Reaction Equilibrium Research Articles

Adsorption of Pesticides, Antibiotics and Microcystin-LR by Graphene and Hexagonal Boron Nitride Nano-Systems: A Semiempirical PM7 and Theoretical HSAB Study

In recent years, graphene (CC) and hexagonal boron nitride (h-BN) have been widely used in water purification and environmental remediation because of their unique physical and chemical properties. Therefore, based on the reaction enthalpy, equilibrium structure, atomic charge, molecular, orbital and electronic spectrum provided by a semiempirical PM7 method, the adsorption of pesticides, antibiotics and microcystin-LR on graphene and hexagonal boron nitride (h-BN) nano-systems was examined. For the adsorption of diazinon, parathion, oxacillin and ciprofloxacin, the results show that as the bond length decreases and the atomic partial charge increases, the adsorption energy increases. The removal efficiency for antibiotics is higher than that for pesticides. Regarding the co-adsorption of pesticides/antibiotics and microcystin-LR on nano-systems, hydrogen bonds play a crucial role in stabilizing the whole structure. In addition, the non-covalent interaction (NCI) diagrams show the adsorption strength of the nano-systems to the pesticides/antibiotics. The energy gap and HSAB global descriptors are calculated based on the energy values of HOMO and LUMO. It is proved that the graphene nano-system has excellent electron-accepting ability, and suitable sensor materials can be designed.

Structure and Dynamics of Associative Exchange Dynamic Polymer Networks

Introducing dynamic covalent bonds can breathe life into polymers by endowing recyclability and tunability to materials, but the characteristic structure and dynamics of associative exchange dynamic polymer networks are yet to be understood. In this study, we present a model to analyze the structure of associative intermediates and the kinetic process of associative exchange. The relationship between the reaction equilibrium constant and the plateau modulus of the associative exchange dynamic polymer networks is established. The model was validated by vinylogous urethane model vitrimers (BPOVU) with different stoichiometric ratios at various temperatures in the equilibrium state. Meanwhile, the thermodynamics and kinetics of BPOVU vitrimers were further analyzed. The model could provide a fundamental understanding of the associative exchange reaction and help direct promising emerging polymer designs and applications.

Design of deep eutectic solvents with multiple-active-sites for HCl separation and storage

The exploiting of efficient, reversible and environmentally friendly hydrogen chloride (HCl) absorbent is of great significance for the recovery and high-value utilization of by-product HCl. Herein, we propose a new strategy to design deep eutectic solvents (DESs) with multiple-active-sites to effectively absorb HCl. Therefore, five new DESs were designed and prepared by pairing 1,3-dimethyl-2-imidazolidinone (DMI) with amide derivatives or LiCl. Among them, DMI + 1,3-dimethylurea (2:1) showed the unprecedented HCl capacity of 2.16 mol/mol at 303.2 K and 1 bar, surpassing that of water, DESs and ILs reported in literature. Spectroscopic characterization and quantum-chemical calculations showed that such high HCl capacity originates from multiple interaction sites between DESs and HCl. DMI + 1,3-dimethylurea (2:1) also exhibited the advantages of fast absorption of HCl, good recyclability, good selectivity and acceptable cost. A new reaction equilibrium thermodynamic model was developed to correlate HCl solubility data. The absorption rate of HCl in DESs was measured systematically for the first time. These DESs with multiple-active-sites offer improvements over commonly used absorbents, indicating the promise for industrial application in HCl separation and storage.

Kinetic, thermodynamic and physical-chemical study of the removal of copper from cachaça using coconut fibers

The use of coconut fiber as a copper adsorbent in cachaça was optimised, and changes in the chemical quality of the beverage were observed by analytical techniques. The influence of the adsorbent mass and copper concentration parameters was investigated using the Central Composite Design, and the optimum condition was obtained through the use of Response Surface Methodology. The equilibrium of the adsorption reaction was obtained within 120 min. The kinetic data were better adjusted for the Elovich model (Elovich and Zhabrova 1939) and the isotherm data for the Sips model (Sips 1948). The maximum adsorption capacity was 1.38 mg g−1. Slight changes in the physicochemical quality of the beverage were observed, including a decrease in volatile acidity and alcohol content. Copper levels in cachaça decreased from 8.57 mg L−1 to 4.97 mg L−1 after adsorption. Therefore, the use of biomass as a metal ion adsorbent in beverages can be successfully employed.

A novel iron phosphate cement derived from copper smelting slag and its early age hydration mechanism

Copper slag (CS), a by-product of copper smelting, is normally stockpiled, leading to wastes of resource and space as well as environment pollution. It has not been massively reutilized as a supplementary cementitious material in Portland cement due to its low reactivity. In the present study, CS is for the first time utilized as the base component to prepare an iron phosphate cement (IPC) by reacting with ammonium dihydrogen phosphate (ADP) at room temperature. The influence of the raw materials mass ratio (CS/ADP) on the microstructure and performance of IPC pastes are investigated. It is found that the compressive strength of IPC pastes at all ages is not a monotonic function of CS/ADP, and the paste with CS/ADP of 2.0 gives the highest strengths, i.e., 26.8, 38.9 and 47.5 MPa at 1, 3 and 28 d, respectively. The crystalline phases including FeH2P3O10·H2O and FePO4 are formed as the main reaction products to bind the unreacted CS particles. The early age hydration of IPC is found to be a multi-stage process, involving the initial dissolution of ADP and iron-containing phases of CS, the formation of FeH2P3O10·H2O, the initial generation of FePO4, and the attainment of the hydration reaction equilibrium. Unlike the magnesium phosphate cement, a redox reaction of Fe(Ⅱ) into Fe(Ⅲ) occurs due to the suitable range of pH and oxidation-reduction potential of the IPC system during the hydration reaction.

A novel formulation representation of the equilibrium constant for water gas shift reaction

In order to meet prominent disagreement for the water gas shift reaction (WGSR) equilibrium constant values obtained from various conventional empirical correlations and mitigate the strong dependence on plenty of experimental data points, here, we report a novel WGSR equilibrium constant formulation representation approach with direct algebraic operation, which only involves experimental data of 3–6 molecular constants for each reactants and products and does not contain the fitting of any experimental equilibrium constant data. The reliability of the developed approach is demonstrated by comparing the predicted values with experimentally measured data and the calculated results with other previous WGSR equilibrium constant correlations. The average absolute deviations between the theoretical values predicted from the developed technique and the directly measured data reported in the literature are 3.993%, 5.970%, 2.418%, 2.083%, 8.659%, 3.733%, and 3.755% for 7 experimental data sets, respectively.

Modeling of propane dehydrogenation combined with chemical looping combustion of hydrogen in a fixed bed reactor

A redox process combining propane dehydrogenation (PDH) with selective hydrogen combustion (SHC) is proposed, modeled, simulated, and optimized. In this process, PDH and SHC catalysts are physically mixed in a fixed-bed reactor, so that the two reactions proceed simultaneously. The redox process can be up to 177.0% higher in propylene yield than the conventional process where only PDH catalysts are packed in the reactor. The reason is twofold: firstly, SHC reaction consumes hydrogen and then shifts PDH reaction equilibrium towards propylene; secondly, SHC reaction provides much heat to drive the highly endothermic PDH reaction. Considering propylene yield, operating time, and other factors, the preferable operating conditions for the redox process are a feed temperature of 973 K, a feed pressure of 0.1 MPa, and a mole ratio of H2 to C3H8 of 0.15, and the optimal mass fraction of PDH catalyst is 0.5. This work should provide some useful guidance for the development of redox processes for propane dehydrogenation.

Perspective on Fe0-PS synergetic effect and reaction mechanism in the thallium(I) contaminated water treatment

Due to extreme toxicity of the element of thallium (Tl), increasing aqueous Tl pollution incidents have aroused growing concerns. As the prevalent and stable form, i.e., monovalent Tl, the highly efficient removal methodologies of Tl(I) from (waste)water remains limited and challenging. In this study, an advanced oxidation method, the feasibility of using zero valent iron (Fe0) coupled with persulfate (PS) to treat Tl(I)-containing synthetic wastewater was investigated. Its influence parameters, including reaction time, initial Tl concentration, dosages of PS and Fe0, initial and coagulation pH, temperature, coexisting ions and organic matter (NO3−, SO42−, Cl− and HA) were examined. The results revealed that the system can be applied to a wide range of pH and temperature and the reaction equilibrium can be reached in about 30 min. Favorable Tl(I) removal rate (>98%) was observed in the synthetic wastewater with medium and relatively high Tl(I) concentration (≤0.250 mM). The analyses of characterization results including electron spin resonance spectrometer and X-ray photoelectron spectroscopy indicated that ·OH played a vital role in the removal of Tl(I), which was oxidized and removed by co-precipitation. Fe0 can be served as a stable source of Fe2+ to efficiently catalyze PS. The remaining Fe0 can be easily separated because of its magnetism, assuring the promising reusability of the reactant. The study aims to provide references for treatment of real Tl polluted wastewater.

Engineering substrate specificity of HAD phosphatases and multienzyme systems development for the thermodynamic-driven manufacturing sugars

Naturally, haloacid dehalogenase superfamily phosphatases have been evolved with broad substrate promiscuity; however, strong specificity to a particular substrate is required for developing thermodynamically driven routes for manufacturing sugars. How to alter the intrinsic substrate promiscuity of phosphatases and fit the “one enzyme-one substrate” model remains a challenge. Herein, we report the structure-guided engineering of a phosphatase, and successfully provide variants with tailor-made preference for three widespread phosphorylated sugars, namely, glucose 6-phosphate, fructose 6-phosphate, and mannose 6-phosphate, while simultaneously enhancement in catalytic efficiency. A 12000-fold switch from unfavorite substrate to dedicated one is generated. Molecular dynamics simulations reveal the origin of improved activity and substrate specificity. Furthermore, we develop four coordinated multienzyme systems and accomplish the conversion of inexpensive sucrose and starch to fructose and mannose in excellent yield of 94–96%. This innovative sugar-biosynthesis strategy overcomes the reaction equilibrium of isomerization and provides the promise of high-yield manufacturing of other monosaccharides and polyols.

Construction of an optimal model for the preparation of C4 olefins based on multiple regression

In this paper, based on the data obtained from a series of experiments conducted by a chemical laboratory for different catalysts at different temperatures, the optimization model and regression relationship model are established by using Gibbs free energy law, chemical equation energy analysis, chemical reaction equilibrium, the preparation of C4 alkenes by ethanol coupling was studied. By analyzing the temperature variation law of ethanol conversion and C4 olefin selectivity under different catalyst combinations, a regression relationship model was established, and the functional relationship between the variables was obtained. Then, the effects of different catalyst combinations and temperatures on ethanol conversion and C4 olefin selectivity were discussed. At the same time, in order to establish two optimization models, the first model is the C4 olefin yield model, which takes the minimum C4 olefin yield as the goal, and takes the range of factors such as temperature, and total mass as constraints. The second optimization model is based on the previous one with a constraint that the temperature is below 350°C, and then solved in MATLAB.

Construction of hydrophobic lauric acid film on aluminum alloy and its corrosion resistance mechanism

6061 aluminum alloy is one of the light metal materials, which has the advantages of good elasticity and lightweight. However, aluminum alloy is susceptible to corrosion in industrial applications. Therefore, in this paper, we successfully prepared an organic lauric acid film on the surface of aluminum alloy by electrodeposition. The film was characterized by SEM, EDS, WCA, XPS, EIS, FT‐IR, and neutral salt spray test. According to the results of the EIS test, impedance value has increased by two orders of magnitude compared to the substrate, and corrosion current density reached 8.51 × 10−7 A/cm2. The salt spray test was conducted for 192 h before the corrosion point appeared, indicating that the film have better anticorrosion ion permeability. Calculated chemical results show that COOH of lauric acid is the dominant reaction group and the carboxyl group is near the aluminum alloy surface for the reaction equilibrium state, which provide a theoretical basis for the study of the film.

Technology Focus: Acidizing (June 2022)

The pulse of our industry is driven not only by simple supply and demand but also by political debate around climate change. It should be kept in mind that the majority of greenhouse-gas emissions is caused by using fossil fuels, not by producing them. Published data showed 5.6% of the global greenhouse-gas emission was from energy production through fugitive gas, compared with 73.2% from the use of energy in various industries, buildings, and transportation. The oil and gas industry is a provider of the basic needs for human activities instead of being the cause of major environmental damage. In fact, the world will have to rely on our knowledge of the subsurface to reach net zero through CO2 sequestration. Nevertheless, today, sustainability is a key matter in our industry. The knowledge we have accumulated in matrix acidizing can play an important role not only in supplying low-cost energy but also in contributing to the reduction of greenhouse gases. It is pleasantly surprising to find a revival in sandstone acidizing. For many years, sandstone acidizing was becoming almost a lost art, overshadowed by carbonate acidizing and hydraulic fracturing. The complex reaction equilibrium of hydraulic fracturing and siliceous minerals, and hence the arduous sequencing of the fluids, impedes its effectiveness. A single-step formulation that works well in carbonate acidizing may mean broader acceptance by operators. Matrix stimulation is not limited to pumping acids. Assessing reservoir properties and well-completion designs to properly integrate chemical formulations and mechanical tools, such as tunneling or jetting, can help extend the reach into the reservoir and, therefore, deliver the optimal economic result of the treatment. Protecting well tubulars from corrosion is another critical consideration during acidizing. The reality of constructing wells with nonmetallic materials is still in the future. Use of corrosion-resistant liner can prove more reliable than chemical inhibitors, especially when long production life of the well is a critical consideration. Acidizing has long been practiced, yet the evolution of chemicals seems slow to stagnant. However, huge amounts of data are available. Collecting and organizing them using artificial-intelligence algorithms will help us improve practices and perhaps even trigger the next breakthroughs. Let’s look forward to integrating the digital transformation with the development of acidizing products and technology in the future. Recommended additional reading at OnePetro: www.onepetro.org. IPTC 21997 - A Delayed In-Situ-Generated Acid System To Enhance Carbonate Acidizing by Albert Bokkers, Nouryon, et al. SPE 208807 - Stimulation Treatment Design Compatible With Glass-Reinforced-Epoxy Lining by Anastasia Bird, BP, et al. IPTC 22665 - Low-Viscosity Polymer Free Acid Retarded System, a Novel Alternative to Emulsified Acid: Successful Application in West Kuwait Field by Salem Hamad Al-Sabea, Kuwait Oil Company, et al.

Determination of Thermodynamic Properties for the Esterification of Levulinic Acid with 1-Butene

The thermodynamic equilibrium of the liquid phase esterification of levulinic acid (LA) with 1-butene (1B) to obtain sec-butyl levulinate (SBL) was studied. Equilibrium experiments were performed in a batch reactor at 2.5 MPa in the temperature range of 363–393 K using Amberlyst-15 as the catalyst. The thermodynamic equilibrium for the side reactions (i.e., isomerization of 1B to trans-2-butene, isomerization of trans-2-butene to cis-2-butene, and esterification of LA with these isomers) was also studied. The thermodynamic properties of the reaction were determined experimentally and compared to theoretical estimations and reported literature values. The enthalpy and entropy changes of the esterification reaction with 1B at 298.15 K were estimated to be −(32.9 ± 1.6) kJ/mol and −(70 ± 4) J/(mol·K), respectively. As for the SBL thermodynamic properties, it was found that the liquid phase enthalpy change of formation and entropy at 298.15 K were −(737.1 ± 0.3) kJ/mol and (423 ± 3) J/(mol·K), respectively.

Enzymatic Preparation of l-Malate in a Reaction System with Product Separation and Enzyme Recycling

Reaction coupling separation systems using calcium fumarate as a substrate can break the reaction equilibrium and promote the production of l-malate. However, the low reusability and stability of fumarase limit its further application. In this study, partially purified fumarase of Thermus thermophilus (87.0 U mg−1) was immobilized within konjac-κ-carrageenan beads. An amalgamation of konjac and carrageenan gum (2%) was used to form the beads, and polyethylene polyamine (0.2%) and glutaraldehyde (0.1%) were used as the cross-linking agents. The pH and temperature profiles of free and immobilized fumarases were remarkably similar. The diffusion limit of immobilized fumarase caused a decline in the maximal velocity (Vmax), whereas the kinetic constant (Km) value increased. Optimization of the parameters for biotransformation by immobilized fumarase showed that 88.3% conversion of 200 mM calcium fumarate could be achieved at 55 °C within 8 h. The beads were stored for 30 days at 4 °C with minimal loss in activity and were reusable for up to 20 cycles with 78.1% relative activity. By recycling the reaction supernatant, a total amount of 3.98 M calcium fumarate was obtained with a conversion of 99.5%, which is the highest value ever reported.

An advanced, comprehensive thermochemical equilibrium model of a downdraft biomass gasifier

A stoichiometric model is formulated for predicting the syngas yield from the reduction zone of a downdraft biomass gasifier. It incorporates the thermodynamic equilibrium of the global gasification reaction, predicts the concentration of the minor gasification products of hydrogen sulphide and ammonia as the sulphur-based and nitrogen-based contaminants, respectively, and implements a new empirical correlation, formulated using existing pertinent experimental data, to account for the mass tar yield. The governing set of model equations is solved in a fully coupled manner, with the boudouard reaction employed to predict char output and the ammonia synthesis reaction used to predict ammonia production. The model does not require the use of correction factors and satisfactorily predicts the concentration of methane, a shortcoming that has tended to plague existing equilibrium models. The syngas composition, tar and char yields, gasification temperature, cold gas efficiency and lower heating value are obtained for various biomass feedstock with a specific ultimate analysis, for different equivalence ratios and varying moisture content. Where possible, predictions are compared with corresponding experimental data and found to be in very good agreement.

Facile preparation of metallic vanadium from consumable V2CO solid solution by molten salt electrolysis

A novel strategy for the preparation of metallic vanadium from V2CO solid solution as consumable anode is proposed by molten salt electrolysis. Controllable synthesis of V2CO solid solution was confirmed based on thermodynamic analysis and carbothermal reduction of V2O3. The constant-current electrolysis process of V2CO was divided into three stages, i.e. induction period (IP), initial depositional period (IDP), and reaction equilibrium period (REP). It was found that V2+ ions from V2CO anode were mainly dissolved into NaCl-KCl molten salts at lower anode current density than 0.2 A cm−2, and then was reduced on cathode. Meanwhile, CO was formed on anode. With the increase of anode current density, the concentrations of vanadium ions in molten salts were increased and induction period was shortened. In addition, particle size of metallic vanadium decreased with the increase of cathode current density. At all anode and cathode current density, metallic vanadium with high purity was obtained by molten salt electrolysis with consumable V2CO anode.

Shift of the reaction equilibrium at high pressure in the continuous synthesis of neuraminic acid

The importance of a compound that helps fight against influenza is, in times of a pandemic, self-evident. In order to produce these compounds in vast quantities, many researchers consider continuous flow reactors in chemical industry as next stepping stone for large scale production. For these reasons, the synthesis of N-acetylneuraminic acid (Neu5Ac) in a continuous fixed-bed reactor by an immobilized epimerase and aldolase was investigated in detail. The immobilized enzymes showed high stability, with half-life times > 173 days under storage conditions (6 °C in buffer) and reusability over 50 recycling steps, and were characterized regarding the reaction kinetics (initial rate) and scalability (different lab scales) in a batch reactor. The reaction kinetics were studied in a continuous flow reactor. A high-pressure circular reactor (up to 130 MPa) was applied for the investigation of changes in the position of the reaction equilibrium. By this, equilibrium conversion, selectivity, and yield were increased from 57.9% to 63.9%, 81.9% to 84.7%, and 47.5% to 54.1%, respectively. This indicates a reduction in molar volume from N-acetyl-ᴅ-glucosamine (GlcNAc) and pyruvate (Pyr) to Neu5Ac. In particular, the circular reactor showed great potential to study reactions at high pressure while allowing for easy sampling. Additionally, an increase in affinity of pyruvate towards both tested enzymes was observed when high pressure was applied, as evidenced by a decrease of KI for the epimerase and KM for the aldolase from 108 to 42 mM and 91 to 37 mM, respectively.

Surface complexation model theory application in NaOL and CTAB collector adsorption differences of diaspore and kaolinite flotation

Although the relevant direct and revers flotation mechanism has been discussed a lot in diaspore and kaolinite separation, the quantitative analysis of surface-active sites and their reaction descriptions during flotation have not been reported yet. In this study, the hydration and collector adsorption reactions of anionic sodium oleate (NaOL) and cationic hexadecyl trimethyl ammonium bromide (CTAB) onto diaspore and kaolinite were quantized. Surface complexation model (SCM) was referred to obtain intrinsic reaction equilibrium constants. It can be found that for NaOL adsorption, the equilibrium constant of diaspore (1013.55) was obviously bigger than that of kaolinite (1011.76 and 1010.35 for ≡AlOH and ≡SiOH, respectively), corresponding to direct flotation of bauxite. While the interaction (103.90 for ≡XNR) between the permanent negatively charged site ≡X− and CTAB was much stronger than other sites. Besides, the single adsorbed amount in mixed minerals were successfully predicted at ratios of 1:2, 1:1 and 2:1. Finally, the fitted potential curves were also acceptable to zeta potential tests. These conclusions from SCM calculation can provide strong supports for collector adsorption differences and then help for separation much more efficiently and economically through saving preliminary exploration cost.

Chemical-Phase Equilibrium of CO–CO2–H2–CH3OH–DME–H2O Mixtures in C–H–O Atom-Mol Fraction Space Using Gibbs Free Energy Minimization

This work employs Gibbs free energy minimization to carry out reaction and phase equilibrium analysis for a CO–CO2–H2–CH3OH–DME–H2O mixture, in a manner that enables a compact representation of the mixture’s feed composition in terms of the feed’s C–H–O atom-mol fractions. The concept of the Atom Species Attainable Region (ASAR) is formally defined, and propositions are developed that identify ASAR in C–H–O atom-mol fraction space for feed compositions consisting of either all six or four of the six aforementioned species. Then, Gibbs free energy minimization is carried out for a broad collection of ASAR points and a wide range of temperatures and pressures, aiming to identify conditions favoring DME production. The results of this comprehensive equilibrium analysis are then presented, and conclusions are drawn.

Influences of variable porosity on CaO/Ca(OH)2 thermochemical energy storage characteristics in direct/indirect heated reactor

• Influence of variable porosity on CaO/Ca(OH) 2 TCES characteristics is investigated. • Variable porosity significantly influences permeability and heat conductivity. • Constant porosity over/underestimates DHR/IHR performance in dehydration by 9%. • Constant porosity underestimates DHR/IHR performance in hydration by 19%. In the present work, the influences of variable porosity of CaO/Ca(OH) 2 , which is normally regarded as constant, on the thermochemical energy storage characteristics in direct/indirect heated reactor (DHR/IHR), are comprehensively investigated by establishing a transient multi-physics coupled model. It is found that, unlike the traditional constant porosity assumption, the variable porosity shows significantly two-fold competitive impacts. On the one hand, increasing/decreasing porosity increases/decreases the permeability of reaction bed, which leads to the drop/rise in pressure field and further the local reaction equilibrium temperature drop/rise. Thus, the local reaction rate increases/decreases correspondingly. On the other hand, increasing/decreasing porosity also decreases/increases the heat conductivity of the reaction bed, which leads to the drop/rise in transient temperature field. Thus, the transient reaction rate decreases/increases instantaneously. The results indicate that the constant porosity assumption may over/underestimate the performance of DHR/IHR during the charging (dehydration) process by around 9%, while underestimate the performances of both DHR and IHR during discharging (hydration) process by up to around 19%. It is also found that the variable porosity demonstrates greater influence on the discharging (hydration) process in DHR and on the charging (dehydration) process in IHR.