3. Results & Discussion
3.1. Biodiesel Purification
3.1.1. Acid value
Even with the increase in the acidity index after the treatment of
biodiesel with Magnesol®, all values of the acidity
index are lower than that established by the ANP standard, where the
document cites that only biodiesel with an acidity index less than 0.5
mg KOH/g sample can be marketed. Figure 3 shows the acid value of the
unpurified biodiesels and biodiesels purified with virgin (purified I)
and recovered Magnesol® (purified II), where occurs
increase acids values due to the affinity of Magnesol®adsorbing basic compounds, such as soap and catalyst residue (KOH)
(Faccini et al., 2011).
3.1.2. Glycerol amount
Figure 4 shows the amount of glycerol in the biodiesel before and after
the use of Magnesol®, and it is observed that the used
of Magnesol®, and the reuse do Magnesol purified
(originally used in the purification of biodiesel from virgin soybean
oil), was not effective to purification of biodiesel, because the amount
of glycerol found in the biodiesel is within the norms (below 5%). But
the Magnesol® used in the purification of biodiesel
from the frying oil, it can be reused with good efficiency, since the
amounts of glycerol found in biodiesel A2.1 (5.03%) and A2.2 (2.7%)
are within the values recommended by the legislation, showing a decrease
in the amount of glycerol when compared to unpurified biodiesel (A2 -
6.41%). Probably, this decrease in glycerol observed in biodiesel after
purification with recovered Magnesol® is due to the
characteristics of the remaining compounds in the THF-purified Magnesol,
because it is demonstrated in the literature that residual compounds
with polar and nonpolar characteristics found in residues of the
biodiesel and remaining in the Magnesol have greater affinity with
glycerol, aiding in the purification of the biodiesel (Panagiotopoulou
and Tsimidou, 2002; Wretensjo and Karlberg, 2002).
3.1.3. Flash point
In three fractions of biodiesels synthesized from virgin oil (A1) and
subsequently purified with virgin Magnesol® (A1.1) and
recovered Magnesol® (A1.2), flash point analyses were
performed and the results obtained were 169°C, 165°C and 167°C,
respectively. The results indicate that all fractions of purified
biodiesel have values accepted by ANP, demonstrating good reusability
after passing through the purification process. The same flash point
analyses were performed with three fractions of biodiesel synthesized
from frying oil (A2) and purified with virgin
Magnesol® (A2.1) and recovered
Magnesol® (A2.2), yielding results of 159 °C, 158°C
and 160 °C, respectively. These results are in accordance with ANP
07/2008 standards that establish a flash point of 100°C as the minimum
value to be used (Lôbo et al., 2009).
3.2. Magnesol®Purification
In Table 1, processes 1 and 3 correspond to the solvents used to purify
the Magnesol® used in the purification of biodiesel
derived from virgin oil, while processes 2 and 4 correspond to the
solvents used to purify the Magnesol® used in the
purification of biodiesel derived from frying oil. Results of the
elemental analysis corresponding to the related process showed the best
results for the Magnesol® used in the purification of
biodiesel from virgin oil. Consequently, after process 4, it was decided
to optimize the adsorbent purification process only for the
Magnesol® used in the purification of biodiesel
derived from virgin oil, and later, to apply this to the
Magnesol® used in the purification of biodiesel
derived from frying oil (Table 1).
The elemental analysis of virgin Magnesol® did not
show any percentage of carbon, thus all carbon found after the
purification of the adsorbent is an impurity derived from biodiesels. In
the Magnesol® recovery process, the parameters
optimized were reaction time, solvent type, solvent ratio and
temperature. Above is Table 1 with the 19 Magnesol®recoveries carried out in this work. As the goal of this analysis was to
determine the amount of carbon, the reactions that were demonstrated to
be more efficient were reactions 9, 10, 14, 15 and 16.
Magnesol® purification was performed using several
solvents of different polarities in order to verify the influence of the
dielectric constant in the purification of biodiesels, because it is
known that the by-products of biodiesel synthesis have polar and
nonpolar characteristics. Knowing the dielectric constant (µ) of the
solvents, it was expected that the solvents with a higher degree of
polarity, such as H2O (used to make the solution of
NaOH), µ = 80; CH3CN, µ = 37 and ethanol, µ = 30, would
be the least effective. The CH2Cl2,
although showing µ = 9.1, very close to µ of THF (µ = 7.5), also does
not provide satisfactory results, perhaps because it did not show
hydrogen interactions with the by-products generated in biodiesel
synthesis. Ethyl acetate (µ = 6.02) is observed to have purification
rates very close to THF because ethyl acetate has a µ slightly smaller
than THF and it has the possibility of having hydrogen interactions with
compounds withdrawn from the process of biodiesel purification.
In relation to the effect of the temperature during the reaction, it is
observed that an increase in temperature (25 to 50°C) in the
purification process of Magnesol® does not contribute
significantly to a better result. This can be seen in the reactions
using hexane (reactions 5 and 6) and ethyl acetate (reactions 07 and 08)
in which a small decrease in impurities (amount of C, 0.54% and 0.06%,
respectively) occurred. In addition, when comparing the THF solvent at
25 and 50 °C a slight variation in the amount of carbon (4.31 and
4.44%, respectively) is seen.
Another parameter analyzed in the reaction optimization was the number
of extractions. When comparing reactions 04 and 05, it is evident that
when three extractions are used (reaction 05) instead of a single
extraction (batch), the purification of Magnesol® is
more effective, even using 25% less solvent. Subsequently, by comparing
the amount of solvent, it was observed that when increasing the amount
of THF in the proportions of solvent/adsorbent from 15:1 (reaction 09)
to 30:1 (reaction 14), Magnesol® was obtained with a C
quantity 0.42% lower, and when testing the purification of
Magnesol® by increasing the proportion of
solvent/adsorbent to 45:1 and 60:1 (reactions 15 and 16, respectively),
a very small decrease in impurity was observed, 0.06 and 0.08%,
respectively, showing that above the solvent/adsorbent ratio 30:1, there
is no considerable gain in impurities reduction. And finally, when the
contact time between the solvent and Magnesol® was
decreased, a decrease in the purification efficiency of the solvent was
observed, indicating that the solvent and the
Magnesol® are required to remain in contact for 30
minutes at each step during the washing process.
3.3. Characterization of Purified and
Unpurified
Magnesol®
In order to justify the efficiency of the recovery of
Magnesol® (purified), SEM-FEG (Scanning Electron
Microscopy-Field Emission Gun) analyses were performed, in which it was
possible to compare the morphology and particle diameter. In addition,
through the FTIR analysis it was possible to compare which chemical
groups the Magnesol® can retain in its structure as
well as evaluate the efficiency of the recovery process. Also,
thermogravimetric analysis was performed, in which the different
degradation temperatures of the virgin and recovered
Magnesol® can be compared.
3.3.1. SEM-FEG
Figure 5 shows the SEM-FEG of virgin Magnesol® and
Magnesol® recovered from the purification of biodiesel
derived from virgin and frying soybean oils. From the micrographs
obtained by SEM-FEG, the particle diameters of (a andd ) Pure Magnesol®, (b ande ) Magnesol® used to purify biodiesel derived
from frying oil and (c and f )
Magnesol® used to purify biodiesel derived from virgin
oil were calculated. A predominant microporous morphology was observed
in the analyzed materials as it was also highlighted by Facicini et al.,
2011.
It is noted that the process of purification and recovery causes
breaking of part of the Magnesol® structure, probably
due to the agitation and temperature of these processes. This
corroborates with previous results regarding the reuse of
Magnesol® because the structure remains porous and the
breaking of part of the spherical structures increases the contact
surface, compensating for the probable decrease in
Magnesol® efficiency that can occur with the small
amount of contamination that remains after the recovery process.
3.3.2. FTIR
Comparing the first spectrum with the RM-1 and RM-2 spectra, not
difference is noted, specifically, the recovered
Magnesol® (RM-1 and RM-2 spectra) demonstrates
compatibility with the virgin Magnesol®. It may be
further noted that the M-1 and M-2 spectra show some characteristic
bands having absorptions between 3000 and 2800 cm-1(C-H), compatible with the presence of carbon sp3(carbon with just sigma bonds (σ)). The bands between 1820 and 1630
cm-1 show carbonyl functions of C=O and the region
1599 to 1500 cm-1 represents sigma (σ) and pi (π)
bonds, i.e., unsaturated bonds between C=C (Lopes and Fascio, 2004;
Silverstein and Bassler, 1962). With this, it can be observed that the
recovered Magnesol® spectra (RM-1 and RM-2) do not
contain the infrared absorption bands found in the M-1 and M-2 spectra,
and thus, resemble the virgin Magnesol® FTIR spectrum
(Figure 6).
3.3.3. Thermal gravimetric analysis
From the thermograms in Figure 7, it is observed that the degradation of
virgin Magnesol® (VM) occurs in a single step.
However, the degradation of the recovered Magnesol®(RM-1 and RM-2) occurs in two steps, because contaminants are present in
the purified biodiesel which the THF solvent was not capable of
removing. This result was proven by the presence of carbon in the
elemental analysis.
As shown in Figure 7, VM, RM-1 and RM-2 experience maximum mass loss
with temperature at 83 °C, 76 °C and 74 °C, respectively. This result is
expected due to the volatile components and water steam beginning to be
released in this first range of temperature starting at 42 °C, 42 °C and
35 °C and finishing at 230 °C, 266 °C and 266 °C, respectively. In
addition, a second maximum mass loss temperature was observed for RM-1
and RM-2 (408 °C and 446 °C, respectively); mass loss in this
temperature range was expected due to the small amount of carbon found
in the products.