Intraparticle Mass Transfer Research Articles

Cationic dye remediation in water treatment with Lizardite–Rice Husk composite: A statistical physics approach

This study presents the development of a novel composite adsorbent, Lizardite-Rice Husk Composite (LRHC), synthesized from lizardite, a mineral derived from chromite ore waste, and rice husk, an agricultural byproduct. The primary objective was to evaluate the efficiency of LRHC in the adsorption of cationic dyes, Malachite Green (MG) and Methylene Blue (MB), from aqueous solutions. Systematic investigations were conducted to assess the influence of adsorbent mass, initial dye concentration, stirring speed, and contact time on adsorption performance. The results revealed that LRHC exhibited optimal adsorption capacities at pH values above 5, with MB and MG adsorption capacities reaching 309.75 mg/g and 51.43 mg/g, respectively. Adsorption equilibrium for MB was achieved within 30 min, indicating rapid dye uptake. Isotherm analysis demonstrated that the Temkin model best described MB adsorption, while the Freundlich model was more suitable for MG, with favorable Langmuir constants. Kinetic studies confirmed that the adsorption followed a second-order model, suggesting chemisorption as the rate-determining step. Intraparticle diffusion and mass transfer were identified as significant contributors to the adsorption process. Thermodynamic studies indicated that MB adsorption was spontaneous (ΔG° = −4.69 kJ/mol for the concentration of 50 mg/L at 298 K) and that MG adsorption was non-spontaneous (ΔG° = 1.52 kJ/mol for the concentration of 50 mg/L at 298 K), with spontaneity increasing at higher initial concentrations. Statistical physics modeling, particularly the monolayer model, provided detailed insights into the adsorption mechanisms and geometry. Furthermore, LRHC demonstrated excellent reusability, maintaining over 80% of its initial adsorption capacity after four regeneration cycles via a heterogeneous Fenton-like reaction. The combination of easy availability, cost-effectiveness, and environmental friendliness makes LRHC a superior adsorbent for the removal of cationic dyes compared to conventional alternatives. This research contributes novel insights into the design and application of composite adsorbents, offering a sustainable solution for water treatment and addressing significant environmental challenges.

Mass Transfer Kinetics of Volatile Organic Compound Desorption from a Novel Adsorbent

The adsorption isotherms and intraparticle mass transfer coefficients of a novel adsorbent with various VOCs at different temperatures during the desorption process are investigated. Firstly, the adsorption isotherms of an HCP-5 adsorbent with o-xylene and ethyl acetate systems were determined at temperatures ranging from 30 to 160 °C, and the data were fitted using the Langmuir adsorption isotherm equation. Subsequently, a mathematical model for the fixed-bed desorption breakthrough of VOCs was established. By combining with fixed-bed desorption breakthrough experiments, the intraparticle mass transfer coefficients of o-xylene and ethyl acetate during the desorption process at different temperatures were obtained through the least squares method. This study revealed that the intraparticle mass transfer coefficients of o-xylene and ethyl acetate during the desorption process were basically equal. The intraparticle mass transfer coefficients increased and then decreased with temperature during the desorption process. Compared with the adsorption process, the contribution of surface diffusion inside the adsorbent pores to intraparticle mass transfer decreased during the desorption process, leading to a significant decrease in the intraparticle mass transfer coefficients, which were approximately one-twentieth of those during the adsorption process.

Kinetic, equilibrium, and thermodynamic studies of adsorptive interactions of eosin-B on chemically treated orange peels

The present study investigated the adsorption of eosin B on the surface of powdered and chemically treated orange peels, along with this process’s condition optimizations, kinetics, and thermodynamics. The adsorbent dose (0.1–0.5 g), temperature (298, 303, 308, and 313 K), contact time (15–120 min), initial pH value (2–11) of the solution, and interfering salts (0.01 and 0.1 mol L−1) were all taken into consideration during the experiments. At all investigated temperatures and pH of 2, adsorption was more favourable. Although the Langmuir model might also represent the adsorption data, the Freundlich and Dubinin–Radushkevich (D–R) models provided a good description. The pseudo-second order kinetic model was followed during the adsorption process. The mechanics of the rate-controlling step were examined by applying the intra-particle diffusion-based mass transfer model to the experimental data. It was discovered that the only process that controlled the rate was intra-particle diffusion. The adsorption process appears to be spontaneous, and endothermic and involves van der Waals forces based on thermodynamic data.

Diffusion behavior of rhodamine 6G in single octadecylsilyl-functionalized silica particle revealed by fluorescence correlation spectroscopy.

We investigated the diffusion behavior of rhodamine 6G (Rh6G) within single octadecylsilyl-functionalized (ODS) silica particle in an acetonitrile (ACN)/water system using fluorescence correlation spectroscopy (FCS). FCS measurements were conducted at the center of the particle to exclusively determine the intraparticle diffusion coefficient (D). The obtained D values were analyzed based on a pore and surface diffusion model, the results of which indicate that surface diffusion primarily governs the intraparticle diffusion of Rh6G. Furthermore, an increase in the concentration of ACN (CACN) resulted in a corresponding increase in the surface diffusion coefficient (Ds), whereas the addition of NaCl did not significantly affect the Ds values. We attributed this dependence of Ds to the dielectric constant change in the interfacial liquid phase formed on the ODS layer. Specially, Ds values of (4.0 ± 0.5) × 10-7, (7.7 ± 1.1) × 10-7, (1.0 ± 0.3) × 10-6, and (1.1 ± 0.2) × 10-6cm2s-1 were obtained for CACN = 20, 30, 40, and 50vol%, respectively. We anticipate that this approach will contribute to advancing research on intraparticle mass transfer mechanisms.

Effect of adsorption/desorption of substrates/products during isobutyl propionate synthesis over CalB Immo Plus™ in solid/gas biocatalysis

This work revisits the potential of Solid/Gas (S/G) biocatalysis for sustainable ester synthesis, focusing on isobutyl propionate (isoPro) production from propionic acid (aciP) and isobutyl alcohol (isoB) using CalB Immo Plus™ (CalB-IP), Candida antarctica lipase B (CalB) supported on ECR1030M (ECR). Our research, conducted in a bench-scale S/G bioreactor, describes the role of adsorption-desorption and intraparticle mass transfer on the production rate of isoPro. Three reaction scenarios were examined at 55°C: simultaneous introduction of both substrates into the reactor; CalB-IP saturation with isoB followed by the supply of aciP; and vice versa, with aciP saturation preceding isoB. Adsorption-desorption-based experiments were conducted to determine breakthrough curves for isoB, aciP, and isoPro over ECR or CalB-IP at 55°C. ECR exhibited significant adsorption capacity, with aciP>isoPro>isoB, in a reversible process. At pseudo-steady state, aciP and isoB were adsorbed at 86% and 84%, respectively, on ECR; while the remaining 14% and 16%, respectively, were adsorbed on the enzyme surface, involving irreversible binding. The experimentation also considered the influence of water activity (aw: 0.11–0.75) on experimental responses. Production rates of isoB adsorption and isoPro were sensitive to aw, while aciP adsorption remained insensitive to aw. At aw = 0.75, isoB adsorbed 35% less over CalB-IP than at aw = 0.11. Additionally, at aw = 0.75, the production of isoPro at the bioreactor outlet in the pseudo-steady state was 33.5% less than when aw = 0.11. These findings offer valuable insights for designing S/G bioreactors, thereby advancing the industrial implementation of sustainable ester synthesis.

Experimental investigation and modeling of the impact of random packings on mass transfer in fluidized beds

This study investigates the impact of two novel settings of bubbling fluidized beds equipped with random metal packings on the mass transfer. To do this, a comprehensive approach is applied that integrates experiments and modeling and explores the relevance of the different underlying mechanisms involved in interphase mass transfer in fluidized beds. Firstly, the mass transfer of water from moisturized silica gel particles to dry air is studied in both a packed-fluidized bed and a freely bubbling bed with no packing. The experimental set-up consists of a cylindrical bubbling fluidized-bed column with an inner diameter of 22 cm. Silica-gel particles with a mean particle diameter of 797 μm are used as bed material. The total bed amount ranges from 4 to 8 kg, while the fluidization number (F) varies between 1.7 and 2.3. Two types of packing, RMSR (stainless steel thread saddle rings) and Hiflow (stainless steel pall rings) are examined and compared to the reference case of a bubbling bed with no packing. The height of the packed section is maintained at 60 cm. The results show that, at all operating conditions, the use of packings enhances the amount of desorbed water in the fluidized bed. The increase is up to 17%, as compared to the bed without packing. The effect is believed to be inhibition of bubble growth in the packed-fluidized bed. To study this further, a mass-transfer model is introduced to analyze the different mass-transfer steps (intra-particle, particle surface to emulsion gas, and emulsion gas to bubble gas) in packed-fluidized beds compared to beds with no packing. TGA experiments are applied to describe the intra-particle mass transfer through a desorption kinetic model. Model analysis shows that the main resistance for mass transfer occurs across the bubble-emulsion boundary. The calculated value of the mass transfer coefficient for this, Kb, at reference conditions (6 kg of silica gel and F = 2.3) is 7.6e-5 s−1 with packings (in average) and 6.2e-5 s−1 without packings, i.e. a 23% improvement in the governing mass-transfer coefficient.

High removal performance of reactive blue 5G dye from industrial dyeing wastewater using biochar in a fixed-bed adsorption system: Approaches and insights based on modeling, isotherms, and thermodynamics study

In an eco-friendly context, an adsorption study was performed in a fixed-bed column system to remove organic pollutants from dyeing wastewater, testing preliminary theoretical models and reactive blue 5G (RB5G) dye as a reference pollutant and tilapia bone-based biochar as an alternative adsorbent. Adsorption approaches in removing RB5G dye molecules from synthetic solutions were performed to understand better based on a reliable mathematical representation and provide insights and strategies into treating dyeing wastewater. Initial dye concentration, pH, temperature, and stirring velocity were used as process variables to search for maximal capacity in batch mode. Thermodynamic analysis and a series of phenomenological kinetic models were applied to understand and interpret the mechanisms and develop a predictive model for a fixed-bed column adsorption system, trying to minimize the total organic carbon (TOC) in dyeing wastewater. An intraparticle mass transfer resistance model and the Langmuir-BET isotherm better represented kinetic and equilibrium data, respectively. In the Langmuir-BET model context, the first monolayer has systematically changed its predicted Langmuir adsorption capacity from 18 mg g−1 to 31 mg g−1 being favored by the increase in temperature of 30 to 60 °C, respectively, with the lowest Gibbs free energies for the multilayer formation ruled by weak physical interaction. Theoretical values of the breakpoint, full saturation time, and useful column height were well predicted related to their experimental ones, including the better fitting of all adsorption curve patterns in a fixed-bed adsorption column system with an adsorption capacity of 30.4 mg g−1 (at 50 °C) for an inlet of 200 mg L−1 RB5G solution resembling almost the same value found in batch mode (30.9 mg g−1). After treating the dyeing wastewater characterized by 75 mg L−1 RB5G dye, the adsorption capacity of 23.3 mg g−1 was attained with a 12% loss in comparison with the expected one for a synthetic RB5G solution due to adsorptive competition with other organic pollutants. Finally, a final TOC value near 5.0 mg L−1, the maximum allowed for the Brazilian environmental council, was attained with an almost zero RB5G concentration after a 5-h breakpoint.

Plantwide Simulation and Operation of a Methanol to Propylene (MTP) Process

BackgroundMethanol to propylene (MTP) process is considered as one of the most important methods for propylene production. The MTP process consists of four sections: conversion of reactants to products, cooling, compression and products separation. In this process, is utilized from multi-stage fixed bed reactors. Due to high exothermicity of the MTP reactors, and existence of recycle loops, a plant-wide control structure is required to be designed for stable, safe and maximum production of propylene. MethodModeling and simulation of the heterogeneous fixed bed MTP reactors with interphase and intra-particle mass and heat transfer were carried out in Aspen Custom Modeler. Steady-state simulations of the MTP process were carried out in Aspen Plus. A simple control strategy was proposed to achieve maximum propylene production with temperature control of the MTP multi-stage reactors by splitting the cold oxygenate feed and the recycled hydrocarbons among the reactor beds. The performance of the proposed control strategy was tested against several disturbances including change in flowrate and composition of feed, using dynamic simulations by Aspen Plus Dynamics. Significant findingDynamic simulation results revealed that simultaneous control of the split range for the 5th and 6th reactor beds and cascade temperature of other reactor beds, could be a suitable temperature control strategy for the reaction section of the MTP process.

Dynamic modelling of removal of binary mixtures of VOCs from indoor air through a carbon-based filter

Carbon-based filters are commonly used to remove volatile organic compounds from indoor air environments. Assessing the filter performance, such as its ability to remove specific pollutants or its efficiency, is crucial to improve air quality in the indoor environment. However, conducting experiments to evaluate the performance of filters for removing volatile organic compounds from indoor air environments can be difficult and time-consuming due to their low indoor concentrations and the presence of complex mixtures of these pollutants. Dynamic models have been used to assist in evaluating the performance of filters for indoor environment applications.In this study, iterative and non-iterative methods were applied to the Dubinin-Radushkevich isotherm, and then they were incorporated into the mass transfer models to represent the adsorption behaviour of a binary mixture of volatile organic compounds (toluene-limonene and toluene- methyl ethyl ketone mixture). Experimental results of binary mixtures containing 9 parts per million volume of each compound were used to measure Dubinin-Radushkevich constants in the iterative method, whereas single-component adsorption experimental results were used in the non-iterative method. Afterwards, the model’s predictions were compared with the experimental results at 0.1 parts per million volume of each compound. The non-iterative method could predict the filter performance for the removal of the toluene and limonene mixture, but there was a systematic deviation for the binary mixture of toluene and methyl ethyl ketone. However, the iterative method, which considers the lateral interaction between the adsorbates, could predict the breakthrough of the filter for the non-ideal mixture of toluene and methyl ethyl ketone correctly. Comparative modelling confirmed the negligible significance of gas-phase diffusion. Also, the comparison between the comprehensive model (Fick’s diffusion for internal mass transfer) and two approximate solutions (linear and quadratic driving force models for internal mass transfer) exhibited the applicability of these intraparticle mass transfer approximations in specific conditions. Finally, the parametric study showed that as the particle size increases, the 100% breakthrough time and initial breakthroughs increase for each component of the binary mixture. However, increasing the air velocity leads to a reduction in 100% breakthrough times and initial efficiencies. At higher inlet concentrations, the breakthrough curves become steeper. Furthermore, the occurrence of the overshoot phenomenon was observed with increasing thickness.

Using Confocal Laser Scanning Microscopy to Analyze the Mass Transfer in the Protein A Medium of a Silica Matrix

Mass transfer in a protein A medium with a silica matrix was analyzed in this study. Using confocal laser scanning microscopy, we monitored the positional and temporal changes in the polyclonal human IgG during batch adsorption. A simple theoretical model based on Fick’s law of diffusion and Langmuir adsorption was used to numerically approximate the external and intraparticle mass-transfer properties of IgG in single particles. The diffusivities found in this study were validated by comparing with the values reported in other studies and also by using numerical calculation to reproduce the experimentally obtained breakthrough curve.

Modeling glucose isomerization in a packed- bed reactor: A complete theoretical and numerical approach

Immobilized enzymes are used in many applications in the food industry presently. Some researchers employ apparent kinetic parameters in immobilized enzyme reactor systems, which only apply to these specific case studies. To increase productivity in a packed bed reactor, it is vital to establish a thorough understanding of all the factors affecting the process, including axial dispersion, convective mass transport, intra-particle diffusive mass transfer, and kinetics. This paper discusses the packed-bed reactor's steady-state model of immobilized glucose isomerase. This model is based on a nonlinear reaction-diffusion equation containing nonlinear terms associated with the enzymatic reaction of Michaelis–Menten kinetics. Akbari-Ganji's method (AGM) and Taylors series with Pade's approximation method are used to calculate the species concentration and normalized current for all possible kinetic parameters and Thiele modulus. The saturated and unsaturated kinetics also have been investigated analytically. A significant agreement between the simulation results and the analytical expression of concentration is observed.

Remediation of water tainted with noxious hexavalent chromium using cetylpyridinium-modified bagasse biomass: adsorption and regeneration studies.

Herein, cetylpyridinium-modified bagasse (SB-CPC) biomass was synthesized and applied for removal of noxious Cr(VI) ions from aqueous matrix. Batch mode analyses were conducted, and the results showed that SB-CPC adsorbent has a maximum uptake capacity (qm) of 70.5 ± 3.2mgg-1 at 303K. The adsorption isotherms and kinetics for elimination of Cr(VI) by SB-CPC were better fitted by Langmuir model and pseudo-second-order model, respectively. The occurrence of pseudo-second-order kinetic could be mainly influenced by the intra-particle diffusion mass transfer. Electrostatic attraction was the dominant underlying reaction mechanism followed by pore filing effect (minor). Thermodynamic study affirms the endothermic behavior and occurrence of physical adsorption process. SB-CPC adsorbent had exhibited an outstanding desorption-regeneration performance using NaOH solution; accordingly, it can practically be applied for remediation of wastewater tainted with Cr(VI) ions.

Effective removal of trace-level toxic metals from flue gas desulfurization wastewater using SiO2 supported hydrogel sorbent

Flue gas desulfurization (FGD) wastewater generated from coal-fired power plants contain potentially harmful heavy metal pollutants that pose a threat to public health and clean water. In this work, we present a water stable polyethylenimine-n,n’-methylenebisacrylamide (PEI-MBAA) functionalized SiO2 solid sorbent material (PMS-1.2/1/4) and investigate its metal adsorption kinetics, selectivity, regenerability, and space velocity. The kinetic studies of six of the toxic heavy metals (As, Cd, Cr, Pb, Se, and Hg) prepared with single elements in Milli-Q water showed the effect of chemical bonding and intraparticle mass transfer resistance on the sorption process. The selectivity studies demonstrated the significant adsorption efficiency toward trace-level heavy metals (Se, Cd, U, Al, etc.) from authentic industrial FGD wastewater. Through five consecutive adsorption−desorption cycles with the FGD (uptake)-citrate (release)-based buffer pair, the sorbent showed high heavy metal removal ability and good reusability. The maximum flow rate for the removal of Se from industrial FGD wastewater was determined to be as high as 8 bed volumes/minute of the sorbent bed. The results demonstrate the PMS-1.2/1.4 sorbent is a promising candidate for the removal of heavy metals from practical aqueous solutions.

Facile Capture of Recombinant Human Erythropoietin on Mesoporous Affinity Hydrogel Matrix Functionalized with Azoboronate.

Boronate affinity ligands (BALs) have gained attention for glycoproteins capture and recognition due to their unique affinity interaction with glycans. In this paper, the effect of azo immobilization of phenylboronic acid on the reduction of adsorption pH of a recombinant glycoprotein (i.e., rhEPO) on hydrogel microparticles was investigated. To evaluate the influence of intraparticle porosity on protein adsorption, microporous (MicroBead) and mesoporous (MesoBead) agarose beads carrying two levels of amine densities were functionalized with azoboronate ligand. Affinity adsorption of the glycoprotein during static and dynamic adsorptions at relatively low pHs of 8 and 7 was studied. Results revealed successful adsorption of rhEPO at pH = 8 through affinity capture of glycans by azoboronate ligands. Increased amine density provided 1.1 and 1.5 times higher static adsorption capacities and dynamic performance efficiencies, respectively. In addition, adsorption capacities and initial adsorption rates of rhEPO on MesoBeads were respectively 1.4 and 2.5-2.8 times of MicroBeads. Also, at pH = 8, MesoBeads recorded higher dynamic recoveries (59 and 91%) compared with microporous ones (46 and 69%) since mesoporosity facilitates intraparticle mass transfer. Reduction of binding pH from 8 to 7 resulted in a sharp decrease in dynamic recovery (14%), indicating the appropriate binding pH of azoPBA to be above 7. The azoboronate affinity ligand is a leading candidate for capturing glycoproteins at relatively low pH. Also, mesoporous microparticles are appropriate tools in more efficient medium-sized protein binding applications.

Particle-scale heat and mass transfer processes during the pyrolysis of millimeter-sized lignite particles with solid heat carriers

• Devolatilization kinetics is coupled with the heat and mass transfer processes. • Evolution of pore structure in coal pyrolysis with solid heat carrier is included. • Multi-physical fields inside a lignite particle during pyrolysis is elaborated. • The intraparticle mass transfer mechanism influences the secondary reaction. The study of mesoscale solid fuel pyrolysis behavior is a key bridge between the microscopic reaction kinetics and macroscopic multiphase reaction flow in a reactor. In this work, a one-dimensional nonstationary model was developed in spherical coordinate system for the pyrolysis of millimeter-scale lignite particles with solid heat carriers, in which a modified multistep kinetic model (MSM) was coupled with a series of correlative transient heat and mass conservation equations in conjunction with the dusty gas model (DGM). The MSM for coal pyrolysis was modified by adding a set of kinetic equations of pseudo-elementary secondary reactions, making the kinetic model comparable to the Chemical Percolation Devolatilization model in terms of accuracy. In addition, a semiempirical submodel for the evolution of pore structure parameters (porosity, pore size, and permeability) was incorporated to obtain the precise mechanism of volatile species transport in the porous coal matrix. The modified MSM and pore evolution submodel were validated against literature data. The coupling effects between intraparticle transport processes and transient devolatilization kinetics were investigated. It was concluded that notable multiphysical fields (pressure, concentration, and velocity) emerged within lignite particles during pyrolysis, governed by the heating history. In addition, it should be noted that the direction and mechanism of volatiles transfer within porous lignite particles varied during pyrolysis, which can significantly affect secondary reactions. Flow reversal and shifts in the dominant mass transfer mode influenced the secondary reaction pathway, in addition to the impact of volatiles flow velocity on the reaction degree.

Analysis of model dimensionality, particle shrinkage, boundary layer reactions on particle-scale modelling of biomass char conversion under pulverized fuel combustion conditions

In this work, the effects of model dimensionality, particle shrinkage, and boundary layer reactions on particle-scale modelling of biomass char conversion under pulverized fuel combustion conditions have been analysed by using six models: zero-dimensional models with constant particle size (0D_Cons) or shrinking particle size (0D_SPM), one-dimensional models with/without considering particle shrinkage (1D_Cons/1D_SPM), and 1D_Cons and 1D_SPM with considering boundary layer reactions (1D_Cons_BH and 1D_SPM_BH). A comparison with existing experimental data shows that the 1D_SPM_BH model with consideration of intra-particle heat and mass transfer, particle shrinkage, and boundary layer reactions is an appropriate model to describe biomass char conversion over a wide range of conditions. The 0D_Cons model is a good approximation for the conditions of small particle size (< 1 mm) at 1273–1473 K, but overestimates the char conversion rate for larger biomass char particle or at high temperatures (regime III). The 0D_SPM model gives a reasonable prediction on char conversion time but predicts a larger contribution of reaction between char and O2 as compared to the 1D_SPM_BH model. The consideration of intra-particle heat and mass transfer in particle-scale modelling (1D_Cons and 1D_SPM) is beneficial to improving the model prediction of char conversion time and the contributions of char oxidation and gasification reactions. The boundary layer reactions have a significant effect on the prediction of char conversion for large particles (> 1 mm) and high temperatures (> 1473 K). An implication for the selection of a particle-scale model in CFD modelling is also given.

Numerical investigations of soot generation during wood-log combustion

• Particle-scale biomass combustion model with soot formation is established. • Virtual-particle-based thermally-thick model and two-equation soot model are integrated. • Improved prediction of soot volume fraction for a single-particle combustion experiment is achieved. • Soot generation during wood log combustion depends highly on flame structure and the packing of wood logs. Soot formation is an important challenge in the design of modern wood stoves, as soot not only deteriorates the combustion efficiency but also poses threats to human health. Although soot formation in biomass combustion has been studied previously, the investigation at wood stove level is still rare due to its complex nature. In this paper, numerical simulations are performed to uncover the basic trends of soot formation during wood log combustion. The soot formation model is developed based on a particle-resolved biomass combustion algorithm, where the intraparticle heat and mass transfer effect, soot mass fraction and particle size are all resolved. Besides, simplified tar and precursor models are used in solving the reaction kinetics of soot formation. The integrated model is first validated through the combustion simulation of a micron-sized coal particle in air, where the predicted flame temperature and the soot volume fraction show improved agreement with experimental data compared to a previous modeling work. Thereafter, the soot formation during wood-log combustion in a confined stove is studied. Different combustion behaviors are observed for varying numbers of wood logs and for variations in the wood-log stacking. Additionally, the flow field temperature, tar, soot, and oxygen concentrations during the combustion are analyzed. Finally, the influences of the air intake rate, the relative distance between wood logs, and temperature boundary condition on the soot formation are discussed. This work provides useful information for the design and the optimization of modern wood stoves.

Application of response surface methodology on photocatalytic degradation of Astrazon Orange G dye by ZnO photocatalyst: Internal mass transfer effects

The present study involves the removal of Astrazon Orange G dye from aqueous solutions by ZnO in a heterogeneous system of using UV-C light as a source of energy. Crystalline structure and BET surface area of the photocatalyst were characterized. The optimum conditions were determined as 200 mg dm-3 of dye concentration, 4 g dm-3 of catalyst amount, pH of 6, the temperature of 40 °C, and 0.2 dm3 min-1 of the rate of airflow. Under these conditions, the dye and TOC removal efficiencies at 75 min were determined as 97.9 % and 54.7 %, respectively. Response surface methodology was also used to investigate the interactive effects of the selected parameters and the optimum conditions for maximum degradation of AOG dye. The kinetics of the Astrazon Orange G dye photodegradation by using ZnO represented by the first-order equation. The effect of the temperature on the AOG dye photodegradation was shown by using of the Arrhenius equation. The activation energy was found to be 4.28 kJ mol-1. In addition, internal mass transfer effects on photodegradation of AOG dye were investigated with different sizes ZnO and effectiveness factors, Thiele modulus, and average effective diffusion coefficient were calculated. These results showed that the intraparticle mass transfer did not have much effect on the reaction rate and the chemical step largely controlled the rate. The potential performance of these photocatalytic processes on the synthetic wastewater was also tested.

Lattice Boltzmann modelling on pore-scale reactive transport in exothermic reactions of solid blocks for thermochemical energy storage

In this study, a pore-scale numerical model of plate-type reactor is developed to simulate and analyze the coupled CaO/Ca(OH)2 thermochemical heat storage processes based on the lattice Boltzmann method. In the research, the fluid flow, chemical adsorption, mass and heat transfer during hydration reaction are considered. Three different structures with the same porosity of solid particles are designed: in-line, staggered and random patterns. The heterogeneous reaction model with the Langmuir adsorption kinetics is implemented on gas–solid interfaces. The interparticle and intraparticle mass transfer processes are both involved with the help of the lattice Boltzmann method. The distributions of concentration in the gas phase and adsorbed amount in the solid phase are obtained in detail. The conversion rates under three different structures with similar porosity are also compared. Moreover, conjugate heat transfer is applied to simulate the transient temperature distributions in these structures. Heat is released from the solid particles and diffuse to the surrounding area along with the fluid flow. The maximum temperatures of the three structures are 550℃. Besides, the trends of characteristic temperatures over time are also obtained, and the durations above 500℃ are calculated, reflecting the heat storage performances of the different structures. The heat release of three different structures is also compared. It is proved that the structure with staggered blocks is recommended.

Numerical analysis of heat pipe-assisted finned adsorber with FAM-Z02/water pair for vehicle air conditioning

• Heat pipe-assisted finned adsorber for vehicle air conditioning. • Heat and mass transport between the heat pipe, fins and adsorbent particles. • Parametric study on SCP, COP and AAMR of FAM-Z02/water adsorber bed. • Optimal bed configuration considering number of fins and minimized weight. Adsorption cooling system (ACS) driven by engine waste heat is an attractive alternative to vehicle air conditioning (A/C) system. To find a compact and efficient solution for onboard application, a heat pipe-assisted finned adsorber unit tube (AUT) packed with FAM-Z02 adsorbent was studied numerically. Based on the integrated physical prototype, a three-dimensional numerical model was developed to investigate adsorption/desorption characteristics combined with experimentally validated heat pipe model and adsorption isotherm model. Moreover, specific cooling power (SCP), coefficient of performance (COP) and adsorber bed to adsorbent mass ratio (AAMR) were quantified to evaluate cooling capacity and system performance. It is found that, compared with adsorber without heat pipe, a 15.3% increment of SCP and 19.1% increment of COP can be achieved in the FAM-Z02/water based adsorber due to the contribution of heat pipe, and the AUT has an optimal SCP of 64.19 W/kg at the cycle time of 8510 s. The smaller adsorbent particle size leads to more refrigerant adsorbing/desorbing under the same cycle time, and FAM-Z02 with 0.1 mm diameter provides optimal SCP of 66.7 W/kg for ACS due to smaller particles possess less intra-particle mass transfer resistance. When the cool source temperature and heat source temperature are 300 K and 365 K respectively, higher SCP can be achieved due to the larger cyclic water uptake. Heat pipe-assisted finned adsorber offers a viable solution for coolant’s application in onboard ACS, and a 6-fin adsorber packed with 0.1 mm-diameter FAM-Z02 is considered optimal under lower adsorption temperature and higher desorption temperature.