Apparatus and process for freeze drying

Claim 1

IN A PROCESS OF FREEZE DRYING HEAT SENSITIVE PRODUCTS WHEREIN THE PRODUCT IS FROZEN AND THE FROZEN PRODUCT IS MAINTAINED IN A CHAMBER HAVING A PARTIAL PRESSURE OF WATER VAPOR OF LESS THAN ABOUT 4 MM. HG ABS., THE IMPROVEMENT WHICH COMPRISES RAISING THE TOTAL PRESSURE WITHIN SAID CHAMBER BY AN AMOUNT IN EXCESS OF 1 MM. HG BY INTRODUCING INTO THE CHAMBER A PARTIAL PRESSURE OF A DRY INERT GAS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, CARBON DIOXIDE, AIR, NITROGEN AND THE NOBLE GASES AND MIXTURES THEREOF, MEANWHILE REMOVING WATER VAPOR FROM THE CHAMBER WITHOUT SIGNIFICANTLY LOWERING THE PARTIAL PRESSURE OF THE INERT GAS, THEN SUBSEQUENTLY DECREASING THE TOTAL PRESSURE WITHIN SAID CHAMBER AND THE PARTIAL PRESSURE OF THE INERT GAS BEFORE THE LOCALIZED PRESSURE OF WATER VAPOR AT THE ICE SURFACE IS RAISED SUFFICIENTLY TO PROVIDE AN IMPEDANCE TO WATER VAPOR TRAVEL WHICH WOULD ALLOW THE ICE IN THE PRODUCT TO REACH A WATER VAPOR EQUILIBRIUM AT HIGH TEMPERATURES EXCEEDING THE MELTING POINT OF THE ICE, SAID DECREASE OF PRESSURE BEING AN AMOUNT IN EXCESS OF 1 MM. HG., AND REPEATING THIS RAISING AND LOWERING OF THE PARTIAL PRESSURE OF THE INERT GAS IN THE CHAMBER AS A SERIES OF PULSES.