Study the fuel characteristics of ethanol and waste engine oil pyrolytic oil blends

This study shows the application of pyrolytic oil derived from waste engine oil (WEOPO) as an alternative fuel by blending with ethanol. For this, the effect of blending of ethanol at 5 %, 10 %, 15 %, 20 %, 25 %, and 30 % on the compositions and fuel properties were analyzed. The utmost blending was established based on the higher heating value. The pyrolytic oil used for this study was produced at 550 °C which was the optimum pyrolytic temperature. A comparison study of the blended oil was performed with commercially available gasoline to observe the similarities in their fuel properties and composition. The study confirmed that ethanol can be blended with WEOPO at 20 % by volume to obtain a fuel of a higher heating value of about 44.24 MJ/kg that can be used as fuel. Since WEOPO contains 65.80 % of C4–C12 (gasoline range), hydrocarbon compounds and the rest 31.48 % C11–C15, 11.84 % C15–C19, and 6.94 % > C19 compounds, it can be used as a future fuel.


Introduction
Energy is the capability of human beings to perform work and available in various forms. The main source of energy that we get is normally available in the form of electricity and fossil fuel. The major reason behind the extensive use of fossil fuels depends on the increasing population and new trends in human lifestyle. Global fossil fuel depletion is the major cause for the hike in the fuel cost which demands an alternative fuel to meet the increasing energy demand (Sonthalia and Kumar 2021;Kumar and Sidharth 2018;Pali and Kumar 2016). Very soon the day will come when the whole world will be in great anxiety due to the inadequacy of fossil fuel. Initiatives have already been taken to meet the energy demand from alternative sources (Rao et al. 2008). With increasing demand and habit, the petroleum reserves are also exhausted.
A billion tonnes of waste materials including biomass (Sathe et al. 2018), waste oil (Chang et al. 2018), and waste plastic (Foschi et al. 2021) are produced annually. The disposal of these waste materials which contain hazardous substances like polyaromatic hydrocarbons (PAHs), hazardous metals, and toxic chemicals affects badly the living beings and environment Shadangi 2020a, 2020b;Patel et al. 2021;Kumar et al. 2013). The increase in the number of automotive vehicles creates a big problem with the disposal of waste engine oil (WEO). WEO is considered to be one of the major waste materials among all which spoil the environment severely. Diesel-like fuel (Arpa et al. 2010a) and gasoline-like fuel (Arpa and Yumrutas 2010) can be produced from the waste engine oil by following a suitable process. It was reported that around 40 million metric tonnes of engine oil are produced every year, and a major portion (around 60 %) were discarded as waste, and the remaining (only 40 %) were recycled (Fuentes et al. 2007;Arpa et al. 2010b;Tripathi et al. 2015). The direct exposure of waste engine oil affects badly the living beings and the environment. Nowadays the WEO is considered an alternative energy source and received much attention. Varieties of techniques are being employed to handle the waste engine oil. The recycling techniques such as distillation (Demirbas et al. 2015), clay treatment (Abu et al. 2015), hydrogenation (Batov et al. 2018), and acidic refining (Osman et al. 2018) are adapted to process the waste engine oil. Such techniques are not widely accepted due to certain drawbacks and require further improvement. Among the gasification, incineration, and pyrolysis techniques, the gasification and incineration process releases more toxic gases directly into the environment and affects severely human health. The emissions of oxidized compounds of metals and PAHs are the major hazardous pollutants released by such processes. These processes can only be able to recover the heating value from the wastes except for many valuable chemicals (Dong et al. 2018). Pyrolysis is one of the suitable thermochemical conversion processes yields pyrolytic oil, gases, and char as the products. Based on the process parameters, the residence time of vapor, and rate of heating, the pyrolysis is termed as either a fast or slow pyrolysis process (Basu 2018). In this regard, Lam et al. (2010) concluded that the char and gas yield increases with the increase in the residence time of the vapor and at a slow rate of heating. The report explained about the microwave-heated pyrolysis reactor, operated in the temperature range of 250-700°C and feed rate of 0.4-5 kg/h with an N 2 purge rate of 0.1-0.75 L/min. The yield of pyrolytic oil yield was found to be optimum (88 wt%) at a feed rate of 5 kg/h and N 2 purge rate of 250 mL/min. Kim and Kim (2000) experimented with the pyrolysis of waste automotive lubricating oil in a tubing bomb microreactor by varying the residence time and heating rate at a fixed temperature. No significant effect was observed in the yield of oil, coke, and gas due to the variation in the residence time. At 420°C temperatures and 5-min residence time, the yield of oil, coke, and gas was found to be 98.15 %, 1.04 %, and 0.81 %, respectively. Shadangi (2020a, 2020b) investigated the fast pyrolysis of waste engine oil. The WEO was pyrolyzed in a semi-batch reactor at 550°C. The condition for the highest yield (76.73 wt%) of WEO pyrolytic oil (WEOPO) was 25°C/min heating rate and 25 mL/min of N 2 flow rate. The literature says that the pyrolytic yield also depends on the chemical composition of feed, reactor design, pyrolysis temperature, pyrolysis pressure, N 2 purge rate, and feed rate (Lam et al. 2012). Sarkar et al. (2014) investigated the pyrolysis kinetics of spent engine oil by varying the pyrolysis temperatures and also studied the effects on the pyrolytic oil calorific value and yield of the pyrolytic oil. The optimum yield of the pyrolytic oil was 58 % at 773 K and 40 min (reaction time). Lam et al. (2012) conducted the pyrolysis of waste automotive engine oil in a microwave-assisted continuous stirred type reactor and observed that hightemperature pyrolysis increased the oil yield due to the cracking of hydrocarbons gas.
Therefore, WEO pyrolysis can be considered an environmentally adequate and proper way to handle this waste. The direct use of pyrolytic oil as a fuel in the combustion engine is not a good option due to few drawbacks and hence it is required to follow any upgrading techniques. Many researchers followed the physical treatment method to upgrade the pyrolytic oil. The pyrolytic oil is blended with diesel, gasoline, and ethanol before using in the engine. Bert et al. (2018) reported a comparison between the engine performance of modified single-cylinder (1C) and four-cylinder (4C) diesel engines fueled with fast pyrolysis bio-oil blended with 20 % mass fraction of ethanol (FPBO20). The four-cylinder, 50kW diesel engine fueled with FPBO20 showed the optimum performance with about 80 % power output. The import parameters like air inlet temperature, fuel injection timing, fuel consumption, and efficiency played a vital role in the engine performance. As reported, it was important to preheat the inlet air to a high temperature in the range of 220-230°C to resolve the poor combustion of FPBO20. The combustion performance indicated that with the decrease in air inlet temperature, the NOx emission decreases along with CO. The maximum efficiency and optimum combustion were achieved by maintaining the fuel injection timing because at lower ΔT, combustion takes place on time and efficiently (Bert et al. 2018). Gadwal et al. (2019) studied the performance and emission characteristics of common rail direct injection (CRDI) fitted with diesel engines which were fueled with plastic pyrolysis oil (PPO) blended with ethanol and diesel at various ratios and loads. The higher heating value of diesel and oxygen content of ethanol is mainly responsible for the increase in the brake thermal efficiency (BTE). BTE increases with the increase in the percentage of ethanol (up to 15 %) in diesel in the blend. Further, it was established that the best performance was observed at 900 bar IP and 10°before the top dead center (10°bTDC) IT with the lowest emission due to the proper oxidation and combustion of the blended sample. The blend of 70PPO+15D+15E showed the engine performance similar to diesel. Kareddula and Puli (2018) investigated the emission and performance of multi-cylinder spark-ignition engines fueled with plastic pyrolysis oil (PPO) blended with ethanol and gasoline. About 15 % of plastic pyrolysis oil (15PPO) was blended with gasoline, and 5 % ethanol (15PPO5E) was also added as an additive. The multi-cylinder Maruti 800 petrol engine was run with pure gasoline, blend with ethanol and blend without using ethanol. The performance characteristics and emission were compared for 15PPO, 15PPO5E, and gasoline. It was concluded that 15PPO5E showed high brake-specific fuel consumption (BSFC) and low BTE of the engine as compared to an engine run with pure gasoline (Kareddula and Puli 2018). It was reported that the mixture of 80 % ethanol and 20 % biomass pyrolytic oil can be an alternative fuel for residential boilers (Martin and Boateng 2014). The pyrolytic oil produced from eucalyptus (low nitrogen content) blended with ethanol gives less NOx emission on combustion. However, the higher heating value of pyrolytic oil generated from protein-rich biomass blended with ethanol was found to be very high. The experimental results showed that the higher heating value of the blended sample decreased with an increase in the concentration of pyrolytic oil (Martin and Boateng 2014).
On the other hand, the wood pyrolytic oil has 1/3 the calorific value of fossil fuel due to its high oxygen content. Only 20-40 % wood pyrolytic oil can be blended with ethanol to prevent lower viscosity and polymerization. Less NOx and PM emission was observed by the combustion of blended oil in diesel engines (Lee and Kim 2015). Hence, it was confirmed that ethanol can be added as an additive to improve the performance of a SI engine and control NOx emission (Kareddula and Puli 2018). Patel and Patel (2012) verified that DP95 E5 (95 % of 85 % diesel and 15 % tire pyrolysis oil and 5 % ethanol) provided the best performance results for a single-cylinder diesel engine without the following any engine modifications. Hence, it was confirmed that the % blending of ethanol with pyrolytic oil mainly depends upon the oil types and source of pyrolysis oil.
However, none of the studies were reported regarding the use of WEO pyrolytic oil and ethanol blends as alternative fuels and characterized also. In this study, the optimum blending condition of ethanol with WEO pyrolytic oil was studied. The utmost ethanol blending ratio was established based on the obtained higher heating value. For this purpose, WEO was pyrolyzed at various temperature ranges to identify the ideal temperature to produce gasoline-rich pyrolytic oil with a higher yield. Further, the physicochemical properties of the blended oil were determined compared with gasoline. The chemical composition of the blended sample at the optimum condition was studied using FTIR and GCMS analysis and compared with gasoline.

Feedstock
The prime feedstock used for the pyrolysis experiment was WEO. It was gathered from Yash Honda service center, Sambalpur, Odisha, India, and the analytical grade ethanol was procured from LOBA Chemical. The solid impurities present in WEO were discarded by using vacuum filtration and stored safely at room temperature for future use.

Pyrolysis process
Thermal pyrolysis of the WEO was performed in a laboratoryscale pyrolyzer. The pyrolyzer was consist of a reactor and a tubular furnace. Approximately, 50g of WEO was occupied in the reactor and inserted vertically into the furnace. The pyrolysis was performed in the temperature range of 450 to 575°C. The temperature was elevated at a heating rate of 25°C min −1 from room temperature to the decided temperature. The reaction temperature was measured by using a thermocouple and regulated with the help of a PID controller. The pyrolysis process was executed in presence of N2, at the flow rate of 25 mL min −1 Shadangi 2020a, 2020b). The experimental setup used is shown in Fig. 1. The pyrolytic vapors released from the top opening of the reactor were condensed by passing through an ice-cooled water condenser. Three condensers were connected in series to ensure proper condensation. The condensed pyrolytic oil was collected in a beaker and weighted. The temperature at which a higher amount of oil was produced was considered the optimum temperature. The char was collected from the reactor once the release of vapors was stopped and weighed accurately. The weight of the non-condensable gases is calculated by subtracting the sum of the yield of pyrolytic oil and char from the feed.

Preparation of ethanol and pyrolytic oil blends
The blended sample of ethanol and pyrolytic oil was prepared on a volume basis. Ethanol at a different volume % (5 to 30 %) was blended with the pyrolytic oil, and the blends were named E5, E10, E15, E20, E25, and E30. The pyrolytic oil used for the blending purpose was produced at the optimum temperature. To achieve proper mixing and observe the effect of blending on the phase separation, the blends were stirred using a magnetic stirrer at 100 rpm for 30 min at room temperature. The blends were stored in a gravity-settling flask for 24 h. As no phase separation was noticed after 24, it was stored in an air-tight container for further use.

Characterization of blended oil samples and pyrolytic oil
The Pensky Martens apparatus (ASTM D-93) and Engler's Viscometer (ASTM D-445) were used to determine the flash point and kinematic viscosity of all the blended oil samples and pyrolytic oil. The higher heating value was estimated by using an automatic bomb calorimeter (IKON instruments). The presence of functional groups was analyzed by using an FTIR analyzer (Bruker, Germany) in wave no. range of 4500-300 cm −1 . A minute quantity (small drop) of pyrolytic oil was taken in a sample holder in absence of KBr, and the spectra noticed in terms of wave no. vs. % transmittance were recorded for further analysis. The attendance of different compounds was studied using a GC-MS analyzer (Shimadzu, JAPAN). For the composition analysis, the GC column was heated at a heating rate of 10°C min −1 from 70 to 300°C with a hold time of 9 min at the final temperature. The column was occupied with about 1 μL of the liquid sample (prepared using hexane as solvent) with a holdup time of 1.7481 min and an average velocity of 28.602 cm s −1 where He was used as the carrier gas at a rate of 1.5 mL min −1 . The total run time of GC was 34 min. The source temperature of the MS ion was kept at 150°C, and the composition was identified with an m/z ratio in the 40-700 range. The gas chromatogram shown by the GC with variations in the retention time was used to identify the respective composition. The mass spectra obtained from the MS showed the composition that is analyzed using the NIST library.

Impact of pyrolysis temperature on yield
The impact of the temperature on the WEO pyrolysis on the yield is shown in Fig. 2. The yield in terms of pyrolytic oil, char, and non-condensable gas with the increase in the temperature is observed from the figure. The pyrolytic oil yield was augmented from 500 to 550°C and descended by further rising in the temperature. The reduction in the pyrolytic oil was noticed from about 74.54 wt% to 65 %. This confirmed that 550°C is the optimum temperature to maximize the yield of oil. At the higher temperature pyrolysis (due to secondary reactions) low molecular weight chemical compounds generated which enhanced the yield of noncondensable gas compared to condensed liquid. However, the non-condensable gas yield was higher at 500°C compared to other elevated temperatures. This may be due to the higher residence time of the pyrolytic vapors inside the reactor that proceeds to secondary reactions at the low temperature compared to higher temperatures. The yield of non-condensable gas was found to be higher about 21.53 % at 575°C compared to 550°C (33.47 %). As the pyrolysis temperature increased from 500 to 550°C, the affinity of secondary reactions reduced and resulted in more condensable pyrolytic vapors as pyrolytic oil.

Impact of ethanol blending on the higher heating value (HHV)
The variations in the higher heating value with the blending of ethanol are depicted in Fig. 3. With the rising in the volume % of ethanol in the blends from 5 to 20 %, the higher heating value was increased. However, the addition of more ethanol (30 %) in the blend reduced the heating value. The higher heating value of the E20-blended sample was 44.24 MJ/kg, and the value is close to petrol. The higher heating value at 20% blending could be due to the better combustion ability of the E20 oil. WEO pyrolytic oil was mainly consist of various   hydrocarbons and very few amount of oxygenated compounds Shadangi 2020a, 2020b). Since oxygen helps in the combustion process, the addition of ethanol increased the oxygen content in the blended oil and resulted in better heating value compared to pyrolytic oil. However, higher oxygen in the fuel oil yields water as a product during combustion; hence, it is important to identify the approximate proportion of the oxygen content in the fuel. From this study, it was observed that increasing the ethanol blending to 30 % resulted in less heating value compared to 20 %. Therefore, it could be considered that the oxygen content was increased up to the optimum level in E20 that helped in the combustion process by resulting better heating value with the formation of less water as one of the products. Hence, it can be stated that blending ethanol at 20 % with WEO pyrolytic oil is possible and can be used as a fuel.

Fuel properties
The fuel properties such as density, absolute viscosity, flash point, and higher heating value of pyrolytic oil and the blended samples are shown in Table 1. These fuel properties of blends were compared with the gasoline. The density of pyrolytic oil was 795 kg/m 3 which was higher than the petrol. However, with an increase in the volume % of ethanol in the pyrolytic oil, the density of blended samples was decreased from 782 to 737 kg/m 3 . The density of the E20 blended sample was 751 kg/m 3 which was approximately the same as gasoline. A similar trend was also perceived for absolute viscosity. The absolute viscosity of the blended samples was declined from 15.34 CST to 5.26 CST with an increase in volume % of the ethanol from 5 % (E5) to 30 % (E30). However, the absolute viscosity of petrol was very less (only 0.71 CST) compared to pyrolytic oil and the blended samples. It was confirmed from the literature that on the blending of ethanol with biomass pyrolytic oil, both density and viscosity decreased by increasing the volume % of ethanol (Bert et al. 2018;Martin and Boateng 2014). A falling tendency was also detected for flash point of all blended samples.

FTIR analysis
The FTIR spectra of WEO pyrolytic oil, E20, and gasoline are shown in Fig. 4 a, b, and c. The absorbance peaks mainly appeared within 2800-3000 cm −1 and 1300-1500 cm −1 in all three cases. The intensity of the peak of gasoline was less and higher in WEOPO and E20 spectra. The three medium peaks at 2952 cm −1 , 2920 cm −1 , and 2854 cm −1 noticed for WEOPO represented the attendance of aliphatic C-H stretching vibrations. Similar peaks were also observed in E20 and gasoline. In all three spectra, a common peak was observed at 2920 cm −1 (C-H stretching vibrations). The weak peak identified at 2646 cm −1 showed the incidences of O-H stretching vibrations. The weak peak at 1647 cm −1 and 1605 cm −1 appeared in both WEOPO and gasoline which showed the existence of alkenes, while such peak was absent in the E20. Further, the presence of C-H bending was confirmed by the peak obtained at 1457 cm −1 and 1378 cm −1 and signified the C=O stretching vibration in the WEOPO. The attendance of C=O stretching vibrations was also present in the E20 and gasoline FTIR spectra, appeared at 1462 cm −1 and 1371 cm −1 in E20 and 1461 cm −1 and 1380 cm −1 in gasoline. Table 2 represents the detailed GC-MS analysis of E20 oil. The retention time, area %, and respective compound name are listed in Table 2. However, Table 3 shows the presence of   Fig. 5 shows the chemical composition of E20 oil and gasoline based on the carbon numbers. E20-blended oil is composed of C7 to C28 hydrocarbon compounds, while gasoline contained compounds having a carbon number in the range of C8-C11. It was reported that gasoline comprised C4-C12 compounds (Teng et al. 1994). However, the presence of C12 to C28 hydrocarbon compounds in the E20 oil may be due to the blending of pyrolytic oil with ethanol. It deliberates that during the blending of ethanol with pyrolytic oil chemical reactions between ethanol and pyrolytic oil

Conclusion
This study concluded that the fuel properties of pyrolytic oil were not similar to gasoline. Its density and kinematic viscosity were very high with low calorific value and cannot be used as a fuel in combustion engines directly. However, blending of ethanol by 20 % volume with the WEO pyrolytic oil provided resulted in a better calorific value around 44.24 MJ/kg and can be considered the utmost blending of ethanol to pyrolytic oil. At 20 % blending condition, the density of the oil is very near to gasoline. So, the improved fuel properties of E20blended oil can be used in SI engines. Further investigation is required to study the engine performance and emission characteristics of SI engines fueled with E20-blended oil.
Availability of data and materials All data generated or analyzed during this study are included in this published article.
Author contribution NP performed the experiment, discussed the results, and prepared the manuscript. KPS set the idea and guidance to conduct the experiment, edited, and corrected the manuscript. All authors read and approved the final manuscript.

Declarations
Ethics approval and consent to participate Not applicable

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Competing interests The authors declare no competing interests.