Effects of coexistent gaseous components and fine particles in the flue gas on CO 2 separation by flat-sheet polysulfone membranes

Experimental Study on Postcombustion Systems Including a Hollow Fiber Membrane and a Packed Column

In this work, a comprehensive lab-scale carbon capture installation was established to study the separation performances of CO₂/N₂ systems for the postcombustion technology. Four kinds of mono-/two-stage carbon capture methods containing membrane separation and chemical absorption processes were investigated. The result shows that the CO₂ capture performance of the one-stage membrane separation method (Memb) exhibits a profitable CO₂ removal efficiency but defective CO₂ concentration, while the one-stage chemical absorption method (Chem) indicates both CO₂ removal efficiency and CO₂ purity of more than 95.0% but suffers a regeneration heat of at least 2.7 MJ/t CO₂. The CO₂ purity of the two-stage membrane separation method (Memb-Memb) is 46.2% higher than the Memb method because of the additional membrane pretreatment. Two-stage methods have a superior gas recovery efficiency of over 99.0%, which is dramatically higher than the homogeneous Memb method. In addition, the investigation on the hybrid chemical absorption-membrane separation method (Memb-Chem) provides an alternative approach to reduce the mass transfer and solve the problems caused by an unequal mass flow distribution.

Getting insight into the influence of coexisting airborne nanoparticles on gas adsorption performance over porous materials

Adsorption as one of the most important air cleaning methods has been extensively applied during which the coexisting airborne nanoparticles (NPs) with sizes close to adsorbent pore sizes could inevitably influence gas adsorption processes. In this work, the influence of sub-20 nm NPs on toluene adsorption on ZSM-5 zeolites exchanged with different cations (Li⁺, Na⁺ and K⁺) were studied based on gas-and-particle coexisting adsorption/filtration tests. Affinities for both toluene and NPs on adsorbents follow Li-ZSM-5 > Na-ZSM-5 > K-ZSM-5 regarding the orders of charge density, pore size, and internal and external specific surface areas. The toluene adsorption was shown to be impaired by coexisting NPs from perspectives of thermodynamics and kinetics. For Li-ZSM-5, Na-ZSM-5 and K-ZSM-5, significant relative reductions of 10.4 %, 10.5 % and 16.0 % in toluene adsorption capacity at the lower feed concentration, and of 20.3 %, 15.2 % and 2.3 % in mass transfer coefficient at the higher feed concentration were observed, respectively. The influential mechanisms regarding competitiveness between toluene and NPs in interaction with cationic and porous surfaces were accordingly proposed, which are of practical significance for selecting robust adsorbents under realistic harsh air conditions.

Evaluation of the Properties, Gas Permeability, and Selectivity of Mixed Matrix Membrane Based on Polysulfone Polymer Matrix Incorporated with KIT-6 Silica

Mixed matrix membranes (MMMs) separation is a promising technology for gas permeation and separation involving carbon dioxide (CO₂). However, finding a suitable type of filler for the formation of defect-free MMMs with enhancement in gas permeability remains a challenge. Current study focuses on synthesis of KIT-6 silica and followed by the incorporation of KIT-6 silica as filler into polysulfone (PSF) polymer matrix to fabricate MMMs, with filler loadings of 0–8 wt %. The effect of KIT-6 incorporation on the properties of the fabricated MMMs was evaluated via different characterization techniques. The MMMs were investigated for gas permeability and selectivity with pressure difference of 5 bar at 25 °C. KIT-6 with typical rock-like morphology was synthesized. Incorporation of 2 wt % of KIT-6 into PSF matrix produced MMMs with no void. When KIT-6 loadings in the MMMs were increased from 0 to 2 wt %, the CO₂ permeability increased by ~48%, whereas the ideal CO₂/CH₄ selectivity remained almost constant. However, when the KIT-6 loading in PSF polymer matrix was more than 2 wt %, the formation of voids in the MMMs increased the CO₂ permeability but sacrificed the ideal CO₂/CH₄ selectivity. In current study, KIT-6 was found to be potential filler for PSF matrix under controlled KIT-6 loading for gas permeation.

Colloidal Force Study of Particle Fouling on Gas Capture Membrane

Membrane fouling induced by industrial flue gas deteriorates their gas capturing efficiency, which is mainly caused by the adhesion of aerosol particles. To fully understand the mechanism of membrane fouling, a quantitative study of the adhesion force of particle on membrane surface was investigated by atomic force microscopy (AFM). The adhesion force of a single particle with flat glass, silicon wafer, PP (polypropylene) membrane, and fly-ash particles were measured within the relative humidity (RH) of 0 ~ 85%. The results showed the adhesion force of a particle with membrane have not much difference from the glass and silica wafer. And the surface roughness of flat substrate has slight effect on the adhesion force of the micrometer scale particle on flat surface at dry condition, while measured adhesion forces show obvious RH dependent for glass and membrane. Additionally, at dry conditions, the adhesion force of inter-particles also shows no obvious quantitative difference but obvious scattering comparing to that on membrane. The adhesion force of inter-particles increased more higher with the RH than that on membrane, which indicates the adhesion between micrometer scale particles can accelerate the deposition of particles on membrane and contributes the most to membrane fouling in industry atmosphere.

Gas permeation properties of polymer membranes containing ethylene glycol monomers

Copolymers based on glassy and rubbery units have been developed to take advantage of both domains to enhance solubility and diffusivity. In this study, a series of gas separation membranes from poly(ether sulfone)s containing ethylene glycol were synthesized via nucleophilic substitution polycondensation. The structures of copolymers were confirmed by proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectra. The permeability and selectivity of the membranes were studied at different temperatures of 25–55°C and pressures of 0.5–1.5 atm using single gases, such as carbon dioxide (CO2) and nitrogen (N2). Gas permeation measurements showed that copolymers with different content of poly(ethylene glycol) (PEG) exhibited different separation performances. For example, the membrane from polysulfone–PEG-20 containing 20 wt% PEG showed a better performance in terms of ideal selectivity over the other three copolymers membranes. The highest ideal CO2/N2 selectivity was 66.8 with CO2 permeability of 6.4 barrer at 1.5 atm and 25°C.

Alkyl amine and vegetable oil mixture-a viable candidate for CO2 capture and utilization

In this present work, the absorption of CO₂ in alkyl amines and vegetable oil mixture has been evaluated. The results showed that the absorption is higher in alkyl amines and vegetable oil mixture compared with the aqueous alkyl amines. In addition to that, by employing the greener and non-toxic vegetable oil media, the CO₂ gas has been captured as well as converted into value-added products, such as carbamates of ethylenediamine, diethylenetriamine, and triethylenetetramine. The carbamates have been isolated and characterized by Fourier transform infrared and ¹H and ¹³C nuclear magnetic resonance spectroscopic techniques. The formation of these products in precipitate form has not been observed in the case of aqueous medium. Among the various alkyl amine and vegetable oil combinations, triethylenetetramine in coconut oil medium showed the maximum CO₂ capture capacity of 72%. The coconut oil used for the process has been recovered, recycled, and reused for 3 cycles. Thus, this novel scheme seems to be a better alternative to conquer the drawback of aqueous amine-based CO₂ capture as well as for the capture and utilization of the CO₂ gas to gain the value-added products.