The Related Experimental Study On The Pyrolysis Of Waste Tires

With the increasing of waste tires, more serious environmental pollution and waste of resources have occurred. Retread, produce of reclaimed rubber and rubber powder, pyrolysis and incineration are all used to the disposal of waste tires. Retread needs waste tires with better appearance, and the retread times are limited. Meantime, retread leads to air pollution. Produce of rubber powder has high cost. Compared with the number and increasing rate of waste tires, rubber powder has less demand and capacity. Incineration can recover waste heat, but it can not recover valuable industrial raw materials. In contrast to the methods above, pyrolysis can recycle the resources as much as possible and it also has large processing capacity and high benefit, and what's more, pyrolysis is environmental acceptable. Therefore, pyrolysis is the main way to treat the waste tires. In this paper, the catalytic pyrolysis of waste tires and the modification of pyrolytic carbon black were studied, and the reuse of modified carbon black was also discussed.First, Fe2O3, CaO, ZnO, fly ash and modified fly ash were chosen as catalysts for pyrolysis of waste tires because of their industrial applicability. The catalysts were mixed with waste tire pieces in a certain proportion. Catalysts, pyrolytic temperature and amount of catalysts were studied on their effects on the yield of pyrolytic products especially the yield of pyrolytic oil. The results showed that the yield of pyrolytic solid residues maintained at about 38%, which had no much matter with the effect factors studied. The yield of pyrolytic oil decreased obviously when added 2% CaO. While added 2% ZnO, the yield of pyrolytic oil was as much as that without catalyst added. At 450℃, added 2% Fe2O3 got most pyrolytic oil, and it was 43%. At 400℃, the pyrolysis was very slow. When the pyrolytic temperature was up to 500℃and 550℃, the yield of pyrolytic oil decreased, and more pyrolytic gas produced. The yield of pyrolytic oil was up to 43% when added 5% modified fly ash at 450℃, which was the same as 2% Fe2O3 added.Then waste tires were pyrolysed at 500℃at atmospheric pressure and without catalysts added. The recovered pyrolytic carbon black was ground and sieved, then carbon black in 120-150 mesh (CBp) was modified. Modification was carried out by acid washing (with 2N H2SO4 and 2N HNO3, SCBp and NCBp for short) and then added with 1.5% stearic acid (SSCBp and SNCBp for short). For contrast,3.6N HNO3 was also used to wash the CBp. Some properties of these samples were characterized. The results show that the ash in CBp was 20.46%, and the ash was reduced to 8.65% after 2N H2SO4 washing. However, by 2N and 3.6 N HNO3 washing, the ash decreased to 4.02% and 1.16%. The fixed carbon in carbon blacks was closed to 90% after acid washing, meantime, the volatile was reduced but the DBP absorption number and BET surface area increased. Changes were more obvious in carbon black washing with nitric acid than sulfuric acid. SEM images showed that the surface of all the carbon blacks in the experiment was very rough, and many nano-level particles gathered into bigger grains with several to tens of microns. There were no inorganic oxides in the surface of CBp. There were carbonaceous deposits on the surface of CBp, and surface C existing in C=O was less than in C-O. Carbonaceous deposits reduced and surface C existing in C=O increased by acid washing. Surface oxygen functional groups existing in C-OR, C-OEt and COOR/COOH were more in SSCBp than in SCBp, which was consistent with the increasing volatile. There was no much difference between NCBp and SNCBp in surface carbon functional groups. Surface double-bonded oxygen in SSCBp and SNCBp increased relatively with SCBp and NCBp due to the dual role of physical and chemical activities. Regardless of the surface elements (C, O, S, N, Zn) content or changes in surface functional groups, the strength of nitric acid modification is greater than sulfuric acid.Finally, CBp and modified CBp in the reuse were forecasted, and the further research on catalytic pyrolysis of waste tires was suggested.