| Waste printed circuit boards (WPCBs) contain many chemical pollutants and high value materials. It is becoming a hot research topic to efficiently and environmental friendly treat and recover WPCBs. Traditional treatment technologies such as pyrometallurgy, hydrometallurgy, mechanical treatment caused serious environmental pollution, and could not recover the valuable materails. Some new treatment technologies such as biological treatment, supercritical fluids, ionic liquids were costly and immature, and their industrial application was limited. Pyrolysis is a promising treatment technology for WPCBs. Researches on pyrolysis characteristics, pyrolysis products distribution and materials recovery and high-value utilization need to be further exploited. Un-controlled decomposition of brominated flame retardants caused the brominated contaminants emission, which need to be controlled. So far, most WPCBs pyrolytic debromination researches did not involve the debromination performance on the products in three phases, and researches on bromine recovery and high-value utilization of pyrolysis products were also limited.In this study, a method of pre-pyrolysis combined with pyrolytic debromination of WPCBs with additives was proposed. At the low pyrolysis tempature, brominated epoxy resin was decomposed, which weaked the bonding of metal and non-metal, thus facilitating the separation and recovery of high-value materials. In addtion, pyrolysis gas and pyrolysis oil could be reutilized as fuel or chemical materials. As for pyrolytic debromination experiment, additives helped to recover the bromide elemental by converting organic bromide into inorganic bromide during the decomposition of brominated flame retardants. The pyrolysis process will not pollute the environment and pyrolytic products could be utilized in more environemtnal friendly manners. A series of experiments were carried out and main conclusions were drawn as follows:(1) Characteraziation results showed that the WPCBs contained a low calorific value (9.18～11.06MJ/kg), high ash content (65%～75%), high metal content (20%～35%). The metal content suggested that WPCBs possessed a high materials recovery value. However, the high bromine content (2%～5%) could cause the brominated pollutant emission. The TG/DTG analysis indicated that pyrolysis process occurred mainly at temperatures between300℃and500℃. In this temperature range, the brominated epoxy resin was decomposed, and various phenolic derivatives were generated together with small molecules gases and bromine-contained components.(2) The tubular pyrolysis experimental results indicated that the examined reaction temperatures (400℃and600℃) exerted a little effect on products distribution. Considering the decomposition degree and energy consumption,500℃was chosed as the optimal pyrolysis temperature. At this temperature, the yields of pyrolysis oil, gas and solid were10%,20%and70%, respectively. As for the gas products, the main components of pyrolysis gas were H2, CO, CO2and CH4with the calorific value of9.35～12.94MJ/Nm3. The GC/MS anlysis indicated that pyrolysis gas contained some harmful gases such as CHs Br, benzene and toluene. As for pyrolysis oil, the main components were phenol and substituted phenols with the calorific value of25.13～26.22MJ/kg containing a high percentage of organic bromides. Pyrolysis solid was easily to be crushed, metal and glass fibers were recovered with recovery rate more than95%.(3) In the pyrolytic debromination experiment, different types of additives were added into WPCBs. The results indicated that the additives did not affect the yields of gas, liquid and solid. However, it was found that NaOH and Ca(OH)2transformed more than85wt.%of total bromine into inorganic bromine and the pyrolysis products were free of organic bromine. Pyrolysis of WPCBs with alkali could recover the high-value materials in a more efficiently and environmetally friendly manners. Pyrolysis with molten salt could fully decompose organic components of WPCBs, and metal and non-metal could be easily separated and recovered. Pyrolysis gas yields were increased and more than90%of pyrolysis gas were combustible gas with a higher calorific value. |
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