An Experimental Study of Moisture and Temperature Distributions During Freeze‐drying

Hatcher, John D.; Lyons, Donald W.; Sunderland, J. E.

doi:10.1111/j.1365-2621.1971.tb02025.x

Cited by 8 publications

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“…The lengthy drying times are caused by resistances to heat and mass transfer and other factors which have been investigated extensively, both experimentally and theoretically, (Saravacos and Stinchfield, 1965;Bralsford, 1967;Sandall et al, 1967;King et al, 1968;Hatcher et al, 1971;King, 1971;Cox and Dyer, 1972;Gentzler and Schmidt, 1972;Meo, 1972;Flink and Aguilera, 1974;Greenfield, 1974;Goldblith et al, 1975;Ma and Peltre, 1975a,b;MacKenzie, 1977a,b;Kerkhof and Thijssen, 1977;Sheng and Peck, 1977;To and Flink, 1978;Liapis and Litchfield, 1979a;Liapis, 1979, 1982;Liapis, 1980a,b;Litchfield et al, 1981a,b;Liapis andMarchello, 1982, 1983a,b). A reduction in the drying time can result in reduced energy and labor costs.…”

Section: Introductionmentioning

confidence: 99%

An analysis of the lyophilization process using a sorption‐sublimation model and various operational policies

1985

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The freeze-drying process is studied under various operational policies through the use of a sorption-sublimation model. The operational policy that provides the shortest drying times keeps the pressure at its lowest value. The upper and lower heating plates are independently controlled so that the material constraints are encountered and held throughout the free water removal phase.Under certain conditions, and for the case of samples of small thickness, the sorbed water profiles may have segments whose bound water concentrations are higher than those at the start of the free water removal phase. It is shown that the criterion used in terminating the freeze-drying process is of extreme importance, since it may lead to an undesirable sorbed water profile which may deteriorate the quality of the dried product. M. J. MILLMAN, SCOPECertain biological materials, pharmaceuticals, biochemical products, and foodstuffs which may not be heated even to moderate temperatures in ordinary drying, are freeze-dried. Recent developments in biotechnology and biochemical engineering (Hill and Hirtenstein, 1983) have established the importance of lyophilization-freeze-drying-in biochemical processing.As a rule, freeze-drying produces the highest quality product obtainable by any drying method (Goldblith et al., 1975;Mellor, 1978). Prominent factors are the structural rigidity of the product, which facilitates rapid and almost complete rehydration at a later time, little loss of flavor and aroma, and minimization of degradative reactions which normally occur in ordinary drying processes, such as nonenzymatic browning, protein denaturation, and enzymatic reactions.However, freeze-drying is an expensive form of drying because of the slow drying rates and the use of vacuum. Thus, it is essential to develop operational policies which would reduce the drying times by improving the drying rates.The interactions in the variables of the freeze-drying process are complex, and an experimental approach of examining the various operational policies is tedious, expensive, and timeconsuming. But the experiment will finally confirm or disprove the validity of operational policies suggested by theoretical work, and which are supposed to improve or minimize the drying times. A mathematical model which can predict known freezedrying experimental results accurately, can be used in the analysis of the freezedrying process and in the examination of various operational policies which may maximize the drying rates. This work develops a sorption-sublimation model which is used to study operational policies that may significantly reduce the drying times. This model is also used to examine the effects on the bound water profiles of the criteria employed to end the terminal drying phase. Skim milk was used as a model material.The development of bound water profiles incorporates an important factor for optimization policies for quality retention in freeze-drying. CONCLUSIONS AND SIGNIFICANCEA sorption-sublimation model is presented and used to simulate the fr...

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