Mass Transfer Conditions Research Articles

Biofilm mass transfer and thermodynamic constraints shape biofilm in trickle bed reactor syngas biomethanation

Syngas (H2, CO2, CO) produced thermochemically from lignocellulosic biomass is an underexploited source for resource recovery and valorisation through its biological conversion for the production of a wide range of chemicals and fuels. Syngas biomethanation is one such promising bioconversion pathway, displaying interesting features such as high conversion efficiency and product selectivity, as methane is the sole product of the process. The biological conversion of syngas to high purity biomethane is still typically associated with a number of challenges related to the syngas composition, CO toxicity, and gas–liquid mass transfer limitations. In this work, the syngas biomethanation process carried out in trickle bed reactors was investigated at its boundary conditions to explore the limits of the process, focusing on syngas composition and mass-transfer conditions potentially limiting process performance. The process was found to be robust when exposed to CO excess, but highly sensitive to H2 excess, which caused severe inhibition even under small amounts of excess H2. This implies that biomethane purity comparable to natural gas can be achieved by addition of renewable H2, but this requires precise control to avoid process failure. Modulating the liquid recirculation rate and gas residence time allowed for a maximum methane productivity of 9.8 ± 0.5 mmol CH4 h−1 Lreactor−1 with full conversion of H2 and CO at a gas residence time of 1 h. Nevertheless, increasing the gas–liquid mass transfer with increasing liquid recirculation rate did not lead to increased methane productivity, which suggested additional rate-limiting bottlenecks in the process. Careful investigation of other factors potentially limiting the process led to the conclusion that diffusive transport of syngas components in the biofilm was the main bottleneck of the process. This diffusive limitation leads to a scenario of severe substrate scarcity in the biofilm phase that conditions the thermodynamic feasibility of the different biochemical reactions involved in syngas biomethanation. In turn, these thermodynamic constraints were found to drive the stratification of microbial groups and sequential consumption of syngas components along the height of the reactor.

Revealing the intricacies of natural convection: A key factor in aqueous zinc battery design

Aqueous zinc-based batteries offer high safety, abundant resources, low cost, and environmental friendliness, making them a promising alternative to lithium-ion batteries for large-scale energy storage markets. However, the natural convection in the electrolyte during operation, which can greatly affect the battery performance, is overlooked for a long time. Through particle tracing experiments, this study demonstrates that in the vertical placement of the battery, natural convection occurs due to the variation of electrolyte density, whereas it does not happen when the cathode is on top. Besides, there is a significant difference in electrochemical performance between these two configurations, with a voltage difference of up to 0.25 V at 10 mA cm⁻² and a peak current difference of up to 3.4 mA in linear sweep voltammetry. Simulation results show that convective mass transfer can be up to 100 times greater than diffusive mass transfer in a bulk solution. This highlights the importance of considering natural convection to improve model accuracy. Further, to increase energy density, batteries are scaled up in practical applications to reduce the weight of the casing. This work simulates mass transfer conditions under various scenarios, illustrating the trade-off between current density and battery size, and offering new guidance for the design of aqueous zinc-based batteries.

Multiplicative Control Problem for the Stationary Mass Transfer Model with Variable Coefficients

Multiplicative Control Problem for the Stationary Mass Transfer Model with Variable Coefficients

Determining the efficient mass ratio of the extractant and the object of extraction and the equilibrium concentrations of the target components in them

The caviar and lecithin complex of freshwater fish can be widely used for the production of various food products, including those of functional orientation. The main technological operations in lecithin technology should include the processes of extraction of the initial caviar raw material and raffinate obtained after the first stage of selective extraction. The purpose of the study is to identify the rational mass ratio of extractant and raw material (module), on which the extraction efficiency depends, as well as the final concentration of extracted substances in the extract to determine its current value in the process of mass transfer to study the kinetics of extraction. The object of the study is the caviar-anchovy complex of fathead carp, carp, pikeperch and catfish, as well as the extract and raffinate from it. Summarizing the experimental data on revealing the rational module, as well as the final concentration of extracted substances in the extracts obtained, we can conclude that for caviar of the fish species under study, the rational hydromodule for its extraction with acetone is the ratio of dry caviar : extractant 1 : 4, and for its extraction with ethyl alcohol is the ratio of dry caviar : extractant 1 : 8. If the mass ratio refers to the fresh caviar of the studied fish species, then its rational indicator at its extraction with acetone is the ratio of fresh caviar : extractant 1 : 1.5, and at its extraction with ethyl alcohol is the ratio of fresh caviar : extractant 1 : 3. The average final concentration of extracted substances from dry caviar of the studied fish species in the extracts obtained, if acetone was used as a solvent under rational conditions of mass transfer, corresponds to the value of 1.3 %, and if ethyl alcohol was used as a solvent under rational conditions of mass transfer, corresponds to the value of 1.0 %.

Novel Approach to Organization of Structured Cobalt-Based Fischer–Tropsch Catalyst

Structured Fischer–Tropsch synthesis catalysts were tested in tubular reactors of industry-standard diameters of 0.5 or 0.75 inches. The structured catalyst bed was manufactured by the obturation of a straight bunch of graphite-based extrudates (D = 1.5 mm, L = 30 mm). A conventional loose bed of granulated catalyst (D = 1.5 mm, L = 3 mm) was tested as a reference. In a 1000–3000 h−1 syngas space velocity range, structured and loose catalyst bed testing showed no significant differences in their main catalytic parameters. Nevertheless, their C5+ hydrocarbon group composition was quite different, i.e., the alkene fraction rose from 9 to 23%, while n-alkanes dropped from 81 to 64%. This could be a result of secondary reaction intensification in the conventional loose bed due to its zeolite acid site’s higher availability. Further FTS testing of the structured catalysts in 4000–6000 h−1 manifested distinctive limits in C5+ productivity for 0.5 and 0.75 inches of 512 kg C5+/(m3 reactor·h) and 362 kg C5+/(m3 reactor·h), respectively. This may be explained by limitations in structured bed thermal conductivity. It suggests that the arrangement of extrudates in the structured catalyst can significantly affect the reaction heat and mass transfer conditions and affords new opportunities for group composition control by means of catalyst bed organization.

Rotating Disk Electrode Study of Sm(III)/Sm(II) in LiCl-KCl Eutectic Molten Salt

Understanding the redox reactions of fission products in molten salts is crucial for developing pyroprocessing techniques for used nuclear fuel. A rotating disk electrode is useful for investigating the electrochemical reactions with controlled mass transfer conditions, but its application has been limited in high-temperature corrosive molten salts. This study employs a tungsten (W) rotating disk electrode (RDE) to measure the electrochemical and kinetic properties of the Sm(III)/Sm(II) redox reaction in a LiCl-KCl eutectic molten salt. The properties of the Sm(III)/Sm(II) redox reaction, including diffusion coefficients, exchange current densities, charge transfer coefficients, activation energies, and Tafel slopes, were determined over a temperature range of 723–803 K using limiting currents in linear sweep voltammetry at various rotating speeds and mass transfer-corrected Tafel plots. The kinetic parameters obtained using the rotating disk electrode system can be useful for optimizing the design of pyroprocessing techniques.

Effect of High Local Diffusive Mass Transfer on Acidic Oxygen Reduction of Pt Catalysis

In this study, we utilize a platinum ultramicroelectrode as a model platform for platinum electrocatalysts in acidic electrolytes to study the effects of local mass transfer on the oxygen reduction reaction (ORR), which plays a significant role in fuel cells with reduced platinum loading. Finite element simulations show that the UME exhibits size-dependent ultrathin diffusion layers during the electrochemical process. Submicron-scale UMEs can achieve ultrahigh localized mass transfer, which is unattainable through other experimental techniques. By conducting catalytic experiments under various mass transfer conditions, we find that the mass transfer limiting current is significantly lower than the value predicted by the four-electron process equation. Additionally, the apparent electron transfer number (napp) decreases as the mass transfer coefficient (m0) increases. Furthermore, as m0 increases, the half-wave potential shifts toward more negative values, allowing for the evaluation of the intrinsic activity of the catalysts over a broader potential range. Due to the UME technique’s capability to conveniently control local mass transfer, we anticipate its potential application in understanding the effects of chemical microenvironments on complex electrochemical reactions, including ORR and other processes.

Soret and Dufour impacts in entropy optimized MHD flow by third-grade liquid involving variable thermal characteristics

Soret and Dufour impacts for third-grade liquid flow are examined. MHD (magnetohydrodynamics), Joule heating, and thermal radiation are studied. Properties beyond constant thermophysical characteristics are discussed. Convective condition of mass and heat transfer is addressed. First-order chemical reaction with entropy generation is deliberated. Finite difference method is implemented. Analysis for involved variables about quantities of interest is organized. The findings show that velocity for material parameters of fluid has increasing trend. Suction variable yields to decay in velocity. Radiation and suction variables reveal enhancement in temperature whereas higher Dufour number lower thermal field. Higher thermal Biot number improved temperature. Higher magnetic field and radiation variables enhance entropy generation rate. Nusselt number against radiation has deceasing behavior whereas Sherwood number for reaction rate shows opposite trend.

Experimental performance analysis of an infrared heating system for continuous applications of drying

One feasible approach for enhancing material quality and expediting the dehydrating procedure is using infrared radiation to provide heat. The impact of infrared power (0.130–0.341 W/cm2), airflow (0.5–1.5 m/s), and slice thickness (2–6 mm) on mass transfer, drying kinetics, colour, shrinkage, and rehydration ratio conditions. During the process, the dried samples' initial moisture content of 86.7 % was decreased to 11 % (w.b.). Eleven statistical factors were used to compare eleven alternative mathematical models. The results of regression analysis indicated that the Midilli et al. model best describes the drying behaviour in both techniques. The outcomes exhibited that the drying period rose at airflow and thickness but decreased with intensity. While the shrinkage ratio increased and declined with air velocity, the rehydration ratio grew and dropped with increasing infrared radiation intensity and airflow. As the intensity and airflow increased, there was a noticeable increase in the overall colour difference between slices of fresh and dry apples. The outcomes of this investigation will offer a further understanding of the ideal drying settings to create apple slices for snacking or other culinary purposes.

The effects of different impeller combinations in the Sphingan WL gum fermentation process

The fermentation of the high-viscosity polysaccharide WL gum has always been associated with poor mass transfer. Appropriate impeller configurations are key factors in maintaining homogeneity and sufficient mass transfer conditions. Therefore, a flat-folded disc turbine impeller (FFDT) taking into account both the reduced cavitation effect and the increased contact area was designed. Besides, a curved cross impeller (CC) and a fishbone-shaped impeller (FS) generating axial flow were also designed. The energy consumption and efficiency of the designed impellers and eight reported impellers were evaluated through fermentation and principal component analysis (PCA). Compared to the commonly-used six-blade flat-blade disc turbine (FBDT), the ungassed power number of FFDT was reduced by 50 %. Combinations of six-blade Brumajin impeller (BM) + FFDT and CC + FFDT produced high WL gum production and viscosity (34.0 g/L, 35.50 g/L, and 62.64 Pa·s, 61.68 Pa·s, respectively) and were suitable impellers for WL biosynthesis. WL gum from BM + FFDT showed higher viscosity, viscoelasticity, and molecular weight than that from FBDT + FBDT. In addition, fewer amino acids and pyruvic acid intermediates were formed using BM + FFDT, indicating a greater metabolic flux towards WL gum synthesis. This work provided an important reference for the design of impellers in high-viscosity fermentation systems.

A modified local thermal non-equilibrium model of transient phase-change transpiration cooling for hypersonic thermal protection

Aiming to efficiently simulate the transient process of transpiration cooling with phase change and reveal the convection mechanism between fluid and porous media particles in a continuum scale, a new two-phase mixture model is developed by incorporating the local thermal non-equilibrium effect. Considering the low-pressure and high overload working conditions of hypersonic flying, the heat and mass transfer induced by capillary and inertial body forces are analyzed for sub-cooled, saturated and super-heated states of water coolant under varying saturation pressures. After the validation of the model, transient simulations for different external factors, including spatially-varied heat flux, coolant mass flux, time-dependent external pressure and aircraft acceleration are conducted. The results show that the vapor blockage patterns at the outlet are highly dependent on the injection mass flux value and the external pressure, and the reduced saturation temperature at low external pressure leads to early boiling off and vapor blockage. The motion of flying has a large influence on the cooling effect, as the inertial force could change the flow pattern of the fluid inside significantly. The comparison of the results from 2-D and 3-D simulations suggests that 3-D simulation shall be conducted for practical application of transpiration cooling, as the thermal protection efficiency may be overestimated by the 2-D results due to the assumption of an infinite width length of the porous plate.

Mechanical properties of solid waste-based composite cementitious system enhanced by CO2 modification

Utilizing CO2 to modify solid waste and produce high-performance cementitious material is a promising strategy. In this study, circulating fluidized bed fly ash (CFBFA), calcium carbide slag (CS) and flue gas desulphurization gypsum (FGDG) were prepared by mixing CO2 to produce cementitious materials. The impacts of CO2 on mechanical properties and carbonation reaction mechanism of composite materials were investigated. The results shown that the microstructure and mechanical properties of the gelling materials were improved by CO2 modification. When the CO2 mass transfer conditions as followed: CO2 flow rate was 1.5 L/min, stirring rate at 600 r/min, and stirring time at 20 min, compressive strength of modified material was 22 % higher than that of the non-CO2 modified material. Additionally, the density increased by 3.2 %, and porosity was reduced by 34.1 %. Among them, TG/DTG analysis found that the highest effective fixed CO2 rate was 11.1 %. The ultrasonic nondestructive testing also shown that the structure of the CO2-modified cementitious material was significantly better than that of the CFBFA-CS-FGDG composite cementitious system, and the ultrasonic loss rate was reduced by 9.4 %. Therefore, the use of CO2 to modify the composite system was of great significance for the realization of CO2 storage and the improvement of the properties of composite materials. One interesting future possibility is solid waste-based grouting materials production at energy plants: CFBFA, CS and FGDG can be used to capture CO2 from flue gases, thus improving the strength of produced grouting materials.

Optimization of a Rare Earth and Aluminum Leaching Process from Weathered Crust Elution-Deposited Rare Earth Ore with Surfactant CTAB

Ammonium sulfate is typically employed as a leaching agent in the in situ leaching of weathered crust elution-deposited rare earth ore. However, it is associated with challenges such as low efficiency in mass transfer for rare earth (RE) leaching, high usage of the leaching agent, and prolonged leaching duration. To address the issues mentioned above, the surfactant cetyltrimethyl ammonium bromide (CTAB) was compounded with 2% ammonium sulfate to form a leaching agent in this paper. The effects of CTAB concentration, temperature, pH, and leaching agent flow rate on the rare earth (RE) and aluminum (Al) leaching mass transfer process from RE ore were investigated using chromatographic plate theory. The results revealed that CTAB addition improved the RE mass transfer process while moderately inhibiting the Al mass transfer efficiency. Increasing the temperature and pH of the leaching solution led to higher theoretical plate numbers for RE and Al leaching, lowered theoretical plate height (HETP), and enhanced leaching mass transfer efficiency. However, under high temperature and alkaline conditions, the mass transfer efficiency begins to decrease, indicating that high temperature and alkaline conditions are not conducive to the synergistic enhancement of RE and Al leaching by CTAB. Considering that clay minerals have good pH buffering properties, adjusting the pH of the leaching solution during rare earth ore leaching operations was deemed unnecessary. The optimal mass transfer conditions for leaching RE and Al were identified as 2% ammonium sulfate concentration, 0.00103 mol/L CTAB concentration, pH range of 5.2–5.5 for the leaching solution, 0.6 mL/min leaching solution flow rate, and room temperature. The rare earth leaching mass transfer effect could be enhanced during summer operations.

Water desalination system via ion immobilization on iron corrosion-based colloids and filtration by kevlar support

An efficient, scalable water desalination line has been introduced based on ion immobilization on the corrosion-based colloids (Diameter: from 10 nm to 20 µm) and filtration by a kevlar support. These particles are generated based on the galvanic cell behavior of some semi-galvanized wiring bundles inside a water medium according to the electrochemical cell schematic: Fe|Fe2+, OH-, H2|H2O with ΔG° of −73.0 KJ mol−1. To have an efficient desalination process, the contributions of different mechanisms such as mixed salt crystals, co-precipitation, and /or formation of various ionic charged species are present. These interactions resulted in the formation of micro/nano colloids (suspensions) with Fe2+ with other cations and anions, randomly, inside the bulk water medium. These particles are sandwiched among the arrays of the kevlar slices (5.0 × 5.0 cm) and play the role of the filter medium. In the introduced water desalination process, the population of the iron-based suspensions is controlled via a descending setting of the mass percentage of the semi-galvanic iron bundling wires along the water desalination line to control the number (population) of iron-based particles. This phenomenon consequently approves the condition for the efficient water desalination process at a laminar mass transfer condition with Reynolds number < 2000. The important factors of the removal efficiency are optimized using a multivariate optimization method based on a controllable waste purification efficiency threshold. This system possesses adequate advantages such as high water desalination efficiency, an acceptable water purification rate (3.0 L h−1, for only one water desalination line), low cost, enough simplicity, no residual water, and no need for any external driving source(s).

Engineering applications development through OHAM in heat and mass transfer during stagnant flow of second-grade nanomaterial

This paper investigates the stagnation point flow of a second-grade nanomaterial, considering nanofluid effects via thermophoresis and Brownian motion. The study addresses convective heat and mass transfer conditions within the flow induced by a stretching cylinder. The transformed systems are solved using the optimal homotopy solutions (OHAM) method, revealing the impact of various parameters on the quantities of interest. The results indicate that an increase in curvature, viscoelasticity, velocity ratio and injection parameters leads to an enhancement in velocity, while the opposite trend is observed due to suction. The viscoelasticity and curvature parameters also increase skin friction. Additionally, thermophoresis enhances the temperature and concentration fields, while Brownian motion reduces mass diffusion.

Intensification of multiphase systems with a jet‐loop reactor: characterization of mass transfer, mixing time, drop oil size, and biomass growth

AbstractBACKGROUNDThe development of processes for transforming vegetable oils into useful products has received increasing attention in the biotechnological field. The reactor used for this purpose should meet adequate mass transfer, mixing, and oil dispersion conditions. In this work, comprehensive research into the use of a jet‐loop reactor as a potential alternative to airlift and stirred tank reactors was conducted in the presence of avocado oil in a water‐air system. Additionally, the assessment of the jet‐loop for biomass growth in the presence of oil was performed.RESULTSThe increase of avocado oil from 1% to 5% v/v resulted in a reduction in the performance of the three reactors. Despite the airlift reactor having the lowest power input, it exhibited the worst performance in terms of mass transfer, mixing, and oil dispersion. The estimation of the energetic oxygen transfer efficiency (Kg O2 KW−1 h−1) allowed the determination that the jet‐loop reactor was superior to the stirred tank. This superiority was attributed to the low values of the mixing time and oil droplet diameter observed in the jet‐loop reactor. Finally, all these parameters had a positive impact on the growth of Wautersia eutropha in the jet‐loop reactor compared with the other two reactors.CONCLUSIONThe results showed that the jet‐loop reactor presented superior performance in most cases compared to the stirred tank and airlift reactors. Particularly, the jet‐loop exhibits an interesting potential to reduce the size of the avocado oil droplets, which could lead to a significative increase in the growth rate of Wautersia eutropha. © 2023 Society of Chemical Industry (SCI).

Screening Electrochemical Phosphorous Recovery Conditions in Real and Synthetic Wastewater Streams

The recovery of phosphorus (P) from wastewater via electrochemical precipitation is a promising route to improved nutrient recovery due to its ability to be coupled with current wastewater treatment processes, the viability of both small- and large-scale implementation (allowing for dispersed nutrient recovery systems), and utilization of electrons as an energy source (as opposed to chemically induced precipitation). In this talk, electrochemical P recovery from real and synthetic wastewater will be demonstrated, discussed, and contrasted. This study highlights the viability of electrochemical P recovery by considering waste stream composition, energetics of separation, and analyses of recovered products.Specifically, both synthetic and real wastewater was tested under similar stirred batch reactor conditions with various mass transfer conditions, electrode types, and applied potentials. The reactor solution chemistry was based upon an analysis of three real waste streams and time series analyses were used to compare the transient stream conditions to conditions used in P recovery studies. Additionally, materials characterization was performed on the product of various recovery conditions and the implications of reactor conditions are discussed.

Review of Micro- and Nanobubble Technologies: Advancements in Theory and Applications and Perspectives on Adsorption Cooling and Desalination Systems

Adsorption refrigerators are a compelling ecological alternative to compressor refrigerators; global warming forces us to constantly look for alternative sources of energy and cold. Cold production in adsorption chillers is based on the use of heat generated by other processes running in the company. Waste heat from production processes, which has, until now, been irretrievably lost, is a potential source of energy for generating cold via an adsorption unit producing chilled water. Cooling optimizes the use of the heating network in summer and can lead to increased electricity production while reducing heat supply losses. Thus far, attempts to implement adsorption refrigerators for widespread use have not been successful as a result of the low efficiency of these devices; this is directly related to the poor heat and mass transfer conditions in the beds and heat exchangers of adsorption refrigerators. The solutions used so far, such as new working pairs, glued beds or modifications to the structure or cycle length, are still not strong enough for these devices. Therefore, it is necessary to look for new solutions. Using micro- and nanobubbles as media to increase mass and heat transfer in refrigerators is an innovative and pioneering solution. Thus, this document describes the most important features of micro- and nanobubble technology applications in adsorption refrigerators. This article is an introduction and a basis for the implementation of further research, consolidating the existing literature as a review.

The Study of Fluid Dynamics Simulation of the Internal Flow Field in a Novel Airlift Oscillation Loop Bioreactor

The three-dimensional flow and mass transfer conditions in 5 L and 40 L airlift oscillation loop reactors were studied and compared with existing two-dimensional simulation and experimental data to verify the accuracy of the method. Then, the fluid dynamics behavior of the 2500 L reactor was simulated via supercomputing and provided guidance for production data. The results indicate that the application of oscillation operation in the 40 L multi-guide tube reactor can effectively improve the gas holdup and mass transfer coefficient in the reactor, with a maximum increase of 38% and 29%. For the 2500 L multi guide tube reactor, oscillation operation oscillation operation can significantly improve gas holdup and mass transfer coefficient increase gas holdup by 46% under 0.5 vvm operating conditions; the mass transfer coefficient increased by 54%. Therefore, oscillation operation can greatly improve the mass transfer coefficient for actual production reactors. After digging a hole in the middle sleeve, the circulating liquid speed has no effect. Although the gas holdup and mass transfer coefficient decreased by 1.3%, the gas holdup inside the entire reactor was more uniform, effectively reducing the average bubble aggregation.

Boron-doped rGO electrocatalyst for high effective generation of hydrogen peroxide: Mechanism and effect of oxygen-enriched air

Different B-doped rGO catalysts were prepared and their 2e- oxygen reduction reaction (ORR) performance was investigated. It was found that the 2e- ORR selectivity of B-doped rGO was related to the B content and oxygen mass transfer conditions. The synthesized catalyst exhibited high 2e- ORR selectivity of 95–98.6%, and the H2O2 yield reached up to 95.63 mg cm−2 h−1 at a current density of 200 mA cm−2. Moreover, increasing the oxygen concentration in the gas supplied to the B-doped rGO modified gas diffusion electrode (GDE) only to 30–40% resulted in almost the same H2O2 yield as using pure oxygen. Experimental analysis and theoretical calculations indicated that the isolated B dopant acts as active site for the 2e- ORR. Furthermore, B-doped rGO modified GDE was applied to the electro-Fenton system to continuously degrade organic pollutants. This work will be beneficial for the study and application of carbon-based ORR catalysts.