P-xylene Yield Research Articles

Insight into the enhanced catalytic performance of phosphate-modified ZrO2/SBA-15 for the conversion of biobased 2,5-dimethylfuran and ethylene into p-xylene

Catalytic conversion of biomass-derived platform chemicals into bulk chemicals p-xylene (PX) is appealing yet challenging due to low catalytic efficiency and severe reaction conditions. In this work, we fabricated a series of phosphate-modified ZrO2/SBA-15 (xP-Zr/SBA-15) via adjusting the addition of phosphoric acid, and used them for the catalytic conversion biomass-derived 2,5-dimethylfuran (DMF) and ethylene to PX. Because of the enhanced adsorption capability for the reactant molecules (DMF and ethylene) and the good synergistic effect between Brønsted acid sites (P-OH) and Lewis acid sites (Zr4+), 30P-Zr/SBA-15 revealed an excellent catalytic performance in the selective conversion of DMF into PX. The DMF conversion was 98.5%, PX yield was 92.0% at 250 °C for 12 h, and the corresponding PX productivity was upto 50.5 mmolPX·gcat−1·h−1. The results are far superior to those obtained on most previously reported catalysts in the literature under similar reaction conditions. The kinetic study revealed that 30P-Zr/SBA-15 has a lower apparent activation energy for the tandem reaction including the Diels-Alder reaction (57.0 kJ·mo−1) and dehydration reaction (37.7 kJ·mo−1). Moreover, the 30P-Zr/SBA-15 catalyst exhibited the excellent recyclability and could be recycled at least six times without a significant loss of activity. On the basis of the temperature-programmed surface reaction of DMF and ethylene, a reasonable reaction mechanism was proposed.

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.

Highly efficient catalytic conversion of biomass-derived 2,5-dimethylfuran into renewable p-xylene over zirconium phosphate catalysts

A series of zirconium phosphates (ZrP-x) with various P/Zr ratios were prepared. Among the catalysts, ZrP-2.5 with a high specific surface area of 410.9 m2·g−1 and abundant mesopores exhibited outstanding catalytic performance in the synthesis of p-xylene (PX) from 2,5-dimethylfuran (DMF) and ethylene. A high PX yield of 89.2% and a productivity of 72.3 mmolPX·gcat−1·h−1 were achieved at 250 °C using a small amount of catalyst. The excellent catalytic performance of ZrP-2.5 was attributed to the synergy between the large quantities of acidic sites with appropriate acid strength distribution, balanced Brønsted and Lewis acidity, and abundant mesopores. In addition, the catalyst had excellent recyclability and stability. In-situ FT-IR spectra of adsorbed DMF and ethylene revealed the crucial roles of P-OH and the coordinately unsaturated Zr(IV) in the adsorption and reaction process, which is beneficial to understanding the reaction mechanism and designing highly efficient catalysts.

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.

Construction of a One-Dimensional Al-Rich ZSM-48 Zeolite with a Hollow Structure.

Diffusion limitation and acid deficiency are two main challenges that the ZSM-48 zeolite faces in practical application. To date, there have been few effective strategies to solve both problems, simultaneously. Also, it is also a challenge to construct a hollow structure in a one-dimensional (1D) zeolite. Herein, an Al-rich ZSM-48 zeolite with a hollow structure is constructed through an alumination-recrystallization strategy, thereby solving the problems related to diffusion and acidity simultaneously. The hollowness and enrichment of aluminum can be controlled by judiciously matching the desilication and recrystallization. The silica to alumina ratio (SAR) of the ZSM-48 zeolite can be tuned from 130 to 45, which breaks the SAR limitation of conventional synthesis. On the basis of the different characterization results, the whole crystallization can be divided into two stages: rapid desilication-alumination and time-consuming recrystallization. In the selective desilication-recrystallization process, the preferential special distribution of the organic template leads to the formation of a hollow structure and the healing of mesopores at the outer shell, as evidenced by structured illumination microscopy images. Due to the enhancement in diffusion ability and acid density, the obtained hollow Al-rich ZSM-48 zeolite exhibits excellent catalytic stability and high p-xylene yield (∼26%) in the m-xylene isomerization reaction (WHSV = 18 h-1), indicating its strong industrial application potential.

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.

Spatiotemporal Coke Coupling Enhances para-Xylene Selectivity in Highly Stable MCM-22 Catalysts.

Identifying zeolite catalysts that can simultaneously optimize p-xylene selectivity and feed utilization is critical to toluene alkylation with methanol (TAM). Here, we show that zeolite MCM-22 (MWW) has an exceptional catalyst lifetime in the TAM reaction at high operating pressure, conversion, and selectivity. We systematically probe the catalytic behavior of active sites in distinct topological features of MCM-22, revealing that high p-xylene yield and catalyst stability are predominantly attributed to sinusoidal channels and supercages, respectively. Using a combination of catalyst design and testing, density functional theory, and molecular dynamics simulations, we propose a spatiotemporal coke coupling phenomenon to explain a multistage p-xylene selectivity profile wherein the formation of light coke in supercages initiates the deactivation of unselective external surface sites. Our findings indicate that the specific nature of coke is critical to catalyst performance. Moreover, they provide unprecedented insight into the synchronous roles of distinct topological features giving rise to the exceptional stability and selectivity of MCM-22 in the TAM reaction.

Selective catalytic synthesis of bio-based terephthalic acid from lignocellulose biomass

_Efficient synthesis of bio-based chemicals from renewable lignocellulosic biomass is of great significance to promote the sustainable development of chemical industry. This work aims to demonstrate that terephthalic acid, a bulk high value chemical in petrochemical industry, can be synthesized using biomass. This novel controllable transformation process was started with the selective catalytic pyrolysis of sawdust biomass to form p-xylene intermediate. The high p-xylene yield of 23.4% was obtained using the Ga2O3/SiO2/HZSM-5 catalyst under the optimized reaction condition. Subsequently, the selective oxidation of the biomass-derived aromatic intermediates to terephthalic acid was realized with the metal oxide catalysts. The highest terephthalic acid yield of 72.8% with the terephthalic acid selectivity of 82.3% was achieved using the CoMn2O4@SiO2@Fe3O4 catalyst. Based on the study of the catalytic conversion of the model compounds and the catalyst characterizations, the reaction pathways and possible reaction mechanism have been proposed.

Selective upgrading of biomass pyrolysis oil into renewable p-xylene with multifunctional M/SiO2/HZSM-5 catalyst

This work indicated that p-xylene, an important bulk chemical in petrochemical industry, was able to be produced using the renewable biomass pyrolysis-derived bio-oil. The multifunctional catalysts (especially 3%Zn/20%SiO2/HZSM-5) simultaneously promoted the selectivity and yield of p-xylene in the catalytic upgrading of the bio-oil or bio-oil/methanol mixture. The SiO2 layer loaded on the catalysts significantly increased the selectivity of p-xylene by decreasing the external acidity of the catalyst surface. The addition of the active elements such as Zn and Ga into the HZSM-5 zeolite further improved the p-xylene yield by promoting the decarbonylation, decarboxylation and aromatization reactions. The optimized catalyst of 3%Zn/20%SiO2/HZSM-5 showed the maximum p-xylene yield of 18.7% with high p-xylene to xylenes ratio of 93.8%. The reaction pathways were proposed according to the detailed investigation for the catalytic cracking of different bio-oils and the functional groups in the products. Potentially, the resulting p-xylene product from the bio-oil can be used for high added value chemical or high octane gasoline additive.

Catalytic conversion of biomass-derived polyols into para-xylene over SiO2-modified zeolites

This work proved that biomass-based polyols (sorbitol, xylitol, erythritol, glycerol and ethanediol) were able to be converted into high-value chemical (p-xylene) by catalytic cracking of polyols, alkylation of aromatics, and the isomerization of xylenes over the SiO2-modified zeolites. Compared to the conventional HZSM-5 zeolite, the SiO2-containing zeolites considerably increased the selectivity and yield of p-xylene due to the reduction of external surface acidity and the narrowing of pore entrance. The influences of the methanol additive, reaction temperature, and types of polyols on the selectivity and yield of p-xylene were investigated in detail. Catalytic cracking of polyols with methanol significantly enhanced the production of p-xylene by the alkylation of toluene with methanol. The highest p-xylene yield of 10.9 C-mol% with a p-xylene/xylenes ratio of 91.1% was obtained over the 15wt%SiO2/HZSM-5 catalyst. The reaction pathway for the formation of p-xylene was addressed according to the study of the key reactions and the characterization of catalysts.

Selective conversion of furans to p‐xylene with surface‐modified zeolites

AbstractBACKGROUNDOwing to the growing consumption of oil and the negative environmental impacts, the production of p‐xylene (PX) from renewable biomass has gained significant attention recently. However, the major challenge for the production of PX from biomass or furans is how to improve the yield and selectivity of PX, along with reducing coke.RESULTSThe para selectivity in the catalytic conversion of furans was greatly enhanced owing to the deactivation of external surface and the adjustment of pore entrance. Co‐catalytic conversion of furans and methanol significantly enhanced the production of PX by the Diels–Alder reactions between furans and olefins and the alkylation of benzene/toluene with methanol. The highest PX yield of 17.8 C‐mol% with a p‐xylene/xylene ratio of 94.5% was obtained by the co‐conversion of 2‐methylfuran with methanol over the 15%La/10%Ce/HZ catalyst.CONCLUSIONThis work proved that furans (2‐methylfuran, 2,5‐dimethylfuran, furfural and furan) were able to be selectively converted into a high‐value chemical (PX) over the 15%La/10%Ce/HZ catalyst. The transformation mainly involved four key reactions: the catalytic cracking of furans, the Diels–Alder reactions, the alkylation of aromatics and the isomerization of xylenes over the surface‐modified zeolite. © 2019 Society of Chemical Industry

Enhancement of Bio-based para-Xylene Selectivity in Catalytic Fast Pyrolysis of Cellulose Using a Surface-modified Mg/P/HZSM-5 Catalyst

With the growing consumption of oil, the production of p-xylene(PX) from renewable biomass has gained significant attention recently. This work demonstrated that cellulose, a main component in lignocellulosic biomass, was directly converted into PX over the Mg/P surface-modified zeolites. The catalysts modified by the incorporation of P2O5 and MgO into HZSM-5(HZ) promoted the isomerization of m-/o-xylenes to p-xylene. The PX selectivity was greatly enhanced using the modified zeolites due to the deactivation of external surface and the adjustment of pore entrance. In addition, the addition of methanol to cellulose was beneficial to increase the selectivity of xylenes due to the alkylation reactions and the Diels-Alder reactions between cellulose-derived furans and methanol-derived olefins. The highest PX yield of 10.7%(molar fraction) with a high PX selectivity in xylenes(97.1%) was obtained over the 10%Mg/5%P/HZ catalyst. The reaction pathway for the formation of p-xylene was addressed according to the study of the key reactions and the characterization of catalysts.

Highly selective production of renewable p-xylene from bio-based 2,5-dimethylfuran and ethylene over Al-modified H-Beta zeolites

H-Beta zeolite with further dealumination and modification with alumina shows excellent and durable performances in the synthesis of renewable p-xylene (PX) via bio-based 2,5-dimethylfuran and ethylene with a PX yield of 97% and much less coke content.

Renewable p-xylene production by co-catalytic pyrolysis of cellulose and methanol

This work developed a one-step process for renewable p-xylene production by co-catalytic fast pyrolysis (co-CFP) of cellulose and methanol over the different metal oxides modified ZSM5 catalysts. It has been proven that La2O3-modified ZSM5(80) catalyst was an effective one for the production of bio-based p-xylene. The selectivity and yield of p-xylene strongly depended on the acidity of the catalysts, reaction temperature, and methanol content. The highest p-xylene yield of 14.5 C-mol% with a p-xylene/xylenes ratio of 86.8% was obtained by the co-CFP of cellulose with 33wt% methanol over 20%La2O3-ZSM5(80) catalyst. The deactivation of the catalysts during the catalytic pyrolysis process was investigated in detail. The reaction pathway for the formation of p-xylene from cellulose was proposed based on the analysis of products and the characterization of catalysts.

Dual-template synthesis of HZSM-5 zeolites with tailored activity in toluene methylation with CH3Br

Abstract Shape-selective zeolites (HZ-x/y) were synthesized by a one-pot method using TPAOH (y) and/or MeEt3N+ I− (x) as templates. The use of MeEt3N+ I− affects the crystal growth and the distribution of acid sites on the external surface of the zeolites. The catalysts show excellent catalytic activity towards toluene alkylation with CH3Br. With toluene conversion of 36.3% and p-xylene selectivity of 66.2%, HZ-40/0 is the most effective among the prepared catalysts, showing a p-xylene yield of 21.2%. The improved para-selectivity is mainly due to the decrease of acid sites on the external surface of the catalysts.

Excellent Performances of Dealuminated H-Beta Zeolites from Organotemplate-Free Synthesis in Conversion of Biomass-derived 2,5-Dimethylfuran to Renewable p-Xylene.

Direct synthesis of renewable p-xylene (PX) by cycloaddition of biomass-derived 2,5-dimethylfuran (2,5-DMF) and ethylene was achieved over Al-rich H-beta zeolites synthesized by an organotemplate-free approach and their dealuminated counterparts with different Si/Al ratios. Among them, H-beta zeolite with an Si/Al ratio of 22, obtained from an Al-rich parent by dealumination, was found to be an excellent catalyst for the synthesis of PX. A PX yield of 97 % and 2,5-DMF conversion of 99 % were obtained under optimized conditions. These results are even better than those of a commercial H-beta zeolite prepared using a organotemplate synthesis with a similar Si/Al ratio of 19. The excellent performance of the H-beta zeolite with Si/Al ratio of 22 is closely related to its acidity and porous structure. A moderate Brønsted/Lewis acid ratio can improve the conversion of 2,5-DMF to as high as 99 %. Furthermore, dealuminated H-beta zeolite has a secondary pore system that facilitates product diffusion, which increases the selectivity to PX. In addition, this catalyst shows better regeneration. After five successive regeneration cycles, the yield of PX was still as high as 85 % without obvious dealumination. This work provides a deeper understanding of the more general Diels-Alder cycloaddition of furan-based feedstocks and olefins and significantly improves the potential for the synthesis of chemicals from lignocellulosic biomass.

The origin of the activity and selectivity of silicalite-1 zeolite for toluene methylation to para-xylene

In this study, a series of MFI-type zeolites with different aluminum contents have been prepared and evaluated for toluene alkylation with methanol. All these zeolite samples are well crystallized and exhibit typical characteristics of MFI structure (as indicated by XRD), and their acid amounts decrease continuously with the decreasing aluminum content of the zeolites (as revealed by NH3-TPD). The weakly-acidic aluminum-free silicalite-1 zeolite is demonstrated to be active in catalyzing toluene methylation for the first time. The content of p-xylene in xylenes, namely the reaction para-selectivity, has been substantially improved by increasing the zeolite diffusion resistance. For the silicalite-1 zeolite, the silanol nests inside the micropores are determined to be the active sites for toluene methylation into p-xylene. Meanwhile, the external surface enriching inert isolated silanols is indicated to be responsible for the enhanced para-selectivity, due to a negligible isomerization of as-formed p-xylene into its isomers. Generally, a greatly improved catalytic performance (with a para-selectivity up to 75% and p-xylene yield ca. 13%) has been obtained for silicalite-1 among the recently reported zeolites.

Heteropolyacid catalysts for Diels-Alder cycloaddition of 2,5-dimethylfuran and ethylene to renewable p-xylene

The Diels-Alder cycloaddition of biomass-derived furans and subsequent dehydration are promising routes for the sustainable production of commodity chemicals such as p-xylene (PX). In this paper, we have investigated the catalytic performances of a range of phosphotungstic acid (HPW) and silicotungstic acid (HSiW) catalysts supported on various oxides, i.e., SiO2, Al2O3, TiO2 and ZrO2 and their structure-activity correlation in the conversion of 2,5-dimethylfuran (DMF) and ethylene to PX. The characterization studies of the catalysts using XRD, BET, Raman and 31P MAS-NMR spectroscopy reveal that all of the supported heteropolyacid (HPA) catalysts (except HPW/ZrO2) retain their Keggin structure on the surface of oxide supports. Results from ammonia- and n-propylamine-TPD studies show that all of the supported HPA catalysts possess well-defined Brønsted acid sites with the total acidity decreasing in the following order: HPA/SiO2>HPA/Al2O3>HPA/ZrO2>HPA/TiO2. The conversion of DMF and the initial rate of PX production generally increase with an increase in the total acidity, with HPA/SiO2 being the most active catalyst. The turnover frequency of PX production for HPA/SiO2 is also considerably greater than those for the HPAs supported on Al2O3, ZrO2, and TiO2, which suggests that the higher activity of HPA/SiO2 is at least partly due to the enhanced strength of Brønsted acid sites. Both the silica-supported HSiW and HPW catalysts demonstrate remarkably high PX selectivity (82–85%) at high DMF conversion (91–94%) at 250°C after 6h reaction. The effects of reaction conditions such as acid loading, reaction temperature, and reaction time have also been investigated with the most active silica-supported HSiW catalysts to optimize the PX yield.

Direct and selective conversion of methanol to para-xylene over Zn ion doped ZSM-5/silicalite-1 core-shell zeolite catalyst

We successfully designed Zn ion doped ZSM-5/silicalite-1 core-shell zeolite catalyst. On methanol to para-xylene (MTpX) over the core-shell catalyst, p-xylene yield was 40.7C-mol% and para-selectivity (para-xylene selectivity in xylene isomers) was higher than 99C-mol%, which substantially exceeds the other results reported in the literature.

Enhancing p-xylene productivity for disproportionation of toluene in microstructured reactors

Microstructured monolith reactors washcoated with ZSM5 and La2O3-loaded ZSM5 (LaZSM5) were used for disproportionation of toluene for studying the effect of washcoat thickness on reactor productivity and yield of the commercially important p-xylene isomer. The toluene conversion and p-xylene yield in the ZSM5 washcoated monolith reactor was superior to that in a packed bed reactor using ZSM5 pellets. Modification of the surface properties of ZSM5 due to addition of La2O3 reduced the toluene conversion but resulted in a substantial enhancement in p-xylene yield. The decrease in catalytic activity and p-xylene yield with increase in washcoat thickness was attributed to the lengthening of the diffusional path length. The reactor productivity was highest with thin washcoats and low conversion on La2O3-loaded ZSM5 washcoated monoliths. The advantage of higher p-xylene productivity using monoliths is offset by the increase in the cost of recycling unreacted toluene.