Freeze-drying of ceftriaxone sodium solution frozen with prefabricated porosity

Initially unsaturated material frozen with prefabricated porosity was prepared to experimentally investigate its effect on freeze-drying of liquid material. Ceftriaxone sodium, a kind of commonly used antibiotic, was selected as the primary solute in an aqueous solution. The liquid nitrogen ice cream-making method was employed to prepare frozen materials with different initial porosities. Results showed that freeze-drying was significantly enhanced with the initially unsaturated frozen material and substantial drying time was saved compared with conventional freeze-drying. Drying time for the unsaturated sample (0.3 of saturation or 0.67 of initial porosity) was more than 20 % shorter than that required for the saturated one (1.0 of saturation without initial porosity). SEM images displayed that the dried products of the unsaturated frozen material had a pierced solid skeleton and uniform pore space with a fine and tenuous structure compared with those of the saturated one. The freezing rate exhibited little influence on the freeze-drying process. Annealing can be moderately beneficial to shortening the drying time and further improving the energy utilization. An appropriate increase in operating temperature was able to enhance the freeze-drying rate while changes in chamber pressure had a negligible effect on the process.