A Study of Growth Kinetics on Sucrose Crystallization

• Main Authors: Ching-Shiang Chuang, 莊晴翔
• Other Authors: Lie-Ding Shiau
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/16899219373041532065

碩士 === 長庚大學 === 化工與材料工程研究所 === 91 === The growth kinetics of sucrose crystals from aqueous solutions is studied using a photomicroscopic technique in an isothermal, continuous-flow chamber. The phenomena of size-independent growth and growth rate dispersion are observed in the experiments. These results indicate that the constant crystal growth model is applicable in the studied crystallization system. A modified two-step model is proposed to account for the observed growth phenomena. In this work, the resistance to crystal growth due to the volume diffusion is eliminated by increasing the solution flow rate through the growth chamber. Thus the crystal growth process becomes surface reaction-controlled and the effects of the sole surface reaction step on the growth kinetics can be investigated. The effects of supersaturation, temperature and solution velocity on the growth rates are investigated in these experiments to recover the mass transfer coefficient and the surface reaction constant. Based on the mean growth rate data in the isothermal, continuous-flow experiments, the activation energy of 14.9 Kcal/mol is obtained for the surface reaction process in sucrose crystal growth. By comparing the growth rate of each individual crystal with the mean growth rate in a purely surface reaction-controlled growth process, it is found that the distribution of the dislocation activity among crystals mainly falls within the range of 50% to 150% of the average dislocation density. The effects of fructose on the growth kinetics of sucrose crystals are also investigated. As one sucrose molecule consists of one fructose and one glucose, the adsorption of fructose on the sucrose crystal surface might cause the formation of new growth sites, resulting in the faster growth rate on the sucrose surface.