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.