Film Mass Transfer Research Articles

Determination of Pore and Surface Diffusivities from Single Decay Curve in CSBR Based on Parallel Diffusion Model

A novel, simple numerical method to determine the pore and surface diffusivities in adsorbents from a single experimental concentration decay curve obtained using the batch adsorption technique was investigated in this study. The pore and surface diffusion coefficients were determined based on the conventional parallel diffusion model in its dimensionless form using a theoretical model correlation. The model assumed that the film mass transfer resistance was negligible, i.e., the condition with a large Biot number, from the single concentration decay curve. The procedure for determining the kinetic parameters was investigated, and the effectiveness of the proposed simple method was validated by comparing the parameters with those reported previously. The single decay curve of p-nitrophenol, obtained by the batch adsorption system using granular activated carbon as an adsorbent, was used for validation. The diffusivities determined by the simple method corresponded fairly well with the diffusivities reported previously.

Microinterface intensification in hydrogenation and air oxidation processes

Hydrogenations and air oxidations usually have low apparent reaction rate, generally controlled by mass transfer rate, and widely exist in the modern chemical manufacturing process. The key to increase the mass transfer rate is the reduction of the liquid film resistance 1/ k L a . In this work, the original concept of microinterface intensification for mass transfer and then for these reactions has been proposed. We derived the regulation model and set up the mathematical calculation method of micron-scale gas-liquid interface structure on mass transfer and reaction, designed the mechanical energy exchange device that can produce gas-liquid microinterface system on a large scale, and established the OMIS system which is able on line to measure the diameter and distribution of millions of microbubbles, interface area a and mass transfer film thickness δ M , as well as developed a series of microinterface intensified reactor systems (MIRs) for the applications of hydrogenation and air oxidation processes. It is believed that this research will provide an up-to-date development for the intensification of hydrogenation and air oxidation reactions.

Polarization-sensitive direct laser patterning of azopolymer thin films with vortex beams.

Laser patterning of thin films of materials is widely used for the fabrication of one-, two- and three-dimensional functional nanomaterials. Using structured laser beams with a complex structure of amplitude, phase, and polarization distributions allows one to significantly simplify and speed up the procedure of manufacturing nano- and microstructures with a complex shape, such as a spiral structure. Here, we demonstrate the use of vortex laser beams with a helical wavefront for the realization of spiral mass transfer in azopolymer films. The polarization sensitivity of this material allows us to demonstrate the formation of different three-dimensional structures in the case of linearly or circularly polarized vortex beams of different orders. The presented theoretical analysis shows that the profile of the fabricated structures is defined by the structure of the longitudinal component of the incident radiation, and thus can be easily controlled with the polarization state of the radiation without the need to change the amplitude-phase structure of the beam.

Different efficiency toward the biomimetic aerobic oxidation of benzyl alcohol in microchannel and bubble column reactors: Hydrodynamic characteristics and gas–liquid mass transfer

The selective aerobic oxidation of benzyl alcohol to benzaldehyde has attracted considerable attention because benzaldehyde is a high value-added product. The rate of this typical gas–liquid reaction is significantly affected by mass transfer. In this study, CoTPP-mediated (CoTPP: cobalt (II) meso-tetraphenylporphyrin) selective benzyl alcohol oxidation with oxygen was conducted in a membrane microchannel (MMC) reactor and a bubble column (BC) reactor, respectively. We observed that 83% benzyl alcohol was converted within 6.5 min in the MMC reactor, but only less than 10% benzyl alcohol was converted in the BC reactor. Hydrodynamic characteristics and gas–liquid mass transfer performances were compared for the MMC and BC reactors. The MMC reactor was assumed to be a plug flow reactor, and the dimensionless variance was 0.29. Compared to the BC reactor, the gas–liquid mass transfer was intensified significantly in MMC reactor. It could be ascribed to the high gas holdup (2.9 times higher than that of BC reactor), liquid film mass transfer coefficient (8.2 times higher than that of BC reactor), and mass transfer coefficient per unit interfacial area (3.8 times higher than that of BC reactor). Moreover, the Hatta number for the MMC reactor reached up to 0.61, which was about 15 times higher than that of the BC reactor. The computational fluid dynamics calculations for mass fractions in both liquid and gas phases were consistent with the experimental data.

Experimental Study for The Effect of Changing Flow on Absorption in Wetted Wall Column.

Gas absorption is the unit operation in which one or more soluble components of gas mixture are dissolved in a liquid. The absorption may be a purely physical phenomenon or may involve chemical reaction with one or more constituents in the liquid solution. In order to obtain the highest rate of absorption, gas and liquid streams flow in opposite directions in counter-current flow. The unit in this work has been designed to help grasp the basic principles of the chemical and physical aspects involved in absorption. This study unit is made of borosilicate transparent glass in order to show the water spread in the column and get the visual distribution of fluids behavior which helps to fully understand the phenomenon. In this work, the wetted wall column is used to determine gas/liquid mass transfer coefficients, which is essential to design absorption towers. This study investigates the absorption of oxygen from air into deoxygenated water (prepared by nitrogen sparing) in liquid film controlled absorption experiment. The liquid film mass transfer coefficient is calculated at various mass flow rates of water and air. This work also studies the effect of water flow and air flow on oxygen concentration in the oxygenation and de-oxygenation process so affect on absorption process .

Experimental Study for The Effect of Changing Flow on Absorption in Wetted Wall Column.

Gas absorption is the unit operation in which one or more soluble components of gas mixture are dissolved in a liquid. The absorption may be a purely physical phenomenon or may involve chemical reaction with one or more constituents in the liquid solution. In order to obtain the highest rate of absorption, gas and liquid streams flow in opposite directions in counter-current flow. The unit in this work has been designed to help grasp the basic principles of the chemical and physical aspects involved in absorption. This study unit is made of borosilicate transparent glass in order to show the water spread in the column and get the visual distribution of fluids behavior which helps to fully understand the phenomenon. In this work, the wetted wall column is used to determine gas/liquid mass transfer coefficients, which is essential to design absorption towers. This study investigates the absorption of oxygen from air into deoxygenated water (prepared by nitrogen sparing) in liquid film controlled absorption experiment. The liquid film mass transfer coefficient is calculated at various mass flow rates of water and air. This work also studies the effect of water flow and air flow on oxygen concentration in the oxygenation and de-oxygenation process so affect on absorption process .

Self-Assembly of Amphiphilic BODIPY Derivatives on Micropatterned Ionic Liquid Surfaces for Fluorescent Films with Excellent Stability and Sensing Performance.

Fluorescent films have been widely recognized as one of the most powerful tools for trace analyte detection. However, their use has been limited due to the poor photochemical stability of fluorophores at a gas-solid interface and inefficient film mass transfer. Herein, novel fluorescent films were developed through self-assembly of amphiphilic BODIPY derivatives on micropatterned ionic liquid surfaces. Unlike solid-state films, the obtained monolayer films exhibit excellent photochemical stability, similar to that of a solution. Moreover, the interfacial assembly of amphiphilic fluorophores can avoid gas diffusion inside the microdroplets, significantly improving the sensing performance. The 1/1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) monolayer exhibits high sensitivity, high selectivity, and a fast response to detect diethylchlorophosphate (DCP) vapor. The detection limit was 226 ppt, with a response time to DCP of 2.0 s. Importantly, the 1/[BMIM]BF4 monolayer can be reused for at least 50 cycles with no obvious signal fading. This study is expected to benefit the development of new strategies for designing fluorescence sensing films and lay a solid foundation for the fabrication of multifunctional sensing devices with excellent photochemical stability and sensing performance.

Computational fluid dynamics modeling of biomass catalytic fast pyrolysis in bubbling fluidized reactor: Effects of catalyst parameters on process performance

AbstractIn this study, a computational fluid dynamics mathematical model has been developed for catalytic fast pyrolysis (CFP) of biomass based on multiphase flow, transfer process, and biomass pyrolysis reactions in a bubbling fluidized bed reactor. The multiphase fluid flow, and the inter‐phase momentum and energy transfer processes are modeled with Eulerian multiphase formulas, representing the flows of gases and solids (catalyst and biomass) within the reactor. The biomass CFP reactions are described by using a two‐stage, semi‐global model. Specified secondary tar catalytic cracking process, which considers both intrinsic reaction rates and mass‐transfer process, is embedded to the developed model by user‐defined function. The model simulation results of pyrolysis product yield and distribution are compared with the experimental data with close agreement. The model is then employed to investigate the effects of structural properties of catalyst, such as specific internal area, average size of active sites, pore diameter, and tortuosity, on products yields and composition. The tar cracking process by the selected catalyst is proposed and the influences of adsorption capability of tar molecule on catalyst surface and external film mass transfer are also analyzed. The developed model can be solved with short computational time and thus it can be employed for further research and engineering designs of the catalytic pyrolysis of carbonaceous materials.

Process evaluation and kinetic analysis of 3D-printed monoliths comprised of CaO and Cr/H-ZSM-5 in combined CO2 Capture-C2H6 oxidative dehydrogenation to C2H4

In this study, dual-function materials (DFMs) comprised of CaO and Cr/H-ZSM-5 were formulated in 3D-printed monolithic structures and investigated in a combined process for capture and utilization of CO2in oxidative dehydrogenation of C2H6 to C2H4 (CO2-ODHE). Various formulation strategies were employed to fabricate these DFM structures. Two bed designs were considered: i) a layered-bed in which adsorbent (CaO) and catalyst were printed separately and stacked on top of each other, and ii) a single-layer bed where the adsorbent-catalyst materials were 3D-printed into a singular monolith and loaded into the bed as DFMs. Between these, the layered-bed displayed enhanced performance as compared to the composite DFMs, as this configuration generated a 3.73 mmol/g CO2 adsorption capacity, 42.5% C2H6 conversion, 90.6% C2H4 selectivity and 38.6% C2H4 yield compared to 2.4 mmol/g CO2 adsorption capacity, 37.9% C2H6 conversion, 89% C2H4 selectivity and 33.8% C2H4 yield in the best singular monolith configuration. The enhanced performance of this configuration was attributed to a higher degree of adsorptive site accessibility and a lesser degree of active site blockage from intraparticle binding (as evident from the textural properties). This work also assessed the effects of monolith cell density on CO2 adsorption and utilization for ODHE by varying the cells per square inch (cpsi) from 200 to 600 cpsi. These experiments revealed that increasing the cell density from 200 to 600 cpsi enhanced the overall mass transfer coefficient from 0.40 × 10-2 to 1.01 × 10-2 s-1 due to a sizable enhancement in film mass transfer between the two geometric designs. Such enhancement improved the C2H4 selectivity and yield to 92 and 45.1% in the 600 cpsi sample. As such, this work also indicated that higher cell densities lead to better performance of the layered-bed configuration, where the optimum configuration is separate stacking of the adsorbent and catalyst phases. Overall, these findings provide a deeper understanding of DFM materials, bed configuration, and establish a groundwork which can be used to optimize their structures for CO2 adsorption-reaction processes.

Ion exchange and adsorption of cadmium from aqueous media in sodium-modified expanded vermiculite.

The use of mineral clays as alternative adsorbent has received attention due to their physicochemical characteristics, superficial negative charge, abundance of vermiculite (especially in Brazil), low cost, and chemical composition, which allows the material modification to increase the adsorptive capacity. This manuscript evaluated the use of expanded vermiculite (EV) and sodium-modified vermiculite (VNa) in the adsorption and ion exchange of Cd2+ ions. The sodification was successfully carried out making the ion exchange capacity greater in the modified clay, confirmed by EDX, cation exchange capacity (CEC), DRX, and FTIR analysis. The CEC was 210 and 233mEq/100g for the EV and VNa, respectively, with 97.8% exchangeable ion (Na+) in the VNa. FTIR spectra showed small variations in the groups related to ion exchange and XRD analysis indicated changes in the distance of the layers with loss of crystallinity after clay modification, which was recovered after cadmium adsorption. The kinetics became faster with an equilibrium time of 10min for VNa and 45min for EV. Cd2+ removal by vermiculite above 99% was achieved. Pseudo-second order model best described the kinetics, in which the resistance to mass transfer in external film is the limiting step of the process and, once this resistance is overcome, the ion exchange happens quickly. Despite the decrease in surface area after sodification, the adsorptive capacity increased 158% in the sodified adsorbent, from 0.107mmol/g for EV to 0.276mmol/g for VNa, under the evaluated conditions.

Silica-functionalized pyrite core-shell particle as a new mesoporous adsorbent for water-soluble dyestuffs: Characterization, kinetic and thermodynamic studies

Environmental problems caused by non-economic minerals in mining processes are among the most significant mining activity challenges. Pyrite is the most abundant sulfide and waste mineral due to acid mine drainage and polluting the environment. The project aims are to synthesize a mesoporous silica-based coating on the surface of natural pyrite (Pyrite@Silica) to prevent oxidation and production of acidic effluent and evaluate its efficiency as an adsorbent for cationic dyes, such as malachite green oxalate (MG) and methylene blue (MB). The study’s strength is that Pyrite@Silica demonstrated a significant adsorption capability in comparison to other natural adsorbents. Pyrite@Silica was prepared during the sol-gel process using tetraethyl orthosilicate (TEOS). In this study, the chemical, mineralogical and morphological characteristics of activated pyrite and Pyrite@Silica were characterized by XRD, XRF, FT-IR, SEM, EDX, TEM, and BET analysis. The optimum conditions of MG and MB adsorption were recorded to be contact time 10 min, Pyrite@Silica dose 2 g L−1, initial concentration 600 mg L−1 for malachite green and 200 mg L−1 for methylene blue at pH 8. The maximum adsorption capacity for MG and MB dyes at 298 K was obtained 349 mg g−1 and 97 mg g−1, respectively. Equilibrium and thermodynamic studies indicated that the adsorption process is heterogeneous, endothermic, chemical, and non-spontaneous. Kinetic studies revealed that both adsorbent and adsorbate effectively affect the adsorption mechanism and also the diffusion mass transfer coefficient is higher than the film mass transfer, which indicates that the resistance of mass transfer is not dependent on the film mass transfer.

Nonlinear thermal radiation and temperature dependent viscosity effects on MHD heat and mass transfer in a thin liquid film over a stretching surface

This paper describes nonlinear thermal radiation effects on MHD heat and mass transfer in a thin liquid film over a permeable unsteady stretching surface taking temperature-dependent fluid viscosity with convective boundary condition. For the non-linearity of the momentum, energy and mass diffusion equations, the problem is solved numerically. At first, Similarity transformations is used to the governing equations to reduce the equations into a set of ordinary differential equations. Then the resulting nonlinear ordinary differential equations are solved using Runge-Kutta-Felberg method with shooting technique. Different physical parameters effects on heat and mass transfer in a thin liquid film are presented graphically. It is found that increase in the unsteadiness parameter leads to increase in the velocity distribution, temperature and concentration gradient. Further, increase in the value of magnetic parameter results in a decrease in the velocity profile and increase in the temperature and concentration gradient. For enhancement of thermal radiation decreases the temperature gradient of the thin film flow. Also, for increase in viscosity variation parameter is to decrease velocity distribution but reverse effects shown in case of temperature and concentration gradient.

Modelling and simulation of the ion exchange process for Zn2+(aq) removal using zeolite NaY

The treatment of water contaminated by toxic metals using ion exchange with zeolites is becoming attractive due to its low capital costs and high potential for removal capacity. Mathematical modelling of this process allows for operational control and estimation of the ability to remove these metals. In this work, the kinetic modelling was performed based on finite bath experimental data, with Intraparticle Diffusion (IPD) and External Liquid Film Mass Transfer (MTEF) models. The models Thomas (TH), Yoon-Nelson (YN) and Solid Film Mass Transfer (MTSF) were used to estimate the saturation time, ion exchange capacity and sizing variables of a fixed bed column. For the finite bath system, the results showed that the mass transfer was better represented by the IPD phenomenon. The breakthrough curve obtained by the Aspen Adsorption (MTSF) model presented the best fit, compared with experimental data, with R2≥0.9923. The average ion exchange capacities calculated for MTSF, TH and YN were respectively 2.22, 2.12 and 2.07 meq Zn2+(aq)/ g of zeolite. The model simulated with Aspen Adsorption was also used to analyze the continuous system behaviour, by varying the height of the bed. It was observed that increasing the height, the saturation time and ion exchange capacity also increase, while reducing the height makes axial dispersion the predominant mass transfer phenomenon, which reduces the diffusion of Zn2+(aq) ions.

A new multi-mechanism adsorption kinetic model and its relation to mass transfer coefficients

A new multi-mechanism kinetic model for batch adsorption is proposed. A dimensionless parameter in the model serves as a mechanism indicator in the sense that the model converts to the pseudo-first-order (PFO), the Vermeulen (intraparticle diffusion) and the film diffusion models as the dimensionless parameter changes its values. Expressions relating the model parameters and the mass transfer coefficients are obtained which allow for the estimation of the film mass transfer and the intraparticle diffusion coefficients from `show that the estimated mass transfer coefficients are in reasonable agreement with literature values.

Strontium adsorption characteristics of natural Zeolites for permeable reactive barrier in Fukushima Daiichi nuclear power station

ABSTRACT Laboratory experiments and model estimates were carried out to evaluate the effectiveness of sorbent for construction of the Permeable Reactive Barrier (PRB) at downstream of H4 tank area in Fukushima-Daiichi Nuclear Power Station in September 2014. Measurement of cation exchange capacity and X-ray diffraction analyses of crystal structures were carried out for natural zeolites. The Sr adsorption isotherms were measured for these zeolites contacted with water containing Sr or the simulated groundwater containing Na, K, Ma, Ca, and Sr. According to these equilibrium characteristics, Akita-Futastui zeolite was selected as candidate. The zeolite was served for the column tests to obtain Sr breakthrough curves with different conditions such as particle size of zeolite, Darcy Flux, Sr concentration in the simulated groundwater, and mixed bed with gravel. From the breakthrough curves, kinetic properties such as the film mass transfer coefficient and the effective intraparticle diffusivity were derived by fitting with adsorption model. Based on these kinetic properties, Sr breakthrough curves were estimated for the simulated groundwater containing 0.3 ppm Sr passed at 10 cm∙day-1 through 1.5 m thick PRB with zeolite and gravel. The breakthrough points for the PRB with 33 wt.% zeolite was evaluated as more than 70 years.

Condensation heat and mass transfer characteristics of low GWP zeotropic refrigerant mixture R1234yf/R32 inside a horizontal smooth tube: An experimental study and non-equilibrium film model development

Condensation heat and mass transfer characteristics of low GWP zeotropic refrigerant mixtures R1234yf/R32 (mass fractions of 0.52:0.48 and 0.77:0.23, respectively) inside a horizontal smooth tube (inner diameter 4 mm) were studied experimentally. Moreover, a non-equilibrium film heat and mass transfer model was also developed by considering the mass transfer resistance on the vapor and the liquid side. Effects of mass flux, vapor quality, thermophysical properties and mass fraction on the heat transfer coefficients (HTCs) were analyzed. The heat transfer characteristics, especially the heat transfer deterioration caused by the mass transfer difference of the zeotropic refrigerant mixture, were evaluated. The experiment data show the HTCs of R1234yf/R32 (0.48:0.52) are lower than that of R1234yf at the inlet nearby of the condenser, then that becomes higher gradually than R1234yf due to mass transfer resistance decreasing. The non-equilibrium film model shows good agreement with the experimental results with the mean deviation in HTC of 22.9% at a mass fraction of 0.77:0.23 and 17.8% at a mass fraction of 0.48:0.52. Furthermore, the heat transfer degradation coefficient, interface temperature, diffusion flux of R32 and mass transfer Nusselt number were also reasonably determined with the non-equilibrium film model.

Adsorption of propranolol hydrochloride from aqueous solutions onto thermally treated bentonite clay: A complete batch system evaluation

Sustainability is an increasingly prominent issue in our modern society. Propranolol, a β-blocker mainly indicated for the control of hypertension, is an emerging contaminant that has already been reported as non-biodegradable, highly persistent, partially removed by the conventional treatment processes of water and wastewater and harmful to aquatic organisms. The removal of propranolol hydrochloride by batch adsorption using calcined Verde-lodo, a thermally modified bentonite clay, was assessed in this work. pH analysis indicated that natural pH could be used in the experiments. The kinetic study, conducted at 25 °C and deeply evaluated by rate laws and mass transfer models, achieved the equilibrium after 15 h, with pseudo-second order model showing the best fit and resistance to mass transfer in external film as the limiting step of adsorption. The isotherms’ study, conducted at 20, 30 and 40 °C, showed a maximum adsorptive capacity of 0.468 mmol.g−1. The thermodynamic analysis revealed a spontaneous, endothermic and entropy-governed adsorptive process (with increase in randomness and disorder level at the solid/liquid interface), and that clay surface is energetically heterogeneous. The energies of the electron-rich and electron-deficient sites, as well as the quantum chemical parameters (based on DFT theory), were determined for propranolol. The effects of molecular sieving could be ignored. Experimental data was supported by characterization results of the clay before and after adsorption, which indicated that the process modified its surface by the effective removal of the drug from aqueous solutions.

Unraveling the mechanism of efficient adsorption of riboflavin onto activated biochar derived from algal blooms

Riboflavin is commercially produced primarily by bio-fermentation. Nonetheless, purification and separation are particularly complex and costly. Adsorption from the fermentation liquor is an alternative riboflavin separation technology during which a cost-efficient adsorbent is highly desired. In this study, a low-cost activated algal biomass-derived biochar (AABB) was applied as an adsorbent to efficiently adsorb riboflavin from an aqueous solution. The adsorption capacity of riboflavin on AABB increased with the increase in pyrolysis temperature and initial riboflavin concentration. The adsorption isotherms were well described by the Freundlich and Langmuir models. The AABB displayed excellent adsorption performance and its maximum adsorption capacity was 476.9 mg/g, which was 6.8, 6.8, and 5.2 times higher than that of laboratory-prepared activated rape straw biochar, activated broadbean shell biochar and commercial activated carbon, respectively, which was mainly ascribed to its larger specific surface area and abundant functional groups. The mass transfer model results showed that mass transfer resistance was dependent on both the film mass transfer and porous diffusion. Raman and Fourier transform-infrared spectra confirmed the presence of π-π interactions and hydrogen bonding between riboflavin and the AABB. The adsorption of riboflavin onto AABB was a spontaneous process, which was dominated by van der Waals forces. These results will be beneficial for developing effective riboflavin recovery technologies and simultaneously utilizing waste algal blooms.

Electrochemically modified adsorbents for treatment of aqueous arsenic: Pore diffusion in modified biomass vs. biochar

Canola straw-based biomass and biochar adsorbents were electrochemically modified and used to remove arsenate (As(V)) from water. Studying the effects of the modification parameters on the As(V) adsorption capacity of the modified materials showed that the materials treated at lower pH (3) and drying temperatures (60 °C) had higher As(V) uptake. The modification conditions were optimized to obtain optimum modified biomass (OBM) and biochar (OBC) with the highest As(V) adsorption capacity. Characterization of the OBM and OBC indicated that the deposited iron oxide on the surface of the adsorbents was goethite. The adsorption isotherms and kinetic data suggested that a hybrid adsorption mechanism took place under the experimental conditions with a higher probability of heterogeneous multilayer chemisorption. Solid-phase speciation of the sorbed As(V) indicated a negligible reduction (2.5%) of As(V) to arsenite (As(III)) on OBM, while no reduction occurred on OBC. The liquid film mass transfer coefficient (kf) and effective pore diffusion coefficient (Dp) were estimated using a shrinking core model combined with a genetic algorithm. A higher tortuosity factor of 3.75 for the OBM was obtained as compared to 2.93 for the OBC. Overall, the applied electrochemical modification successfully enhanced the As(V) sorption capacity of both the biomass and biochar from 8 to 766 and 25 to 922 µg/g, respectively, indicating promising potential of this method for preparation of high performance adsorbents.

Modeling of Fixed‐Bed Rapid Temperature Swing Adsorber for Butanol Dehydration

AbstractA fixed‐bed system of rapid temperature swing adsorption (RTSA), which uses a solid absorbent for dehydration of butanol, was studied. The packed bed was simulated using proper partial and algebraic equations which were solved by the central difference method in MATLAB software. The equilibrium relationship and fixed‐bed breakthrough curves were determined experimentally. The value of unknown parameters such as equilibrium constants, liquid film mass transfer coefficient, intraparticle diffusion coefficient, and axial diffusivity were estimated by appropriate equations. The model fitted well to experimental breakthrough data. The results proved that it would be possible to operate a complete RSTA cycle in just a few hours to allow a large quantity of organic solvent dehydrated with reasonable concentration.