Biofuels - Alcohols
Most ethanol made from plants at present is made from corn. However for every unit of energy used to produce it, the process yields only 1.4 units of energy. A profit, but not much.
Sugar cane in Brazil has a profit of 8X. Agave in the arid regions of Mexico, and sugar palms from the tropics, sugar beet from the cold areas, are promising much better energy profits than for corn.
Energy from cellulose covered in the next page is promising to be very profitable. Same for seaweed.
The numbers vary with: the region, the climate, the soils, the accounting method, and the story teller. It is impossible to get a definitive answer to which is the best process.
Every process claims to be better than corn.
Biofuels - Ethanol from sugar
Biofuels are fuels made from any life form. Here we will divide them into alcohols and oils. Bio-char will be included with oil.
Producing ethanol by fermenting sugar or starch is ancient technology. (man's most ancient chemical reaction, after fire and cooking) Nowadays we are developing ways of extracting the sugar from more difficult sources such as cellulose and the alignate in seaweed.
Biofuels face tremendous problems in replacing oil from underground. It is unlikely they will be able to. They require too much agricultural land. At present the total biomass harvested from crops, wood, and waste, is equivalent to 20% of our liquid fuel energy use. It is unlikely we will be able to increase this dramatically.
There are many different processes being researched and trialed. It is impossible to tell which is the most suitable as everyone is out to sell their process and will sometimes, shall we say, present their project in the best light.
Octane number (RON) is a measure of how much the fuel can be compressed before igniting. This allows higher compression ratio. Higher compression means higher temperature. Higher temperature means higher efficiency.
Click on images for source and more information.
(Note: there is quite a variation in reported octane numbers.)
Glucose, starch and cellulose
The sun’s energy falling on chlorophyll combine carbon dioxide with water, producing carbohydrate, mainly glucose. The name says it: carbo-hydrate.
A plant will often store the glucose as a more stable for starch. The glucose is stacked in a simple regular pattern.. Starch is easy to ferment.
To make cellulose, the plant stacks glucose so it alternates. This forms crystals and is very stable. Cellulase enzymmes can break it down into sugar for fermentation
Glucose - is a 6 carbon sugar - easy to ferment
An excellent summary of carbohydrates can be found at:
Starch - glucose stacked same side up - easy to ferment
Cellulose - glucose stacked alternately - must be pretreated then split with cellulase enzymes to make glucose available
Sugar for ethanol
Sugar for ethanol comes from: sugar cane, sugar beet, Sugar palm, and agave.
The debate is whether food crops should be used for fuel. The fuel option is keeping the food prices high so there is commercial and political pressure in this debate.
The other question is over how much energy is used to produce the ethanol.
Sugar cane grows in most tropical countries, but Brazil has taken the production of ethanol much more seriously than anywhere else. Ethanol is 25% of all petrol, but this varies according to the crop yields. Because the cane waste fibre, bagasse, is used to power the sugar and distillation processes, the production of this ethanol has a very low greenhouse footprint.
One third of the world's sugar comes from sugar beet. Most of it is grown in the colder parts of
So the beet must be processed as soon as possible, meaning the mill must operate only in the season and be idle the rest of the year. Cane sugar has the same problem. This capital lying idle increases the cost.
There is a new beet called “energy beet” and is being used for ethanol. There are plans to produce ethanol in UK. Although the beet mill will run only during the season, the distillery would run 365 days a year.
Sugar palm covers several species of palm producing sugar.
Arenga pinnata (syn. A. saccharifera)
Nypa fruiticans or Nipah is a palm classified as a mangrove growing in SE Asia and northern Australia
Nipah has a very high sugar-rich sap yield. According to one study (Hamilton and Murphy 1988), nipah sap can produce 6,480-15,600 liters of ethanol per hectare, compared to 3,350-6,700 liters/hectare from sugarcane and 2,000 litres/Hectr/yr for corn.
Agave is a native of Mexico and is used to produce tequila and rope. Agave-derived ethanol has been shown to have the potential to produce good yields on hot, dry land with minimal environmental impact.
Professor Remigio Madrigal Lugo Autonomous University of Chapingo.
Sugar palm - Nypa fruiticans
Ethanol from starch
The plant stores sugar as starch, cellulose, or hemicellulose. These are covered in the next two pages.