Method and catalysts for the production of ammonia synthesis gas
In a process for the production of ammonia synthesis gas from a hydrocarbon-containing feedstock, comprising steam reforming of the feedstock and treatment of the synthesis gas obtained, the shift of the synthesis gas comprises two shift steps, both including stable catalysts, whereby the formation of hazardous by-products is avoided or at least reduced to an acceptable low level. The two shift steps can both be HTS, or they can be one HTS and one LTS or one HTS and one MTS. The catalyst used in the HTS and the LTS steps is based on zinc oxide and zinc aluminum spinel, and the catalyst used in the MTS and the LTS steps can be based on copper.
1. A process for the production of ammonia synthesis gas from a hydrocarbon-containing feedstock, comprising the steps of:
steam reforming of the feedstock, thereby obtaining a synthesis gas comprising hydrogen (H 2 ), carbon monoxide (CO) and carbon dioxide (CO 2 ), and
treatment of the synthesis gas obtained, including shift of CO and subsequent removal of CO 2 ,
wherein
a primary reactor and a secondary reactor are used, at least one of said reactors being an autothermal reformer and steam/carbon ratio being less than 2.6,
the shift of the synthesis gas comprises two shift steps, wherein at least one of said shift steps is an HTS step, and
in both shift steps, stable catalysts based on zinc oxide and zinc aluminum spinel are used,
whereby the formation of hazardous by-products is avoided or at least reduced to an acceptable low level.
2. The process according to claim 1 , wherein the two shift steps both are high temperature shift (HTS) steps.
3. The process according to claim 1 , wherein the two shift steps are a step of high temperature shift (HTS) and a step of low temperature shift (LTS).
4. The process according to claim 1 , wherein the two shift steps are a step of high temperature shift (HTS) and a step of medium temperature shift (MTS).
5. The process according to claim 3 , wherein the catalyst used in the low temperature shift (LTS) step is based on copper.
6. The process according to claim 5 , wherein the carrier for the copper-based catalyst is zinc oxide.
7. The process according to claim 1 , wherein the two shift steps are combined to a single reactor provided with suitable inter-bed cooling.
8. The process according to claim 1 , wherein the two shift steps are combined to a single isothermal reactor.
9. The process according to claim 1 , wherein any hazardous by-products are removed in a downstream process.
10. The process according to claim 4 , wherein the catalyst used in the medium temperature shift (MTS) step is based on copper.
11. The process according to claim 10 , wherein the carrier for the copper-based catalyst is zinc oxide.
12. The process according to claim 1 , wherein methanol is at a level below 2000 ppm, acetic acid is at a level below 1000 ppm, and methyl formate is at a level below 50 ppm.