US2785998A - Process of decolorizing sugar solutions with a porous quaternary ammonium anion exchanger - Google Patents

Description

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United States Patent C PROCESS OF DECOLORIZING SUGAR SOLUTIONS WITH A POROUS QUATERNARY AMMONIUM ANION EXCHANGER Frederick H. Harding, Manhasset, and Frederick Bruder,

Ozone Park, N. Y., assignors to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware No Drawing. Application November 25, 1953, Serial No. 394,504

7 Claims. (Cl. 127-46) This invention relates to the manufacture of refined sugar solutions and refined sugar. It relates to the removal of color-bodies from sugar solutionspreferably from hot sugar solutions-by means of strongly basic quaternary ammonium anion-exchange resins in the salt form.

, It is conventional, in the manufacture of refined sugar solutions such as syrups and of refined crystallized sugar, to treat sugar solutions after affination and clarification with a variety of sorbing materials such as bone-char or powdered carbon or other forms of carbon in an effort to remove by absorption or adsorption the various extraneous materials which are present as impurities in the sucrose solutions. This is done because such impurities, including color-bodies, lower the quality of the syrups and reduce the quantity and/ or quality of the sugar which can be crystallized from the solutions.

It has also been shown, for example in U. S. Patents 2,551,519, 2,578,937, 2,578,938 and 2,635,061, that vari ous combinations of cation-exchange materials and quaternary ammonium anion-exchange resins in the hydroxyl form can be used in the treatment of sugar solutions.

An object of this invention is to provide a methodof' purifying sugar solutions which has commercial advantages over processes known heretofore. An object is to provide a method which produces a better quality 'of refined syrups and a greater yield of refined sugar and lower quantitiesof molasses. Still another object isto furnish a method whereby larger amounts of more con-- centrated sugar solutions can be decolorized in a given evident are accomplished by the process of this invention which comprises treating-preferably at elevated temperatures-a solution of sucrose which contains colorbodies with a quaternary ammonium anion-exchange resin which is in the salt form.

In the preferred embodiment of this invention, a hot sucrose solution, which may or may not contain some invert sugar and which does contain color-bodies, is passed through a bed or layer of particles of a quaternary ammonium anion-exchange resin in the chloride form. Colorbodies are adsorbed on the resin and anions in solution, particularly sulfate, phosphate and carbonate ions, are simultaneously exchanged for chloride ions on theresin. When the resin has adsorbed its full capacity as evidenced by the fact that the efiluent sugar. solution is not sufiiciently lighter in color than the influent solution the resin is considered exhausted and requires regeneration. The sugar solution remaining in the bed of resin is drained off and the layer of resin is rinsed with water. The resin is then treated with aqueous solutions of sodium chloride and sodium hypochlorite which remove the color-bodies, replace the adsorbed anions with chlon'deions, andrestore ice the resin to its original condition. Rinsing with wateror preferably with a dilute solution of ammonium hydroxidecompletes the cycle.

While the description above is that of the preferred embodiment it is evident from the following discussion that variations in the process can be made without depart: ing from the spirit of the invention.

The process of this invention can be applied to any sugar solution however dark in color and it will efiect a real reduction in color. It is more reasonable, however, to apply the process to sugar solutions which have been alfinated and also clarified with lime and phosphates. At least seventy percent of the color can be removed from such a solution by a single rapid treatment with the resin. Since other adsorbents such as bone-char, activated'charcoal and powdered carbon also remove substantial quantities of color-bodiesbut not all-and since their use up to a point is economical it is also practical to use them first to remove the color bodies which are most readily adsorbed and then to remove essentially all of the remaining color-bodies by adsorption on the quaternary ammonium ion-exchange resin. It appears that the ion-exchange resins have a specificity for the color-bodies which are least readily adsorbed by conventional adsorbents and therefore they can be used most advantageously to remove the final traces of color from sugar solutions which have been partially decolorized.

The ion-exchange resins which are employed are those which contain quaternary ammonium salt groupspreferably chloride groupsas their polar groups. They are cross-linked, and hence insoluble, resins in granular or preferably spheroidal form and they contain in their structure quaternary ammonium salt groups. The quaternary ammonium salt groups are the functional groups on which adsorption of the anions take place and adsorption of the color-bodies is also believed to take place. Such resins are well known and are available commercially. Suitable resins are those which are made, for example, according to the processes of U. S. Patents 2,591,573 and 2,614,099 by first forming an insoluble, cross-linked copolymer of a monovinyl hydrocarbon and a copolymerizable crosslinking agent such as divinylbenzene, then haloalkylating the copolymer whereby alkylene halide groups become joined to the insoluble copolymer and finally aminating the haloalkylated resin with a tertiary amine such as trimethylamine or dimethylamino ethanol. Other quaternary ammonium anion-exchange resins are made by the process of U. S. Patent 2,540,985. While quaternary ammonium resins are ordinarily sold in the basic or hydroxyl form they are readily converted to the salt form by treatment with a solution of an inorganic salt or mineral acid.

What is required here is an insoluble quaternary ammonium anion-exchange resin of the strongly basic type which is in the salt form. What is also desired is that the resin be as porous as possible. As is well known, the degree of porosity of such a resin is inversely proportional to the amount of cross-linking agent which is employed and accordingly it is recommended that the quaternary ammonium anion-exchange resin be as lowly cross-linked as is consistent with other required properties such as insolubility and degree of swellability. For example, in the case of the resins which are made by the processes of U. S. Patents 2,591,573 and 2,614,099, it is most desirable that the amount of copolymerized cross-linker be not over 4% and preferably from about 0.5% to about 2% on a molar basis. Here again, resins of this kind are available commercially as quaternary ammonium anion-exchange resins of the porous grade. '7

When employed in this process of sugar refining the resin is in the salt form-preferably in the chloride form. It can also be used in the bromide form which is fully crystallized sugar than chlorides and also cause turbid-- ity in the syrups. The quaternary ammonium anionexchange resin in the chloride form not only adsorbs color-bodies but also. exchanges its chloride. ions for. sulfate ions. This is most advantageous because sugars. of lower ashecontent are obtained, presumably because chlo-. ride salt re not occluded so tenaciously by sugar crystals asare fsu v ate salts and can befar more. readilyremoved.

Itis much preferred thatthe sugar solutions which-are Pyliified by; this 1 process be hot. .When the process-is operated at -elevated temperatures the volume of sucrose solution w 1c ,can betreated with agivenamount of resin; in any g ventime, is far greater than. when low temperatures are employed. Also of .real importance is the. fact that rnpre concentrated solutionscan. be purified. Syrups at a temperaturewithinthe rangeof 130 to.2 l- B. have been treated and decolorized very successfully,. but,it is. preferred thatthetemperature of the solutionsbef rom lm" to 190-F. Undertheseconditio ns solutions having a concentration at leastas high as about. joffiBrix, have been rapidly and efficiently puri-' color-bodiesand other anions and ultimately becomese xhaju sted. At this point it is freed of the sugarsolution is usually rinsed, and is then regenerated. Two inds of regenerants are required to restore thesresin to its original condition; namely a solution .of a waters olub le Salton-mineral acidv and .a solution of. a. mild oxidigin'g agent. While .these two kinds of regenerants can be mixed in the same. solution. it is preferred that they be used-separately, Thefirst kind of.regenerantifhichs is ordinarily sodium. chloride or sulfuric -acid s adsorbed; anions ,but failsto remove all of the ed color-bodies from; the .resin. The color-bodies are removed Afte eatment with the two .kinds of I re generants the r in s in condition to. treat and purifymoresugar l ilQ r...

Sodium; chloride solutions are much preferred as regenerants and these can be of any reasonable andlconve'nient concentration, .Inpractice it is preferred to. employ solutions containing about 1% ,to 15% salt. Solutions of Qth'er witter-soluble chlorides such as hydrochloric acid, potassium chloride, calcium chloride and magnesium chloridehave been used but these have no'advantage over solutions of sodiumchloride. What is evident from this h o weven is that acheap sodium chloride brine which contains other water-solublechlorides as impurities can be usedif desired. Hot solutions of sodium chloride at 130? toabout 2 00 F, are particularly efficient.

iqcause .the watensoluble chloride regenerant alone doe not remove ,all of the color-bodiesand hence fails instselftorestorethe resin to its full capacity, it is nece ss ary .to employ in .adiiitiona solution of a mild oxidib in g agent suchas a solution of a water-soluble hypo halite particularly a .hypochlorite-.or asolution of hydrogen peroxide. Solutions of sodium hypochlorite are QCOngmended .although other hypohalites such as potassiumhypochlorite, potassiumhypobromite, sodium-hypo:

, however, by .the mild oxidizingagent.

bromite and calcium hypochlorite can likewise be used.

. Strong oxidizing agents. including potassiumepermangw nate, nitric acid and chromic acid have also been used; and while these are effective in removing the color-bodies they are less satisfactory than the hypochlorites or hydrogen peroxide because they; tend, to degrade the resins. Solutions containing up to peroxideor sodium hypochlorite have been used but the particular concentration employed is a matter of choice. Usually. more dilute solutions are preferred.

Under those conditions: where the-quantities of -color-- bodies in the sugar solutions are high'andthe amounts which are adsorbed are also high in comparison with the amounts of other anions which. are-simultaneously adsorbed, it is suggested;thatregeneration with both salt and oxidizing agent be carried out each time the resin becomes exhausted. In such cases it appears best to treat the exhausted resin first with a hot solution containing about 1% to 1 0%. of the mineralacidor-salt thereof, then with a 0.25%. to 5%- solution ofah'ypochlorite or of hydrogenperoxide at room-or ambient temperature and then again with a hot solution of the mineral acid or salt.

On the other hand, when the ratio of adsorbed colorbodies to other adsorbed anions is low,- it may be-preferred, to regenerate the resin a number of-times with only a mineral acid or salt of a mineral acid, allow the color-bodies to accumulate, and then only occasionally to regeneratewith the mild oxidizing agent.

In any case what is required is that theexhaustedresin be regenerated with an aqueous solution of a mineral acid; or a salt thereof.preferably with a solution of sodium chloride-insofar as is possible and that-the color-bodies whichare adsorbed more tenaeiously and which are not removed by the first regenerant be removed by means of a solution of a mild oxidizing agent.

Thefollowing examples serve to further illustrate this invention. In the examples the colors which are recorded are based on the American Molasses Companys Color Standards which are described in Analytical Chemistry, vol. 2.4, page 832 (May 1952).

Example 1 andiin ally: reacting the chloromethylated copolymer: with trirnethylarnine. The column of resin beadswas 2.4- inches. ingdepth. The sugar solution-was flowed at a-rateof '62i5 gals. per square foot of column area per hour. A'total quantity of sugar solution equivalent to 1500.pounds of solid sugar per-cubicyioot of resinwas passed through the column. The efiiuent had aconcentration. of 58'.7 Brix, .a pH of 5.9, ;a color-of 3. and contained 3.3. color units- Thus,. a;total of 88.5% ofthe colorhadbeenremoyedo The-ionexchange resin was regeneratedas follows:v A 10% .aqueous solution of sodiurnrchloride, aha-tempera ture of,175 F., was slowly percolated throughtheibedrof resinover a-total contact time of 20 minutes. The bed of resinwas then washed thoroughly .with water.

The whole procedurewhich comprisesthe treatment of the sugar solution, the removal of the color therefrom. and 'the regeneration of the resin constitutes onecycleof operation.

Example 2 Th ,B QQ'iSS. .of, .-Example ,1 was repeated fl mesin avenues the manner described, with essentially the same kind of washed raw sugar melt. The 75th cycle was run as follows: A washed raw sugar melt having a concentration of 60 Brix, a pH of 7.0, a color of 16, and containing 31 color units was percolated through the same column of anion-exchange resins. Here, as in the previous cycles, a total quantity of sugar solution equivalent to 1500 pounds of solid sugar per cubic foot of resin was passed through the column of resin at a rate of 62.5 gals/sq. ft./hour. The efliuent had a concentration of 59 Brix, a pH of 6.3, a color of 6+, and contained 6.2 units of color.

It will be noted that about 80% of the color was removed. While this represents a real and very worthwhile improvement in the quality of the sugar solutions it is not as great a removal as was obtained in earlier cycles. The gradual loss of the capacity of the resin to remove color-bodies is due to the fact that some of the colorbodies are not removed from the resin by the step of regeneration, as explained above.

In this case, however, the same column of resin was used for 75 more cycles in the same manner described above. In the 150th cycle the same equivalent amount of washed raw sugar melt was passed through the same column of resin at the same rate and at the same temperature. The influent had a concentration of 60 Brix, a pH of 7, a color of 16+, and contained 32 color units. The effluent had a concentration of 59 Brix, a pH of 6.2, a color of 10+, and contained 8.6 color units. In this cycle about 73% of the color was removed.

After the sugar solution had drained from the column of resin and the latter had been rinsed with hot water (sweetening off) the resin was regenerated as follows: A 10% aqueous solution of sodium chloride, at a temperature of 175 F., was slowly percolated through the bed of resin over a total contact time of 20 minutes. The bed of resin was thoroughly rinsed first with hot water and then with cold Water. Next the bed was treated with a 2% aqueous solution of sodium hypochlorite at 80 F. for a total contact time of 60 minutes. Finally the column of resin was thoroughly rinsed with hot water.

In the 151st cycle, after the bed of resin had been regenerated with sodium chloride and with sodium hypoohlorite as above described, a washed raw sugar melt was decolorized. The influent had a temperature of 180 F., a concentration of 60 Brix, a pH of 7.1, a color of and contained 26 color units. The quantity of sugar solution and rate of flow were the same as described in Example 1. The efiiuent had a concentration of 59 Brix, a pH of 6.2, a color of 5, and contained 5.2 color units. In this cycle approximately 80% of the color was removed. This represents an improvement over the results of cycle No. 150 and shows the value and importance of using an oxidizing agent, at least periodically, in the regeneration of the ion-exchange resins.

Treatment of sugar solutions was continued in the manner described above using the same column of resin, the same rate of fiow, the same regenerating procedure with sodium chloride every cycle and also employing the regenerating procedure with sodium chloride and sodium hypochlorite every thirtieth cycle. In the 410th cycle over 74% of the color was removed.

Example 3 The purpose of this example is to compare the decolorizing ability of a quaternary ammonium anion-exchange resin in the chloride form with that of powdered activated carbon. The same washed raw sugar melt was employed and initially it had a concentration of 60 Brix, a pH of 7.0, a color of 16 and contained 31 color units.

A portion of this solution was treated in the conventional manner with powdered activated carbon in an amount equal to 1% of the weight of solid sugar in the solution. The resultant solution had a color of 9 and contained 8 units of color indicating that 74% of the color had been removed by the carbon.

Another portion of the washed raw sugar melt was treated in exactly the manner described above in Example 1. The product had a color of 3+ and contained 3.5 color units indicating that the resin had removed more than 88% of the color.

Example 4 A partially decolorized and filtered whole raw sugar melt having a concentration of 62 Brix, a pH of 5.5, a color of 22 and containing 123 color units was passed at a temperature of 170 F. through a column of anionexchange resin in the chloride form. The resin was the the same quaternary ammonium chloride resin described and employed in Example 1 above and the rate of flow was 71.2 gals/sq. ft./hr. An amount equivalent to 320 pounds of solid sugar per cubic foot of resin was thus treated. The efiluent had a concentration of 60.0 Brix, a pH of 5.7, a color of 13 and contained 14.0 color units. From this it is evident that 88.7% of the color had been removed by the resin.

Example 5 In some cases, particularly where the quantities of color-bodies to be removed by the resin are high and many of the color-bodies are adsorbed tenaciously and are not removed by salt or acid alone during regeneration, it is preferred to regenerate the resin every cycle with a mild oxidizing agent, such as hydrogen peroxide or sodium hypochlorite. In such cases a very dilute so-. lution of oxidizing agent can be used and/or the time of contact of the oxidizing agent with the resin can be decreased.

Accordingly, many portions of a washed raw sugar melt were passed through a column of the anion-exchange resin described in Example 1 above. The solutions all had an average concentration of 60 Brix, a pH of about 7.0, a color of 16-17, and contained about 31-34 color units. They were passed through the column at the rate of 62.5 gals/sq. ft./hour until the equivalent of 1500 lbs. of solid sugar had passed through per cubic foot of resin. The resin was then regenerated by means of a 2.5% aqueous solution of sodium chloride at 175 F. during a contact time of 20 minutes and with .a 0.25% aqueous solution of sodium hypochlorite at F. during a contact time of 20 minutes, followed in each case by thorough rinsing with water.

The efiluent from the 75th cycle had a color of 3+ and contained 3.5 color units, indicating a removal of color. The effluent from the 150th cycle had a color of 3-4 and contained 3.7 color units, thus showing that 88% of the initial color had been removed.

We claim:

1. The process of purifying a sucrose solution which contains dissolved impurities including color-bodies which comprises bringing said solution, at a temperature from F. to 210 E, into contact with a porous quaternary ammonium anion-exchange resin which is in the salt form.

2. The process of purifying a sucrose solution which contains dissolved impurities including color-bodies which comprises bringing said solution, at a temperature from 130 F. to 210 F., into contact with a porous quaternary ammonium anion-exchange resin which is in the chloride form.

3. The process of purifying an afiinated and clarified sucrose solution which contains dissolved impurities including color-bodies which comprises bringing said solution, at a temperature from 130 F. to 210 F., into contact with a porous quaternary ammonium anion-exchange resin which is in the chloride form.

4. The process of purifying a sucrose solution which contains dissolved impurities including color-bodies which comprises passing said solution at a temperature from 130 F. to 210 F. through a layer of particles of a porous quaternary ammonium anion-exchange resin which islinnthe chloride.= form, thereby removing. said colorzbodies frornsaid-solution and adsorbing themlon said" resin, separating-the. resultant solution from said resirLandT finally: regenerating said resin and removing saidadsorbed color-bodies from it by treating it With a solution of a Water-Soluble chloride and with a solution of a mild oxidizing agent.

5. The process of purifying a sucrose solution which contains? dissolved impurities including color-bodies which comprises passing said solution atl a temperature from 140T'FJ. to 190 F. through awla yer of particles of a porous quaternary ammonium anion-exchange resin which is.in-the 'chloride form, thereby removing said color-bodies from said solution and adsorbing them on said .resin,. separating the resultant solution from said resin and finally regenerating said resin and removing saidia'dsorbed color-bodiesirom it by treating it with a solution of a Water-soluble chloride and with a solution offa mild oxidizingaagent.

61The process of purifying an aflinated and clarified sucrose solution which is at a concentration of 40 to about 70 Brix and Which contains dissolved impurities including color-bodies which comprises passing said solution at'a'temperature'from 140 F. to 190 F. through a layer: of particles of a porous quaternary ammonium anion-exchange resin inthe chloride form, thereby removingsaid color-bodies from said'solution and adsorbingfthem'on said-resin, separating the resultant'solution from'saidresin and finally regenerating said resin and saidiadsorbed color-bodies from it by treating it with a: solution of sodiumchloride and with an solution of sodium hypochlorite 7; The process of -purifying an afiinatedand clarified said adsorbed color-bodies from it by treating it with a solution of sodium-chloride and with a solution-of 2 hydrogen peroiide.

' ReferencesCited'in the file of this patent UNITED STATES PATENTS 2,578,938 Kunin Dec. 18, 1951 2,650,177 Menard-"mm Aug. 25, 1953 FOREIGN PATENTS 489,173 Great Britain Jan; 20, 1937 OTHER REFERENCES Serial N6. 359,575, Sinit (AP. 0. published May 11,1943.

Claims (1)

1. THE PROCESS OF PURIFIYING A SUCROSE SOLUTION WHICH CONTAINS DISSOLVED IMPURITIES INCLUDING COLOR-BODIES WHICH COMPRISES BRINGING SAID SOLUTION, AT A TEMPERATURE FROM 130* F. TO 210* F., INTO CONTACT WITH A PROOUS QUATERNARY AMMONIUM ANION-EXCHANGE RESIN WHICH IS IN THE SALT FORM.