Abstract:

The porous frozen materials with prefabricated porosity were prepared to verify the effect on freeze-drying of liquid materials experimentally. Ceftriaxone sodium, a kind of commonly used antibiotics for injection, was selected as the primary solute in aqueous solution. Liquid nitrogen ice-cream making method was adopted to fabricate frozen materials with certain initial porosity. Freeze-drying experiments were conducted at the same operating conditions for two kinds of frozen materials, the initially unsaturated and saturated ones for comparison. The results showed that freeze-drying could be enhanced significantly using the porous frozen materials with prefabricated porosity. The drying time for the initially unsaturated frozen sample (S₀=0.3 or 0.67 of initial porosity) can be 21.3% shorter than that required for the saturated one (S₀=1.00 or zero porosity). SEM images of dried products displayed that the unsaturated materials had more tenuous solid matrix and continuous void space than those of the conventional one. This would be beneficial to migration of sublimated vapor and desorption of adsorbed moisture, favoring reduction of mass transfer resistance. Freezing rate had a little effect on freeze-drying of two kinds of frozen materials. Annealing could decrease the drying times, which were 16.2% saved for the initially unsaturated sample and 14.8% for the saturated one. Appropriately increasing ambient temperature had a positive impact on the freeze-drying process, and the change in chamber pressure had little contribution to the process.

Key words: drying, porous media, experimental validation, initial porosity, freezing rate, annealing

摘要：

实验探究了具有初始预制孔隙多孔物料对冷冻干燥过程的强化作用。以注射用抗生素药剂——头孢曲松钠为主要溶质，采用“液氮制作冰激凌法”制备了具有不同初始孔隙率的冷冻物料，在相同的条件下进行冷冻干燥实验。结果表明，初始饱和度为0.3的冷冻物料（初始孔隙率为0.67）干燥时间比饱和物料（初始孔隙率为0）缩短了21.3%。干燥产品的SEM图显示，初始非饱和冷冻物料的固体骨架和孔隙结构连续而均匀，初始饱和度越低，骨架越纤细，可大大地降低传质阻力。对冷冻速率和退火处理的研究表明，冷冻速率对于两种物料干燥过程的影响甚微；退火处理能够提高冷冻干燥速率。适当提高操作温度可以明显缩短两种物料的干燥时间；操作压力对冷冻干燥过程几乎没有影响。

关键词: 干燥, 多孔介质, 实验验证, 初始孔隙, 冷冻速率, 退火