331.    BRATZLER, K.  [Sorption Methods for the Analytical and Preparative Separation of Gases.]  Oel u. Kohle, vol. 39, 1943, pp. 953-960; Chem. Abs., vol. 38, 1944, p. 6154. 

                  Briefly discusses theory of the separation of gases by adsorption and desorption.  Because of the lowered vapor pressure of the adsorbed gases the difference in the relative volatility of various adsorbed gases becomes great enough for purposes of separation at temperatures that would be too high for effective separation by fractional distillation.  Pure C₃H₈ is obtained from the commercial gas containing C₂H₆ and C₄H₁₀ by passing it slowly at 0° or room temperature over activated charcoal that had been degassed at 200° and 0.1 mm. Hg.  After atmospheric pressure has been reached, which may require 20-30 min., an electric oven is placed over part of the adsorption tube and some of the gas is desorbed; the desorbed gas comes in contact with the adsorbed gas in the cold part of the tube and exchange of the heavier and lighter components of the gas takes place. In this way the light impurities are driven off first followed by pure C₃H₈, and the heavy impurities remain adsorbed.  The same principle is applied to analytical methods that give satisfactory results if allowance is made for the material that remains adsorbed.  This difficulty is avoided by carrying out the desorption under vacuum. The latter method is particularly suited to the determination of small concentrations of a volatile component in a less volatile gas (C₂ hydrocarbons in commercial C₃H₈).  For the determination of C₃ and C₄ hydrocarbons in coke-oven gas or residual gas from the adsorption plant connected with a Fischer-Tropsch synthesis plant, it is best to concentrate these compounds by adsorption on activated charcoal and desorb them by steaming (Carbotox process). If the hydrocarbon mixture to be adsorbed contains olefins, the breakthrough of olefins, and thereby of the other hydrocarbons through the adsorbent, can be controlled automatically by bromination of the olefins with Br made in an electrolytic cell and measuring the amount of current used in the preparation of Br.