Production Process of Methanol


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
Syngas Methanol synthesis
 CO + 2H2    CH3OH
 CO + 3H2         CH3OH + H2O
Cu/ ZnO/Al2O3
Cu/ ZnO/Cr2O3
Syngas Two step methanol synthesis
 CH3OH + CO    HCOOCH3
 HCOOCH3 + 2H2    2CH3OH
Potassium methaoxide,
Cu chromite
Methane Direct oxidation
CH4 + ½ O2              CH3OH
Metal oxides,
 (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
Mass balance block diagram of methanol produced from carbon monoxide and hydrogen, units in Kg/h
The hydrocarbon feed is mixed with steam and fed to the reforming furnace, nickel catalyst is packed in its vertical tubes having 3-4 inches diameter and 20-25 feet long. Heat for the endothermic reaction is supplied by burners by combustion of the fuel gas. Reaction temperature is maintained in the range of 700 -1000oC; high temperature alloy steel is used for the tubes and whole steel wall of the furnace is refractory lined. A space velocity of 500-600 Kg/hr is maintained in reformer tubes. The effluent reformer gas is cooled to 35oC and pumped to a hot potassium carbonate scrubbing system to remove CO2.

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 from synthesis gas process flow diagram
Methanol Production by Synthesis Gas