The rapid depletion of conventional fossil fuels and day-by-day growth of environmental pollution due to use of extensive use of fossil fuels have raised concerns over the use of the fossil fuels; and thus search for alternate renewable and sustainable sources for fuels has started in the last few decades. In this context biomass derived fuels seems to be the promising path; and various routes are available for the biomass processing such as pyrolysis, transesterification, hydrothermal liquefaction, steam reforming, etc.; and the hydrothermal liquefaction (HTL) of wet biomass seems to be the promising route. Therefore, this article briefly enlightened a few concepts of HTL such as the elemental composition of bio-crude obtained by HTL, different types of feedstock adopted for HTL, mechanism of HTL processes, possible process flow diagrams for HTL of both wet and dry biomass and energy efficiency of the process. In addition, this article also enlisted possible future research scope for concerned researchers and a few of them are setting up HTL plant suitable for both wet and dry biomass feedstock; analysing influence of parameters such as temperature, pressure, residence time, catalytic effects, etc.; deriving optimized pathways for better conversion; and development of theoretical models representing the process to the best possible accuracy depending on nature of feedstock.

A review on hydrothermal liquefaction of biomass

Due to the finite stock of fossil fuels and its negative impact on the environment, many countries across the world are now leaning toward renewable sources energies like solar energy, wind energy, biofuel, hydropower, geothermal and ocean energy to ensure energy for the countries development security. Biodiesel is one kind of biofuel that is renewable, biodegradable and has similar properties of fossil diesel fuel. The aim of this paper is to provide the substantial information on biodiesel to the researchers, engineers and policy makers. To achieve the goal, this paper summarizes the information on biofuel development, feedstocks around the world, oil extraction technic, biodiesel production processes. Furthermore, this paper will also discuss the advantages of biodiesel compared to fossil fuel. Finally, the combustion behavior of biodiesel in an internal combustion engine is discussed and it will help the researchers and policy maker and manufacturer. To determine the future and goal of automotive technology the study found that, feedstock selection for biodiesel production is very important as it associates 75% production cost. Moreover, the test of fuel properties is very important before using in the engine which depends on the type of feedstocks, origin country, and production process. Most of the researchers reported that the use of biodiesel in diesel engine reduces engine power slightly but reduces the harmful emission significantly. Finally, the study concludes that biodiesel has the potential to be used as a diesel fuel substitute in diesel engines to solve the energy and environment crisis.

Production, characterization and performance of biodiesel as an alternative fuel in diesel engines – A review

The green chemistry era has pushed the scientific community to investigate and implement new solvents in phenolic compounds (PC) extraction as alternatives to organic solvents, which are toxic and may be dangerous. Recently, deep eutectic solvents (DES) have been applied as extraction solvents for PC. They have the advantages of biodegradability and ease of handling with very low toxicity. Nevertheless, the extraction process is affected by several factors: affinity between DES and the target compounds, the water content, the mole ratio between DES’ starting molecules, the liquid/solid ratio between the DES and sample, and the conditions and extraction method. On the other hand, PC recovery from DES is a challenge because they can establish a strong hydrogen bond network. Alternatively, another possibility is to use DES as solvent extraction as well as formulation medium. In this way, DES can be suitable for cosmetics, pharmaceutical, or food applications.

Application of Deep Eutectic Solvents (DES) for Phenolic Compounds Extraction: Overview, Challenges, and Opportunities.

In recent decades, the concern over depletion of the world׳s petroleum reserves and environmental pollution has increased the demand to develop a renewable and environmental friendly fuel. Biodiesel, which mainly consists of Fatty Acid Methyl Esters (FAME) is one of the best substitutes for diesel fuel. Currently, vegetable oils, edible or non-edible, are the main resources of biodiesel. This review aims at providing comprehensive information and analyzes on biodiesel produced from edible and non-edible vegetable oils, their composition and specifications. Accordingly, the Fatty Acid (FA) profiles of 28 edible vegetable oils and 40 non-edible vegetable oils were collected. Their main specifications including sulfur content, density, viscosity, flash point, cloud point, pour point, cold filter plugging point, cetane number, iodine number, heating value, acid value and carbon residual before and after transesterification (vegetable oil and biodiesel, respectively) were analyzed in detail. Many researchers have developed prediction models to quantify biodiesel specifications to optimize its manufacturing and obtain biodiesel with the best specifications. Three factors that are especially influential are the fatty acids profiles, the degree of unsaturation within the FA structures and molecular weight. Accordingly, many models have been constructed on these features. There are also models that quantify the relationship between the biodiesel specifications and its thermodynamic properties or other specifications. Accordingly, the second part of this work was conducted on the existing prediction models. All the models were discussed along with their deviation in prediction.

A comprehensive review on properties of edible and non-edible vegetable oil-based biodiesel: Composition, specifications and prediction models

State of the art and prospective of lipase-catalyzed transesterification reaction for biodiesel production

Co-solvents transesterification of cotton seed oil into biodiesel: Effects of reaction conditions on quality of fatty acids methyl esters

Performance and emission characteristics of an agricultural diesel engine fueled with blends of Sal methyl esters and diesel.

Hydrothermal liquefaction of de-oiled Jatropha curcas cake using Deep Eutectic Solvents (DESs) as catalysts and co-solvents.

High acid content and low calorific value of pyrolysis oil (PO) hindered its application as transportation fuel. This work investigates the supercritical esterification of the acids in PO, as a method of improving its fuel properties using novel green catalysts and co-solvents. Deep eutectic solvents (DESs), prepared from choline chloride (ChCl) with either urea, p -toluene sulfonic acid ( p -TsOH) or glycerol serving as hydrogen bond donors were used both as catalysts and co-solvents. The optimization of reaction conditions for the production of maximum yields of fatty acids methyl esters (FAMEs), which was been monitored by measuring the reduction in its total acid number (TAN) and its corresponding FAMEs conversion is reported. Highest TAN reduction (86.62%) was obtained with ChCl/ p -TsOH DES, in which the ChCl/ p -TsOH DES mixing ratio was 1:4. The FAMEs obtained under optimum reaction conditions showed improvements in the fuel properties, especially using methanol as solvent. In contrast, the use of ChCl/urea DES and ChCl/glycerol DES as catalysts and co-solvents, showed 52.12% and 48% optimum TAN reduction respectively. However, on checking the fuel properties, it were found to be improved. Conclusively, supercritical esterification of PO using DES was effective technique in improving fuel properties, with only carbon residue been below the standard acceptable limits.

Yahaya Alhassan

Papers

Co-solvents transesterification of cotton seed oil into biodiesel: Effects of reaction conditions on quality of fatty acids methyl esters

Performance and emission characteristics of an agricultural diesel engine fueled with blends of Sal methyl esters and diesel.

Hydrothermal liquefaction of de-oiled Jatropha curcas cake using Deep Eutectic Solvents (DESs) as catalysts and co-solvents.

Catalytic upgrading of waste tire pyrolysis oil via supercritical esterification with deep eutectic solvents (green solvents and catalysts)

Co-liquefaction of whole Jatropha curcas seed and glycerol using deep eutectic solvents as catalysts