Research Of Carbon Deposition On Basic Lithium Phosphate Surface

Allyl alcohol is an important petrochemical product due to its double and hydrogen bonds in the molecular structure, which can participate in oxidation reaction, reduction reaction, esterification reaction, etherification reaction and so on. At present, allyl alcohol is produced by the isomerization of gas phase propylene oxide in industry. This method has advantages as simple process, high efficiency and less pollution, but also has the disadvantage as catalyst deactivation, which brings great inconvenience to continuous production. Basic lithium phosphate catalyst has high catalytic activity and selectivity for the isomerization of gas phase propylene oxide, and this paper mainly studies the carbon deposition behavior of basic lithium phosphate by a variety of characterization methods.Deactivated Li3PO4 catalysts were analyzed by FTIR,13C CP-MAS-NMR and XPS characterization, to study the composition of carbon deposition. Results showed that the carbon deposition was very complex and mainly composed of alkanes and aromatic hydrocarbons containing oxygen element. There may also exist olefins and graphite carbon. Thermogravimetric results showed that carbon deposition on catalyst surface of different reaction time was different, and the decomposition situation of which was also different. The decomposition of carbon deposition for longer reaction time was harder compared to that for shorter reaction time. Besides, the decomposition of carbon deposition became easier with the attendance of oxygen, especially for the situation of long reaction time.In-situ DRIFTS was used to investigate carbon decomposition by recording the real-time infrared spectrogram. Results showed atmosphere and temperature both had influence on the decomposition of carbon deposition. Oxygen can lower the decomposition temperature of carbon deposition. Carbon deposition can’t be decomposed at 300℃ in pure N2 atmosphere, but could be decomposed in atmosphere containing O2. Under low temperature, temperature had little influence on carbon decomposition, while the decomposition rate changed largely when the temperature was improved to 500℃.The conversion ratio and specific surface area of fresh catalyst were 87% and 27.8 m2/g, but those of deactivated catalyst declined to 33.6% and 2.5 m2/g. After deactivated catalyst was calcined at 500℃for 8 h, catalytic activity and specific surface area of the regenerated catalyst both returned to the level of fresh catalyst, showing that calcination under high temperature is a kind of effective regeneration methods to basic lithium phosphate catalyst.Carbon formation and decomposition dynamics are discussed in this paper. According to the rate equation of carbon generation during the isomerization of propylene oxide with basic lithium phosphate, the reaction grade of carbon formation reaction is 1.482 and the reaction activation energy is 30 kJ/mol. This shows that carbon formation rate can be affected easily by the content of propylene oxide, and carbon deposition reaction happens easily. The research on carbon decomposition reaction shows that the reaction grade of carbon decomposition reaction is 2 and the reaction activation energy is 30.096 kJ/mol.