So, I was trying to find the “Octane” rating of a CO + H2 mixture (“synthesis gas” or “producer gas” – the stuff from a “gasifier”) as I was pondering making a device to turn “yard waste” into fuel for one of my Diesels. You can ‘fumigate’ high octane fuels into the air intake up to about 75% of full power. Natural gas can be used this way. It doesn’t pre-detonate, then when the Diesel injection happens, that acts like a spark plug to ignite the co-fuel. Low octane fuels (like ‘regular gasoline’) would knock or ping and as you approach a stoichiometric mix the knock tendency rises as well.
It would be “nice” to know if the fuel could be used this way before building a unit… and the “octane” rating would give me the information. But as so often happens, you trip over something else along the way… I still have not found the octane rating for synthesis gas (almost all the links I found contain “octane” as something related to gasoline produced via synthesis gas…), but did find this interesting paper:
First off, I noticed that the page numbers start at 282 and run to 287. It’s 5 pages from something larger. There is a lot of information out there on fuel synthesis…
Second, it’s from Argonne National Laboratory, a place I’ve not looked at much. This implies they may have more interesting stuff to find… Finally, it is a PDF of what looks like old typewriter font material. This stuff has been around for a while. This implies things ought to have improved since then.
OK, the nub of it:
They talk about some things I’d not seen in more “popular press” type articles. One is the use of liquid phase reactors. Catalyst particles carried in a liquid bed of inert oil (there may be some “typos” in this as the “cut / paste” process was sometimes “creative” in how the software turned shapes into letters…and I may not have caught them all):
Chem Systems, Inc. has developed a liquid phase reactor system to improve the thermal efficiency of methanol production ( 1 ) . This Liquid Phase Methanol process is being further investigated under a cost shared contract in a 5 TPD process development unit (PDU) which is located at La Porte, Texas, on a site owned by the prime contractor Air Products and Chemicals, Inc. The PDU has operated very successfully with a Cu/Zn catalyst powder less than 50 microns in diameter slurried in an inert oil in the reactor through which the synthesis gas is passed. Operating conditions are 5.27 MPa (765 psia) and 25O oC (482 F ) . During its most recent 40-day run (May-June 1985) the PDU operated with a nominal 25 wt. percent catalyst slurry and the catalyst activity declined 0.34 percent per day.
It also talks a bit about the ability to choose between alcohol production and the production of gasoline and Diesel type hydrocarbons. The main point being “selectivity” in the process and catalyst. The original Fischer Tropsch process being rather un-selective leads to a need to crack waxes (or make a lot of candles ;-) along with less ability to control how much is gasoline, Diesel, or propane.
If one makes Methanol first, then the path to gasoline is more directly controllable via a zeolite catalyst named ZSM-5 (the M being for Mobil, I think… I’ve seen Mobil Oil involved with an M5 catalyst before. They used that zeolite catalyst with Methane, i.e. natural gas, in a facility in New Zealand to turn their natural gas production into liquid fuels back in the late ’70s or early ’80s). Zeolites are a kind of mineral / rock material. One kind is commonly found in water softeners, for example. They are a bit tricky to make (as small changes in process result in large changes of what they produce, so there is “black magic” involved in finding the “right” incantation to make any exact zeolite… but once the process is known, you can fairly reliable make batches of each unique mix.)
At any rate, you have one path:
Synthesis gas -> hydrocarbons -> cat cracking -> motor fuels
and a competing path:
Synthesis gas -> methanol -> ZSM-5 -> motor fuels.
Each will have a different set of reaction conditions (such as using copper instead of iron as the catalyst) and each has a different “selectivity” of product. Also, cat crackers are not cheap nor easy to make so you have a cost issue. ( Or a lot of candles…)
I found the discussion of liquid phase / slurry phase reactors interesting too. It mostly speaks to some process issues like the ease of keeping the catalyst fresh, but it was not something I’d thought about much in the context of fuel. An exothermic reaction can be made more efficient if you extract the heat (while keeping the temperature in the best reaction zone), so a liquid phase may also allow more thermal efficiency by better heat extraction; while the article states a better working temperature is possible.
liquid , or slurry phase, reactors are recognized as having a potential to significantly improve thermal efficiency over more traditional reactor designs for highly exothermic reactions.
A number of existing projects are investigating liquid phase reactors, but we need much more data describing the hydrodynamics of such systems under process conditions. Actual operating data are required from a reactor which can be operated in a commercially viable churn turbulent flow regime. Results from research to date are encouraging in processing a lower H2/C0 ratio syngas and producing a flexible product slate. The liquid phase Fischer-Tropsch reactor also operates at a higher, more productive, temperature (260 C-270 C) than is feasible with the Arge or Synthol reactors using the current iron catalyst at Sasol.
But notice that last line. “more productive”…
The other bit that caught my eye was a chart about relative performance. Sasol is making gasoline and Diesel fuels (along with a suite of process chemicals) in South Africa today with their process. The cost of gasoline made this way is about $2.75 / gallon US at present. (Price varies over time as the US Dollar depreciates… at one time it was 70 CENTS per gallon, but that was when oil derived gasoline was 50 CENTS per gallon and going to the movie cost about $2…) At any rate, any process that comes in cheaper than that is something I want to know about.
Unit product cost*, market basis, all liquid output Case Relative Cost Sasol (dry Lurgi/Synthol) 1.00 Modified Sasol (BGC Lurgi/Synthol) 0.83 Liquid Phase Fischer-Tropsch (BGC Lurgi/Kolbel) 0.69 Liquid Phase Fischer-Tropsch (BGC/Mobil)** 0.73 * All liquid hydrocarbon fuels valued the same. ** Upgrading of Fischer-Tropsch liquids to marketable fuels based on ZSM-5 catalyst.
So this is saying that by taking a tour through liquid phase catalysts and ZSM-5 you can get the costs of fuels down to about 73% of the costs using the Sasol process. Assuming (and it is a big assumption, times have moved on…) that SASOL is still using that Sasol process, this implies that one could make gasoline in the USA (where this study took it’s cost basis and coal source data) at about $2 / gallon U.S.
So, we are not doing this because?…
For More Information
An interesting, and short, note about ZSM-5 and how it works / what makes it “special”:
General FT orientation:
If you would like to buy a Lurgi Methanol reactor ‘turn key’:
There is an online archive of F-T materials:
That has some interesting stuff. Like this one…
It looks like Fluor has built these for folks:
Even folks at school “get it”. This is a nice paper that has an overview of approaches. It also looks at DME (Di-Methyl-Ether) production as an alternative path to motor fuels and finds it has significant production advantages. Nice color charts of reactor designs too:
Summer School September 2009
Bifunctional metal (Cu, Zn, etc.)-zeolite
catalysts have been developed, which can
convert syngas very selectively to DME
with high carbon monoxide (CO)
conversion (this reaction is far more
favorable thermodynamically than
methanol synthesis from syngas).
• Syngas to DME breaks the thermodynamic limit
of syngas to methanol system with up to over 90
percent CO conversion, 5-8 percent investment
savings and 5 percent operational cost savings
So if you are willing to use DME as a motor fuel (and it has been done) then you can get the costs down even more…
IMHO, the path to freedom from OPEC does not run through a multi-$Trillion “20+ year” change of all our vehicles to some other power source (be it hydrogen, electricity, whatever). What I’ve termed the “Fleet Change” problem. The path to energy freedom runs directly through F-T conversions and Zeolites. Feedstock can be any of: Coal, trash (paper, cardboard, animal by-products), wood chips, “yard waste”, biomass (from trees and switchgrass to corn stalks and farmed algae), and any other carbon containing material. The products are gasoline and Diesel that can be run in the exiting fleet and through the existing fuel delivery systems. The costs are lower than OPEC derived fuels and the money would stay in our home country.
Why this is not being done is a really big “Dig Here”…