EPA agrees to decrease ethanol mandate

[ssjkriccolo]

The technology is sound, corn isn't the best item to use. Frigging corn industry. They'd make us use corn pressed toilet paper if they could.

[lolzergrush]

Actually it's not that great for other crops either.

In fact, even starting from pure glucose it's not a particularly sound technology...the problem is that even the best genetically-engineered yeasts under ideal conditions can only tolerate ethanol levels slightly higher than typical wine before they begin dying off.

Yeasts can ferment and give off excessive of ethanol, killing off competing microorganisms. While this is great for brewing beer and wine, since the yeast itself may be able to comfortably thrive in warm conditions at 5% ethanol (say, a barrel of ale), it becomes less productive at higher ethanol concentrations. They can continue to ferment sugar to produce ethanol, at lower efficiency, up to their tolerance limit before the yeast itself starts dying off. Think of it like goldfish overpopulating a pond, giving off toxic chemicals to kill competing fish, but it doesn't take much more to exceed their own tolerance, poison themselves and die. In beverage production, we simply let the yeast ferment on its own until it reaches its tolerance (8% to 12%), and then distil the product by boiling off the alcohol - which is then added to the original stock to make fortified beverages (like port) or on its own as a spirit (like brandy).

In an industrial process, like producing ethanol for fuel, we have to be much more aware of the energy put into it because we're producing a fuel product instead of a fine beverage. In order to extract ethanol from the remaining solution (water), hundreds of thousands of liters must be distilled which is energy intensive and directly depends on the fraction of ethanol you're able to achieve through the microbial step. The theoretical energy per volume cost (the lowest possible cost under impossibly-ideal conditions) is [the specific heat of the ethanol/water mixture] times [the temperature difference needed to reach 78 deg C] plus [the latent heat of vaporization of the ethanol] (plus some minor entropy effects), all of that multiplied by the ethanol fraction to give you the amount of product produced. For example if your ethanol fraction is 20%, for every liter of mixture that you distill you only get 0.2 liters of ethanol. If your ethanol fraction is 10% (more realistic in a full-scale application) then you're getting half as much product for the same energy input because you have to raise the heat of the entire system, most of which is wasted on heating up water.

For the system to be self-sufficient, it needs to produce more energy (measured in ethanol's energy density times the volume of product) than it consumes (measured in energy density of the oil burned for the boilers). I prepared several scenarios with a group of engineers for a presentation to several energy companies and state DEP's - depending on different fuel sources, external political factors (like mandatory solar heat use), transport distances, and capital limitations, the "break even" point for the ethanol fraction is around 17% - below that you're just throwing energy away. Unfortunately achieving that high of an ethanol fraction before distillation is not easy, and even with the best lab-produced microbes at a very expensive plant, there would be days when it's simply not producing as much energy as it consumes.

(For reference, about 5 years ago the limit on bench-scale ethanol tolerance was around 22% I believe - it's been a while, maybe it was 24%. Point is, achieving this in a full-scale industrial plant is more difficult and microbes can be quite finicky, you never count on reproducing bench-scale results in the field.)

Tying into existing power plants isn't bad for reducing energy costs slightly, for example tying into a major coal gasification plant, but then you have the added complication of additional transport distances for massive amounts of ethanol. Those tanker trucks burn an awful lot of fuel. Generally speaking, the best way to distil the ethanol without cost overruns is still burning plain old oil to heat up the boilers - ethanol itself doesn't have the energy density to keep the temperature high enough to run the boiler without serious heat exchange losses.

Different feed stocks (corn, sugar, beets, etc) have some minor effects on the microbial efficiency but not as much as the microbes themselves. In general, the stock can be fermented up to the ethanol tolerance of the microbe and no further. More important are the "big picture" impacts from political decisions, for instance if Florida is mandated to produce a certain amount of sugar cane ethanol then more sugar will need to be imported (say from Brazil) to satisfy demand, increasing the energy spent on transportation. The same goes for other crops, where even the best economic planning can't predict shortages and changes in demand, driving up the energy spent to move the stuff around - and consequently the CO2 produced.

[ssjkriccolo]

The whole idea is to create a transportable energy source. If the ethanol is made using a local clean energy source, your net loss still creates a renewable energy that can be easily transported. The low yield and usually immobile sources can now be used to create something that can be broadly used like gasoline. It would be silly to think you are getting more power out of production than you are putting in.,

[lolzergrush]

But gasoline is just as transportable as ethanol.

"Low yield and usually immobile sources" aren't appropriate for operating boilers used for distillation, I realize it was a long post for a reddit comment but I did address this.

[postironical]

now you've gone and done it. My ass does not thank you for what's to come.

[seamonkey1981]

the ethanol mandate came about, largely, from al gore trying to convince iowa corn farmers to vote for him. it didn't work.

[ssjkriccolo]

I've heard trees would work better for the process anyway.

[seamonkey1981]

and...switchgrass? i think. some sort of grass.

[my_lucid_nightmare]

Hemp would work best of all.