Recovery of triphenyl phosphate from waste printed circuit boards by solvothermal process

• A process for triphenyl phosphate (TPPO) recovery from PCBs was established.
• The structure of recycled TPPO was in good agreement with TPPO standard material.
• The PCBs became phosphorus-free with structure and inorganic components maintained.
• The kinetics analysis of solvothermal process was evaluated and better understood.

Organophosphorus flame retardants (PFRs) have been largely used in waste printed circuit boards (PCBs) because of the regulation of brominated flame retardants (BFRs) in recent years. In the present study, triphenyl phosphate (TPPO), a typical PFR, contained in waste PCBs was tentatively subjected to solvothermal treatment in order for efficient recycling of this type of valuable resource. Experimental results showed that the optimum operation temperature, time and liquid to solid ratio for TPPO removal were 90 °C, 120 min and 10:1, respectively. After solvothermal treatment, TPPO was transferred into the solvents and solid TPPO powder was easily recovered through vacuum rotary evaporation. The TPPO recovery efficiency reached 84.4% in a purity of 93.4% and dephosphorization efficiency of waste PCBs reached 97.3%. Shrinking core model (SCM) indicated that both interface transfer and internal diffusion affected the recovery rate of TPPO in the solvothermal process. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) profiles of the recycled TPPO were in good agreement with TPPO standard material indicating that the structure of the recycled TPPO maintained after the recovery process. This work provides a clean and applicable process for PFRs recovery from waste PCBs.