正丁烷水蒸汽催化转化反应动力学

KINETICS OF CATALYTIC STEAM REFORMING OF n—BUTANE

用内循环式无梯度反应器研究了正丁烷和水蒸汽在 Z409催化剂上的转化反应动力学。实验结果表明在实验条件范围内反应产物除氢、一氧化碳、二氧化碳及甲烷以外,不含其他烃类,而且水煤气变换反应始终接近热力学平衡。提出了该反应系统的反应模式。假定催化剂表面上存在两类活性位,且烃类的 C-C 键很快地断裂而生成单碳中间化合物,继而转变为碳-组分(即 CO,CO_2及 CH_4)。根据所提出的反应模式导出了各个反应的速率方程,与实验结果甚相符合。

The steam reforming kinetics of n—butane on Z409 catalyst has been studied at atmospheric pressure with an internal recycle gradientless reactor.The reaction temperature was varied in the range of 743—853 K,and the steam to carbon molar ratio in the feed was 3,4 or 5. No hydrocarbon other than methane was found experimently among the reaction products.Al- though the number of independent reactions is three for this reaction system,the kinetic behaviour may be described with four reactions,i.e.n—butane hydrogenolysis and oxygenolysis reactions, the methanation reaction and the water—gas shift reaction,However,experimental findings showed that the last one is often to be at equilibrium. Assuming that there exist two kinds of different active sites on the catalyst surface and the car- bon—carbon bonds of n—butane can break rapidly to form single carbon intermediates,either car- bon monoxide or methane A reaction sequence was proposed for the system.According to this se- quence,kinetic expressions were derived: For n—butane hydrogenolysis reaction r_1=(K_1P_(C_4H_(10))P_(H_2)/A+4KP_(C_4H_(10)) For n—butane oxygenolysis reaction r_2=K_2P_(C_4H_(10))P_(H_2O)/(A+4KP_(C_4H_(10)))(P_(H_2)+K_(H_2O)P_(H_2O) For the methanation reaction K3PcoP^2A(1 -- fl) r_3=K_3P_(CO)P_(H_2)~2A(1-β)/(A+4KP_(C_4H_(10)))(P_(H_2)+K_(H_2O)P_(H_2O)) where P_i—partial pressure of species i,MPa;k_j—rate constant of reaction j;K—constant,equal to 123;K_(H_2O)—adsorption equilibrium constant of steam;A=p_(H_2)+K_1p_(H_2O)/K_2(p_(H_2)+ K_(H_2)p_(H_2O))β=p_(CH_4)p_(H_2O)/p_(CO)p_(H_2)~3K_P,where K_P is the equilibrium constant of methanation reaction. The average absolute percent deviations for production rates of CO,CH_4 and CO_2 and the con- version fraction of n—butane were 5.81%,9.71%,5.26% and 4.27% respectively.