Environmental Engineering Reference
In-Depth Information
taBle 14.6
effect of Phospholipids on Pre-esterification
level
Particulars
I
II
III
Phospholipid content before pretreatment, %
0.33
1.03
1.62
Phospholipid content after pretreatment, %
0.04
0.05
0.12
Removal of phospholipids, %
87.9
95.1
92.6
Initial acid value of oil, mg KOH/g
20.5
20.9
20.6
Acid value after pretreatment, mg KOH/g
1.18
1.34
2.04
Pretreatment conversion, %
94.2
93.6
90.1
Source:
Data from Lu, H., et al.,
Comput Chem Eng
, 33, 1091-1096, 2009.
(Lu et al. 2009). However, the FFA contents of the feedstock is the important criterion for selecting
a suitable processing technology for production of biodiesel because production process parameters
are dependent on it and the yield of biodiesel is influenced by the methanol-to-oil ratio, catalyst-to-
oil ratio, reaction temperature, reaction time, and agitation speed.
It is reported that the FFA level of jatropha oil varies between 0.29% and 0.4% (Caboverde variety),
0.60% and 1.27% (Nicaragua variety), 7 and 15% (China and Indonesia variety), and 1.76 and 14%
(India variety) (Foidl et al. 1996; Akintayo 2004; Chitra et al. 2005; Tiwari et al. 2007; Berchmans
and Hirata 2008; Lu et al. 2009; Vyas et al. 2009). A process such as acid- or base-catalyzed trans-
esterification may be followed for production of biodiesel from oil having an FFA level less than 1%
(Ma and Hanna 1999; Canakci and Gerpen 2001; Ghadge and Raheman 2005); for oils with higher
F FAs (>1%),
a two-step process (i.e., an acid pretreatment process followed by base transesterifica-
tion process, supercritical fluid process, and a solid catalysis process) may be followed for producing
biodiesel (Canakci and Gerpen 2001; Ghadge and Raheman 2006; Wang et al. 2006; Sahoo et al.
2007; Tiwari et al. 2007; Berchmans and Hirata 2008; Shi and Bao 2008; Hawash et al. 2009).
The yield of biodiesel following the two-step process is between 90 and 99%. Heterogeneous
catalysis processes such as enzymatic catalysis and solid catalysis are reported to be time-consum-
ing and give an average yield of biodiesel between 70% and 92.8% (Shah et al. 2004; Modi et al.
2007a, 2007b; Tamalampudi et al. 2008;
Vyas et al. 2009). The supercritical methanol process was
found to be better among the processes because of its homogeneity and better yield of biodiesel up
to 100% (Hawash et al. 2009), but the process requires higher temperature, pressure, and a large
amount of methanol, hence it involves a higher production cost (Saka and Kusdiana 2001). The
detailed technologies followed and developed for producing biodiesel from jatropha oil are sum-
marized in Table 14.7.
14.4.2.1 reaction chemistry for transesterification
Vegetable oils and animal fats are principally composed of triacylglycerols (TAGs) consisting of
long-chain fatty acids chemically bound to a glycerol (1,2,3- propanetriol) backbone (Moser 2009).
Transesterification or alcoholysis is the process in which triglycerides or TAGs of oil react with
an alcohol to produce esters (known as biodiesel) and glycerin (glycerol) in the presence of a cata-
lyst, as shown in Figure 14.4, where R
1
, R
2
, and R
3
are long hydrocarbon chains, sometimes called
fatty acid chains (Gerpen 2005). The catalyst could be alkali catalyst, acid catalyst, or enzymatic
catalyst. The whole process is normally a sequence of three consecutive steps that are reversible
reactions (Figure 14.5). In the first step, diacylglycerol is obtained from TAG (step 1); from diacyl-
glycerol, monoacylglycerol is produced in the second step (step 2); and in the last step, glycerol is
obtained from monoacylglycerol (step 3). In all of these steps, esters are produced, which are called
biodiesel (Marchetti et al. 2007).
