MISPA

microreactor for spectroscopic applications

MISPA system is intended for contemporary or new users of various spectroscopic measuring instruments, chemical laboratories, universities and research institutes focused on material or catalytic research [1][2][3], who need a hermetically sealed environment for in situ observations with programmable reaction conditions that can be correlated with time dependent data capture, a device compatible with synchrotron measurements or who need to reduce the size of their currently used setups. MISPA is a laboratory device that has narrower geometry, supplementary measurement and control systems, preciselly controlled input conditions and is compatible with various spectroscopic systems, unlike other comparable vacuum and pipe furnaces or autoclaves.

main capabilities and utilization

Most of todays analytical methods utilize static observation approaches, meaning a measurement is carried out on an unchanging sample or a system. For a more precise observation it can be beneficial to carry out the measurent in situ (in its original place of creation) or to prevent any unwanted changes in your sample due to possible material degradation, or you just want reduce to size of your current setup.

The Microreactor for spectroscopic applications (MISPA) is a device that can fulfil these requirements. The device is designed in a way so that most "dry method" reactions can carried out in the interior of MISPA. The device combines the best from existing vacuum and tube furnaces, autoclaves and reaction cells, all of that in a compact narrow manner and with preciselly controlled interior conditions.

MISPA can find its utilization in many branches of material research, study of reaction kinetics, sample treatment processes such as forced oxidation [4], and catalytic research in petroleum industry. Our device can be anchored and applied in variety of used spectroscopic methods (e.g. Mössbauer spectroscopy [5]), be it in a laboratory environment or an industrial facility. The geometry of the device's integration can be suited to the customers, be it a simple laboratory environment (E.g. small fume cupborads), open industrial halls, synchrotron and other particle physics systems.

The microreactor for spectroscopic applications has a robust and sturdy design with high modularity

Views of the MISPA from different angles.

Main advantages

- Shorter device length compared to similar products (higher signal yield)
- Robust design resistant to aggressive external conditions
- Precisely controlled reaction conditions – programmable temperature, atmosphere type, and gas flow
- Simple handling of components during sample exchange
- Usable as a sample preparer/chemical reactor
- Modularity enabling a wider variety of applications for different analytical methods
- Control application enables long-term reaction management
- Compatible with in situ Mössbauer spectroscopy
- Device anchoring can be tailored to the customer’s needs

Technical Parameters

Narrow size of 117 mm in the transmission axis
Pressurable interior of up to 15 bar
Regulated mass flow in the range of 5–250 ml/min
Vacuum compatible sealing (UHV)
Adjustable sample temperature in the range of RT - 500°C
Variable exterior cooling of down to 5°C
Low window attenuation for gamma (>2 cm-1)
Compatible with a wide variety of reaction gases (hydrogen, methane, carbon monoxide, and more)

Technical description

Transmission geometry with customizable flanges

MISPA is designed for a transmission geometry and for that purpose, the dismountable windows are assembled in a compact way that assures easy dismounting and sample manipulation. The default aperture material enables the employment of gamma spectroscopy (thanks to low gamma radiation absorbance) or can be swapped for different materials that are compatible with VIS applications. The modularity of the system is assured thanks to the use of standardized flanges (KF and CF).

Example of a dismountable window in MISPA designed for gamma spectroscopic applications that require low attenuation for high energy photons (E.g. mössbauer spectroscopy, synchotron experiments).

Inside view of the heating control and measurement structure in the sample area together with the thre active coolers. Two thermocouples are used to measure sample and heating coil temperature.

Temperature control and measurement

Two thermocouples constantly measure temperature of the heating coil and sample area. That in conjunction with a PID control creates a programmable temperature system for custom heating slopes and enables time-dependent energy input estimation for the study of energy kinetics of reactions [6].

The heated sample area is thermally isolated from the main body of the microreactor and rest of the system. However, to reduce any potential unnecessary temperature gradients on the main body and to ensure safety when handling with the device during operation, the system is equipped with three active coolers that regulate the outer temperature and can rapidly cool the system in case of overheat.

Adjustable gas flow and pressure

Programmatically controlled feedback control loop (C + K) ensures a precise volume flow rate of a reaction gas that can be pressurized up to 15 bar. A condensation container for liquid product capture was added to the distribution and can be easily disconnected from the system. To eliminate any cooling of the sample due to gas flow, a pre- and post-heater are present in the system to heat the gas to a desired temperature.

To ensure maximum safety, the gas system contains a discharge (I) and overpressure (J) valve that in case of an unexpected behavior can purge and stop the system in a matter of seconds.

Schematic overview of the gas management system connected to the MISPA (F). Two electrically driven Bronkhorst™ valves control the gas pressure and flow in the sample area. The system also contains three coupled safety valves (C, I, J).

Example employment - Mössbauer spectroscopy

An example how the MISPA can be employed in mössbauer spectroscopy. The anchoring is tailored to the specific needs of the spectroscopic method.

Mössbauer spectroscopy is a powerful technique to study any iron containing material in solid form to identify local chemical and phase composition [7][8]. In combination with the MISPA system and a modified data acquisition, an in situ observation was carried out [9].

MISPA has the right parameters to be compatible with a mössbauer spectrometer. Low window attenuation and narrow size of the microreactor allows for efficient data capture and observation of time-evolving spectra.

A simple thermal decomposition of iron oxalate dihydrate was studied in the temperature range of 25–400 °C under the dynamic nitrogen atmosphere of 1.5 bar. The temperature ramp was set 2 °C/min. The first spectrum (a) shows the studied material before the heat treatment. The next three consecutive (b–d) spectra display the transformation of the material to different material phases. The last spectrum (e) shows the post-heating evolvement of the material during the cooling.

Different mössbauer spectra captured at relevant izotherms during an in situ observation in the MISPA system. [9]

References

[1] B. A. Rizkin, F. G. Popovic, R. L. Hartman, "Spectroscopic microreactors for heterogeneous catalysis", Journal of Vacuum Science & Technology, A 37, 050801, Aug. 2019, doi: 10.1116/1.5108901.

[2] Motjope, T. R., Dlamini, H. T., Hearne, G. R., Coville, N. J., "Application of in situ Mössbauer spectroscopy to investigate the effect of precipitating agents on precipitated iron Fischer-Tropsch catalysts", Catalyst Today, vol. 71, no. 1, pp. 335-341, Jan. 2002, doi: 10.1016/S0920-5861(01)00460-6.

[3] Jian Xu, C. H. Bartholomew, "Temperature-Programmed Hydrogenation (TPH) and in Situ Mössbauer Spectroscopy Studies of Carbonaceous Species on Silica-Supported Iron Fischer-Tropsch Catalysts", J. Phys. Chem. B 2005, 109, 6, 2392–2403, Sept. 2004, doi: 10.1021/jp048808j.

[4] S. Hejda, M. Drhova, J. Kristal, D. Buzek, P. Krystynik, P. Kluson, "Microreactor as efficient tool for light induced oxidation reactions", Chemical Engineering Journal, vol. 255, no. 1, pp. 178-184, Nov. 2014, doi: 10.1016/j.cej.2014.06.052.

[5] J.W. Niemantsverdriet, W.N. Delgass, "In situ Mössbauer spectroscopy in catalysis", Topics in Catalysis, vol. 8, pp. 133–140, May 1999, doi: 10.1023/A:1019144607553.

[6] V. Burkle-Vitzthum, F. Moulis, Jie Zhang, Jean-Marc Commenge, E. Schaer, Paul-Marie Marquaire, "Annular flow microreactor: An efficient tool for kinetic studies in gas phase at very short residence times", Chemical Engineering Research and Design, vol. 94, no. 1, pp. 611-623, Feb. 2015, doi: 10.1016/j.cherd.2014.10.003.

[7] G. Klingelhöfer et al., “Athena MIMOS II Mössbauer spectrometer investigation,” J. Geophys. Res. Planets, vol. 108, no. E12, pp. 8067–8084, Dec. 2003, doi: 10.1029/2003JE002138.

[8] G. Longworth, “The use of Mössbauer spectroscopy in non-destructive testing,” NDT Int., vol. 10, no. 5, pp. 241–246, Oct. 1977, doi: 10.1016/0308-9126(77)90119-5.

[9] M. Jirus, J. Kopp, L. Kouril, J. Pechousek, "Mössbauer Microreactor for In Situ Observations", conference ICAME 2019, doi: 10.13140/RG.2.2.15203.91681.

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