Vacuum drying process with pure gas supply - to avoid stationary evapn. equilibrium conditions

摘要

A vacuum drying process is optimised by supplying fresh gas (pure gas or gas mixt. in which the partial vapour pressure of the liq. to be evaporated is below the equilibrium partial pressure under the prevailing drying conditions) into the drying chamber while maintained defined conditions of gas compsn., gas vol./unit time, pressure, temp. and time-variable vacuum. When e.g. acetonitrile-contg. liquids are being evaporated by drying at room temp. and 0.05 Pa vacuum, a supply of ultra-pure nitrogen, contg. no partial pressure of acetonitrile, is provided. The vacuum pumps must produce a much higher vacuum than the drying pressure, when the fresh gas supply is shut off, so that a sufficient amt. of fresh gas can be supplied to attain the drying pressure without too great a redn. in the vacuum. ADVANTAGE - The drying process is optimised w.r.t. time and quality and the materials are given more protection against losses, which is important in micro-analytical processes.