US3508965A - Sugar purification - Google Patents

Description

United States Patent 3,508,965 SUGAR PURIFICATION John R. Harrison, West Chester, Pa., and Ronald D.

Lees and Daniel J. Monagle, Wilmington, Del., assignors to Hercules Incorporated, Wilmington, Del., a corporation of Delaware No Drawing. Filed Nov. 15, 1966, Scr. No. 594,365 Int. Cl. B01d 21/01; C13d 3/00, 3/12 US. Cl. 127-48 11 Claims ABSTRACT OF THE DISCLOSURE Manufacturing sugar and especially purification of aqueous sugar slurry by contacting same with certain acrylamide-acrylate copolymers as a processing aid (e.g. as a fiocculant, settling, filtering, etc. aid).

The present invention relates to sugar manufacture and more particularly to the use of fiocculants as processing aids in the manufacture of sugar.

Sugar beets and sugar cane are the two major raw materials from which sugar is obtained. There is not much difference between a typical conventional process of manufacturing sugar from beets and one of manufacturing sugar from cane. These processes will now be described very briefly to aid in understanding the present invention.

After the raw whole sugar beets are washed and shredded they are passed through a diffuser countercurrent to a flow of water which dissolves out substantially all of the sugar and leaves behind the beet pulp for drying as livestock feed. The effluent from the diffusion process includes water containing about 15% dissolved sugar as well as both dissolved and undissolved impurities. By means of at least one step each of screening, liming and carbonating much of these impurities are removed. Additional impurities are removed by allowing the aqueous sugar solution to settle. The efiiuent (supernatant) from the settling (clarification) step contains in solution substantially all of the original sugar in a relatively pure form. The final pure white sugar product is obtained from the settling step efiluent by further processing this effluent in accordance with conventional steps such as evaporating, crystallizing, centrifuging, drying and grinding. The material which settles during the settling step is vacuum filtered, the filtrate (sweet water) being recirculated to the liming steps. Either the lime is recovered from the filter cake of the vacuum filtration step and reused in the process, or this filter cake is simply discarded.

Raw sugar cane is cut to a fibrous pulp and slurried in hot water to dissolve the sugar from the pulp. Impurities (pulp, dirt, etc.) are removed from the slurry by settling. The effiuent (supernatant) from the settling (clarification) step is processed to the final sugar product by subjecting this effluent to conventional steps such as evaporating, .crystallizing, centrifuging, drying and grinding. The material which settles from this slurry is vacuum filtered, the filtrate (sweet water) being recirculated to the process and the filter cake being discarded.

The present invention is useful in the manufacture "ice of sugar from cane and beets in either the settling step or in the filtration step, or in both steps.

Although the process steps employed in the manufacture of sugar from cane and beets are very similar, the impurities encountered in the two processes are quite different. The impurities in beets are primarily organic whereas those in cane are primarily inorganic. In addition, the amount of impurities in cane is considerably greater than in beets. In view of this it cannot be predicted that merely because a given fiocculant processing aid is useful in the manufacture of sugar from cane it will also be useful in the manufacture of sugar from beets, or vice versa.

The sugar industry, both cane and beet, has been striving for increasing product yields as well as for decreasing stream pollution.

In accordance with the present invention it has been found that these objectives of the sugar industry are accomplished to a surprisingly high degree by contacting an aqueous slurry containing sugar and impurities (either from cane or beet) just prior to the settling or vacuum filtration steps with a small amount of a certain acrylamide-alkali metal or ammonium acrylate copolymer. The use of said copolymer in the settling (clarification) step results in the copolymer flocculating the sugar impurities into large dense fiocs which increases the settling rate of the impurities and the amount thereof settled. The use of said copolymer in the vacuum filtration step results in the copolymer flocculating the sugar impurities into large dense flocs which causes the fiocculated particles to release their bound water (to dehydrate) far more readily during vacuum filtration.

The effectiveness has been determined of the particular copolymer of the present invention to facilitate the settling (clarification) step and the vacuum filtration step in the manufacture of sugar from both cane and beets.

The following examples illustrate various embodiments of the present invention. These examples are not intended to limit the present invention beyond the scope of the appended claims. In these examples and elsewhere herein and ratios parts and percent are by weight unless otherwise indicated. All molecular weights given in the examples and elsewhere herein of the copolymers were measured as reduced specific viscosity (RSV) employing the well known Ubbelohde viscometer on a 0.1% solution of the copolymer in 0.1 M KCl at 25 C.

EXAMPLES 1-3 Cane sugarsettling (during clarification) qualitative These examples are carried out to determine the effect of various polymeric flocculating agents on the settling characteristics of suspended solids impurities in cane sugar aqueous slurries.

l-liter portions of cane sugar juice slurry (formed by cutting raw sugar cane to a fibrous pulp and slurrying in hot water) were placed in each of several l-liter graduated cylinders. Flocculating agent was mixed with each portion by adding the fiocculating agent thereto and pouring 5 times back and forth from filled to empty graduated cylinders. The resulting mixtures were allowed to stand 5 minutes and the settling characteristics of the suspended solids impurities were observed.

Further details appear in Table 1 hereinafter.

TABLE L-CANE SUGAR, SETTLING (DURING CLARIFICATION) QUALITATIVE [Efiect of various flocculating agents on settling characteristics of suspended solids impurities in cane sugar aqueous slurriesl Floceulating Agent Visual observations Name a Amount b RSV after standing 5 mins.

Example No.1

1 None 2 Commercial ilocculating agent No. 1.

3 90% aerylamide, 10% sodium aerylate None Very slow settling. Turbid supernatant.

I Example 2 used an aerylamide-based anionic floeeulating agent available commercially as {Separan AP-30. h P.p.m. dry weight basis by weight of total slurry treated, added as a 0.01% aqueous solution.

EXAMPLES 4-16 Beet sugarsettling (during clarification) qualitative These examples were carried out to determine the effect of various polymeric flocculating agents on the settling characteristics of suspended solids impurities in beet sugar aqueous slurries.

l-liter portions of beet sugar juice slurry (effiuent after completion of the liming-carbonation steps) were placed in each of several l-liter graduated cylinders. Flocculating agent was mixed with each portion by adding the fioccnlating agent thereto and pouring 5 times back and forth from filled to empty graduated cylinders. The resulting mixtures were allowed to stand 5 minutes and the settling characteristics of the suspended solids impurities were observed.

Further details appear in Table 2 hereinafter.

EXAMPLES 17-26 I Cane sugarsettling (during clarification) quantitative These examples were carried out to determine the eifect of various polymeric flocculating agents on the settling rate of suspended solids impurities in cane sugar aqueous slurries.

l-liter portions of cane sugar juice slurry (formed by cutting raw sugar cane to a fibrous pulp and slurrying in hot water) were placed in each of several l-liter graduated cylinders. Flocculating agent was mixed with each portion by adding the flocculating agent thereto and pouring 5 times back and forth from filled to empty graduated cylinders. The resulting mixtures were allowed to stand 5 minutes and the settling rate of the suspended solids impurities was determined by measuring the amount of supernatant which formed during this time.

TABLE 2.BEET SUGAR, SETTLING (DURING CLARIFICATION) QUALITATIVE [Effect of various floceulatlng agents on settling characteristics of suspended solids impurities in beet sugar aqueous slurries] Flocculating Agent Visual observations Name Example N o.

4 Nona...

5 Commercial floceulating agent N o. 1.

Amount after standing RSV 5 minutes None {Very slow settling.

Turbld supernatant.

ery slow settling.

urbid supernatant. Very fast settling. 0. 1 Hazy supernatant with many fines.

Very fast settlin 0 25 g Clear supernatant with many fines. Very fast settling. 1 0 Clear supernatant with only few fines. Very fast settling.

1 5 Clear supernatant without fines.

17 {Slow settling.

Turbid supernatant;

{Very fast settling.

Hazy supernatant. Very fast settling. Clear supernatant with many fines. Very fast settling. 17 Very clear supernataut with only few fines. Extremely large floor Very fast settlingn Very clear supernatant without fines.

Extremely large floc.

Very fast settling.

2. 5 17 Very clear supernatant without fines.

Extremely large floc. Very fast settling. 5. O 17 Very clear supernet-ant without fines.

lglgiarnples 5-9 used an aerylamidebase danionlc flooculating agent available eommerioally as Separan b P.p.m. dry weight basis by weight of total slurry treated, added as a 0.01% aqueous solution.

Further details appear in Table 3 hereinafter.

filtrate from this mud contains dissolved sugar (sweet TABLE 3.-CANE SUGAR, SETTLING (DURING CLARIFICATION) [Efiect of various flocculating agents on settling rate of suspended solids impurities in cane sugar aqueous slurries] Example 18 used an aerylamide-based anionic flocculating agent available commercially as Naleo D-1941. Example 19 used an acrylamide-based anionic flocculating agent avail able commercially as Separan AP-.

b P.p.m. dry weight basis by weight of total slurry treated, added as a 0.01% aqueous solution.

EXAMPLES 27-32 Beet sugarsettling (during clarification) quantitative These examples were carried out to determine the effect of various polymeric fiocculating agents on the settling rate of suspended solids impurities in beet sugar aqueous slurries.

l-liter portions of beet sugar juice slurry (efiluent after completion of the liming-carbonation steps) were water) and is recirculated to the process and the filter cake is discarded.

250-ml. portions of cane sugar mud were placed in each of several 500-ml. graduated cylinders. Flocculating agent was mixed with each portion by adding flocculating agent thereto and inverting the cylinders 5 times. The resulting mixtures were allowed to stand 2 minutes and the settling rate of the suspended solids impurities determined.

TABLE 5.CANE SUGAR, sETILlNglggUD TO BE FILTERED) QUANTITA [Eflcct of various flocculating agents on settling rate of suspended solids impurities in cane sugar mud] Flocculating Agent Ml. supernatant after standing 2 minutes None B Examples 34-37 used an acrylamide-based anionic fioceulating agent available commercially as Separan AP-BO.

b P.p.m. dry weight basis by weight of total dry solids in mud treated, added as a 0.1%

aqueous solution.

placed in each of several l-liter graduated cylinders. Flocculating agent was mixed with each portion by adding the flocculating agent thereto and pouring 5 times back and forth from filled to empty graduated cylinders. The resulting mixtures were allowed to stand 1 minute and the settling rate of the suspended solids impurities was determined.

Further details appear in Table 4 hereinafter.

EXAMPLES 41-48 Beet sugar-settling (mud to be filtered) quantitative These examples were carried out to determine the effect of various polymeric flocculating agents on the settling rate of suspended solids impurities in beet sugar mud (wet solids settled from the settling, i.e. clarification,

step). This mud is very wet (very concentrated slurry) TABLE 4.BEET SUGAR, SETTLING (DURING CLARIFICATION) QUANTITATIVE [Effect of various flocculating agents on settling rate of suspended solids impurities in beet sugar aqueous slurries Floceulating Agent Ml. supernatant Example RSV after standing No. Name Amount b 1 minute 27 None 1 Comimercial flocculating agent No. 1.... 138

o. 50% acrylamide, 50% sodium acrylate 126 do... 132 "do".-. l 189 1 Examples 28 and 29 used an aerylamide-based anoinic flocculating agent available commercially as Separan AP-SO."

b P.p.m. dry weight basis by weight of total slurry treated, added as a 0.01% aqueous solution.

EXAMPLES 33-40 Cane sugar-settling (mud to be filtered) quantitative These examples were carried out to determine the effect of various polymeric flocculating agents on the settling rate of suspended solids impurities in cane sugar mud (wet solids settled from the settling, i.e. clarification, step). This mud is very wet (very concentrated slurry) and is vacuum filtered. As mentioned hereinbefore the filtrate from this mud contains dissolved sugar (sweet water) and is recirculated to the process and the filter cake is discarded either before or after recovering the lime therefrom.

ZSO-ml. portions of beet sugar mud were placed in each of several SOD-ml. graduated cylinders. Flocculating agent was mixed with each portion by adding fiocculating agent and is vacuum filtered. As mentioned hereinbefore the thereto and inverting the cylinders 5 times. The resulting mixtures were allowed to stand 1 minute and the settling was mixed with each portion by adding flocculating agent rate of the suspended solids impurities determined. thereto and inverting the slurries 5 times. The resulting Further details appear in Table 6 hereinafter. slurries were poured into Buchner funnels lined with No.

TABLE 6.-BEET SUGAR, SETTLING (MUD TO BE FILTE RED) QUANTITATIVE [Efieet of various fioeculating agents on settling rate oi suspended solids in purities in beet sugar mud] Floeeulating Agent Ml. supernatant Example RSV after standing No. Name B Amount b 1 minute 41 None None 42 Commercial fluocculating Agent N0. 1 205 43 do 210 44 90% daerylamide, sodium aerylate... 2 46 70% acrylamide, sodium aerylate. 0"--. 48 acrylarnide, 50% sodium acrylate 355 11 Examples 42 and 43 used an acrylamide-based anionic ilocculating agent available commercially as SeparanAP-ZiO. v

b P.p.m. dry weight basis by weight of total dry solids in mud treated, added as a 0.1% aqueous solution.

EXAMPLES 49-53 20 4 Whatman filter paper. A 22-inch mercury vacuum was applied to the funnels and the filtrates collected in 250- ml. graduated cylinders. These examples were carried out to determine the Further details appear in Table 8 hereinafter.

TABLE 8.BEET SUGAR, FILTRATION (MUD) QUANTITATIVE [Etleet of various fiooculating agents on filtration rate of suspended solid impurities in beet sugar mud] Cane sugarfiltration (mud) quantitative Flocculating Agent Ml. filtrate Example No. Name a Amount b RSV minutes n Examples -58 used an aerylamide-based anionic floceulating agent available commerclally as Separan AP-30.

b P.p.m. dry weight basis by Weight of total dry solids in mud treated, added as a 0.1% aqueous solution.

effect of various flocculating agents on the filtration rate From the foregoing examples it will be readily apparent of suspended solids impurities in cane sugar mud aqueous 45 that the particular copolymer flocculating agent of the slurries. present invention, as compared with typical flocculant ZSO-ml. portions of cane sugar mud were placed in agents of the prior art, gives substantially better performeach of several SOO-ml. graduated cylinders. Flocculating ance (even at lower concentrations) from the standpoint agent was mixed with each portion by adding flocculatof flocculation, settling, and filtration. The amount of the ing agent thereto and inverting the cylinders 5 times. The 50 particular copolymer flocculating agent applicable in the resulting slurries were poured into Buchner funnels lined present invention is not critical and may vary considerawith No. 4 Whatman filter paper. A 22-inch mercury bly. In the settling (clarification) step the amount of covacuum was applied to the funnels and the filtrates colpolymer fiocculating agent of the present invention usually lected in 250-ml. graduated cylinders. will be about 0.01%5%, preferably 0.05%-2.5%, dry

Further details appear in Table 7 hereinafter. weight basis by weight of the total aqueous sugar slurry TABLE 7.CANE SUGAR, FILTRATION (MUD) QUANTITATIVE [Effect oi various fiocculating agents on filtration rate oi suspended solids impurltles m cane 1\ Examples 50 and 51 used an aerylamlde-based anionic floeculating agent available commercially as Beparan AP-30.

b P.p.m. dry weight basis by weight of total dry solids in mud treated, added as a 0.1%

aqueous solution.

EXAMPLES 54-68 irheated. The amount of copolymer flocculating agent of e present invention in the filtration step usually will be Beet Sugar filtram'n (mud) quantltfmve about 0.05%100%, preferably about 0.1%40%, dry These examples were carried out to determine the effect weight basis by weight of the dry solids in the aqueous of various flocculating agents on the filtration rate of sugar slurry treated. Those skilled in the art to which the suspended solids impurities in beet sugar mud. present invention relates will appreciate that aqueous 250-ml. portions of beet sugar mud were placed in each sugar slurries and muds vary considerably and that the of several SOO-ml. graduated cylinders. Flocculating agent amount of any given flocculating agent employed will vary accordingly. The foregoing examples were carried out on the same aqueous sugar slurries and muds.

The copolymer flocculating agents of the present invention consist of acrylamide and alkali metal or ammonium acrylate. The preferred acrylate is sodium acrylate. These copolymers consist by weight thereof essentially of 95 25% acrylamide and %75% acrylate, preferably 90%- 50% acrylamide and %50%acrylate. The weight percentage compositions given herein and in the claims are calculated on sodium acrylate, and it will be obvious that these will vary somewhat (and to what extent they will vary) when other acrylates (e.g. potassium acrylate) are used in place of sodium acrylate.

Preparation of the particular copolymer employed in the present invention is not claimed herein nor is it per se a part of present invention. However, the preparation of said copolymer is quite important. In fact, applicants know of only one process which will produce a product having the properties of the particular copolymer applicaable in the present invention. For the sake of completeness this process will now be disclosed. It may be referred to as precipitation polymerization.

This precipitation process broadly comprises polymerizing a solution of acrylamide and acrylate monomers in aqueous tertiary butanol, aqueous acetone or aqueous tertiary butanolacetone in the substantial absence of air while agitating the solution to give a copolymer product that can be isolated by filtration, the aqueous tertiary butanol and aqueous acetone being solvents for the monomers but non-solvents for the copolymeric product.

Several of the conditions of this precipitation polymerization process are critical, and these conditions will now be discussed.

The solvent for the monomers must be aqueous tertiary butanol, aqueous acetone or aqueous tertiary butanol-acetone (i.e. mixtures of water with tertiary butanol or acetone alone or with both). The concentrations of water in said mixtures must be 30%65%, preferably 45 %-60%, by weight of said mixtures.

The polymerization reaction temperature must be 0 C.-60 C., preferably 0 C.-40 C.

The polymerization may be carried out either in the presence of absence of a polymerization catalyst (initiator), but preferably a polymerization initiator will be used. Both the types and amounts of free radical initiator applicable are well known in this art. Peroxygen compounds are quite suitable, including e.g. ammonium persulate, potassium persulfate and hydrogen peroxide. Other free radical initiators include e.g. a,a'-azo-bis-isobutyronitrile. The peroxygen initiators may be used alone or in combination with activators (also well known in this art) including e.g. sodium bisulfite, sodium thiosulfate, tetramethylethylenediamine, thiourea and ferrous chloride, said combination forming a redox system. The amount of initiator usually will not exceed 0.5%, preferably is 0.05%- 0.2%, 0.05% being specifically preferred, by weight of the combined weight of monomers.

Although not necessary, preferably the precipitation polymerization is carried out in the presence of a salt dissolved in the polymerization reaction mixture. By polymerizing in the presence of a salt, or a bufier system comprising one or more salts in combination with another material to complete the buffer system, recovery of the copolymer product is substantially facilitated. These salts and buffer systems include, e.g., (l) alkali metal and; ammonium acetates, carbonates, bicarbonates, chlorides, phosphates, sulfates, bisulfates, borates; (2) buffer systems comprising (a) mixtures of weak acid or weak base and their salts including (b) phthalates, citrates, borates, phosphates, acetates, ammonium hydroxide, ammonium acetate; ammonium chloride, (c) specific combinations including mixtures of boric acid-borax, citric acid-sodium acid phosphate, sodium carbonate-sodium bicarbonate, ammonium chloride-ammonium hydroxide, ammonium acetate-ammonium hydroxide; or (3) any combination of (1) and (2).

The amount of salt which may be used is about 0.1%- 2.0%, preferably about 0.2%-0.7%, by weight of the reaction mixture. If the amount of salt exceeds about 2.0%, usually there is a tendency for the granules of the polymeric product to agglomerate in the polymerization reaction mixture. The manner of adding the salt and the point at which it is added are not critical.

The following is a specific example wherein the precipitation process was used in preparing the particular copolymer applicable in the present invention.

To a glass reactor fitted with a stirrer and reflux condenser cooled with ice water were charged 26.6 parts of sodium hydroxide and 210 parts of water. After dissolving and cooling, 47.9 parts of acrylic acid was added gradually with cooling to maintain the temperature below 20 C. The pH of this solution was 6.4. Then 62.5 parts of acrylamide, 222 parts of tertiary butanol, and 0.425 part of 30% hydrogen peroxide were added. The atrnosphere and dissolved air were replaced with nitrogen by a series of evacuations and repressurizations with nitrogen. The temperature was raised to 25 C. and the vacuum adjusted to maintain reflux at that temperature. Then 25 parts of a 2.28% solution of thiourea in 1:1 water:tertiary butanol was pumped in at a uniform rate during 2.9 hours. During this time the copolymer formed and precipitated. After 3 hours the slurry was diluted first with 200 parts of tertiary butanol and then 200 parts of acetone. After filtering off the liquid, the copolymer was washed with acetone and then dried at 50 C. in a vacuum oven. There was obtained 115 parts of copolymer containing 94.5% solids. The RSV of the copolymer was 73. The copolymer contained 50 weight percent acrylamide and 50 weight percent acrylate.

The copolymer flocculating agents of the present invention have surprisingly high molecular weights. These were determined, as indicated hereinbefore, by measuring the reduced specific viscosity (RSV-Ubbelohde) of a 0.1% solution of the copolymer in 0.1 111. KCl at 25 C. The RSV varies directly with the amount of acrylate in the copolymer. The copolymers disclosed and claimed herein have an RSV of about 8-110, preferably about 17-80. Stated in another way, the following copolymers, e.g., of the present invention have the following approximate RSV values:

8-28, preferably 14-28, for a 95% acrylamide-5% acrylate copolymer 10-35, preferably 17-35, for a acrylamide-10% acrylate copolymer 30-80, preferably 40-80, for a 50% acrylamide-50% acrylate copolymer 43-110, preferably 54-110, for a 25% acrylamide-75% acrylate copolymer.

Operating within the conditions of the processes disclosed hereinbefore for making the copolymers applicable in the present invention, RSV varies directly with total monomer concentration and inversely with polymerization temperature and amount of initiator.

Although the flocculating agent in accordance with the present invention may be added in dry form to the sugar juice slurry being treated, it is preferred to add it as an aqueous solution in order to get faster and more complete dispersion thereof throughout said slurry.

As many apparent and widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

What we claim and desire to protect by Letters Patent is:

1. Process of purifying an aqueous sugar slurry which comprises contacting said slurry with an acrylamideacrylate copolymer, allowing the resulting slurry to settle, thereby (1) increasing the rate at which suspended solids flocculate and settle out of said slurry, and (2) increasing the amount of suspended solids which flocculate and settle out of said slurry, said copolymer being prepared by copolymerizing the monomers of acrylamide and acrylate at a temperature of about C.60 C. in a mixture of water with a member of the group consisting of (a) tertiary butane], (b) acetone, or (c) mixtures of (a) and (b), the amount of water in said mixture being about 30%-65% by weight thereof.

2. Process of claim 1 wherein said copolymer is acrylamide-alkali metal acrylate and the amount thereof is about 0.0'52.5 p.p.m., dry weight basis by weight of the total sugar slurry treated.

3. Process of claim 1 wherein the copolymer consists by weight thereof essentially of 95%-25% acrylamide and 5%75% sodium acrylate.

4. Process of claim 1 wherein the copolymer consists by weight thereof essentially of 90%50% acrylamide and %50% sodium acrylate.

5. Process of purifying an aqueous sugar slurry which comprises stirring a mixture of said slurry and about 0.015 p.p.m., dry weight basis by weight of the total sugar slurry treated, of an acrylamide-acrylate copolymer, thereby (1) increasing the rate at which suspended solids flocculate and settle out of said slurry, and (2) increasing the amount of suspended solids which flocculate and settle out of said slurry, said copolymer being prepared by copolymerizing the monomers of acrylamide and acrylate at a temperature of about 0 C.60 C. in a mixture of water with a member of the group consisting of (a) tertiary butanol, (b) acetone, or (c) mixtures of (a) and (b), the amount of water in said mixture being about 30%-65% by weight thereof.

6. Process of purifying an aqueous sugar slurry which comprises contacting said slurry with an acrylamideacrylate copolymer, and then dewatering said resulting slurry, said copolymer being prepared by copolymerizing the monomers of acrylamide and acrylate at a temperature of about 0 C.60 C. in a mixture of water with a member of the group consisting of (a) tertiary butanol, (b) acetone, or (c) mixtures of (a) and (b), the amount of water in said mixture being about 30%-65% by weight thereof.

7. Process of purifying an aqueous sugar slurry which comprises stirring a mixture of said slurry and 005-100 p.p.m., dry weight basis by weight of the solids in said slurry, of an acrylamide-acrylate copolymer, and then dewatering said resulting slurry while continuing to stir same, said copolymer being prepared by copolymerizing the monomers of acrylamide and acrylate at a temperature of about 0 (3. 60 C. in a mixture of Water With a member of the group consisting of (a) tertiary butanol, (b) acetone, or (c) mixtures of (a) and (b), the amount of water in said mixture being about 30%65% by weight thereof.

8. Process of claim 7 wherein said copolymer is acrylamide-alkali metal acrylate and the amout, there is about 01-40 p.p.m., dry weight basis by weight of the solids in said slurry.

9. Process of claim 7 wherein the copolymer consists by weight thereof essentially of 95%25% acrylamide and 5 sodium acrylate.

10. Process of claim 7 wherein the coplymer consists by weight thereof essentially of %50% acrylamide and 10%50% sodium acrylate.

11. Process of purifying an aqueous sugar slurry which comprises contacting said slurry with an acrylamideacrylate copolymer allowing the resulting slurry to settle, removing the resulting settled material (mud) from the supernatant thus formed, contacting said mud with an acrylamide-acrylate copolymer, and then dewatering said mud, said copolymer being prepared by copolymerizing the monomers of acrylamide and acrylate at a temperature of about 0 C.-60 C. in a mixture of water with a member of the group consisting of (a) tertiary butanol, (b) acetone, or (c) mixtures of (a) and (b), the amount of water in said mixture being about 30%65% by weight thereof.

References Cited UNITED STATES PATENTS 2,937,143 5/1960 Goren 121--50 3,171,805 3/1965 Suen et al. 2l054 3,276,998 10/ 1966 Green 2l054 3,278,506 10/1966 Chamot et a1. 2l054 3,374,143 3/1968 Stephenson 2l054 2,718,497 9/1955 Oldham et al.

FOREIGN PATENTS 1,095,926 12/1954 France.

OTHER REFERENCES Clarification of Sugar Cane Juice with Polyelectrolytes, A. B. Bonneville, Sugar, November, 1953, pp. 36- 39.

Ionic Properties Foreign Electrolytes, Bourdais, Chem. Abst. 55: 15089 (1961).

Michaels, Aggregation of Suspensions by Polyelectrolytes, 1&EC, vol. 46, No. 7, pp. 14854490 (1954).

MORRIS O. WOLK, Primary Examiner D. G. CONLIN, Assistant Examiner US. Cl. X.R.