Studies on a New Spinning Disc Spinning Bowl ContactorMixer

Abstract

Increased focus on continuous synthesis of fine chemicals and pharmaceuticals has led to resurgence of process intensification. In this thesis we introduce a new continuous contactor. It works on the principle of impinging fine drops of one liquid, produced by a spinning disc, on thin flowing film of another liquid, on inner wall of a spinning bowl, and sweeping the mixture away from the impingement zone. The device offers the (largest) length scale of segregation itself equal to film thickness, intense mixing, and substantially reduced back-mixing. The device is first demonstrated for the synthesis of drug nanoparticles of curcumin by using anti-solvent precipitation route. The SEM measurements confirm the device can produce spherical nanoparticles of curcumin below 100 nm in continuous mode of operation, free from choking in corresponding microfluidic operations. Experiments with the diagnostic iodide-iodate competing parallel reaction combined with a model yield time scale of micro-mixing of 4 ms. High resolution static images of the inner surface of the transparent bowl reveal perfect wetting by organic liquids and poor wetting by water as an explanation of the poor mixing observed at low rotational speeds. Several bowl geometries with tapered cylindrical wall and film flowing downward and upward are studied. The drop formation from a spinning disc at low flow rates is studied in using high resolution static imaging by controlled duration of flash light. The images at high disc speeds also capture vivid detail, which allow primary and secondary drops to be measured separately, without ambiguity, for the first time. The size ratio of primary to the first secondary drops lies in range 2.2-2.6, and 6-9% of the incoming liquid appears as first secondary drops. The polydispersity of primary drops alone is far smaller than when all the drops are considered together...