The mechanism of coke formation on silica-alumina cracking catalysts was studied by analysis of cracking experiments with seven pure hydrocarbons at 445' C. and n-hexadecane at 500" C. under a variety of process conditions. Coke deposits were isolated from selected catalyst samples for infrared spectral examination. Aromatic skeletal vibrations were observed a t 1580 to 1590 cm.-' Although the cokes were low in hydrogen content, it was possible to identify -Ctlz, -CH3, and aromatic -CH groups by infrared absorption in the C-H stretch region. Mechanism of coke formation involves initial adsorption of hydrocarbons followed by chemical reactions of adsorbed materials. The latter include condensation reactions followed b y hydrogen elimination either by direct dehydrogenation to form hydrogen gas or by a hydrogen transfer process. Coke formation in fixed beds is shown to b e a complex function of length of

for use of data on which temperature calculations of EVis were based, and to Wladimir Philippoff for helpful advice and suggestions. This work was conducted under contract between the Chemical Corps, U. S. Army, and Rensselaer Polytechnic Institute.

The purpose of this study was to develop methods for the isolation and characterization of sulfur compounds i n vacuum gas oils. Two separation schemes were devised. One method involved oxidation of the sulfur compounds to sulfones using an excess of hydrogen peroxide followed by separation from the hydrocarbons using liquid-solid chromatography. Characterization was achieved by mass spectrometric analysis of the sample before and after removal of the thermally unstable sulfones and by direct examination of the isolated sulfones using ultraviolet and infrared spectrophotometry and nuclear magnetic resonance spectrometry. The second and more desirable technique involved stepwise oxidation of the sulfur compounds to sulfoxides using a limited amount of hydrogen peroxide followed by separation of the polar sulfoxides f r o m the hydrocarbons by liquid-solid chromatography. The sulfoxides were reduced back t o the parent sulfur compounds and isolated in relatively pure state by liquid-solid chromatography. These sulfur compound concentrates, being free of hydrocarbon contamination, were then analyzed by mass spectrometry, thin layer chromatography, ultraviolet spectrophotometry, and nuclear magnetic resonance spectrometry. For comparison, a third method was used which was based upon dealkylation over alumina at 500° C followed by gas chromatography using a microcoulometric sulfur detector for separation and measurement by compound classes. The results of the isolation and characterization work confirmed the reliability of the dealkylation method for the rapid routine analysis of high-boiling petroleum fractions for sulfur compound types. These methods were useful in studying the kinetics and mechanisms of hydrodesulfurization during process development.O'DONNELL ( I ) isolated sulfur compounds from a California coastal asphalt by oxidation of the sulfur compounds to sulfones, then separated them from the hydrocarbons by liquidsolid chromatography. The sulfones, being much more polar than the aromatic hydrocarbons, were easily isolated without contamination from the hydrocarbons and vice versa. However, O'Donnell did not fully characterize the isolated materials by instrumental techniques. Drushel and Miller (2) converted sulfur compounds in petroleum fractions to sulfones, rendering them amenable to polarographic reduction. In their studies it was not necessary to isolate the sulfones. The oxidized sample yielded polarographic reduction waves corresponding to benzo-and dibenzothiophene dioxides (listed as thiophenes and diary1 sulfides). Good recovery for a wide range of samples from kerosine to molecular still cuts (mol wt 200 to 1000) indicated essentially quantitative conversion of the sulfur compounds to sulfones by oxidation with hydrogen peroxide.A number of workers have successfully isolated sulfur compounds from petroleum by controlled oxidation of the sulfur compounds to sulfoxides with hydrogen peroxide. (1) G. O'Donnell, ANAL. CHEM., 23, 894 (1951). (2) H. V. Drushel and J. F. Miller, Ibid., 30, 1271 (1958...

No abstract

No abstract