Upfront

The 16 electrodes in each plane were repeatedly oven-fired, ensuring minimal protrusion into the process fluid to avoid disturbing the flow. During trials, current applied in a very fast predetermined sequence between the electrodes provided data which, fed through a specially-written algorithm, gave a real-time picture of material distribution in that plane on a computer screen. Using electrodes in several planes offered a 3-D view of the whole reactor (Image). In mixing evaluations, ERT can cover the whole vessel, rather than summing values taken in many different locations, as with other techniques using local conductivity probes. Ethyl acetate hydrolysis was chosen for testing ERT because the hydroxide ions consumed and acetate ions produced during the reaction have very different conductivities, and ERT can track the change. Glaxo compared the ERT results in a stirred tank with a tried-and-tested on-line monitoring technique: Raman spectroscopy. Starting materials and products have different Raman spectra. Trials made allowance for the relative insensitivity of the Raman system and its long spectrum acquisition time, but the graphs of conversion against time for the two systems were virtually identical. ITS is working to make ERT more flexible, so that users won't have to line electrodes around a vessel and wire them up. Along with the glass-lined reactor manufacturer, Pfaudler, ITS is developing a glass Optomix probe (Photo) that would be placed inside a glass-lined reactor, and would play the same role as a baffle. The Optomix electrodes would perform the same function as those on the circumference of the vessel, but the data-conversion algorithm would take their different geometries into account. The probe promises greater flexibility and could be used in any vessel where two phases, such as solids and liquids, are being mixed or are reacting together. ITS team members and a laboratory-scale version of the Optomix