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Catalytic hydrodeoxygenation of algae biooil over bimetallic Ni-Cu/ZrO catalysts 2

Qingjie Guo, Man Wu, Kai Wang, Liang Zhang, and Xiufeng Xu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie5042935 • Publication Date (Web): 02 Jan 2015 Downloaded from http://pubs.acs.org on January 6, 2015

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Industrial & Engineering Chemistry Research

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Catalytic hydrodeoxygenation of algae bio-oil over

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bimetallic Ni-Cu/ZrO2 catalysts

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Qingjie Guoa,*, Man Wua, Kai Wang a, Liang Zhanga, Xiufeng Xub1

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a Key Laboratory of Clean Chemical Processing of Shandong Province, College of Chemical Engineering,

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Qingdao University of Science & Technology, 53 Zhengzhou Road, Qingdao 266042, PR China;

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b Institute of Applied Catalysis, Yantai University, 32 Qingquan Road, Yantai 264005, PR China

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*Corresponding author. Tel./fax: 86 53284022757 E-mail address: [email protected]

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Abstract:

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Bio-oil from the catalytic pyrolysis of algae biomass is an attractive energy

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source. To improve algae bio-oil properties for co-feeding applications in

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conventional oil refineries, bimetallic Ni-Cu/ZrO2 catalysts, with various Cu/Ni ratios

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(0.14 to 1.00 w/w) at a fixed total metal loading of 22 wt. %, were synthesized and

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used for hydrodeoxygenation (HDO) of bio-oils via the catalytic pyrolysis of

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Chlorella and Nannochloropsis sp. at 350 °C and a hydrogen pressure of 2 MPa in a

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trickle-bed reactor. It was found that the Ni-Cu/ZrO2 catalysts were more attractive

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than Ni/ZrO2 catalysts in HDO, as the addition of copper could facilitate the reduction

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of nickel oxide. As the loading of Cu increased, the HDO efficiency of the

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Ni-Cu/ZrO2 catalyst for crude bio-oil increased and thereafter decreased. The

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15.71Ni6.29Cu/ZrO2 catalyst showed the highest activity, with an HDO efficiency of

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82% for Chlorella bio-oil. Moreover, the Ni-Cu/ZrO2 catalyst was stable with low

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sintering and little coking according to transmission electron microscopy (TEM),

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X-ray diffraction (XRD) and thermal gravimetric analysis (TGA) analyses of the

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catalysts before and after reaction. In addition, this catalyst exhibited the favorable

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properties of product bio-oils. In particular, the cetane number of the upgraded bio-oil

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from Nannochloropsis sp. reached the EN 590-09 standard (specification of diesel

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fuel for vehicles).

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Key words: Bio-oil; Algae; Catalytic hydrodeoxygenation; Bimetallic Ni-Cu/ZrO2

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catalyst

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1 Introduction

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Biomass, or bio-energy, has been recognized as a renewable energy source that

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can replace fossil fuels, with the added bonus that the biomass can absorb CO2 from

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the atmosphere and reduce the greenhouse effect. Bio-oil, obtained from the pyrolysis

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of biomass in an inert gas atmosphere, has a significant appeal for use in

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transportation fuels, both economically and technologically.1 Algae can produce more

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oil than other biofuel feed stocks.2 In addition, algae, as a type of photosynthetic

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organism, even grows on waste water generated by the agricultural, food, and coal

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gasification industries.3, 4 In this case, the development of bio-oil from algae, as a

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biofuel, is an innovative field of research, and this technology has been widely

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considered as an ‘algal bio-refinery’.5

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According to Chaiwong et al.2, the main groups of aromatic hydrocarbons,

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including heterocyclic, phenol, amine, amide, indole, alkane and nitrile, were found in

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algae crude bio-oil. The length of the carbon chain in the crude bio-oil was in the

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range of C7-C17, and the oil boiling point was approximately 100 °C-300 °C. As a

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refined fuel, diesel is made up of hydrocarbons with approximately 10 to 22 carbons,

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mainly composed of aromatic hydrocarbon, cycloparaffin hydrocarbon and alkane.

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Thus, the chemo-physical properties of the crude bio-oil were similar to those of

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diesel oil.6 However, the crude bio-oil normally contained a high water content and

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high level of oxygen and could not be directly used as a transportation fuel. Due to its

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oxygen-rich compositions, crude bio-oil had some undesirable properties for

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application in fuels, such as a low heating value, immiscibility with hydrocarbon fuels,

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thermal and chemical instability, high viscosity and corrosiveness.7,

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reasons, as an alternative energy source, an upgrading process was required for crude

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bio-oil. Catalytic hydrotreatment, commonly known as “hydrodeoxygenation” (HDO), 3 ACS Paragon Plus Environment

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For these


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was one of the most promising technologies for improving the properties of crude

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bio-oil.9

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In the process of HDO, the crude bio-oil reacted with hydrogen in the presence

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of a catalyst. Hence, the development of a catalyst with a high activity and stability

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was a significant challenge for the HDO of crude bio-oil.10, 11 In many reports, the

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conventional hydrotreating catalysts, such as sulfided or unsulfided Co-Mo or Ni-Mo,

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were investigated.12, 13 However, these catalysts were unstable in the hydrotreating

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process. Therefore, some researchers focused on noble metals, such as Pt-, Pd- and

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Ru-based catalysts, for HDO of crude bio-oil from the pyrolysis of biomass.

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Wildschut et al.14 studied Ru-based catalysts in the HDO process of crude bio-oil

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from the pyrolysis of lignocellulosic biomass. It was found that the Ru/C catalyst

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reached the de-oxygenation level of 90 wt.% and was superior to the classical HDO

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catalysts, such as sulfided Ni-Mo/Al2O3 and Co-Mo/Al2O3. In particular, the new

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bio-oil contained less acids and water than the original crude bio-oil after the HDO

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process. Unfortunately, the high cost of noble metal catalysts may limit their

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application.

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While developing a non-noble metal catalyst with high activation and stability

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for HDO, nickel was found to be a good choice as an active component of the

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catalyst.15, 16 In addition, the loading of Cu to an Ni-based catalyst may enhance the

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activity of hydrogenation reactions by reducing the reduction temperature of nickel

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species,17 preventing the formation of carbon and limiting the sintering of active

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phases in the catalyst.18 Initial screening studies on bimetallic Ni-Cu catalysts showed

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their potential for model compounds, such as anisole, o-cresol19-21 and crude bio-oils

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from lignocellulosic biomass.18,22

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The components of crude bio-oil from algae biomass were different than the 4 ACS Paragon Plus Environment

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components of lignocellulosic bio-oil. On the one hand, the algae bio-oil included

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carbonyls, aromatic hydrocarbons, phenols and nitrogen-containing compounds,

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which were absent in the terrestrial bio-oil.23 On the other hand, the crude bio-oil from

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lignocellulosic biomass had a number of compounds and contained the guaiacyl group,

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which had a low conversion rate compared to carboxyl or carbonyl compounds and

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caused high coke formation during HDO. These compounds were absent in the algae

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bio-oil.23, 24 To the best of our knowledge, the upgrading process of crude bio-oil from

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algae using a bimetallic Ni-Cu catalyst has not been investigated, and further research

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is needed.

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In the present study, a series of HDO experiments were carried out using

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bimetallic Ni-Cu catalysts with different Cu/Ni (w/w) proportions in a lab-scale

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trickle-bed reactor to develop a low-cost, highly active and stable catalyst. In the

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HDO process of producing bio-oil from the pyrolysis of algae, the effect of Cu on the

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activity and stability of bimetallic Ni-Cu catalysts was examined in detail. ZrO2 was

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selected as a support for bimetallic Ni-Cu catalysts because ZrO2 possesses rich acid

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sites on the surface and could supply many adsorption sites for oxy-compounds.25

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Furthermore, the activity of the Ni-Cu/ZrO2 catalyst was compared with that of a

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sulfide Ni-Mo/Al2O3 catalyst. The purpose of the present study was to upgrade the

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quality of algae bio-oil by using bimetallic Ni-Cu catalysts. The upgraded bio-oil

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could partially substitute for fossil carbon in liquid transportation fuels.

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2 Experimental

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2.1 Preparation of crude bio-oils from algae

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The algaes used in this study were Chlorella and Nannochloropsis sp. in powder

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form, which came from the first institute of oceanography, China’s State Oceanic

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Administration. They were dried at room temperature for one week before being fed

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into the pyrolysis reactor. The algaes were characterized by ultimate, proximate and

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component analyses. Ultimate analysis of a biomass sample was conductedin a

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CHNS/O analyzer (CUBE, German vario EL). The moisture content of a biomass

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sample (dry basis) was determined by calculating the weight loss after heating in an

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oven at 103 °C for 16 hours according to the ASTM E 871 standard, and the ash

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content was measured using the ASTM E 1755 standard. The fixed carbon and

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volatile matter were measured using the ASTM E 1756 and ASTM E 872 standards,

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respectively. Relevant properties of the Chlorella and Nannochloropsis sp. are

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compiled in Table 1.

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Table 1. Relevant properties of the Chlorella and Nannochloropsis sp. used in this study.

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The crude bio-oil from Chlorella was produced by the fast pyrolysis of Chlorella

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over a mixed MCM-41 catalyst, and crude bio-oil from Nannochloropsis sp. was

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obtained by the fast pyrolysis of Nannochloropsis sp. on a mixed CaO catalyst in a

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tube furnace reactor. Nitrogen was fed into the reactor at a flow rate of 0.6 L/min for

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30 min at room temperature. Then, heat in the reactor was increased at a ramping rate

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of 20 °C/min until a temperature of 550 °C was reached and held iso-thermally for 1 6 ACS Paragon Plus Environment

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hour for the pyrolysis of Chlorella and Nannochloropsis sp. in an N2 atmosphere. Via element analysis, the mass fractions of the oxygen element in the crude

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bio-oils from Chlorella and Nannochloropsis sp. were found to be 7.19 and 5.81 wt. %

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(dry base), respectively. As listed in Table 2, abundant aliphatic acids, amides and

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alcohol exist in the crude bio-oil from Chlorella, while aldehyde, ketone, aliphatic

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acids and alcohol are the primary oxygen-containing compounds in the crude bio-oil

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from Nannochloropsis sp.

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Table 2. Main organic components in crude bio-oils from Chlorella and Nannochloropsis sp.

2.2 Preparation of HDO catalysts

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The ZrO2 used was in the form of monoclinic crystals with an average particle

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size of 2µm. Before use, ZrO2 was calcined at 500 °C for 3 hours to remove water and

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other impurities.

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ZrO2-supported catalysts were synthesized by impregnating ZrO2 with an

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aqueous solution of Ni(NO3)2·6H2O and Cu(NO3)2·3H2O or Ni(NO3)2·6H2O alone

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under strong agitation. After ultrasonic treatment for 3 hours, the catalysts were

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heated while stirring to form a viscous substance. Then, the samples were dried at

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110 °C for 10 hours and calcined in air at 550 °C for 5 hours. Before the HDO

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reaction, the catalysts were reduced by hydrogen for activation. The reduction

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temperature was determined by the temperature programmed reduction (TPR)

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procedure. In the case of bimetallic Ni-Cu catalysts, the total percentage of Ni and Cu

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was 22 wt. %, with different levels of the Cu/Ni mass ratio. For the single Ni catalyst, 7 ACS Paragon Plus Environment


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it contained 22 wt. % of nickel.

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The Ni-Mo/Al2O3 catalyst was provided by the Qilu petrochemical catalyst plant.

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The mass fractions of Ni and Mo, counted in terms of metal oxide, were 4 wt. % and

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16 wt. %, respectively.

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2.3 Catalyst characterization

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The weight fractions of Ni and Cu metals in the catalyst samples were

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determined by inductively coupled plasma-optical emission spectrometry (ICP-OES),

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with microwave digestion as the sample pretreatment method. Accurately weighed

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50-150 mg samples werecompletely dissolved in 16 mL of aqua regia using

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microwave digestion. Then, the samples were diluted with deionized water and

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analyzed by ICP-OES (Prodigy XP, Leeman, USA). The contents of Ni and Cu were

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quantified with the calibration curves of standards in known concentrations.

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Bulk phases of catalysts were characterized by XRD (Rigaku, D/Max-3C) using

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Cu-Kα radiation (λ=1.54056 Å) operated at 40 kV and 100 mA. 2θ scanning was

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operated in the range of 40° to 70° with a step size of 0.02°. The average crystallite

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size of the active phase was calculated by Scherrer’s formula, shown in Equation 1:

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଴.଼ଽ஛

݀ = ஒୡ୭ୱ஘d

(1)

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where d is the crystallite size (nm), B is the FWHM of the characteristic peak, θ is the

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characteristic diffraction angle (°) and λ is the wavelength of the X-ray.

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The reducibility of NiO-CuO/ZrO2 and NiO/ZrO2 was examined by

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temperature-programmed reduction (TPR) via the following steps: 0.03 g

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NiO-CuO/ZrO2 or NiO/ZrO2 with a particle size of 80-180 µm was fed into a silica 8 ACS Paragon Plus Environment

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tube, and then, a reducing gas (5% H2-95% N2) was pumped into the tube with a flow

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rate of 30 mL/min. The temperature was raised to 800 °C with a heating rate of

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5 °C/min, and hydrogen consumption was detected by a thermal conductivity detector

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(TCD).

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Catalyst morphology was characterized by transmission electron microscopy

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(TEM, JEOL, JEM-2100) with an accelerating voltage of 200 kV. The samples were

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prepared via ultrasonic dispersion in ethanol. Consequently, the suspension was

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deposited upon a “holey” carbon film supported on a copper grid.

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The amount of coking on the used catalyst was measured by a thermogravimetric

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analyzer (TG 209F1, Netzsch, Germany). The used catalysts were washed with

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alcohol to remove residual oil on the surface and dried at 200 °C for 2 hours, and then,

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a 0.05 g dried sample was heated to 700 °C, with a heating rate of 10 °C/min in

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flowing air. The amount of coking is calculated by Equation 2: Coke (%) =

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m1 − m2 ×100% m1

(2)

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where coke (%) represents the amount of coking on the used catalyst, and m1 and m2

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are the sample weights at 200 °C and 700 °C, respectively.

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2.4 HDO experimental setup

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As shown in Scheme 1, the experimental setup includes a trickle-bed reactor,

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pump, temperature controller, condenser and liquid collecting system. The reactor

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was made of 022Cr17Ni12Mo2 stainless steel with a diameter of 11.8 mm and a

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length of 48.4 mm. 9 ACS Paragon Plus Environment


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Four milliliters (approximately 8.0 g) HDO catalyst was placed in the reactor, and

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the reaction temperature was increased from room temperature to 350 °C in 15 min in

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a nitrogen atmosphere. After reaching the desired temperature, the flow gas was

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switched from nitrogen to hydrogen, and then, the bio-oil was pumped into the reactor.

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Subsequently, the HDO products were cooled in the condenser, and the liquid sample

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was centrifuged to separate the aqueous phase and oil phase. The oil phase was

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analyzed using various techniques (see Section 2.6).

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Scheme 1. Schematic layout of the hydrogenation equipment.

2.5 HDO reaction conditions

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Before the HDO reaction, catalysts with an average size of 150 µm were

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pre-reduced using hydrogen in the reactor. The reduction temperature was 450 °C for

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bimetallic Ni-Cu/ZrO2 precursors and 500 °C for monometallic Ni/ZrO2 precursors,

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according to the TPR analysis for the catalysts (see Section 3.1). These catalysts were

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reduced for 2 hours in hydrogen under a pressure of 2 MPa and at a flow rate of 80

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mL/min. The Ni-Mo/Al2O3 catalyst, before HDO reaction, was pre-sulfided in situ at

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500 °C for 2 hours using dimethyl disulfide with a volume flow rate of 0.2 mL/min.

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The pre-sulfided Ni-Mo/Al2O3 catalyst was marked as S-Ni-Mo/Al2O3.

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The crude bio-oil derived from the catalytic pyrolysis of Chlorella was selected

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for studying the effects of the Ni/Cu mass ratio on the catalytic activity of Ni-Cu/ZrO2

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catalysts. For the typical HDO procedure, the operation conditions were selected

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according to previous research.16, 26 The operation pressure was 2 MPa, operation 10 ACS Paragon Plus Environment

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temperature was 350 °C, liquid hourly space velocity (LHSV) of feeding was 3.5

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h-1and volume ratio of H2/oil was 450 N m3/m3. Two grams silica sand, with a size of

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150-250 µm, was mixed with the catalyst to enhance heat transfer. The upgraded

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bio-oil was collected after accumulating for 3 hours in the HDO process, and the

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component and element composition of the upgraded bio-oil was measured by a

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GC-MS analyzer and elemental analyzer, respectively. It should be noted that 0.5%

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dimethyl disulfide was added to the crude bio-oil when S-Ni-Mo/Al2O3 was used as

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the HDO catalyst.

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The stability of the bimetallic Ni-Cu/ZrO2 catalyst was analyzed using crude

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bio-oil from Chlorella under the same conditions as above. In addition, the catalyst

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was sampled after running 3, 6, 12, 18, and 24 hours, separately, and their bulk phases

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and amount of coking were measured by XRD and TGA analyses, respectively. The

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HDO efficiency of upgraded bio-oil under different accumulated times was evaluated

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on the basis of elemental analysis data.

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2.6. The analysis of HDO products

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The heat value of bio-oil was measured by an automatic quick calorimeter

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(WELL800, Shanghai ouri instrument equipment co., LTD). The kinematic viscosity

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of bio-oil at 40 °C was measured by an oil kinematic viscosity analyzer (SYD-265,

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Shanghai changji geological instrument co., LTD). The cetane number of bio-oil was

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measured in accordance with the standard test methods described by ASTM D613.27

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A trace moisture analyzer (Zibo zifen instrument co., LTD) was employed for mass

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fraction analysis of water in bio-oil. In the experiments, the elemental composition of 11 ACS Paragon Plus Environment


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bio-oil was measured by an elemental analyzer (CUBE, German vario EL).

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The analysis of crude bio-oils and upgraded bio-oils was performed by a Trance

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GC/Trace MS (Thermo Finnigan, American) with an HP-5MS column (60 mm×0.25

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mm i.d.; 0.25 µm film thickness). The injection volume was 0.4 µL. An injector

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temperature of 300 °C and a split ratio of 1:40 were used. The oven temperature was

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raised to 100 °C and maintained for 5 min, then increased to 280 °C at a rate of

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20 °C/min and maintained for 20 min.

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The hydrodeoxygenation efficiency was calculated by Equation 3: HDO efficiency =

ω1 − ω2 ×100% ω1

(3)

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where ω1 and ω2 are the oxygen contents (wt. %, dry basis) of the crude bio-oil and

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upgraded bio-oil, respectively.

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3 Results and discussion

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3.1 Effect of Cu doping on the physicochemical properties of Ni-Cu/ZrO2 catalysts

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The catalysts were prepared via wet impregnation of Ni and Cu metals on the

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ZrO2 support. An overview of the catalyst formulation used in this study is given in

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Table 3. The total loading of active metals (Ni and Cu, 22 wt.%) is the same, while

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the Ni to Cu weight ratios vary considerably. For comparison, a monometallic catalyst

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of Ni/ZrO2 was prepared and tested as well.

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Table 3. Chemical composition of the reduced fresh catalysts determined by the ICP method.

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The phase composition of the active component of the catalysts after reduction

251

was determined by XRD, and the results are given in Fig. 1. According to the XRD

252

data, the characteristic diffraction peaks of Ni/ZrO2 catalyst at 44.5° and 51.8°

253

demonstrated that the active phase of the Ni/ZrO2 catalyst existed in the form of metal

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Ni.28 Compared with the Ni/ZrO2 catalyst, the diffraction peaks of

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15.71Ni6.29Cu/ZrO2 at 44.0° and 51.3° were shifted toward smaller angles. This

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indicated the formation of a NixCu1-x alloy (or solid solution), where X depends on the

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initial loading.17 Therefore, the active phase of the bimetallic Ni-Cu/ZrO2 catalyst

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existed in the form of a Ni1-xCux alloy. Meanwhile, the characteristic diffraction peaks

259

of the Ni1-xCux alloy were wider than those of metal Ni on Ni/ZrO2. This result

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indicated that the particle size of the active phase decreased, and the growth of Ni was

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suppressed due to the introduction of Cu. The small particle size of the active phase

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showed that the active phase was well dispersed on the surface of the ZrO2 support.29 13 ACS Paragon Plus Environment


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Fig. 1. XRD patterns of monometallic Ni/ZrO2 and bimetallic Ni-Cu/ZrO2 catalysts. a. Ni/ZrO2; b. 17.6Ni4.4Cu/ZrO2; c. 15.71Ni6.29Cu/ZrO2.

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Both of the catalysts (Ni/ZrO2 and 15.71Ni6.29Cu/ZrO2) were analyzed, in

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reduced form, by TEM, and the results are given in Fig. 2. Large and non-uniformly

267

dispersed metal clusters are visible in the results of the monometallic Ni/ZrO2 catalyst

268

(Fig. 2(a)). In the results of the bimetallic Ni-Cu/ZrO2 catalyst, the metal clusters are

269

small and evenly distributed on the support (Fig. 2(b)). The observations shown in the

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TEM figures were in accordance with the XRD measurements.

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Fig. 2. TEM images of the reduced Ni/ZrO2 (a) and 15.71Ni6.29Cu/ZrO2 (b).

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The reduction behavior of the active phase precursor was studied to determine

273

the activation temperature before the HDO reaction. The reduction profiles of the two

274

samples are given in Fig. 3. A strong peak, centered at approximately 500 °C, was

275

observed in the Ni/ZrO2 sample, which was attributed to the reduction of NiO. For the

276

15.71Ni6.29Cu/ZrO2 catalyst, several peaks, centered at approximately 275 °C,

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310 °C and 450 °C, were present in the TPR curve. Note that the reduction peak

278

between 230 and 300 °C was likely associated with the reduction of Cu(II) to Cu(0).30

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Peaks above 300 °C were associated with the reduction of bimetallic NixCu1−x

280

species16 and the reduction of Ni(II) to Ni(0)18. The reduction of weakly bound NiO

281

also took place in this temperature region, as the defective structure facilitated

282

reduction at a lower temperature compared to the well-crystallized bulk NiO31.

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For the TPR curve of the bimetallic Ni-Cu catalyst, the reduction peaks of NiO 14 ACS Paragon Plus Environment

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shifted to a lower temperature (centered at approximately 310 °C and 450 °C)

285

compared with that of monometallic Ni/ZrO2, demonstrating that the addition of Cu to

286

the Ni-Cu/ZrO2 catalyst promoted the nickel oxide reduction.19 This was also

287

observed by Robertson et al., who attributed the more facile reduction of CuO in the

288

bimetallic Ni-Cu sample to the molar free energy of reduction being lower for this

289

oxide (-100.65 kJ/mol at 25 °C) than for NiO (-12.31 kJ/mol at 25 °C).19, 32 Therefore,

290

the positions of the hydrogen consumption peaks for the bimetallic samples were

291

shifted to a lower temperature. Moreover, as illustrated in Fig. 3, for the same weight

292

samples, the integral area of the Ni-Cu/ZrO2 curve is larger than that of Ni/ZrO2. For

293

the Ni-Cu/ZrO2, the consumption of hydrogen was 160 mL per gram catalyst

294

precursor, while for the Ni/ZrO2, the consumption of hydrogen was 52.4 mL per gram

295

catalyst precursor. It is implied that the hydrogen consumption of Ni-Cu/ZrO2 was

296

more than that of Ni/ZrO2. Therefore, the high hydrogen consumption contributed to

297

the formation of reduced active particles on the Ni-Cu/ZrO2 catalyst.

298

299

Fig. 3. TPR profiles for the Ni/ZrO2 and 15.71Ni6.29Cu/ZrO2 catalysts.

3.2 Effect of Cu doping on the HDO performance of Ni-Cu/ZrO2 catalysts

300

The HDO performance of Ni-Cu/ZrO2 catalysts with different Cu/Ni weight

301

ratios for the crude Chlorella bio-oil was investigated, as shown in Fig. 4. Fig. 4

302

illustrates that mono- and bimetallic catalysts are both active in crude bio-oil, with

303

HDO efficiencies between 31.8 % and 81.9 %. The HDO efficiency for the

304

monometallic Ni/ZrO2 catalyst was lower (31.8 %) than those for bimetallic catalysts, 15 ACS Paragon Plus Environment


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305

which indicated a positive effect of Cu. For the bimetallic catalysts, the HDO

306

efficiency of crude bio-oil has a relationship with the Cu/Ni ratio. The activity of the

307

Ni-Cu/ZrO2 catalysts was first increased and then reduced with increasing Cu/Ni ratio.

308

The 15.71Ni6.29Cu/ZrO2 catalyst was the most active in this series with a maximum

309

HDO efficiency of 82 %.

310

Such changes in the HDO efficiency were caused by the changing of the

311

electronic properties in the Ni xCu1-x alloy particle. According to the electron-band

312

theory, as a Group VIII metal, nickel has free d-orbitals delocalized in the

313

conductivity band, whereas copper, as a Group 1B, has free d-electrons. Therefore, a

314

significant change in the catalytic activity of Ni-based alloys can be expected because

315

the Ni interaction with the Group 1B metal caused the filling of the d-zone19.

316

According to the modern catalytic theory, catalysts with moderate adsorption strength

317

have higher activities. Due to the fewer d-band holes in Ni1-xCux compared to that of

318

Ni, the absorption strength of active hydrogen was weakened when moderate Cu was

319

introduced. Thus, active hydrogen could easily migrate on the catalyst’s surface,

320

promoting a hydrogenation reaction.33, 34 However, with the further increase of Cu,

321

the absorption strength of active hydrogen would be too weak. In this case, little

322

active hydrogen could be supplied to the HDO reaction. As expected, the activity of

323

the catalyst decreased.35 Moreover, an analogous effect can also occur in the

324

interaction with the desired oxygenated molecules. The Cu broke the Ni ensembles on

325

the catalyst’s surface, and the potential for back-donation from d-orbitals to the

326

adsorbed oxygenated molecules was lower for the alloy than for the pure Ni, thus 16 ACS Paragon Plus Environment

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limiting the adsorption strength of the desired oxygenated molecules, as previously

328

proposed by other researchers 36. These reasons would explain the observed changes

329

in the HDO efficiency of crude Chlorella bio-oil with the loading of Cu, as seen in

330

Fig. 4. This is especially true in the case of Cu/Ni=40 wt.%, for which the catalytic

331

activity reached its maximum point.

332

Fig. 4. Effect of Cu/Ni weight ratios of the Ni-Cu/ZrO2 catalyst on the product yield and the catalytic

333

HDO efficiency for crude Chlorella bio-oil.

334

(Reaction conditions: Pressure, 2 MPa; Temperature, 350 °C; Liquid hourly space velocity, 3.5

335

h-1, H2/Oil (volume ratio), 450 N m3/m3; Time, 3 hours)

336

This result is also supported by XRD, TEM and TPR analyses. As demonstrated

337

from XRD and TEM, the high dispersion of the active phase was obtained via the

338

introduction of moderate Cu. Therefore, the relatively high activity of the bimetallic

339

Ni-Cu catalyst compared to the monometallic Ni-based catalyst could be forecasted,

340

due to the presence of relatively small metal clusters. In addition, a high reducibility

341

of the bimetallic Ni-Cu catalyst was observed. The formation of reduced particles was

342

also high for the bimetallic Ni-Cu catalyst, as shown by TPR analysis. Eventually, an

343

increase in the HDO activity of the Ni-Cu/ZrO2 catalyst was caused.

344

3.3 The stability of bimetallic Ni-Cu catalysts

345

For the HDO reaction, one of the major challenges was catalyst stability.

346

Therefore, the stability of the catalyst was studied in a trickle-bed reactor using

347

Chlorella crude bio-oil under constant reaction conditions, with the exception of time. 17 ACS Paragon Plus Environment


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348

The structure, morphology and texture of the catalysts may be affected over long time

349

periods. To obtain a better understanding of the deactivation phenomena for the

350

bimetallic Ni-Cu catalyst, the spent catalysts were analyzed by XRD, TEM and TGA,

351

and the data were compared with those for the fresh catalysts.

352

After a 24 hours reaction, the 15.71Ni6.29Cu/ZrO2 catalyst showed no major

353

changes in appearance by visual observation. The color of the catalyst was slightly

354

dark after the reaction, most likely due to carbon deposition, and the particle size of

355

the 15.71Ni6.29Cu/ZrO2 catalyst was minimally different.

356

Carbon deposition on the surface of the catalyst was measured by TGA analysis

357

using the spent catalysts in air. Fig. 5 shows the variation of catalytic HDO efficiency

358

and the amount of coking on the 15.71Ni6.29Cu/ZrO2 catalyst with different

359

operation times during the HDO process for crude bio-oil from Chlorella. The

360

experiments were carried out at different times, showing that the HDO efficiency

361

decreased with running time, whereas the coke deposition increased. Even for a

362

long-termrun of 24 hours, the HDO efficiency for crude oil was still larger than 77%;

363

meanwhile, the amount of coking on 15.71Ni6.29Cu/ZrO2was only 2%, indicating

364

that the stability of the bimetallic Ni-Cu catalyst was very high.

365

In this study, the reaction data presented in Fig. 5 show that HDO efficiency

366

decreases over a 24 hours run time but declines more slowly in the latter portion of

367

the run. This can be explained by the following reasons. On the one hand, the HDO

368

efficiency was the average during the reaction time. It can be seen that the HDO

369

efficiency per hour was high at the beginning and then declined with the increase of 18 ACS Paragon Plus Environment

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370

time-on-stream in the latter period. Thus, the average of the HDO efficiency

371

decreased with increasing time. On the other hand, during the experiment, the

372

fluctuation of HDO efficiency, determined by elemental analysis, was inevitably

373

caused by experimental error. When the time increased from 18 hours to 24 hours, the

374

average of the HDO efficiency only changed from 77.5 % to 77 %. That small

375

decrease in the HDO efficiency was a normal fluctuation. Therefore, the

376

15.71Ni6.29Cu/ZrO2 catalyst is stable.

377

Coking and sulfur poisoning are two important constraints for the activity of

378

hydrotreating catalysts. The surface’s active sites can be covered by the generated

379

coke, and in addition, sulfur poisoning can result in a decline in catalyst activity. As

380

shown in Table 6, due to the insignificant amounts of sulfur in the algae bio-oil, sulfur

381

poisoning via the Ni-Cu catalyst could be ignored during the HDO process.

382

Conversely, polymerization reactions were the major reactions leading to coke on the

383

catalyst’s surface.37,

384

nitrogen-containing heterocyclic compounds in the algae bio-oil, polymerization

385

reactions rarely occurred during the HDO process using the bimetallic Ni-Cu catalyst.

386

Hence, coking on the catalyst was not considered significant during the HDO process.

387

Fig. 5. Effect of continuous operating time on the coking amount of the 15.71Ni6.29Cu/ZrO2 catalyst

38

Due to having few condensed aromatic compounds and

388

and the catalytic HDO efficiency of 15.71Ni6.29Cu/ZrO2 and S-Ni-Mo/Al2O3 for the crude

389

Chlorella bio-oil.

390

(Reaction conditions for the 15.71Ni6.29Cu/ZrO2 catalyst: Pressure, 2 MPa; Temperature, 350 °C;

391

Liquid hourly space velocity, 3.5 h-1, H2/Oil (volume ratio), 450 N m3/m3).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

392

The XRD characterizations of the fresh and spent 15.71Ni6.29Cu/ZrO2 catalysts

393

are depicted in Fig. 6. The average particle size of active phase NixCu1-x was

394

calculated using Scherrer’s formula. After running 12 and 24 hours, the average size

395

of active phase NixCu1-x on the catalysts increased to 15.2 nm and 15.8 nm,

396

respectively, which were almost the same as the fresh catalyst value of 14.3 nm. The

397

stability of active phase NixCu1-x indicated that the growth and agglomeration of the

398

active phase was low, which led to the stable activity of the 15.71Ni6.29Cu/ZrO2

399

catalyst over a long operational time.

400

Fig. 6 XRD patterns of 15.71Ni6.29Cu/ZrO2 catalysts.

401

a. fresh catalyst; b. 12 hours running; c. 24 hours running.

402

The TEM images of the 15.71Ni6.29Cu/ZrO2 catalyst, before and after reaction,

403

are given in Fig. 7. It illustrates that the active metal particles of the bimetallic

404

Ni-Cu/ZrO2 catalyst were stable. Sintering during the hydrotreatment reaction was not

405

serious, which was also supported by the XRD analysis.

406

Fig. 7. TEM images of fresh (a) and spent (b) 15.71Ni6.29Cu/ZrO2catalysts.

407

The results show that the activity of the bimetallic Ni-Cu/ZrO2 catalyst was

408

stable in the bio-oil HDO process, even over long operational times. Therefore, using

409

bimetallic Ni-Cu/ZrO2 catalysts can be considered a promising method in the

410

hydrotreatment of algae bio-oil.

411

3.4 Properties of the upgraded bio-oil 20 ACS Paragon Plus Environment

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412

To investigate the changes in the main components of crude and upgraded

413

bio-oils, a GC-MS analysis was carried out. The results for Chlorella bio-oil are listed

414

in Table 4, while Nannochloropsis sp. bio-oil results are listed in Table 5. Chlorella

415

was a typical algae with a protein content of 44.6 wt.%. The 15.71Ni6.29Cu/ZrO2

416

catalyst showed a good HDO performance for the crude bio-oil from the catalytic

417

pyrolysis of algae with high protein. In this study, the HDO efficiency for the crude

418

Chlorella bio-oil reached up to 82 %. The acid and amide in the bio-oil, from the

419

pyrolysis of proteins, were completely converted during the catalytic hydrotreatment

420

reaction, as seen in Table 4. For the Nannochloropsis sp. crude bio-oil, the

421

15.71Ni6.29Cu/ZrO2 catalyst also showed a high HDO performance, with an HDO

422

efficiency of 90 %. Table 5 shows that acids, aldehydes and ketones have been almost

423

completely removed in the upgrading of the crude bio-oilvia pyrolysis of

424

Nannochloropsis sp.. Hence, the bimetallic Ni-Cu/ZrO2 catalyst can be applied to the

425

upgrading process of algae bio-oils.

426

Table 4. Distribution and content of oxygenates in bio-oil from the catalytic pyrolysis of Chlorella and

427

its upgraded bio-oil (% mass).

428

Table 5. Distribution and content of oxygenates in bio-oil from the catalytic pyrolysis of

429

Nannochloropsis sp. and its upgraded bio-oil (% mass).

430

To evaluate the properties of upgraded bio-oil, low heat value, viscosity and

431

water content are quantified in Table 6, and the elemental compositions are also listed

432

in Table 6.

433

After the Chlorella crude bio-oil was hydrotreated on a 15.71Ni6.29Cu/ZrO2 21 ACS Paragon Plus Environment


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434

catalyst, the hydrogen content in the bio-oil increased from 9.61 to 11.53 wt.%,

435

revealing that the hydrotreatment occurred during the upgrading process. For the

436

Nannochloropsis sp. bio-oil, the hydrogen content increased from 6.20 to 11.39 wt.%.

437

Additionally, the oxygen content decreased significantly, possibly because the water

438

affected by the dehydration reactions was removed prior to the elemental analysis of

439

the upgraded bio-oil. Meanwhile, the 15.71Ni6.29Cu/ZrO2 catalyst could similarly be

440

employed to convert the organic compounds containing N and S. Compared to the

441

crude bio-oils, the content of nitrogen and sulfur elements in the upgraded bio-oils

442

was significantly lower, as shown in Table 6.

443

When considering the bio-oils for use in co-feeding in existing oil refinery units,

444

the relevant product properties of upgraded bio-oils, such as viscosity, heat value,

445

water content and cetane number, should be determined. As shown in Table 6, the

446

properties of low heat value, kinematic viscosity at 40 °C and water content all

447

effectively improvedin both of the upgraded bio-oils, with the removal of oxygen in

448

the crude bio-oils. The low heat value, kinematic viscosity at 40 °C and cetane

449

number of the upgraded Nannochloropsis sp. bio-oil were 40 MJ/kg, 3.5 mm2/s and

450

50, respectively. In particular, the cetane number met the standard of the EN 590-09

451

specification of diesel fuel for vehicles.39 In addition, the water content in the

452

upgraded bio-oil was reduced to 1.0 %. Therefore, the properties of the upgraded

453

bio-oils were improved significantly.

454

Earlier studies40, 41 have noted that the H/C molar ratio of the bio-oil was an

455

important indicator for its suitability. The H/C ratios of the upgraded bio-oils from 22 ACS Paragon Plus Environment

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456

Chlorella and Nannochloropsis sp. were 1.77 and 1.93, which were higher than the

457

values of the crude bio-oils (1.57 and 0.93). This was partly due to the hydrogen

458

uptake, and a high hydrogen uptake led to a high H/C ratio.22

459

Interestingly, as shown in Table 6, it seems that there is a relation between the

460

kinematic viscosity and H/C molar ratio of the upgraded bio-oil. In the case of high

461

H/C molar ratio, the kinematic viscosity of the bio-oil was low in both types of algae.

462

These findings may be rationalized by considering the reaction network established

463

by Venderbosch et al.42 for the hydrotreatment reaction on a Ru/C catalyst. In the

464

initial phase of the hydrotreatment process, catalytic hydrogenation and thermal,

465

non-catalytic re-polymerization occurred in a parallel pathway. Recently, Ardiyantia

466

et al.22 studied this reaction network and found that the catalytic hydrogenation

467

pathway was dominant in the HDO reactions on Ni-Cu catalysts and eventually

468

determined the ultimate product properties. The hydrogenation pathway involved the

469

hydrogenation of thermally labile components in the bio-oil, forming stable molecules

470

that were not prone to polymerization. Subsequent reactions (hydrogenations and

471

hydrocracking), on a time scale of hours, led to products with low oxygen contents

472

and high H/C ratios. High H/C ratios caused low molecular weights, which is

473

associated with the low viscosity of the bio-oil.

474

475

476

Table 6. Properties of crude and upgraded bio-oils from Chlorella and Nannochloropsis sp.

3.5 Catalytic performance comparison of Ni-Cu/ZrO2 and S-Ni-Mo/Al2O3

During the HDO process of crude bio-oil from Chlorella, the HDO performances 23 ACS Paragon Plus Environment


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477

of bimetallic Ni-Cu/ZrO2 and S-Ni-Mo/Al2O3 catalysts were compared. For the

478

different running times, the Ni-Cu/ZrO2 catalyst showed a high HDO activity.

479

Specifically, when the continuous running time extended from 3 hours to 24 hours,

480

the HDO efficiency of the Ni-Cu/ZrO2 catalyst for the crude bio-oil changed from 82 %

481

to 77 %, while the HDO efficiency of the S-Ni-Mo/Al2O3 catalyst decreased from 78 %

482

to 67 %, as shown in Fig. 5, indicating that the activity of the Ni-Cu/ZrO2 catalyst was

483

not only higher but also more stable than that of the S-Ni-Mo/Al2O3 catalyst.

484

The activity and stability of the S-Ni-Mo/Al2O3 catalyst was largely affected by

485

the composition of the crude bio-oil. The S-Ni-Mo/Al2O3 catalyst was not appropriate

486

for the HDO process of algae bio-oil because of the low sulfur content in this

487

bio-oil.16, 43 Therefore, the sulfiding agent was added to the crude bio-oil to improve

488

the HDO performance.44 Meanwhile, to obtain optimal activity, the proper

489

concentration of SOX must be maintained in the reaction environment.45 However, it

490

was hard to maintain the concentration of SOX, which was controlled by many factors,

491

such as the amount of sulfur donor compounds, the content of sulfur compounds in

492

the bio-oil and the operating conditions.46 Therefore, all these reasons led to the

493

instability of the Ni-Mo/Al2O3 catalyst in the HDO process of crude bio-oil from

494

Chlorella.

495

Because the application of the bimetallic Ni-Cu/ZrO2 catalyst was not limited by

496

the sulfur content in the crude bio-oil, it showed a higher stability than that of the

497

Ni-Mo/Al2O3 catalyst. Therefore, the Ni-Cu/ZrO2 catalyst has a high activity and

498

stability for the HDO process of algae bio-oil. 24 ACS Paragon Plus Environment

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499

4 Conclusions

500

The bimetallic Ni-Cu/ZrO2 catalystwas used for the hydrodeoxygenation of

501

crude bio-oils from Chlorella and Nannochloropsis sp. The addition of copper to the

502

Ni-Cu/ZrO2 catalyst decreased the reduction temperature of the active components

503

and prevented excessive carbon deposition on the surface. Thus the catalyst’s

504

deactivation rate was reduced. As the loading of Cu increased, the HDO efficiency of

505

Ni-Cu/ZrO2 catalysts for crude bio-oil increased and thereafter decreased, and a

506

maximum value of 82 % was reached using the 15.71Ni6.29Cu/ZrO2 catalyst.

507

Moreover, the HDO activity of the Ni-Cu/ZrO2 catalyst was higher than that of the

508

S-Ni-Mo/Al2O3 catalyst. After the HDO reaction using the 15.71Ni6.29Cu/ZrO2

509

catalyst, the properties of low heat value, kinematic viscosity at 40 °C and water

510

content in the upgraded bio-oils were effectively improved. In particular, the cetane

511

number of the upgraded bio-oil from Nannochloropsis sp. met the standard of EN

512

590-09. In summary, Ni-Cu/ZrO2 is a good catalyst for use in hydrotreating and

513

upgrading crude algae bio-oils.

514



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515 516

Acknowledgments The authors gratefully acknowledge financial support from the special fund of

517

marine renewable

energy of China (GHME2001SW02), Qingdao application

518

foundation research project (14-2-4-5-jch) and Natural Science Foundation of China

519

(21276129).

520


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References:

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(1) Sadhukhan, J.; Ng, K. S. Economic and European Union Environmental Sustainability Criteria

523

Assesment of Bio-Oil-Based Biofuel Systems: Refinery Integration Cases. Ind. Eng. Chem. Res.

524

2011, 50, 6794-6808.

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(2) Chaiwong, K.; Kiatsiriroat, T.; Vorayos, N.; Thararax, C. Study of Bio-oil and Bio-char Production from Algae by Slow Pyrolysis. Biomass Bioenerg. 2013, 56, 600-606.

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(3) Reddy, H. K.; Muppaneni, T.; Sun, Y.; Li, Y.; Ponnusamy, S.; Patil, P. D.; Dailey, P.; Schaub, T.;

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Holguin, F. O.; Dungan, B.; Cooke, P.; Lammers, P.; Voorhies, W.; Lu, X.; Deng, S.; Subcritical

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Water Extraction of Lipids from Wet Algae for Biodiesel Production. Fuel 2014, 133, 73-81.

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(4) Hamawand, I.; Yusaf, T.; Hamawand, S. Growing Algae using Water from Coal Seam Gas Industry

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(5) Mu, D.; Min, M.; Krohn, B.; Mullins, K. A.; Ruan, R.; Hill, J. Life Cycle Environmental Impacts of Wastewater-Based Algal Biofuels. Environ. Sci. Technol. (Accepted) DOI: 10.1021/es5027689.

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(6) Francis, W.; Peters, M. C. Fuels and fuel Technology. 2nd ed. Michigan: Pergamon Press; 1980.

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(7) Graça, I.; Lopes, J. M.; Cerqueira, H. S.; Ribeiro, M. F. Bio-oils Upgrading for Second Generation

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Biofuels. Ind. Eng. Chem. Res. 2013, 52, 275-287. (8) Lu, Q.; Li, W. Z.; Zhu, X. F. Overview of Fuel Properties of Biomass Fast Pyrolysis Oils. Energ. Convers. Manage. 2009, 50, 1376-1383. (9) Tang, Z.; Lu, Q.; Zhang, Y.; Zhu, X.; Guo, Q. One Step Bio-oil Upgrading through Hydrotreatment, Esterification, and Cracking. Ind. Eng. Chem. Res. 2009, 48, 6923-6929. (10)Chaudhari,

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Kinetics, Mechanism, and Reaction Engineering. Ind. Eng. Chem. Res. 2013, 52, 15226-15243.

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(11) Shi, W.; Gao, Y.; Song, S.; Zhao, Y. One-Pot Conversion of Bio-oil to Diesel- and Jet-Fuel-Range Hydrocarbons in Supercritical Cyclohexane. Ind. Eng. Chem. Res. 2014, 53, 11557-11565.

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(12) Srifa, A.; Faungnawakij, K.; Itthibenchapong, V.; Viriya-Empikul, N.; Charinpanitkul, T.;

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Assabumrungrat, S. Production of Bio-hydrogenated Diesel by Catalytic Hydrotreating of Palm

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Oil over NiMoS2/γ-Al2O3 Catalyst. Bioresource. Technol. 2014, 158, 81-90.

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(13) Krár, M.; Kovács, S.; Kalló, D.; Hancsók, J. Fuel Purpose Hydrotreating of Sunflower oil on CoMo/Al2O3 catalyst. Bioresource Technol. 2010, 101, 9287-9293. (14) Wildschut, J.; Mahfud, F. H.; Venderbosch, R. H.; Heeres, H. J. Hydrotreatment of Fast Pyrolysis Oil Using Heterogeneous Noble-metal Catalysts. Ind. Eng. Chem. Res. 2009, 48, 10324-10334. (15) Duan, P.; Savage, P. E. Hydrothermal Liquefaction of a Microalga with Heterogeneous Catalysts. Ind. Eng. Chem. Res. 2011, 50, 52-61.

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Novopashina, V. M.; Lebedev, M. Yu.; Bulavchenko, O.; Parmon, V. N. Development of New

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Ni Cu-based catalysts. Catal. Today 2009, 145, 176-185.

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(18) Ardiyanti A. R.; Khromova, S. A.; Venderbosch, R. H.; Yakovlev, V. A.; Melián-Cabrera, I. V.;

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Heeres, H. J. Catalytic Hydrotreatment of Fast Pyrolysis Oil Using Bimetallic Ni-Cu catalysts on

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Various Supports. Appl. Catal. A-Gen. 2012, 449, 121-130.

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(19) Khromova, S. A.; Smirnov, A. A.; Bulavchenko, O. A.; Saraev, A. A.; Kaichev, V. V.;

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Table captions: Table 1. Relevant properties of the Chlorella and Nannochloropsis sp. used in this study. Table 2. Main organic components in crude bio-oils from Chlorella and Nannochloropsis sp. Table 3. Chemical composition of the reduced fresh catalysts determined by the ICP method. Table 4. Distribution and content of oxygenates in bio-oil from the catalytic pyrolysis of Chlorella and its upgraded bio-oil (% mass). Table 5. Distribution and content of oxygenates in bio-oil from the catalytic pyrolysis of Nannochloropsis sp. and its upgraded bio-oil (% mass). Table 6. Properties of crude and upgraded bio-oils from Chlorella and Nannochloropsis sp.


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Table 1. Relevant properties of the Chlorella and Nannochloropsis sp. used in this study. Chlorella

Nannochloropsis sp.

C (wt.%)

44.93

49.07

H (wt.%)

6.42

7.59

O (wt.%)

40.67

35.63

N (wt.%)

6.41

6.29

S (wt.%)

1.57

1.42

Moisture (wt.%)

4.13

5.0

Volatile matter (wt.%)

69.45

79.69

Properties Ultimate analysis

Proximate analysis

Component analysis

Fixed carbon (wt.%)

16.22

10.24

Ash (wt.%)

10.20

5.03

Protein (wt.%)

42.70

44

Polysaccharide (wt.%)

9.42

21

Lipid (wt.%)

2.51

30

Others(wt.%)

45.37

5



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Table 2. Main organic components in crude bio-oils from Chlorella and Nannochloropsis sp. Bio-oil from Chlorella

Formula

Bio-oil from Nannochloropsis sp. Area

Structure

Area Formula

Structure

(%)

(%)

O

C16H32O2

10.32

C20H40O

10.17

OH

C20H40O

OH

5.36

OH

C17H32O

5.11 O

O

C18H37NO

O

NH2

4.95

C3H6O

2.88

O

O

C22H43NO

3.46

N

C11H28N2O2

1.93

NH

NH2 O

O

O OH

C18H28O2

OH

C17H32O

3.05

C18H28O2

2.07

C15H28O2

HO

1.92

OH

1.71 O

C15H26O2

O O

1.04


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Table 3. Chemical composition of the reduced fresh catalysts determined by the ICP method. Metal loading (wt. %) Catalyst Ni

Cu

22Ni/ZrO2

22.00

-

19.25Ni2.75Cu/ZrO2

19.25

2.75

18.6Ni3.4Cu/ZrO2

18.60

3.40

17.6Ni4.4Cu/ZrO2

17.60

4.40

15.71Ni6.29Cu/ZrO2

15.71

6.29

14.67Ni7.33Cu/ZrO2

14.67

7.33

13.2Ni8.8Cu/ZrO2

13.20

8.80

11Ni11Cu/ZrO2

11.00

11.00



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Table 4. Distribution and content of oxygenates in bio-oil from the catalytic pyrolysis of Chlorella and its upgraded bio-oil (% mass). Acids

Alcohols

Amides

Distribution

Original Bio-oil

Upgraded bio-oil

Distribution

Original Bio-oil

Upgraded bio-oil

Distribution

Original Bio-oil

Upgraded bio-oil

C15H26O2

1.04

0.00

C14H30O

0.95

1.43

C18H37NO

4.95

0.76

C16H32O2

10.32

1.16

C15H32O

1.42

0.00

C22H43NO

3.46

0.41

C18H28O2

3.05

0.32

C17H32O

2.07

0.00

C20H40O

5.36

0.28

Sum

9.80

1.71

Sum

8.41

1.17

Sum

14.41

1.48

34


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Table 5. Distribution and content of oxygenates in bio-oil from the catalytic pyrolysis of Nannochloropsis sp. and its upgraded bio-oil (% mass). Acids

Aldehydes and Ketones

Alcohols Phenols

Amides Upgraded

Distribution

Original Bio-oil

Upgraded bio-oil

Distribution

Original Bio-oil

Upgraded bio-oil

Distribution

Original Bio-oil

Original

Upgraded

Bio-oil

bio-oil

C11H18N2O2

1.93

0.00

SUM

1.93

0.00

Distribution bio-oil

C15H28O2

1.71

0.00

C3H6O

2.88

0.00

C7H14O

0.33

0.00

C16H32O2

0.48

0.00

C10H14O

0.56

0.00

C14H30O

0.67

0.00

C18H28O2

1.92

0.00

C9H12O3

0.57

0.00

C20H40O

10.17

0.46

C15H30O

1.63

0.00

C20H42O

0.46

0.00

C17H32O

5.11

0.00

C20H38O2

0.66

0.00

C22H42O

0.33

0.00

C17H14O

0.00

0.32

C5H10O

0.00

0.46

C6H6O

0.00

0.78

C12H22O

0.00

0.30

C11H28O

0.00

0.50

SUM

11.08

0.76

SUM

12.29

2.06

SUM

4.01

0.00

35



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Table 6. Properties of crude and upgraded bio-oils from Chlorella and Nannochloropsis sp. Chlorella

Nannochloropsis sp.

Quality parameters

C (wt. %) H (wt. %)

Crude Bio-oil

Upgraded bio-oil

Crude Bio-oil

Upgraded bio-oil

73.2

78.3

80.2

83.2

9.61

①

11.5

6.20

13.4

O (wt. %)

7.19

1.30

5.81

1.63

N (wt. %)

9.25

8.73

6.20

1.42

S (wt. %)

0.721

0.142

1.59

0.356

H/C molar ratio

1.57

1.76

0.928

1.93

O/C molar ratio

0.0736

0.0125

0.0543

0.0147

Low heat value (MJ/kg)

31.5

36.0

37.2

40.0

40°C Kinematic viscosity (mm2/s)

20.5

8.1

12.5

3.5

8.0

2.2

3.8

Water content (%)

①

1.0 50.0

Cetane number

Oxgen in the water of the bio-oil was not included in the value.


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Figure Captions: Scheme 1. Schematic layout of the hydrogenation equipment. Fig. 1. XRD patterns of monometallic Ni/ZrO2 and bimetallic Ni-Cu/ZrO2 catalysts. a. Ni/ZrO2; b. 17.6Ni4.4Cu/ZrO2; c. 15.71Ni6.29Cu/ZrO2. Fig. 2. TEM images of the reduced Ni/ZrO2 (a) and 15.71Ni6.29Cu/ZrO2 (b). Fig. 3. TPR profiles for the Ni/ZrO2 and 15.71Ni6.29Cu/ZrO2 catalysts. Fig. 4. Effect of Cu/Ni weight ratios of the Ni-Cu/ZrO2 catalyst on the product yield and the catalytic HDO efficiency for crude Chlorella bio-oil. (Reaction conditions: Pressure, 2 MPa; Temperature, 350 °C; Liquid hourly space velocity, 3.5 h-1, H2/Oil (volume ratio), 450 N m3/m3; Time, 3 hours) Fig. 5. Effect of continuous operating time on the coking amount of the 15.71Ni6.29Cu/ZrO2 catalyst and the catalytic HDO efficiency of 15.71Ni6.29Cu/ZrO2 and S-Ni-Mo/Al2O3 for the crude Chlorella bio-oil. (Reaction conditions for the 15.71Ni6.29Cu/ZrO2 catalyst: Pressure, 2 MPa; Temperature, 350 °C; Liquid hourly space velocity, 3.5 h-1, H2/Oil (volume ratio), 450 N m3/m3). Fig. 6 XRD patterns of 15.71Ni6.29Cu/ZrO2 catalysts. a. fresh catalyst; b. 12 hours running; c. 24 hours running. Fig. 7. TEM images of fresh (a) and spent (b) 15.71Ni6.29Cu/ZrO2catalysts.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Scheme 1. Schematic layout of the hydrogenation equipment.


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Fig. 1. XRD patterns of monometallic Ni/ZrO2 and bimetallic Ni-Cu/ZrO2 catalysts. a. Ni/ZrO2; b. 17.6Ni4.4Cu/ZrO2; c. 15.71Ni6.29Cu/ZrO2.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 2. TEM images of the reduced Ni/ZrO2 (a) and 15.71Ni6.29Cu/ZrO2 (b).


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Fig. 3. TPR profiles for the Ni/ZrO2 and 15.71Ni6.29Cu/ZrO2 catalysts.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 4. Effect of Cu/Ni weight ratios of the Ni-Cu/ZrO2 catalyst on the product yield and the catalytic HDO efficiency for crude Chlorella bio-oil. (Reaction conditions: Pressure, 2 MPa; Temperature, 350 °C; Liquid hourly space velocity, 3.5 h-1, H2/Oil (volume ratio), 450 N m3/m3; Time, 3 hours)


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Fig. 5. Effect of continuous operating time on the coking amount of the 15.71Ni6.29Cu/ZrO2 catalyst and the catalytic HDO efficiency of 15.71Ni6.29Cu/ZrO2 and S-Ni-Mo/Al2O3 for the crude Chlorella bio-oil. (Reaction conditions for the 15.71Ni6.29Cu/ZrO2 catalyst: Pressure, 2 MPa; Temperature, 350 °C; Liquid hourly space velocity, 3.5 h-1, H2/Oil (volume ratio), 450 N m3/m3).



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Fig. 6 XRD patterns of 15.71Ni6.29Cu/ZrO2 catalysts. a. fresh catalyst; b. 12 hours running; c. 24 hours running.


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Fig. 7. TEM images of fresh (a) and spent (b) 15.71Ni6.29Cu/ZrO2catalysts.


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