Markus Paananen

High-alkali low-temperature polysulfide pulping (HALT) of Scots pine

High-alkali low-temperature polysulfide pulping (HALT) was effectively utilised to prevent major polysaccharide losses while maintaining the delignification rate. A yield increase of 6.7 wt% on wood was observed for a HALT pulp compared to a conventionally produced kappa number 60 pulp with comparable viscosity. Approximately 70% of the yield increase was attributed to improved galactoglucomannan preservation and 30% to cellulose. A two-stage oxygen delignification sequence with inter-stage peroxymonosulphuric acid treatment was used to ensure delignification to a bleachable grade. In a comparison to conventional pulp, HALT pulp effectively maintained its yield advantage. Diafiltration trials indicate that purified black liquor can be directly recycled, as large lignin fractions and basically all dissolved polysaccharides were separated from the alkali-rich BL.

Stabilization, degradation, and dissolution behavior of Scots pine polysaccharides during polysulfide (K-PS) and polysulfide anthraquinone (K-PSAQ) pulping

Abstract The behavior of Scots pine (Pinus sylvestris L.) polysaccharides was studied during modified kraft pulping processes of wood meal by polysulfide (K-PS) and polysulfide anthraquinone (K-PSAQ) at the hydroxide ion concentrations of 0.50 and 1.55 M [OH-] with a high liquor-to-wood (L/W) ratio of 200. The high L/W ratio was selected for avoiding diffusion phenomena and to be able to focus on the chemistry of polysaccharides. A comparison with the kraft process reference at 160°C revealed a substantial increase in pulp yield (6–7% in K-PS pulping and 7.5–10.5% in K-PSAQ pulping) mainly attributed to galactoglucomannan (GGM) stabilization. Due to the rapid delignification rate at 1.55 M [OH-] concentration, the temperature could be lowered from 160°C to 130°C without a notable prolongation of cooking time. In K-PS pulping at 130°C, no additional GGM stability was observed compared to 160°C, whereas cellulose and arabinoxylan preservation was improved. In K-PSAQ pulping, GGM preservation was also significantly improved. At 130°C, pulp yield increase of approximately 8% in PS pulping and more than 11% in PSAQ pulping was observed. The amount of dissolved softwood hemicelluloses in black liquor was significantly increased at the higher [OH-] level and even further in the presence of PS and AQ. Simultaneously, the formation of hydroxy acids was decreased, indicating a significant stabilization of the dissolved polysaccharide fraction parallel to the pulp polysaccharides.

Effect of hydroxide and sulfite ion concentration in alkaline sulfite anthraquinone (ASA) pulping – a comparative study

Abstract Pulp and black liquor produced by alkaline sulfite anthraquinone (ASA) process were comprehensively characterized to evaluate the effects of ion concentration on the delignification and polysaccharide preservation. Scots pine wood meal was pulped at 160°C with a sulfite-to-hydroxide ion ratio of 0.75 and liquor-to-wood ratio of 200:1. Two concentration levels were studied in presence and absence of anthraquinone (AQ). Contrary to the expectations, already the lower concentration level (L-ASA) revealed rapid delignification in presence of AQ, while only moderate acceleration was obtained at the high concentration level (H-ASA). However, H-ASA liquor resulted in a slightly higher pulp yield of 1–2% (based on wood) but only in case of pulps with kappa numbers (KN) above 60. With progressing delignification, the yield advantage was gradually lost. The higher pulp yield at H-ASA conditions was mainly due to improved galactoglucomannan retention, which was around 2% on KN60 pulp and around 0.5% after prolonged delignification. The xylan content, on the other hand, was found to be 1% (based on wood) lower under H-ASA conditions compared to L-ASA conditions, which may be attributed to an increased solubility of short-chain polysaccharides at high alkali concentration.

Novel insight in carbohydrate degradation during alkaline treatment

Abstract A mathematical model is presented, in which the yield loss (YL) and the decline in polymerization of carbohydrates is comprehended. The model is applicable to the treatment of cellulose and hemicelluloses in alkaline media, and it features the actions of peeling, stopping, and alkaline hydrolysis of the polymer chains. The peeling reaction is further subdivided into primary and secondary peeling depending on whether it originates from an initial reducing end-group (REG) or from an REG created by alkaline hydrolysis. Fitting the model to experimental data provides estimates of the various reaction rate constants. When available, simultaneous observations of the YL and the decrease in chain length contribute to the evaluation of the parameters. Alternatively, if the data are limited to the YL, the obtained parameter estimates allow for a projection of the time development of chain length. The model has been applied on data from two types of experiments: soda-anthraquinone treatment of cotton linters and kraft treatment of Scots pine. It was possible to evaluate the impact of the different processes on degradation as well as the portions of polymer chains possessing active or stabilized REGs.