Mechanically mixed ZnO‐Al₂O₃ catalysts in the synthesis of propylene carbonate via alcoholysis of urea

Abstract

Alcoholysis of urea with 1,2-propylene glycol (PG) is a potential industrial process for the synthesis of propylene carbonate (PC) with many advantages. However, the preparation of industrial catalysts such as Zn-Al oxide by the coprecipitation method will inevitably produce a large amount of salty water and building desalting equipment will increase the investment cost. The present work attempts to use a mechanically mixed catalyst consisting of commercial ZnO and Al 2 O 3 to solve these problems. This type of catalyst was capable of catalyzing the reaction more than 5 times. The PC yield was gradually increased with each use. The best PC yield of 96.7% is comparable to the coprecipitated Zn-Al oxide catalysts and was achieved during the third use. In the reaction, ZnO and Al 2 O 3 were dissolved into the reactants to form complexes, which homogenously catalyzed the reaction. It was found that the dissolved Zn and Al complex significantly influenced the PC yield and re-precipitated in the late stage of the reaction. Furthermore, the partial dissolution of Al assisted the dissolution and precipitation of Zn, which improved the PC yield. After several dissolution-precipitation cycles, ZnO-Al 2 O 3 was homogeneously mixed at the atomic scale. Interestingly, there was an adequate linear relationship between the amount of dissolved Zn and Al in each reaction, the linear correlation coefficient improved after each reaction, and the slope of the line (the ratio of dissolved Zn/Al) was 7.26 in the third use. K E Y W O R D S mechanically mixed catalyst, propylene carbonate, urea alcoholysis, ZnO-Al 2 O 3 catalyst

Efficient Propylene Carbonate Synthesis from Urea and Propylene Glycol over Calcium Oxide–Magnesium Oxide Catalysts

“…The stability of CaO–MgO was determined by consecutive reuse in the following manner: After completion of the first reaction of PC synthesis, the catalyst was recovered by centrifuge, washed with ethanol, dried in an oven at 60 °C for 6 h, and then reused. The catalyst was again reused by the same procedure two more times and then regenerated by calcining it at 700 °C for 5 h after drying according to the previously described procedure [ 40 , 41 ]. This regenerated catalyst was used for PC synthesis, and the recovered catalyst after completion of the reaction was reused again two more times, the results of which are shown in Figure 6 .…”

Synthesis of Ethylene Carbonate by Urea Transesterification Using Zeolitic Imidazolate Framework Derived Fe-Doped ZnO Catalysts

“…Li et al conducted the same reaction over various catalysts, including CaO, La 2 O 3 , ZrO 2 , Al 2 O 3 , MgO, and ZnO, and found that ZnO exhibited the highest activity and selectivity . Jia and Zhao reported Al-containing and Fe-containing ZnO catalysts for urea transesterification. , Fakhrnasova investigated the mechanisms of acid–base catalyzed reactions by performing in situ dip-in attenuated total reflection infrared spectroscopic measurements . Although various catalysts have been considered for this purpose, their conversion efficiency and selectivity should be further improved through the more efficient utilization of acidic and basic reactive sites based on an in-depth understanding of the catalytic reaction mechanism.…”

Preparation of propylene carbonate by alcoholysis of urea from the perspective of homogeneous reaction: Influence of dissolution and precipitation of metal oxide catalysts

“…Li et al [ 5 ] investigated the effect of acid–base properties of metal oxides for this reaction and found that ZnO with appropriate acidity and basicity has the best activity. Jia et al [ 15 ] used a mechanically mixed catalyst consisting of industrial ZnO and Al 2 O 3 and found that both of the two oxides dissolved when they participated in the reaction.…”