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Study shows gasoline pre-blending in ethanol production could cut energy requirements of separation by 17-40%

Researchers at the University of Witwatersrand and the University of South Africa are proposing replacing the final purification steps of conventional bio-ethanol production with a simple gasoline-blending step.

In a paper published in the ACS journal Energy & Fuels, they show that gasoline pre-blending results in a spontaneous liquid phase split which produces a viable fuel with desirable ethanol content and high recovery of ethanol; reduces the energy requirements of separation by between 17 and 40%; reduces operating costs of the process; and also eliminates capital expenses.

The most prevalent use of bioethanol is not as a fuel in its pure form but rather as an additive to petrol. Conventional processes, however, fully purify bioethanol prior to blending it in petrol. This is an energy-intensive and costly process and is typically achieved through distillation. This paper examines the possibility of blending partially purified fermentation products directly into petrol, allowing for the spontaneous liquid-phase separation to eliminate the bulk of the remaining water without the addition of separation energy.

… The nature of the fermentation process dictates that fermentation products are dilute, comprised primarily of water. For bioethanol to be used as a fuel, this water must be eliminated. This separation is conventionally achieved using distillation. Because distillation requires the evaporation of liquids, it tends to require substantial energy inputs. This is exacerbated in this case by the high heat capacity of water and the existence of a binary azeotrope in the ethanol/water mixture, resulting in a particularly energy-intensive separation process. This paper examines the possibility that some of this energy consumption can be alleviated by the use of simple flowsheet improvement.

—Stacey et al.

Conventional fermentation processes to produce ethanol make use of either one or two distillation columns that produce an azeotropic mixture (a mixture of liquids that has a constant boiling point because the vapor has the same composition as the liquid mixture) of water and ethanol. This precludes the use of simple distillation to produce pure ethanol. Azeotropic distillation—the introduction of another component (an entrainer) to produce two immiscible liquid phases—delivers the final purification.

The South African researchers are proposing replacing the final purification step with a simple liquid-liquid phase split, thereby eliminating between 17.3 and 40.8% of the total separation energy, potentially saving between 0.916 and 2.04 MJ/L of ethanol produced.

The proposed approach uses equipment already in place is used for the bulk of the separation, but uses a two-stage liquid−liquid extraction to transfer ethanol into gasoline in the overflow stream while eliminating water in the underflow stream. The wastewater stream will still contain ethanol and should therefore be recycled to the distillation circuit if possible, to improve overall ethanol recovery. Click to enlarge.

In their study, they found that blending 8.75 L of gasoline for each liter of ethanol in the azeotropic mixture yielded an enriched gasoline stream with an ethanol content of 10% while achieving an ethanol recovery of 97.5%.

The process can also be modified slightly to cater to different objectives in terms of ethanol composition. For example, a two-stage blending process with a blending ratio of 48 delivered an ethanol content of 2% and an ethanol recovery of 99.9%.

It is important to put this result into context. Globally, over 20 billion gallons of bioethanol are produced per year. Most of that bioethanol is purified for use in fuels, using energy-intensive azeotropic distillation methods. Converting even a fraction of those existing processes to instead use the direct blending method would result in energy savings on the order of terajoules per year, cutting global carbon dioxide emissions significantly while reducing the cost of renewable fuels. The content of this paper sets out the groundwork for developing processes to achieve this goal.

It must also be noted that this approach is equally applicable to the separation of other alcohols for fuel usage. Ongoing work is underway to develop a similar process for biobutanol separation, with the expectation of even larger energy savings, owing to the fact that butanol is a less polar molecule and will therefore tend to dissolve into the fuel phase more preferentially than ethanol, allowing for a lower purity mixture to be blended while achieving the desired recovery and alcohol content.

—Stacey et al.


  • Neil T. Stacey, Aristoklis Hadjitheodorou, and David Glasser (2016) “Gasoline Preblending for Energy-Efficient Bioethanol Recovery” Energy & Fuels doi: 10.1021/acs.energyfuels.6b01591



Of course, instead of blending EtOH it could be held separately and used as an octane-on-demand additive to prevent knock under high-power conditions.  The downsized, high-compression engines this allows would save far more fuel than is displaced by blended ethanol.

EtOH used as an octane booster can contain even more water than the solvent-extracted input shown here; it can easily be 20% water.  This would require much less energy input than even this new, improved scheme.


This scheme would also work on old Lycoming and Continental aircraft engines that now burn 100 low lead (which is actually only lower in lead content that old military grade 130/150 octane fuel).


Will the fuel systems tolerate EtOH?  I seem to recall that the STCs for autogas use required non-gasohol.


Sounds like a really good idea to me.
Biofuels are far from perfect, but if we can generate them with less energy input, what's not to like ?
There is no reason to assume you can't use this with "non-food" crops.


NYT- "More than one-third of our corn crop is used to feed livestock. Another 13 percent is exported, much of it to feed livestock as well. Another 40 percent is used to produce ethanol. The remainder goes toward food and beverage production.Jul 30, 2012"

I see up to date the ethanol portion of the corn harvest is reduced from 40 percent to one-third, but one-third of that corn is returned as high value live stock feed. Feed that is actually contains all the valuable protein of the original corn and added nutrition of natural distillery fermentation leftovers. So, not much here to fret over when using corn first as starch feed stock for ethanol. Also, we must tabulate the coproducts of ethanol production that often go unaccounted for. The vegetable corn oil for example. Non the least the new cellulosic processes that are just getting started to contribute to the ethanol production. These dry grind plants are expected to quickly adapt the very cost efficient process and push ethanol to 3.1 gallons per bushel with additional corn oil. They expect to advance to accepting a portion of field corn stover in future as well that will push production 50% or so.

Notice the Times report that "food" is merely 14% of a bushel if doing the math. Most of that has to be for corn syrup of which is of modern day health concern giver our saturation of commercial food with the sugar. So, fear not of starving. Note the fattening of cattle with corn is under scrutiny as well given the unhealthy fat production profile.


I will take issue with the comment the "ethanol" is far from perfect fuel".

One will have to put that into perspective as if ethanol is far from perfect, gasoline must be a disaster. The quality of ethanol from purity ratings and exact chemical makeup is about perfect as consistency goes from production of the simple compound verses crude oil myriad chemical complexity and formulations. So, you tell me the ease to control combustion and emissions as comparing the two fuels. Consider ethanol anti knock character of which is one of the primary drivers of engine efficiency. Ethanol the champ. Compare the cost of oxygenates, pollution, emissions, octane boost and one would conclude ethanol the champ. Ethanol's high flame speed propels engine efficiency as well that translates to higher engine torque. Ethanol's ability to decrease combustion temperature results in a decrease in NOX emissions. How about small business job creation upon domestic companies.

You see our automotive manufacturers have just starting to optimize ethanol fuel portion of our fuel. So, the path forward is much brighter for ethanol abilities as compared to fossil fuels that have decades of optimizing done to make the fuel efficient.


What should be the EPA actions be to decrease environmental and unhealthy vehicle emissions? First given the convenience, cost effectiveness, and current fleet of cars one would presume any motor fuel that minimizes the emission damage these vintage cars produce would be priority number one. Seems higher ethanol blends would come to the rescue on that one and do so at a cost savings. Even our four cycle small engines, especially if the fuel character was consistent and the small engines were actually tuned to proper air fuel mix.

Second I can see no advantage to emissions if comparing an efficient ethanol hybrid as opposed to battery grid power cars. Meaning, both should be receive incentives to proceed at a quicker pace. EPA federal and state should afford battery car incentives to a high efficient ethanol vehicle. Note, that for ethanol to advance and optimize the fuel's natural ability for carbon efficiency, there is a need to drop the gasoline portion. Also, that pure ethanol would require a new range of technology to advance. It's does not require break through technology, just experimenting with typical engineering choices and the experience that proceeds out. Already, Cummings have demonstrated that down sizing, down speeding an E85 vehicle produces more torque than diesel and better mileage than gasoline. Read their test data to gain info that E100 is superior to E85 with efficiency gain. That half sized engines will produce more power than modern day typical engine technology. Were talking of better than diesel torque, higher efficiency, and upon a cheaper engine as compared to diesel. The fuel cost per mile about the same or lower. Emissions much lower. Forget gasoline. The fuel doesn't compete.


Distillers Dried Grain goes to feed live stock after ethanol is made. Using corn stalks and cobs produces ethanol, four cellulose ethanol plants in the mid west have been doing this for years.


In 2015, only 123 million gallons of cellulosic ethanol were required by the EPA (127.64 million RINs generated).  This was about 4% of the EISA requirement.  The shortfall was due to woefully insufficient capacity.  There is no direct translation from RINs to gallons linked on the page or its associated spreadsheet.

For the uninformed, 123 million gallons is less than 3 million barrels.  The USA consumes almost 9 million barrels of gasoline per day; cellulosing EtOH was less than 0.1% of US gasoline-equivalent consumption, and less than 0.05% of total petroleum product consumption.

Whoever thinks cellulosic anything is going to replace petroleum is smoking something strong.



Most of the older aircraft engine fuel systems are not made compatible with ethanol. However, if you ran a new separate ethanol or ethanol/water injection system to prevent detonation, this would not be a problem. This was actually done on a number of WW2 aircraft to prevent detonation at high power setting and low altitude and is currently used on race planes. A similar system was also used on the 1983 turbo-charged Oldsmobile F85 Starfire.

To use such a system on certified aircraft would require additional certification. However, with experimental aircraft, this would not be a problem. I am currently building an experimental aircraft with a turbo-charged Rotax engine. While it is possible to run 100 LL, it is not recommended. The best thing is to run high octane gasoline without ethanol but it is better to run E-10 autogas than 100 LL.


Cellulosic ethanol is in daily production. Soon to be three dry grind plants with the capability. This is low volume production stuff, nonetheless successful application of cellulosic with very comfortable margins. Payback is in months. If all dry grind plants would add the ability and most analysis believe they will, the corn kernel feed stock will produce one additional billion gallons of cellulosic and apparently the industry is planning for those plants to up production to two billion cellulosic gallons. This is good for cellulosic, to have daily production, as the learning curve will never end.

Poet's large cellulosic plant is operational, but without production quantities. This year I believe they finished the commissioning phase. New processes and new equipment will make for a large environment for just about everything to go wrong. They had problems with stover bale dirt, corrosion of pumps, and production bottlenecks. They did run a railroad car of production then shut it down. They claim the process is capable of production, but the current economics of the market make the gallons produced a net loss. I would suppose this is the case for all the stover cellulosic plants. Gasoline goes to $4/gallon, Katie bar the door.


Farmers have found they can take all the stover off the field if they plant a cover crop.


Source ascr-discovery magizine 9/16

The magazine article has a good description of cellulosic ethanol process problems. The major cost of cellulosic fuel is not the feed stock, it's the enzymes. Below, they describe why so much expensive enzyme additive is needed. Also, note that the science is indicating a path of enzymatic hydrolases in which lignin left overs provide an excellent feed stock for the valuable chemical industry.

"A critical question was how lignin interacts with hydrolases to convert cellulose to simple sugars for fermentation into ethanol. Bioengineers knew lignin inhibited enzymatic reactions but not how. Using simulations, Petridis, Smith and colleagues showed that lignin binds to the hydrolase enzymes in the exact location where those enzymes bind to cellulose to cleave it apart, effectively blocking the decomposition reaction".

"scientists Charles Wyman and Charles Cai, who were trying to figure out why pretreatment with a common, nontoxic chemical solvent, tetrahydrofuran (THF), made ethanol production from cellulose more efficient.
So the ORNL-UT team went to work with molecular dynamics simulations. The calculations showed that THF inserts itself between lignin and cellulose, Smith says. “It stops the lignin and the cellulose from sticking to each other and stops the lignin from sticking to itself.” The strategy could prove useful as a way to split off lignin, Petridis adds, which could prove useful as DOE researchers look for ways to use other biomass components to produce energy and other useful products".


For news on biofuels, I suggest:



I wrote "1983 turbo-charged Oldsmobile F85 Starfire". It should have been "1963 turbo-charged Oldsmobile F85 Starfire". Over 50 years ago!

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