Promotion of Activated Carbon on the Nucleation and Growth Kinetics of Methane Hydrates.

Guodong Zhang,Kun Chao,Xiaoyun Shi,Runcheng Zhang,Fei Wang

doi:10.3389/fchem.2020.526101

Abstract

Due to the hybrid effect of physical adsorption and hydration, methane storage capacity in pre-adsorbed water-activated carbon (PW-AC) under hydrate favorable conditions is impressive, and fast nucleation and growth kinetics are also anticipated. Those fantastic natures suggest the PW-AC-based hydrates to be a promising alternative for methane storage and transportation. However, hydrate formation refers to multiscale processes, the nucleation kinetics at molecule scale give rise to macrohydrate formation, and the presence of activated carbon (AC) causes this to be more complicated. Although adequate nucleation sites induced by abundant specific surface area and pore texture were reported to correspond to fast formation kinetics at macroperspective, the micronature behind that is still ambiguous. Here, we evaluated how methane would be adsorbed on PW-AC under hydrate favorable conditions to improve the understanding of hydrate fast nucleation and growth kinetics. Microbulges on AC surface were confirmed to provide numerous nucleation sites, suggesting the contribution of abundant specific surface area of AC to fast hydrate nucleation and growth kinetics. In addition, two-way convection of water and methane molecules in micropores induced by methane physical adsorption further increases gas–liquid contact at molecular scale, which may constitute the nature of confinement effect of nanopore space.

Highlights

As one of the most promising energy resources, natural gas hydrates gradually get more and more attention, which are stored in permafrost and marine with huge reserves (Sloan, 2003)
Here we report how methane would be absorbed on pre-adsorbed water-activated carbon (PW-activated carbon (AC)) under hydrate-favorable conditions and evaluate potential micromechanisms behind the fast nucleation and growth kinetics
The point one should keep in mind is that regardless of what the nature of fast nucleation and growth kinetics of hydrates loaded by AC is, the reason behind that at macroperspective must depend on the increased tremendous potential nucleation sites caused by abundant specific surface area and pore texture

Summary

INTRODUCTION

As one of the most promising energy resources, natural gas hydrates gradually get more and more attention, which are stored in permafrost and marine with huge reserves (Sloan, 2003). We found a three-stage kinetic behavior during hydrate formation as shown, methane physical adsorption occurs soon after the experimental pressure is reached, followed by a hydration induction period, and eventually hydrates form causing methane quick consumption Another promising finding for PW-AC-based hydrates is that the presence of AC significantly enhances hydrate nucleation and growth kinetics. Mass ratio of water to activated carbon used in hydrate formation experiments

Findings

DISCUSSION

CONCLUSION