Effects of Pressure Driving Force on Carbon Dioxide Hydrate Formation in the L-Met System Under Constant Pressure

Abstract

Carbon dioxide (CO₂) hydrate technology is a key approach to achieving carbon capture, utilization, and storage (CCUS). Traditional studies are often based on isochoric (constant-volume) systems, and due to the effects of driving force decay, they struggle to reveal the intrinsic kinetic characteristics of hydrate growth. In this study, a high-precision mobile-piston constant-pressure apparatus was employed to systematically investigate the effects of pressure driving force (ΔP) on the kinetics and morphological evolution of CO₂ hydrates in an L-methionine (L-Met) system within a temperature range of 1.0–2.5°C and a pressure range of 2.8–3.4 MPa. The results indicate that: (1) The induction time decreases as ΔP increases, dropping by 63.4% at 1.0°C. However, within the range of 1.5–2.0°C, it exhibits a nonlinear behavior characterized by an initial increase followed by a decrease, revealing the stochastic nature of nucleation under low driving forces. (2) Hydrate formation exhibits a unique bimodal (double-peak) phenomenon under constant-pressure conditions. The first peak is suppressed by the loss of local undercooling caused by the exothermic nature of interfacial nucleation, while the second explosive peak is driven by the compensatory effect of the constant-pressure driving force, inducing the vertical expansion of the hydrate into the bulk phase. (3) The water conversion rate generally increases with rising ΔP, reaching a maximum of 89.8%. However, under extreme conditions (1.0°C and 2.0 MPa), the rapid formation of a dense hydrate layer induces significant thermal resistance, restricting heat dissipation and mass transfer, which ultimately results in a decreased conversion rate. This study demonstrates the superiority of the moving-piston method in eliminating mechanical disturbances and revealing true kinetic behavior, providing a theoretical foundation for heat management and pressure control in industrial carbon sequestration processes.