Nonsteady-state mathematical modelling of H2SO4-catalysed alkylation of isobutane with alkenes

Elena Ivashkina,Emiliya Ivanchina,Vyacheslav Chuzlov,Alexander Kotelnikov,Igor Dolganov,Irena Dolganova,Rustam Khakimov

doi:10.2516/ogst/2021017

Abstract

H2SO4-catalysed isobutane alkylation with alkenes is an important industrial process used to obtain high-octane alkylate. In this process, the concentration of H2SO4 is one of the main parameters. For alkylation, sulphuric acid containing 88%–98% monohydrate is typically used. However, only a H2SO4 concentration of 95%–96% enables alkylate with the maximum octane number to be obtained. Changes in H2SO4 concentration due to decontamination are the main cause of process variations. Therefore, it is necessary to maintain the reactor acid concentration at a constant level by regulating the supply of fresh catalyst and pumping out any spent acid. The main reasons for the decrease in the H2SO4 concentration are accumulation of high-molecular organic compounds and dilution by water. One way to improve and predict unsteady alkylation processes is to develop a mathematical model that considers catalyst deactivation. In the present work, the formation reactions of undesired substances were used in the description of the alkylation process, indicating the sensitivity of the prediction to H2SO4 activity variations. This was used for calculation the optimal technological modes ensuring the maximum selectivity and stability of the chemical–technological system under varying hydrocarbon feedstock compositions.

Highlights

In context of tightening motor fuel requirements, in relation to aromatic hydrocarbon content, there is an increasing demand for alkylate, i.e., the product of the alkylation process of isobutane with alkenes
The other reason for using sulphuric acid is that alkylation gasoline may be contaminated by Hydrogen Fluoride (HF) and fluorinated organic compounds that are highly toxic
The developed model of H2SO4-catalysed isobutane alkylation was software implemented in a high-level language

Summary

Introduction

In context of tightening motor fuel requirements, in relation to aromatic hydrocarbon content, there is an increasing demand for alkylate, i.e., the product of the alkylation process of isobutane with alkenes. The alkylation of isobutane with alkenes is mainly performed using two types of catalyst, i.e., sulphuric or hydrofluoric acids [5,6,7]. In 1996, most industrial alkylation plants used Hydrogen Fluoride (HF) as a catalyst; owing to its high toxicity, technologies that used a relatively safe analogue, i.e., sulphuric acid, were subsequently developed. The other reason for using sulphuric acid is that alkylation gasoline may be contaminated by HF and fluorinated organic compounds that are highly toxic. Despite other concerns such as the high operating costs, sulphuric acidcatalyzed processes are less hazardous. Sulfuric acid is a corrosive liquid, but not so volatile, making its handling easier [14]

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