Borohydride Ionic Liquids as Hypergolic Fuels: A Quest for Improved Stability

Abstract

Hydrazine and its derivatives are used as fuels in rocket propellant systems; however, due to high vapor pressure, toxicity, and carcinogenicity, handling of such compounds is extremely hazardous. Hypergolic ionic liquids have shown great promise to become viable replacements for hydrazines as fuels. Borohydride-containing ionic liquids have now been synthesized using a more efficient synthetic pathway that does not require liquid ammonia and halide precursors. Among the eight new compounds, 1-allyl-3-n-butyl-imidazolium borohydride (1) and 1, 3-diallylimidazolium borohydride (5) exhibit very short ignition-delay times (ID) of 8 and 3 ms, respectively. The hydrolytic stability of borohydride compounds has been greatly improved by attaching long-chain alkyl substituents to the imidazole ring. 1,3-Di-(n-octyl)-imidazolium borohydride (3) is a water stable borohydride-containing ionic liquid. 1,3-Di-(n-butyl)-imidazolium borohydride (2) is a unique example of a borohydride liquid crystal. These ionic liquids have some unusual advantages, including negligible vapor pressures, good ignition delay (ID) times, and reduced synthetic and storage costs, thereby showing good application potential as environmentally friendly fuels in bipropellant formulations. In addition, they also have potential applications in the form of reducing agents and hydrogen storage materials.

Prospective Symbiosis of Green Chemistry and Energetic Materials

“…[144] Some of them had unique properties, in particular, ah igh density (0.85-0.93 vs. 0.78 gcm À1 for UDMH), prominent specific impulse value (I sp up to 213 vs. 198 sf or UDMH), positive heat of formation,a nd ultrafastI Dt ime ( 3msw ith WFNA). [144] Some of them had unique properties, in particular, ah igh density (0.85-0.93 vs. 0.78 gcm À1 for UDMH), prominent specific impulse value (I sp up to 213 vs. 198 sf or UDMH), positive heat of formation,a nd ultrafastI Dt ime ( 3msw ith WFNA).…”

Synthesis and Improved Properties of Hypergolic Boronium‐Based Ionic Liquids

“…All the resulting ILs were fully characterized by 1 H and 13 C NMR, IR spectroscopy, elemental analysis or high resolution mass spectrum. The characterization data supported the structures of new ILs (see the Supporting Information).…”

“…[26] All the resulting ILs were fully characterized by 1 H and 13 C NMR, IR spectroscopy, elemental analysis or high resolution mass spectrum. They exhibited moderate thermal stability with decomposed temperature ranging from 123 ℃ to 168 ℃.…”

“…− -based ILs, [13] dicyanamide (DCA − )-based ILs, [7] borohydridebased ILs [1,[14][15][16][17][18] and some others. [4] Considerable efforts have been made in the design and synthesis of HILs from the known hypergolic fuels such as hydrazine-based ILs, [12] amine-based ILs, [4] B-H bonds-rich ILs, [1,[14][15][16][17][18] and so forth.…”

Azetidinium‐based Hypergolic Ionic Liquids with High Strain Energy

“…[7] This provided an opportunity to replace the toxic hydrazine derivatives with green bipropellant fuels. Since then, attentions have been increasingly paid to ILs due to their characteristics, such as negligible vapor pressure, high thermal stability, low toxicity, [2,[8][9][10] Currently, many studies focus on the design of ILs with good hypergolicity and fluidity, including cations such as alkyl-substituted imidazolium, triazolium, pyrrolidinium, pyridinium, [11,12] and anions such as N(CN) 2 À , [13] BH 4 À , [14,15] BH 3 CN À , [16][17][18] BH 2 (CN) 2 À , [19] N 3 À , [20][21][22] …”