Crude glycerol is the main byproduct of biodiesel manufacturing from oleaginous crops and other biomass-derived oils. Approximately 10% crude glycerol is produced with every batch of biodiesel. Worldwide, there is a glut of glycerol and the price of it has decreased considerably. There are real opportunities for valorizing crude glycerol into higher value-added chemicals which can improve the economic viability of biodiesel production as an alternative fuel. Exploring new potential applications of glycerol in various sectors is needed such as in pharmaceuticals, food and beverages, cosmetics, and as a transportation fuel. However, crude glycerol produced directly from biodiesel often contains impurities that hinder its direct industrial usage and thus, a refining process is needed which is typically expensive. Hence, this review reports on current upgrading crude glycerol technologies—thermo-, bio-, physico-, and electrochemical approaches—that valorize it into higher value-added chemicals. Through comparison between those viable upgrading techniques, future research directions, challenges, and advantages/disadvantage of the technologies are described. Electrochemical technology, which is still underdeveloped in this field, is highlighted, due to its simplicity, low maintenance cost, and it working in ambient condition, as it shows promising potential to be applied as a major glycerol upgrading technique.

The quest for sustainable and environmentally friendly fuel feedstocks has led to the exploration of green solvents for the extraction of bio-oil from various biomass sources. This review paper provides a comprehensive analysis of the challenges and future research outlooks for different categories of green extraction solvents, including bio-based solvents, water-based solvents, supercritical fluids, and deep eutectic solvents (DES). The background of each solvent category is discussed, highlighting their potential advantages and limitations. Challenges such as biomass feedstock sourcing, cost fluctuations, solvent properties variability, limited compatibility, solute solubility, high costs, and potential toxicity are identified and examined in detail. To overcome these challenges, future research should focus on alternative and abundant feedstock sources, the development of improved solubility and separation techniques, optimization of process parameters, cost-effective equipment design, standardization of DES compositions, and comprehensive toxicological studies. By addressing these challenges and advancing research in these areas, the potential of green extraction solvents can be further enhanced, promoting their widespread adoption and contributing to more sustainable and environmentally friendly industrial processes.

The start of art SAFs production routes and HTL potential for overcoming challenges.

The food wastage problem and its associated issues have become a significant threat to sustainable development, particularly in developing countries. Cooked rice, which has been reported to be one of the most abundant regional food wastes, is a substantial feedstock for biofuel production due to its rich carbon content. In this study, both solid-state and acetone–butanol–ethanol (ABE) fermentations were conducted in series with Aspergillus oryzae and aero-tolerant Clostridium acetobutylicum YM1 for the biobutanol production. To validate the process parameters for an industrial-scale process, it is critical to examine the effects of process parameters using a process simulation tool. To this end, by adapting lab-scale process results, a techno-economic evaluation of the biobutanol production from the cooked rice by two-step fermentation was performed using SuperPro Designer®. This study aims to examine various scenarios for cooked rice utilization to produce butanol while examining process optimization and minimization of operational expenses for the aerobic ABE fermentation and microbial saccharification. According to the simulation results, butanol production cost was estimated to be 1.24 $ kg⁻¹, incorporating a cost reduction of 0.58 $ kg⁻¹ from heat integration, steam and power generation, while eliminating costs for the unnecessary commercial enzymes and N₂ gas for purging. Finally, sensitivity analysis was applied to demonstrate the plant feasibility concerning potential fluctuations in the changing biofuel market and environmental conditions.