Page 147 - Biofuels Refining and Performance

130 Chapter Four

were also obtained using KOH and methanol instead of NaOH and
ethanol, which decreases transesterification rates. The reaction was
optimized at an ambient temperature, using 1.26% KOH and 12%
methanol, and stirring for 1 min [40]. Some authors have optimized the
reaction by using methanol (alcohol–waste oils molar ratios between 3.6
and 5.4) and 0.2–1% NaOH [146], or methanol (molar ratios in the range
of 1:74 to 1:245) and acid catalyst (sulfuric acid) [147]. Al-Widyan and
Al-Shyoukh have performed waste palm oil transesterification under
SO
various conditions. The best process combination was 2.25 M H 2 4
with 100% excess ethanol in about 3 h of reaction time [148].
Several parameters (e.g., heating conditions, FFA composition, and
water content) can influence conversion from waste oils into biodiesel.
Mittelbach et al. have found that heating over a long period led to a sig-
nificantly higher FFA content, which can reach values up to 10% and
have detrimental effects during the transesterification process.
Nevertheless, in most cases, simple heating and filtering of solid impu-
rities is sufficient for further transesterification [20]. The methyl and
ethyl esters of fatty acids obtained by alcoholysis of triglycerides seem
to be excellent fuels [5]. Anggraini found that it was also important to
keep the water content of used cooking oils as low as possible [149].
Dorado et al. have compared biofuels from waste vegetable oils from sev-
eral countries (different FFA composition) including Brazil, Spain, and
Germany. The transesterification process was carried out in two steps,
using a stoichiometric amount of methanol and the necessary amount
of KOH, supplemented with the exact amount of KOH to neutralized
acidity. Both reactions were completed in 30 min [41]. Results revealed
that to carry the reaction to completion, an FFA value lower than 3% is
needed. The two-step transesterification process (without any costly
purification step) was found to be an economic method for biofuel pro-
duction using waste vegetable oils. To reduce FFA content, a two-step
transesterification using 0.2% ferric sulfate and 1% KOH with methanol
(mole ratio 10:1) was also developed [150]. Acid-catalyzed pretreatment
to esterifiy the FFA before transesterification with an alkaline catalyst
was also proposed [151]. This procedure can reduce the acid levels to less
than 1%. Some authors have proposed a three-step process in a fixed-
bed bioreactor with immobilized Candida antarctica lipase [152].
Brenneis et al. also developed a process involving C. antarctica through
alcoholysis of waste fats, with excess of water. The optimum amount of
water was found to be 80–10% of the amount of fat [153]. Chen et al.
preferred the use of immobilized lipase Novozym-435 in transesterifi-
cation of both waste oil and methyl acetate. However, they found that
the reaction rate decreased with increasing water content [154].
Engine tests have been performed with biodiesel from different
kinds of waste oils. Al-Widyan et al. tested several ester–diesel blends in