In 1972 a kind of high-silica zeolite was found and reported by Argauer and Landolt from Mobil Oil Corporation which was called ZSM-5. This zeolite has received much attention due to its particular structure and physical-chemical performance, shape selectivity, stability and the flexibility, so it has been used in a variety of processes, such as dehydration of methanol, conversions of methanol to olefins (MTO) and gasoline (MTG), and FCC process[12–17]. Since 1972, extensiveresearch has been carried out particularly to find catalysts having higher selectivity for the ether formation and less tendency to coke formation to prevent catalyst deactivation and ultimately stop dehydration process. Accordingly, many researchers have tried to find a modified catalyst structure and/or formulation in order to optimize the DME production as well as improve the catalyst stability [18–22].
ported on NaY. A result was explained on the basis that the incorporation of HPA in ZSM-5 and mordenite leads to 20% reduction of their surface area whereas; the surface area reduction was around 50% in case of NaY zeolite. This refers to that HPA is mostly located on the external surface and not in the pores of ZSM-5 and mordenite zeolites. While the Anderson types were mostly incor- porated in the pores of NaY zeolite. The degradation efficiency of DB1 dye on the samples was 43% and 28% after one min. of reaction time then reached to
In the same line, the separation of normal pentane from a light gasoline isomerate through a MFI zeolite composite membrane was investigated by Baudot et al. . They discovered that increasing the total hydrocarbon pressure at the upstream side of the membrane led apparently to an increased sorption of the slowest compounds (branched paraffins), which in turn slowed down the diffusion of the fastest species (linear paraffins) across the selective zeolite layer. They observed Maximal permeate flux, close to 2 kg/m2.h at 250°C - 2 bar total hydrocarbon pressure. In 2013, Bayati et al.  synthesized a B-ZSM-5zeolite membrane layer supported on a porous tubular alumina support for the separation of n-C 5 from the mixture of n-C 5 and 2-MB. They
structure during the synthesis. As the crystals continue to grow with time, the pressure inside the crystallization kettle increases; and thereby, the density of the crystal skeleton is increased. Moreover, pH value affects the polymerization degree of silicate ions; therefore, adjusting the pH to an appropriate value will increase the thermal and hydrothermal stabilities of the zeolite catalyst . Consequently, for determining the potential of ZSM-5 in the reaction of alkanes, it is necessary that its preparation conditions be optimized. In this study, the effects of the crystallization temperature, crystallization time, and pH value on the textural properties of synthetic ZSM-5 were investigated by the orthogonal test method. As there are many C6 components in hydrocarbons obtained from heavy oil cracking, the effects of the ZSM-5 catalysts synthesized under different preparation conditions on the conversion of n-hexane during catalytic cracking have been investigated. Moreover, the selectivity and yield of ethylene and propylene were evaluated using a small fixed bed reactor. Thus, the suitability of various textural properties of ZSM-5 for catalytic cracking reactions was characterized, and the optimal conditions for the synthesis of ZSM-5 for the n-hexane cracking reaction were determined. Finally, in this study, it is expected that these findings will provide basic data for the selection and preparation of catalysts for deep cracking of alkanes to produce low-carbon olefins.
Preparation of ZeoliteZSM-5: The synthetic compounds with a composition ratio of 2O:60SiO2:0.5Al2O3:936H2O TPA (12-O- tetradecanoylphorbol-13-acetate) was prepared by adding aluminum sulfate and silica to ammonium hydroxide solution 20% w/w in boiling water. After 10 minutes of stirring under reflux condition, a clear homogeneous solution was obtained. Then, the solution temperature was lowered to 25 °C. This transparent solution was poured into flasks that were placed in an oil bath containing reflux. Crystallization occurred at ambient pressure and at a temperature of 80 ºC for 72 hours. The obtained zeolite nanoparticles were separated from the solution via centrifugation at 5000 rpm. They were poured into distilled water and separated again using ultrasonic bath in order to obtain the concentrated colloidal suspension. To classify the sizes of ZSM-5 standard sieves with a mesh of 20 and 40 (ASTM, PA, USA) were, respectively, used to separate particle sizes of 0.85 and 0.425 mm. ZSM-5 with 20-40 mesh included particles that passed through the 20-mesh sieve, but remain on the 40-mesh sieve. Scanning electron microscopy (SEM), X-ray powder
by Polshettiwar, et al. (2010), the addition amount of urea affects the morphology of dendrimeric silica fiber. However, excess addition of urea could increase the particle size of the catalyst due to the rapid hydrolysis of silica precursor. Zeolite crystal-seed crystallization was used instead of direct zeolite crystallization. This was to avoid interaction competition between microemulsion and zeolite structure directing agent and the aluminosilicate species (Li, et al., 2011). The presence of other electrolyte from zeolite precursor, such as Na + , could change the critical micelle concentration of CTAB, which will result in different formation of supramolecular structure. Thus, zeolite crystal-seed crystallization was best suited to be used in synthesis method to avoid the competition and minimizing the changes in CTAB critical micelle concentration. The preparation also involved protonation, in which both Si@ZSM-5 as well as commercial ZSM-5 catalysts were converted into ammonium form by ion- exchange and followed by calcination to convert the NH 4 + species into H + . The first
This is a comprehensive review of the recent progresses made in the field of zeolitemembranes. It describes zeolitic materials and methods of membrane fabrication, followed by a summary of applications for gas separation, pervaporation and separation of liquid mixtures. Special attention is called to polymer mixed matrix membranes (MMMs) and membranes based on metal organic frame works (MOFs). In this comprehensive survey, the following trends were observed during the past 5 – 10 years. New zeolitic materials and new synthesis methods, such as hydrothermal synthesis, seeding and microwave heating, have been continuously reported in the literature. Many efforts have been devoted to the synthesis of hybrid or mixed matrix membranes (MMMs) since MMMs clearly outperformed polymeric membranes. MOFs also showed improved performance in gas separation. Many attempts have been made to develop thin (1µm) supported zeolite layers on a variety of carriers such as capillaries, fibers, tubes, etc. The assembly of nanozeolite building blocks and nanosheets is the starting point for the synthesis of thin defect free zeolitemembranes. The present review presents the recent progresses made in the field of zeolite/zeotype membranes. Different types of zeolitemembranes, methods of preparation and application aspects especially for separation of gases have been focused on, including the individual zeolites which are in use or are to be used as inorganic fillers in mixed matrix membranes (MMMs). Despite the enormous efforts of researchers, the commercialization of zeolitemembranes has been achieved only in a limited area. The future works necessary to change the current situation are hence suggested.
Ion infiltration into zeolite powders was carried out by mixing 1 g high silica MFI- type zeolite powder with 5 mL ion solution in a 50 mL centrifuge tube, and shaking in a water bath at room temperature (21 °C) for 48 h. Ion behaviour due to the zeolite was also assessed by exposing them only to DI water. After powder infiltration experiments, the mixture was centrifuged (4000 RPM, 10 min) and supernatant decanted from the powder immediately to avoid any further interactions. The supernatant was analysed for cations (including S) by ICP-OES (Shimadzu ICPE-9000). The ion infiltrated zeolite powders were washed with DI water three times to remove any free solution and oven dried at 80 ºC overnight for further characterisation. The adsorbed amount of cations was estimated from ion concentrations measured by ICP-OES and presented as the amount of ion i adsorbed per gram zeolite, C z,i , (mmol g -1 ) according to:
This study showed that ZSM-5 was able to rapidly adsorb the common groundwater contaminant TCE from the aqueous phase even from dilute solutions. Adsorption from dilute solutions followed linear and Freundlich isotherm models. Desorption of TCE from ZSM-5 occurred, however the linear isotherm still models the sorption of TCE from the aqueous phase well. As the adsorption and desorption isotherms were so close, it can be concluded that hysteresis was not observed to a great extent, and the adsorption process was essentially reversible. This suggests a physical adsorption process occurred between TCE and ZSM-5.
The objective of this work is to develop a new class of nanocomposite ultrafiltration (UF) membranes with excellent solute rejection rate and superior water flux using zeolitic imidazolate framework-8 (ZIF- 8) and multi-walled carbon nanotubes (MWCNTs). The effect of ZIF-8 and MWCNTs loadings on the properties of polyvinyldifluoride (PVDF)-based membrane were investigated by introducing respective nanomaterial into the polymer dope solution. Prior to filtration tests, all the membranes were characterized using several important analytical instruments, i.e., SEM-EDX and contact angle analyzer. The addition of the nanoparticles into the membrane matrix has found to increase the membrane pore size and improve its hydrophilicity compared to the pristine membrane. The separation performance of membranes was determined with respect to pure water flux and rejections against bovine serum albumin (BSA) and humic acid (HA).The experimental findings indicated that the nanocomposite membranes in general demonstrated higher permeation flux and solute rejection compared to the pristine membrane and the use of ZIF-8 was reported to be better than that of MWCNTs in preparing nanocomposite UF membranes owing to its better flux and high percentage of solute rejection.
This method was used as early as 1918 by Zsig- mondy. A cast R lm, consisting of a polymer and a solvent, is placed in a vapour atmosphere where the vapour phase consists of a nonsolvent saturated with the solvent. The high solvent concentration in the vapour phase prevents the evaporation of solvent from the cast R lm. Membrane formation occurs because of the penetration (diffusion) of nonsolvent into the cast R lm. This results in a porous membrane without a top layer. With immersion pre- cipitation an evaporation step in air is sometimes introduced and, if the solvent is miscible with water, precipitation from the vapour will start at this stage. An evaporation stage is often introduced in the case of hollow R bre preparation by immersion precipita- tion (‘wet } dry spinning’) exchange between the sol- vent and nonsolvent from the vapour phase, leading to precipitation.
Semipermeable membranes allow us to manipulate processes that take place at the interface between two (miscible or nonmiscible) phases. They can be used in the gas phase for sampling purposes (e.g. membrane- assisted headspace injection in GC, membrane inlet mass spectrometry, MIMS) or in the liquid phase for sample preparation (e.g. dialysis) or sample concen- tration. Membranes used for gas sampling usually consist of simple R bres made of polymeric materials, such as polysiloxanes. More sophisticated separ- ations, such as af R nity chromatography, require more sophisticated membranes with dedicated selec- tivities. Also when in contact with liquid phases, most of the R bres used in analytical chemistry are based on organic (polymeric) materials.
In the discussions of IFC membranes that follow, technical milestones are highlighted with emphasis on commercially signi R cant developments. The early period of membrane development shown in Table 2 began in 1967 with the investigation of various aque- ous diamine and hexane } diacyl chloride interfacial solutions upon polysulfone porous supports by Rozelle et al. at North Star Research Institute. These R rst IFC membranes had low salt rejections, probably due to lack of R lm integrity since the resultant poly- mers were not cross-linked. This pioneering work, however, is signi R cant in that the essential elements for the preparation of IFC membranes were demon- strated. Shortly thereafter, in 1970, the R rst high salt-rejecting IFC membrane, NS-100, was also de- veloped at North Star Research. This membrane was made from polyethylenimine (PEI) in the aqueous solution and toluene diisocyanate (TDI) in the hexane solution. The coated and drained polysulfone support was subsequently dried at 110 3 C to yield a dry composite membrane with greater than 99% salt rejection on a synthetic seawater feed at 1000 psig (6.9 MPa). A later related membrane, des- ignated NS-101, substituted isophthaloyl chloride (IPC) for TDI as the cross-linker and provided similar results. The selective layers in these membranes con- sisted of cross-linked polyurea and polyamide R lms, respectively. The membranes demonstrated high perm- selectivity but were mechanically delicate and highly vulnerable to attack by chlorine disinfectant.
Reverse osmosis (RO) is currently the most important desalination technology, experiencing significant growth. It is a separation process that uses hydrostatic pressure to drive a solution (usually a saline brine) passes through a membrane. In better words, RO membrane retains the solute on one side and allows the solvent to pass to the other side. RO is an efficient desalination technology for providing safe drinking water from saline resources, including brackish and sea water. The membranes used for RO have a thin dense barrier layer at the top of the membrane, where most separation occurs (i.e. selective layer). In most cases, the membrane is designed to allow only water to pass through this dense layer, while preventing the passage of solutes (such as salt ions). In RO, chemical potential difference of the solvent is the driving force for the solvent flow through the membrane, which is achieved by applying hydrostatic pressure on the feed to overcome the osmotic pressure difference between the feed and permeate. Recently, many review papers on RO have appeared demonstrating historical background, development and etc. In the proposed review papers, nano-structured membranes are often discussed, including zeolitemembranes, thin film nano-composite membranes, carbon nano-tube membranes, and biomimetic membranes [1-4]. It is proposed that these novel materials represent the most likely opportunities for enhanced RO performance in the future, but a number of challenges remain with regard to their practical implementation.
Cross-linked composite membranes of sulfonated poly(ether ether ketone) (SPEEK) with a chitosan content up to 50 wt%, were prepared by solution cast technique and ultraviolet (UV) curing. A mixture of sulfonated poly(ether ether ketone)-chitosan (SPEEK-CS) membranes was prepared by dissolving SPEEK in dimethyl sulfoxide (DMSO) and chitosan (CS) in acetic acid. The homogen formed was later irradiated with an UV source to induce crosslinking. The membranes were then characterized by evaluating infrared spectra, proton conductivity, water uptake, degree of swelling and ion exchange capacity (IEC). The Fourier transform infrared (FTIR) study revealed considerable interaction between the sulfonic acid functions of SPEEK and amino groups of chitosan. Proton conductivity decreases with increasing of chitosan content from 8.51 x 10 -3 to 2.85 x 10 -7 S cm -1 . Meanwhile, water uptake decreases with increasing of chitosan content from 52% to 29% and IEC 0.188 to 0.018 mequi. However, the swelling properties unchanged as the chitosan content increases.
The purple membranes (PM) of the Halobacterium salinarum cells and bacteriorhodopsin (major retinal-containing trans-membrane protein of these bacteria are the most promising photosensitive biopolymers in terms of bionanotechnology, developing photosensitive devices, etc. The article is devoted to the improvement of the cultivation system for Halobacterium salinarum cells and the PM production; the study of the properties and functional characterization of bacteriorhodopsin - the biological components of the bionanomaterials. The optimal conditions for the production of the biomass are the following: the volume of incubation media must be 10% of the working volume (the volume of the cuvette); the cell “age” must be close to the end of the exponential phase of growth; the lighting must be maximum (4 light bulbs LD-20); the temperature must be 37°Ñ; the time must be 8 days; the aeration must be 0.45 (L air)/(L of environment)/min. The yield of the product is about 5 g of biomass containing 45 mg of bacteriorhodopsin. The purple membranes and their major protein - bacteriorhodopsin were obtained with the required parameters.
Results of previous studies have shown that H-ZSM-5zeolite was an active catalyst for this reaction [9-12], however, this catalyst without any treatment demonstrated low stability. It is known that impregnation of some of 1A, 2A, 3A and B groups of metals of the periodic table of elements onto zeolites modify the zeolites acidic property. Furthermore, elements like Zn, Zr, Al, Na and Mg previously displayed good results presented in other studies [4, 5, and 7]. These reasons made them a legitimate choice to be utilized in this research where attempts were made to improve the properties of H-ZSM-5 for production of DME from methanol. In this direction, the effects of some additives such as Zn, Zr, Al, Na and Mg on properties of H-ZSM-5 were investigated. This ultimately led to an optimum catalyst for the aforementioned production.
The synthesized catalysts were evaluated in benzylation of acetic acid with benzyl alcohol, which was carried out in a three-necked glass round bottom flask of 250 mL capacity equipped with a reflux condenser to prevent the escape of acetic acid, a thermometer and a magnetic stirrer. The flask was charged with acetic acid and benzyl alcohol both weighted sequentially, followed by the addition of the catalyst. Then, the system was heated up to desire temperature (383 K), the reaction was carried out for 3 h, and finally the product was collected after removing the catalyst. For deter- mination of free fatty acids conversion, 1 g sample was mixed with 5 mL of 96 % ethanol and 5 mL n-hexane. Then the 3 drops of phenolphthalein indicator was added and titrated with 0.1 N KOH solution. Previously, the KOH has been standardized with oxalic acid 0.1 N. The titration was stopped when the color of the solution changes to pink which can last up to 30 seconds.
acid in water with pH = 0.5; then, pH of the mixture adjusted at about 9 using concentrated sulfuric acid. Then TPABr was added; and the obtained gel was maintained at room temperature for about 4 h under vigorous stir- ring. The resulting gel was transferred into Teflon-lined stainless-steel autoclave. Na[Cr]ZSM-5 or K[Cr]ZSM-5 or Cs[Cr]ZSM-5 was obtained after about 100 h of hydrothermal treatment of the mixtures at 155˚C. After crys- tallization, the as-synthesized solids were washed several times with distilled water and dried overnight in an oven at 120˚C. Calcination of the samples was made under air for 5 h at 550˚C. At this point, the obtained prod- uct (MCS) was washed with distilled water in order to remove chromium species. Thus, KCS samples before and after washing, were labeled as KCS BW and KCS AW , respectively. By the same way, NCS samples before and