**3.1 Thermal extraction of gong oil**

The extracted gong oil presented a physical aspect, with medium viscosity, straw yellow coloration, clear and free of impurities as shown in **Figure 4**.

In the course of this work, three thermal extractions of the gong oil collected from the tucum coconut (Bactris setosa) were performed. A gravimetric yield in the range of 29 to 38% was obtained. The following equation shows the gravimetric yield of the second extraction. A total of 599 g of gong was used and 208.17 g of oil was obtained.

$$Incomect = \frac{208,17}{599} \times 100 = 34,7596\tag{7}$$

It is believed that the production of biodiesel from the oil extracted from the gong is an innovative idea. In the literature to date no work has been found on this energy input. Comparing the gravimetric yield of some oilseed plants, such as: corn kernels with 4%, cottonseed with 15%, linseed with 34%, and soybeans with 18%. It must be agreed that the yield of thermal extraction of gong oil is of excellent quality.

## **3.2 Physicochemical profile of gong oil**

**Table 1** shows the physicochemical profile revealed for the oil extracted from the gongo in its raw or in natura form. The gongo oil was divided into two samples in order to perform its physicochemical characterization. In turn, each sample was divided into three aliquots, the analyses were performed in triplicates totaling 30 assays.

Acid value and moisture content are the main parameters affecting the sustainable production of biodiesel by the homogeneous alkaline transesterification route. A free fatty acid (FFA) content higher than 0.5% and a moisture content higher than 0.25% limit biodiesel production by basic homogeneous catalysis.

The acidity index is a quality parameter that indicates the amount of free fatty acids originating from the hydrolysis of glycerides. A high FFA content is indicative

**Figure 4.** *Physical aspect of gong oil in natura [20].*


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

#### **Table 1.**

*Physical–chemical characterization of gong oil* in natura *[20].*

that the oil is undergoing breakdown in the glycerol chains, releasing its main constituents. The acidity of oils tends to increase with prolonged storage due to the oxidation of free fatty acids, which can compromise their aroma, color, and flavor due to their rancidity process [23]. In this sense, the high acidity values found in **Table 1** may be related to the storage time of the samples (6 months) and also to the rudimentary way in which the oil was extracted.

In this work we obtained AI:3.26 mg KOH/g ( 0.41) and FFA:1.63% (0.20) for sample 1 and AI:3.41 ( 0.00) and FFA: 1.74 (0.00) for sample 2. Obtained the following results for tucum oil extracted by mechanical pressing IA: 37.5 mg KOH/g (0.40) and FFA:18.86% (0.26) [24], it is noted when comparing the results that in both cases the acidity of the oil extracted from the gong contained in the tucum coconut or properly from the tucum almonds present a high acidity index indicating that the gong oil was not appropriate for biodiesel production, requiring a treatment to adapt it to the biofuel production process.

Another parameter that influences the biodiesel production is water. This substance deactivates the catalyst forming soap, hinders the separation of product phase (biodiesel) and byproduct (glycerin), besides generating effluents that contaminate the environment. **Table 1** shows that the average water content was 0.17% ( 0.05) and 0.19 ( 0.00) for samples 1 and 2, respectively. On the other hand, [25], obtained a moisture content of 0.13% ( 0.00) for tucum extracted oil. Regarding the moisture content, it can be inferred that the gong oil in natura was within the specification for biodiesel production.

The saponification index (Is) is a property that has a strong influence on the quality of an oil. The saponification reaction can indicate the degree of deterioration and stability of an oil. The gong oil revealed Is:103 mg KOH/g ( 2.16) for sample 1 and for sample 2, Is:204 ( 0.00). According to the British standard an oil that is considered first quality should have a saponification index in the range of 177 to 187 mg KOH/g of the sample. The higher the saponification index, the greater is its application for food purposes [23]. In the view of the English standard, the Is of sample 1 is not first quality. The Is of sample 2, on the other hand, [24], is ideal for human consumption and coincidentally this input is widely used for this among the countryside populations. The difference in Is between the analyzed samples may be related to regional climatic conditions, since sample 1 was collected in the dry season (summer) and sample 2 was collected in the rainy season. The rainy season contributes greatly to the rancidity of the oil in natura (crude) because with the increase in moisture content there is hydrolysis of the oil, release of fatty acids and decomposition by the action of microorganisms.

Density is a physicochemical parameter of high relevance in the quality of biodiesel. This parameter is directly related to the chemical composition of the oil used for biodiesel production. The stronger the intermolecular interactions existing in the raw materials the higher the density will be. These interactions increase with the number of carbons in the chain (single bonds) and decrease the greater the number of unsaturated bonds (double bonds) contained in the oil composition. The analysis of the chemical composition of the gong oil performed by gas chromatography (GC) revealed as the majority acid, the C12:0 (lauric acid). In **Table 1** the mean density value for gongo oil was 915 Kg/m3 ( 0.00) and 887 Kg/m3 for samples 1 and 2 respectively. On the other hand, found similar density (D:889 kg/m3 0.00) [24], for the oil extracted from tucum by the physical method.When an oil suffers the influence of temperature there is a reduction in its density, in biodiesel the density is linked to the cetane number, which is an indicative property in the ignition delay time of diesel cycle engines and the calorific value, directly affecting the engine performance [23]. Fuel injection systems, thus, suffer changes in fuel density and influence engine power, in view of the addition of different mass to be injected. In addition, fuel density and viscosity affect injection pressure, fuel atomization, and engine performance.
