Sample | Sulfuric acid/mL | Temperature/˚C | Time/h |
1 | 0 | 200 | 24 |
2 | 1 | 200 | 24 |
3 | 2 | 200 | 24 |
4 | 3 | 200 | 24 |
5 | 4 | 200 | 24 |
6 | 5 | 200 | 24 |
7 | 3 | 180 | 24 |
8 | 3 | 200 | 12 |