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Urea Degradation by Electrochemically Generated Reactive Chlorine Species: Products and Reaction Pathways

Cho, Kangwoo and Hoffmann, Michael R. (2014) Urea Degradation by Electrochemically Generated Reactive Chlorine Species: Products and Reaction Pathways. Environmental Science and Technology, 48 (19). pp. 11504-11511. ISSN 0013-936X. http://resolver.caltech.edu/CaltechAUTHORS:20141120-111400084

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Abstract

This study investigated the transformation of urea by electrochemically generated reactive chlorine species (RCS). Solutions of urea with chloride ions were electrolyzed using a bismuth doped TiO_2 (BiOx/TiO_2) anode coupled with a stainless steel cathode at applied anodic potentials (E_a) of either +2.2 V or +3.0 V versus the normal hydrogen electrode. In NaCl solution, the current efficiency of RCS generation was near 30% at both potentials. In divided cell experiments, the pseudo-first-order rate of total nitrogen decay was an order of magnitude higher at E_a of +3.0 V than at +2.2 V, presumably because dichlorine radical (Cl_2–•) ions facilitate the urea transformation primary driven by free chlorine. Quadrupole mass spectrometer analysis of the reactor headspace revealed that N_2 and CO_2 are the primary gaseous products of the oxidation of urea, whose urea-N was completely transformed into N_2 (91%) and NO_3– (9%). The higher reaction selectivity with respect to N_2 production can be ascribed to a low operational ratio of free available chlorine to N. The mass-balance analysis recovered urea-C as CO_2 at 77%, while CO generation most likely accounts for the residual carbon. In light of these results, we propose a reaction mechanism involving chloramines and chloramides as reaction intermediates, where the initial chlorination is the rate-determining step in the overall sequence of reactions.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/es5025405 DOIArticle
http://pubs.acs.org/doi/abs/10.1021/es5025405PublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/es5025405PublisherSupporting Information
ORCID:
AuthorORCID
Hoffmann, Michael R.0000-0002-0432-6564
Additional Information:© 2014 American Chemical Society. Received: May 23, 2014; Revised: September 2, 2014; Accepted: September 14, 2014; Published: September 15, 2014. We acknowledge the financial support of the Bill and Melinda Gates Foundation (BMGF RTTC Grant OPP1037491 and OPP109500C). This project benefited from the use of instrumentation made available by the Caltech Environmental Analysis Center. Korea Institute of Science and Technology supported the graduate study of Kangwoo Cho.
Funders:
Funding AgencyGrant Number
Bill and Melinda Gates FoundationOPP1037491
Bill and Melinda Gates FoundationOPP109500C
Korea Institute of Science and Technology (KIST)UNSPECIFIED
Record Number:CaltechAUTHORS:20141120-111400084
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141120-111400084
Official Citation:Urea Degradation by Electrochemically Generated Reactive Chlorine Species: Products and Reaction Pathways Kangwoo Cho and Michael R. Hoffmann Environmental Science & Technology 2014 48 (19), 11504-11511
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52003
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:20 Nov 2014 19:28
Last Modified:19 Jun 2015 22:23

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