| With the rapid development of science and technology, the number of the electronics is on the increase, meanwhile, their service life becomes shorter, which has produced a large amount of waste electrical and electronic equipment (WEEE),and have brought enormous pressure on the ecological environment. As the severer laws and regulations are enforced, higher requirements for electronic waste disposal and recycling are needed. Printed circuit board (PCB) is an indispensable component of electrical and electronic equipment. WEEE is generally crushed mechanically to separate the metal, and then the residues are buried or burned. This processing method is resource-wasting as well as harmful to environment. As an environment-friendly technology of disposing waste PCB, vacuum pyrolysis can not only change the organic components in the PCBs into industrial chemicals and energy, but also separate the metal and nonmetal components effectively. Aiming at these questions, the typical kind of PCB named FR4was chosen as experimental materials and the involved studies are as follows:The pyrolysis characteristics of waste printed circuit boards were investigated by a thermogravimetric analyzer at different atmosphere and vacuum condition. The kinetics parameters were obtained by different kinetic data processing methods from the basic kinetics parameters such as thermogravimetric loss, initial and final pyrolysis temperature, the temperature at the maximum pyrolysis rate, and so on. The results showed that the pyrolysis under vacuum can significantly reduce the activation energy compared with decomposition under inert atmospheres. The pyrolysis actions under nitrogen and vacuum both belong to the same mechanism.After a self-designed fixed-bed pyrolysis experimental device was set up and pyrolysis liquid, solid, gas products of waste PCBs were collected, a series of experiments were carried out to study the pyrolysis law of waste PCB, and the effect of process parameters such as pyrolysis temperature, heating rate, condensing temperature, vacuum degree and heat preservation time on the vacuum pyrolysis procedure was detected. The results showed that the most effect of the pyrolysis oil yield is pyrolysis temperature, next is condensing temperature. Based on an overall consideration of factors, the optimum process condition for the liquid yield is as follows:the pyrolysis temperature is500℃, the system pressure at15kPa, the heat preservation time at30min, the heating rate at30℃/min and the condensing temperature at-25℃.The pyrolysis products were analyzed by GC-MS, FT-IR and SEM-EDS. The formation and distribution of brominated organic component during the thermal pyrolysis process was analyzed by combining the results of TG and FTIR, and the possible decomposition mechanism of epoxide resin in the PCB was studied. The main gaseous product is CO2, CO, H2and CH4, which can be recycled as combustible gas. The most considerable product in the liquid product was phenol followed by4-isopropylphenol,4,4’-(promane-2,2-diyl) diphenol and their substituent. The pyrolysis residues mainly consist of glass-fiber and carbon, and they can be separated and recycled easily. The residues contain several elements such as carbon, oxygen, silicon, aluminum, calcium, etc. Comparing with the pyrolysis at atmosphere, the solid product from vacuum pyrolysis contains less carbon, and the glass-fiber is barely destroyed after pyrolysis and can be reused.Nine kinds of additives were used to study the influence of additive on the vacuum pyrolysis of WPCB. According to the results of SEM, EDS and thermodynamic analysis, metallic iron, copper oxide and iron oxide have better debromination ability, among which the debromination reaction of iron is completest with quite low equilibrium HBr pressure. It was found that the produced metal bromide has some catalytic on the pyrolysis reaction. |
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