Evaluation of chipping and impregnation of Scots pine heartwood with sulfite cooking liquor
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Evaluation of chipping and impregnation of Scots pine heartwood with sulfite cooking liquor Jessica Gard Timmerfors1 · Madhavi Latha Gandla1 · Torbjörn Sjölund2 · Leif J. Jönsson1 Received: 18 August 2020 / Accepted: 6 November 2020 © The Author(s) 2020 OPEN
Abstract Heartwood and sapwood of Scots pine were procured and chipped using a newly developed pilot drum chipper, which for the heartwood resulted in a combined fraction of pin chips and fines of ~ 3%. Heartwood wood chips were processed using a set of 15 different reaction conditions that differed with respect to impregnation and cooking procedures. The result was evaluated with regard to absorption of impregnation liquid, pulp yield, fraction of reject, viscosity, kappa number, brightness, fiber properties, and chemical composition measured using two different techniques (compositional analysis using two-step hydrolysis with sulfuric acid and Py-GC/MS). The chemical analyses provided detailed information about how all main organic constituents of the wood, cellulose, hemicelluloses, and lignin, were affected by operational parameters. Inclusion of a pressurized (9 bar) impregnation step resulted in a more efficient cook, but the duration of the impregnation step (five minutes and four hours were compared) was not decisive for the outcome. Omission of the impregnation step or using low-pressure impregnation resulted in high fractions of reject, poor delignification, and, with a cooking time of two hours, no advantages with regard to fiber length and fraction of fines. The results indicate that the conditions used during impregnation, such as pressure, temperature, and acidity of impregnation liquid, warrant further attention in future studies. Keywords Drum chipper · Cellulose · Impregnation · Heartwood · Scots pine · Sulfite cooking
1 Introduction The sulfite process has been of considerable interest for the development of forest-based biorefineries, where one possible product is dissolving pulp that can be utilized for textile production and production of cellulose derivatives. Even though the production of dissolving pulp peaked in 1975, the demand has typically increased since 2000. Thus, the global production, 4.5 million metric tons in 2010, was lower than the 5.3 million metric tons in 1975, but higher than the 2.3 million metric tons in 2000 [1]. The increase is mostly due to an increasing demand for highly pure cellulose fibers for textile applications, but also for manufacture of cellulose acetate for high value-added films, plastics,
and coatings, cellulose ethers, and cellulose powder [2]. Today, dissolving pulp is mainly produced by using the acid sulfite process, but in some cases, by using the Kraft process [3]. One advantage with the acid sulfite process is the high recovery rate for the cooking chemicals. Sulfite cooking could be performed in different pH ranges: acidic, neutral, or alkaline. In the acid sulfite process, the active chemicals are sulfurous acid ( H2SO3) and bisulfite ions ( HSO3−) [4]. There could be a single-step
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