P-xylene Research Articles

3D-printed zeolite with combined structure for xylene isomerization

Para-xylene (PX) is an important material for the production of polyester fibers and resins; it is widely used in fuel and medical fields. To alleviate the low strength and unsatisfactory mass-transfer performance of conventional catalysts during xylene isomerization, a combined-structure catalyst is fabricated using three-dimensional (3D) printing technology. In this study, a catalyst ink formulation and preparation method suitable for 3D printing is designed, and a wet ball-milling process is adopted to improve the stability of the ink during 3D printing. The mass-transfer performance of the structured catalysts are investigated via computational fluid dynamics simulation; thus, combined-structure catalysts with high diffusivity and high specific surface area are realized. Compressive strength tests and xylene isomerization reaction experiments are conducted on the three-dimensionally printed catalysts and extrudates. Compared with the extrudates, the three-dimensionally printed catalyst exhibits higher mechanical strength and better catalytic performance. Among the structured catalysts, the combined linear-staggered/wave-vertical (LS/WV) catalyst demonstrates the best overall performance with a PX concentration in xylene of 22.89% and a high ethylbenzene conversion of 36.70%, which is approximately 21.68% higher than the extrudates.

Excellent catalytic performance of Cu+ modified HZSM-5 to produce para-xylene via the toluene methylation reaction: High catalytic active site combining with channel shape selectivity

The toluene methylation reaction via methanol is an important process to produce high-value para-xylene (PX), it has always been our goal to explore a catalyst with high activity and selectivity for PX. Cu+ is used to modify HZSM-5 (BAS/Cu+-HZSM-5) zeolite, and the microscopic reasons for the excellent catalytic performance to produce PX on BAS/Cu+-HZSM-5 are investigated according to the intrinsic reaction and molecular diffusion. The intrinsic activation energies of methanol dissociation and xylene formation on BAS/Cu+-HZSM-5 are obtained by the density functional theory (DFT). Calculations indicate that the energy required for methanol dissociation is 109.7 kJ mol−1, which is lower than that on pure HZSM-5. In addition, PX, meta-xylene (MX) and ortho-xylene (OX) formed with little activation energies of 12.7, 11.8 and 14.2 kJ mol−1, respectively. Therefore, the formation of these xylenes on BAS/Cu+-HZSM-5 has high activity and strong competition. On the other hand, the self-diffusion coefficients of three xylenes on BAS/Cu+-HZSM-5 are analyzed by molecular dynamics (MD) simulation. And the self-diffusion coefficient of PX is found to be much larger than that of MX and OX in all cases, which indicates that the channel characteristics of BAS/Cu+-HZSM-5 are beneficial to the diffusion and separation of PX. Therefore, it can be concluded that BAS/Cu+-HZSM-5 has better catalytic performance and high PX selectivity for the toluene methylation reaction via methanol.

Separation of p-xylene and m-xylene by simulated moving bed chromatography with MIL-53(Fe) as stationary phase

The separation of p-xylene (PX) and m-xylene (MX) isomers with near boiling points is a worldwide problem. The metal-organic framework material is an ideal stationary phase for chromatographic separation because of its high porosity, homogeneous pore diameter and good chemical stability. In this paper, a simulated moving bed (SMB) chromatography system with MIL-53(Fe) as the stationary phase and petroleum ether-dichloromethane as the mobile phase was designed to separate PX and MX at ambient temperature. Firstly, according to the elution curves of a single column, nonlinear competitive Langmuir adsorption isotherm equation was confirmed by equilibrium dispersive chromatography model. Then, the SMB separation zone was determined based on triangle theory, and the SMB operating conditions were optimized. Finally, the purity, recovery and productivity of PX reached 100.0%, 99.1% and 93.1 g/L/h, respectively; the purity, recovery and productivity of MX reached 96.4%, 100.0% and 23.5 g/L/h, respectively; the solvent consumption was 0.42 L/g.

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.

Lignin-based sulfonated carbon as an efficient biomass catalyst for clean benzylation of benzene ring compounds

Low-temperature carbonization–sulfonation two-step process or one-step sulfonation process was employed to draft sodium lignosulfonate (SLS), the primary biological macromolecule ingredient of papermaking black liquor, into lignin-based sulfonated carbon. The two-step lignin-based sulfonated carbon named SLC400,1S was found to be an efficient catalyst for clean Benzyl-alcohol (BA) route Friedel-Crafts (F-C) benzylation of benzene ring compounds. FT-IR, XRD, Raman spectra, XPS, SEM with EDX-mapping, TGA-DSC, acid-base titration, and n-butylamine–acetonitrile titration characterizations demonstrated that the specific two-step process could introduce porous properties and a large number of surface sulfonic, hydroxyl, and carboxyl active groups into the structure of the prepared material, which was found to account for the good catalytic performance for benzylation. Similar to that of hierarchical mesoporous ZSM-5 under optimal conditions, the apparent activation energy for benzylation of paraxylene (PX) with BA over SLC400,1S was estimated to be 119 kJ·mol−1. The common by-product of BA route benzylation, dibenzyl ether (DBE), was almost inhibited because of the extraordinary activity of SLC400,1S and the optimized reaction conditions. A 12-run recycling test demonstrated easy recovery and steady reusability of the above lignin-based sulfonated carbon catalyst.

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.

Toluene methylation with syngas to para-xylene by bifunctional ZnZrOx-HZSM-5 catalysts

Toluene methylation with methanol on H-ZSM-5 (Z5) zeolite for the directional transformation of toluene to xylene has been industrialized. However, great challenges remain because of the high energy barrier of methanol deprotonation to the methoxy group, the side reaction of methanol to olefins, coke formation, and the deactivation of zeolites. Herein, we report the toluene methylation coupled with CO hydrogenation to showcase an enhancement in para-xylene (PX) selectivity by employing a bifunctional catalyst composed of ZnZrOx (ZZO) and modified Z5. The results showed that a PX selectivity of up to 81.8% in xylene and xylene selectivity of 64.8% in hydrocarbons at 10.3% toluene conversion can be realized over the bifunctional catalyst on a fixed-bed reactor. The selectivity of gaseous hydrocarbons decreased to 10.9%, and approximately half of that was observed in methanol reagent route where the PX selectivity in xylene was 38.8%. We observed that the acid strength, the quantity ratio of Brönsted and Lewis acid sites, and the pore size of zeolites were essential for the PX selectivity. The investigation of the H2/D2 kinetic isotope effect revealed that the newborn methyl group in xylene resulted from the hydrogenation of CO rather than toluene disproportionation. Furthermore, the catalyst showed no evident deactivation within the 100 h stability test. The findings offer a promising route for the production of value-added PX with high selectivity via toluene methylation coupled with syngas conversion.

Bifunctional catalysts with versatile zeolites enable unprecedented para-xylene productivity for syngas conversion under mild conditions

The direct conversion of syngas to aromatics has received considerable attention. The development of a highly active and stable catalyst with tunable selectivity for the synthesis of aromatics remains a great challenge, notwithstanding the understanding of the reaction mechanism. In this study, we fabricated a series of high-performance bifunctional catalysts comprising CoMnAl catalysts, which contain Co 2 C nanoprisms as the active phase, and versatile HZSM-5@silicalite-1 zeolites, with a hollow nanostructure and a scaly shell, for the transformation of syngas into aromatics. The catalysts achieve a CO conversion >70% under mild reaction conditions (280°C, 2 MPa), with ultrahigh stability. The selectivity toward aromatics is higher than 63% with <2.9% selectivity toward CH 4 , and the para -xylene (PX) fraction of the aromatics produced reaches 34.7%, leading to unprecedentedly high space-time yield of PX. Furthermore, the reaction pathway and the intermediates involved in the formation of the aromatic products are also determined. • ZSM-5@silicalite-1 zeolite with a hollow nanostructure and a scaly shell is prepared • CoMnAl/HZSM-5@S1 composite catalyst shows high activity, selectivity, and stability • Versatile HZSM-5 zeolite enables unprecedentedly high yield of para -xylene at 280°C • Oxygen-containing aromatic compounds play a crucial role in aromatics formation The direct transformation of syngas to aromatics, especially para -xylene (PX), has received considerable attention and can be achieved using tandem catalysts through methanol or olefin intermediates. However, it remains a great challenge to develop efficient catalysts with high catalytic activity, selectivity, and stability. We fabricated nanosized HZSM-5 with a hollow structure to enhance the diffusion of the intermediates and products, improving both the CO conversion and the aromatic selectivity. The addition of a scaly silicalite-1 layer grown epitaxially on the HZSM-5 crystals effectively inhibits side reactions from occurring without affecting the diffusion property of the zeolites; thus, the conversion of syngas to PX is improved, and catalyst shows ultrahigh stability. In addition to the development of a high-performing catalyst with industrial application potential, this work significantly improves our understanding of the complex reaction network of syngas to aromatics. To develop a highly active and stable catalyst with tunable selectivity for syngas to aromatics, especially para -xylene, versatile zeolites with a hollow nanostructure and a scaly shell were fabricated and combined with CoMnAl catalysts, with Co carbide nanoprisms as the active phase. The combined catalyst exhibited ultrahigh catalytic activity, selectivity, and stability under mild reaction conditions. Oxygen-containing aromatic compounds produced through the coupling of CO with olefins or higher oxygenates play a crucial role in the formation of aromatics.

Catalytic Transformation of PET and CO2 into High‐Value Chemicals

AbstractPolyethylene terephthalate (PET) and CO2, two chemical wastes that urgently need to be transformed in the environment, are converted simultaneously in a one‐pot catalytic process through the synergistic coupling of three reactions: CO2 hydrogenation, PET methanolysis and dimethyl terephthalate (DMT) hydrogenation. More interestingly, the chemical equilibria of both reactions were shifted forward due to a revealed dual‐promotion effect, leading to significantly enhanced PET depolymerization. The overall methanol yield from CO2 hydrogenation exceeded the original thermodynamic equilibrium limit since the methanol was in situ consumed in the PET methanolysis. The degradation of PET by a stoichiometric ratio of methanol was significantly enhanced because the primary product, DMT was hydrogenated to dimethyl cyclohexanedicarboxylate (DMCD) or p‐xylene (PX). This synergistic catalytic process provides an effective way to simultaneously recycle two wastes, polyesters and CO2, for producing high‐value chemicals.

Catalytic Transformation of PET and CO2 into High-Value Chemicals.

Polyethylene terephthalate (PET) and CO2 , two chemical wastes that urgently need to be transformed in the environment, are converted simultaneously in a one-pot catalytic process through the synergistic coupling of three reactions: CO2 hydrogenation, PET methanolysis and dimethyl terephthalate (DMT) hydrogenation. More interestingly, the chemical equilibria of both reactions were shifted forward due to a revealed dual-promotion effect, leading to significantly enhanced PET depolymerization. The overall methanol yield from CO2 hydrogenation exceeded the original thermodynamic equilibrium limit since the methanol was in situ consumed in the PET methanolysis. The degradation of PET by a stoichiometric ratio of methanol was significantly enhanced because the primary product, DMT was hydrogenated to dimethyl cyclohexanedicarboxylate (DMCD) or p-xylene (PX). This synergistic catalytic process provides an effective way to simultaneously recycle two wastes, polyesters and CO2 , for producing high-value chemicals.

Niobium grafted mesoporous silica for the production of biorenewable p-xylene from concentrated 2,5-dimethylfuran

The Diels–Alder cycloaddition of bio-based 2,5-dimethylfuran (DMF) and ethylene and the subsequent dehydration of the cycloadduct intermediate hold promise to produce renewable p-xylene (PX) from biofeedstocks.

Information Dissemination and Control of NIMBY Projects under Stigmatization

NIMBY (Not in My Backyard) projects are easily stigmatized due to their environmental risk. Stigmatization enlarges residents’ risk perception, urges residents to spread information, and takes actions to resist project implementation, causing environmental mass emergency. Taking paraxylene (PX) project as an example, information dissemination model of NIMBY project under stigmatization based on SEIR model in small world network was established, and the information dissemination process and characteristics of NIMBY project under stigmatization were simulated and analysed. The results show that (1) the public risk perception deviation caused by stigmatization promotes residents to disseminate information; (2) stigmatization has a greater impact on the information dissemination of NIMBY project with low environmental risk; (3) stigmatization accelerates the speed of information dissemination and increases the number of residents participating in information dissemination in different dissemination environment. The contribution of this paper is that SEIR model in small world network is used to verify the role of stigmatization in promoting information dissemination of NIMBY project by comparing the information dissemination before and after stigmatization.

Enhancement of p-xylene selectivity in the reaction between 2,5-dimethylfuran and ethanol over an ammonium fluoride-modified ZSM-5 zeolite

A renewable synthesis of p-xylene (PX) via 2,5-dimethylfuran (2,5-DMF) and ethanol was achieved on a hierarchical MFI zeolite, which shows excellent performances with PX selectivity of 78% and yield of 55%.

Effect of Wood-Based Panels and Varnish Types on VOC Emissions in Furniture Production

This study investigated the effects of varnishes on VOCs emissions from wood-based panels of standard particle panels (PB) and medium density fiber panels (MDF) which are covered by beech veneer and varnished by three different types of varnishes. The highest value was 624,90 ppm for Toluene, while the lowest was 0,30 ppm for Para xylene in respect to the Particleboards which were covered by beech veneered and varnished with cellulosic varnish. However, samples of beech veneered and varnished with synthetic and polyurethane varnishes yielded less gas emission than cellulosic varnish. The samples of MDF, covered with beech veneer and varnished polyurethane varnished yielded gas emission more than the synthetic (100%) and cellulosic varnishes (220%). All values show that gas emission reduces its effect within time in respect to the manufacturing time, after drying period, 15- and 30-days measurements.

Civic Participation in Chinese Cyberpolitics: A Grounded Theory Approach of Para-Xylene Projects.

The internet provides a free and convenient platform for the public to obtain political information and participate in political life. Meanwhile, there occurs fierce confrontation of various values and ideologies, shaping a complicated and changeable field of public opinion. The strategies of civic participation and the generation of public opinion show quite different characteristics in such a mediatized society. This article aimed to study civic participation in Chinese cyberpolitics and to find its patterns and the logic behind it. Due to the natural advantage of the environmental issues in its commonality, the internet events in the last decade related to the PX (para-xylene) project were selected as the research object. This study used grounded theory as the method and conducted a cross-case analysis on the original data captured on Weibo—one of the most popular social media sites in China. Finally, four patterns of civic participation in internet events were found and summarized, as well as the intervention and influence of media logic in different modes. However, it is political logic, rather than media logic, that reveals greater vitality in the civic participation of cyber deliberation. Mediatization does exist but is far from dominance. It has certain significance for the supervision and management of public opinion and the rational and harmonious development of civic participation in public issues.

Capsule-like zeolite catalyst fabricated by solvent-free strategy for para-Xylene formation from CO2 hydrogenation

An efficient Na-FeMn/HZSM-5@Silicalite-1 catalyst was rationally designed for direct conversion of CO2 to aromatics. The tailor-made HZSM-5@Silicalite-1 core-shell zeolite was prepared by a facile solvent-free method. The solvent-free synthesis of core-shell zeolite could not only address pollution issues by eliminating the large utilization of organic reagents, but also exhibit a better performance for separating para-Xylene (PX) from xylenes with the assistance of capsule-like zeolite oriented synthesis. For CO2 to aromatics reaction, Na-FeMn combining with capsule-like HZSM-5@Silicalite-1 catalyst could reach 81.1% PX/X (the C-mol ratio of PX to all xylenes) ratio, which was higher than those of conventional core-shell zeolites, such as HZSM-5@SiO2 and HZSM-5@Silicalite-1 core-shell zeolites which were obtained from traditional chemical liquid deposition and hydrothermal methods. The as-synthesized zeolite paves a new route for efficient conversion of CO2 molecules into valuable PX, and provides a facile method for regulating surface acid properties of zeolite.

Diels–Alder Cycloaddition of Biomass-Derived 2,5-Dimethylfuran and Ethylene over Sulfated and Phosphated Metal Oxides for Renewable p-Xylene

In this work, sulfated and phosphated metal oxides were studied as catalysts for the Diels–Alder cycloaddition of biomass-derived 2,5-dimethylfuran (DMF) and ethylene to understand the effect of acid strength on the reaction. Four catalysts with varied acidity, namely sulfated SiO2, sulfated TiO2, phosphated SiO2, and phosphated TiO2, were prepared via wet impregnation using sulfuric acid and phosphoric acid as precursors, and their structural and acid properties were examined using X-ray diffraction, Brunauer–Emmett–Teller analysis, Fourier transform infrared spectroscopy, solid state 31P magic angle spinning nuclear magnetic resonance spectroscopy, and temperature programmed desorption of ammonia. The results revealed that the acidity of the catalysts was largely influenced by the type of the acid functional group and the support as well as the calcination temperature. The conversion of DMF and the selectivity toward p-Xylene (PX) were generally correlated with the total acid site density and the acid–metal oxide interaction strength, which in turn affected the acid strength. Overall, phosphated SiO2 and TiO2 calcined at 773 K were identified as the most active and selective catalysts, exhibiting a high PX selectivity of over 70% and DMF conversion of 80% at 523 K after 6 h. The origin of the stability of the highly active phosphated catalysts was also investigated in detail.

A nonchlorinated solvent-processed polymer semiconductor for high-performance ambipolar transistors.

Ambipolar polymer semiconductors are potentially serviceable for logic circuits, light-emitting field-effect transistors (LFETs) and polymer solar cells (PSCs). Although several high-performance ambipolar polymers have been developed, their optoelectronic devices are generally processed from toxic chlorinated solvents. To achieve the commercial applications of organic FETs (OFETs), the polymers should be processed from nonchlorinated solvents, instead of chlorinated solvents. However, most conjugated polymers show poor solubility in nonchlorinated solvents. It is of great importance to develop ambipolar polymers that can be processed from nonchlorinated solvents. Here, we develop a nonchlorinated solvent processed polymer named poly[7-fluoro-N, N′-di(4-decyltetradecyl)-7′-azaisoindigo-6′,6″-(thieno[3,2-b]thiophene-2,5-diyl)-7‴-fluoro-N″, N‴-di(4-decyltetradecyl)-7″-azaisoindigo-6,6‴-([2,2″-bithiophene]-5,5″-diyl)] (PITTI-BT) by designing a monomer with a large molar mass. The polymer displays good solubility in p-xylene (PX). Well-aligned films of PITTI-BT are achieved by an off-center spin-coating (SC) method. Based on the high-quality films, the OFETs fabricated from PX solution achieve record ambipolar performance with hole and electron mobilities of 3.06 and 2.81 cm2 V−1 s−1, respectively. The combination of nonchlorinated solvents and good alignment process offers an effective and eco-friendly approach to obtain high-performance ambipolar transistors.

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.

Effect of Lewis/Brønsted acid sites in HZSM−5 zeolite on the selectivity of para-xylene during methylation of toluene with methanol

• The participation of Lewis acid site is good for the dissociation of methanol. • The activity of methanol dissociation has positive correlation with the acid strengths of HZSM-5 zeolites. • ZnOH + /BAS-HZSM−5 with the moderate acid strength is conducive to the formation of PX. The methylation reaction of methanol and toluene to xylenes has been carried out in Brønsted Acid Sites (BAS)−HZSM−5, AlOH 2+ /BAS−HZSM−5 and ZnOH + /BAS−HZSM−5 catalysts. The stronger acid strengths are produced in AlOH 2+ /BAS−HZSM−5 and ZnOH + /BAS−HZSM−5 due to the synergistic effect of Lewis Acid Sites (LAS) and BAS compared to BAS−HZSM−5, which is beneficial to the dissociation of methanol. AlOH 2+ /BAS−HZSM−5 shows the highest activity for methanol dissociation with the strongest acid strength. The Gibbs free energy barrier is only 68.2 kJ·mol −1 , but the formation of Para -xylene (PX) needs to overcome a high barrier of 129.2 kJ·mol −1 . However, ZnOH + /BAS−HZSM−5 exhibits relative high activity for the formation of methoxy with the Gibbs free energy barrier of 113.9 kJ·mol −1 , and 92.9 kJ·mol −1 for PX. Meanwhile, the formation of PX is easiest among three xylenes. Therefore, ZnOH + /BAS−HZSM−5 can be as the promising catalyst for the preparation of PX during methylation of toluene with methanol.