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    The electrochemistry of alcohols in aqueous phosphate electrolytes under reducing conditions : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Chemistry, Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Wise, Nessha M.
    Few methods are available for the routine reduction of alcohols in synthetic chemistry. These few are dominated by reduction with HI/I2, LiAlH4 or Li/NH3 and typically involve severe conditions for other functionalities and there is little research into less severe synthetic or electrochemical methods. There is also limited mechanistic or kinetic information available for these reduction methods. This leaves an interesting area for development within fundamental knowledge. The development of an effective process for the reduction of alcohols could have many applications in pharmaceutical and chemical industries along with many environmental and economical benefits. A preliminary study on a range of electrodes established an electrochemical reduction response observed for a number of water-soluble alcohols on rotating disc copper, tin and lead electrodes in 0.1 M phosphate buffers. A response was observed for ethanol, propanol, propan-2-ol and butanol on copper rotating disc electrodes in the 0.1 M phosphate buffer. Reduction of the alcohols at the copper disc electrodes was observed at pH 8.1 with the production of a limiting current plateau. The reduction was found to be continuous and reproducible. The observed limiting current was found to increase with both increasing concentration and increasing electrode rotation rate. A Koutecky-Levich study suggested the reduction of the alcohol occurred through both mass transport and kinetic processes. A discrete, reproducible response was observed for ethanol, propanol and propan-2-ol on tin rotating disc electrodes in the 0.1 M phosphate buffer electrolyte at pH 7.3. A reductive peak was observed at −1.1 V vs Ag/AgCl in cyclic voltammetry. This formation of a reductive peak suggests that the reduction becomes progressively hindered, proposed to be due to a passivating layer forming on the surface of the electrode. The charge associated with the peak is relatively invariant with alcohol concentration (in the range 7−20 mM) and with scan rate (over the range 10−500 mV s−1). In the case of ethanol, the peak charge is typically found to be in the range 2.9−3.6 C m−2 suggesting that a passivating layer of reaction products forms with an area of 8.8−10.8 Ǻ2 for each adsorbed molecule (assuming a 2-electron process and a surface roughness factor of one). This suggests formation of a monolayer with sparsely located binding sites. The peak charge does not change with increasing electrode rotation rate, not inconsistent with the formation of a passivating layer on the surface of the electrode inhibiting any further reduction. A discrete response was also observed for ethanol, propanol and propan-2-ol on lead rotating disc electrodes in the 0.1 M phosphate buffer electrolyte at pH 8.1. A reduction peak is observed at −0.9 V vs Ag/AgCl in cyclic voltammetry. This suggests that the reduction becomes progressively hindered due to a proposed passivating layer. The passivating layer is not permanent – employing a > 30 second open-circuit rest period or having an anodic limit more positive than −0.6 V will result in the new reduction peak for each subsequent voltammogram. Multiple-cycle voltammograms exhibit only the background response if these conditions are not met. The charge associated with the peak decreases with scan rate (over the range 10−500 mV s−1) but is relatively invariant with alcohol concentration (in the range 7−20 mM). In the case of ethanol, the peak charge is typically found to be in the range 0.5−4.0 C m−2 suggesting that a passivating layer of reaction products forms with an area of 19−58 Ǻ2 for each adsorbed molecule (assuming a 2−electron process and a surface roughness factor of one). This suggests formation of a monolayer with sparsely located binding sites. The peak charge decreases with increasing electrode rotation rate. It is proposed that this is due to a surface chemical reaction following the electrochemical process – it is the product of this chemical reaction that results in a transient passivating monolayer. FT−IR analyses of the lead disc systems suggest possible products to be propandiol and butandiol.
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    Intensification of the acetone, butanol, ethanol fermentation using whey permeate and Clostridium acetobutylicum : a preliminary study : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biotechnology at Massey University
    (Massey University, 1987) Ennis, Brett Mills
    The use of whey permeate as the fermentation substrate for the production of acetone:butanol:ethanol (solvents), using C. acetobutylicum P262 was studied. Initial experiments were conducted in a batch mode using sulphuric acid casein whey permeate medium, in an attempt to optimize the culture conditions for maximal extent of lactose utilization and solvents production. A high initial lactose concentration (65-75 g/l) in combination with a culture pH maintained in the region pH 5.4 to 5.6 were the most favourable conditions for solvent production. An inverse relationship between the lactose utilization rate and solvents yield was observed. Solvent productivities were only 60% however, of that achievable with this strain of organism on an industrial scale using a molasses medium, but comparable productivities were obtained using a semi-synthetic medium containing glucose. Hydrolysed-lactose sulphuric acid casein whey permeate medium was investigated as a medium for solvent production. Glucose and galactose were utilized simultaneously, although glucose was used preferentially. Only a small increase in solvents productivity was obtained compared with that obtained using non-hydrolysed permeate. Experiments were performed in continuous culture using cheese whey permeate medium and alginate-immobilized cells. Significantly greater solvent productivities were obtained, compared with those achieved using free cells in batch culture. Fermentations were operated for over 650 hours with no detectable loss in fermentation performance. The extent of lactose utilization was low, however (less than 40%), and attempts to increase this by the use of pH regulation or a two-stage process were unsuccessful. This fermentation process was described as a biomass volume process (volumetric fraction of alginate beads in the reactor), where the lactose utilization and hence the solvents production, was defined by an inhibitory concentration of butanol, approximately 5 g/l. An alternative continuous fermentation process using free cells and cheese whey permeate medium was investigated. External cell recycle using cross-flow microfiltration (CFM) membrane plant to continuously separate cells from the fermentation culture and recycle them back to the fermenter was utilized. Biomass was continuously removed from the fermenter in order to achieve a stable biomass concentration. Stable solvents production was not achieved under the range of culture conditions investigated; culture degeneration was attributed to the complex interactive morphological cyclic behaviour of the organism. A tubular CFM unit which could be periodically backflushed to maintain the filtrate flux, was found to be the most suitable of those tested. The integration of in-situ or in-line solvents recovery with batch culture using free cells, and continuous fermentation using cells immobilized by adsorption to bonechar, was investigated in order to remove toxic solvents and so increase the extent of lactose utilization and solvents productivity. A novel process using gas-stripping with an inert gas, and solvents recovery from the vapour phase by condensation using a cold trap, was described. An increase in lactose utilization and solvents productivity was achieved in both fermentation modes compared with control fermentations. The use of adsorbent resins and a molecular sieve for integrated fermentation solvents recovery was also demonstrated. However, the adsorption of medium components may mitigate against the usefulness of such a process option. The batch refermentation of batch fermentation effluent treated by gas-stripping to remove solvents was investigated. However, solvent production was favoured only when lactose and nutrients were supplemented to concentrations similar to those present originally. Conversely, fermentation medium treated by gas-stripping to remove solvents could be readily refermented to produce solvents when an existing cell population was used, suggesting that this option of an integrated continuous fermentation-product recovery process may be promising for whey permeate solvent production.