Selective two-stage hydroprocessing system and method
Aromatic extraction and hydrocracking processes are integrated to optimize the hydrocracking units design and/or performance. By processing aromatic-rich and aromatic-lean fractions separately, the hydrocracking operating severity and or catalyst reactor volume requirement decreases.
1. An integrated hydrocracking process for producing cracked hydrocarbons from a feedstock including:
a. separating the hydrocarbon feed into an aromatic-lean fraction and an aromatic-rich fraction;
b. hydroprocessing the aromatic-rich fraction in a first stage hydroprocessing reaction zone to produce a first stage hydroprocessing reaction zone effluent;
c. fractionating the first stage hydroprocessing reaction zone effluent to produce one or more fractionating zone product streams and one or more fractionating zone bottoms streams;
d. hydroprocessing a mixture of at least a portion of fractionating zone bottoms stream and aromatic-lean fraction in a second stage hydroprocessing reaction zone to produce a second stage hydroprocessing reaction zone effluent; and
e. conveying the second stage hydroprocessing reaction zone effluent to the step of fractionating.
2. The process of claim 1 , wherein the first stage hydroprocessing reaction zone is operated under relatively severe conditions effective to remove heteroatoms from, and to hydrocrack, at least a portion of aromatic compounds contained in the aromatic-rich fraction.
3. The process of claim 1 , wherein the second stage hydroprocessing reaction zone is operated under relatively mild conditions effective to remove heteroatoms from, and to hydrocrack, at least a portion of paraffin and naphthene compounds contained in the mixture of fractionating zone bottoms stream and aromatic-lean fraction.
4. The process of claim 1 , wherein the aromatic-rich fraction includes aromatic nitrogen compounds including pyrrole, quinoline, acridine, carbazole and their derivatives.
5. The process of claim 1 , wherein the aromatic-rich fraction includes aromatic sulfur compounds including thiophene, benzothiophenes and their derivatives, and dibenzothiophenes and their derivatives.
6. The process of claim 1 , wherein separating the hydrocarbon feed into an aromatic-lean fraction and an aromatic-rich fraction comprises:
subjecting the hydrocarbon feed and an effective quantity of extraction solvent to an extraction zone to produce
an extract containing a major proportion of the aromatic content of the hydrocarbon feed and a portion of the extraction solvent and
a raffinate containing a major proportion of the non-aromatic content of the hydrocarbon feed and a portion of the extraction solvent;
separating at least substantial portion of the extraction solvent from the raffinate and retaining the aromatic-lean fraction; and
separating at least substantial portion of the extraction solvent from the extract and retaining the aromatic-rich fraction.
7. An integrated apparatus for processing heavy hydrocarbon feedstocks to produce clean transportation fuels comprising:
an aromatic separation zone operable to extract aromatic compounds from the hydrocarbon feed, the aromatic separation zone including an inlet for receiving the hydrocarbon feed, an aromatic-rich outlet and an aromatic-lean outlet;
a first stage hydroprocessing reaction zone having an inlet in fluid communication with the aromatic-rich outlet and an outlet for discharging first stage hydroprocessing reaction zone effluent;
a fractionating zone having an inlet in fluid communication with both the first stage hydroprocessing reaction zone effluent and a second stage hydroprocessing reaction zone effluent, one or more outlets for discharging product and one or more outlets for discharging fractionating zone bottoms; and
a second stage hydroprocessing reaction zone having an inlet in fluid communication with both the fractionating zone bottoms stream and the aromatic-lean outlet, and an outlet for discharging second stage hydroprocessing reaction zone effluent.
8. The process of claim 1 , wherein the one or more fractionating zone product streams include diesel and/or naptha.
9. The process of claim 1 , wherein at least a portion of the one or more fractionating zone bottoms streams are recycled back to step (a) and/or step (b).
10. The process of claim 1 , wherein separating the hydrocarbon feed into an aromatic-lean fraction and an aromatic-rich fraction is carried out in a mixer-settler apparatus.
11. The process of claim 1 , wherein separating the hydrocarbon feed into an aromatic-lean fraction and an aromatic-rich fraction is carried out in a centrifugal contactor.
12. The process of claim 1 , wherein separating the hydrocarbon feed into an aromatic-lean fraction and an aromatic-rich fraction is carried out in a contacting column.
13. The process of claim 12 , wherein the contacting column is a tray column.
14. The process of claim 12 , wherein the contacting column is a packed bed column.
15. The process of claim 12 , wherein the contacting column is a rotating disc contactor.
16. The process of claim 12 , wherein the contacting column is a pulse column.