| The flame retarded plastics in waste electric and electronic equipments (WEEE) are usually disposed by landfill or incineration which not only wastes resource but also brings giant pollution on environment. Pyrolysis is the unique way to transform the plastics into oil, and is one of the effective approach to recycle plastics as well. However, because of the brominated flame retardants in WEEE plastics which raise a challenge of utilizing the oil with brominated compounds. Although the debrominated oil can be used as chemical feedstock after distillation, complexity of the oil hinders the development in industrialization. Fuel oil is in great need in China, if the physical and chemical properties of the treated pyrolysis oil can be up to the national standard of fuel oil ,and then can be used in industrial fields, that will have practical significance in energy saving and environmental protection.Taking the waste brominated flame retarded TV shells as research object, we select the technical route of two-step vacuum pyrolysis to degrade the brominated flame retarded WEEE, furthermore the nanotechnology is adopted to debrominate the main bromides in the oil collected from the second step. The related technical and theoretical studies are as follows: Several analytical techniques such as SEM, FTIR, GC/MS and TG/DTG were used to study the TV shells′physical and thermal properties. It has been found that TV shells are the typical high impact polystyrene(HIPS), and contain three polybrominated diphenyl ether(decabrominated diphenyl ether, nanobrominated diphenyl ether and octabrominated diphenyl ether in which decabrominated diphenyl ether is the major component ). As for the thermal property, the TV housings underwent two weight loss step, and the vacuum can significantly decrease the apparent activation energy.Pyrolysis experiments of TV housings under vacuum were carried out in a tube furnace. Influence of flash pyrolysis and two-step controlled pyrolysis on the products yield and distribution was studied. Experimental results showed, two-step controlled pyrolysis remarkably influence on the distribution and yield of main components and bromides. Pentabromobenzene and low bromine number polybrominated diphenyl ether are the main bromides.Taking 1,2,4,5-tetrabromobenzene (1,2,4,5-TBB) and decabrominated diphenyl ether as debrominated objects, nanoscaled Pd/C as catalyst, isopropyl alcohol as main solvent and hydrogen donor, meanwhile by means of GC/MS, HPLC and SEM, various factors which have effects on debromination were probed into. The debromination kinetics mode of 1,2,4,5-TBB was developed and the debromination mechanism was studied. The following conclusions could be drown: the reaction conditions remarkably influence the debromination efficiency. The high temperature, the more catalysts, the longer reaction time and temperate pH are benefit to debromination. Because of different properties, the additional hydrocarbons produce different influence on debromination rates and effects. The debromination rates are strongly suppressed in the presence of aromatic hydrocarbon such as toluene, but the debromination rates are hardly affected by the addition of aliphatic hydrocarbon such as n-hexane.Catalytic debromination and purification studies on pyrolysis oil of TV shells were carried out. The main components and bromides in the treated oil were analyzed, meanwhile the main physical and chemical properties were tested based on the standard of SH/T0356-1996. The results showed that the debromination efficiency was up to 95.5%. As for the oil quality, three indexes were obtained, flashpoint is about 25℃, kinematic viscosity is 5.6 mm2.s-1, sulfur content is 0.0738%. Comparing with the fuel oil, the flashpoint is lower, kinematic viscosity and sulfur content is both up to the standard of SH/T0356-1996. |
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