Clay Support Research Articles

Synthesis of sodalite octahydrate zeolite-clay composite membrane and its use in separation of SDS

A simple two-step process for synthesis of sodalite octahydrate zeolite-clay composite, charged ultrafiltration membrane is described wherein the active layer is obtained by partial plugging of the pore-mouth of macroporous clay support with in situ grown zeolite particles. Dip-coating of zeolite synthesis solution at pH 12 is found to give higher deposition of zeolite on the clay support. Increase in amount of zeolite in the active layer obtained by repeated deposition of zeolite particles on clay-support is quantified using membrane potential measurements and it is found that four cycles of zeolite deposition gives optimum results. The membrane is characterized using SEM for surface morphology, XRD for zeolite characterization, water flux and separation of surfactant (SDS) above cmc concentration. SDS separation results show observed-rejection in the range of 10–45%. The observed-rejection is found to decrease with increase in the applied pressure difference and increase with increase in the surfactant concentration. The permeate flux is found to reduce significantly to about 0.2–0.46 times the pure water flux. The trend is similar to that reported in literature for separation of surfactant micelle by ultrafiltration membrane of pore size much larger than the size of surfactant micelle.

Solid‐State Regioselective Cyclization Initiated by the Electrophilic Attack on the Double Bond by N‐Bromosuccinimide on Montmorillonite K‐10 Clay Support under Microwave Irradiation.

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Investigation of performance of a low ZnAl 2O 4–TiO 2 ultrafiltration membrane in relation with speciation and membrane solutes interactions

The low ultrafiltration (UF) membranes performances depend mainly on the nature of the interactions between the solutes and the membrane material. This paper reports the filtration tests of different salts: CH 3COONa, Na 2HPO 4 and NaF by means of a TiO 2–ZnAl 2O 4 membrane prepared by sol–gel route deposed on a moroccan clay support. The measured rejections depend at once on the pH, on ionic strength of the solution; their interpretation needs to precise the exact speciation of the filtered species.

Solid‐State Regioselective Cyclization Initiated by the Electrophilic Attack on the Double Bond by N‐Bromosuccinimide on Montmorillonite K‐10 Clay Support under Microwave Irradiation

3‐Allyl‐4‐hydroxy‐coumarins and pyrones were regioselectively cyclized with N‐bromosuccinimide (NBS) on solid phase under microwave irradiation in excellent yield. NBS on montmorillonite K‐10 clay under microwave irradiation for expeditious solvent‐free regioselective cyclization has been used for the first time.

Al-pillared clay supported CuPd catalysts for nitrate reduction

PdCu catalysts on clay and Al-pillared clay supports were prepared by wet impregnation procedure and characterized by powder x-ray diffraction (PXRD), Scanning Electron Microscope Dispersive x-ray analysis (SEM-EDAX) and Transmission Electron Microscopy (TEM). The incorporation of [Al13O4(OH)24(H2O) 12]7+ clusters in the clay interlayers and subsequent formation of Al-pillared clays was confirmed from PXRD patterns. The EDAX analysis indicated good homogeneous mix of metallic components, in the form of monometallic or inhomogeneous bimetallic particles, on the clay and pillared clay surfaces. TEM pictures showed striking particle size differences upon Al2O3-pillaring. The metallic particles were much smaller in size on Al-pillared clay than those formed on parent clay. The clay supported PdCu catalysts were tested for nitrate ion reduction in aqueous phase under hydrogen atmosphere. Preliminary results show that the catalysts with Pd and Cu components together exhibit superior performance in activity and selectivity to nitrogen compared to their monometallic particles supported on both clay samples. This study indicates the possibility of using PdCu catalysts supported on pillared clays as environmental friendly and efficient catalysts for nitrate reduction reactions.

HDS and deep HDS activity of CoMoS-mesostructured clay catalysts

The goal of this work is to identify more promising supports from synthetic clay materials to advance hydrotreating catalyst development. Silica sol can be used as the silicon-containing starting material when creating nanoporous layered silicate catalysts with a certain portion of unreacted sol particles incorporated into the final matrix. The resulting structure then has mesoporosity and a unique morphology. Hectorite-based clays have been prepared using different silica sols in order to ascertain the importance of sol characteristics on the final matrix. Several techniques have been applied to characterize the materials, including XRD, TGA, N 2 porosimetry, and TEM. For hydrodesulfurization (HDS), the conversion of dibenzothiophene (DBT) to biphenyl was examined at 400 °C using CoMoS-loaded mesostructured clay supports. No hydrogenation or hydrocracking was observed with any of the clay supports. The most active clay was derived from Ludox silica sol AS-30 with an activity of 65% DBT conversion and 100% selectivity to biphenyl (BP). For comparison, a reference commercial catalyst displayed 94% BP selectivity. For deep HDS, the conversion of 4,6-dimethyldibenzothiophene was tested at 325 and 350 °C. At 325 °C, conversions are 92% of commercial catalysts for a CoMoS-loaded mesostructured clay derived from Ludox AM-30 silica sol. A commercially available synthetic hectorite called laponite has very low activity, indicating that the unique morphology of the mesostructured clays is important. Hydrogenolysis vs. hydrogenation pathways are compared for the deep HDS reaction. HR-TEM of the most active deep HDS catalyst revealed a multilayered MoS 2 morphology.

A new application of clay-supported vanadium oxide catalyst to selective hydroxylation of benzene to phenol

The highly selective direct hydroxylation of benzene with hydrogen peroxide to phenol was observed on a clay-supported vanadium oxide catalyst. Under mild reaction conditions at 313 K, high selectivity to phenol of 94% was realized on the clay-supported vanadium oxide catalyst at 14% conversion of benzene, comparable with the well-known TS-1 catalyst. On the other hand, vanadium on other supports and other metals on the clay support gave inferior catalytic performances. V–O–Al and V–O–Si bridges in the catalyst may be responsible for the reaction.

Effect of the Platinum Content on the Microstructure and Micropore Size Distribution of Pt/Alumina-Pillared Clays

The aim of this work is to study the effect of the platinum content (0-1.8 wt % Pt) on the microstructure of an alumina-pillared clay. For this purpose, the nitrogen physisorption data at -196 degrees C, the micropore size distributions of the supported platinum catalysts, and the hydrogen chemisorption results at 30 degrees C have been analyzed and compared. The preparation of the catalysts has modified the textural properties of the Al-pillared clay support, giving rise to a loss of surface area and micropore volume. After reduction at 420 degrees C, the presence of dispersed metallic platinum with mean crystallite size in the 22-55 A range has been found by hydrogen adsorption. Comparison of all results reveals that the platinum species block the micropore entrances by steric hindrance to nitrogen access as the platinum content increases.

Preparation and characterization of iron salt embedded electrodialysis Analcime-C zeolite clay composite membrane

Metal salt embedded electrodialysis zeolite clay composite membrane has been prepared by in situ hydrothermal crystallization of Analcime-C zeolite over the mesoporous clay support followed by deposition of a suitable salt (FeCl 2) inside the pores. To characterize the membrane, it has been used for the electrodialysis of sodium chloride solution in the low current regimen and the results reported in terms of current efficiency and energy requirements. When the membrane is fresh after metal loading, its current efficiency is low (42.8%) which gradually rises and takes a value of 93% asymptotically at room temperature. Once this value is reached, the effect of the current density, flow rate, salt and alkali concentration and temperature on the performance of membrane are measured and reported in this work. The current efficiency of our membrane is found to decrease slightly for higher current densities, increase at higher temperatures and is little affected by flow rate and salt and alkali concentrations. This membrane gives a current efficiency of 93% at room temperature (25 °C, 0.1117 kWh/mol NaOH, 275 A m −2 and 4.2N NaCl solution) which increases with increase in temperature. Impurities, like calcium and magnesium salts, in the feed have small effect on the performance of the membrane and on washing it with dilute HCl, it is restored to the original level. The membrane has been studied over 1 year and its efficiency is not affected with time.

Chromium (VI) separation from aqueous solution using anion exchange membrane

AbstractThe preparation is reported of a chemically modified crosslinked poly(methyl methacrylate–ethylene glycol dimethacrylate) (PMMA–EGDM) copolymer anion exchange ultrafiltration membrane on a macroporous clay support. This is obtained by nitrating a PMMA–EGDM membrane using NOx (a mixture of NO and NO2), which is further reduced to an amine group using hydrazine hydrate to form an anion‐exchange membrane (AEM). The membrane thus formed is characterized for its properties such as ion‐exchange capacity, membrane swelling, contact angle measurements, and membrane morphologies. The results show that the membrane becomes highly hydrophilic on the introduction of a charge and the separation experiments on the chromium (VI) salt solution show that the permeate flux (keeping the same rejection level of 90%) is considerably increased (by 100‐fold). The analysis of separation of Cr(VI) from its aqueous solution has been done by solving a two‐dimensional (in cylindrical coordinates) space‐charge model (SCM). A series solution of the nonlinear Poisson–Boltzmann equation has been generated, which leads to a considerable reduction in the computational time (from 15 h of batch time using the method reported earlier to 15 min for our method). The effective pore radius and wall potential of the unmodified and AEMs are evaluated by fitting the experimental data of the separation. The permeate flux calculated from this model matches well with the experimental values and a correlation is developed between the separation characteristic (rejection) and the wall charge developed by the chemical modification of the membrane. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Oxidative Deprotection of Oximes, Phenylhydrazones and Semicarbazones Using Pyridinium Chlorochromate in Catalytic Amount with t‐Butyl Hydroperoxide and in the Solid State on Montmorillonite K‐10 Clay Support under Microwave Irradiation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Michael reaction of β-ketoesters with vinyl ketones by iron(III)-exchanged fluorotetrasilicic mica: catalytic and spectroscopic studies

Michael reaction of β-ketoesters with vinylketones at room temperature under solvent-free condition is investigated with various Fe 3+ catalysts, including FeCl 3 ⋅ 6H 2O supported on various supports (Fe–mica, Fe–mont, Fe–SiO 2, Fe–Al 2O 3, Fe–NaY) and homogeneous catalysts, FeCl 3 ⋅ 6H 2O and Fe(NO 3) 3 ⋅ 9H 2O. Fe 3+-exchanged fluorotetrasilicic mica (Fe–mica) shows highest activity. Fe–mica exhibits almost quantitative yields of Michael adducts, high turnover numbers (TON = 1000), and a low level of Fe leaching. After simple work-up procedures, Fe–mica can be recycled without a loss in activity. The relationship between catalytic activity and the catalyst structure determined by XRD, UV–vis, and Fe K-edge XANES/EXAFS is discussed in terms of the effect of clay support on the structure and reactivity of Fe 3+ species. The Fe 3+ cation, highly dispersed in the interlayer of clay (mica or mont) or on SiO 2, is more active than the cluster-like Fe 3+ oxide or hydroxide species in Fe–NaY and Fe–Al 2O 3. UV–vis and XAFS results for the catalysts treated with reactants suggest that, during the reaction, the FeCl 2(O) 4 octahedral species in FeCl 3 ⋅ 6H 2O or those on Fe–SiO 2 are converted to the β-diketonato complexes with two β-diketonato ligands, whereas in Fe–mica β-diketonato complexes with one β-diketonato ligand are formed. The formation of β-diketonato complexes results in a slight lowering of the Fe oxidation number from 3+, probably as a result of the electron donation from the β-diketonato ligand to Fe 3+ as a Lewis acid site. The lower numbers of β-diketonato ligand coordinated with Fe 3+ in Fe–mica should result in a larger coordination strength for β-diketonato ligand than that in Fe–SiO 2, which was confirmed by acetylacetone-TPD. Thus, the central carbon atom of the β-diketonato ligand in Fe–mica is more reactive toward nucleophilic attack by the coordinated enone, leading to higher activity for the Michael reaction.

Purification of water effluent from a milk factory by ultrafiltration using Algerian clay support

A milk factory sited at Boudouaou (40 km from Algiers) rejects a great quantity of effluent which contains soft whey. 8,000 1 are treated twice a week and are rejected into a river which supplies drinking water to the town population. Some analyses have shown an increase in the water acidity and both the BDO (biological demand of oxygen) and CDO (chemical demand of oxygen) attained 40,000 and 1,800 respectively. This is due to the presence of the lactose coupled with some organic matter. In this work, the purification of water is attempted by ultrafiltration using both gamma alumina and Ti0 2 membranes. Commercial mineral supports were used and their performance was compared to other supports elaborated from a natural Algerian clay (attapulgite). The results obtained have shown a good retention of lactose and total proteins giving rise to a pure water with a BDO of 90 and a DCO of 62. Moreover, the study of the influence of the pressure and the variation of the water flux has shown an improvement of the process through the use of the local clay support. Thus, this is appropriate for an economical and safe treatment of this water. Moreover, it combines a recovery of a valuable matter, which is the whey.

Ecofriendly Solid‐State Oxidative Deprotection of 1,3‐Dithianes and 1,3‐Dithiolanes Using Ammonium Persulfate on Wet Montmorillonite K‐10 Clay Support under Microwave Irradiation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Oxidative deprotection of oximes, phenylhydrazones and semicarbazones using pyridinium chlorochromate in catalytic amount with t-butyl hydroperoxide and in the solid state on montmorillonite K-10 clay support under microwave irradiation

Pyridinium chlorochromate (PCC) and other oxochromium(vt) reagents have been extensively employed in excess of the stoichiometric amount (2 equivalents or more) for efficient cleavage of oximes to carbonyl compounds. The aim of this study is to replace excess use of toxic chromium(VI) reagents and develop cleaner environment-friendly general methods of cleavage of imine derivatives such as oximes, phenylhydrazones and semicarbazones using PCC in catalytic or stoichiometric amount. Two approaches of greening the deprotection process with PCC are conceived of which the first one is based on the catalytic use of the reagent (0.1 equiv.) in combination with an excess of 70% t-butyl hydroperoxide as the cooxidant. Mild selective regeneration of carbonyl compounds from oximes, phenylhydrazones and semicarbazones has been accomplished in good-to-excellent yields (70-98%) by this method. With focus on rate enhancement coupled with efficiency of cleavage, an alternative microwave-assisted solid-state solventless protocol of deprotection employing a stoichiometric amount of PCC dispersed on montmorillonite K-10 clay is also evaluated. It offers an expeditious efficient (74-98% yields) general route of cleavage of these procarbonyl compounds. Absence of overoxidation, particularly for oxidation-prone aryl aldehydes, is the key advantage of both these methods.

Ecofriendly Solid-State Oxidative Deprotection of 1,3-Dithianes and 1,3-Dithiolanes Using Ammonium Persulfate on Wet Montmorillonite K-10 Clay Support under Microwave Irradiation

Solid-state microwave-assisted oxidative deprotection of 1,3-dithianes and 1,3-dithiolanes of aromatic aldehydes and ketones, cyclic ketones, α,β-unsaturated aldehydes and aliphatic aldehydes and ketones has been accomplished using ammonium persulfate on wet montmorillonite K-10 clay support.

Studies on Regioselectivity of Nitration of Coumarins with Cerium(IV) Ammonium Nitrate: Solid‐State Nitration of 6‐Hydroxycoumarins on Montmorillonite K‐10 Clay Support under Microwave Irradiation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Studies on Regioselectivity of Nitration of Coumarins with Cerium(IV) Ammonium Nitrate: Solid-State Nitration of 6-Hydroxy-Coumarins on Montmorillonite K-10 Clay Support Under Microwave Irradiation

6-Hydroxycoumarins and their O-methyl ethers were selectively nitrated in the carbocyclic ring even in the presence of activating 4-Me group in the 2-pyrone ring with cerium(IV) ammonium nitrate (CAN) in acetic acid and acetonitrile in acceptable-to-excellent yields. Acetonitrile was found to be a better solvent for regioselective nitration than acetic acid. Use of CAN on montmorillonite K-10 clay under microwave irradiation for expeditious solvent-free regioselective nitration has been revealed for the first time.

Hydrogenation of benzene on Ni/Al-pillared saponite catalysts

Benzene hydrogenation has been employed as a test reaction for examining Nickel on Al-pillared saponite systems as hydrogenation catalysts. Catalytic activity was evaluated over a temperature range of 70–160 °C under atmospheric pressure, in a differential bench scale reactor. Surface area measurements and X-ray diffraction were used as tools for characterizing the catalysts. The influence of the support’s acidity on the catalyst activity was studied via diverse modifications of the pillared clay support. The evolution of catalyst activity with nickel loading is also discussed and the results are compared to those previously obtained for nickel on Al-pillared montmorillonite catalyst.

Effect of gas phase modification of analcime zeolite composite membrane on separation of surfactant by ultrafiltration

Ceramic–analcime zeolite composite membranes have been synthesized by hydrothermal crystallization of zeolite over clay supports. The zeolite layer is characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and pore size distribution determined using the bubble point technique. The XRD pattern of the zeolite is found to match with JCPDS file #19-1180 which is an analcime-o zeolite of molecular formula NaAlSi 2O 6·H 2O having orthorhombic crystal structure with lattice parameters: a=13.72 Å, b=13.714 Å and c=13.714 Å. In this paper, we report a gas phase nitration scheme, in which we show through the elemental analysis that the modification of entire matrix (and not limited to pores and channels) occurs. The nitrated zeolite was reduced to aminated zeolite membrane by reacting it hydrazine hydrate. Separation of surfactant (CPC) was performed using these three types (unmodified, nitrated and aminated) of membranes and it showed about 300% increase in the retention of the surfactant after its modification. Its hydrophilic nature also increases as shown by the increase in the permeate flux. In order to find the reason for this enhanced performance, structural analysis of the modified membranes was carried out. The XRD patterns of these were found to be identical and they did not match with those of any of the compounds given in the JCPDS files. The patterns were therefore indexed, using first principle, to find their crystal structure and it was found that the structure changed from orthorhombic for unmodified to tetragonal geometry for the modified zeolites. This also caused about 10% increase in the unit cell volume of the modified zeolites. Anion exchange capacity and the elemental analysis showed that the nitration occurred over the entire zeolite matrix (not restricted to the pores and channels) and on an average about one amine group was present in every second formula unit of the zeolite. This extensive presence of nitrate or amine group in the zeolite matrix makes the modified zeolite membrane highly hydrophilic and may be responsible for the increase in the retention of the surfactant and permeate flux for the modified membranes.