Thermodynamic Study and Experimental Verification on the Product Distribution of the Synthesis of Dipropylene Glycol from Propylene Oxide and Propylene Glycol

Propylene oxide(PO) is an important petrochemical materials used to produce downstream products such as propylene glycol(PG), polyether polyols, and dipropylene glycol(DPG). Among these, DPG is commonly used as a solvent for fragrances, cosmetics, food additives, and detergents, and can also be served as a moisturizer in cosmetics, showing broad application prospects. The distribution of DPG isomers in the products synthesized from PO and PG has a significant impact on the quality of the products. Therefore, conducting thermodynamic calculation on the reaction of PO and PG to synthesize DPG can provide a theoretical basis for practical operations and product distribution regulation. So, in this paper, the thermodynamic parameters of PO, 1,2-PG, H2O, tripropylene glycol (TPG) and three isomers of DPG under different reaction conditions is calculated. Additionally, the , and ln K for four potential reactions at various reaction temperatures and pressures are calculated. By designing isodesmic reactions and combining the results of thermodynamic calculations, the and for the isomers of DPG are obtained, and the relative error is less than 7%. The results show that in the process of preparing DPG by PO and PG, when PO: PG = 1, the reaction temperature ranges from 298.15 K to 413.15 K, and the pressure ranges from 101.325 kPa to 506.325 kPa, the reactions of and are thermodynamically spontaneous. While the reactions of and are thermodynamically unspontaneous. The optimal reaction temperature and pressure are 413.15 K and 101.325 kPa. The thermodynamic stability of the three isomers is DPG1>DPG2>DPG3 under standard conditions. The accuracy of the computational results is verified through experimental design, and based on this, the factors affecting product distribution are analyzed.