Biohydrogen production from Imperata cylindrica bio-oil using non-stoichiometric and thermodynamic model

This paper presents a non-stoichiometric and thermodynamic model for steam reforming of Imperata cylindrica bio-oil for biohydrogen production. Thermodynamic analyses of major bio-oil components such as formic acid, propanoic acid, oleic acid, hexadecanoic acid and octanol produced from fast pyrolysis of I. cylindrica was examined. Sensitivity analyses of the operating conditions; temperature (100–1000 °C), pressure (1–10 atm) and steam to fuel ratio (1–10) were determined. The results showed an increase in biohydrogen yield with increasing temperature although the effect of pressure was negligible. Furthermore, increase in steam to fuel ratio favoured biohydrogen production. Maximum yield of 60 ± 10% at 500–810 °C temperature range and steam to fuel ratio 5–9 was obtained for formic acid, propanoic acid and octanol. The heavier components hexadecanoic and oleic acid maximum hydrogen yield are 40% (740 °C and S/F = 9) and 43% (810 °C and S/F = 8) respectively. However, the effect of pressure on biohydrogen yield at the selected reforming temperatures was negligible. Overall, the results of the study demonstrate that the non-stoichiometry and thermodynamic model can successfully predict biohydrogen yield as well as the composition of gas mixtures from the gasification and steam reforming of bio-oil from biomass resources. This will serve as a useful guide for further experimental works and process development.     

On the dynamics and reversibility of the deactivation of a Rh/CeO2ZrO2 catalyst in raw bio-oil steam reforming

The deactivation mechanism of a commercial Rh/CeO₂ZrO₂ catalyst in raw bio-oil steam reforming has been studied by relating the evolution with time on stream of the bio-oil conversion and products yields and the physicochemical properties of the deactivated catalyst studied by XRD, TPR, SEM, XPS, TPO and TEM. Moreover, the reversibility of the different deactivation causes has been assessed by comparing the behavior and properties of the catalyst fresh and regenerated (by coke combustion with air). The reactions were carried out in an experimental device with two units in series: a thermal treatment unit (at 500 °C, for separation of pyrolytic lignin) and a fluidized bed reactor (at 700 °C, for the reforming reaction). The results evidence that structural changes (support aging involving partial occlusion of Rh species) are irreversible and occur rapidly, being responsible for a first deactivation period, whereas encapsulating coke deposition (with oxygenates as precursors) is reversible and evolves more slowly, thus being the main cause of the second deactivation period. The deactivation selectively affects the reforming of oxygenates, from least to greatest reactivity. Rh sintering is not a significant deactivation cause at the studied temperature.     

Application of exhaust gas fuel reforming in diesel and homogeneous charge compression ignition (HCCI) engines fuelled with biofuels

This paper documents the application of exhaust gas fuel reforming of two alternative fuels, biodiesel and bioethanol, in internal combustion engines. The exhaust gas fuel reforming process is a method of on-board production of hydrogen-rich gas by catalytic reaction of fuel and engine exhaust gas. The benefits of exhaust gas fuel reforming have been demonstrated by adding simulated reformed gas to a diesel engine fuelled by a mixture of 50% ultra low sulphur diesel (ULSD) and 50% rapeseed methyl ester (RME) as well as to a homogeneous charge compression ignition (HCCI) engine fuelled by bioethanol. In the case of the biodiesel fuelled engine, a reduction of NO_x emissions was achieved without considerable smoke increase. In the case of the bioethanol fuelled HCCI engine, the engine tolerance to exhaust gas recirculation (EGR) was extended and hence the typically high pressure rise rates of HCCI engines, associated with intense combustion noise, were reduced.     

Indirect land use change and biofuels: Mathematical analysis reveals a fundamental flaw in the regulatory approach

In the Renewable Fuel Standard (RFS2) program, the United States Environmental Protection Agency (U.S. EPA) has used partial equilibrium models to estimate the overall indirect land use change (iLUC) associated with the biofuel scenario mandated by the Energy Independence and Security Act of 2007 (EISA). For regulatory purposes, the U.S. EPA “shocks” (changes) the amount of each biofuel in the economic models one at a time to estimate the threshold values for specific biofuels (single-shock analysis). The primary assumption in the single-shock analysis is that iLUC is a linear process with respect to biofuels, i.e., that interactions between different biofuels are trivially small. However, the assumption of linearity in the single-shock analysis is not appropriate for estimating the threshold values for specific biofuels when the interactions between different biofuels are not small.Numerical results from the RFS2 program show that the effects of interactions between different biofuels are too large to be ignored. Thus, the threshold values for specific biofuels determined by the U.S. EPA are scenario-dependent and value choice-driven. They do not reflect real impacts of specific biofuels. Using scenario-dependent values for regulation is arbitrary and inappropriate. Failure to deal appropriately with interactions between different biofuels when assigning iLUC values to specific biofuels is a mathematical and systematic flaw; it is not an “uncertainty” issue. The U.S. EPA should find better ways to differentiate the contribution of one biofuel versus another when assigning iLUC values or find better means of regulating the land use change impact of biofuel production.     

Progress and recent trends in homogeneous charge compression ignition (HCCI) engines

HCCI combustion has been drawing the considerable attention due to high efficiency and lower nitrogen oxide (NO_x) and particulate matter (PM) emissions. However, there are still tough challenges in the successful operation of HCCI engines, such as controlling the combustion phasing, extending the operating range, and high unburned hydrocarbon and CO emissions. Massive research throughout the world has led to great progress in the control of HCCI combustion. The first thing paid attention to is that a great deal of fundamental theoretical research has been carried out. First, numerical simulation has become a good observation and a powerful tool to investigate HCCI and to develop control strategies for HCCI because of its greater flexibility and lower cost compared with engine experiments. Five types of models applied to HCCI engine modelling are discussed in the present paper. Second, HCCI can be applied to a variety of fuel types. Combustion phasing and operation range can be controlled by the modification of fuel characteristics. Third, it has been realized that advanced control strategies of fuel/air mixture are more important than simple homogeneous charge in the process of the controlling of HCCI combustion processes. The stratification strategy has the potential to extend the HCCI operation range to higher loads, and low temperature combustion (LTC) diluted by exhaust gas recirculation (EGR) has the potential to extend the operation range to high loads; even to full loads, for diesel engines. Fourth, optical diagnostics has been applied widely to reveal in-cylinder combustion processes. In addition, the key to diesel-fuelled HCCI combustion control is mixture preparation, while EGR is the main path to achieve gasoline-fuelled HCCI combustion. Specific strategies for diesel-fuelled, gasoline-fuelled and other alternative fuelled HCCI combustion are also discussed in the present paper.     

Steam enhanced carbon dioxide reforming of methane in DBD plasma reactor

Considering the inevitable high energy input to implement the CO₂ reforming of methane under high-temperature operation using conventional catalysis method, the low temperature conversion of CO₂ and methane in the coaxial dielectric barrier discharge (DBD) plasma reactor was investigated in this work. Steam was introduced to enhance the CO₂ reforming of methane with synergetic catalysis effect by cold plasma and catalyst. The experimental results showed that a certain percent of steam could promote the conversion of both CH₄ and CO₂. Meanwhile, the carbon deposition was evidently reduced compared with the dry reforming of methane. With the increase of steam input, the steam reforming occurred predominantly. As a result, the hydrogen volume percentage in the product gases increased. In this way, the products with different H₂/CO ratio could be achieved by changing the mole ratio of CH₄/CO₂/H₂O at the reactor inlet. In particular, when the mole ratio of H₂O/CH₄ increased to almost 3 corresponding to the pure steam reforming process, the conversion of CH₄ reached almost 0.95 and the selectivity to H₂ was almost 0.99 at 773K.     

Simultaneous production of ultrapure hydrogen and gasoline in a novel thermally coupled double‐membrane reactor

In this study, simultaneous production of ultrapure hydrogen and gasoline via a novel catalytic fixed‐bed double‐membrane reactor with co‐current flow was investigated, mathematically. The thermally coupled double‐membrane reactor (TCDMR) consists of two Pd/Ag membranes, one for separation of pure hydrogen from endothermic side and another one for permeation of hydrogen from endothermic into exothermic side. Ammonia decomposition reaction is coupled with the Fischer–Tropsch Synthesis (FTS) reaction to improve the heat transfer between endothermic and exothermic sides. Some of the produced hydrogen via ammonia decomposition reaction is utilized in FTS reaction, and the other is extracted and stored. A steady‐state heterogeneous model of the two fixed beds predicts the performance of this novel configuration. The achieved results of this simulation have been compared with the results of the conventional fixed‐bed reactor (CR) at identical process conditions. The simulation results show 67.34% hydrogen production in the permeation side and 32.66% hydrogen utilization in the exothermic side for compensates of hydrogen lack in the FTS reaction through the TCDMR configuration. Moreover, the gasoline yield in TCDMR increases about 18.42% because of a favorable profile of temperature along the TCDMR in comparison with the one in CR. Therefore, this approach utilizes and produces large amounts of pure hydrogen and decreases environmental impacts owing to ammonia emission. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over trimethylbenzene-assisted ordered mesoporous nickel–alumina catalyst

A trimethylbenzene (TMB)-assisted ordered mesoporous nickel–alumina catalyst (denoted as TNA) was prepared by a single-step evaporation-induced self-assembly (EISA) method, and it was applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, an ordered mesoporous nickel–alumina catalyst (denoted as NA) was also prepared by a single-step EISA method in the absence of TMB. Pore volume and average pore diameter of TNA catalyst were larger than those of NA catalyst due to structural modification caused by TMB addition in the preparation of TNA catalyst. In addition, TNA catalyst showed less ordered mesoporous array than NA catalyst. Both NA and TNA catalysts exhibited diffraction patterns corresponding to nickel aluminate phase, and they retained surface nickel aluminate phase with high stability and reducibility. Crystallite size of metallic nickel in the reduced TNA catalyst was smaller than that in the reduced NA catalyst due to strong nickel–alumina interaction of surface nickel aluminate phase over TNA catalyst. In the hydrogen production by steam reforming of LNG, TNA catalyst with small crystallite size of metallic nickel showed a better catalytic performance than NA catalyst in terms of LNG conversion and hydrogen yield. Furthermore, steam reforming reaction rather than water–gas shift reaction favorably occurred over TNA catalyst.     

Progress and recent utilization trends in combustion of Chinese oil shale

The gradual decrease in conventional energy resources, and the growth of heavy industry, have placed great pressure on China's energy supplies. As a result of technological development, clean and diverse energy utilization facilities have become available in the energy market. Oil shale with combustible organic materials is widespread throughout the earth; many researchers have been motivated to investigate efficient means to use oil shale as an alternative energy as soon as possible.

In China, the conventional utilization of oil shale is concentrated mainly on oil shale retorting, and burning oil shale in pulverized furnaces, or bubbling fluidized beds. To improve the availability of oil shale, many specialists have advocated burning oil shale in a circulating fluidized bed (CFB), which has a satisfactory combustion efficiency, low NO_X and SO₂ emission, adaptability to low-grade coal, etc. In Huadian, China, a plant incorporating three units of 65 t h⁻¹ oil shale-fired CFB began successful commercial operation in 1996, proving that burning oil shale in a CFB produces both high combustion efficiency and environmental protection. For effective utilization of oil shale, its pyrolysis and combustion characteristics, emission performance of gaseous pollutants from an oil shale-fired CFB pilot setup, co-combustion characteristics of oil shale and high sulfur coal—as well as the operating performance of the Huadian CFB boiler—were further studied. The resulting experimental data and theoretical analysis prove that oil shale resources have significant potential use in the combustion field.

This paper introduces these fundamental characteristics and the industrial application of oil shale in combustion. Three projects are recommended for the future use of oil shale, based on the current status of energy and the characteristics of oil shale: (1) co-combustion of oil shale and high sulfur fuel for furnace desulfurization; (2) large-scale development of oil shale-fired CFBs; (3) a comprehensive oil shale utilization project to produce shale oil, burn oil-shale semicoke in a CFB boiler to generate electricity and supply heat, and produce building materials with oil shale ash.     

Catalysts for hydrogen production in a multifuel processor by methanol,dimethyl ether and bioethanol steam reforming for fuel cell applications

Methanol, dimethyl ether and bioethanol steam reforming to hydrogen-rich gas were studied over CuO/CeO₂ and CuO–CeO₂/γ-Al₂O₃ catalysts. Both catalysts were found to provide complete conversion of methanol to hydrogen-rich gas at 300–350 °C. Complete conversion of dimethyl ether to hydrogen-rich gas occurred over CuO–CeO₂/γ-Al₂O₃ at 350–370 °C. Complete conversion of ethanol to hydrogen-rich gas occurred over CuO/CeO₂ at 350 °C. In both cases, the CO content in the obtained gas mixture was low (<2 vol.%). This hydrogen-rich gas can be used directly for fuelling high-temperature PEM FC. For fuelling low-temperature PEM FC, it is needed only to clean up the hydrogen-rich gas from CO to the level of 10 ppm. CuO/CeO₂ catalyst can be used for this purpose as well. Since no individual WGS stage, that is necessary in most other hydrogen production processes, is involved here, the miniaturization of the multifuel processor for hydrogen production by methanol, ethanol or DME SR is quite feasible.     

Steam reforming of methanol for ultra-pure H2 production in a membrane reactor: Techno-economic analysis

Process simulation and design as well as economic analysis were carried out to evaluate technical and economic feasibility of steam reforming of methanol in a membrane reactor (MR) for ultra-pure H₂ production. Using a commercial process simulator, Aspen HYSYS®, comparative studies were conducted to investigate the effect of operating conditions including the H₂ permeance (1 × 10⁻⁵ - 6 × 10⁻⁵ mol m⁻² s⁻¹ Pa⁻¹), a H₂O sweep gas flow rate (1–20 kmol h⁻¹), and a reaction temperature (448–493 K) in a conventional packed-bed reactor (PBR) and the MR using a previously reported reaction kinetics. Improved performances such as methanol conversions and H₂ yields were observed in the MR compared to the PBR and several design guidelines for the MR were obtained to develop H₂ separation membranes with optimal H₂ permeance and to select a suitable H₂O sweep gas flow rate. In addition, economic analysis based on itemized cost estimations was conducted for a small-sized H₂ fueling station by calculating a unit H₂ production cost for both the PBR and the MR reflecting a current economic status in Korea. As a result, a cost saving of about 23% was obtained in the MR (7.24 $ kgH₂⁻¹) compared to the PBR (9.37 $ kgH₂⁻¹) confirming the benefit of employing the MR for ultra-pure H₂ production.     

Integrating safety and economics in designing a steam methane reforming process

The recent explosion at a steam reforming facility producing hydrogen in California, U.S., suggests the need to revisit the design of the traditional steam methane reforming (SMR) process from a safety perspective to further enable the growth of the hydrogen economy. Specifically, it is important to analyze the interaction between process, economic and safety variables within the SMR process through an integrated model approach to maintain positive economics of hydrogen production while making the process safer. The integrated model described within this study consists of process synthesis, quantitative risk assessment and economic analysis sub-models facilitating a holistic design for the SMR process. The usefulness of the integrated model is demonstrated by evaluating alternatives based on the inherently safer design philosophy. For the considered base design, it was found that decreasing the pressure of purge gas exiting the purge gas compressor leads to a reduction in the jet-fire axial risk distance of purge gas with minor economic benefits. Also, increasing the temperature of syngas entering the condensation unit leads to a reduction in the jet-fire axial risk distance for both purge gas and syngas with slight decrease in process economics.     

Production of hydrogen via steam reforming of acetic acid over Ni and Co supported on La2O3 catalyst

Nickel (Ni)-cobalt (Co) supported on lanthanum (III) oxide (La₂O₃) catalyst was prepared via impregnation technique to study the steam reformation of acetic acid for hydrogen generation by using one-step fixed bed reactor. Moreover, in order to specify the physical and the chemical attributes of the catalyst, X-ray diffraction (XRD), nitrogen physisorption, temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia and carbon dioxide (TPD-NH₃ and CO₂), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) methods were employed. The nitrogen physisorption analysis showed that the presence of Co on Ni/La₂O₃ improved the textural properties of the catalyst by increasing the surface area, the pore diameter and the pore volume of the catalyst. This improved the dispersion of metal particle and caused a reduction in the size of metal particle, and consequently, increased the catalytic activity, as well as the resistance to coke formation. On top of that, the condensation and the dehydration reactions during acetic acid steam reforming created carbon deposition on acidic site of the catalyst, which resulted in the deactivation of catalyst and the formation of coke. Besides, in this study, Ni/La₂O₃ contributed to a high acetic acid conversion (100%) at 700 °C, but it produced more coking compared to Ni–Co/La₂O₃ and Co/La₂O₃ catalysts.     

Transient reaction and exergy analysis of catalytic partial oxidation of methane in a Swiss-roll reactor for hydrogen production

Catalytic partial oxidation of methane (CPOM) is a promising method for hydrogen production with autothermal reaction. To figure out the unsteady reaction characteristics of CPOM in a Swiss-roll reactor along with heat recirculation, a numerical method is employed to simulate the transient reaction dynamics, with emphasis on energy recovery using exergy analysis. Three different gas hourly space velocities (GHSVs) of 5000, 10,000 and 50,000 h⁻¹ with the condition of atomic O/C ratio of 1 are considered. The predictions indicate that increasing GHSV substantially shortens the transient period of chemical reactions; however, it also reduces the methane conversion, as results of more reactants sent into the reactor and shorter residence time of the reactants in the catalyst bed. Within the investigated range of GHSV, the methane conversion with energy recovery at the steady state is larger than 80%, much higher than the reaction without heat recovery. The selectivities of H₂ and CO in the product gas are always larger than 90%. The exergy recovery is in the range of 66–80%, implying that over two-third useful work contained in the product gas can be reused to preheat the reactants in the reactor, thereby enhancing the performance of CPOM.     

Green synthesis,properties, and catalytic application of zeolite (P) in production of biofuels from bagasse

This study reports the technical and economic feasibilities of converting sugar cane residue (bagasse) into biofuel by using novel zeolite (P) catalyst. Using silica gel, aluminum powder, and sodium hydroxide as a precursor material, zeolite (P) has been successfully fabricated by template free hydrothermal synthesis. The as‐prepared catalyst is used for the conversion of sugarcane residue into valuable hydrocarbons by an autoclaving process. The effect of various parameters on catalytic and conventional (noncatalytic) pyrolysis was scrutinized and compared. It has been recognized that conventional pyrolysis (without catalyst) and catalytic pyrolysis (with Cat (I) and Cat (II)) produced 25.06%, 80.31%, and 55.26% of combustible liquid. The facial synthesis, high thermal stability, and economic and environmental feasibilities of the as‐synthesized zeolite (P) makes it a promising catalyst for biofuel production from biomass.     

Energy balance and GHG-abatement cost of cassava utilization for fuel ethanol in Thailand

Since 2001, in order to enhance ethanol's cost competitiveness with gasoline, the Thai government has approved the exemption of excise tax imposed on ethanol, controlling the retail price of gasohol (a mixture of ethanol and gasoline at a ratio of 1:9) to be less than that of octane 95 gasoline, within a range not exceeding 1.5 baht a litre. The policy to promote ethanol for transport is being supported by its positive effects on energy security and climate change mitigation. An analysis of energy, greenhouse gas (GHG) balances and GHG abatement cost was done to evaluate fuel ethanol produced from cassava in Thailand. Positive energy balance of 22.4 MJ/L and net avoided GHG emission of 1.6 kg CO₂ eq./L found for cassava-based ethanol (CE) proved that it would be a good substitute for gasoline, effective in fossil energy saving and GHG reduction. With a GHG abatement cost of US$99 per tonne of CO₂, CE is rather less cost effective than the many other climate strategies relevant to Thailand in the short term. Opportunities for improvements are discussed to make CE a reasonable option for national climate policy.     

The role of aluminum in the formation of Ni–Al–Co-containing porous ceramic converters with high activity in dry and steam reforming of methane and ethanol

The role of aluminum in the formation of Ni–Al–Co-containing porous ceramic membrane-catalytic converters (MCC) obtained by SHS method, which are high-active in dry and steam reforming of methane, ethanol and fusel alcohols into synthesis gas, was discovered. It was shown that the aluminum introduced into the charge through mechanical alloying leads to a significant increase in the catalytic activity of the converter in the studied processes, as compared to aluminum introduced by mechanical mixing. In this case, the addition of 5% aluminum to the initial nickel charge allows achieving of maximum productivity for syngas against other studied concentrations of Al. The Al content increase above the optimum leads to a significant formation of the catalytically inactive phase of Ni₃Al intermetallide. TEM and X-ray diffraction methods show that due to oxidation-reduction phase transformations involving aluminum there occurs the formation of metal oxides on the basis of γ-Al₂O₃ with the structure of spinel having nanosized Ni–Co alloy particles formed on its surface during the reductive activation stage.     

Hydrogen-rich gas production by steam gasification of char derived from cyanobacterial blooms (CDCB) in a fixed-bed reactor: Influence of particle size and residence time on gas yield and syngas composition

Char derived from cyanobacterial blooms (CDCB), by-product of fast pyrolysis of cyanobacterial blooms from Dianchi Lake (Yunnan Province, China) at a final pyrolysis temperature of 500 °C were used as feedstock material in this study. Steam gasification characteristics of CDCB were investigated in a fixed-bed reactor to evaluate the effect of particle size (below 0.15 mm, 0.15–0.3 mm, 0.3–0.45 mm, 0.45–0.9 mm, 0.9–3 mm) and solid residence time (3, 6, 9, 12, 15 min) on gas yield and composition, and experiments were carried out at bed temperature range of 600–850 °C, steam flow rate of 0.178 g/min. The results showed that solid residence time played an important role on steam gasification process, while particle size presented less effect on gasification process; proper particle size and longer residence time were favorable for dry gas yield and carbon conversion efficiency (CCE). At the same time, higher reaction temperature reduced influence of particle size on gasification process, and smaller particle size required less residence time for reaction completed. Maximum dry gas yield and CCE reached 1.84 Nm³ kg⁻¹ and 98.82%, respectively, achieved at a temperature of 850 °C, flow rate of 0.178 g/min, solid residence time of 15 min and particle size range of 0.45–0.9 mm.     

Optimizing the production of hydrogen and 1,3-propanediol in anaerobic fermentation of biodiesel glycerol

The conversion of glycerol in biodiesel waste streams to valuable products (e.g. hydrogen and 1,3-propanediol (1,3-PD)) was studied through batch-mode anaerobic fermentation with organic soil as inoculum. The production of hydrogen in headspace and 1,3-PD in liquid phase was examined at different hydrogen retention times (HyRTs), which were controlled by gas-collection intervals (GCIs) and initial gas-collection time points (IGCTs). Two purification stages of biodiesel glycerol (P2 and P3) were tested at three concentrations (3, 5 and 7 g/L). Longer HyRT (longer GCI and longer IGCT) led to lower hydrogen yield but higher 1,3-PD yield. The P3 glycerol at the concentration of 7 g/L had the highest 1,3-PD yield (0.65 mol/mol glycerol_consumed) at the GCI/IGCT of 20 h/65 h and the highest hydrogen yield (0.75 mol/mol glycerol_consumed) at the GCI/IGCT of 2.5 h/20 h), respectively. A mixed-order kinetic model was developed to simulate the effects of GCI/IGCT on the production of hydrogen and 1,3-PD. The results showed that the production of hydrogen and 1,3-PD can be optimized by adjusting HyRT in anaerobic fermentation of glycerol.     

Fundamentals and recent advances in polymer composites with hydride-forming metals for hydrogen storage applications

Hydrogen has unique properties that make it a promising energy vector to replace fossil fuels. However, it is still required to develop safe and efficient storage methods before being widely implemented. Storing hydrogen in hydride-forming metals (HFM) is an approach that has been extensively studied in the last decades. But only recently the preparation of polymer composites with HFM have been explored. Air resistance, volumetric stability and processability are some of the HFM properties that could be improved by incorporating a polymer phase. This review presents the fundamentals concepts of gas transport in dense polymers, and the evolution and trends of incorporating HFM particles into a polymer matrix. The most recent findings are summarized and discussed. The potential improvement of the most relevant classes of HFM and the mechanisms of how different classes of polymers could be advantageously used are reported.