Tall oil production process and characterization

Abstract

Existing kraft pulp mills have seen the necessity to branch out from traditional pulp and paper products to alternative value-added products such as bioenergy and biomaterials as a result of increasing competition in the forest products industry and the need for divergence from fossil fuels. Consequently, by-products from kraft pulp mills, including tall oil from extractives and modified lignin from black liquor, have seen a rise in valorization recently. In this study, tall oil soap was received from a kraft pulp mill and transformed via acidification to crude tall oil. The reaction conditions of water content, reaction pH, reaction time, along with the application of settling additives were varied in order to determine optimized conditions. Optimized conditions without the use of settling additives were 100 wt.% H2O, pH of 2.5 – 3.0, reaction time of 20 min, and incorporated industrially accepted values of reaction temperature (90 – 100 °C) and settling time (2 h). When employing settling additives, both anionic and cationic polymers were tested. The InfinityTM PS 3040 Pulp Processing Aid was an anionic polymer with the charge density -4.73 mmol/g and a molecular weight of 7.00 x 104 g/mol. When employed at a dry basis dosage of 0.0185 wt.% (0.05 wt.% wet basis), it produced crude tall oil with a 57.1 wt.% yield and an acid number of 142 mg KOH/g oil, based on the initial amount of raw soap added. These were increased compared to crude tall oil produced with no additive with a yield of 52.9 wt.% and acid number of 137 mg KOH/g oil. The second settling additive was xylan-AETAS-APS, a cationic xylan copolymer with a charge density of 3.81 mmol/g and molecular weight of 1.26 x 105 g/mol. The yield of crude tall oil was optimized with a dry dosage of 0.01109 wt.% (0.03 wt.% wet dosage), at 53.7 wt.%. A maximum acid number of 138 mg KOH/g oil was achieved with a dry dosage of 0.00729 wt.% (0.02 wt.% wet). Finally, an H-lignin copolymer, DMC-HL10, with a cationic charge density of 3.47 mmol/g and a preliminary molecular weight of approximately 32,000 g/mol was employed. With a dry dosage of 0.0037 wt.% (0.01 wt.% wet), a crude tall oil yield of 53.1 wt.% and acid number of 136 mg KOH/g oil were produced. Ultimately, analysis of variance (ANOVA) and Statistical Package for the Social Sciences (SPSS) analysis determined that no statistical optimal conditions were present. The waste lignin from the tall oil production process was also characterized by charge density, solubility, CHNS, and molecular weight analysis, in order to determine if sulfonation with sulfuric acid during tall oil production had occurred. It was found that the anionic charge density increased from approximately 0 with unmodified kraft lignin to 0.2 – 0.4 mmol/g depending on the production process of tall oil. There was an increase in solubility from approximately 0 g/L to over nearly 2 g/L and an increase in sulfur content from as low as 0.23 wt.% to a maximum of 2.1 wt.%. Molecular weight of tall oil lignin was found to be approximately 1,700 g/mol, i.e. lower than those of unmodified kraft lignin (up to 25,000 g/mol) and lignosulfonates (up to 150,000 g/mol). Thus, it can be inferred that sulfonated kraft lignin may be produced from waste tall oil lignin, but further studies must be conducted before determining potential implementation in industrial processes such as dispersion and flocculation.