Abstract:
A method for the separation of water soluble carbohydrates from a feed solution by the utilization of a fractionation medium. The solution contains carbohydrates A and B in major amounts and carbohydrate A has a volume distribution coefficient at least 0.05 units greater than carbohydrate B when determined on said medium.

Description:
BACKGROUND OF THE INVENTION 
     There are a number of publications and patents which disclose methods of separating water soluble carbohydrates and other materials. British Pat. No. 731,335 discloses the separation of a mixture of at least two water soluble organic compounds each having an ionization constant of not more than 1.4 × 10 -   3 . In this separation method, cation exchange resins which contain sulphonate radicals as the functional groups are utilized. U.S. Pat. No. 3,044,904 to Serbia and U.S. Pat. Nos. 3,044,905 and 3,044,906 both to Lefevre, disclose the utilization of various salts of a nuclearly sulfonated styrene resin to separate dextrose and fructose. In U.S. Pat. No. 3,184,334 to Sargent the separation of dextran from fructose by the utilization of ion exchange resins in the salt form and acid-and salt-forms is disclosed and U.S. Pat. No. 3,483,031 to Lauer et al. teaches the separation of glucose and fructose by using an ion exchange resin charged with calcium ions. 
     There are a number of problems associated with the separation of various water soluble carbohydrates by the use of resins. Generally, large quantities of water are involved with such separations and, due to the dilution factors involved, removal of water to obtain the carbohydrates in a relatively pure and concentrated state requires high energy costs. Moreover, the equipment necessary to effect an efficient separation is generally quite complex and requires a number of holding tanks or similar devices and thereby entails a costly capital investment. Gross, Intl. Sugar J., Vol 73, p. 330 (1971), discloses a partial solution to this problem whereby holding tanks, used for storage of recycle liquid, are eliminated by the utilization of two columns of resins positioned in series. However, this process does not result in the desired degree of separation. 
     OBJECTS 
     It is a principal object of the present invention to provide an efficient and economical method for separating carbohydrates from aqueous solutions which overcomes the problems heretofore encountered in such separations. 
     It is another object of the present invention to provide an effective method for separating carbohydrates wherein minimum amounts of water are utilized. 
     It is still another object of the present invention to provide a method for separating carbohydrates wherein only one recycle holding tank is necessary. 
     Other objects and advantages of this invention will be apparent from the following discussion and drawings. 
     SUMMARY OF THE INVENTION 
     This invention relates to a method for the separation of water soluble carbohydrates from a feed solution containing carbohydrates A and B in major amounts by the utilization of a fractionation medium. Carbohydrate A has a volume distribution coefficient at least 0.05 units greater than carbohydrate B when determined on said medium. The method comprises: 
     I. Admitting sequentially predetermined volumes of the feed solution and elution water to a column of the medium; 
     II. Separating the effluent from the column sequentially into the following fractions: 
     (a) carbohydrate A rich fraction, 
     (b) carbohydrate A rich fraction highly contaminated with carbohydrate B, 
     (c) carbohydrate B rich fraction highly contaminated with carbohydrate A, 
     (d) carbohydrate B rich fraction and 
     (e) dilute carbohydrate B rich fraction; 
     III. Admitting sequentially into the column: 
     (a) carbohydrate A rich fraction highly contaminated with carbohydrate B, 
     (b) a volume of feed solution approximately equal to the volume of carbohydrate B rich fraction, 
     (c) carbohydrate B rich fraction highly contaminated with carbohydrate A, 
     (d) dilute carbohydrate B rich fraction and 
     (e) a volume of elution water approximately equal to the volume of the carbohydrate A rich fraction, the carbohydrate A rich fraction highly contaminated with carbohydrate B and the dilute carbohydrate B rich fraction being recycled directly to the column and the carbohydrate B rich fraction highly contaminated with carbohydrate A being collected while the feed solution is introduced into the column and then admitting said collected fraction into the column and 
     IV. Repeating steps II and III in a cyclic manner. 
    
    
     DRAWINGS 
     FIG. 1 shows a diagrammatic arrangement of the method for the separation of carbohydrates from a water solution. 
     FIG. II graphically depicts the separation of glucose from other carbohydrates. 
    
    
     DESCRIPTION OF THE INVENTION 
     For purposes of the present invention, the volume distribution coefficient (D) is determined by the procedure of Olaf Samuelson, Methods in Carbohydrate Chemistry, VI, 1972, pp. 65-75, using the formula: ##EQU1## where v is the retention volume (volume of effluent to attain peak maximum dry substance concentration), x is the volume of the fractionation medium and y is the interstitial volume of the medium. 
     A number of types of fractionation media may be used in the method of the present invention so long as the volume distribution coefficients of the carbohydrates sought to be separated thereon differ by at least 0.05 units. Preferably, the volume coefficients will differ by at least 0.1 units and most preferably by at least 0.2 units. 
     The preferred fractionation media are porous particulate ion exchange resins. In Table I, below, the volume distribution coefficients of various carbohydrates on a number of resins are illustrated: 
     
                                           TABLE I__________________________________________________________________________ Volume Distribution Coefficients of Various Carbohydrates On IonExchange Resins__________________________________________________________________________Temperature  Ion Exchange          Ionic° C   Resin  Form   Xylose                     Arabinose                           Galactose                                 Dextrose                                      Fructose__________________________________________________________________________40     Dowex 1-X8          Bisulfite              1.49 0.9540     Dowex 1-X4          Carbonate                 1.47                     1.27  1.2740     Dowex 50W-X4          Hydrazinium                 1.90                     2.31  2.30  2.09 1.1040     Dowex 50W-X4          Calcium                 1.15                     1.3570     Dowex 50W-X4          Calcium                 1.07                     1.21  1.11  1.00 1.2240     Dowex 50W-X4          Strontium                 1.14                     1.28        1.05 1.3370     Dowex 50W-X4          Strontium                 1.13                     1.23  1.18__________________________________________________________________________ 
    
     While the present method has application for the separation of a wide variety of carbohydrates, it is contemplated that it will be most applicable for the separation of fructose and glucose. Fructose-and glucose-containing solutions may be produced by processes well known in the art, such as the inversion of sucrose and the alkaline and enzymatic isomerization of glucose. Because of the low levels of impurities generally contained in enzymatically produced glucose-fructose solutions, such are preferred feed solutions in the present process. The presence of excessive quantities of impurities, such as saccharide degradation products, salts and the like, may decrease the effectiveness of the resin over extended periods of use. 
     The temperature, concentration of feed solution, height of column, particular fractionation medium utilized, number of recycles, volume of fractions and contact period all affect the efficiency of the separation. 
     The temperature at which separation is affected should not be so high as to cause breakdown of the carbohydrates and it must not be so low as to increase the viscosity of the solution to such a degree that the flow rate thereof through the column is deleteriously affected. In general, temperatures from about 40° to about 80° C. provide satisfactory results. 
     The method of the present invention may be performed in an apparatus depicted in the diagrammatic arrangement shown in FIG. I. Components of the apparatus shown in FIG. I are identified as follows: 
     reservoir or source of feed solution 1, 
     reservoir or source of elution water 2, 
     holding tank 3 for carbohydrate A rich fraction, 
     holding tank 4 for carbohydrate B rich fraction, 
     storage tank 5 for recycle liquor, 
     vertical column 6 charged with a fractionation medium and fitted at the top thereof with a distributor for admitting solutions uniformly to the upper surface of the resin and at the bottom with a distributor for drawing off effluent fractions, 
     pump 7 for circulating various fractions, 
     heating means 8 for maintaining the temperature of the column of resin constant and 
     valves 1 to 7 for directing the flow of the various fractions to and from the column in accordance with the desired method of operation. 
     The following relationships must be satisfied to return recycle fractions directly to the column without storage. 
      (1) Volume of feed solution = Volume of carbohydrate B rich fraction 
      (2) Volume of elution water = Volume of carbohydrate A rich fraction 
      (3) The volume of water which is initially displaced from the resin bed by the feed solutions prior to emergence of carbohydrate A plus the volume of carbohydrate A rich fraction must equal the cycle volume (total volume of carbohydrate A rich fraction, carbohydrate B rich fraction and recycle fractions). Note: The volume of water which is displaced from the resin will vary with different carbohydrates. 
     The volume of feed solution, elution water and recycle fractions can be varied within the constraints of the above relationships. Choice of volumes to satisfy the above stated equalities are identified below as predetermined. 
     At the start of the present process, column 6 is substantially full of a water-immersed resin. Valves 1 and 5 are opened and all other valves are closed. A predetermined volume of feed solution containing carbohydrates A and B is transferred from reservoir 1 through pump 7 to the top of column 6. The effluent from the column is directed through valve 5 and stored in tank 5. When the predetermined volume of feed liquor has been introduced via pump 7 to column 6 valve 1 is closed and valve 6 opened. The stored liquor in tank 5 is pumped to the column and the effluent continues to be directed to tank 5 for a predetermined volume. Valve 5 is then closed and valve 4 is opened. The remaining liquor in tank 5 is then pumped to the column while the carbohydrate B rich effluent is directed through valve 4 and collected in tank 4. The volume collected in tank 4 is about equal to the volume of feed liquor previously introduced. Valves 4 and 6 are then closed and valve 7 opened and the effluent rich in B but too dilute for use as product is recycled to the column directly. Valve 7 is then closed and valves 2 and 3 are opened. Elution water is introduced to column 6 and the carbohydrate A rich effluent liquor collected in tank 3. When the elution water has been introduced valves 2 and 3 are closed and valve 7 opened to recycle directly the liquor which is rich in carbohydrate A but too highly contaminated with carbohydrate B. After this recycling step the cycle is begun again by introducing feed liquor through valve 1 and storing the effluent which is rich in carbohydrate B, but highly contaminated with carbohydrate A in tank 5. 
     Since the dry substance concentration of the stored recycle fraction decreases during collection, the introduction of this fraction to the top of storage tank 5 will result in a layering effect which maintains the concentration gradient emerging from the column. Withdrawing this recycle fraction from the bottom of the tank allows the introduction of higher dry substance concentrations at the start of the recycle step. 
     The above described separation procedure may be performed continuously utilizing automatic sensing devices whereby the amounts of the various fractions are electronically determined so that valves depicted in the drawings are opened and closed according to a programmed sequence. 
     While the present method has been particularly described in regard to the separation of two carbohydrates, it should be understood that the separation process may be carried out so that an individual carbohydrate may be separated from a group of carbohydrates or that one group of carbohydrates may be separated from another group of carbohydrates. 
     EXAMPLE I 
     This example illustrates the separation of fructose and glucose from an enzymatically produced fructose-glucose containing solution. 
     A double-walled glass column having a 2.42 cm I.D. was filled with the calcium form of Dowex 50W-X4 cation exchange resin to a depth of 305 cm. The resin had a particle size of 35 to 70 U.S. Standard mesh. Water at 70° C. was circulated through the column jacket to maintain the temperature of the resin at 68° C. An enzymatically produced fructose-glucose containing solution having a dry substance of 50 percent was fractionated on the resin column using a 10 ml/min flow rate in accordance with the method of the present invention. The sequence of collecting and recycling fractions shown in Table II below was repeated 12 times to approach equilibrium of the system. 
     
                                           TABLE II__________________________________________________________________________ Separation of Glucose and Fructose on Calcium Form of Cation ExchangeResin__________________________________________________________________________Influent                     Effluent               Volume             Volume  Fraction     (ml)     Fraction  (ml)__________________________________________________________________________Recycle I           160 glucose rich fraction                                  328  (glucose rich fraction highly  contaminated with fructose)Feed                120 Recycle I (glucose rich                                  160  (fructose containing solution)                   fraction highly contami-                   nated with fructose)Recycle II          260 Recycle II (fructose rich                                  260  (fructose rich fraction highly                   fraction highly contami-  contaminated with glucose)                   nated with glucose)Recycle III         160 fructose rich fraction                                  120  (dilute fructose rich fraction)Elution water       328 Recycle III (dilute                                  160                   fructose rich fraction)__________________________________________________________________________ 
    
     Recycles I and III were returned directly to the fractionation column. Recycle II was stored until the feed liquor was introduced into the column and then Recycle II was introduced into the column. 
     At the end of the 12th cycle the carbohydrate content of the collected fractions and of the feed solution were determined and are set forth below: 
     
                       TABLE III______________________________________      Percent      Dry     Carbohydrates %Fraction     Substance Dextrose Fructose                                  Other______________________________________Feed         49.9      48.4     43.0   8.6Glucose rich fraction        13.9      79.5      7.4   13.1Fructose rich fraction        20.7       2.0     97.0   1.0______________________________________ 
    
     EXAMPLE II 
     This Example illustrates the separation of glucose from other carbohydrates in an enzymatically produced glucose containing solution. 
     A column of cation exchange resin described in Example I was prepared except that the resin volume was 1420 cm 3 . 
     An enzymatically produced glucose containing solution having a dry substance content of 53.5 percent was fractionated on the resin column using a 10 ml/min flow rate in accordance with the method of the present invention. 
     The separation sequence followed is set forth in Table IV below: 
     
                                           TABLE IV__________________________________________________________________________Separation of Glucose and Oligosaccharides on Calcium Form of CationExchange Resin__________________________________________________________________________Influent                  Effluent                Volume                Volume   Fraction     (ml) Fraction                           (ml)__________________________________________________________________________Recycle I            160  Oligosaccharide rich fraction                                      300  (oligosaccharide rich fraction  highly contaminated with glucose)Feed                 130  Recycle I (oligosaccharide                                      150  (glucose containing substrate)                     rich fraction highly con-                     taminated with glucoseRecycle II           250  Recycle II (glucose rich frac-                                      250  (glucose rich fraction highly                     tion highly contaminated with  contaminated with oligosaccharides)                     oligosaccharides)Recycle III          150  Glucose rich fraction                                      130  (dilute glucose rich fraction)Elution water        300  Recycle III (dilute glucose                                      130                     rich fraction)__________________________________________________________________________ 
    
     Recycles I and III were returned directly to the column. Recycle II was stored until the feed liquor had been introduced into the column. The sequence was repeated nineteen times to approach equilibrium of the system and then the carbohydrate content of the collected fractions and of the feed liquor were determined and are set forth in Table V below: 
     
                       TABLE V______________________________________   Percent    Carbohydrates % Fraction Dry Substance                  Glucose  Oligosaccharides______________________________________Feed      53.5         79.5     19.8Oligosaccharide      6.3         22.9     76.4rich fractionGlucose rich     35.6         95.4      3.7fraction______________________________________ 
    
     In FIG. II, a graph is set forth relating effluent volumes at equilibrium to the concentration of glucose and oligosaccharides. The relative slope and dispositions of the oligosaccharide and glucose curves are constant under these conditions.