PNNL

Abstract

Microfluidics have many potential applications including characterization of chemical processes at reduced scale. The use of in situ characterization of process streams from lab-scale and microscale experiments on the same chemical system can provide comprehensive understanding and in-depth analysis of any similarities or differences between process conditions at the different scales. A well characterized PUREX extraction of ?Nd(NO?_3 )_3 from an aqueous phase of varying ?NO?_(3 (aq))^- concentration with tributyl phosphate (TBP) in dodecane was the focus of this micro-scale study and was the focus of an earlier lab-scale study. In the prior lab-scale study, it was demonstrated on lab-scale counter current extraction equipment that the extraction follows a linear relationship between the natural log of the distribution coefficient, D, for Nd between the aqueous and organic phases and the natural log of the ?NO?_(3 (aq))^- concentration. Here we verify that this same extraction process can be followed on the microscale using spectroscopic methods adapted for microfluidic measurement. The PUREX extraction was carried to completion in advance of the microfluidic flow experiment by pre-contacting aqueous Nd solutions with the organic phase. The contacted phases were separated, and alternating aliquots of post-contact aqueous and organic phases were passed back-to-back through the microfluidic device (MFD). These were analyzed during the sequential flow using simultaneous application of micro-Raman and micro-UV-vis spectroscopies. The ?NO?_(3 (aq))^- concentration was chemometrically measured during the flow experiment using Raman spectra and the distribution coefficient for Nd, DNd, was chemometrically measured using UV-vis spectra recorded for both the aqueous and organic phases. Extraction distributions measured on the micro-scale after recognizing differently competing aqueous phase and organic phase flow behaviors through the MFD were consistent and compared favorably with those determined on the lab-scale in the earlier study. Both micro-Raman and micro-UV-vis can be used to determine fundamental parameters with significantly reduced sample size as compared to traditional lab-scale approaches. This leads naturally to time, cost, and waste reductions.