Diesel Trees - Bioenergy Crop Plants - page 626

Monoterpenes and sesquiterpenes are volatile cyclic hydrocarbons. The major sesquiterpene
present in most Copaifera species, β-caryophyllene, has a chemical structure most similar to a
cyclic olefin, or a naphthene, which contains two double bonds. In general, naphthenes have a
midrange cetane rating, good low-temperature properties, and an acceptable volumetric heating
value. Biofuels from oilseed sources such as soybean and canola have a pour and cloud point of
approximately 0°C, making them impractical in areas with cold climates. In addition, fuel additives
to improve low temperature properties are not very effective because of the high level of saturated
compounds present in the oils (U.S. Department of Energy 2004). Addition of terpenoid components
(such as sesquiterpenes) to these types of biofuels could increase their low-temperature properties
and complement their high cetane ratings.
Not much is known about the chemical and physical properties of Copaifera oleoresin as a
diesel fuel. Calvin (1980) submitted a sample of Copaifera oleoresin to the Mobil Corporation and
obtained a cracking pattern: 50% aromatics, 25% liquid petroleum gas (LPG), 3-4% low-molecular-
weight fuel gas, and coke. Later, cracking of C. officinalis oleoresin with a zeolite catalyst, ZSM-5,
led to production of over 200 compounds from 34 sesquiterpenes present in the original oleoresin
(Stashenko et al. 1995). The great variety of resulting products could indicate the utility of these
oleoresins in not only fuels but also additional value-added products from a renewable resource.
As mentioned before, the seeds of Copaifera species not only produce sesquiterpene hydrocarbons
but also produce various fatty acids when pressed and extracted (Lima Neto 2008; Stupp et al.
2008). In C. langsdorfii, , oleic acid (C18:1) made up 33.1% of the fatty acid profile, whereas palmitic
acid (C16:0) made up 20.2% of the fatty acid profile. According to Stupp et al. (2008), the major
fatty acid that was extracted was linoleic acid (C18:2) which made up 45.3% of the fatty acids and
oleic acid making up 30.9%. It would be interesting to test oil pressed from these seeds against
other biodiesels and to compare their overall chemical structure to see how the percentages of
sesquiterpenes versus fatty acids are present in the seed oil.
24.7 Future scoPe oF research and develoPment
For reasons described earlier, it does not seem economically feasible to create plantations of
Copaifera trees to produce oleoresin for biodiesel markets. In brief, long generation times, low
and sporadic yields per tree, and their tropical nature limit production of oleoresin. Instead,
characterization of the unique terpenoid biosynthesis pathway and expressing it in other species
already suited for production of biodiesel offers a more reasonable avenue.
Why these oleoresins produce higher amounts of certain terpenoids, sesquiterpenes mostly, is not
well understood. Possible mechanisms include differential regulation of sesquiterpene synthesis, or
even higher TPS efficiency. Although there has been a lot of work accomplished to characterize the
chemical nature of oleoresins, there has been a surprising lack of molecular biology and biochemistry
research as to how these oleoresins are created, stored, and transported. Identification, isolation,
and characterization of the TPS responsible for the production of the oleoresin constituents will be
crucial not only in first determining how these proteins function, but also in localizing them within
tissue types to understand production of oleoresin constituents.
Detailed studies on the emission and performance standards of oleoresins as a diesel fuel will also
be necessary. The host of traditional diesel classification tests for physical and chemical properties,
including density, cloud and pour points, viscosity, heat of combustion, cetane number, etc., should
be performed to gauge the usefulness of these compounds in today's markets with current engine
technology. This work will also need to include several different possible species because each one
has a varying chemical makeup and properties associated with that makeup. These studies will
be instrumental in determining whether oleoresin constituents are better suited as a stand-alone
biodiesel fuel or as an additive for other petroleum or biofuels.
However, there are barriers to further research on Copaifera species. Many publications and
historical records about Copaifera trees are in Portuguese; this presents a barrier to the larger scientific