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Patent of the Month - Microfluidic Desalination

Patent of the Month – Microfluidic Desalination

| On 26, Sep 2018

Darrell Mann

Patent of the month this month takes us to a trio of inventors at the University of Texas. US9,932,251 was granted on April 3. The wonderfully succinct background description describes the motivation for the invention as follows:

The global demand for freshwater is growing rapidly. Many conventional sources of freshwater, including lakes, rivers, and aquifers, are rapidly becoming depleted. As a consequence, freshwater is becoming a limited resource in many regions. In fact, the United Nations estimates two-thirds of the world’s population could be living in water stressed regions by 2025.

Currently, approximately 97% of the world’s water supply is present as seawater. Desalination–the process by which salinated water (e.g., seawater) is converted to fresh water–offers the potential to provide dependable supplies of freshwater suitable for human consumption or irrigation. Unfortunately, existing desalination processes, including distillation and reverse osmosis, require both large amounts of energy and specialized, expensive infrastructure. As a consequence, desalination is currently expensive compared to most conventional sources of water, and often prohibitively expensive in developing regions of the world. Therefore, only a small fraction of total human water use is currently satisfied by desalination. More energy efficient methods for water desalination offer the potential to address the increasing demands for freshwater, particularly in water stressed regions.

The contradiction here is best seen through the lens of the conventional ‘mechanical’ (i.e. physical barrier) means of achieving the salt-separation function. Here’s what that contradiction looks like when mapped on to the Contradiction Matrix:

And here’s the solution found in the new patent in Claim 1…

A microfluidic device comprising (a) a desalination unit comprising an inlet channel fluidly connected to a dilute outlet channel and a concentrated outlet channel, wherein the dilute outlet channel and the concentrated outlet channel diverge from the inlet channel at an intersection; and (b) an electrode in electrochemical contact with the desalination unit in proximity to the intersection; wherein the electrode is configured to generate an electric field gradient in proximity to the intersection.

It’s another good example of the significance of Principle 28, Mechanics Substitution and the replacement of a mechanical solution (i.e. the membrane) with a ‘field’. Using an ‘electrical field gradient’ is, of course, not the only field-based attempt at the desalination problem (see ‘capacitive desalination’), but what I think makes this one stand out is the (Principle 3, Local Quality) shift to solving the problem at the micro-scale:

Making ‘fields’ work over large distances is not so easy; making them work to achieve a function over a few microns makes all the difference. Then the only need is to economically configure lots of these micro-features. Which is where the micro-fluidics part of the story comes in.