| Methane hydrate,also known as"combustible ice",is a kind of non-stoichiometric crystal compound with ice-like appearance.It is composed of subject-water molecules and guest molecules-gas small molecules.The main water molecules are connected by hydrogen bonds to form a cage structure and the guest small molecules are covered in the cavity of the cage structure.Methane hydrate has high application potential in natural gas storage and transportation due to its advantages of high gas storage density,mild storage and transportation conditions,good safety and economic performance.But the realization of large-scale industrialization needs to solve the problems of long induction period,slow reaction rate and low water conversion rate.In order to accelerate the process of industrial application of hydrate technology,a lot of researches have been carried out on the accelerators of hydrate formation.The experimental results show that the surfactant,especially the anionic surfactant sodium dodecyl sulfate（SDS）,has the best effect on the formation of hydrate.However,the hydrate generated by such accelerators grows upward along the inner wall of the reaction kettle,the utilization rate of the reaction kettle is low,and a lot of foam is generated during the dissociation process of hydrate,which is not conducive to the recovery and reuse of the accelerator.Produce a certain degree of pollution to the environment.Nanofluids formed by nanoparticles are regarded as a new accelerator due to their excellent mass and heat transfer properties.For example,metal-based nanofluids formed by Ag nanoparticles and Cu nanoparticles and carbon-based nanofluids such as carbon nanotubes and graphene have significant promoting effects when applied to hydrate formation experiments.In this paper,graphite phase carbon nitride（g-C3N4）was used as the base material,which was modified and used in the methane hydrate generation experiment.The specific contents and research results are as follows:（1）Study on the promotion of g-C3N4to methane hydrate formation based on SDS ultrasonic dispersion.When only g-C3N4was used as accelerator,the gas storage ratio of methane hydrate reached 138±7.35V/V,but the whole reaction time was 700min.The complex system g-C3N4and SDS were doped under the action of ultrasound to obtain the complex system g-C3N4-SDS.The complex system was used in the experiment of methane hydrate formation.The experimental results showed that the shortest induction time of hydrate formation was 24.33±6.66min,and the highest gas storage ratio was 151.93±5.63V/V.Compared with SDS of the control group,the induction time of the compound system was shortened by 28.23%,and the gas storage capacity was increased by 16.98%.In addition,in seven experiments of methane hydrate formation and dissociation cycle,the gas storage multiple of the hydrate is basically the same,indicating that the complex system has a good cycle performance.（2）Study on the promotion of methane hydrate formation based on the modification of g-C3N4nanotubes with sulfonate type macromolecules.g-C3N4nanotubes were prepared by self-assembly method using melamine,and then the large molecule long chain polymer of styene-styrene sulfonate（c PSSS）synthesized in laboratory was coated on g-C3N4nanotubes by means of soap-free emulsion polymerization to obtain the composite material g-C3N4NT@c PSSS,which was used in the experiment of methane hydrate generation.The experimental results showed that the induction time of hydrate formation was reduced to 10.71±3.45min,the growth rate was increased to 1.00±0.21mmol/min,and the gas storage ratio was up to 153.47±3.86V/V.Compared with g-C3N4NT as accelerator,the induction time of hydrate formation was reduced by 82.91%.Growth rate increased by 42.85%,gas storage ratio increased by 356.75%.In addition,compared with SDS of the control group,the formation of hydrate in g-C3N4NT@c PSSS system did not produce foam during the dissociation process,which was conducive to the recycling of accelerator.（3）Study on the promotion of methane hydrate formation supported by Ag nanoparticles on graphitic carbon nitride nanosheets.g-C3N4nanosheets were prepared by concentrated acid peel,and then loaded with Ag nanoparticles on g-C3N4nanosheets by electrostatic attraction and in-situ reduction,to obtain the composite accelerator Ag@g-C3N4NS.The experimental results show that,when g-C3N4NS is used as the accelerator,The gas storage ratio of the hydrate was only64.97±4.87V/V in 1200min,and the gas storage ratio of the compound accelerator was as high as 145.65±6.64V/V in the methane hydrate formation experiment,87.7%of the theoretical gas storage ratio.In addition,compared with the control group SDS,no foam was generated in the process of methane hydrate formation and dissociation,which was conducive to the recovery and utilization of the accelerator. |
