Accelerated natural gas hydrate formation is important for the promotion of natural gas storage, gas separation and CO2 capture technologies based on hydrate method. The kinetic characteristics of methane hydrate of 0.05 wt% functionalized (hydroxylated, carboxylated and aminated) multi-walled carbon nanotubes and 1.0 wt% L-leucine complexed system were investigated by constant temperature and constant volume method. It is shown that the compounding of multi-walled carbon nanotubes, carboxylated and hydroxylated multi-walled carbon nanotubes with L-leucine can significantly reduce the nucleation time of natural gas hydrate induction to about 25, 22 and 13 min, the promotion effect is comparable to that of typical promoter sodium dodecyl sulfate, and the promotion effect is better than that of the single additive system. The methane storage density of the compounded system has good performance up to 136-142 mg/g. The analysis of the average and instantaneous methane uptake rate shows that the multi-walled carbon nanotubes have little effect on the growth kinetics of methane hydrate in the growth phase. The growth of methane hydrate in the compounded and L-leucine systems had similarities, both showed a rapid increase of uptake rate to the maximum value, follwed by a rapid decrease and completion of growth. The comprehensive analysis indicates that the compounding system of multi-walled carbon nanotubes and L-leucine has a synergistic enhancement effect on the nucleation rate of methane hydrate, while the process and rate of the growth phase are mainly influenced by L-leucine. This study provides a new idea to explore the differentiation mechanism of different types of additives in enhancing the kinetics of methane hydrate generation.
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