{"id":6186,"date":"2024-12-19T10:17:54","date_gmt":"2024-12-19T09:17:54","guid":{"rendered":"https:\/\/www.perfectsamplegas.de\/sample-gas-dryer-perma-pure\/"},"modified":"2025-08-15T15:20:20","modified_gmt":"2025-08-15T13:20:20","slug":"sample-gas-dryer-perma-pure","status":"publish","type":"page","link":"https:\/\/www.perfectsamplegas.de\/en\/sample-gas-dryer-perma-pure\/","title":{"rendered":"Sample gas dryer Perma Pure"},"content":{"rendered":"

Perma Pure
\nNafion\u00ae Sample gas dryer<\/p><\/h2><\/div>

There are many reasons for drying sample gases for analysis, be it that the operating temperature of the analyzer is below the dew point temperature of the sample gas or that the analysis is disturbed by higher water concentrations. Conventional sample gas dryers such as condensate coolers, adsorption dryers or permeation dryers often change the composition of the sample gas by partially precipitating the sample component with the condensate, adsorbing it with the water or permeating it with the water. Drying with a Nafion\u00ae membrane, on the other hand, is based on a water-specific chemical process.<\/p>\n<\/div>

Principle of drying with Nafion\u00ae sample gas dryers<\/strong>
\nNafion\u00ae is a copolymer of perfluoro-3,6-dioxa-4methyl-7octene sulfonic acid and tetrafluoroethylene.<\/p>\n<\/div><\/div><\/div>

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Nafion\u00ae spontaneously absorbs water while its in its gaseous phase.<\/h3><\/div>

Each sulphonic acid group is surrounded by a maximum of 13 water molecules. The sulfonic acid groups form ion channels within the polymer through which water molecules can be transported. When water touches a sulfonic acid group on the outside of the Nafion\u00ae film, it is momentarily bound by the group. Other sulfonic acid groups inside the wall now have a higher affinity for water because they have not yet bound any water. The water is consequently transported through the ion channels until the other side of the wall is reached and the Nafion\u00ae wall is saturated. This transport is rapid. If the water vapor partial pressure in the vicinity of the Nafion\u00ae wall is lower than in the Nafion\u00ae membrane itself, water is released into the atmosphere in the form of vapor – until the difference in water vapor partial pressure between the atmospheres on both sides of the wall is equalized. Water is always transported in the direction of the lower water vapor partial pressure. For the continuous drying of gases, the Nafion\u00ae is extruded as a pipe. A Nafion\u00ae tube or a bundle of Nafion\u00ae tubes is surrounded by a housing and can thus be supplied with a drying gas in counterflow. This continuously maintains a water vapor – partial pressure gradient.<\/p>\n<\/div>

\"Nafion-Rohrbuendel\"<\/i> <\/a><\/i> <\/a><\/i> <\/a><\/i> <\/a><\/i> <\/a><\/i> <\/a><\/div><\/div><\/div><\/div><\/div><\/div>

Temperature and pressure influences, material properties<\/h3><\/div><\/div><\/div>

Nafion\u00ae is stable up to a temperature of 160\u00b0 C, but the housing material and the head of a tube bundle set lower limits. A gas temperature of 150\u00b0 C must not be exceeded even when using PTFE or stainless steel housings. The amount of residual water in the Nafion\u00ae wall is very temperature-dependent. At higher temperatures, the water is retained more by the wall than at lower temperatures and therefore cannot be released into the dry gas. The water concentration inside the Nafion\u00ae wall corresponds to the water concentration in the atmosphere outside the Nafion\u00ae. If the water concentration value in the moist sample gas reaches the water concentration value in the Nafion\u00ae wall, no more water can be absorbed and drying stagnates. The remaining concentration of water in the Nafion\u00ae at the corresponding operating temperature determines the minimum water dew point that can be reached in the sample gas. At room temperature (20\u00b0C), the residual water remaining in the Nafion\u00ae corresponds to a water dew point in the gas of -45\u00b0 C. This means that no lower dew point than -45\u00b0C can be reached at room temperature.<\/p>\n<\/div><\/div><\/div>

At higher temperatures, there is an approximate parallel shift in the minimum dew point, i.e. a dryer temperature of 60\u00b0 C corresponds to a minimum dew point of -5\u00b0 C. As condensation due to falling below the dew point must not occur under any circumstances, Perma Pure dryers must be heated when operating with gases of higher humidity. Heated dryers should have a temperature gradient over their length so that optimum drying is achieved. The optimum configuration would be one in which the temperature is just above the dew point of the sample gas at every point of the dryer. The differential pressure across the Nafion membrane influences drying via the water vapor partial pressures. At 13 bar, the burst pressure of the Nafion\u00ae tube is well above the maximum operating pressure of approx. 2 bar (differential pressure), depending on temperature and dryer type. The absolute pressure is of secondary importance. Nafion\u00ae is extremely corrosion-resistant. At the application temperatures and in the gas phase, there are hardly any known substances that attack Nafion\u00ae. The application is limited by the materials of the dryer housing (stainless steel, PTFE, PVDF or polypropylene) and the seals (fluororubber FPM).<\/p>\n<\/div><\/div><\/div><\/div><\/div>

Selectivity of the drying process<\/h4><\/div>

The only known components that are also transported through the Nafion\u00ae membranes are those with a hydroxyl group. As most inorganic hydroxides do not occur in the gas phase (except as aerosols), this group of components is essentially limited to:<\/p>\n<\/div>