Experimental Study On Strengthening CO 2 Hydrate Formation In A Self-priming Stirred Reactor

CO₂ is the primary greenhouse gases.As we all know,the increase of this content will lead to global warming,and even seriously affect the ecological environment and human's survival environment,so it is of great significance to CO₂ gas storage.The rapid formation of CO₂ hydrate becomes a hot spot in the researches of CO₂ storage,separation and transportation,because of the simple process without pollution or corrosion and the convenience of CO₂ transport or storage.However,there are many problems such as small hydrate gas storage capacity,low formation rate and poor stability which restrict its industrial application.In order to solve these problems,the effects of mechanical and chemical means on the process of C02 hydrate formation were studied in depth in this work.A gas-inducing agitated reactor and chemical additives were used to promote CO₂ hydrate formation.The effects of the gas-inducing agitated reactor,surfactant?Sodium dodecyl sulfate and sodium dodecyl benzene sulfonate?and nanofluids?SiO2,TiO2,multi walled carbon nanotubes?on the induction time,the amount of gas consumption and gas storage capacity of the hydrate formation were detailly studied in this work.The main conclusions are as follows:CO₂ hydrate formation can be effectively promoted by increasing the rotational speed of the gas-inducing agitater,reducing the initial temperature and increasing the initial pressure.With the gas-inducing agitated speed increased from 0 rpm to 800 rpm,the induction time of C02 hydrate formation was shortened from 261 minutes to 24 minutes;with the temperature reduced from 278.35 K to 274.15 K,the molar mass of dissolved C02 was increased from 0.18 mol to 0.25 mol.The initial pressure was conducive to the improvement of hydrate nucleation.With the initial pressure increased from 2.09 MPa to 6.02 MPa,the induction time of C02 hydrate formation was shortened from 185 minutes to 51 minutes,and the gas storage capacity increased from 41.38 V/VH to 140.94 V/VH.The analysis showed that the gas-inducing agitated reactor combined the stir and bubble that can greatly improve the efficiency of gas-liquid contact and opportunely take the heat of CO₂ hydrate formation away.It can greatly shorten the induction time of hydrate formation and increase the hydrate formation rate.The surfactants can shorten the induction time of CO₂ hydrate formation and enhance the stability of CO₂ hydrate,but have no obvious effects on the amount of gas consumption and the gas storage capacity of CO₂ hydrate.At the initial pressure of 5 MPa and the temperature of 274.15 K,the induction time of CO₂ hydrate formation measured in pure water,the 0.5 g/L twelve sodium dodecyl sulfate solution?SDS?and 0.3 g/L twelve benzene sulfonic acid solution?SDBS?were 50 minutes,35 minutes and 35 minutes,respectively.At the same time,the gas storage capacity of CO₂ hydrate calculated in pure water,the 0.5 g/L SDS and 0.3 g/L SDBS were 89.62 V/VH,92.67 V/VH and 92.62 V/VH,respectively,which indicated that surfactants can not increase the gas storage capacity of CO₂ hydrate.But the decomposition time of CO₂ hydrate formation in pure water,0.5 g/L SDS and 0.3 g/L SDBS were 148 minutes,276 minutes and 230 minutes,respectively,which indicated that surfactants can enhance the stability of CO₂ hydrate,and SDS behaved more pronounced.SDS and SDBS can reduce the surface tension of the solution and promote gas dissolution and hydrate nucleation,while reducing the adhesion of hydrate intermolecular.Nanofluids can reduce the induction time of CO₂ hydrate formation,but have no obvious effects on the amount of gas consumption and the gas storage capacity of CO₂ hydrate.The average induction time of CO₂ hydrate formation measured in SiO2,TiO2 and multi-walled carbon nanotubes?MWNTs?nanofluids under the same experimental conditions were 15 minutes,20 minutes and 11 minutes,less than the 35 minutes in SDS and SDBS solution under the same conditions,which indicated that the nanofluids could efficiently reduce the induction time of CO₂ hydrate formation,and WNTs promoted more significantly.But the amount of gas consumption and gas storage capacity of CO₂ hydrate caculated in nanofluids were close to that in pure water,which indicated that single nanofluids had effects on neither of the amount of gas consumption and gas storage capacity of CO₂ hydrate.Nanofluids can not only increase the thermal conductivity of the solution and improve heat conduction rate of the system,but also can enhance the gas-liquid mass transfer and strengthen the process of CO₂ hydrate nucleation.