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 Made  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

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