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Abstract

The contribution of biofuels is expected to continuously increase in the global fuel market, as they are environmentally-friendly and provide renewable energy. Four generations of biofuels are categorized and are primarily based on their feedstock sources and the production technologies that are used. The influence of promising feedstock types and the availability on the production technologies and the fuel properties of advanced-generation biofuels are not systematically examined in the literature. Hence, this research extensively reviews the potential impact of feedstock sources and their variability on the production and characteristics of biofuels. The approaches of theoretical analysis and inference referred to relevant works in the literature were applied. The findings suggest that the potency of the commercialized mass production of advanced-generation biofuels is facilitated by a much more flexible selection and the sufficient availability of promising feedstocks. Lignocellulose biomass is recognized as the most significant feedstock source for second-generation biofuels, while microalgae do the same for third-generation biofuels. Moreover, the microalgae of some strains are able to produce the highest amount of bio-alcohol of all available feedstock sources. The cell walls of lignocellulose biomass and microalgae mostly consist of lignin compounds and cellulose materials, respectively. Biological pretreatment is considered to be the most promising process, prior to biofuel production. The biofuel yields from lignocellulose biomass and microalgae, using biological pretreatments, could increase by 120% and 22-159%, respectively, in comparison with those of any other pretreatment process. Moreover, more double bonds and larger unsaturated fatty acids in raw lipids cause the inferior oxidative stability, but superior fluidity of biofuel. The possible impact of Genetically-Modified Crops (GMC) on the eco-environment and human genes remains a serious concern and requires further tracking and analysis. Genetically-modified technology is still immature to achieve the expected characteristics of biofuels from those modified crops. The unceasing exploitation of promising biomass feedstock sources is crucial for the rapid and steady development of advanced-generation biofuels.

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