Studies in the Liquefaction of Biomass

Abstract

When cellulose is heated to 350°C in aqueous phenol in the presence of zinc chloride a variety of products are formed; these were fractionated chemically into five classes: A, water soluble carbohydrate products; B, acidic products; C, neutral, organic soluble compounds; D, gases; C, char. Qualitative and quantitative analysis of the compounds in each of these classes (primarily by gas chromatography and gas chromatography-mass spectrometry techniques) accounted for the fates of greater than 90% of the cellulose carbon atoms after liquefaction. Under the conditions used in the majority of this study xanthene (1) comprised 80% of the non-polar products and was formed in 16% molar yield. This rose to 53% when pure phenol was used as solvent together with 10% zinc chloride. By employing 13C labelled cellulose model compounds the origins of the carbon atoms in xanthene were investigated. The methylene carbon atom was derived totally from the carbohydrate were similarly derived, the remainder originating from the solvent Phenol. It was concluded that a minimum of 8% of the carbohydrate carbon was converted to xanthene carbon during the liquefaction of cellulose at 350°C in aqueous phenol containing zinc chloride. The major component of the dichloromethane-soluble fraction of the products of the zinc chloride catalysed hydrothermolysis of methyl α-D-glucopyranoside is phenol and, by use of labelling experiments this product was found to be formed by two pathways: i, by the direct conversion of the hexose carbon skeleton into the aromatic ring and ii, by a fragmentation-recombination mechanism. Schemes were proposed to account for both of these pathways. The knowledge obtained in this study may assist which gaining control over the thermal degradation of cellulose to produce specific aromatic compounds, thus increasing the avaliability of liquefaction products as chemical feedstocks or as fuels and therefore the value of biomass as an energy resource.