c 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim10.1002/14356007.a06233.pub2Chlorinated Hydrocarbons 1Chlorinated HydrocarbonsManfred Rossberg, Hoechst Aktiengesellschaft, Frankfurt/Main, Federal Republic of GermanyWilhelm Lendle, Hoechst Aktiengesellschaft, Frankfurt/Main, Federal Republic of GermanyGerhard Peiderer, Hoechst Aktiengesellschaft, Frankfurt/Main, Federal Republic of GermanyAdolf T ogel, Hoechst Aktiengesellschaft, Frankfurt/Main, Federal Republic of GermanyEberhard-Ludwig Dreher, Dow Chemical GmbH, Stade, Federal Republic of GermanyErnst Langer, BASF Aktiengesellschaft, Ludwigshafen, Federal Republic of GermanyHeinz Rassaerts, Chemische Werke H uls AG, Marl, Federal Republic of GermanyPeter Kleinschmidt, Bayer AG, Dormagen, Federal Republic of GermanyHeinz Strack, formerly Dynamit Nobel AG,Richard Cook, ICI Chemicals and Polymers, Runcorn, United KingdomUwe Beck, Bayer AG, Leverkusen, Federal Republic of GermanyKarl-August Lipper, Bayer AG, Krefeld, Federal Republic of GermanyTheodore R. Torkelson, Dow Chemical, Midland, Michigan, United StatesEckhard L oser, Bayer AG, Wuppertal, Federal Republic of GermanyKlaus K. Beutel, Dow Chemical Europe, Horgen, SwitzerlandTrevor Mann, INEOS Chlor Limited, Runcorn, United Kingdom (Chap. 7)1. Chloromethanes ........... 31.1. Physical Properties.......... 41.2. Chemical Properties ......... 71.3. Production ............... 91.3.1. Theoretical Bases ........... 91.3.2. Production of Monochloromethane 121.3.3. Production of Dichloromethane andTrichloromethane ........... 131.3.4. Production of Tetrachloromethane . 181.4. Quality Specications ........ 211.4.1. PurityoftheCommercialProductsand Their Stabilization ........ 211.4.2. Analysis ................. 221.5. Storage, Transport, and Handling 221.6. Behavior of Chloromethanesin the Environment ......... 231.6.1. Presence in the Atmosphere ..... 241.6.2. Presence in Water Sources ...... 241.7. Applications of theChloromethanesand Economic Data ......... 252. Chloroethanes ............. 262.1. Monochloroethane .......... 292.1.1. Physical Properties .......... 292.1.2. Chemical Properties .......... 292.1.3. Production................ 302.1.4. Uses and Economic Aspects..... 322.2. 1,1-Dichloroethane .......... 322.2.1. Physical Properties .......... 322.2.2. Chemical Properties .......... 332.2.3. Production................ 332.2.4. Uses and Economic Aspects..... 342.3. 1,2-Dichloroethane .......... 342.3.1. Physical Properties .......... 342.3.2. Chemical Properties .......... 352.3.3. Production................ 352.3.4. Uses and Economic Aspects..... 422.4. 1,1,1-Trichloroethane ........ 422.4.1. Physical Properties .......... 422.4.2. Chemical Properties .......... 422.4.3. Production................ 432.4.4. Uses and Economic Aspects..... 462.5. 1,1,2-Trichloroethane ........ 472.5.1. Physical Properties .......... 472.5.2. Chemical Properties .......... 472.5.3. Production................ 472.5.4. Uses and Economic Aspects. .... 492.6. 1,1,1,2-Tetrachloroethane ..... 492.6.1. Physical Properties .......... 492.6.2. Chemical Properties .......... 492 Chlorinated Hydrocarbons2.6.3. Production................ 492.7. 1,1,2,2-Tetrachloroethane ..... 502.7.1. Physical Properties .......... 502.7.2. Chemical Properties .......... 502.7.3. Production................ 512.7.4. Uses and Economic Aspects..... 522.8. Pentachloroethane .......... 522.8.1. Physical Properties .......... 522.8.2. Chemical Properties .......... 532.8.3. Production................ 532.8.4. Uses and Economic Aspects..... 532.9. Hexachloroethane .......... 532.9.1. Physical Properties .......... 542.9.2. Chemical Properties .......... 542.9.3. Production................ 542.9.4. Uses and Economic Aspects..... 543. Chloroethylenes ............ 543.1. Vinyl Chloride (VCM) ....... 553.1.1. Physical Properties .......... 553.1.2. Chemical Properties .......... 563.1.3. Production................ 563.1.3.1. Vinyl Chloride from Acetylene ... 573.1.3.2. Vinyl Chloridefrom 1,2-Dichloroethane ....... 593.1.3.3. Vinyl Chloride from Ethyleneby Direct Routes ............ 633.1.3.4. Vinyl Chloride from Ethane ..... 643.1.3.5. Vinyl Chloride by Other Routes .. 663.1.4. Uses and Economic Aspects..... 663.2. 1,1-Dichloroethylene(Vinylidene Chloride, VDC) .... 673.2.1. Physical Properties .......... 673.2.2. Chemical Properties .......... 673.2.3. Production................ 673.2.4. Uses and Economic Aspects..... 693.3. 1,2-Dichloroethylene......... 703.3.1. Physical Properties .......... 703.3.2. Chemical Properties .......... 703.3.3. Production................ 713.3.4. Uses and Economic Aspects..... 713.4. Trichloroethylene........... 713.4.1. Physical Properties .......... 713.4.2. Chemical Properties .......... 723.4.3. Production................ 723.4.4. Uses and Economic Aspects..... 743.5. Tetrachloroethylene ......... 753.5.1. Physical Properties .......... 753.5.2. Chemical Properties .......... 753.5.3. Production................ 753.5.4. Uses and Economic Aspects..... 793.6. Analysis and Quality Controlof Chloroethanesand Chloroethylenes ......... 803.7. Storage and Transportationof Chloroethanes andChloroethylenes ............ 803.8. Environmental Aspects in theProduction of Chloroethanes andChloroethylenes ............ 814. Chloropropanes ............ 824.1. 2-Chloropropane ........... 824.2. 1,2-Dichloropropane......... 834.3. 1,2,3-Trichloropropane ....... 845. Chlorobutanes ............. 855.1. 1-Chlorobutane ............ 855.2. tert-Butyl Chloride .......... 865.3. 1,4-Dichlorobutane.......... 866. Chlorobutenes ............. 876.1. 1,4-Dichloro-2-butene ........ 876.2. 3,4-Dichloro-1-butene ........ 876.3. 2,3,4-Trichloro-1-butene ...... 886.4. 2-Chloro-1,3-butadiene ....... 886.4.1. Physical Properties .......... 886.4.2. Chemical Properties .......... 896.4.3. Production................ 896.4.3.1. Chloroprene from Butadiene .... 896.4.3.2. Chloroprene from Acetylene .... 906.4.3.3. Other Processes ............ 916.4.4. Economic Importance ........ 916.5. Dichlorobutadiene .......... 916.5.1. 2,3-Dichloro-1,3-butadiene ..... 916.5.2. Other Dichlorobutadienes ...... 926.6. 3-Chloro-2-methyl-1-propene ... 926.6.1. Physical Properties .......... 926.6.2. Chemical Properties .......... 926.6.3. Production................ 936.6.4. Quality Specications and ChemicalAnalysis ................. 946.6.5. Storage and Shipment ......... 956.6.6. Uses ................... 956.7. Hexachlorobutadiene ........ 957. Chlorinated Parafns ........ 967.1. Physical Properties.......... 977.2. Chemical Propertiesand Structure ............. 977.3. Production ............... 997.4. Analysis and Quality Control ... 1017.5. Storage and Transportation .... 1017.6. Toxicology, EnvironmentalImpact and Regulation ....... 1027.7. Uses ................... 1037.8. Summary ................ 1048. Nucleus-ChlorinatedAromatic Hydrocarbons ...... 1048.1. Chlorinated Benzenes ........ 1058.1.1. Physical Properties .......... 1058.1.2. Chemical Properties .......... 105Chlorinated Hydrocarbons 38.1.3. Production................ 1098.1.3.1. Monochlorobenzene.......... 1128.1.3.2. Dichlorobenzenes ........... 1138.1.3.3. Trichlorobenzenes ........... 1148.1.3.4. Tetrachlorobenzenes ......... 1148.1.3.5. Pentachlorobenzene .......... 1158.1.3.6. Hexachlorobenzene .......... 1158.1.4. Quality and Analysis ......... 1158.1.5. Storage and Transportation ..... 1158.1.6. Uses ................... 1168.2. Chlorinated Toluenes ........ 1168.2.1. Physical Properties .......... 1168.2.2. Chemical Properties .......... 1178.2.3. Production................ 1178.2.3.1. Monochlorotoluenes ......... 1218.2.3.2. Dichlorotoluenes ............ 1218.2.3.3. Trichlorotoluenes ........... 1228.2.3.4. Tetrachlorotoluenes .......... 1228.2.3.5. Pentachlorotoluene .......... 1238.2.4. Quality and Analysis ......... 1238.2.5. Storage and Transportation ..... 1238.2.6. Uses ................... 1248.3. Chlorinated Biphenyls ....... 1248.3.1. Physical and Chemical Properties . 1258.3.2. Disposal ................. 1258.3.3. Analysis ................. 1268.3.4. Storage and Transportation ..... 1268.3.5. Uses ................... 1278.4. Chlorinated Naphthalenes ..... 1278.4.1. Physical Properties .......... 1278.4.2. Chemical Properties .......... 1288.4.3. Production................ 1298.4.4. Quality and Analysis ......... 1298.4.5. Storage and Transportation ..... 1298.4.6. Use .................... 1308.5. Environmental Protection ..... 1308.6. Economic Facts ............ 1319. Side-Chain Chlorinated AromaticHydrocarbons ............. 1329.1. Benzyl Chloride ............ 1329.1.1. Physical Properties .......... 1329.1.2. Chemical Properties .......... 1339.1.3. Production................ 1349.1.4. Quality Specications and Analysis 1369.1.5. Storage and Transportation ..... 1379.1.6. Uses ................... 1379.2. Benzal Chloride ............ 1379.2.1. Physical Properties .......... 1379.2.2. Chemical Properties .......... 1389.2.3. Production................ 1389.2.4. Quality Specications and Analysis 1389.2.5. Storage and Transportation ..... 1389.2.6. Uses ................... 1399.3. Benzotrichloride ........... 1399.3.1. Physical Properties .......... 1399.3.2. Chemical Properties .......... 1399.3.3. Production................ 1409.3.4. Quality Specications and Analysis 1409.3.5. Storage and Transportation ..... 1419.3.6. Uses ................... 1419.4. Side-Chain Chlorinated Xylenes . 1419.4.1. Physical and Chemical Properties . 1419.4.2. Production................ 1429.4.3. Storage and Transportation ..... 1439.4.4. Uses ................... 1439.5. Ring-Chlorinated Derivatives ... 1439.6. Economic Aspects .......... 14510. Toxicology and OccupationalHealth .................. 14510.1. Aliphatic ChlorinatedHydrocarbons ............. 14510.1.1. Chloromethanes ............ 14610.1.2. Chlorinated C2 Hydrocarbons ... 14810.1.3. Chloropropanes andChloropropenes ............ 15210.1.4. Chlorobutadienes ........... 15210.1.5. Ecotoxicology and EnvironmentalDegradation ............... 15210.2. Chlorinated AromaticHydrocarbons ............. 15410.2.1. Chlorinated Benzenes ......... 15410.2.2. Chlorotoluenes ............. 15410.2.3. Polychlorinated Biphenyls ...... 15510.2.4. Chlorinated Naphthalenes ...... 15610.2.5. Benzyl Chloride ............ 15610.2.6. Benzoyl Chloride ........... 15710.2.7. Benzotrichloride ............ 15710.2.8. Side-Chain Chlorinated Xylenes .. 15711. References ............... 1571. ChloromethanesAmong the halogenated hydrocarbons, thechlorine derivatives of methane monochloro-methane (methyl chloride) [74-87-3], dichloro-methane (methylene chloride) [75-09-2], tri-chloromethane (chloroform) [67-66-3], andtetrachloromethane(carbontetrachloride)[56-23-5] play an important role fromboth industrialand economic standpoints. These products ndbroad application not only as important chemi-cal intermediates, but also as solvents.4 Chlorinated HydrocarbonsHistorical Development. Monochloromethanewas produced for the rst time in 1835 by J. Du-masandE. Peligotbythereactionofsodiumchloride with methanol in the presence of sulfu-ric acid. M. Berthelot isolated it in 1858 fromthe chlorination of marsh gas (methane), as didC. Groves in 1874 from the reaction of hydro-gen chloride with methanol in the presence ofzinc chloride. For a time, monochloromethanewasproducedcommerciallyfrombetainehy-drochloride obtained in the course of beet sugarmanufacture. Theearliestattemptstoproducemethyl chloride by the chlorination of methaneoccurredbeforeWorldWar I, withtheintentof hydrolyzingit tomethanol. Acommercialmethane chlorination facility was rst put intooperation by the former Farbwerke Hoechst in1923. In the meantime, however, a high-pressuremethanol synthesis based on carbon monoxideand hydrogen had been developed, as a result ofwhich the opposite process became practical synthesis of methyl chloride from methanol.Dichloromethane waspreparedforthersttime in 1840 by V. Regnault, who successfullychlorinatedmethylchloride. Itwasforatimeproduced by the reduction of trichloromethane(chloroform) with zinc and hydrochloric acid inalcohol, but thecompoundrst acquiredsig-nicance as a solvent after it was successfullyprepared commercially by chlorination of meth-ane andmonochloromethane (Hoechst AG, DowChemical Co., and Stauffer Chemical Co.).Trichloromethane was synthesized indepen-dentlybytwogroupsin1831: J. vonLiebigsuccessfullycarriedout thealkalinecleavageofchloral,whereasM.E.Soubeirainobtainedthe compound by the action of chlorine bleachon both ethanol and acetone. In 1835, J. Dumasshowedthat trichloromethanecontainedonlyasinglehydrogenatomandpreparedthesub-stance by the alkaline cleavage of trichloroaceticacid and other compounds containing a termi-nal CCl3 group, such as -trichloroacetoacrylicacid. In analogy to the synthetic method ofM.E. Soubeirain, the use of hypochlorites was ex-tended to include other compounds containingacetyl groups, particularly acetaldehyde. V. Reg-naultpreparedtrichloromethanebychlorina-tion of monochloromethane. Already by themiddle of the last century, chloroform was be-ingproducedonacommercialbasisbyusingthe J. von Liebig procedure, a method which re-tained its importance until ca. the 1960s in placeswhere the preferred starting materials methaneand monochloromethane were in short supply.Today, trichloromethane along with dichloro-methaneispreparedexclusivelyandonamassivescalebythechlorinationofmethaneand/ormonochloromethane. Trichloromethanewas introduced into the eld of medicine in 1847by J. Y. Simpson, who employed it as an inhaledanaesthetic. As a result of its toxicologic proper-ties, however, it has since been totally replacedby other compounds (e.g., Halothane).Tetrachloromethane was rst prepared in1839 by V. Regnault by the chlorination of tri-chloromethane. Shortly thereafter, J. Dumas suc-ceeded in synthesizing it by the chlorination ofmarshgas. H. Kolbeisolatedtetrachlorometh-anein1843whenhetreatedcarbondisuldewith chlorine in the gas phase. The correspond-ingliquidphasereactioninthepresenceofacatalyst, giving CCl4 and S2Cl2, was developeda short time later. The key to economical practi-cality of this approach was the discovery in 1893by M uller and Dubois of the reaction of S2Cl2with CS2 to give sulfur and tetrachloromethane,thereby avoiding the production of S2Cl2.Tetrachloromethane is produced on an indus-trial scalebyoneoftwogeneral approaches.The rst is the methane chlorination process, us-ing methane or mono-chloromethane as startingmaterials. The other involves either perchlorina-tion or chlorinolysis.Starting materials in thiscaseincludeC1toC3hydrocarbonsandtheirchlorinated derivatives as well as Cl-containingresidues obtainedinother chlorinationprocesses(vinyl chloride, propylene oxide, etc.).Originally, tetrachloromethane played a roleonly in the dry cleaning industry and as a reextinguishingagent. Its productionincreaseddramatically, however, with the introduction ofchlorouoromethane compounds 50 years ago,these nding wide application as non-toxic re-frigerants, as propellants for aerosols, as foam-blowing agents, and as specialty solvents.1.1. Physical PropertiesThemostimportantphysicalpropertiesofthefour chloro derivatives of methane are presentedin Table 1; Figure 1 illustrates the vapor pressurecurves of the four chlorinated methanes.Chlorinated Hydrocarbons 5Table 1. Physical properties of chloromethanesUnit Monochlorometh-aneDichloromethaneTrichloromethane Tetrachloro-methaneFormula CH3Cl CH2Cl2CHCl3CCl4Mr50.49 84.94 119.39 153.84Melting pointC 97.7 96.7 63.8 22.8Boiling point at 0.1 MPaC 23.9 40.2 61.3 76.7Vapor pressure at 20 C kPa 489 47.3 21.27 11.94Density of liquid at 20 C kg/m3920 1328.3 1489 1594.7(0.5 MPa)Density of vapor at bp kg/m32.558 3.406 4.372 5.508Enthalpy of formation H0298kJ/mol 86.0 124.7 132.0 138.1Specic heat capacity of liquid at 20 C kJ kg1K11.595 1.156 0.980 0.867Enthalpy of vaporization at bp kJ/mol 21.65 28.06 29.7 30.0Critical temperature K 416.3 510.1 535.6 556.4Critical pressure MPa 6.68 6.17 5.45 4.55Cubic expansion coeff. of liquid (0 40 C) K10.0022 0.00137 0.001399 0.00116Thermal conductivity at 20 C W K1m10.1570 0.159 0.1454 0.1070Surface tension at 20 C N/m 16.2 10328.76 10327.14 10326.7 103Viscosity of liquid at 20 C Pa s 2.7 1044.37 1045.7 10413.5 104(0.5 MPa)Refractive index n20D1.4244 1.4467 1.4604Ignition temperatureC 618 605 Limits of ignition in air, lower vol% 8.1 12 Limits of ignition in air, upper vol% 17.2 22 Partition coefcient air/water at 20 Cmg/L(air)mg/L(water)0.3 0.12 0.12 0.91Figure 1. Vapor pressure curves of chloromethanesThe following sections summarize additionalimportant physical properties of the individualcompoundsmakingupthechloromethanese-ries.Monochloromethane is a colorless, am-mable gas with a faintly sweet odor. Its solubilityinwaterfollowsHenryslaw;thetemperaturedependence of the solubility at 0.1 MPa (1 bar)is:t, C 15 30 45 60g of CH3Cl/kg of H2O 9.0 6.52 4.36 2.64Monochloromethane at 20Cand 0.1 MPa (1bar) is soluble to the extent of 4.723 cm3in 100cm3of benzene, 3.756 cm3in 100 cm3of tetra-chloromethane, 3.679 cm3in 100 cm3of aceticacid, and 3.740 cm3in 100 cm3of ethanol. Itforms azeotropic mixtures with dimethyl ether,2-methylpropane, and dichlorodiuoromethane(CFC 12).Dichloromethane is a colorless, highlyvolatile, neutral liquid with a slightly sweetsmell, similar to that of trichloromethane. Thesolubility of water in dichloromethane is:t, C 30 0 + 25g of H2O/kg ofCH2Cl20.16 0.8 1.98Thesolubilityofdichloromethaneinwaterand in aqueous hydrochloric acid is presented inTable 2.Dichloromethane forms azeotropic mixtureswith a number of substances (Table 3).6 Chlorinated HydrocarbonsTable 2. Solubility of dichloromethane in water and aqueous hydrochloric acid (in wt %)SolventTemperature, C15 30 45 60Water 2.50 1.56 0.88 0.5310 % HCl 2.94 1.85 1.25 0.6020 % HCl 2.45 1.20 0.65Table 3. Azeotropic mixtures of dichloromethanewt % Compound Azeotropic boilingpoint, in C, at101.3 kPa30.0 acetone 57.611.5 ethanol 54.694.8 1,3-butadiene 5.06.0 tert-butanol 57.130.0 cyclopentane 38.055.0 diethylamine 52.030.0 diethyl ether 40.808.0 2-propanol 56.67.3 methanol 37.851.0 pentane 35.523.0 propylene oxide 40.639.0 carbon disulde 37.01.5 water 38.1Dichloromethane is virtually nonammableinair, asshowninFigure2, whichillustratesthe range of ammable mixtures with oxygen nitrogen combinations [1, 2]. Dichloromethanethereby constitutes the only nonammable com-mercialsolventwithalowboilingpoint. Thesubstance possesses no ash point according tothedenitionsestablishedinDIN51 755andASTM5670 as well as DIN51 758 and ASTMD 9373. Thus, it is not subject to the regula-tions governing ammable liquids. As a resultof the existing limits of ammability (CH2Cl2vapor/air), it is assigned to explosion category G1 (VDE 0165). The addition of small amountsof dichloromethane to ammable liquids (e.g.,gasoline, esters, benzene, etc.) raises their ashpoints; additionof10 30 %dichloromethanecan render such mixtures nonammable.Trichloromethane is a colorless, highly vol-atile, neutral liquid with a characteristic sweetodor. Trichloromethane vapors form no explo-sive mixtures with air [2]. Trichloromethane hasexcellent solvent propertiesfor manyorganicmaterials, including alkaloids, fats, oils, resins,waxes, gums, rubber, parafns, etc. As a resultof its toxicity, it is increasingly being replaced asa solvent by dichloromethane, whose propertiesin this general context are otherwise similar. Inaddition, trichloromethane is a good solvent foriodine and sulfur, and it is completely misciblewithmanyorganicsolvents. Thesolubilityoftrichloromethane in water at 25 C is 3.81 g/kgof H2O, whereas 0.8 g of H2O is soluble in 1 kgof CHCl3.Figure 2.RangeofammabilityofmixturesofCH2Cl2with O2 and N2 [1]Important azeotropic mixtures of chloroformwith other compounds are listed in Table 4.Table 4. Azeotropic mixtures of trichloromethanewt % Compound Azeotropic boilingpoint, in C, at101.3 kPa15.0 formic acid 59.220.5 acetone 64.56.8 ethanol 59.313.0 ethyl formate 62.796.0 2-butanone 79.72.8 n-hexane 60.04.5 2-propanol 60.812.5 methanol 53.423.0 methyl acetate 64.82.8 water 56.1Chlorinated Hydrocarbons 7Ternaryazeotropes alsoexist betweentri-chloromethane and ethanol water (boilingpoint 55.5C, 4 mol%ethanol + 3.5 mol%H2O), methanol acetone, and methanol hex-ane.Tetrachloromethane isacolorlessneutralliquid with a high refractive index and a strong,bitter odor. It possesses good solubility proper-ties for many organic substances, but due to itshigh toxicity it is no longer employed (e.g., as aspot remover or in the dry cleaning of textiles).It should be noted that it does continue to ndapplication as a solvent for chlorine in certainindustrial processes.Tetrachloromethane is soluble in water at 25C to the extent of 0.8 g of CCl4/kg of H2O, thesolubility of water in tetrachloromethane being0.13 g of H2O/kg of CCl4.Tetrachloromethaneforms constant-boilingazeotropic mixtures with a variety of substances;corresponding data are given in Table 5.Table 5. Azeotropic mixtures of tetrachloromethanewt % Compound Azeotropic boilingpoint, in C, at101.3 kPa88.5 acetone 56.417.0 acetonitrile 71.011.5 allyl alcohol 72.381.5 formic acid 66.6543.0 ethyl acetate 74.815.85 ethanol 61.171.0 2-butanone 73.82.5 butanol 76.621.0 1,2-dichloroethane 75.612.0 2-propanol 69.020.56 methanol 55.711.5 propanol 73.14.1 water 66.01.2. Chemical PropertiesMonochloromethane as compared to otheraliphatic chlorine compounds, is thermally quitestable. Thermal decomposition is observed onlyat temperaturesinexcessof 400C, eveninthe presence of metals (excluding the alkali andalkaline-earth metals). The principal products ofphotooxidation of monochloromethane are car-bon dioxide and phosgene.Monochloromethane forms with water or wa-ter vapor a snowlike gas hydrate with the com-position CH3Cl 6 H2O, the latter decomposingintoitscomponentsat+7.5 Cand0.1MPa(1 bar). To the extent that monochloromethanestill nds application in the refrigeration indus-try, its water content must be kept below50 ppm.This specication is necessary to prevent poten-tial failure of refrigeration equipment pressurerelease valves caused by hydrate formation.Monochloromethaneishydrolyzedbywa-teratanelevatedtemperature. Thehydrolysis(tomethanol andthecorrespondingchloride)is greatly accelerated by the presence of alkali.Mineral acidsshownoinuenceonthecom-pounds hydrolytic tendencies.Monochloromethane is converted in the pres-ence of alkali or alkaline-earth metals, as wellas by zinc and aluminum, into the correspond-ing organometallic compounds (e.g., CH3MgCl,Al(CH3)3 AlCl3). These have come to play arole both in preparative organic chemistry andas catalysts in the production of plastics.Reaction of monochloromethane witha sodium lead amalgam leads to tetra-methyllead, an antiknocking additive to gasolineintended for use in internal combustion engines.The use of the compound is declining, however,as a result of ecological considerations.Averysignicant reactionisthat betweenmonochloromethane and silicon to producethe corresponding methylchlorosilanes (the Ro-chow synthesis), e.g.:2CH3Cl+SiSiCl2(CH3)2The latter, through their subsequent conver-siontosiloxanes, serveas important startingpoints for the production of silicones.Monochloromethane is employed as a com-ponent inthe Wurtz-Fittigreaction; it is alsousedin Friedel-Crafts reactions for the production ofalkylbenzenes.Monochloromethane has acquiredparticu-larly great signicance as a methylating agent:examples include its reaction with hydroxylgroups to give the corresponding ethers (methyl-cellulose from cellulose, various methyl ethersfrom phenolates), and its use in the preparationofmethyl-substitutedaminocompounds(qua-ternarymethylammoniumcompoundsforten-sides). Allofthevariousmethylaminesresultfromitsreactionwithammonia.TreatmentofCH3Cl withsodiumhydrogensulde under pres-sureandatelevatedtemperaturegivesmethylmercaptan.8 Chlorinated HydrocarbonsDichloromethane is thermally stable to tem-peratures above 140 C and stable in the pres-enceofoxygento120 C. Itsphotooxidationproduces carbon dioxide, hydrogen chloride,and a small amount of phosgene [3]. Ther-mal reactionwithnitrogendioxidegivescar-bon monoxide, nitrogen monoxide, and hydro-genchloride[4]. Inrespecttomostindustrialmetals (e.g., iron, copper, tin), dichloromethaneisstable, exceptionsbeingaluminum, magne-sium, and their alloys; traces of phosgene rstarise above 80 C.Dichloromethane forms a hydrate with water,CH2Cl2 17 H2O, which decomposes at 1.6 Cand 21.3 kPa (213 mbar).Nodetectablehydrolysisoccursduringtheevaporation of dichloromethane fromextracts orextraction residues. Only on prolonged action ofsteam at 140 170 C under pressure are form-aldehyde and hydrogen chloride produced.Dichloromethane can be further chlorinatedeither thermallyor photochemically. Halogenexchange leading to chlorobromomethane ordibromomethanecanbecarriedout byusingbromine and aluminum or aluminum bromide.In the presence of aluminum at 220 C and 90MPa (900 bar), it reacts with carbon monoxidetogivechloroacetyl chloride[5]. Warmingto125 Cwithalcoholicammoniasolutionpro-duceshexamethylenetetramine. Reactionwithphenolates leads to the same products as are ob-tained in the reaction of formaldehyde and phe-nols.Trichloromethane is nonammable, al-thoughit does decompose ina ame or incontactwithhotsurfacestoproducephosgene.Inthepresence of oxygen, it is cleaved photochemical-ly by way of peroxides to phosgene and hydro-gen chloride [6, 7]. The oxidation is catalyzed inthe dark by iron [8]. The autoxidation and acidgeneration can be slowed or prevented by sta-bilizers such as methanol, ethanol, or amylene.Trichloromethaneformsahydrate,CHCl3 17H2O, whosecriticaldecompositionpointis+1.6C and 8.0 kPa (80 mbar).Upon heating with aqueous alkali, trichloro-methane is hydrolyzed to formic acid, orthofor-mate esters being formed with alcoholates. Withprimary amines in an alkaline mediumthe isoni-trilereactionoccurs, aresultwhichalsondsuseinanalytical determinations. Theinterac-tion of trichloromethane with phenolates to givesalicylaldehydes is well-known as the Reimer-Thiemann reaction. Treatment with benzeneunder Friedel-Crafts conditions results intri-phenylmethane.The most important reaction of tri-chloromethaneisthat withhydrogenuoridein the presence of antimony pentahalides to givemonochlorodiuoromethane(CFC22), apre-cursorintheproductionofpolytetrauoroeth-ylene (Teon, Hostaon, PTFE).Whentreatedwithsalicylicanhydride, tri-chloromethaneproducesacrystallineadditioncompoundcontaining2moloftrichlorometh-ane. This result nds application in the prepa-ration of trichloromethane of the highest purity.Under certain conditions, explosive and shock-sensitive products can result from the combina-tion of trichloromethane with alkali metals andcertain other light metals [9].Tetrachloromethane is nonammableandrelatively stable even in the presence of light andair at room temperature. When heated in air inthe presence of metals (iron), phosgene is pro-duced in large quantities, the reaction starting atca. 300 C [10]. Photochemical oxidation alsoleads to phosgene. Hydrolysis to carbon dioxideand hydrogen chloride is the principal result in amoist atmosphere [11]. Liquid tetrachlorometh-ane has only a very minimal tendency to hydro-lyze in water at room temperature (half-life ca.70 000 years) [12].Thermal decomposition of dry tetrachlor-omethaneoccurs relativelyslowlyat 400Ceven in the presence of the common industrialmetals (withtheexceptionof aluminumandother light metals). Above 500 600Can equi-librium reaction sets in which is shifted signi-cantly to the right above 700C and 0.1 MPa (1bar) pressure. At 900Cand 0.1 MPa (1 bar), theequilibrium conversion of CCl4is >70 % (seeChaps. 3.5, cf. Fig. 6).Tetrachloromethane forms shock-sensitive,explosive mixtures with the alkali and alkaline-earth metals. With water it forms a hydratelikeaddition compound which decomposes at +1.45C.The telomerization of ethylene and vinylderivatives with tetrachloromethane under pres-sure and in the presence of peroxides hasChlorinated Hydrocarbons 9acquired a certain preparative signicance[13 15]:CH2 = CH2+CCl4CCl3CH2CH2ClThemost important industrial reactionsoftetrachloromethane are its liquid-phase con-version with anhydrous hydrogen uoridein the presence of antimony (III/V) uo-rides or its gas-phase reaction over alu-minumor chromiumuoride catalysts, bothofwhichgivethewidelyusedandimportantcompounds trichloromonouoromethane (CFC11), dichlorodiuoromethane (CFC12), andmonochlorotriuoromethane (CFC 13).1.3. Production1.3.1. Theoretical BasesThe industrial preparation of chloromethanederivativesisbasedalmost exclusivelyonthetreatment of methane and/or monochlorometh-ane with chlorine, whereby the chlorinationproducts are obtained as a mixture of the indi-vidual stages of chlorination:Thermodynamic equilibrium lies entirely onthe side of the chlorination products, so that thedistribution of the individual products is essen-tially determined by kinetic parameters.Monochloromethane can be used in place ofmethane as the starting material, where this inturncanbepreparedfrommethanolbyusinghydrogen chloride generated in the previous pro-cesses. The corresponding reaction is:Inthisway, theunavoidableaccumulationof hydrogenchloride(hydrochloricacid) canbe substantially reduced and the overall processcan be exibly tailored to favor the productionofindividualchlorinationproducts.Moreover,given the ease with which it can be transportedand stored, methanol is a better starting mate-rialforthechloroderivativesthanmethane, asubstancewhoseavailabilityistiedtonaturalgas resources or appropriate petrochemical fa-cilities. There has been a distinct trend in recentyears toward replacing methane as a carbon basewith methanol.Methane Chlorination. The chlorination ofmethane and monochloromethane is carried outindustrially by using thermal, photochemical, orcatalytic methods [16]. The thermal chlorinationmethodispreferred, anditisalsotheoneonwhich the most theoretical and scientic inves-tigations have been carried out.Thermal chlorinationof methane andits chlo-rine derivatives is a radical chain reaction initi-ated by chlorine atoms. These result from ther-mal dissociation at 300 350 C, and they leadto successive substitution of the four hydrogenatoms of methane:The conversion to the higher stages of chlori-nation follows the same scheme [17 21]. Thethermal reaction of methane and its chlorinationproductshasbeendeterminedtobeasecond-order process:dn(Cl2) /dt = kp (Cl2) p (CH4)It has further been shown that traces of oxy-gen strongly inhibit the reaction. Controlling thehigh heat of reaction in the gas phase (which av-erages ca. 4200 kJ per m3of converted chlorine)at STP is a decisive factor in successfully carry-ing out the process. In industrial reactors, chlo-rineconversionrst becomesapparent above250to270C, but it increases exponentiallywithincreasingtemperature[22],andintheregionof commercial interest 350 to 550 C thereaction proceeds very rapidly. As a result, it isnecessary to initiate the process at a temperaturewhich permits the reaction to proceed by itself,but also to maintain the reaction under adiabaticconditions at the requisite temperature level of320 550Cdictatedbybothchemical andtech-nical considerations. If a certain critical temper-atureisexceededinthereactionmixture(ca.550 700 C, dependent both on the residencetime in the hot zone and on the materials makingup the reactor), decomposition of the metastablemethanechlorinationproductsoccurs. Inthatevent, the chlorination leads to formation of un-desirablebyproducts, includinghighlychlori-nated or high molecular mass compounds (tetra-chloroethene, hexachloroethane, etc.). Alterna-tively, the reaction with chlorine can get com-10 Chlorinated Hydrocarbonspletely out of control, leading to the separationofsootandevolutionofHCl(thermodynami-callythemoststableendproduct).Oncesuchcarbon formation begins it acts autocatalytically,resulting in a progressively heavier buildup ofsoot, whichcanonlybehaltedbyimmediateshutdown of the reaction.Propertemperaturecontrolofthisvirtuallyadiabaticchlorinationisachievedbyworkingwith a high methane : chlorine ratio in the rangeof 6 4 : 1. Thus, a recyclingsystemis em-ployed in which a certain percentage of inert gasis maintained (nitrogen, recycled HCl, or evenmaterials such as monochloromethane or tetra-chloromethane derived from methane chlorina-tion). Inthis way, the explosive limits of methaneand chlorine are moved into a more favorable re-gion and it becomes possible to prepare the morehighlysubstitutedchloromethaneswithlowerCH4 : Cl2 ratios.Figure 3 shows the explosion range of meth-ane andchlorine andhowit canbe limitedthroughtheuseof diluents, usingtheexam-ples of nitrogen, hydrogen chloride, and tetra-chloromethane.Figure3. Explosive range of CH4 Cl2mixtures con-taining N2, HCl, and CCl4Test conditions: pressure 100kPa; temperature 50 C; ignition by 1-mm sparkThe composition and distribution of the prod-ucts resultingfromchlorinationis a denitefunction of the starting ratio of chlorine to meth-ane, as can be seen from Figure 4 and Figure 5.Figure 4. Product distribution in methane chlorination, plugstream reactora) Methane; b) Monochloromethane; c) Dichloromethane;d) Trichloromethane; e) TetrachloromethaneFigure 5. Product distributioninmethane chlorination, idealmixing reactora) Methane; b) Monochloromethane; c) Dichloromethane;d) Trichloromethane; e) TetrachloromethaneChlorinated Hydrocarbons 11Theserelationshipshavebeeninvestigatedfrequently [23, 24]. The composition of the re-action product has been shown to be in excel-lentagreementwiththatpredictedbycalcula-tions employing experimental relative reactionrateconstants[25 28]. Theproductsarisingfrom thermal chlorination of monochlorometh-ane and from the pyrolysis of primary productscan also be predicted quantitatively [29]. The re-lationships among the rate constants are nearlyindependent of temperature in the region of tech-nical interest. If one designates as k1 through k4the successive rate constants in the chlorinationprocess, thenthefollowingvaluescanbeas-signed to the relative constants for the individualstages:k1 =1 (methane)k2 =2.91 (monochloromethane)k3 =2.0 (dichloromethane)k4 =0.72 (trichloromethane)With this set of values, the selectivity of thechlorination can be effectively established withrespect to optimal product distribution for reac-torsofvariousresidencetime(streamtypeormixing type, cf. Fig. 4 and Fig. 5). Additionalrecyclingintothereactionofpartiallychlori-nated products (e.g., monochloromethane) per-mits further control over the ratios of the indi-vidual components [30, 31].It has been recognized that the yield of par-tially chlorinated products (e.g., dichlorometh-ane and trichloromethane) is diminished by re-cycling. This factor has to be taken into accountin the design of reactors for those methane chlo-rinations which are intended to lead exclusivelyto these products. If the emphasis is to lie moreon the side of trichloro- and tetrachloromethane,then mixing within the reactor plays virtually norole, particularly since less-chlorinated materi-als can always be partially or wholly recycled.Details of reactor construction will be discussedbelow in the context of each of the various pro-cesses.Chlorinolysis. The technique for the produc-tion of tetrachloromethane is based on what isknownasperchlorination, amethodinwhichanexcessofchlorineisusedandC1-toC3-hydrocarbonsandtheirchlorinatedderivativesare employed as carbon sources. In this process,tetrachloroethene is generated along with tetra-chloromethane, the relationship between the twobeing consistent with Eq. 1 in page 13 and de-pendentonpressureandtemperature(cf. alsoFig. 6).Figure 6. Thermodynamic equilibrium 2 CCl4C2Cl4 +2 Cl2a) 0.1 MPa; b) 1 MPa; c) 10 MPaIt will be noted that at low pressure (0.1 to 1MPa, 1 to 10 bar) and temperatures above 700C,conditionsunderwhichthereactiontakesplace at an acceptable rate, a signicant amountoftetrachloroethenearises. Foradditional de-tailsseeChap. 3.5. Underconditionsofhighpressuregreaterthan10MPa(100bar) thereactionoccursatatemperatureaslowas600 C. As a result of the inuence of pressureandbytheuseofalargerexcessofchlorine,the equilibrium can be shifted essentially 100 %to the side of tetrachloromethane. These circum-stances are utilized in the Hoechst high-pressurechlorinolysis procedure (see below) [32, 33].Methanol Hydrochlorination. Studieshavebeenconductedfor purposes of reactordesign [34] on the kinetics of the gas-phase re-actionofhydrogenchloridewithmethanol inthepresenceofaluminumoxideascatalysttogive monochloromethane. Aging of the catalysthas also been investigated. The reaction is rstorder in respect to hydrogen chloride, but nearlyindependent of the partial pressure of methanol.The rate constant is proportional to the specicsurface of the catalyst, whereby at higher tem-peratures(350 400C) aninhibitionduetopore diffusion becomes apparent.12 Chlorinated Hydrocarbons1.3.2. Production of MonochloromethaneMonochloromethane is produced commerciallyby two methods: by the hydrochlorination (es-terication) of methanol using hydrogen chlo-ride, and by chlorination of methane. Methanolhydrochlorination has become increasingly im-portant in recent years, whereas methane chlo-rination as the route to monochloromethane asnal product has declined. The former approachhastheadvantagethat it utilizes, rather thangenerating, hydrogen chloride, a product whosedisposal generallyashydrochloricacidhas become increasingly difcult for chlorinatedhydrocarbon producers. Moreover, this methodleadstoasingletarget product, monochloro-methane, in contrast to methane chlorination (cf.Figs. 4 and 5). As a result of the ready and low-cost availability of methanol (via the low pres-sure methanol synthesis technique) and its faciletransport and storage, the method also offers theadvantage of avoiding the need for placing pro-ductionfacilitiesinthevicinityofamethanesupply.Sinceinthechlorinationof methaneeachsubstitution of a chlorine atom leads to gener-ation of an equimolar amount of hydrogen chlo-ride cf. Eqs. 2 5 in page 7a combinationof the two methods permits a mixture of chlori-nated methanes to be produced without creatinglarge amounts of hydrogen chloride at the sametime; cf. Eq. 6.Monochloromethane production from meth-anolandhydrogenchlorideiscarriedoutcat-alyticallyinthegasphaseat0.3 0.6MPa(3 6 bar) and temperatures of 280 350 C. Theusual catalyst is activated aluminum oxide. Ex-cess hydrogen chloride is introduced in order toprovide a more favorable equilibrium point (lo-cated 96 99 % on the side of products at 280 350C) and to reduce the formation of dimethylether as a side product (0.2 to 1 %).The raw materials must be of high purity inorder to prolong catalyst life as much as possi-ble. Technically pure (99.9 %) methanol is em-ployed, alongwithverycleanhydrogenchlo-ride. In the event that the latter is obtained fromhydrochloric acid, it must be subjected to spe-cial purication (stripping) in order to removeinterfering chlorinated hydrocarbons.Process Description. In a typical productionplant (Fig. 7), the two raw material streams, hy-drogen chloride and methanol, are warmed overheatexchangersandled,aftermixingandad-ditional preheating, into the reactor, where con-version takes place at 280 350 C and ca. 0.5MPa (5 bar).The reactor itself consists of a large numberof relatively thin nickel tubes bundled togetherand lled with aluminumoxide. Removal of heatgenerated by the reaction (33 kJ/mol) is accom-plishedbyusingaheatconductionsystem. Ahot spot forms in the catalyst layer as a result ofthe exothermic nature of the reaction, and thismigrates through the catalyst packing, reachingthe end as the latters useful life expires.The reaction products exiting the reactor arecooled with recycled hydrochloric acid (>30 %)in a subsequent quench system, resulting in sep-aration of byproduct water, removed as ca. 20 %hydrochloric acid containing small amounts ofmethanol. Passage through a heat exchanger ef-fects further cooling and condensation of morewater, aswell asremoval of most of theex-cess HCl. The quenching uid is recovered andsubsequentlyreturnedtothe quenchcircula-tionsystem.Thegaseouscrudeproductisledfrom the separator into a 96 % sulfuric acid col-umn,wheredimethyletherandresidualwater(present in a quantity reective of its partial va-por pressure) are removed, the concentration ofthe acid diminishing to ca. 80 % during its pas-sage through the column. In this step, dimethylether reacts with sulfuric acid to form oniumsaltsandmethylsulfate.Itcanbedrivenoutlater by further dilution with water. It is advan-tageous to use the recovered sulfuric acid in theproduction of fertilizers (superphosphates) or todirect it to a sulfuric acid cleavage facility.Dry, crude monochloromethane is subse-quentlycondensedandworkedupina high-pres-sure (2 MPa, 20 bar) distillation column to givepureliquidmonochloromethane. Thegaseousproduct emerging from the head of this column(CH3Cl +HCl), along with the liquid distillationresiduetogethermakingupca.5 15 %ofthe monochloromethane product mixture canbe recovered for introduction into an associatedmethane chlorination facility. The overall yieldof the process, calculated on the basis of meth-anol, is ca. 99 %.The commonly used catalyst for vapor-phasehydrochlorinationofmethanol is-aluminumoxide with an active surface area of ca. 200 m2/g.Chlorinated Hydrocarbons 13Figure 7. Production of monochloromethane by methanol hydrochlorinationa) Heat exchangers; b) Heater; c) Multiple-tube reactor; d) Quench system; e) Quench gas cooler; f) Quenching uid tank;g) Sulfuric acid column; h) CH3Cl condensation; i) Intermediate tank; j) CH3Cl distillation columnCatalystsbasedonsilicateshavenotachievedany technical signicance. Catalyst aging can beascribed largely to carbon deposition. Byprod-uct formation can be minimized and catalyst lifeconsiderably prolonged by doping the catalystwith various components and by introduction ofspecic gases (O2) into the reaction components[35]. The life of the catalyst in a production fa-cility ranges from about 1 to 2 years.Liquid-Phase Hydrochlorination. Theonce commonliquid-phase hydrochlorinationof methanol using 70 % zinc chloride solutionat 130 150Cand modest pressure is currentlyof lesser signicance. Instead, new productiontechniques involving treatment of methanol withhydrogenchloride inthe liquidphase without theaddition of catalysts are becoming preeminent.The advantage of these methods, apart from cir-cumventing the need to handle the troublesomezinc chloride solutions, is that they utilize aque-ous hydrochloric acid, thus obviating the needfor an energy-intensive hydrochloric acid distil-lation. The disadvantage of the process, whichisconductedat 120 160C, isitsrelativelylowyieldonaspace timebasis, resultinginthe need for large reaction volumes [36 38].Other Processes. Other techniques for pro-ducingmonochloromethaneareof theoreticalsignicance, but are not applied commercially.Monochloromethane is formed when a mix-ture of methane and oxygen is passed into theelectrolytes of analkali chloride electrolysis[39]. Treatment of dimethyl sulfatewithalu-minumchloride[40]orsodiumchloride[41]results in the formation of monochloromethane.Methane reacts with phosgene at 400C to giveCH3Cl [42]. The methyl acetate methanol mix-ture that arises during polyvinyl alcohol synthe-sis can be converted to monochloromethane withHCl at 100Cin the presence of catalysts [43]. Ithas also been suggested that monochlorometh-ane could be made by the reaction of methanolwith the ammonium chloride that arises duringsodium carbonate production [44].The dimethyl ether which results frommethylcellulose manufacture can be reactedwith hydrochloric acid to give monochlorometh-ane [45]. The process is carriedout at 80 240Cunder sufcient pressuresothat wa-terremainsasaliquid. Similarly, cleavageofdimethyl etherwithantimonytrichloridealsoleads to monochloromethane [46].Inmethanolysisreactionsforthemanufac-tureofsilicones, monochloromethaneisreco-vered and then reintroduced into the process ofsilane formation [47]:Si+2CH3ClSiCl2(CH3)2(11)1.3.3. Production of Dichloromethane andTrichloromethaneThe industrial synthesis of dichloromethane alsoleads to trichloromethane and small amounts of14 Chlorinated Hydrocarbonstetrachloromethane, asshowninFigure4andFigure 5. Consequently, di- and trichlorometh-ane are prepared commercially in the same fa-cilities. In order to achieve an optimal yield ofthese products and to ensure reliable tempera-ture control, it is necessary to work with a largemethane and/or monochloromethane excess rel-ative to chlorine. Conducting the process in thisway also enables the residual concentration ofchlorinetobekept inthefullyreactedprod-uct at an exceptionally low level ( 98 % based on chlo-rine.Other Processes. Oxychlorination as a wayof producing tetrachloromethane (as well as par-tiallychlorinatedcompounds) has repeatedlybeen the subject of patent documents [80 82],particularlysinceit leadstocompleteutiliza-tionof chlorinewithout anyHCl byproduct.Pilot-plant studies using uidized-bed technol-ogy have not succeeded in solving the problemof the high rate of combustion of methane. Onthe other hand the Transcat process, a two-stageapproach mentioned in page 13 and embodyingfusedcoppersalts, canbeviewedmoreposi-tively.Direct chlorination of carbon to tetrachloro-methane is thermodynamically possible at atmo-spheric pressure below 1100 K, but the rate ofthe reaction is very low because of the high acti-vation energy (lattice energy of graphite). Sulfurcompounds have been introduced as catalysts inthese experiments. Charcoal can be chlorinatedChlorinated Hydrocarbons 21Figure 10. Production of tetrachloromethane by stepwise chlorination of methane (Hoechst process)a) Reactor; b) Cooling; c) First condensation (air); d) Second condensation (brine); e) Crude product storage vessel;f) Degassing/dewatering column; g) Intermediate tank; h) Light-end column; i) Column for pure CCl4; j) Heavy-end column;k) HCl stream for hydrochlorination; l) Adiabatic HCl absorption; m) Vapor condensation; n) Cooling and phase separation;o) Off-gas coolerto tetrachloromethane in the absence of catalystwith a yield of 17 %in one pass at 900 to 1100 Kand 0.3 2.0 MPa (3 20 bar) pressure. None ofthese suggested processes has been successfullyintroducedonanindustrialscale.Areviewofdirect chlorination of carbon is found in [83].In this context it is worth mentioning the dis-mutation of phosgene2COCl2CCl4+CO2another approach which avoids the formation ofhydrogen chloride. This reaction has been stud-ied by Hoechst [84] and occurs in the presenceof 10 mol%tungsten hexachloride and activatedcharcoal at 370 to 430 C and a pressure of 0.8MPa. The process has not acquired commercialsignicance because the recovery of the WCl6is very expensive.1.4. Quality Specications1.4.1. Purity of the Commercial Productsand Their StabilizationThestandardcommercial gradesofall ofthechloromethanes are distinguished by their highpurity (>99.9 wt %). Dichloromethane, the sol-vent with the broadest spectrum of applications,is also distributed in an especially pure form (>99.99 wt %) for such special applications as theextraction of natural products.Monochloromethane and tetrachlorometh-ane do not require the presence of any stabilizer.Dichloromethane and trichloromethane, on theother hand, are normally protected fromadverseinuencesofairandmoisturebytheadditionof small amountsof efcient stabilizers. Thefollowing substances in the listed concentrationranges are the preferred additives:Ethanol 0.1 0.2 wt %Methanol 0.1 0.2 wt %Cyclohexane 0.01 0.03 wt %Amylene 0.001 0.01 wt %Othersubstanceshavealsobeendescribedas being effective stabilizers, including phenols,amines, nitroalkanes, aliphatic and cyclic ethers,epoxides, esters, and nitriles.Trichloromethane of a quality correspondingtothat speciedintheDeutscheArzneibuch,8th edition (D.A.B. 8), is stabilized with 0.6 1 wt % ethanol, the same specications as ap-pear in the British Pharmacopoeia (B.P. 80). Tri-22 Chlorinated Hydrocarbonschloromethane is no longer included as a sub-stance in the U.S. Pharmacopoeia, it being listedonly in the reagent index and there without anyspecications.1.4.2. AnalysisTable6liststhoseclassical methodsfortest-ingthepurityandidentityofthechlorometh-anes that are most important to both producersand consumers. Since the majority of these aremethods with universal applicability, the corre-spondingDeutscheIndustrieNorm(DIN)andAmerican Society for the Testing of Materials(ASTM) recommendations are also cited in theTable.Table 6. Analytical testing methods for chloromethanesParameter MethodDIN ASTMBoiling range 51 751 D 1078Density 51 757 D 2111Refraction index 53 491 D 1218Evaporation residue 53 172 D 2109Color index (Hazen) 53 409 D 1209Water content (K. Fischer) 51 777 D 1744pH value in aqueous extract D 2110Apart fromthese test methods, gas chro-matographyisalsoemployedforqualitycon-trol bothinthe productionandshipment ofchloromethanes. Gaschromatographyisespe-cially applicable to chloromethanes due to theirlowboiling point. Even a relatively simple chro-matographequippedonlywithathermalcon-ductivity (TC) detector can be highly effectiveat detecting impurities, usually with a sensitivitylimit of a few parts per million (mg/kg).1.5. Storage, Transport, and HandlingDrymonochloromethaneisinert withrespecttomostmetals,thuspermittingtheirpresenceduring its handling. Exceptions to this general-ization, however, are aluminum, zinc, and mag-nesium, as well as their alloys, rendering theseunsuitablefor use. Thusmost vesselsfor thestorage and transport of monochloromethane arepreferentially constructed of iron and steel.Since it is normally handled as a com-pressedgas, monochloromethanemust, intheFederal Republic of Germany, be stored in ac-cord with Accident Prevention Regulation (Un-fallverh utungsvorschrift, UVV) numbers 61 and62bearingthetitleGasesWhichAreCom-pressed, Liquied, or DissolvedUnder Pres-sure (Verdichtete, ver ussigte, oder unterDruck gel oste Gase) and issued by the TradeFederationoftheChemicalIndustry(Verbandder Berufsgenossenschaften der chemischen In-dustrie). Additional guidelines are providedby general regulations governing high-pressurestoragecontainers.Storedquantitiesinexcessof 500 t also fall within the jurisdiction of theEmergency Regulations (St orfallverordnung) ofthe GermanFederal lawgoverningemissionpro-tection.Gas cylinders with a capacity of 40, 60,300, or 700kgaresuitablefor thetransportof smaller quantities of monochloromethane.Shut-off valves on such cylinders must be left-threaded. Larger quantities are shipped in con-tainers, railroad tank cars, and tank trucks, thesegenerally being licensed for a working pressureof 1.3 MPa (13 bar).The three liquid chloromethanes are also nor-mallystoredandtransportedinvessels con-structed of iron or steel. The most suitable ma-terial for use with products of very high purity isstainless steel (material no. 1.4 571). The use instorage and transport vessels of aluminum andotherlight metalsortheiralloysispreventedby virtue of their reactivity with respect to thechloromethanes.Storage vessels must be protected against theincursion of moisture. This can be accomplishedbyincorporatingintheirpressurereleasesys-tems containers lled with drying agents such assilica gel, aluminum oxide, or calcium chloride.Alternatively, the liquids can be stored under adry,inertgas.Becauseofitsverylowboilingpoint,dichloromethaneissometimesstoredincontainersprovidedeitherwithexternalwatercooling or with internal cooling units installedin their pressure release systems.Strict specications withrespect tosafetyconsiderationsareappliedtothestorageandtransfer of chlorinated hydrocarbons in order toprevent spillage andoverlling. Illustrative is thedocument entitled Rules Governing FacilitiesfortheStorage, Transfer, andPreparationforChlorinated Hydrocarbons 23Shipment of Materials Hazardous to Water Sup-plies(Verordnungf urAnlagenzumLagern,Abf ullen und Umschlagen wassergef ahrdenderStoffe, VAwS). Facilities for this purpose mustbe equipped with the means for safely recover-ing and disposing of any material which escapes[94].Shipment of solvents normally entails the useof one-waycontainers (drums, barrels) madeof steel andif necessarycoatedwithprotec-tive paint. Where product quality standards areunusuallyhigh, especiallyasregardsminimalresidue on evaporation, stainless steel is the ma-terial of choice.Largerquantitiesareshippedincontainers,railroadtankcars, tanktrucks, andtankersofboth the transoceanic and inland-waterway va-riety. So that product specications may be metfor material long in transit, it is important duringinitial transfer to ensure high standards of purityand the absence of moisture.Rules for transport by all of the various stan-dardmodes havebeenestablishedonanin-ternational basisintheformofthefollowingagreements: RID, ADR, GGVSee, GGVBinSch,IATA-DGR. The appropriate identicationnum-bers and warning symbols for labeling as haz-ardous substances are collected in Table 7.Table 7. Identication number and hazard symbols ofchloromethanesProduct Identication Hazard symbolnumberMonochloromethane UN 1063 H (harmful)IG (inammablegas)Dichloromethane UN 1593 H (harmful)Trichloromethane UN 1888 H (harmful)Tetrachloromethane UN 1846 P (poison)The use and handling of chloromethanes bothbyproducers andbyconsumers of thesubstances and mixtures containing themaregovernedintheFederalRepublicofGermanyby regulations collected in the February 11, 1982version of the Rules Respecting Working Mate-rials (Arbeitsstoff-Verordnung). To some ex-tent, at least, these have their analogy in otherEuropean countries as well. Included are stipu-lationsregardingthelabelingofthepuresub-stancesthemselvesaswell asofpreparationscontaining chloromethane solvents. The centralauthorities of the various industrial trade organi-zations issue informational and safety brochuresfor chlorinated hydrocarbons, and these shouldbe studied with care.The standard guidelines for handling mono-chloromethane as a compressed gas are thePressure Vessel Regulation (Druckbeh alter-Verordnung) of February 27, 1980, with the re-lated Technical Rules for Gases (TechnischeRegeln Gase, TRG) and the Technical Rulesfor Containers (Technische Regeln Beh alter,TRB), as well as Accident Prevention Guide-line 29 Gases (Unfallverh utungsvorschrift[UVV] 29, Gase).ForMAKvalues, TLVvalues, andconsid-erationsconcerningthetoxicologyseeChap.10. Theecologyandtheecotoxicologyofthechloromethanes are described in Chapter 10.1.5.1.6. Behavior of Chloromethanes in theEnvironmentChloromethanesareintroducedintotheenvi-ronment frombothnatural andanthropogenicsources. Theyare foundinthe lower atmosphere,and tetrachloromethane can even reach intothe stratosphere. Trichloromethane andtetra-chloromethanecanbedetectedinmanywatersupplies.The chloromethanes, like other halogenatedhydrocarbons, are viewedas water contami-nants. Thus, they are found in both national andinternational guidelines related to water qualityprotection [85, 86].Therearefundamentalreasonsforneedingtorestrictchlorocarbonemissionstoanabso-lute minimum. Proven methods for removal ofchloromethanesfromwastewater, off-gas, andresidues areVapor stripping with recyclingAdsorptiononactivatedcharcoal andrecy-clingRecovery by distillationReintroduction into chlorination processes[87]Combustion in facilities equipped with offgascleanup24 Chlorinated HydrocarbonsTable 8. Atmospheric concentration of chloromethanes (in 1010vol.%) [90]Compound Continents Oceans Urban areasCH3Cl 530 . . . 1040 1140 . . . 1260 834CH2Cl236 35 300C), theyaresusceptibletothe eliminationof hydrogenchloride. Inthepresence of light and oxygen, oxidation occursyielding phosgene, carbon oxides, and acetyl orchloroacetyl chlorides. The latter easily hydro-lyzewithtracesofmoistureformingthecor-responding chloroacetic acids, which are well-knownas stronglycorrosive agents. Topre-vent this unwanted decomposition, most indus-trially used chlorinated hydrocarbons are stabi-lized with acid acceptors such as amines, unsat-uratedhydrocarbons, ethers, epoxidesorphe-nols, antioxidants, and other compounds able toinhibit free radical chain reactions. Longer stor-age periods and use without appreciable effecton tanks and equipment is then possible.Of all chlorinated ethanes, approxi-mately half are of industrial importance.Monochloroethane (ethyl chloride) is an inter-mediate in the production of tetraethyllead andiswidelyusedasanethylatingagent. 1,2-Di-chloroethane has by far the highest productionrates. It isanintermediatefortheproductionof 1,1,1-trichloroethane and vinyl chloride (seepage 43 and 3.1.3.2), but it is also used in syn-Chlorinated Hydrocarbons 27Table 12. Demand and use pattern of chloromethanes (1983)Western United JapanEurope StatesMonochloromethane 230 000 t 250 000 t 50 000 tSilicone 52 % 60 % 83 %Tetramethyllead 12 % 15 % Methylcellulose 15 % 5 % 1 %Other methylation reactions, e.g., tensides,pharmaceuticals ca. 21 % ca. 20 % ca. 16 %Dichloromethane 210 000 t 270 000 t 35 000 tDegreasing and paint remover 46 % 47 % 54 %Aerosols 18 % 24 % 19 %Foam-blowing agent 9 % 4 % 11 %Extraction and other uses 27 % 25 % 16 %Trichloromethane 90 000 t 190 000 t 45 000 tCFC 22 production 78 % 90 % 90 %Other uses, e.g., pharmaceuticals, intermediate 22 % 10 % 10 %Tetrachloromethane 250 000 t 250 000 t 75 000 tCFC 11/12 production 94 % 92 % 90 %Special solvent for chemical reactions 6 % 8 % 10 %thetic applications (e.g., polyfunctional amines)and as a fuel additive (lead scavenger).Table 13. Physical properties of chlorinated ethanesCompound Boiling point Relative(at 101 kPa), C density, d204Monochloroethane 12.3 0.92401,1-Dichloroethane 57.3 1.17601,2-Dichloroethane 83.7 1.23491,1,1-Trichloroethane 74.1 1.32901,1,2-Trichloroethane 113.5 1.44321,1,1,2-Tetrachloroethane 130.5 1.54681,1,2,2-Tetrachloroethane 146.5 1.5958Pentachloroethane 162.0 1.6780Hexachloroethane mp 186 187 2.09401,1,1-Trichloroethane, trichloroethylene,(seeSection3.4)andtetrachloroethylene(seeSection 3.5) are important solvents widely usedin dry cleaning, degreasing, and extraction pro-cesses.Theotherchlorinatedethaneshavenoim-portant end uses. They are produced as interme-diates(e.g.,1,1-dichloroethane)orareformedas unwanted byproducts. Their economical con-version into useful end products is achieved ei-ther by cracking tetrachloroethanes yield tri-chloroethylene or more commonly by chlori-nolysis, which converts them into carbon tetra-chloride and tetrachloroethylene (see page 76 ).Basic feedstocks for the production of chlo-rinated ethanes and ethylenes (see Chap. 3) areFigure 11. Vapor pressure as a function of temperature forchlorinated hydrocarbonsethane or ethylene and chlorine (Fig. 12). Theavailability of ethylene fromnaphtha feedstockshas shifted the production of chlorinated C2 hy-drocarbons during the past three decades in theWestern World from the old carbide acetylene vinyl chloride route toward the ethylene route.Withthedramaticincreaseof naphthapricesduring the past decade, the old carbide route hasregained some of its attractiveness [106]. Eventhough a change cannot be justied presently in28 Chlorinated HydrocarbonsFigure 12. Chlorinated hydrocarbons from ethane and ethylene (simplied)most countries, it could offer an alternative forcountries where cheap coal is readily available.Theuseofethanolderivedfrombiomassasastarting material could likewise also be consid-ered [107, 108].Inafewcases, ethaneis useddirectlyasahydrocarbonfeedstock. Thisdirectethaneroute could offer an attractive alternative in somecases, because of the substantial cost differencesbetweenethaneandethylene. Itbecomesevi-dent whynumerous patents onethane-basedpro-cesses have been led. However, the major costadvantage of such processes is the reduced cap-ital investment for cracker capacity. The directethane route must certainly be considered for fu-ture grass-root-plants, but at present, the conver-sions and selectivities obtained seem not to jus-tify the conversion of existing plants if crackercapacity is available.Less is known about the situation in Easternblock countries. The available information indi-cates, however, that in some Eastern Europeancountries the acetylene route is still used.Because chlorine is needed as a second feed-stock, most plants producing chlorinated hydro-carbons are connected to a chlor-alkali electrol-ysisunit. Thehydrocarbonfeedstockiseithersuppliedfromanearbycracker, typical forU.S. gulf coast, or via pipelines and bulk shiptransports. The chlorine value of the hydrogenchloride produced as a byproduct in most chlo-rination processes can be recovered by oxychlo-rination techniques, hydrochlorination reactions(for synthesis of methyl and ethyl chloride) or,lesseconomically byaqueousHCl elec-trolysis.Aminorbuthighlyvaluableoutletisultrapure-grade anhydrous HCl used for etchingin the electronic industry.Although most unwanted byproducts can beused as feed for the chlorinolysis process [109](see page 76 ), the byproducts of this process,mostly hexachloroethane, hexachlorobutadiene,andhexachlorobenzenetogetherwithresidualtars from spent catalysts and vinyl chloride pro-duction, represent a major disposal problem. Theoptimal ecological solution is the incineration ofthese residues at a temperature above 1200 C,which guarantees almost complete degradation.Presently, incinerationisperformedat seaonspecial ships [110] without HCl scrubbing or onsite with subsequent HCl or chlorine recovery.The aqueous HCl recovered can then be used forChlorinated Hydrocarbons 29pHadjustment in biological efuent treatment orbrine electrolysis.Due to their unique properties, the market forchlorinated C2hydrocarbons has shown excel-lent growth over the past 30 years and reached itsmaximum in the late 1970s. With increasing en-vironmental consciousness, the production rateof some chlorinated hydrocarbons such as ethylchloride, trichloroethylene(seepage73), andtetrachloroethylene (see 3.5.4) will in the longrun decrease due to the use of unleaded gasoline,solvent recoverysystems, andpartial replace-ment by other solvent and extraction chemicals.However, newformulationsforgrowingmar-kets such as the electronic industry, the availabil-ity of ecologically safe handling systems, know-how in residue incineration, and the difculty innding superior replacements causing fewerproblems guaranteechlorinatedethanesandethylenes a long-term and at least constant mar-ket share.2.1. MonochloroethaneMonochloroethane (ethyl chloride) [75-00-3] isthoughttobetherstsynthesizedchlorinatedhydrocarbon. It was produced in 1440 by Valen-tine by reacting ethanol with hydrochloric acid.Glauberobtaineditin1648byreactingetha-nol (spirit of wine) with zinc chloride. Becauseof the growing automotive industry in the early1920s, monochloroethane became an importantbulk chemical. Its use as a starting material forthe production of tetraethyl-lead (Lead Com-pounds) initiated a signicant increase in ethylchlorideproductionandisstillitsmajorcon-sumer. Thetrendtowardunleadedgasolineinmost countries, however, will inthelongrunlead to a signicant decrease in production.2.1.1. Physical PropertiesMr64.52mp 138.3 Cbp at 101.3 kPa 12.3 C of the liquid at 0 C 0.924 g/cm3 of the vapor at 20 C 2.76 kg/m3n20D1.3798Vapor pressure at50 C 4.480 kPa20 C 25.090 kPa10 C 40.350 kPa0 C 62.330 kPa+ 10 C 92.940 kPa+ 20 C 134.200 kPa+ 30 C 188.700 kPa+ 60 C 456.660 kPa+ 80 C 761.100 kPaHeat of formation (liquid) H0298133.94kJ/molSpecic heat at 0 C 1.57 kJ kg1K1Heat of evaporation at 298 K 24.7 kJ/molCritical temperature 456 KCritical pressure 5270 kPaViscosity (liquid, 10 C) 2.79104PasViscosity (vapor, bp) 9.3105PasThermal conductivity (vapor) 1.09 103Wm1K1Surface tension (air, 5 C) 21.18103N/mDielectric constant (vapor, 23.5 C) 1.0129Flash point (open cup) 43 CIgnition temperature 519 CExplosive limits in air 3.16 15 vol%monochloroethaneSolubility in water at 0 C 0.455 wt %Solubility of water in monochloroethane at 0 C 0.07 wt %Atambienttemperature,monochloroethaneis a gas with an etheral odor.Monochloroethane burns with a green-edgedame.Combustion products are hydrogen chloride,carbon dioxide, and water.Binary azeotropic mixtures of monochloro-ethane have been reported [111]. The data, how-ever, have not been validated.2.1.2. Chemical PropertiesMonochloroethane has considerable thermalstability. Onlyat temperaturesabove400C,considerable amounts of ethylene and hydrogenchloride are formed due to dehydrochlorination[111]a. This decomposition can be catalyzed bya variety of transition metals (e.g. Pt), transition-metal salts, and high-surface area oxides such asalumina and silica. Catalyzed decomposition iscomplete at temperatures slightly above 300Caccording to the thermodynamic equilibrium.At ambient atmospheric conditions, both,hydrolysis(toethanol)andoxidation(toacet-aldehyde) are moderate.30 Chlorinated HydrocarbonsAt temperatures up to 100 C, monochloro-ethane shows no detrimental effect on moststructural materials if kept dry. Contact with alu-minum, however, shouldbeavoidedunderallcircumstances for safety reasons.Monochloroethane has the highest reactivityof all chlorinated ethanes. It is mainly used asanethylatingagent inGrignard- andFriedel-Crafts-typereactions, forether, thioether, andamine synthesis. Halogene exchange [111]b anduorination is also possible [111]c.2.1.3. ProductionMonochloroethane can be produced by a varietyof reactions. Only two are of industrial impor-tance: the hydrochlorination of ethylene and thethermal chlorination of ethane.Hydrochlorination of Ethylene. Exother-mic hydrochlorination of ethylene can be carriedout in either the liquid or gas phase.C2H4+HClC2H5ClH = 98kJ/molThe liquid-phase reaction is carried out mostlyat near ambient temperatures (10 50 C) andmoderate pressure (0.1 0.5 MPa) in a boiling-bed type reactor. The heat of reaction is used tovaporize part of the monochloroethane formed,which in turn is then cooled down, puried, orpartiallyrecycled. Thereactor temperatureiscontrolledbythe recycle ratioandthe feedrate ofthe reactants. Unconverted ethylene and hydro-gen chloride from reux condensers and over-head light end columns are recycled back to thereactor. Sufcientmixingandcatalystcontacttime is achieved through recirculation of the re-actor sump phase. Aluminum chloride in a 0.5 5 wt % concentration is mostly used as a cat-alyst. Apartofitiscontinuouslyorintermit-tentlyremovedviaarecirculationslipstream,together with unwanted high boiling impuritiesconsisting mostly of low molecular mass ethyl-ene oligomers formed in a Ziegler-type reactionof the catalyst with the ethylene feed. New cat-alyst is added to the system either by a hopperas a solid or preferably as a solution after pre-mixing with monochloroethane or monochloro-ethane/ethylene. AgaseousfeedofvaporizedAlCl3hasalsobeensuggested[112]. Asim-plied process diagram is shown in Figure 13;an optimized process has been patented [113].Inotherprocessvariations,theformedmono-chloroethane(sumpphase)iswashedwithdi-luted NaOHto remove catalyst and acid and thendried and distilled. Excess ethylene is recycled.Figure 13. Schematic diagram (simplied) of an ethylenehydrochlorination processa) Reactor; b) Cooler; c) Knock-out drum; d) Light-endcolumns; e) Reboiler; f) Stripper column (heavy ends)Ethylene andHCl yields for hydrochlori-nationarealmost quantitative; selectivitiesof98 99 %have beenreported. InadditiontoAlCl3, other Lewis-acid catalysts, such as FeCl3[114], BiCl3 [116], and GaCl3 [117], have beenpatented. Suggestions to perform the reaction inbenzene or higher boiling hydrocarbons [118],in1,1,2-trichloroethane [119] or tocomplexAlCl3 by nitrobenzene [120] have not found in-dustrial acceptance.The troublesome handling of the catalyst isminimizedwhenethyleneandhydrogenchlo-ride are reacted in the gas phase. Although thereaction equilibrium becomes unfavorable at atemperature above 200C, the process is carriedout at temperatures of 250 450 C in order toachieve sufcient conversion. Ethylene and HClarepreheated, mixed, andsentacrossthecat-alyst, whichcanbeusedasxedoruidizedbed. The chloroethane formed is separated andpuried. Unreacted ethylene and HCl are recy-cled. Selectivities are comparable to those of theliquid-phase process, conversion per pass, how-ever, may not exeed 50 %, so that relatively highrecycle rates are necessary. Because high pres-sure favors the formation of monochloroethane,the reaction is preferably carried out at 0.5 1.5MPa.Chlorinated Hydrocarbons 31Thoriumoxychlorideonsilica[121], pla-tinium on alumina [122], and rare-earth oxideson alumina and silica [123] have been patentedas catalysts.Chlorination of Ethane. Thermal chlorina-tion of ethane for the production of monochloro-ethane canbe usedindustriallyina tandemprocessdevelopedbytheShell Oil Company(Fig. 14) [124]. This process was especially de-signed for a plant in which sufcient ethylenefeedstockcouldonlybesuppliedbyincreas-ingthecrackercapacity. Ethaneandchlorinewere available, but not hydrogen chloride. Forthis feedstock constellation, the tandem processseems advantageous.Figure 14.ProductionofmonochloroethanebytheShellprocess [124]a) Preheater; b) Ethane chlorinator; c) Cooler; d) Lightendtower; e) Crude chloroethane storage; f) Hydrochlorinator;g) CompressorIn the rst stage, ethane and chlorine are re-acted noncatalytically after sufcient preheatingat 400 450 C in an adiabatic reactor. The re-action gases are separated after cooling in a rstmonochloroethane distillation tower. The heavybottomsofthistowercontainingchloroethaneandmorehiglychlorinatedproducts (mostly1,1-dichloroethane and 1,2-dichloroethane) aresent to the purication stage. The overheads con-sistingmainlyof unconvertedethane, hydro-gen chloride, and ethylene are sent to a secondisothermal xed-bedreactor. Before enteringthis reactor, fresh ethylene is added to achieve a1 : 1 ethylene to HCl feed ratio. Even though thetypeofcatalystusedintheisothermalsectionis not described, any of the catalysts mentionedfor gas-phase hydrochlorination in the previoussectioncanbeused. Conversionat thisstageis50 80 %. Theproductsarethenseparatedinasecondtower. Unconvertedethane,ethyl-ene, and hydrogen chloride are recycled to therst reactor. The monochloroethane formed byhydrochlorination is drawn off and puried to-gether with the stream from the rst tower.Even though the recycled ethylene from thehydrochlorinationstepispresent duringther-mal chlorination, the formation of 1,2-dichloro-ethane is insignicant. Because the rst reactionis carried out at high temperatures, chlorine ad-dition to the ethylene double bond is suppressed.The process is balanced by the overall reac-tion equation:C2H6+Cl2C2H5Cl+HClHCl+C2H4C2H5ClA 90 % overall yield for ethane and ethyleneand a 95 % chlorine yield to monochloroethaneare reported.Monochlorinationof ethaneisfavoredbe-causeethanechlorinationisfour timesfasterthan the consecutive chlorination of mono-chloroethane to dichloroethanes.Major byproducts from the chlorination stepare 1,1-, 1,2-dichloroethane and vinyl chloride.Toachieveahighselectivityformonochloro-ethane, a high ethane surplus preferably a 3 5-fold excess over chlorine [125, 126] andgoodmixingisrequired.Insufcientheatdis-sipationmayenhancecrackingandcoking. Athermal chlorination reactor providing thoroughpremixing and optimal heat transfer by meansof a uidized bed has been described in [126].Other patents claimcontact of the reaction gaseswith metal chlorides [127] or graphite [128].The photochemical chlorination of ethane de-scribed in several patents [129] is less important,because it is difcult to implement in large vol-ume plants and offers no major advantages overthe thermal process.Monochloroethane as a Byproduct of theOxy-EDCProcess. Monochloroethane is a ma-jor byproduct in the Oxy-EDCprocess (see page35), in which it is formed by direct hydrochlo-rinationof ethylene. It canbecondensedorscrubbed fromthe light vent gases and recoveredafter further purication.32 Chlorinated HydrocarbonsMonochloroethane from Ethanol. The es-terication of ethanol with HCl is possible in theliquid phase by using ZnCl2or similar Lewis-acidcatalysts at 110 140C[130]. Similartotheproductionofmonochloromethane(see1.3.2), thereactioncanalsobecarriedout inthe gas phase by using -alumina [131], ZnCl2and rare earth chlorides on carbon [132] or zeo-lites[133]ascatalysts.Atthepresentethanolprices, theseproceduresareprohibitive. Withsome modication, however, they can offer out-lets for surplus byproducts such as ethyl acetatefromPVAproduction which can be converted tomonochloroethane by HCl using a ZnCl2/silicacatalyst [134].OtherSyntheticRoutes toMonochloro-ethane. Non-commercial routes to mono-chloroethane consist of electrolytic chlorinationof ethane in melts [135], reactions with diethylsulfates [136], metathesis of 1,2-dichloroethane[137], hydrogenationof vinyl chloride[138],and conversion of diethyl ether [139]. The oxy-chlorination of ethane is discussed later in thisChapter.Small amounts of monochloroethane areformedduringthereactionof synthesisgas chlorine mixtures over Pt/alumina [140] andmethane chlorine mixtures in the presence ofcation-exchange resins complexedwithTaF5[141].2.1.4. Uses and Economic AspectsMonochloroethanebecameindustriallysignif-icant as a result of the developing automo-tive industry. It is the starting material fortetraethyllead, the most commonly used octanebooster. IntheUnitedStates, about 80 90 %and in Europe ca. 60 %of the monochloroethaneproductionisusedfortheproductionoftetra-ethyl lead.Production has already been cut signicantlydue to the increased use of unleaded fuel for en-vironmentalreasons. U.S. projectionsindicatean average annual decline of ca. 10 % per year.With some delay, the same trend can also be pre-dicted for Western Europe.Minor areas of use for monochloroethane arethe production of ethyl cellulose, ethylating pro-cessesfor nechemical production, useasablowingagent andsolvent forextractionpro-cesses for the isolation of sensitive natural fra-grances.Production in 1984 in the Western World wasabout 300 000 t. Almost all processes in use atpresent are ethylene based.2.2. 1,1-Dichloroethane1,1-Dichloroethane [75-34-3] is the less impor-tant of the two dichloroethane isomers.It occurs oftenas anunwantedbyprod-uct in many chlorination and oxychlorinationprocesses of C2 hydrocarbons.The most important role of 1,1-dichloro-ethaneisasanintermediateintheproductionof 1,1,1-trichloroethane.Other uses are negligible.2.2.1. Physical PropertiesMr98.97mp 96.6 Cbp at 101.3 kPa 57.3 C at 20 C 1.176 g/cm3n20D1.4164Vapor pressure at0 C 9.340 kPa10 C 15.370 kPa20 C 24.270 kPa30 C 36.950 kPaHeat of formation (liquid)H0298160.0 kJ/molSpecic heat at 20 C 1.38 kJ kg1K1Heat of evaporation at 298K30.8 kJ/molCritical temperature 523 KCritical pressure 5070 kPaViscosity at 20 C 0.38103Pa sSurface tension at 20 C 23.5103N/mDielectric constant at 20C10.9Flash point (closed cup) 12 CIgnition temperature 458 CExplosive limits in air at 25C5.4 11.4 vol%1,1-dichloroethaneSolubility in water at 20 C0.55 wt %Solubility of water in1,1-dichloroethane at 20C0.97 wt %1,1-Dichloroethane is a colorless liquid. It isreadily soluble in all liquid chlorinated hydro-carbons and in a large variety of other organicsolvents (ethers, alcohols).Chlorinated Hydrocarbons 33Binary azeotropes are formed with water andethanol: with 1.9 % water, bp 53.3 C (97 kPa)and with 11.5 % ethanol, bp 54.6C (101 kPa).2.2.2. Chemical PropertiesAt room temperature, 1,1-dichloroethane is ad-equately stable. Cracking to vinyl chloride andhydrogen chloride takes place at elevated tem-peratures.However,comparedtootherchlori-nated C2hydrocarbons, the observed crackingratesaremoderate. Thisreactioncanbepro-moted by traces of chlorine and iron [142]. 2,3-Dichlorobutane is often found as a dimeric by-product of decomposition.1,1-Dichloroethane was alsofoundtoen-hance 1,2-dichloroethane cracking when addedin lower concentrations (10 wt %) [143].Corrosionrates for dry1,1-dichloroethaneare marginal, increase however, with water con-tent andtemperature. Aluminumiseasilyat-tacked.In the presence of water or in alkaline solu-tion, acetaldehyde is formed by hydrolysis.2.2.3. ProductionTheoretically 1,1-dichloroethane can be pro-duced by three routes:1) Addition of HCl to acetylene:2) Thermal or photochemical chlorination ofmonochloroethane:3) Addition of HCl to vinyl chloride:For thesynthesis of 1,1-dichloroethaneasanintermediateintheproductionof1,1,1-tri-chloroethaneonlythelatterrouteisimportantand industrially used.1,1-Dichloroethane via the 1,2-Di-chloroethane Vinyl Chloride Route. Hydro-gen chloride and vinyl chloride obtained from1,2-dichloroethane cracking see page 58) are re-acted in a boiling-bed-type reactor [144] in thepresence of a Friedel-Crafts catalyst, preferablyferricchloride(FeCl3). 1,1-Dichloroethaneisused as solvent and the temperature ranges from30 to 70C.Depending on the process design, hydrogenchloride can be used in excess to achieve com-plete conversion of the vinyl chloride. The heatof reaction, which differs only slightly from theheat requiredfor1,2-dichloroethanecracking,can be used to distill the 1,1-dichloroethane andrecoverpartoftheenergyinput. Downstreamhydrogen chloride and unconverted vinyl chlo-ride are separated and recycled. If necessary, the1,1-dichloroethane can then be further puriedbydistillation. Duetotheformationofheavybyproducts (vinyl chloride polymers) and deac-tivationofthecatalyst, aslipstreamfromthereactor bottom must be withdrawn and new cat-alyst added.Improvedprocessesusecolumn-typereac-torswithoptimizedheight [145] (hydrostaticpressuretoavoidashingof vinyl chloride!)and recycled 1,1-dichloroethane with intermit-tent cooling stages. In this case, the stoichiomet-ric ratio of hydrogen chloride to vinyl chloride,asobtainedfrom1,2-dichloroethanecracking,can often be used. In such a process, the down-stream distillation equipment can be less com-plexandexpensive, becausealmost completeconversionisachievedandbecausenoexcesshydrogen chloride or the entrained vinyl chlo-ride must be separated. However, the energy re-quirements may be higher because most of theheat of formation must be dissipated by cooling.Both process variations yield between ca. 95and 98 %. Yield losses result through polymer-ization of vinyl chloride. The concentration aswell as the nature of the catalyst determine thissidereaction. Zincchloride(ZnCl2) andalu-minumchloride (AlCl3), which also can be usedas catalysts, promote the formation of high mo-lecular mass byproducts more than ferric chlo-ride (FeCl3) [120, 146]. The removed spent cat-alyst canbeburnedtogether withtheheavybyproductsinanincinerator,iftheventgasesare subsequently scrubbed and the wash liquorappropriately treated. Environmental problems34 Chlorinated Hydrocarbonscaused by the residues are thereby almost elim-inated.1,1-Dichloroethane via the AcetyleneRoute. As with the synthesis of vinyl chlo-ride (see 3.1.3.1), 1,1-dichloroethane can beproduced fromacetylene by adding 2 mol of hy-drogen chloride. For the rst reaction sequencetheformationof vinyl chloride mercurycatalyst is required [147].Because ethylene has become the major feed-stock for chlorinated C2 hydrocarbons, this pro-cess has lost its importance.1,1-Dichloroethane fromEthane. 1,1-Di-chloroethane may also be obtained by ethane orchloroethane chlorination. This chlorination canbe carriedout as thermal chlorination[148], pho-tochlorination, or oxychlorination [149]. Theseprocesses,however,areimpairedbyalackofselectivity and are not used industrially.2.2.4. Uses and Economic AspectsAs mentioned earlier, 1,1-dichloroethane is pri-marily used as a feedstock for the production of1,1,1-trichloroethane.Although several other applications havebeen patented [150], currently 1,1-dichloro-ethane is rarely used for extraction purposes oras a solvent.Basedonestimatedproductiongures of1,1,1-trichloroethane and disregarding otheruses, the total WesternWorldproductionof1,1-dichloroethane is estimated at 200 000 250000 t for 1985.2.3. 1,2-DichloroethaneThe rst synthesis of 1,2-dichloroethane (ethyl-ene dichloride, EDC) [107-06-2] was achievedin 1795.Presently, 1,2-dichloroethane belongs tothose chemicals with the highest productionrates. Averageannual growthratesof >10 %were achieved during the past 20 years.Although these growth rates declined duringthepast several years, inthelongrun1,2-di-chloroethane will maintain its leading positionamong the chlorinated organic chemicals due toits use as starting material for the production ofpoly(vinyl chloride) (Poly(Vinyl Chloride)).2.3.1. Physical PropertiesMr98.97mp 35.3 Cbp at 101.3 kPa 83.7 C at 20 C 1.253 g/cm3n20D1.4449Vapor pressure at0 C 3.330 kPa20 C 8.530 kPa30 C 13.300 kPa50 C 32.000 kPa70 C 66.650 kPa80 C 93.310 kPaHeat of formation (liquid)H298157.3 kJ/molSpecic heat (liquid, at 20 C) 1.288 kJ kg1K1Heat of evaporation at 298 K 34.7 kJ/molCritical temperature 563 KCritical pressure 5360 kPaViscosity at 20 C 0.84103Pa sSurface tension at 20 C 31.4103N/mCoefcient of cubical expansion(0 30 C) 0.00116 K1Dielectric constant 10.5Flash point (closed cup) 17 CFlash point (open cup) 21 CIgnition temperature (air) 413 CExplosive limits in air at 25 C 6.2 15.6 vol%1,2-dichloroethaneSolubility in water at 20 C 0.86 wt %Solubility of water in1,2-dichloroethane at 20 C 0.16 wt %1,2-Dichloroethane is a clear liquid at ambi-ent temperature, which is readily soluble in allchlorinated hydrocarbons and in most commonorganic solvents.Binaryazeotropes with1,2-dichloroethaneare listed in Table 14.Table 14. Binary azeotropes formed by 1,2-dichloroethanewt % Component Azeotropeboiling point(101.3 kPa),C18.0 2-propen-1-ol 79.938.0 formic acid 77.437.0 ethanol 70.319.5 1,1-dichloroethane 72.043.5 2-propanol 74.732.0 methanol 61.019.0 1-propanol 80.779.0 tetrachloromethane 75.618.0 trichloroethylene 82.98.2 water 70.5Chlorinated Hydrocarbons 352.3.2. Chemical PropertiesPure 1,2-dichloroethane is sufciently stableevenatelevatedtemperaturesandinthepres-ence of iron. Above 340C, decomposition be-gins, yielding vinyl chloride, hydrogen chloride,andtraceamountsofacetylene[111]a, [151].This decompositionis catalyzedbyhalogens andmorehighlysubstitutedchlorinatedhydrocar-bons [152].Long-termdecompositionat ambient tem-perature caused by humidity and UV light canbe suppressed by addition of stabilizers, mostlyamine derivatives. Oxygen decient burning andpyrolytic and photooxidative processes convert1,2-dichloroethane to hydrogen chloride, carbonmonoxide, and phosgene.Bothchlorineatomsof 1,2-dichloroethanecan undergo nucleophilic substitution reactions,which opens routes to a variety of bifunctionalcompounds such as glycol (by hydrolysis or re-actionwithalkali), succinicaciddinitrile(byreactionwithcyanide), orethyleneglycol di-acetate (by reaction with sodium acetate). Thereaction with ammonia to ethylenediamine anduse of 1,2-dichloroethane for the production ofpolysuldes is of industrial importance.Iron and zinc do not corrode when dry 1,2-di-chloroethane is used, whereas aluminum showsstrong dissolution. Increased water content leadstoincreasedcorrosionof ironandzinc; alu-minum, however, corrodes less [153].2.3.3. Production1,2-Dichloroethane is industrially produced bychlorination of ethylene.Thischlorinationcaneitherbecarriedoutby using chlorine (direct chlorination) or hydro-gen chloride (oxychlorination) as a chlorinatingagent.In practice, both processes are carried out to-gether and in parallel because most EDC plantsareconnectedtovinyl chloride(VCM) unitsand the oxychlorination process is used to bal-ance the hydrogenchloride fromVCMpro-duction(seepage62andFig.24).Dependingon the EDC/VCM production ratio of the inte-grated plants, additional surplus hydrogen chlo-ride from other processes such as chlorinolysis(perchloroethylene and tetrachloromethane pro-duction, see page 18 and Section 3.5.3) or 1,1,1-trichloroethane (see page 43) can be fed to theoxychlorination stage for proper balancing andchlorine recovery.The use of ethane as a starting material, al-though the subject of numerous patent claims,is still in the experimental stage. It could offereconomic advantages if the problems related tocatalyst selectivity, turnover, and long-term per-formance are solved.Direct Chlorinationinthe Ethylene LiquidPhase.. In the direct chlorination process, ethyl-ene and chlorine are most commonly reacted inthe liquid phase (1,2-dichloroethane for temper-ature control) and in the presence of a Lewisacidcatalyst, primarily iron(III) chloride:Toavoidproblemsinproduct purication,the use of high-purity ethylene is recommended.Especially its propane/propene content must becontrolledinordertominimizetheformationofchloropropanesandchloropropenes, whichare difcult to separate from 1,2-dichloroethanebydistillation.Puriedliquidchlorineisusedto avoid brominated byproducts. Oxygen or airisoftenaddedtothereactants, becauseoxy-gen was found to inhibit substitution chlorina-tion, yielding particularly 1,1,2-trichloroethaneand its more highly chlorinated derivatives [154,155]. Through this and an optimized reactor de-sign, the use of excess ethylene is no longer re-quired to control byproduct formation. In mostcases, thereactantsareaddedinthestoichio-metricchlorine/ethyleneratioorwithaslightexcess of chlorine. This simplies the process-ingequipmentbecauseanexcessofethylene,which was often used in the past [156], requirescomplicated condensor and post reactor equip-ment to avoid the loss of expensive ethylene inthe off-gas [155, 157].Although several other Lewis-acid catalystswith higher selectivities such as antimony, cop-per, bismuth, tin, and tellurium chlorides [158]have been patented, iron chloride is widely used.Because the reaction selectivities are not depen-dent on the catalyst concentration, it is used ina diluted concentration between ca. 100 mg/kg36 Chlorinated Hydrocarbonsand0.5wt %. Someprocessesuseironllerbodies in the reactor to improve mass and heattransfer or use iron as a construction material.This equipment generates sufcient FeCl3insitu[159].In the liquid-phase reaction, ethylene absorp-tionwasfoundtobetherate-controllingstep[160].In addition to the distinct process modica-tions with which each producer of 1,2-dichloro-ethane has improved his process during the pastyears,twofundamentalprocessvariationscanbe characterized:1) low-temperature chlorination (LTC) and2) high-temperature chlorination (HTC)In the LTC process, ethylene and chlorine re-act in 1,2-dichloroethane as a solvent at temper-atures (ca. 20 70 C) below the boiling pointof 1,2-dichloroethane.The heat of reaction is transferred by exter-nal cooling either by means of heat exchangersinside the reactor or by circulation through ex-terior heat exchangers [161].Thisprocesshastheadvantagethatduetothe lowtemperature, byproduct formation is low.The energyrequirements, however, are consider-ably higher in comparison to the HTC process,becausesteamisrequiredfortherecticationof 1,2-dichloroethane in the purication section.Conversions up to 100 % with chlorine and eth-ylene selectivities of 99 % are possible.In the HTC process, the chlorination reactionis carried out at a temperature between 85 and200 C, mostly, however, at about 100 C. Theheat of reaction is used to distill the EDC. In ad-dition, EDC from the Oxy-EDC process or un-converted EDC from the vinyl chloride sectioncan be added, since the heat of formation equalsthe heat required for vaporization by a factor ofca. 6.By sophisticated reactor design and thoroughmixing conversion, and yields comparable to theLTCprocess may be obtained with considerablylower energy consumption for an integrated DC-Oxy-VCM process [162].Descriptionof theHTCProcess (Fig. 15).Gaseous chlorine andethylene are fedthor-oughly mixed into a reaction tower which is alsosupplied with dry EDC from oxychlorination orrecycled EDC from the VCM section.Figure 15. Simplied DC HTC processa)Reactor; b) Cooler; c) Knock-out drum; d) Heavy-endtower; e) ReboilerThe light ends are drawn off from the headsection, and ethylene is condensed and recycled.In the following condensation section, vinylchloride is separated and can then be processedwithvinyl chloridefromEDCcracking(seepage 58). The remaining vent gas is incinerated.Pure EDC is taken from an appropriate sectionand condensed. In order to maintain a constantcomposition in the reactor sump phase, a slip-stream is continuously withdrawn, from whichthe heavy byproducts are separated by rectica-tion and sent to a recovery stage or incinerated.In some designs, the reactor is separated fromthe distillation tower [164]. In others, two tow-ers are used for light ends/EDCseparation. Solidadsorption has been patented for iron chlorideremoval [165].For optimal heat recovery, crossexchangecan be used for chlorine feed evaporation [166].Due to the relatively low temperatures and an-hydrous conditions, carbon steel equipment canbe used [167].Processdevelopmentsusingcrackinggasesinstead of highly puried ethylene [168] and theuse of nitrosyl chloride [169] as a chlorinatingagent have not found any industrial importance.DirectChlorinationintheGasPhase. Acatalytic gasphase process was patented by theSoci et e Belge de lAzote [170]. Because of thehighly exothermic reaction, adequate dilution isChlorinated Hydrocarbons 37necessary. Several catalysts have been patented[171].Thenoncatalyticchlorineadditionreactionhas been thoroughly studied [172], but is not in-dustriallyused,