The Use of Food-Grode Phosphoric Acid in Processing Sugarbeet Diffusion Juice to Obtain a By-Product Feed Supplement'

Transcription

1 The Use of Food-Grode Phosphoric Acid in Processing Sugarbeet Diffusion Juice to Obtain a By-Product Feed Supplement' S. T. DEXTER, \II. C. FRAKES, C. E. YlrLES, AND J. W. LYONS" Received for publicalion JanualJ The warm diffusion juice from sugarbee~ cossettes is commonly processed by adding about 2% to 2.5% CaO (pli over 12 at 25C) to decompose invert sugars etc. and to remove impurities in the form of insoluble calcium salts. _'\ddition of carbon dioxide to remove excess lime and adsorbed impurities occurs in two stages. ~ost of the impurities are removed after the first carbonation to a ph of ahout A second carbonation of the relatively clear "first carbonation juice" brings the ph to about 9.2 with relatively slight precipitation. Filtration then gives a clear, somewhat amber-colored "clear, or thin" juice, which is ready for evaporation and further processing. The voluminous precipitate of CaC0 3 and organic matter that is discarded in the lime pond approximates 100 pounds of dry matter per ton of beets. The availability of low cost, high purity, food-grade phosphoric acid, made via the electric furnace, has led to ~xpanded use throughoul the food industry and increased production of dicalcium phosphate for use as a feed supplement. In the processing o[ sugar beets, it seemed of interest to attempt to replace the massive amounts of lime and carbonic acid with adequate quantities of lime and phosphoric acid, since the reaction product would have a commercial m~rket. The present paper describes experiments to determine the minimum amounts o[ lime and acid needed to produce a clarified juice equal in purity to that presently produced by the factory, and to find out the quantity and composition of tbe resultant " mud" in terms of its value as a feed supplement. Rate of filtration etc. after different treatments was determined. Literature Review Sugar textbooks (5, 6) ', patent literature and journal papers describe the infinite variations, difhculties and complications of 1 Journal article 4272 Mich. Agl'. Ex p. Sta.. East Lansing, Michigan. 2 Professor of Crop Science, ivri chigan Sta te Lniv., East Lansi ng.. Director Agr. R esea rch, MiChigan Sugar Co., Saginaw. and Senio r Research Chemist and Research Section Manager. Monsa nto Co., St. Louis, Mo., respectivel y.

2 168 JOURNAL OF TIlE A. S. S. B. T. the purification process, together with proposals for improvement. Among these reports are many that involve the addition of phosphates or phosphoric acid to remove calcium and other impurities. A patent search has shown at least eight reports since 1924 of patented methods by means of which phosphates have heen claimed to give improved clarification, color, etc. (7). For the most part, cane and fruil juices have been involved, with primary emphasis on the means of facilitating removal of the precipitate. Journal articles, as Frankenhoff (3) and Cummings (2), are in agreement that "the use of calcium phosphate as a defecant in the refining of sugars is an old practice," which was rather generally discarded when pressure filters were introduced. "Calcium phosphate plugs the pores and openings in the diatomaceous filter cake" and leads to slow filtration. It still has the advantage that its use promotes the production of a very clear juice, and it can be used in relatively minute amounts to assist in removing colloidal material by flotation, filtering- or settling. The Carruthers-Oldfield (1) method of using phosphoric acid with massive amounts of lime to produce clear juice for purity determinations has shown clearly that this method will remove impurities from expressed juice fully as well as by carbonation of limed diffusion juice, and will produce a clear juice of good color by ordinary lahoratory filtration. Materials and Methods Factory personnel took hourly samples of diffusion juice and thin juice during one shift each day throughout the campaigns of and These samples were frozen. At the end of the season they were thawed and composited, by weeks. These weekly composited samples, about 15 each year, were used in the individual experiments described. Using standard precision instruments, analyses for purity, lime salts, alpha amino nitrogen, potassium and sodium were made on juice purified with" phosphate in the laboratory in comparison with that purified with carbonate in the factory. Rates of filtering, settling, etc. were determined with ordinary filter paper, graduated cylinders, etc. with no attempt to accurately simulate factory conditions. Experimental Results The 15 composited diffusion juices, for each year, were individually purified with CaO-H3PO, in the laboratory and compared with those purified with CaO-C0 2 in the factory. Table 1 summarizes the data for the two seasons. Lime salts were determined by the company chemist. During the campaign, treatment of the diffusion juice :) Numbers in parentheses refer to literature cired.

3 VOl. 15, No.2, JULY by Ca0 3 PO. consistently gave a higher purity than that processed by the factory (CaO-C0 2 ). In either year, when correction was Table I.-The 15-week averages of analyses of juice aher purification with CaO H"PO. (laboratory) versus CaO C02 ([actory), during the and calnpaigns CaO H,PO. CaO CO, CaO.a,po, CaO CO, Clear juice purity % 'i'] 9293 Mg. amino Ni loo g sucros~ 'I 2 1 ~ 201.v, g. Potass i L1m/ 100 g sucrose ~ [ Mg. Sodium/ JOO g sucrose J20 464' I~O 2 1 : ~.. Lime salts,% O.O~ {S Sodium addeu by factory. made for the sodium carbonate added to the juice in the factory, the juices were almost identical. 1\0 significant difference was found in the content of potassium or amino nitrogen in the juices processed WiLh CaO-H3PO, and CaO-C0 2 Although sodium carbonate was added to factory purified juices for the purpose (among others) of reducing the soluble calcium salts, the "lime salts" content of the factory juice was regularly about double that of the phosphated juice to which no soda was added. Obviously the additional sodium reduces purity and is avoided when adequate purification can be attained without it. Jvr inimum amount of lime to jjroduce a satisfactory clear Juice In about 60 separate trials, factory diffusion juices " 'ere brought to various ph values with lime or phosphoric acid, heated at various temperatures and filtered. Fase and clarity of filtration and color of filtered juice were noted. In the resultant clear juices, purity and content of sodium, potassium and amino nitrogen per 100g sugar were determined. Initial liming to a minimum of ph 11.8 (2 5C) was necessary to produce a juice as good as the factory juice. After adjusting the ph to 11.2 (25C) with acid, optimum purities were obtained by bringing the juice to a temperature of about 70C (during 8 minutes oe heating) before filtration. After the first filtration, the addition of acid to ph 9.2 (25C) to juice of about 60C seemed to give' optimum clarity but no improvement of purity over somewhat lower temperatures. The minimum amount of lime required to bring 2400 pounds of diffusion juice (equivalent to about 1 ton oe beets) to pit 11.8 was determined to be approximately 8.8 pounds of CaO. To bring this juice to ph 11.2 required about 5.5 pounds oe 85% phosphoric acid. Obviously, the more lime is added, the more acid must be used to accomplish this. After the first filtra

4 170 JOURNAL OF THE A. S. S. B. T. tion, about 10% additional acid was required to reach ph 9.2, or a total acid requirement of about 6 pounds per ton of beets. Following the second addition of acid, the precipitate was light and cloudy and was not saved for weighing. A mount of jjrec pi ta Le formed in the fi rs t phosj)hatation mud T he "mud" from I :\.6 pounds of diffusion juice, treated with minimum lime as indicated above, was collected, oven dried, and found to weigh slightly over 20 pounds per ton of beets, va rying somewhat wi th different juices. Since the phosphate is precipitated as (approximately) Ca,o (O H )z (PO.,),; (hydroxyapatite), (Ca/ P 2. 13) under these conditions, {4) the acid used could precipitate a maximum of 8 pounds of apatite in the first phosphatation mud, per ton of beets. The rest of the precipitate would be mainly in the form of organic matter, and calci um sa lts of acids, removed in increasing the purity from that of diffusion juice to that of clear juice. A nalyses of the m ud Analyses by two independent la boratories gave the following figures (Table 2) on a dry matter basis of two lots of mud. From the analyses, it would appear that a little less than one- half the dry matter in the first phosphatation mud was organic matter, '",ith a protein (KjeJdahl N X 6.2 5) content of about 20%. Since all of this organic matter was in solution or colloi dal suspension, one would expect its digestibility to approach 1009(. The proportion of calcium to phosphorus (about 2: 1) indicates that considerably more phosphoric acid would need to be added to the mud to make the mud equal to the commercial dicalcium phosphate in ca lcium phosphorus ratio (Ca / P = 1. 3: I ). C"iee discussio n ). Table 2.-Analyses of Mud Precipitated with CaO and a,po., H C:: mmcc'cial dicalcium phcsphate PhosphOI'LlS 5.7 % 5.8 % 19% Protein 9.28% 9.22% ::\'one Calci um 10.9 % 22-23% As h 53.79% j\lfoist ure 3.88% Stability of phosjjhated clear juice during evajjoration The quality of the factory diffusion juice was such that about 1.6 pounds of sodium ca rbonate vvas added per ton of juice the first year, on the average, and less than half this amount the second year in order to get proper de~ecation, lower lime salts, etc. T o give some indication of the stability of thin juice prepared

5 VOL. 15, No.2, JULY 19fi8 171 with CaO-H3P04' but without sodium carbonate, it was evaporated by heating under the vacuum of a water-aspirator to 65% solids. A drop in ph from 9. 2 to 9.0 indicated a rather stable juice, without the addition of sodium carbonate. Filtration of untreated first-phosj)hatation juice Beca use enormous amounts of processed juice must be filtered per minute in a sugarbeet factory, ease of filtration or other means of separation of insoluble solids is a primary necessity for operation. In the laboratory, we tried the ordinary practices used to get larg er crystals or floccs as by "seeding", avoiding high degree of supersaturation, recirculation of crystals already formed, etc. In no case did we get substantial improvement in flltration rate. Use of extra CaO, in general, decreased filtration rate, both in Michigan and :Monsanto experiments, but sometimes improved purity slightly. Us e of flocwlants in the separation of mud by filtration, settling or centrifuging The use of several flocculants (Separan AP-30, Kelco Gel LV, Polyhall 295)1 in various concentrations produced pronounced improvement in the rates of filtration, settling or separation by centrifuging. Addition of the flocculant in low concentrations was more effective than addition in high concentration. T able 3 gives an idea of the effect of one of the flocculants used. _\ddition of flocculant to carbonated juice did not improve filtration or settling rate. Vacuum or pressure filtration of CaO-H3PO. treated juices was more difficult than gravity filtration, primarily due to the small particle size and the compressible nature of the solids relative to the CaO-C0 2 precipitate. About twice as much flocculant was required to achieve clarity and rapidity of filtration in vacuum or pressure filtration as in gravity filtration. Rate of settling was enormously accelerated in laboratory tests by use of flocculants. Still lower levels of flocculants ( pounds per ton of juice) appeared to be satisfactory if the solids were removed by centrifuging. This may be the easiest, and, in the long run, the cheapest way to remove waste solids from this juice. No effort was made to approximate closely the practices that could be used in a factory, or to conduct an exhaustive survey of the efficacy of possible acceptable flocculants, either alone or in combination, or to estimate their effects on sugar quality or the acceptability of the mud as a feed supplement. However, Polyhall 295 is approved by the Food and Drug Administration for use in sugarbeet juice purifications. It seemed likely that Dow Chem. Co., Midland, Michigan, Kelco Co., Clark, New Jersey, and Stein Hall & Co., New York, New York respectively.

6 ...:) "" Table 3.---Comparative l'ates of gravity and pre"...re fuu'ation of CaO-C02 and CaO H;;PO, treated ben juices, with various amounts ami W,IS of flocculant (Polyhall 295) added. Filtration Cone. of 1'lo(culam Treating Level Time, 20 cc Rate" Flocculant PolyhaU 295 Ibs. a(th~(~7i{)n- Gravity nlmulativc yolume Ion solution~ C( 100 juice min. 20('«:75«:t~ o 0 0 2:00-4: :30 ditto ,0\ 4:15 ditto :35 ditto ;) l:ot) CaO-CO, 0 0 CaO-H,PO, 0.02 dilto Filler arca 9.6 em', -'!o. 1 filler paper Report :"\0, G921 "L.-.c of Phosphoric Acid in Rc:i'inlog oi Reet Sugar", ilnd o "I,\fon'ianto Comp"IOY, SL LOllis, :\10. >-l :r: t'l > v; :n ~ ~

7 VOL. 15, No.2, JULY lhe acceptability or the complications in industrial application could not be accurately inferred from small scale laboratory trials, no matter how comprehensive. vvhether separation was by gravity filtration, suction or pressure filtration, settling or centrifuging, an expense of from $0.01 to $0.05 for flocculant per ton of beets appeared likely to solve the problem of large scale separation of the precipitate from the juice. Discussion In the context of these trials, some discussion of the probable cost of materials, and value and uses of the pr0duct seems pertinent. The probable costs of materials seem relatively easy to establish. When the lime and acid were used at the minimum rate of produce a thin juice equal in purity, but superior in color, to the CaO-C0 2 thin juice, a total of about 9 pounds of CaO and 6 pounds of 85% H apo. was needed per ton of beets. This includes all acid used for purification, but not the acid required to convert the apatite and lime salts into feed-gtade dicalcium phosphate (CaHPO,. 2H"O). With CaO at about 1.4 and acid at 6.5 per pound, this would amount to about 52 per ton of beets. An additional cost for flocculant of about 3 per ton of beets would bring the processing cost to about 55 for materials. The 6 pounds of 85% acid would precipitate about 22 pounds of total dry matter in the mud from a ton of beets, including the precipitate from the second addition of acid. Of this, about 9 pounds would be organic matter containing about 20% protein, 9 pounds would be hydroxyapatite and about 4 pounds would be CaO combined with weak organic acids. If the phosphorus and calcium from the beet roots were not considered, the rate of calcium to phosphorus would be about 4: 1, on the basis of the purchased calcium oxide and phosphorit: acid that was used. This ratio is somewhat high for most nutritional purposes. (Commercial "dical" has a Ca/ P ratio of about 1.3 to 1.) Analyses of the mud, with a Ca/ P ratio of about 2: 1 shown in Table 2, indicate that the contributions from the roots may be of significant economic value. Although it would be expected that this contribution would vary widely in different regions, analyses of beets, pulp, molasses and mud indicate that the phosphorus recovered from a ton of beets (about 0.8 lb.) would have a value of about $0.20, if sold as dical. If the analys es shown in Table 2 are representative of the Ca/ P ratios to be generally expected, no further addition of acid would be required to make the mud marketable for many nutritional purposes.

8 174 JOURNAL OF THE A. S. S. B. T. Nutritionists tell us that in many regions, where corn silage and urea are replacing legume hays (high in calcium) a Ca:P ratio in the supplement of 2 to 3: I might be more generally acceptable for cattle than the 1.3: 1 ratio in dical. As a supplement for hogs, where the ratio is high in grain, and thus in phosphorus, a still higher ratio of calcium might be advantageous. In Michigan, for example, in feeding swine on a standard comsoybean meal ration, ground limestone as well as dical is needed in the supplement, on a weight basis, to obtain the optimum Ca:P ratio of 3.6: 1. If such a product could be furnished swine feeders at a competitive price, they would rather handle one material than two. In such a case, payment for the phosphorus content only would not be realistic, since the calcium also must be purchased. Thus, it might not be desirable to add sufficient acid to convert all the CaO to the dical ratio of calcium to phosphorus. If this were done, ho\\'ever, and there were no contribution of phosphorus or calcium from the beets, an additional 12 pounds of 85 % acid would be needed. This would be in the form of a cheaper "feed grade" acid. The total of 9 pounds of CaO and 18 pounds of acid would produce about 28 pounds of feed-grade dicalcium phosphate (Ca/P 1.3: 1) mixed with about 9 pounds of organic matter with approximately 20% protein content. Each of these ingredients should be valued at going prices, - about $90 per ton for dical, and $60 for the protein supplement. The commercial value of feed-grade clical is roughly equivalent to that of the lime and acid used. In any case, any desired ratio of calcium to phosphorus could be provided at varying prices, regardless of whether the lime and phosphate are purchased as such, or come partly from the beets. The operation at the sugar factory level might stop,,,ith the separation of the traditional,vet mud, which could he sold to and processed further by a concern interested in the feed supplement. Although prices have been proposed, this seems a matter for inter-company bargaining. From the standpoint of the beet sugar company, the operation of the lime kiln might be eliminated and the traditionally offensive lime pond rendered obsolete. The greatly reduced quantity of mud-perhaps one fifth- would be expected to affect [titration practices considerably and to lower the loss of sucrose in the mud. All lime and acid purchased (as well as phosphorus from the beets) ' could be sold as a feed supplement. The organic matter removed- about 0.5 % on beets- would contain about 20% protein and its value might pay the processing costs of the mud. A thin juice equal to or better than CaO-C0 2 juice

9 VOL. I:>, No. ~, JULY ly in lime salts, purity, color and sllbility on boiling should be produced, possibly without the necessity of adding soda ash. Use of phosphoric acid, without the necessity of bubbling 'with carbon dioxide containing free oxygen, should reduce the alkaline oxidation of sucrose (6). The literature generally reports less trouble with evaporator scaling when phosphate is used (6). The lower color and the lack of bicarbonates should favorably affect the sulphitation process- or even eliminate it-and the use of a strong acid should reduce the problem of high viscosity due to potassium carbonate (6). Since we are not dealing 1.llith a volatile acid, - C0 2, and the alkalinity of the juice might be more stable on evaporation, the ph after completion of the second filtration might be reduced somewhat to reduce sucrose and amide hydrolysis due to - OH ions (5). In general, one might expect that the use of a non-volatile and highly heat-stable acid would enable a precision to be reached in processing diffusion juice that is difficult or impossible to attain with carbonic acid. The yearly production of by-product from a factory processing about 200,000 tons of beets per year would approximate 3000 tons of dicalcium phosphate and 1000 tons of 20% protein supplement. Summary Slightly less than 0.5% CaO, on beets was sufficient to bring factory diffusion juice to ph 11.8 (25C) which was the minimum alkalinity required to produce a clarified juice as good or better than factory " thin" juice..'\bout 0.3% of 85% H ~ P0 4 ' on beets, was needed to bring the limed juice to ph 11.2 (25C), (heat and filtration) and to a final ph 9.2. Purity of the juice thus treated, \'as essentially identical 'with that of factory thin juice, with sodium, potassium and amino nitrogen almost the same when adjustment for added soda ash was made. Lime salts were about half as high in laboratory phosphated juice (without soda) as in the factory carbonated thin juice, to 'which soda ash had been added. Flocculants were required at the rate of about pounds per ton to promote filtration or settling at a rate as rapid as that found with carbonated juice, with or without ftocculant. \;\/ith the quantities of chemicals specified above, slightly over 1% of dry matter on beets was precipitated. This dry matter contained over 40 % organic matter, with a protein content of about 20%. The precipitate had a calcium/ phosphorus ratio of about 2: 1. The addition of about 12 pounds of additional acid (assuming no phosphorus from the beets) would bring the calcium/ phosphorus ratio up to about 1.3: I, which is the ratio in commercial dicalcium phosphate feed supplement.

10 176 JOURNAL OF THE A. S. S. B. T. It is proposed that all of the lime and phosphoric acid purchased can be sold. The additional high protein supplement that is mixed with it should also have a considerable market value. The phosphorus from the beets, commonly discarded in the lime pond, would have a substantial value when recovered and sold as a feed supplement. Literature Cited (I) CARRUTHERS, A. and J. F. T. OLDFIELD Methods for the assessment of beet quality. The technological value of the sugar beet. Elsevier Publishing Co., New York. (2) CUMMINGS, A. B Calcium phosphate in the filtration of sugar liquors. Ind. and Eng. Chem. 34: (3) FRANKEN HOFF, C. A Pressure filtration of phosphoric acid and lime-defecated refinery and whole raw sugar liquors. Ind. and Eng. Chem. 34: (4) LYONS, J. W. and C. O. SJEBENTHAL On the binding of co n densed phosphates by proteins. Biochem. Biophys. Acta 120: (5) MCGINNIS, R. A Beet sugar technology. Reinhold Publishing Co., New York. (6) SILIN, P. M T echnology of beet-sugar production and refining. Translated from the Russian by Israel Translations, J erusalem. U. S. Dept. of Commerce, Washington, D.C. (7) Somewhat pertinent patents: U. S. Pat. 1,486,091; 1,653,491; 2,408,418; 2,416,683; 2,421,376; 2,470,332; 2,964,428.