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

Towards Sustainable Production of Polybutylene Adipate Terephthalate: Non-Biological Catalytic Syntheses of Biomass-Derived Constituents

Renewable chemicals, which are made from renewable resources such as biomass, have attracted significant interest as substitutes for natural gas- or petroleum-derived chemicals to enhance the sustainability of the chemical and petrochemical industries. Polybutylene adipate terephthalate (PBAT), which is a copolyester of 1,4-butanediol (1,4-BDO), adipic acid (AA), and dimethyl terephthalate (DMT) or terephthalic acid (TPA), has garnered significant interest as a biodegradable polymer. This study assesses the non-biological production of PBAT monomers from biomass feedstocks via heterogeneous catalytic reactions. The biomass-based catalytic routes to each monomer are analyzed and compared to conventional routes. Although no fully commercialized catalytic processes for direct conversion of biomass into 1,4-BDO, AA, DMT, and TPA are available, emerging and promising catalytic routes have been proposed. The proposed biomass-based catalytic pathways toward 1,4-BDO, AA, DMT, and TPA are not yet fully competitive with conventional fossil fuel-based pathways mainly due to high feedstock prices and the existence of other alternatives. However, given continuous technological advances in the renewable production of PBAT monomers, bio-based PBAT should be economically viable in the near future.

Thermodynamic and Mechanistic Analyses of Direct CO2 Methylation with Toluene to para-Xylene

Direct CO₂ methylation with toluene, as one of the CO₂ hydrogenation technologies, exhibits great potential for the CO₂ utilization to produce the valuable para-xylene (PX), but the tandem catalysis remains a challenge for low conversion and selectivity due to the competitive side reactions. The thermodynamic analyses and the comparation with two series of catalytic results of direct CO₂ methylation are conducted to investigate the product distribution and possible mechanism in adjusting the feasibility of higher conversion and selectivity. Based on the Gibbs energy minimization method, the optimal thermodynamic conditions for direct CO₂ methylation are 360-420 °C, 3 MPa with middle CO₂/C₇H₈ ratio (1:1 to 1:4) and high H₂ feed (CO₂/H₂ = 1:3 to 1:6). As a tandem process, the toluene feed would break the thermodynamic limit and has the higher potential of >60% CO₂ conversion than that of CO₂ hydrogenation without toluene. The direct CO₂ methylation route also has advantages over the methanol route with a good prospect for >90% PX selectivity in its isomers due to the dynamic effect of selective catalysis. These thermodynamic and mechanistic analyses would promote the optimal design of bifunctional catalysts for CO₂ conversion and product selectivity from the view of reaction pathways of the complex system.

p-Xylene Oxidation to Terephthalic Acid: New Trends

Large-scale terephthalic acid production from the oxidation of p-xylene is an especially important process in the polyester industry, as it is mainly used in polyethylene terephthalate (PET) manufacturing, a polymer that is widely used in fibers, films, and plastic products. This review presents and discusses catalytic advances and new trends in terephthalic acid production (since 2014), innovations in terephthalic acid purification processes, and simulations of reactors and reaction mechanisms.

Effects of Silicalite-1 Coating on the p-Xylene Selectivity and Catalytic Stability of HZSM-5 in Toluene Methylation with Methanol

The methanol–toluene alkylation process over zeolites catalysts offers a promising route for the production of p-xylene from low-cost feedstocks. Herein, we present a catalyst by preparing a core-shell aluminosilicate zeolite with an epitaxial silicalite-1 shell that passivates acid sites on the exterior surfaces. The para-selectivity was obviously increased due to the inhibition of the unselective isomerization of p-xylene over the external acid sites, and the open porous structure of the silicalite-1 shell ensured the mass transfer of reactants and products. Meanwhile, the carbon deposition was suppressed over HZSM-5@silicalite-1 catalysts, as a result of the decreased external acid sites. Furthermore, pulse chromatographic experiments revealed that the silicalite-1 coating could also improve the separation efficiency of p-xylene over o-xylene and m-xylene, due to the steric hindrance and extended diffusion path, resulting in a higher selectivity for p-xylene compared to that of the parent HZSM-5. The HZSM-5@4%S-1 catalyst showed the highest p-xylene selectivity (>80%) and methanol efficiency (66%), with good catalytic stability throughout the 170 h reaction time.

Progress of Methylation of C6-8~Arene with Methanol: Mechanism, Catalysts, Kinetic/Thermodynamics and Perspectives

High-efficiency production of xylene/trimethylbenzene from benzene/toluene with methanol is a potential way to promote the implementation on the coupled cycle development strategy of petrochemical and coal chemical industry and optimize the resource structure. At the same time, relying on the innovation of catalytic new materials, physical chemistry, intelligent capture technology, process engineering, and other principles and methods, p-xylene (PX) and trimethylbenzene (TMB) with higher added value were prepared by C6-8~arene methylation, which could elevate the level of methylation field and improve the competitiveness of the industry. This paper focuses on the one-step methylation reaction of benzene with methanol or toluene with methanol to obtain high-purity p-xylene (BM-PX/TM-PX), and the one-step methylation reaction of xylene with methanol to obtain mesitylene (XM-TMB). The methylation reaction mechanism and the preparation strategy of a high-performance catalyst were reviewed. The high selectivity of PX obtained by precisely controlling the pore size and acid site distribution of zeolites was emphasized. Meanwhile, the current research progress of TMB, the kinetic/thermodynamics of the BM-PX/TM-PX, and XM-TMB methylation reaction were described. Based on a literature research and the conclusion of our research group, the mechanism of methylation reaction process was expounded. Finally, the new research direction of catalysts used and reaction process in methylation reaction were prospected in order to guide the rapid development of this field.