直馏石脑油催化裂解反应中甲烷的生成

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CH4产率和选择性的影响规律，分析了导致CH4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CH4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CH4生成的主要反应路径；分子筛催化剂中较强Brnsted酸中心是石脑油催化裂解反应生成CH4的重要活性中心。烃类热裂解反应中CH4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CH4来自于C2原子连接的C-C键或C-H键的质子化裂化反应。

Methane Formation in Catalytic Cracking of Straight Run Naphtha

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 CH4 yield and selectivity between catalytic cracking and thermal cracking were analyzed, and the reaction paths of CH4 formation were explored with n octane as model compound. Results showed that CH4 was produced by a process involving both free radicals and carbocation intermediates, in which the carbonium ion reaction was a main path to form CH4 in the reaction temperature range of 600-700℃. During SRN catalytic cracking over zeolite catalyst, stronger Brnsted acidic sites were the key active centers for CH4 formation. CH4 came from homolytic cleavage occurring at primary C-C bond of hydrocarbon in its thermal cracking, while in its catalytic cracking, CH4 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.