Study On Crystal Growth Behavior

Crystallization process is one of the major unit operations for manufacture of a widerange of chemicals in the food, mineral, fine chemical, petrochemical and pharmaceuticalindustries. For product quality evaluation, the particle shape is of critical importance not onlybecause it will influence the end-use properties of the products such as the bioavailability ofthe pharmaceuticals, flowability and adhesion, but also it has been found to be associated withtheir downstream processing such as in filtration and handling and also in transport andstorage. Crystal shape was formed in a growth process, which depends on the growthbehavior of its different crystallographic face. Measurement of crystal growth rates inreal-time and within processing reactors could open the way for the development of moreeffective process and product quality control. Research on crystal growth behavior is of greatsignificance to the controlling of crystal’s shape. On-line imaging has shown to be the mostpromising method for real-time measurement of crystal behavior in cooling crystallization. Byobtaining crystal projection in the two-dimensional space, imaging could real-time show2-Dshape with crystal growth. However, some important information about real3D crystal shapeis missing in the process. So at the moment, it is a big challenge to realize the measurement ofreal3D facet growth behavior of crystals for further crystal shape control.In this thesis, an in-house developed system is introduced that uses two cameras tosimultaneously capture two2-D images from different angles of crystals grown from solution.Using the2-D image pairs, the three dimensional shape of crystals can be reconstructed andfacet crystal growth rate estimated. The on-line imaging system was used for monitoring theparticle shape evolution during crystallization process. In combination of Attenuated TotalReflection-Fourier Transform Infrared (ATR-FTIR) spectroscopy, the on-line imaging systemwas used to study crystal facet growth kinetics. Crystal growth rates were deduced with thehelp of imaging and image analysis system. While the on-line sensor, ATR-FTIR was usedfor the real-time measurement of solution concentration in dense crystal slurries; Partial leastSquare regression (PLS) were used to develop the calibration model which represents therelationship between the IR spectra and predicted variable (concentration). The vision systemwas tested by monitoring the dynamic morphological evolution of potassium dihydrogenphosphate crystal growth in aqueous solution. The results achieved in this paper, showed thatthe stereo vision system is valid and effective for monitoring3D crystal growth behavior andvalidated the growth kinetics by KDP crystals. Using the system, real-time online measurement of KDP growth kinetics inthree-dimensions was achieved. The information is helpful for real optimization and shapecontrol of crystals during crystallization process. The empirical power law for facet growthkinetics of KDP was determined as well.