MMA-grade ammonium sulphate arises from methyl methacrylate manufacture by the acetone cyanohydrin route, in which acetone cyanohydrin is hydrolysed in concentrated sulfuric acid to methacrylamide sulfate and then esterified with methanol. The spent acid stream is neutralised with ammonia and crystallised. The resulting crystal is typically finer and more uniform than caprolactam material and normally white to off-white.
Substance identity
| Chemical name | Ammonium sulfate |
| Synonyms | Ammonium sulphate, diammonium sulfate, AMSUL |
| Formula | (NH₄)₂SO₄ |
| CAS No. | 7783-20-2 |
| PubChem CID | 6097028 |
| Molar mass | 132.14 g/mol |
| Appearance | White to off-white crystalline solid, medium crystal size |
Specification
— typical commercial ranges for this route; not a guaranteed specification
| Parameter | Typical range | Note |
|---|---|---|
| Total nitrogen (N), dry basis | 21.0 % min (20.5 % min in some contracts) | stoichiometric 21.2 % |
| Sulfur (S) | 24 % min | stoichiometric 24.3 % |
| Moisture (H₂O) | ≤ 0.3 – 1.0 % | finer crystal retains more surface moisture than coarse capro crystal |
| Free acid (as H₂SO₄) | ≤ 0.05 – 0.10 % | commonly slightly higher than caprolactam grade |
| Water-insoluble matter | ≤ 0.05 – 0.10 % | |
| pH, 5 % aqueous solution | 5.0 – 6.0 | |
| Predominant particle size | 0.5 – 2 mm | medium/fine crystal, comparatively uniform |
| Bulk density | ≈ 0.95 – 1.1 t/m³ | fine crystal packs more densely than coarse |
Properties
Physical and chemical behaviour is that of ammonium sulphate: high water solubility (about 74–76 g per 100 g water at 20–25 °C), critical relative humidity near 79–81 % at 30 °C, no true melting point, decomposition from roughly 235 °C, and strong soil acidification on nitrification of the ammonium fraction.
Two properties follow from the route rather than the compound. First, crystal size: a finer, tighter size distribution dissolves faster than coarse crystal but flows and spreads less well, and it segregates from coarse blend partners. Second, impurity character: the residual impurities are organic and derived from the acetone cyanohydrin process chain, so specification attention belongs on free acid, insolubles and any contractual organic-carbon limit rather than on heavy metals.
Applications
Straight application as a nitrogen-plus-sulfur fertiliser, and feed material for compaction into granules where a uniform, fine feed compacts well. The fast dissolution of medium crystal suits dissolving-tank operations where the material must go into solution quickly and completely. Where the destination is a coarse bulk blend, either screen to the blend partner’s size band or compact first, otherwise the fine fraction migrates to the bottom of the pile and the field application becomes uneven.
Handling and storage
Dry, covered storage; keep away from lime, caustic and other strong alkalis, which liberate ammonia. Finer crystal carries a higher dust load than caprolactam grade — use extraction at bag-filling and transfer points and provide eye and respiratory protection. Not classified as dangerous goods for transport.
Notes
Cyanide-derived species from the acetone cyanohydrin step are destroyed and removed upstream in commercial operation; where a contract needs assurance on this point, it should be raised as a specific analytical requirement rather than assumed. For the fertiliser-use view of the same material see the MMA grade page under nitrogen fertilizer.