Reaction Equilibrium Research Articles

Fabrication of biogenic carbon-based materials from coconut husk for the eradication of dye

The highly biocompatible nature of carbon dots (CQDs) and potential usage in waste water treatment makes them as one of the effective alternative for treating water pollution. Herein, biogenic carbon dots (CQDs) with size range of 2 nm were prepared from waste coconut husk as a precursor source. The hydrophilic nature and higher surface area of as prepared CQDs has further supported the superior adsorption efficiency of more than 90% for Victoria blue B (VB) dye from waste water samples. Different dye adsorption parameters including adsorbate and adsorbent dosage, pH of reaction media and equilibrium time have been optimized and found that 8 mg of adsorbent was sufficient to remove 70 mg VB dye in 4 mL aqueous solution in 60 min at pH = 7. The adsorption kinetic (2nd order) and isotherms (Freundlich-type) were well followed on prepared CQDs. The reusability studies up to 5 times with minimal decrement of 4% confirm the constancy of CQDs for the adsorptive removal of VB. The methodology presents a greener way for overcoming ecological issues with sustainable materials in an economical manner.

Biomass steam gasification for hydrogen-rich syngas production over fly ash-based catalyst pretreated by coupling of washing and calcination

Biomass gasification to produce syngas is promising, but the limited hydrogen content of the syngas restricts its potential applications. This study proposed an efficient thermochemical approach that used cost-effective fly ash pretreated with washing and calcination (WCFA) as a catalyst to enhance hydrogen-rich syngas production from biomass steam gasification. Catalyst characterizations indicated that washing removed most chloride salts in raw fly ash by dissolution, and subsequent calcination decomposed Ca-containing compounds into CaO, resulting in smaller catalyst grains, more developed pore structure, and greater capability and reaction rate of CO2 sorption. With WCFA, the H2 release during gasification was prolonged by ∼10 min and its release peak increased by over 1.5 times, compared to no catalyst. Consequently, the cold gas efficiency, syngas yield, and H2/CO ratio increased from 53%, 792 mL/gbiomass, and 0.39 for no catalyst to 72%, 1132 mL/gbiomass, and 1.05 for WCFA. The WCFA catalyst calcined at 800 °C for 60 min was optimal for H2 formation, due to its enriched CaO composition and improved porosity, which effectively catalyzed volatiles cracking/reforming and absorbed CO2 to lead the chemical equilibrium of water gas shift reaction move foward.

A convenient method for measuring gas-liquid volumetric mass transfer coefficient in micro reactors

The research on gas-liquid multiphase reactions using micro reactors is becoming increasingly widespread, given their excellent mass transfer performance. Establishing an accurate and reliable method to measure the gas-liquid mass transfer performance of micro reactors is crucial for evaluating and optimizing the design of micro reactor structure. In this paper, the physical absorption method of aqueous solution-CO2 and the chemical absorption method of sodium carbonate solution-CO2 were proposed. By analyzing the chemical reaction equilibrium during the absorption process, the relationship between the mass transfer of CO2 and the solubility of hydroxide ions in the solution was established, and the total gas-liquid mass transfer coefficient was immediately obtained by measuring the pH value. The corresponding testing platform and process have been established based on the characteristics of the proposed method to ensure fast and accurate measurement. In addition, the chemical absorption method takes into account temperature factors that were not previously considered. The volumetric mass transfer coefficient measured by these two methods is in the same range as those measured by other methods using the same microchannel structure in previous literature. The methods have the advantages of low equipment cost, faster measurement speed, and simpler procedures, which can facilitate its wide application to the evaluation of the mass transfer performance and hence can guide the structure optimization of microchannel reactors.

Eliminating Concentration Polarization with Cationic Covalent Organic Polymer to Promote Effective Overpotential of Nitrogen Fixation.

Electrocatalytic nitrogen reduction reaction offers a sustainable alternative to the conventional Haber-Bosch process. However, it is currently restricted by low effective overpotential due to the concentration polarization, which arises from accumulated products, ammonium, at the reaction interface. Here, a novel covalent organic polymer with ordered periodic cationic sites is proposed to tackle this challenge. The whole network exhibits strong positive charge and effectively repels the positively charged ammonium, enabling an ultra-low interfacial product concentration, and successfully driving the reaction equilibrium to the forward direction. With the given potential unchanged, the suppressed overpotential can be much liberated, ultimately leading to a continuous high-level reaction rate. As expected, when this tailored microenvironment is coupled with a transition metal-based catalyst, a 24-fold improvement is generated in the Faradaic efficiency (73.74 %) as compared with the bare one. The proposed strategy underscores the importance of optimizing dynamic processes as a means of improving overall performance in electrochemical syntheses.

Eliminating Concentration Polarization with Cationic Covalent Organic Polymer to Promote Effective Overpotential of Nitrogen Fixation

AbstractElectrocatalytic nitrogen reduction reaction offers a sustainable alternative to the conventional Haber‐Bosch process. However, it is currently restricted by low effective overpotential due to the concentration polarization, which arises from accumulated products, ammonium, at the reaction interface. Here, a novel covalent organic polymer with ordered periodic cationic sites is proposed to tackle this challenge. The whole network exhibits strong positive charge and effectively repels the positively charged ammonium, enabling an ultra‐low interfacial product concentration, and successfully driving the reaction equilibrium to the forward direction. With the given potential unchanged, the suppressed overpotential can be much liberated, ultimately leading to a continuous high‐level reaction rate. As expected, when this tailored microenvironment is coupled with a transition metal‐based catalyst, a 24‐fold improvement is generated in the Faradaic efficiency (73.74 %) as compared with the bare one. The proposed strategy underscores the importance of optimizing dynamic processes as a means of improving overall performance in electrochemical syntheses.

Bioleaching of oceanic manganese nodules: Current progress and future prospects

AbstractThe extraction of manganese elements and other strategic elements from oceanic manganese nodules has become a strategic decision to ensure the security of global metal resources and the high‐quality green development of metal resource processing and metallurgy industry due to the gradual depletion of high‐quality terrestrial metal resources and the increase of difficult‐to‐select and difficult‐to‐smelt deposits. In order to achieve the enrichment and separation of diverse elements within oceanic manganese nodules, it is imperative to initiate chemical reactions that facilitate the breakdown of complex oxides, particularly manganese dioxide. Bioleaching is a viable treatment option for oceanic manganese nodules with low operating costs and environmental damage. However, the mechanism of oceanic manganese nodules bioleaching is not fully studied, and the prospect of technology development is uncertain. We have reviewed five influencing factors on bioleaching of oceanic manganese nodules: mineralogical characteristics, chemical reaction equilibrium, thermodynamic characteristics, microbial properties, and operational variables. It then makes new development recommendations and technological system suggestions for the future improvement of oceanic manganese nodule bioleaching, primarily focusing on the development of new technologies for challenging to select and difficult to smelt ores, the practicality of strategic energy metal development, the cell design and its materials revolution, environmental protection and management, and all‐round resource utilization. Solving the above critical technical issues will boost the high‐quality development of metal industry and environmental protection.

Hydrolysis phase equilibrium in various reactor configurations of the thermochemical Cu–Cl cycle

This study examines the phase equilibrium trends of the hydrolysis process in the thermochemical Cu–Cl cycle of hydrogen production. Various temperatures, pressures, and steam to copper ratios are modelled to predict CuCl2 conversion and progression of side reactions within the hydrolysis reactor. Novel reactor configurations, such as Moving Bed Reactors (MBRs), reactors in series and outlet gas recirculation are introduced within the analysis. Optimal conversion of CuCl2 and minimal by-product generation are obtained at a reactor temperature of 375 °C and pressure of 1 bar with improved conversion at higher temperatures and lower pressures. Improved reaction conversion is identified at higher steam to copper ratios. A 10:1 steam to copper ratio was used for the remaining reactor configuration scenarios. Reactors in series were simulated to mimic MBR behaviour. Three reactors in series with 10 kmol total steam consumption showed better conversion of 1 kmol of CuCl2 by 17% compared to a single reactor with the same steam inlet conditions. Mitigation of CuCl2 and Cu2OCl2 decomposition was also observed. The outlet gas recirculation improved the total desired product yield, however, the maximum conversion of CuCl2 was significantly impacted due to the high level of HCl concentrated steam. A combination of the gas outlet stream and reactors in series provide a method to improve the conversion rate. This reactor configuration is a challenging approach unless there is a separation technique to shift the reaction equilibrium or reduce HCl concentration within the gas stream.

Constructing biocatalytic nanochannel membranes for unidirectional isomer conversion and separation

AbstractIsomer conversion and separation are crucial in the chemical, pharmaceutical, and food industries. However, this process remains challenging due to the reversed conversion of isomers and their similar boiling points and kinetic diameters. Herein, an enzyme‐catalyzed nanochannel membrane with a hierarchical structure is fabricated for selective and directional isomeric conversion and separation. The enzyme is embedded in a confined polymer network that shows high stability and retains 95% of its initial activity after 50 reaction cycles. Studying the transport mechanisms between isomers through the membrane shows that the hierarchical layers of the membrane impose unequal energy barriers to the forward and backward transport of products, promoting unidirectional diffusion of products and interrupting the equilibrium of the isomerization reaction to increase the conversion rate by 43%. Overall, this work opens a new avenue for the design of biocatalytic nanochannel membranes and the directional production and in situ separation of isomers.

Comprehensive analysis of thermodynamic models for CO2 absorption into a blended N,N‐diethylethanolamine‐1,6‐hexamethyl diamine (DEEA‐HMDA) amine

AbstractIn this work, CO2 equilibrium solubility of 1M N,N‐diethylethanolamine (DEEA):2M 1,6‐hexamethyl diamine (HMDA), 1.5M DEEA:1.5M HMDA and 2M DEEA:1M HMDA was studied with a temperature range of 298–333 K and CO2 partial pressure range of 8–100 kPa. Seven thermodynamic models including Empirical model, Kent and Eisenberg (KE) model, Hu–Chakma model, Austgen model, Helei Liu model, Liu et al. model, and Li–Shen model were developed by correlating reaction equilibrium constants with observed equilibrium solubility of CO2 in mixed amine solvents. The evaluation of those models was conducted in terms of the average absolute relative deviation (AARD). The results indicated that Liu et al. model considering T, [Amine], Ptotal and [CO2(aq)] can better represent this complex system with an AARD of 8.06%. Meanwhile, comprehensive comparison and analysis were also performed to identify the contribution of parameters to develop models, which could provide a guideline for the development of accurate thermodynamic models for representation of thermodynamic behaviors.

Persistent Free Radicals in Petroleum

The persistent free radical content in petroleum is of the order 1018 spins/g (1 μmol/g), with higher and lower values found depending on origin and in different distillation fractions. The field of persistent free radicals in petroleum was reviewed with the aim of addressing and explaining apparent inconsistencies between free radical persistence and reactivity. The macroscopic average free radical concentration in petroleum is persistent over geological time, but individual free radical species in petroleum are short-lived and reactive. The persistent free radical concentration in petroleum can be explained in terms of a dynamic reaction equilibrium of free radical dissociation and association that causes a finite number of species at any given time to be present as free radicals. Evidence to support this description are observed changes in free radical concentration related to change in Gibbs free energy when the bulk liquid properties are changed and responsiveness of free radical concentration to dynamic changes in temperature. Cage effects, solvent effects, steric protection, and radical stabilization affect free radical reaction rate but do not explain the persistent free radical concentration in petroleum. The difference between persistent free radicals in straight-run petroleum and converted petroleum is that straight-run petroleum is an equilibrated mixture, but converted petroleum is not at equilibrium and the free radical concentration can change over time. Based on the limited data available, free radicals in straight-run petroleum appear to be part of the compositional continuum proposed by Altgelt and Boduszynski. Persistent free radical species are partitioned during solvent classification of whole oil, with the asphaltenes (n-alkane insoluble) fraction having a higher concentration of persistent free radicals than maltenes (n-alkane soluble) fraction. Attempts to relate persistent free radical concentration to petroleum composition were inconclusive.

Numerical study of the dehydration and hydration processes of the Ca(OH)2/CaO system in an indirect-direct reactor

Energy storage is important for the application of the discontinuous and unstable renewable energy. The CaO/Ca(OH)2 thermochemical system of high energy density and little heat lose is promising for thermal energy storage, yet the heat and mass transfer processes related to dehydration reaction needs further improvement and the regulation manner related to the hydration reaction needs further investigation. In this work, a hybrid indirect-direct reactor of the CaO/Ca(OH)2 system is proposed with the physicochemical model developed to study the dehydration and hydration processes under different operating and structural conditions, and five indicators are defined to evaluate the overall reaction performance. During the dehydration process, the reactant is indirectly heated by the electrical heater at the reactor outside wall and the reaction proceeds in radial direction which is mainly limited by the poor heat transfer, leading to low energy storage efficiency of 6.1 %. The increase of reactant thermal conductivity and application of high-thermal-conductivity porous channel greatly enhance the heat transfer leading to significant reduction of reaction time and increase of energy storage efficiency up to 25.63 %. During the hydration process, the gas mixture directly contacts and reacts with solid reactant and the reaction proceeds in axial direction with reaction region of “U” shape which is mainly restricted by the reaction equilibrium. The thermal power density and reaction temperature of the hydration process can be regulated by the inlet mass flow rate and the inlet steam mass fraction respectively. The increase of inlet mass flow rate and inlet steam mass fraction leads to higher heat exchange efficiency at the same reaction extent and shorter hydration reaction time. The present study demonstrates the superiority of the indirect-direct type reactor and the performance of which can be further improved by optimizing the geometrical and operating conditions.

Enhancing the Equilibrium of Dynamic Thia-Michael Reactions through Heterocyclic Design.

Although the catalyst-free dynamic thia-Michael (tM) reaction has been leveraged for a range of significant applications in materials science and pharmaceutical development, exploiting its full potential has been limited by relatively low equilibrium constants. To address this shortcoming, a new series of catalyst-free, room-temperature dynamic thia-Michael acceptors bearing an isoxazolone motif were developed and utilized to access both dynamic covalent networks and linear polymers. By leveraging the generation of aromaticity upon thiol addition and tuning the electronic-withdrawing/donating nature of the acceptor at two different sites, a wide range of equilibrium constants (Keq ∼1000 to ∼100,000 M-1) were obtained, constituting a 2 orders of magnitude increase compared to their noncyclic benzalcyanoacetate analogues. Integration into a ditopic isoxazolone-based Michael acceptor allowed access to both bulk dynamic networks and linear polymers; these materials not only exhibited tailorable thermomechanical properties based on thia-Michael acceptor composition, but the higher Keq tM bonds resulted in more mechanically robust materials relative to past designs. Furthermore, solution-state formation of linear polymers was achieved thanks to the increased Keq of the isoxazolone-based acceptors.

REACTION KINETICS OF ACETIC ACID WITH ETHANOL TO ETHYL ACETATE WITH SULFURIC ACID CATALYST

Ethyl acetate is an ester of ethanol and acetic acid. This compound is a colorless liquid with a characteristic odor. Ethyl acetate is widely used as a solvent because of its high solubility. The manufacture of ethyl acetate (ethyl ester) is referred to as the esterification process. This esterification reaction is an exothermic reaction, is reversible and generally runs very slowly so it requires a catalyst to obtain maximum ester. Domestic demand for ethyl acetate is increasing, while production in Indonesia is still lacking. Reactor design requires a reaction mechanism and kinetic data in the form of reaction rate equations and reaction rate constants. This study aims to determine the kinetics of the etherification of acetic acid presented in the form of the reaction rate equation, the value of the reaction rate constant, and the reaction equilibrium constant. In addition, this research also studied how the influence of sulfuric acid catalyst on the reaction rate constant and the reaction balance. The esterification reaction was carried out in a batch reactor. 99% acetic acid and H2SO4 catalyst whose concentrations are varied, are mixed in a reactor equipped with a magnetic stirrer which is operated at 400 rpm, then 96% ethanol is poured with a volume ratio of 1:1 to acetic acid, 5 mL of sample is taken to analyze the remaining acid after The reaction takes place, every certain time interval a sample is taken to be analyzed until an equilibrium point is obtained. From the results of this study it can be concluded that the esterification reaction of acetic acid with ethanol to produce ethyl acetate is a second order reaction with the reaction rate equation (-rA) = k1CACB – k2CCCD. By using a reaction temperature of 34oC and a stirring speed of 400 rpm, the best conditions were obtained using a catalyst of 5.3% by volume, with the reaction rate constant to the right (k1) being 0.014 L/(gmol min), the value of the equilibrium constant (K=k1/k2) is 5.51 and the balance conversion is 77%.

Exploring the hygroscopicity and chemical composition evolution in organic-inorganic aerosols: A study on internally mixed malonic acid-metal (Na+, Ca2+, Mg2+) nitrates

Chemical transformations in mixed aerosols alter the particulate physical properties. Nitrates and water soluble dicarboxylic acids, such as malonic acid (MA), are major components of ambient aerosol particles. Various metal ions such as, Na+, Ca2+, Mg2+ also become part of these complex aerosol systems during their atmospheric lifetime. Interactions among the co-existing ionic and molecular species govern the chemical changes in the aerosol particles. In this work, we provide a comparative account of the effect of metal ion identity (Na+, Ca2+, Mg2+) on such chemical changes arising from ion-molecular interactions in NaNO3-MA, Ca(NO3)2-MA and Mg(NO3)2-MA mixed inorganic-organic aerosols. In-situ micro-Raman spectroscopy has enabled us to gain molecular level insight on formation of organic salt and simultaneously estimate nitrate depletion in these mixed aerosols during different stages of their hygroscopic cycle. In addition to the nitrate depletion often reported during the drying phase, this study has brought to light an intriguing observation: depletion of nitrate in the humidification phase as well, a phenomenon that has hitherto remained undocumented. For the mixed systems studied here, the extent of nitrate depletion follows the order Mg-MA (58%) > Ca-MA (43%) > Na-MA (15%). The comparatively huge forward shift in the acid displacement reaction equilibrium for the systems, Ca-MA and Mg-MA is driven by complexation. Our results highlight the profound effect of ion-molecular interactions on the acid displacement reaction equilibria in aerosols.

Physical–chemical coupling machine learning approach to exploring reactive solvents for absorption capture of carbonyl sulfide

Most of machine learning (ML) models only explain one (chemical or physical) aspect of the reaction-involved absorption and therefore fail to predict solubilities of reactive species in chemical solvents. Herein, we propose a physical–chemical coupling ML approach to exploring absorption solvents for capturing a reactive organosulfide, COS. COS solubilities for 2,824 molecules were obtained by integrating physical absorption calculated using Henry's law and chemical absorption derived from reaction equilibrium calculation. ML model of ΔG of the reaction was established to examine the contributions of physical and chemical absorption. The coupling ML method was constructed by combining three absorption models. Experimental results of four commercial solvents verify that coupling ML method predicts COS solubilities in reactive and non-reactive solvents well. Furthermore, a descriptor-based molecule generation method was utilized to find 96 COS-preferred compounds. Present research highlights the coupling ML model for predicting absorption of COS and provides a general strategy for designing molecules/materials for intensified physical–chemical synergism.

Considerations for the Scale‐up of in vitro Transaminase‐Catalyzed Asymmetric Synthesis of Chiral Amines

AbstractIn vitro transaminase catalyzed asymmetric synthesis is not a new phenomenon in the biocatalytic toolbox. Our group published a review on process consideration for these reactions in 2011, in which process metrics and the unfavorable reaction equilibrium was deduced to be the main bottlenecks at the time. Now, a decade later, this has been solved by different process methods presented in this review, with the development of enzymatic cascades one of the main solutions. Today, the new bottleneck is the downstream processing, due to the complexity of transaminase reactions, in which a ketone and an amine as substrates and a new ketone and a new amine as products. How to recover the produced amine from the resulting product mixture is considered and will be the key challenge for scale‐up of such systems in the near future.

Systematic study of prescission neutron multiplicity: Revealing the role of entrance channel magicity

The prescission neutron multiplicities (νpre) are studied for a systematic understanding of the influence of entrance-channel shell closure in fusion-fission dynamics. The existing νpre data are analyzed for reactions with a wide variety of target and projectile combinations. For completeness, the measured νpre data for the fusion-fission reactions with the doubly closed shell 16O projectile on the targets having either proton (204,206Pb) or both proton and neutron (208Pb) shell closure is reanalyzed. Although the measured νpre for 224Th disagree with the available data reported by Rossner et al. (1992) [1], our results are found to be more consistent and follow a systematic trend as described in this letter. Theoretical analysis is performed within the standard statistical model framework, where dissipation strength is used as a tunable parameter. It is observed that irrespective of the compound nuclear excitation energy, the entrance channel magicity imparts an intriguing impact on the dissipation strength. A similar entrance channel effect in the evaporation residue cross-section is also demonstrated. In conclusion, the present analysis establishes an entanglement of the exit channel observables with the entrance channel shell closure. It contradicts the hypothesis of complete equilibrium in compound nuclear reactions.

Visualize intracellular β-galactosidase using an asymmetric near-infrared fluorescent probe with a large Stokes shift

β-galactosidase (β-Gal) is an important biomarker of cell senescence and primary ovarian cancer. Therefore, it is of great significance to construct a near-infrared fluorescent probe with deep tissue penetration and a high signal-to-noise ratio for visualization of β-galactosidase in biological systems. However, most near-infrared probes tend to have small Stokes shifts and low signal-to-noise ratios due to crosstalk between excitation and emission spectra. Using d-galactose residues as specific recognition units and near-infrared dye TJ730 as fluorophores, a near-infrared fluorescence probe SN-CR with asymmetric structure was developed for the detection of β-Gal. The probe has a fast reaction equilibrium time (<12 min) with β-Gal, excellent biocompatibility, near-infrared emission (738 nm), low detection limit (0.0029 U/mL), and no crosstalk between the excitation spectrum and emission spectrum (Stokes shifts 142 nm) of the probe. Cell imaging studies have shown that SN-CR can visually trace β-Gal in different cells and distinguish ovarian cancer cells from other cells.

Global Renormalised Solutions and Equilibration of Reaction–Diffusion Systems with Nonlinear Diffusion

The global existence of renormalised solutions and convergence to equilibrium for reaction–diffusion systems with nonlinear diffusion are investigated. The system is assumed to have quasi-positive nonlinearities and to satisfy an entropy inequality. The difficulties in establishing global renormalised solutions caused by possibly degenerate diffusion are overcome by introducing a new class of weighted truncation functions. By means of the obtained global renormalised solutions, we study the large-time behaviour of complex balanced systems arising from chemical reaction network theory with nonlinear diffusion. When the reaction network does not admit boundary equilibria, the complex balanced equilibrium is shown, by using the entropy method, to exponentially attract renormalised solutions in the same compatibility class. This convergence extends even to a range of nonlinear diffusion, where global existence is an open problem, yet we are able to show that solutions to approximate systems converge exponentially to equilibrium uniformly in the regularisation parameter.

Continuous microflow visible-light photocatalytic N-formylation of piperidine and its kinetic study

N-formylation of amines, a class of synthetically important reactions, is typically conducted using metal catalysts that are relatively expensive or not readily available and usually needs harsh conditions to increase the reaction efficiency. Here, an efficient continuous microflow strategy was developed for the gas-liquid visible-light photocatalytic N-formylation of piperidine, which achieved a reaction yield of 82.97% and a selectivity of >99% at 12 min using cheap organic dye photocatalyst under mild reaction conditions. The influence of essential parameters, including light intensity, temperature and equivalents of the gas, additive and photocatalyst, on the reaction yield was systematically studied. Furthermore, kinetic investigations were conducted, exhibiting the dependence of reaction rate and equilibrium yield of N-formylpiperidine on light intensity, temperature and photocatalyst equivalent. The microflow photocatalytic approach established in this work, which realized a markedly higher space-time yield than the conventional batch method (37.9 vs. 0.212 mmol·h−1·L−1), paves the way for the continuous, green and efficient synthesis of N-formamides.