For many years, GreenTech
leaders have been saying renewables are never going to make
a major contribution to our energy needs until we have a better
method for storing off-peak clean energy. For even longer,
environmentalists and national security analysts have been
seeking an alternative to fossil oil for our transportation
For more than five years, we at Doty Windfuels have been working
on “RFTS”, for Renewable
Fischer Tropsch Synthesis. The process will use off-peak excess
wind energy to recycle CO2 into standard fuels that
work seamlessly in the one billion cars and trucks on the road
today around the
world. The chemistry is fundamentally simple and well understood.
First, variable off-peak energy is used to electrolyze water
into hydrogen and oxygen; some of the hydrogen is used to reduce
CO2 into CO and H2O in
a catalyzed reaction called Reverse Water Gas Shift (RWGS);
the balance of the hydrogen is combined with
CO in a Fischer Tropsch reactor to form a synthetic oil – a
mixture of mostly gasoline, jet fuel, and diesel, just like the
stuff from petroleum, but with no contaminants. The co-produced
oxygen from the electrolysis is a valuable by-product.
Fischer Tropsch chemistry has been well understood for seven decades. During
World War II, Germany synthesized some of its fuel by combining CO and H2 (derived
from coal) in an FT reactor. Today, this process is commonly referred to
as coal-to-liquids, or CTL. South Africa has the longest history of FTS generation
of fuels. Unfortunately, traditional coal-to-liquids production is more environmentally
destructive even than tar sands or oil-shale based petroleum because of its
enormous on-site release of CO2. However, if the H2 is obtained
from water and excess carbon-neutral energy, and the CO is derived from CO2,
are carbon neutral, as we explain in greater detail on other pages on this
There is no question that it should be possible to synthesize standard liquid
fuels from CO2 and water using off-peak clean energy. The only step that
has not been commercialized is the RWGS process – reducing CO2 to CO.
The question has not been whether such a system would work, but whether it
compete with traditional petroleum derived fuels.
Our analysis concludes that if the correct paths and system design are chosen,
overall system efficiency (from input electrical energy to output energy
in the liquid fuels) will exceed 58%. If done at a reasonable scale, the
fuels will sometimes compete when oil is as low as $50/bbl – and always
when oil is above $95/bbl. After the R&D phase, the equipment capital
costs are expected to be low enough to be recovered in 2 to 3 years. Our
to develop a process that will allow the world to replace the use of petroleum
and tar sands with clean, competitive, carbon-neutral fuels synthesized efficiently
from CO2 and off-peak clean energy.
One of the team’s recent technical papers: Toward Efficient Reduction
of CO2 to CO for renewable fuels. shows that the somewhat related direct-solar-fuels
processes face daunting practical barriers because of fundamental laws of
thermodynamics governing equilibria in one or more of the required steps.
The RFTS process, on the other hand, eliminates such bottlenecks by starting
with electrical energy rather than thermal energy or photons to get the needed
hydrogen. The technology for electrolysis is mature and efficient. After
the electrolysis, there are no highly endothermic reactions, so there are
no reactions that are difficult to get to work.
CARMA-GTL – A bridging technology. In
spite of the above reasoning, thus far general enthusiasm for
Windfuels has been limited – essentially for one valid
reason: the current cost of electrolyzers. While analysis shows
ROI (return on investment) should be attractive for Windfuels
even at current electrolyzer and fuel prices in some regions,
the capital outlay for the electrolyzers would be beyond what
most investors wish to consider in today’s risk-averse
That has motivated us to begin developing a less expensive “bridging” approach
to synthesizing fuels from a combination of CO2, methane, and
renewable energy. The outcome of this research is a process we
have dubbed CARMA-GTL, for Carbon dioxide Advanced Reforming
of Methane Adiabatically, with GTL. As explained later, as long
as low-cost natural gas is available, our CARMA-GTL process reduces
the electrolyzer requirements by a factor of three to ten while
actually increasing efficiency.
The Demand for Oil. The strong upward trend
of the past three years in the price of oil is bringing gasoline
prices back into the media spotlight. We expect to be showing
by the time the public is again insisting on solutions that show
real promise for competing with OPEC.
Windfuels provides the potential for the U.S. to transition from
the worlds largest importer of oil to the world’s largest
exporter of carbon-neutral transportation fuels.
The company is working on scaling windfuels plant designs down as small as
practical with acceptable efficiency and capital cost, since changes in the
financial markets argue that the more likely scale-up path would be thousands
of 10-MW plants though out the wind corridor rather than a much smaller number
of GW plants near large nuclear reactors. Recent simulations are showing 45%
efficiency at the 2-MW plant size, 53% at 20 MW, and 58% at 250 MW.
of Cheap, Off-peak Clean Energy. The “Windfuels” moniker
is apt because the vast majority of the inexpensive,
clean, off-peak energy that has come online in the past several
years in the
U.S. has been wind, but nuclear energy may be the best option
in some places. A few facts here put the scalability, climate
benefit, and expected competitiveness of Windfuels into perspective.
Approximately 10 TWh (yes, 10 tera-watt-hours) of wind energy
was curtailed (idled) in the U.S. last year to keep the off-peak
grid energy price from frequently going negative. That is
more than the energy in 200 million gallons of gasoline – thrown
away. Curtailed wind energy is the U.S. appears likely to
continue to grow.
Economically recoverable wind energy potential in the U.S.
exceeds 70 PWh/yr – enough energy to synthesize twice
the current U.S. transportation fuel needs and supply all our
• Point-source CO2 emissions
in the U.S. total about 4 Gt/yr – enough
to synthesize twice the current domestic transportation fuel
usage – about 0.7 Gt/yr. Windfuels are expected to
be 85% carbon neutral (fully burdened), while most domestic
are only 5-15% carbon neutral when land-use change is fully
One of the greatest advantages
of RFTS is that the electrolyzers would be well positioned to
stabilize the grid by ramping up
or tamping down in real time to adjust to the amount of excess
energy on the grid. This will eliminate negative pricing and
curtailment, and ensure that the fuels are completely carbon-neutral
(100% of the energy entering the electrolyzers will be matched
by additional energy coming onto a grid from otherwise curtailed
renewable energy). More information can be found here.
(Note: Much of the above
appeared on GreenTechMedia on 2/2/2011,
and a lively discussion followed.)
Choosing the Best
Chemical Paths. It is useful to look briefly,
in broad strokes, at some of the reasons why our synthesis choices
lead not only to the best option for a renewable fuel today,
but also for many decades to come.
There are a number of options
for converting CO2 and
water into liquid fuels – and we have looked
carefully at all of them. Unfortunately, with the perspective
we gained, we concluded that there is nothing that looks like
more than a minor percentage of the world's fuels. All may play
a part, but there is something (like land use for biofuels)
that will limit their
scale up to the demand. In our view, only our RFTS (process 7)
can be scaled to provide enough transportation fuels.
1. Make ethanol from biomass.
2. Make biodiesel using microalgae and solar energy.
3. Use genetically engineered cyanobacteria and solar energy to make gasoline
4. Use extremely concentrated solar energy (at above 1100 K) to make gasoline
and diesel from CO2 and water.
5. Inject renewable hydrogen into conventional CTL plants.
6. Use stranded wind energy to make methanol or ammonia.
7. Develop a novel CARMA-GTL process that is as efficient as possible,
scalable from 2-200 MW, that can make all the fuels and chemicals we need
from CO2, shale gas, and
Below, we look briefly at
the above options, some of which are discussed in more detail
in a 2010 ASME-ES paper, “Deployment Prospects for Proposed
Sustainable Energy Alternatives in 2020”.
1. Ethanol from biomass.
Most of the cellulosic ethanol plants are now failing financially,
even though they are using feedstocks
that are currently nearly free (sometimes even at negative
price), and they are getting a high price plus subsidies
for their ethanol. They are generally located in areas where
their feedstocks will remain nearly free for at least several
years – in some cases even for a decade. However, the
only truly competitive use for biomass today is in home heating
and co-firing in coal power plants. The demand from these markets
exceeds the total potential biomass supply in most regions
of the world by factors ranging from 2 to 100. The global average
is probably 14. That is, the global demand for home-heating
and co-firing exceeds the total potential biomass supply by
a factor of 14.
When we already know that the market demand for biomass for
home-heating and co-firing could exceed the available supply
by a factor of 14 within two decades – and
possibly much sooner – it is foolish to advocate making ethanol from
a feedstock that will become extremely expensive. Also, using biomass for fuel
will inevitably place upward pressure on the price of food. Both of these applications
use limited resources on this planet – land, fresh water, nutrients,
and human labor.
2. Biofuels from microalgae. This
is undoubtedly the most distorted alternative of all alternative
research has been well supported financially for three decades.
Our analysis (beginning six years ago, and updated
annually) of the various approaches using photosynthetic microalgae
has concluded that photosynthetic algae will never produce
fuels for under $90/gal – except as a co-product during
the treatment of waste water. Some fuels will be able to be
made profitably from waste-water (sewage) treatment facilities
because the municipalities must pay to have the sewage treated
anyway, and it probably doesn’t cost much more to make
fuels at the same time. The amount of fuels that can be made
profitably from waste-water treatment could supply about 0.5%
of the total demand.
A recent DOE-supported study (Lawrence Berkeley
National Laboratory) thinks that photosynthetic algae without subsidy from
waste-water treatment will eventually be produced for $10/gal. Of course, the
authors of this study have all been supported (at least to some extent) by
DOE grants for the development of fuels from algae.
The data clearly show otherwise. HRBP spent $22M and showed they could produce
fuels from microalgae for $40,000/gal. GreenFuels spent $70M and showed they
could produce fuels from algae for $200,000/gal.
Algenol will spend $35M of your tax dollars (DOE plus local support) along
over $70M from partners and investors over the next few years. They claim they
will produce ethanol from a genetically modified hybrid microorganism at the
rate of 100,000 gal/yr from a 40 acre demonstration facility. The upper-level
managers of Algenol have a 25-year history of over-stating what they will achieve
by factors of 100 to 10,000.
Algenol’s CEO finally let a useful cost number out. They are expecting
their photo-bioreactors (PBRs) in large scale production will cost $10M/ha.
So if they spend $60M on PBRs, they will be able to afford 6 ha (14.8 acre)
of PBRs. The best, credible, short-term, algae production we have see (by Seambiotic)
would produce diesel fuels at the rate of 5400 gal/ha/yr in race-track ponds.
A reasonable assumption is that long-term production in PBRs might exceed short-term
production in ponds by 30%. If the fuel from the micro-organism is ethanol
rather than jet fuel, an additional 60% gain in production volume might be
possible. So perhaps Algenol will produce ethanol at the rate of 67,000 gal/yr.
If they produce 67,000 gal/yr, and if their bioreactors last 20 years, and
if their operating costs are all included in the initial estimate of $100M
total, they might be producing ethanol for $127/gal, or $200/gge (gallon gasoline
equivalent). However, we suspect their PBRs (which are more fragile and complex
than most) will only last 7 years. In which case their ethanol could could
cost $256/gal, or $400/gge.
Sapphire has even bigger plans. They will spend over $120M of your tax dollars
plus at least $300M of investor’s dollars over the next 4 to 6 years.
They might be producing 250,000 gal/yr by 2016 from the initial 400 acres being
developed. If their facility then produces steadily with relatively low operating
and maintenance costs for 20 years, the fuels they produce will cost about
$160/gal. However, with likely O&M costs, their fuels could cost $200/gal.
3. Gasoline from cyanobacteria. The PR
campaign of Joule Unlimited made Direct Solar Fuels one
of the hottest
topics in 2011. They claim they will produce
gasoline from genetically engineered cyanobacteria at the rate
of 15,000 gal/acre/yr. A peer-reviewed paper with some semblance
of scientific objectivity has recently appeared:
From this and other materials, it appears reasonable to expect
that highly engineered cyanobacteria could be 70% more efficient
than microalgae. The theoretical
gross solar efficiency limit for bioenergy from cyanobacteria is 12% – the
same as the theoretical limit for bioenergy from microalgae. The theoretical
limit for motor-grade fuels from microalgae products is probably 7%, as there
are losses associated with turning lipids and carbohydrates into motor-grade
fuels. Note that gross solar efficiency is defined as the ratio of the energy
in the fuels to that in the incident solar energy, and it ignores all the other
energy inputs, which thus far have generally exceeded the energy in
the fuels produced – often by a factor of 2 to 5. One of the best references
here is by Williams and Laurens, 2010,
The promoters of Joule Unlimited continually make numerous claims
that are simply not supported by any data or valid reasoning. First of all,
they claim that 12% efficiency is 7 times the theoretical limit for microalgae.
This is plain disinformation. A practical gross solar efficiency has been
in the range of 1-3%, but the losses have much less to do with the nature of
the hydrocarbons produced than with many other factors that will still limit
practical efficiency from cyanobacteria. A few of these cost factors will be
reduced a little by cyanobacteria that can directly produce mostly alkanes
rather than mostly lipids, triglycerides, proteins, polysaccharides, etc. The
problem of separation of the desired products from the culture is also reduced
with cyanobacteria compared to most microalgae approaches – though Algenol’s
approach is similar.
The PBRs needed by Joule Unlimited to get 15% of the gain they are counting
on will probably cost 20% more than those Algenol finds acceptable (where we
expect their fuels to cost $200-400/gge). Thus, if there is a
70% inherent theoretical advantage for motor-grade fuels from highly engineered
cyanobacteria compared to highly engineered microalgae, plus a (possible)
20% cost savings associated with reduced harvesting costs, a reasonable estimate
is that the fuels produced by Joule Unlimited could cost $110-180/gge from
a $100M facility. However, it appears their first demonstration will likely
be less than 5 acres of the 1200-acre site (that was earlier to be 5000 acres)
in Hobbs, New Mexico. Our suspicion is that Joule will go the way of GreenFuels,
as all of their publicly released information looks the same – nothing
but marketing hyperbole.
4. Fuels from super-concentrated
solar heat. Solar Driven
Thermo-chemical Conversion (STCC) uses highly concentrated
solar energy (much more concentrated than PowerTower CSP) in
attempts to produce standard liquid fuels (or just hydrogen)
from CO2, water, and sometimes methane. Government
research support (especially in Switzerland, Germany, the U.S.,
the UK) has grown rapidly over the past four years, though
this is an area that has received very little public and investor
attention. STCC is related to Windfuels RFTS in that it seeks
to produce standard liquid fuels from CO2 and
water via a syngas (CO+H2) route.
Some of the processes are referred to as “dry reforming”, carbo-reduction, “solar
water splitting”, and many more. In fact, we should point out that there
is no standard name, but we refer to all as STCC for convenience.
The best experimental results for STCC thus far have achieved under 2% efficiency
(most have been under 0.1%), at enormous costs (over $50/W), and from apparatus
having very short useful lifetime – sometimes only a few days.
Sadly, these results are as we projected from our theoretical analyses many
years ago. Since we have presented more details on the fundamental challenges
facing the various STCC processes in a recent publication here (and since STCC
appears to be falling out of favor), there is no reason to belabor the point
here. We simply note that we believe STCC is much further away from being economically
practical than microalgae.
We should emphasize that while there are some similarities between the chemistry
of STCC and RFTS, the similarities end there. The economics are worlds apart.
If you have any doubts – just follow the above link to get a better appreciation
for challenges facing STCC.
For comparison, the Windfuels RFTS processes show 45% efficiency will be practical
in a small (2 MW) plant, and 55% efficiency can be expected at 80 MW. Moreover,
the cost of the source energy in Windfuels will be much less because it will
use cheap, off-peak wind energy and thus allow renewables to grow without any
concerns about grid stability. STCC, on the other hand, cannot do anything
to improve grid stability.
5. Inject renewable hydrogen into
CTL plants. Coal-to-liquids
(CTL) plants get the CO (carbon monoxide) needed in the Fischer
Tropsch (FT) reactor from partial oxidation of coal. Some of
the CO can then be reacted with steam in the water-gas-shift
(WGS) reaction to get the hydrogen also needed in the FT reactor.
Both of these processes (especially the second) also produce
a lot of CO2, which is vented. If renewable hydrogen – as
from wind energy – is used instead of CO followed by
WGS, the total amount of CO2 released is greatly reduced. Not
surprisingly, coal supporters are advocating injecting renewable
H2 into CTL plants to make them sound cleaner.
There are problems with this concept. The first problem is
that the economics don’t make sense. The biggest part
of the cost in CTL is cleanup of the syngas (the CO +
H2) before it goes to the FT reactor. The clean-up
process is still required and just as expensive even if some
H2 is used during
off-peak hours, but now one also must add the electrolyzers and deal with variable
rates in the partial oxidation reactor. The economics for using renewable
H2 work only if one completely eliminates the expensive
gas cleanup problems – the gas cleanup cost is the largest
reason for FT’s reputation of being expensive and not
workable at small scale.
6. Wind methanol, DME, and ammonia. The company
Blue Fuel Energy http://www.bluefuelenergy.com/index.html ,
begin a rather large scale demonstration of methanol production
from CO2 and water using stranded wind energy. This is clearly
a much more competitive and scalable option than any of the
preceding options (other than Windfuels). They expect to pay
about $55/MWh for the energy from an exceptionally windy ridge.
Some researchers have said that methanol production
can work efficiently with the right catalysts starting with
just CO2 and H2 in the syngas,
but commercial methanol production processes always begin with
a mixture of CO2+CO+
the syngas, and (wisely) that is what Blue Fuel Energy plans to use. They will
get the needed CO by sending some of the CO2 and
H2 through an RWGS
The methanol can then easily be made into dimethyl ether (DME), and the DME
can easily be made into gasoline, though there are efficiency losses of
at least 5% for each step along the way. The company plans to sell all three
products – methanol, DME, and gasoline.
The problem with this plan lies in the economics. Blue Fuel Energy plans to
operate from largely stranded wind – wind with little other market. Our
model for Windfuels, on the other hand, is to operate primarily from off-peak
wind – which is less than one-third as expensive because the wind farms
are largely supported by the high prices they get for their energy during peak-demand
Many others (most famously, the late Mat Simmons) have advocated making ammonia
from stranded wind energy and air. The process is straight forward, but again
the problem lies in the economics. Ammonia from stranded natural gas is much
cheaper, and will remain cheap for decades. It is true that ammonia could be
used as a motor fuel, but ammonia is much more hazardous and less efficient
than hydrocarbons or ethanol, so ammonia will never be accepted as a motor
fuel. There is a strong and growing need for ammonia for fertilizers, but that
need will be met by natural gas and coal for decades.
Returning to Blue Fuel Energy, we expect they will not make money from carbon-neutral
methanol, as methanol from coal is much cheaper per unit energy than any other
liquid fuel – usually about half as expensive as diesel. Demand for methanol
blending into gasoline will be limited (as that makes the gasoline more toxic
and less suited for hot climates), and there is also not likely to be much
demand for carbon-neutral DME. DME has numerous drawbacks as a motor fuel compared
to gasoline, ethanol, diesel, and propane. We suspect most of their methanol
will be converted to gasoline, for which there is a strong market. The price
per energy for jet fuel and diesel is stronger than for gasoline, but a simple
process for efficiently making jet fuel or diesel from methanol, DME, or gasoline
has not been developed.
7. RFTS – Make
jet fuel and diesel from off-peak wind.
This is where we started at the top of this page, and we will not repeat those
comments here, but rather go a little further into the technical justification
One advantage of RFTS is that it is extremely flexible. If market conditions
change, it will be relatively easy to change the primary product emphasis from
jet fuel to gasoline or diesel.
The primary basis for the sentiment against FTS is the perception that it is
capital intensive, and that it cannot be made competitive at small scale – because
there are too many complicated sub-processes. Indeed, that’s what Shell,
BP, Sasol, and other big oil companies would have you believe – because
they don’t want a small company to even think of trying to compete. (But
you probably already know that you can’t believe everything big oil says.)
There has also been considerable sentiment against FTS on the basis that the
reaction products are not highly selected, so much more effort is required
in the separations than for methanol synthesis, for example. However, the advances
in our patents and proprietary technology now make that a non-issue.
It is important to appreciate how much easier it will be to scale down a Windfuels/CARMA
plant than a conventional FTS plant making diesel from coal or natural gas.
The biggest single factor driving conventional GTL plants toward large scale
is that it has been very expensive to get the high-purity oxygen they need
for partial oxidation in the syngas production at a plant size below 30,000
bbl/day. This, of course, is not needed in the RFTS plant (we don’t need
high purity oxygen – we produce it). The other major drivers toward large
plants have been the costs of syngas clean-up and product upgrading. Both of
these are now greatly simplified. The CO2 coming into the RFTS plant will be
three orders of magnitude cleaner than coal, and its final cleanup is much
simpler for other reasons too. Elsewhere on this website some of the innovations
that further help are discussed in more detail – but naturally, some
The arguments against biomass to liquids (BTL), as advocated by Enerkem and
Rentech, are even more compelling:
(1) Biomass has half the energy density of
coal, so transportation and initial processing costs are doubled;
(2) Biomass has more impurities than coal, and of greater unpredictability,
so syngas cleanup costs are 50% greater from biomass than from coal;
(3) BTL plants are always much smaller, because the feedstocks are not
available nearby in sufficient supply for large BTL plants;
(4) The BTL feedstocks are usually much more expensive after the first few
(5) The BTL companies are usually not motivated to make the process competitive – they’re
primarily motivated by the value of the initial PR.
(6) The waste stream from BTL is greater than from CTL.
Of course, when the feedstock is at negative price, as it
sometimes is, BTL should work. But there is only the potential
for enough negative-priced biomass to supply 0.5% of our demand
for liquid fuels.
it is important to emphasize that the FTS reactor, when properly
designed, can be scaled down by
more than four orders of magnitude from typical commercial
CTL or GTL sizes with little effect on cost effectiveness,
general design, or engineering parameters. (The diameter of
the tubes used in the FTS reactor will be the same whether
the fuel production is 3 gal/day or 30,000 bbl/day.) The same
is true of most of the other major plant components except
the waste heat conversion, so efficiency suffers a little at
smaller scale. Still, our detailed simulations are showing
33% efficiency at the 200 kW size, 45% efficiency at the 2-MW
plant size, 53% at 20 MW, and 58% at 250 MW.
The other major difference
between our approach and that of some other groups advocating “closing the carbon cycle” (making
fuels from CO2) is that we have concluded the best
routes will all begin by reducing CO2 to CO in an
RWGS or CARMA process. Others have said that it would be better
to instead put several
decades of work into developing catalysts that might make it
possible to get the desired level of conversion and selectivity
with the CO2 and H2 sent directly into an FT reactor.
There have been a number of laboratory experiments suggesting
might eventually be possible; but if the slow progress over
the past decade is a valid indicator, it is many decades away.
The Windfuels RWGS-FTS and CARMA processes, on the other hand,
will work today.
Making an RFTS plant work optimally requires numerous changes compared to a
fossil-diesel FTS plant. Not surprisingly, many of the features disclosed in
detail in the pending Doty patents are somewhat at odds with current trends
in the design of fossil-diesel plants (most notably, the primary separations
processes, waste heat utilization methods, the reactor design, and operating
conditions). However, the bottom-line results from the simulations speak for
themselves. The combination of the various innovations permits a factor of
two increase in efficiency compared to what most have expected, and capital
costs will be less than those for a cellulosic ethanol plant of similar capacity.
1. S Phillips, A Aden, J Jechura, and D Dayton, “Thermochemical
Ethanol via Indirect Gasification and Mixed Alcohol Synthesis
of Lignocellulosic Biomass”, NREL/TP-510-41168, 2007. http://www.nrel.gov/docs/fy07osti/41168.pdf
2. M Xiang, D Li, H Qi, W Li, B Zhong, Y Sun, “Mixed
alcohols synthesis from CO hydrogenation over K-promoted ?-Mo2C
catalysts”, Fuel 86, 1298-1303, 2007.
3. JE Whitlow and C Parrish, “Operation, Modeling and
Analysis of the Reverse Water Gas Shift Process”, 2001
NASA/ASEE summer program, JFK Space Center, http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020050609_2002079590.pdf
4. PL Spath and DC Dayton, “Preliminary Screening – Technical
and Economic Assessment of Synthesis Gas to Fuels and Chemicals
with Emphasis on the Potential for Biomass-Derived Syngas”, http://www.fischer-tropsch.org/DOE/DOE_reports/510/510-34929/510-34929.pdf , NREL/TP-510-34929, 2003.
5. X Li, L Feng, Z Liu, B Zhong, DB Dadyburjor, and
DL Kugler, “Higher
Alcohols from Synthesis Gas Using Carbon-Supported Doped Molybdenum-Based
Catalysts”, Ind. Engr. Chem. Res. 37, 3853-3863, 1998.