Gas permeation and pervaporation of water/alcohols through the microporous carbon membranes prepared from resorcinol/formaldehyde/quaternary ammonium compounds

Ultra-Selective CMSMs Derived from Resorcinol-Formaldehyde Resin for CO2 Separation

A resorcinol-formaldehyde precursor was synthesized to fabricate the CO₂ selective Carbon Molecular Sieve Membranes (CMSMs) developed in this study. The degree of polymerization (DP) was analyzed via Gel Permeation Chromatography (GPC) and its effect on the CO₂/N₂ perm-selectivity and CO₂ permeance was investigated. The membrane that was polymerized at 80 °C (named R80) was selected as the best performing CMSM after a preliminary test. The post treatment with oxidative atmosphere was performed to increase the CO₂ permeance and CO₂/N₂ perm-selectivity on membrane R80. The gas permeation results and Pore Size Distribution (PSD) measurements via perm-porometry resulted in selecting the membrane with an 80 °C polymerization temperature, 100 min of post treatment in 6 bar pressure and 120 °C with an oxygen concentration of 10% (named R80T100) as the optimum for enhancing the performance of CMSMs. The 3D laser confocal microscopy results confirmed the reduction in the surface roughness in post treatment on CMSMs and the optimum timing of 100 min in the treatment. CMSM R80T100 exhibiting CO₂/N₂ ideal selectivity of 194 at 100 °C with a CO₂ permeability of 4718 barrier was performed higher than Robeson's upper bound limit for polymeric membranes and also the other CMSMs fabricated in this work.

Process Variable Optimization in the Manufacture of Resorcinol⁻Formaldehyde Gel Materials

Influence of process parameters of resorcinol–formaldehyde xerogel manufacture on final gel structure was studied, including solids content, preparation/drying temperature, solvent exchange, and drying method. Xerogels produced using a range of solids content between 10 and 40 w/v% show improved textural character up to 30 w/v% with a subsequent decrease thereafter. Preparation/drying temperature shows a minimal threshold temperature of 55 °C is required to obtain a viable gel structure, with minimal impact on gel properties for further thermal increase. Improving the solvent exchange method by splitting the same amount of acetone used in this phase over the period of solvent exchange, rather than in a single application, shows an increase in total pore volume and average pore diameter, suggesting less shrinkage occurs during drying when using the improved method. Finally, comparing samples dried under vacuum and at ambient pressure, there seems to be less shrinkage when using vacuum drying compared to ambient drying, but these changes are insubstantial. Therefore, of the process parameters investigated, improved solvent exchange seems the most significant, and it is recommended that, economically, gels are produced using a solids content of 20 w/v% at a minimum temperature of 55 °C, with regular solvent replenishment in the exchange step, followed by ambient drying.