Study On Synthesis Of Propylene Carbonate From Carbon Dioxide And 1, 2-Propylene Glycol

Dimethyl carbonate is mainly produced by transesterification rout in China. In this process, a lot of 1,2-propylene glycol(PG) is cogenerated as a byproduct. Furthermore, the feed propylene carbonate (PC) is a petrochemical and its supply is controlled by petrochemical industry inevitably. In this paper, PG is converted back to PC by the reaction of PG and carbon dioxide in order to make full use of PG and to increase the utilization of PC.Among a series of alkali metal salts and alkaline earth salts, potassium carbonate shows the highest catalytic activity in the reaction for the synthesis of PC from carbon dioxide and PG. And then the catalytic activity of potassium carbonate and supported potassium carbonate catalysts has been systemically studied. Finally, the catalytic activity of 1,1,3,3-tetramethyguanidine(TMG), supported TMG and TMG ionic liquid catalysts has been preliminarily studied.The optimal reaction conditions for the synthesis of PC from carbon dioxide and PG over potassium carbonate catalyst are as follows: n(acetonitrile):n(PG):n(CO₂) =19.2:3:4, reaction time 12 h, reaction temperature 423.15 K, weight percentage of potassium carbonate 2.0 %, and initial pressure of carbon dioxide 2.0 MPa;the highest yield of PC is 12.6 %, the conversion of PG is 23.8%, and the selectivity of PC is 52.9%. The reaction products have been qualitatively analyzed by GC-MS, and three important side-reactions, ie. Hydrolysis of acetonitrile to acetamide, the reaction of acetamide and PG to acetate of PG, and the condensation reaction of PG to dipolymer of PG have been determined.Supported potassium carbonate catalysts have been prepared by an incipient impreganation method to facilitate separation and recovering of the catalyst from the reaction system. And the catalytic properties of the supported potassium carbonate catalyst for the synthesis of PC from carbon dioxide and PG have been studied. The results show that potassium carbonate supported on activated carbon (AC) is an excellent catalyst. The optimal preparation conditions are as follows: the loading of potassium carbonate is 15 wt %, and the calcinations temperature is 423.15K. Under the following reaction conditions: n(acetonitrile):n(PG):n(CO₂)=19.2: 3:4, reaction time 12 h, reaction temperature 443.15 K, weight percentage of the supported potassium carbonate catalyst 2.0%(wt), and initial pressure of carbon dioxide 2.0 MPa, the yield of PC is 9.6%, the conversion of PG is 12.9%, and the selectivity of PC is74.4%. X-ray diffraction analysis shows that both K2O and K2CO3 are observed in the supported potassium carbonate catalyst. BET measurement result suggests that the effect of the specific surface area of the support on the catalytic properties of the supported potassium carbonate is more important.The catalytic activity of TMG and the TMG ionic liquids in the reaction for the synthesis of PC from carbon dioxide and PG has been studied. Silica-supported TMG catalysts have been prepared by an anchoring method and have been characterised by means of IR, element analysis, H-NMR, ICP and BET analysis, etc. And then their catalytic activity of the different TMG catalysts in the reaction for the synthesis of PC from carbon dioxide and PG has been studied. The results show that they possess a little catalytic activity.