(664f) Singlet-Oxygen Generation Via Microscale Trickle-Bed Reactor Array: Experiments and Modeling

The theoretical and experimental investigation of a miniaturized, low-pressure trickle-bed reactor for generating singlet-oxygen is presented. The reaction of chlorine gas with concentrated alkaline hydrogen peroxide solution under low-vacuum (~ 20 – 200 torr) is a challenging and unique chemistry, which produces significant quantities of singlet-oxygen, O₂(¹Δ), for use as either a reagent for organic synthesis or as an efficient energy-transfer species for chemical laser systems. The advantages of microreactors, specifically (i) enhanced mass transfer rates, (ii) enhanced heat transfer rates resulting in isothermal reactor operation, and (iii) inherent safety for hazardous chemistries, all serve to address the immediate challenges to existing singlet-oxygen generator design.

A series of parallel microscale post-bed reactors are fabricated in silicon via photolithography and deep reactive-ion etching (DRIE) methods analogous to those employed in manufacture of microelectromechanical systems (MEMS). Each reactor is 350 micron depth, 650 micron width and 6000 micron in length, and contains a hexagonally-packed array of 70 micron-diameter posts, uniformly spaced 30 micron apart to approximate a two-dimensional packed-bed (ε=0.40). Individual post-beds are connected to a capillary separator for immediate phase separation within the microchemical device. Cooling channels are incorporated into the resulting chip design to remove heat of reaction and maintain favorable reaction temperature (~ 263 – 273K). Mass spectrographic analysis of the effluent gas is employed to measure chlorine conversion, while spectroscopic analysis enables measurement of singlet-oxygen yield via observed diol emission at 1280 nm. Incorporation of a glass capping layer during microdevice fabrication additionally enables visual identification of gas-liquid flow patterns within the structured post-bed, as well as visual confirmation of capillary separator performance.

Results obtained experimentally for both reacting- and non-reacting flows within the microreactor are compared with existing correlations and findings for macroscale trickle-bed reactors. Reaction data obtained from operation of the microdevice are compared with previously developed isothermal model of the microchemical system¹. Results demonstrate the need for further understanding of gas-liquid and gas-liquid-solid microreactors.

¹ B.A. Wilhite et al., “Design of a MEMS-Based microChemical Oxygen-Iodine Laser (μCOIL) System,” IEEE J. Quant. Elect., 40(8), 1041-1055.