Synthesis Of Propylene Carbonate From Urea Alcoholysis Catalyzed By ABO₃-type Catalysts

Propylene Carbonate(PC) as an excellent polar organic solvent with high boiling point has been widely used in the fields of organic synthesis, gas separation and electrochemical techniques. At present, PC is mostly used to produce dimethyl carbonate(DMC) through transesterification with methanol.The methods for the synthesis of PC include phosgene processes, transesterification of alkyl carbonate with propylene glycol(PG), reaction of carbon dioxide with o-chloropropanol, cycloaddition of propylene oxide with CO2, and urea alcoholysis. Among them, the urea alcoholysis, in which PC is prepared from urea and 1,2-propylene glycol, shows many advantages: cheap and easily available raw material, mild reaction conditions, and conforming to the development of green chemical industry requirements. Many catalysts have been reported, but their performances are difficult for industrialization. Therefore, this process mainly focuses on the investigation of novel and efficient catalysts.In this thesis, the ABO3-type catalysts were prepared to catalyze urea alcoholysis to PC. Combined with the catalytic characterizations of XRD, EDS, BET, SEM, CO2-TPD and H2-TPR, the reasons, that preparation conditions affected the catalytic activities and the stable of catalysts, were investigated. Effect of the technigical conditions including reaction temperature, reaction time, molar ratio of raw materials and amount of the catalyst on the alcoholysis was discussed in detail in a batch reactor.1. Comparison with the activities of ABO3-type catalysts prepared with different metal ion including Mg、Ca、Sr、Ba、Zn、Pb and Ni. Mg Ti O3 with the strongest alkali intensity and the most quantity on its surfaces showed the highest activity. The yield and the selectivity of PC were up to 95.7% and 99.7%, respectively.2. The quantity and intensity of strong basic centers could be changed by the synergistic effect between Mg Ti O3 and Mg O aggregated on the surface of Mg Ti O3.When Mg Ti O3 was prepared under the conditions of the Mg/Ti molar ratio of 1.0, the calcined temperature of 700°C and the calcined time of 3h, the synergistic effect between Mg Ti O3 and Mg O was the strongest. With the rise of the reuse times, the synergy between Mg O and Mg Ti O3 was weakened due to the loss of Mg O from the surface of Mg Ti O3, which leaded to the reduction of the catalytic activity.3 With the metal salt solution as raw material, polymerization of acrylamide to provide a polymer network framework, and crosslinking effect of N, N ’-methylene acrylamide to extended three-dimensional network space, the solution containing the required cations was evenly dispersed in three-dimensional space, providing a suitable environment for the formation of crystal nucleus and the growth of the particle during the calcination. Under the optimal conditions of p H value of 5, citric acid as the complex agent, acrylamide as monomer, N, N’- methylene acrylamide as crosslinking agent, calcined temperature of 800 ℃ and calcined time of 8h, a Co-doped perovskite, La0.5Pb0.5Mn0.9Co0.1O3, was prepared with a pure phase. When it was used as the catalyst in the urea alcoholysis, the PC yield was 84.5% with the selectivity of 84.2%.4. With the rise of the reuse times, the oxygen content and the valence of metal ions on the surface of La0.5Pb0.5Mn0.9Co0.1O3 were reduced due to the reducibility of 1,2-propylene glycol, leading to the increase of the moderate alkaline active center on the surface. The catalytic activity was promoted and remained stable because the middle-strong alkaline active center was of benefit to the formation of PC from the Urea alcoholysis. When the catalyst was recycled for eight times, the yield and the selectivity of PC can still maintain about 90%.