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Improved methods of manufacturing at the micro scale are opening up new avenues for the development of compact devices for functions ranging from reactions to extraction and separation. Much of the initial work in this field has concentrated on the development of systems using single phase flow with diffusive transfer between parallel reacting fluid streams.


Work within our department has however focused on the more complex system of multiphase flow in narrow channels and in particular immiscible liquid-liquid processes. The main method adopted to perform multiphase reactions is the use of slug flow to allow both convective and diffusive processes to operate within the reactor channel. An illustration of the mechanisms involved is provided in the diagram below.


Circulation patterns within slug flow provide high mass transfer performance between phases


Generation of Slug Flow

Slug generation within glass or polymer based on-chip style reactors is generally achieved by the continuous pumping of both phases into a “T” or “X” channel configuration. The photograph below shows the generation of slug flow for a two-phase oil-water experiment being performed on a glass chip with 0.38mm wide/deep channels.


Reaction Visualisation

Flow visualisation of reaction and mass transfer between slugs was performed as part of the on-going modelling of slug flow.


A titration process involving acetic acid transfer from kerosene into an aqueous solution of NaOH and KOH was used to visualise the mass transfer. This triggers a colour change in a pH indicator as show in the photograph below. In this example the aqueous slug turns completely yellow after at least 50% of the acetic acid has transferred, which in this case occurred after 3.6s.



Use of Slug Flow for Chemical Production

Experiments using slug flow reactors were also performed for the industrially relevant process of organic nitration. A PTFE capillary tube reactor was used with slug flow generated by use of a modified tee as shown here.



Images of slug flow generated by this device using a dyed organic phase are shown in the photograph below. In this system a 0.15mm internal diameter PTFE tube was used to carry the slugs.



Results from Benzene and Toluene nitration shown that slug flow could be used to provide significant conversion to nitrobenzene and nitrotoluene in seconds using coiled PTFE reactors of 30cm to 180cm length and compared favourably with industrial processes.




  1. Burns, J. and Ramshaw, C. (May 1999) “Development of a Microreactor for Chemical Production.” Trans IChemE, vol. 77, Part A

  2. Burns, J. and Ramshaw, C. “A Multiphase Microreactor for Organic Nitration.” 4th International Conference on Process Intensification for the Chemical Industry: Better Processes for Better Products, Brugge, Belgium, 10-12 September 2001.

  3. Burns, J.R. and Ramshaw, C. (2001) “The Intensification of Rapid Reactions in Multiphase Systems using Slug Flow in Capillaries.” R.S.C. Lab-on-a-Chip Journal, vol. 1, pp.10-15.


Dr Kamelia Boodhoo




 Last modified: 11-Jan-2019