Interfacial Reaction Model Research Articles

Preparation of ultrafine Mo powder by the H2 reduction of MoO2: Parameter optimization, reaction kinetic, and its reduction mechanism

The influences of different parameters, such as reaction temperature, yttrium (Y) content, and H2 concentration, on the particle size and morphological structure of Mo powder prepared via the H2 reduction of MoO2, were investigated in the work. TG, XRD, FE-SEM, laser particle size analysis, model fitting, and orthogonal design experiment methods were adopted to analyze the reaction kinetic and reduction mechanism. The results showed that the optimum conditions for preparing ultrafine Mo powder were recognized as 1073 K, 1 mass% Y content, and a H2 concentration of 0.000576 mol·cm−2·min−1, which enabled the as-prepared Mo powder with a particle size as small as 107 nm. A new interfacial chemical reaction model with the consideration of reaction temperature, H2 concentration, and sample thickness, was proposed to analyze the reaction kinetic. It was found that the curves predicted by the model agreed well with the experimental data, with the apparent activation energy extracted to be 94.686 kJ/mol. The effect of different individual parameter on the reaction rate and the possible reduction mechanism were also elucidated.

Research on gold leaching of carbonaceous pressure-oxidized gold ore via a highly effective, green and low toxic agent trichloroisocyanuric acid

In this work, trichloroisocynauric acid (TCCA) are used for gold leaching with the advantages of fast reaction rate, high leaching efficiency, low toxicity and environmentally friendly. In addition, an important feature is the continuous hydrolysis of TCCA in an aqueous solution to produce oxidants (HClO) while maintaining the effective chlorination concentration at a high level. The various factors affecting TCCA leaching carbonaceous pressure-oxidized gold ore were investigated and the leaching kinetics were established. According to the results of orthogonal experiments, the optimal conditions of TCCA concentration 0.25 mol L−1, NaCl concentration 50 g L−1, pH 5.5, leaching temperature 45 °C and solid-liquid ratio 1:6 could be obtained, and the gold leaching efficiency reached (88.64 ± 0.37) % within 3 h. After the three stages of TCCA leaching, a gold leaching efficiency was increased to 94.39%. Furthermore, TCCA leaching process could be divided into three steps, the findings of kinetic models revealed that in the early leaching step (0–2 h), TCCA leaching was controlled by solid products layer diffusion model, and yet shifted to be controlled by interfacial chemical reaction model in the final step. Importantly, TCCA leaching solution might be converted into a disinfectant with an effective chlorination concentration of 16.075% treated with resin adsorption and alum removal, enabling the secondary utilization of wastewater resources.

Interfacial Reaction Model of High-Al Steel in Continuous Casting Mold

Interfacial Reaction Model of High-Al Steel in Continuous Casting Mold

Thermokinetics synergistic effects on co-pyrolysis of coal and rice husk blends for bioenergy production

In-depth thermodynamic and kinetic synergistic effects of the coal and rice husk blends on co-pyrolysis have been investigated for bioenergy production. The thermokinetic rate parameters were determined for chemical, one-dimensional diffusional, and phase interfacial reaction models especially when fitted to the Coats-Redfern method. The fitted models exhibited thermokinetic rate parameters. The thermogravimetric analysis in view of the thermodynamic parameters including enthalpy, Gibbs free energy, and entropy imparted the prominent degradation temperature ranges (Stage A: 200 °C–400 °C, Stage B: 410 °C–560 °C) for co-pyrolysis reactions of blends. The proportional increase of rise husk into coal for Stage A caused an increase in the apparent values of activation energy, enthalpy specifically for one-dimensional diffusional, and phase interfacial reaction models. In case of Stage B, the increasing share of rice husk into coal proved to be beneficial in decreasing values of activation energy and enthalpy. Positive synergies for 80:20 and 60:40 coal-rice husk blends were calculated. In addition to characterisation analysis of all samples; co-pyrolysis and co-gasification experiments were completed in a tubular fixed bed reactor at Stage B and onwards temperatures for synergised blends. The resultant co-pyrolysis biochar samples revealed honeycomb structure useful in adsorption applications. The gas chromatography-mass spectrometry analysis of the bio-oil yields 23% phenols, 11% acids, and methoxy phenols for the 60:40 coal-rice husk blend. The product gas composition of 2% H2, 14% CH4, and 4% CO2 for the 80:20 coal-rice husk blend increased to 3% H2, 12% CH4, and 5% CO2 for the 60:40 blend. The co-gasification process substantially increased the production of H2 up to 14%-17% when compared to co-pyrolysis results. The approach used in this study can be utilized to capitalize on synergy to enhance co-pyrolysis of appropriate blends and their products can be used in further future applications upon upgradation.

Pyrolysis of date seeds loaded with layered double hydroxide: Kinetics, thermodynamics, and pyrolytic gas properties

Development of date seeds in-situ pyrolysis utilizing layered double hydroxide (LDH)-based catalysts is still in its infancy. This study investigates the thermokinetics of date seeds (DS) loaded with LDH by thermogravimetric analysis. Three different LDHs, namely Mg-Fe (MF), Ni-Fe (NF), and Co-Fe (CF), were synthesized by the co-precipitation method and loaded with dried date seed powder in a 1:10 ratio, which were then pyrolyzed in-situ in a custom-designed pyrolytic reactor (semi-batch cracking furnace) at an operating temperature and heating rate of 500 °C and 10 °C/min under inert atmosphere (N2). Under optimized operating conditions, the LDH-loaded DS provided a bio-oil yield between 65 and 67 wt%, while the pyrolysis–gas yield was about 20 wt%. The FT-IR analysis of LDH-derived bio-oil confirmed the presence of aliphatic and aromatic hydrocarbons that can be used effectively for energy applications. The pyrolysis kinetics, pyrolysis gas composition, and thermodynamic properties of biomass-loaded with LDH were also investigated. Thermokinetic analysis was performed using data from Coats-Redfern, which fitted the kinetic model at five different reaction mechanisms: chemical reaction order, phase interfacial reaction, power-law, diffusion-controlled, and nucleation and growth models for biomass conversion rates of 20–40% and 40–80%. The results showed that the diffusion-controlled parabolic law (D1) and the fourth-order reaction model (F4) are likely mechanisms in the conversion range of 20–40% and 40–80% for LDH-loaded date seeds. Based on the ascending order of activation energy (Ea), the biomasses can be classified as DS > MF-DS > NF-DS > CF-DS. In addition, the main gasses released and detected from the decomposition of pure biomass (date seeds) and LDH-loaded biomass through a micro GC-Varian were CH4, H2, CO, and CO2. A plausible reaction mechanism for the role of layered double hydroxides in the conversion of bio-oils and pyrolytic-gas components was also presented. This study demonstrates the role of LDH-based catalysts in the pyrolysis of date seeds to produce value-added chemicals and biofuels.

Transport of Carbamazepine, Ciprofloxacin and Sulfamethoxazole in Activated Carbon: Solubility and Relationships between Structure and Diffusional Parameters.

The transport of carbamazepine, ciprofloxacin and sulfamethoxazole in the different pores of activated carbon in an aqueous solution is a dynamic process that is entirely dependent on the intrinsic parameters of these molecules and of the adsorbent. The macroscopic processes that take place are analyzed by interfacial diffusion and reaction models. Modeling of the experimental kinetic curves obtained following batch treatment of each solute at 2 µg/L in tap water showed (i) that the transport and sorption rates were controlled by external diffusion and intraparticle diffusion and (ii) that the effective diffusion coefficient for each solute, with the surface and pore diffusion coefficients, were linked by a linear relationship. A statistical analysis of the experimental data established correlations between the diffusional parameters and some geometrical parameters of these three molecules. Given the major discontinuities observed in the adsorption kinetics, the modeling of the experimental data required the use of traditional kinetic models, as well as a new kinetic model composed of the pseudo first or second order model and a sigmoidal expression. The predictions of this model were excellent. The solubility of each molecule below 60 °C was formulated by an empirical expression.

Innovative technology for defluorination of secondary aluminum dross by alkali leaching

Secondary aluminum dross (SAD) contains harmful fluorides, so it requires a harmless treatment before recycling. In this paper, an innovative SAD defluorination technology was developed. It extracts all the soluble sodium fluoride and active cryolite of SAD; besides, it can also stabilize the harmful fluorides towards deep detoxification. The defluorination process gave a novel idea for the comprehensive wet processing treatment of SAD. A NaOH solution was used to leach active fluorides, including cryolite and soluble fluorides, from SAD. The Effects of NaOH concentration, temperature, liquid-to-solid ratio, and leaching time on the fluoride leaching rate were investigated. The leaching rate of active fluorides was 95.8% at a NaOH concentration of 10 wt%, a leaching temperature of 80 °C, a liquid-to-solid ratio of 4, and a leaching time of 20 min. The kinetic analysis showed that the fluoride leaching occurred according to the hybrid control model of solid product layer in-diffusion and interfacial chemical reaction. The apparent activation energy was 39.64 kJ/mol. Meanwhile, 99.9% of fluoride ions in the alkaline solution were converted into CaF2 by adding CaO, stabilizing the active fluorides. The concentration of fluorides in the alkaline solution was 5.944 mg/L, satisfying the Chinese National Standard.

Evaluation of reaction mechanisms and emissions of oily sludge and coal co-combustions in O2/CO2 and O2/N2 atmospheres

Oxy-fuel combustion technology presents promising potential for the thermal disposal of hazardous waste to alleviate the global greenhouse effect on the environment and human well-being. In this study, the co-combustion reaction mechanisms and cleaner and efficient performances of oily sludge (OS) and coal in the oxy-fuel (O2/CO2) and air (O2/N2) atmospheres were characterized. With O2 concentration of 21% and at 20 °C/min, the ignition and burnout temperatures of the OS combustion were slightly worse in the oxy-fuel (403 and 531 °C) than air (407 and 535 °C) atmosphere. The rising O2 concentration increased the comprehensive combustion characteristic index from 1.11 × 10−7 to 4.29 × 10−7 in the air atmosphere and 1.02 × 10−7 to 4.10 × 10−7 in the oxy-fuel atmosphere. Based on the master-plots method, the three combustion stages of light oil, heavy oil, and fixed carbon were best described by the three-dimensional diffusion, interfacial reaction, and random nucleation growth models, respectively. The reaction mechanisms were independent of heating rate, O2 concentration, and atmosphere type. The co-combustion interaction between 70% OS and 30% coal reduced NO and SO2 emissions. Our findings can provide new insights into achieving their cleaner and more efficient co-combustion performance and its operational optimization.

Recovery and regeneration of Al2O3 with a high specific surface area from spent hydrodesulfurization catalyst CoMo/Al2O3

Aluminum recovery is a key issue for the overall recycling of valuable metals from spent catalysts. This paper focuses on the recovery and regeneration of alumina with high additional value from the spent hydrodesulfurization catalyst CoMo/Al2O3. The results indicate that 98.13% alumina is successfully leached from the treated spent catalysts by an alkaline leaching process under the conditions of 5 mol·L−1 sodium hydroxide, a liquid/solid ratio of 20 ml·g−1, a temperature of 160 °C and a reaction time of 4 h. In the leaching residue, no difficult leaching compound is found and cobalt and nickel are enriched, both of which are conducive to the subsequent metal recovery step. The reaction order of aluminum leaching is 0.99. This reaction fits well with the interfacial chemical reaction model, and its apparent activation energy is calculated as 45.50 kJ·mol−1. Subsequently, γ-Al2O3 with a high specific surface area of 278.3 m2·g−1, a mean size of 2.2 μm and an average pore size of 3.10 nm is then regenerated from the lixivium, indicating its suitability for use as a catalyst carrier. The recovery and regeneration of alumina from spent catalysts can not only significantly contribute to the total recycling of such hazardous spent catalysts but also provide a new approach for the preparation of γ-Al2O3 with a high specific surface area using spent catalysts as the aluminum sources.

Extraction kinetics of neodymium from chloride medium using HEH/EHP saponified with magnesium bicarbonate solution

Magnesium bicarbonate solution is considered as an environmentally friendly extractant saponification agent for the solvent extraction of rare earth elements due to its advantage of minimum water pollution. In order to reveal the extraction regularity, optimize production-process and guide the use of this new extraction system, the extraction of Nd(Ⅲ) in chloride medium with HEH/EHP saponified by magnesium bicarbonate solution was investigated with the self-designed constant interfacial area cell. Besides, the effects of stirring rate, temperature, specific interfacial area and concentration of Mg-HEH/EHP on the extraction rate of Nd(Ⅲ) were systematically investigated. Results show that, the rate of extraction is governed by both diffusion and chemical reaction, and the extraction reaction takes place at the interface. The apparent activation energy of the extraction reaction is 16.88 kJ/mol. The corresponding rate equation is deduced. The mechanisms and rate-determining step are speculated based on interfacial reaction models, which is consistent with the experimental results.

Kinetics analysis of the forward extraction of cerium(III) by D2EHPA from chloride medium in the presence of two complexing agents using a constant interfacial area cell with laminar flow

AbstractThe kinetic studies performed on the forward extract of cerium(III) from chloride solution with the complex agents, citric acid (H3Cit) and lactic acid (HLac) in the presence of di-(2-ethylhexyl)phosphoric acid (D2EHPA, H2A2) have been investigated using a constant interfacial area cell with laminar flow. The effects of stirring speed, temperature, and specific interfacial area on the extraction rate are discussed separately, and the results show that the extraction process is a diffusion-controlled kinetics process with an interfacial reaction. Studies on the effect of pH value and H2A2concentration on the extraction rate are used to obtain the rate equation. The rate-controlling step is also suggested by the predictions derived from the interfacial reaction models, and the rate equation obtained by the kinetic model is consistent with that obtained by the experimental results. The information on the extraction kinetics in this extraction system will provide some knowledge of its application.

Interfacial reactions in SiCf/C/Ti17 composites dominated by texture of carbon coatings

Two kinds of turbostratic carbon coatings with different texture were deposited on SiC fibers using single filament chemical vapor deposition by changing substrate temperature: 920 and 1000 °C, labeled as C920 and C1000, respectively, followed by coating Ti17 matrix, and then SiCf/C920/Ti17 and SiCf/C1000/Ti17 composites were fabricated by hot isostatic pressing (HIP). C1000 possesses much stronger texture than C920, evidenced by combined tests of X-ray photoelectron spectrum, Raman spectroscopy and transmission electron microscope (TEM). Interfacial reactions of SiCf/C920/Ti17 and SiCf/C1000/Ti17 composites are found to depend strongly on texture of turbostratic carbon coatings after HIP, revealing that C1000 with stronger texture can hinder the outward diffusion of C and inward diffusion of matrix elements more efficiently than C920, which is elucidated by the results of scanning electron microscope, TEM and energy-dispersive spectroscopy. Interdiffusion between C coating and Ti17 matrix results in formation of C gradient distribution in interfacial reaction layer for both composites, in which interfacial zone of fiber and matrix can be described as turbostratic C||amorphous C||fine-grained TiC||transition TiC||coarse-grained TiC, however, each sub-layer thickness is determined by the texture of C coating. Based on these results, the model of interfacial reactions dominated by texture of C coatings was proposed.

A sectioning method for the kinetics study on anthracite pulverized coal combustion

The combustion process of pulverized coal is widely used in different industries as a supplier of energy. Taking Gaoping coal as an example, combustion reaction kinetic of anthracite was studied by thermal analysis curves at different heating rates. Based on the physical and chemical characteristics of combustion process, the characteristic temperatures of combustion process are obtained. Then, anthracite combustion process is divided into two ranges from ignition to burnout temperatures at the temperature where the mass loss rate reaches the maximum. At first range, the combustion reaction temperature is relatively low and the ash layer (solid reaction product) is thin. The primary limiting element is the chemical reaction stage. With the temperature rising and the reaction going on, the chemical reaction rate is increased. Simultaneously, as the solid product is accumulated, the gaseous diffusion process is impeded. The rate-controlling step is turned into the diffusion process. Therefore, interfacial chemical reaction model and internal diffusion model are developed to describe the two ranges of combustion process. The results illustrate that the experimental data are fitted well and correlation coefficients (r 2) exceed 0.90. Finally, the corresponding kinetic parameters are obtained for the utilization of coal resource.

Kinetic study on reactive extraction of metoprolol enantiomers with cyclohexyl (D)-tartrate and boric acid as combined chiral selector

Abstract This paper reports on the kinetic study on reactive extraction of metoprolol (MT) enantiomers using cyclohexyl (D)-tartrate (DT) and boric acid (BA) as combined chiral selector in a modified Lewis cell. An interfacial reaction model is applied to understanding the experimental data. The MT enantiomers are extracted enantioselectively from aqueous phase through the interfacial reaction among BA, DT and MT. Important factors that influence the kinetics of extraction are investigated. The optimal conditions for kinetic study were as follows: agitation speed of 75 rpm, interfacial area of 12.56 cm2, pH of 6, initial DT concentration of 0.075 mol/L, initial BA concentration of 0.1 mol/L, and initial MT concentration of 5 mmol/L at temperature of 5 °C. Important parameters concerning extraction kinetics are evaluated through multiple linear regression analysis of the experimental data. The interfacial reaction is 0.4, 0.6 and 1 order separately with respect to BA, MT and DT, and the total order of reaction is about 2. The forward rate constants have been found to be 5.24 × 10−4 L/(mol s) for (R)-MT and 2.73 × 10−4 L/(mol s) for (S)-MT.

Direct preparation of hierarchical macroporous β-SiC using SiO2 opal as both template and precursor and its application in water splitting

β-SiC is a suitable photocatalyst for hydrogen evolution reaction because of its proper band structure (2.36 eV) and high chemical stability. Porous β-SiC has a large surface area that can increase the number of reactive sites and shorten the charge transport pathways between the material interior and surface, thereby significantly improving the hydrogen evolution reaction performance. In the present study, hierarchical macroporous β-SiC monolith composed of nanocrystals was directly prepared using SiO2 opal as both template and precursor via the magnesiothermic reduction method at 750 °C. An interfacial magnesiothermic reaction model was presented as well. The β-SiC sample exhibited high photoelectric conversion performance and stability as a catalyst for hydrogen evolution.

Thermal behavior and kinetic study on the pyrolysis of Shenfu coal by sectioning method

According to the physical and chemical characteristics of Shenfu coal pyrolysis process, the kinetics process is divided into three parts at the temperature where the variation of mass loss rate reaches the maximum. First of all, the adsorbed gas and crystal water are removed in the low temperature range; secondly, with a large amount of coal gas and tar vapors evaporating off, coal is transformed into semi-coke in the middle temperature range; thirdly, the semi-coke is further coked with the obvious volume shrinkage in the high temperature range. And then, interfacial chemical reaction model, internal diffusion model with the constant volume of resultant and internal diffusion model with the shrinking volume of resultant are developed to describe the different ranges of pyrolysis process. The results illustrate that the experimental data are fitted well, and all the correlation coefficients (r 2) exceed 0.95. Finally, the kinetic parameters of each temperature range are obtained for the utilization of coal resource.

Extraction kinetics of neodymium(III) from chloride medium in the presence of two complexing agents by D2EHPA using a constant interfacial area cell with laminar flow

Kinetic studies of the extraction of neodymium (Nd) from chloride medium in the presence of two complexing agents lactic acid (HLac) and citric acid (H3Cit) by D2EHPA (H2A2) in kerosene have been investigated using a constant interfacial area cell with laminar flow. The different parameters affecting the extraction rate such as stirring speed, temperature, specific interface area, hydrogen ion concentration, and H2A2 concentration are separately studied and a rate equation is deduced. The experimental results demonstrate that, the rate of Nd(III) extraction is a diffusion controlled process at the interface rather than in the bulk phase, and it is first order with respect to H2A2 and H+ concentrations. The rate-determining step is proposed on the basis of predictions derived from interfacial reaction models, and is in good agreement with the analysis of the experimental results.

Mass transfer kinetics of lanthanum (III) extraction in the presence of two complexing agents by D2EHPA using a constant interfacial area cell with laminar flow

The lanthanum (La) extraction kinetics from chloride medium containing two complexing agents lactic acid (HLac) and citric acid (H3cit) by D2EHPA (H2A2) have been investigated using constant interfacial area cell with laminar flow. The stoichiometry of the complex formation reaction between La and H2A2 has been evaluated. The extraction kinetics data have been analyzed in terms of pseudo-first order constants. From the effects of stirring speed, temperature and specific interfacial area on the extraction rate, it is found that the extraction process is a diffusion-controlled kinetics process with an interface reaction. The rate-determining step is made by predictions derived from interfacial reaction models, and the rate equation has been evaluated from analysis of the experimental results, also, the extraction model has been proposed.

Kinetics study on reactive extraction of d-p-hydroxyphenylglycine by BINAP–palladium complex in Lewis cell

This paper reports the kinetics study on the reactive extraction of d-p-hydroxyphenylglycine (d-HPG) with PdCl2-(S)-BINAP (BINAP–Pd) complex as chiral selector. Experiments were performed in a modified Lewis cell and d-HPG was extracted by BINAP–Pd from the aqueous phase to the organic phase. The theory of extraction accompanied by a chemical reaction and an inter-facial reaction model were applied for an insightful understanding of the kinetics data. Results show that modeling is in good agreement with the experimental data. The effects of agitation speed, interface area, pH value of aqueous phase, initial concentration of d-HPG and initial concentration of BINAP–Pd on the specific rate of extraction were investigated. The forward rate constant of the reaction in the reactive extraction process have been found to be 1.0×10−3.5m2.2/(mol0.4s) for d-HPG.

Kinetics Study on Reduction of CaWO4 by Si from 1423 K to 1523 K

Abstract Investigation on reduction kinetics of scheelite(CaWO4) provides important fundamental knowledge to control and optimize process of Ferrotungsten manufacturing and direct reduction of scheelite in steelmaking. In this work, the isothermal reduction kinetics of CaWO4 powder by Si powder at 1,423 K, 1,473 K and 1,523 K, where all reactants and products are in solid state, was investigated by using X-ray diffraction quantitative analysis. Scanning electronic microscopy (SEM) attached with energy dispersive spectra (EDS) was also employed to investigate the microstructure of reaction interface. Both Jander model and Ginstling–Brounshtein model could describe kinetics of reduction of CaWO4 well, whereas 3D interfacial reaction model could not describe the kinetics of reduction of CaWO4. The rate determining step for reduction of CaWO4 could be diffusion of Si across product layer. The values of activation energies obtained by fitting kinetic data using Jander and Ginstling–Brounshtein model are as great as 379.93 kJ/mol and 387.16 kJ/mol respectively. The oxygen partial pressure during reduction has impact on the kinetics of reduction. The reduction was retarded by increase of oxygen partial pressure.