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Ecofuel conversion technology of inedible lipid feedstocks to renewable fuel 267

used as the saponification agent to release carotenoids at a lower temperature (60°C)
[126]. Solvent extraction is used to separate nonwater-soluble compounds from the
saponified extract. Hexane or a mixture of ethanol-water-CH 2 Cl 2 can be used as
the extraction solvent. Purification of carotenoids is carried out by crystallization
or chromatography [117]. Carotenoids usually are obtained in a separate extraction
process. However, lutein as one of the carotenoids can be obtained along with biodie-
sel production in one process, which resulted 6mg lutein/g and 94mg FAME/g [117].
Including carotenoids as a product in biodiesel production could improve its eco-
nomic feasibility. However, improving technologies and methods to cut down cost in
separation and purification of carotenoids is necessary.

9.4.3 Biorefinery approach in the biodiesel production from spent
coffee grounds

As shown in Table 2.4, spent coffee grounds are a complex biomass with high poten-
tial to produce various chemicals and fuels. Assuming that all extractable antioxidants
were depleted in spent coffee grounds, the remaining useful compounds are lipids and
carbohydrate fibers. However, such assumption is dubious because some studies indi-
cated that spent coffee grounds still contained antioxidant compounds such as chlo-
rogenic acid, which can be recovered easily by extraction using pure water or aqueous
ethanol [127]. The extraction method selected and the brewing process from which
spent coffee grounds originated may determine the yield of the recovered antioxi-
dants. Andrade et al. reported that Soxhlet and ulrasound-assisted extraction by using
ethanol as the solvent gave the highest yield of crude antioxidant extract: about 15%
and 12.2%, respectively [128]. Supercritical CO 2 extraction resulted in a lower yield
but the use of ethanol as a cosolvent (15wt% of dried spent coffee grounds) increased
the extraction yield to 14%. A brewing process involving a pressurized system
resulted in fewer remaining antioxidants in spent coffee grounds, which is reasonable
as pressure facilitated the extraction of antioxidants during the brewing process [51].
Lipid extraction prior to the utilization of the carbohydrate component was shown to
benefit sugar recovery from acid hydrolysis and enzymatic saccharification of carbohy-
drate, where dilapidated spent coffee grounds produced higher glucose concentration
than that of original spent coffee grounds (18g/L versus 15g/L glucose) [55].Withcon-
sideration to the higher energy obtainable from bioethanol (20MJ/kg spent coffee gro-
unds) than the other options of biofuel, such as biogas (12.5MJ/kg spent coffee grounds)
and bio-oil from pyrolysis (14.5–16MJ/kg), this coincidentally directs lipid extraction
and biodiesel production as the second stage of good biorefinery practice in the utiliza-
tion of spent coffee grounds [129]. Although direct combustion of spent coffee grounds
might generate higher energy in a single step ( 25MJ/kg spent coffee grounds), such
aan pproach is not recommended due to considerable NO x emission from the combus-
tion of nitrogenated compounds, such as protein and caffeine [130].As somesugars
released from hemicellulose (xylose, arabinose, galactose, rhamnose, and mannose)
are often not readily digestible to the common fermenting microorganism strains,
genetic engineering must be applied as an effort to maximize the attainable products