Suitability of raw materials and processes for the production of dissolving pulps

The world dissolving pulp production decreased from approx. 5 mio. t in 1978 to 2.8 mio, t in 1996. In the future, increasing production rates are predicted; based on positive developments in the area of cellulose acetate and cellulose ethers as well as advances in direct solvent spinning of cellulose. In the area of raw materials, only cotton linters play a certain role among the annual plants. The corresponding pulp production amounts to 200,000 t/year. Also in future other annual plants will be of minor importance. Hardwood and softwood dissolving pulps are dominating, and it can be assumed that in future the capacities for production of dissolving pulps from hardwoods will exceed those from softwoods. Among the pulping processes the sulfite process is the dominating one with a share of 2/3 of the total production, followed by the kraft process. Environmentally friendly alternatives are soda/AQ and the ASAM process. A comparison of these processes for the production of dissolving pulps based on hardwoods demonstrates distinct advantages for the ASAM process. As the capacities for dissolving and paper pulp production deviate more and more, it is required to develop an independent technology for dissolving pulp production which counteracts the cost disadvantages of low capacities. In this respect integrated plants for dissolving pulp production and processing are beneficial. In particular, chemical recovery in pulp production is costly. Trials showed that ASAM black liquors have good dispersing properties and could be used for this purpose as an alternative to combustion and chemical recovery. Filtrates from chlorine-free bleaching can be disposed in the same way which renders a closed mill operation possible.