Inhibition of Natural Gas Hydrates in the Presence of Liquid Hydrocarbons Forming Structure H

Abstract

The effects of LMGS (large molecule guest substance) amount on the thermodynamics of natural gas hydrates, as well as structural characteristics of mixed hydrates of LMGS and natural gas, have been studied. The addition of 1.7 wt % neohexane (NH) to water induced inhibition of natural gas hydrates, and this inhibition effect increased with increased addition of NH up to 7.8 wt %. However, the hydrate equilibrium condition changed slightly when the concentration of NH further increased from 7.8 to 14.5 wt %. Investigations on structural characteristics were carried out by analyzing (13)C NMR spectra of mixed hydrates formed from the mixture of natural gas and NH. They indicate that two hydrate structures of II and H coexist simultaneously, and the ratio of structure H to II decreased from 0.97 to 0.43 when the NH concentration decreased from 14.5 to 7.8 wt %. In addition, it was confirmed that ethane, propane, and iso-butane gas molecules do not participate in the formation of structure H and only enclathrated in large cages of structure II. These results indicate the existence of multiple hydrate structures, which must be considered in many industrial applications when mixed hydrates are formed from multicomponent gas mixtures and liquid hydrocarbons.

Instrumental Methods for Cage Occupancy Estimation of Gas Hydrate

“…At conventional high pressure (<200 bar), hydrates have three main crystallographic structures (Figure 1), which are known as structure I (sI), structure II (sII), and structure H (sH) [1][2][3]. sI comprises two different type cages, a small pentagonal dodecahedral cage with 12 pentagonal faces (5 12 ) and a large tetrakaidecahedral cage with 12 pentagonal and 2 hexagonal faces (5 12 6 2 ). sII also contains the small 5 12 cage in addition to large hexacaidecahedral cage with 12 pentagonal and 4 hexagonal faces (5 12 6 4 ).…”

“…sI comprises two different type cages, a small pentagonal dodecahedral cage with 12 pentagonal faces (5 12 ) and a large tetrakaidecahedral cage with 12 pentagonal and 2 hexagonal faces (5 12 6 2 ). sII also contains the small 5 12 cage in addition to large hexacaidecahedral cage with 12 pentagonal and 4 hexagonal faces (5 12 6 4 ). sH is composed of the small 5 12 cages, middle 4 3 5 6 6 3 cages (with 3 square, 6 pentagonal, and 3 hexagonal faces), and large icosahedral cages, 5 12 6 8 (containing 12 pentagonal and 8 hexagonal faces) [4][5][6][7].…”

“…sII also contains the small 5 12 cage in addition to large hexacaidecahedral cage with 12 pentagonal and 4 hexagonal faces (5 12 6 4 ). sH is composed of the small 5 12 cages, middle 4 3 5 6 6 3 cages (with 3 square, 6 pentagonal, and 3 hexagonal faces), and large icosahedral cages, 5 12 6 8 (containing 12 pentagonal and 8 hexagonal faces) [4][5][6][7]. The type of hydrate structure is primarily determined by the size of the guest molecule, i.e., most small molecule gases (methane, ethane, carbon dioxide, hydrogen sulfide, etc.)…”

P‐67: Wet Etching of Gallium Indium Zinc Oxide (GIZO) Semiconductor for Thin Film Transistor Application

“…It is a noticeable result that the GIZO film exhibits the increase of the etch rate in acid solutions as increasing oxygen partial pressure. Such unique etch behavior has been reported as regards with the Zinc oxide(ZnO) film with varying oxygen partial pressure in a highly concentrated hydrochloric acid solution [4]. They showed that the etch rate of the ZnO film increased as the crystallinity of the film increased.…”

Thermodynamic inhibition of 4-methylmorpholine while forming sH hydrate with methane

“…Many LMGSs that form sH hydrates, such as tert-butyl methyl ether (TBME), methylcyclohexane (MCH), methylcyclopentane (MCP), and neohexane (NH) have been suggested (Ripmeester and Ratcliffe, 1990). A large number of studies have been carried out to identify phase equilibrium conditions, formation kinetics, and structural characteristics (Lee et al, 2010;Seo et al, 2010). Moreover, new LMGSs enclosed in sH hydrates with CH 4 gas are being explored for gas storage application and separation media, since sH hydrates commonly have superior storage capacity and thermodynamic stability compared to sI and sII hydrates (Shin et al, 2011;Jin et al, 2013;Strobel et al, 2008).…”