【作者】 邵平；

【导师】 姜绍通；

【作者基本信息】 合肥工业大学 ， 农产品加工及贮藏工程， 2007， 博士

【摘要】 分子蒸馏适用于高沸点、热敏性、易氧化物质的分离，在食品和化学工业中的应用逐步受到重视。目前对分子蒸馏的应用基础理论研究尚不够深入，工艺参数的确定主要依靠具体操作经验总结和试验操作的优化：分子蒸馏在菜籽油脱臭馏出物(Rapeseed Oil Deodorizer Distillate，RODD)有效成分分离中尚缺乏系统性。本论文目的是对分子蒸馏过程进行数值模拟，开展基于分子蒸馏的RODD有效成分分离研究，为RODD再资源化提供技术支持。课题通过分析分子蒸馏液膜表面流体流动和传质传热特性，根据物料在进料、蒸馏和冷凝时物性变化，建立蒸发和冷凝液膜性质关联的二组分分子蒸馏模型；以RODD为研究对象，运用分子蒸馏、酸催化酯化和脂肪酶催化分离维生素E、甾醇和脂肪酸甲酯(FAME)，模拟预测分离维生素E(V_E)，指导实际分离过程。主要研究内容及结果如下：1、分析分子蒸馏液膜表面流体流动和传质传热特性，根据物料物化性质变化，建立蒸发和冷凝液膜性质关联的二组分分子蒸馏液膜模型。(1)对建立的分子蒸馏液膜模型利用平均隐式差分法Crank-Nicholson数值求解，过程稳定。通过EHP-EHS验证，模拟计算结果与实际试验结果最大误差低于5.1％。通过DBP-DBS物系数值模拟，系统研究进料温度、冷凝温度、进料浓度和进料速率对分子蒸馏过程的影响。进料温度增加，蒸发液膜的厚度和表面浓度沿轴向不断降低的趋势更加明显，液膜表面温度较快达到平衡稳态温度，DBP的蒸发速率增大的趋势越加明显。冷凝温度增高，冷凝液膜表面分子返蒸发严重。进料浓度增加，液膜表面温度降低，蒸馏率提高；进料速率增加，液膜表面温度达到稳态较慢，蒸馏量降低。(2)经DBP-DBS物系数值模拟，系统研究分段冷凝和分段蒸发对分子蒸馏过程的影响。分子蒸馏等温分段冷凝可以降低返蒸发效应的影响，得到浓度梯度较大的目标组分，增大了蒸馏量，避免实际蒸馏过程中“喷溅”现象对产品的不良影响。通过温度梯度冷凝则可以得到浓度梯次更大的目标组分。通过分子蒸馏分段蒸发，蒸发液膜表面温度随蒸发温度梯度的升高逐渐以“爬坡式”达到恒定值，实现了不同挥发组分在相应冷凝面上收集。采用脉冲示踪法研究刮膜式分子蒸馏中物料的停留时间分布，为刮膜转速选择提供依据。2、以RODD为研究对象，运用分子蒸馏、酸碱催化酯化和脂肪酶催化技术分离维生素E、甾醇和FAME。(1)系统研究并优化了RODD经甲酯化途径分离甾醇、FAME和V_E工艺。建立菜籽油脱臭馏出物甲酯化过程甾醇分离的数学模型，考察分子蒸馏操作参数对酯化物中相继分离FAME和维生素E的影响。当酯化反应液固比100ml／100g、甲酯化时间1.65h、催化剂用量4.4ml，酯化率达98％。当分子蒸馏系统压力为5.3Pa、蒸发面温度120℃、进料温度70℃、刮膜转速150 r／min、进料速率120mL／h时，FAME回收率达到41g／100mL。当系统压力2.66Pa、分子蒸馏蒸发面温度200℃、进料速率90ml／h、刮膜转速150r／min时，V_E的浓度和回收率分别达34.7％和89.5％。采用分子蒸馏直接分离游离脂肪酸(FFA)浓缩V_E时，维生素E浓度和回收率达26.32％和69.23％，相对分离FAME浓缩维生素E方法，浓度和回收率均降低。(2)采用脂肪酶催化酯化和分子蒸馏浓缩维生素E，运用响应曲面建立了脂肪酶反应时FAME含量的数学模型，并与动量梯度下降神经网络模型做了对比分析。当20g反应原料，初始加入水量11.77ml；单次加入甲醇量1.32ml，同时加入脂肪酶15U；初始加入酶量30.78U；水解时间16h，总反应时间40h，酯化率达到55％，二次蒸馏操作后V_E纯度达到25.2％以上。响应曲面优化分析结果相对神经网络结果较佳。3、利用建立的分子蒸馏液膜模型模拟预测分离油脚中的维生素E和FFA，与实际试验数据进行了比较，为分子蒸馏操作参数优化提供理论依据。(1)V_E分离模拟预测结果与试验结果曲线趋势相近。随着蒸馏温度和进料温度的增加，V_E浓度增大。达到较高浓度V_E时的模拟蒸馏温度较试验结果降低了20K，V_E浓度相差15％。随着蒸馏温度的增加，FFA分离时的蒸馏量增大，模拟值与实验值的相对误差不超过16％，同时重组分中FFA含量不断降低，模拟值与实际值随蒸馏温度的变化趋势相近。(2)应用Visual Basic 6.0中Matrix VB技术把Visual Basic的可视化设计同Matlab处理数据的优越性相结合，初步建立了分子蒸馏过程仿真软件，具有界面友好、操作简便的特点。更多还原

【Abstract】 Molecular distillation （MD） process is useful in the separation and purification of materials of high boiling point, as well as those that are thermally sensitive. It has been gotten more and more applications in food and chemistry industries. However, there remain unexplored larger and more important fields of molecular distillation. Parameters of practical production still depend upon experience and optimization methods. Application of MD on the separation of active components from rapeseed oil deodorizer distillate （RODD） is not systematically studied.The objective of study is to carry out numerical simulation of molecular distillation and separation of components from RODD, which provides technical support for recycling of RODD.In this study, balanced equations of a binary mixture for MD were derived on the basis of relation of heat and mass transfer in liquid films on both the evaporating and condensing surface, allowing for the feed, evaporating and condensing physical-chemical properties. The separation of vitamin E, sterols and fatty acid methyl ester （FAME） with acid and lipase esterification by MD from RODD and simulation for separation of vitamin E from RODD were carried out. The main work and results were as follows.1. Balanced equations of a binary mixture for MD were derived on the basis of relation of heat and mass transfer in liquid films taking account of the properties change of mixture.（1）The stable implicit finite differences Crank-Nicholson method was used for the transformation of partial differential equation into discrete form. The model values agreed well with the experimental values. The maximum relative error did not exceed 5.1%. The effects of feed temperature, condenser temperature, feed concentration and feed rate on MD process were investigated by the simulation of DBP-DBS mixture distillation. As the feed temperature increased, film thickness and surface concentration decreased sharply. It was more remarkable with an increase of feed temperature. The length of the evaporating cylinder along with the surface temperature of evaporating film reached steady-state was decreasing with increasing feed temperature. Evaporation rate of DBP increased with an increase of feed temperature. Evaporation rate decreased and re-evaporation on condensing film taken place with increasing of condensing temperature. Evaporating film surface temperature decreased while degree of evaporation and separation factor increased with the increase of feed concentration. Evaporating film thickness, surface concentration and composition of distillate increased, while degree of evaporation decreased when feed rate increased. The length of the evaporating cylinder along with the surface temperature of evaporating film reached steady-state decreasing with increasing feed rate.（2） Influences of divided evaporator and condenser on MD process were investigated by the simulation of DBP-DBS mixture distillation. Results showed that influence of splashing on desired substance caused by insufficient removal of gases and re-evaporation were minimized by the divided condenser. Gradient concentration of desired substance and increased degree of evaporation were obtained. Desired product concentration could be obtained by adjusting correspond condensing temperature. Evaporating film surface temperature was gradient increased nearly to the evaporator temperature through the gradient temperature increase of divided evaporator. Degree of evaporation increased with the increase of evaporator temperature. Different components could be collected on correspond condenser. The residence time distribution was carried out for wiped film molecular distillation by impulse response method.2. The separation of vitamin E, sterols and FAME with acid and lipase esterification by molecular distillation from RODD.（1） Optimization of sterols, FAME and vitamin E separation from RODD was studied systematically on basis of acid catalyzed methyl esterification. A mathematical regression model was presented for separation of sterols in methyl esterification of RODD. The effects of MD operation parameters on separation of FAME and vitamin E from RODD were investigated. The results showed that the methyl ester rate was above 98% when methyl esterification temperature 60℃, time 1.65hrs ,catalyst 4.4%, methanol/material ratio 100ml/100g. It indicated that the recovery of FAME was 41g/100mL when pressure 5.2Pa, evaporating temperature 120℃, feed temperature 70℃, wiper rolling speed 150 rpm and feed rate 120mL/h.. when experiments with an evaporating temperature of 200℃, feed flow rate of 90 ml h^-1 and wiper rolling speed of 150 rpm was conducted, the content and recovery of V_E was above 34.7%, 89.5% respectively after molecular distillation. Vitamin E was concentrated by molecular distillation by eliminating free fatty acid （FFA）, content and recovery in the residue were 26.32% and 69.23%, respectively. Compared to the FAME separation to concentrate vitamin E, vitamin E concentration and recovery of vitamin E by this method was lower.（2） MD and lipase catalyzed methyl esterification were applied for vitamin E concentration. The model of FAME content produced by enzymatic reaction was presented by RSM and compared with the BP neural network model with algorithm with momentous factor. The results indicated that when RODDTGF 20g, reaction temperature 37℃, the amount of water 11.7ml and lipase 30.78 U for hydrolysis time 16 h followed by amount of methanol added 1.32ml with lipase 15 U per time of three times, and total reaction time 40h, the content of V_E was 25.2% after twice MD. Optimization by RSM was better compared to the BP neural network model. 3. Molecular distillation simulation for separating desired components was carried out. Model value of V_E concentration was compared with experimental value.（1） Simulation for separation of V_E from RODD and separation of FFA from soapstock were carried out. Results showed that the tendency of model value was similar to that of experimental value. V_E concentration increased with the increase of evaporator and feed temperature. Evaporator temperature of model was lower 20K than experimental value and relative error of V_E concentration was below 15% when high concentration was obtained. Degree of evaporation increased with the increase of evaporator temperature when FFA separation took place. The relative error between model and experimental value was below 16%. The FFA content in residue decreased when evaporator temperature increased and was similar to model values.（2） MD process software was developed combining the advantages of Matlab data-processing with object oriented design of Visual Basic 6.0 by Matrix VB. The software had the characteristics of friendly interface and conveniently processing.更多还原