Shell–Paques process
Introduction
The Shell-Paques/Thiopaq process is technology for the conversion of hydrogen sulfide from natural, refinery, synthesis and bio-gas. It is based on the biocatalytical conversion of sulfide into elemental sulfur. It operates at near-ambient conditions of temperature (i.e. 30-40°C) and pressure which results in inherent safety. It is an alternative to for example the Claus process.
Process chemistry
Each reaction can be applied individually or sequentially as dictated by the characteristics of the stream to be treated.
The process consist of two main step: A gas washing section and a sulfide oxidation section as pictured in the Figure below:
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The process block scheme of the Shell-Paques/Thiopaq process.
The washing step uses a dilute sodium carbonate solution to remove hydrogen sulfied (H2S) from the gas according to:
H2S + Na2CO3 --> NaHS + NaHCO3
The loaded washing liquid is transported to a bioreactor where a biocatalyst oxidises the aqueous NaHS to elemental sulfur with about 95% selectivity according to:
NaHS + ½ O2 --> S° + NaOH
NaOH + NaHCO3 --> Na2CO3 + H2O
Combined reaction equation: NaHS + NaHCO3 + ½ O2 --> S° + Na2CO3 + H2O
The regenerated washing liquid is send back to the washing column.
The controlled partial oxidation of sulfide to elemental sulfur (2) is catalyzed by naturally occurring microorganisms of the genus Halothiobacillus in the bioreactor. These natural, living microorganisms present in the bioreactor catalyse the sulfur conversions and are, by their nature, resilient and adaptive.
In many situations the process can be used for sulfur removal and recovery. When sulfur recovery is desired, the elemental sulfur produced in the aerobic bioreactor will be separated from the aqueous effluent in a separator inside of the reactor. The excess sulfur will be removed as aqueous slurry of 10% dry solids content. There are several options for handling this slurry and to convert int into products for sulfuric acid generation, fertiliser or fungicide.
The system is flexible and has several processing options that have ready application in the petroleum refinery or petrochemical complex for managing a variety of sulfur-containing streams including sulfidic caustic, LPG, hydrotreater offgas and fuel gas.