OVERVIEW

Separation of the components of a fluid can be effected by contacting them with a solid that has a preferential attraction for some of them. Such processes are quantitatively significant when the specific surfaces of the solids are measured in hundreds of m ²/g. Suitable materials are masses of numerous fine pores that were generated by expulsion of volatile substances. The most important adsorbents are activated carbon, prepared by partial volatilization or combustion of a carbonaceous body, and activated alumina, silica gel, and molecular sieves which are all formed by expulsion of water vapor from a solid. The starting material for silica gel is a coagulated silicic acid and that for molecular sieves is hydrated aluminum silicate crystals that end up as porous crystal structures. Porous glasses made by leaching with alkai have some application in chromatography. Physical properties of common adsorbents are listed in Tables 15.1 and 15.2. Representative manufacturing processes are represented on Figure 15.1.

Table 15.1: Physical Properties of Adsorbents

	Particle Form [*]	Mesh Size	Effective Diameter D p, ft.	Bulk Density P b, Lb/cu.ft.	External Void Fraction F a	External Surface a v, sq.ft.	Specific Heat C x, Btu/lb F	Reactivation Temperature F	Examples
Activated Carbon	P	4 6	0.0128	30	0.34	310	0.25	200-1000	Columbia L
P	6 8	0.0092	30	0.34	446	"	" "	" "
P	8 10	0.0064