Critical conditions for improved fermentability during overliming of acid hydrolysates from spruce.
ABSTRACT Bioethanol can be produced from wood via acid hydrolysis, but detoxification is needed to achieve good fermentability. Overliming was investigated in a factorial designed experiment, in which pH and temperature were varied. Degradation of inhibitory furan aldehydes was more extensive compared to monosaccharides. Too harsh conditions led to massive degradation of sugars and formation of inhibiting acids and phenols. The ethanol productivity and yield after optimal overliming reached levels exceeding reference fermentations of pure glucose. A novel metric, the balanced ethanol yield, which takes both ethanol production and losses of fermentable sugars into account, was introduced and showed the optimal conditions within the investigated range. The findings allow process technical and economical considerations to govern the choice of conditions for overliming.
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ABSTRACT: Ethanol produced from various lignocellulosic materials such as wood, agricultural and forest residues has the potential to be a valuable substitute for, or complement to, gasoline. This paper reviews the research activities in Sweden on development of the technology for ethanol production from lignocellulosics. The paper focuses on hemicellulose and cellulose hydrolysis and fermentation as well as on process integration and techno-economic evaluation of the overall process.
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ABSTRACT: One of the major problems in commercial production of lignocellulosic ethanol and xylitol, are the toxic compounds generated during the hydrolytic process. A concentrated hemicellulosic hydrolyzate from olive tree pruning residue has been detoxified using several methods in order to minimize the presence of inhibitory compounds, improving subsequent fermentation stage with yeasts. Thus, in a first stage, activated charcoal has been used to study the influence of pH, agitation, temperature and the proportion of this type of adsorbent, using a 24 experimental design. Further, liming and overliming processes were performed with three different alkalis, CaO, Ca(OH)2 and NaOH. Finally, the use of three organic solvents, chloroform, n-hexane and ethyl acetate, in four different proportions, 2:1, 1:1, 1:2 and 1:3 (hydrolyzate:solvent, v/v), was tested to achieve the toxic compounds elimination. In all assays we have checked the reduction in acetic acid, total phenolic compounds, furfural, hydroxymethylfurfural and total sugars concentrations. The volume loss of hydrolyzate has also been determined. In the adsorption processes with activated charcoal, the variables that have proved most influential on the responses tested were the percentage of this compound and pH. It could be an excellent alternative to decrease inhibitors from olive tree pruning residue hydrolyzates (removing 46% of acetic acid, 81% of phenolic compounds and 98% of total furans). The detoxification treatments with solvents revealed that the experimental conditions which combined the best inhibitor removal and lower alteration of sugar yields could be achieved using ethyl acetate because this extractor agent was able to remove near 50% of total phenolic compounds and 57% of total furans. Less favorable results were obtained when n-hexane was employed. The liming and overliming processes allowed a significant reduction of acetic acid (in some case up to 53%), lignin-derived compounds (close to 72%) and total furans (near 83%) mainly furfural, but also hydroxymethylfurfural.Industrial Crops and Products 08/2013; 49:196–203. · 3.21 Impact Factor
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ABSTRACT: Two treatments, an induced autohydrolysis and an acid hydrolysis, were applied to Eucalyptus globulus wood chips prior to the cooking stage to extract the hemicellulosic fraction that otherwise would be dissolved in the black liquor and burnt in the recovery boiler. The obtained hydrolysates, rich in xylose, were detoxified by overliming and used for ethanolic fermentation. Impacts of each wood pretreatment on the kraft cooking process and on the quality of the produced pulp were evaluated. Both pretreatments promoted an increase in the cooking rate, but had a negative effect on pulp quality and overall yield. Autohydrolysis showed a less negative influence. However, autohydrolysates led to lower values of ethanol concentration, productivity and yield compared to the fermentation of acid hydrolysates. To get more profit from the autohydrolysates they were also submitted to secondary acid hydrolysis and vacuum evaporation processes. Overliming followed by evaporation (with a concentration factor of 3) gave better results than the inverse method. This procedure raised the fermentable sugar content and led to the production of ethanol with a concentration of ~10 geth L-1 (productivity of 0.23 geth L-1 h-1 and yield of 0.50 geth gxyl eq -1) which compares well with the results obtained with the fermentation of acid hydrolysates.XXI TECNICELPA Conference and Exhibition - VI Iberoamerican Congress on Pulp and Paper Research - CIADICYP 2010; 10/2010