**3.4 Characterization of gongo oil and biodiesel**

#### *3.4.1 Fourier transform infrared spectroscopy*

The elucidation of the chemical behavior of the products of the homogeneous acid esterification and homogeneous alkaline transesterification reactions of gong oil was investigated using Fourier transform infrared absorption spectroscopy (FTIR).

**Figure 5.** *Physical aspect of gong and its crude and esterified oils [20].*

#### **Figure 6.**

*Products obtained from the biodiesel processing steps. Caption: a: gongo sludge; b: gongo oil in natura; c: esterified gongo oil and d: gongo biodiesel [20].*

The IR spectra of the esterified gong oil (**Figure 7a**) and biodiesel (**Figure 7b**) samples are shown in **Figure 5**. They showed similar band positions, intensity and wave number. [22, 26, 27] Characterized vegetable oils and biodiesels produced from different vegetable oils and obtained FTIR results similar to the results revealed in this work.

In the region of the functional groups that comprises the range 4000–1650 cm<sup>1</sup> few bands were observed. There, three sets of well-defined bands were revealed, two bands in the range 2853–2925 cm<sup>1</sup> referring to the CH2 stretching of alkanes and one at 1744 cm<sup>1</sup> indicative of the C=O (carbonyl) stretching that characterizes the double bond region.

The region between 1650 and 500 cm<sup>1</sup> is called the fingerprint region. In this region more bands were found in relation to the region of the functional groups, however, the bands obtained between 1171 and 1172 cm<sup>1</sup> allusive to the vibrations of the C-O bond, indicative of the stretching of the ester grouping, stand out. Between 722 and 723 cm<sup>1</sup> bands referring to asymmetric CH deformation, characteristic of long hydrocarbon chains, were revealed. Another relevant factor observed in **Figure 7a** and **b** was the absence of absorption of broad bands in the region between 2500 and 3300 cm<sup>1</sup> , showing that the gongo oil and biodiesel had low moisture content. This fact was confirmed in the course of the immediate chemical analyses shown in **Table 2**.

**Figure 7.** *FTIR spectrum. (a) Gong oil; (b) Biodiesel.*

*Processing of Gong Oil (*Pachymerus nucleorum*) to Obtain Biodiesel by Methyl Route DOI: http://dx.doi.org/10.5772/intechopen.97721*

#### *3.4.2 Fat profile of biodiesel obtained by GC-FID*

In Brazil, the National Agency of Petroleum, Natural Gas and Fuel (ANP) is the body responsible for overseeing the quality parameters of biodiesel through Resolution No. 45, dated August 13, 2014. It regulates the characteristics of biofuels. The quality parameters are used to determine whether a given product is fit for consumption and not harmful to the population and the environment.

The ideal biodiesel for Resolution 045/2014-ANP should contain in its chemical constitution 100% of fatty acid methyl esters (FAME), however, in view of the low conversion of monoacylglycerols (MAG), diacylglycerols (DAG) and triacylglycerols (TAG) and competition between the secondary reactions throughout the transesterification process it becomes difficult to separate the esters formed and the reaction impurities. Consequently, at the end of the transesterification reaction, a mixture containing biodiesel and impurities is formed. Hence the importance of characterization of biodiesel and the feedstock that gave rise to it.

Among the specific quality parameters for biodiesel determined by the ANP is the ester content. The ANP has established an ester content of at least 96.5%. A low ester content directly influences the physical–chemical properties of biodiesel. Therefore, to obtain a high quality biofuel, the transesterification reaction must be complete and the purification process after the reaction must be effective. Thus, the content of remaining contaminants (FFA, methanol traces, water, etc.) should be low, so that the ester content meets the ANP specifications.

The methyl biodiesel produced from the esterified gong oil was characterized by gas chromatography with flame ionization detector (GC-FID) technique for ester conversion. The chromatographic profile in terms of fatty acid methyl esters (FAME) of the biodiesel is presented in **Figure 8**.

The FAME centesimal composition of the biodiesel is shown in **Table 3**. Therein it was observed that the majority constituent was dodecanoic acid methyl ester (methyl laurate, C 12:0) with 36.85%; followed by octadecanoic acid methyl ester (methyl stearate, C18:0) with 25.47%, tetradecanoic acid methyl ester (methyl myristate, C14:0) with 23.37% and hexadocanoic acid methyl ester (methyl palmitate, C16:0) with 14.31%.

The technique of gas chromatography with flame ionization detector (GC-FID) is suggested by standards EN 14103 and NBR 15764 for determining the content of fatty acid methyl esters (FAME) from the transesterification reaction of vegetable oils and, to confirm the results are necessary to use analytical standards for each FAME.

**Figure 8.** *Chromatographic profile of methyl esters contained in gong biodiesel. Source: the author himself.*


#### **Table 3.**

*Composition of fatty acid methyl esters from gong biodiesel [20].*

According to the ANP (2014), the determination of the ester content can be done following the EN 14103 methodology. The ester content based on this standard is performed by internal standardization with methyl heptadecanoate (C17:0) and only considers the esters of chain from C14:0 to C24:1 in the calculation of the ester content. Since in the characterization of biodiesel produced from gong oil it was revealed that the majority fatty acid methyl ester was C12:0 (methyl laurate), the EN 14103 technique did not allow determining the conversion of esterified gong oil into biodiesel (methyl esters). Due to financial and technical difficulties that permeate our institution it was not possible to use other means to do the conversion. On the other hand, comparing the FTIR results for the esterified gongo oil and biodiesel with the results revealed for the fat profile of gongo biodiesel through the GC-FID technique is notable the presence of bands in the infrared absorption region allusive to the axial deformation of carbonyl (C=O) indicating the presence of fatty acid methyl esters, which were confirmed in the GC-FID tests, and the absence of bands between 2500 and 3300 cm<sup>1</sup> indicating low percentage of water in biodiesel studied. Such occurrences allow us to predict the results of some quality control parameters of biodiesel. For example, the values shown in **Table 3** (methyl ester composition) for gongo biodiesel lead us to infer as to the degree of FAME saturation that the gongo biodiesel will have:


*Processing of Gong Oil (*Pachymerus nucleorum*) to Obtain Biodiesel by Methyl Route DOI: http://dx.doi.org/10.5772/intechopen.97721*

2500 to 3300 cm<sup>1</sup> allows us to predict that gong biodiesel contains low moisture content.
