From residual to useful oil: Revalorization of glycerine from the biodiesel synthesis

The reaction kinetics for the synthesis of glycerol triacetate (triacetin) from glycerol and acetic acid has been studied in the frame of revalorization of residual glycerol in biodiesel production. The reaction has taken place in a stirred reactor at a pressure of 1070 kPa. No external catalyst has been added because the reaction performs better by using as catalyst an excess of acetic acid. Kinetic parameters were obtained at 120 and 160 °C and a model of three reactions with monoacetin, diacetin and triacetin formation was proposed with a good agreement with the experimental results. Arrhenius constants were determined for the involved reactions.     

Transesterification of triglycerides in high and low quality oil feeds over an HT2 hydrotalcite catalyst

The use of a heterogeneous catalyst, in the transesterification reaction of refined and acidic cottonseed oil for the production of methyl-esters (biodiesel) has been studied. The basic Mg-Al-CO3 hydrotalcite catalyst used showed a high activity for methanolysis and esterification reactions in a refined and an acidic cottonseed oil as well as in a representative high water content animal fat feed. The experiments were performed in a temperature range between 180 and 210 degrees C, in a batch reactor. The methanol to vegetable oil molar ratio was 6 to 1, while the catalyst concentration was fixed at 1 wt.% of the oil mass. Non-calcined and calcined forms of the catalyst were tested. The activity of the calcined catalyst was lower than the initial activity of the non-calcined catalytic system but it appeared the same with the reused non-calcined system.     

Highly efficient Brønsted acidic ionic liquid-based catalysts for biodiesel synthesis from vegetable oils

Biodiesel has been produced by transesterification of canola oil with methanol in the presence of highly Br?nsted acidic ionic liquids based on 1-benzyl-1H-benzimidazole, and the effect of reaction temperature, type and amount of catalyst, molar ratio and reaction time investigated. The results show that the 4B ionic liquid has the highest catalytic activity and best recyclability under the optimised reaction conditions. Thus, this ionic liquid is able to catalyze the transesterification of canola oil to its methyl esters in 5 h with yields of more than 95%. Density functional calculations (B3LYP), using the 6-311G basis set, have been performed to have a better understanding on the reactivity of these catalysts. The catalytic activity of 4B for the transesterification of other vegetable oils and alcohols has also been studied.     

发酵体系中氨态氮含量的测定及影响因素的探讨

靛酚蓝-分光光度法是一种灵敏度高、设备要求简单、线性相关性好、重现性高的氨态氮检测方法。本文对该方法的检测波长,反应温度、时间以及催化剂浓度等条件进行了优化,确定了最佳的检测波长为637nm,最佳的反应条件为37℃、25 mg.L-1的催化剂和20 m in的反应时间。并由此得到一条线性相关系数为0.9996的氨态氮检测标准曲线。同时,对靛酚蓝法测定氨态氮用于普通发酵体系进行了探讨。对常用发酵基质如炭源、氮源、金属离子以及消泡剂等进行了考察,结果发现这些常用基质基本不影响本法用于氨态氮的测定。最后,将这种氨氮测定方法用于泰乐菌素和阿维菌素的发酵实践,取得了良好效果,由此证明该方法是一种切实可行的发酵中氨态氮的检测方法。     

Reaction pathways in the decomposition of hydrogen peroxide catalyzed by copper(II)

The kinetics of the decomposition of H(2)O(2) catalyzed by Cu(II) has been studied by the initial-rate method in aqueous phosphate media at near physiological pH. The activity of the catalyst is increased by [Fe(CN)(6)](3-) and decreased by VO(3)(-), CrO(4)(2-) and Zn(II). Three reaction pathways are involved in the Cu(II)-H(2)O(2) reaction, the kinetic orders of the catalyst being 1 (rate constant k1), 2 (rate constant k2) and 3 (rate constant k3). The three pathways present fractional apparent orders (>1) in H(2)O(2) and base catalysis. The apparent activation energies associated to rate constants k1, k2 and k3 are 102+/-4, 65+/-8 and 61+/-5 kJ mol(-1). Free-radical chain mechanisms are proposed for the three pathways.     

Carboxymethylation of pine wood subjected to microwave irradiation after pretreatment in an “acetic acid-hydrogen peroxide-water-catalyst” system

Pretreatment of pine wood in a mixture containing acetic acid, hydrogen peroxide, water, and catalyst has been performed in order to minimize wood component destruction and analyze the behavior of the principal components of pine wood upon carboxymethylation. The effects of catalysts (sulfuric acid or ammonium molybdate) and the characteristics of the microwave radiation on the composition of the solid residue have been investigated. The reaction of pine wood carboxymethylation after pretreatment in a mixture of acetic acid, hydrogen peroxide, water, and catalyst has been studied. Formation of highly substituted carboxymethylated derivatives containing 17–29% carboxymethyl groups has been demonstrated for pine wood. Solubility of carboxymethylated pine wood depended on the nature of the catalyst used during pretreatment. Carboxymethylation products obtained with sulfuric acid as catalyst had the highest solubility.     

Dynamic kinetic asymmetric transfer hydrogenation of racemic 2,4-diaryl-2,3-dihydrobenzo[b][1,4]diazepines catalyzed by chiral phosphoric acids

Dynamic kinetic Transfer hydrogenation reaction of 2-methyl-2,4-diaryl-2,3-dihydrobenzo[b][1,4]diazepines, using phosphoric acids as catalysts and Hantzsch ester as hydride source, has been studied. A 3,3′-H8-binol derived phosphoric acid has been identified the optimal chiral catalyst for this transformation, affording 1,3-diamine derivatives with up to 8/1 dr, 86% ee and 94% ee for the major and minor diastereomers, respectively.     

Optimization Studies and Chemical Kinetics of Silica Sulfuric Acid-Catalyzed Biodiesel Synthesis from Waste Cooking Oil

In the present study conversion of waste cooking oil to biodiesel has been carried out via simultaneous esterification and transesterification reaction over silica sulfuric acid as a solid acid catalyst. The process variables that influence the fatty acid methyl ester (FAME) conversion, such as reaction temperature, reaction time, catalyst concentration and methanol to oil molar ratio were investigated and optimized using Taguchi method. Highest FAME production obtained under the optimized condition was 98.66 %. Analysis of variance revealed that temperature was the most significant factor effecting the FAME production among four factors studied. From the kinetic study, the reaction was found to follow pseudo first-order kinetics and rate constant of the reaction under optimum condition was 0.00852 min^?1.     

One-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones using CuBr2 as catalyst

A simple, efficient procedure and improved conditions have been found to carry out the Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives. This synthesis was performed using CuBr2 as the catalyst in ethanol solution. The optimum conditions were as follows: the molar ratio of aldehyde to alpha,beta-diketone to urea or thiourea is 1:1:1:0.5, the molar ratio of catalyst to aldehyde is 25%, and the reaction time is 4 h.Under the above conditions, the highest yield of dihydropyrimidinones was up to 95%. Compared with the classical Biginelli reaction conditions, this new method has the advantage of excellent yields and short reaction times.     

Energetics of ribonuclease A catalysis. 2. Nonenzymatic hydrolysis of cytidine cyclic 2',3'-phosphate

Various kinetic aspects of the nonenzymatic hydrolysis of cytidine cyclic 2',3'-phosphate and uridine cyclic 2',3'-phosphate have been studied in order to provide a basis for comparison with the ribonuclease A catalyzed hydrolysis reaction. Studies of the pH dependence of the nonenzymatic reaction reveal mechanisms that are first order in hydroxide concentration and second order in hydrogen ion concentration, in addition to a "water" reaction. The rate constant for the water reaction was found to be very small, approximately equal to 2.5 X 10(-6) min-1. General base catalyzed hydrolysis reactions were also studied with imidazole as the catalyst. At pH values in which both the protonated and neutral forms of imidazole are present, a kinetic mechanism was observed that appears to be second order in total imidazole concentration, thus suggesting that bifunctional catalysis occurs. The activation enthalpy for the hydroxide, hydrogen ion, water, and imidazole catalyzed reactions was determined.     

Anchoring of palladium(II) in chemically modified mesoporous silica: An efficient heterogeneous catalyst for Suzuki cross-coupling reaction

The synthesis and characterization of a highly efficient and reusable catalyst, Pd(II) immobilized in mesoporous silica MCM-41, are described. Pd(II) Schiff-base moiety has been anchored onto mesoporous silica surface via silicon alkoxide chemistry. The catalyst has been characterized by small-angle X-ray diffraction (SAX), FTIR and electronic spectroscopy as well as elemental analysis. The catalyst is used in Suzuki cross-coupling reaction of various aryl halides, including less reactive chlorobenzene, and phenylboronic acid to give biaryls in excellent yields without any additive or ligand. High selectivity for the bi-aryl products containing both electron-donating and electron-withdrawing substituents, mild reaction conditions and possibility of easy recycle makes the catalyst highly desirable to address the industrial needs and environmental concerns.     

Solvent effects on biocatalysis in organic systems: equilibrium position and rates of lipase catalyzed esterification

Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.     

Synthesis of cyclic silyl nucleosides having bulky groups on the silicon atom

Synthesis of cyclic silyl nucleosides having bulky tert-butyl groups on the silicon atom has been investigated. Cyclic silyl deoxyribonucleosides having one tert-butyl group on the silicon atom was obtained without difficulty in the standard silylation reaction using dichlorosilane and imidazole. However, under similar conditions the reaction with di-tert-butyldichloro-silane proceeded only slowly by virtue of steric hindrance. The reaction has been largely improved by the use of 1-hydroxy-benzotriazole as a catalyst for silyl transfer and silver salts of acids to generate silylating reagents of high reactivity.     

Molecular modeling approach to elucidate gas phase hydrodeoxygenation of guaiacol over a Pd(111) catalyst within DFT framework

Excessive amounts of oxy-functional groups in unprocessed bio-oil vitiate its quality as fuel; therefore, it has to be channelized to upgrading processes, and catalytic hydrodeoxygenation is one of the most suitable routes for the upgrading of crude bio-oil. In this computational work, catalytic hydrodeoxygenation (HDO) of guaiacol, which is an important phenolic compound of crude bio-oil, has been carried out using density functional theory (DFT) over a Pd(111) catalyst. The Pd(111) catalyst surface does not endorse direct eliminations of functional groups of guaiacol; however, it is found to perform excellently in stepwise dehydrogenation reactions of oxy-functionals of guaiacol according to present DFT results. The catechol product, formed through dehydrogenation of the methoxy group, followed by elimination of CH₂ and association of the hydrogen atom, has been identified as one of the major products. The overall reaction rate is controlled by scission of CH₂ from 2-methylene-oxy-phenol with an activation energy demand of 23.06 kcal mol^–1. Further, the kinetic analysis of each reaction step involved in HDO of guaiacol over the Pd(111) catalyst surface has also been carried out at atmospheric pressure and at a wide range of temperatures from 473 to 673 K, with temperature intervals of 50 K. In the kinetic analysis part, various kinetic parameters, such as forward and reverse reaction rate constants, Arrhenius constants, and equilibrium rate constants, are reported. The kinetic modeling of the dominating reaction steps has revealed that even a lower temperature of 473 K provides a favorable reaction environment; and the temperature increment further improves the reaction favorability.     

Labeling study of avidin by modular method for affinity labeling (MoAL)

We studied the specific labeling of avidin with biotinylated modular ligand catalysts via MoAL, which we recently established. The labeling yield was found to depend on the linker length connecting the catalytic site to biotin in the modular ligand catalyst 1, and the maximum yield was obtained with 1d possessing octamethylene linker. The labeling reaction reached a maximum rate with only 4 equiv of the ligand catalyst. Presumably, all the subunits of avidin with homotetrameric structure formed a stable complex with 4 equiv of the catalyst because of the extremely high affinity. The ligand catalyst bound to avidin first catalyzed N-triazinylation of the ε-amino group of Lys111, and the resulting regenerated catalyst then catalyzed the reaction of Asp108 and CDMT.     

The modulation of membrane fluidity by hydrogenation processes. II. Homogeneous catalysis and model biomembranes

A homogeneous catalyst, chlorotris (triphenylphosphine) rhodium (I) has been incorporated into model biomembrane structures in the form of lipid bilayer dispersions in water. This enables the hydrogenation of the double bonds of the unsaturated lipids within the bilayers to be accomplished. To decide the optimum conditions for efficient hydrogenation the reaction conditions have been varied. The effect of catalyst concentration, hydrogen gas pressure and lipid composition (with and without cholesterol) have all been studied. The partition of the catalyst into the lipid medium was checked by rhodium analysis. The results show that an increase of catalyst concentration or an increase of hydrogen gas pressure leads to increasing rates of hydrogenation. Successful hydrogenation was accomplished with different types of lipid dispersions (mitochondrial, microsomal and erythrocyte lipids). A selectivity of the homogeneous hydrogenation process is indicated. The polyunsaturated fatty acyl residues are hydrogenated at an earlier stage and at a faster rate than the monoenoic acids. Furthermore, an increase in the proportion of cholesterol to lipid within the bilayer structures causes a progressive decrease in the rate of hydrogenation. The fluidity of the lipid bilayers can be altered to such an extent by the hydrogenation process that new sharp endotherms corresponding to the order-disorder transition of saturated lipids occur at temperatures as high as 319 K. Some potential uses of hydrogenation for the modulation of cell membrane fluidity are discussed as well as the design of new types of catalyst molecules.     

Autocatalytic enzyme system for amplification of light signals

High-sensitivity systems are considered in which a low trypsin (EC 3.4.21.4) concentration can be increased by several factors by means of an autoactivation reaction. This amplification of a catalyst makes it possible to reveal weak effects resulting in trypsin generation. For this purpose, the pH-dependent and light-sensitive systems inducing active trypsin have been studied in the presence of trypsinogen. The application of such systems to detect superweak light signals has been shown to be practicable.     

Etherification of biodiesel-derived glycerol with ethanol for fuel formulation over sulfonic modified catalysts

The present study is focused on the etherification of biodiesel-derived glycerol with anhydrous ethanol over arenesulfonic acid-functionalized mesostructured silicas to produce ethyl ethers of glycerol that can be used as gasoline or diesel fuel biocomponents. Within the studied range, the best conditions to maximize glycerol conversion and yield towards ethyl-glycerols are: T = 200 °C, ethanol/glycerol molar ratio = 15/1, and catalyst loading = 19 wt%. Under these reaction conditions, 74% glycerol conversion and 42% yield to ethyl ethers have been achieved after 4 h of reaction but with a significant presence of glycerol by-products. In contrast, lower reaction temperatures (T = 160 °C) and moderate catalyst loading (14 wt%) in presence of a high ethanol concentration (ethanol/glycerol molar ratio = 15/1) are necessary to avoid the formation of glycerol by-products and maximize ethyl-glycerols selectivity. Interestingly, a close catalytic performance to that achieved using high purity glycerol has been obtained with low-grade water-containing glycerol.     

A novel preparation of methyl-β-cyclodextrin from dimethyl carbonate and β-cyclodextrin

A novel green synthesis process about methyl-β-cyclodextrin has been investigated through the reaction between β-cyclodextrin and dimethyl carbonate by anhydrous potassium carbonate as catalyst in DMF. The influence of experimental factors including the molar ratio of dimethyl carbonate to β-cyclodextrin, reaction temperature, and reaction time on the average degree of substitution of methyl-β-cyclodextrin was studied. The results show that the average degree of substitution of methyl-β-cyclodextrin can be dependent on the reaction temperature and the molar ratio of raw material primarily. The structures of methyl-β-cyclodextrin were characterized by TLC, IR, MS, ¹H NMR, and ¹³C NMR.     

Influence of vegetable oils fatty-acid composition on biodiesel optimization

Biodiesel is an alternative fuel for diesel engines produced through transesterification of oleaginous feedstocks. To analyze the influence of the fatty-acid composition on biodiesel optimization, transesterification of several vegetable oils has been studied. Reactions were carried out in flasks filled with vegetable oils, heated to the reaction temperature and stirred at 1100 rpm. The reactions started when the methanol and potassium hydroxide solutions were added to the flasks. Concentration of catalyst, amount of methanol, reaction temperature and time were optimized using a factorial design and a surface response design. Also, a kinetics study was carried out to optimize the reaction time. Results showed that reaction parameters optimal values depend on the oil chemical and physical properties. It can be concluded from this field trial that the effect of both catalyst concentration and reaction time over the transesterification yield is greatly influenced by the saturation degree and fatty-acid chain length.