STUDIES ON ENVIRONMENTALLY COMPATIBLE PULPING AND BLEACHING OF BAGASSE

Abstract

Bagasse is an important raw material resource for pulp and papermaking in India. It has all the requisite properties to replace the conventional raw .material like bamboo and wood for economical manufacturing of high grade of paper. Conventionally, bagasse is being cooked with soda to a reasonable Kappa number ranging between 20-24. The addition of a small fraction (0.05-0.1% on o.d. basis) of AQ has helped reduce the Kappa number of the pulp significantly (sometimes it is reduced by 40-50% of kappa number of'soda pulps). The brown stock washed pulp is normally being bleached with elemental chlorine. The chloride ions generated from chlorine reacts with lignin and appear in bleach plant effluent as "original chlorine" resulting in increased pollution load to the stream. Considering environmental impact of chlorine, it is imperative to restrict the use of it to maximum possible extent in the bleaching process. As the amount of chlorine is directly related to the kappa number of the pulp to be bleached, the first and foremost need is to look back into the cooking process and explore the possible remedial solution for reducing the kappa number of the pulp as minimum as possible. As the delignification has. its own limitations, the most suitable eco-friendly way of achieving the kappa number could be pre-bleaching of pulp with molecular oxygen. The pre-bleaching of brown stock pulp in the presence of caustic soda has the advantages of low - bleach chemicals consumption and higher bleaching efficiency in later stages. Modification of bleaching process is generally the least expensive and simplest means of reducing environmental load of bleach plants. The replacement of chlorine by chlorine dioxide (D/C ratio as 70/30) has helped reduce the color and toxicity of bleach plant effluent significantly. The development of chlorine free bleaching employing oxygen, hydrogen peroxides and ozone has reduced the AOX generation to nil and the effluent so generated may be utilised for burning in chemical recovery for generation of steam. In this experimental work it has been planned to study the various pulping and bleaching techniques for bagasse, a promising future raw material for countries like India, compatible to environment.