Valorization of banana peel waste via in-situ catalytic pyrolysis using Al-Modified SBA-15

Accepted Manuscript Valorization of banana peel waste via in-situ catalytic pyrolysis using Al-Modified SBA-15 Nurgul Ozbay, Adife Seyda Yargic, Rahmiye Zerrin Yarbay Sahin, Elif Yaman PII:

S0960-1481(19)30376-3

DOI:

https://doi.org/10.1016/j.renene.2019.03.071

Reference:

RENE 11343

To appear in:

Renewable Energy

Received Date: 21 June 2018 Revised Date:

6 March 2019

Accepted Date: 13 March 2019

Please cite this article as: Ozbay N, Yargic AS, Yarbay Sahin RZ, Yaman E, Valorization of banana peel waste via in-situ catalytic pyrolysis using Al-Modified SBA-15, Renewable Energy (2019), doi: https:// doi.org/10.1016/j.renene.2019.03.071. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

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Valorization of Banana Peel Waste via in-situ Catalytic Pyrolysis Using Al-Modified SBA-15

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Nurgul Ozbay a,b,*, Adife Seyda Yargic a,b, Rahmiye Zerrin Yarbay Sahina,b,c, Elif Yamand

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a

Chemical Engineering Department, Engineering Faculty, Gulumbe Campus, Bilecik Seyh Edebali University,

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11210, Bilecik, Turkey b

Biotechnology Research Center, Gulumbe Campus, Bilecik Seyh Edebali University, 11210, Bilecik, Turkey

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c

Department of Advanced Materials for Energy Applications, Catalonia Institute for Energy Research (IREC),

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Jardins de les Dones de Negre 1, Sant Adrià del Besòs, 08930, Barcelona, Spain d

Central Research Laboratory, Gulumbe Campus Bilecik Seyh Edebali University, 11210, Bilecik, Turkey

* Corresponding author. Chemical Engineering Department, Engineering Faculty, Gulumbe Campus, Bilecik

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Seyh Edebali University, 11210, Bilecik, Turkey. Fax: +90 (228) 2141222.

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E-mail address: [email protected]

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Abstract

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The present study is aimed to investigate thermal and catalytic pyrolysis of banana peel. In the

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first part of the study, banana peel was pyrolyzed by varying the temperatures between 400

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and 700°C. It was seen that higher temperature caused in lower bio-oil and bio-char yields but

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higher gas yields and optimum temperature was determined as 550°C. In the second part, the

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mesoporous material Al-SBA-15 with the typical hexagonal arrangement of SBA-15 verified

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via XRD possesses Lewis and Brönsted acid sites (NH3-TPD), large surface area and wide

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pore diameter (N2 physisorption) was able to catalyzing of banana peel biomass resulting in

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bio-oil yields of 18–28% with varying catalyst/biomass ratios (0, 5, 10, 15, 20 wt%). The

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highest bio-oil yield from the catalytic pyrolysis was 18.64% with 15 wt% catalyst/biomass

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ratios. The composition and physical properties of the bio-oils were reported that the catalyst

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increased oxygen removal from the bio-oil and also developed the production of desirable

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products like phenolics and aromatic compounds. The results confirmed the catalytic

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pyrolysis of banana peel was well related to the textural properties of catalysts.

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Keywords: Al-SBA-15, Banana peel, Biomass, Catalytic Pyrolysis, Mesoporous catalysts.

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ACCEPTED MANUSCRIPT 1. Introduction

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There is a growing attention to alternative resources to replace conventional resources,

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because of the global oil crisis of the 1970s and the greenhouse effect [1]. In the last decades,

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biomass has been a promising alternative among alternative energy resources due to it’s

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negligible amount of sulphur, nitrogen and ash [2, 3].

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The common way to achieve bio-energy is the growing of energy crops which has led to two

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drawbacks which are competition with food production and the destruction of forests [4]. On

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the other hand, waste biomass which is a bio-energy source does not cause any of these

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drawbacks. Hence, improving technologies for degradation of waste to energy has drawn the

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interest of many scientists [5-8].

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Biomass can be converted to valuable products that could be utilised as fuels using several

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processes. Thermal conversion via pyrolysis is a promising process as it produces valuable

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products and byproducts [9, 10]. In pyrolysis, the organic matter is heated in an inert

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atmosphere and converted into non-condensable gases, condensable gases which also

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recovered as the liquid product and a solid product (char) [11]. Especially, the liquid product

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which is called as bio-oil is generally the most desired product in pyrolysis [8].

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Biomass catalytic pyrolysis has some advantages like promoting the yield of energy and

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getting directional chemical products [12]. Catalytic pyrolysis consists of two stages; firstly

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pyrolysis of biomass takes places and catalytic transformation of pyrolysis vapors occurs. In

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the first step, biomass is converted into pyrolysis vapors, non-condensable gases and bio-char

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when it is heated. Then, the vapors are met with the catalyst surface. In this surface, the

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oxygenated compounds can be turned into aromatics and aliphatics via deoxygenation [3].

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Catalysts take a role not only making easier the cracking of carbon–carbon bonds and de-

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oxygenation reaction but also producing bio-oil that is lower in oxygenates, has a higher

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calorific value and better hydrocarbon distribution. Thus, the quality and stability of bio-oil

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ACCEPTED MANUSCRIPT are enhanced, making the handling, upgrading and transporting of bio-oils are easier as well

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as reduction of processes costs [9, 13–17].

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As agricultural wastes, banana leaves, pseudostem, empty fruit bunch and peel are getting

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more attention in recent years [18-26]. Although there are few studies regarding the pyrolysis

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of banana waste reported in the literature, there is a lack of implementation of catalytic

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pyrolysis; especially there is no study related to using metal loaded catalysts in banana

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pyrolysis [27- 29]. The novelty of the current study lies in the direct comparison of thermal

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and catalytic pyrolysis using mesoporous (SBA-15) acidic catalysts, as well as their parent

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materials, for investigation of degradation of pyrolysis vapours from banana peel. Besides,

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detailed investigation of sub-fractions of one of the pyrolysis’ products (liquid bio-oil) is lack

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in the literature. This study will provide fruitful evaluations of products especially when

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mesoporous materials used for the first time in banana peel waste.

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In the present work, laboratory scale results were evaluated on thermal and catalytic pyrolysis

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of banana peel. In the thermal pyrolysis experiments, banana peel pyrolysis was performed to

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investigate the effect of temperature on product distributions. In the catalytic part, the effect

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of Al-SBA-15 catalyst on product yields and bio-oil compositions were studied and compared

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with thermal pyrolysis. Besides, char produced from pyrolysis was also characterized.

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2. Materials and methods

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Bananas which are grown in the Mediterranean region in Turkey were collected. The peel

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samples were dried naturally in open air in the dark room up to two months, ground, milled

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and sieved. An average particle size was calculated as 0.902 mm. Proximate analysis was

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applied in order to detect the volatile matter, ash, moisture and fixed carbon. Leco CNH628

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S628 elemental analyzer was used to detect carbon, hydrogen, nitrogen and oxygen contents

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by using helium, dry air and oxygen gases.

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ACCEPTED MANUSCRIPT Thermal behaviour of the banana peel was investigated by Setaram Labsys Evo

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thermogravimetric analyzer (TGA) in a nitrogen environment. In each run, 10 mg of sample

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was used from 10 to 1000ºC. Fourier Transform Infrared Spectroscopy (FT-IR) analysis of

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banana peel was carried out using a Perkin Elmer Spectrum 100 to identify structural groups

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in the range of 4000-400 cm-1 wavelength by using the ATR technique. The particle

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morphology of banana peel was studied by using a scanning electron microscope (Zeiss Supra

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VP 40).

2.1. Synthesis and characterization of the mesoporous material

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Al-SBA-15 catalyst was synthesized according to a procedure which can be found in the

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literature [30, 31]. The chemicals used in preparation were tetraethyl orthosilicate (TEOS-

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Sigma-Aldrich) and aluminumchloride (Sigma-Aldrich) as silica and aluminium precursors,

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respectively. Nonionic triblock copolymer surfactant EO20PO70EO20 (pluronic P123;

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average MW 5800, Sigma-Aldrich) was the structure-directing agent. Concentrated HCl

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solution was chosen as the acid source.

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First, SBA-15 was synthesized separately. In the synthesis procedure, 4 g of pluronic P123

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was weighed to dissolve in 20.59 mL of HCl and 125 mL of deionize water. 9.04 mL of

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TEOS was added slowly after dissolving solution while stirring at 35°C. This solution was

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mixed at 35°C for 24 h and aged in a teflon bottle at 120°C for 24 h. After cooling to room

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temperature, the obtained product was filtered, washed with deionized water, dried at 65°C

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for a night and then calcined at 550°C for 5 h under dry air atmosphere.

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Al-SBA-15 was prepared by the traditional incipient wet impregnation of SBA-15 with

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aluminum chloride dissolved in ethanol (99.5%). Then the resulting powder was calcined

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again at 550°C for 5 h under dry air atmosphere.

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The synthesized catalyst was characterized by using X-ray diffraction (XRD), scanning

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electron microscopy (SEM) and N2 adsorption-desorption isotherms techniques. Small-angle

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XRD pattern of catalyst was determined on a Panalytical Empyrean diffractometer operated at

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40 kV. The SEM images were carried out using a Zeiss Supra VP 40 instrument. N2

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adsorption-desorption isotherms were evaluated over a Micromeritics ASAP 2020 apparatus.

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Solid-state

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resonance spectrometer.

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The temperature-programmed desorption with ammonia (NH3-TPD) was carried out in

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Autochem II-2920, Micromeritics. The catalyst was saturated with a flow of 15 (v./v.)% NH3

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in He at 50°C. Subsequently, NH3 was desorbed in a He flow of 25 cm3/min up to a

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temperature of 700°C with ramp rate of 10 K/min.

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2.2. Pyrolysis experiment

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Al-NMR spectra were collected using a JEOL ECZ500R nuclear magnetic

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The pyrolysis experiments were implemented in a Heinze retort type reactor made of 316

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stainless steel under static atmosphere. The reactor is externally heated by an electric furnace

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and the temperature inside the reactor is measured by a thermocouple inside the bed.

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The experiments were performed in two groups. In the first group, in order to determine the

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temperature effect on product yields, 15 g of biomass was put inside the reactor and the

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temperature was upraised to a final temperature (400, 450, 500, 550, or 700°C) at 7°C/min

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and held for 20 min. The liquid phase condensed in collecting bottles conserved at about 0°C

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was recovered by washing with solvent. Bio-oil and water contents of liquid product were

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separated using a separating funnel. Bio-oil was dried first by using anhydrous sodium

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sulphate; then the dichloromethane solvent was evaporated at 313 K and 790 mbar using a

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rotary evaporator. When the reactor was cooled to room temperature, the obtained solid

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product was weighed and verified as char yield. The number of gaseous products was

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calculated by subtraction of sum of solid, water and liquid yields from the initial banana peel

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amount.

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The second group of experiments were performed in order to determine the catalyst/biomass

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weight ratio effect on the pyrolysis yields. The experiments were implemented in

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catalyst/biomass ratio of 5, 10, 15, or 20% at the optimum temperature for all these

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experiments.

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2.3. Product analysis

The obtained bio-oils were characterized using several chromatographic and spectroscopic

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techniques including elemental analysis, FT-IR TGA/DTG analysis, GC–MS and column

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chromatography. Elemental results (Leco CNH628 S628) which were calculated on a dry

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ash-free basis were performed on bio-oil samples. Additionally; higher heating values of the

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bio-oils were calculated using elemental analyses data via Dulong’s Formula [22]:

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HHV (MJ/kg) =33.83C + 144.3(H-O/8) + 9.42S

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A thermogravimetric analyzer (Setaram Labsysevo) was used to evaluate the thermal

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behaviour of the biomass. Gas chromatography/mass spectroscopy (GC/MS) analysis for bio-

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oils and n-pentane subfractions were performed using a QP2010 Model gas chromatograph

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and a mass selective detector (Shimadzu, Japan); a thin film (30 m × 0.25 mm, 0.25 µm film

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thickness) TRB-5 MS capillary column supplied from Teknoroma was used. Carrier gas was

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helium with a flow rate of 1 cm3/min. The temperature program was 40 °C for 5 min followed

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by 4 °C/min heating rate to 260 °C. The compounds were identified using NIST library.

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The FT-IR spectrum of bio-oil was recorded using a Perkin Elmer Spectrum 100 Model.

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Chemical compositions of the bio-oils were established by liquid column chromatographic

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fractionation. The adsorption column was eluated with pentane, toluene, and methanol to

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achieve aliphatic, aromatic, and polar fractions, respectively. Each fraction was dried and

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weighed and then subjected to elemental, FT-IR analyses and GC-MS chromatography.

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Char product derived from thermal pyrolysis at optimum temperature was further

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characterized using SEM techniques and N2 adsorption-desorption isotherms.

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3. Results and discussion 3.1. Characterization of raw material

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The proximate, ultimate and structural analysis of the banana peel was carried out and results

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were presented in Table 1. The ultimate analysis determined the presence of carbon (39.95%),

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oxygen (52.28%), hydrogen (7.06%), and nitrogen (0.71%) in the banana peel. The results

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confirmed that banana peel restrained maximum volatile matters (62.62%) ash (13.36) and

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fixed carbon (14.53) with lower % of moisture (9.49) contents. More volatile matter generally

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release more liquid and gas fuel during the pyrolysis process. The presence of volatiles

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determines the combustibility of biomass, the existence of extractives provides a higher

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impact on the heating value as well as the yield of pyrolytic liquid. The extractive content was

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determined by using toluene and ethanol as a solvent in a Soxhlet apparatus. The results also

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indicated that maximum 11.71% of extractives were present in the banana peel. It can be seen

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from the elemental analysis that the sum of C, H, and O values of the banana peel was about

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99.3% wt and calorific value of banana peel was calculated as 14.27 MJ/kg [32, 33].

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Table 1. Proximate, structural and ultimate analyses (wt.%) of banana peel. Proximate analysis (%) 9.49

Volatile

62.62

Fixed carbon

14.53

Ash

13.36

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Moisture

Structural analysis (%)

11.71

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Extractives Hemmicellulose

10.50

24.28

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40.15

Holoselüloz

34.20

Oil

8.65

Ultimate analysis (%, dry basis)

39.95

Hydrogen

7.06

Nitrogen

0.71

Oxygen (by difference)

52.28

H/C

2.12

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Carbon

O/C

0.98

HHV(MJ/kg)*

14.27

*Calculated using Dulong Formula.

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Banana peel was also characterized on the basis of thermal degradation temperature. The

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degradation temperature depends on the composition where cellulose, hemicellulose and

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lignin play a vital role [34]. Cellulose and hemicellulose decompositions are known to cause

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ACCEPTED MANUSCRIPT the formation of organic volatiles, where lignin devolatilization increases the formation of

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char. Decomposition of lignin happened through the temperature in the range of 200–500°C,

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however, the essential weight loss took place at higher temperatures [35]. The degradation

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profile was observed by TGA/DTG analysis and depicted in Fig. 1. The TGA of banana peel

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showed an initial weight loss between 100 and 200°C. This could have been related to the

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elimination of physically absorbed water related to the moisture of the biomass.

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Devolatilization started at about 200°C and removal of volatiles was finished at about 500°C.

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After 550°C, there was no visible loss of weight essentially. This stated that the main

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reactions like decarboxylation, depolymerization, and cracking took place over the

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temperature range. The lower temperature of DTG peak of banana peel mainly represented

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the moisture, while the higher temperature of DTG peak represented the degradation of

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hemicellulose and cellulose. According to results, it could be stated that since most of the

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weight loss, due to volatilization of hydrocarbons, happened at temperatures lower than 550

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°C, choosing optimum pyrolysis temperature as 550 °C was suitable to maximize of bio-oil

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[36-40].

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wt. %

80 60 40 20 0

0

200

400 600 800 Temperature (°C)

%/min

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1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3 -3.5 -4 1000

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Fig. 1. Thermogravimetric analysis of banana peel

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group compositional analysis of banana peel. The band at 3292 cm-1 was assignable to (O–H)

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vibrations in hydroxyl groups indicating alcohols, phenols or carboxylic acids. According to

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the spectra, the bands between 2918 and 2762 cm-1 (asymmetric or symmetric aliphatic C–H

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stretching vibration) show the aliphaticity of the bio-oils. The existence of the olefinic

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compounds was confirmed by the band between 1733-1595 cm-1, denoted C=O stretching

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vibration.

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T%

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1200

1000

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600

400

-1

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Fig. 2. FT-IR spectrum of banana peel

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The SEM photograph of the banana peel taken at 1000x magnification was given in Fig. 3.

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SEM image showed layered-like structures whilst recess ledge particle was available. The

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non-porous structure of the biomass resulted in the low specific surface area. EDX results

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gave us information about the inorganic composition of the biomass. However biomass has

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heterogeneous structure, the results could be different. Considering the EDX results, it could

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be seen that the structure of banana peel consisted of carbon (52.57%) and oxygen (43.08%)

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essentially. Besides, potassium (3.31%) was found in the structure. 10

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Fig. 3. SEM image of the banana peel obtained at 1000x magnification. 3.2. Catalyst characterization

The properties of the ordered mesoporous structure of SBA-15 and Al-SBA-15 catalysts were

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attained by XRD analysis, N2-adsorption measurements and SEM analysis.

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3.2.1. XRD

Fig. 4 depicted the X-ray diffractograms, corresponding to samples of SBA-15 and Al-SBA-

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15 at low angles due to the mesoporous hexagonal structure. SEM images of the catalysts

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were given in Fig. 5. The XRD pattern of SBA-15 showed three diffraction peaks indexed to

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(100), (110) and (200) which were characteristics of the ordered hexagonal mesostructures of

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the SBA-15 [40-42]. It is obvious that Al-species forms other structure different to the SBA-

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15. SBA-15 is formed by channels of worms, while Aluminum forms different structure.

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When aluminum incorporated SBA-15, d001 diffraction peak observed more intense. This

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situation can be related to the evidence the transformation of the metallic precursors into the

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corresponding oxides after the calcination stage. This result suggests strengthening of ordered

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mesoporosity in the Al-SBA-15 when the aluminum is envolved.

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3.2.2. BET

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The mesoporous structures of SBA-15 and Al- SBA-15 catalysts were verified by the results

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of N2 adsorption/desorption and pore size distributions given in Fig. 6. There was a sharp

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increase in uptake volume in the P/P0 = 0.5–0.85 range indicating IV isotherms and typical of

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and Al-SBA-15 catalysts were well and uniformly distributed about at 5 nm sizes. 1.4 1.2 1 0.8 0.6 0.4 0.2 0 50 Pore diameter (nm)

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mesoporous structures with well-defined pores [42-44]. The pores in structures of SBA-15

Pore volume (cm3/g.nm)

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0

0

50 Pore diameter (nm)

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a

b

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Fig. 6. Adsorption–desorption isotherms and pore size distribution of a) SBA-15 and b)AlSBA-15.

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was a decrease in pore volume and specific surface area. The reduction in the specific surface

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area could be changed to the density rise related to metal inclusion in SBA-15, and the

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reduction in pore volume to metal presence inside the mesoporous channels [45-47].

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Table 2. Specific surface area and pore structure of the catalysts. Average pore diameter (nm)

SBA-15

634.30

5.67

Al/SBA 15

560.85

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Total pore volume (cm³/g)

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SBET (m2/g)

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Al/SBA-15

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SBA-15

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1

2 3 Bragg Angle, 2Θ

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Fig. 4. X-ray diffractions of SBA-15 and Al-SBA-15.

3.2.3. SEM

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According to SEM images (Fig. 5); the pore system, hexagonally ordered structure and rod-

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like particles of SBA-15 samples were observed. They exhibited irregular spherical shape.

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When aluminium loaded, hexagonally ordered structure and rod-like particles were preserved. 13

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Fig. 5. SEM images of a) SBA-15 obtained (1000x) and b) Al/SBA-15 (30000x)

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3.2.4.

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Al-NMR

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NMR study was performed to determine the location of the heteroatom in the framework. The

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specific coordinated states of aluminum were clearly revealed through the 27Al-NMR spectra

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in Fig. 7 for the Al-SBA-15. Two resonance signals are observed. The intense resonance at 62

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ppm can be assigned to tetrahedral framework aluminium (AlO4 structural unit) formed in the

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mesoporous wall of the materials. The other signal at 6 ppm is probably due to octahedral

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aluminium (AlO6 structural unit) caused by the sample calcination [48]. Thus, it could be

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ACCEPTED MANUSCRIPT concluded that alumina was deposited on the silica support mainly in the form of octahedral

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Al(VI) and tetrahedral Al(IV).

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δ (ppm) Fig. 7. Al NMR spectra of Al-SBA-15 material 27

3.2.5. NH3-TPD

The temperature-programmed desorption of ammonia (NH3-TPD) provides information on

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the total acidity of the solids, since ammonia is a suitable probe molecule due to its small size

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and high basicity, which allows it to interact with the majority of acid sites. Thus, the amount

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of ammonia desorbed at some characteristic temperatures is taken as a measurement of the

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number of acid centers, while the temperature range in which the ammonia is desorbed is an

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indicator of the strength of the acid sites [49-51]. The integration of the curves representing

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the amount of NH3 desorbed as a function of the temperature, using different temperature

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ranges, provides us with the histograms displayed in Fig. 8. Generally, the desorption peaks at

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temperatures of 200-400°C correspond to the medium acidity sites, and peaks at lower (25-

15

200°C) and higher temperatures (>400°C) indicate the weak and strong acid sites,

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respectively [51]. The NH3-TPD curve showed three ammonia desorption peaks at 100, 200

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and 680°C in the temperature range of 100-700°C corresponding to the weak acid site,

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medium acid sites, and strong acid sites, respectively. The NH3-TPD result showed that Al-

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SBA-15 had both weak and strong acid sites, which could be assigned to Lewis and Brønsted

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acid sites, respectively.

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0.8

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0.6 0.4 0.2 0 0

100

200

400

500

600

700

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Fig. 8. NH3-TPD curve of Al-SBA-15.

3.3. Effect of temperature on product yield

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Temperature (°C)

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Temperature is known the most important factor for pyrolysis of lignocellulosic biomass and

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it affects the product distribution comprehensively. Fig. 9a showed the product yields for the

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pyrolysis of banana peel in connection with pyrolysis temperatures of 400, 500, 550 or 700 °C

10

with a constant heating rate (7°C/min). As it could be seen, the pyrolysis temperature

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influenced bio-oil and gas yields, especially. When the bio-oil yield was 24.94% at 400 °C, it

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performed to go through a maximum of 28.03% at 550°C. Then at the final temperature of

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700°C, the bio-oil yield reduced to 20.19%. Further temperature increase resulted in bio-oil

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liquid yields due to cracking and gasification reactions. In addition, some researchers also

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stated optimum temperature of pyrolysis for maximizing the bio-oil yield lay between 500 and

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ACCEPTED MANUSCRIPT 600 °C [35, 52-55]. Therefore, 550 °C is the optimum temperature to reach maximum bio-oil

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yields in our studied temperature range. 40

Bio-oil %

Water %

Gas %

a

20

10

60

Bio-oil %

50

Char %

b

40 30 20 10 0 0

4

550

700

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Product Distribution (%)

3

450 500 Temperature (°C)

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30

400

Water %

5 10 15 Catalyst/Biomass Ratio(%)

Gas %

20

Fig. 9. Products yield distributions of a) thermal and b) catalytic experiments.

TE D

5

Char %

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Product Distribution(%)

1

6

In Fig. 9a, altering the pyrolysis temperature, there was a little effect on water and char yields.

8

The rise in gas yield was suggested to be related to secondary reactions of the pyrolysis

9

vapors. Besides, at higher temperatures, the secondary decomposition of the char may also

10

provide some non-condensable gaseous products, which also contributes to the increase in gas

11

yield [56]. Definitely, when the temperatures of primary degradation are increased or the

12

residence times of primary vapors inside the cracked particle have to stay shorter, the char

13

yields decline [33, 52].

AC C

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14 15 16

17

ACCEPTED MANUSCRIPT 1

3.4. Effect of catalysts on product yield In banana peel, oxygen represents 52.28% of the tomato waste. Dehydration and

3

decarboxylation are two main reactions that can eliminate oxygen in the form of H2O and

4

CO2. Decarboxylation which releases CO2 and reduces the chain size can be described as the

5

long chain carboxylic acids’ thermal cracking. Using catalyst has been developed as an

6

effective approach to improve deoxygenation reactions, thus improving the bio-oil quality.

7

When catalysts are used, volatiles coming from pyrolysis and liquefaction processes are

8

exposed to various reactions like dehydration, deoxygenation, decarboxylation, and

9

decarbonylation which were the results hydrocarbons production [57, 58].

M AN U

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2

In this part, catalytic pyrolysis experiments were carried out at the optimum pyrolysis

11

temperature of 550ºC to obtain maximum bio-oil yields with a constant heating rate of 7°C

12

min−1 in the presence of Al-SBA-15 (catalyst/biomass ratio of either 5, 10, 15 or 20 by

13

weight). Experimental results were shown in Fig. 9b. As seen from Fig. 9b, the maximum

14

liquid yield obtained as 18.64% with catalyst/biomass blending ratio of 15 wt% among the

15

catalytic pyrolysis results, while the highest gas yield was achieved with catalyst/biomass

16

blending ratio of 20 as 51.72%. When blending ratio was changed from 5 to 20% wt., bio-oil

17

yields were decreased up to 10.14%. Water contents were improved due to the dehydration

18

reactions which took place in acid sites in large pores of Al-SBA-15. The decline in bio-oil

19

yields and a rise in gas yields at higher catalyst loadings were related to the formation of

20

secondary cracking reactions of the pyrolysis vapors. In addition, secondary decomposition of

21

the bio-chars resulted in the production of non-condensable gaseous yields, helping to a rise in

22

gas yields at higher catalyst loadings.

23

Lee et. al studied pyrolysis and co-pyrolysis of polypropylene and Laminaria japonica using

24

mesoporous Al-SBA-15 catalyst [59]. According to them, when only biomass was pyrolyzed,

25

catalytic conversion slightly increased the gas and water and decreased the bio-oil yield.

AC C

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18

ACCEPTED MANUSCRIPT 1

These findings were valid for our work as well. The results showed that the amount of catalyst

2

was affected not only char and bio-oil yields but also the structure of bio-oils. According to

3

this information, GC-MS spectrum of the catalytic bio-oils was further investigated.

4

3.5. Catalyst effectiveness

RI PT

5

Adjaye et al. were used catalyst effectiveness term in order to compare the used catalysts and

7

establish their effectiveness based on bio-oil production. The catalyst effectiveness term is

8

described as:

SC

6

9

M AN U


 =     where Yield is expressed by:

 . % =

and Selectivity is defined as:

TE D

10

 −    100    

  !  "  . % #$   !  "  . %

EP

=

Where desired product is bio-oil fraction and undesired product is sum of char, gaseous and

12

aqueous fractions [60].

13

The catalyst effectiveness was given in Fig. 10 for comparison. It can be seen that

14

catalyst/biomass ratio of 15% by weight was the most effective in bio-oil production while

15

catalyst/biomass ratio of 20% was the least effective due to losing its activity. Besides, 10%

16

and 15% were quite effective with effectiveness of 3.2 and 3.7, respectively. The results

17

indicate that in order to optimize the yield, the pyrolysis should be carried out using 15%

18

catalyst/biomass ratio.

AC C

11

19

5 4 3 2 1 0 5%

10% 15% Catalyst/Biomass Ratio

20%

1

4

SC

3

Fig. 10. Comparison of the effectiveness of different catalyst/biomass ratios. 3.6. Characterization of bio-oils

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2

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Catalyst effectiveness (%)

ACCEPTED MANUSCRIPT

3.6.1. Elemental analysis of bio-oils

Elemental analysis results of bio-oils were shown in Table 3. Elemental analysis presented

6

that the catalyst helped to reduction the amount of oxygen which was found in the bio-oil

7

fraction and rise the carbon and hydrogen content. The carbon content of bio-oils was

8

increased up to 15% catalyst blending ratio, then decreased when 20% blending ratio used.

9

An evaluation of H/C ratios with conventional fuels showed that the H/C ratios of the bio-oils

11

lie among those of heavy and light petroleum products [32].

EP

10

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5

Table 3. Physical properties of the catalytic bio-oils.

AC C

Al/SBA-15

5%

10%

15%

20%

C(wt.%)

54.67 79.33 83.65 82.03

H(wt.%)

7.90

10.8

8.84

8.80

N(wt.%)

2.64

3.54

3.43

5.41

O*(wt.%)

34.79

6.33

4.08

3.76

H/C(wt.%)

1.72

1.63

1.27

1.29

O/C(wt.%)

0.47

0.06

0.04

0.03

HHV**(Mj/kg) 23.61 41.27 40.31 39.76 12 13

*By difference. **Calculated using Dulong Formula. 20

ACCEPTED MANUSCRIPT The higher heating value of the banana peel was calculated as 14.27 MJ/kg which is

2

noteworthy but the catalysts further improved the heating value of bio-oils into a range of

3

23.61–41.27 MJ/kg which was comparable to other conventional fuels such as petroleum (43

4

MJ/kg), kerosene (41 MJ/kg), or LPG (45.75 MJ/kg) [61]. This increase could be attributed to

5

the reduction in oxygen [62-64].

6

3.6.2. FT-IR analysis of bio-oils

7

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1

Bio-oils which were obtained from pyrolysis of biomass have a very wide range of complex

9

organic chemicals. FT-IR spectra of the bio-oils were given in Fig. 11 and they were found

M AN U

SC

8

quite similar to each other.

11

The O-H stretching vibrations between 3200 and 3600 cm-1 indicate the existence of phenols

12

and alcohols. The presence of alkanes was shown by the peak of C-H vibrations between

13

3000 and 2800 cm-1 and by 1490–1325 bands related to the C-H bending. The C=O stretching

14

vibrations with absorbance peaks between 1650 and 1775 cm−1 represented the presence of

15

aldehydes, ketones and carboxylic acids. The presence of O-H and C=O stretching vibrations

16

together indicated the presence of carboxylic acids and derivatives. The absorbance peaks

17

between 1680 and 1575 cm-1 indicated the incidence of alkanes and nitrogenated compounds

18

The peaks between 1575 and 1675 cm−1 represented C=C stretching vibrations which

19

indicated the existence of alkenes and aromatics [64]. The peaks between 1300 and 950 cm-1

20

were indicated to the occurrence of primary, secondary and tertiary alcohols and phenols

21

displaying the C=O stretching and O-H bending. The presence of polycyclic, single, and

22

substituted aromatic groups could be seen from the absorbance peaks between 900 and 650

23

cm-1.

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24

21

ACCEPTED MANUSCRIPT

Thermal

T%

RI PT

5% Al-SBA-15

10% AlSBA-15

SC

15% AlSBA-15

M AN U

20% AlSBA-15

4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900

800

700

600

500

-1

Wavenumber (cm )

1

4

TE D

3

Fig 11. FT-IR spectrum of bio-oils obtained at 550°C.

3.6.3. GC-MS analysis of bio-oils

EP

2

Adjaye and Bakshi had investigated the reaction pathways for decomposition of bio-oil in

6

detail. According to their studies, the bio-oil was converted to tar, char, heavy organics, light

7

organics, coke and hydrocarbons over each catalyst, first, by thermal effects. Then, it is

8

considered that these products decomposed secondly by thermocatalytic effects. The products

9

obtained as a result were similar in nature thus it is accepted that thermal effects on the bio-oil

10

were similar for each catalyst. On the other hand, the thermocatalytic effect resulted in

11

different product distributions on the bio-oil and changed with the catalyst [60].

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22

400

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ACCEPTED MANUSCRIPT

1 2

Fig. 12. The reaction pathway developed for acidic catalyst (like zeolite) [60].

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3

Mainly, three different reaction pathways were recommended for the conversion of bio-oil

5

based on catalyst acidity, crystallinity and non-crystallinity. The reaction pathway developed

6

for acidic catalyst (like zeolite) was shown in Fig. 12. In this pathway, the light organics

7

which comprises of various acids and esters, ketones, alcohols, ethers and phenols undertook

8

a number of reactions like deoxygenated and cracked within the catalyst bed (step 6). Water

9

and carbon oxides were produced by the deoxygenation. Dehydration was assumed as the

10

main deoxygenation reaction. Decarboxylation and decarbonylation which occured during the

11

secondary cracking took easily place over acidic catalysts. Alkanes and carbon dioxides were

12

formed during decarboxylation. Alkenes, water and carbon monoxides formed during

13

decarbonylation as shown by the following equations:

AC C

EP

4

% −
&&' → % − ' +
&*  + ,+$

23

ACCEPTED MANUSCRIPT % −
&&' → %- − ' +
& + '* &  + ,$+$ where R denotes saturated alkyl group and R1 denotes unsaturated alkyl group [60, 65]. Al-

2

SBA-15 is known as an acid catalyst [66]. According to our experimental results, the light

3

organics were effectively converted over acidic Al-SBA-15 catalyst to hydrocarbons

4

compared to thermal pyrolysis results which were compatible with literature [60, 65].

5

Fig. 13 presents the main product distribution of the bio-oils obtained by thermal and catalytic

6

pyrolysis experiments. As established in the literature, acids, PAHs, esters and ethers are the

7

undesired products from pyrolysis, whereas phenols, hydrocarbons, furans, and alcohols are

8

desirable for fuel and valuable chemical production [67]. Compounds that could not be

9

identified by the GC-MS system were classified as unidentified. Impregnation of Aluminum

10

metal onto mesoporous SBA-15 persuaded a significantly rise in the relative area of phenolic

11

compounds. The presence of phenols was also apparent from FT-IR results. Using 20 wt%

12

Al-SBA-15 catalyst which can be considered to be improved dehydrogenation and

13

deoxygenation reactions on its surface is also effective to formation of the highest amount of

14

phenols and alcohols. Because of being industrially important, phenolic compounds could be

15

utilized to produce solvents or phenolic-based adhesives like novolac and resole resins [67].

SC

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17

AC C

16

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1

24

ACCEPTED MANUSCRIPT Phenolics

30

Alcohols Furans

20

Aldehyde 15 Hydrocarbons 10 5 0

Thermal

5 wt.% AlSBA-15

10 wt.% AlSBA-15

15 wt.% AlSBA-15

20 wt.% AlSBA-15

SC

1

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Chromatogram area, %

25

Fig. 13. Chemical composition of thermal and catalytic pyrolysis bio-oils (Data adapted from GC-MS results).

4

Typically, bio-oil is known to have acidic structures due to the decomposition of biomass

5

[64]. Because of this, this process has a disadvantage, which is the formation of oxygenated

6

compounds that make the product acid, which can, as a result, damage the engine [65].

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2 3

8

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7

3.6.4. Column chromatography of bio-oils The bio-oils, produced by either thermal and 15% catalyst blending ratio used catalytic

10

pyrolysis at optimum temperature were extremely oxygenated complex mixtures of hundreds

11

of different constituents that could be clustered into many chemical classes. The chemical

12

class composition of the bio-oils was detected by liquid column chromatographic

13

fractionation [69]. The results of the column chromatography of the bio-oils were given in

14

Table 4. Bio-oils obtained from thermal and catalytic pyrolysis involved 77.27 and 78.19% of

15

an n-pentane soluble fraction, respectively and the rests were asphaltenes. Bio-oil obtained by

16

thermal pyrolysis consists of 38.38% aliphatics, 34.62% aromatics and 27% polar compounds,

17

whereas bio-oil obtained by catalytic pyrolysis consists of 55.05% aliphatics, 25.11%

18

aromatics and 19.84% polar compounds. For both bio-oils, the aliphatic and aromatic sub-

AC C

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25

ACCEPTED MANUSCRIPT 1

fractions fell between ∼73-80 % and appeared to be more applicable for the production of

2

hydrocarbons and chemicals [36, 64]. Table 4. Results of column chromatography. N-pentane Non-solubles (%) Asphaltenes

Aliphatic Aromatics Polars 77.27

22.63

38.38

Catalytic pyrolysis’ bio-oil

21.81

55.05

Column chromatography FT-IR

27.00 19.84

M AN U

3.6.4.1.

34.62 78.19 25.11

SC

Non-catalytic pyrolysis’ biooil

4 5

N-pentane Solubles (%)

RI PT

3

FT-IR spectra of the asphaltenes, aliphatic, aromatic and polar sub-fractions from thermal and

7

catalytic runs were given in Fig. 14. Very similar FT-IR spectra were obtained for same

8

fractions of thermal and catalytic bio-oils. In both figures except n-pentane fractions, the O–H

9

stretching vibrations between 3150 and 3400 cm-1 directed the presence of phenols and

10

alcohols. In only methanol fractions, N-H groups about 3300-3200 cm-1 were detected. The

11

presence of aliphatic CH2 ve CH3 groups was indicated by the peak of C-H vibrant symmetric

12

C-H stretching vibration ions between 2900 and 2850 cm-1 for all fractions. Stretching

13

vibration of ester carbonyl was only observed in toluene fractions at 1700 cm-1. The aromatic

14

C=C stretching vibrations with absorbance peaks represented between 1669 and 1510 cm−1.

15

The absorbance peak observed at 1459 cm-1 indicated the presence of asymmetric C-H

16

bending vibration (aliphatic CH3 groups) and scissoring vibration (aliphatic CH2 groups).

17

symmetric C-H bending vibration (aliphatic CH3 groups) at 1370 cm-1 were detected in all

18

fractions except asphaltenes. Ether (C-O) stretching vibration at 1200 cm-1 was observed in

19

only methanol fractions. Bending stretching vibration of carbonyl groups between 1125-1199

20

cm-1, in-plane C-H stretching vibration at 1036 cm-1 were found for only toluene fractions.

21

The region between 700 and 900 cm-1 comprises many bands associated with the aromatic,

AC C

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6

26

ACCEPTED MANUSCRIPT out of plane C–H bending for all fractions. The FT-IR spectrum of pentane sub-fractions

2

indicated the higher content of functional groups of hydrocarbons proved the presence of

3

hydrocarbons. The band in the FT-IR spectrum of toluene sub-fraction indicated the higher

4

content of CH3 groups as aliphatic chains. For both methanol fractions, the absorbance at 750

5

cm-1 indicated the occurrence of four C–H vibrations located near the aromatic ring.

RI PT

1

6

SC

7

thermal

M AN U

T%

TE D

15% AlSBA-15

4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900

800

700

600

500

400

-1

EP

Wavenumber (cm )

AC C

8

a

27

ACCEPTED MANUSCRIPT thermal

b

T%

SC

RI PT

15% AlSBA-15

4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900

800

700

600

500

400

-1

Wavenumber (cm )

M AN U

1

T%

AC C

EP

15% AlSBA-15

c

TE D

thermal

4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900

2

800

700

600

500

-1

Wavenumber (cm )

28

400

ACCEPTED MANUSCRIPT

thermal

d

RI PT

T%

SC

15% AlSBA-15

4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900

800

700

600

500

400

-1

Wavenumber (cm )

1

Fig. 14. FT-IR spectrum of a) asphaltenes, b) n-pentane, c)toluene and d)methanol fractions

3

obtained at 550°C from (a) thermal and used (b) 15% Al-SBA-15.

M AN U

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4 5

3.6.4.2.

Column chromatography GC-MS

GC-MS analyses of the aliphatic sub-fractions of n-pentane soluble were connected with the

7

pyrolysis oils achieved from thermal and catalytic pyrolysis experiments. The objective was

8

to establish the nature and type of compounds of aliphatic sub-fractions, in order to state the

9

possible ways of reusing or treating and reusing them. Table 5 showed the GC-MS

10

chromatogram of n-pentane soluble from banana peel obtained thermal and catalytic

11

pyrolysis, respectively.

13

EP

AC C

12

TE D

6

14 15 16 17

29

ACCEPTED MANUSCRIPT Table 5. Identification and yield (area%) of n-pentane sub-fraction. Area (%)

Product

Thermal Catalytic

Undecane

1.49

-

Tetradecane

6.10

5.30

1-Heptadecene

4.17

4.09

Hexadecane

19.15

1-Nonadecene

6.19

n-Decylbenzene

4.41

5.70

-

2.61

10.33

23.06

M AN U

Hexatriacontane

5.44

SC

2-Hexadecene, 3,7,11,15-tetramethyl-

2.11

-

1.17

3.20

-

1.60

68.10

66.20

n-Alkenes

12.47

10.69

Branched

19.43

15.59

Tetrapentacosan 1-Nonadecene

TE D

n-Alkanes

2

17.24

0.59

Hexadecane, 2,6,10,14-tetramethyl-

1-Eicosene

RI PT

1

The aliphatic fractions consisted of n-alkanes, alkenes and hydrocarbons branched. While

4

considering the results of GC/MS detailed analysis, the total amounts of n-alkanes, n-alkenes

5

and branched hydrocarbons were 68.10%, 12.47%, and 19.43% for thermal and 66.20%,

6

10.69%, and 15.59% for catalytic pyrolysis, respectively. Using Al-SBA-15 as catalysts was

7

favoured branched hydrocarbons and decreased n-alkenes and n-alkenes.

AC C

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3

8 9

3.7. Characterization of char

10

SEM technique and N2 adsorption-desorption isotherms were utilised to characterize the

11

surface of materials. The surface morphology of the bio-char obtained at 550°C was given in 30

ACCEPTED MANUSCRIPT Fig. 15. Due to high temperature during thermal conversion, new pores led to increase in the

2

surface area of banana peel after pyrolysis as a result of decomposition. This situation is due

3

to the fast volatile coming from pyrolysis produced substantial interior overpressure effect

4

and the merging of the small pores. This occurred large interior cavities and more open

5

structure [70, 71]. According to EDX analysis, carbon (65.83%) which was the main element

6

of the char beside oxygen (21.07%), and potassium(13.09%) were detected inside the

7

structure.

b

M AN U

a

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1

25 μm 8

10

Fig. 15. SEM images of thermal bio-char obtained at a) 2000x, b) 10000x magnifications.

TE D

9

5 μm

The BET surface area and pore structure of bio-char had a significant impact on its adsorption

12

performance [23, 72]. The mesoporosity of bio-chars was verified by the BET surface area

13

and the average pore diameter. BET surface of bio-char was obtained as 3.65 m2/g. Moreover,

14

the average pore diameter of the bio-char was established as 25.40 nm, indicated that the

15

obtained activated carbon was in the mesopores region due to the International Union of Pure

16

and Applied Chemistry (IUPAC). Pores are categorized as micropores (<2 nm diameter),

17

mesopores (2–50 nm diameter) and macropores (>50 nm diameter) [73].

AC C

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18

19

31

ACCEPTED MANUSCRIPT 4. Future perspectives

2

Fundamental research about pyrolysis of biomass is carried out not only to maximize the bio-

3

oil yield but also to improve the quality of the bio-oil in recent years. The major limitation in

4

this area is the developing new catalysts to enhance both yield and quality besides being

5

stable after many uses. The earlier works were focused on developing cheaper catalysts [2, 10,

6

11, 13, 40, 59, 69]. Despite high/low bio-oil yields obtained by using cheaper metal catalysts,

7

these catalytic systems are not suitable for large scale bio-oil production. Besides, more

8

experiments, observations, calculations for reuse and scale-up are essentially required. The

9

Life cycle assessment (LCA) is a popular and useful approach as per sustainability of biomass

10

conversion. This new approach also precludes assessment of all inputs and outputs of

11

production system (mainly processing, manufacturing, distribution, use and maintenance, and

12

disposal or recycling). In addition, the raw biomass, catalysts, chemical procedure involved in

13

biomass conversion barely follows the approach. In consideration of this application, its scope

14

in near future and economical value has made catalyst synthesis an inquisitory tool in today’s

15

biofuel based research network [74].

16

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1

5. Conclusions

18

Bio-oil can be utilized as one of the blending component with conventional fuels while it is

19

possible to benefit for chemical production. This study involved both the influence of

20

temperature and the usage of Al-SBA-15 catalyst with different catalyst/biomass blending

21

ratios (5, 10, 15, 20 %wt.) to improve the quality of bio-oils achieved from pyrolysis of

22

banana peels. The highest yield of bio-oil was found as 28.03% at the temperature of 550°C.

23

The catalyst lead only enhancement of bio-oil production in terms of quality, not quantity.

24

Besides, very similar product yields were achieved for all catalyst/biomass blending ratios.

AC C

17

32

ACCEPTED MANUSCRIPT The Al-SBA-15 catalyst enhanced gasification. Use of catalyst induced a rise in gas yields

2

and a decline in liquid product yields. The maximum bio-oil yield of 18.64% was achieved

3

with 15% blending ratio whereas the lowest bio-oil yield was achieved with 20% blending

4

ratio. It increased the aliphatic compounds in the bio-oil which was supported by column

5

chromatography results. The experiments presented that the pyrolysis temperature and

6

catalyst presence had vital roles on the bio-oil yield and composition. Consequently, catalyst

7

choice and evaluation for higher product selectivity were essential in industrial applications.

8

The study of catalyst application for the pyrolysis of oil is very important for the future of

9

biorefinery. In this sense, new research in the area is necessary and welcome.

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1

10

Acknowledgments

12

The authors appreciate the financial support from the Scientific Research Projects

13

Commissions of Bilecik Şeyh Edebali University [grant numbers 2014-01.BİL.03-01].

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16

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EP

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14

Y. H. Chan, K. V. Dang, S. Yusup, M. T. Lim, A. M. Zain, Y. Uemura, Studies on

catalytic pyrolysis of empty fruit bunch (EFB) using Taguchi’s L9 Orthogonal Array,

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EP

17

the

Energy

Institute 87.3

(2014):

227-234.

AC C

of

20

10. M.H. Nilsen, E. Antonakou, A. Bouzga, A. Lappas, K. Mathisen, M. Stöcker,

21

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ACCEPTED MANUSCRIPT Highlights The thermal and catalytic pyrolysis of banana peel was perfomed.

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Al- SBA-15 was prepared by the incipient wet impregnation of SBA-15.

•

The mesoporous material Al-SBA-15 showed the typical hexagonal arrangement of

RI PT

•

SBA-15, large surface area and Lewis and Brönsted acid sites which were verified via SEM, XRD, BET and NH3-TPD. 27

Al-NMR spectra showed that alumina was deposited on the silica support mainly in

SC

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the form of octahedral Al(VI) and tetrahedral Al(IV).

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and quality of bio-oils.

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Catalyst/biomass blending ratio affected the yields of products and the composition

AC C

•