Study of Reaction Conditions for the Synthesis of Methyl Oleic from Used Cooking Oil

Research on the study of the reaction conditions for the synthesis of methyl oleic from used cooking oil has been carried out. This study aims to: (1) reduce levels of free fatty acids (FFA) used cooking oil using activated charcoal adsorbent avocado seed; (2) determining the optimum conditions for the synthesis of methyl oleic from used cooking oil; (3) determining the quality of methyl oleic; (4) characterized methyl oleic by FTIR. Methyl oleic was obtained in two stages, namely the purification and synthesis stages. In the purification stage, 150 mL of used cooking oil was adsorbed with (2, 4, 6, 8, and 10) g of avocado seed activated charcoal for 2 hours at 70 o C. The purification results showed that the avocado seed activated charcoal could reduce the FFA content of used cooking oil by 93.79% (w/w). In the synthesis stage, methyl oleic was synthesized using the mol ratio (triolein : methanol) (1 : 3), (1 : 6), and (1 : 9), as well as the concentration of NaOH (1, 8, and 16)% (w/w) by weight of oil. The results showed that the optimum condition for the synthesis of methyl oleic from used cooking oil with the highest yield (84.32% w/w) was the mol ratio (triolein : methanol) (1 : 9) with a concentration of NaOH 1% (w/w). The quality of the resulting methyl oleic meets the requirements as biodiesel according to INS 04-7182-2015 with an iodine number value of 4.44 g I 2 /sample, saponification number of 114.44 mg KOH/g sample, cetane number of 82.96, water content of 0.03% (w/w), and the acid number of 0.71 mg KOH/g sample. The results of characterization of methyl oleic by FTIR showed that methyl oleic had a typical functional group absorption type of unsaturated fatty acid esters.


Introduction
Domestic demand for fuel oil is estimated to increase from 327 million barrels in 2011 to 578 million barrels in 2030 [1]. If this increase in fuel demand is not matched by an increase in production, then the availability of fuel in the future is a serious problem for us. Therefore, we need to make efforts to develop alternative fuels from renewable sources such as vegetable oils and animal fats. One of the vegetable oils that is quite abundant and wasted is used cooking oil. Used cooking oil contains triglycerides, so that used cooking oil can be used as a raw material for making methyl oleic (biodiesel) [2].
Biodiesel is an environmentally friendly alternative fuel. The advantages of biodiesel are reducing exhaust gas emissions which include hydrocarbon (HC), carbon monoxide (CO), sulfur monoxide (SO), and other particles [3]. Biodiesel also has a fairly high cetane number (CN), excellent lubricity, a relatively high flash point at 154ºC, and is biodegradable [4] [5]. Biodiesel can be synthesized from vegetable oil derived from renewable natural resources and Indonesia is rich in vegetable natural resources [6] [7].
Used cooking oil contains 84% (w/w) of oleic acid as FFA [20] [21]. If the FFA level of used cooking oil is > 2% (w/w) directly transesterified with an alkaline catalyst, the triolein or FFA will be hydrolyzed by the base (saponification) to form soap and glycerol ( Figure 1). If a large enough amount of soap is formed, it can inhibit the separation of glycerol from methyl ester because emulsions can be formed during washing [2].
There are two ways that you can do to reduce the FFA level of used cooking oil. First, the method of purification using activated charcoal as an adsorbent. One of the activated charcoal that can be used as adsorbent is avocado seeds. The use of avocado seeds as an adsorbent has been studied by Fitriani [22] and Kartika [23].
Second, the method of esterification by reacting FFA with methanol using a 98% (v/v) H2SO4 catalyst. The method of esterification can reduce the FFA level of used cooking oil by 78.34% (w/w), namely from 1.57 -0.34% (w/w) [2].
The reaction used to synthesize methyl ester from used cooking oil is transesterification. The transesterification reaction is an interconversion reaction from an ester, triester or triglyceride to an ester by heating with an alcohol and an acid or base catalyst [24].  Methyl oleic was washed with aquabidest until the pH of the solution became neutral.
Methyl oleic was dried with anhydrous magnesium sulfate until it became water free [32]. The same procedure was carried out for mol ratios (oil : methanol) (1 : 6) and (1 : 9), yield was calculated using equation (2). %Yield = Mass of methyl oleic obtained Total mass of oil x 100% (2) f. Quality Test of Methyl Oleic [29] Methyl oleic quality was tested based

a. Purification of Used Cooking Oil
The color change of used cooking oil before and after refining using avocado seed activated charcoal is shown in Figure 3. Figure   3 shows

b. Determination of FFA Content
The results of determining the FFA content of used cooking oil in various variations of the active charcoal mass of avocado seeds can be seen in Figure 4. Figure   4 shows that avocado seed activated charcoal can reduce the FFA content of used cooking oil by 93.79% (w/w), namely from 7.08% (w/w) before purification (0 g of avocado seed activated charcoal) to 0.44% (w/w) after purification (10 g of avocado seed activated charcoal). These results indicate that the higher the activated charcoal mass of the avocado seeds used, the lower the FFA content of used cooking oil. The decrease in the FFA content of used cooking oil was due to the -OH sites on the surface of the avocado seed activated charcoal reacting with FFA to form methyl oleic (ester) through an esterification reaction ( Figure 5).  Figure 4 also shows that the FFA content of used cooking oil after purification using 10 g of avocado seed activated charcoal is 0.44% (w/w) < 2.00% (w/w). Therefore, the synthesis of methyl oleic in this study only went through the transesterification stage.    (Figure 7). This is consistent with Le Chatelier's equilibrium principle, which states that when an external pressure is applied to an equilibrium system, the system adjusts in such a way that some of the pressure is balanced. The data in  The results of the interpretation of the FTIR spectrum of triolein and methyl oleic (biodiesel) are shown in Table 3.
The FTIR spectrum data in Table 3 shows that both triolein and methyl oleic  The results of the methyl oleic quality test are shown in Table 4. The data in Table 4 appears that the quality of the methyl oleic produced is in accordance with the quality requirements of biodiesel according to INS 04-7182-2015.

Iodine Number
The analysis results in Table 4 show that the iodine number of methyl oleic is 4.44. The higher the iodine number, the more double bonds >C=C< there will be in the methyl oleic. Therefore, the high iodine number is an unfavorable property for methyl oleic. This is because methyl oleic which has a double bond >C=C< in high amounts will be easily oxidized to form epoxide when the methyl oleic comes in contact with epoxy acid. This process is known as epoxidation.
The epoxidation reaction above appears that peroxy acid breaks down into carboxylic acids. This carboxolic acid will cause corrosion in the combustion engine when methyl oleic is used as fuel.

Saponification Number
The

Conclusion
Avocado seed activated charcoal can reduce the FFA content of used cooking oil by 93.79% (w/w), from 7.08% (w/w) before purification (0 g of avocado seed activated charcoal) to 0.44% (w/w) ) after purification (10 g of avocado seed activated charcoal).
The optimum condition for the synthesis of methyl oleic from used cooking oil with the highest yield (84.32%) was the mol ratio