| Practices and procedures developed during this project resulted in a fivefold increase in ethanol production compared to the results from initial batches of wood extracts. One of the most significant contributors to the gain in ethanol production came from a decision to convert sugars from oligomer to monomer form. Other factors of importance were inhibitor content, and selection of a promising microorganism.;As the second most abundant polysaccharide found in nature, hemicellose is a potential feedstock for ethanol production. Compared to cellulose, hemicellulose is advantageous because it is relatively easy to extract and hydrolyze to monomeric units. The carbohydrate content in hemicellulose extract is an important factor in ethanol fermentation as hemicellulose is a heteropolymer of 5- and 6- carbon sugars, which can contain both oligomer and monomer units, however many microorganisms can only utilize monomers. Another important factor influencing ethanol yield were inhibitory compounds released or formed during extraction and hydrolysis of the hemicellulose. It was determined that nano-filtration/diafiltration was an effective in reducing inhibitor concentrations. A third influential factor was the microorganism; six xylose fermenting microorganisms were tested for their capability to ferment ethanol from the Sugar Maple hemicelluloses extracts. One strain, Scheffersomyces (Pichia) stipitis NRRL Y-11543 was selected for further experiments due to consistently producing higher ethanol concentrations than the other strains. Fermentation of initial batches resulted in ethanol concentrations of about 5-7 g/L ethanol while later batches produced 35 g/L ethanol with a yield of 0.38 g/g without further detoxification following the membrane diafiltration.;In order to study the fermentation of hydrolysates, several different analytical methods were used in the analysis of the hemicellulosic fermentation broth including high performance liquid chromatography (HPLC), gas chromatography (GC), spectrophotometric methods, and both proton and two dimensional nuclear magnetic resonance (NMR) spectroscopy. A 1H-13C heteronuclear single quantum coherence (HSQC) NMR method was determined to be the best for the analysis of the hemicellulosic hydrolysates used in this project, because NMR has the ability to distinguish between the different monosaccharides and oligomers present in the media, as well as several of the inhibitory compounds and the ethanol in the fermentation broth. |
