Author: Claire Delacour, KU Leuven

The Microfluidic domain has known important development over the last two decades. In 1990, only less than 10 patents were published whereas in 2004 more than 350 patents were published in the USA[1]. This study showed the large range of microfluidic applications, and impacts in Biology and Chemistry.

A microchannel reactor is a continuous flow-type reactor with the channels’ characteristics dimension under a millimeter in size. Two types of flow rectors can be distinguish depending on their sizes[2]:

  1. Microfluidics: 10-500 µm
  2. Millifluidics: 500 µm to several mm

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Figure 1: Microreactor on a chip

Reactions carried under continuous conditions are divided into three categories [3]:

  • Type A reactions which are very fast (<1s), micro- or milli-reactors allow a controlled by the mixing process, yield is increased through better mixing and heat transfer
  • Type B reactions: which are rapid reactions (10s to 20 min), those reactions are kinetically controlled. The use of micro reactors avoids overcooking and increases yield
  • Type C reactions: are slow reactions (>10 min); micro reactors can increase the safety

One of the main challenge of the actual chemistry is to respect the 12 principles of the Green chemistry. Wiles and al. described[4] the 12 principle of the green chemistry applied to continuous flow reactors. The aim of this 12 principle is to develop a sustainable chemical research and production.

Micro- or milli-reactors can have a significant impact on the way chemists conduct their reactions. Table 1 presents some advantages and their corresponding green chemistry principle and disadvantages of microfluidic processes.

AdvantagesDisadvantages
  • High throughput scanning of reaction conditions
  • Precise control of reaction variables (temperature, pressure, etc.) due to high surface-volume ratio[2]
  • Use of small quantities of reagents and solvent – Principle 1 (prevention of waste)
  • Increased safety parameters (enable a safe use of highly toxic or explosive reactants) because of the small volume used – Principle 3 (less hazardous chemical synthesis)
  • Ready scale-up of synthetic procedures
  • Single or multiphase reactions can be conducted –  Principle 5 (safer solvent and auxiliaries)
  • Isolation of sensitive reactions to air or moisture
  • Reduction of hazardous waste – Principle 1, 3
  • Handling of highly reactive or hazardous intermediate – Principle 3
  • Reduction of CAPEX (Lonza [3])
  • New emerging technology
  •  Today micro-, milli-reactors cannot be applied to all chemistries (reaction type C [3])
  •  Limited reaction time range
  •  High sensitivity to precipitating products
  •  Reactor clogging

Table 1: Advantages and drawbacks of using Microfluidic process

Continuous flow reactors have commonly flourished in the chemical and biochemical industrial environment. But, to expand the area of applications of micro- and milli-fluidics, it is necessary to find solution for solid handling. In fact, in chemistry, solids can occur under different forms: catalysts, reagent, product, side-product. As a solution, ultrasonic power can be used to prevent clogging in channels. It has been previously shown that ultrasound could prevent solid clogging, enhance particle morphology and particle size distribution.

[1]      H. Carsten, “Microfluidics in commercial applications; an industry perspective,” Lab Chip, vol. 6, pp. 118–1121, 2006.[2]      J. Wegner, S. Ceylan, and A. Kirschning, “Ten key issues in modern flow chemistry,” Chem. Commun., vol. 47, no. 16, p. 4583, 2011.[3]      Lonza, “Microreactor Technology at Lonza,” no. June, 2009.[4]      C. Wiles and P. Watts, “Green Chemistry Continuous flow reactors: a perspective,” Green Chem., vol. 14, pp. 38–54, 2012.

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