Types Of Biofuel

Biofuels, like fossil fuels, come in a number of forms and meet a number of different energy needs. The class of biofuels is subdivided into two generations, each of which contains a number of different fuels that will be explored in this article.

First Generation Biofuels

First generation biofuels are made from sugar, starch, or vegetable oil. They differ from “second generation biofuels” in that their feedstock (the plant or algal material from which they are generated) is not sustainable/green or, if used in large quantity, would have a large impact on the food supply. First generation biofuels are the “original” biofuels and constitute the majority of biofuels currently in use.

Second Generation Biofuels

Second generation biofuels are “greener” in that they are made from sustainable feedstock. In this use, the term sustainable is defined by the availability of the feedstock, the impact of its use on greenhouse gas emissions, its impact on biodiversity, and its impact on land use (water, food supply, etc.). At this point, most second generation fuels are underdevelopment and not widely available for use.

Biofuel Table

This table breaks biofuels down by generation and then explores their uses, energy densities, and greenhouse gas impacts. Specific biofuels from the table are selected for further exploration on subsequent pages.

Fuel

Feedstock

Energy Density

(megajoules/kilogram)

Greenhouse Gas

CO2(kg/kg)

Notes

First Generation

Bioalcohol

         Ethanol

         Propanol

         Butanol

Starches from wheat, corn, sugar cane, molasses, potatoes, other fruits

By Type

         30

         34

         36.6

By Type

         1.91

         N/A

         2.37

 

Biodiesel

Oils and fats including animal fats, vegetable oils, nut oils, hemp, and algae

37.8

2.85

 

Green Diesel

Made from hydrocracking oil and fat feedstock

48.1

3.4

Chemically identical to fossil fuel diesel

Vegetable Oil

         Castor Oil

         Olive Oil

         Fat

         Sunflower Oil

Unmodified or slightly modified

By Type

         39.5

         39

         32

         40

By Type

         2.7

         2.8

         N/A

         2.8

 

Bioethers

Dehydration of alcohols

N/A

N/A

These are additives to other fuels that increase performance and decrease emissions, particularly ozone

Biogas

Methane made from waste crop material through anaerobic digestion or bacteria

55

2.74 (does not take into account the direct effect of methane, which is 23X more effective as a GHG than CO2

Same properties as methane from fossil fuels

Solid Biofuels

         Wood

         Dried plants

         Bagasse

         Manure

         Seeds

Everything from wood and sawdust to garbage, agricultural waste, manure

By Type

         16-21

         10-16

         10

         10-15

         15

By Type

         1.9

         1.8

         1.3

         N/A

         N/A

This category includes a very wide variety of materials. Manure has low CO2 emissions, but high nitrate emissions.

Second Generation

Cellulosic ethanol

Usually made from wood, grass, or inedible parts of plants

 

 

 

Algae - based biofuels

Multiple different fuels made from algae

Can be used to produce any of the fuels above, as well as jet fuel

See specific fuels above

More expensive, but may yield 10-100X more fuel per unit area than other biofuels

Biohydrogen

Made from algae breaking down water.

Hydrogen compressed to 700 times atmospheric pressure has energy density of

123

Does not have any greenhouse effect.

Used in place of the hydrogen produced from fossil fuels

Methanol

Inedible plant matter

19.7

1.37

More toxic and less energy dense than ethanol

Dimethylfuran

MadeĀ  from fructose found in fruits and some vegetables

33.7

 

Energy density close to that of gasoline. Toxic to respiratory tract and nervous system

Fischer-Tropsch Biodiesel

Waste from paper and pulp manufacturing

37.8

2.85

Process is just an elaborate chemical reaction that makes hydrocarbon from carbon monoxide and hydrogen