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Bio-oil production by thermochemical catalytic liquefaction of bloom-forming cyanobacteria: Optimization using response surface methodology (RSM) Fanghua Li, Zhiquan Hu, and Bo Xiao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02595 • Publication Date (Web): 14 Nov 2017 Downloaded from http://pubs.acs.org on November 19, 2017
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Energy & Fuels
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Bio-oil production by thermochemical catalytic liquefaction of bloom-
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forming cyanobacteria: Optimization using response surface methodology
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(RSM)
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Fanghua Li1,2, Zhiquan Hu1*, Bo Xiao1
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1. School of Environmental Science and Engineering, Huazhong University of Science and
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Technology, 1037 Luoyu Road, Wuhan 430074, China
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2. Department of chemical engineering, Monash University, Wellington Rd, VIC 3800, Australia
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Fax: +86-27-87557464. E-mail:
[email protected] (Z. Hu),
* To whom correspondence should be addressed. Phone: +86-27-87557464.
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Abstract
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Experimental research on thermochemical catalytic liquefaction of bloom-forming
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cyanobacteria (BC) was carried out to determine the effects of solvent, catalyst, reaction
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time, temperature, the ratio of raw material to solvent and catalyst dosage on liquefaction
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performance. The liquefaction conditions were optimized by central composite design (CCD)
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experiments as follows: the concentrated H2SO4 content of 6.6%, the reaction temperature of
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175°C, the reaction time of 30 min and the ratio of material to solvent of 1:4. The
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liquefaction yield and oil yield (chloroform phase) reached 93.85% and 37.96% at above-
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mentioned conditions. The ultimate analysis and calorific value of the oil were determined,
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and the chemical composition of the oil was investigated using gas chromatography-mass
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spectrometry (GC-MS) technique and Fourier-transform infrared (FT-IR) spectroscopy. The
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analysis of bio-oil composition showed that bio-oil from BC mainly contains ethyl palmitate
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which is the main composition of palm oil biodiesel, with a heating value of 32.7MJ/kg.
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Keywords: Bio-oil production; Bloom-forming cyanobacteria; Thermochemical catalytic
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liquefaction; Bio-oil characterization
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1. Introduction
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the current society. The reserves of fossil fuel are decreasing gradually; this reduction is
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coupled with an increase in greenhouse gas emissions (mainly CO2) contributing to global
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warming. Thus, it is essential to develop a process to reduce the emissions of greenhouse
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gases. This requirement has led to an increasing interest in the utilization of renewable
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sources. Biomass, as a renewable source, will play an important role in sustainable energy
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systems due to being non-toxic, biodegradable and environment-friendly. Compared with the
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terrestrial biomass, the aquatic biomass (such as algae) possessed the advantages of rapid
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growth, high photosynthetic efficiency, high lipid productivity, capability of capturing flue
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gas, especially CO2, tolerance to a wide range of water sources, potential to provide
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transportation fuels and no competition with arable land [1]. Therefore, there had been a
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growing interest in using algae as a promising candidate for biofuel production [2]. In recent
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decades, there is an increasing concern of lake eutrophication in China. Sixty-six percent of
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the lakes are at the level of over eutrophication and the lakes at severe and extreme
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eutrophication level constitute 22% of the total lakes [3]. Lake Dianchi ranked number six in
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the case of area among all the freshwater lakes in China and located in Kunming City,
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Yunnan Province, Southwestern of China.
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cyanobacteria (BC) have appeared frequently in Lake Dianchi due to the raise of heavy
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eutrophication. Because of the heavy metals and toxins in algal cells, heavy BC posed a
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threat to human and animal health and was not available for food and feed [4]. As a result, it
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is quite necessary to remove BC as a reduction of nitrogen and phosphorus level in the lake in
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order to remediate eutrophication of Lake Dianchi [5]. However, the large quantities of
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harvested bloom algae can cause serious secondary-environmental pollution without an
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effective technology for converting the collected biomass. Thus, using the large amounts of
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biomass collected from eutrophic lakes as feedstock for useful products may be a promising
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solution [6].
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Recently, many researches have been carried out to recover energy from algae through
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thermochemical technologies, including gasification [7], direct combustion [8], pyrolysis [8-
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12] and liquefaction [13]. Among them, efforts on liquefaction of algae are quite limited. In
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the open literatures, Huang et al. [14] studied the thermochemical liquefaction of Spirulina
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with the solvent of sub- and supercritical ethanol in an autoclave. Various liquefaction
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parameters were investigated such as the reaction temperature, the ratio of solid to liquid, the
Energy shortage and environmental pollution problems are the most significant issues facing
At present, large area bloom-forming
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solvent filling ratio, and the type and dosage of the catalyst. They found that the bio-oil yield
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increased generally with increasing temperature and solvent filling ratio, while the bio-oil
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yields reduced with increasing solid to liquid ratio. The FeS catalyst played an important role
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in the liquefaction of Spirulina due to its contribution on the production of bio-oil and the
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reduction of residue. Under catalytic liquefaction, the liquid products showed higher heating
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values than non-catalytic liquefaction and the dominant compounds in bio-oil were fatty acid
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ethyl ester for both catalytic and non-catalytic liquefaction. Xu et al. [15] investigated the
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bio-oil production from planktonic algae biomass by thermochemical catalytic liquefaction
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with the catalyst of NaOH. Reaction conditions such as reaction time, temperature and the
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ratio of algae to solvent were explored. With the increase of reaction time and temperature,
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the liquefaction yield increased first and then decreased. The maximum liquefaction yield
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was 61.6%. The chemical components of the bio-oil including acid, ester derivatives, furan
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and phenol were reported. Zou et al. [16] investigated the thermochemical catalytic
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liquefaction of Dunaliella tertiolecta in the solvent of ethylene glycol with H2SO4 as a
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catalyst. They achieved 97.05% of liquefaction yield from the microalgae. The main bio-oil
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compositions were fatty acid methyl ester, fatty acid hydroxyethyl ester and benzofuranone.
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However, the main issue of these studies is the energy-consuming process of cultivation,
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especially the laboratory-grown cultures [17-20], which hinders the commercial application
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of bio-oils produced by thermochemical liquefaction. Pyrolysis conversion of BC into bio-oil
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had been carried out in our previous study [21]. The results showed that the BC had a great
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potential for transportation fuel production, however, there was a low bio-oil yield with an
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energy intensive process. After the experiments, there was still a large portion of the residual
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solid left as waste. Therefore, it is necessary to find an approach by which the algae sample
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can be converted with higher yields. Up to date, there were few reports, if any, were
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concerned on particular liquefaction characteristics of BC under different reaction
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parameters, which is just the point to be explored in depth in this paper.
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The aims of this study are to (1) examine the effects of solvent and catalyst, reaction time,
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temperature, ratio of material to solvent and catalyst dosage on the product yields, (2)
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understand the properties and composition of bio-oil obtained under the conditions of
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maximum liquid yield, (3) evaluate the potential of bio-oil produced from BC as a potential
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source of renewable fuel.
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2. Materials and methods 3
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2.1. Raw materials and sample preparation In this study, BC biomass used as the raw material, mainly comprised of Microcystis species
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(>90%), was collected from Lake Dianchi of Yunnan Province in China and dried under
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natural summer sunlight for 7 days. Before the experiment, the preserved algae biomass was
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dried again in an oven at 60 °C overnight. The dried biomass obtained was sieved (
