Hydrocracking process in several stages and regulating the hydrocracking by varying the amount of hydrogen sulfide in the reaction zones

Claim 1

A MULTI-STAGE HYDROCRACKING PROCESS FOR CONVERTING A HYDROCARBON FEDSTOCK CONTAINING SULFUR COMPOUNDS AND AT LEAST ABOUT 20% BY VOLUME OF AROMATIC HYDROCARBONS AND BOILING ABOVE THE GASOLINE RANGE TO RELATIVELY HIGH-OCTANE AROMATIC GASOLINE, WHICH COMPRISES: (1) SUBJECTING SAID FEEDSTOCK PLUS ADDED HYDROGEN TO CATALYTIC HYDROFINING WITHOUT SUBSTANTIAL CRACKING OF HYDROCARBONS; (2) SUBJECTING TOTAL HYDROGEN SULFIDE-CONTAINING EFFLUENT FROM SAID HYDROFINING TO A FIRST STAGE OF CATALYTIC HYDROCRACKING; (3) SEPARATING THE EFFLUENT FROM SAID FIRST-STAGE HYDROCRACKING INTO A GASOLINE PRODUCT, A SUBSTANTIALLY SULFUR-FREE UNCONVERTED GAS OIL, AND A SOUR RECYCLE GAS WHICH IS AT LEAST IN PART RECYCLED TO SAID HYDROFINING STEP; (4) SUBJECTING SAID UNCONVERTED GAS OIL PLUS ADDED HYDROGEN TO A SECOND STAGE OF CATALYTIC HYDROCRACKING OVER A FIXED BED OF CATALYST, INTIALLY AT A TEMPERATURE BETWEEN ABOUT 525* AND 650*F., AND CONTINUING FOR AN EXTENDED RUN PERIOD AND AT INCREMENTALLY RISING HYDROCRACKING TEMPERATURE WITHIN THE RANGE OF ABOUT 525-750*F., SAID HYDROCARCKING CATALYST COMPRISING A SOLID REFRACTORY CRACKING BASE HAVE AN ACTIVITY GREATER THAN THAT CORRESPONDING TO A CAT.-A ACTIVITY INDEX OF 40, AND COMBINED THEREWITH A MINOR PROPORTION OF A GROUP VIII NOBLE METAL HYDROGENAING COMPONENT; (5) SEPARATING THE EFFLUENT FROM SAID SECOND-STAGE HYDROCRACKING INTO A GASOLINE PRODUCT, A SECOND-STAGE RECYCLE OIL, AND A SECOND-STAGE RECYCLE GAS HAVING A RELATIVELY LOW CONCENTRATION OF HYDROGEN SULFIDE WHICH IS RECYCLED TO SAID SECOND HYDROCRACKING STAGE; (6) DURING A FIRST PART OF SAID SECOND-STAGE HYDROCRACKING RUN, BLENDING A PORTION OF SAID SOUR RECYCLE GAS WITH SAID SECOND-STAGE RECYCLE GAS SO AS TO MAINTAIN A RELATIVELY HIGH CONCENTRATION OF HYDROGEN SULFIDE IN SAID SECOND-STAGE RECYCLE GAS; (7) REDUCING SAID SOUR RECYCLE GAS PORITON DURING A LATER PORTION OF SAID SECOND-STAGE HYDROCARCKING RUN SO AS TO MAINTAIN A RELATIVELY LOW CONCENTRATION OF HYDROGEN SULFIDE THEREIN, AND THEREAFTER CONTINUING SAID RUN UNTIL A TERMINAL TEMPERATURE BETWEEN ABOUT 675* AND 750*F. IS REACHED; AND (8) CONTROLLING AND CORRELATING THE HYDROCRACKING TEMPERATURE WITH THE HYDROGEN SULFIDE CONCENTRATION SO AS TO OBTAIN THROUGHOUT SAID SECOND-STAGE RUN AT LEAST ABOUT 40% BY VOLUME CONVERSION TO AN AROMATIC GASOLINE PRODUCT, SAID GALOLINE PRODUCT CONTAINING AT LEAST ABOUT 10% BY VOLUME OF AROMATIC HYDROCARBONS IN THE C7-400*F. FRACTION AT ALL HYROCRACKING TEMPERATURES ABOVE ABOUT 600*F.