5_1-Methanol-le-2008
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Transcript of 5_1-Methanol-le-2008
Methanol from synthesis gasMethanol from synthesis gas
Applications of methanolApplications of methanolProduct (in w.%) 1988 1996 2005Formaldehyde 39 35 38Acetic acid 6 7 11Methyl halides 7 7 7MTBE 12 27 20Dimethyl terephthalate 3 2 2Methyl amines 4 4 4Methyl methacrylate 3 3 4Solvents 9 4 4Others 17 11 13Sum (in mio t/a) 17,3 24,3 32,1
Methanol from syngasMethanol from syngas(ΔH = -92 kJ/mol)
(ΔH = -50 kJ/mol)
CO + H2O ⇌ CO2 + H2 (ΔH = -41 kJ/mol)
• Several side-products that are thermodynamically more stable than methanol.
• As the reactions are exothermic➜ Good temperature control in the
reactor important.
• The catalyst needs to be active and selective towards methanol
CO + 2H2 ⇌ CH3OH
CO2 + 3H2 ⇌ CH3OH + H2O
Mechanism of methanol formationMechanism of methanol formation
Methanol synthesis mechanismMethanol synthesis mechanism
Rate determining step
Cu/ZnO/AlCu/ZnO/Al22OO33 catalystscatalysts
H2 H2 : H2O = 1 : 3 H2 : CO = 95 : 5
CuO (wt %) > 55ZnO (wt %) 21-25Al2O3 (wt %) 8-10
Equilibrium CO conversion to methanolEquilibrium CO conversion to methanol
Zn/Cr2O3
Cu/ZnO/Al2O3
Synthesis gas for methanol productionSynthesis gas for methanol production
• Optimum H2/CO ratio : 2– Lower ratio: increased production of by-products– Higher ratio: excess hydrogen needs to be purged
• A small amount of CO2 increases the catalyst activity
ATR
Module M = 2 = H2 – CO2
CO + CO2
Purification of syngas
Low concentrations of impurities, such as sulfur (especially newer catalysts are very sensitive against poisoning)
The feed (syngas) purification section may consist of the following steps:
• Hydrogenation • Chlorine Absorption • Sulphur Absorption • Trace removal of Sulphur (final purification)
Industrial processesIndustrial processes
• ICI/LINDE – low pressure process• Lurgi – low pressure process• BASF – high pressure process• UK – Wesseling high pressure process
Desulfurization
Methanol product
Distillation
Methanol synthesis
Compression
Cooling
ReformingNatural
gas
Types of reactors used for efficient coolingTypes of reactors used for efficient cooling
•(a) Cooling with water bath; (b)cooling with water coils; (c) cooling with cold feed;(d) feed gas quench; (e) feed–effluent heat exchange by periodic flow reversal;
(f) lateral flow; (g) fluidised bed.
Linde/ICI low pressure synthesisLinde/ICI low pressure synthesis
Boiler feed waterGas
Steam
Circulating water
Circulating water Gas exit
Linde/ICI Linde/ICI –– low pressure synthesislow pressure synthesis• Temperature 240 – 260 °C• Pressure 50 – 100 bar• Catalyst Cu-Zn-Al-Oxides
→ catalyst is very sensitive against poisoning and requires very low concentrations of impurities.
99.9% MeOH
The Lurgi The Lurgi –– low pressure processlow pressure process• Temperature: 250 – 260 °C• Pressure: 50 – 80 bar• Catalyst: modified CuO-ZnO catalyst• Reactor type: multi-tubular reactors Mega methanol plants
(5000 tons/d)
Syngas is partially converted in the 1st
reactor and is sequentially fed to the 2nd
where the cooling medium is cold syngas
BASF BASF –– high pressure processhigh pressure process
• Temperature: 320 – 380 °C• Pressure: 340 bar• Catalyst: ZnO-Cr2O3 (Zn:Cr ratio: 70:30)
Catalyst is very resistant against poisons in low concentrations→ long life time (several years)
• Very short residence time to avoid side reactions (1-2 sec) • Low conversions per one single pass (12-15%)• At several inlets along the reactor cold feed is added to control
the temperature.
UK UK –– Wesseling high pressure processWesseling high pressure process
• Temperature: 350°C• Pressure: 300 bar• Catalyst: ZnO-Cr2O3
→ similar conditions like in the BASF process
Difference:Lower partial pressure for CO (13 bar) used:• Reactor can be built from steal as Fe(CO)5 is not produced• Purity of methanol very good
New industrial developmentsNew industrial developments
Company Catalsty Temperature (°C) Pressure (bar)
Haldor-Topsøe CuO-ZnO-Cr2O3 230-260 100-150
Vulcan ZnO-Cr2O3 270-330 150-250
Pritchard CuO Unknown 100-250
Catalyst & Chemical Inc.
CuO-ZnO-Al2O3 240-250 100-250
BASF CuO-ZnO-Al2O3 200-350 50-250
Mistubishi Gas Chemical
CuO + promoters 200-280 50-150
Methanol production with medium pressure processes
Methanol synthesis slurry processMethanol synthesis slurry process
Methanol future
Reducing the cost of production by installing “Mega”production facilities using asraw material low-cost natural gas is opening up new promising areas for methanoluses as a motor fuel, gasoline additive, feedstock for chemical synthesis, sourceof carbon for protein production
New applications of MeOH for the production of• Ethylene and/or propylene, MTP• Dimethyl ether as a substitute for diesel fuel• Liquid fuels (substitute of gasoline or raw material for gasoline production
MTG process • Hydrogen or feed material for power generating systems or• Use in integrated schemes combined with an ammonia/urea complex• Methanol consumption for fuel cells to be used in automobiles, for power
generation and portable equipment is bound to increase in the near future.