Applications Of Zeolite Membranes Research Articles

A novel preparation of high permeation SiC supports for NaA zeolite membrane by in situ reaction bonding

The performance of zeolite membrane supports directly determines the synthesis performance and industrial application of zeolite membranes. In this study, a novel and high permeation SiC supports for NaA zeolite membrane were prepared by carrying out in situ reaction bonding at high temperature in the air atmosphere to coat the SiC particles with aluminum sol. The effects of process parameters on the formation of porous structure of SiC supports were systematically investigated, and the underlying mechanism was explored. During the sintering process, high-temperature Al2O3 from aluminum sol reacted with SiO2 generated by oxidation of the surface of SiC particles to form mullite, which exhibited excellent chemical stability and improved the mechanical properties and chemical stability of the supports. The porous SiC supports for zeolite membrane displayed obvious three-dimensional connected pore structure, with smooth inner surface of the pores and obvious connection neck between the particles. The porous SiC supports for zeolite membrane showed good in situ mullite bonding between the particles, and high permeability. It has a porosity of 36.3%, an average pore size of 1.42 µm and a bending strength of 32.4 MPa. All these figures indicate good comprehensive properties that are consistent with the rigorous requirements of zeolite membrane synthesis and industrial application.

Application of Zeolite Membranes to Dehydrate a Bio-Ethanol Solution Produced by High-Temperature Fermentation

The combination of high-temperature fermentation and membrane separation has the potential to realize a simple on-site process to produce concentrated bioethanol. The performance of dehydration membranes in separating bioethanol was investigated in this study. Three types of zeolite membranes, LTA, MFI, and MOR, were synthesized. Their dehydration ability was compared using a bioethanol solution produced by high-temperature fermentation followed by vacuum distillation. The LTA zeolite membranes deformed and became amorphous while treating the distillate. On the contrary, no significant changes were observed in the MFI and MOR zeolite membranes analyzed by X-ray diffraction after treating the distillate. However, the flux declined when the membranes were in contact with the distillate (pH = 3.8). Neutralizing the distillate to pH 6.6 with sodium hydroxide did not prevent the flux decline. Even though flux decreased by about 20–30%, the MOR membrane showed quite high water-selectivity, with a water concentration of over 99.9% in the permeate, suggesting the feasibility of its application to concentrate bioethanol.

Mass transfer model, preparation and applications of zeolite membranes for pervaporation dehydration: A review

Pervaporation (including vapor permeation) is a kind of new membrane separation technology, possessing the advantages of high efficiency, energy saving and convenient operation. It has promising application in the separation and purification of organic solvents. Dehydration is an important step in the production and recovery of organic solvents. Zeolite membranes have attracted wide attention for pervaporation dehydration due to their high separation performance and good thermal/chemical stability. So far, zeolite membranes have been preliminarily industrialized for dehydration of organic solvents. This paper reviews the recent development of zeolite membranes for pervaporation dehydration, including mass transfer models, preparation and applications of zeolite membranes. The review also discusses the current industrial applications of zeolite membranes and their future development in pervaporation.

Ionothermal Synthesis of Aluminophosphate Molecular Sieve Membranes through Substrate Surface Conversion

Applications of zeolite membranes in separation, chemical sensors, and catalytic membrane reactors have led to extensive studies on their fabrication. To date, mainly silicatebased zeolite membranes of the structure types MFI, DDR, LTA, and FAU have been synthesized on different substrates and evaluated for singleor multiple-gas permeation. Routes for the synthesis of zeolite membranes can be broadly classified into two categories: in situ and secondary growth synthesis, both of which are derived from the strategy of hydrothermal zeolite synthesis. However, the high autogenous pressure associated with hydrothermal procedures is inconvenient for preparation of zeolite membranes, especially for large-scale production, due to safety concerns and the risk of molecular sieve collapse. On the other hand, although aluminophosphate and silicoaluminophosphate membranes for gas separation have been prepared, there are few reports on the preparation of aluminophosphate molecular sieve membranes, which suggests that hydrothermal preparation of such membranes may be difficult. Ionothermal synthesis, which uses ionic liquids as reaction media instead of water or organic solvents, allowed highly efficient preparation of aluminophosphate molecular sieves under ambient pressure. Ionic liquids (ILs) are commonly defined as salts that consist of organic cations and inorganic anions with melting temperatures below 100 8C. ILs are well known as environmentally benign and designable solvents, which endow ionothermal synthesis with interesting features and many potential advantages over the hydrothermal method. As a result of the negligible vapor pressure of ILs, ionothermal synthesis can take place at ambient pressure, which eliminates safety concerns. The organic cation of the IL can act as a structure-directing agent (SDA), or play a cooperative structure-directing role together with introduced amines and quaternary ammonium compounds. AEL, AFI, CHA, LTA, and CLO types of aluminophosphate molecular sieves have been successfully synthesized by ionothermal methods. Ionothermal synthesis is a promising method for the preparation of aluminophosphate molecular sieve membranes under ambient pressure. Yan and co-workers prepared AlPO-11 and SAPO-11 films on aluminum alloys as anticorrosion coatings by in situ ionothermal synthesis. To the best of our knowledge, no permeable membrane has been previously prepared on a porous substrate by the ionothermal method. Here we report an ionothermal method for the synthesis of permeable aluminophosphate molecular sieve membranes on porous alumina disks by substrate-surface conversion. Molecular sieve membranes of types AEL, AFI, CHA, and LTA were prepared by placing homemade d-alumina substrates (2.0 mm thickness, 20 mm diameter, and 10 nm average pore size; see Supporting Information for details) in a solution of IL, phosphoric acid, hydrofluoric acid, and, if required, organic amines with no additional source of Al. Table 1 lists the initial solution composition, crystallization

Characterization of the formation of NaA zeolite membrane under microwave radiation

Zeolite membranes have gained much attention in recent years, due to their potential application in various fields such as catalysis, gas separation, pervaporation, etc. [1–4]. There are many reports on the synthesis, characterization and applications of zeolite membranes [1–4], but literatures about the formation mechanism of zeolite membrane are fewer [5–7]. To prepare zeolite membranes, many methods have been developed, including hydrothermal crystallization [8], vapor phase synthesis [9], and microwave heating [10, 11]. It was reported that microwave heating and crystal seeding could help the formation and improve the performance of zeolite membranes [10]. It was proposed that the formation of zeolite membranes included the following three stages: sol or gel adhesion on the substrate to form the gel layer, the nucleation and crystallization stage, and the dissolving stage [10, 12, 13]. However, there are few reports on the direct observation of these stages, especially under microwave radiation. In this report, by using scanning electron microscopy (SEM), the formation stages of zeolite NaA membrane in microwave radiation environment were observed and confirmed with the results from X-ray diffraction (XRD) and gas permeation measurements. The disk shaped substrates (30 mm in diameter, 3 mm in thickness) used were porous α-Al2O3 made by casting, with pore radius of 0.3–0.5 μm and ca. 50% porosity. The precursor of the gel was prepared by mixing sodium hydroxide, sodium aluminate, water glass and water, and aging for 24 h with vigorous stirring. The final molar composition of the gel was 3Na2O: Al2O3: 2SiO2: 200H2O. After one face of the substrates was rubbed with zeolite NaA crystals as seeds, the substrates were put vertically in Teflon vessels containing 120 ml gel. Then the vessels were transferred into a microwave oven, heated up to 90 ◦C within 1 min, and reacted for a range of specified times. After the reaction, the membranes were vigorously ultrasonically vibrated in water for 10 min to remove the species physically absorbed on the substrates, washed by de-ionized water to pH = 7.0 and dried at 150 ◦C for 3 h. The membranes were characterized by scanning electron microscopy (SEM) on a JEM-1200E scanning electron microscope and Xray diffraction (XRD) using Cu Kα (λ = 0.154 nm) radiation operating at 40 kV and 100 mA on a Rigaku D max /b powder diffractometer. The integrity of the membrane was evaluated with gas permeation tests.