Purification of used cooking oil using natural corn cob and carbon corn cob as adsorbent with batch operation

Adsorption is one of the processes used to purify used cooking oil by using adsorbents from natural and carbonized corn cob as part of sustainability. The adsorption process is chosen because it is more economical, efficient, relatively affordable cost, and can be regenerated. This study was conducted in batches to observe changes in the quality of used cooking oil at certain time intervals and to determine the modeling of adsorption kinetics on natural corn cob and carbonized corn cob adsorbents. The sample of this study is 100 ml of used cooking oil with adsorbents in the form of natural corn cob and carbonized corn cob with a mass of 3 grams and a particle size of 70 mesh. This study’s best adsorption result is corn cob carbon adsorbent. This can be seen from the final turbidity value of 37.3 NTU compared to the natural corn cob adsorbent of 37.6 NTU. This study found that the adsorption process that occurs has chemical interactions as evidenced by second-order pseudo-modeling, which has a correlation coefficient close to one.


Introduction
Cooking oil is a glyceride compound vegetable oil from various fatty acids.Cooking oil repeatedly causes fatty acids to become saturated and can change color [1].Cooking oil used through the heating process will experience a decrease in quality, which can be seen from its increasingly unpleasant aroma, darker color, fatty acid levels, viscosity and higher peroxide levels [2].
If used cooking oil is not managed properly, it can pollute the environment, one of which can be characterized by increasing levels of Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD) in waters.[3].Used cooking oil is also very bad for health due to carcinogenic, mutagenic and genotoxic potential.Some of the diseases that can be caused are hypertension, atherosclerosis, cardiovascular disease, lipid peroxidation, increased LDL, and impaired vasorelaxation response.[4].
Used cooking oil, if purified, can provide excellent benefits for life.If properly purified, used cooking oil can be used to make products or assist existing production processes, such as soap making and biodiesel, considering environmental issues and renewable energy that is eco-friendly and sustainably sourced.
There are various ways to purify or remove unnecessary substances and contaminants in used cooking oil, including steam injection, centrifugation, neutralization with bases, and adsorption.Most of these processes require high temperatures, many solvents, and enormous costs.The choice of adsorption as a cooking oil purification process is considered more efficient, low energy costs, and relatively simple [5].Adsorption is absorbing or separation process of a specific component in fluid phase called adsorbate that transferred to the surface of adsorbent [6].There are two types of adsorption systems, batch and continuous (column).Batch adsorption provides an overview of the adsorbent's capabilities by mixing it with several solutions and observes the quality changes at specified intervals [7].
In the adsorption process, adsorbents, which are used to purify used cooking oil, are needed.The materials used in the manufacture of adsorbents in this study were selected to help reduce waste by utilizing them as adsorbents sustainably.One such potential waste is corn cob.Corn cobs are often thrown away, relatively cheap, available, and indeed contain components that are suitable for use as adsorbents, namely cellulose, and hemicellulose [8] So that further use of corn cobs as a cooking oil purification adsorbent can be carried out sustainably.
Pyrolysis is one of the appropriate methods for making carbon adsorbents because this process is more environmentally friendly.Pyrolysis is also known as carbonization.Carbonization with closed or minimal air can provide better carbon results, as seen from the carbon produced close to the equilibrium limiting value.The length of the carbonization process carried out also dramatically affects the results.This process generally requires temperatures of 400°C -500°C [9].This research was conducted to compare the adsorbent capacity of natural corn cob and corn cob carbon in the cooking oil purification batch adsorption process.

Materials and tools
The materials used in this research are corn cob as adsorbent and used cooking oil to be refined.While the tools used in this research are aluminum foil, ball mill, beaker glass, cutter, digital balance, furnace, measuring cup, and sieve.This research begins with manufacturing corn cob carbon adsorbent by carbonization method using a pyrolysis reactor at 500 ℃ for 30 minutes.The resulting charcoal was crushed using a ball mill and sieved using a 70 mesh sieve.After the adsorbent preparation was completed, continued with the cooking oil purification process using 100 ml of used cooking oil put into a glass beaker and added corn cob carbon adsorbent sized 70 mesh as much as 3 grams.The operation was batch operation for 5 hours, where every 20 minutes 5 ml was sampled to measure the turbidity by a turbidimeter.impurities or contaminants, so it has high turbidity.In contrast to Figure 3d and Figure 3e, the used cooking oil has been purified using natural corn cob adsorbent and corn cob carbon adsorbent, which has a decreased turbidity value.

Adsorption ability
Adsorption ability is strongly influenced by the surface area of the adsorbent used.The larger the surface area of the adsorbent means that more adsorbate can be absorbed so that the adsorption process increases.The particle size of the adsorbent that has been carbonized can increase the surface area of the adsorbent [10].To increase adsorption ability, researchers use carbon-type adsorbents, namely corn cob carbon, using the pyrolysis process.Smaller particle size, larger surface area, and suitable surface functional groups can increase the adsorption capacity.Pyrolysis can help the formation of corncob whose surface area is more porous so as to increase the adsorption ability [11].The pyrolysis process on corn cobs causes non-carbon elements to disappear, such as nitrogen and hydrogen.The pyrolysis process can reduced essential compounds in corn cobs, such as cellulose, hemicellulose, and lignin, to produce carbon with good adsorption ability [12].The research conducted by the researchers used a shakerless non-active corn cob carbon adsorbent with a size of 70 mesh and a weight of 3 grams.Adsorption was carried out for 5 hours with turbidity data taken every 20 minutes.The initial turbidity was 122 NTU. Figure 2 shows the effect of natural corn cob and corn cob carbon adsorbent types on the turbidity of used cooking oil.Based on Figure 4, it can be seen that there is a difference in turbidity within 5 hours in each adsorption process using natural corn cob adsorbent and corn cob carbon in batches.The adsorption process without adsorbent has a much higher turbidity, with an initial turbidity of 122 NTU and a final turbidity at the 300th minute of 55.8 NTU.Then, natural corn cob adsorbent has an initial turbidity of 122 NTU and a final turbidity of 37.6 NTU.Furthermore, corn cob carbon adsorbent has an initial turbidity of 122 NTU and a final turbidity of 32.2 NTU.Based on these results, the lowest turbidity was achieved using corn cob carbon adsorbent.The better adsorption ability indicates that corn cob carbon has a larger surface area and pores than natural corn cob adsorbent.
Figure 5 compares the total turbidity reduction of cooking oil without adsorbent, using corn cob natural adsorbent and corn cob carbon in batch operation.Adsorption without adsorbent resulted in a total turbidity reduction of 66.2 NTU.Furthermore, the corn cobs natural adsorbent obtained a total turbidity reduction of 84.4 NTU.Then, using a corn cob carbon adsorbent, the total turbidity reduction was 89.8 NTU.From these results, it can be concluded that the best adsorption ability occurs when using corn cob carbon adsorbent to purify used cooking oil sustainably.The results obtained using corn cob carbon adsorbents are better because the adsorbent has been carbonized so that components that are not needed as adsorbents have been reduced, and the pore size and surface area also increase.

Kinetics of adsorption
Determination of adsorption kinetics aims to understand and investigate adsorption rates controlled by batch process mechanisms.Commonly used kinetic models are Pseudo First Order and Pseudo Second Order.The equations for Pseudo First Order and Pseudo Second Order are as follows.First Order Pseudo Equations (1) [13]: (mg/g) is the amount of adsorbate that can be adsorbed at time t (min), qe (mg/g) is the equilibrium adsorption capacity, and k1 (min -1 ) is the rate constant of Lagergren's first-order pseudo equation.Furthermore, the equation is integrated with the limits t = 0, qt = 0, and t = t, qt = qt , so that equation 2 : ln(q e − q t ) = ln q e − k 1 .t The equation can also be derived to equation 3 [X], log(q e − q t ) = log q e − k 1 2,303 t Next, the Second Order Pseudo equation 4 : k 2 is the rate constant of the second-order pseudo model.
The above equation is integrated with the boundaries of t = 0, qt = 0, and t = t, qt = qt, thus equation 5 and 6 : The values of k2 and qe can be calculated from the intercept and slope of the linear line on the graph when plotted.  Figure 7 shows the second-order pseudo-modeling of corn cob natural adsorbent and corn cob carbon for batch process cooking oil purification.When using natural corn cob adsorbent, the R 2 = 0.9996.Then, using corn cob carbon adsorbent resulted in R 2 = 0.9984.To determine whether the data follows the first-order or second-order pseudo modeling can be seen from the correlation coefficient value close to 1.The results showed that the second-order pseudo is more appropriate and more suited to fit the experimental data on adsorption capacity and equilibrium, It can be concluded that the rate-determining phase of the pseudo second-order model is chemisorption, where valence force interaction occurs through electron exchange between adsorbent and adsorbate.[14].Based on these results, second-order pseudo modeling is better than first-order.

Conclusion
The use of corn cob is considered a sustainable step to reuse by utilizing corn cob waste to create something of value.The best adsorption result in the batch process of this research is corn cob carbon adsorbent.This can be seen from the final turbidity value of 32.2 NTU, which, compared to natural corn cob adsorbent of 37.6 NTU, shows that corn cob carbon adsorbent absorbs more impurities in used cooking oil.This study found that the adsorption process that occurs has chemical interactions as evidenced by second-order pseudo-modelling, which has a correlation coefficient close to one.This study shows that the adsorption process increases rapidly at the beginning of the process and then decreases with increasing time.It has also been shown that natural and corn cob carbon can be used as adsorbents in the cooking oil adsorption process.

Figure 3 .
a) Natural Corn Cob, b) Corn Cob Carbon, c) Used Cooking Oil Before Purification, d) Used Cooking Oil After Purification with Natural Corn Cob, and e) Used Cooking Oil After Purification with Corn Cob Carbon Based on Figure3a, it can be seen that the natural corn cob adsorbent has a bright ivory-white color, in contrast to the Figure3bcorn cob carbon adsorbent, which is black because it has gone through a pyrolysis process.In Figure3c, it can also be seen that the used cooking oil before purification has many Used

Figure 4 .Figure 5 .
Figure 4. Effect of adsorbent type on used cooking oil turbidity

Figure 6 .Figure 6
Figure 6.First-Order Pseudo-Modeling of Natural Corn Cob and Corn Cob Carbon Adsorbent on Used Cooking Oil Purification

Figure 7 .
Figure 7. Second-Order Pseudo-Modeling of Natural Corn Cob and Corn Cob Carbon Adsorbent on Used Cooking Oil Purification