Destruction of Hazardous Heterocyclic Nitrogen Containing Hydrocarbons By Supercritical Water Oxidation

SCWO of Nitrogen Containing Heterocyclic Hydrocarbons Found in Hazardous Aqueous Waste Streams: Process Enhancement by Addition of Isopropyl Alcohol

B. Al-Duri^1* and F. Alsoqyiani¹

¹School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom. Email: B.Al-Duri@Bham.ac.uk

Abstract

This work investigates the destruction nitrogen-containing heterocyclic hydrocarbons frequently encountered in hazardous wastes, by supercritical water oxidation (SCWO), considering the process enhancement by adding isopropyl alcohol (IPA) as co-fuel. DBU$ is selected for SCWO in a continuous plug flow reactor, under a temperature range of 400 to 575¡C, oxidant ratio of 0.8 to 2 times stoichiometric value, initial DBU concentration of 5mM (reactor conditions) and 25 MPa reactor pressure.  IPA was premixed with DBU at various IPA/DBU ratios (0.5 to 3.5). Experimental results were presented in terms of total organic carbon (TOC) removal %, and nitrogenous products yield %.  Based on GC-MS analysis exit streams, a reaction pathway from DBU to benign small compounds was proposed. 

Results indicated that the destruction of N-containing hydrocarbons occurs by virtue of the vigorous free radical mechanism where HO¥ and HO₂¥ were responsible for the scission of the C-N bonds, followed by a series of C-C and C-N scissions.  Temperature was found to be the main factor to influence overall destruction of DBU, while oxidant ratio predominantly affected the N speciation in the exit stream.  Alcohol addition enhanced the destruction of DBU in terms of TOC removal %. Specifically, it enhanced the conversion of recalcitrant ammonia (NH₄⁺) to gaseous nitrogen, which is highly advantageous in SCWO applications to nitrogenous waste destruction.

---

* Corresponding Author

$ 1,8-Diazabicyclo [5.4.0] undec-7-ene