US3325308A - Process for the refining of sugar with two or more solvents - Google Patents

Description

June i3, 1967 D. F. OTHMER 3W325,308

PROCESS FOR THE REFINING OF SUGAR WITH TWO OR MORE SOLVENTS Filed June 19. 1965 DONALD F. OTHMER United States Patent O M 3,325,308 PROCESS FOR THE REFINING F SUGAR WITH TW() 0R MORE SOLVENTS Donald F. Othmar. Coudersport. Pa. (333 Jay St., Brooklyn, N.Y. H201) Filed June 19., 1963. Ser. No. 289,083 19 Claims. (Cl. 127--63) This invention relates to a method for the refining of crystalline, so-called raw sugar, customarily produced by pressing the juice from sugar cane, concentrating this juice and crystallizing out the sugar, then centrifuging the crystals of raw sugar Which are formed from a residue of the mother liquor, called blackstrap molasses. It has now been found possible to remove and separate the impurities which remain in and on the crystals of raw sugar by two successive solvent treatments. A washing with a first solvent of the raw crystals allows them to be recovered as refined sugar merely by being centrifuged free of solvent. Evaporation of the washing liquor results in the recovery of the first solvent and yields a first molasses. An extration of the first molasses with a second solvent gives an extract stream from which the second solvent is recovered to give a residue which may be separated by a third solvent (usually water) into crude acids and crude fats and waxes.

. The impurities on the raw sugar of commerce largely remain from the blackstrap molasses on or near the surface of the crystals. They may be almost entirely removed lby the hot extraction and physical washing action on the raw sugar of certain first solvents, sometimes acidified with mineral acid. This leaves nearly pure sugar crystals from which the solvent may be centrifuged. Undissolved solids Washed out and suspended in the first solvent effluent may be settled by gravity therefrom. Most of the first solvent is then evaporated from the effluent stream for reuse to give as residue an impure liquid, or rst molasses. This liquid molasses, in turn, is extracted with a secon-d solvent in a liquid-liquid extractor: the rainate molasses from the extractor is further concentrated by evaporation to a massecuite, from which is centrifuged a light colored raw sugar (usually in the range of one percent of that originally charged). The solvent extract stream from the liquid-liquid extractor is evaporated to recover a residue of a crude mixture of fats, waxes, and solid acids. Further treatment with a third selected solvent (often water) will separate the waxes and fats from the mixture of acids, chiefly aconitic.

The preferred first solvents for this invention are watersoluble, have the same number of oxygen atoms as carbon atoms in their molecules, and boil between about 50 C. and 150 C. A preferred one is methanol (methyl alcohol).

The preferred second solvents have a solvent action for acids and fats. Acetone is preferred, but methyl ethyl ketone, methyl isobutyl ketone, or other ketones, containing up to six carbon atoms, aromatic or staright chain hydrocarbons, or ethers, may be used, also in a preferred boiling range of 50 to` 150 C.

The preferred third solvent is water, although methanol and ethanol may have advantages in some cases.

There may be listed the several simple and more or less standard operations which have been found successful for refining the sugar and separating the impurities into useful and valuable products.

(a) Washing-The impurities of the raw sugar are removed therefrom by a simple countercurrent washing in a horizontal ribbon conveyor, Iby the first solvent (e.g., methanol), either anhydrous or containing a small amount of Water. An acid, sulfuric or hydrochloric, may be added; a very small amount gives free solid acids from the salts.

3,325,308 Patented .lune 13, 1967 ICC (b) Centrifugng rened Sagan-The refined sugar is produced immediately by centrifuging the crystals in a substantially pure form from the solvent, which is immediately reused. The refined sugar is almost white, consists of the same crystals as the original raw sugar (fines removed), but has a purity above 99.5%. It is obtained in a yield of 94 to 97% of the weight of the original raw sugar.

(c) Settling--1nsoluble impurities, dirt, lint, ctc., as well as very fine crystals of sugar which are mechanically Washed or flushed away from the raw sugar crystalsby the methanol washing, are settled out in a settling tank, in an amount usually less than about 0.5% of the original raw sugar. If sulfuric acid has been added, calcium sulfate will also be presented; if hydrochloric acid has been added, there is a lesser amount of settling due to dissolution of salts of aconitic acid. The slimy precipitate includes various gums, etc.

(d) Evaporation-lst solvent-The methanol solution of impurities, after settling, is evaporated to remove the methanol, but not the water.

(e) Liquid-liquid exlraclon.-The aqueous solution of impurities (a molasses, preferably of about 50 to 80% total solids) substantially free of methanol, is extracted counter-currently in a liquid-liquid extractor by a selected second solvent (e.g., acetone) which removes fats and waxes, aconitic and other acids, chlorophyl, gums, etc.

(f) Evapraron-Znd solvent from raffinata- The raffinate layer of the liquid-liquid extraction is evaporated to recover acetone and to concentrate the sugar to a massecuite;

(g) Cenzrfugz'ng raw sugar.-Raw sugar-above 94% purityis crystallized out of this massecuite and centrifuged out in an amount of about 1% of the original raw sugar charged. It may be recharged 'with the original raw sugar and increases the overall yield by approximately this amount.

Residual molasses is obtained from the centrifuge. This has been freed of the usual impurities of fats and waxes, aconitic and other acids; chlorophyl, gums, etc. It thus has a pleasant taste and light color and contains almost all of the vitamins and minerals originally present in the original raw sugar.

(h) Evaporation-2nd solvent from extracl.-The extract layer from the liquid-liquid extractor is removed as a solution in the second solvent of the sugar cane wax and fats, chlorophyl, aconitic acid, other acids, gums, etc. The 2nd solvent is evaported from this solution for reuse, and these solids are discharged to solidify out as a crude mixture.

(i) Dissolution of crude acida-This crude mixture of solids is agitated with a third solvent, e.g., Water, which dissolves at an elevated temperature, aconitic and other acids, etc. These may be purified further by standard techniques for their respective uses, as may also be the water insoluble fats and waxes.

STANDARD `SUGAR REFINllNG PROCESS Raw sugar has sucrose as the principal constituent, usually 95 to 97%, but there are also present invert sugars (glucose), a small amount of water, suspended materials, and various other organic chemicals such as aconitic acid, sugar cane fats and waxes, chlorophyl, and other constituents of the original sugar cane plant which have come into the juice either because of their solubility in the juice which has been expressed in the rolls, or be cause of mechanical inclusion as impurities. Most of these impurities are present in a thin film of molasses on the surface.

RaW sugar is dissolved in water, then refined in a sequence of operations. The aqueous solution is purified by treatment with materials which adsorb the impurities, the sugar is crystallized from the purified solution; and the final mother liquid (molasses) is removed, containing all of the impurities which were-not adsorbed. These impurities including valuable wax, vitamins, and aconitic acid, are wasted in the molasses or lost on the adsorbent solid, with considerable expense in removing therefrom, or discarded.

All standard refining methods are expensive because of (a) Large heat cost in evaporating water used for dissolution;

(b) Revivication cost of the solid adsorbing agent, such as bone black, carbon black, or various ion exchange resins, and the loss of discard of such adsorbents;

(c) Complete loss of the value of the impurities;

(d) Mechanical and other losses (inversion) of the sugar, itself, in the numerous steps, and

(e) Large size and investment in plant because of numerous steps and much equipment necessary.

ADVANTAGES OF NEW PROCESS Now it has been found possible to separate from the crystalline raw sugar the impurities without first dissolving the crystals in water, and then to separate the impurities into useful products; whereas, in the normal process of sugar refining, the impurities are immediately discarded to waste by whatever means they may be removed from the sugar. In the new process, since about 95% of the raw sugar is immediately recovered in the final, refined form without dissolution of anything but the impurities, the subsequent steps of separating the impurities are operated on a very small scale, relatively; with relatively very small amounts of materials, a few percent at most of the original amount of raw sugar handled. Therefore, only small units of equipment are necessary at small cost.

A considerable saving in time of the sugar in process, and hence of inventory, is also accomplished. Also, there is a considerable saving in steam or other form of heat energy and a great saving in the elimination of solid adsorbents, also a greater productive efficiency of the refinery as a whole is reached by reason of the large percentage of the sugar which is obtained as pure refined sugar, also the impurities are obtained in a salable form to give additional revenue. Furthemore, the equipment which is utilized is relatively cheap and inexpensive, and it may be economically operated in relatively small units of low capacity.

Because of incompatability of bacteria, spores, etc. with the preferred first solvents, and the fact that the refined sugar is discharged from an ultimate drying off of the first solvent, the sugar is free of bacteria. Even after standing, tests showed it to contain no bacteria, against an average from 12 fine granulated sugars from standard `refining processes, of 17 per gram, an average from 7 commercial turbinado sugars of 63 per gram. The count for Flat Sour Spores Was per gram of sugar by the present process, against 43 per gram for the average of l2 sugars by standard refining, and 144 per gram for the average of 7 turbinado sugars. This much greater biological purity makes the new sugar ideal for canning, bottling, and similar purposes where fermentation in later use must be prevented.

BRIEF DESCRIPTION OF THE FIGURES FIGURE 1 consists of two cross-sectional views-one longitudinal and one horizontal-of a multi-cell evaporator to be used in the process.

FIGURE 2 is a flow sheet of one embodiment of the invention showing diagrammatically the several operations which are being conducted in equipment shown schematically in cross-section.

CHOICEl OF FIRST SOLVENT i It has been found that the most desirable solubility relations for the first solvent in its use for separating impurities from raw sugar are met with in those having the same number of oxygen atoms in the molecule as the number of carbon atoms. Such compounds are always watersoluble and have good solvent properties for the impurities present in raw sugar. (Solvents with molecules containing chlorine, nitrogen, or other atoms, than C, H, and O are not useful.) Thus methanol and ace-tic acid are good; and because of the desirable boiling point of methanol below water, it is preferred; although acetic acid may also be used.

Ethylene glycol and glycerol may also be used as the first solvent; but their high boiling points make the subsequent separation of solvent from the impurities which are dissolved much more difficult. Also, formaldehyde and methyl formate have useful solvent properties for the impurities, and they fall in the class of having the same num-- ber of oxygen and carbon atoms; but they both have boil-- ing points too low for use conveniently, and both are too unstable for use.

It has been found that, in many cases, it an advantage to use from one tenth percent to eight percent of water inthe first solvent to aid in the extraction of the impurities from the sugar. Increasing the amount of water improves the eiciency of the solvent, but decreases its selectivity; i.e., the presence of a small amount of water increases the solubility of many of the impurities considerably, and also increases the solubility of sugar in the solvent. Thus the presence of this small amount of water reduces the yield of refined sugar while increasing its purity somewhat for a given amount of solvent used.

In the usual washing operation, the highest temperature, up to the boiling point of the solvent, gives the maximum efficiency 'in the minimum of time. In washing of sugar, the highest temperature must always be Well below the point of carmelization. With methanol and no acidification (as discussed below) good washing is secured when operating at its boiling point, 65 C., or at a temperature between about 60 and 65 C., with a washing time of from one to two hours, using a weight ratio of methanol to raw sugar of unity. Lower temperatures require somewhat longer times of contacting, or higher ratios of methanol to raw sugar.

When acetic acid is used as the first solvent, temperatures up to its boiling point, 118 C., may be used. The higher washing temperature possible with acetic acidwithout pressure-compared to methanol allows the solvent to dissolve the impurities in less time. At temperatures from to 110 C., the refining of raw sugar is usually accomplished in from 45 minutes to 90 minutes.

The nearly complete recovery of the solvent must always be possible. Higher boiling solvents are preferable in this respect. However, it has been found possible to recover all but about 1% of the methanol cycled by using a closed system such as is standard for washing solids with solvents. The ease of separation of methanol from water and from aqueous sugar solutions by distillation makes it a most convenient material to use.

The use of acetic acid poses a dierent problem of solvent recovery, since the distillation -of the acetic acid removes the water from the impurities, i .e., the rst molasses. Other methods of separation of the solvent may be used-as will be described hereinafter.

Usually and most conveniently, the washing with the first solvent is done under atmospheric pressure at a temperature up to the boiling point of the solvent acting; however, by increasing the pressure above the atmospheric pressure a higher temperature may be used and more rapid extraction obtained with methanol. Such an advantage gained must be balanced against the disadvantage of operating under pressure. In any case, it has been found that a temperature of 120 C. is as high as is ever necessary and any higher temperature tends to cause carmeliz'ation. With methanol, this high temperature requires the operation under considerable pressure, up to 5 or 6` atmospheres.

As is usual in washing operati-ons, the presence of a very small amount of surface active agent Was found to improve the rate of washing, i.e., reduce the time. A sucrose ester of a high molecular weight fatty acid, such as sebacic, is suitable; and in amounts of 0.001 to 0.01% of the raw sugar, this showed a reduction of time necessary for extraction :of 25 to 30%.

ACIDIFICATION OF FIRST SOLVENT The refined sugar, when washed with methanol, is a light straw color. When acetic acid is used as a solvent, a very much lighter colored refined sugar, with lower ash, is obtained. This led to the consideration that the better product obtained with the use of acetic acid might be due to the acid or ionizing capabilities of the acetic acid with the small amount of water present, rather than to the physical solvent effect of the nearly anhydrous organic liquid.

` Therefore, the addition of an inorganic acid to the methanol was tried; and it was found that acidification to a pH of about 1.25 reduced the color of the refined sugar to a very much lower valuea very faint yellow tint. Also, the polarization, or corresponding percent sucrose, usually was found to increase by from 0.1 to 0.25% sucrose purity by the washing with methanol which had been acidified. Furthermore, the ash content of the refined sugar was reduced from 0.12 to 0.15% without acidification, to 0.05 to 0.1% with acidification.

The total free and combined aconitic acid was reduced from about 0.05% to 0.15% to about 0.01 to 0.02%. Removal of the aconitic acid was found to lbe related directly to the removal of the color (also, to a lesser degree, to the removal of ash), indicating that the color-giving impurities and ash reacted similarly, or were related in some way.

From about 0.1 to 0.2% total acids determined as aconitic acid is present in raw sugar. This may include possibly some small amount, a few percent, of the total acid, as oxalic acid and malic acid; all of these acids act much the same in the washing process. About half of the total acid may be in the free form and about half in the form of calcium or magnesium salts-or mixed salts. All of these salts are even much more insoluble in methanol than in water. When the raw sugar is washed with methanol, these salts may be partially entrained or suspended by the hydraulic washing action and be carried out in a slimy mass with gums, pectins, etc., which are also removed, while the free acids are dissolved in the methanol.

Acidification to a pH of 1.25 requires only the correspondingly small amount of inorganic acid to spring the fractional percent of organic acid 'by releasing all three of the carboxyl groups of all of the aconitic acid from its combination with calcium and magnesium.

As is usual in treatment of sugar with acids, there is the tendency for inversion. To minimize this, the time of washing may be reduced to as low as 15 minutes, and the temperature from room temperature up to 30 to 40 C. The same results are obtained as with 60 to 90 minutes and 50 C. without acidification.

Invert sugar was not noticeably increased in the refined sugar, but was often slightly higher in the final molasses. Acidification to a pH of 4.0l gave much less danger of inversion and gave a much improved color as compared to no acidification, but not as good as when the pH was 1.25 to 1.3. About one half again as much ash remained in the refined sugar when a pH of 4 was used as compared to a pH of 1.3. In general, the low range of pH, from 1.25 to 1.3, would be used only with a short time and a low temperature of washing because of possible inversion, and a range from pH 4.0 downto 1.25 to 1.3 would be desirable, depending on particular raw sugar analysis, time and temperature used for washing, etc.

A slight addition of mineral acid to acetic acid used as first solvent decreased the time necessary for the extraction; and again the practical lower value of pH may be taken as 1.25 to 1.3.

When hydrochloric acid is used for acidification, the resulting calcium and magnesium chlorides are soluble in the methanol and 4remainin solution in the liquid stream, and then stay in solution throughout subsequent steps to be discharged in the final molasses. However, hydrochloric acid leaves a minimal amount of ash in the refined sugar, 0.05% to 0.07%.

When sulfuric acid, or particularly phosphoric acid, is used for acidification, the corresponding salts formed are insoluble in methanol. If the very fine crystals of these salts form on the sugar crystals, they may be removed readily by the minor mechanical abrasion of the sugar crystals rubbing against each other during the washing; and they are fiushed away by the hydraulic action of the stream of methanol. They are then settled out with other fine solids.

Phosphoric acid gives the best results since its salts Iare the most insoluble and easily removed by settling. Thus, they can cause no trouble in scaling of heat transfer surfaces in the subsequent evaporation steps. Sulfates are not as insoluble in Water, but are quite .insoluble in methanol. Sulfuric `acid is usually preferred, however, because of its cheapness and ready availability.

By the use of sulfuric acid sufficient to spring the aconitic acid and to reduce the pH to 1.25 to 1.3, it was found that, as compared to the use -of unacidified methanol, a slightly purer refined sugar, 99.8% sucrose, with a much better color, could be made with a washing time of not over 30 minutes and a temperature of washing of 30 to 40 C.

In acidification, it has been found preferable to add the acid mixed with from 2 to 10% of the recycle methanol at ,an intermediate point in the washing-after 10 to 75% of the distance of travel of the bulk of the methanol and a corresponding washing time in a countercurrent washer. The refined crystals discharged are thus entirely washed free `of acid by the bulk of the methanol before acid is added thereto, and the time of contact of the acidified methanol with the raw sugar entering the washer iS minimized.

CHOICE OF SECOND SOLVENT As noted above, the first solvent, desirably, Should separate out solid crystals, which are essentially sucrose, with a minimum dissolution of the sucrose itself. It should remove all impurities, both organic and inorganic, including insolubles, dirt, Water, ash, `and particularly glucose or invert sugars. The second solvent has a narrower assignment. Desirably it should separate, in this case, from a liquid-the First Molasseshthose materials which may have a value ras solid acids, fats or oils, and waxes, and possibly coloring matter. Already the dirt and other insolubles have been removed; and the water and invert sugar are to remain and be left with the final molasses.

Besides having the normal requirements -of cheapness `and availability, the second solvent must have an ability t-o dissolve the aconitic acid and the fat and wax materials, and must be selective in not dissolving sucrose or invert sugar.

Furthermore, the solvent phase `and water phase (molasses) must separate rapidly and completely, without emulsification.

Yet another requirement is that the solvent must be readily recoverable for reuse by separation from the extractables in the extract layer. Since the desirable solvents for acids invariably have also a solubility for water, the ready separation of the solvent from any water which it dissolves from the molasses which is extracted is essential.

Hydrocarbons and chlorinated hydrocarbons form bad emulsions in the extraction step. They dissolve the fats and waxes but have been found to have poor efiiciency in extracting the aconitic acid (including other solid acids).

Alcohols containing four and more carbons have been 'found to have increasing efficiency in extracting the fats and waxes and decreasing efiiciency in extracting aconitic acid as the number of carbon atoms in the molecule in- 7 L creases. They also form emulsions which are separable only with difficulty. Also, there has been found to be esteritication with the aconitic acid, which prevents complete recovery.

Ethers have been found to decrease rapidly in extraction eiciency for aconitic acid with increase in molecular weight. Ethyl ether has a usable extraction efficiency for both aconitic acid and wax, and it does notform stable emulsions. However, it is very volatile; and solvent losses are high in its use.

Esters have the basic disadvantage as solvents of possible ester-interchange with aconitic acid. Furthermore, their eiciency in extraction of either the aconitic acid or the wax were found to he not as good as desired, and the emulsication formed during extraction always presented a problem.

The ketones were found to give the best phase separation, but desirability in this regard was found to decrease with increasing molecular Weight as was also the eiciency of the aconitic acid extraction. Thus, methyl isobutyl ketone was less desirable on both counts than methyl ethyl ketone; i.e., emulsions were more slow in separating and partitions coeicient of acid in solvent to acid in molasses was less. Ketones above 6 carbon atoms were unusable.

By far the best solvent found on all counts was acetone. This solvent, at first discarded lfrom consideration, without trial, because -of its complete miscibility with water, was found on experimental tests to be quite usable with molasses concentrations of at least about 50% total solids concentration. When acetone is used alone, the total solids concentration in the molasses is preferably above about 60%. Emulsions are not formed, phase separation is rapid; and the partition coetcient for aconitic acid (i.e., acid in solvent to acid in water-in presence of the toatl solids) is from 2.5 to 4, or even higher, at higher total solids than 60%. Thus, extraction is relatively easy; i.e., smaller amounts of solvent are required, and less efficient extracting equipment is required than with any other solvent used.

The extracting efficiency of the solvent, acetone, for the aconitic acid and fats and waxes, has been found to be Ibetter at higher temperatures, even those above the normal boiling point of acetone. The extraction operation may be conducted at higher temperatures and corresponding Vpressures to keep the acetone in a liquid phase-up to about 100 C. to 110 C. Here the vapor pressures of acetone are respectively about 4 and 5 atmospheresand these temperatures and pressures have been found to be the maximum desirable. Extraction at lower temperatures, down to 40 to 50 C., may be used; however, the time required is longer land the viscosity of the molasses is much greater.

While the acetone has, -by itself, excellent properties as a solvent, in the present case, these may be improved by the addition of a co-solvent; and a preferred one has been found to be isopropyl ether, while both benzol and chloroform also contribute the same desirable properties to `a different degree. All of these make the solvent phase less miscible with lower concentrations of total solids in the molasses; and both increase the selectivity of the principal solvent, acetone, for the waxes. Isopropyl ether is a particularly desirable co-solvent, land it for-ms a constant boiling mixture with the acetone at 53 C., which aids in the distillation of the acetone from the extract layer. The amount of isopropyl ether is from l to 30%, preferably; and in no case more than 43%, the amount in the constant boiling mixture. With 30%, the molasses concentration may be as low as 40% total solids. The opti- -mum amount of benzol or chloroform to be added if it is the co-solvent, is between 1 and 25% of the total.

Furthermore, in the choise of a second solvent such as acetone, and a co-solvent such as isopropyl ether, the formation of a minimum constant boiling mixture with methanol by the liquid or liquids of the second solvent,

tends to strip completely any trace of methanol which may have remained from the washing and the removal thereof.

If the first solvent is acetic acid, the second solvent may desirably be chosen as above; however, toluene, which has an excellent solvent eiciency for the fats and waxes, but not nearly so high an eicieucy for the aconitic acid, may be used. In the use of toluene, it forms a minimum constant boiling mixture with acetic acid which helps to remove any acetic acid remaining from the washing operation.

With acetic acid as the first solvent, it is impossible to remove it completely from the First Molasses by evaporation without at the same time removing all of the water. Thus, only a part of the acetic acid is removed; the last of the acetic acid may be removed along with the fats, oils, waxes, and aconitic acid by the acetone (or acetone cosolvent) as the second solvent. The acetic acid and acetone are then evaporated from the crude wax-aconitic mixture and separated for their respective recovery and reuse.

If the First Mollasses has a concentration of total solids above about it may be desirable to dilute it with water to 75% or lower, to obtain a material which may be efficiently extracted. Higher temperatures allow higher concentrations in the extraction step.

CHOICE OF THIRD SOLVENT The second solvent is removed from the extract stream of the liquid-liquid extraction by evaporation or distillation. There remains as residue a solid or semi-solid mass containing aconitic and other acids, oils, fats, and waxes. This may be leached by a third solvent-desirably wateralthough both ethanol and methanol may also be advantageously used. The mass is broken up if solid, and thoroughly agitated in a batch system, with successive amounts of the third solvent, eg., water.

Almost exactly ten times as much aconitic acid dissolves in water at 100 C. as at 15 C. The speed of solution is also many times greater. An agitated batch leaching at the boiling point of water is used, preferably with successive batches, each washed several times countercurrently with leachings of two to three times as much water as aconitic acid present in the original mass. A relatively strong solution is thus obtained in the final liquor from which the aconitic acid may be crystallized out immediately by cooling to as low a temperature as the cooling water allows. Mother liquor may be recycled several times to successive batches. Finally, impurities build up to a point where discard, or separation of the other acids, sucrose, invert, etc. is necessary.

Alternately, the oils, fats, and waxes may be removed Y from the acids by a leaching with a hydrocarbon or chlorinated hydrocarbon of which toluene is an example (see Balch U.S. Patent 2,381,420), after which the ,fats and waxes may be separated by the method of Balch, or other usual method.

A better separation is possible than by the use simply of a solvent for the aconitic acid, water, or a solvent for the waxes, toluene. Both solvents may be used simultaneously. The agitated leaching operation is conducted continuously with both solvents (e.g., water and toluene) at as high a temperature as practical (these two liquids have a minimum boiling point at one atmosphere pressure of C.). The toluene-water mixture is run off the leaching tank and separated, the toluene solution-mainly of fats and waxes-is then washed countercurrently in a liquid-liquid extractor with the entering hot water, and the water solution is washed countercurrently in a liquidliquid extractor by the incoming hot toluene. The simultaneous use of the two solvents gives an increased selectivity in the separation.

9 MULTI-CELLULAR EVAPORATION One of the important features of the process of the present invention is the use of a special evaporation step which has been found most effective with solutions of solids in a mixture of two liquids of different relative volatiles; one of which is water. Particularly is this important where, as in the present case, the relative volatility of the water is greatly depressed by the presence of a large amount of dissolved solids.

Evaporation is done in from 4 to 8 stages in a singleeifect. The single body of the evaporator is divided by partitions or baffles into sections or cells, each supplied with heating surface. Free movement of liquid is possible in the general direction of flow from inlet to outlet, but not free circulation among the cells, and particularly not backwardly towards the inlet. The partitions or baliles dividing the cells may be placed so as to give a passage of liquid reversing in direction as it passes through each cell, or by using perforated plates for baffles, a direct forward flow may be maintained. They do not extend completely to the top of the evaporation chamber. Heat is transferred to the solution in the cell; and vapors are formed.` Vapors from all cells join in their outflow through a common exit pipe.

There may be considered, as an example, the separation of methanol, a preferred first solvent, from the water, sucrose, invert sugar, and impurities dissolved away from the raw sugar.

The vapors going off of the evaporator contain a mixture of methanol and water-but with much less water than if only a single-cell was effective for the entire evaporation process, and there was, as usually, a complete mixing of the liquid in all parts of the evaporator body. The composition of the vapors depends on the relative volatilities of the methanol and the water from the solution in that cell. As the feed liquid proceeds from one end to another, through or around the series of baffles which divide the body of the evaporator into 4 to 8 sections or cells, the liquid rapidly loses methanol to the vapors.

In this operation, the solution is concentrated from cell to cell; and the nal discharge at the far end from the feed may be of a syrup of the sugar dissolved only in Water. Meanwhile, the methanol has been evaporated practically completely therefrom and with little water in the vapors. No such separation of methanol can be achieved in the usual continuously operated, single-body evaporator.

FIGURE 1 diagrams such `an evaporation process conducted in a long horizontal cylindrical vessel with longitudinal steam coils. There are four bafes of the shape shown in the view on the right, with open vapor space above, and holes to allow freedomy of liquid passage in the direction of flow, but little or no baclcmixing. Methanol containing water and solids dissolved from the raw sugar flows from left to right through the five cells in series. The methanol is effectively distilled out of the residual molasses in this arrangement, as it passes from the inlet cell to the outlet. Vapors of methanol arise from each cell and join in passing to the condenser. Only a small amount of water vaporizes because of its vapor pressure lowering by the sucrose and glucose. A rst molasses discharges from the right, containing the water present in the original raw sugar. This concentration is controlled so that no sugar grain forms.-

This multi-cellular evaporation is a stagewise exhausting operation, similar to, but not as efficient as, an exhausting distillation in a column still would be for separating `all of the methanol. `A distilling oolumn'is not usually necessary in the present` usage with either methanol, a preferred first solvent; or acetone, a preferred second solvent. In those few cases where'water must be separated from the vapors to prevent a build-up in the system by recycling the condensate, the vapors are passed to the mid-point of a column still with the solvent going out the top for re-use and the water going out the bottom as waste. Thus, the concentration of water in the methanol passing to the cycling operation may be controlled at the optimum point for the particular raw sugar being processed.

A further improvement of the multi-cellular evaporation system, which has been found particularly effective, is the combination of two such operations, usually at the same pressure. They may be at different pressures, and

possibly even arranged in a double-effect. The description so far covers an operation which delivers most of the solvent free of water. As the molasses is exhausted of solvent, evaporation in the later cells gives more and more water in the vapors. Also, it may be necessary to remove a substantial amount of water to obtain the desired grain in a massecuite. Hence, another multi-cellular evaporation may be used: (a) to exhaust the last of the solvent with whatever water evaporates therewith, and (b) to concentrate the sugar solution to obtain the desired grain. This second object may be the controlling requirement in operation of this additional unit.

A relatively larger amount of water is in the vapors from this second multi-cellular evaporation, as. compared to the vapors from the first; and, in one case, where two such operations, each of ive cells, were conducted, the combined vapors from five cells ofthe first or solvent operation contained only about 1% water, while the combined vapors from the second or graining operation contained almost 50% water. The first vapors, after condensation, may be used directly as the solvent in the washer; while the second vapors may be separated by distillation or condensed and then separated into water and solvent. r

Both of the multi-cellular evaporations may be conducted in a single shell or body, although a separate body for each may be more convenient. If in a single body, one baile may extend across the entire cross-section to prevent mixing of vapors, which then have separate ydrawoffs. In any case, separate control of heat supply is desirable. A double-effect arrangement reduces heat cost, but makes control less flexible. The grainiiig operation is conducted at the higher temperature, and this would be the rst ejject, supplying vapors to the solvent operation as the second effect which loperates at a lower temperatu-re due to the greater amount of methanol present. Condensate from the first effect goes to a. still for separation, from the second effect directly back to the washer.

FLOW SHEET OF WASHING METHOD OF REFINING Washer FIGURE 2 is a diagram of one embodiment of the invention. In a washer, a standard ribbon type of conveyor or mingler, raw sugar is contacted countercurrently with methanol as an exemplary first solvent. The raw sugar passes through the washer from left to right. Nearly anhydrous methanol, 01.1% or containing water, never more than 8%, is fed in the right end at about its boiling point. The two ows are in counter-current and desirably about 1 part methanol to 1 part raw sugar, although this ratio may be varied from 0.3 to 1, to 1 to 0.3 with good results.

Methanol is passed from right to left through the washer at such a velocity `as to lift into suspension by simple hydraulic action, all fine solids. Liquid velocity is controlled so that it will carry ofic line particles of dirt, fiber, lint, and other extraneous materials which are present, but not carry 0H crystals of sugar in the usual size range. It will, however, `carry off very small particles of sugar as powder, thus removing such fines from the product. It dissolves, in its time of Contact, desirably from 15 minutes to 2 hours, the water and solids which are present as impurities on the surface, or near the surface, of the sugar crystals. The lifting action and agitating action of the ribbon or scrolls of the washer on the crystals forcing them in one direction, and the washing action of the solvent flowing against them, combine to rub the crystals one against the other, and to help in scrubbing off the film of impurities. Also, any crystals which adhere in clusters are broken apart. The contacting action must not be violent enough, however, to break up the usual crystal.

All of the water, invert sugar, the wax, the aconitic and other acids, the chlorophyl, the vitamin bodies, minerals, and other extraneous materials, are dissolved, while sucrose is only very slightly dissolved. A mineral acid to spring aconitic acid may be added in the washer at a point, A, to 75% of the length of the washer from the right where sugar is discharged, and is thus completely removed from the product. From 2% to 10% of the recycling methanol is first used to dilute this acid. Acid addition is controlled so that the discharge to the solids settler has a pH of from 4.0 down to 1.25 to 1.3.

Solids settler The methanol, with its dissolved impurities and its suspended impurities, is discharged at the end where the raw sugar is fed into the washer, the left end in FIG- URE 2. Thus, a true countercurrent action is achieved. The suspended solids present in the hot methanol discharge may be in amount from 0.1% to 1.0% of the total raw sugar fed to the system, depending on its previous history; i.e., whether it has been bagged and shipped, or whether it comes directly from the raw sugar production, the amount of dirt included, the amount of fines in the raw sugar, the amount of agitation in the washer, and other conditions. From one quarter to one half of these solids will usually be sugar nes. The methanol solution containing all of these insoluble solids, labelled DIRT on FIGURE 2, is possed to a gravity solids settler. Here the suspended solids settle to the bottom, since they have a higher density than that of the hot solvent. They are drawn off, and separated as such by centrifuge 1. The sugar fines may then be separated from the insoluble DIRT by dissolution in water after the centrifuging. This is not indicated. If sulfuric acid or phosphoric acid is added to the washer, the insoluble salts formed-*or if no acid is added, a part of the salts of aconitic acid present-will settle out. The solvent is decanted off the solids separator containing the free aconitic acid.

1st solvent evaporator The methanol solution of impurities is then passed into one end of the 1st solvent evaporator, containing a multiplicity of cells. The discharge is from the opposite or last cell of the series. An effective stripping of the methanol from the residual molasses is achieved due to this cellular construction and the depression of the partial pressure of water by the invert sugar and sucrose in the solution. Individual heating units may be used in the cells, or a single heating coil or other type of heater may extend throughout all of them, as diagrammed in FIGURE 2. The vapors combine from all cells and pass to the first solvent condenser. This condenser gives substantially pure methanol which is then returned directly to the washer for reuse. A small amount of water is not usually disadvantageous to the process-particularly if the raw sugar does not contain more than 0.75% water, as is usual. This water returned in the condensate recycles around with solvent each time, the water entering in the raw sugar goes out in this 1st molasses.

After substantially all of the methanol is evaporated off, the solvent of the lst molasses discharging from this evaporator is, as usual, water. Water may be controlled by addition or removal, as desired, by standard methods to obtain the optimum solvent action. After the first solvent evaporator returns solvent for recycle, a second multi-cell unit may remove vapors containing water and a small amount of solvent, then to be separated.

12 Extraction of 1st molasses with second solvent The 1st molasses leaves the 1st solvent evaporator at a concentration of about 65 to 80% of solids in water, and is passed to a countercurrent liquid-liquid extractor where approximately the same volume of second solvent, such as acetone in the present example is counter-currently contacted therewith in a liquid-liquid extraction. (While acetone is miscible with water, it has been found that it is not miscible under the present conditions with a concentrated molasses and thus may be used as an extracting solvent.)

The Wax, oils or fats, aconitic and other acids, and other impurities, including chlorophyl, are extracted by the second solvent from the aqueous solution which is usually maintained at a temperature below the boiling point of the second solvent. Since the extracting action has been found to be improved at higher temperatures than the normal boiling point, 56.5 C., of acetone, the liquid-liquid extractor may operate at a higher pressure than atmospheric. Thus, at C., the pressure may have to be about 4 atmospheres, and a lower ratio of solvent than 1 to 1 may be used; i.e., as low as 0.5 part solvent to 1 part molasses. The solvent efficiency in removing the two general classes of materials, fats or waxes and acids, may be improved with many raw sugars by using an added solvent; eg., from 1 to 30%, or up to 43%, of isopropyl ether. This decreases the miscibility with water, greatly reduced already by the large amount of solids present; i.e., allows a molasses of lower Brix to be extracted.

The counter-current action of the extractor is accomplished as shown in FIGURE 2 by feeding the heavier liquid-the hot molasses--into the top of the extractor column in the form of droplets which settle downwardly as they contact counter-currently a slowly rising body of solvent in a continuous upper layer. At the interface, the molasses droplets coalesce to give a lower continuous layer of molasses. Near the bottom of the extractor is introduced a stream of droplets of solvent which rise upwardly through the continuous molasses layer. The large amount of the surface of the respective droplets passing in contact with the opposite liquid phase allows the extraction action to proceed efficiently. (Any one of numerous other types of liquid-liquid extractors may be used.)

Molasses of high viscosity is difficult to extract. Heating or dilution to a concentration of 65 to 75% solids usually makes it workable.

2nd solvent evaporator from extract layer By the counter-current solvent action, an extract layer of many of the impurities of the 1st molasses, which are preferentially soluble in the second solvent, is withdrawn at the top of the extractor. This extract layer contains the impurities not preferentially soluble in the water which is still present in the 1st molasses, and particularly fats, oil, and sugar cane wax, and aconitic and other acids. This passes into a 2nd solvent evaporator of the same multi-cell type as the 1st solvent evaporator. Here the extract layer is concentrated until substantially free of the second solvent and in a melted, oily form. Again, the stripping or exhausting effect-similar to that of a beer still-is effective in this multicellular evaporator.

The melted wax-oil mixture from the last cell at the discharge end of the 2nd solvent evaporator is then run offdnto a pan to allow the wax to solidify. The amount of crude wax so recovered was approximately 0.2% of the original raw sugar. This Wax mixture may be worked up to separate into the crude wax into its components, including aconitic and other acids.

Some` small amount of water may be in the feed to this evaporator. Because its vapor pressure is reduced by the acinotic acid, the acetone may evaporate leaving most of the water behind to discharge with the solids. If the 13A vapors contain water, these may be passed to a column still (not shown) for separation.

Dissolution of crude acids The crude wax mixture is agitated with to l0 volumes of a third solvent, e.g., water, at 90-95 C. This dissolves the acids-principally aconitic. Aconitic acid may be crystallized out by cooling the mother liquor containing also sucrose, invetts, salts, and other acids. After re-use, the mother liquor is limed to remove acids and recycled to the first molasses to recover sucrose and inverts. Alternately, the aqueous extract may be treated with lime and calcium chloride to obtain the calcium salt. This is filtered off and converted to the free acid by adding sulfuric acid. From this solution a purified aconitic 'acid is obtained. Approximately 0115 of the original raw sugar was obtained in one case as aconitic acid, but this varies with the source of the raw sugar.

2nd solvent evaporator from raffinate The rainate molasses from the bottom of the liquidliquid extractor is an aqueous solution containing original impurities, particularly invert sugar, and a small amount of the s-olvent, acetone. It iiows from the bottom of the extractor, to a third multi-cell unit, another second solvent evaporator. This evaporates the small amount of dissolved second solvent and a small amount of water. These vapors pass to the same condenser used for the second solvent evaporator for the extract stream.

In order to improve the operation of both second solvent evaporators on the two streams (extract-top, and raffinate-bottom) from the extractor, the second solvent may be selected as an azeotropic withdrawing agent to distill ofi completely any trace of residual methanol from these streams. The azeotrope of methanol with acetone biols at about 55 C.; with benzene at about 57 C.; with hexane at about 50 C.

The small amount of water which evaporates from the concentrated molasses is usually not important. If acetone, water may be removed in a standard distillation procedure. If the second solvent is water-insoluble, such as toluene, two layers form in the condensate; and the water layer is discarded.

If the amount of water present warrants, a second evaporator of the same multi-cell type may follow that for removal of the second solvent. This will produce a massecuite from which sugar crystallizes; and the vapors therefrom, relatively low in solvent concentration, may be passed to a column still either before or after condensation. The solvent is dehydrated for reuse and the water is discarded.

Neither the use of a second multi-cellular evaporator nor a column still for separating solvent and water, is indicated in FIGURE 2.

However, this is the point in the system where added water may be removed--and may have to be removedto` obtain a massecuite from which may be crystallized the sugar dissolved in the washer. Thus, if any small amount of water, preferably never more than 8%, has been added to the first solvent, e. g., methanol, any excess above that removed for recycle in the first solvent evaporator may be removed here. (This allows the amount of water added with the first solvent in the first solvent washing step to be controlled as to (a) solubility relations for impurities, and (b) crystallization of sugar.) On the other hand, any water added to the first molasses to dilute it to a suitable total solids content so that it may be extracted, will be removed here.

In any case, the equipment involved at this stage is very small since less than about two percent of the original raw sugar is present, and the volumes are relatively small.

Centrifuging of raw sugar Evaporation is continued in the second solvent evaporator either in a single unit or the second of a double unit, until an impure or raw sugar begins to crystallize out in the massecuite. The mixture of molasses and the fine sugar crystals is then withdrawn. Sugar grain is allowed to grow; and, when centrifuged, from one to two percent of the original raw sugar is obtained as a sucrose of a very light color, often a light yellow color, comparable to that of the original raw. This has a sucrose content from 93 to 98%; and it is returned to the original raw sugar feed to the process with accompanying increase in overall yield.

The molasses which is spun off in this centrifuge is about 2 to 2.5% of the raw sugar originally fed, of which the sucrose accounts for only about 0.5% of that in the original ra-w sugar. It contains most of the moisture present in the original raw sugar, as well as most of the invert sugars originally present, the minerals originally present, and the vitamins originally present. This molasses has a light color, is relatively clear of cloudiness, and has a pleasant fiavor `because of the elimination of -the normal impurities of molasses, aconitic, and other acids, fats, waxes, chlorophyl, etc., by the extraction action of the second solvent. This is an edible grade molasses.

If the methanol in the washer has not been acidified, the calcium `or magnesium salts of aconitic acid (mono, di, trior mixed), which are insoluble in methanol, will be precipitated and removed in the solids settler. If the methanol has been acidifed with phosphoric acid or sulfuric acid, most of the aconitic acid will be in the free form; and the corresponding calcium and magnesium salts are removed even `more completely in the solids settler. If hydrochloric acid is used, the calcium and magnesium chlorides will stay in solution and discharge in this second molasses, to make a less desirable product here.

EXAMPLE By way of example, there may be considered the treatment of 100,000 pounds of raw sugar from Puerto Rico, having the following analysis:

The analysis did not distinguish between free and combined acids; and the undetermined included fats, waxes, gums, cellulosics, and hemicellulosics, pentosans, chlorophyll, and other materials. The acids are analyzed here and later as aconitic, and so expressed.

To the tot-al fresh raw sugar fed to the washer, there Was added approximately 1360 pounds recycle or recovered raw sugar from the sugar centrifuged from the second molasses and 300 pounds recovered from the water solubles of the settled solids, as explained later.

Washing was with 1 to 1 methanol recycling in the system, with a total time in the washer controlled at one hour, and with an acidification with sulfuric acid so that a pH of 4.0 was maintained at the discharge of impurity laden solvent. Acid was added at a point two-thirds of the distance from the sugar discharge of the extractor. A total of pounds of sulfuric acid (as 100%) was added. This was diluted with a small stream of methanol taken from the main stream to the washer. The time of washing after the addition of sulfuric acid was thus 20 minutes. Inlet of methanol was at 60 C., of raw sugar was at 20 C., no heat was `supplied to the Washer, although a heating jacket for circulation of hot waterl is desirable for controlling the temperature of washing when desired. The acidification was thus at the relatively cool side of the washer, where the temperature was between 25 C. and 35 C. The refined sugar discharged at 55 C., and its average temperature during the washing was thus between 35 C. and 40 C.

The discharge of the slurry of refined sugar in methanol was by an enclosed tube to an enclosed centrifuge. Refined sugar was washed lightly in the centrifuge with methanol and, after discharge, was dried in an enclosed dryer with recycling hot air. Vents in the centrifuge were minimized; and the air from the centrifuge and the dryer discharged through a scrubbing system to minimize solvent loss, which, on the system as a whole, did not exceed 1% of that cycled.

The total refined sugar made from the original raw, plus the recycle raw (from the second molasses and the settled solids) had the following analysis:

16 This was only about 400 gallons in total, representing 4.31% of the original raw sugar. It was diluted with water to -bring the total solids contents to 75% for ease in further processing. This water added amounted to 5 714.7 pounds, to give a total water content of 1256.2

pounds. (As noted above, the aqueous extract -of the settled solids may be added here, with its several solid contents, which `are also -recoverable similarly. The resulting mother liquor of the aqueous extract of aconitic acid may be added at this point. Dilution t0 the desired total solids content would be after such additions.)

The rst molasses, now diluted to 75% total solids, was extracted with one-half as much acetone on a volume basis (approximately 250 gallons) in a countercurrent tower extractor having an eiciency equivalent to 5 theoretical stages. The partition coetiicient for aconitic acid averaged about 4 to 1, in favor of Ithe actone throughout the various stages. The acetone extracted layer was withdrawn containing a little water; and the acetone was removed in a Second solvent evaporator, which discharged a semi-solid mixture nearly acetone-free. This had the following approximate amounts of solids:

The capacity 0f the solids settler allowed one and a urtse half hour settling. A slimy solids fraction was drawn olf 25 1 l 12 and separated. It contained many of the trace impurities, As.d 138 and amounted to some 550 pounds or 0.55% of the Umd st--"d 565 original feed. It was extracted with water, filtered with the n e ermme help of iilter aid. The resulting sugar solution was crystal- 795 lized and returned to the raw. Alternately it may be added This mass was leached with boiling water, from which to the first molasses: was crys-tallized 125 pounds of aconitic acid. The mother Analysis of Weight 0i Water Extract Discard In- Settled Solids, Settled Solids, Concentrated soluble in Percent Pounds and Recycled, Water or Pounds Lost, Pounds 51.0 1.9 1.1 0.1 3. 0 16.5 10.0 40.0 0.1 0.5 Undetermined 34, 8 191. 0

'rtm1 100. 0 550. o 300 250. 0

Undetermined materials included gums, dirt, cellulosics, pentosans, etc., and were not further identified. These, With the insoluble inorganics (ash) were discarded,

The methanol solution was decanted from the solids settler and passed through the six cells of a 'first solvent evaporation where about three-quarters of the methanol was exhausted as vapors from the methanol solution of molasses. This solution in methanol and water was discharged to the kettle of a 20-plate column still operated by batches (this is not shown in FIGURE 2, since it is only one -of several alternate methods of operation). The distillation gave 99.8% methanol which was passed with that from the `condenser of the first solvent evaporator back to the Washer. Five percent of this stream (about 5,000 pounds) was added to the sulfuric acid for its dilution before its addition two thirds of the 'distance in the washer from the point of addition of the major part of the methanol.

The tirst molasses, now discharging hot from the methanol recovery still, had the following composition based on a water balance from the original raw sugar. Actually, the water content may be varied in this evaporation to prevent grain formation or crystallization; while liquids .were `re-used until the impurities, mainly sucrose and inve-rt sugars, built up to an objectionable amount. Then the remaining small amounts of molasses (high in acids and ash) which resulted, was recycled for re-use with the first molasses. This recovery and recycle is not shown in FIGURE 2 nor on the material balance.

The undetermined in the last list of amounts represented the crude oil and wax mixture, containing also chlorophyll and other coloring materials. Some 550 pounds was separated from the hot water leachings. The chlorophyll may be extracted with hot methanol. The balance may be worked up for further separation by the method of Balch (U.S. Patent 2,381,420).

The raflinate layer from the liquid-liquid extractor had the acetone which was dissolved therein exhausted in a multi-cell evaporator as was used Vfor the methanol previously. Again, some water was evaporated containing some acetone in a crystallizing evaporator. Acetone was recovered to the total extent of about 98% and recycled.

A massecuite resulted from the grain formation with solids of the following composition:

Recovered Second Molasses Massecuite, "Raw" Sugar,

Pounds Pounds Percent Pounds sucrose 1,835.1 1, 330 24.8 505. 1 14 37.8 766. 9 6 20. 2 410.0 6 15. 9 322.0 0 0.1 1. 5 Undetermlned. 28. 0 4 1. 2 24.0

l It was impossible to obtain a water balance in this series.

The raw sugar produced was recycled to the original raw sugar feed to the washer-representing only 1.36% of the total feed. The second molasses was only about 200 gallons in volume. It was high in ash, and particularly high in invert sugars, compared to blackst-rap. This was to be expected from its prior history. As was to be expected, since there had been removed already insoluble (gums, etc.) and extracta'bles, (fats, waxes, etc.) it was relatively light in color land clean in appearance and of agreeable taste. Analysis showed it to have substantial amounts of various vitamins, and from ve to ten times as much as does the usual blaclrstrap of the important vitamin constituents. Niacin (B), pantothenic acid, and pyredoxine (B6). Much of the nutritional mineral content was also present, as evidenced by the high ash content.

The methanol loss was approximately one percent of the amount cycled, the relatively smaller amount of acetone recycled is in a somewhat easier system to keep tight and its loss was also between about one percent and two percent.

No exa-ct balance of the water could be accounted, because of the evaporation for graining, dilution of molasses for extraction, etc. Hence, the totals of water in and out are not exactly the same in these figures, which actually represent a composite of various experimental determinations. A larger number of signiiicant gures are used in the material balances than warranted by the experimental accuracy, in order to indicate the distribution of materials throughout the system.

The total s-ucrose recovery inthe relined sugar was above 99%; and with the complete recycling operation, this high yield is not unexpected. A very slight improvement is to be expected in a complete operation, wherein there would be recovered the small amounts of sucrose removed from lthe extract stream from the liquid-liquid extractor. Here, the aqueous leaching liquor for separating aconitic `acid from the fats and waxes had the acid crystallized out. It then may be recycled back to the system, into the first molasses. Credit could be given then for the sugars which would be recovered. This has not been done in this example.

VARIATIONS OF FLOW SHEET Another -first solvent besides the methanol of the example, which may be utilized, is acetic acid. It may be used either with or without acidification by a mineral acid to a pH as low as 1.25 to 1.30; In its use, some of the water removed from the raw sugar is distilled with the solvent in the first solvent evaporator. Thus, there may result a molasses containing as its partial solvent the acetic acid; and this also may then be extracted from the first molasses in the liquid-liquid extractor with the second solvent.

In this case, the preferred second solvent again is acetone, which will extract the acetic acid along with the aconitic acid, fats, oil, and waxes. The extractthen Will have to be worked up for the subsequent separation of the acetic acid which would be re-used.

While acetone is the preferred second solvent, toluene may be used instead in some cases. Thus, again, the second solvent may be chosen so it will act as an azeotropic agent to withdraw any residual acetic acid from the extract layer and from the raffinate layer, which leave the extractor to pass to the respective evaporators. Toluene `forms an azeotropic mixture with acetic acid at 105 C., and helps remove the acetic acid in the second solvent evaporator. Provision (not shown) must be made to separate the acetic acid from the second solvent if this mixture is formed here. In those cases where toluene is used, much of the aconitic acid is not extracted, and thus is lost in the second molasses, since toluene is principally useful as a solvent for the fats, waxes, and oils when they are desired in the extract layer without aconitic acid.

The refined sugar recovered may represent a yield from a raw sugar containing 97% sucrose, between 95% and 96% of the original material, plus a recycle of the raw sugar from the second centrifuging, which may add over 1%. Also, there may be included from 0.2 to 0.5% of sugar settled out with the dirt, probably as iines; and a much smaller amount recovered from the aconitic acid purification. In both cases, this comes from a water leaching step, in the case of aconitic acid, the mot-her liquor, which has become a molasses, after the aconitic acid crystallization is returned to the first molasses and the sugar is obtained as raw sugar from the second molasses. Thus the total refined sugar recovered may be as much as 96.5%; or the rened sugar may be well above 99% of the sucrose in the original raw sugar, depending on the completeness of the various steps. These represent relatively small items of equipment and processing and would only be economic on a large scale operation. If the solvent retining process was installed alongside of other sugar operations, some of these streams of small amounts may more economically feed into other operations.

As previously mentioned, one of the features of the present invention is the utilization of multi-cell evaporation, either in one operation or two. This makes practical the separation of the methanol `from the water in the rst solvent evaporator to give a solvent-free rst molasses; also the separation of the second solvent from the extract layer from the extractor, to give a nearly solvent-free wax, which then may be crystallized out by cooling and iinal drying 01T of any trace of solvent therein.

Also, in the working up of the raliinate stream from the extractor, multi-cell evaporation allows the elimination of the second solvent from the massicuite of the second molasses and raw sugar before this mixture is separated. As explained above, a iirst operation may secure an almost water-free solvent which may be re-used immediately, and the second operation may give a much smaller amount of the solvent diluted with a large amount of water. This water-solvent mixture-a small part of the total solvent-must be separated to re-use the solvent. Instead of using a second multi-cellulor evaporator here or in recovery of methanol, the molasses discharging from the -iirst of these units with some solvent may pass to the kettle of a batch still with column, which allows pure solvent to be recovered as an overhead product.

The separation of the small amount of chlorophyl originally present in raw sugar may be accomplished by a further preferential extraction in the purification of the crude wax after the removal of the acids if there is a market for this material as such. A suitable solvent is methanol. Methanol dissolved all of the constituents of the crude wax in the washer, in its relatively large ratio' to fat, wax, and chlorophyll because there was some hundreds of times as much methanol as the combined amounts of these materials; and all were dissolved from the sugar which was thereby relined; At this later stage, several volumes of methanol may be used to extract the chlorophyll from the wax fraction. 'Ethanol has a better solubility (i.e., efliciency) -for the chlorophyll, but less selectivity; and more oils and waxes are found in the crude chlorophyll fraction on evaporation of ethanol as the solvent. Thus, methanol is usually preferred for this separating extraction.

Many other variations are possible in the several operations of refining sugar and separating the impurities by the use of two or more solvents. One reason for these process variations is that the raw sugars of commerce have great differences in. the constituents and their relative amounts in the 3 to 5% impurities present. Raw sugars come from widely different parts of the world, from different climatic and growing conditions, from different species of cane, and from widely different processing. Hence, there are variations in the composition, not

so much in the amount of sucrose, but in the various' impurities, largely analyzed only empirically, and not identified as such. The process to remove and separate these impurities will necessarily vary somewhat-often also empirically, in changing from raw sugar to another. No best conditions for all raw sugars can be stated. Different modifications of processing are necessary, as indicated above, and no fixed specification can be made methods of arrangement of more or less standard items of equipment and processing steps. Furthermore, there may be chosen many alternate standard processing steps, eg., centrifuging or filtering instead of settling for solids 5 separation, without changing the fundamental advantages which will be optimum for all conditions. of the method.

SUMMARY OF MATERIAL BALANCE In Out Recycle Out Raw Sugar Rened Sugar Settled Solids Water In- Water soluble, Percent Pounds Percent Pounds Percent Pounds Extract, Pounds Pounds Sucrose 97. 97, 150 99. 80 96, 608 51. 0 1.9 Invert Sugars. 85 85 0. 04 38 1.1 0.1 at 60 600 0. U5 48 3. 0 16. 5 .45 450 0. 08 76 10. 0 40. 0 15 150 0. 01 10 0. 1 0. 5 80 800 O. 02 2() 34. 8 191. 0

Out Recycle Out First Molasses (l) Raflinate Second Molasses Extract, Pounds Masse- Recovered Percent Pounds cuite, Raw Percent Pounds Pounds Sugar,

Pounds Sucrose 43. 4 1, 870. 1 35 1, 835. 1 1, 330 24. 8 505. 1 Invert Sugar 19.2 825. 9 45 780. 9 14 37. 8 766. 9 Water.. 12. 5 2 541. 5 (3) (3) 6 20. 2 410.0 Ash 7.9 340. 0 12 328. 0 6 15.9 322.0 Acids (as aconitic) 3. 2 139. 5 138 1. 5 0 0.1 1. 5 Undetermined 13. 8 593. 0 565 28. 0 4 1. 2 24. 0

Total. 100.0 4,310. o 795 2, 876. 5 1, 360 100. c 2, 029. 5

1 Extracted with water to give 125 pounds Aconitie Acid as crystals, balance recycled. 2 Plus water added to dilute the First Molasscs before extraction. 3 Water lost during evaporation ol solvent.

Also, it must be noted that the washer is the only unit which handles all of the throughput. All but a few percent goes out as product, refined sugar, through the first centrifuge. The other units handle progressively less, often relatively insignificant amounts (e.g., the centrifuge for t-he raw sugar produced from the second molasses handles only 1 to 1.5% as much as the first centrifuge) and the aconitic acid to be recovered is only one-tenth of that small amount.

Hence, under conditions of the different raw sugars to be handled, of different analyses, and particularly the amount to be handled per day, different methods of operation will be used. Large plants will find it economic to separate all of the products in `all of the steps suggested. Even the small fractional percents of aconitic acid and other items indicate worthwhile revenues at their higher unit values when the throughput of raw sugar runs into millions of pounds daily.

Most items of equipment are standard: the washer, the centrifuges, pumps, liquid-liquid eXtractors, dryers, and other items are completely familiar to all in the industry. The multi-cellular evaporator involves a simple modification of a standard unit. Thus, the unexpected and novel results which have been secured are mainly through different arrangements and operations of standard items of equipment. Furthermore, the figures and the description do not show or discuss the various standard equipment and steps, i.e., pumps, valves, temperature and other controllers, or their operation, since such are basically standard and a background of, but not a part of, this invention.

Also processing storage, solvent recovery, materials handling, heat transfer, extraction, rectification, etc. are not discussed by themselves as being familiar to those in this industry. The novelty and advantages reside in the I claim:

1. The method of removing and separating impurities from raw sugar, comprising:

(a) washing the crystals of said raw sugar with a first solvent selected from the group consisting of acetic Y acid and methanol;

(b) removing from said washing operation refined crystals of sugar and a separate solution of said first solvent containing said impurities;

(c) evaporating off for re-use said first solvent from said solution of impurities, to give a molasses;

(d) extracting said molasses with a second solvent comprising a ketone having no more than six carbon atoms in the molecule, so as `substantially to separate acid, oil, fat, and Wax impurities from the invert sugar impurity.

2. The method of claim 1, wherein the separated solution of said first solvent containing said impurities after said washing operation is allowed to stand so as to settle out those impurities which are insoluble and are decanted therefrom, While holding in solution other of the impurities which are soluble.

3. The method of claim 1, wherein the first solvent contains water in an amount of from 0.1% to 8%.

4. The method of claim 1, wherein the second solvent comprises acetone. i

5. The method of claim 1, wherein the second solvent comprises a mixture of acetone and from 1% to 43% of isopropyl ether.

6. The method of claim 1, wherein the second solvent comprises a mixture of acetone and from 1% to 25% of a solvent selected from the group consisting of benzene and chloroform.

7. The method of claim 1, wherein the first solvent is evaporated from the said solution of impurities washed 21 from the said raw sugar while passing through a series of cells, all at the same pressure, with the concentration of the lirst solvent decreasing from cell to cell and vapors from all cells being combined to discharge in one stream.

8. The method of claim 1, wherein:

an extract stream is removed from said extraction containing the bulk of said second solvent with dissolved acid, oil, fat, and wax impurities of the original raw sugar; and

said second solvent is evaporated oi from said extract stream for re-use, so as to leave a residue containing said acid, oil, fat, and wax impurities of the original raw sugar.

9. The method of claim 8, wherein:

said residue containingr said dissolved acid, oil, fat, and Wax impurities from the original raw sugar is leached with water so as to obtain an aqueous solution of the said acid impurities; and

said aqueous solution of the said acid impurities is concentrated so that said acids originally present as impurities in the raw sugar crystallize out of said solution.

10. The method of claim 8, wherein:

said residue containing said dissolved acid, oil, fat, and wax impurities from the original raw sugar is leached with a solvent selected from the group consisting of a hydrocarbon and a chlorinated hydrocarbon so as to obtain a solution of the said oil, fat, and wax impurities of the original raw sugar;

said solvent selected from the group consisting of a hydrocarbon and a chlorinated hydrocarbon is evaporated from said solution so as to obtain the said oil, fat, and wax impurities of the original raw sugar.

11. The method of claim 1, wherein:

a raffinate stream is removed from said extraction of said molasses containing some of said second solvent which is evaporated therefrom for re-use; and

a concentrated aqueous sugar solution is thus left as a residue containing most of the invert sugar present in the original raw sugar.

12. The method of claim 11, wherein the second solvent in said raffinate stream from said liquid-liquid extraction is evaporated from the said concentrated aqueous sugar solution, While passing through a series of cells, all at the same pressure, with the concentration of the second solvent decreasing from cell to cell and all vapors being combined to discharge in one stream.

13. The method of claim 11, wherein:

an impure, light brown sugar is crystallized from the said concentrated aqueous sugar solution containing most of the invert sugar present in the original raw sugar; and

said impure, light brown sugar is separated from a second molasses.

14. The method of claim 1, wherein a mineral acid selected from the group consisting of hydrochloric acid, sulfuric acid, and phosphoric acid is added to the iirst solvent in an amount sufficient to spring the acids originally present in the raw sugar as salts.

15. The method of claim 14, wherein said addition of said mineral acid is made in a counter-current washing of the raw sugar at a point to 75% of the length of its travel before its place of discharge, so that the rst solvent-as yet unacidiiied with said mineral acid--may wash 22 out any of said mineral acid otherwise remaining in the sugar being washed.

16. The method of removing from a molasses which contains sucrose and invert sugar, the acid, oil, fat, and wax impurities, comprising:

(a) extracting said molasses with a solvent comprising a ketone having no more than six carbon atoms in the molecule, so as substantially to separate from the said molasses the said acid, oil, fat, and wax impurities;

(b) removing as the extract stream from said extraction, the bulk of said solvent with dissolved acid, oil, fat, and wax impurities of the original molasses; and

(c) evaporating oli from said extract stream for reuse, said solvent so as to leave a residue containing said acid, oil, fat, and wax impurities of the original molasses.

17. The method of claim 16, wherein:

a raflinate stream is removed from -said extraction of said molasses containing some of said solvent which is evaporated therefrom for re-use;

a concentrated aqueous sugar solution is thus left as a residue containing most of the invert sugar present in the original molasses;

an impure, light brown sugar is crystallized from the said concentrated aqueous sugar solution left as a residue; and

said impure, light brown sugar is separated from a sec ond molasses.

18. The method of claim 16, wherein:

said residue containing said dissolved acid, oil, fat, Iand wax impurities from the original molasses is leached with water so as to obtain an aqueous solution of the said acid impurities; and

said aqueous solution of the said acid impurities is concentrated so that said acids originally present as impurities in the original molasses crystallize out of said solution.

19. The method of claim 16, wherein:

said residue containing said dissolved acid, oil, fat, and wax impurities from the original molasses is leached with a solvent selected from the group consisting of a hydrocarbon and a chlorinated hydrocarbon so as to obtain a solution of the said oil, fat, and wax impurities ofthe original molasses; and

said solvent selected from the group consisting of a hydrocarbon and a chlorinated hydrocarbon is evaporated from said solution so `as to obtain the said oil, fat, and wax impurities of the original molasses.

References Cited UNITED STATES PATENTS 1,558,554 10/ 1925 Leonis 99-141 X 2,000,202 5/ 1935 Vazquez 127-47 3,174,877 3/ 1965 Bohrer 127-64 FOREIGN PATENTS 439,873 3/ 1934 Great Britain.

MORRIS O. WOLK, Primary Examiner.

MICHAEL E. ROGERS, Examiner..

Claims (1)

1. THE METHOD OF REMOVING AND SEPARATING IMPURITIES FROM RAW SUGAR, COMPRISING: (A) WASHING THE CRYSTALS OF SAID RAW SUGAR WITH A FIRST SOLVENT SELECTED FROM THE GROUP CONSISTING OF ACETIC ACID AND METHANOL; (B) REMOVING FROM SAID WASHINGTON OPERATION REFINED CRYSTALS OF SUGAR AND A SEPARATE SOLUTION OF SAID FIRST SOLVENT CONTAINING SAID IMPURITIES; (C) EVAPORATING OFF FOR RE-USE SAID FIRST SOLVENT FROM SAID SOLUTION OF IMPURITIES, TO GIVE A MOLASSES; (D) EXTRACTING SAID MOLASSES WITH A SECOND SOLVENT COMPRISING A KETONE HAVING NO MORE THAN SIX CARBON ATOMS IN THE MOLECULE, SO AS SUBSTANTIALLY TO SEPARATE ACID, OIL, FAT, AND WAX IMPURITIES FROM THE INVERT SUGAR IMPURITY.

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