A simple protocol to overcome the explosive pentafluoroethylation of carbonyl compounds by HFC-125 is described The use of potassium (K) bases with triglyme or tetraglyme as a solvent safely yield

Pentafluoroethylation of Carbonyl Compounds by HFC-125 via the Encapsulation of the K Cation with Glymes.

Trifluoroethylene (HFO-1123) and its mixtures are useful as the next generation refrigerants because their global warming potential (GWP) are lower than that of those ordinarily used. HFO-1123, however, has the potential to disproportionate explosively as does tetrafluoroethylene. In this report, the explosive disproportionation of mixed gases of HFO-1123 and other gases were investigated by the fusing of Pt wires ignition method at 10 MPa and 488 K which was the upper limit of the conditions in typical refrigerant usage. It was found that there was a roughly linear correlation between the lower limit of HFO-1123 concentration at which disproportionation occurred and the molar heat capacity at a constant volume of mixed gas. This experimental finding strongly suggests that an explosive disproportionation consists of a thermal explosion process.

Analysis of disproportionation process of trifluoroethylene mixtures

A medical grade nitrous oxide (N2O) and gaseous oxygen (GOX) “Nytrox” blend is investigated as a volumetrically-efficient replacement for GOX in SmallSat-scale hybrid propulsion systems. Combined with 3-D printed acrylonitrile butadiene styrene (ABS), the propellants represent a significantly safer, but superior performing, alternative to environmentally-unsustainable spacecraft propellants like hydrazine. In a manner analogous to the creation of soda-water using dissolved carbon dioxide, Nytrox is created by bubbling GOX under pressure into N2O until the solution reaches saturation. Oxygen in the ullage dilutes N2O vapor and increases the required decomposition energy barrier by several orders of magnitude. Thus, risks associated with inadvertent thermal or catalytic N2O decomposition are virtually eliminated. Preliminary results of a test-and-evaluation campaign are reported. A small spacecraft thruster is first tested using gaseous oxygen and 3-D printed ABS as the baseline propellants. Tests were then repeated using Nytrox as a “drop-in” replacement for GOX. Parameters compared include ignition reliability, latency, initiation energy, thrust coefficient, characteristic velocity, specific impulse, combustion efficiency, and fuel regression rate. Tests demonstrate Nytrox as an effective replacement for GOX, exhibiting a slightly reduced specific impulse, but with significantly higher volumetric efficiency. Vacuum specific impulse exceeding 300 s is reported. Future research topics are recommended.

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1198&context=mae_facpub

Nytrox as “Drop-in” Replacement for Gaseous Oxygen in SmallSat Hybrid Propulsion Systems

The protocol of micro-flow nucleophilic pentafluoroethylation using pentafluoroethane (HC2F5, HFC-125), a nontoxic, inexpensive, and commercially available greenhouse gas, is described. The micro-flow pentafluoroethylation by HFC-125 proceeded smoothly at room temperature or at -10 °C in DMF or toluene in the presence of a potassium base, namely, t-BuOK or KHMDS. A broad range of ketones, aldehydes, and chalcones with various substituted benzene rings were successfully converted to the corresponding pentafluoroethyl carbinols instantly with good to high yields.

Pentafluoroethylation of Carbonyl Compounds Using HFC-125 in a Flow Microreactor System.

This Review examines the gas-phase oxidations of hydrogen and other fuels (ammonia, hydrazine, hydrocarbons) with nitrous oxide, running as self-ignitions, deflagrations, or detonations. Taking into account the main feature of nitrous oxide, i.e., its ability to decompose exothermally, this Review summarizes also the conditions determining an explosive evolution of N2O decomposition, and the characteristic parameters of this process, as self-ignition or after ignition by local energy sources. For fuel–nitrous oxide explosive combustion, this Review is focused on conditions where the explosive combustion takes place (flammability limits, minimum ignition energy) or it is quenched (quenching distance, Maximum Experimental Safe Gap) and on the characteristic properties of explosion development and propagation. These properties are separately examined for deflagrations and detonations. The DDT (Deflagration-to-Detonation) process is also taken into account, because it occurs in most technical applications of fuel–N2O combustion in enclosures. This Review is completed by a discussion of processes where nitrous oxide is promoter of fuel–oxygen or fuel–air explosive combustion. 

Nitrous Oxide: Oxidizer and Promoter of Hydrogen and Hydrocarbon Combustion

The minimum energies required to initiate the combustion of gaseous tetrafluoroerthy1ene (TFE) and mixtures thereof with nitrogen, argon, and helium at various initial pressures and temperatures are determined. Flame transition from the gas to the liquid phase of TFE is investigated. Liquid TFE is demonstrated to be virtually nondetonable. The fuel-lean flammability and detonability limits of TFE-air mixtures under normal conditions are demonstrated to be identical, 12.2 vol %.

Explosive characteristics of tetrafluoroethylene

The minimum energies of ignition of gaseous nitrous oxide are measured at pressures up to 3 MPa. The minimum pressure at which nitrous oxide burnt out in the reactor completely was 0.5 MPa. It is shown that this pressure depends on the length of the vertically installed cylindrical reactor. At the optimal length, the minimum pressure was as low as 0.3 MPa. The effect of organic lubricants on the ignition energy is discovered. Liquid nitrous oxide failed to be ignited by a flame torch.

Critical conditions for nitrous oxide ignition

The characteristics of the propagation of a nitrous oxide decomposition flame in a tube with an internal diameter of 70 mm were measured. It was demonstrated that the pattern of flame propagation and the extent of burnout are determined by the convective motion of the flame kernel because of a very slow burning of nitrous oxide. The laminar flame speed estimated from pressure oscillograms and calculated using thermal theory of flame propagation was found to be ∼1 cm/s. The critical diameter of flame quenching in channels were measured to decrease from 10 to 4 mm as the pressure was increased from 15 to 20 atm. Because of the possibility of reignition of the fresh mixture behind the flame arrester by the outflowing combustion products, the channel should be significantly longer than 200 mm.

Yu. S. Biryulin

Papers

Explosive characteristics of tetrafluoroethylene

Critical conditions for nitrous oxide ignition

Flame propagation in gaseous nitrous oxide