Márcio José da Silva

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.

Fe(NO 3 ) 3 -Catalyzed Monoterpene Oxidation by Hydrogen Peroxide: An Inexpensive and Environmentally Benign Oxidative Process

Simple Fe(NO3)2·9H2O was demonstrated to be able to catalyze the oxidation of monoterpenes by hydrogen peroxide in methyl alcohol solution. Compared with the previous iron-catalyzed methods, the present procedure avoids the use of stabilizing ligands, additives, and corrosive peroxide organic oxidants. A novel, simple and highly efficient catalyst system was developed for oxidizing monoterpenes into a valuable derivates using hydrogen peroxide, an environmentally friendly oxidant.Graphical AbstractPossible steps involved in the Fe(III)-catalyzed oxidation of β-pinene by hydrogen peroxide into myrtenol methyl ether in methyl alcohol

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.

A Highly Selective Na 2 WO 4 -Catalyzed Oxidation of Terpenic Alcohols by Hydrogen Peroxide

Sodium tungstate was found to be an active and highly selective catalyst to oxidation of various primary or secondary origin renewable alcohols by hydrogen peroxide as green oxidant. Borneol, nerol, geraniol and β-citronellol were efficiently and selectively converted to respective carbonyl derivatives by hydrogen peroxide. ATR/FT-IR measurements confirmed that Na2W(O2)4 was the specie active catalytically. The role of the main reaction variables, including temperature, reactants and catalyst concentration, solvent, and nature of substrate were also assessed. In addition to use a green oxidant, this simple and environmentally friendly catalyst system did not require additive to control pH, molecular sieves or phase transfer catalyst.Graphical Abstract

Catalysis of vegetable oil transesterification by Sn(II)-exchanged Keggin heteropolyacids: bifunctional solid acid catalysts

Keggin heteropolyacid protons (i.e., H3PW12O40, H3PMo12O40, H4SiW12O40) were partially exchanged with Sn(II) cations generating solid acid catalysts that were used for vegetable oil transesterification reactions. These catalysts have double acidity properties, i.e., Lewis acidity and Brønsted acidity that are suitable for the conversion of vegetable oil into biodiesel. The highest efficiency (ca. 100%) was achieved on the Sn1.2H0.6PW12O40-catalyzed transesterification reactions. The relationship between the catalytic activity and acidic properties was deeply discussed and the effects of main reaction parameters were assessed. The activity of the precursor HPA, tin salts and physical mixture were compared and confirmed a synergism between Sn(II) cations and PW12O403− anions. The reusability of catalyst was investigated.

An Efficient Benzaldehyde Oxidation by Hydrogen Peroxide over Metal Substituted Lacunary Potassium Heteropolyacid Salts

Keggin heteropolyacids (i.e. H3PW12O40, H3PMo12O40 and H4SiW12O40) were converted to potassium lacunary salts and afterwards their vacancy were filled by metal cations (i.e. Cu2+, Co2+, Fe3+, Ni2+ or Al3+). These solid catalysts were assessed on oxidation of benzaldehyde to benzoic acid by hydrogen peroxide. Remarkably, among heteropoly salts investigated, the K6SiW11CoO39 was the most active catalyst. High conversion (ca. 90%) and benzoic acid selectivity (ca. 90%) were achieved. The activity of solid catalyst remained unaltered after successive cycles of reuse. Effect of catalyst nature, temperature, reactants concentration on conversion and selectivity were assessed.Graphical Abstract

Monolacunary K8SiW11O39-Catalyzed Terpenic Alcohols Oxidation with Hydrogen Peroxide

Abstract Lacunar potassium undecasilicotungstate salt catalyst was highly efficient in oxidation reactions of terpenic alcohols with hydrogen peroxide. Carbonylic products were selectively obtained from alcohols such as borneol, nerol, geraniol and β-citronellol. The K8SiW11O39 catalyst was synthesized in one pot reaction starting from precursor salts (KCl, Na2WO4, and Na2SiO3). The catalyst salt was characterized by FT-IR, TG/DSC, BET, XRD analyses and potentiometric titration. The main reaction parameters were assessed. Based on experimental data, a reaction pathway was proposed. In borneol oxidation, TON of 2720 was achieved, indicating the high catalytic activity. As far we know, it is the first time where the monolacunar catalyst is used without an additional introduction of metal transition into Keggin anion. A comparison of the catalytic performance of different lacunar silicotungstic acid salts exchanged with different cations was performed. The K8SiW11O39 catalyst was used without loss activity.Graphical Abstract

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.