Vol. 34, No. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
864
The coefficients for air are calculated by the writer on the assumption that air consists of 1 mole of oxygen mixed with 3.78 moles of nitrogen. The results from the air equation for c p check the tabulation of Heck (W) as s h o ~ mby Table 11.
multiplying this equation by dT and integrating between these limits. The resulting equation is: AH
+ 2 ~ ( T 2 ”-~
a(T2 - Ti)
where AH 600
0.2408 Heck Combinedequatiqn 0.2390
~
enthalpy change, B. t. u./mole
1000
2000
3000
4000
5000
The mean specific heat, cpn, may be found from this equation by dividing through by (T,- TI) :
0.2488
0.2773 0.2790
0.2930 0.2940
0.3021 0.3018
0.3079 0.3080
~ p m=
TABLE 11. INSTANTANEOUS SPECIFIC HEATOF AIR T ,O R. c p , B . t . u./lb./’ F.
=
+ ylog, TT’I + z (T&$) __
0.2500
Heck’s computations are based on assumed air composition of 1 mole of oxygen to 3.80 moles of nitrogen and argon. The molal specific heat of the argon is taken as constant at 4.962. Despite these differences in assumptions of air composition, there is an agreement in Table I1 well within 1 per cent. From the combined equation, the enthalpy change between any tpvo temperature limits, TI and TP,may be found by
u
+ z/T’Ti + [22(T2”’
- Ti”’)
+
21+-
loge-
(2‘2 - T I )
Similarly an expression for entropy change may be deduced. Appropriate values of a, z, y, and z for any mixture of the gases listed are readily obtained from Table I. Literature Cited (1) Heck, R. C. H., ilIech. Eng., 62, 9-12 (1940). (2) Ibid., 63,126-35 (1941).
(3) Sweigert and Beardsky, Georgia School of Tech., Bull. 2 (1938).
Production of a Palatable Artichoke Sirup Application of Organic Exchanged D. T. ENGLIS AND H. A. FIESS University of Illinois, Urbana, Ill.
T
HE factors responsible for the initiation of the studies relating to the production of a palatable levulose sirup from Jerusalem artichokes were discussed and a general procedure for the preparation of the product was outlined in a previous paper ( 7 ) . Briefly this process consists in the preparation of an aqueous ext’ract from the sliced and dried tubers, hydrolysis of the soluble polysaccharides in the extract, then decolorization and concentration of the resulting solution. I n order to effect hydrolysis, the pH of the original extract must be lowered considerably. The quantit’y of acid necessary is moderately large because of the high buffer capacity of the natural extract. Examination of the ash of the extract shows a high potash value and indicates bhat the buffer action may be assigned chiefly to the potassium salts of organic acids. Dykins and Englis (6) established the conditions of hydrolysis with hydrochloric acid n-hich leaves a minimum of salt in the final product. Heubaum (11) studied the electrolytic acidification in a three-compartment system, and Hardy (9) worked out the details regarding the efficiency of the process. Although sirups of excellent quality can be produced by the electrodialytical treatment, the cost of the equipment and certain difficulties in operation may have a retarding effect upon the adoption of the procedure commercially. An effort was made by Henry (10) to hydrolyze the extract through the agency of enzymes. However, 1
The first three pnpers in this series appeared in 1933 ( 6 , 7, 9),
the inulases which have been isolated so far do not show sufficient activity unless the p H is lowered to a point (3.5-4) where hydrolysis can be accomplished more satisfactorily by heating under pressure. Shannon (15) hydrolyzed the polysaccharides of the extract with the aid of sulfuric acid, neutralized the solution v,-ith lime, and, after removal of the precipitated calcium sulfate by filtration, replaced the residual calcium ion by passing the sirup through a sodium Doucil exchanger. Satisfactory sirups have been produced but the salt content of the final product is still relatively high. During the cation exchange the solutions tend to become basic, which causes increased darkening of the solution. Another disadvantage encountered is a frequent failure to secure the full advantage of the fairly insoluble nature of the calcium sulfate. The salt tends to persist in a supersaturated condition or a dispersed state so that it is not removed in the first filtration. Some salt may crystallize out in further concentration, or persist and leave a corresponding amount of sodium sulfate after the exchange reaction. The development of the new organic exchangers appears to offer the most satisfactory answer to the original problem. By use of a cation exchanger, employing the hydrogen cycle, the potassium and other metallic ions can be replaced and the acidity brought into the desired range for hydrolysis. Then by means of a supplementary treatment with an anion exchanger, the acids may be removed. The introduction of a base and a corresponding increase in salt content is thus avoided.
INDUSTRIAL AND ENGINEERING CHEMISTRY
July, 1942
Organic exchangers are used in this procedure for the production of a palatable sirup from Jerusalem artichokes. The aQueous extract from the dried material is treated with a cation exchanger, using the hydrogen cycle, and the pH is lowered to a value near 3.5. The solution is drawn off, treated under a pressure of 15-20 pounds for 30 minutes, and decolorized with an active carbon; the acid content is reduced with an anion exchanger, and the solution is concentrated to a sirup of 80 per cent solids. Sirup superior to that of earlier methods is produced.
Resin Exchangers The first major contribution to the preparation and use of acid resin exchangers was made by Adams and Holmes ( I ) . The capacities of many of these synthetic resins are equal to or greater than the capacities of inorganic zeolites previously in use as ion adsorbents. A review of the development and applications of materials of this nature is given by Myers, Eastes, and Myers (IS). Adsorption of anions from solution is a comparatively new development and gives promise of being adapted to many processes hitherto impracticable. An equation for the reaction of the cation exchanger in the hydrogen cycle may be written HR K+ + K R HS
+
+
where K+ is the ion to be removed and HR represents the hydrogen form of the cation exchanger. The anion exchange materials are thought to adsorb complete molecules, not ions, and the action is represented by the equation, RX HA RX.HA
+
where RX is the exchange material. Myers and Eastes (12) reported studies of the capacity, rates of regeneration, and other factors of significance in the performance of Amberlite resins in water purification. Several interpretations have been made of the nature of the exchange process. Austerweil (4)considers the reaction to be analogous to the extraction of material from an aqueous solution by a nonmiscible solvent. Myers, Eastes, and Urquhart (14) consider it a species of adsorption and correlate the break through capacities with adsorption isotherms. Beaton and Furnas (5) believe the phenomenon may be accounted for by mass action considerations and formulate an equilibrium constant which gives good correlations with experimental data in the range of concentrations studied. Whether the nature of the phenomenon is physical or chemical or both probably will be more conclusively demonstrated as more data are accumulated. The object of the present work was to make a preliminary study of the general applicability of resin exchangers to the production of a palatable sirup from artichoke extract.
Exchange Materials and Artichoke Extract A considerable number of synthetic exchangers are now in commercial production, and several of them were examined in this study. Most of the attention was given to Nalcite A, Zeo-Karb H, and t8heAmberlite exchangers.
865
Flocculation of impurities as the pH of
the extract is lowered slows down the rate of flow in the cation exchanger and makes the column method of treatment impracticable. The batch method of operation is satisfactory. Lowering the pH of the extract to 3.5 is accompanied by a reduction of the ash content to two thirds its original value; lowering the pH further to 2.4 reduces the ash to one fourth the initial quantity. After twenty complete cycles the exchangers show no apparent loss in efficiency.
The solution which was to undergo the exchange treatment was prepared by subjecting the sliced dried artichoke material to extraction with hot water in a modified diffusion battery as described in one of the previous papers ( 7 ) . Although concentrations as high as 35 per cent total solids may be attained, these experiments were conducted 'with various concentrations. I n most cases an extract of about 12 per cent solids, which is near the value obtainable from fresh artichokes, was employed. In other cases extracts with total solids up to 25 per cent were utilized.
Procedure for Exchange Studies The raw extract is characterized by dijficulty of filtration. A certain amount of colloidal material is present which seems to be adsorbed upon the filter medium, and the rate of flow of the solution slows down rapidly and eventually almost ceases. Filter aids are of little benefit and their addition usually results in loss of polysaccharide material. However, if the pH of the solution is lowered and the solution is heated to hydrolyze the polysaccharides, flocculation of the colloidal materials takes place. At this stage the flocculated material can be easily filtered out. These characteristics of the extract immediately come up for consideration in establishing the type of operation to be applied. For most purposes the column treatment appears advantageous over the batch method since it lends itself more easily to continuous operation. COLUMNTREATMENT OF RAWEXTRACT. The American Water Works Association ( 2 ) proposed a method for examination of zeolites which is more or less standard for other materials of similar nature. Following this general procedure, a Pyrex glass tube of 34-mm. diameter with a stopcock a t the bottom was used for the column. I n the tube above the stopcock a layer of glass beads and glass wool was placed and moist Nalcite A was introduced until a contracted depth of 34 inches (86.4 cm.) was obtained. In order to prepare the exchanger for the hydrogen cycle the exchanger was treated with a 5 per cent solution of sulfuric acid and washed thoroughly with distilled water. Artichoke extract of an apparent total solids content of 11.67 per cent, as indicated by the refractive index and Schonrock's tables (S),was heated to 65" C. and allowed to percolate through the column a t an initial rate of 30 ml. per minute. The lowering of the pH of the first liter of juice was from 5.45 to 1.70. Measurements of pH were made with the glass electrode and the industrial model Beckman pH meter.
866
INDUSTRIAL A N D ENGINEERING CHEMISTRY
TABLE I. EFFECT OF EXHAUSTION OF EXCHANGE MATERIALON pH AND TOTAL SOLIDSOF ARTICHOKE EXTRACT (Exchange material, 250 grams Zeo-Karb H ; initial pH of artichoke extract, 5.46) 7 Apparent Total Sample Volume, ,M1. ----pHd l i d a by RefraoNo. Expt. 1 Expt. 2 Expt. 1 Expt. 2 tometer, Expt. 2 1.95 2.30 11.25 1 250 250 250 2.00 2.78 15.00 2 250 250 2.80 3.31 3 500 17.20 4 250 250 3 2 3.50 18.20 3.72 3.70 19.15 5 250 250 250 3.82 3.90 64 250 19.62 250 250 4.08 4.00 19.93 7
- -
-
Total combined portions 2000 1750 3.40 3.45 16.93 The exchanger was oleaned at this oint of adhering protein and carboh drate with two 400-ml. portions of Rot water; there was no apparent d a n g e in effectiveness.
The column became clogged when one liter of juice had passed through, and operations had to be discontinued. Subsequent experiments using Zeo-Karb H and Amberlite IR-1 exchangers of a slightly larger mesh gave similar results with this type of operation. BATCH TREATMENT OF RAWEXTRACT. After the standard column treatment had failed to give satisfactory performance upon the raw extract, it was discarded and the batch method of operation was tried. This procedure consisted simply in treating the extract in a suitable container with a specified amount of exchange material, agitating for a short period t o permit equilibrium to be established, and then separating the exchange material from the solution by decantation or filtration. No difficulty was encountered in the manipulations, As was to be expected, the pH of the treated solution was slightly higher and the exchange was less complete than in the column method where the break-through point had not been reached. I n practical operation, exhaustion of the material will not be obtained by a single-batch treatment. However, if a series of batch treatments are carried out, employing the countercurrent principle as in a diffusion battery extraction (where fresh extract first comes in contact with most nearly depleted exchanger and in the last operation with fresh exchanger), the method would be very practicable. I n laboratory testing operations, the batch method has the added advantage of speed. Using the proper amount of exchange material to attain the desired pH of the extract, apparent equilibrium was reached in less than 3 minutes. After allowing a few more minutes for the exchanger to settle, the extract was filtered and was ready for the hydrolysis treatment. CAPACITYOF EXCHANGE MATERIALS.For economic reasons it is necessary that the synthetic exchangers have a relatively high capacity and that they do not disintegrate or diminish in capacity with repeated use. The previous experiment demonstrated that the artichoke extract may be treated successfully by the batch method, but it is essential to establish the rate a t which the capacity is reduced by successive portions of an extract of given total solids up to a point of depletion of the exchanger. Furthermore, it must be determined if there is an accumulation of flocculated or adsorbed impurities which will alter the performance of the exchanger.
Cation Exchanger Studies Capacity as indicated by p H change with repeated use of the cation exchangers was the next topic of study. Zeo-Karb H was utilized in the experiments. As originally received, it contained many fine particles which were removed by repeated washing with water. It was then prepared for the hydrogen cycle by regeneration with 5 per cent hydrochloric acid. The artichoke extract to be treated had an initial pH
Vol. 34, No. 7
of 5.45 and a total solids content of nearly 20 per cent. The extract was heated t o 65" C. in order to lower the viscosity and increase the rate of exchange. Portions of 250 ml. each (in all instances except one when 500 ml. were used) were heated with about 250 grams of moist Zeo-Karb H and gently agitated for several minutes In the previous studies it was shown that the exchange took place rapidly and the time factor was not important. After treatment the liquid was drawn off, a fresh 250-ml. portion of extract added, and the operation repeated until the p H of a new portion reached or exceeded 4.0. After five portions had been treated, the Zeo-Karb H was suspended in water and washed to see if there would be any effect upon the next exchange. When the seventh portion had been treated, the experiment was stopped and the exchanger was regenerated. I n the second experiment a similar series of operations were carried out. I n this experiment the refractive index of the treated portions was taken and apparent total solids noted. The data obtained are shown in Table I. In the first portion the pH is lowered to 1.95. Seven portions of extract may be treated successively before the capacity of the exchanger is reduced to the point where the pH will not be below 4. Washing the exchanger with water after the fifth portion had been passed seemed t o have little effect, and it is believed that any flocculation of impurities which takes place as the pH is lowered does not interfere seriously with the action of the exchanger. After the ZeoKarb H had been regenerated and the experiment repeated slightly higher results were obtained with the initial portions, but the general results were similar. When the portions from each experiment were combined, the pH values of the mixtures were nearly the same. Since the exchanger was moist after the regeneration process, the total solids of the first few portions was lowered by dilution. At first it was feared that some polysaccharides might have been adsorbed upon the Zeo-Karb H. Other later tests showed that washing of the exchanger seemed to give complete recovery. It is evident that under these conditions of operation, 250 grams of the moist exchanger without regeneration is capable of lowering the pH of 2 liters of extract (containing about 400 grams of dissolved artichoke solids) to a value of 3.5 a t which a satisfactory hydrolysis may be accomplished by the methods previously described.
Exchange Capacity and Repeated Cycling The previous experiments had given some information on the performance of Zeo-Karb H with repeated use, but it was desirable to make a more extended test of this property. In the treatment of water some carbonaceous exchangers have been used in thousands of complete cycles without loss of capacity. However, the treatment of artichoke extract, which contains a high concentration of organic solids, involves other factors not characteristic of natural waters. In order to investigate this point, a number of complete cycles were run using the same material but regenerating in the prescribed manner after each treatment. For the cation exchange 25 grams of moist Zeo-Karb H were employed. The artichoke extract was then subjected t o treatment with 10 grams of moist Amberlite IR-4 for the anion exchange. Since these results were for comparative purposes only, an excess of artichoke extract was used-namely, 200 ml. of an extract having an initial pH of 5.45 and a total solids content of 25.1 per cent. After the Zeo-Karb H treatment, the extract was separated from the resin by filtration with the aid of suction. The pH of the extract was taken, and it was then treated with Amberlite IR-4 for exactly 15 minutes since the time factor is important in this reaction. Again the pH was taken, and both exchangers were regenerated in the manner previously
July, 1942
INDUSTRIAL A N D ENGINEERING CHEMISTRY
TABLE11. CAPACITYOF EXCHANGE MATERIALSAFTER REPEATED CYCLING WITH ARTICHOKE EXTRACT (Volume of extraat used 200 ml. or volume to oontain 50 grams of soluble solids; exchAnger regenerated after each treatment) Amberlite Zeo-Karb H Treatment IR-4 Treatment Cyole No. Vol., ml. pH Deviation pH Deviation -0.12 3.92 -0.01 4.67 1 200 +0.01 3.92 4.80 -0.01 2 200 +0.28 -0.01 3.92 5.07 3 200 $0.17 -0.04 4.96 3.89 4 200 +0.19 3.90 -0.03 4.98 6 200 4-0.17 +o.oo 3.93 4.96 6 200 +0.27 +0.03 3.96 5.06 200 7 -0.01 +0.04 3.97 4 . 7 8 200 8 -0.02 +0.05 3.98 4.77 200 9 +o.oo f0.02 3.93 4.81 10 200 -0.12 +0.01 3.94 4.67 212 11" -0.07 4.72 -0.05 3.88 12 212 -0.03 4.76 -0.16 3.78 212 13 -0.21 4.58 -0.06 3.88 14 200 -0.03 -0.03 4.00 4.76 200 15 -0.11 -0.07 3.97 4.68 200 16 -0.11 -0.04 3.99 4.68 200 17 -0.11 -0.04 3.99 4.68 200 18 -0.10 -0.03 3.90 4.69 190 19 -0.11 -0.03 3.90 4.68 190 20 a The volume of sirup used in oyoles 11-20 was varied somewhat so that comparative results oould be obtained, as the total solids content of these samples differed among themselves and from the first ten samples.
described. The anion exchange resin was treated for exactly 15 minutes After the regeneration and washing, a fresh lot of artichoke was treated for the second cycle. This process of exchange was repeated for twenty separate cycles. The results are given in Table 11. With Zeo-Karb H the pK dropped to an average of 3.93, and the deviations are within the range of experimental error. After the anion exchange the pH was raised to an average value of 4.79. The deviations from the mean are slightly greater than in the case of the cation exchange. This may be expected since the time factor is of greater significance. However, it is apparent that there is no loss in exchange capacity of either exchanger after twenty complete cycles, and it is probable that longer cycling will have no adverse effect except perhaps some slight physical disintegration.
Effect of Double Cycling upon pH and Ash Content The next experiment was designed to test the effect of single and double cycling upon the removal of the mineral elements from the artichoke extract. In the first step the p H was reduced by Zeo-Karb H to the point satisfactory for hydrolysis and then subjected to the anion exchange. In this step Amberlite IR-3 was used, the more effective Amberlite IR-4 not then being available. The treated extract was put through a second cycling with the regenerated exchangers. As a check the experiment was repeated. Samples were withdrawn after each step, and the pH and ash were determined. The results are given in Table 111.
TABLE111. EFFECT OF REPEATED ALTERNATE CYCLING WITH ANIONAND CATIONEXCHANGERS UPON THE pH AND ASH CONTENT OF ARTICHOKE EXTRACT h1500 ml. of artichoke extrect oontaiGng 18.1% solids; 160 grams moist eo-Karb H , 226 grams moist Amberlite IR-8. regeneration of exohanger after eaoh treatment) -pH-Ash, Gram-Expt. 1 Expt.2 Expt. 1 Expt.2 5.46 0.81 5.46 0.81 Originel extraot 3.40 3.47 1st oation exohange 0.51 0.49 4.25 4.10 1st anion exohange 0.44 0.49 2nd oation exohange 2.40 2.56 0.26 0.25 2nd anion exohange 4.15 3.87 0.18 0.21
The ash content of the extract is reduced to about two thirds of its original value when the pH is dropped to 3.4-3.5,
867
but when lowered to a pH of 2.4-2.6 by the second cation exchange, the ash content is only about one fourth its original value. Further experimentation will be necessary to determine the relative values of a single complete cycle (one cation and one anion exchsnge) and of a repeated cycle, from the standpoint of cost and efficiency. Some preliminary tests (8) were made in an effort to determine what constituents are removed by the anion exchanger, and additional work is in progress. The marked reduction in ash content is a favorable factor toward the production of a palatable sirup, and the next experiment was concerned with this problem.
Use of Organic Cation and Anion Exchangers The general procedure for the preparation of the extract was the same as that outlined previously (7). After heating the extract to 60" C., it was treated with the Zeo-Karb H in a large beaker and the mixture was stirred gently. Sufficient Zeo-Karb H was added to reduce the pH to 3.4, then the solution was decanted from the exchanger and hydrolyzed in an autoclave a t 15 pounds per square inch (1.05 kg. per sq. cm.)pressure for 30 minutes. The hydrolyzate was decolorized with Darco and treated with Amberlite IRA, and the pH was raised to 6.7. The solution was again decanted from the resin, iiltered, and finally concentrated under reduced pressure a t a temperature not over 50" C. until the solids had reached 80 per cent. The final sirup was of a light amber color. The flavor waa excellent and was rated superior to samples previously made by other procedures. The use of the anion exchanger not only eliminates the necessity of adding sodium carbonate or some other base to neutralize the acidity produced by the cation exchange employing the hydrogen cycle, but also removes certain acid bodies. Elimination of these seems t o improve the quality and flavor of the sirup. Several samples of the sirup have been prepared with good success in every instance. It is not necessary for the production of highquality sirup that the exchangers be used in a manner to effect a maximum removal of foreign material. However, work is now in progress in which they will be utilized to this degree with the belief that the purity of the sirup may be improved to a point where direct crystallization of levulose will be possible. Acknowledgment Several of the resins studied were supplied through the courtesy of the manufacturers-National Aluminate Corporation, The Permutit Company, and The Resinous Products and Chemical Company, Inc.
Literature Cited (1) Adams, B. A., and Holmes, E. L., J . Soo. Chem. I d . , 54, 1-6T (1935). (2) Am. Water Works Assoc., Tentative Methods for Examination of Zeolites, 1940. (3) Assoc. of Offioial Agr. Chem., Officialand Tentative Methods of Analysis, 5th ed., p. 667 (1940). (4) Austerweil, G. V., J . Soo. Chem. I d . , 53, 185T (1934). (5) Beaton, R. H., and Furnas, C. C., IND. ENG.CHEM.,33, 1600 (1941). (6) Dykins, F. A., and Englis, D. T., Ibid., 25, 1165 (1933). (7) Dykins: F.A., Kleiderer, E. C., Heubaum, U., Hardy, V. R., and Enghs, D. T., Ibid., 25,937 (1933). (8) Gast, L. E., B.S. thesis, Univ. of Ill., 1941. (9) Hardy, V. R., IND. ENG.CHEM.,25, 1395 (1933). (10) Henry, R. E., Ph.D. thesis, Univ. of Ill., 1937. (11) Heubaum, U., Fads About Sugar, 28, 284 (1933). (12) Myers, R. J., and Eastes, J. W., IND. ENQ. CHEW,33, 1203 (1941). (13) Myers, R. J., Eastes, J. W., and Myers, F. J., I b g . , 33, 697 (1941). (14) Myers, R.J., Eastes, J. W., and Urquhart, J. D., Ibid., 33,1270 (1941). (15) Shannon, W. J., Ph.D. thesis, Univ. of Ill., 1941.
