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- Genre: Masters Thesis
Description
Emergent environmental issues, ever-shrinking petroleum reserves, and rising fossil fuel costs continue to spur interest in the development of sustainable biofuels from renewable feed-stocks. Meanwhile, however, the development and viability of biofuel fermentations remain limited by numerous factors such as feedback inhibition and inefficient and generally energy intensive product recovery processes. To circumvent both feedback inhibition and recovery issues, researchers have turned their attention to incorporating energy efficient separation techniques such as adsorption in in situ product recovery (ISPR) approaches. This thesis focused on the characterization of two novel adsorbents for the recovery of alcohol biofuels from model aqueous solutions. First, a hydrophobic silica aerogel was evaluated as a biofuel adsorbent through characterization of equilibrium behavior for conventional second generation biofuels (e.g., ethanol and n-butanol). Longer chain and accordingly more hydrophobic alcohols (i.e., n-butanol and 2-pentanol) were more effectively adsorbed than shorter chain alcohols (i.e., ethanol and i-propanol), suggesting a mechanism of hydrophobic adsorption. Still, the adsorbed alcohol capacity at biologically relevant conditions were low relative to other `model' biofuel adsorbents as a result of poor interfacial contact between the aqueous and sorbent. However, sorbent wettability and adsorption is greatly enhanced at high concentrations of alcohol in the aqueous. Consequently, the sorbent exhibits Type IV adsorption isotherms for all biofuels studied, which results from significant multilayer adsorption at elevated alcohol concentrations in the aqueous. Additionally, sorbent wettability significantly affects the dynamic binding efficiency within a packed adsorption column. Second, mesoporous carbons were evaluated as biofuel adsorbents through characterization of equilibrium and kinetic behavior. Variations in synthetic conditions enabled tuning of specific surface area and pore morphology of adsorbents. The adsorbed alcohol capacity increased with elevated specific surface area of the adsorbents. While their adsorption capacity is comparable to polymeric adsorbents of similar surface area, pore morphology and structure of mesoporous carbons greatly influenced adsorption rates. Multiple cycles of adsorbent regeneration rendered no impact on adsorption equilibrium or kinetics. The high chemical and thermal stability of mesoporous carbons provide potential significant advantages over other commonly examined biofuel adsorbents. Correspondingly, mesoporous carbons should be further studied for biofuel ISPR applications.
ContributorsLevario, Thomas (Author) / Nielsen, David R (Thesis advisor) / Vogt, Bryan D (Committee member) / Lind, Mary L (Committee member) / Arizona State University (Publisher)
Created2011
Description
ABSTRACT Among the major applications of pervaporation membrane processes, organic separation from organic/water mixtures is becoming increasingly important. The polydimethylsiloxane (PDMS) is among the most interesting and promising membranes and has been extensively investigated. PDMS is an "organicelastomeric material, often referred to as "silicone rubber", exhibiting excellent film-forming ability, thermal stability, chemical and physiological inertness. In this thesis incorporation of nanosilicalite-1 particles into a PDMS matrix and effect of particle loading and temperature variation on membrane performance was studied. A strong influence of zeolite was found on the pervaporation of alcohol/water mixtures using filled PDMS membranes. The mixed matrix membrane showed high separation factor at higher zeolite loading and high flux at higher temperature.
ContributorsYadav, Amit Binodkumar (Author) / Lind, Mary L (Thesis advisor) / Lin, Jerry Ys (Committee member) / Nielsen, David R (Committee member) / Arizona State University (Publisher)
Created2012
Description
Freshwater is becoming more and more scarce, and the need to make use of other water resources is critical. Although processes such as Sea Water Reverse Osmosis (SWRO) exist, these processes are not without drawbacks, such as a brine with a high salt concentration being a byproduct of SWRO. Pervaporation is a potential solution to this problem, however the membranes used in these processes are prone to fouling and the high salt conditions are difficult to work around. Incorporating zwitterions into the polymeric backbone of these membranes has proven to be an effective way to increase fouling resistance. In this work, sulfobetaine – based zwitterions were incorporated into the backbone of poly(arylene ether sulfone) to synthesize sulfobetaine – modified poly(arylene ether sulfone) (SB-PAES) membranes, which were then tested in a cross-flow pervaporation apparatus to analyze salt rejection. SB-PAES membranes were cast with two different methods to create a consistent casting protocol. It was determined that casting solutions with a lower weight percent in petri dishes was optimal, but still needs more exploration. The SB-PAES membranes were tested with feed solutions of pure water and salt solutions with concentrations of 1 g/L, 5 g/L, and 10 g/L. Both 50% and 25% charge SB-PAES membranes were tested. The 50% charge membranes showed good flux and salt rejection over 99.9% for a 10 g/L feed solution, while the 25% charge membranes showed less flux and salt rejection around 85% for a feed solution of 10 g/L.
ContributorsMartin, Adam Lau (Author) / Green, Matthew D (Thesis advisor) / Lind, Mary L (Committee member) / Seo, Soyoung E (Committee member) / Arizona State University (Publisher)
Created2022