Cellulose-driven supported liquid membranes with (choline chloride)-based deep eutectic solvents for CO2 separation from biogas.

Introduction. Gas separation membranes enable technologies that use selective permeation to separate gas mixtures of interest, such as biogas or flue gas, thereby reducing greenhouse gas emissions. Adding liquid additives to the polymer matrix creates supported liquid membranes (SLMs), which can improve their CO₂ capture performance. Neoteric additives like deep eutectic solvents (DESs) can be used for SLM production due to their highly adjustable compositions, suitable to tailor task-specific membranes. In this work, This study investigates the impact of different choline chloride (ChCl)-based DES on the stability, physicochemical properties and CO₂/CH₄ separation of DES-based SLMs (DSLMs) using different cellulose-based materials as a polymeric substrate, such as regenerated cellulose (RC), cellulose nitrate (CN) and cellulose acetate (CA).

Methods. DES used in this work were based on ChCl as a hydrogen bond acceptor and different hydrogen bond donors: urea (U), glycerol (Gly) or Malic acid (MalAc) among others. DSLMs were produced by a vacuum assisted method. Structural, morphological and thermal properties of membranes were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX).

Results Single- and mixed-gas tests were conducted and permeability and selectivity of CO₂/CH₄ (αCO₂/CH₄) was calculated. FTIR spectroscopy confirmed the presence of DESs within the polymeric structure. In general, αCO₂/CH₄ of the studied membranes resulted to be competitive with those reported in specialized literature, above 100 in some cases such as ChCl:U SLMs.

Conclusions. DES-based SLMs developed in this work demonstrated strong potential for selective CO₂ separation while also presenting a greener approach within carbon capture technologies, making them promising candidates for carbon capture technologies, including environmental applications such as biogas upgrading.