Rapid and facile chemical actinometric protocol for photo-microfluidic systems using azobenzene and NMR spectroscopy

Achi, Nassim El; Bakkour, Youssef; Chausset‐Boissarie, Laëtitia; Penhoat, Maël; Rolando, Christian

doi:10.1039/c7ra01237c

Cited by 19 publications

(18 citation statements)

References 21 publications

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“…[14][15][16] Simplified models, as used in photochemical and actinometric studies, implicitly consider plug flow and homogeneous illumination, and these models yield a very good match to experimental results when used in micro-and millichannel reactors, and are considered in this work. [17][18][19][20][21] In the following section, three different models are derived: cross-current, co-current, and counter-current illumination related to the relation between the light and flow direction. Cross-current illumination is the current state-of-the-art in photochemical reactor operation and will be treated first, see Figure 1.…”

Section: Photochemical Reactor Frameworkmentioning

confidence: 99%

“…In this model, we explicitly assume plug flow, which is implicitly using in most articles and justified by experimental validation. [17][18][19][20][21] The residence time distribution (RTD) factor will be added to the model in a further step. The mass balance over a small volume element (dV) can be described as:…”

Section: Geometry and Mass Balancementioning

confidence: 99%

“…Commonly, millireactor, microreactor and thin film reactors are used which are designed for homogeneous illumination, thus having low up to very low absorbance values (eg, <0.1). [2,4,5,15,18] If one was to operate these reactors at higher absorbances, the selectivity of the reaction might suffer. Furthermore, at an absorbance of 1, half of the light is absorbed in the first quarter of the reactor, losing homogeneous illumination.…”

Section: Cross-currentmentioning

confidence: 99%

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Principles of co‐axial illumination for photochemical reactions: Part 1. Model development

Meir

Leblebici

Fransen

et al. 2020

J Adv Manuf & Process

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Photochemical reactors with conventional homogeneous illumination suffer from a light efficiency problem, which is inherent to their design: Dark zones arise near the reagent-rich inlet whereas the reagent depleted outlet is overilluminated. Any attempt to mitigate dark zones at the inlet will only increase photon losses further downstream. This study reports the principles and model equations for co-and counter-current illumination in photochemical reactors, along with an optimization study to determine the most efficient and productive operating point. This work proves that the use of co-and counter-current illuminated reactors increases the energy efficiency while easing scalability by implementing larger path lengths, without altering the reactor's geometry. We report a simple model to determine the conversion obtained by such novel illumination techniques and compare it to the current state-of-the-art. Two nondimensional groups where derived that describe all possible reactor configurations, these are the initial absorbance (A) and the quantum photon balance (ρϕ). Variation of both parameters leads for noncompetitive photochemical reactions to an optimal point for the current state-of-the-art as well as the novel co-axial illumination. Ultimately, we recommend the use of an initial absorbance value (A) of at least 1, and a quantum photon balance (ρϕ) equal to 1 to introduce sufficient light and enable near complete absorption of light.

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Section: Photochemical Reactor Frameworkmentioning

confidence: 99%

Section: Geometry and Mass Balancementioning

confidence: 99%

Section: Cross-currentmentioning

confidence: 99%

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Principles of co‐axial illumination for photochemical reactions: Part 1. Model development

Meir

Leblebici

Fransen

et al. 2020

J Adv Manuf & Process

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“…The reactor is illuminated radially by a series of 10 LEDs for cross-current illumination, mounted to a heat sink (3), and illuminated axially by an LED mounted to a bigger heat sink (4) the isomerization via absorption of UV-light and can be omitted as the samples are measured immediately after production. [7] The actinometric method used in this work is based on the model of Achi et al [7] and the measuring technique is based on the technique employed by Gauglitz and Hubig, [8] quantum yield values are reported by Gauglitz and Hubig [8] and absorbance values for cisazobenzene are reported by Vetrakova et al [20] This actinometer is used for cross-and co-current illumination validation. The method utilizes azobenzene (98%, VWR, Geel, Belgium) dissolved in methanol (Chromasolv 99.9%, Sigma Aldrich, Diegem, Belgium) at various concentrations that are pumped through the reactor and illuminated via either cross-or co-current illumination.…”

Section: Actinometric Validationmentioning

confidence: 99%

“…In the first step, the received light flux of the reactor's LEDs is measured via spectrometry and validated via actinometry using the isomerization of azobenzene. [7][8][9] In the second step, the conversion of 2-chloroacetophenone is used as a model reaction for a noncompetitive, nonreversible photochemical reaction. [10] 1.1 | Photochemical reactor model…”

Section: Introductionmentioning

confidence: 99%

Principles of coaxial illumination for photochemical reactions: Part 2. Model validation

Meir

Leblebici

Kuhn

et al. 2020

J Adv Manuf & Process

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This study reports the principles and model equations for co-and counter-current illumination, validated by experimental data. Current photochemical reactors which are homogeneously illuminated suffer from a light efficiency problem resulting in low light absorption and subsequent low productivity. Hence, the use of co-and counter-current illuminated reactors, implementing larger path lengths, without altering the reactor's geometry, is of interest. In this article, we report a simple model to determine the conversion obtained by co-and counter-current illumination techniques and compare against the current state-of-the-art. Via experimental validation, we report the use of co-and counter-current illumination to significantly boost the PSTY, a measure for photochemical reactor productivity, by a factor of 5 to 6 for same input concentration of reagent, solemnly by illuminating the reactor via co-and countercurrent (axially) instead of cross-current (radially). Furthermore, we report that simply increasing the reagent concentration, thus absorbance, has a large influence on productivity, thus PSTY, of the reactor. By assessing the reactor's performance parameters, derived by modeling, which are the initial absorbance value (A) and the quantum photon balance (ρϕ), the reactor's operating point can be determined and adapted to operate in a more productive and efficient regime.

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Riboflavin as a Bioorganic Solar Fuel: Photoredox Chemistry Rationalized and Accelerated in a Miniaturized Flow Photoreactor

et al. 2019

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With the depletion of fossil‐fuel‐based energies and the corresponding growing environmental concerns, the design of new strategies to store renewable solar energy is highly attractive. Herein, we studied a biomimetic organic solar fuel (Riboflavin – Vitamin B2) to photochemically store solar light into its amphoteric form (leucodeuteroflavin), working as a charge carrier towards a flow fuel cell. We demonstrate that miniaturization of the photoreactor permits significant reduction of the full time solar charge. Nevertheless, due to inherent leucodeuteroflavin (LDH2) degradation into lumichrome (LC), the maximum system charge (at pH=5) is limited to 13 % corresponding to a maximum power density of 0.11 mW cm−2 after 90 min. In comparison with other described photoredox electroactive systems (e. g. polyoxometalates, quinones), organic solar fuels based on flavins appear particularly promising and their chemical structure should be optimized to fit both photostability and economical requirements. In any case, this study enables a clear rationalization and quantification of the mechanism of riboflavin degradation under anaerobic conditions, which has been the topic of many discussions during the last century, and opens the way towards the development of a new generation of low‐cost renewable organic solar fuels.

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Rapid and facile chemical actinometric protocol for photo-microfluidic systems using azobenzene and NMR spectroscopy

Abstract: A new protocol for determining the photon flux inside a photomicroreactor is described using (E)-azobenzene and NMR spectroscopy which does not require the determination of the quantum yield of the unstableZisomer.

Cited by 19 publications

References 21 publications

Principles of co‐axial illumination for photochemical reactions: Part 1. Model development

Principles of co‐axial illumination for photochemical reactions: Part 1. Model development

Principles of coaxial illumination for photochemical reactions: Part 2. Model validation

Riboflavin as a Bioorganic Solar Fuel: Photoredox Chemistry Rationalized and Accelerated in a Miniaturized Flow Photoreactor

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