Removal of thiophene in air stream by absorption combined with electrochemical oxidation

Abstract

Abstract As typical heteroaromatic compounds, thiophene is an air pollutant that pose serious environmental and health related impacts due to its volatility and toxicity. This work reports a hybrid process of absorption combined with electrochemical oxidation to degrade thiophene. The ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) was employed as the absorbent to capture thiophene from air stream. Linear sweep voltammetry (LSV) demonstrated that thiophene could be oxidized on β-PbO2 anode modified with fluoride at 1.28 V versus Ag/Ag + electrode (RE) with a scan rate of 100 mV/s while [BMIM]BF4 was used as the electrolyte. Results of bulk electrolysis showed that thiophene could be thoroughly degraded within 60 min in [BMIM]BF4 under 50 mA/cm2 due to the successive attack of hydroxyl radicals (·OH) produced by electrolysis on the surface of β-PbO2 anode. Acetic acid was determined as the main intermediate and could be further mineralized to fumaric acid, maleic acid and oxalic acid, while sulfur atom in thiophene was finally converted to sulfate ions (SO42−). Based on the HPLC analysis and a precipitation of BaSO4, degradation pathway of thiophene was proposed and the thiophene sulfur could be degraded completely into sulfate. The kinetics of the electrochemical oxidation process for thiophene can be described by the pseudo-first order model. This absorption-electrochemical oxidation method with continuous operation would be a promising way for the clean and safe removal of heteroaromatic compounds from waste gases.