Abiney Lemos Cardoso

Tin-catalyzed esterification and transesterification reactions: a review.

The recent increase in the world biofuels demand, along with the need to reduce costs while improving the environmental sustainability of the biodiesel production, have led to the search for catalysts that should be economically viable, efficient, and environmentally friendly. This paper reviews recent research and development of organic and inorganic tin catalysts; focusing on kinetic properties and catalytic activity in two key reactions for biodiesel production: free fatty acids (FFA) esterification and triglycerides (TG) transesterification. First the basic knowledge of homogeneous tin catalysts in esterification reactions of different carboxylic acids is provided. Second, main advances obtained in the study of FFA esterification reactions catalyzed by tin chloride are covered. The effect of the principal parameters of reaction on the yield and rate of alkyl esters production is described. Kinetic measurements allowed the determination of the activation energy (46.79 kJ mol−1) and a first-order dependence in relation to both FFA and tin chloride catalyst concentration. Aspects related to recycling of the tin chloride catalyst in phase homogeneous are discussed. Third the advances obtained in the development of homogeneous catalysts based on tin complexes in transesterification reactions are summarized. Finally, results obtained from the use of tin organometallics compounds in reactions of vegetable oils transesterification reactions are concisely presented. The optimization of processes catalytic homogeneous utilized in the transesterification reactions can contribute to the improvement of the technology biodiesel production.

Heterogeneous Tin Catalysts Applied to the Esterification and Transesterification Reactions

The interest in the development of efficient and environmentally benign catalysts for esters synthesis has increased exponentially, mainly due to the demand for biodiesel. In general, fatty esters are used as bioadditive, cosmetic ingredients, polymers, and, more recently, biofuel. Nevertheless, most of the production processes use nonrecyclable and homogenous alkaline catalysts, which results in the reactors corrosion, large generation of effluents, and residues on the steps of separation and catalyst neutralization. Heterogeneous acid catalysts can answer these demands and are an environmentally benign alternative extensively explored. Remarkably, solid acid catalysts based on tin have been shown highly attractive for the biodiesel production, mainly via FFA esterification reactions. This review describes important features related to be the synthesis, stability to, and activity of heterogeneous tin catalysts in biodiesel production reactions.

p-Sulfonic acid calix[n]arenes: the most active and water tolerant organocatalysts in esterification reactions

This work reports the novel results obtained from an in situ kinetic study, which was conducted via1H NMR, of the palmitic acid esterification reaction with deuterated methanol in the presence of organocatalysts: p-sulfonic acid calix[6]arene, p-hydroxybenzenesulfonic acid and p-toluenesulfonic acid. The kinetic order of reaction relative to the catalyst concentration and the main thermodynamic properties, such as the activation energy (ΔE), entropy variation (ΔS), enthalpy variation (ΔH) and Gibbs free energy variation (ΔG), were obtained. The results indicated that p-sulfonic acid calix[6]arene was the most active organocatalyst in esterification reactions, regardless of temperature or catalyst concentration employed. Additionally, by performing the reactions in the presence of increasing amounts of water, it was found that p-sulfonic acid calix[n]arenes are more tolerant to water than the other catalysts investigated. This result, when combined with the kinetic and thermodynamic measurements, may explain their highest catalytic activity.

Bioenergy II: Tin Catalysed Esterification of Free Fatty Acids

Tin(II) chloride dihydrate (SnCl2.2H2O) has been an efficient Lewis acid catalyst in the ethanolysis of saturated and saturated free fatty acids (FFA). This compound is stable under aerobic conditions and it has shown to be as active as the mineral acid H2SO4, a common acid catalyst in the conventional production of biodiesel. The carbon chain length of FFA and the fatty acid/alcohol molar ratio were parameters of investigation herein in association with the yield and reaction rate of free fatty ethyl esters (FAEE) formation. The efficiency of the process of recovery of SnCl2 also has been evaluated. It was verfified that the catalytic activity of the recovered SnCl2 has remained unaltered in successive reactions with oleic acid. The residual content of catalyst in the biodiesel was determinated by spectrophotometry of atomic absorption. The use of SnCl2 has advantages in comparison with mineral acid catalysts. For instance, the absence of corrosion in the reaction vessel as well as the unnecessary neutralization of the catalyst after the reaction finishes. The results in this work put forward the SnCl2 as a promising catalyst for the production of biodiesel.

Assessing the Activity of Solid-Suported SnCl2 Catalysts on the Oleic Acid Esterification for Biodiesel Production

The search for cleaner methodologies has forcing the chemical industry to seek environmentally benign acid catalysts. SnCl2.2H2O is an affordable commercially Lewis acid, water tolerant and easy to handling, cheaper, and less corrosive. Recently, we have demonstrated that it is an efficient catalyst to produce biodiesel in homogeneous catalysis conditions. In this work, we have supported SnCl2.2H2O over different solid matrix (i.e., such as SiO2, Nb2O5 and ZrO2) and evaluated its catalytic activity in FFA esterification reactions. In this case, the reaction occurs in heterogeneous phase bringing with itself all the pertinent advantages to this rational system as the best separation of products and reuse of the catalyst. It was appraised reaction parameters such as thermal treatment temperature nature of the support; leaching test was also accomplished.

Heterogeneous Catalysts Based on H3PW12O40 Heteropolyacid for Free Fatty Acids Esterification

1.1 Biodiesel chemical background The inevitable exhaustion of the fossil diesel reserves, besides the environmental impact generated by the green-house effect gas emission by these fuels has provoked the search by renewable feedstokes for energy production (Srivastava & Prasad, 2000; Sakay et al., 2009). Due to this crescent demand, the industry chemistry in all parts of world has search to develop environment friendly technologies for the production of alternative fuels (Di Serio et al., 2008; Marchetti et al., 2007). Biodiesel is a “green” alternative fuel that has arisen as an attractive option, mainly because it is less pollutant than its counterpart fossil and can be obtained from renewable sources (Maa & Hanna, 1999). Although it is undeniable that biodiesel is a more environmentally benign fuel, its actual production process cannot be classified as “green chemistry process” (Kulkarni et al., 2006). The major of the biodiesel manufacture processes are carry out under alkaline or acid homogeneous catalysis conditions, where is not possible the recycling catalyst, resulting in a greater generation of effluents and salts from neutralization steps of the products and wastes (Kawashima et al., 2008). Moreover, there are some important points related to raw materials commonly used, such as high costs, besides to crescent requirements of large land reserves for its cultivation.