Method for recovery of paraxylene with reduced crystallization load
A method for the recovery paraxylene with reduced crystallization. Paraxylene is recovered from a mixture of C8 aromatic hydrocarbons in a pressure swing adsorption zone and a crystallization zone. The invention provides for lower throughput through the crystallization zone, resulting in lower capital costs, reduced electricity in operating separation equipment, as well as reduced refrigeration duty.
1. A process for the recovery of a paraxylene product from a mixture of C8 aromatic hydrocarbons, the process comprising:
separating a C8-rich aromatic hydrocarbon mixture in a pressure swing adsorption zone to form a first paraxylene-rich stream and a first paraxylene-lean stream, wherein the first paraxylene-rich stream comprises less than 75 wt % paraxylene;
separating at least a portion of the first paraxylene-rich stream in a crystallization zone to form a paraxylene-rich product stream and a second paraxylene-lean stream; wherein a ratio of the total mass of the first paraxylene-rich stream to the total mass of the paraxylene-rich product stream is less than 4; and
isomerizing at least a portion of the second paraxylene-lean stream to form an isomerate having a paraxylene concentration greater than the paraxylene concentration of the second paraxylene-lean stream; wherein at least a portion of the isomerate is used to form said C8-rich aromatic hydrocarbon mixture.
2. The process of claim 1 , wherein the ratio of the total mass of the first paraxylene-rich stream to the total mass of the paraxylene-rich product stream is less than 2.
3. The process of claim 1 , further comprising isomerizing at least a portion of the first paraxylene-lean stream to form a secondary isomerate having a paraxylene concentration greater than the paraxylene concentration of the first paraxylene-lean stream.
4. The process of claim 3 , wherein at least a portion of the secondary isomerate is used to form said C8-rich aromatic hydrocarbon mixture.
5. The process of claim 1 , further comprising separating a feedstock containing aromatic hydrocarbons in a fractionation zone to form said C8-rich aromatic hydrocarbon mixture.
6. A process for the recovery of a paraxylene product from a mixture of C8 aromatic hydrocarbons, the process comprising:
separating a C8-rich aromatic hydrocarbon mixture in a pressure swing adsorption zone to form a first paraxylene-rich stream and a first paraxylene-lean stream, wherein the first paraxylene-rich stream comprises less than 75 wt % paraxylene;
separating at least a portion of the first paraxylene-rich stream in a crystallization zone to form a paraxylene-rich product stream and a second paraxylene-lean stream; wherein a ratio of the total mass of the second paraxylene-lean stream to the total mass of the paraxylene-rich product stream is less than 3; and
isomerizing at least a portion of the second paraxylene-lean stream to form an isomerate having a paraxylene concentration greater than the paraxylene concentration of the second paraxylene-lean stream; wherein at least a portion of the isomerate is used to form said C8-rich aromatic hydrocarbon mixture.
7. The process of claim 6 , wherein the ratio of the total mass of the second paraxylene-lean stream to the total mass of the paraxylene-rich product stream is less than 1.
8. The process of claim 6 , further comprising isomerizing at least a portion of the first paraxylene-lean stream to form a secondary isomerate having a paraxylene concentration greater than the paraxylene concentration of the first paraxylene-lean stream.
9. The process of claim 8 , wherein at least a portion of the secondary isomerate is used to form said C8-rich aromatic hydrocarbon mixture.
10. The process of claim 6 , further comprising separating a feedstock containing aromatic hydrocarbons in a fractionation zone to form said C8-rich aromatic hydrocarbon mixture.