Improvement of the p-xylene and benzene production process through the disproportionation of the toluene

Abstract

This document contains the extension of the thesis carried out during the degree which consisted of the design of a plant to obtain p-xylene and benzene by disproportionation reaction of the toluene that is present in the bottom stream of the hydrocarbon column that is currently sent to the gasoline blend. The expansion of the work consists of the purification of the xylene mixture and maximization of the production of p-xylene, as well as the realization of elements not designed during the reference project. The new unit starts with the modification of the xylene separation column in which previously p-xylene and m-xylene were obtained by means of a 132-tray distillation column, now separating the heavy aromatics from the rest. The stream containing the xylenes is sent to the continuous adsorption column, using hydrated Y-type zeolite as adsorbent, the physisorption is carried out by means of SMB technology, simulated moving bed technology. The stream rich in p-xylene which is separated by means of a distillation column obtaining the product, the desorbent is obtained which is recirculated to the adsorption chamber. The stream that does not contain p-xylene is sent to the desorbent recovery zone and the desorbent-free stream is sent to the reaction zone where the isomerization of the xylenes and the dealkylation of the ethylbenzene is carried out in order to obtain benzene at 10 bar and 420 °C. The output stream from the isomerization unit is sent to the benzene separation zone and then sent back to the adsorption column. Once the process and equipment had been designed, the corresponding P&IDs were drawn up together with the list of pipes. Finally, in order to check the feasibility of the project and its possible implementation, an economic study was carried out. To carry out the process, an initial investment of 108 M€ is required. Considering the current market, assuming that the price of raw materials, products and their demand remains constant and, a IRR of 21.1 % and a NVP of 25.2 M€ are obtained in a period of 5 years. In addition, the payback of the process is 3 years.