刮膜式分子蒸发器上液体的停留时间分布

Residence Time Distribution of Liquid in Wiped Film Molecular Distillation

以水及质量分数分别为50%、70%的丙三醇-水溶液为介质,采用脉冲示踪法与紫外分光光度法对刮膜式分子蒸馏器上液体的停留时间分布(RTD)进行研究,分别研究了进料速率、转子转速及物料黏度对停留时间分布的影响.结果表明:在实验范围内,停留时间随着进料速率的增大而减小;进料速率增大时,分子蒸发器上的液膜混合程度也随之增强;随着转子转速增大,停留时间先增大,当达到一定转速后,停留时间反而减小;停留时间随物料黏度的增大而增大,液膜轴向返混程度也随之增强.通过对实验过程的观察与分析,采用2种不同的组合流动模型对刮膜式分子蒸馏过程进行描述,经与实验数据的对比可知,模型2(2个N级全混流串联模型进行并联,其中一个区域中每个全混流模型分别与一个平推流区域进行交换)在实验条件下较为适用,模型的模拟值与实验数据吻合较好.

The residence time distribution(RTD)of wiped film molecular distillation was studied based on impulse response method which was performed with pure water,50%(mass percent)and 70%(mass percent)glycerin-water solution and UV-VIS measurement.The dependent variables in the study were the feeding flow rate,rotate speed of rotor and liquid viscosity.The results indicated that the mean residence time decreased with the increase of the feeding flow rate.As the flow rate increased,the mixing degree was enhanced.In the beginning,the mean residence time increased with the increase of the rotate speed;however,it decreased after the rotate speed reached a certain speed.Both the mean residence time and the axial back-mixing degree increased with the liquid viscosity increasing.Wiped film molecular distillation was described by two different flow models.After observation and analysis of the experi-ment data,it has been found that model 2(two N-level continuous stirred tank reactors are in parallel,and one of them are exchanged with corresponding plug flow reactors) is more suitable under experimental condition,since its estimated value has a better agreement with experimental value.