First highly effective non-catalytic nitrobenzene reduction in UV/dithionite system with aniline production – Advanced reduction process (ARP) approach

Abstract

Advanced reduction processes (ARPs) are currently intensively investigated as an alternative to Advanced Oxidation Processes (AOPs). The study presents efficient reduction of nitrobenzene under non-catalytic conditions through reaction with free radicals having reductive potential. Effective conversion of nitrobenzene in a model wastewater solution, was obtained for sodium dithionite (SDT)/ dithionite (DTN). The developed process provide a nitrobenzene reduction efficiency of > 99.9 % within 10 min under neutral conditions, ambient temperature, with a molar ratio of reductant to pollutant (rred) of 3. Additional UV radiation lowered by 10 % the dose of DTN. Interestingly, addition of titanium dioxide (TiO2) as a photocatalyst did not show a positive effect. An extremely significant conclusion of this study is the observed excellent resistance of the reaction system to the negative influence of inorganic anions, with a reduction in efficiency in the following order: CO32-22%>NO3-6%>SO42-2%>Cl-2%>NO2-<1%>S2O32-<1%>N3-<1% and dissolved organic matter (DOM) (<13%). The study showed that the process works effectively across the pH range from 3 to 12. Studies on the reaction mechanism revealed that sulfur dioxide anion radical (SO2∙-)) was responsible for the main reduction effect. The main product of nitrobenzene reduction was aniline (>99.9 %). The total cost of purification process was USD 0.77/m3. The high efficiency, short process time, low cost, and lack of need for complicated equipment make this developed process potentially widely applicable in the industry. The developed method for the reduction of nitrobenzene to aniline is the first non-catalytic method with such high efficiency and without the formation of intermediate reaction products.