Browsing by Subject "carboxylic acids"
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Item Anaerobic fermentation of rice straw and chicken manure to carboxylic acids(Texas A&M University, 2007-04-25) Agbogbo, Frank KwesiIn this work, 80% lime-treated rice straw and 20% lime-treated chicken manure were used as substrates in rotary fermentors. Countercurrent fermentation was performed at various volatile solid loading rates (VSLR) and liquid residence times (LRT). The highest acid productivity of 1.69 g/(L????d) was at a total acid concentration of 32.4 g/L. The highest conversion and yield were 0.692 g VS digested/g VS fed and 0.29 g total acids/g VS fed, respectively. The continuum particle distribution model (CPDM) was used to predict product concentrations at various VSLR and LRT. CPDM predicted the experimental total acid concentration and conversion at an average error of 6.41% and 6.55%, respectively. A fixed-bed fermentation system was designed to perform pretreatment and fermentation in the same unit. High product concentrations (~48 g/L) as well as high conversions (0.741 g VS digested/g VS fed, F4, Train B) were obtained from the same fermentor. CPDM was extended to predict product concentrations in the fixed-bed fermentation system. The model gave a good estimate of the product concentrations and retention time. After biomass fermentation, the residue can be combusted to generate heat. For pretreatment purposes, the use of ash can replace lime. A study was performed using ash as a potential pretreatment agent. Ash from raw poplar wood was effective in pretreating poplar wood; however, ash from bagasse fermentation residues was not useful in pretreating bagasse. Previous modeling studies indicate that a conversion of 95% could be achieved with bagasse using countercurrent fermentation. Because lignin constitutes 13% of the dry weight of bagasse, this means lignin would have to be digested to obtain a conversion of 95%. Experiments on the fermentation of enzymatically liberated lignin from both poplar wood and bagasse do not show that solubilized lignin was fermented to organic acids by using a mixed culture of marine microorganisms. Two buffer systems (ammonium bicarbonate and calcium carbonate) were used to compare product concentrations of carboxylic acid fermentations using office paper and chicken manure. It has been demonstrated that the total product concentration using ammonium bicarbonate is almost double the product concentration using calcium carbonate.Item Conversion of CO2 to Polycarbonates and Other Materials: Insights through Computational Chemistry(2014-09-25) Yeung, Andrew DThe use of carbon dioxide as a chemical feedstock for the copolymerization with epoxides to give polycarbonates, and for coupling with hydrocarbons to give carboxylic acids, was probed using computational chemistry. Metal-free systems were modeled at high levels using composite methods that give ?chemical accuracy?, whereas metal-bound systems were studied using density functional theory, benchmarked to these high-accuracy results for confidence. The thermodynamics of polymer vs. cyclic carbonate formation was calculated, and polymer is the exothermic product, whereas cyclic carbonate is the entropic product. The barriers for the metal-free carbonate and alkoxide backbiting reactions were also determined, carbonate backbiting having a higher barrier than alkoxide backbiting. The base degradation of polymers to epoxide co-monomers, and the acid- and base-catalyzed degradation of glycerol carbonate to glycidol were investigated too. Poly(cyclopentene carbonate) preferentially degrades to epoxide co-monomer instead of cyclic carbonate due to angle strain for alkoxide backbiting. Conversely, glycerol carbonate only yields glycidol instead of the isomeric 3-hydroxyoxetane because formation of the latter has a higher barrier. The (salen)Cr(III)- and (salen)Co(III)-catalyzed copolymerization reactions were studied for a variety of epoxides, and the overall displacement of a polymeric carbonate by an epoxide, followed by ring-opening, was found to be rate limiting. Chromium(III)-catalyzed systems have higher free energy barriers than cobalt(III) systems due to enthalpy, which explains why such polymerization reactions have to be run at higher temperatures. The metal-bound polymer carbonate and alkoxide backbiting reactions generally have higher barriers than when unbound, due to the terminal oxygen atoms? reduced nucleophilicity. The carboxylation of metal-hydride and metal-carbon bonds was studied for a series of trans-ML2XY complexes, and thermodynamics of carboxylation of the M-X bond are influenced by M, L, and Y, in decreasing order. Similar cis-complexes did not exhibit as clear trends. Examination of these complexes indicated that the three steps for the overall conversion of hydrocarbons to carboxylic acids (oxidative addition of hydrocarbon, carboxylation, and reductive elimination of the carboxylic acid) must be optimized in parallel for the successful direct synthesis of carboxylic acids.Item Conversion of sugarcane bagasse to carboxylic acids under thermophilic conditions(2009-05-15) Fu, ZhihongWith the inevitable depletion of the petroleum supply and increasing energy demands in the world, interest has been growing in bioconversion of lignocellulosic biomass (e.g., sugarcane bagasse). Lignocellulosic biomass is an abundant, inexpensive, and renewable resource. Most of current conversion technologies require expensive enzymes and sterility. In contrast, the patented MixAlco process requires no enzymes or sterility, making it attractive to convert lignocellulosic biomass to transportation fuels and valuable chemicals. This study focuses on pretreatment and thermophilic fermentation in the MixAlco process. Ammonium bicarbonate (NH4HCO3) was discovered to be a better pH buffer than previously widely used calcium carbonate (CaCO3) in anaerobic fermentations under thermophilic conditions (55?C). The desired pH should be controlled within 6.5 to 7.5. Over 85% acetate content in the product was found in paper fermentations and bagasse fermentations. Hot-lime-water-treated bagasse countercurrent fermentations buffered by ammonium bicarbonate achieved 50?60% higher total product concentrations than those using calcium carbonate. It was nearly double in paper batch fermentations if the pH was controlled around 7.0. Ammonium bicarbonate is a ?weak? methane inhibitor, so a strong methane inhibitor (e.g., iodoform) is still required in ammonium bicarbonate buffered fermentations. Residual calcium salts did not show significant effects on ammonium bicarbonate buffered fermentations. Lake inocula from the Great Salt Lake, Utah, proved to be feasible in ammonium bicarbonate buffered fermentations. Under mesophilic conditions (40?C), the inoculum from the Great Salt Lake increased the total product concentration about 30%, compared to the marine inoculum. No significant fermentation performance difference, however, was found under thermophilic conditions. The Continuum Particle Distribution Model (CPDM) is a powerful tool to predict product concentrations and conversions for long-term countercurrent fermentations, based on batch fermentation data. The experimental acid concentrations and conversions agree well with the CPDM predictions (average absolute error < 15%). Aqueous ammonia treatment proved feasible for bagasse. Air-lime-treated bagasse had the highest acid concentration among the three treated bagasse. Air-lime treatment coupled with ammonium bicarbonate buffered fermentations is preferred for a ?crop-tofuel? process. Aqueous ammonia treatment combined with ammonium bicarbonate buffered fermentations is a viable modification of the MixAlco process, if ?ammonia recycle? is deployed.Item Recovery of Carboxylic Acids from Fermentation Broth via Acid Springing(2010-01-14) Dong, JipengA proprietary technology owned by Texas A