S Cycle

Page 1

S CYCLE – PART 2 Chemical amines: combine the basicity necessary to promote the chemical reaction with H2S, with the presence of OH group we have good solubility in water. Hybrid solvents: high efficiency at low and high concentration of H2S in the gas phase Sulfinol is the commercial name of hybrid solvent which approximates the behaviour at high concentration of the physical solvent (sulfulane) and the one of chemical solvent (sulfinol) at low concentration. Storage capacity of the solvent with respect to the temperat ure: T1 is generally lower that T2 (T1=50°C, T2=80°C). These are all commercial processes: RECTISOL (use of methanol as physical solvent, low operating temperature, there is the need of a refrigerating system, regeneration obtained by simple flashing or stripping); AMISOL and SULFINOL (hybrid sorbent, very deep desulfurization, generally a higher energy input is required for regeneration, flash and heating uses in series). CLAUSIUS PROCESS From absorption we come out with a gaseous phase with a high concentration of H2S . We need to covert H2S into S, generally we use the CLAUS PROCESS. CLAUS PROCESS: bring S as H2S (where we have S- -) to elemental S (with zero oxidation state). S has different allotropic forms, Sx, where x can vary between 2 to 8 depending on the temperature: at low temperature the stable allotropic form of S is S8, while at high temperature is S2. In this process we have a PARTIAL OXIDATION : for example SO 2, this is a deep oxidation (S4+), with Claus process we want to stop at zero oxidation state, that’s why we say that it is a partial oxidation process. To increase oxidation state we need oxygen, an oxidizing agent. In Claus process we have combination of H2S and sub stoichiometric air (because we don’t want a deep oxidation, we…