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Offline paulyt

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Ethanol Question - Please help
« on: 22/07/2007 17:07:38 »
Hi please could someone help my confusion.  I am interested in ethanol as an alternative and renewable fuel but I am confused as to why so much emphasis is placed on producing ethanol with wheat and other grains, surely if ethanol is produced by fermentation and distillation then would it not be more efficient to ferment raw sugar rather than grains?


 

another_someone

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Ethanol Question - Please help
« Reply #1 on: 22/07/2007 17:14:30 »
Raw sugar has to be produced from something - most commonly from sugar cane or sugar beet.

I suspect that grains are simply cheaper and simpler to grow, so there is a probably cost advantage (in both money, and as importantly, in energy and materials) is using cereals rather than sugar beet or cane.

Bear in mind that the drinks industry itself has always tended to use grains or fruit for fermentation, with grain generally being used for the cheaper alcoholic beverages.
 

Offline paulyt

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Ethanol Question - Please help
« Reply #2 on: 22/07/2007 17:36:15 »
Thanks for your reply. I suppose there must be some cost advantage as you say, you would imagine that there would be more sugar content in sugar cane than wheat.
 

another_someone

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Ethanol Question - Please help
« Reply #3 on: 22/07/2007 18:53:09 »
Thanks for your reply. I suppose there must be some cost advantage as you say, you would imagine that there would be more sugar content in sugar cane than wheat.

Sugar per unit weight, maybe - but sugar per unit cost may well be different to sugar per unit weight, and if you have limited resources (money, energy, land, whatever), then your primary concern is how you can get the highest level of sugar within the available resources rather than what crop contains the highest level of sugar per weight of crop.
 

Offline Bored chemist

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Ethanol Question - Please help
« Reply #4 on: 22/07/2007 20:17:05 »
Industrial fermentation (including breweing beer) uses the starches as well as the sugars. The total carbohydrate content of grain is very high. It's also cheaper per ton than things like sugar beet.
If they can find a bug that will do the job well then fermenting cellulose would help even more.
 

paul.fr

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Ethanol Question - Please help
« Reply #5 on: 22/07/2007 23:02:54 »
Paul, most likely the push for ethanol from grain is because vast area's of the US are grain economies.
While ethanol can be produced from other plants - including corn, native US switchgrass, sugar beets and tapioca - sugar cane offers the highest energy balance of any ethanol option.

About one unit of energy input is required for every eight units produced, compared with 1.5 units of ethanol from corn, which is widely used in US biofuel, and 0.8 units of traditional gasoline from crude oil.

Take Brazil as an example, Brazil is the world's largest sugar cane harvester and producer of ethanol, with 16.5 billion litres in 2005. More than 90 per cent of gas stations sell ethanol alongside conventional fuel - and even the latter is a mix of one-quarter ethanol and three-quarters petrol, the world's highest percentage.

But there is a price to pay, Brazil now exports less sugar cane to the rest of the world than it once did. I believe it was the, if not one of the largest exporters. This has lead to higher sugar prices.

The same will happen to corn, should there be a massive push to ethanol from corn. One plus is that what is left of the corn ,after being made in to ethanol, can be fed to livestock. The downside is, that there will be less corn for the human population.

We need to get the balance right. fast growing and high yielding willow is a good alternative, it can grow up to 15 foot a year and be harvested for ethanol every two years.

 

another_someone

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Ethanol Question - Please help
« Reply #6 on: 23/07/2007 06:34:12 »
But sugar cane is only really grown in tropical climates - it has never been grown in European climates, and I imagine it could not do so.
 

Offline eric l

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Ethanol Question - Please help
« Reply #7 on: 23/07/2007 09:06:26 »
Sugar or sucrose or sacharose is a molecule consisting of 1 glucose unit and 1 fructose unit.  Starch is a polymer of many glucose units, the same goes for cellulose.
In the currently used fermentation process, cellulose can not be easily fermented to ethanol. 
When you try to ferment sacharose (using the traditional process), the fructose part is not converted into ethanol - which means a yield reduction by 50 %.
Potatoes are also a source of starch, and are used to make alcohol (e.g. vodka), but need to be processed shortly after harvesting.
Cereals in general can be dried, so that when you transport 1 ton of grain, you easily transport twice the amount of starch compared to transporting 1 ton of potatoes.
There is of course a lot of research going on after processes for converting cellulose - and fructose - into alcohol, but for the time being, cereals are the best base product for making industrial ethanol.
 

Offline Bored chemist

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Ethanol Question - Please help
« Reply #8 on: 23/07/2007 20:08:17 »
My home-brew frements sucrose perfectly well thanks. It doesn't leave the fructose behind, if it did the density wouldn't fall to below 1. Fructose and glucose can be interconverted easilly enough by enzymes. That's where we get the high fructose corn syrup that is alegedly responsible for so much obesity.
http://en.wikipedia.org/wiki/HFCS
The yeast must have a similar enzyme.
 

paul.fr

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Ethanol Question - Please help
« Reply #9 on: 23/07/2007 20:12:52 »
But sugar cane is only really grown in tropical climates - it has never been grown in European climates, and I imagine it could not do so.

This is where balance and diversity come in. Brazil does a wonderful job with sugar cane, but it's not for everyone. Which is why i reccomended willow as an alternative to grain.
 

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Ethanol Question - Please help
« Reply #9 on: 23/07/2007 20:12:52 »

 

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