RESUMO A substituição parcial do óleo diesel pelo biodiesel tem contribuído para o aumento da disponibilidade de glicerina no mercado mundial. Cerca de 10 m3 e glicerina são obtidos para cada 100 m3 de triacilglicerídeos (principal componente de óleos vegetais e gorduras animais) processados na principal rota tecnológica para produção do biodiesel, a transesterificação alcalina em meio homogêneo. Naturalmente, a glicerina obtida como coproduto no processo precisa ser aproveitada em processos complementares. Isso usualmente é possível após a glicerina passar por vários processos de purificação. Com a intenção de evitar tais processos complementes para aproveitamento da glicerina, estamos propondo a síntese do biodiesel por interesterificação do óleo de soja com acetato de metila, uma rota tecnológica que possibilita a obtenção da glicerina na forma de triacetina, ou seja, já quimicamente modificada. Os catalisadores utilizados no processo foram o hidróxido duplo lamelar (HDL) Zn2 Al/NO3 e o estearato de zinco comercial (EZ), um carboxilato lamelar. Ambos estes materiais lamelares ainda não haviam sido testados como catalisadores em reações de interesterificação. Foram obtidas conversões em ésteres metílicos de ácidos graxos de 50,8±4,2 % e 82,9±1,0 % (m m-1) utilizando os catalisadores EZ e HDL, respectivamente; quando as reações foram conduzidas utilizando 5 % de catalisador (m m-1), por 10 h de reação e razão molar acetato de metila: óleo de soja de 24:1.

ABSTRACT The partial replacement of diesel oil with biodiesel has contributed to the increased availability of glycerin on the world market. About 10 m3 of glycerol is obtained for every 100 m3 of triacylglycerides (main component of vegetable oils and animal fats) processed in the main technological route for biodiesel production, the alkaline transesterification in homogeneous medium. Of course, the glycerin obtained as a coproduct in the process needs to be harnessed in complementary processes. This is usually possible after the glycerin undergoes several purification processes. With the intention of avoiding such complementary processes, we are proposing the synthesis of biodiesel by interesterification of soybean oil with methyl acetate, a technological route that makes it possible to obtain glycerol in the form of triacetin, that is, already chemically modified. The catalysts used in the process were the layered double hydroxide (HDL) Zn2 Al/NO3 and the commercial zinc stearate (EZ), a layered carboxylate. Both these layered materials had not yet been tested as catalysts in interesterification reactions. Conversions were obtained in fatty acid methyl esters of 50.8 ± 4.2% and 82.9 ± 1.0% (m m-1) using the EZ and HDL catalysts, respectively; when reactions were conducted using 5% catalyst (m m-1), for 10 h reaction and molar ratio methyl acetate: soybean oil of 24:1.

Palm oil containing 40% fatty acids was converted to methyl esters using zinc carboxylates as the esterification/transesterification catalyst. The reaction was optimized using a factorial design in which the effects of the alcohol:fatty acids molar ratio (MRAG) and the catalyst concentration (CAT) were assessed. The best conversion was achieved with CAT at 4 wt% and MRAG at 4:1. However, the solid catalyst presented significant structural changes after use. For instance, laurate anions were replaced by carboxylates of higher molecular mass, leading to the formation of a new catalytically active layered structure. Also, the glycerin obtained as a co-product contained 86 wt% glycerol.

Glicerolatos de metais divalentes foram sintetizados e investigados na transesterificação metílica de óleo de soja refinado. Altas conversões foram obtidas para os monoglicerolatos de estrôncio e bário e diglicerolato de cálcio. O diglicerolato de cálcio se mostrou estável até o terceiro ciclo de reuso, se decompondo em uma mistura inativa de CaCO3 e Ca(OH)2.

Divalent metal glycerolates were synthesized and investigated in the methyl transesterification of refined soybean oil. Higher conversions to monoacylesters were obtained for strontium and barium monoglycerolates and calcium diglycerolate. Calcium diglycerolate was shown to be stable up to a third reuse cycle, decomposing to an inactive mixture of CaCO3 and Ca(OH)2.

Sodium bismuthate dihydrate and two species derived from its thermal treatment were investigated as catalysts for soybean oil methanolysis and, regardless of the type of solid used, ester yields always above 76 wt% were obtained. After a single reaction course, both liquid and solid phases were characterized using several analytical methods such as X-ray diffraction and thermogravimetric analysis. As a result, the catalytic phenomenon was shown to be solely due to the leaching of alkalinecatalytic species from the solid materials.

The recent increase in the world biodiesel demand, along with the need to reduce costs while improving the environmental sustainability of the entire biodiesel production chain, have led to the search for heterogeneous catalysts that would be efficient and highly amenable to recycling. Many classes of materials have been tested for these purposes. Among these are zeolites, ion-exchange resins, inorganic oxides, guanidines, metal complexes, layered compounds and ionic liquids. This review article describes the structure, properties, synthesis and performance of compounds that are catalytic active in both esterification and transesterification reactions.