Inert Purge Gas

Instead of using an inert purge gas to blanket the polymer in the chamber the chamber atmosphere can also be evacuated to remove air/oxygen. Pyrolysis under vacuum reduces the incidence of secondary reactions in the gas phase in contrast to pyrolysis at atmospheric pressure. Under vacuum, the residence time of the pyrolysis products is short and so the secondary reactions are limited. 

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Use Figure 1 to determine the quantity of inert purge gas required. 

An example of an actual physical activation procedure is as follows [176] the dried raw material is crushed, and sieved then the furnace temperature is increased at a rate of 10 [°C/min] up to 600°C for about 3 h, under inert purge gas flow. The resulting chars are then activated at 500°C-900°C for 10-60 min under purified C02 flush. In Figure 3.16 [175], a flow chart of the physical activation method is shown. 

Basically, a graphite-furnace atomizer (Fig. 8.1 A) consists of a graphite tube, electrical contacts, an enclosed water-cooled housing and inert purge gas controls. 

Ventilation in special rooms or chambers. Lower-cost standard motors are enclosed with light sheet metal and pressurized with uncon-taminated air or other inert purge gas. A housing pressure of 1 to 2 lb is sufficient to exclude hazardous gas from the equipment enclosure. In some cases, positive-pressure ventilation of an entire room or building is recommended to allow use of less expensive standard electrical equipment throughout. 

If the make-up gas contains inerts, purge gas is drawn from the loop after the second cold exchanger just before addition of the make-up gas. At this point the gas has the maximum content of inerts. The purge gas is usually transferred to a purge gas recovery unit for recovery of hydrogen. Recovered hydrogen is recycled to the process and introduced at a relevant stage of the synthesis gas compressor. 

In principle, recovering hydrogen from the inert purge gas is an easy apphca-tion for membranes. However, as hydrogen is removed through the membrane, the remaining gas becomes enriched in hydrocarbons, and the dew point increases to 60 °C or more. To avoid condensation of hydrocarbons on the membrane, the gas should be heated to at least 60 °C. In practice, to provide a safety margin and to minimize plasticization of the membrane, the gas must be heated to 15-20 °C above the expected dew point, in other words to above 80 °C. 

Inert-purge gas stripping cycle. In this cycle the adsorbate is removed by passing a nonadsorbing or inert gas through the bed. This lowers the partial pressure or concentration around the particles and desorption occurs. Regeneration cycle times are usually only a few minutes. 

Commercial high-pressure DTA instruments use an inert purge gas to attain a maximum operating pressure of 10 MPa. The DTA heating curves of polyethylene measured over a range of pressures are presented in Figure 2.16. 

Inert purge gas for graphite furnace atomizer compressed gas cylinder of purified argon. 

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