Krypton‐xenon separation properties of SAPO‐34 zeolite materials and membranes

Separation of the radioisotope ⁸⁵Kr from ¹³⁶Xe is an important target during used nuclear fuel recycling. We report a detailed study on the Kr and Xe adsorption, diffusion, and membrane permeation properties of the silicoaluminophosphate zeolite SAPO‐34. Adsorption and diffusion measurements on SAPO‐34 crystals indicate their potential for use in Kr‐Xe separation membranes, but also highlight competing effects of adsorption and diffusion selectivity. SAPO‐34 membranes are synthesized on α?alumina disk and tubular substrates via steam assisted conversion seeding and hydrothermal growth, and are characterized in detail. Membrane transport measurements reveal that SAPO‐34 membranes can separate Kr from Xe by molecular sieving, with Kr permeabilities around 50 Barrer and mixture selectivity of 25–30 for Kr at ambient or slight sub‐ambient conditions. The membrane transport characteristics are modeled by the Maxwell‐Stefan equations, whose predictions are in very good agreement with experiment and confirm the minimal competing effects of adsorption and diffusion. © 2016 American Institute of Chemical Engineers AIChE J, 63: 761–769, 2017     

Deactivation by coke of a catalyst based on a SAPO‐34 in the transformation of methanol into olefins

When methanol is converted to olefins on a SAPO‐34 catalyst between 350 and 425°C, there is a rapid initial formation of coke, followed by a slower rate of coke deposition. The rate of coke formation decreases with increasing temperature, and with progression through the catalyst bed. The coke completely blocks the internal channels of the SAPO‐34 crystals and subsequently blocks the mesopores (intercrystalline and those of the bentonite). Coke deposition mainly blocks sites of acidic strength above 175 kJ mol⁻¹. The presence of water in the feed lessens coke formation, either by converting Lewis to Brønsted sites or by competing for surface sites with coke precursors. © 1999 Society of Chemical Industry     

Regeneration of a catalyst based on a SAPO‐34 used in the transformation of methanol into olefins

The regeneration by coke combustion of a catalyst based on a SAPO‐34 used in the transformation of methanol into olefins (ethene and propene) has been studied. It has been observed that coke combustion kinetics are strongly dependent on the nature of the coke (H/C ratio), which in turn is a consequence of the reaction conditions (especially of the water content in the feed) and of the ageing level of the coke prior to its combustion. A severe ageing treatment is needed in order for combustion kinetics to be reproducible. Combustion is delayed due to the fact that coke is not an inert material but is bound to the acid sites. © 1999 Society of Chemical Industry     

Transalkylation of diisopropylbenzene with benzene over SAPO‐5 catalyst: a kinetic study

BACKGROUND: The objective of this work was to improve the selective yield of cumene by transalkylating the (diisopropylbenzene) DIPB formed in benzene alkylation with propene and select the optimum process conditions for this transalkylation over SAPO‐5 catalyst. RESULTS: Higher benzene/DIPB mole ratios and higher space velocities were found to give better cumene selectivity. An apparent activation energy value of 130.2 kJ mol^?1 was obtained for the reaction with SAPO‐5 as the catalyst. CONCLUSION: SAPO‐5 shows promise when loaded with a small quantity of platinum (0.005% w/w) in the transalkylation of commercial DIPB (cumene column bottoms) with benzene. The kinetic investigations help in selecting optimum process operating conditions for maximizing the cumene yields in transalkylation of commercial DIPB over SAPO‐5. Copyright © 2008 Society of Chemical Industry     

Alkylation of benzene with isopropanol over SAPO‐5: A kinetic study

The kinetics of benzene alkylation with isopropanol has been studied in vapour phase over SAPO‐5 catalyst. On the basis of the product distribution pattern obtained over this large pore molecular sieve, a reaction mechanism has been proposed. Based on this reaction network, suitable phenomenological models have been derived and fitted to the kinetic data. A Langmuir‐Hinshelwood model with surface reaction involving single site mechanism fitted the data better than the other models. The deactivation kinetics has also been investigated in the low temperature chosen. The activation energy for the deactivation reaction in this range is found to be lower than that for the main reaction.     

Adsorption Mechanism for 2‐Methylpyridine on Hypercross‐linked Fibers

Two types of novel hypercross‐linked fiber adsorbents, ZH‐01 and ZH‐02, were prepared by cross‐linking PP‐ST‐DVB fibers in solution with p‐xylylenedichloride and monochloromethylether according to the Friedel‐Crafts reaction. A series of static adsorption tests were performed. The results showed that the adsorbents have excellent adsorption capacities for 2‐methylpyridine and the adsorption equilibrium data can be fitted well by the Freundlich model. The thermodynamic studies supported the conclusion that the mechanism of adsorption for 2‐methylpyridine on the adsorbents is physical adsorption and a lower temperature is favorable to the exothermic physisorption process. In addition, kinetic studies were also carried out. The hypercross‐linked fiber adsorbents showed a faster adsorption rate than the base PP‐ST‐DVB fiber. The faster attainment of adsorption equilibrium for 2‐methylpyridine on the adsorbents (within 2 h), is advantageous for practical use. A first‐order reaction rate equation was assumed for the adsorption system and was suitable to describe the process. The equilibrium rate constants of the adsorbents correlated well with their adsorption capacities.     

Modeling of the Wall Effect in Packed Bed Adsorption

A model developed for catalytic packed bed reactors and consistently accounting for the influence of the tube wall on porosity, flow and transport phenomena is used in order to simulate the operation of packed bed adsorbers. By comparison of simulation results with reduced versions of the model the influence of the wall on the adsorber performance is worked out and found to be major at low ratios between tube and particle diameter. The interaction between maldistribution, thermal effects and intraparticle resistances in such adsorber tubes is discussed.     

Experimental Investigation and Modeling of Adsorption of Water and Ethanol on Cornmeal in an Ethanol‐Water Binary Vapor System

The adsorption capacity of water and ethanol on cornmeal in an ethanol‐water binary vapor system was investigated in a fixed‐bed apparatus for ethanol dehydration. Experiments were performed at temperatures of 82–100 °C for different relative humidities of ethanol‐water vapor. Adsorption equilibrium models, including those based on the adsorption potential theory of Polanyi and Sircar's model, have been used to fit the experimental data for water adsorption on cornmeal, and all gave good fits. For ethanol adsorption, pseudo‐equilibrium was defined as the mass adsorbed on the cornmeal within the time needed for the equilibrium for water on the same adsorbent. Based on this limiting condition, adsorption behaviors and mechanisms were analyzed.     

Fixed‐Bed Adsorption of Allura Red Dye on Chitosan/Polyurethane Foam

The potential of a chitosan/polyurethane foam (CTS/PU) fixed‐bed column for the removal of Allura Red dye (AR) from aqueous solutions was evaluated. Breakthrough curves were constructed under different conditions and optimized using response surface methodology (RSM). The empirical models Thomas, Yoon‐Nelson, and Bed Depth Service Time (BDST) were fitted to the experimental data. The dynamic models of Yoon‐Nelson and BDST accurately fitted the experimental data. As a result, CTS/PU can be successfully applied in a fixed‐bed adsorption operation to remove AR dye.     

Kinetics and Equilibrium Modeling of Sterol Adsorption on Styrene‐Divinylbenzene Cation‐Exchange Resins

The potential of recovering phytosterols from fatty acid methyl esters by an adsorption‐desorption process is demonstrated using a strong‐acid ion‐exchange styrene‐divinylbenzene resin (SA‐R) as an adsorbent and ethanol as a desorbent. Since the operating cost of the overall process significantly depends on the efficiency of SA‐R in the adsorption step, the behavior of SA‐R in sterol adsorption is investigated in detail using a model solution of stigmasterol in n‐heptane. The results indicate that stigmasterol was associatively and exothermically adsorbed on SA‐R. Based on the experimental results, a simple pseudo‐second‐order model and a modified Langmuir isotherm with their parameters, which well predicted kinetics and adsorption capacity of SA‐R, are proposed.     

Binary Adsorption of n‐Butane or Toluene and Water Vapor

To clean the air in cars of noxious gases by adsorption, predominantly activated carbon is used. The height of the activated carbon layer is especially small in cabin air filtration. As test substances for adsorptive filters in cabin air filtration, toluene and n‐butane are prescribed in several engineering standards, e.g., ISO TS 11155‐2. In the study presented, the differences in binary adsorption between toluene or n‐butane and water vapor are investigated with emphasis on adsorption equilibrium and kinetics at temperatures between 15 °C and 33 °C, and relative humidity varying between 0 % and 90 %. The range of input concentrations is from 2 ppm_V up to 80 ppm_V.     

Efficient Water Purification by Photocatalysis and Rapid Adsorption of Dip‐Coated Metal Foam with Nanostructured Bismuth Vanadate

Rapid removal of the organic methylene blue (MB) dye was achieved by simple stirring of highly porous Ni–Fe–Cr–Al metal foam coated with bismuth vanadate (BiVO₄). The metal foam was dip‐coated with the BiVO₄ solution precursor and annealed for an hour, through which the foam surface was decorated with the highly porous nanostructure, yielding high adsorptivity. This bismuth‐decorated metal foam was characterized by X‐ray diffraction, X‐ray photoelectron, and scanning electron microscopy to elucidate its physical, chemical, and morphological properties. The modeled pollutant, MB, was stirred with the metal foam both in darkness and in light. Complete decolorization was observed for both of these conditions, which indicates that adsorption dominates over photocatalysis; we found that photocatalysis contributed to less than 10% of the purification process. We also demonstrated that it would be possible to recycle the metal foam as many as 20 times, beyond which its purification capability degrades. However, the MB residues on the foam can be removed by simple annealing; thus, in theory the foam can be recycled indefinitely.     

Effect of different organic amino cations on SAPO‐34 for PES/SAPO‐34 mixed matrix membranes toward CO2/CH4 separation

Mixed matrix membranes (MMMs) embedded with functionalized SAPO‐34 were successfully synthesized and characterized. Two different types of organic amino cation, namely ethylenediamine (EDA) and hexylamine (HA), were used to functionalize SAPO‐34 particles prior to MMM synthesis. In this work, the effects of different functionalizing agents on the membrane morphology, pore size, and CO₂/CH₄ gas separation properties were investigated. Surface modification of SAPO‐34 was confirmed via X‐ray photoemission spectroscopy (XPS) where the presence of nitrogen atom was observed for the samples functionalized with amino cations. The dispersion of EDA‐functionalized SAPO‐34 particles was found to have better polymer/filler interface morphology as shown by field emission scanning electron microscopy (FESEM) analysis. The gas separation performance revealed that PES containing EDA‐functionalized SAPO‐34 exhibited better CO₂/CH₄ separation performance as compared to the MMMs containing HA‐functionalized SAPO‐34. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43387.     

Predicting and Controlling the Effect of Solubilized Flavor Oil on Foam Properties of Surfactant through Study of the Adsorption Activity and Configuration

In the wide application of foam products, the effect of oil additive on foam property is a critical issue that has gained increasing attention; the effect on foam induced by various flavor oils is still a puzzling question, and relative study is rare. In this article, a series of typical flavor oils were studied for their effects on the foam properties of sodium dodecylsulfate. Measurements of foamability, foam stability, foam elasticity, and surface activity were taken; meanwhile, molecular dispersion and interfacial arrangement behavior of surfactant and oil molecules were explored by molecular dynamics simulation. Through a combination of macroscopic phenomenon and microscopic information, how flavor oils with different chemical structures affected the foaming properties of surfactants was demonstrated, and an evaluation scheme for predicting the level of influence on foam properties by different flavor oils was constructed. This investigation may help better understand the role of flavor oils in foam systems and provide a theoretical foundation for optimizing the application of flavor oils in relevant industries.     

Adsorption of 2,4,6‐Trinitrotoluene on MFI Zeolite

2,4,6‐Trinitrotoluene (TNT) was adsorbed onto all silica MFI zeolite. These TNT doped zeolite samples were examined using Fourier Transform Infrared Spectroscopy (FTIR) and X‐ray Diffraction (XRD). Results indicate that, using FTIR with an Attenuated Total Reflection (ATR) accessory, mass loading percentages as low as 2.5 mass percent TNT in zeolite are detectable. It was also observed that adsorption of TNT onto MFI did not suppress the IR absorbing vibrations of TNT. TNT doped zeolite samples were washed, using vacuum aspiration, with water and acetone, both of which stripped the TNT from the zeolite samples, indicating that the adsorption of TNT onto MFI zeolite is a physisorption, rather than chemisorption, phenomenon. Finally, a lack of strain‐induced peak broadening from XRD studies indicate that TNT does not enter the zeolitic pore structure, rather, it is adsorbed onto the zeolite surface.     

The Kinetics and Equilibrium of Ethanol Adsorption from Aqueous Phase Using Calcined (Na‐1,6‐Hexanediol)‐ZSM‐5

Na‐ZSM‐5, synthesized using 1,6‐hexanediol as the structure directing agent, has been found to have a suitable selectivity and adsorbing capacity for ethanol adsorption from aqueous solutions. In contrast to quaternary ammonium based Na‐ZSM‐5 zeolites, this Na‐ZSM‐5 did not show any catalytic interaction with ethanol during thermal desorption. The dynamics of the adsorption process were investigated using the finite volume “uptake rate” route. The data predicted from the governing relations of the process were correlated with experimental results. The micro‐diffusion coefficient was determined as a function of temperature.The macropore diffusional mass transfer contribution for biporous zeolite particles was found to be negligible.     

Adsorption of C6–C8 Aromatics over Ba‐Exchanged Zeolite X at High Temperature

The adsorption of C₆–C₈ aromatics was investigated at higher temperatures than normally used in the industry in the absence of water to assess the adsorption equilibrium properties under conditions that can be suitable for a simulated moving‐bed reactor for the production of p‐xylene. Batch experiments were conducted on a dry Ba‐exchanged zeolite X at various temperatures in the liquid phase. Pseudo‐single‐component adsorption equilibrium isotherms from binary mixtures with i‐octane were obtained based on the adsorbed amount with different initial concentrations. The Langmuir model was applied to describe the adsorption equilibrium data. The estimated parameters predicted very well the equilibrium in the adsorbent.     

Synthesis of Carbon‐Rich Hybrid Foam from GAP‐Modified Polyurethane

4,4′‐Diisocyanato diphenylmethane (MDI)‐based polyurethanes melt and start to burn at 150–200 °C. Mainly H₂O, CO₂, CO, HCN, and N₂ are formed. The new modified polyurethane shows a different pyrolysis behavior. GAP‐diol (glycidyl azide polymer), which was used as a modifying agent, is a well‐known energetic binder with a high burning velocity and a very low adiabatic flame temperature. The modified polyurethane starts to burn at approximately 190 °C because of the emitted burnable gases, but it does not melt. The PU foam shrinks slightly and a black, solid, carbon‐rich hybrid foam remains. TGA and EGA‐FTIR revealed a three‐step decomposition mechanism of pure GAP‐diol, the isocyanate‐GAP‐diol, and PU‐GAP‐diol formulations. The first decomposition step is caused by an exothermic reaction of the azido group of the GAP‐diol. This decomposition reaction is independent of the oxygen content in the atmosphere. In the range of 190–240 °C the azido group spontaneously decomposes to nitrogen and ammonia. This decomposition is assumed to take place partly via the intermediate hydrogen azide that decomposes spontaneously to nitrogen and ammonia in the range of 190–240 °C. The second decomposition step was attributed to the depolymerization of the urethane and bisubstituted urea groups. The third decomposition step in the range of 500–750 °C was attributed to the carbonization process of the polymer backbone, which yielded solid, carbon‐rich hybrid foams at 900 °C. In air, the second and the third decomposition step shifted to lower temperatures while no solid carbon hybrid foam was left. Samples of PU‐GAP‐diol, which were not heated by a temperature program but ignited by a bunsen burner, formed a similar carbon‐rich hybrid foam. It was therefore concluded that the decomposition products of the hydrogen azide, ammonia and mainly nitrogen act as an inert atmosphere. FTIR, solid‐state ¹³C‐NMR, XRD, and heat conductivity measurements revealed a high content of sp²‐hybridized, aromatic structures in the hybrid foam. The carbon‐rich foam shows a considerable hardness coupled with high temperature resistance and large specific surface area of 2.1 m²⋅g⁻¹.