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Comprehensively utilization of spent bleaching clay for producing high quality bio-fuel via fast pyrolysis process
Journal Pre-proof Comprehensively utilization of spent bleaching clay for producing high quality bio-fuel via fast pyrolysis process Lujiang Xu, Shijia Chen, He Song, Yang Liu, Chenchen Shi, Qiang Lu PII:
S0360-5442(19)32066-3
DOI:
https://doi.org/10.1016/j.energy.2019.116371
Reference:
EGY 116371
To appear in:
Energy
Received Date: 1 August 2019 Revised Date:
26 September 2019
Accepted Date: 15 October 2019
Please cite this article as: Xu L, Chen S, Song H, Liu Y, Shi C, Lu Q, Comprehensively utilization of spent bleaching clay for producing high quality bio-fuel via fast pyrolysis process, Energy (2019), doi: https://doi.org/10.1016/j.energy.2019.116371. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
Comprehensively utilization of spent bleaching clay for producing high quality biofuel via fast pyrolysis process
Lujiang Xu,*1 Shijia Chen,1 He Song,2 Yang Liu,1 Chenchen Shi,1 Qiang Lu*3
1. College of Engineering, Nanjing Agricultural University, No. 40 Dianjiangtai Road, Nanjing, Jiangsu Province, 210031, PR China 2. Water and Environmental Engineering Group, Faculty of Engineering and the Environment, University of Southampton, University Road, Southampton SO17 1BJ, UK 3. National Engineering Laboratory for Biomass Power Generation Equipment, North China Electric Power University, Beijing, 102206, PR China
* Corresponding author. Lujiang Xu ([email protected]; [email protected]); Qiang Lu ([email protected]; [email protected])
Submitted to Energy September 2019
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ABSTRACT: High-quality bio-fuel (low oxygen content and acid value, high calorific value) was produced by catalytic pyrolysis of clay oil over calcined clay. Both feedstock (clay oil) and catalyst (calcined clay) were obtained from spent bleaching clay (SBC) deriving out of edible oil plants. The calcined clay was characterized with inductively coupled plasmaatomic emission spectrometry (ICP-AES), N2 adsorption/desorption analyses, X-Ray Diffraction (XRD), temperature programmed desorption of ammonia and carbon dioxide (NH3-TPD and CO2-TPD). Catalytic pyrolysis experiments were conducted to investigate the effects of several parameters on the product distribution, including pyrolysis temperature, weight hourly space velocity (WHSV) and residence time. The optimal conditions for produce high quality bio-fuel were 550 ºC with WHSV of 2.5 h-1 and residence time of 1.65 s. The low heating value of bio-oil was increased by 13% to 46.36 KJ/g, as long as the acid value was decreased by 97% to 1.16 mg/g KOH. The calcined clay catalyst showed slight deactivation after 4 cycles. Therefore, fast pyrolysis process is a rapid and efficient method of valorising spent bleaching clay from waste oils for high quality bio-fuel. Keywords: high quality bio-fuel; catalytic pyrolysis; clay oil, calcined clay; characterization
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1. INTRODUCTION
With the development of social economy and the improvement of human's living standards, individual's annual edible oil consumption has increased a lot. In 2015/2016 crop year, China’s consumption of edible oil reached about 30 million tons and kept with an annual growing of 5 % (Xu et al., 2016). For the industrial production of edible oil, crude oil needs to undergo a decolorization process to remove the pigment and other impurities (eg. proteins, mucus, resins, soap, etc) in order to improve the quality of edible oil (Dijkstra, 2013; Boukerroui et al., 2018). Activated clay is widely used as an adsorbent, it is estimated that 2% to 5% of activated clay is consumed to refine per ton of crude oil (Akinwande et al., 2015). After the decolorization process, the inactivated clay (spent bleaching clay, SBC), as one type of solid waste, is produced more than 1 million tons each year (Su et al., 2018). About 20%-40% of residual oil (triglyceride) still remains in the spent bleaching clay (Loh et al., 2006). However, the spent bleaching clay is mainly discarded or landfilled directly, which not only wastes the resource, but also causes the soil and groundwater pollution. The recovery and utilization of waste clay become the top priority. Recently, SBC can also be reused to produce clay bricks, fertilizer and sorbents (Tsai et al., 2002; Eliche-Quesada and Corpas-Iglesias, 2014; Loh et al., 2013; Beshara and Cheeseman, 2014; and Su, et al., 2018). Besides, lots of studies also focused on the recycling of the adsorbed oil on SBC. The adsorbed oil on SBC can be converted to biodiesel (Huang and Chang, 2010). The residual oil of SBC can be extracted via squeezing, solvent leaching or supercritical carbon dioxide (scCO2) extraction, then transesterified with methanol to produce biodiesel. Boey et al. (Boey et al., 2011) directly 3
produced methyl esters from the crude palm oil adsorbed on SBC via ultrasound aided in situ transesterification. Additionally, Sedghamiz et al. (Sedghamiz et al. 2019) produced biodiesel from residual vegetable oil in SBC via in-situ transesterification with alkali catalysts (KOH and NaOH), and the optimum operating conditions (e.g., temperature, catalyst to SBC ratio, etc) were investigated systematically by the response surface method based on the central composite approach (RSM-CCD model). Besides producing biodiesel via transesterification, pyrolysis process was also used to recycle spent bleaching clay. Sapawe et al. (Sapawe and Hanafi, 2018) pyrolyzed the SBC from palm oil factory by modifying tubular furnace to produce the bio-oil, whereas carboxylic acids and esters were the major pyrolytic compounds in the obtained bio-oil, which also indicated that the direct pyrolysis of SBC is not a good way to produce high quality biofuel. Due to low process costs, compatibility with refining instruments, feedstock flexibility and high pyrolytic oil quality, catalytic pyrolysis is becoming a promising technology for catalytic triglycerides deoxidation for production of high quality biofuel (Khan et al. 2019). Plenty of works about catalytic pyrolysis of triglycerides to produce high quality bio-fuels were presented (Lam et al., 2016; Xu et al., 2016), whereas different kinds of triglycerides (e. g., vegetable oils, animal fats, waste cooking oil etc) served as feedstock were widely reported. Araújo et al. (Araújo et al., 2017) used sunflower oil to produce diesel-like oil via catalytic pyrolysis with AlMCM-41. Adebanjo et al. (Adebanjo et al., 2005) also used lard to produce diesel-like fuel and other value-added chemicals by pyrolysis process, the heating value of pyrolytic oil reached 40 MJ/kg. Li et al. (Li et al., 2013) used waste cooking oil to produce liquid hydrocarbon fuels by catalytic pyrolysis
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in the presence of K2O/Ba-MCM-41. In addition, different types of catalysts (molecularsieve catalysts, metal oxides, hydroxides, carbonates, hydrotalcite, activated carbon, etc) were used in previous studies. Abdelfattah et al. (Abdelfattah et al., 2018) produced different types of castor based bio-fuels by using slow pyrolysis process of castor raw oil in the presence of Al2O3, NaOH, NaCO3 and ZSM-5, the obtained biofuels could be used alternative diesels. Yigezu et al. (Yigezu and Muthukumar, 2014) screened the metal oxides (Co3O4, V2O5 and ZnO) to catalytic pyrolysis of sunflower oil to produce biofuel, and identified V2O5 to be the best catalytic activity. Romero et al. (Romero et al., 2015) catalyzed pyrolysis of Jatropha oil over calcined hydrotalcite to produce bio-fuels, and found it could reduce the production of saponifiables effectively. Lam et al. (Lam et al., 2016) observed that activated carbon showed good deoxygenation performance and could efficiently catalyze conversion of waste palm oil to form diesel-like fuel by microwave catalytic pyrolysis process. Furthermore, different pyrolytic oils (e.g., rich aromatics oils, rich diesel fraction oils, rich gasoline fraction oils, etc) could also be produced via regulating catalysts and reaction conditions. Ngo et al. (Ngo et al., 2010) produced aromatics-rich bio-oil by catalytic pyrolysis of soybean oil over HZSM-5 (Proton-exchange of ZSM-5) in a fixedbed reactor, whereas brønsted acid and specific channel structure of HZSM-5 catalyst promoted the formation of aromatics during the catalytic pyrolysis. Xu et al. (Xu et al., 2009) produced diesel-like oil from soybean oils by using Na2CO3 and K2CO3 as catalyst during the catalytic pyrolysis process. Zandonai et al (Zandonai et al., 2016) produced gasoline-rich bio-oil by catalytic hydrocracking of crude soybean oil over Na-ZSM-5, and carbon numbers of main pyrolytic bio-oil components were less than 12, which could
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be used as a gasoline additive. Although many studies about producing high quality biooils from triglycerides via catalytic pyrolysis were carried out, few studies were reported about integral valorization of spent bleaching clay to produce high quality bio-fuel via pyrolysis process. Herein, in order to realize the comprehensive utilization of SBC and the poor properties of SBC direct pyrolsis bio-oil, the SBC was squeezed to produce the waste clay oil and solid residual. Meanwhile the SBC residual was calcined in air to produce the calcined clay. Then, the obtained calcined clay served as the catalyst to catalyze pyrolysis of waste clay oil to produce high quality bio-fuel. The detailed properties of calcined clay was characterized with inductively coupled plasma-atomic emission spectrometry (ICPAES), N2-adsorption/desorption analyses, X-Ray Diffraction (XRD), temperature programmed desorption of ammonia and carbon dioxide (NH3-TPD and CO2-TPD). The parameters of pyrolysis temperature, weight hourly space velocity (WHSV) and residence time, which affected the bio-oil quality significantly, were investigated systematically. For each experiment, the product distributions, chemical components in bio-oil and bio-oil elements were analyzed regularly. Furthermore, the stability and the deactivation mechanism of the calcined clay were also investigated by 4 recycles experiments. Finally, the fuel properties (e.g., elemental compositions, acid value, density, water content and low heating value) of bio-oil obtained at the optimal conditions were also analyzed and compared with the commercial diesel and other catalytic bio-fuels.
2. MATERIALS and METHODS
2.1 Materials
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The spent bleaching clay and clay oil were obtained from Xinhuan utilization of regenerated grease Co. LTD (Taizhou, Jiangsu province, China). Methanol (≥99.5%) was purchased from Sinopharm Chemical Reagent Co. Ltd. (Beijing, China). Air, NH3 (≥99.995%, AR), N2 (99.999%), Ar (99.999%), He (99.999%), 7.90% NH3 and 92.1% He gas mixture for NH3-TPD test and CO2 (99.999%) for CO2-TPD test were purchased from Nanjing Special Gases Factory (Nanjing, Jiangsu province, China). All the raw materials, chemicals and gases were used without further purification. 2.2 Calcined clay preparation and regeneration A certain amount of residual is still remained in the pressed SBC residual, which will affect the catalytic performance of clay. In order to remove the adsorptive material on SBC, the SBC residual was regenerated by calcining in air at 700 °С for 6 h to obtain the calcined clay catalyst. For catalyst regeneration, the used catalyst was also calcined in air at 700 °С for 6 h to remove the coke decomposed on the catalyst. 2.3 Pyrolysis experiments Catalytic pyrolysis of clay oil over calcined clay was carried out in a quartz tube reactor heated by an electric furnace with 3 kW (height of 400 mm, internal diameter of 10 mm, Anhui Kemi machinery technology Co. LTD, Hefei, China) at 450-650 °C. In each run, 1.0 g of calcined clay were fixed in the reaction tube that was heated to a desired temperature, and clay oil was subsequently fed batch by a peristaltic pump (Longer Precision Pump Co., Ltd, Baoding, China) at a certain rate (0.5g/h-4g/h) and purged with carrier gas (100 mL/min N2). The volatile oil products were trapped in a cold trap (100 mL) by liquid nitrogen. The oil was diluted with 25 mL of methanol for GC-MS 7
analysis. The non-condensable gas products were collected with a gas bag (2000 mL) for GC analysis. Fig.S1 in the supplementary information shows the detailed schematic diagram of the experiments. 2.4 Characteristic and analysis The elemental contents of calcined clay were measured by Inductive Coupled Plasma Emission Spectrometer (ICP, Optima 5300DV, Perkin Elemer, USA). Before the characterization, 20 mg of calcined clay was dissolved in the 100 ml of 5% HF solution for 24 hours under stirring. Then, the obtained solution was characterized by the ICPAES. XRD patterns were conducted on a theta rotating anode X-ray diffractometer (TTPIII, Rigaku, Tokyo) using CuKα radiation at 40 kV and 40 mA, with the scattering angle 2θ of 10-70º at a scan rate of 10 º/min. The nitrogen adsorption/desorption isotherms of the catalysts were measured by Autosorb-iQ (Quantachrome, Boynton Beach, FL). The surface area and total volume were determined by the Barrett-Emmet-Taller (BET) method and Barrett-Joyner-Halenda (BJH) method, respectively. The NH3-TPD and CO2TPD for acidity and basicity tests of the catalyst were conducted with Chembet PULSAR TPR/TPD (Quantachrome, Boynton Beach, FL). Four different volumes (0.5, 1, 1.5, 2 mL) of a standard NH3 gas (7.9% NH3 and 92.1% He) were used to calibrate total acid density with R2 > 0.999. The detailed procedures of analysis could refer to the previous work (Xu et al., 2016 and 2019a). The surface morphology of calcined clay was investigated by SEM on an S4800 instrument (Hitachi, Tokyo). The CO2-TPD for basicity test of calcined clay was conducted with Chembet PULSAR TPR/TPD (Quantachrome, Boynton Beach, FL). Four different volumes (0.5, 1, 1.5, 2 mL) of a standard CO2 gas were used to calibrate total basic density with R2 > 0.999. About 100 8
mg of sample were put in a reactor and pre-treated in situ for 4 h at 550 °C in a flow of argon. After cooling to 100 °C, CO2 adsorption was performed by feeding pulses of CO2 to the reactor. After the catalyst surface became saturated, the sample was kept at 100 °C for 2 h to remove the base excess. CO2 was thermally desorbed by rising the temperature with a linear heating rate of approximately 10 °C/min from 100 °C to 500°C (Xu et al, 2019b). The C, H, O, N, S contents of pyrolytic bio-oils were determined by elemental analysis (EA, Vario MACRO cube, Elemnet). The bio-oil density was measured by accurately weighing the mass of bio-oil in a unit volume. Calorific value was measured by a fully automatic calorimeter. The acid value of bio-oil was measured through the indicator method with 0.05 mol/L KOH ethanol solution. The liquid samples were analyzed by GC-MS (Agilent 7890-5977B, Santa Clara, CA) equipped with an HP-5 MS capillary column (30 m × 0.25 mm × 0.25 mm). Split injection was performed at a split ratio of 50 using helium (99.999%) as carrier gas. The oven temperature was held at 40 °C for 3 min, heated to 280 °C at 10 °C /min, and held at 280 °C for 5 min. MSD Chem Station was used to analyze data using the Chem Station Integrator and the integration parameters were listed in detail in Table S1, and the compounds in the bio-oil product were identified through the NIST library. The yields of bio-char, bio-oil and gases were calculated based on Equations (1)-(3), respectively. bio˗char yield % = ˗ ⁄ ! " # × 100 % 1 bio˗oil yield % = ˗
# ⁄ ! " #
× 100% 2
gases yield % = 1 − bio˗char yield − bio˗oil yield × 100% 3
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2.5 Product Analysis 3. RESULTS AND DISCUSSION 3.1 Calcined clay characterization The SEM image of the calcined clay was displayed in Fig. 1a. The calcined clay showed a complex surface structure, as many macro-pore structures of different sizes displayed on the surface of calcined clay, the particle size was different. Fig. 1b displayed that about 20 peaks shown in the X-ray diffraction pattern (XRD) of calcined clay. The highest peak was at 2θ of 26.6º, and other characteristic peaks were at 2θ of 20.9º, 39.4º, 50.1º and 68.4º, which corresponded to quartz (SiO2), as the main component of calcined clay. Small amounts of various silicates, such as aluminium oxide (Al2O3, characteristic peaks at 2θ of 20.6, 27.4º, 45.7º and 54.7º), anorthite (CaAl2Si2O8, characteristic peaks at 2θ of 27.7º, 35.8º and 42.3º), calcite (CaCO3, characteristic peaks at 2θ of 21.8º and 36.4º), and almandine (Al2Fe(SiO4)3, characteristic peaks at 2θ of 40.2º and 54.7º) and actinolite (Ca2(Mg,Fe)Si2O6 characteristic peaks at 2θ of 59.8º), were presented in XRD patterns of calcined clay. The detailed XTD PDF reference number is listed in the Table S2. Table 2 displays the element contents and physical properties of calcined clay. The element content of Si, Al, Fe, Mg, Ca and K of calcined clay was 29.83%, 7.19%, 3.83%, 2.74% 2.02% and 1.79%, respectively. In addition, N2 adsorption-desorption measurements were performed to determine the porosity of the calcined clay. The BET surface area and pore volume of calcined clay were 118.33 m2/g and 0.174 cm3/g respectively. NH3/CO2-TPD were used to determine the acidity and basicity of the calcined clay (Fig.S2). The total acid amounts and basic amounts of
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calcined clay were 103.15 µmol NH3/g and 36.73 µmol CO2/g, which indicated that calcined clay had both acid-base functions, and the acidity was stronger than basicity. The acid sites of calcined clay were probably derived from Al and Fe, and the basic sites were probably derived from Mg, and Ca. (Sugawara et al. 2007; Di Cosimo et al., 1998) 3.2 Comparison of direct pyrolysis and catalytic pyrolysis of clay oil The direct pyrolysis and catalytic pyrolysis of clay oil were compared at 500 °C. The pyrolytic product distributions (a), GC-MS spectra of bio-oils (b), chemical compositions of bio-oils (c), and elemental compositions of bio-oils (d) of direct pyrolysis and catalytic pyrolysis are shown in Fig.2. The detailed product distributions of bio-oils are shown in Table S3 and S4 in the supplementary information. As shown in Fig.2a, the calcined clay changed the pyrolysis behavior of clay oil significantly. Higher yields of bio-char and gases, lower yield of bio-oil were obtained during the catalytic pyrolysis process. With 1.0g of calcined clay catalyst, the yields of bio-char and gases increased from 5.59% and 13.99% to 10.05% and 17.27%, respectively. Meanwhile, the yield of bio-oil decreased from 80.42%to 72.73%. Fig. 2b and Fig. 2c show the GC-MS spectra, the peak area (%) of different chemical classes of directly pyrolytic bio-oil and catalytically pyrolytic bio-oil. Fig. 2b shows that the typical GC-MS spectras of direct pyrolysis and catalytic pyrolysis were different, the retention time of main components in pyrolytic bio-oil was much later than those in the catalytically pyrolytic bio-oil. The main organic components of bio-oils were classified into six groups, i.e., acid and esters (A&E), alcohols (AL), ethers (E), hydrocarbons (HC), ketones and aldehydes (K), and N-contained chemicals (N) based on the chemical structures of main components. Hydrocarbons were the complex mixtures of 11
cycloalkanes, aromatics, straight-chain alkenes, and straight-chain alkanes. As shown in Fig. 2c, the relative peak area (%) varied greatly, especially for acid and esters, alcohols, hydrocarbons, ketones and aldehydes, and N-contained chemicals. The peak area (%) of alcohols, hydrocarbons and ketones increased from 4.46%, 14.09% and 5.88% to 12.20%, 74.79% and 8.59%, respectively. Meanwhile, the peak area (%) of acid and ester decreased from 72.11% to 2.42%, all of which indicated that calcined clay could effectively promote the deoxygenation of acids and esters to form hydrocarbons, alcohols, ketones and aldehydes via during the pyrolysis process. To further verify the catalytic deoxygenation effect of calcined clay, the elemental compositions of directly pyrolytic bio-oil and catalytically pyrolytic bio-oil were determined by elemental analysis (Fig. 2d). The element contents of C, H, O and N of directly pyrolytic bio-oil were 73.74%, 10.70%, 15.35% and 0.65%, respectively. When calcined clay served as the catalyst, the oxygen content in the bio-oil decreased to 3.75%, which was only 24.4% of directly pyrolytic bio-oil. Meanwhile, the carbon content of catalytically pyrolytic bio-oil increased to 85.37%. Therefore, calcined clay showed good potential to catalyze deoxygenation of clay oil to high quality bio-fuel via pyrolysis process. For further determination of the liquid products, the gas products of direct pyrolysis and catalytic pyrolysis were analyzed by gas chromatography. Table 3 shows the selectivity (%) of direct pyrolysis and catalytic pyrolysis. The gas products of direct pyrolysis were composed of C3, CO, CO2, CH4, etc. Compared to direct pyrolysis, higher selectivity of CO and CO2 in catalytic pyrolysis gas products indicated calcined clay could effectively catalyze deoxidation of waste clay oil during the catalytic pyrolysis
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process. In addition, higher selectivities of H2, C2, C4 and C5 and lower selectivities of C3 and CH4 indicated the calcined clay could accelerate the cracking reactions during the catalytic pyrolysis process. The above gases products are combustible, could provide the energy for waste clay regeneration to reduce the additional energy input. Based on above results and previous studies (Zhang et al., 2014; Xu et al., 2016; Botton et al., 2016), the possible mechanism of catalytic pyrolysis of waste clay oil to produce high quality bio-fuel was proposed in Fig. 3. During the catalytic pyrolysis process, the waste clay oil underwent a thermal decomposition process to form fatty acids, ketenes and acrolein in the first step (Fig. 3a). Then, the fatty acid underwent a SBC catalyzed decarboxylation reaction to form straight-chain alkanes (Fig. 3b). Ketones were mainly generated from acids and esters via alkali-catalyzed decarboxylation into ketones reactions in third step (Fig. 3c). Alcohols were probably generated from ketenes via hydrogenation process (Fig. 3d). Straight-chain alkenes were probably via acidiccatalytic cracking of ketenes and the acidic-catalytic dehydration of alcohols in the following steps (Fig. 3 e and f). Moreover, some other reactions (e.g., dehydrogenation, isomerization, aromatic cyclization, alkylation and polymerization etc) occurred during the calcined clay catalytic pyrolysis of waste clay oil process (Xu et al., 2016). 3.3 Effect of Pyrolysis temperature Pyrolysis temperature is an important factor during the catalytic pyrolysis process, which could affect the reactions of pyrolysis process dramatically. Herein, different pyrolysis temperatures (450, 500, 550, 600 and 650 °C) were selected to investigate their influence on product distributions, chemical compositions, carbon number distributions,
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and elemental components of bio-oils by fixing the catalyst dosage (1g), WHSV (2 h-1) and N2 flow rate (100 ml/min) (Fig. 3). The detailed GC-MS spectra of bio-oils obtained at different temperatures are given in Fig.S3. In Fig. 4a, pyrolysis temperature affected the pyrolytic product distributions obviously. Lower pyrolysis temperature promoted to form more bio-oil and char, whereas higher temperature promoted to produce more gases, these changes were on the grounds that higher temperature enhanced cracking reactions. When pyrolysis temperature reached 450 °C, the yields of bio-oil, bio-char and gases were 75.20%, 12.00% and 12.80%, respectively. With the pyrolysis temperature up to 650 °C, the yields of bio-oil and biochar decreased to 52.10% and 5.04%, respectively, and gases yield increased to 42.86%. Pyrolysis temperature also affected the quality of bio-oil dramatically. Fig. 4b, 4c and 4d show the effect of pyrolysis temperatures on chemical compositions, carbon number distributions of chemical components and elemental components of bio-oil. In Fig. 3b, the peak area (%) of oxygenic components (acid & esters, alcohols, and ketones) decreased whereas peak area (%) of hydrocarbons increased significantly along with the pyrolysis temperature increasing from 450 to 650 °C. When pyrolysis temperature reached 450 °C, the peak area (%) of oxygenic components (54.39%) was much higher than that of hydrocarbons (44.31%), and the peak area (%) of acid & esters, alcohols, ethers and ketones were 34.72%, 6.88%, 0.15% and 12.63%, respectively. With the pyrolysis temperature increased to 650 °C, the main components in the bio-oil were hydrocarbons, and the peak area (%) of hydrocarbons, and the total amount of above mentioned was up to 98.58%, the peak area (%) of oxygenic components was only 1.32%, and acids and esters (A&E) was not detected in the bio-oil. It indicated that the
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deoxygenation effect of calcined clay was affected by pyrolysis temperature greatly, higher pyrolysis temperature promoted the deoxygenation reaction during the catalytic pyrolysis of clay oil over calcined clay process. In addition, the main organic components of bio-oils were classified into three types, i.e.,C16, based on the chemical structures of main components in bio-oil. The carbon number distribution of bio-oil components was summarized in Fig. 4c. With the pyrolysis temperature increasing from 450 to 650 °C, the peak area (%) of C16 decreased from 26.76% to 2.64%. The above results indicated that higher pyrolysis temperature promoted the cracking reaction during the catalytic pyrolysis process. Furthermore, the element contents of C, H, O, N of bio-oils obtained at different pyrolysis temperatures were analyzed and shown in Fig. 4d. The oxygen and carbon contents in the bio-oils changed obviously along with the pyrolysis temperature increasing. With the temperature from 450 to 650 °C, the oxygen content decreased from 5.62% to 1.34%, and carbon content increased from 85.37% to 87.28%. It also implied that higher temperature promoted the deoxygenation. When the pyrolysis temperature was at 550 °C, the oxygen content of bio-oil obtained could be decreased to 1.60%, the peak area (%) of hydrocarbons was more than 90%, and the bio-oil yield was up to 68.82%, which was much higher than that of 650 °C. Besides, higher pyrolysis temperature meant higher cost investment. Therefore, the optimal pyrolysis temperature for producing high quality bio-fuel was determined at 550 °C through comprehensively consider of the bio-oil properties, yield and investment.
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3.4 Effect of WHSV Besides the pyrolysis temperature, the effect of WHSV (clay oil feeding rate/calcined clay dosage) was investigated by changing the WHSV from 1.5 to 3 h-1 at fixed pyrolysis temperature (550 °C), catalyst dosage (1g), and residence time (1.65 s). Fig.5 showes the effect of WHSV on (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distributions of bio-oil component, and (d) elemental components of biooil. The detailed GC-MS spectra of bio-oils obtained with different WHSV are given in Fig.S4. It is shown in Fig. 5a that WHSV affected the yields of bio-oil, bio-char and gases when the WHSV increased from 1.5 to 3.0 h-1, higher yield of bio-oil, and lower yields of bio-char and gases were produced. When WHSV was at 2.5 and 3.0 h-1, the bio-oil yields increased up to 71.09% and 73.91%,which were much higher as that of 1.5 h-1 (63.95%). Fig. 5b, 5c and 5d show the effect of WHSV on the quality of pyrolytic bio-oils. Fig. 4b showed that the WHSV had an effect on the chemical compositions. As shown in Fig. 5b, the peak area (%) of hydrocarbons decreased slightly and kept around 90% during WHSV increase. Higher WHSV caused a small higher peak area (%) of oxygenic components (acid & esters, alcohols, ethers and ketones). Fig. 5c showed that WHSV affected carbon number distribution of bio-oil components. With WHSV increased from 1.5 to 3.0 h-1, the peak area (%) ofC16 at 3.0 h-1 was highest. Fig.5d showed that WHSV didn’t change elemental components when WHSV was less than 2.5 h-1, and C, H and O contents of pyrolytic bio-oils were around 86.5%, 10.95% and 1.6%, respectively. With the subsequent increasing of WHSV to 3 h-1, the oxygen content increased to 2.239%, and C content decreased to 85.71%. Therefore, the optimal WHSV for this catalytic process was
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fixed at 2.5 h-1. 3.5 Effect of residence time The residence time between the pyrolytic vapor and the calcined clay catalyst also influenced the product distributions during the catalytic pyrolysis process. Herein, the effect of residence time (from 0.83s to 3.30s) between the pyrolytic clay oil vapors and calcined clay was investigated by changing the N2 flow rate (from 50 ml/min to 200 ml/min) under optimized condition of pyrolysis temperature (550 ºC), catalyst dosage (1g) and WHSV (2.5 h-1). Fig. 6 shows the effect of residence time on (a) product distributions and (b) elemental components of bio-oil. Short residence time could cause higher bio-oil yield (Fig. 6a). When the residence time was at 0.83 s, the bio-oil yield increased to 75.5%. The bio-oil yield of 1.1s (71.09%) was comparable to that of 1.65 s (70.87%). It is worth noted that short residence time caused higher oxygen content in the pyrolytic bio-oil (Fig. 6b). The oxygen content of 0.83 s was up to 2.60%. 1.65s was the optimal residence time and N2 flow rate was selected at 100 ml/min to produce high quality biofuel from clay oil via catalytic pyrolysis process. Therefore, the optimal conditions for producing high quality bio-fuel from clay oil by catalytic pyrolysis with calcined clay process was at 550 ºC with WHSV at 2.5 h-1 and residence time at 1.65s. 3.6 Catalyst cycles The stability of the calcined clay was investigated at optimal conditions. For each cycle, the used catalyst was calcined at 700 °C for 6 h to remove the coke formed on the surface of the catalyst. Fig. 7 shows the overall yields of bio-oil, gases, bio-char and the oxygen content in bio-oil of each catalyst recycle. The yield of bio-oil increased after 5 cycles,
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while the yields of bio-char and gases decreased. Meanwhile, the oxygen content in the bio-oil increased gradually together with catalyst cycle times increase. Based on the results, the catalyst had slight deactivation after 4 cycles. To investigate the reasons of catalyst deactivation, the catalyst after 4 cycles was characterized with N2adsorption/desorption and NH3/CO2-TPD (Table S5). After 4 recycles, BET surface area and pore volume of calcined clay decreased to 95.70 m2/g and 0.135 cm3/g. The total acid amounts decreased from 103.15 µmol NH3/g to 55.45 µmol/g. The total basicity amounts decreased from 36.73 µmol CO2/g to 18.26 µmol/g. Therefore, the deactivation of calcined clay could be caused by the structure changes and acid site loss. 3.7 The fuel properties of bio-oil obtained at optimal conditions The fuel properties (e.g., elemental analysis, chemical compositions, carbon number distribution, acid value, density, water content and LHV) of bio-oil obtained under the optimal conditions were also analyzed. No sulfur was detected in the bio-oil. The C, H, O and N contents of bio-oil were 86.47%, 10.86%, 1.63%, 1.04%, respectively. Compared to the raw clay oil, 86.4% of oxygen in the clay oil could be removed efficiently through the catalytic pyrolysis over calcined clay. As shown in Table S4, the peak area (%) of acid & esters, alcohols, ethers, hydrocarbons, ketones and N-containing chemicals in the biooil were 1.17%, 3.23%, 0.79%, 90.58%, 2.82% and 1.39%, respectively. The oxygen compositions in the bio-oil were alcohols and ketones. The peak area (%) ofC16 were 20.72%, 65.11% and 14.17%, respectively. The main carbon number distribution was C10~C16. The results showed the potential of pyrolytic bio-oil to be used as jet fuel and diesel. Furthermore, the density of bio-oil was about 0.83 g/cm3, which was similar to density of commercial diesel (0.82-0.85 g/cm3) and much lower 18
than that of direct pyrolytic bio-oil (0.89g/cm3) (Jiang et al., 2015). In addition, the acid value of bio-oil was only 1.16 mg KOH/g, which was much lower than the clay oil (42.62 mg KOH/g). The water content of bio-oil was about 0.32%. The lower heating value of bio-oil reached 46.36 kJ/g, which was much higher than that of waste clay oil (41 kJ/g). Furthermore, the fuel properties of bio-fuel obtained via catalytic fast pyrolysis are also cpmpared with the bio-fuels obtained by catalytic pyrolysis over different catalysts (e.g. CaO, Al2O3 and zeolites, etc). (Wang et al., 2019; Xu et al., 2019) The results also showed that calcined clay showed as good catalytic catalytic performance as other kinds of catalysts. The above results showed catalytic pyrolysis over calcined clay was an efficient method to upgrade waste clay oil and also a promising technology to integrally valorize spent bleaching clay from edible oil plant to high quality bio-oil.
4. CONCLUSIONS High quality bio-oil with high heating value was produced by catalytic pyrolysis of clay oil over calcined clay. Both waste oil (extracted from clay) and catalyst (calcined clay) were obtained from SBC from edible oil plants. During the catalytic pyrolysis process, the calcined clay showed a good catalytic performance. Under the optimal conditions (550 ºC with WHSV at 2.5 h-1 and residence time at 1.65 s), the peak area (%) of hydrocarbons in the bio-oil was around 90%. The calcined clay deactivated slightly after 4 cycles. Compared with biodiesel and 0 # diesel, waste clay oil-based bio-fuel has the advantages of high calorific value. Both inorganics and organics in the SBC waste were fully utilized for the production of oil with fast pyrolysis technology. ACKNOWLEDGMENT 19
The authors are grateful to the financial supports from the Natural Science Foundation of Jiangsu Province (No. BK20180548), Natural Science Foundation of China (No. 51906112), China Postdoctoral Science Foundation (2019M651852), Nanjing Agricultural University (77J-0603), Open Funding of Key Laboratory of Energy Thermal Conversion and Control of the Ministry of Education of China at Southeast University, “Innovation & Entrepreneurship Talents” Introduction Plan of Jiangsu Province. REFERENCES [1]
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Tables
Table 1. Physical properties of clay oil Acid value
Lower heating value
(mg KOH/g clay oil)
(LHV) (kJ/g)
42.62
41.02
Elemental analysis (%)
C
H
O
N
S
76.43
11.01
11.99
0.70
0
Table 2. The chemical and physical properties of calcined clay Elemental analysis Si
Al
Fe
Mg
Ca
K
29.83%
7.19%
3.83%
2.74%
2.02%
1.79%
Physical Properties
Acidity and basicity
BET surface area
Pore volume
Total acid amounts
Total basic amounts
(m2/g)
(cm3/g)
(µmol NH3/g)
(µmol CO2/g)
118.33
0.174
103.15
36.73
Table 3. The gas selectivity (%) of direct pyrolysis and catalytic pyrolysis H2
CO
CO2
CH4
C2
C3
C4
C5
Direct pyrolysis
0.23
9.53
4.36
8.52
0.64
73.79
2.87
0.06
Catalytic pyrolysis
0.89
22.83
7.10
0.45
0.93
56.81
10.80
0.19
Table 4. Typical properties of bio-oil obtained under optimal conditions Bio-oil elemental analysis C
H
O
N
S
86.47
10.86
1.63
1.04
0
Acid value
Density
Water content
Lower heating value (LHV)
(mg KOH/g)
(g/cm3)
(%)
(kJ/g)
1.16
0.83
0.32
46.26
Figure captions: Fig.1 (a) SEM and (b) XRD pattern of the calcined clay catalyst Fig.2 Yields and products of direct pyrolysis and catalytic pyrolysis of clay oil (a) product distributions, (b) GC-MS spectra of bio-oils, (c) chemical compositions of bio-oils, and (d) C, H, O, N, S of bio-oil Fig.3 The possible mechanism of catalytic pyrolysis of waste clay oil to produce high quality bio-fuel Fig. 4 Effect of pyrolysis temperature on yields and products of catalytic pyrolysis of clay oil (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distribution of bio-oil component, and (d) C, H, O, N, S of bio-oil. Fig.5 Effect of WHSV on yields and products of catalytic pyrolysis of clay oil (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distribution of bio-oil component, and (d) C, H, O, N, S of bio-oil Fig.6 Effect of residence time (a) product distributions and (b) elemental components of bio-oil of catalytic pyrolysis of clay oil Fig.7 Catalyst cycles (a) Overall yield, and oxygen content in bio-oil
Fig.1 (a) SEM and (b) XRD pattern of the calcined clay catalyst
Fig.2 Yields and products of direct pyrolysis and catalytic pyrolysis of clay oil (a) product distributions, (b) GC-MS spectra of bio-oils, (c) chemical compositions of bio-oils, and (d) C, H, O, N, S of bio-oil; Pyrolysis conditions: feeding rate, 2 g/h; pyrolysis temperature 500 °C; N2 flow rate: 100 ml/min; WHSV of catalytic mode: 2 h-1. (Abbreviation in Fig. 2C, A&E: acids & esters; AL: alcohols; E: ethers; N: N-compounds; HC: hydrocarbons; K: ketones and aldehydes)
Fig. 3 The possible mechanism of catalytic pyrolysis of waste clay oil to produce high quality bio-fuel
Fig.4 Effect of pyrolysis temperature on yields and products of catalytic pyrolysis of clay oil (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distribution of bio-oil component, and (d) C, H, O, N, S of bio-oil (Pyrolysis conditions: catalyst dosage, 1g; feeding rate, 2 g/h; N2 flow rate: 100 ml/min; WHSV: 2 h-1).
Fig.5 Effect of WHSV on yields and products of catalytic pyrolysis of clay oil (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distribution of bio-oil component, and (d) C, H, O, N, S of bio-oil (Pyrolysis conditions: pyrolysis temperature, 550 °C; catalyst dosage, 1g; residence time, 1.65 s, N2 flow rate, 100 ml/min).
Fig.6 Effect of residence time (a) product distributions and (b) elemental components of bio-oil of catalytic pyrolysis of clay oil (Pyrolysis conditions: pyrolysis temperature: 550 °C; catalyst dosage: 1g; clay oil feeding rate: 2.5 g/h, WHSV: 2.5 h-1).
Fig.7 Catalyst cycles (a) Overall yield, and oxygen content in bio-oil (Reaction conditions: pyrolysis temperature: 550 °C; catalyst dosage: 1g; clay oil feeding rate: 2.5 g/h; residence time: 1.65s; WHSV: 2.5 h-1)
Spent bleaching clay was Comprehensively used to produce high quality bio-fuel
The calcined clay was served as catalyst and showed good deoxidation efficiency
Catalyst characterizations & pyrolysis parameters were investigated systematically
The calcined clay catalyst showed slight deactivation after 4 cycles
The LHV of bio-oil increased by 13% and the acid value decreased by 97%
S0360-5442(19)32066-3
DOI:
https://doi.org/10.1016/j.energy.2019.116371
Reference:
EGY 116371
To appear in:
Energy
Received Date: 1 August 2019 Revised Date:
26 September 2019
Accepted Date: 15 October 2019
Please cite this article as: Xu L, Chen S, Song H, Liu Y, Shi C, Lu Q, Comprehensively utilization of spent bleaching clay for producing high quality bio-fuel via fast pyrolysis process, Energy (2019), doi: https://doi.org/10.1016/j.energy.2019.116371. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
Comprehensively utilization of spent bleaching clay for producing high quality biofuel via fast pyrolysis process
Lujiang Xu,*1 Shijia Chen,1 He Song,2 Yang Liu,1 Chenchen Shi,1 Qiang Lu*3
1. College of Engineering, Nanjing Agricultural University, No. 40 Dianjiangtai Road, Nanjing, Jiangsu Province, 210031, PR China 2. Water and Environmental Engineering Group, Faculty of Engineering and the Environment, University of Southampton, University Road, Southampton SO17 1BJ, UK 3. National Engineering Laboratory for Biomass Power Generation Equipment, North China Electric Power University, Beijing, 102206, PR China
* Corresponding author. Lujiang Xu ([email protected]; [email protected]); Qiang Lu ([email protected]; [email protected])
Submitted to Energy September 2019
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ABSTRACT: High-quality bio-fuel (low oxygen content and acid value, high calorific value) was produced by catalytic pyrolysis of clay oil over calcined clay. Both feedstock (clay oil) and catalyst (calcined clay) were obtained from spent bleaching clay (SBC) deriving out of edible oil plants. The calcined clay was characterized with inductively coupled plasmaatomic emission spectrometry (ICP-AES), N2 adsorption/desorption analyses, X-Ray Diffraction (XRD), temperature programmed desorption of ammonia and carbon dioxide (NH3-TPD and CO2-TPD). Catalytic pyrolysis experiments were conducted to investigate the effects of several parameters on the product distribution, including pyrolysis temperature, weight hourly space velocity (WHSV) and residence time. The optimal conditions for produce high quality bio-fuel were 550 ºC with WHSV of 2.5 h-1 and residence time of 1.65 s. The low heating value of bio-oil was increased by 13% to 46.36 KJ/g, as long as the acid value was decreased by 97% to 1.16 mg/g KOH. The calcined clay catalyst showed slight deactivation after 4 cycles. Therefore, fast pyrolysis process is a rapid and efficient method of valorising spent bleaching clay from waste oils for high quality bio-fuel. Keywords: high quality bio-fuel; catalytic pyrolysis; clay oil, calcined clay; characterization
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1. INTRODUCTION
With the development of social economy and the improvement of human's living standards, individual's annual edible oil consumption has increased a lot. In 2015/2016 crop year, China’s consumption of edible oil reached about 30 million tons and kept with an annual growing of 5 % (Xu et al., 2016). For the industrial production of edible oil, crude oil needs to undergo a decolorization process to remove the pigment and other impurities (eg. proteins, mucus, resins, soap, etc) in order to improve the quality of edible oil (Dijkstra, 2013; Boukerroui et al., 2018). Activated clay is widely used as an adsorbent, it is estimated that 2% to 5% of activated clay is consumed to refine per ton of crude oil (Akinwande et al., 2015). After the decolorization process, the inactivated clay (spent bleaching clay, SBC), as one type of solid waste, is produced more than 1 million tons each year (Su et al., 2018). About 20%-40% of residual oil (triglyceride) still remains in the spent bleaching clay (Loh et al., 2006). However, the spent bleaching clay is mainly discarded or landfilled directly, which not only wastes the resource, but also causes the soil and groundwater pollution. The recovery and utilization of waste clay become the top priority. Recently, SBC can also be reused to produce clay bricks, fertilizer and sorbents (Tsai et al., 2002; Eliche-Quesada and Corpas-Iglesias, 2014; Loh et al., 2013; Beshara and Cheeseman, 2014; and Su, et al., 2018). Besides, lots of studies also focused on the recycling of the adsorbed oil on SBC. The adsorbed oil on SBC can be converted to biodiesel (Huang and Chang, 2010). The residual oil of SBC can be extracted via squeezing, solvent leaching or supercritical carbon dioxide (scCO2) extraction, then transesterified with methanol to produce biodiesel. Boey et al. (Boey et al., 2011) directly 3
produced methyl esters from the crude palm oil adsorbed on SBC via ultrasound aided in situ transesterification. Additionally, Sedghamiz et al. (Sedghamiz et al. 2019) produced biodiesel from residual vegetable oil in SBC via in-situ transesterification with alkali catalysts (KOH and NaOH), and the optimum operating conditions (e.g., temperature, catalyst to SBC ratio, etc) were investigated systematically by the response surface method based on the central composite approach (RSM-CCD model). Besides producing biodiesel via transesterification, pyrolysis process was also used to recycle spent bleaching clay. Sapawe et al. (Sapawe and Hanafi, 2018) pyrolyzed the SBC from palm oil factory by modifying tubular furnace to produce the bio-oil, whereas carboxylic acids and esters were the major pyrolytic compounds in the obtained bio-oil, which also indicated that the direct pyrolysis of SBC is not a good way to produce high quality biofuel. Due to low process costs, compatibility with refining instruments, feedstock flexibility and high pyrolytic oil quality, catalytic pyrolysis is becoming a promising technology for catalytic triglycerides deoxidation for production of high quality biofuel (Khan et al. 2019). Plenty of works about catalytic pyrolysis of triglycerides to produce high quality bio-fuels were presented (Lam et al., 2016; Xu et al., 2016), whereas different kinds of triglycerides (e. g., vegetable oils, animal fats, waste cooking oil etc) served as feedstock were widely reported. Araújo et al. (Araújo et al., 2017) used sunflower oil to produce diesel-like oil via catalytic pyrolysis with AlMCM-41. Adebanjo et al. (Adebanjo et al., 2005) also used lard to produce diesel-like fuel and other value-added chemicals by pyrolysis process, the heating value of pyrolytic oil reached 40 MJ/kg. Li et al. (Li et al., 2013) used waste cooking oil to produce liquid hydrocarbon fuels by catalytic pyrolysis
4
in the presence of K2O/Ba-MCM-41. In addition, different types of catalysts (molecularsieve catalysts, metal oxides, hydroxides, carbonates, hydrotalcite, activated carbon, etc) were used in previous studies. Abdelfattah et al. (Abdelfattah et al., 2018) produced different types of castor based bio-fuels by using slow pyrolysis process of castor raw oil in the presence of Al2O3, NaOH, NaCO3 and ZSM-5, the obtained biofuels could be used alternative diesels. Yigezu et al. (Yigezu and Muthukumar, 2014) screened the metal oxides (Co3O4, V2O5 and ZnO) to catalytic pyrolysis of sunflower oil to produce biofuel, and identified V2O5 to be the best catalytic activity. Romero et al. (Romero et al., 2015) catalyzed pyrolysis of Jatropha oil over calcined hydrotalcite to produce bio-fuels, and found it could reduce the production of saponifiables effectively. Lam et al. (Lam et al., 2016) observed that activated carbon showed good deoxygenation performance and could efficiently catalyze conversion of waste palm oil to form diesel-like fuel by microwave catalytic pyrolysis process. Furthermore, different pyrolytic oils (e.g., rich aromatics oils, rich diesel fraction oils, rich gasoline fraction oils, etc) could also be produced via regulating catalysts and reaction conditions. Ngo et al. (Ngo et al., 2010) produced aromatics-rich bio-oil by catalytic pyrolysis of soybean oil over HZSM-5 (Proton-exchange of ZSM-5) in a fixedbed reactor, whereas brønsted acid and specific channel structure of HZSM-5 catalyst promoted the formation of aromatics during the catalytic pyrolysis. Xu et al. (Xu et al., 2009) produced diesel-like oil from soybean oils by using Na2CO3 and K2CO3 as catalyst during the catalytic pyrolysis process. Zandonai et al (Zandonai et al., 2016) produced gasoline-rich bio-oil by catalytic hydrocracking of crude soybean oil over Na-ZSM-5, and carbon numbers of main pyrolytic bio-oil components were less than 12, which could
5
be used as a gasoline additive. Although many studies about producing high quality biooils from triglycerides via catalytic pyrolysis were carried out, few studies were reported about integral valorization of spent bleaching clay to produce high quality bio-fuel via pyrolysis process. Herein, in order to realize the comprehensive utilization of SBC and the poor properties of SBC direct pyrolsis bio-oil, the SBC was squeezed to produce the waste clay oil and solid residual. Meanwhile the SBC residual was calcined in air to produce the calcined clay. Then, the obtained calcined clay served as the catalyst to catalyze pyrolysis of waste clay oil to produce high quality bio-fuel. The detailed properties of calcined clay was characterized with inductively coupled plasma-atomic emission spectrometry (ICPAES), N2-adsorption/desorption analyses, X-Ray Diffraction (XRD), temperature programmed desorption of ammonia and carbon dioxide (NH3-TPD and CO2-TPD). The parameters of pyrolysis temperature, weight hourly space velocity (WHSV) and residence time, which affected the bio-oil quality significantly, were investigated systematically. For each experiment, the product distributions, chemical components in bio-oil and bio-oil elements were analyzed regularly. Furthermore, the stability and the deactivation mechanism of the calcined clay were also investigated by 4 recycles experiments. Finally, the fuel properties (e.g., elemental compositions, acid value, density, water content and low heating value) of bio-oil obtained at the optimal conditions were also analyzed and compared with the commercial diesel and other catalytic bio-fuels.
2. MATERIALS and METHODS
2.1 Materials
6
The spent bleaching clay and clay oil were obtained from Xinhuan utilization of regenerated grease Co. LTD (Taizhou, Jiangsu province, China). Methanol (≥99.5%) was purchased from Sinopharm Chemical Reagent Co. Ltd. (Beijing, China). Air, NH3 (≥99.995%, AR), N2 (99.999%), Ar (99.999%), He (99.999%), 7.90% NH3 and 92.1% He gas mixture for NH3-TPD test and CO2 (99.999%) for CO2-TPD test were purchased from Nanjing Special Gases Factory (Nanjing, Jiangsu province, China). All the raw materials, chemicals and gases were used without further purification. 2.2 Calcined clay preparation and regeneration A certain amount of residual is still remained in the pressed SBC residual, which will affect the catalytic performance of clay. In order to remove the adsorptive material on SBC, the SBC residual was regenerated by calcining in air at 700 °С for 6 h to obtain the calcined clay catalyst. For catalyst regeneration, the used catalyst was also calcined in air at 700 °С for 6 h to remove the coke decomposed on the catalyst. 2.3 Pyrolysis experiments Catalytic pyrolysis of clay oil over calcined clay was carried out in a quartz tube reactor heated by an electric furnace with 3 kW (height of 400 mm, internal diameter of 10 mm, Anhui Kemi machinery technology Co. LTD, Hefei, China) at 450-650 °C. In each run, 1.0 g of calcined clay were fixed in the reaction tube that was heated to a desired temperature, and clay oil was subsequently fed batch by a peristaltic pump (Longer Precision Pump Co., Ltd, Baoding, China) at a certain rate (0.5g/h-4g/h) and purged with carrier gas (100 mL/min N2). The volatile oil products were trapped in a cold trap (100 mL) by liquid nitrogen. The oil was diluted with 25 mL of methanol for GC-MS 7
analysis. The non-condensable gas products were collected with a gas bag (2000 mL) for GC analysis. Fig.S1 in the supplementary information shows the detailed schematic diagram of the experiments. 2.4 Characteristic and analysis The elemental contents of calcined clay were measured by Inductive Coupled Plasma Emission Spectrometer (ICP, Optima 5300DV, Perkin Elemer, USA). Before the characterization, 20 mg of calcined clay was dissolved in the 100 ml of 5% HF solution for 24 hours under stirring. Then, the obtained solution was characterized by the ICPAES. XRD patterns were conducted on a theta rotating anode X-ray diffractometer (TTPIII, Rigaku, Tokyo) using CuKα radiation at 40 kV and 40 mA, with the scattering angle 2θ of 10-70º at a scan rate of 10 º/min. The nitrogen adsorption/desorption isotherms of the catalysts were measured by Autosorb-iQ (Quantachrome, Boynton Beach, FL). The surface area and total volume were determined by the Barrett-Emmet-Taller (BET) method and Barrett-Joyner-Halenda (BJH) method, respectively. The NH3-TPD and CO2TPD for acidity and basicity tests of the catalyst were conducted with Chembet PULSAR TPR/TPD (Quantachrome, Boynton Beach, FL). Four different volumes (0.5, 1, 1.5, 2 mL) of a standard NH3 gas (7.9% NH3 and 92.1% He) were used to calibrate total acid density with R2 > 0.999. The detailed procedures of analysis could refer to the previous work (Xu et al., 2016 and 2019a). The surface morphology of calcined clay was investigated by SEM on an S4800 instrument (Hitachi, Tokyo). The CO2-TPD for basicity test of calcined clay was conducted with Chembet PULSAR TPR/TPD (Quantachrome, Boynton Beach, FL). Four different volumes (0.5, 1, 1.5, 2 mL) of a standard CO2 gas were used to calibrate total basic density with R2 > 0.999. About 100 8
mg of sample were put in a reactor and pre-treated in situ for 4 h at 550 °C in a flow of argon. After cooling to 100 °C, CO2 adsorption was performed by feeding pulses of CO2 to the reactor. After the catalyst surface became saturated, the sample was kept at 100 °C for 2 h to remove the base excess. CO2 was thermally desorbed by rising the temperature with a linear heating rate of approximately 10 °C/min from 100 °C to 500°C (Xu et al, 2019b). The C, H, O, N, S contents of pyrolytic bio-oils were determined by elemental analysis (EA, Vario MACRO cube, Elemnet). The bio-oil density was measured by accurately weighing the mass of bio-oil in a unit volume. Calorific value was measured by a fully automatic calorimeter. The acid value of bio-oil was measured through the indicator method with 0.05 mol/L KOH ethanol solution. The liquid samples were analyzed by GC-MS (Agilent 7890-5977B, Santa Clara, CA) equipped with an HP-5 MS capillary column (30 m × 0.25 mm × 0.25 mm). Split injection was performed at a split ratio of 50 using helium (99.999%) as carrier gas. The oven temperature was held at 40 °C for 3 min, heated to 280 °C at 10 °C /min, and held at 280 °C for 5 min. MSD Chem Station was used to analyze data using the Chem Station Integrator and the integration parameters were listed in detail in Table S1, and the compounds in the bio-oil product were identified through the NIST library. The yields of bio-char, bio-oil and gases were calculated based on Equations (1)-(3), respectively. bio˗char yield % = ˗ ⁄ ! " # × 100 % 1 bio˗oil yield % = ˗
# ⁄ ! " #
× 100% 2
gases yield % = 1 − bio˗char yield − bio˗oil yield × 100% 3
9
2.5 Product Analysis 3. RESULTS AND DISCUSSION 3.1 Calcined clay characterization The SEM image of the calcined clay was displayed in Fig. 1a. The calcined clay showed a complex surface structure, as many macro-pore structures of different sizes displayed on the surface of calcined clay, the particle size was different. Fig. 1b displayed that about 20 peaks shown in the X-ray diffraction pattern (XRD) of calcined clay. The highest peak was at 2θ of 26.6º, and other characteristic peaks were at 2θ of 20.9º, 39.4º, 50.1º and 68.4º, which corresponded to quartz (SiO2), as the main component of calcined clay. Small amounts of various silicates, such as aluminium oxide (Al2O3, characteristic peaks at 2θ of 20.6, 27.4º, 45.7º and 54.7º), anorthite (CaAl2Si2O8, characteristic peaks at 2θ of 27.7º, 35.8º and 42.3º), calcite (CaCO3, characteristic peaks at 2θ of 21.8º and 36.4º), and almandine (Al2Fe(SiO4)3, characteristic peaks at 2θ of 40.2º and 54.7º) and actinolite (Ca2(Mg,Fe)Si2O6 characteristic peaks at 2θ of 59.8º), were presented in XRD patterns of calcined clay. The detailed XTD PDF reference number is listed in the Table S2. Table 2 displays the element contents and physical properties of calcined clay. The element content of Si, Al, Fe, Mg, Ca and K of calcined clay was 29.83%, 7.19%, 3.83%, 2.74% 2.02% and 1.79%, respectively. In addition, N2 adsorption-desorption measurements were performed to determine the porosity of the calcined clay. The BET surface area and pore volume of calcined clay were 118.33 m2/g and 0.174 cm3/g respectively. NH3/CO2-TPD were used to determine the acidity and basicity of the calcined clay (Fig.S2). The total acid amounts and basic amounts of
10
calcined clay were 103.15 µmol NH3/g and 36.73 µmol CO2/g, which indicated that calcined clay had both acid-base functions, and the acidity was stronger than basicity. The acid sites of calcined clay were probably derived from Al and Fe, and the basic sites were probably derived from Mg, and Ca. (Sugawara et al. 2007; Di Cosimo et al., 1998) 3.2 Comparison of direct pyrolysis and catalytic pyrolysis of clay oil The direct pyrolysis and catalytic pyrolysis of clay oil were compared at 500 °C. The pyrolytic product distributions (a), GC-MS spectra of bio-oils (b), chemical compositions of bio-oils (c), and elemental compositions of bio-oils (d) of direct pyrolysis and catalytic pyrolysis are shown in Fig.2. The detailed product distributions of bio-oils are shown in Table S3 and S4 in the supplementary information. As shown in Fig.2a, the calcined clay changed the pyrolysis behavior of clay oil significantly. Higher yields of bio-char and gases, lower yield of bio-oil were obtained during the catalytic pyrolysis process. With 1.0g of calcined clay catalyst, the yields of bio-char and gases increased from 5.59% and 13.99% to 10.05% and 17.27%, respectively. Meanwhile, the yield of bio-oil decreased from 80.42%to 72.73%. Fig. 2b and Fig. 2c show the GC-MS spectra, the peak area (%) of different chemical classes of directly pyrolytic bio-oil and catalytically pyrolytic bio-oil. Fig. 2b shows that the typical GC-MS spectras of direct pyrolysis and catalytic pyrolysis were different, the retention time of main components in pyrolytic bio-oil was much later than those in the catalytically pyrolytic bio-oil. The main organic components of bio-oils were classified into six groups, i.e., acid and esters (A&E), alcohols (AL), ethers (E), hydrocarbons (HC), ketones and aldehydes (K), and N-contained chemicals (N) based on the chemical structures of main components. Hydrocarbons were the complex mixtures of 11
cycloalkanes, aromatics, straight-chain alkenes, and straight-chain alkanes. As shown in Fig. 2c, the relative peak area (%) varied greatly, especially for acid and esters, alcohols, hydrocarbons, ketones and aldehydes, and N-contained chemicals. The peak area (%) of alcohols, hydrocarbons and ketones increased from 4.46%, 14.09% and 5.88% to 12.20%, 74.79% and 8.59%, respectively. Meanwhile, the peak area (%) of acid and ester decreased from 72.11% to 2.42%, all of which indicated that calcined clay could effectively promote the deoxygenation of acids and esters to form hydrocarbons, alcohols, ketones and aldehydes via during the pyrolysis process. To further verify the catalytic deoxygenation effect of calcined clay, the elemental compositions of directly pyrolytic bio-oil and catalytically pyrolytic bio-oil were determined by elemental analysis (Fig. 2d). The element contents of C, H, O and N of directly pyrolytic bio-oil were 73.74%, 10.70%, 15.35% and 0.65%, respectively. When calcined clay served as the catalyst, the oxygen content in the bio-oil decreased to 3.75%, which was only 24.4% of directly pyrolytic bio-oil. Meanwhile, the carbon content of catalytically pyrolytic bio-oil increased to 85.37%. Therefore, calcined clay showed good potential to catalyze deoxygenation of clay oil to high quality bio-fuel via pyrolysis process. For further determination of the liquid products, the gas products of direct pyrolysis and catalytic pyrolysis were analyzed by gas chromatography. Table 3 shows the selectivity (%) of direct pyrolysis and catalytic pyrolysis. The gas products of direct pyrolysis were composed of C3, CO, CO2, CH4, etc. Compared to direct pyrolysis, higher selectivity of CO and CO2 in catalytic pyrolysis gas products indicated calcined clay could effectively catalyze deoxidation of waste clay oil during the catalytic pyrolysis
12
process. In addition, higher selectivities of H2, C2, C4 and C5 and lower selectivities of C3 and CH4 indicated the calcined clay could accelerate the cracking reactions during the catalytic pyrolysis process. The above gases products are combustible, could provide the energy for waste clay regeneration to reduce the additional energy input. Based on above results and previous studies (Zhang et al., 2014; Xu et al., 2016; Botton et al., 2016), the possible mechanism of catalytic pyrolysis of waste clay oil to produce high quality bio-fuel was proposed in Fig. 3. During the catalytic pyrolysis process, the waste clay oil underwent a thermal decomposition process to form fatty acids, ketenes and acrolein in the first step (Fig. 3a). Then, the fatty acid underwent a SBC catalyzed decarboxylation reaction to form straight-chain alkanes (Fig. 3b). Ketones were mainly generated from acids and esters via alkali-catalyzed decarboxylation into ketones reactions in third step (Fig. 3c). Alcohols were probably generated from ketenes via hydrogenation process (Fig. 3d). Straight-chain alkenes were probably via acidiccatalytic cracking of ketenes and the acidic-catalytic dehydration of alcohols in the following steps (Fig. 3 e and f). Moreover, some other reactions (e.g., dehydrogenation, isomerization, aromatic cyclization, alkylation and polymerization etc) occurred during the calcined clay catalytic pyrolysis of waste clay oil process (Xu et al., 2016). 3.3 Effect of Pyrolysis temperature Pyrolysis temperature is an important factor during the catalytic pyrolysis process, which could affect the reactions of pyrolysis process dramatically. Herein, different pyrolysis temperatures (450, 500, 550, 600 and 650 °C) were selected to investigate their influence on product distributions, chemical compositions, carbon number distributions,
13
and elemental components of bio-oils by fixing the catalyst dosage (1g), WHSV (2 h-1) and N2 flow rate (100 ml/min) (Fig. 3). The detailed GC-MS spectra of bio-oils obtained at different temperatures are given in Fig.S3. In Fig. 4a, pyrolysis temperature affected the pyrolytic product distributions obviously. Lower pyrolysis temperature promoted to form more bio-oil and char, whereas higher temperature promoted to produce more gases, these changes were on the grounds that higher temperature enhanced cracking reactions. When pyrolysis temperature reached 450 °C, the yields of bio-oil, bio-char and gases were 75.20%, 12.00% and 12.80%, respectively. With the pyrolysis temperature up to 650 °C, the yields of bio-oil and biochar decreased to 52.10% and 5.04%, respectively, and gases yield increased to 42.86%. Pyrolysis temperature also affected the quality of bio-oil dramatically. Fig. 4b, 4c and 4d show the effect of pyrolysis temperatures on chemical compositions, carbon number distributions of chemical components and elemental components of bio-oil. In Fig. 3b, the peak area (%) of oxygenic components (acid & esters, alcohols, and ketones) decreased whereas peak area (%) of hydrocarbons increased significantly along with the pyrolysis temperature increasing from 450 to 650 °C. When pyrolysis temperature reached 450 °C, the peak area (%) of oxygenic components (54.39%) was much higher than that of hydrocarbons (44.31%), and the peak area (%) of acid & esters, alcohols, ethers and ketones were 34.72%, 6.88%, 0.15% and 12.63%, respectively. With the pyrolysis temperature increased to 650 °C, the main components in the bio-oil were hydrocarbons, and the peak area (%) of hydrocarbons, and the total amount of above mentioned was up to 98.58%, the peak area (%) of oxygenic components was only 1.32%, and acids and esters (A&E) was not detected in the bio-oil. It indicated that the
14
deoxygenation effect of calcined clay was affected by pyrolysis temperature greatly, higher pyrolysis temperature promoted the deoxygenation reaction during the catalytic pyrolysis of clay oil over calcined clay process. In addition, the main organic components of bio-oils were classified into three types, i.e.,
15
3.4 Effect of WHSV Besides the pyrolysis temperature, the effect of WHSV (clay oil feeding rate/calcined clay dosage) was investigated by changing the WHSV from 1.5 to 3 h-1 at fixed pyrolysis temperature (550 °C), catalyst dosage (1g), and residence time (1.65 s). Fig.5 showes the effect of WHSV on (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distributions of bio-oil component, and (d) elemental components of biooil. The detailed GC-MS spectra of bio-oils obtained with different WHSV are given in Fig.S4. It is shown in Fig. 5a that WHSV affected the yields of bio-oil, bio-char and gases when the WHSV increased from 1.5 to 3.0 h-1, higher yield of bio-oil, and lower yields of bio-char and gases were produced. When WHSV was at 2.5 and 3.0 h-1, the bio-oil yields increased up to 71.09% and 73.91%,which were much higher as that of 1.5 h-1 (63.95%). Fig. 5b, 5c and 5d show the effect of WHSV on the quality of pyrolytic bio-oils. Fig. 4b showed that the WHSV had an effect on the chemical compositions. As shown in Fig. 5b, the peak area (%) of hydrocarbons decreased slightly and kept around 90% during WHSV increase. Higher WHSV caused a small higher peak area (%) of oxygenic components (acid & esters, alcohols, ethers and ketones). Fig. 5c showed that WHSV affected carbon number distribution of bio-oil components. With WHSV increased from 1.5 to 3.0 h-1, the peak area (%) of
16
fixed at 2.5 h-1. 3.5 Effect of residence time The residence time between the pyrolytic vapor and the calcined clay catalyst also influenced the product distributions during the catalytic pyrolysis process. Herein, the effect of residence time (from 0.83s to 3.30s) between the pyrolytic clay oil vapors and calcined clay was investigated by changing the N2 flow rate (from 50 ml/min to 200 ml/min) under optimized condition of pyrolysis temperature (550 ºC), catalyst dosage (1g) and WHSV (2.5 h-1). Fig. 6 shows the effect of residence time on (a) product distributions and (b) elemental components of bio-oil. Short residence time could cause higher bio-oil yield (Fig. 6a). When the residence time was at 0.83 s, the bio-oil yield increased to 75.5%. The bio-oil yield of 1.1s (71.09%) was comparable to that of 1.65 s (70.87%). It is worth noted that short residence time caused higher oxygen content in the pyrolytic bio-oil (Fig. 6b). The oxygen content of 0.83 s was up to 2.60%. 1.65s was the optimal residence time and N2 flow rate was selected at 100 ml/min to produce high quality biofuel from clay oil via catalytic pyrolysis process. Therefore, the optimal conditions for producing high quality bio-fuel from clay oil by catalytic pyrolysis with calcined clay process was at 550 ºC with WHSV at 2.5 h-1 and residence time at 1.65s. 3.6 Catalyst cycles The stability of the calcined clay was investigated at optimal conditions. For each cycle, the used catalyst was calcined at 700 °C for 6 h to remove the coke formed on the surface of the catalyst. Fig. 7 shows the overall yields of bio-oil, gases, bio-char and the oxygen content in bio-oil of each catalyst recycle. The yield of bio-oil increased after 5 cycles,
17
while the yields of bio-char and gases decreased. Meanwhile, the oxygen content in the bio-oil increased gradually together with catalyst cycle times increase. Based on the results, the catalyst had slight deactivation after 4 cycles. To investigate the reasons of catalyst deactivation, the catalyst after 4 cycles was characterized with N2adsorption/desorption and NH3/CO2-TPD (Table S5). After 4 recycles, BET surface area and pore volume of calcined clay decreased to 95.70 m2/g and 0.135 cm3/g. The total acid amounts decreased from 103.15 µmol NH3/g to 55.45 µmol/g. The total basicity amounts decreased from 36.73 µmol CO2/g to 18.26 µmol/g. Therefore, the deactivation of calcined clay could be caused by the structure changes and acid site loss. 3.7 The fuel properties of bio-oil obtained at optimal conditions The fuel properties (e.g., elemental analysis, chemical compositions, carbon number distribution, acid value, density, water content and LHV) of bio-oil obtained under the optimal conditions were also analyzed. No sulfur was detected in the bio-oil. The C, H, O and N contents of bio-oil were 86.47%, 10.86%, 1.63%, 1.04%, respectively. Compared to the raw clay oil, 86.4% of oxygen in the clay oil could be removed efficiently through the catalytic pyrolysis over calcined clay. As shown in Table S4, the peak area (%) of acid & esters, alcohols, ethers, hydrocarbons, ketones and N-containing chemicals in the biooil were 1.17%, 3.23%, 0.79%, 90.58%, 2.82% and 1.39%, respectively. The oxygen compositions in the bio-oil were alcohols and ketones. The peak area (%) of
than that of direct pyrolytic bio-oil (0.89g/cm3) (Jiang et al., 2015). In addition, the acid value of bio-oil was only 1.16 mg KOH/g, which was much lower than the clay oil (42.62 mg KOH/g). The water content of bio-oil was about 0.32%. The lower heating value of bio-oil reached 46.36 kJ/g, which was much higher than that of waste clay oil (41 kJ/g). Furthermore, the fuel properties of bio-fuel obtained via catalytic fast pyrolysis are also cpmpared with the bio-fuels obtained by catalytic pyrolysis over different catalysts (e.g. CaO, Al2O3 and zeolites, etc). (Wang et al., 2019; Xu et al., 2019) The results also showed that calcined clay showed as good catalytic catalytic performance as other kinds of catalysts. The above results showed catalytic pyrolysis over calcined clay was an efficient method to upgrade waste clay oil and also a promising technology to integrally valorize spent bleaching clay from edible oil plant to high quality bio-oil.
4. CONCLUSIONS High quality bio-oil with high heating value was produced by catalytic pyrolysis of clay oil over calcined clay. Both waste oil (extracted from clay) and catalyst (calcined clay) were obtained from SBC from edible oil plants. During the catalytic pyrolysis process, the calcined clay showed a good catalytic performance. Under the optimal conditions (550 ºC with WHSV at 2.5 h-1 and residence time at 1.65 s), the peak area (%) of hydrocarbons in the bio-oil was around 90%. The calcined clay deactivated slightly after 4 cycles. Compared with biodiesel and 0 # diesel, waste clay oil-based bio-fuel has the advantages of high calorific value. Both inorganics and organics in the SBC waste were fully utilized for the production of oil with fast pyrolysis technology. ACKNOWLEDGMENT 19
The authors are grateful to the financial supports from the Natural Science Foundation of Jiangsu Province (No. BK20180548), Natural Science Foundation of China (No. 51906112), China Postdoctoral Science Foundation (2019M651852), Nanjing Agricultural University (77J-0603), Open Funding of Key Laboratory of Energy Thermal Conversion and Control of the Ministry of Education of China at Southeast University, “Innovation & Entrepreneurship Talents” Introduction Plan of Jiangsu Province. REFERENCES [1]
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Tables
Table 1. Physical properties of clay oil Acid value
Lower heating value
(mg KOH/g clay oil)
(LHV) (kJ/g)
42.62
41.02
Elemental analysis (%)
C
H
O
N
S
76.43
11.01
11.99
0.70
0
Table 2. The chemical and physical properties of calcined clay Elemental analysis Si
Al
Fe
Mg
Ca
K
29.83%
7.19%
3.83%
2.74%
2.02%
1.79%
Physical Properties
Acidity and basicity
BET surface area
Pore volume
Total acid amounts
Total basic amounts
(m2/g)
(cm3/g)
(µmol NH3/g)
(µmol CO2/g)
118.33
0.174
103.15
36.73
Table 3. The gas selectivity (%) of direct pyrolysis and catalytic pyrolysis H2
CO
CO2
CH4
C2
C3
C4
C5
Direct pyrolysis
0.23
9.53
4.36
8.52
0.64
73.79
2.87
0.06
Catalytic pyrolysis
0.89
22.83
7.10
0.45
0.93
56.81
10.80
0.19
Table 4. Typical properties of bio-oil obtained under optimal conditions Bio-oil elemental analysis C
H
O
N
S
86.47
10.86
1.63
1.04
0
Acid value
Density
Water content
Lower heating value (LHV)
(mg KOH/g)
(g/cm3)
(%)
(kJ/g)
1.16
0.83
0.32
46.26
Figure captions: Fig.1 (a) SEM and (b) XRD pattern of the calcined clay catalyst Fig.2 Yields and products of direct pyrolysis and catalytic pyrolysis of clay oil (a) product distributions, (b) GC-MS spectra of bio-oils, (c) chemical compositions of bio-oils, and (d) C, H, O, N, S of bio-oil Fig.3 The possible mechanism of catalytic pyrolysis of waste clay oil to produce high quality bio-fuel Fig. 4 Effect of pyrolysis temperature on yields and products of catalytic pyrolysis of clay oil (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distribution of bio-oil component, and (d) C, H, O, N, S of bio-oil. Fig.5 Effect of WHSV on yields and products of catalytic pyrolysis of clay oil (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distribution of bio-oil component, and (d) C, H, O, N, S of bio-oil Fig.6 Effect of residence time (a) product distributions and (b) elemental components of bio-oil of catalytic pyrolysis of clay oil Fig.7 Catalyst cycles (a) Overall yield, and oxygen content in bio-oil
Fig.1 (a) SEM and (b) XRD pattern of the calcined clay catalyst
Fig.2 Yields and products of direct pyrolysis and catalytic pyrolysis of clay oil (a) product distributions, (b) GC-MS spectra of bio-oils, (c) chemical compositions of bio-oils, and (d) C, H, O, N, S of bio-oil; Pyrolysis conditions: feeding rate, 2 g/h; pyrolysis temperature 500 °C; N2 flow rate: 100 ml/min; WHSV of catalytic mode: 2 h-1. (Abbreviation in Fig. 2C, A&E: acids & esters; AL: alcohols; E: ethers; N: N-compounds; HC: hydrocarbons; K: ketones and aldehydes)
Fig. 3 The possible mechanism of catalytic pyrolysis of waste clay oil to produce high quality bio-fuel
Fig.4 Effect of pyrolysis temperature on yields and products of catalytic pyrolysis of clay oil (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distribution of bio-oil component, and (d) C, H, O, N, S of bio-oil (Pyrolysis conditions: catalyst dosage, 1g; feeding rate, 2 g/h; N2 flow rate: 100 ml/min; WHSV: 2 h-1).
Fig.5 Effect of WHSV on yields and products of catalytic pyrolysis of clay oil (a) product distributions, (b) chemical compositions of bio-oils, (c) carbon number distribution of bio-oil component, and (d) C, H, O, N, S of bio-oil (Pyrolysis conditions: pyrolysis temperature, 550 °C; catalyst dosage, 1g; residence time, 1.65 s, N2 flow rate, 100 ml/min).
Fig.6 Effect of residence time (a) product distributions and (b) elemental components of bio-oil of catalytic pyrolysis of clay oil (Pyrolysis conditions: pyrolysis temperature: 550 °C; catalyst dosage: 1g; clay oil feeding rate: 2.5 g/h, WHSV: 2.5 h-1).
Fig.7 Catalyst cycles (a) Overall yield, and oxygen content in bio-oil (Reaction conditions: pyrolysis temperature: 550 °C; catalyst dosage: 1g; clay oil feeding rate: 2.5 g/h; residence time: 1.65s; WHSV: 2.5 h-1)
Spent bleaching clay was Comprehensively used to produce high quality bio-fuel
The calcined clay was served as catalyst and showed good deoxidation efficiency
Catalyst characterizations & pyrolysis parameters were investigated systematically
The calcined clay catalyst showed slight deactivation after 4 cycles
The LHV of bio-oil increased by 13% and the acid value decreased by 97%