Abstract:
A continuous Liquid-Solids Circulating Fluidized Bed (LSCFB) preferably for use as an ion exchanger consists of two fluidized bed columns, a fluidized bed adsorber (downer) operating in conventional fluidized bed mode for adsorption of ions of interest and a fluidized bed riser for desorption of ions (operating as a riser fluidized bed) to provide regenerated particles. Ion exchange particles circulate continuously between the riser and the downer i.e. the particles that have adsorbed ions in the absorber pass from the adsorber (downer) to the desorber where they are regenerated and the so regenerated particles are return to the adsorber near the top of the adsorber column. The LSCFB can be used in processes for continuous recovery of the ions of interest.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION 
     This patent application is a Divisional application of the U.S. patent application Ser. No. 09/676,453 entitled LIQUID-SOLIDS CIRCULATING FLUIDIZED BED, filed Oct. 2, 2000, in the name of the same inventors, now U.S. Pat. No. 6,716,344 and which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a fluidized bed, more specifically, a liquid-solids circulating fluidized bed arrangement specially suited for ion exchange processes. 
     BACKGROUND TO THE INVENTION 
     Fluidized beds have been used for a number of different applications such as gas-liquid, gas-liquid-solid contactors and to carry out a variety of different processes such as chemical reactions. 
     Fluidized beds have found application in ion exchange process. For example Chase, H. A., “Purification of Proteins by Adsorption Chromatography in Expended Beds”, TIBTECH 12, 296-303 (1994) describes a batch ion exchange process using a conventional fluidized bed for recovering proteins from whole fermentation broth with the presence of bacterial cells. It eliminates the difficult solids separation step and recovers the desired products directly from unclarified whole broth. This process is a batch process employing a conventional fluidized bed. 
     Burns, M. A. and D. J. Graves, “Continuous Affinity Chromatography Using a Magnetically Stabilized Fluidized Bed”, Biotechnology Progress 1, 95-103 (1995) suggested a two-column magnetically stabilized fluidized bed system for the continuous chromatography of biochemical products. The magnetically stabilized fluidized bed system is considered to be complicated and costly. 
     Gordon, N. F., H. Tsujimura and C. L. Cooney, “Optimization and Simulation of Continuous Affinity Recycle Extraction”, Bioseparation 1, 9-12 (1990) describes a process using mixed reactors as opposed to fluidized bed and reported the continuous affinity recycle extraction of proteins using well-mixed reactors. This system, although simple and easy to control, has the disadvantage of a stirred tank system—the ion exchange efficiency is low and large processing volumes are essential for even a moderate throughput requirement. 
     Porter and Robert, U.S. Pat. No. 3,879,287, “Continuous ion exchange process and apparatus” (1975) relates to an apparatus for continuous ion exchange. However, the process described is a semi-continuous process as the recommended eluting means is a batch wise conventional fixed bed ion exchange process. 
     Himsley and Alexander, U.S. Pat. No. 4,279,755: Continuous countercurrent ion exchange process (1993) teaches a continuous countercurrent ion exchange process for absorbing ions of interest onto ion exchange particles from a feed liquor containing ions which when absorbed on the particles cause the density of the particles to increase. The process comprises the steps of (1) flowing the feed liquor upwardly through a main bed of ion exchange resin particles contained in a main chamber of an absorption column and thereby maintaining the bed in fluidized state; (2) continuously collecting the denser loaded particles from the lower region of the absorption column; (3) passing an outflow of the feed liquor from the upper region of the main chamber upwardly into the lower region of the polishing chamber containing a secondary bed of fluidized ion exchange resin particles whereby residual ions of interest are polished from the liquor, and (4) producing a barren liquor flowing out of the upper region of the polishing chamber. Again, this is a semi-continuous process as the stripping and the regeneration of the loaded ion exchange particles cannot be performed in this device. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a process for continuous recovery of the ions of interest for example contaminants in liquid streams or value added products from waste streams using a Liquid-Solids Circulating Fluidized Bed (LSCFB) ion exchange system. 
     Broadly the present invention relates to a method for recovering ionic products of interest comprising passing ion exchange particles in countercurrent flow with a feed stream of a first fluid through a first fluidized bed for adsorption of ionic products of interest from said feed stream of said first fluid, transferring said particles with adsorbed ionic products of interest from said first fluidized bed to a second fluidized bed through a packed moving bed which forms a dynamic seal between said first and second fluidized beds, and passing said ion exchange particles with absorbed ionic products in co-current flow with an extract buffer of a second fluid through said second fluidized bed for desorption of said adsorbed ionic products of interest, separating said second fluid containing said ionic products of interest desorbed from said ion exchange particles by said second fluid to provide regenerated ion exchange particles and returning said regenerated ion exchanged particles into said first fluidized bed to flow in countercurrent with said first fluid. 
     Preferably said ion exchange particles with absorbed ionic products are washed before being introduced into said second fluidized bed. 
     Preferably said regenerated ion exchange particles are washed before being returned to said first fluidized bed 
     Preferably said ionic product is a protein and said first fluid is a fermentation broth. 
     Preferably said ionic product is a metal and said first fluid is seawater. 
     Preferably said ionic product is an enzyme and said first fluid is dextrose syrup. 
     It is also an object of the present invention to provide a circulating fluidized bed system for liquid solids contact and interaction, more specifically a Liquid-Solids Circulating Fluidized Bed (LSCFB) ion exchanger. 
     Broadly the present invention also relates to a fluidized bed system comprising a first fluidized bed, means to feed solids into said first fluidized bed adjacent to a first end of said first fluidized bed and means to feed a first fluid into said first fluidized bed adjacent to a second end of said first fluidized bed, said second end being remote from said first end so that said solids and said first fluid flow in counter current, a second fluidized bed, said second fluidized bed being an entraining fluidized bed wherein a means for introducing solids and a means for introducing a second fluid into said second bed are both adjacent to the one end of said second fluidized bed so that said solids and said second fluid introduced into said second bed flow concurrently through said second bed from said one end toward another end of said second fluidized bed remote from said one end, first means connecting said first fluidized bed to said second fluidized bed adjacent to said second end of said first fluidized bed and said one end of said second fluidized bed and said first means connecting including said means to feed solids into said second fluidized bed, and second means connecting said first and said second fluidized beds adjacent said first end of said first bed and said other end of said second fluidized bed, and said second means connecting including said means to feed solids into said first fluidized bed. 
     Preferably said first and second fluidized beds are substantially vertical columns. 
     Preferably said second means connecting said first and said second fluidized beds includes a separator means for separating solids from fluid and exhausting such separated fluid to provide separated solids. 
     Preferably second means connecting said first and said second fluidized beds further includes a washer for washing said solids before they are feed into said first end of said first fluidized bed. 
     Preferably said first means connecting said first and said second fluidized beds includes a second washer for washing solids adjacent to said second end of said first fluidized bed before they are introduced into said second fluidized bed. 
     Preferably said first fluidized bed is an absorber for separating ionic products of interest and said second fluidized bed is a desorber for desorption of ionic products and said solids are ion exchange particles. That is, the said liquid-solid circulating fluidized bed system can preferably be used to recover ionic products of interest by passing ion exchange particles in countercurrent flow with a feed stream of a first fluid through a first fluidized bed for adsorption of ionic products of interest from said feed stream of said first fluid, transferring said particles with adsorbed ionic products of interest from said first fluidized bed to a second fluidized bed and passing said ion exchange particles with absorbed ionic products in cocurrent flow with an extract buffer of a second fluid through said second fluidized bed for desorption of said adsorbed ionic products of interest, separating said second fluid containing said ionic products of interest desorbed from said ion exchange particles by said second fluid to provide regenerated ion exchange particles and returning said regenerated ion exchanged particles into said first fluidized bed to flow in countercurrent with said first fluid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, objects and advantages will be evident from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings in which; 
         FIG. 1  is a schematic illustration of the method and apparatus of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1  the present invention is composed of a pair of fluidized beds a first fluidized bed  10  and a second fluidized bed  12  interconnected at their adjacent ends by solid transfer and washing systems generally indicated at  14  and  16  respectively. The first fluidized bed  10  is a conventional counter-current flow bed wherein solids (solid particles such as ion exchange beads) as indicated at  18  enter adjacent to the top of the bed  10  as indicated by the line  17  and flow downward and a first fluidizing fluid namely the feed liquor  20  enters the bed  10  as indicated schematically at  22  at the lower end  24  of the bed  10  and flows upward in counter current with the particles  18 . 
     The second fluidized bed  12  on the other hand is a riser fluidized bed wherein the solid particles  18  transferred from bed  10  via transfer system  14  enter the bed  12  adjacent to the lower end  26  of the bed  12  and flow upward in co-current relation with a second fluidizing fluid  28  (such as extract buffer) which enters the bed  12  under pressure in the illustrated arrangement via nozzle  30  and inlet  32  both adjacent to the lower end  26  of the bed  12  and flows upward through the bed  12  carrying the particles  18  in its flow. 
     The distributor of the second fluidized bed  12  divides the incoming stream of extracting buffer  28  into two sub-streams: the primary  60  and the auxiliary  62  streams. The primary stream  60  is introduced through nozzle  30  which projects into the second fluidized bed column  12 . This design increased the pressure drop across the bottom solids return pipe  42  and makes the system more stable. The auxiliary stream  62  is introduced into the bottom  26  of the second fluidized bed  12  through a perforated plate inlet  32 . The function of the auxiliary stream  62  is to stir up the particles at the bottom of the second fluidized bed  12  to be entrained up the second fluidized bed by the combination of the primary and auxiliary liquid streams  60  and  62 . The two streams  60  and  62  may also be combined into a single stream and the fed through a single distributor at the second fluidized bed  12  bottom end  26 . 
     As above indicated the solid particles  18  enter at inlet  17  and travel downward through the bed  10 . After they have traversed the fluidized bed  10  the particles  18  enter into the transfer system  14  which includes a washing stage  34  in a conical or funnel shaped bottom end  35  of the housing containing the bed  10  and into which wash water from a source is injected via nozzle  38  positioned adjacent to the apex of the cone in the bottom outlet  40  of the bed  10 . The injected wash water  36  travels in counter current to and washes the particles  18  when they leave the fluidized bed  10 . The wash water dilutes the feed stream and exits from the top of bed  10  through outlet  44 . The washed particles  18  then pass via transfer pipe  42  and are introduced into the second fluidized bed  12 . 
     The function of the wash section  34  is to rinse the loaded particles  18  and to prevent the feed stream  20  from being carried to the second fluidized bed  12  by the particles  18 . The bottom solids return pipe  42  is located below the wash section  34 . It connects the bottoms of the first fluidized bed  10  and the second fluidized bed  12 . During operations, loaded ion exchange particles are transported into the base of the second fluidized bed  12  through the bottom solids return pipe  42  to make up the particles  18  entrained up along the second fluidized bed  12 . The bottom solids return pipe  42  operates as a packed moving bed. This is the most important mechanism for forming the dynamic seal between the second fluidized bed  12  and the first fluidized bed  10 . The dynamic seal is critical for the success of this continuous ion exchange process, which employs two liquid streams of different properties. 
     The distributor of the second fluidized bed  12  divides the incoming stream of extracting buffer  28  into two sub-streams: the primary  60  and the auxiliary  62  streams. The primary stream  60  is introduced through nozzle  30  which projects into the second fluidized bed column  12 . This design increased the pressure drop across the bottom solids return pipe  42  and makes the system more stable. The auxiliary stream  62  is introduced into the bottom  26  of the second fluidized bed  12  through a perforated plate inlet  32 . The function of the auxiliary stream  62  is to stir up the particles at the bottom of the second fluidized bed  12  to be entrained up second fluidized bed by the combination of the primary and auxiliary liquid streams  60  and  62 . The two streams  60  and  62  may also be combined into a single stream and the fed through a single distributor at the second fluidized bed  12  bottom end  26 . 
     The feed liquor  20  as above described enters at the bottom of the bed  10 , travels in countercurrent to the particles  18  through the bed  12  and leaves at the top of the bed as indicated at  44 . The fluid exiting from  44  is discarded as waste or as a purified stream in the case of contaminant removal. 
     The second fluidizing fluid (extract buffer)  28  and the particles  18  from line  42  travel in co-current fashion upward through the bed  12  and are regenerated and then enter the transfer system  16  which includes a separator such as the fluid vortex type separator  46  having a fluid outlet  48  through which the second fluidizing fluid  28  is removed and a solids outlet through a washing stage  50  at the bottom. This fluid exiting from outlet  48  contains the ions of interest and may be subjected to further downstream processing or membrane treatment to concentrate the ions of interest. Washing fluid is injected via nozzle  52  at the bottom of the washing stage  50  and flow upward in countercurrent with the downcoming solids (regenerated solid particles)  18  and the so washed particles  18  enter the inlet tube delivering the regenerated particles  18  into the top of the bed  10 . The washing fluid dilutes the extract buffer and exits from the outlet  48 . 
     The operation of the invention will be described in relation to ion exchange process, but it may be used in other potential application as described below. 
     In the process of ion exchange, the feed liquor  20  is introduced via inlet  22  into the bottom (second) end of the first fluidized bed  10  (downcomer  10 ) and the regenerated particles  18  from the bed  12  are introduced via line  17  adjacent to the first or the top of the first fluidized bed  10 , i.e. the feed  20  and regenerated beads are introduced at opposite ends of the first fluidized bed  10 . 
     The falling particles  18  and the up-flowing feed liquor  20  contact counter-currently and the target ions in the feed  20  are adsorbed onto the ion exchange particles  18  in the first fluidized bed  10 . The de-ionized liquor leaves from the top of the first fluidized bed through the raffinate outlet  44  and the loaded particles  18  fall into the washing stage  34  at the base of the first fluidized bed  10  are rinsed and then transferred via line  42  to the base of the second fluidized bed  12 . 
     During operations, as above described loaded ion exchange particles are transported into the base of the second fluidized bed  12  through the bottom solids return pipe  42  to make up the particles  18  entrained up along the second fluidized bed  12 . The bottom solids return pipe  42  operates as a packed moving bed forming the dynamic seal between the second fluidized bed  12  and the first fluidized bed  10 . The extracting buffer  28  is applied to the second fluidized bed  12  at the bottom. The superficial liquid velocity in the second fluidized bed  12  is maintained in a range higher than the terminal velocity of the ion exchange particles  18  so that the loaded particles are carried upward by the upflowing buffer  28 . The buffer  28  and the loaded ion exchange particles  18  hence contact co-currently while desorption and regeneration of the particles  18  proceed in the second fluidized bed  12 . The extract  28  and the regenerated ion exchange particles  18  are separated by a liquid-solids separator  46  adjacent to the top of the second fluidized bed  12 . 
     The extract is then collected from the extract outlet  48  and the regenerated ion exchange particles  18  returned to the first fluidized bed  10  through the top solids return pipe  17 , after being rinsed through the wash section  50 . 
     The liquid-solids separator  46  in the illustrated arrangement is a hydraulic (but can be any other type of separator) cyclone, which separates the regenerated particles  18  from the extract  28 . The extract outlet  48  is located on the separator preferably at the same level as that of the raffinate outlet  44  on the top of the first fluidized bed  10  to maintain the pressure balance between the second fluidized bed  12  and the first fluidized bed  10 . To prevent the loss of particles through the extract outlet, a stainless steel mesh (not shown) is preferably used to cover the extract outlet  48 . 
     The top washing section  50  comprises of the funnel bottom of the separator and return pipe  17 . The upward washing water slows down the falling of the particles  18  and creates a solids layer in the funnel bottom of the separator  46 . It also rinses the particles  18  before their falling into the top solids return pipe  17  and minimizes the inter-mixing between the extract in the second fluidized bed  12  and the de-ionized liquor at the top of the first fluidized bed  10 . The return pipe  17  (particle inlet to the first fluidized bed  10 ) enters the first fluidized bed  10  sufficiently below the outlet  44  to maintain a freeboard section  64  in the upper part of the first fluidized bed  10  of sufficient height to substantially eliminate carry over of particles  18  through the outlet  44 . 
     Although the invention has been illustrated with the feed liquor flowing upwards in countercurrent with the particles in the first fluidized bed and the extract buffer flowing upwards in cocurrent with the particles in the second fluidized bed, it will be clear to those skilled in the art that the two fluidizing fluids can be switched with the feed liquor flowing upwards in cocurrent with the particles in the second fluidized bed and the extract buffer flowing upwards in countercurrent with the particles in the first fluidized bed. 
     Applications of the Present Invention 
     A feed liquor  20  from which ions can be recovered, such as a fermentation broth, usually contains a large amount of small solids and relatively low concentration of desired product(s). Hence, the first task in developing a new downstream treatment process usually focuses on the selection of an appropriate procedure for handling the solids present in the feed. This is typically achieved by filtration or centrifugation. However, the presence of colloidal solids and the viscous properties of many feeds frequently make those methods both costly and inefficient. The LSCFB ion exchange system of the present invention is an integrated unit operation which can recover desired ions from unclarified whole broth continuously. 
     The desorption of the target ions and the regeneration of the ion exchange particles are carried out in the second fluidized bed  12 . The loaded ion exchange particles  18  are transported into the base of the second fluidized bed  12  through the bottom solids return system  14  and flow co-currently upward with the extracting buffer  28  along the second fluidized bed  12 . The loaded particles are stripped of the target ions and regenerated in the second fluidized bed  12  before being entrained into the liquid-solids separator  46  of the transfer system  16 . As the second fluidized bed  12  is operated in the circulating fluidization regime with high liquid velocity, the contact efficiency and the mass transfer rate between the liquid and solids are very high. 
     In the liquid solids circulating fluidized bed (LSCFB), diagrammed in  FIG. 1 , the adsorption in the first fluidized bed or downcomer  10  and the desorption in the second fluidized bed or second fluidized bed  12  can be carried out in a continuous mode with the ion exchange particles circulated continuously between the two columns. The ion exchange particles  18  employed in this system should have reasonably large adsorption capacity to the target or desired ions and the density of the ion exchange particles  18  in the swollen state should be larger than that of the feed liquor. As the first fluidized bed  10  is maintained in the conventional fluidization regime, the bed voidage could be adjusted to allow the passage of the particulates in an unclarified feed by controlling the superficial liquid velocity in the first fluidized bed. In other words, this system can be used to purify the target ions directly from an unclarified whole broth so that the costly pre-clarification process is eliminated. 
     In the LSCFB, the adsorption of the target ions are carried out in the first fluidized bed  10  and the desorption and the regeneration in the second fluidized bed  12 . This is a continuous process with the ion exchange particles  18  circulated continuously between the two columns  10  and  12 . Two different liquid streams, the feed  20  in the first fluidized bed  10  and the extracting buffer  28  in the second fluidized bed  12 , are used in this system. The second fluidized bed  12  is operated in the circulating fluidization regime and the first fluidized bed in the conventional fluidization regime. 
     Although the above description uses the first fluidized bed for adsorption and the second fluidized bed for desorption, it will be understood by those skilled in the art that one can also use the second fluidized bed for adsorption and the first fluidized bed for desorption. 
     EXAMPLES 
     In an arrangement as shown in  FIG. 1 , the second fluidized bed  12  is an acrylic column of I.D. 38.1 mm and 3 m in height. The distributor of the second fluidized bed  12  divides the incoming stream of extracting buffer into two substreams: the primary  60  and the auxiliary  62  streams. The primary stream  60  is introduced through a stainless steel pipe (I.D. 11 mm) (nozzle  30 ). It projects 36 mm into the second fluidized bed column  12 . Since the liquid velocity in the second fluidized bed is maintained in a range higher than the terminal velocity of the ion exchange particles, the high liquid velocity enhances the contact efficiency and also the mass transfer rate between the liquid and the particles. 
     The top washing section  50  as above described comprises of the funnel bottom of the separator  46  and an acrylic pipe of 40 mm in diameter and 200 mm in height (pipe  17 ). 
     The first fluidized bed is a Plexiglas column of I.D. 120 mm and 2.5 m in height. The particle entrance  17  on the first fluidized bed  10  is located 0.813 m below the raffinate outlet  44  to prevent the direct loss of particles through the raffinate outlet  44 . The distributor  22  of the first fluidized bed  10  is a perforated stainless steel pipe. This distributor allows the particles to fall through to the bottom solids return pipe  42  while introducing the feed  20  to the first fluidized bed  10 . 
     The bottom washing section  34  is comprised of the funnel bottom of the first fluidized bed  10  and a vertical pipe  40  of 40 mm I.D. and 200 mm in height. Wash water is introduced from the base of this column and goes upward (nozzle  38 ). 
     In the LSCFB ion exchange system, the solids circulation rate is controlled as above described by a butterfly valve  70  located on the bottom solids return pipe  42 . 
     Table 1 summarizes the experimental result conducted using the apparatus as above described, with whole whey which contains approximately 5.4 g/L proteins and with an artificial protein solution, the 2 g/L bovine albumin serum (BSA) solution. The protein recovery from BSA solution was much higher than that from the whey solution. This is because the high ionic strength and the fouling effects of the milk-fats in whey solution reduced the dynamic capacity of the system. 
                                                                                 TABLE 1                   Summary of parameters of whey protein recovery under different       conditions                            Protein                   Protein   Feed   Protein   Conc. in       Through-           Conc.   Flow   Loading   Raffinate   Overall   put       Feed   in Feed   rate   Rate   (waste feed)   Recovery   (g/hr · (kg       Type   (g/L)   (L/hr)   (g/hr)   (g/L)   (%)   beads))                    Whey   5.4   5.7   31.2   0.77   78.4   8.2       BSA   2.0   38.4   76.8   0.79   84.0   21.5       Solu-       tion                    
Potential Technology Applications
 
     Potential applications of the invention that the invention is believed to be suitable for include but are not limited to:
         a) The recovery of ionic products from biological or non-biological feeds such as protein recovery from fermentation broth, metal recovery from sea water, etc. where suitable ion exchange particles are available;   b) The removal of ionic contaminants from products or intermediate products, e.g., removal of enzyme from dextrose syrup after the conversion;   c) The desalination of water;   d) Wastewater treatment.
 
In Summary
 
Ion Exchange of Target Ions Occurs by:
   1. Regenerated ion exchange particles are fed to the first fluidized bed through the top solids return pipe; those particles flow down to the lower part of the first fluidized bed to form a particulate bed;   2. The feed liquor flows upward through the down moving bed of ion exchange particles and maintains the bed in the conventional fluidized regime;   3. The target ions are adsorbed onto the ion exchange particles when the ion exchange particles and the feed contact counter-currently in the particulate bed;   4. The de-ionized liquid is discarded from the raffinate outlet and the loaded ion exchange particles fall into the bottom wash section;   5. The rinsed ion exchange particles are continuously transported to the second fluidized bed through the bottom solids return pipe;   6. Extracting buffer is fed into the base of the second fluidized bed and flows upward at a velocity higher than the terminal velocity of the particles, thereby maintained in a circulating fluidization regime;   7. The loaded particles are desorbed and regenerated while being entrained up continuously along the second fluidized bed;   8. The regenerated particles are separated from the extract in the liquid-solids separator at the top; the extract is collected from the extract outlet on the liquid-solid separator and the regenerated particles are rinsed in a wash section below the separator;   9. The rinsed particles are fed to the first fluidized bed by gravity. Another cycle begins.       

     As used herein, the terms “comprises”, “comprising”, “including” and “includes” are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in this specification including claims, the terms “comprises”, “comprising”, “including” and “includes” and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components. 
     Having described the invention, modifications will be evident to those skilled in the art without departing from the spirit of the invention as defined in the appended claims. Therefore the foregoing description of the preferred embodiments of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiment illustrated. It is intended that the scope of the invention be defined by all of the embodiments encompassed within the following claims and their equivalents.