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The conversion of heavy reformate into high-value xylenes was studied over a series of H-mordenite-based catalysts in a fluidized-bed reactor at 400 °C. The results show that methyl-ethyl-benzenes (MEBs) were more reactive than trimethylbenzenes (TMBs) over all the catalysts studied. Mordenite catalyst with higher acid site concentration (M1) favor...
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Upgrading of the heavy reformate fraction (HR), containing mainly C9+ aromatics, is usually performed by dealkylation or by transalkylation with added benzene and/or toluene to obtain the more valuable xylenes. However, when the costs related to the use of benzene and toluene are considered, the one-step dealkylation/transalkylation of the C9+ alky...
Citations
... 7,8 Xylene isomerization is typically catalyzed by Brønsted acids, [9][10][11][12] therefore, zeolite is deemed suitable for catalyzing this reaction. [13][14][15][16] ZSM-5 is a crucial high-silicon zeolite with a threedimensional ten-membered annular channel structure. It exhibits high hydrothermal stability and strong acidity, making it extensively employed in various petrochemical applications such as uid catalytic cracking, hydroisomerization, xylene isomerization, among others. ...
The isomerization process of xylene in the liquid phase has garnered significant attention due to its low energy consumption and high selectivity. However, conventional ZSM-5 zeolites have exhibited significantly diminished activity in this process, primarily attributed to diffusion barriers. To address this issue, Nano-ZSM-5 zeolite was synthesized using tetrapropylammonium hydroxide (TPAOH) as a structure direct agent (SDA) and introducing silicate-1 (S-1) as a crystallization seed. The impact of OH⁻/SiO2 molar ratio on the sample morphology was investigated. The structure of Nano-ZSM-5 zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 physical -sorption analysis. The results demonstrate that the addition of S-1 crystal seeds enables the formation of ZSM-5 crystallites with diminutive particle sizes (∼20 nm). Furthermore, variations in the OH⁻/SiO2 molar ratio within the synthetic system impact crystallite aggregation, excessively high or low ratios result in severe aggregation, leading to decreased specific surface area and mesoporous volume. By optimizing the OH⁻/SiO2 molar ratio to 0.2, the sample exhibits exceptional dispersibility with a specific surface area of 420 m² g⁻¹ and a mesoporous volume extending to 0.57 cm³ g⁻¹. When utilized as a catalyst for liquid-phase xylene isomerization, nano-ZSM-5 demonstrates superior catalytic performance compared to traditional zeolite.
... The authors stated that Y ensured higher performance than Mordenite and that high temperatures were in favour of transalkylation, but this was negative in terms of coke deposition. Among the studies that have utilized commercial heavy reformate and fluidized bed reactors, Ali et al. (2011) used Mordenite and ZSM-5 catalyst mixtures and obtained the highest xylene yield by feeding 70:30 (w/w) heavy reformate: toluene. Syed et al. (2015) suggested that Mordenite and ZSM-5 dual zeolites provide improvement in xylene yield and selectivity compared to single ones. ...
... Compared to H-Beta, Ce-Beta, Ce-ZSM-5, Pd-Beta, highest yield of total xylenes, respectively was achieved with H-ZSM-5 catalyst. Since H-ZSM-5 has higher acidity and highest toluene conversion hence this resulted in a higher yield of xylenes (Ali et al., 2011). The results of this study are in accordance with the results obtained in the study of Ali et al. (2011). ...
... Since H-ZSM-5 has higher acidity and highest toluene conversion hence this resulted in a higher yield of xylenes (Ali et al., 2011). The results of this study are in accordance with the results obtained in the study of Ali et al. (2011). ...
A feasible and cost-effective process for utilization of toluene and heavy reformate is the conversion of its streams by transalkylation reaction into highly valuable xylenes. The process is usually catalysed by zeolites and the challenges to overcome in transalkylation of heavy reformate with toluene over zeolites are their selectivity, activity, long-term stability, and coke formation. Current study aimed to investigate xylenes production by transalkylation reaction on the synthesized metal-doped zeolite catalysts and to characterize prepared catalysts by FTIR, SEM, EDS and BET analysis. Toluene/heavy reformate modelled mixture was utilized as a feed. For the first time Beta and ZSM-5 catalysts with 10% (w/w) cerium and 0.1% (w/w) palladium were synthesized by calcination and wet impregnation method. Catalytic tests were performed by continuous-flow gas/solid catalytic fixed bed reactor at atmospheric pressure, 2 h⁻¹ and 5 h⁻¹ and 250, 300, 350 and 400 °C. Experimental results revealed that the highest heavy reformate conversion (98.94%) and toluene conversion (9.82%) were obtained over H-ZSM-5, at 400 °C and 2 h⁻¹ WHSV. The highest xylene selectivity (11.53) was achieved over H-ZSM-5, and the highest p-xylene percentage (62.40%), using Ce-ZSM-5 catalyst. ZSM-5 catalysts showed more resistance to coke deposition than Beta zeolites. The present study delivers novel approach and catalysts, which have immense potential for developing safer and inexpensive transalkylation process in industry.
... The xylene producing process comprises of dealkylation, transalkylation and disproportionation reactions [2,3]. Medium-and large-pore zeolites such as ZSM-5, NU-87, ZSM-12, faujasite, Beta, mordenite, and zeolite L were investigated as the catalysts for these reactions [4][5][6][7][8][9][10][11][12]. The zeolite topology as well as the type and strength of acid sites significantly influence their catalytic performance [13]. ...
... The metal-acid bifunctional catalysts are reported to promote desirable reactions in the conversion of heavy reformate. Thus, the impact of incorporating Mo, Ni, W, Pt, Re, Pd, Ni, and other active metals are reported [2,3,11,[13][14][15]. Multi-zeolite and multi-metal catalysts were also found to demonstrate better performance [16]. ...
Hierarchical composites of MCM-41 on zeolite Beta were synthesized by in-situ hydrothermal technique, characterized and their catalytic performance for converting heavy reformate into valuable xylenes was evaluated. Systematic optimization of the hierarchical pore generation was carried out by varying the strength of the alkaline solution (0.10-0.45 M NaOH) during disintegration of zeolite Beta. The nanocomposites obtained were extruded with alumina binder and impregnated with 4.0 wt% Mo. The characterization results indicate the transition of mesophase occurs from distinct disordered phase to ordered/disordered and then to ordered mesophase with increasing alkaline concentration. The xylene yield over the hierarchical composite zeolite was 1.4 times more than the parent zeolite Beta. Incorporation of a well-dispersed mild hydrogenation function (4 wt.% Mo) was advantageous in improving the xylene yield and selectivity. The formulation prepared with moderately alkaline (0.2 M NaOH) solution exhibited optimum bimodal pore structure and improved dealkylation and transalkylation conversion resulting in a xylene yield of 33.0 wt.% and 1.7 times enhancement in xylene selectivity over parent zeolite Beta. A 30 h stability test showed steady performance and xylene yields. Hence, a potential application of hierarchical zeolite Beta and MCM-41 composite catalysts for the conversion of heavy aromatics to produce xylenes has been successfully demonstrated.
... These reactions include transalkylation, dealkylation, disproportionation and isomerization reactions, forming a mixture of products, including benzene, m-xylene, p-xylene, o-xylene, 1,2,3-TMB and 1,3,5-TMB. [28][29][30] Which of these different reaction pathways take place, is largely dependent on the acidity of the zeolite that is employed. Dumitriu et al. [31] showed that transalkylation and disproportionation mainly occur on strong acid sites, while isomerization can take place on weak acid sites. ...
The performance of zeolite‐based catalyst extrudates can be largely influenced by the choice of binder material. To investigate these binder effects in zeolite‐based catalyst extrudates in more detail, high spatiotemporal resolution techniques need to be further developed and employed. In this work, we present a new methodology to investigate binder effects in catalyst extrudates at different reaction pressures using operando UV‐vis diffuse reflectance (DR) micro‐spectroscopy coupled with on‐line gas chromatography. We have studied mm‐sized zeolite H‐ZSM‐5‐containing extrudates with either Al2O3 or SiO2 binder material, during the transalkylation of toluene with 1,2,4‐trimethylbenzene at 450 °C and at a pressure of either 1 or 5 bar. Using this technique, it was revealed that the binder material significantly influenced catalyst deactivation at different reaction pressures. By subsequent mapping of the cross sections of the cylindrical catalyst extrudates using UV‐vis micro‐spectroscopy, it was shown that the SiO2‐bound extrudate formed poly‐aromatic coke molecules homogeneously throughout the entire extrudate, whereas for the Al2O3‐bound extrudate a coke ring formed that moved inwards with increasing reaction time. Notably, the developed methodology is not limited to the transalkylation reaction, and can also be used to gain more insight into binder effects during a variety of important catalytic reactions.
... However, the reaction of toluene and TMB on zeolites is rather complex, as multiple chemical reactions do occur. [9][10][11][12] Besides the transalkylation reaction, dealkylation, disproportionation and isomerization reactions can take place. In such instances, not only does the transalkylation pathway yield xylene, but also the disproportionation of two molecules of toluene or TMB can form xylene. Furthermore, the dealkylation of toluene forms benzene and the dealkylation of TMB results in the formation of xylene. ...
The choice of binder material, added to a zeolite‐based catalyst body, can significantly influence the catalyst performance during a reaction, i. e. its deactivation and selectivity. In this work the influence of the binder in catalyst extrudates on the formation of hydrocarbon deposits was explored during the transalkylation of toluene with 1,2,4‐trimethylbenzene (1,2,4‐TMB). Using in situ UV‐vis micro‐spectroscopy and ex situ confocal fluorescence microscopy approach, coke species were revealed to predominantly form on the rim of zeolite crystals within Al2O3‐bound extrudates. It was found that this was due to Al migration between the zeolite crystals and the Al2O3‐binder creating additional acid sites near the zeolite external surface. In contrast, minimal isomerization of 1,2,4‐TMB in the SiO2‐bound extrudate allowed greater access to the zeolite internal pore network, creating a more homogeneous coke distribution throughout the zeolite crystals.
... A third option is the one-step dealkylation/transalkylation of a 100% heavy reformate feed, which can be economically attractive due to the higher value of benzene and toluene as compared to that of the heavy aromatic fraction [1]. A recent study over a series of H-Mordenite based catalysts in a fluidized bed reactor at 400°C [26] showed that EMB was more reactive than TMB in the conversion of a heavy reformate. Thus, the combination of a first step of EMB dealkylation to toluene, followed by the reaction of this toluene with the TMB, also present in the feed, to produce xylenes by transalkylation, is feasible. ...
Upgrading of the heavy reformate fraction (HR), containing mainly C9+ aromatics, is usually performed by dealkylation or by transalkylation with added benzene and/or toluene to obtain the more valuable xylenes. However, when the costs related to the use of benzene and toluene are considered, the one-step dealkylation/transalkylation of the C9+ alkylaromatics to xylenes becomes economically attractive. Thus, in a first step, ethylmethylbenzenes (EMB) will have to be dealkylated to toluene, which will then react with the trimethylbenzenes (TMB) present in the HR feed to produce xylenes by transalkylation. Medium pore zeolites will favor dealkylation, whereas large pore zeolites will be more adequate for carrying out the transalkylation reaction. In this work, we present the one-pot synthesis of beta-pentasil aggregates with tunable ratios of the large pore beta to the medium pore component. We show that the close proximity of the beta and pentasil nanocrystals obtained by one-pot co-crystallization synthesis, results in a highly efficient catalyst for the consecutive dealkylation/transalkylation process. The bifunctional catalyst based on the co-crystallized aggregate is more active and selective to xylenes than a catalyst based on a physical mixture of equivalent beta and pentasil nanozeolites synthesized following an analogous procedure. The small crystallite sizes of the co-crystallized zeolites provide the additional advantage of a lower deactivation rate as compared to a reference benchmark catalyst. Results are shown on both, model molecules and industrial HR feed.
... The reactor feed is divided into aromatics (TOL, MX, B, PX, OX, TMB, EB, MEB, PB and A 10 ), naphthenes (N 7 and N 8 ) and paraffins (P 1 to P 5) , and 39 related reactions offer a reliable reaction network. The reactions include transalkylation [1], disproportionation [50], dealkylation [1,51], paring reaction [52,53], ring saturation [1], isomerization [54] and cracking [55][56][57]. [46] 360 Inlet pressure (bar) [46] 29.4 Feed composition (wt%) [ 10 3.01 Typical properties of catalyst [46] Chemical name: zeolite (Al 2 O 3 ·y SiO 2 ) - ...
In this paper, an optimized membrane-assisted thermally coupled reactor, as well-known equipment for process intensification (PI), is proposed for simultaneous production of highly-valuable xylenes and pure hydrogen. In the proposed configuration, transalkylation process (exothermic reaction) and dehydrogenation of methylcyclohexane (endothermic reaction) take place simultaneously in two different sides, and a hydrogen perm-selective Pd/Ag membrane is utilized to separate pure hydrogen from the endothermic side. A comprehensive reaction network is applied for the exothermic side with the aim of providing a reliable reactor model. The operating conditions of the membrane-assisted thermally coupled reactor are optimized using Differential Evolution (DE) method with 10 decision variables. The model results of conventional reactor are validated with the plant data and a reasonable agreement is achieved. In order to verify the performance of the membrane-assisted thermally coupled reactor configuration, the modeling results are compared with that of the conventional reactor, which reveals that the optimized thermally coupled membrane reactor results in more xylenes yield and lower temperature in exothermic side.
... Moreover, higher liquid flow rates give greater liquid hold up which evidently decreases the contact of liquid and gas reactants on active site by increasing the film thickness. While at low liquid flow rate, the liquid resides in the reactor for longer time, and therefore undergoes more conversion and agrees with [22][23] . ...
The recent economic climate, impact of government regulation, and new market trends has impacted the catalyst designers to improve the performance of catalyst. To achieve this goal, a series of experiments were conducted to focus on the influence of Ga and Re addition on the catalytic activity of Pt–Re/Al2O3 naphtha reforming catalysts. To supported γ-Al2O3 the Ga-Re-Pt prepare by using incipient wetness impregnation method. Many characterization tests are used such as scanning electron microscopy, temperature programmed desorption, X-ray diffraction and BET surface area. The liquid product yield tested by PONA method. In this study the benzene content is used as main performance criteria throughout many experiments performed at different liquid hourly space velocity, hydrogen/ hydrocarbon ratios and different operating temperature. According to the catalyst characterization tests the coimpregnation method showed good result in term of performance and properties. The catalyst exhibited good liquid product distribution and significant minimization of benzene content.
The recent economic climate, impact of government regulation, and new market trends has impacted the catalyst designers to improve the performance of catalyst. To achieve this goal, a series of experiments were conducted to focus on the influence of Ga and Re addition on the catalytic activity of Pt–Re/Al2O3 naphtha reforming catalysts. To supported γ-Al2O3 the Ga-Re-Pt prepare by using incipient wetness impregnation method. Many characterization tests are used such as scanning electron microscopy, temperature programmed desorption, X-ray diffraction and BET surface area. The liquid product yield tested by PONA method. In this study the benzene content is used as main performance criteria throughout many experiments performed at different liquid hourly space velocity, hydrogen/ hydrocarbon ratios and different operating temperature. According to the catalyst characterization tests the coimpregnation method showed good result in term of performance and properties. The catalyst exhibited good liquid product distribution and significant minimization of benzene content.
... Transalkylation of TMB with toluene is also an important process for production of xylene, which is practiced commercially (Serra, Guillon, and Corma 2005; Aitani et al. 2010; Wang et al., 2010). Transalkylation of TMB with toluene with various zeolite catalysts has Downloaded by [Thapar University] at 03:28 15 September 2015 gained interest recently due to its commercial and environmental benefits like low toxicity, reusability and non hazardous nature of zeolite catalyst (Barman, Pradhan, and Basu 2005; Maity, Seetaram, and Pradhan 2006) . ...
... Large pore zeolites like Mordenite, faujasite Y, SAPO-5 are found to actively catalyze this transalkylation reaction due to their pore size and structure (Dumitriu et al. 2002; Tsai et al. 2002; Al-Khattaf et al. 2007; Krejči et al. 2010). A number of studies reveal that the Si/Al ratio, which varies with the pore size, affects the conversion of reactant and selectivity of the product (Al-Khattaf et al. 2007; Krejči et al. 2010; Wang et al., 2010). Zeolite pore size and geometry were also found to have a direct influence on dealkylation and transalkylation of the different alkyl groups (Serra, Guillon, and Corma 2005). ...
H-beta zeolite was modified by the ion exchange method to replace its H+ ions with Ce4+ ions. The catalytic performance of this cerium exchanged beta zeolite was evaluated for vapor phase transalkylation of 1,2,4 TMB (1,2,4 trimethylbenzene) with toluene for the production of xylene in a fixed bed, down-flow reactor. The modified zeolite was found to be highly active for this transalkylation reaction. The response surface methodology (RSM) is used for designing the experiments. The effect of three important reaction parameters viz. temperature, reactant ratio, and space time on response variables (toluene conversion and xylene selectivity) is studied and discussed. All the three selected reaction parameters were found to be significant for the toluene conversion; whereas, xylene selectivity was not much influenced by the temperature. The optimum values of the reaction parameters predicted by the model (temperature: 409.7°C, reactant ratio: 2.024, and space time: 4.451) were validated by an experimental run. The results of the experimental run were in close agreement with the model predicted results.
... Transalkylation of TOL with TMB Isomerization of 1,2,4-TMB Disproportionation of TOL Disproportionation of TMB Dealkylation of MEB Mordenite 400 3.45 Ali et al. 2011 [23] Dealkylation of MEB ...
In the present study, an accomplished reaction network is developed for commercial conversion of heavy reformates to more valuable xylenes. The proposed kinetic model is based on 18 pseudo-components and 39 related reactions in which 7 different types of reactions are included. Thermodynamic principles are also applied to predict the reversibility of the reactions. To estimate the reaction rate constants, the absolute deviation between the model results and observed data are minimized applying differential evolution (DE) optimization method. To prove the accuracy of the proposed model, simulation results are compared with the plant data and an acceptable agreement is achieved. Then, the effect of operating conditions on the reactor performance is verified. The results of this work show that increasing the inlet temperature and molar flow rate up to certain values would improve the xylenes production.
