With biofuel ferment
A solution potash mine operator likely would not want to become a producer of biofuels. However, it would be mutually beneficial for both the miner and such a biofuel maker to become closely associated. Here’s why ….
Ferments are one path to making biofuels, and a potash mine can provide an inexpensive means of isolating the desired products from a ferment. A strong brine is the means of doing this. Bear in mind that the ferment products will be present only in minor amounts: that is to say, in dilute solution.
One of two types of ferments may be involved, the more obvious being the production of solvents. Ethanol is the most widely known, but butanol, isopropanol, acetone, and butanediol are among other candidate solvents. Here, mixing the ferment liquid with a saturated NaCl brine in some proportion, and likely in small batches, will float the solvent(s) atop the mixed brine so that this minor layer of concentrated product is readily decanted and the solvents then distilled from it. The volume involved being small, the amount of heat required is small also, certainly compared with heating the entire ferment liquid. Also, the distilling apparatus is smaller and less costly.
The other type of ferment is production of organic acids that may be made into biofuels. Here, too, a strong brine is useful in isolating them. The three most likely acids are butanoic, propanoic and acetic (ethanoic), though hexanoic is another possibility. ..Often the organic acids will be present in the ferment as their calcium salts, of which any hexanoate, then butanoate, is least soluble.
Say the ferment produces mainly butanoate plus some acetate. When the ferment ends, adding about an equal volume of saturated NaCl brine should drop any Ca:butanoate out of solution, leaving any Ca:acetate in solution. Here also this is likely to be done in small batches withdrawn from the fermenter.
{note: _these ferments also produce COO (carbon dioxide) made from the annual plantstuff being fermented. This is a recycling of COO that the plants took from the atmosphere during their growth. So such recycling does not augment atmospheric levels of carbon dioxide, and it is not a factor in worsening those levels.}
Ca:acetate__ is so close to NaCl in solubility below circa 35 degrees C that another means of isolating it is needed. Perhaps the simplest is adding Na:carbonate which will drop Ca:carbonate leaving Na:acetate behind. ..This becomes useful to the potash miner in reducing the costs of crystallising KCl from the upwelled brine. __The scenario here is as follows:
1. Crystallise KCl from upwelled brine until KCl to NaCl ratio is something like 1:6 or 1:5;
2. While transferring the brine from the crystalliser, add Na:acetate to it (in an NaCl solution from fermenter), and send brine to top of a solvent extraction column *;
3. Solvent rising in the column removes K:acetate such that brine exiting at the bottom is wholly NaCl, which may be downwelled or sent back to the fermenter;
4. Solvent may be methanol or ethanol, perhaps something else;
5. Doing the above keeps the upwelled brine less long in the crystalliser, upping its throughput. Also, the K product obtained is more valuable than ordinary KCl.
At this point the miner has several options regarding the solvent exiting the top of the column — [a] distil the solvent leaving K:acetate as the product; or [b] instead, contact it with COO, which drops either the carbonate or bicarbonate out of the solvent (depending on whether any water is present) while the freed acetic is said to cling to a K:acetate molecule (according to an old British patent). The solvent can then be distilled away, followed at higher temperature by acetic vapour. This K:acetate can be recycled if acetic acid is to be the product.
{_Of course, what is claimed in a patent is not always reliably workable in practice, and perhaps that may be the case here. It happens. However, adding ammonia to the solvent before contacting the solution with COO would give Am:acetate which would remain in the solvent. At a higher temperature it dissociates into acid and ammonia gas. But it would be more convenient, surely, if that patent claim turned out to be workable, sans need for ammonia.}
{{* A column might not work readily unless the solution is less than saturated, due to Na:acetate being likely to cause deposition of one of the chloride salts. However, in batch mode with a long enough period of mixing, when the mixing is stopped a solvent layer on top would contain the K:acetate, while the salt layer should have little or no potassium salts in it.}}
Another brine:__ The solution mine might also have a brine that is mainly KCl but contains somewhat more NaCl than is wanted in a commercial fertiliser. Adding K:bicarb to it would drop out Na:bicarb sufficient to correct that situation. Heating Na:bicarb converts it into the carbonate.
Products
If butanoate is produced in the ferment, this would be the fermenter’s, presuming this entity is separate from the miner. Ca:butanoate is not obviously a fuel itself — though surprisingly it may be to a cement producer. Added as a slurry to the kiln, the high heat dries the slurry then destroys the Ca salt to yield lime (CaO) one COO and burnable other gases as fuel, the equivalent of 4:heptanone (dipropyl:ketone). Thus to the cement maker it is a biofuel that ought not carry any carbon tax, should that become of importance to any cement maker.
The butanoate can be made into the ketone elsewhere as well.
Electrolysis of butanoate yields hexane, itself a fuel, and which can be made into a gasoline. _See the item Green Gasoline. ..
Hexane is a good solvent for butanoic acid, and hexane will separate from the ferment carrying the acid with it, so this can be done continuously instead of neutralising the acid by forming a salt. …Or, if indeed salt formation is done, then later mixing with COO and hexane will see free butanoic acid taken by the hexane while the bicarbonate of the other part of the salt forms (and drops out of solution, most probably).
Certainly, it would be simpler if the ferment was solely to acetic acid, likely as Ca:acetate. ..As indicated above the products may be K:acetate, or K:bicarbonate plus acetic acid. ..And this latter may be made into acetone by passing the vapour over hot MnO as a catalyst, (or apparently by a fermentation route). ..Butanoic acid vapour similarly produces a ketone, which can be used as a fuel, or made into one that is more energy dense.
These potassium products and the acetic are each worth considerably more than fertiliser potash. K:acetate is sold as a sidewalk de:icer, a somewhat pricey one, but relatively benign and a fertiliser, which any sodium product is not, be it NaCl or Na:acetate. A limited market, but still. Oddly enough, K:acetate is not produced on this continent but is imported, likely from Europe.
K:bicarbonate would be more valuable as a fertiliser than KCl to certain overseas buyers, because it is really two products in one. Mixing it with a strong NaCl solution precipitates Na:bicarbonate, leaving KCl in solution. Heating the bicarb to no great degree creates Na:carbonate (soda). So then the importer has fertiliser KCl plus soda that can be readily sold to industrial users, or to a packager marketing washing soda. Obviously, such an overseas importer would be willing to pay rather more for K:bicarbonate than for ‘muriate of potash’ which is the name KCl carries as a fertiliser.
{_It would be tempting to ship K:carbonate from the mine due to weight reduction relative to the bicarb, but being very deliquescent, attracting moisture, it could not be sent as a dry bulk product unless in air:tight containers. Or as a slurry would be fine. Besides, K:bicarbonate is more useful for many an overseas buyer.}
To sum up, a solution potash mine would have somewhat lower operating costs per tonne of product, due to greater utilisation of crystalliser capacity, were it coupled with a biofuels fermenter outfit. Also, it may market potassium products having higher value per tonne than the usual fertiliser potash, products that may be especially attractive in particular overseas markets. Meanwhile, the fermenter also has lower operating costs due to this synergistic association with the potash miner.