The LPMeOH® Process
(Liquid Process Methanol)
An Initial Look
Traditionally, methanol has been produced by bringing compressed syngas into contact with a solid catalyst that's hot. The resulting reaction gives off heat (i.e., it's exothermic). While this means that given the right conditions the reaction will proceed without a need to continue heating the reactants, which is good, the reaction can easily become too hot, which is bad because overheating will ruin the catalyst.
The reaction generates heat on the surface of the catalyst, and the reaction's limiting factor is the inherently low heat transfer involved in interactions between a solid and a gas. In order to keep the reaction from proceeding too quickly and ruining the catalyst, the traditional practice was to throttle back the reaction by limiting the amount of CO in the syngas.
The liquid process route gets around this problem by grinding the catalyst into a powder (thereby increasing its surface area) and suspending it as a slurry in mineral oil. The syngas is then bubbled up through the slurry. Because the catalyst is immersed in a liquid, the reaction is able to take advantage of the much-more-rapid transfer of heat from a solid to a liquid.
The result is that an LPMeOH reactor can reliably generate more than five times as much methanol per pass through the reactor, which translates into considerable savings in the cost of compressing, heating, cooling and decompressing the syngas passing through the reactor. This also significantly lessens the problem of accumulating ever greater percentages of inert gases in the recirculating syngas.
Note: LPMeOH® is a registered trademark of Air Products and Chemicals, Inc.