Molecular simulation study of liquid sulfur adsorption and diffusion in calcite nanoscale slits under varying temperature and pressure conditions

Abstract

In the late stages of extensive development of high-sulfur carbonate gas reservoirs, pressure decline leads to sulfur enrichment, and when the temperature exceeds sulfur's melting point, sulfur precipitates in a liquid form, severely restricting the exploitation of high-sulfur carbonate gas reservoirs. However, the adsorption mechanism of sulfur deposition remains poorly understood. In this study, we investigated the microscopic adsorption mechanism of liquid sulfur in calcite nanopores using molecular simulation methods. Our research revealed that liquid sulfur adsorption in calcite nanopores is primarily influenced by pore size. When the pore size is less than 160 Å, multilayer adsorption dominates, with a single-layer sulfur film thickness of approximately 5 Å. At the nanoscale, 1 g of calcite with a 40 Å nanopore structure exhibits excess adsorption of liquid sulfur ranging from 0.00734 to 0.0279 g. As pressure increases, the adsorption of two or more layers intensifies, while the diffusion coefficient decreases. Conversely, as temperature rises, the density of each layer decreases, and the diffusion coefficient increases. Simultaneously, the diffusion coefficient of liquid sulfur in calcite slits exhibits a power function increase as the pore size enlarges. Under a pressure of 15 MPa, when the temperature increases from 420 K to 480 K, the diffusion coefficient increases from 6.96 × 10−11 m²/s to 3.51 × 10−10 m²/s. This study provides valuable insights into the adsorption and diffusion behavior of liquid sulfur in calcite nanopores, which can inform the development of high-sulfur carbonate reservoirs.