The BASF process is conducted at 320-380°C and ca. 340 bar. The ZnO-Cr2O3 catalyst has a maximum activity when the Zn/Cr ratio is about 70: 30. Cold gas is injected at many places in the catalyst bed to avoid high temperatures that would shift the equilibrium away from methanol. Being very resistant to the usual catalyst poisons at low concentrations, the oxide mixture has a service life of several years. Byproducts such as dimethyl ether, methyl formate, and the higher alcohols are separated by distillation with a low- and high-boiling column. In order to suppress side reactions, a short residence time (1 -2 s), which completely prevents equilibration from taking place, is employed. Conversions of only 12- 15% are usual for a single pass through reactor.
The industrial process has been made highly efficient. The use of high pressure centrifugal compressors - normally employed in NH3 plants - has made a particularly strong contribution.
UK Wesseling has developed a process operating at a low CO partial pressure (1 3 bar in gas recycle). The reaction conditions (300 bar and 350 °C) are similar to those of the BASF process.