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How to choose the degree of vacuum in the drying process of the freeze dryer? It is a scientific method to determine the appropriate pressure for freeze drying by the vapor pressure of ice. A basic criterion for selecting system pressure: ice is in the range of 20% to 30% of the vapor pressure at the target product temperature. Sublimation occurs when the vacuum level set point is lower than the vapor pressure at which the ice is at the current product temperature.
Normally, the freeze-drying vacuum level is controlled between 50 and 300 mTorr (0.06 to 0.40 mbar), and 100 to 200 mTorr (0.13 to 0.26 mbar) is the most common range.
As can be seen from the table below, there is a direct relationship between temperature and pressure. The lower the temperature of ice, the lower the saturated vapor pressure. If the lyophilizer is not continuously controlled to very low vacuum levels, it will not be possible to have the system pressure set point at 20% to 30% of the ice vapor pressure at very low product temperatures (below -40oC). between. Therefore, freeze drying will proceed very slowly at very low product temperatures.
| Temp | Vapor Pressure | ||
|---|---|---|---|
| [Deg C] | [milliTorr] | [milliBar] | [pascals] |
| 0 | 4,584.000 | 6.1115 | 611.148 |
| -2 | 3,883.000 | 5.1769 | 517.689 |
| -4 | 3,281.000 | 4.3743 | 437.429 |
| -6 | 2,765.000 | 3.6864 | 368.635 |
| -8 | 2,325.000 | 3.0997 | 309.974 |
| -10 | 1,949.000 | 2.5984 | 259.845 |
| -12 | 1,630.000 | 2.1731 | 217.315 |
| -14 | 1,359.000 | 1.8118 | 181.185 |
| -16 | 1,130.000 | 1.5065 | 150.654 |
| -18 | 936.800 | 1.2490 | 124.896 |
| -20 | 774.400 | 1.0324 | 103.245 |
| -22 | 638.200 | 0.8509 | 85.086 |
| -24 | 524.300 | 0.6990 | 69.901 |
| -26 | 429.400 | 0.5725 | 57.248 |
| -28 | 350.500 | 0.4673 | 46.729 |
| -30 | 285.100 | 0.3801 | 38.010 |
| -32 | 231.200 | 0.3082 | 30.824 |
| -34 | 186.800 | 0.2490 | 24.905 |
| -36 | 150.300 | 0.2004 | 20.038 |
| -38 | 120.600 | 0.1608 | 16.079 |
| -40 | 96.300 | 0.1284 | 12.839 |
| -42 | 76.700 | 0.1023 | 10.226 |
| -44 | 60.800 | 0.0811 | 8.106 |
| -46 | 48.000 | 0.0640 | 6.399 |
| -48 | 37.700 | 0.0503 | 5.026 |
| -50 | 29.500 | 0.0393 | 3.933 |
| -52 | 23.000 | 0.0307 | 3.066 |
| -54 | 17.900 | 0.0239 | 2.386 |
| -56 | 13.800 | 0.0184 | 1.840 |
| -58 | 10.600 | 0.0141 | 1.413 |
| -60 | 8.100 | 0.0108 | 1.080 |
| -62 | 6.160 | 0.0082 | 0.821 |
| -64 | 4.660 | 0.0062 | 0.621 |
| -66 | 3.510 | 0.0047 | 0.468 |
| -68 | 2.630 | 0.0035 | 0.351 |
| -70 | 1.960 | 0.0026 | 0.261 |
| -72 | 1.450 | 0.0019 | 0.193 |
| -74 | 1.060 | 0.0014 | 0.141 |
| -76 | 0.780 | 0.0010 | 0.104 |
| -78 | 0.570 | 0.0008 | 0.076 |
| -80 | 0.410 | 0.0005 | 0.055 |
| -82 | 0.290 | 0.0004 | 0.039 |
| -84 | 0.210 | 0.0003 | 0.028 |
| -86 | 0.150 | 0.0002 | 0.020 |
| -88 | 0.100 | 0.0001 | 0.013 |
| -90 | 0.072 | 0.0001 | 0.010 |
| -92 | 0.049 | 0.0001 | 0.007 |
| -94 | 0.034 | 0.0000 | 0.005 |
| -96 | 0.023 | 0.0000 | 0.003 |
| -98 | 0.015 | 0.0000 | 0.002 |
