Studies Of Gas Hydrate Formation Characteristic Under The Coupling Action Of Porous Media And Thermodynamic Additives

Gas hydrate has been considered as a potential material for gas storage in recent years due to its large gas storage capacity and high flexibility.At the same time,due to the different phase equilibrium conditions for the formation of different gas hydrates,the purpose of gas separation can also be achieved by controlling the conditions for the formation of hydrates.However,current research shows that the development of these technologies generally has the problems of slow hydrate formation rate and low gas lift.In order to strengthen the formation of gas hydrates,scientists have proposed a variety of methods including mechanical strengthening methods and chemical physical methods.But the specific research on these two methods is still insufficient.In recent years,the construction of highly dispersed hydrate systems through porous media has also been shown to greatly enhance the formation of gas hydrates.However,most of these porous media have disadvantages such as complex manufacturing process,high cost,and environmentally unfriendly production process.As a kind of agricultural waste,corn cobs has a natural porous structure from the naked eye.It is worthwhile to build a highly dispersed hydrate system with the help of the porous structure of corn cobs,so as a question of inquiry to achieve a win-win result of waste utilization and hydrate strengthening.Therefore,this paper uses corn cobs as porous media,methane and IGCC synthesis gas to simulate natural gas and IGCC power plant gas,respectively.Under the synergistic effect of corn cob particles and tetrahydrofuran(THF),the synthesis of THF-methane mixed hydrate and THF-IGCC are studied.The kinetic characteristics of the gas mixture hydrate formation process are used to evaluate the strengthening effect of the system.Finally,powder X-ray diffraction(PXRD),Raman spectroscopy(Raman)and Fourier infrared transform spectroscopy(FTIR)were used to study the microstructure of the mixed hydrates generated in the above system.The following research results have been achieved:(1)Using scanning electron microscopy(SEM)and thermogravimetric analysis(TGA)was observed that the corn cob has many nano-scale pores and a large specific surface area.It is clear that its saturated water absorption rate is as high as 87.23%.The effect of the synergistic effect of corn cob particles and tetrahydrofuran(THF)on the formation of methane hydrate under static reaction conditions at a temperature of 274.15K and an initial pressure of 7.2MPa was explored.The experimental results show that when the pressure reaches 7.2MPa,hydrate is immediately formed.Moreover,multiple stages of hydrate formation have been observed during the entire hydrate formation process,indicating that the following three possible hydrate formation mechanism steps may occur during the hydrate formation process:(1)pure THF hydrate formation;(2)CH₄molecules enter the small cages(5¹²)of pure THF hydrate to form THF-CH₄mixed hydrate.In addition,from the CH₄ hydrate formed in the 3g corn cob particles+3.0 mol%THF solution system,a gas consumption of up to 98.40mmol/mol H₂O was obtained,and only 90%of the gas consumption was obtained in about 3.12 hours.(2)The effect of the synergistic effect of corn cob particles and tetrahydrofuran(THF)on the formation of IGCC synthesis gas gas hydrate under static reaction conditions at a temperature of 276.15 K and an initial pressure of6.0 MPa was explored.The experimental results show that for all experiment cases(with or without corn cobs),the induction time is within 180s.Besides,the induction time obtained from the system containing corn cobs is slightly longer than that in the system without corn cobs and this difference disappeared almost as the THF concentration increase to 4.0 mol%and 5.6 mol%.Further,relative to the system without corn cobs,the time required to complete hydrate formation is longer in the presence of corn cobs.It is noted that as the THF concentration increase,less time is required for achieving 90%of final gas consumption in the presence of corn cobs.In addition,at a certain THF concentration,the gas consumptions in the presence of corn cobs are larger than that in the system without corn cobs.These indicate that the addition of corn cobs has a positive effect on the kinetics of IGCC syngas hydrates formation and the CO₂ recovery.(3)Clarified the effects of corn cob particles and tetrahydrofuran(THF)on the structure and composition of methane hydrate and IGCC synthesis gas gas hydrate,the experimental results show that he hydrate types generated in the corn cob+THF+CH₄ system are all s II type,and CH₄ molecules occupy both the small cage(5¹²)and the large cage(5¹²6⁴)of the s II hydrate.The test results of IGCC synthesis gas hydrate show that whether it contains corn cob particles or not,the IGCC synthesis gas hydrate generated in the THF solution system contains carbon dioxide hydrate.And its structure is s II type.While in the pure water system,the generated IGCC synthesis gas hydrate structure contains both s I type and s II type.