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UBC Theses and Dissertations

Black liquor extraction of lodgepole pine (Pinus Contorta var. Latifolia Engelm.) tree residues Wang, I-Chen


As a new feature of complete tree utilization, lodgepole pine (Pinus contorta var. latifolia Engelm) bark and technical foliage (foliage with twigs 6 mm or less in diameter) milled materials were extracted with commercial kraft black liquors. Thereby, residual liquor alkali was used to saponify lipids and dissolve organic components in the materials; The original liquors are reinforced by adding crude tall oil, phenolic substances and solid residue from the bark and foliage. Crude tall oil refers to the analytical recovery of lipids according to the Saltsman and Kuiken method. Potential lipid yields of these tree residues and the effects of various drying treatments were assessed as petroleum ether extracts. Lodgepole pine bark and technical foliage contained 9.3 and 7.5% petroleum ether soluble fractions, respectively; Similar amounts of crude tall oils were recovered in the main study. Special freeze-drying and short period air-drying preserved the lipid content, while oven-drying at 70 and 100°C substantially decreased extractive recovery. Subsequently, bulk materials for the main study were air-dried for 4 to 6-days before milling and thereafter meals were stored in the cold (ca. 2°C) under nitrogen. Black liquor extractions of the sample materials were carried out in bomb cooks including two liquor strengths (original and original plus 5 g/1 sodium hydroxide), three particle sizes (coarse, medium and fine fractions) and 1:7 liquor to material ratio. Maximum cooking temperatures of 80°, 100°, 120°, 145° and 170°C were examined in combination with various times at maximum temperature; Approximately one-third of the solid materials were dissolved following mixing and standing overnight at room temperature. These portions were not relevant to the cooking process and based on this correction the solid residue yields were found to exhibit kinetics close to a second order reaction. Empirical expressions relating time-temperature cooking conditions to solid residue yields were developed from the Arrhenius equation. These contained exponentially adjusted time terms, i.e., 0.45 for bark and 0.333 for technical foliage. Correlations were established between crude tall oil and solid residue yields; Black liquor extraction provided an efficient means of recovering bark and foliage lipids. Even with the milder conditions studied (1.5-hr at 80°C) better than 60% lipid recovery was achieved. Saponification seemed to be less important in controlling the crude tall oil yield than physical entrainment of tall oil soaps in the solid residue. Thus, higher temperature and longer cooking time tended to dissolve more solid material and liberate more crude tall oil soap. In order to gain information on progress of reaction between black liquor components and sample materials, direct potentiometric measurements were made during course of the reaction at 70°C with pH and sodium ion selective electrodes; Measurements indicated that when samples were added to the liquor, there was an immediate three orders decrease in hydroxide ion activity. Subsequent bulk liquor alkali consumption showed a slow and linear decrease in hydroxide activity. This implies that alkali consumption was close to a first order reaction. Black liquor extraction is advanced as a means for recovering valuable chemical components from abundant and underused coniferous forest residues. Constraints on implementing the process are discussed.

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