Internal Mass Transfer Research Articles

Effects of Chelating Surfactants on Competitive Adsorption of Lead and Zinc on Loess Soil

The study of competitive adsorption of heavy metals on soil is important for heavy metals contaminated soil remediation. However, there have been few studies on the impact of desorption reagents on heavy metal adsorption in soil. Batch adsorption studies were used to investigate the competitive adsorption mechanism of two heavy metals, Pb and Zn, on a loess soil in the presence of a new chelating surfactant, sodium N-lauroyl ethylenediamine triacetate (LED3A). Results showed that competitive adsorption equilibria of Pb and Zn were reached at 3 and 10 h, respectively. The maximum equilibrium adsorption capacities were 19.55 and 18.35 g.kg-1, respectively. LED3A affected the competitive adsorption kinetics of Pb and Zn by increasing the change in external mass transfer and reducing the change in internal mass transfer. LED3A reduced Pb and Zn adsorption capacities onto the soil through competitive chelation of the heavy metals. The heavy metal chelating ability of LED3A was higher for Zn than for Pb. When its concentration was larger than 5 g.L-1, LED3A showed a significant effect on the competitive adsorption of Pb and Zn. In the competitive system, the effect of Pb concentration on the Zn adsorption capacity was greater than the effect of Zn concentration on the Pb adsorption capacity. LED3A weakened the effect of Pb concentration and enhanced the effect of Zn concentration. LED3A showed a significant potential for efficiently leaching remediation of Pb and Zn co-contaminated soil.

Partial loading of performance reference compounds in passive samplers and its effect on the fractional approach to steady state

Passive sampling for hydrophobic organics in soils and sediments is typically accomplished by measuring the equilibrium accumulation of the target compounds onto a sorbing polymer. Because the samplers do not often achieve equilibrium in the environment, the release of performance reference compounds (PRCs) pre-loaded on the sampler is used to estimate the extent of equilibrium uptake of a similar target compound. In this work, we evaluate the effect of non-equilibrium loading of PRCs on the estimated equilibration of target compounds. A numerical transport model considering both internal and external mass transfer resistances to the polymer during loading from a finite reservoir was constructed to predict PRC distribution polymer sheets. An analytical internal diffusion, external mass transfer limited model is then employed to simulate the release of the PRCs and predict both the apparent and actual approach to equilibration for the uptake of target compounds. Partial equilibration during loading of PRCs does not lead to inaccuracies in target compound equilibration except when internal resistances control both PRC release and target compound uptake, under which conditions the PRCs overestimate the extent of equilibration of target compounds. This is likely to occur during short PRC loading times (e.g., <1 month) and thick polymer sheets (e.g., >100 µm in thickness). If external mass transfer resistances control PRC release and target compound uptake, even partially loaded PRCs can accurately indicate the extent of equilibration of target compounds as long as the initial PRC loading is adequately characterized.

Verification of a 0D model for the heat and mass transfer inside a moving spherical catalyst for steam methane reforming

This work is devoted to the verification of a new 0D model for the steam reforming of methane inside a spherical catalyst particle (Ni/α-Al2O3) moving in a hot methane/steam atmosphere. The submodel includes six gaseous chemical species (CH4, CO2 , CO, H2O, H2, N2) and uses experimentally defined reaction rate expressions taken from the literature. The distinguishing feature of the subgrid model is its ability to take into account the internal heat and mass transfer coupled with the heat and mass transfer on the catalyst surface influenced by convection and diffusion around the particle. The sub-model was verified against a comprehensive 1D-based model resolving diffusion and conduction processes inside the porous catalyst particle using 1D differential equations for the temperature and chemical species written in spherical coordinates. Comparisons between the 0D model and 1D model have been made for the particle diameters, d, 2 mm, 1 cm and 2.54 cm. The ambient temperature was varied between 650 K and 1000 K, respectively. Good agreement (less than 1%–2%) was achieved between predictions obtained using the new 0D model and results calculated using the 1D-based model for all particle diameter ranges for the ambient gas temperatures below 900 K. The increase in the ambient temperature and in the particle diameter leads to the deviations of up to 5%–10% between both models.

Повышение эффективности снятия покровной ткани с плодов томата импульсным электрическим полем

Electrophysical technologies are a global trend of sustainable agriculture and food industry. Peeling is an energy-intensive procedure of fruit and vegetable processing. The research featured the effect of pulsed electric field (PEF) treatment on tomato peeling effectiveness. The assessment included such factors as specific effort, energy costs, and product losses in comparison with thermal and electrophysical methods.&#x0D; Tomatoes of Aurora variety underwent a PEF treatment at 1 kV/cm. The expended specific energy was 1, 5, and 10 kJ/kg. The tomatoes were visually evaluated with optical microscopy before and after processing. The peeling effectiveness and mass loss were measured with a texture analyzer and digital scales.&#x0D; The PEF treatment decreased the specific force of mechanical peel removal by 10% (P &lt; 0.05). The mass loss decreased by 4% (P &lt; 0.05) at 1 kJ/kg. The PEF method resulted in cell electroporation, which activated the internal mass transfer of moisture from the endocarp region between the mesocarp and the integumentary tissue. The hydrostatic pressure produced a layer of liquid, which facilitated the peeling.&#x0D; In comparison with thermal treatment (blanching), ohmic heating, and ultrasonic processing, the PEF technology had the lowest production losses and energy costs. The research proves the prospects of the PEF treatment in commercial tomato processing.

Fast and continuous synthesis of 2,5-furandicarboxylic acid in a micropacked-bed reactor

Oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) is of great importance for the production of biopolymer. It is regarded as a representative of the heterogeneous process, in which the reactant in the gas phase and liquid phase interact with each other over the solid catalysts. Due to the low mass-transfer efficiency and co-existence of O2 and organic compounds in the batch reactor, low catalytic efficiency and safety concerns hiders the commercial application. Herein, a micropacked-bed reactor was used to realize the efficient and ultrafast continuous-flow synthesis of FDCA. Au/CeO2 was used as a catalyst and O2 was used as a green oxidant. Owing to the enhanced gas − liquid mass transfer efficiency, an HMF conversion of 100% and an FDCA selectivity of 90 % were achieved within only 41 s, which represents a space–time-yield of 1–2 orders of magnitude higher than that of traditional reactors. By virtue of the minimized internal and external mass transfer resistances, kinetic parameters of the reaction were determined. The rate constants were more than one order of magnitude higher than those of other strategies. In addition, the oxidation of HMFCA to FFCA was determined to be the rate-controlling step. Overall, this work not only delineates an efficient strategy for synthesizing FDCA from HMF, but also opens a new avenue for enhancement of heterogeneous reactions suffering from limited mass transfer.

Performance assessment of a novel solar distiller with a double slope basin covered by coated wick with lanthanum cobalt oxide nanoparticles

Solar distillers are simple desalination systems used to produce freshwater from saline water by utilizing solar energy. The low water yield is the key drawback of solar distillers. In this work, a novel double slope wick type solar distiller (DSWSD) coated with lanthanum cobalt oxide (LaCoO 3 ) nanoparticles doped in black paint is experimentally investigated. The nano LaCoO 3 /black paint is uniformly speared on the jute wick surface to boost the absorption improvement of solar irradiance for effective desalination. The influence of water flow rate (namely; 0.050, 0.10, and 0.20 kg/min) on the internal mass and heat transfer of the proposed DSWSD is analyzed. The mass and heat transfer coefficients (HTCs) are computed using the experimental results and compared with those computed according to Dunkle’s correlations. Experiments have been conducted on the established DSWSD under climatic conditions of Vijayawada, Andhra Pradesh (16.4419° N, 80.6226° E), India. It is observed that there is an increase in the internal HTCs as well as distilled yield at low flow rates of saline water for the DSWSD. The daily productivity of the proposed DSWSD coated with and without 20 wt % LaCoO 3 /black paint is 5.40 and 3.85 kg/m 2 . day, respectively, at saline water flow rate of 0.05 kg/min. Moreover, the average values of evaporative and convective HTCs as well as energy efficiency are found higher by 11.20%, 17.54%, and 24.86%, respectively, than that of the solar distiller without LaCoO 3 /black paint.

A visual mass transfer study in the ejector considering phase change for multi-effect distillation with thermal vapour compression (MED-TVC) desalination system

The multi-effect distillation with thermal vapour compression (TVC) seawater desalination system provides an excellent energy-saving scheme by escalating the low-level energy. The internal mass and heat transfer in ejectors is an important element to improve efficiency. In this study, a visual mass transfer simulation model considering real thermodynamic properties is used to observe the inner-mixing process. The assessment is from the perspective of visible mixing layer growth and the effect on entrainment ratio. As shown in the mass percentage distribution graph, there is an inescapable phase change on mixing layer boundary, where the wetness of wet steam can reach to 16.0%. Meanwhile, the mixing layer length predicted by dry model is 25.1% higher than wet model. The condensation weakens the mixing process and leads to shorter length. Under subcritical mode, the cross-sectional area of the entrained flow is deducted and the mixing layer cannot develop completely. The critical pressure range predicted without condensation is 18.5% lower, which causes a misjudgment in entrainment ratio because overvaluing the influence of outlet pressure on entrained flow. Thus, mass transfer during development of the two-phase mixing layer has great impact for MED-TVC system.

Sustainability assessment of acid-modified biochar as adsorbent for the removal of pharmaceuticals and personal care products from secondary treated wastewater

This study investigated the adsorption behavior and sustainability of biochar to remove four pharmaceutical and personal care products (PPCPs). The biochar (PEBC) was prepared via slow pyrolysis of empty palm bunch (PEB) at three temperatures (250–750 °C). To improve the adsorption capacity further, PEBC450 was acid treated with H2SO4 to develop PEBC450-A. The adsorption behavior of target pollutants (methyl paraben (MPB), carbamazepine (CZP), ibuprofen (IBP), and triclosan (TCS)) onto PEBC450-A was studied in batch experiments, and phenomenological and statistical models were applied to understand the sorption mechanism. Results demonstrated that the adsorption system was able to achieve fast equilibrium (in 4 h), with maximum adsorption capacities as 60.2 mg/g (MPB), 51.7 mg/g (CZP), 38.8 mg/g (IBP), 35.4 mg/g (TCS). The modeling results showed heterogeneous adsorption of PPCPs involving the participation of multiple functional groups in parallel and non-parallel orientations. The mass transfer kinetic models identified the internal mass transfer resistance as the rate-limiting step. The PPCPs adsorption was significantly affected by the change in solution pH and the presence of humic acid. However, no substantial change in PPCPs removal was observed in the presence of co-existing ions and different ionic strengths. In multi-pollutant systems and real water samples, PEBC450-A maintained more than 75% removal of target pollutants, indicating the developed material as a promising adsorbent for wastewater treatment. The sorption mechanism was found to be channel diffusion, hydrogen bonding, n-π and π-π interactions, and van der Waals force. The comparative life cycle assessment of PEBC450-A and commercial activated carbon showed that the total impact contribution of PEBC450-A was 20 times less than commercial activated carbon. The overall finding makes PEBC450-A a low-cost and sustainable adsorbent for water treatment.

Advanced modelling of adsorption process on activated carbon

To gain a deeper insight into the adsorption kinetics mechanism, the adsorption of p-chlorophenol (PCP) from water, cyclohexane, and heptane on surface chemistry modified activated carbons was modeled by the general rate (GR) differential mass transport model, which takes into account external and internal mass transfer resistance. Due to the fact that the particles of AC are characterized by a wide particle size distribution (PSD) and pore diameter distribution (PDD), which are usually not considered for the simulation, our experimental dates were modeled with the GR model, in which PSD and PDD were included. It was found that, for organic phases, mainly the slow surface adsorption–desorption process controls mass transfer. In the case of water, the mass transfer was controlled by molecular diffusion in pores or by slow surface adsorption depending on AC. It was also shown that neglecting the PSD can lead to errors in the evaluation of the values of the adsorption model parameters, whereas, on the other hand, the pore diameter distribution can be successively approximated by average pore diameter.

Effect of catalytic hydrodynamics over microagglomerates of Mn2O3 and PdO supported on γ-χ-Al2O3 for dimethyl ether production

In this study, we synthesize microagglomerates of PdO and Mn2O3 supported over γ-χ-Al2O3 via the impregnation method, for their application in the methanol dehydration to dimethyl ether, under reaction conditions of 240 °C to 290 °C and 1 pressure atm. It was determined by XRD, TEM and XPS that when PdO (Pd2+) is present at 3% by weight over γ-χ-Al2O3, conversions of 57% and selectiveness of 100% towards dimethyl ether can be reached at 250 °C due to at a higher density of moderate acid sites (a moderate acidity difference of 0.5276 mmol/g with respect to Mn2O3/γ-χ-Al2O3). Additionally, our theoretical and experimental results between the correlation of the textural and morphological properties of the PdO/γ-χ-Al2O3 and Mn2O3/γ-χ-Al2O3 materials with the hydrodynamics and kinetics of the reaction, showed that when PdO agglomerates with a size of ∼79.2 µm are used, higher internal mass transfer rates predominate when compared to using Mn2O3 agglomerates of a larger size, ∼124 µm. Finally, the relative stability shown by the PdO/γ-χ-Al2O3 catalyst during 10 h of reaction was correlated with its low apparent activation energy (111 kJ/mol) and with its inactive phase change of PdO measured by XPS after the reaction.

Multi-mode reduced order models for real time simulations of monolith reactors with micro-kinetics

We present a novel procedure for computing washcoat diffusional effects in monolith reactors with detailed micro-kinetic models. First, we show that the short time scales associated with the adsorption/desorption steps of micro-kinetic models requires using a significantly larger number of mesh points within the washcoat to obtain a solution that is independent of the mesh size. Next, we present a multi-mode reduced order model that eliminates the degrees of freedom associated with species diffusion in the washcoat using the local property dependent internal mass transfer coefficient matrix. This matrix is shown to be diagonal for most micro-kinetic models of practical interest and can be calculated accurately. We illustrate the new approach with an example of H2/CO/C3H6 oxidation over a Pt/Al2O3 catalyst with a 20 step micro-kinetic model. Even for this simple single site model, the small time (and length) scales associated with the species adsorption steps make the computation of the mesh size independent solution of the 1＋1D model time consuming. However, the reduced order model leads to an accurate solution while speeding-up calculations by about three orders of magnitude.

Ultrasound enhancing the mass transfer of droplet microreactor for the synthesis of AgInS2 nanocrystals

Droplet microreactors are powerful tools for synthesizing chemicals, nano materials and biomolecules, but traditional methods, such as mechanical stirring, are hard to enhance the internal mass transfer of droplet microreactor due to its small reaction space. In this study, we propose a novel ultrasonic-enhancing method for droplet microreactor, and report the effect of bubbles inside micro-droplets for the first time. On this basis, the synthesis of AgInS2 nanocrystals is selected as model reaction to study the enhancement mechanism. It is discovered that the flow field in micro-droplet is significantly improved owing to acoustic streaming and cavitation microstreaming. Benefiting from them, the mass transfer coefficient is enhanced by 72.5 %, and AgInS2 nanocrystals are successfully synthesized with smaller, more uniform particle size, as well as more adjustable performance compared with no ultrasonic radiation condition. This work provides a new method and a deep insight of ultrasound enhancing droplet microreactor, enabling the continuous production of fine chemical synthesis.

Insight into mass transfer mechanism and equilibrium modeling of heavy metals adsorption on hierarchically porous biochar

One-step pyrolysis of biomass/zinc salts composites was investigated to clarify the effects of zinc salts on the pore structure of biochar and its performance for removing heavy metals from wastewater. The characterization results indicated that zinc salts not only promoted the pyrolysis of biomass but also decomposed to generate volatile gas and thermally removable pores templates in situ that established the hierarchical porous biochar (HPBC). More specifically, HPBC exhibited a significantly increased pore volume compared with pristine biochar (by a factor of up to 80) and large specific surface areas ranging from 769.91 to 1192.37 m2/g. To connect these improved properties with the heavy metals removal performance, the pore volume and surface diffusion model (PVSDM) was used to numerically simulate the adsorption process and investigate the diffusion and mass transfer mechanism. Notably, the fitted pore volume diffusion coefficient of HPBCs (DpHPBC) was at least three orders of magnitude larger than their surface diffusion coefficient (DSHPBC), whereas these two parameters (DpBC&DSBC) for pristine biochar (BC) were of the same order of magnitude but were much smaller in value than those obtained by HPBCs. These results suggested that the improved biochar pore structure by co-pyrolyzing with zinc salts mainly enhanced the pore volume diffusion of heavy metals during their adsorption. The adsorption process of Pb2+ on HPBCs was controlled by the intra-particle diffusion mechanism, while the adsorption process of Cd2+ was controlled by external and internal mass transfer.

Biosorption investigation of Cu(II) ions from aqueous solutions using sericin–alginate particles: Kinetic, equilibrium, and thermodynamic

In this study, sericin–alginate particles are produced for use as a biosorbent to remove Cu(II) ions from an aqueous solution in a batch biosorption system. Sericin is a protein present in silkworm cocoons and is considered a byproduct of the silk industry. Its use in the production of biosorbents has emerged as an environmentally friendly alternative. Sericin–alginate particles are characterized using N2 physical adsorption analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, and point of zero charge. Additionally, they are evaluated via kinetic, isothermal, and thermodynamic biosorption tests. Kinetic modeling is performed using Lagergren pseudo-first-order, pseudo-second-order, Weber–Morris intraparticle diffusion, homogeneous solid diffusion, and external liquid-film diffusion models. For equilibrium modeling, the Langmuir, Freundlich, and Temkin isotherm models are applied. The Cu(II) ions biosorption is spontaneous and exothermic, as biosorption capacity decreases with temperature: 87.27 mg g-1 (20 °C), 82.54 mg g-1 (40 °C), and 76.18 mg g-1 (60 °C). Based on kinetic modeling, it is verified that internal mass transfer limits the biosorption rate. The Langmuir isotherm model shows a better fit for the biosorption equilibrium, indicating that biosorption occurs in the monolayer. Tests to evaluate the reusability of sericin–alginate particles are performed. It is discovered that even after five adsorption–desorption cycles, the biosorbent shows excellent biosorption capacity. The obtained results and a comparison of the biosorption capacity of different biomaterials demonstrate the high potential of the sericin–alginate particles as a biosorbent for Cu(II) ions.

Separate Effect of Turbulent Pulsation on Internal Mass Transfer in Porous Biofilms

Separate Effect of Turbulent Pulsation on Internal Mass Transfer in Porous Biofilms

Mathematical Modeling of Unsteady Mass Transfer in the Cement Concrete-Liquid Medium System, Limited by Internal Diffusion and External Mass Transfer

Mathematical Modeling of Unsteady Mass Transfer in the Cement Concrete-Liquid Medium System, Limited by Internal Diffusion and External Mass Transfer

Modeling and optimization of a honeycombed adsorbent bed for efficient moisture capture

Adsorption-based atmospheric water harvesting has received significant interest owing to its promise of decentralized water supply and a wide applicability. In this study, the adsorbent bed is specially designed and optimized for efficient moisture capture. A transient three-dimensional non-equilibrium model has been developed that takes both internal and external mass transfer resistances into account. It is found that the simulation results agree better with the experimental results, which indicates the reliability of the model. Then this model was applied to investigate the influence of the adsorbent bed structure, and the operating parameters on the transient distributions of the adsorbent temperature, adsorption kinetics, dynamic up-taken moisture capture, mass transfer resistance and relative capture efficiency of the adsorbent bed. ASLi30 (Activated carbon fiber + Silica gel + 30 wt% LiCl)-vapor is selected as the working pair. It has been found that generally, the effects of the air channel aspect ratio on the investigated indexes are negligibly small. A thinner layer thickness and a smaller air channel length characterize an excellent moisture capture, small vapor transport resistance and faster adsorption kinetics. By considering different parametric variations for performance optimization and the effect of operating conditions, these results provide important insights and design guidelines of adsorbent bed for efficient moisture capture.

Approximate Models of Microbiological Processes in a Biofilm Formed on Fine Spherical Particles

This paper concerns the dynamical modeling of the microbiological processes that occur in the biofilms that are formed on fine inert particles. Such biofilm forms e.g. in fluidized-bed bio-reactors, expanded bed biofilm reactors and biofilm air-lift suspension reactors. An approximate model that is based on the Laplace–Carson transform and a family of approximate models that are based on the concept of the pseudo-stationary substrate concentration profile in the biofilm were proposed. The applicability of the models to the microbiological processes was evaluated following Monod or Haldane kinetics in the conditions of dynamical biofilm growth. The use of approximate models significantly simplifies the computations compared to the exact one. Moreover, the stiffness that was present in the exact model, which was solved numerically by the method of lines, was eliminated. Good accuracy was obtained even for large internal mass transfer resistances in the biofilm. It was shown that significantly higher accuracy was obtained using one of the proposed models than that which was obtained using the previously published approximate model that was derived using the homotopy analysis method.

The droplets and film behaviors in supersonic separator by using three-field two-fluid model with heterogenous condensation

Supersonic separator is a kind of natural gas dehydration device with great potential, but its internal mass and heat transfer process has not been fully studied. In this study, a novel three-field two-fluid model described by Eulerian-Eulerian approach for supersonic separator considering the heat and mass transfer between gas, liquid droplets, and liquid film was developed and validated. The interphase slip, latent heat, film heat flux, and film phase change rate were studied. It revealed that the maximum centrifugal slip velocity of droplets can reach 24.9 m s−1. The maximum latent heat is 5.3 × 108 J m−3 from droplets to gas phase during condensation, and the minimum latent heat is -3.4 × 108 J m−3 during evaporation. The thickness of swirling liquid film at wet gas outlet is 21 μm, 47 μm, 74 μm and 89 μm, respectively. The liquid film temperature decreases to a minimum 304.1 K due to droplets deposition, where the maximum heat flux is 0.74 MW m−2. Besides, the frequency and velocity of the interfacial wave of liquid film were obtained by using the cross-correlation algorithm, and their maximum values was 11.07 Hz and 1.49 m s−1, respectively. In addition, for achieving higher dehydration efficiency, the optimal value of the foreign droplet mass concentration should be 0.01 kg m−3. The maximum separation efficiency and dew point depression of separator A are 85.11% and 40.32 °C, respectively. The model without considering the liquid film over-predicts the separation efficiency.

Lead Biosorption Characterisation of Aspergillus piperis

In this study, the Pb(II) adsorption capabilities of the heavy metal tolerant strain of fungus, Aspergillus piperis, were studied. This study involved finding optimal growth conditions using a plating technique, and optimal adsorption conditions using submerged fermentation and fractional factorial experimental design. The adsorption behaviour was then elucidated using isotherm and kinetic models, of which the one surface Langmuir isotherm provided the best fit, with a maximum predicted adsorption capacity of 275.82 mg g−1. The kinetic models suggested that internal mass transfer is the driving force behind the reaction rate. After adsorption, biomass surface characterisation was undertaken using FESEM, EDS, and ATR-FTIR to explain observations. The system was characterised by a cation exchange mechanism with strong carboxyl and organophosphorus group interactions. This study demonstrates that due to the ease of propagation and high adsorption capacity, this locally sourced fungal strain is an ideal adsorbent for industrial Pb(II) bioremediation.