Pyrolysis and Combustion Characteristics of Newly Discovered Coals from Nigeria: Physicochemical, Microstructure, Mineralogy, and Thermal Properties

Despite Nigeria’s vast mineral and energy resources, the nation lacks sucient electricity generation capacity to stimulate sustainable growth and infrastructural development. However, the discovery of vast coal deposits across the nation’s sedimentary basins could provide cheap, reliable, and abundant energy supplies. However, the lack of comprehensive data on the fuel characteristics, energy recovery, and potential emissions of Nigeria’s coals currently hampers the quest for coal-red electricity generation. Hence, this study examined the physicochemical, microstructural, mineralogical, and thermal fuel properties of three (3) newly discovered coals from Akunza (AKZ), Ome (OME), and Shiga (SHG) in Nigeria for potential energy recovery through combustion and pyrolysis. Physicochemical analysis revealed high combustible but low levels of polluting elements. The higher heating values ranged from 18.65 MJ/kg for AKZ to 26.59 MJ/kg for SHG. Microstructure analysis revealed rough textured and surfaced particles with a glassy lustre ascribed to metals (such as Ti and Fe), quartz, and kaolinite. Mineralogical analyses revealed the major elements (C, O, Si, and Al), along with minor (Ca, Cu, Fe, K, Mg, S, and Ti) associated with clays, salts, or the porphyrin constituents of coal. Thermal analysis showed mass losses (M L ) ranging from 30.51% to 87.57% and residual mass (R M ) from 12.44% to 69.49% under oxidative (combustion) and non-oxidative (pyrolysis) conditions due to the thermal degradation of organic matter and macerals (vitrinite, inertinite and liptinite) during TGA. Overall, the coals are potential feedstocks for energy recovery through pyrolysis and combustion.


Introduction
Coal is a biogenic sedimentary rock derived from complex biochemical and metamorphic processes termed coali cation in the earth's crust (Gräbner 2014;Speight 2013). In the context of energy recovery, coal is considered a brown-to-black combustible material that contains high carbon content (60-87 wt.%) and higher heating values (14-34 MJ/kg) (Reddy 2013;Speight 2012). Consequently, coal is predominantly utilised for electric power generation due to its high energy content, widespread availability, and low processing costs. Over the years, coal has also become an important feedstock for the production of fuels, chemicals, and industrial raw material for numerous applications (Dorf 2017;Miller 2016).
According to analysts, coal currently accounts for 38-41% of the global electricity generation (Dai and  Mozambique have also begun to invest heavily in coal-red electricity generation due to the growing energy demands required to catalyse socio-economic growth and infrastructural development (Baruya 2017; Kutani and Anbumozhi 2015; Zhao and Alexandroff 2019). Over the years, such investments have ensured a steady supply of low-cost and consistent energy, which have stimulated scal growth, infrastructural development, and poverty alleviation (IEA-CCC 2020; IEA 2018).
In the same vein, the discovery of new coal deposits in Nigeria presents numerous opportunities not only for the power and energy sectors but for socioeconomic growth, infrastructural and industrial development (Gbadebo and  Therefore, this study seeks to comprehensively characterise the physicochemical, calori c, microstructural, mineralogical, and thermal properties of three (3) newly discovered Nigeria coal samples from Nasarawa State in Nigeria. Furthermore, the study also examines the energetic fuel properties of the selected coals as potential feedstocks for pyrolysis and combustion through non-isothermal oxidative and non-oxidative thermogravimetric analysis (TGA). Lastly, the study attempts to categorise the new coals into various ranks (lignite, sub-bituminous, and bituminous) based on ASTM Standards along with suggestions for potential applications. It is envisaged that the study ndings will avail engineers and policymakers with the comprehensive data required to effectively design, develop, and implement strategic plans for the future power plants in Nigeria.

Raw Materials
The coal samples were obtained from the middle Benue Trough, as described in the detailed section on geological settings. Samples were collected from coal mines in Akunza, Ome, and Shiga in Obi Local Government Area of Nasarawa State in Nigeria. The coal samples were bagged, tagged, and labelled AKZ, OME, and SHG for Akunza, Ome, and Shiga, respectively, for ease of identi cation. Large chunks of the samples were broken down using a handheld hammer and then pulverised in a dry miller (Panasonic Mixer Grinder MX400C, Malaysia). Subsequently, the pulverised coal samples were sifted using an analytical sieve (W.S. Tyler, USA) to obtain homogeneous sized particles below 250 µm prior to physicochemical, microstructure, mineralogical, and thermal analyses.

Geological Settings
The Benue Trough is an Inland basin that originated from the early Cretaceous age, forming as a split from the Central West African basement during the separation of African and South American continents known as the breakup of Gondwanaland. This break up was followed by the separation of these continents, opening up of the South Atlantic, and growth of the Mid Atlantic Ridge (Benkhelil 1989;Olade 1975). It forms a regional structure 150 km wide, which is exposed from the northern frame of the Niger Delta running North-East for about 1000 km and terminating underneath Lake Chad. The trough contains 6 km thick Cretaceous-Tertiary sediments, including sections pre-dating the middle Santonian, which have been compressed, deformed, folded, faulted, and uplifted in several places, producing more than 100 anticlines and synclines (Benkhelil 1989). Recent evidence from petrographic studies and signi cant element abundance suggest a passive margin tectonic environment for the Benue Trough  (Fig. 1). In both basins, the Albian Bima Sandstone lays unconformably on the basement (Fig. 2) and is conformably overlain by the Cenomanian transitional/coastal Yolde Formation, which represents the beginning of marine incursion into the upper Benue Trough. In the middle Benue Trough, around La a-Obi, six upper Cretaceous lithogenic formations make up the stratigraphic successions (Fig. 2). The succession is made up of the Albian Arufu, Uomba, and Gboko Formations generally termed the Asu River Group (Offodile 1976). These formations are overlain by the Cenomanian Keana, Awe, and the Cenomanian-Turonian Ezeaku Formations. The late Turonian early Santonian coal-bearing Awgu Formation lies conformably on the Ezeaku Formation. The post-folding Campanian-Maastrichtian La a Formation ended the sedimentation in the middle Benue Trough, after which widespread volcanic activity took over in the Tertiary. The late Turonian /early Santonian coal-bearing Awgu Formation are exposed at La a-Obi.
In the lower Benue Trough lies the oldest geological formation overlying the basement is the Asu river group, which is Albian in age. It is marine-based and consists of dark shales, siltstones and ne-grained sandstones passing upwards into shales and limestones (Offodile 1980). This is overlain by the Cross river group, which consists of Odukpani, Agala, Nkalagu and Agbani formations. The only known marine Cenomanian in the coastal basin is found in the Odukpani formation, and it consists of a series of limestone and calcareous sandstones. The Cross River group deposition is followed by the major Santonian folding and erosion episodes. The coal-bearing Mamu Formation is exposed at Okoba, Enugu, Imiegba, Ezimo, Ogboyoga, Orukpa, Udi, on the Enugu -Onitsha Expressway and Agwu -Enugu Escarpment (Ogala 2018).

Physicochemical Fuel Properties
The physicochemical fuel properties of the AKZ, OME, and SHG coal samples were determined by ultimate, proximate, and calori c analyses. Ultimate analysis was performed using the elemental analyser (vario MACRO CUBE, Germany) based on the ASTM standard D5373 for determination of carbon

Microstructural and Mineralogical Analyses
The microstructure and mineral composition of the coal samples were examined by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) spectroscopy. For each test, the powdered coal samples were spray-coated on the carbon epoxy tapes placed on the SEM sample grain mounts. Next, the samples were sputter-coated with a thin layer of gold (Quorum Q150R S, UK) to eliminate errors due to the charging effect, electron beam damage, and to enhance the clarity of the SEM micrographs. The charged samples were then transferred to the sample chamber of the SEM (JEOL JSM IT-300, Germany) for analysis at 20 kV and 5 mm, operating voltage and working distance, respectively. Subsequently, the samples were scanned based on the mapping technique to examine the surface microstructure at a magni cation of × 1000. Lastly, the mineral composition of each sample in weight per cent (wt.%) was computationally elucidated by point ID analysis (AZTEC EDX software, Oxford Instruments, UK) based on charge balance.

Thermal Analyses
The thermal properties of the coals were examined by thermogravimetric (TG) analysis. For each TG test, about 12-15 mg of each sample was placed in an alumina crucible and heated at 20 °C/min from room temperature (RT) to 900 °C, based on the non-isothermal heating program of the TG thermal analyser (Shimadzu TG-50, Japan). For the non-oxidative characteristics tests, the TGA furnace was ushed with ultrapure nitrogen (N 2 , 99.99%) gas at the ow rate of 100 mL/min from ramp heating to the cooling stage of the process to maintain an inert environment for pyrolysis. In contrast, during the oxidative TGA, the furnace was ushed with air at the ow rate of 100 mL/min from ramp heating to cooling to ensure an oxidative atmosphere for combustion. On completion, the raw TG data were converted in mass loss (%) and derivative mass loss (%/min) before plotting against temperature (°C) in Microsoft Excel (version 2013) to determine the thermogravimetric (TG) and derivative (DTG) plots. Consequently, the temperature pro le characteristics (TPC) of each sample were deduced according to the tangent method for thermally decomposing materials in TGA (Cai et al. 2017). In this study, the TPCs were deduced based on the data analysis using the Shimadzu software (Workstation TA-60WS, Japan). The TPCs deduced were; the ignition (T i ) temperature, midpoint (T m ) temperature, peak decomposition (T d ) temperature, and offset (T o ) temperature, mass loss (M L , %) and residual mass (R M , %). Table 1, presents the physicochemical properties of the AKZ, OME, and SHG coal samples. The elemental composition of carbonaceous materials such as coal is an indicator of its potential energy recovery, rank classi cation, and or evolved gas emissions during thermal conversion. As observed in Table 1  44.80-58.38 wt%. The highest moisture content was observed in OME coal, whereas the lowest was in AKZ coal. The moisture content of coal is an important parameter that affects its ignitability and potential utilisation (Speight 2012). As such, high moisture is unsuitable for the processing and utilisation of coal. In this study, the moisture content of all the coals are below 10%, which is within the acceptable limits for electric power generation or conversion into value-added products (Akinyemi et al.

Physicochemical properties
2020a; Chukwu et al. 2016). In contrast, the volatile matter (VM) is an important variable for determining not only the coal rank but also its suitability for potential energy recovery from thermal processes such as combustion and pyrolysis (carbonisation) (Nyakuma 2016;Speight 2012). In this study, the highest VM was observed for SHG coal, whereas the lowest was in AKZ. The ndings indicate that SHG could be a more suitable feedstock for gasi cation compared to AKZ, which is more suited for pyrolysis into coke.
The ndings also showed that AKZ contains the highest xed carbon (FC) content, which is typically inversely proportional to the VM content. The FC of coal is a measure of the approximate coke yield after devolatilization during carbonisation or slow pyrolysis. As such, it indicates that AKZ may be most suitable for pyrolysis, as earlier surmised, due to its low VM and high FC. Furthermore, the highest AC was observed in OME coal, whereas the lowest was observed in AKZ. Typically, ash represents the bulk mineral matter, inorganic or non-combustible residue arising from the coal combustion, which has potential impacts on the environment (Akinyemi et al. 2020b). According to various studies, the chemical composition of coal ash is crucial to coal conversion due to its in uence on slagging, agglomeration or viscosity of bed materials (Cebeci et al. 2002;Özer et al. 2017). Based on the foregoing, it can reasonably be surmised that OME coal could potentially pose more ash related problems compared to SHG and AKZ during combustion.
The higher heating value (HHV) of the coals ranged from 18.65 MJ/kg to 26.59 MJ/kg, with the SHG sample reporting the highest value while the AKZ reported the lowest value. The HHV is a measure of the heat content or energy value of any coal sample (Speight 2012). It is also employed to predict the rank, classi cation, and or assess the suitability of any coal for various applications (ASTM D388-12 2012

Microstructure and Mineralogical Properties
The SEM micrographs and EDX spectra for the coal samples are shown in Figs. 3-5 (a & b). The results present insights into the surface morphology, microstructure, and chemistry of the constituent elements in the coal samples. For all the samples, the SEM micrographs displayed particles with rough textures and surfaces characterised by a distinct glassy sheen, which is typically ascribed to the presence of metallic elements, minerals, or aluminosilicates such as quartz and kaolinite (Karayigit et al. 2001). In addition, the scanned particles were composed of closely packed strati ed layers of materials with contoured outlines owing to deposition of organic material during the coali cation process. Lastly, the particles were found to be devoid of surface pores or crevices, which indicates a dense, compact and sintered microstructure.
The mineralogical properties of AKZ, OME, and SHG were examined by energy-dispersive X-ray (EDX) spectroscopy, as shown in Table 2 that Sulphur and Potassium were undetected in OME and SHG, respectively. Typically, the occurrence of metals is related to the clay, salt, or the porphyrin constituents in the coal structure, and they serve as a measure of the level of coali cation (Speight 2012). For all cases, the major elements detected as de ned by composition > 2.50 wt. %, were in the order C > O > Si > Al. The highest composition of C was detected in SHG, whereas the lowest was observed in OME. However, the highest and lowest compositions of O were observed in AKZ and SHG, respectively. The higher C but lower O of SHG compared to the other samples account for its high calori c value (26.59 MJ/kg) reported in Table 1. Hence, the results of the mineralogical study are consistent and agree with the physicochemical analyses. The highest composition of Si was observed in OME, whereas the lowest was observed in SHG. Typically, Si exists in coal in the form of silicon dioxide (SiO 2 ) otherwise termed quartz (Speight 2012), which accounts for 40-90% of the major inorganic components of ash formed in coal and other combustible matter (Wong et al. 2020). Quartz is the primary constituent of various granite, quartz, porphyry, and rhyolite rocks and tends to occur due to proximity to coal beds during the process of silicate weathering or coali cation (Akinyemi et al. 2020b; Speight 2012). Hence, the high Si indicates the presence of SiO 2 in OME, which is in good agreement with the high ash content of OME as earlier reported in Table 1.
Similarly, the highest composition of Al was observed in OME, whereas SHG contains the lowest composition. Typically, Si and Al exist as clay minerals or aluminosilicates, which account for the highest inorganic constituents of coal (Gluskoter 1975 (Liu and Peng 2015). In addition, the clay found in coals is a signi cant contributor to ash formation, loss of calori c value, and increased cost of ash handling/disposal during the combustion of coal in power plants (Spears 2000). Lastly, the presence of clay minerals along with other metal elements such as Ti and Fe (Sengupta et al. 2008) may account for the distinct lustre observed in the coals, as reported earlier in our previous study (Nyakuma et al. 2019b). In general, the minor elements detected were in the order Fe > K > Ti > Cu > Ca > Mg > S particularly for AKZ. For OME no sulphur (S) was detected and the composition of Ti > K, whereas for SHG no K was detected and the composition of S > Ca. The highest composition of Fe, Ti, K, Ca, and Mg was detected in OME, which indicates high mineral compositions of pyrite (FeS 2 ), anastase or ilmenite (Ti), illite (K), calcite (CaCO 3 ), and oxides of Mg.

Thermal Degradation Properties
The thermal properties of AKZ, OME, and SHG were examined under oxidative and non-oxidative conditions based on non-isothermal heating to examine the burning (combustion, CMB) and devolatilization (pyrolysis, PYR) pro les of the coal samples, as depicted in Figs. 6 and 7.
The burning and devolatilization pro les of the coals depicted in the TG plots showed the typical downward "Z" curves, which slope from left to right for most thermally degrading carbonaceous materials. The ndings indicate that the non-isothermal increase in temperatures from 30 °C to 900 °C resulted in signi cant thermal degradation during TGA. As observed in Fig. 6, the burning pro les resulted in steeper plots particularly between 300 °C and 500 °C compared to the devolatilization pro les (Fig. 7).
The steeper TG plots (Fig. 6) observed for the burning pro les indicate more signi cant thermal degradation, loss of mass, and mass-loss rates in the coals compared to during the devolatilization process. This is ascribed to the exothermic nature of the oxidative (combustion) process, which ensures the higher heat or thermal energy supply to the coal particles during the TG degradation process.
The thermal degradation observed during TGA could also be ascribed to the degradation of the organic fractions or maceral components of coals. The term macerals describe the microscopic, and rock-rich constituents of coal comprising the vitrinite, inertinite, and liptinite groups. Typically, the compositions range from 50-90% for vitrinites, 5-10% for liptinites, and 50-70% for the inertinites depending on the rank, classi cation, and source of the coal. Furthermore, the macerals are physico-chemically and structurally comprised of polymers, lignin, cellulose, resins, spores, and cuticles derived from plants, algae, and fungi residues (Speight 2012;Sun et al. 2003;Xie et al. 2013). Hence, the loss of mass during TGA could be ascribed to the thermal degradation of plant cell wall matter (or organic fractions) present in the coal samples. Košina and Heppner (1984); Landais et al. (1989) demonstrated that the degree of the thermal degradation, physicochemical behaviour, and potential conversion products greatly depends on the maceral composition, rank, and atomic ratios of coals. Hence, the effect of the oxidising and nonoxidising environments on the thermal degradation of AKZ, OME, and SHG was examined by temperature pro le characterization. Table 3 presents the temperature pro le characteristics (TPCs) of the coals under oxidative (combustion) and non-oxidative (pyrolysis) conditions during TGA. As observed, the oxidative conditions resulted in a high loss of mass ranging from 69.61% for AKZ to 87.57% as observed for SHG. Due to the oxidative nature of the process, it can be reasonably inferred that the mass loss during the process results in ue gas mixture along with coke and ash, which are collectively termed the residual mass. In this study, the residual masses for the oxidative process ranged from 12.44-30.40% as observed for SHG and AKZ, respectively. Compared to the ash contents of the coals in Table 1, it can be reasonably surmised that the residual mass comprises largely ash (9.45 wt.% to 11.59 wt.%) along with the coke or unreacted coal particles arising from incomplete combustion during TGA. Hence, higher temperatures (above 900 °C), longer residence and isothermal conditions are required for complete combustion of the coals.
For the non-oxidative conditions, the mass loss ranged from 30.51% for AKZ to 43.05% as observed for SHG, which resulted in the residual mass ranging from 56.95% for SHG to 69.49% for AKZ. Based on the nature of the process, the predicted products of the mass loss could be pyrolysis gas (fuel gases), oil, and tar, whereas the solid products could be largely coke, char and ash. This view is corroborated by Sun et al. The ndings indicated that pyrolysis of coals is largely dependent on the reactivity of individual macerals particularly inertinite compared to vitrinite. Furthermore, the study showed that the distribution of pyrolysis products is comprised of tar, fuels gas, and char. These ndings are corroborated by Zou et al. (2017) whose study showed that coal pyrolysis results in a fuel gas mixture comprising; hydrogen (H 2 ), carbon dioxide (CO 2 ), carbon monoxide (CO), methane (CH 4 ) and water vapour (H 2 O) and ethylene (C 2 H 2 ) based on the TG-MS and gas evolution. Overall, the mass loss for the oxidative process in this study was higher than the non-oxidative process, whereas the residual masses were higher during the non-oxidative compared to the oxidative processes. The plausible explanation can be found in the higher thermal energy and exothermic nature of the oxidative process, which provides the heat required to break the bonds of the macerals in the coal structure. This assertion is veri ed by the higher mass-loss rates observed during the oxidative thermal degradation (17.70%/min to 19.91%/min) compared to the non-oxidative process (2.26%/min to 5.3%/min) along with other TPC values shown in Table 3.
As observed in Table 3 . For all cases, the TPC values T ons , T mid and T end were higher for the non-oxidative degradation of the coals compared to the oxidative process. As earlier surmised, this is due to the exothermic nature of the oxidative process, which provides higher heating energy and hence higher massloss rates required to thermally degrade the coal components compared to the non-oxidative process during TGA. Furthermore, the oxidative reaction conditions provide suitable conditions for the secondary cracking or thermal degradation of condensable products and char/coke produced during the TGA process.
The degradation pathway for the oxidative and non-oxidative thermal degradation of the coals was examined by derivative thermogravimetry (DTG) plots, as shown in Figs. 8 and 9.
The DTG plots in Figs. 8 and 9 each reveal two sets of symmetric and asymmetric peaks. The rst sets of smaller peaks occurred from 30 °C to 200 °C for the oxidative and non-oxidative processes, whereas the second larger set of peaks were from 200 °C to 500 °C for the oxidative and 200 °C to 600 °C for the nonoxidative thermal degradation. The non-oxidative process occurred over a wider temperature range compared to the oxidative process. This is veri ed by the temperature difference of the T ons and T end for the non-oxidative thermal degradation, which was; 230.97 °C, 170.16 °C, and 151.90 °C for AKZ, OME, and SHG, respectively, compared to 87.02 °C, 79.19 °C, and 84.46 °C for the oxidative process. The peaks for the oxidative process were found to be asymmetric with shoulder protuberances on the left-hand side of the large peak between 300 °C and 350 °C for all samples and between 400 °C and 450 °C for the OME and SHG coal samples. In contrast, the non-oxidative process resulted in symmetric peaks devoid of shoulder peaks between 200 °C and 600 °C. Furthermore, the observed peaks for the non-oxidative process exhibited lower derivative mass-loss rates (Table 4) and signi cantly smaller peaks from 200 °C to 600 °C compared to the oxidative process. This observation indicates the devolatilization process, which governs thermal degradation and softening is largely endothermic, as similarly reported in the literature (Agroskin et al. 1972;Hanrot et al. 1994).
Based on the thermal degradation ranges, peak sizes and symmetry, it can be reasonably inferred that the oxidative and non-oxidative thermal degradation processes occur in three (3) stages. The rst stage could be ascribed to drying or loss of coal surface moisture along with low molecular weight volatile components below 200 °C (Xie et al. 2013). Zou et al. (2017) reported that the loss of mass during this stage of coal degradation is also ascribed to the evolution of moisture, free radical groups, and hydrogen (H 2 ). Accordingly, the second stage observed between 200 °C and 500 °C and from 200 °C to 600 °C for the oxidative and non-oxidative processes, respectively, could be attributed to the bond cleavage or cracking of tar along with the evaporation and transport of evolved gases during the thermal degradation of coal macromolecules (Zou et al. 2017). Likewise, this stage could also be due to the thermal degradation of coal components such as macerals, as earlier surmised.
Hence, the mass loss during the TGA of the coals in this study could be largely due to vitrinite, which is the most abundant maceral fraction compared to inertinite and liptinite in decreasing order. In addition, the high temperature (typically 400-800 °C) degradation of coal is considered an exothermic process which is mainly due to vitrinite degradation alongside coke graphitization ( The temperature pro les characteristics (TPC) for the DTG plots were deduced to examine the reactivity, mechanism and mass-loss rates for the drying and devolatilization processes under oxidative and nonoxidative conditions, as presented in Table 4.  Table 4 DTG plot -Temperature Pro les Characteristics For all cases, the peak drying temperatures were observed from 60.38 °C (SHG) to 77.27 °C (AKZ) for the non-oxidative process compared to the oxidative process, which was observed from 65.87 °C (AKZ) to 68.27 °C (SHG). However, mass loss rates for both oxidative and non-oxidative conditions were similar indicating the reactivity of the coals was similar during the drying stage. However, the peak devolatilization temperatures were observed from 470.29 °C (OME) to 475.95 °C (AKZ) for the nonoxidative process compared to the oxidative process, which was observed from 385.44 °C (AKZ) to 405.26 °C (SHG). However, the mass-loss rates for both oxidative and non-oxidative conditions were markedly different indicating the mechanism and thermal reactivity of the coals. The ndings indicate that thermal degradation behaviour of coals is also signi cantly dependent on the nature of the oxidising environment as similarly observed for the composition of the organic materials or maceral components in the literature.

Conclusions
The study comprehensively examined the physicochemical, microstructural, mineralogical, and thermal fuel properties of three (3) newly discovered coal samples from Nigeria for potential energy recovery through combustion and pyrolysis. The ndings showed that the new coal samples contain high compositions of the combustible elements along with low polluting elements such as sulphur and nitrogen as required for enhanced energy recovery. The higher heating values (HHV) of the coals were in the range from 18.65 MJ/kg (AKZ) to 26.59 MJ/kg (SHG) and comparable with other similarly ranked lignite, subbituminous and bituminous coals. Microstructure analysis revealed the coal particles with rough textures and surfaces characterised by a distinct glassy sheen typically ascribed to the presence of metallic elements, minerals, and aluminosilicates such as quartz and kaolinite. Lastly, the thermal properties performed under non-isothermal oxidative and non-oxidative thermogravimetric analysis (TGA) indicated the samples are potential feedstock for coal pyrolysis and combustion. Overall, the ndings of this study identi ed and highlighted the prospects of coal-based energy along with prospects for coke, chemicals, and fuels production.

Declarations
Availability of data and materials All the data in the manuscript are presented in the form tables and gures.  DTG Plots for Devolatilization of AKZ, OME, and SHG