Polyethyleneglycol-Modified Cellulose Acetate Membrane for Efficient Olefin/Paraffin Separation

Olefin/paraffin separation is one of the most challenging processes in the gas separation field. Nowadays, membrane technology has emerged as a promising alternative for the current energy-intensive cryogenic distillation. Due to the demonstration of higher selectivity of glassy polymers, these polymers are preferred in this regard. Herein, polyethylene glycol (PEG), known as a plasticizer, was used to blend with glassy cellulose acetate (CA) and enhanced its permeability and separation factor over ethylene and propylene. The existence of all specific bands for CA and PEG was proved using Fourier transform infrared analysis. Changes in the glass-transition temperature (T-g) of the membrane were investigated through differential scanning calorimetry analysis, which confirmed that a uniform blending was attained. With the addition of PEG up to 30 wt %, T-g and crystallinity of the membranes also decreased. The scanning electron microscopy results indicated a uniform dense structure for the pristine membrane, which changed into a grooved structure upon addition of PEG due to the created intermolecular interaction. The gas separation test indicated that upon addition of different amounts of PEG to the polymer matrix at 2 bar pressure, the gas separation performance of all the blended membranes improved. Ethylene permeability showed 56% increase from 0.59 in neat CA to 0.92 Barrer in a CA/30 wt % PEG membrane. A similar enhancement was also seen in propylene permeability, which increased from 0.57 to 0.91 Barrer. Addition of PEG into the polymer matrix increased the selectivity of ethylene/ethane from 2.185 for the pristine membrane to 2.484 for the 30 wt % PEG membrane. Moreover, the selectivity of propylene/propane increased from 2.375 to 3.033. The gas separation performance of all the blended membranes also enhanced upon increasing the feed pressure in all membranes. The selectivity of ethylene/ethane enhanced from 2.48 to 2.57 and that of propylene/propane increased from 3.033 to 3.52 at a pressure of 10 bar.

Automated summary

In this study, polyethylene glycol modified glassy cellulose acetate membranes were developed to enhance their permeability and separation performance for ethylene/propylene. The addition of polyethylene glycol resulted in a decrease in the glass transition temperature and crystallinity of the membranes, and a change in the membrane structure was observed. Gas separation tests showed that the addition of polyethylene glycol improved the gas separation performance of the membranes, and the performance further enhanced with increasing feed pressure.