Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

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A. Santhoshkumar, R. Anand Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, India

Nomenclature ASTM ASR CH4 CO CO2 GC-MS H2 HHV DSC FEO FTIR MAP MSW MPO NCG PAHs PWEO SiC TGA WEO

5.1

American Standard for Testing Material auto shredder residues methane carbon monoxide carbon dioxide gas chromatography and mass spectrometry hydrogen higher heating value differential scanning calorimeter fresh engine oil Fourier Transform Infrared Spectroscopy microwave-assisted pyrolysis municipal solid waste microwave pyrolysis oil noncondensable gases polynuclear aromatic hydrocarbons pyrolysis waste engine oil silicon carbide thermogravimetry analysis waste engine oil

Pyrolysis process in waste management

Waste management is essential for a green and clean environment for a sustainable civilization. The disposal of waste is the biggest challenge that humankind is facing today. With increasing population and industrialization, discarded waste is increasing continuously. Solid and liquid waste such as plastics and waste oil are health hazards [1]. At the same time, the science community is focusing on finding new fuel alternatives proportional to the population growth to fulfill the energy demand [2]. Waste generation is always proportional to the population, with some waste fractions being Advances in Eco-Fuels for a Sustainable Environment. https://doi.org/10.1016/B978-0-08-102728-8.00005-X © 2019 Elsevier Ltd. All rights reserved.

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difficult to recycle. The utilization of these fractions for energy purposes should be further investigated (Statistical Review of World Energy, June 2016) [3]. According to certain studies, the energy has been utilized from gas approximately next 150 years and coal for long period [4]. Consequently, the researchers and the analysts of the whole world currently endeavour to find a new alternative energy for the future, while seeking to develop innovations allowing to re-use the substantial surpluses like a source of vitality. Waste materials can be of many types, mainly biodegradable such as biomass and nonbiodegradable such as plastics, waste oils, metallic wastes, and many more. Many research works have addressed the application of discarded lubricating oils from waste oil for the diesel engine as a source of energy [5, 6]. The surplus lubricating oils can be reclaimed as fuel or finished into diesel-like fuel. Every year, about 40 million metric tons of waste engine oil are generated, and around 60% of the waste is particularly misused. Less than 45% of the available surplus oil was gathered universally in 1995 [7]. Waste lubricating oil is hazardous and toxic as it contains additives such as lead, zinc, phosphorous, magnesium, etc. [8]. The methods adopted to recycle and reuse the waste oil vary from one country to another. There are various thermochemical methods available for the conversion of waste lubricant oil to some useful energy. The thermochemical conversion processes are combustion, gasification, and pyrolysis. Pyrolysis occurring in the absence of oxygen is thermal decomposition to extract liquid oil, gaseous fuel, and solid char. The yield of these three products varies according to the variation of the operation parameter [9, 10]. There are various methods available for heating the waste lubricant oil. Among them, conventional heating and microwave heating have been carried out previously. Real world wastes can be treated very efficiently in the microwave pyrolysis process as compared to the conventional pyrolysis process. In the traditional pyrolysis technique, the heating mechanism is less efficient and slower as it is based on conduction and convection, whereas in microwave pyrolysis it heats all the substances equally due to the diffuse character of the electromagnetic field. Thus, microwave pyrolysis provides equal distribution of heat and efficient heat transfer, and heating methods can be controlled easily. Microwaves penetrate and create the hotspot only on dipole materials. So, the hotness created substantially on the pyrolysis feed causes higher process efficiency than conventional heating [11]. Huang et al. [12] states that microwave heating is better than conventional heating because of various advantages. Hotspots, which form under microwave irradiation, would have a significant influence on the return and features of microwave processing products. The solid goods of microwave pyrolysis at proper microwave power levels can have high heating values and specific surface areas with higher gas and solid yields but lower liquid yield than conventional pyrolysis. By using microwave pyrolysis, almost half the lignocellulosic biomass can be converted into a gas product, which is mainly composed of H2, CH4, CO, and CO2, with more bioenergy because of its high H2 and CO yields. The addition of proper catalysts provides a substantial influence on the product selectivity of microwave pyrolysis. The gas and liquid yields

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as well as the warming presentation of microwave pyrolysis can be dramatically promoted by adding catalysts. The addition of proper susceptors in the microwave method can increase the yield value of the liquid oil. Silicon carbide activated carbon and fly ash have been used as susceptors in the microwave pyrolysis of polypropylene, and the liquid yield percentage are 31.89%, 29.80%, and 21.07%, respectively [13]. Moreover, the heating rate for silicon carbide as a susceptor is higher compared to the other two. Municipal solid waste is used in the pyrolysis process, and different susceptors have been used for increasing the efficiency of the microwave pyrolysis process. For municipal solid waste activated carbon, solid beads, fly ash, and aluminum are the suitable susceptors. The temperature rise for an activated carbon susceptor is more than flyash. However, the liquid oil yield percentage for silicon beads as the susceptor is higher than other susceptors [14]. So, suitable susceptors need to be chosen depending upon the feed for pyrolysis process.

5.2

Microwave heating mechanism

As mentioned in the international agreement, the preferred frequencies of microwave heating are 915 MHz (λ ¼  33 cm) and 2.45 GHz (λ ¼  12 cm) [15]. The electromagnetic radiation generated by the magnetron causes the dipolar molecules to try and rotate in phase with the alternating electric field. At the molecular level, resistance to this rotation leads to the friction between the molecules and causes the heating effect [16]. In conventional thermal heating, the process is regulated by the temperature of the surface and also by some physical properties of the material being heated, such as heat capacity, density, and thermal diffusivity. Whereas, in microwave heating, the heating effect is due to the interaction of dipoles with electromagnetic radiation. In microwave heating, the material gets high temperatures and heating rates [17]. The efficiency of electrical energy to heat energy conversion is high (80%–85%) in microwave heating [18]. The microwave heating technique is a volumetric heating method that includes other heating procedures such as heating due to conduction in the operating frequency range of 0–6 Hz and heating due to induction in the operating frequency range of 50 Hz–30 kHz. Ohmic heating occurs in the frequency range between the induction and conduction. Radio frequency heating in the frequency range of 1–100 MHz is used for workloads with high resistivity when placed between electrodes [15]. Meredith [19] gives a typical electromagnetic spectrum with examples of applications performed at different frequency ranges. There are many principles and theories available in textbooks that explain the microwave heating mechanism. In general, there are three mechanisms by which the heating effect is achieved in microwave heating methods, which are summarized as follows. Dipole reorientation or polarization: This mechanism explains how the heating effect is achieved in polar compounds. When a polar compound is subjected to

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microwave radiation, it displaces the atomic nuclei from their equilibrium position (atomic polarization) or the electrons around the nuclei (electronic polarization), forming induced dipoles. These dipoles tend to reorient themselves under the influence of an alternating electric field. This realignment occurs at the rate of a trillion times per second [15, 20]. As a result, friction is developed between the rotating molecules, thereby generating heat within the whole volume of the material. The dipolar orientation was clearly explained in the section basics of the microwaves by Denshi CO, Ltd. [21], for example, water contains an atom of oxygen and two hydrogen atoms under an angle of 104.5 degrees [22]. This unequal division of the electrons gives to the water molecule a light negative charge close to its oxygen atom and a light positive charge close to its hydrogen atoms. The dipole was formed due to this atoms take a little charge of each plus (+) and minus (). This dipole or dielectric material is exposed to an electric field such as a radio wave or microwaves; it vibrates 2450 million times more or less to be replaced a second [23]. At a lower frequency in the radio wave, the water is not able to generate heat because the permanent dipole suddenly follows the electric field direction. Similarly, at the high-frequency range, dipoles will not be able to follow the fast changes in the electric field direction. So heat does not generate by water. In a moderate frequency range, the water is exposed to the dipole orientation. In this case, behind the electric field, the permanent dipole changes a bit. Water takes the energy from the radio wave and generates heat during the delay time in this nominal frequency range [21]. Interfacial or Maxwell-Wagner polarization: This mechanism explains how the heating effect is achieved in heterogeneous systems. Here, polarization is produced due to differences in dielectric constants and conductivities of the substances at the interfaces. The dielectric loss and field distortions due to a collection of space charge lead to the heating effect. Conduction mechanism: In an electrically conductive material, the electric currents of charged particles or carriers (electrons, ions, etc.) move through the material due to the externally applied electromagnetic field. These moving electric currents go through a relatively high electrical resistivity within the structure of material, generating heat [15, 20]. Dielectric properties are essential to determine the maximum heating of a material when exposed to electromagnetic radiation (microwave radiation). The dielectric loss tangent (Tan δ) of the microwave absorber is mainly affected by the dielectric constant (ε0 ) and the dielectric loss factor (ε00 ). The dielectric constant determines how much energy is absorbed and how much is reflected, thereby showing the ability of a material to get polarized by an electric field. The dielectric loss factor determines the efficiency of conversion. The ratio of these two gives the dissipation factor of the material. Tan δ ¼

ε00 ε0

(5.1)

Thus, a good microwave receptor has to have a material with a high value of ε00 and a moderate value of ε0 [15].

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Influence of microwave heating on the pyrolysis

In the application of microwave heating for pyrolysis, refreshing circumstances related to temperature distribution, the heating rate, and the residence time of volatiles have been noticed when equated with the conditions obtained from conventional heating. Thus, different pyrolysis products outputs are authorized to form a different chemical profile for each heating system [24]. The conventional electrical heating method describing the heat energy is transferred from the outermost layer to the innermost layer by conduction, convection, and radiation [25, 26]. On microwave pyrolysis, the conversion of electromagnetic energy represents the formation of heat and thermal energy. The electromagnetic waves (microwaves) can penetrate through the pyrolysis feed and generate the heat energy. Microwaves can penetrate materials and deposit energy due to the formation of a hotspot on the pyrolysis feed, not in the mode of heat transfer. Therefore, both heating systems have different thermal gradients. The heat generation occurs in the entire volume of the material. Microwave heating recognizes the complex reactions due to volumetric heating. Therefore, microwave heating is energy conversion contrary to heat transfer [27]. The higher heating rate can be achieved in case of microwave heating because heat can be directly transferred through molecular interaction with the electromagnetic field, and there is no necessity to heat the surroundings. Moreover, due to higher heating rates, residence times of volatiles can be reduced because they travel faster from the inner hot regions to the outside cold regions, hence avoiding secondary vapor phase reactions. Reactions of devolatilization and conventional heating is ameliorated in the gas-phase homogeneous reactions, in the same manner with the reactions that take place extraterrestrially. Moreover, the lesser temperatures in the microwave cavity help to condense the terminal vapors of pyrolysis and to overturn inappropriate reactions [28]. Men
endez et al. [29] observed that microwave pyrolysis used to obtain higher pyrolysis evolved a gas yield and less char residue. Compared to conventional technology, the microwaves in heterogeneous processes are to eliminate the heat transfer resistance in the conventional chemical process. Thus, the main advantages of microwave pyrolysis concerning conventional pyrolysis would be higher efficiency and a higher heating rate, therefore a more significant saving of time. Solid Char acts like a reactive catalyst because of the active metal centres located at the surface. Moreover, some of the heterogeneous reactions observed in a microwave pyrolysis compared to conventional pyrolysis. With certain specific reactions such as methane decomposition reaction, solid metal char will act as a catalyst to obtain better conversion rates in heating by microwaves [30]. If a material has a significant moisture content, microwave pyrolysis shows a unique pattern in the heating process of the particle. Water molecules have good harmony with microwaves. The steam generated by the vaporization of moisture in the core of the particle is swiftly exited into the adjacent area. It sweeps not only the vapours but also creates favourable channels in the solid, which increases the permeability and supports the vapour release at low temperature [31]. Microwave pyrolysis offers an alternate worldview in molecule warming wherever the electromagnetic field penetrates the strong and collaborates straightforwardly with dipoles in

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substance arrangement. Because of the high preference of water atoms with microwaves, humidity content inside a particular biomass molecule is focused explicitly on accidental microwaves. Microwaves evaporate humidity in the deepness of the molecule before volatilizing the natural substance. The produced mist is quickly rejected into the surrounding area, thus eliminating the volatile substances and creating single deviations in the carbonaceous fort which increase its absorptivity. Thus, that supports the arrival of volatile substances at low temperatures and, consequently, its response to the emitted mist which supports partial oxidation and creation of perpetual gases (CH4, CO2, H2, CO). Microwave heating and conventional heating are distinguished based on differential heating rates of the material being heated, as the microwave energy is directly delivered into the material through molecular interaction with the electromagnetic field. Savings of energy and time are attained in microwave pyrolysis due to higher heating rates because of electromagnetic radiation. High heating rates improve the devolatilization of material, which decreases the conversion time. The residence time of the volatile matters is also controlled by the heating rate. The faster heating was decreased the volatile residence time and obtained the more volatile substances that reach to the external cold area or condenser, which reduces the activity of the products in the vapour phase in the part of the secondary reactions. That gives high liquid yield and a reduction in the deposit on char in the internal surface of the refractory material [32].

5.4

Factors affecting the pyrolysis process

The pyrolysis temperature, heating rate, and residence time majorly influence the pyrolysis product and pyrolysis fuel quality. Morin et al. [33] investigated the effect of the biomass nature and the pyrolysis conditions on the reactivity of char and the physicochemical properties. Table 5.1 shows the effect of properties on the pyrolysis product. Pyrolysis processes were divided into three subgroups based on the operating parameters. Each parameter resulted in a different product composition. These subgroups are slow pyrolysis, fast pyrolysis, and flash pyrolysis. The parameters that describe slow pyrolysis are a temperature of 400°C with a residence time of more than 30 min and a heating rate of (0.1–1°C/s). The product composition yield for slow pyrolysis as explained by the investigators is 35% biochar (solid), 30% bio-oil (liquid), and 35% syn-gas (gas) [34]. Slow pyrolysis has the lowest yield of liquid products that is the focus of most experiments. Fast pyrolysis is the second type of pyrolysis that is explained. The operating parameters that describe fast pyrolysis are a temperature of 500°C with a residence time about 10–20 s and a heating rate of (1–200°C/s). The product composition yield for fast pyrolysis is 20% biochar (solid), 50% bio-oil (liquid), and 30% syn-gas (gas) [34]. The yield for bio-oil under fast pyrolysis conditions is better than that of slow pyrolysis. The third operating parameter is flash pyrolysis, which has operating parameters that include a residence time of about 1 s, a temperature of 500°C, and a heating rate that is greater than 1000°C/s. The composition of product yield of flash

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Table 5.1 Effect of properties on the pyrolysis product Effect on yield with increasing value of the property

Effect on the reactivity of char

Sl. No.

Property

1

Heating rate

Decrease the char yield Increase the gas and liquid yield

Reactivity of char increased due to higher heating rate

2

Pyrolysis temperature

Increases gas yield; decreases char yield

Decreases reactivity of char

3

Pyrolysis pressure

Increases the yield of char and CO2; decreases the yield of CO, CH4, and H2

Decreases char reactivity

4

Residence time

Increases the yield of char

Decreases char reactivity

5

Biomass nature

No effect

No effect

Other comments Higher heating rate activates oxygen and hydrogen content and also increases the surface area and the availability of active sites CO2 concentration is decreased by increasing pyrolysis temperature; char reactivity reduces due to the enhancement in the presence of a larger aromatic ring and system structural ordering of the char by increasing the temperature of pyrolysis The decrease of reactivity of the char with pyrolysis pressure is due to the rise of the char’s carbonaceous structure Prolonged heating reduced reactivity at the final temperature of pyrolysis, which improves the loss of active sites and structural ordering of the char The determining parameter is the initial biomass pertaining to the reactivity of the char as well as its properties and the structure of the char

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pyrolysis is 13% syn-gas (gas), 2% biochar (solid), and 75% bio-oil (liquid) [35]. So, fast and flash pyrolysis is proven to be apt for max efficiency. Miandad et al. [36] states that with pyrolysis of liquid oil from polystyrene waste at 400°C with 75 min reaction time, the char yield was 16% of the mass, the liquid oil yield was 76% of the mass, and the gas yield was 8% of the mass. Increasing the temperature to 450°C reduced the char production to 6.2%, increased the liquid oil yield to 80.8% by mass, and increased the gas production to 13% by mass. The response time and optimum temperature were found to be 75 min and 450°C. At optimum conditions, the liquid oil had an absolute viscosity of 1.77 mPa s, a pour point of 60°C, a kinematic viscosity of 1.92 cSt, a density of 0.92 g/cm3, a flash point of 30.2°C, a high heating value (HHV) of 41.6 MJ/kg, and a freezing point of 64°C; this is similar to conventional diesel. Compared to conventional electrical pyrolysis, microwave pyrolysis has a higher heating rate and efficiency and provides uniform volumetric heating of the substances. The microwave assisted pyrolysis to increase the gas production and decrease the char formation due to hot spot formations [37]. Lam et al. [11] reported that the microwave assisted pyrolysis created an 88 wt% income of condensable pyrolysis oil with fuel assets (calorific value, density) practically identical to conventional transport fuels. Inspection of the species of the oils demonstrated that they contain light aliphatic hydrocarbon. The element of pyrolysis oils which it is shown that an excellent recovery (90%) of the quantity of energy from the surplus engine oil is restored in the pyrolysis oil and it is also free from impurities and contains few contaminants of sulphur, oxygen and dangerous mixtures of PAH. The great return of pyrolysis oil can be recognized in microwave-assisted pyrolysis with appropriate heating in an inert atmosphere. This review amplifies current discoveries on the impacts of pyrolysis process situations on the overall yield and arrangement of the recuperated oils, by exhibiting that encouraged addition rate, stream rate of cleansing gas, and warming source impacts the focus and the atomic way of the various hydrocarbons shaped in the pyrolysis oils. Huang et al. [38] investigated whether the corn stover, which is a standout among the most abundant rural deposits over the world, could be changed into significant biofuels and biobased items by a method of microwave pyrolysis. After the response at the microwave control level of 500 W for the processing time of 30 min, the response obtained under the N2 environment was superior to the CO2 environment. This might be because of the better heating absorbability of CO2 particles to decrease the hotness of stover pyrolysis. The more significant part of the metal-oxide impetuses viably expanded the most extreme temperature and mass lessening proportion; however, they brought down the calorific estimations of massive deposits. The more CO gas was formed under the N2 atmosphere, but higher CO2 was formed under the CO2 atmosphere. Catalyst expansion brought down the arrangement of polycyclic aromatic hydrocarbons and in this way, made fluid items less dangerous. Lam et al. [39] investigated the pyrolysis of WEO using a metallic char catalyst to increase the heterogeneous reaction such as methane decomposition and attain the required temperature quickly. Moreover, the metals get converted into metal oxides and absorb the sulfur existing in the oil. The high volatile materials Cd and Cr may vaporize at the pyrolysis temperature, which is above 400°C.

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Designation of microwave heating on the materials

The efficiency of microwave pyrolysis is a function of the dielectric nature of the material. Apart from the conventional classification of materials according to their nature of interaction with the microwaves, as a conductor, insulator, and an absorber, there exists a fourth type of interaction called mixed absorption. Mixed absorption refers to the selective absorption of the microwaves by a multiphase compound, where the material having a high dielectric loss acts as an absorber and the material with the low dielectric loss as a conductor. Due to this phenomena, new chemical reactions may be initiated, which is otherwise not possible with convention heat addition that will be added uniformly [40, 41]. Owing to their poor dielectric properties, the waste materials are unable to generate sufficient heat in the microwave pyrolysis process. The presence of water makes it more difficult, with the quantity of heat absorbed being barely sufficient to dry the mixture. This necessitates the use of dopants that are sensitive to the microwaves and readily absorb them. The activated carbon, coal, char and graphite are used like receptors in the microwave field because of their polar nature. It is thus evident that the effect of microwave assisted pyrolysis will depend mainly on nature on the receptors [42–44]. The temperature variation of the material can be explained in four stages. The initial step is the dielectric relaxation of the water molecules, which leads to initial heating. Dielectric relaxation means the adjustment of dielectric displacement or polarization to the time-dependent electrical field. The second stage involves attaining constancy in temperature, which mainly depends upon the nature of the receptor. In the third stage, the temperature rises rapidly with a sharp drop in mass, and this is followed by the last stage, which is the attainment of thermal equilibrium. The final pyrolysis temperature is a function of the heat absorbed by the dopant as well as the heat absorbed by the solid residue. Sometimes, due to the concentration of heat within receptors, the rate of absorption increases drastically. This phenomenon is known as thermal runaway [45]. Initially, the receptor absorbs microwaves and then heats up the remaining molecules. This removes the volatile component, leaving behind char, which absorbs microwaves further and hence the process of pyrolysis is sustained. Depending upon the dispersion of the receptors, the first, second, and third generation of receptors may be found. The lower the generation, the better the dispersal of the receptor. There have been instances where the pyrolysis process has been sustained without the addition of receptors. In some instances, the pyrolysis of wood has been achieved by heating water alone. Some biomass derivatives also do not require the addition of microwave absorbers. Apart from microwave absorption, the receptors can also alter the pyrolysis products. Dominguez et al. [46] showed with experiments that the oil yield obtained by using char as a receptor was higher than that obtained by using graphite as a receptor. Use of graphite, however, favored the cracking of large aliphatic chains. The microwave-assisted pyrolysis of polystyrene was affected by the variation of size and shape of the iron mesh used as an antenna. From this study, the cylindrical antenna gave a better result than others.

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Effect of microwave absorber on pyrolysis process

Suriapparao and Vinu [47] inferred that microwave pyrolysis of waste engine oil yield varied with increasing the temperature. The saturated hydrocarbons are 40%, 55%, and 50%, obtained at the temperatures of 300°C, 400°C, and 500°C, respectively. Also, this study revealed that there was a high content of aromatic benzene derivatives at higher and lower temperatures and the chain length decreases as temperatures increase. This shows the temperature at which the work should be carried on. This study revealed that the temperature must be around 400°C for maximum output of saturated hydrocarbons. The microwave absorbers, catalysts, or susceptors have a tremendous effect on the pyrolysis temperature, the pyrolysis time, and the time taken to reach the temperature. In the selective production of products in bio-oil, a uniform composition mixture of municipal solid waste (MSW) was subjected to microwave-assisted pyrolysis by using 10 different susceptors, which also served as catalysts. The susceptors were associated with different categories such as metal powders (aluminum, iron), carbonaceous materials (activated carbon, graphite), silica beads and nano-TiO2, oxide mixtures (cement, garnet, fly ash), and a ceramic material (SiC). The primary goals in employing these susceptors were to evaluate (i) bio-oil, char, and gas yields, (ii) composition and quality of bio-oil, from model MSW mixtures, and (iii) the average heating rates achieved with these materials. These experiments were conducted using 20 g of municipal solid waste at a 5:1 mass ratio of MSW, and a susceptor and a microwave power of 450 W [14]. This experiment depicts the ratio of higher heating value (HHV) of pyrolysis oil to the HHV of municipal solid waste or the initial raw material of the pyrolysis process. The HHV ratio (1.99) was higher while using the graphite as the microwave absorber with a 1:1 feed to catalyst ratio. Then it is followed by the other susceptors, including garnet (1.87), aluminum (1.82), and iron (1.75) with a 5:1 ratio [14]. The same works show that both saturated and unsaturated hydrocarbons are equally obtained when SiC and activated carbon are used as the susceptors and gives more saturated hydrocarbons than the silica beads and others. Aluminum and silica beads also give a good amount of required composition. Considering the oil composition, the percentages of bio-oil were 42.34%, 32.38%, 30.78%, 26.14%, 41.09%, 26.46%, 19.29%, 37.44%, 44.52%, and 15.61% when aluminum, activated carbon, garnet, iron, silica beads, cement, titanium oxide, silicon carbide, granite, and flew ash were used, respectively [14].

5.7

Pyrolysis of automotive waste

The automotive industry mainly comprises production and maintenance sectors. The recycling process of the parts and the material can be used for automobile components manufacturing through automotive waste management. Automobile manufacturing increased to 58 million units by 2002 [48]. There has been a subsequent increase in automotive waste in recent years. The wastes are converted into valuable products and energy for further uses [39]. Out of large amounts of automotive wastes, most of

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them can be subjected to microwave pyrolysis (MP) for conversion into valuable products. About 75% of the weight of the vehicles is recycled every year and the remaining 25% is known as auto shredder residues (ASR). The ASR is obtained from the automobile after the separation of iron and steel particles through magnetic separation [49]. These solid ASR materials cannot be disposed of through a landfill due to their complexity. The ASR materials mostly consist of heavy metals such as zinc-lead and copper. A Canadian ASR sample consists of 6% moisture, 18% metals, and 37% fines as well as some other particles in small fractions such as plastics, woods, textiles, and fiber materials. Because of complex chemical composition and diversity in the materials, heat treatment is emphasized by minimizing the mechanical recycling. The current trend is for microwave pyrolysis and plasma arc thermal destruction process for low treating ASR for reducing costs. Donaj et al. [50] have developed a process in which microwave pyrolysis and high-temperature gasification have been combined to be used in ASR waste management. This method can be applied to automobile waste (tires, wire tubes, oils), construction and demolition waste, residues from oil refineries, and petrochemicals. In this method, metals can be preserved and organic wastes can be converted into valuable products. The MP process occurs in molecular level thermal decomposition at temperatures ranging from 275°C to 300°C [51]. The solid and liquid products after microwave pyrolysis of ASR could be further subjected to hightemperature steam gasification (HTSG) for fuel gas production [24]. Due to the fast depletion of fossil fuels, there is a need to search for alternate fuels for internal combustion engines. Moreover, there is a requirement to discover new alternative fuels due to a drastic increase in energy demand and regulations in emission norms. One of the methods to derive alternate fuels is the conversion of a waste substance to energy. On the other hand, we have a large number of vehicles that offer a significant amount of used engine oil every year. It is easy to derive usable and valuable products rather than to dispose of waste oil. The waste engine oil can be converted into highly potential fuel through the pyrolysis method. This waste engine oil is environmentally hazardous, and when mixed with nature it will cause pollution. Globally, nearly 24 million metric tons of waste oil are generated every year. This high-quantity waste is difficult to dispose of and to treat due to the presence of elements such as polycyclic aromatic hydrocarbons (PAHs), soot, and impurities from additives such as polychlorinated biphenyls (PCBs) and chlorinated paraffin [24, 52]. Recent studies have proved that the best disposal method for waste oil is pyrolysis. The aim of recycling waste lubricant oil is through conversion into reusable products such as gasoline and oil. It has been discovered that through microwave pyrolysis, they can recover most of the commercially valuable products from waste engine oil [52]. Pyrolysis of waste oil can be carried out by mixing of excellent microwave receptor materials such as particulate carbon [32]. More particularly, they understood the potential for recovering gaseous hydrocarbons with liquid hydrocarbon oils containing benzene derivatives, BTX, and light olefins. When compared with conventional pyrolysis processes, the microwave pyrolysis process showed improved cracking reactions [24]. However, there is a considerable effect of temperature on the formation and overall yield of the recovered pyrolysis liquids and gases.

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From the previous research, nearly 40 million tires every year are scrapped in the United Kingdom. Out of all the scrap tires, 74% by weight were recovered in 1997, and about 20% of the recovered tires were recycled for reusable purposes; this can be used for energy recovery. Waste and used tires can be converted into value-added products such as olefins, chemicals, and surface-activated carbons through conventional pyrolysis processes. They consist of compounds such as elastomers, vulcanizing agents, reinforcing agents, and plastificants [37]. The main advantage of this process is the recovery of material and structural damage reduction. Changes in pyrolysis temperature can change the mass reduction percentage. Increases in pyrolysis temperature will lead to a decrease in the solid char percentage [53]. Sulfur and nitrogen oxide emissions can be reduced compared to conventional pyrolysis. High temperatures can be achieved easily in microwave pyrolysis tires, which is a disadvantage of conventional pyrolysis.

5.8

Experimental setup and procedure

The experiment was conducted by electrical and microwave heating mechanisms. Both pyrolysis processes maintained an equal power-to-volume ratio for the comparison of results. The electrical heating method is explained by the following steps. Heat is supplied through the heating mantle, the power supplied is 450 W, and 600 mL of waste lubricant oil is taken inside the three-neck, round-bottom reactor. It is heated at different temperatures (250°C, 300°C, and 350°C). The water-cooled condenser cools the vapor that evolved from the waste lubricant oil. A k-type thermocouple was used in the process to monitor and control the temperature. An ero-therm data acquisition system is additionally attached to collect temperature and time data in the microwave process. The microwave pyrolysis quartz vessel is used as a reactor due to the favorable properties of this material. A 1.5-L vessel is placed in a microwave oven, and the power rating can be varied between 1.1 and 2.2 kW. In this experiment, 1 L of waste engine oil has been used, and the heating is given through a pair of magnetrons to attain a temperature range of 300–400°C. The oven has two pairs of magnetrons, and each pair is organized by a distinct button, which controls the power supplied to the magnetron. Only one pair of magnetrons is powered at a time to supply the necessary heat, and the other pair is kept inactive. The power supply is exchanged between the pair of magnetrons every 3 min to avoid overheating. The susceptors are used in the microwave heating for a better energy transformation and it is used to reach the maximum effectiveness of the pyrolysis process because of the microwave absorbance. The susceptor used in this process is silicon carbide (SiC). Alumina bricks were placed between silica carbide and the quartz to avoid direct contact of susceptors on the quartz vessel, as direct contact may lead to the thermal crack on the vessel. Pure nitrogen of 99.99% at a range of 2–5 L/min is supplied in both processes to maintain the inert atmosphere. The gas from the heated waste engine oil was directed to the double tube lei bag condenser, which condenses the gases at three stages. Water at room temperature circulates around the condenser, and the liquid fuel is obtained and collected in the vessels. The char (residue) inside the reactor was measured at the end of the pyrolysis process. The noncondensable gases left out were passed into the water to reduce the release of the toxic gases into the atmosphere.

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Fig. 5.1 Schematic layout of electrical pyrolysis setup. (1) Nitrogen cylinder. (2) Data acquisition system. (3) Electrical mantle. (4) Three-neck borosil vessel. (5) Stirrer motor. (6) Supporting stand. (7) Condenser. (8) Water tank with pump. (9) Nitrogen flow regulator.

Therefore, the data obtained from the total yield of fuel, the amount of noncondensable gases, and the char secreted in both electrical heating and microwave heating are compared to know the respective efficiencies of the processes. The electrical and microwave pyrolysis experimental setup shown in Figs. 5.1 and 5.2, respectively.

5.9

TG/DSC analysis for waste engine oil and microwave pyrolysis oil

TG/DSC analysis was performed by using a TGA NETZSCH STA 449F3 thermogravimetric analyzer to study the thermal decomposition of waste engine oil and pyrolysis oil. The experiments were conducted at a temperature ranging from room temperature to 600°C with a heating rate of 10°C/min and a flow rate of 200 mL/min N2 controlled atmosphere. Figs. 5.3 and 5.4 show a TG/DSC curve of WEO and PWEO, the decomposition of both the samples was completely stable at 597.7°C with a residual weight of 3.1% and 4.4%, respectively. It was absorbed that the initial weight loss for pyrolysis oil was 0.3% at 154.6°C, and for the waste engine oil, it was 0.1% at 212.2°C due to the removal of moisture and volatile content. Also, it was noticed that the second weight loss related to the main devolatilization of carbon and hydrogen compounds was released at 344.5°C and 389.8°C with the weight reduction of 48.5% and 43.7% for pyrolysis oil and waste engine oil, respectively. The change of heat content in terms of the exothermic and endothermic reaction was absorbed for waste engine oil and pyrolysis oil as a function of temperature under the controlled heating condition; it is shown in Figs. 5.3 and 5.4. The exothermic peak for pyrolysis oil in the DSC occurs at 344.3°C with a differential heat rate of

132

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Fig. 5.2 Schematic layout of microwave pyrolysis setup. (1) Nitrogen cylinder. (2) Data acquisition system. (3) Magnetron. (4) Blower. (5) Quartz vessel. (6) Stirrer motor. (7) Control panel. (8) Water tank with pump. (9) Condenser. (10) Nitrogen flow regulator.

DSC (mW/mg)

TG (%)

 exo

Value: 211.2°C, 99.9%

[1]

100 Value: 465.5°C, 6.316 mW/mg

8 7

80

6 5 Value: 389.8°C, 56.2%

60

4 Value: 390.3°C, 4.145 mW/mg

3

40

Residual mass: 3.1% (597.7°C)

2 20

1 [1]

0 100 WEO

200

400 300 Temperature (°C)

Fig. 5.3 TGA and DSC curve for waste engine oil (WEO).

500

0

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels TG (%)

133 DSC (mW/mg)

Value: 154.6°C, 99.7%

Peak: 344.3°C, 2.156 mW/mg

 exo

100

2.0 1.5

80

1.0

Value: 344.5°C, 51.2%

60 0.5 40

20

Value: 457.0°C, –0.8661 mW/mg

–0.5

Value: 67.2°C, –0.4928 mW/mg [1] [1]

0

–1.0

Residual mass: 4.4% (597.7°C)

100 PWEO

0.0

200

300 400 Temperature (°C)

500

Fig. 5.4 TGA and DSC curve for pyrolysis waste engine oil (PWEO).

2.156 mW/mg. It denoted the thermal decomposition of carbon and hydrogen compounds. The reaction range found for the pyrolysis oil was from 67°C to 457°C, where the initial endothermic peak occurs at 67.2°C with the differential heat rate of 0.4928 mW/mg due to that heat absorption of moisture in the pyrolysis oil. The final endothermic peak occurs at 457°C with the differential heat rate of 0.88 mW/mg denoting the reaction was completed. Similarly, for waste engine oil, the differential heat rate gradually increased, and no endothermic reaction takes place. One peak occurs at 390.3°C with the differential heat rate of 4.145 mW/mg; it denotes releasing of carbon and hydrogen components. Another peak occurs at 465.5°C with the differential heat rate of 6.316 mW/mg, which is due to melting of zinc present in the WEO. Also, a further increase in heat rate due to other metal components and contaminants was present in the WEO.

5.10

Comparison of electrical and microwave pyrolysis temperature profile and energy consumption

5.10.1 Temperature profile Fig. 5.5 shows the temperature rise through the different heating processes and the time taken to reach the maximum temperature through the different pyrolysis processes. From the graph temperature profile, we can infer that the heating process through electrical heating takes the longest time of 105 min. In microwave pyrolysis, the use of susceptors is to increase the heat generation of the waste oil. When compared with the electrical heating process, microwave-assisted pyrolysis (MAP) without susceptors with 1.1 and 2.2 kW reaches its maximum in 100 and 95 min,

134

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Fig. 5.5 The temperature profile for different pyrolysis mechanisms.

respectively. However, when compared with the electrical heating process, MAP with susceptors with 1.1 and 2.2 kW reaches its maximum in 40 and 30 min, respectively. The SiC susceptors have been used here for improving the process efficiency. It can be observed that MAP with susceptors at 2.2 kW is the fastest way to achieve maximum temperature.

5.10.2 Specific energy consumption Fig. 5.6 is drawn between the specific energy consumption of the pyrolysis process and the temperature rise through the different heating mechanisms. For reaching the same maximum temperature of 350°C, electrical heating takes 5040 kJ/kg. When compared to electrical heating, MAP without susceptors with 1.1 and 2.2 kW will require 7837 and 12,200 kJ/kg of specific energy consumption, respectively. MAP without susceptors will need 55% and 142% more of the specific power consumption value compared to electrical pyrolysis. When compared to electrical pyrolysis, MAP with silicon carbide susceptors in 1.1 and 2.2 kW will require 3441 and 3112 kJ/kg, respectively, which is 32% and 38% less of the specific energy consumption value of electrical heating. It can be observed that MAP with susceptors at 2.2 kW has less amount of specific energy consumption to achieve maximum temperature and also that MAP without susceptors takes a significant amount of power per kg because of the weak microwave-absorbing characteristics of the waste engine oil. The use

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

135

Fig. 5.6 Specific energy consumption for different pyrolysis mechanisms.

of susceptors has been beneficial in reducing the specific energy consumption by nearly four times compared to microwave pyrolysis without susceptors.

5.11

Comparison of electrical and microwave pyrolysis process yield at different conditions

5.11.1 Pyrolysis liquid yield In electrical heating pyrolysis, pyrolysis oil yields increased with an increase in temperature. Due to the increase in temperature, the kinetic energy of gas increased and decreased the retention time, resulting in a significant amount of liquid fraction obtained at a temperature of 350°C. An increase in nitrogen flow rate also enhanced the increase in the amount of liquid fraction from 2 to 3 L/min. A further increase in nitrogen flow rate along with temperature did not make any difference in improving the liquid fraction obtained. An increase in stirrer speed, a further increase in kinetic energy needed for pyrolysis, and hence more yield of the liquid fraction was obtained. Complete evaporation happened beyond the temperature of 350°C, and a broad optimum region of oil yield was obtained at 20 rpm of stirrer speed, as shown in Fig. 5.7. In MAP, due to high localized heat generation over conventional heating, the pyrolysis oil yield increased with an increase in temperature but the optimum temperature at which the maximum fraction obtained was 350°C. Moreover, an increase in the nitrogen flow also improved the yield of pyrolysis oil, but beyond the N2 flow rate

136

Advances in Eco-Fuels for a Sustainable Environment Electrical pyrolysis with stirrer speed 20 rpm 5.0

4.5

4.5 Nitrogen flow rate (L/min)

Nitrogen flow rate (L/min)

Electrical pyrolysis with stirrer speed 10 rpm 5.0

4.0

3.5

3.0

3.0

2.0

2.0 260

280

320

300

60% 65% 70% 75% 80%

340

Temperature (°C) Microwave pyrolysis with stirrer speed 10 rpm 5.0

260

280

320

300

340

Temperature (°C) Microwave pyrolysis with stirrer speed 20 rpm 5.0

4.5 Nitrogen flow rate (L/min)

4.5 Nitrogen flow rate (L/min)

3.5

2.5

2.5

4.0

3.5

3.0

4.0

3.5

3.0

2.5

2.5

2.0 300

4.0

320

340

360

Temperature (°C)

380

400

2.0 300

320

340

360

380

400

Temperature (°C)

Fig. 5.7 Comparison pyrolysis liquid yield for electrical and microwave pyrolysis.

of 3 L/min, the yield of pyrolysis oil had decreased. This is because the retention time of the pyrolysis gases in a condenser was reduced beyond an optimum (i.e., 3 L/min) nitrogen flow rate. An increase in stirrer speed further increased the amount of localized heat generation as well as the kinetic energy of the gases, which reduced the amount of sufficient retention time, hindering the process of condensation. This led to the decrease in the amount of the pyrolysis oil yield. Moreover, a broad range of optimum pyrolysis oil yield was observed at a 10 rpm stirrer speed. The pyrolysis oil yield obtained in microwave pyrolysis was high when compared with electrical pyrolysis at 10 rpm stirrer speed. The maximum amount of oil yield was obtained at 350°C temperature and a 3 L/min nitrogen flow rate in microwave pyrolysis. At 20 rpm stirrer speed, improved oil yield was observed in electrical pyrolysis when compared to microwave pyrolysis, due to a very high amount of localized heat generation happening in microwave pyrolysis due to the insufficient retention rate. The broad area of the optimum range was observed and is shown in Fig. 5.7.

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

137

5.11.2 Noncondensable gases yield In electrical pyrolysis with minimum nitrogen flow rate at 20 rpm stirrer speed has increased the noncondensable gas yield fraction because of the secondary cracking due to lower kinetic energy and retention time. However, in the case of 10 rpm stirrer speed and low nitrogen flow rates, as the temperature increased slightly, this decreased the noncondensable gas yield fraction due to optimum kinetic energy to reduce the secondary cracking of the pyrolysis gases. Stirrer speed did not affect much more on the gas yields obtained due to the constant heating rate of the electrical pyrolysis process. The slight difference was only observed in electrical pyrolysis. However, at 300°C and 10 rpm stirrer speed, as the nitrogen flow rate increased, there was a decrease in the percentage of gas yield due to the reduction of secondary cracking reactions because of its optimum kinetic energy condition. At low temperatures, an increased nitrogen flow rate improved the noncondensable gas yield because of low retention time roots in the condenser. On the other hand, at a low nitrogen flow rate, an increase in temperature decreased the gas yield due to the reduced amount of retention time as well as secondary cracking at 10 rpm stirrer speed. However, at 20 rpm stirrer speed and low nitrogen flow rates, an increase in temperature increased the amount of noncondensable gases when compared with gas yield obtained at 10 rpm stirrer speed because of secondary cracking. Secondary cracking increased due to stirrer speed, and it splashed out the feed, which came in contact with the surface of the reactor vessel and caused secondary cracking. In microwave pyrolysis, an increase in temperature as well as nitrogen flow rate improved the amount of noncondensable gas yield due to very high localized heat generation and low retention time (i.e.) from 20% to 25% at 10 rpm stirrer speed. Moreover, there was an improvement in the gas yield from 20% to 30% with 20 rpm stirrer speed as temperature and nitrogen flow rate increased. At low temperatures, increased nitrogen flow rate improved the gas yield because of the low retention times and instantly carried away the gases that were produced. From Fig. 5.8, it can be concluded that MAP improved the amount of noncondensable gases obtained when compared with electrical pyrolysis for any stirrer speed.

5.11.3 Char yield The percentage of char formed in electrical pyrolysis decreased with increasing temperature and nitrogen flow rate. However, the percentage of char yield was high with a reduction in the temperature. This is due to partial evaporation of feed at low temperatures and implying high elimination volatile components. The latent heat of evaporation was not reached for the whole of the species, which involved a weaker cracking of the hydrocarbon chain, which improved the percentage of char in the residue. The higher rate of evaporation caused by increased temperature led to an increase in kinetic energy, which reduced the amount of char formation. In electrical pyrolysis, the trend of change of char formation was the same for both stirrer speeds (i.e., 10 and 20 rpm). At low temperatures, an increase in nitrogen flow rate decreased the char yield for both stirrer speeds. An increase in stirrer speed resulted in a decrease of char

138

Advances in Eco-Fuels for a Sustainable Environment Electrical pyrolysis with stirrer speed 20 rpm 5.0

4.5

4.5 Nitrogen flow rate (L/min)

Nitrogen flow rate (L/min)

Electrical pyrolysis with stirrer speed 10 rpm 5.0

4.0

3.5

3.0

3.0

2.0

2.0 260

280

320

300

10% 15% 20% 25% 30%

340

Temperature (°C) Microwave pyrolysis with stirrer speed 10 rpm 5.0

4.5

260

280

320

300

340

Temperature (°C) Microwave pyrolysis with stirrer speed 20 rpm 5.0

4.5 Nitrogen flow rate (L/min)

Nitrogen flow rate (L/min)

3.5

2.5

2.5

4.0

3.5

3.0

4.0

3.5

3.0

2.5

2.5

2.0 300

4.0

320

340

360

Temperature (°C)

380

400

2.0 300

320

340

360

380

400

Temperature (°C)

Fig. 5.8 Comparison of noncondensable gas yield for electrical and microwave pyrolysis.

yield because of decreased deposition of char on the walls of the reactor vessel. Increased deposition of char reduced the rate of heat transfer and promoted the formation of char due to slow heating observed at 10 rpm stirrer speed. Fig. 5.9 shows the formation of char with different temperature and nitrogen flow rate for the electrical and microwave pyrolysis. The percentage of char formation in microwave pyrolysis was less compared to electrical pyrolysis due to the higher localized heat generation, which was the primary cause of decreased char formation. In this microwave region, the generation of localized heat was increased and increased the temperature of the spots involving rich in carbon. Carbon converts the energy of the microwaves into heat and finally evaporates because of the high localized temperature. Thus, the yield of char formation was reduced in microwave heating. Increased temperature and nitrogen flow rates decreased the amount of char formation from 16% to 8% at 10 rpm stirrer speed. However, at 20 rpm stirrer speed, the nitrogen flow rate did not affect the yield of char with

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels Electrical pyrolysis with stirrer speed 20 rpm 5.0

4.5

4.5 Nitrogen flow rate (L/min)

Nitrogen flow rate (L/min)

Electrical pyrolysis with stirrer speed 10 rpm 5.0

4.0

3.5

3.0

3.5

3.0

08% 2.0 10% 12% 14% 16% 18% 20% 5.0 22% 24%

2.0 260

280

320

300

340

Temperature (°C) Microwave pyrolysis with stirrer speed 10 rpm 5.0

4.5

260

280

300

320

340

Temperature (°C) Microwave pyrolysis with stirrer speed 20 rpm

4.5 Nitrogen flow rate (L/min)

Nitrogen flow rate (L/min)

4.0

2.5

2.5

4.0

3.5

3.0

4.0

3.5

3.0

2.5

2.5

2.0 300

139

320

340

360

Temperature (°C)

380

400

2.0 300

320

340

360

380

400

Temperature (°C)

Fig. 5.9 Comparison of char yield for electrical and microwave pyrolysis.

an increase in temperature due to an added advantage of the further increase in localized heat generation.

5.12

Hydrocarbon analysis of electrical and microwave pyrolysis

GC-MS results show that the pyrolysis waste engine oil contains alkanes, alkenes, cycloalkanes, ketones, and others. Table 5.2 shows the hydrocarbon constituents present in the electrical and different microwave pyrolysis oil. Figs. 5.10 and 5.11 show the area percentage of carbon chain analysis at different pyrolysis mechanisms. The hydrocarbon formation for the electrical and microwave pyrolysis with 1.1 kW power is nearly the same at 350°C but a higher power rating in the microwave pyrolysis with

Table 5.2 GC-MS constituents for different pyrolysis oil Electrical pyrolysis

MAP with 1.1 kW

MAP with 2.2 kW

Area%

Compounds

R. Time

Area%

Compounds

R. Time

Area%

Compounds

1

2.14

0.3265

2.13

1.0515

Cyclopentane, methyl-

4.188

3.07

2

2.32

0.4018

Cyclopentane, methylHeptane

2.26

0.5061

1-Heptene

4.322

1.84

3

2.93

0.3795

Heptane, 2-methyl-

2.32

0.9897

Heptane

4.505

1.19

4

3.03

0.1758

2.45

0.1996

6.18

3.25

0.4168

2.55

0.1475

6.184

0.4

Heptane (CAS)

6

3.35

1.4366

Octane

2.8

0.147

1-Pentene, 2,4,4trimethylZ-3,4,4-Trimethyl-2pentene 2,4-Dimethyl-1-hexene

4.951

5

Heptane, 3,4,5trimethyl1-Octene

Pentane, 2-methyl(CAS) Pentane, 3-methyl(CAS) Butane, 2-isothiocyanato(CAS) Cyclopentane, methyl-

6.91

0.6

7

4.34

0.7861

2.93

0.4738

Heptane, 2-methyl-

8.133

0.4

8

4.46

0.589

Cyclohexane, 1-(1,1dimethylethyl)-4methylOctane, 3-methyl-

Cyclohexane, methyl(CAS) Benzene, methyl(CAS)

3.06

0.6504

8.482

0.39

9 10 11 12

4.73 4.84 4.98 5.63

0.4374 1.0859 1.9976 0.2548

3.25 3.36 4.34 4.47

1.0672 1.0783 0.673 0.7562

8.743 9.02 10.233 10.345

0.38 1.15 0.42 0.5

13

5.76

0.3534

4.73

0.4087

1-Octene, 2-methyl-

11.233

0.77

Cyclohexane, 1,3-dimethyl-, cis1-Octene Octane (CAS) 1-Octanol, 2-butylCyclohexane, ethyl(CAS) Octane, 4-methyl-

14

5.95

0.2611

1-Octene, 2-methyl1-Nonene Nonane Octane, 2,6dimethylCyclohexane, 2-propenyl1-Undecene, 7-methyl-

2,2,4,4,5,5,7,7Octamethyloctane 1-Octene Octane Nonane, 4-ethyl-5-methylHexanal, 5,5-dimethyl-

4.85

0.8125

1-Nonene

11.496

0.57

Octane, 3-methyl-

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R. Time

140

Peak

6.07

0.4606

1.3727

Nonane

11.571

1.07

5.65 5.78

0.2099 0.3202

12.101 12.169

0.33 0.38

6.44

0.3156

Nonane, 3-methyl-

5.97

0.2531

12.479

2.79

Nonane (CAS)

19

6.77

0.4988

2-Methyl-1-nonene

6.07

0.4958

13.676

0.34

20 21 22

6.91 7.09 7.42

1.6453 2.2687 0.29

1-Decene Decane 1-Decene, 4-methyl-

6.23 6.78 6.93

0.3314 0.4146 1.2146

Octane, 2,6-dimethyl4-Hexen-3-one, 4,5dimethylPentane, 3-ethyl-2-methyl1,1,3,3,5Pentamethylcyclohexane Nonane, 4-methyl2-Methyl-1-nonene 1-Decene

Benzene, 1,2dimethyl- (CAS) Cyclododecane 1-Octanol (CAS)

16 17

6.22 6.28

18

13.734 14.632 14.719

0.36 0.32 0.41

23

7.57

0.2075

Decane, 4-methyl-

7.11

1.5011

Decane

14.812

0.56

24

7.88

0.1933

7.44

0.2757

1-Decene, 4-methyl-

15.462

0.41

25

8.25

0.5232

7.59

0.1965

Decane, 4-methyl-

15.63

0.52

26

8.41

0.5311

Heptane, 4-(1methylethyl)Decane, 2,2,3trimethylHeptane, 4-ethyl-

Octane, 3,6-dimethyl(CAS) Cyclohexane, propylNonane, 4-methylNonane, 2-methyl(CAS) Benzene, 1-ethyl-3-methylBenzene, 1,3,5trimethyl- (CAS) 1-Decene

7.88

1.1944

15.921

2.08

Decane

27

8.48

0.2418

Decane, 4-methyl-

8.41

0.3121

17.184

0.59

28

8.58

0.4873

Decane, 2-methyl-

8.54

0.9235

17.984

0.61

Cyclohexylmethyl dodecyl sulfite Octane, 4-ethyl-

29 30

8.74 9.1

0.4489 0.4863

8.75 9.13

0.358 0.4559

18.841 19.101

0.37 1.11

1-Undecene (CAS) Undecane (CAS)

31

9.27

1.7817

Decane, 3-methyl4-Decene, 2-methyl-, (Z)1-Undecene

3-Heptene, 2,2,4,6,6pentamethylHeptane, 3-ethyl-2-methylHeptane, 2,2,6,6tetramethyl-4- methyleneDecane, 3-methyl4-Decene, 2-methyl-, (Z)-

9.3

1.2953

1-Undecene

19.907

0.38

32

9.46

2.9504

Undecane

9.49

1.8812

Undecane

20.753

0.52

Bicyclo[4.1.0]heptan3-one, 4,7,7trimethyl-, 2,6-Dimethyldecane Continued

141

4.99

0.2991 0.2773

2-Decene, 5-methyl-, (Z)Heptane, 3-ethylNonane, 2-methyl-

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

15

Table 5.2 Continued Electrical pyrolysis

MAP with 1.1 kW

MAP with 2.2 kW

Area%

Compounds

R. Time

Area%

Compounds

R. Time

Area%

Compounds

33

9.91

0.2538

9.84

0.202

2,6-Dimethyldecane

21.055

0.4

Cinnamyl carbanilate

34 35

10.08 10.71

0.1671 1.0578

9.94 10.09

0.2505 0.1724

1-Nonene, 4,6,8-trimethylDecane, 3,7-dimethyl-

21.791 22.022

0.4 1.45

1-Dodecene (CAS) Dodecane (CAS)

36

10.87

0.3778

1-Undecene, 4-methylUndecane, 4-methyl1-Undecene, 8-methylUndecane, 4-methyl-

11

0.4034

23.754

0.31

Dodecane, 2-methyl-

37

10.98

0.5736

Undecane, 2-methyl-

11.15

0.7072

24.351

0.33

38

11.14

0.7146

Undecane, 3-methyl-

11.54

0.5918

24.505

0.35

Piperidine, 4-(4methylphenyl)1-Tridecene (CAS)

39

11.52

0.7057

11.72

1.4893

24.719

1.94

Tridecane (CAS)

40

11.69

1.9192

5-Undecene, 2-methyl-, (Z)1-Dodecene

4-Undecene, 3-methyl-, (Z)Benzene, 1-methyl-3-(1methylethyl)5-Undecene, 2-methyl-, (Z)1-Dodecene

11.89

2.0851

Dodecane

25.22

0.38

41

11.87

0.2988

Dodecane

12.02

0.2449

5-Dodecene, (E)-

25.725

0.36

42

11.99

0.3241

2-Dodecene, (Z)-

12.17

0.6183

Undecane, 2,6-dimethyl-

26.081

0.4

43

12.14

0.5715

13.09

0.4335

Undecane, 2,6-dimethyl-

26.321

0.51

44

13.36

0.7609

Undecane, 2,6dimethylDodecane, 2-methyl-

13.39

0.5664

Undecane, 4,8-dimethyl-

26.455

0.81

45

13.52

0.7572

Dodecane, 3-methyl-

13.55

0.6392

Dodecane, 3-methyl-

26.511

0.35

46

13.89

0.8094

Cyclopentane, 3-hexyl-1,1dimethyl-

13.91

0.8071

Cyclopentane, 3-hexyl-1,1-dimethyl-

26.667

0.48

Naphthalene, 2-methyl- (CAS) 2-Cyclopenten-1-ol, 1-phenyl- (CAS) Decane 4-cyclohexyl-, 4-cyclohe Tetradecane, 2,6,10trimethyl2,4,4,6,6,8,8Heptamethyl-2-nonene Tetradecane, 2-methyl- (CAS) Hexadecane, 2,6,10,14-tetramethy

Advances in Eco-Fuels for a Sustainable Environment

R. Time

142

Peak

2.5503 3.3705 0.5137

6-Tridecene Tridecane Tridecane, 5-methyl-

14.1 14.27 14.61

1.9962 2.4199 0.5516

6-Tridecene Tridecane Tridecane, 6-methyl-

27.033 27.228 27.323

0.36 3.04 0.64

1-Hexadecene Tetradecane 2,4,4,6,6,8,8Heptamethyl-1-nonene Benzoic acid, 4-chloro-, (1methyl-4-piperidi Hexadecane, 1,1-bis (dodecyloxy)Hexadecane

50

15.53

0.6897

Tridecane, 4-methyl-

15.57

0.3566

Tridecane, 4-methyl-

28.404

0.4

51

15.86

0.5784

Tridecane, 3-methyl-

15.9

0.4979

Tridecane, 3-methyl-

28.601

0.53

52

15.95

0.2234

16

0.6783

0.88

16.27

0.6663

16.31

0.64

Dodecane, 2,6,10trimethyl2-Methyl-n-1-tridecene

28.708

53

28.903

0.31

54

16.47

1.7899

Dodecane, 2,6,10trimethyl2-Methyl-n-1tridecene 5-Tetradecene, (E)-

16.52

2.5766

1-Tridecene

29.255

0.36

55

16.67

3.6918

Tetradecane

16.75

4.1673

Tetradecane

29.326

0.36

56

18.06

0.7722

18.21

0.1986

Tetradecane, 5-methyl-

29.391

0.48

57

18.16

0.3142

Tridecane, 2,5dimethylTetradecane, 5-methyl-

18.56

0.5533

Hexadecane

29.485

0.41

58

18.51

0.6655

18.77

0.5148

Tetradecane, 3-methyl-

29.572

3.24

59

18.71

0.4314

19.25

0.5718

0.68

Hexadecane

19.21

0.7333

19.47

1.3767

Cyclopropane, 1-(1methylethyl)-2-nonyl9-Octadecene, (E)-

30.597

60

30.725

0.33

61

19.42

2.006

Tetradecane, 2-methylTetradecane, 3-methyl2Methyl-1-tetradecene 1-Pentadecene

Decahydro-8a-ethyl1,1,4a,6tetramethylnaph Pentadecane (CAS)

19.7

3.7503

Pentadecane

30.862

0.66

62

19.62

3.7972

Pentadecane

21.16

0.6882

Pentadecane, 5-methyl-

30.966

1.07

Pentadecane, 5-methyl- (CAS) Pentadecane, 4-methyl- (CAS) Pentadecane, 2-methyl-

Tetradecane, 3-methyl2Methyl-1-tetradecene Cycloheptasiloxane, tetradecamethyl1-Pentadecene

Continued

143

14.05 14.22 15.39

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

47 48 49

Table 5.2 Continued Electrical pyrolysis

MAP with 1.1 kW

MAP with 2.2 kW

Area%

Compounds

R. Time

Area%

Compounds

R. Time

Area%

Compounds

63

21.1

0.4489

21.34

0.8575

Dodecane, 2-methyl-

31.147

0.34

64 65

21.27 21.45

0.9041 0.9205

21.51 21.73

0.8611 0.5713

Pentadecane, 2-methylPentadecane, 3-methyl-

31.609 31.774

0.44 3.67

Pentadecane, 3-methyl1-Octadecene Hexadecane

66

21.67

0.5729

22.21

0.7859

0.44

22.15

0.8654

22.42

1.3716

Cyclopropane, 1,2dimethyl-3-pentyl-, 1-Nonadecene

32.712

67

32.795

1.07

68

22.36

0.1687

Heptane, 3,4,5trimethylTridecane, 3-ethylDodecane, 2-methyl-6-propylPentadecane, 3-methylPentadecane, 8-methylene1-Hexadecene

22.65

3.9039

Hexadecane

32.987

0.45

69

22.55

3.6295

Hexadecane

23.89

1.8367

33.264

0.33

70

23.8

2.1426

24.24

0.4324

33.856

3.54

71

24.17

0.4286

24.41

0.8843

Hexadecane, 2-methyl-

33.984

2.92

72

24.34

0.9235

24.62

0.7176

Hexadecane, 3-methyl-

34.765

1.27

73

24.56

0.7303

Pentadecane, 2,6,10trimethylHexadecane, 4-methylHexadecane, 2-methylHexadecane, 3-methyl-

Pentadecane, 2,6,10trimethylHexadecane, 4-methyl-

24.84

0.7975

34.865

0.37

74

25.23

1.2444

9-Octadecene, (E)-

25.3

0.7307

Cyclohexane, 1-(1,5dimethylhexyl)-4-(4methylpentyl)5-Eicosene, (E)-

35.095

0.32

75 76

25.4 26.77

3.7322 0.9567

Heptadecane Octadecane, 6-methyl-

25.52 26.62

5.5669 1.3453

Heptadecane Heptadecane, 2,6,10,15tetramethyl-

35.691 35.824

0.41 3.61

Heptadecane, 8-methyl- (CAS) Pentadecane, 2,6,10trimethylHexadecane, 4-methylHexadecane, 3-methyl- (CAS) Heptadecane (CAS) Pentadecane, 2,6,10,14-tetramethyl2,6,10Trimethylpentadecane Hexadecane, 2-methylHeptadecane, 2-methyl- (CAS) 1-Octadecene (CAS) Octadecane

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R. Time

144

Peak

26.97

0.6464

0.5956

Heptadecane, 4-methyl-

36.027

1.17

78

27.12

0.7959

27.2

0.7655

Heptadecane, 2-methyl-

36.5

0.38

79

27.34

0.4512

28.06

0.7837

9-Octadecene, (E)-

36.607

0.87

80

27.99

28.26

4.5763

Octadecane

36.7

0.31

81

28.14

3.6934

Octadecane

29.5

0.2577

Heptadecane, 9-hexyl-

36.784

0.34

82

29.21

0.3649

29.7

0.3878

Octadecane, 4-methyl-

37.001

0.32

83

29.77

0.4103

30.08

0.6084

Octadecane, 3-methyl-

37.176

0.33

84

30

0.702

30.87

4.1871

Nonadecane

37.57

0.44

85 86

30.76 31.87

3.1649 0.1177

32.24 32.4

0.4315 0.5528

Nonadecane, 4-methylNonadecane, 2-methyl-

37.695 38.419

3.51 0.76

87

32.17

0.408

32.6

0.7237

Nonadecane, 3-methyl-

38.739

0.46

88

32.32

0.5732

33.38

3.4257

Eicosane

38.814

0.33

89

32.53

0.7863

33.46

0.083

3.71

33.25 34.16

3.1316 0.6351

34.68 35.03

0.2091 0.8776

2,4,4,6,6,8,8Heptamethyl-1-nonene Heptadecane, 9-hexylPentadecane, 2,6,10trimethyl-

39.473

90 91

Octadecane, 3-methylOctadecane, 2-methylOctadecane, 3-methylNonadecane Heptadecane, 9-hexylNonadecane, 4-methylNonadecane, 2-methylNonadecane, 3-methylEicosane Heptadecane, 9-hexyl-

40.141 40.354

0.67 0.75

92

34.74

0.4317

Eicosane, 2-methyl-

35.75

2.5783

Heneicosane

41.01

0.61

93

35.64

3.0386

Heneicosane

37.03

0.2112

Eicosane, 3-methyl-

41.172

4.01

Hexadecane, 2,6,10,14-tetramethyl1-Dodecanol, 2-octylNonadecane, 9-methylDodecane, 5,8-diethyl(CAS) Octadecane, 5-methyl(CAS) Octadecane, 2-methyl(CAS) Octadecane, 3-methyl(CAS) 1-Decanol, 2-octylNonadecane (CAS) Nonadecane, 9-methyl- (CAS) 2-Thiopheneacetic acid, 2-tridecyl ester Octadecane, 3-methyl(CAS) Eicosane (CAS) Eicosane Sulfurous acid, cyclohexylmethyl pentadecyl 2,4,4,6,6,8,8Heptamethyl-1-nonene Heneicosane (CAS) Continued

145

27.03

0.4994

Heptadecane, 4-methylHeptadecane, 2-methylHeptadecane, 2,3dimethyl9-Octadecene, (E)-

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

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146

Table 5.2 Continued Peak

Electrical pyrolysis

MAP with 1.1 kW

MAP with 2.2 kW

Area%

Compounds

R. Time

Area%

Compounds

R. Time

Area%

Compounds

94

36.93

0.2029

Eicosane, 3-methyl-

37.17

0.3159

Eicosane, 2-cyclohexyl-

41.289

0.61

95

37.27

0.4369

38.05

2.0994

Docosane

41.786

0.71

96 97

37.93 39.68

2.6076 0.2442

38.83 39.28

0.4479 0.1243

Eicosane, 10-methylHeneicosane, 3-methyl-

42.369 42.835

0.32 3.01

3-Methylheneicosane Docosane (CAS)

98 99 100

40.14 42.32 43.06

1.7723 1.5212 0.8017

Heneicosane, 3-methylDocosane Docosane, 2,21dimethylTricosane Tetracosane Hexadecane, 2,6,11,15tetramethyl-

9-Octadecenoic acid, methyl ester (CAS) Eicosane

39.64 40.27 42.46

0.2055 1.3131 0.8591

Docosane, 2,21-dimethylTricosane Tetracosane

43.478 44.619 45.312

0.52 2.91 0.55

Tetratriacontane Tricosane Octacosane

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R. Time

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

Fig. 5.10 Comparison of hydrocarbon group for different pyrolysis techniques.

Fig. 5.11 Comparison of hydrocarbon chain length for different pyrolysis techniques.

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2.2 kW slightly deviated from others due to high heating rate causes for carbon evaporation and secondary cracking. The percentage of alkanes present in pyrolysis oil produced from both electrical as well as microwave pyrolysis was nearly same. However, the percentage of alkanes present in the oil that is produced from electrical pyrolysis was slightly higher than the alkanes present in the pyrolysis oil produced from microwave pyrolysis. The percentage of alkanes present in pyrolysis oil that was produced from MAP at 2.2 kW heating rate, and the percentage of alkanes in pyrolysis oil that was produced from electrical pyrolysis were nearly the same. The percentage of alkenes present in the pyrolysis oil that was produced from microwave pyrolysis at 1.1 kW heating rate and the percentage of alkenes present in the pyrolysis oil that was produced from the electrical pyrolysis were the same. The low kinetic energy of the molecules and the high retention time enhances the secondary cracking and leads to the production of alkenes. Alcohol and other species also formed, and this was higher in microwave pyrolysis at a 2.2 kW heating rate compared to the microwave pyrolysis at 1.1 kW as well as electrical pyrolysis. This was due to high temperatures and heating rates, and the energy required to form such other species was sufficient enough in microwave heating at 2.2 kW heating rate. The similar percentages of C6–C9 and C10–C19 carbon chain lengths were observed in pyrolysis oil that was produced from both electrical pyrolysis and microwave pyrolysis at 1.1 kW. There was an increase in the percentage of C6–C9 chain length in the pyrolysis oil that was produced from microwave pyrolysis at 2.2 kW heating rate. Moreover, there was a decrease in the percentage of C10–C19 chain length in the pyrolysis oil that was produced from microwave pyrolysis at 2.2 kW heating rate. The percentage of other compounds observed in pyrolysis oil that was produced from both electrical pyrolysis as well as microwave pyrolysis at 1.1 kW was nearly the same. There was an increase in the percentage of other components in the pyrolysis oil that was produced from microwave pyrolysis at 2.2 kW heating rate compared with both electrical and microwave heating at 1.1 kW.

5.13

Analysis of FT-IR spectroscopy of different products

Fig 5.12 shows that comparison of the FT-IR spectrum for different pyrolysis products. FT-IR results showed that most of the hydrocarbons found in microwave pyrolysis oil (MPO) were alkanes and C]H bending alkenes. The results indicate that most hydrocarbons present in the waste engine oils (WEO) were alkanes C–H stretching it is shown in the frequency range of 2750–3000 cm1. The compounds with inflection similar to C–H stretching in the frequency range of 675–850 cm1 are cyclic single ring aromatics in the pyrolysis oil present only in modest amounts. Most of the hydrocarbons found in diesel were CdH stretching alkanes and minor quantities of single ring aromatics. Results revealed that the hydrocarbons found in the electrical pyrolysis oil (EPO) and microwave pyrolysis oil (MPO) were alkanes and minor amounts of alkenes. Chemical compounds present in the char produced by the electrical pyrolysis

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

149

Fig. 5.12 FT-IR spectrum for different pyrolysis fuels.

were CdH stretching alkanes, minor amounts of C]H bending/deformation alkanes, and a very few C]H bending alkenes. Similarly, chemical compounds found in char produced from the MAP were CdH stretching alkanes, minor amounts of C]H bending/deformation alkanes, and a very few C]H bending alkenes as well as single ring aromatics are shown in Table 5.3.

Table 5.3 FT-IR spectroscope with frequency range Frequency range (cm21)

Functional groups

Classification of compounds

3200–3400

OdH stretching

2750–3000 1700–2100

CdH stretching C]O stretching

1575–1675 1345–1500

C]C stretching C]H bending/ deformation C]H bending CdH out of plane bending

Alcohols, phenols, or carboxylic acid Alkanes Aldehydes, ketones, or carboxylic acid Alkenes Alkanes

900–1200 675–850

Alkenes Single ring aromatics

150

5.14

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Comparison of calorific value for the different pyrolysis oil

Fig. 5.13 shows that variation of the calorific value of different pyrolysis oil with respect to the temperature and heating rate. The calorific value of the pyrolysis oil produced depends on temperature, a heating mechanism, and heating rate. The calorific value of the oil obtained from MAP was more than the oil obtained from the electrical pyrolysis. This is because the length of the hydrocarbon chain is less in the pyrolysis oil produced by MAP. In electrical pyrolysis, the hydrocarbon chain length of the oil produced varies from C9 to C25 and in microwave pyrolysis, the hydrocarbon chain length varies from C6 to C36. The calorific value of the oil increases as the hydrocarbon chain length decreases but a decrease in hydrocarbon chain length decreases the density as well as the viscosity of the oil. The average chain length of oil being produced from microwave pyrolysis was less. Hence, the calorific value of the oil was more. An increase in temperature increases the calorific value to a specific temperature because the increase in temperature decreases the chain length of a hydrocarbon. Moreover, this is the reason why the increase in temperature improves the calorific value of the oil being produced. In electrical pyrolysis, the temperature at which higher calorific value of the oil being produced is at 300°C when compared with 250°C and 350°C. Similarly, in microwave pyrolysis, the range of temperature at which high calorific value oil was obtained was from 350°C to 400°C.

Fig. 5.13 Comparison of calorific value for different pyrolysis fuels.

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

151

The calorific value of the oil was improved with an increase in heating rate. The calorific value of the pyrolysis oil was more for a 2.2 kW heating rate when compared with a 1.1 kW heating rate. This was due to the increased cracking of hydrocarbon chain into smaller molecules. The calorific value decreases for microwave pyrolysis at 2.2 kW heating and above 350°C were because of the chances of decreased H/C ratio due to the formation of cycloalkanes and alkenes.

5.15

Comparison of kinematic viscosity of the different pyrolysis oils

Fig. 5.14 shows that variation of kinematic viscosity of different pyrolysis oil with respect to the temperature and heating rate. In electrical pyrolysis, kinematic viscosity increases with an increase in temperature because of viscous species. Also, additives present in the waste engine oil will also evaporate along with volatile matter and condensation of this increases the viscosity of the pyrolysis oil. The viscosity of the pyrolysis oil being produced depends on temperature, a heating mechanism, and heating rate. The pyrolysis oil produced from electrical pyrolysis has a low viscosity when compared with oil produced from microwave pyrolysis due to the surface evaporation from the reactor wall, and secondary cracking was the essential cause of this low viscosity. In microwave heating, pyrolysis oil has a higher kinematic viscosity because of the high kinetic energy of the particles, the low retention time, and fewer chances for secondary cracking. However, increasing the heating rate in microwave pyrolysis

Fig. 5.14 Comparison of kinetic viscosity for different pyrolysis fuels.

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reduces the viscosity of the pyrolysis oil being produced of the pyrolysis oil has a low hydrocarbon chain length. Temperature plays a primary role in the variation of the viscosity of the pyrolysis oil produced. If the temperature rose over 350 °C, the viscosity of the pyrolysis fuel increased due to the evaporation of the heavier and longer hydrocarbon chain in the engine waste oil.

5.16

Conclusions

The following conclusions were drawn from this investigation.    

    

The microwave pyrolysis with SiC was an energy-efficient process compared to the electrical pyrolysis and microwave pyrolysis without a microwave absorber. The time taken for reaching pyrolysis temperature in microwave pyrolysis without an absorber was 4.7% and 9.5% faster than electrical pyrolysis. In microwave pyrolysis with an absorber, it was 61.9% and 71.4% faster than electrical pyrolysis. Microwave-assisted pyrolysis with silicon carbide susceptors with 1.1 and 2.2 kW consumes 32% and 38% less specific power consumption value compared to electrical pyrolysis. The optimum temperature was found in the range of 350–400°C for microwave pyrolysis with a nitrogen flow rate of 2–3 L/min. The maximum pyrolysis oil obtained in the microwave pyrolysis with 1.1 and 2.2 kW power was 3% and 10% less than electrical pyrolysis, respectively. The microwave with 1.1 kW power was more suitable compared to the microwave with 2.2 kW power rating. Higher heating rate increases the noncondensable gas yield and decreases the pyrolysis oil yield and char yield due to secondary cracking and higher kinetic energy. The GC-MS results indicate that the pyrolysis oil obtained by the electrical and microwave pyrolysis was nearly the same alkane percentage, but alkenes and other elements are slightly higher in the microwave pyrolysis oil. FT-IR spectrum confirmed the same alkane present in the electrical and microwave pyrolysis processes. The calorific value obtained in the microwave pyrolysis with 2.2 kW power was 2% higher than electrical pyrolysis.

The study recommended for the future research can refer to different hazardous wastes, which result from a microwave pyrolysis operated by solar energy, in order to achieve a maximum energy recovery during the pyrolysis process. Extensive research will be carried out on microwave susceptors to find the suitable and highest efficiency microwave absorber for the pyrolysis process. Microwave susceptors prepared with the addition of different ceramics and metals will enhance the process efficiency and fuel quality. The future research will be focused on better utilization of pyrolysis yields such as liquid, char, and noncondensable gases for various applications to increase the efficiency.

Acknowledgments The authors would like to acknowledge the Department of Science and Technology—Science and Engineering Research Board (DST-SERB) for providing valuable support and sanctioning

Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

153

the grant for successful completion of this project (Project No. DST/SB/EMEQ-251). The authors also acknowledge the Director, National Institute of Technology, Tiruchirappalli, Tamilnadu, India for extending the facility to carry out this experimentation.

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Microwave-assisted fast pyrolysis of hazardous waste engine oil into green fuels

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