Enhancing reaction rate of transesterification of glycerol monostearate and methanol by CO(2)

The effect of CO2 as a green additive on the reaction rate of transesterification of glycerol monostearate with methanol was studied at 333.15 and 343.15 K up to 10.5 MPa. It was demonstrated that addition of CO2 in the reaction system could increase the reaction rate significantly. The phase behavior of the CO2+methanol+ glycerol monostearate ternary system was also determined at 333.15 and 343.15 K. It is shown that addition of CO2 can enhance the miscibility of the reactant. The main reasons for the reaction rate enhancement are that CO2 can enhance the miscibility of the reactants, reduce the viscosity of the reaction mixture, and increase the diffusion coefficients of the reactants.     

Understanding the role of noncovalent interactions on the rate of some Diels-Alder reactions in different solvents

In this article, the role of noncovalent interactions (NCI) on four types of cycloaddition reactions in different solvents was investigated by employing quantum chemistry calculations. For this purpose, explicit and implicit solvation models were applied in the experimental conditions of temperature and pressure. NCI analysis indicates that van der Waals (vdW) interactions, as a part of NCI, change the stability and Gibbs energy of the transition states (TSs), which in turn affects the rate of the reaction. On the basis of NCI analysis, a partial covalent nature of the forming C C bonds at the TSs was confirmed. Energy analysis confirms that vdW interactions can be considered as the main part of the solute-solvent interactions in the cycloaddition reactions. Moreover, cycloaddition reactions of the polar reactants are faster in polar solvents, while nonpolar solvents induce a contrast effect on the rate of these reactions.     

The rate constant of the reaction HO2 + COCO2 + OH

The high-temperature oxidation of formaldehyde in the presence of carbon monoxide was investigated to determine the rate constant of the reaction HO₂ + CO ? CO₂ + OH (10). In the temperature range of 878–952°K from the initial parts of the kinetic curves of the HO₂ radicals and CO₂ accumulation at small extents of the reaction, when the quantity of the reacted formaldehyde does not exceed 10%, it was determined that the rate constant k₁₀ is A computer program was used to solve the system of differential equations which correspond to the high-temperature oxidation of formaldehyde in the presence of carbon monoxide. The computation confirmed the experimental results. Also discussed are existing experimental data related to the reaction of HO₂ with CO.     

Theoretical study of the mechanism and rate constant of the B + CO2 reaction

The different stationary points on the potential energy surface relative to the title reaction have been reinvestigated at the B3LYP/aug-cc-pVDZ level with relative energies computed at the CCSD(T)/aug-cc-pVTZ level with B3LYP/aug-cc-pVDZ optimized geometries and by using the G3B3 composite method. Two entrance channels have been identified. The first one corresponds to boron addition at one of the oxygen atoms of the CO 2 molecule leading to trans-BOCO, which is found to be about 27 kcal/mol exothermic with a potential energy barrier of 16.4 kcal/mol (G3B3). The second channel, which has not been identified in previous theoretical works, corresponds to a direct insertion of the boron atom into a CO bond and leads to OBCO. The B + CO 2 --> OBCO step is found to be about 84 kcal/mol exothermic and needs to overcome a potential energy barrier of only 3.6 kcal/mol (G3B3). The rate constant at 300 K of the insertion step, calculated by using TST theory with G3B3 calculated activation energy value, is 5.4 10 (-14) cm (3) molecule (-1) s (-1), in very good agreement with the experimental data ((7.0 +/- 2.8) 10 (-14) cm (3) molecule (-1) s (-1), DiGiuseppe, T. G.; Davidovits, P. J. Chem. Phys. 1981, 74, 3287). The one corresponding to the addition process is found to be several orders of magnitude smaller because of a much higher potential energy barrier. The addition channel would not contribute to the title reaction even at high temperature. A modified Arrhenius equation has been fitted in the 300-1000 K temperature range, which might be useful for chemical models.     

Tautomeric equilibrium of ethyl acetoacetate in compressed CO2 + ethanol and CO2 + methanol mixtures

Tautomerism equilibrium of ethyl acetoacetate (EAA) in compressed CO2 + methanol and CO2 + ethanol mixtures was studied by UV-Vis spectroscopy at 308.15 K and different pressures. The volume expansion coefficient (alpha) of the solvents at different pressures was also determined. The relative permittivity (epsilon) of CO2 + methanol and CO2 + ethanol mixtures at different conditions was calculated using the Kc and Onsager solvent parameter. The equilibrium constant (Kc) of EAA in the binary mixtures increases considerably with increasing pressure or volume expansion coefficient. The relative permittivity or the polarity of the binary mixtures decreases sharply with increasing volume expansion coefficient in the range of 0 < alpha < 1.5. However, as the volume expansion coefficient exceeds 1.5, the relative permittivity decreases slowly. In other words, the dissolution of CO2 in the polar solvents can reduce the polarity of the solvents significantly in the low volume expansion coefficient range, and the polarity of the solution is not sensitive to the volume expansion coefficient as its value is large enough. The difference in polarity of the two solvents reduces with increasing pressure and becomes negligible after volume expansion coefficient exceeds about 2.5.     

On the properties of methylbenzoate/n-hexane mixed solvents: a theoretical and experimental study

This paper reports on an experimental and theoretical study of methylbenzoate/n-hexane mixed solvents as a function of pressure and temperature in the whole composition range. We have measured the pressure-volume-temperature (PVT) behavior of these fluids over wide temperature and pressure ranges; from the experimental data, relevant derived coefficients required for the fluid's characterization were calculated. The structure of mixed fluids was analyzed from macroscopic data according to excess and mixing properties. The statistical associating fluid theory (SAFT) and perturbed chain (PC)-SAFT molecularly based equations of state were used to predict the PVT behavior with model parameters for pure fluids fitted from correlation of available saturation literature data. The results provided by the PC-SAFT equation of state were clearly superior. Using the fitted PC-SAFT parameters, the global phase behavior of the mixture was predicted, and a type I pattern was inferred according to the van Konynenburg systematic. The molecular level structure was studied through classical molecular dynamics simulations in the NPT ensemble using the optimized potential for liquid simulations (all atom version) (OPLS-AA) force field. Molecular dynamics provides, on one hand, theoretical values of thermophysical properties, which are compared with the experimental ones to check the quality of simulations, and, on the other hand, valuable molecular level structural and dynamic information. Based on both macroscopic and microscopic studies, fluid structure was inferred.     

A study on the phase behavior of the system CO2 + CO + H2 + 1-hexene + heptanal

The phase behavior of a system of importance for the hydroformylation reaction of 1-hexene in supercritical CO₂ has been studied in the range of 303.2–348.2 K with different CO₂ mole fractions. The conversion of 1-hexene varies from 0 to 1. The density of the reaction mixture at different conditions are also determined. It is demonstrated that the phase behavior changes with conversion of 1-hexene. At zero conversion, the phase separation pressure increases with increasing concentration of the reactants in the reaction system and decreases slightly with the increase of temperature. At other conversions, the phase separation pressure increases as temperature rises. The density of the reaction mixture at phase separation point is higher at the larger conversions.     

The reaction of selenoaldehydes with 2-methoxyfuran using their generation by retro Diels-Alder reaction

Selenoaldehydes, regenerated by thermal retro Diels-Alder reaction of anthracene cycloadducts under neutral conditions, reacted with 2-methoxyfuran to give methyl penta-2,4-dienoates along with the deposition of elemental selenium. In a similar reaction with 2-methoxyfuran using thioaldehyde, thiirane compound was isolated. This suggests the formation of selenirane intermediates in the above reaction.     

Enhancing the process of CO2 reduction reaction by using CTAB to construct contact ion pair in Li-CO2 battery

Aprotic Li-CO₂ batteries have attracted growing interest due to their high theoretical energy density and its ability to use green house gas CO₂ for energy storage.However,the poor ability of activating CO₂ in organic electrolyte often leads to the premature termination of CO₂ reduction reaction （CO₂RR） directly.Here in this work,cetyl trimethyl ammonium bromide （CTAB） was introduced into a dimethyl sulfoxide（DMSO） based Li-CO₂ ba...     

Complexation and abstraction channels in the Al + CO2 reaction

The AI + CO₂ reaction is studied in the gas phase at 296 K by laser-induced fluorescence monitoring of Al and AlO. Pressure dependence of the effective bimolecular rate constant in the range 10–600 Torr (Ar+CO₂) indicates a complex formation channel yielding a stable Al·CO₂ adduct. Observation of AlO confirms the presence of an abstraction channel. A simple chemical activation mechanism is used to interpret the pressure dependence of the effective bimolecular rate constant. The activation energy for Al·CO₂ complex formation is estimated at ⪢ 1.0 kcal mol⁻¹, and the binding energy is estimated at ⪢ 9 kcal mol⁻¹.     

Absolute rate constants for F + CH3CHO and CH3CO + O2, relative rate study of CH3CO + NO,and the product distribution of the F + CH3CHO reaction

Using a pulse-radiolysis transient UV–VIS absorption system, rate constants for the reactions of F atoms with CH₃CHO (1) and CH₃CO radicals with O₂ (2) and NO (3) at 295 K and 1000 mbar total pressure of SF₆ was determined to be k₁=(1.4±0.2)×10⁻¹⁰, k₂=(4.4±0.7)×10⁻¹², and k₃=(2.4±0.7)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹. By monitoring the formation of CH₃C(O)O₂ radicals (λ>250nm) and NO₂ (λ=400.5nm) following radiolysis of SF₆/CH₃CHO/O₂ and SF₆/CH₃CHO/O₂/NO mixtures, respectively, it was deduced that reaction of F atoms with CH₃CHO gives (65±9)% CH₃CO and (35±9)% HC(O)CH₂ radicals. Finally, the data obtained here suggest that decomposition of HC(O)CH₂O radicals via C C bond scission occurs at a rate of <4.7×10⁵ s⁻¹. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 913–921, 1998     

The pressure dependence of the rate constant for the reaction: HO + CO → H + CO2

Relative rate measurements of the reactions of the HO-radical with CO [HO + CO → H + CO₂ (1)] and with isobutane [HO + iso-C₄H₁₀ → H₂O + t-(or iso-)C₄H₉ (3)] have been made through the photolysis of dilute mixtures of HONO with CO, iso-C₄H₁₀, NO₂, and NO in simulated air at 700 and 100 torr pressure and 25 ± 2°C. In situ, long path, FT-IR analysis of the reactants and products provided essentially continuous monitoring of the reactions during the course of the experiments. The kinetic analysis of the data coupled with Greiner's estimate of k₃ give new estimates of k₁ = 439 ± 24 ppm^?1 min^?1 in air at 700 torr and k₁ = 203 ± 29 ppm^?1 in air at 100 torr. The results confirm the recent conclusions of Cox and Sie and their co-workers that the rate constant for reaction (1) is pressure dependent. Modeliers of the chemical changes which occur in the troposphere should adopt a new value for the rate constant k₁ which is about a factor of two larger than that in current use by most groups.     

Solvatochromic behavior of phenol blue in CO2+ethanol and CO2+n-pentane mixtures in the critical region and local composition enhancement

The UV-Vis spectra of probe phenol blue in CO(2)+ethanol and CO(2)+n-pentane binary mixtures were studied at 308.15 K and different pressures. The experiments were conducted in both supercritical region and subcritical region of the mixtures by changing the compositions of the mixed solvents. On the basis of the experimental results the local compositions of the solvents about phenol blue were estimated by neglecting the size difference of CO(2) and the cosolvents. Then the local composition data were corrected by a method proposed in this work, which is mainly based on Lennard-Jones sphere model. It was demonstrated that the local mole fraction of the cosolvents is higher than that in the bulk solution at all the experimental conditions. In the near critical region of the mixed solvents the local composition enhancement, defined as the ratio of cosolvent mole fraction about the solute to that in the bulk solution, increased significantly as pressure approached the phase boundary from high pressure. The local composition enhancement was not considerable as pressure was much higher than the critical pressure. In addition, in subcritical region the degree of composition enhancement was much smaller and was not sensitive to pressure in the entire pressure range as the concentration of the cosolvents in the mixed solvents was much higher than the concentration at the critical point of the mixtures.     

Rapid microfluidic screening of CO(2) solubility and diffusion in pure and mixed solvents

We present a high-throughput method to determine rapidly and simultaneously the solubility and the diffusivity of CO(2) in pure solvents and mixtures using segmented flow in a microchannel. Gas bubbles are injected via a T-junction into the liquid stream and the evolution of the bubbles' lengths are followed visually. We measure both solubility and diffusion coefficient from the shrinkage and expansion of the bubbles. The presented method is used to study the physical absorption of CO(2) in various pure solvents and to screen the complete composition space of binary and ternary mixtures.     

Vibrational mode and collision energy effects on reaction of H2CO+ with CO2

The effects of collision energy (Ecol) and five different modes of H2CO+ vibration on the title reaction have been studied over the center-of-mass Ecol range from 0.1 to 3.2 eV, including measurements of product ion recoil velocity distributions. Electronic structure and Rice-Ramsperger-Kassel-Marcus calculations were used to examine properties of various complexes and transition states that might be important along the reaction coordinate. Two product channels are observed, corresponding to Hydrogen Transfer (HT) and Proton Transfer (PT). Both channels are endothermic with similar onset energies of approximately 0.9 eV; however, HT dominates over the entire Ecol range and accounts for 70-85% of the total reaction cross section. Both HT and PT occur by direct mechanisms over the entire Ecol range, and have similar dependence on reactant vibrational and collision energy. Despite these similarities, and the fact that the two channels are nearly isoenergetic and differ only in which product moiety carries the charge, their dynamics appear quite different. PT occurs primarily in large impact parameter stripping collisions, where most of the available energy is partitioned to product recoil. HT, in contrast, results in internally hot products with little recoil energy and a more forward-backward symmetric product velocity distribution. Vibration is found to affect the reaction differently in different collision energy regimes. The appearance thresholds are found to depend only on total energy, i.e., all modes of vibration are equivalent to Ecol. With increasing Ecol, vibrational energy becomes increasingly effective, relative to Ecol, at driving reaction. For HT, this transition occurs just above threshold, while for PT it begins at roughly twice the threshold energy.     

Conductometric study of complexation reaction between 15-crown-5 and Cr3+, Mn2+ and Zn2+ metal cations in pure and binary mixed organic solvents

The stability constants (K_f) for the complexation reactions of Cr³⁺, Mn²⁺ and Zn²⁺ metal cations with macrocyclic ligand, 15-crown-5 (15C5), in acetonitrile (AN), ethanol (EtOH) and also in their binary solutions (AN–EtOH) were determined at different temperatures, using conductometric method. 15C5 forms 1:1 complexes with Cr³⁺, Mn²⁺ and Zn²⁺ cations in solutions. A non-linear behaviour was observed for changes of logK_f of the metal ion complexes versus the composition of the mixed solvent. The order of stability of the metal–ion complexes in pure AN and in a binary solution of AN–EtOH (mol% AN?=?52) at 25?°C was found to be: (15C5Zn)²⁺?>?(15C5·Mn)²⁺?>?(15C5·Cr)³⁺, but in the case of pure EtOH at the same temperature, it changes to: (15C5·Zn)²⁺?>?(15C5·Cr)³⁺?>?(15C5·Mn)²⁺. The results also show that the stability sequence of the complexes in the other binary solutions of AN–EtOH (mol% AN?=?26 and mol% AN?=?76) varies in order: (15C5·Cr)³⁺?~?(15C5·Zn)²⁺?>?(15C5·Mn)²⁺. The values of the standard thermodynamic quantities (ΔH_C°, ΔS_C°) for formation of (15C15-Cr³⁺), (15C5-Mn²⁺) and (15C5-Zn²⁺) complexes were obtained from the temperature dependence of the stability constants and the results show that the thermodynamics of complexation reactions is affected by nature and composition of the solvent systems and in most solution systems, the complexes are enthalpy stabilized but entropy destabilized.     

CuMgAlO_x复合氧化物催化甲醇乙醇Guerbet反应:M~(2+)/Al~(3+)比的影响

以类水滑石为前驱体,通过调控M~(2+)/Al~(3+)比制备了系列具有不同表面性质的MgAlO_x(MA)和CuMgAlO_x(CMA)催化剂,并分别应用于甲醛乙醛缩合反应(甲醇乙醇Guerbet反应的第二步反应)和甲醇乙醇Guerbet反应。采用NH_3/CO_2-TPD、XPS、H_2-TPR和H_2-TPD技术对催化剂表面酸碱性以及铜物种的性质进行了表征。结果表明,甲醇乙醇Guerbet反应性能与催化剂表面Cu~0比表面积和中强碱数目有关,提高Cu~0比表面积有利于甲醇乙醇脱氢生成甲醛和乙醛,增强中强碱数目能促进甲醛乙醛缩合反应。