From pollutant to valuable phenolic resin: a novel reutilization strategy of industrial semi-coking wastewater

Semi-coking wastewater is a highly pollutive side product from coal chemical industry. In this study, we present a novel reutilization strategy of semi-coking wastewater that convert the abundant phenols and highly concentrated ammonias into thermoset phenolic resin via facile reaction with formaldehyde. The effects of reaction temperature, formaldehyde amount, and reaction time on the yield and quality of the acquired phenolic resin were investigated, and the water quality of the semi-coking wastewater after reaction was determined and compared with the untreated ones. The results showed that the optimal reaction condition was 95 °C for 2 h, under which 1.986 g phenolic resin was obtained from reacting 1.2 mL of formaldehyde with 80 mL of semi-coking wastewater. The obtained phenolic resin had a spherical microstructure, and its FT-IR spectrum was in good consistence with that of the standard phenolic resin with low content of residual phenol and formaldehyde. The reaction with formaldehyde endows efficient removal of phenols, COD and ammonia nitrogen in the semi-coking wastewater, with removal rates of 99.19%, 44.46% and 60.10%, respectively. Furthermore, the scale-up experiment was conducted, and 0.86 kg phenolic resin was generated from 40 L semi-coking wastewater, indicating the robustness of the process and the reliability for up-scaling. The presented strategy realizes the economic reutilization of semi-coking wastewater with synergetic pollutant remediation and value-added production, which sheds light on the treatment of other wastewater rich in phenol and ammonia too.