Algae fuel
Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that use algae as the source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made from seaweed it can be known as seaweed fuel or seaweed oil. These fuels have no practical significance but remain an aspirational target in the biofuels research area.
History
In 1942, Harder and Von Witsch were the first to propose that microalgae be grown as a source of lipids for food or fuel. Following World War II, research began in the US, Germany, Japan, England, and Israel on culturing techniques and engineering systems for growing microalgae on larger scales, particularly species in the genus Chlorella. Meanwhile, H. G. Aach showed that Chlorella pyrenoidosa could be induced via nitrogen starvation to accumulate as much as 70% of its dry weight as lipids. Since the need for alternative transportation fuel had subsided after World War II, research at this time focused on culturing algae as a food source or, in some cases, for wastewater treatment.Interest in the application of algae for biofuels was rekindled during the oil embargo and oil price surges of the 1970s, leading the US Department of Energy to initiate the Aquatic Species Program in 1978. The Aquatic Species Program spent $25 million over 18 years to develop liquid transportation fuel from algae that would be price-competitive with petroleum-derived fuels. The research program focused on microalgae cultivation in open outdoor ponds, systems that are low in cost but vulnerable to environmental disturbances like temperature swings and biological invasions. 3,000 algal strains were collected from around the country and screened for desirable properties such as high productivity, lipid content, and thermal tolerance, and the most promising strains were included in the SERI microalgae collection at the Solar Energy Research Institute in Golden, Colorado and used for further research. Among the program's most significant findings were that rapid growth and high lipid production were "mutually exclusive" since the former required high nutrients and the latter required low nutrients. The final report suggested that genetic engineering may be necessary to be able to overcome this and other natural limitations of algal strains and that the ideal species might vary with place and season. Although it was successfully demonstrated that large-scale production of algae for fuel in outdoor ponds was feasible, the program failed to do so at a cost that would be competitive with petroleum, especially as oil prices sank in the 1990s. Even in the best-case scenario, it was estimated that unextracted algal oil would cost $59–186 per barrel, while petroleum cost less than $20 per barrel in 1995. Therefore, under budget pressure in 1996, the Aquatic Species Program was abandoned.
Other contributions to algal biofuels research have come indirectly from projects focusing on different applications of algal cultures. For example, in the 1990s Japan's Research Institute of Innovative Technology for the Earth implemented a research program with the goal of developing systems to fix using microalgae. Although the goal was not energy production, several studies produced by RITE demonstrated that algae could be grown using flue gas from power plants as a source, an important development for algal biofuel research. Other work focusing on harvesting hydrogen gas, methane, or ethanol from algae, as well as nutritional supplements and pharmaceutical compounds, has also helped inform research on biofuel production from algae.
Following the disbanding of the Aquatic Species Program in 1996, there was a relative lull in algal biofuel research. Still, various projects were funded in the US by the Department of Energy, Department of Defense, National Science Foundation, Department of Agriculture, National Laboratories, state funding, and private funding, as well as in other countries. More recently, rising oil prices in the 2000s spurred a revival of interest in algal biofuels and US federal funding has increased, numerous research projects are being funded in Australia, New Zealand, Europe, the Middle East, and other parts of the world.
In December 2022, ExxonMobil, the last large oil company to invest in algae biofuels, ended its research funding.
In March 2023, researchers said that the commercialization of biofuels would require several billion dollars of funding, plus a long-term dedication to overcoming what appear to be fundamental biological limitations of wild organisms. Most researchers believe that large scale production of biofuels is either "a decade, and more likely two decades, away."
Food supplementation
Algal oil is used as a source of fatty acid supplementation in food products, as it contains mono- and polyunsaturated fats, in particular EPA and DHA. Its DHA content is roughly equivalent to that of salmon based fish oil.Fuels
Algae can be converted into various types of fuels, depending on the production technologies and the part of the cells used. The lipid, or oily part of the algae biomass can be extracted and converted into biodiesel through a process similar to that used for any other vegetable oil, or converted in a refinery into "drop-in" replacements for petroleum-based fuels. Alternatively or following lipid extraction, the carbohydrate content of algae can be fermented into bioethanol or butanol fuel.Biodiesel
Biodiesel is a diesel fuel derived from animal or plant lipids. Studies have shown that some species of algae can produce 60% or more of their dry weight in the form of oil. Because the cells grow in aqueous suspension, where they have more efficient access to water, and dissolved nutrients, microalgae are capable of producing large amounts of biomass and usable oil in either high rate algal ponds or photobioreactors. This oil can then be turned into biodiesel which could be sold for use in automobiles. Regional production of microalgae and processing into biofuels will provide economic benefits to rural communities.As they do not have to produce structural compounds such as cellulose for leaves, stems, or roots, and because they can be grown floating in a rich nutritional medium, microalgae can have faster growth rates than terrestrial crops. Also, they can convert a much higher fraction of their biomass to oil than conventional crops, e.g. 60% versus 2-3% for soybeans. The per unit area yield of oil from algae is estimated to be from 58,700 to 136,900 L/ha/year, depending on lipid content, which is 10 to 23 times as high as the next highest yielding crop, oil palm, at 5 950 L/ha/year.
The U.S. Department of Energy's Aquatic Species Program, 1978–1996, focused on biodiesel from microalgae. The final report suggested that biodiesel could be the only viable method by which to produce enough fuel to replace current world diesel usage. If algae-derived biodiesel were to replace the annual global production of 1.1bn tons of conventional diesel then a land mass of 57.3 million hectares would be required, which would be highly favorable compared to other biofuels.
Renewable diesel
Algae can be used to produce 'green diesel' through a hydrotreating refinery process that breaks molecules down into shorter hydrocarbon chains used in diesel engines. It has the same chemical properties as petroleum-based diesel meaning that it does not require new engines, pipelines or infrastructure to distribute and use. It has yet to be produced at a cost that is competitive with petroleum. While hydrotreating is currently the most common pathway to produce fuel-like hydrocarbons via decarboxylation/decarbonylation, there is an alternative process offering a number of important advantages over hydrotreating. In this regard, the work of Crocker et al. and Lercher et al. is particularly noteworthy. For oil refining, research is underway for catalytic conversion of renewable fuels by decarboxylation. As the oxygen is present in crude oil at rather low levels, of the order of 0.5%, deoxygenation in petroleum refining is not of much concern, and no catalysts are specifically formulated for oxygenates hydrotreating. Hence, one of the critical technical challenges to make the hydrodeoxygenation of algae oil process economically feasible is related to the research and development of effective catalysts.Biobutanol
Butanol can be made from algae or diatoms using only a solar powered biorefinery. This fuel has an energy density 10% less than gasoline, and greater than that of either ethanol or methanol. In most gasoline engines, butanol can be used in place of gasoline with no modifications. In several tests, butanol consumption is similar to that of gasoline, and when blended with gasoline, provides better performance and corrosion resistance than that of ethanol or E85.The green waste left over from the algae oil extraction can be used to produce butanol. In addition, it has been shown that macroalgae can be fermented by bacteria of genus Clostridia to butanol and other solvents. Transesterification of seaweed oil is also possible with species such as Chaetomorpha linum, Ulva lactuca, and Enteromorpha compressa.
The following species are being investigated as suitable species from which to produce ethanol and/or butanol:
- Alaria esculenta
- Laminaria saccharina
- ''Palmaria palmata''
Biogasoline