直馏石脑油催化裂解反应中甲烷的生成

Methane Formation in Catalytic Cracking of Straight Run Naphtha

采用小型固定流化床装置,对比研究了反应温度对直馏石脑油热裂解和催化裂解反应中CH4产率和选择性的影响规律,分析了导致CH4产率和选择性差异的主要原因.以正辛烷作为探针分子,分析了催化裂解和热裂解反应中CH4生成的反应路径.结果表明,反应温度在600～700℃范围内,直馏石脑油催化裂解反应中CH 4的生成是烃类自由基反应和正碳离子反应共同作用的结果,其中正碳离子反应是CH4生成的主要反应路径;分子筛催化剂中较强Br（o）nsted酸中心是石脑油催化裂解反应生成CH4的重要活性中心.烃类热裂解反应中CH4的生成来自于伯C-C键的均裂反应,而其催化裂解反应生成的CH4来自于C2原子连接的C-C键或C-H键的质子化裂化反应.

The effects of reaction temperature on the yields and selectivity of methane produced in catalytic cracking and thermal cracking of straight run naphtha（SRN） were investigated on a fixed fluidized bed reactor. The differences of CH4 yield and selectivity between catalytic cracking and thermal cracking were analyzed, and the reaction paths of CH4 formation were explored with n-octane as model compound. Results showed that CH4 was produced by a process involving both free radicals and carbocation intermediates, in which the carbonium ion reaction was a main path to form CH4 in the reaction temperature range of 600--700℃. During SRN catalytic cracking over zeolite catalyst, stronger Br6nsted acidic sites were the key active centers for CH4 formation. CH4 came from homolytic cleavage occurring at primary C--C bond of hydrocarbon in its thermal cracking, while in its catalytic cracking, CH4 was formed by the protolytic cracking taking place on C--C bond or C--H bond adjacent to the second carbon atom in carbon chain.