Rheometric measurements of molten sulfur might lead to safer transport

Molten liquid sulfur from oil refining and gas processing plays a crucial role in the production of fertilizer worldwide. To avoid equipment failure and design more realistic models for liquid sulfur transportation, scientists collect the rheometric and viscoelastic properties of the material.

Due to the complexities in dealing with liquid sulfur, Mitchell Stashick and Robert Marriott used a modified Anton-Paar Modular Compact Rheometer, which had been hermetically sealed, to obtain viscoelastic measurements of pure liquid sulfur. They found relaxation times relevant to the motion of entangled polymeric sulfur chains (reptation) and shorter chains due to bond breaking at a similar timescale.

The authors had to use a large temperature range and lengthy measurement times to study the viscoelastic behavior of the material. Using a hermetically sealed rheometer allowed them to avoid vapor loss during the experiments.

“Interpretation of the viscoelastic plots allow us to support a modified reptation model, where reptative motion is mitigated by homolytic sulfur bond scission and recombination at a similar timescale,” said Marriott. “This explains why sulfur shows both viscous and elastic type behavior.”

The slow relaxation time related to reptative behavior, was discovered to be between 0.24 seconds and 0.28 seconds at 190 degrees Celsius. Based on the Maxwell relation, this corresponded with a viscosity range predicted in former studies. Using a Cole-Cole plot, the authors identified what type of relaxation was taking place.

In the future, the authors suggest the effect of hydrogen sulfide solubility should be studied in relation to the concentrations found in oil refineries and natural gas processing plants to continue to develop fundamental and applicable viscosity models.

Source: “Viscoelastic behavior corresponding to reptative relaxation times across the λ-transition for liquid elemental sulfur,” by Mitchell J. Stashick and Robert A. Marriott, Journal of Chemical Physics (2020). The article can be accessed at https://doi.org/10.1063/1.5138942 .