《结晶分离（crystallization separation）》由会员分享，可在线阅读，更多相关《结晶分离（crystallization separation）（14页珍藏版）》请在金锄头文库上搜索。
1、结晶分离（Crystallization separation）General properties of crystals(1) anisotropy: the main difference between crystal and non crystal amorphous material in many properties such as optical and electrical has direction, which has the same properties in the same direction, are different in different direct
2、ions; but polycrystalline macro has no anisotropy.(2) uniformity: the crystal is a structure formed by the arrangement of the same molecules, atoms and ions in order to form crystals only when they reach a certain degree of purity.(3) crystal (single crystal) has regular geometrical shape and good s
3、ymmetry.(4) it has a certain melting point.(5) the same kind of material will form different crystalline morphology, homogeneous polycrystalline phenomenon.Crystallization processCrystallization - a substance from a liquid (liquid or molten body) or gasThe process by which crystals are formed is cal
4、led crystallization.? - crystallization in certain conditions. The crystalline form of the solute precipitation from solution, to achieve the purpose of separation, which is the traditional method of material separation and purification, widely used in chemical industry, biological engineering, food
5、 and pharmaceutical industries, such as sugar, monosodium glutamate, various amino acid production.The analysis and determination of crystalline products were carried out by optical microscope, polarizing microscope and X- ray diffraction.Conditions for crystallization(1) material characteristics (i
6、nternal causes)(2) the purity of the sample(3) the saturation of solution: in a slightly supersaturated state, the crystal formation rate is slightly larger than the rate at which the crystal dissolves, so that the crystal can be obtained(4) the effect of solvent: solvent can react with crystalline
7、substance, can not affect the biological activity of a crystalline substance; with high temperature coefficient, in order to take advantage of the temperature change of crystallization; a higher solubility of impurities, or at different temperatures and different crystalline substance impurity solub
8、ility; safety and easy recovery.Formation mechanism of crystallizationCrystallization consists of three processes:Formation of supersaturated solutions;Nucleation of nuclei;Crystal growth.Supersaturation of solution is the premise of crystallization, supersaturation is the driving force of crystalli
9、zation.Formation of supersaturated solutionsCooling crystallization:The heat saturated solution is cooled, and the temperature of the solution is lowered directly so that the solute is crystallized out of supersaturation. The cooling method is suitable for the occasions where solubility decreases wi
10、th the decrease of temperature.Evaporation crystallization:The solution is heated under pressure, atmospheric pressure or reduced pressure, evaporating, removing partial solvent, and crystallizing the supersaturated solution. This method is mainly applicable to occasions where solubility changes lit
11、tle with temperature, or solubility decreases with increasing temperature.Chemical reaction crystallization:A new substance with lower solubility is formed by adding a reactant or regulating pH value, and crystallization is precipitated when its concentration exceeds its supersaturated solubility.An
12、alytic method:The addition of certain substances to the solution reduces the solubility of the solute and forms a supersaturated solution and crystallizes. These substances are called anti solvent or precipitant, they can be solid or liquid or gas. Commonly used solid sodium chloride, hydrophilic or
13、ganic solvents, such as methanol, ethanol, acetone and so onNucleationCrystal nucleus (crystal, nucleus) - tiny particles precipitated first in supersaturated solutions. The size of the nuclei is usually in the range of several nanometers to tens of nanometers.Nucleation rate - the number of new nuc
14、lei produced in unit volume solutions per unit time.Small nuclei have larger solubility than normal crystals and dissolve in saturated solutions, and nuclei can only exist when they reach a certain supersaturationThere are three mechanisms of nucleation:(1) primary homogeneous nucleation: solution a
15、t higher supersaturationThe process of spontaneous nucleation.(2) primary heterogeneous nucleation: the process of producing nuclei under the guidance of foreign matter can occur at lower supersaturation.(3) two times nucleation: a solution containing crystals occurs when crystals collide with each
16、other or crystals are induced by tiny crystals produced by collisions with a stirrer or wallIndustrial crystallization(1) natural crystallization;This is an ancient method of crystallization.The solution is evaporated and cooled to an unstable region, i.e., in the unstable region, the nuclei are precipitated.The formati
