Experimental study on atomization characteristics of energetic ionic liquid for green monopropellant of RCS thruster

Energetic ionic liquids (EILs) are of great interest. They offer enhanced stability, higher densities, no vapor pressure, and, hence, no vapor toxicity. As a general principle, the stability of energetic ionic compounds can be greatly enhanced by making the cation the fuel and the anion the oxidizer. The formal positive charge increases the ionization potential of the fuel cation, and the formal negative charge decreases the electron affinity of the anion. In this manner, the fuel cation becomes more oxidizer-resistant, and the oxidizer anion is protected against premature reduction by the cation. For environmental reasons, it is also desirable to avoid halogen-containing ingredients, such as perchlorates. The previously known EILs consist of small oxidizing anions, such as ClO4 , NO3 , or N(NO2)2 , and large fuel cations containing quaternary nitrogen heterocycles with long, asymmetric, poorly packing side chains. The most serious drawback of these EILs is that they are underoxidized. The small anions do not carry sufficient oxygen for complete oxidation of the large fuel cations to carbon monoxide, resulting in poor performance. In rocket propulsion, a low molecular weight of the exhaust products is very important. 5] Furthermore, at high flame temperatures CO2 is dissociated almost completely to CO and O2 (Boudouard equilibrium). Therefore, it is often sufficient to oxidize the carbon content only to CO and not to CO2 to achieve nearmaximum performance. The aim of this study was the preparation of halogen-free, CO-balanced, EILs. In 1998, the concept of oxidizer-balanced EILs was proposed, and in 2002, its practicability was shown by the preparation of 1-ethyl-3-methylimidazolium tetranitratoborate, a compound that turned out to be indeed an ionic liquid with a freezing point of 25 8C. However, its energy content and thermal stability were marginal. Herein, we report on a significantly improved compound using the tetranitratoaluminate anion as a thermally more stable highoxygen carrier and the 1-ethyl-4,5-dimethyltetrazolium cation as a more energetic counterion (imidazole, DH o f = + 49.8 kJmol ; tetrazole, DH o f =+ 237.1 kJmol 1 ). These are the first CO-balanced EILs. Although an oxygenbalanced tetrazolium salt, 5-aminotetrazolium nitrate, was recently reported, its melting point of 173 8C does not classify it as an ionic liquid. Polynitratoaluminates were first studied in the 1960s in the USA and, subsequently, during the 1970s in the USSR. Several examples of alkali metal, NO2 , and ethylammonium salts of tetra-, penta-, and hexanitratoaluminate anions are known. The tetranitratoaluminate anion contains 12 oxygen atoms; of these, 10.5 are available to oxidize a fuel cation. Alkylated tetrazolium cations were used in this work because of their large positive heats of formation and their potential to form ionic liquids. Ionic salts of the tetranitratoaluminate anion can be prepared in essentially quantitative yields in one-pot reactions in nitromethane solution. The starting materials are the chloride salt of the cation, aluminum trichloride, and dinitrogen tetroxide. The synthesis of 1-ethyl4,5-dimethyltetrazolium tetranitratoaluminate (3) is shown in Scheme 1. The starting material 1-ethyl-4,5-dimethyltetrazo-

N,N‐Bis(1H‐tetrazol‐5‐yl)amine anions (HBTA–/BTA2–) were used as suitable nitrogen‐rich components for the construction of energetic ionic liquids. Seven ionic liquids, namely, 1,3‐dimethylimidazolium (1, [C1mim]HBTA), 1‐ethyl‐3‐methylimidazolium (2, [C2mim]HBTA), 1‐butyl‐3‐methylimidazolium (3, [C4mim]HBTA), 1‐hexyl‐3‐methylimidazolium (4, [C6mim]HBTA), 1‐methyl‐3‐octylimidazolium (5, [C8mim]HBTA), and 1,2,3‐trimethylimidazolium (6, [C1mmim]HBTA) cations with the HBTA– anion and di‐1,2,3‐trimethylimidazolium N,N‐bis(1H‐tetrazol‐5‐yl)amine (7, [C1mmim]2BTA), were synthesized. All materials were fully characterized by IR and NMR spectroscopy, elemental analysis, and high‐resolution mass spectrometry. The crystal structures of 1 and 7 were determined by single‐crystal X‐ray diffraction [1: monoclinic, P21/n, a = 14.0653(4) Å, b = 6.9507(2) Å, c = 22.4699(7) Å, β = 93.996(3)°, V = 2191.38(12) Å3, Z = 8, ρ = 1.511 g cm–3; 7: monoclinic, P21/c, a = 17.5869(3) Å, b = 12.8757(2) Å, c = 21.9203(6) Å, β = 125.0580(10)°, V = 4063.15(15) Å3, Z = 8, ρ = 1.221 g cm–3]. The nitrogen contents of 1–7 exceed 40 %, and 1 has the highest value of 61.78 %. The ionic liquids 1–7 are thermally stable to 220 °C, and 2–5 are room‐temperature ionic liquids. The heats of formation of 1–7 obtained by both experimental and theoretical methods are all positive. The ionic liquids 1–7 are insensitive towards impact (>40 J) and friction (>360 N). They can be ignited in air. These new energetic ionic liquids contain only C, H, and N and are of interest as potential propellants with high energy, high thermal stability, low sensitivity to impact and friction, and environmentally friendly decomposition gases.

Anion assisted extraction of U(VI) in alkylammonium ionic liquid: Experimental and DFT studies

Salts being liquid below 100 °C are defined as ionic liquids. Due to their unique properties, they are attracting increasing interest and are also being investigated in the field of energetic materials. Combining nitrogen‐rich cations and oxygen‐rich anions, it is possible to obtain energetic ionic liquids (EILs). Potential applications are plasticizers, high explosives, gun and rocket propellants. However, only few works have been done in the field of EILs which show a glass transition temperature less than −40 °C, the so called low‐temperature EILs (LT‐EILs). LT‐EILs with dinitramide as an anion are an almost unknown group with interesting properties and potential. In this paper we present synthesis, characterization and combustion properties of 4‐amino‐1‐butyl‐1,2,4‐triazolium dinitramide (C4 DN) as a low temperature dinitramide‐based EIL in its entirety for the first time. A classic synthesis route and a metal‐free route are presented. The physical properties were measured and compared to conventional non‐ionic energetic plasticizers like BDNPA/F, TMETN/BTTN, Bu‐NENA and DNDA‐57. The combustion behaviour was studied using an optical window bomb and compared to non‐ionic energetic liquids in use. To evaluate the performance as an energetic plasticizer or additive, the interaction with the energetic binder GAP is investigated by manufacturing of dog bone‐shaped test specimen and comparing their mechanical properties and their glass transition temperatures with conventional energetic plasticizers, based on non‐ionic energetic compounds. As one result, C4 DN showed an intense softening effect. Based on the result, propellant samples were prepared and characterized.

Energetic ionic liquids (EILs) have various industrial applications because they release chemically stored energy under certain conditions. They can avoid some environmental problems caused by traditionally used toxic fuels. EILs, which are environmentally friendly and safer, are emerging as an alternative source for hypergolic bipropellant fuels. This review focuses on the crucial thermophysical properties of the EILs. The properties of imidazolium and triazolium-based ionic liquids (ILs) are discussed here. The thermophysical properties addressed, such as glass transition temperature, viscosity, and thermal stability, are critical for designing EILs to meet the need for sustainable energy solutions. Imidazolium-based ILs have tunable physical properties making them ideal for use in energy storage while triazolium-based ILs have thermal stability and energetic potential. As a result, it is important to understand and compile thermophysical properties so they can help researchers synthesize tailored compounds with desirable characteristics, advancing their application in energy storage and propulsion technologies.

Starting from N-methylimidazole, 1,2-dimethylimidazole and 2-chloroethanol, a series of imidazolium-based ener- getic ionic liquids were synthesized via quaternization, nitration and metathesis reactions. All the energetic ionic liquids were characterized by ultraviolet visible spectrum (UV-Vis), infrared spectrum (IR), mass spectrometry (MS), nuclear magnetic resonance (NMR) and elemental analysis. The solubility study of these ionic liquids was carried out with commonly used or- ganic solvents, which showed that the energetic ionic liquids dissolved easily in polar solvents. Moreover, the ionic liquids had good thermo-stabilities indicated by thermal gravimetric analysis (TG-DTG) and differential scanning calorimetry (DSC). TG-DTG analyses showed that N-nitrooxyethylimidazolium nitrate decomposed at about 160 ℃ and N-hydroxyethylimida- zolium ionic salts decomposed above 190 ℃. Furthermore, there was an obvious glass transition process for the energetic ionic liquids based on 1-(2-nitrooxyethyl)-3-methylimidazolium and N-hydroxyethylimidazolium during the secondary heating process of DSC, which was the unique property of ionic liquids. Their densities and standard enthalpies of formation and det- onation properties were calculated and analyzed. Keywords energetic materials; quaternary ammonium; metathesis; thermal properties; detonation properties

Ionic liquids (ILs) are pure salts with melting points typically less than 100°C. ILs exhibit several advantages over conventional molecular liquids in disparate applications because of their remarkable physical properties, which include wide electrochemical stability windows, high ionic conductivity and negligible vapor pressure. IL applications, either already realized or currently under development, encompass many diverse areas such as analytics, catalysis, chemical synthesis, separation technologies, electrochemistry, capacitors, batteries, fuel cells, solar cells, and tribology. Many of these applications involve reactions at the IL/solid interface. Hence, a detailed understanding of the structure of this interface is important and cannot be overstated. ILs exhibit behavior that is very different from common molecular liquids. As ILs are composed entirely of charged species, they usually exhibit a more pronounced structure in the bulk and at surfaces than molecular liquids.1 ILs are subject to a range of cohesive interactions (Coulombic, van der Waals, hydrogen bonding and solvophobic forces), resulting in a well-defined nanostructure both in the bulk and at interfaces.2 The nanostructure of ILs evolves as a consequence of electrostatic interactions between charged groups that produce polar domains. Cation alkyl chains are solvophobically repelled3 from these charged domains and cluster together to form apolar regions, that in turn produce a sponge-like phase-separated nanostructure.4 This spongelike structure present in the bulk changes immediately adjacent to a smooth solid surface. Atomic force microscopy (AFM) force curves5,6 and reflectivity experiments7 both reveal the formation of discrete ion or ion pair layers immediately adjacent to the solid surface. This layered surface structure decays to the bulk sponge morphology over a length-scale of a few nanometers.8 The IL/solid interface has been the subject of extensive experimental and theoretical studies. Various spectroscopic and scattering methods have been applied to examine this interface.7,9-21 Electrochemical impedance spectroscopy (EIS) measurements have been used to study the structure and dynamics of ILs.22-24 Theoretical descriptions of the IL/electrode interface using molecular dynamics and Monte Carlo simulations,25-35 and mean field theory,36,37 have predicted “bell-” and “camel-” shaped capacitance curves and oscillating ion density profiles at the electrode surface, consistent with experimental results. However, a proper theoretical model of the electrified IL/solid interface does not yet exist and further experimental studies are required for better understanding the IL/electrode interfacial structure. During the last decade, in situ atomic force microscopy (AFM) and scanning tunneling microscopy (STM) have been extensively used to probe the IL structure at the IL/solid interface.1,5,8,38-50 The mechanism of operation of the AFM experiment is presented schematically in Fig. 1. The solid electrode substrate and the AFM tip and cantilever are completely immersed within the IL (Fig. 1a). The layers close to the surface are shown schematically as single (blue) layers. As the AFM tip moves towards the surface, it is deflected away due to the forces imparted by the interfacial IL

Friction sensitivity is an important safety parameter for assessment when working with new energetic ionic liquids (EILs) during mixing, pouring, sieving, priming and consolidation operations in working places. This work introduces a reliable method to predict friction sensitivity of quaternary ammonium‐based EILs, which are based on elemental composition of cation and anion of a desired ionic liquid as well as the contribution of specific cations and anions. For 47 EILs, the values of coefficient of determination (R2) and Root Mean Squared Error (RMSE) of the new model are 0.9057 and 33 N, respectively. High accuracy of the novel method confirms that prediction of friction sensitivity of quaternary ammonium‐based EILs is not necessarily enhanced by greater complexity.

Boron nanoparticles prepared by milling in the presence of a hypergolic energetic ionic liquid (EIL) are suspendable in the EIL and the EIL retains hypergolicity leading to the ignition of the boron. This approach allows for incorporation of a variety of nanoscale additives to improve EIL properties, such as energetic density and heat of combustion, while providing stability and safe handling of the nanomaterials.

Exploring the possibilities of energetic ionic liquids as non-toxic hypergolic bipropellants in liquid rocket engines

Today, the use of polymer electrolyte membranes (PEMs) possessing ionic liquids (ILs) in middle and high temperature polymer electrolyte membrane fuel cells (MT-PEMFCs and HT-PEMFCs) have been increased. ILs are the organic salts, and they are typically liquid at the temperature lower than 100 °C with high conductivity and thermal stability. The membranes containing ILs can conduct protons through the PEMs at elevated temperatures (more than 80 °C), unlike the Nafion-based membranes. A wide range of ILs have been identified, including chiral ILs, bio-ILs, basic ILs, energetic ILs, metallic ILs, and neutral ILs, that, from among them, functionalized ionic liquids (FILs) include a lot of ion exchange groups in their structure that improve and accelerate proton conduction through the polymeric membrane. In spite of positive features of using ILs, the leaching of ILs from the membranes during the operation of fuel cell is the main downside of these organic salts, which leads to reducing the performance of the membranes; however, there are some ways to diminish leaching from the membranes. The aim of this review is to provide an overview of these issues by evaluating key studies that have been undertaken in the last years in order to present objective and comprehensive updated information that presents the progress that has been made in this field. Significant information regarding the utilization of ILs in MT-PEMFCs and HT-PEMFCs, ILs structure, properties, and synthesis is given. Moreover, leaching of ILs as a challenging demerit and the possible methods to tackle this problem are approached in this paper. The present review will be of interest to chemists, electrochemists, environmentalists, and any other researchers working on sustainable energy production field.

Electrically-driven vapor compression or thermally-driven ammonia water absorption refrigeration systems are commonly used for cooling below 0°C. Due to the non-negligible vapor pressure of water, usually a rectification during regeneration is required for the ammonia water system. Ionic liquids (IL) present an alternative to conventional working pairs. Ionic liquids are versatile absorbents since they extend the use of natural refrigerants other than ammonia in thermally driven absorption technology. Furthermore, room temperature ionic liquids do not crystallize at ambient temperature even at high ionic liquid mass fractions just like water in ammonia water chillers. In addition, they exhibit a nearly zero vapor pressure allowing for regeneration without rectification. In the present paper, the first experimental results of a single stage absorption refrigerator using ethanol as the refrigerant and the ionic liquid [EMIM][DEP] as the absorbent are presented. For 10°C and 30°C as external evaporator and absorber inlet temperatures the experimental thermal efficiency (COP) ranges from 0.4 to 0.62 and the refrigeration power from 0.7 to 1.9kW for varying driving temperatures from 66°C to 110°C. The simulated thermal efficiency is rather high with 0.75. This discrepancy to the experiment most likely is due to a thermal loss in the experiment.

This paper presents a numerical, and experimental study on atomization characteristics and droplet distribution of a twin-fluid two-phase internal mixing atomizer. Using the discrete phase model and Eulerian–Lagrangian numerical study, internal and external flow fields are simulated to describe two-phase flow in mixing chamber. The exterior region near the exit nozzle in the combustion chamber is simulated by particle trajectory method. Internal-mixing atomizer is manufactured and tests are carried out to verify the numerical results by applying shadowgraph method visualizing flow near the exit nozzle of the atomizer and downstream in combustion chamber. In order to study atomization characteristics including droplet dimension and velocity distribution in different gas to liquid ratio, an advanced twin-fluid test stand for two-phase flow atomizers is designed and built. By changing operating parameters of gas phase pressure and liquid flow rate a reasonable agreement for spray cone angle, maximum penetration depth and droplet diameter and velocity distributions is found between numerical and experimental result. As result, turbulence modeling assists to estimate atomization characteristics of complicated twin-fluid two-phase atomizers precisely to avoid time-taking and costly experimental tests although an advanced test stand is developed and built to cover all types of atomizer.

To develop a new type of energetic ionic liquid (EIL) that has a catalytic effect on the thermal decomposition of ammonium perchlorate (AP) and can be ignited in white fuming nitric acid (WFNA), six borane‐containing ionic liquids based on biferrocene were successfully synthesized, and their structures were determined by x‐ray crystallography. Except for iodized salts, four EILs with high thermal stability burned rapidly in WFNA, one of which, bis[1‐(ferrocenylmethyl)imidazole‐3‐yl] dihydroboronium cyanoborohydride, [Fcmim][BH3CN], produced the shortest ignition delay (ID) time of 5 ms. However, iodized salts demonstrated a better catalytic effect on AP than did BH3CN−‐ or N(CN)2−‐based EILs and bis[1‐(ferrocenylmethyl)benzimidazole‐3‐yl] dihydroboronium iodide, [Fcbemim][I], could advance the final thermal decomposition temperature of AP by 50°C. Anions have a significant effect on the structures and performances of ionic liquids.

Ionic liquid is a new type of green solvent, because of the nonvolatility, good dissolution properties, and high chemical stability. It is expected to replace the current extensive use of volatile solvents, to design environmental friendly new chemical process. However each cations and anions different from each other, combination into a huge number of ionic liquids, if its physical and chemical properties determined through the experiment, the cost is high. So it is highly needed to develop an effective and reliable method to predict the thermodynamic properties of the systems containing ionic liquid. Ammonia (NH3) solubility studies about the design and production of natural gas plays an important role. In this paper the solubility of NH3 in different ionic liquids are studied, and compared with the results predicted by UNIFAC model. The accurate calculation of the NH3 solubility in ILs is important in natural gas purification. UNIFAC model is selected to predict the solubility of NH3, which can decrease a plenty of experimental work in the laboratory. The new group NH3 is defined by regression of the experimental data collected from the literatures published to obtain the group-group interaction parameters between the components of NH3 and ionic liquids. The consistency test is carried out to examine the accuracy of prediction results. The solubility predicted by UNIFAC model is verified a perfect agreement with the experimental data provided in the literature at temperature range from 282.2 K to 355.8 K and pressure up to 25 bar, with an average relative deviation (ARD) less than 10 %. The results demonstrate that for system studied in this work, UNIFAC model can realize the solubility prediction successful. This predictive model is useful for predicting the NH3 solubility in imidazolium-based ionic liquids and providing the phase equilibrium data for the application of liquid natural gas and the relevant mass transfer separation in chemical engineering.