Production Of P-xylene Research Articles

Highly Selective Production of Biobased p-Xylene from 2,5-Dimethylfuran over SiO2–SO3H Catalysts

Aimed at highly selective production of p-xylene (PX) from biomass-derived 2,5-dimethylfuran with a high carbon balance, SiO2 supported with sulfonic acid was especially designed and prepared. As one kind of the most widely used Bronsted acid, sulfonic acid groups were chosen as the active sites of probes. The density of sulfonic acid groups in the whole composite was highly adjustable, ranging from 4.7–540.6 μmol/g. The catalytic activity was strongly related to the acid concentration and location: the one with active sites mainly on the exterior surface exhibited much better catalytic activity by facile mass transfer through mesopores. The suitable acid species and structures of the as-prepared catalyst contributed to the improved activity: a selectivity of 89% and a carbon balance of 95% were achieved at 523 K. Overall, this new reusable catalyst provided an alternative for highly efficient production of biobased PX.

Effect of Silica Content on Production of p-Xylene from Dimethylfuran/Ethylene Over Mesoporous SiO₂–Al₂O₃ Catalysts.

Mesoporous SiO₂–Al₂O₃ (SA) catalysts with different SiO₂ contents were prepared, for the selective production of p-xylene from dimethylfuran/ethylene through the combination of cycloaddition and dehydrative aromatization reactions, by a co-precipitation method. For comparison, commercial SiO₂–Al₂O₃ and ZSM-5 zeolites (Si/Al₂ = 30, Si/Al₂ = 80) were also employed as catalysts in the same reaction. The pore size of the catalysts played an important role in determining the catalytic performance in the production of p-xylene. Among the catalysts tested, the order of the yield and production rate of p-xylene was as follows: mesoporous SA > commercial SiO₂–Al₂O₃ > commercial ZSM-5. In the mesoporous SA catalysts in particular, p-xylene yields showed a volcano-shaped trend with respect to the catalyst’s SiO₂ content. The SA-60 catalyst, with SiO₂ = 52.3, showed the highest yield (75%) and production rate (57.7 mmol/g-cat · h) because of a catalyst structure with moderate pore size, which prevented side reactions.

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.

Diffusion of Trimethylbenzenes and Xylenes in Zeolites with 12- and 10-Ring Channels as Catalyst for Toluene-Trimethylbenzene Transalkylation

A molecular dynamics study of the diffusion of trimethylbenzene (TMB) and xylene molecules involved in toluene and TMB transalkylation reaction has been performed over 6 different pure-silica zeolites, containing 10- and 12-ring channels: BOG, MSE, IWR, SFS, SOF, and UWY. The shape selective properties of these six frameworks have been tested using two different loadings: one loading characteristic of the early stage and another of the late stage of the reaction. The collected data explains the diffusion behavior of these molecules in the zeolite frameworks and allows researchers to obtain trends and also rationalize their performance as candidates for the selective production of p-xylene during transalkylation of toluene and TMB. UWY appears a promising zeolite that allows the reaction of the TMBs in the 12-ring channels, is able to host the transition states, and favors the preferential diffusion of p-xylene in the 10-ring channels.

Catalytic transformation of lignin to aromatic hydrocarbons over solid-acid catalyst: Effect of lignin sources and catalyst species

Catalytic pyrolysis of two lignin samples extracted from Chinese fir and rice straw was investigated by Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), concerning the effect of reaction temperatures (550–900°C) and catalyst species (HZSM-5 (25), HZSM-5 (50), HZSM-5 (210), H-β and H-USY) on the production of specific aromatic hydrocarbons (such as benzene, toluene and xylene). The yield of specific aromatic hydrocarbons from catalytic pyrolysis of the two lignin samples with HZSM-5 (25) achieved the maximum value at 650°C. Formation of p-xylene was remarkably promoted with the decreased Si/Al ratio of HZSM-5 over that of toluene. Production of o-xylene from two lignin samples under 650°C was selectively enhanced by H-USY due to its compatible pore structure. HZSM-5 (25) with suitable distribution of acidic sites identified by NH3-TPD was estimated to be the potential commercial catalyst for production of toluene and p-xylene from catalytic pyrolysis of lignin. Yield of oligo-aromatic hydrocarbons (naphthalene and methylnaphthalene) from catalytic pyrolysis of Chinese fir lignin under 650°C is remarkably higher than that from rice straw lignin possibly due to their different oxygen contents.

Methylation of toluene with methanol in sub/supercritical toluene using H-beta zeolite as catalyst

Production of xylene isomers and other alkylbenzene products in normal, near and supercritical toluene using unmodified beta zeolite catalyst and methanol were investigated. The effect of different parameters such as toluene/methanol ratio, temperature, pressure, and flow rate of the reacting materials were investigated. The production optimum conditions for alkylbenzenes are temperature of 623K, pressure of 55bar and flow rate of 0.2mLmin−1 using 1g beta zeolite as catalyst with Si/Al=38. The selectivity of 47% was achieved for p-xylene production, conversion of methanol and toluene were 100 and 65%, and the production yield and liquid selectivity of xylenes were 72 and 97%, respectively. The catalyst's activity was investigated in a 20h period and the catalyst were characterized by XRD, TGA, and FT-IR methods.

Inhibition of Xylene Isomerization in the Production of Renewable Aromatic Chemicals from Biomass-Derived Furans

Inhibition of p-xylene isomerization in the presence of H-Y (Si/Al 2.6) and H-BEA (Si/Al 12.5) zeolites was studied under conditions relevant to p-xylene production from 2,5-dimethylfuran (DMF) and ethylene. Through examination of the reaction components, it was shown that both DMF and 2,5-hexanedione inhibit transalkylation and methyl shift reactions of p-xylene, while other reaction components, water and ethylene, do not. Retention of Bronsted acid sites after the reaction was shown through the use of 27Al NMR for both H-Y and H-BEA zeolites, but with a reduction in the ratio of tetrahedrally coordinated aluminum (strong acid sites) to octahedrally coordinated aluminum (Lewis acid sites) coinciding with the disappearance of the framework aluminum. Diffuse reflectance spectroscopy has shown preferential adsorption of DMF and 2,5-hexanedione (DMF + H2O) relative to p-xylene to the Bronsted acid sites located in the super and sodalite cages of the H-Y. Desorption characteristics for DMF and p-xylene in H-Y...

Simulated moving bed reactor for p-xylene production: Dual-bed column

A dual-bed Simulated Moving Bed Reactor (SMBR) is developed under the framework of a proposed aromatics complex where the extract product, with 70wt% p-xylene, is further purified by a crystallization unit to obtain the final product. Each column within the unit contains an adsorbent/catalyst homogeneous mixture as first bed followed by another bed of just adsorbent. A method of dynamic optimization is applied to estimate the optimum adsorbent/catalyst proportion within the first bed so p-xylene production is equal to its adsorption. Afterwards, the unit is optimized through successive simulations using the SMBR model giving a productivity of 226.27kg/m3h (produced p-xylene per volume of adsorbent and catalyst within the columns), a desorbent consumption of 0.07m3/kg (volume of desorbent per produced p-xylene), and a produced p-xylene to fed p-xylene ratio of 1.75at 200°C. Finally, using the commercial software gPROMS, an integrated method that combines less time-consuming results from True Moving Bed Reactor (TMBR) approach with the rigorous SMBR calculations to develop the dual-bed SMBR unit is presented.

Selective p-xylene production from biomass-derived dimethylfuran and ethylene over zeolite beta nanosponge catalysts

p-Xylene can be synthesized via a renewable route from biomass-derived 2,5-dimethylfuran (DMF) and ethylene with zeolite catalysts. Here, we propose mesoporous beta zeolite with a nanosponge-like morphology (NSP-BEA) as a highly efficient catalyst for the cycloaddition of DMF with ethylene. The NSP-BEA zeolite was synthesized through a hydrothermal synthesis route using multi-ammonium surfactants as a meso–micro dual structure-directing agent. From structural analyses and measurements of the surface acidity, the NSP-BEA was found to be composed of ultrathin zeolitic nanocrystals with intercrystalline mesopores (∼4.5nm). It also possessed a large number of Brønsted acid sites on its external surfaces and in its internal micropores. This NSP-BEA catalyst exhibited high catalytic performance upon a cycloaddition of DMF with ethylene as compared to the commercial beta zeolite, alumina, and silica–alumina catalysts reported previously.

Production of renewable p-xylene from 2,5-dimethylfuran via Diels–Alder cycloaddition and dehydrative aromatization reactions over silica−alumina aerogel catalysts

We report the selective conversion of biomass-derived 2,5-dimethylfuran (DMF) to p-xylene (~70% selectivity) through Diels–Alder cycloaddition and subsequent dehydration with silica−alumina aerogel (SAA) catalysts. The high activity of SAA can be attributed to its high surface area, large mesoporous volume, and high acid site concentrations. The conversion of DMF and the yield of p-xylene were strongly dependent on the silica alumina ratio of SAA. A higher aluminum content in SAA led to a progressive increase in the concentration of Brønsted acid sites and a corresponding increase in the p-xylene production rate. The effect of solvent on the production of p-xylene was examined, and it was found that the p-xylene production rate increases significantly in polar aprotic solvents (i.e. 1,4-dioxane).

Kinetic Regime Change in the Tandem Dehydrative Aromatization of Furan Diels–Alder Products

Renewable production of p-xylene from [4 + 2] Diels–Alder cycloaddition of 2,5-dimethylfuran (DMF) and ethylene with H–Y zeolite catalyst in n-heptane solvent is investigated. Experimental studies varying the solid acid catalyst concentration reveal two kinetic regimes for the p-xylene production rate: (i) a linear regime at low acid site concentrations with activation energy Ea = 10.8 kcal/mol and (ii) a catalyst-independent kinetic regime at high acid site concentrations with activation energy Ea = 20.1 kcal/mol. We carry out hybrid QM/MM calculations with a three-layer embedded cluster ONIOM model to compute the energetics along the main reaction pathway, and a microkinetic model is constructed for the interpretation of the experimental kinetic data. At high solid acid concentrations, p-xylene production is limited by the homogeneous Diels–Alder reaction, whereas at low acid concentrations, the overall rate is limited by the heterogeneously catalyzed dehydration of the Diels–Alder cycloadduct of DMF an...

Life Cycle Assessment of Biobased p-Xylene Production

A general framework implementing process design, simulation, heat integration, and life cycle assessment (LCA) is illustrated to develop a sustainable route, which is particularly exploited to evaluate the environmental impacts of the p-xylene production from both generation biomass feedstocks. Noticeably, the lignocellulose-based p-xylene is comparable with the petroleum-based p-xylene, while the starch-based p-xylene appears less environmentally friendly. In the latter case, the cultivation and processing of maize starch and heating requirements dominate total environmental impacts. The main contributions for the lignocellulose-based p-xylene arise from the cultivation of biomass and the large requirements of nonrenewable chemicals (i.e., the makeup solvent (THF) and ethylene). Sensitivity analysis indicates that high selectivity is also favored to achieve better environmental performance, while the impacts of conversion are negligible and discovers a large variance from different biomass feedstocks. The uncertainties caused by the assumptions and developing technologies are assessed by uncertainty analysis.

Current technologies, economics, and perspectives for 2,5-dimethylfuran production from biomass-derived intermediates.

Since the U.S. Department of Energy (DOE) published a perspective article that described the potential of the top ten biomass-derived platform chemicals as petroleum replacements for high-value commodity and specialty chemicals, researchers around the world have been motivated to develop technologies for the conversion of biomass and biomass-derived intermediates into chemicals and fuels. Among several biorefinery processes, the conversion of biomass carbohydrates into 2,5-dimethylfuran (DMF) has received significant attention because of its low oxygen content, high energy content, and high octane value. DMF can further serve as a petroleum-replacement, biorenewable feedstock for the production of p-xylene (pX). In this review, we aim specifically to present a concise and up-to-date analysis of DMF production technologies with a critical discussion on catalytic systems, mechanistic insight, and process economics, which includes sensitivity analysis, so that more effective catalysts can be designed. Special emphasis has been given to bifunctional catalysts that improve DMF yields and selectivity and the synergistic effect of the bifunctional sites. Process economics for the current processes and the scope for further improvement are discussed. It is anticipated that the chemistry detailed in this review will guide researchers to develop more practical catalytic processes to enable the economic production of bio-based DMF. Processes for the upgrade of DMF to pX are also described.

Mechanochemical approach for selective deactivation of external surface acidity of ZSM-5 zeolite catalyst.

The acid sites associated with the external surface of zeolite particles are responsible for undesirable consecutive reactions, such as isomerization, alkylation, and oligomerization, resulting in a lower selectivity to a target product; therefore, the selective modification (deactivation) of the external surface of zeolite particles has been an important issue in zeolite science. Here, a new method for surface deactivation of zeolite catalyst was tested via a mechanochemical approach using powder composer. Postsynthetic mechanochemical treatment of ZSM-5 zeolite causes a selective deactivation of catalytically active sites existing only on the external surface, as a potentially useful catalyst for highly selective production of p-xylene.

1,2,4-Trimethylbenzene disproportionation over large-pore zeolites: An experimental and theoretical study

While 1,2,4-trimethylbenzene (TMB) disproportionation is one of the potential technologies for p-xylene production, its reaction intermediates have been neither experimentally observed nor identified yet. Here we present GC–MS evidence that not only pentamethylated diphenylmethane (5mDPM) derivatives but also hexamethylated diphenylmethane (6mDPM) ones are serving as key reaction intermediates of 1,2,4-TMB disproportionation over large-pore zeolites. We also propose a new bimolecular diphenylmethane-mediated reaction pathway for the formation of tetramethylbenzenes (TeMBs) and xylenes over large-pore zeolites based on the GC–MS results obtained. Comparison with the GC–MS results from LaNa-Y after transalkylation reactions of three different TeMB isomers with three xylene and three TMB isomers, respectively, allows us to rationally identify most of the seven 5mDPM and three 6mDPM derivatives at their isomer level. A combination of GC–MS and DFT calculation results demonstrates that the bimolecular 1,2,4-TMB disproportionation over LaNa-mordenite, a practically one-dimensional 12-ring zeolite with regard to this reaction, is a new example of transition state shape selectivity in zeolite catalysis.

Optimizing the distribution of aromatic products from catalytic fast pyrolysis of cellulose by ZSM-5 modification with boron and co-feeding of low-density polyethylene

This study investigated the effects of ZSM-5 impregnation with boron on its catalytic properties in catalytic fast pyrolysis (CFP) of cellulose, low-density polyethylene (LDPE), and their mixtures. A series of boron-modified ZSM-5 zeolites were prepared by impregnating a conventional ZSM-5 with different boron loadings (0.5–3wt.%). Due to boron deposition, the acidity and pore size of ZSM-5 decreased with increasing the boron loading. When impregnated with 1wt.% boron, ZSM-5 preserved sufficient catalytic activity for the production of valuable monoaromatic hydrocarbons and decreased the formation of undesired polyaromatic hydrocarbons in CFP of cellulose. In addition, the pore narrowing of ZSM-5 by boron deposition greatly enhanced p-xylene production over m- and o-xylenes in CFP. This result indicates that slightly decreasing the pore size of ZSM-5 can improve aromatic distribution toward more valuable products in CFP. Co-feeding of cellulose with LDPE in CFP further improved the product distribution. As a result of boron modification and co-feeding, the monoaromatic yield increased from 20.0 C% for CFP of cellulose alone with the parent ZSM-5 to 24.6 C% for co-feed CFP of cellulose and LDPE mixture (mixing ratio of 4:1) with the boron-modified ZSM-5, while the polyaromatic yield decreased from 11.3 C% to 6.0 C%. The yield for p-xylene also increased from 2.23 C% to 5.57 C% while the selectivity increased from 47.9% to 75.2%. The results indicate that ZSM-5 modification with boron and co-feeding of plastics have a beneficial effect for improving aromatic product distribution in CFP of biomass.

Simulated moving bed reactor for p-xylene production: Adsorbent and catalyst homogeneous mixture

Abstract This work analyzes the use of process intensification in the production of p- xylene. Both separation and isomerization processes are combined in the simulated moving bed unit currently used for p- xylene separation. In addition, based on larger yields required for p- xylene and benzene, a modification to the aromatic complex is proposed including a new single stage crystallization unit allowing further purification of high p- xylene content streams. Based on the aforementioned, a lower p- xylene purity is defined in the extract (0.70) along with a purity of 0.95 of the rest of the aromatics in the raffinate; a Simulated Moving Bed Reactor unit combining adsorbent and catalyst within the columns is projected instead of the commonly used simulated moving bed facility. Keeping the same physical characteristics of the unit, several configurations with different flow rates were analyzed with the purpose of obtaining the highest productivity by means of simulations using a commercial software and the true moving bed reactor approach. The results showed that the amount of adsorbent shall be high in order to achieve the desired purity due to the nature of the reverse reaction. The columns arrangement that offered the best performance is 2-6-14-2 with a desorbent consumption and productivity of 0.06 m 3 kg −1 and 412 kg m −3 h −1 , respectively.

Role of complex equilibrium in the shape-selective performances of MgO/MCM-22 catalysts prepared by complexing impregnation

The role of complex equilibrium in the shape-selectivity of the MgO/MCM-22 catalysts prepared by complexing impregnation was investigated. The presence of hydrochloric acid during the complexing impregnation process resulted in a significant improvement of selectivity for p-xylene production by toluene methylation with dimethyl carbonate over MgO/MCM-22 catalysts. The dramatic performance was ascribed to the designated shifting of the complex equilibrium of malonic acid and Mg2+, which may alter the coverage of acidic sites on the external surface of zeolite, adjust the pore size of zeolite, and therefore affect the shape-selective performances of the catalysts.

Solvent-tuned hydrophobicity for faujasite-catalyzed cycloaddition of biomass-derived dimethylfuran for renewable p-xylene

Phase equilibria of the high temperature/high pressure heterogeneous catalytic reaction of 2,5-dimethylfuran (DMF), a biomass-derived furan, with ethylene to produce p-xylene was studied as a function of DMF conversion in a constant-pressure reactor. Adsorption of reactants and products onto a zeolite catalyst was computed using a configurational-bias Grand Canonical Monte Carlo (CB-GCMC) simulation, and the vapor–liquid behavior was computed using ASPEN Plus with an appropriate equation of state. It was found that the amount of water adsorbed in H–Y (Si/Al = 2.6) increases significantly as DMF is consumed, but is small in the presence of an aliphatic solvent, here n-heptane, even at high DMF conversion. The presence of the solvent reduces side reactions with water, such as hydrolysis followed by oxyalkylation, and increases p-xylene selectivity, in agreement with experiment. The decrease in the amount of water adsorbed is due to the increased hydrophobic environment in the zeolite as a result of the addition of n-heptane. The increase of ethylene inside the cage by the addition of n-heptane results in a slight increase of p-xylene alkylation. This work presents the first use of molecular simulation to understand mechanistic effects of solvents on the catalytic production of p-xylene in an H–Y zeolite.

Alternative Approaches for p-Xylene Production from Starch: Techno-Economic Analysis

Two alternatives for the production of p-xylene from starch are investigated using detailed techno-economic analysis. The first route is based on the patents by GEVO Inc. and uses fermentation followed by the catalytic conversion, whereas the second one utilizes CCEI-discoveries - solely the catalytic conversion. The minimum p-xylene price for the GEVO and CCEI processes is found as $4121 and $3637/metric ton, respectively, without accounting for the byproduct values, while taking into consideration that the byproduct value leads to $3481 and $2885/metric ton. Using sensitivity analysis, the biomass feedstock cost is determined as a major contributor of the total cost. Other significant contributors include biocatalyst cost in the GEVO process and ethylene and solvent (THF) costs in the CCEI process. The impacts of selectivity and conversion on the p-xylene price for the CCEI process are investigated. High selectivity is favorable compared to high conversion due to recycling used to improve the performanc...