Closing the loops in the pulp and paper industry with membrane technology

To catch successfully the new opportunities that arise from the development of new paper-product markets, pulp and paper producers are facing the need to improve the profitability and the environmental profile of their processes. Pulp and paper producers are therefore seeking all means to “close the loops”: the water loop, the chemical loop and the by-product loop. This lecture reviews the opportunities of the use of “membrane technology” to close those loops.
The first part of the lecture aims to give an overview of where membrane technology can be applied in the different loops. For the water loop the use of membrane technology for water recycling from the pulping process and the paper making process will be presented, e.g. white water recirculation at the paper machine. The membrane applications in the by-product loop include e.g. the concentration of lignin and black liquor and recycling of the permeate back to the pulp mill. In the chemicals loop, the focus will amongst others be on the recovery of coating colour and recycling of the permeate.
The second part of the lecture will demonstrate the successful integration of membrane technology in the pulp and paper industry by focusing on the extraction of lignosulphonate from spent sulphite liquor. In the case study presented, ultrafiltration is used to extract and concentrate lignosulphonate in the retentate, while the permeate is polished with reverse osmosis and then recycled to the pulp mill.
Overall, it will be shown that the integration of membrane technology can have a significant impact by improving the water balance in the pulp and paper industry.