Stable water-in-oil emulsions with water volume fraction ranging from 10 to 70 vol % have been developed with mineral oil 70T, Span 80, sodium di-2-ethylhexylsulfosuccinate (AOT), and water. The mean size of the water droplets ranges from 2 to 3 μm. Tests conducted show that all emulsions are stable against coalescence for at least 1 week at 2 °C and room temperature. Furthermore, it was observed that the viscosity of the emulsion increases with increasing water volume fraction, with shear thinning behavior observed above certain water volume fraction emulsions (30 vol % at room temperature and 20 vol % at 1 °C). Viscosity tests performed at different times after emulsion preparation confirm that the emulsions are stable for 1 week. Differential scanning calorimetry performed on the emulsions shows that, for low water volume fraction emulsions (<50 vol %), the emulsions are stable upon ice and hydrate formation. Micromechanical force (MMF) measurements show that the presence of the surfactant mixture has little to no effect on the cohesion force between cyclopentane hydrate particles, although a change in the morphology of the particle was observed when the surfactant mixture was added into the system. High-pressure autoclave experiments conducted on the model emulsion resulted in a loose hydrate slurry when the surfactant mixture was present in the system. Tests performed in this study show that the proposed model emulsion is stable, having similar characteristics to those observed in crude oil emulsions, and may be suitable for other hydrate studies.

The large demand of natural gas consumption requires an effective technology to purify and store methane, the main component of natural gas. Metal–organic frameworks and gas hydrates are highly appealing materials for the efficient storage of industrially relevant gases, including methane. In this study, the methane storage capacity of the combination of methane hydrates and HKUST-1, a copper-based metal–organic framework, was studied using high pressure differential scanning calorimetry. The results show a synergistic effect, as the addition of HKUST-1 promoted hydrate growth, thus increasing the amount of water converted to hydrate from 5.9 to 87.2% and the amount of methane stored, relative to the amount of water present, from 0.55 to 8.1 mmol/g. The success of HKUST-1 as a promoter stems mainly from its large surface area, high thermal conductivity, and hydrophilicity. These distinctive properties led to a kinetically favorable decrease in hydrate growth induction period by 4.4 h upon the addition of HKUST-1. Powder X-ray diffraction and nitrogen isotherm suggests that the hydrate formation occurs primarily on the surface of HKUST-1 rather than within the pores. Remarkably, the HKUST-1 crystals show no significant changes in terms of structural integrity after many cycles of hydrate formation and dissociation, which results in the material having a long life cycle. These results confirm the beneficial role of HKUST-1 as a promoter for gas hydrate formation to increase methane gas storage capacity.

In this work Tb 3+ is revisited as a laser ion for efficient visible laser operation. In detailed spectroscopic investigations of absorption and fluorescence properties we reveal, that neither the spin-forbidden transitions nor the widespread belief of excited state absorption or upconversion into 4f 7 5d 1 -states ultimately prevent efficient visible laser operation in Tb 3+ -doped fluorides. In contrast, the rise of blue semiconductor-based pump sources enabled us to achieve slope efficiencies up to 58% around 545 nm in the green spectral region in highly Tb 3+ -doped LiLuF 4 , LiYF 4 , KY 3 F 10 , β-BaLu 2 F 8 and LaF 3 crystals. In addition, we obtained laser emission from Tb 3+ in the yellow spectral region around 585 nm with slope efficiencies approaching 20%. To the best of our knowledge, these results represent the first continuous wave laser operation of Tb 3+doped crystals and demonstration of laser oscillation on the 5 D 4 → 7 F 4 -transition in this ion.

The demand for natural gas globally is rising due to the need for energy caused by population and economic growth. This demand calls for more effective approaches to store and transport natural gas, which consists primarily of methane. Gas hydrates, icelike materials that encapsulate gas molecules, possess the potential for high energy density. The feasibility of this methane storage method relies upon the efficiency of hydrate formation, which must be improved before it can be developed commercially. In this study, two microporous zeolitic imidazolate frameworks, ZIF-8 (zinc based) and ZIF-67 (cobalt based), were evaluated as methane hydrate formation promoters. ZIF-8 and ZIF-67 increased the water-to-hydrate conversion in a water-and-methane system from 4.5% to 85.6% and 87.7%, respectively, thus remarkably improving the gas storage by a factor of 14.4 and 14.7, respectively. Isothermal tests revealed that ZIF-8 and ZIF-67 reduced the methane hydrate nucleation induction time by 51.6% and 92.2%, respectively. Both ZIFs maintained their structural integrity and exhibited consistent recyclability, which indicates that the materials would have a long lifecycle as promoters. These results show that ZIF-8 and ZIF-67 are effective gas hydrate growth promoters, and application of these ZIFs makes methane storage in gas hydrates industrially appealing.

In recent years, there has been growing interest in gas hydrates as technological applications, such as for energy (methane and hydrogen) storage and transportation, separation (gas and desalination), and carbon capture. However, there are several challenges that deter large-scale applications and commercialization of these hydrate-based technologies. One of the main challenges is the long induction time and slow growth of hydrate particles, which can increase the overall operating costs of these technologies. It has been reported that the addition of additives (known as hydrate promoters) can help improve the nucleation and growth rate of hydrates. In general, there are two types of hydrate promoters: thermodynamic hydrate promoters and kinetic hydrate promoters. Thermodynamic hydrate promoters shift the hydrate equilibrium curve to milder conditions (i.e., lower pressures and higher temperatures), while kinetic hydrate promoters reduce the induction time for hydrate formation and increase the growth rate. In this review, we provide a comprehensive review of the two types of hydrate promoters (thermodynamic and kinetic) and their effects on hydrate phase equilibria, induction time, and growth rate.