Selection and modeling of simultaneous cooled microwave system for polycondensation of L-lactic acid

Abstract In this study, a simultaneous cooled-microwave (MW) system operating in isothermal conditions under constant and continuous MW irradiation was designed using outside cooling for glycerin. To design an appropriate simultaneous cooled-MW experimental system, many simultaneous cooling methods, cooling liquids and MW experimental systems have been tried. Among these MW systems, the coil-cooled-MW system was considered most suitable experimental system. On the other hand, o-xylene was selected as the cooling liquid with the cooling efficiency (1.56°Cmin−1) for the MW system. Then, a basic mathematical relation was derived by means of a dynamic thermal model of the system to estimate required MW power (P) and to ensure isothermal conditions. Consequently, the time-dependent glycerin temperature was shown with an average model error of 2%. For further testing the validity of the model in reactive mediums, MW-assisted polycondensation reaction of LA was performed at 120 °C by applying 245 W MW power calculated from the model equation. The experiment revealed that the temperature (TR) was kept constant at desired value with an error of 5.7%. In addition, that, polymerization rate, yield of products and energy saving in the MW system were higher than conventional heating (CH) counterparts.   Abbreviations: MW: microwave; CH: conventional heating; FO: flouroptic sensor; IR: infrared sensor; LA: L-Lactic acid; PLLA: poly-(L-lactic acid); b.p.: boiling point (°C); pTsOH: p-Toluenesulfonic acid; DMP: direct melt polycondensation; ROP: ring opening polymerization