# A Review of Reactor Designs for Hydrogen Storage in Clathrate Hydrates
## 2 Hydrate-Formation Technologies
### Water-In-Oil Emulsion  
Compared with aqueous solutions, [PERSON] et al. proposed a new method as the absorption-hydration hybrid separation method [35; 36; 37; 38] in which water and oil emulsion was used for hydrate formation. In a water/oil emulsion, gas-water contact area is significantly increased due to the presence of nano-droplets of water in the oil phase, which will be followed by a high yield in gas-hydrate production. Furthermore, a good 'flowability' of formed hydrate/oil slurry can be achieved with the addition of a suitable anti-agglomerant agent. This can be a great breakthrough in which most of the difficulties in hydrate production, such as a low formation yield, slow kinetics, and difficulty in realizing a continuous production operation can be solved by using water/oil emulsion in hydrate production [35].  
In the research presented by [PERSON] and co-workers, a reverse-micelle process was used to enhance hydrogen-hydrate formation in minutes, using water-insoluble co-guests [39]. The marked enhancement in hydrate-formation rate was due to a very substantial increase of surface-to-volume ratio of the water 'pseudo-phase'. Indeed, this general concept of an 'inverted phase' using oil emulsions as the continuous phase to manipulate surface-to-volume ratios [40] represents an intriguing advance in the formation of hydrogen hydrates, and the economics and operability of this process has been gauged, as well as hydrogen hydrate as a storage medium in general, relative to competing hydrogen-storage technologies, with largely favourable results [41].  
In another design proposed by [PERSON] et al. [42], the operation was characterised by use of two liquid jets impinging on each other in a loaded reactor with high-pressure hydrate-forming gas (HFG) (Figure 6). Liquid water is ejected from one jet and, a hydrophobic liquid with a considerably low freezing point is coming from the second jet. In case of using a large-molecule guest substances (LMGSs) as the hydrophobic component, in addition to the main HFG, the liquid will serve as a companion hydrate guest, which will fit into the \(5^{12}6^{8}\) cages of the structure-H hydrates [43]. The schematic design of a twin-jet system is illustrated in Figure 6. To control the reaction temperature, each liquid component is being circulated after passing through heat exchangers and introduced into the high pressure chamber in a way that a rapidly expanding sheet will form at the point of liquids' collision in the gas area which will result in the formation of water/LMGS droplets in the gas phase [44]. Hydrate will crystalize in the surface of the droplets and will coalesce into a liquid pool, allowing for water and LMGS to be separated due to a different density profile at the top and bottom of the hydrate layer.  
Figure 6: Conceptual illustration of a twin-jet hydrate-forming system.  
Major disadvantages of conventional water-spray systems, such as (a) a relatively large power consumption for pressurizing water to be sprayed, and (b) an insufficient function of discharging heat released by the hydrate formation will be eliminated by using a twin-jet scheme, liquid circulation and external heat exchangers (Figure 6) [42].