Biofuel applications of botryococcene

Last updated September 10, 2023

Botryococcenes are the major oil constituents of the green algae Botryococcus braunii. The hydrocarbons these species produce can be chemically converted into fuels.

Transesterification cannot be used to make biodiesel from botryococcenes, the major oil of Botryococcus braunii. This is because Botryococcene oil is not a 'vegetable oil' (which is a fatty acid triglyceride) but is instead a triterpene, and lacks the free oxygen for transesterification. It can be used as feedstock for hydrocracking in an oil refinery to produce octane (gasoline, a.k.a. petrol), and kerosene. Up to 86% of its dry weight can be long-chain hydrocarbons.

Background

The colonial green microalgae Botryococcus braunii is a species of algae that accumulates oily hydrocarbons that consist mainly of botryococcenes. This algae grows well in a variety of conditions, including treated sewage. These hydrocarbons make up 17 to 86 percent of the dry weight of the algae.^[1] An experimental study in 1980 found that hydrocracking the oil that was found in a naturally-occuring bloom of the algae in Australia produced a 67% gasoline fraction, 15% jet fuel fraction, 15% diesel fuel fraction, and 3% residual oil.^[2] Further study of the gasoline fractions that can be extracted from the algae found that it has a high enough octane rating to make it suitable to use directly as an automotive fuel.^[3]

Challenges

There are several challenges which must be met in order to economically produce the desired alkanes such as gasoline. This will only be briefly covered in this article at this time, as it has only just begun.

Growth phase

Initial studies of the hydrocarbon content of Botryococcus braunii found contradictory data about the hyrdocarbon content. It was later found that the dry cellular weight of the algae was around 0%, 17%, or 86%, depending on whether the algae was tested during its green resting, green active, or brown resting growth phases, respectively.^[4]

Suitable strain

First, a suitable strain of Bb (Botryococcus braunii) must be found. Several strains are available from algae specimen banks, but there is no guarantee that these are high-producing strains. Some plant patent applications have been filed and patents granted, for high producing strains. It is not likely within reason for even a small scale producer of boytrococcenes to breed successively higher producing strains of Bb, due to the reasonably slow generation rate. However, in selecting Bb strains for high Botryococcene production, it is likely that other beneficial attributes may be bred out. For instance, resistance to disease, competitive advantages against other organisms, and survivability in less than ideal climates. In this case, a photobioreactor may be needed. Botryococcus Braunii are relatively cosmopolitan so this is not a major factor.

The practice of farming algae is known as algaculture. However, there are properties of Botryococcus braunii which make its harvest a bit different from the harvest of other algae. Compared to other green algae species it has a relatively thick cell wall that is accumulated from previous cellular divisions; making extraction of cytoplasmic components rather difficult. Fortunately, much of the useful hydrocarbon oil is outside of the cell. This gives rise to the hope that the algae will not have to be killed in order to extract its useful oil. Several methods are available to extract the botryococcene. One that shows the most promise is the use of hexane as a solvent. If used at the proper molarity, it does not kill the majority of the Bb, while extracting the botryococcene.

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<span class="mw-page-title-main">Biofuel</span> Type of biological fuel produced from biomass from which energy is derived

Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. Biofuel can be produced from plants or from agricultural, domestic or industrial biowaste.

<span class="mw-page-title-main">Cracking (chemistry)</span> Process whereby complex organic molecules are broken down into simpler molecules

In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of catalysts. Cracking is the breakdown of a large hydrocarbons into smaller, more useful alkanes and alkenes. Simply put, hydrocarbon cracking is the process of breaking a long chain of hydrocarbons into short ones. This process requires high temperatures.

Natural-gas condensate, also called natural gas liquids, is a low-density mixture of hydrocarbon liquids that are present as gaseous components in the raw natural gas produced from many natural gas fields. Some gas species within the raw natural gas will condense to a liquid state if the temperature is reduced to below the hydrocarbon dew point temperature at a set pressure.

<span class="mw-page-title-main">Catalytic reforming</span> Chemical process used in oil refining

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Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies exist: (i) direct partial combustion of methane to methanol and (ii) Fischer–Tropsch-like processes that convert carbon monoxide and hydrogen into hydrocarbons. Strategy ii is followed by diverse methods to convert the hydrogen-carbon monoxide mixtures to liquids. Direct partial combustion has been demonstrated in nature but not replicated commercially. Technologies reliant on partial combustion have been commercialized mainly in regions where natural gas is inexpensive.

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Botryococcus braunii is a green, pyramid-shaped planktonic microalga that is of potentially great importance in the field of biotechnology. Colonies held together by a lipid biofilm matrix can be found in temperate or tropical oligotrophic lakes and estuaries, and will bloom when in the presence of elevated levels of dissolved inorganic phosphorus. The species is notable for its ability to produce high amounts of hydrocarbons, especially oils in the form of Triterpenes, that are typically around 30–40% of their dry weight. Compared to other green alge species it has a relatively thick cell wall that is accumulated from previous cellular divisions; making extraction of cytoplasmic components rather difficult. Much of the useful hydrocarbon oil is outside of the cell.

Scenedesmus is a genus of green algae, in the class Chlorophyceae. They are colonial and non-motile. They are one of the most common components of phytoplankton in freshwater habitats worldwide.

Second-generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of non-food biomass. Biomass in this context means plant materials and animal waste used especially as a source of fuel.

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References

↑ Ogi, T.; Inoue, S.; Sawayama, S.; Dote, Y. (1997). "Fuel Oil Production from Hydrocarbon-Rich Microalgae Botryococcus Braunii". In Bridgewater, A.V.; Boocock, A.V. (eds.). Developments in Thermochemical Biomass Conversion. Springer, Dordrecht. pp. 339–348. doi:10.1007/978-94-009-1559-6_27. ISBN 978-94-010-7196-3.
↑ Hillen, L. W.; Pollard, G.; Wake, L. V.; White, N. (January 1982). "Hydrocracking of the oils of Botryococcus braunii to transport fuels". Biotechnology and Bioengineering. 24 (1): 193–205. doi:10.1002/bit.260240116. PMID 18546110. S2CID 43310427.
↑ Kitazato, H.; Asaoka, S.; Iwamoto, H. (1989). "Catalytic cracking of hydrocarbons from microalgae". Journal of the Japan Petroleum Institute (in Japanese). 32 (1): 28–34. doi:10.1627/jpi1958.32.28.
↑ Lornabene, T.G. (1982). "Microorganisms as hydrocarbon producers". In Mislin, H.; Bachofen, R. (eds.). New Trends in Research and Utilization of Solar Energy through Biological Systems. Basel: Birkhäuser. pp. 49–52. doi:10.1007/978-3-0348-6305-6_10. ISBN 978-3-0348-6307-0.

External links

Japanese scientists create diesel-producing Botryococcus braunii algae.

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[ogi1997-1] Ogi, T.; Inoue, S.; Sawayama, S.; Dote, Y. (1997). "Fuel Oil Production from Hydrocarbon-Rich Microalgae Botryococcus Braunii". In Bridgewater, A.V.; Boocock, A.V. (eds.). Developments in Thermochemical Biomass Conversion. Springer, Dordrecht. pp. 339–348. doi:10.1007/978-94-009-1559-6_27. ISBN 978-94-010-7196-3.

[Hillen1982-2] Hillen, L. W.; Pollard, G.; Wake, L. V.; White, N. (January 1982). "Hydrocracking of the oils of Botryococcus braunii to transport fuels". Biotechnology and Bioengineering. 24 (1): 193–205. doi:10.1002/bit.260240116. PMID 18546110. S2CID 43310427.

[Kitazato1989"-3] Kitazato, H.; Asaoka, S.; Iwamoto, H. (1989). "Catalytic cracking of hydrocarbons from microalgae". Journal of the Japan Petroleum Institute (in Japanese). 32 (1): 28–34. doi:10.1627/jpi1958.32.28.

[tornabene1982-4] Lornabene, T.G. (1982). "Microorganisms as hydrocarbon producers". In Mislin, H.; Bachofen, R. (eds.). New Trends in Research and Utilization of Solar Energy through Biological Systems. Basel: Birkhäuser. pp. 49–52. doi:10.1007/978-3-0348-6305-6_10. ISBN 978-3-0348-6307-0.

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