HOMOGENEOUS GAS-PHASE OXIDATION OF METHANE USING OXYGEN AS OXIDANT INAN ANNULAR REACTOR

The gas-phase partial oxidation of methane with oxygen has been invest igated in a high-pressure quartz-lined annular reactor. The work under taken consists of a systematic investigation of the effects of reactor tube wall temperature, pressure, feed oxygen concentration, and gas f low rate on methane conversion and methanol yield and selectivity. Met hanol yields in the range of 1.5-2.3 mol % and selectivities in the ra nge of 23-47 mol % have been observed, depending on the process parame ters used. Increasing the oxygen concentration in the feed is found to decrease methanol selectivity dramatically, while yield exhibits a tr ade-off between decreasing selectivity and increasing conversion. The influence of pressure is most noticeable between 1.5 and 3.0 MPa, wher e substantially more methanol is produced at the higher pressure. The effect is less pronounced as the pressure is increased further. The mo st significant outcome of this study is the recognition of the importa nce of the interaction of the chemistry of the system and the heat-tra nsfer properties of the reactor system. The system is very sensitive t o heat release rate and exhibits a discontinuity in methane conversion , with hysteresis being observed under process conditions employing hi gh feed oxygen concentrations and total gas flow rates. More important ly, highest methanol yields are observed on the downward sweep of reac tor wall temperature, reinforcing the concept that the reaction is mos t sensitive to temperature and that low temperatures favor methanol pr oduction.