Optimization of the content of isobutane in the feed stream of the plant for sulfuric acid alkylation of isobutane with olefins

Abstract

The raw materials for the industrial production of moto- and air-alkylates are isobutane and butane-butylene fractions containing in their composition a component, n-butane, which is inert for the reaction of sulfuric acid alkylation of isobutane with olefins. In accordance with the Specifications TU 0272-024-00151638-99, the content of n-butane in the isobutane fraction, depending on the grade of the fraction, is 0.7÷20% wt. Its presence reduces the useful reaction volume of the alkylation reactor, and when separating the components of the alkylation reaction mass, it is necessary to use a distillation column (debutanizer). The possibility of including an additional column in the technological scheme for removing n-butane from the composition of the fraction (respectively, isobutane concentration) before it is fed into the alkylation reactor is being considered. This is of particular importance for factions with a brand below "High Brand". The study is conducted using the Honeywell UniSim Design software system. The Peng-Robinson method was used to calculate the properties of process stream components. The theoretically optimal design of the apparatus was calculated: when using a distillation column with a pressure in the apparatus of about 400 kPa to reduce the content of n-propane in the distillate (obtained isobutane fraction) to 0.001 mol. the share will require 48 theoretical plates, the accepted reflux ratio R = 8.9, the temperatures in the condenser and reboiler are 26.88 and 47.27 °C, respectively. A computational experiment has shown that in order to achieve the practical absence of n-butane in the obtained isobutane fraction (concentration of about 0.1% wt.), it is possible to use a distillation column with the following technological modes: the number of plates is 60, the feed plate is 15, the efficiency of contact devices is 0.8; the pressure in the column is about 400 kPa, the temperature in the condenser and reboiler is Тk=28.91÷29.05 ℃ and Тр=46.72÷47.25 ℃, respectively, reflux ratio R=20.41. This fraction also does not contain pentanes.