Production Of P-xylene Research Articles

Controlling soft rot of green pepper by bacteriocin paracin wx3 and its effect on storage quality of green pepper

A bacteriocin paracin wx3 was investigated as a candidate of natural preservative to control green pepper soft rot. Firstly, paracin wx3 was heterologously expressed in Pichia pastoris X33 with an improved yield of 0.537 g/L. Its size and amino acid sequence were confirmed by Tricine-SDS-PAGE and LC-MS/MS. Then, result of antibacterial activity showed that its MIC value against Pectobacterium carotovorum was 16 μg/mL. In vitro, paracin wx3 completely killed the pathogen at high concentrations ≥8 × MIC. In vivo, disease incidence of green pepper soft rot was decreased from 90% (control) to <2% (8 × MIC). Subsequently, results of action mode showed that paracin wx3 inhibited the growth of pathogen by pore-formation on cell membrane. Last, paracin wx3 treatment reduced losses of weight, firmness, total soluble solid, Vc of green pepper during storage. It also inhibited the production of soft rot volatile p-xylene, 1-butanol, 2-methyl-2-propanol, 3-hydroxybutan-2-one-D, 2-pentyl furan, butanal, etc.

On the reactivity and selectivity trends in the tandem Diels-Alder cycloaddition and dehydrative aromatization between dimethylfuran and ethene over solid acids

Tandem Diels-Alder (DA) cycloaddition and dehydration reactions between bio-derived furans and dienophiles offer a sustainable route potentially able to meet the growing demands of aromatic chemicals worldwide. In particular, efforts to maximize the production of p-xylene from dimethylfuran (DMF) and ethene have led to an expanding list of solid acids with, reportedly, outstanding catalytic performances. In this work, we have revisited the kinetic complexities of this reaction that are characterized by a distinct shift in the rate-limiting step depending sensitively on catalyst mass, and addressed the possible origins of reactivity and selectivity trends across a range of solid acids that hold promise for the target reaction, including aluminosilicates and a series of mesoporous metal phosphate catalysts (MOPOx; M = Sn, Ti, Zr, Hf, Nb and Ta), in both dehydration- and cycloaddition-limiting regimes. In contrast to initial p-xylene formation rates in the dehydration-limiting regime, which benefit from an increased acid strength of Brønsted acid sites, p-xylene formation rates within the cycloaddition-limiting regime are essentially unaffected by variations in acid site densities, Lewis and Brønsted acid strength, and pore confinement. Such weak dependences of DA reactivity on a multitude of acid properties provide strong hints that DA cycloaddition between DMF and ethene follows an inverse-electron-demand [4 + 2] route, most likely as a consequence of a more favorable adsorption of DMF than that of ethene on the acid sites enhancing so the electrophilicity of DMF, but not that of ethene as required by the normal-electron-demand cycloaddition. Product selectivities and carbon balances were tracked as functions of reaction time, conversion and reactant pressure or concentration to identify the side reactions and acid properties responsible for p-xylene selectivity losses and the ultimate formation of carbonaceous deposits. These findings deepen our understanding of the roles of Lewis acid sites and Brønsted acid sites for the chemical reactivities toward the DA cycloaddition, the consecutive cycloadduct dehydrative aromatization and undesired acid-catalyzed side reactions, and inform strategies to enhance DA reactivities and suppress deleterious side reactions from the standpoint of both materials and process design.

An efficient one-pot synthesis of p-xylene from bio-based 2,5-hexanedione and ethanol

A brand-new p-xylene (PX) production route via 2,5-hexanedione (HDO) and ethanol was put forward. And the reaction was successfully catalyzed by organic base - tetrapropylammonium hydroxide modified HZSM-5 zeolite. Under optimum condition, the conversion of 2,5-HDO and selectivity to PX was 89.6 % and 35.2 %, respectively, much higher than the patent HZSM-5 zeolite. For comparison, PX was also produced from 2,5-dimethyfuran (2,5-DMF) and ethanol or 2,5-HDO and ethylene under the same conditions. However, the PX selectivity and yield obtained from 2,5-HDO and ethanol was much poorer than that when 2,5-DMF or ethylene as reactant due to the series competitive dehydration reactions. To investigate the relationship between catalyst properties and performance, the physicochemical properties of catalysts were comprehensively characterized by XRD, N2 adsorption-desorption isotherms, ICP, NH3/CO2-TPD, pyridine-IR, SEM, TEM and MAS NMR. Conclusion can be drawn that the appropriate acidity and hierarchical pore structure in T0.5-HZ catalyst (HZSM-5 modified by 0.5 M tetrapropylammonium hydroxide) were beneficial to high PX selectivity and yield. Among them, the acid site with weak acid site would catalyze 2,5-HDO intramolecular aldol condensation to 3-methylcyclopentenone (MCO), while strong acid site was beneficial for 2,5-DMF hydrolysis to 2,5-HDO. Thus, acid site with moderate strength was advantageous to the conversion of 2,5-HDO to 2,5-DMF. Besides, the enough amount of acid sites and suitable B/L ratio of 0.98 can satisfy the requirements of various dehydration reactions and Diels-Alder reaction between 2,5-DMF and dienophiles, enhancing PX selectivity and yield. Additionally, the hierarchical pore structure enhanced mass transfer efficiency and improved the reaction rate. The promising production for bio-based PX via 2,5-HDO and ethanol lay solid foundation for industrialized production route from lignicellulose.

Selective production of para-xylene from biomass-derived 2,5-dimethylfuran through tandem Diels–Alder/dehydration reactions with a bifunctional Ga,Al-zeolite catalyst

Here we demonstrate that Ga,Al-*BEA zeolites are effective bifunctional catalysts for para-xylene (p-xylene) production from bio-derived 2,5-dimethylfuran (DMF) through tandem Diels–Alder/dehydration reactions.

The role of Ni-containing species on methanol-toluene methylation to p-xylene over ZSM-5 zeolite

The methylation of toluene with methanol is an important process for the preparation of p-xylene (PX). The modification of Ni-containing species in HZSM-5 can improve the yield of PX. However, the active site existence form of Ni is unclear. The intrinsic reaction mechanisms for methylation of toluene with methanol over HZSM-5 with NiOH+ and Ni2+ as Lewis acid have been investigated. The results indicate that the introduction of Ni2+ decreases the activity for the methanol dissociation, whereas NiOH+ enhances the activity with a reduction in activation energy of 100.7 kJ/mol. Furthermore, the generation of three xylenes, as well as the conversion of PX to 1,2,4-Trimethylbenzene (1,2,4-TMB) have also been studied over NiOH+/HZSM-5. It is shown that PX is most easily formed with the lowest energy barrier of 84.8 kJ/mol in four products, implying the introduction of NiOH+ in HZSM-5 favors the formation of PX. In addition, molecular dynamics simulations show that toluene reacts with methanol to form xylenes mainly at the intersection of channels. PX exhibits a much higher self-diffusion coefficient than MX and OX when the temperature rises from 498 to 698 K. It can be concluded that NiOH+ is the active Ni-containing species and NiOH+/HZSM-5 is an excellent catalyst for the production of PX via the methylation of toluene with methanol.

Zirconium-tin phosphate as an efficient catalyst for renewable p-xylene synthesis from biobased 2,5-dimethylfuran and ethylene

Efficient production of renewable p-xylene (PX) from bio-based 2,5-dimethylfuran (DMF) and ethylene is challenging. Herein, novel nanoflake-like zirconium-tin phosphate catalysts were synthesized, and their catalytic performance was evaluated in the conversion of DMF and ethylene to PX. The DMF conversion, PX selectivity and PX yield reached up to 99%, 95.2% and 94.2%, respectively over Zr0.6Sn0.4P under relatively mild conditions. The PX productivity was 61.1 mmolPX·gcat−1·h−1, which is better than that of previously reported catalysts. By combining characterization with activity test, it was found that enhanced DMF and ethylene adsorption is beneficial to promoting the reaction between DMF and ethylene. Precise regulation of acid sites is crucial for inhibiting the occurrence of side reactions and improving the selectivity of PX. The kinetic analysis revealed that Zr0.6Sn0.4P had a relatively low apparent activation energy (39 kJ·mol−1) for this reaction than previously reported catalysts. In addition, the Zr0.6Sn0.4P catalyst exhibited an excellent reusability.

Hollow STW-Type Zeolite Single Crystals with Aluminum Gradient for Highly Selective Production of p-Xylene from Methanol-Toluene Alkylation.

Zeolites with uniform micropores are important shape-selective catalysts. However, the external acid sites of zeolites have a negative impact on shape-selective catalysis, and the microporosity may lead to serious diffusion limitation. Herein, we report on the direct synthesis of hierarchical hollow STW-type zeolite single crystals with a siliceous exterior. In an alkalinous fluoride medium, the nucleation of highly siliceous STW zeolites takes place first, and the nanocrystals are preferentially aligned on the outer surface of the gel agglomerates to grow into single crystalline shells upon crystallization. The lagged crystallization of the internal Al-rich amorphous gels onto the inner surface of nanocrystalline zeolite shells leads to the formation of hollow cavities in the core of the zeolite crystals. The hollow zeolite single crystals possess a low-to-high aluminum gradient from the surface to the core, resulting in an intrinsic inert external surface, and exhibit superior catalytic performance in toluene methylation reactions.

SCM-36 zeolite nanosheets applied in the production of renewable p-xylene from ethylene and 2,5-dimethylfuran

SCM-36 zeolite nanosheets applied in the production of renewable p-xylene from ethylene and 2,5-dimethylfuran

Process simulation for enhanced p-xylene production via aromatics complex integrated toluene methylation with low-cost methanol feedstock

Enhancing the p-xylene (PX) yield for the process of direct crude to chemicals will keep more technological competitiveness and sustainable economics. However, the enhancement would be limited by the ratio of benzene ring to methyl groups in the feedstock. To maximize the PX capacity, the toluene methylation unit is integrated to the traditional aromatic complex with the low-cost methanol as additional feedstock. The detailed process modeling and simulation are presented for the mass balance, energy consumption and technoeconomic analyses. The results show that the PX yield is significantly improved by integrating toluene methylation unit and the additional methanol feedstock to break the limitations of ratio of benzene ring to methyl groups in the original feedstock. By comparing with the traditional aromatic complex, the PX product increases with a growth of 31.24% from 869.70 kmol·h−1 to 1140.92 kmol·h−1 for the methylation integrated process, and the effective utilization rate of benzene ring in the feedstock enhances from 65.74% to 86.23%. Under the minimum temperature difference of 10 °C, the integrated process reduces the unit energy consumption by 5.59% equaling 7.55% of standard oil. Besides, the integrated process needs less total capital investment but produces more annual sales revenues due to the high PX yield and low energy consumption, which exhibits more sensibility to the prices of feedstock and products and greater techno-economic performance than that of traditional aromatic complex.

Decarboxylative [4 + 2] cycloaddition via ligand-to-metal charge transfer photoexcitation of a Cu-MOF

Production of p-xylene (PX) via a broad biomass-derived furan cycloaddition has received incremental interest because of its renewable character.

A comprehensive kinetics for p-xylene increment by isomerizing C8 aromatics over Pt/HZSM-5

Isomerization of C8 aromatics is an indispensable process for industrial production of p-xylene, but there is still a lack of rigorous kinetics of this reacting system. In this paper, the experiments for isomerization of C8 aromatics over Pt/HZSM-5 have been carried out in an isothermal fixed bed reactor under a wide range of operating conditions to obtain the rate laws for isomerization, disproportionation and deethylation reactions. A detailed kinetic model is developed from experimental data to accurately describe the reacting system of C8 aromatics, and the apparent kinetic parameters are estimated by genetic algorithm and least square method. The kinetic model verified by fitting experimental data can well predict the reaction trends of o-xylene, m-xylene and industrial feeds to exhibit good feed adaptability. Therefore, this model will support reactor design and operation.

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 (&gt;80%) and methanol efficiency (66%), with good catalytic stability throughout the 170 h reaction time.

Selective toluene methylation to p-xylene: current status & future perspective

ABSTRACT Industrially, petroleum naphtha reforming and steam cracking are two major multistep and energy-intensive sources for p-xylene production. Additionally, p-xylene is also produced by selective toluene disproportionation, heavy (C9) aromatics trans-alkylation and isomerization of xylenes. Rapidly changing market dynamics from fuels to petrochemicals coupled with growing petrochemicals demand has led to the further exploration of economical and highly p-xylene selective processes by using surplus low-value aromatics. Methylation of toluene with methanol has been envisaged as one such potential opportunity to produce p-xylene. For the purpose, significant efforts have been made in the past forty years to develop suitable shape selective zeolite catalysts and technologies to make toluene methylation a highly p-xylene selective process. Current paper briefly highlights various advancements in the toluene methylation process development and aims to provide an extensive review of several works put up in the past to design suitable catalysts, catalyst’s limitations and developmental challenges for toluene methylation. Further, this paper provides an useful insight for two competing chemistries of toluene alkylation and side-by-side methanol reactions. Finally, motivated by competitive chemistry of methanol conversion reactions, existing catalytic limitations and novel synthesis opportunities in engineering shape selective zeolite catalysis, a way forward is proposed to arrive at a logical and futuristic catalyst design strategy for p-xylene production via toluene methylation. The proposed strategy is envisaged to offer low-to-moderate catalyst acidity, improved toluene methylation activity, high p-xylene selectivity and improved catalyst life which, otherwise, up till now have been the bottlenecks to develop distinctly economical toluene alkylation to p-xylene process.

MOF derived 2.x-dimensional trimetallic catalysts for selective aromatization to p-xylene

Aromatization to p-xylene is challenging in which the catalyst should be designed and tuned. A series of layered MOF(Al, Cr, Fe)der catalysts derived from trimetallic MIL-53(Al, Cr, Fe) have been synthesized by one-pot method and systematically investigated for selective production of p-xylene from diisobutylene. The catalyst showed the p-xylene yield of 21% with p-xylene selectivity of 91% in aromatics under relative milder conditions. The highly homogenously dispersed of Al, Cr and Fe elements greatly enhanced the formation of the active monochromate species. The mesoporous 2.x dimensional structure comprised of stacking layers exposed more available active Cr species. The coordination unsaturated active sites by introduction of Fe was favorable for the aromatization of diisobutylene. The regeneration and recycle experiments showed the catalyst had fine structure stability and regeneration performance.

Renewable p-xylene synthesis via biomass-derived 2,5-dimethylfuran and ethanol by phosphorous modified H-Beta zeolite

The sustainable production of p-xylene (PX), via Diels-Alder cycloaddition between biomass-derived 2,5-dimethylfuran (2,5-DMF) and ethanol followed by subsequent dehydration, was catalyzed by a series of nitric acid and phosphoric acid modified H-Beta zeolites. It is tentatively suggested that the multifold increase of p-xylene selectivity and reduction of coke amount for NPB-2 (H-Beta zeolite modified by 2 M HNO3 combining with H3PO4) was attributed to existence of acid sites with appropriate amount and strength. NH3-TPD and multiple ss MAS NMR results revealed that nitric acid can remove framework and extraframework Al species effectively, leading to the decrease of total acid amount. While by further phosphoric acid modification, not only P species was introduced in the crystal, the tetrahedrally coordinated framework Al was also turned into octahedrally coordinated framework Al, resulting in the reduction of strong acid sites and increase of weak acid sites, which can slow down the dehydration reaction rate of 2,5-hexanedione (2,5-HDO) to 3-methyl-2-cyclopentenone (MCO) and promote dehydration of cycloaddition to p-xylene. Besides, the N2 physical adsorption showed the specific surface area and pore volume were increased after modification, further enhancing accessibility and utilization efficiency of acid sites. This study promotes the development and application of P-containing zeolite in acid catalyzed reactions.

Rational Design of Zinc/Zeolite Catalyst: Selective Formation of p-Xylene from Methanol to Aromatics Reaction.

The production of p-xylene from the methanol to aromatics (MTA) reaction is challenging. The catalytic stability, which is inversely proportional to the particle size of the zeolite, is not always compatible with p-xylene selectivity, which is inversely proportional to the external acid sites. In this study, based on a nano-sized zeolite, we designed hollow triple-shelled Zn/MFI single crystals using the ultra-dilute liquid-phase growth technique. The obtained composites possessed one ZSM-5 layer (≈30 nm) in the middle and two silicalite-1 layers (≈20 nm) epitaxially grown on two sides of ZSM-5, which exhibited a considerably long lifetime (100 % methanol conversion >40 h) as well as an enhanced shape selectivity of p-xylene (>35 %) with a p-xylene/xylene ratio of ≈90 %. Importantly, using this sandwich-like zeolite structure, we directly imaged the Zn species in the micropores of only the ZSM-5 layer and further determined the specific structure and anchor location of the Zn species.

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

Is hydrolysis a bad news for p-xylene production from 2,5-dimethylfuran and ethylene? Mechanism investigation into the role of acid strength during 2,5-hexanedione conversion

Although a precise understanding of acid strength would be essential to elucidate the reaction mechanism and boost the catalytic activity, it is still severely deficient during p-xylene (PX) production from 2,5-dimethylfuran (DMF). Herein, a series of metal phosphate catalysts featuring varied acid strength are prepared and afford an ideal platform. A combination study including kinetic analysis, converting pathway investigation and isotopic labelling experiments reveal the reversible reaction between DMF and 2,5-hexanedione (HDO) and the vital role of strong acid sites during the further conversion of HDO. DMF hydrolysis to HDO is not the intrinsic cause for decrease in PX selectivity, but further condensation of HDO over the strong acid sites is to blame. It destroys the equilibrium state of the reversible reaction and leads to loss in PX selectivity and carbon balance. Besides, the process starting with HDO and ethylene for PX production and strategies to improve PX selectivity have also been proposed. This work provides a much deeper insight into the crucial role of acid strength, which would be constructive for rational design of new catalysts and the corresponding mechanistic understanding.

Simultaneous Optimization and Heat Integration of an Aromatics Complex with a Surrogate Model

The aromatics complex is essential in the production of p-xylene and contains several distillation towers and reactors, making this process highly energy intensive. To save energy for the aromatics...

Catalytic synthesis of renewable p-xylene from biomass-derived 2,5-dimethylfuran: a mini review

In this work, the renewable synthesis of p-xylene (PX) from biomass-derived carbohydrates has been reviewed. PX is a crucial chemical feedstock and an essential starting material of polyethylene terephthalate (PET). PX can be produced selectively by the Diels-Alder reaction between ethylene and 2,5-dimethylfuran (DMF) followed by catalytic dehydration of the oxanorbornene adduct. DMF is primarily produced by the catalytic hydrogenation of 5-(hydroxymethyl)furfural (HMF), a furanic intermediate produced by the acid-catalyzed hydrolysis/dehydration of biomass-derived hexoses. With ethylene being sourced by dehydrating bioethanol, PET can be made biorenewable in its entirety. The atom economy and carbon efficiency of converting glucose into PX have been calculated. The existing literature (both theoretical and experimental) on the catalytic production of PX from DMF and ethylene are summarized, and future directions on this research have been proposed. The effect of Bronsted and Lewis acidity, porosity, and surface area of the heterogeneous catalysts on the selectivity and yield of PX have been highlighted. In addition, the techno-economic analysis of renewable PET, its future prospects based on the petroleum market, and the possibility of a circular economy of PET using chemical and enzymatic recycling strategies have been discussed.