Abstract
Surface wettability-tailored porous ceramic/metallic membranes (in the tubular and planar disc form) were prepared and studied for both vapor-phase separation and liquid pervaporative separations of water-ethanol mixtures. Superhydrophobic nanoceramic membranes demonstrated more selective permeation of ethanol (relative to water) by cross-flow pervaporation of liquid ethanol–water mixture (10 wt % ethanol feed at 80 °C). In addition, both superhydrophilic and superhydrophobic membranes were tested for the vapor-phase separations of water–ethanol mixtures. Porous inorganic membranes having relatively large nanopores (up to 8-nm) demonstrated good separation selectivity with higher permeation flux through a non-molecular-sieving mechanism. Due to surface-enhanced separation selectivity, larger nanopore-sized membranes (~5–100 nm) can be employed for both pervaporation and vapor phase separations to obtain higher selectivity (e.g., permselectivity for ethanol of 13.9 during pervaporation and a vapor phase separation factor of 1.6), with higher flux due to larger nanopores than the traditional size-exclusion membranes (e.g., inorganic zeolite-based membranes having sub-nanometer pores). The prepared superhydrophobic porous inorganic membranes in this work showed good thermal stability (i.e., the large contact angle remains the same after 300 °C for 4 h) and chemical stability to ethanol, while the silica-textured superhydrophilic surfaced membranes can tolerate even higher temperatures. These surface-engineered metallic/ceramic nanoporous membranes should have better high-temperature tolerance for hot vapor processing than those reported for polymeric membranes.
Highlights
While there are many alternative energy sources starting to emerge for stationary power, the transportation energy market is primarily driven by the volatile price of fossil fuels
Results show that the perfluoro decyl trimethoxy silane (PDTMS)-based membrane was studied by both visual inspection and contact angle measurements (Figure 7)
◦ C, which is high enough for superhydrophobicity ofthe thePDTMS-based membrane surface can be stable up to show that superhydrophobicity of 300 the membrane surface can be stable up to 300 the example testing application conditions discussed in this paper
Summary
While there are many alternative energy sources starting to emerge for stationary power, the transportation energy market is primarily driven by the volatile price of fossil fuels. Membranes 2018, 8, 95 biomass to biofuels represents a vital option for producing a liquid renewable green energy source. The United States’ energy consumption is projected to rise by about 12% from 2012 to 2040. Renewable liquid fuels are projected to have the largest increase in production for meeting the United States’. Biochemical conversion [2,3], such as fermentation, is a major pathway for transforming solid biomass or sugar to liquid fuel, such as ethanol. Challenges exist to integrate separation technologies into the fermentation process to directly produce high-quality ethanol with high efficiency. Removing inhibitors (such as n-butanol) from the fermentation broth can increase ethanol production [4]. Ethanol produced at low concentrations in the bio-fermentation broth needs to be efficiently concentrated and dehydrated (purified) to qualify as a gasoline blend. The traditional distillation process utilized to concentrate ethanol is energy-intensive and has an azeotropic limitation for ethanol purification [5]
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