A simple method for extraction of Ricinus communis L. oil and its application for biodiesel production by ethylic route

Biodiesel is a clean fuel, and an alternative to the environmental complications ascribed to fossil fuels. However, the forms of its production are still the object of research in the literature because some issues related to its process improvement and economical viability remain a challenge. Consequently, this research aims to produce biodiesel by the ethylic route from Ricinus communis L. oil extracted with a simple solid liquid extraction method without the use of the soxhled extractor and inspired from rural communities practices. In this sense, Ricinus communis L. was extracted by n-hexane as solvent, obtaining biodiesel through ethyl transesterification via alkaline catalysis. The characterization of biodiesel in terms of—acid value (AV), combustibility and corrosivity to copper. The results indicated that the yield of the extracted oil was 14% in relation to the mass of seeds used, the value of the AV was 0.96 mg NaOH/g, showing in this case that the oil can be used in the transesterification process to obtain biodiesel. The biodiesel yield obtained was 37% and the AV was 1.98 mg NaOH/g, being considered above the acceptable value for its use in diesel engines, and should be neutralized to at least 0.8 mg NaOH/g. Based on this work, biodiesel was obtained via ethyl esterification of Ricinus communis L. oil extracted from a simple and easy method.


Introduction
Biodiesel is fuel from biomass; this is renewable, clean, biodegradable, non-toxic, sulfur free among other advantages. For these reasons, it is considered the promisor fuel to overcome most of challenges ascribed to fuel from crude oil [1,2]. Besides that, in its structure, it possesses oxygen atoms resulting in enhancement combustion process. As consequence, the combustion reaction is complete, avoiding the production of high quantities of carbon monoxide (CO), unburned hydrocarbons and particulate matters [3,4]. Generally, biodiesel is produced from transesterification reaction of vegetal oils and other oils. In addition, in the biodiesel production, Fur glycerin is also produced as byproduct [5,6]. Several crops such as, sunflower, coconut and others are used as a source of biodiesel. However, the oils from abovementioned crops are expensive and compete with areas for food productions. Thus, non-edible source of oils are the paramount for biodiesel productions. There are several types of non-edible crops for oil production [7]. The Ricinus communis L., belongs to the family Euphorbiaceae, it can nowadays be found in most of tropical countries [8]. The seeds of Ricinus communis, are generally used for biodiesel productions, because they allow an easy production [7][8][9][10]. Soxhalet and solvent extraction are commonly used for Ricinus communis L. oils production. The yields in terms of oils is better than 1 3 other sources such as (soyben: 15-20% (p/p), sunflower: 25-35% (p/p), colza: 38-46% (p/p) e palm: 30-60% (p/p) [12]. Furthermore, the biodiesel produced from Ricinus communis L. oil presents properties that are in agreement with the quality standard of biodiesel [13]. Many methods such as hydrodynamic cavitation are applied for biodiesel production. The hydrodynamic cavitation is an interesting method, because it allows the biodiesel with yields between 40 and 80% in only 100 min [11]. In addition, for biodiesel production two routes are the cited in the literature, ethylic and methylic. Generally, the methylic route is most used for biodiesel production from Ricinus communis L. oil. The use of methanol is more common than ethanol because of its low cost and high reactivity, but there is a growing interest in the use of ethanol because it is renewable, non-toxic and is safe [14,15]. Methanol is generally added in higher proportions than the stoichiometric ratio (3:1), to change the equilibrium position of the reaction towards the product side. However, this fact strongly increases the final cost of the process, due to the fact that expenses with methanol are higher [16].
The extraction of Ricinus communis L. oil, is mainly performed applying sophisticated techniques, such as, Soxhlet, CO 2 supercritical fluid and among others [17,18]. However, as far as we known, no works in literature was found that applied a simple and traditional approach to obtain Ricinus communis L. oils for biodiesel production. This extraction method is mainly applied by rural communities in Mozambique and other countries to obtain Ricinus communis L. oil for application in traditional medicine.
Therefore, the present work aims to produce biodiesel by ethylic route using Ricinus communis L. oil extracted applying a simple method.

Materials
Ricinus communis L. oil was produced applying a simple method. Ricinus communis L. seeds were collected in Lichinga, Mozambique. The following was used used in this process; n-hexane (Supra Solvs), 95% diethyl ether (Rochelle Chemical); 99.9% ethanol and 37% HCl-RPE, Brande: CARLO ERBA. The tests for oil extraction and transesterification were carried out at the chemistry laboratory of Rovuma University and at Agrarian Institute of Lichinga, respectively.

Methods
Ricinus communis L. oil was extracted with a simple solid liquid extraction method without the use of the soxhled extractor.

Collection and treatment of Ricinus communis L. seeds
The Ricinus communis L. seeds were collected in the city of Lichinga. These seeds were harvested without regard to their varieties, in so doing; it was a random collection, as the Ricinus communis L. variety issue was not being studied. The seeds collected, firstly were peeled and dried at 25 °C. The dried and peeled seeds were then weighted and dried in oven (Ø 3871112-48/228 V-758 W) at 70 °C for 30 min. Following this, the seeds were toasted at 60 °C for 30 min and then weighed again. After drying, 600 g of dry seeds were weighed and crushed by mortar and pistil, until an oily and pasty mass was obtained.

Solvent extraction of Ricinus communis L. oil
The seeds treated in the previous step were mixed with hexane in 1:2 proportion (600 g of seeds to 300 mL of n-hexane). The mixture was heated at 68 °C for 10 min and was kept for 15 h. After 15 h the oil mass was filtered through a paper filter coupled to a funnel, using an Erlenmeyer flask to collect the oil. The mixture containing oil and solvent was submitted to a vacuum evaporator under constant heating of 68 °C for 50 min. Thereafter, the oil was left to cool naturally and was kept in a glass container Fig. 6c. Finally, the amount of oil produced by seeds of Ricinus communis was evaluated by weighing the oil obtained compared to the initial weight of the seed (Eq. 1).

Biodiesel production
The production of biodiesel from Ricinus communis L. is based on the methodology proposed by [19]. Having changed some parameters such as the solvent. In this experiment 74 g of Ricinus communis L. oil was used in the biodiesel production. Firstly, the oil was heated at 65-70 °C. In parallel experiment, an ethanolic solution containing 45 mL of ethanol and 1 g of NaOH was prepared, using magnetic stirrer, it was then necessary to elevate the temperature to 50 °C for 48 min. After the dissolution, of NaOH, the solution was added to Ricinus communis L. The process was kept under constant stirring for 2 h at 70 °C. Figure 1 illustrates all the steps followed until biodiesel synthesis.

Purification of the product obtained from transesterification
The mixture of biodiesel and glycerol was removed from the funnel and heated to 80 °C until it returned to a liquid state, after it had solidified. Subsequently, 2 mL of HCl was added to neutralize the catalyst used in the transesterification. Then the product was added back to the separating funnel and the biodiesel was separated from the glycerol. The biodiesel was washed with warm water until the washing water reached neutral pH. The biodiesel yield was then calculated using Eq. 2.
The total weight (g) of the biodiesel produced during transesterification was divided by the weight (g) of the oil used as raw material to determine the production yield of biodiesel.

Experimental characterization of biodiesel
The biodiesel of ricinus communis was characterized by its physicochemical properties such as the acid value, combustibility test and corrosion test. The experimental procedures of each property are presented below.
(1) Oil Yield(%) = weight of oil weight of the seed × 100% (2) Biodiesel yield (%) = Total wt.of product produced wt. of. oil × 100% The acid value of Ricinus communis L. oil was determined in triplicate. About 4.30 g of Ricinus communis L oil was placed in an Erlenmeyer flask, with 25 mL of ethyl ether/ethyl alcohol in a 2:1 (v/v) ratio, 3 drops of phenolphthalein and titrated with 0.1 KOH solution mol L −1 . The same procedure was used to determine the acid value of biodiesel. The results obtained were compared with the values standardized in the standards described in Table 1. The acid value was determined using Eq. 3.
Being, AV = Acid value (mg NaOH/g); V NaOH = Volume (mL) of the NaOH solution spent on the titration; V white = Volume of the titrant solution in mL for titration of the blank, C = Concentration of the titrant solution in mol L −1 ; M sample = mass of the sample in grams.

Combustibility test
Four cotton pads were embedded separately with 3 mL of Ricinus communis L oil (OR), 3 mL of Ricinus communis L. biodiesel (BR), 3 mL of petroleum diesel (DP) and 3 mL of the mixture of 20% Ricinus communis L. biodiesel with petroleum diesel (B20), respectively. The pads were placed in porcelain crucibles (one crucible for each pad) identified as OR, biodiesel of Ricinus communis L. (BR), DP and B20. A matchstick was used as a heat source to see which one would be flammable and observation of the characteristics of its flame was made.

Corrosion test
Two copper wires were placed in beaker cups and the beakers were identified as BR and DP. 2 mL of Ricinus communis L. biodiesel was pipetted into the BR beaker until the copper wire was soaked. Following this, 2 mL of petroleum diesel was pipetted into the DP beaker until the copper wire was embedded. The mixtures were left to stand for 48 h. After 48 h the wires were removed from the beakers and compared with the new wires (not used in the test-control). Figure 2 shows the results regarding seeds mass variation after two drying cycles. According to Fig. 2, after the first drying procedure the seeds lost 8% mass compared to fresh seeds. Whereas, after the second drying procedure the mass loss was 9% in relation with fresh seeds. These results are yet expected because the fresh seeds present humidity and after drying a part of humidity was lost. Figure 3 shows a pasty mass after seeds pulverization. The formation of this pasty mass is due to high content of oil and the reduction of particle size allowing the interaction between particles. Furthermore, this step is particularly important because it allows the interaction between the grounded seeds with hexane.  Figure 4 presents the macroscopically aspect of pulverized seeds in contact with hexane. In Fig. 4a, the phase separations are observable, suggesting that the solubilization had not started due to high viscosity of the mixture. Then, after the heating at 80 °C, the phase separations disappeared, forming a homogenous like mixture (Fig. 4b).

Solvent extraction of Ricinus communis L. oil
After 35 min (Fig. 4c), a separation into unstable oily phases could already be seen; these phases were stable and very visible when the mixture was left to stand for another 15 h. The phenomena observed in (Fig. 4b and c), is consequence of heating process that resulted in decrease of viscosity, leading to enhancement of dissolution of oil in hexane [20]. As a result, the extraction process accelerated. Subsequently, Fig. 4d, presents three phases after additional 15 h. Phase 1 (from bottom to top) consisted of husks, thicker grains and contained less oil, phase 2 consisted of finer grains and contained a greater amount of oil compared to phase 1, and, finally, phase 3 consisted of oil and some seed grains. Figure 4d shows that in addition to the action of the solvent in this process, the granulometry also influenced a lot, since in each phase, particles with different granulometry were arranged and the phase with the highest granulometry (finer particles) has higher concentration of oils, which is why it is necessary to use the press to obtain finer grains in relation to those obtained in grinding, allowing a greater homogenization of the material to be extracted with the solvent, in addition to reducing the density of the flakes.   Figure 5a shows the upper part of the mixture being decanted into a filter paper attached to the long-stem funnel to start the filtration of the crude oil. In Fig. 5b, it is observed that all phases are being filtered under the same conditions. Figure 5c shows the filtered oil being collected into a single container, as the filtration was done separately due to the size of the materials used and due to the difference in appearance at each stage of the mixture, believing that this would facilitate the filtration of each phase. The crude oil can be seen in Fig. 5d.
When the flask containing the oil was left open for natural evaporation of the solvent, there was a reduction in viscosity resulting from the reduction of the solvent by evaporation, but the process was slow (it took a week to notice the difference in viscosity) therefore, the oil was subjected to evaporation under heating. During heating intense bubbles were formed (Fig. 6a). These bubbles were the result of the solvent being heated above its P.E, so the bubbles represented the boiling solvent. The bubbles reduced with the passage of time, until they disappeared completely (Fig. 6b), and the solvent elimination process ended. After removing the solvent, 75 mL of oil was obtained whose weight was 88.76 g. In this case, the oil yield was 14% in relation to the mass of the seeds used (Fig. 6c).
By the method used to eliminate the solvent, it cannot be concluded that there was total elimination of the solvent in the oil, the most important being to ensure that there is a minimum of substances that can interfere in the transesterification process. Evaporation under continuous heating can be a good option when the solvent elimination process is to be efficient. However, care must be taken with the solvent used in the extraction process and the temperature to be used for heating.

Ricinus communis L. oil transesterification
The preparation of sodium ethoxide took 48 min, as the dissolution of sodium hydroxide in ethyl alcohol was slow and the transesterification was maintained for 2 h. During the addition of sodium ethoxide to the oil under heating and continuous stirring (Fig. 7c), there was an immediate change in the colour of the oil, which changed from light yellow to orange (Fig. 7c and d). In addition, it was observed that the oil became lighter. After 2 h of reaction, under constant stirring and heating, the process was stopped. When the product was placed in the separating funnel, it dried immediately, with no phase separation (Fig. 7d). this is due to the high value of free fatty acids that this oil presents, which in turn can make it difficult to separate phases after the transesterification reaction and can still cause problems with the formation of soap (saponification) [21] Filtration (a, b), collection (c), Ricinus communis L. oil collected (d)

Biodiesel purification
The biodiesel was purified eliminating the excess of NaOH by titration. After the addition of 35% HCl with the purpose of neutralizing the remaining catalyst and removing the salts of the product obtained in the transesterification process [12]. In the transesterification product, effervescence was registered which ended with the appearance of a white liquid which was separated by decantation. The final yield was 37% in relation to the OR mass used in transesterification. The final product of this process can be seen in Fig. 8d. Effervescence was the result of the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) used as a catalyst in transesterification. The production of Ricinus communis L biodiesel requires higher level of control as it involves several parameters for the yield to be satisfactory [22,23]. The yields shown in Table 1 refer to the conventional methods which involve a conventional reactor and the method of extracting oil from the seed of Ricinus communis L oil, but for the research in question no conventional extraction method was used and the reactor used was of low cost. However, the biodiesel yield obtained was considered satisfactory under the conditions of the study.

Acid value
The acid value of biodiesel was 1.98 mg NaOH/g, which shows an increase (Table 2). According to the norms of the ANP legislation, the established specification is that the acid value is between 0.1 and 0.5 mg NaOH/g [24]. However, it is observed that, having the acid value of the oil as well as the biodiesel obtained, they presented values outside the established norm due to their high content of ricinoleic acid [9].  Table 3 presents the phenomena observed in the combustibility test of Ricinus communis L. biodiesel. It compares combustibility of Ricinus communis L oil with petroleum diesel, as well as the mixture between DP and BR. The flame intensity of the OR (Ricinus communis L. oil) was extremely low compared to that of the BR (Ricinus communis L. biodiesel) Table 3. It is suggested that these differences were influenced by the cetane number of each substance, which is a parameter directly associated with fuel combustibility, so with the transesterification there was an increase in the cetane number of Ricinus communis L. oil (converted into BR) [12]. Generally, the cetane number of biodiesel is much higher than that of mineral diesel, which justifies the fact that biodiesel has a more controlled ignition and burns better in the engine than mineral diesel oil itself [16]. On the other hand, the BR, DP and B20 flame were similar, with the advantage that the BR flame was controlled. Table 3 also presents that OR and DP showed a reduced flame duration than BR and BR 20. Being that the flame of the BR had a much longer extension and OR much smaller in relation to another sample (B20 and DP), with that it can be said that the BR is economical from the point of view of consumption in the engine, when compared with the DP. Table 3, shows the smoke release behavior of all samples. There was a greater release of smoke in the burning of DP (oil diesel) and the mixture of DP and BR, having been lower in the mixture compared to pure DP, whereas in the BR a lower release of smoke was verified and when burning the OR the smoke release was not noticeable. Such aspects can be seen in Fig. 9. Figure 9d, presents the feature after the burning process of oil diesel and Ricinus communis L. biodiesel, until the end of the process, the capsules that contained DP and B20 showed a greater amount of carbon black compared to  the capsule in which the BR was burned. BR, the presence of carbon black was practically not verified at the end of the process, a fact that demonstrates the advantage of using BR in terms of the impacts of emissions when compared to DP. In this way, these observations are in agreement with studies that reported that fuels like ethanol and biodiesel release less pollutants than crude oil derivatives [25].

Corrodibility
The corrosibility of Ricinus communis L. biodiesel was performed using copper as a model metal (Fig. 9c). The BR presented a green color after 48 h of copper. However, the DP did not change the color, but the copper was corroded. The BR changed the color due to the oxidation reaction caused by copper [26]. The BR possess double bonds in the structure that can easily break, originating reactive radicals that can react with Cu 0 resulting in Cu 2+ (green color). For these reasons, additives are necessary to inhibit the oxidation [27]. It can be seen from Fig. 10c, that DP did not change in colour, but the wire that was dipped in the DP turned black (Fig. 10b), showing stability from the point of view of corrosion stability. Diesel has a greater corrosion stability compared to biodiesel. For the corrosion to be observed in a diesel environment, the metal must be exposed for a long period of time, unlike biodiesel that oxidizes when exposed to air and high temperatures, forming organic acids and hydroperoxides, which impair the quality of the product and promote corrosive processes [28].

Conclusions
A simple and rural communities practices inspired extraction process was applied in Riccinus communis L oil for biodiesel production. In this work, extraction with n-hexane proved to be efficient, since a yield of 14% was obtained in relation to the mass of seeds used in the process and the acid value (0.69 mg NaOH/g), considering within standards for the transesterification process (≥ 3 mg NaOH/g). Biodiesel was obtained through the ethyl route with a yield of 37% in relation to the Ricinus communis L. oil mass, with an acid value of 1.98 mg NaOH/g, being outside the parameters of ANP 045, with the need to correct the acidity as that this oil has a high index of ricinoleic acid. The combustibility of Ricinus communis L. biodiesel was better than petroleum diesel. However, by the corrosivity test, biodiesel proved to be very unstable, having suffered a degradation that resulted in the oxidation of the copper wire. The results of the acid value of Ricinus communis L. biodiesel are in agreement with its effect on corrosivity under the same study conditions.