Abstract:
Solvent regeneration to recover a polar hydrocarbon (HC) selective solvent substantially free of hydrocarbons (HCs) and other impurities from a solvent-rich stream containing selective solvent, heavy HCs, and polymeric materials (PMs) generated from reactions among thermally decomposed or oxidized solvent, heavy HCs, and additives is provided. A combination of displacement agent and associated co-displacement agent squeezes out the heavy HCs and PMs from the extractive solvent within a solvent clean-up zone. Simultaneously, a filter equipped with a magnetic field is positioned in a lean solvent circulation line to remove paramagnetic contaminants. The presence of the co-displacement agent significantly enhances the capability of the displacement agent in removing the heavy HCs and PMs from the extractive solvent. As a result, the solvent regeneration system operates under milder conditions and minimizes or eliminates the need for including a high temperature, energy intensive and difficult-to-operate thermal solvent regenerator.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/606,829 which was filed on Mar. 5, 2012. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to removing heavy hydrocarbons and polymeric sludge from a selective solvent after the solvent contacts a feed mixture containing aromatic and non-aromatic hydrocarbons and more particularly to solvent regeneration techniques whereby a co-displacement agent is used to enhance the capability of a primary displacement agent. 
       BACKGROUND OF THE INVENTION 
       [0003]    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 (PMs), that have boiling points higher than that of the solvent, are removed as sludge from the bottom of the solvent regenerator. 
         [0004]    U.S. Pat. No. 4,048,062 to Asselin discloses a 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 part of the non-aromatic product. 
         [0005]    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 9   + ) 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. 
         [0006]    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 PMs 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 PMs not only changes the solvent properties (selectivity and solvency) significantly but the polymers also plug process equipment to render the ED process inoperable. 
         [0007]    U.S. Pat. Nos. 7,666299 to Wu, et al. and 7,871,514 to Lee, et al. disclose a technique for removing heavies from solvent that is based on the observation that most of extractive solvents for ED and LLE are water soluble. In practice, a split solvent stream is introduced into a water washing zone and contacts a stream of process water, which is circulated in a closed loop. Solvent dissolves into the water phase while the heavy HCs and PMs are rejected by the water. In this fashion, the heavy HCs and PMs are removed from the solvent stream and accumulate in the HC phase. Because this water wash method requires much water, it is often difficult to achieve the proper balance and distribution of the process water in the closed system. 
         [0008]    U.S. Pat. No. 8,246,815 to Wu, et al. describes a method of removing heavy HCs and PMs that are trapped in the closed solvent loop in an ED or LLE process for aromatic HCs recovery. Light hydrocarbons, such as non-aromatic HCs in the raffinate stream, function as “displacement agents.” The light HCs “squeeze” the heavy HCs and PMs from the extractive solvent, especially when the heavy HCs in the solvent are in the C 9   30  molecular weight range. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is based in part on the development of techniques for using a co-displacement agent to significantly enhance the capability of a displacement agent in removing the heavy HCs and PMs from the extractive solvent. The novel methods are particularly suited for incorporation into processes wherein a feed mixture containing aromatic and non-aromatic HCs is contacted with a selective solvent in an extraction zone consisting of an extractive distillation column (EDC), liquid-liquid, extraction (LLE) column, or combination thereof. A rich solvent stream comprising the solvent and aromatic HC is generated and fed to a solvent recovery column or zone to recover the purified aromatic HCs and the lean solvent which contains solvent and measurable amounts of heavy HC&#39;s and polymeric sludge. 
         [0010]    In one aspect, the invention is directed to a method for recovering a polar HC selective solvent substantially free of HCs and other impurities from a solvent-rich stream containing the selective solvent, measurable amounts of heavy HCs, and PMs generated from reactions among thermally decomposed or oxidized solvent, heavy HCs, and additives, which method includes the steps of: 
         [0011]    (a) introducing a feed containing polar and less polar HCs into a middle portion of an extractive distillation column (EDC) and introducing a solvent-rich stream into an upper portion of the EDC as a selective solvent feed; 
         [0012]    (b) recovering a water-containing, less polar HC-rich stream from a top of the EDC and withdrawing a first solvent-rich stream containing solvent and polar HCs from a bottom of the EDC; 
         [0013]    (c) introducing the first solvent-rich stream into a middle portion of a solvent recovery column (SRC), recovering a polar HC-rich stream, that is substantially free of solvent and less polar HCs, from a top of the SRC, and removing a second solvent-rich stream from a bottom of the SRC; 
         [0014]    (d) introducing a first portion of the second solvent-rich stream into the upper portion of the EDC in step (a) as the selective solvent feed; 
         [0015]    (e) cooling a second portion of the second solvent-rich stream in step (c), mixing the cooled solvent-rich stream with a portion of water phase from step (h), and introducing the mixture into an upper portion of a solvent clean-up zone to form a solvent phase; 
         [0016]    (f) introducing a light HC-rich stream into a lower portion of the solvent clean-up zone, as a heavy HC displacement agent, to squeeze out heavy HCs and PMs from the solvent phase into a HC phase; 
         [0017]    (g) withdrawing an accumulated HC phase containing heavy HCs, PMs and minor amounts of solvent from an upper portion of the solvent clean-up zone, and recovering a solvent phase containing solvent and light HCs, which serves as heavy HC displacement agents, and has substantially reduced levels of heavy HCs and PMs, from a lower portion of the solvent clean-up zone; 
         [0018]    (h) introducing the HC phase from the solvent clean-up zone in step (g) into a water wash zone to remove the minor amounts of solvent from the HC phase into the water phase; and 
         [0019]    (i) introducing the solvent phase from the solvent clean-up zone in step (g) into a lower portion of the EDC in step (a) as part of a selective solvent feed to recycle purified solvent into a solvent loop. 
         [0020]    In another aspect, the invention is directed to a method for recovering a polar HC selective solvent substantially free of HCs and other impurities from a solvent-rich stream containing the selective solvent, measurable amounts of heavy HCs, and PMs generated from reactions among thermally decomposed or oxidized solvent, heavy HCs, and additives, which method includes the steps of: 
         [0021]    (a) introducing a feed containing polar and less polar HCs into a middle portion of a LLE column and introducing a solvent-rich stream into an upper portion of the LLE as a selective solvent feed; 
         [0022]    (b) recovering a 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 and minor amounts of less polar HCs from a bottom of the LLE; 
         [0023]    (c) introducing a mixture comprising the first solvent-rich stream and a minor portion of a third solvent-rich stream from a bottom of a solvent recovery column (SRC), 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, which is condensed and recycled to a lower portion of LLE column as the reflux, and withdrawing a second solvent-rich stream containing solvent and polar HCs, which is substantially free of less polar HCs, from a bottom of the ESC; 
         [0024]    (d) introducing the second solvent-rich stream in step (c) into a middle portion of the SRC, withdrawing a polar HC-rich stream, which is substantially free of solvent and non-polar HCs, from a top of the SRC, and removing a third solvent-rich stream from a bottom of the SRC; 
         [0025]    (e) introducing a portion of the third solvent-rich stream into the upper portion of the LLE column in step (a) as the selective solvent feed; 
         [0026]    (f) cooling a minor portion of the third solvent-rich stream in step (d), mixing the cooled solvent-rich stream with a portion of water phase from step (i), and introducing the mixture into an upper portion of a solvent clean-up zone to form a solvent phase; 
         [0027]    (g) introducing a light HC-rich stream into a lower portion of the solvent clean-up zone, as a heavy HC displacement agent, to squeeze out heavy HCs and PMs from the solvent phase into a HC phase; 
         [0028]    (h) withdrawing an accumulated MC phase containing heavy HCs, PMs, and minor amounts of solvent from an upper portion of the solvent clean-up zone and recovering the solvent phase containing solvent, light HCs, which serves as heavy hydrocarbon displacement agents, and having substantially reduced levels of heavy HCs and PMs, from a lower portion of the solvent clean-up zone; 
         [0029]    (i) introducing the HC phase from the solvent clean-up zone in step (h) into a water wash zone to remove the minor amounts of solvent from the HC phase into the water phase. 
         [0030]    (j) introducing the solvent phase from the solvent clean-up zone in step (h) into a lower portion of the ESC in step (c) as a way to recycle purified solvent into a solvent loop. 
         [0031]    A filter enhanced with a magnetic field can be installed in the lean solvent circulation line to work simultaneously with the solvent clean-up zone to remove paramagnetic contaminants in the lean solvent to minimize the function of or eliminate the need for a high temperature, energy intensive and difficult-to-operate thermal solvent regenerator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  illustrates an ED process with a solvent clean-up system that includes a counter-current extractor, a magnetically enhanced filter, and a thermal regenerator; 
           [0033]      FIG. 2  illustrates an ED process with a solvent clean-up system that includes a counter-current extractor and a magnetically enhanced filter; 
           [0034]      FIG. 3  illustrates a LLE process with a solvent clean-up system including a counter-current extractor, a magnetically enhanced filter, and a thermal regenerator; and 
           [0035]      FIG. 4  illustrates a LLE process with a solvent clean-up system including a counter-current extractor and a magnetically enhanced filter. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    The techniques of the present invention can be integration into an ED or LLE process for the selective separation and recovery of polar HCs from a mixture containing the polar and less polar HCs. The inventive processes will be described in relation to the separation and recovery of aromatic HCs from mixtures containing aromatics and non-aromatics, comprising paraffins, isoparaffins, naphthenes, and olefins, but it is understood that the techniques are applicable to a multitude of mixtures. Suitable extractive solvents include, for example, sulfolane, alkyl-sulfolane, N-formyl morpholine, N-methyl pyrrolidone, tetraethylene glycol, triethylene glycol, diethylene glycol, and mixtures thereof, with water as the co-solvent. For aromatic HC recovery, the preferred solvents for the ED process comprise sulfolane with water as the co-solvent and non-aqueous N-formyl morpholine; the preferred solvents for the LLE process comprise sulfolane and tetraethylene glycol and both with water as the co-solvent. The most preferred solvent for both the ED and LLE processes is sulfolane with water as the co-solvent. 
         [0037]    In one feature of the invention for aromatic HC recovery as depicted in  FIGS. 1 and 3 , a portion of the lean solvent in an ED or LLE process, which contains measurable amounts of heavy HCs and PMs, is withdrawn from the bottom of a solvent recovery column (SRC) and combined with regenerated solvent from an overhead of a thermal solvent regenerator. The combined lean solvent stream, after cooling, is then mixed with a slip water-rich stream from the bottom of the water wash column (WWC) (as co-displacement) and introduced into the solvent clean-up system or zone (SCZ). The SCZ preferably consists of a column with trays, packings or rotating discs, or a pulse column, or a multi-stage mixer/settlers. A portion of the raffinate stream from the EDC overhead in the ED process (or the LLE column overhead in the LLE process), is also fed to the SCZ to contact the mixed lean solvent stream with increased water content. 
         [0038]    Preferably, the raffinate stream, as a displacement agent, contacts the mixed solvent stream with increased water content, with the water being the co-displacement agent, in a counter-current fashion in order to squeeze out the heavy HCs and polymeric PMs from the solvent phase into the HC phase. The higher water content augments the raffinate stream in displacing the heavies from the solvent phase. The solvent phase, which contains essentially the solvent, most of the benzene and other aromatic components from the raffinate stream (the displacement agent), and much reduced levels of heavy HCs and PMs, is withdrawn continuously from the SCZ and fed into the lower portion of the EDC (or the lower portion of the extractive stripping column (ESC) of a LLE process), as a way to enhance the solvent selectivity in the single phase region in the EDC (or ESC) with increased water content (the co-displacement agent), to recycle purified solvent into the closed solvent loop, and to recover the aromatic HCs, especially benzene, which is lost to the raffinate stream. A HC phase from the SCZ, containing the “squeezed” heavy HC&#39;s and PMs as well as most of non-aromatic components in the raffinate stream, is removed continuously from the SCZ and fed to a WWC to remove any solvent in the HC phase. The SCZ is operated such that the benzene content of its HC phase after combining with the raffinate stream from the EDC (or LEE column), before or after the WWC, is controlled at a desirable level. For example, if the combined HC stream is used for gasoline blending, its benzene concentration should be below one volume percent. 
         [0039]    Alternatively, any desulfinized light HC mixture can be used to replace the EDC or LLE column raffinate stream as the displacement agent to remove the heavy HCs and PMs from the lean solvent. With the present invention, the incorporation of a SCZ to remove a substantial portion of the heavy HCs and PMs will greatly reduce the loading requirements of the thermal solvent regenerator, when the latter is employed, and renders the process easier to operate, especially for the ED process. 
         [0040]    A filter, preferably one that is enhanced with a magnetic field, can be installed in the solvent loop to selectively remove the paramagnetic contaminants generated from the interaction among decomposed solvent, various solvent additives and the heavy HCs with iron sulfides and iron oxides. Suitable filters with magnets are described in U.S. Pat. Publication Nos. 20090272702, 20100065504, 20120165551, and 20120228231, which are incorporated herein by reference. 
         [0041]    In another feature of the invention as depicted in  FIGS. 2 and 4 , a solvent regeneration scheme employs an efficient, low temperature and energy-saving solvent clean-up zone or system. The process does not require any high temperature and energy-intensive thermal solvent regenerator. A portion of a lean solvent stream that is withdrawn from the bottom of a SRC is diverted and, after cooling, combined with a water-rich slip stream from the bottom of the WWC (as a co-displacement agent), before introducing into a SCZ. A portion of raffinate stream from the overhead of the EDC in the ED process (or the LLE column in the LLE process) is also fed to the SCZ as a displacement agent, to contact said diverted lean solvent stream with increased water content. 
         [0042]    The solvent clean-up operation is typically conducted in a continuous multi-stage contacting device, and preferably in one that is designed for counter-current extraction. Suitable designs includes columns with trays, packings, or rotating discs, pulse columns, any other rotating type contactors, and multi-stage mixers/settlers. The solvent phase containing essentially the solvent, increased amount of water, most of aromatic components from the raffinate stream (the displacement agent), especially benzene, and much reduced levels of heavy HCs, is withdrawn continuously from the SCZ and fed to the lower portion of the EDC or ESC, as a way to enhance the solvent selectivity in the single phase region of the EDC (or the ESC), to recycle purified solvent into the closed solvent loop, and to recover the aromatic HCs, especially benzene, which is lost to the raffinate stream. The HC phase containing the “squeezed” heavy HCs and PMs is removed periodically from the SCZ. The SCZ is operated such that the benzene content of its HC phase after combining with the raffinate stream from the EDC (or LLE column), before or after the WWC, is controlled at a desirable level. 
         [0043]    Alternatively, any desulfurized light HC mixture can be used to replace the raffinate stream as the displacement agent remove heavy HCs and PMs from the lean solvent and to recover the aromatics from the raffinate stream, especially benzene. Again, a filter that is enhanced with a magnetic field can be installed in the solvent loop to selectively remove the paramagnetic contaminants from the lean solvent stream. 
         [0044]    In the above-described embodiments, since the C 9   +  heavy HCs are recovered from the lean solvent in the SCZ, the EDC in the ED process is preferably operated under further relaxed conditions by releasing the maximum allowable benzene to the overhead raffinate stream and by keeping substantially all C 9   +  HCs in the bottom of the EDC with the rich solvent (extract) stream. The SRC is preferably operated under such conditions as to strip only C 8  and lighter HCs from the rich solvent stream and to keep substantially all C 9  and heavier HCs in the bottom of the SRC with the lean solvent stream. 
         [0045]      FIG. 1  depicts an ED process for aromatic HCs recovery which employs an extractive distillation column (EDC)  300 , solvent recovery column (SRC)  302 , thermal solvent regenerator (SRG)  304 , solvent clean-up column (SCC)  310 , and water washing column (WCC)  314 . A HC feed containing aromatic and non-aromatic HCs is fed via line  1  to the middle portion of EDC  300 , while a lean solvent from the bottom of SRC  302  is fed via lines  16 ,  19 , and  22  to near the top of EDC  300  below the overhead reflux entry point for line  4 . 
         [0046]    Non-aromatics vapor exiting the top of EDC  300  through line  2  is condensed in a condenser (not shown) and the condensate is transferred to an overhead receiver D 1   316 , 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  300  as reflux via lines  3  and  4  and a second portion is withdrawn as the raffinate stream through line  5 . 
         [0047]    A part of the raffinate stream in line  5  is withdrawn as a raffinate product through lines  10  and  34 . A rich solvent consisting of solvent, aromatics free of non-aromatics, and measurable amounts of heavy HCs and PMs is withdrawn from the bottom of EDC  300  and transferred to the middle portion of SRC  302  via line  6 . Stripping steam is injected from steam generator SR 1   312  via line  27  into the lower portion of SRC  302  to assist in removing the aromatic HCs from the solvent. A portion of the rich solvent heated in reboiler R 1   320  and recycled to the bottom of EDC  300  via line  7 . An aromatic concentrate, containing water and being substantially free of solvent and non-aromatic HCs, is withdrawn as an overhead vapor stream from SRC  302  and introduced into an overhead receiver D 2   322  via line  11  after being condensed in a cooler (not shown). In order to minimize the bottom temperature of SRC  302 , receiver D 2   322  is connected to a vacuum source to generate sub-atmospheric conditions in SRC  302 . 
         [0048]    Overhead receiver D 2   322  serves to effect a phase separation between the aromatic HCs and the water phases. A portion of the aromatic HC phase in line  12  is recycled to the top of SRC  302  as reflux via line  13 , while the remaining portion is withdrawn as aromatic HC product through line  14 . The water phase that accumulates in the water leg of overhead receiver D 2   322  is fed via line  15  to WWC  314  as wash water at a location below the interface between the HC phase and the water phase near the top of WWC  314 . Solvent is removed from the HC phase from SCC  310  through a counter-current water wash and the solvent-free non-aromatics, which accumulate in the phase, are then withdrawn from the top of WWC  314  as solvent-free non-aromatic products through line  32 . A water phase, containing the solvent, exits through lines  33 ,  30  from the bottom of WWC  314  and is combined with line  8 , which is the water phase from overhead receiver D 1   316 , and is fed to SR 1   312  via line  26  where it is transformed into stripping steam that is introduced into SRC  302  via line  27  and into SRG  304  via line  24 . 
         [0049]    A greater proportion of the lean solvent from the bottom of SRC  302  is recycled through a magnetic enhanced filter MF  328  via lines  16 ,  19 , and  22  and is supplied to the upper portion of EDC  300  for extracting the aromatic HCs. A split stream of the lean solvent from the SRC bottom is diverted into SRG  304  via line  18  and steam is introduced into SRG  304  through line  24 , at a location below the lean solvent feed entry point. A portion of the lean solvent is heated in reboiler R 2   324  and recycled to the bottom of SRC  302  via line  17 . Deteriorated solvent and polymeric sludge are removed as a bottom stream through line  25 , while the regenerated solvent and substantially all the stripping steam, are recovered as an overhead stream  23 . This vapor in line  23  and a split lean solvent from the bottom of SRC  302  in line  20  are combined to form the mixture in line  21 , which contains the solvent, measurable amounts of heavy HCs and substantially all the stripping steam from SRG  304 . After cooling and condensing in the cooler C 1   318 , a slip water-rich stream from the bottom of WWC  314  is added to the stream in line  21  to provide a controlled amount of water via line  31  to the lean solvent stream as a co-displacement agent, which is then introduced into the upper portion of SCC  310  below the location of solvent/HC interface. 
         [0050]    A portion of the raffinate stream from EDC  300  is fed to the lower portion of SCC  310  via line  9  as the displacement agent to contact the solvent phase counter-currently to squeeze out the heavy HCs and PMs from the solvent phase into the HC phase in SCC  310 . Alternatively, any external desulfurized light HC stream can be used effectively as the displacement agent. A solvent phase containing essentially purified solvent, most of the aromatics components from the raffinate stream (the displacement agent), and substantially reduced levels of heavy HCs and PMs is continuously withdrawn from the bottom of SCC  310  and introduced through line  28  into the lower portion of EDC  300 , as a way of recycling the purified solvent into the solvent loop, to recover the aromatic HCs, especially benzene, which is lost to the raffinate stream, and to enhance the solvent selectivity in the single phase region of EDC  300  due to increased water content (the co-displacement agent) in the recycled solvent phase from SCC  310 . 
         [0051]    The HC phase accumulates continuously at the top of SCC  310  and is removed periodically from the overhead of SCC  310  and fed to WWC  314  via lines  29  under interface level control. The solvent clean-up operation can also be achieved by employing other contacting devices. Preferred apparatuses include continuous multi-stage contacting devices configured for counter-current extraction, such as multi-stage mixers/settlers or rotating type contactors. 
         [0052]    In an application of the ED process using sulfolane as the solvent, EDC  300  is operated at a reduced solvent-to-HC feed weight ratio of 2.0 to 4.0, preferably 1.5 to 3.0, depending upon the boiling range of the HC feedstock, to allow 1 to 10 wt %, preferably 2 to 5 wt % benzene in the raffinate stream from the EDC overhead. The temperature of the overhead vapor from SRG  304  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. The mixture comprising of solvent vapor from SRG  304  and lean solvent from SRC  302  is condensed and cooled in cooler C 1   318  to a temperature in the range of approximately 0 to 100° C., and preferably of 25 to 80° C. The temperature of the raffinate stream from EDC  300 , which is fed to SCC  310  as the displacement agent, ranges from 0 to 100° C., preferably from 25 to 50° C. The raffinate feed-to-lean solvent feed weight ratio in SCC  310  is typically from 0.1 to 100, and preferably from 0.1 to 10. The contacting temperature in SCC  310  typically ranges from 0° to 100° C., and preferably from 25 to 80° C. The operating pressure of SCC  310  typically ranges from 1 to 100 atm., and preferably from 1 to 10 atm. The weight ratio between the cooled solvent-rich stream mixture in line  21  and the water-rich stream in line  31  is in the range of 200:1 to 10:1, preferably in the range of 100:1 to 20:1; the desired ratio is achieved by adjusting the flow rate of the water-rich stream in line  31 . The solvent phase from SCC  310 , containing essentially all the solvent, the added amount of water, most of aromatic components from the raffinate stream (the displacement agent), especially benzene, and much reduced levels of heavy HCs and polymeric materials, is fed to the lower portion of EDC  300  to enhance the solvent selectivity in the single liquid phase region due to added water in the solvent phase. 
         [0053]    The operation conditions of the SCZ are preferably selected to achieve the following three main objectives: (1) The benzene content in the HC phase is at such a level that the benzene concentration in the raffinate stream through combination of lines  10  and  32  meets product specifications. For example, the benzene concentration in the raffinate stream in line  34  should below one volume percent for gasoline blending. (2) The content of heavy HCs and PM s in the solvent phase withdrawn in line  28  is kept at a desirable range to maintain the solvent performance. (3) The water content in the lean solvent feed to the SCZ is controlled by adjusting water addition in order to maximize the heavy HCs removal from the solvent phase and minimize benzene loss to the HC phase (raffinate product after water wash). 
         [0054]      FIG. 2  illustrates an ED process for aromatic HCs recovery in which SCC  340  uses the EDC raffinate, as the displacement agent, and the added water to the lean solvent, which functions the co-displacement agent, are employed to regenerate the solvent. The conventional high temperature and energy intensive thermal solvent regenerator is not required in this solvent regeneration scheme. This ED process employs extractive distillation column (EDC)  330 , solvent recovery column (SRC)  332 , a solvent clean-up column (SCC)  340 , water washing column (WWC)  344 , and inline magnetic filter (MF)  358 . 
         [0055]    A HC feed containing a mixture of aromatic and non-aromatic HCs is fed via line  41  to the middle portion of EDC  330 , while lean solvent from the bottom of SRC  332  is fed via lines  56 ,  58 , and  61  to near the top of EDC  330  below the overhead reflux entry point for line  44 . The lean solvent from SRC  332  can be filtered with a magnet-enhanced filter MF  358  that removes iron rust particulates and other polymeric sludge that are paramagnetic in nature. Non-aromatics vapor exiting the top of EDC  330  through line  42  is condensed in a condenser (not shown) and the condensate is transferred to an overhead receiver D 1   346 , which serves to effect a phase separation between the non-aromatic HCs and the water phases. A portion of the non-aromatic HC phase in line  43  is recycled to the top of EDC  330  as reflux via line  44  while a second portion is withdrawn as through line  45 . A part of the raffinate stream in line  45  is withdrawn as the raffinate product through lines  50  and  70 . 
         [0056]    A rich solvent consisting of the solvent, purified aromatics and measurable amounts of heavy HCs and PMs is withdrawn from the bottom of EDC  330  and transferred to the middle portion of SRC  332  via line  46 . Rich solvent is also heated in reboiler R 1   350  and recycled to the bottom of EDC  330  via line  47 . Stripping steam is injected from steam generator SR 1   342  via line  64  into the lower portion of SRC  332  to assist in the removal of aromatic HCs from the solvent. An aromatic concentrate, containing water and being substantially free of solvent and non-aromatics, is withdrawn as an overhead vapor stream from SRC  332  and introduced into an overhead receiver D 2   352  via line  51  after being Condensed in a cooler (not shown). In order to minimize the bottom temperature in SRC  332 , receiver D 2   352  is connected to a vacuum source to generate sub-atmospheric conditions in SRC  332 . 
         [0057]    Overhead receiver D 2   352  serves to effect a phase separation between the aromatic HC and the water phases. A portion of the aromatic HC phase in line  52  is recycled to the top of SRC  332  as reflux via line  53 , while the remainder portion is withdrawn as aromatic HC product through line  54 . A portion of the lean solvent from the bottom of SRC  332  is heated in the reboiler R 2   354  and recycled to the bottom of SRC  332  via line  57 . The majority of the lean solvent exiting from the bottom of SRC  332  is transferred into EDC  330  via lines  56 ,  58 , and  61 . 
         [0058]    The water phase that accumulates in the water leg of overhead receiver D 2   352  is fed via line  55  to WWC  344  as wash water at a location below the interface between the HC and the water phases near the top of WWC  344 . Solvent is removed from the HC phase from SCC  340  through a counter-current water wash and the solvent-free non-aromatics, which accumulate in the HC phase, are withdrawn from the top of WWC  344  as a product through lines  69  and  70 . A water phase, containing the solvent, exits through lines  62  and  67  from the bottom of WWC  344  and is combined with line  48  that is the water phase from overhead receiver D 1   346  and is fed to steam generator SR 1   342  via line  63  where it is transformed into stripping stem that is introduced into SRC  332  via line  64 . 
         [0059]    A split stream  59  of the lean solvent from SRC  332  in line  58  containing a measurable amount of heavy HCs is cooled in the cooler C 1   348 . After being cooling, a slip water-rich stream from the bottom of WWC  344  is then added via lines  62  and  68  to the stream  59  to form stream  60  to provide a controlled amount of water to the lean solvent stream as the co-displacement agent. This lean solvent stream with increased water content is introduced via line  60  into the upper portion of SCC  340  below the location of the solvent/HC interface. 
         [0060]    A portion of the raffinate stream from EDC  330  is fed to SCC  340  via line  49  to contact the solvent phase as the displacement agent to squeeze out the heavy HCs and PMs from the solvent phase into the HC phase in SCC  340 . A solvent phase, that contains essentially purified solvent, most of the aromatic components from the raffinate stream (the displacement agents), and substantially reduced levels of heavy HCs and PMs, is continuously withdrawn from lower portion of SCC  340  and introduced through line  65  to the lower portion of EDC  330  where the single liquid phase region exists. This is the way to recycle the purified solvent into the solvent loop, to recover the aromatic HCs, especially benzene, which is lost to the raffinate stream, and to improve the solvent selectivity in the single liquid phase region of EDC  330  due to higher water content in the solvent. 
         [0061]    The HC phase accumulating continuously at the top of SCC  340  is removed periodically from the overhead of SCC  340  and fed to WWC  344  via line  66 , where any solvent in the final raffinate product is removed. 
         [0062]    In an application of the ED process of  FIG. 2  using sulfolane as the solvent, the EDC is operated at a reduced solvent-to-HC feed weight ratio of 2.0 to 4.0, preferably 1.5 to 3.0, depending upon the boiling range of the HC feedstock, to allow 1 to 10 wt %, preferably 2 to 5 wt % benzene the raffinate stream from the EDC overhead. Preferably, the portion of the lean solvent that withdrawn from the bottom of SRC  332  and directed to cooler C 1   348  is cooled to a temperature typically in the range of approximately 0 to 100° C., and preferably of 25 to 80° C. Temperature of the raffinate stream fed to SCC  340  as the displacement agent ranges from 0 to 100° C., preferably from 25 to 50° C. In addition, raffinate feed-to-solvent feed weight ratio in SCC  340  typically ranges from 0.1 to 100, and preferably from 0.1 to 10. The contacting temperature in SCC  340  typically ruins 0 to 100° C. and preferably from 25 to 80° C. The operating pressure of SCC  340  typically is from 1 to 100 atm., and preferably from 1 to 10 atm. The weight ratio between the cooled solvent-rich stream mixture in line  59  and the water-rich stream in line  68  is in the range of 200:1 to 10:1 preferably in the range of 100:1 to 20:1, by adjusting the flow rate of the water-rich stream in line  68 . Again, operation condition of SCC  340  is selected to achieve the objectives outlined for the process of  FIG. 1 . 
         [0063]      FIG. 3  is a LLE process for aromatic HC recovery, employing liquid-liquid extraction (LLE) column  400 , solvent recovery column (SRC)  402 , solvent regenerator (SRG)  404 , solvent clean-up column (SCC)  406 , water washing column (WCC)  408 , extractive stripper column (ESC)  410  and inline magnetic filter (MF)  412 . A HC feed containing aromatics and non-aromatics is fed via line  102  to the middle portion of LLE column  400 , while lean solvent is introduced near the top of LLE column  400  via line  103  to counter-currently contact the HC feed. The aromatic HCs in the feed typically comprise benzene, toluene, ethylbenzene, xylenes, C 9   +  aromatics, and mixtures thereof, and the non-aromatic hydrocarbons typical comprise C 5  to C 9   +  paraffins, naphthenes, olefins, and mixtures thereof. 
         [0064]    A raffinate phase containing essentially the non-aromatics with minor amounts of solvent is withdrawn from the top of LLE column  400  as stream  104  and is fed to a middle portion of WWC  408  via line  132  after combining stream in line  130 . An extract phase from the bottom of LLE column  400  in line  105  is mixed with a secondary lean solvent from line  106 ; the combined stream  107  is fed to the top of ESC  410 . 
         [0065]    The vapor flow through ESC  410  is generated by the action of reboiler R 1   414 , whereby a portion of the rich solvent in the bottom is recycled to ESC  410  via line  111  through reboiler R 1   414  which is normally 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  410  is condensed in a cooler (not shown) and the condensate is transferred via line  108  to an overhead receiver D 1   416 , which serves to effect 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 LEE column  400  as reflux via line  109 . The water phase is transferred via lines  110  and  125  to steam generator SR 1   418  to generate stripping steam for SRC  402 . A rich solvent consisting of the solvent, aromatics free of non-aromatics, and measurable amounts of heavy HCs and PMs is withdrawn from the bottom of ESC  410  and transferred to the middle portion of SRC  402  via line  112 . Stripping steam is injected from steam generator SR 1   418  via line  126  into the lower portion of SRC  402  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  402  and introduced into an overhead receiver D 2   420  via line  113  after being condensed in a cooler (not shown). in order to minimize the bottom temperature of SRC  402 , overhead receiver D 2   420  is connected to a vacuum source to generate sub-atmospheric conditions in SRC  402 . 
         [0066]    Overhead receiver D 2   420  serves to effect a phase separation between the aromatic HC and the water phases. A portion of the aromatic HC phase in line  114  is recycled to the top of SRC  402  as reflux via line  115 , while the remainder portion is withdrawn as aromatic HC product through line  116 . The water phase that accumulates in the water leg of overhead receiver D 2   420  is fed via line  136  to WWC  408  as wash water at a location below the interface between the HC phase and the water phase near the top of WWC  408 . The solvent is removed from the LLE raffinate and the HC phase from SCC  406  through a counter-current water wash and the solvent-free non-aromatics, which accumulate in the HC phase, are then withdrawn from the top of WWC  408  as solvent-free non-aromatic products through line  137 . A water phase, containing the solvent, exits through lines  133  and  134  from the bottom of WWC  408  and is combined with line  110 , that is the water phase from overhead receiver D 1   416 , and is fed to steam generator SR 1   418  via line  125  where it is transformed into stripping steam that is introduced into SRC  402  via line  126  and into SRG  404  via line  122 . 
         [0067]    A greater proportion of the lean solvent from the bottom of SRC  402  is recycled through a magnetic enhanced filter MF  412  via lines  118 ,  120 ,  121  and  103  and is supplied to the upper portion of LLE column  400  for extracting the aromatic HCs in LLE column  400 . A split stream of the lean solvent from the SRC bottom is diverted into SRG  404  via line  119  and steam is introduced into SRG  404  through line  122 , at a location below the lean solvent feed entry point. A portion of the lean solvent is heated in reboiler R 2   422  and recycled to the bottom of SRC  402  via line  117 . Deteriorated solvent and polymeric sludge are removed as a bottom stream through line  124 , while the regenerated solvent and substantially all the stripping steam, are recovered as an overhead stream  123 . This vapor in line  123  and a split lean solvent from the bottom of SRC  402  in line  127  are combined to form the mixture in line  128 , which contains the solvent, a measurable amount of heavy HCs and substantially all the stripping steam from SRG  404 . In operation, after the vapor is cooled and condensed in cooler C 1   424 , a slip water-rich stream from the bottom of WWC  408  is added to the stream in line  128  to provide a controlled amount of water via line  135  to the lean solvent stream as a co-displacement agent. The mixture is then introduced into the upper portion of SCC  406  below the location of solvent/HC interface. 
         [0068]    A portion of the raffinate stream from the LLE column is fed to the lower portion of SCC  406  via line  129  as the displacement agent to contact the solvent phase counter-currently to squeeze out the heavy HCs and PMs from the solvent phase into the HC phase in SCC  406 . Alternatively, a external desulfurized light HC stream can be used effectively as the displacement agent. A solvent phase containing essentially purified solvent, most of the aromatics components from the raffinate stream (the displacement agent), and substantially reduced levels of heavy HCs and PMs is continuously withdrawn from the bottom of SCC  406  and introduced through line  131  into the lower portion of ESC  410 , to recycle the purified solvent into the solvent loop, to enhance the solvent selectivity in the single phase region of the ESC due to increased water content (the co-displacement agent) in the recycled solvent phase from SCC  406 . 
         [0069]    The HC phase that accumulates continuously at the top of SCC  406  is removed periodically from the overhead of SCC  406  via lines  130  under interface level control, which is then mixed with the raffinate stream from the overhead of LLE column  400  and fed via line  132  to WWC  408 . The solvent clean-up operation may also be conducted in any other continuous multi-stage contacting device, preferably one that is designed for counter-current extraction, such as multi-stage mixers/settlers, or any other rotating type contactors. 
         [0070]    In an application of the LLE process of  FIG. 3  using sulfolane as the solvent, the temperature of the overhead vapor from SRG  404  typically ranges from 150° to 200° C. and preferably from 160° to 180° C., under a pressure of 0.1. to 10 atm., and preferably of 0.1 to 0.8 atm. The mixture comprising of solvent vapor from SRC 1   404  and lean solvent from SRC  402  is condensed and cooled in the cooler C 1   424  to a temperature in the range of approximately 0 to 100° C., and preferably of 25 to 80° C. The temperature of the raffinate stream from LLE column  400 , which is fed to SCC  406  as the displacement agent, ranges from 0 to 100° C., preferably from 25 to 50° C. The raffinate feed-to-lean solvent feed weight ratio in SCC  406  is typically from 0.1 to 100, and preferably from 0.1 to 10. The contacting temperature in SCC  406  typically ranges from 0° to 100° C. and preferably from 25 to 80° C. The operating pressure of SCC  406  typically ranges from 1 to 100 atm., and preferably from 1 to 10 atm. The weight ratio between the cooled solvent-rich stream mixture in line  128  and the water-rich stream in line  135  is in the range of 200:1 to 10:1, preferably in the range of 100:1 to 20:1 and is achieved by adjusting the flow rate of the water-rich stream in line  135 . The operational requirements of SCC  406  are the same as for SCC  310  and SCC  340  for the schemes of  FIGS. 1 and 2 , respectively. 
         [0071]      FIG. 4  illustrates a LLE process for aromatic HCs recovery from the mixture containing aromatic HCs and non-aromatic HCs, in which a solvent clean-up column (SCC)  436  uses the raffinate from LLE column  430  as the displacement agent to regenerate the lean solvent. A high temperature and energy intensive conventional thermal regenerator is not required. 
         [0072]    The process employs liquid-liquid extraction (LLE) column  430 , solvent recovery column (SRC)  432 , solvent clean-up column (SCC)  436 , water washing column (WCC)  438 , extractive stripper column (ESC)  440 , and inline magnetic filter enhanced with magnetic field (MF)  442 . A HC feed containing aromatic and non-aromatics is fed via line  202  to the middle portion of LLE column  430 , while lean solvent is introduced near the top of LLE column  430  via line  203  to counter-currently contact the HC feed. A raffinate phase in stream  204  containing essentially the non-aromatics with minor amounts of solvent is withdrawn from the top of LLE column  430  and is fed to a middle portion of WWC  438  via line  227  after combining the stream in line  226 . An extract phase is transferred from the bottom of LLE column  430  via line  205  and is mixed with a secondary lean solvent from line  206 ; the combined stream  207  is fed to the top of ESC  440 . 
         [0073]    The vapor flow through ESC  440  is generated by the action of reboiler R 1   444 , whereby a portion of the rich solvent in bottom is recycled to ESC  440  via line  211  through reboiler R 1   444  which is normally 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  440  is condensed in a cooler and the condensate is transferred via line  208  to an overhead receiver D 1   446 , which serves to effect 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  430  as reflux via line  209 . The water phase is transferred via lines  210  and  221  to steam generator SR 1   448  to generate stripping steam for SRC  432 . A rich solvent consisting of the solvent, purified aromatics and measurable amounts of heavy HCs and PMs is withdrawn from the bottom of ESC  440  and transferred to the middle portion of SRC  432  via line  212 . Stripping steam is injected from steam generator SR 1   448  via line  222  into the lower portion of SRC  432  to assist in the removal of aromatic HCs from the solvent. An aromatic concentrate, containing water and being substantially free of solvent and non-aromatics, is withdrawn as an overhead vapor stream from SRC  432  and introduced into an overhead receiver D 2   450  via line  213  after being condensed in a cooler. In order to minimize the bottom temperature of SRC  432 , overhead receiver D 2   450  is connected to a vacuum source to generate sub-atmospheric conditions in SRC  432 . 
         [0074]    Overhead receiver D 2   450  serves to effect a phase separation between the aromatic HC and the water phases. A portion of the aromatic HC phase in line  214  is recycled to the top of SRC  432  as reflux via line  215 , while the remainder portion is withdrawn as aromatic HC product through line  216 . A portion of the lean solvent from the bottom of the SRC  432  is heated in the reboiler R 2   452  and recycled to the bottom of SRC  432  via line  217 . Preferably, the majority of the lean solvent exiting from the bottom of SRC  432  is transferred into LLE column  430  via lines  218 ,  220 , and  203 . 
         [0075]    The water phase that accumulates in the water leg of overhead receiver D 2   450  is fed via line  231  to WWC  438  as wash water at a location below the interface between the HC and the water phases near the top of WWC  438 . Solvent is removed from the LLE raffinate through a counter-current water wash and the solvent-free non-aromatics, which accumulate in the HC phase, are withdrawn from the top of WWC  438  as a product through line  232 . A water phase, containing the solvent, exits through lines  228  and  229  from the bottom of WWC  438  and is combined with line  210  that is the water phase from overhead receiver D 1   446  and is fed to steam generator SRI  448  via line  221  where it is transformed into stripping steam that is introduced into SRC  432  via line  222 . 
         [0076]    A split stream  219  of the lean solvent from SRC  432  in line  218  which contains measurable amounts of heavy HCs is cooled in cooler C 1   454 . A slip water-rich stream from the bottom of WWC  438  is then added via line  230  to stream  219  to form stream  223  which provides a controlled amount of water to the lean solvent stream as the a co-displacement agent. This lean solvent stream with enhanced water content is introduced via line  223  into the upper portion of SCC  436  below the location of the solvent/HC interface. 
         [0077]    A portion of the raffinate stream from LLE column  430  contacts the solvent phase as the displacement agent to squeeze out the heavy HCs and PMs from the solvent phase into the HC phase in the SCC. A solvent phase, that contains essentially purified solvent, most of the aromatic components from the raffinate stream (the displacement agents), and substantially reduced levels of heavy HCs and PMs, is continuously withdrawn from lower portion of SCC  436  and introduced through line  225  to the lower portion of ESC  440  where the single liquid phase region exists. This recycles the purified solvent into the solvent loop and to improve the solvent selectivity in the single liquid phase region of ESC  440  due to higher water content in the solvent. A filter MF  442  that is enhanced with a magnetic field is positioned in the main lean recycle line between SRC  432  and LLE column  430 . 
         [0078]    The HC phase which accumulates continuously at the top of SCC  436  and is removed periodically from the overhead of SCC  436  via line  226  under interface level control, which is then mixed with the raffinate stream from the overhead of LLE column  430  before being fed via line  227  to WWC  438  where any solvent in the final raffinate product is removed. 
         [0079]    In an application of the LLE process that is depicted in  FIG. 4  with sulfolane as the solvent, the portion of the lean solvent that withdrawn from the bottom of SRC  432  and directed to cooler C 1   454  is cooled to as temperature typically in the range of approximately 0 to 100° C., and preferably of 25 to 80° C. Temperature of the raffinate stream fed to SCC  436  as the displacement agent ranges from 0 to 100° C., preferably from 25 to 50° C. In addition, raffinate feed-to-solvent feed weight ratio in SCC  436  typically ranges from 0.1 to 100, and preferably from 0.1 to 10. The contacting temperature in the SCC typically ranges from 1 to 100° C., and preferably from 25 to 80° C. The operating pressure of SCC  436  typically is from 1 to 100 atm., and preferably from 1 to 10 atm. The weight ratio between the cooled solvent-rich stream mixture in line  219  and the water-rich stream in line  230  is in the range of 200:1 to 10:1, preferably in the range of 100:1 to 20:1, by adjusting the flow rate of the water-rich stream in line  230 . Operation conditions of SCC  436  are selected to achieve the objectives outlined in the process of  FIG. 1 .