Chemical Recovery in TEMPO Oxidation

To be regarded as environmentally friendly and economical, an industrial process using 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) oxidation requires recycling and/or recovery of chemicals. In this work, hypochlorite recycling via electrolysis was evaluated and potential means for TEMPO recovery were explored. The most important variable affecting electrochemical hypochlorite conversion was the concentration of sodium chloride in the feed solution. With 30 g/L NaCl salt, a sufficient hypochlorite concentration of 0.8% could be obtained for pulp oxidation of up to 5% consistency. The regeneration of hypochlorite in the treated TEMPO solution was possible by electrolysis and further oxidation performed with only a small addition of make-up chemicals. During electrolysis, some TEMPO degradation took place; therefore, recovery of TEMPO should be done prior to electrolysis. For the recovery of TEMPO, solid phase extraction (SPE) was tested. The best recovery of TEMPO was obtained using a combination of hydrophobic SPE resin material and distillation (yields between 52% and 87%).