Catalytic pyrolysis of chemical extraction residue from microalgae biomass
Graphical abstract
Introduction
With the global energy consumption increasing year by year, the status of renewable energy in the energy market is becoming more and more significant [1]. As an important part of renewable energy, microalgae has become a hotspot in the fields of energy, ecological environment medicine and food because the advantage of large total amount, rapid reproduction, strong environmental adaptability, convenient cultivation and rich nutrition [2,3].
Biomass has long been an important source of renewable energy, and its utilization has become a hotspot in the field of energy and ecological environment [4]. Microalgae biomass (MA) is an important part of biomass energy, typically found in freshwater and marine systems. It has attracted widespread interest because of its fast growth, short breeding cycle, environmental adaptability, no need for arable land and so on [5,6]. Generally, MA can be converted to biofuels by thermochemical, transesterification, extraction and other biochemical methods [7]. Among them, the solvent extraction method is widely used in lipid extraction because of its convenient operation, good selectivity, and high efficiency [8]. However, a large amount of microalgae residue (MR) can be produced with a certain amount of energy substances after the extraction. Moreover, previous work has indicated that MR can be converted to bio-fuels through thermochemical methods, which mainly includes pyrolysis, gasification and hydrothermal liquefaction [9]. Pyrolysis can efficiently recover most of the available energy in biomass. In order to improve pyrolysis performance of biomass, it is necessary to add catalysts during pyrolysis. At present, researchers have done a lot of work on the catalytic pyrolysis of MA. Du et al. [[10], [11], [12]] confirmed that HZSM-5 could effectively increase the yield of aromatics by the catalytic pyrolysis of MA. It can also greatly increase the yield of light olefins during the pyrolysis in steam [13]. In addition, the use of Ni-loaded zeolite can effectively improve the quality of bio-oil [14]. Zeolite catalyst can achieve the selective production of valuable chemical intermediates in the pyrolysis of MA [15]. Studies have shown that some alkali and alkaline earth metal compounds can effectively shorten the reaction time of the pyrolysis and reduce the temperature required for reaction [16]. It can be seen that emphasis has been placed on the pyrolysis of MA with or without catalyst, while catalytic pyrolysis behavior of MR from chemical extraction of MA has rarely been reported. Chemical extraction for high-valued nutrients from MA leaves considerable amount of residue, which is generally regarded as a solid waste. Pyrolysis could produce hydrocarbons with lower molecular weight in condensation (i.e. liquid), non-condensable gases, and solid chars, which is an effective utilization for MR treatment. However, efficient and effective pyrolysis of MR has yet to be developed.
In order to solve the comprehensive utilization of the waste residue and improve its utilization efficiency, catalysts of KCl, KOH, K2CO3, Al2O3, CaO, MgO and pyrolysis char of MR (MRC) under 600 °C in N2 were selected to study the catalytic pyrolysis performance of MR through a thermogravimetric analyzer and a tube furnace reactor. The aim was to evaluate on a quantitative base the yields of catalytic pyrolysis products, and demonstrate the effects of the catalysts on the potential ecological risk of heavy metals in the pyrolysis char of MR. The results will aid current understanding of pyrolysis processes of the solid waste, and provide valuable information for its potential utilization.
Section snippets
Sample preparation
The MR samples used in this study were from chemical extraction of Haematococcus pluvialis, which was supplied by Qingdao Xuneng Biological Engineering Co. Ltd. A large amount of a mixture containing the extractant and the MR will be left after breaking the wall by ultrasonic and extracting the astaxanthin oil from the MA. The MR powder can be obtained with further filtration, separation and drying. After that, the MR sample was grounded and passed through an 80 mesh screen and then placed in a
Properties analysis of MR
The proximate, ultimate and biochemical composition analysis of MR are shown in Table 1. The mineral content of MR was presented in Table 2. It can be seen that the volatile and ash content of MR is as high as 45.67% and 47.91%, respectively.
Thermogravimetric analysis of MR
Fig. 2 shows the weight loss curves (TG) and the weight loss rate curves (DTG) of MR at different heating rates. It can be seen that there were three stages during the pyrolysis of MR. The first stage (0–185 °C) corresponded to a small amount of weight loss
Conclusion
In the present work, catalysts of KCl, KOH, K2CO3, Al2O3, CaO, MgO and pyrolysis char of microalgae residue (MRC) under 600 °C in N2 were selected to study the catalytic pyrolysis performance of microalgae residue (MR) through a tube furnace reactor. The addition of KCl, KOH, K2CO3, Al2O3, CaO, MgO and pyrolysis char of MR (MRC) can promote the oil yield from MR pyrolysis. The order of the strength on increasing the oil yield was: MRC > Al2O3>CaO > K2CO3>MgO > KCl > KOH. The potential
Acknowledgments
The research was supported by the Natural Science Foundation of Shandong Province (No. ZR2017BEE042), the Fundamental Research Funds for the Central Universities (NO. 18CX02150A), and the Talent Introduction Project of China University of Petroleum (East China) (No. 2017010068).
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