# Three-Dimensional-Printed Polymeric Cores for Methane Hydrate Enhanced Growth
## 4 Discussion
Indeed, the surface reduction due to water volume increase for ABS and ePC equals 56 and 59% (Table 3), with the water-to-hydrate conversion decreasing by 49-50%. On the other hand, three-phase water-gas-polymer contact (partial filling of porous space) was provided in experiments with PLA, regardless of the water volume (due to the different core positions; Figures 5b and 11, Videos S2 and S7). For 5 mL of water, the surface of the polymer insert in the gas phase even increased by 21%. At the same time, the conversion for 2 and 5 mL of water differed by more than 2 times (100% and 43%, respectively). This may indicate the anisotropy of the direction of the connected channels in the printed PLA core. Conducting studies with polymer bodies with straight channels at different angles to the water surface might reveal the optimal configuration. Another reason for this behavior may be the driving force of hydrate growth. Table 3 shows that the final pressure in the system varies slightly for different volumes of water. From the point of view of the growth regimen and hydrate morphology, the presence of a polymeric core contributes to the manifestation of three main features. (1) The type of polymer allows hydrate growth to be directed either under the insert (transfer of gas into the water volume) or on its top (migration of water into the gas volume; compare Figure 10c,d); compare Figures 5b, 7, 8, 11, S4 and S5 with Figure Figure 9 (also Videos S2 and S5-S7 with S3). The ABS core (in the case of 2 mL of water; partial filling of the pore volume) ensures the growth of the hydrate due to the transfer of water to gas. This exciting feature can be used to separate water from non-hydrate-forming water-soluble impurities. At the same time, this feature was not observed in experiments with 5 mL  
Figure 11: Methane hydrate formation from 5 mL of deionized water with PLA insertion; the blue arrow indicates the front of initial hydrate growth, the red one shows the start of hydrate growth at the sapphire; the lower right photo shows the system’s appearance after 12 h since the hydrate onset. of water (complete filling of the pore space). This again indicates the importance of the experiment's configuration and the possible anisotropy in the coupled channel network. In addition, repeated hydrate formation just after hydrate dissociation revealed growth predominantly proceeded in the bulk of water (Video S4). This indicates that some channels responsible for the upward water migration remained inactive after the hydrate decomposition (probably due to the formation of water-gas layers). (2) A blowing of hydrate crystals into the volume of water (Figure 10g; for PLA--Video S2 and S7, Figure 11 (7.5 min); for ePC--Videos S6 and S9; for UltraX--Video S5; for ABS--Videos S6 and Figure S4 (picture 5)). After such blowing, the hydrate often grew in bubbles from the ends of the insert into the water volume (apparently, after the hydrate film overgrew the outlets of the channels). (3) Sometime after blowing out the hydrate crystals, hydrate arrays start to grow from the steel cell's walls in the direction of the polymer core (Figure 10g). Notably, this growth mode does not manifest itself without a polymer core. Obviously, the polymer cannot \"attract\" the hydrate growing from the wall. It seems to be likely that the morphology of the hydrate crust formed on the water surface is responsible for this. It can be assumed that defects are created in it, providing additional contact between water and gas. The observed features of hydrate growth are probably controlled by the hydrophobicity of the pore surface. It is evident that the hydrate film growth rate along the gas\(-\)water interface inside the pores depends on the thermobaric conditions, the efficiency of heat dissipation, the type of gas, but weakly on the pore size (for sizes greater than 100 nm), and the gas flow rate (for example, [58]). However, the latter parameters can significantly impact the hydrate's ability to linger in these pores or grow continuously through them.