Editor's note: From the birth of ionic liquids in 1914 to the present, it has gone through nearly 100 years. With the continuous updating and development of science and technology, the ionic liquids developed by modern times are increasingly used by scientists from various countries in the development of clean energy. Go. In May this year, Chinese and American scientists have made the latest breakthrough in the field of ionic liquid research and development.
Ionic liquid
Ionic liquid (IL) refers to ionic compounds in liquid state. All salts that can be melted without decomposition or gasification can be used as ionic liquids, such as sodium chloride at high temperature, which contains sodium ions and chloride ions. Ionic liquids generally generate ionic solids on cooling, which may be crystalline or amorphous.
Relevant data show that substances composed of ions that are liquid at or near room temperature are called room temperature ionic liquids, room temperature molten salts, organic ionic liquids, etc. There is currently no uniform name, but they tend to be referred to as ionic liquids. In ionic compounds, the force between the anions and cations is the Coulomb force, and its size is related to the number and radius of the charge and anion of the anions and cations. The larger the ion radius, the smaller the force between them and the melting point of this ionic compound. low. Some ionic compounds have a large volume of anions and cations and a loose structure, resulting in a low force between them, so that the melting point is close to room temperature.
The main reason for the low melting point of ionic liquids as ionic compounds is due to the asymmetry of certain substituents in their structure, which prevents ions from stacking regularly into crystals. It is generally composed of organic cations and inorganic anions. Common cations include quaternary ammonium salt ions, quaternary phosphonium salt ions, imidazole salt ions and pyrrole salt ions. Anions include halogen ions, tetrafluoroborate ions, hexafluorophosphate ions, etc. .
The history of ionic liquids can be traced back to 1914, when Walden reported the synthesis of (EtNH3) HNO3- (melting point 12 ° C). This substance is made by the reaction of concentrated nitric acid and ethylamine. However, because it is very unstable in the air and it is easy to explode, its discovery did not arouse people's interest at the time. This is the earliest ionic liquid.
Until 1976, Robert of Colorado State University in the United States used AICl3 / [N-EtPy] Cl as an electrolyte to conduct organic electrochemical research and found that this room temperature ionic liquid is a good electrolyte, which is miscible with organic matter, not Containing protons, the electrochemical window is wider. In 1992, Wilkes synthesized 1-methyl-3-ethylimidazole chloride with 1-methyl-3-ethylimidazole as a cation. In the presence of AICl3 with a mole fraction of 50%, its melting point reached 8 ° C. After this, the application research of ionic liquids has really been widely carried out.
Ionic liquid as carbon precursor modified electrode material
In mid-May, from the Institute of Physics of the Chinese Academy of Sciences, the research team of Hu Yongsheng, the Beijing National Laboratory for Condensed Matter Physics, used ionic liquids as carbon precursors for the first time to coat porous Li4Ti5O12. Compared with the traditional solid carbon source precursors, ionic liquids are easier to penetrate into porous materials due to their flow properties, and at lower vapor pressures, the cracking temperature range is wider (400-1000 ℃), and it is not accompanied by rapid Evaporation of the solvent is beneficial to form a uniform thin coating on the particle surface. In addition, the composition of the coating layer can be adjusted by selecting different types of ionic liquids. Therefore, the use of ionic liquids as a precursor has obvious advantages in adjusting the composition and properties of the coating layer and the surface interface, which is particularly important for the design and optimization of materials.
In fact, in 2012, China has made significant progress in the research of ionic liquids. It is reported that the "Twelfth Five-Year" National Science and Technology Support Plan project undertaken by the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences has made significant progress in independent research and key research on the key technology and application demonstration of oxygenated compounds for the synthesis of polyethers from methanol via paraformaldehyde The pilot plant with an annual output of 100 tons of polymethoxy dimethyl ether (DMMn) developed at the Baiyin Pilot Base of Lanzhou Institute of Chemical Research was successfully commissioned and commissioned in mid-August. The pilot test was completed and the entire process was completed. The key technological processes such as stable operation, catalytic separation, and product processing were realized, and the laboratory results were reproduced.
With its profound research and accumulation in the construction of functionalized ionic liquids and its catalytic reaction performance, Lanzhou Institute of Chemical Research took the lead in breaking through the research work on the new technology of ionic liquid catalytic synthesis of DMMn in China in 2007. There are nearly forty related invention patents and more than nine patents have been granted in China and the United States. This technology will promote the development of carbon-chemical chemicals using methanol as a raw material, and have a significant impact on non-petroleum raw material synthesis of clean fuel technology.
Ionic liquid or future rocket fuel
According to foreign media reports, from the launch of rockets in the 1970s to the most advanced Curiosity rover mission in the beginning of this century, relatively "primitive" power was used. Hydrazine is still the fuel for rocket launches, and the chemical substance has also been It is called hydrazine. Although hydrazine can release a lot of energy, the substance is highly toxic. After years of exploration by the US Air Force Institute, it has finally found a rocket fuel that replaces hydrazine. It is not only safer than hydrazine fuel, but also environmentally friendly. The fuel releases energy Also very high.
This new type of propellant is an ionic liquid. The molecule has a positive charge or a negative charge and exists in the form of a liquid. The characteristics of ionic liquids make this substance very safe and conducive to transportation and storage, but in previous experiments, ionic liquids did not have a strong energy release feature, which means that when they burned, they did not produce the energy required to propel the rocket.
Tom Hawkins, a scientist from the US Air Force Rocket Propulsion Research Group, believes that ionic liquids will be a potential source of rocket fuel. The professional name of the current ionic liquid rocket propellant is AF-M315E, which is presented in the form of liquid. If it is processed with low pressure, it will slowly evaporate, which means that the ionic liquid rocket propellant is more stable and less flammable than hydrazine. It is also easy to handle and use. In terms of toxicity, AF-M315E only releases non-toxic gases, such as water vapor, hydrogen, and carbon dioxide. It is understood that the rocket using this type of green propellant will conduct its first test flight in 2015. If the test is successful, it will open a new era of manned spaceflight.
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