Kinetics modeling of disproportionation and ethylation of ethylbenzene over HZSM-5: Effects of SiO₂/Al₂O₃ ratio

This article deals with the effects of SiO₂/Al₂O₃ ratio of HZSM-5 catalysts in disproportionation and ethylation of ethylbenzene to produce para-diethylbenzene (p-DEB). The physicochemical characterization of the catalyst samples shows that the variation of SiO₂/Al₂O₃ has minimal impact on the crystallinity of HZSM-5 samples. On the other hand, the acidity of the materials decreased while specific surface area increased with increasing the SiO₂/Al₂O₃ ratios. The catalytic experiment in the CREC Riser Simulator shows that low temperature favors the EB ethylation reaction while higher temperature is favorable for disproportionation. The DEB selectivity is found to be significantly higher in ethylation of EB with ethanol than disproportionation. Among the five HZSM-5 catalysts, the sample with SiO₂/Al₂O₃=80 gives highest EB conversion and is more selective to DEB although the p-DEB/m-DEB for the catalysts are comparable with other samples. The value of the activation energy for EB cracking is comparable to the activation energy of EB disproportionation which is consistent to the high benzene selectivity in this route. During the EB ethylation with ethanol, a small amount of benzene was formed via the cracking of EB, which is reflected by higher activation energy of the EB cracking reaction. The kinetics analysis also confirms that during EB ethylation, the disproportionation and cracking of EB is negligible. In EB ethylation, the HZSM-5 catalyst with SiO₂/Al₂O₃=80 requires lowest amount of activation energy to form DEB which is reflected in higher DEB selectivity of the catalyst.