https://www.cti2000.it/Bionett/BioD-1999-101%20Biodiesel%20production%20review.pdf

Biodiesel production : a review

Biodiesel is gaining more and more importance as an attractive fuel due to the depleting fossil fuel resources. Chemically biodiesel is monoalkyl esters of long chain fatty acids derived from renewable feed stock like vegetable oils and animal fats. It is produced by transesterification in which, oil or fat is reacted with a monohydric alcohol in presence of a catalyst. The process of transesterification is affected by the mode of reaction condition, molar ratio of alcohol to oil, type of alcohol, type and amount of catalysts, reaction time and temperature and purity of reactants. In the present paper various methods of preparation of biodiesel with different combination of oil and catalysts have been described. The technical tools and processes for monitoring the transesterification reactions like TLC, GC, HPLC, GPC, 1H NMR and NIR have also been summarized. In addition, fuel properties and specifications provided by different countries are discussed.

Technical aspects of biodiesel production by transesterification—a review

Hydrothermal technologies are broadly defined as chemical and physical transformations in high-temperature (200–600 °C), high-pressure (5–40 MPa) liquid or supercritical water. This thermochemical means of reforming biomass may have energetic advantages, since, when water is heated at high pressures a phase change to steam is avoided which avoids large enthalpic energy penalties. Biological chemicals undergo a range of reactions, including dehydration and decarboxylation reactions, which are influenced by the temperature, pressure, concentration, and presence of homogeneous or heterogeneous catalysts. Several biomass hydrothermal conversion processes are in development or demonstration. Liquefaction processes are generally lower temperature (200–400 °C) reactions which produce liquid products, often called “bio-oil” or “bio-crude”. Gasification processes generally take place at higher temperatures (400–700 °C) and can produce methane or hydrogen gases in high yields.

/pdf/thermochemical-biofuel-production-in-hydrothermal-media-a-57itjyvhnt.pdf

Thermochemical biofuel production in hydrothermal media: A review of sub- and supercritical water technologies

Various novel techniques including ultrasound-assisted extraction, microwave-assisted extraction, supercritical fluid extraction, and accelerated solvent extraction have been developed for the extraction of nutraceuticals from plants in order to shorten the extraction time, decrease the solvent consumption, increase the extraction yield, and enhance the quality of extracts. A critical review was conducted to introduce and compare the conventional Soxhlet extraction and the new alternative methods used for the extraction of nutraceuticals from plants. The practical issues of each extraction method were discussed. Potential uses of those methods for the extraction of nutraceuticals from plant materials was finally summarized.

Recent advances in extraction of nutraceuticals from plants

Hydrothermal liquefaction of biomass: A review of subcritical water technologies

Water, in its subcritical state, can be used as both a solvent and reactant for the hydrolysis of triglycerides. In this study, soybean, linseed, and coconut oils were successfully and reproducibly hydrolyzed to free fatty acids with water at a density of 0.7 g/mL and temperatures of 260−280 °C. Under these conditions the reaction proceeds quickly, with conversion of greater than 97% after 15−20 min. Some geometric isomerization of the linolenic acids was observed at reaction temperatures as low as 250 °C. Reactions carried out at higher temperatures and pressures, up to the critical point of water, produced either/or degradation, pyrolysis, and polymerization, of the oils and resultant fatty acids.

Hydrolysis of Vegetable Oils in Sub- and Supercritical Water

Supercritical fluid technology in oil and lipid chemistry

https://zenodo.org/record/1230004/files/article.pdf

Hydrolysis of soybean oil. in a subcritical water flow reactor

An alternative extraction method for the removal of fats from meat samples is described employing supercritical carbon dioxide as the extracting medium. Experiments conducted at 35-70 MPa and 80 “C have shown that dense COz is an effective agent for selective removal of fat from a variety of meat matrices. Results obtained on meats varying in fat content from 2 to 35% by weight indicate that over 96% of the theoretical fat content can be removed. .Rapid extraction fluxes are realized when comminution and dehydration are performed on the samples prior to extraction. The described technique generates minimal toxicological risk to laboratory personnel and eliminates disposal problems of residual solvents.

Extraction of fat tissue from meat products with supercritical carbon dioxide

Hydrogenation of vegetable oils under supercritical conditions can involve a homogeneous one-phase system, or alternatively two supercritical components in the presence of a condensed phase consisting of oil and a solid catalyst. The former operation is usually conducted in flow reactors while the latter mode is more amenable to stirred, batch-reactor technology. Although many advantages have been cited for the one-phase hydrogenation of oils or oleochemicals using supercritical carbon dioxide or propane, its ultimate productivity is limited by the oil solubility in the supercritical fluid phase as well as unconventional conditions that affect the hydrogenation. In this study, a dead-end reactor has been utilized in conjunction with a head-space consisting of either a binary fluid phase consisting of varying amounts of carbon dioxide mixed with hydrogen or neat hydrogen for comparison purposes. Reaction pressures up to 2000 psi and temperatures in the range of 120–140°C have been utilized with a conventional nickel catalyst to hydrogenate soybean oil. Depending on the chosen reaction conditions, a wide variety of end products can be produced having different iodine values, percentage trans fatty acid content, and dropping points or solid fat indices. Although addition of carbon dioxide to the fluid phase containing hydrogen retards the overall reaction rate in most of the studied cases, the majority of products have low trans fatty acid content, consistent with a nonselective mode of hydrogenation.

Jerry W. King

Papers

Hydrolysis of Vegetable Oils in Sub- and Supercritical Water

Supercritical fluid technology in oil and lipid chemistry

Hydrolysis of soybean oil. in a subcritical water flow reactor

Extraction of fat tissue from meat products with supercritical carbon dioxide

Hydrogenation of vegetable oils using mixtures of supercritical carbon dioxide and hydrogen