Esterification biodiesel manufacturing

Fatty acid methyl esters (FAME) are currently manufactured mainly by trans-esterification with an alcohol, using a homogeneous base catalyst (NaOH/KOH). Methanol is more suitable for biodiesel manufacturing, but other alcohols can in principle also be used, depending on the feedstock available. The... 

Fatty acids react with alkaline catalysts to form catalytically inactive soaps (3). The chemical reaction consumes one mole of fatty acid per mole of alkaline catalyst. Although fatty acid composition of the starting material varies, the content determined by titration reflects the amount of catalyst that would be consumed in a chemical reaction. By calculation, it may be determined that one gram of fatty acid (expressed as oleic acid) will react with about 0.2 g of anhydrous potassium hydroxide or 0.14g of anhydrous sodium hydroxide. Often, additional catalyst must be added to esterify a vegetable oil containing higher levels of fatty acids (3). Conversely, acid catalysts are not inactivated by fatty acids (3). In a unique reaction, fatty acids produced during biodiesel manufacture are actually used as a catalyst in their own esterification (see below). 

During the last decade many industrial processes shifted towards using solid acid catalysts (6). In contrast to liquid acids that possess well-defined acid properties, solid acids contain a variety of acid sites (7). Sohd acids are easily separated from the biodiesel product they need less equipment maintenance and form no polluting by-products. Therefore, to solve the problems associated with liquid catalysts, we propose their replacement with solid acids and develop a sustainable esterification process based on catalytic reactive distillation (8). The alternative of using solid acid catalysts in a reactive distillation process reduces the energy consumption and manufacturing pollution (i.e., less separation steps, no waste/salt streams). 

The benefits of using biodiesel as renewable fuel and the difficulties associated with its manufacturing are outlined. The synthesis via fatty acid esterification using solid acid catalysts is investigated. The major challenge is finding a suitable catalyst that is active, selective, water-tolerant and stable under the process conditions. The most promising candidates are sulfated metal oxides that can be used to develop a sustainable esterification process based on continuous catalytic reactive distillation. 

Methyl esters of soya, rapeseed and palm oil fatty acids used as biodiesel (Chapters 7 and 8) are preferentially manufactured by transesterification." The acid catalyzed esterification and the alcoholysis of triacylglycerides apply also for the manufacture of higher alcohol monoesters as well as for fatty acid polyol esters. Due to their oily consistency and to their solubilizing properties fatty acid esters of low Mw alcohols are components in odorous substances like perfumes, and cosmetic and drug formulations such as ointments, creams or lotions. 

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