lincomycin (Augugliaro et al. 2005, 2006), and others (Choo et al. 2008a, b) can be
decontaminated through photocatalytic membrane reactors.
An alternative process to membrane reactors which emerged the past years
consists in implementing photocatalytic micro-reactors.
2.5.2 Continuous-Flow Photochemical Micro-Reactor
Flow Reactors
A micro-reactor (or flow reactor, microfluidic reactor) is a chemical reactor where
the reaction occurs in a confined channel with a diameter below 1 mm (Zhang et al.
2017). Such micro-reactors and their applications undergone intense development
and were extensively reviewed the past years (Hartman and Jensen 2009; Jensen
et al. 2014; Gemoets et al. 2015; Cambié et al. 2016; Rossetti and Compagnoni
2016: Heggo and Ookawara 2017; Jensen 2017; Zhang et al. 2017). Thanks to their
small size, micro-reactors exhibit a high surface-to-volume ratio, which favors
mixing, heat, and mass transfer (Gemoets et al. 2015; Zhang et al. 2017). Consequently, flow reactors allow favoring heterogeneous reactions such as liquid-liquid,
liquid-gas, liquid-solid, and gas-liquid-solid reactions by favoring the contact area
between reactants and catalyst. Indeed, it was reported that specific interfacial areas
can reach values as high as liquid–liquid, 1000–10,000 m
2 /m
3 and gas–liquid,
160–1300 m
2 /m
3 , thus improving mass transfer as compared to conventional batch
reactors (Nieves-Remacha et al. 2012, 2013). Mass transfer coefficients were found
to be liquid–liquid, 1.9–41 s
À1 and gas–liquid, 0.2–3 s
À1 (Yue et al. 2009; Woitalka
et al. 2014). As a result, the general trend is that the use of micro-reactors results in a
better efficiency as compared to conventional ones (Anderson 2012; Mizuno et al.
2016; Cambié et al. 2016). Moreover, thanks to the small reactor volume, safety of
the process is improved, even for harsh conditions (Hessel et al. 2011; Gutmann
et al. 2015). Indeed, such reactors allow implementing high-temperature and/or
high-pressure reactions, as well as explosive reactants/products. Additionally,
micro-reactors also present many advantages from a point of view of green chemistry since they allow improving the safety of the process, the energy efficiency,
higher yields, and reduced wastes (Newman and Jensen 2013; Rossetti and
Compagnoni 2016). The reproducibility and low-cost scale-up are often spotlighted
among advantages of micro-reactors. Indeed, it is often claim that the scaling up
simply consists of multiplying the number of reactors, but the reality is not as
straightforward (Rossetti and Compagnoni 2016). Indeed, the fluid distribution to
ensure an accurate control of the flow and the cost of scaling up still represent a
major challenge. Three main scaling-up strategies were reported in the literature:
parallel numbering-up (reactors in parallel), consecutive numbering-up (reactors in
series), and scale-out by suitable dimension enlarging (Zhang et al. 2017; Kuijpers
et al. 2017). Flow reactors can be made of glass, polymer, silicon, ceramic, or metal
72
B. Lebeau et al.
decontaminated through photocatalytic membrane reactors.
An alternative process to membrane reactors which emerged the past years
consists in implementing photocatalytic micro-reactors.
2.5.2 Continuous-Flow Photochemical Micro-Reactor
Flow Reactors
A micro-reactor (or flow reactor, microfluidic reactor) is a chemical reactor where
the reaction occurs in a confined channel with a diameter below 1 mm (Zhang et al.
2017). Such micro-reactors and their applications undergone intense development
and were extensively reviewed the past years (Hartman and Jensen 2009; Jensen
et al. 2014; Gemoets et al. 2015; Cambié et al. 2016; Rossetti and Compagnoni
2016: Heggo and Ookawara 2017; Jensen 2017; Zhang et al. 2017). Thanks to their
small size, micro-reactors exhibit a high surface-to-volume ratio, which favors
mixing, heat, and mass transfer (Gemoets et al. 2015; Zhang et al. 2017). Consequently, flow reactors allow favoring heterogeneous reactions such as liquid-liquid,
liquid-gas, liquid-solid, and gas-liquid-solid reactions by favoring the contact area
between reactants and catalyst. Indeed, it was reported that specific interfacial areas
can reach values as high as liquid–liquid, 1000–10,000 m
2 /m
3 and gas–liquid,
160–1300 m
2 /m
3 , thus improving mass transfer as compared to conventional batch
reactors (Nieves-Remacha et al. 2012, 2013). Mass transfer coefficients were found
to be liquid–liquid, 1.9–41 s
À1 and gas–liquid, 0.2–3 s
À1 (Yue et al. 2009; Woitalka
et al. 2014). As a result, the general trend is that the use of micro-reactors results in a
better efficiency as compared to conventional ones (Anderson 2012; Mizuno et al.
2016; Cambié et al. 2016). Moreover, thanks to the small reactor volume, safety of
the process is improved, even for harsh conditions (Hessel et al. 2011; Gutmann
et al. 2015). Indeed, such reactors allow implementing high-temperature and/or
high-pressure reactions, as well as explosive reactants/products. Additionally,
micro-reactors also present many advantages from a point of view of green chemistry since they allow improving the safety of the process, the energy efficiency,
higher yields, and reduced wastes (Newman and Jensen 2013; Rossetti and
Compagnoni 2016). The reproducibility and low-cost scale-up are often spotlighted
among advantages of micro-reactors. Indeed, it is often claim that the scaling up
simply consists of multiplying the number of reactors, but the reality is not as
straightforward (Rossetti and Compagnoni 2016). Indeed, the fluid distribution to
ensure an accurate control of the flow and the cost of scaling up still represent a
major challenge. Three main scaling-up strategies were reported in the literature:
parallel numbering-up (reactors in parallel), consecutive numbering-up (reactors in
series), and scale-out by suitable dimension enlarging (Zhang et al. 2017; Kuijpers
et al. 2017). Flow reactors can be made of glass, polymer, silicon, ceramic, or metal
72
B. Lebeau et al.