Solid at low pressure

Figure 5.19 shows an idealized form of the adsorption isotherm for physisorption on a nonporous or macroporous solid. At low pressures the surface is only partially occupied by the gas, until at higher pressures (point B on the curve) the monolayer is filled and the isotherm reaches a plateau. This part of the isotherm, from zero pressures to the point B, is equivalent to the Langmuir isotherm. At higher pressures a second layer starts to form, followed by unrestricted multilayer formation, which is in fact equivalent to condensation, i.e. formation of a liquid layer. In the jargon of physisorption (approved by lUPAC) this is a Type II adsorption isotherm. If a system contains predominantly micropores, i.e. a zeolite or an ultrahigh surface area carbon (>1000 m g ), multilayer formation is limited by the size of the pores. 

Ksenzhek (K8) developed a model for a porous body by representing it as a cube with regularly spaced intersecting capillaries. Liquid under pressure penetrates against the capillary forces. He showed that small pores block large ones, and this accounts for the fact that the liquid is not uniformly distributed throughout the solid. At low pressure, liquid penetrates only to a limited depth. 

Thus finally we have a mixture of 64.5 wt % sulfuric acid that has an enthalpy of O kJ/kg. (Note that we have used the fact that for liquids and solids at low pressure, the internal energy and enthalpy are essentially equal.) From Fig. 8.1-1 we see that a mixture containing 64.5 wt % sulfuric acid has an enthalpy of 0 kJ/kg at about 150 C. Therefore, if water and sulfuric acid are adiabatically mixed in the ratio of 3 1, the mixture will achieve a temperature of 150°C, which... 

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