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  • 1.
    Ji, Xiaoyan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Xie, Yujiao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Zhang, Yingying
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lu, Xiaohua
    Key Laboratory of Material and Chemical Engineering, Nanjing University of Technology.
    CO2 capture/separation using choline chloride-based ionic liquids2013Conference paper (Refereed)
    Download full text (pdf)
    FULLTEXT01
  • 2.
    Xie, Yujiao
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Zhang, Yingying
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lu, Xiaohua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, College of Chemistry and Chemical Engineering, Nanjing University of Technology.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Energy consumption analysis for CO2 separation using imidazolium-based ionic liquids2014In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 136, p. 325-335Article in journal (Refereed)
    Abstract [en]

    CO2 solubility in ionic liquids has been measured extensively in order to develop ionic liquid-based technology for CO2 separation. However, the energy consumption analysis has not been investigated well for such technology. In order to carry out the energy consumption analysis for CO2 separation using ionic liquids based on available experimental data, in this work, the experimental data of the CO2 solubility in imidazolium-based ionic liquids at pressures below 10 MPa was surveyed and evaluated by a semi-empirical thermodynamic model firstly. Based on the reliable experimental solubility data, the enthalpy of CO2 absorption was further calculated by the thermodynamic model. The results show that the CO2 absorption enthalpy in the studied ionic liquids is dominated by the enthalpy of CO2 dissolution and the contribution of excess enthalpy increases with increasing CO2 solubility in ionic liquids. The magnitude of the CO2 absorption enthalpy decreases with increasing chain length in cation and strongly depends on the anion of ionic liquids. Furthermore, the energy consumption for a CO2 separation process by pressure swing and/or temperature swing was investigated. For the pressure swing process, the Henry’s constant of CO2 in ionic liquids is an important factor for energy consumption analysis; If CO2 is absorbed at 298 K and 1 MPa and ionic liquid is regenerated by decreasing the pressure to 0.1 MPa at the same temperature, among the studied ionic liquids, [emim][EtSO4] is the solvent with the lowest energy consumption of 9.840 kJ/mol CO2. For the temperature swing process, the heat capacity of ionic liquids plays a more important role; If CO2 is absorbed at 298 K and desorbed at 323 K and 0.1 MPa, [emim][PF6] is the solvent with the lowest energy demand of 888.9 kJ/mol CO2. If the solvent is regenerated by releasing pressure and increasing temperature, both the Henry’s constant of CO2 in ionic liquids and the heat capacity of ionic liquids are important for analyzing the energy consumption; If CO2 is absorbed at 298 K and 1 MPa and ionic liquid is regenerated at 323 K and 0.1 MPa, [bmim][Tf2N] is the solvent with the lowest energy consumption of 57.71 kJ/mol CO2.

  • 3.
    Zhang, Yingying
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Thermodynamic Analysis and Screening ILs/DESs-based Absorbents for CO2 Separation2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    CO2 separation plays an important role in both biofuel production, and CO2 capture and storage (CCS) implementation to deal with global warming. The available CO2 separation technologies are either energy-intensive or require large-scale operations, and it is crucial to develop novel CO2 separation technology in order to optimize the energy uses and the amounts of CO2-absorbents/adsorbents.Recently, ionic liquids (ILs) have been proposed as potential liquid absorbents for CO2 separation with remarkable properties. A lot of ILs have been synthesized for this purpose. The CO2 absorption capacity/selectivity and the energy use have been considered in screening ILs, while the amounts of ILs needed have seldom been considered in the screening process. Meanwhile, the high-cost, toxicity and poor biodegradability of the conventional ILs limit their applications in large-scale. Deep eutectic solvents (DESs) have emerged as a new type of ILs, and in particular, those based on choline salts (i.e. choline-based DESs) show additional advantages in cost, environmental impact and synthesis. Choline-based DESs have been synthesized and the research work related to CO2 separation with this series of DESs and their aqueous solutions has been carried out. However, it is still unclear which absorbent can achieve a better performance for CO2 separation.The choice of absorbents for CO2 separation depends on gas streams, and the performances of absorbents for CO2 separation relate to the energy uses and the amounts of absorbents needed. In this thesis work, four gas streams (i.e. flue gas and lime kiln gas from the combustion of fossil-fuels, biogas from the anaerobic digestion of biomass as well as bio-syngas from the gasification of biomass) with different temperature, pressure, CO2 concentration and gaseous components were considered, and CO2 separation from four gas streams was analyzed thermodynamically based on Gibbs free energy change. The analysis shows that biogas is the CO2 stream with the lowest theoretical energy penalty. Therefore, biogas was chosen as a specific CO2 stream for further evaluating the performances of CO2 absorbents.In evaluation, the conventional ILs were first analyzed and screened for CO2 separation from biogas with three options (i.e. option 1: the CO2 dissolution enthalpy and CO2 working capacity, option 2: the energy use, and option 3: the energy use and the amount of IL needed). The investigation shows that the screen of ILs is strongly related to the operational condition and the screening criteria. In the option of “the energy use and the amount of IL needed”, the operational condition was optimized based on the minimum Gibbs free energy change, and the energy use and the amount of IL needed were considered in screening. While in other screening options, the operational conditions were presumed and the amounts of ILs needed were not considered. Therefore, the option of “the energy use and the amount of IL needed” is more reasonable compared to the other two options. The performances of these screened conventional ILs were further compared with those of the commercial CO2 absorbents. It shows that the conventional ILs are promising CO2 absorbents due to lower energy uses or lower amounts of ILs needed combined with the advantage of non-volatility.The research work on choline-based DESs and their aqueous solutions for CO2 separation was surveyed and reviewed. Generally, the properties of choline-based DESs are similar to those of conventional ILs. Considering the additional advantages of low-cost, non-toxicity and biodegradability, choline-based DESs are more promising for CO2 separation. However, due to the limited available research work, further studies need to be carried out from experimental measurements to model developments. The performances of choline-based-DESs for CO2 separation from biogas were analyzed. Based on the option of “the energy use and the amount of absorbent needed”, the choline-based-DESs were screened and then compared with the conventional ILs and the commercial CO2 absorbents. The comparison results show that the choline-based-DESs are more promising for CO2 separation from biogas due to the non-volatility, lower energy uses or lower amounts of absorbents needed. In addition, CO2 separation from other CO2 streams was further investigated. It shows that the physical absorbents are more suitable for the CO2 streams with high CO2 concentration (i.e. biogas, lime kiln gas and bio-syngas), while the chemical CO2 absorbents are more suitable for that with low CO2 concentration and high temperature (i.e. flue gas). Considering the high amounts of physical absorbents, further study needs to be carried out with techno-economic analysis.

    Download full text (pdf)
    FULLTEXT01
  • 4.
    Zhang, Yingying
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lu, Xiaohua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology.
    Application of choline-based deep eutectic solvents in CO2 capture and separation2014In: Huagong Xuebao/Journal of Chemical Industry and Engineering, ISSN 0438-1157, Vol. 65, no 5, p. 1721-1728Article in journal (Refereed)
    Abstract [en]

    Choline-based deep eutectic solvents (DESs) are a new class of ionic liquids. With similar properties to ionic liquids, choline-based DESs have the advantages of easy synthesis, low price, low toxicity and biodegradability. In this work, the properties of choline-based DESs related to CO2 capture and separation were investigated, such as gas solubility, CO2 absorption-desorption, density, thermal stability, viscosity and surface tension. The influence of the structure of choline-based DESs on their properties were analyzed. The comparison of choline-based DESs with traditional ionic liquid showed that choline-based DESs could be used as absorbents for CO2 capture and separation due to high CO2 solubility and low viscosity. However, more research needs to be done before commercial application, for example, CO2 selectivity compared to other components in gas mixtures, surface tension as well as thermal-stability.

  • 5.
    Zhang, Yingying
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lu, Xiaohua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, College of Chemistry and Chemical Engineering, Nanjing University of Technology.
    Choline-Based Deep Eutectic Solvents for Mitigating Carbon Dioxide Emissions2015In: Novel Materials for Carbon Dioxide Mitigation Technology, Elsevier, 2015, p. 87-116Chapter in book (Refereed)
    Abstract [en]

    Global warming is a critical issue facing human beings due to greenhouse gas emissions, especially CO2 emissions. Mitigating CO2 emissions by Carbon capture and storage (CCS) has become a hot topic today. CO2 separation is a crucial step in CCS and is an energy-intensive process. Ionic liquids (ILs) as green solvents have gained tremendous attention for use as liquid absorbents for CO2 separation. However, the high price, toxicity, and poor biodegradability limit the application of ILs. Recently, deep eutectic solvents (DESs) based on choline chloride (ChCl) (i.e., choline-based DESs) were proposed as a new type of ILs but with additional advantages in cost, environmental impact, and synthesis. To promote the application of choline-based DESs in CO2 separation, the research work on the microstructure and physicochemical properties of choline-based DESs as well as the water effect were surveyed and compared with traditional ILs. The potential applications of choline-based DESs in CO2 separation and the challenges were further analyzed. It is shown that choline-based DESs are promising for use as liquid absorbents for CO2 separation, and the performance of ChCl/urea (1:2) is better than that for other choline-based DESs. However, uncertainties and bottlenecks still exist, and further study on the microstructure and properties needs to be carried out from experimental measurements to model developments

  • 6.
    Zhang, Yingying
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lu, Xiaohua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology.
    Energy consumption analysis for CO2 separation from gas mixtures2014In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 130, no S1, p. 237-243Article in journal (Refereed)
    Abstract [en]

    CO2 separation is an energy intensive process, which plays an important role in both energy saving and CO2 capture and storage (CCS) implementation to deal with global warming. To quantitatively investigate the energy consumption of CO2 separation from different CO2 streams and analyze the effect of temperature, pressure and composition on energy consumption, in this work, the theoretical energy consumption of CO2 separation from flue gas, lime kiln gas, biogas and bio-syngas was calculated. The results show that the energy consumption of CO2 separation from flue gas is the highest and that from biogas is the lowest, and the concentration of CO2 is the most important factor affecting the energy consumption when the CO2 concentration is lower than 0.15 in mole fraction. Furthermore, if the CO2 captured from flue gases in CCS was replaced with that from biogases, i.e. bio-CO2, the energy saving would be equivalent to 7.31 million ton standard coal for China and 28.13 million ton standard coal globally, which corresponds to 0.30 billion US$ that can be saved for China and 1.36 billion US$ saved globally. This observation reveals the importance of trading fossil fuel-based CO2 with bio-CO2.

  • 7.
    Zhang, Yingying
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Xie, Yujiao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lu, Xiaohua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, College of Chemistry and Chemical Engineering, Nanjing University of Technology.
    Screening of conventional ionic liquids for carbon dioxide capture and separation2016In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 162, p. 1160-1170Article in journal (Refereed)
    Abstract [en]

    CO2 capture and storage could efficiently mitigate CO2 emissions, wherein CO2 capture is a crucial energy-intensive process. Ionic liquids (ILs) have been proposed as potential liquid absorbents for CO2 separation. The CO2 absorption capacity and selectivity of ILs have also been investigated extensively. Although ILs have been screened for CO2 separation, only specific ILs have been examined in terms of energy consumption. In this study, 76 conventional ILs were collected and screened in terms of energy consumption to establish potential ILs for CO2 separation. Seventeen ILs were screened according to the CO2 dissolution enthalpy and CO2 working capacity criteria obtained from the Henry’s law constant in the preliminary screening. Seven ILs were then screened from the 17 ILs according to the CO2 working capacity from the measured CO2 solubility in the final screening. The energy consumptions of the seven screened ILs (i.e., [Emim][NTf2], [Bmim][BF4], [Bmim][PF6], [Bmim][NTf2], [Hmim][NTf2], [Bmpy][NTf2], and [Hmpy][NTf2]) were calculated, and the corresponding gas solubility selectivities were discussed. The energy consumptions and properties of the seven screened ILs were compared with those of the commercial CO2 absorbents of 30 wt% MEA, 30 wt% MDEA, and dimethyl ethers of polyethylene glycol (Selexol™ or Coastal AGR®). The results showed that the energy consumptions of the seven screened ILs were lower than those of the commercial CO2 absorbents. [Hmpy][NTf2] showed the lowest energy consumption among the seven screened ILs under the operating conditions set in this study.

  • 8.
    Zhang, Yingying
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lu, Xiaohua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology.
    Feng, Xin
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Properties and applications of choline-based deep eutectic solvents2013In: Huaxue jinzhan, ISSN 1005-281X, Vol. 25, no 6, p. 881-892Article in journal (Refereed)
    Abstract [en]

    Choline-based deep eutectic solvents (DESs) are considered as a new class of ionic liquids. Comparing to traditional ionic liquids, choline-based DESs are low-toxic, biodegradable, and the price is generally low, which make them more and more attractive in green chemistry and industrial chemistry. In the current work, the properties of choline-based DESs, such as freezing point, melting point, solubility, viscosity, surface tension and conductivity, were collected and summarized. The dependences of these properties with different factors, such as temperature, mole ratios and water content, and the models which can be used to predict the properties were studied and discussed. The applications of choline-based DESs in the area of lubrication, functional material preparation, electrochemistry, organic synthesis and catalytic conversion of biomass were introduced. Finally, the problems and difficulties in research and applications were illustrated and then prospective was provided.

  • 9.
    Zhang, Yingying
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Xie, Yujiao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Zhu, Yudan
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology.
    Lu, Xiaohua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, College of Chemistry and Chemical Engineering, Nanjing University of Technology.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Energy Consumption Analysis for CO2 Separation from Gas Mixtures with Liquid Absorbents2014In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 61, p. 2695-2698Article in journal (Refereed)
    Abstract [en]

    CO2 separation is an energy intensive process, and it plays an important role in both energy saving and CO2 capture and storage (CCS) to deal with global-warming. CO2 can be from different sources in a wide temperature, pressure and concentrations range. Meanwhile, new liquid absorbents are under-development to cost-effectively separate CO2 from gas mixtures. All this makes it crucial to analyze the energy consumption for CO2 separation from different streams and with different absorbents. In this work, the theoretical energy consumption of CO2 separation from flue gas (CO2/N2), lime kiln gas (CO2/N2), biogas (CO2/CH4) and bio-syngas (CO2/H2/CO) was calculated. The results show that the energy consumption of CO2 separation from flue gas is the highest and that from biogas is the lowest. If the CO2 captured from flue gases was substituted by that from biogases, the energy saving would be equivalent to 28.13 million ton standard coal globally. The energy consumption of CO2 separation from biogas using traditional absorbent of 30%MEA and new developed ionic liquids (ILs) was further studied, in which 1-ethyl-3-methy- limidazolium bis[(trifluoromethyl)sulfonyl]imide ([Emim][NTf2]), 1-butyl-3-methylimida- zolium tetrafluoroborate ([Bmim][BF4]), 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide ([Hmim][Tf2N]) and 1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide ([Bmpy][Tf2N]) were screened from 75 ILs. The energy consumptions of CO2 separation using ILs are lower than those of 30%MEA and that of [Bmim][BF4] is the lowest in the four screened ILs. With a very low vapor pressure and high CO2 solubility, it's promising to use ILs as absorbents for CO2 separation.

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