Ethyl chloride, adsorption

Fig. 4.25 Adsorption isotherms showing low-pressure hysteresis, (a) Carbon tetrachloride at 20°C on unactivated polyacrylonitrile carbon Curves A and B are the desorption branches of the isotherms of the sample after heat treatment at 900°C and 2700°C respectively Curve C is the common adsorption branch (b) water at 22°C on stannic oxide gel heated to SOO C (c) krypton at 77-4 K on exfoliated graphite (d) ethyl chloride at 6°C on porous glass. (Redrawn from the diagrams in the original papers, with omission of experimental points.)...

The swelling of the adsorbent can be directly demonstrated as in the experiments of Fig. 4.27 where the solid was a compact made from coal powder and the adsorbate was n-butane. (Closely similar results were obtained with ethyl chloride.) Simultaneous measurements of linear expansion, amount adsorbed and electrical conductivity were made, and as is seen the three resultant isotherms are very similar the hysteresis in adsorption in Fig. 4.27(a), is associated with a corresponding hysteresis in swelling in (h) and in electrical conductivity in (c). The decrease in conductivity in (c) clearly points to an irreversible opening-up of interparticulate junctions this would produce narrow gaps which would function as constrictions in micropores and would thus lead to adsorption hysteresis (cf. Section 4.S). 

Fig. 4.27 Swelling and low-pressure hysteresis in the adsorption of n-butane on compacts of coal at 273 K. The following are plotted against the relative pressure (a) the amount adsorbed (b) the percentage increase on length (c) the decrease —Ajc in electrical conductivity. The curves for ethyl chloride were very similar to the above curves.

Since 1950, the scope and nature of these effects have been studied in greater detail. Amberg and McIntosh 67) were the first to use porous glass as the adsorbent and studied water adsorption. In later work 68, 69) butane, ethyl chloride, and ammonia were adsorbed. Flood and Heyding... 

Fig. 1. Expansions of an activated charcoal rod produced by the adsorption of ethyl chloride (O) at 10 C. and dimethyl ether (-f) at 6.5 C. (64).

Fig. 2.2. Adsorption isotherms of ethyl chloride on charcoal (ct stands for 0 labels on curves indicate different temperatures in °C)...

Solution The answer to this is obtained by comparing Equations (31) and (62). When p/p0 is used instead of p, we obtain c, not K, from the linearized Langmuir equation via Equation (41). The exponential energy term evaluated from the analysis of In K versus 1/7 is seen by Equation (62) to be the difference between the adsorption energy and the energy of vaporization of the adsorbate. For ethyl chloride Ev = 23 kJ mole-1 therefore E = 23 + 14 = 37 kJ mole-1 this is the actual adsorption energy for the ethyl chloride-charcoal system discussed in Example 9.3. 

For an arbitrarily chosen extent of adsorption, a horizontal line such as the dashed line in Figure 9.7 may be drawn that cuts the various isotherms at different pressures. The pressure coordinates of these intersections can be read off the plot. According to Equation (90), a graph of In p versus l/T should be linear with a slope of ( — qs,/R). From Figure 9.7, for example, when the adsorption is 0.10 g ethyl chloride (g charcoal)-1 (which corresponds to 8 = 0.2), the equilibrium pressures are 0.20, 0.63, and 2.40 torr at —15.3, 0, and 20°C, respectively. When plotted in the manner just described, these data yield a line of slope — 5330 K. Multiplication by R gives qst = 44.3 kJ mole -1 as the isosteric heat of adsorption for this system at 8 = 0.2. Table 9.3 lists values of qst for different 8 values as calculated from the data in Figure 9.7. 

We shall just give one example. The adsorption of ethyl chloride on charcoal at 331°K., measured by Pearce and Taylor 198), can be described as a case where the adsorbed molecule moves and rotates freely over the surface. When the surface is covered with adsorbed molecules to about 27%, the heat of adsorption is 9.1 kcal./mole. The value of h/kT is 1.45 X 10 13 sec. hence... 

Comparing the adsorption of ethyl chloride on charcoal (see 2 above) with the adsorption of water on charcoal, mentioned here, we obtain... 

Despite the somewhat lower temperature and the higher heat of adsorption, the time of adsorption of the water molecules is roughly ten times shorter than that of ethyl chloride molecules. 

Schwab has pointed out that the following relationship between the two parameters of the Arrhenius equation is frequently encountered. A decrease in the activation energy of a given reaction, for a series of catalysts, often does not increase the reaction rate to the extent calculated, because of a simultaneous decrease of the frequency factor. Cremer (106) confirmed this for the decomposition of ethyl chloride on various chloride catalysts. These findings will be discussed here with due regard to the relation between adsorption and elementary reaction rates dealt with in the preceding section. 

In all cases the mechanism is adsorption of A, reaction on the surface to form adsorbed B, and desorption of B into the gas phase. Sketch the rate of reaction (per unit mass of catalyst) vs total pressure in each of the above three cases. Also, for comparison, include a sketch of the rate of the homogeneous reaction, assuming that it is first order. Sketches should be for constant composition. 9-11. Thodos and Stutzmanstudied the formation of ethyl chloride, using a zirconium oxide catalyst (on silica gel) in the presence of inert methane,... 

Figure 3.17. Adsorption isotherms of ethyl chloride on charcoal.

Examples of mono-layer adsorption isotherms obtained for chloroform and butyl chloride are shown in Figure 5. The adsorption isotherms of the more polar solvents, ethyl acetate, isopropanol and tetrahydro-furan from -heptane solutions on silica gel were examined by Scott and Kucera [4]. Somewhat surprisingly, it was found that the experimental results for the more polar solvents did not fit the simple mono-layer... 

Homogenization of sample (adding water if needed) and adsorption on activated Florisil to produce a free-flowing powder. Elution with ethyl acetate or methylene chloride. 

Vinyl acetate-ethyl acetate Propane-propylene Ethanol-isopropanol Hydrochloric acid-water Nitric acid-water Close-boiling Close-boihng Close-boihng Maximum-boiling azeotrope Maximum-boiling azeotrope Phenol, aromatics Acrylonitrile Methyl benzoate Sulfuric acid, calcium chloride for salt process Sulfuric acid, magnesium nitrate for salt process Alternative to simple distillation Alternative to simple distillation, adsorption Alternative to simple distillation Sulfuric acid process rehes heavily on boundary curvature Sulfuric acid process rehes heavily on boundary curvature... 

In certain processes currently being developed, it is proposed to withdraw the ferric chloride by adsorption on alumina or activated charcoal to avoid excessive product losses. As a rule, most of the equipment is built of carbon steeL The main license holders are Dow, Ethyl, Goodrich, Hoechst, Hills, Mitsui Totasu, Monsanto, PPG (Pittsburgh Plate Glass Company), Rhdne-Poulenc, Solvay, Stauffer. Toa Gosei, Tokuyama Soda, Toyo-Soda, etc. In the 1970s, Diamond Alkali and Oronzo de Nora developed a process for the chlorination of dilute ethylene called Dianor. 

Hydroxyl groups cause a greater increase than do chlorine atoms methyl and ethyl alcohols have a higher heat of adsorption than have the corresponding chlorides. 

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