ARCANUM | DESIGN: Nanofluidic bulk active ion pump using porous pyrolytic carbon

ORIGINALITY

Original, to the best of my knowledge, as of March 2011.  Idea date approximately January 2007.  May share some similarities to ideas explored in research into implantable artificial dialyzers.


SOURCES OF INSPIRATION

Dialysis; animal kidneys; mass spectrometry; cyclotrons


EXPOSITION

The removal of ions from solution touches on many disparate areas of modern life, such as medicine, engineering, public health, process chemistry, and farming, to name but a few.  An efficient means of selectively transporting ions against a concentration gradient would almost certainly lead to cheaper and cleaner water supplies, more efficient industrial processes, less pollution, and possibly even medical advances such as fully-functional implantable artificial kidneys.

Removing ions from aqueous solution has traditionally been the province of bulk techniques, such as reverse osmosis[1], ion-exchange[2], distillation[3], and electrodialysis[4].  These share the common feature of being energetically and/or economically expensive, as well as relatively nonselective.  Ion-exchange resins have the added problem that the resin beads must be periodically recharged, during which time they cannot be used for ion removal (duty cycle <100%), and that they must replace the captured ion with one or more ions totaling the same charge, meaning no net decrease in dissolved solid concentration.

In animals, the job of maintaining appropriate ion concentrations in the bloodstream is largely accomplished by the kidneys.  In order to efficiently maintain control of blood ion concentrations, very efficient and selective nanoscale ion-transport systems have evolved to "pump" ions in the proper direction, usually against a concentration gradient.  A major problem is that most of these biological ion-pumps are powered by transport of some other substance along its concentration gradient (ex:  the sodium-glucose antiporter pump SGLT1[5]), by co-transport of some other substance along the same concentration gradient (ex:  the Na-K-Cl symporter system in the kidney[6]), or by active powering by ATP.  The first case leads to a "Hobbes' choice" where the increasing concentration of some other potentially undesirable contaminant in the diluate must be tolerated in order to remove another, less-desirable contaminant; the second leads to a case where one must remove other, potentially-desirable ions from the diluate in order to facilitate removal of undesirable ions; the final case leads to the requirement of multiple entire biochemical pathways to produce the chemical power necessary to power the transport system.

In gaseous or plasma phase, however, ions are easy to separate individually, owing to their unique interactions with magnetic and electric fields.  Every elemental ion has a different charge and mass; using these unique physical characteristics, ions can be separated from one another easily, as in a cyclotron or mass spectrometer.  However, this is of little use in industrial processes, as converting substances to gas or plasma is extremely expensive energetically and economically, and the flow rate is minimal at best; it is of even less use in biological systems, for the obvious reasons.


DESCRIPTION

The core of this idea is the observation of the electrical anisotropy and biocompatibility of pyrolytic carbon sheets[7].  Pyrolytic carbon is a form of graphite, consisting of parallel sheets of graphene, with some impurities.  Graphene's planar structure allows electron transport within sheets at conductivities potentially higher than silver[8], while cross-sheet electron transport is significantly less efficient.  (I shall refer to each sheet of graphene henceforth as a "sheet", and of the collection of parallel sheets as a whole as a "sheaf".)


This would seem to lead to the possibility of providing different amounts of charge to each sheet, with relatively limited current leakage between sheets.  If the sheaf were constructed or machined such that a small cylindrical "tunnel" oriented perpendicular to the sheet existed, the tunnel would have a spatially-inhomogeneous electric field inside it, owing to the relative difference in charge between individual sheets.  If charge could be pumped in and out of these sheets in a controlled fashion, the time-varying electric field in the tunnel would create a time-varying force on a charged particle inside it.  Since different ions would have different mass-to-charge ratios, this would seem to offer the possibility of selectively accelerating particular ions in aqueous solution, using electrical power to "pump" them from one side of the sheaf to another by carefully applying particular charge pulses to various sheets within the sheaf at particular intervals.


Careful control of the charge applied to each sheet should permit "gating" of particular batches of ions once within the tunnel; ions of mass lower than that desired should move faster through the tunnel, where they can be "reflected" by appropriately-charged sheets, and ions of mass higher than that desired should move much more slowly, thereby enabling "cutoff" of transport at a certain separation from the "desired" group of ions.  This should lead to relatively selective transport of ions through the sheaf, presumably as a function of the total thickness of the sheaf.


If such a device is feasible, the applications are obvious.  Pyrolytic carbon is a highly-biocompatible material; such a device could serve as an artificial glomerulus, enabling the construction of an electrically-powered implantable dialyzer that should function adequately as a replacement for those suffering from kidney disease.  (In some ways, such a device might even be an improvement over the natural model, since it would be immune to various poisons and toxins that can damage biological kidneys.)  Pyrolytic carbon is also resistant to most forms of chemical attack, thereby enabling its use in industrial processes.  It would also enable selective recovery of ions in wastewater and possibly even from the active process, potentially improving the efficiency and reducing pollution from those processes.  It may, if efficient enough, be useful as a means of desalinating drinking water.




BENEFITS

1. Outlined above.  Obviously, this is highly speculative.

PROBLEMS

1. Obviously, there's no guarantee that you can make pyrolytic carbon, or any other substance, do this.  The addition of transverse holes to the sheaf may be impossible, or may lead to changes in the electronic structure of the sheet that lead to increased inefficiency, difficulty of production, or both.
2. The envelope-level description above does not take into account solvation effects.  Ions in aqueous solution are surrounded by configurations of water molecules, significantly altering their behavior. These solvation effects may well preclude the efficient transport of ions in this manner.
3. The ions may interact with the pyrolytic carbon in some fashion, changing its electrical characteristics over time.  The electrical characteristics of pyrolytic carbon are highly dependent on the level of impurities embedded in it; electronic "pumping" may abstract impurities from the solution, and may even propagate them within the structure.
4. The tunnels within the sheaf may become filled, irreversibly, with ions that come out of solution.  If an ion is able to abstract an electron, or donate an electron, to the sheaf itself, then it will lose its charge and will no longer be susceptible to forces imposed by the electric field.  (It may be possible to re-ionize the substance by applying an electric field of the appropriate magnitude, though.)
5. Artificially segregating ions in solution may lead to situations where insoluble salts are produced by accident, either in the solution or within the sheaf.
6. It will be significantly less efficient at lower ion concentrations.
7. It may require some form of mechanical mixing or turbulence to homogenize ion distribution within the solution.

CALCULATIONS

To be added.



DRAWINGS


To be added.



REFERENCES

1. http://en.wikipedia.org/wiki/Reverse_osmosis
2. http://en.wikipedia.org/wiki/Ion_exchange
3. http://en.wikipedia.org/wiki/Distillation
4. http://en.wikipedia.org/wiki/Electrodialysis 
5. http://en.wikipedia.org/wiki/SGLT1
6. http://en.wikipedia.org/wiki/Na-K-2Cl_symporter
7. http://www.espimetals.com/index.php/online-catalog/353-carbon-c
8. http://en.wikipedia.org/wiki/Graphene#Electronic_transport
9. Applied Surface and Colloid Chemistry, R.M. Pashley and M.E. Karaman, Wiley, 2004, ISBN 0-470-86883-X

ARCANUM | DESIGN: Subsurface oceanic bio-crude station

ORIGINALITY

Original, to the best of my knowledge, as of March 2011.  Idea first conceived roughly 2006.

 

EXPOSITION

Some time back, I had read an article or two on the process of thermal depolymerization[1], and, hey!  I had an idea.

This process is designed to turn organic material into what is essentially crude oil.  The story highlighted a pilot plant using the process, turning castoff turkey guts from a turkey-processing plant into moderately useful amounts of rather heavy crude.

The basic idea is that, when placed under high pressure and heated, carbon chains inside the organic goo rearrange themselves into the sorts of chains one ordinarily finds in petroleum products.  These can then be refined to produce more useful products, such as gasoline and lubricating oil.

One major problem in industrial processes is that pressure is typically not cheap; it is economically and energetically expensive.  Heat is likewise expensive, unless the heat exhaust can be harvested from another industrial process.

Another major contributor to this idea was the story of iron fertilization[2].  Apparently, oceanographer John Martin discovered that iron, when added to the surface layers of ocean water, significantly increased the growth rate of plankton.  Plankton is a wonderful source of biomass; many algae-based biofuels processes are currently in development.[3]

The keystone of the idea was my discovery that there were such things as dead hydrothermal vents on the seafloor, i.e. vents around which a highly-localized biosphere either does not exist or has already disappeared.  Dead vents are key to this process, since they do not have an existing biosphere to disrupt; most vents have sulfide-based biocommunities surrounding them, and any disruption of flow from the hydrothermal vent would presumably be destructive to these unusual creatures.


DESCRIPTION

The basic idea is this:

After finding a dead hydrothermal vent system, preferably with "smoker" vents, an converted offshore oil platform can be positioned over it, and the vent tapped to feed the process.  A reactor column would be sunk to the sea floor; this column could be relatively thin compared to the requirements for a land-based reactor column, as the static pressure within the column would be opposed by the water pressure outside it.  Hot, sulfide-laden water would be extracted from the vent and brought up through the column to power the thermal-depolymerization process, and if any excess heat was available, to power refining and/or electricity-generation processes on the surface.

Water from hydrothermal vents is typically rich in iron sulfide.  This can be oxidized to iron sulfate, which, when added to the surface water surrounding the platform, should stimulate phytoplankton growth and thereby biomass generation.  A collection system, possibly using converted tanker vessels or flexible suction pipelines, would strain the plankton from the water and move it to to the column top, where it would enter the depolymerization process.  Since plankton are ubiquitous in water, this is essentially an algae-farming operation in the open ocean.  Specific natural algae that produce higher-quality lipids can be "seeded" in the area; if the process is carefully tuned, they may naturally dominate the farming area.

The column, when full, should achieve a "steady-state" thermal and reaction distribution; withdrawal of synthetic crude from the column to the surface can take place from an experimentally-observed, optimal depth.  This can then be fed to a surface refining process - possible powered by residual heat from the vents, from heat supplied by other vents, or from burning fractions of the synthetic crude - to yield useful fractions, which can then be offloaded to tankers, disposing of the need to transport raw crude to centralized refineries elsewhere.


BENEFITS

1. The process is carbon-neutral.  The biomass to be refined is produced from CO2 in the atmosphere, effectively "recycling" CO2 released from burning fossil fuels.
2. It is, at least notionally, more efficient in several ways.  It allows for selective tanker transport to market of finished products instead of crude oil, allowing lower transport cost per unit.  It uses currently-unused waste heat from naturally-occurring processes, and has naturally-occurring feedstocks, thereby reducing the lower bound for pollution to zero.
3. Since vent fields can be found in international waters, production can take place in less-politicized, secure, and royalty-free environments.
4. Since the upper bound of crude oil storage is the volume of the subsurface column plus any external storage tanks, any leaks are automatically limited, unlike deepwater drilling of oil reservoirs, where the upper bound of the potential leak is the size of the reservoir.
5. Any organic material is theoretically a feedstock for this process; carbonaceous waste such as plastics (a major component of the Great Pacific Garbage Patch[4]), waste biomass, fish-processing residues, &c., can theoretically be processed as well.  While these would require transport to the column, it may be economically feasible, depending on the capital costs of construction.
6. The refining process, generally considered to be a source of pollution and unpleasant odor, is by definition remotely located, away from human population centers.

PROBLEMS

1. It requires a particular oceanic feature - a hydrothermal vent field - to work as designed.  There are only some charted vent fields in the world.
2. As described, it requires vents that are "dead", i.e. have no biospheres surrounding them; these comprise an unknown fraction of vent fields, but apparently a minority of them.  While a "live" vent field is technically as usable for this purpose, there are potential political and scientific objections to appropriation of the critical materials (heat and sulfides) of a functioning biosphere for industrial processes.
3. There may be political or ecological objections to the use of oxidized iron sulfides to "fertilize" stretches of open ocean, regardless of the natural origin of the sulfides.
4. Since this is essentially a permanent placement, the construction must be robust to weather extended exposure to normal marine-environment conditions, including storms, rogue waves, tsunami, corrosion, &c.

DRAWINGS

To be added.


CALCULATIONS

To be added.


REFERENCES

1. http://en.wikipedia.org/wiki/Thermal_depolymerization
2. http://en.wikipedia.org/wiki/Iron_fertilization 
3. http://en.wikipedia.org/wiki/Algae_fuel
4. http://en.wikipedia.org/wiki/Great_Pacific_Garbage_Patch 

About Tricks

This section is similar to Fearpoop, but somewhat broader.  Basically, any neat trick - typically involving computers, naturally - belongs here.  This is a repository for ways to do things that I have found to be useful.

Commentary is welcome.  If I'm using a trick that was independently developed by someone else, let me know in the comments section, and I will update each post with a link to the originator.

About Writing

This is the section in which my prose flows freely.  I will restrict myself to general observations, mostly on technical subjects, with occasional divergences.  I will endeavor to avoid subjects touching on religion, politics, political economy, economics, and so forth.  While I certainly have opinions on these topics, I have decided that those properly belong elsewhere.

You may discuss things in the comments section, but I will not respond or meaningfully interact there, or likely even read them, except for occasional scans for comment spam.  Not to put too fine a point on it, you're reading it because you care what I think, not vice versa.  If you don't like it, feel free to vent in the comments, but don't expect me to pay any attention to it.

About the Arcanum

I have a wide-ranging interest and background in various scientific and engineering fields, and dream up many strange things at the oddest times.  I have come to the realization that 99% of these are probably worthless, and I will never in any event be able to exploit or do anything with most of them anyway, so it costs me nothing to describe them here.  Somebody may find them interesting.

You will not find my secret plans for a 500mpg carburetor or free-energy perpetual-motion machine here.  That's because I don't have any, because I have more than a passing familiarity with the laws of thermodynamics.  By the same token, you will find your designs for such things also not here, and any comments about them deleted.  I do not tolerate tinfoil craziness well.

This is for things that... well, maybe, could exist.  Strange designs.  Imaginary envelope-pushing.  That sort of thing.  If there are flaws in my reasoning here, in any aspect, I encourage more skilled readers to point them out.  (Note that arguments of the form "well, that just can't be done", without some coherent reasoning of "why not" - preferably backed up with actual math, physics, or chemistry - will be about as poorly-received as tinfoil.)

If it is demonstrated that the designs are flawed, already explored by others, encumbered by patents, or suffer any other fatal flaws, I will nonetheless leave them standing as monuments to my folly.  That seems only fair.

First Post

Once upon a time, some years ago, I remarked to a friend of mine that blogging was a sign of mental illness.  While I have not changed my mind on this topic, I have elected to succumb to hypocrisy and engage in this particular mental illness myself.

Hell, why not.  We're never gonna survive unless we get a little crazy.  A wise man once said that.

This blog exists to expose the varied and astonishing contents of my mind to the scrutiny of the cold, cold world.  It is also designed to accomplish a small portion of my larger goal of staking claim to my name on the big, bad Intarwebs.  I have elected to do this before somebody else does it for me.  The only thing worse than being unfairly judged on the basis of one's Internet presence is being unfairly judged on the basis of somebody else's Internet presence, or on the lack of an Internet presence to evaluate.

I may update it.  I may not update it.  It exists for my amusement and convenience, and not anybody else's.

My rough envisioning of the layout - which I have little intention of deviating from - is five sections:

1. The Arcanum (ideas, designs, free-ranging novelties; these may be updated from time to time; I will care about comments in this section, please make them useful)
2. Writings (personal observations and creations; I don't care what you think of them, and will not read or answer comments)
3. Tricks (clever ways I have discovered to manipulate technology; comments will be incorporated in post updates if they extend or improve things in some way)
4. Fearpoop (stories of situations going horribly wrong, lifted shamelessly from my experience, others' experience, Internet stories, &c. ALONG WITH tales of how recovery from those situations was achieved; again, this mostly involves computers, and comments are welcome [and may be mined for future posts], again, so long as they are useful) 
5. Miscellaneous (things that do not belong in one of the above categories)

This blog's existence is the extent of my narcissism.  I will not brag.  I will not whine.  I will not post anecdotes of my life, any more than I do anywhere else.  To the extent possible, I will not post opinions; I have done that elsewhere, and while fun, an untrammeled stream of opinion (overt or covert) is the cancer that is killing the Internet.  I will not flame.  (That last is a bit of work for me, it being my natural response; please don't test me, that's not why this is here.)  You will not see pictures of me, my dog, my cousins, the mountains, the last thing I ate, or squirrels with lightsabers.  Everything I post will be either interesting, or useful, or both.  Just the facts, ma'am.