Abstract:
A method for cross connecting the lean solvent supply lines between the liquid liquid extraction (LLE) and the extractive distillation (ED) processes thereby using the LLE column as the outlet for removing accumulated heavy hydrocarbons (HCs) and polymeric materials from the solvent loop of both processes to maintain their solvent performance. The unique capabilities of the LLE column in rejecting heavy HCs from the solvent into a raffinate product stream that leaves the system enable the removal of the accumulated heavy HCs and polymeric materials from the closed solvent loop of the ED process when their lean solvent loop are cross connected. Cross connection requires minimum equipment change. In the revamped system, the solvent recovery column (SRC) in LLE process supplies lean solvent for the extractive distillation column while the SRC of the ED process supplies lean solvent for LLE column.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to techniques for integrating existing liquid-liquid extraction (LLE) and extractive distillation (ED) processes whereby the LLE column serves as the outlet for removing accumulated heavy hydrocarbons and polymeric materials from the solvent loop of both processes. 
     BACKGROUND OF THE INVENTION 
     In extractive distillation (ED) and liquid-liquid extraction (LLE) processes for aromatics recovery, the solvent is circulated in a closed loop indefinitely. The feedstock is typically treated in a prefractionator to remove the heavy portion before being fed into the EDC or LLE column. Nevertheless, measurable amounts of heavy hydrocarbons (HCs) pass through even a well-designed prefractionator operating under normal conditions. The level of heavy HCs in the feed stream is significantly higher for a poorly operated or malfunctioned prefractionator. To remove the heavy HCs and the polymerized heavy materials derivate from oxidized solvent, conventional commercial LLE processes use a thermal solvent regenerator where a small slip stream of the lean solvent is heated to recover the regenerated solvent and heavy components that have boiling points lower than that of the solvent. The heavy polymeric materials, that have boiling points higher than that of the solvent, are removed as sludge from the bottom of the solvent regenerator. 
     U.S. Pat. No. 4,048,062 to Asselin discloses an LLE process for aromatics recovery in which a portion of lean solvent from the bottom of a solvent recovery column (SRC) is introduced into a solvent regenerator (SRG). A stripping steam that is introduced into the SRG separately is recovered with the regenerated solvent and then introduced into the SRC as a portion of the total stripping steam. This solvent regeneration scheme works because, within the same type of molecules, the higher the boiling point, the lower the polarity (affinity with the extractive solvent). Consequently, a major portion of the measurable heavy (C 9  to C 12 ) HCs in the feedstock is rejected by the solvent phase in the LLE column and is removed with the raffinate phase as a pan of the non-aromatic product. 
     In an ED process for aromatics recovery, the heavy HCs tend to remain in the rich solvent at the bottom of the extractive distillation column (EDC) due to their high boiling points. Even for a narrow boiling-range (C 6 -C 7 ) feedstock, there can be measurable amounts of heavy (C) HCs that are trapped and accumulated in the solvent, which can only be removed from the solvent by increasing the severity of the SRC (higher temperature and vacuum level, and more stripping steam) and/or by increasing the loading of the SRG. Neither alternative is desirable. Moreover, for the full boiling-range (C 6 -C 8 ) feed, the boiling points of the heavy HCs are too high to be stripped from the solvent in the SRC and, as a result, they accumulated in the solvent as the solvent is circulated between the EDC and the SRC indefinitely in a closed loop. 
     The solvent regeneration of the Asselin scheme is not suitable for the ED process. The scheme was designed for LLE processes to remove minor amounts of polymeric materials generated from reactions between the oxidized or decomposed solvent components and traces of the heavy HCs in the solvent. When this scheme is applied to ED processes, heavy HCs inevitably accumulated and polymerized in the closed solvent loop until the polymerized materials reach boiling points that are higher that of sulfolane (&gt;285° C.) before they can be removed from the bottom of the solvent regenerator. This accumulation is potentially disastrous since the presence of excessive polymeric materials not only changes the solvent properties (selectivity and solvency) significantly but the polymers also plug process equipment to render the ED process inoperable. 
     SUMMARY OF THE INVENTION 
     The present invention is based in pan on the discovery that, among the heavy (C 9 -C 12 ) HCs, the C 9  aromatic compounds are most likely to be the only ones that are extracted by the solvent in the LLE column; most of the C 9  aromatics can then be stripped from the solvent in the SRC of the LLE process under normal operating conditions. In the ED process, however, these heavy hydrocarbons (HCs) remain in the rich solvent at the bottom of the EDC due to their high boiling points and quickly accumulate in the closed solvent loop. 
     The invention provides a method for cross connecting the lean solvent supply lines between the LLE and the ED processes. In this fashion, the LLE column becomes the outlet for removing the accumulated heavy HCs and polymeric materials (PMs) from the solvent loop of both processes to maintain their solvent performance. The invention takes advantage of the unique capability of the LLE column for rejecting the heavy HCs from the solvent as a way of removing the heavy HCs and PMs from the closed solvent loop of an ED process. The invention can be implemented by cross connecting their lean solvent loops together using low-cost revamping that requires only some piping changes to cross connect the lean solvent supply lines for the LLE column and the EDC. In other words, the revamp causes the SRC of LLE process to supply the lean solvent for the EDC, and the SRC of ED process to supply the lean solvent for LLE column. 
     The invention can also be implemented by incorporating, a simple mixing tank to combine the lean solvent generated from the SRC of the LLE process (containing reduced heavy HCs) and that of the ED process (containing higher heavy HCs). The mixed lean solvent supplies both the LLE column and the EDC. 
     In one aspect, the invention is directed to a method of integrating (i) a LLE process for producing polar HCs from mixtures comprising polar and less polar HCs wherein the LLE process employs (1) a LLE column into which a first HC feed containing polar and less polar HCs is introduced and from which a first water-containing, less polar HC-rich stream is recovered from a top of the LLE column and from which a first solvent-rich stream containing solvent, polar HCs, minor amounts of less polar HCs, and measurable but reduced heavy HCs and PMs is withdrawn from a bottom of the LLE column, (2) an extractive stripper column (ESC) into which the first solvent-rich stream is introduced and from which a less polar HC-rich stream but containing a significant of polar HCs is withdrawn from a top of the ESC and recycled to the lower portion of the LLE column as reflux and from which a second solvent-rich stream containing solvent, polar HCs, and measurable but reduced heavy HCs and PMs which is substantially free of less polar HCs is withdrawn from a bottom of the ESC and (3) a first solvent recovery column (SRC) into which the second solvent-rich stream is introduced and from which a first polar HC-rich stream, which is substantially free of solvent and less polar HCs is withdrawn and from which a third solvent-rich stream is withdrawn from a bottom of the first SRC and (ii) an extractive distillation (ED) process for producing, polar HCs from mixtures comprising polar and less polar HCs wherein ED process employs (1) an ED column into which a second HC feed containing polar and less polar HCs is introduced and from which a second water-containing, less polar HC-rich stream is recovered from a top of the EDC and from which a fourth solvent-rich stream containing solvent, polar HCs, and measurable heavy HCs and PMs is withdrawn from a bottom of the EDC (2) a second SRC into which the fourth solvent-rich stream is introduced and from which a second polar HD-rich stream, which is substantially free of solvent and less polar HCs is recovered and from which a fifth solvent-rich stream is withdrawn from a bottom of the second SRC, which method includes the steps of: 
     (a) diverting the majority portion (typically more than 90%) of the fifth solvent-rich stream into an upper portion of the LLE column as a selective solvent feed; 
     (b) diverting a minor portion (typically less than 10%) of the fifth solvent-rich stream into the ESC; and 
     (c) diverting the third solvent-rich stream into the ED column, thereby removing heavy hydrocarbons and polymeric materials from the fifth solvent-rich stream of the extractive distillation process which contains a polar HC selective solvent, measurable amounts of heavy HCs (typically 1-5 wt %), and polymeric materials that are generated from reactions among thermally decomposed or oxidized solvent, heavy HC&#39;s, and additives. 
     In another aspect, the invention is directed to a method for removing HCs and PMs from a solvent-rich stream of an ED process, containing a polar HC selective solvent, measurable amounts of heavy HCs, and PMs generated from reactions among; thermally decomposed or oxidized solvent, heavy HCs, and additives, by cross connecting said solvent-rich stream with that of an adjacent LLE process, which method includes the steps of: 
     (a) introducing a first HC feed containing polar and less polar HCs into a middle portion of a LLE column and introducing a major portion (typically more than 90%) of the fifth solvent-rich stream in step (g) into an upper portion of the LEE column as a selective solvent feed; 
     (b) recovering a first water-containing, less polar HC-rich stream from a top of the LLE column and withdrawing the first solvent-rich stream containing solvent, polar HCs, minor amounts (typically 10-20 wt %) of less polar Ms, and measurable but reduced heavy HCs and PMs (typically 0.1-1 wt %) from a bottom of the LLE column; 
     (c) introducing a mixture comprising the first solvent-rich stream and a minor portion (typically less than 10 wt %) of a fifth solvent-rich stream from step (g), into an upper portion of an extractive stripping column (ESC), recovering a HC-rich vapor containing less polar HCs and a significant amount of benzene and heavier aromatics (typically 30-50 wt %) from a top of the ESC, which is condensed and recycled to a lower portion of LLE column as the reflux, and withdrawing a second solvent-rich stream containing solvent, polar HCs, and measurable but reduced heavy HCs and PMs (typically 0.1 to 2 wt %) which is substantially free of less polar HCs, from a bottom of the ESC; 
     (d) introducing the second solvent-rich stream in step (c) into a middle portion of the first solvent recovery column (SRC-1), withdrawing a first polar HC-rich stream, which is substantially free of solvent and less polar HCs, from a top of the SRC-1, and removing a third solvent-rich stream from a bottom of the SRC-1; 
     (e) introducing a second HC teed containing polar and less polar HCs into a middle portion of an EDC and introducing a major portion of said third solvent-rich stream from step (d) into an upper portion of the EDC as a selective solvent feed; 
     (f) recovering a second water-containing, less polar HC-rich stream from a top of the EDC and withdrawing a fourth solvent-rich stream containing solvent, polar HCs, and measurable heavy HCs and PMs (typically 1-5 wt %) from a bottom of the EDC; 
     (g) introducing said fourth solvent-rich stream into a middle portion of a second solvent recovery column (SRC-2), recovering a second polar HC-rich stream, that is substantially free of solvent and less polar HCs, from a top of the SRC-2, and removing a fifth solvent-rich stream from a bottom of the SRC-2; and 
     (h) installing a transfer line between the third solvent-rich stream in step (d) and the fifth solvent-rich stream in step (g) to adjust the flow rate of the solvent-rich streams to the LLE column in step (a) and to the EDC in step (e). 
     In yet another aspect, the invention is directed to a method for removing heavy HCs and PMs from a solvent-rich stream of an ED process, containing, a polar HC selective solvent, measurable amounts of heavy HCs, and PMs generated from reactions among thermally decomposed or oxidized solvent, heavy HCs, and additives, by mixing of said solvent-rich stream with that of an adjacent LLE process, which method includes the steps of 
     (a) introducing a first HC feed containing polar and less polar HCs into a middle portion of a LLE column and introducing a portion of sixth solvent-rich stream from step (h) into an upper portion of the LLE column as a selective solvent feed; 
     (b) recovering a first water-containing, less polar HC-rich stream from a top of the LLE column and withdrawing a first solvent-rich stream containing solvent, polar HCs, minor amounts of less polar HCs (typically 10-20 wt %), and measurable but reduced heavy HCs and PMs (typically 0.1-1 wt %) from a bottom of the LLE column; 
     (c) introducing a mixture comprising the first solvent-rich stream and a minor portion of sixth solvent-rich stream from step (h), into an upper portion of an extractive stripping column (ESC), recovering a HC-rich vapor containing less polar HCs and a significant amount of benzene and heavier aromatics (typically 30-50 wt %) from a top of the ESC, which is condensed and recycled to a lower portion of LLE column as the reflux, and withdrawing a second solvent-rich stream containing solvent, polar HCs, and measurable but reduced heavy HCs and PMs (typically 0.1-2 wt %) which is substantially free of less polar HCs, from a bottom of the ESC; 
     (d) introducing the second solvent-rich stream in step (c) into a middle portion of the first solvent recovery column (SRC-1), withdrawing a first polar HC-rich stream, which is substantially free of solvent and less polar FICs, from a top of the SRC-1, and removing a third solvent-rich stream from a bottom of the SRC-1 and transferring said stream to a mixing tank; 
     (e) introducing a second HC feed containing polar and less polar HCs into a middle portion of an EDC and introducing a portion of sixth solvent-rich stream in step (h) into an upper portion of the EDC as a selective solvent feed; 
     (f) recovering a second water-containing, less polar HC-rich stream from a top of the EDC and withdrawing a fourth solvent-rich stream containing solvent, polar HCs, and measurable heavy HCs and PMs (typically 1-5 wt %) from a bottom of the EDC; 
     (g) introducing said fourth solvent-rich stream into a middle portion of a second solvent recovery column (SRC-2), recovering a second polar HC-rich stream, that is substantially free of solvent and less polar HCs, from a top of the SRC-2, and removing a fifth solvent-rich stream from a bottom of the SRC2 and transferring said stream to said mixing tank in step (d); and 
     (h) withdrawing a sixth solvent-rich stream from said mixing tank in step (d) and introducing a portion of said stream to the upper part of the LLE column in step (a) and another portion to the upper part of the EDC in step (e) as the solvent feeds, at predetermined flow rates. 
     The inventive processes are particularly suited for separation and recovery of aromatic HCs from mixtures containing aromatics and non-aromatics, including paraffins, isoparaffins, naphthenes, and/or olefins, but it is understood that the techniques are applicable to a multitude of HC mixtures. Suitable extractive solvents include, for example, sulfolane, alkyl-sulfolane, N-formyl morpholine, N-methylpyrrolidone, tetraethylene glycol, triethylene glycol, diethylene glycol, and mixtures thereof, with water as the co-solvent. For aromatic HC recovery, the most preferred solvent jointly use for both the ED and the KKE processes is sulfolane with water as the co-solvent. 
     The invention can be readily adapted to a large petrochemical complex that has existing, adjacent but separate LLE and ED processes that are using the same selective solvent, for producing purified polar HCs from the mixtures comprising polar and less-polar HCs generated from different sources. The invention affords a simple, low-cost method to take the advantage of the nature of the LLE and ED processes to simultaneously remove the heavy HCs and polymeric materials from both processes, 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of side-by-side LLE Process and ED Process (Base Case); 
         FIG. 2  is a schematic diagram of an LLE and ED processes with cross connection of lean solvent supply lines; and 
         FIG. 3  is a schematic diagram of LLE and ED processes that are connected with a common lean solvent supply tank, 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a side-by-side LLE process and ED process for aromatic HC recovery. The LLE process employs among other devices, a liquid-liquid extraction (LLE) column  100 , solvent recovery column 1 (SRC-1)  102 , solvent regenerator  128 , water washing column (WCC)  104 , and extractive stripper column (ESC)  106 . Sulfolane with water as co-solvent is used as the selective solvent. HC feed  1  containing a mixture of aromatics and non-aromatics is fed to a lower portion of the LLE column  100 , while lean solvent is introduced near the top of LLE column  100  via line  2  to counter-currently contact the HC feed. The aromatic HCs in the feed typically comprise benzene, toluene, ethylbenzene, xylenes, and C 9   +  aromatics and the non-aromatic hydrocarbons typical comprise C 5  to C 9   +  paraffins, naphthenes and olefins. 
     A raffinate phase containing essentially the non-aromatics (enriched in C 9   +  HCs) with a minor amount of solvent is withdrawn from the top of LLE column  100  and fed to a middle portion of the WWC  104  via line  3 . An extract phase (with reduced heavy HCs) from the bottom of LLE column  100  in line  4  is mixed with a secondary lean solvent from line  5 ; the combined stream  6  is fed to the top of ESC  106 . The vapor flow through ESC  106  is generated by the action of a bottom reboiler which is heated by steam at a rate that is sufficient to control the column bottom temperature, the overhead stream composition and the flow rate. Overhead vapor exiting the top of ESC  106  is condensed in a cooler (not shown) and the condensate is transferred to an overhead receiver  114 , which serves to elect a phase separation between the HC and the water phases. The HC phase, containing the non-aromatics and up to 30-40% benzene and heavier aromatics, is recycled, to a lower portion of LIE column  100  as reflux via line  7 . The water phase is transferred via line  115  to a steam generator  116  to generate a part of the stripping steam for SRC-1  102 . 
     Rich solvent consisting of the solvent, aromatics free of non-aromatics, and measurable amounts but reduced heavy HCs and polymeric materials is withdrawn from the bottom of ESC  106  and transferred to the middle portion of SRC-1  102  via line  11 . Stripping steam is injected through line  117  from steam generator  116  into a lower portion of the SRC-1  102  to assist the removal of aromatic HCs from the solvent. An aromatic concentrate, containing water and being substantially free of solvent and non-aromatic HCs, is withdrawn as an overhead vapor stream from SRC-1  102  and introduced into an overhead receiver  118  via line  12  after being condensed in a cooler (not shown). In order to minimize the bottom temperature of SRC-1  102 , overhead receiver  118  is connected to a vacuum source to generate sub-atmospheric conditions in SRC-1  102 . Overhead receiver  118  serves to effect a phase separation between the aromatic HC and the water phases. A portion of the aromatic HC phase is recycled to the top of SRC-1  102  as reflux via line  13 , while the remainder portion is withdrawn as aromatic HC product through line  14 . 
     The water phase that accumulates in the water leg, of overhead receiver  118  is fed via line  8  to WWC  104  as wash water at a location that is below the interface between the HC phase and the water phase near the top of WWC  104 . The solvent is removed from the LLE raffinate through a counter-current water wash and the solvent-free HCs, which accumulate in the HC phase of WWC  104 , are then withdrawn from the top of the column as solvent-free raffinate product through line  9 . A water phase, containing the solvent, exits through line  10  from the bottom of WWC  104  and is fed to steam generator  116  along with the water phase from ESC overhead receiver  114 , where the water is transformed into stripping steam that is introduced into the SRC-1 via line  117  and also into a thermal solvent regenerator  128 . The majority of the lean solvent (with reduced heavy HCs) from the bottom of the SRC-1  102  is recycled via lines  15  and  2  as a lean solvent feed that is supplied to an upper portion of LLE column  100  for extracting the aromatic HCs in the LLE column. A minor portion of said lean solvent is recycled through lines  15  and  5  as a secondary solvent for ESC. 
     Another minor portion of the lean solvent stream from the bottom of the SRC-1  102  is diverted into thermal solvent regenerator  128  and steam is introduced therein to assist the stripping of the solvent and heavy HCs from the sludge. To minimize the bottom temperature of solvent regenerator  128 , it is preferably operated under reduced pressure (vacuum). Still another minor portion of the lean solvent is heated in a reboiler and recycled to the bottom of SRC-1  102 . 
       FIG. 1  also depicts a separate ED process for aromatic HC recovery, which employs an extractive distillation column (EDC)  110 , solvent recovery column 2 (SRC-2)  112 , and thermal solvent regenerator  129 . Sulfolane with water is used as the selective solvent. HC feed  16  containing a mixture of aromatic and non-aromatic HCs is fed to the middle portion of EDC  110 , while a lean solvent from the bottom of SRC-2  112  is fed via line  24  to near the top of EDC  110  below the overhead reflux entry point for line  18 . 
     Non-aromatics vapor exiting the top of EDC  110  through line  17  is condensed in a condenser (not shown) and the condensate is transferred to an overhead receiver  120 , which serves to effect a phase separation between the non-aromatic HCs and the water phases. A portion of the non-aromatic HC phase is recycled to the top of EDC  110  as the reflux via lines  18  as a second portion is withdrawn as the raffinate product through line  19 . The water phase in line  121  from overhead receiver  120  and the water from SRC-2 overhead  122  via line  123  are transferred to a steam generator  124  to form stripping steam that is introduced into SRC-2  112  via line  25  and into solvent recovery generator  129 . The rich solvent stream containing the solvent, aromatics, and measurable levels of heavy HCs is withdrawn from the bottom of EDC  110 . A portion of the rich solvent is heated in an EDC reboiler (not shown) and recycled to the bottom of EDC  110  to generate vapor stream in the column, while the rest of the rich solvent is fed to the middle portion of SRC-2  112  through line  20 . 
     Stripping steam when injected via line  25  into the lower portion of SRC-2  112  assists in the removal of aromatic HCs from the solvent. An aromatic concentrate, containing water and which is substantially free of solvent and non-aromatic HCs, is withdrawn through line  21  as an overhead vapor stream from SRC-2  112 ; after the steam is condensed in a condenser (not shown) the liquid is introduced into an overhead receiver  122  which serves to effect a phase separation between the aromatic HC phase and the water phase. A portion of the aromatic HC phase is recycled to the top of SRC-2  112  as the reflux via line  22 , while the remaining portion is withdrawn as the aromatic HC product through line  23 . The water phase in stream  123 , along with the water from EDC overhead  120 , are transferred to a steam generator  124  to form stripping steam for SRC-2  112 . 
     In order to minimize the bottom temperature of SRC-2  112 , overhead receiver  122  is connected to a vacuum source to generate sub-atmospheric conditions in SRC-2  112 . A lean solvent stream containing measurable amounts of heavy HCs is withdrawn from the bottom of SRC-2  112 . The majority proportion thereof is recycled via line  24  as the lean solvent feed to the upper portion of EDC  110  for extracting the aromatic HCs in EDC  110 . A minor portion of the lean solvent stream from the bottom of the SRC-2  112  is diverted into thermal solvent regenerator  129  and steam is introduced therein to assist the stripping of the solvent and heavy HCs from the sludge. To minimize the bottom temperature of solvent regenerator  129 , it is preferably operated under reduced pressure (vacuum). Another minor portion of the lean solvent is heated in a reboiler and recycled to the bottom of SRC-2  112 . 
     In one embodiment of the invention for aromatic HC recovery, the above side-by-side LLE and ED processes are revamped with some piping changes to cross connect the lean solvent supply lines for the LLE column and the EDC, with no additional process equipment necessary. The modified integrated configuration causes the solvent recovery column of the LLE process to supply the lean solvent for the EDC, and the solvent recovery column of the ED process to supply the lean solvent for LLE column. 
     As shown in  FIG. 2 , in operation an HC feed  31  containing a mixture of aromatics and non-aromatics is fed to a lower portion of LLE column  130 , while lean solvent from the bottom of SRC-2  138  (the solvent recovery column for the ED process) is introduced near the top of LLE column  130  via lines  54 ,  57 , and  32  to counter-currently contact the HC feed. The aromatic HCs in the feed typically comprise benzene, toluene, ethylbenzene, xylenes, and C 9   +  aromatics and the non-aromatic HCs typical comprise C 1  to C 9   +  paraffins, naphthenes and olefins. 
     A raffinate phase containing essentially the non-aromatics (enriched in C 9   +  HCs) with a minor amount of solvent is withdrawn from the top of LLE column  130  and fed to a middle portion of WWC  134  via line  33 . An extract phase (with reduced heavy HCs and polymeric materials) from the bottom of LLE column  130  in line  34  is mixed with a secondary lean solvent from line  35 ; the combined stream  36  is fed to the top of ESC  136 . The vapor flow through ESC  136  is generated by the action of a bottom reboiler which is heated by steam at a rate that is sufficient to control the column bottom temperature, the overhead stream composition and the flow rate. Overhead vapor exiting the top of ESC  136  is condensed and the condensate is transferred to an overhead receiver  142 , which effects a phase separation between the HC and the water phases. The HC phase, containing the non-aromatics and up to 30-40% benzene and heavier aromatics, is recycled to the lower portion of LLE column  130  as reflux via line  37 . The water phase is transferred via line  143  to a steam generator  144  to generate stripping steam for SRC-1  132 . Rich solvent consisting of the solvent, aromatics free of non-aromatics, and measurable amounts but reduced heavy HCs and polymeric materials is withdrawn from the bottom of ESC  136  and transferred to the middle portion of SRC-1  132  via line  41 . Stripping steam is injected from steam generator  144  into a lower portion of SRC-1  132  via line  145  to assist in the removal of aromatic HCs from the solvent. An aromatic concentrate, containing water and being substantially free of solvent and non-aromatic HCs, is withdrawn as an overhead vapor stream from SRC-1  132  and introduced into an overhead receiver  146  via line  42  after being condensed. In order to minimize the bottom temperature of SRC-1132, overhead receiver  146  is connected to a vacuum source to generate sub-atmospheric conditions in SRC-1  132 . 
     Overhead receiver  146  effects a phase separation between the aromatic HC and the water phases. A portion of the aromatic HC phase is recycled to the top of SRC-1  132  as reflux via line  43 , while the remainder portion is withdrawn as aromatic HC product through line  44 . The water phase that accumulates in the water leg of overhead receiver  146  is fed via line  38  to the WWC  134  as wash water at a location below the interface between the HC phase and the water phase near the top of WWC  134 . The solvent is removed from the LLE raffinate through a counter-current water wash and the solvent-free HCs, which accumulate in the HC phase of WWC  134 , are then withdrawn from the top of the column as solvent-free raffinate product through line  39 . A water phase, containing the solvent, exits through line  40  from the bottom of WWC  134  and the water phase from ESC overhead receiver  142  via line  143  are fed to steam generator  144  where it is transformed into stripping steam that is introduced into the SRC-1  132  via line  145  and also into the thermal solvent regenerator  148 . 
     The majority of the lean solvent (with reduced heavy HCs and polymeric materials) from the bottom of SRC-1  132  is recycled via lines  45  and  56  to an upper portion of EDC  140 , instead of LLE column  130 , as the lean solvent feed. Another minor portion of the lean solvent stream from the bottom of SRC-1  132  is diverted into thermal solvent regenerator  148 . Steam is introduced into solvent regenerator  148  to assist the stripping of the solvent and heavy HCs from the sludge. It is preferable to operate solvent regenerator  148  under reduced pressure (vacuum) in order to minimize its bottom temperature. A still another minor portion of the lean solvent (not shown) is heated in a reboiler (not shown) and recycled to the bottom of SRC-1  132 . 
     As further shown in  FIG. 2 , an HC feed containing a mixture of aromatic and non-aromatic HCs is fed via line  46  to the middle portion of EDC  140 , while a lean solvent from the bottom of SRC-1  132  (the solvent recovery column for the LLE process) is fed via lines  45  and  56  to near the top of EDC  140  below the overhead reflux entry point of line  48 . 
     Non-aromatics vapor exiting the top of EDC  140  through line  47  is condensed and the condensate is transferred to an overhead receiver  150 , which effects a phase separation between the non-aromatic HC and the water phases. A portion of the non-aromatic HC phase is recycled to the top of EDC  140  as the reflux via lines  48  as a second portion is withdrawn as the raffinate product through line  49 . The water phase  151  from overhead receiver  150  and water stream  153  from SRC-2 overhead  152  are transferred to a steam generator  154  to form stripping steam that is introduced into SRC-2  138  via line  58  and into a solvent recovery generator  158 . The rich solvent stream containing the solvent, aromatics, and measurable levels of heavy HCs and PMs is withdrawn from the bottom of EDC  140 . A portion of the rich solvent is heated in an EDC reboiler and recycled to the bottom of EDC  140  to generate vapor stream in the column, while the rest of the rich solvent is fed to the middle portion of SRC-2  138  through line  50 . 
     Stripping steam when injected via line  58  into the lower portion of the SRC-2 assists in the removal of aromatic HCs from the solvent. An aromatic concentrate, containing water and which is substantially free of solvent and non-aromatic HCs, is withdrawn through line  51  as an overhead vapor stream from SRC-2  138  and after the vapor is condensed, the liquid is introduced into an overhead receiver  152 . The overhead receiver  152  effects a phase separation between the aromatic HC phase and the water phase. A portion of the aromatic HC phase from receiver  152  is recycled to the top of SRC-2  138  as the reflux via line  52 , while the remaining portion is withdrawn as the aromatic HC product through line  53 . The water phase  153  and water  151  from EDC overhead  150  are transferred to a steam generator  154  to form stripping steam for SRC-2  138 . 
     To minimize the bottom temperature of SRC-2  138 , overhead receiver  152  is connected to a vacuum source to generate sub-atmospheric conditions in SRC-2  138 . A lean solvent stream containing measurable amounts of heavy HCs and PMs is withdrawn from the bottom of SRC-2  138 . The majority thereof is recycled via lines  54 ,  57 , and  32  as the lean solvent feed to the upper portion of LLE column  130  for extracting the aromatic HCs; and a minor proportion is recycled via line  35  as a secondary solvent to ESC  136 . Another minor portion of the lean solvent stream from the bottom of SRC-2  138  is diverted into thermal solvent regenerator  158 . Steam is introduced into solvent regenerator  158  to assist the stripping of the solvent and heavy HCs from the sludge. It is preferable to operate solvent regenerator  158  under reduced pressure (vacuum) in order to minimize its bottom temperature. A still another minor portion of the lean solvent (not shown) is heated in a reboiler (not shown) and recycled to the bottom of SRC-2  138 . 
     For the process configuration in  FIG. 2 , the flow rate of the crossed lean feeds to LLE column and EDC is preferably adjusted with a crossover line (line  55 ) even if a similar amount of HC feedstock with similar composition is fed to each of the processes. This is because the LLE process and the ED process are operated under different Solvent-to-HC feed ratios (S/F). Thus, for example, if the S/F of LLE column  130  is higher than that of EDC  140 , line  55  moves lean solvent from line  45  to line  54 , and vice versa. 
     In another embodiment of the invention for aromatic HC recovery, the side-by-side LLE and ED processes depicted in  FIG. 1  are converted into the flow scheme as shown in  FIG. 3 , wherein a lean solvent mixing tank (ST)  178  is installed to mix the lean solvent that is generated from SRC-1  172  (of the LLE process) and SRC-2  182  (of the ED process). In this integrated configuration, LLE column  170 , ESC  176 , SRC-1  172 , WWC  174 , along with overhead receiver  214 , steam generator  216 , overhead receiver  218  and thermal solvent generator  228  in the LLE process generally operate in the same manner as their corresponding unit operations in the scheme shown in  FIG. 1 . Similarly, ED column  180 , SRC-2  182 , along with overhead receiver  210 , steam generator  224 , overhead receiver  222  and thermal solvent regenerator  229  in the ED process generally operate in the same manner as their corresponding unit operations in the scheme shown in  FIG. 1 . 
     In operation, as shown in  FIG. 3 , an HC feed containing a mixture of aromatics and non-aromatics is fed via line  71  to a lower portion of LLE column  170  while an HC feed containing a mixture of aromatics and non-aromatics is fed via line  86  to the middle portion of EDC  180 . In this modified process, a greater portion of the lean solvent from the bottom of SRC-1  172  is transferred to ST  178  via lines  95  and  97  whereas a greater portion of the lean solvent from the bottom of the SRC-2  182  is introduced to ST  178  through lines  96  and  97 . Subsequently, a common lean solvent feed, with reduced heavy HCs and PMs which is attributable to the function of LLE column  170  for removing the heavies, is fed to both LLE column  170  and EDC  180 . 
     EXAMPLES 
     Example 1 
     This example demonstrates that a major portion of the heavy (C 9   + ) HCs in the feed are removed in the liquid-liquid extraction (LLE) column by the raffinate stream. Only a minor portion of the C 9   +  HCs in the feed remains in the closed lean solvent loop and is eventually removed from the lean solvent through a solvent regenerator. This is one of the features that enable LLE process to recover benzene, toluene, and xylene (BTX) aromatics from the full-boiling range (C 6 -C 8 ) HC feed. All the data were generated from a process model which was upgraded with actual experimental data. 
     Referring to  FIG. 1 , a full-boiling range feed is fed to the lower portion of a LLE column via line  1 . The feed composition and flow rate are given in Table 1. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Hydrocarbon Feed Flow Rate: 50,000 Kg/Hr 
               
             
          
           
               
                   
                 n-Paraffins 
                 Isoparaffins  
                 Olefins 
                 Naphthenes 
                 Aromatics 
               
             
          
           
               
                   
                 (Unit in weight %) 
               
               
                   
               
             
          
           
               
                 C 5   −   
                 0.633 
                 0.558 
                 0.042 
                 0.294 
                 0.0 
               
               
                 C 6   
                 3.25 
                 3.904 
                 0.226 
                 4.470 
                 20.950 
               
               
                 C 7   
                 2.338 
                 7.758 
                 0.427 
                 2.043 
                 20.313 
               
               
                 C 8   
                 0.766 
                 1.796 
                 0.102 
                 0.772 
                 22.937 
               
               
                 C 9   
                 0.247 
                 0.574 
                 0.0 
                 0.188 
                 5.034 
               
               
                 C 10   
                 0.019 
                 0.092 
                 0.0 
                 0.04 
                 0.148 
               
               
                 C 11   
                 0.0 
                 0.0 
                 0.024 
                 0.0 
                 0.011 
               
               
                 C 12   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.037 
               
               
                   
               
             
          
         
       
     
     Lean solvent (sulfolane with water) from the bottom of the SRC column is fed to the upper portion of the LLE column via lines  15  and  2  under a pre-determined solvent-to-feed ratio. The raffinate stream is then withdrawn from the top of LLE column through line  3  and fed to the middle portion of a water washing column (WWC) to remove minor amount of sulfolane from the raffinate. The washing water is collected from overhead of the SRC and introduced into upper portion of the WWC via line  8 . The washed raffinate product is taken from overhead of the WWC through line  9 . The composition and flow rate of the raffinate product are presented in Table 2. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Raffinate Product Flow rate: 15,599 Kg/Hr 
               
             
          
           
               
                   
                 n-Paraffins  
                 Isoparaffins 
                 Olefins 
                 Naphthenes 
                 Aromatics 
               
             
          
           
               
                   
                 (Unit in weight %) 
               
               
                   
               
             
          
           
               
                 C 5   −   
                 2.029 
                 1.857 
                 0.128 
                 0.869 
                 0.0 
               
               
                 C 6   
                 11.072 
                 13.673 
                 0.59 
                 12.606 
                 0.066 
               
               
                 C 7   
                 7.681 
                 25.073 
                 1.559 
                 6.257 
                 0.024 
               
               
                 C 8   
                 2.458 
                 5.181 
                 0.243 
                 3.318 
                 0.165 
               
               
                 C 9   
                 0.797 
                 1.269 
                 0.0 
                 1.313 
                 1.041 
               
               
                 C 10   
                 0.022 
                 0.266 
                 0.0 
                 0.0 
                 0.311 
               
               
                 C 11   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.015 
               
               
                 C 12   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.058 
               
               
                   
               
             
          
         
       
     
     An extract stream of the LLE column is withdrawn from the bottom and fed to the top of an extractive stripper column (ESC) via lines  4  and  6 . Vapor of the light non-aromatic rich HCs is removed from the top of ESC and recycled to the lower portion of LLE column via line  7  after condensing and separating the water phase in a phase separator. Water from the phase separator is sent to a steam generator for generating a part of stripping steam for the SRC and the SRG. 
     Rich solvent is withdrawn from the bottom of ESC and sent to the middle of portion of the SRC through line  11 . As mentioned above, stripping steam generated from a steam generator is fed to lower portion of the SRC via line  117  to strip the aromatic HCs from the rich solvent. The vaporous aromatic HCs and steam are withdrawn from the top of SRC via line  12  and the extract (aromatic) product is taken from line  14  after condensing and separating the water phase in a phase separator (not shown), and after a portion of which is recycled to the SRC as the reflux via line  13 . Water from the phase separator is sent as washing water to the WWC through line  8 . The composition and flow rate of the extract product is summarized in Table 3. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Extract Product Flow rate: 34,083 Kg/Hr 
               
             
          
           
               
                   
                 n-Paraffins 
                 Isoparaffins 
                 Olefins 
                 Naphthenes 
                 Aromatics 
               
             
          
           
               
                   
                 (Unit in weight %) 
               
               
                   
               
             
          
           
               
                 C 6   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 30.363 
               
               
                 C 7   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 30.034 
               
               
                 C 8   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 33.514 
               
               
                 C 9   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 6.084 
               
               
                 C 10   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.005 
               
               
                 C 11   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
               
               
                 C 12   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
               
               
                   
               
             
          
         
       
     
     Based on the stream compositions and flow rates presented in Tables 1 to 3, the portion of heavy (C 9   + ) HCs removed by the raffinate stream of LLE column are summarized in Table 4. 
     
       
         
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 (Unit: Kg/Hr)  
                 % Removal 
               
             
          
           
               
                   
                 Feed 
                 Raffinate 
                 Extract 
                 Lean Solvent 
                 By Raffinate 
               
               
                   
               
             
          
           
               
                 C 9   
                 3021.5  
                 689.5 
                 2093.0 
                 239.1 
                 22.8* 
               
               
                 C 10   
                 149.5 
                 93.4 
                 1.7 
                 54.4 
                 62.5 
               
               
                 C 11   
                 17.5 
                 2.3 
                 0.0 
                 15.2 
                 13.4 
               
               
                 C 12   
                 18.5 
                 9.1 
                 0.0 
                 9.4 
                 48.9 
               
               
                 Total 
                 3207.0 
                 794.3 
                 2094.7 
                 318.1 
               
               
                   
               
               
                 *Although the raffinate stream removes only 22.8% C 9  HCs in the feed, roughly 69.3% C 9  HCs in the feed are stripped from the solvent as a part of the extract product and only 7.9% are left in the lean solvent. 
               
             
          
         
       
     
     As shown in Table 4, roughly 50 to 60% of C 10   +  HCs is removed by the raffinate stream of the LLE column, except C 11  HCs which contain only olefins (more polar than the paraffins) and aromatics (more polar compounds tend to stay in extract stream with sulfolane). The remaining portion of C 10   +  HCs circulates in the closed solvent loop until the HCs polymerized into heavier species having boiling point higher 285° C. (boiling point of sulfolane) and are removed as sludge from the bottom of a conventional thermal solvent regenerator. To continuously remove the sludge and the impurities generated from decomposed or oxidized sulfolane from the lean solvent, a split stream of the lean solvent is fed a thermal solvent regenerator, where sulfolane and lower boiling components were recovered under heating and steam stripping. 
     Example 2 
     This example demonstrates that, in recovering BTX aromatics from the full-boiling range (C 6 -C 8 ) HCs feed by an ED process, nearly all of the heavy (C 9   + ) HCs in the feed remains circulating in the closed lean solvent loop and cannot be removed from the loop until becoming heavier species having boiling point higher 285° C. (boiling point of sulfolane) through polymerization, which are then removed as sludge from the bottom of a solvent regenerator (SRG). All the data presented in this example were generated from a process model which was upgraded with actual experimental data from a continuous ED process for recovering BTX aromatics from a full-boiling range pyrolysis gasoline, disclosed in article: “Two Liquid-Phase Extractive Distillation for Aromatics Recovery”, Ind. Eng. Chem. Res. (26) No. 3, 564-573, 1987. 
     Referring to  FIG. 1 , a full-boiling range feed is fed to the middle portion of the extractive distillation column (EDC) via line  16 . The feed composition and flow rate are given in Table 1. Lean solvent (sulfolane with water) from the bottom of the SRC is fed to the upper portion of the EDC via line  24 , under a pre-determined solvent-to-feed ratio. The raffinate stream is then withdrawn from the top of EDC through line  17  through a condenser (not shown) into a phase separator (not shown) to decant the water phase. A portion of the raffinate is recycled to the EDC as the reflux via line  18  and the remaining portion is taken the raffinate product through line  19 . Composition and flow rate of the raffinate product is presented in Table 5. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Raffinate Product Flow rate: 14,815 Kg/Hr 
               
             
          
           
               
                   
                 n-Paraffins 
                 Isoparaffins 
                 Olefins 
                 Naphthenes 
                 Aromatics 
               
             
          
           
               
                   
                 (Unit in weight %) 
               
               
                   
               
             
          
           
               
                 C 5   −   
                 2.136 
                 1.955 
                 0.135 
                 0.915 
                 0.0 
               
               
                 C 6   
                 11.658 
                 14.397 
                 0.620 
                 13.274 
                 0.174 
               
               
                 C 7   
                 8.088 
                 26.401 
                 1.642 
                 6.588 
                 0.069 
               
               
                 C 8   
                 2.588 
                 5.455 
                 0.256 
                 3.494 
                 0.025 
               
               
                 C 9   
                 0.050 
                 0.080 
                 0.0 
                 0.020 
               
               
                   
               
             
          
         
       
     
     Rich solvent is withdrawn from the bottom of EDC and send to the middle of portion of the SRC through line  20 . The composition of the rich solvent is presented in Table 6 on a solvent-free basis. 
     
       
         
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                   
                 n-Paraffins 
                 Isoparaffins 
                 Olefins 
                 Naphthenes 
                 Aromatics 
               
             
          
           
               
                   
                 (Unit in weight % on Solvent-Free Basis) 
               
               
                   
               
             
          
           
               
                 C 6   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 29.458 
               
               
                 C 7   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 28.598 
               
               
                 C 8   
                 0.102 
                 0.0 
                 0.0 
                 0.158 
                 32.619 
               
               
                 C 9   
                 0.333 
                 0.782 
                 0.0 
                 0.259 
                 7.159 
               
               
                 C 10   
                 0.028 
                 0.131 
                 0.0 
                 0.057 
                 0.210 
               
               
                 C 11   
                 0.0 
                 0.0 
                 0.034 
                 0.0 
                 0.016 
               
               
                 C 12   
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.053 
               
               
                   
               
             
          
         
       
     
     As shown in Table 6, nearly all the heavy (C 9   + ) hydrocarbons in the feed stay at the bottom of the EDC with the rich solvent, while the raffinate stream from the top of the EDC contains only trace of C 9   +  hydrocarbons (see Table 5). In normal operations, the SRC is operated with stripping steam at a reboiler temperature in the range of 170 to 185° C. under a reduced pressure in the range of 0.4 to 0.7 atmospheric pressure. Higher temperatures would cause accelerated thermal decomposition of sulfolane (hourly decomposition rate is approximately 0.001 to 0.01% when temperatures exceed 200° C.). Under normal operating condition, the SRC overhead (aromatic) product contains all the C 6  to C 8  aromatics, a portion of C 9  aromatics, and trace of C 10  aromatics as shown in Table 3 in Example 1. Therefore, a portion of C 9  hydrocarbons and essentially all the C 10   +  hydrocarbons in the rich solvent as shown in Table 6, will stay at the bottom of the SRC with the lean solvent. For a ED process with 50,000 Kg/Hr throughput, the accumulation rate of C 9   +  HCs in the lean solvent loop is estimated to be 1,091 Kg/Hr (almost 3.5 times of the rate of the LLE process with same throughput). This amount of heavies in the lean solvent would overburden the conventional thermal solvent regenerator and could cause the solvent performance to deteriorate quickly rendering the ED process inoperable, even at much higher solvent regeneration rates.