Development of hydrophobic PVDF membranes using sustainable solvents and the incorporation of PEG and Gly as pore-formers for gas-liquid contactors

DEVELOPMENT OF HYDROPHOBIC PVDF MEMBRANES USING SUSTAINABLE SOLVENTS AND THE INCORPORATION OF PEG AND GLY AS PORE-FORMERS FOR GAS-LIQUID CONTACTORS A. Gálvez-Subiela*, R. Jiménez-Robles, G. Marco-Velasco, J. D. Badia, M. Izquierdo-Sanchis, V. Martínez-Soria Research Group in Materials Technology and Sustainability (MATS), Department of Chemical Engineering, School of Engineering, Universitat de València, Avda. Universitat s/n, 46100 Burjassot, Spain. ([email protected]). www.uv.es/mats PID2021-122495OA-I00: Development of functionalized polymer membrane contactors for improving the capture of CO2 and CH4 from industrial emissions TED-2021-131276-I00: Sustainable manufacturing of superhydrophobic membranes for the decarbonization of dissolved methane emissions from anaerobic digesters. PROJECTS Introduction Conclusions References Acknowledgements Project PID2021-122495OA-I00 financed by: Project TED2021-131276A-I00 financed by: In porous polymeric membrane contactors, pore wetting can occur in gas-liquid separation applications. This phenomenon is caused by the partial or total occupation of the pores by the liquid, increasing the membrane resistance to mass transfer and decreasing the separation efficiency. There are two key parameters in membrane properties that mitigate this phenomenon: hydrophobicity and pore size. Traditional manufacture of polymeric membranes involves the use of toxic solvents, such as N,N-dimethylformamide or N-methyl pyrrolidone. A modification of the preparation processes based on less toxic solvents such as triethyl phosphate (TEP) [1] could reduce the environmental impact of polymeric membrane manufacture. This work is focused on green poly (vinylidene fluoride) (PVDF) membrane preparation by the non-solvent induced phase separation method (NIPS), which is one of the focus of our projects controlling the hydrophobicity and pore size of membranes to improve its performance in dissolved methane (D-CH4) recovery from water. For this purpose, influence of polyethylenglycol (PEG) and glycerol (GLY) as pore-formers was studied. Membrane preparation 1. D. Kim, S.P. Nunes, Green solvents for membrane manufacture: Recent trends and perspectives, Curr Opin Green Sustain 28 (2021) 100427. 2. R. Jiménez-Robles, C. Gabaldón, J.D. Badia, M. Izquierdo, V. Martínez-Soria, Recovery of dissolved methane through a flat sheet module with PDMS, PP, and PVDF membranes, Sep Purif Technol 282 (2022) 120057. ✓ The use of TEP as green solvent has resulted in PVDF membranes with high hydrophobicity, near to 140°. ✓ The highest overall porosity was obtained using GLY at 2.5%wt as additive, whilst at higher concentrations porosity was decreased. On the other hand, PEG did not modify the overall porosity of the membrane until it exceeded 7.5%wt. ✓ The reduction in pore size observed at concentration of GLY of 7.5%wt could improve the membrane wetting resistance, thought its reduction in WCA and the overall porosity suggest to avoid GLY concentrations higher than 5%wt. ✓ Membranes prepared and used in D-CH4 recovery from water showed similar RE to commercial PVDF membranes. oMembrane contactor in flat-sheet configuration [2]. oWater saturated with CH4. (QL ≈ 21 L h-1) oN2 as sweep-gas. (QG ≈ 1 L min-1) oClosed water loop. [Removal efficiency (RE,%) at 5 hours] oGas chromatography analysis for determining dissolved CH4 concentration. RE =(D − CH4)t=0 h−(D − CH4)t=5 h (D − CH4)t=0 h x100 Dope preparation - 15%wt PVDF concentration using TEP as solvent. - PEG or GLY as additives between 0.0 and 10.0%wt. - Agitation at 200 rpm and 80ºC for 6 hours. Film casting - Automatic casting film applicator. - 500 µm casting knife height. - 30 mL sample volume. - 20 mm/s casting velocity at 80ºC. Membrane formation - Ethanol 96% non-solvent bath. - 500 mL non-solvent volume. - 3 hours of coagulation process. - Room temperature. Washing and drying - Distilled water to wash the surface. - 0.5 L min-1 synthetic air flow in a drying chamber. - Overnight drying at room temperature ( ≈ 25 ºC). 0.0 2.5 5.0 7.5 10.0 90 105 120 135 150 WCA (º) Additive concentration (%wt) PVDF PEG GLY Characterization techniques ➢Water ContactAngle (WCA): sessile drop method for quantification of surface hydrophobicity. ➢Overall porosity: gravimetric method with 1-octanol to mesure the internal porosity of membrane. ➢Scanning Electron Microscopy (SEM): for the inspection of the different structures of the membrane surface and cross-section. Results and discussion 0.0 2.5 5.0 7.5 10.0 0 20 40 60 80 100 Overall porosity (%) Additive concentration (%wt) PVDF PEG GLY Water contact angle and overall porosity oPVDF membranes with TEP as green solvent and without additives showed WCA of 140°, near to superhydrophobic regime (>150º). oThe use of PEG as a pore-forming additive did not decrease the WCA up to concentrations >7.5%wt. oThe increase in GLY concentration in the solution generated a loss of hydrophobicity in the material, unlike PEG. oIt was not possible to prepare membranes at GLY 10.0%wt due to the gelation of the solution under the tested conditions. oThe overall porosity of the obtained membranes using a green solvent and without additives was around 80%. oIncrease in PEG concentrations did not change the overall porosity of the membranes until it exceeded 7.5 %wt. oThe addition of GLY at low concentrations generated the highest overall porosity (86.2 ± 2.6%). oHigher concentrations of 2.5%wt of GLY showed decreases in the overall porosity of the membranes, reaching a minimum value near to 50% at a concentration of 7.5%wt. 0 10 20 30 40 50 RE (%), t = 5 h 2.5 %wt PEG 7.5 %wt PEG Commercial PVDF (Durapore Merk) oThe tested membranes showed good resistance and integrity in their application for D-CH4 recovery from water. oThe membranes produced with TEP as green solvent and PEG concentrations of 2.5 and 7.5%wt showed a similar RE to that of the commercial PVDF membrane after 5 hours of application. Surface and cross-section morphology Surface Cross-Section Additives 0.0%wt PEG 2.5%wt PEG 7.5%wt GLY 2.5%wt GLY 7.5%wt oThe surface of membranes with low PEG content (2.5%wt) showed an increase in the number of surface pores. A sponge-like structure was observed from the cross-section analysis, showing the presence of small channels inside. However, the channels presented a low uniformity. oWhen the PEG content was increased, the surface morphology and internal structure gain uniformity. The surface increased its pore size and the presence of pores, while the cross-section showed smaller but longer channels, keeping its sponge-like structure. oThe use of GLY as a pore-forming additive at 2.5%wt presented a morphology and surface porosity similar to that seen with PEG at 2.5%wt. The internal structure was composed of larger internal channels than PVDFPEG membranes. oWhen GLY content was increased to 7.5%wt the surface pore size was significantly and uniformly reduced. Also its cross-section changed to a dense internal structure that did not show the presence of pores. oThe SEM images of PVDF membranes showed the presence of non-homogeneous surface pores. The cross-section of the membrane showed large channels with an intermediate morphology between a finger-like and sponge-like structure. Liquid Feed tank Persitaltic pump Membrane module Liquid sampling point, CL Mass flow controller Gas sampling point, CG N2 Saturation column Mass flow controller CH4 On/off valve 3-way valve Degassed water Recirculated water Saturated water Recovered gas Out gas D-CH4 Performance of the membranes in dissolved-methane recovery from water PhD grant of R. Jiménez-Robles was funded by Ministerio de Universidades, Spain (Beca de Formación de Profesorado Universitario FPU19/02478).