Protic thiocyanate ionic liquids as fuels for hypergolic bipropellants with hydrogen peroxide

Abstract

The combination of ionic liquids (ILs) and hydrogen peroxide is one of the most promising approaches for the substitution of conventionally used hypergolic bipropellants consisting of nitrogen tetroxide and hydrazines. In this work, protic ionic liquids with imidazolium-based cationic structures and thiocyanate anions are presented as new fuels for green hypergolic bipropellants for the first time. All seven presented substances are hypergolic with hydrogen peroxide and surpass the density specific impulse of the previously mentioned conventional bipropellant. One of them stands out in particular, as no other transition metal-, hydride- and boron-free ionic liquid with an ignition delay time as short as 7.3 ms was found with hydrogen peroxide so far. This extremely good ignition behavior of the, at room temperature solid, IL offers great potential not only for hybrid propellants, but also for liquid hypergolic bipropellant combinations: out of a mixture of 35 wt% [Him][SCN] and 65 wt% [Emim][SCN], a remarkable new liquid bipropellant combination (named HIM_35) is formed with a very low ignition delay time of 16.7 ms and a particularly high maximum density specific impulse ρ Isp of 429 s·g·cm−3.