Process of p-Xylene Production by Highly Selective Methylation of Toluene

Abstract

p-Xylene is an important industrial compound, and its demand has been increasing in recent years. It is mostly produced from cracking of naphtha, but there is a need for new and cost-effective methods for the production. Toluene alkylation with methanol over an alumino-silicate zeolite catalyst, such as ZSM-5, produces a mixture of xylene isomers with low p-xylene selectivity. Due to the very close boiling points of xylene isomers, it is very expensive to separate them. There has been some success in enhancing p-xylene selectivity by modifying the ZSM-5 catalyst. This results in reduced separation cost, which makes toluene methylation a competitive process for p-xylene production. Based on these findings, a novel process for the production of p-xylenes by the catalytic methylation of toluene followed by reactive distillation for the separation of p-xylene (instead of the more costly conventional technique of separation based on crystallization and adsorption) is developed and a complete process flow diagram is simulated using Aspen Plus. Using the built-in optimization tool in Aspen Plus, we optimized reactor parameters for a maximum p-xylene selectivity of 97.7%. After separation, a p-xylene product stream purity of 99.7% is achieved. High p-xylene selectivity in the reactor and use of reactive distillation reduces the separation cost and renders the new process economically competitive.

Production of bio‐based p‐xylene via catalytic pyrolysis of biomass over metal oxide‐modified HZSM‐5 zeolites

“…Industrially, various aromatic chemicals have been usually obtained from the refining of petroleum. p ‐Xylene can be produced from various subsequent catalytic transformations such as aromatic disproportionation, alkylation and isomerization processes . With the growing consumption of oil and its negative environmental impacts, there is considerable interest in producing commodity chemicals using renewable biomass resources …”

“…The oxygenates (like furans, acids and phenolics) formed from pyrolysis of biomass can be catalytically converted into aromatics such as benzene, toluene and xylenes over zeolite catalysts . The catalytic pyrolysis of cellulose to aromatics over zeolites involves a complex pathway: the formation of anhydrous sugars from cellulose; the dehydration of these sugars to furanics; and acid‐catalysed decarbonylation, decarboxylation, dehydration and oligomerization of furanics to aromatic products . The catalytic cracking of lignin into aromatics using a zeolite catalyst involves the formation of phenols and other oxygenates by thermal depolymerization of lignin through the cleavage of the CC and CO bonds in the lignin polymer, followed by the formation of the aromatics through catalytic cracking, deoxygenation, aromatization and oligomerization over zeolites .…”

Biomass‐Derived Renewable Aromatics: Selective Routes and Outlook for p‐Xylene Commercialisation

“…Currently, most of the TA used in the manufacture of PET is derived through variation of oxidation of p ‐xylene by the Mid‐Century/BP, Witten and Eastman processes, making p ‐xylene both a valuable and very important commodity chemical. Industrially, p ‐xylene, along with various other aromatics, is typically obtained from refining of gasoline followed by a series of subsequent separation processes . More recently, new methods of p ‐xylene production have been explored although they are all ultimately reliant on the use of petroleum‐derived chemicals.…”

“…Industrially, p-xylene, along with variouso ther aromatics, is typicallyo btained from refining of gasoline followed by as eries of subsequent separation processes. [5] More recently, new methodso fp-xylene productionh ave been explored [6] althought hey are all ultimately reliant on the use of petroleumderived chemicals. Gradually diminishing oil and fossil-fuel reserves, coupled with the negative environmental stigma that the use of such resources creates, has generatedi nteresti n the development of renewable and more sustainable alternatives.…”

A Facile Strategy to Prepare Shaped ZSM-5 Catalyst with Enhanced para-Xylene Selectivity and Stability for Toluene Methylation

“…However, mixed xylenes with composition close to thermodynamic equilibrium distribution (ortho:meta:para xylene ratio of ~22:53:25 [9]) are produced over unmodified ZSM-5 zeolites, especially nano-sized ZSM-5 zeolites [10]. para-Xylene is separated from other xylene isomers through a very expensive and energy-intensive process of distillation, adsorption and cryogenic crystallization [11,12]. Thus, improving para-selectivity in xylene product, as an effective way to reduce the cost, is the first priority for catalyst design.…”