Gas purification by adsorption of hydrogen sulfide
Hydrogen sulfide is removed from a hydrogen rich gas stream using adsorbents having a low loss of carbon dioxide adsorption capacity upon sulfur loading including high purity silica gels, titania or highly cross-linked, non-chemically reactive resins. The adsorbents may be used to adsorb both carbon dioxide and hydrogen sulfide, or may be used as a guard bed upstream of a separate carbon dioxide adsorbent.
1. A PSA process for the removal of hydrogen sulfide from a feed gas containing at least hydrogen sulfide as an impurity, said process comprising contacting the feed gas with an adsorbent for hydrogen sulfide, adsorbing hydrogen sulfide from said feed gas on said adsorbent to produce a hydrogen sulfide depleted feed gas, and periodically regenerating said adsorbent by desorption of hydrogen sulfide therefrom under PSA conditions wherein said adsorbent for hydrogen sulfide has a sulfur deposition rate of less than 0.04 wt % S per day H 2 S exposure when continuously exposed to a 1% H 2 S dry gas at 20° C. for seven (7) days; wherein the adsorbent comprising a silica gel having an SiO 2 content of at least 99.2%.
2. A process as claimed in claim 1 , wherein said adsorbent for hydrogen sulfide has loss of adsorption capacity for carbon dioxide upon accumulation of sulfur on the adsorbent produced by continuous seven day exposure to a 1% H 2 S dry gas at 20° C. of less than 2.0% capacity loss/wt % S loading.
3. A process as claimed in claim 1 , wherein the feed gas contains at least 0.2 vol % hydrogen sulfide.
4. A process as claimed in claim 1 , wherein the feed gas contains at least 50 vol % hydrogen.
5. A process as claimed in claim 1 , wherein the feed gas contains at least 80 vol % of hydrogen and carbon dioxide.
6. A process as claimed in claim 1 , wherein the feed gas contains hydrogen as a desired component and at least hydrogen sulfide and carbon dioxide as impurities and purified hydrogen is obtained as an end product by contacting the feed gas with a said adsorbent in the form of a single homogeneous adsorbent.
7. A process as claimed in claim 1 , wherein said feed gas is synthesis gas produced by steam reforming of a carbon source which is solid or liquid at STP, followed by a water gas shift reaction.
8. A process as claimed in claim 1 , wherein said feed gas contains at least both hydrogen sulfide and carbon dioxide as impurities, and said hydrogen sulfide depleted feed gas is passed from said adsorbent for hydrogen sulfide to contact an adsorbent for carbon dioxide, and carbon dioxide is adsorbed from said hydrogen sulfide depleted feed gas by said adsorbent for carbon dioxide to form a hydrogen sulfide and carbon dioxide depleted feed gas.
9. A process as claimed in claim 8 , wherein said adsorbent for hydrogen sulfide is contained in a first column and said adsorbent for carbon dioxide is contained in a second column connected for gas flow to said first column.
10. A process as claimed in claim 9 , wherein said adsorbent for hydrogen sulfide is regenerated at intervals by desorption of hydrogen sulfide therefrom.
11. A process as claimed in claim 10 , wherein said adsorbent for hydrogen sulfide is regenerated at first intervals by desorption of hydrogen sulfide therefrom and wherein said adsorbent for carbon dioxide is regenerated at second intervals by desorption of carbon dioxide therefrom.
12. A process for the purification of a hydrogen rich feed gas containing at least carbon dioxide and hydrogen sulfide as impurities, comprising contacting the feed gas with a first adsorbent contained in a first adsorbent vessel and thereby removing hydrogen sulfide from said feed gas to form a hydrogen sulfide depleted feed gas and contacting said hydrogen sulfide depleted feed gas with at least a second adsorbent contained in a second adsorbent vessel to remove at least carbon dioxide from said hydrogen sulfide depleted feed gas, and at intervals regenerating said first adsorbent and at different intervals regenerating said second adsorbent, wherein said first adsorbent is silica gel having an SiO 2 content of at least 99.2% and has a sulfur deposition rate of less than 0.04 wt % S per day H 2 S exposure when continuously exposed to a 1% H 2 S dry gas at 20° C. for seven (7) days.