In situ alkaline transesterification: An effective method for the production of fatty acid esters from vegetable oils

Abstract

The production of simple alkyl FA esters by direct alkali-catalyzed in situ transesterification of the acylglycerols (AG) in soybeans was examined. Initial experiments demonstrated that the lipid in commercially produced soy flakes was readily transesterified during agitation at 60°C in sealed containers of alcoholic NaOH. Methyl, ethyl, and isopropyl alcohols readily participated in the reaction, suggesting that the phenomenon is a general one. Statistical experimental design methods and response surface regression analysis were used to optimize reaction conditions, using methanol as alcohol. At 60°C, the highest yields of methyl ester with minimal contamination by FFA and AG were predicted at a molar ratio of methanol/AG/NaOH of 226:1:1.6 with an approximately 8-h incubation. An increase in the amount of methanol, coupled with a reduced alkali concentration, also gave high ester yields with low FFA and AG contamination. The reaction also proceeded well at 23°C (room temperature), giving higher predicted ester yields than at 60°C. At room temperature, maximal esterification was predicted at a molar ratio of 543:1:2.0 for methanol/AG/NaOH, again in 8 h. Of the lipid in soy flakes, 95% was removed under such conditions. The amount of FAME recovered after in situ transesterification corresponded to 84% of this solubilized lipid. Given the 95% removal of lipid from the soy flakes and an 84% efficiency of conversion of this solubilized lipid to FAME, one calculates an overall transesterification efficiency of 80%. The FAME fraction contained only 0.72% (mass basis) FFA and no AG. Of the glycerol released by transesterification, 93% was located in the alcoholic ester phase and 7% was on the post-transesterification flakes.Paper no. J10571 in JAOCS 81, 83-89 (January 2004).KEY WORDS: Biodiesel, fats and oils utilization, fatty acid ester, in situ transesterification, transesterification.The simple alkyl esters of FA have numerous established uses in the food, textile, cosmetic, rubber and metal processing, and synthetic lubricant industries. FAME are the predominant esters consumed, with a year 2000 global consumption of 1 million metric tons (MMT) (1). In addition, FAME are the favored starting material for the production of fatty amides, more complex esters, ester sulfonates, and fatty alcohols. Fatty alcohols alone were consumed at a world rate of 6.2 MMT in 2000 (1). Production and consumption of the methyl esters of FA are rapidly increasing due to their growing use as biodiesel, a renewable replacement for petroleum-based diesel engine fuel.Contemporary industrial technology for the synthesis of fatty acyl esters of vegetable oils involves isolation of oilseed acylglycerides by extrusion or solvent extraction, degumming and refining of the oil, and its alkali-catalyzed transesterification. Hexane extraction is the main technology for oil recovery in the United States. Extraction plants achieve high levels of solvent recovery, with a typical soybean processing plant losing less than 1.25 L of solvent per metric to...

Soybeans Processing for Biodiesel Production

“…8. In general, increasing the methanol to oil volumetric ratio, increased the biodiesel yield (Haas et al, 2004). Also, increasing ultrasound power from 70 % to 90 % at different methanol levels showed significant effect on oil yield.…”

Biodiesel production from jatropha seeds: Solvent extraction and in situ transesterification in a single step

“…As the cost of vegetable oil production accounts for approximately 70% of biodiesel production costs [24][25][26], there is a need for the development of a new biodiesel production process that is simple, compact, efficient, low-cost, and that consumes less energy.…”

“…Recently, the preparation of biodiesel using in situ transesterification has been successfully carried out with various oilseeds [24][25][26][27][28][29][30][31][32]. In situ transesterification is a biodiesel production method that uses the original agricultural products as the source of triglycerides, instead of purified oil, with direct transesterification, and works with virtually any lipid-bearing material.…”

Esterification of Oleic Acid for Biodiesel Production Catalyzed by SnCl2: A Kinetic Investigation

“…Biodiesel fuel has become more attractive because of its environmental benefits, due to the fact that plants and vegetable oils and animal fats are renewable biomass sources [2]. Currently, most of the biodiesel comes up from transesterification of edible resources such as animal fats, vegetable oils, and even waste cooking oils, under alkaline catalysis conditions [3][4][5]. However, the high consumption of catalysts, the formation of soaps, and the low yields, make biodiesel currently more expensive than petroleum-derived fuel [6].…”