Hot Water Extraction and Subsequent Kraft Pulping of Pine Wood Chips

Abstract

This research investigated the effects of pre-extraction time, temperature, and pH on the rate and quantity of sugars recovered from Loblolly pine wood chips and the impact this treatment has on pulp kappa number and yield. Composition analysis of raw chips, extracted chips, pulp, and hydrolyzate were performed to assess the hemicellulose extraction efficiency and subsequent loss during kraft pulping of Loblolly pine. A pseudo kinetic model of prehydrolysis extraction was developed from the hydrolyzate sugar concentration data. Preliminary experiments demonstrated the potential for influencing pulp properties and sugar recovery in hydrolyzate through on-line control of prehydrolysis pH, reaction temperature, and time. A second set of experiments examined these factors and added a presoak period to the design matrix. A third set of experiments used a best case of pre-extraction conditions to test five potential pulping additives. It was concluded that the extraction rate for all sugars was increased with either increasing temperature from 140 to 170°C or decreasing pH from 4.5 to 3.0. The hydrolysis was selective for hemicellulose as opposed to cellulose by using temperature at 140°C. Both pH and temperature also impacted the degradation rate of sugars in solution. The 24 hour presoak at 25°C with various pH levels had no measurable effect on hydrolysis rate or pulp yield. The additives tested in this research: anthraquinone, acetaldehyde, ethanolamine, lithium aluminium hydride, and hydroxylamine, were not successful in recovering pulp yield from extracted chips to that of a standard kraft cook with the conditions tested. More work could be justified with hydroxylamine or to test the use of anthraquinone in conjunction with hydroxylamine or another successful additive. A pseudokinetic model of the extraction was calculated using an activation energy of 27 kcal/mole for hemicellulose hydrolysis and a term for the acid concentration. This modified H-factor model described the sugar extraction data except when significant degradation of sugars was observed. The data for chip weight loss and pulp yield also fit a smooth curve when plotted against the modified H-factor.