The effect of compaction on the surface characteristics of some synthetic zeolites: Compaction versus porosity

Abstract

The surface characteristics of loose and compacted 3A, 5A and 10A zeolite samples were investigated by nitrogen adsorption at — 195 °C. Three series of samples were examined: (i) untreated A zeolites; (ii) acid-activated zeolites; (iii) zeolites which had been deactivated by presoaking in water-soluble polymers. Compaction at 5 and 10 tonf in -2 produced changes in the shapes of the isotherms from type I to type II of the Brunauer-Emmett-Teller classification and high pressure hysteresis loops were formed. Activation of the parent zeolites with a 1:1 hydrochloric acid solution produced an increase in the porosity, whereas presoaking in polyglycol solution led to deactivation of the zeolites due to blockage of the pores with the long-chain polymer molecules. Compaction of the parent zeolites at 5 tonf in -2 produced a more noticeable decrease in their nitrogen adsorption capacities over the monolayer and multilayer regions owing to the destruction of micropores that were originally accessible for nitrogen adsorption in the loose powder. An increase in the compaction to 10 tonf in -2 resulted in the isotherm being moved upwards. However, it still lay below the isotherm for the loose powder, and this effect is correlated with the occurence of plastic deformation that partially compensates the adhesion effects that exist at the lower compaction pressure of 5 tonf in -2. Compaction of the acid-activated zeolite samples led to downward shift of the isotherm to below that of the loose zeolite samples; this is due to the effect of the solid-solid interface formed by compaction. Compaction of deactivated zeolite samples at a pressure of 5 tonf in -2 invariably produced a marked upward shift in the nitrogen isotherm above that for the corresponding loose powder; this effect is assumed to indicate the occurrence of a controlling plastic deformation effect. However, increasing the compaction pressure to 10 tonf in -2 produced a downward shift in the nitrogen isotherm to below that obtained for the sample compacted at 5 tonf in -2 but still above that obtained for the loose sample. This observation indicates the influence of adhesion effects that partially compensate the plastic deformation effects. Thus the effect of compaction on the surface characteristics of zeolites is different in the untreated, acid-activated and deactivated series of zeolites and depends on the porosity of the original loose powder. In view of the complications arising from the adhesion and fragmentation of compacted particles, the present results indicate that a systematic and comparative study is required to determine the limits on the various effects involved in the compaction of solids.