Reaction Equilibrium Research Articles

Catalytic pyrolysis of biomass with Ni/Fe-CaO-based catalysts for hydrogen-rich gas: DFT and experimental study

The H2-rich gas produced by biomass pyrolysis with Ni-based catalysts were studied by DFT, thermodynamic simulation, and pyrolysis experiment. The complex reaction between volatiles of biomass pyrolysis was clarified through DFT calculation. The results proved that the Ea of key reactions for H2 production on Ni-Fe/CaO surface were lower than that on NC, which facilitates to produce H2. The order of the Ea of the rate determining step on Ni-Fe/CaO surface is toluene cracking reaction < water-carbon reaction < Boudouard reaction < methane steam reforming reaction < methane dry reforming reaction < water gas shift reaction, indicating water gas shift reaction is the key control reaction. When the temperature is 650 ℃, Ni-Fe/CaO can effectively adsorb CO2 to break the thermodynamic equilibrium of the water gas shift reaction and promote the forward reaction to generate H2. Thermodynamic simulation and pyrolysis experiments determined that 650℃ and Ni-Fe/CaO are the most suitable reaction condition for H2 formation. Under this condition, the liquid yield of biomass pyrolysis decreased by 18.32% and the gas yield was increased by 26.27% compared to that of Ni /CaO. More importantly, the H2 yield was increased by 18.29% to 453.34 mL/g-biomass.

A phospholipase B from Pseudomonas aeruginosa with activity towards endogenous phospholipids affects biofilm assembly

Pseudomonas aeruginosa is a severe threat to immunocompromised patients due to its numerous virulence factors and biofilm-mediated multidrug resistance. It produces and secretes various toxins with hydrolytic activities including phospholipases. However, the function of intracellular phospholipases for bacterial virulence has still not been established. Here, we demonstrate that the hypothetical gene pa2927 of P. aeruginosa encodes a novel phospholipase B named PaPlaB. At reaction equilibrium, PaPlaB purified from detergent-solubilized membranes of E. coli released fatty acids (FAs) from sn-1 and sn-2 positions of phospholipids at the molar ratio of 51:49. PaPlaB in vitro hydrolyzed P. aeruginosa phospholipids reconstituted in detergent micelles and phospholipids reconstituted in vesicles. Cellular localization studies indicate that PaPlaB is a cell-bound PLA of P. aeruginosa and that it is peripherally bound to both membranes in E. coli, yet the active form was predominantly associated with the cytoplasmic membrane of E. coli. Decreasing the concentration of purified and detergent-stabilized PaPlaB leads to increased enzymatic activity, and at the same time triggers oligomer dissociation. We showed that the free FA profile, biofilm amount and architecture of the wild type and ΔplaB differ. However, it remains to be established how the PLB activity of PaPlaB is regulated by homooligomerisation and how it relates to the phenotype of the P. aeruginosa ΔplaB. This novel putative virulence factor contributes to our understanding of phospholipid degrading enzymes and might provide a target for new therapeutics against P. aeruginosa biofilms.

Extraction equilibrium of molybdenum(VI) and tungsten(VI) in aqueous solutions containing hydrogen peroxide by synergistic solvent extraction with TRPO and TBP

The separation of molybdenum from peroxotungstate solution with neutral phosphorus extractant such as trialkyl phosphine oxide (TRPO), tri-butyl phosphate (TBP) is often accompanied by extraction loss of tungsten, which greatly reduces the separation efficiency. To solve the above problems and optimize process, clarifying the reaction equilibrium of extraction is necessary. However, relevant research, especially the TRPO-TBP synergistic system, has not been reported. Here, based on the effect of extractant concentration and equilibrium pH on Mo and W extraction with three extraction systems (TRPO, TBP and TRPO-TBP), the Mo and W distribution equations in the two phases and the stoichiometry of chemical reactions were determined via slope analysis. The apparent extraction equilibrium constants and cumulative protonation constant of [Mo2O3(O2)4]2− were calculated by successive-approximation method. The order of the extraction equilibrium constants is as follows: logKMo-TRPO-H (5.8) > logKMo-TRPO-TBP-H (4.3) > logKMo-TRPO (3.8) > logKW-TRPO (3.7) > logKMo-TRPO-TBP (2.3). The synergistic mechanism of TBP for Mo and W extraction was revealed through Raman, FT-IR and 31P NMR spectroscopy, proposing a synergistic extraction compound TBP·[H2Mo2O3(O2)4·2H2O]·TRPO. The experimental results showed that keeping a higher equilibrium pH (2–2.5) can improve the separation efficiency of W and Mo, which verified the feasibility of optimization measure proposed based on equilibrium data. This study reveals the extraction mechanism of W and Mo in H+-H2O2/TRPO-TBP system, which can provide some reference for the optimization of separation process.

Kinetic study of the zeolite membrane-assisted transesterification reaction with methanol removal

The removal of methanol with permselective membranes can improve the conversion of the transesterification reaction with methanol as the byproduct by shifting the equilibrium. However, the required membrane performance and favorable reaction conditions (e.g., catalyst weight, temperature, and the molar ratio of the reaction substrate) are not fully understood yet regarding membrane-assisted transesterification. We investigated the effect of methanol removal by the FAU-type zeolite membrane in the transesterification of methyl hexanoate and 1-hexanol theoretically and experimentally. First, we propose a kinetic model considering the catalytic reaction rate and methanol removal rate by the membrane. The reaction rate, equilibrium, and permeation rate constants were individually determined at 333–373 K by the catalytic reactions and vapor permeation experiments. The FAU-type zeolite membrane showed sufficiently high methanol separation performance for the reaction solutions. Moreover, the highest conversion was achieved 96% at the initial molar ratio of 1-hexanol/methyl hexanoate of 3 and 373 K. The improvement in the conversion could be explained by the equilibrium shift with the selective removal of methanol via the membrane. These suggest that our kinetic model is valid for the estimation of conversion increment for membrane-assisted transesterification.

Osmolyte effect on enzymatic stability and reaction equilibrium of formate dehydrogenase.

Osmolytes are well-known biocatalyst stabilisers as they promote the folded state of proteins, and a stabilised biocatalyst might also improve reaction kinetics. In this work, the influence of four osmolytes (betaine, glycerol, trehalose, and trimethylamine N-oxide) on the activity and stability of Candida bondinii formate dehydrogenase cbFDH was studied experimentally and theoretically. Scanning differential fluorimetric studies were performed to assess the thermal stability of cbFDH, while UV detection was used to reveal changes in cbFDH activity and reaction equilibrium at osmolyte concentrations between 0.25 and 1 mol kg-1. The thermodynamic model ePC-SAFT advanced allowed predicting the effects of osmolyte on the reaction equilibrium by accounting for interactions involving osmolyte, products, substrates, and water. The results show that osmolytes at low concentrations were beneficial for both, thermal stability and cbFDH activity, while keeping the equilibrium yield at high level. Molecular dynamics simulations were used to describe the solvation around the cbFDH surface and the volume exclusion effect, proofing the beneficial effect of the osmolytes on cbFDH activity, especially at low concentrations of trimethylamine N-oxide and betaine. Different mechanisms of stabilisation (dependent on the osmolyte) show the importance of studying solvent-protein dynamics towards the design of optimised biocatalytic processes.

Structure of the Star with Ideal Gases

In this paper, we calculate some structure functions of an idealized stellar model, which can be solved by the total mass and radius of a star. These functions have enlightening and pedagogical significance. We find that the equation of state of matter is decisive to the fate of a star. Only if the equation of state includes the driving effect of gravity on particles, then it satisfies some increasing and causal conditions and is compatible with Einstein’s field equation. In this case, we always have singularity-free balanced star, no matter how heavy the star is. Usually, we believe that the main factor determining the stellar structure is the pressure equilibrium of the thermonuclear reaction against gravity. But this opinion is inadequate. The calculation of this paper shows that, the pressure generated by the driving effect of gravity on particles is dominant.

Synthesis and characterization of Fe0@chitosan/cellulose biocompatible composites from natural resources as advanced carriers for ibuprofen drug: reaction kinetics and equilibrium

Fe0@chitosan/cellulose was synthesized as a carrier for Ibuprofen drug. It has achieved a loading capacity of 553 mg g−1 and a slow release profile for 260 h, which is controlled by complex diffusion and erosion mechanisms.

Theoretical and experimental studies on the size- and morphology-dependent thermodynamics of nanoparticle electrodes

The morphology and size of nanoparticles have a significant effect on the thermodynamics of nanoparticle electrodes due to the nanometer effect. However, the influencing mechanism and regularity of morphology and particle size on electrochemical thermodynamics of nanometer electrodes are still unclear. Herein, the universal thermodynamics equations of nanometer electrodes which consisting of nanoparticles with different morphologies and particle sizes are deduced theoretically and we discuss the influencing mechanism and regularity of morphology and size on electrochemical thermodynamics. Experimentally, we adopt a hydrothermal method to prepare nanometer In2O3 particles with different particle sizes and morphologies and make them into nanometer electrodes. The electrode potentials at different temperatures are measured by a potentiometer, the standard electrode potentials, temperature coefficients of electrode potential, reaction equilibrium constants, reaction thermodynamic properties, and reversible reaction heats are obtained for the nanometer electrode with diverse particle morphologies and sizes. The effects of particle size and morphology on these thermodynamic properties are discussed and we find that the experimental results conform to the corresponding theoretical relations. The electrochemical thermodynamics theory of nanoparticle electrodes can quantitatively describe the electrochemical thermodynamic behavior of nanometer electrodes with different morphologies and particle sizes, explain relevant experimental phenomena, and provide theoretical guidance and support reference to design, research, and apply various nanometer electrode.

Dimensionless analysis of reverse water gas shift Packed-Bed membrane reactors

A dimensionless analysis was performed on the reverse water gas shift packed-bed membrane reactors (RWGS PBMRs) to shift the equilibrium of the RWGS reaction by in-situ H2O removal at low temperatures. Using Damköhler, Péclet, and Stanton dimensionless numbers, the effects of sweep to reactor flow and pressure ratios, flow configuration, temperature, and H2O/H2 perm-selectivity were studied for CuO/ZnO/Al2O3 and Ru-Cu/ZnO/Al2O3 catalysts. The counter-current configuration resulted in higher CO2 conversions at milder sweep pressures when compared to the co-current configuration. It was determined that the application of RWGS PBMRs had to be limited to temperatures below 300 °C to shift the reaction equilibrium. It was concluded that to meaningfully intensify the RWGS reaction by PBMRs, weight hourly space velocities should be lowered to values below 1 hr-1 using membranes with H2O/H2 perm-selectivities greater than 100 and H2O permeance in the range of 10-6-10-5 mol m-2 s-1 Pa-1.

Transaminase Engineering and Process Development for a Whole-Cell Neat Organic Process to Produce (R)-α-Phenylethylamine

The production of (R)-α-phenylethylamine ((R)-α-PEA) from acetophenone is a classic reaction for the characterization of transaminases. However, developing a commercially viable transaminase process to manufacture (R)-α-PEA usually suffers from two drawbacks. One is related to the biocatalyst itself, since transaminases are easily inhibited by (R)-α-PEA at low concentrations. The other drawback is a common low space-time yield of typical transaminase processes, because the reaction equilibrium greatly favors the formation of acetophenone over (R)-α-PEA. In this study, an (R)-selective amine transaminase (TA) from Aspergillus fumigatus Af293 was engineered by a directed evolution for an efficient process to produce (R)-α-PEA. The evolved variant showed an over 3000-fold increase in activity and a tolerance with 2.0 M isopropylamine as well as the complete absence of inhibition by (R)-α-PEA. At the same time, using this evolved TA variant, a continuous neat organic process using whole-cells was developed where the biocatalyst and remaining acetophenone can be efficiently separated from (R)-α-PEA and reused repetitively. This not only decreases the overall cost and waste generation but also achieves a very high space-time yield of up to 168 g L–1 d–1 of (R)-α-PEA in an industrial pilot scale setup.

Transaminase-Mediated Amine Borrowing via Shuttle Biocatalysis.

Shuttle catalysis has emerged as a useful methodology for the reversible transfer of small functional groups, such as CO and HCN, and goes far beyond transfer hydrogenation chemistry. While a biocatalytic hydrogen-borrowing methodology is well established, the biocatalytic borrowing of alternative functional groups has not yet been realized. Herein, we present a new concept of amine borrowing via biocatalytic shuttle catalysis, which has no counterpart in chemo-shuttle catalysis and allows efficient intermolecular amine shuttling to generate reactive intermediates in situ. By coupling this dynamic exchange with an irreversible downstream step to displace the reaction equilibrium in the forward direction, high conversion to target products can be achieved. We showcase the potential of this amine-borrowing methodology using a biocatalytic equivalent of both the Knorr-pyrrole synthesis and Pictet–Spengler reaction.

Effect of initial aluminium-oxygen concentration product on alumina-based inclusions in high carbon Al-killed steels during the ladle refining process

ABSTRACT The effect of different aluminium-oxygen concentration products at the start of deoxidation on the evolution of alumina-based inclusions in high carbon Al-killed steels during the ladle refining process was investigated. Results showed that the higher aluminium-oxygen concentration product at the start of deoxidation, the higher area fraction and the number density of large-sized inclusions before the slag melting, then clustered alumina-based inclusions gradually became ripening. Thermodynamic equilibrium results indicated that initial contents of the [O] were 100, 200, 300 and 400 ppm in the molten steel, then contents of the [O] at the final reaction equilibrium were 4.6, 4.9, 5.8 and 9.5 ppm, respectively. The relationship between oversaturation and size of Al2O3 inclusions showed that the larger the critical radius of nucleus, the lower the oversaturation. Meanwhile, the evolution mechanism of alumina-based inclusions during the LF refining process was also revealed.

Understanding How Coacervates Drive Reversible Small Molecule Reactions to Promote Molecular Complexity

Liquid-liquid phase-separated coacervate droplets give rise to membraneless compartments that play an important role in the spatial organization and reactivity in cells. Due to their molecularly crowded nature and ability to sequester biomolecules, coacervate droplets create distinct environments for enzymatic reaction kinetics and reaction mechanisms that markedly differ from bulk solution. In this work, we use a combination of experiments and quantitative modeling to understand how coacervate droplets promote reversible small molecule reaction chemistry. In particular, we study a model condensation reaction generating an unstable fluorescent imine in polyacrylic acid-polyethylene glycol coacervate droplets over a range of conditions. At equilibrium, the concentration of the imine product in coacervate droplets is approximately 140-fold larger than that in bulk solution, which arises due to preferential partitioning of reactants and products into coacervate droplets and a reaction equilibrium constant that is roughly threefold larger in coacervate droplets than in solution. A reaction-diffusion model is developed to quantitatively describe how competing reaction and partitioning equilibria govern the spatial distribution of the imine product inside coacervate droplets. Overall, our results show that compartmentalization stabilizes kinetically labile reaction products, which enables larger reactant concentrations in coacervate droplets compared to bulk solution. Broadly, these results provide an improved understanding of how biomolecular condensates promote multistep reaction pathways involving unstable reaction intermediates and suggest how coacervates provide a potential abiotic mechanism to promote molecular complexity.

Experimental and Theoretical Equilibrium Insights in the Reactive Extraction of Pimelic Acid with Tri-n-octylamine in Natural Solvents

The theoretical and experimental studies on the reactive extraction of pimelic acid (PA) from dilute aqueous solutions with tri-n-octylamine (TOA) in three different green and natural solvents namely, rice bran oil, sunflower oil (SFO), and soybean oil are carried out. In addition, physical extraction (extraction with pure solvent, natural oil) is also studied to determine the partition and dimerization constants. The experiments on reaction equilibria were performed to calculate the extraction efficiencies with variable TOA concentration, PA concentration, type of diluent/solvent, and temperature at atmospheric pressure (101.325 ± 1 kPa). The acid distribution coefficient (KD), degree of extraction (E, %), and loading factor (Z) were calculated as the extraction efficiencies to recover the PA from aqueous solution. The maximum KD (7.76) and extraction yield (88.58%) were obtained for initial PA concentration (CH2P,o= 0.2497 kmol·m–3) with 0.687 kmol·m–3 TOA concentration (C̅S,o) dissolved in sunflower oil. The overall stoichiometry and reaction equilibrium constant (KE) and individual acid-extractant complexation constants (K11, K12, K21, and K31) of 1:1, 1:2, 2:1, and 3:1 PA–TOA complexes in the organic phase and their complex concentrations (C11, C12, C21, and C31) are determined using an equilibrium chemical model and bioinspired genetic algorithm, differential evolution, for better understanding of the reaction mechanism. Moreover, based on extraction conditions, the thermodynamic study is carried out to determine the change in enthalpy (−1320.11 J·mol–1), entropy (−3.63427 J·mol–1·K–1), and Gibbs free energy (−254.72 J·mol–1·K–1) of reactive separation of PA with TOA–SFO.

Synthesis of γ-valerolactone from ethyl levulinate hydrogenation and ethyl 4-hydroxypentanoate lactonization over supported Cu-Ni bimetallic, bifunctional catalysts

A stable and highly efficient supported Cu-Ni catalysts for the conversion of ethyl levulinate (EL) to γ-valerolactone (GVL) was developed. The catalysts were characterized by XRD, TEM, TPD, TPR, and XPS. The support effect of metal oxides (Al2O3, SiO2, ZrO2, and TiO2) revealed that Cu-Ni supported on Al2O3 showed the highest activity for EL hydrogenation to ethyl 4-hydroxypentanoate (EHP) and the subsequent intramolecular esterification of EHP to GVL. EHP intramolecular esterification to GVL in the ethanol solution was a reversible reaction with an equilibrium constant of 24 at 453 K. A simplified reaction kinetic network was established. The solvent had a significant influence on the reaction equilibrium and the catalyst stability. Cu-Ni/Al2O3 in n-hexane solvent gave a higher GVL yield than that in ethanol solvent, and showed better recyclability than that in toluene solvent. With optimizing the conditions, Cu-Ni/Al2O3 gave 99.9% conversion and 98% selectivity to GVL with a space–time yield of 1.13 gGVL gcat-1h−1 in n-hexane solvent with good recyclability.

Theoretical Thermodynamic Efficiency Limit of Isothermal Solar Fuel Generation from H2O/CO2 Splitting in Membrane Reactors

Solar fuel generation from thermochemical H2O or CO2 splitting is a promising and attractive approach for harvesting fuel without CO2 emissions. Yet, low conversion and high reaction temperature restrict its application. One method of increasing conversion at a lower temperature is to implement oxygen permeable membranes (OPM) into a membrane reactor configuration. This allows for the selective separation of generated oxygen and causes a forward shift in the equilibrium of H2O or CO2 splitting reactions. In this research, solar-driven fuel production via H2O or CO2 splitting with an OPM reactor is modeled in isothermal operation, with an emphasis on the calculation of the theoretical thermodynamic efficiency of the system. In addition to the energy required for the high temperature of the reaction, the energy required for maintaining low oxygen permeate pressure for oxygen removal has a large influence on the overall thermodynamic efficiency. The theoretical first-law thermodynamic efficiency is calculated using separation exergy, an electrochemical O2 pump, and a vacuum pump, which shows a maximum efficiency of 63.8%, 61.7%, and 8.00% for H2O splitting, respectively, and 63.6%, 61.5%, and 16.7% for CO2 splitting, respectively, in a temperature range of 800 °C to 2000 °C. The theoretical second-law thermodynamic efficiency is 55.7% and 65.7% for both H2O splitting and CO2 splitting at 2000 °C. An efficient O2 separation method is extremely crucial to achieve high thermodynamic efficiency, especially in the separation efficiency range of 0–20% and in relatively low reaction temperatures. This research is also applicable in other isothermal H2O or CO2 splitting systems (e.g., chemical cycling) due to similar thermodynamics.

Fluorinated nitrile-butadiene rubber (F-NBR) via metathesis degradation: Closed system or open system?

Fluorinated nitrile-butadiene rubber (F-NBR) could be designed via the metathesis degradation of nitrile-butadiene rubber (NBR) with perfluoroalkylethyl acrylates as fluorination chain transfer agent (F-CTA). Ethylene was produced during the metathesis degradation. Different from the reported works in the open system in which the ethylene escaped, the reaction in a closed system is greener. Here, the metathesis degradation of NBR was investigated in a closed system for the first time, with 2,2,3,4,4,4-hexafluorobutyl acrylate (F6) or 1H,1H,2H,2H-perfluorooctyl acrylate (F13) as F-CTA, respectively. Compared with the reaction in the open system, the metathesis degradation in the closed system with F6 was suppressed due to the reaction equilibrium, while that with F13 was promoted owing to the ethenolysis reaction, which was caused by the ethylene produced during the metathesis degradation. With the proposed green and efficient approach, the fluorinated liquid nitrile-butadiene rubber (F-LNBR) could be designed for various applications.

Performance enhancement of equilibrium regeneration in a gasoline particulate filter based on field synergy theory

The optimization of exhaust parameters is conducive to improving the regenerative performance of the gasoline particulate filter(GPF) in the reaction equilibrium process. In this work, firstly, the regenerative model of the GPF is established to explore the effect of exhaust parameters on the index of the regenerative performance in the reaction equilibrium process. Secondly, based on the method of extreme difference analysis, a large number of parameters are optimized to intuitively study the variation law of the regenerative performance in the reaction equilibrium process. Finally, the multi-field synergy theory is used to analyze the field synergy effect after optimizing exhaust parameters. Research results show that when the exhaust mass flow, carbon loading amount, and m(NO2)/m(NO) decrease, while the oxygen concentration increases, both the regenerative performance and the effect of the field synergy are greatly improved. Through the calculation and analysis, after the exhaust parameters are optimized, the maximum increment of the soot oxidation rate is 30.38%, and the maximum decrement of the temperature non-uniformity coefficient(CTU), pressure drop in the reaction equilibrium process, and local maximum pressure drop gradient(GMP) are 23.40%, 69.38%, and 70.35% respectively. In addition, the increasing range of the field synergy coefficient of the GPF is 2.64–3.52%.

Influence of air content on thermal degradation of poly(ethylene terephthalate)

Abstract: The aim of these research is to investigate the air content on aging of poly(ethylene terephthalate) (PET) preforms. Three air pressures were selected and in each pressure 5 samples were aged during 21 days in 80oC. Three samples were selected to cut and measure their density with the use of hydrostatic method. Sample mass, Young modulus and surface roughness were measured for each sample before and after aging and differences between those parameters were presented as results. The changes of parameters may lead to a conclusion that mechanism of polymeric chain oxidation is dominant during thermal aging of PET. However the aging is not the fastest in atmospheric pressure but in lower air contents. This effect may be caused by greater evaporation of small molecule degradation products and shifting of reaction equilibrium in the direction of further decomposition.

Insights into enhanced removal of U(VI) by melamine sponge supported sulfurized nanoscale zero-valent iron

Radioactive pollutants have always been the top priority in wastewater, and searching a green and efficient treatment technology remains a significant challenge. In this study, a novel melamine sponge supported sulfurized nanoscale zero-valent iron (MS@S-NZVI) material with high dispersion was firstly designed to effectively capture U(VI) from water environment. The target material could retain its original structure in water due to the excellent mechanical strength of MS, which greatly inhibited the aggregation of S-NZVI. A series of characterization techniques, such as SEM, XRD, FTIR, TGA and XPS, had proved the effective synthesis and excellent structural properties of the MS@S-NZVI. The faster reaction equilibrium (<1 h) and higher maximum adsorption capacity (180 mg/g at pH = 5 and 298 K) exposed the perfect performance of target material in the elimination of U(VI). In addition, further researches in different water systems exhibited that MS@S-NZVI had a significant U(VI) removal rate in simulated wastewater systems. Finally, the removal process of MS@S-NZVI to U(VI) could be divided into three pathways through the XPS technique, adsorption and reduction were the main reaction mechanisms. This study provides a new insight into the utilization of melamine sponge and a prospect for the practical application of S-NZVI in the removal of radionuclide.