A long time ago in a galaxy not so far, far away someone had the novel idea to take plant matter and convert it to liquid fuel. What started with first generation (or conventional) biofuels has rapidly evolved to biofuels made from 'sustainable' feedstocks and beyond.
Now. Before the comment board fills up with comments pertaining to the terrible Star Trek / Star Wars references – Biofuels: The Next Episode just didn't have the same ring to it.
Biofuels have been getting a lot of attention lately from everyone from multinational oil companies to President Obama. But what exactly are they talking about? And are we all talking about the same technology? The short answer is no.
What I'd like to do here – as succinctly as I can – is provide a rundown of the different biomass-to-fuel technologies. So bear with me and if you think I've missed something 'mission critical' or glossed over a key issue please provide your two cents in the comments section!
First, a definition: biofuel is any fuel whose energy is derived from biological carbon fixation. What I will be discussing in this post is liquid biofuels that are being developed as petroleum replacements.
At the beginning we started with conventional biofuels (generation 1), which refers to fuel made from sugar, starch or vegetable oil. Bioethanol biofuel is the most common and is produced by fermenting plant sugars into ethanol. This technology has been getting a lot of attention in places like Brazil, the USA, Canada etc. Basically countries where a lot of corn can be grown at pretty low cost and there is some political will. Biodiesel is also pretty common, and growing due to favourable legislation in the US, and is produced from plant oils, sometimes waste oil. In the US most gasoline is now blended with 10% ethanol. Furthermore, the US recently reinstated the biodiesel tax credit along with changing regulation requirements under the Renewable Fuel Standard. According to the Energy Information Agency, replacement fuel use increased 187% between 2007 and 2011. This growth was led by biodiesel which grew by 240%! So that talk about fast food powering your car? – not so far off! It is also conventional (biofuel 1.0) that has probably generated the most controversy. There has been ample discourse on water requirements, carbon intensity, deforestation, and of course it has provided fodder for the food vs. fuel debate.
Next we have second generation, biofuels which refers to fuel made from lignocellulosic biomass such as woody biomass or agricultural waste. Second generation biofuels address some of the concerns about the sustainability of feedstocks. One of the challenges with lignocellulosic biomass is that the sugars are locked up in more complex carbohydrates (hemicellulose and cellulose), which can make it more difficult to break down for fermentation. A number of second generation technologies exist including thermochemical processes such as gasification, pyrolysis, and torrefaction, and biochemical routes using a pretreatment step such as ionic liquids, a strong acid, and/or enzymes to accelerate the hydrolysis process. This class of biofuels addresses some of the concerns around biofuel such as carbon balance, land use, and non-food based feedstocks.
And then we move on to 3rd generation biofuels, or advanced biofuels, which are fuels derived from algae and bacteria. This generation of biofuels is based on biological processes and is an area of intense R&D. Many species of algae naturally produce low levels of long chain fatty acids when they are stressed. Algae species can be screened and/or modified to increase the production yields of long chain fatty acids. Some of the leading edge research around maximizing algae growth and oil production involve treating algae with common antioxidants which has demonstrated increases in oil production by as much as 85% (UC Davis). Additionally, through synthetic biology, organisms such as e-coli bacteria can be manipulated to produce a drop in biofuel using sugar as a feedstock.
Well – there you have it. A quick high level rundown of the different classes of biofuels. Gen 1 biofuel or conventional biofuel is the main source of biofuel today. Gen 2 fuels and advanced biofuels are much further away from commercialization and are an area of considerable research by bodies such as the DOE and others. Alternative feedstocks and advances in the conversion technology make these next generation fuels promising contenders.