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Raw Materials to Produce Low-Cost Biodiesel 129

as a source of dietary fiber in food technology, as a high-quality cooking/
salad oil, as a source of starch, as an antioxidant-containing food, and
so forth [139]. The oil extracted from yellow nutsedge can be used as food
oil as well as for industrial purposes. Since the tubers contain 20–36%
oil, the crop has been suggested as a potential oil crop for the produc-
tion of biodiesel [138]. Preliminary tests using pure nutsedge oil as fuel
in a diesel engine have indicated that the engine operated near its rated
power [140]. Currently, it is being studied as an oil source for fuel pro-
duction in Africa [53].

4.4 Used Frying Oils
Currently, world oil crop production is about 139,000,000 ton [141]. In
particular, developing countries (97,370,185 ton) and developed coun-
tries (41,193,308 ton) are the largest producers, while least developed
countries contribute 4,141,535 ton. Most of this oil is used for deep-
frying processes, after which it becomes a disposal problem. Disposal
methods often contaminate environmental water and contribute to world
pollution. Due to high oxidative thermal stress, such waste frying fats
should not be used for human food [142]. Also, since 2002, the EU has
enforced a ban on feeding these mixtures to animals, because during
frying many harmful compounds are formed, which could result in the
return of harmful compounds back into the food chain through the
animal meat [143].
Used oils can be recycled through conversion into soap by saponifi-
cation and reused as lubricating oil or hydraulic fluid. Nevertheless, bio-
fuel production seems to be the most attractive alternative for waste oil
treatment. Certainly, it will not solve the energy problem, because only
a small percentage of diesel demand can be supplied by this source [20],
but it will decrease the dependence on fossil oil while reducing an envi-
ronmental problem.
For economic reasons, used frying oil is an interesting feedstock for
biodiesel production. In this sense, Nye et al. were the first to describe
the transesterification of used frying oil using excess of alcohol under
both acidic and basic conditions. The best result was obtained using
methanol with catalysis by KOH [144]. The tests were carried out using
frying margarine and partially hydrogenated soybean oil. The reaction
was carried out at 50 C for 24 h, using methanol in a methanol–triglyceride
molar ratio of 3.6:1 and 0.4% KOH. At the same time, Mittelbach et al.
investigated the use of waste oils to produce biodiesel and found that
the increase in the amount of polymers during heating of the oil is a
good indicator for the suitability for biodiesel production [42]. They
proposed a low-temperature process (40 C) under alkaline catalysis
and excess of methanol [145]. Considering used olive oil, better results