Can FAS be combined with Hydrogen Peroxide?
Direct Answer
Direct Answer Yes, and it is one of the most common combinations in papermaking, but the two stages must be run separately and never in the same bath.
Why not in the same bath
Hydrogen peroxide is an oxidiser and formamidinesulfinic acid (FAS) is a reducing agent. In the same liquor they consume each other, so both chemicals are wasted and brightness can fluctuate.
Recommended stage sequence
| Stage | Chemicals | Purpose |
|---|---|---|
| First | Hydrogen peroxide plus alkali and chelant | Oxidative bleaching to lift brightness and remove part of the colour |
| Middle | Washing or thorough draining | Remove residual peroxide and dissolved material |
| Second | FAS plus alkali | Reductive post-bleaching to pull colour down and correct the shade |
Can the order be reversed
Yes, but it is less common. A reduce-then-oxidise route is used on certain furnishes, mainly to remove easily reduced colour first and then lift final brightness in the oxidative stage. That route places stricter demands on the intermediate washing.
Control points
- Residual peroxide must be brought low enough between stages, normally by washing, or destroyed with a reducing agent
- Alkali for the second stage has to be calculated separately and not carried over from the oxidative stage
- Temperature and time are set separately: typically 70 to 90 C for oxidation and 60 to 80 C for reduction
Bottom line
They work well together and the combination is a mainstream route, provided the stages are separate, the intermediate wash is adequate and the two are never dosed into the same bath.
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
- 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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