Kraft chemical pulping bleached paper production

Kraft Chemical Pulped Bleached Paper Production... 

The US pulp and paper industry operates over 550 facilities which employ over 200,000 people. Total shipments are 60 billion with an additional 80 billion in converted products. Several proeesses eontribute to the emission of solvents. These include chemical pulping kraft process (terpenes, alcohols, methanol, acetone, chloroform), bleaching (acetone, dichloromethane, chloroform, methyl ethyl ketone, carbon disulfide, chloromethane, and trichloroethane), wastewater treatment (terpenes, alcohols, methanol, acetone, chloroform and methyl ethyl ketone), and evaporators in chemical recovery systems (alcohols and terpenes). 

A bleached kraft pulp mill requires 15,140 to 45,420 L (4000 to 12,000 gal) of water and 8.56 to 12.22 million chu (14 to 20 million Btu) of energy per ton of pulp, of which ca. 4.44 to 5.56 million chu (8 to 10 million Btu) are typically derived from biomass-derived fuel from the pulping process itself.4 Across all facilities, the pulp, paper, and allied products industry is the largest consumer of process water and the third largest consumer of energy (after the chemicals and metals industries).5,6 The large amounts of water and energy used, as well as the chemical inputs, lead to a variety of environmental concerns. 

The most important application of cellulosic materials is the production of paper. Thus wood is transformed first into pulp by mechanical or chemical modification. Hardwood trees such as eucalyptus, birch, and softwood trees like pinus and spruce are used. In the Kraft process woodchips are treated with sodium hydroxide and sodium sulfide to promote the breakdown of the linkage between lignin, some hemicelluloses, and cellulose. This produces cellulose containing residual lignin. The latter is removed by a bleaching process that can apply several oxidizing agents. White pulp is pure cellulose that is used to produce paper. 

The chemical bleaching of paper pulp is currently performed using chlorine or chlorine dioxide, which for kraft pulp results in the production of between 45 and 90 kg of organic waste/ton of pulp, containing 4-5 kg of organically-bound chlorine/ton. (1,2.) Bleaching of paper... 

---