Improved Method for Kinetic Studies in Microreactors Using Flow Manipulation and Noninvasive Raman Spectrometry

Abstract

A novel method has been devised to derive kinetic information about reactions in microfluidic systems. Advantages have been demonstrated over conventional procedures for a Knoevenagel condensation reaction in terms of the time required to obtain the data (fivefold reduction) and the efficient use of reagents (tenfold reduction). The procedure is based on a step change from a low (e.g., 0.6 μL min(-1)) to a high (e.g., 14 μL min(-1)) flow rate and real-time noninvasive Raman measurements at the end of the flow line, which allows location-specific information to be obtained without the need to move the measurement probe along the microreactor channel. To validate the method, values of the effective reaction order n were obtained employing two different experimental methodologies. Using these values of n, rate constants k were calculated and compared. The values of k derived from the proposed method at 10 and 40 °C were 0.0356 ± 0.0008 mol(-0.3) dm(0.9) s(-1) (n = 1.3) and 0.24 ± 0.018 mol(-0.1) dm(0.3) s(-1) (n = 1.1), respectively, whereas the values obtained using a more laborious conventional methodology were 0.0335 ± 0.0032 mol(-0.4) dm(1.2) s(-1) (n = 1.4) at 10 °C and 0.244 ± 0.032 mol(-0.3) dm(0.9) s(-1) (n = 1.3) at 40 °C. The new approach is not limited to analysis by Raman spectrometry and can be used with different techniques that can be incorporated into the end of the flow path to provide rapid measurements.

Beyond Organometallic Flow Chemistry: The Principles Behind the Use of Continuous-Flow Reactors for Synthesis

“…Time-series data can be obtained in microflow reactors by using a controlled ramp of the flow rate and inline analysis methods. 128,129 Obtaining reaction kinetics can be a time-consuming undertaking and, recently, a lot of effort has been devoted to develop completely automated systems. 130 This allows to reduce the manual labor, to increase the efficiency of results collection and to implement Design of Experiment methods (DOE).…”

Efficient kinetic experiments in continuous flow microreactors

“…[29][30][31][32] Recent studies have shown that transient flow data could be used to quickly generate kinetic data. [33][34][35][36] Mozharov used the transient data generated from a step change in flow to scan different reaction times and fit kinetic data collected with inline Raman spectroscopy. 33 However it was concluded that the method was limited since the procedure to extract kinetics was based on estimating when the transient flow started and stopped.…”

“…[33][34][35][36] Mozharov used the transient data generated from a step change in flow to scan different reaction times and fit kinetic data collected with inline Raman spectroscopy. 33 However it was concluded that the method was limited since the procedure to extract kinetics was based on estimating when the transient flow started and stopped. Moore and Jensen improved the method by gradually increasing the flow rate, allowing for a more accurate tracking of reaction times, utilizing infrared spectroscopy.…”

Real-Time Raman Monitoring during Photocatalytic Epoxidation of Cyclohexene over V-Ti/MCM-41 Catalysts

“…For example, cyclohexane 1,2-diol, 2-cyclohexene-1-ol and 2-cyclohexene-1-one might be observed by gas chromatography analyses, although Raman result suggested that 1,2-epoxycyclohexane was the only product obtained in the reaction. It is important to mention that among many powerful techniques, which might be used to provide unique fingerprints for molecular analysis and monitoring of chemical reactions, Raman spectroscopy is particularly suitable to study in situ catalytic reaction [17][18][19][20][21][22]. Considering them together in this study, gas chromatography is used to screen the catalytic activity by determining cyclohexene conversion values while Raman technique is used to identify the reactants and selective products of epoxidation in real-time.…”