Solid Mass Transfer Research Articles

Liquid – Solid mass transfer characteristics of a heterogeneous reactor made of separated horizontal woven screens impinged by a submerged jet

The mass transfer characteristics of a submerged liquid jet impinging on a stack of separated screens were investigated by the electrochemical limiting current technique. The effects of changing the jet velocity, the nozzle diameter, and the screens’ porosity were studied. The present mass transfer data were found to be much higher than the data obtained by previous studies on jet impinging on flat surfaces. The mass transfer data also revealed that using the impinging jet greatly enhanced the mass transfer at screen surfaces with respect to other conventional forced convection methods used in previous studies. The mass transfer data were correlated by the equation: ShR=0.253Sc0.33ReN0.66ε0.745 for the conditions: Sc=1898, 8071 ≤ ReN≤ 33631, 0.668≤ε≤ 0.809. The importance of the above equation in the scale up and design of electrochemical and catalytic reactors suitable for diffusion-controlled reactions was highlighted. The calculated high energy utilization efficiency (kA/e) of the reactor lends support to its use in practice in preference to reactors made of flat surfaces impinged by a submerged jet. By supporting catalyst on the screens, the reactor also can replace stirred slurry reactors usually used in conducting biochemical and photochemical reactions in order to eliminate the time consuming and the costly step of separating the final product from the catalyst particles.

Ethyl levulinate ketalization with glycerol promoted by H,Y-Zeolite: Kinetic analysis in batch and continuous milli-reactor scale

Ketals from levulinic acid are considered emerging compounds which have obtained growing interest in last years. Their possible applications are different, from additives for fuels to plasticizers, polymers and solvents. Ketals can be obtained starting from levulinic acid and its esters. The advantages in using the esters, such as ethyl levulinate, can be found in avoiding the occurrence of the competitive esterification reaction. In this work, the attention was focused on the reaction between ethyl levulinate and glycerol to obtain the five-membered ketal. The reaction was made in the presence of H,Y-zeolite as catalyst investigating the kinetics in batch reactor and in a continuous milli-reactor simulating all the experimental data with a mathematical model. The activation energy was measured both without catalyst (Ea = 104 kJ/mol) and for the catalyzed experiments (Ea = 48 kJ/mol). The reaction showed an endothermic behavior as demonstrated by the reaction enthalpy (ΔrH = 41 kJ/mol). The feasibility of the operation in flow was demonstrated using a milli-reactor. From data interpretation, the fluid–solid mass transfer coefficient was calculated for each volumetric flow. The present study tracks the basis for a future scale-up of the process.

Elucidating the Role of Mass Transfer in Electrochemical Redox Reactions on Electrospun Fibers

Mass transfer can tune the surface concentration of reactants and products and subsequently influence the catalytic performance. The morphology of nanomaterials plays an important role in the mass transfer of reaction microdomains, but related studies are lacking. Herein, a facile electrospinning technique utilizing cellulose was employed to fabricate a series of carbon nanofibers with different diameters, which exhibited excellent electrochemical nitrate reduction reaction and oxygen evolution reaction activities. Furthermore, the microstructure of electrocatalysts could influence the gas–liquid–solid interfacial mass transfer, resulting in different electrochemical performances.Graphical abstract

DEM-CFD coupled simulation of limestone calcination and fuel combustion in beam type lime shaft kiln

This paper presents the development and simulation analysis of a coupled DEM-CFD model of the gas–solid heat and mass transfer process in an industrial-scale beam lime shaft kiln, which uses Computational Fluid Dynamics (CFD) to simulate the combustion of gaseous fuels and the three-dimensional transport of mass, momentum and energy in the gas, and the Discrete Element Method (DEM) to simulate the movement of limestone particles and calcination reactions in the kiln are simulated using the Discrete Element Method. A beam lime kiln uses five burner beams staggered up and down to provide heat for the decomposition of limestone particles in the kiln, and natural gas is injected as fuel from the burners on the burner beams into the limestone bed of the kiln for combustion, while cooling air enters the kiln from the bottom air cap to cool the calcined products and then enters the calcination zone as secondary air to participate in the combustion. In this paper, a 250 m3 beam lime shaft kiln in normal production is used as the research object to simulate and analyze the data of temperature, gas and solidity field and limestone decomposition rate in the kiln. The simulation results show that the overall limestone calcination temperature in the kiln is low and the temperature distribution is uneven, and the decomposition degree of limestone near the kiln wall is higher than that in the center of the kiln. It's caused by the wall effect, the particle porosity is larger near wall, and combustion gas penetration is therefore enhanced in the vicinity. Meanwhile, the simulation results are in good agreement with the actual measured data, which verifies the reasonableness of the model for application in industrial-grade lime kiln.

Liquid Fluidization of Short Hollow Cylinders

We perform numerical simulations on fluidized dense suspensions of solid spheres, solid cylinders, and hollow cylinders in a Newtonian liquid. The simulations are three-dimensional and time-dependent and aim to resolve the flow around and─for the hollow particles─inside individual particles. We use a lattice-Boltzmann scheme that includes an immersed boundary approach for imposing no-slip at solid surfaces. The overall solids volume fraction is 0.5 for the solid particles and 0.375 for hollow cylinders. The latter have a length over outer diameter aspect ratio in the range of 0.56–1.58, while the ratio of outer to inner diameter is 2. Archimedes numbers of the order 103–104 are such that we expect inhomogeneous fluidization with wave-type voidage instabilities. We have a particular interest in the flow through the inner diameter of the hollow cylinders and the extent to which it could contribute to liquid–solid mass transfer.

Optimizing dense particles for efficient thermochemical fuel generation through a unified particle-level model

This study presents a consistent modeling framework that accounts for gas–solid mass transfer, surface reactions, and bulk diffusion in reacting particles to identify the rate-limiting factors for thermochemical cycles.

Implementation of the moving control volume and filling front concepts in modelling solid-liquid extraction of vegetable oil from porous and non-porous solids in a fixed bed

Solid-liquid extraction (SLE), in which a solute is transferred from a fixed bed of solids with different porosities into a liquid phase, involves solid matrix diffusivity or intra-particle porosity ( ε p ) to reflect the mass transfer resistance within the solid phase and mass transfer coefficients to describe the resistance within the liquid phase. Models that consider intra-particle porosity do not adequately describe the overall mass transfer, especially when the porosity values are low. For such cases, it is common to employ models based on solid matrix diffusivity. However, such models do not describe the non-linear solute concentration profiles commonly encountered in the liquid loading zone of extractors. A new mathematical model based on a control volume that moves along with the liquid phase is proposed to describe the solute concentration within the particle and liquid phases. Such an approach also enables calculation of the transient and local solute concentrations in the loading zone. The model parameter sets were fitted to the experimental results from the porous systems (soybean layer). The global mean deviation (11.6%) between the model and experimental results demonstrates that the proposed model is consistent and can be used to simulate solid-liquid extraction operations for porous and low-porosity solids. • New mathematical method for improved simulation of the solid-liquid extraction. • Description of the mass transfer phenomena for particles with different porosities. • Column loading zone is assumed and treated by three approaches. • Strategies to improve the numerical stability and convergence of the model. • Adjustment and validation with experimental results from vegetable oil extraction.

Intensified CO2 capture in wall-coated microreactors with immobilized carbonic anhydrase: Experimental and modeling

An intensified enzymatic CO2 capture process in a wall-coated enzyme-immobilized microreactor (WCEI_MR) was investigated experimentally and numerically under diverse flow conditions, at different human carbonic anhydrase II (hCA II) enzyme and buffer concentrations, and using different buffers. The motivation for using this type of microreactor for the CO2 capture process is to enhance the absorption rate by improving the flow and mass transfer through Taylor gas–liquid flow to efficiently accommodate the reduced time scales of CO2 absorption associated with the CA enzyme. hCA II enzyme was covalently immobilized on the internal surface of experimental microreactor (priori amine-functionalized via polydopamine & polyethyleneimine co-deposition) through glutaraldehyde. An unsteady-state two-scale model involving volume-averaged continuity and momentum balance equations, mass transport/reaction in bulk liquid & gas, and diffusion/enzymatic reaction equations in immobilized-enzyme layer was developed to simulate the wall-coated enzyme-loaded microreactor. Gas-liquid two phase Taylor flow in wall-coated microreactor generates an intensified gas–liquid/liquid–solid mass transfer which, coupled with the large surface area and small axial dispersion and backmixing, enhances the utilization of the enormous hCA II enzyme turnover number and ensures an enhanced enzyme-mediated CO2 absorption process at low pressure drop. WCEI_MR favors low enzyme concentrations, buffers with higher pKa2 constant that generates higher driving force for CO2 hydration or higher buffer concentration that improves enzymatic activity and the intermolecular proton-transfer step that stimulate the absorption process, all of which mitigate the impact of resistance to mass transfer. These findings suggest that WCEI_MR has a high potential for CO2 absorption and, when connected in flexible small-scale modular parallel systems, could represent a promising approach for large-scale green CO2 capture.

Supercritical fluid extraction of turmeric root oil using CO2: Experimental analysis and process modelling

The present study focuses on supercritical fluid extraction (SFE) of essential oil from turmeric root waste. It is an analytical extension of our previous experimental work (Priyanka and Khanam, 2018a, Priyanka and Khanam, 2018b). As one of the objectives, a physico-chemical characterization study shows that turmeric root oil is rich in oleic acids, making it suitable for use in the pharmaceutical and cosmetics industries. The other objective is to gain more insights into the experimental observations through two analytical methods – Mathematical Modelling (MM) and Artificial Neural Network (ANN). Through MM, it is seen that the SFE of turmeric root has an initial fast extraction followed by a slow extraction phase, and the solid phase mass transfer resistance dominates the process. The most optimized conditions for maximum oil yield OY are found through ANN since ANN can predict OY values for conditions for which experimental results do not exist. Phenomena like solute-solvent repulsion, volatility, and the role of intra-cellular structures are investigated through optimization of pressure, temperature, solvent/ co-solvent flow rates, and particle size. Through this work, the significance of turmeric root oil is established, a method of extraction is proposed, the physics involved in extraction is investigated, and optimized parameters for the extraction are suggested.

Effects of chemical potential differences on methane hydrate formation kinetics

To underpin the increasing interest in practical applications of gas hydrates, for gas storage and separation for instance, the formation and growth of hydrates at liquid-gas interfaces are of fundamental importance. Although the thermodynamics of hydrate formation has been widely studied and is well understood, the kinetics of these processes is not well characterised. In this work, a high-pressure, low-temperature stirred reactor was used to conduct hydrate formation kinetic studies in a temperature range from 276.5 to 283.5 K and a pressure range from 5 to 10.5 MPa, with a special focus on 1) the impact of agitation conditions on the available water-gas interfacial surface area for mass transfer and growth rate during hydrate formation, and 2) the effect of the chemical potential driving force on the formation rate. Five hydrate growth regimes were identified, with varying degrees of gas mass transfer control across the gas-water interface depending on the extent to which hydrate layers built up at this interface, gas needed to move through solid hydrate layers, and the extent to which the gas was entrained within the water phase. The formation rate in the initial linear growth regime, before the onset of solid hydrate gas mass transfer effects, was found to depend in an essentially exponential manner on the chemical potential difference from the equilibrium state. Semi-empirical models related to Arrhenius-type kinetic models were used to correlate the data, the best of which reproduced the formation rates from the chemical potential differences to within ± 5 %. The approach has general applicability to help determine the balance between kinetic and thermodynamic factors in identifying the optimum pressure-temperature conditions for processes for gas storage, gas separation and other hydrate applications.

Experimental study on CO2 adsorption with silica-supported ionic liquid in a high gravity reactor

For the problem of mass transfer limitation in the process of CO2 adsorption, the high gravity reactor-Rotating Adsorption Bed (RAB) is used as a device to intensify the gas–solid mass transfer in this paper. The rapidly updated gas–solid interface formed by mean of rotation and peristalsis of dynamic adsorbent in the RAB, is the key reason for improving mass transfer effect and diffusion rate. Firstly, as filler of the RAB, mesoporous silica modified by tetraethylammonium lysine ionic liquid (N2222Lys-Si) is prepared by ultrasonic impregnation method and then characterized by FT-IR, TGA, BET, and SEM. Results show that N2222Lys is uniformly layered on silica by the interaction of electrostaticity and hydrogen bonding. When the N2222Lys loading was 16.7 %, the specific surface area, pore volume and average pore size of the adsorbent were 141.9 m2·g−1, 0.47 cm3·g−1 and 8.72 nm, respectively. The sufficient remain available pores of N2222Lys-Si facilitate the diffusion of CO2. Then, the influence of different operating factors including initial CO2 volume concentration (C0), simulated gas flow rate (Qa), high gravity factor (β), and temperature (Ta) to the adsorption capacity (qe) are explored systematically. The qe reaches 23.33 mg·g−1 at the optimal operating conditions within the experimental range, which are N2222Lys loading of 16.7 %, C0 of 10.0 %, Qa of 600 mL·min−1, Ta of 298.15 K, and β of 7.68. The adsorption process is consistent with Freundlich multi-layer adsorption and Avrami kinetic adsorption, and the adsorption rate in the RAB is intensified by increasing the external and internal diffusion rate from 1.43 and 0.46 mg·g−1·s−1/2 to 2.30 and 0.77 mg·g−1·s−1/2, respectively, with the increase of β from 1.72 to 15.88. Expectedly, excellent mass transfer characteristic makes the RAB a potential intensification device in the process of CO2 adsorption.

A readily available and efficient Pt/P25 (TiO2) catalyst for glycerol selective oxidation

AbstractIn this work, a commercial P25 (TiO2) with phase junctions between (101) and (110) faces supported Pt catalyst was prepared for glycerol selective oxidation, giving a decent 76.8% glyceric acid (GLYA) yield, and good stability. The kinetic experiments calculated apparent activation energy, turnover frequency (TOF), and reaction rates, demonstrating Pt/P25 could facilitate glyceraldehyde (GLYAD) formation and inhibit GLYA over‐oxidation. Series of structural techniques confirmed the 101/110 junctions in P25 contributed electronic effect on Pt through metal‐support interface, which improved the oxygen activation ability and optimized the GLYAD/GLYA adsorption modes. Furthermore, progressive scale‐up reactions were tested and the mass transfer limitations under different conditions were thoroughly studied. The obtained mass transfer factors suggested the gas–liquid and liquid–solid mass transfer were severely limited. Finally, through optimizing the conditions, Pt/P25 catalyst achieved 75.8% GLYA yield at 300 ml‐scale reaction, realizing equivalent magnification with the 5 ml‐scale experiment.

Hydrodynamics and liquid–solid mass transfer in micropacked bed reactors with copper foam packing

Hydrodynamics and liquid–solid mass transfer in micropacked bed reactors (μPBRs) with copper foam packing are investigated. Effects of fluid superficial velocities, liquid viscosity, pore diameter of foam packing on the residence time distribution, liquid holdup, axial dispersion coefficient, and liquid–solid mass transfer coefficient are discussed. The liquid holdup of μPBRs can reach 0.23 ∼ 0.39, which is larger than that of packed bed reactors (0.05). The axial dispersion coefficient of μPBRs is 3.17 × 10-6 ∼ 2.30 × 10-5 m2/s, which is similar with that of packed bed reactors. The value of liquid–solid volumetric mass transfer coefficient with effect of axial dispersion coefficient in μPBRs can reach 0.033 ∼ 0.13 s−1, which is higher than that of packed bed reactors (0.006 ∼ 0.09 s−1). The empirical models of liquid holdup, axial dispersion coefficient, and liquid–solid mass transfer coefficient in single liquid phase flow and gas–liquid two phase flow of μPBRs are established and their predictions are in good agreement with experimental values.

Geometric improvement of hydrolysis reactor structure to enhance the sustainable production of hydrogen from MgH2

Hydrogen is an important clean renewable energy carrier and has the advantages of high calorific value, low environmental impact, and wide availability. Magnesium hydride (MgH2) has attracted extensive attention due to its high hydrogen storage density; however, its poor hydrolysis kinetics limit its application. In this paper, the hydrolysis performance of MgH2 was studied in a self-made hydrolysis reactor, which included both a single tube structure and a plate tower structure. The hydrolysis reactor with the plate tower structure was conducive to achieving controllable and continuous MgH2 hydrolysis. Specifically, the plate tower structure can effectively strengthen the distribution of MgH2 materials, improve the liquid–solid mass transfer and reduce the surface coating. The results of this paper can expand the application of traditional reactors and provide a novel approach for the design of hydrolysis reactors for controllable continuous MgH2 hydrolysis.

Eulerian–Eulerian modeling of the formation and deposition of SiO2 in the outside vapor deposition process

Understanding the complex phenomena in the outside vapor deposition (OVD) process is critical to improvement of the quality and production rate of optical fibers. In the current work, an Eulerian–Eulerian multiphase model based on Computational Fluid Dynamics (CFD) is proposed to simulate the physico-chemical behavior in the OVD process. The model considers the gas–solid flow, heat and mass transfer, species transport, thermodynamics of chemical reactions, as well as growth and deposition of SiO2 comprehensively. The predicted flame structure and flow characteristics are validated against experimental measurements taken from literature. Typical transport phenomena of the OVD process are captured successfully for deeper insights into the mechanisms of the SiO2 growth and deposition. The sensitivity of the key model constants for the solid phase is analyzed. The model predictions are insensitive to the initial particle number density of the seeds introduced. The initial particle size of the seeds critically affects the growth and deposition of SiO2 in the OVD process. The model provides a profound understanding of the mechanism of SiO2 growth and deposition, which plays an important role in process optimization and product attributes control.

Solid-gas adsorption kinetics of the naphthalene on silica and XAD-2

Polycyclic aromatics hydrocarbons (PAH) are an important class of pollutants ubiquitous in the environment, being spread from their source to different parts of the world and has already been related to many health issues. Its major font ofproduction is on the burning or pyrolysis of fuels and during asphalt applications. Adsorption process has been used on-air samplers and polluted media remediation and to a better result kinetics information of the process is necessary. A system tomonitor the gas  solid mass transfer was developed to represent the presence of PAH on the air. Adsorption of naphthalene in XAD-2 and silica, as separated adsorbents and as mixtures, were studied and a mixture of them in a proportion of 2:1 XAD-2/silicagave the best results in terms of the mass of PAH adsorbed and process kinetics. Improvements on the system developed have to be made for future experiments with PAH with a higher molecular weight.

Chemical Looping Combustion in a Packed Fluidized Bed Reactor─Fundamental Modeling and Batch Experiments with Random Metal Packings

The conversion of gaseous fuels during chemical looping combustion (CLC) was investigated in a packed fluidized reactor. The experimental setup consisted of a cylindrical laboratory-scale bubbling fluidized bed reactor with an inner diameter of 78 mm and a height of 1.27 m. Two types of fuel, syngas (50:50% H2/CO) and carbon monoxide (100% CO), were used. Two different types of packings were assessed and compared to the reference case, which was a bubbling bed with no packings. The investigated packings were 25 mm stainless-steel thread saddle rings (RMSR) with a bulk density of 195 kg/m3 and 25 mm stainless-steel pall rings (Hiflow) with a bulk density of 271 kg/m3. The height of the packed reactor section was kept constant at 1 m. Ilmenite concentrate particles in the size range of 90–212 μm was used as an oxygen carrier. The unfluidized bed height was varied between 10 and 60 cm. The results show that the fuel conversion increases as the bed height increases and that the use of packings have a positive effect on fuel conversion. For RMSR packings, the syngas conversion at 840 °C improves from 0.84 (for 10 cm bed height) to 1.00 (for 60 cm bed height). This should be compared to the bed with no packings, for which the corresponding improvement was from 0.69 to 0.98. The general pattern is consistent for all fuels, packings, and bed heights. The results are interpreted as an improvement in gas–solid mass transfer when packings are used, mainly as a result of the reduced bubble size. A fundamental analysis of the variance in the pressure drop over the bed to estimate the bubble diameter supports this interpretation. It is also shown that the mass-based first-order effective reaction contact factor kf improves up to 109% in the bed with RMSR packings compared to the bed without packings.

Modeling of three‐phase continuously operating open‐cell foam catalyst packings: Sugar hydrogenation to sugar alcohols

AbstractAn advanced comprehensive and transient multiphase model for a trickle bed reactor with solid foam packings was developed. A new simulation model for isothermal three‐phase (gas–liquid–solid) catalytic tubular reactor models was presented where axial, radial, and catalyst layer effects were included. The unique feature of this model is that the material balances include most of the individual terms (i.e., internal diffusion, gas–liquid, and liquid solid mass transfer, kinetics) for solid foam packing which is seldom done. Hydrogenation of arabinose and galactose mixture on a ruthenium catalyst supported by carbon‐coated aluminum foams was applied as a fundamentally and industrially relevant case study. Parameter estimations allowed to obtain reliable and significant parameters. The effect of the kinetic parameters and the operation conditions on the arabinose and galactose conversions was studied in detail by sensitivity analysis. The model described is applicable for other three‐phase continuous catalytic reactors with solid foam packings.

Numerical and Experimental Investigation of Pressure Drop in Periodic Open Cellular Structures for Intensification of Catalytic Processes

Periodic Open Cellular Structures are envisioned as potential enhanced catalyst substrates for heat and mass transfer-limited processes. To enable their rational design, in this study, we propose a combined numerical and experimental approach to assess the pressure drop in the tetrakaidekahedral and diamond lattices since generalized correlations are not present in the literature. Deviations are observed between the model predictions available in the literature, which are possibly due to the different methods of investigation, that is, numerical on ideal geometries and experimental on reproductions. To reconcile the two approaches and prevent discrepancies, careful attention is paid here to the quality of 3D-printed replicas for experimental investigation to obtain results representative of ideal lattices. Computational Fluid Dynamics simulations and experiments are then employed together to cross-validate the results and then to perform a parametric analysis of the effect of the morphological properties on the pressure drop. The effect of the cell size and the porosity are discussed, enabling the derivation of engineering correlations for the prediction of the pressure drop across the lattices within the range of 1 < Reds < 300. Finally, the performances of lattice materials are compared with those of conventional structured supports by evaluating the trade-off between the fluid–solid mass transfer rate and the pressure drop, which is crucial for several catalytic processes. Results show that the diamond lattice outperforms other cellular materials and can outperform ceramic honeycomb monoliths at low Reynolds numbers.

Revisiting a large-scale FCC riser reactor with a particle-scale model

Understanding gas–solid hydrodynamics, heat and mass transfer, and multiphase reactions is of great importance to the design of a large-scale fluid catalytic cracking (FCC) riser reactor. FCC catalyst particles in a large-scale (e.g., demo-scale or industrial-scale) riser reactor are generally simulated using Eulerian methods since Lagrangian approaches are often avoided because of their high computational cost. As a result, information about the flow at the particle scale is not considered. In this study, the catalyst behaviors in a large-scale FCC riser reactor are investigated with a particle-scale model that is based on the multiphase particle-in-cell (MP-PIC) scheme. Cracking reactions are taken into account through the incorporation of an eight-lump kinetic model. Numerical predictions are found to be in very close agreement with the available plant data. Detailed particle-scale information, including the particle trajectory, residence time (i.e., internal age), and coke content of the catalysts in the large-scale riser reactor, are fully quantified. Catalyst particles may be entrapped in the diameter-enlarged section, leading to high mean residence time (i.e., 1.67 s) and coke content (more than 3.0% of 3.20% catalyst particles therein), and thereby low catalytic activities (e.g., 0.77 at the height of 2.0 m). It is believed that these findings should help better understand the particle-scale physical and chemical phenomena in large-scale FCC multi-regime riser reactors and assist the design, scale-up, and optimization of similar industrial devices.