Optimization of pyroliysis of polypropylene and polyethylene based plastic waste become an alternative oil fuel using bentonite catalyst

. The conversion is accomplished by pyrolyzing plastic bag waste at relatively low temperatures, around 50-225 O C, and using a bentonite catalyst. The four products are alternative oils consisting of gasoline, kerosene, diesel, and non-condensable gas. The pyrolysis procedure is as follows: (a). 3 kg of chopped plastic waste mixed with a mass fraction of bentonite catalyst of around 0.035-0.0125 of the weight of plastic waste and then put into the pyrolysator; (b). the pyrolysator is heated with 1.5 kg of liquid petroleum gas (LPG) for 2-3 hours at a temperature ranging from 50-225 o C; (c). pyrolysis results are stored separately in 3 pots: gasoline, kerosene, and diesel; (d). to clarify pyrolysis results by adsorption using a sand filter. The variables studied were the polypropylene (PP) and polyethylene (PE) plastic materials type and the effect of the mass fraction of bentonite catalyst ranging from 0.035 to 0.125. The research obtained relatively good results as follows. Pyrolysis of 3 kg of PP plastic waste with the mass fraction catalyst of 0.100 yielded 44.00% alternative gasoline, 10.76% alternative kerosene, 21.07% alternative diesel, and the remaining non-condensable gases. The flash (ASTM D7094) points of alternative gasoline, alternative kerosene, and alternative diesel


Introduction
Waste is a severe problem in Indonesia that has not yet been resolved optimally.The increase in population causes an increase in the amount of waste accumulated due to human activities.The entire population of Indonesia in 2016 was able to produce 0.8 kg of waste per person, or a total of 189,000 tons of plastic waste/day.Of this amount, 15% is in plastic waste, or 28,400 tonnes of plastic waste/day [1].In 2022, waste generation in Indonesia is estimated at 69.2 million tonnes/year [2].In line with this, economic growth in Surabaya continues to increase, currently reaching 4.85%.This economic growth has made Surabaya one of the five cities in Indonesia with the highest waste generation in Indonesia.2018 Surabaya produced 2,164.4tonnes/day of waste [3].The national waste management information system data recorded 1,477 tonnes/day at the Benowo Final Disposal Site.
Of this amount, around 54.31% comes from food waste, plastic (rice sacks, aqua bottles, plastic straws) 19.44%, paper 14.63%, and textiles 1.47% [4].This plastic waste also has various types, including polypropylene (PP), which is a type of plastic that is often used as packaging for dry food/snacks and plastic straws.Polyethylene (PE) is a plastic-type commonly used to package drinks such as ice cubes, syrup, and rice sacks.Apart from that, there is also a type of high-density polyethylene (HDPE), which is a type of plastic that is clean white and is used as tissue bags, detergent bottles, cooking oil, plastic pipes, and shopping bags because it is flexible and has high strength.Low-density polyethylene (LDPE) plastic is also used for can linings, food wrapping plastic, and bread wrapping.In 1907, the use of plastic was discovered for the first time, and plastic-based items continued to increase.The increase in plastic use impacts population development, technology, and industry.Plastic cannot be separated from everyday life; this can be seen in several items made of plastic or those composed of plastic materials.In general, plastic waste is thrown away or burned in landfills, and some is recycled.Burning waste is an ineffective treatment and has negative impacts because it produces dangerous gas emissions [5].This problem requires alternative ways to convert plastic waste into a product that is more useful and has a higher selling value, including alternative fuel oil.
The technology for converting plastic waste into fuel oil is the thermal cracking process, which is a process of breaking down hydrocarbon chains from long-chain compounds into smaller-chain hydrocarbons with the help of heat.A thermal cracking process aims to obtain petroleum fractions with a lower boiling range than the feed.In this process, gas, gasoline (naphtha), diesel, residue, or coke are produced.In the thermal cracking reaction, C-C bond scission (C-C bond scission), dehydrogenation, isomerization, and polymerization will occur [6].Plastic is a hydrocarbon compound that has a long chain resulting from polymerization: polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET).Polyethylene has a molecular weight of around 200-500 thousand, while polypropylene has a molecular weight of around 10-12 thousand [7].Thermal cracking is also known as the pyrolysis process, where the pyrolysis process is a thermal decomposition process of organic material without the involvement of oxygen in it.This process results in the breaking of the chain of chemical compounds, resulting in the production of new compounds that have shorter bond chains.Plastic, as a form of polymer with the main monomer in the form of a hydrocarbon chain, has the opportunity to be processed by pyrolysis in the hope that hydrocarbon compounds with shorter C chains can be produced [8].Due to the problem of plastic waste, most of which is still not managed well, the authors intend to participate in overcoming this problem, namely by pyrolyzing plastic waste into alternative fuel with the help of a bentonite catalyst.Plastic waste is in the form of plastics used for household needs, including rice sacks, rice containers (plastic boxes), mineral water bottle packaging, mineral water cup packaging, and soft drink cups.This research is aimed at studying the process of converting polyethylene (PE) and polypropylene (PP) plastic into alternative fuel oil using the pyrolysis process and studying and analyzing the effect of the mass % of bentonite as a catalyst.

Utilization of plastic waste
Much research has been carried out on handling the problem of plastic waste, and alternative fuel oil has been produced from these studies.Some of these alternative fuels are used, among others, as fuel in industry to replace the role of diesel, as a substitute for fuel for 3-wheeled motorbikes, and as fuel to drive tractors in agricultural businesses at a more affordable price.The studies carried out by previous researchers are listed according to raw materials, the weight of raw materials, pyrolysis conditions, and results, as presented in Table 1.From Table 1, it can be seen that the researchers did not report, among other things, the type of raw material, the type and properties of fuel, and the length of pyrolysis time.The use of plastic waste as raw material for the pyrolysis process into fuel oil is often encountered.Every year plastic waste in Indonesia increased by 189,000 tons/year in 2016, so it is necessary to use plastic waste recycling so that it does not pollute the surrounding environment [1].Plastic waste, especially those made from polyethylene and polypropylene, is used as alternative fuel oil.
Polypropylene-type plastic is a thermoplastic polymer material made by the polymer industry and used in various applications as fiber or plastic.Polypropylene is a light polymer because it has a density ranging from 0.90-0.92g/mL, a molecular weight ranging from 10,000-12,000, and has the highest level of brittleness and is less stable to heat [13].Apart from using polypropylene plastic, polyethylene plastic is also used.Polyethylene is a white transparent thermoplastic material that has good flexibility, has a melting point varying between 110-137 0 C, and has a molecular weight of 200,000-500,000 [14].The plastic waste has been recycled using pyrolysis; this can be considered profitable by turning plastic into fuel that can be reused.The pyrolysis process is a thermochemical decomposition process using organic material (biomass) through a heating process without contact with oxygen, where the raw material will experience a chemical structure breakdown into a gas phase at temperatures ranging from 200-500 0 C [15].
This pyrolysis process uses conventional steam distillation as a pyrolysis process tool, which has quite good results, but sometimes it still has several shortcomings.Research continues to be carried out to find the use of steam distillation as a pyrolysis process tool that can meet needs efficiently and effectively.One of the research being carried out is designing a distillator with a condenser without fluid cooling.The use of this distillator is still the same as a regular distillator, but it has several advantages.The design of a distillator with a condenser without fluid cooling has shown better results in terms of design, production costs, equipment, and higher oil yields [16].The principle of this fluidless condenser has a working principle where the hot steam is cooled using a Peltier so that it can absorb the heat of condensation, which changes the phase of the pyrolysis product from a gas phase to a liquid.The condenser has twelve peltiers placed on each bottom side of each inner side of the condenser wall.To speed up the decomposition reaction process in a steam distillation apparatus, a catalyst can be added.
In the pyrolysis process, a catalyst can be added to speed up the decomposition reaction and shorten the hydrocarbon chain so that it can be easily condensed into oil.Research by adding a catalyst has been carried out by several researchers where the presence of a catalyst can minimize the production of heavy oil that can be produced during the pyrolysis process without a catalyst.Various types of catalysts can be used in the pyrolysis process, such as alumina, bentonite, and zeolite.
According to Buchari and Harsini (1996), bentonite has high plastic and colloidal properties, with the main content of skit minerals (montmorillonite), has exchangeable cations and has a specific pore size and can expand (swelling), so that bentonite can be used as a catalyst in this pyrolysis process [17].The main requirement for using a catalyst in the pyrolysis process is a large surface area and a large pore volume.The method that can be used to expand the catalyst's surface and volume is by activating sulfuric acid.

Bentonite catalyst activation using sulfuric acid
Activation of the bentonite catalyst using sulfuric acid aims to clean the catalyst from impurities.Meanwhile, to adsorb impurities contained in alternative fuel products, you can use bentonite.Activation of bentonite using acid will produce an adsorbent with more significant active sites and a greater surface acidity level [18].So, the adsorption ability of bentonite increases higher compared to before, thus making the adsorption process easier.Furthermore, bentonite that has been activated was tested using SEM instrument to determine the morphological structure.Bentonite contains montmorillonite minerals ranging from 80-85%.

Research novelty
Different from research carried out by previous researchers, this research was carried out at relatively low pyrolysis temperatures, with the highest temperature being 225 0C, and the pyrolysis results were separated directly into alternative gasoline, alternative kerosene, and alternative diesel.Thus, the overall pyrolysis costs are lower.

Equipment
In this research, the leading equipment used is a series of pyrolysis reactors consisting of a reactor with a capacity of 5 kg, which is equipped with a pressure indicator, temperature indicator, condenser, burner, alternative diesel reservoir, alternative kerosene reservoir, and alternative gasoline reservoir.Apart from that, there are tools used for catalyst preparation, catalyst characterization, and testing of the physical properties of alternative fuels, as well as infrared thermometers and LPG gas as a heating source.Equipment for bentonite catalyst preparation includes a hot plate, magnetic stirring, centrifuge, and oven, while the tool for catalyst characterization is an SEM instrument.The equipment for testing the physical properties of alternative fuels are pycnometers, Ostwald viscometers, and flash point apparatus.

Material
In this research, the raw materials used were plastic waste made from polypropylene (PP), which came from drinking water cups, soft drink containers, and thin wall rice boxes, and plastic waste made from polyethylene (PE), which came from rice sacks., sugar packaging plastic, and instant noodle packaging plastic.Plastic waste made from polypropylene (PP) and made from polyethylene (PE) is each washed to clean the remaining dirt (food scraps and dust), then dried, namely by drying it in the sun for one day to ensure the plastic is dry.The dried plastic is cut into small pieces around 1cm x 1 cm to increase the contact area.

Bentonite catalyst preparation
Bentonite powder is soaked in hydrogen peroxide solution for 24 hours to remove the organic compounds contained in it.After washing, the bentonite is then dried in an oven at a temperature of around 100 0 C for 12 hours.Next, acid activation is carried out on the bentonite powder by weighing 100 grams of bentonite and adding excess distilled water to make it a slurry.Then, 98% concentrated sulfuric acid was added with a mass ratio of sulfuric acid to bentonite mass of 0.35.Then, the mixture is placed in a water bath with a temperature of around 90 0 C for 12 hours.At the end of the activation time, an excess amount of water is added to the mixture to stop the activation reaction; then, the solid is separated from the liquid using a centrifuge.The separated solid was then washed repeatedly to remove residual acid and then dried at 100 °C for 24 hours.Next, the bentonite catalyst is ready to be used.

Plastic waste pyrolysis process without using a catalyst
First, 3 kg of plastic waste made from polypropylene (PP) and polyethylene (PE), which has gone through the washing, drying, and cutting process, is weighed; after that, the plastic waste is put into a pyrolysis reactor with a capacity of 5 kg.Next, the pyrolysis reactor is closed with bolts so that it does not leak during the heating process and is sealed from outside air.The next step is to prepare a 3 kg LPG gas cylinder and turn on the burner right under the pyrolysis reactor so that the heat is even.The heating process of the pyrolysis reactor with a gas cylinder is carried out for 3 hours 30 minutes with a temperature of 100-225°C which can be read on a thermocouple device, and the pressure in the pyrolysis reactor is kept constant at l atm, read on a pressure gauge.About 1.5 kg of LPG gas was used for one experiment.In the pyrolysis reactor, plastic waste will soften, melt, and then undergo a breakdown process to produce gases in the form of alternative gasoline, alternative kerosene, and alternative diesel.These gases are then channeled into the condenser.The gases in the condenser will undergo a phase change process from vapor to liquid, which will then release droplets at the condenser output so that they are collected in bottles.The resulting droplets from this process are alternative gasoline, alternative kerosene, and alternative diesel, all three of which are stored in bottles, and non-condensable gases are released into the air.Next, an analysis was carried out on the three alternative fuels: calorific value, octane number (RON) rating, flash point, density, and viscosity.

Plastic waste pyrolysis process using a bentonite catalyst
Plastic waste made from polypropylene (PP) or polyethylene (PE), which has gone through the washing, drying, and cutting process, is weighed at 3 kg, after which it is put into a pyrolysis reactor with a capacity of 5 kg and a catalyst is also added with a mass to mass ratio of plastic waste of 3 .5%.Next, the pyrolysis reactor is closed with bolts to prevent leaks during the heating process.Then, a 3 kg LPG gas cylinder was prepared, and the burner was lit right under the pyrolysis reactor so that the heat was even [16].The heating process of the pyrolysis reactor with LPG gas cylinders is carried out for around 2-3 hours with a temperature ranging from 100-2250C, which can be read on a thermocouple, and the pressure in the pyrolysis reactor is maintained at a constant level that can be read on a pressure gauge.The role of this catalyst occurs when the plastic material has melted, and the catalyst can help break down hydrocarbon chains with a significant molecular weight into new hydrocarbon compounds with a lower molecular weight.Next, these compounds are stored in a tank, which will help the condensable vapor flow to the condenser to be condensed.The PP plastic in the condenser will have a condensation process, which will then produce droplets at the output of the condenser, which are then collected in the bottle.The resulting droplets from this process are alternative gasoline, alternative kerosene, and alternative diesel.The alternative fuel results were then analyzed at the Energy and Environment Laboratory, ITS, Surabaya, to determine the heating value, octane number rating, flash point, density, and viscosity.The same steps above were repeated on different catalyst variations of 5%, 7.5%, 10%, and 12.5% (catalyst weight/material weight).

Bentonite catalyst
Bentonite characterization using scanning electron microscopy (SEM) was carried out to determine the surface morphology and type of mineral constituents, as seen in Figure 1.From Figure 1 (a), it can be seen that the surface of the bentonite catalyst is covered by other components even though the structure and pores of the bentonite are still clearly visible.It also shows the smaller pore size seen in the activated bentonite catalyst with a magnification of 20,000x.The pore size of bentonite greatly influences the adsorption process [19,20].The more pores that are open on the bentonite surface, the better the adsorption process will be, with more adsorbate being adsorbed on the surface of the adsorbent pores.impurities cover the pores on the surface of bentonite without activation.When the pores are still filled with impurities, the adsorption process will be hampered because the adsorbate to be adsorbed cannot be adsorbed either on the catalyst surface or inside the catalyst pores.In Figure 1 (b), it can be seen that the morphological image was analyzed using SEM at a distance of 200 µm with a magnification of 40,000x, which shows more precise,surface contours and morphology.

Effect of adding bentonite catalyst on pyrolysis of PP-based plastic
The effect of adding bentonite catalyst on the yield of alternative fuel oil is shown in Figure 2.

Fig. 2. Effect of bentonite catalyst mass fraction on alternative fuel oil yield
Based on Figure 2, the total yield in the PP plastic waste pyrolysis process shows that the two dominating pyrolysis products are alternative gasoline and alternative diesel.By increasing the mass fraction the bentonite catalyst from 0.035 to 0.100, the alternative gasoline yield will increase from 10.67% to a peak of 44%.On the other hand, by increasing the bentonite catalyst from 3.5% to 10%, the alternative diesel yield will decrease from 40.34% to its lowest at 21.07%.This shows that the bentonite catalyst plays an active role in explicitly directing alternative gasoline products.The selling prices per liter of gasoline, kerosene, and diesel, respectively, are as follows: IDR 10,000.00,IDR 8,400.00,and IDR 6,800.00,so the total selling price of alternative gasoline, alternative kerosene, and alternative diesel in these conditions are also the largest, namely IDR 26,413.81.The bentonite catalyst plays a role in increasing the formation of alternative gasoline and, conversely, reducing the formation of alternative diesel [21].The use of bentonite catalyst is profitable, considering that the selling price of alternative gasoline is higher than the selling price of alternative diesel.
Furthermore, by increasing the weight fraction of the bentonite catalyst from 0.100 to 0.125, the alternative gasoline yield will decrease from 44.00% to 28.82%, and the alternative diesel yield will increase from 21.07% to 31.57%.This shows that under these conditions, the role of the bentonite catalyst to direct the formation of alternative gasoline is no longer effective.The selling price of pyrolysis products under these conditions is IDR 23,989.73.From this description, the condition of the 0.100 bentonite catalyst heavy fraction is considered optimum with yields of alternative gasoline, alternative kerosene, and alternative diesel, respectively, at 44.00%, 10.76%, and 21.07%.

Characteristics of the Physical Properties of Alternative Fuels Results from Pyrolysis of PP Plastic Waste
For alternative fuel oil produced from the pyrolysis process of glass plastic (PP) waste using a bentonite catalyst with a weight fraction of 0.100, characteristic tests were then carried out, including density, viscosity, flash point, heating value, and octane number rating.The test results are presented in Table 2.  2, the density and viscosity values of alternative fuels were obtained for each type of liquid product, which met standard commercial specifications, so that the results of alternative fuel products with the bentonite catalyst addition of weight fraction of 0.100 is good quality for further flash point testing.The flash points of alternative gasoline, alternative kerosene, and alternative diesel products are, respectively, 84 o C, 68 o C, and 100 °C.Data on the calorific value of the test results for each alternative fuel product are 10,970 cal/g for alternative gasoline, 10,965 cal/g for alternative kerosene, and 10,816 cal/g for alternative diesel.From the parameter aspect of the octane number (RON) rating value, the RON value for alternative gasoline and alternative kerosene both have RON values greater than 97.This shows that the calorific value of alternative fuel from plastic waste made from PP raw materials has met the calorific value standard and appropriate qualifications, as produced by PT Pertamina, Indonesia.

The effect of bentonite catalyst on alternative fuels through pyrolysis of pe plastic waste
The effect of using a bentonite catalyst on the yield of alternative fuel oil is shown in Figure 3. Based on Figure 3, it can be seen that with the increase in the weight fraction of the bentonite catalyst, the yield of alternative gasoline, alternative kerosene, and alternative diesel also fluctuates.The highest alternative gasoline yield of 32.54% was achieved at a bentonite catalyst weight fraction of 0.050, the highest alternative kerosene yield of 17.11% was achieved at a bentonite catalyst weight fraction of 0.100, and the highest alternative diesel yield of 53.90% was achieved at a bentonite catalyst weight fraction of 0.035.Figure 3 reveals that with the increase in the weight fraction of the bentonite catalyst from 0.035 to 0.100, the non-condensable gas yield will also decrease from 25.88% to its lowest point at 11.45%, whereas with the increase in the weight fraction of the bentonite catalyst from 0.100 to 0.125, then the yield of noncondensable gases will increase from 11.45% to around 21.09%.This shows that the bentonite catalyst plays a role in conditioning and directing the pyrolysis product phase to the liquid phase [22,23].Optimization is based on the highest sales results from alternative gasoline, alternative kerosene, and alternative diesel products.
Optimum conditions with the highest sales yield of IDR 27,000.00were achieved with pyrolysis products with an alternative gasoline yield of 27.65%, an alternative kerosene yield of 17.11%, and an alternative diesel yield of 43.79% on a bentonite catalyst weight fraction of 0.100.

Characteristics of the physical properties of alternative fuels resulting from pyrolysis of PE plastic waste
For alternative fuels produced from the pyrolysis process of plastic waste made from PE using a bentonite catalyst with a weight fraction of 0.100, characteristic tests were then carried out, including testing density, viscosity, flash point, heating value, and rating octane number.The results are presented in Table 3.Based on Table 3, the density and viscosity values of alternative fuels for each type of liquid product meets the standard commercial specifications for fuel oil according to the provisions of the Directorate General of Oil and Gas, Ministry of Energy and Mineral Resources of the Republic of Indonesia number 146.k/10/DJM/2020, so that the results of alternative fuel products with a bentonite catalyst weight fraction of 0.100 has quality that meets the requirements [24,25].Furthermore, the alternative fuel products also have flash points (ASTM D7094) and provide consecutive flash point data: alternative gasoline 84 0 C, alternative kerosene 70 0 C, and alternative diesel 98°C.Data on the calorific value of the test results for each alternative fuel product is for alternative gasoline 10,979 cal/g, alternative kerosene 11,008 cal/g, and alternative diesel 11,027 cal/g.From the parameter aspect of the rating octane number (RON), the RON value for alternative gasoline and alternative kerosene both have RON values greater than 98 [26].This shows that the calorific value of alternative fuel from plastic waste made from PE has met the calorific value standard and has the appropriate qualifications, the same as liquid fuel produced by PT Pertamina.Therefore, PE based oil is a promising altermative to replace petroleum based fuel.

Conclusion
The pyrolysis of plastic waste derived from polypropylene (PP) and polyethylene (PE) was investigated under controlled conditions, specifically employing a 0.1 weight fraction of bentonite catalyst and a pyrolysis temperature range spanning 50-225°C.For PP-based plastic waste, the process yielded alternative gasoline, kerosene, and diesel products at notable rates of 44.00%,

Fig. 3 .
Fig. 3. Effect of the amount of bentonite catalyst on the yield of alternative fuel oil

Table 1 .
Raw materials, weight, and pyrolysis conditions

Table 2 .
Physical Characteristics of Alternative Fuels -Based on Table

Table 3 .
Characteristics of the physical properties of alternative fuel from PE-based plastic waste 10.76%, and 21.07%, respectively.These products exhibited flash point values of 84°C, 68°C, and 100°C, as well as heating values of 10,970 cal/g, 10,965 cal/g, and 10,816 cal/g, with research octane number (RON) values exceeding 97 for both alternative gasoline and kerosene.Likewise, in the case of PE-based plastic waste, the optimal conditions resulted in alternative gasoline, kerosene, and diesel yields of 27.65%, 17.11%, and 43.79%.These alternative fuels demonstrated flash point values of 84°C, 70°C, and 98°C, and heating values of 10,979 cal/g, 11,008 cal/g, and 11,027 cal/g, with RON values surpassing 98 for the gasoline and kerosene fractions.Notably, the alternative fuel oils meet the commercial fuel oil standards outlined by the Directorate General of Oil and Gas, Ministry of Energy and Mineral Resources, Republic of Indonesia (Regulation Number 146.k/10/DJM/2020), showcasing density, viscosity, and heating values within the specified ranges.This underscores their viability as environmentally responsible options for plastic waste valorization and the sustainable production of fuel resources.