Alcohol Dehydration using New Shape Selective Zeolites

Alcohol Dehydration using New Shape Selective Zeolites. - The shape selectivity of zeolites has been referred to and exploited in numerous ways. Nevertheless, within the last ten years a new class of zeolite (Type ZSM-5) has been reported, which possesses pore openings, intermediate in size between the large and small pore zeolites its sieving properties in respect of alkyl aromatics and various aliphatic hydrocarbons have been reported. 

Since Meisel et al. reported the reaction, the new zeohte has received a good deal of attention and among the first workers to discuss the possible reaction mechanism were Chang and Silvestri, who reported the conversion of methanol and other oxygenated hydrocarbons to hydrocarbons. 

Increasing the partial pressure to 50 atm increased the production of aromatics, and there appeared to be greater overlap between dehydration and aromatization steps thus enhancing the probability of alkylation. 

The acidic properties of H-ZSM-5 have been studied using i.r. and e.s.r. spectroscopy and microcalorimetry.The i.r. results indicated that two different hydroxyl groups are present. It was postulated that one resulted from the interaction of similar OH groups, or OH-water molecule interactions, to give (H20) H species. The second was linked to the presence of the group Si-OH-Al. 

Bronsted and Lewis acid sites were shown to exist, but the strength of the former decreased with increasing calcination temperature, and the most strongly acidic groups could be removed permanently by calcination at 1173K. 

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