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BACKGROUND Polybenzoxazine ( PBZ) membranes have received increasing attention for serving as a high performance membrane for pervaporation processes owing to their good mechanical properties, high chemical resistance, high thermal stability, and low synthesis cost. This study aims to develop PBZ membrane and NaA-PBZ mixed matrix membrane ( MMM) for purification of ethanol/water mixtures using a pervaporation process and to investigate the effects of preparation parameters on the membrane performance, including precursor concentrations, number of dippings, amount of NaA zeolite loading, temperature, and ethanol concentration. RESULTS It was found that PBZ membrane and NaA-PBZ MMM exhibited excellent stability in all feed ethanol concentrations tested, with a low degree of swelling. The highest separation factor of the pure PBZ membrane was more than 10 000 while the NaA-PBZ MMM was even higher, up to and, in some cases, higher than 100 000 with the highest permeation flux of 1071 g m−2 h−1 when using 25 wt% PBZ precursor with 15 wt% NaA zeolite loading. The permeation flux of MMM increased with increase in temperature or a decrease in the feed ethanol concentration. Swelling increased when the ethanol concentration was increased, revealing the hydrophobic behavior of NaA-PBZ MMM. CONCLUSION The membranes are capable of purifying ethanol over a wide feed ethanol concentration range with excellent performance and properties that promise great potential for use in bioethanol purifying applications. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Hydrogen desorption/absorption of the LiBH/MgH mixture milled for 5 h was investigated with different initial pressures. The results showed that the initial pressure played an important role in the reversibility of the LiBH/MgH mixture. The stability of the hydrogen capacity in the subsequent desorption was improved with a higher initial pressure. A possible reason was from the increase in the formation of MgB and the lower degree in the decomposition of both LiBH to the amorphous phases of LiBH and B; and MgH to Mg, during the hydrogen desorption. However, the higher initial pressure increased the hydrogen desorption temperature. The desorption temperature was increased from 310 °C for the sample decomposing under 0.1 MPa hydrogen pressure to 360 °C for other cases. This may be due to the higher energy required to overcome the suppression of MgH and LiBH decomposition. [ABSTRACT FROM AUTHOR]

SUMMARY TiCl3 has been considered as the best catalyst for the hydrogen desorption/re-absorption of NaAlH4 in terms of kinetic enhancement. However, the formation of NaCl as a by-product leads to the decrease in the reversible hydrogen capacity of NaAlH4. In this work, TiO2 and metallic Ti were selected as catalysts for the reaction to avoid the formation of the by-product. The comparison of the catalytic activity of Ti, TiCl3, TiO2 and Ti(OBu)4 on the hydrogen desorption/absorption NaAlH4 were carried out. It was found that TiO2 doped NaAlH4 exhibits similar behavior as TiCl3 doped NaAlH4 with the reversible hydrogen capacity about 3.8 wt% (H/M). In addition, TiO2 doped NaAlH4 exhibits the superior hydrogen re-absorption rate to the one doped with TiCl3. That may be due to the Ti3+ defect sites on the surface of TiO2 would facilitate the hydrogen dissociation. Moreover, high surface area of TiO2 prevents the segregation and the morphological change of the desorbed substances (NaH and Al). This benefits to the mass transfer into the hydride system. However, doping with TiO2 also produces sodium oxide and hydroxide as by-products. Unexpectedly, metallic Ti doped NaAlH4 shows the lowest hydrogen desorption/re-absorption among the tested samples. Its hydrogen reversible capacity is around 1 wt% (H/M). The formation of TiHx (1 < x < 2) was detected in the sample after the hydrogen desorption/reabsorption. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The hydrogen desorption/absorption behaviors of LiAlH4/LiBH4 with a focus on the effects of catalysts, namely TiCl3, TiO2, VCl3, and ZrCl4, were investigated using a thermal-volumetric apparatus. The hydrogen desorption was performed from room temperature to 300 °C with a heating rate of 2 °C min-1. The LiAlH4-LiBH4 mixture with a molar ratio of 2:1 decomposed between 100 and 220 °C, and the hydrogen desorption capacity reached up to 6.6 wt %. Doping 1 mol % of a catalyst to the mixture resulted in the two-step decomposition and a decrease in the hydrogen desorption temperature. All the doped samples provided lower amountz of desorbed hydrogen than that obtained from the undoped one. No hydrogen absorption was observed under 8.5 MPa of hydrogen pressure and 300 °C for 6 h. Despite the fact each of the catalysts may affect the hydrogen storage behaviors of the mixture differently, none resulted in a change in the sample reversibility [ABSTRACT FROM AUTHOR]

Sodium aluminum hydride or sodium alanate (NaAlH4) has been considered as a potential material for hydrogen storage. Although its theoretical hydrogen storage capacity is 5.5 wt.% at 250 °C, the material still has its drawback in the regeneration issue. With the use of certain catalysts, the regeneration problem can somewhat be alleviated with added benefits in the decrease in the hydrogen decomposition temperature and the increase in the decomposition rate. This work summarizes what we have learned from the decomposition of NaAlH4 with/without catalysts and co-dopants. The decomposition was carried out using a thermovolumetric apparatus. For the tested catalysts—HfCl4, VCl3, TiO2, TiCl3, and Ti—the decomposition temperature of the hydride decreases; however, they affect the temperature in the subsequent cycles differently and TiO2 appears to have the most positive effect on the temperature. Sample segregation and the morphological change are postulated to hinder the reversibility of the hydride. To prevent the problems, co-dopants—activated carbon, graphite, and MCM-41—were loaded. Results show that the hydrogen reabsorption capacity of HfCl4- and TiO2-doped NaAlH4 added with the co-dopants increases 10–50% compared with that without a co-dopant, and graphite is the best co-dopant in terms of reabsorption capacity. In addition, the decomposition temperature in the subsequent cycles of the co-dopant doped samples decreases about 10–15 °C as compared to the sample without a co-dopant. Porosity and large surface area of the co-dopant may decrease the segregation of bulk aluminum after the desorption and improve hydrogen diffusion in/out bulk of desorbed/reabsorbed samples. [ABSTRACT FROM AUTHOR]

A novel silver ion-exchange treatment of zeolite was introduced in this work to change the physical and chemical adsorption properties of penetrants in the zeolite. EDX data confirm the complete replacement of sodium ion in zeolite NaA by silver ion, whereas XRD patterns and BET results show no changes in some physical properties of zeolite after the silver ion-exchange treatment. Polyethersulfone (PES)-zeolite NaA mixed matrix membranes (MMMs) and PES-zeolite AgA MMMs were fabricated at high processing temperatures with different zeolite loadings. Cross-sectional SEM images of these two types of MMMs indicate the interface between polymer and zeolite phases is comparable before and after the silver ion-exchange treatment. The effects of silver ion-exchange treatment of zeolite and zeolite loadings on the gas separation performance of these MMMs were investigated. CO2 permeability of PES-zeolite AgA MMMs is higher than that of PES-zeolite NaA MMMs, whereas their CH4 permeability is lower than that of PES-zeolite NaA MMMs. This trend is the result of the reversible reaction between silver ion and CO2 molecule. CO2 and CH4 permeability of PES-zeolite AgA MMMs decreases with increasing zeolite content arising from the effects of partial pore blockage of zeolite and polymer chain rigidification, whereas their CO2/CH4 selectivity increases with an increase in zeolite loadings and the highest value reaches 59.6 at 50 wt % zeolite loading because of a combined effect of the facilitated transport mechanism of silver ion and the molecular sieving mechanism of zeolite. Both CO2-induced plasticization test and CO2/CH4 mixed gas measurement were performed to examine the applicability of these developed PES-zeolite AgA MMMs in industry. Results prove that this type of composite membrane material is a superior candidate for the practical separation of natural gas. [ABSTRACT FROM AUTHOR]

It has been demonstrated that a novel p-xylenediamine/methanol soaking method could efficiently remove the polymer--zeolite interface defects of the mixed-matrix structure. In this work, the mixed-matrix structure is in the form of an ultrathin (1.5-3 µm) polysulfone/ zeolite beta mixed-matrix layer that is supported by a neat Matrimid® layer in dual-layer composite hollow fibers. The particle's loading in this thin layer has reached 30 wt %. The ideal selectivities of the mixed-matrix hollow fibers (30 wt % of zeolite)for O2/N2 and CO2/CH4 separation were roughly 30 and 50% superior to that of the neat PSF/Matrimid® hollow fibers, respectively. Investigation of the morphology of the mixed-matrix selective layer and its relation with gas separation performance indicated that without p-xylenediamine/methanol solution treatment, the outer layer showed various polymer--zeolite interface structures in different fibers with the same heat treatment procedures; this situation might lead to the different selectivities after coating. However, by applying p-xylenediamine/methanol processing on the fibers before thermal treatment, the fibers obtained a more uniform structure and improved attachment between polymer matrix and zeolite surface. Hydrogen bonding was proposed as the possible mechanism for the tighter attachment between the two phases. The improvement of separation efficiency was presumably related to the polymer chain rigidification, partial pore blockage, and/or favorable interaction between the gas penetrants and zeolite framework. [ABSTRACT FROM AUTHOR]

Abstract: Although hydrogen has a great potential as clean energy, safe practical storage of hydrogen for applications such as fuel cells has been a major challenge. NaAlH4 is one of the metal hydrides, which are candidates for hydrogen storage in vehicles. However, the rather slow absorption/desorption kinetics is still a significant drawback. To alleviate this problem, purified NaAlH4 was ground with TiCl3, ZrCl4, or HfCl4. Desorption kinetics and capacities were observed under TPD-like operation. Absorption efficiency was determined by raising the temperature up to 125°C. Of the three doped metals investigated for the positive effect on facilitating NaAlH4 decomposition, TiCl3 assists the best on the first reaction while ZrCl4 and HfCl4 do for the second one. Despite the kinetics enhancement directly involves with the ZrCl4 amount, there is a threshold of ZrCl4-content which affects. 6% ZrCl4 is considered as an appropriate amount to improve the hydrogen release because it simultaneously decreases the desorption temperature and gives the outstanding rate. In hydrogen desorption, ZrCl4 provides the most amount of released hydrogen, but for hydrogen absorption TiCl3-doped NaAlH4 possesses the highest capacity. It is believed that the metal size is one of the key factors resulting in such the behavior. [Copyright &y& Elsevier]

Phenol hydroxylation with TS-1 was studied in a chromatographic reactor. TS-1 not only acts as the catalyst for the reaction but also the adsorbent for the separation. The reaction/separation was carried out at 60°C with water and 0.2 wt% of aqueous H2O2 as the desorbent. Separation of hydroquinone(HQ) can be achieved in all cases. With water as the desorbent, separation of catechol(CT) depends on the phenol feed concentration, which has been confirmed from both reaction/separation in the chromatographic reactor and equilibrium competitive adsorption experiment. Some unknown by-products not commonly reported in batch experiments have been observed here. TS-1 can also be regenerated using just water. With the aqueous mixture of H2O2 as the desorbent, separation of HQ and CT is possible. Reactive separation schemes based on the simulated counter-current technology have been proposed according to the experimental results. [ABSTRACT FROM AUTHOR]

Two widely investigated methane hydrate promoters, tetra-n-butyl ammonium bromide (TBAB) and cyclopentane (CP), for methane hydrate formation and dissociation were comparatively investigated in the quiescent reactor at 2.5 °C and 8 MPa. The results indicated that the increase in the mass fraction TBAB decreased the induction time. However, it did not significantly affect the methane uptake. In the presence of CP, the increase in the CP concentration resulted in an increase in the induction time due to the increasing thicknesses of the CP layer in the unstirred reactor. Moreover, the methane uptake was varied proportionally with the CP concentration. The addition of TBAB resulted in a higher methane uptake than that of CP, since the presence of TBAB provided the cavities in the hydrate structure to accommodate the methane gas during the hydrate formation better than that of CP. On the contrary, the presence of CP significantly increased the induction time. Although the methane recovery remained relatively the same regardless of TBAB and CP concentrations, the recovery was higher in the presence of TBAB. [ABSTRACT FROM AUTHOR]