Method of minimizing transition metal ions during chemical pulping in a digester by adding chelating agent to the digester
US6475338B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | Jun 5, 1996 |
| Grant date | Nov 5, 2002 |
| Priority date | — |
| Expiry date | Jan 20, 2019 |
Classification
- Technology area (CPC D)Textiles; Paper
- CPC primaryD21C3/22
- WIPO fieldTextile and paper machines
- WIPO sectorMechanical engineering
Abstract
The production of chemical (e.g., kraft) cellulose pulp much more suited to totally chlorine free or elemental chlorine free bleaching is produced by reducing the bleaching chemical consumability of the produced pulp. The effective alkalinity of the pulp during at least the majority of the cooking stage is maintained at about 15 g/l or above (e.g., about 18-25 g/l), expressed as sodium hydroxide, so as to reduce the charged acid groups (including hexeneuronic acids) by at least 30% (e.g., at least about 50%) compared with pulp cooked at conventional alkalinity. Instead—or in addition to—the cellulosic material which produces the pulp may be heated to a temperature (at least about 100° C., preferably at least about 130° C.) to release significant quantities of the transition metals within it, and preferably while it has this elevated temperature and a dissolved organic solids concentration of about 120 g/l or less, a chelating agent (such as EDTA) is added to combine with a significant quantity of the released transition metals to produce complexes. At least a majority of the complexes are preferably removed (e.g., using an extraction screen in a digester) before…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.