Study On Pyrolysis Of Printed Circuit Boards At Medium-level Temperature

As the development of electronic industry, people enjoy the huge benefit. At the same time, lots of printed circuit boards fall into disuse. If these waste PCBs are filled into the dumping site or combustion furnace, the products will be very harmful and will do lots of damage on the environment and the health of the human beings.Until now, waste PCBs treatment approaches can be roughly divided into several categories: (1) mechanical means; (2) fire metallurgy under high temperature; (3) wet-process metallurgy; (4) biological method; (5) electrochemical process; (6) pyrolysis method and so on. The first three of them are traditional ones and are more widely used. But there are also some faults that are difficult to overcome. At the same time, pyrolysis is a new way and is not fully developed so far. Under this circumstance, this article does some research on the weight loss of PCBs under medium temperature when the whole device is filled with nitrogen. Also, a new miniature stationary bed are designed and made to study the chemical reaction. The result of the research will provide some gist for the industry. During the process, some gas and liquid are gathered and some metal are obtained from the solid residue. There are also some experiments to check what chemical materials are produced in the chemical reaction and their effect on the environment.The analyses of the curve of DTA show that, the chemical reaction starts at around 300 Celsius degree, and reaches the highest reaction rate at 320~370℃. When the temperature reaches 330~430 Celsius degree, the reaction finished. Caused by the heat transfer, the starting temperature becomes high as the temperature rising rate rises, the whole reaction process takes less time, and the reaction becomes more acute. After the reaction, the result shows that the weight of gas takes 18.91% of the products, liquid takes 8.33%, and solid 72.76%. The activation energy of the pyrolysis reaction is 102.65kJ/mol, and the pre-exponential factor is 386972.8min-1 according to the Kissinger and they are 8827.428min-1 and 130.4572 kJ/mol according to Coats-Redfern .The result of the chemical analysis shows that: the main component of the gas mainly is carbon monoxide,carbon dioxide,propene,ethyl bromide,methylene chloride, and some other micro-molecule organic substance which contains 3~11 carbon atoms; The light fraction separated from the oil is acetone, phenol and some other aromatic compound. The molecular weight of them is between 50~240 and the number of carbon is between 3~17. Other than these, there are also some thick oil and some waxy bitumen. The solid residue consists of brittle coke and metal. The copper sheet which is in the outer layer contains copper,nickel,iron,gold and some carbon attaching on the sheet which is difficult for scavenging. The internal sheet contains carbon and copper only.In this paper, a new method, pyrolysis at medium-level temperature is used in the treatment and reclamation of the waste PCBs. The result of the research shows that the nest condition is: the final temperature is 500 Celsius degree. The heating-up rate can be decided according to the experiment. Finally, the metal we get from the experiment is about 8% to 8.8%; gaseous product account for 18.91%, the oil takes 8.33% and the other solid products take 72.76%.