Off-white is a colour classification, not a separate chemical grade. Caprolactam-route ammonium sulphate ranges from bright white to a pale cream or light beige tint depending on how much organic material from the process liquor is occluded in or adhering to the crystal. This page covers only that distinction; route chemistry, full specification and agronomy are on the caprolactam grade page.
Substance identity
| Chemical name | Ammonium sulfate |
| Formula | (NH₄)₂SO₄ |
| CAS No. | 7783-20-2 |
| PubChem CID | 6097028 |
| Molar mass | 132.14 g/mol |
| Appearance | Cream to pale beige crystalline solid; tint uniform through the crystal mass rather than as visible dark specks |
Specification
— typical commercial ranges; colour is the only parameter that systematically differs from white caprolactam grade
| Parameter | Typical range | Note |
|---|---|---|
| Total nitrogen (N) | 21.0 % min | unaffected by colour |
| Sulfur (S) | 24 % min | unaffected by colour |
| Moisture (H₂O) | ≤ 0.2 – 0.5 % | |
| Free acid (as H₂SO₄) | ≤ 0.05 % | |
| pH, 5 % aqueous solution | 5.0 – 6.0 | |
| Water-insoluble matter | ≤ 0.05 % | |
| Colour | off-white / cream / light beige | assessed visually against a retained reference sample |
| Predominant particle size | 2 – 4 mm | as white grade |
Properties
Solubility, hygroscopicity, thermal behaviour and soil acidification are those of ammonium sulphate generally and are unchanged by the tint. One property does differ in degree: dissolved off-white material can leave a faint haze or a very small amount of floating organic film in a clear stock tank, and it can carry a weak process odour that becomes noticeable in a warm, closed store. Neither indicates a low assay.
Applications
For direct field application, bulk blending and compaction into granules, off-white material performs identically to white and is normally the sensible choice. The tint is only a genuine constraint where the buyer’s own specification names colour: retail-bagged consumer product, products dyed to a defined shade where the base colour shifts the result, clear-solution fertigation systems with visible tanks, and industrial or food-adjacent uses where colour is part of the purchase specification.
Handling and storage
As caprolactam white grade. Because the residual organics are the source of any odour, ventilate closed stores before entry and avoid long storage at elevated temperature, which makes the odour more noticeable.
Notes
Colour is not a proxy for purity across routes. An off-white caprolactam lot is chemically cleaner than a pale-grey coke-oven lot, despite similar apparent lightness. Judge purity by free acid, insolubles and trace metals on the certificate of analysis, not by shade.