Pyrolysis of waste printed circuit boards
In recent years, organic waste pyrolysis technology has been increasingly used for its low pollution emissions and high energy recovery rate. The use of pyrolysis technology to treat waste printed circuit boards can not only recover the metal in the circuit board, but also realize the recycling of non-metallic components such as resin and glass fiber, which has certain appeal.
Pyrolysis is the process of heating organic matter to a certain temperature under anoxic or anaerobic conditions to decompose it into gas, liquid (oil), solid (coke) and recover it.
General process flow of circuit board pyrolysis
First remove the components on the circuit board, then crush the board to a certain size and send it to the reactor for pyrolysis. Polymer materials such as epoxy resin are heated to a certain temperature under the protection of inert gas to thermally decompose, producing substances with low molecular weight. The pyrolysis oil and gas from the reactor is condensed to obtain non-condensable gas and liquid pyrolysis oil. The metal and glass fiber and other components do not change in nature, and remain in the reactor as solid phase residue, which can be separated and recovered by a simple physical method.
Pyrolysis products circuit board pyrolysis gas main components are CO2, CO, HBr, lower aliphatic hydrocarbons and some low molecular weight aromatic hydrocarbons. The pyrolysis gas has a certain calorific value, which can be recovered as a heat source for the pyrolysis process.
The composition of pyrolysis oil is complex, the boiling point range is large, the calorific value is high, and it has properties similar to crude oil. Pyrolysis oil contains many valuable components. If it can be recycled reasonably, the economics of the entire pyrolysis process will be greatly improved.
Pyrolysis oil recycling
Use as fuel When the processing scale is not large and the pyrolysis oil output is low, it is simple and feasible to use it as fuel. Chien et al. Obtained four fractions of light naphtha, heavy naphtha, light oil and gas, and heavy oil and gas by pyrolysis oil at atmospheric pressure. The high-temperature fractions with higher calorific value are sold as low-grade fuel oil, and the low-temperature fraction naphtha and light oil and gas that have undergone moderate hydrogenation, deoxidation, and dehydration treatments can be recycled as the main components of gasoline and diesel.
Extraction of high value-added substances as the main components of chemical raw materials pyrolysis oil phenol and isopropyl phenol are important organic chemical raw materials, widely used in plastics, medicine, pesticides, dyes, paints and other fields. If these substances can be separated and extracted, they will be more valuable than pure fuel oil. Wang Qing et al. Explored the separation process conditions of phenol, isopropylphenol and water in pyrolysis oil through intermittent rectification test. The content of the separated product isopropylphenol is not less than 90, and the phenol complies with GB3079-1997 standard. Iji et al. Used a rotary kiln to pyrolyze glass fiber reinforced epoxy resin waste to obtain high-purity glass fiber, which was used as an epoxy resin polymer filler and insulation material for recycling, and achieved good results.
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