【摘要】 在积分反应器内,确定消除外扩散和内扩散影响的传统方法是改变流速和改变粒度。其判断标准一般都是在同一温度和同一接触时间比较转化率是否相同。但由于该反应器存在温度梯度和浓度梯度,容易出现假象,因此这种方法不太可靠。本文以甲烷水蒸汽转化反应为例,建议在改变流速和改变粒度时,从不同温度下的转化率(x)与接触时间(τ)曲线,求出视活化能作为判断内扩散和外扩散是否消除的标准,则较为可靠。我们用活化能法由实验确定,在850-900℃,压力为1.5-1.6大气压和水碳比为1.5:1时,要消除大孔、低表面积和低活性的S-4镍催化剂内扩散影响的粒度须小于0.045毫米。更多还原

【Abstract】 Traditional methods of eliminating the effects of internal and external diffusion over a porous catalyst are simply to reduce the pellet size of catalyst and to increase the linear velocity of reactant gases through the catalyst bed, and whether or not the conversion remains constant for various pellet sizes at the same temperature and the same contact time is regarded as a criterion.Results of the methane steam reforming in this paper indicate that the criterion mentioned above is unreliable, especially in the case of integral reactors, because there will be temperature and concentration gradients in the catalyst bed, and therefore an incorrect conclusion is often drawn. It is suggested that the apparent activation energy may be used as the criterion of diffusion effect elimination.It is assumed that the function f(x) is independent of temperature in a limited range of temperature and conversion,and the rate expression is C0dx/ dr-kf(x). When x1= x2,then the activation energy E=Rln(r2/r1)/(1/T2-1/ T1), where x is the conversion, k is the rate constant,r is the contact time, and C0 is the initial concentration. Therefore, in order to obtain the activation energy, x~r curves must be plotted for catalysts of different pellet sizes at various temperatures. The experimental results show that the method taking activation energy as criterion is more reliable and diffusion effects are difficult to be eliminated at high temperature. For methane steam reforming, to eliminate the diffusion effects, the pellet size must be smaller than 0.045mm in a reaction temperature range of 850-900℃ even using a catalyst with large pore, low surface urea and low activity.更多还原