超临界条件下甲醇合成的气液传质系数测定

Determination of gas-liquid mass transfer coefficient for methanol synthesis under supercritical condition

以液体石蜡为惰性液相载体,正己烷为超临界介质,合成气制甲醇为研究体系,测定了超临界条件下三相浆态床中甲醇合成的气液传质系数。在反应温度238℃、合成气分压3.7 MPa、气体空速2744 h-1条件下,通过不断增加催化剂浓度提高气液传质阻力和反应阻力的相对大小,采用外推法获得完全处于气液传质控制下的气液传质系数。计算结果表明:催化剂浓度对CO的气液传质系数的影响较大,而对CO2的气液传质系数的影响较小;液相条件下CO、CO2的气液传质系数分别是0.161、0.03 s-1,而超临界三相甲醇合成中CO、CO2的气液传质系数分别是0.199、0.042 s-1,说明三相浆态床甲醇合成中引入超临界流体利于气液传质,验证了超临界介质中三相甲醇合成的优越性。

Gas-liquid mass transfer coefficient for methanol synthesis was determined in a mechanically agitated slurry reactor with paraffin oil as the inert liquid medium and n-hexane as the supercritical medium. The ratio of gas-liquid mass transfer resistance to reaction resistance increased with increasing of catalyst concentration under the reaction condition of temperature 238 ℃, syngas pressure 3.7 MPa, and space velocity 2744 h-1. As gas-liquid mass transfer was the control step, gas-liquid mass transfer coefficients were obtained by extrapolation. Catalyst concentration had a much bigger effect on gas-liquid mass transfer of CO than that of CO2. Gas-liquid mass transfer coefficients of CO and CO2 in the liquid-phase reaction were 0.161 s^-1 and 0.03 s^-1 respectively, while they were 0.199 s^-1 0.042 s^-1 under supercritical condition. Supercritical fluid is conductive to gas-liquid mass transfer in the three-phase methanol synthesis process.