Purification of glycerol as a by-product of biodiesel based on palm oil and castor oil

The government program requires the use of biodiesel B35, which is 35% fatty acid methyl ester and 65% diesel oil from petroleum, which would impact the rise of biodiesel production and is accompanied by an increase in the by-product of crude glycerol. Crude glycerol requires purification to increase its selling value. This product still contains a lot of impurities such as methanol, soap, catalyst, fatty acids, and water. Crude glycerol, a by-product of making biodiesel based on palm oil and castor oil, has a purity of 39.10 and 37.30%. In this research, purification of crude glycerol was carried out using 10% w/v activated carbon. The results of glycerol after purification were 64.90 and 66.90%, it shows that the addition of activated carbon can absorb impurities contained in glycerol. The increase in levels from 37.30 to 64.90% and 66.90% due to the loss of water, alcohol, residue base (KOH), soap and fatty acids. It can be concluded that activated carbon is quite effective for the glycerol purification process with an addition of 10% (w/v). A further process is required, namely separation by distillation, to obtain glycerol with a purity above 80% to comply with SNI 7182-2015 standards.


Introduction
The policy for using biodiesel was established in 2015 and updated in 2018 through Regulation of the Minister of Energy and Mineral Resources No.41.In 2020, the government stipulates mixing diesel fuel & biodiesel with a ratio of 70:30 or known as B30, and will continue to increase the biodiesel content to B40, B50 and so on.For 2020 with the B30 program, around 9.6 million KL of biodiesel from palm oil is needed.The biodiesel production process produces at least 10% crude glycerol [1, 2, 3].The B30 program will produce around 960 thousand KL of glycerol.Even shortly B40 and B50 will be implemented, Currently, the installed capacity of the Indonesian biodiesel industry is 13.8 million KL/year, which will produce around 1.38 million tons of glycerol/year, which needs to increase its added value.The increase in biodiesel production capacity led to crude glycerol production.Suppose this increase in production is not accompanied by advances in utilization technology and its transformation into products with higher added value and market expansion.In that case, the excess availability of crude glycerol will increase the by-products of biodiesel production.Based on data from the Directorate of Agro and Chemical Industries in 2019, the utilization of 1308 (2024) 012059 IOP Publishing doi:10.1088/1755-1315/1308/1/012059 2 glycerol by industry has reached 370,000 tons, compared to the current total production of glycerol getting 960,000 tons (assumed only from FAME production for biodiesel).
Crude glycerol is a by-product of biodiesel produced around 10-20% v/v , which has many uses, including as a solvent for pharmaceuticals and cosmetics.With the determination of biodiesel currently used by the government in the B35 program, the by-product of glycerol is increasing.In one biodiesel production cycle, the by-product in the form of glycerol reaches 10% of the total biodiesel production [10].
This product still contains a lot of impurity compounds such as methanol, soap, catalysts, fatty acids, water, and others [4].If this product is purified, it will increase revenue for the biodiesel industry.Research about the purification of crude glycerol has been carried out by several researchers.Aziz [6,7] performed crude glycerol purification using phosphoric acid (H3PO4), glycerol extraction using polar solvents, and adsorption with commercial activated carbon.The novelty of this research is part of the integration research into making biodiesel and purifying the glycerol by-product produced.So that the glycerol produced can be reused.
The results of the glycerol quality analysis obtained were 96.2% glycerol levels; ash content 2.08%; MONG content (Matter Organic Non-Glycerol) 1.50%; and the resulting glycerol is colorless or transparent [5].The purification of crude glycerol was also carried out by Aziz et al., (2019) [5] using acidification and adsorption methods using Lampung natural zeolite.The optimum conditions for zeolite adsorption in crude glycerol purification were obtained at 75 minutes, the zeolite concentration was 12% of the sample mass, the adsorption temperature was 60 ºC, and the zeolite diameter was 0.2 mm with the glycerol quality obtained after the adsorption process at optimum conditions meeting the quality requirements of SNI 06-1564-1995 [8], with a moisture content of 7.38%; ash content 3%; does not contain sugar; and glycerol content of 88.91%.The aim of this research is to purify glycerol as a by-product of biodiesel using activated carbon as an absorbent to improve the quality of glycerol and the resulting color.

Glycerol purification as a by-product of biodiesel production [8]
A total of 200 ml of crude glycerol was added to 85% technical phosphoric acid, as much as 5% (v/v) heated at 60°C for 30 minutes at 300 rpm.After settling for 1 hour, three layers: form fatty acids, glycerol, and phosphate salt crystals.The fatty acids and phosphate salt crystals were separated, and the glycerol, as a result of settling, was filtered and bleached using 10% (w/v) activated carbon and kept overnight at room temperature .After that, the filtrate was separated to get purified glycerol.The glycerol purification flow chart can be seen in Figure 1.As much as 0.5 g of crude glycerol dissolved in 50 ml of distilled water.Then 5 drops of BTB indicator were added and the solution was acidified with 0.2N H2SO4 until a green or greenish-yellow color was formed.The solution was neutralized with 0.05N NaOH until a blue color was formed.A blank of 50 ml of aquadest was made and the same procedure was carried out as for the sample.A total of 50 ml of NaIO4 solution was added to the sample solution and blank, stirred gently, covered and allowed to stand in a dark room at room temperature (no more than 35°C) for 30 minutes.After that, 10 ml of 1:1 Gliserol, % = Analysis of physicochemical properties ethylene glycol solution was added and allowed to stand in a dark room at room temperature (no more than 35°C) for 20 minutes.The solution was diluted with 300 ml of distilled water, 3 drops of BTB indicator, and titrated with 0.5N NaOH until a blue color was formed.

Results and Discussion
Purification of glycerol as a by-product of biodiesel production In this research, the purification of glycerol as a by-product of biodiesel production was carried out using activated carbon.Based on SNI 7182-2015 [9] the requirements and quality for the density of crude glycerol are 0.85-0.89gr/cm 3 at 40°C.In this experiment, the density value of crude glycerol was 0.8787 gr/cm 3 at 40°C.This means that the crude glycerol produced still meets the specifications according to SNI 7182-2015 [9].Furthermore, glycerol purification was carried out to obtain glycerol with better purity.The stages and results of glycerol purification are visualized in Figure 2. The requirements and product quality for total glycerol for crude glycerol are stated in SNI 7182-2015 [9], namely a minimum of 80% by mass.This study obtained total glycerol content before refining for palm oil of 39.10% and 37.30% for castor oil (Table 1).Judging from the results obtained for crude glycerol content, the glycerol results from this experiment are still far from the standard that should be, namely 80%.Meanwhile, for commercial standard glycerol and purity, >90% purity is required [11].Coarse glycerol is brownish red as shown in Figure 2 which shows that glycerol still contains impurities in the form of soap containing free fatty acids, while the brownish yellow/brick red color is caused by the presence of beta-carotene pigment from palm oil which is the raw material for making biodiesel.
The initial stage of purifying glycerol from crude glycerol is the separation of glycerol and phosphate salt crystals with the addition of H3PO4 5% (v/v).Adding phosphoric acid to crude glycerol causes a reaction with the remaining KOH to become a phosphate salt and precipitate.Crude glycerol is reddish brown and alkaline because it uses a KOH catalyst.Nanda et al. (2014) [6] used phosphoric acid (H3PO4) to separate soap and fatty acids contained in crude glycerol sourced from palm oil; the optimum pH obtained was 5.Meanwhile, Sinaga et al. (2018) [12] also conducted the same thing, but the vegetable oil used is coconut oil, and the optimum pH is 7. Differences in raw material sources can cause differences in the refining process (pH) conditions in refining crude glycerol from biodiesel by-products.
In addition, phosphoric acid will react with the soap formed in the transesterification reaction to become free fatty acids [13].The purpose of adding this acid is to attract potassium ions contained in dirty glycerol.The reaction is as follows: Apart from the purpose of attracting potassium ions, the addition of acid is also to change the soap formed in the biodiesel production reaction into free fatty acids.The addition of 5% phosphoric acid to dirty glycerol causes the formation of 3 layers, as shown in Figure 2. The top layer is free fatty acids, the middle layer is glycerol, while the bottom layer is methanol residue and potassium phosphate precipitate.
The fatty acids, glycerol and phosphate salts were separated, some of the salts suspended in glycerol/water were then filtered using vacuum filtration and filter paper.Phosphate salts can be used as fertilizers.The resulting phosphate salt can be seen in Figure 1.After the phosphate salt is separated from the crude glycerol, the next step is glycerol purification by removes the glycerol color.
The next stage removes the glycerol color by adding activated carbon as much as 6.155 grams (w/v) and 10 grams (w/v) of activated carbon, as shown in Figure 2. A type of adsorbent that is non-polar and relatively inexpensive.Activated carbon can absorb inorganic components with Van der Waals attractions.The impurity components are expected to be absorbed by inorganic salts and FFA from crude glycerol, which is a less polar compound when compared to glycerol.The adsorption process in bleaching with activated carbon lasts 12-24 hours or more until the glycerol solution becomes clear.
Purification with activated carbon is quite effective for purifying glycerol.Activated carbon can absorb impurities in glycerol on its surface.Activated carbon has a large surface area so it is able to absorb impurities in glycerol.Activated carbon is carbon that has been activated to increase its surface area using acids or bases.After the addition of activated carbon, the resulting glycerol color becomes clear (colorless) like the color of pure glycerol (Figure 3).In this study the activated carbon used is technical activated carbon.
Requirements and product quality for total glycerol for crude grade are contained in SNI 7182-2015 [9] with a minimum of 80% mass.Glycerol content after purification IOP Publishing doi:10.1088/1755-1315/1308/1/0120596 were 64.90 and 66.49% (Table 2).The purity of glycerol is still below the SNI standard, which is 80%, possibly because the final stage of this purification is just bleaching, while the impurities such as water are still present.
It can be concluded that activated carbon is quite effective for the glycerol purification process with an addition of 10% (w/v).The addition of 6 g of activated carbon resulted in slightly cloudy glycerol.This can be seen from the color, but the addition of 10 g of activated carbon produces clear glycerol.Activated carbon can function as a good absorbent in various liquids, so the addition of large amounts will increase its effectiveness as an absorbent.Then a further process is needed, namely separation by distillation, to obtain glycerol with a purity above 80%.

Conclusion
Purification of biodiesel by-products using activated carbon 10% w/v can purify glycerol by-products of biodiesel based on palm oil and castor oil from 39.10 and 37.30% to 64.90 and 66.49%.The purity of the glycerol produced still needs further development to achieve 80% purity according to SNI 7182-2015 [9] standards.

Figure 1 .
Figure 1.Diagram of purification of glycerol as a by-product of biodiesel production

Figure 2 .
Figure 2. Stages of purification of glycerol as a by-product of the biodiesel process in palm oil

Table 1 .
Calculation of total glycerol content in crude glycerol before purification

Table 2 .
Calculation of total glycerol content in crude glycerol after purification