Acid Sulfite Digesters

The relatively severe conditions in an acid sulfite digester dictate the use of a multiple layer acid brick lining. The lining must be carefully selected and specified since these units operate at elevated temperatures and pressures with very acidic chemicals. Improper selection, design, specification, or installation can result in an unacceptably short lining life, lining failure, or vessel failure. 

Because of the severity and cyclic nature of acid sulfite digester operating conditions it is imperative that inspection and repair take place on a routine basis. The face course obviously will receive the most attention but no opportunity to inspect and repair the intermediate layer of brick, such as during face course replacement, should be missed. The steel digester shell should also be inspected for integrity and thickness whenever the opportunity is available. 

Routine lining inspection and maintenance procedures must be followed to obtain suitable lining life. Maintenance procedures described for acid sulfite digesters apply here with one addition, replacement of brick "fall-outs." This problem can be caused by movements of the lining and the steel shell, low compression in the lining, and the low bond strength between the Portland cement mortar and the carbon brick. Proper design considerations will normally reduce or eliminate this problem. 

During acid sulfite pulping a-pinene and some monocyclic terpenes are partially converted to p-cymene (Fig. 7-18). Crude cymene can be separated from the digester gas relief condensates and purified by distillation. With spruce and fir the distilled product is 99% p-cymene and only minor quantities of other products, such as borneol and sesquiterpenes, are present. Pine wood contains 3-carene, which affords appreciable quantities of m-cymene besides p-cymene. The crude cymene can be used within the mill as a resin-cleaning solvent. The distilled p-cymene finds use in the paint and varnish industry. 

Digestion liquor for acid sulfite pulping consists of a solution of sulfur dioxide in water containing calcium ion. Sulfur dioxide is obtained by... 

C. accounts for more of the earth s biomass than any other compound. The total amount is equivalent to about 50% of the carbon dioxide in the atmosphere about 100 billion metric tonnes are produced each year. It is degraded by organisms that possess Cellulases (see) lower plants, wood-destroying fungi and some bacteria. Termites, ruminants and some rodents harbor symbiotic bacteria in their digestive tracts which enable them to utilize cellulose. In animals that cannot digest it (e.g. humans and carnivores), C. is a ballast substance. C. is a very important industrial product, obtained primarily by acid (sulfite... 

Sodium hypochlorite Sulfamic acid Sulfite cooking liquor Sulfite digester acid (calcium bisulfite + sulfur dioxide)... 

Kilian, A., de Vaal, P.L (20(X)) Potential for improved control of an acid sulfite batch digester using a fundamental model, TAPPI Journal (83) November. 

Silica. The siUca content of natural waters is usually 10 to (5 x lO " ) M. Its presence is considered undesirable for some industrial purposes because of the formation of siUca and siUcate scales. The heteropoly-blue method is used for the measurement of siUca. The sample reacts with ammonium molybdate at pH 1.2, and oxaUc acid is added to reduce any molybdophosphoric acid produced. The yellow molybdosiUcic acid is then reduced with l-amino-2-naphthol-4-sulfoiiic acid and sodium sulfite to heteropoly blue. Color, turbidity, sulfide, and large amounts of iron are possible interferences. A digestion step involving NaHCO can be used to convert any molybdate-unreactive siUca to the reactive form. SiUca can also be deterrnined by atomic... 

In the sulfite pulp process, the digestion fluid is typically made by dissolving sulfur dioxide in water in the presence of limestone until the solution contains 7.0% by weight S02, three-quarters of which is in the form of bisulfite ion. Why is this done In support of your answer to this question, calculate the pH of (a) the digestion solution prepared as above, (b) a hypothetical 7% solution of S02 alone, and (c) an actual saturated solution of S02 alone (2.9% S02), if the first acid dissociation constant of sulfurous acid is 1.7 x 10-2, at ambient temperature and pressure. 

Chemical. In addition to its intrinsic interest, sulfur serves as a starting point for the synthesis of many labeled molecules. Digestion of sulfur in aqueous sulfites yields thiosulfates, which when heated with iodine lead to tetra-thionates and trithionates. Digestion of sulfur in alcoholic cyanide solutions yields thiocyanates, thence thiocyanogen and thiourea with its derivatives and coordination complexes. Oxidation of sulfur to sulfur dioxide is a potential route to labeled sulfamic acid and its derivatives and to labeled sulfuryl chloride. The intermediate sodium sulfide readily yields hydrogen sulfide and metallic sulfides. 

Methods for recovering lignin are the alkali process, the sulfite process, ball milling, enzymatic release, hydrochloric acid digestion, and organic solvent extraction. Alkali lignins are produced by the kraft (22) and soda (23) methods for wood pulping. These... 

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