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Process for oxygen pulping of lignocellulosic material and recorvery of pulping chemicals

  • US 6,770,168 B1
  • Filed: 08/14/2001
  • Issued: 08/03/2004
  • Est. Priority Date: 02/15/1999
  • Status: Expired due to Fees
First Claim
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1. A substantially sulfur-free process for the production of a chemical pulp from lignocellulosic material and the recovery of chemicals used in said process comprising the steps of:

  • a) providing a feed stream of comminuted lignocellulosic material, b) subjecting said feed stream of comminuted lignocellulosic material to a pretreatment, c) reacting the pretreated lignocellulosic material from step b) with oxygen or oxygen-containing gas, in the presence of an alkaline buffer solution comprising at least one sodium or potassium compound in order to obtain a stream of at least partially delignified lignocellulosic material, d) further treating said at least partially delignified material from step c) to obtain a chemical pulp product, e) extracting spent liquor comprising dissolved lignin components and spent chemical substances from step b) or both steps b) and c), f) recovering chemical substances from the spent liquor obtained in step e) and preparing fresh alkaline buffer solution to be charged to step c) or both steps c) and b), wherein in step b) said comminuted lignocellulosic material is subjected to a mild prehydrolysis in an aqueous solution and thereafter precooked in the presence of an alkaline buffer solution, and in step b) an aromatic organic compound is added to promote selective delignification, and in step f) the recovery of chemical substances from the spent liquor obtained in step e) comprises, f1) treating at least part of said spent liquor to form a concentrated stream of cellulose spent liquor, f2) reacting said concentrated cellulose spent liquor stream with an oxygen containing gas at elevated temperature in a gas generator to form a hot gas comprising carbon dioxide and molten droplets of sodium or potassium compounds or an aerosol of sodium or potassium compounds, f3) dissolving said sodium or potassium compounds in water to form an alkaline buffer solution and f4) recycling and charging at least a portion of said alkaline buffer solution to step c) or both steps c) and b).

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