Studies Of Hydrate Adhesion Mechanism On Wall Surfaces And Coating Preventions

In oil and gas transportation,the formation of hydrates will cause pipeline plugged,resulting in economic losses and safety hazards.The adhesion between particles and wall deposition are the two main reasons of hydrate plugging.For flow safety,hydrate inhibitors are usually injected to prevent the formation of hydrate blockage.In recent years,researchers have proposed a new hydrate mitigation method-wall coating method,which modifies the pipe wall to make the hydrate on its surface“easy to remove”.Therefore,in order to solve the problem of hydrate plugging in the pipeline,the influence of traditional hydrate inhibitors on the interparticle adhesion forces was studied using microscopic manipulation and imaging system,and the corresponding adhesion mechanism was discussed.Then,the regularities of contact angle,sliding angle,and functional groups of hydrophobic surfaces on the adhesion forces of hydrates were investigated.Finally,two functional wall coatings were successfully prepared,and their anti-hydrate performance and applicability to various hydrate systems were systematically studied,and the anti-hydrate mechanism was explored.First,the effects of thermodynamic inhibitors and anti-agglomerant inhibitors on the adhesion force of hydrate interparticle were studied.The results suggested that the thermodynamic inhibitors increased adhesion force,while the anti-agglomerant inhibitors reduced adhesion force.The hydrophilic thermodynamic inhibitors lead to the existence of a large amount of unconverted free water on the outer surface of hydrate,which forms macroscopic capillary bridges.However,the anti-agglomerant inhibitors with hydrophobic groups（-RCH₃）can weaken the capillary bridge between particles in a relatively short time（60s）,and reduce the adhesion force to 0.3 m N/m.Therefore,the hydrophobic surfaces are expected to achieve“easy to remove”of hydrates.Second,the hydrophobic surface is adopted to reduce the hydrate-wall adhesion.The hydrophobic surfaces with contact angle of 143°-150°and sliding angle of 12°-45°were prepared by filling the porous copper with carbon nanomaterials.The adhesion forces of hydrate on the hydrophobic surfaces are only 0.003-0.015m N/m,which was reduced at least 99.6%compared with bare metal substrate.The sliding angle has a great influence on the cyclic anti-hydrate performance,and the smaller the sliding angle,the better the cyclic performance.The hydrophobic surface with-CH₃as the terminal group has high chemical affinity to cyclopentane（CP,-CH₂ groups）,which causes the mechanical interlocking of hydrate during the cyclic test,and increases the adhesion force to 2.5 m N/m.However,the maximum adhesion force on hydrophobic surface with-F as the terminal group was 0.13 m N/m.Therefore,the preparation of excellent anti-hydrate coatings can be considered as follows:high hydrophobicity,low sliding angle,and surface fluorine content.A superhydrophobic anti-hydrate coating with high hydrophobicity and low sliding angle was designed and prepared,and the coating was modified by fluorine containing low surface energy materials.A biomimetic flower like Ce O₂/p DA coating was first fabricated on X80surface using static self-assembly method.The coating reduced the adhesion forces of CP hydrate by 98.9%and tetrahydrofuran（THF）hydrate by 99.8%compared with pipeline steel X80.When the coating thickness was worn from 20μm to 420 nm,the adhesion force of CP hydrate can still be reduced by 93.2%.Due to the hydrophobic functional groups and oil barrier film,the coating can drastically avoid the strong adhesion of hydrate on the pipe wall in the presence of deposited water.The unique properties of polydopamine（p DA）give the coating mechanical stability and oil resistance.The adhesive ability of the coating was satisfied with the requirements of Grade 2,and it can maintain superhydrophobicity after soaking in various oil phases for 30 days,which has potential application value in light crude oil environments.Then,based on the superhydrophobic coating,an amphiphobic anti-hydrate coating was prepared by designing the multilayer structure and increasing the fluorine content.And a biomimetic mulberry like PF/ZSM-5 coating was first fabricated on X80 surface using self-assembled ZSM-5.Subsequently,a hydrate nucleation model was established,and the results showed that the critical nucleation barrier of hydrate increases with the contact angle of substrate increases.The experimental results suggested that the amphiphobic coating can effectively slow down the nucleation of hydrate on the wall due to the high contact angle and persistent droplet bouncing phenomenon on surface.And the adhesion force of the hydrate decreases with the increase of the contact angle.The coating can reduce the adhesion force between CP hydrate and the wall to 0 m N/m.The amphiphobic coating can repel crude oil,and the anti-hydrate durability in crude oil is significantly better than that of the superhydrophobic coating,which has potential application value in high viscosity crude oil environments.Final,the amphiphobic coating was applied to semi-clathrate hydrate system.The tetrabutylammonium bromide（TBAB）hydrate readily nucleated on the metal surface.In contrast,the coating effectively inhibited the hydrate nucleation on the surface.The coating is stable in TBAB solution,and the anticorrosion efficiency can reach 98.5%.The chemical stability and surface nucleation inhibition can effectively avoid the residue of crystal nucleus of hydrate on the surface of the coating,making the anti-hydrate performance superior to commercial coatings.