Influence of textural properties and iron content on the activated carbon performance for catalytic wet air oxidation of phenol
Advancing the chemical engineering fundamentals
Catalysis (T2-13P)
Keywords: activated carbon, catalyst, phenol oxidation, porosity modification
Nowadays, wastewater treatment is a key issue in chemical process industry. Increasingly stringent regulations about the disposal of hazardous chemical substances force waste water treatment industry to not only improve the existing techniques but also develop new alternatives for the treatment of effluents. Many of the available wastewater treatment methods are based on the oxidation of the substances at high temperature and pressure using some oxidants. Subsequently, the use of a catalyst allows to temper the operation conditions. On the other hand, activated carbon (AC) has been used for years in water remediation (1), typically, in adsorption. AC can be made from almost any carbonaceous source such as wood and coal.; even great results have been obtained using sewage sludge as raw material (2). Different physico-chemical characteristics of AC, as porosity and surface chemistry, can be obtained by controlling the media and conditions during the activation step. Also, post-manufactured treatments look like alternatives to improve the performance of AC in different applications. For instance, heat treatment under inert atmosphere has shown to be effective in reducing the surface oxygen content and increase the adsorption capacity towards phenolic compounds, which are well-known pollutants because of their high toxicity and poor biodegradability (3,4). AC has also shown to possess catalytic activity for certain reactions. Pereira et al (5), and Stüber et al (6) have used AC carbon as catalyst in oxidative dehydrogenation (ODH) of ethyl benzene and catalytic wet air oxidation (CWAO) of phenol, respectively. However, the specific physical and/or chemical characteristics that provided these catalytic activities are not yet well identified. Using heat treatment to partially remove surface oxygen, Pereira et al (5) found that surface quinones groups were responsible for the catalytic activity shown by AC in ODH. Nevertheless, the surface oxygen groups that might be partially responsible for the catalytic activity of AC in the CWAO of phenol have not been clearly identified. In order to clarify which properties could influence the catalytic behaviour, a commercial AC with proven catalytic activities has been modified using several modification methods. It was found that a basic and stable to reoxidation AC surface, such as that obtained after a heat treatment under H2, can increase the steady state phenol conversion up to 10%. Previous results obtained after acid treatment of the AC demonstrated that an increase in the surface oxygen content gave worse final phenol conversion (7). Moreover, Fe content also seems to have some impact on the catalytic activity shown by AC, since previous studies made with demineralised samples showed a lower phenol conversion. However, the effect of textural properties has not been sufficiently studied, as all the treatments conducted until now have not practically changed either the surface area or the porosity. The aim of this work is to study the impact of porosity and Fe/Ca content on the CWAO of phenol. A commercial AC was initially subjected to either Ca or Fe impregnation by ion exchange, then heat treated under N2 at 1000°C. An enhancement in the mesoporosity of the samples was observed due to carbon pore enlargement. Surface area and pore size distribution of carbons were characterised by N2 adsorption and mercury porosimetry. The oxygen content was determined by elemental analysis while surface oxygen groups were characterised by Boehm method. The performance of these modified samples was evaluated by phenol adsorption and CWAO of phenol in a trickle bed reactor.
References
1. Dabrowski, A., P. Podkoscielny, Z. Hubicki and M. Barczak, Adsorption of phenolic compounds by activated carbon - a critical review. Chemosphere, 2005. 58(8):1049-1070.
2. Rio, S., Faur-Brasquet, C., Le Coq, L., Lecomte, D., and P. Le Cloirec, Preparation and characterization of activated carbon from sewage sludge: carbonization step. Water Sci. Technol., 2004. 49(1): 139-146.
3. Ania, C.O., J.B. Parra, and J.J. Pis, Influence of oxygen-containing functional groups on active carbon adsorption of selected organic compounds. Fuel Process. Technol. 2002. 79(3):265-271.
4. Tessmer, C.H., R.D. Vidic, and L.J. Uranowski, Impact of oxygen-containing surface functional groups on activated carbon adsorption of phenols. Environ. Sci. Technol. 1997. 31(7):1872-1878.
5. Pereira, M.F.R., J.J.M. Orfao, and J.L. Figueiredo, Oxidative dehydrogenation of ethylbenzene on activated carbon catalysts. I. Influence of surface chemical groups. Appl. Catal., A 1999. 184(1):153-160.
6. Stüber, F., I. Polaert, H. Delmas, J. Font, A. Fortuny, and A. Fabregat, Catalytic wet air oxidation of phenol using active carbon: performance of discontinuous and continuous reactors. J. Chem. Technol. Biotech., 2001. 76(7): 743-751.
7. Santiago, M., F. Stuber, A. Fortuny, A. Fabregat and J. Font, Modified activated carbons for catalytic wet air oxidation of phenol. Carbon, 2005. 43(10): 2134-2145.
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Presented Wednesday 19, 13:30 to 15:00, in session Catalysis (T2-13P).
