Process Design Strategies To Produce p-Xylene via Toluene Methylation: A Review

Abstract

It is envisaged that the future refineries will be reconfiguring for the direct conversion of crude oil to chemicals to improve their profitability. In this direction, the toluene methylation process offers a promising route for the production of high-value p-xylene from low-cost feedstocks such as toluene and methanol. There is a growing commercial interest in the toluene methylation process, because it can theoretically produce double the amounts of p-xylene with high selectivities, when compared with the other existing processes (such as disproportionation and transalkylation), and it can be the next-generation method of producing p-xylene. Past and current research approaches were mainly focused on improving the catalyst activity (high toluene conversion and para-selectivity) by introducing several modifying agents. However, still the major challenge of this process lies in the development of an efficient catalyst without compromising on the methylation activity and para-selectivity. In addition, catalyst deactivation is another major issue that is mainly due to the coking precursors derived from methanol conversion. To address these issues, a good understanding of the mass transfer plays a vital role in the catalyst design, as well as process design and optimization strategies. This review summarizes the fundamental aspects of possible reaction mechanisms that occur in the process, useful reaction kinetics data for the process optimization studies and scaleup, with emphasis on recent developments in the catalyst design, deactivation mechanism, and process development strategies. A future perspective is also provided related to the catalyst design and process design strategies for addressing the gaps in this field.

Study on a Novel Process for the Synthesis of P‐Xylene by Selectivity Intensification in Benzene Alkylation with Methanol

“…(3) O-xylene (OX) and m-xylene (MX) was produced by isomerization of PX; (4) The rate constants of the further alkylation of xylene to produce trimethylbenzene were the same; (5) The reaction of methanol dehydration to olefin would take ethylene as lumped; (6) According to the thermodynamic analysis of benzene alkylation system with methanol, the equilibrium constant of each reaction was very large and the reverse reaction was ignored. [13] The specific reactions included the alkylation of benzene with methanol to toluene (R1,Table 1" the same below), toluene then with methanol to p-xylene (R2), isomerization of xylene (R3 and R4), the deep alkylation of xylene to trimethylbenzene (R5, R6 and R7), and methanol to olefin (R8).…”

“…PR-BM method was selected as the physical property method, and the thermodynamic equilibrium reactor was used to obtain toluene from benzene with methanol. Based on the literature research [3][4][5][6][7][8][9] and simulation study, the optimization of the benzene alkylation process with methanol to prepare PX was conducted. The results showed that the selectivity of PX reached more than 99.70 %, which had reached the purity standard of industrial application.…”

Novel Short Process for p-Xylene Production Based on the Selectivity Intensification of Toluene Methylation with Methanol

“… 1 , 2 PX is mainly produced via aromatic extraction, toluene disproportionation, C8 aromatic isomerization, and transalkylation of heavy aromatics. 3 − 5 These methods are typically accompanied by adsorptive separation, crystallization, and reactive distillation technologies for C8 isomers with relatively low m -xylene (MX) and o -xylene (OX) values. These separation technologies require more energy and expensive raw materials, which increases the production costs due to very similar boiling points of xylene isomers, low PX selectivity, and the considerable amount of byproducts that are produced.…”

“…These separation technologies require more energy and expensive raw materials, which increases the production costs due to very similar boiling points of xylene isomers, low PX selectivity, and the considerable amount of byproducts that are produced. 3 , 6 Correspondingly, toluene methylation with methanol offers a potential molecular engineering process for the production of PX, based on shape-selective catalysts. 1 , 7 − 9 …”

“…p -Xylene (PX) is an important intermediate for the polyester, pharmaceutical, chemical fiber, and pesticide industries with an annual global market compound growth rate of 12.05% between 2016 and 2022. , PX is mainly produced via aromatic extraction, toluene disproportionation, C8 aromatic isomerization, and transalkylation of heavy aromatics. − These methods are typically accompanied by adsorptive separation, crystallization, and reactive distillation technologies for C8 isomers with relatively low m -xylene (MX) and o -xylene (OX) values. These separation technologies require more energy and expensive raw materials, which increases the production costs due to very similar boiling points of xylene isomers, low PX selectivity, and the considerable amount of byproducts that are produced. , Correspondingly, toluene methylation with methanol offers a potential molecular engineering process for the production of PX, based on shape-selective catalysts. ,− …”