Study On Extraction Of Flame Retardants From Electronic Printed Circuit Board By Supercritical Carbon Dioxide

Flame retardant is a kind of additives contained in the resin material of electronic products to avoid inflammation. Most of flame retardants are halogenated organic substances or phosphorous compounds, and triphenyl phosphate (TPP) as an environment- friendly flame retardant have been widely used recently.The disposal of waste electrical and electronic equipment is an urgent requiring problem to all over the country in this century. Waste printed circuit board (PCB) contains various metals, flame retardants and other renewable resources. In the conventional incineration and burial disposal process, it cannot be avoided producing some of pernicious components, which bring serious hazards to environment and human health. Moreover, these disposal processes waste vast resources. In this work, wet flotation and supercritical CO₂ extraction technique were use to recover metals and flame retardants from waste PCB respectively.Wet smash flotation method was employed to separate the metals and resin material containing flame retardants, and recover the metals from waste PCB. Several typical leftover PCB were acted as materials, the yield of copper obtained was up to 90 %. The Soxhlet extraction was used to determine the content of TPP in the resin material obtained by flotation. Under the different temperature and extraction time, the experimental results of toluene extraction indicate that extraction temperature is the main factor on the yield of TPP, and TPP yield increased with increases in the extraction temperature. The extraction rate of TPP was faster within 0.5 hours than other periods, and the yield of TPP achieved 60～80 %.The solubility of TPP in supercritical CO₂ was measured by a static equilibrium apparatus. The solubility of naphthalene was measured to test the feasibility of the apparatus, and the experimental data were in good agreement with the values of literature. Under the temperature range of 313～343 K and the pressure range of 10～25 MPa, the solubility of TPP in supercritical CO₂ were measured and correlated with the Peng-Robinson equation of state combining vdW-1 hybrid rules. Under the above experimental conditions, model calculations agreed roughly with the experimental results well.Flame retardant TPP from the mixture of the resins ground powder obtained by flotation and smash of waste PCB was extracted by supercritical CO₂. The composition of the extract was identified by infrared spectroscopy (IR) and gas chromatography/mass spectrometry (GC/MS), and the amount of the components was determined by GC. All the experiments were performed under the pressure of less than 25 MPa for the mixture of resin powder as material, and the effects of experimental parameters including extraction time, temperature, pressure and CO₂ flow rate on the extraction efficiency of TPP were investigated. A maximum extraction efficiency of TPP can be achieved at 98.72 % and higher significantly than that by toluene extraction. The yield of TPP increased with increase in both pressure and temperature. When extraction time was extended to 2.0 hours, the yield of TPP up to 80 % was achieved, and increased with increase in CO₂ flow rate.At higher pressure conditions, several resin powder of typical PCB acted as materials were experimented respectively by a pilot plant scale supercritical extraction apparatus. The extraction efficiency of TPP was obviously higher than that under low-pressure conditions. When pressure rose up to 30 MPa, the yield of TPP up to 90 % was obtained within 1.0 hours, and the TPP concentration of the extract achieved a maximum of 68 %.In conclusion, the extraction of flame retardants from electronic printed circuit board by supercritical CO2 is one of promising way in the reutilization of resources of waste electrical and electronic equipment.