Fossil fuels have been a major contributor to greenhouse gases, the amounts of which could be reduced if biofuels such as bioethanol and biodiesel were used for transportation. One of the most promising biofuels is ethyl alcohol. In 2015, the world production of ethanol was 25.6 billion gallons and the USA, Brazil, China, the European Union, and 28 other countries have set targets for blending ethanol with gasoline. The two major bio-source materials used for ethanol production are corn and sugarcane. For 1st generation biofuels, sugarcane and corn feedstocks are not able to fulfill the current demand for alcohol. Non-edible lignocellulosic biomass is an alternative bio-source for creating 2nd generation biofuels and algae biomass for 3rd and 4th generation biofuels. This review discusses the significance of biomass for the different generations of biofuels, and biochemical and thermochemical processes, and the significance of biorefinery products.

Microwave-assisted deep eutectic solvent (DES) has received attention as an ultrafast pretreatment method in lignocellulose fractionation. This study investigated the improvement of milled softwood mixture (MSM) fractionation with chlorine chloride-formic acid (ChCl:FA) to obtain residues with high glucan retention and purity while removing majority of the lignin and hemicelluloses. At the optimum pretreatment conditions i.e., ChCl:FA (1:4), 140 °C, 14 min, 800 W and 15 % (w/v), 96.2 % hemicellulose removal, 90.1 % delignification and 93.5 % glucan retention were achieved. About 85 % lignin was recovered with a 95 % purity when solid loading was 10-20 % (w/v). This study showed that microwave assisted ChCl:FA pretreatment was a suitable means to fractionate MSM to achieve high quality glucan and lignin at high solid loading.

Growing interest in lignocellulosic bioethanol stems from the European Union's renewable energy directive, targeting a global bioethanol output of 130 billion L to achieve a minimum threshold of 42.5%. Despite industrialization challenges, recent advancements, especially in crucial stages like pretreatment, hydrolysis, and fermentation, are transforming the landscape. This review delves into the progress of bioethanol production, addressing technological, environmental, and economic hurdles. Innovations such as deep eutectic solvent pretreatment and mechanocatalysis, offering advantages like 30% and 100% solid loading, respectively, surpass traditional techniques and enzymatic hydrolysis in yielding better results. Improved pretreatment methods, enzyme exploration, saccharification techniques, genetic engineering, and integrated biorefineries contribute to overall economic viability. Ongoing research involves techno-economic analysis for cost-effective strategies, aiming to enhance the competitiveness of lignocellulosic bioethanol production. Scrutinizing the feasibility of these innovative approaches not only highlights their potential to overcome existing shortcomings but also envisions a more attractive future for industrial bioethanol production. Embracing these advancements could pave the way for a vibrant and sustainable bioethanol industry.