Influence of cooking conditions and wood species on the formation of Hexeneuronic acids in kraft cooking | |
| Author | Sah, Jainath Prasad |
| Call Number | AIT Thesis no.PP-03-9 |
| Subject(s) | Pulping Wood-pulp--Bleaching |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science |
| Publisher | Asian Institute of Technology |
| Abstract | Hexenuronic acid content in the pulp is an important factor for the production of bleached kraft pulp. Formation rate of Hexenuronic acid is a function of cooking parameters. Accordingly, content of Hexenuronic acid in unbleached kraft pulps can be somewhat reduced by choosing right combination of cooking conditions. Detailed characterization of hexenuronic acid content in hardwood species such as Eucalyptus and Acacia from laboratory kraft pulping in various pulping conditions were conducted and investigated in this study. Hexenuronic acid contribution to the pulp kappa number was investigated. Hexenuronic acid contents at different pulps correlate with kappa reduction through Hexenuronic acid hydrolysis, and these correlations vary with wood species. Evaluation results include cooking yield, hexenuronic acid concentration, pentosan content and viscosity. Difference between different species is very large in many respects. Use of highest effective alkali charge and concentration, sulfidity and cooking time higher than average, and highest practical temperature gives low content ofhexenuronic acid. Pulps from Eucalyptus and Acacia had highest hexenuronic acid content 81.7 and 66.5 mmol/kg BD pulp respectively, detrimentally affecting pulp viscosity and yield of the pulping process. Pulps after cooking of a both species are compared to pulps by conventional kraft cooking, all having almost same delignification degree. High alkali charge and temperature for both species as well as sulphidity higher than average, 33% and very high sulphidity 40% in the subsequent cook results pulps with 56% and 72% reduction of hexenuronic acid in case of Eucalyptus and Acacia, respectively. At the same time viscosity and yield are clearly reduced. On the other hand, Eucalyptus and Acacia using different cooking conditions result in pulps with 28% and 45% reduction of hexenuronic acid, without detrimentally affecting the pulp viscosity or yield. Also evaluation was made to reduce use of chlorine dioxide compared to reference HexA case pulp. Use of chlorine dioxide can indeed be reduced, but also this will affect other parameters. Finally low, average and high hexeneuronic acid pulps of both species were bleached in D0ED 1 sequence. Each of three different pulps (with different hexenuronic acid level) was bleached using ECF bleaching. This is beneficial because of low chlorine dioxide consumption and still other pulp characteristics like pulp viscosity and yield may remain on acceptable level. It is found that a pulp produced applying the optimum cooking conditions to Acacia is reducing of 30 kg/ ADt active chlorine, i.e. 34% lower compared to consumption in conventional bleaching. |
| Year | 2003 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Pulp and Paper Technology (PP) |
| Chairperson(s) | Malinen, Raimo |
| Examination Committee(s) | Viljakainen, Esa;Kolehmainen, Heikki |
| Scholarship Donor(s) | Government of Japan;AIT Fellowship |
| Degree | Thesis (M.Sc.) - Asian Institute of Technology, 2003 |