Methane, the main component of natural gas, is "reformed" by reaction with water, and sometimes oxygen, to synthesis gas, or syngas, which contains carbon monoxide and hydrogen. Since this step requires the most energy and cost, research has focused on making this step more efficient or eliminating it altogether.
Synthesis gas is converted to a mixture of methanol and other substances with the use of a catalyst at low temperature and high pressure. Several different reactor designs exist to deal with the large amount of heat produced during this process while keeping the reaction temperature relatively low.
The raw methanol produced in this manner also contains water, dissolved gases and trace byproducts. The design of this step to remove all or some of these other substances depends on how the methanol will be used once it's purified.