Process for the Preferential Separation of Fructose From Glucose

According to U.S. Pat. No. 3,440,159, the electrical separation of low molecular weight substantially un-ionized substances from liquid mixtures thereof with other substances is known. That patent relates to such separation of un-ionized or only partially ionized substances of low molecular weight (crystalloids) from high molecular weight substances (colloids) in aqueous solution by causing the former to migrate under the influence of an electric potentional across ion selective membranes which are substantially impermeable to the high molecular weight substances (colloids). As examples of this process it is disclosed that such low molecular weight un-ionized substances as phenol, furfurol, xylose, arabinose, sucrose, lactose, fructose, mannose, maltose, and dextrose may be separated from such high molecular weight substances as albumin, casein, polysaccharides, lignin and dextrin, for example. Moreover, U.S. Pat. No. 3,718,560 discloses the removal of salts from sugar solutions by electrodialysis in a cell having ion permeable membranes alternately disposed between the electrodes. This same patent discloses that ionizing salts have also been removed from sugar solutions by means of cation and anion exchange resins. Furthermore, U.S. Pat. No. 3,806,363 discloses the following methods of separating glucose and fructose from mixtures containing such sugars: (1) converting fructose into a calcium-fructose complex by treatment with calcium hydroxide; (2) use of a calcium form cation-exchange resin bed; (3) use of a strontium form cation-exchange resin bed; (4) use of a silver form cation-exchange resin bed; (5) use of a borate form anion-exchange resin bed; (6) use of a hydrazine form cation-exchange resin bed, and (7) a method involving the use of a bisulfite form anion-exchange resin bed. According to U.S. Pat. No. 3,806,363, only the method utilizing calcium hydroxide has been adopted for commercial operation, but in poor yield. Furthermore, the cation exchange resin processes are not very flexible and result in highly dilute process streams since water is used as the desorbent. This results in high evaporation cost.

It has now been found that fructose may be preferentially separated from a mixture of glucose and fructose. This result is accomplished by a process comprising the steps of (1) passing a liquid mixture of fructose and glucose through a first feed chamber of an electro-osmosis cell comprising at least two chambers defined between ion exchange membranes having alternating high and low permeability coefficients with respect to each other, (2) passing a direct electric current transversely through said membranes and chambers in a direction to cause the fructose to pass from said feed chambers through said high permeability coefficient membrane into a second chamber with said fructose being substantially retained in the second chamber, and (3) recovering a glucose enriched and a fructose enriched effluent from the separate chambers. Preferably, the ion-exchange membranes are in the form of a cation of an alkaline earth metal selected from the class consisting of calcium, magnesium and barium.

The process of this invention may be described by reference to FIG. 1 wherein:

E.sub.a =anode electrode

C.sub.L =relatively high permeability membrane

C.sub.T =relatively low permeability membrane

F=fructose

G=glucose

*=indication of enriched product

E.sub.c =cathode electrode

FIG. 1 shows schematically a stack of electrodialysis membranes in a configuration designed for electroosmatic transfer. A complete discussion of electrodialysis membranes is contained in the publication entitled "Principles and Applications of Electrodialysis and Related Membrane Processes" by William B. Iaconelli, published by Ionics, Inc., Watertown, MA 02172 (july 1970). A charge of electricity is shown being applied to the cathode electrode. The concept of alternating high and low permeability coefficients of cation and anion exchange membranes is described in U.S. Pat. No. 3,440,159. A solution of fructose, glucose and salt is shown being introduced between alternating high permeability and low permeability membranes. Also an aqueous salt solution is shown being introduced between alternating membranes. In accordance with the process of this invention the salt comprises a salt of an alkaline earth metal selected from the group consisting of calcium, magnesium and barium. This operating electrodialysis stack effectively produces the two effluents shown, that is a glucose enriched stream and a fructose enriched stream. The surprising fact about this result is that such separation is made between fructose and glucose which have the same molecular weight.

The records of actual runs of the electrodialysis method in accordance with the process of this invention are summarized in Tables 1 and 2, as follows: Fructose/Glucose Separation Basis: Enriched Stream Analysis Description Run DILUTE STREAM DESCRIPTION Sugar transferred Power Sugar Transfer Run temp, Duration INITIAL FINAL Flux No. of Consump. g/Faraday R = KWH/ # salt, conc, .degree. C. pH minutes gFr gDx Vol, 1 gFr gDx Vol, 1 gFr gDx lb/hr ft.sup.2 Faradays Whrs. Fr Dx F/G lb Fr 2 MgCl.sub.2, 10, 45, 3-4 60 0 504 1.242 39 480 1.287 39 -24 0.013 1.491 149.8 26.2 -16.1 -1.6 1.744 3 " 20, 43, 3-4 60 0 517 1.189 30 486 1.179 30 -31 0.001 1.278 94.3 23.4 -24.2 -0.97 1.427 4 " 5, 43, 3-4 60 0 516 1.231 33 497 1.276 33 -19 0.012 1.137 137.0 28.9 -16.7 -1.73 1.885 5 " 10, 38, 3-4 60 0 502 1.149 29 491 1.204 29 -11 0.016 1.141 114.7 25.4 -9.6 -2.6 1.796 6 " 10, 44, 3-4 60 RESULTS NOT AVAILABLE 1.502 120.8 -- -- -- -- 17 " 10, 49, >6 60 0 496 1.215 42 490 1.310 42 -6 0.032 1.434 144.1 29.3 -4.2 -6.98 1.558 18 " 10, 47, >6 60 0 512 1.185 40 495 1.265 40 -17 0.020 1.385 139.2 28.9 -12.3 -2.35 1.580 7 CaCl.sub.2 20, 42, 3-4 60 0 502 1.242 38 496 1.312 38 -6 0.028 1.502 120.8 25.3 -4.0 -6.33 1.443 8 " 10, 42, 3-4 60 0 512 1.166 36 511 1.251 36 -1 0.031 1.166 93.8 30.8 -0.9 -34.2 1.183 9 " 20, 41, 3-4 60 0 528 1.242 25 529 1.312 25 1 0.023 1.218 81.6 20.5 0.8 25.6 1.482 10 " 20, 53, 3-4 60 0 518 1.317 49 514 1.397 49 -4 0.040 1.763 118.1 28.0 -2.3 -12.2 1.094 11 " 10, 47, >7 60 55 426 1.100 96 402 1.150 41 -22 0.017 1.203 96.8 34.1 -18.3 -1.86 1.072 12 " 10, 49, 3-4 60 0 555 1.273 548 19 1.303 -7 19 0.011 1.054 84.8 -6.6 18.0 .37 13 " 10, 47, 3-4 60 0 511 1.148 26 463 1.223 26 -48 -0.019 1.234 99.3 21.1 -38.9 -.54 1.734 14 " 5, 49, 3-4 60 0 491 1.182 44 499 1.297 44 8 0.046 1.194 128.0 36.9 6.7 5.5 1.321 15 " 10, 49, >6 60 0 484 1.274 67 461 1.379 67 -23 0.039 1.438 115.7 46.6 -16.0 -2.91 0.784 16 " 10, 49, >6 60 17 465 1.134 62 455 1.214 45 -10 0.031 1.205 96.4 37.0 -8.3 -4.46 0.973 19 KCl, 10, 50, 3-8 35 0 500 1.340 34 503 1.440 34 3 0.056 2.241 180.2 15.2 1.3 11.7 2.406 20 KCl, 5, 49, 3-4 40 0 509 1.270 29 514 1.355 29 5 0.045 1.828 196.0 15.8 2.7 5.85 3.068 21 BaCl.sub.2, 10, 46, 3-4 80 0 509 1.270 52 518 1.415 52 9 0.040 1.317 132.0 39.5 6.8 5.81 1.152 22 BaCl.sub.2, 10, 45, >6 80 0 515 1.310 51 516 1.445 51 1 0.034 1.254 126.0 40.7 0.8 50.9 1.122 Fructose/Glucose Separation Basis: Dilute Stream Analysis Description Run DILUTE STREAM DESCRIPTION Sugar transferred Power Sugar Transfer Run temp, Duration INITIAL FINAL Flux No. of Consump. g/Faraday R = KWH/ # salt, conc, .degree.C. pH minutes gFr gDx Vol,1 gFr gDx Vol,1 gFr g Dx lb/hr ft.sup.2 Faradays Whrs. Fr Dx F/G lb Fr 2 MgCl.sub.2, 10, 45, 3-4 60293 237 1.242 236 235 1.162 57 2 0.052 1.491 149.8 38.2 1.3 28.5 1.193 3 " 20, 43, 3-4 60 283 253 1.176 241 254 1.121 42 -1 0.036 1.278 94.3 32.8 -0.8 -40.1 1.019 4 " 5, 43, 3-4 60 283 251 1.213 227 240 1.131 56 11 0.059 1.137 137.0 49.3 9.7 5.1 1.111 5 " 10, 38, 3-4 60 273 253 1.196 226 247 1.126 47 6 0.047 1.141 114.7 41.2 5.3 7.8 1.108 6 " 10, 44, 3-4 60 208 189 1.174 162 174 1.079 46 15 0.054 1.502 120.8 30.0 10.0 3.0 1.192 17 " 10, 49, >6 60 277 250 1.325 225 245 1.220 52 5 0.050 1.434 144.1 36.3 3.5 10.4 1.258 18 " 10, 47, >6 60 286 246 1.302 238 250 1.212 48 -40.039 1.385 139.2 34.7 -2.9 -12.0 1.317 7 CaCl.sub.2, 20, 42, 3-4 60 282 244 1.235 227 235 1.160 55 9 0.056 1.502 120.8 36.6 6.0 6.1 0.997 8 " 10, 42, 3-4 60 270 247 1.181 217 236 1.081 53 11 0.056 1.166 93.8 45.5 9.4 4.8 0.803 9 " 20, 41, 3-4 60 295 266 1.260 245 251 1.160 54 15 0.061 1.218 81.644.3 12.3 3.6 0.686 10 " 20, 53, 3-4 60 283 262 1.317 220 245 1.202 63 17 0.070 1.763 118.1 30.1 9.6 3.7 0.854 11 " 10, 47, >7 60 255 256 1.138 203 246 1.038 52 10 0.055 1.203 96.8 43.2 8.3 5.2 0.845 *12 " 10, 49, 3-4 60 269 236 1.168 274 210 1.113 -5 26 0.019 1.054 84.8 -4.7 24.7 -0.2 -- 13 " 10, 47, 3-4 60 267 281 1.199 210 272 1.104 57 9 0.058 1.234 99.3 46.2 7.3 6.3 0.791 14 " 5, 49, 3-4 60 265 237 1.121 204 222 1.001 61 15 0.067 1.194 128.0 51.1 12.6 4.1 0.953 15 " 10, 49, >6 60 266 242 1.293 210 235 1.162 56 7 0.056 1.438 115.7 38.9 4.9 8.0 0.938 16 " 10, 49, >6 60 279 261 1.173 223 244 1.073 56 17 0.0641.205 96.4 46.5 14.1 3.3 0.782 19 KCl, 10, 50, 3-8 35 284 247 1.350 235 234 1.250 49 13 0.094 2.241 180.2 21.9 6.2 3.5 1.670 20 KCl, 5, 49, 3-4 40 283 240 1.195 237 232 1.125 46 8 0.071 1.828 196.0 25.2 4.4 5.8 1.934 21 BaCl.sub.2, 10, 46, 3-4 80 281 249 1.210 205 224 1.055 76 25 0.067 1.317 132.0 57.7 19.0 3.0 0.789 22 BaCl.sub.2, 10, 45, >6 80 289 247 1.310 222 226 1.140 67 21 0.058 1.254 126.0 53.4 16.7 3.2 0.854 *Fructose in conc. Compt.

In all of the above runs, in the incoming stream a mixture of fructose and glucose was used. A ten-cell membrane pair stack with a diluting and a concentrating stream was employed. The analytical results obtained are based on differential polarimetry for fructose/glucose. The solids content was monitored by a hand sugar refractometer and the specific gravity determined from tables for corn syrups. The fructose used was almost free of moisture, whereas the glucose (cerelos) was found to contain 9% moisture. In each run, flow rates, stream volumes, pressures, voltage and current were monitored. A heat exchanger system was incorporated to maintain temperatures of the dilute and enriched streams.

It is apparent from the results shown in Tables I and II that glucose-fructose separation may be achieved by electrodialysis in accordance with the process of this invention. Magnesium, potassium, barium and calcium alkaline earth metals are practical equivalents in mediating the preferential separation of these sugars. The separation can be achieved at salt concentrations as low as 5 gram/liter without significant loss of separation efficiency. Separation factors of at least 1.3 are indicated. Fructose enrichment can be effected even when the same syrup composition is used in both the dilute and enriched chambers initially.