Abstract:
Extractive distillation for recovering aromatic hydrocarbons employs an extractive distillation column with a novel overhead system including a partial condenser. The process enables (i) efficient removal of heavy non-aromatics, particularly C 8  naphthenic compounds, from the EDC bottom stream to increase the purity of aromatic products, especially of the mixed xylenes and (ii) reduction (or better control) of benzene loss to the raffinate product stream to maintain its quality as a gasoline blend stock and, as a result, enhance benzene recovery in the aromatic products. Feedstock includes a full-range feedstock, such as pyrolysis gasoline, or a narrow-range feedstock, such as reformate.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to techniques for recovering aromatic hydrocarbons from mixtures containing aromatic and non-aromatic hydrocarbons and particularly to methods that employ an extractive distillation column with a novel overhead system. 
     BACKGROUND OF THE INVENTION 
     Recovering aromatic hydrocarbons from mixtures containing the aromatic and non-aromatic hydrocarbons (HCs) can be achieved with liquid-liquid extraction (LLE) or extractive distillation (ED). In ED, a nonvolatile polar solvent is added to an extractive distillation column (EDC) to increase the relative volatility between the more-polar and less-polar components that have close-boiling points. In general, the solvent is added to the upper portion of the EDC and a hydrocarbon (HC) feed is introduced to the middle portion of the EDC. As the nonvolatile solvent descends through the column, it preferentially extracts the more-polar components to form a rich solvent that moves toward the bottom of the EDC while the less-polar component vapor ascends to the top. The overhead vapor is condensed and a portion of the condensate is recycled to the top of the EDC as reflux and the other portion of the condensate is withdrawn as raffinate product. The rich solvent containing the solvent and the more-polar components is fed to a solvent recovery column (SRC) to recover (i) the more-polar components as the overhead product and (ii) the lean solvent (free of the feed components) as the bottom product, which is recycled to the upper portion of the EDC. A portion of the overhead product is recycled to the top of the SRC as the reflux to knock down any entrained solvent in the overhead vapor. The SRC is optionally operated under reduced pressure (vacuum) and/or with a stripping medium to lower the column bottom temperature. 
     ED processes for recovering aromatic HCs are described in U.S. Pat. No. 7,078,580 to Tian et al., U.S. Pat. No. 4,053,369 to Cines, and F. Lee, et al., “Two Liquid-Phase Extractive Distillation for Aromatics Recovery,” Ind. Eng. Chem. Res. (26) No. 3, 564-573, 1987. 
     Although the ED process is simpler to implement than the LLE process, ED has a number of crucial operational limitations. For instance, the ED process is more restricted by the boiling range of the feedstock than is the LLE process. In order to achieve acceptable aromatic HCs purity and recovery, the solvent needs to keep essentially all the benzene (which is the heavy key with the lightest aromatic compound boiling at 80.1° C.) at the EDC bottom thereby driving virtually all of the heaviest non-aromatics into the overhead of the EDC. For a narrow boiling-range (C 6 -C 7 ) aromatic feedstock, the non-aromatic components (the light key) are the C 7  naphthenes, such as ethylcyclopentane (boiling point of 103.5° C.). For a full boiling-range (C 6 -C 8 ) aromatic feedstock, the non-aromatic components (the light key) are the C 8  naphthenes, such as ethylcyclohexane (boiling point of 131.8° C.). These compounds become the light key components not only because of their higher boiling points but also because of their stronger tendency to stay with the solvent and aromatic compounds due to their higher polarity as compared to other non-aromatic compounds in the feed. It is much more difficult to recover benzene, toluene and xylenes (BTX) aromatics from the full boiling-range feedstock, such as the full range pyrolysis gasoline, than to recover benzene and toluene from the narrow boiling-range feedstock, such as the C 6 -C 7  reformate. However, even a well defined narrow boiling-range feedstock contains at least two percent of C 8  hydrocarbons including C 8  aromatics and naphthenes. 
     SUMMARY OF THE INVENTION 
     It has been shown that in prior art ED processes, the level of naphthenic impurities in the C 8  aromatic product is noticeably higher than that produced by the LLE process. High concentrations of C 8   +  naphthenic impurities can cause significant problems in the subsequent xylene isomerization and purification units in p-xylene production. This presents a challenge to ED technology, especially for the BTX aromatics production from a full-range (C 6 -C 8 ) feedstock. The present invention recognizes the importance of reducing the naphthenes content in the aromatics product, especially in C 8  aromatics. 
     The present invention provides a novel EDC configuration and attendant operations to significantly improve the removal of heavy non-aromatics, especially the C 8  naphthenic compounds, from the EDC bottom solvent-rich stream in order to enhance the purity of aromatic products, especially of C 8  aromatic HCs. The inventive aromatic recovery process reduces (or controls) benzene loss to the EDC overhead raffinate (non-aromatic) product stream so as to maintain its quality as a suitable gasoline blend stock and thus increase recovery of benzene in the aromatic product. The efficiency of the lower section of the modified EDC is superior to conventional EDCs. The invention is based, in part, on the recognition improved aromatics recovery can be achieved by adding a solvent-rich stream to the overhead system to extract benzene in the EDC overhead raffinate stream, recycling the solvent phase to the lower portion of the EDC, and withdrawing the hydrocarbon phase as the overhead product after traces of solvent are removed. 
     In conventional EDC operations, benzene is essentially the only aromatic HC that is lost to the EDC overhead raffinate stream due to its low boiling point. With the present ED process, benzene in the EDC overhead raffinate stream is extracted by a solvent-rich stream and recycled to a lower portion of the EDC, so more heavy non-aromatic HCs, especially C 8  naphthenes, is driven to the EDC overhead without concern with the loss of benzene from the aromatic product stream that is withdrawn from the bottom of the EDC. 
     Therefore, the present invention provides an improved EDC operation for the ED process to recover benzene, toluene and xylenes and C 8  aromatic HCs from a full-range feedstock, such as pyrolysis gasoline, or from a narrow-range feedstock, such as reformate. The amount of heavy non-aromatic HCs, especially C 8  naphthenes, in the aromatic products is significantly reduced thereby enhancing the purity of the mixed xylenes to levels comparable to those produced by the LLE process. 
     In one aspect, the invention is directed to an ED process with improved configurations and operations in the EDC for recovering aromatic HCs with reduced non-aromatic HC contaminants, and increased benzene recovery from a HC feed mixture comprising aromatic and non-aromatic HCs, which process includes the steps of: 
     (a) introducing a feed containing aromatic and non-aromatic HCs into a middle portion of an EDC and introducing a first solvent-rich stream containing essentially the solvent and water into an upper portion of the EDC as a selective solvent feed; 
     (b) withdrawing a non-aromatic HCs-rich stream containing water, non-aromatic HCs, benzene, and trace of other aromatic HCs from a top of the EDC and recovering a second solvent-rich stream containing the solvent, aromatic HCs and trace of non-aromatic HCs from a bottom of the EDC; 
     (c) mixing a third solvent-rich stream having the same composition as the first solvent-rich stream, with said non-aromatic HCs-rich stream in step (b) to generate a solvent phase and a raffinate phase. 
     (d) recycling the solvent phase in step (c) containing, benzene, water, and trace of other aromatic HCs to a lower portion of the EDC. 
     (e) withdrawing at least a portion of the raffinate phase in step (c) as the raffinate product after water washing to remove trace of the solvent; and recycling the other portion to a top of the EDC as a reflux. 
     (f) introducing the second solvent-rich stream in step (b) into a middle portion of a solvent recovery column (SRC), recovering an aromatic HCs-rich stream, that is substantially free of solvent and non-aromatic HCs, from a top of the SRC, and removing a fourth solvent-rich stream containing essentially the solvent and water from a bottom of the SRC; 
     (g) introducing a major portion of said fourth solvent-rich stream (first solvent-rich stream) into an upper portion of the EDC in step (a) as a selective solvent feed; mixing a minor portion of said fourth solvent-rich stream (third solvent-rich stream) with said non-aromatic HCs-rich stream in step (b); and introducing another minor portion of said fourth solvent-rich stream (fifth solvent-rich stream) into an upper portion of a thermal solvent regeneration zone, removing heavy sludge from a lower portion of the solvent regeneration zone, and recovering a sixth solvent-rich stream containing solvent, water, and hydrocarbons and other compounds having boiling points below that of the solvent, from a top of the solvent regeneration zone for recycling to a lower portion of the SRC in step (f). 
     In another aspect, this invention is directed to an ED process with improved configurations and operations in the EDC for recovering aromatic HCs with reduced non-aromatic HC contaminants, and increased benzene recovery from a hydrocarbon HC feed mixture of aromatic and non-aromatic HCs, which process includes the steps of: 
     (a) introducing a feed containing aromatic and non-aromatic HCs into a middle portion of an EDC and introducing a first solvent-rich stream containing essentially the solvent and water into an upper portion of the EDC as a selective solvent feed; 
     (b) withdrawing a non-aromatic HCs-rich stream containing water, non-aromatic HCs, benzene, and trace of other aromatic HCs from a top of the EDC and recovering a second solvent-rich stream containing the solvent and aromatic HCs from a bottom of the EDC; 
     (c) partially condensing a non-aromatic HCs-rich stream from a top of the EDC in step (b) to partially remove water and heavier HCs to form a water and heavier HCs reduced non-aromatic HCs-rich stream; 
     (d) mixing a third solvent-rich stream having the same composition as said first solvent-rich stream, with the water and heavier HCs reduced non-aromatic HCs-rich stream in step (c) and introducing the mixture to an EDC overhead system to generate a solvent phase and a raffinate phase. 
     (e) recycling the solvent phase in step (d) containing, benzene, water, and trace of other aromatic HCs to a lower portion of the EDC. 
     (f) withdrawing at least a portion of the raffinate phase in step (d) as the raffinate product after water washing to remove trace of the solvent; and recycling the other portion to a top of the EDC as a reflux. 
     (g) introducing the second solvent-rich stream in step (b) into a middle portion of a solvent recovery column (SRC), recovering an aromatic HCs-rich stream, that is substantially free of solvent and non-aromatic HCs, from a top of the SRC, and removing a fourth solvent-rich stream containing essentially the solvent and water from a bottom of the SRC; 
     (h) introducing a major portion of said fourth solvent-rich stream (first solvent-rich stream) into an upper portion of the EDC in step (a) as a selective solvent feed; mixing a minor portion of said fourth solvent-rich stream (third solvent-rich stream) with the water and heavier HCs reduced non-aromatic HCs-rich stream in step (c); and introducing another minor portion of said fourth solvent-rich stream (fifth solvent-rich stream) into an upper portion of a thermal solvent regeneration zone, removing heavy sludge from a lower portion of the solvent regeneration zone, and recovering a sixth solvent-rich stream containing solvent, water, and HCs and other compounds having boiling points below that of the solvent, from a top of the solvent regeneration zone for recycling to a lower portion of the SRC in step (g). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a process for extracting benzene from the EDC overhead raffinate stream in an in-line static mixer, allowing increased removal of heavy naphthenes from the EDC bottom solvent-rich stream for improving C 8  aromatic purity and benzene recovery; and 
         FIG. 2  illustrates a process for extracting benzene from the EDC overhead raffinate stream with reduced water content in the solvent in an in-line static mixer, allowing increased removal of heavy naphthenes from the EDC bottom solvent-rich stream for improving C 8  aromatic purity and benzene recovery. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Testing results on full-range feedstock demonstrate that with prior art ED processes the content of non-aromatic HCs (consisting mostly C 8  naphthenic HCs) in the aromatic extract product is in the range of 0.4 to 0.7 wt % thereby generating a C 8  aromatic product with purity below 98.5 wt % (which is a minimum purity requirement). In contrast, with similar feedstock, LLE processes yield an extract product with less than 0.1 wt % non-aromatic HCs. 
     It is generally recognized that the solubility of hydrocarbons in sulfolane or other polar solvent is in sequence of: Aromatics&gt;&gt;Naphthenes&gt;Olefins&gt;Paraffins. In other words, the solubility of aromatics is significantly higher than that of naphthenes. Therefore, a feature of the present invention for reducing naphthenic HCs in aromatic product is to incorporate a secondary solvent to the EDC overhead stream to preferentially extract benzene and other aromatic components in the stream to form a solvent phase, leaving most of the naphthenes and other less polar non-aromatic components in the raffinate phase to be withdrawn as the raffinate product after a water wash to remove traces of solvent. 
     The solvent phase is then recycled to the EDC to recover mainly benzene and minor amounts of other aromatic compounds. This adaptation allows the EDC reboiler to drive more, if not all, of the heavy non-aromatics, especially C 8  naphthenes (the light key component) to the EDC overhead, without concerned with loss of benzene (the heavy key component) from the EDC bottom rich solvent stream. Indeed, benzene recovery is improved and controlled since most benzene loss to the EDC overhead is recovered by recycling the benzene extracted with the secondary solvent. 
     Normally, the water content is controlled in the lean solvent which is fed to near the top of the EDC. As the high-boiling (non-volatile) solvent flowing down the EDC, low-boiling water in the lean solvent is vaporized and raised to the top of the EDC. Therefore, water content in the solvent is highest at the top and lowest at the bottom of the column. Since water is an anti-solvent, this means that the solvent mixture at the top has the lowest solubility (highest selectivity) and the top is where the less soluble non-aromatic HCs are concentrated. Conversely, the solvent mixture at the bottom has the highest solubility (lowest selectivity) and the bottom is where the highly soluble aromatic HCs are present. This water concentration profile is very undesirable. 
     Since less soluble non-aromatic HCs are concentrated in the upper portion of the EDC, the undesired two liquid phases are present in the upper portion of the EDC when ED solvent such as sulfolane is used. Co-solvent such as water can be beneficial or detrimental to the selectivity of the ED solvent such as sulfolane. Under a single liquid phase, selectivity of sulfolane solvent is significantly enhanced as its water content increased from 0 to 5 wt %. However, the reverse is true when two liquid phases are present. Therefore, selection of the location in EDC to recycle the solvent phase is important to the EDC operation, especially when this solvent phase contains more water than the solvent feed (water in solvent feed plus at least a part of water in the EDC overhead). With the present invention, the EDC overhead stream and the secondary solvent can be mixed in a static mixer or in a multi-stage contactor such as multi-stage mixer/settler. 
     It is conceivable that adding solvent containing more water to the lower portion of EDC will reverse the undesirable water concentration profile in the EDC. This should lead to better column performance with a reduction in the C 8   +  naphthenic content in the aromatic product that is withdrawn from the bottom of the EDC. 
       FIG. 1  depicts an aromatics recovery process that employs an extractive distillation column (EDC)  40 , solvent recovery column (SRC)  48 , thermal solvent regenerator (SRG)  46 , water wash column (WWC)  45  and inline static mixer (SM)  43 . Alternatively, instead of the SM, a multi-stage contactor can be employed. A full-range HC feedstock or a narrow-range HC feedstock is fed via line  1  to the middle portion of EDC  40 . The full-range feedstock comprises C 6 -C 8  aromatics including benzene, toluene, ethylbenzene and xylenes, and C 6 -C 8  non-aromatics including paraffins, naphthenes and olefins. The narrow-range feedstock comprises C 6 -C 7  aromatics including benzene, toluene and less than 2% C 8  aromatic HCs, and C 6 -C 7  non-aromatic HCs comprising paraffins, naphthenes, and olefins. A major portion of the fourth solvent-rich stream (the first solvent-rich stream) from the bottom of SRC  48  is fed via lines  31 ,  2  and  3  to near the top of EDC  40  below the overhead reflux entry point for line  8 . Typically, 50 to 95 wt % and preferably 90 to 95 wt % of the fourth solvent-rich stream is diverted. The first solvent-rich stream, which enters the EDC, contains an extractive distillation solvent which comprises sulfolane, alkyl-sulfolane, N-formyl morpholine, N-methyl pyrrolidone, tetraethylene glycol, triethylene glycol, diethylene glycol, and mixtures thereof, and preferably with water as the co-solvent. The preferred solvent is sulfolane with up to 5 wt % water and preferably up to 1 wt % water. 
     The EDC reboiler  41  is operated to drive essentially all of the C 8  naphthenes from the second solvent-rich stream from the EDC bottom, without being restricted by the benzene loss from the second-rich stream. The amount of first solvent-rich stream added to the top of the EDC and the EDC reboiler temperature are adjusted to control the benzene content in the EDC overhead raffinate stream in the range of 0 to 10 wt % and preferably 0 to 5 wt %. 
     Non-aromatics vapor exiting the top of EDC  40  through line  5  is condensed in condenser  42  and the condensate is fed to SM  43  to mix with a third solvent-rich stream having the same composition as the first solvent-rich solvent from line  4 . The mixture from SM  43  is fed via line  6  to an overhead receiver  44 , which serves to effect a phase separation between the raffinate (non-aromatic HCs) and the solvent phases, wherein the benzene content in the raffinate phase is preferably in the range of 0.1 to 1.0 wt %. 
     A portion of the raffinate phase is recycled to the top of EDC  40  as reflux via lines  7  and  8  and a second portion is transferred to a lower portion of WWC  45  through lines  7  and  9 . Since the stream in line  8  contains increased amounts of C 8  naphthenes, the reflux ratio should be minimized to 0.25 or less so as to avoid introducing excess C 8  naphthenes into EDC  40 . Water is withdrawn from SRC overhead receiver  49  via lines  22  and  23 , and is fed to an upper portion of WWC  45 , to counter-currently contact with the raffinate stream from receiver  44  in line  9  for removing any trace amount of solvent. Solvent-free raffinate product is then withdrawn from the top of WWC  45  via line  12 . The benzene level in the raffinate product is typically 0.1 to 1.0 wt %. A water phase from WWC  45  containing traces of solvent is transferred from the bottom via lines  13  and  16 , and combined with the water from receiver  49  through lines  22  and  24 . The combined stream is fed to a steam generator (SR)  47  via line  25  to generate stripping steam that is then fed to a lower portion of SRC  48  through line  30 . 
     A solvent phase is withdrawn from receiver  44  via line  10  and combined with a water make-up stream  14 , if required, to form a mixed stream in line  15  which is recycled to the single liquid phase region in a lower portion of the EDC  40  to recover the extracted benzene and provide additional solvent for enhancing the EDC operation. The C 8  naphthenes content in the rich solvent from the bottom of EDC  40  is reduced not only by the presence of additional solvent, but also by the higher solvent water content in the single liquid phase region which promotes solvent selectivity. 
     A second rich-solvent consisting of solvent, aromatic HCs, and reduced amounts of non-aromatic HCs (mainly C 8   +  naphthenes) is withdrawn from the bottom of EDC  40  and transferred to the middle portion of SRC  48 , which is equipped with reboiler  50 , via line  11 . The volume ratio between the first solvent-rich stream and the HC feedstock steam varies in the range of 1.0 to 5.0 and preferably 2.0 to 4.0. This ratio is adjusting along with the EDC reboiler temperature in order to control the concentration of the C 8   +  naphthenes in the second solvent-rich stream to be within the range 0.1 to 1.0 wt % and preferably 0.1 to 0.5 wt %, after being stripped of solvent in SRC  48 . The second solvent-rich stream is transferred to the middle portion of SRC via line  11 . Stripping steam is injected from steam generator SR  47  via line  30  into the lower portion of SRC  48  to assist in removing the aromatic HCs from the solvent. An aromatic concentrate, containing water and being substantially free of solvent and typically having no more than 1.0 wt % and preferably no more than 0.5 wt % C 8  naphthenes and other non-aromatic HCs, is withdrawn as an overhead vapor stream from SRC  48  and introduced into an overhead receiver  49  via line  17  after being condensed in a condenser (not shown). In order to minimize the bottom temperature of SRC  48 , overhead receiver  49  is connected to a vacuum source via line  18  to generate sub-atmospheric conditions in SRC  48 . 
     Overhead receiver  49  serves to effect a phase separation between the aromatic HCs and the water phases. A portion of the aromatic HC phase in line  19  is recycled to the top of SRC  48  as reflux via line  20 , while the remaining portion is withdrawn as aromatic HC product with reduced C 8  naphthenes through line  21 . A part of water phase that accumulates in the water leg of overhead receiver  49  is fed via lines  22 ,  24  and  25  to steam generator SR  47  to produce stripping steam for SRC  48 . The other part of water phase is introduced to an upper portion of WWC  45  via lines  22  and  23  to remove the trace of solvent from receiver  44  raffinate stream and produce a solvent-free raffinate stream containing less than 1 wt % benzene via line  12  suitable for gasoline blending. 
     A major portion of the fourth solvent-rich stream (the first solvent-rich stream) from the bottom of SRC is recycled via lines  31 ,  2  and  3  to upper portion of EDC  40  for extracting the aromatic HCs. Typically 50 to 95 wt % and preferably 90 to 95 wt % of the fourth solvent-rich stream is diverted to form line  3 . A minor portion of the fourth solvent-rich stream (the third solvent-rich stream) is fed via line  4  to inline SM  43  to extract benzene and minor amount of other aromatics. Typically 1 to 10 wt % and preferably 1 to 5 wt % of the fourth solvent-rich stream is diverted to form line  4 . A split stream of the fourth solvent-rich stream (the fifth solvent-rich stream) from SRC  48  bottom is diverted into SRG  46  via line  26  and steam is introduced into SRG  48  through line  28 , at a location below the lean solvent feed entry point. Typically 1 to 5 wt % of the fourth solvent-rich stream is diverted to form line  26 . Deteriorated solvent and polymeric sludge are removed as a bottom stream of SRG  46  through line  29 , while the regenerated solvent and substantially all the stripping steam, are recovered as an overhead stream  27  and recycled to the lower portion of SRC  48  via line  30 . 
     In an application of the ED process of  FIG. 1  with sulfolane as the solvent, EDC  40  is operated at a solvent-to-HC feed volume ratio of 1.0 to 5.0, preferably 2.0 to 4.0, depending upon the boiling range of the HC feedstock, to allow 0 to 10 wt %, preferably 0 to 5 wt % benzene in the EDC overhead raffinate stream by adjusting the reboiler temperature and the solvent-to-HC feed volume ratio. In extracting the benzene in the EDC overhead raffinate stream, the ratio of the third solvent-rich stream in line  4  to the first solvent-rich stream in line  3  is in the range of 0.1 to 1.0 and preferably 0.01 to 0.1. The water content in the recycled solvent stream in line  15  is in the range of 5 to 25 wt %, depending upon the ratio of the third solvent-rich stream to the first solvent-rich stream. 
     The temperature of the overhead vapor from SRG  46  typically ranges from 150° to 200° C., and preferably from 160° to 180° C., under a pressure of 0.1 to 10 atmospheres, and preferably of 0.1 to 0.8 atm. SRC  48  is typically operated with stripping steam at a reboiler temperature in the range of 170° to 185° C. under a reduced pressure in the range of 0.4-0.7 atmospheric pressure. Higher temperatures would cause accelerated thermal decomposition of sulfolane (hourly decomposition rate is 0.001 to 0.1% when temperatures exceed 200° C.). 
       FIG. 2  depicts another aromatics recovery process that employs an extractive distillation column (EDC)  60 , solvent recovery column (SRC)  68 , thermal solvent regenerator (SRG)  66 , water wash column (WWC)  65  and inline static mixer (SM)  63 . The flow scheme also incorporates a partial condenser  70  that removes a part of water and heavier non-aromatic HCs, especially C 8  naphthenes from the EDC  60  overhead raffinate stream. This process can accommodate the same feed mixtures and use the same solvents as employed with the scheme of  FIG. 1 . 
     As a co-solvent, the presence of water strongly affects solvent selectivity and solvency and thus water influences the effectiveness of benzene extraction in inline static mixer SM  63 . The addition of partial condenser  70  also reduces the amount of heavier non-aromatic HCs, especially C 8  naphthenes, in the reflux in line  90 . This improves the performance of the upper portion of EDC  60  where two liquid phases exist and assists in the removal of C 8  naphthenes from the EDC  60  bottom aromatic product. 
     Referring to  FIG. 2 , an HC feedstock is fed via line  81  to the middle portion of EDC  60 , while a major portion of the fourth solvent-rich stream (the first solvent-rich stream) from the bottom of SRC  68 , which is equipped with reboiler  114 , is fed as the solvent feed via lines  113 ,  82  and  83  to near the top of EDC  60  below the overhead reflux entry point for line  90 . Typically, 50 to 95 wt % and preferably 90 to 95 wt % of the fourth solvent-rich stream is diverted to form line  83 . EDC reboiler  61  is operated to drive essentially all the C 8  naphthenes from the second solvent-rich stream from the EDC  60  bottom, without being restricted by the benzene loss from the second solvent-rich stream. The amount of first solvent-rich stream introduced to the top of EDC  60  and the reboiler temperature are adjusted in order to control the benzene content in the EDC  60  overhead raffinate stream to be within the range of 0 to 10 wt % and preferably 0 to 5 wt %. 
     Non-aromatics vapor exiting the top of EDC  60  through line  85  is partially condensed in a partial condenser  70  and the condensate containing mainly water and heavier non-aromatic HCs, especially C 8  naphthenes, is fed to a lower portion WWC  65  via line  86 . Uncondensed vapor from partial condenser  70  containing mainly benzene, lighter non-aromatic HCs, and having a lowered water content is introduced to a total condenser  62  through line  87 , and the condensate is fed to SM  63  to mix with a third solvent-rich stream (a split stream from the first solvent-rich solvent) from line  84 . Typically 1 to 10 wt % and preferably 1 to 5 wt % of the fourth solvent-rich stream is diverted to form line  84 . Instead of SM  63 , a multi-stage contactor can be employed. The mixture from SM  63  is transferred to an overhead receiver  64  via line  88 , which serves to effect a phase separation between the raffinate (non-aromatic HCs) and the solvent phases, wherein the benzene level in the raffinate phase should be in the range of 0.1 to 1.0 wt %. 
     A portion of the raffinate phase is recycled to the top of EDC  60  as reflux via lines  89  and  90  and a second portion is transferred to a lower portion of WWC  65  through lines  89  and  91 . Water is withdrawn from SRC overhead receiver  69  via lines  104  and  105  and is fed to an upper portion of WWC  65 . The water counter-currently contacts the raffinate stream from overhead receiver  64  in line  91  and the condensate from partial condenser  70  in line  86  to remove trace amounts of solvent and produce a solvent-free raffinate stream containing less than 1 wt % benzene via line  94  which is suitable for gasoline blending. A water phase containing traces of solvent from WWC  65  is transferred from the bottom via lines  95  and  98 , and combined with the water from overhead receiver  69  through lines  104  and  106 . The combined stream is fed to a steam generator SR  67  via line  107  to generate stripping steam to be fed to a lower portion of SRC  68  through line  112 . 
     A solvent phase is withdrawn from overhead receiver  64  via line  92  and combined with a water make-up stream  96 , if required, to form a mixed stream in line  97  which is recycled to the single liquid phase region in a lower portion of the EDC  60  to recover the extracted benzene and provide additional solvent for enhancing the EDC  60  operation. 
     In an application of the ED process of  FIG. 2  with sulfolane as the solvent, EDC  60  is operated at a solvent-to-HC feed volume ratio of 1.0 to 5.0 and preferably 2.0 to 4.0, depending upon the boiling range of the HC feedstock. The process yields 0 to 10 wt % and preferably 0 to 5 wt % benzene in the EDC overhead raffinate stream  85  by adjusting the reboiler  61  temperature and the solvent-to-HC feed volume ratio. The EDC operations simultaneously controls the concentration of C 8  naphthenes in the second solvent-rich stream from the bottom of EDC  60  for generating an aromatic concentrate containing 0.1 to 1.0 wt % and preferably 0.1 to 0.5 wt % C 8  naphthenes. In extracting the benzene in EDC overhead raffinate stream  85 , the ratio of the third solvent-rich stream in line  84  to the first solvent-rich stream in line  83  is preferably in the range of 0.01 to 0.1. The partial overhead condenser  70  removes at least a part of the water in EDC overhead raffinate stream  85 . The water content in the recycled solvent stream in line  97  is reduced and controlled at a preferred range of 1 to 5 wt %, depending upon operating condition of partial condenser  70  as well as the ratio of the third solvent-rich stream to the first solvent-rich stream. The ratio of the third solvent-rich stream to first solvent-rich stream is typically ranges from 0.01 to 1 and preferably from 0.01 to 0.1. 
     In this integrated configuration of  FIG. 2 , the solvent recovery column, water washing column, solvent regenerator generally operate in the same manner as their corresponding unit operations in the scheme shown in  FIG. 1 . As a corollary, SRG  66  and attendants lines  109 ,  110  and  111  operate in the same manner as SRG  46  and lines  27 ,  28  and  29  of  FIG. 1 , respectively. Similarly, overhead receiver  69  and attendant lines  99 ,  100 ,  101 ,  102 ,  103  and  104  operate in the same manner as overhead receiver  49  and attendant lines  17 ,  18 ,  19 ,  20 ,  21 , and  22  of  FIG. 1 , respectively.