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The growth in the global fuel consumption is expected to continue unabated. At the same time, nations around the globe are trying to reduce greenhouse gas emissions resulting from the transportation sector. These factors have led researchers to look for alternative sources of fuels. Biodiesel is one such alternative fuel that can complement or displace petroleum diesel with a potentially lower carbon footprint fuel, depending upon the feedstock and the production process. Biodiesel refers to the monoalkyl esters derived from a wide range of raw materials, like vegetable oils, animal fats, and algae lipids. Conventionally, biodiesel is produced by transesterification with the help of an acid, base or enzyme catalyst. Certain drawbacks, like slow reaction times, soap formation and intense pre‐ and post‐processing, are associated with conventional transesterification, ultimately leading to increased capital and production costs. Supercritical transesterification is a relatively new technique promising to provide advantages, such as faster reaction times, catalyst‐free operation, and higher purity of final product, over the conventional transesterification method. The most common feedstocks are virgin and used edible oils from crops like soybean, rapeseed, and African palm. There is an increasing interest in algae to avoid the utilization of food resources for energy production. Using algae as a lipid source, a more sustainable biodiesel production process could be developed to achieve large‐scale production capabilities on a long‐term basis without adverse effects on the food chain. This paper presents a critical review of supercritical transesterification and its prospects for biodiesel production. WIREs Energy Environ 2017, 6:e252. doi: 10.1002/wene.252 This article is categorized under: Bioenergy > Science and Materials Bioenergy > Systems and Infrastructure Energy and Development > Science and Materials

Summary Carbon black (CB) obtained from used car tire rubbers were treated with concentrated sulfuric and nitric acids. The oxidized CB (CB‐COO‐Na+) is subsequently modified with epichlorohydrin (ECH) and amines including polyethylene imine (PEI). These modified CBs such as CB‐PEI are used as metal‐free catalysts in methanolysis of sodium borohydride (NaBH4) to produce hydrogen. The hydrogen generation rate (HGR) of 3089 ± 44.69 mL.min‐1.g‐1 is accomplished at room temperature with CB‐PEI‐hydrochloric acid (HCl) catalyst. The resulting activation energy of 34.7 kJ/mol for the temperature range of −20°C to +30°C compares favorably to most of alternative catalysts reported in literature while reaction catalyzing capabilities of CB‐PEI‐HCl particles extend to the subzero temperature range (−20°C‐0°C). The reuse and regeneration studies conducted for the CB‐PEI‐HCl catalyst showed that these catalysts do provide complete conversion at every use up to five consecutive runs and retain 50 ± 2.5% of the original hydrogen generation rate at the fifth consecutive reuse. The CBs‐based catalysts are fully regenerated with HCl treatment.