What is it?
Many chemical processes involve the separation of liquid mixtures into their components. For example, crude oil is a mix of hydrocarbons (wax, oil, kerosene, gasoline) that are separated at a refinery. In the ethanol industry, fermentation produces a mix of water and ethanol called ‘broth’. Broth is 90 – 95% water, but auto fuel requires >99% ethanol and <1% water. Distillation columns separate most of the ethanol from the broth. But other (hybrid) techniques must be used to remove the rest of the water.
How does it work?
In ethanol distillation columns, heat is applied to the mixture. Stacked plates or other packing materials in the column increase surface area and allow rising vapor, stripped or evaporated from the mix, to interact with falling liquid. Water remains at the bottom, while ethanol concentrates toward the top, where it is removed and condensed.
After most of the water has been removed, a hybrid technique called ‘Pressure Swing Adsorption’ (PSA) is commonly used to dehydrate ethanol further. However, “Membrane assisted” distillation (MAD) promises to do the job even more efficiently. Membranes made of polymers or inorganic zeolite materials selectively pass water but retain ethanol.
What are the most appropriate applications?
Experts predict that MAD could be incorporated into new and existing plant designs.
What are the savings?
20% – 30% energy savings were reported in an actual installation in Japan in 2008. Some researchers expect savings up to 80% to 90% eventually, once the technology matures.
What are the non-energy benefits?
Recovery of ethanol from low concentration waste streams would increase productivity and improve the feasibility of small-scale facilities.
What is the cost?
MAD has not been widely commercialized, so cost is hard to predict. Polymer membranes are cheap but fragile. Other membrane materials are more expensive. The cost of adsorption media currently used in PSA would be avoided.
What is the status/availability of the technology?
Research and development activity is strong (judging from the number of relevant papers); however, the technology is not yet widely available
What kinds of incentives/programs are available?
When projects of this type begin to appear, they would be served by utility custom incentive programs.
