Green Gasoline
Mostly green for sure, and wholly green is possible. .. As instance, some cars today will run on a blend of 85% ethanol and 15% hydrocarbons. And of course, it may be fermentation ethanol.
Burning an alcohol derived from fermentation does not contribute to greater atmospheric CO2 levels, because the plant parts fermented were built from carbon dioxide the growing plants had earlier removed from the air. Hence, it is a recycling event, not a net addition to atmospheric CO2 levels, whereas burning a fossil fuel is.
However, I am not referring here to ethanol being green, but to a gasoline being so. Ethanol is not sufficiently energy dense to be called a gasoline, though it can be made into one.
For a dozen years in New Zealand a Mobil subsidiary made gasoline from methanol. ..Though not an especially good way to produce gasoline, nonetheless it has been done on a commercial scale. ..Fermentation ethanol (which need not be anhydrous) may instead be the feedstock for that process, producing a gasoline entirely green. ..[However, the methanol used in NZ was made from natural gas, so that gasoline was completely fossil in origin.]
From organic acids
First, I’ll mention butanoic acid (or butyric acid, if you prefer that name). According to an old British patent [565.773], this can be got by a septic ferment of material such as cereal chaff or straw using a combination of unselected wild bacteria together with one that provides butanoic acid mainly. In effect it benefits from the enzymes the wild ones produce. Given a long enough ferment, the end result is almost all butanoic acid.
Isolating it and passing it over a catalyst will provide the ketone, here mostly PPK (di~propyl~ketone). It has a pleasant odour and may be blended with gasoline. Unlike ethanol it does not attract water: ..indeed, it is not soluble in water. That alone makes it superior to ethanol for use in gasoline, plus it has greater energy density.
Similarly, a ferment to acetic acid with catalytic creation of acetone as the ketone could be done. More convenient would be a bacterial process to accomplish the same thing. ..A thermophilic bacteria that will produce acetone from acetic acid at a temp near 60 degrees has been engineered in a laboratory. ..As this is about the distilling point for acetone, product isolation would be by a condenser withdrawing its vapour from the ferment. However, a stable bacteria for industrial use is not yet available.
Also, in a one~step transformation acetone together with hydrogen makes MiBK (methyl.isobutyl.ketone), which is used in gasoline in Canada though not allowed in California. ..This product would also be entirely green in its carbon content, if the acetone came from a ferment – directly or indirectly. Petroleum refiners do this today with acetone that does not. Should work with butanone instead of acetone. …{{Just as an aside, the H2 is only there to saturate a created double bond, which instead an alcohol molecule could instead do.}}
From ketones
Dow Chemical once looked seriously at making a high octane gasoline extender on a commercial basis. They got US patents in 1956 on a process combining two methanol molecules with one of acetone over an acidic resin at temperatures well below freezing. [No doubt today there are catalysts that work well at more convenient temperatures.]
That yields di~methoxy~propane (DMP), which has a central carbon atom with four attachments, two methyl and two methoxy. Its density is about that of water and it distills at ~145 degrees.
The process also works with ethanol instead of methanol. Ketone + 2 Alcohols <-> Product + HOH is the general formula. ..Note that the reaction is reversible, and that product is not favoured at room temp. ..However, removing the water leads to product being made. ..Experience in breaking the ethanol azeotrope in order to remove the water and get pure ethanol could be valuable here.
The ketone may be butanone instead of acetone. ..Butanone is also known as MEK (methyl~ethyl~ketone). ..It is readily made by passing 2,3-butanediol over an acidic resin or other acid catalyst. Butanediol can be had by fermentation, though only some bacteria that do this are safe to use, with no need for special precautions.
One of these is a strain of Bacillus subtilis, another is Paenibacillus polymixa, which latter can utilise quite a broad range of materials, including glucose, mannose, starches, cellobiose, pectin and xylose. ..So it can use starches directly, such as potato peels or wastewater from a potato processor.
It produces several enzymes, xylanase among them. ..But the bacteria have a strong preference for six:carbon sugars rather than five, and won’t consume xylose if any glucose, cellobiose or starch is available. ..This means the ferment can be halted at a point where much xylose has accumulated but not yet been used. …Very handy for making furfural or xylitol, or having some other use for xylose.
Product isolation from a ferment may be by salting out, which creates a very salty lower layer atop which float the solvents produced (alcohols, diol, ketone). ..That top layer may be decanted and distilled to separate any ethanol from the diol, and to ensure no salt is carried with them. Among many salts that can be used are NaCl, seasalt, and KCl (potassium fertiliser).
If using a cheap salt, NaCl or seasalt, after product isolation the overly salty water with fermenter debris may be slowly sent into the sea where it disperses and a plankton feast on the debris ensues. The harvest of fitre feeders and fish in that area should then increase.
If using KCl, the salty layer may be sent to an outdoor evaporation pond for salt recovery. ..Fermenter debris will be included, so the recovered salt may be marketed as enhanced potassium fertiliser that includes also some nitrogen, phosphorus, and various micro-nutrients. Pellet to provide a flowing product.
|< Just as an aside, 2,3-butanediol will itself combine with acetone to yield a gasoline component, in this case a cyclic di:ether with two oxygen and three carbon atoms in the ring with an ethyl and several methyl attachments where you’d expect.
Note that since the butanone can be made from the diol (and it a ferment product), butanediol alone can provide a gasoline that is entirely green.>|
Electrolysis route
At least one longer organic acid may be turned into gasoline in quite a different manner. Circa 1850 it was discovered that sodium or potassium butanoate in aqueous solution upon electrolysis will give mostly hexane at the anode and the hydroxide plus hydrogen gas at the cathode.
Hexane is a linear hydrocarbon having six carbon atoms which can serve as a diesel fuel. ..Also, it is readily re:arranged over a catalyst into several branched isomers, all still having six carbon atoms, which make a good gasoline with an octane rating of ~85.
However, this electrolysis typically has some side products, in particular an alkene. ..Indeed, this may be deliberately done so as to produce as much alkene as hexane (and other alkanes, depending on what the feed is). ..The alkene may be combined with alkanes to give a product useful as a gasoline component, or as a fuel for a furnace or cooker (stove). ..Petroleum refineries do this routinely in a process they term alkylation.
Fermenting starch to acetic and butanoic acids was being done on a commercial scale in 1917, though the acids were not the object of the process. ..Instead, the ferment was continued in a second phase that transformed the acids into acetone and butanol, the first being the desired product at the time. ..But after the Great War, butanol became the more desired product, for use in making lacquers for automobiles, the butanol being part of a solvent for them.
The same ferment done today could use xylose as the substrate. Certain bacteria tend to produce mainly butanoic acid, which could undergo electrolysis to provide hexane.
Butanoic acid may be separated from any acetic by use of an appropriate extractant. But if the amount of acetic acid is minor, such a step may be foregone, and the electrolysis will then also yield some butane by combining one acetate with one butanoate. ..[Perhaps a little ethane as well from two acetates, which may be added to natural gas, or otherwise burnt to prevent its release into the air.]
Butane and hexane are easily separated. The butane may be used in heaters or gas barbecues, where it has the advantage of lighter weight containers than propane requires. (Butane distils at ~O degrees Centigrade.)
Note that this is a more efficient use of electricity to power vehicles. Powering vehicles directly with electricity does not get you very far. ..Using electrolysis to make a green gasoline powers vehicles far greater distances. ..All~electric vehicles are really (overall) an inefficient use of electricity.
|[note: Gasoline is not required for an EC engine (external combustion), which can use a wider range of fuels. See page: Biofuels/Enviro .]
To sum up: __There are several routes to a green gasoline from fermenting cheap cellulosic waste materials (or even hay) that would be beneficial in reducing net additions to atmospheric carbon dioxide levels.
It is up to political will to pursue this route by making producing these profitable. (See item: Biofuels Production as Critical Infrastructure. _again the page: Biofuels/Enviro.)