Biodiesel production from free fatty acids

Apart from a few reports" on solid acid catalyzed esterification of model compounds, to our knowledge utilization of solid catalysts for biodiesel production from low quality real feedstocks have been explored only recently. 12-Tungstophosphoric acid (TPA) impregnated on hydrous zirconia was evaluated as a solid acid catalyst for biodiesel production from canola oil containing up to 20 wt % free fatty acids and was found to give ester yield of 90% at 200°C. Propylsulfonic acid-functionalized mesoporous silica catalyst for esterification of FFA in flotation beef tallow showed a superior initial catalytic activity (90% yield) relative to a... 

The process involves reacting the degummed oil with an excess of methyl alcohol in the presence of an alkaline catalyst such as sodium or potassium methoxide, reaction products between sodium or potassium hydroxide and methyl alcohol. The reaction is carried out at approximately 150°F under pressure of 20 psi and continues until trans-esterification is complete. Glycerol, free fatty acids and unreacted methyl alcohol are separated from the methyl ester product. The methyl ester is purified by removal of residual methyl alcohol and any other low-boiling-point compounds before its use as biodiesel fuel. From 7.3 lb of soybean oil, 1 gallon of biodiesel fuel can be produced. See FIGURE 12-5. 

FAME production of rapeseed oil by alkali-catalyzed transesterification reaction was investigated. To obtain optimum conversion yield, anhydrous methanol and rapeseed oil with a free fatty acid content of <0.5% were used. The optimum conditions for alkali-catalyzed transesterification using KOH were determined as follows an oil to methanol molar ratio of 1 8 to 1 10 KOH, 1.0% (w/w) on the basis of oil weight, as catalyst a reaction temperature of 60°C and reaction time of 30 min. At these conditions, the FAME conversion yield was approx above 98%. From the refined FAME product (biodiesel), the FAME purity was obtained above 99% through posttreatment such as washing and centrifugation. 

As a simulation example we treat the production of biodiesel from rapeseed in a plant capacity of 200 ktonne per year. The feedstock has a high content of oleic acid triglyceride, around 65%, such that the kinetic data from Section 14.6 can be used for sketching the design of the reaction section. For simplification, we consider that the oil was pretreated for removing impurities and gums, as well as FFA by esterification over solid catalyst. The free fatty acids and water content in oil feed should be less than 0.5%w. NaOH and KOH in 0.5 to 1.5% w/w are used as catalysts. 

Canakci, M., and Van Gerpen, J. 2001. Biodiesel production from oils and fats with high free fatty acids. Trans. ASAE, 44(6), 1429-1436. 

It is generally accepted that the production of biodiesel meeting the E. U. standards is possible from crude oils with a free fatty acid content lower than 2-2.5%, and levels of phospholipids up to 300ppm (Dorado et al., 2004). However the presence of a high amount of phospholipids results in poor biodiesel-glycerol and biodiesel-water separations which in turn results in a lower yield. Due to the lower concentration of P-compounds in palm oil and animal fat, these raw materials can be used without further degumming treatment. 

As Upases are able both to esterify free fatty acids and catalyze the alcoholysis of acylglycerols, they can in theory eliminate the need for multiple catalyst systems during biodiesel production from waste greases. Several groups have investigated... 

For biodiesel fuels, the basic idea is to convert natural glycerides to liquid products that have properties closer to those of diesel fuels than those of gasolines. The feedstocks for conversion to biodiesel are usually triglyceride oils from oilseeds. These oils normally contain small amounts of monoglycerides, diglycerides, and free fatty acids. Animal fats and natural non-seed-oil triglycerides are also suitable starting materials. 

Biodiesel (long-chain monoalkyl fatty acid esters), a renewable and green fuel, is made from vegetable oil or animal fats. At present, the high cost of biodiesel, of which the raw material amounts to 75%, prohibits its wide application. Compared with chemical method, enzymatic process seems to be a promising alternative because of its mild reaction conditions, easy recovery of product, being free of chemical wastes and low demangding on raw materials, which makes it possible to use waste oil as substrate for enzymatic production of biodiesel. 

Presently industrial production of biodiesel from waste edible oil is performed by chemical alkaline catalysts, but it has been found that high content of free fatty acid (FFA) in waste edible oil (FFA>2%) would decrease the yield sharply due to soaps formed in the process (7). Several studies showed that enzymatic methanolysis with waste edible oil was a promising alternative owing to its mild reaction condition and free of chemical waste (2, 5). However, this conventional protocol was associated with many drawbacks such as deactivation of lipase caused by methanol and absorption of glycerol to lipase surface, thus resulting in serious negative effect on the reaction (4,5). 

Lou, W., Zong, M., Duan, Z. (2008). Efficient production of biodiesel from high free fatty acid-containing waste oils using various carbohydrate-derived solid acid catalysts. Bioresource Technology, 99, 8752—8758. 

Biodiesel can also be produced from noncatalytictransesterification with supercritical alcohol. Supercritical alcohol transesterification is a process that has several advantages, such as reduced reaction time and easy separation and purification of the products, besides allowing the use of raw material with high contents of free fatty acids. However, this technique requires relatively severe operating conditions, therefore requiring special equipment that makes the costs associated with the process very expensive (Shimoyama et al., 2009 Tan et al., 2010 Atadashi et al., 2011). 

Recent studies have demonstrated the use of oleic acid as an efficient substrate for production of biodiesel by esterification using lipase. Mulalee et al. (2013) studied the production of biodiesel from oleic acid and bioalcohols (ethanol and butanol) using immobilized lipase (Novozym 435) as biocatalyst in a batch esterification process. The optimal conditions were 45 C, oleic acid to alcohol molar ratio of 1 2, Novozym 435 loading at 5% based on oleic acid weight and 250 rpm, in which the free fatty acid conversion at 91.0% was obtained after 12 hours of the reaction. 

Canakci, M., and J. Van Gerpen. 2001. Biodiesel Production from Oils and Fat with High Free Fatty Acids. American Society of Agricultural Engineers 44 (6) 1429-1436. 

Chen, L., T. Liu, W. Zhang, X. Chen, and J. Wang. 2012. Biodiesel Production from Algae Oil High in Free Fatty Acids by Two-Step Catalytic Conversion. Bioresource Technology 111 208-214. 

Ghadge, S. V, and H. Raheman. 2005. Biodiesel Production from Mahua Madhuca Indica) Oil Having High Free Fatty Acids. Biomass and Bioenergy 28 (6) 601-605. 

Shi, W., J. Li, B. He, F. Yan, Z. Cui, K. Wu, L. Lin, X. Qian, and Y. Cheng. 2013. Biodiesel Production from Waste Chicken Fat with Low Free Fatty Acids by an Integrated Catalytic Process of Composite Membrane and Sodium Methoxide. Biosource Technology 139 316-322. 

Beichmans HJ, Hirata S. Biodiesel production from crude Jatropha curcas L. seed oil with a high content of free fatty acids. Bioresour Technol 2008 99 1716—1721. 

Naik M, Meher LC, Naik SN, Das LM. Production of biodiesel from high free fatty acid Karanja (Pongamia pinnata) oil. Biomass Bioenergy 2008 32 354-357. 

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