Development of 3D-Printed Membranes for the Production of Low-Carbon Intensity Biofuels

Rising energy demands and the excessive consumption of fossil fuels have led to increased greenhouse gas emissions, scarcity of resources, and fluctuating fuel prices, prompting the exploration of sustainable and viable alternative energy sources. Of them, renewable bioethanol has been widely considered due to the availability of biomass and recent efficiency gains in corn-to-ethanol conversion. However, despite these gains, the efficiency of bioethanol processing remains limited, largely due to the energy-intensive distillation and molecular sieving processes currently used to purify dilute aqueous solution from fermentation. Pervaporation, a method of membrane separation, is an alternative that has the potential to address the limitations of both distillation and molecular sieving given they can demonstrate the stability, selectivity, and low capital cost required for commercial viability. Minimizing capital cost, in particular, poses a challenge to conventionally casted pervaporation membranes as their uncontrolled and relatively high thickness limits their throughput and requires larger membrane areas. In this study, a novel 3D-printing process known as electrospray was implemented to fabricate one of the first thin-film composite pervaporation membranes in order to obtain greater control over membrane thickness and improve flux without any decrease in selectivity for ethanol dewatering. Electrospray works by depositing layers of nanoscale monomer droplets in the presence of a strong electric field, which then polymerize to create a thin film. Using this method, 1, 3, and 5% polyvinyl alcohol (PVA), the benchmark standard material used for ethanol dewatering membranes, and a 10% glutaraldehyde crosslinking solution were sequentially deposited on a polyacrylonitrile (PAN) substrate. Using profilometry, crosslinked 5% PVA membranes produced through additive manufacturing were found to range from 0.404 to 1.013 microns thick for 8 to 15 layers, noticeably thinner than the 30-plus micron range typically observed for casted PVA membranes. Membrane testing using a pervaporation system is currently in progress to determine the performance of printed membranes in separating a mixture of 90% ethanol and 10% water relative to commercially available as well as conventionally casted membranes.