TiO₂ reactivation in photocatalytic destruction of gaseous diethyl sulfide in a coil reactor

Diethyl sulfide (DES) photocatalytic oxidation was carried out in a flow research reactor with TiO₂ Hombikat UV 100 deposited onto the internal surface of a Pyrex coil. The reactor allowed easy catalyst reactivation by washing with water. Mass transfer limitations were not detected in the reactor. Catalyst deactivated after several hours of complete DES mineralization, which was expressed by decrease of effluent CO₂ concentration and appearance of gaseous intermediates. Catalyst reactivation was achieved by two procedures: (1) irradiating photocatalyst until complete mineralization of adsorbed organic products with subsequent water washing; and (2) immediate washing with water. The water used after the first procedure contained only H₂SO₄, while after the second procedure it contained organic intermediates. The second procedure was much faster. Lower water concentration and higher catalyst loading allowed longer catalyst stability in DES oxidation. Low feed DES concentration resulted in much longer deactivation. Twelve consecutive runs were done to test reactivation completeness. Some permanent catalyst deactivation was noted and explained by TiO₂ etching with H₂SO₄. Gaseous and surface intermediate products were detected in the reactor effluent and catalyst wash water using solid phase microextraction (SPME) and trimethylsilyl derivatization. Main gaseous products were acetaldehyde, diethyl disulfide, ethylene, SO₂, and main surface products were diethyl disulfide, diethyl trisulfide, 1,2-bis(ethylthio)ethane, ethanesulfinic, ethanesulfonic acids, diethyl sulfoxide, diethyl sulfone, and sulfuric acid.