Mass Transfer Steps Research Articles

Scale-up and mass transfer of the adsorption/desorption process of anthocyanins in amorphous silica

The purification and recovery of anthocyanins are important to maintain the stability of the purified solution, ensuring that the health-beneficial properties of this substance are not altered. This work aimed to obtain and compare solutions of commercial and natural grape and red cabbage anthocyanins, suitable process conditions, as well as purification and recovery through detailed analysis called two-stage, estimation of phenomenological parameters of mass transfer and scale-up using Bugram Protect® as amorphous silica. The adsorbent was characterized as amorphous and with a high silicon dioxide composition. The pH 3.0 potentiated the stability of flavylium cation in solution. The Freudlich isotherm represented the equilibrium data. The phenomenological parameters KE and Ds and the limiting step of mass transfer were estimated. Scale-up indicated dosages of adsorbents to meet the process specifications. This work presented additional results in phenomenological aspects and industrial scale in the recovery and purification of anthocyanins.

Continuous air purification by front flow photocatalytic reactor: Modelling of the influence of mass transfer step under simulated real conditions

In this work, a solution for the treatment of toxic gases based on a photocatalytic process using TiO2 coated on a cellulosic support, has been investigated. Here, cyclohexane was chosen as the reference for testing its removal efficiency via a continuous front flow reactor as type A anti-gas filters. The photocatalytic support was firstly characterized by EDX, to confirm its elemental composition. Then, the experiments were carried out, starting with a batch reactor in order to evaluate the degradation efficiency of the photocatalytic media, as well as the monitoring of the photocatalytic process which allowed the establishing of a carbon mass balance corresponding to the stoichiometric number of our target pollutant. The transition to a continuous treatment with a front flow reactor aims to highlight the influence of the input concentration (0.29–1.78 mM m−3) under different flow rates (12, 18 and 36 L min−1). The relative humidity effect was also investigated (from 5 to 90% of humidity) where an optimum rate was obtained around 35–45%. In addition, the mineralization rate was monitored. The major rates obtained were for a cyclohexane input concentration of 0.29 mM m−3 in wet condition (38%) at an air flow rate of 18 L min−1, where the CO2 selectivity reached 77% for an abatement of 62%. In order to understand the limiting steps of the photocatalytic process, a model considering the reactor geometry and the hydraulic flow was developed. The obtained results showed that the mass transfer must be considered in the photocatalytic process for a continuous treatment. The Langmuir-Hinshelwood bimolecular model was also developed to represent the influence of the humidity.

Modeling of indoor air treatment using an innovative photocatalytic luminous textile: Reactor compactness and mass transfer enhancement

Indoor air pollution is a complex problem that involves a wide range and diversity of pollutants that threaten human health. In this context, significant efforts must be made to improve the quality of indoor air. It is therefore important to start controlling the sources of indoor pollution. However, where eliminating or minimizing sources of emissions is not technically feasible, technologies to reduce them should be used. The present work deals with the photocatalytic depollution of hospitals indoor air, using a continuous photocatalytic process. In order to get closer to real conditions, two model pollutants representing the indoor air of hospitals were chosen as targets; chloroform (CHCl3) and glutaraldehyde (C5H8O2). The photocatalytic oxidation of VOCs alone and their mixture (binary mixing system) has been studied on a pilot scale. Indeed, the experiments were carried out in a continuous planar reactor using a new technology based on the TiO2/optical fiber photocatalyst.The effects of experimental conditions such as air flow rate (4–12 m3.h−1), VOCs inlet concentration (4–40 mg.m−3) and humidity levels (5–90%) were pointed out. The photocatalytic effect of the OF-TiO2 composite was found to be improved under UV irradiation as compared to TiO2. The presence of water molecules in small amounts (less than RH = 30%) can promote the degradation process due to the formation of •OH radicals. Biomolecular Langmuir-Hinshelwood model including mass transfer step has been developed to represent the process behavior. Reusability test show that the optical fiber -based photocatalysts presented good photocatalytic activities towards CHCl3/C5H8O2 removal.

Separation of lithium and cobalt with N-salicylideneaniline from sulfate solution by hollow fiber membrane contactors

The study of the equilibrium concentrations for the extraction separation of cobalt from mixed sulfate solution with N-salicylideneaniline in membrane contactors is investigated. The reaction equilibrium constant (Kex) of 4.7 L2mol−2 was obtained from the modeling of the equilibrium distribution curves, which is carried out from the mass action law. A separation factor of 30,74 of cobalt was obtained. The calculation of the distribution coefficient (D) in the membrane contactors is carried out from global mass balances (operating line) and linear extraction isotherms in membrane contactors. The extraction kinetics of cobalt in the aqueous and organic phases in hollow fiber membrane contactors became slow and steady state is quickly reached. The steady state experimental concentration in aqueous and organic phase does not correspond to the concentration predicted by the calculation this deviation between the steady state concentration and calculated data could be explained that the diffusion of metal complex in the microporous is the main limiting step of mass transfer..

Biosorption of Dye by Malt Bagasse in a Fixed-Bed Column: Experimental and Theoretical Breakthrough Curves

The fixed-bed column biosorption process is the most widely used system, which aims to expand to industrial scale in wastewater treatment, and requires for its design thermodynamic equilibrium data. In this study, fixed-bed column experiments using malt bagasse, an industrial byproduct, were performed to quantitatively evaluate the dye biosorption capacity, as well as perform mathematical modeling of the breakthrough curves and obtain mass transfer parameters. The FTIR spectrum of malt bagasse was performed before and after the dye biosorption process. The best operating condition of the column occurred at the feed flow of 4mLmin− 1. The Langmuir isotherm (qmax = 38.44mgg− 1; R2 = 0.98) was used to represent the equilibrium data between the phases (fluid/solid) in column. The phenomenological mathematical model, which considered the resistance to internal diffusion as a limiting step of mass transfer, was able to adequately predict the dynamic behavior of the biosorption column operation, constituting a useful tool for analysis, description, and design of dye biosorption in fixed-bed column.

Adsorption Separation of l-Tryptophan Based on the Hyper-Cross-Linked Resin XDA-200.

l-Tryptophan (l-Trp) was separated from its aqueous solution by hyper-cross-linked resins. The adsorption and desorption performances of l-Trp on different resins were compared. The weakly polar resin XDA-200 was selected as an excellent adsorbent with high adsorption amount and easy elution. The resin has a high adsorption selectivity and strong salt resistance. The adsorption mechanism of l-Trp on resin XDA-200 was elucidated based on adsorption thermodynamics experiments, molecular dynamics simulations, and adsorption kinetics experiments. The dynamic separation process of l-Trp was finally studied. The adsorption of l-Trp on resin XDA-200 is a spontaneous process driven by adsorption enthalpy. l-Trp± is the most favorable form for l-Trp adsorption on resin XDA-200 because of the strongest affinity of l-Trp± to the resin and relatively low water solubility. The adsorption of l-Trp is mainly based on π–π and hydrophobic interactions. Surface diffusion is the sole rate-limiting step of l-Trp mass transfer on resin XDA-200. l-Trp was separated satisfactorily from l-glutamic acid (l-Glu) and NaCl with both the recovery rate and purity of l-Trp higher than 99% in the fixed bed packed with resin XDA-200.

Investigation of the smelting reduction mechanism and of iron extraction from high-iron red mud

High-iron red mud presents a problem due to its alkalinity which leads to significant risks to the environment. In order to realize the harmless and large-scale utilization of high-iron red mud, the smelting reduction experiments were carried out to investigate the reaction mechanism for extraction iron from high-iron red mud. FactSage 6.4 software was used to conduct thermodynamic analysis of the carbon thermal reduction system. The results showed that the direct reduction with carbon involved a process of Fe2O3 → Fe3O4 → FeO → Fe, in which the theoretical required molar ratio of C/O (oxygen in Fe2O3) was 1:1. The maximum degree of iron extraction was 92.8% with anthracite as reductant and 88.8% without anthracite smelting at 1500 °C for 30 min in a graphite crucible. XRD was conducted to analyze the mineral phase of the samples and slags. The results showed that the minerals contained in high-iron red mud were hematite, quartz, rutile, and sodium aluminosilicate hydrate. The blank sample was consisted of hematite, nepheline quartz, and the reduced slag without quenching consisted of perovskite and gehlenite, indicating that the reaction processes occurred from sodium aluminosilicate hydrate to nepheline and then occurred from nepheline to gehlenite in slagging process. The overall smelting reduction process was described as three mass transfer steps and three chemical reaction steps. These results provide useful information for large-scale and harmless utilization of high-iron red mud.

Influence of the amine alkyl-chain upon carbon dioxide absorption in G-L-L reactor

Abstract Present work analyzes the behavior of several gas-liquid-liquid systems for carbon dioxide separation using chemical absorption. The type of amine center in a solvent with two liquid phases (organic and aqueous) shows a high importance in relation to the overall behavior. The experimental results for these solvents have been compared with a previous study using octylamine in the chemical solvent because it has shown suitable results for carbon dioxide loading, absorption rate and energy cost associated to solvent regeneration. Present study analyzes the carbon dioxide absorption mechanism in multiphasic reactors (specifically G-L-L) using different types of amines in order to understand the overall behavior that involves steps of mass transfer and chemical reaction.

TiO2 electrocatalysis via three-electron oxygen reduction for highly efficient generation of hydroxyl radicals

The use of heterogeneous catalysts to improve the Electro-Fenton (EF) process has attracted significant attention. However, complex redox reactions and multiple mass transfer steps during the EF process result in limited current efficiency with only a low rate of generation of hydroxyl radicals (OH). Herein, we establish a three-electron oxygen reduction reaction (ORR) process coupling adsorbed H2O2 (H2O2ad) generation with an in situ EF-like reaction on TiO2 during cathodic electrolysis. Anatase TiO2 was composited with graphite, enabling the electrochemical reduction of Ti4+ to Ti3+. H2O2ad was formed during the ORR, electrocatalyzed by TiO2, then the H2O2ad was reduced in situ to OH without desorption. The generation and decomposition of Ti-OH during the electrochemical reduction were directly observed by in situ Raman spectroscopy. This result was further confirmed by density functional theory (DFT) calculations. Based on this three-electron ORR mechanism, the OH yield reached 2.69 μg cm−2 min−1 and the current efficiency approached 92.8% at a current density of −0.80 mA cm−2 within 2 h during ORR on the TiO2/graphite (TiO2/C) cathode.

Cycling Performance and Kinetic Mechanism Analysis of a Li Metal Anode in Series-Concentrated Ether Electrolytes.

Li metal batteries are facing unprecedented opportunities because of the urgent demand for high-energy-density rechargeable batteries as well as enormous challenges due to their low Coulombic efficiency and notorious safety issues. Recently, high-concentration electrolytes have attracted much attention owing to their superior properties. However, Li metal plating is an exceedingly complicated process including several elementary steps; it is not comprehensive enough to uncover the mystery of concentrated electrolytes by studying the structure of electrolytes, the existence of anions, cations, and solvent molecules using only conventional means. Here, we first report the apparent cycling performance of Li metal anode in series-concentrated LiTFSI/DOL-DME electrolytes. It shows that the Li metal anode in 4 M LiTFSI/DOL-DME electrolyte can operate 180 cycles stably at 2 mA cm-2 with an average Coulombic efficiency of 98%, in which the Li plating layer is more compact and without dendrites. Subsequently, the kinetic parameters were obtained by the microelectrode technique. We found that appropriate mass transfer, interface, and surface step kinetic parameters (migration number, exchange current density, nucleation rate, and corrosion rate) and their good matching degree are favorable for the cycling of Li metal anodes. This work reveals the relationship between the elementary steps and the apparent cycling performance during the Li plating process under certain operating conditions; it is a major breakthrough in the study of high-concentration electrolytes and can provide a new perspective for future research.

The essential mass transfer step in hierarchical/nano zeolite: surface diffusion.

The essential mass transfer step in hierarchical/nano zeolite: surface diffusion.

Impact of atrazine concentration on bioavailability and apparent isotope fractionation in Gram-negative Rhizobium sp. CX-Z

Compound-specific stable isotope analysis of micropollutants has become an established method for the qualitative and quantitative assessment of biodegradation in the field. However, many of environmental factors may have an influence on the observed isotope fractionation. Herein, we investigate the impact of substrate concentration on the observed enrichment factor derived from Rayleigh plot of batch laboratory experiments conducted to measure the atrazine carbon isotope fractionation of Rhizobium sp. CX-Z subjected to the different initial concentration level of atrazine. The Rayleigh plot (changes in bulk concentration vs. isotopic composition) derived from batch experiments shown divergence from the linear relation towards the end of degradation, confirming bioavailability of atrazine changed along with the decay of substrate concentration, consequently, influenced the isotope fractionation and lowered the observed enrichment factor. When microbial degradation is coupled to a mass transfer step limiting the bioavailability of substrate, the observed enrichment factor displays a dependence on initial atrazine concentration. Observed enrichment factors (ε) (absolute value) derived from the low concentration (i.e. 9.5 μM) are below 3.5‰ to the value of −5.4‰ determined at high bioavailability (membrane-free cells). The observed enrichment factor depended significantly on the atrazine concentration, indicating the concentration level and the bioavailability of a substrate in realistic environments should be considered during the assessment of microbial degradation or in situ bioremediation based on compound-specific stable isotope analysis (CSIA) method.

Investigation of potassium vapor time-resolved adsorption and potassium-sodium competitive adsorption by modified kaolinite

Frequent corrosion of heat transfer tubes in boilers, which was closely related to the massive corrosion sources, such as KCl and NaCl vapors in flue gas, restricted the safe and economic development of MSW incineration technology. This study attempted to alleviate corrosion by using the method of modified kaolinite adsorbing alkali vapors in furnace. Firstly, an ingenious alkali vapor adsorption platform with the advantage of simple operation and precise control was established. Based on this, the time-resolved adsorption of K vapors and the competitive adsorption of K/Na vapors by kaolinite and modified kaolinite were investigated. Four classical adsorption models were applied to mathematically describe the adsorption process. The pseudo-first order model was suitable for kaolinite and pseudo-second order model can be used to fit modified kaolinite. The corresponding rate-controlling steps were external mass transfer and chemisorption step. Accordingly, the equilibrium adsorption capacity of kaolinite and modified kaolinite was estimated as 17.41 and 32.30 mg/g, respectively. During the competitive adsorption of K/Na vapors, it was obvious that more K was captured by kaolinite than Na. It might be caused by the higher alkalinity of potassium, which had a higher tendency to react with acidic kaolinite. Maximum K-loading capacity of kaolinite occurred at the K/Na atomic ratio of approximately 1:1. After the structural calculation of alkali feldspar based on DFT, the most stable state of alkali feldspar occurred at the K/Na atomic ratio of 1:1, which might explain the maximum loading capacity at the K/Na ratio of 1:1.

Process intensification in catalytic wet air oxidation of phenol via coupling gas‐liquid microdispersion with trickle bed reactors

AbstractIntensified trickle bed reactors were developed for catalytic wet air oxidation (CWAO) of phenol, by generating microbubbles before gas/liquid fluid flows along catalyst packed‐beds. By coupling gas‐liquid microdispersion module, phenol disappearance rate significantly increases under the same operating conditions and phenol conversion reaches 92% in 22 seconds at 160°C and 1000 kPa. Effects of operating conditions were studied systematically and results demonstrated characteristics of high‐interaction regime at low Reynolds number. Comparison of effects among mass transfer and reaction steps shows CWAO reaction is controlled by resistance to liquid‐solid mass transfer of phenol in most cases, while gas‐liquid mass‐transfer‐resistance is ignorable. A dimensionless correlation, Sh = 2.29φ−0.91(ReL + ReG)0.04, was established, by considering influences of liquid film thickness and fluid flow situations on liquid‐solid mass transfer coefficient in microbubble‐in‐liquid/catalyst‐particle system. The study would provide an effective method for intensifying CWAO and other liquid‐solid‐mass‐transfer‐resistance‐controlled gas/liquid/solid catalytic reactions and help understand mass transfer mechanism in new gas/liquid/solid system.

Engineering the Low-Temperature Performance of Li-S Batteries

For the last few decades, lithium-ion batteries employing insertion-compound cathodes and graphite anodes have become the standard in consumer electronics and have even become commonplace in applications with extreme-operating environments, such as missions to space.1 As such missions increase in complexity and applications continue to require increasingly greater specific energy, the energy density of secondary batteries needs to similarly increase. Lithium-sulfur (Li-S) batteries have the potential to offer significant improvements due to the sulfur cathode’s high theoretical capacity of 1,672 mA h g-1 and system’s theoretical energy density of 2,500 W h kg-1.2 Conventional lithium-ion batteries experience a sharp loss in energy and power density at temperatures below 0˚C, which significantly impacts design parameters for applications like space missions. During charge and discharge, low temperatures kinetically impede all steps of mass transfer of lithium ions through the battery, particularly through the increasingly viscous electrolyte as well as the electrode-electrolyte interface. This ultimately leads to reduced capacity and utilization of active material.3 In this work, we show that many of these same trends hold true for Li-S batteries at low temperatures. Not only is there a severe drop in accessible capacity with decreasing temperatures, but this loss is primarily exhibited by a shortening in length of the second voltage plateau.4 This plateau corresponds to the formation of the insoluble Li2S discharge product, and from the low temperature behavior, we see that the nucleation and growth of this species is a primary kinetically limiting barrier to low temperature operation of Li-S cells. This presents opportunities for investigation into the kinetic behavior of sulfur reduction and the dynamic interplay between soluble and insoluble species in nonaqueous solvents at low temperatures. We explore this behavior in detail and discuss our efforts in electrolyte co-solvent and additive engineering towards designing a Li-S battery capable of operating at low temperatures. Acknowledgement: This work was supported by a NASA Space Technology Research Fellowship.

The phenomenological mass transfer kinetics model for Sr2+ sorption onto spheroids primary microplastics

In this paper, the equilibrium and mass transfer kinetics of Sr2+ sorption onto 3 types of microplastics, including polyethylene terephthalate (PET), polyethylene (PE), and polyvinyl chloride (PVC) were investigated. A novel film-pore mass transfer (FPMT) model was developed and used to study the sorption kinetics and mechanisms. This model can be used to describe the external mass transfer (EMT) and the internal mass transfer (IMT) processes and to calculate the diffusion rate. The FPMT model could successfully predict the kinetics data of Sr2+ sorption onto microplastics. The maximum value of the EMT rate achieved at the beginning of sorption was 103 μg g−1·h−1 for PET, 247 μg g−1·h−1for PE, and 854 μg g−1·h−1 for PVC, and then it decreased dramatically with time. The IMT rate was far less than the EMT rate, and decreased slowly with time. The overall sorption rate of Sr2+ onto microplastics was controlled by the external mass transfer step.

Sorption of sulfamethoxazole onto six types of microplastics

Microplastics and sulfamethoxazole (SMX) are ubiquitous in aquatic environment. In this study, we investigated the sorption of SMX onto six types of microplastics (polyamide (PA), polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC) and polypropylene (PP)). The sorption rate and mass transfer steps of SMX was studied by using the phenomenological kinetics models. The effect of pH and salinity on SMX sorption was examined. The results showed that the sorption of SMX onto microplastics reached equilibrium within 16 h. The external mass transfer was the slowest sorption step. The linear and Freundlich isotherms fitted well the sorption equilibrium data. PA had the highest sorption capacity (2.36 mg g−1 at SMX concentrations of 12 mg L−1), with high distribution coefficient (Kd) value (284 L kg−1). The Kd values of PE, PS, PET, PVC, and PP ranged from 22.2 to 30.9 L kg−1. The sorption capacity of SMX decreased with increase of pH and salinity in the solution.

A Multiscale Model of Oxidation Kinetics for Cu-Based Oxygen Carrier in Chemical Looping with Oxygen Uncoupling.

Copper oxide is one of the promising oxygen carrier materials in chemical looping with oxygen uncoupling (CLOU) technology, cycling between Cu2O and CuO. In this study, a multiscale model was developed to describe the oxidation kinetics of the Cu-based oxygen carrier particle with oxygen, including surface, grain, and particle scale. It was considered that the solid product grows with the morphology of disperse islands on the grain surface, and O2 contacts with two different kinds of grain surfaces in the grain scale model, that is, Cu2O surface (solid reactant surface) and CuO surface (solid product surface). The two-stage behavior of the oxidation reaction of the Cu-based oxygen carrier was predicted successfully using the developed model, and the model results showed good agreement with experimental data in the literature. The effects of oxygen partial pressure, temperature, and particle structure on the oxidation performance were analyzed. The modeling results indicated that the transition of the conversion curve occurs when product islands cover most part of the grain surface. The oxygen partial pressure and particle structure have an obvious influence on the duration time of the fast reaction stage. Furthermore, the influence of the external mass transfer and the change of effectiveness factor during the oxidation reaction process were discussed to investigate the controlling step of the reaction. It was concluded that the external mass transfer step hardly affects the reaction performance under the particle sizes normally used in CLOU. The value of the effectiveness factor increases as the reaction goes by, which means the chemical reaction resistance at grain scale increases resulting from the growing number of product islands on the grain surface.

Accelerating and Parallelizing Lagrangian Simulations of Mixing‐Limited Reactive Transport

AbstractRecent advances in random walk particle tracking have enabled direct simulation of mixing and reactions by allowing the particles to interact with each other using a multipoint mass transfer scheme. The mass transfer scheme allows separation of mixing and spreading processes, among other advantages, but it is computationally expensive because its speed depends on the number of interacting particle pairs. This note explores methods for relieving the computational bottleneck caused by the mass transfer step, and we use these algorithms to develop a new parallel, interacting particle model. The new model is a combination of a sparse search algorithm and a novel domain decomposition scheme, both of which offer significant speedup relative to the reference case—even when they are executed serially. We combine the strengths of these methods to create a parallel particle scheme that is highly accurate and efficient with run times that scale as 1/P for a fixed number of particles, where P is the number of computational cores (equivalently, subdomains, in this work) being used. The new parallel model is a significant advance because it enables efficient simulation of large particle ensembles that are needed for environmental simulations and also because it can naturally pair with parallel geochemical solvers to create a practical Lagrangian tool for simulating mixing and reactions in complex chemical systems.

The influence of biochar and compost mixtures, water content, and gas flow rate, on the continuous adsorption of methane in a fixed bed column

Biofiltration is an excellent alternative for the treatment of diffuse emissions of methane (CH4) that cannot be treated by physical/chemical means or recovered for energy. Despite the advances on CH4 biological treatment technologies, they are limited by the low aqueous solubility of CH4 into the biofilm where CH4 mineralization occurs. In this study, the CH4 adsorption kinetics, adsorption capacity and transport behavior of CH4 was studied in batch experiments and in a fixed-bed column by varying the biochar and compost mixtures under 5-levels, 3 different water contents (dry, 15% and 30% water holding capacity), and 2 inlet flow rates. Experimental results were formally tested using analysis of variance (ANOVA) in order to draw objective conclusions based on statistical inference. As CH4 biofiltration requires water addition to maintain microbial activity, these results indicate adsorption capacity is not lost with water addition if biochar content is the dominant packing material. The Langmuir isotherm described the data best (R2 = 0.99). Maximum adsorption capacity by monolayer adsorption, or qmax, is relatively similar with or without the addition of water as long as the biochar component is the dominant material at 3.5 mg CH4/g medium for a 7:1 biochar: compost, v/v mixture. Empirical regression models for qo, kTh, (Thomas model) and τ and KYN (Yoon-Nelson model) were developed for the break through curves of CH4. The current work demonstrates the applicability of utilizing biochar, a relatively inexpensive adsorbent, can compensate for the low solubility of CH4 and overcome the rate-limiting step of mass transfer from the gas phase and into the methanotrophic biofilm. Further, biochar may be a reliable back-up system for CH4 storage especially for fluctuating inlet loads that may be encountered in industrial applications adsorbing up to 13 mg CH4/g biochar under dry conditions.