Effects And Mechanisms Of Dextran On The Carbonatization And The Crystallization Of Sucrose

The Sugar industry was acknowledged crucial importance to the national economy andpeople’s livelihood. Emissions and wastes are becoming the bottleneck problem to the sugarindustry with survival and sustainable development. In addition, recent research detailed thepresence of dextran in the sugar factories leads to processing problems like increased ofsucrose loss to molasses, that how to remove or reduce the dextran was urgently concerned inthe sugar industry.Dextran in the sugar industry was the main research object in this thesis. Effect of themolecular weights of dextran on physicochemical properties of calcium carbonate obtained bycarbonation in the juice and the nucleation process of sucrose in pure sucrose solutions wereinvestigated. With the method of ultrasound to assist carbonation in the juice and sectionalcarbonation to figure out the low concentration, fluctuation and low absorption rate of CO₂inthe boiler flue gas were proposed. Which make foundation for practical application on greenprocessing and energy savings of sugar industry in the future.The ethanol sedimentary method was used to extract dextran from the sucrose. Theweight-average molecular weight of the dextran was between1.04×10⁴and2.24×10⁶Da bysize-exclusion chromatography, using a refractive index detector. Then, the effect ofmolecular weights of dextran on the calcium carbonate obtained by carbonation in the milk oflime was investigated. Chord length range and unweighted median chord length of thecalcium carbonate increased with the increase of the molecular weight of dextran. The dextranin the milk of lime can raised lattice distortion in the calcium carbonate. And we found thephysical adsorption was exist between the dextran and the calcium carbonate.The effect of molecular weights of dextran on the calcium carbonate obtained bycarbonation in the calcium saccharate solution was investigated. The morphology of thecalcite was changed from bifurcation stalactite into irregular shape with the increasing ofdextran molecular weight. In addition, both of chord length range and unweighted medianchord length of the calcite decreased with the increase of the dextran molecular weight. Thedextran in the calcium saccharate solution could not cause lattice distortion in the calciumcarbonate. The calcium carbonate obtained by carbonation with presence of dextran T40waspositively effect to clarify juice.And also we found the effect of ultrasonic on the calcium carbonate obtained bycarbonation in the calcium saccharate solution with dextran, the number of the calcite with the irregular shape was increased by the increasing of ultrasonic power. Furthermore, both ofchord length range and not weighted median chord length of the calcite decreased with theincrease of ultrasonic power. Both ultrasonic and dextran could not cause lattice distortion inthe calcium carbonate. The calcium carbonate obtained by carbonation with presence ofdextran T40and ultrasonic power2w/cm²was positively effect to clarify juice.The effect of dextran on the calcium carbonate obtained by Ca（HCO₃）₂also wasinvestigated. The calcium carbonate which could include calcite and aragonite was producedusing the decomposition of Ca（HCO₃）₂by heat treatment and the percentage of aragonite was67.0±0.5%. The shape of the calcium carbonate was cubic, columnar and fusiform. Thedextran and sucrose in the Ca（HCO₃）₂solution could not cause lattice distortion in thecalcium carbonate. However, the calcium carbonate produced by reacting betweenCa（HCO₃）₂and Ca（OH）₂was calcite. The shape of the calcite was globular, cubic andneedlelike. Both sucrose and dextran could cause lattice distortion in the calcium carbonate.the existence of dextran and sugar could can cause lattice distortion in the calcium carbonate.Clarified juice was better with the calcium carbonate obtained by reacting betweenCa（HCO₃）₂and Ca（OH）₂.The supersolubility of sucrose in the water solution increased with the increase of thehigher molecular weights of dextran. The spontaneous nucleation of sucrose, mitigation andreducing the counts of sucrose crystal in the syrup could be obviously inhibited by the highermolecular weight of dextran in sugar liquid. The development of the crystals faces of sucrose（110and110） were inhibited by the increasing of molecular weights of dextan.With the center combination design optimization of the test results, the concentration ofsolid matter in the solution, the dosage of enzyme and the temperature of the soltuion affectedthe dextran in the syrup digestion rate extremely. By controlling the concentration of solidmatter at the end of the effect evaporation tank and the dosage of the dextranase can reducethe content of dextran in the syrup.