PEER-REVIEW ARTICLE PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3144 Production of Bio-oil via Catalytic Pyrolysis of Medlar Seeds Fatıma Topak, and Mehmet Kuddusi Akalin * The pyrolysis of medlar seeds was performed at 350, 450, 550, and 650 C with and without K2CO3, MgO, and expanded perlite (10 wt%). The maximum dichloromethane extract yield (6.70 wt%) was obtained at 450 °C in the pyrolysis experiments without catalyst, while the maximum bio- oil yield (50.3 wt%) was obtained at 650 °C in the presence of perlite. The dichloromethane extract and bio-oil yields decreased noticeably with the use of MgO and K2CO3. The bio-oils obtained from the non-catalytic runs mainly consisted of phenolic compounds. The use of catalysts had a noticeable effect on the composition and higher heating values of the bio- oils. The use of K2CO3 increased the relative content of 2-methoxyphenol at all tested temperatures and the relative content of 2,6-dimethoxyphenol and 2,6-dimethoxy-4-methylphenol increased with the use of expanded perlite at above 550 °C, while the use of MgO led to an increase in the relative content of 2,6-dimethoxy-4-methylphenol at above 550 °C. The bio-oil with the maximum higher heating value (30.4 MJ/kg) was obtained at 450 °C with the use of perlite. This study showed that medlar seeds are a good alternative source of waste biomass in the production of bio-oil that can be used as a biofuel. DOI: 10.15376/biores.18.2.3144-3159 Keywords: Pyrolysis; Medlar seeds; Bio-oil Contact information: Department of Environmental Engineering, Karabuk University, 78050, Karabuk, Turkey; *Corresponding author: mehmetakalin@karabuk.edu.tr INTRODUCTION Biomass is one of the promising renewable resources to obtain products that can replace fossil fuels products. In addition to being renewable, biomass is an abundant and environmentally friendly resource because of its carbon neutrality when compared to fossil fuels. The use of fossil fuels causes a significant increase in emission of carbon dioxide and other pollutants such as NOx and SOx. Further, non-renewability and depletion of fossil resources cause fluctuations in fossil fuel prices, posing major economic problems in the world (Hu and Golizadeh 2019). Because of its abundancy, renewability, and the diversity of products that can be used in various applications, biomass has a great potential to be an alternative to fossil resources (Guedes et al. 2018). Thermochemical conversion is one of the important and efficient ways to utilize biomass, in which pyrolysis occupies an important place among thermochemical conversion methods. Pyrolysis is a widely used thermal process to transform biomass under an inert atmosphere into value added solid, liquid, and gas products (Tan et al. 2022; Vuppaladadiyam et al. 2022). Yields of products (liquid, solid, and gas) vary depending on the process parameters such as pyrolysis temperature, residence time, heating rate, biomass type, etc., in pyrolysis. Feedstock composition, which is related to the biomass PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3145 type, is an important factor that affects yields and characteristics of products as well as determining the experimental conditions for desired products and their subsequent applications (Chen et al. 2020; Al-Rumaihi et al. 2022). Therefore, a wide variety of biomass including agricultural residues (e.g., peanut shell, hazelnut shell, or wheat straw) and forestry residues (i.e., wood residues), which are considered as waste, have been used in the pyrolysis process (Al-Rumaihi et al. 2022). The most abundant form of biomass is lignocellulosic biomass, primarily consisting of hemicellulose, cellulose, and lignin, which can be converted into biofuels and value-added products via pyrolysis (Zhou et al. 2022). The hemicellulose and cellulose content of biomass mainly contributes to the formation of bio-oil, which is also known as pyrolysis oil, pyrolysis liquid, tar, and bio-crude. The pyrolysis oil is mixture of various types of compounds, and it has a high oxygen content which leads to a low heating value in comparison to coal. The pyrolysis oil can be used as a fuel in furnaces, boilers, diesel engines, and turbines with minor modifications to existing equipment, or it can be used in the production of chemicals and phenolic resins; furthermore, it can be upgraded to enhance its fuel properties by using various catalysts (Kim 2015; Krutof and Hawboldt 2016; Pawar et al. 2020). The char (also known as biochar, solid product, or charcoal) formation is mainly promoted by lignin decomposition. The char mainly consists of carbon, and it can be used as an adsorbent, fertilizer, or catalyst. The bio-oil is a dark brown liquid, and it contains a considerable amount of water depending on the moisture content of the biomass. Despite its undesirable properties, such as high oxygen content, low pH value, high corrosiveness, and high viscosity, bio-oil can be considered as a potential fuel for turbines, diesel engines, boilers, furnaces, and combustors in short term. It also has potential to be a chemical feedstock for resin manufacturing, fertilizer, pharmaceutical, and the food industry (Kan et al. 2016; Makepa et al. 2022; Liu et al. 2023). The medlar fruit (Mespilus germanica L.) is a member of the Rosaceae family. It is shaped like a pear and apple with brown (sometimes reddish tinged) color in various sizes ranging from 1.5 to 3 cm. The weight of the fruit is around 10 to 80 g, and it generally contains five large seeds with diameters around 1 to 1.25 cm. The plant can grow wild in different regions of the Middle East, and it is also cultivated for jam, marmalade, and jellies production in the food industry (Solgi et al. 2017). It is a widely consumed fruit in Turkey, and it is also used in many local recipes such as in jams and jellies. In addition, it can be used for medicinal purposes. It was reported that medlar has the ability to act as a diuretic, and blatted pulp or syrup of the medlar fruit can be used for treatment of kidney and bladder stones (Ayaz et al. 2008; Gruz et al. 2011). Therefore, high amounts of seeds are produced as waste every year, serving various usage areas. Activated carbon was produced from medlar seeds via chemical activation with KOH (mass of seed/mass of KOH, 1:3) at 450 to 750 °C for chromium removal (Solgi et al. 2017). Experimental analysis and modeling of chromium removal were investigated using artificial neural network and support vector regression. It was reported that maximum adsorption capacity was achieved with the use of activated carbon produced at 750 °C, and it could be considered as a good alternative for removal of Cr(VI) from wastewaters. Pyrolysis of different biomass (including plum seed, pine seed, and date seed) waste was performed at 400 to 600 °C for liquid oil production (Islam et al. 2013). The effect of temperature, particle size, and time on the yields and composition of products from biomass wastes was investigated. PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3146 The optimum operating temperatures were 500, 500, and 520 °C with a running time of 120 min for pine seed (liquid product yield 40%), date seed (liquid product yield 50%), and plum seed (liquid product yield 39%), respectively. The higher heating values of all liquid products were higher than the corresponding raw biomass waste. The higher heating values of bio-oils obtained from the pyrolysis of pine seed, date seed, and plum seed were reported as 20.00, 28.64, and 22.39 MJ/kg, respectively. Perlite is a naturally occurring alumino-silicate amorphous volcanic rock. Raw perlite contains combined water (2 to 6 wt%), whereas expanded perlite is produced from raw perlite by rapid heating at high temperatures (900 to 1200 °C). In this process, water that is held in the structure of perlite vaporizes rapidly. As a consequence, perlite expands up to 5 to 20 times of its original volume, resulting in hollow and porous particles with a low bulk density. Expanded perlite is a lightweight and porous material that has insulating properties. Thus, expanded perlite is a commonly used material in construction, petrochemical, and chemical industries (Rashad 2016; Różycka and Pichór 2016; Papa et al. 2018). Turkey, Greece, USA, China, Japan, Hungary, and Italy are the countries that have a large share in world’s total perlite production (Rashad 2016; Różycka and Pichór 2016). Perlite was also used in the pyrolysis process in the literature. Balat and Balat (2010) used perlite (2.5 to 10 wt%) in the pyrolysis of black locust wood. It was reported that liquid product yield increased with increasing the perlite ratio from 2.5 to 10 wt% between 5 to 15 min reaction times (Balat and Balat 2010). Pyrolysis of car tire waste was carried out using different ratios (0.05 to 0.25) of expanded perlite as a catalyst at 425 C with 10 C/min heating rate (Kar 2011). It was reported that maximum pyrolytic oil yield (65.11 wt%) was obtained with the use of perlite at a ratio of 0.10. The yield increase achieved by using expanded perlite was 8.48 wt% when compared to the non-catalytic pyrolysis experiments. A further increase in perlite ratio up to 0.25 resulted in a decrease in pyrolytic oil yield. In another study, using perlite (9 wt%) in the catalytic pyrolysis of hazelnut shell at 500 °C increased the liquid yield from 41% to 46% while using higher amount of perlite (18 wt%) resulted in a slight decrease in the liquid yield (40%) (Aydinli and Caglar 2012). It was reported that this may be due to the high adsorption capacity of perlite. Catalytic pyrolysis of Styrax officinalis L. seeds were carried out at 450 °C with a heating rate of 25 °C/min in the presence of natural zeolite and expanded perlite (Kar and Sen 2012). The authors reported that the bio-oil yields were lower in the catalytic pyrolysis experiments than the bio-oil yields that were obtained from the non-catalytic experiments in their previous study. They also reported that increasing the amount of perlite from 10 wt% to 30 wt% led to an increase in bio-oil yield from 35.23% to 37.49%. To the best of the authors’ knowledge, there has been no study regarding the bio- oil production from the medlar seeds via pyrolysis in the literature so far. The main objective of the study is to produce bio-oil from medlar seeds and investigate the effect of pyrolysis temperature on the yields of bio-oil and biochar. The effect of the temperature on composition of the bio-oils was also investigated. In the second part of the study, the effect of the temperature on the yields and composition of bio-oils in the presence of natural expanded perlite, MgO, and K2CO3 was investigated. PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3147 EXPERIMENTAL Feedstock The medlar fruits were purchased from a local market in Karabük. The seeds were separated from the fruits and washed several times. The seeds were air-dried for 2 days at room temperature, ground, and sieved to achieve a homogeneous mixture with a particle size of less than or equal to 1 mm. Then the ground seeds were air-dried for 2 days at room temperature again. The proximate and ultimate analysis of the medlar seeds were shown in Table 1. Table 1. Proximate and Ultimate Analysis of the Medlar Seeds Proximate Analysis (wt%) Ultimate Analysis (%) Moisture 6.34 C 43.210 Volatile matter 81.78 H 6.634 Fixed carbon 10.90 N 0.514 Ash 0.98 Oa 49.64 HHVb (MJ/kg) 15.22 a by difference b by Dulong formula: HHV = 0.338C + 1.428(H - O/8) + 0.095S Pyrolysis Experiments The pyrolysis experiments were performed at 350, 450, 550, and 650 °C in a 250- mL stainless steel fixed bed reactor under nitrogen atmosphere. In a typical pyrolysis experiment, 10 g of medlar seeds (dry basis) were placed in the reactor. Before heating the reactor to the set temperature, the nitrogen gas passed through the system for 30 min, and nitrogen gas continued to pass through the system throughout the entire pyrolysis process. Then, the reactor was heated (10 °C/min) to the set temperature. After the reactor reached the set temperature, the system was held at that temperature for 1 h. There have been some studies regarding the pyrolysis of biomass at long holding time (30 min<) (Abnisa et al. 2011; Güngör et al. 2012; Fan et al. 2014; Ling et al. 2015); thus the justification for selecting a pyrolysis holding time of 1 h was to ensure entire pyrolysis vapors flowed to the collection flasks. The pyrolysis vapors were passed through the collection flasks by nitrogen gas flow, and they were collected in the collection flasks that were cooled with an ice-water mixture. Liquid product, which includes water, was collected in the collection flasks and it was labeled as “bio-oil”. The bio-oil was subjected to extraction with dichloromethane (20 mL), and after evaporating dichloromethane from the organic phase, the resulting product was labeled as dichloromethane extract. The same procedure was used in the catalytic experiments with the addition of catalyst (10 wt% of the biomass) into the reactor. All experiments were repeated three times. No investigation regarding the yield and composition of the gas product was performed in this study. Analysis Procedure The compounds in the bio-oils were determined by gas chromatography-mass spectrometry analysis (GC-MS). The analysis was performed using an Agilent GC-MSD- 7890B+5977MSD with HP5-MS column (Agilent Technologies, Santa Clara, CA, USA). The temperature program for the GC oven was as follows: started at 40 °C and held at that temperature for 1 min, raised to 250 °C with 5 °C/min, and held for 15 min; finally raised PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3148 to 270 °C with a heating rate of 5 °C/min and held for 20 min. The elemental composition of the bio-oils and the raw material was determined by using a LECO CHNS 932 (LECO Corporation, St. Joseph, MI, USA). RESULTS AND DISCUSSION Effect of the Pyrolysis Temperature on Product Yields Bio-oil, dichloromethane extract, and biochar yields that were obtained from the pyrolysis of medlar seeds at different temperatures (350 °C, 450 °C, 550 °C, and 650 °C) at a heating rate of 10 °C/min are shown in Fig. 1. The pyrolysis temperature had a noticeable effect on the product yields. The highest bio-oil yield (49.9 wt%) was obtained at 550 °C. Increasing the temperature from 350 to 550 °C led to an increase in the bio-oil yield from 44.5 wt% to 49.9 wt% and led to a decrease in biochar yield from 36.6 wt% to 30.1 wt%. At the highest temperature, the bio-oil yield decreased to 47.2 wt% while the biochar yield remained almost the same. This may be due to the formation of secondary cracking of pyrolysis vapors (Yorgun and Yildiz 2015). A similar trend was observed in the case of dichloromethane extract yields. However, the highest dichloromethane extract yield was 6.70 wt% at 450 °C. A further increase in the pyrolysis temperature resulted in a decrease in the dichloromethane extract yield. Fig. 1. Product yields obtained from the pyrolysis of medlar seeds at different temperatures Effect of the Catalysts on the Product Yields at Different Temperatures Figure 2 shows the product distribution from the pyrolysis of medlar seeds at different temperatures in the presence of 10 wt% perlite. The use of perlite noticeably affected the product yields. The bio-oil yield increased in the presence of perlite at all pyrolysis temperatures. However, the rate of increase was less at 550 °C, which was the optimum temperature for the non-catalytic experiments, when compared to other temperatures. The bio-oil yield increased from 44.5 wt% to 46.3 wt% and from 47.2 wt% to 49.0 wt% at 350 and 450 °C, respectively. The highest bio-oil yield (50.3 wt%), which was also higher than the maximum bio-oil yield in the non-catalytic runs, was obtained at the highest temperature. PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3149 Fig. 2. Product yields from the pyrolysis of medlar seeds at different temperatures in the presence of perlite (10 wt%) The dichloromethane extract yield increased, and the biochar yield decreased when increasing the pyrolysis temperature in the catalytic experiments, and the dichloromethane extract yield reached the maximum (6.38 wt%) at the highest pyrolysis temperature. When compared to non-catalytic runs, the use of perlite resulted in a decrease in dichloromethane extract yields at below 550 °C. The use of perlite had no noticeable effect on the dichloromethane extract yield at 550 °C. The only pyrolysis temperature at which the dichloromethane extract yield (6.38 wt%) from the experiment in the presence of perlite was higher than dichloromethane extract yield (5.95 wt%) from the non-catalytic experiment at the same temperature, was 650 °C. The biochar yields in the catalytic runs with perlite were lower than the biochar yields from the non-catalytic runs at 450 °C and at higher temperatures. Product yields obtained from the pyrolysis of medlar seeds in the presence of MgO are shown in Fig. 3. The dichloromethane extract and bio-oil yields obtained from the catalytic runs were lower than that of non-catalytic runs at all pyrolysis temperatures. The highest bio-oil yield (45.3 wt%) and dichloromethane extract yield (5.67 wt%) were obtained at 450 and 550 °C, respectively. Fig. 3. Product yields from the pyrolysis of medlar seeds at different temperatures in the presence of MgO (10 wt%) PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3150 The biochar yields were higher than the yields from the non-catalytic experiments at all temperatures except 650 °C. Increasing the temperature from 350 to 650 °C led to a decrease in biochar yields from 38.2 to 28.5 wt%, respectively. Figure 4 shows the bio-oil, biochar, and dichloromethane extract yields obtained from the pyrolysis experiments with the use of K2CO3. The use of K2CO3 noticeably decreased the dichloromethane extract and bio-oil yields when compared to non-catalytic runs. The highest bio-oil yield (43.2 wt%) was obtained at 550 °C while the highest dichloromethane extract yield (3.97 wt%) was obtained at 450 °C. However, the yields of all products (dichloromethane extract, biochar, and bio-oil) were lower than that of the product type obtained from the non-catalytic runs. The yield of biochar decreased from 33.8 wt% to 26.4 wt% by increasing the pyrolysis temperature from 350 to 650 °C, respectively. Increasing the temperature from 350 to 450 °C led to an increase in the dichloromethane extract yield from 2.59 to 3.97 wt%. However, an increase in temperature from 550 to 650 °C had no noticeable difference on the dichloromethane extract yields. Fig. 4. Product yields from the pyrolysis of medlar seeds at different temperatures in the presence of K2CO3 (10 wt%) Characterization of Bio-oils The identified compounds in the bio-oils obtained from the non-catalytic pyrolysis of medlar seeds are listed in Table 2. Bio-oils from the non-catalytic pyrolysis mainly consisted of phenolic compounds. The pyrolysis temperature had a noticeable effect on the composition of bio-oils. The compound 2,6-dimethoxyphenol was the major component in the bio-oils at all tested temperatures, while it was followed by 2,6-dimethoxy-4- methylphenol at lower temperatures (350 and 450 °C). Increasing the pyrolysis temperature from 450 to 550 °C had a noticeable effect on the relative concentrations of both compounds as the area percentages of compounds decreased from 18.7% to 11.1% and from 12.1% to 7.66% for 2,6-dimethoxyphenol and 2,6-dimethoxy-4-methylphenol, respectively. However, the relative concentrations of 2-methoxyphenol, 4-ethyl-2- methoxyphenol, and 2-methoxy-4-methylphenol increased when increasing the temperature from 350 to 550 °C. The second major compound was 2-methoxy-4- methylphenol in the bio-oil obtained at 550 °C. The pyrolysis of medlar seeds resulted in production of bio-oils with rich phenolic content which can be used as a chemical source and/or production of phenolic resins. PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3151 Table 2. Composition of Bio-oils Obtained from the Non-Catalytic Pyrolysis Experiments Retention Time (min) Quality Compound Area (%) 350 °C 450 °C 550 °C 650 °C 5.447 91 2-furancarboxaldehyde 6.95 7.299 93 2-methyl-2-cyclopenten-1-one 0.74 8.940 94 5-methyl-2-furancarboxaldehyde 3.25 9.543 90 phenol 0.45 2.60 10.837 96 2-hydroxy-3-methyl-2- cyclopenten-1-one 1.79 1.45 2.73 11.696 97 2-methyl-phenol 0.61 1.65 12.328 97 4-methyl-phenol 0.88 1.95 4.03 12.659 97 2-methoxy-phenol 6.41 6.36 6.85 4.85 13.201 95 2,6-dimethyl-phenol 0.49 14.436 97 2,4-dimethyl-phenol 1.54 15.053 93 3,4-dimethyl-phenol 1.31 15.294 90 1,4-dimethoxy-benzene 0.98 15.384 95 benzoic acid 1.27 15.686 97 2-methoxy-4-methyl-phenol 5.69 5.95 8.09 3.43 16.559 93 benzothiazole 2.13 1.79 18.110 94 4-ethyl-2-methoxy-phenol 4.89 5.12 5.29 3.23 19.058 96 2-methoxy-4-vinylphenol 1.81 1.61 1.94 20.082 97 2,6-dimethoxy-phenol 18.23 18.73 11.11 12.65 20.232 97 2-methoxy-4-(2-propenyl)-phenol 1.07 21.362 96 4-hydroxy-3-methoxy- benzaldehyde 0.90 22.536 93 2,6-dimethoxy-4-methylphenol 10.15 12.12 7.66 7.33 22.596 98 2-methoxy-4-(1-propenyl)-phenol 4.56 3.51 2.69 23.590 93 1-(4-hydroxy-3-methoxyphenyl)- ethenone 0.83 24.478 90 1,2,5-trimethoxy-3-methyl- benzene 7.16 8.25 4.44 4.55 24.614 70 methyldopa-M 1.10 24.659 92 4-hydroxy-3-methoxy- homovanillic acid 0.90 1.06 25.412 91 2,6-dimethoxy-4-vinyl-phenol 2.04 1.39 26.285 98 2,6-dimethoxy-4-(2-propenyl)- phenol 1.39 1.53 0.96 0.89 26.436 91 2,6-dimethoxy-4-propyl-phenol 2.50 2.70 1.33 27.384 96 2,6-dimethoxy-4-(2-propenyl)- phenol 0.79 0.61 0.34 27.595 97 4-hydroxy-3,5-dimethoxy- benzaldehyde 0.64 1.42 28.498 94 2,6-dimethoxy-4-(2-propenyl)- phenol 2.64 2.27 29.191 97 1-(4-hydroxy-3,5- dimethoxyphenyl)-ethanone 1.01 1.32 1.67 32.473 98 Nonadecane 5.70 34.160 98 Eicosane 8.14 33.753 90 5-(6-Methylbenzothiazol-2- yl)furan-2-carbaldehyde 3.11 PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3152 Table 3 shows the relative abundance of compounds identified in the bio-oils obtained from pyrolysis of medlar seeds in the presence of perlite. The bio-oils mainly consisted of phenolic compounds, and 2,6-dimethoxyphenol and 2,6-dimethoxy-4- methylphenol were the major compounds in the bio-oils. However, their relative concentrations increased while increasing the temperature from 550 to 650 °C in contrast to non-catalytic runs. Table 3. Composition of Bio-oils Obtained from the Pyrolysis Experiments in the Presence of Perlite Retention Time (min) Quality Compound Area (%) 350 °C 450 °C 550 °C 650 °C 5.463 94 2-furancarboxaldehyde 9.19 8.956 94 5-methyl-2-furancarboxaldehyde 2.83 9.573 93 phenol 1.75 10.823 97 2-hydroxy-3-methyl-2- cyclopenten-1-one 1.92 11.711 98 2-methyl-phenol 1.38 12.343 96 3-methyl-phenol 2.02 2.00 1.91 12.659 97 2-methoxy-phenol 6.60 7.03 5.85 7.95 14.481 97 2,4-dimethyl-phenol 0.73 15.068 91 3,4-dimethyl-phenol 0.71 15.686 97 2-methoxy-4-methyl-phenol 4.99 5.86 4.81 7.95 16.559 91 benzothiazole 2.47 0.34 3.15 17.763 90 3-methoxy-1,2-benzenediol 0.95 18.110 93 4-ethyl-2-methoxy-phenol 4.48 5.36 3.84 5.69 19.058 95 2-methoxy-4-vinylphenol 1.97 1.71 1.96 20.067 97 2,6-dimethoxy-phenol 17.55 17.5 14.08 20.15 20.233 95 2-methoxy-4-(2-propenyl)-phenol 0.78 21.558 95 2-methoxy-4-(1-propenyl)-phenol 0.69 22.521 93 2,6-dimethoxy-4-methyl-phenol 10.21 10.43 9.99 11.80 22.596 98 2-methoxy-4-(1-propenyl)-phenol 4.65 4.39 2.55 6.07 24.478 90 1,2,5-trimethoxy-3-methyl- benzene 7.48 7.43 6.19 7.60 24.614 87 methyldopa-m 0.94 25.397 90 2,6-dimethoxy-4-vinyl-phenol 1.77 1.45 2.54 26.285 98 2,6-dimethoxy-4-(2-propenyl)- phenol 1.25 1.21 1.37 1.63 26.436 91 2,6-dimethoxy-4-propyl-phenol 2.40 1.99 27.384 97 2,6-dimethoxy-4-(2-propenyl)- phenol 0.86 0.64 1.29 27.595 97 4-hydroxy-3,5-dimethoxy- benzaldehyde 1.61 28.483 94 2,6-dimethoxy-4-(2-propenyl)- phenol 2.89 2.52 0.75 5.90 29.191 97 1-(4-hydroxy-3,5- dimethoxyphenyl)-ethanone 0.80 1.65 PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3153 The identified compounds obtained from the pyrolysis of medlar seeds in the presence of MgO are shown in Table 4. The use of catalyst noticeably affected the composition of bio-oils. The relative abundance of phenols reduced and the formation of compounds, such as ketones and carboxylic acids, were observed in the bio-oils, unlike the runs without catalyst. However, 2,6-dimethoxyphenol and 2,6-dimethoxy-4-methylphenol still remained as two of the abundant compounds in the bio-oils. Table 4. Composition of Bio-oils Obtained from the Pyrolysis Experiments in the Presence of MgO Retention Time (min) Quality Compound Area (%) 350 °C 450 °C 550 °C 650 °C 7.564 90 2-furancarboxaldehyde 9.60 8.83 6.81 8.482 95 2-furanmethanol 2.26 2.48 1.70 2.27 10.078 94 2-methyl-2-cyclopenten-1-one 0.74 0.75 0.95 13.315 72 phenol 1.66 2.23 1.69 1.23 14.580 94 3-methyl-1,2-cyclopentanedione 1.68 1.46 14.685 93 2-hydroxy-3-methyl-2- cyclopenten-1-one 1.64 1.32 15.619 95 2-methyl-phenol 1.15 1.34 1.33 1.48 16.341 96 4-methyl-phenol 0.76 1.17 0.90 1.00 16.537 95 2-methoxy-phenol 4.67 4.85 4.12 4.38 17.004 92 2-methyl-benzofuran 0.25 17.094 90 2,6-dimethyl-phenol 0.19 17.531 94 3-ethyl-2-hydroxy-2-cyclopenten- 1-one 0.50 0.50 0.39 18.524 95 2,4-dimethyl-phenol 0.86 1.24 0.75 1.13 19.217 90 3,5-dimethyl-phenol 0.80 19.744 97 2-methoxy-4-methyl-phenol 3.66 4.06 3.49 3.85 20.271 90 2-vinyl-2,3-dihydrobenzofuran 0.47 0.42 0.50 21.009 95 3,4-dimethoxytoluene 0.23 21.897 94 3-methoxy-1,2-benzenediol 0.83 22.198 94 4-ethyl-2-methoxy-phenol 3.56 3.74 3.60 3.64 22.514 94 1-methyl-naphthalene 0.24 0.35 23.147 96 2-methoxy-4-vinylphenol 1.79 1.70 1.83 1.49 23.824 90 (trimethyl-[3-(3- phenylcyclopentylidene)-1- propynyl]silane 0.21 23.839 90 5-methyl-2-phenyl-4,6- diisopropylpyrimidine 0.28 24.321 96 2,6-dimethoxy-phenol 8.36 8.74 7.85 8.64 25.496 94 1,2,3-trimethoxy-5-methyl- benzene 0.43 0.40 0.46 25.646 95 2-methoxy-4-(1-propenyl)-phenol 0.75 0.55 1.02 0.72 26.790 95 2-methoxy-4-(1-propenyl)-phenol 1.28 1.71 26.805 90 2,6-dimethoxy-4-methyl-phenol 7.87 8.72 9.44 11.36 27.754 90 1-(4-hydroxy-3-methoxyphenyl)- ethanone 0.36 28.687 90 1,2,5-trimethoxy-3-methyl- ethanone 4.70 5.34 4.59 5.90 28.718 90 homovanillyl alcohol 1.05 28.808 87 methyldopa-m 0.94 1.00 PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3154 29.546 90 2,6-dimethyl-3-(methoxymethyl)- p-benzoquinone 1.63 30.434 98 2,6-dimethoxy-4-(2-propenyl)- phenol 1.20 1.28 1.26 1.43 30.584 91 4-propyl-syringol 1.73 1.90 1.80 2.11 31.533 93 2,6-dimethoxy-4-(2-propenyl)- phenol 0.88 0.89 1.11 1.06 31.819 97 4-hydroxy-3,5-dimethoxy- benzaldehyde 1.14 1.02 1.21 1.03 32.692 94 2,6-dimethoxy-4-(2-propenyl)- phenol 2.78 3.15 3.07 3.48 33.415 96 1-(4-hydroxy-3,5- dimethoxyphenyl)- ethanone 1.06 1.00 1.17 1.13 35.312 87 4-propionyl–syringol 0.78 0.78 37.149 98 hexadecanoic acid methyl ester 0.40 0.38 0.41 0.33 38.007 97 n-hexadecanoic acid 0.98 0.84 0.85 1.17 38.459 92 3,5-dimethoxy-4- hydroxycinnamaldehyde 0.40 0.40 40.341 99 9,12-octadecadienoic acid 0.30 0.30 0.29 0.27 40.461 99 9-octadecenoic acid methyl ester 1.05 1.11 0.96 0.92 40.928 98 octadecanoic acid methyl ester 0.12 0.13 0.10 0.10 41.334 99 9-octadecenoic acid 1.76 1.22 1.26 1.47 41.651 95 octadecanoic acid 0.12 41.681 90 oleic acid 0.09 42.027 95 8,11-octadecadienoic acid methyl ester 0.03 Table 5 shows the composition of bio-oils obtained in the presence of K2CO3. The composition of bio-oils was noticeably affected using catalyst when compared to the composition of bio-oils from the non-catalytic runs. 2,6-dimethoxyphenol and 2- methoxyphenol were the major compounds in the bio-oils. The formation of high molecular weight compounds and decrease in the low molecular weight products was observed with the use of catalyst, which can be related to promotion of coking. The pyrolysis conditions and the interactions between bio-oil components strongly affects the formation of coke. It was reported that temperature and heating rate are the pyrolysis parameters which have a noticeable effect on coke formation and high heating rate lowers the coke yields (Xiong et al. 2019). Table 5. Composition of Bio-oils Obtained from the Pyrolysis Experiments in the Presence of K2CO3 Retention Time (min) Quality Compound Area (%) 350 °C 450 °C 550 °C 650 °C 8.452 94 2-furanmethanol 1.55 1.86 1.34 10.078 93 2-methyl-2-cyclopenten-1-one 0.88 1.19 12.216 92 3-methyl-2-cyclopenten-1-one 1.79 2.02 1.90 2.02 14.565 93 3-methyl-1,2-cyclopentanedione 0.76 14.655 93 2-hydroxy-3-methyl-2- cyclopenten-1-one 0.42 14.775 78 2,3-dimethyl-2-cyclopenten-1-one 1.25 1.28 1.96 1.68 15.453 74 3,5-dimethyl cyclopentenolone 0.66 0.79 15.694 94 2-methyl-phenol 1.51 2.29 1.94 2.58 16.357 96 4-methyl-phenol 0.82 1.32 1.97 PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3155 16.537 94 2-methoxy-phenol 7.28 6.78 10.10 7.61 17.109 95 2,6-dimethyl-phenol 0.50 17.531 95 3-ethyl-2-hydroxy-2-cyclopenten- 1-one 0.58 18.615 96 2,4-dimethyl-phenol 1.82 2.35 2.97 3.41 19.112 94 3,5-dimethyl-phenol 1.42 2.9 19.202 90 2,3-dimethyl-phenol 0.28 2.85 0.89 19.548 81 2,4-dimethyl-phenol 2.19 19.729 97 2-methoxy-4-methylphenol 2.62 2.91 3.58 3.33 19.880 95 3,4-dimethyl-phenol 0.80 20.060 90 2,3,5-trimethyl-phenol 0.32 0.58 20.919 89 2-ethyl-6-methyl-phenol 0.45 20.933 89 2,3,6-trimethyl-phenol 0.84 0.53 0.73 1.19 21.114 93 4-ethyl-3-methyl-phenol 0.28 0.40 0.56 21.235 93 3-ethyl-5-methyl-phenol 0.63 22.018 96 2,3,5-trimethyl-phenol 0.89 22.033 87 2,4,5-trimethyl-phenol 0.51 0.78 0.76 0.91 22.213 93 4-ethyl-2-methoxy-phenol 4.35 4.66 6.31 4.74 22.996 90 2-methyl-naphthalene 0.28 23.147 94 2-methoxy-4-vinylphenol 1.79 1.78 1.43 23.342 90 5-methyl-2-(1-methylethyl)- phenol 0.49 24.231 97 2,6-dimethoxy-phenol 11.47 11.49 9.25 12.78 25.556 90 1,2,5-trimethoxy-3-methyl- benzene 0.35 0.54 0.46 0.47 25.556 81 2,4-dimethyl-3- (methoxycarbonyl)-5-ethylfuran 0.46 25.616 91 2-methoxy-4-(2-propenyl)-phenol 0.53 26.700 94 2,6-dimethoxy-4-methyl-phenol 5.96 7.16 7.90 26.836 90 2-methoxy-4-(1-propenyl)-phenol 1.42 1.18 27.904 90 pentadecane 0.34 28.657 90 1,2,5-trimethoxy-3-methyl- benzene 5.56 5.44 8.11 5.95 29.561 78 1,4-dihydrophenanthrene 1.32 30.464 96 2,6-dimethoxy-4-(2-propenyl)- phenol 1.12 1.05 1.07 1.25 30.615 91 4-propyl-syringol 2.52 3.40 2.53 31.518 90 2,6-dimethoxy-4-(2-propenyl)- phenol 0.56 0.64 31.789 97 4-hydroxy-3,5-dimethoxy- benzaldehyde 0.72 0.78 32.527 91 heptadecane 0.23 0.26 0.26 0.35 32.692 93 2,6-dimethoxy-4-(2-propenyl)- phenol 0.61 1.00 1.66 0.62 33.385 94 1-(4-hydroxy-3,5- dimethoxyphenyl)-ethanone 0.40 0.52 0.43 35.282 74 4-propionyl-syringol 0.32 0.38 37.134 97 hexadecanoic acid methyl ester 0.27 37.149 96 14-methyl-pentadecanoic acid methyl ester 0.28 0.21 37.977 99 n-hexadecanoic acid 0.76 0.89 0.65 40.341 99 9,12-octadecadienoic acid methyl ester 0.18 0.14 0.16 40.461 99 9-octadecenoic acid methyl ester 0.34 0.31 0.31 41.304 99 9-octadecenoic acid 1.10 1.52 0.66 PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3156 Elemental compositions of bio-oils obtained from the experiments with and without catalysts are shown in Table 6. The pyrolysis process led to deoxygenation, as the oxygen content of the bio-oils were noticeably lower than that of the raw material. The higher heating values of the bio-oils were higher than the HHV of raw material, while the bio-oil with maximum HHV (27.4 MJ/kg) was obtained at 450 °C in the non-catalytic runs. The highest higher heating value was 30.4 MJ/kg from the pyrolysis of medlar seeds in the presence of perlite at 450 °C. The use of MgO noticeably reduced the carbon content and HHV of bio-oils when compared to non-catalytic experiments. The higher heating value of bio-oils increased from 23.5 to 24.7 MJ/kg when the temperature was increased from 350 to 450 °C, respectively. A further increase in temperature resulted in a slight decrease in HHV of bio-oils. For K2CO3, the higher heating values of bio-oils were between 26.1 and 29.0 MJ/kg. The higher heating values of bio-oils obtained with the use of K2CO3 at 350 °C (27.9 MJ/kg) and 550 °C (29.0 MJ/kg) were found to be higher than that of the bio-oils from other experiments at the related temperatures. Table 6. Elemental Compositions of Bio-oils Obtained from the Experiments With and Without Catalysts Bio-oil Type C (%) H (%) N (%) Oa (%) O/C H/C HHVb (MJ/kg) Raw material 43.21 6.634 0.514 49.64 0.86 1.84 15.22 350 °C/ - 65.64 6.726 0.484 27.15 0.31 1.23 26.94 450 °C/ - 67.38 6.470 0.584 25.56 0.28 1.15 27.45 550 °C/ - 65.66 6.803 0.470 27.06 0.31 1.24 27.08 650 °C/ - 66.64 6.621 0.679 26.06 0.29 1.19 27.33 350 °C/ Perlite 65.12 6.928 0.470 27.48 0.32 1.28 27.00 450 °C/ Perlite 66.36 8.626 0.549 24.46 0.28 1.56 30.38 550 °C/ Perlite 66.00 7.740 0.598 25.66 0.29 1.41 28.78 650 °C/ Perlite 67.14 7.541 0.601 24.71 0.28 1.35 29.05 350 °C/ MgO 60.29 6.339 0.261 33.11 0.41 1.26 23.52 450 °C/ MgO 60.97 6.847 0.356 31.82 0.39 1.35 24.71 550 °C/ MgO 60.83 6.679 0.388 32.10 0.40 1.32 24.37 650 °C/ MgO 60.64 6.701 0.472 32.18 0.40 1.33 24.32 350 °C/ K2CO3 65.89 7.203 0.702 26.20 0.30 1.31 27.88 450 °C/ K2CO3 63.73 6.813 0.597 28.86 0.34 1.28 26.12 550 °C/ K2CO3 67.21 7.422 1.434 23.93 0.27 1.33 29.04 650 °C/ K2CO3 65.39 6.394 0.533 27.68 0.32 1.17 26.29 (a): By difference (b): Higher heating value calculated by Dulong formula (HHV) = 0.338C + 1.428(H - O/8) + 0.095S CONCLUSIONS 1. The pyrolysis of medlar seeds was performed at different temperatures with and without catalysts. In the non-catalytic experiments, the maximum bio-oil yield was obtained at 550 °C while the maximum dichloromethane extract yield was obtained at 450 °C. 2. The use of K2CO3 and MgO noticeably affected the yields and composition of the bio- oils. The maximum bio-oil yields were obtained at 550, 450, and 650 °C in the presence of K2CO3, MgO, and perlite, respectively. PEER-REVIEWED ARTICLE bioresources.com Topak & Akalin (2023). “Medlar seeds for bio-oil,” BioResources 18(2), 3144-3159. 3157 3. The higher heating values of the bio-oils obtained from the pyrolysis experiments in the presence of perlite were higher than that of the non-catalytic runs at all tested temperatures. Therefore, bio-oils with increased higher heating values can be obtained with the use of a relatively cheap and an abundant material in the pyrolysis of medlar seeds. 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