| The PRENOX Process - Pulp Pre-Treatment with NO2 | France | - | Pilot Scale |
MANUFACTURE OF PAPER AND PAPER PRODUCTS # 39
Background
This case study was submitted on the part of the Working Group on Cleaner Production in Pulp and Paper Industries in the framework of the UNEP IE/PAC Cleaner Production Program with the support of the Technical Research Center of Finland's Non-Waste Technology Research Unit.
Cleaner Production Principle
New technology.
Cleaner Production Application
The Prenox (TM) process consists of pretreating the pulps prior to oxygen-delignification with NO2. This process has been developed by the Swedish companies AGA, KemaNord, MoDo and Sunds Defibrator.
A research effort has been made in order to find ways of delignification to still lower kappa numbers. Special attention has been paid to the ability of nitrogen oxides to activate the lignin degradation. In the Prenox process the softwood pulp can be treated with nitrogen dioxide in acid conditions prior to oxygen delignification. In laboratory conditions it is possible to extend the delignification down to the kappa number 7 without severely impairing the papermaking properties of the pulp. On a pilot scale the practical kappa number limit is about 10.
The tests have been made using a normally cooked softwood pulp with an initial kappa number of about 30. The test figures show that at low charges (5 and 6 kgs per ton respectively) NO2 is as efficient as molecular chlorine. At increased concentrations molecular chlorine shows a more selective delignification.
Laboratory pre-treatment tests using already oxygen delignified softwood pulp have also been made. With a nitrogen dioxide pre-treatment at 10% consistency and subsequent delignification in a pressurised (EOM) stage, an acceptable pulp with the kappa number 7 has been obtained.
This process is in the pilot stage and is not yet commercially available.
Environmental and Economic Benefits
The Prenox process increases the selectivity of the oxygen toward lignin in the oxygen delignification stage. The amount of the bleaching chemicals needed is reduced and the environmental effect of the bleach plant effluent decreased.
| Material Category | QTY Before | QTY After |
| Waste Generation : TOCl | N/A | 1,5 kg/t |
| Feedstock Use: | N/A | N/A |
| Water Use: | N/A | N/A |
| Energy Use: | N/A | N/A |
Constraints
All effective pretreatments occur in acidic conditions, which is a drawback, because the pulp is alkaline after the cook. If nitrous compounds are used, the NOX emissions from the recovery boiler are likely to increase. Using nitrogen dioxide would pose serious questions related to health and safety at work.
Contacts
Review Status
This case study was submitted by the UNEP Working Group on Cleaner Production in the Pulp and Paper Industries, based at the Technical Research Center of Finland (address above) in 1992, as part of a contract for UNEP IE. Before submission, the case studies were reviewed at the Center. They were edited for the ICPIC diskette in June 1997.
Subsequently the case study has undergone another technical review by Dr Prasad Modak at Environmental Management Centre, Mumbai, India, in September 1998.