Application of Na3PO4/NaX catalyst for the side chain alkylation reaction of toluene with methanol

Styrene is a basic organic chemical raw material for synthetic rubber and plastics. At present, there are many ways to synthesize styrene in industry, but most of them are catalytic dehydrogenation of ethylbenzene. This process has many shortcomings such as long process and high energy consumption, which are not in line with the current concept of environmental protection and energy saving. The side-chain alkylation of toluene with methanol has many advantages, such as the wide source of raw materials, short process flow, low energy consumption. Therefore, this reaction has become the focus of research. A large number of studies have found that side-chain alkylation of toluene with methanol is a synergistic reaction on acid and base catalyst, and the catalyst needs to have suitable weak acid sites and base sites at the same time. In our recent research, we found that the moderate addition of cheaper Na3PO4 decreased the amount of middle acid and increased the strength and amount of middle base sites. Based on the unique role of Na3PO4 in regulating acidity and basicity, catalysts with different acidity and basicity were prepared in this paper and the relationship between the catalytic performance and the distribution of acid and base sites were investigated. The catalysts were characterized by XRD, SEM, FT-IR, BET, UV-Vis, NH3-TPD, and CO2-TPD. It is found that the catalysts prepared by ion-exchange of Na3PO4 solution with NaX zeolite, the distribution of the acid-base sites changes with the concentration of Na3PO4 solution. While the catalyst prepared by a modified method which cannot be opened at present has a better performance for the side chain alkylation of toluene with methanol. The reason is that Na3PO4 and NaX can provide a suitable base site, a weak acid site respectively and they both form a suitable space structure required for the reaction. The reaction of toluene and methanol were very sensitive to the basicity and acidity of the catalyst, there were some competitive activations for toluene and methanol over middle acid and middle base sites. In the absence of strong acid sites on the catalyst, when the more middle base sites and the less middle acid sites there were on the surface of the catalyst, the more products of side-chain alkylation of toluene formed. If the middle base sites were enough, the stronger base sites there were on the surface of the catalyst, the more formaldehyde formed, so, the selectivity of styrene should be higher. That is, enough middle and strong base sites were both very important for the side-chain alkylation of toluene with methanol to styrene.

Author(s): Faraz Ahmad

Abstract | PDF

Share This Article