Methanol production process description table, which gives some brief about the chemical reactions and catalysts used in each method, established in modern production plants:
|Feed stocks||Process technology and main reactions||Catalyst|
CO + 2H2 ↔ CH3OH
CO + 3H2 ↔ CH3OH + H2O
|Syngas||Two step methanol synthesis
CH3OH + CO ↔ HCOOCH3
HCOOCH3 + 2H2 ↔ 2CH3OH
CH4 + ½ O2 → CH3OH
(eg MoO3 based)
|Methane||Bio processing||Enzymes eg., cytochrome P450, methanotropes|
Production of Syngas (synthesis gas) from natural gas:
Synthesis gas (Syngas) is obtained from natural gas. Natural gas is desulphurised by passing over activated carbon, preheated and mixed with steam and CO2 under 2 atm pressures. CO2 required for the reaction is obtained by burning natural gas in excess of air.
CH4 + 2O2 (air) →
CO2 + H2O
3CH4 + CO2 + 2H2O →
4CO + 8H2
|Mass balance block diagram of methanol produced from carbon monoxide and hydrogen, units in Kg/h|
Methanol from Syngas:
A simplified flowsheet for production of methanol from Synthesis gas is shown below. Hydrogen and Carbon monoxide in a mole ratio of 2.25(12% greater than theoretical) is compressed to 3000-5000 psi, mixed with recycle gas, and fed to a high pressure converter. Internal preheat is usually employed. The reactor is copper lined and contains a mixed catalyst of Zinc, Chromium, Manganese or Aluminum oxides. The temperature is maintained at 300-375oc by proper space velocity and heat exchange design.
The reaction is highly exothermic and takes place with a decrease in volume. The enhanced pressure would, therefore result in more favorable equilibrium (Le Chatlier’s principle). The exit gases are cooled by heat exchange with reactants, then with water to 0-20oC and then condensed in high pressure condensers, where methanol is condensed at 3000-4000 psi. The liquid methanol is drawn off and the residual gases are recycled. The methanol condenses under full operating pressure to maximize yields (50%conversion per pass). The liquid methanol is depressurized, purified by permanganate to remove traces of ketones, aldehydes, and other such impurities, sent to a stripper to remove light ends such as dimethylether, and to fractionators to separate methanol from higher molecular weight compounds. The methanol from stripper on distillation gives 99% pure methanol. The yield is around 98% with recycling. Dimethyl-ether (1-2%) and higher alcohols, such as n-propanol and isopropanol (0.3-0.5%) are obtained as by-products.
|Methanol Production by Synthesis Gas|