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Graphical abstract Highlights • Biofuel production by supercritical ethyl acetate was studied in fixed-bed reactor. • Synthesized biofuel properties nearly met the biodiesel standards. • The excess of triacetin content greatly increased density of biofuel. • Thermal stress strongly affected on cold flow properties of biofuel. • The utilization of alumina balls contributed to cleanliness of biofuel. Abstract This study aimed to investigate the effects of temperature, ethyl acetate to palm oil molar ratio, residence time, and packing alumina balls on triglyceride conversion, ethyl ester, and acetin contents. The complete triglyceride conversion was observed at 1.35 ± 0.05 times of the transition temperature. The packed alumina enhanced the ester content up to 20%; but it had no effect on the acetin content. Furthermore, this study also intended to determine the effects of the acetin content and thermal cracking on 19 fuel properties of lipid-based biofuel samples synthesized by supercritical ethyl acetate. The optimal condition was found at 380 °C, 20 MPa and ethyl acetate to oil molar ratio of 30:1. First, the density and kinematic viscosity of the biofuels were slightly higher than the maximum values specified by standards because of the presence of triacetin and polymerized products. Second, packing alumina balls increase the mixing intensity and thermal conductivity inside the tubular reactor resulted in higher contents of sulfated ash and carbon residue. Third, the acid values of the biofuel samples were considerably higher than the standard value of biodiesel. However, copper strip corrosion testing resulted in slight tarnishing (level 1A). The corrosiveness of fuels mainly originates from their sulfur compound content, neither biofuel sample was classified as a corrosive material. Furthermore, the high acid values of the samples interfered with the testing of oxidation stability. Finally, beneficial effects of triacetin on cold flow properties were revealed in this study. The cloud point and cold filter plugging point of lipid-based biofuels strongly depended on the thermal stress of the reaction conditions rather than the triacetin concentration. [ABSTRACT FROM AUTHOR]

Abstract: This review aims to provide up-to-date knowledge on existing feedstocks for biofuels production (mainly biodiesel) from lipid-based biomasses. The 1st generation of lipid-based feedstocks was edible plant oils, whilst other alternative feedstocks were discovered and reported as the 2nd generation feedstocks. The 2nd generation feedstocks that are summarized in this work include non-edible oils, waste vegetable oil, animal fats, industrial wastes and by-products, lipid derived from insects and microorganisms. The general strong points of the 2nd generation feedstocks are that they are inexpensive, of high productivity and typically do not compete ethically or economically with food crops (edible oils). However, all 2nd generation feedstocks usually have a high level of moisture and free fatty acids that cause an extremely negative effect on conventional biodiesel production process. Thus, this article provides basic information on the processing techniques that are capable of handling 2nd generation feedstocks as well. [Copyright &y& Elsevier]

The techno-economic analysis of biodiesel production with supercritical methanol (SCM) at a low methanol: oil molar ratio (L-SCM) of 12:1, as well as with a homogeneous alkali-catalyzed process (Alkali-cat) and conventional SCM (C-SCM) with a methanol: oil molar ratio of 42:1 was investigated. The process simulation was performed using the Aspen plus ® software based on the plant biodiesel production capacity of 40,000 tonnes/y. Even though the L-SCM had a higher total capital investment than the Alkali-cat process ($7.19 million versus $4.91 million), it was economically viable. The L-SCM process provided a lower manufacturing cost of $37.28 million and the highest net present value (NPV) of $45.48 million. However, the C-SCM process was not financially profitable because of the large amount of methanol employed in the recycling loop. Sensitivity analysis of all the processes was investigated based on variations in the feedstock and products selling price and revealed that the biodiesel selling price and palm oil price were the major effects on the sensitivity of the NPV. [ABSTRACT FROM AUTHOR]

The high energy consumption and high environmental impact in the supercritical methanol (SCM) process primarily originates from the preheating of reactants and the recovery of excess alcohols. This work demonstrated the synthesis of biofuel using a lowered methanol to oil molar ratio of 12:1, instead of the 40:1–42:1 ratios that are commonly employed in conventional SCM. The apparent density of the reacting mixture was measured and applied to accurately calculate residence times in a continuous reactor. The effects of residence time were considered from 10 to 25 min. The results revealed that excessive residence times reduced the ester content, especially for unsaturated esters, in the resulting biofuel. A residence time of 20 min was recommended to simultaneously achieve a maximum ester content of 90% and a triglyceride conversion of up to 99%. Used palm olein oil with high free fatty acid (4.56 wt.%) can be employed as a feedstock and give a maximum ester content of 80%. In addition, the side reaction between glycerol and methanol at 400 °C and 15 MPa showed a positive effect in increasing fuel yield by 2%–7%. [ABSTRACT FROM AUTHOR]

The interesterification of palm oil in supercritical ethyl acetate (ETA) to produce fatty acid ethyl ester (FAEEs) or biofuel was conducted in a continuous tubular reactor. The density of the mixtures in the system was estimated using the Peng–Robinson equation of state process simulator, and the residence time was calculated. The effects of the reaction conditions, including the molar ratios of palm oil to ethyl acetate, the temperature, and the pressure, were investigated under various mass flow rates of the mixtures and optimized. The results showed that reaction temperatures above 653 K and long residence times affected the content of FAEEs and triacetin, a valuable by-product. The addition of water to the mixture in a 1:30:10 M ratio of palm oil to ethyl acetate to water at 653 K, 16 MPa, and a mixture mass flow rate of 1.5 g/min increased the total production of FAEEs and triacetin from 90.9 to 101.5 wt% in 42.4 min. The main finding of the present study is that triglyceride associated with ETA hydrolysis used to form acetic acid protected the products from decomposition at high temperatures and long residence times. The results will aid the selection of an efficient and economical process for alternative biofuel production from palm oil in supercritical ETA. [ABSTRACT FROM AUTHOR]

Abstract: A recent life cycle assessment (LCA) reported that biodiesel production in supercritical alcohols (SCA) produces a higher environmental load than the homogeneous catalytic process because an enormous amount of energy is required to recover excess alcohol. However, the excess alcohol could be dramatically reduced by increasing the operating temperature to 400°C; although the product would have to be considered as an alternative biofuel instead of biodiesel. A comparative LCA of the biodiesel production in two SCA at 300°C (C-SCA) and novel biofuel production in the same two SCA at 400°C (N-SCA) is presented. It was clear that the N-SCA process produces a dramatically reduced environmental load over that of the C-SCA process due to a lower amount of excess alcohol being used. The N-SCA process could be improved in terms of its environmental impact by changing from fossil fuel to biomass-based fuels for the steam generation. [Copyright &y& Elsevier]

Abstract: Biofuel production from palm oil with supercritical methanol (SCM) and supercritical ethanol (SCE) at 400°C and 15MPa were evaluated. At the optimal alcohol to oil molar ratios of 12:1 and 18:1 for the SCM and SCE processes, respectively, the biofuel samples were synthesized in a 1.2-L reactor and the resulting biofuel was analyzed for the key properties including those for the diesel and biodiesel standard specifications. Biofuel samples derived from both the SCM and SCE processes could be used as an alternative fuel after slight improvement in their acid value and free glycerol content. The remarkable advantages of this novel process were: the additional fuel yield of approximately of 5% and 10% for SCM and SCE, respectively; the lower energy consumption for alcohol preheating, pumping and recovering than the biodiesel production with supercritical alcohols that use a high alcohol to oil molar ratio of 42:1. [Copyright &y& Elsevier]