The present invention relates to a method for fractionating a solution into two or more fractions en- riched with different components. In particular, the invention relates to a method for fractionating a solu¬ tion by a chromatographic simulated moving bed method in which the liquid flow is effected in a system comprising at least two chromatographic sectional packing material beds in different ionic forms, in which the dissolved substances present in the solution are separated from each other, and if the solution to be treated comprises substantial amounts of ions, the system also comprises a unit where the ion equilibrium of the solution is changed.

Fractionation of a solution comprising many dis¬ solved substances into fractions enriched with different components is often necessary to recover the desired components as pure as necessary. The method of the invention can be employed to carry out such fraction¬ ation. A sulphite cooking liquor, for instance, can be fractionated by the method so as to give a fraction rich in monosaccharides and/or a fraction rich in lignosul- phonates; furthermore, molasses or vinasse can be fractionated in this way to obtain fractions rich in a sugar, such as sucrose, and/or betaine.

The method of the invention is particularly well suitable for recovering monosaccharides from a sulphite cooking liquor, particularly for recovering xylose from a hardwood sulphite cooking liquor, in a continuously operated process by which also a fraction enriched with lignosulphonates can be recovered, if desired.

Sulphite cooking liquor in this context denotes liquor employed in sulphite cellulose cooking, liquor obtained after such cooking, or a part thereof.

It is known per se to use ion exchange resins of different ionic forms in chromatographic separation methods. Finnish Patent 59 388 describes chromatographic separation of polyols, employing columns packed with a cation exchange resin in different ionic forms (resin with a polystyrene skeleton cross-linked with divinyl- benzene and activated with sulphonic acid groups) . Fin¬ nish Patent 69 296 discloses a chromatographic method for the fractionation of polyols, in particular to ob- tain pure xylitol. Also this method employs a resin with a polystyrene skeleton cross-linked with divinylbenzene and activated with sulphonic acid groups, packed in parallel columns; in some columns, the resin is in earth alkaline form and in the other columns in Al ^3* or Fe ³⁺ form.

U.S. Patent 4 631 129 discloses the separation of sugars and lignosulphonates from a sulphite spent liquor by a process comprising two chromatographic treatments with ion exchange resins in different ionic forms. In the first treatment, the sulphite spent liquor is intro¬ duced into a chromatographic column comprising a strong acid resin used as column packing material in metal salt form; the metal ion is preferably a metal ion of the spent liquor, usually calcium or sodium. A substantially sugarless fraction rich in lignosulphonates and a frac¬ tion rich in sugars are obtained from this column by elution. The latter fraction is subjected to a softening treatment, and its pH is adjusted to be in the range 5.5 to 6.5, whereafter it is introduced into the second chromatographic column containing resin in monovalent form, and a second fraction rich in sugars and a second fraction rich in lignosulphonates and salts are obtained therefrom by elution. It is stated in this patent that the process is capable of recovering sugars, e.g. xylose contained in hardwood sulphite spent liquor, in a very

high purity and high yields. However, a drawback of the method is that the dry solids profile which has been formed in the first chromatographic treatment and in which the components are already partly separated is destroyed in the softening treatment and pH adjustment and thus cannot be utilized in the second chromato¬ graphic treatment. The method is also complicated by the steps of concentration and additional pumping to which the solution is subjected. All of these factors add to investment costs. Furthermore, this method and all prior art chromatographic separation methods in which ion ex¬ change resins of different ionic forms are used are attended by the drawback that they are typically batch methods and are not suitable for fractionating solutions on an industrial scale.

Continuously operated chromatographic separation processes nowadays commonly employ the simulated moving bed method, which is known in modifications developed for a variety of different applications. The simulated moving bed method enables a separ¬ ating performance as high as several times that of the batch method, and also significantly lower dilution of the products (consumption of eluent) .

The simulated moving bed method may be either continuous or sequential, as described in the copending Finnish patent applications 930321 and 932108 (corres¬ ponding to international patent applications WO 94/17213 and WO 94/26380, respectively). In the continuous simu¬ lated moving bed method, typically all flows are con- tinuous. These flows are: supply of feed solution and eluent, recycling of liquid mixture, and withdrawal of products. The flow rate for these flows may be adjusted in accordance with the separation goals (yield, purity, capacity). Normally, 8 to 20 sectional packing material beds are combined into a single loop. The feed and prod-

uct withdrawal points are shifted cyclically in the downstream direction in the packing material bed. On account of the supply of eluent and feed solution, the withdrawal of products, and the flow through the packing material bed, a dry solids concentration profile is formed in the packing material bed. Components having a lower migration rate in the packing bed are concentrated in the back slope of the dry solids concentration pro¬ file, and respectively components having a higher mig- ration rate in the front slope. The points of intro¬ duction of the feed solution and eluent and the with¬ drawal points of the product or products are shifted gradually at substantially the same rate at which the dry solids concentration profile moves in the packing material bed.

The feed and withdrawal points are shifted cycli¬ cally by using feed and product valves located along the packing material bed typically at the upstream and down¬ stream end of each sectional packing material bed. If it is desired to recover product fractions of very high purity, short cycle times and a plurality of sectional packing material beds must be employed (the apparatus has the requisite valves and feed and withdrawal equip¬ ment) . In the sequential simulated moving bed method, not all flows are continuous. In the sequential simul¬ ated moving bed method, the flows are: supply of feed solution and eluent, recycling of liquid mixture, and withdrawal of products (eluting phase; 2 to 4 or more products) . The flow rates and the volumes of the dif¬ ferent feeds and product fractions may be adjusted in accordance with the separation goals (yield, purity, capacity). The method comprises three basic phases: feeding, elution and recycling. During the feeding phase, a feed solution, and possibly also an eluent

during a simultaneous eluting phase, is introduced into predetermined sectional packing material beds, and simultaneously a product fraction or fractions are with¬ drawn. During the eluting phase, eluent is introduced into a predetermined sectional packing material bed or predetermined sectional packing material beds, and dur¬ ing these phases two, three or even four product frac¬ tions are withdrawn. During the recycling phase, no feed solution or eluent is supplied to the sectional packing material beds and no products are withdrawn.

Sequential simulated moving bed methods are disclosed in British published application 2 240 053 and U.S. Patent 4 970 002, for instance. A sequential simul¬ ated moving bed method applied to the recovery of beta- ine and sucrose from beet molasses is disclosed in Fin¬ nish Patent 86 416 (U.S. Patent 5 127 957). Also the above-mentioned copending Finnish patent applications 930321 (filing date January 26, 1993) and 932108 (filing date May 19, 1993) relate to a sequential simulated mov- ing bed method, the first applied to the fractionation of molasses and the latter to the fractionation of sul¬ phite cooking liquor. As is described in these applica¬ tions, the simulated moving bed method may be a multi- step process. The object of the present invention is a chrom¬ atographic method for the continuous fractionation of solutions, employing ion exchange resins of two or more different ionic forms, so that the dry solids concentra¬ tion profile formed upon passage of the solution through the chromatographic packing material having a first ionic form is passed to the chromatographic packing material having a second ionic form without the parti¬ ally separated components being remixed, and/or that the concentration and pumping stages of the solution, in- eluded in the prior art methods for fractionating solu-

tions with packing material of two different ionic forms, can be avoided.

By the method of the invention, valuable com¬ ponents of solutions produced as by-products in industry, such as monosaccharides and lignosulphonates from sulphite cooking liquor in the pulping industry and sugar, such as sucrose, and/or betaine from molasses produced in the sugar industry or vinasse produced in the fermentation industry, can be advantageously recov- ered. The method of the invention is particularly suit¬ able for the recovery of xylose from a hardwood sulphite cooking liquor.

The present invention relates to a simulated mov¬ ing bed method in which the liquid flow is effected in a system comprising at least two sectional packing mater¬ ial beds of different ionic forms. Between fractionation operations performed in packing materials of different ionic forms, the solution may be subjected to an addi¬ tional treatment step. For example, if the solution con- tains ions, the ion equilibrium of the solution is changed to be suitable for fractionation in the packing material having another ionic form. A change in the pH is also a change in the ion equilibrium.

A preferred embodiment of the invention is a sequential simulated moving bed in which the products are recovered during a multi-step sequence.

A sectional packing material bed may comprise one column; it is nevertheless also possible to pack several successive sectional packing material beds in a single column, depending on the column structure. On the other hand, several successive columns may be connected to form one or more loops.

Changing of the ion equilibrium of the solution to be suitable for fractionation with a packing material having another ionic form may comprise removal of

specific ions from the solution by ion exchange or precipitation, pH adjustment, and/or filtration, for instance. When the feed solution is sulphite cooking liquor having calcium as the base, this can be exchanged into sodium by ion exchange, or the calcium may be pre¬ cipitated for example as calcium sulphite or calcium sulphate with a sodium sulphite solution or sulphuric acid. The dry solids profile can be maintained essen¬ tially intact when the precipitation is performed for example in a tube reactor. The apparatus for carrying out such treatments can be connected in series between the sectional packing material beds having different ionic forms.

The ionic form of the packing material in this context means the ion equilibrium; for instance one sec¬ tional packing material bed may be predominantly in the calcium form and partly in the magnesium and/or sodium form. The ionic form of the packing material is equi¬ librated according to the ionic form of the feed solu- tion employed, and/or it is separately adjusted to suit the solution to be treated in each case.

The ionic form of the sectional packing material beds is selected in accordance with the solution to be fractionated. When the feed solution is sulphite cooking liquor, for instance, the packing material bed for the first fractionation treatment is preferably in the base form of the cooking liquor (often calcium or magnesium) and the packing material bed for the second fraction¬ ation treatment in monovalent metal ion form, e.g. Na ⁺ and/or K ⁺ form. In the fractionation of vinasse, prefer¬ ably the monovalent form (e.g. Na ^* or K ^* ) is first used, followed by the divalent form (e.g. Ca ²⁺ or Mg ^2t ) .

The method of the invention may be employed to fractionate sugar solutions as well. For example from a solution obtained from lactose by alkaline isomerization

and containing lactose, lactulose and galactose, a frac¬ tion enriched with galactose can be separated with a packing material in Na ⁺ form, and fractions enriched with lactulose and lactose can be separated from one another with packing material in Ca ²⁺ form. Likewise, salts can be removed from molasses, or maltose can be removed from syrup, with a packing material in K ⁺ /Na ^* form, and after subsequent inversion of sucrose, being carried out as an intermediate step, fractions enriched with glucose and fructose can be separated from one another with a pack¬ ing material in Ca ^2t form.

In a preferred sequential simulated moving bed method of the invention, the product or products are re¬ covered by employing a multi-step sequence comprising the following operations, i.e. phases: feeding phase of the solution to be fractionated, eluting phase and re¬ cycling phase.

During the feeding phase, the solution to be fractionated (feed solution) is supplied to the sec- tional packing material bed, and a corresponding amount of a product fraction is recovered at a point downstream in the flow direction, which may be either in the same sectional packing material bed as the feed point (in which case the other sectional packing material beds in the system may be in the eluting or recycling phase, for instance) or in a sectional packing material bed differ¬ ent than the feed point, and connected in series (pos¬ sibly through other sectional packing material beds and/or a unit changing the ion equilibrium) with the sectional packing material bed to which feed solution is supplied.

During the recycling phase, the liquid present in the sectional packing material beds with dry solids pro¬ file is recycled in a loop comprising one, two or more sectional packing material beds.

In the eluting phase, eluent is introduced into a sectional packing material bed and a corresponding amount of product fraction or fractions are recovered at a downstream point of the packing material bed, from the same or a downstream sectional packing material bed.

A process step comprises one or more of the above simultaneous identical or different phases. A step can consist of, for example, a feeding phase, recycling phase or eluting phase only, a feeding phase and a simultaneous recycling and/or eluting phase or phases, an eluting phase and a simultaneous recycling phase or phases, a recycling phase and a simultaneous eluting phase or phases, etc. These steps are repeated one or several times during the sequence. These phases are employed to form sequences com¬ prising several successive process steps. In accordance with the invention, a sequence comprises 4 to 20, pre¬ ferably 4 to 10 steps.

A sequence comprising the above steps is repeated about 6 to 8 times to equilibrate the system, whereafter the process is continued in a state of equilibrium.

Typically 2 to 12, preferably 2 to 7, chromato¬ graphic sectional packing material beds grouped into one or more loops are employed in the method of the inven¬ tion. A loop may comprise one, two or more sectional packing material beds packed in one or more columns.

In the method of the invention, recycling is em¬ ployed such that one, two, three or even more discrete successive loops are formed in the recycling phase. For example, when the number of sectional packing material beds is three, these may form one loop or preferably two loops (in which case the method is called a two-phase metho ), one of the loops comprising one and the other two sectional packing material beds. When the system

comprises several successive discrete loops, each of these may be closed or open, that is, when the liquid is recycled in one loop, eluent can be introduced into the other loop and a product fraction can be withdrawn there- from. During the feed and elution, the flow through the packing material beds may be effected between the suc¬ cessive loops, the flows conveying material from one loop to another. During the recycling phase, the loop is closed and isolated from the other loops. A separate dry solids profile is recycled in each of the discrete loops. Each sectional packing material bed may form one discrete loop. On the other hand, a loop may comprise one or more sectional packing material beds.

A particularly preferred embodiment of the inven- tion is a simulated moving bed method employing sec¬ tional packing material beds in two different ionic forms for simultaneous recovery of xylose and lignosul¬ phonates from a hardwood sulphite cooking liquor on an industrial scale in high yields and advantageous purity for further processing or use. Furthermore, the salts, oligosaccharides and other components in the sulphite cooking liquor which are harmful to the production of pure crystalline xylose, for instance, can be advantage¬ ously removed from the xylose fraction by this method. If a softwood sulphite cooking liquor is employed as the raw material, the prevailing monosaccharide is mannose and a mannose-rich fraction is obtained by the method.

If in the method only a monosaccharide (e.g. xylose) fraction and a residue fraction are separated from the sulphite cooking liquor, the lignosulphonates are eluted with organic and inorganic salts into the residue fraction. However, the method of the invention yields a dry solids profile in which lignosulphonates are concentrated in relation to salts at the front slope

of the dry solids profile, and they can be recovered by suitably selecting the product withdrawal point.

The implementation of the method (e.g. the ionic forms of the sectional packing materials; number of loops to be forme ) and the process parameters are chosen for example in accordance with the composition of the feed solution employed as the raw material so as to yield an optimum result with regard to product purity and yield and the separation capacity of the packing material.

Preferably a strong acid gel-type cation exchange resin (e.g. "Finex", "Amberlite" or "Dowex" ) is employed as the packing material, and in the first chromato¬ graphic fractionation treatment it preferably has the ionic form of the feed solution. Prior to separation, the solids present in the solution are removed therefrom by filtration.

If the solution to be fractionated is e.g. a sul¬ phite cooking liquor, vinasse or molasses, it is heated to 40 to 100°C, preferably 50 to 85°C, prior to being fed into the separation process. In such a case, the eluent employed can be water or a solution obtained from con¬ centration of dilute fractions (e.g. condensate obtained from evaporative concentration) at a temperature 40 to 100°C, preferably 50 to 85°C. The linear flow rate of the liquid in the columns is 0.5 to 12 m/h, even 20 m/h, preferably 2 to 10 m/h.

The following examples illustrate the invention in greater detail. These examples are not to be con- strued as limiting the field of the invention, but they are only illustrative of the special embodiments of the invention.

The dry solids contents indicated have been determined by the Karl Fischer method, unless otherwise indicated.

Example 1

Two-phase separation method for sulphite cooking liquor

A chromatographic separation apparatus comprising four columns connected in series was employed. Three of these were separation columns and one was a column re¬ moving divalent cations. The apparatus further comprised a feed pump, recycle pumps, an eluent water pump, flow and pressure regulators, and inlet and product valves for the process streams. Columns 1, 2 and 4 were separ¬ ation columns and column 3 a column for removing di¬ valent cations. The two first columns comprised four sectional packing material beds (8 m), the column for removing divalent cations comprised one sectional pack- ing material bed (1.5 m), and the fourth column com¬ prised two sectional packing material beds (4 m).

Each of the four columns was packed with a strong acid cation exchange resin (Finex V09 C™). The resin had a polystyrene skeleton; it was cross-linked with divinyl- benzene and activated with sulphonic acid groups, and had a mean bead size (in Na ⁺ form) of 0.39 mm. The resin had a DVB content of 5.5%. The resin of the first two columns had been regenerated into Ca ^2* form and the sec¬ tional packing material of columns 3 and 4 into Na ⁺ form prior to the test.

Test conditions: Diameter of columns 0.11 m

Height of resin bed in the column for removing divalent cations 1.5 Total height of resin bed in separation columns 12 m

Temperature 75°C

Volume flow rate 14-75 1/h

The feed solution was hardwood sulphite cooking liquor whose composition was analyzed by HPLC. The cook¬ ing liquor was in calcium base form. The analysis res¬ ults are shown in Table 1, where the percentages of the different components are given as per cent by weight on dry solids basis.

Table 1 Analysis of feed solution

Fractionation was performed by a four-step sequence. The sequence had a cycle length of 92 minutes, and it comprised the following steps:

Step 1: 17 1 of feed solution was introduced ( feeding phase) into column 1 at a volume flow rate 33 1/h, and 17 1 of residue (residue 1) was eluted from the downstream end of the same column at the same volume flow rate. Simultaneously 25 1 of eluent water was sup¬ plied (eluting phase) to column 2 at a volume flow rate 45 1/h, and 25 1 of residue (residue 4) was withdrawn from column 4 at a volume flow rate 45 1/h. In this

eluting phase, the column for removing divalent cations was connected to this open elution loop. The volume flow rate in the column for removing divalent cations during the elution was 45 1/h, and the feed volume from this column was 25 1. Subsequent to the column for removing divalent cations, the pH of the solution was adjusted to be within the range 5.5 to 6.5. After pH adjustment, the solution was filtered. The feed from the column for re¬ moving divalent cations was introduced into the upper portion of the fourth column.

Step 2: Recycling (recycling phase) in the loop formed by columns 1 and 2 (13.0 1; 50 1/h) with simul¬ taneous supply of 4.5 1 of water to column 4 (eluting phase) at a volume flow rate 35 1/h, and elution of a recycle fraction from column 4 (4.5 1; 35 1/h).

Step 3: 20 1 of water was introduced into the upper portion of column 1 at a volume flow rate 75 1/h, and a residue was eluted (residue 2) from the bottom of column 2 (20 1; 75 1/h). Simultaneously 21.5 1 of water was supplied to the upper portion of column 4 at a vol¬ ume flow rate 35 1/h and a xylose fraction was eluted from column 4 (21.5 1; 35 1/h).

Step 4: Recycling (recycling phase) in the loop formed by columns 1 and 2 (4.8 1; 75 1/h) and in the separate loop formed by column 4 (4.2 1; 14 1/h).

After the sequence was carried to completion, the process control program was continued and it returned to the beginning, starting the sequence anew from step 1. By repeating this sequence six to eight times the system was equilibrated. The method was proceeded with in a state of equilibrium, and the progress of the separation process was monitored with a density meter, a meter for optical activity, and a conductivity meter, and the separation was controlled by a microprocessor which controlled precisely the volume flow rates and volumes

of feeds, employing quantity/volume measuring devices, temperature controllers, valves and pumps.

In this method, four product fractions were frac¬ tionated: a xylose fraction from column 4, one residue fraction from column 1, one residue fraction from column 2 and one residue fraction from column 4. An analysis of the product fractions and recycle fraction obtained dur¬ ing one sequence in a state of equilibrium is shown in Table 2, where the percentages of the different com- ponents are given as per cent by weight on dry solids basis.

The xylose yield from this fractionation was 90.9% calculated from the product fractions.

Table 2

Analysis of product fractions and recycled fraction

The calcium balance during one sequence in this fractionation in a state of equilibrium was the fol¬ lowing:

In feed solution into column 1: 271 g Separation from packing material in Ca ²⁺ form (columns 1 and 2) into product fractions: residue 1 60.3 g (3.7% d.s. ) residue 2 150.3 g (3.4% d.s.) Into column for removal of divalent cations (column 3): 60.4 g

Into packing material in Na ⁺ form (column 4): 196 mg Separation from packing material in Na ⁺ form into product fractions: residue 4 100 mg xylose fraction 77 mg recycle 19 mg

Example 2

Two-phase separation method for sulphite cooking liquor

Fractionation was performed employing the chrom¬ atographic separation apparatus described in Example 1, which comprised two loops, removal of divalent cations, and pH adjustment. The sequence carried out differed from the procedure of Example 1 in regard to step 2, in which a residue fraction and a recycle fraction were successively eluted with water from column 4. In this sequence, a fraction rich in lignosulphonates was addi¬ tionally eluted. The volume parameters and volume flow rates of the feeds and recovered fractions were modi¬ fied. These modifications were due to the fact that a different packing material (Relite C-360) was employed in the column for removal of divalent cations, and the sectional packing material bed in column 4 had a greater height. The resin Relite C-360™ had a polystyrene

skeleton cross-linked with divinylbenzene, and it was activated with sulphonic acid groups; the bead size was 0.3 to 1.2 mm and the DVB content 16%. The sectional packing material in the other columns was the same as in Example 1. The feed solution was the same as above. Test conditions: Diameter of columns 0.11 m

Height of resin bed in the column for removing divalent cations 1.5 m Total height of resin bed in separation columns 13 m

Temperature 75°C

Volume flow rate 22-50 1/h

A lignosulphonate-rich fraction was eluted from column 2.

Fractionation was performed by a four-step sequence. The sequence had a length of 98 minutes, and it comprised the following steps: Step 1: 20 1 of feed solution was introduced

(feeding phase) into column 1 at a volume flow rate 22 1/h, and a 20 1 residue fraction (residue 1) was eluted from the downstream end of the same column. Simultane¬ ously 33 1 of water was supplied (eluting phase) to column 2 at a volume flow rate 40 1/h and a residue fraction (residue 4/1, 33 1; 40 1/h) was eluted from column 4.

Step 2: Recycling (recycling phase) in the loop formed by columns 1 and 2 (11 1; 35 1/h). Simultaneously 8 1 of water was supplied to column 4, and 4 1 of res¬ idue fraction (residue 4/2) was first eluted from column 4 at a volume flow rate of 35 1/h and thereafter 4 1 of recycle fraction was eluted from column 4 at the same volume flow rate.

Step 3: 16 1 of water was introduced into the upper portion of column 1 at a volume flow rate 45 1/h, and a lignosulphonate-rich fraction was eluted from the bottom of column 2 (16 1; 45 1/h). Simultaneously 22 1 of water was supplied to the upper portion of column 4 at a volume flow rate 40 1/h, and a xylose fraction was eluted from column 4 (22 1; 40 1/h).

Step 4: Similar to step 4 in Example 1 (recycling in the loop formed by columns 1 and 2 4.8 1, 75 1/h; in the loop formed by column 4 0 1; 0 1/h).

This sequence was repeated six to eight times, whereafter the system was equilibrated, and the method was proceeded with in a state of equilibrium until the column for the removal of divalent cations required re- generation.

An analysis of the product fractions and recycle fraction obtained in this fractionation during one sequence in a state of equilibrium is shown in Table 3.

The percentages of the components are calculated as per cent by weight on dry solids basis.

The xylose yield from this fractionation was 94.7%.

Figure 1 shows the separation curves of column 1, Figure 2 the separation curves of column 2, Figure 3 the separation curves of column 3 for the removal of dival¬ ent cations, and Figure 4 the separation curves of col¬ umn 4 for this fractionation.

The lignosulphonate content has been determined by means of UV absorbance measurement (absorptivity 14.25 1 ^• g- ^{1 •} cm ^"1 ) .

Table 3

Analysis of product fractions

Xylose Residue 1 Residue 4/1 Residue 4/2 LJQnosul + recycle phonate fraction

Volume, 1 22.0 20.0 37.0 4.0 16

Dry solids content, K-F, g/100 g

Xylose, %

Monosaccharides, %

Oligosaccharides, %

Lignosulphonates, %

Others

Example 3

Two-phase separation method for sulphite cooking liquor

Fractionation was performed with a chromato- graphic separation apparatus comprising four columns. The first loop comprised columns 1 and 2 (packing mater¬ ial in Ca ^2* form), column 3 was a column for the removal of divalent cations in the solution, and a pH adjustment unit was connected between column 3 and column 4. Column 4 constituted the latter loop, and its packing material was in the Na ^* form. The feed solution and the sectional packing material for the columns were the same as in Ex¬ ample 2.

Test conditions: Diameter of columns 0.11 m

Height of resin bed in the column for removing divalent cations 1.5 m Total height of resin bed in separation columns 13 m Temperature 75°C

Volume flow rate 22-50 1/h

Fractionation was performed by a five-step sequence. The sequence had a length of 100 minutes, and it comprised the following steps: Step 1: 20 1 of feed solution was introduced

(feeding phase) into column 1 at a volume flow rate 22 1/h, and a 20 1 residue fraction (residue 1) was eluted from the downstream end of the same column. Simultane¬ ously 34 1 of water was supplied (eluting phase) to column 2 at a volume flow rate 40 1/h, and a residue (residue 4) was eluted from column 4 (34 1; 40 1/h).

Step 2: Recycling (recycling phase) in the loop formed by columns 1 and 2 (11 1; 35 1/h). Simultaneous recycling (recycling phase) of 3 1 at a volume flow rate 40 1/h in the loop formed by column 4.

Step 3: 16 1 of water was introduced into column 1 at a volume flow rate 45 1/h, and a residue was eluted from column 2 (residue 2, 16 1; 45 1/h). At the same time, 4 1 of water was supplied to column 4 at a volume flow rate 40 1/h, simultaneously eluting a recycle frac¬ tion from the bottom of column 4 (4 1; 40 1/h).

Step 4: Recycling (recycling phase) in the loop formed by columns 1 and 2 (3.5 1; 50 1/h). 18 1 of water was supplied to column 4 at a volume flow rate 40 1/h, and 18 1 of xylose fraction was eluted from column 4 at a volume flow rate 40 1/h.

Step 5: Further recycling (recycling phase con¬ tinued) in the loop formed by columns 1 and 2 (3.5 1; 50 1/h). Simultaneous recycling (recycling phase) in the loop formed by column 4 (4 1; 30 1/h). During this step, the two recycling phases were synchronized to end at the same time.

This sequence was repeated six to eight times, whereafter the system was equilibrated, and the method was proceeded with in a state of equilibrium until the column for the removal of divalent cations required re¬ generation.

An analysis of the product fractions and recycle fraction obtained in this fractionation during one sequence in a state of equilibrium is shown in Table 4.

The percentages of the components are calculated as per cent by weight on dry solids basis.

The xylose yield from this fractionation was 92.7%.

Table 4

Analysis of product fractions and recycled fraction

The fractionation described above was performed also in a variant where the divalent ions were removed, instead of ion exchange, by precipitating the calcium in a tube reactor, as described hereinbelow. A. Precipitation of calcium as calcium sulphite

The pH of the solution obtained from column 2 and introduced into column 3 was adjusted with sodium hydr¬ oxide to about 7 at about 60°C. A quantity of an aqueous solution of sodium sulphite (about 1 M) was added such that the amount of added sulphite ions was about 1.3 times the molar amount of calcium to be precipitated. Kenite 300 diatomaceous earth was employed as an aid in the filtration. Thus it was possible to remove about 90% of the calcium present in the solution. Xylose losses in the calcium removal thus performed were negligible.

B. Precipitation of calcium as calcium sulphate The procedure was similar to that of variant A above, but the precipitation was carried out by adding an amount of sulphuric acid in which the number of sul- phate equivalents was about 1.5 times that of calcium equivalents, and the pH of the solution was adjusted to be in the range 5.5 to 6 with sodium hydroxide. In this way, it was possible to remove about 70% of the calcium.

Example 4 Three-stage separation method for vinasse

A pilot plant scale chromatographic test appar¬ atus was used. The apparatus comprised three chromato¬ graphic separation columns connected in series, a pH adjustment unit, a filtration unit, a feed pump, recycl- ing pumps, an eluent water pump, flow and pressure regu¬ lators, and inlet and product valves for the process streams. Each of the three columns was packed with a strong acid cation exchanged resin (Finex C13 S™). The resin had a polystyrene skeleton, it was cross-linked with divinylbenzene and activated with sulphonic acid

groups and had a mean bead size (in Na ^* form) of 0.36 mm.

The resin had a DVB content of 8%. The packing material of columns 1 and 2 was in K ^* form and column 3 was in Ca ^2* form. The pH adjustment unit and filtration unit were connected between columns 2 and 3. The pH was adjusted with Ca(0H) ₂ . The total height of the packing material beds in the two first columns was 10 m, and the height of the packing material bed in the third column was 5 m.

The feed solution was vinasse whose composition is shown in Table 5. The percentages of the different components are given as per cent by weight on dry solids basis.

Table 5 Analysis of feed solution Inositol, % 0.4

Glycerol, % 6.3

Betaine, % 13.8

Trisaccharides, % 0.4

Disaccharides, % 1.6 Monosaccharides, % 7.9

Others, % 69.6

Water was used as eluent.

Fractionation was performed by an eight-step sequence. The sequence had a cycle length of 93 minutes, and it comprised the following steps:

Step 1: 7 1 of feed solution was introduced (feeding phase) into column 1 at a volume flow rate 90 1/h, and a fraction enriched with betaine (7 1; 90 1/h) was eluted from column 2. Simultaneous recycling (recycling phase) in the loop formed by column 3 (6 1; 75 1/h).

Step 2: Feed was continued (feeding phase) into column 1 (5 1; 90 1/h), and a residue was eluted from the bottom of the same column (5 1; 90 1/h). Simultane- ously eluent was supplied (eluting phase) to column 2 (6

1; 120 1/h), and a fraction enriched with betaine was eluted from the bottom of this column (6 1; 120 1/h). The recycling phase was continued in the loop formed by column 3 (recycling 4 1; 75 1/h). Step 3: Feed was continued into column 1 (28 1;

90 1/h), and 28 1 of residue was eluted from the bottom of the same column at the same volume flow rate. Columns 2 and 3, together with the pH adjustment and precipi¬ tation unit connected between them, formed an open elu- tion loop; 40 1 of eluent was supplied to column 2 at a volume flow rate 130 1/h, and a fraction enriched with betaine was withdrawn from column 3 (40 1; 130 1/h).

Step 4: Recycling in the loop formed by columns 1 and 2 (55 1; 120 1/h) and simultaneously in the loop formed by column 3 (12 1; 75 1/h).

Step 5: 35 1 of eluent was introduced into column 1 at a volume flow rate 120 1/h, and 35 1 of residue was eluted from column 2 at the same volume flow rate. Sim¬ ultaneously 36 1 of eluent was supplied (75 1/h) to col- umn 3 and 36 1 of residue was eluted from the bottom of the same column at the same volume flow rate.

Step 6: Recycling in the loop formed by columns 1 and 2 (48 1; 130 1/h). Simultaneously 9 1 of eluent was supplied to column 3 at a volume flow rate 75 1/h, and 9 1 of a fraction enriched with inositol was eluted from the bottom of column 3 (75 1/h).

Step 7: Recycling was continued in the loop formed by columns 1 and 2. Simultaneously 28 1 of eluent was supplied to column 3 at a volume flow rate 75 1/h and 28 1 of a fraction enriched with glycerol was eluted from the bottom of column 3 (75 1/h).

Step 8: Recycling was continued in the loop formed by columns 1 and 2. Simultaneous recycling in the loop formed by column 3 (8 1; 75 1/h).

This sequence was repeated six to eight times, whereafter the system was equilibrated, and the method was proceeded with in a state of equilibrium.

The following product fractions were fraction- ated in this method: betaine fractions from columns 2 and 3, an inositol fraction from column 3, a glycerol fraction from column 3, two residue fractions from col¬ umn 1, one residue fraction from column 2 and one res¬ idue fraction from column 3. An analysis of the product fractions (with residue fractions combined) obtained in a state of equilibrium during one sequence is shown in Table 6, where the percentages of the components are given as per cent by weight on dry solids basis.

Table 6

Example 5

Two-phase concentration of lactulose A two-loop apparatus comprising five chromato¬ graphic separation columns was used to separate a solu- tion prepared from lactose as follows: The lactose was isomerized by the conventional method with alkali into a lactulose-containing syrup. The resulting syrup was pur¬ ified in the conventional manner by ion exchange em¬ ploying ion exchange resins. The lactulose content of the resulting syrup was 22% on dry solids basis.

Lactose was crystallized from the ion-exchanged syrup twice, so that the lactulose content of the mother

solution obtained was 50% on dry solids basis and the contents of lactose and other components (e.g. galac¬ tose) 30% and 20%, respectively.

The columns were packed with the same ion ex- change resin as in Example 1. The packing material of the three first columns was in Ca ^2* form and the packing material of the two last two columns in Na ^* form.

Fractions enriched with lactose and other com¬ ponents (e.g. galactose) were withdrawn from all three columns having a packing material in Ca ^2* form. The first fraction to be recovered was the lactose fraction, and the last fraction was the fraction enriched with other components (galactose) . The lactulose-containing concen¬ trate with average retention was introduced into the packing material having Na ^* form.

A lactose fraction was withdrawn from both col¬ umns having a packing material in Na ^* form, and a frac¬ tion enriched with other components (galactose) was with¬ drawn from the last column (fifth column in the system). The lactulose fraction obtained had a lactulose content of 85% on dry solids basis and a lactose content of 10% on dry solids basis. The combined lactose frac¬ tions contained 15% of lactulose on dry solids basis and 74.7% of lactose on dry solids basis. The lactulose and lactose contents of the combined by-product fraction (which comprised mainly galactose) were 22% and 18.8% on dry solids basis, respectively. Example 6

Two-phase separation of maltose, glucose and fructose

A two-loop apparatus comprising five chromato¬ graphic separation columns was used to separate a syn¬ thetic maltose-containing syrup containing also glucose and fructose. The solution contained 20% of maltose, 40%

of glucose and 40% of fructose, all calculated on dry solids basis.

The columns were packed with the same ion exchange resin as in Example 1. The packing material of the first column was in Na ^* form and the packing material of the next four columns in Ca ²⁺ form. A maltose fraction was withdrawn from the first column, and a glucose- fructose-containing concentrate was introduced into the packing material having Ca ^2* form. A glucose fraction and a fructose fraction were withdrawn from the third and fifth column having a pack¬ ing material in Ca ^2* form (the fructose fraction was eluted more slowly).

The withdrawn maltose fraction contained 90% of maltose on dry solids basis and 10% of glucose on dry solids basis.

The combined glucose fractions contained 3% of maltose and 95% of glucose, and the combined fructose fractions contained 1% of maltose and 99% of fructose (all on dry solids basis).

Example 7

Two-phase separation of cane molasses

Cane molasses was softened and clarified in the conventional manner by phosphatization treatment and by removing the resulting solids by centrifugation. After the centrifugation, the solution was subjected to fil¬ tration with diatomaceous earth as an aid.

A two-loop apparatus comprising seven columns was used to separate cane molasses thus pretreated, which contained 30% of non-sugars, 40% of sucrose, 15% of glucose and 15% of fructose.

The packing material of the first three columns was in Na*,K ^* form (in equilibrium with cations in the molasses) , and the packing material of the other four columns of the apparatus was in Ca ^2* form.

A non-sugar fraction was withdrawn from all three columns and a sucrose fraction with average retention was withdrawn from the third column, having a packing material in Na ^* ,K ^* form. The glucose-fructose-containing concentrate which was the slowest to elute was introduced into the packing material having Ca ^2* form.

A glucose fraction and a fructose fraction were withdrawn from the fifth and seventh column having a packing material in Ca ^2* form. The combined non-sugar fractions withdrawn contained 85% of non-sugars and 15% of sucrose; the sucrose fraction obtained contained 10% of non-sugars and 85% of sucrose (all on dry solids basis). The glucose fractions obtained contained 96% of glucose and 2% of fructose on dry solids basis; the fructose frac¬ tions contained 95.6% of fructose and 2% of glucose.