SOLVENT REGENERATION METHODS

FIELD OF THE IN VENTION

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

in extractive distillation (ED) and liquid-liquid extraction (LLE) processes for aroma tics 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.

U.S. Patent 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 (S G). 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 ((¾ to Cn) 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-aroma tic 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 (Ce-C?) feedstock, there can be measurable amounts of heavy (Q> ⁺ ) 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 le vel and more stripping steam) and/or by increasing the loading of the SRGL Neither alternative is desirable. Moreover, for the full boiling-range (C<,-Q) 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 regeneratio 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 sol vent components and traces of the heav HCs in the sol vent. When this scheme is applied to ED processes, heavy HCs inevitably accumulated and polymerized in the closed solvent loo until the polymerized materials reach, boiling points that are higher that of sulfolane (> 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.

U.S. Patents 7,666,299 to Wu, et a!. and 7,871 ,514 to Lee. et at, disclose a technique for temovwm heavies from solvent that is based on the observation that most of extractive solvents tor 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 ate rejected by the water. m 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.

5 U.S. Patent 8,246,81 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 raffmate stream, function as "displacement agents." The light HCs "squeeze" the heavy HCs and PMs from the extractive solvent, especially when the heaw HCs in the solvent are in the tV molecular wei.aht ran¾e.

10

SUMMARY OF THE INVENTION

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 foi ^¬ l s incorporation into processes wherei a feed mixture containing aromatic and non-aromatic HCs is contacted with a selective solvent in an. extraction, zone consisima 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 0 measurable amounts of heavy HCs and polymeric sludge.

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:

5 (a) introducing a teed 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;

(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;

(c) introducing the first sol vent-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 ^" ;

(d) introducing a first portion of the second solvent-rich stream into the upper portion of the EDC i step (a) as the selective solvent feed;

(e) cooling a second portion of the second solvent-rich stream in step (c), mixing the cooled solvent-rich stream wit 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;

(f) introducing a light HC-rich stream into a lower portion of the solvent clean-up zone, as a heavy HC displacement agent, to sqtieeze out heavy HCs and PMs from the solvent phase into a HC phase;

(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 ami light HCs, which serves as heav HC displacement agents, and has substantially reduced levels of heavy HCs and PMs, from a lower portion of the solvent clean-up zone;

(h) introducing the HC phas 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

(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 seieciive solvent feed to recycle purified solvent into a solvent loop.

Sri 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 FMs generated from reactions among thermally decomposed or oxidized solvent, heavy HCs, and additives, which method includes the steps of:

(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;

(b) recovering a water-containing, less polar HC-rich stream, from a top of die L LE 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 ;

(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 aroraatics, 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 substantiall 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 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;

(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;

(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;

(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 P s from the solvent phase into a HC phase;

(h) 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 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;

(j) 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.

(j) introducing the solvent phase from the solvent clean-up zone in step ( ) into a lower portion of the ESC in step (c) as a way to recycle purified solvent into a solvent loop.

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

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;

Fig. 2 illustrates an ED process with a solvent clean-up system that includes a counter-current extractor and a magnetically enhanced filter;

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

Fig. 4 illustrates a LLE process with a solvent clean-tip system including a counter-current extractor and a magnetically enhanced filter. DETAILED DESCRI PTION OF THE INVENTION

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 b described in relation to the separation and recovery of aromatic HCs from raixtuxes containing aromatics and non-aromatics, comprising paraffins, isoparaffms, naphthenes, and olefins, but it is understood that the techniques are applicable to a multitude of HC mixtures. Suitable extractive solvents include, for example, sulfolane, alkyS~sul.foi.ane, N-formyl nioq holine, N-methyl pyrrolidone, tetraethy!ene glycol, methylene glycol, diethylene glycol, and mixtures thereof, with water as the co-solvent. For aromatic HC recovery, the preferred solvents for the ED proces comprise sulfolane with water as the co-solvent and non-aqueous N-formyi morpholine; the preferred solvents fo 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.

In one feature of the invention for aromatic EC recovery as depicted in Figs, I and 3, a portion of the lean solvent in an ED or LL E 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 o 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.

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 a d 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 stopping 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 raffmate stream. A HC phase from the SCZ, containing the "squeezed" heavy HCs 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 raffmate stream from the EDC (or LLE 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.

Al ernatively, any desulfurized light HC mixture can be used to replace the EDC or LLE column raffmate stream as the displacement agent to remove the heavy HCs and PMs from the lean sol vent. 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.

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 sol vent additives and the heavy HCs with iron sulfides and iro oxides. Suitable filters with magnets are described in U.S. Pat. Publication Nos. 20090272702, 20100065504, 20120165551 , and 201.20228231, which are incorporated herein by reference.

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 n the LLE process) is also fed to the SCZ as a displacement agent, to contact said diverted lean solvent stream with increased water content.

The solvent clean-op 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 wa ter, most of aromatic compon en ts from the raffinate stream, (the displacement agent), especially benzene, and much .reduced levels of hea vy 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.

Alternatively, any desul.furiz.ed light EC mixture can. be used to replace the raffinate. stream as the displacement agent to 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 lea solvent stream.

in the above-described embodiments, since the CV heav HCs are recovered from the lean solvent in the SCZ, the EDC in the ED process is preferabiy operated under further relaxed conditions by releasing the maximum allowable benzene to the overhead raffinate stream and by keeping substantially all CV 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 £¾ and lighter HCs from the rich, solvent stream and to keep substantially ah &> and heavier HCs in the botiom of the S C with the lean solvent stream.

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 colum (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, 1 , and 22 to near the top of EDC 300 below the overhead reflux entry point for line 4.

on-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 Dl 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 Hoes 3 and 4 and a second portion is withdrawn as the raffinate stream through line 5.

A part of the raffniate stream in Sine 5 is withdrawn as a raffinate product through lines 10 and 34. A rich, solvent consisiinu of solvent, aromatics free of non-aromatics, and measurable amounts of heavy HCs and PM is withdraw 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 S I 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 is heated in rehoile l 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 D2 322 via line 1 1 after being condensed in a cooler (not shown). In order to minimize the bottom temperature of SRC 302, receiver D2 322 is connected to a vacuum source to generate sub-atmospheric conditions in SRC 302,

Overhead eceiver D2 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 D2 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 H phase from SCC 310 through a counter-current water wash and the solvent-free non-aromatics, which accumuiate in the HC phase, are then withdrawn from the top of WWC 314 as sol vent-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 Dl. 316, and is fed to SRI 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.

A greater proportion of the lean solvent from the bottom of SRC 302 is recycled through a magnetic enhanced filter MP 328 via lines 16, 1 , 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 solven t is heated in rehoiler 2 324 and recycled to the bottom of SRC 302 via line 17. Deteriorated sol vent 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 S G 304. After cooling and condensing in the cooler Cl 318, a slip water-rich stream from the bottom of WWC 3 14 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 3 10 below the location of solveni HC interface.

A portion of the raffinate stream from EDC 300 is fed to the lowe portion of SCC 3 10 via l ine 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 desulfijrized light HC stream can be used effectively as the displacement agent. A solvent phase containing essentially purified solvent, most of the aroraaiics 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 31 .

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 continuou multi-stage contacting devices configured for counter-current extraction, such as multistage mixers/settlers or rotating type contactors.

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 L5 to 3.0, depending upon the boiling range of the HC feedstock, to allow 1 to 10 wt%, preferably 2 to 5 t% benzene in the raffinate stream from the E.DC overhead The temperature of the overhead vapor from SRG 304 typically ranges from 150° to 200° C, and preferably from 160° to 1 80° C, under a pressure of 0.1 to 10 atmospheres, and preferably of 0.1 to 0.8 aim. The mixture comprising of solvent vapor from SRG 304 and lean solvent from SRC 302 is condensed and cooled in cooler C i 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, whic is fed to SCC 10 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 31 is typically from 0.1 to 1 0, and preferably from 0.1 to 10. The contacting temperature in SCC 310 typically ranges from 0° to 1 0" C, and preferably from 25 to 80° C. The operating pressure of SCC 310 typically ranges from 1 to 100 arm., 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 regio due to added water in the solvent phase.

The operation conditions of the SCZ are preferably selected to achieve the following three main objectives: (! ) 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 i the raffinate stream i line 34 should below one volume percent for gasoline blending. (2) The content of heavy HCs and PMs. 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).

Fig. 2 illustrates an ED process for aromatic HCs recovery in which SCC 340 uses the EDC raffinate, as the displacemem 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, solven recovery column (SRC) 332, a solvent clean-up column (SCC) 340, water washing column (WWC) 344. and inline magnetic filter (MF) 358.

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 Sean solvent from the bottom of SRC 332 is fed via lines 56, 58, and 61 to near the to 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. N n-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 Dl. 346, which serves to effec 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 withdra wn as the rafimate product through lines 50 and 70.

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 rehoiler R l 350 and recycled to he bottom of EDC 330 via line 47. Stripping steam is injected from steam generator SRI 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 substantiall tree of solvent and non-aromattcs, is withdrawn as an overhead vapor stream from SRC 332 and introduced into an overhead receiver D2 352 via line 51 after being condensed in a cooler (not shown). In order to minimize the bottom temperature in SRC 332, receiver D2 352 is connected to a vacuum source to generate sub-atmospheric conditions in SRC 332.

Overhead receiver D2 352 serves to effect a phase separation between the aromatic HC and the water phases. A portion of the aromatic EC 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 R2 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.

The water phase that accumulates in the water leg of overhead receiver D2 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 i 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 Dl 346 and is fed to steam generator SRI 342 via line 63 where it is transformed into stripping steam that is introduced into SRC 332 via line 64.

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 I. 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 mto the upper portion of SCC 340 below the location of the solveni HC interface.

A portion of the raffinate stream from EDC 330 is fed to SCC 340 via line 49 to contac 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 heav HCs and PMs, is continuously withdrawn from iower 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.

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 remo ed.

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 in 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 I 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 SO^C. In addition, raffinate feed-to-solvent feed weight ratio in. SCC 340 typically ranges from 0. 1 to 100, and preferabl .from 0.1 to 10. Th contacting temperature m SCC 340 typically ranges 0 to 100 ^> C, and preferably from 25 to 80" C, The operating pressure of SCC 340 typically is from 1 to 100 aim., and preferably from. 1 to 10 aim. The weight ratio between the cooled sol vent-rich stream mixture in Hue 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.

tg. 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 aroraatics and non~aromaties is fed via line 102 to the middle portion of LLE column 400, while lean sol vent 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, etlrylbenzene, xylenes, C aromatics, and mixtures thereof, and the nan- aromatic hydrocarbons typical comprise Cj to CV paraffins, naphthenes, olefins, and mixtures thereof

A raffinate phase containing essentially the «on~aromaiies with minor amounts of solvent, is withdrawn from the top o LLE column 400 as stream 104 and is ted 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 1 6; the combined stream. 107 is fed to the top of ESC 410.

The vapor flow through ESC 410 is generated by the action of reboiler R l 414, whereby a portion of the rich solvent in the bottom is recycled to ESC 410 via line 1 1 1 through reboiler Rl 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 to of ESC 410 is condensed in a cooler (not shown) and the condensate is transferred via line 108 to an overhead receiver Dl 4.16, 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 arotnatics, is recycled to the lower portion of LLE column 400 as reflux via line 109. The water phase is transferred via. lines 110 and 125 to steam generator SRI 41 S 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 1 12. Stripping steam is injected from steam generator SRI 418 via line 126 into the lower portion of SRC 402 to assist in the removal of axomatic 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 D2 420 via line 1 13 after being condensed in a cooler (not shown). In order to minimize the bottom temperature of SRC 402, overhead receiver D2 420 is connected to a vacuum source to generate sub-atmospheric conditions in SRC 402,

Overhead receiver D2 420 serves to effect a phase separation between the aromatic HC and the water phases. A portion of the aromatic HC phase in line 1 14 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 1.16. The water phase that accumulates in the water leg of overhead receiver D2 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 raffi naie and the HC phase from SCC 406 through a counter-current water wash and the solvent-free non-aromaiics, which accumulate in the HC phase, are then withdrawn from the top of WWC 408 as solvent-free non-aromatic products through Sine 337. A water phase, containing the solvent, exits through lines 133 and 134 from the bottom of WWC 40S and is combined with line J 10, that is the water phase from overhead receiver Dl 416, and is fed to steam generator SR I. 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. 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 LL E column 400 for extracting the aromatic HCs in LLE column 400. A split steam of the lean solvent f om 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 Sean solvent is heated in reboilet R2 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 fine 123 and a split lean solvent f om 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 substantiall all the stripping steam from SRG 404. In operation, after the vapor is cooled and condensed in cooler C I 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.

A portion of the raffina e stream .from the LLE column is fed to the lower portion of SCC 406 via line 129 a 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, 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 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. The HC phase- that accumulates continuously at the top of SCC 406 is removed pe.fiodical.iy 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,

in an application of the LLE process of Fig. 3 using sulfolane as the solvent, the temperature of the overhead vapor .from. S G 404 typically ranges from .150" to 200° C, and preferabiy from. 1 0" to 180" C, under a pressure of 0.1 to 10 aim., and preferably of 0.1 to 0.8 ami. The mixture comprising of solvent vapor from SRG 404 and lean solvent from SRC 402 is condensed and cooled In the cooler CI 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 KM 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 preferabiy from 0.1 to 10. The contacting temperature in SCC 406 typically ranges from 0" to 00" C, and preferably from 25 to 80" C. The operating pressure of SCC 406 typically ranges rom. 1 to 100 aim., and preferably from 1 to 10 aim. The weight ratio between the cooled solvent-ric 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, respecti vely.

Fig. 4 illustrates a LLE process for aromatic HCs recovery from the mixture containing aromatic EC's 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. The process employs !iqaid-Hquid extraction (LLE) column. 430, solvent recovery colum

(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 (MP) 442. A HC feed containing aiOmatic 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 lin 226. An extract phase is transferred front the bottom of LLE column 430 via line 205 and is mixed with a secondary lea solvent from line 206; the combined stream 207 is fed to the top of ESC 440.

The vapor flow through ESC 440 is generated by the action of reboiler Rl 444, whereby a portion of the rich solvent in bottom is recycled to ESC 440 via line 211 through reboiler Rl 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 Dl 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 aroraatics, is recycled to the lower portion of LLE column 430 as reflux vi line 209. The water phase is transferred via lines 210 and 221 to steam generator SRI 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 S I 448 vi 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 withdraw as an overhead vapor stream from SRC 432 and introduced into an overhead receiver D2 450 via line 21.3 after being condensed in a cooler. In order to .minimize the bottom temperature of SRC 432, overhead receiver D2 450 is connected to a vacuum source to generate sub-atmospheric conditions in SRC 432.

Overhead receiver D2 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 R2 452 and recycled to the bottom of SRC 432 via line 217. Preferably, the majority of the ean solvent exiting from the bottom of SRC 432 is transferred into LLE column 430 via lines 218, 220, and 203.

The water phase that accumulates in the water leg of overhead receiver D2 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 2 -that is. the water phase from overhead receiver D.1 446 and is led to steam generator SR I 448 via line 221 where it is transformed into stripping steam that is introduced into SRC 432 via line 222.

A split stream 219 of the lean solvent from SRC 432 in. line 2.18 which, contains measurable amounts of heavy HCs is cooled in cooler CI 454. A slip water-rich stream from the bottom of WWC 438 is then added via Sine 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.

A portion of the raffinate stream from ^' LLE column 430 contacts the solvent phase as the displacement agent to squeeze out. the hea vy HCs and PMs from the sol vent phase into the HC phase in the SCC. A solvent phase, that contains essentially purified solvent, most of the aromatic components from the raffinate streaoi (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.

The HC phase which accumulates continuously at the top of SCC 436 and is removed periodically from the overhead of SCC 436 via Hue 226 under interface level control, which is then mixed with the raffinate stream from the o verhead of LLE column 430 before being fed via line 227 to WWC 438 where any solvent in the final raffinate product is removed.

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 I 454 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 436 as the displacement agent ranges from 0 to 100"C _S 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 0 to 1 0" C, and preferably from 25 to 80" C. The operating pressure of SCC 436 typically is from I to 100 atm., and preferably from 1 to 10 aim. 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. I .