Date of Award

12-2008

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

Adriaan R.P. van Heiningen

Second Committee Member

Martin Ocen Lawoko

Third Committee Member

Joseph M. Genco

Abstract

Chemical pulping of wood leads to fiber yields of only about 50% because most hemicelluloses and almost all the lignin end up in the spent pulping stream. The latter is combusted for steam and electricity generation. The heating value of wood carbohydrates is only half that of lignin. Therefore it has been proposed that a more economical use of hemicelluloses is extraction as oligomers from wood chips prior to pulping followed by conversion to high value-added products such as ethanol, polymers and other chemicals. Recently, it has been shown that all lignin in soft wood is chemically linked to carbohydrates and especially to the hemicelluloses by covalent bonds (Lawoko et. 2005). The main LCC bonds proposed are of the ester-, a-ether-, phenyl glycosidic- and carboncarbon type. Selective cleavage of LC bonds will be essential when extracting hemicellulose mostly free of lignin in an extraction step prior to pulping. In this study the cleavage of the phenyl glycosidic bond of a model compound, phenyl-B-D-glucopyranoside, was studied. The hydrolysis conditions were chosen to simulate different pretreatment methods such as auto hydrolysis, green liquor pretreatment and acid hydrolysis. It was found that hydrolysis of the phenyl glucoside model compound at near neutral aqueous conditions (pH 6) was minimal (4 %) at 170°C. On the other hand hydrolysis was nearly complete (95 %) at this temperature with the addition of acetic acid at a concentration expected to be generated from deacetylation of xylan in hardwoods (about 10 g/L). At acid conditions of pH 1.65 the temperature may be lowered to 105 or 121°C while still obtaining a significant (80-90 %) hydrolysis yield. The hydrolysis experiments performed simulating green liquor extraction showed as previously reported that the hydrolysis of phenyl-glucoside produces phenol and levoglucosan while no glucose is formed. The result showed that hydrolysis of the phenyl glucoside at 155 °C was essentially complete with quantitative formation of levoglucosan and phenol rather than glucose and phenol. Incomplete mass balances were obtained between the amount of the phenyl glucoside reacted and phenol and glucose formed after hydrolysis at pH 1.65 at all temperatures studied (70, 90, 105 and 121°C). Based on the curved nature of the phenyl glucoside calibration curve and quantification of the TOC of the starting and final reaction mixtures, it is suggested that the alditol acetylation method does not work properly at strong acidic conditions. No other degradation products than glucose, phenol and levoglucosan were observed at any of the experimental conditions studied.

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