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An experimental and modelling study of CO2 removal from a simulated biogas feed by chemical absorption in an organic solution of 2-amine-2-methyl-1-propanol in an ethylene glycol and n-propanol solvent is presented. Absorption was carried out under different temperature, feed flow rate, and feed recirculation conditions. Regeneration was carried at different temperatures. Cyclability tests showed that the absorption capacity remained stable starting from the fourth cycle. In the conditions analyzed, higher temperatures and liquid recirculation favor absorption. With all other conditions constant, the CO2 absorption efficiency increased from 72% to 87% when the temperature increased from 23 to 45°C. At 33°C, liquid recirculation enhanced the absorption efficiency from to 93%–97%. A model was developed and validated against experimental results. Absorption and desorption rates are proportional to the carbon dioxide and AMP concentrations and to the alkyl carbonate concentration, respectively. The two rate constants were fitted from the experimental data: their values at 30°C are 0.033 s−1 (kmol/m3)−1 and 1.5 × 10−6 s−1, respectively. The model indicates that the beneficial effect of temperature and liquid recirculation is due to the increased mass transfer coefficient of CO2 from the gas to the liquid solution, which increased from 4 × 10−3 s−1 at 20°C to 1.3 × 10−2 s−1 at 70°C and by a factor of 8.8 as a consequence of feed recirculation. An increase in the biogas flow rate reduced the absorption efficiency by decreasing the contact time. Higher temperatures also increased the rate of CO2 desorption.

The very high theoretical capacity of the silicon (4200mAh/g more than 10 times larger than graphite), environmental-friendly, abundant and low-cost, makes it a potential candidate to replace graphite in high energy density Li-ion batteries. As a drawback, silicon suffers from huge volume changes (300%) on alloying and dealloying with Li, leading a structural deformation that induces disruption. The use of nanostructured silicon materials has been shown to be an effective way to avoid this mechanical degradation of the active material. In this paper the synthesis of silicon nanowires, grown on a highly porous 3D-like carbon paper substrate by CVD using Cu as the catalyst, is presented. The use of carbon paper allows to achieve remarkable loadings of active material (2-5 mg/cm2) and, consequently, high capacity densities. The silicon electrode was investigated both morphologically and electrochemically. To improve the electrochemical performance various strategies have been carried out. It was observed that a very slow first cycle (C/40), which helps the formation of a stable solid electrolyte interphase on the silicon surface, improves the performance of the cells; nevertheless, their cycle life has been found not fully satisfactory. Morphological analysis of the Si-NWs electrodes before and after cycling showed the presence of a dense silicon layer below the nanowires which could reduce the electrical contact between the active material and the substrate.

Magnesium hydride is a promising material for hydrogen storage due to its high storage capacity i.e.7.6wt%. But its high stability i.e. high desorption temperature (~350 o C) limits its practical application towards hydrogen economy. Moreover the kinetics is also too slow even at high temperatures. Composite formation with Zr based laves phase alloys, especially ZrCr2 family, is an effective method to improve the hydriding properties of MgH2. This work presents the synthesis, structural, morphological, and hydrogenation properties of Mg-x wt% ZrCrMn composites. Both phases i.e. Mg & ZrCrMn remain their presence after milling and several hydriding cycles as well. SEM results suggest the homogeneous distribution of alloy particles on Mg matrix. Pressure composition temperature (PCT) analysis shows a reduction in desorption temperature down to 250 o C for these composites. TG experiments suggest a total hydrogen capacity of 5.9% and 4.35% for x =25, 50 in Mg-x wt% ZrCrMn composites respectively. The enthalpy of hydride formation is also calculated using Van't Hoff plots, which is found similar to the parent material i.e. MgH2. A remarkable enhancement in the kinetics of hydrogen absorption / desorption is reported here by forming these composites. Copyright © 2014 VBRI press.

In this paper the preparation of silicon nanowires and their electrochemical characterization as an anode in lithium batteries is reported. The nanowires were synthesized by CVD and characterized by XRD, SEM and EDS. The nanostructured materials were used as electrodes in lithium cells and their electrochemical properties were investigated by galvanostatic charge-discharge cycles at various discharge rates. To evaluate the dependence of the specific capacity and charge coefficient on the end charge potential this parameter was varied during the experimentation. The evolution of the charge transfer resistance, specific capacity, and charge coefficient as a function of the number of the cycles was also investigated. © 2014 Elsevier B.V. All rights reserved.

In this paper the morphological, structural and electrochemical properties of crystalline lithium iron phosphate (LiFePO4) obtained from ferrous ammonium phosphate (FAP) have been studied. The FAP was obtained following four different processes, namely: (1) homogeneous phase precipitation, (2) heterogeneous phase precipitation from stoichiometric sodium phosphate, (3) heterogeneous phase precipitation from stoichiometric ammonium phosphate, and (4) heterogeneous phase precipitation from over stoichiometric ammonium phosphate. Lithium iron phosphate was prepared by solid state reaction of FAP with lithium hydroxide. In order to evaluate the effect of reaction time and synthesis temperature the LiFePO4 was prepared varying the heating temperatures (550, 600 and 700 C) and the reaction times (1 or 2 h). The morphology of the materials was evaluated by scanning electron microscopy while the chemical composition was determined by electron energy loss spectroscopy. X-ray diffraction was used to evaluate phase composition, crystal structure and crystallite size. The so obtained LiFePO4's were fully electrochemical characterized and a correlation was found between the crystal size and the electrochemical performance. © 2013 Elsevier Ltd. All rights reserved.

Magnesium hydride has a high theoretically storage capacity, which amounts to 7.6 wt%. It is therefore a promising candidate for hydrogen storage applications. However, its major drawback is its high desorption temperature of well over 300 °C, which is related to the high stability of the Mg–H bonds and expressed in the high enthalpy of hydride formation (77 kJ/mol). The preparation of Mg composites with other hydrogen storage compounds is an effective method to improve the hydrogen storage properties of Mg. Thus we prepared Mg-50 wt% ZrCrFe alloy composite by high energy ball milling under argon atmosphere. X-ray diffraction (XRD) studies on the composite before and after hydriding cycles suggest no intermetalic phase is formed between Mg and the elements of the alloy. The morphological studies carried on by Scanning Electron Microscope (SEM) technique suggest that the alloy particles are homogeneously distributed throughout the Mg surface. A particle reduction after hydrogenation is also visible. Hydriding/dehydriding properties of the composites are investigated by PCT measurements using a dynamic system. The maximum hydrogen capacity for this composite is found to be 4.5 wt%. The reaction kinetics have also been recorded in a temperature range from RT to 300 °C and the thermodynamic parameters calculated from Van’t Hoff plot. From the results it is found that the alloy reacts with hydrogen also when cooled to room temperature while at higher temperature it works as catalyst.

Chemical hydrides have already been pointed out as great potential hydrogen storage materials. In this paper, the hydrolysis of two solid hydrides, namely sodium borohydride (NaBH4) and lithium hydride (LiH) was studied to check their performance as hydrogen generators. The simplicity of the reactor design, the absence of high pressure or very high temperatures as well as the benignity of the spent fuel make this hydrogen storage approach conceptually feasible. Several devices have been developed and tested. The devices have been designed to generate hydrogen flows in the 0.5–1.0 L min−1 range. Batches up to 500 g of sodium borohydride powder were hydrolyzed with liquid water. 10.0 wt. % nickel acetate was used as catalyst. Hydrogen flows in the desired range have been continuously produced for several hours (up to 30 h). Due to the high reactivity lithium hydride was hydrolyzed without any catalyst. In this case batches of about 50 g have been hydrolyzed with steam for 4 h.

In this paper nickel acetate catalyzed sodium borohydride cartridges have been prepared and hydrolyzed with water for hydrogen production. Two technological solutions have been tested to increase the overall hydrogen yield, namely a porous water diffuser and a hydrophobic membrane. The first was used to improve water diffusion inside the hydride while the second to confine water inside the cartridge. The generated hydrogen flow showed a very reproducible behavior. Hydrogen promptly evolved just after water was pumped into the cartridge. After some initial peaks, a constant hydrogen flow has been recorded for the whole reaction time. The constant flow was related to the presence of the porous diffuser. The use of a hydrophobic membrane to confine the water inside the cartridge allowed to increase the overall hydrogen yield: about 6 water molecules per mol of hydride were required to complete the reaction. The reaction product was identified by XRD as Na2B2O4*8H2O. The cartridge hydrogen gravimetric content, based on water and sodium borohydride weight, was as high as 4.64%.

Steam hydrolysis of lithium hydride was studied at various temperatures (20°C–80°C). To monitor the reaction rate, hydrogen flow was recorded as a function of time. Phase composition of the reaction products was analyzed by XRD spectroscopy. A variation in the reaction mechanism was found for temperatures lower than 70°C when lithium hydride was reduced to 10% of the initial amount. Using XRD analysis it was found that the main product obtained at temperatures ranging from 20°C to 70°C was LiOH.H2O. By increasing the temperature, the percentage of dehydrate slowly increases, and at 80°C the dehydrate represents the main product. A simple model for steam hydrolysis of lithium hydride is proposed taking into consideration the experimental results. The behavior of hydrogen flow was related to water vapor pressure and unreacted lithium hydride amount. The change in the reaction mechanism was related to a variation of water uptake (from the solid phase to the gas phase) to the lithium hydride surface.

The hydrolysis of sodium-borohydride (SBH) to produce hydrogen has been studied at various temperatures using salts of nickel (II) or iron (III) as catalyst. Excess of water has been added to a mixture of solid SBH and catalyst to start hydrolysis reaction and the evolved hydrogen measured as a function of time. After a sudden peak a constant hydrogen flow was observed when Ni is used as catalyst. The activation energy has been evaluated from the dependence of the reaction time and of the hydrogen flow on the inverse of temperature. If Ni is substituted by a Fe based catalyst, after the initial increase, a different shape is observed in the hydrogen flow: it reaches a maximum and then monotonously decrease to zero. The different shape has been related to the different activity of the catalyst. The reaction activation energy was evaluated to be 73 KJ/mol.

A system for a controlled production of hydrogen from solid NaBH 4 has been designed and built. Cartridges of catalysed or non-catalysed NaBH 4 in powder form are fed by water or catalyst solution into a reactor; the reaction is started and tuned by controlling the input water (or water/catalyst solution) flow. We designed, built and tested different reactor layouts and geometries. Tests have been carried out in order to monitor operative parameters (i.e., water flow, reactor temperature) and to evaluate their influence on hydrolysis performance. The facility allows hydrogen flow in the 5–30 L/h range for several hours. The paper reports on the experimental runs and on the main achieved goals.

A device has been designed to generate hydrogen for a fuel cell powered cellular phone. The device is based on the chemical reaction between NaBH 4 and hydrochloric/water solution to satisfy the hydrogen request at room temperature and pressure. The operation mechanism and controlling method is based on the Kipp's gas generating apparatus. A prototype has been built and tested to evaluate the optimum salt/acid and acid/solution ratios and check the hydrogen mass flow rates upon operation and the pressure variation in stand-by condition. The system works delivering hydrogen flows ranging between 0 and 10 ml min −1 . In a typical test the hydrogen flow was set to 5 ml min −1 to match a 1 W power fuel cell. The working pressure was slightly higher than the atmospheric one. The hydrogen capacity was as high as 2.5% (w/w). By converting this amount of hydrogen in electricity by a fuel cell working at 0.8 V it is possible to achieve a system energy density of about 720 Wh kg −1 , four times larger than commercial high energy density lithium-ion batteries.

The thermal decomposition of borane–ammonia complex as well as of milled and doped samples was studied by volumetric titrations. The samples were heated at fixed temperature and the volume of the evolved gas recorded as a function of time. Milled and doped samples were prepared by mechanical and mechanochemical reactions, respectively. Samples containing 1 and 2 mol% hydrogen hexachloroplatinate hydrate were prepared. The materials were characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Mechanical alloying was effective to modify the crystallinity of the complex and to change the material morphology enhancing the amount of gas evolved. Both the milled and the doped samples showed an increase of the pre-exponential factor in the Arrhenius equation. The activation energy decreased for the doped sample, and it increased for the milled sample. As a result it was found that the decomposition of 1 mol% doped sample could be provided by waste heat coming from polymer electrolyte membrane fuel cell.

A fast and easy way to produce LiFePO4 starting from FePO4, used as iron and phosphorus source, is proposed. 5% hydrogen is employed as a reducing agent and various compounds containing lithium as lithiation agents. The selected lithiation agents included: LiCl, CH3COOLi, LiOH, Li2S, LiH, and Li2CO3. Solid state synthesis is used for the LiFePO 4 preparation and the so obtained materials are structurally characterized by XRD. The materials are used to fabricate composite electrode and their specific capacity is evaluated by low rate galvanostatic charge/discharge cycles (C/10 rate). Among the various lithium salts, the acetate give rise to the LiFePO4 with the best electrochemical performance. The morphology of this material is further investigated by SEM microscopy and the specific capacity is evaluated as a function of the discharge rate and the cycle number. © 2014 AIP Publishing LLC.

Biogas utilized for energy production needs to be free from organic silicon compounds, as their burning has damaging effects on turbines and engines; organic silicon compounds in the form of siloxanes can be found in biogas produced from urban wastes, due to their massive industrial use in synthetic product, such as cosmetics, detergents and paints. Siloxanes removal from biogas can be carried out by various methods (Mona, 2009; Ajhar et al., 2010 May; Schweigkofler and Niessner, 2001); aim of the present work is to find a single practical and economic way to drastically and simultaneously reduce both the hydrogen sulphide and the siloxanes concentration to less than 1ppm. Some commercial activated carbons previously selected (Monteleone et al., 2011) as being effective in hydrogen sulfide up taking have been tested in an adsorption measurement apparatus, by flowing the most volatile siloxane (hexamethyldisiloxane or L2) in a nitrogen stream, typically 100-200ppm L2 over N2, through an activated carbon powder bed; the adsorption process was analyzed by varying some experimental parameters (concentration, grain size, bed height). The best activated carbon shows an adsorption capacity of 0.1g L2 per gram of carbon. The next thermogravimetric analysis (TGA) confirms the capacity data obtained experimentally by the breakthrough curve tests. The capacity results depend on L2 concentration. A regenerative carbon process is then carried out by heating the carbon bed up to 200. °C and flushing out the adsorbed L2 samples in a nitrogen stream in a three step heating procedure up to 200. °C. The adsorption capacity is observed to degrade after cycling the samples through several adsorption-desorption cycles. © 2013 Elsevier Ltd.

In this paper a general method to obtain a mixture of a transition metal embedded in a matrix of lithium fluoride is proposed. The method consists in the reduction of the oxide of the transition metal with lithium hydride to form the correspondent transition metal and lithium oxide. This latter is then converted into lithium fluoride by solid state reaction with ammonium fluoride. In this work the proposed method was applied to iron(III) oxide to obtain a mixture of iron metal and lithium fluoride. The crystal structure and phase purity of the intermediate as well as the final product were analyzed by X-ray diffraction measurement and the crystallite dimensions evaluated by using the Scherrer's formula. The iron metal/lithium fluoride mixture was used as a conversion material and its electrochemical properties evaluated by galvanostatic charge discharge cycles, impedance spectroscopy and galvanostatic intermittent titration technique. As the conversion material is in its reduced state it can be coupled with a carbonaceous negative electrode to build a lithium ion battery, opening new perspectives for using conversion materials in lithium ion batteries technology. © 2013 Elsevier Ltd. All rights reserved.

The hydrogen storage properties of doped and undoped NaAlH4 samples are studied after mixing them with different percentages of high surface carbon. Manually mixed samples are compared with ball milled ones; it was found that manual mixing was a simple and effective way to dope NaAlH4. A morphological and micro-structural analysis has been carried out in order to understand the effect of carbon. Carbon added samples show a marked enhancement of hydrogen desorption rate. The desorption temperature and the total hydrogen content remain almost unchanged for undoped sample. The desorption temperatures of Ti-doped samples increase with carbon content. (C) 2006 Elsevier B.V. All rights reserved.