Green solvents for Novolac-based carbon membranes production

Over the last three decades, carbon membranes (CMs) have gained attention as technology for gas separation. However, their fabrication often involves toxic and hazardous solvents with significant environmental impact, like N-methyl-2-pyrrolidone (NMP). In this work, Novolac-based CMs were developed using two greener and safer organic solvents, Cyrene™ and γ-valerolactone (GVL). Single gas permeation tests with He, H 2 , N 2 and CH 4 were conducted at temperatures from 20 °C to 200 °C and pressure differences (ΔP) between 1 and 5 bar. GVL led to the best performing CM, achieving an ideal selectivity of 340 the H 2 /CH 4 system at 20 °C. The GVL-derived CM exhibited a pore size distribution similar to that of the NMP-derived one, with 85.6 % ultra-micropores, 13.7 % micropores and 0.7 % mesopores. Raman spectroscopy, organic elemental analysis (OEA) and perm-porometry confirmed structural and chemical differences among the CMs fabricated with different solvent. This study highlights the potential of GVL as a safer and greener solvent for fabricating H 2 -selective Novolac-based CMs, representing a step forward towards a more sustainable CMs production. • Green solvents replace N-methyl-2-pyrrolidone in Novolac-based carbon membranes. • γ-Valerolactone enables defect-free Novolac-based carbon membranes for H 2 separation. • An isothermal step at 400 °C reduces pore size and enhances H 2 separation. • γ-Valerolactone membrane has 85.6 % ultra-micropores and 13.7 % micropores. • Selectivity of 270 (H 2 /N 2 ) and 340 (H 2 /CH 4 ) achieved at 20 °C with γ-valerolactone.