Gas-liquid Separation Research Articles

Process Intensification of Gas–Liquid Separations Using Packed Beds: A Review

The gas–liquid multiphase process plays a crucial role in the chemical industry, and the utilization of packed beds enhances separation efficiency by increasing the contact area and promoting effective gas–liquid interaction during the separation process. This paper primarily reviews the progress from fundamental research to practical application of gas–liquid multiphase processes in packed bed reactors, focusing on advancements in fluid mechanics (flow patterns, liquid holdup, and pressure drop) and the mechanisms governing gas–liquid interactions within these reactors. Firstly, we present an overview of recent developments in understanding gas–liquid flow patterns; subsequently we summarize liquid holdup and pressure drop characteristics within packed beds. Furthermore, we analyze the underlying mechanisms involved in bubble breakup and coalescence phenomena occurring during continuous flow of gas–liquid dispersions, providing insights for reactor design and operation strategies. Finally, we summarize applications of packed bed reactors in carbon dioxide absorption, chemical reactions, and wastewater treatment while offering future perspectives. These findings serve as valuable references for optimizing gas–liquid separation processes.

Influence of guide groove structure on in-flow drag reduction in spiral axial gas-liquid mixing pumps

Abstract With the onset of the fossil energy crisis, demand for oil has skyrocketed, and the spiral axial flow gas-liquid mixing pump has emerged as the primary piece of equipment for deep-sea oil extraction. However, at high gas content, the problems of separation of mixed media from hydraulic components, gas-liquid separation and gas phase aggregation are faced. The difficulties of gas-phase aggregation and bubble trajectory in the impeller channel have received much attention, while the problem of increased medium flow resistance induced by flow separation has received less attention. The spiral axial gas-liquid mixing pump is numerically calculated using the Eulerian multiphase flow model and the SST k- turbulence model in this work. The pump is designed with the design flow rate Q = 100 m3/h, rotational speed n = 4500 rmin, and head H = 30m by arranging guide slots with different relative depths and different number of slots to reduce the dissipative vortices, thus reducing the flow resistance in the 1/5 region behind the suction surface. The findings reveal that when the relative depth of the slots is 1/7 and the number of guide slots arranged is 5, the highest drag reduction rate in this location is 69.6% under the design flow condition. When the relative depth of the guide channel is1/7 and the number of guide channels is 3, the performance of the mixing pump is improved most, with an efficiency increment of 1.9% and a head increment of 4.2%, which can provide technical support for the flow resistance reduction of gas-liquid mixing pumps.

Recent Research Progress of Porous Graphene and Applications in Molecular Sieve, Sensor, and Supercapacitor.

Porous graphene, including 2D and 3D porous graphene, is widely researched recently. One of the most attractive features is the proper utilization of graphene defects, which combine the advantages of both graphene and porous materials, greatly enriching the applications of porous graphene in biology, chemistry, electronics, and other fields. In this review, the defects of graphene are first discussed to provide a comprehensive understanding of porous graphene. Then, the latest advancements in the preparation of 2D and 3D porous graphene are presented. The pros and cons of these preparation methods are discussed in detail, providing a direction for the fabrication of porous graphene. Moreover, various superior properties of porous graphene are described, laying the foundation for their promising applications. Owing to its abundant morphology, wide distribution of pore size, and remarkable properties benefited from porous structure, porous graphene can not only promote molecular diffusion and electron transfer but also expose more active sites. Consequently, a serious of applications containing gas sieving, liquid separation, sensors, and supercapacitors, are presented. Finally, the challenges confronted during preparation and characterization of porous graphene are discussed, offering guidance for the future development of porous graphene in fabrication, characterization, properties, and applications.

Numerical investigation of dynamic gas–liquid separator by population balance model

Dynamic gas–liquid separator (DGLS) can efficiently separate gas and liquid phases and are widely used in aerospace, chemical, and petroleum engineering. The energy loss and separation efficiency within the DGLS are studied through the combination of numerical simulations and experiments. Three-dimensional transient Reynolds-Averaged Navier–Stokes equations were solved to analyze the fluid dynamics within the DGLS. The bubble aggregation and breakup in oil were simulated by using the population balance model. Experimental data were meticulously compared with numerical results to validate the accuracy and reliability of the numerical methods. The findings revealed a direct correlation between the inlet flow rate and various performance metrics of the DGLS. Specifically, as the inlet flow rate increased, the energy loss within the DGLS escalated, resulting in higher power consumption. The degassing rate of the DGLS exhibited a decreasing trend with increasing inlet flow rate, while the de-oiling rate showed an inverse relationship. The optimal performance of the separator was observed at an inlet flow rate of 140 m3·d−1, with ηg* and ηl* reaching 0.94 and 0.99, respectively. The relationship between the Qo and the η* and Po was fitted by a second-order polynomial. Moreover, the rotational speed of the DGLS demonstrated a positive correlation with energy consumption, accompanied by an increase in power output. However, the separation efficiency of the DGLS exhibited a non-linear relationship with rotational speed, peaking at a specific value before marginally declining. The optimization of degassing and dewatering rates occurred at a rotational speed of 2500 r·min−1. These findings underscore the importance of carefully adjusting operational parameters to achieve optimal performance and energy efficiency within DGLS.

Research on the jet active control mechanism of gas-liquid separation in helical-axial multiphase pumps

In the field of deep-water oil and gas extraction, the intermittent gas blocking phenomenon in helical-axial multiphase pumps leads to decreased pump performance and reliability, severely limiting their large-scale application and promotion in engineering projects. To address this challenge, this study is based on the principle of jet flow field control to flow separation, utilizing external energy for active intervention to suppress the separation phenomena and improve the hydraulic efficiency within the impeller flow channel. The research reveals that the jets achieved a reconstruction of the internal flow in the helical-axial gas-liquid mixed transport pumps. Using orthogonal experimental methods, a preliminary predictive analysis of the factors influencing the effectiveness of the jet system was conducted. The study explored the impact of jet parameters on enhancing the performance of helical-axial gas-liquid mixed transport pumps from the perspective of diminishing gas aggregation at the trailing edge of the rotor cascade and curtailing backflow conditions, and established a mathematical model for the head and efficiency of helical-axial multiphase pumps under jet active control. Research indicates that the jet velocity significantly impacts the efficiency enhancement of multiphase pumps, with an optimal jet speed coefficient, Cjet = 10, identified. Beyond this speed, the benefits brought by increased jet velocity do not compensate for the costs of introducing high-speed jets, and instead, may lead to a reduction in the efficiency of the pump. Jet flow field control methods alleviate the suction side gas aggregation downstream of the jet holes and in the flow domain traversed by the jets, effectively reducing the aggregation of gas phases in the rear channel of the rotor and suppressing backflow near the trailing edge of the rotor cascade. Jet control measures strengthen the working capacity of the blade in the flow direction beyond 0.35 times the length of the streamline, expanding the working range of the blade and enhancing the work efficiency of the multiphase mixed transport pump. Higher jet velocities result in more significant enhancements of blade working power, especially under conditions of high initial gas content, where the relative increase in blade load is more pronounced.

Numerical Modeling of Water Transport in a Microporous Layer-Coated Porous Transport Layer for a Polymer Electrolyte Membrane Water Electrolyzer with an Interdigitated Flow Field for Internal Gas-Liquid Separation

A novel design for interdigitated flow fields in polymer electrolyte membrane electrolyzers has been developed for both ground and space applications. This design separates oxygen and liquid water internally, eliminating the need for water circulators to remove bubbles and external gas-liquid separators with buoyancy. The capillary pressure in the hydrophobic microporous layer (MPL) of the anode porous transport layer facilitates internal separation of oxygen gas and pressurized liquid water. A finite element model (COMSOL Multiphysics) simulates water transport in the MPL, while electrochemical impedance spectra determine the electrochemical kinetic parameters for the model. The model takes into account the oxygen bubble coverage of the cathode, liquid water saturation in the MPL, and the current ratio between liquid water and water vapor at the MPL-cathode layer interface. The vapor from liquid water in the MPL is modeled to mix with oxygen for diffusion. A volumetric water evaporation rate as a linear function of liquid water saturation in the MPL is assumed, where the rate constant is estimated from vapor permeation tests.

Numerical Modeling of Water Transport in a Microporous Layer-Coated Porous Transport Layer for a Polymer Electrolyte Membrane Water Electrolyzer with an Interdigitated Flow Field for Internal Gas-Liquid Separation

A novel design for interdigitated flow fields in polymer electrolyte membrane electrolyzers has been developed for both ground and space applications. This design separates oxygen and liquid water internally, eliminating the need for water circulators to remove bubbles and external gas-liquid separators with buoyancy. The capillary pressure in the hydrophobic microporous layer (MPL) of the anode porous transport layer facilitates internal separation of oxygen gas and pressurized liquid water. A finite element model (COMSOL Multiphysics) simulates water transport in the MPL, while electrochemical impedance spectra determine the electrochemical kinetic parameters for the model. The model takes into account the oxygen bubble coverage of the cathode, liquid water saturation in the MPL, and the current ratio between liquid water and water vapor at the MPL-cathode layer interface. The vapor from liquid water in the MPL is modeled to mix with oxygen for diffusion. A volumetric water evaporation rate as a linear function of liquid water saturation in the MPL is assumed, where the rate constant is estimated from vapor permeation tests.

Performance analysis of a novel gas-liquid separator with industrial application

This paper presents a novel gas-liquid separator characterized by its distinctive geometric design, capable of handling different volume fractions and mass flow rates. The separator's performance is comprehensively assessed across various gas volume fractions, bubble sizes, and mass flow rate fluctuations. The study reveals that variations in vapor volume fraction substantially affect both separation efficiency and pressure loss. An increase in vapor volume fraction from 0.1 to 0.5 leads to a 25% reduction in separation efficiency and a 3.3-fold decrease in pressure loss. In contrast, changes in mass flow rate exert a relatively minor influence on separation efficiency. Specifically, increasing the mass flow rate from 15 to 30 kg/s results in a mere 4% decrease in separation efficiency, whereas pressure loss increases by a factor of 3.2.Additionally, a reduction in bubble size from 1000 µm to 200 µm causes a 33% increase in pressure loss and a 14% decrease in separation efficiency. The incorporation of a meshpad in this design promotes the formation of a forced vortex, thereby enhancing the separation process.

Novel rate-based modeling and mass transfer performance of CO2 absorption in rotating spiral contactor

For the process of CO2 absorption, existing gas-liquid contactors suffer from low mass transfer performance and low gas-liquid ratios. In this study, a rotating spiral contactor was developed to overcome these drawbacks and a novel rate-based model was developed to predict the CO2 absorption performance. The effective interfacial area (ae), overall volumetric mass transfer coefficient (KGae) and CO2 absorption efficiency (η) were investigated. The results showed that the ae was 913–1125 m2/m3 superior to the conventional contactor. In the range of gas–liquid ratio of 200–1800, the KGae and η were 1.4–10.1 kmol.m-3.h-1.kPa-1 and 40.5–99.6 %, respectively. The rate-based model predicted the KGae and η with the AARD of 6.71 % and 1.90 %, respectively. Also, it has better robustness even in highly nonlinear temperature and composition distributions. This study provides a potential contactor and a new modeling tool for CO2 capture and other gas-liquid separation.

Kinetics and dynamics of Gas-liquid separation and bubble generation in surfactant solutions: Role of bulk/interfacial properties and hydrodynamic conditions

Understanding the kinetics and dynamics of gas–liquid separation and bubble generation in surfactant solutions is important for many industrial applications. To explore the potential mechanisms affecting the physical properties (expansion ratio, bubble size, and foam stability) of foams and bubbles, the surface tension of the solution, including the equilibrium and dynamic properties, was investigated. Then, the morphology of the surfactant aggregates was explored by cryo-transmission electron microscopy (cryo-TEM). Based on these experimental results, the effects of various physical and chemical factors (including the relative concentration of surfactant, dynamic surface tension, surface coverage, surface elasticity, surface mobility, aggregate morphology, etc.) on the expansion ratio and bubble size were analysed to identify which “universal” parameters can explain the phenomenon for all aqueous solutions in the gas–liquid separation process. Research has shown that the morphology of aggregates in a solution largely determines the surface properties of the solution at 1.5 ms (surface tension, surface coverage, surface elasticity, and so on). These surface properties significantly affect the expansion ratio. However, no good correlation was found between bubble size and these surface properties because surfactant vesicles can directly affect bubble size. In addition, the liquid flow rate and gas–liquid ratio have a significant impact on the expansion ratio and bubble size. Ultimately, we found that the foam stability, bubble size, and expansion ration can be described by a simple linear relationship. Our research provides new opinions for further understanding the effects of bulk/interfacial properties and hydrodynamic conditions on the physical properties of bubbles in the gas–liquid separation process.

Experimental investigation on pressure drop characteristics of adiabatic two-phase flow in a Gyroid-structured channel

Recent advancements in additive manufacturing techniques have enabled the fabrication of intricate structures. Among these structures, triply periodic minimal surfaces (TPMSs) such as the gyroid, are particularly promising for heat and mass transfer applications owing to their higher surface area to volume ratios compared to conventional structures such as heat exchangers. This study experimentally investigates the pressure drop characteristics of single- and two-phase flows in a gyroid-structured channel under adiabatic conditions. In particular, using an additively manufactured test section with a gyroid-structured channel, the pressure drop characteristics of both single- and two-phase flows are analyzed. The results ofsingle-phase flow experiments reveal that the friction factor depends on the hydraulic diameter, which is defined by the internal volume and surface area of the channel. This suggests that in addition to the hydraulic diameter, other parameters such as porosity and wall thickness must also be considered. Subsequently, the two-phase pressure drop predictions of homogeneous and separated models are compared with the pressure drop data obtained from two-phase flow experiments. The results reveal that gas–liquid separation must be considered to accurately predict the pressure drop in regions influenced by gravitational effects. Furthermore, correlations for predicting the pressure drops both single- and two-phase flows within the operating constraints are proposed.

Computational fluid dynamics modeling of gas bubble separation efficiency in downhole separators and vertical / inclined annulus: An experimental validation and analysis

This study presents a comprehensive investigation into gas bubble separation efficiency in a vertical downhole separator using computational fluid dynamics (CFD) modeling, which is validated with experimental data. The research aims to provide detailed insights into the separation mechanisms and the factors affecting them, such as liquid velocity, gas bubble sizes, and positions. Using an Euler-Lagrange multiphase model, the behavior of individual gas bubbles within the liquid-gas mixture was simulated. The results demonstrate that separation efficiency decreases as the liquid flow rate increases. This reduction in efficiency occurs because the increased liquid flow rate drags more bubbles within the stream, making it harder for them to separate. The separation process is primarily driven by the buoyancy force acting on the bubbles and the velocity profile of the liquid flow. Smaller bubbles, which tend to be near the casing wall, separate more efficiently, while larger bubbles are predominantly located between the second and third quarters of the annulus space. The "quarters" refer to radial divisions from the casing wall to the tubing wall, with the first quarter closest to the casing wall and the fourth quarter closest to the tubing wall. The study introduces a nonlinear regression model based on the numerical results to predict liquid slug separation efficiency. This model, validated against experimental data, accurately predicts separation efficiency and offers a robust methodology for estimating the efficiency of gravity-driven gas-liquid separators. This methodology is crucial for refining separator design and improving the operational efficiency of downhole separation systems, which are vital for enhancing the performance of pumping systems in oil and gas wells. The contributions of this study include a deeper understanding of the downhole separation process, the development of a simplified model for assessing bubble separation efficiency, and the potential application of the proposed methodology to different gas-liquid separator designs and inclination angles, thereby informing the design and operation of downhole separation systems.

Highly Porous Co-Al Intermetallic Created by Thermal Explosion Using NaCl as a Space Retainer.

Co-Al porous materials were fabricated by thermal explosion (TE) reactions from Co and Al powders in a 1:1 ratio using NaCl as a space retainer. The effects of the NaCl content on the temperature profiles, phase structure, volume change, density, pore distribution and antioxidation behavior were investigated. The results showed that the sintered product of Co and Al powders was solely Co-Al intermetallic, while the final product was Co4Al13 with an abundant Co phase and minor Co2Al5 and Co-Al phases after added NaCl dissolved out, due to the high Tig and low Tc. The open porosity of sintered Co-Al compound was sensibly improved to 79.5% after 80 wt.% of the added NaCl dissolved out. Moreover, porous Co-Al intermetallic exhibited an inherited pore structure, including large pores originating from the dissolution of NaCl and small pores in the matrix caused by volume expansion due to TE reaction. The interconnected large and small pores make the open cellular Co-Al intermetallic suitable for broad application prospects in liquid-gas separation and filtration.

Cyclone-coalescence separation technology for enhanced droplet removal in natural gas purification process

Natural gas is increasingly recognized as a clean energy source due to its high quality, low pollution levels, and abundant availability. However, certain gas fields contain complex components that require purification for efficient transportation and utilization. Addressing these issues involves efficient gas–liquid separation technology. Existing gas–liquid separation units face challenges such as efficiency, liquid entrainment, energy consumption, and the need for consumable replacement. This study focuses on a novel cyclone-coalescence separator that combines centrifugal and coalescence principles. Implemented in a high-acid natural gas purification plant in China, the cyclone-coalescence separator demonstrated efficiency primarily influenced by gas velocity and diameter. Optimal performance was observed with a 75 mm diameter reactor at velocities of 8–12 m s−1, achieving a peak efficiency of 96%. The hydrophilic glass fiber with a monofilament structure can coalesce droplets effectively. In practical industrial use, under operational conditions, the hydrocyclone's liquid discharge rate is 89.6 kg·h−1 with an inlet concentration of 382.7 g·m3. Over a 400-h cycle, the cyclone-coalescence separator demonstrated superior separation performance with an average liquid discharge volume of 9.09 mg·kg−1, compared to 4.93 mg·kg−1 for the precision filter. This successful industrial implementation presents a promising approach to natural gas purification.

Bionic Janus microfluidic hydrogen production with high gas–liquid separation efficiency

Water electrolysis offers the advantages of emission-free and highly efficient energy conversion in terms of sustainable energy development and environmental pollution. However, water electrolysis is strongly affected by the detachment of bubbles from the electrodes commonly enabled by buoyancy, thereby reducing the performance of the electrolytic cells in harsh environments like in space. Herein, a bionic Janus microchannels with active gas–liquid separation for water electrolysis is proposed. There is a Janus membrane with superaerophilic top surface and inner micropores over the microchannels, and such a unique type of microchannels can capture and unidirectionally manipulate the hydrogen (H2) bubbles generated on the surface of the electrode during the water electrolysis reaction at high speed with long-term stability. It is worth noting that the gas–liquid separation through the Janus membrane does not hinder the flow of electrolyte in the microchannel due to its hydrophilic inside surfaces, which can maintain the great stability of the electrolysis. Moreover, mimicked leaves and trees for water catalysis are further demonstrated with ultrahigh electrolysis efficiency based on the active detachment of H2 bubbles enabled by Janus micropores. The present bionic Janus microchannels for high-efficient water electrolysis to produce H2 is intended to provide a new power supply solution for human space living and exploration.

Preparation and regulation of high-strength and high-permeability porous ceramic/PDMS composite membranes for gas-liquid separation

Methane detection is crucial in identifying combustible ice within the energy sector. The gas–liquid separation membrane, a key component of methane sensors, plays a critical role in effectively separating methane and water. It significantly enhances the efficiency and stability of detecting methane concentration in situ. However, the related permeability and mechanical property present conflicting requirements in order to achieve optimal membrane performance. This work proposes an investigation into the mass transfer performance of a high-strength composite membrane, utilizing PDMS as the functional layer and porous ceramics as the supporting layer. By adjusting the pore distribution of the porous ceramics, particularly through the use of spherical graphite as a porogen, the study examines the impact of spherical graphite (SG) on the support layer’s morphology and its ability to regulate pore structure. Results indicate that incorporating spherical graphite with a porogen content of 10 wt% and a particle size of 25 μm enhances connections between ceramic grains, resulting in a flexural strength of 56.36 MPa and a permeability coefficient of 1861.57 barrer. This configuration demonstrates good waterproof and breathable performance. Overall, this research presents a novel approach for fabricating methane-water separation membranes, offering valuable insights for underwater methane detection efforts.

Energy and exergy analysis of a novel two-stage ejector refrigeration cycle using binary zeotropic mixtures

To improve the ejector refrigeration cycle performance, this paper presents a theoretical thermodynamic analysis of a novel two-stage ejector refrigeration cycle (TSERC) with a gas-liquid separator using R134a/R32 and R600a/R290 as refrigerant. By separating the relatively low-boiling-point and high-boiling-point refrigerants, the cycle compression ratio decreases, the cycle performance increases, and the energy utilization efficiency can be improved. Energy and exergy analysis were conducted for the traditional single-stage ejector refrigeration cycle (SSERC) and TSERC. The effect of the mixture mass fraction on cycle performance under a fixed external heat source operating condition was studied, and the cycle performance comparisons between TSERC and SSERC at different evaporation temperature, condensation temperature and generation temperature were conducted. Results show that for TSERC, the maximum COP values 0.126 and 0.11, the maximum exergy efficiency 4.51 % and 4 % are obtained as the low-boiling-point mass fraction equals 0.6 and 0.4 respectively for R134a/R32 and R600a/R290. It is found that exergy destruction mainly occurs in the low-pressure sub-cycle of TSERC, the top three largest exergy destruction components are ejector 1, condenser 1 and generator 1, while the smallest exergy destruction occurs in pump 2. In addition, cycle performance comparison between SSERC and TSERC shows that the maximum COP improvement increased by 41.6 % and 89.6 % for 134a/R32 and R600a/R290 for TSERC, while the maximum entrainment ratio improvement increased by 32.4 % and 87.6 %. Moreover, it is concluded that the cycle performance improvement of TSERC is more significant at lower evaporation temperature, higher condensation temperature, and lower generation temperature compared to SSERC.

Membrane electrolysis distillation for volatile fatty acids extraction from pH-neutral fermented wastewater

Volatile fatty acids (VFAs) serve as building blocks for a wide range of chemicals, but it is difficult to extract VFAs from pH-neutral wastewater using evaporation methods because of the ionized form. This study presents a new membrane electrolysis distillation (MED) process that extracts VFAs from such fermentation solutions. MED uniquely integrates pH regulation and joule heating to facilitate the efficient evaporation of VFAs. This integration occurs alongside a hydrophobic membrane that ensures effective gas-liquid phase separation. Operating solely on electricity, MED achieved an acid flux rate of 12.03 g/m2/h at 6V. In contrast, the control results without the joule heating or pH swing only obtained a 0.23 g/m2/h and 0.32 g/m2/h flux, respectively. In addition, a physicochemical model was developed to assess the impacts of temperature on membrane surface pH. This system enhances resource recovery from waste streams and helps achieve a circular carbon economy.

Co2+ - assisted continuous flow UV-induced Hg vapor generation coupled with a modified MSIS gas–liquid separator and microwave plasma atomic emission spectrometry

Co2+ - assisted continuous flow UV-induced Hg vapor generation coupled with a modified MSIS gas–liquid separator and microwave plasma atomic emission spectrometry

Facile scalable one-flow synthesis of ionizable cationic lipid library as precursors of nanoparticle carriers

A variety of ionizable and cationic lipids have been synthesized as precursors for nanoparticle carriers. However, the laborious synthetic routes in batch reactors often involve the use of toxic and carcinogenic agents, as well as challenge of removing gaseous byproducts. In this study, we present facile one-flow micro-reaction process that enables the synthesis of 11 ionizable lipids as well as 7 cationic lipids, including the well-known DODAP and DOTAP. These lipids can be scaled up to produce approximately ∼10g/h by using a straightforward size-up approach. The development of the lipid library was involved generating highly moisture-sensitive acyl chloride at 25 °C for 1.5 min. The toxic byproducts such as HCl, CO2 and CO were subsequently removed using a liquid–gas separator. The esterification with dimethylamino-1,2-diol at 25 °C for 3 min, monitored in-line with FTIR, completed the process. Additionally, the synthesized ionizable lipids were converted to cationic lipids with methyl sulfate, chloride ions via dimethyl sulfate and Steglich esterification in a continuous flow system. Finally, the produced DODAP was transformed into a uniform-sized LNPs (64 nm, PDI 0.07) and liposomal nanoparticles (72 nm, PDI 0.05) while DOTAP was converted to liposomes (55 nm, PDI 0.08) using a custom micro-mixer. This efficient platform for lipid synthesis significantly contributes to the practical applications of lipid-based nanomedicines.