PARTⅤ SOLVOLYSISMICROWAVE-BASED CHEMICAL RECYCLINGTECHNOLOGY RESEARCH FOR WASTE PCB
Xiao-Yong Pan*, Lian Wang, Hui Zhi
Sichuan Changhong Electec Co.,Ltd , Mianyang 621000, China.
Abstract: Because epoxy condensate can be completely decomposed in nitric acid solution,
the glass fiber and epoxy resin in PCB can be fully recycled through this way and much morevalue can be obtained from the waste PCB. However, the decomposition efficiency is low,and several resultants are very toxic to human 0 . To solve this problem, this paper studied thedecomposition efficiency of the non-metallic powder from PCB and the resultants by using
microwave as an assistant tool. First of all, through a series of experiments, find the best
reaction conditions without the assistant of microwave. Then, study the acidolysis of thenon-metallic powder with the assistant of microwave through the orthogonal experiments. An
analysis on the composition of reaction resultants was done, the result showed that theassistant of microwave changed the chemical reaction of degradation, and also improved thereaction efficiency.
Key words: PCB; recycle; microwave1. Introduction
With the rapid development of electronic technology, the upgrading of products becomes
more frequent. Almost all the electronic products have some PCBs. After the separation ofelectronic components and solders, the PCB is smashed into powder, and then copper, tin,lead and other metal components in the powder would be seperated 000 . Finally, thenon-metal remains, which mainly contained epoxy resin and glass fiber, and the main
treatment of this non-metal can be classified as physical method and chemical method 0.
Among these treatment methods, the solvent chemical method is the most completed one.
This experiment used microwave’s high digestion capacity, to adjust the reaction kinetics ofsystem and improve the reaction efficiency at last 0.
The Green Manufacturing Department of Changhong Engineering Technology Centerhas done some research on chemical decomposition of epoxy condensate from the waste TV’sPCB. The study shows that in the decomposition reaction of epoxy condensate, microwave
can greatly accelerate the reaction speed, and change the reaction process. In this way, itsolves the issues of low efficiency, high energy consumption as well as large environmental
hazard, etc.

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2. Experiments
2.1 Experiment materials
The main materials required by this experiment include: self-made non-metallic powderof PCB, nitric acid, sodium hydroxide, acetone and so on.
2.2 Experiment process
According to a special proportion, put the non-metallic powder and a certain
concentration of nitric acid into a tree-neck flask with a reflux condenser. Heat it with theassistant of microwave, in different temperature, power, and time duration. Then, take out
reaction products from the flask. After the filtration and washing, place them into a drying
oven in 80 oC. Then, calculate the decomposition rate by weighting. Finally, The ScanningElectron Microscopy (SEM) analysis was carried out on the reaction resultants, test andcharacterize the reaction solution by Gel Permeation Chrommatograph and Gas
Chromatography-Mass Spectrum.
2.2.1 The experimental situation in different material ratios without the microwave

Fig. 1 The data of complete reaction in different material ratios (80°C / 40%)
Fig. 1 shows: the reaction temperature is 80 °C; nitrate acid concentration is 40%;
material ratio is 10 g/100 ml, 20 g/100 ml respectively. In these conditions, the reaction rateincreases gradually with the reaction time until 56h, when the reaction fully done, thenfollowed by a gradual equilibrium. Meanwhile, Fig.1 also shows that the reaction effect of 10g/100 ml is better than that of 20 g/100 ml, and the reaction rate is 61.69%. This result isalmost consistent with the study results of Liu Yuyan0 and others (reach a reactionequilibrium at 50 h).

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PARTⅤ SOLVOLYSIS
2.2.2 The effect of material ratio on the microwave-assisted nitric acid decomposition of thenon-metallic powder
Tab.1 shows the influence of different material ratios on the decomposition rate of thenonmetallic powder, when the reaction temperature is 80 °C, the microwave power is 800 w,
and reaction time is 8 h.
Tab. 1 The effect of different material ratios on
the decomposition rate of the nonmetallic powder
Material Ratio / g/100 mL

3.3101520

Decomposition rate / %68.0064.47

51.20

35.01

Tab. 1 also shows that: with the increase of material ratio, the decomposition rate of thenon-metallic powder declines rapidly within the specified time. According to a preliminary
analysis, it is due to the reducing of effective contact area between the non-metallic powder
and nitric acid, while the material ratio is increasing.
2.2.3 The orthogonal experiment of microwave-assisted decomposition of the nonmetallic
PowderFixing the material ratio at 10 g/100 ml and the reaction time at 8 h, considering theeffect of 3 factors on the microwave-assisted decomposition rate of the onmetallic powder:microwave power, temperature, and acid concentration.
2.2.4 Analysis of the composition of the reaction resultants
2.2.4.1 Analysis of High-Performance Gel Chromatography
Neutralizing the reaction solution with sodium hydroxide, and using the gel
chromatography (AGILENT HP1100, US) to test the molecular weight distribution of theresultants. The mobile phase is tetrahydrofuran; the flow rate is 1 mL·min-1; the standard
substance is polystyrene; the chromatographic column is plgel①5 min*104 A, plgel②5min*100 A; the detector temperature is 35 °C. The results are shown in Tab.2.
Tab. 2 The molecular weight distribution of the neutralized resultantsNo.

Mn/ g·mol-1

Mω/g·mol-1

Mz/g·mol-1

Mv/ g·mol-1

D1
2

172.94169.84256.26259.56371.45399.79256.26259.561.48171.5283

Tab. 2 shows that after the neutralization of sodium hydroxide, the molecular weight
distribution of the resultants is in a range from 100 to 1000 g·mol-1, which means that with the- 279 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
assistant of microwave, the high molecular polymer in the nonmetallic powder has been fully
degraded to low molecular weight compounds.
2.2.4.2 Analysis of Gas Chromatography-Mass Spectrum (GC-MS)
Making the neutralized resultans dissolved in acetone solution, and using the GC-MSanalyzer (VARIAN 3900-Saturn 2100T, US) to analyze the components. The
chromatographic column: VF-5MS (30 m×0.25 mm×0.25µm) fused silica capillary column;
the column flow rate is 0.5 mL·min-1; the column temperature rises from 100℃ to 200℃ at aspeed of 20 °C·min-1; the injection mode: split stream with a ratio 1:10; the carrier gas: He;
GC-MS interface temperature: 250 °C; EI source: 70 eV; the scan range: 40-650. Fig.2 shows
the corresponding gas chromatography.

Fig. 2 The gas chromatography of the resultants (800W / 80°C / 40%)
According to Fig. 2., the major resultants include: 2- hexylamine, dcpd dioxide, 1,1,3,3tetramethyl -1,3- diphenyl disiloxane, butyl cyclohexyl phthalate, etc. Almost all of them are
low or no toxic products. On the contrary, LIU Yuyan and others used water bath as theheating medium of nitric acid decomposition reaction. The main resultants are the compounds
like 2, 4-dinitrophenol and 2-nitro-4-carboxy-phenol, which are fairly toxic and harmful to theenvironment.
3. Conclusion(1) Assisted by microwave, the decomposition rate of the PCB nonmetallic powder
grows with the increase of microwave power and acting time. The microwave power can onlychange the proportion of the resultants’ compounds.
(2) The best material ratio is 10 g/100 ml, while the decomposition rate is 64.47%.
Through orthogonal experiment, the best reaction conditions are: microwave power 800 w,microwave temperature 80 °C, acid concentration 40%.

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PARTⅤ SOLVOLYSIS(3) In this microwave-assisted decomposition experiment for the PCB nonmetallic
powder, the molecular weight distribution of the resultants was within 100-1000 g·mol-1,
which proves that the microwave-assisted decomposition of the powder works well.
(4) The major resultants through the process of microwave-assisted decomposition
include: 2- hexylamine, dcpd dioxide, 1,1,3,3- tetramethyl -1,3- diphenyl disiloxane, butyl
cyclohexyl phthalate, etc. Almost all of them are low or no toxic. It implies that the chemical
reactions in the microwave-assisted decomposition are totally different with the ones in otherways.
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