Selective hydrogenation method
The present subject matter relates generally to methods for selectively saturating the unsaturated C 2 -C 4 . More specifically, the present subject matter relates to methods for saturating butadiene and butenes from a hydrocarbon stream before it is combined with a fresh feed and enters a reaction zone. Removing the unsaturates from the hydrocarbon stream before the hydrocarbon stream enters the reaction zone prevents the reactor internals from coking.
1. A method for saturating hydrocarbons comprising:
providing a hydrocarbon stream comprising paraffins having 4 or less carbon atoms, C2-C4 olefins, diolefins, aromatics, H 2 O, H 2 S, and other sulfur containing compounds, wherein the hydrocarbon stream comprises a portion of an effluent from a dehydrocyclodimerization reaction zone;
passing the hydrocarbon stream to a guard bed and contacting the hydrocarbon stream with an adsorbent to remove H 2 O, H 2 S, and other sulfur containing compounds and form a treated hydrocarbon stream; and
passing the treated hydrocarbon stream and a hydrogen stream to a reaction zone containing a hydrogenation catalyst to selectively hydrogenate the olefins and diolefins in the treated hydrocarbon stream and form a reaction zone effluent stream, wherein greater than about 60% by weight of the olefins are saturated, greater than about 80% by weight of the diolefins are saturated, and no more than 20% by weight of the aromatics are saturated.
2. The method of claim 1 , wherein the guard bed contains molecular sieves to remove H 2 O.
3. The method of claim 1 , wherein the guard bed contains molecular sieves to remove H 2 O and H 2 S.
4. The method of claim 1 , wherein the guard bed contains molecular sieves and metal or metal oxides that are capable of going through reduction-oxidation cycle to remove H 2 S and other sulfur containing compounds.
5. The method of claim 1 , wherein the reaction zone comprises multiple reactors in series having inter-stage quenching.
6. The method of claim 5 , wherein the inter-stage quenching includes dividing H 2 and injecting it into individual reactors.
7. The method of claim 1 , wherein the reaction zone operates at a temperature from about 60° C. (140° F.) to about 350° C. (662° F.).
8. The method of claim 1 , wherein the reaction zone operates at a pressure from about 40 psig to about 300 psig.
9. The method of claim 1 , wherein the hydrogenation catalyst comprises at least one active metal chosen from Groups 6 through 10.
10. The method of claim 1 , wherein the hydrogenation catalyst comprises one or more transition metals selected from nickel, palladium, platinum, rhodium, iridium and mixtures thereof supported on inorganic metal oxides.
11. The method of claim 1 , wherein the hydrogenation catalyst comprises at least one Group VIII metal selected from nickel, palladium, platinum and mixtures thereof supported on an inorganic oxide.
12. The method of claim 1 , wherein an overall H 2 to olefin molar ration in the reaction zone range from 0.5 to 5.0.
13. The method of claim 1 , wherein the guard bed operates over a cycle from 2 to 48 hours.
14. The method of claim 1 , wherein the diolefins comprise greater than 50% by weight butadiene.
15. The method of claim 1 , further comprising:
passing a feed stream comprising aliphatic hydrocarbons to a dehydrocyclodimerization reaction zone to form a reaction mixture comprising aromatics, C4+ non-aromatics byproduct, a light ends byproduct comprising C1-C2 hydrocarbons, C2-C4 olefins, diolefins, unconverted aliphatic hydrocarbons, H 2 O, H 2 S, and other sulfur containing compounds;
separating the reaction mixture to form the hydrocarbon stream.
16. The method of claim 15 , further comprising:
recycling the reaction zone effluent stream to the dehydrocyclodimerization reaction zone.