•CP decreases CO2 hydrate phase equilibrium pressure by forming CO2-CP hydrates.•The increase of CP can’t decrease hydrates phase equilibrium pressure unlimitedly.•Higher CP concentration lowers CO2 hydrate gas uptake.•The optimal CP molar ratio is 0.01 based on hydrate phase equilibrium and gas uptake.Cyclopentane (CP) is considered to be a potential co-guest molecule in carbon dioxide (CO2) hydrate-based desalination. The experimental thermodynamic data of CO2-CP hydrates were measured for a salt solution, where CP was chosen as a hydrate promoter. Seven experimental cases (62 cycles) were studied with different molar ratios of CP/water (0, 0.0025, 0.005, 0.0075, 0.01, 0.02, and 0.03). Hydrate phase equilibrium data were generated using an isochoric method, and the hydrate saturations were calculated based on gas uptake. The results indicated that the increase in CP concentration significantly decreased the CO2 hydrate equilibrium pressure to a certain limit; the hydrate saturation also decreased during this process. Also, it was determined that CP encouraged the formation of s-II double CO2-CP hydrates, which are different from s-I simple CO2 hydrate. The CO2-CP guest provides a strengthened stability and moderate hydrate phase equilibrium conditions for hydrate-based desalination. The recommended optimal molar ratio of CP is 0.01 when the increase in equilibrium was more than 10 K, and the decrease in hydrate saturation was less than 2%.

•Reformation Sh increment and MH dissociation percentage are positively correlated.•Percentage of reformation Sh increment increases with methane injection rate.•Sw2 is the main factor influencing the hydrate reformation amount and Rmax.•Constant methane flow in MH reformation process influence water distribution.The hydrate reformation that occurs in natural gas hydrate (NGH) exploration reduces mining efficiency and safety. To elucidate the hydrate formation/reformation characteristics during NGH exploration, methane hydrate (MH) was formed/reformed in two different modes to simulate mining of NGH sediment. The effects of residual water, residual MH and methane flow rate on MH reformation in a porous medium were investigated experimentally. Magnetic resonance imaging (MRI) was used to analyze MH saturation and distribution in the porous medium. In reformation, a positive correlation exists between the hydrate saturation (Sh) increment and MH dissociation. Moreover, the percentage of reformation Sh increment increases with the methane injection rate. That demonstrates MH dissociation by depressurization improves the contact area of gas-liquid and enhance the nucleation rate, which contributes to hydrate reformation. In addition, the residual Sw and MH reformation rate maximum (Rmax) are positively correlated in the rapid-reformation period. According to MRI images, crack-like pathways exist in the porous medium after MH dissociates completely in the first experimental mode. However, constantly flowing methane in the MH reformation process can render the water distribution uniform after MH dissociation in the second experimental mode. That means the methane flow affects the capillary force distribution then further influences the pore water distribution in porous medium.Download high-res image (123KB)Download full-size image

Many tetrahydrofuran (THF) hydrate properties are similar to those of gas hydrates. In the present work THF hydrate dissociation in four types of porous media is studied. THF solution was cooled to 275.15 K with formation of the hydrate under ambient pressure, and then it dissociated under ambient conditions. THF hydrate dissociation experiments in each porous medium were conducted three times. Magnetic resonance imaging (MRI) was used to obtain images. Decomposition time, THF hydrate saturation and MRI mean intensity (MI) were measured and analyzed. The experimental results showed that the hydrate decomposition time in BZ-4 and BZ-3 was similar and longer than that in BZ-02. In each dissociation process, the hydrate decomposition time of the second and third cycles was shorter than that of the first cycle in BZ-4, BZ-3, and BZ-02. The relationship between THF hydrate saturation and time is almost linear.

Hydrate-based gas separation is one of the potential methods of carbon dioxide capture from fuel gases (CO2/H2) for an integrated coal gasification combined cycle (IGCC) power plant. In this study, the influences of selected factors, including porous properties, tetrahydrofuran (THF) concentration, sodium dodecyl sulfate (SDS) concentration, and initial pressure, of the operation system on hydrate phase equilibria, gas consumption, and gas separation are experimentally investigated by a designed orthogonal test method. It is found that the porous property is the most important factor on hydrate phase equilibria and CO2 gas separation, where the gas separation becomes better in silica gel. The presence of THF moderates the hydrate phase equilibrium and improves the gas consumption and CO2 gas recovery, and 3 mol % THF should be a suitable value for gas separation. The initial pressure has an important effect on the hydrate equilibrium pressure. With the increase of the driving force, the gas consumption increases, while the gas separation effect becomes worse.