Miniaturized Tubular Cooling Crystallizer With Solid-Liquid Flow for Process Development

Production of fine chemicals and pharmaceuticals often includes solid-liquid suspension flow. For continuous cooling a tubular crystallizer was designed based on the coiled flow inverter (CFI) concept, providing a narrow residence time distribution (RTD) of the liquid phase. Counter-current cooling allows for a smooth adjustment of the axial temperature profile. Successful operation of up to 50 g min⁻¹ in a prototype with 4 mm inner diameter was scaled down to a tube-in-tube CFI crystallizer (CFIC) with an inner diameter of 1.6 mm and varying length from 7.8 to 54.6 m. This leads to a significantly lower consumption of chemicals in process development with lower total mass flow rates of 15–20 g min⁻¹. Due to modular design, mean residence time (3.8 to 6.9 min) and mean cooling rate (0.6 to 1.4 K·min⁻¹) were varied at constant mass flow rate. Crystallization growth rate and yield are analyzed with the L-alanine/water test system and seed crystals of 125–180 μm.