IN SITU FORMATION OF HYDROGEN PEROXIDE FOR THE CATALYTIC REMOVAL OF PHARMACEUTICAL COMPOUNDS IN WASTEWATER USING HYDROGEN IN EXCESS OF OXYGEN/AIR

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1 Proceedings of the 13 th International Conference of Environmental Science and Technology Athens, Greece, 5-7 September 13 IN SITU FORMATION OF HYDROGEN PEROXIDE FOR THE CATALYTIC REMOVAL OF PHARMACEUTICAL COMPOUNDS IN WASTEWATER USING HYDROGEN IN EXCESS OF OXYGEN/AIR N.A. PANTELIDOU, C.P. THEOLOGIDES, G.G. OLYMPIOU, P.G. SAVVA and C.N. COSTA 1 1 Cyprus University of Technology, Department of Environmental Science and Technology, P.O.BOX 5329, 33 Limassol-Cyprus costas.costa@cut.ac.cy ABSTRACT To date, very few such prescriptive studies have been reported in the literature concerning the catalytic removal of pharmaceutical substances in wastewater using H 2 in excess of O 2, while the mechanism of the reaction have not been studied yet. For the first time ever the reactions of the in situ production of hydrogen peroxide and the catalytic wet oxidation of pharmaceuticals will be studied simultaneously, in order to find a novel catalytic system for the oxidation of pharmaceuticals in water medium. In the present work an attempt has been made, to elucidate the actual effects of the in situ production of hydrogen peroxide on the catalytic wet air oxidation of pharmaceuticals. Therefore, the effects of the chemical composition of the support, the nature of the active phase (Pd, Pt, Rh etc), as well as the reaction conditions (feed gas composition, temperature etc) have been examined towards the reaction at hand. Various pharmaceutical substances commonly appeared in wastewater, such as Paracetamol, Diclofenac Sodium and Ibuprofen have been chosen for the study of the pre-referred process. The physicochemical properties of the catalysts, the effectiveness of the alumina-coating procedure, the effect of several experimental parameters, the nature of active species, and the steps in a sequencing reaction will be thoroughly examined with a series of advanced techniques (BET, SEM-EDX, ICP-MS, SSITKA-DRIFTS). It should be noted that the present work provides quality evidences for the catalytic removal of paracetamol from water medium over monometallic (1 wt % Pd, Pt and Rh) catalysts supported on alumina spheres, especially in the case where high levels of H 2 appear in the air feed stream. In particular, it has been proven, that the conversion of paracetamol is enhanced in the case of 1 wt % Pd/γ-Al 2O 3 and 1 wt % Rh/γ-Al 2O 3 catalysts. However, the monometallic Rh catalyst seems to be preferred due to its ability to completely convert the paracetamol in less than 3 min of reaction, minimizing the cost of the process. Keywords: oxidation; pharmaceuticals; catalytic removal; hydrogen peroxide. 1. INTRODUCTION In the last decades, the consumption of pharmaceutical substances increased exponentially, with the environment to be especially burdened from their rejection. Human and veterinary drugs are rejected to the environment mainly as a result of manufacturing processes, improper disposal or metabolic excretion. In addition to that, the conventional technologies used for the treatment of organic pollutants are not refereed to completely remove the pharmaceutical residues from wastewater. Based on the literature [1-5], the amount of residues (ng/l to low μg/l) that remains even after going through wastewater treatment is still high to induce toxic effects. An alternative method is the catalytic wet air oxidation (CWAO), which reduces the severity of reaction conditions compared to Wet Air Oxidation (WAO) and more easily decomposes even refractory substances. Heterogeneous catalysts are advantageous compared to homogeneous catalysts since

2 they do not require an additional separation step to recover the metal ions from the effluent, which will increase the operation costs. Strong oxidizing agents like ozone, hydrogen peroxide and UV radiation which involve the generation of hydroxyl radical (OH) with high oxidative power can also be used in CWAO to further reduce the severity of reaction conditions. Methods involving ozone and UV radiation due to the specialized equipment needed are too expensive to be used widely. Hydrogen peroxide can be used as the radicals OH source due to its low cost. In addition, using hydrogen, in excess of oxygen/air, in the presence of a catalyst can lead to the in-situ production of hydrogen peroxide, which further reduces the cost of operation. Only very few research studies have been reported to the literature [6, 7] concerning the heterogeneous CWAO in excess of oxygen (air) and in the presence of hydrogen, while the mechanism of the reaction have not been studied yet. The scope of the present research is to develop a suitable, innovative catalytic system, which will show high reactivity and selectivity towards the CWAO of pharmaceutical substances in excess of oxygen and in the presence of hydrogen. For the first time ever the reactions of the in situ production of hydrogen peroxide and the catalytic wet oxidation of pharmaceuticals will be studied simultaneously, so as to find the best catalytic system for the oxidation of pharmaceuticals in water medium. In the present work an attempt has been made, to elucidate the actual effects of the in situ production of hydrogen peroxide on the catalytic wet air oxidation of pharmaceuticals. According to other researches [7, 8], the introduction of small amount of hydrogen gas into air feed stream leads to an appreciable increase of the of the wet oxidation activity of the catalyst, making the operation costs significantly lower. Other advantages of the proposed catalytic system are the low cost of installation and maintenance, the transformation of pharmaceutical compounds to innocuous compounds, such as carbon dioxide and water, no bacterial contamination of the effluent and the environment occurs, and iit can be used for the degradation of a wide spectrum of organic compounds in aqueous solutions since the method is not selective. More specifically, the proposed work will include the following: a. the study of the catalytic behavior of the prepared solids in the respect of reactivity and selectivity towards carbon dioxide (CO 2), and the selection of the most appropriate catalytic system for the reaction at hand. Therefore, the development and in-depth physicochemical characterization of novel metal-supported catalysts will take place. In particular, supported catalysts of different metals, such as platinum (Pt), iron (Fe), molybdenum (Mo), copper (Cu), ruthenium (Ru), palladium (Pd) and rodhium (Rh) on alumina (Al 2O 3) or other oxide-type supports, will be examined at reaction at hand. Various substances such as Paracetamol, Diclofenac Sodium and Ibuprofen are possible candidates to be used as references for the these studies. b. the characterization of the catalysts surface composition and morphology (BET, Scanning-Electron Microscopy- SEM, and Temperature Programmed Desorption- TPD) c. the detailed study of the mechanism of the reaction (determination of the active species) thoroughly advanced techniques (Temperature Programmed Surface Reaction, TPSR and Steady State Isotopic Transient Kinetic Analysis combined with Diffuse Reflectance Fourier Infrared Transform Spectroscopy, SSITKA-DRIFTS). It is worth mentioning that in the present paper are demonstrated the first promising results derived from the study of the conversion of paracetamol by the use of different reaction mixture (% vol H 2 in air) over various monometallic 1 wt % M (M=Pd, Pt and Rh) catalysts supported on γ-al 2O 3 speres.

3 2. EXPERIMENTAL The catalysts were prepared via modified wet impregnation method in accordance to our previous work [8]. Catalytic experiments were conducted in a custom-built autoclave (batch) reactor (Autoclave Engineers, U.S.A., and PID Eng &Tech, Spain) equipped with a Mahoney-Robinson catalyst basket. Paracetamol was chosen as the xenobiotic substances at a 1 mg/l concentration in water medium at 25 o C. Samples were taken at, 3, and 1 min and were tested using Ultraviolet Spectrophotometry at 243 nm and Total Organic Carbon Analyzer (TOC). The physicochemical properties of the catalysts, the effectiveness of the alumina-coating procedure, the effect of several experimental parameters, and the surface composition of species will be thoroughly examined with a series of advanced techniques (BET, SEM- EDX, ICP-MS, SSITKA-DRIFTS) [8]. 3. RESULTS AND DISCUSSION 3.1. Catalysts Characterization Physicochemical characterization of solid catalysts involved the in-depth study of both the bulk and the surface of the catalysts before and after the reaction. The determination of the physicochemical properties of the catalysts was made using a series of cutting-edge characterization techniques aiming at the elucidation of the chemical composition, morphology and electron state of the bulk and surface of the solid catalysts examined. The Pd, Pt and Rh content in the present 1 wt % M/γ-Al 2O 3 (M=Pd, Pt and Rh) catalysts compositions were determined either by using Atomic Absorption Spectroscopy (AAS) or Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The chemical analysis showed that most of the metal precursor salts were actually deposited on the support. In particular Pd, Pt and Rh loadings were found to vary in the wt % range. The specific surface area of the examined catalysts was measured in the range of g/m 2. SEM-EDX analyses revealed an egg-shell distribution of metal clusters on alumina spheres Catalytic Studies The remarkable effect of the presence of hydrogen in the reaction s feed stream on the catalysts behaviour towards the conversion of paracetamol with oxygen was reported for first time in a batch mode system. The conversion of paracetamol was studied over three monometallic catalysts, 1 wt % Pd/γ-Al 2O 3 (a) and 1 wt % Pt/γ-Al 2O 3 (b) and 1 wt % Rh/γ- Al 2O 3 (c) catalyst using different reducing feed gas composition. Based on comparative evidence showing in Figures 1a, 1b, and 1c, different paracetamol s conversion profile obtained by the examined catalysts with respect to hydrogen concentration. As shown in Figure 1b, no significant conversion of Paracetamol was observed over 1 wt % Pd/γ-Al 2O 3 catalyst (X par.= %), in comparison with the other catalysts which provide a complete conversion under high levels of Hydrogen. The latter result is probably due to the in situ production of Hydrogen Peroxide, which is a source of OH radicals production. However, the monometallic Rh catalyst seems to be preferred for the examined reaction at high H 2 concentration due to its ability to completely convert the paracetamol in less than 3 min of reaction (Fgure 2).

4 Conversion of wt % Pd/γ-Al 2O 3 1 wt % Pt/γ-Al 2O 3 Conversion of % vol of H 2 % vol of H 2 Conversion of 1 1 wt % Rh/γ-Al 2O % vol of H 2 Figure 1. Conversion of Paracetamol as a function of H 2 concentration (% vol) over monometalic 1 wt % Pd (a), 1 wt % Pt (b), 1 wt % Rh (c) supported on γ-al 2O 3 spheres. Reaction conditions: Reaction Temperature = 25 o C; [Paracetamol] o = 1 mg/l; W cat= 4 g (dp=1.8mm); T= 25 o C; P= 1.2 atm. The comparative results presented in Figure 1 indicate that the conversion of paracetamol is clearly affected by the active phase of the catalyst, especially when Rh was used. Therefore, the catalytic performance of 1 wt % Rh/γ-Al 2O 3 catalyst was examined in detail using different reducing feed gas composition. Figure 2 presents the paracetamol conversion profile obtained during 1.5 h of reaction over wt % Rh/γ-Al 2O 3 catalyst, when 95 vol.% H 2 in air, pure H 2 and O 2 are used as a reaction gas. As shown in Figure 2, the conversion of paracetamol is not practically affected by the only presence of oxygen (air) in the reaction s gas feed stream. A completely different catalyst s behaviour was observed when using pure H 2 or 95% H2 in air as a reducing gas. In more detail, significantly higher paracetamol s conversion values (up to %) were obtained after 2h in the cases of both 95% vol. H 2/5% vol. air and 1% vol. H 2. It can clearly be seen from the Figure 2 that the conversion of Paracetamol almost reached the peak only after 3min (steady-state) of reaction. The latter result clearly indicates that this process is extremely promising in elimination of xenobiotic substances from water medium, probably due to reduction instead of oxidation of the substance.

5 Conversion of Time (min) % vol. H 2/5% vol. air 1% vol. H 2 1 % vol. air Figure 2. Conversion of Paracetamol as a function of time over 1 wt % Rh/γ-Al 2O 3 by the use of different gas feed stream composition. Reaction conditions: Gas Feed Stream Composition= 95% vol. H 2/5% vol. air, 1% vol. H 2, 1 % vol.air; Reaction Temperature = 25 o C; [Paracetamol] o = 1 mg/l; W cat= 4 g (dp=1.8mm); T= 25 o C; P= 1.2 atm. CONCLUSIONS Based on the results of the present research catalytic wet air oxidation in excess of O 2 using H 2 seems to be a very promising technique for the complete removal of pharmaceutical residues from wastewater such as paracetamol, mostly by the use of the monometallic Rh catalyst supported on γ-al 2O 3 spheres. Therefore, is expected to reduce the residence time for the oxidation/reduction of pharmaceutical substances to innocuous substances, as well the cost of the process. Future experiments will be conducted for further optimization of the method. Therefore, catalysts with other metal loadings and support oxides (TiO 2, CeO 2 and Fe 2O 3) will be tested. The catalysts that will be found to be the most suitable for the oxidation of pharmaceutical substances will be further studied thoroughly advanced techniques (TPSR, SEM-EDX, SSITKA-DRIFTS). Mechanistic experiments are expected to provide significant information about the mechanism of the reaction at hand. Moreover, the effect of the concentration of the pollutant, as well as the effect of the temperature of the reaction on the oxidation of paracetamol will be studied. REFERENCES 1. Hernando M.D., Heath E., Petrovic M. and Barcelo D. (6) Environmental risk assessment of pharmaceutical residues in wastewater effluents, surface waters and sediments. Anal. Bioanal. Chem., 385, Ollers S., Singer H.P., Fassler P. and Muller S.R. (1) Analysis of trihalomethanes in drinking water using headspace-spme technique with gas chromatography. Chromatogr J., A 911, Hernando M.D., Mezcua M., Gomez M.J., Malato O., Aguera A. and Fernandez-Alba A.R. (4) Comparative study of analytical methods involving gas chromatography mass spectrometry after derivatization and gas chromatography tandem mass spectrometry for the determination of selected endocrine disrupting compounds in wastewaters. J. Chromatogr., A 147, Stackelberg P.E., Furlong E.T., Meyer M.T., Zaugg S.D., Henderson A.K., and Reissman D. B. (4) Persistence of pharmaceutical compounds and other organic wastewater contaminants in a conventional drinking-water-treatment plant. Sci. Total Environ., 329,

6 5. Makris, K.C. and Snyder S.A. (1) Screening of pharmaceuticals and endocrine disrupting compounds in water supplies of Cyprus. Water Sci. & Technol., 62 (11), Kim S.C., Park H.H. and Lee D.K (3) Pd-Pt/Al2O3 bimetallic catalysts for the advanced oxidation of reactive dye solutions. Catal. Today, 87, Lee D.K, Cho I.C., Lee G.S., Kim S.C., Kim D.S. and Yang Y.K. (4) Catalytic wet oxidation of reactive dyes: Preparation of Al Cu with H2/O2 mixture on Pd Pt/Al2O3 catalysts. Sep. Purif. Technol., 34, Theologides P.C., Savva, G.S. and Costa, N.C. (11) Catalytic removal of nitrates from waters in a continuous flow process: The remarkable effect of liquid flow rate and gas feed composition. Applied Catalysis B: Environmental, 12,

Catalytic Removal of Pharmaceutical Compounds in Water Medium under a H2 stream over Various Metal Supported Catalysts: A Promising Process

Catalytic Removal of Pharmaceutical Compounds in Water Medium under a H2 stream over Various Metal Supported Catalysts: A Promising Process N.A. Pantelidou 1, C.P. Theologides 1, G.G. Olympiou 1, P.G.