Temperature, 2-propanol decomposition

Temperature-Programmed Decomposition of 2-Propanol on the Zinc-Polar, Nonpolar, and Oxygen-Polar Surfaces of Zinc Oxide... 

The dehydrogenation reaction produces acetone and hydrogen, and is dominant over basic oxides ( ) The dehydration reaction produces propene and water, and is dominant over acidic oxides. It would be interesting to see if the competition between these two pathways depend on the exposed crystal planes of ZnO. We report here the results of such an investigation. 2-Propanol was decomposed on ZnO single crystal surfaces by the temperature programmed decomposition technique. To assist the interpretation of data, the temperature programmed desorption of propene and acetone were also studied. 

The decomposition of 2-propanol showed both similarities and differences among the surfaces. The most notable similarity is the fact that propene and acetone were produced at about the same ratio on all surfaces. Dehydrogenation to form acetone was the dominant reaction, as has been observed on ZnO powders ( ). The desorption temperatures of the reaction products, acetone, propene, and hydrogen were always higher than the temperature of desorption of the adsorbed acetone, propene, and hydrogen (hydrogen does not adsorb on ZnO under our conditions). Thus the evolution of acetone and propene are reaction limited in 2-propanol decomposition. 

From the temperature at which the decomposition products evolved, it would seem that the 0-polar surface should be the most active in 2-propanol decomposition. However, a close examination of the temperatures in Table I shows that on the 0-polar surface, the desorption temperature of the minor product water was actually rather high - higher than any of the products from the nonpolar surface. Thus in a steady state reaction at temperatures below about 100 C, the 0-polar surface could be easily poisoned by adsorbed water, leaving only the nonpolar surface active. 

Recent developments for reactive C02 sorbents include sterically hindered amines such as 2-amino-2-methyl-l-propanol (AMP) and 1,8-p-methanediamine (MDA) and 2-piperidine ethanol (PE), which are claimed to have good reversible C02 capacity (Veawab et al., 1998) and low-temperature molten salts called ionic liquids (Bates et al., 2002). Ionic liquids are attractive due to their negligible vapor pressure up to their decomposition at... 

Let us compare the ratio of radicals in oxidized 2-propanol and cyclohexanol at different temperatures when oxidation occurs with long chains and chain initiation and termination do not influence the stationary state concentration of radicals. The values of the rate constants of the reactions of peroxyl radicals (kp) with alcohol and decomposition of the alkylhydroxy-peroxyl radical (k ) are taken from Table 7.4 and Table 7.5. 

Propane was selected as solvent for the isobutene for experiments down to -145° the aluminium chloride was dissolved in ethyl chloride, for the work at lower temperatures a mixture of ethyl chloride and vinyl chloride was used. Although these catalyst solutions were made up at -78° they were yellow, and as stated above, they probably contained some hydrogen chloride and other catalytically active decomposition products. The polymerisations were carried out by running the cooled catalyst solution into the monomer solution. Polymer was formed, and came out of solution, almost immediately, and the reaction was very fast even at the lowest temperature (-185°) and lowest monomer concentration (0.6 mole/1). After the reaction was over, propanol at the reaction temperature was added to the reaction mixture to deactivate the catalyst. 

The ternary hydride was purified by reprecipitation from aqueous methanolic sodium hydroxide. Na2ReH9 was soluble in water and methanol, slightly soluble in ethanol, and insoluble in 2-propanol, acetonitrile, ether, and THF. Decomposition started at approximately 245°C when heated in a vacuum, with the evolution of hydrogen and sodium as the temperature increased. Na2ReH9 was a precursor for the preparation of the tetraethylammonium salt, the potassium salt, and the mixed potassium sodium salt of nonahydridorhenate(VII). 

To improve process economics, further work is needed to improve catalyst lifetimes. A more stable system employed a noble metal-loaded potassium L-zeolite catalyst for the condensation of ethanol with methanol to produce a 1-propanol and 2-methyl-l-propanol (US patent no. 5,300,695) (18). However, yields were small compared with the large amounts of CO and C02 produced from the methanol. More recently, Exxon patented a noble metal-loaded alkali metal-doped mixed metal (Zr, Mn, Zn) oxide (US patent nos. 6,034,141 and 5,811,602) (19,20). The catalyst was used in a syngas atmosphere. As with other catalysts, the higher temperatures resulted in decomposition of methanol. Changes in catalyst composition were noted at higher temperatures, but the stability of the catalyst was not discussed. Recently, compositions including Ni, Rh, Ru, and Cu were investigated (21,22). 

A solution of the above compound in a mixture of ethanol (20 ml) and acetic acid (20 ml) is shaken with a 30% palladium-on-charcoal catalyst (0.1 g) in an atmosphere of hydrogen at laboratory temperature and pressure until 250 ml of hydrogen is absorbed. The mixture is filtered, the filtrate is evaporated to dryness under reduced pressure and to the residue is added a hot solution of fumaric acid (1.25 g) in ethanol (15 ml). The mixture is kept at 5°C for 12 hours and is then filtered, and the solid residue is washed with hot ethanol and then dried. There is thus obtained l-p-hydroxyphenoxy-3-beta-(morpholinocarbonamido)ethyl-amino-2-propanol hydrogen fumarate, m.p. 168-169°C (with decomposition). 

Thermal decomposition of RuCl, tiHjO at different temperatures in a stream of oxygen in the presence of Spherosil (silica beads 100 pm in diameter). Silica beads, 100 pm in diameter, were calcined at 900°C. They were then dipped in 2 mass% RuCl, solution in 2-propanol, and calcined in an oxygen stream at 300-700°C. 

The second difference among the surfaces is the fact that, except H2O, the other three decomposition products, H2, acetone, and propene, were evolved at the same temperature on the two polar surfaces, but H2 was evolved at a lower temperature on the nonpolar surface. It is interesting to compare these results with the observations by Koga et al. who studied the decomposition of 2-propanol at 100 C on ZnO powder (13) They found that if the gas phase 2-propanol was suddenly removed from the gas phase, the evolution of hydrogen continued, but the evolution of acetone stopped. The evolution of acetone resumed after readmission of 2-propanol. This behavior can be explained by the fact that the major exposed face of their ZnO powder sample was the nonpolar plane. It is only on this surface that H2 can be evolved without concurrent evolution of acetone in the absence of gaseous propanol. 

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