Hydrocracking process and system including separation of heavy poly nuclear aromatics from recycle by ionic liquids and solid adsorbents

A process for the treatment of a hydrocracking unit bottoms stream obtained from a hydrocracking operation containing heavy poly-nuclear aromatic (HPNA) compounds that are derived from the hydrocracking operation prior to use within the hydrocracking operation to reduce the content of HPNA compound, the process comprising:

• a. introducing the bottoms stream from the hydrocracking operation into an extraction unit with one or more ionic liquids for a predetermined period of time to extract the HPNA compounds and to produce an extraction unit effluent stream containing extracted HPNA compounds and ionic liquid, and an ionic liquid treated stream having a reduced content of HPNA compounds and residual ionic liquid;
• b. introducing the extraction unit effluent stream containing the extracted HPNA compounds and ionic liquid into a separation unit for contact with an organic polar solvent;
• c. mixing the extraction unit effluent stream containing the extracted HPNA compounds and ionic liquid in the separation unit for a time that is sufficient to form a solution of the HPNA compounds in the organic polar solvent;
• d. recovering ionic liquid from the separation unit for re-use in the extraction unit and discharging a stream containing solvent and HPNA compounds;
• e. transferring the stream containing solvent and HPNA compounds to a solvent recovery unit, and recovering a solvent stream for re-use in the separation unit;
• f. transferring from the extraction unit the ionic liquid treated stream having a reduced content of HPNA compounds to a liquid-liquid separator and recovering as separate streams
• (i) an ionic liquid treated hydrocarbon stream having a substantially reduced content of HPNA compounds, and
• (ii) a stream containing residual ionic liquid and HPNA compounds;
• g. contacting the ionic liquid treated hydrocarbon stream with an effective amount of adsorbent material to produce an adsorbent-treated hydrocarbon stream having a reduced content of HPNA compounds;
• h. recovering the adsorbent-treated stream having a reduced content of HPNA compounds;
• and
• i. using all or a portion of the adsorbent-treated stream having a reduced content of HPNA compounds as feed within the hydrocracking operation.