z Potassium Industries 2007 2

8/6/2019 z Potassium Industries 2007 2

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Treating Chamber

Flotation Cells

Potassium Industries

Potassium, K

Potassium occurs in nature only in the form of its compounds. It is one of the ten most commonelements in the earths crust. Potassium compounds are obtained almost entirely by the mining of saltdeposits. The more important salt minerals are halite, anhydrite, sylvanite, sylvite, carnallite, andkieserite that were obtained from USA, Canada, Russia and Germany.

In 1807, potassium metal was first isolated using an electrolysis apparatus. When potassium metalreacts with oxygen in dry air, it produces a powerful oxidizing agent, potassium superoxide (K2O).With moisture air, potassium hydroxide is produced.

Manufacturing Processes. Potash ores are treated today by three basic processes:1. Leaching-crystallization (originally cooked in open vessels, an oldest process; vacuum

cooling was introduced in 1918 in the United States)

2. Flotation (introduced in 1935 in the United States)3. Electrostatic treatment (first used on a large scale in the German potash industry in 1974)

Importance and Uses. The most important function of potassium is the activation of more than 80enzymes. It is also integral to a number of other plant processes, translocation of carbohydrates, and

protein synthesis. As a result, potassium deficiencies cause numerous problems from decreasing ratesof photosynthesis to the weakening of straw in grain crops. In addition it has important effects onquality factors of plants.

Economics. The world potash production is amounted to 25.8 x 106 t K2O in 2001. However, potassium chloride is not a versatile potassium source. The more favourable potassium sources forthe production of multi-component fertilizers are potassium sulfate and potassium nitrate.

Compounds of Potassium

Potassium Chloride, KCl

It occurs in many salt deposits mixed with halite and other salt minerals. It is also occurred in naturalsylvite, which is usually opalescent or milky white. When this compound is mixed with magnesiumchloride, they formed the double salt carnallite (KClMgCl26H2O), which is also commonly foundin salt deposits.

Manufacturing and Production. Hot Leaching Process An oldest industrial process used to produce potassium chloride from potash ore (1860). Two different processes are used, depending on thecomposition of the ore:

Ksalts

Carnallite Leach Tank Deslimator Hydroseparator

Separator

Fine KCl

Coarse KCl

Crushed CarnalliteBrine Amine/Starch

Figure 1. Flow Chart of K salts production from carnallite


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1. Syl i it t L i (t

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iti t KCl

N Cl l l i l i t

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2. Hard SaltL achi (sol tions cont in appreciable amounts ofMgCl2 and MgSO4)

Process:1. Potash ore, ground to a fineness of


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2KOH + CO2 K2CO3 + H2O

Steps:1. Solid potassium carbonate is then obtained by crystalli ation (under vacuum and with

cooling) from liquors orin the fluidi ed-bed process.2. Until the hydrate K2CO31.5H2O finally precipitates in the crystalli er after cooling

under vacuum.3. The motherliquoris separated from the crystal suspension in hydrocyclones.

4. Motherliquor centrifuges.5. Motherliquoris then filtered.6. Motherliquorthatis separated is fed backto the process.7. The crystals are dried at ca.110C120C. Impurities such as soda, sulfate, silicic acid,

and iron that concentrate in the mother liquors can be partially removed by removing apartial stream ofthe motherliquor or by drying process.

8. Crystals are calcined at 200C350Cto give 98%100% K2CO3.9. The resulting potassium carbonate is very pure and meets the requirements ifthe process

is operated in appropriate manner.

Steps:1. Aqueous potassium

hydroxide solution is sprayed into afluidi ed-bed reactor from above andexposed to a countercurrent of CO2-containing hot gas.Carboni ation andcalcinations take place in the samereactor.

2. Hard, spherical potassiumcarbonate prills are formed having ahigh packing density.

3. The prills are dischargedand sieved.

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a) CarboniB ation; b) Crude liquor filter; c) Fresh liquortank; d) Mixed liquortank;e1,2) Preliminary evaporation; f) Vacuum/ cooling crystalliB ation (ChemietechnikMesso system);g) Preheater; h) Vapor condenser; i) Vacuum pump; j) Hydrocyclone;k) Centrifuge; l) Centrifugeliquortank; m) Motherliquor filter; n) Motherliquortank; o) Drying/ calcining rotary kiln; p)Cooling device for calcined K2CO3; q) Hydrated potash storage; r) Calcined potash storage.

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4. The coarse grains are ground and returned to the reactor together with the very finegrains, where they act as crystallization seeds.

5. The salable, dust-free, medium grains are cooled and packed. Because no mother liquor isformed, the quality of the potassium carbonate depends on that of the raw materials.

Other processes of manufacturing potassium carbonate were included, yet these processes areuneconomical today because of high energy consumption and poor product quality, and are nolonger used:

1. Amine Process2. Nepheline Decomposition Process

y The mineral nepheline is decomposed with limestone by sintering at 1300C:

(Na, K)2Al2O32SiO2 + 4CaCO3 (Na, K)2OAl2O3+ 2(2CaOSiO2) + 4CO2

The sinter product is leached with a Na2CO3NaOH solution. After filtration, a filter cakeis obtained that is processed to give portland cement and an aluminate solution containingsilicic acid. After precipitation of the silicic acid as alkaline aluminum silicate the purifiedaluminate solution is reacted with carbon dioxide:

2(Na, K)AlO2 + CO2 + 3H2O 2Al(OH)3 + (Na, K)2CO3

3. The magnesia process (Engel Precht process; limited interest):

3(MgCO33H2O) + 2KCl + CO2 2(MgCO3KHCO34H2O) + MgCl2

In hot water the double salt (MgCO3KHCO34H2O) decomposes under pressure intomagnesium carbonate and dissolved potassium carbonate.

4. Le Blanc process:

K2SO4 + CaCO3 + 2C CaS +K2CO3 + 2CO2

5. Formate process:

K2SO4 + Ca(OH)2 + 2CO 2HCOOK + CaSO4HCOOK + KOH+ 1.5O2 K2CO3 + H2O

6. Piesteritz process :

K2SO4 + 2CaCN2 + 2H2O 2KHCN2 + CaSO4 + Ca(OH)22KHCN2 + 5H2O K2CO3 + 4NH3 + CO2

7. Ion-Exchange Process

Economics. About 4% to 5% of potash production is used in industrial applications. In 1996, theworld supply of industrial grade potash was close to 1.35Mt K2O. This industrial material is 98%-99% pure, compared with the agricultural potash specification of 60% K2O minimum (equivalent to95% KCl). Industrial potash should contain at least 62% K2O and have very low levels of Na. Mg,Ca, SO4 and Br.

Uses. Since 1860, potash salts have replaced wood as a raw material for the manufacture ofpotassium carbonate. Potassium carbonate is used for fertilizer, for production of commercial soap,as a compound found in gunpowder and for making glass. Large amounts are also required for

potassium silicate manufacture; used for many organic syntheses; electrical industry, the dyeindustry, the printing trade, the textile industry, the leather goods industry, and the ceramic industry.


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2. 2KCl +K2SO4MgSO46H2O+ xH2O 2K2SO4 + MgCl2 (aq)

From Potassium Chloride and Kainite.Kainite, KClMgSO4 2.75H2O, is obtained from a potash oreby flotation.

Steps:1. Kainite, KClMgSO42.75H2O is obtained from a grinned potash ore by flotation.2. Kainite is converted into schoenite at 25C with motherliquor containing the sulfates of

potassium and magnesium.3. Schoenite is filtered off and decomposed with water at 48C.4. Most ofthe potassium sulfate to crystalli e.5. Sulfate motherliquoris recycled to the kainite

schoenite conversion stage.

6. Contains 30% of thepotassium used, istreated with gypsum,CaSO42H2O causingsparingly solublesyngenite,K2SO4CaSO4H2O, to

precipitate.7. Syngenite isdecomposed with

water at 5C, whichdissolves potassium

sulfate andreprecipitates gypsum.

8. Potassium sulfatesolution is recycled to the schoenite decomposition stage.

9. Gypsum is reused to precipitate syngenite.

From Potassium Chloride and Sodium Sulfate. The production of potassium sulfate from

potassium chloride and sodium sulfate takes place in two stages, with glaserite, Na2SO43K2SO4,as an intermediate, according to the following equations:

1. 4Na2SO4 + 6KCl Na2SO43K2SO4 + 6NaCl2. Na2SO43K2SO4 + 2KCl 4K2SO4 + 2NaCl

Potassium chloride and sodium sulfate are reacted at 20C50C in water and recycled process brines to form glaserite, which is filtered and then reacted with more potassiumchloride and water to form potassium sulfate. Because the mother liquor from the glaseritestage has a high potassium and sulfate content, the maximum potassium yield is 73%, and themaximum sulfate yield is 78%. The yield can be increased considerably by cooling the

motherliquorto produce more crystals and byincluding a final evaporation stage.

Other processes of manufacturing potassium sulfate include:

1. From Potassium Chloride and Calcium Sulfate (processes based on gypsum,CaSO42H2O)

2. From Alunite, K2SO4Al2(SO4)34Al(OH)33. Single-Stage Process from Sodium Sulphate:

Forthe sake of thermodynamics constraints, the process of potassium sulfate productionfrom the sodium sulfate proceeds in two steps:

1. 6KCl + 4Na2SO4 2K3Na(SO4)2 + 6NaCl

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2. 2KCl + 2K3Na(SO4)2 4K2SO4 + 2NaCl

4. From Potassium Chloride and Langbeinite:

K2SO42MgSO4 + 4KCl 3K2SO4 + 2MgCl2

Economics. Worldwide, almost all technical grade potassium sulfate production, >99%, is used inagriculture. Moreover, sulfate of potash production since the mid-80s has been characterized by anup and down cycle. The latest upward trend ended in 1998 due to development of new sulfate of

potash sources that outpaced demand, and a massive destruction of tobacco cropping acreage in theUS and China. (According to industry representatives, the sulfate of potash market is characterized

by major over-capacities in production with further increase expected.)

Importance and Uses. Potassium sulfate is, after potassium chloride, the most important potassium-containing fertilizer, being used mainly for special crops. Potassium sulfate constitutes 5% of theworld demand for potash fertilizer and used in a wide range of industrial uses, for manufacturing

potassium alum, for manufacturing potassium carbonate and for manufacturing glass.

Potassium Hydroxide, KOH

Commonly called caustic potash. It is a caustic compound of strong alkaline chemical dissolvingreadily in water, giving off much heat and forming a caustic solution.

Manufacture and Production. Today, potassium hydroxide is manufactured almost exclusively bypotassium chloride electrolysis. There are three different processes:

1. Diaphragm process (KCl-containing, 8%10 % potassium hydroxide solution is initially formed, whose salt content can be reduced to 1.0%1.5% KCl by evaporation to a 50%

liquor)

2. Mercury process [very pure KCl brine must be utilized, because even traces (ppb range) ofheavy metals such as chromium, tungsten, molybdenum, and vanadium, as well as smallamounts ( ppm range) of calcium or magnesium; very pure potassium hydroxide solution

running off the decomposers is cooled, freed from small amounts of mercury in precoated

filters]3. Membrane process [cell liquor has a low chloride content (1050 ppm); the KOH

concentration is 3t

%; before dispatch, it is concentrated to 45%50% by evaporation]

Economics. World production is estimated at 700800 10 3 t/a. Main producers are the United States,Germany, Japan, and France.

Uses. Pure-quality potassium hydroxide is used as a raw material for the chemical andpharmaceutical industry, in dye synthesis, for photography as a developer alkali, and as an electrolytein batteries and in the electrolysis of water; raw material in the detergent and soap industry; as astarting material for inorganic and organic potassium compounds and salts; for the manufacture ofcosmetics, glass, and textiles; for desulfurizing crude oil; as a drying agent; and as an absorbent for

carbon dioxide and nitrogen oxides from gases.

Potassium Dichromate, K2Cr2O7

Potassium dichromate is a major patent chromium chemical of commerce. In 1880, Germanyintroduced Na2CO3 as a substitute for K2CO3 in manufacturing, since then sodium dichromategradually replaced K2Cr2O7.

Manufacture and Production. Potassium dichromate process starts:1. Reaction of potassium hydroxide and chromium trioxide in a reactor creating a mother liquor:


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CrO + 2KOH K2Cr2O7 + H2O

2. The mother liqour is filtered and the resultant filter solids are sent off-site for disposal to afacility.

3. The mother liquor is then sent to a crystallizer to precipitate crystalline K2Cr2O7, which isrecovered by centrifuging.

4. The resulting mother liquor from the product centrifuge is returned to the reactor.

It is also prepared from chromite ore (FeCr2O4). Chromite ore is finely powdered and is heated withsodium carbonate in the presence of air in a reverberatory furnace. The reaction produces sodiumchromate:

4FeCr2O4 + 8Na2CO3 + 7O2 8Na2CrO4 +2Fe2O3+ 8CO2Na2CrO4+ H2SO4 Na2Cr2O7 + Na2SO4+ H2ONa2Cr2O7 + KCl K2Cr2O7 + 2NaCl

Uses. Wide variety of uses in leather tanning, dyeing, painting, porcelain decorating, printing,photography, pigment-prints, staining wood, pyrotechnics, safety matches, and for blending palm oil,wax and sponges; for water-proofing fabrics, as an oxidizer in the manufacture of organiccompounds, in electrical batteries, and as a corrosion inhibitor, and in oil refining.

Potassium Nitrate,KNO3

It was first known by Hasan al-Rammah (Arab, 1270). Into the 20th century, niter-beds wereprepared by mixing manure with mortar or wood ashes. It usually under a cover from the rain, keptmoist with urine, turned often to accelerate the decomposition and leached with water afterapproximately one year. The product was ammonia from the decomposition of urea and othernitrogenous materials would undergo bacterial oxidation to produce various nitrates.

From 1903, fertilizer was produced on an industrial scale from nitric acid produced via theBirkelandEyde process. Haber process (1913) was combined with the Ostwald process after 1915,allowing Germany to produce nitric acid for the war.

Manufacture and Production. Almost all potassium nitrate, now used only as a fine chemical, is produced from basic potassium salts and nitric acid. Potassium nitrate can be made by combiningammonium nitrate and potassium hydroxide:

NH4NO3 (aq) + KOH (aq) NH3 (g) + KNO3 (aq) + H2O (l)

without a by-product ammonia:

NH4NO3 (aq) + KCl (aq) NH4Cl (aq) + KNO3 (aq)

Resultant solids

mother liquor

mother liquor

Reactor

Filtration Crystallizer*centrifuging

CrO3

KOH

1facility

crystals

2

3

4

Figure 8. Flow diagram of the production of

potassium dichromate


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from neutrali ation and the reaction is highly exothermic:

KOH (aq) + HNO3 KNO3 (aq) + H2O (l)

Uses. Potassium nitrate fertili eris the most widely used application ofthe compound. It contains allthe macro nutrients needed for growth of plant species. It has potassium that is vital for growth of

plants. Nitrogen helps the crops to fully mature, rather than delaying their growth.Used as foodpreservatives during the Middle Ages; used in many processes like curing meat, production of brineand making corned beef.Seventy five percent potassium nitrate is found in the "Chinese Snow" or "Devil's Distillate", a black power that is now commonly known as gunpowder and also frequentlyused ingredientin cigarettes.

Nitrogen Industries

Nitrogen, N

The nitrogen cycle represents one ofthemost important nutrient cycles found interrestrial ecosystems. Nitrogen is used

by living organisms to produce a

number of complex organic molecules.The store of nitrogen found in theatmosphere, where it exists as a gas(N2), plays an important role for life.Despite its abundance in theatmosphere, nitrogen is often the mostlimiting nutrient for plant growth.This

problem occurs because most plants canonly take up nitrogen in two solid

forms: ammonium ion (NH4+) and the ion nitrate (NO3

-).

Manufacture and Production. Nitrogen in the form of ammonium can be absorbed onto the surfacesof clay particles in the soil.The ion of ammonium has a positive molecular charge is normally held

by soil colloids.This process is sometimes called micellefiu ation. Ammonium is released from thecolloids by way of cation exchange. When released, most of the ammonium is often chemicallyaltered by a specific ty pe of autotrophic bacteria (genus Nitrosomonas) into nitrite (NO2

-);

modification by another ty pe of bacteria (genus Nitrobacter) converts the nitrite to nitrate (NO3-).

Both ofthese processes involve chemical oxidation and are known as nitrification.

Economics. Scientists estimate that biological fixation globally adds approximately 140 millionmetric tons of nitrogen to ecosystems everyyear.

Importance and Uses. Almost all ofthe nitrogen found in anyterrestrial ecosystem originally camefrom the atmosphere.Significant amounts enterthe soilin rainfall orthrough the effects oflightning.The majority, however, is biochemically fixed within the soil by speciali ed micro-organisms like

bacteria, actinomycetes, and cyanobacteria.Members of the bean family(legumes) and some otherkinds of plants form mutualistic symbiotic relationships with nitrogen fixing bacteria. In exchangefor some nitrogen, the bacteria receive from the plants carbohydrates and special structures(nodules)in roots where they can existin a moist environment.

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Compounds ofNitrogen

Nitri Acid, HNO3

Nitric Acid is a strong, highly corrosive and toxic mineral acid and one of the most importantinorganic acids. Itis one ofthe few substances capable of dissolving gold and platinum, which wereknown as the royalornoble metals. Pure Nitric Acid is a colourless liquid but older samples maytake on a yellowish colour due to the accumulation of oxides of Nitrogen.

Manufacture and Production.Nitric Acid is produced in two methods:1. Weak Nitric Acid (yields 30%-90%; oxidation, condensation, and absorption)2. High-strength Nitric Acid (yields 90%; dehydrating, bleaching, condensing, and absorption)

Weak Nitric Acid. Manufactured by the high-temperature catalytic oxidation of ammonia.Processes include:

1. Ammonia oxidation2. Nitric oxide oxidation3. Absorption

Processes:1. A 1:9 ammonia/air mixture is oxidi ed at a temperature of 1380F to 1470F as it

passes through a catalytic convertor:

4NH3 + 5O2 4NO + 6H2O; exothermic reaction

2. Underthese conditions the oxidation ofammonia to nitric oxide (NO)

proceeds a range of 93 to 98percent yield. Oxidationtemperatures can vary from1380F to 1650F. Highercatalyst temperaturesincrease reactionselectivity toward NO

production. Lowercatalysttemperatures tend to

be more selective towardless useful products:nitrogen (N2) and nitrousoxide (N2O).

3. The nitrogen dioxide/dimermixture then passes througha waste heat boiler and a

platinum filter.4. The process stream is

passed through acooler/condenser and cooledto 100F orless at pressuresup to 116 psia. The nitricoxide reacts noncatalyticallywith residual oxygen toform nitrogen dioxide (NO2) and its liquiddimer, nitrogen tetroxide:

2NO + O2 2NO2 N2O4

13

AIRPREHEATER

WASTEHEATBOILER

STEAM

AIRTAILGAS

EMMISIONPOINT

EFFLUENTTANK

AMMONIA

VAPOR

AMMONIAOXIDIZER

ENTRAINEDMISTSEPARATOR

WATER

AIR

COOLING

WATER

COOLER/CONDENSER

SECONDARYAIR

PLATINUMFILTER

NITROGENDIOXIDE

PRODUCT:30%-70%HNO3

NITRIC OXIDEGAS

COMPRESSSOREXPANDER

NOX EMISSIONSCONTROL

CATALYTICREDUCTIONUNITS

2FUEL

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A secondary air stream is introduced into the column to re-oxidize the NO that isformed instep 8. This air also removes NO2 fromstep 4.

5. The final step introduces the nitrogen dioxide/dimer mixture into an absorptionprocess after being cooled. The mixture is pumped into the bottom of the absorptiontower.

6. Air with liquid dinitrogen tetroxide is added at a higher point.7. Deionized process water enters the top of the column.8. The absorption trays are usually sieve or bubble cap trays. The exothermic reaction

occurs as follows:

3NO2 + H2O 2HNO3 + NO

9. An aqueous solution of 55% to 65% (typically) nitric acid is withdrawn from the bottom of the tower. The acid concentration can vary from 30% to 70% nitric acid.The acid concentration depends upon the temperature, pressure, number of absorptionstages, and concentration of nitrogen oxides entering the absorber.

10.The absorber tail gas (distillate) is sent to an entrainment separator for acid mistremoval.

11.The tail gas is reheated in the ammonia oxidation heat exchanger to approximately392F.

12.The nitric acid formed in the absorber(bottoms) is usually sent to an external bleacherwhere air is used to remove (bleach) any dissolved oxides of nitrogen. The bleachergases are then compressed and passed through the absorber.

13.The thermal energy produced in this turbine can be used to drive the compressor. Tailgases from the absorption tower are heated to ignition temperature, mixed with fuel(natural gas, hydrogen, propane, butane, naphtha, carbon monoxide, or ammonia) and passed over a catalyst bed.

14.Two seldom-used alternative control devices for absorber tailgas are molecular sievesand wet scrubbers. In the presence of the catalyst, the fuels are oxidized and the NOxare reduced to N2.

High-Strength Nitric Acid Production. It can be obtained by concentrating the weak nitric

acid (30% to 70% concentration) using extractive distillation.Processes:

1. Nitric Acid from the Wweak nitric acid production is mixed with concentrated sulfuricacid (60%) as a dehydrating agent. The acid mixture flows downward, countercurrentto ascending vapors.

2. Concentrated nitric acidleaves the top of the columnas 99 percent vapor,containing a small amount of

NO2 and oxygen (O2)resulting from dissociation ofnitric acid.

3. The concentrated acid vaporleaves the column and goes toa bleacher and acountercurrent condensersystem to effect thecondensation of strong nitric acid and the separation of oxygen and oxides of nitrogen(NOx) byproducts.

4. These byproducts then flow to an absorption column where the nitric oxide mixeswith auxiliary air to form NO2, which is recovered as weak nitric acid. Inert andunreacted gases are vented to the atmosphere from the top of the absorption column.

H2SO4 HNO3

BLEACHER

CONDENSER

O2 , NO

WEAKHNO3

INERT,UNREACTEDGASES

COOLINGWATER

DEH

DRATINGAGENT

O2 , HNO3, NO2

AIR

ABSORPTIONCOLUMN

Figure 10.Flow diagram of high strengthnitric acid production from wea

nitric acid


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Economics. In 1991, there were approximately 65 nitric acid (HNO3) manufacturing plants in theU.S. with a total capacity of11 million tons of HNO3 peryear.The plants range in si e from 6,000tons to 700,000 tons per year. About 70 percent of the nitric acid produced is consumed as anintermediate in the manufacture of ammonium nitrate (NH4NO3).

Uses. Another 5% to 10% of the nitric acid produced is used for organic oxidation in adipic acidmanufacturing. Nitric acid is also used in organic oxidation to manufacture terephthalic acid andother organic compounds.Explosive manufacturing utili es nitric acid for organic nitrations. Nitricacid nitrations are used in producing nitrobenzene, dinitrotoluenes, and other chemicalintermediates.Other end uses of nitric acid are gold and silver separation, military munitions, steel and brass

pickling, photoengraving, and acidulation of phosphate rock.

Ammonia, NH3

As the active product of smellingsalts, the compound can quicklyrevive the faint of heart and light of

head. Ammonia contributessignificantly to the nutritional needsof terrestrial organisms by serving

as a precursorto food and fertilizers.Ammonia, either directly orindirectly, is also a building block

for the synthesis of manypharmaceuticals.

Manufacture and Production.

Ammonia is produced in a process

known as the Haber process, in

which nitrogen and hydrogen react

in the presence of an iron catalystto

form ammonia.The hydrogen isformed by reacting natural gas andsteam at high temperatures and thenitrogen is supplied from the air.Other gases (such as water andcarbon dioxide) are removed from

the gas stream and the nitrogen and

hydrogen passed over an ironcatalyst at high temperature and

pressure to form the ammonia.

Natural gas

Desulfuriser

Steam reformerflue gases

steam

atmosphere

waterWaste heat

boilerAir reformerAir

steam

waterWaste heat

boiler

water

saturated UCARSOL

Shift converter

CO 2 removal UCARSOL

CO2 stripper Methanation water

CO 2

Urea plant

Compression and

cooling

MixerNH3 unreacted gases

NH3 converter

cool to 30C

NH3Decompression

impuritiesNH 3 recovery

purge gas

NH3

Ammonia

Industry Urea plant

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Steps:1. Natural gas may contained sulfrous element or compound.2. All sulfurous compounds must be removed from the natural gas to prevent catalyst

poisoning. These are removed by heating the gas to 400C and reacting it with zinc oxide:

ZnO + H2S ZnS + H2O

3. Primary reformer where superheated steam is fed with methane. The gas mixture heatedwith natural gas and purge gas to 770oC in the presence of a nickel catalyst:

CH4 + H2O 3H2 + COCH4 + 2H2O 4H2 + CO2CO + H2O H2 + CO2

4. Synthesis gas (cooled to 735C) flows to the secondary reformer where it is mixed withcalculated air:

CO + H2O CO2 + H2O2 + 2CH4 2CO + 4H2O2 + CH4 CO2 + 2H2

2O2 + CH4 2H2O + CO2

5. Carbon monoxide is converted to carbon dioxide (which is used later in the synthesis ofurea):

CO + H2O CO2 + H2

Achieved in two steps:1. Gas stream is passed over a Cr/Fe3O4 catalyst at 360C.2. Gas stream is passed over a Cu/ZnO/Cr catalyst at 210C.

6. Water condenses out and is removed from 40C.

7. Gas with carbon dioxide is passed through a stripper chamber and removal chamber toremove and to stripped carbon dioxide with UCARSOL. Carbon dioxide in the mixturedissolves.

8. Saturated UCARSOL from carbon dioxide removal chamber is feed to carbon dioxidestripper to strip the remaining carbon dioxide for urea manufacturing.

9. Remaining carbon dioxide is passed through the methanation chamber where water isproduced and is removed by condensation at 40C. Carbon dioxide is converted tomethane using a Ni/Al2O3 catalyst at 325C:

CO + 3H2 CH4 + H2OCO2 + 4H2 CH4+ 2H2O

10.Gas mixture is cooled and compressed.11.Gas stream is mixed with the mixture of ammonia and unreacted gases and cooled to 5C.12.Ammonia is removed and is passed through decompression with another ammonia.13.Unreacted gases is heated to 400C with P = 330 barg and passed over an iron catalyst

and is converted to ammonia.14.Outlet gas is cooled from 220C to 30C. This process condenses more ammonia.15.Ammonia after cooling is passed through decomposition with the ammonia from thestep

11:

N2 + 3H2 2NH3; P = 24 barg


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16.Impurities such as methane and hydrogen become gases and are sent to the ammoniarecovery unit. Purge gas (used for primary or steam reformer) and recovered ammoniaare removed.

Economics. Annually 105 000 tonnes of pure ammonia (300 T day-1) are produced in Kapuni, andmost of this is converted to urea. Ammonia is produced in large petrochemical plants typically 400000 tonnes to 800 000 tonnes per year and costing $150m to $250m. Ammonia is produced in about80 countries and 85 per cent is for nitrogen fertiliser production including about 6 per cent for directuse in agriculture. Production capacity has grown strongly doubling from 62 million tonnes in1974 to 130 million tonnes in 2000.

Importance and Uses. Most of the ammonia is used on site in the production of urea. The remainderis sold domestically for use in industrial refrigeration systems and other applications that requireanhydrous ammonia. It is an industrial chemical, but its most important use is as the building blockof nitrogen fertilizers urea and ammonia chemicals.

Urea, NH2CONH2

Also called carbamide, is an organic chemical compound which essentially is the waste producedwhen the body metabolizes protein. It is a compound not only produced by humans but also by many

other mammals, as well as amphibians and some fish. Urea was the first natural compound to besynthesized artificially using inorganic compounds a scientific breakthrough.

Manufacture and Production. Urea is produced from ammonia and carbon dioxide in twoequilibrium reactions:

2NH3 + CO2 NH2COONH4(ammonium carbamate)NH2COONH4 NH2CONH2(urea) + H2O

The urea manufacturing process is designed to maximize these reactions while inhibitingbiuret formation:

2NH2CONH2 NH2CONHCONH2(biuret) + NH3

Steps:1. Carbon dioxide and ammonia is mixed in a reactor to form ammonium carbamate

Synthesis

urea, excess NH3,carbamate, H2O

heat Decomposition

urea, H2O

heat Concentration

urea

Granulation

U e le

H3

NH3, CO2 Recovery cooling

H2O H2O


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(exothermic reaction):

2NH3 + CO2 NH2COONH4(ammonium carbamate); P = 240 barg

First reactor achieves 78% conversion of carbon dioxide to ureaSecond reactor receives the gas from the first reactor and recycle solution from thedecomposition and concentration sections; 60% conversion of carbon dioxide to ureaat P = 50 barg.

2. Water and unconsumed reactants (ammonia, carbon dioxide, ammonium carbamate) areremoved ; pressure is reduced from 240 barg to 17 barg and the solution is heated:

NH2COONH4 2NH3 + CO2(decomposition of ammonium carbamate)NH2CONH2 + H2O 2NH3 + CO2(urea hydrolysis)2NH2CONH2 NH2CONHCONH2 + NH3(biuret formation)

3. Ammonia and carbon dioxide is passed through a recovery chamber. Unconsumedreactants are passed through the second reactor and purified excess ammonia is passedthrough the first reactor.

4. Urea and water from the decomposition of ammonia carbamate is concentrated from 68%w/w to 80% w/w. Seventy percent of the urea solution is heated at 80C-110C under

vacuum, which evaporates off some water. Molten urea is produced at 140C; remaining25% of the 68% w/w solution is processed under vacuum at 135C.

5. Urea that is 80% w/w is processed under granulation. Dry, cool granules classified usingscreens. Oversized granules are crushed and combined with undersized ones for use asseed. The final product is cooled in air, weighed and conveyed to bulk storage ready forsale.

Economics. Global urea production increased by 3.6% in 2009 to reach 146m tonnes, estimated theInternational Fertilizer Industry Association (IFA). Currently 182 000 tonnes of granular urea are

produced annually (530 T day-1), but this is soon expected to increase to 274 000 tonnes. The IFAforecasted that world urea capacity will increase by 51m tonne/year between 2009 and 2014 to reach222m tonne/year, a growth rate of 6%/year. Global demand for urea is forecast to grow at 3.8%/year

to around 175m tonnes in 2014. Much of the increase was from fertilizer demand while industrialapplications for urea, accounting for 12% of total consumption, is expected to grow at 7%/year.

Uses. The urea is used as a nitrogen-rich fertilizer, and as such is of great importance in agriculture.It is also used as a component in the manufacture of resins for timber processing and in yeastmanufacture. Urea is also used in the manufacture of urea-formaldehyde (UF) resins produced by thecondensation reaction between urea and formaldehyde. Urea is also a constituent of cattle feeds, andis a useful viscosity modifier for casein or starch-based paper coatings. Small quantities are used asan intermediate in the manufacture of polyurethanes, pharmaceuticals, toothpaste, cosmetics, flame-

proofing agents, sulphamic acid and fabric softeners.

Ammonium Nitrate, NH4NO3

A salt of ammonia and nitric acid, is a colourless, crystalline substance. Ammonium Nitrate reactswith combustible and reducing materials as it is a strong oxidant. It is prepared commercially byreaction of nitric acid and ammonia.

Manufacture and Production. Ammonium nitrate (NH4NO3) is produced by neutralizing nitric acid(HNO3) with ammonia (NH3).

Steps:1. Ammonia and nitric acid are reacted in a solution formation chamber which is resulted a melt

stream:


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HNO3 + NH3 NH4NO3

2. As the melt stream is feed to a solution concentration chamber, an additive magnesiumnitrate or magnesium oxide is injected. Purposes:

1. to raise the crystalline transition temperature ofthe final solid product;2. act as an desiccant, drawing waterinto the final productto reduce caking;3. to allow solidification to occur at a low temperature by reducing the freezing

point of molten ammonium nitrate.3. Melt stream fromstep 2 is passed

to solids formationchamber by prillingand by granulating.

4. Solid NH4NO3 is passed to solidsfinishing chamber by drying andcooling.

5. Dried solids are processed againfor screening.These solids vary insizes and must be screened forconsistently sized prills orgranules. Offsize prills are

dissolved and recycled to thesolution concentration process.6. Screened prills is processed for

coating for bulk shipping and bagging.

Economics. In 1991, there were 58 U.S. ammonium nitrate plants located in 22 states producingabout 8.2 million megagrams (Mg; 9 million tons) of ammonia nitrate.

Uses. Approximately 15% to 20% of this amount was used for explosives and the balance forfertilizers. The commercial grade contains about 34 percent nitrogen, all of which is in formsutilizable by plants; it is the most common nitrogenous component of artificial fertilizers.Ammonium nitrate also is employed to modify the detonation rate of other explosives, such as

nitroglycerin in the so-called ammonia dynamites, or as an oxidizing agent in the ammonals.Ammonium nitrate is also used in the treatment oftitanium ores and in solid-fuel rocket propellants,in pyrotechnics.

Ammonium Sulfate, [NH4]2SO4

Manufacture and Production.About 90% of ammonium sulfate is produced in three differentprocesses:

1. caprolactam [(CH2)5COHN] by-product

2. synthetic manufacture3. coke-oven by-product

Processes:1. Synthetic ammonium sulfate is

produced by combininganhydrous ammonia and sulfuricacid in a reactor.

2. Coke-oven by-productammonium sulfate is produced byreacting the ammonia recovered

from coke-oven offgas with sulfuric acid.3. Ammonium sulfate crystals are formed by

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Ammonia

Nitric Acid

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circulating the ammonium sulfate liquorthrough a water evaporator, which thickens thesolution.

4. Ammonium sulfate crystals are separated from the liquorin a centrifuge.5. The crystals are fed to either a fluidized-bed or rotary drum dryer.6. Dryers are continuously steam heated, while the rotary dryers are fired directly.7. Rotary vacuum filters may be used in placed of a centrifuge and dryer.8. Crystallayeris removed as product; not generally screened;carried by conveyors to bulk

storage.9. Dryer exhaust gases pass through a particulate collection device, wet scrubber.10.After being dried, the ammonium sulfate crystals are screened into course and fine crystals.

Economics. In 1991, U.S. facilities produced about 2.7 million megagrams(Mg; 3 million tons) ofammonium sulfate in about 35 plants. Production rates atthese plants range from 1.8Mg to 360Mg (2tons to 400 tons) peryear.

Uses. Itis commonly used as fertilizer.

Ammonium Phosphate, NH4H2PO4

Manufature and Production.Two basic mixer designs are used by ammoniation-granulation plants:

pugmill ammoniator and rotary drum ammoniator.

Processes:1. Phosphoric acid is mixed in an acid surge tank with 93% sulfuric acid and with recycled acid

from wet scrubbers.2. Mixed acids are then partially neutralized with liquid or gaseous anhydrous ammonia in a

brick-lined acid reactor.3. A slurry of ammonium phosphate and 22% water are produced and sentthrough steam-traced

lines to the ammoniator-granulator.4. Ammonia-rich

offgases passthrough a wet

scrubber beforeexhausting to theatmosphere.

5. Granulation, byagglomeration and

by coatingparticulate withslurry, takes place inthe rotating drumand is completed inthe dryer.

6. Primary scrubbers use raw materials mixed with acid.

7. Secondary scrubbers use raw materials mixed with pond water.8. Moist ammonium phosphate granules are transferred to a rotary concurrent dryer.9. Then transferred to a cooler.10.Before being exhausted to the atmosphere, these offgases pass through cyclones and wet

scrubbers.

11.Cooled granules pass to a double-deck screen, in which oversize and undersize particles areseparated from product particles.

12.Oversized granules are crushed, mixed with undersized.13.They recycled backto the ammoniator-granulator.

Economics.Total ammonium phosphate production in the U.S.in 1992 was estimated to b e 7.7

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5 8

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million megagrams (Mg; 8.5 million tons).

Uses. Ammonium phosphate is used as an ingredient in some fertilizers as a high source of elementalnitrogen. It is also used as a flame retardant in thermoplastic compositions. It is analytically used as

buffer solutions.

Documents

z Potassium Industries 2007 2