What is pulp manufacture
cellulose, Fibrous material obtained from fibrous plants (wood or annual plants) through chemical and mechanical processing, which consists primarily of cellulose. The aim of pulp production is both the separation of the fibers from the cell structure of the woody plant material (e.g. wood, straw) and the production of unbleached and bleached fiber material with optimal properties (quality development) for further processing in undissolved (paper pulp) or dissolved (Chemical or textile pulp) shape.
Manufacturing. The pulp production process is based on the penetration of digestion solutions into the wood and the removal of cell wall components (lignin, hemicelluloses, wood constituents) from the wood. The fiber structure of the wood can also be separated mechanically. In this way the so-called. Wood pulp. Transitions between the actual pulp and wood pulp production are the so-called semi-chemical (e.g. NSSC: neutral-sulfite-semi-chemical pulp and chemomechanical processes (e.g. CMP: chemomechanical pulp, CTMP: chemo-thermomechanical pulp), in which a partial dissolution and softening of the lignin with chemical solutions takes place and a mechanical defibration follows. Based on the mass of the debarked wood used, the yields in the wood pulp production are 80-99%, with the CMP and CTMP processes 65- 97% and between 30 and 60% in pulp production processes. Pulp, wood pulp and waste paper are the fibers in paper production.
The technically important processes of pulp production are subdivided into the alkaline (soda- and Sulphate process) and the Sulphite process. In both cases, the wood is debarked in the form of so-called wood chips and transferred to the cellulose digester. Both alkaline process the lignin is dissolved as sodium lignate. At the same time, other phenols (e.g. the tannins in wood and bark) are transferred into the solution as phenolates and the resins and fatty acids as salts ("soaps"). Therefore, after the sulfate process, for. For example, wood rich in resin (e.g. pine wood) and wood that has not been barked so well can be used. In addition to the dissolution of the wood components through salt formation, the sodium sulfide contained in the digestion solution in the sulfate process cleaves the ether bonds in the lignin nucleophilically, which significantly increases its solubility. At the Sulphite process the wood chips are treated with an acidic bisulfite solution. The ether bonds in the lignin are also split nucleophilically by the hydrogen sulfite ions. The actual solution of the lignin is achieved by the sulfitation reaction (formation of lignosulfonates). Some of the wood polysaccharides - especially the hemicelluloses - are hydrolyzed and converted into the digestion solution in the form of simple sugars. In these processes, resins, fats and phenols essentially remain in the pulp, so that the sulfite process can only be used for wood that is poor in wood content and well debarked (spruce, fir, beech, poplar). The table shows a comparison of some parameters of the two digestion methods.
The pulping processes can be designed either discontinuously or continuously.
Cellulose. Tab .: Some typical parameters of the sulphate process and the sulphite process for pulp production.
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