NOVEMBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
Literature Cited Barnes, R . B., J . Optical SOC.Am., 28, 140 (1938). Bridgman, P. W., Proc. Am. Acad. Arts Sci., 60, 305 (1925). Cartwright, C. H., J. Optical SOC.Am., 29, 350 (1939). Gundelach, E., Z. P h y s i k , 66, 775 (1930). Gyulai, Ibid., 46, 80 (1927). Hohls, H. W., Ann. Physik, [5] 29, 433 (1937). International Critical Tables, Vol. VII, p . 24, New York, MoGraw-Hill Book Co., 1930. Ibid., Vol. VII, p. 26. Kyropolous, 2. anorg. albem. Chem., 154, 308 (1926). Melvin, E. H., P h y s . Rev., 37, 1230 (1931). Mentzel, A,. Z.P h y s i k , 88, 178 (1934).
(12) (13) (14) (15) (16) (17) (18) (19) (20) (21)
1483
Paschen, Ann. P h y s i k , [1]26, 120 (1908). Ramsperger and Melvin, J. Optical SOC.A m . , 15, 359 (1927). Rubens, Ann. Physik, [N.S.] 54, 476 (1895); 60, 724 (1897). Schneider, E. G., J . Optical SOC.Am., 27, 72 (1937) Schneider, E. G., Phgs. Rev., 45, 152 (1934). Sohneider, E. G., Ibid., 49, 341 (1936). Slater, Proc. Am. Acad. A r t s Sci., 61, 136 (1925). Stockbarger, D. C., J . Optical SOC.Am., 27, 416 (1937). Stockbarger, D. C., Rev. Sci. Instruments, 7, 133 (1936). Stockbarger and Cartwright J. Optical SOC.Am. 29, 29 (1939).
PRESENTED before the Division of Physical a n d Inorganic Chemistry a t t h e 99th Meeting of the American Chemical Society, Cincinnati, Ohio.
Wet Milling of Corn Recovery and Utilization of Process Losses In the early days of the wet milling of corn, one of the largest plants in the industry lost dry-substance materials in its various process waters which were sewered, and caused a pollution load of the factory effluent equivalent to about 400,000 persons (in population equivalents) per 24 hours. This has been reduced to a n average of below 40,000 persons during 1938 w-itha lowest figure achieved during the last half of the year 1936 of 22,000 persons. Reviewing the work of the several investigators during this period, the greatest reduction and consequent recovery of product losses was accomplished through the recirculation and countercurrent flow of starch and gluten wash waters. Instituting a department to control losses continuously, devising a scheme for recovering volatile losses, study and subsequent improvement of processes and equipment, and a general survey of all openings to thc sewers from process departments contributed to this reduction with a corresponding saving of materials and products for a financial gain in all instances. Present work involving the recovery of ethyl alcohol and other volatile substances and the treatment of other process waters indicates that it may be possible to reduce the pollution load below 20,OOO persons and perhaps to less than 10,000, should these recovery processes work out as well in practice as they have in the pilot-plant stage.
I
N 1910thisindustry became conscious of the material losses in its process (5) because of the objections of residents in the vicinity of a plant located a t Waukegan, Ill., which disposed of its untreated process waters directly into Lake Michigan. The condition was improved by treating the waters with lime and iron sulfate and filtering to remove the solids, but the economic importance of these trade wastes did not receive significant attention until a study was started in 1920 by the Chicago Sanitary District in cooperation with the Corn Products Refining Company at the factory located a t Argo, 111. (3) Laboratory facilities were established on the factory premises, and an extensive investigation was car1
Ind
Present address, Yational Starch Prodrirts C o m p a n y , Inc
, Indianapolis,
-4. L. PULFREY’, RALPH W. KEKH, &NDH.
R . REINTJES
Corn Products Refining Company. Argo, 111.
ried out between 1920 and 1928. Before reviewing the results of their work, a brief description of this 24-hour continuous process is essential. Air-cleaned shelled corn is steeped in a weak solution of sulfurous acid. The corn is then milled, and the material is separated into the following fractions: starch, germ, gluten, fibrous material, and soluble solids. Dextrins, gums, food starches, corn sirups, dextrose sugar, and many other products are manufactured from the starch. Though zein and other products are derived from the gluten, the greater part is either combined with the soluble solids and fibrous materials or prepared directly as an animal feeding material. The entire process of steeping, grinding, and separation of the above components is a wet-milling process and all materials are handled as slurries to the last manufacturing steps. Deep wells furnish process waters. Before 1920 only the countercurrent, water used in the steeping operation was evaporated for the recovery of the solids, and even this practice was not followed a t all plants in the industry. Other process waters were sewered, which caused the total effluent losses reported by Mohlman and Beck (4) as amounting to over 2 per cent of the total dry substance ground. The pollution load of the entire factory effluent ranged from 250,000 to about 400,000 population equivalents per day ( 3 ) . “Bottling up” those process waters originating from the starch washing and the gluten settling processes, by recirculating and eventually concentrating them with the steep waters in the vacuum evaporators, contributed the first substantial reduction in the pollution load. Closer control of the escaping solids by automatic sampling, regular reports of excessive entrainment in the evaporation processes, and the recirculation of starch and of gluten wash waters reduced the pollution load to a range of 50,000 to 100,000 population equivalents (4) by 1928 and continiied in this range through 1935 (Table I). To concentrate all wet-starch process solubles eventually as steep water, however, involves two problems, one related to the other. First, efficient evaporation of the water in gallons of water evaporated per pound of exhaust steam must be
INDUSTRIAL AND ENGINEERING CHEMISTRY
1484
VOL. 32, NO. 11
Steep-Water Evaporation
O F THE TABLEI. AVER.4OE DAILYPOPULATION EQUIVALEXTS Three types of losses from steepwater evaporators are ARGO FACTORY, REPORTED BY THE COOKCOUNTYSANITARY DISTRICT LABORATORYO known: (a) entrainment losses of solids, ( b ) noncondensed
1930 1931 1932 1933 1934 1935 1936 1937 1988
First 6 Mo. 71,000 84,000 76000 56,000 95,000 66,000 37,000 43,000 36,000
L a s t 6 nfo. 56,000 72,000 51,000 62.000 87,000 54,000 22,000 34,000 43,000
0 Oxygen demand a n d metered volumes of t h e effluent a r e determined daily. Averages are used t o compute t h e population equivalents monthly a n d semiannually (Figure 1).
maintained. To reduce the load on the evaporators, most of the table-house liquors must be re-used; a cycle is built up that not only increases to the saturation point the concentration of undesirable solids which slows down evaporation, due to a scaling effect. but also favors the production of low-temperature fermentation products which increases the volatiles from the evaporators to the sewer.
FIGURE 1,
RE-
PLANT W.4STE POPULATION EQUIVALENTS PORTED BY THE SANITARY DISTRICT LABORATORY
Both problems were solved, in part, by one of the writers.
A system of high-temperature fermentation was devised to treat steep water. This treatment produced negligible quantities of volatiles and a t the same time produced steep water which would boil with maximum efficiency (3). Secondly, recycling of table-house liquors was reduced to a minimum; the result was a straightforward flow of countercurrent water throughout the process by a more careful study of the principles of separation, principally starch-table separation, which permitted table-house operation with less than half the volume of process water used previous to 193233. By adoption of this heavier gravity process (at Argo in 1934-35) the bottled-up system was further improved in that, without recycling, it was necessary neither to draw a prohibitive volume of water through the steeps nor to sewer it. Mohlman and Beck (4) reported that in 1928 the vapors from the steep-water concentration process and the water sewered after washing and preparing bone black for decolorizing sirup and sugar liquors contributed well over 7 5 per cent of the total pollution load. Periodic surveys made since 1935 (typical samples in Table 11) show marked reduction only during the last half of 1936, though the population equivalents since 1936 are lower than for the period prior to 1935. Each of these effluents has been studied individually and will be discussed separately.
vapors, volatile a t the pan operation temperatures, and (c) condensable organic materials passing over in the vapors. Vigilant supervision of pan operation, regular maintenance inspections, and the use of properly designed liquor separators have reduced entrainment losses from over 50 to less than 20 grains per gallon. Considering that over half a million gallons of condensed vapors are sewered per day, this reduction amounts to a recovery of over a ton of dry substance per 24 hours. A method was devised for evaluating the amount of volatiles in the steep waters receiving different preliminary treatments: One thousand cubic centimeters of the treated and untreated steep water were each distilled under standard conditions. The distillate condensed at 0" C. was collected. A 5-day B. 0. D. was made on each fraction, and the cumulativti average concentration of volatiles in the distillate, as evidenced by the B. 0. D., was plotted against the fractional volume of steep water distilled. Using logarithmic paper, a straight line resulted. By extrapolating t o a theoretical 100 per cent of the steep water being distilled, an index value was obtained representing the total B. 0. D. equivalent of the volatiles present in each sample and called a '(B. 0. D. index". Comparison of the B. 0. D. indices between control samples and treated samples was used as a measurement of the value of the treatment being studied. Many types of treatment were tried in the laboratory, but the most spectacular results were obtained simply by heating the steep water in open vessels and aerating t h e steep water a t elevated temperatures (Figure 2). Accordingly, a process was devised in the factory whereby the water from the steeping operation was heated t o 180' F. by heat exchangers, and then passed over wet-system dust collectors used for recovering dust losses from the hot vapors and gases from feed and gluten meal rotary dryers. A reduction of 52 per cent was obtained in the B. 0. D. of the steep water vapors in the
7.BY V O L O F STEEP W A T E R D I S T R
FIGURE 2. REDUCING R. 0. D. BY PREHEATING STEEPWATER IN OPEN TANKS (above) AND BY AERATION OF STEEPWATER(below)
NOVEMBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
1485
substance in the form of these volatiles has inspired work along the lines of identifying and recovering the subPopulation Equivalents % ' of Total stances or modifying the manufacturing Process or Operation Jan., 1935 Sept., 1936 Jan., 1937 Jan., 1935 Sept., 1936 Jan., 1937 process so that they will not be formed. Steep-aater evapn. 38,500 15,400 24,600 54 71 61 Concn. of corn sirup and Steep-water vapors were shown ( 4 ) sugar liquors 2.400 1,700 1,000 3 8 2 to contain aliphatic alcohols, acids, and Waste water from washing and preparing bone esters in 1928. Recently an analysis black for suyar-decolorizing process 11,900 3,000 9,300 17 14 23 was made on steep water as follows: Filtrates from modified In the laboratory 10 liters of regularly starch proress 4,200 None 3,000 6 0 7 Other sources (by differincubated ( 1 ) water from the steeps, 14,700 1,500 __ 2,500 20 7 6 ence) taken over 4 consecutive days, were Total 71,700 21,600 40,400 fractioned in a laboratory distilling column: the distillates were composited' and fractioned until the volafactory as shown in Table 111. The slight increase in the tiles were concentrated in a fraction containing 75 per cent density of the steep water after passing through the collectors ethyl alcohol. Ethyl acetate was prepared from the alcohol, may be due either to evaporation of water (as indicated from and the ester was positively identified by boiling point, the temperature drop) or by the removal of the volatiles. saponification equivalent, and odor. Acetaldehyde was found to be the next major constituent in this fraction and was identified by forming its 2,4-dinitrophenylhydrasone OF STEEPWATERBEFORE CONCENTRATABLE 111. AERATION (6). This steep water was found to contain, in per cent by TION IN VACUUMPANS" volume, 0.23 ethyl alcohol and 0.03 acetaldehyde. TABLE11. RELATIVERESPONSIBILITY OF DIFFERENT PROCESSES FOR THE TION EQUIVALEKTS IN THE TOTAL FACTORY EFFLUENT
PoPUL.4-
t
-
Analvsis of SteeD Water BB. of ateep water (at 60' F.), degrees Acidity (8s HCI). 5% Temperntur~ O F. B. 0. D. indkx Reduction in volatiles having an oxygen demand, % a Average of three %-hour test rum.
To Wet Dust T o Vacuum ColIPctors 4 6 0.67 172 3190 52
Pana 4 9 0.67 131 1540 52
Steep water passes through a three-stage evaporator and then to single-effect pans for its final concentration into a heavy liquor. The condensing temperatures are not low enough to condense all of the low-boiling organic vapors passing over from the first- and second-effect stages. These vapors were vented from the second- and third-effect heating chambers to the barometric condenser on the third effect and thus entered the sewered effluent. By installing steam-jet pumps (2) to these heating chambers, these noncondensed volatilcs were pumped directly to the atmosphere. To d o termine the effect of venting these volatiles to the atmosphere, the operation was alternated every 24 hours, and observations were made on the sewer receiving the condensed vapors from all three effects as shown in Table TV. Installation of these jet pumps reduced the pollution load by 3800 population equivalents.
X
0
2
4
6
8 IO 12 14 16 NUMBER O F PLATES
18
21
FIGURE 3. DISTILLATION OF STEEP-WATER CONDENSATE
A method for removal and recovery of the volatiles was demonstrated as commercially practical by the installation of a small, experimental bubble-cap column, capable of handling a maximum of about 8 gallons per minute of steep-water condensate. Three representative runs are summarized in Table V and show that a t least 90 per cent of the volatiles responsiTABLEIV. REDUCTION OF SEWERPOLLUTION BY VENTING ble for B. 0. D. could be removed by this column from the NONCONDENSED VOLATILES TO THE ATMOSPHERE FROM SECONDHEATIKGCHAhIBERS O F THREE-STAGE water treated. Run 3 shows the effect of using a deficiency of A N D THIRD-EFFECT EVAPORATORS steam, which gives a low reduction in B. 0. D. Figure 3 Vapors Vented shows the effect of B. 0. D. of steep-water condensate when T o sewer T o atniosphere scrubbed with different amounts of steam as well as the rela&day B. 0. D. of combined vapors, p. p. m. 183 70 Population equivalent/24 hr. 5380 1570 tion of the number of plates in the column.
r
It may be expected that the total pollution load from the steepwater evaporation processes may be held to a population equivalent below 10,000 persons by the described methods of control of the three types of losses causing the pollution. The lowest population equivalent (below 7000) for the effluent from this process was obtaincd in September, 1936. Heat requirements for warming the steep water before aeration and for the operation of the jet pumps have been excessive. Consequently, i t has been economically prudent to liold this figure near 20,000 a t present which represents a reduction of 50 per cent of the population equivalent found before and during 1935. This fact plus the actual loss of dry
TABLEV. Run NO.
1 2 3
DATA ON REMOVAL AND RECOVERY OF VOLATILES IN BUBBLE-CAP COLUMN Feed, Gal./ Min. 6.0 5.6 5.1 5.2 4.3 3.8 7.8 7.8 9.0
Steam Required, Lb /lo00 Gal. 1000 920 1200 1140 1 800 1400 G80
580 520
To column 5.000 10,000 8,300 9.900 10,000 8,000 7.700 5,300 7,700
5-Day B. 0. D. From % coluiun reduction 800 86 200 98 450 95 240 97 200 9.9 120 98 2400 69 2000 51 2800 64
1486
INDUSTRIAL AND ENGINEERlNG CHEMISTRY
After the experimental work was completed, a system was designed for the removal and recovery of the volatiles present in steep waters. Originally it was intended to reduce the B. 0. D. by such a procedure with no thought of recovery of alcohol. Calculatious show that the recovery of alcohol is economically justified.
VOL. 32, NO. 11
Bone Black W a s h W a t e r s Corn sirup and sugar liquors described above are decolorized by passing over bone black. To prepare this bone black for service, i t is first tempered hy an acid wash followed by fresh hot water until the proper pH and temperatures are reached. The bone char is then drained and placed into liquor service. Kear the conclusion of the service cycle, fresh water is added to sweeten off or to remove the adhering liquors. This is sent forward with the liquor until the concentration of solids in the wash waters is small. Water used in continued washing is sewered. Table VI shows that of the total bone wash waters, the 60 per cent used in washing the bone after liquor service contained 87 per cent of the pollution toad, and therefore little thought has been given to the losses from the tempering process. During 1936 the population equivalent in this effluent was reduced to 3000 persons (Table 11) by utilizing the 182,oM)gallons of wash water in a recirculah ing system diluting the starch slurry to the hydrolyzing process. After 3 months this had to be abandoned because the cycle built up in the refining process too high a concentration of inorganic ash. ~
~~~~
TABLE VI. DATA1'EaTAINING TO EFFLUENTS FROM BONE BLACK TREATMENT PROCESSES (JANUARY. 1936) From*; 4. REMOVAL AND RECoVERV STEEP WATER
OF
ALCOHOL FROM
Our prtiposed system is shown diagrammatically in Figure 4. I n this system steep water will be taken directly from the incubators to the first effect of an efficient triple-effect evaporator, without aeration. The vapors from the first effect will be condensed in the second effect, whereupon they will be sent to the scrubbing column. Vapors from the second effect go to the third effect, are condensed, and go with the condensate from the second effect to the still. The scrubbing column will be 6 feet in diameter with eighteen stripping and three rectifying plates, and should remove better than 90 per cent of the volatiles of the treated steepwater condensate responsible for B. 0.D. Vapors from thescrubhiugcolumn are condensed and then pass to a rectifying column for recovery of alcohol. This column will be 20 inches in diameter and will contain eighteen stripping plates and twenty-six rectifying plates. The total steam required will be approxim t e l y 1.4 pounds of steam per gallon of steep-water condensate treated. The practice of using steam jets to vent the noncondensable volatiles from the evaporators to the atmosphere will be discontinued. With this installation we would expect to reduce the population equivalent in the waste from this process well belov thc present level, with a corresponding recovery of materials and products of sufficient economic importance to more than justify the cost of the improvement in operations.
Corn Sirup and Sugar Liquor E v a p o r a t i o n Processes Starch is hydrolyzed to m k e corn sirups and liquors from which pure dextrose i s crystallized. Concentration of these liquors during their refining process bas never contributed much of a pollution load to the factory effluent and has been found due solely to entrainment losses a t the vacumn pans. The reduction of these losses hy close supervision, correct installation and proper maintenance of equipment, and controlled automatic sampling has reduced the pollution load from about 2500 population equivalents in 1935 to less than 1000 a t present.
Tempezing PrDeeSs Av. gsllon~geper 24 hr. Rstes of eBpente b y YoI.. 7 AT. population equivale?tsh4 hr. Ratia of po*ulatiuo equ'ualents, yo Total aolrds sewered, W 2 4 hr. Inorgsnio solids (ash). lb./24 hr.
PH
273,000
Wash Water after SweetTotal ening-oK Effluent
Prooea
tosewer
1s2.000
455.000
60
40
1550
10,350
13 IS90
87 6370
1090 4.2
100 8260
840 8.6
1930
IC0
11,900
6.0
A study of the detailed washing operations resulted in a more closely controlled and supervised cutoff of the
washing operation in the factory, with the result that the present total pollution load is held below 9000 population equivalents. Further investigation bas shown that this SO00 papulation equivalents possibly might be eliminated by either of the following changes: (a) Replace the present bone black proeess with a process using a vegetable carbon (which involves the discarding of a 3,500,000-pound stock of bone black, kilns, Uters, and other costly equipment now in use), or ( 6 ) develop a countercurrent process for washing the spent bone char in a series of tanka with agitation. The first proposal h a s n o t y e t been shown to be ewnomi1401 1 eally feasible. Laboratory-scele te.sts (Figure 5) have indicated that spent bone char could be washed more efficiently than a t present by the second plan, but the cost might he prohibitive on a factoryscale operation. The solids would be collected in approximately 60,000 gallons of wash water (one third of the present volume) which would be concentrated with steep watera and FIGWE5. BONEWASHINUBY thesolids thusrecovered. A Q ~ A T I NIN Q TANKS
*
NOVEMBER. 1940
IXDUSTRIAL .4ND ENGINEERING CHEMISTRY
1487
Filtrates from Modified Starch Process
Colic111sions
Starch slurries are treated with acids and other chemicals to modify the physical-chemical characteristics of the starch for a large range of products. Some organic solubles are created, but over 50 per cent of the solids in the sewered filtrates are inorganic in nature and of little commercial importance. For several months during 1936 these filtrates were concentrated in a vacuum evaporator, and the solids were recovered which eliminated a population equivalent of over 4000 persons from the total factory effluent. The damage to the equipment caused by the chemicals present far exceeded expectations, and the practice had to be abandoned. -1bout 25 per cent. of this effluent is used for wetting coal and cinders at the power plant. Studies are in progress to alter the present manufacturing process.
Sources of pollution load of the seivered water from the Corn Products Refining Plant at Argo have been carefully analyzed, and their respective proportions of the total load have been evaluated. Developments leading to the curtailment of these sewered waste waters and the recovery of losses, where possible, in the remaining portion sewered, have been traced over the past two decades u p to the present time. The net result has been a reduction of pollution load from a total of 250,000 to 400,000 population equivalent per day to around 40,000, with a corresponding recovery of materials and products of sufficient economic importance to more than justify the cost of the improvement in operations. Experimental work has been given to indicate that i t may be commercially possible to reduce this load still further.
Other Sources
Acknowledgment
A complete survey of the factory sewer system was made in 1935 to determine the origin of the 15,000populationequivalent unaccounted for in the total factory effluent. Samples were taken daily at each sampling station along the principal sewers, and the oxygen demand was determined. These results were watched closely for any sudden “shots” which would lead to a new source of process loss. Every opening in the sewer was traced back to its origin, a list prepared of all drains or outlets to the sewers, and each one investigated individually. It was found that material from careless process spills, due to drains being located too near tanks, pumps, presses, etc , was escaping to the sewer. Removing drains, changing equipment, and treating particularly bad effluents before sewering, such as the wash waters from washing machines for press cloths, reduced this pollution te a present range of 1000 to 2500 persons.
The direct cooperation of the Sanitary District Laboratories has helped to make many of the described innovations possible without resorting to methods involving sewage treatment where no recovery of materials or products could be attained.
Literature Cited (1) Berlin, H., and Kerr, R. U’. ( t o International Patents Devclopment Corp.), U. S. Patent 1,918,812 (1933). (2) McCoy, R. (to International Patentr Development Corp.).
Ibid., 2,126,568 (1938). (3) Mohlman, F. W., IND.ENG.CHEM.,18, 1076 (1926). (4) Mohlman, F. W., and Beck, A. J., Ibid., 21, 205 (1929). (5) Sjostrom, 0, Ibid., 3, 100 (1911) (6) Strain, H. H., J. Am. Chem. SOC.,57, 738 (1933). PRESENTED as p a r t of t h e Symposium o n t h e Utilization of Agricultural Wastes before t h e Division of Sgricultural Chemistry at t h e 99th Meeting of t h e iimerican Chemical Society, Cinrinnati, Ohio.
ALUMINA FLOC-
X-Ray Diffraction Study
H-ARRI- I). WEISER, W. 0. JIILLIG.Ah7, . .iND W. R. PURCELL T h e Rice Institute, Houston, Texas
RESHLY precipitated alumina gives an x-ray diffraction pattern consisting of broad bands or lines corresponding to y-A1203.H20or y-A100H (1). The gel precipitated from aluminum sulfate solution gives much broader diffraction bands of yA1z03.HzO than the gel from chloride or nitrate (8,s). This means that the crystal size of the particles in the gel from chloride is larger than in the gel from sulfate, and hence that the gel from sulfate possesses the greater adsorption capacity. Since the alumina floc made from aluminum sulfate is widely used in water purification, additional information concerning the composition of this gel is of interest. The purpose of this paper is to report the results obtained from a n x-ray diffraction study of the constitution of the alumina floc thrown down a t varying pH values from highly dilute solutions of aluminum sulfate such as are used in water purification.
F
Effect of pH with Various Precipitants An amount of A12(S01)3.18Hz0,equivalent to a concentration of 50 p. p. m. in 5000 ml., was diluted to 1 liter in a volumetric flask and transferred to a separatory funnel. Various amounts of a standard sodium hydroxide solution correspond-
ing to 60,80, 100, 120, and 140 per cent of the amount equivalent to the dlz(S04)3.18H20 mere diluted to 1 liter and transferred to a second separatory funnel mounted beside the first one. The two solutions were allowed to run together at a uniform rate into a glass jar containing 3 liters of water while the mixture was stirred rapidly.
FIGURE1.
TITRATION CURVES SULFATE
ALrJMrNmf
FOR
