283394 High Pressure Heterogeneous Catalysis with Continuous Flow Microreactors

Tuesday, October 30, 2012: 8:30 AM
316 (Convention Center )
Baris Ünal and Klavs F. Jensen, Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA

 

 

Microreactors enable precise control of reaction parameters (e.g. temperature, pressure).

The improved heat and mass transfer aspects provide kinetics to be probed at isothermal conditions in the absence of mass transfer effects. Due to the small footprint of these devices it is possible to access to high temperatures and high pressure operations, especially for hydrogenation reactions.

We developed a high pressure and high temperature microreactor platform to investigate heterogeneous catalysis at industrially relevant conditions. The system is operable up to 100 bar from 25 ºC to 300 ºC. A packed-bed microreactor which can stand for high pressures has been microfabricated from silicon and Pyrex as shown in figure 1a. The system has inline analysis tools as well as a sampling unit for off line liquid analysis with gas or liquid chromatography. A microfluidic device was fabricated, which enabled to sample reactor effluents at elevated pressures of up to 100 bar. With this unit it became possible to couple the high pressure microreactor with a quadrupole mass spectrometer. The system also involves a microfluidic cell with attenuated total reflection section for inline Fourier transform infrared spectroscopy (FTIR) analysis at pressures of up to 100 bar. A pulse chemisorption microfluidic device has been developed to characterize surface area of a catalyst in a few mg scales. Carbon monoxide (CO) chemisorption curves for the fresh (red) and spent (blue) Pt/silica catalysts are given in figure 1b. The areal difference between the red and the blue curves represents the active area loss of the catalyst.

Using the microreactor platform with the inline characterization tools, several catalytic systems have been explored. Conversion of syngas to methanol has been studied with homemade catalyst. Effect of several process parameters such as temperature, pressure, residence time and feed composition on reaction rates has been determined. Apparent activation energy has been found. Hydrogenation reactions of bio-oil model compounds (furan derivatives) were also studied. For this system, mass transfer effects were delineated and operation conditions under which intrinsic kinetics can be measured were identified. Apparent activation energies have been found as well.

 

Figure 1. A) Silicon-Pyrex high pressure microreactor for heterogeneous catalysis. B) CO pulsed chemisorption curves for fresh and spent 5wt% Pt/silica catalysts. The catalyst amount was 2 mg.

 


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