Influence of Silica Gel and Silicone Oil on HFC-134a Hydrate Formation in Seawater

Abstract

Gas hydrates (or clathrate hydrates) are ice-like crystalline molecular complexes formed when water mix with suitably sized 'guest' gas molecules. The hydrogen bonding in water (host) molecules lead lattice structures with several interstitial cavities to be formed. The guest gas molecules can occupy the lattice cavities. When a minimum number of cavities are filled, the crystalline structure will be stable and it will form solid gas hydrates, even at temperatures well above the melting point of water ice. HFC (Hydro Fluoro Carbon)-134a has been used in this report as the guest gas since it is a refrigerant. Several kinds of commonly used refrigerants are CFC (Chloro Fluoro Carbon), HCFC (Hydro Chloro Fluoro Carbon), and HFC. However, CFC and HCFC consist of chlorine destroying the ozone layer and giving the bad effect of global warming. Porous medium such as silica gel have significant influence on hydrate formation rate. Silica gel can reduce the chemical barrier which hydrate formation must overcome and promote hydrate formation. Silicone oil can effectively prevent the hydrate dissociation. In this experiment, three sizes of silica gel and one silicone oil were used and for each type, five different weights were conducted. Operation condition for each variables are remained same. Adding every 0.4 g/L of silica gel make the hydrate formation time slower and it also happens with adding every 0.4 ml/L of silicone oil. This phenomena happens because the bond between silica gel and water is stronger than that between water and gas. The bond between silica gel and water is electrostatic attraction and the bond between water and gas is intermolecular force (Van der Waals). The bond between silicone oil and water which is hydrogen bonding also stronger than that between water and gas. Therefore silica gel and silicone oil inhibit the hydrate formation. Silica gel and silicone oil may not be used for desalination. Silica gel and silicone oil can be used for preventing the pipeline blockage in petroleum industry.