Batch Study of Glycerol Decomposition in One-Stage Supercritical Production of Biodiesel

Abstract

The objective of this work was to assess some of the points that need to be elucidated in order to define the economic viability of the noncatalytic supercritical biodiesel process. Net yield of the supercritical process, consumption of methanol, and the quality of the fuel issuing from the reactor were studied. Biodiesel was prepared by reacting refined soy oil with supercritical methanol at T ) 280 °C and methanol-to-oil molar ratios of 15 and 20. After the reaction, unreacted methanol, water, and other volatile compounds were removed from the product by stripping with nitrogen at 110 °C. Biodiesel production by the reaction of oils in supercritical methanol under the conditions used in this work produces practically no glycerol byproduct. This fact simplifies the downstream refining of the produced biodiesel. Glycerol is transformed into products of smaller molecular size and water. At first this water reacts with the triglycerides of the reacting mixture to form free fatty acids (FFA), thus increasing the acidity of the product. At longer reaction times the acids are converted into methyl esters again. Glycerol methanolysis reactions increase the methanol consumption. The small amount of glycerides and FFA contaminants in the biodiesel product makes a final step of refining by silica adsorption convenient. No liquid effluents are issued with such a refining step. After the FFA and glycerides are recycled, the yield of the process is 94-96%.

An entirely renewable biofuel production from used palm oil with supercritical ethanol at low molar ratio

“…Moreover, the 2-ethoxy-1,3-propanediol in the biofuel sample implied that the product from the ethanol-glycerol reactions can dissolve in the fuel phase and can increase the fuel yield by approximately 8.15%. As proposed in the previous study, the reaction products of glycerol, mainly ether isomers of glycerol, could be directly used as part of the biofuel and improve some fuel properties (Marulanda et Anitescu et al, 2008;Aimaretti et al, 2009). Aimaretti et al (2009) reported that approximately 10 % of glycerol reaction products has a marginal influence on the kinematic viscosity.…”

“…As proposed in the previous study, the reaction products of glycerol, mainly ether isomers of glycerol, could be directly used as part of the biofuel and improve some fuel properties (Marulanda et Anitescu et al, 2008;Aimaretti et al, 2009). Aimaretti et al (2009) reported that approximately 10 % of glycerol reaction products has a marginal influence on the kinematic viscosity. However, the compatibility of those compounds with diesel fuels, and their influence on engine performance, should be investigated in further research.…”

Biodiesel production through non-catalytic supercritical transesterification: current state and perspectives

“…Anistescu et al (2008) performed alcoholysis reactions using supercritical methanol at temperatures around 623-673 K and reported the absence of glycerol in the reaction products; the authors cogitated that reaction of glycerol with other compounds may have occurred. Aimaretti et al (2009) evaluated the reaction of refined soybean oil with supercritical methanol under different conditions. In the conditions studied by the authors, glycerol was not formed.…”

“…One advantage of removing the glycerol formed in the reaction mixture is to allow the reaction to occur at lower ratios of alcohol to oil increasing the reaction rate for the production of biodiesel (Crawford et al, 2007). As cited by Aimaretti et al (2009), during the reaction, the alcohol used in the process is required by secondary reactions, which occur with glycerol.…”

Transesterification in Supercritical Conditions

“…Under these conditions it was reported that triglyceride and glycerol convert to oxygenate liquid fuel with a conversion of up to 99.5%. The glycerol dehydration both increases the fuel yield by up to 10% and reduces the amount of glycerol by-products (Aimaretti et al, 2009). By using the high-temperature process, the simultaneous conversion of triglyceride, free fatty acids and glycerol to liquid fuel is an alternative option that will increase the feasibility and profitability of supercritical transesterification.…”