• Due to ongoing issues caused by Search, it has been temporarily disabled
  • Please excuse the mess, we're moving the furniture and restructuring the forum categories
  • You may need to edit your signatures.

    When we moved to Xenfora some of the signature options didn't come over. In the old software signatures were limited by a character limit, on Xenfora there are more options and there is a character number and number of lines limit. I've set maximum number of lines to 4 and unlimited characters.

CO2+H20+?->CH4 or C8H18

Meadmaker

Guest
Meadmaker
Joined
Apr 27, 2004
Messages
29,033
I was thinking about ethanol one day. I think corn based ethanol grown in temperate latitudes is really stupid. I would much rather eat the corn.

While discussing it one day, I found myself saying, "There has to be a more efficient way to capture sunlight than by using chlorophyll to produce one organic compound, then using yeast to make a different compound, then burning that compound." Surely, there must be.

The crux of the problem is that we are growing corn, then throwing away most of the corn plant, but taking some of the captured sugar, then converting it to alcohol which we can burn. It's a marvel of nature that plants evolved to convert energy like they did, but when we want to capture energy, we aren't limited to those things which were randomly created and then survived because they happened to increase reproductive capacity of similiar molecules.

Plants take energy from the sun and using some complex chemistry convert CO2 to sugar. Do we know enough to describe any way that we can take CO2 and water, and end up with some burnable compound, using the energy of the sun, but not going through some complex chain of living organisms? Chlorophyll is a wonder of nature, but surely we can find something better suited for industrial use?
 
CO2 to burnable products is a tricky one since it is already fully oxidised. You have to put lots of energy in to convert it to usefully burnable products.

There are a couple of processes that produce gasoline from lower hydrocarbons. The Fischer-Tropsch synthesis WP converts CO and hydrogen (syngas) into long hydrocarbons. This process is traditional transition metal redox catalysis using metals such as iron or cobalt.

There is also the Mobil "Badger" process, also known more usefully as the MTG (Methanol to Gasoline) process WP. This process uses an acidic catalyst (Zeolite Socony-Mobil 5) to build up long hydrocarbons from methanol, either biological in origin or from natural gas.

Both of these processes can be economically viable, if the price of crude oil is high enough.
 
A couple questions:

For the F-T process, whats the source for hydrogen ?

For the MTG process, whats the source for methanol?

You can't get energy out that hasn't been put in. Catalysts will save on the energy needed to make bonds, but will not add energy that isn't in the substrates.

What is needed is some catalyst or enzyme that will put the energy from the sun into the substrate made from corn stalks. Not an original concept, I which I had 1% of the funds being spent on it today.
 
I know virtually nothing about biofuels. But if I were to design a research project, I would try to bioengineer and algae that could produce hydrocarbons. No planting, no harvesting: grow it in tanks anywhere with sun. Doubling times could be hours. Centrifuge it, extract the oil.

Sounds simple. Almost too simple...

Wait, who's that at the door?!

AAAAH! It's the ExxonMobil Police Swat tea.....................................
 
From the first link:
Extensive research is currently being conducted to determine the utilization of microalgae as an energy source, with applications being developed for biodiesel, ethanol, methanol, methane and even hydrogen. Independent studies have demonstrated that algae is capable of producing 30 times more oil per acre than the current crops now utilized for the production of biofuels. Algae biofuel contains no sulfur, is non-toxic and highly biodegradable.

The Office of Fuels Development, a division of the Department of Energy, funded a program from 1978 through 1996 under the National Renewable Energy Laboratory (NREL) known as the "Aquatic Species Program." The focus of this program was to investigate high-oil algae that could be grown specifically for the purpose of wide-scale biodiesel production. According to the release, some species of algae are ideally suited to biodiesel production due to their high oil content, in excess of 50%, and extremely rapid growth rates.
Click to expand...

Like I said, it sounds too good to be true. There must be a catch.
 
ah. From the second link:

Making biodiesel from algae is not easy, but it might be worth the trouble because of economies of scale. ...(snip)... And second, bringing algae to an industrial scale for biodiesel production, takes time and money.
Click to expand...

If there are algae out there that are 50% oil, and it seems there are, someone will find out how to make this work. sounds much more promising than ethanol from cellulose.
There have been successful projects using the CO2 from smokestacks to speed up the algae growth, adding in the possibility of a carbon credit and increasing yield per acre per year. This presents a great opportunity for the power plants because it is taking something with a cost associated with it, CO2 emissions, and turning it into something of value, liquid fuel.
Click to expand...

genius. Use waste CO2 from burning fossil fuels to increase the yield of biodiesel.
 
Evilgiraffe said:
CO2 to burnable products is a tricky one since it is already fully oxidised. You have to put lots of energy in to convert it to usefully burnable products.
Click to expand...

I understand that. (I wish everyone did, especially the people who cite hydrogen as a perfect fuel because you can get it from water.) I just know that plants do it, but I figured that there might be a way to figure out what they are doing, and use a non-plant based method to do the same thing, but with a solar power input.

Thanks, everyone, for inputs. I, too, had wondered about using algae as a source. One thing I wondered was how much water would be used up. I pictured a closed tank which would theoretically mean that all the water could be recycled. However, I suspect that in practice there would have to be at least some water loss. I wondered if, when all was said and done, the energy required to make it wouldn't be more than the energy extracted, because of the need to pump in water.
 
Much of the water could be recovered. Plus, it's not like water is not used for irrigating the corn used in biodiesel. Even oil extraction often involves pumping water into the ground to help force the oil out, IIRC.
 
casebro said:
A couple questions:

For the F-T process, whats the source for hydrogen ?

For the MTG process, whats the source for methanol?
Click to expand...

I believe all of the feedstock for these processes is currently sourced from fossil fuels. Gassification of coal gives CO and H2 for the F-T process and steam reforming of natural gas gives methanol for the MtG process.

This is obviously unsustainable but they are useful for converting difficult to handle fuels into more useful, energy dense forms.
 
You must log in or register to reply here.
Back
Top Bottom