The flash point of elemental sulfur: Effect of heating rates, hydrogen sulfide, and hydrocarbons

Facilities for the storage and handling of liquid sulfur are designed to avoid fires to prevent (a) deflagration, (b) breaching of hot-liquid and (c) the emission of highly toxic sulfur dioxide. To aid design and operation, current literature reports a wide range of flash points from 160 to 207 degrees C. This work aims to help clarify why this wide variance in measurements exists and which values are more applicable for safety and vessel integrity. The effects of heating rate, dissolved hydrogen sulfide, and hydrocarbon impurities on the apparent flash point were studied using a Pensky-Martens closed cup flash point apparatus following the standardized procedure outlined in American Society for Testing and Materials test method D93-20. The heating rate significantly affected the sulfur flash point, where slower rates yielded consistent flash points of 207 +/- 3 degrees C. Flash points as low as 167 degrees C were observed when using faster rates, including the American Society for Testing and Materials recommended heating rates. Freely dissolved hydrogen sulfide lowered the flash point to 175 degrees C for concentrations greater than 100 ppmw, irrespective of the amount of dissolved polysulfanes. No effect on the flash point was observed for decane or hexadecane impurities up to 333 and 512 ppmw, respectively.