Hello, this is my first post here so please forgive me if this board is not the best place for it.
I just finished my 2nd year of a chemistry degree and subsequently Organic Chemistry 1 & 2. While we were learning about the aldol reaction, I
read about a reaction pathway for the conversion of three equivalents of acetone into one equivalent of 1,3,5-trimethylbenzene. This struck me as a
potentially useful reaction, as the product has been proposed as a motor gasoline (https://patents.google.com/patent/US20140357908). I looked into this reaction on Organic Syntheses (http://www.orgsyn.org/demo.aspx?prep=CV1P0341) and was disappointed to find that it had a very low yield and selectivity (as well as a lengthy
workup) when catalyzed by sulfuric acid. After this, I decided to continue searching for a more efficient catalyst and found a document that
references a paper by G. A. Olah in which the reaction is catalyzed by Nafion-H, (http://reag.paperplane.io/00002063.htm). Unfortunately, I am unable to find the paper anywhere. However, I was able to find another paper that
details a similar reaction, that substitutes acetone for substituted acetophenones (https://link.springer.com/article/10.1007/BF00764000). I would like to perform the reaction of acetone to 1,3,5-trimethylbenzene and possibly
scale it up in the future. That being said, I have never worked with a solid acid catalyst and do not know the procedures or conditions of this
reaction. If anyone here has a link to the original paper, or even an improvised procedure for the reaction. I would be very grateful. Melgar - 20-7-2018 at 05:57
Trimethylbenzene is a common component of crude oil. Additionally, the technology for separating the various methylbenzenes from each other is very
well-developed, since para-xylene is especially valuable as a precursor to PETE (polyester). For this reason, it's almost never synthesized, because
it's so much more cost-effective to extract it from petroleum.
You might be thinking "But what about when we run out of oil?" Well, the truth is, we're never going to totally run out of oil. We'll just
eventually get to a point where it's too expensive to use for fuel. It'd still be worth extracting for use as a chemical feedstock though, just
because of how incredibly useful oil is for that purpose.
Since you mentioned wanting to scale up, I'm assuming you're thinking about commercial applications, which is why I'm trying to talk you out of
attempting that.
edit: So that I don't seem like I'm all negativity, if you want to research something that has real potential, look into ammonia-based fuel cells.
Hydrogen is ridiculously difficult to store, since it embrittles metals, needs incredibly high pressures to store in liquid form, and can escape from
just about any container you might try to store it in. However, ammonia (NH3) can be converted to H2 and N2 on demand, in an exothermic catalytic
reaction. The N2 is released to the atmosphere, and the H2 is immediately used in a fuel cell. This is very convenient, since NH3 can be stored in
the same tanks that are used for propane. Jet engines can also be run on the combustion of NH3, although it's only about half the energy density of
the jet fuel in current use.
The nice thing about NH3 is that we already have decades of experience manufacturing it on a huge scale (millions of tons a year) for use primarily as
fertilizer. It also doesn't need fossil fuel energy to power it, since plants that make ammonia need most of their energy in the form of electricity,
so they could theoretically run entirely on renewables. Current plants typically produce hydrogen from natural gas and water because that's a lot
cheaper, but if the economics changed, they could also produce hydrogen electrolytically.
[Edited on 7/20/18 by Melgar]j_sum1 - 20-7-2018 at 06:03
Welcome to SM, Arenium.
Interesting idea. Even if it is probably uneconomic as Melgar said.
I will move this to OC where it more properly belongs.clearly_not_atara - 20-7-2018 at 08:00
All synthetic fuel cycles must compete with the very simple:
CO2 + 6 e- + 6 H+ + hv + (Cu or Pd complexes) >> MeOH
2 MeOH + heat + (acidic clay) >> Me2O + H2O
Dimethyl ether has excellent combustion properties in a diesel engine -- way cleaner than normal diesel or biodiesel -- but it suffers from low energy
density. It's stored at the same pressures as ammonia but isn't as corrosive. Melgar - 20-7-2018 at 09:18
All synthetic fuel cycles must compete with the very simple:
CO2 + 6 e- + 6 H+ + hv + (Cu or Pd complexes) >> MeOH
2 MeOH + heat + (acidic clay) >> Me2O + H2O
Dimethyl ether has excellent combustion properties in a diesel engine -- way cleaner than normal diesel or biodiesel -- but it suffers from low energy
density. It's stored at the same pressures as ammonia but isn't as corrosive.
First, I'd argue that anhydrous ammonia isn't actually very corrosive at all, and probably no moreso than water. It's a fairly easy problem to solve
just by designing things properly.
I'd posit that ammonia could be produced a lot more easily than dimethyl ether, due to the relative ease of large-scale extraction of nitrogen from
air. CO2 only makes up less than half of 1% of the atmosphere, and if you were trying to extract it, you'd be competing with chloroplasts. Also, the
Haber process has been economical since the 1930s, and has a lot fewer steps to it.
Just my take on it though, I could easily be wrong.unionised - 21-7-2018 at 05:20
Since acetone is made commercially from propene, it's probably more efficient to turn propene into a suitable fuel directly.
It depends on whether there is a market for acetone produced as a byproduct from phenol production. If demand for acetone doesn't keep up with supply,
there could be a lot of surplus acetone available.
I'm not sure that fuel is really the best use for it.Dr.Bob - 26-7-2018 at 09:25
Just my take on it though, I could easily be wrong.
Saying that making ammonia from air is easier than extracting CO2 since air is 70+% nitrogen is ignoring that producing fuels is more about
thermodynamics than any other factor. Any method to produce liquid fuels must get its energy from another course, and trying to reduce CO2 back to a
useful fuel is ALWAYS going to use more energy than it produces in useful fuels, many processes use more than twice the energy of the final fuel to
make it. Finding CO2 is easy, just look at the output of a fossil fuel electric plant, concrete kiln, or brewery to find concentrated CO2. And
making ammonia is one of the most energy intensive processes known. So concentration in air does not matter.
More importantly, why try to make fuel from CO2, much better to just not burn something to make CO2 in the first place, as saving energy is almost a
log order cheaper than making liquid fuels from CO2. Having worked in alternative energy and conservation for a short time, there are several ways
to reduce energy use that are far more practical and affordable than others. Using solar thermal energy is very simple, cheap, and practical, where
it is planned ahead of time (passive solar heating, hot water intensive processes, concentrated solar to heat things).
Just insulating houses, driving less miles and using efficient cars, turning off lights when not used, installing LED lights, and a few other tricks
can cut your electric and gasoline usage in half, often with no real effort, and many pay for themselves in a year or less. I don't understand why
some people want to do all PV solar, complicated batteries, and other very expensive systems, when simple things can save 50% of your energy costs.
It is far simpler to avoid using a fuel than to remake it back from the CO2 it generated by burning it. Yellow12 - 28-7-2018 at 03:24
Saying that making ammonia from air is easier than extracting CO2 since air is 70+% nitrogen is ignoring that producing fuels is more about
thermodynamics than any other factor.
Yeah, and my point is that these reactions need to be in liquid phase, which requires liquefying air via the application of high pressures. If the
fraction that you're collecting from the air is the largest component, (as nitrogen is) then this is much, much more efficient than trying to collect
the CO2 portion.
I could see where this conversation is going though, since I'm also interested in alternative fuel chemistry. The real question being, what vehicle
fuel could most easily be chemically produced solely from renewable resources and electricity? Personally, I think ammonia is our best bet, but it's
far from settled. Incidentally, ammonia is probably the best with regard to energy stored in the fuel too, since with modern Haber Bosch plants, they
can retain 60% of the input energy as chemical energy.
So the main rule of this game is it's got to be carbon neutral, and produce a fuel that can power say, jet engines.
On page 9 it states that the Ammonia Decomposition to hydrogen is endothermic.
It makes it a less convenient reaction.
Yeah, you're right about it being endothermic. However the reaction is strongly favored due to the stability of N2 gas, I also haven't studied PEM
fuel cells very well because in my experience they're expensive, require PGM catalysts, and are easily poisoned. I think SOFCs (solid oxide fuel
cells) are a much more promising technology, and they can run on ammonia too. Also, SOFCs run at a much higher temperature than PEMs, and this
temperature is hot enough to catalyze the decomposition of ammonia with really cheap, durable catalysts like nickel.Dr.Bob - 28-8-2018 at 18:33
The challenge is that very few chemicals are cheaper per gallon than gasoline, due to the scale of its production, and that it is basically made from
something dug up from the ground. Natural gas is one of the few cheaper chemicals, which is why methanol can be made as cheap or cheaper per gallon
than gasoline (as low as $1/gallon), but few chemicals ar cheaper per gallon than those two. Acetone costs more than either (phenol is not made via
the acetone route as much now, so little surplus acetone is made now), but is surprisingly cheap in bulk ($3-5/gallon), but still more than gasoline
before taxes. So only if you could make a really valuable fuel additive like trimethylbenzene in very high yields could you justify the cost of the
starting material.
Don't get me wrong, I am all for trying to make chemicals and test ideas of chemistry, but if you are going to speculate on making chemicals for
economic reasons, then it is a good idea to have some idea of the economics of chemicals first. Since methanol is very cheap (due to being made from
abundant natural gas), making dimethyl ether as a fuel makes great sense, as did using TBME as an octane booster until idiots in government stopped
that. Ethanol is really more expensive than gasoline to make, but tax breaks keep it just under the price of fossil fuel gasoline. I would love to
see the people who ask about various scheme to make a useful chemical do some basic research to find the cost of the starting materials before posting
so that can give a complete picture of what they are proposing, and its value.
Sadly, several schemes to make liquid fuel from coal, clean gas from coal, fuels from biomass, etc have been thought up, created, optimized, and built
into pilot plants or full factories, and have seen many of them then closed due to the price fluctuations of oil, natural gas, and other energy
sources. Most are interesting science, many are engineering marvels, but if they go bankrupt and loose money and jobs for scientists, it makes me
sad. Sadly, there are still many reasonable methods to save energy that make more sense, but are politically incorrect, less exciting or not as
sexy, so many go undone. clearly_not_atara - 28-8-2018 at 18:45
Actually, that reminds me -- there is a fermentation process that produces a mixture of mostly acetone and butanol with some ethanol. Butanol is an
excellent fuel, so in order to make this workable I thought you could form the dimethyl ketal of the acetone:
Unfortunately, you'd probably have to separate the fuel, react acetone with methanol, and recombine it. Ketals with alkanes other than methyl might
form explosive peroxides, which is bad.
Also, biofuel isn't great by environmental standards, because it increases the amount of land that has to be dedicated to agriculture, and it releases
nitrous oxide as a consequence of fertilizer degradation. It's nice to have on hand for stuff batteries just can't do, but it's never going to replace
oil, because the fundamental economics don't work out even if you postulate a magical machine that turns sugar into gasoline.JJay - 28-8-2018 at 18:50
