How do I choose a reducing agent? Four options compared

Direct answer

Textiles and paper use four reducing agents: sodium hydrosulfite (sodium dithionite), thiourea dioxide, Rongalite (sodium formaldehyde sulfoxylate) and sodium bisulfite. Choosing between them comes down to five things: reducing power, formaldehyde, storage and transport risk, dosage, and total cost per tonne. For most dye houses thiourea dioxide gives the best overall balance of the five.

1. The four options side by side

2. Four reasons to choose thiourea dioxide

• The customer applies ZDHC MRSL, a brand restricted-substance list, or a formaldehyde-free requirement
• The plant wants lower odour and a better working environment
• Storage and transport are constrained and water-reactive self-heating goods are unwelcome
• Dosage is about one third of hydrosulfite for the same result, so unit cost falls

3. Three reasons to stay with hydrosulfite

• A proven recipe already runs, with risk control in place
• Very fast, near-instant reduction is needed, as on some continuous lines
• The customer specifies it

4. What to watch with Rongalite

Discharge printing and similar duties that depend on its specific decomposition behaviour still use Rongalite, but it releases formaldehyde as it decomposes. Orders covered by a brand formaldehyde limit must avoid it.

5. Where sodium bisulfite fits

Its reducing power is weak. It suits dechlorination and mild reduction only, and cannot replace hydrosulfite or thiourea dioxide.

6. Three steps to a decision

1. Bench trial: run a dose gradient on the same process and compare whiteness, shade and strength

2. Cost it: compare total chemical cost per tonne of fabric, or per oven-dry tonne of pulp, not price per kilogram

3. Check compliance: ask for the MRSL conformance report, the SDS and an SVHC declaration

Sources

Reduction potentials and relative dosages are the recommended ranges from our technical data sheet and published literature; confirm the actual dose by bench trial on your own process.