| Dihydrate oxalic acid was prepared from soybean dregs. The effects of mass fraction of sulphuric acid, immersion time of dry soybean dregs, dosage of nitric acid, reaction time, reaction temperature and dosage of catalyst(mass ratio of antimony pentoxide to ferric chloride 1∶?1) on the yield of oxalic acid were studied. The product quality was also determined.The results showed that the optimal conditions were obtained as follows: mass fraction of sulphuric acid 70%, immersion time of dry soybean dregs 3 h, mass ratio of nitric acid to dry soybean dregs to catalyst 2.1∶?1∶?0.002, reaction temperature 65-70?℃, and reaction time 5-6 h. Under these conditions, nine batches of materials were continuously operated by mother liquid recycle, and the yield and purity of oxalic acid dihydrate were 76.5% and 99.5%, respectively. The product was determined as oxalic acid by IR, and its melting point, iron salt and sulfate contents, and buring residule content at 850?℃ were 1015?℃, 0.002%, 0.04% and 0.07%, respectively. |
