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Accurate Measurement of the Photon Flux Received Inside Two Accurate Measurement of the Photon Flux Received Inside Two Continuous Flow Microphotoreactors by Actinometry Tristan Aillet, Karine Loubiere, Odile Dechy-Cabaret, Laurent E. Prat To cite this version: Tristan Aillet, Karine Loubiere, Odile Dechy-Cabaret, Laurent E. Prat. Accurate Measurement of the Photon Flux Received Inside Two Continuous Flow Microphotoreactors by Actinometry. International Journal of Chemical Reactor Engineering, De Gruyter, 2014, vol. 12 (n° 1), pp. 1-13. 10.1515/ijcre- 2013-0121. hal-01153086 HAL Id: hal-01153086 https://hal.archives-ouvertes.fr/hal-01153086 Submitted on 19 May 2015 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Open Archive TOULOUSE Archive Ouverte (OATAO) OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 11825 To link to this article : DOI:10.1515/ijcre-2013-0121 URL : http://dx.doi.org/10.1515/ijcre-2013-0121 To cite this version : Aillet, Tristan and Loubiere, Karine and Dechy-Cabaret, Odile and Prat, Laurent E. Accurate Measurement of the Photon Flux Received Inside Two Continuous Flow Microphotoreactors by Actinometry. (2014) International Journal of Chemical Reactor Engineering, vol. 12 (n° 1). pp. 1-13. ISSN 1542-6580 Any correspondance concerning this service should be sent to the repository administrator: [email protected] Tristan Aillet, Karine Loubiere*, Odile Dechy-Cabaret, and Laurent Prat Accurate Measurement of the Photon Flux Received Inside Two Continuous Flow Microphotoreactors by Actinometry Abstract: In this study, the photon flux received in two 1 Introduction continuous flow microphotoreactors was measured by acti- nometry (potassium ferrioxalate). The microphotoreactors Recently, microreactor technology has been successfully had two different geometries and were irradiated by either investigated in the organic chemistry field. The micro-scale a polychromatic or a monochromatic light source. A model offers several advantages, such as short molecular diffusion considering the partial absorption of photons through the distances, intensified heat and mass transfers, and small reactor depth and, if required, the polychromatic character amounts of reactants used. In the case of photochemistry, of the light source and the dependence of the actinometer microreactors also allow efficient light penetration even for properties on the wavelength were formulated to describe relatively concentrated solutions. For these reasons, micro- the variation of the actinometer conversion with the irra- reactors are increasingly being adopted for photochemical diation time. The photon flux received in the microphotor- reactions, including photocycloadditions, photooxygena- eactors could be thus accurately calculated as a function of tions, photoisomerizations and photocatalytic reactions the emitted wavelength. The same methodology was then (Coyle and Oelgemöller 2008; Oelgemoeller 2012; Knowles, applied to measure the photon flux received in a batch Elliott, and Booker-Milburn 2012). Although the benefits of immersion well photoreactor. The radiant power received microreactors for photoconversion are now accepted, there in each photoreactor was compared to that emitted by the is still a lack of objective criteria for understanding and lamp and major differences were found, thus confirming modelling the positive effect of the microspace, and thus the need for this kind of in situ measurement. Finally, for rigorously transposing photochemical synthesis from some guidelines based on a knowledge of the photon flux batch to intensified continuous flow reactors. This requires were proposed to compare various photoreactors. They a modelling approach in which hydrodynamic and radiative revealed in particular that the choice of the most efficient transfer phenomena are coupled via the reaction kinetics photoreactor depended on the criteria chosen to evaluate term. In addition, microreactors are widely used for studying the performances (i.e. productivity, Space Time Yield). reactions and acquiring the associated kinetic data (Mozharov et al. 2011). By analogy, we could imagine using photochemistry, microphotoreactor, chemical Keywords: microreactors to determine some intrinsic properties of a actinometry, photon flux photochemical reaction, such as the quantum yield. In all cases, for modelling, for data acquisition pur- poses, or for optimizing reaction performance, it is essential *Corresponding author: Karine Loubiere, Université de Toulouse, −1 INPT, ENSIACET, F-31432 Toulouse, France; CNRS, Laboratoire de to know the photon flux (einstein s ) actually received in the Génie Chimique (LGC UMR 5503), 4 allée Emile Monso, BP 84234, continuous flow microphotoreactor. Up to now, this photon F-31432 Toulouse, France, E-mail: [email protected] flux has not been accurately measured in such systems, and Tristan Aillet, Université de Toulouse, INPT, ENSIACET, F-31432 most studies have estimated this parameter either by a mod- Toulouse, France; CNRS, Laboratoire de Génie Chimique (LGC UMR elling approach (Aillet et al. 2013) or from the characteristics 5503), 4 allée Emile Monso, BP 84234, F-31432 Toulouse, France, E-mail: [email protected] of the light source (Sugimoto et al. 2009; Shvydkiv et al. 2011; Odile Dechy-Cabaret, Université de Toulouse, INPT, ENSIACET, Aida et al. 2012). For example, Sugimoto et al. (2009) carried F-31432 Toulouse, France; CNRS, Laboratoire de Chimie de out the Barton reaction of a steroidal substrate in various Coordination (LCC UPR 8241), 205 route de Narbonne, BP 44099, continuous microphotoreactors and compared the reaction F-31077 Toulouse, France, E-mail: [email protected] performances according to the light sources and the material Laurent Prat, Université de Toulouse, INPT, ENSIACET, F-31432 of the microreactor glass top. To do this, they measured the Toulouse, France; CNRS, Laboratoire de Génie Chimique (LGC UMR 5503), 4 allée Emile Monso, BP 84234, F-31432 Toulouse, France, characteristics of the light transmitted through each type of E-mail: [email protected] reactor top. Shvydkiv et al. (2011) compared the performances of a batch Rayonet reactor and various micro- actinometer conversion with the irradiation time and thus reactors. They used the data given by the lamp manufacturer to accurately calculate the photon flux received in the micro- and evaluated, for example, the lamp power per unit of photoreactor as a function of the wavelength emitted by the irradiated surface (W cm−2). In a recent paper (Aillet et al. lamp. The same methodology was then used to measure the 2013), we deduced the photon flux from a modelling photon flux received in a batch immersion well photoreactor. approach in which the polychromatic light source was Finally, the radiant power received in each photoreactor was assumed to be monochromatic, and hence pointed out the compared to that emitted by the lamp, and some guidelines important role of the photon flux when comparing different based on a knowledge of the photon flux were proposed to photoreactors. Thus, in all cases, the photon fluxes consid- compare various photoreactors. ered remain approximate in so far as they are not equal to the fluxes actually received in the microphotoreactor, which depend, of course, not only on the characteristics of the 2 Material and methods light source but also on the reactor exposition to the source, on the reflectance and transmittance of the reactor material. In classical photoreactors, the photon flux is com- 2.1 Microphotoreactors and batch monly determined by direct measurements using a radio- photoreactor meter. However, this method cannot be applied in microreactors since their dimensions are smaller than The first continuous flow microphotoreactor (A) used in this those of the sensor and also because, in most cases, the study (Figure 1a) had a design encountered in many different irradiated area remains difficult to determine accurately. studies (Aillet et al. 2013; Hook et al. 2005; Lainchbury et al. An efficient alternative is to use an actinometer, which 2008; Vaske et al. 2010), classically named “capillary tower”. involves a simple photochemical reaction with a known It was constructed by winding Fluorinated Ethylene quantum yield. Despite that this well-established method Propylene (FEP) tubing (508 μm inner diameter d, 1587.5 μm is commonly applied in photochemical reactors of large outer diameter, 4 m length) in a single pass around an immer- scale (see for example (Yang, Pehkonen, and Ray 2004; sion well made of Pyrex, which contained a high-pressure Hg Yang et al. 2005; Cornet, Marty, and Gros 1997; Zalazar lamp. The temperature was not measured directly inside the et al. 2005)), we have not found any works implementing microphotoreactor, only the stability of the temperature (8°C) actinometry in microphotoreactors. of the cooling water circulating
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