Green Energy&Environment

2019, 4(2): 93-94. doi: 10.1016/j.gee.2019.04.003

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Application of deep eutectic solvents in biomass pretreatment and conversion

Yu Chen, Tiancheng Mu

2019, 4(2): 95-115. doi: 10.1016/j.gee.2019.01.012

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Biomass is renewable, abundant, cheap, biocompatible, and biodegradable materials and has been used to produce chemicals, materials, energy, and fuels. However, most of the biomass, especially most of the biomass polymers are not soluble in common solvents, which hinders their pretreatment and conversion. Deep eutectic solvents (DESs) are environmental-friendly, cheap, and highly tunable, with high solubility, which renders them potential applications in biomass pretreatment and conversion. They could be used as solvents or catalysts and so on. This paper intends to review the application of DESs for the pretreatment of biomass and conversion of biomass to value-added products. We focus on the following topics related to biomass and DESs: (1) DESs for the pretreatment of biomass; (2) DESs for the dissolution and separation of biomass or extraction of chemicals from biomass; (3) DESs for biomass conversion; (4) Drawbacks, and recyclability of DESs for pretreatment and conversion of biomass.

Redox active ionic liquid as efficient mediator and solvent for visible light-driven B1₂ catalytic reactions

Hisashi Shimakoshi, Noriyuki Houfuku, Li Chen, Yoshio Hisaeda

2019, 4(2): 116-120. doi: 10.1016/j.gee.2019.03.001

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The redox active ionic liquid, 1-ethyl-4-(methoxycarbonyl)pyridinium bis(trifluoromethanesulfonyl)amide ( RIL ), was synthesized from its iodide form by an anion exchange reaction of Li(NTf₂) with viscos liquid (η = 122 cP at 25 °C) and characterized by NMR, IR, and elemental analysis. The compound showed reversible redox couples at −0.65 V and −1.48 V vs. Ag/AgCl and worked as an electron mediator in the B₁₂ complex/[Ru(bpy)₃]Cl₂ photosensitizer catalytic system under visible light irradiation. The catalytic efficiency in the RIL was higher than those in DMF, MeOH, and the redox inactive ionic liquid, 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide.

Degradation mechanism of tin phosphide as Na-ion battery negative electrode

Hiroyuki Usui, Yasuhiro Domi, Ryota Yamagami, Hiroki Sakaguchi

2019, 4(2): 121-126. doi: 10.1016/j.gee.2019.01.001

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The degradation mechanism of an Sn₄P₃ electrode as Na-ion battery anode was investigated by using a transmission electron microscopic observation. At the first desodiation, we confirmed that Sn nanoparticles with 6 nm in size were dispersed in an amorphous-like P matrix. Compared to this, we observed aggregated Sn particles with sizes exceeding 50 nm after the drastic capacity fading. The capacity fading mechanism was for the first time confirmed to be Sn aggregation. To improve the capacity decay, we carried out the two kinds of charge−discharge cycling tests under the reduced volume changes of Sn particles and P matrix by limiting desodiation reactions of NaSn and Na₃P, respectively. The Sn₄P₃ electrode exhibited an excellent cyclability with the discharge capacity of 500 mA h g⁻¹ for 420 cycles under the limited desodiation, whereas the capacity decay was accelerated under the limited sodiation. The results suggest that the Sn aggregation can be improved by the reduced volume change of the P matrix, and that it is very effective for improving anode performance of Sn₄P₃ electrode.

Hand-holding and releasing between the anion and cation to change their macroscopic behavior in water

Kosuke Kuroda, Yumiko Shimada, Kenji Takahashi

2019, 4(2): 127-130. doi: 10.1016/j.gee.2018.12.004

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Despite the similarity of ionic liquid and zwitterion, their some properties such as conductivity and hydrophobicity are different. Here we developed a novel phosphonium salt having a dynamic covalent bond between anion and cation, enabling reversible structural shift between free ion pair and zwitterion. With the phosphonium salt, control of the macroscopic phase behavior in aqueous solution, i.e. forming mono- or bi-phasic systems, upon exposure to an acid or base was reversibly achieved, based on the structural shift of the phosphonium salt. CO₂/N₂ bubbling reversibly changed the phase behavior as well as acid/base, leading to green separation systems.

Anionic structural effect in liquid–liquid separation of phenol from model oil by choline carboxylate ionic liquids

Zhiyong Li, Ruipeng Li, Xiaoqing Yuan, Yuanchao Pei, Yuling Zhao, Huiyong Wang, Jianji Wang

2019, 4(2): 131-138. doi: 10.1016/j.gee.2019.01.011

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Phenolic compounds exist in crude oil as pollutants, and their removal is vital important for the refining and further application of oils. In traditional separation approaches, strong acid and strong base have to be used to remove these compounds, which may cause serious environmental problems. In this work, 19 kinds of cholinium ionic liquids have been developed to separate phenol from model oil by liquid–liquid extraction. Structural effect of anions of the ionic liquids in the separation is systematically investigated. It is found that depending on the chemical structure of ionic liquids, phenol can be removed from toluene with single-step removal efficiency from 86 to 99% under optimal conditions. The type of substituent groups and the -CH₂ number between two carboxylates have obvious effect on the removal efficiency, and more hydrophilic ionic liquids have a stronger extraction performance for phenol. Furthermore, thermodynamic, ¹³C NMR, ¹H NMR and density functional theory calculations have been performed to characterize the extraction process and to understand the extraction mechanism. It is shown that the extraction of phenol from oil to ionic liquid is a favorable process, and this process is mainly driven by enthalpy change. The formation of the hydrogen bond between anion of the ionic liquid and -OH of phenol is the main driving force for the extraction of phenol from oil to the ionic liquids.

Design of ionic liquids as liquid desiccant for an air conditioning system

Haruki Watanabe, Takuro Komura, Ryo Matsumoto, Kenta Ito, Hiroshi Nakayama, Toshiki Nokami, Toshiyuki Itoh

2019, 4(2): 139-145. doi: 10.1016/j.gee.2018.12.005

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Suitable control of the humidity can contribute to electric energy savings. However, the present dehumidification system has many weak points. The liquid desiccant air-conditioning system has recently gained growing interest from the stand point of reducing energy consumption during dehumidification. In order to find the appropriate ionic liquids (ILs) as a desiccant for the liquid desiccant air-conditioner system, we conducted a systematic evaluation of the humidification capability of 16 types of ILs. Among the tested ILs, tributyl(methyl)phosphonium dimethyl phosphate ([P₄₄₄₁][DMPO₄]) exhibited the best dehumidification capacity and had a less corrosive effect on four types of metals as possible piping materials. It should be noted that this [P₄₄₄₁][DMPO₄] has a very stable nature and produced no odor while conducting the experiment and storing for over 1 year at room temperature under ambient conditions. Furthermore, it was revealed that a 77% (w/w) aqueous solution of [P₄₄₄₁][DMPO₄] worked as an efficient desiccant liquid for the liquid desiccant air-conditioner system.

Ionic liquid/tetraglyme hybrid Mg[TFSI]₂ electrolytes for rechargeable Mg batteries

Zheng Ma, Maria Forsyth, Douglas R. MacFarlane, Mega Kar

2019, 4(2): 146-153. doi: 10.1016/j.gee.2018.10.003

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The electrochemical reversibility of Mg in hybrid electrolytes based on mixtures of ionic liquid and glyme based organic solvents was investigated for applications in rechargeable magnesium batteries (RMBs). The electrolytes demonstrate reversible reduction and oxidation of Mg only after being pre-treated with the dehydrating agent, magnesium borohydride, Mg[BH₄]₂, highlighting the importance of removing water in Mg based electrolytes. The addition magnesium di[bis(trifluoromethanesulfonyl)imide] (Mg[TFSI]₂) (0.3 M) to N-butyl-n-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide [C4mpyr][TFSI]/tetraglyme at a mole ratio of 1:2 showed stable CV cycling over almost 300 cycles while scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirmed Mg deposition, showing non-dendritic morphology and a well-aligned growth. Further thermogravimetric analysis (TGA) demonstrated a mass retention of 79% at 250 °C for this electrolyte suggesting that the presence of the ionic liquid increases thermal stability substantially making these hybrid electrolytes compatible for RMBs.

Computer-aided ionic liquid design for alkane/cycloalkane extractive distillation process

Zhen Song, Xinxin Li, He Chao, Fan Mo, Teng Zhou, Hongye Cheng, Lifang Chen, Zhiwen Qi

2019, 4(2): 154-165. doi: 10.1016/j.gee.2018.12.001

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A computer-aided ionic liquid design (CAILD) study is presented for the frequently encountered alkane/cycloalkane separations in petrochemical industry. Exhaustive experimental data are first collected to extend the UNIFAC-IL model for this system, where the proximity effect in alkanes and cycloalkanes is considered specifically by defining distinct groups. The thermodynamic performances of a large number of ILs for 4 different alkane/cycloalkane systems are then compared to select a representative example of such separations. By applying n-heptane/methylcyclohexane extractive distillation as a case study, the CAILD task is cast as a mixed-integer nonlinear programming (MINLP) problem based on the obtained task-specific UNIFAC-IL model and two semi-empirical models for IL physical properties. The top 5 IL candidates determined by solving the MINLP problem are subsequently introduced into Aspen Plus for process simulation and economic analysis, which finally identify 1-hexadecyl-methylpiperidinium tricyanomethane ([C₁₆MPip][C(CN)₃]) as the best entrainer for this separation.

Depolymerization of polyamide 6 in hydrophilic ionic liquids

Akio Kamimura, Yuto Shiramatsu, Takuji Kawamoto

2019, 4(2): 166-170. doi: 10.1016/j.gee.2019.01.002

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Polyamide 6 underwent an efficient depolymerization in hydrophilic ionic liquids under microwave irradiation at 300 °C. The depolymerization completed within 60 min. Caprolactam was readily separated by simple extraction procedure and the ionic liquids were recovered and reused for several times. Addition of catalytic amounts of DMAP (N,N-dimethylaminopyridine) promoted the depolymerization effectively. The present improved procedure provides a method to avoid direct distillation procedure, which consumes energy for the separation of caprolactam from ionic liquids. Although some contamination of ionic liquids was observed, the present procedure provides a new possibility for the use of ionic liquids for plastic chemical recycling from the viewpoint of development of an energy-saving methodology. Use of solubility switchable ionic liquids is also examined to explore a possibility for better separation although depolymerization did not work well.

Dominant role of wettability in improving the specific capacitance

Tongtong Liu, Kai Wang, Yongxiu Chen, Shuangliang Zhao, Yongsheng Han

2019, 4(2): 171-179. doi: 10.1016/j.gee.2019.01.010

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Here we report a strategy to enhance the energy density of supercapacitors by increasing the utilization rate of the specific surface area (SSA) via wettability improvement. The nonporous gold (NPG) film is used as the electrodes and the ionic liquid [EMIM]BF₄ is the electrolyte. When the electrode is coated by paraffin, an increase of the contact angle leads to a remarkable reduction of the specific capacitance. While when acetonitrile is added into the electrolyte, the contact angle is decreased and the utilization rate of SSA is improved, which results in an increase of the specific capacitance. The addition of isopropyl acetate into the electrolyte leads to a further increase of the specific capacitance. To generalize the role of the wettability in improving the energy density, a carbon-based electrode is evaluated in the solution of potassium hydroxide. An addition of propyl alcohol into the potassium hydroxide solution leads to an increase of the specific capacitance, as well as a long-term stability of the supercapacitor. The role of conductivity in this study is excluded by designing experiments. This paper highlights the significance of wettability in determining the specific capacitance, showing an alternative to improve the energy density of supercapacitors.

Highly active and stable supported Pd catalysts on ionic liquid-functionalized SBA-15 for Suzuki–Miyaura cross-coupling and transfer hydrogenation reactions

Etty N. Kusumawati, Takehiko Sasaki

2019, 4(2): 180-189. doi: 10.1016/j.gee.2019.02.003

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Highly dispersed palladium nanoparticles were synthesized in the presence of immobilized ionic liquid on mesoporous silica SBA-15. PdNPs(2.4 nm)_me-Im@SBA-15 catalyst was prepared by the reduction using NaBH₄ as the reducing agent with controlled feed rate and has been investigated as ligand-free catalyst for Suzuki–Miyaura cross-coupling reaction at room temperature in aqueous solution under air. PdNPs catalyst was also prepared in situ from PdCl₄_me-Im@SBA-15 during the reaction and demonstrated high activity and stability towards nitrobenzene hydrogenation at high temperature. Both catalysts were reusable at least for four recycle processes without significant loss in activity with simple procedure. The catalysts were characterized by TEM, EXAFS, FTIR and XPS.

Removal of gaseous acetic acid using ionic liquid [EMIM][BF₄]

Mingli Mu, Jun Cheng, Chengna Dai, Ning Liu, Zhigang Lei, Yanzhou Ding, Jianjiang Lu

2019, 4(2): 190-197. doi: 10.1016/j.gee.2019.01.004

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This work proposed to use the ionic liquid [EMIM][BF₄] as absorbent for the absorption of gaseous acetic acid. The feasibility of this technology was investigated from molecular level to industrial scale. The acetic acid absorption experiment was carried out using [EMIM][BF₄], and the removal ratio of acetic acid in the gas product can achieve 88.6% at 20 °C under atmospheric pressure at the laboratory scale. Based on the experimental results, a reliable strict equilibrium phase model embedding the parameters of the UNIFAC model was established. On this basis, the conceptual process design and optimization of acetic acid removal by [EMIM][BF₄] at an industrial scale was done, and the most suitable design and operation parameters were obtained. For a further step, the binding energy between [EMIM][BF₄] and acetic acid was calculated to give some insights into the separation mechanism, and the results indicate that the interaction between acetic acid and IL is much stronger than that between nitrogen and IL. Moreover, hydrogen bond can be formed between the cation-acetic acid as well as the anion-acetic acid.

Boosting photocatalytic degradation of RhB via interfacial electronic effects between Fe-based ionic liquid and g-C₃N₄

Xiaowei Li, Bin Wang, Yuhong Huang, Jun Di, Jiexiang Xia, Wenshuai Zhu, Huaming Li

2019, 4(2): 198-206. doi: 10.1016/j.gee.2019.02.002

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The Fe-based ionic liquid doped g-C₃N₄ (FeCN) photocatalyst was firstly prepared base on ultrathin g-C₃N₄ obtained by multiple calcination method with a metal-based reactive ionic liquid [Omim]FeCl₄ for the degradation of Rhodamine B (RhB). Experimental results revealed that Fe³⁺ species were doped into the framework of g-C₃N₄. The effect of the amount of Fe-doping on the catalytic activity was performed. The result showed that the FeCN could effectively degrade RhB under the condition of visible light irradiation. The photocurrent analysis showed that the incorporation of Fe³⁺ into g-C₃N₄ material could accelerate the separation of the photogenerated carriers significantly. At the same time, the reactive species generated during the photodegradation process were tested by radicals trapping experiments and electron spin resonance (ESR). It was proposed that the synergistic effect of O₂^•− and ·OH contributed to degrade RhB efficiently.

2019 Vol. 4, No. 2

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Special Issue: Molecular Thermodynamics for Green Engineering

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