Claudio J. A. Mota

Water-tolerant zeolite catalyst for the acetalisation of glycerol

We studied the acid-catalysed reaction of glycerol with aqueous formaldehyde and acetone in absence of solvents and using heterogeneous catalysts. The reactivity of acetone was usually higher than formaldehyde and the glycerol conversion was over 90% within 40 min of reaction time for all the heterogeneous acid catalysts studied. With aqueous formaldehyde solution, the glycerol conversion was within 60 to 80%, depending upon the acid catalyst used (Amberlyst-15, K-10 montmorillonite, p-toluene-sulfonic acid), due to the high amount of water in the reaction medium, which shifts the equilibrium and weakens the acid sites. However, the use of zeolite Beta, with Si/Al ratio of 16, leads to a conversion of over 95% within 60 min of reaction time. The hydrophobic character of the zeolite, due to the high silicon content, prevents the diffusion of the water to the interior of the pore, preserving the strength of the acid sites. In addition, the water formed during the acetalisation is expelled off from the pore environment, impairing the reverse reaction, and avoiding the use of hazard solvents, commonly employed to distil off the water formed.

Glycerol acetals as anti-freezing additives for biodiesel.

Glycerol acetals from butanal, pentanal, hexanal, octanal and decanal were prepared with the use of Amberlyst-15 acid resin as catalyst. The glycerol conversion decreases with the size of the hydrocarbon chain. This fact has been associated with formation of micelles and aggregates of the aldehyde to minimize the interaction between the polar glycerol molecule with the hydrocarbon chain. The Z+E mixture of the acetals with five and six-member rings were produced in all cases. The distribution of the acetal isomers varied with the reaction time, especially for the long chain aldehydes. Addition of 5 vol.% of the butanal-glycerol acetal reduced the pour point of animal fat biodiesel (methyl ester) from 18 to 13 degrees C. The decrease in the pour point of the glycerol acetals-biodiesel mixtures were dependent on the size of the hydrocarbon chain and the percent blended.

Gliceroquímica: novos produtos e processos a partir da glicerina de produção de biodiesel

Glycerol is a byproduct of biodiesel production through transesterification of oils and fat. This article discusses the chemical transformation of glycerol in ethers, acetals and esters of high technological applications, especially in the fuel sector. Glycerol hydrogenolysis, dehydration to acrolein and oxidation are discussed as well, to show the potential use of glycerol for production of plastic monomers. Finally, the article shows other transformations, such as syn gas production, epichloridrin and glycerin carbonate.

Etherification of glycerol with benzyl alcohol catalyzed by solid acids

In this work we present the results of glycerol etherification with benzyl alcohol, catalyzed by different solid acids. The mono-benzyl-glycerol ether was the main product in the reactions catalyzed by β zeolite and Amberlyst-35 acid resin, whereas di-benzyl-ether was formed in higher yield with the use of p-toluene-sulfonic acid and K-10 montmorillonite as catalyst. Niobic acid was inactive in this reaction. The porous structure of the zeolite impaired the formation of di and tri-benzyl-glycerol ethers.

Reactivity of glycerol/acetone ketal (solketal) and glycerol/formaldehyde acetals toward acid-catalyzed hydrolysis

The effect of temperature, molar ratio and catalyst loading on the acid-catalyzed hydrolysis of glycerol/acetone ketal (solketal) and glycerol/formaldehyde acetals was studied. The reactivity of the solketal was significantly higher than the glycerol/formaldehyde acetals. At 80 oC, 5:1 water/ketal molar ratio and 3.0 mmol of catalyst loading (amberlyst-15) the hydrolysis of the solketal was almost complete, whereas the glycerol/formaldehyde acetals showed around 40% conversion. The higher reactivity of solketal toward hydrolysis is associated with the formation of a tertiary carbocation intermediate, whereas in the case of glycerol/formaldehyde acetals hydrolysis takes place through direct nucleophilic displacement. DFT theoretical calculations of the relative stability of the ketal and acetal isomers, having five and six-membered rings, explain the experimental distribution.

Iron-Exchanged Zeolite as Effective Catalysts for Friedel–Crafts Alkylation with Alkyl Halides

Friedel–Crafts alkylation of benzene and ethylbenzene with butyl halides has been investigated in the presence of iron-exchanged zeolites. The catalysts showed high conversions and selectivity for monoalkylated products with tertiary and secondary halides under mild reaction conditions (45–60°C). Alkylation of ethylbenzene with 2-chlorobutane can be achieved in 99% yield and 100% selectivity to the monoalkylated product.

Oxidative dehydration of glycerol to acrylic acid over vanadium-impregnated zeolite beta

The oxidative dehydration of glycerol to acrylic acid was studied over vanadium-impregnated zeolite Beta. Catalysts were prepared by wet impregnation of ammonium metavanadate over ammonium-exchanged zeolite Beta, followed by air calcination at 823 K. Impregnation reduced the specific surface area, but did not significantly affected the acidity (Bronsted and Lewis) of the zeolites. The catalytic evaluation was carried out in a fixed bed flow reactor using air as the carrier and injecting glycerol by means of a syringe pump. Acrolein was the main product, with acetaldehyde and hydroxy-acetone (acetol) being also formed. Acrylic acid was formed with approximately 25% selectivity at 548 K over the impregnated zeolites. The result can be explained by XPS (X-ray photoelectron spectroscopy) measurements, which indicated a good dispersion of the vanadium inside the pores.

Heterogeneous basic catalysts for biodiesel production

Biodiesel is one the main biofuels used as an alternative to fossil sources. It is mainly produced through the transesterification of oils and fats with methanol, under acid, basic or enzymatic catalysis. Today, the majority of the biodiesel production processes employ homogeneous base catalysts, such as NaOH or NaOCH3, which require expeditious purification procedures and yield significant amounts of waste. This review covers recent achievements in the field of basic heterogeneous catalysts for biodiesel production, focusing on the main systems being employed, their advantages and disadvantages. The present drawbacks and future challenges on basic heterogeneous catalytic systems for biodiesel production are also addressed in the concluding remarks.

Theoretical study of protonation of butene isomers on acidic zeolite: the relative stability among primary, secondary and tertiary alkoxy intermediates

A density functional theory (DFT) study of the protonation of but-1-ene, (E)-but-2-ene and isobutene over a cluster representing the zeolite acid site (HT3) was carried out. At the B3LYP/6-31+G** level of calculation all the reactions were exothermic, with respect to the isolated reactants, in forming an alkoxy species. Formation of a π-complex involving the double bond and the acidic proton was the first step and shows a small dependence with the olefin structure. The proton transfer involves a transition state with carbenium ion like character, which is reflected in the calculated ΔH‡, being higher for the but-1-ene (to afford the 1-butoxy intermediate) and lower for the isobutene (to afford the tert-butoxy intermediate). However, the stability of the alkoxy formed shows a different trend. The tert-butoxy was computed to be only 1.5 kcal mol−1 lower in energy than the π-complex between isobutene and HT3 at the B3LYP/6-31+G** level of calculation, but the reaction becomes endothermic by 2.5 kcal mol−1 when computed at B3LYP/6-311++G**. The calculated order of stability among the alkoxy species was 2-butoxy > 1-butoxy > tert-butoxy. These results show that electronic effects dominate ΔH‡, which is associated with the kinetics of the protonation process, while steric effects play a major role in the stability of the alkoxy, which in turn is related to the thermodynamics of protonation.

Rearrangement, Nucleophilic Substitution, and Halogen Switch Reactions of Alkyl Halides over NaY Zeolite : Formation of the Bicyclobutonium Cation Inside the Zeolite Cavity

Rearrangement and nucleophilic substitution of cyclopropylcarbinyl bromide over NaY and NaY impregnated with NaCl was observed at room temperature. The first-order kinetics are consistent with ionization to the bicyclobutonium cation, followed by internal return of the bromide anion or nucleophilic attack by impregnated NaCl to form cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl chlorides. The product distribution analysis revealed that neither a purely kinetic distribution, similar to what is found in solution, nor the thermodynamic ratio, which favors the allylcarbinyl halide, was observed. Calculations showed that bicyclobutonium and cyclopropylcarbinyl carbocations are minimal over the zeolite structure, and stabilized by hydrogen bonding with the framework structure. A new process of nucleophilic substitution is reported, namely halogen switch, involving alkyl chlorides and bromides of different structures. The reaction occurs inside the zeolite pores, due to the confinement effects and is an additional proof of carbocation formation on zeolites. The results support the idea that zeolites act as solid solvents, permitting ionization and solvation of ionic species.