Studies On The Microwave Pyrolysis Gas Of Wasted Circuit Boards

At present,a lot of the recycling disposal methods of waste printed circuit board have been proposed both at home and abroad, but it is not difficult to find that the method of microwave combined with pyrolysis is more efficient and energy-saving by comparison of disposal methods in recent ten years. This method can not only reduce the recycling time of waste circuit board, but also the reagent used less relative,so the processing cost is cheap. Therefore our experiment adopts the method of microwave pyrolysis of waste circuit board.In our experiment, the waste circuit board components were characterized in a full range at first by using scanning electron microscope, X ray diffraction, X ray photoelectron spectroscopy and Fourier transform infrared spectra of four kinds of methods. The characterization results confirmed the elemental composition and the content of each element of waste circuit board, also confirmed the chemical composition and molecular structure of waste circuit board. It is provides the theoretical foundation for the pyrolysis gas study of waste circuit board.Secondly, approximately inferred the composition of microwave pyrolysis gas through the analysis of literatures on microwave pyrolysis products of waste circuit board in recent years. By this, it’s not only provides the general direction of the study on the composition of pyrolysis gas, but also provides the guidance of detection method for composition of pyrolysis gas.Experimental study on the microwave pyrolysis gas composition of waste circuit board was carried out under the following conditions:microwave time15min, microwave power633W,the size of circuit board is about lcm2.Under the experimental circumstance, the composition and molecular structure of the collected pyrolysis oil was analyzed by GC/MS, also analyze of volatile components in it. The experimental results show that the pyrolysis gas contains organic gases like phenol、cresol and phenol substitutions and phenol polymer. It’s determined that the most serious pollution factor is phenol in our experimental processing through the analysis of the composition of the pyrolysis gas. Combining the characteristics of phenol, and the harm to human body and environment to determine the approach to processing of phenol is adopting absorbing device with ethanol to absorb the phenol, the device is in series with three ethanol absorption bottle. In order to figure out whether the phenol has been absorbed completely, behind the absorption device there is a bottle which contains ferric chloride solution for indication. if the indication bottle’s colour turned XX into purple, it means that the phenol wasn’t absorbed completely, and more ethanol absorption device should be added to ensure the complete absorption of phenol. During the whole experiment, the experimenters must wear radiation protection lab coat, a gas mask and corrosion resistant gloves, moreover, the experiment should be performed in a fume hood.Because the experiment was carried out on the basis of the previous research, the treatment and disposal of the microwave pyrolysis residue of waste circuit board should be consistent with the previous:preparation of activated carbon after pyrolysis residue modified by nitric acid. The previous experimental result shows that the Pyrolysis residue imports oxygen-containing groups after soaking by Nitric acid. The oxygen-containing groups in the surface of pyrolysis residue exist in hydroxyl、carbonyl、carboxyl and lactone base forms, The hydroxyl content increased considerably, but lactone content declined. From the characterization of scanning electron microscopy results also show that compared with the unprocessed pyrolysis residue, the pyrolysis residue after soaking with nitric acid and hydrochloric acid has more irregular structure, after oxidized some skeleton appeared skeleton collapse and holes increase, ect. And the surrounding of the hole changed more smoother. All the results show that, the pyrolysis residue can be prepared for activated carbon by acid activation, and had a good result.Throughout the experiment, it is no secondary pollution basically. It reflected in the follows:after processing the pyrolysis residue,it can be prepared for activated carbon, pyrolysis oil can be used for the preparation of phenolic resin, after determined the pollution factor in the pyrolysis gas is phenol,to avoid the secondary pollution caused by phenol,we added the phenol absorption device; by precipitation with sulphide, waste water contains acid and alkali could avoid the pollution of heavy metal, and then by using natural neutralizationto to avoid secondary acid-alkali wastewater pollution, Therefore, our experiment achieved the maximum utilization of resources, and satisfied the requirements of processing friendly for environment, With the dual benefit for environment protection and resources utilization.