Study On Catalytic Process Of Solid Phosphoric Acid Catalyst In Propylene Oligomerization

Fischer-Tropsch(FT) synthesis is an effective way to produce clean liquid fuels, such as gasoline and diesel. Meanwhile, the exhaust contains about 25% of low carbon olefins. After the cool separation, ethylene can be converted into linear alpha olefins and propylene can be translated into polypropylene. Through these methods, utilization rate of olefins and economic benefit increase. Nevertheless, there is still a part of low carbon olefins in tail gas. Compared to separate them continually, transformation of them to oil additives is a valid way to shorten downstream industry chain and reduce investment cost. According to the characteristics of olefins in the FT synthesis product, it is a key technology to choose appropriate oligomerization catalyst and corresponding process. Currently, due to the simple preparation process, mild operation condition, low cost and high octane number of product, solid phosphoric acid catalyst(SPAC) has been used generally in olefin oligomerization. In addition, there have been relatively mature techniques both at home and abroad. However, the catalyst pulverizing is easy to cause catalyst deactivation in oligomerization process. Moreover, the regulation of product selectivity is particularly necessary to increase the carbon chain length and added value of product.This thesis was based on the background of oil processing technology development in HT/LTFT synthesis, aimed at researching propylene oligomerization process over SPAC, and investigated two problems: the suitable method to reduce the degree of catalyst pulverizing under the precondition of maintaining the reactivity; the regulation range of product selectivity and influence factors of the carbon chain growth process. Detailed content is as follows:1) The method to reduce the degree of catalyst pulverizing was put forward by means of combining with silicon phosphate hydrolysis and acid loss processes.2) The effects of acid strength of catalyst and reaction conditions on product selectivity and influence factors of the carbon chain growth process were studied and analyzed by combining with catalyst property.The conclusions were as follows:1) There is no need to active catalyst before reaction. Water can be added after 80 h of reaction and the amount of it can be set to 0~0.025 mol·g-1·h-1. The degree of catalyst pulverizing may be reduced by this way.2) SPAC has the ability to translate propylene into C6~C12 olefins andthere is a limitation on the carbon chain growth process under the action of it.It is impossible to produce oligomers greater than C12.3) Acid strength of SPAC is the key limiting factor of carbon chain growth process in oligomerization.