High efficiency process for producing methanol from a synthesis gas

A process for converting natural gas to methanol comprising the steps of:

• partially oxidizing natural gas with an oxidant stream to form a synthesis gas containing H2, CO and CO2 in a ratio of (H2)/(2CO+3CO2) less than 1.0, said oxidant stream secured by diffusion of compressed air through a semipermeable membrane preferential for permeation of O2 in preference to N2 into a low pressure permeate stream enriched in oxygen compared to air and leaving a high pressure non-permeate stream which is poor in oxygen content compared to air;
• combining the synthesis gas with a hydrogen rich recycle gas stream, said hydrogen rich recycle gas stream being used in an amount that provides a combined synthesis-recycle gas stream containing H2, CO and CO2 in a ratio of (H2)/(2CO+3CO2) which is greater than that of the synthesis gas;
• passing said combined synthesis-recycle gas stream into a plurality of contacts with a methanol conversion catalyst with recovery of methanol from said gas stream between contacts with the methanol conversion catalyst to form after the last methanol recovery step a tail gas stream which is subjected to diffusion through a semipermeable membrane preferential for permeation of H2 in preference to N2 to produce as a low pressure permeate stream the hydrogen rich gas stream for recycle and leaving a high pressure non-permeate stream which is of a reduced hydrogen content;
• passing said high pressure non-permeate stream which is poor in oxygen content into admixture with said high pressure non-permeate stream which is of a reduced hydrogen content over an oxidizing catalyst to form an oxidized gas stream, and
• recovering energy from said oxidized gas stream.