Experimental Study On Hydrate Fromation Characterstics In Systems Containing ZIF-8

The study of hydrate formation and decomposition is of great significance to the prevention of oil-water multiphase pipeline plugging and other hydrate-based technologies.In this paper,the porous medium ZIF-8 was added to water or oil-water systems to study the effect of ZIF-8 on the hydrate formation in gas storage and anti-aggregation process.The main research contents are as follows:1.The adsorption-hydration sequence method was developed to improve the gas storage density of clathrate hydrate for methane by using the hydrate slurry with porous material added as gas storage medium.In the study of improving hydrate formation,porous materials could increase the water conversion in the fixed bed whose gas storage density is small and accelerate the hydrate nucleation in the suspension with low water conversion.In this work,the porous material slurry was adopted as the gas storage media and an adsorption-hydration sequence method was developed to increase the gas storage density.The methane storage and release in the ZIF-8 slurry and fixed bed were investigated.In the ZIF-8 fixed bed,the methane storage density of 127.41 V/V_bed was obtained,while the gas loss accounted for 21.50%of the total gas uptake during the depressurization.With the adsorption-hydration sequence method,the gas storage density of the slurry was effectively increased and reached 107.51 V/V_bed,meanwhile,the gas loss was much smaller than that in the fixed bed during the depressurization.In the slurry,the gas uptake and loss decreased with the decrease of cooling temperature.The largest amounts of gas uptake and storage density were 78.84 mmol and 133.59V/V_bed,respectively,in the slurry with ZIF-8 content of 40%at 268.15 K,meanwhile,the gas loss just accounted for 14.04%of the total gas uptake.The self-preservation effect was observed in the slurry,and the temperature for the slowest gas release was found to be 263.15 K.Considering the high gas release ratio under atmospheric pressure,the release pressure was increased and it was found that the gas release rate could be effectively controlled by increasing the back pressure.The gas release ratio at 1.1 MPa was just 11.08%within 10 h,which was 43.42%at atmospheric pressure.The results showed that the application of adsorption-hydration sequence method in ZIF-8 slurry is a prospective approach for gas transportation.2.For the prevention and control of hydrate risk,the anti-aggregation effect of thermodynamic inhibitor ethylene combined with porous media in oil-water system was evaluated,and the effect of combination of low-dose ZIF-8 and ethylene glycol(EG)on the hydrate slurry in oil-water system at different water cuts and different degree of undercooling was investigated.The slurry system containing 0.5 wt%of Span20 and 5.0wt%of ZIF-8/EG had a good anti-aggregation effect at the water cut ranging from 5 to25 vol%,and the agglomeration began to occur when the water content reached 30vol%.Meanwhile,when the water content was 20 vol%,the system could bear a higher degree of supercooling to 7.01 K.It was also found that pour point depressant and diesel oil can play a certain role in inhibiting hydrate formation,and the combination of two of that with ZIF-8/EG slurry can prevent hydrate deposition and agglomeration to a certain extent.This indicates that ZIF-8/EG slurry has a good effect in hydrate anti-aggregation and has a broad application prospect in oil and gas pipeline blockage prevention.