Ethanol

Ethanol can be directly blended with gasoline, reacted with isobutylene to form the oxygenated fuel additive ethyl tert-butyl ether (ETBE), or burned directly as a neat fuel. Blends of either ethanol or ETBE with gasoline force engines set for gasoline to run lean and can substantially reduce carbon monoxide emissions. ETBE also lowers the overall vapor pressure, thereby cutting back on smog-forming emissions. Neat ethanol further reduces smog formation since it has a low volatility, the photochemical reactivity of ethanol and its combustion products is low, and low levels of smog producing compounds are formed by ethanol combustion. Neat ethanol also offers good engine performance owing to its high heat of vaporization, high octane, and low flame temperature. Fermentation stoichiometry reveals that many feedstocks are expensive for fuels production even considering coproduct credits and ignoring conversion costs, whereas lignocellulosic feedstocks cost much less than their value. Furthermore, the quantities of lignocellulosics are projected to be ample even for neat ethanol production. Release of carbon dioxide during fermentation concentrates almost all the heat of combustion from the solid carbohydrate portion in liquid ethanol. Since the carbon dioxide released during production and use of ethanol is recycled during growth of biomass, ethanol utilization doesn’t contribute to the accumulation of carbon dioxide in the atmosphere and possible global warming.     

Impact of fluid velocity on hot water only pretreatment of corn stover in a flowthrough reactor

Flowthrough pretreatment with hot water only offers many promising features for advanced pretreatment of biomass, and a better understanding of the mechanisms responsible for flowthrough behavior could allow researchers to capitalize on key attributes while overcoming limitations. In this study, the effect of fluid velocity on the fate of total mass, hemicellulose, and lignin was evaluated for hot water only pretreatment of corn stover in tubular flow through reactors. Increasing fluid velocity significantly accelerated solubilization of total mass, hemicellulose, and lignin at early times. For example, when fluid velocity was increased from 2.8 to 10.7 cm/min, xylan removal increased from 60 to 82% for hot water only pretreatment of corn stover at 200°C after 8 min. At the same time, lignin removal increased from 30 to 46%. Dissolved hemicellulose was almost all in oligomeric form, and solubilization of hemicellulose was always accompanied by lignin release. The increase in removal of xylan and lignin with velocity, especially in the early reaction stage, suggests that chemical reaction is not the only factor controlling hemicellulose hydrolysis and that mass transfer and other physical effects may also play an important trole in hemicellulose and lignin degradation and removal.     

Simultaneous saccharification and fermentation of lignocellulose

Simultaneous saccharification and fermentation (SSF) processes for producing ethanol from lignocellulose are capable of improved hydrolysis rates, yields, and product concentrations compared to separate hydrolysis and fermentation (SHF) systems, because the continuous removal of the sugars by the yeasts reduces the end-product inhibition of the enzyme complex. Recent experiments using Genencor 150L cellulase and mixed yeast cultures have produced yields and concentrations of ethanol from cellulose of 80% and 4.5%, respectively. The mixed culture was employed because B.clausenii has the ability to ferment cellobiose (further reducing end-product inhibition), while the brewing yeastS. cerevisiae provides a robust ability to ferment the monomeric sugars. These experimental results are combined with a process model to evaluate the economics of the process and to investigate the effect of alternative processes, conditions, and organisms.     

High solids simultaneous saccharification and fermentation of pretreated wheat straw to ethanol

Wheat straw was pretreated with dilute (0.5%) sulfuric acid at 140°C for 1 h. Pretreated straw solids were washed with deionized water to neutrality and then stored frozen at –20°C. The approximate composition of the pretreated straw solids was 64% cellulose, 33% lignin, and 2% xylan. The cellulose in the pretreated wheat straw solids was converted to ethanol in batch simultaneous saccharification and fermentation experiments at 37°C using cellulase enzyme fromTrichoderma reesei (Genencor 150 L) with or without supplementation with β–glucosidase fromAspergillus niger (Novozyme 188) to produce glucose sugar and the yeastSaccharomyces cerevisiae to ferment the glucose into ethanol. The initial cellulose concentrations were adjusted to 7.5, 10, 12.5, 15, 17.5, and 20% (w/w). Since wheat straw particles do not form slurries at these concentrations and cannot be mixed with conventional impeller mixers used in laboratory fermenters, a simple rotary fermenter was designed and fabricated for these experiments. The results of the simultaneous saccharification and fermentation (SSF) experiments indicate that the cellulose in pretreated wheat straw can be efficiently fermented into ethanol for up to a 15% cellulose concentration (24.4% straw concentration).     

Peroxycarbenium-mediated C-C bond formation: applications to the synthesis of hydroperoxides and peroxides

The Lewis acid-mediated reaction of alkene nucleophiles with peroxyacetals provides an effective route for the synthesis of homologated peroxides and hydroperoxides. In the presence of Lewis acids such as TiCl(4), SnCl(4), and trimethylsilyl triflate, peroxyacetals and peroxyketals undergo reaction with allyltrimethylsilane, silyl enol ethers, and silyl ketene acetals to afford homoallyl peroxides, 3-peroxyketones, and 3-peroxyalkanoates, respectively. Reactions of peroxyacetals are Lewis acid dependent; TiCl(4) promotes formation of ethers while SnCl(4) and trimethylsilyl triflate promote formation of peroxides. Lewis acid-promoted reactions of silylated hydroperoxyacetals furnish silylated hydroperoxides, which can be deprotected to homologated hydroperoxides. Hydroperoxyketals undergo Lewis acid-mediated allylation to furnish 1,2-dioxolanes via attack of hydroperoxide on the intermediate carbocation. Lewis acid-mediated cyclization of unsaturated peroxyacetals furnishes 1,2-dioxanes, 1,2-dioxepanes, and 1,2-dioxacanes through 6-endo/exo, 7-endo/endo, and 8-endo/endo pathways. The corresponding reactions involving 6-endo/endo and 5-endo/exo pathways were unsuccessful.     

Initial evaluation of simple mass transfer models to describe hemicellulose hydrolysis in corn stover

The uncatalyzed hydrolysis and removal of xylan from corn stover is markedly enhanced when operation is changed from batch to continuous flow through conditions, and the increase in hemicellulose removal with flow rate is inconsistent with predictions by widely used first-order kinetic models. Mass transfer or other physical effects could influence the hydrolysis rate, and two models reported in the literature for other applications were adapted to investigate whether incorporation of mass transfer into the kinetics could explain xylan removal in both batch and continuous flow through reactors on a more consistent basis. It was found that a simple leaching model and a pore diffusion/leaching model could describe batch and flow through data with accuracy similar to that of conventional batch models and could provide a more rational explanation for changes in performance with flow rate.     

Polymethacrylate Networks as Substrates for Cell Culture

Summary: methacrylate networks have a long history of applications in medical technology and much is known of their non-fouling properties. However, in recent times it has become clear that the swollen nature of these materials may provide some advantages if they are used as scaffolds in tissue engineering. In general however these hydrogels are resistant to protein adsorption and human cells do not easily adhere. In this work we provide an overview of several strategies that are designed to improve the cell-adhesive properties of hydrogels while maintaining their useful properties, mainly ease of diffusion of nutrients and growth factors. We describe our early attempts at modifying hydrogels based on 2,3-propandiol -1-methacrylate, with either hydrophobic units or acid groups. Modification with lauryl methacrylate produced an improvement but acid modification failed to provide surfaces that were conducive to cell culture. Much better scaffolds were prepared by amination of epoxy functional 2,3-propandiol-1-methacrylate networks. Optimized materials in this class were shown to be good substrates for the co-culture of bovine keratocytes with human corneal epithelial cells. We also describe the synthesis and biological properties of methacrylate conetworks, which phase separate during synthesis to give porous amphiphilic materials. Optimization of these materials produces materials that perform as well as tissue culture plastic so that confluent sheets of human dermal fibroblasts can be produced using standard culture techniques.