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Algae Biofuels — Why Not Now?
September 2, 2012
odern societies are built around cheap energy that has been extracted for about 150 years. Our food, shelter, transportation and lifestyles consume massive amounts of fossil fuels. Globally, peak oil occurred in 2008 even though demand for fossil fuels continues to increase. Consequently, fuel prices continue to rise while supplies diminish.
Fossil fuels are composed of algae fossilized under tremendous pressure and heat over 400 million years. Therefore, anything made from fossil fuels can be made from algae. Algae biofuel production is sustainable and occurs in weeks rather than eons.
Algae biofuels are not a practical substitute for coal or natural gas for making electricity. Algae biofuels are excellent substitutes for fossil liquid transportation fuels that include ethanol, biobutanol, hydrogen, gasoline, diesel, aviation gas and jet fuel.
Fossil fuel extraction and use create severe economic and ecological damage. Most of the cheap crude oil has been extracted from easily accessed land areas. Additional supplies lie in difficult terrain such as the artic circle or deep in oceans. Hard to access oil supplies not only drive up oil prices but amplify the probability of spills that create ecological catastrophes. Extracting and burning fossil fuels not only create a heavy carbon load for the atmosphere but also spread damaging black soot particulates on ice packs, cities and homes.
Renewable algae liquid transportation fuels provide three critical values for human societies. Unlike fossil fuels that damage human, animal and ecological health, algae biofuels can:
- Be produced with abundant rather than fossil resources, thereby saving those resources for our next generations.
- Recover, recycle and repurpose waste stream nutrients that not only avoid pollution but regenerate air, soils and water while producing biofuels.
- Recycle carbon dioxide, reducing the carbon load while burning clean, with no black soot particulates. (Algae biofuels burn cleanly because they are not fossilized; they are similar to vegetable oil.)
How are algae biofuels made?
Algae are most productive when the cells have access to solar energy. For algae, oil production is strategic and operates as stored energy and access to light. Algae that produce oil tend to move closer to the top of the water column because oil is lighter than water. Algae have no natural propulsion so oil production enables access to more photons that fuel photosynthesis. In natural settings, typically the algae specie on top holds the most oil.
Recent technologies enable producers to scan thousands of algae cells to find those that produce robustly and rapidly while offering high oil content, often around 40%. Some producers stress the algae by withholding a nutrient such as nitrogen, which causes the algae to protect itself by overproducing oil.
The harvested algae biomass undergoes lysis, which bursts the cells and enables the oils to float to the surface of the liquid. Lysis may occur by solvents such as hexane, enzymes, electrical, mechanical pressure, (press) or lasers. Carbon dioxide acts as the supercritical fluid when pressurized and heated to change its composition from gas to liquid. Supercritical CO2 mixed with the algae extracts nearly 100% of the oil, but the process is more costly than other oil extraction methods.
Producers refine the algae oil to the target biofuel, bioplastics or fine green chemicals. Oil refining uses transesterification on the fatty acid chains. An alcohol such as methanol and an ester compound are mixed to create a reaction to produce a different type of alcohol and ester. The same process is used to make polyester fabrics. Esters are chemical compounds in which an acid has had one of its hydroxy groups – a molecule of hydrogen and oxygen bonded together – replaced by a molecule of oxygen. The transesterification chemical reaction converts algae oil to biodiesel.
Considerable R&D focuses on alternative methods to convert algae oil extracts to biofuels including enzymatic conversion, catalytic cracking and sweating algae oil. Enzymatic conversion employs natural or synthetic enzymes to do the transesterification work. Catalytic cracking is used to convert the high-boiling, high-molecular weight hydrocarbon fractions of fossil crude oil petroleum to gasoline and other products. Catalytic cracking produces more gasoline with a higher octane rating than thermal cracking and provides more valuable compounds.
Sweating algae oil offers novel solutions to several challenges. Growers chose an algae species that has no cell wall such as blue-green algae, cyanobacteria, or a highly permeable cell wall. Producers use either GMO algae or accelerated evolution to train algae to release oil naturally. The algae culture does not have to be harvested, saving considerable time and cost. Growers “milk” the algae and the oil rises to the top of the water column where a skimmer removes the oil. The algae oil can then be refined using traditional methods. Alternatively, a few algae companies have developed genetically modified species that sweat 90- octane gasoline that requires no conversion.
The residual biomass, mostly protein and carbohydrates, may be used for food, feed, nutrients, fertilizers or many other products. Large-scale algae biofuel production will generate substantial feed for animals and plants. Typically, biofuel protein co-products are insufficiently clean for use in human foods. However, one of the strongest benefits from biofuel production is the R&D lift that will benefit all algae producers.
Why not now?
Algae biofuels make so much sense; several companies have invested millions of dollars trying to develop one or multiple fuels. Those companies have not succeeded because scale-up from the laboratory is far more complex than expected. Total scale for biofuel cultivation requires hundreds and possibly thousands of acres. Construction costs require investment of hundreds of millions of dollars and operational costs are non-trivial. With current technologies, the probability of a large-scale culture crash poses too much risk for most investors.
Each step of the algae-to-biofuels process needs additional refinements including species selection, inoculation, culture growth, culture metrics and automation, harvest, dewatering, oil separation and refinement. Breakthroughs in each of the areas will make algae biofuels production reliable and economically competitive within a few years. Fortunately, excellent minds are working on algae innovations that will benefit all human societies.