ZSM-5 Membranes Research Articles

Chemical vapor deposition of CuO on ZSM-5 membrane for catalytic wet peroxide oxidation of phenol in a fixed bed reactor

Complete removal of phenol and high TOC reduction (around 60%) can be achieved over CuO supported on ZSM-5 membrane.

Proton-Selective Ion Transport in ZSM-5 Zeolite Membrane

The ionic ZSM-5 zeolite membranes were investigated for proton-selective ion separation in electrolyte solutions relevant to redox flow batteries. The zeolite membrane achieved exceptional selectivity for proton over V4+ (VO2+), Cr2+, and Fe2+ via size-exclusion at the zeolitic channel openings, and remarkably low area specific resistance resulted from its hydrophilic surface, copious extraframework protons, and micron-scale thickness. The ZSM-5 membrane, as a new type of ion separator, demonstrated substantially reduced self-discharge rates and enhanced efficiencies for the all-vanadium and iron–chromium flow batteries as compared to the benchmark Nafion membrane. Findings of this research show that ionic microporous zeolite membranes can potentially overcome the challenge of trade-off between ion selectivity and conductivity associated with conventional polymeric ion separators.

Preparation and High Permeance of SiO₂-Modified Substrate Supported ZSM-5 Membrane by Pre-Seeding and Secondary Nucleation.

SiO₂-modified substrate supported compact ZSM-5 membranes with high permeance were prepared using the secondary nucleation method. The synthesis mixture had a molar composition of 10Na₂O:84SiO₂: 100NaCI:5TPABr:3500H₂O. In order to obtain high permeance, a SiO₂ meso- porous top layer was added to the macroporous substrate in this study. The SEM images of the seed layer indicate that about 400-500 nm round shaped seeds consisting of 60 nm zeolites fully covered the modifying substrate. The XRD patterns of the zeolite membranes show the purity of the ZSM-5 crystal phase, and reveal the formation of a random orientation on the SiO₂-modified substrate. The SEM images of the zeolite membranes indicate that the membranes consist of highly intergrown crystals, with a maximum thickness of about 30 µm. The results of gas permeability studies indicate that the SiO₂-modified substrate supported ZSM-5 membranes show good permeance, with the maximum H₂permeance achieved being 12.5 x 10⁻⁷ mol s⁻¹ m⁻² Pa⁻¹. The maximum H₂/N₂ and H₂/CO permselectivities were 4.01 and 4.37 respectively, which are higher than those of the corresponding Knudsen diffusion. The method used resulted in high permeance, while keeping the sustainable permselectivity, and is therefore desirable for practical applications.

Catalytic wet peroxide oxidation of phenol wastewater over a novel Cu–ZSM-5 membrane catalyst

A novel Cu–ZSM-5 membrane catalyst was prepared and characterized for catalytic wet peroxide oxidation (CWPO) of phenol wastewater in a continuous reactor. The Cu–ZSM-5 membrane catalyst was first prepared by the secondary growth process and incipient wetness impregnation method, and then characterized by thermal gravimetric (TG) analysis, N2 adsorption–desorption, X-ray diffraction (XRD), scanning electron microscopy (SEM) and H2-temperature programmed reduction (H2-TPR), respectively. This catalyst exhibited an excellent catalytic performance (complete phenol conversion and TOC conversion about 65% without toxic quinones detected).

Total oxidation of isopropanol over manganese oxide modified ZSM-5 zeolite membrane catalysts

Manganese oxide modified ZSM-5 membrane catalysts were prepared for the catalytic combustion of a volatile organic compound (isopropanol) over a zeolite membrane reactor.

Preparation and Characterization of Water Perm-selectivity ZSM-5 Zeolite Membrane Using Fluoride Route

Water perm-selectivity ZSM-5 zeolite membranes were prepared from fluoride media without organic template on the low cost macroporous α-Al2O3 tubular support by secondary growth. A varying temperature hot dip-coating method with different size of crystal was used to form a flat and continuous perfect seed layer. The effects of concentration of the small seed solution on the surface of seed layer, the morphology and pervaporation property of the ZSM-5 membrane were investigated. The results show that when the concentration of the small seed solution is 0.2wt%, the prepared ZSM-5 zeolite membrane displays high water perm-selectivity properties in the pervaporation dehydration of 10wt% H2O/IPA and 10wt% H2O/Ac OH mixtures at 75℃, which fluxes are 3.64 kg/(m2·h) and 0.61 kg/(m2·h), separation factor up to 3204 and 1321, respectively.

TPAOH Template Removal from High-Silica ZSM-5 by Low-Temperature Hydrocracking

zeolite membranes, especially the mfi-type zeolite membranes, have attracted significant attention for decades because of their special properties. while organic templates such as tetrapropylammonium hydroxide (tpaoh) have typically been used for the synthesis of zsm-5 zeolite and zeolite membranes, the templates remain trapped in the as-synthesized zeolite crystals. a common method for removing organic templates and generating porous frameworks is calcination; however, during this process, the channel structure may be affected. in particular, for zsm-5 membranes, membrane defects may be produced and the separation efficiency therefore may decrease to some extent. in this study, the low-temperature hydrocracking of tpaoh in zsm-5 zeolite crystals was studied under h-2/n-2, while n-2 adsorption, thermogravimetric (tg) analysis, fourier transform infrared (ftir) spectroscopy, temperature-programmed desorption of ammonia (nh3-tpd), and raman spectroscopy were used to characterize zeolite samples. the results show that the organic template in the pores of zsm-5 can be effectively removed below 350 degrees c by low-temperature hydrocracking. characterization analyses by bet specific surface area, tg, ftir, and raman spectroscopy demonstrated that a reducing atmosphere containing h-2 was more conducive to template removal at low temperature than atmospheres of air or n-2. the degree of template removal increased with temperature increasing. the bet surface area of the crystal after hydrocracking at 280 degrees c reached 252 m(2).g(-1), although a small amount of organic residue remained. furthermore, after hydrocracking at 350 degrees c, the bet surface area reached 399 m(2).g(-1), and only trace amount of inorganic carbon residue remained. in addition, the introduction of hydrogen at low temperatures could prevent coke deposits on acid sites and thus zsm-5 zeolite crystals had greater numbers of acidic sites after low-temperature hydrocracking.

Tuning aluminum spatial distribution in ZSM-5 membranes: a new strategy to fabricate high performance and stable zeolite membranes for dehydration of acetic acid

A novel ZSM-5 membrane with a low Si/Al ratio and homogeneous aluminum spatial distribution was achieved from an organic template-free inorganic gel in the presence of both OH(-) and F(-) ions and the obtained ZSM-5 membrane exhibited excellent selectivity and high flux and stability for dehydration of acetic acid in a wide AcOH content range.

Maxwell–Stefan modeling of high flux tubular silicalite-1 membranes for CO2 removal from CO2/H2 gas mixtures

In this work, a Maxwell–Stefan model for high flux tubular silicalite-1 membranes for separation of CO2 from a CO2/H2 mixture was developed. The model concerns tubular membranes operating in a counter flow module and includes transport through flow-through defects in the silicalite-1 film and pressure drop over the graded alumina support. Adsorption and diffusion parameters for perfect silicalite-1 crystals were taken from the literature. The flux and selectivity predicted by the model were in reasonably good agreement with experimentally observed data for a ZSM-5 membrane without any fitting of the model. However, the CO2 flux and selectivity measured experimentally for the ZSM-5 membrane were higher than that predicted by the model for a silicalite-1 membrane.The model was used to investigate a case with a 20,000Nm3/d feed comprised of a 50/50 mixture of CO2/H2 at pressure of 25bar and a membrane temperature of 296K. The permeate pressure was 1bar and 90% of the CO2 permeated the membrane. In this case, the membrane permselectivity and CO2 flux varied along the length of the tubes between 20–26 and 950–396kg/(m2h), respectively. Further, both defects and pressure drop over the support were shown to have an adverse effect on the selectivity, which indicates that membrane selectivity can be improved by reducing the flow-through defects and/or by preparing supports with less flow resistance. For a one-stage process, the required membrane area is as small as ca. 0.85m2 and the hydrogen loss through the membrane was 12.4%. For a two-stage process the required membrane area almost doubled to 1.6m2, however the hydrogen loss through the second membrane is reduced to as little as 2.5%. In summary, this work shows that high flux zeolite membranes may be an interesting option for CO2 removal from synthesis gas.

STUDY OF PERMEATION OF GASES THROUGH CERAMIC SUPPORTED POLYMERIC AND ZEOLITE MEMBRANES

Membrane separation process is one of the novel techniques for separation of CO2 from various effluent gas mixtures. Membrane operations are recognized as feasible and economical operations over conventional technologies for gas separation due to a higher flexibility to tolerate fluctuations in feed composition and flow rate. In this present work Hydroxy Ethyl Cellulose (HEC) membrane prepared on Silicon carbide (SiC) tube and ZSM-5 membrane casted on α-Al2O3 tube support is used to study the permeation characteristics of various gases. Pour and decanting technique is used to coat HEC membrane on SiC tube whereas seed growth hydrothermal technique is used to prepare ZSM-5 zeolite membrane. Scanning electron microscope (SEM) and X-ray diffraction techniques (XRD) are used to characterize the membranes.

Influence of support morphology on the detemplation and permeation of ZSM-5 and SSZ-13 zeolite membranes

In this work we prepared α-alumina hollow-fiber supported SSZ-13 and ZSM-5 membranes by hydrothermal secondary growth. The effects of support surface roughness and porosity, zeolite topology and zeolite film thickness on the thermal behavior of composite membranes during detemplation were investigated. The quality of prepared membranes was characterized by SEM, single and mixture gas permeation tests and adsorption-branch permporometry. The surface roughness of α-alumina hollow fiber supports is shown to strongly influence the thermal stability of zeolite films. SSZ-13 and ZSM-5 membranes prepared on supports with rough surface could be safely detemplated without formation of cracks by calcination (450–500°C), whereas membranes prepared on very smooth surface supports were cracked under similar conditions. In such case ozonication at lower temperature was found to be effective to detemplate the membranes without formation of cracks.

The synthesis of super-hydrophilic and acid-proof Ge–ZSM-5 membranes by simultaneous incorporation of Ge and Al into a Silicalite-1 framework

A new method for synthesis of super-hydrophilic and acid-proof zeolite membranes was presented. It involved simultaneous incorporation of suitable amounts of Ge and Al into a Silicalite-1 framework. The precursor sol was prepared in an ice-water bath, and the alcohols in the precursor sol were removed at about 80°C. It was shown that using the ice-water bath would prevent the formation of GeO2 and removing the alcohols at a relatively high temperature would lead to suitable amounts of Ge and Al in the membranes. The obtained Ge–ZSM-5 membranes were acid-proof and showed high pervaporation performance for dehydrating acetic acid and ethanol solutions. At 353K, for feed acetic acid solutions in a concentration range of 30–98wt%, the permeation flux of water was almost constant (about 0.57kg/m2h), and very little acetic acid permeated through the membrane, resulting in a very high separation factor. Similarly, for dehydration of ethanol solutions (10–98wt%) at 343K a water flux of approximately 2.4kg/m2h was obtained.

Crystallite-pore network model of transport and reaction of multicomponent gas mixtures in polycrystalline microporous media

Abstract A three-dimensional pore network model has been developed to simulate anisotropic multicomponent diffusion and reaction in polycrystalline microporous media with coexisting intracrystalline micropores and intercrystalline mesopores (i.e., defects). Transport in these pores is modeled with the generalized Maxwell–Stefan surface diffusion model proposed by Krishna [11] and the Knudsen diffusion model, respectively. A new feature highlight of this model is the representation of polycrystalline media with a crystallite-pore network model. In contrast to previous pore network models, the crystallite-pore network model has the novel aspect of modeling the anisotropic transport inside the crystallites forming a polycrystalline layer by assigning to every crystallite two parameters to describe its orientation. The model was applied to simulate xylene isomerization in a polycrystalline ZSM-5 zeolite membrane, which had been experimentally investigated in a Wicke-Kallenbach cell by Haag et al. [13] . First, their experimental data were used to estimate adsorption and diffusion parameters of the xylene isomers in the ZSM-5 membrane via fitting single-gas permeance data of the xylene isomers. Second, adopting these parameters, the experimental data for xylene isomerization were used to determine kinetic parameters for xylene isomerization in the ZSM-5 membrane. Finally, effects of selected structural parameters – concentration of defects, connectivity of defects, crystallite orientation, and crystallite size – were investigated using the obtained adsorption, diffusion, and reaction parameters. The simulation results show that high selectivity towards p-xylene requires a low concentration of defects in the polycrystalline layer and a low loading of xylene isomers in the membrane. The novel crystallite-pore network model is also applicable to many other reaction systems.

Fabrication of porous copper/manganese binary oxides modified ZSM-5 membrane catalyst and potential application in the removal of VOCs

Abstract Copper-manganese binary oxides modified ZSM-5 membrane catalysts were synthesized by using incipient wetness impregnating method. Specifically, the PSSF (paper-like sintered stainless steel fibers) support was fabricated by wet lay-up papermaking/sintering process and the ZSM-5 membranes were synthesized on the surface of stainless steel fibers by using secondary growth process. The catalysts were characterized by using scanning electron microscopy (SEM), Energy dispersive X-ray spectrometer (EDS) mapping, X-ray diffraction (XRD), N 2 adsorption–desorption, X-ray photoelectron spectra (XPS) as well as H 2 -TPR (Temperature programmed reduction). The most efficient catalyst was Cu–Mn(1:6)/ZSM-5/PSSF, exhibiting best catalytic activity (% of isopropanol conversion was 210 °C) and excellent reaction rate. It can be also demonstrated that the zeolite membrane reactor performs better for isopropanol oxidation, giving a T 90% that is around 70 °C lower than obtained in the traditional particles fixed bed. The excellent catalytic performance of the Cu–Mn(1:6)/ZSM-5/PSSF catalysts can be attributed to the presence of ZSM-5 zeolite membrane, well dispersion of catalysts actives, reasonable mass/heat transfer efficiency, excellent oxygen storage ability as well as higher contacting efficiency. Furthermore, the Cu–Mn(1:6)/ZSM-5/PSSF catalyst exhibits a high stability after being used at 260 °C for 50 h.

Gradient porous Co–Cu–Mn mixed oxides modified ZSM-5 membranes as high efficiency catalyst for the catalytic oxidation of isopropanol

Novel gradient porous mixed cobalt–copper–manganese mixed oxides modified ZSM-5 membrane catalysts were synthesized by the incipient wetness impregnating method. The paper-like sintered stainless steel fibers (PSSF) support was fabricated by the wet lay-up papermaking/sintering process, and the ZSM-5 membranes were synthesized on the surface of stainless steel fibers by using secondary growth process. These novel modified membrane catalysts have been characterized by a series of techniques including SEM, EDS mapping, XRD, N2 adsorption–desorption, XPS and H2-TPR method. Catalytic performances of isopropanol oxidation over these novel catalysts were investigated. Among the series of catalysts, the as-prepared Co–Cu–Mn (1:1:1)/ZSM-5/PSSF catalysts have exhibited the best catalytic activity, demonstrating by a lowest T90% at 210°C. The gradient porous modified ZSM-5 membrane as high efficiency catalyst can offer a much higher catalytic activity, excellent reaction stability, and higher contact efficiency.

Catalytic activity and stability of porous Co–Cu–Mn mixed oxide modified microfibrous-structured ZSM-5 membrane/PSSF catalyst for VOCs oxidation

Porous microfibrous-structured ZSM-5 membrane catalyst possesses excellent catalytic activity and stability.

Catalytic Combustion of Volatile Organic Compounds over a Structured Zeolite Membrane Reactor

A novel structured zeolite membrane reactor based on a Cu–Mn (1:6)/ZSM-5/PSSF catalyst was developed for catalytic combustion of volatile organic compounds (VOCs). First, the ZSM-5 membrane/PSSF (paper-like sintered stainless steel fibers) composite was fabricated by the wet layup papermaking/sintering process and secondary growth process. The copper/manganese binary oxides modified ZSM-5 membrane catalyst was synthesized by an incipient wetness impregnation method. Catalytic combustion of VOCs in single and binary components was investigated over these structured zeolite membrane reactors using different gas hourly space velocity (GHSV) (3822–11466 h–1). Results showed that the complete destruction of isopropyl alcohol or ethyl acetate in a single component can be achieved below the temperature of 300 °C. The study exhibited that the presence of toluene in the binary mixture had a slight effect on the conversion of isopropyl alcohol or ethyl acetate. Isopropyl alcohol and ethyl acetate were found to be more reactive than toluene in the binary mixture. A higher temperature above 300 °C was needed to totally destroy toluene in the binary mixture. The structured zeolite membrane reactor exhibited a relatively lower bed pressure drop, excellent reaction stability, reasonable mass/heat transfer efficiency, and excellent contacting efficiency as well as relatively lower diffusion resistance.

Adsorption of CO2, CH4, and H2O in Zeolite ZSM-5 Studied Using In Situ ATR-FTIR Spectroscopy

Biogas and natural gas are interesting fuels with high H/C ratio. However, these gases frequently contain carbon dioxide and water which lowers the heat value of the gas and may induce corrosion. Therefore, the development of more efficient processes, such as membrane processes and improved adsorbents, for the separation of carbon dioxide and water from biogas and natural gas is of great importance. Zeolite ZSM-5 membranes are promising for this separation which is controlled by the adsorption and diffusion of the different species in the zeolite. Multicomponent adsorption data are therefore required for development of new membrane and adsorption processes. In the present work, the adsorption of water, carbon dioxide, and methane in a Na-ZSM-5 zeolite film at various temperatures was studied by in situ Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy for the first time. Adsorption isotherms were retrieved from the experimental data and the Langmuir model fitted the isotherms very well. Limiting heat of adsorption was determined from the Henrýs law regime and the values determined agreed well with previously reported data. A few experiments were conducted with multicomponent mixtures and the experimentally determined amounts adsorbed were compared with values predicted by the Ideal Adsorbed Solution Theory (IAST). It was found that for the binary mixture of carbon dioxide and methane there was good agreement between the experimental values and those predicted by the IAST. However, when water was also introduced, the IAST could not fully capture the adsorption behavior of the multicomponent mixture, probably because the adsorbed phase is not ideal. These findings are in line with previous reports for adsorption in zeolites. The multicomponent adsorption behavior of this system will be further investigated in forthcoming work.

Dehydration of acetic acid and esterification product by acid-stable ZSM-5 membrane

ZSM-5 membranes were prepared on mullite supports by a static secondary hydrothermal synthesis without applying organic structure directing agents. The ZSM-5 membrane had Si/Al ratio of 13.1 and selectively permeated water from the binary acetic acid/water mixtures and the quaternary acetic acid/ethanol/water/ethyl acetate (HAc/EtOH/H2O/AcOOEt) mixtures by pervaporation. The deviation of the dehydration performance of the membranes prepared in different batch was small, suggesting the high reproducibility of the synthesis. Part of the Na+ in the ZSM-5 membrane was replaced to H+ during the dehydration of acetic acid solution. Cation type was changed back to Na+ by immersing the membranes in 0.1M sodium hydroxide (NaOH) or sodium chloride (NaCl) solutions. The perm-selectivity of the membranes was maintained even after applying pure HAc liquid for 77h and applying esterification product of ethanol and acetic acid for 98days. No change in the membrane structure was observed before and after the dehydration of acidic solutions by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis characterizations. These results confirm the high acidic stability of the membrane.

Eco-friendly fabrication of hydrophilic ZSM-5 membranes for alcohol upgrading

The synthesis of continuous and low-siliceous ZSM-5 membranes was achieved without organic templates under mild conditions (a low temperature of 100 °C and ambient pressure). The resultant high-quality membranes with good water perm-selectivity were further applied in water-alcohol separation, exhibiting an extraordinarily high separation factor of above 10,000 and an improved water flux (3.43-6.88 kg m(-2) h(-1)) for ethanol and isopropanol aqueous azeotropes.