Micro-Channel Distillation

Capability Title Micro-channel Distillation
Laboratory Pacific Northwest National Laboratory (PNNL)
Capability experts Ward TeGrotenhuis and Danny Bottenus
Description

PNNL has unique capabilities in micro-channel-based distillation, with demonstrated heights of a theoretical plate (HETP) of < 3.3 millimeters.  This is nearly two orders of magnitude less than commercial structured packings that report HETP values of 300 to 600 millimeters.  The technology platform has been applied to close-boiling-point component separations, at both elevated temperatures and cryogenic temperatures, including isotope enrichment.  The technology is also amenable to reactive distillation approaches.

The microchannel distillation concept involves thin, porous wicking structures that transport liquid through the device in one direction while gas flows countercurrently in adjacent vapor channel.  Capillary forces prevent vapor intrusion into the wicks. Vapor exiting the device is condensed and refluxed back to the microchannel device, thereby creating a recirculating flow necessary for total reflux distillation.

The alternating configuration of vapor channel and liquid wicks allows mass transfer to occur in both directions along the flow length which enhances the characteristic mass transfer time by a factor of 4.   The current microchannel distillation device is 10 inches long, 1.6 inches wide, and is comprised of 20 thin (0.004 inches) liquid wicks stacked alternately between 21 thicker (0.02 inches) vapor channels.

Limitations  Feed stocks must be amenable to processing and, in particular, wetting of the stainless steel surface of the micro-wick structures by the liquid in order to contain the liquid in the micro-channels.  Other limitations such as maximum siphon and subsequent liquid flow rate will depend on the feed stock wettability and surface tension.
Unique aspects Micro-channel distillation offers the potential for the smallest tray heights of any current distillation approach.  This makes it an attractive option for compact/modular processing and distributed manufacturing.
Availability  The technology is available for consideration on new/ future projects
Citations/references
  1. TeGrotenhuis, W.E. and M.R. Powell.  2012. “Packing Structure Capable of Sub-Centimeter HETP for High Purity Distillation of Low Relative Volatility Compounds.”  American Institute of Chemical Engineers Conference Proceedings.
  2. Bottenus, D., et al., Process Intensification of Distillation using a Microwick Technology to Demonstrate Separation of Propane and Propylene. AIChE Journal, 2018. Submitted.
  3. Bottenus, D., et al., Isotope Enrichment of 13C from Methane in Microchannel Distillation Devices at Cryogenic Temperatures. AIChE Journal, 2018. Submitted.