Rocket fuels do create environmental pollution, and the degree ofpollution varies with the nature of the fuel used. Propellantscontaining high grade kerosene, rubber and chemicals like hydrazine,nitrogen tetroxide and nitrous oxide produce toxic products, while those constituting hydrogen and oxygen are much cleaner. Making a majorbreakthrough, the US military researchers have innovated a “green rocket fuel” that emits less corrosive and toxic chemicals than theconventional rocket propellants.
Rocket propellants require a hypergolic mixture, where thecomponents are capable of igniting spontaneously as soon as they come in contact with each other. Producing a less hazardous hypergolicpropellant is tough as the oxidizer and fuel need to achieve therequired ignition point to give out the best performance. According tothe propellant expert John Bellerby of Cranfield University, UK,hydrogen peroxide is a better option as the oxidizer releasing minimumamounts of hazardous chemicals, but finding a matching hypergolic fuelis tough.
Stefan Schneider and his colleagues of Air Force Research Laboratory at Edwards, California are highly optimistic about the use of hydrogenrich ionic-liquid as the green rocket fuel that will produce the samepropelling force as the conventional rocket fuels. Schneider’s team isof the view that highly dense form of hydrogen ions can be createdcombining an ionic liquid with aluminum borohydride that producedcomplex anions being stabilized by the aluminum cations. The higherdensity of hydrogen will produce less toxic substances on burning.
Ionic liquids are nothing but salts that remain in liquid state atthe room temperature. These are fast emerging as “green solvents” forthe future due to its extremely low vapor pressure that produce lesstoxic vapors. This property makes them attractive replacements forhydrazine in the rocket fuels. The team experimented withtrihexyltetradecylphosphonium (THTDP) chloride, where the negativechloride ion was substituted with the borohydride anion. The complexproduct (THTDP)BH4, when reacted with excess aluminum borohydride,produced an ionic liquid at room temperature containing higher densityof hydrogen ions. The aim of the experiment was to increase theconcentration of hydrogen to produce clean and green bi propellant.
Repeated tests have proved the hypergolicity of the hydrogen richionic-liquid fuels with hydrogen peroxide as the oxidizing agent, whichcan be considered as green bipropellants for the future. The researchers declared this type of ionic liquids as the pioneer in liquid bipropellants that will bring out better performance besides emitting less hazardous chemicals.