Optimization of the propylene content in the propane-propylene fraction fed to benzene alkylation in order to obtain isopropylbenzene

Abstract

One of the critical units for isopropylbenzene production plants is the unit for preparation of reactant fractions, in particular, the used propane-propylene fraction. In accordance with the Specifications TU 0272-024-00151638-99, the content of propylene in this fraction must be at least 65% wt. Such a sufficiently low content of propylene to carry out the reaction of benzene alkylation leads to inefficient use of the reaction volume of the alkylation reactor. The operation of the unit for the concentration of propylene from the propane-propylene fraction of the industrial production of isopropylbenzene by alkylation of benzene with propylene is considered. The study is carried out using the Honeywell UniSim Design modeling system. The flow of the process in one distillation column and when using two columns is simulated. A computational experiment has shown that in order to obtain propylene (calculated propylene content 99.1% wt.) and propane (estimated propane content 90% wt. propylene - 4.47% wt.) fractions that meet the parameters of current regulatory documents, it is possible to use one distillation column with technological modes: Тlow=31.4 ℃, Тup=21.17 ℃, apparatus pressure 1050kPa, reflux ratio R=13.43. When using two columns, the first one qualitatively "forms" the propylene fraction (calculated content of propylene 99.1% wt., propane 0.8% wt.), and the second column - the propane fraction with the practical absence of propylene in it (propane content 94.42% wt., propylene - 0.03% wt.). The developed models of technological schemes for the concentration of propylene from the propane-propylene fraction can be used to evaluate the operating and design parameters of columns and analyze the achieved process indicators. Calculations show that at the industrial site, the probable cause of the high propane content in the resulting propylene fraction is about 7% wt. is the maintenance of non-optimal technological regimes. Values of expedient operating parameters are given.