| Methane hydrate,also known as“burning ice”,is an ideal storage medium for methane.However,under static conditions,the slow formation rate and low storage capacity of methane hydrate seriously hinder the industrial application of hydrate technology.Rapid formation and higher storage capacity of methane hydrate can be achieved by adding surfactants,especially sodium dodecyl sulfate（SDS）.Nevertheless,surfactants are mainly derived from petrochemical feedstock,and a large amount of foam will be generated during the production process,which will block and pollute the pipelines.Herein,based on inorganic compounds,this study explored the formation and gas storage performance of methane hydrate in inorganic systems.According to the structure-performance relationship of the effective promoters,composite promoters were designed from a molecular perspective to further enhance the formation rate and the storage capacity of methane hydrate.In addition,the mechanism of inorganic promoters was preliminarily studied and explored.The main research contents and conclusions are as follows:（1）Through the high-throughput experiments on gas storage performance of 170 kinds of inorganic compounds,it was found that 28 kinds of inorganic compounds,such as boric acid and sodium silicate,could promote the formation of methane hydrate.The structures of effective promoters were analyzed and compared in order to preliminarily judge their influence on methane hydrate formation.Meanwhile,the synergistic effects of 130 kinds of inorganic composite systems on hydrate formation were also investigated.（2）After magnifying the formation kinetics of methane hydrate in boric acid aqueous solutions and optimizing the concentration of boric acid,it was found that maximum gas storage capacity was 112.2 mg/g when the boric acid concentration was 0.5 wt%.Boric acid can be used as an effective promoter for the formation of methane hydrate without foaming phenomenon upon degassing under static conditions.（3）Boric acid had a good synergistic effect with inorganic alkali,magnesium carbonate and amino acid,and these composite promoters can significantly enhance the gas storage performance of methane hydrate.In addition,the influence of concentration,metal cation,driving force and amino acid structure on methane hydrate formation kinetics was investigated.It was found that the gas storage capacity in boric acid plus calcium hydroxide composite system was up to 131.8 mg/g,which was similar to the promotion effect of SDS,the benchmark promoter.More importantly,the gas storage capacity in boric acid plus L-leucine composite system was 146.2 mg/g,which was close to the theoretical storage capacity of methane hydrate（154.9 mg/g）.11B-NMR measurements confirmed the excellent promoting effect of the inorganic composite promoters was due to the combined effect of boric,monoborate anion,and metal cation.Moreover,the results of Raman spectroscopy and X-ray diffraction showed that the methane hydrate formed in the composite systems was still structure I（s I）methane hydrate.（4）The rice husk extract and its main component lignin plus alkali compounds could promote the formation of methane hydrate efficiently,and the gas storage capacity was better than that of SDS under the same conditions.Raman spectroscopy was used to determine the hydrate structure and the results showed that the promoters could improve the gas storage performance of the hydrate without changing the crystal structure of s I methane hydrate. |
