With all the talk about Ethanol lately, why not use Hemp as a source? Hemp doesn’t need fertilizer or pesticides and requires a lot less irrigation than corn. Wouldn’t it be a better source of the cellulose needed to produce ethanol?
In simple terms, ethanol can only be produced from sugar and starch. Hemp contains very little of either. Instead hemp contains large amounts of cellulose, which produces methanol (wood alcohol) when fermented. Methanol is toxic, doesn’t burn very well in engines and you get relatively little of it in return for the input material.
Hemp certainly does need fertiliser, as any grower will tell you. Hemp perhaps needs less pesticide than maize at the moment because it is only grown on a small scale. Put a couple of thousand million hectares under hemp and watch the bug population explode. I have never seen any suggestion that hemp requires any less pesticide than cane.
Huh? How can it require less than nothing? IIRC most of the world’s maize is a dry land crop.
Ethanol isn’t produced from cellulose. It is produced form corn starch or cane sugar.
If we just want cellulose we plant trees, which can grow with no fertiliser and no water in conditions that are totally unsuitable for any other form of agriculture. We don’t grow a rather finicky and wasteful crop like hemp on prime agricultural land.
I don’t know where people get the idea that hemp is some sort of magical wonder crop. It isn’t. I suspect that Cecil was right, people with no interest in or knowledge of agriculture are enthusiatsic about hemp because they see it as some back door way to legalise pot.
Just to add to Blake’s excellent analysis, even if the technology to produce cellulosic ethanol becomes practical on a large scale, there are many other native plants (switchgrass, for example) that would be a better choice than hemp.
I’m hearing more talk about switchgrass all the time. Is it kinda like alfalfa? Something you plant once, and it comes back for several years without replanting, doesn’t need fertilizer, herbicides, or pesticides, and is easy to harvest?
I hear that the corn-based ethanol plants being built in Iowa are using almost as much energy as they’re producing, so it seems like other options should be explored.
But I worry that the herbicide/pesticide/fertilizer interests – not to mention the farm implement people – will do their best to push corn and nothing else.
Corn is definitely being pushed by the corn lobbies. Which is unfortunate, since corn isn’t really well suited for ethanol production. I’m not familiar with alfalfa, but switchgrass is a grass that’s native to the American prairie. The prairies are a fairly dry place, so switchgrass shouldn’t require much in the way of irrigation.
Kinda. It’s a perrennial bunch grass, which means that it grows back from the stump every year. Like all crops it will need fertiliser, herbicides and pesticides once it goes into commercial production. With any luck though it should require less of those things than many alternatives.
You heard wrong. Maize based ethanol plants use much more energy than they produce. They are net energy consumers. The best thing you can say about them is that if the energy comes entirely from renewables or nuclear then they are carboin neutral. Essentially they enable us to convert nuclear or wind electricity into vehicle fuels. Theyd don’t produce any energy whatsoever and they consume quiet a lot.
The biggest push at the moment comes from the maize growers themselves, rather than from chemical companies.
You’re correct but entirely wrong in what you are talking about.
Maise plants are energy inefficent if you factor in the energy used to produce them which is provided free of charge by the sun and earth.
Outside of that you are completely wrong.
Site
http://www.ethanolinvestments.com/Does_it_take_more_energy.pdf
Here is another that explains it simply
Site
You really need to read past the headlines.
And if your tractors run on solar power, and your fertilizers are made out of light, and if you don’t have to process the corn into ethanol. Now, it is not inconceivable that all of these factors could be made energy-efficient, in which case corn ethanol would become energy-positive. But the technology isn’t there yet, so for the moment, it’s still a net loss. If you want to convince folks otherwise, find one example, anywhere, of an ethanol production facility which doesn’t ship in petroleum derivatives.
Oh, and you gave the same link twice, there, for your two cites.
Chronos
You didn’t read the whole article did you.
It says that the cost to plant and harvest is only .87 and the processing cost is .89 . So as it says add the 2 numbers and find that it takes 1.76 to produce 2.83 gallons of ethanol. So now we only have the cost of fertilizer.Dunno.
I don't know if his .87 tractor fuel is biodiesel or not.
So why does anyone care if they do or do not ship in petroleum derivitives?
I don’t even care if they power their boilers with natural gas.
On the other hand Blake hasn’t put a cost on producing nuclear powered cars or checked out the even stated the cost to produce a solar powered car.
Sorry about the 2 sites. I lost the url for the other one.
This is a 1995 study.
From
http://www.carbohydrateeconomy.org/library/admin/uploadedfiles/How_Much_Energy_
Does_it_Take_to_Make_a_Gallon_.html
HTML1DocumentEncodingutf-83. How do we divide the energy used among
the products produced?
If we add the amount of energy currently used in growing corn on the average farm to the
amount of energy used to make ethanol in the average processing plant today, the total is
81,090 BTUs per gallon (Table 1, Column 1). Under the best-existing practices, the
amount of energy used to grow the corn and convert it into ethanol is 57,504 BTUs per
gallon. Ethanol itself contains 84,100 BTUs per gallon. Thus even without taking into
account the energy used to make co-products, ethanol is a net energy generator.
But an analysis that excludes co-product energy credits is inappropriate. The same energy
used to grow the corn and much of the energy used to process the corn into ethanol is
used to make other products as well. Consequently, we need to allocate the energy used
in the cultivation and production process over a variety of products. This can be done in
several ways.
One is by taking the actual energy content of the co-products to estimate the energy
credit. For example, 21 percent protein feed has a calorie content of 16,388 BTUs per
pound. The problem with this method is that it puts a fuel value on what is a food and
thus undermines the true value of the product.
Another way to assign an energy value to co-products is based on their market value.
This is done by adding up the market value, in dollars, of all the products from corn
processing, including ethanol, and then allocating energy credits based on each product’s
proportion of the total market value. For example, Table 4 shows the material balance
and energy allocation based on market value for a typical wet milling process. Here the
various co-products account for 43 percent of the total value derived from a bushel of
corn, and thus are given an energy credit of 36,261 BTUs per gallon of ethanol.
check out the site for the real straight dope
As I mentioned above this is a 1995 study. Don’t have current data. Consider the technical advancements in the last decade.
What the hell are you on about? The financial costs are totally irrelevant to everything Chronos, Myself and AuntiPam posted. We are discussing the energetic costs.
The simple fact is that to produce one joule of ethanol enegry it takes more than one joule of energy input in the form of fertilisers, transport, refining, irrigation, cultivation, storage etc
That is because nobody but you has mentioned the financial cost. You don’t seem to understand that financial cost and energetic cost are not the same.
Just want to clarify, we’re talking about limitations of efficiency, not thermodynamics here, aren’t we?
Well I guess it’s true on both counts. 
But yeah, we’re talking limitaions in the technology. As the technology improves and the processing plants get larger we might eventually break even, but not today.
Why? They sell all kinds of farm implements.
Corn planters & pickers, true. But also the cutters & balers used by grass hay (and probably the same would be used for switchgrass or prairie grass). And the plows, cultivators, and fertilizer applicators would be much the same for any such crop.
No reason for the implement people to push any particular crop. In fact, they do best when farmer grow a mixture of several crops, so they need both corn pickers, grass cutters, wheat combines, etc. Implement dealers (and nearly everybody else in farming communities) have an incentive to support ethanol, but no particular crop – just any starch crop that grows well in their area.
Why no talk about using sugar beets?
Last I heard (from friends in the Minnesota-North Dakota Red River Valley, a big sugar beet growing area) was that the leftover beet pulp was more valuable for animal feed than it would be for ethanol production. But that was a couple years ago, when gas was only about $1.50/gallon.
That’s after it’s been crushed to extract the primary crop of sugar though, isn’t it? What about growing it specifically to use that primary crop for ethanol production? (and still selling the pulp byproduct for animal fodder)
I think the cart got in here before the horse. Why hasn’t there been research to determine which plants are most efficacious for producing ethanol, before the farm lobby decides that corn is the chosen crop. As I recall, corn is one of the more soil depleting crops. Are we simply trading one set of problems for another.
As far as hemp, I’m certainly not advocating it to ease the way for marijuana production. Nor am I claiming that it’s a good source of bio-fuel.
Hemp makes a very fine paper w/ much less processing that wood pulp, while take up much less space to cultivate than trees. Hemp fibers do not require chlorine bleaching, like wood fiber, a process that is the source of much river pollution. Hemp also makes an excellent cloth and there are other byproducts, such as oil from the seeds.
Do you have cites for these claims? And, please, cites that are NOT from a pro-legalized-marijuana site.
Yes, of course, the sugar is extracted first. I would think that would always be true. It’s the pulp that contains the starch used for ethanol, I thought.