Transesterification Of Tributyrin Research Articles

Increasing the catalytic efficiency of Candida rugosa lipase for the synthesis of tert-alkyl butyrates in low-water media

Reactions involving tert-alcohols and their esters are generally not catalyzed by lipases. Candida rugosa lipase is one of the few lipases which shows at least limited catalytic activity towards tert-alcohols and their esters. Using transesterification of tributyrin with tertiary butyl and amyl alcohols as a model reaction, it is shown that precipitation of lipase by a tertiary alcohol in the presence of a buffer with optimum concentration enhances the catalytic activity 7 fold as compared to rates obtained with lyophilized powders. Optimization of the ratio of triglyceride to tert-alcohols and medium engineering gave an initial rate which was 41 times higher than that obtained with lyophilized powders. Hence, use of a simple enzyme formulation, coupled with optimization of reaction conditions led to Candida rugosa lipase becoming a useful catalyst for catalyzing transesterification involving tertiary alcohols.

Glycerol-Intercalated Mg-Al Hydrotalcite as a Potential Solid Base Catalyst for Transesterification

AbstractGlycerol is a byproduct of biodiesel synthesis by transesterification of triglycerides with short-chain alcohols in the presence of solid base catalysts. Because hydrotalcite is a potentially useful basic catalyst for the transesterification reaction, the interaction of glycerol with hydrotalcite is the focus of this work. Glycerol was intercalated into Mg-Al hydrotalcite with a Mg/Al molar ratio of 4 under elevated temperatures of 4432/503 K in the absence and presence of NaOH. The resulting materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and N2 adsorption. The amount of glycerol incorporated into hydrotalcite increased with increasing temperature of intercalation. However, the brucite-like sheets of hydrotalcite partially decomposed during the intercalation process at the highest temperature. The presence of NaOH stabilized the hydrotalcite layers against decomposition under high temperature (503 K). The intercalated materials exposed large surface areas ranging from 142 to 663 m2 g−1, depending on the preparation conditions. The glycerol-intercalated hydrotalcites were less catalytically active than hydrotalcite with OH− counterions for the transesterification of tributyrin with methanol. The lower reactivity of glycerol-intercalated hydrotalcite was probably the result of a strong interaction between the intercalated glycerolate (HOCH2-CHOH-CH2O−) and the partially decomposed brucite-like sheets.

Cs Promoted Triglyceride Transesterification Over MgO Nanocatalysts

The influence of Cs on the structure and basicity of nanocrystalline MgO was assessed via electron microscopy, CO2 chemisorption, XRD and XPS. Caesium incorporation via co-precipitation under supercritical conditions generates Cs2Mg(CO3)2 nanocrystallites with an enhanced density and strength of surface base sites. Wet impregnation proved less effective for modifying MgO nanocrystals. A strong synergy between Cs and Mg components in the co-precipitated material dramatically enhanced the rate of tributyrin transesterification with methanol relative to undoped MgO and homogeneous Cs2CO3 catalysts. On-stream deactivation of Cs-doped MgO reflects heavy surface carbon deposition and loss of the high activity Cs2Mg(CO3)2 phase due to limited Cs dissolution.

Intercalation of Ethylene Glycol into Yttrium Hydroxide Layered Materials

Intercalation of ethylene glycol into layered yttrium hydroxide containing nitrate counterions was accomplished by heating the reagents in a methanol solution of sodium methoxide under autogenous pressure at 413 K for 20 h. The resulting crystalline material had an expanded interlayer distance of 10.96 A, confirming the intercalation of an ethylene glycol derived species. Characterization of the material by FT-IR spectroscopy, thermogravimetric analysis, and the catalytic transesterification of tributyrin with methanol was consistent with direct bonding of ethylene glycolate anions (O(2)C(2)H(5)(-)) to the yttrium hydroxide layers, forming Y-O-C bonds. The layers of the material are proposed to be held together by H-bonding between the hydroxyls of grafted ethylene glycol molecules attached to adjacent layers. Glycerol can also be intercalated into yttrium hydroxide layered materials by a similar method.

Transesterification of tributyrin with methanol over basic Mg:Zr mixed oxide catalysts

Two series of Mg:Zr mixed oxides, prepared by either co-precipitation or sol–gel synthesis, were characterized and evaluated in the base catalyzed transesterification of tributyrin with methanol. A co-precipitated Mg-rich mixed oxide catalyst with Mg:Zr 11:1 was approximately 300% more active than MgO on a surface area basis, whereas pure ZrO2 was inactive for the reaction. To explore the nature of the activity enhancement, samples were characterized by X-ray diffraction, N2 adsorption, CO2 adsorption microcalorimetry and DRIFTS of adsorbed CO2 and CH3OH. Although the sol–gel synthesis method provided better atomic level mixing of Mg and Zr, the resulting catalysts were not as effective as mixed oxides prepared by co-precipitation. The most active mixed oxide (Mg:Zr 11:1) exhibited a high initial heat of CO2 adsorption and modified modes of methanol adsorption compared to MgO. However, the CO2 adsorption capacity did not correlate to catalyst activity.

In situ studies of structure–reactivity relations in biodiesel synthesis over nanocrystalline MgO

High temperature processing of solvothermally synthesised MgO nanoparticles promotes striking changes in their morphology, and surface chemical and electronic structure. As-prepared NanoMgO comprised ∼4 nm cubic periclase nanocrystals, interspersed within an amorphous Mg(OH)(OCH 3) matrix. These crystallites appear predominantly (1 0 0) terminated, and the overall material exhibits carbonate and hydroxyl surface functionalities of predominantly weak/moderate base character. Heating promotes gradual crystallisation and growth of the MgO nanoparticles, and concomitant loss of Mg(OH)(OCH 3). In situ DRIFTS confirms the residual precursor and surface carbonate begin to decompose above 300 °C, while in situ XPS shows these morphological changes are accompanied by the disappearance of surface hydroxyl/methoxide species and genesis of O − centres which enhance both the surface density and basicity of the resulting stepped and defective MgO nanocrystals. The catalytic performance in tributyrin transesterification with methanol is directly proportional to the density of strong surface base sites.

Influence of textural properties and trace water on the reactivity and deactivation of reconstructed layered hydroxide catalysts for transesterification of tributyrin with methanol

Magnesium–aluminum hydrotalcites with a Mg/Al molar ratio of 2 were prepared by coprecipitation or by urea hydrolysis. The as-prepared samples, as well as their activated analogues, were characterized by N 2 physisorption, phenol chemisorption, SEM, XRD, TGA, and DRIFTS. The base-catalyzed transesterification of tributyrin with methanol at 333 K was used to probe the reactivity of the materials. The reconstructed hydrotalcite samples exhibited much higher catalytic activity than the mixed oxides of Mg and Al. Nevertheless, the turnover frequency for the reaction was about two orders of magnitude lower than that of homogeneous sodium methoxide. Variations in the textural properties of the reconstructed hydrotalcite catalysts did not significantly affect the surface base site density or the turnover rate of transesterification. However, the presence of trace water not only enhanced the transesterification reaction rate but also led to severe catalyst deactivation. Characterization of deactivated catalysts revealed a replacement of the interlayer Brønsted base sites with butyric anions, which led to an expansion of the interlayer distance.

Transesterification of tributyrin with methanol over calcium oxide catalysts prepared from various precursors

Abstract Calcium oxide catalysts were prepared by calcining various precursors such as calcium acetate, carbonate, hydroxide, nitrate and oxalate and their catalytic activities were examined in the transesterification of tributyrin with methanol. The prepared calcium oxide catalysts were characterized using thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption and temperature programmed desorption (TPD) of CO2. The calcium oxide catalyst obtained by calcining calcium hydroxide at 600–800 °C showed the highest tributyrin conversion and methyl butyrate yield. The large desorption peak of CO2 TPD confirmed that its numerous basic sites were responsible for its high activity. The low-temperature decomposition of calcium hydroxide provided many nano-sized pores with strong basic sites. Although the activity of the calcium oxide catalyst prepared from calcium hydroxide was high, its activity was one order of magnitude less than that of sodium hydroxide catalyst. The dissolution of calcium oxide catalysts in products and their repeated uses were also investigated to discuss their advantages as heterogeneous catalysts in the production of biodiesel.

The exceptional activity of a phosphazenium hydroxide catalyst incorporated onto silica in the transesterification of tributyrin with methanol

A phosphazenium hydroxide catalyst incorporated onto silica showed exceptional activity in the transesterification of tributyrin with methanol and could be used repeatedly without suffering any appreciable deactivation.

Influence of water on the activity and stability of activated Mg [sbnd]Al hydrotalcites for the transesterification of tributyrin with methanol

Magnesium–aluminum hydrotalcite with a Mg/Al molar ratio of 4 was synthesized by a coprecipitation method. Thermally-decomposed and rehydrated Mg–Al hydrotalcites were used to catalyze the transesterification of tributyrin, a model triglyceride, with methanol (tributyrin:methanol molar ratio 1:30) at 333 K to produce methyl butyrate, monobutyrin, dibutyrin, and glycerol. The pseudo first order rate constants of a three step reaction sequence for tributyrin transesterification were determined by fitting a kinetic model to the experimental data. Although decomposed and rehydrated Mg–Al hydrotalcite was one order of magnitude more active than decomposed Mg–Al hydrotalcite based on surface area measured by N 2 adsorption, the activity correlated well to the CO 2 adsorption capacity. The most active rehydrated samples also deactivated faster, presumably because butyric acid produced by hydrolysis of ester with adsorbed water reacted with the base sites. The areal rate and CO 2 adsorption capacity of decomposed-rehydrated Mg–Al hydrotalcite decreased as the interlayer water was removed by heating.

Comparative study of triglyceride transesterification in the presence of catalytic amounts of sodium, magnesium, and calcium methoxides

Abstract A solution of Mg(OCH3)2 in methanol, in-house prepared solid MgOx(OCH3)2−2x, and commercial Ca(OCH3)2 were tested at 60 °C in transesterification of tributyrin with methanol—a model reaction for biodiesel production. The homogeneous magnesium methoxide acts fast at the beginning of the reaction but quickly forms a suspension/precipitate mixture of much lower catalytic activity. The precipitate was found to be a complex composition including glycerol and butyric acid derivatives. The reaction over solid MgOx(OCH3)2−2x is catalytic but sluggish with deactivation taking place in ca. 4 h. Analysis of the used catalyst revealed surface butyric acid as the most likely species responsible for the catalyst deactivation. In the presence of Ca(OCH3)2, the yields of the products reach final values in about 4 h. The reaction starts as a heterogeneous process, however, interaction of Ca(OCH3)2 with reaction products such as glycerol gives rise to catalytically active homogeneous species. Formed in a side reaction calcium butyric acid derivatives contribute to Ca(OCH3)2 dissolution but do not deactivate the surface of the catalyst.

Structure–activity relations in Cs-doped heteropolyacid catalysts for biodiesel production

A series of insoluble heteropolytungstate (H 3PW 12O 40 HPW) salts, Cs x H 3− x PW 12O 40 ( x = 0.9 – 3 ), were synthesized and characterized using a range of bulk and surface sensitive probes including N 2 porosimetry, powder XRD, FTIR, XPS, 31P MAS NMR, and NH 3 calorimetry. Materials with Cs content in the range x = 2.0 – 2.7 were composed of dispersed crystallites with surface areas ∼100 m 2 g −1 and high Brönsted acid strengths [ Δ H ads 0 ( NH 3 ) = − 150 kJ mol −1 ], similar to the parent heteropolyacid. The number of accessible surface acid sites probed by α-pinene isomerization correlated well with those determined by NH 3 adsorption calorimetry and surface area measurements. Cs x H 3− x PW 12O 40 were active toward the esterification of palmitic acid and transesterification of tributyrin, important steps in fatty acid and ester processing for biodiesel synthesis. Optimum performance occurs for Cs loadings of x = 2.0 – 2.3 , correlating with the accessible surface acid site density. These catalysts were recoverable with no leaching of soluble HPW.

Preparation of cross-linked enzyme aggregates by using bovine serum albumin as a proteic feeder

Addition of bovine serum albumin (BSA) as a proteic feeder facilitates obtaining cross-linked enzyme aggregates (CLEAs) in cases where the protein concentration in the enzyme preparation is low and/or the enzyme activity is vulnerable to the high concentration of glutaraldehyde required to obtain aggregates. CLEAs of Pseudomonas cepacia lipase and penicillin acylase were prepared. CLEA of lipase prepared in the presence of BSA retained 100% activity whereas CLEA prepared without BSA retained only 0.4% activity of the starting enzyme preparation. Lipase CLEA showed 12-fold increase in activity over free enzyme powder when the CLEA was used in transesterification of tributyrin. For the transesterification of Jatropha oil, while free enzyme powder required 8 h and 50 mg lipase to obtain 77% conversion, CLEA required only 6 h and 6.25 mg lipase to obtain 90% conversion. In the case of penicillin acylase, 86% activity could be retained in CLEA prepared with BSA whereas CLEA made without BSA retained only 50% activity. CLEA prepared without BSA lost 20% activity after 8 h at 45 °C whereas CLEA with BSA retained full activity. CLEA prepared with BSA showed V max/ K m of 36.3 min −1 whereas CLEA prepared without BSA had V max/ K m of 17.4 min −1 only. Scanning electron microscopy analysis showed that CLEAs prepared in the presence of BSA were less amorphous and closer in morphology to CLEAs of other enzymes described in the literature.

Regioselective lipase‐catalyzed transesterification of tributyrin. Influence of salt hydrates on acyl migration

The influence of the nature of solid salt hydrates on the rate of hexanoic acid catalyzed acyl migration in 1,2‐dibutyrin has been examined in hexane. The results show that the rate of acyl migration is faster when hydrogen phosphate salts are included compared to sulfate salts. The rate is essentially the same in the presence of sulfate salts and without salts. In regioselective lipase‐catalyzed acidolysis of tributyrin with hexanoic acid, the use of hydrogen phosphate salts to control water activity leads to a higher rate of migration than the use of sulfate salts. Minor differences are observed in interesterification with ethyl hexanoate.

Lipase-catalyzed transesterification in organic solvent: effects of water and solvent, thermal stability and some applications

The lipase-catalyzed transesterification of tributyrin with various alcohols in a heterogeneous system was investigated using powdered enzyme suspended in numerous organic solvents. There is an optimum water content, (H 2O) op, where the enzyme shows the maximal activity and its value is affected by the hydration of the enzyme and the substrate, coagulation of the enzyme, the nature (water-miscible/immiscible) of the solvent and the water equilibrium between the enzyme and the substrate solution. In a water-restricted environment, Pseudomonas lipases were very stable and showed enzymatic activities, parts of which were restored by water supplementation. This suggests that a thermally azeotropic dehydration plays a part in the thermoinactivation of the enzyme in organic solvents. The catalytic activity of the enzyme was predominantly determined by the polarity and the structure of the solvent, and the dehydration of the enzyme by the solvent. The reactivity of an aliphatic primary alcohol bearing a straight chain was dependent on the nature of the solvent and differed from that for enzymatic hydrolysis of the corresponding alkyl butyrate in aqueous solution. Investigations of the transesterification with 2-alkanol confirmed a synthetic strategy of the optically active esters and optical resolution of the alcohol.

Quantitative analysis and determination of the enantiomeric purity of glycerides by 13C NMR spectroscopy. Application to the lipase‐catalysed transesterification of triacylglycerides

Abstract13C NMR spectroscopy can be used for the quantitative analysis of mixtures of glycerides and the enantiomeric purity can be determined by using Eu(hfbe)3‐d reagent. This technique was applied to the study of the reaction mixture obtained from the transesterification of tributyrin catalysed by My‐lipase (Candida cylindracea). A ‘preference’ of this lipase for the pro‐R ester function of tributyrin is demonstrated.