Exploring Sulfur Recovery in a Eutectic Mixture of Biphenyl and Diphenyl Ether
Committee MemberRoesler, Roland
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AbstractA proof-of-concept liquid phase sulfur recovery process was explored in a eutectic solvent of biphenyl and diphenyl ether. Sulfur conversions up to 99.96% could be achieved within the solvent over commercial alumina and titania catalyst for a simulated tail-gas feed containing up to 5% sulfur species. A temperature range of 120 to 150 °C was explored to take advantage of a higher Claus equilibrium, favoured at lower temperatures, and to enable a liquid-liquid phase separation of the formed sulfur. CS2 destruction was explored in the same temperature range for a 2:1 and 2.3:1 H2S/SO2 ratio, with higher ratios giving higher CS2 conversions. For all conditions explored, the highest conversions were observed at 150 °C. In the presence of the 2.3:1 H2S/SO2 ratio, CS2 conversions were 95 and 98% over Al2O3 and TiO2, respectively. The effects of the addition of 28% water and sulfur saturation were also determined over Al2O3 and TiO2. It was found that the large excess of water had little impact on CS2 conversion over Al2O3 (92% destruction) but showed a negative impact over TiO2 (79% destruction). When saturating the eutectic solvent with sulfur, CS2 destruction was not affected on titania; however, a drop in conversion was observed over alumina (83% versus 95% in the absence of sulfur saturation) due to sulfur condensation on the catalyst surface (pore condensation). The benefits of the eutectic solvent were demonstrated in a regeneration study which enabled effective removal of deposited sulfur on both Al2O3 and TiO2. To support further design of the process, sulfur solubility in the eutectic mixture was measured from 25 to 130 °C. High-pressure densities of sulfur in the eutectic solvent were measured from 25 to 100 °C and pressures up to 40MPa to determine the volumetric properties of dissolved sulfur. An apparent molar volume of V2 = 139 ± 19 cm3·mol-1 was calculated which is similar to the molar volume of elemental sulfur. The solubility measurements and the molar volume changes were used in a closed-form calculation method using a van’t Hoff model to determine the enthalpy of dissolution and change in heat capacity for the α-sulfur, β-sulfur and the liquid-sulfur phase for the general treatment of sulfur in physical sulfur solvents. Using changes in molar volumes from the density data, the calculated solubility showed a very low-pressure dependence. Gas solubilities for H2S, SO2, COS and CO2 were measured by determining the vapour-liquid equilibrium of selected tail-gas species in the eutectic solvent. Solubilities were measured at 25, 50 and 75 °C at low pressures to determine the Henry’s law constants. The (phi/gamma) method and the Krichevsky-Kasarnovksy (KK) equation were used to correlate the solubility data. The (phi/gamma) method was found to give a better fit for the solutes studied. As expected, the Henry’s Law constants were found to increase with increasing temperature which corresponded to lower solubilities at high temperatures.
CitationPrinsloo, R. (2022). Exploring sulfur recovery in a eutectic mixture of biphenyl and diphenyl ether (Unpublished doctoral thesis). University of Calgary, Calgary, AB.
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