2. Materials and methods
2.1. Materials
The WPCB without electronic components used for the experiments
originated from a local PCB factory. There was only copper
coating on the epoxy base plates. And the WPCB wasmulti-layered
structure, containing epoxy resin, woven glass fiber, brominated
epoxy resin flame retardant and copper. The components of WPCB
were given in Table 1.
2.2. Methods
The recycling process comprised vacuum pyrolysis and mechanical
processing. At the first stage of this work, approximately 3 kg
of WPCB were first cut into fragments of about 5 cm×5 cm using
an electrical saw and then pyrolyzed under vacuum in a fixed bed
reactor to separate and recover organic resins. At the second stage,
the residues obtained at the first stage were investigated to separate
and recover the copper and glass fiber through mechanical
processing, such as crushing, screening, as well as gravity separation.
A schematic diagram investigated for recycling WPCB was
shown in Fig. 1.
2.2.1. Vacuum pyrolysis
The vacuum pyrolysis experiments were carried out by using
a self-made batch pilot-scale fixed bed reactor according to our
previous research [31]. The reactor measured 350mmin length by
an internal diameter of 160mm and was externally heated by a
10kW electric heating furnace. Fig. 2 showed a schematic diagram
of the vacuum pyrolysis apparatus, which included electric heating
furnace, stainless steel fixed bed reactor, temperature control system,
condensing system, vacuum system and gases treatment and
collection system.
In a typical run, approximately 3 kg of WPCB pieces of about
5cm×5 cm were placed into the reactor at the start of the experiment,
and the reactor was then sealed and vacuumed to the total
pressure of 20 kPa by water ring vacuum pump before being heated
to 550 ◦C at a rate of 10 ◦C/min. Once the reactor had reached 550 ◦C
it was held at this temperature for 120 min to ensure that vacuum
pyrolysis of the sample was complete, and then natural cooling
to room temperature under vacuum. After exiting the fixed bed
reactor, the pyrolysis gases and oils passed through awater-cooledcondenser and then an ice-cooled condenser (ice salt water less
than −5 ◦C) that collected any oils and waxes released during the
vacuum pyrolysis process. In addition, a glass wool trap was used to
remove any oils or waxes that were not trapped by the condensers.
The water trunk contained 5 wt.% sodium hydroxide solution was
used to collect water-soluble compounds in the exhaust gas. The
organic and permanent gases were sampled by drawing off gas
samples into a syringe in order to analyze by gas chromatography
and collected using a gas bag. The pyrolysis residues and oils yields
were determined in each experiment by weighing the amount of
each obtained, while the pyrolysis gases yields were calculated by
difference.