Thermal characteristics of biomass pyrolysis oil and potential

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Biofuels and Biomass

Thermal characteristics of biomass pyrolysis oil and potential hydrogen production by catalytic steam reforming Ningbo Gao, Cui Quan, Zhengzhao Ma, and Chunfei Wu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00365 • Publication Date (Web): 18 Mar 2018 Downloaded from http://pubs.acs.org on March 18, 2018

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Thermal characteristics of biomass pyrolysis oil and potential hydrogen production

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by catalytic steam reforming

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Ningbo Gaoa, Cui Quana*, Zhengzhao Mab, Chunfei Wuc*

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a

School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an, China, 710049 b

China Offshore Environmental Service Ltd, Tianjin, China, 300452 c

School of Engineering, University of Hull, Hull, UK, HU6 7RX

*Corresponding author: Tel/Fax: +86-29-82668572; E-mail: [email protected]

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Abstract: In order to facilitate the further processing and utilization of biomass pyrolysis oil, the chemical

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composition and thermal properties of biomass pyrolysis oil from pyrolysis of rice husk were investigated.

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The chemical composition analysis revealed that the pyrolysis oil contained large amount of oxygenated

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compounds, i.e., acid, ketones and phenols. Thermal degradation behaviors and kinetics of pyrolysis oil

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were investigated at different heating rates (5, 20, 35 and 50 oC min-1) under N2 and air atmosphere by TG.

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Pyrolysis oil decomposition mainly experienced three stages either in N2 or air atmosphere, and the

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corresponding activation energies vary with the degree of conversion. Py-GC/MS analysis of the pyrolysis

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oil reveals that ketones and aromatics are the main pyrolysis products of biomass pyrolysis oil. When the

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temperature increased from 600 to 700 oC during Py-GC/MS analysis, the content of ketones increased

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while the content of aromatics decreased. Subsequently, the feasibility of catalytic steam reforming of

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pyrolysis oil to produce renewable hydrogen was performed in a fixed-bed reactor with a NiO/ceramic foam

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catalyst. The effects of calcination temperature and metal content on the hydrogen yield were investigated.

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It is indicated that higher calcination temperature and loading content lead to the aggregation and sintering

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of NiO particles. A maximum hydrogen yield of 105.28 g H2 kg-1 pyrolysis oil (up to 81.1% of the

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stoichiometric yield) was obtained at reaction temperature of 700 oC, S/C ratio of 1, NiO loading content of 1

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3.54%.

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Keywords: Biomass pyrolysis oil; Reforming; Hydrogen; NiO/ceramic foam catalyst

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1.

Introduction

In recent years, energy shortage and environment problems caused by fossil fuel utilization have

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threatened the sustainable development of our society. Biomass is a promising renewable source, it can be

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converted into energy or chemicals using thermal-chemical technologies, such as pyrolysis for biomass

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pyrolysis oil, gasification for syngas, and hydrolysis for sugar, etc1-4. Among these conversion processes,

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biomass pyrolysis for oil production is an important technological route. The biomass pyrolysis oil can have

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a volumetric energy density up to ten times larger than biomass and is therefore more suitable for the

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transportation.

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Depending on the biomass feedstock and pyrolysis conditions employed (reactor type, carrier gas,

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temperature, residence time, and heating rate, etc), the composition of pyrolysis oil is varied. However, the

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pyrolysis oil mainly consists of oxygenated hydrocarbons, such as acids, ketones, alcohols, phenols and

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sugars. As a renewable liquid fuel, biomass pyrolysis oil can serve as a substitute for fuel oil or diesel in

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many static applications including boilers, furnaces, engines, and turbines for electricity generation.

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Alternatively, pyrolysis oil could serve as a raw material for the production of adhesives,

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phenol-formaldehyde-type resin, wood flavors, etc. Due to the complex composition and unstable nature of

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pyrolysis oil, it is necessary to understand the chemical structure and thermal properties of biomass

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pyrolysis oil in order to facilitate its further utilization and enhance the performance of the resultant

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materials.

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However, until now, the properties of biomass pyrolysis oil are still not very good and the undesired

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properties such as high water content, low heating value, high viscosity and corrosiveness have limited the

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range of pyrolysis oil application. Upgrading of biomass pyrolysis oil is needed to improve its properties for

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liquid fuel. These upgraded techniques are focused on catalytic hydrotreating for deoxygenation,

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hydro-cracking to make large quantities of light products, supercritical fluids or solvent addition for

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producing fuels with higher caloric value and lower viscosity, catalytic steam reforming for hydrogen

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production, or a combination of these technologies5, 6. Among the technologies above, biomass pyrolysis oil

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catalytic steam reforming for hydrogen production will be a promising way.

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In recent years, steam reforming of biomass pyrolysis oil and biomass derived model compounds has been

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extensively investigated 7-9. Ni has been extensively used as an active metal for the steam reforming of

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oxygenates due to its high activity, high hydrogen selectivity and low cost compared to noble metals. The

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Ni-based catalysts such as Ni/Al2O3, Ni/CNTs, Ni/MCM-41, Ni/Ru-Mn/Al2O3, Ni-CeO2/γ-Al2O3 have been

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developed 10-12. Published reports indicate that the biggest bottleneck for hydrogen and syngas production

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via steam reforming of pyrolysis oil in a large scale is the catalyst deactivation caused by carbon deposition

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13-15

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reforming of pyrolysis oil. Traditionally, the Ni was loaded on pellet-type or powder-type catalyst support

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16-18

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high effective catalyst recycle and high resistance to coke deposition because of its special hole structure

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and the heat and mass transfer ability 15. As one of monolithic catalyst supports, ceramic foam is a porous

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material with three-dimensional space truss structure and high specific heat capacity. In our previous study,

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NiO was loaded on the porous ceramic or ceramic foam to prepare a monolithic catalyst for biomass

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pyrolysis oil and its model compound reforming. The results indicated that the prepared monolithic Ni

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catalysts exhibited excellent ability for pyrolysis oil reforming 19-21.

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. Therefore, the exploration of effective catalyst with high resistance to coke deposition is vital for steam

. The use of monolithic catalyst emerges as interesting catalytic type due to its high mechanical strength,

Rice husk is largely available in China. Recently, a demonstration scale pyrolysis of rice husk has been

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developed in China (Shandong Province), and the fixed-bed pyrolysis reactor with a manufacturing capacity

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of 500kg/h was adopted. This work aims to examine the properties of the pyrolysis oil produced from the 4


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demonstration plant and explore the possibility of upgrading the raw pyrolysis for the production of high

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value product such as hydrogen enriched syngas.

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Therefore, in this paper, the thermal stability of the pyrolysis oil is evaluated by thermogravimetric

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analysis (TGA) including kinetic assessment. Pyrolysis gas chromatography mass spectrometry (Py-GC/MS)

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was applied to analyze the pyrolysis products of biomass pyrolysis oil, providing insights for the steam

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reforming process. In addition, NiO/ceramic foam catalyst was prepared and its physicochemical properties

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were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2 isothermal

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adsorption. Steam reforming of bio-oil for hydrogen production over NiO/ceramic foam was assessed.

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2. Materials and methods

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2.1. Feedstock

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The real biomass pyrolysis oil used in this study was obtained from Shangdong Gerun New Energy Co.

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Ltd, Zibo, China, which was produced by rapid pyrolysis of rice husk at 550 oC. The pyrolysis oil sample

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was black brown liquid with relatively good fluidity and strong pungent odor at ambient temperature. The

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ultimate analysis, proximate analysis and caloric value of the pyrolysis oil are given in Tab.1. Ultimate

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analysis of the oil was performed on VarioEL Elementar (Germany). The calorific value of the pyrolysis oil

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was determined by burning a weighed sample in an oxygen bomb calorimeter (Hebi HongTai Electronic

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technology Co., Ltd, China). From Tab.1, it is observed that the water content of the pyrolysis oil is 46.1%,

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and the pyrolysis oil has a relative high content of C and O. The calorific value of the pyrolysis oil is

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13.43MJ/kg.

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2.2. Preparation of catalyst

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The ceramic foam used in this study was purchased from Nantong Tianjian New Material Technology Co., Ltd, China. The preparation procedure for NiO/ceramic foam catalyst includes pretreatment of ceramic

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foam support, immersion ceramic foam into Ni(NO3)2 solution and calcination. First, the ceramic foam was

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rinsed with deionized water to remove impurities. The dried ceramic foam support was then dipped into a

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certain amount of Ni(NO3)2 solution for 2 h. The loading content of the catalyst was adjusted by changing

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the concentration of Ni(NO3)2 solution. After immersion, the catalyst was dried at 105 oC in an oven for 12

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h, then was put into a muffle furnace and calcined at different calcination temperatures.

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2.3 Experimental apparatus and method

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2.3.1 TG analysis

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TG analysis of pyrolysis oil feedstock was carried out using a TG/DTG analyzer (6300, SEIKO Co., Japan). The pyrolysis and combustion characteristics of pyrolysis oil were performed in TG in an

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atmosphere of nitrogen and air, respectively. During each analysis, approximately 20 mg pyrolysis oil

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sample was loaded into an Al2O3 crucible. Nitrogen or air was introduced into the TG system with a flow

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rate of 150 mL min-1 for 15min to ensure the gas flow stability in apparatus. After the baseline of TG

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reached stable, the pyrolysis oil sample was heated from room temperature to 800 oC at four different

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heating rates of 5, 20, 35, 50 oC min-1, respectively, and then remains at 800 oC for 10 min.

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2.3.2 Catalytic steam reforming apparatus

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Figure 1 shows a schematic of the apparatus of catalytic pyrolysis oil steam reforming. The fixed bed

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reactor used in the experiment has an inner diameter of 40 mm and was heated by an electric furnace. The

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temperature of the reactor was controlled by a temperature controller and monitored by a K-type

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thermocouple. NiO/ceramic foam catalyst with the size of φ37mm×150 mm was placed in the middle of the

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reaction tube. When the reaction temperature reached the preset value, the pyrolysis oil and water were

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simultaneously injected into the reaction tube by a double channel micro-infusion pump. N2 of 30 ml min-1

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was used as carrier gas. The volatile evolved from the reactor was cooled down by ice water, and the

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condensable portion was collected by liquid collector while the non-condensable gas was collected by a gas

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bag after passing through a flowmeter.

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2.4 Product characterization

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The component of produced gas was off-line analyzed by gas chromatograph (GC7890II, Techcomp,

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China) with thermal conductivity detector (TCD) for determining H2, O2, N2, CO and CO2 analyses, and

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with a flame ionization detector (FID) for alkane gases analyses. Fourier transform infrared (FTIR)

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spectrometer (IRPrestige-21, Shimadzu, Japan) was used to characterize the main functional groups in

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biomass pyrolysis oil. The scanning wavenumber of the analysis process was set at 400-4000 cm-1. The

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sequence of FTIR analysis was as follows: initially, an appropriate amount of pyrolysis oil sample was

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taken from the container to remove the moisture via the addition of anhydrous sodium sulfate. Then, 1-2 mg

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dehydrated samples were directly coated on the KBr crystalline salt to form a thin film. After the treatment

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of the original sample, the determination could be carried out on the infrared spectrometer.

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Comparative analysis of the main compounds and their content in the pyrolysis oil and in the liquid

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condensates obtained from catalytic reforming of pyrolysis oil was carried out by a Gas chromatography–

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mass spectrometry (GC/MS) (HP 6980N/5973, Agilent, America). Anhydrous sodium sulfate was used to

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remove the moisture in pyrolysis oil and then the pyrolysis oil was diluted with acetone at a ratio of 1:20.

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The testing condition of GC-MS was as follows: GC conditions (DB-5 quartz capillary column, 30 m×0.132

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mm×0.125 um; oven: 50 oC to 300 oC with a heating rate of 4 oC min-1, then maintain at 300 oC for 10 min;

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injector: 280 oC; FID: 270 oC; Carrier gas: high purity helium) and the MS conditions (EI source: 70 eV;

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source temperature: 230 oC).

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Decomposition properties of the pyrolysis oil feedstock were evaluated using a Py-GC/MS that was consisted of a Curie point pyrolyzer (JHP-5, JAI, China) and a GC/MS (6890N-5975B, Agilent, America).

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The temperature of Curie point pyrolyzer was set at 600 and 700 oC, respectively. The temperature of the

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chromatographic column (DB-5MS) was ramped from 50 oC (held for 5 min) to 250 oC (held for 10 min) at

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the heating rate of 5 oC min-1 and the split ratio was 20:1. Mass spectra were recorded in EI (230 oC) at

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scanning range of 35-600 amu. The decomposition products were identified by means of the comparison

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between the experimental mass spectrum and the mass spectrum library attached to the GC/MS apparatus.

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The identification of each product can be confirmed if the qualification percentage reaches 85% and even

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higher. The relative content of main component (peak area %) was obtained by integration and

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normalization of the peak area of each material in the spectrum.

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The morphology of the catalyst was measured by SEM (S-4800, Hitachi, Japan) with the scan voltage of

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15kV and resolution of 1nm. The crystalline structure of the catalyst was carried out by XRD (EMPYREAN,

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PANalytical, Holland) using Cu Kα as radiographic source and with tube current of 40mA, scanning rate of

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5°C min-1, scanning scope of 20-70°. The Brunauer-Emmett-Teller (BET) surface areas of catalysts were

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obtained by nitrogen adsorption at 77K using a F-Sorb3400 automatic surface area analyzer. The catalysts

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were crushed to a powder with particle size less than 0.15mm previous to its characterization by nitrogen

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adsorption, SEM and XRD.

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3. Results and discussion

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3.1 Thermal characteristic of biomass pyrolysis oil

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3.1.1 FTIR analysis of pyrolysis oil

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The FTIR spectrum of biomass pyrolysis oil (raw material in this work) is shown in Figure 2. It is

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indicated that the component of the pyrolysis oil is complex which typically includes acids, alcohols,

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aldehydes, sugars, phenolic compounds, etc. The typical functional groups and the IR signal in some of

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these compounds are similar. As observed in Figure 2, the O-H stretching vibration in carboxyl and 8


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hydroxyl functional group is presented at 3404.6 cm-1, the C=O stretching vibration in the ketone group and

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the carboxyl functional group is presented at 1717.2 cm-1, the alcohols (C-O) and ethers (C-O-C) skeletal

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vibration appears at 1268.9 cm-1 and 1052.3 cm-1, respectively. The above analysis results indicate that the

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oxygen compounds which mainly exists in the form of carboxylic acids, ketones, alcohols and ethers may

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be the main components in the pyrolysis oil. Due to its oxygen-rich composition, the biomass pyrolysis oil

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presents low heating value, immiscibility with hydrocarbon fuels, chemical instability, high viscosity,

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corrosiveness, etc.

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The content of oxygen mainly affects the intensity of carbonyl absorption bands while the hydroxyl and

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methoxyl bands are less affected 22. The obvious characteristic peaks of aromatic ring (C=C) skeletal

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vibration band at 1639.8 cm-1 and 1515.3 cm-1 reflect the existence of aromatic compounds or their

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derivatives in pyrolysis oil. The deformation vibration band of N-H at 617.6 cm-1 corresponds to the

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presence of a certain amount of nitrogen-containing organic compounds in pyrolysis oil.

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3.2.2 TG and kinetic analysis

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TG was used to assess the thermal characteristics, including pyrolysis and combustion process of pyrolysis

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oil feedstock. The TG and DTG curves for the pyrolysis and combustion of pyrolysis oil are presented in

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Figure 3. Pyrolysis oil is a thermally unstable material, and it tends to undergo decomposition processes and

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polymerization when heated. As shown in Figure 3 (a) and (b), TG and DTG curves obtained at different

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heating rates for the same sample are similar in appearance, an increase in heating rate resulted in small

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change of the pattern of the thermal decomposition; the shifts of the TG and DTG curves to higher

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temperature have been observed with the increase of heating rate under both N2 and air atmosphere,

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respectively. In addition, the intensity of DTG peak is increased with the increase of heating rate, revealing

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that the reaction rate is intensified as the heating rate increased. A broad thermal decomposition temperature

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range is observed due to the complex composition of the pyrolysis oil. As shown in DTG curves, the pyrolysis process of pyrolysis oil can be divided into three stages: i)

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volatilization stage, ii) primary pyrolysis stage and iii) char forming stage. The combustion process of the

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pyrolysis oil can also be divided into three stages: i) volatilization stage, ii) pyrolysis stage and iii) char

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combustion stage. By comparing the DTG peaks between pyrolysis and combustion process of the pyrolysis

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oil, it is noticed that the temperature range and the weight loss of the first stage (volatilization stage) and the

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secondary stage (primary pyrolysis stage) in pyrolysis and combustion process are similar, implying that

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oxygen in air atmosphere has almost no impact on decomposition of pyrolysis oil in these two stages. This

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phenomenon was also observed in the pyrolysis and combustion of other types of wastes 23.

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The temperature range of volatilization stage occurred between 60 and 160 oC. It is suggested to be linked

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to the valorization of moisture and small molecular organic substances with low boiling points, i.e.,

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HCOOH, CH3COOH, CH3COCH3 presented in the pyrolysis oil. The volatilization stage is endothermic

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and is mainly a physical process. The weight loss was about 44%, revealing that the pyrolysis oil contains a

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large amount of moisture or low molecular weight compounds.

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The second TG stage (primary pyrolysis stage) occurs in a temperature range of 160-350 oC with about 20%

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weight loss. This stage belongs to the thermal cracking stage of heavy components and volatile process of

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components with high boiling points. Along with the thermal cracking of large molecular organic substances,

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the intermolecular random nucleation and recombination process of different molecular may occur

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simultaneously. Under a low heating rate, the volatilization and thermal cracking process of the organic

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compounds with different boiling points occurred in different time zones. With the increase of heating rate,

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the required time for reaching the same pyrolysis temperature will be shortened, but there was not sufficient

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residence time for the volatile matters to be evolved at that pyrolysis temperature range. Thus, at a high 10


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heating rate, the volatilization and thermal cracking process of these large organics may overlaps. The

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boiling point of most valuable phenolic compounds, i.e., 2-methoxyphenol, phenol, p-cresol, in the

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pyrolysis oil is in the temperature range of 200-350oC, so more weight loss occurred in this

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temperature range, the higher proportion of phenolic compounds contained in the pyrolysis oil.

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The third stage for pyrolysis oil occurred in the temperature range of 350-500 oC with the mass loss of

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8.5-9.6%. The weight loss in this stage tends to be slow. Carbonization and char formation may occur in this

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stage, releasing small molecular gases such as H2, CO, CO2 etc. and eventually forming honeycomb carbon

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residue after pyrolysis. When the pyrolysis temperature exceeded 500 oC, the TG curves become flat,

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indicating that the pyrolysis was nearly complete.

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However, the third stage for pyrolysis oil combustion is char combustion stage, which occurs in the

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temperature range of 350-700 oC with the mass loss of 15.9-22.9%. The honeycomb carbon residue formed

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after pyrolysis process reacted with oxygen, releasing CO, CO2 etc. The end of the char combustion process

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was at 700 oC. After 700 oC, the coke was totally burned with little ash remained.

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The combustion and pyrolysis process of pyrolysis oil not only contains a variety of chemical reactions

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simultaneously, but also generates a wide range of intermediate products. The kinetic analysis has an

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important significance in the study of combustion and pyrolysis process of pyrolysis oil. In this study,

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non-isothermal analysis was chosen to analyze the thermal conversion process of pyrolysis oil. The rate

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equation for the kinetics analysis can be simplified as 23, 24:

219 ln[-ln(1-a)/T2]=ln(AR/βE)-E/RT

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(3.1)

where, a is the conversion ratio at the time t (min), T is the reaction temperature (K), A is a pre-exponential

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factor (min-1), R is the universal gas constant (8.314 J mol-1 K-1), β is the heating rate (K min-1), E is the

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activation energy (J mol-1). 11


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The term of ln[-ln(1-a)/T2] varies linearly with 1/T as slope of the line is -E/R. Meanwhile, the intercept of

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the line with y-axis is related to the pre-exponential factor A. Table 2 presents the activation energies E and

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the Arrhenius pre-exponential factors A for pyrolysis and combustion process of pyrolysis oil at different

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heating rate, respectively. The value of correlation coefficient, R, is in the range 0.9911-0.9988. The good

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correlation coefficient indicates that the applied kinetic model fits the experimental data very well.

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It is expected that the reactions involved in the pyrolysis and combustion of pyrolysis oil are very complex

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and the corresponding activation energies may vary with the degree of conversion. As indicated in Table 2,

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during pyrolysis process of pyrolysis oil, an increase in the heating rate appeared to increase the start and

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end temperatures of each stage. The activation energy for primary pyrolysis stage is in the range of

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33.5-50.3 kJ mol-1. This stage belongs to the thermal cracking stage of heavy components and volatile

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process of components with high boiling points and more reactions were triggered simultaneously at higher

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heating rates25. Thus, the E values for primary pyrolysis increase with the increase of heating rate. As the

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reaction progress to above 350 oC, carbonization and more porous char formation may occur. The porous

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chars enhance the diffusion of the volatiles. High heating rate is conductive to form higher activity char

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which causes the activation energy lower. Therefore, the E values in this stage decrease with the increase of

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heating rate. At low heating rate (5, 20 oC min-1), the E values of primary pyrolysis stage are lower than

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those of char forming stage. However, at high heating rate (35, 50 oC min-1), the E values of primary

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pyrolysis stage are higher than those of char forming stage, indicating that the char forming is easier to

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occur at higher heating rate.

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As shown in Table 2, during combustion process of pyrolysis oil, the activation energy of the char

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combustion stage decreases with the increase of the heating rate, and the E values are in the range of

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79.8-124.2 kJ mol-1, indicating that the higher the heating rate, the easier for the carbon residue to burn. 12


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3.2.3. Py-GC/MS analysis of pyrolysis oil feedstock Py-GC/MS is a significant method for online analysis of the composition and structure of pyrolysis

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products. To further investigate the effect of temperature on pyrolysis behavior of pyrolysis oil samples,

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Py-GC/MS was used to estimate the pyrolysis products from pyrolysis oil at different pyrolysis

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temperatures, providing a theoretical basis for the utilisation of pyrolysis oil via thermochemical technology.

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Py-GC/MS results of volatiles evolved from oil feedstock with final temperature at 600 oC and 700 oC are

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illustrated in Table 3. The compounds were ordered according to their retention times. The relative content

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of main component (peak area %) was obtained by integration and normalization of the peak area of each

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material in the spectrum.

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From Table 3, 27 compounds were detected in the pyrolysis of pyrolysis oil obtained at 600 oC. The main

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pyrolysis products are found to be aromatic compounds (44.78%), including phenylethylene, phenol,

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o-methoxyphenol and ethyl-phenol. The content of chain compounds is found to be 14%, which is mainly

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consisted of vinyl acetate, 2-butanone, hydroxy-acetone, 2-hydroxy-3-methyl-2-cyclopentane etc.

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Heterocyclic substances account for 5.46%, mainly including furfural, 2,3-dihydro benzofuran etc. A small

259

amount of dehydrated glucose was also contained in the pyrolysis products.

260

When Py-GC/MS was carried out with a final temperature of 700 oC (Table 3), 21 compounds were

261

determined. The aromatic compounds and ketones are the main pyrolysis products. The content of aromatic

262

compound was found to be 25.49%, mainly including phenol, o-methoxyphenol, ethyl-phenol etc. The

263

content of ketones, such as hydroxy-acetone, 2-hydroxy-3-methyl-2-cyclopentane, was found to be 23.04%.

264

Heterocyclic compounds account for 4.40%, mainly consisted of 2,3-dihydro benzofuran. And also a small

265

amount of anhydro glucose is found in the pyrolysis products.

266

The compositions of pyrolysis volatiles are commonly divided into nine categories according to their

13


Energy & Fuels 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

267

functions: acids, ketones, phenols, aldehydes, furans, esters, N-containing compounds, sugars and others 26.

268

The distribution of pyrolysis oil pyrolysis products obtained at two different temperatures was compared in

269

Figure 4. It is shown that, with the increase of Py-GC/MS temperature from 600 to 700oC, the relative

270

content of aromatic compounds significantly reduces from 44.78% to 25.49%, agree with the results

271

reported by Wang et al27. The relative content of ketones significantly increases from 8.62% to 23.04%. The

272

content of furans and dehydrated glucose decreases slightly, while the contents of acid and esters slightly

273

increase as the pyrolysis temperature increases. It is noticeable that aldehydes disappear when the

274

Py-GC/MS temperature was increased to 700 oC.

275

It is known that higher temperature can provide more energy for pyrolysis oil pyrolysis, increasing the

276

chance of long chain material breaking or the formation of free radicals attributed to the ring-opening of

277

single ring materials. High oxygen content of pyrolysis oil makes it easy for oxygen atom to form a stable

278

C=O structure with carbon atoms at high temperature. Thus, the relative content of ketones increases

279

remarkably with the increase of pyrolysis temperature. In addition, high temperature also increases the ring

280

opening chance of heterocyclic ring and polycyclic compounds, i.e., promoting the occurrence of

281

ring-opening fracture of the furan compound. The ring opening reaction of these compounds may lead to the

282

formation of chain hydrocarbons which then experience secondary pyrolysis at high temperature and

283

produce small molecular compounds. As indicated in Table 3, with the pyrolyzer temperature of Py-GC/MS

284

increase from 600 to 700oC, the number of the compounds detected in the volatile of pyrolysis oil decreases,

285

revealing that most of the compounds in pyrolysis oil are directly cracked into small molecular compounds

286

at higher temperature.

14


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287

3.3 Steam catalysis reforming of pyrolysis oil

288

3.3.1. Effect of catalyst calcination temperature

289

In this section, the pyrolysis oil feedstock was steam reformed in the presence of a Ni-ceramic foam

290

catalyst. The reaction conditions were: reaction temperature of 700 oC, S/C ratio of 1:1, NiO loading content

291

of 3.74% and the weight hourly space velocity (WHSV) is 4.68 h-1. The effect of calcination temperature of

292

catalyst on hydrogen yield with time on-stream is depicted in Figure 5. It seems that before 80 min, the

293

catalysts calcined at 800 and 900 oC have higher ability of hydrogen production than the catalysts calcined

294

at 600 and 700 oC. After 80 min of reaction, there was a significant decline in hydrogen yield for the

295

catalysts calcined at 600 oC, 800 oC and 900 oC. However, the H2 yield using the catalyst calcined at 700 oC

296

maintained at a stable value of 97 g H2 kg-1 pyrolysis bio-oil in an 160 min test, revealing that the catalyst

297

calcined at 700 oC has higher catalytic efficiency and better stability. The average H2 yields under the

298

calcination temperature of 600, 700, 800 and 900 oC is 92.91, 97.48, 95.79 and 96.02 g H2 kg-1 pyrolysis

299

bio-oil, respectively.

300

XRD patterns of NiO/ceramic foam catalyst under different calcination temperatures are presented in

301

Figure 6. It is observed that the α-Al2O3 (at 2θ=25.6°, 35.2°, 37.8°, 43.4°, 52.6°, 57.6°, 66.6° and 68.3°) and

302

SiO2 (at 2θ=21.6°) are the main crystalline phase despite the calcination temperature. Furthermore, the

303

peaks related to NiO are identified and visible at 2θ=37.3°, 43.3°, 62.9°. According to Scherrer equation, the

304

crystallite sizes of NiO particles at 2θ=43.3° calcined at 600 oC, 700 oC, 800 oC and 900 oC are 23.4 nm,

305

27.6 nm, 28.8 nm and 32.8 nm, respectively. The particle size of the NiO particles increased with the

306

increase of calcination temperature. It is known that catalyst deactivation (e.g. caused by coke formation on

307

the surface) can happens during steam reforming of pyrolysis oil. Coke deposition occurs more easily on

308

lager particles than smaller ones, and a significant decrease in Ni particles would resist the formation of

15


Energy & Fuels 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

309

filamentous carbon 28-30.

310

Table 4 presents the BET surface area of pure ceramic foam and its derived NiO catalysts calcined at

311

different temperature (600, 700, 800 and 900oC). It is observed that after loading with NiO, the surface area

312

of ceramic foam increases. This increase is due to the contribution of dispersed NiO on the ceramic foam’s

313

surface. In addition, as recognized from Table 4, catalyst calcined at 700oC possesses the largest specific

314

surface area of 3.114m2/g. When the temperature exceeds 700oC, the porosity of the support was blocked

315

due to agglomeration and sintering of NiO particles, leading to the decrease in surface area.

316

SEM images of NiO/ceramic foam catalyst under different calcination temperatures with 7000 times

317

magnification were shown in Figure 7. Porous structure of ceramic foam can be clearly observed. Catalysts

318

had a higher activity at lower calcination temperature because the nickel oxides showed a high dispersion

319

and strong interaction with the support. As the calcination temperature is higher than 700 oC, the activity of

320

catalyst declines since large amount of NiO particles aggregated into clusters covering the surface of the

321

support, which may block support’s pore and reduce the surface area of the catalyst 11. Surface area analysis

322

also evidenced that catalyst calcined at 700oC possesses the largest specific surface area of 3.11m2/g. Based

323

on the above analysis, 700oC was considered as the optimum calcination temperature, which is conducive to

324

the formation of NiO particle size that is suitable for bio-oil catalytic reforming.

325

3.3.2. Effect of NiO loading content

326

As the active component, NiO loading content is an important factor affecting the catalyst activity. In our

327

study, the catalysts were prepared with different NiO contents: 2.50%, 3.01%, 3.54 %, 4.68% and 5.29%

328

relative to total weight of catalyst, the gas samples were collected after 2 hours running. Table 5 shows the

329

gas composition and hydrogen yield using catalysts with different metal loading amount at reaction

330

temperature of 700oC, S/C ratio of 1 and WHSV of 4.6 h-1.

16


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Energy & Fuels

331

From Table 5, when the NiO loading was increased, the H2 content in the produced gas firstly increased

332

and then decreased with a maximum value of 63.13% at the NiO loading content of 3.54%. The trend of H2

333

yield is similar to that of H2 content in the produced gas. The H2 yield is in the range of 76.27-105.28 g H2

334

kg-1 pyrolysis oil and reached its maximum value of 105 g H2 kg-1 pyrolysis oil at 3.54% NiO loading

335

content. It is known that catalytic activity of a metal-supported catalyst is strongly dependent on active

336

metal particle size, shape, and its distribution or dispersion over the support. In general, the metal catalyst

337

should be dispersed on the surface of supports with a smaller particle size in order to get more active sites.

338

An appropriate amount of loading can promote the distribution of the active component of NiO on the

339

surface of the carrier. Excessive loading of Ni may lead to an inhomogeneous distribution of active

340

component, causing low catalytic efficiency due to aggregation sintering NiO crystal particle 8, 13, 31. Wang

341

et al. 32 found the catalyst activity for butanol steam reforming increases to a maximum and then declined as

342

the loading of NiO from 5.7-25%.

343

During catalytic reforming of pyrolysis oil, the pyrolysis oil was cracked or transformed into gas

344

molecules. In overall stoichiometric condition, only H2 and CO2 were obtained from steam reforming of

345

pyrolysis oil, and the stoichiometric maximum yield of hydrogen equals 129.8 g H2 kg-1 pyrolysis oil. In

346

actual conditions, overall stoichiometric steam reforming reaction cannot be achieved due to some

347

accompanied side reactions, such as the thermal decomposition, methanation and boudouard reactions 13, 14.

348

Thus other gas components like CO, CH4 also exist in the produced gas. As indicated in Table 5, the CO

349

content in the produced gas is in the range of 5.75-17.74%, and the yield of CO generally experiences a

350

decrease and then an increase trend by increasing the Ni content in the investigated range. The content of

351

CO2 in the produced gas is in the range of 19.01-35.36%, whilst the content of CH4 maintains in a low value

352

and is in the range of 0.25-4.68%. In terms of the production of H2, the optimal loading content of NiO is 17


Energy & Fuels 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

353

suggested to be 3.54%, as the maximum H2 yield of 105g H2 kg-1 pyrolysis oil (up to 81.1% of the

354

stoichiometric yield) was obtained, higher than the highest hydrogen yield reported by other researchers 14,

355

33

356

model compounds of biomass fast-pyrolysis oil using two commercial nickel-based catalysts (UC G-90C

357

and ICI 46-1), the H2 hydrogen yield ranged from 70 to 90% of the stoichiometric potential, indicating that

358

the performance of NiO/ceramic foam catalyst is comparable with commercial Ni-based steam reforming

359

catalysts.

360

3.3.3. Liquid condensate analysis by GC/MS

361 362 363

. In the study of Marquevich et al34, they investigated the hydrogen production by steam reforming of

Liquid condensates obtained after steam reforming of pyrolysis oil feedstock, and the original pyrolysis oil sample were analyzed by GC-MS (Table 6). As indicated in Table 6, acids account for 25.69%, which mainly consist of acetic acid, propionic acid and

364

butyric acid. Ketones including hydroxy-acetone, 1-hydroxy-2-methyl ethyl ketone and cyclopentenone

365

account for 23.55%. Phenols and its derivatives account for 18.8%. Furans are around 11.74% mainly

366

including furaldehyde and alkyl-substituted furans. The condensates after steam reforming also contain

367

alcohols and aldehydes were found of less content, and also a number of dehydrated glucose and nitrogen

368

containing organic compounds are detected in the pyrolysis oil.

369

After steam reforming, the amount of the compounds in the liquid phase significantly decreased, only 10

370

kinds of compounds were detected in liquid condensate from steam reforming of the pyrolysis oil. After

371

catalytic reforming, the main products were phenols and its derivatives (48.55%), including phenol, methyl

372

phenol and 3-methyl phenol, etc. Acids (18.36%), such as acetic acid and 4-hydroxybutyric acid, were also

373

found in the liquid condensates. Ketones (11.83%), mainly includes 2- acetone and cyclopentanone. Furans

374

account for 2.77%, mainly in the form of furaldehyde. A few nitrogen-containing organic compounds were

18


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375 376

Energy & Fuels

also found. The distribution of the compound types before and after the catalytic reforming of pyrolysis oil was

377

illustrated and compared in Figure 8. After steam reforming, aromatics were the most abundant components

378

followed with ketones and acidic. Chain hydrocarbons and furans contents were significantly reduced after

379

steam catalytic reforming of pyrolysis oil. Torren 35 reported the biomass-drerived feedstocks fast catalytic

380

pyrolysis and the dehydration reactions were proposed to produce water and the dehydrated species which

381

were further converted into aromatics, carbon monoxide, carbon dioxide, water, and coke. Compared to the

382

original pyrolysis oil, the content of acids reduced from 25.69% to 18.36%, ketones decreased from 23.55%

383

to 11.83%, the decline of the furans were from 11.74% to 2.77% for the condensate obtained from steam

384

reforming process.

385

Aldehydes and dehydration glucoses were completely decomposed in the reforming process. The content

386

of aromatic compounds increased significantly from 18.80% to 48.54%. Nitrogen-containing organic

387

content increased slightly from 0.84% to 3.05%. From these analyses, it is possible to state that in steam

388

reforming process, the pyrolysis oil component was activated on the catalyst surface, Ni as the active

389

constituent can promote C-C bond and C-O bond rupture with the occurrence of decarboxylation,

390

dehydrogenation reaction and ring opening reactions of heterocyclic compounds, small molecule gas was

391

produced simultaneously. The content of aromatic compounds mainly phenols increased significantly from

392

3.44% to 34.12%, indicating that C=C structure in the benzene ring is stable enough and cannot be easily

393

destroyed. Ni as the active component mainly promotes the fracture of C-C bond on benzene ring and C-O

394

bond on branched chain.

395

4. Conclusions

396

In this study, thermal properties of pyrolysis oil and its potential application for hydrogen production by 19


Energy & Fuels 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

397

catalytic steam reforming over NiO/ceramic foam catalysts were presented. TG analysis reveals that the

398

pyrolysis or combustion process of the pyrolysis oil feedstock could be divided into three stages. The first

399

stage is the volatilization process of water and light components of low boiling points. The second stage is

400

the primary pyrolysis process, consisting of the thermal cracking of heavy components and volatilization

401

process of components with high boiling points. Oxygen in air atmosphere has almost no impact on the

402

decomposition of pyrolysis oil in these two stages. The third stage for pyrolysis oil pyrolysis in TG is

403

carbonization and char forming stage, while the third stage for pyrolysis oil combustion in TG is char

404

combustion stage. The result of Py-GC/MS analysis to the original pyrolysis oil showed that increasing temperature from 600

405 406

o

407

Hydrogen production by catalytic steam reforming of pyrolysis oil showed that Ni was an active constituent

408

promoting C-C bond and C-O bond rupture. A maximum hydrogen yield of 105.28 g H2/kg Pyrolysis oil

409

was obtained at reforming temperature of 700 oC, S/C ratio of 1, NiO loading content of 3.54%. The

410

performance of NiO/ceramic foam catalyst is comparable with commercial Ni-based steam reforming

411

catalysts.

412

Acknowledgement

413

The authors would like to appreciate the support of the National Natural Science Foundation of China (No.

414

51476023, 51306029), China Postdoctoral Science Foundation (No.2016M602828, No.2016M600790), the

415

the Fundamental Research Funds for the Central Universities (No. xjj2016048) and Science and Technology

416

Support (Industry) Project of Shaanxi Province (2017GY-167).

417

Reference

418 419 420 421

C to 700 oC significantly decreased the contents of aromatics, while the content of ketones was increased.

1.

Coimbra, M. C.; Duque, A.; Saéz, F.; Manzanares, P.; Garcia-Cruz, C. H.; Ballesteros, M., Sugar

production from wheat straw biomass by alkaline extrusion and enzymatic hydrolysis. Renewable Energy 2016, 86, 1060-1068. 2.

Galadima, A.; Muraza, O., In situ fast pyrolysis of biomass with zeolite catalysts for 20


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bioaromatics/gasoline production: A review. Energy Conversion and Management 2015, 105, 338-354. 3.

Ge, H.; Guo, W.; Shen, L.; Song, T.; Xiao, J., Biomass gasification using chemical looping in a 25

kWth reactor with natural hematite as oxygen carrier. Chemical Engineering Journal 2016, 286, 174-183. 4.

Guedes, R. E.; Luna, A. S.; Torres, A. R., Operating parameters for bio-oil production in biomass

pyrolysis: A review. Journal of Analytical and Applied Pyrolysis 2018, 129, 134-149. 5.

Xiu, S.; Shahbazi, A., Bio-oil production and upgrading research: A review. Renewable and

Sustainable Energy Reviews 2012, 16, (7), 4406-4414. 6.

Zhao, X.-Y.; Ren, J.; Cao, J.-P.; Wei, F.; Zhu, C.; Fan, X.; Zhao, Y.-P.; Wei, X.-Y., Catalytic Reforming

of Volatiles from Biomass Pyrolysis for Hydrogen-Rich Gas Production over Limonite Ore. Energy Fuels 2017, 31, (4), 4054 - 4060. 7.

Wang, S.; Li, X.; Zhang, F.; Cai, Q.; Wang, Y.; Luo, Z., Bio-oil catalytic reforming without steam

addition: Application to hydrogen production and studies on its mechanism. International Journal of Hydrogen Energy 2013, 38, 16038-16047. 8.

Quan, C.; Xu, S.; Zhou, C., Steam reforming of bio-oil from coconut shell pyrolysis over Fe/olivine

catalyst. Energy Conversion and Management 2017, 141, 40-47. 9.

Dou, B.; Zhang, H.; Cui, G.; Wang, Z.; Xu, Y., Hydrogen production by sorption-enhanced chemical

looping steam reforming of ethanol in an alternating fixed-bed reactor: Sorbent to catalyst ratio dependencies. Energy Conversion and Management 2018, 155, 243-252. 10. Surachai Karnjanakom, G. G., Bayu Asep, Xiao Du, Xiaogang Hao, Chanatip Samart, Abuliti Abudula, Catalytic steam reforming of tar derived from steam gasification of sunflower stalk over ethylene glycol assisting prepared Ni/MCM-41. Energy Conversion and Management 2015, 98, 359-368. 11. Valle, B.; Aramburu, B.; Remiro, A.; Bilbao, J.; Gayubo, A. G., Effect of calcination/reduction conditions of Ni/La2O3-Al2O3 catalyst on its activity and stability for hydrogen production by steam reforming of raw bio-oil/ethanol. Applied Catalysis B: Environmental 2014, 147, 402-410. 12. Remón, J.; Giménez, J. R.; Valiente, A.; García, L.; Arauzo, J., Production of gaseous and liquid chemicals by aqueous phase reforming of crude glycerol: Influence of operating conditions on the process. Energy Conversion and Management 2016, 110, 90-112. 13. Seyedeyn-Azad, F.; Salehi, E.; Abedi, J.; Harding, T., Biomass to hydrogen via catalytic steam reforming of bio-oil over Ni-supported alumina catalysts. Fuel Processing Technology 2011, 92, 563-569. 14. Fu, P.; Yi, W.; Li, Z.; Bai, X.; Zhang, A.; Li, Y.; Li, Z., Investigation on hydrogen production by catalytic steam reforming of maize stalk fast pyrolysis bio-oil. Internation Journal of Hydrogen Energy 2014, 39, 13962-13971. 15. Wang, C.; Wang, T.; Ma, L.; Gao, Y.; Wu, C., Steam reforming of biomass raw fuel gas over NiO-MgO solid solution cordierite monolith catalyst. Energy Conversion and Management 2010, 51, 446-451. 16. Blanco, P. H.; Wu, C.; Onwudili, J. A.; Williams, P. T., Characterization and evaluation of Ni/SiO2 catalysts for hydrogen production and tar reduction from catalytic steam pyrolysis-reforming of refuse derived fuel. Applied Catalysis B: Environmental 2013, 134-135, 238-250. 17. Heo, D. H.; Lee, R.; Hwang, J. H.; Sohn, J. M., The effect of addition of Ca, K and Mn over Ni-based catalyst on steam reforming of toluene as model tar compound. Catalysis Today 2016, 265, 95-102. 18. Karnjanakom, S.; Guan, G.; Asep, B.; Du, X.; Hao, X.; Samart, C.; Abudula, A., Catalytic steam reforming of tar derived from steam gasification of sunflower stalk over ethylene glycol assisting prepared Ni/MCM-41. Energy Conversion and Management 2015, 98, 359-368. 19. Gao, N.; Wang, X.; Li, A.; Wu, C.; Yin, Z., Hydrogen production from catalytic steam reforming of benzene as tar model compound of biomass gasification. Fuel Processing Technology 2016, 148, 380-387. 21


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20. Gao, N.; Liu, S.; Han, Y.; Xing, C.; Li, A., Steam reforming of biomass tar for hydrogen production over NiO/ceramic foam catalyst. International Journal of Hydrogen Energy 2015, 40, 7983-7990. 21. Gao, N.; Li, A.; Quan, C.; Gao, F., Hydrogen-rich gas production from biomass steam gasification in an updraft fixed-bed gasifier combined with a porous ceramic reformer. International Journal of Hydrogen Energy 2008, 33, (20), 5430-5438. 22. Scholze, B.; Meier, D., Characterization of the water-insoluble fraction from pyrolysis oil (pyrolytic lignin). Part I. PY-GC/MS, FTIR, and functional groups. Journal of Analytical and Applied Pyrolysis 2001, 60, 41-54. 23. Quan, C.; Li, A.; Gao, N., Combustion and pyrolysis of electronic waste: thermogravimetric analysis and kinetic model. Procedia Environmental Sciences 2013, (18), 776-782. 24. Gao, N.; Li, A.; Quan, C.; Du, L.; Duan, Y., TG-FTIR and Py-GC/MS analysis on pyrolysis and combustion of pine sawdust. Journal of Analytical and Applied Pyrolysis 2013, 100, 26-32. 25. Mui, E. L. K.; Cheung, W. H.; Lee, V. K. C.; McKay, G., Compensation effect during the pyrolysis of tyres and bamboo. Waste Management 2010, 30, 821-830. 26. Zhang, S.; Dong, Q.; Zhang, L.; Xiong, Y., Effects of water washing and torrefaction on the pyrolysis behavior and kinetics of rice husk through TGA and Py-GC/MS. Bioresource Technology 2016, 199, 352-361. 27. Wang, J.; Zhang, B.; Zhong, Z.; Ding, K.; Xie, Q.; Ruan, R., Catalytic fast co-pyrolysis of mushroom waste and waste oil to promote the formation of aromatics. Clean Technologies and Environmental Policy 2016, 18, (8), 2701 - 2708. 28. García, V.; Fernández, J. J.; Ruíz, W.; Mondragón, F.; Moreno, A., Effect of MgO addition on the basicity of Ni/ZrO2 and on its catalytic activity in carbon dioxide reforming of methane. Catalysis Communications 2009, 11 240-246. 29. Xu, J.; Zhou, W.; Wang, J.; Li, Z.; Ma, J., Characterization and analysis of carbon deposited during the dry reforming of methane over Ni/La2O3/Al2O3 catalysts. Chinese Journal of Catalysis 2009, 30, 1076-1084. 30. Naeem, M. A.; Al-Fatesh, A. S.; Abasaeed, A. E.; Fakeeha, A. H., Activities of Ni-based nano catalysts for CO2-CH4 reforming prepared by polyol process. Fuel Processing Technology 2014, 122, 141-152. 31. Zhang, R.; Wang, H.; Hou, X., Catalytic reforming of toluene as tar model compound: Effect of Ce and Ce-Mg promoter using Ni/olivine catalyst. Chemosphere 2014, 97, 40-46. 32. Jia Wang; Bo Zhang; Zhaoping Zhong; Kuan Ding; Qinglong Xie; Roger Ruan, Catalytic fast co-pyrolysis of mushroom waste and waste oil to promote the formation of aromatics,. Clean Technologies and Environmental Policy 2016, 18, (8), 2701 - 2708. 33. Chen, G.; Yao, J.; Liu, J.; Yan, B.; Shan, R., Biomass to hydrogen-rich syngas via catalytic steam reforming of bio-oil. Renewable Energy 2016, 91, 315-322. 34. Marquevich, M.; Czernik, S.; Chornet, E.; Montane, D., Hydrogen from Biomass: Steam Reforming of Model Compounds of Fast-Pyrolysis Oil. Energy & Fuel 1999, 13, 1160-1166. 35. Carlson, T. R.; Tompsett, G. A.; Conner, W. C.; Huber, G. W., Aromatic Production from Catalytic Fast Pyrolysis of Biomass-Derived Feedstocks. Topics in Catalysis 2009, 52, 241-252.

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Energy & Fuels

508 509

Captions

510

Table 1 The properties of the pyrolysis oil

511

Table 2 Kinetic parameters of pyrolysis oil pyrolysis at different heating rate

512

Table 3 Main components and relative content of pyrolysis oil pyrolysis products at 600oC and 700 oC

513

Table 4 Effect of calcinations temperature on surface area of the catalyst

514

Table 5 Effect of catalyst loading content on gas composition and hydrogen yield

515

Table 6 Main components and their relative content in origin pyrolysis oil and the liquid condensate after

516

steam reforming

517 518

Figures

519

Figure 1 Schematic diagram of catalytic pyrolysis oil steam reforming set-up

520

Figure 2 FTIR spectrum of biomass pyrolysis oil

521

Figure 3 TG and DTG curves of pyrolysis oil pyrolysis (a) and combustion (b) at different heating rates

522

Figure 4 Relative contents of different groups of chemicals in volatiles from pyrolysis oil pyrolysis

523

Figure 5 Effect of calcination temperature of catalyst on hydrogen yield

524

Figure 6 XRD patterns of NiO/ceramic foam catalyst under different calcination temperature

525

Figure 7 SEM images of NiO/ceramic foam catalysts under different calcination temperature

526

Figure 8 Distribution of compounds before and after reforming of pyrolysis oil

527 528

23


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Page 24 of 39

529 530 Table 1 The properties of the pyrolysis oil

531 Proximate analysis(wt% ad)

532

Ultimate analysis(wt% daf)

Calorific value

M

V

A

FC

C

H

O1)

N

(MJ/kg)

46.12

30.37

2.50

21.24

34.12

8.28

55.60

2.00

13.43

1)

by difference

533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 24


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Energy & Fuels

548 549 Table 2 Kinetic parameters of pyrolysis oil pyrolysis at different heating rate

550

Heating rate

Temperature

E

A

(oC min-1)

Range (oC)

(kJ mol-1)

(min-1)

160-242

33.5

6.52×102

-0.9952

327-486

44.2

6.83×103

-0.9933

171-275

40.8

9.00×103

-0.9963

324-491

43.5

5.49×103

-0.9952

188-296

46.9

4.45×104

-0.9957

330-490

41.6

6.20×102

-0.9925

201-304

50.3

1.08×105

-0.9961

333-490

39.2

1.06×102

-0.9911

5

363-496

124.2

1.54×108

-0.9988

20

417-648

91.2

2.31×105

-0.9962

35

433-675

87.6

1.18×105

-0.9968

50

525-692

79.8

8.30×104

-0.9970

R

5

20 Pyrolysis 35

50

Combustion

551 552 553 554 555 25


Energy & Fuels 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

Page 26 of 39

556 557 Table 3 Main components and relative content of pyrolysis oil pyrolysis products at 600oC and 700 oC

558

Compound No.

RT (min)

Content (area%)

Content (area%)

600 oC

700 oC

Formula

1

4.161

Carbon dioxide

CO2

3.43

4.84

2

5.919

2-Methylfuran

C5H6O

0.97

-

3

6.201

Vinyl acetate

C4H6O2

2.95

1.60

4

6.278

2-Butanone

C4H8O

2.64

2.11

5

9.588

Hydroxyacetone

C3H6O2

3.13

17.41

6

19.25

Furfural

C5H4O2

1.11

0.98

7

19.776

Phenylethylene

C8H8

6.20

-

8

22.650

Butyl methacrylate

C5H14O2

9

24.664

Phenol

C6H5O

1.54 3.305

3-Methyl-1,210

3.4 2.83

27.288

C6H8O2

2.85

cyclopentanedione 11

27.455

o-Cresol

C7H8O

1.32

-

12

28.250

m-Cresol

C7H8O

3.12

3.01

13

29.155

Guaiacol

C7H8O2

4.82

4.41

14

30.637

2,4-Dimethylphenol

C8H10O

1.24

1.37

15

31.291

4-Ethylphenol

C8H10O

4.26

3.70

16

32.292

2-Methoxy-4-methylphenol

C8H10O2

3.78

3.09

26


Page 27 of 39 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

Energy & Fuels

17

32.793

Pyrocatechol

C6H6O2

4.18

-

18

33.440

2,3-Dihydrobenzofuran

C8H8O

3.38

3.42

19

34.672

4-Ethyl-2-methoxyphenol

C9H12O

1.84

1.74

20

35.173

3-methoxy-2-benzenediol

C7H8O3

1.10

-

21

35.628

4-Methylcatechol

C7H8O2

2.41

-

22

36.270

C9H10O2

1.98

4-Hydroxy-3-

1.89

methoxystyrene 423

37.065

(e)-isoeugenol

C10H12 O2

1.64

-

24

38.047

2,6-Dimethoxyphenol

C8H10O3

1.50

1.25

Phenol,2-methoxy-425

39.958

1.63 C10H12O2

2.09

C8H8O3

1.49

C6H10O5

2.05

C16H32O2

0.933

1.09

69.72

62.91

(1Z)-1-propen-1-yl26

40.125

27

43.833

Vanillin 1,6-anhydro-beta-d-

1.6

glucopyranos 28

49.119

Palmitic acid Total

559 560 561 562 563 564 27


Energy & Fuels 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

Page 28 of 39

565 Table 4 Effect of calcinations temperature on surface area of the catalyst

566

Calcination temperature (oC) Sample type

Surface area (m2/g)

Pure ceramic

1.715

600

700

800

900

2.803

3.114

2.009

1.757

567

28


Page 29 of 39 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

Energy & Fuels

568 Table 5 Effect of catalyst loading content on gas composition and hydrogen yield

569

Hydrogen yield Loading content/%

H2

CO

CO2

CH4

(g H2/kg) 2.50

76.27

56.63

8.59

30.61

3.52

3.01

93.87

59.37

5.75

33.11

1.58

3.54

105.28

63.13

12.32

24.29

0.25

4.68

87.28

57.46

17.74

19.01

4.68

5.29

79.69

53.88

16.89

25.58

3.77

570 571 572 573 574 575 576 577 578 579 580 581 582 583

29


Energy & Fuels 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

Table 6 Main components and their relative content in origin pyrolysis oil and the liquid condensate after

584 585

Page 30 of 39

steam reforming

Content (area %) No.

RT(min)

Compound

Formula

After steam Pyrolysis oil reforming

1

14.468

2-Propanone

C3H6O2

-

8.20

2

14.494

Hydroxyacetone

C3H6O2

15.50

-

3

16.038

2-Cyclopenten-1-one

C5 H 6 O

1.73

2.34

4

16.514

1-hydroxy-2-butanone

C4 H 8 O

1.57

-

5

18.546

Acetic acid

C2H4O2

22.11

16.38

6

18.978

Furfural

C5H4O2

4.30

2.77

7

20.759

Propanoic acid

C3H6O2

1.94

-

8

20.763

Ethanol,2-nitro-,propionate

C5H9O4N

-

3.05

9

23.031

4-hydroxy butanoic acid

C4H8O3

-

1.98

10

25.883

2(5H)-Furanone

C4H4O2

1.71

-

C6H8O2

3.91

-

3-methyl-1,211

27.270 cyclopentanedione

12

27.928

2-methoxyphenol

C7H8O2

5.41

-

13

29.807

Creosol

C8H10O2

2.70

-

14

30.592

Phenol, 2-methyl-

C7H8O

1.09

-

15

30.650

Phenol

C6 H 6 O

3.44

34.12

30


Page 31 of 39 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

Energy & Fuels

16

31.796

p-cresol

C7 H 8 O

2.54

9.61

17

31.883

3-methylphenol

C7H8O

-

4.81

18

33.011

4-ethylphenol

C8H10O

2.88

-

19

34.254

α-D-glucopyranoside

C14H23O16

1.16

-

C11H20O2

1.66

-

C8H8O3

1.60

-

5-heptyldihydro-2(3H)20

35.551 furanone 3-hydroxy-4-

21

37.222 methoxybenzaldehyde Total

75.25

586 587

31


8 83.26

Energy & Fuels 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

Page 32 of 39

588

Ceramic Foam

589 590

Figure 1 Schematic diagram of catalytic pyrolysis oil steam reforming set-up

591

1-syringe pump; 2-N2 cylinder; 3-air pump; 4-temperature controller; 5-mass flow meter; 6-thermocouple;

592

7-fixed-bed reactor; 8-furnace; 9-NiO/ceramic foam catalyst; 10-condensate collector; 11-condenser; 12-gas

593

bag.

594

32


Page 33 of 39

595 100

617

80

1052.3

1717.2

40

1639.8

2939.6

60

1268.9

1515.3

Transmittance (%)

20 3404.6

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

Energy & Fuels

0 4000

596 597

3500

3000

2500 2000 -1 Wavenumber (cm )

1500

1000

Figure 2 FTIR spectrum of biomass pyrolysis oil

598

33


500

Energy & Fuels

599 600 100 o

Mass loss (%)

42.8-46.3%

60

40

volatilization

40

5 C/min o 20 C/min o 35 C/min o 50 C/min

dm/dt (%/min)

80

19.7-21.9%

30 primary pyrolysis

20

char forming

10

20

0

8.5-9.6% 0

0

100

601

200

300 400 o Temperature ( C)

500

600

0

700

100

200

300 400o Temperature ( C)

500

600

700

(a)

602

50

100

volatilization

o

5 C/min o 20 C/min o 35 C/min o 50 C/min

42.4-46.5%

40

dm/dt (% /min)

80 M ass loss (% )

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

Page 34 of 39

30

60

20

40

pyrolysis

19.4-21.6%

10

20

char combustion

15.9-22.9%

0

603

0 0

100

200

300 400 o 500 Temperature ( C)

600

700

0

800

100

200

300 400 o 500 Temperature ( C)

600

700

800

604

(b)

605

Figure 3 TG and DTG curves of pyrolysis oil pyrolysis (a) and combustion (b) at different heating

606

rates

607

34


Page 35 of 39

608 609 50 o

40 Relative content (%)

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

Energy & Fuels

600 C o 700 C

30

20

10

610 611

0

Ketones Aldehydes Acidic

Esters

Aromatics Furans

Glucose

Figure 4 Relative contents of different groups of chemicals in volatiles from pyrolysis oil pyrolysis

612

35


Energy & Fuels

613 614

100 H2 yield /(g H2/kg pyrolysis oil)

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

Page 36 of 39

80

o

600 C o 700 C o 800 C o 900 C

60

40

20

0 615 616

60

90 Time/min

120

150

Figure 5 Effect of calcination temperature of catalyst on hydrogen yield

617

36


Page 37 of 39

618 619

∆

∆

∆

Fe-Ni

NiO ∆ ∆

∆

900 C

SiO 2

Al2O3

∆ o

Intensity (a.u)

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

Energy & Fuels

∆∆

o

800 C

o

700 C

o

600 C

20 620 621

30

40 50 o 2Theta/

60

70

Figure 6 XRD patterns of NiO/ceramic foam catalyst under different calcination temperature

622 623 624 625 626 627 628 629 630 631 632 37


Energy & Fuels 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

Page 38 of 39

633 634 635

5µm

5µm

o

o

600 C

700 C

5µm

5µm

o

900 C

800oC 636 637

Figure 7 SEM images of NiO/ceramic foam catalysts under different calcination temperature

638 639 640 641 642

38


Page 39 of 39

643 644 50

Before reforming After reforming 40

Relative content (%)

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

Energy & Fuels

30

20

10

645

0

Ketones Aldehydes Acidic Aromatics Furans

GlucoseNitrogenous

Chemical components

646

Figure 8 Distribution of compounds before and after reforming of pyrolysis oil

647 648 649 650 651

39


Thermal characteristics of biomass pyrolysis oil and potential

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