Further development of chemical and biological processes for production of bioethanol: Optimisation of pre-treatment processes and characterisation of products

A.B. Thomsen, A.S. Schmidt

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    Abstract

    The efficiency of several processes for pre-treatment of lignocellulose has been investigated to provide suitable feedstock for enzymatic hydrolysis and fermentation. Wet oxidation (with and without alkaline) has been investigated for wheat straw, birchwood, and willow treating 60 g/L. The conditions for willow and birchwood was selected based on the optimal conditions for wheat straw. Three different harvest years of wheat straw were included to evaluate the effect of crop variation from year to year. Comparative studies were made using steaming and steam explosion of wheat straw. Alkaline wet oxidation fractionated wheat straw efficiently into solubilised hemicellulose and a highly convertible cellulose fraction. High oxygen (12 bar) during treatment and low lignin in treated fibres resulted in highly convertible cellulose. Different optimal reaction conditions were found for different harvest years. For straw 1993 and 1997, the conditions were 185°C, 15 minutes resulting in 9-10 g/L solubilised hemicellulose and 63-67% cellulose convertibility. For straw 1994, the conditions were 195°C, 5 minutes resulting in 7.5 g/L solubilised hemicellulose and 96% cellulose convertibility. For willow, the optimal pretreatment was wet oxidation without alkaline using 185°C, 15 minutes (from 60 g willow/L). These conditions gave 8.2 g/L hemicellulose in solution and 50% cellulose convertibility, which was lower than that of wheat straw. High recoveries were obtained for willow compared to wheat straw. Addition of alkaline significantly decreased fractionation and degree of convertible cellulose. For birchwood, the best process conditions were hydrothermal treatment (without oxygen and alkaline). At 200°C and 15 minutes, 8 g/L hemicellulose was solubilised with high recoveries for both polysaccharides, however, poor cellulose convertibility was found (<30%). The addition of oxygen (wet oxidation) also resulted in a high fractionation but decreased the recoveries. Alkaline wet oxidation resulted in the highest cellulose convertibility but low content of solubilised hemicellulose (< 4 g/L). In general, formation of furfurals was avoided by adding alkaline to wet oxidation. In the absence of alkaline, furfural formation was higher (up to 130 mg/100 g wheat straw) than that of steam explosion (43 mg/100 g straw). Formation of carboxylic acids was highest during alkaline wet oxidation and highest for birchwood (up to 8 g/L). Minor amounts of phenolic compounds were identified after alkaline wet oxidation of wheat straw. However, some residual total organic carbon presumably high molecular weight components remained unidentified.
    Original languageEnglish
    Place of PublicationRoskilde
    PublisherRisø National Laboratory
    Number of pages73
    ISBN (Print)87-550-2533-1
    ISBN (Electronic)87-550-2535-8
    Publication statusPublished - 1999
    SeriesDenmark. Forskningscenter Risoe. Risoe-R
    Number1110(EN)
    ISSN0106-2840

    Keywords

    • Risø-R-1110
    • Risø-R-1110(EN)

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