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Hybrid rocket propulsion can contribute to reduce launch costs by simplifying engine design and operation. Hypergolic propellants, i.e. igniting spontaneously and immediately upon contact between fuel and oxidizer, further simplify system integration by removing the need for an ignition system. Such hybrid engines could also replace currently popular hypergolic propulsion approaches based on extremely toxic and carcinogenic hydrazines. Here we present the first demonstration for the use of hypergolic metal-organic frameworks (HMOFs) as additives to trigger hypergolic ignition in conventional paraffin-based hybrid engine fuels. HMOFS are a recently introduced class of stable and safe hypergolic materials, used here as a platform to bring readily tunable ignition and combustion properties to hydrocarbon fuels. We present an experimental investigation of the ignition delay (ID, the time from first contact with an oxidizer to ignition) of blends of HMOFs with paraffin, using White Fuming Nitric Acid (WFNA) as the oxidizer. The majority of measured IDs are under 10 ms, significantly below the upper limit of 50 ms required for functional hypergolic propellant, and within the ultrafast ignition range. A theoretical analysis of the performance of HMOFs-containing fuels in a hybrid launcher engine scenario also reveals the effect of the HMOF mass fraction on the specific impulse (Isp) and density impulse (ρIsp). The use of HMOFs to produce paraffin-based hypergolic fuels results in a slight decrease of the Isp and ρIsp compared to that of pure paraffin, similar to the effect observed with Ammonia Borane (AB), a popular hypergolic additive. HMOFs however have a much higher thermal stability, allowing for convenient mixing with hot liquid paraffin, making the manufacturing processes simpler and safer compared to other hypergolic additives such as AB.

There will be common challenges to scaling-up any ionic liquids separations technologies which require very large volumes of ionic liquid. Some of these challenges are illustrated in this personal account which chronicles the extraction of chitin from shrimp shell from discovery to current commercialization efforts. The road being taken from discovery in an academic laboratory, through attempts to navigate the scaling-up to commercial scale using the vehicle of a faculty startup company is rewarding, but fraught with roadblocks, detours, and unexpected challenges. The differences in 'technically feasible' and 'commercially viable' are not always evident from the beginning of the journey, however, one wonders what achievements we miss as a Society because it was assumed to not be commercially viable.

In search of ionic liquids (ILs) with multiple types of soft donor atoms capable of preferentially complexing a range of soft metal ions over harder ions, we investigated structural clues to the role of hydrogen bonding in IL behavior through a series of salts with anions containing both N- and S-donor atoms based on azole thiolates. Reaction of equimolar amounts of triethylamine (Et3N) or diisobutylamine (DBA) with 1-phenyl-1H-tetrazole-5-thiol (PhTzSH), 1-methyl-1H-tetrazole-5-thiol (MeTzSH), or 5-methyl-1,3,4-dithiazole-2-thiol (MeDiTSH) yielded [Et3NH][MeTzS] (1), a yellow liquid, and the low melting yellow solids [DBAH][MeTzS] (2), [Et3NH][PhTzS] (3), [DBAH][PhTzS] (4), [Et3NH][MeDiTS] (5), and [DBAH][MeDiTS] (6). Thermal analysis revealed that all of them qualify as ILs with melting points below 100 °C. Single crystal X-ray structure analysis of 2-6 revealed the presence of an extensive H-bonding network that includes the rare N-H⋯S hydrogen bonds in 3, 4, and 6. These weaker interactions appear to significantly influence thermal behavior, where strong bonding leads to higher melting temperatures and lower decomposition points.

A reversible amine-carbamate approach has been developed to reduce the use of antisolvents such as water in the coagulation of biopolymers from ionic liquid (IL) solution and thus improve the economy of IL recycle. Cellulose and chitin were recovered from 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) solution by introducing the miscible amines triethanolamine (TEA), ethylenediamine (EDA), or butylamine (BA) and bubbling CO2 at 40 °C and atmospheric pressure through the solutions to form carbamate salts in situ which resulted in biopolymer coagulation. BA gave the best results because of its low boiling point and low viscosity, which benefited both biopolymer recovery and IL recycle. Cellulose films and fibers could be formed by extrusion of an MCC/[C2mim]‐[OAc] solution into a coagulating bath comprised of a 1:1 M mixture of [C2mim][OAc] and butylammonium butylcarbamate (BA-carbamate). The cellulose, IL, amine, and CO2 were easily separated, although the cellulose recovered required some water washings to remove traces of IL. Up to 96.5% of the [C2mim][OAc] could be recovered, 76.2% from the coagulation bath and 20.2% from the water washings. The recycled IL was suitable for another cycle of cellulose dissolution and extrusion and 84.6% of the IL used for the second cycle was recovered. Although further work is needed, not the least of which will be reducing the amount of water needed for washing steps, some promising features of this process point the way for new directions for more economically viable IL recycling processes in biomass treatment with ILs.

Aqueous solutions of a series of short carbon chain tetra(n-alkyl)ammonium hydroxides, [Nnnnn][OH] with n = 2: n-ethyl, 3: n-propyl, 4: n-butyl, have been serendipitously found to be potential candidates for direct air carbon capture (DAC) when being used as reagents in more complicated reactions. Aqueous solutions of [N3333][OH], [N2222][OH], or [N3333][OH] with UO2SO4·3H2O and 1,4-diamidoximylbenzene, and [N4444][OH] with cytosine (HCyt) directly absorb CO2 from the atmosphere upon mild heating in the open atmosphere crystallizing in complexes reaching up to 2 : 1 CO2/[Nnnnn]OH ratio. [N2222][HCO3]·3H2O (1), [N2222]2[H(HCO3)3]·5H2O (2), [N3333][HCO3]·0.5H2O (3), [N3333][H(HCO3)2] (4), [N3333]2[(tpa)(H2CO3)2] (5; tpa = terephthalate), [N4444][H(Cyt)(HCO3)]·H2O (6) and [N4444][H2(Cyt)2(HCO3)]·H2O (7) have been isolated in crystalline form and structurally characterized by single crystal X-ray diffraction. The compounds are characterized by complex polyanionic formations from bicarbonate dimers ([(HCO3)2·(H2O)]24−) or chains ([H(HCO3)2]nn− or [H2(tpa)(HCO3)2]n2n−) to water-bicarbonate associates ([(HCO3)2·6H2O]2− and [(H2CO3·(HCO3)2)2·6H2O·2H2O]2−) and three-component anionic layers ([H(Cyt)(HCO3)·H2O]nn− and [H2(Cyt)2(HCO3)·H2O]nn−) frequently showing proton sharing. While some hydroxides themselves can maintain a high CO2/[Nnnnn][OH] ratio, particularly 2 and 4, the presence of secondary hydrogen bond donors/acceptors may increase the sorption efficiency through decreased solubility and enhanced crystallization.

Continuing our investigations of ionic liquid (IL) based routes to a library of f-element/soft donor complexes which could be studied crystallographically, we have explored the dissolution of f-ele...

A fresh look back at the chemistry of Bi3+ spanning solid state structural studies, aqueous biphasic separations, and a chromatographic purification of 213 Bi in support of its clinical use in targ...

Four mono-substituted N-butylpyridinium salts, 1-butyl-4-dimethylaminopyridinium chloride [b4dmapy]Cl, 1-butyl-4-methylpyridinium bromide [b4mpy]Br, 1-butyl-4-methylpyridinium hexafluorophosphate [...

The metal–organic material UVO(UVIO2)2(OH)5(Triaz)2 (Triaz = 1,2,4-triazolate) has been isolated from the reaction of UO2(NO3)2·6H2O with 1,2,4-triazole in the ionic liquid 1-ethyl-3-methylimidazol...

Three chloroaluminate ionic liquids (ILs), triethylammonium tetrachloroaluminate ([HN222][AlCl4]), triethylammonium heptachlorodialuminate ([HN222][Al2Cl7]), and tetraethylammonium heptachlorodialu...

The two most common commercial catalysts for the acylation of isobutylbenzene to produce the major ibuprofen intermediate 4-isobutylacetophenone are HF and AlCl3; however, both of these catalysts s...

A robust general route to lanthanide dicyanamide (DCA–) complexes has been developed where f-element salts are dissolved in DCA–-based ionic liquids (ILs) directly or formed in situ, forcing coordination of these normally weakly coordinating soft N-donor anions, even in an ambient, non-moisture-excluding environment. A series of lanthanide complexes [C2mim][Ln(DCA)4(H2O)4] (C2mim = 1-ethyl-3-methylimidazolium; Ln = La, Nd, Eu, Tb, Dy, and Yb) and [C2mim]3n[La(OH2)4(μ2-DCA)4]n[La(OH2)2(μ3-DCA)3(μ2-DCA)4]2n(Cl)4n were crystallized under a variety of conditions using this methodology and structurally characterized using single crystal X-ray diffraction. Although not all examples were isostructural, the dominant feature across the series was the presence of [Ln(DCA)4(H2O)4]− anionic nodes with all terminal DCA– ligands accepting hydrogen bonds from the coordinated water molecules forming a 3D metal organic framework. To determine if any structural clues might aid in the further development of the synthetic methodology, the metal-free IL [C1mim][DCA] (C1mim = 1,3-dimethylimidazolium), a room-temperature solid, crystalline analogue of the reaction IL, which is liquid at room temperature, was also prepared and structurally characterized. The ready isolation of these compounds allowed us to begin an investigation of the physical properties such as the luminescence at room and low temperatures for the Eu, Tb, and Dy representatives., Direct dissolution of lanthanide chloride hydrates in the DCA− ionic liquids leads to coordination of DCA− anions to Ln3+ under full displacement of chloride and partial displacement of water ligands leading to the formation of metal organic frameworks under ambient conditions. X-ray analyses reveal a significant influence of the hydrogen bonding and lanthanides’ size on crystallographic disorder in their crystal structures.

A non-stoichiometric approach to control the solid-state behavior of protic ionic liquids (PILs) was demonstrated by direct mixing of 4,5-dicyanoimidazole (HDCNim) with either 1-ethylimidazole (C2i...

We investigated whether the relatively Lewis basic imidazole-2-thiones could be used to substitute water ligands bound to f-element cations and generate f-element soft donor complexes. Reactions of 1,3-diethylimidazole-2-thione (C2C2ImT) with Nd(NO3)3·6H2O and UO2Cl2·3H2O led to the isolation of the anhydrous thione complexes Nd(NO3)3(C2C2ImT)3 and UO2Cl2(C2C2ImT)2, characterized by single crystal X-ray diffraction. Differences in the strength of metal-thione interactions have been examined by means of the crystal structure analysis and density functional theory (DFT) calculations. The C2C2ImT ligands were found to be affected by both coordination and noncovalent interactions, making it impossible to deconvolute the effects of one from the other. Calculated partial atomic charges indicated greater ligand-to-metal charge transfer in the [UO2]2+ complex, indicative of a stronger interaction. The reactivity of C2C2ImT demonstrates its usefulness in the preparation of f-element soft donor complexes from readily available hydrates that could be useful intermediates for promoting the coordination and studying the effects of soft donor anions.

Characterization of the biodegradability of herbicidal ionic liquids (HILs) using the industry standard activated sludge methodology is thought to be insufficient to fully understand the biodegradation of HILs in the environment because cations and anions of the HILs may have different potential for biodegradation in aquatic and terrestrial systems. To test this hypothesis, we conducted laboratory microcosm experiments using C-13-labeled cations and anions forming benzyldodecyldimethylammonium 4-chloro-2-methylphenoxyacetate ([C-12-BA][MCPA]) and evaluated their biodegradation potential in soil with a known history of herbicide exposure, and in water (mineral medium) augmented with microorganisms present in activated sludge. The biodegradability of the cation and anion was found to depend on the test system (water or soil). The cation was mineralized in water, whereas the anion was fully utilized in soil. These results suggest that performing biodegradation tests using differently C-13-labeled species of the target HIL and mimicking various environmental compartments (e.g., soil, activated sludge) is needed to provide a better understanding of the fate of HILs in the environment. They also indicate that biodegradation kinetic parameters of HILs derived from experiments performed in aqueous systems should not be used to estimate biodegradation rates in terrestrial environments.

Because the very high molecular weight of biopolymers extracted from biomass using ionic liquids (ILs) cannot be accurately determined using conventional methodologies (e.g., gel permeation chromatography, intrinsic viscosity measurements, etc.) due to their insolubility in the solvents used for such measurements, we have developed a new method for Mw determination based on static light scattering (SLS) in IL solution. The method, based on using SLS measurements to calculate weight average molecular weight (Mw) via the Rayleigh equation, was validated by determining the Mw for both commercially available (practical grade, PG-) chitin and chitin extracted from raw shrimp shell using 1-ethyl-3-methylimidazolium acetate. We have shown that on average the IL-extracted chitin has a high average Mw value, almost two and a half times larger than that for PG-chitin, has a comparatively low polydispersity, and has a degree of acetylation nearly ideal (98(1)% vs. PG-chitin at 82(1)%), thus making the IL-extracted polymer preferable for utilization in materials preparation.

Lewis acid/base catalysts of AlCl3/N-methyl-2-pyrrolidone (O-NMP) and AlCl3/1-methylimidazole (N-Mim) were prepared and found to have higher catalytic activity in the Friedel-Crafts alkylation of benzene than the known super acidic ionic liquid chloroaluminate [HN222][Al2Cl7] ([HN222]+ = triethylammonium). Crystals structures were obtained for AlCl3(N-Mim), [AlCl2(O-NMP)2][AlCl4], and [Al(O-NMP)6][AlCl4]3·(C6H6)3 supporting the assignments of neutral and charged catalytic species.

By dehydrating actinide salts with an ionic liquid containing a common anion and subsequent reaction with N-heterocyclic ligands, we challenge the concept that actinides prefer O- over N-donors; rather the acidic hydrogen atoms of protic solvents hinder the formation of more elusive f-element N-donor coordination complexes.

In pursuit of bioplastics which require a controlled biopolymer molecular weight, consistency, and supply, we have examined the chitin in the molts of farm raised Hybrid (H1) Pacific whiteleg shrimp (Litopenaeus vannamei) by collecting the molts during the shrimp growth cycle, sorting by shrimp average body weight (ABW), and extracting the chitin from the molts using the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]). The amount of available chitin in the molts increases with the age/size of the molting shrimp, 19% in juveniles to 22% in adults. As expected from the biology of molting, the chitin in the final shell peeled from the adult shrimp contained the most chitin (29%). It is neither easier nor harder to extract the chitin from molts or peels, and the extracted chitin was equivalent in purity and degree of acetylation with comparable extraction efficiency (67% for molts, 63% for peels). In addition, the weight average molecular weight (MW) of the chitin has the potential to be controlled by shrimp age/size. The MWs of the chitin in the smaller animals (5–10 and 10–20 g ABW) were comparable at ∼4–5 MDa, while the chitin obtained from the large adult molts (30–40+ g ABW) exhibited a significantly higher MW of 23 MDa. Thus, by collecting and using the shrimp molts, the industrial viability of chitin can be improved by providing both a larger amount of chitin per shrimp (an ca. 8-fold increase) and by providing the opportunity to extract chitin of a specific MW.

Our attempts to use an ionic liquid strategy to force f-element coordination of soft donor adenine and 4,5-dicyanoimidazole using 1-pot reactions in water using hydrated lanthanide salts failed, instead resulting in the isolation of anhydrous lanthanide nitrate salts. Reactions of previously ground mixtures of 40 % aq. [P 4444][OH] and adenine with Nd(NO 3) 3·6H 2O or Sm(NO 3) 3·6H 2O followed by hand grinding and heating to 90 °C for 10 h led to hot crystallization of anhydrous [P 4444] 2[Nd(NO 3) 5] and [P 4444] 2[Sm(NO 3) 5]. The same reaction with 4,5-dicyanoimidazole and Nd(NO 3) 3·6H 2O but without heating (10 h, room temperature) to prevent ligand decomposition, led to crystallization of anhydrous [P 4444] 3[Nd(NO 3) 6]. [P 4444] 3[Nd(NO 3) 6] could also be isolated by conducting the first reaction without using adenine. The single crystal X-ray diffraction structures of the three new anhydrous salts were examined to provide clues to the observed behavior. The [P 4444] + cations allow charge balance while forming box-type encapsulations around the anionic counterpart which has been previously reported in similar structures. The fact that these anhydrous salts were prepared from water with hydrated starting materials and no precautions taken to keep the crystal growing process anhydrous, suggests synthetic strategies that can potentially be beneficial for more advanced separations procedures.

We demonstrate the unprecedented ability to induce hypergolic behavior, i.e. rapid and spontaneous ignition upon contact with an oxidizer, in non-hypergolic metal fuels by blending them with hypergolic metal-organic frameworks (HMOFs). Using magnesium, aluminum or zinc metal as the fuel, we demonstrate materials with ignition delays (IDs) below 50 ms, and calculated specific impulse (Isp) in the 220-250 s range. These parameters are comparable to those of toxic and carcinogenic hydrazine-based hypergols conventionally used in aerospace technologies, suggesting a route to develop cleaner, safer propulsion systems.