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Production of bio-oil from a Botryococcus Braunii residue
Accepted Manuscript Title: Production of bio-oil from a Botryococcus Braunii residue Author: Kazuhisa Murata Yanyong Liu Makoto M Watanabe Megumu Inaba PII: DOI: Reference:
S0165-2370(15)30050-4 http://dx.doi.org/doi:10.1016/j.jaap.2015.05.017 JAAP 3501
To appear in:
J. Anal. Appl. Pyrolysis
Received date: Revised date: Accepted date:
15-3-2015 25-5-2015 26-5-2015
Please cite this article as: Kazuhisa Murata, Yanyong Liu, Makoto M Watanabe, Megumu Inaba, Production of bio-oil from a Botryococcus Braunii residue, Journal of Analytical and Applied Pyrolysis http://dx.doi.org/10.1016/j.jaap.2015.05.017 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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Production of Bio-Oil from a Botryococcus Braunii Residue
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Kazuhisa Murata*, Yanyong Liu, Makoto M Watanabe2ǂ, Megumu Inaba
Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8565, Japan.
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ǂ Faculty
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Ibaraki 305-8572, Japan
of Life & Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba,
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KEYWORDS. Pyrolysis; Botryococcus Braunii residue; Liquid hydrocarbons; Hydrothermal
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liquefaction
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*Corresponding author. Tel.: +81 298614776. E-mail address: [email protected] (K.Murata). Highlights
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Renewable green bio-oil can be produced by pyrolysis of Botryococcus (B.) Braunii residue after B. Braunii oil extraction. Hydrocarbon selectivities accounted for 85–90% and the organic liquid yield was found to be above 30%. Hydrothermal liquefaction of the B. Braunii residue yielded hydrocarbons of 36.8%.
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ABSTRACT: The aim of the present study is to obtain bio-oil from Botyococcus (B.) Braunii
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residue after B. Braunii oil (Bot-oil) extraction. For this, one of a probable method is fast
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pyrolysis, in which the effect of zeolite catalyst was examined. From Py-GC/MS analyses at 550
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ºC using H-ZSM-5 (80) (Z80) catalyst, total selectivities of aromatic and aliphatic hydrocarbons
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accounted for 88.6%, being much higher than 35.2% without catalyst. At fast pyrolysis using
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reactor, the organic liquid product (bio-oil) yield was found to be above 30%, approximately 3
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times higher than that of jatropha residue. The higher heating value (HHV) of the liquid product
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was approximately 35-37 MJ/kg, which was close to a HHV value of crude triglyceride. The
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highest overall hydrocarbon yield was 24.58 % at 600 ºC. In order to briefly compare with fast
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pyrolysis, hydrothermal liquefaction (HTL) of the residues under H2 pressure conditions was
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tried using PtRe/SiO2-Al2O3 catalyst, which has been extremely effective for hydrocracking of B.
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Braunii oil into aviation-range fuel. In the HTL of the B.Braunii residue at 400 ºC, the
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hydrocarbon yield was 36.8 % which was a little higher yield than that from pyrolysis. The n-
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alkanes predominantly formed over aromatic hydrocarbons, due to lower temperature of 400 ºC
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and the catalyst different from pyrolysis. Postulated scheme was presented through cracking,
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hydrodeoxygenation and dehydroaromatization..
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1. INTRODUCTION
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Microalgae are among the aquatic biomass feedstocks that are considered to be one of the best
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sources of liquid fuels [1]. Recently, bio-harvesting and pyrolysis of Botryococcus braunii have
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been successfully investigated [2]. They can accumulate lipids that can be converted into
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biofuels. After extraction of algae oil, there remain algae residues with a high water content. In
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order to reduce process cost of algae-based biofuel production, our present interest is to produce
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another biofuels from these residues with an energy-saving consideration. Generally,
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thermochemical conversions such as fast pyrolysis [3 ] and hydrothermal liquefaction (HTL)[4]
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have been suggested for production of biofuel oil from algae [5,6]. Possibly, these methods can
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be acceptable for wet residues with moderate energy consumtion. These processes have the great
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advantage of converting the whole microalgae residue. Bio-oils derived from biomass have
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energy densities higher than the initial biomass feedstock. Moreover it can be also upgraded in
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order to obtain biofuels such as bio-diesel or bio-kerosene. Bio-oil production from fast pyrolysis
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has been investigated for many microalgae strains [7-11] The pyrolysis bio-oil quality depends
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greatly on the microalgae strains and the operating onditions. For example, Harman et al. [8] and
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Gong et al. [10] produced fast pyrolysis bio-oils from Scenedesmus sp., Chlorella vulgaris and
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Dunaliella salina characterized by a higher heating value (HHV) relatively low (18-25 MJ kg-1,
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as a comparison the HHV of diesel is 48 MJ kg-1). However despite bio-oils production with low
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HHV, Belotti et al. [11] and Miao and Wu [9] showed that fast pyrolysis (heating rate = 600 K s1
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) produced more energy from bio-oil combustion than the energy required for thermochemical
conversion.
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Although pyrolysis has been extensively reported for a wide variety of lignocellulosic biomass
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including different species of wood [12], there is not much information about laboratory scale
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pyrolysis of algal biomass except the ones on fast pyrolysis of microalgae Chlorella
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protothecoides and Microcystis aeruginosa [13] and the slow pyrolysis of Botyococcus Braunii
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residue [14]. Bio-oil yields of 17.5% and 23.7% were reported from the fast pyrolysis of C.
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protothecoides and M. aeruginosa, respectively. The fuel properties of bio-oils from algae in the
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above studies were found superior to that obtained from wood.
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Hydrothermal liquefaction (HTL) of microalgae biomass has been widely reported to result in
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higher bio-oil yields [15-17]. HTL is a potential conversion routes for biomass with a high water
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content [18]. In this process, water has both the role of solvent and of reactant. HTL operating
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conditions bring the water near its critical point (Tc = 374 ºC and Pc = 22.1 MPa) leading to a
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low dielectric constant and an increased solubility of organic molecules [19]. Toor et al.
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described the basic reaction mechanism of biomass hydrothermal liquefaction [4] consisting of -
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depolymerisation of biomass, decomposition of biomass monomers by cleavage, dehydration,
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decarboxylation and deamination and recombination of reactive fragments.
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To our knowledge, typical studies can be reported on the comparison between pyrolysis and
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HT, using Scenedesmus and Spirulina [20] and Spirulina platensis [21]. In these cases, the
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energy consumption ratio (ECR, energy required for thermochemical conversion over the energy
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that can be recovered from bio-oil combustion, while accounting for combustion energy loss and
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heat recovery) of pyrolysis was very competitive with HTL.
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However, although an overall investigation of the fuel properties of bio-oil from fast pyrolysis
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with hydrothermal liquefaction were reviewed from algae residues [22], little is reported for the
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fast pyrolysis of Botyococcus Braunii (B. Braunii) residues to give organic liquid product, as
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well as the HTL of the residue. Considering the ongoing research attention centered on liquid
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fuel production from biomass and rapid developments in the fields of pyrolysis and hydrothermal
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liquefaction, further information is needed.
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In our previous study, we have reported the hydrocracking of Botryococcene oil (Bot-oil) into
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aviation-range fuel using PtRe/SiO2-Al2O 3 catalyst [23] and the fast pyrolysis of jatropha
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residues with catalysts to form organic liquid product [24-25]. These studies stimulated us to try
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bio-oil production from B. Braunii residues, which could be expected to reduce process cost for
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fuel production from algae. Thus, the aim of the present study is to obtain bio-oil from
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Botyococcus (B.) Braunii residue after B. Braunii oil (Bot-oil) extraction. For this, one of a
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probable method is fast pyrolysis, in which the effect of zeolite catalyst was examined. Then, in
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order to briefly compare with fast pyrolysis, hydrothermal liquefaction (HTL) of the residues
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under H2 pressure conditions was performed using PtRe/SiO2-Al2O3 catalyst [23]. Now we
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report on the bio-oil production from B.Braunii residues.
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2. Materials and methods 2.1. Materials.
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Three zeolites (H-ZSM-5(Si/Al2 =80)(Z80), Beta (Si/Al 2 =116)(B116), and USY (Si/Al2
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=20)(U20), Zeolyst) powder were first calcined at 500oC for 6 h with a heating rate of 3oC/min
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and were used for Py-GC/MS analyses. Other cylindrical-shape pellet zeolites (2 x 5.5 mm,
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such as H-ZSM-5 (Si/Al 2 = 80)) were purchased from JGC C&C Co. Ltds and used after
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calcination at 500 ºC. SiO2-Al 2O3 (abbreviated as SA) were purchased from JGC C&C Co.Ltds.
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Pt(NH3)4Cl2·H2O and NH4ReO4 were purchased from Soekawa Chemicals, Japan. The 1wt%Pt-
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3wt%Re/SiO2-Al 2O3 (SA)
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Pt(NH3)4Cl2·H2O and NH4ReO4, followed by drying at 100 C and calcination for 5 h at 500 C.
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The PtRe/SA catalyst was pre-reduced in an autoclave at 250oC for 5 h under a 4 MPa hydrogen
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atmosphere.
was
prepared
by immersion
impregnation
of SA with
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The Botryococcus braunii residue was isolated by Prof. Watanabe. Briefly, the oil fraction was
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extracted from air-dried B. braunii cells by rinsing several times with n-hexane. After oil
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extraction, remaining residue was obtained and .used without any treatment as the residue for
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subsequent catalytic conversion. Preliminary studies of the fast pyrolysis of the residue were
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performed using Py-GC/MS and stainless-steel reactor was used for 10g-scale reaction under
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atmospheric pressure. The hydrothermal liquefaction of the residue was carried out using batch-
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type reactor. Proximate ultimate analyses of the residue were given in Table 1. The experimental
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methods are described in the 2.2 section.
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2.2. Analysis.
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BET surface area, total pore volume (Vp), and mean pore diameter (dp) of all catalysts were
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determined by N2-physisorption using a BELSORP MAX apparatus (Nippon Bell Co. Ltd.) at
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liquid-N2 temperature. Vp and dp were estimated from the BET surface area [26]. The metal
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particle size of the reduced Pt particle was measured by CO chemisorption method, which was
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carried out by using the BEL-CAT apparatus. Before chemisorption of CO, the catalysts (50 mg)
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were pretreated in He for 35 min and then reduced for 30 min in a 5% H2/Ar gas flow of 50
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ml/min and in He for 15 min at 400 ºC in a reaction chamber. After this pretreatment, the
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samples were cooled down at 50 ºC under He gas flow and CO pulse measurements were carried
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out using 5% CO/He gas flow of 50 ml/min. Finally, particle size of each metal was determined
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from CO pulse data. For comparison, particle size of Re is estimated, based on the assumption
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that Pt and Re are independently present on the SA surface.
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NH3 temperature-programmed desorption (TPD) experiments were carried out for (Z80),
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(U20) and (B116), on a special NH3-TPD apparatus (BELCAT, Nippon Bel), which was
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connected to a TCD detector for measuring the solid acidity of the catalysts. After pretreatment
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under He flow at 500 C for 60 min, adsorption of NH3 at 100 C for 90 min, and desorption of
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the weakly adsorbed NH3 under He flow at 100 C for 30 min, TPD profiles were recorded under
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He flow between 100 C and 700 C (heating rate: 10 C min–1).
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Thermo-gravimetric analysis (TGA) of B. Braunii residue [27] and used catalysts was carried
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out by using TG 2000, Bruker AXS. Approximately 10 mg of sample was heated from 40°C to
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800°C at a typical ramp rate of 20°C/min at a total flow rate of 50 ml/min. The moisture content
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was considered to account for the weight loss when the sample was heated up to 160ºC. Two
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step devolatilization began after the temperature reached 160ºC and was completed at 600ºC.
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TGA pyrolysis showed a gradual loss in mass above 600ºC which can be attributed to volatile
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metal loss and carbonate decomposition. Argon gas was used for a proximate analysis of
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B.Braunii, while air flow was used for deposit carbon combustion of used catalysts. Ultimate
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analysis was performed using a CE INSTRUMENTS EA1110 analyzer.
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Py-GC/MS analysis was performed on a PY-2020iS pyrolyser (Frontier Lab) connected to a
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Agilent model 7890A gas chromatograph (GC) interfaced with a Agilent model 5975C mass
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spectrometer (MS). B.Braunii residue samples of 0.4 mg in holder were rapidly pyrolysed at
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prescribed temperature by dropping the sample holder into furnace. When catalyst was used, the
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catalyst to residue sample weight ratio was typically 6.25 and these reactants were prepared by
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physically mixing the residue and the catalyst. The products were separated on an Ultra alloy
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DX-30 30 m capillary column, 0.25 i.d., 0.15 mm film thickness. The GC oven was programmed
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with the following temperature regime: hold at 40 ◦C for 3 min, ramp to 200 C at 5 C min−1,
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ramp to 400 C at 10 C min -1, hold at 400 C for 5 min. Mass chromatograms were taken at m/z
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57 (alkanes), m/z 55 (alkenes) and m/z 91 (alkylbenzenes) [14]. Full scan data were acquired
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over a range of 50-550 m/z at 2.9 scans/s. Product selectivities were evaluated by area % of each
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peak detectable in GC/MS.
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2.3. Methods.
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The B.Braunii residue was pyrolyzed in a stainless steel reactor with a diameter of 6 cm and
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height of 40 cm (Fig. 1). Four traps, one ice trap and three liquid nitrogen traps, and a plastic gas
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reservoir of volume 100 l were connected with the reactor. The ratio of the residue to catalyst
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was 1:1 by weight. Approximately 20 g of quartz sand and 10 g of catalyst were first put into the
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reactor. Then the reactor was heated up to typically 600oC under N2 at a flow rate of 1,900
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ml/min. After reaching 600oC, the B.Braunii residue was poured into the reactor from the No.1
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inlet of Fig.1 immediately. Products, gas and liquid phase, were collected in the liquid traps and
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plastic gas reservoir. The liquid (organic phase and water phase) and solid char products were
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weighed and the remaining small amount of liquid products were rinsed out from the trap tubes
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using a mixture of 1:1 by volume of dichloromethane and methanol. All the obtained liquid
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products were analyzed by off-line flame ionization detector (FID) gas chromatography (Agilent
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Technologies 7890A GC system, UA-DX30 column) and GC/MS (Agilent Technologies 5975C
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insert XL MSD). FID analysis used dioxane as the internal standard. The gaseous products were
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collected in a plastic bag and analyzed by off-line TCD gas chromatography. Porapak Q and MS
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5A columns were used for the TCD. FID analysis of gaseous hydrocarbon product was
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performed using a KCl-PLOT column. The amount of carbon deposited over the catalyst surface
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was analyzed by TGA, as described above. Thus, the yields of gas, liquid, and char were
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estimated from the sum of the carbon in B.Braunii residue initially introduced. The carbon
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selectivity for each of the organic liquid products was estimated from the relative area % by
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GC/MS analysis.
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For the batch reaction for hydrothermal liquefaction, the pre-reduced catalyst (0.1 g) and
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B.Braunii residue (1g) were introduced with H2O (5g) into a 100-cm3 autoclave-type reactor. The
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autoclave was pressurized with 5.2 MPa of H2/N2 gas mixture (H2/N2=90/10 vol.%). The
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reaction was carried out at 400 ºC for 12 h. After reaction, the gas product was collected into gas
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reservoir, while liquid products weighted and were collected with dichloromethane and analyzed
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by off-line FID and TCD gas-chromatographies, which were equipped with CP-Al2O3/KCl
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PLOT for C1-C4 hydrocarbons and UA-DX30 columns for C5+ hydrocarbons for FID and
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Porapak Q and MS 5A columns for inorganic gases (CH4, CO, CO2 and H2) for the TCD
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detector. TCD analysis was performed using N2 internal standard, while, for FID analysis,
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dioxane was used as internal standard. Here, from off-line GC analysis, the selectivity was
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classified, for convenience, as seven fractions such as gas [C1-C4], [C5-C9], [C10-C15], [C16-
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C20], [C21+], [Coke] and [Unidentified]. The selectivity of [C1-C4] = sum of carbon (mmol) of
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C1-C4 divided by the total carbon (mmol) in the B.Braunii residue initially introduced (1g).
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Other selectivities such as [C5-C9] and [C10-C15] are estimated similarly. The selectivity of
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carbon deposit over the catalyst surface [Coke] was estimated by TGA analysis under air
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conditions. [Unidentified] = 100- ([C1-C4] + [C5-C9] + [C10-C15] + [C16-C20] + [C21+] +
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[Coke]). Overall hydrocarbon yield = (organic liquid yield) x (sum of aromatic and aliphatic
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hydrocarbons selectivities)/100. The ultimate analysis was carried out using organic phase
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product.
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3. RESULTS AND DISCUSSION
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3.1 Properties of original B.Braunii residue.
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Proximate and ultimate analyses of the residue has been performed in nitrogen using a
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thermogravimetric analyzer (TGA) (TG 2000, Bruker AXS) [27]. Approximately 10 mg of
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sample was heated from 40 ºC to 800 ºC at a typical ramp rate of 20 ºC min−1 in a total flow rate
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of 50 ml min−1. As shown in Fig.2, the moisture content was considered to account for the
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weight loss (Peak I) when the sample was heated up to 180 ºC. Three step devolatilizations
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began once the temperature was at 180 ºC and was completed at 635 ºC through intermediate
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temperatures of 343 ºC and 484 ºC. The peak II component corresponds to weight fraction from
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180 ºC to 343 ºC, which would be botryococcene for the residue sample [28]. Peak III around
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343 ºC-484 ºC would be usually correspond to proteins and/or polysaccharides, because 3.52%
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of nitrogen was estimated by ultimate analysis (Table 1) [28-29]. Peak IV around 484 ºC-635 ºC
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should derive from algaenan, which is chemically resistant bio-polymers presumably synthesized
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from the hydrocarbons [30-31]. TGA pyrolysis shows gradual loss in mass above 635 ºC which
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can be attributed to volatile metal loss and carbonate decomposition. The results of proximate
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and ultimate analyses of the B.Braunii and jatropha residues are given in Table 1.
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3.2 Catalyst properties.
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Table S1 shows catalyst properties employed. The BET surface area of porous materials were
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(U20) > (Z80) > 1wt%Pt3wt%Re/SA > (B116) and the pore diameters were (B116) >
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1wt%Pt3wt%Re/SA > (U20) > (Z80). CO adsorption measurements of the catalysts make it
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possible to estimate each metal particle sizes. As shown in Table S1, the values of Pt particle size
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for 1wt%Pt3wt%Re/SA are 0.29 nm, while the particle size of Re is estimated as 1.10 nm.
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The NH3-TPD patterns of zeolites are shown in Fig. 3 and two-stage desorption of NH3 is
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observed. The peak at 100–250 ºC (first peak) is to weak acid sites and the peak at 300–650 ºC
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(second peak) is to strong acidic sites [32]. As shown in table S1, the number of acid sites of each
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zeolite expressed as mmol NH3.g -1 are in the orders: for first peak, (B116) > (U20) > (Z80),
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while, for second peak, (U20) > (B116) > (Z80). The peak temperatures are the order: for first
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peak, (B116) > (Z80) > (U20), while for second peak, (U20) > (B116) > (Z80), as shown in
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Fig.3 [33]. Thus, the total acid natures of three zeolites would be (B116) > (U20) > (Z80).
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Figure 4 shows TPR profile of 1wt%Pt-3wt%Re/SA. The reduction profile of Pt-Re/SA
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shows a reduction peak at ca. 259 C, indicating reduction of Re 7+ to Re0 [34], while Pt reduction
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peak (Pt4+ to Pt0) would not be clear, probably due to small content of Pt of 1wt%.
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3.3 Fast pyrolysis of B.Braunii residue using Py-GC/MS.
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The catalytic fast pyrolysis of B.Braunii residue was carried out with three different catalysts.
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Table 2 shows the product selectivity as estimated by Py-GC/MS analysis at 550 ºC, by
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measuring the relative peak area % of liquid products. The carbon mass balance remained
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unknown, since gaseous and solid products were not measured. In this case, gaseous products
238
contained C2-C4 hydrocarbons as well as CH4, CO, and CO2. Three porous catalysts were
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calcined at 500 ˚C prior to use. The distribution of compounds in bio-oils was determined using a
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semi-quantitative study based on the percentage area of the chromatographic peaks. Compounds
241
were identified using a combination of a mass spectral database and retention data for standard
242
components. Analysis of bio-oil products indicated the production of a range of mono-aromatic
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hydrocarbons, MAH, polyaromatic, PAH [35], alkanes and alkenes, Alkane-alkene, phenols,
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Phenol, oxygenates, Oxy, alcohols + ketones + ethers + acids and esters and nitrogen-containing
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compounds, N-comp.. The MAH included, typically, benzene, toluene, xylenes, methylindene,
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while the PAH included, typically, methylnaphthalene and anthracene. The Alkane-alkene
247
included, typically, dodecene, pentadecane, hexadecane, heptadecene, octadecene and higher
248
aliphatic hydrocarbons. In the Oxy products, the acids and esters predominantly formed and they
249
contained hexadecanoic acid (palmitic acid), octadec-9-enoic acid (oleic acid), and octadecanoic
250
acid (stearic acid) [36].
251
In the absence of a catalyst, fast pyrolysis of B.Braunii residue resulted in the major fraction
252
consisting of 56.0% of Oxy and 24.9% of Alkane-alkene. MAH accounted for 10.3 %, and
253
Phenols, N-comp. and PAH were also found in lesser quantities. Addition of porous catalysts
254
such as USY (20) (U20), ZSM (80) (Z80), Beta (116) (B116) significantly changed the product
255
distribution, as seen in Table 2. The proportions of MAH and PAH compounds increased to 50-
256
55% and 8-14%, whereas Oxy compounds were greatly reduced to 9-16%, and Phenol and N-
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257
comp. were somewhat decreased. As a result, total selectivities of aromatic and aliphatic
258
hydrocarbons accounted for 85-90%, being higher than 75-80% of hydrocarbon selectivities
259
from pyrolysis of jatropha wastes (Table 2). Under the pyrolysis conditions employed, similar
260
effects were observed for three zeolite catalysts.
261
As shown in table 3 in the absence of a catalyst, the MAH selectivity slightly increased with
262
the increase in the reaction temperature from 450 ºC to 600 ºC, while Alkane-alkene selectivity
263
decreased with the increased temperature. The total hydrocarbon selectivities decreased from
264
64.3% to 33.8%. In the presence of porous catalysts, MAH selectivity accounted for 60.6%-
265
65.5%, even at 450 ºC, but the MAH selectivity slightly decreased with the increased
266
temperature, whereas the Alkane-alkene selectivity increased. Thus, the total hydrocarbon
267
selectivities were approximately constant: 84.3%-92.3% for (Z80), 90.9%-85.6% for (U20) and
268
83.8%-92.5% for (B116).
269
Table 3 shows the effects of weight ratio of catalyst to B.Braunii residue from 4 to 10. The
270
total hydrocarbon selectivities remained constant at 90.2%-91.2% for (Z80) with the increased
271
catalyst/B.Braunii residue ratio. On the contrary, for (U20), the total hydrocarbon selectivities
272
increased with the increased weight ratio from 87.1% to 94.9%. Also, for (B116), the total
273
hydrocarbon selectivities increased with the increased weight ratio from 68.4% to 97.7%. Thus,
274
the hydrocarbon selectivities at the catalyst/B.Braunii residue ratio of 10 were found to be
275
(B116) > (U20) > (Z80), which could be consistent with trends of structural and acid properties,
276
obtained from pore diameter and NH3-TPD (Table S1), but the difference of the selectivities is
277
not so large.
278
279
3.4 Fast pyrolysis of B.Braunii residue using stainless-steel reactor.
13
280
The object of runs using reactors was to estimate the yields of liquid products and to compare
281
product selectivity with the Py-GC/MS results. The B.Braunii residue was pyrolyzed in the
282
stainless-steel reactor at 550 oC-650 ºC without and with catalyst. The products consist of Gas,
283
Water-soluble phase, Organic phase, Char, and Unidentified. The two liquid phases were directly
284
obtained from the traps of the stainless steel reactor without any rinsed solvent and the organic
285
phase, which appeared as black liquid, was subjected to GC-MS analysis, as mentioned later.
286
Each yield is shown in Fig.5(A). The highest organic phase yield of 33.1wt% was achieved at
287
600 ºC without catalyst, while, at 650 ºC, the organic phase yield decreased and the char yield
288
increased. In the presence of (Z80) catalyst at 550 ºC, the organic phase yield was 27.8 wt%,
289
being three times higher than that of jatropha waste of 10.2 wt% yield. As shown in Table 4, the
290
ultimate analysis of the organic liquid product exhibited 75-77% of carbon, which was higher
291
than that of starting B.Braunii residue (63 %), while 11-15% of oxygen content was lower than
292
that of the starting residue (24 %). The estimated higher heating values (HHV) were 35-37
293
MJ/kg, which was close to a HHV value of crude triglyceride [37].
294
Organic liquid products were analyzed by GC-MS. Relative selectivities are shown in
295
Fig.5(B) and Table 5 and the chromatograms are shown in Fig.S1. The mono-aromatic
296
hydrocarbons included typically ethylbenzene, toluene, xylenes. The MAH selectivities were in
297
the order (650 ºC, no catalyst) (74.2%) > (550 ºC, (Z80)) (47.8%) > (600 ºC, no catalyst)
298
(42.7%) > (550 ºC, no catalyst) (19.8%). Poly-aromatic hydrocarbons (PAH) [35], included
299
naphthalene, alkylnaphthalenes, alkylfluorenes, and phenanthrene. For PAH, the order was (550
300
ºC, (Z80)) (30.0%) > (600 ºC, no catalyst) (24.4%) > (550 ºC, no catalyst) (13.0%) > (650 ºC, no
301
catalyst) (9.70%). The Alkane-Alkene included mainly long-chain aliphatic hydrocarbons such
302
as decene, pentadecene, 1-octadecene and cyclotetracosane. For alkane-alkene selectivity, the
14
303
order was (550 ºC, no catalyst) (31.1%) > (600 ºC, no catalyst) (7.20%) > (550 ºC, (Z80)) (3.4%)
304
> (650 ºC, no catalyst) (0.9%).
305
The oxygenates contain alcohols, ketones, ethers and acid and ester. These included 5-hexen-
306
2-one, 5-methyl-3-methylene, 4-dodec-3-en-1-ol, methyl 12,15-octadecadienoate, hexadecanoic
307
acid, methyl ester. The oxygenates selectivities decreased with the increase in reaction
308
temperature from 550 ºC to 650 ºC and the order was (550 ºC, no catalyst) (20.3%) > (600 ºC, no
309
catalyst) (12.1%) > (550 ºC, (Z80)) (11.1%) > (650 ºC, no catalyst) (2.4%) [36]. The N-
310
compounds were typically indole, alkylindole, quinoline, benzylnitrile. For N-compounds, the
311
order was (550 ºC, no catalyst) (12.7%) > (600 ºC, no catalyst) (10.1%) > (650 ºC, no catalyst)
312
(8.2%) > (550 ºC, (Z80)) (6.4%). The value of 6.4% was much lower than that of jatropha of
313
18.3%, due to lower N content. The main phenolic compounds were phenols and alkylphenols.
314
The total percentage of these compounds were below 5%.
315
Thus, at pyrolysis of B.Braunii residue, the organic liquid product yield was found to be above
316
30%, approximately 3 times higher than that of jatropha residue. Examinations of Fig.5 and
317
Table 5 indicate that hydrocarbon selectivities were greatly affected by reaction temperature and
318
(Alkane-alkene) was found to be comparable to sum of aromatic hydrocarbons at 550ºC. As the
319
temperature increased, the aromatic hydrocarbon selectivities dramatically increased and, at
320
650ºC, the MAH selectivity was as high as 74.2%. The MAH and PAH selectivities at 550 ºC
321
were improved by the presence of (Z80) catalyst. Taking organic liquid yield and hydrocarbon
322
selectivities into account, table 5 summarizes overall hydrocarbon yield, which is in the order: no
323
catalyst at 600 ºC (24.58%) > (Z80) at 550 ºC (22.57%) > no catalyst at 550 ºC (20.6%) > no
324
catalyst at 650 ºC (19.32%).
15
325
326
3.5 A comparative brief study on hydrothermal liquefaction of B. Braunii residue. In order to compare a nature of hydrothermal liquefaction (HTL) with pyrolysis, the HTL
327
reaction was briefly carried out with or without catalyst using batch reactor, where the Pt3Re/
328
SiO2-Al 2O3 (SA) catalyst was used [23]. As shown in Table 6, the selectivity of liquid
329
hydrocarbons (C5-C21+) was 51.08% with Pt3Re/SA catalyst, which was found to be a little
330
higher than the 32.02% without catalyst. As shown in table 5, the overall hydrocarbon yield with
331
catalyst was 36.8%, which was higher than the yield of 24.58% for pyrolysis at 600 ºC. Table 5
332
also shows the estimated higher heating values (HHV) were 34.72 MJ/kg, which was
333
approximately close to a HHV value of pyrolysis oil [37].
334
The coke selectivity of 1.81% with catalyst was much lower than 11.4% without catalyst. As
335
shown in Fig.6(A) and (C), the GC-MS chromatogram of organic liquid obtained by HTL of
336
B.Braunii residue were found to be rather similar to that of pyrolysis at 550 ºC without catalyst
337
(Figure S1(a)). The mass chromatogram analyses revealed the presence of a homologous series
338
of C9−C32 of n-alkanes (m/z 57) and smaller portion of n-alkenes (m/z 55). Also present but in
339
much lower abundance are C8−C18 of n-alkylbenzenes (m/z 91) and alkylnaphthalenes
340
(m/z=141) ((B) and (D) of Fig.6, respectively) [14]. The n-alkanes predominantly formed over
341
aromatic hydrocarbons, even in the presence of catalyst, due to low temperature of 400 ºC.
342
3.6 Summary of reaction pathways.
343
A reaction pathway for conversion of B. Braunii residue into hydrocarbons is shown in Fig. 7.
344
The residue mainly contains Botryococcene and algaenan with polysaccharide and protein.
345
Aliphatic
346
hydrodeoxygenation (HDO) from Botryococcene, algaenan and polysaccharide, by pyrolysis as
hydrocarbons
were
formed
through
cracking,
dehydrogenation
(DH),
16
347
well as hydrothermal liquefaction (HTL). Aromatic hydrocarbons were produced through
348
dehydrocyclization (DHC) and dehydroaromatization (DHA), from aliphatic hydrocarbons. In
349
the presence of zeolite catalyst, the aromatization of aliphatic hydrocarbons could be accelerated.
350
Protein [38] would undergo cracking, DHA and DHC to form N-containing monoaromatic
351
product, followed by DH, DHA and DHC to give heterocyclic compounds. Thus, in the pyrolysis
352
of B. Braunii residue, the aromatization could be enhanced by use of zeolite catalyst [24].
353
4. CONCLUSION
354 355
The aim of the present study is to obtain bio-oil from Botyococcus (B.) Braunii residue after B.
356
Braunii oil (Bot-oil) extraction. The study concludes that pyrolysis can be employed for
357
generating bio-oil from B.Braunii residue. From Py-GC/MS analyses using the residue and
358
zeolite catalyst, total selectivities of aromatic and aliphatic hydrocarbons accounted for 88.6%,
359
being much higher than 35.2% without catalyst. At fast pyrolysis of B.Braunii residue using
360
reactor, the organic liquid product (bio-oil) yield was found to be above 30%, approximately 3
361
times higher than that of jatropha residue. The higher heating value (HHV) of the liquid product
362
was approximately 35-37 MJ/kg, which was close to a HHV value of crude triglyceride. The
363
hydrocarbon yields were 19.3-24.6%. As a brief comparison with pyrolysis, the hydrothermal
364
liquefaction (HTL) of the residue at 400 ºC with PtRe/SiO2-Al 2O3 catalyst under H2 conditions
365
yielded liquid hydrocarbons of 36.8 % which was a little higher than that of pyrolysis at 600 ºC.
366
The n-alkanes predominantly formed over aromatic hydrocarbons, due to low temperature of 400
367
ºC. Postulated scheme was presented, where liquid hydrocarbons are formed from B. Braunii
368
residue through cracking, dehydrogenation, hydrodeoxygenation and dehydroaromatization and
369
dehydrocyclization.
370
17
371
ACKNOWLEDGMENT
372
The authors are grateful to the AFFRC grant of Ministry of Agriculture, Forestry and Fisheries of
373
Japan (MAFF).
374
375
376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412
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461 462 463 464
19
465
Figure captions:
466
Figure 1: Illustraion of stainless-steel reactor system.
467 468
1: B.Braunii residue, 2:N2 flow, 3: Thermocouple, 4: Catalyst-bed, 5: Mesh filter, 6: Electric furnace, 7: Iced trap, 8: Liquid N2 trap, 9: Plastic waste gas reservoir.
471
Figure 2: TG and DTA profiles recorded for B.Braunii residue in the nitrogen atmosphere. (A) TG, (B): DTA. Measurement conditions: See text. Figure 3: NH3-TPD of fresh zeolite catalysts. 1: Beta (116), 2:H-ZSM-5(80), 3: USY(20).
472
Figure 4:TPR profile of 1wt%Pt-3wt%Re/SiO2-A2O3 (SA).
469 470
473 474
475
Figure 5: Yields of oil, gas and char in pyrolysis of B.Braunii residue and product selectivities of bio-oil (organic phase) using stainless-steel reactor. (A): Yield; ()Gas, ()Water-soluble, ()Organic, ()Char, ()Unidentified
479
(B): Selectivities of organic phase. NCat denotes no catalyst. ()MAH: Mono-aromatic hydrocarbons, ()PAH: Poly-aromatic hydrocarbons, ()Aliphatic: sum of alkane and alkene, ()Phenol: sum of phenolic compounds, ()Oxy: sum of (alcohol + ketone + ether + acid and ester), ()N-Comp.: sum of N-compounds.
480
Figure 6: Mass chromatograms of organic liquid obtained from hydrothermal liquefaction (HTL)
481
of B.Braunii residue. (A) and (B) with PtRe/SA catalyst, (C) and (D) with no catalyst. (A)
482
and (C): Total chromatogram, (B) and (D): Mass chromatograms: m/z 57 (n-alkanes), m/z
483
55 (n-alkenes), m/z 91 (n-alkylbenzenes), m/z 141 (alkylnaphthalenes). Conditions: See
484
text.
476 477 478
485
Figure 7: Summary of reaction scheme.
486
Figure S1: GC/MS chromatograms of organic liquid product.
487 488
a: No catalyst at 550 ºC, b: No Catalyst at 600 ºC, c: No catalyst at 650 ºC, d: (Z80) at 550ºC.
489
490
491
492
493
494
495
20
496
497
Table 1Proximate and Ultimate Analyses of Botryococcus (Bot) and Jatropha residues. Proximate analysis (%)
Bot Residue
Jat Residue
moisture
10.94
volatile matter
81.13
81.0
0
0.76
ash content fixed carbon
4.95
7.93
11.39
C
63.3
46.39
H
9.30
6.55
N
3.52
4.53
O
23.88
42.53
Ultimate analysis (%)
498
499
500
Table 2. Effects of catalyst on the product selectivities in the fast pyrolysis of B.Braunii and Jatropha residues
a
501
Organic productselectivityb Catalyst
Residue
1
2
3
4
5
6
B.Braunii
10.27
0
24.90
2.43
55.98
6.39
c
B.Braunii
50.97
9.95
27.65
1.39
8.83
1.23
c
B.Braunii
55.04
7.95
26.72
0.48
9.36
0.45
Beta (116) (B116)
B.Braunii
49.87
13.93
19.75
0.11
15.57
0.77
Non
Jatropha
1.26
0
3.06
11.11
72.54
12.0
c
Jatropha
58.06
5.36
18.32
1.14
12.34
4.74
c
Jatropha
50.17
9.65
14.78
6.01
8.37
11.04
Jatropha
52.04
12.67
14.41
2.86
13.50
4.53
Non ZSM(80) (Z80) USY (20) (U20) c
ZSM(80) (Z80) USY (20) (U20) c
Beta (116) (B116) 502
503 504
a
b
Conditions: Catalyst/residue ratio =2.5/0.4, 550ºC. Remark: 1: Mono-aromatic hydrocarbon (MAH), 2: Poly-aromatic
hydrocarbons (PAH), 3: Alkane andalkene, 4.:Phenol, 5: Oxygenates (Alcohol + ketone + Ether + Acid and ester), 6: Ncompounds c
505
The number in parentheses denotes Si/Al2 ratio.
21
506 507 508
Table 3. Effects of reaction temperature and catalyst/residue ratio on the product selectivities in the fast pyrolysis of B.Braunii residue
509
b
Catalyst Non
Temp./ºC
1
2
3
4
5
6
450
6.2
3.77
0
60.57
0.38
33.84
1.16
500
6.2
4.58
2.68
41.05
1.70
46.76
3.26
550
6.2
10.27
0
24.9
2.43
55.98
6.39
600
6.2
9.58
0.52
23.7
1.79
62.27
2.15
ZSM (80)
450
6.2
62.34
6.22
15.76
0.30
13.38
1.66
(Z80)
500
6.2
57.89
15.48
9.57
0.43
15.46
1.19
550
6.2
50.97
9.94
27.65
1.39
8.83
1.23
600
6.2
52.26
7.16
32.91
1.02
2.25
4.37
USY (20)
450
6.2
65.49
11.89
13.50
0.47
7.35
1.29
(U20)
500
6.2
64.21
8.18
10.07
0
14.76
2.81
550
6.2
55.04
7.95
26.72
0.48
9.36
0.45
600
6.2
49.40
8.81
27.34
0.42
10.84
3.23
Beta (116)
450
6.2
60.60
17.73
5.46
0
15.79
0.43
(B116)
500
6.2
61.62
16.88
14.02
0
6.78
0.69
550
6.2
49.87
13.93
19.75
0.11
15.57
0.77
600
6.2
36.96
16.24
35.25
0.52
10.6
0.40
ZSM(80)
550
4
39.17
7.45
43.61
0.61
7.99
1.15
(Z80)
550
6.2
50.97
9.95
27.65
1.39
8.83
1.23
550
10
49.17
9.32
32.71
0
8.07
0.74
USY (20)
550
4
57.70
13.38
16.04
0
11.96
0.93
(U20)
550
6.2
55.04
7.95
26.72
0.48
9.36
0.45
550
10
52.70
12.52
29.73
0.46
4.59
0
Beta (116)
550
4
38.57
11.85
17.98
0.15
30.81
0.33
(B116)
550
6.2
49.87
13.93
19.75
0.11
15.57
0.77
550
10
51.11
16.66
29.94
0.21
2.06
0
a 510
Organic product selectivitya
Catalyst/Residue ratio
b
Remark:See footnote of Table 3. The number in parentheses denote Si/Al2 ratio.
22
511
512
513
Table 4. Elemental composition and energy content of pyrolysis bio-oil and HTL oil (organic phase) from B.Braunii residue..
514
515
HTL oil
Pyrolysis Bio-oil
Overall a yield(C5+)
hydrocarbon
No Catalyst/ 650ºC
No Catalyst/ 600ºC
19.32
24.58
No Catalyst/ 550ºC
(Z80) / 550ºC
516
Pt3Re/SiO 2517 Al2O3/ 400ºC 518
20.60
22.57
36.80
519
520
Ultimate analysis
b
521
C
-
77.28
77.26
74.69
H
-
8.92
7.84
9.14
8.73
523
N
-
2.63
1.84
1.33
1.92
524
O
-
11.17
13.06
14.84
15.01
525
-
36.97
35.08
35.64
34.72
526
HHV/ MJ/kg
c
73.81
522
527
528
529
530
a
Overall hydrocarbon yield = (organic liquid yield) x (sum of aromatic and aliphatic hydrocarbons selectivities)/100.
The ultimate analysis was carried out using organic phase product. b
531
Estimated by Dulong’s equation.
532
533
23
534
Table 5. Main Componenta of the Algal Bio-Oils Obtained from Fast Pyrolysis of B.Braunii Residues a
Organic products
RT , min
Area% NoCat550
NoCat600
NoCat650
(Z80)-550
2.08
0.69
1.487
Benzene
0
0.88
1.954
Toluene
2.99
8.04
2.625
Ethylbenzene
2.73
2.25
1.97
1.87
2.724
o-Xylene
5.41
7.11
6.37
8.25
2.934
Styrene
2.945
p-Xylene
3.90
5.49
3.60
5.02
3.333
Phenol
1.18
1.82
1.36
0.75
3.694
Acetic acid, chloro-, isobutyl ester
1.87
1.57
0.85
1.27
3.704
1-Decene
3.788
-Methylstyrene
3.972
Benzene, 1-ethyl-3-methyl-
4.029
Benzene, 1-propenyl-
4.114
2-Chloro-N-ethylacetamide
1.95
4.287
Benzene, 1,2,3-trimethyl-
1.34
4.297
4-Ethylphenethylamine
4.381
Phenol, 4-methyl-
1.83
1.80
3.03
4.522
Indene
1.28
2.63
3.88
3.29
4.722
Undecene
1.94
4.80
1,8-Nonadien-3-ol
1.02
4.905
Benzene, 1-ethyl-2,4-dimethyl-
1.38
1.03
0.61
5.403
Benzene, 1-methyl-4-(2-propenyl)-
0.98
1.05
2.40
1.07
5.67
1H-Indene, 1-methyl-
1.71
2.73
0.30
4.25
5.686
Benzene, 1-butynyl-
4.12
2.55
2.25
5.754
2-Dodecene, (E)-
5.827
Azulene
1.35
4.00
7.79
5.57
4.60
2.04 1.31 3.93
1.62
1.44
3.84
1.19
5.26
0.69
1.22 5.53
1.26
2.34
1.26
2.89
24
6.121
Naphthalene
0.78
6.299
1,4-Cyclohexanedimethanamine
1.64
6.514
Butanoic acid, 3-oxo-, 2,2,2-trichloroethyl ester
1.11
6.74
1-Tridecene
1.94
6.865
1H-Indene, 4,7-dimethyl-
7.043
Indole
7.279
1.65
4.36
0.75
0.80
3.02
2.13
6.40
1.33
1.51
1.14
1.23
Naphthalene, 1-methyl-
0.82
1.71
3.86
0.60
7.442
Naphthalene, 2-methyl-
1.53
1.09
2.78
1.63
7.683
7-Tetradecene, (Z)-
1.87
8.218
Naphthalene, 2,3-dimethyl-
0.96
8.574
1-Pentadecene
1.59
8.637
Pentadecane
0.96
8.821
Biphenylene
9.424
1-Hexadecene
9.428
Naphthalene, 1,6,7-trimethyl-
9.963
Fluorene
10.08
8-Heptadecene
0.59
10.99
1-Octadecene
0.69
11.68
Phenanthrene
11.72
1-Nonadecene
0.94
12.41
3-Eicosene, (E)-
0.36
12.71
Anthracene, 2-methyl-
0.45
0.25
13.83
Pyrene
0.21
0.18
14.33
1-Docosene
0.48
14.91
9-Tricosene, (Z)-
0.41
15.48
Cyclotetracosane
0.34
16.55
Hexacosane
0.35
1.34 4.52
5.08
6.70
1.90
0.41
0.98
1.69
4.28
0.19
1.83
0.79
1.16
0.66
1.08
0.16 0.12
0.23
a 535
RT: Retention time.:
536
25
537
538
539
540
541
542
543
Table 6Hydrothermal liquefaction of B.Braunii residue using batch reactor. a Catalyst
544
Selectivity%
b
C1-C4
C5-C9
C10-C15
C16-C20
C21+
Coke
Unidentified
Non
12.89
5.50
8.38
7.23
10.91
11.40
43.89
Pt3Re/SiO2-Al2O3
16.40
9.39
14.36
13.06
14.27
1.81
30.72
a
Conditions and Selectivity: See Experimental section.
545
546
26
S0165-2370(15)30050-4 http://dx.doi.org/doi:10.1016/j.jaap.2015.05.017 JAAP 3501
To appear in:
J. Anal. Appl. Pyrolysis
Received date: Revised date: Accepted date:
15-3-2015 25-5-2015 26-5-2015
Please cite this article as: Kazuhisa Murata, Yanyong Liu, Makoto M Watanabe, Megumu Inaba, Production of bio-oil from a Botryococcus Braunii residue, Journal of Analytical and Applied Pyrolysis http://dx.doi.org/10.1016/j.jaap.2015.05.017 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.
1
2
Production of Bio-Oil from a Botryococcus Braunii Residue
3
4
5
6
Kazuhisa Murata*, Yanyong Liu, Makoto M Watanabe2ǂ, Megumu Inaba
Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8565, Japan.
7
ǂ Faculty
8
Ibaraki 305-8572, Japan
of Life & Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba,
9
10
KEYWORDS. Pyrolysis; Botryococcus Braunii residue; Liquid hydrocarbons; Hydrothermal
11
liquefaction
12
13 14
15
16
*Corresponding author. Tel.: +81 298614776. E-mail address: [email protected] (K.Murata). Highlights
17 18
19 20
Renewable green bio-oil can be produced by pyrolysis of Botryococcus (B.) Braunii residue after B. Braunii oil extraction. Hydrocarbon selectivities accounted for 85–90% and the organic liquid yield was found to be above 30%. Hydrothermal liquefaction of the B. Braunii residue yielded hydrocarbons of 36.8%.
21 22 23
ABSTRACT: The aim of the present study is to obtain bio-oil from Botyococcus (B.) Braunii
24
residue after B. Braunii oil (Bot-oil) extraction. For this, one of a probable method is fast
25
pyrolysis, in which the effect of zeolite catalyst was examined. From Py-GC/MS analyses at 550
1
26
ºC using H-ZSM-5 (80) (Z80) catalyst, total selectivities of aromatic and aliphatic hydrocarbons
27
accounted for 88.6%, being much higher than 35.2% without catalyst. At fast pyrolysis using
28
reactor, the organic liquid product (bio-oil) yield was found to be above 30%, approximately 3
29
times higher than that of jatropha residue. The higher heating value (HHV) of the liquid product
30
was approximately 35-37 MJ/kg, which was close to a HHV value of crude triglyceride. The
31
highest overall hydrocarbon yield was 24.58 % at 600 ºC. In order to briefly compare with fast
32
pyrolysis, hydrothermal liquefaction (HTL) of the residues under H2 pressure conditions was
33
tried using PtRe/SiO2-Al2O3 catalyst, which has been extremely effective for hydrocracking of B.
34
Braunii oil into aviation-range fuel. In the HTL of the B.Braunii residue at 400 ºC, the
35
hydrocarbon yield was 36.8 % which was a little higher yield than that from pyrolysis. The n-
36
alkanes predominantly formed over aromatic hydrocarbons, due to lower temperature of 400 ºC
37
and the catalyst different from pyrolysis. Postulated scheme was presented through cracking,
38
hydrodeoxygenation and dehydroaromatization..
39 40
1. INTRODUCTION
41
Microalgae are among the aquatic biomass feedstocks that are considered to be one of the best
42
sources of liquid fuels [1]. Recently, bio-harvesting and pyrolysis of Botryococcus braunii have
43
been successfully investigated [2]. They can accumulate lipids that can be converted into
44
biofuels. After extraction of algae oil, there remain algae residues with a high water content. In
45
order to reduce process cost of algae-based biofuel production, our present interest is to produce
46
another biofuels from these residues with an energy-saving consideration. Generally,
47
thermochemical conversions such as fast pyrolysis [3 ] and hydrothermal liquefaction (HTL)[4]
48
have been suggested for production of biofuel oil from algae [5,6]. Possibly, these methods can
49
be acceptable for wet residues with moderate energy consumtion. These processes have the great
2
50
advantage of converting the whole microalgae residue. Bio-oils derived from biomass have
51
energy densities higher than the initial biomass feedstock. Moreover it can be also upgraded in
52
order to obtain biofuels such as bio-diesel or bio-kerosene. Bio-oil production from fast pyrolysis
53
has been investigated for many microalgae strains [7-11] The pyrolysis bio-oil quality depends
54
greatly on the microalgae strains and the operating onditions. For example, Harman et al. [8] and
55
Gong et al. [10] produced fast pyrolysis bio-oils from Scenedesmus sp., Chlorella vulgaris and
56
Dunaliella salina characterized by a higher heating value (HHV) relatively low (18-25 MJ kg-1,
57
as a comparison the HHV of diesel is 48 MJ kg-1). However despite bio-oils production with low
58
HHV, Belotti et al. [11] and Miao and Wu [9] showed that fast pyrolysis (heating rate = 600 K s1
59
60
) produced more energy from bio-oil combustion than the energy required for thermochemical
conversion.
61
Although pyrolysis has been extensively reported for a wide variety of lignocellulosic biomass
62
including different species of wood [12], there is not much information about laboratory scale
63
pyrolysis of algal biomass except the ones on fast pyrolysis of microalgae Chlorella
64
protothecoides and Microcystis aeruginosa [13] and the slow pyrolysis of Botyococcus Braunii
65
residue [14]. Bio-oil yields of 17.5% and 23.7% were reported from the fast pyrolysis of C.
66
protothecoides and M. aeruginosa, respectively. The fuel properties of bio-oils from algae in the
67
above studies were found superior to that obtained from wood.
68
Hydrothermal liquefaction (HTL) of microalgae biomass has been widely reported to result in
69
higher bio-oil yields [15-17]. HTL is a potential conversion routes for biomass with a high water
70
content [18]. In this process, water has both the role of solvent and of reactant. HTL operating
71
conditions bring the water near its critical point (Tc = 374 ºC and Pc = 22.1 MPa) leading to a
72
low dielectric constant and an increased solubility of organic molecules [19]. Toor et al.
3
73
described the basic reaction mechanism of biomass hydrothermal liquefaction [4] consisting of -
74
depolymerisation of biomass, decomposition of biomass monomers by cleavage, dehydration,
75
decarboxylation and deamination and recombination of reactive fragments.
76
To our knowledge, typical studies can be reported on the comparison between pyrolysis and
77
HT, using Scenedesmus and Spirulina [20] and Spirulina platensis [21]. In these cases, the
78
energy consumption ratio (ECR, energy required for thermochemical conversion over the energy
79
that can be recovered from bio-oil combustion, while accounting for combustion energy loss and
80
heat recovery) of pyrolysis was very competitive with HTL.
81
However, although an overall investigation of the fuel properties of bio-oil from fast pyrolysis
82
with hydrothermal liquefaction were reviewed from algae residues [22], little is reported for the
83
fast pyrolysis of Botyococcus Braunii (B. Braunii) residues to give organic liquid product, as
84
well as the HTL of the residue. Considering the ongoing research attention centered on liquid
85
fuel production from biomass and rapid developments in the fields of pyrolysis and hydrothermal
86
liquefaction, further information is needed.
87
In our previous study, we have reported the hydrocracking of Botryococcene oil (Bot-oil) into
88
aviation-range fuel using PtRe/SiO2-Al2O 3 catalyst [23] and the fast pyrolysis of jatropha
89
residues with catalysts to form organic liquid product [24-25]. These studies stimulated us to try
90
bio-oil production from B. Braunii residues, which could be expected to reduce process cost for
91
fuel production from algae. Thus, the aim of the present study is to obtain bio-oil from
92
Botyococcus (B.) Braunii residue after B. Braunii oil (Bot-oil) extraction. For this, one of a
93
probable method is fast pyrolysis, in which the effect of zeolite catalyst was examined. Then, in
94
order to briefly compare with fast pyrolysis, hydrothermal liquefaction (HTL) of the residues
95
under H2 pressure conditions was performed using PtRe/SiO2-Al2O3 catalyst [23]. Now we
4
96
report on the bio-oil production from B.Braunii residues.
97
5
98
99
2. Materials and methods 2.1. Materials.
100
Three zeolites (H-ZSM-5(Si/Al2 =80)(Z80), Beta (Si/Al 2 =116)(B116), and USY (Si/Al2
101
=20)(U20), Zeolyst) powder were first calcined at 500oC for 6 h with a heating rate of 3oC/min
102
and were used for Py-GC/MS analyses. Other cylindrical-shape pellet zeolites (2 x 5.5 mm,
103
such as H-ZSM-5 (Si/Al 2 = 80)) were purchased from JGC C&C Co. Ltds and used after
104
calcination at 500 ºC. SiO2-Al 2O3 (abbreviated as SA) were purchased from JGC C&C Co.Ltds.
105
Pt(NH3)4Cl2·H2O and NH4ReO4 were purchased from Soekawa Chemicals, Japan. The 1wt%Pt-
106
3wt%Re/SiO2-Al 2O3 (SA)
107
Pt(NH3)4Cl2·H2O and NH4ReO4, followed by drying at 100 C and calcination for 5 h at 500 C.
108
The PtRe/SA catalyst was pre-reduced in an autoclave at 250oC for 5 h under a 4 MPa hydrogen
109
atmosphere.
was
prepared
by immersion
impregnation
of SA with
110
The Botryococcus braunii residue was isolated by Prof. Watanabe. Briefly, the oil fraction was
111
extracted from air-dried B. braunii cells by rinsing several times with n-hexane. After oil
112
extraction, remaining residue was obtained and .used without any treatment as the residue for
113
subsequent catalytic conversion. Preliminary studies of the fast pyrolysis of the residue were
114
performed using Py-GC/MS and stainless-steel reactor was used for 10g-scale reaction under
115
atmospheric pressure. The hydrothermal liquefaction of the residue was carried out using batch-
116
type reactor. Proximate ultimate analyses of the residue were given in Table 1. The experimental
117
methods are described in the 2.2 section.
118
2.2. Analysis.
119
BET surface area, total pore volume (Vp), and mean pore diameter (dp) of all catalysts were
6
120
determined by N2-physisorption using a BELSORP MAX apparatus (Nippon Bell Co. Ltd.) at
121
liquid-N2 temperature. Vp and dp were estimated from the BET surface area [26]. The metal
122
particle size of the reduced Pt particle was measured by CO chemisorption method, which was
123
carried out by using the BEL-CAT apparatus. Before chemisorption of CO, the catalysts (50 mg)
124
were pretreated in He for 35 min and then reduced for 30 min in a 5% H2/Ar gas flow of 50
125
ml/min and in He for 15 min at 400 ºC in a reaction chamber. After this pretreatment, the
126
samples were cooled down at 50 ºC under He gas flow and CO pulse measurements were carried
127
out using 5% CO/He gas flow of 50 ml/min. Finally, particle size of each metal was determined
128
from CO pulse data. For comparison, particle size of Re is estimated, based on the assumption
129
that Pt and Re are independently present on the SA surface.
130
NH3 temperature-programmed desorption (TPD) experiments were carried out for (Z80),
131
(U20) and (B116), on a special NH3-TPD apparatus (BELCAT, Nippon Bel), which was
132
connected to a TCD detector for measuring the solid acidity of the catalysts. After pretreatment
133
under He flow at 500 C for 60 min, adsorption of NH3 at 100 C for 90 min, and desorption of
134
the weakly adsorbed NH3 under He flow at 100 C for 30 min, TPD profiles were recorded under
135
He flow between 100 C and 700 C (heating rate: 10 C min–1).
136
Thermo-gravimetric analysis (TGA) of B. Braunii residue [27] and used catalysts was carried
137
out by using TG 2000, Bruker AXS. Approximately 10 mg of sample was heated from 40°C to
138
800°C at a typical ramp rate of 20°C/min at a total flow rate of 50 ml/min. The moisture content
139
was considered to account for the weight loss when the sample was heated up to 160ºC. Two
140
step devolatilization began after the temperature reached 160ºC and was completed at 600ºC.
141
TGA pyrolysis showed a gradual loss in mass above 600ºC which can be attributed to volatile
142
metal loss and carbonate decomposition. Argon gas was used for a proximate analysis of
7
143
B.Braunii, while air flow was used for deposit carbon combustion of used catalysts. Ultimate
144
analysis was performed using a CE INSTRUMENTS EA1110 analyzer.
145
Py-GC/MS analysis was performed on a PY-2020iS pyrolyser (Frontier Lab) connected to a
146
Agilent model 7890A gas chromatograph (GC) interfaced with a Agilent model 5975C mass
147
spectrometer (MS). B.Braunii residue samples of 0.4 mg in holder were rapidly pyrolysed at
148
prescribed temperature by dropping the sample holder into furnace. When catalyst was used, the
149
catalyst to residue sample weight ratio was typically 6.25 and these reactants were prepared by
150
physically mixing the residue and the catalyst. The products were separated on an Ultra alloy
151
DX-30 30 m capillary column, 0.25 i.d., 0.15 mm film thickness. The GC oven was programmed
152
with the following temperature regime: hold at 40 ◦C for 3 min, ramp to 200 C at 5 C min−1,
153
ramp to 400 C at 10 C min -1, hold at 400 C for 5 min. Mass chromatograms were taken at m/z
154
57 (alkanes), m/z 55 (alkenes) and m/z 91 (alkylbenzenes) [14]. Full scan data were acquired
155
over a range of 50-550 m/z at 2.9 scans/s. Product selectivities were evaluated by area % of each
156
peak detectable in GC/MS.
157
2.3. Methods.
158
The B.Braunii residue was pyrolyzed in a stainless steel reactor with a diameter of 6 cm and
159
height of 40 cm (Fig. 1). Four traps, one ice trap and three liquid nitrogen traps, and a plastic gas
160
reservoir of volume 100 l were connected with the reactor. The ratio of the residue to catalyst
161
was 1:1 by weight. Approximately 20 g of quartz sand and 10 g of catalyst were first put into the
162
reactor. Then the reactor was heated up to typically 600oC under N2 at a flow rate of 1,900
163
ml/min. After reaching 600oC, the B.Braunii residue was poured into the reactor from the No.1
164
inlet of Fig.1 immediately. Products, gas and liquid phase, were collected in the liquid traps and
165
plastic gas reservoir. The liquid (organic phase and water phase) and solid char products were
8
166
weighed and the remaining small amount of liquid products were rinsed out from the trap tubes
167
using a mixture of 1:1 by volume of dichloromethane and methanol. All the obtained liquid
168
products were analyzed by off-line flame ionization detector (FID) gas chromatography (Agilent
169
Technologies 7890A GC system, UA-DX30 column) and GC/MS (Agilent Technologies 5975C
170
insert XL MSD). FID analysis used dioxane as the internal standard. The gaseous products were
171
collected in a plastic bag and analyzed by off-line TCD gas chromatography. Porapak Q and MS
172
5A columns were used for the TCD. FID analysis of gaseous hydrocarbon product was
173
performed using a KCl-PLOT column. The amount of carbon deposited over the catalyst surface
174
was analyzed by TGA, as described above. Thus, the yields of gas, liquid, and char were
175
estimated from the sum of the carbon in B.Braunii residue initially introduced. The carbon
176
selectivity for each of the organic liquid products was estimated from the relative area % by
177
GC/MS analysis.
178
For the batch reaction for hydrothermal liquefaction, the pre-reduced catalyst (0.1 g) and
179
B.Braunii residue (1g) were introduced with H2O (5g) into a 100-cm3 autoclave-type reactor. The
180
autoclave was pressurized with 5.2 MPa of H2/N2 gas mixture (H2/N2=90/10 vol.%). The
181
reaction was carried out at 400 ºC for 12 h. After reaction, the gas product was collected into gas
182
reservoir, while liquid products weighted and were collected with dichloromethane and analyzed
183
by off-line FID and TCD gas-chromatographies, which were equipped with CP-Al2O3/KCl
184
PLOT for C1-C4 hydrocarbons and UA-DX30 columns for C5+ hydrocarbons for FID and
185
Porapak Q and MS 5A columns for inorganic gases (CH4, CO, CO2 and H2) for the TCD
186
detector. TCD analysis was performed using N2 internal standard, while, for FID analysis,
187
dioxane was used as internal standard. Here, from off-line GC analysis, the selectivity was
188
classified, for convenience, as seven fractions such as gas [C1-C4], [C5-C9], [C10-C15], [C16-
9
189
C20], [C21+], [Coke] and [Unidentified]. The selectivity of [C1-C4] = sum of carbon (mmol) of
190
C1-C4 divided by the total carbon (mmol) in the B.Braunii residue initially introduced (1g).
191
Other selectivities such as [C5-C9] and [C10-C15] are estimated similarly. The selectivity of
192
carbon deposit over the catalyst surface [Coke] was estimated by TGA analysis under air
193
conditions. [Unidentified] = 100- ([C1-C4] + [C5-C9] + [C10-C15] + [C16-C20] + [C21+] +
194
[Coke]). Overall hydrocarbon yield = (organic liquid yield) x (sum of aromatic and aliphatic
195
hydrocarbons selectivities)/100. The ultimate analysis was carried out using organic phase
196
product.
197
198
3. RESULTS AND DISCUSSION
199
3.1 Properties of original B.Braunii residue.
200
Proximate and ultimate analyses of the residue has been performed in nitrogen using a
201
thermogravimetric analyzer (TGA) (TG 2000, Bruker AXS) [27]. Approximately 10 mg of
202
sample was heated from 40 ºC to 800 ºC at a typical ramp rate of 20 ºC min−1 in a total flow rate
203
of 50 ml min−1. As shown in Fig.2, the moisture content was considered to account for the
204
weight loss (Peak I) when the sample was heated up to 180 ºC. Three step devolatilizations
205
began once the temperature was at 180 ºC and was completed at 635 ºC through intermediate
206
temperatures of 343 ºC and 484 ºC. The peak II component corresponds to weight fraction from
207
180 ºC to 343 ºC, which would be botryococcene for the residue sample [28]. Peak III around
208
343 ºC-484 ºC would be usually correspond to proteins and/or polysaccharides, because 3.52%
209
of nitrogen was estimated by ultimate analysis (Table 1) [28-29]. Peak IV around 484 ºC-635 ºC
210
should derive from algaenan, which is chemically resistant bio-polymers presumably synthesized
10
211
from the hydrocarbons [30-31]. TGA pyrolysis shows gradual loss in mass above 635 ºC which
212
can be attributed to volatile metal loss and carbonate decomposition. The results of proximate
213
and ultimate analyses of the B.Braunii and jatropha residues are given in Table 1.
214 215
3.2 Catalyst properties.
216
Table S1 shows catalyst properties employed. The BET surface area of porous materials were
217
(U20) > (Z80) > 1wt%Pt3wt%Re/SA > (B116) and the pore diameters were (B116) >
218
1wt%Pt3wt%Re/SA > (U20) > (Z80). CO adsorption measurements of the catalysts make it
219
possible to estimate each metal particle sizes. As shown in Table S1, the values of Pt particle size
220
for 1wt%Pt3wt%Re/SA are 0.29 nm, while the particle size of Re is estimated as 1.10 nm.
221
The NH3-TPD patterns of zeolites are shown in Fig. 3 and two-stage desorption of NH3 is
222
observed. The peak at 100–250 ºC (first peak) is to weak acid sites and the peak at 300–650 ºC
223
(second peak) is to strong acidic sites [32]. As shown in table S1, the number of acid sites of each
224
zeolite expressed as mmol NH3.g -1 are in the orders: for first peak, (B116) > (U20) > (Z80),
225
while, for second peak, (U20) > (B116) > (Z80). The peak temperatures are the order: for first
226
peak, (B116) > (Z80) > (U20), while for second peak, (U20) > (B116) > (Z80), as shown in
227
Fig.3 [33]. Thus, the total acid natures of three zeolites would be (B116) > (U20) > (Z80).
228
Figure 4 shows TPR profile of 1wt%Pt-3wt%Re/SA. The reduction profile of Pt-Re/SA
229
shows a reduction peak at ca. 259 C, indicating reduction of Re 7+ to Re0 [34], while Pt reduction
230
peak (Pt4+ to Pt0) would not be clear, probably due to small content of Pt of 1wt%.
231 232
3.3 Fast pyrolysis of B.Braunii residue using Py-GC/MS.
233
11
234
The catalytic fast pyrolysis of B.Braunii residue was carried out with three different catalysts.
235
Table 2 shows the product selectivity as estimated by Py-GC/MS analysis at 550 ºC, by
236
measuring the relative peak area % of liquid products. The carbon mass balance remained
237
unknown, since gaseous and solid products were not measured. In this case, gaseous products
238
contained C2-C4 hydrocarbons as well as CH4, CO, and CO2. Three porous catalysts were
239
calcined at 500 ˚C prior to use. The distribution of compounds in bio-oils was determined using a
240
semi-quantitative study based on the percentage area of the chromatographic peaks. Compounds
241
were identified using a combination of a mass spectral database and retention data for standard
242
components. Analysis of bio-oil products indicated the production of a range of mono-aromatic
243
hydrocarbons, MAH, polyaromatic, PAH [35], alkanes and alkenes, Alkane-alkene, phenols,
244
Phenol, oxygenates, Oxy, alcohols + ketones + ethers + acids and esters and nitrogen-containing
245
compounds, N-comp.. The MAH included, typically, benzene, toluene, xylenes, methylindene,
246
while the PAH included, typically, methylnaphthalene and anthracene. The Alkane-alkene
247
included, typically, dodecene, pentadecane, hexadecane, heptadecene, octadecene and higher
248
aliphatic hydrocarbons. In the Oxy products, the acids and esters predominantly formed and they
249
contained hexadecanoic acid (palmitic acid), octadec-9-enoic acid (oleic acid), and octadecanoic
250
acid (stearic acid) [36].
251
In the absence of a catalyst, fast pyrolysis of B.Braunii residue resulted in the major fraction
252
consisting of 56.0% of Oxy and 24.9% of Alkane-alkene. MAH accounted for 10.3 %, and
253
Phenols, N-comp. and PAH were also found in lesser quantities. Addition of porous catalysts
254
such as USY (20) (U20), ZSM (80) (Z80), Beta (116) (B116) significantly changed the product
255
distribution, as seen in Table 2. The proportions of MAH and PAH compounds increased to 50-
256
55% and 8-14%, whereas Oxy compounds were greatly reduced to 9-16%, and Phenol and N-
12
257
comp. were somewhat decreased. As a result, total selectivities of aromatic and aliphatic
258
hydrocarbons accounted for 85-90%, being higher than 75-80% of hydrocarbon selectivities
259
from pyrolysis of jatropha wastes (Table 2). Under the pyrolysis conditions employed, similar
260
effects were observed for three zeolite catalysts.
261
As shown in table 3 in the absence of a catalyst, the MAH selectivity slightly increased with
262
the increase in the reaction temperature from 450 ºC to 600 ºC, while Alkane-alkene selectivity
263
decreased with the increased temperature. The total hydrocarbon selectivities decreased from
264
64.3% to 33.8%. In the presence of porous catalysts, MAH selectivity accounted for 60.6%-
265
65.5%, even at 450 ºC, but the MAH selectivity slightly decreased with the increased
266
temperature, whereas the Alkane-alkene selectivity increased. Thus, the total hydrocarbon
267
selectivities were approximately constant: 84.3%-92.3% for (Z80), 90.9%-85.6% for (U20) and
268
83.8%-92.5% for (B116).
269
Table 3 shows the effects of weight ratio of catalyst to B.Braunii residue from 4 to 10. The
270
total hydrocarbon selectivities remained constant at 90.2%-91.2% for (Z80) with the increased
271
catalyst/B.Braunii residue ratio. On the contrary, for (U20), the total hydrocarbon selectivities
272
increased with the increased weight ratio from 87.1% to 94.9%. Also, for (B116), the total
273
hydrocarbon selectivities increased with the increased weight ratio from 68.4% to 97.7%. Thus,
274
the hydrocarbon selectivities at the catalyst/B.Braunii residue ratio of 10 were found to be
275
(B116) > (U20) > (Z80), which could be consistent with trends of structural and acid properties,
276
obtained from pore diameter and NH3-TPD (Table S1), but the difference of the selectivities is
277
not so large.
278
279
3.4 Fast pyrolysis of B.Braunii residue using stainless-steel reactor.
13
280
The object of runs using reactors was to estimate the yields of liquid products and to compare
281
product selectivity with the Py-GC/MS results. The B.Braunii residue was pyrolyzed in the
282
stainless-steel reactor at 550 oC-650 ºC without and with catalyst. The products consist of Gas,
283
Water-soluble phase, Organic phase, Char, and Unidentified. The two liquid phases were directly
284
obtained from the traps of the stainless steel reactor without any rinsed solvent and the organic
285
phase, which appeared as black liquid, was subjected to GC-MS analysis, as mentioned later.
286
Each yield is shown in Fig.5(A). The highest organic phase yield of 33.1wt% was achieved at
287
600 ºC without catalyst, while, at 650 ºC, the organic phase yield decreased and the char yield
288
increased. In the presence of (Z80) catalyst at 550 ºC, the organic phase yield was 27.8 wt%,
289
being three times higher than that of jatropha waste of 10.2 wt% yield. As shown in Table 4, the
290
ultimate analysis of the organic liquid product exhibited 75-77% of carbon, which was higher
291
than that of starting B.Braunii residue (63 %), while 11-15% of oxygen content was lower than
292
that of the starting residue (24 %). The estimated higher heating values (HHV) were 35-37
293
MJ/kg, which was close to a HHV value of crude triglyceride [37].
294
Organic liquid products were analyzed by GC-MS. Relative selectivities are shown in
295
Fig.5(B) and Table 5 and the chromatograms are shown in Fig.S1. The mono-aromatic
296
hydrocarbons included typically ethylbenzene, toluene, xylenes. The MAH selectivities were in
297
the order (650 ºC, no catalyst) (74.2%) > (550 ºC, (Z80)) (47.8%) > (600 ºC, no catalyst)
298
(42.7%) > (550 ºC, no catalyst) (19.8%). Poly-aromatic hydrocarbons (PAH) [35], included
299
naphthalene, alkylnaphthalenes, alkylfluorenes, and phenanthrene. For PAH, the order was (550
300
ºC, (Z80)) (30.0%) > (600 ºC, no catalyst) (24.4%) > (550 ºC, no catalyst) (13.0%) > (650 ºC, no
301
catalyst) (9.70%). The Alkane-Alkene included mainly long-chain aliphatic hydrocarbons such
302
as decene, pentadecene, 1-octadecene and cyclotetracosane. For alkane-alkene selectivity, the
14
303
order was (550 ºC, no catalyst) (31.1%) > (600 ºC, no catalyst) (7.20%) > (550 ºC, (Z80)) (3.4%)
304
> (650 ºC, no catalyst) (0.9%).
305
The oxygenates contain alcohols, ketones, ethers and acid and ester. These included 5-hexen-
306
2-one, 5-methyl-3-methylene, 4-dodec-3-en-1-ol, methyl 12,15-octadecadienoate, hexadecanoic
307
acid, methyl ester. The oxygenates selectivities decreased with the increase in reaction
308
temperature from 550 ºC to 650 ºC and the order was (550 ºC, no catalyst) (20.3%) > (600 ºC, no
309
catalyst) (12.1%) > (550 ºC, (Z80)) (11.1%) > (650 ºC, no catalyst) (2.4%) [36]. The N-
310
compounds were typically indole, alkylindole, quinoline, benzylnitrile. For N-compounds, the
311
order was (550 ºC, no catalyst) (12.7%) > (600 ºC, no catalyst) (10.1%) > (650 ºC, no catalyst)
312
(8.2%) > (550 ºC, (Z80)) (6.4%). The value of 6.4% was much lower than that of jatropha of
313
18.3%, due to lower N content. The main phenolic compounds were phenols and alkylphenols.
314
The total percentage of these compounds were below 5%.
315
Thus, at pyrolysis of B.Braunii residue, the organic liquid product yield was found to be above
316
30%, approximately 3 times higher than that of jatropha residue. Examinations of Fig.5 and
317
Table 5 indicate that hydrocarbon selectivities were greatly affected by reaction temperature and
318
(Alkane-alkene) was found to be comparable to sum of aromatic hydrocarbons at 550ºC. As the
319
temperature increased, the aromatic hydrocarbon selectivities dramatically increased and, at
320
650ºC, the MAH selectivity was as high as 74.2%. The MAH and PAH selectivities at 550 ºC
321
were improved by the presence of (Z80) catalyst. Taking organic liquid yield and hydrocarbon
322
selectivities into account, table 5 summarizes overall hydrocarbon yield, which is in the order: no
323
catalyst at 600 ºC (24.58%) > (Z80) at 550 ºC (22.57%) > no catalyst at 550 ºC (20.6%) > no
324
catalyst at 650 ºC (19.32%).
15
325
326
3.5 A comparative brief study on hydrothermal liquefaction of B. Braunii residue. In order to compare a nature of hydrothermal liquefaction (HTL) with pyrolysis, the HTL
327
reaction was briefly carried out with or without catalyst using batch reactor, where the Pt3Re/
328
SiO2-Al 2O3 (SA) catalyst was used [23]. As shown in Table 6, the selectivity of liquid
329
hydrocarbons (C5-C21+) was 51.08% with Pt3Re/SA catalyst, which was found to be a little
330
higher than the 32.02% without catalyst. As shown in table 5, the overall hydrocarbon yield with
331
catalyst was 36.8%, which was higher than the yield of 24.58% for pyrolysis at 600 ºC. Table 5
332
also shows the estimated higher heating values (HHV) were 34.72 MJ/kg, which was
333
approximately close to a HHV value of pyrolysis oil [37].
334
The coke selectivity of 1.81% with catalyst was much lower than 11.4% without catalyst. As
335
shown in Fig.6(A) and (C), the GC-MS chromatogram of organic liquid obtained by HTL of
336
B.Braunii residue were found to be rather similar to that of pyrolysis at 550 ºC without catalyst
337
(Figure S1(a)). The mass chromatogram analyses revealed the presence of a homologous series
338
of C9−C32 of n-alkanes (m/z 57) and smaller portion of n-alkenes (m/z 55). Also present but in
339
much lower abundance are C8−C18 of n-alkylbenzenes (m/z 91) and alkylnaphthalenes
340
(m/z=141) ((B) and (D) of Fig.6, respectively) [14]. The n-alkanes predominantly formed over
341
aromatic hydrocarbons, even in the presence of catalyst, due to low temperature of 400 ºC.
342
3.6 Summary of reaction pathways.
343
A reaction pathway for conversion of B. Braunii residue into hydrocarbons is shown in Fig. 7.
344
The residue mainly contains Botryococcene and algaenan with polysaccharide and protein.
345
Aliphatic
346
hydrodeoxygenation (HDO) from Botryococcene, algaenan and polysaccharide, by pyrolysis as
hydrocarbons
were
formed
through
cracking,
dehydrogenation
(DH),
16
347
well as hydrothermal liquefaction (HTL). Aromatic hydrocarbons were produced through
348
dehydrocyclization (DHC) and dehydroaromatization (DHA), from aliphatic hydrocarbons. In
349
the presence of zeolite catalyst, the aromatization of aliphatic hydrocarbons could be accelerated.
350
Protein [38] would undergo cracking, DHA and DHC to form N-containing monoaromatic
351
product, followed by DH, DHA and DHC to give heterocyclic compounds. Thus, in the pyrolysis
352
of B. Braunii residue, the aromatization could be enhanced by use of zeolite catalyst [24].
353
4. CONCLUSION
354 355
The aim of the present study is to obtain bio-oil from Botyococcus (B.) Braunii residue after B.
356
Braunii oil (Bot-oil) extraction. The study concludes that pyrolysis can be employed for
357
generating bio-oil from B.Braunii residue. From Py-GC/MS analyses using the residue and
358
zeolite catalyst, total selectivities of aromatic and aliphatic hydrocarbons accounted for 88.6%,
359
being much higher than 35.2% without catalyst. At fast pyrolysis of B.Braunii residue using
360
reactor, the organic liquid product (bio-oil) yield was found to be above 30%, approximately 3
361
times higher than that of jatropha residue. The higher heating value (HHV) of the liquid product
362
was approximately 35-37 MJ/kg, which was close to a HHV value of crude triglyceride. The
363
hydrocarbon yields were 19.3-24.6%. As a brief comparison with pyrolysis, the hydrothermal
364
liquefaction (HTL) of the residue at 400 ºC with PtRe/SiO2-Al 2O3 catalyst under H2 conditions
365
yielded liquid hydrocarbons of 36.8 % which was a little higher than that of pyrolysis at 600 ºC.
366
The n-alkanes predominantly formed over aromatic hydrocarbons, due to low temperature of 400
367
ºC. Postulated scheme was presented, where liquid hydrocarbons are formed from B. Braunii
368
residue through cracking, dehydrogenation, hydrodeoxygenation and dehydroaromatization and
369
dehydrocyclization.
370
17
371
ACKNOWLEDGMENT
372
The authors are grateful to the AFFRC grant of Ministry of Agriculture, Forestry and Fisheries of
373
Japan (MAFF).
374
375
376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412
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461 462 463 464
19
465
Figure captions:
466
Figure 1: Illustraion of stainless-steel reactor system.
467 468
1: B.Braunii residue, 2:N2 flow, 3: Thermocouple, 4: Catalyst-bed, 5: Mesh filter, 6: Electric furnace, 7: Iced trap, 8: Liquid N2 trap, 9: Plastic waste gas reservoir.
471
Figure 2: TG and DTA profiles recorded for B.Braunii residue in the nitrogen atmosphere. (A) TG, (B): DTA. Measurement conditions: See text. Figure 3: NH3-TPD of fresh zeolite catalysts. 1: Beta (116), 2:H-ZSM-5(80), 3: USY(20).
472
Figure 4:TPR profile of 1wt%Pt-3wt%Re/SiO2-A2O3 (SA).
469 470
473 474
475
Figure 5: Yields of oil, gas and char in pyrolysis of B.Braunii residue and product selectivities of bio-oil (organic phase) using stainless-steel reactor. (A): Yield; ()Gas, ()Water-soluble, ()Organic, ()Char, ()Unidentified
479
(B): Selectivities of organic phase. NCat denotes no catalyst. ()MAH: Mono-aromatic hydrocarbons, ()PAH: Poly-aromatic hydrocarbons, ()Aliphatic: sum of alkane and alkene, ()Phenol: sum of phenolic compounds, ()Oxy: sum of (alcohol + ketone + ether + acid and ester), ()N-Comp.: sum of N-compounds.
480
Figure 6: Mass chromatograms of organic liquid obtained from hydrothermal liquefaction (HTL)
481
of B.Braunii residue. (A) and (B) with PtRe/SA catalyst, (C) and (D) with no catalyst. (A)
482
and (C): Total chromatogram, (B) and (D): Mass chromatograms: m/z 57 (n-alkanes), m/z
483
55 (n-alkenes), m/z 91 (n-alkylbenzenes), m/z 141 (alkylnaphthalenes). Conditions: See
484
text.
476 477 478
485
Figure 7: Summary of reaction scheme.
486
Figure S1: GC/MS chromatograms of organic liquid product.
487 488
a: No catalyst at 550 ºC, b: No Catalyst at 600 ºC, c: No catalyst at 650 ºC, d: (Z80) at 550ºC.
489
490
491
492
493
494
495
20
496
497
Table 1Proximate and Ultimate Analyses of Botryococcus (Bot) and Jatropha residues. Proximate analysis (%)
Bot Residue
Jat Residue
moisture
10.94
volatile matter
81.13
81.0
0
0.76
ash content fixed carbon
4.95
7.93
11.39
C
63.3
46.39
H
9.30
6.55
N
3.52
4.53
O
23.88
42.53
Ultimate analysis (%)
498
499
500
Table 2. Effects of catalyst on the product selectivities in the fast pyrolysis of B.Braunii and Jatropha residues
a
501
Organic productselectivityb Catalyst
Residue
1
2
3
4
5
6
B.Braunii
10.27
0
24.90
2.43
55.98
6.39
c
B.Braunii
50.97
9.95
27.65
1.39
8.83
1.23
c
B.Braunii
55.04
7.95
26.72
0.48
9.36
0.45
Beta (116) (B116)
B.Braunii
49.87
13.93
19.75
0.11
15.57
0.77
Non
Jatropha
1.26
0
3.06
11.11
72.54
12.0
c
Jatropha
58.06
5.36
18.32
1.14
12.34
4.74
c
Jatropha
50.17
9.65
14.78
6.01
8.37
11.04
Jatropha
52.04
12.67
14.41
2.86
13.50
4.53
Non ZSM(80) (Z80) USY (20) (U20) c
ZSM(80) (Z80) USY (20) (U20) c
Beta (116) (B116) 502
503 504
a
b
Conditions: Catalyst/residue ratio =2.5/0.4, 550ºC. Remark: 1: Mono-aromatic hydrocarbon (MAH), 2: Poly-aromatic
hydrocarbons (PAH), 3: Alkane andalkene, 4.:Phenol, 5: Oxygenates (Alcohol + ketone + Ether + Acid and ester), 6: Ncompounds c
505
The number in parentheses denotes Si/Al2 ratio.
21
506 507 508
Table 3. Effects of reaction temperature and catalyst/residue ratio on the product selectivities in the fast pyrolysis of B.Braunii residue
509
b
Catalyst Non
Temp./ºC
1
2
3
4
5
6
450
6.2
3.77
0
60.57
0.38
33.84
1.16
500
6.2
4.58
2.68
41.05
1.70
46.76
3.26
550
6.2
10.27
0
24.9
2.43
55.98
6.39
600
6.2
9.58
0.52
23.7
1.79
62.27
2.15
ZSM (80)
450
6.2
62.34
6.22
15.76
0.30
13.38
1.66
(Z80)
500
6.2
57.89
15.48
9.57
0.43
15.46
1.19
550
6.2
50.97
9.94
27.65
1.39
8.83
1.23
600
6.2
52.26
7.16
32.91
1.02
2.25
4.37
USY (20)
450
6.2
65.49
11.89
13.50
0.47
7.35
1.29
(U20)
500
6.2
64.21
8.18
10.07
0
14.76
2.81
550
6.2
55.04
7.95
26.72
0.48
9.36
0.45
600
6.2
49.40
8.81
27.34
0.42
10.84
3.23
Beta (116)
450
6.2
60.60
17.73
5.46
0
15.79
0.43
(B116)
500
6.2
61.62
16.88
14.02
0
6.78
0.69
550
6.2
49.87
13.93
19.75
0.11
15.57
0.77
600
6.2
36.96
16.24
35.25
0.52
10.6
0.40
ZSM(80)
550
4
39.17
7.45
43.61
0.61
7.99
1.15
(Z80)
550
6.2
50.97
9.95
27.65
1.39
8.83
1.23
550
10
49.17
9.32
32.71
0
8.07
0.74
USY (20)
550
4
57.70
13.38
16.04
0
11.96
0.93
(U20)
550
6.2
55.04
7.95
26.72
0.48
9.36
0.45
550
10
52.70
12.52
29.73
0.46
4.59
0
Beta (116)
550
4
38.57
11.85
17.98
0.15
30.81
0.33
(B116)
550
6.2
49.87
13.93
19.75
0.11
15.57
0.77
550
10
51.11
16.66
29.94
0.21
2.06
0
a 510
Organic product selectivitya
Catalyst/Residue ratio
b
Remark:See footnote of Table 3. The number in parentheses denote Si/Al2 ratio.
22
511
512
513
Table 4. Elemental composition and energy content of pyrolysis bio-oil and HTL oil (organic phase) from B.Braunii residue..
514
515
HTL oil
Pyrolysis Bio-oil
Overall a yield(C5+)
hydrocarbon
No Catalyst/ 650ºC
No Catalyst/ 600ºC
19.32
24.58
No Catalyst/ 550ºC
(Z80) / 550ºC
516
Pt3Re/SiO 2517 Al2O3/ 400ºC 518
20.60
22.57
36.80
519
520
Ultimate analysis
b
521
C
-
77.28
77.26
74.69
H
-
8.92
7.84
9.14
8.73
523
N
-
2.63
1.84
1.33
1.92
524
O
-
11.17
13.06
14.84
15.01
525
-
36.97
35.08
35.64
34.72
526
HHV/ MJ/kg
c
73.81
522
527
528
529
530
a
Overall hydrocarbon yield = (organic liquid yield) x (sum of aromatic and aliphatic hydrocarbons selectivities)/100.
The ultimate analysis was carried out using organic phase product. b
531
Estimated by Dulong’s equation.
532
533
23
534
Table 5. Main Componenta of the Algal Bio-Oils Obtained from Fast Pyrolysis of B.Braunii Residues a
Organic products
RT , min
Area% NoCat550
NoCat600
NoCat650
(Z80)-550
2.08
0.69
1.487
Benzene
0
0.88
1.954
Toluene
2.99
8.04
2.625
Ethylbenzene
2.73
2.25
1.97
1.87
2.724
o-Xylene
5.41
7.11
6.37
8.25
2.934
Styrene
2.945
p-Xylene
3.90
5.49
3.60
5.02
3.333
Phenol
1.18
1.82
1.36
0.75
3.694
Acetic acid, chloro-, isobutyl ester
1.87
1.57
0.85
1.27
3.704
1-Decene
3.788
-Methylstyrene
3.972
Benzene, 1-ethyl-3-methyl-
4.029
Benzene, 1-propenyl-
4.114
2-Chloro-N-ethylacetamide
1.95
4.287
Benzene, 1,2,3-trimethyl-
1.34
4.297
4-Ethylphenethylamine
4.381
Phenol, 4-methyl-
1.83
1.80
3.03
4.522
Indene
1.28
2.63
3.88
3.29
4.722
Undecene
1.94
4.80
1,8-Nonadien-3-ol
1.02
4.905
Benzene, 1-ethyl-2,4-dimethyl-
1.38
1.03
0.61
5.403
Benzene, 1-methyl-4-(2-propenyl)-
0.98
1.05
2.40
1.07
5.67
1H-Indene, 1-methyl-
1.71
2.73
0.30
4.25
5.686
Benzene, 1-butynyl-
4.12
2.55
2.25
5.754
2-Dodecene, (E)-
5.827
Azulene
1.35
4.00
7.79
5.57
4.60
2.04 1.31 3.93
1.62
1.44
3.84
1.19
5.26
0.69
1.22 5.53
1.26
2.34
1.26
2.89
24
6.121
Naphthalene
0.78
6.299
1,4-Cyclohexanedimethanamine
1.64
6.514
Butanoic acid, 3-oxo-, 2,2,2-trichloroethyl ester
1.11
6.74
1-Tridecene
1.94
6.865
1H-Indene, 4,7-dimethyl-
7.043
Indole
7.279
1.65
4.36
0.75
0.80
3.02
2.13
6.40
1.33
1.51
1.14
1.23
Naphthalene, 1-methyl-
0.82
1.71
3.86
0.60
7.442
Naphthalene, 2-methyl-
1.53
1.09
2.78
1.63
7.683
7-Tetradecene, (Z)-
1.87
8.218
Naphthalene, 2,3-dimethyl-
0.96
8.574
1-Pentadecene
1.59
8.637
Pentadecane
0.96
8.821
Biphenylene
9.424
1-Hexadecene
9.428
Naphthalene, 1,6,7-trimethyl-
9.963
Fluorene
10.08
8-Heptadecene
0.59
10.99
1-Octadecene
0.69
11.68
Phenanthrene
11.72
1-Nonadecene
0.94
12.41
3-Eicosene, (E)-
0.36
12.71
Anthracene, 2-methyl-
0.45
0.25
13.83
Pyrene
0.21
0.18
14.33
1-Docosene
0.48
14.91
9-Tricosene, (Z)-
0.41
15.48
Cyclotetracosane
0.34
16.55
Hexacosane
0.35
1.34 4.52
5.08
6.70
1.90
0.41
0.98
1.69
4.28
0.19
1.83
0.79
1.16
0.66
1.08
0.16 0.12
0.23
a 535
RT: Retention time.:
536
25
537
538
539
540
541
542
543
Table 6Hydrothermal liquefaction of B.Braunii residue using batch reactor. a Catalyst
544
Selectivity%
b
C1-C4
C5-C9
C10-C15
C16-C20
C21+
Coke
Unidentified
Non
12.89
5.50
8.38
7.23
10.91
11.40
43.89
Pt3Re/SiO2-Al2O3
16.40
9.39
14.36
13.06
14.27
1.81
30.72
a
Conditions and Selectivity: See Experimental section.
545
546
26