Studies on the Pyrolysis of Silica Gels Surface-treated with C₅-Alcohols

Abstract

The pyrolysis of the silica gels treated with C₅ alcohols, i. e., 1-pentanol, 1-2-methyl-1-butanol, d-2-pentanol, 1-2-pentanol and cyclopentanol and the pyrolysis of these alcohols in gaseous phase or over silica gel have been investigated through the identification and analysis of these products by means of the quadrupole mass spectra or of the gas chromatograph-quadrupole mass spectra. Both dehydration and dehydrogenation of the alcohols proceed simultaneously for the pyrolysis of those alcohols in gaseous phase. Since dehydration proceeds selectively for their pyrolysis over silica gel at lower temperature than that of their pyrolysis in gaseous phase, it is recognized that silica gel proceeds catalytically dehydration reaction of the alcohols. At higher temperature, both dehydration and dehydrogenation reactions proceed. The main products of pyrolysis of the surface-treated silica gels were observed to be water, alcohols used and the corresponding olefins. The evolution of water observed under 130°C and the alcohols observed under 250°C were considered to be due to the elimination of physisorbed ones. Although the olefines and water were observed at the range of 250°C and 500°C, the ratio of the amount of water to that of olefines was not constant against the decomposition temperature. Thus, these pyrolysis products were recognized to be formed under the different reaction mechanism. These surface groups are perceived to be combined chemically with substrate in the form of>SiOR.