BACKGROUND - FIELD OF INVENTION This invention relates to the process of solvent regeneration of activated carbon, specifically to a number of processing improvements that result in increased extent of regeneration, decreased hazard of explosion associated with combustible vapor mixtures, decreased regeneration cycle time, reduced solvent recovery requirement and/or reduced equipment complexity for the overall process. These improvements also expand the utility of the solvent regeneration technology to vapor-phase carbons and allow the efficient use of water-immiscible solvents in the regeneration of all applications of activated carbon.

BACKGROUND - DESCRIPTION OF PRIOR ART Aasorption by activated carbon is a technology widely applied for the removal of chemical species from waters and waste waters, as well as the removal of organic chemicals from vapor streams. In normal applications, the activated carbon gradually accumulates the chemical species removed from the liquid or vapor stream being purified, causing a progressive reduction in the carbon's ability to remove additional chemicals from the stream being treated. At some interval, i.e., when the activated carbon has become "spent", it must be replaced or regenerated to restore the adsorptive capacity.

Two methods of regeneration of spent activated carbon have found wide-spread industrial application: steam regeneration and thermal regeneration. Solvent regeneration has been utilized on occasion, but in far fewer instances than the other two mainstream regeneration methods.

Steam regeneration uses direct contact steam to strip the adsorbed organics away from the surface of the carbon and is routinely used for vapor-phase carbon. This technique exploits the phenomenon that the volatility of the adsorbed compounds

increases with temperature. Thus, by increasing the temperature of the carbon, the adsorption equilibrium of the adsorbed chemical scan be shifted from condensed liquid in the internal pores of the carbon to the vapor phase, desorbing some of the adsorbate out of the carbon. This results in the regeneration of some of the carbon's capacity for subsequent adsorption.

Steam regeneration can successfully be utilized for volatile organic adsorbates with atmospheric boiling points up to about 120 degrees Celsius. This method has the advantage that regeneration conditions are mild and the internal pore structure of the carbon is unaffected by the regeneration conditions, but has the disadvantage that less volatile compounds, if present, are not effectively removed and reduce the adsorptive capacity of the carbon.

Sometimes, a hot inert gas is used in place of steam. Steam and hot inert gases regenerate carbon in the same manner, by heating the carbon and volatizing adsorbates directly from the surface of the internal pores of the carbon.

Thermal regeneration involves heating the activated carbon up to temperatures as high as 900 degrees Celsius, which desorbs and oxidizes the adsorbed chemicals. Unfortunately, some of the internal pores of the carbon are also deteriorated during thermal regeneration, leading to gradual atrophy and eventual loss of adsorption capability by the activated carbon. Thermal regeneration has the additional disadvantages of being energy intensive and destroying the adsorbed material during the thermal regeneration process, precluding the recovery of the adsorbates intact.

Solvent regeneration occupies the niche between steam regeneration and thermal regeneration. Solvent regeneration provides for effective removal of adsorbed organic adsorbates from the internal pores of the carbon, presuming the organics are favorably soluble in the solvent, yet avoids both the extreme temperatures, which destroy the adsorbates, and the high energy requirements of thermal regeneration. The key to the solvent regeneration process is the utilization of a solvent that

efficiently solubilizes the contaminants out of the carbon pores, yet can be subsequently removed from the pores of the carbon itself, typically by steaming with direct cont t steam, as in the steam regeneration process.

The concept of organic solvents desorbing the adsorbates from activated carbon is not new. The original patent on the solvent regeneration of adsorbates was issued in 1932 (US Patent 1,866,417). The patent was issued as an improvement over the then current practice of regenerating liquid-phase activated carbon with superheated steam, a method that was only partially successful for carbon used on the phenolic waste water from coking plants. After describing the then current practice, the patent notes "the aforesaid drawbacks can be obviated in a simple manner by treating the charged adsorption media with solvents which are capable of dissolving out the adsorbed constituents from the adsorption media. . . . ".

In addition, US Patent 1,866,417 provides the principle method of removing the solvent after regenerating the carbon: "these solvents may be expelled again from the adsorption media in the simplest manner, for example by steaming out or by treatment with boiling water."

In the current development and practice of the solvent regeneration of activated carbon, the term "solvent" has a broad definition. The "solvenfrepresents the class of regenerating fluids that exhibit favorable solubilities for the adsorbates present in the spent activated carbon and, upon being properly contacted with the spent carbon, effectively desorb the adsorbates. As such, the appropriate solvents for a given application are application-specific.

Additionally, since virtually all applications of solvent regeneration involve the recovery and reuse of the regenerating fluids from the eluants associated with the regeneration process, the recycled solvent will likely contain varying amounts of impurities, such as water and trace adsorbates. These impurities have been demonstrated to be acceptable to the regeneration process. Similarly,the application of solvent blends, sequences

of solvents and recycled unpurified eluants have been shown to be effective regenerating fluids and would be within the broad classification of "solvent", as applied to the solvent regeneration of activated carbon (US Patent 3,274,104 and US Patent 3,965,036) . In the current development and practice of the solvent regeneration of activated carbon, the "solvent" may be best defined in terms of those non-aqueous constituents of the regenerating fluids, supplied to the carbon for the purpose of effecting the desorption of the adsorbates contained within the internal pores of the spent carbon. As such, the terms solvent and regenerating fluid are synonymous, but should be distinguished from the term "eluant", which is the fluid stream exiting the solvent regeneration process, consisting of the original regenerating fluid and the newly desorbed adsorbates removed from the carbon, in addition to any residual water, if present.

Solvent regeneration of activated carbon is not without shortcomings. As noted in US Patent 3,965,036: "Solvent regeneration can be unfeasible because very large amounts of solvent must be employed to recover the sorbed species from the bed and the large quantity of solvent must then be treated to recover the chemical species from the solvent. " That patent develops a method of reducing the amount of solution requiring distillation by up to 85%. It is this reduction of regenerant fluid, without loss of regeneration effectiveness, that constitutes the essence of that invention.

Solvent regeneration has further shortcomings in the current practice that prevent the efficient use of solvents immiscible with water. In addition, the technology has not been applied to the regeneration of activated carbon used in vapor-phase adsorption applications. These shortcomings result from the difficulty in achieving effective solvent penetration into the internal pores of the activated carbon, where the adsorbates are physically located.

In the case of activated carbon used in aqueous applications, the internal pores are flooded with water. When

solvents that are immiscible with water are used to solvent regenerate the adsorbate-loaded carbon, water becomes trapped in the internal pores of the carbon, inhibiting the regeneration process. This situation is contrasted with the case of water-miscible sol-'^nts, where the intrapore water is diluted upon contact with vent and extracted from the carbon during the regeneration p_ ess.

In the case of activated carbon used in vapor-phase applications, the internal pores are occupied b\ ir. Analogous to the case of the immiscible solvent -water situ .tion, air trapped in the internal pores is sparingly soluble in the regenerating solvent, resulting in a physical barrier to the penetration of the solvent into the pores of the carbon.

OBJECTS AND ADVANTAGES Accordingly, the solvent regeneration of activated carbon adsorption processes,as currently developed and practiced in industry, has been improved in the following manner by the scope of this patent: a) the extent of regeneration achieved over the current practice has been increased; b) the hazard of explosion, due to combustible vapor mixtures, has been decreased or elimi: ed during the regeneration cycle, allowing the solvent regeneration of activated carbons used in vapor-phase applications; c) the overall solvent regeneration cycle time has been decreased, principally through the elimination of unnecessary regeneration steps; d) the overall amount of solvent requiring recovery has been reduced; and e) the complexity of the equipment required for the overall process has been reduced.

These improvements expand the utility of the solvent regeneration technology to vapor-phase carbons and allow the efficient use of water-immiscible solvents in the re^aneration of all applications of activated carbon.

Still further objects, features, and advantages of the present invention will become readily apparent to one skilled in the art from consideration of the description of the invention and the appended claims.

SUMMARY OF THE INVENTION The invention described herein provides improvements to the current development and practice of the solvent regeneration of activated carbon. The current development of the solvent regeneration process requires the initial fluid in the carbon pores to be water or waste water. The intrapore water is then diluted upon contact with a miscible solvent and extracted from the carbon during the initial phases of the regeneration process. Specifically, the improvements focus on the conditions and sequence of events that result in the replacement of the initial fluid in the carbon's internal pores with solvent at the start of the solvent regeneration cycle. This invention provides for the transport of solvent as a vapor into the internal pores of the activated carbon, thereby allowing the solvent to condense inside the carbon pores and efficiently surrounding with solvent the adsorbates contained on the surface of the internal pores of the carbon. The creation and exploitation of the vapor transport pathway into the carbon pores for the regenerating solvent is the essence of this invention. By improving the efficiency and effectiveness of the flooding of the carbon pores with solvent,the solvent regeneration process is improved in manners that will be subsequently elaborated.

DETAILED DESCRIPTION OF THE INVENTION The invention consists of modifying the conditions and sequence of events at the start of the solvent regeneration process to affect the replacement the initial fluid in the internal pores of the activated carbon with solvent. Once this replacement is achieved, the remaining solvent regeneration process proceeds in accordance with the current development and practice of the solvent regeneration technology. That

methodology consists of eluting the adsorbates out of the carbon bed with additional solvent, followed by removal of the residual solvent, typically by heating the carbon with steam or hot inert gas.

Several considerations influence the choice of the primary regenerating solvent, i. e. , the principal component of the regenerating fluid. These include the solubility of the adsorbates in the solvent, the energy of adsorption of the solvent on carbon, the miscibility of the solvent with water, the ease of removing the residual solvent, and the ease of separation of the solvent from the other eluted constituents from the regeneration process, typically the adsorbates and water. Additional considerations include the cost and availability of the solvent, flammability, explosive potential, environmental concerns and health concerns.

For water-immiscible solvents, the presence of an azeotrope with water is desirable, since this feature can be used to displace the water from the carbon pores at the start of the regeneration and facilitate the removal of the residual solvent at the end of the regeneration. However, water- iscible solvent that form aqueous azeotropes are not desirable, since the recovery of the solvent by distillation is complicated by the presence of the azeotrope.

These multiple considerations result in several solvents being excellent candidates for solvent regeneration, assuming the solubility for the adsorbates is sufficient to provide for effective regeneration of the activated carbon. For water-miscible solvents, the preferred solvents are acetone and methanol, since the higher homologues form azeotropes with water and other water-miscible solvents, such as ethers, have cost and safety concerns.

For water-immiscible solvents, those that form azeotropes with water are attractive candidates for regenerating solvents. These include toluene, xylenes and ethyl benzene for the aromatic solvents and pentanes (C _s ) through nonanes (C _y ) for the aliphatic solvents. Additionally, refinery cuts that contain suitable

boiling point ranges of aliphatics and aromatics, such as hexane cuts, heptane cuts, naphthas, and light straight run gasolines, are acceptable solvents if the solubility for the adsorbates is sufficient.

Benzene and chlorinated solvents such as methylene chloride, ethylene dichloride and trichloroethylene have environmental and health concerns which require additional attention during the design of a full-scale regeneration process, but do not eliminate these solvents from further consideration. In particular, the low solubility in water and flame resistance of chlorinated solvents make them attractive candidates for those sites where these solvents are currently in use.

As discussed, the current development and practice of solvent regeneration process requires the initial fluid in the carbon pores to be water or waste water. This precludes the solvent regeneration of activated carbon containing air in the carbon pores, such as encountered in vapor-phase adsorption applications. In addition, substantial operational problems are encountered when water-immiscible solvent are used as the regenerating fluid for liquid-phase activated carbon. These problems arise from the difficulties achieving efficient replacement of the initial fluid in the carbon's internal pores with solvent at the start of the solvent regeneration cycle.

In the case of activated carbon used in vapor-phase applications, the internal pores are occupied by air. The invention described herein provides several methods for facilitating the exchange of the air trapped in the internal pores with solvent. The methods provided are:

1) Admitting the solvent initially as a vapor and allowing the solvent to condense inside the carbon pores and the remaining solvent vapor to displace the residual air from the carbon pores and the carbon bed. Subsequently, the carbon bed can be flooded with liquid solvent.

2) Flooding the carbon bed with liquid solvent and providing a quiescent period for the solvent to migrate into the carbon pores due to the vapor pressure of the solvent. The

displaced air is allowed to accumulate in the interstitial voids of the carbon bed..

3) Flooding the carbon bed with liquid solvent and cycling the external pressure to alternately drive the solvent into the internal pores and evacuate the carbon bed to release the air trapped in the interstitial voids of the carbon bed. This procedure facilitates the solvent transport of method 2 above.

4) Heating the carbon initially, by steaming or other means, and introducing the solvent into the carbon bed as a liquid under conditions that result in significant vaporization of the solvent. The vaporizing solvent condenses in the carbon pores, displacing any residual water or non-condensible vapor from the pores of the carbon, while cooling the carbon to allow the subsequent flooding of the internal pores and the entire carbon bed with liquid solvent.

In the case of activated carbon used in aqueous applications, the internal pores are flooded with water. The invention described herein provides methods for facilitating the exchange of the water trapped in the internal pores with either a water-miscible or water-immiscible solvent. The methods provided are:

1) Heating the carbon initially, by steaming or other means, and introducing the solvent into the carbon bed as a liquid under conditions that result in significant vaporization of the solvent. The vaporizing solvent condenses in the carbon pores, displacing any residual water or non-condensible vapor from the pores of the carbon, while cooling the carbon to allow the subsequent flooding of the internal pores and the entire carbon bed with liquid solvent.

2) Admitting the solvent initially as a vapor and allowing the solvent vapor to displace the water in the carbon bed. This method is essentially the inverse of removing a solvent from activated carbon by steaming the carbon bed. As the solvent vapor condenses in the carbon bed, the carbon is heated, facilitating the removal of the water in the pores by extraction as a liquid and/or vaporization.

carbon are filled with water, simulating a liquid-phase activated carbon.

3) Each regeneration utilized 300 grams of untreated carbon, contained in a column of 3 inches diameter and carbon bed height of 4. 5 inches. The total amount of solvent utilized for each example was 600 grams. In all cases, the initial solvent was introduced over a period of one-half hour, followed by the removal of the solvent uniformly over the next one and one-half hours. Subsequently, the carbon bed was steamed at atmospheric pressure for approximately one-half hour to remove the residual solvent and dried at 100 degrees centigrade for five hours with a slow sweep of air to remove the residual moisture.

4) The regenerated carbons were assayed in the same manner as the untreated carbon, by slurrying the dried treated carbon with two parts tetrahydrofuran for twenty hours and analyzing the extract with size exclusion chromatography. The effectiveness of the regeneration was evaluated by measuring the height of the highest peak in the region of molecular weight 300 and comparing the peak height to the corresponding peak of the untreated carbon. All assays were performed in duplicate, the highest peak measured in millimeters and the results averaged.

The solvents used for the demonstrations were acetone and toluene. These solvents were chosen based on their ability to solubilize the adsorbates present on the starting carbon. The choice of solvent for each example is not intended to preclude the suitability of other solvents. The use of acetone is representative of the behavior of all water-miscible solvents and the use of toluene is representative of the behavior of all water-immiscible solvents. As discussed previously, several considerations influence the choice of regenerating solvent for 'a specific application.

In addition, the durations of the individual steps of the regeneration sequence in the examples were chosen to provide effective regenerations and facilitate the comparison of the regeneration efficiencies. These intervals are representative, but not unique, to each demonstrated regeneration technique. In

practice, the duration of each phase is adjusted by equipment constraints and operating considerations, with longer intervals generally providing improved regeneration efficiency. Similarly, volume of solvent used as regenerant fluid is a variable that is adjustable for a specific application.

For the purposes of the examples and convenience, all regenerating fluids are introduced above the carbon bed and all eluants are removed below the carbon bed. This configuration is not necessary for any of the regeneration techniques demonstrated nor considered a requirement in any application of this invention.

The pressure levels for the examples are given in inches of mercury, with 0" Hg corresponding to atmospheric pressure and 30" Hg corresponding to approximately full vacuum.

EXAMPLE 1 In this example, the current development and practice of the solvent regeneration of activated carbon technology is demonstrated. The following conditions and sequence of events provided the regeneration of the activated carbon.

1) Load dry spent carbon, steam carbon at 0" Hg

2) Flood carbon bed with cold water

3) Float acetone on top of water and desorb downflow

4) Discard initial water from carbon column prior to solvent appearance

5) Collect all subsequent column eluants

6) After all solvent eluted, steam at 0" Hg for one half hour

7) Total collected from steps 5 & 6: 1030 gms

8) SEC Height: 42.8 mm, 51.2 % of Untreated Carbon Sample The starting carbon was initially converted to a liquid-phase carbon by steaming to remove the residual air and flooding the carbon bed with cold water. Subsequently, the current solvent regeneration methodology, as applied with a water-miscible solvent, is used to regenerate the activated carbon.

The regeneration technique of Example 1 is substantially less effective with water-immiscible solvents due to the water trapped in the internal pores of the carbon, inhibiting the regeneration process.

EXAMPLE 2 In this example, the starting carbon is regenerated by admitting the solvent initially as a vapor and allowing the solvent to condense inside the carbon pores and the remaining solvent vapor to displace the residual air from the carbon pores and the carbon bed. The following conditions and sequence of events provided the regeneration of the activated carbon.

1) Load dry spent carbon, evacuate to 15" Hg

2) Vaporize acetone overhead onto the carbon bed

3) Seal exit of column when bottom temperature reaches 35 degrees centigrade

4) Provide remaining acetone as a liquid and flood carbon with solvent

5) Collect all column eluants

6) After all solvent eluted, steam at 0" Hg for one half hour

7) Total collected from steps 5 & 6: 831 gms

8) SEC Height: 42.0 mm, 50.3 % of Untreated Carbon Sample Example 2 demonstrates an improvement over Example 1 by avoiding the initial conversion of the carbon to a liquid-phase carbon, thereby avoiding the associated equipment requirements, cycle time, energy consumption and creation of contaminated water. This improvement allows the direct solvent regeneration of activated carbon used in vapor-phase adsorption applications.

In addition, the initial evacuation of the starting carbon decreases the hazard of explosion by reducing the oxygen partial pressure below the level that can sustain flame propagation. Alternately, the hazard of explosion could have been avoided by inerting the starting carbon with an oxygen-depleted vapor stream.

This improvement applies principally to vapor-phase

activated carbon adsorption applications. However, the improvement can be applied to liquid-phase activated carbon if the carbon is dried prior to solvent regeneration. The regeneration technique of Example 2 is applicable to all water-miscible and water-immiscible solvents suitable for solvent regeneration of activated carbon.

EXAMPLE 3 In this example, the starting carbon is regenerated by flooding the carbon bed with liquid solvent and providing a quiescent period for the solvent to migrate into the carbon pores. The quiescent period allows for the evaporation of the solvent into the air within the internal pores and subsequent adsorption on the surface inside the carbon pore. The displaced air is allowed to accumulate in the interstitial voids of the carbon bed. The following conditions and sequence of events provided the regeneration of the activated carbon.

1) Load dry spent carbon

2) Spray liquid acetone onto the top of the carbon bed to flood the carbon

3) Hold quiescent for 1/2 hour - air bubbles appear in carbon bed

4) Collect all column eluants

5) After all solvent eluted, steam at 0" Hg for one half hour

6) Total collected from steps 4 & 5: 816 gms

7) SEC Height: 40.3 mm, 48.2 % of Untreated Carbon Sample Example 3 demonstrates an improvement over Example 2 by avoiding the initial vaporization of the solvent, thereby avoiding the associated equipment requirements, cycle time, and energy consumption. This improvement allows the direct solvent regeneration of activated carbon used in vapor-phase adsorption applications.

The preferred embodiment of this improvement would include measures to decrease the hazard of explosion by evacuating or inerting the vapor space in the carbon column prior to

4) Collect all column eluants

5) After all solvent eluted, steam at 0" Hg for one half hour

6) Total collected from steps 4 & 5: 826 gms

7) SEC Height: 41.3 mm, 49.4 % of Untreated Carbon Sample Example 4 demonstrates an embellishment of Example 3 by facilitating the removal of the air from carbon bed and promoting the migration of solvent into the internal pores of the carbon. This improvement is advantageous for solvents with lower vapor pressures and higher surface tensions, such as aromatic solvents and higher molecular weight aliphatic hydrocarbons.

The preferred embodiment of this improvement would include measures to decrease the hazard of explosion by avoiding explosive conditions within any vapor pockets formed within the carbon vessel, as discussed in Example 2.

This improvement applies principally to vapor-phase activated carbon adsorption applications. However, the improvement can be applied to liquid-phase activated carbon if the carbon is dried prior to solvent regeneration. The regeneration technique of Example 4 is applicable to all water-miscible and water-immiscible solvents suitable for solvent regeneration of activated carbon.

EXAMPLE 5 In this example, the starting carbon is regenerated by steaming the carbon initially, replacing the air in the carbon pores with water vapor. Subsequently, a water-miscible solvent is introduced into the carbon bed as a liquid under conditions that result in significant vaporization of the solvent. The vaporizing solvent drives the residual water and water vapor from the pores of the carbon, while cooling the carbon to allow the condensation of the solvent inside the carbon's internal pores. The following conditions and sequence of events provided the regeneration of the activated carbon.

1) Load dry spent carbon, steam carbon at 0" Hg

2) Spray liquid acetone overhead at 2" Hg

3) Seal exit of column when bottom temperature reaches 55 degrees centigrade

4) Flood carbon with remaining acetone

5) Collect all column eluants

6) After all solvent eluted, steam at 0" Hg for one half hour

7) Total collected from steps 5 & 6: 1000 gms

8) SEC Height: 29.5 mm, 35.3 % of Untreated Carbon Sample Example 5 demonstrates an improvement over the current development and practice of solvent regeneration of activated carbon by providing greater extent of regeneration, avoiding the hazard of explosion by removing the residual air from the carbon bed prior to introducing the solvent and avoiding the equipment requirements associated with vaporizing the solvent.

The essence of this improvement is to provide the heat for vaporizing the solvent by preheating the carbon bed. In this example, the heating was provided by steaming the carbon prior to introducing the solvent into the carbon bed. Alternately, the carbon bed could be preheated by an alternate means, such as supplying hot inert gas to the carbon bed or external heating of the carbon vessel. In addition, the pressure within the carbon bed can be adjusted to facilitate the vaporization of liquid solvent to an extent optimal for the overall regeneration process.

This improvement applies to both liquid-phase and vapor-phase activated carbon adsorption applications. The regeneration technique of Example 5 is applicable to all water-miscible solvents suitable for solvent regeneration of activated carbon.

EXAMPLE 6

In this example, the starting carbon is regenerated by steaming the carbon initially, replacing the air in the carbon pores with water vapor. Subsequently, a water-immiscible solvent is introduced into the carbon bed as a liquid under conditions that result in significant vaporization of the solvent. The vaporizing solvent drives the residual water and water vapor from

the pores of the carbon, while cooling the carbon to allow the condensation of the solvent inside the carbon's internal pores. The following conditions and sequence of events provided the regeneration of the activated carbon.

Load dry spent carbon, steam carbon at 0" Hg

Spray liquid toluene overhead at 2" Hg

Seal exit of column when bottom temperature reaches 80 degrees centigrade

Flood carbon with remaining toluene

Collect all column eluants

After all solvent eluted, steam at 0" Hg for one half hour

7) Total collected from steps 5 & 6: 1085 gms

8) Solvent recovery steam in two phases: toluene rich on top, aqueous on bottom

9) SEC Height: 29.0 mm, 34.7 % of Untreated Carbon Sample Example 6 demonstrates an improvement over the current development and practice of solvent regeneration of activated carbon by providing greater extent of regeneration, avoiding the hazard of explosion by removing the residual air from the carbon bed prior to introducing the solvent, avoiding the equipment requirements associated with vaporizing the solvent, and reducing the overall amount of solvent requiring recovery by distillation. This distillation requirement reduction results from the use of a water-immiscible solvent and the resulting two liquid phase eluant, allowing isolation of the solvent-rich phase prior to distillation.

The essence of this improvement is to provide the heat for vaporizing the solvent by preheating the carbon bed. In this example, the heating was provided by steaming the carbon prior to introducing the solvent into the carbon bed. Alternately, the carbon bed could be preheated by an another means, such as supplying hot inert gas to the carbon bed or external heating of the carbon vessel.

In addition, the pressure within the carbon bed can be adjusted to facilitate the vaporization of liquid solvent to an

extent optimal for the overall regeneration process. In addition, solvents that exhibit a minimum boiling azeotrope with water expedite the displacement of the water in the carbon pores. The vaporizatic of the water, as the azeotrope, effectively strips the wate from the carbon's pores and facilitates the solvent exchange with the water in the pores of the carbon.

This improvement applies to both liquid-phase and vapor-phase activated carbon adsorption applications. The regeneration technique of Example 6 is applicable to all water-immiscible solvents suitable for solvent regeneration of activated carbon.

EXAMPLE 7 In this example, the starting carbon is regenerated by draining the carbon bed of interstitial water, then admitting the solvent initially as a vapor and allowing the solvent to migrate into and condense inside the carbon pores. As the solvent vapor condenses in the carbon bed, the carbon is heated and the water in the pores is displaced. The following conditions and sequence of events provided the regeneration of the activated carbon.

1) Load dry spent carbon, steam carbon at 0" Hg

2) Flood carbon bed with cold water

3) Drain column of excess water and evacuate to 15" Hg

4) Vaporize toluene overhead onto the carbon bed

5) Seal exit of column when bottom temperature reaches 63 degrees centigrade

6) Provide remaining toluene as a liquid and flood carbon wit^ solvent

7) Collect all column eluants

8) After all solvent eluted, steam at 0" Hg for one half hour

9) Total collected from steps 8 & 9: 1050 g s

10) Solvent recovery steam in two phases: toluene rich on top, aqueous on bottom

11) SEC Height: 38.8 mm, 46.4 % of Untreated Carbon Sample Example 7 demonstrates an improvement over Example 6 by

eliminating initial steaming of the activated carbon, thereby decreasing the overall cycle time and energy consumption of the regeneration process. When applied to a full-scale regeneration process, the preferred embodiment of this improvement would include utilization of the solvent recovery facilities to provide the solvent vapor stream, thereby avoiding the cooling cost associated with condensing the distilled solvent in solvent recovery.

In this example, the excess water was drained from the carbon bed prior to the introduction of the solvent vapor. This feature is not necessary and the water in the carbon bed can be directly replaced by solvent by providing solvent vapor until the water in the carbon bed is displaced. This technique is essentially the inverse of removing a solvent from activated carbon by steaming the carbon bed.

Alternately, the carbon bed can be steamed prior to introduction of the solvent vapor, which would further reduce the amount of solvent vapor necessary to displace the water from the carbon and reduce the amount of water in the subsequent eluants.

In addition, solvents that exhibit a minimum boiling azeotrope with water expedite the displacement of the water in the carbon pores. The vaporization of the water, as the azeotrope, effectively strips the water from the carbon's pores and facilitates the solvent exchange with the water in the pores of the carbon.

This improvement applies principally to liquid-phase activated carbon adsorption applications. However, the improvement can be applied to vapor-phase activated carbon if the carbon is wetted prior to solvent regeneration. The regeneration technique of Example 7 is applicable to all water-miscible and water-immiscible solvents suitable for solvent regeneration of activated carbon.

CONCLUSION. RAMIFICATIONS. AND SCOPE Thus the reader will see that the invention provides a substantial broadening of the flexibility and domain of

applications for solvent regeneration of activated carbon. This invention extends the current development and practice by allowing the efficient use of solvents which are immiscible with water and providing the application of the technology to vapor-phase activated carbon.

While my above description contains many specificities, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of preferred embodiments thereof. Many other variations are possible. For example, depending on the requirements of a specific adsorbate or solvent choice and other characteristics of an individual application, the conditions and sequence of events associated with the execution of individual improvements may be modified without deviating from the underlying phenomenon constituting the invention. Accordingly, the scope of the invention should be determined not by the embodiment(s) , but bv the appended claims and their legal equivalents.