# Three-Dimensional-Printed Polymeric Cores for Methane Hydrate Enhanced Growth
## 1 Introduction  
Gas hydrates are ice-like solids composed of water and gas molecules. The water molecules form defined cage structures and networks via hydrogen bonding, which are stabilized by the enclathration of the gas molecules [1]. Gas hydrates have wide distribution in nature [2], with large gas storage capacity (about 160/140 volumes of methane/carbon dioxide per hydrate volume); this encourages researchers to employ them as gas storage containers and gas/water absorbers [3; 4]. In addition, the different hydrate-forming ability of a components mixture allows gases to be separated via hydrate phase enrichment with hydrate-forming components [5; 6]. Hydrate-based water desalination is also possible [7]. However, the efficiency of hydrate-based solutions turned out to be inferior to traditional methods, primarily due to the high energy consumption for gas compression and reactor cooling as well as the low hydrate formation rate. The latter can be increased, for example, by adding water-soluble surfactants and helping hydrate formers (dioxolane, tetrahydrofuran, cyclopentane, etc.) [8; 9] or by intensive mixing [10]. The stirring also helps resolve the slow nucleation issue. In turn, cold energy from liquefied natural gas reduces the cost of maintaining the required temperature for the hydrate formation process. These optionsundoubtedly increase the hydrate formation's energy efficiency and make it competitive with well-developed techniques [11; 12; 13; 14]. However, such solutions can decrease the hydrate gas capacity, need promoter regeneration/water remediation, and significantly complicate the apparatus for continuously producing hydrates, especially at high pressures. A possible alternative is the creation of efficient surfaces catalyzing the nucleation and growth of hydrates, which would ensure the formation of hydrate particles immediately after water-gas contact under suitable thermodynamic conditions with a satisfactory hydrate growth rate. Hydrate nucleation most often occurs near the liquid-gas interface due to the necessary supersaturation of the fluid with dissolved gas in this region [15]. The influence of artificially introduced surfaces in contact with water and gas, which serve as centers of heterogeneous nucleation, on the hydrate's formation is intensively studied [16]. So far, the characteristics of surfaces that favor the gas hydrates formation are not yet sufficiently understood. One can only indicate the importance of the particle surface's composition and morphology on the hydrate nucleation's kinetics. The development of such substrates requires preliminary scientific research. However, it is reliably known that an increase in the water-gas contact surface also makes it possible to accelerate hydrate nucleation even at low driving forces. Moreover, the water-to-hydrate conversion will be more significant in the case of an increased water-gas contact surface at the same aqueous phase volume [17]. Indeed, after water surface overgrowth, the further hydrate growth rate is controlled by the diffusion of gas and/or water molecules into the reaction zone. Thus, porous materials containing uniformly distributed water are promising systems for obtaining hydrates [18; 19]. Moreover, studying the gas hydrates formation and decomposition in natural porous media is relevant for understanding the formation process of these compounds in nature and the production of gas from hydrate-bearing sediments [20; 21; 22]. Utilizing various visualization methods allows the features of the processes under consideration to be identified [23; 24], making it possible to develop ways to control them in the future. At the same time, not only surfactants promote hydrate phase growth [25; 26] but also the chemical modification of surfaces [27; 28; 29]. Moreover, the growth efficiency of hydrates of various gases (or structures) in the porous medium in the presence of surfactants varies significantly [30]. An intensive upward hydrate growth was recently found for poplar wood shavings [31].