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Petrochemicals
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Lower alkenes Chemicals industry uses 10% of available
petroleum and NG as feed, 4-5% as fuel
Ethylene, Propylene, butadiene Produced from steam cracking of various
refinery streams.
Dehydrogenation reactions.
Lower alkenes or olefins an important feedfor products we will discuss (ex. LDPP orHDPP)
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Steam cracking: Free radical reactions form and propagate, decompose
to an olefin plus hydrogen radical, etc.
Obeys first order kinetics
Reaction rate increases with partial pressure, and
secondary reactions do as well.
Uncatalysed reaction takes place in furnace tubes.
Near atmospheric pressure, 30-40% steam,
temperatures 750 oC -850 oC but as high as 900 oC.
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Rate constants as a function of T
Reactivity increases with chain length
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Industrial Process A mixture of HC and steam is passed through
tubes inside a furnace
Heating occurs by convection and radiation Considerable heat input at a high temperature
level
Limited HC partial pressure
Very short residence times (
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Dehydrogenation Recently, the demand for propenes and
butenes has been increasing.
Direct production for these specificalkenes is important
Selectively dehydrogenate the specific
alkane (ie propane to form propylene) Alkane dehydrogenation is highly
endothermic
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Variables in these processes include:
Type of catalyst used
Reactor design
Method of heat supply
Method for catalyst regeneration
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Major dehydrogenation processes
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Major outlets for alkenes
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Uses of ethylene LDPE 15%
HDPE 23 %
LLDPE 13 %
Ethylene oxide 13 %
Dichloroethane 10-11 % (to make vinyl chloride)
Ethylbenzene 7% ( to make styrene)
Vinyl acetate 3 %
Acetaldehyde 2 % Ethanol 1 %
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Synthesis Gas, Syngas A mixture of CO and H in varying ratios
Uses:
refinery hydrotreating, hydrocracking
Ammonia
Alkenes (via Fischer Tropsch reaction)
Methanol, higher alcohols Aldehydes
acids
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Produced from coal, natural gas, etc.
Major processes:
Steam reforming of NG or light HC in thepresence of O2 or CO2
Partial oxidation of heavy HC with steam
(H2O) and O2
Partial oxidation of coal with steam (H2O) and
O2
Raw materials depend on cost and availability
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Reactions to form SyngasGeneral reactions
(1) C + H2O CO + H2 (steam reforming, endothermic)
(2) C + O2 CO (partial oxidation, exothermic)
(3) CO + H2O CO2 + H2 (water gas shift)
NG as a feed:
(1) CH4 + H2O CO + 3H2 (steam reforming, endothermic)
(2) CO + H2O CO2 + H2 (water gas shi ft)
(3) CH4 + CO2 2CO + 2H2(4) CH4 C + CO
(5) 2COC + CO2(6) CH4 + O2 CO + H2 (partial oxidation)
(7) CH4 + 2O2 CO2 + 2H2O
(8) CO + O2 CO2(9) H2 + O2 H2O
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Production of Syngas
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Steam reforming High temperatures
Nickel catalyst contained in tubes heated by afurnace
May contain 500-600 tubes that are 7-12 m longwith ID of 70-130 mm
Convection section and radiation section
Feed pretreatment required to remove sulfur
Coke deposits can form that deactivate thecatalyst and can block the furnace tubes, soexcess steam is used to prevent this
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Steam reforming
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Ammonia synthesis
3H2+N2 2NH3 DH+ -91.44 kJ/ml
A major product of the CPI
Early sources were natural (saltpeter), or byproduct of coke ovens
Major use in fertilizers (agricultural), explosives (increasing due toWWI)
In 1909 Fritz Haber established the conditions under which nitrogen,
N2(g), and hydrogen, H2(g), would combine using
medium temperature (~500oC)
very high pressure (~250 atmospheres, ~351kPa)
a catalyst (a porous iron catalyst prepared by reducing magnetite, Fe3O4).Osmium is a much better catalyst for the reaction but is very expensive.
Requires a H2:N2 ratio of 3:1
N2 sources is air, H2 from syngas
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The key to development of the Haber process was the availability of reliable thermodynamic data At atmospheric P it was noted that NH3 did not form from a mixture of the reactants
Haber extrapolated to lower T and concluded that a feasible process could be developed
Low T and high P are favoured
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Uses of ammonia
Fertiliser ammonium sulfate, (NH4)2SO4
ammonium phosphate, (NH4)3PO4
ammonium nitrate, NH4NO3
urea, (NH2)2CO
Chemicals nitric acid, HNO3, which is used in making explosives such as TNT (2,4,6-trinitrotoluene),
nitroglycerine which is also used as a vasodilator (a substance that dilates blood vessels) and PETN(pentaerythritol nitrate).
sodium hydrogen carbonate (sodium bicarbonate), NaHCO3
sodium carbonate, Na2CO3
hydrogen cyanide (hydrocyanic acid), HCN
hydrazine, N2H4 (used in rocket propulsion systems)
Explosives ammonium nitrate (NH4NO3)
Fibres & Plastics nylon, -[(CH2)4-CO-NH-(CH2)6-NH-CO]-,and other polyamides
Refrigeration used for making ice, large scale refrigeration plants, air-conditioning units in buildings and plants
Pharmaceutical used in the manufacture of drugs such as sulfonamide which inhibit the growth and multiplication of bacteria thatrequire p-aminobenzoic acid (PABA) for the biosynthesis of folic acids, anti-malarials and vitamins such as the B
vitamins nicotinamide (niacinamide) and thiamine
Pulp & Paper ammonium hydrogen sulfite, NH4HSO3, enables some hardwoods to be used
Mining & Metallurgy used in nitriding (bright annealing) steel,used in zinc and nickel extraction
Cleaning
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MethanolCO+ 2H2 CH3OH
CO2+3H2 CH3OH+H2O
Coupled by: CO+H2O CO2+H2
Second large scale process involving catalyst and high P
Equilibrium data:
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Catalyst selectivity is very important, as other products
may form. Cu/ZnO/Al2O3 catalysts are newer catalysts that enable
lower P
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Methanol synthesis
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Methanol uses Formaldehyde
Methyl tert-butyl ether (MTBE) used as
octane booster
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Fischer Tropsch Synthesis German scientist who discovered in 1923 that syngas
could be converted to a wide range of HC and alcohols
Economically not competitive
Used in South Africa (Sasol) to produce fuels from coal
Recently used to convert NG to liquid fuels
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