Hydrogen is considered to be the most viable energy carrier for the future. Producing hydrogen from ethanol steam reforming would not only be environmentally friendly but also would open new opportunities for utilization of renewable resources, which are globally available. This paper reviews the current state of the steam reforming process of ethanol, examines different catalysts, and, finally, makes a comparative analysis. Different catalysts have been used for the steam reforming of ethanol. Depending on the type of catalysts, reaction conditions, and the catalyst preparation method, ethanol conversion and hydrogen production vary greatly. It was observed that Co/ZnO, ZnO, Rh/Al 2 O 3 , Rh/CeO 2 , and Ni/La 2 O 3 -Al 2 O 3 performed the best, in regard to the steam reforming of ethanol. Currently, hydrogen production from ethanol steam reforming is still in the research and development stage.

Conventional resources mainly fossil fuels are becoming limited because of the rapid increase in energy demand. This imbalance in energy demand and supply has placed immense pressure not only on consumer prices but also on the environment, prompting mankind to look for sustainable energy resources. Biomass is one such environmentally friendly renewable resource from which various useful chemicals and fuels can be produced. A system similar to a petroleum refinery is required to produce fuels and useful chemicals from biomass and is known as a biorefinery. Biorefineries have been categorized in three phases based on the flexibility of input, processing capabilities, and product generation. Phase I has less or no flexibility in any of the three aforementioned categories. Phase II, while having fixed input and processing capabilities, allows flexibility in product generation. Phase III allows flexibility in all the three processes and is based on the concept of high-value low-volume (HVLV) and low-value high-volume (LVHV) outputs. This paper reviews the concept of biorefinery, its types, future directions, and associated technical challenges. An approach of streamlining biorefineries with conventional refineries in producing conventional fuels is also presented. Furthermore, twelve platform chemicals that could be major outputs from an integrated biorefinery are also discussed.

About 80% of the present world energy demand comes from fossil fuels. Unlike using fossil fuels, using hydrogen as an energy source produces water as the only byproduct. Use of hydrogen as an energy source could help to address issues related to energy security including global climate change and local air pollution. Moreover, hydrogen is abundantly available in the universe and possesses the highest energy content per unit of weight compared to any of the known fuels. Consequently, demand for hydrogen energy and production has been growing in the recent years. Membrane separation process is an attractive alternative compared to mature technologies such as pressure swing adsorption and cryogenic distillation. This paper reports different types of membranes used for hydrogen separation from hydrogen-rich mixtures. The study has found that much of the current research has been focused on nonpolymeric materials such as metal, molecular sieving carbon, zeolites, and ceramics. High purity of hydrogen is obtainable through dense metallic membranes and especially palladium and its alloys, which are highly selective to hydrogen. Thin membranes would not only reduce the cost of materials but also increase the hydrogen flux. Metal alloys or composite metal membranes have been used for hydrogen purification. However, metallic membranes are sensitive to some gases such as carbon monoxide and hydrogen sulfide. Therefore, ceramic membranes, inert to poisonous gases, are desirable. Inorganic microporous membranes offer many advantages over thin-film palladium membranes. More importantly, in microporous membranes, the flux is directly proportional to the pressure, whereas in palladium membranes, it is proportional to the square root of the pressure. The paper also discusses the advantages and disadvantages of different hydrogen separation membranes. Also, the paper reports performance of selected membranes in terms of hydrogen selectivity and permeability.

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The demand for energy around the world is increasing, specifically the demand for petroleum-based energy. Appeasing this growing energy demand without irreparably damaging the environment is of primary concern. With rising fuel prices and environmental concerns, alternative fuels could satisfy the need for renewable energy with low environmental impact. Some of the more popular alternative fuels for new vehicles are ethanol, hydrogen, and biodiesel. Although gasoline engines are expected to be replaced by hydrogen-powered fuel cells, compression-ignition engines, the diesel engines, are expected to remain in use for high-power applications because of limitations of hydrogen-storage densities. The viable environmental friendly alternative fuel for compression-ignition engines is methyl esters (commonly known as biodiesel), which is derived from vegetable oils or animal fats. Using biodiesel instead of conventional diesel fuel reduces emissions such as the overall life cycle of carbon dioxide (CO2), particulate matter, carbon monoxide, sulfur oxides (SOx), volatile organic compounds (VOCs), and unburned hydrocarbons significantly. However, biodiesel increases nitrogen oxides (NO x ) emissions, mostly NO and NO2, which are considered as zone A hazardous compounds. This paper reviews the kinetics of NO x formation in relation to thermal, prompt, and fuel NO x formation processes and critically reviews the techniques that have been attempted to reduce NO x emissions from mechanisms to effectively reduce the NO x formation with biodiesel fuel.

A glut of inexpensive glycerol has resulted from expanding biodiesel production around the world. This glycerol could be used as a good renewable source to produce hydrogen fuel. Hydrogen production from glycerol via a steam reforming process over Ni/CeO2, Ni/MgO, and Ni/TiO2 catalysts was studied. The catalysts were characterized by using X-ray diffraction, thermogravimetric analysis, BET surface area analysis, metal dispersion, active surface area analysis, and hydrogen temperature programmed reduction. Ni/CeO2 had the highest surface area (67.0 m2/g) followed by Ni/TiO2 (64.9 m2/g) and Ni/MgO (50.2 m2/g). Also, Ni/CeO2 showed the highest metal dispersion (6.14%) compared to Ni/MgO (0.38%) and Ni/TiO2 (0.29%). Effects of reaction temperatures, feed flow rates (FFRs), and water/glycerol molar ratios (WGMRs) on hydrogen selectivity and glycerol conversion were analyzed. Ni/CeO2 was found to be the best performing catalyst compared to Ni/MgO and Ni/TiO2 under the experimental conditions investigated. Ni/CeO2 gave the maximum hydrogen selectivity of 74.7% at a WGMR of 12:1, temperature of 600 °C, and FFR of 0.5 mL/min compared to Ni/MgO (38.6%) and Ni/TiO2 (28.3%) under similar conditions.

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