Supercritical water oxidation of chlorinated waste from pulp and paper mill

The article presents the research results of the oxidation of watered toxic waste from the pulp and paper industry (sludge-lignin, the empirical formula of organic matter CH1.51N0.05S0.03Cl0.01O0.54) in supercritical water-oxygen (SCW/O-2) fluid. The experiments were carried out using a flow tube reactor at a pressure of 25 MPa, temperature gradient along its vertical axis (from top to bottom: 390-600 degrees C), sludge-lignin flow rate of 9.5-14.5 g/min, oxygen ratio OR = 0.73-2.52, using NaOH (1.6 wt%) as a catalyst. Employing gas chromatography - mass spectrometry, polychlorophenols were identified in the composition of sludge-lignin, in which 2,4,6-trichlomphenol was the main component. The total yield of extracted phenols and chlomphenols per sludge-lignin organic matter was 20.82 and 2.88 mu g/g, respectively. It is revealed that the conversion rate of sludge-lignin in SCW/O-2 fluid is limited by heterogeneous oxidation of the carbonized residue, and is determined by the O-2 content in the reaction mixture. At OR >= 1.16, only CO2, CO, N-2, and N2O were detected in the volatile oxidation products. An increase in OR from 0.73 to 2.52 leads to a decrease in the total content of phenols (from 45540.1 to 129.3 mu g/dm(3)) and chlorophenols (from 51.4 to 2.2 mu g/dm(3)) in the water collected at the reactor outlet. It is shown that 2,6-dichlomphenol and 2-chlorophenol are the most resistant to oxidation. From the analysis of the initial sludge-lignin and mineral residues, it follows that the bulk of the chlorine contained in its organic matter is converted into NaCl in the course of oxidation.

Automated summary

This study investigated the oxidation of watered toxic waste from the pulp and paper industry in supercritical water-oxygen fluid, revealing that only CO2, CO, N2, and N2O were detected in volatile oxidation products at higher oxygen content. Increasing the oxygen ratio led to a decrease in phenols and chlorophenols produced, with 2,6-dichlorophenol and 2-chlorophenol being the most resistant to oxidation.