Esterification Equilibrium Research Articles

Equilibrium of esterification in Chinese distilled liquor (Baijiu) during ageing

Different Baijiu varieties are characterised by their specific flavours and ester aromas. These flavours originate from the process of esterification during long-term ageing. Despite their wide popularity and long history, the mechanism of esterification during ageing has not been experimentally demonstrated. This study aimed to elucidate the esterification mechanism experimentally to promote advances in the ageing technology for Baijiu and to help advance the Baijiu brewing industry to transform it into a carbon-neutral industry. In this study, traditional acid-catalysed conditions were applied and esterification during ageing was accelerated. Equilibrium constants were obtained for the major esters via thermodynamic calculations and these constants were corrected using the experimental results. These corrected constants can predict the acid and ester contents of the liquor during ageing. Thus, the results can also help standardise Baijiu brewing technology.

Enhancing esterification of small molecular acids with alcohols by molten salt hydrates

A novel approach is reported for efficient esterifying low molecular acids with alcohols in molten salt hydrate (MSH) without additional catalyst. A series of MSHs (LiCl, CaCl2, ZnCl2 and ZnBr2) were evaluated for catalytic esterification of chloroacetic acid (CA) with methanol to methyl chloroacetate (MC). The effects of coordination water number also examined. It was found that appropriate coordination water number not only can promote the protonation of the reactant acids, but also enhance the activity of the protons as well as esterification equilibrium towards ester formation. A MC yield of 98.1% with concentration of 92.1% in the organic-phase could be readily achieved after reacting at 80 °C for 2.0 h in CaCl2·4H2O. MSH also demonstrated excellent performance in esterification of other acids (acetic, mercaptoacetic, propionic, n-butyric and levulinic acids) with alcohols (ethanol, n-propanol and n-butanol). After removing portion of the water from MSH, it can be reused without any difficulty. The promotion effects of MSH on the esterification reaction can be categorized to three aspects: (1) accelerating the reaction rate due to the enhanced protonation of the reactant acids and reduction in the hydration degree of the protons; (2) facilitating phase-splitting by virtue of the poor solubility in MSH and thus expelling the formed esters into organic-phase, as a result, boosting up esterification conversions; and (3) promoting the esterification reaction equilibrium owing to the strong hygroscopicity of MSH.Economic analysis shows, compared with the conventional esterification of CA with ethanol, in which organic solvents is used as the water-carrying agent, that esterification in MSH could not only accelerate the reaction rate and strengthen the equilibrium conversion, but also save energy input.

Promotion effect of molten salt hydrate on co-esterification of biomass-derived levulinic and formic acids

Efficient esterification of biomass-derived levulinic acid (LA) to levulinate was investigated in molten salt hydrates (MSH) for the first time. A series of molten salt hydrates (LiBr·3H2O, LiCl·3H2O, ZnCl2·3H2O, CaCl2·3H2O and CaBr2·3H2O) were examined in terms of their catalytic activity and Hammett acidity (H0). Among them, CaBr2·3H2O, ZnBr2·3H2O and ZnCl2·3H2O exhibited excellent activity. It was found that formic acid (FA), a compound that is cogenerated with LA in converting cellulose and hemicellulose as well as their derived sugars, can significantly enhance esterification of LA when reacting in MSHs. Mechanism analysis demonstrated that the promotion effect of FA on the formation of levulinate was resulted from transesterification of LA with butyl formate (BF). Under same conditions, as high as 99.8 % of butyl levulinate (BL) yield was obtained in CaCl2·3H2O, while it was merely 19.6% in the absence of CaCl2·3H2O. Hammett acidity measurement confirmed that CaCl2·3H2O is able to promote the protonation of LA and FA, and thus accelerating the esterification and transesterification reactions. Besides, reacting in CaCl2·3H2O can spontaneously form a biphasic reaction system: an organic phase that mainly consists of BL and n-butanol, and an aqueous phase composed of CaCl2, acids and water. Such a biphasic system help boost the esterification equilibrium and the subsequent separation and purification of the synthesized esters.

Simulation and Parametric Study of the Innovative Process to Produce High Purity Isopropyl Acetate with Ethylene Oxide Hydration as an Auxiliary Reaction

Production of high purity isopropyl acetate by esterification is a difficult process since the equilibrium conversion is relatively low and there are azeotropes between isopropyl acetate with water and between isopropyl acetate with the reactants. In this research, an innovative process to produce high purity isopropyl acetate with auxiliary reaction of ethylene oxide hydration was proposed. The process consisted of a reactor and a simple distillation column. The auxiliary reaction abolished the water/isopropyl acetate azeotrope and shifted the esterification equilibrium to the right. Impacts of the reactor type, the feed temperature, the reflux ratio, and the bottoms rate were investigated by simulating the process in Aspen Plus software. The results revealed that the innovative IpAc production with auxiliary reaction of EO hydration gave very high esterification conversion (up to 99.8%) and very high purity of IpAc (up to 99.7%). These results were achieved when the reactor type was isothermal at feed temperature, the feed temperature was 77°C, the reflux ratio was 1, and the bottoms rate was 10 kmol/h.

CaLB Catalyzed Conversion of ε-Caprolactone in Aqueous Medium. Part 1: Immobilization of CaLB to Microgels.

The enzymatic ring-opening polymerization of lactones is a method of increasing interest for the synthesis of biodegradable and biocompatible polymers. In the past it was shown that immobilization of Candida antarctica lipase B (CaLB) and the reaction medium play an important role in the polymerization ability especially of medium ring size lactones like ε-caprolactone (ε-CL). We investigated a route for the preparation of compartmentalized microgels based on poly(glycidol) in which CaLB was immobilized to increase its esterification ability. To find the ideal environment for CaLB, we investigated the acceptable water concentration and the accessibility for the monomer in model polymerizations in toluene and analyzed the obtained oligomers/polymers by NMR and SEC. We observed a sufficient accessibility for ε-CL to a toluene like hydrophobic phase imitating a hydrophobic microgel. Comparing free CaLB and Novozym® 435 we found that not the monomer concentration but rather the solubility of the enzyme, as well as the water concentration, strongly influences the equilibrium of esterification and hydrolysis. On the basis of these investigations, microgels of different polarity were prepared and successfully loaded with CaLB by physical entrapment. By comparison of immobilized and free CaLB, we demonstrated an effect of the hydrophobicity of the microenvironment of CaLB on its enzymatic activity.

New heterogeneous catalyst for the esterification of fatty acid produced by surface aromatization/sulfonation of oilseed cake

In this work, an efficient heterogeneous acid catalyst for the esterification of oleic acid was prepared directly from oilseed cake by a simple sulfonation with concentrated H2SO4. Characterization by SEM/EDS, IR, Raman, TG, TG/MS, potentiometric titration showed that treatment with H2SO4 for 1, 2 and 4h at 120°C partially dehydrates the cake to form a carbon/cellulose composite which is sulfonated to produce strong SO3H acidic sites. These surface sites were active for the esterification of oleic acid with yields ca. 84%, 88% and 94% in the presence of 5, 10 and 20wt% catalyst, respectively. These results are comparable to 98% yield obtained with 1wt% H2SO4 and higher than 75% observed for a high surface area (880m2g−1) sulfonated activated carbon with similar number of SO3H active groups. These results are discussed in terms of two effects: (i) the number of sulfonic surface acidic groups and (ii) the presence of a hydrophilic cellulosic fraction in the catalyst that adsorbs/traps water formed in the reaction shifting the esterification equilibrium and improving the yield.

Decarboxylative allylation of arylglyoxylic acids with allyl alcohol

A decarboxylative allylation of arylglyoxylic acids with allyl alcohol has been developed. In the presence of catalytic amounts of Pd(dba)2 and PPh3, the substrates are in an esterification equilibrium with the allyl arylglyoxylates, which are continuously decarboxylated to give α,β-unsaturated ketones along with CO2 and water as the only byproducts.

Esterification equilibrium constants of arsonic and arsinic acids

The esterification equilibrium constants between CD3OD and five arsonic acids (methyl, pentyl, phenyl, 2,3- dipalmitoyloxypropyl, and 2,3,4-tripalmitoyloxybutyl) and one arsinic acid (cacodylic acid) were measured in the solvent system CDCl3/CD3OD at 25.0 C. Equilibrium concentrations of the diester, monoester, and free acid for each compound were calculated from the integrations of the corresponding 1 H NMR peaks. It was found that the nature of the organic part of the arsonic acids essentially did not affect the measured equilibrium constants which were around 0.114 and 0.014 for K1 and K2, respectively. However, the equilibrium constant K1 of cacodylic acid was 0.053. Dies- ters and monoesters are very easily hydrolyzed, and in particular the diesters are extensively hydrolyzed even in the presence of tiny amounts of water. Thus, esters of arsonic or arsinic acids with monohydric alcohols are expected to be in very low concentrations inside cells, a conclusion that may be of interest to the ''arsenic bacterium debate''.

Chemical equilibrium of esterification in AcOH-EtOH-H2O-EtOAc system at 293.15 K

New experimental data on the chemical equilibrium of esterification in an acetic acid-ethanol-water-ethyl acetate system at 293.15 K and atmospheric pressure are presented.

Conceptual Design of a Butyl-levulinate Reactive Distillation Process by Incremental Refinement

Butyl-levulinate has been identified as a promising fuel candidate with high oxygen content. Its combustion in diesel engines yields very low soot and NO x emissions. It can be produced by the esterification of butanol and levulinic acid, which themselves are platform chemicals in a biorenewables-based chemical supply chain. Since the equilibrium of esterification limits the conversion in a conventional reactor, reactive distillation can be applied to overcome this limitation. The presence of the high-boiling catalyst sulfuric acid requires a further separation step downstream of the reactive distillation column to recover the catalyst for recycle. Optimal design specifications and an optimal operating point are determined using rigorous flowsheet optimization. The challenging optimization problem is solved by a favorable initialization strategy and continuous reformulation. The design identified has the potential to produce a renewable transportation fuel at reasonable cost.

Pervaporation membrane reactor study for the esterification of acetic acid and isobutanol using polydimethylsiloxane membrane

In this study, isobutyl acetate, a valuable solvent in cosmetics, aroma and paint industries, is produced by pervaporation–esterification equilibrium reaction in a batch pervaporation membrane reactor (PVMR) using homogeneous (sulphuric acid) and heterogeneous (Dowex 50W-X8) catalysts. The effects of catalyst loading, catalyst type, reaction time, membrane thickness, temperature and initial molar ratio of reactants were investigated. A cross-linked polydimethylsiloxane (PDMS) membrane selective to esters was prepared and used in PVMR. Batch reactions were carried out also in a simple batch reactor (SBR) without pervaporation under the same conditions to compare the conversions for the reactions with and without pervaporation. In conclusion, PVMR experiments showed that the PDMS membrane can be used to remove the isobutyl acetate formed selectively with acceptable conversions and pervaporation fluxes.

Sulfonated polystyrene: A catalyst with acid and superabsorbent properties for the esterification of fatty acids

In this work, catalysts with acid and superabsorbent properties were obtained by sulfonation of expanded polystyrene and used to promote the esterification of oleic acid with ethanol. The prepared superabsorbent polymers (SAP) showed high concentration of active sulfonic acid sites (0.7–5.9 mmol acid sites g −1) and high water absorption capacity (445–900 g water g −1). It was observed that the catalytic activity increased with the number of acid site and water absorption capacity. Turnover frequencies suggested that the catalytic activity depends on the accessibility/diffusion processes determined by the crosslinks in the polymer. Commercial sulfonic acid resins and polyacrylate based superabsorbent polymers showed very low activities compared with the SAP produced. The SAP also showed higher activity compared to the homogeneous catalyst p-toluenesulfonic acid. The higher activity of the prepared SAP is discussed in terms of the acidity of sulfonic groups combined with the water absorption which shifts the esterification equilibrium.

Fluorous Biphase System of C 9F 18 and Its Use in Esterification

Some apolar organic solvents is miscible with perfluorous nonene to form fluorous biphase systems. Perfluorous nonene could be used as a green solvent in equimolar esterification of carboxylic acids with alcohols without removal of water or ester formed. Perfluorous nonene made the esterification equilibrium to move right and the yields of esterification to enhance in different degrees as compared with that in the absence of perfluorous nonene. After esterification perfluorous nonene is easy to be recovered and recycled.

In Silico Prediction of Medium Effects on Esterification Equilibrium Using the COSMO-RS Method

This paper presents a new approach for predicting solvent effects on esterification reactions of industrial importance in the field of biocatalysis. The COSMO-RS method has been used to calculate the activity coefficients of the chemical species involved in various reactions, carried out in different solvents. For comparison we also used the traditional UNIFAC method. Three lipase-catalyzed esterifications were considered: (1) 1-dodecanoic acid with menthol in n-hexane, n-heptane, cyclohexane, 2,2,4-trimethylpentane, toluene, acetonitrile, and 2-methyl-2-butanol; (2) 1-dodecanoic acid and 1-dodecanol in n-hexane, n-heptane, cyclohexane, 2,2,4-trimethylpentane, and toluene; and (3) glycerol and n-octanoic acid in acetonitrile, benzene, and toluene and in the neat reaction mixture (without any solvent). Predicted activities were used to calculate the thermodynamic equilibrium ratio. This should be independent of medium, and the variation in COSMO-RS values is at most 9-fold (corresponding to a DeltaG degrees of about 5.5 kJ/mol, which would still be a very useful prediction) and often only 2-fold (corresponding to less than 2 kJ/mol or 0.5 kcal/mol, therefore comparable with experimental error). UNIFAC is weaker, especially when important roles are played by conformational freedom, intramolecular interactions, strong polar effects, and charge distribution of molecules in the mixture. The relative percent deviations from the mean of equilibrium constants in different solvents range between 17 and 49 for COSMO-RS versus 32 to 65 for UNIFAC. The COSMO-RS method opens up new perspectives for the development of theoretical models for solvent selection with general applicability.

Effect of Ionic Liquids on the Chemical Equilibrium of Esterification of Carboxylic Acids with Alcohols.

The esterification of carboxylic acids with alcohols catalyzed by paratoluene sulfonic acid (pTSA) was studied in different room temperature ionic liquids. The chemical equilibrium of esterification can be tuned by using ionic liquids as solvents.

Effect of Ionic Liquids on the Chemical Equilibrium of Esterification of Carboxylic Acids with Alcohols

The esterification of carboxylic acids with alcohols catalyzed by para-toluene sulfonic acid (pTSA) was studied in different room temperature ionic liquids. The chemical equilibrium of esterification can be tuned by using ionic liquids as solvents.

Pressure Tuning of Reaction Equilibrium of Esterification of Acetic Acid with Ethanol in Compressed CO2

The esterification of acetic acid and ethanol in compressed CO2 was studied at 333.2 K and at pressures up to 16 MPa, and the original molar ratio of the components was CO2:CH3COOH:CH3CH2OH:p-toluenesulfonic acid (catalyst) = 90:5:5:0.05. The phase behavior and the isothermal compressibility (kT) of reaction system was also determined under the reaction conditions. The conversion increases with increasing pressure in the two-phase region and reaches a maximum in the critical region of the reaction system where the system just becomes one phase. Then the conversion or apparent equilibrium constant Kx decreases with pressure after the pressure is higher than the critical value. In the supercritical region where the system is one phase, Kx is closely related to the isothermal compressibility and degree of inhomogeneity of the fluid, which is often referred to as the local density and/or local composition enhancement. At the higher pressures the “clustering” in the reaction system is not significant and the Kx is close to that of the reaction in the absence of CO2.

Kinetic model for an esterification process coupled by pervaporation

A basic kinetic model of an esterification process coupled by pervaporation and a new method for measuring the model parameter had been established. Various effects on the shift of chemical equilibrium of esterification were taken into consideration in this kinetic model. The simulation results of this model coincided well with the experimental results.

Esterification, condensation, and deprotonation equilibria of trimethylsilanol

We investigate by 29Si NMR the equilibrium behavior of trimethylsilanol in both acidic and alkaline ethanol/water solutions. This system is of interest not only for passivation (silylation) of organic and inorganic hydroxide-containing compounds, but also as a model of higher silane functionality systems yielding silica coatings, silicones, gels, and zeolites. Because silanol esterification, condensation, and deprotonation reactions are often coupled, one cannot easily monitor the individual reaction equilibria in multifunctional silane systems. Here, though, we measure the equilibrium species distribution in a monofunctional model system to estimate the equilibrium constants – including for the first time the esterification equilibrium constant of a silanol in alkaline conditions. Our main findings are: (1) the measured esterification equilibrium constants agree with previous values from dioxane-based solutions and with pseudoequilibrium data for multi-functional silanes in ethanol–water solutions (suggesting that substitution effects for silanol esterification equilibrium coefficients are negligible), (2) the measured equilibrium deprotonation constant agrees with silanol acidities reported in a dioxane-based system, and (3) the solvent environment affects the apparent silanol condensation equilibrium constants significantly. In alkaline systems, while silanol deprotonation affects solution pH even at low base concentrations, it affects the silicate speciation only at high base concentrations. Finally, we find a strong and nearly linear correlation between 29Si NMR chemical shift and the degree of trimethylsilanol deprotonation.

Measurement of equilibrium constants for the formation of esters from aliphatic carboxylic acids and alcohols

A method for assessing the magnitude of esterification equilibrium constants for a series of alkyl acetates is described. The constants are quite sensitive to electronic effects, with the largest values being obtained for those in which the alkyl groups are electron donating