Research On Increasing Quality And Yield Of 1,2-propylene Glycol Via Transesterification

1,2-propylene glycol is one of the most important raw materials in chemical industry. In this paper, the depurated processes of 1,2- propylene glycol obtained in DMC production via transesterification are studied. CH3ONa is used as the catalyst for the synthesis of DMC. The evaporation method at high temperature is used to separate 1,2-propylene glycol from the catalyst of CH3ONa. However, the color of 1,2- propylene glycol is easy to change and its irritant smell is large. The quality of propylene glycol is poor and the yield is low, too. In order to improve the economic benefits, electrodialysis desalination, membrane desalination, neutralization desalination and carbonization desalination are studied to modify the existing process. Result shows that carbonization desalination is the best process on the technology improvement of DMC production.The optimum conditions of the carbonization reaction are obtained as follows: the temperature is 120℃, the water content in reaction sysytem is 5%, the CO2 content is 0.8% and the carbonation time is 40min. After the carbonization desalination, the purity of 1,2-propylene glycol is increased from 99.70% to 99.9%, and the yield is increased to 93% from 88%. So the economic benefit of 16540000.0RMB is obtained every year.The optimum reaction conditions for producing 1,2-propylene glycol meeting the standard of pharmaceutical grade are determined. They ar as follows: the temperature is 70℃, the time is 1h, the content of additive is 10μg/L, and the water content is 20%. The purified 1,2 - propylene glycol can come up to the standard of pharmaceutical grade. The purity of 1,2 - propylene glycol is greater than 99.95%, and the color (APHA) is smaller than 10. The water content in the product is smaller than 0.10%.