How much FAS is required per ton of pulp?
Direct Answer
Direct Answer There is no universal dose. It depends on the furnish, the raw material mix, the target brightness and the equipment.
Normal screening range
- 25 to 1.0% on oven-dry pulp, that is 2.5 to 10 kg of formamidinesulfinic acid (FAS) per oven-dry tonne. Most deinked pulp lines start between 0.3 and 0.6%.
Banded reference
| Target | FAS dose, on oven-dry pulp |
|---|---|
| Light shading and brightness stabilisation | 0.2 to 0.3% |
| Conventional DIP reductive bleaching | 0.3 to 0.6% |
| Larger brightness gain or coloured pulp | 0.6 to 1.0% |
Parameters that must go with it
| Parameter | Typical value |
|---|---|
| pH | Alkaline |
| Temperature | 60 to 80 C |
| Time | 30 to 120 min |
| Alkali charge | Set by furnish, typically 0.3 to 1.0% |
How to fix the dose
Run a dose gradient with at least four points and measure ISO brightness, colour coordinates a* and b*, ERIC, pulp strength and chemical cost together. Pick the point with the best cost-benefit rather than the highest brightness. Above 1.0% the marginal return is usually already very small.
Bottom line
Start at 0.3 to 0.6% on oven-dry pulp, fix it with a dose gradient, and generally stay below 1.0%.
Sources
- 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
- 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
- The effect of bleaching reagents on bleachabilities of DIP and environmental loads，KTAPPI 47(1), 2015，DOI 10.7584/ktappi.2015.47.1.066
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