Biomedical Engineering Reference
In-Depth Information
akin to a petrochemical refinery, where petroleum is fractionated to produce home and
transportation fuels, chemical intermediates, lubricants, asphalt, and so on (Hatti-Kaul
et al
., 2007; Hill, 2007). As shown in the figure, several chemical intermediates (italicized
in the figure) can serve as components of bio-based surfactants.
At the heart of bio-based surfactant preparation is the utilization of long-chain fatty acids
found primarily in seed oil in the form of triacylglycerols (TAGs) for the lipophile. The ideal
fatty acyl group for industrial, non-food utilization is C
12
-C
16
saturates, while for food-based
products monounsaturates are more acceptable. Feedstocks enriched in medium-chain
saturates include palm, palm kernel particularly palm stearine, a palmitic acyl-rich
by-product from the purification and fractionation of palm kernel oil (Santosa, 2008), and
coconut oils (Edser, 2004). Cuphea is under investigation in the United States as a future
feedstock (Pandey
et al
., 2000). Other potentially valuable sources of fatty acyl groups for
surfactants and detergents are inexpensive feedstocks such as tallow, used cooking oils, and
algal oils and oils from jatropha and soapnut (Scheibel, 2007; Chetri
et al
., 2008 ; Chisti,
2007). These sources consist mainly of C
16
and C
18
saturates and C
18
monoenes and dienes.
Fatty acyl groups can also be derived from oleochemical co-products enriched in free
fatty acids and/or phospholipids, such as soapstock. Many surfactants employ oxygenated
fatty acids, particularly hydroxy acids, such as ricinoleic acid (R-18:1-9
cis
OH-12) from
castor oil, lesquerolic acid (R-20:1-11
cis
OH-14) from lesquerella oil, and dimorphecolic
acids (S-18:2 10
trans
,12
trans
OH-9) from dimorphotheca oil (and their oligomers) (Hayes,
2004), and epoxidized fatty acids, which are readily prepared from common oils such as
soybean (Doll and Erhan, 2009). In addition to fatty acyl groups, other potential bio-based
lipophiles include sterols (Svensson and Brinck, 2003) and lignin (Johansson and Svensson,
2001 ; Holladay
et al
., 2007 ).
Typically the fatty acyl groups obtained from TAGs are converted into free fatty acids
(FFA) or fatty acid methyl or ethyl esters (FAME and FAEE, respectively)
via
hydrolysis
and transesterification, respectively (Figure 10.1). Methyl and ethyl esters are anticipated to
be abundant materials in an oleochemical biorefinery due to their use in biodiesel (Ahmad
et al
., 2007). Methanol and ethanol would be common at biorefineries, readily produced
from gasification and fermentation of polysaccharides after their saccharification,
respectively. FFA, FAME, and FAEE are typically joined to hydrophiles
via
ester linkages,
which enhance biocompatibility and biodegradability, but are readily hydrolyzed under
acidic and basic conditions. FAMEs and FAEEs are readily converted to fatty alcohols to
fatty amines
via
heterogeneous catalytic reactions (Giraldo
et al
., 2010 ; Egan, 1968 ). Also,
bio-based long-chain carbonates have been recently produced, through a catalytic or
biocatalytic reaction between fatty alcohol and diphenyl or diethyl carbonate (Kenar
et al
.,
2004 ; Banno
et al
., 2007 , 2010 ; Matsumura, 2002 ). The latter, known as a non-toxic
replacement for hazardous chemicals such as phosgene and dimethyl sulfate, is formed from
the catalytic oxidation of ethanol (Rudnick, 2006).
As illustrated in Figure 10.1, hydrophiles can also be derived from natural resources.
Many of the bio-based hydrophiles are polyhydric alcohols, or polyols, useful for covalent
attachment of fatty acyl groups
via
ester bonds or fatty alcohol groups
via
ether bonds.
Glycerine, an inexpensive co-product from the manufacture of biodiesel, can be conjugated
to fatty acyl groups to produce monoacylglycerols (MAGs), which are common emulsifiers.
(Alternatively, MAGs can be obtained from hydrolysis of seed oils.) In addition, glycerine
can be converted into other “head group” moieties: 1,2-propanediol, or propylene glycol,
via
a catalytic process, a technological approach under development by Dow, Huntsman,
and others; 1,3-propanediol through a fermentation process developed by DuPont Tate and
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