| Summary: | 碩士 === 長庚大學 === 化工與材料工程研究所 === 93 === The influences of fructose on the growth kinetics of sucrose crystals from aqueous solution are studied using a photomicroscopic technique in an isothermal, continuous-flow chamber. The phenomena of size- independent growth and growth rate dispersion are observed. The presence of fructose is found to enhance growth rate of sucrose crystals in the aqueous sucrose solution. A model is presented to describe the enhanced growth phenomenon studied here. As a sucrose molecule consists of one fructose and one glucose , fructose might be incorporated into sucrose crystal lattice, which promotes growth rate of sucrose crystals by forming more new growth sites. An effectiveness factor ( ) is introduced to take into account the growth promoting ability of the impurity adsorbed on the crystal surface. When , the impurity adsorbed on the crystal surface has a promoting effect on crystal growth. When , the impurity adsorbed on the crystal surface has a retarding effect on crystal growth. When , the impurity adsorbed on the crystal surface does not affect crystal growth. As the diffusion process proceeds very fast in this work, the adsorption process of the impurity on the crystal surface is assumed to reach the equilibrium state and the Langmuir adsorption isotherm is applied to relate the fractional coverage of the impurity on the crystal surface with the impurity concentration in solution. In the end, and the Langmuir constant ( ) are determined by fitting the experimental data with the proposed model.
|
|---|
