08/03/2018

Types Of Biofuel

By htblog Biodiesel 0 Comments

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