Economical and environmentally-friendly pulp bleaching

A simulation model for pulp bleaching was created in the Virtual Pulp Bleaching (VIP) project led by Professor Tapani Vuorinen from the Aalto University School of Chemical Technology. The model will yield information of phenomena taking place during pulp bleaching, especially about reactions between lignin and bleaching chemicals that cause the pulp's brown colour. The chemicals used in pulp bleaching are costly. In addition, water and energy are used in the bleaching process. With the help of the knowledge produced by the VIP model, pulp can be bleached more economically and in a more environmentally friendly way.

The VIP model developed includes a library of chemical reactions for most commonly used bleaching chemicals. The models of the chemical reactions and other phenomena which participate in the bleaching process function as a part of process equipment models with the combination of which it is possible to construct flow diagrams used in the bleaching process at the plant. In addition, the model can be used to simulate experimental arrangements at the laboratory scale.

The simulation model will be used in research and teaching, especially at Aalto University. In industry, the model can be used for planning of the bleaching process, training of personnel, as well as optimization of the existing processes.

Bleaching is the process used after pulping to remove lignin residual

Cellulose is one of the raw materials of paper and cardboard, which is obtained from wood pulping process. Pulping takes place in a high temperature with the help of chemicals; lignin that glues the wood fibres together partially dissolves and the fibres separate from each other. After the pulping process is over, the cellulose is bleached aiming to remove the rest of the lignin, the so-called residual lignin, with different chemicals. Lignin removal is important because lignin gives the fibres their brown colour. Pulps pronounced brightness is important in the production of fine grade paper.

Lignin polymer consists of different chemical groups, which differ from each other in their reactivity with different bleaching chemicals and, for example, in the extent they affect the colour of the fibre. For the construction of the VIP model, attention was directed to these types of different chemical groups to allow the model to provide a sufficiently realistic picture of the effect of different conditions, such as those due to temperature and chemical doses, on the success of bleaching.

The project was multidisciplinary: it drew together scientists from the fields of wood chemistry and the modelling of chemical processes as well as experts from the pulping industry. This kind of cooperation was necessary to obtain a useful model.

The Virtual Pulp Bleaching project is one of the awarded projects of the Forestcluster's EffTech program. The five-year Intelligent and resource efficient production technologies (EffTech) program started in 2008, and its total budget is € 40 million. The VIP project includes Aalto University, VTT Technical Research Centre of Finland and the Lappeenranta University of Technology.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Aalto University.

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