Can FAS replace Sodium Hydrosulfite?

Direct Answer

Direct Answer Yes. In the paper industry formamidinesulfinic acid (FAS) was originally introduced as a safer alternative to sodium hydrosulfite.

The basis for substitution

On equal reducing equivalents, 1 kg of pure sodium hydrosulfite corresponds to roughly 0.62 kg of FAS. Allowing for the unavoidable losses hydrosulfite suffers in hot alkali and in contact with air, the practical substitution ratio is usually more favourable than the theoretical one.

What changes

Three points to watch

• The dose cannot be substituted weight for weight; convert on equal reducing equivalents first, then run a bench trial
• The temperature, pH and time windows differ from hydrosulfite and have to be re-established rather than carried over
• Many mills run a transition blend of FAS with a small amount of hydrosulfite, which is more stable and easier for the mill crew to accept

Bottom line

It can replace hydrosulfite and is a well-established route in reductive pulp bleaching, but convert on equal reducing equivalents and re-establish the process window rather than substituting weight for weight.

Sources

1. 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
2. The effect of bleaching reagents on bleachabilities of DIP and environmental loads，KTAPPI 47(1), 2015，DOI 10.7584/ktappi.2015.47.1.066
3. 我司产品 SDS 与 TDS（危害分类、运输分类、热分解温度、溶解度等物性数据）
4. 我司产品安全数据表《Material Safety Data Sheet — THIOUREA DIOXIDE》（MSDS，签发日期 2023-03-03）
5. 我司产品技术数据表《THIOUREA DIOXIDE Technical Data Sheet》（TDO-TDS，签发日期 2024-05-08）