US2067362A

US2067362A - Purification of sugar juices

Info

Publication number: US2067362A
Application number: US725894A
Authority: US
Inventors: Stietz George E G Von
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1934-05-16
Filing date: 1934-05-16
Publication date: 1937-01-12
Anticipated expiration: 1954-01-12

Description

G. E. G. voN sTlETz PURIFICATION OF SUGAR JUICES Filed May 16, 1934 l. niv a.J ou T S51 Ewa@ @Eg I@ SM2, nous@ si l,5 -U I@ Re orive Time Fodor 514 hi Mmmm? atented jan. L l2, 1937 lili* CATION OF SUGAR JUECES Application May 16, 1934, Serial No. 725,894

11 Claims. (01.*127-48) This invention relates to the manufacture of sugar, and particularly toimprovements in the carbonation process for purifying Juices and syrups.

The disadvantages of the universally used carbonation processes have long been recognized.

These include the use of excessive quantities of lime; the necessity for'high juice temperatures to avoid ltration difliculties; the addition of sodium compounds which increase the losses of sugar as molasses; and inemciency of purification, particularly as regards removal of colloidal material and residual calcium.

Many variations on the usual procedure such as the step-wise addition of the lime and the fractional removal of impurities under diierent conditions of alkalinity, as well as the use of supplementary reagents, including ammonia and its salts, have been suggested as improvements. In

spite of these disclosures, a commercially feasible process which permits full realization of the benents to be derived from such procedures has not heretofore been developed. This was inevitable because the optimum conditions of operation,

Particularly control of hydrogen ion concentration and temperature, had not previously been discovered.

In the following description of my invention and of a preferred method of carrying it out, particular reference is made to the manufacture of beet sugar although the principles involved are equally applicable to kindred arts, such as cane sugar manufacture, by proper adjustment of the conditions to meet the well known differences in character of the juices involved.

Sugar renners have recognized the fact that the degree of clarication is related, inversely, to the amount of residual calcium salts left in the juice, provided the nal calcium oxide elimination takes place at the optimum point pH 8.4 or

hydrogen ion concentration of 2.5x10-9.

In present processes alkali'metal compounds, e. g. soda aga, are used to reduce the nal calcium content of the juice, but the undesirability of the practice is universally admitted. Asit is impossible to remove these compounds in `later operations they increase the molasses losses. The use of ammonia has been suggested in this connection becauseit is'capable of subsequent removal.

, But it has not been applied successfully commercially .because of failure to properly control the hydrogen ion concentration and temperature oftion is insuflicient to bring about a pronounced reduction in dissolved calcium. It is not only necessary to assure a certain definite ammonia alkalinity, but it is also necessary to have in the solution suilcient suitable acid ions such as SO3= or preferably carbonate ions obtained by carbonation to force the precipitation of the' residual calcium.

The ammonia used may advantageously be made the carrier of useful acid radicals which 10 form precipitates with lime possessing high sorptive capacity. Under these conditions the ammonium salt is introduced as the first step in the clariflcation, although further amounts may be added at later stages. In general the best results 15 are obtained by introducing the ammonium salt before the addition of lime. By the mixing of the two reagents in solution a more rapid precipitation results than is possible in the standard methods now in use. 'I'he precipitate formed is 20 more finely divided and a more effective 'sorptive agent. The sulilte has been found exceptionally effective but the carbonate, oxalate, phosphates, tartrate, or other such salts may also be used.

For economic commercial application of this 25 invention a relatively low temperature procedure of carbonation is to be preferred because of the ammonia losses which accompany any evaporation of the juice. By operating at relatively lower temperatures substantial heat economies are 30 also possible. A further advantage to be derived from cold operation, is a marked improvement in the sorption of colloidal material by the precipitates formed. Carbonation at temperatures below 85 C. has never previously been practicable 35 because of the poor flltrability of the precipitates obtained. My procedure of control of hydrogen ion concentration, however, permits these operations to be carriedout at much lower temperatures than 85 C. I can successfully operateat 40 temperatures as low as to 65 C.

This is made possible by the discovery of the possibility of arrivingat a zone of clarication and rapid settling in the hydrogen ion concentration range of 3x109to 10-10 or pH range of 45 8.5 to 10.0 by carbonating the limed sugar juice beyond the first zone of good settling; which usually occurs at about the hydrogen ion concentration 5 1011 to 2x10-12 (pH 10.7 to 11.2). In this zone of hydrogen ion concentration 3x10-g 50 to 10-10 the juices are of a red-brown color instead of the usual light yellow. They have been termed burnt uices .when inadvertently encountered in the industry and have been studiously avoided from fear of their darker color. I 55 bonation which follows.

however, because it is readily eliminated in the subsequent steps cf my process. f

By first eliminating a part of the impurities in the zone of rapid settling where the pH=8.5 to 10 (hydrogen ion concentration 3X109 to l01) a. relatively small compact mud of comparatively high organic content is obtained. Because of its small amount, this precipitate can be of poor filtrability without reducing factory capacity below that of existing processes, even when the operations are carried out at low temperatures. vThis is in no way possible with any other process which has been suggested, for all involve as an essential feature the removal of the first impurities in a bulky precipitate representing an appreciable proportion of all the muds which have to be filtered.

Due to the fact that most of the disturbing organic substances will have been eliminated by this pre-carbonation treatment, filtration. without settling is practicable after the main car- In this step the impurities are removed at a lower hydrogen ion concentration than in the rst treatment. Again due to the previous removal of colloidal material, a more efficient sorption of that remaining is possible as the operations can be carried out nearer the true iso-electric point of such material as remains.

In the following description of a preferred method of carrying out my invention as applied to beet sugar manufacture, it will be understood that the well known variations in the character of the beets sliced will require corresponding variations in the quantities of reagents used and in the conditions of operation. This applies particularly to the hydrogen ion concentrations Y specified, it being recognized in present practice that the optimum may vary widely as from a hydrogen ion concentration of 6 X 10-11 to 6X 10-12 (or pH 10.8 to 11.8) during the same campaign and even more for differenty campaign years.

According to my invention, raw diffusion juiceat about to 65 C. is treatedwith about 0.1% ammonium sulte (all quantities of reagents will be expressed as percentages of the juice weight) followed by the addition of about 0.4% calcium oxide as milk of lime (or as calcium saccharate when' operating in conjunction with the Steffen process). The resulting mixture, having a hydrogen ion concentration of about 10"11 to 10-12 or a pH value of about 11.0 to 12.0 is brought by carbonation in the usual way to a hydrogen ion concentration of about 3x109 to 3 101 or a. pH of about 8.5 to 9.5, preferably more than a hydrogen ion concentration of 10-9 (pH 9). The resulting precipitate is settled, preferably in the Dorr thickener commonly employed for the rst stage of separation in continuousA methods of operation, and then filtered. The temperature during filtration need not be higher, than 65 C. If desired, small quantities of lime, about 0.01- 0.02%, may be added to the mud toffacilitate filtration. y

To the clear juice from the settling tank (Dorr overflow) about 0.05% (NHDaSOs is added followed by about 0.4% CaO and the mixture carbonated in the usual way to a hydrogen ion concentration of about 3 10n to 10-12' or a` pH of about 10.5 to 12.0, preferably a hydrogen ion concentration between V3 10L2 to 10--12y after ltration without settling, the carbonation of the filtrate is continued to a hydrogen ion concentration of about 10-8 to 2X109 or a pH value of about 8.0 to 8.2. The alkalinity of the juice may unfiltered juice may be heated in the usual open boilers until this hydrogen ion concentration is.

attained as the result of the more rapid evolution of CO2 as compared with NH3. In either case, a time interval at the lower hydrogen ion concentration of at least 10 minutes should be provided to allow an opportunity for the completion of'precipitation before filtration.

The purified juice is then treated by the usual processes for recovery of the sugar.

When the ammonia content of th'e clarified thin juice is below 0.070% where the juice has a hydrogen ion concentration less than 3X 10-9 there is no danger of appreciable corrosion of copper and brass apparatus or fittings. `Where higher hydrogen ion lconcentrations are present even greater amounts of ammonia may be present without causing corrosion difiiculties. It is not desirable, however, to allow the clariiied thin juice to reach a hydrogen ion concentration higher than 10-a as the subsequent elimination of ammonia thezbecomes difficult. It is to be noted that the total amount of ammonium sulte used in the above described illustration of an application of my process, represents only about 0.045% ammonia or far below the amounts which produce corrosion.

By the use of automatic control apparatus of the hydrogen ion concentration of the juices, my invention may be carriedout without permitting the alkalinity of the y.juices to materially exceed. during any one step of the operations, that at which the precipitated impurities are to be removed.

.Both methods of operation are indicated dial grammatically in the drawing, wherein Figure 1 represents a How-sheet of' my process as carried out in batch operation, and Figure 2 a ow-sheet of the operations as carried out by continuous methods with automatic control of the pH value of the juices. s

The relative time factor denoted in these figures is intended merely to show the order of the operations. The widths of the plateaus indicating iiltration, for example, are not, in any sense, measures of the time required for these operations as compared with the other steps in the process.

The order of the various operations is designated by the labels and their effect on the pH value of the juice is indicated by the scale shown. The particular points used in the drawing are only representations of the pH ranges previously defined for the steps to which they refer. In Figure l no definite pH value has been assigned to the juice` after the second addition of ammonium sulfite and lime because this may be varied widely by the use of different amounts of those reagents.

The present invention accordingly provides a practical commercially vavailable process for pur- A ifying sugar juices which obviates the difficulties eration of thejui during clarification in the zone g5 `tion are improved and the difdculties of foaming reduced. v

The introduction of (NH4)2SO3 at the beginning of the clarification produces juices and sugars of greatly improved color. Another important feature of my invention is the presenceA of ammonium sulte at each separation stage up to the evaporation stage.A This results in greatly improved precipitation and in the formation of precipitates of increased sorptive capacity, settling rate and ltrability.

The thorough removal of calcium in the final stage of treatment results in juices which not only form no scale in the evaporators and heaters, but actually have been observed to dissolve'the scale left in the apparatus by juices purified in the usual way. Moreover, this .elimination of calcium results in lower sugar losses because less molasses is produced.

Some of the advantages of my process over the i standard procedure of double carbonation Jand sulfur dioxide saturation are shown by the following results determined during various factory and small scale tests of my method. l

. Standard Improved procedure process Consumption oi CaO as milk oi lime as l percent oi iuice weight 2. 12 l. 64 Consumption oi soda ash as percent oi juice weight 0. l None Consumption ot sulfur as percent oi juice weight 0. 07 Nono Consumption of ammonium sulte as percent ol juice weight.. None 0. 12 Purity oi clarified juice; 90. 9 92. 4 CaO content of clarided juice as grams per f 100 Brix 0.084 0. 010 Color oi clarified juice (pure water as zero) (lproduct oi standard ocedure ns,100) 100 78 Su fur content oi du sugar as suliite parts per 1,000,000 0. 30 2. 33 ,f Color oi final sugar (scale pure water=0). f 11 9 My invention is'capable of many modications. Where it may seem desirable not Ito make changes in equipment already installed .or for other reasons the nrst step described above of removal of impurities in the -range of hydrogen ion concendetail the preferred embodiment of my invention and some variants thereof, it will be understood that this is only for. the purpose` of making the invention more clear and thatthe invention is not to be regarded as limited to the details of operation described, nor is it dependent upon the soundness or accuracy of the theories which I have advanced as to the advantageous results attained. On the other hand, the invention is to be regarded as limited only by the terms of the accompanying claims, in which it is my intention to claim all novelty inherent therein asl broadly as is possible in View of the prior art.

I claim as my, invention:

l. A method of purifying sugar solutions from which the bulk of the precipitable material has beenl removed, comprising carbonating the solution to a hydrogen ion concentration within the` `range 2X 1 0-9 to i0-8 and adding ammonia thereto to reduce the hydrogen ion concentration thereof to a value within the range of 3x10-9 to lil-1 and subsequently removing the resulting precipitate.

l2. A method of purifying sugar solutions prior to evaporation thereof comprising introducing at least one basic agent comprising free ammonia to bring the hydrogen ion concentration of said solution `to a value not greater than about -a while containing an ammonia concentration not greater than 0.07% and then evaporating said solution whereby scale formation in 'the vaporator and corrosion of copper-containing equipment is`substantial1y avoided.

3. A method vofpurifying sugar solutions comprising as the first step the separation of precipitated impurities by carbonating the limed solutin to a hydrogen ,ion concentration between 3X109. and 3 10-1, then liming and carbonatprising valkalinizing the solution then acidifying to a hydrogen ion concentration of about 3x10-V9 to 3X 101 removing the resulting precipitate and subsequently separating further impurities by treatment with alkaline and acid electrolytes to bring the hydrogen ion concentration first within the' range 5 1O-`11 to 10l12 and subsequently within the range 3X109 to 3X10,1. 5. A method of purifying sugar solutions from which the bulk of the precipitable'material has been removed by acidifying the alkaline solution to a hydrogen ion concentration of about 5X 10-11 to l0 12 comprising the adiustment of the hydrogen ion concentration thereof by treatment with Y acid and alkaline electrolytes to a point within the range 10Ta to 2X10-9, then reduction of the hydrogen ion concentration before removal of impurities is effected toa point within the range 3 X 10'*9 t0 3 X 10-10.

6. A method of purifying sugarlsolutio'ns from which the bulk of the precipitable material has been removed by acidifying the alkaline solution to a hydrogen ion concentration of about 5X 10"l1 to 10,l comprising carbonating the solution in the presence of an ammonium salt to a hydrogen ion concentration of about'lOa to 2x10, thenI heating the solution to remove carbon dioxide therefrom and reduce the hydrogen ion concentration to a valueof about 3X109 to 3X101.

7. A method of purifying sugar solutions coinprising as the rst step carbonating the limed so- Alution in the presence of an ammonium salt at a temperature below 85 C. to a hydrogen ion con-. centration of about 3X109 to 3X101 whereat Y precipitable material iscaused to settle out, liming effecting a iinal removal of impurities at a hydrogen ion concentration o f about 3 10-9 to 3 10-10.

8. A method of purifying sugar juices wherein the juice has been treated so as to be strongly alkaline, which comprises carbonating the juice to a hydrogen ion concentration of about 3X 10-9 to 3X 10-10, whereat rapid settling of precipitable material takes place, ltering, strongly alkalinizing the ltrate and carbonating to a hydrogen ion concentration of -about 5 10-11 to 10-12, again removing precipitated material and acidifying and eiecting a third separation of impurities at a hydrogen ion concentration of about 3 109 to 3X101.

9. A method of purifying sugar solutions com-v prising treating the alkaline solution with an acid electrolyte in the presence of an ammonium salt aoezaee prising carbonating alkalinized juice to a hydrogen ion concentration of about 3x10-s to 3X 10-10, removing the material precipitated thereby, alkalinizing and carbonating the partially puried juice to a hydrogen ion concentration of about 5X 10-11 to 1012, removing further precipitated material, carbonating to a hydrogen ion concentration of about 10*8 to 2X 10-9 and subsequently lowering the hydrogen ion concentration to about .3x 10-9 to 3X 10-1o before nal removal of impurities.

11. A method of purifying sugar solutions comprising treating the solution with ammonium suliite and alkaline and acid electrolytes to bring the hydrogen ibnA concentration of the alkaline solution irst to about 3X 10V-9 to 3X 10-10 and then to about 5x 1li-11 to 10-12, removing precipitated impurities in each'of said hydrogen ion concentration ranges, acidifying the resulting solution to a hydrogen ion Y concentration of about 10-8 to 2x10-9 and subsequently lowering the hydrogen ion concentration to about 3X 10-9 to 3X 10-1o before final removal of impurities.

GEORGE E. G. VON STIETZ.