Science Forums 2

[CraigD]

Originally Posted by Michaelangelica

Someone wrote about an American plant Gopher Weed on these forums some time ago. i can't find the post.
Apparently you can just turn that sstraight into usable (CO2 producing?) oil.

Gopher weed (I think it’s the sativa variety of Camelina) sounds like a cool plant – able to grow productively in poor soil and climate, a high-quality, healthy food-grade oil-producing plant.

As to the question “What plants might be grown, just for bio-fuel?”, I suspect this could be any of them, or none. All of the food-grade vegi oils (including corn oil) filtered properly to remove solids, make good pure oil fuels. Perhaps there is one that doesn’t taste good enough for food, or is unpopular for health reasons (like palm oil), so would be valuable only as a fuel, but I’ve never heard of it, and have no reason to suspect that the best plant fuel oils aren’t also good food oils. A near bit of tech trivia is that Rudolf Diesel’s first engines were designed to run on peanut oil (a nice, low-viscosity oil), then modified to use petro-based kerosene because the latter was (and still is) cheaper to produce (source: Vegetable oil used as fuel - Wikipedia, the free encyclopedia).

Though it’s not quite true that any diesel engine and fuel system can easily be modified to run on pure vegetable oil, many of them can, and there are a number of mature systems, companies, and user communities existent now – see Straight vegetable oil as diesel fuel: Journey to Forever. No ethanol, gasoline, or other additives or refining processes are required – though good filters, fuel line heating, and other elaborations are.

AFAIK, the big drawback with vegi oil as a fuel now is not engine system design, fuel distribution, etc, but cost. As of 2007, the average cost of vegetable oil in the US – sold as a food - is $10.28/gallon. The stuff is about as energy-dense as petro-diesel, which currently has a average US cost of $3.803/gallon. Not a huge difference – about 270% - but enough to keep businesses and ordinary consumers from flocking to it, even if the capability to produce it in large quantities existed.

Waste vegi oil – popular because it can be had essentially for free from restaurants, which currently have to pay to have the nasty stuff carted off – takes a good bit of refinement, involving separating, pH adjusting, and other complicated and energy-expensive stuff. There’ll never be enough WVO available for large-scale needs, though, only for the niche market that exists while demand for SVO and bio-diesel is tiny.

The main challenge presented in the use of plant oil as a petro-fuel replacement, as best I can see, is production. Consider the following, based on the goal of America becoming fuel-self sufficient through the near 100% replacement of petroleum with plant oils:

• From https://www.cia.gov/library/publicat.../print/us.html, the US oil consumption rate (in 2004) was 318,008,565,000 gal/year.
• From United States Fact Sheet: US agriculture income population food education employment farms top commodities exports counties financial indicators poverty organic farming farm income America USDA, the US had 945,530,000 total acres of farmland in 1992, 938,280,000 in 2002, about 1/3rd of it actually producing crops in a given year.
• From Vegetable oil yields, characteristics: Journey to Forever, we have the following oil yields for various plants:
  • Corn: 18 gallons/acre/year
  • Peanut: 113 gallons/acre/year
  • Coconut: 287 gallons/acre/year
  • Palm: 635 gallons/acre/year

Doing the math, we find that, for the US to grow enough plant oil using all of its farmland (ignoring the need to grow food) to meet 100% of its current oil needs, requires a productivity of about 335 gallons/acre/year, a rate reached only by palmseed. Palmseed and coconut, the 2 top-producers, are tropical plants, however, not effectively growable in the US (former rainforest apparently is ideal palmseed-growing land). The best US-growable crop appears to be peanut, at 113 gallons/acre/year.

At first glance, the goal of America becoming fuel-self sufficient through the near 100% replacement of petroleum with plant oils appears unachievable. Some refinements to the data make it look a bit more feasible:

• Only about 50% of current petroleum use could not practically be replaced by other fuels and energy sources. What’s left are primarily vehicles, which require an easy-to-handle, portable fuel.
• Vehicle fuel efficiency is currently at historic lows. It’s reasonable to assume that, as part of an industry-wide shift to specialized plant-oil-burning diesel engines (or even better systems – closed-cycle steam, perhaps?), efficiency could be about doubled.

Taking this into account, the required production rate becomes about 85 gallons/acre/year. In principle, then, the US could become completely renewable oil based with about 705,000,000 acres of continuously producing peanut.

It’s a close call, however, and ignores issues like emissions. I’ve heard accounts that plant oil combustion bi-products are in some areas cleaner than petroleum, but think that, for approximation purposed, they’re about the same as present-day diesel, worse than present-day gasoline. For CO2 emission, I believe essentially all carbon-based fuels are roughly equivalent

When considering possibilities for large-scale oil production, one rather disturbing possibility can’t be ignored. The oceans, we know well, are rich sources of plant energy. Until the mid 19th century, US demand for oil – about 15,000,000 gallons/year, primarily for lamps and machine lubricants - supporting a thriving industry based on an efficient natural converter of aquatic plants to high-quality, readily obtainable and refinable oil – whales. (source: ”How the Oil Industry Saved the Whales”)

Using modern techniques to increase breeding rates and weed-out undesirable wild traits – essentially domesticating oil whales – it’s conceivable that a renewable oil supply exceeding than any land-based agriculture could be created. Personally, I cringe at the though of an industry based on the wholesale slaughter of vast numbers of intelligent animals, and hope this outlandish (I can’t recall having heard it before this post) possibility is never realized.

Yeah solar.