Green Synthesis of Cellulose Acetate Mixed Matrix Membranes: Structure–Function Characterization

Although membrane technology is widely used indifferent gas separation applications, membrane manufacturers need toreduce the environmental impact during the membrane fabricationprocess within the framework of the circular economy by replacing toxicsolvents, oil-based polymers, and such by more sustainable alternatives.These include environmentally friendly materials, such as biopolymers,green solvents, and surfactant free porous fillers. This work promotes theuse of environmentally sustainable and low toxic alternatives, introducingthe novel application of cellulose acetate (CA) as a biopolymer incombination with dimethyl carbonate (DMC) as a greener solvent anddifferent inorganic fillers (Zeolite-A, ETS-10, AM-4 and ZIF-8) preparedwithout the use of toxic solvents or reactants. Hansen Solubility Parameters were used to confirm the polymer−solvent affinity. PureCA and mixed matrix membranes were characterized regarding their hydrophilicity by water uptake and contact anglemeasurements, thermal stability by TGA, mechanical resistance, ATR-FTIR and scanning electron microscopy before evaluating thegas separation performance by single gas permeability of N2, CH4, and CO2. Conditioning of the CA membranes is observed causingreduction of the CO2 permeability values from 12,600 Barrer for the fresh 0.5 wt % ETS-10/CA membrane to 740 Barrer for the 0.5wt % ZIF-8/CA membranes, corresponding to 24% and 4.2% reductions in CO2/CH4 selectivity and 30% and 24% increase in CO2/N2 selectivity for the same membranes. The structure−relationship was evaluated by phenomenological models which are useful atlow filler loading considering flux direction and particle shape and size but still fail to explain the interactions between the DMCgreen solvent and CA matrix and fillers that are influencing gas transport performance different than other CA membranes.