The Study On Process Of Xylitol Crystallization From The Broth

Xylitol is widely used in the medicine and food trade. One of its production methods is fermentation that has favorable foreground. But the product's separation and purification were not settled well. The thesis aims at this problem.Thermodynamics of xylitol crystallization is researched first. After studying the relationship between xylitol solubility with temperature, solvent's ingredients, impurities and pH', xylitol crystallization method that conjoins the cooling method and "solventing-out" method is determined. Moreover, the value of limit supersaturation is about 0.22, which is obtained from the width of metastable region based on the broth.The effect of impurities, temperature, original supersaturation, crystal seed size and magma density on crystal growth rate is pondered. The kinetics equation of xylitol crystal growth is established on power-law-equation, G= kg o n and Arrhenius-type equation. By the way, the value of activation energy for crystal growth is also calculated. Some of the results seem to indicate that surface integration may be the most significant mechanism in the process of crystal growth. However, this conclusion can't be corroborated by the expected trend in the "order" of the equation.In this thesis, getting crystalline xylitol from its broth is studied emphatically, which is based on thermodynamics and kinetics.Before crystallization, the broth should be pretreated. The pretreatments consist of decoloration, chromatographic separation and concentration. By applying artificial neural network and genetic algorithm, the optimum decoloration condition is found, and overall efficiency is enhanced to 82.7%.By means of uniform design, stepwise regression and xylitol crystal morphology observed with SEM, the technique of xylitol crystallization from its broth is optimized. At the same time, crystal productivity is 88.5% and crystal purity is 79.2%.Being operated under the optimum conditions, recrystallization is executed. The results of analyzing and detecting on the last crystalline xylitol show that the crystalline product is satisfying: Its purity is up to 99%; it appears white and has homogeneous granularity without crystalline water; furthermore, there is no phenomena of agglomeration.