MODELING OF FIXED BED REACTOR FOR HYDROGENATION OF PYROLYSIS GASOLINE

Abstract

This work deals with the development of mathematical model of industrial fixed bed reactor for two stage hydrogenation of pyrolysis gasoline. Pyrolysis gasoline is aromatic rich by-product of steam cracking of naphtha or light gas oil for the production of olefin, can be used as blending agent for motor gasoline or feed for benzene production. In the present study, various types of catalyst used for hydrogenation of pygas, the kinetic models for hydrogenation of hydrocarbons and mathematical models for the fixed bed reactor are discussed. Most of the models are pseudo homogeneous and considering plug flow behaviour. First stage reactor for pygas hydrogenation is trickle bed reactor. To simulate the operating behaviour of the reactor, one dimensional pseudohomogeneous model developed after mass and energy balance and lumped kinetic model is used for three pseudo components diolefins olefins and paraffins. However, second stage reactor hydrogen and pygas are in gaseous phase as reaction carried out at high temperature and pressure. The catalysts used are Ni/A1203 and alumina supported Co-Mo-Ni for first and second stage reactor respectively. The model for first stage reactor is simulated by using odel5s toolbox, while second stage reactor model is simulated by ode45 toolbox in MATLAB 7.6 to predict the concentration and temperature behaviour of the different components along the length of the reactor. Simulated results are verified using the experimental values of the existing first stage fixed bed reactor for pygas hydrogenation, observed by Arpornwichanop et al (2008). The maximum error obtained after comparison between experimental and simulated value is 3%. However experimental result obtained by Cheng et al (2008) for existing second stage hydrogenation of pygas fixed bed reactor is used to verify the simulated results, and got very good agreement. Simulation results are used to show the impact of different parameters on hydrogenation and rise in temperature, such as inlet temperature, inlet pressure, inlet superficial velocity, and catalyst wetting efficiency.