Sensitivity of methanol-to-olefin reaction to axial gas dispersion: determination in a vibrated-bed microreactor

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Virginia Tech


A microreactor has been developed to study the sensitivity of Methanol-To-Olefin (MTO) reaction to axial gas dispersion. It comprises a rectangular horizontal duct, 12.7 mm in height, 25.4 mm in width, variable in length, charged with a 1-mm-deep layer of HZSM-5 catalyst. The microreactor is constructed of aluminum alloy and heated with cartridge heaters. A glass reference duct with the same catalyst loading is mounted directly above the microreactor to provide visual check of the coherent-expanded vibration state achieved by vibrating the setup at 24 hertz and 4.3-mm vertical displacement. In this. state, catalyst powder expands to full duct height during a portion of each vibration cycle, with intense vertical mixing of powder and little horizontal.

Axial gas dispersion coefficient varies linearly with superficial gas velocity, and axial Peclet Number (Peax) can be studied over a wide range of values simply by varying duct length while holding weight hourly space velocity constant.

Conducting the MTO reaction in microreactors of 7.62-, 15.24-, and 22.86-cm length (Peax = ca. 2, 9, and 19 respectively) revealed the reaction to be sensitive to axial gas mixing. Trend in light olefin yield versus Peax agrees with earlier turbulent fluid-bed data. Loss in olefins with increase in axial gas dispersion (decrease in Peax) suggests that a circulating fluid bed may be the preferred reactor for this reaction.

Researchers can use the microreactor to determine, quickly and inexpensively, how reaction outcomes vary with axial gas dispersion. The microreactor could help R&D managers to avoid expense of a fluid bed R&D effort where an economically significant outcome of a reaction is acutely sensitive to axial gas dispersion, and where a fixed bed is an acceptable alternative.