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In this research, the separate production of hydrogen (H 2 ) and methane (CH 4 ) from cassava wastewater with added cassava residue was investigated using a two-stage upflow anaerobic sludge blanket (UASB) system under thermophilic temperature (55 °C) in a continuous mode of operation and steady state condition. The two-stage UASB system was operated under an optimum chemical oxygen demand (COD) loading rate of 10.29 kg/m 3 d (based on the total volume of both bioreactors) of the cassava wastewater with different concentrations of added cassava residue. The recycle ratio of the effluent from the second bioreactor to the feed flow rate was fixed at 1:1 (v/v). In addition, the solution pH in the first bioreactor was controlled at 5.5, while that in the second bioreactor was not controlled. Under the optimum cassava residue concentration of 1200 mg/L, the produced gas from the first bioreactor contained 42.3% H 2 , 55% carbon dioxide (CO 2 ) and 2.70% CH 4 , while that from the second bioreactor contained 70.5% CH 4 , 28% CO 2 and 1.5% H 2 . Apart from a high H 2 and CH 4 production performance (45.2 and 150% improvement, respectively, as compared to the system without added cassava residue) under the optimum cassava residue concentration (1200 mg/L) and the controlled COD loading rate (10.29 kg/m 3 d) of the cassava wastewater, the degradation performance of cellulose and hemicellulose were 41% and 22%, respectively, for the first bioreactor and 23% and 11%, respectively, for the second bioreactor. The digestibility of the cassava residue at thermophilic operation was higher than that at mesophilic temperature., (Copyright © 2018 Elsevier B.V. All rights reserved.)

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]

The main objective of this work was to investigate the effect of two transition metals (0–9mol% ZrCl4 and HfCl4) on hydrogen desorption/absorption of NaAlH4 and LiAlH4. The hydrogen desorption was carried out over a wide temperature range of 25– while the hydrogen absorption took place at and between 50– for NaAlH4 and LiAlH4, respectively, with the same pressure of 11MPa. The result revealed that the transition metals (Zr and Hf) could improve the kinetics of the hydrogen desorption on NaAlH4. NaAlH4 doped with HfCl4 released hydrogen at the lower temperature than that of ZrCl4-doped NaAlH4. In addition, the rate of hydrogen desorption increased with increasing the amount of HfCl4 doping. However, the maximum hydrogen capacity of was obtained from the first desorption, and dropped to 2.2–2.6wt% in the subsequent cycles. This may be because of, after the hydrogen desorption, the hydrides melt due to the high temperature resulted in agglomeration of the hydrides and segregation of Al. XRD results showed the formation of NaCl after milling of NaAlH4 with 4mol% HfCl4 and no evidence of any Hf-containing phase. However, with 10mol% HfCl4, the formation between Al and Hf in the form of Al3Hf was observed. This compound may act as catalyst in the reversible hydrogen desorption/absorption. For LiAlH4, ZrCl4 or HfCl4 also enhanced the kinetics of desorption of LiAlH4. Moreover, it was observed that LiAlH4 released hydrogen during the milling. After the hydrogen desorption from LiAlH4, no hydrogen absorption was observed for the undoped hydride or that doped with HfCl4 or ZrCl4. This may be because of the instability of LiAlH4. Moreover, milling and dopant may also destabilize the structure of LiAlH4 causing the irreversibility of hydrogen desorption/absorption on LiAlH4. [Copyright &y& Elsevier]

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]

Abstract: Effects of temperature variation in microwave-induced system of tetralin dehydrogenation on the enhancement of reactivity were investigated. The enhancement of heating ability of Pt-supported activated carbon catalyst (Pt/AC) particle and decreasing of an existing temperature gradient (non-uniformed heat distribution) in tetralin solution under microwave heating and boiling-reflux condition were examined by three methodologies: an employment of Dewar-like insulation reactor (DIR), addition of an ionic liquid as an optional microwave absorber in the system, and optimization of the catalyst to the reactant in the reaction system. The Dewar-like insulation reactor was used to prevent heat loss in the heterogeneous solution. Under microwave heating with DIR, the reaction can be heated approximately 3°C above the normal boiling point of tetralin. In comparison to the reaction carried out in a conventional reactor, tetralin conversion increased from 31% to 56% under 190W microwave irradiation. Addition of an ionic liquid to the system to function as a heating promoter remarkably enhanced the heating rate of tetralin. However, the ionic liquid deactivated the activity of the catalyst in the reaction. Optimization of tetralin to Pt/AC catalyst in the reaction system improved heat distribution and showed an interesting result. It was found that the reaction performed under the liquid film state showed the highest tetralin conversion, 69% with the microwave irradiation for 60min. [Copyright &y& Elsevier]