Trialkylphosphonium ionic liquids, methods of making, and alkylation processes using trialkylphosphonium ionic liquids

1. An alkylation process comprising:

contacting an isoparaffin feed having from 4 to 10 carbon atoms and an olefin feed having from 2 to 10 carbon atoms in the presence of a trialkylphosphonium ionic liquid catalyst composition in an alkylation zone under alkylation conditions to generate an alkylate,

wherein the trialkylphosphonium ionic liquid catalyst composition comprises one or more trialkylphosphonium haloaluminate compounds having a formula:

where R 1 , R 2 , and R 3 are the same or different and each is independently selected from C 1 to C 8 hydrocarbyl; and

X is selected from F, Cl, Br, I, or combinations thereof;

wherein the trialkylphosphonium haloaluminate compound comprises tri-n-butylphosphonium Al 2 Cl 7 , tri-isobutylphosphonium Al 2 Cl 7 , or di-n-butyl-sec-butylphosphonium Al 2 Cl 7 ; and

wherein an initial kinematic viscosity of the trialkylphosphonium ionic liquid catalyst composition is less than 50 cSt at 25° C.

2. The process of claim 1 wherein an initial kinematic viscosity of the trialkylphosphonium ionic liquid catalyst composition is about 30 cSt or less at 25° C.

3. The process of claim 1 wherein a molar ratio of aluminum to phosphorous in the ionic liquid catalyst composition is in the range of 1.8 to 2.2.

4. The process of claim 1 wherein the trialkylphosphonium ionic liquid catalyst composition further comprises a quaternary phosphonium haloaluminate compound having a formula:

where R 5 -R 7 are the same or different and each is independently selected from a C 1 to C 8 hydrocarbyl;

R 8 is different from R 5 -R 7 and is selected from a C 1 to C 15 hydrocarbyl; and

X is selected from F, Cl, Br, I, or combinations thereof.

5. The process of claim 1 wherein the trialkylphosphonium ionic liquid catalyst composition further comprises a co-catalyst.

6. The process of claim 5 wherein the co-catalyst comprises a Brønsted acid selected from the group consisting of HCl, HBr, HI, and mixtures thereof, or a Brønsted acid precursor.

7. The process of claim 1 further comprising:

separating the alkylate and unreacted isoparaffin feed from the trialkylphosphonium ionic liquid catalyst composition to form a hydrocarbon stream comprising the alkylate and the unreacted isoparaffin feed and an ionic liquid stream comprising the trialkylphosphonium ionic liquid catalyst composition;

separating the hydrocarbon stream into an alkylate stream and an unreacted isoparaffin stream; and

recycling at least one of the unreacted isoparaffin stream and the ionic liquid stream.

8. The process of claim 1 further comprising:

regenerating at least a portion of the trialkylphosphonium ionic liquid catalyst composition in the ionic liquid stream; and

recycling the regenerated trialkylphosphonium ionic liquid catalyst to the alkylation zone.

9. The process of claim 1 wherein the trialkylphosphonium ionic liquid catalyst is present in an amount of about 1 vol % to about 75 vol % of a total volume of material in the alkylation zone.

10. The process of claim 1 wherein the alkylation conditions include a temperature of from about 0° C. to about 100° C., a pressure from about 0.3 MPa(g) to about 2.5 MPa(g), an overall paraffin to olefin molar ratio from about 2 to about 20, and a residence time of about 1 min to about 1 hour.

11. The process of claim 1 wherein the isoparaffin feed has from 4 to 8 carbon atoms and the olefin feed has from 3 to 8 carbon atoms.

12. The process of claim 11 wherein the isoparaffin has from 4 to 5 carbon atoms and the olefin has from 3 to 5 carbon atoms.