Precipitation of mandelic acid with a supercritical antisolvent process:: Experimental and theoretical analysis, optimization, and scaleup

An experimental and theoretical analysis of the precipitation of mandelic acid with a semicontinuous supercritical antisolvent (SAS) process is presented. The experimental section comprises a study of the effect of different operating parameters on particle size, including pressure, temperature, solution concentration, and flow rates. Prismatic or needlelike particles with lengths of 30-200 mu m have been obtained, with precipitation yields between 20% and 80%. The parameter with a stronger influence on particle size is temperature, while an increase in the initial concentration allows a large increase in the precipitation yield with small variations in particle size. Variations in the injection velocities in the nozzle had only a minor influence on particle size. In the theoretical section the application of a detailed mathematical model of the SAS process to this system is discussed. The model is used for the interpretation of the different experimental trends and to propose the optimum process parameters. The model is also used to study the scale-up of the process and particularly the design of the nozzle for higher flow rates. As experimentally it has been found that the parameters of the nozzle do not affect particle characteristics, this discussion is focused on the determination of the required precipitator volume for different nozzle designs. Finally, a scaled-up process with a 5-20 times increase in flow rates and product amount has been tested experimentally, obtaining results similar to those in the lower scale experiments.