High Mass Transfer Performance Research Articles

Side chain sulfonic acid polymers with intrinsic pores in the main chain as proton exchange membranes for fuel cells and redox flow battery

The high proton conductivity, good dimensional stability and acceptable mechanical properties of proton exchange membranes (PEMs) are important indicators for the practical application of membrane materials in clean energy storage and conversion systems. In this work, we prepared SPDI-x, a membrane material with rigid and twisted main chains and intrinsic channels by an efficient and simple route. It combined a rigid and twisted skeleton with a flexible sulfonic acid side chain to achieve high conductivity and a limited swelling rate. The conductivity of SPDI-x at 80 °C was 233 mS cm−1, and the swelling rate was lower than 14%. SPDI-x demonstrated higher coulomb efficiency, energy efficiency and voltage efficiency than commercial Nafion212 in redox flow battery. In addition, it had more stable long-term cycle performance under the same test conditions. The H2–O2 fuel cell has a maximum peak power density of 823 mW cm−2, which is also higher than the battery performance of commercial PEMs under the same test conditions. The high mass transfer performance and good battery performance of SPDI-x provide a new idea for the structural design of high-performance proton exchange membranes.

Design of Baffled Flasks with High Mass Transfer Performance and the Application in Aerobic Microbial Culture

Tae Wan Kim, Sangmin Jung, Chae Il Lim, Si Jae Park, Jinwon Lee, Byung-Keun Oh, and Jeong-Geol Na. Korean Society for Biotechnology and Bioengineering Journal 2022;37:107-11. https://doi.org/10.7841/ksbbj.2022.37.3.107

Alleviating mass transfer limitations in industrial external-loop syngas-to-ethanol fermentation

Mass transfer limitations in syngas fermentation processes are mostly attributed to poor solubility of CO and H2 in water. Despite these assumed limitations, a syngas fermentation process has recently been commercialized. Using large-sale external-loop gas-lift reactors (EL-GLR), CO-rich off-gases are converted into ethanol, with high mass transfer performance (7–8.5 g.L-1.h−1). However, when applying established mass transfer correlations, a much poorer performance is predicted (0.3–2.7 g.L-1.h−1). We developed a CFD model, validated on pilot-scale data, to provide detailed insights on hydrodynamics and mass transfer in a large-scale EL-GLR. As produced ethanol could increase gas hold-up (+30%) and decrease the bubble diameter (≤2 mm) compared to air–water mixtures, we found with our model that a high volumetric mass transfer coefficient (650–750 h−1) and mass transfer capacity (7.5–8 g.L-1.h−1) for CO are feasible. Thus, the typical mass transfer limitations encountered in air–water systems can be alleviated in the syngas-to-ethanol fermentation process.

Coupling influences of electrode and flow field geometry on species transport behavior and battery performance for organic redox flow battery

Abstract The organic redox flow battery (ORFB) was regarded as one of the promising commercial technologies for the large-scale energy storage, the battery performance of which was influenced by the electrodes and flow fields. The battery performance and mass transfer behaviors of four different electrodes (rectangular electrode with serpentine flow field (RS), rectangular electrode with rotary flow field (RR), circular electrode with serpentine flow field (CS), circular electrode with rotary flow field (CR)) were investigated based on a rigorous numerical model, which was verified by the experiments. The results showed that discharge voltages of RS design were highest and voltage of RS design was 24.3% higher than that of RR design, which was lowest. The uniformity factor of RS design was 13.2% higher than that of RR design. The average concentration of RS design was 4.5% higher than that of CS design. Therefore, RS design electrode was the best design due to high mass transfer performance. And performance superiorities of RS design were further highlighted by comparing voltage and concentration distribution of RS design and traditional serpentine flow field (TS). All above can enrich the research of mass transfer behavior in ORFB.

Hierarchically mesoporous carbon spheres coated with a single atomic Fe–N–C layer for balancing activity and mass transfer in fuel cells

AbstractNovel cost‐effective fuel cells have become more attractive due to the demands for rare and expensive platinum‐group metal (PGM) catalysts for mitigating the sluggish kinetics of the oxygen reduction reaction (ORR). The high‐cost PGM catalyst in fuel cells can be replaced by Earth‐abundant transition‐metal‐based catalysts, that is, an Fe–N–C catalyst, which is considered one of the most promising alternatives. However, the performance of the Fe–N–C catalyst is hindered by the low catalytic activity and poor stability, which is caused by insufficient active sites and the lack of optimization of the triple‐phase interface for mass transportation. Herein, a novel Fe–N–C catalyst consisting of mono‐dispersed hierarchically mesoporous carbon sphere cores and single Fe atom‐dispersed functional shells are presented. The synergistic effect between highly dispersed Fe‐active sites and well‐organized porous structures yields the combination of high ORR activity and high mass transfer performance. The half‐wave potential of the catalyst in 0.1 M H2SO4 is 0.82 V versus reversible hydrogen electrode, and the peak power density is 812 mW·cm−2 in H2–O2 fuel cells. Furthermore, it shows superior methanol tolerance, which is almost immune to methanol poisoning and generates up to 162 mW·cm−2 power density in direct methanol fuel cells.

Effect of Monoethanolamine Concentration on CO2 Removal using Continuous High Frequency Ultrasonic Reactor

Chemical absorption is the most common technology used for the process of CO2 removal from natural gas due to its ability to reduce the level of the acid gas to a very low level as well as higher mass transfer performance due to the chemical kinetic reaction. Higher solvent concentration resulted in higher capacity to remove CO2, however reduces the diffusivity as well as its ability to spread on the packing due to its high solvent viscosity. This has hindered the used of high viscosity solvent in the operation of conventional packed column. However, recent technology of using high frequency ultrasonic irradiation for absorption process has shown possibility to operate high viscosity solvent due to the absence of packing in the reactor. From this work, it is shown that high viscosity solvent does not affect the mass transfer performance under ultrasonic irradiation due to the presence of acoustic streaming, fountain and atomization that reduced the film resistance thus increases the diffusivity. This work has demonstrated that this technology has high flexibility of solvent selection for the absorption process.

Comparative investigation of fine bubble and macrobubble aeration on gas utilityand biotransformation productivity.

The sufficient provision of oxygen is mandatory for enzymatic oxidations in aqueous solution, however, in process optimization this still is a bottleneck that cannot be overcome with the established methods of macrobubble aeration. Providing higher mass transfer performance through microbubble aerators, inefficient aeration can be overcome or improved. Investigating the mass transport performance in a model protein solution, the microbubble aeration results in higher kL a values related to the applied airstream in comparison with macrobubble aeration. Comparing the aerators at identical kL a of 160 and 60 1/h, the microbubble aeration is resulting in 25 and 44 times enhanced gas utility compared with aeration with macrobubbles. To prove the feasibility of microbubbles in biocatalysis, the productivity of a glucose oxidase catalyzed biotransformation is compared with macrobubble aeration as well as the gas-saving potential. In contrast to the expectation that the same productivities are achieved at identically applied kL a, microbubble aeration increased the gluconic acid productivity by 32% and resulted in 41.6 times higher oxygen utilization. The observed advantages of microbubble aeration are based on the large volume-specific interfacial area combined with a prolonged residence time, which results in a high mass transfer performance, less enzyme deactivation by foam formation, and reduced gas consumption. This makes microbubble aerators favorable for application in biocatalysis.

Novel Wire Mesh Packing with Controllable Cross-Sectional Area in a Rotating Packed Bed: Mass Transfer Studies

Wire mesh packing has been extensively utilized in laboratory and industry applications in rotating packed bed (RPB) because of the high mass transfer performance and low cost. Conventional wire me...

Theoretical and Experimental Research on a novel adsorption refrigerator based on low temperature geoethermal water

In view of the problems existing in adsorption refrigeration based on low temperature geothermal water, the adsorbent with high mass transfer performance was prepared by carbonization activation method. The specific methods are as follows: firstly, Chinese fir sawdust is immersed in calcium chloride solution, then taken out and dried, and the mixture is carbonized and activated at high temperature to form a porous activated carbon/calcium chloride composite adsorbent, and then expanded graphite is added to enhance the thermal conductivity of the composite adsorbent.The results show that: The proportion of calcium chloride in the composite adsorbent can be significantly increased by carbonization activation method, which makes the composite adsorbent have abundant microporous structure and uniform element distribution. The thermal conductivity of the composite adsorbent can be improved by adding expanded graphite.

Liquid–Liquid Microdispersion Method for the Synthesis of TS-1 Free of Extra-Framework Ti Species

A novel liquid–liquid microdispersion method for the synthesis of TS-1 has been developed by continuous preparation of the precursor. In the novel process, the solution of TBOT in n-hexane could be very uniformly dispersed into the oligomeric silicate prehydrolysis mixture to form microdroplets by a microsieve pore reactor. Due to the fast mixing and very high mass transfer performance of the microdispersion process, the Ti species could be uniformly distributed into the mixture and were more likely to condense into the oligomeric silicate precursor species rather than appear with self-condensation. The prepared samples had a minimum molar ratio of Si/Ti at 51 without extra-framework Ti species. Furthermore, the solvent of n-hexane can be recycled by simple phase separation rather than evaporation under the conditions of using isopropanol, which reduced energy consumption. This continuous microdispersion technology could be controllable and a reliable scaling-up for the preparation of TS-1.

Mass transfer in a rotating packed bed reactor with a mesh-pin rotor: Modeling and experimental studies

A rotating packed bed (RPB) reactor with full stainless steel wire mesh packing loaded in the rotor has excellent mass transfer performance. However, it has the blockage problem when applied to the reactions with solid generated on the surface of the packing. In this work, a mesh-pin rotor (MPR), combining an inner wire mesh packing zone (IMZ) and an outer resin pin zone (OPZ), was designed with the purpose of anti-blockage for the first time, expecting to possess the high mass transfer performance of wire mesh packing and self-cleaning performance of cylindrical pins. With the assistance of liquid holdup measurement by X-Ray CT scan technology, a mass transfer model was proposed for the RPB reactor with MPR and the liquid-side volumetric mass transfer coefficient (kLae) was measured by using an oxygen-water desorption system. The predicted results by the model showed good agreement with the experimental results within a deviation of ±20%, displaying potential application prospects.

Mass Transfer Performance of a String Film Reactor: A Bioreactor Design for Aerobic Methane Bioconversion

The mass transfer performance of a string film reactor (SFR)—a bioreactor design for the aerobic bioconversion of methane—was investigated. The results showed that the SFR could achieve high mass transfer performance of gases, and the highest values of the mass transfer coefficients for oxygen and methane were 877.1 h−1 and 408.0 h−1, respectively. There were similar mass transfer coefficients for oxygen and methane in absorption experiments using air, methane, and air–methane mixed gas under the same liquid flow rate conditions, implying that each gas is delivered into the liquid without mutual interaction. The mass transfer performance of the SFR was significantly influenced by the liquid flow rate and the hydrophilicity of the string material, whereas the magnitude of the gas flow rate effect on the mass transfer performance depended on both the tested liquid flow rate and the gas flow rate. Furthermore, the mass transfer performance of the SFR was compared with those of other types of bioreactors.

Heat and mass transfer performance comparison between a direct-contact liquid desiccant packed bed and a liquid-to-air membrane energy exchanger for air dehumidification

Entrainment of liquid desiccant droplets into the airstream and flow maldistribution are two challenges for liquid desiccant packed beds. Liquid-to-air membrane energy exchangers are novel liquid desiccant exchangers that have the potential to overcome these challenges by using membranes to separate the air and solution flows but have higher heat and moisture transfer resistances. As a new contribution of this study, the heat mass transfer performance of these two exchangers with the same volume and operating condition are compared at two conditions: (1) with the same pressure drop on the air side and (2) with the same total heat/mass transfer area. Results show that liquid-to-air membrane energy exchanger gets up to 13 and 20% higher latent and total effectiveness respectively than the packed bed at the same air pressure drop. Reversely, the packed bed achieves up to 16% higher mass transfer performance than the liquid-to-air membrane energy exchanger with the same heat/mass transfer area. The flow maldistribution and its influences in the packed bed and liquid-to-air membrane energy exchanger are also discussed. Finally, the impact of membrane on the heat mass transfer in the liquid-to-air membrane energy exchanger is evaluated. The membrane accounts for 6∼12% and 26∼43% of the overall heat and mass transfer resistance, respectively, depending on the width of the air channel.

Structure optimization of cathode microporous layer for direct methanol fuel cells

Abstract To obtain the cathode microporous layer (CML) with high mass transfer performance and high electronic conductivity, a pore-forming technology was introduced to optimize CML microstructure for direct methanol fuel cells. In this paper, the effects of carbon material type, carbon material loading and pore-forming agent loading in CML on fuel cell performance were discussed systematically. The results indicated that the optimized CML consisted of carbon nanotubes and ammonium oxalate with the loading of 1.5 and 3.5 mg cm−2 respectively. The fuel cell performance was improved by 30.3%, from 224 to 292 mW cm−2 at 80 °C under 0.3 MPa O2. Carbon nanotube was found to be the most suitable carbon material for the CML due to its great specific surface area and small particle size, resulting in increasing the number of the hydrophobic sites and the contact area between the support and the catalyst layer. The carbon material and pore-forming agent loading directly influenced the pore distribution and the contact resistance of membrane electrode assembly. The water removal capacity and the gas mass transfer property of diffusion layer were improved by optimizing the amount of micropore and macropore structures.

A novel reactive 4-diethylamino-2-butanol solvent for capturing CO2 in the aspect of absorption capacity, cyclic capacity, mass transfer, and reaction kinetics

In the present work, the performance of a novel reactive solvent, 4-diethylamino-2-butanol (DEAB), was comprehensively investigated and compared with the conventional solvents (e.g., MEA and MDEA) in terms of CO2 absorption capacity, cyclic capacity, mass transfer performance, and absorption kinetics. The results showed that DEAB can be considered as alternative promising solvent for capturing CO2 because its outstanding performance on much higher absorption capacity, higher cyclic capacity, and higher mass transfer performance; comparing with those of MEA and MDEA. In addition, the CO2 absorption kinetics of DEAB was found to be faster than that of conventional tertiary MDEA, but slower than that of conventional primary MEA.

Mass transfer of CO2 absorption in hybrid MEA-methanol solvents in packed column

The mass transfer performance of CO2 absorption into three solvents (i.e., 5M MEA in methanol, 5M MEA in 1:1 water-methanol volume ratio, and 5M MEA aqueous solutions) in an absorption column packed with DX structured packing at various CO2 loading, liquid flow rate, and inert gas flow rate. The mass transfer performance was evaluated in terms of volumetric overall mass transfer coefficient (KGav) and mass flux. The results showed that 5M MEA in methanol has higher mass transfer performance than those of 5M MEA in 1:1 water-methanol volume ratio and 5M MEA aqueous solutions, respectively. In addition, CO2 loading and liquid flow rate had significant effect on mass transfer performance, but inert gas flow rate has insignificant effect on mass transfer performance.

Gas–Liquid Effective Interfacial Area in a Rotating Packed Bed

Stainless steel wire mesh packing is widely used for experimental and industrial applications in rotating packed beds (RPBs) for gas–liquid contacting because it has a higher mass-transfer performance than other conventional packings. In this work, the gas–liquid effective interfacial area of a conventional RPB was studied with eight types of stainless steel wire mesh packings, consisting of four different stainless steel fibers. Gas–liquid chemisorption with CO2 in NaOH solution was employed to measure the effective interfacial area for all types of packings with different rotational speeds and gas–liquid ratios. An empirical correlation that takes the effects of the fiber diameter and opening size of the wire mesh into consideration was proposed for the calculation of the gas–liquid effective interfacial area of stainless steel wire mesh packings in a conventional RPB.

Gas Absorption of Slug Flow in Microchannel (1st Report, Experimental Study with C02/Water System)

Gas absorption and pressure drop characteristics of a slug flow in microchannel were experimentally studied with CO2 and water system in expectation of high absorption performance by large specific interface area, toroidal flow in slug and high heat transfer capability of microchannel. Absorption rate was measured by detecting volume change of gas bubble along the channel with photo-interrupters, and then absorption time constant was formulated as a function of inner diameter, bubble velocity, and liquid slug length. Pressure drop was also formulated by fitting experimental data to an equation modeled as a sum of Poiseuille flow part and toroidal flow part. Based on the formulas, high mass transfer performance and compactness of the proposed system was demonstrated by comparison with typical gas absorption systems such as falling liquid film and dispersion bubbles. The microchannel gas absorber, of which channel length was set to keep outlet liquid concentration a specified value, was estimated to be more compact by reducing a channel diameter with a slight increase of pressure drop.

Effect of swelling on mass transfer performance in membrane extraction

The membrane extraction experiments were performed with tributyl phosphate/acetic acid (HAc)/water, n-butanol/HAc/water and 20% Alamine (in kerosene); HAc; and water as working systems. HAc was transferred from the aqueous phase to the organic phase. The effect of flat membranes swelling on mass transfer was studied. The membranes were microporous polysulfone and microporous polytetrafluoroethylene. The overall mass transfer coefficients based on the water phase were calculated and compared between nonswollen and swollen membranes. The experimental results show that the physical structure of the flat membranes used in our experiments was changed if soaked by organic solvents; however, change in thickness was not found. The overall mass transfer coefficients clearly were decreased after the flat membranes were swollen. The most likely reason is that the mass transfer resistance was increased because of the change of the membrane structure. The results also show that it is better to choose a hydrophilic membrane to reach high mass transfer performance when the equilibrium constant is very low.

Mass transfer behaviour of gas‐liquid jet loop reactors

AbstractA special type of jet loop reactor (JLR), designed for continuous operation and short residence times was investigated with regard to its mass transfer behaviour, described by the volumetric mass transfer coefficient kLa. The jet stream and superficial gas velocities are varied in two JLRs of different sizes, equipped with different nozzles. Fully desalinated water, 0.08 molar NaCI solution and solutions of different concentration of carboxymethyl cellulose (CMC) are used as the liquid phase. A steady‐state physical method is employed to determine kLa: air oxygen is purged from the liquid phase by gaseous nitrogen. The measurements show that the reactor is characterized by high power density and high mass transfer performance. No limit of mass transfer capacity was observed in the chosen ranges of volumetric gas and liquid flow rates, i.e. at a given jet stream velocity, the relationship between kLa and the superficial gas velocity is nearly linear. The investigations show that the mass transfer contributed by the jet stream largely depends on liquid phase composition.