What Temperature and Reaction Time Does FAS Bleaching Require?
Direct Answer
Direct Answer The typical window for formamidinesulfinic acid (FAS) bleaching is 60 to 80 C for 30 to 120 minutes, and the two have to be set together rather than one at a time.
How temperature and time trade off
Temperature and time are partly interchangeable: high temperature with a short dwell, or low temperature with a long dwell. For brightness stability and fibre protection, a moderate temperature with a longer dwell is usually the safer of the two.
| Temperature | Typical time | Where it suits |
|---|---|---|
| 60 C | 90 to 120 min | Where fibre protection matters and the brightness target is modest |
| 70 C | 60 to 90 min | The usual working point on most deinked pulp lines |
| 80 C | 30 to 60 min | Where a larger brightness gain is needed and the plant can heat the stock |
What else drives the choice
- Consistency: mass transfer is slower at high consistency, so allow more time
- Alkali charge: more alkali speeds the reaction, but time should not be compressed by adding alkali
- Metal ions: iron and manganese consume the reducing agent, so higher levels call for a larger dose or a longer dwell
- Downstream stages: if a further reductive or shading stage follows, the earlier stage does not need to be pushed to the limit
How to set it
Hold pH and dose constant and run a temperature-time matrix of at least three temperatures by two times, six runs, measuring brightness, colour and strength, then take the best overall combination.
Bottom line
Start at 70 C for 60 minutes, then adjust within 60 to 80 C and 30 to 120 minutes to suit the furnish and the equipment.
Sources
- US5958184A, Process for producing thiourea dioxide（还原当量质量比、碱中水解式、木浆与脱墨浆等当量漂白实施例），https://patents.google.com/patent/US5958184A/en
- US3384534A, Bleaching of wood pulps with thiourea dioxide（对绝干浆用量范围与白度提升数据），https://patents.google.com/patent/US3384534A/en
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