Experimental and numerical investigation binary mixture mass transfer in a gas – Liquid membrane contactor

CO2 Absorption Using Hollow Fiber Membrane Contactors: Introducing pH Swing Absorption (pHSA) to Overcome Purity Limitation

Recently, membrane contactors have gained more popularity in the field of CO₂ removal; however, achieving high purity and competitive recovery for poor soluble gas (H₂, N₂, or CH₄) remains elusive. Hence, a novel process for CO₂ removal from a mixture of gases using hollow fiber membrane contactors is investigated theoretically and experimentally. A theoretical model is constructed to show that the dissolved residual CO₂ hinders the capacity of the absorbent when it is regenerated. This model, backed up by experimental investigation, proves that achieving a purity > 99% without consuming excessive chemicals or energy remains challenging in a closed-loop system. As a solution, a novel strategy is proposed: the pH Swing Absorption which consists of manipulating the acido–basic equilibrium of CO₂ in the absorption and desorption stages by injecting moderate acid and base amount. It aims at decreasing CO₂ residual content in the regenerated absorbent, by converting CO₂ into its ionic counterparts (HCO3− or CO32−) before absorption and improving CO₂ degassing before desorption. Therefore, this strategy unlocks the theoretical limitation due to equilibrium with CO₂ residual content in the absorbent and increases considerably the maximum achievable purity. Results also show the dependency of the performance on operating conditions such as total gas pressure and liquid flowrate. For N₂/CO₂ mixture, this process achieved a nitrogen purity of 99.97% with a N₂ recovery rate of 94.13%. Similarly, for H₂/CO₂ mixture, a maximum H₂ purity of 99.96% and recovery rate of 93.96% was obtained using this process. Moreover, the proposed patented process could potentially reduce energy or chemicals consumption.

Superhydrophobic Surface-Constructed Membrane Contactor with Hierarchical Lotus-Leaf-Like Interfaces for Efficient SO2 Capture

An organic-inorganic polyvinylidene fluoride/polyvinylidene fluoride-silica (PVDF/PVDF-SiO₂) mixed matrix membrane contactor is fabricated via a facile and efficient hydrophobic modification method. The solubility parameters of the PVDF particle are precisely regulated, the PVDF particles are blended with SiO₂ nanoparticles to form PVDF-SiO₂ suspension, and then the suspension is introduced onto the surface of the PVDF substrate by an in situ spin coating strategy. The PVDF particles are partly etched and incorporated to construct the adhesive PVDF-SiO₂ core-shell layer on the PVDF substrate, which results in a more stable PVDF-SiO₂ coating layer on the substrate. The surface structure is precisely regulated by changing the etching morphology of PVDF particles and amount of doped PVDF and SiO₂ particles, forming an integrated porous PVDF-SiO₂ layer and constructing hierarchical lotus-leaf-like interfaces. The resultant PVDF/PVDF-SiO₂ membrane contactors display the relatively regular distribution of pore size with ∼420 nm and excellent hydrophobic property with a water contact angle of ∼158°, which noticeably lightens wetting phenomena of membrane contactors. The SO₂ absorption fluxes can reach as high as 1.26 × 10^-3 mol·m^-2·s^-1 using 0.625 M of ethanolamine (EA) as liquid absorbent. The high stability of the SO₂ absorption flux test indicates the excellent interface compatibility between the PVDF-SiO₂ coating layer and the PVDF substrate. The versatile organic-inorganic layer exhibits super hydrophobic property, which prevents wetting of membrane pores. In addition, the membrane mass transfer resistance (H/K_m) and membrane phase transfer coefficient (K_m) are explored.

Hollow Fiber Membrane Contactors for Post-Combustion Carbon Capture: A Review of Modeling Approaches

Hollow fiber membrane contactors (HFMCs) can effectively separate CO2 from post-combustion flue gas by providing a high contact surface area between the flue gas and a liquid solvent. Accurate models of carbon capture HFMCs are necessary to understand the underlying transport processes and optimize HFMC designs. There are various methods for modeling HFMCs in 1D, 2D, or 3D. These methods include (but are not limited to): resistance-in-series, solution-diffusion, pore flow, Happel’s free surface model, and porous media modeling. This review paper discusses the state-of-the-art methods for modeling carbon capture HFMCs in 1D, 2D, and 3D. State-of-the-art 1D, 2D, and 3D carbon capture HFMC models are then compared in depth, based on their underlying assumptions. Numerical methods are also discussed, along with modeling to scale up HFMCs from the lab scale to the commercial scale.

Modeling and Simulation of the Simultaneous Absorption/Stripping of CO2 with Potassium Glycinate Solution in Membrane Contactor

Global warming is an environmental problem caused mainly by one of the most serious greenhouse gas, CO₂ emissions. Subsequently, the capture of CO₂ from flue gas and natural gas is essential. Aqueous potassium glycinate (PG) is a promising novelty solvent used in the CO₂ capture compared to traditional solvents; simultaneous solvent regeneration is associated with the absorption step. In present work, a 2D mathematical model where radial and axial diffusion are considered is developed for the simultaneous absorption/stripping process. The model describes the CO₂/PG absorption/stripping process in a solvent–gas membrane absorption process. Regeneration data of rich potassium glycinate solvent using a varied range of acid gas loading (mol CO₂ per mol PG) were used to predict the reversible reaction rate constant. A comparison of simulation results and experimental data validated the accuracy of the model predictions. The stripping reaction rate constant of rich potassium glycinate was determined experimentally and found to be a function of temperature and PG concentration. Model predictions were in good agreement with the experimental data. The results reveal that the percent removal of CO₂ is directly proportional to CO₂ loading and solvent stripping temperature.