(278g) Effect of ZIF-8 and Lignin Nanoparticles in Pervaporation Separation of N-Butanol from Aqueous Solutions Using PDMS Based Mixed Matrix Membranes

Global energy demands are primarily met through non‐renewable sources such as coal, natural gas, and oil. However, the scarcity and rising prices of fossil fuels, coupled with environmental challenges lead researchers to find out a microbial alternative to address these issues. Biofuel has emerged as an attractive solution which can be effectively used in the current scenario. Among the probable list of alternatives, biobutanol is an important renewable biofuel, which can be easily integrated into existing fuels due to its better performance and other enviable advantages over other biofuels. It can be directly used in existing car engines without requiring any modifications.

Butanol is produced via acetone-butanol-ethanol (ABE) fermentation from renewable resources such as agricultural by-products. Therefore, it avoids the food vs. fuel debate. However, there are significant challenges to produce this alcohol as an economically viable biofuel. The most important challenge is improving fermentation performance to achieve higher butanol concentration and higher productivity. To improve the productivity in ABE fermentation process, the in-situ removal of the fermentation products, especially butanol as the most toxic one, from fermentation broth is essential.

In this study, pervaporation, a membrane-based process was studied for in situ separation of butanol. This technique has the greatest potential due to its high selectivity, low energy requirement and high efficiency. The primary objective of this study was to improve the performance of the Polydimethylsiloxane (PDMS) membrane for the pervaporation separation and the recovery of butanol by adding fillers into its matrix to make mixed matrix membranes (MMM). Lignin, the second most abundant natural polymer resin, and in situ synthesized Zinc-based Metal Organic Frameworks (ZIF-8) were used as fillers. Different lignin percentages and different membrane thicknesses along with the different sizes of ZIF-8 nanoparticles were used and the separation performances of these MMMs were compared to the neat PDMS. Different characteristics of lignin and ZIF-8 with their impact on the performance of the host membrane were discussed. Results showed that increasing lignin particles up to 10 wt% will improve MMM performance by 280% and 60% for flux and selectivity, respectively. This enhancement was reasonable due to the presence of hydrophobic porous lignin, which enlarged the free volume within the PDMS matrix and provided more permeation pathways for penetrants. On the other hand, by increasing the filler particle amount to 15 wt%, flux was improved by 40% but selectivity was reduced dramatically by 70%. The lignin agglomeration and low filler-polymer bonds at excessive loadings would be responsible for the water molecules (with smaller kinetic diameter than butanol) to more easily bypass the hydrophobic lignin particles, then diffuse to the next layer and make the membrane less selective. Also, by decreasing the membrane thickness, an improvement on flux was observed. In this scenario, in spite of the decreased selectivity, pervaporation separation index of the membrane improved.

Furthermore, separation performance of different ZIF-8/PDMS MMMs emphasized the effect of particle sizes and interfacial bond between particles and polymer so that decreasing the particle size up to 50% resulted in 92% and 218% improvement in the flux and selectivity, respectively.