Adsorption and diffusion properties of xylene isomers and ethylbenzene in metal–organic framework MIL-53(Al)

Adsorption and diffusion behaviour of C8 aromatic isomers, including para-xylene (PX), ortho-xylene (OX), meta-xylene (MX), and ethylbenzene (EB), in metal–organic framework Mil-53(Al) has been systematically investigated by using intelligent gravimetric analyzer, thermogravimetric analysis and molecular simulation respectively. The results indicate that adsorptions of xylene isomers and ethylbenzene molecules in Mil-53(Al) at 303 K present type-I isotherms. The deviation from normal Langmuir model of the isotherms at higher temperature can be, however, found because of the breathing effect of Mil-53(Al) framework. In order to well understand the selective adsorption process of above adsorbates, the diffusion behaviour has been determined and the diffusion coefficient is in the order: OX > PX > MX > EB. The adsorption thermodynamics have been determined by the isotherms at different temperature. A sharp increase of the heat of sorption Q _st suggests that a strong interaction between sorbates molecules and between sorbates and the framework appears as the increase of the loading. Two desorption peaks in DTG curves suggests that two sorption locations exist in Mil-53(Al) to C8 alkylaromatics. The molecular simulation results have been used to successfully explain the experimental phenomena and to well understand the underlying adsorption and diffusion features of the systems.     

Synthesis and Characterization of Platinum Impregnated Zn-ZSM5 Nanocatalysts for Xylene Isomerization Reactions

The influence of zinc to the synthesis of ZSM-5 nanocatalysts (Si/Al?=?24) was investigated in xylene isomerization reactions. Pt was doped through partial vacuum impregnation method on both the parent and Zn-ZSM-5. The synthesized nanocatalyst were characterized by ICP, BET, XRD, FE-SEM, XPS, ²⁷Al MAS NMR, FTIR, NH₃-TPD, and TG analysis. The concentration of weak acid sites of ZSM-5 nanocatalyst slightly decreased while that of strong acid sites increased with the addition of Zn to the nano zeolite structure. Reducing weak acidity resulted in lower coke formation and remarkable catalytic stability in Zn-ZSM-5 nanocatalysts. The precence of Pt on the Zn-containing ZSM-5 illustrated simultaneous high PX yield and high catalytic stability. (0.1 wt%)Pt/(0.8 wt%) Zn-ZSM-5 as an active and stable nanocatalyst for xylene isomerization reactions demonstrated high PX yield (32.6 wt%), high level of EB conversion (68%) and low xylene loss (2.1%).

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Preparation of PFSA‐PVA/PSf hollow fiber membrane for IPA/H2O pervaporation process

Using Na⁺ form of perfluorosulfonic acid (PFSA) and poly(vinyl alcohol) (PVA) as coating materials, polysulfone (PSf) hollow fiber ultrafiltration membrane as a substrate membrane, PFSA‐PVA/PSf hollow fiber composite membrane was fabricated by dip‐coating method. The membranes were post‐treated by two methods of heat treatment and by both heat treatment and chemical crosslinking. Maleic anhydride (MAC) aqueous solution was used as chemical crosslinking agent using 0.5 wt % H₂SO₄ as a catalyst. PFSA‐PVA/PSf hollow fiber composite membranes were used for the pervaporation (PV) separation of isopropanol (IPA)/H₂O mixture. Based on the experimental results, PFSA‐PVA/PSf hollow fiber composite membrane is suitable for the PV dehydration of IPA/H₂O solution. With the increment of heat treatment temperature, the separation factor increased and the total permeation flux decreased. The addition of PVA in PFSA‐PVA coating solution was favorable for the improvement of the separation factor of the composite membranes post‐treated by heat treatment. Compared with the membranes by heat treatment, the separation factors of the composite membranes post‐treated by both heat treatment and chemical crosslinking were evidently improved and reached to be about 520 for 95/5 IPA/water. The membranes post‐treated by heat had some cracks which disappeared after chemical crosslinking for a proper time. Effects of feed temperature on PV performance had some differences for the membranes with different composition of coating layer. The composite membranes with the higher mass fraction of PVA in PFSA‐PVA coating solution were more sensitive to temperature. It was concluded that the proper preparation conditions for the composite membranes were as follows: firstly, heated at 160°C for 1 h, then chemical crosslinking at 40°C for 3 h in 4% MAC aqueous solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

基于PX选择性强化的短流程甲苯甲醇甲基化PX生产新工艺

基于改性的高硅铝ZSM-5催化剂反应动力学模型,本文探讨了甲苯甲醇甲基化反应中影响对二甲苯（PX）选择性的因素,提出了基于选择性强化的短流程甲苯甲醇甲基化PX生产工艺,并从原料利用率、能耗以及经济指标等角度,与已有工艺进行了对比分析。结果表明,在短停留时间、高甲苯/甲醇进料比、高稀释剂/甲醇进料比、较低反应温度和压力条件下,可以促使PX在二甲苯异构体中的选择性达到99.7 %以上。短流程PX生产工艺规避了二甲苯异构体的分离,具有原料利用率高、能耗低、工艺简单的特点,具有良好的经济性。当前工艺研究进一步提升了甲苯甲醇甲基化PX生产工艺的技术竞争力,利用非石油基的甲醇,有助于形成煤化工和石油化工技术互补、协调发展的新格局。     

对二甲苯结晶过程的固液相平衡研究

使用Van’t Hoff方程、Hildebrand方程和冰点降低常数法计算了PX-MX二元体系的固液平衡相图,计算结果表明,3种计算方法均与实验结果吻合很好。使用冰点降低常数法计算混合二甲苯多元体系的低共熔点组成,计算结果表明,含有EB的多元体系,其液相不能当作是理想溶液,不含EB的多元体系,其液相可以近似当作是理想溶液,在工业生产分析时,PX-MX-OX-EB可以近似为PX-MX-OX三元体系。根据冰点降低常数法的计算结果,绘制了PX-MX-OX三元体系的固液平衡立体相图,并分析了不同工业原料中对二甲苯的结晶过程,计算结果表明,PX结晶过程的回收率都受到低共熔点的限制,对于PX质量分数为21.5%的低含量进料,PX最大回收率为67%,对于PX质量分数为83.72%的高含量进料,PX最大回收率为97%。     

Separation of ethylbenzene from C7+‐cut naphtha

A fractional distillation process for separating ethylbenzene (EB) from a feed mixture C7⁺‐cut naphtha, comprising nonaromatics, BTX, EB, styrene, and C8⁺ fraction, was used. Primarily, 29.63 wt % EB in the bottom was obtained. Redistillation of the bottom component produced 63.98 wt % EB in the 2nd cut; finally, this cut was used as a feed to distillation process and 83.21 wt % EB was obtained in distillate, and this feed was used directly for dehydrogenation process to produce styrene monomer. All of the distilled fractions were analyzed by gas chromatography instrument. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2795–2798, 2006     

Transformation of ethylbenzene–m-xylene mixture on zeolites with different structures

Hierarchical zeolite ZSM-5 synthesized by applying amphiphilic organosilane as mesopore template, nanosized zeolite Beta and zeolite MCM-22 have been studied, for the first time in the conversion of mixed ethylbenzene–m-xylene feed. The effects of the channel structure, nanosizing and presence of mesopores in these zeolite materials with close Si/Al molar ratio on the catalytic activity and selectivity have been discussed. It was found that the diverse zeolites have different advantages and disadvantages in dependence on their structure and morphology. MCM-22 zeolite provides promising ethylbenzene conversion at low xylene loss with high production of the p-isomer among xylene.     

Effects of simultaneous chemical cross-linking and physical filling on separation performances of PU membranes

The novel modified polyurethane (PU) membranes were prepared by β-cyclodextrin (CD) cross-linking and SiO₂/carbon fiber filler, simultaneously. The structures, thermal stabilities, morphologies, and surface properties were characterized by FTIR, TGA, SEM, and contact angle. The results showed that the addition of inorganic particles increased the thermal stabilities of PU membranes. The modified PU membranes possessed more hydrophobic surfaces than pure PU. In the swelling investigation, PU and its modified membranes were swelled gradually with increasing phenol content in the mixture. The membranes modified by CD cross-linking (PUCD) demonstrated the highest swelling degree. Pervaporation (PV) performances were investigated in the separation of phenol from water. Three kinds of modified membranes obtained better permeability and selectivity than PU membranes. With the feed mixture of 0.5 wt% phenol at 60 °C, the modified PU membrane by CD cross-linking and SiO₂ filler (PUCD-S) obtained the total flux of 5.92 kg μm m^?2 h^?1 which was above doubled that of PU (2.90 kg μm m^?2 h^?1). The modified PU membrane by CD cross-linking and carbon fiber filling (PUCD-C) obtained the separation factor of 51.31 which was nearly tripled that of PU (17.72). The PUCD membranes showed both better permeability and selectivity than the pure PU membranes. The increased phenol content induced an increased separation factor of PUCD and PU, but a decreased selectivity of PUCD-S and PUCD-C. The methods of CD cross-linking and inorganic particle filling were effective to develop the overall separation performances, greatly.     

Crystallinity of large single crystals of FAU-type zeolites with a wide range of Si/Al ratios

Large colorless single crystals of FAU-type zeolites were synthesized from gels with the composition xSiO₂ : 2.0NaAlO₂ : 7.5NaOH : 454H₂O : 5.0TEA, where x = 2.0–6.0. FAU-type zeolite with Si/Al = 1.26(4) was nearly pure and the maximum size of the single crystals was ca. 150 μm. In case of FAU-type zeolites with Si/Al = 1.54(5), the maximum size of single crystals was ca. 200 μm and the ratio of FAU/impurity was 0.07. The framework Si/Al ratio of the as-synthesized FAU-type zeolite tended to increase with the Si/Al ratio of gel composition. All of the large single crystals had good crystallinities for single-crystal X-ray diffraction, leading to enough numbers of significant reflections which have strong intensity. The structure of a single crystal of dehydrated zeolite Na-X (Si/Al = 1.41(4)) with composition |Na₈₀|[Si₁₁₂Al₈₀O₃₈₄]-FAU per unit cell was determined by X-ray diffraction methods in the cubic space group \( Fd \bar{3} m; \) a = 24.9434(6) Å at 294 K. The structure was refined by using all intensities to the final error indices (using only the 771 reflections for which F _o > 4σ(F _o)), R ₁ = 0.048 (based on F) and R ₂ = 0.188 (based on F ²). In the crystallographic studies, the Si/Al ratio of the synthetic FAU-type zeolite is 1.41(4) which is quite consistent with the SEM–EDS analysis.     

Influence of support layer and PDMS coating conditions on composite membrane performance for ethanol/water separation by pervaporation

A systematic study was performed on the combination of support properties and polydimethylsiloxane (PDMS) coating conditions for the lab‐scale preparation of a defect‐free, thin film composite membrane for organophilic pervaporation. Support layers having comparable surface porosities were prepared from three polymers with different chemical composition (PVDF, PSF, PI). Their exact role on the deposition of the PDMS coating (i.e., wetting and intrusion) and the final membrane performance (i.e., effect on mass transfer of the permeants) was studied. The crosslinking behavior of dilute PDMS solutions was studied by viscosity measurements to optimize the coating layer thickness, support intrusion and wetting. It was found essential to pre‐crosslink the PDMS solution for a certain time prior to the coating. Dip time for coating the PDMS solution on the supports was varied by using automated dip coating machine. The performance of the synthesized membranes was tested in the separation of ethanol/water mixtures by pervaporation. Both flux and selectivity of the membranes were clearly influenced by the support layer. Resistance of the support layers increased by increasing the polymer concentration in the casting solutions of the supports. Increasing the dip time of the PDMS coating solution led to increased selectivity of the composite membranes. Scanning Electron Microscopy analysis of the composite membranes showed that this leads to a minor increase in the thickness of the PDMS top layer. Top layer thickness increased linearly with the square root of the dip time (t^0.5) at a constant withdrawal speed of the support. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43670.     

Modified silicone–PVDF composite hollow‐fiber membrane preparation and its application in VOC separation

Polydimethylsiloxane^vi–poly(vinylidene fluoride) (PDMS^vi–PVDF) composite membranes were prepared using asymmetric PVDF hollow‐fiber membranes as the substrate where a very thin layer of silicone‐based coating material was deposited via a developed dip coating method. The preparation of the composite membranes under various conditions were investigated. In the optimal coating procedure, homogenous and stable oligo‐PDMS^vi coating layers as thin as 1–2 μm were successfully deposited on the surface of PVDF membranes. The developed PDMS^vi–PVDF composite membranes were applied for separation of a wide variety of volatile organic compounds (benzene, chloroform, acetone, ethyl acetate, and toluene). The results showed that the PDMS^vi–PVDF hollow‐fiber composite membranes that had been developed exhibited very high removal efficiency (>96%) for all the VOCs examined under favorable operating conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Comparative Study Between Ethylbenzene Disproportionation Reaction and its Ethylation Reaction with Ethanol over ZSM-5

Ethylation of ethylbenzene with ethanol has been studied over ZSM-5 catalyst in a riser simulator that mimics the operation of a fluidized-bed reactor. The feed molar ratio of ethylbenzene:ethanol is 1:1. The study was carried out at 350, 400, 450, and 500 °C for reaction times of 3, 5, 7, 10, 13, and 15 s. Comparisons are made between the results of the ethylbenzene ethylation reaction with that of ethylbenzene disproportionation reaction earlier reported. The effect of reaction conditions on ethylbenzene reactivity, p-diethylbenzene selectivity, total diethylbenzene (DEB) isomers selectivity, p-DEB-to-m-DEB ratio, benzene-to-DEB molar ratio, and benzene selectivity, are reported. Benzene selectivity is about 10 times more in the EB disproportion reaction as compared to its ethylation reaction with ethanol at 350 °C. In addition, the results showed a p-DEB/m-DEB ratio for the EB ethylation reaction varying between 1.2–1.7, which is greater than the equilibrium values. Increase in temperature shifts the alkylation/dealkylation equilibrium towards dealkylation, thereby decreasing conversion and selectivity to DEB.     

Preparation of PDMS—Silica Nanocomposite Membranes with Silane Coupling for Recovering Ethanol by Pervaporation

In this article, the composite polydimethylsiloxane (PDMS) membranes supported by cellulose-acetate (CA) microfiltration membrane were successfully prepared by adding nano-fumed silica particles modified with a silane coupling reagent, NH₂-C₃H₆-Si(OC₂H₅)₃. The effects of silica content, feed concentration, and feed temperature on the pervaporation performances of the nano-composite PDMS membranes were investigated for recovering ethanol from aqueous solution by pervaporation. It was found that adding the modified silica particles significantly improved the pervaporation performances of the composite membranes. When the silica content in the membrane was 5 wt%, for a 5 wt% ethanol/water mixture at 40°C, the permeation flux of the membrane maintained about 200 g · m^?2 · h^?1 and separation factor reached the maximum value of 19.     

Enhanced gas separation performance of PSF membrane after modification to PSF/PDMS composite membrane in CO2/CH4 separation

Asymmetric polysulfone (PSF) membrane was developed and modified to PSF/polydimethylsiloxane (PSF/PDMS) composite membrane by dip coating technique. Effect of PDMS coating time on membrane properties was examined by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, attenuated total reflectance‐Fourier transform infrared, and water contact angle. The increase in PDMS coating time resulted in a decrement in the thermal strength of PSF membrane. Surface contact angle values revealed that increase in PDMS coating time had increased the surface hydrophobicity in membranes. CO₂/CH₄ separation performance of membranes was evaluated, and an increase in CO₂/CH₄ ideal selectivity was observed with the increase of PDMS coating time. At feed pressure of 10 bar, the selectivity of PSF has increased up to 65% after dip coating with PDMS for 30 min. Modification of polymeric membrane into composite membrane provided a way forward towards the enhancement of gas separation performance in polymeric membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45650.     

Divinyl benzene cross‐linked HTPB‐based polyurethaneurea membranes for separation of p‐/o‐xylene mixtures by pervaporation

Cross‐linked hydroxy terminated polybutadiene (HTPB)‐based polyurethaneurea (PU), HTPB‐divinyl benzene (DVB)‐PU, was synthesized by a three‐step polymerization process. It was first used as membrane material to separate p‐/o‐xylene mixtures by pervaporation (PV). The effects of the content of cross‐linker DVB, feed concentration, and operating temperature on the PV performance of HTPB‐DVB‐PU membranes were investigated. The membranes demonstrated p‐xylene permselectivity as well as high total flux. The introduction of DVB significantly enhanced the temperature resistance ability of the HTPB‐DVB‐PU membranes. With increasing DVB content, the separation factor increased while the total flux decreased a little. The highest separation factor reaches 2.01 and the total flux is 33 g/m²h with feed concentration of 10 wt % p‐xylene at 30°C. These PV performances with increasing DVB content were explained in terms of the view point of chemical compositions and physical structures of the HTPB‐DVB‐PU membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Pervaporation Separation of p-/o-Xylene Mixtures Using HTPB-Based Polyurethaneurea Membranes

Hydroxy terminated polybutadiene (HTPB)-based polyurethaneurea membranes with and without cross-linkage were synthesized and first used as membrane material to separate p-/o-xylene mixtures by pervaporation. Compared with HTPB-PU (without cross-linkage) membranes, HTPB-DVB-PU (cross-linked HTPB-PU with divinyl benzene) membranes demonstrated a lower degree of swelling in xylene isomer solutions and noticeable improved separation factor of p-/o-xylene. On the other hand, the amount of p-xylene adsorbed in HTPB-DVB-PU membranes increased significantly rather than that of o-xylene. While the separation factor of p-/o-xylene increased but the total flux decreased with increasing DVB content, which can be ascribed to the improved chemical structure and more homogeneous chain structures of the HTPB-DVB-PU membranes. The p-xylene normalized permeation rate and separation factor of p-/o-xylene of HTPB-DVB-PU membrane reached 2.70 kgµm/m²h and 2.23, respectively, at a feed concentration of 10 wt% p-xylene at 30°C.     

Pervaporation dehydration of ethyl acetate aqueous solution using the doubly modified polyvinyl alcohol (PVA) composite membrane

Polyvinyl alcohol–tetraethoxysilane–perfluorosulfonic acid (PVA–TEOS–PFSA) hybrid membrane was prepared by sol–gel method through PVA being modified doubly by PFSA and TEOS. With polyacrylonitrile (PAN) ultrafiltration membrane as a substrate membrane, PVA–TEOS–PFSA/PAN composite membrane was fabricated by dip-coating method for pervaporation (PV) dehydration of ethyl acetate (EAc) aqueous solution. The hybrid membrane was characterized by swelling degree, static contact angle, Fourier transform infrared spectra and scanning electron microscope. Effects of PFSA and TEOS contents in coating solution on PV performance of composite membrane were investigated, respectively. With increasing PFSA content, the permeation flux of composite membrane increased, while the separation factor decreased. Just the opposite, the increase of TEOS content resulted in the decrease in permeation flux and the increase in separation factor. In addition, the PV performances of composite membranes were also investigated at different feed temperatures and water concentrations in feed, respectively. The PVA–TEOS–PFSA/PAN composite membrane, which was prepared from coating with PVA/PFSA mass ratio of 80/20 and TEOS content of 20 wt%, exhibited the permeation flux of 347.9 g m^?2 h^?1 and the separation factor of 2218 for PV dehydration of 2 wt% water of EAc solution at 40 °C.     

High‐performance zeolite T membrane for dehydration of organics by a new varying temperature hot‐dip coating method

A new seeding method, namely, varying‐temperature hot‐dip coating (VTHDC), is proposed for synthesis of zeolite T membranes by secondary hydrothermal growth. The VTHDC method is composed of hot‐dip coating at higher temperature, rubbing off the superfluous crystals, and hot‐dip coating at lower temperature. It was found that the method was flexible and effective for combined control over the seed suspension concentration, seed size, and coating temperature, leading to combined control of properties of the seed layer over the seed size, thickness, coverage, and defect. A thin continuous, smooth defect‐free asymmetric seed layer was achieved consisting of large and small zeolite T seed crystals. The resulting zeolite T membrane M5 exhibited high pervaporation performance with the flux reaching 2.12 and 2.52 kg/m² h for the dehydration of 90 wt % EtOH/H₂O and IPA/H₂O mixture, respectively, at 348 K. The corresponding separation factor was up to 1301 and 10,000, respectively. © 2012 American Institute of Chemical Engineers AIChE J, 59: 936–947, 2013     

SAPO-34 membranes for CO2/CH4 separations: Effect of Si/Al ratio

Silicoaluminophosphate (SAPO) membranes with Si/Al gel ratios from 0.05 to 0.3 were synthesized by in situ crystallization onto porous, tubular stainless steel support. Pure SAPO-34 membranes were obtained when the Si/Al ratio was 0.15 or higher. The adsorbate polarizability correlated with the adsorption capacity on SAPO-34, and the amounts of gases adsorbed were in the order: CO₂ > CH₄ > N₂ > H₂. The Si/Al ratio did not affect the pore volume significantly, but it changed the CO₂ and CH₄ adsorption equilibrium constants. The SAPO-34 membranes effectively separated CO₂ from CH₄ for feed pressures up to 7 MPa. At 295 K, for a pressure drop of 138 kPa and a 50/50 feed, the CO₂/CH₄ selectivity was 170 for a membrane with a Si/Al gel ratio of 0.15. At 7 MPa, the CO₂/CH₄ selectivity was 100 and the CO₂ permeance was 4 × 10⁻⁸ mol/(m² · s · Pa) at 295 K. This membrane was also separated CO₂/N₂ (selectivity = 21) and H₂/CH₄ (selectivity = 32) mixtures at 295 K and a pressure drop of 138 kPa. Competitive adsorption and difference in diffusivities are responsible for CO₂/CH₄ and CO₂/N₂ separations, whereas the H₂/CH₄ separation was due to diffusivity differences. For a membrane with Si/Al gel ratio of 0.1, a mixture of SAPO-34 and SAPO-5 formed, and the CO₂/CH₄ selectivity was lower.     

Separation of p‐xylene from ternary xylene mixture using silicalite‐1 membrane: process optimization studies

BACKGROUND: The design of experiments (DoE) is applied to the process optimization of p‐xylene (pX) separation from its isomers m‐xylene (mX) and o‐xylene (oX) mixture using silicalite‐1 membrane supported on α‐alumina. A central composite design (CCD) coupled with response surface methodology (RSM) was used to correlate the effect of two separation process variables, temperature (150–250 °C) and pX feed partial pressure (0.10–0.26 kPa) to three responses: (i) pX flux; (ii) pX/oX separation factor; and (iii) pX/mX separation factor. The significant factors affecting each response were elucidated from the analysis of variance (ANOVA). The interaction between two variables was investigated systematically based on three‐dimensional response surface plots. RESULTS: The optimization criteria were used to maximize the value of pX flux, pX/mX separation factor and pX/oX separation factor. The optimum pX flux of 5.94 × 10^?6 mol m^?2 s^?1, pX/oX separation factor of 19 and pX/mX separation factor of 20 were obtained at a temperature of 198 °C and pX feed partial pressure of 0.22 kPa. CONCLUSIONS: The experimental results were in good agreement with the simulated values obtained from the proposed models, with an average error of ± 2.90%. In comparison with the conventional approach, DoE provides better flexibility of the process studies and a useful guideline for the membrane process operation for pX separation. Copyright © 2009 Society of Chemical Industry