Continuous Reactive Precipitation in a Coiled Flow Inverter: Inert Particle Tracking, Modular Design, and Production of Uniform CaCO₃ Particles

Abstract

A multiphase flow profile inside a helically coiled tubular device (HCTD) was observed by using a high-speed camera. Gas−liquid slug flow observations revealed that the Taylor vortices are influenced by secondary flow due to the centrifugal force acting perpendicular to the flow direction. Hence, mixing inside the liquid slug is enhanced by the combination of Dean and Taylor vortices in HCTD. The modular design of a specific type of HCTD, that is, the coiled flow inverter (CFI) is elucidated by the representation of a new design space diagram. Continuous precipitation of calcium carbonate (CaCO 3 ) was investigated for modular CFI made of polyvinyl chloride (PVC) tubes (d i = 3.2 mm) with slug flow patterns. CaCO 3 was continuously precipitated along CFI with a conversion of ca. 90%. CFI provided a narrower particle size distribution with median particle diameters around 28 μm and more uniform morphology in comparison to a batch reactor.

Modular Coiled Flow Inverter with Narrow Residence Time Distribution for Process Development and Production

“…Here, the pressure drop Δ p is the limit for pump operation. The modular setup assists the design, since the arrangement of two or four coils can be multiplied for the necessary reactor length , .…”

“…In general, Dean vortices are fully developed for Dn > 1.5 and improve the RTD up to Dn = 3 . Numerical studies indicated for T * > 1000 that the velocity profile is nearly symmetrical and torsion effects can be neglected . At values of T * < 1000, the secondary flow pattern becomes asymmetrical until just one vortex dominates the flow .…”

“…For chemical reactions the flow profile is an important aspect, since it provides good radial mixing and a narrow residence time distribution. Coiled tubes and CFIs have been applied for various unit operations such as liquid‐liquid extraction , , precipitation , crystallization , , and gas‐liquid reactions , , underpinning its flexibility and potential for process development.…”

Continuous Downstream Processing of Amino Acids in a Modular Miniplant

“…For the cooling agent, a bypass was used with a separate tube (PFA, d i = 3.2 mm). This tube size was small enough to form a gas‐liquid slug flow , . Hence, gases desorbing from the cooling agent during the process could be removed from the cooling circuit.…”

Equipment and Separation Units for Flow Chemistry Applications and Process Development

“…Among others, single‐phase flow , liquid‐liquid extraction system , gas‐liquid reaction and mass transfer , gas‐liquid‐solid precipitation , and liquid‐solid suspension behavior was investigated in the CFI.…”