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Zeolites embark as a promising inorganic filler for hybrid membrane fabrication. However, small size of microporous structure and long diffusion path length of zeolites may restrict gas transport across the pore channel. Thus, hierarchical zeolites have been introduced as a prominent approach to overcome the diffusion limitation via the presence of bimodal porous structures of micropore and mesopore. In the present work, pristine PEBAX 1657 and hierarchical Linde Type-T (h-LTT) zeolite particles were prepared for the fabrication of hybrid membrane in CO2/CH4 separation. The resultant particles and membrane were characterized using field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD) and thermogravimetric analysis (TGA). FESEM analysis demonstrates the dense symmetric structure of pristine PEBAX 1657 membrane and column-shape morphology of h-LTT zeolite particles with average particle size of 1.38 µm. On the other hand, pristine PEBAX 1657 membrane also exhibit a semi-crystalline structure and a thermal stability up to 370 °C. In addition, the permeation properties of the pristine membrane for single gas was also tested. The pristine membrane demonstrates CO2 permeability and CO2/CH4 selectivity of 74.27 Barrer and 14.26, respectively.

This work reported on the fabrication of mixed matrix membranes by incorporating NH2-MIL-125 (Ti) nanofiller into 6FDA–durene polymer matrix for CO2/CH4 separation. The structural properties and morphology of the nanofillers and resultant membranes were investigated by X-ray diffraction, Brunauer Emmett and Teller, field emission scanning electron microscope, energy-dispersive X-ray spectroscopy mapping, thermogravimetric analysis and free fractional volume. The results showed that the CO2 and CH4 single gas permeability, as well as CO2/CH4 ideal selectivity were improved by incorporating NH2-MIL-125 (Ti) into the polymer matrix. Membrane loaded with 7.0 wt% of NH2-MIL-125 (Ti) filler showed the highest CO2 permeability of 1115.70 Barrer and CO2/CH4 selectivity of 37.10, surpassing the 2008 Robeson upper bound. Furthermore, improvement of CO2 permeability of 119% and increment of 331% for gas pair selectivity in comparison with pure membrane were achieved. The results obtained in this work is due to the high porosity of nanofillers besides the attraction of amine functional group towards CO2. Overall, incorporation of amine-functionalized MIL-125 (Ti) nanofillers into 6FDA–durene polymer matrix has enhanced the separation performance of the membrane in CO2/CH4 separation.

In this work, we systematically study the performance of tubular ZIF-8 membranes in the separation of small molecules including H

Presently, composite membranes emerged as a promising approach to overcome the limitations of polymeric and inorganic membranes particularly in acid gas separation. In the present work, composites membranes were fabricated by combining hierarchical T-Type (h-zeolite T) zeolite and PEBA-1657 at different filler composition that ranging from 5 wt% - 30 wt% for the CO

The attractive features of this work lies on the optimization of spinning parameters including, take-up speed and air-gap distance on the fabrication of NH2-MIL-53(Al)/CA Hollow fiber mixed matrix membranes (HFMMMs) for gases separation. The morphology and distribution of particles in the resultant HFMMMs were characterized by using FESEM and EDX mapping, respectively. FESEM images showed that the increase in take-up speed and air-gap distance reduced the outer diameters of HFMMMs from 275.5 µm to 110.1 µm and 719.1 µm to 648.4 µm, respectively. The gas permeation results exhibited that the permeance values were reduced and ideal selectivities were improved with the increment of take-up speed. Increasing trend of ideal selectivities could be because of progression of polymer orientation, packing and mono-disperse space which suppressed the non-selective voids and Knudsen pores in the HFMMMs. However, variation of air-gap distance produced “V” and “A” pattern for permeance and ideal selectivity values, respectively, for all HFMMMs spun at different take-up speeds. The HFMMM spun at optimum spinning condition at take up speed of 12.2 m/min and air gap distances of 5.0 cm showed the highest CO2/CH4 ideal selectivity of 16.0 and CO2/N2 ideal selectivity of 12.0. Hence, optimization of spinning parameters can be considered as feasible and efficient method in order to fabricate HFMMMs with higher separation performance. The enhanced CO2 permeance and ideal selectivities demonstrated that NH2-MIL-53(Al)/CA HFMMM spun at optimum condition is potential for industrial gas separation.

In the current work, effect of spinning conditions including, take-up speed and air-gap distance and post-treatment methods on the fabrication of cellulose acetate hollow fiber membranes (CA-HFMs) for CO2/N2 and CO2/CH4 separations have been reported. The gas permeation results obtained in this work revealed that permeances of gases were decreased with increase in take-up speed from free fall to 12.2 m/min. Meanwhile, gas pair selectivities increased with increasing take-up speed. Subsequently, increment in air-gap distance produced the “V” pattern for gases permeances and “A” pattern of gas pair selectivities for all CA-HFMs spun at different take-up speeds. Therefore, optimum take-up speed and air gap distance of CA-HFMs of 12.2 m/min and 5.0 cm were obtained, respectively. CA-HFM spun at optimum spinning conditions showed the highest CO2/CH4 and CO2/N2 ideal selectivities of 7.9 and 6.0, respectively. On the other hand, permeation results also demonstrated that the CO2/CH4 and CO2/N2 ideal selectivities of PDMS coated CA-HFMs were higher about 70.9% and 84.1%, respectively, compared to those values obtained from thermally treated CA-HFMs. Therefore, PDMS coating is considered as an effective approach to seal the macro-voids of HFMs compared to the thermal treatment in order to achieve higher permeation performance for CO2 separations. In addition, permeation results also manifested that the CA-HFM fabricated at optimum conditions has incredible worth from the prospective of industrial separations of CO2 from flue and natural gas.

In this study, the effect of solution alkalinity towards zeolite crystallization and growth were investigated for NaX zeolite crystals and NaX zeolite membrane grown via secondary growth. NaX zeolite crystals were synthesized by using different Na2O/Al2O3 ratios of 15, 16, 17, 18 and 19. XRD and FESEM results indicated that Na2O/Al2O3 ratio of 17 and above produced NaX zeolite crystal with high crystallinity ad single phase NaX zeolite. NaX zeolite membrane were also synthesized by varying Na2O/Al2O3 ratios of 17 and 19 in order to study the growth of NaX zeolite membrane via secondary growth. Na2O/Al2O3 ratio of 17 resulted in better intercrystalline growth of the membrane layer compared with the membrane synthesized using mixture solution with Na2O/Al2O3 ratio of 19.

Exploring the efficient synthesis method is essential in producing zeolite membranes with minimum defects. Seeding prior hydrothermal synthesis (HT) is the major parameters that affecting the quality of zeolite membrane formed. The colloidal stability of the NaY seed solution and its attachment to the support were studied by varying the pH of the seed solutions. Three seeding methods, including dip-coating, spin coating and vacuum coating, were studied in forming NaY zeolite seed layer. Then, the seeded alumina supports were subjected to hydrothermal treatment (HT) in order to form NaY zeolite membranes. The effect of NaY seeds solution colloidal stability, electrostatic attachment between seeds and support and the seeding methods on the properties of the quality of the formed NaY zeolite membranes were investigated. The zeta potential of the seed solution was measured with respect to different pH of the seed solution. The formed NaY zeolite membrane samples were characterized with X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) and Energy dispersive X-Ray spectroscopy (EDX). Spin coating and vacuum coating displayed better seeds coverage onto the alumina support due to the vacuum lock mechanism however excessive seeds accumulation onto the alumina support will inhibit zeolite growth and expansion hence to produce NaY zeolite membranes with cracks. Nonetheless, seeded supports by dip coating method display less coverage on the support however with a proper selection pH of the seeding solution with relates to its zeta potential, stable aqueous colloidal dispersion of the seeds solution and better attachment between the zeolite seeds and the support could be achieved in order to form zeolite NaY membranes with least defects.

Sonochemistry is the implementation of ultrasound wave to chemical reactions and processes. Remarkable progress has been achieved over the years on ultrasonic-assisted hydrothermal synthesis in zeolites. Ultrasonic irradiation is gaining popularity among researchers due to its ability in enhancing the zeolite crystallization and shortening significantly zeolite synthesis duration. In this project, zeolite RHO were synthesized via ultrasonic irradiation and followed by hydrothermal synthesis. The effect of ultrasonic irradiation on the synthesis of zeolite RHO was investigated. The zeolite RHO samples were characterized with X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) coupled with Energy Dispersive X-ray (EDX). The application of ultrasonic irradiation treatment in current study has significantly shortened the synthesis duration of zeolite RHO from 7 days to 2 days compared to the conventional hydrothermal synthesis without ultrasonic irradiation treatment.

In this work, composite membranes were fabricated by incorporating amine-functionalized zeolitic imidazolate framework 8 (ZIF-8) into 6FDA-durene polyimide. ZIF-8 particles was functionalized by N-[3-(Dimethoxymethylsilyl)propyl] ethylenediamine (AAPTMS) and N1-(3-Trimethoxysilylpropyl) diethylenetriamine (AEPTMS). Functionalization of ZIF-8 by amine-functional group may possibly enhance the CO2/CH4 separation performances by improving the compatibility between ZIF-8 and 6FDA-durene polymer. The resultant membranes were analysed by using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersion X-ray (EDX). Then, the separation performance test were performed using pure carbon dioxide (CO2) and methane (CH4) gases. The results showed that CO2 permeability of 548 Barrer and CO2/CH4 ideal selectivity of 17 were obtained using 1.0 wt% AAPTMS-ZIF-8/6FDA-durene composite membrane, while 1.0 wt% AEPTMS-ZIF-8/6FDA-durene composite membrane exhibited CO2 permeability of 533 barrer and CO2/CH4 gas pair selectivity of 12. On the other hand, 1.0 wt% ZIF-8/6FDA-durene composite membrane showed CO2 permeability and CO2/CH4 selectivity of 610 barrer and 15, respectively. Therefore, it can be concluded in this work that, selection of another suitable amine functionalization group for the modification of ZIF-8 is needed in later works to further improve the performance of the membrane in CO2 removal from CH4.

In the current study, new types of MMMs are fabricated by incorporating NH2-MIL-53(Al) filler into cellulose acetate (CA) polymer. Subsequently, crystallinity, morphology, thermal stability, functional groups and density measurement of the resultant MMMs were verified by using different analytical tools. The results showed that the presence of NH2-MIL-53(Al) in CA matrix had enhanced the CO2 permeability, CO2/N2 and CO2/CH4 ideal selectivities from 15.5 Barrer to 52.6 Barrer, 8.8 to 23.4 and 10.7 to 28.7, respectively. The present study revealed that the addition of 15 wt% NH2-MIL-53(Al) MOF into the CA matrix resulted in highest enhancement of FFV. Furthermore, MMM loaded with 15 wt% NH2-MIL-53(Al) demonstrated highest CO2 permeability as well as CO2/CH4 and CO2/N2 selectivities of 52.6 Barrer, 28.7 and 23.4, respectively. Besides, the resultant MMM showed CO2 plasticization resistance of up to 30 bar, which is 200% increment in comparison of pristine CA membrane which is only 10 bar. This work also revealed that the resultant MMMs showed significantly higher CO2 separation performance compared to the results previously reported for CA-based MMMs. Thus, it can be concluded that the MMMs fabricated in the present work has potential for CO2 removal from the flue gas and natural gas at industrial scale.

In this work, zeolite T particles were modified with three different types of silane groups including, 3-Aminopropyltrimethoxysilane (APTMS), N-(2aminoethyl)-3-aminopropyl-trimethoxysilane (AAPTMS) and 3-(2-(2-aminoethylamino) ethylamino) propyltrimethoxysilane (AEPTMS) which contain monoamine, diamine and triamine group, respectively, before incorporated into 6FDA-durene polyimide. The physicochemical properties of the particles and the resultant membranes were characterized using XRD, FESEM, EDX, FTIR, TGA and DSC. The results demonstrated that the incorporation of APTMS modified zeolite T particles into 6FDA-durene polymer matrix failed to improve the interfacial adhesion between filler and polymer phases. This phenomenon subsequently contributes to the reduction of CO2 permeability of 9.3% and decrement of CO2/CH4 selectivity of 29.5% as compared to membrane incorporated with unmodified zeolite T, which showed CO2 permeability and CO2/CH4 selectivity of 844 Barrer and 19.1, respectively. Meanwhile, composite membranes loaded with AAPTMS and AEPTMS modified zeolite T particles have effectively enhanced the filler/polymer interfacial adhesion and separation properties of the membranes. Although the incorporation of AAPTMS zeolite T particles into 6FDA-durene polymer demonstrated 2.7% reduction of CO2 permeability, increment of CO2/CH4 selectivity up to 26.4 was obtained, which successfully lies on Robeson upper limit 2008. Meanwhile, composite membrane embedded with AEPTMS modified zeolite T particles has resulted in the increment of both CO2 permeability and CO2/CH4 selectivity of 857.7 Barrer and 22.5, respectively. Overall, the effect of different amine groups in the modification of zeolite T surface on the performance of the composite membranes has been demonstrated in this work.

In this work, the incorporation of ZIF-8 nanofiller for the improvement of the transport properties of 6FDA-durene membrane in CO 2 /CH 4 separation is investigated. Central composite design (CCD) coupled with response surface methodology (RSM) were utilized for the optimization of the separation process variables over ZIF-8/6FDA-durene MMM in CO 2 /CH 4 separation. Three models correlating the independent parameters including, pressure (3.5–12.5 bar), temperature (30–50 °C) and CO 2 concentration (10–90 vol%) with the responses including, CO 2 permeability, CH 4 permeability and CO 2 /CH 4 selectivity were developed based on the experimental data. The optimum parameters for achieving the highest separation performance were obtained at pressure of 4.76 bar, temperature of 30 °C and CO 2 concentration of 90 vol%, which resulted in CO 2 permeability of 687.20 Barrer, CH 4 permeability of 71.03 Barrer and CO 2 /CH 4 selectivity of 8.92. The deviation of the corresponding experimental data was found to be in an acceptable range, confirming the suitability of RSM for predicting the membrane performance and consequently optimizing the separation process variables.

In the recent years, zeolite T has been demonstrated as a potential materials for adsorption, catalysis, pervaporation as well as gaseous separation processes. However, the reported literature on the application of zeolite T as inorganic filler for the fabrication of mixed matrix membranes (MMMs) in CO 2 /CH 4 separation is not available. Therefore, in the present work, different loadings of zeolite T particles are embedded in 6FDA-durene polyimide. The morphology and structural properties of the resultant membranes were investigated using different analytical tools and the performance of the membranes in CO 2 and CH 4 gases separation were tested. The results showed that CO 2 permeability of 843.6 Barrer and CO 2 /CH 4 ideal selectivity of 19.1 were obtained using 1 wt% loaded zeolite T/6FDA-durene MMM, which were 80% and 172% higher than the CO 2 permeability and CO 2 /CH 4 ideal selectivity attained using pristine 6FDA-durene. Besides, the membrane showed improvement in CO 2 plasticization resistant up to 20 bar as compared to pristine 6FDA-durene membrane, which showed only 5 bar. Overall, zeolite T/6FDA-durene mixed matrix membranes fabricated in this work exhibited significant enhancement in CO 2 /CH 4 separation, which makes them an attractive candidate for industrial gas separation especially for natural gas purification.

Membrane separation has been used successfully in numbers of industrial applications especially in CO2 removal from CH4 because it’s involved less energy consumption and low maintenance. The aim of this research is to fabricate ZIF-8/6FDA-durene mixed matrix membranes for enhancement of CO2 capture and consequently to optimize its fabrication method. The results showed that membrane fabricated using total dispersion duration of 3 h with filler priming procedure demonstrated homogenous distribution of ZIF-8 in 6FDA-durene matrix and improved the separation performance. Therefore, the membrane is potential for the large scale production via the method optimized in this work.

In the present work, the effects of CO 2 feed composition (15%–90%), pressure difference (100 kPa–700 kPa) and temperature (303 K–343 K) on the separation of CO 2 from CH 4 via ZIF-8 membrane were investigated. The membrane was synthesized through a simple, feasible and reproducible solvent evaporation seeding method coupled with microwave-assisted secondary solvothermal growth. Subsequently, the membrane was characterized by using scanning electron microscopy. The results showed that, for single gas permeation, CO 2 permeances remained constant while CH 4 permeances increased slightly with the increasing pressure differences at temperature of 303 K. Besides, CO 2 permeances decreased while CH 4 permeances increased slightly with the increase in temperature at pressure difference of 100 kPa. For binary gas separation, maximum CO 2 /CH 4 separation factor of 5.07 and CO 2 permeance of 6.595 × 10 −8 mol m −2 s −1 Pa −1 were obtained at CO 2 feed composition of 15%, pressure difference of 100 kPa and temperature of 303 K. Besides, CO 2 fluxes approached constant value with the increasing CO 2 partial pressure differences at CO 2 feed composition of 15%, which was mainly attributed to the competitive adsorption between CO 2 and CH 4 . On the other hand, CH 4 fluxes increased with increasing CH 4 partial pressure differences even at higher CO 2 composition in the feed, owing to its adsorption capacity and gas transport pathway via membrane intercrystalline pores.

In the current work, the synthesis duration of DD3R membrane has been successfully reduced from 27 days to 3 days using DD3R seeds prepared in 1 day via ultrasonic irradiation coupled with conventional hydrothermal heating method. Two DD3R membranes have been grown on α-alumina support using vacuum-assisted seeding secondary growth method. A DD3R membrane has been synthesized in 2 days at 160 °C using DD3R seeds prepared in 1 day via ultrasonic irradiation coupled with hydrothermal heating method. Similarly, another DD3R membrane has also been synthesized in 2 days at 160 °C using DD3R seeds prepared in 25 days without ultrasonic irradiation pretreatment. Characterization tools including; XRD and FESEM confirmed the formation of DD3R topology for the resultant membranes. Subsequently, the effect of temperature, pressure and CO 2 feed composition on the performance of resultant DD3R membrane in CO 2 /CH 4 separation has been conducted based on the experimental conditions suggested by the statistical tool: response surface methodology. Overall, the single gas permeation result showed that high CO 2 permeance of 2.46 × 10 −7 mol/m 2 sPa obtained in the present work was comparable with the CO 2 permeance reported in the literature. Besides, DD3R membrane showed ideal CO 2 /CH 4 selectivity about 5.22 which was also comparable with the results reported in the literature. In CO 2 /CH 4 separation study, the experimental data were fitted well with the model suggested by response surface methodology, with R 2 value near to 0.99. The optimum condition for the separation has been obtained at temperature of 30.1 °C, feed pressure of 1 bar and CO 2 feed composition of 10 vol% which yielded CO 2 permeance, CH 4 permeance and CO 2 /CH 4 selectivity of 8.23 × 10 −8 mol/m 2 sPa, 4.64 × 10 −8 mol/m 2 sPa and 3.81, respectively. Thus, in the present study, it was concluded that the performance of DD3R membrane still need to be improved in order to meet the industrial requirement for CO 2 separation from CH 4 .

In the current research, mixed matrix membranes (MMMs) comprising of 5, 10, 15 and 20 wt% of zeolitic imidazolate framework-8 (ZIF-8) were incorporated into 6FDA-durene polyimide phase. The effect of ZIF-8 loading on the membrane performance of CO 2 and CH 4 separation was investigated. The excellent compatibility and good distribution of ZIF-8 nanofiller in 6FDA-durene polyimide phase even at higher ZIF-8 loading up to 20 wt% has resulted in the increment of CO 2 permeability and CO 2 /CH 4 selectivity compared to pure membrane. In this work, 6FDA-durene loaded with 10 wt% ZIF-8 demonstrated impressive CO 2 permeability of 1426.75 Barrer with CO 2 /CH 4 selectivity of 28.70, which successfully surpassed the Robeson 2008 upper bound.

In this paper, the effect of synthesis parameters including temperature, pressure and volume of the synthesis solution towards the formation of ZIF-8 under microwave-assisted solvothermal synthesis was investigated. The resultant ZIF-8 samples were characterized using X-ray diffraction and nitrogen physisorption. The surface morphology was examined via scanning electron microscopy. The results exhibited that, highly crystalline ZIF-8 was successfully synthesized within 0.5 hours at 120 C, with the BET surface area up to 690.75 m 2 /g and micropore volume of 0.32 cm 3 /g. It was found that, at higher temperature and pressure, the formation of ZIF-8 can be affected by the expansion of solvent, which reduced the initial concentration of the reactant ions. Hence, further increased of the temperature did not cause higher crystallinity and larger size of ZIF-8 particles.

In this study, response surface methodology (RSM) was used to optimize the experimental conditions in nitrate removal processes using 20% AEPTMS amine-functionalized MCM-41 as the adsorbent. The adsorbent was synthesized via co-condensation method and then characterized by using scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). Subsequently, total 19 adsorption experiments with different experimental conditions generated by the Design of Experiments (DoE) software have been conducted. The experimental results were fitted well with the quadratic model suggested by the software and the R2 value obtained was 0.9935. It was found that the highest percentage removal of nitrate was 70% obtained at initial nitrate concentration of 0.25 mM, adsorbent dosage of 0.50 g and contact time of 1 h. On the other hand, the optimum nitrate removal of 56% was obtained at the optimum conditions suggested by the software, with the initial nitrate concentration of 0.25 mM, adsorbent dosage of 0.124 g, and contact time of 1 h.

Controlled growth of Faujasite zeolite with NaX topology by manipulating the synthesis parameters has been successfully demonstrated in this work. The effects of solution aging durations and Na2O/Al2O3 ratios toward the formation of NaX zeolite are investigated. The morphology, Si/Al ratio, crystallinity and purity, particle size distribution of the resultant NaX zeolite crystals were determined by using field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analyser (XRD) and dynamic light scattering (DLS), respectively. The results showed that, longer aging duration and higher Na2O/Al2O3 ratio resulted in smaller particle size of NaX. On the other hand, high purity of NaX zeolite particle with mean particle size of 750 nm was produced at aging duration of 48 h and Na2O/Al2O3 ratio of 19. Overall, this work has proved that, the growth of NaX zeolite particles could be controlled via a simple synthesis method without using an organic structure directing agent.

Conventional hollow fiber models in process simulators usually assume constant membrane permeance i.e., independent of pressure and temperature. In this work, hollow fiber membrane model has been proposed to cater the effects of temperature and pressure on membrane permeance. The proposed model is incorporated with Aspen HYSYS as a user defined unit operation in order to study the performance of gas separation system. The simulated model is validated by experimental and published data. The temperature drop due to Joule Thomson effect and its contribution to the change in membrane permeance has also been investigated. Similarly, the effect of pressure on membrane permeance has been studied. The influence of these effects on the separation performance and process economics has been investigated for the separation of CO 2 from natural gas. The proposed hollow fiber membrane model has potential to be applied for design, optimization and scale up of wide range of gas separation systems.

We have successfully designed amendable polybenzoxazole materials with enhanced gas transport properties via incorporation of cardo moiety into thermally rearrangeable polymer chains. A series of cardo-copoly(hydroxyimide) have been synthesized by polycondensation of dianhydride with various molar ratios of two different ortho -functional diamine sources: 3,3′-dihydroxybenzidine (non-cardo) and 9,9-bis(3-amino-4-hydroxyphenyl)fluorene (cardo). The effect of cardo-containing diamine composition in the range of 5–50 mol% on the structural and gas transport properties of the copolybenzoxazole membranes have been systematically investigated in the present work. It is found that the incorporation of cardo group has increased the gas permeability significantly. Thermally rearranged copolybenzoxazole membrane with the addition of 10 mol% of cardo moiety has shown the largest enhancement in gas permeability. An increment of 3 times in CO 2 permeability has been achieved as compared to the CO 2 permeability in the non-cardo counterparts. The excellent features of the cardo-copolybenzoxazole shows a promising approach for the future cavity engineering in the field of high performance materials.

The permeation of single component and binary mixture containing p -xylene and o -xylene through silicalite-1 membrane was studied experimentally in the temperature range of 150–250 °C at feed partial pressure of 0.26 kPa for p -xylene and 0.22 kPa for o -xylene. The model for single component flux based on the combination of dual-site Langmuir isotherm and Maxwell–Stefan formulation was derived. The adsorption parameters were estimated by minimizing the difference between the experimental flux and simulated flux. The heat of adsorption and entropy values obtained were in good agreement with the reported values. The effect of feed partial pressure in the range of 0.20–1.50 kPa on xylene flux was predicted using the adsorption parameters and compared with the experimental values. The Maxwell–Stefan diffusion model, in combination with the ideal adsorbed solution (IAS) theory and single-component adsorption parameters was used to predict the permeation flux of p -xylene and o -xylene for binary xylene mixture through the silicalite-1 membrane. The simulated results were in good agreement with the experimental data. The simulated adsorption isotherm in higher temperature range of 150–250 °C using the model and derived adsorption parameters could provide useful information for adsorption of xylene molecules on silicalite-1 membrane at a higher operating temperature.

A mathematical model representing m-xylene isomerization reaction and subsequent separation of xylene isomers in a catalytic membrane reactor is proposed. Propylsulfonic acid-functionalized silicalite-1 and arenesulfonic acid-functionalized silicalite-1 membranes were used as the catalytic membranes. A triangular reaction scheme was used as the reaction model while m-xylene conversion, p-xylene selectivity, p-xylene yield, p-xylene flux and p-/o-xylene separation factor under isothermal condition were calculated from the model. The simulated results were analyzed and showed good agreement with the experimental data within an error of ±5%. The effects of p-xylene diffusivity on m-xylene conversion, p-xylene flux and p-/o-xylene separation factor were investigated. Simulated results showed that the increase in p-xylene flux enhanced m-xylene conversion. p-Xylene yield increased with an increase in m-xylene conversion. m-Xylene conversion by arenesulfonic acid functionalized silicalite-1 membrane was higher compared to that of propylsulfonic acid functionalized silicalite-1 membrane due to higher diffusion rate of p-xylene. The removal of p-xylene through the membrane contributed to higher m-xylene conversion in both of the membranes.

Propylsulfonic acid-functionalized silicalite-1 membrane and arenesulfonic acid-functionalized silicalite-1 membrane were synthesized over α-alumina support via one-step in situ hydrothermal crystallization and subsequent post-synthesis modification. Propylsulfonic acid-functionalized silicalite-1 membrane was synthesized using 3-mercaptopropyltrimethoxysilane (3MP) as an organosilane source whereas for arenesulfonic acid silicalite-1 membrane, phenethyltrimethoxysilane (PE) was used as an organosilane source. The acid capacity of the membrane was varied by adjusting the concentration of organosilane from 5 mol% to 20 mol%. The membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen gas permeation. Ammonia temperature-programmed desorption (NH 3 -TPD) and Fourier transform infrared spectroscopy (FT-IR) showed the presence of strong Bronsted acid sites in both membranes. The total acid capacity increased with increase in organosilane concentration in the synthesis mixture. Both membranes were tested for their catalytic activity in m -xylene isomerization reaction in the temperature range of 355–450 °C. Due to higher acid density, arenesulfonic acid-functionalized silicalite-1 membrane gave higher catalytic activity compared to propylsulfonic acid-functionalized silicalite-1 membrane. At 450 °C, m -xylene conversion of 57% with 33% p -xylene yield was achieved using arenesulfonic acid-functionalized silicalite-1 membrane with 15 mol% of phenethyltrimethoxysilane, while m -xylene conversion of 46% with 28% p -xylene yield was achieved using propylsulfonic acid-functionalized silicalite-1 membrane with 15 mol% of 3-mercaptopropyltrimethoxysilane. The enhancement in p -xylene yield was due to the simultaneous isomerization reaction and separation of the reaction products through the catalytic membrane. Both catalytic membranes exhibited good structural stability after subjected to isomerization reaction study for 120 h.

m-Xylene isomerization kinetics has been studied using acid-functionalized silicalite-1 catalytic membrane in the temperature range of 355–450 °C. Two types of catalytic membranes: (1) propylsulfonic acid-functionalized silicalite-1 membrane and (2) arenesulfonic acid-functionalized silicalite-1 membrane were synthesized on α-alumina support via one-step in situ hydrothermal crystallization and subsequent post-synthesis modifications. The membranes were characterized by scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH3-TPD) and Fourier transform infrared spectroscopy (FT-IR). Arenesulfonic acid-functionalized silicalite-1 membrane with its higher acidity gave better catalytic activity as compared to propylsulfonic acid-functionalized silicalite-1 membrane. The continuous removal of reaction products over the membrane contributed in the higher p-xylene yield. A triangular reaction scheme based on time on stream (TOS) model was used to analyze the experimental data. The simulated results were in good agreement with the experimental results, within an error less than ±5%. The estimated activation energies indicated that conversion of m-xylene to p-xylene in both acid-functionalized silicalite-1 membranes is affected by the mass transfer rate through the membrane, while conversion of m-xylene to o-xylene is controlled by the reaction rate.

The process optimization of p -xylene separation from p -/ o- xylene binary mixture through silicalite-1 membrane using statistical design of experiments (DoE) is reported in the present study. The silicalite-1 membrane was synthesized and characterized using different analytical techniques. The effect of three important process variables, temperature (150–250 °C), p -xylene feed partial pressure (0.04–0.50 kPa) and p -xylene feed composition (0.20–0.80) on the separation performance of the membrane was studied. The response surface methodology (RSM) coupled with central composite design (CCD) was used to develop three models to correlate the effect of process variables to three responses: (i) p -xylene flux, (ii) o -xylene flux and (iii) p -/ o- xylene separation factor. The most influential factor on each of the response was identified using the analysis of variance (ANOVA). The interaction between the three variables was systematically investigated based on three-dimensional response surface plots. The optimum operating condition for the process was determined by setting the optimization criteria to maximize the p -xylene flux and p -/ o -xylene separation factor, and to minimize the o -xylene flux. The optimum p -xylene flux of 3.83 × 10 −6 mol/m 2 s and p -/ o -xylene separation factor of 46 were obtained at a temperature of 198 °C, p -xylene feed partial pressure of 0.15 kPa and p -xylene feed composition of 0.80. The simulated values obtained from the statistical model were in agreement with the experimental results within an average error of ±2.70%. The mass transport of xylene isomers and its separation in the silicalite-1 membrane was related with the characteristics of the membrane.

A series of partially crystalline silicalite-1 based materials were synthesized by varying the molar ratio of organosilane source, phenethyltrimethoxysilane (PE) to tetraethylorthosilicate (TEOS) in the range of 0.05–0.50, using one step co-condensation hydrothermal synthesis method. The phenethyl group was subsequently sulfonated to arenesulfonic acid group following strong acid treatment. The resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and desorption and elemental analysis. The structure of these materials was determined by Fourier transform infrared spectroscopy (FTIR), 29 Si and 13 C solid state NMR. The % crystallinity of the partially crystalline silicalite-1 as determined from XRD was in the range of 33–73%. The average crystallite size decreased with the increase of PE concentration in the synthesis mixture. The thermogravimetric analysis shows that the structures were thermally stable up to 550 °C after elimination of the structure directing agents (SDAs) by calcination at 420 °C. The acid capacities of these materials ranged from 2.52 to 6.63 mmol H + /g.