Environmental Engineering Reference
In-Depth Information
To address these technical issues, feedstocks with inherently different fatty acid profiles or that
have been altered to provide such profiles are of interest. Esters of palmitoleic acid [9(
Z
)-hexadecenoic
acid; C16:1] would be especially desirable to be enriched in a biodiesel fuel (Knothe 2008) because
the cetane number and low melting point (melting point of methyl palmitoleate is approximately
-34°C) are of interest. Macadamia nut oil is a model feedstock that is moderately enriched in
palmitoleic acid, but its content of saturated fatty acids precludes improvement of the cold-flow
properties of the corresponding biodiesel fuel (Knothe 2010). When considering saturated fatty
acid chains, esters of capric acid (decanoic acid; C10:0) offer a compromise of properties (cetane
number of methyl decanoate 51.6, melting point of -13°C) because esters of octanoic acid possess
cetane numbers that are too low. Esters of dodecanoic (lauric) acid possess melting points that are
too high (melting point of methyl laurate is ~4.5°C) (Knothe 2008). Accordingly, methyl esters of a
variety of cuphea oil (PSR 23, a cross of
Cuphea viscosissima
and
Cuphea lanceolata
) containing
approximately 65% methyl decanoate, 12.2% methyl oleate, 7% methyl palmitate, and 6.7% methyl
linoleate with the rest consisting of other saturated esters showed a cloud point of -9 to -10°C and a
cetane number of 55-56 (Knothe et al. 2009). Other work dealt with fuel properties of the genetically
altered
C. viscosissima
strain VS-320, which contains C6:0 and C8:0, in the untransesterified form
(Geller et al. 1999). Although cuphea oil, of which approximately 260 species with greatly varying
fatty acid profiles are known (Isbell 2002), has not been commercialized because of issues such as
seed shattering, the fatty acid profile of the C
10
-enriched oil used here can serve as model for other
oils that are potentially enriched in this fatty acid.
An oil containing high amounts of unsaturated fatty acid chains in the C
20
-C
22
range is
meadowfoam; however, the corresponding biodiesel fuel exhibits relatively high oxidative stability,
which may be due to the position of the double bonds in the chain (Moser et al. 2010).
33.2.7 J
oJoBa
Jojoba (
Simmondsia chinensis
) is a woody perennial bush shrub native to arid regions such as
the deserts of the southwestern United States and neighboring areas of Mexico (Miwa 1971),
but it is now also commercially grown in other countries such as Australia, Argentina, Chile,
Egypt, India, Peru, and South Africa (International Jojoba Export Council 2009). It has a seed
containing approximately 45-55% of a wax-like material known as “jojoba oil.” Jojoba oil is
not a typical oil consisting mainly of triacylglycerols; rather, it is a mixture of long-chain esters
containing smaller amounts of triacylglycerols and other materials such as phospholipids and
tocopherols. The esters that largely comprise jojoba oil are those of monounsaturated fatty acids
with alcohols of C
16
-C
24
chain length. The major fatty acids and alcohols are C20:1 and C22:1,
with double bond positions at C
11
and C
13
, respectively, but minor amounts of acids and alcohols
with double bonds in other positions are also present (Miwa 1971; Hamilton et al. 1975). Because
of its properties, it has largely found application in skin care products and cosmetics. Work on
producing a biodiesel fuel from jojoba oil was reported (Canoira et al. 2006), but the resulting
methyl esters still contained approximately 21% jojoba alcohols and therefore the viscosity was
high (9-10 mm
2
/s), well above the prescribed maximal values in the ASTM D6751 and EN 14214
biodiesel standards.
33.2.8 t
Tall
o
il
Tall oil fatty acids are obtained from the wood pulp industry from the digestion of pine wood chips
with an alkaline solution of sodium sulfate or an acidic solution of sodium sulfite (Gunstone and
Harwood 2007). Upon acidification with sulfuric acid of the aqueous alkaline solution, a mixture of
resin acids and fatty acids results. Tall oil is produced mainly in North America and Scandinavia.
However, the compositions vary because of the nature of the pulped wood.
