Methanol production by direct oxidation of methane in a plasma reactor

Abstract

Methanol is one of the most widely-produced chemicals in the world. It is a key raw material in the production of many chemicals in the petrochemical industry. Methanol also has vast potential for expanded applications as a fuel. It is currently produced by an energy intensive and expensive two step process. An economically feasible one step process could significantly reduce methanol production cost, saving millions of dollars. A methane-to-methanol process, built at remotely located methane reserves, would convert methane into a different energy form that is much easier to transport. This would make methane a much more attractive and valuable energy source. The purpose of this investigation was to evaluate the feasibility of producing methanol by direct oxidation of methane using a plasma reactor. The chemistry of methane oxidation is well understood and free radicals play a central role in methane oxidation reactions. Low pressure experiments by other researchers indicated that methanol can be produced by direct oxidation of methane in plasma reactors. However, the viability of a plasma-based methanol production process depends on its ability to convert large quantities of methane. This work was directed at plasma reactor operation near atmospheric pressure to increase the amount of material processed. The focus of this mvestigation was the design and construction of an experimental apparatus which could achieve methanol synthesis in a plasma reactor by direct oxidation of methane at atmospheric pressure. A microwave source provided the energy to generate the plasma. The system was designed to study the effects of reactant concentration and flow configurations on methanol production. Since high levels of methanol selectivity are the primary consideration in direct synthesis of methanol from methane, improvements in methanol selectivity were desired. The objective of the four experimental phases was to investigate reactor operating conditions and improve methanol production and selectivity. Methanol production at atmospheric pressure was demonstrated in this plasma system and steady improvements in methanol selectivity were achieved as the investigation proceeded. Experiments showed that high concentrations of water and low concentrations of oxygen improved methanol selectivity. In the last experimental phase, oxygen was divided into both reactant streams, but this approach did not improve methanol production. It was observed that higher methanol selectivities were obtained only at low methane conversions. As in other plasma studies, methanol production did not approach what would be required for commercial feasibility.