Effect Of Internal Diffusion Research Articles

Effect of multi-component gas on removal of trace hydrogen sulfide activity from blast furnace gas using activated carbon adsorbent

Abstract In the steel industry, blast furnace gas (BFG) is huge with complex components. The existence of hydrogen sulfide (H2S) in the BFG can produce sulfur dioxide (SO2) after combustion, which will increase the source of SO2 pollution and make the desulphurization more difficult, to be threat to people health. At present, the removal of H2S by dry adsorption with modified activated carbon adsorbent is a high-precision and low-cost desulphurization method. However, the effect of complex gas components in BFG on the adsorption of H2S by activated carbon adsorbent is not sufficient. Based on the fixed bed adsorbent evaluation system, a new type of highly efficient copper-cerium oxide (Cu–Ce–O) modified activated carbon H2S adsorbent was developed. And the effects of carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), oxygen (O2), sulfur dioxide and hydrogen chloride (HCl) in BFG on the desulfurization activity of adsorbents were investigated. The results showed that the performance of H2S removal decreased in the presence of CO, CO2, HCl and SO2, and improved in the presence of H2 and O2. Other parameters were also studied which might influence the process. The application of modified activated carbon adsorbent in simulated BFG is basically stable. According to the fitting results of adsorption kinetics for the five adsorption models, as the atmosphere becomes BFG from N2, pore diffusion becomes the main adsorption form. However, the effects of internal diffusion, chemical adsorption and external mass transfer decreased. The Bangham model is the most suitable model to describe H2S adsorption process.

Determination of effective liquid-phase diffusion coefficients by tracer method in continuous packed columns

Many industrially relevant chemical processes are affected by the liquid-phase diffusion resistance in porous materials, for example in heterogeneous catalysts. Therefore, reliable experimental methods for the determination of effective diffusion coefficients in porous structures are highly desirable. In this work, a method was developed to study the internal diffusion effects in porous media by step response experiments with tracers injected to fixed beds filled with porous particles and inert material. The tracer responses were recorded at the outlet of the bed by UV–vis spectrometry. Ethanol was used as the tracer and water as the solvent. Porous aluminum oxide particles were selected as the model material. The step responses were described with a dynamic axial dispersion model, i.e. partial differential equations for the inert and catalyst sections of the bed. The partial differential equations describing the model were discretized with finite differences and the resulting ordinary differential equations were solved numerically with a solver for stiff ordinary differential equations. From the experimental data, the dispersion coefficients of the bed and the effective diffusion coefficient in the porous aluminum oxide particles were successfully determined by non-linear regression analysis. The values of the effective diffusion coefficents had a good agreement with the liquid-phase diffusion coefficients estimated from correlations. The method is applicable for any porous material.

Study of the Adsorption and Separation Behavior of Scandium and Zirconium by Trialkyl Phosphine Oxide-Modified Resins in Sulfuric and Hydrochloric Acid Media.

Zirconium is recognized as one of the main impurities of the rare earth element scandium during purification. It presents significant challenges due to its similar chemical properties, making separating it difficult. This study used trialkyl phosphine oxide (TRPO) as a functional ligand, and the effects of carrier type and acidity on adsorption performance were first investigated. Among these, the novel extraction resin SiO2-P as a carrier for TRPO demonstrated more prominent separation performance in 0.2 M H2SO4 and 5 M HCl solutions. The kinetic and isotherm data were consistent with the pseudo-secondary kinetics and Langmuir model, respectively, and the adsorption process could be regarded as homogeneous monolayer adsorption subject to the dual effects of chemisorption and internal diffusion. In addition, thermodynamic analysis showed that the adsorption process of zirconium under the experimental conditions was a spontaneous endothermic process. Combined with the results of SEM-EDS, FT-IR, and XPS analyses, scandium and zirconium were successfully adsorbed by the resin and uniformly distributed on its surface, and the greater affinity of the P=O groups on the resin for zirconium was the critical factor contributing to the separation of scandium and zirconium. Finally, scandium and zirconium in sulfuric acid and hydrochloric acid media were extracted and separated by column experiments, and the purity of scandium could reach 99.8% and 99.99%, respectively.

Gas-phase oxidation of benzene using Cu-loaded MFI binderless zeolite compacts

Phenols are essential raw materials for various fields, and several studies have focused on their synthesis. The development of an efficient one-step synthetic method for the industrial production of phenols is highly important in terms of cost, energy, and environmental impact. In this study, we investigated the formation of phenols via the gas-phase oxidation of benzene using copper-loaded MFI zeolite compacts prepared via a binderless zeolite synthetic method. The catalytic activity of the zeolite in the gas-phase phenol one-step synthetic reaction was investigated, in addition to the effect of benzene diffusion in the molded zeolite and the reaction due to water vapor addition to the reaction gas. The results showed that the activity of the copper-loaded MFI zeolite compacts was almost equivalent to that of powdered copper-loaded MFI zeolites. An effect of diffusion was observed on the external boundary film diffusion where the linear velocity was low. However, no effect of diffusion or internal diffusion was observed in the area where the linear velocity was high. Furthermore, the addition of water vapor to the reaction gas suppressed the decrease in phenol formation activity due to the formation of coke on the catalyst surface.

Semi-batch extraction of phenolic compounds from Rosmarinus officinalis: Kinetic study and dimensionless modeling

A transient and one-dimensional mathematical model with two partial differential equations is developed to simulate the extraction of de-oiled rosemary plant in a vertical fixed-bed reactor. The effect of the dimensionless numbers which appear in the final governing equations (Peclet and Damköhler numbers) is studied. The influence of solvent composition, solid particle size and temperature is also investigated. The process is controlled by internal diffusion effects, with the smallest particle size exhibiting the smallest internal diffusion coefficient. Among the different solvents, 80% ethanol shows the highest total phenolics recovery. The antiradical activity is also enhanced by increasing the temperature and the smaller particle size leads to an improvement in the extraction selectivity. Peclet number has a small effect on the results, while Damköhler number strongly affects the process. An increase in bed porosity causes a significant increase in the internal diffusion time.

Kinetics and mechanism insights into the heterogeneous methylation of nitroguanidine with aqueous methylamine

This study investigated the kinetics and mechanism of the heterogeneous methylation of nitroguanidine with aqueous methylamine. The experiments were conducted in the temperature range of 303–318 K. To eliminate the effect of external diffusion, sufficient agitation was provided. Additionally, a shrinking core model and a dissolution model were developed to research the effects of dissolution, internal diffusion, and chemical reaction. The kinetic parameters of these models were fitted using experimental data, and the calculated results were compared with experimental data to assess the model’s applicability. The developed model was used to study the influence of the initial concentration of methylamine and particle diameter of nitroguanidine on the reaction. This work presents a case for the kinetic modeling of solid-liquid reactions considering non-constant liquid reactant concentrations, aiming to optimize the overall process efficiency of organic solid-liquid phase reactions.

Nickel-Copper Oxide Catalysts Deposited on Stainless Steel Meshes by Plasma Jet Sputtering: Comparison with Granular Analogues and Synergistic Effect in VOC Oxidation

A novel method for the preparation of Ni-Cu oxide catalysts—deposition on stainless steel meshes using hollow cathode plasma jet sputtering—was studied. This method allows the preparation of thin oxide films. Consequently, the whole volume of the active phase is readily accessible for the reactants and can be employed in the catalytic reaction due to the negligible effect of internal diffusion. As a result, the activity of our sputtered catalyst was seven times higher in ethanol oxidation and 61 times higher in toluene oxidation than that of the corresponding granular catalyst. Moreover, due to stainless steel meshes used as a catalyst support, the pressure drop across the catalyst bed was lower. Finally, the catalytic activity of the sputtered Ni-Cu oxide catalyst with Ni:Cu molar ratio of 1:1 in ethanol oxidation was 1.7 times higher than that of the commercial EnviCat® VOC-1544 catalyst, while the amount of the active phase in the catalyst bed was 139 times lower. The outstanding performance of the Ni0.5Cu0.5 catalyst was ascribed to the synergistic effect between the copper and nickel components.

Continuous hydrogenation of 2-(4-nitrophenyl) butanoic acid: Kinetics study in a micropacked-bed reactor

Hydrogenation still faces unmet technical challenges in relation to heterogeneous reactions and potential safety issues. In this work, a continuous flow Pd/C-catalyzed hydrogenation of 2-(4-nitrophenyl) butanoic acid (NBA) was developed within a micropacked-bed reactor. Catalytic hydrogenation of NBA involves the interaction of gaseous and liquid reactants on solid catalysts and the mechanism has not been clearly reported. Therefore, the Langmuir-Hinshelwood-Hougen-Watson (LHHW) approach was used to investigate the kinetics and attempted to explain the possible mechanistic path. The effects of internal diffusion, external diffusion, and salt formation were characterized, the intrinsic kinetic model was established and corresponding parameters were obtained. The model showed that the reaction proceeds through the dual site molecular adsorption of reactant specie and NBA can be reduced to 2-(4-aminophenyl) butanoic acid (ABA) either through the generation of hydroxylamine intermediates or directly.

Plasma Jet Sputtering as an Efficient Method for the Deposition of Nickel and Cobalt Mixed Oxides on Stainless-Steel Meshes: Application to VOC Oxidation

Hollow cathode plasma sputtering is an advantageous method of preparing catalysts in the form of thin oxide films on supports. Such catalysts are particularly suitable for processes such as catalytic total oxidation of volatile organic compounds (VOCs), representing an economically feasible and environmentally friendly method of VOC abatement. Catalysts with Ni:Co molar ratios of 1:4, 1:1, and 4:1 were prepared on stainless-steel meshes and compared with single-component Ni and Co oxide catalysts. The properties of the catalysts were characterized by EDX, SEM, powder XRD, temperature-programmed reduction (H2-TPR), Raman spectroscopy, and XPS. Powder XRD revealed the formation of various crystalline phases that were dependent on molar the Ni:Co ratio. NiO and Co3O4 were identified in the single-component Ni and Co oxide catalysts, whereas Ni-Co mixed oxides with a spinel structure, together with NiO, were found in the catalysts containing both Ni and Co. Raman spectra of the catalysts prepared at high working pressures showed a slightly lower intensity of bands, indicating the presence of smaller oxide particles. The TPR profiles confirmed the improved reducibility of the Ni-Co oxide catalysts compared to the single-component Ni and Co catalysts. Catalytic activity was investigated in the deep oxidation of ethanol and toluene, which were used as model volatile organic compounds. In ethanol oxidation, the activity of sputtered catalysts was up to 16 times higher than that of the commercial Cu-Mn oxide catalyst EnviCat® VOC-1544. The main benefits of the sputtered catalysts are the much lower content of Ni and Co oxides and a negligible effect of internal diffusion. Moreover, the process of plasma jet sputtering can be easily implemented on a large scale.

Effective Maxwell−Stefan diffusion model of near ambient air drying validated with experiments on Thomson seedless grapes

AbstractWith 8% of the world's grapes being dried into raisins, grape drying constitutes a sizable part of agricultural revenue. The drying process in the developing regions of the world struggles with a lack of reliable drying techniques and rising energy costs. In this work, we report a systematic study to elucidate the intrinsic drying kinetics of Thomson seedless grapes. The grapes are subjected to drying by warm air (40−55°C) rather than hot air (>60°C), which has the advantage of producing the sought‐after green raisins. The air velocity is varied between 0.05 and 0.15 m/s to isolate the effect of external mass transfer resistance. A 1D mathematical model was developed that incorporates the effects of internal diffusion and external mass transfer resistance as well as the effects of temperature and relative humidity on the kinetics and driving forces. In addition, the model incorporates a novel thermodynamic model to describe the vapour pressure of water at the surface of the grape. The uniqueness of the model is that it combines thermodynamics and mass transfer in a single framework. Therefore, the parameters that describe the evaporation are the same parameters that describe the internal diffusion within the matrix, making the model robust. This robust, experiment‐trained model can be reliably transferred to develop detailed computational protocols to model cost‐effective grape drying processes in the field.

Transportation of binary chemical reaction in entropy optimized micropolar fluid flow with activation energy and internal diffusion effects

Current investigation manages an analytical research on motion of micropolar fluid due to stretching sheet. Porosity is considered over a stretching sheet. Heat and mass transfer analysis is done under the effects of Joule heating, thermal radiation (nonlinear), viscous dissipation and activation energy for chemical reaction. Partial differential expressions are converted to ordinary ones by using similarity variables. Velocity, temperature and concentration profiles are examined against different physical variables like radiation parameter, Prandtl number, Eckert number, activation energy parameter, etc. Rate of irreversibility in the present flow system is also examined. Outcomes of different physical parameters are analyzed through graphs. Analysis of Sherwood number, drag force of surface and heat transfer rate is done through tables.

Model Analysis of the Role of Kinetics, Adsorption Capacity, and Heat and Mass Transfer Effects in Sorption Enhanced Dimethyl Ether Synthesis.

The role of kinetics, adsorption capacity, and heat and mass transfer effects in the sorption enhanced dimethyl ether synthesis (SEDMES) is investigated by means of a 2D+1D model of a single tube of an industrial-scale, externally cooled, multitubular reactor that simulates the reaction/adsorption step of the SEDMES cycle. The effect of the adsorbent/catalyst weight ratio is analyzed, showing that a trade-off between DME productivity and yield originates from the balance of kinetics and adsorption capacity in the reactor tube. The effects of internal diffusion in catalyst particles are shown to have a strong impact on effective reaction rates: significant yield/productivity improvements are obtained when using a mechanical mixture of catalysts with small particle diameters or by rearranging the distribution of the two active phases in hybrid or core@shell pellets. The thermal effects in the reactor, which are increasingly critical upon intensifying the SEDMES process conditions, are also addressed.

The catalytic kinetics and cfd simulation of multi-stage combined removal of acrylonitrile tail gas

There is no kinetic data and rate equation that can be used directly for catalytic combustion of acrylonitrile tail gas, which leads to the multi-stage combined catalytic kinetic model of acrylonitrile tail gas collaborative removal. In the actual application process, affected by the internal and external diffusion, this paper proposes the multi-stage combined catalytic kinetic research and CFD simulation analysis of acrylonitrile tail gas collaborative removal. Based on the judgment of multi-stage combined catalytic reaction rules of acrylonitrile tail gas collaborative removal, the multi-stage combined catalytic reaction network of acrylonitrile tail gas collaborative removal is solved by matrix transformation. The possible reaction path in the multi-stage combined catalytic reaction network of acrylonitrile tail gas collaborative removal is solved. For quantitative calculation of product distribution, each step of reaction parameters and dynamic factors are required. According to the mechanism of positive carbon ion reaction, materials were used Studio software and genetic algorithm are used to calculate the dynamic factors and determine the dynamic parameters; the grid automatic generator AutoGrid5 embedded in the Fine/TurboTM software package is used to generate the CFD simulation network, and the iterative algorithm is used to calculate the limit value of the CFD simulation; the S-A model in the CFD simulation platform is used to get the modified value of the dynamic mathematical model, and the dynamic factors and parameters are brought into it to establish the CA mathematical model of multi-stage combined catalytic kinetics for the CO removal of olefine and nitrile tail gas. The experimental results show that, under the same experimental device and parameters, the internal and external diffusion effects of the multi-stage combined catalytic kinetic model of acrylonitrile tail gas collaborative removal are detected. The multi-stage combined catalytic kinetic model of acrylonitrile tail gas collaborative removal in this study uses 10-20 mesh catalyst, and the retention time of acrylonitrile tail gas is less than 4.62 s, the internal and external diffusion will not affect the acrylonitrile tail gas collaborative removal The practical application of the kinetic model for the removal of multi-stage combined catalysis.

Cobalt Based Catalysts on Alkali-Activated Zeolite Foams for N2O Decomposition

In this work, we studied the effect of alkali-activated zeolite foams modifications on properties and catalytic activity of cobalt phases in the process of catalytic decomposition of N2O. The zeolite foam supports were prepared by alkali activation of natural zeolite followed by acid leaching and ion exchange. The cobalt catalysts were synthesised by a different deposition technique (direct ion exchange (DIE) and incipient wetness impregnation (IWI) method of cobalt on zeolite foams. For comparison, catalysts on selected supports were prepared and the properties of all were compared in catalytic tests in the pellet form and as crushed catalysts to determine the effect of internal diffusion. The catalysts and supports were in detail characterized by a variety of techniques. The catalyst activity strongly depended on the structure of support and synthesis procedure of a cobalt catalyst. Ion exchange method provided active phase with higher surface areas and sites with better reducibility, both of these factors contributed to higher N2O conversions of more than 80% at 450 °C. A large influence can also be attributed to the presence of alkali metals, in particular, potassium, which resulted in a modification of electronic and acid base properties of the cobalt oxide phase on the catalyst surface. The promotional effect of potassium is better reducibility of cobalt species.

Reaction kinetics and internal diffusion of Zhundong char gasification with CO2

Mass transfer usually affects the rate of chemical reactions in coal. The effect of internal diffusion on char gasification with CO2 in the temperature range from 1123 K to 1273 K was investigated via thermogravimetric analysis and assessment of char morphology features. The results revealed that the effect of internal diffusion on the initial reaction rate was more significant with an increase of particle size, due to the concentration gradient of the gasification agent within the solid particles. In the early stage of gasification, the generation of new micropores and the opening of closed pores led to an increase in specific surface area. As the reaction proceeded, the openings were gradually expanded and the specific surface area continued to increase. However, with further reaction, disappearance of edge pores, melting and collapse of the pore structure led to a decrease in specific surface area. The intrinsic activation energy and reaction order based on the nth-order model were 157.67 kJ·mol−1 and 0.36, respectively. Thus, temperature zones corresponding to chemical reaction and diffusion control were identified. Moreover, the calculated effectiveness factor provided a quantitative estimation of internal diffusion in the initial stage.

Effect of the properties of MFI zeolites on the esterification of isopentyl acetate

Fusel oil is a by-product from the fermentation of sugar to produce ethanol. With the increase in ethanol production in the last years, thousands of liters of fusel oil are also generated. Thus, alternatives for reusing fusel oil involving the transformation of isopentanol, its main constituent, into products relevant to industry have aroused interest. In this work, the use of MFI zeolites with different contents of aluminum in the transformation of isopentyl into its ester, isopentyl acetate, was studied. Its main objective was to investigate the effects of the aluminum content of zeolites on textural and chemical properties and how they influence the catalytic activity. In the work it was verified that the catalysts with larger external surface obtained better catalytic performance, suggesting that, due to the small pore diameter of the MFI structure, the reaction is limited by the effects of internal diffusion and occurs mainly at the external surface of the MFI particles.

Measurement of coal pyrolysis reaction heat by empirical baseline method

ABSTRACT Pyrolysis can be considered as the initial stage or/and paralleling part of coal combustion, gasification, and direct liquefaction, and pyrolysis itself constitutes one of the fundamental technologies in coal conversion. Reaction heat of coal pyrolysis is an important thermodynamic parameter used in reactor design, mechanism study, and energy efficiency assessment. In this study, thermogravimetric & differential scanning calorimetry technique (TG-DSC) was exploited to determine and plot the total heat flux curve along with pyrolysis temperature of Shenmu coal sample, and the varying curves of heat flux baselines in different reaction areas were analyzed and discriminated by empirical method, then the coal pyrolysis reaction heat was figured out. Moreover, the effects of primary test parameters on coal pyrolysis reaction heat were investigated. Results show that during the measurement rational settings including open crucible, ca. 15 mg sample amounts and – 0.074 mm particle size and 80 ml/min carrier gas flows could eliminate both internal and external diffusion effects and help to reduce secondary reactions of coal pyrolysis and heat resistance. When the heating rate increases from 3°C/min to 20°C/min, the total pyrolysis reaction heat of Shenmu coal sample shows an upward trend. Low hysteresis effect of heat transfer and high resolution of heat effect could be observed when the heating rate is 5°C/min, and the reaction heat measured is −12985 J/g, which can objectively express the reaction heat of coal pyrolysis. It could be concluded that coal pyrolysis reaction heat can be conveniently measured by the empirical baseline method with TG-DSC technique.

Hydrogen in zirconium: Atomistic simulations of diffusion and interaction with defects using a new embedded atom method potential

A new interatomic embedded atom method (EAM) potential, called BMD19, has been developed for simulations of hexagonal zirconium with dissolved hydrogen. The parameters are fitted to data from density functional calculations and calibrated using the experimental room-temperature density of zirconium. The new potential overcomes the unphysical negative thermal expansion coefficient between 0 and 200 K obtained with the frequently used Mendelev-Ackland potential (MA#3). It reproduces the geometry around self-interstitial atoms (SIA’s) obtained with DFT while the MA#3 and the COMB3 potentials yield structures with the SIA between basal planes. The energies of forming vacancies and self-interstitials as well as the elastic coefficients are of similar quality for all potentials investigated in the present work. Compared with DFT results, the new potential describes the interactions of H with Zr better overall than any previously published interatomic potentials. This includes the binding energy of interstitial H and its dependence on lattice strain for tetrahedral and octahedral sites, the trapping energy in vacancies, surface segregation energy, and the energy of diffusion barriers. The present work illustrates the usefulness of the BMD19 potential by showing the dependence of diffusion coefficients on lattice strain, the accumulation of H in vacancy c-loops and by correctly describing the Soret effect, i.e. the diffusion of H from hotter to colder regions of the material. Simulations of the effect of grain boundaries and internal surfaces (e.g. nano-voids) and diffusion on surfaces provide further demonstrations of the usefulness of this new potential.

Effect of support size for stimulating hydrogen production in phenol steam reforming using Ni-embedded TiO2 nanocatalyst

Fabrication of reducible titanium dioxide (TiO2) loaded with nickel (Ni) to maximize metal-support interaction for stimulating hydrogen (H2) production via phenol steam reforming (PSR) has been investigated. Catalysts, synthesized by sol-gel assisted impregnation method, were characterized by XRD, FE-SEM, EDX, BET, H2-TPR and TEM techniques. The effects of three different catalyst sizes namely Ni/TiO2-A (11−49 nm), Ni/TiO2-B (22−196 nm) and Ni/TiO2-C (69−205 nm) for their mass transfer limitation, catalytic activity and coke formations were evaluated. Using smaller particle sizes of TiO2 higher BET surface area with good morphology and Ni dispersion was achieved. The Ni/TiO2-A sample shows highest phenol reforming activity with phenol conversion and H2 yield of 98.3 and 76.9 %, respectively. When large sizes TiO2 particles in Ni/TiO2-B and Ni/TiO2-C samples were employed, phenol conversion of 93.7 and 73.1 % and H2 yield of 71.2 and 55.6%, respectively, were achieved. This reveals that smaller support particle sizes have higher conversion and yields, and activity was declined when support size was increased to larger particle sizes. This was obviously small particle sizes resulted in larger surface area, higher metal dispersion and efficient surface reactions with minimum internal diffusion effects. Furthermore, stability analysis reveals continuous H2 production over smaller particles without obvious deactivation, however, activity was declined over time on stream using large support size due to obvious coke depositions. Thus, supports sizes and interaction of metal and support has significant contribution to maximize activity and stability and can be further employed in reforming systems for renewable hydrogen production.

Kinetics of Hydrogenation of Acetic Acid to Ethanol

The intrinsic kinetic behaviour of catalytic hydrogenation of acetic acid in vapour phase was studied over a multi-metallic catalyst. The rate expression was derived from the sequence of elementary reaction steps based on a Langmuir-Hinshelwood-model involving two types of active sites. Experiments were carried out in a fixed bed reactor, which is similar to an isothermal integral reactor designed to excluding the negative effects of internal and external diffusion. The reaction conditions investigated were as follow:reaction temperature 275-325 ºC, reaction pressure1.5-3.0 MPa, liquid hourly space velocity (sv) 0.3-1.2 h-1, molar ratio of hydrogen to acetic acid (H/AC) 8:20. The results show that conversion of acetic acid increases with increasing the reaction temperature and pressure, but decreases with increasing the space velocity and H/AC. Furthermore, reducing the reaction pressure and increasing reaction temperature, space velocity and H/AC can improve the reaction selectivity of acetic acid to ethanol. The established kinetic model results agreed with experimental results. The relative difference between the calculated value and the experimental value is less than 6 %. The values of model parameters are consistent with the three thermodynamic constraints. The study provided evidence that the intrinsic kinetic model is suitable both mathematically and thermodynamically, and it could be useful in guiding reactor design and optimization of operating conditions.