Clarification of Acid-Hvdrolvzed Mash and Beer for the P;od&ion of 2,3-Butanediol from Corn A. J. STROHMAIERl Joseph E . Seagram & Sons, Inc., Louisville, Ky.
C. L. LOVELL Purdue University, Lafayette, Ind. T h e filtration and centrifugation characteristics of unfermented and fermented acid-hydrolyzed corn mashes used in the pilot plant production of 2,3-butanediol were determined with small scale laboratory apparatus. It was found that the clarification of these materials is greatly influenced by their hydrogen ion concentration and temperature. Optimum pH varies, depending on the type of mash. Thus, highest filtration rates were obtained at pH 5.0 with laboratory cooked unfermented mash (batch process); pH 5.0 and 6.2 with pilot plant cooked unfermented mash (continuous process); and pH 4.8 with pilot plant fermented beer. At constant pH, highest filtration rates were obtained at the highest temperature (210"F.). The clarification of these corn mashes by either filtration or centrifugation was further improved by the use of small amounts of bentonite (swelling type) added to the mash at pH 2.0 to 3.0 and high temperatures. It was disrobered that unferiuerited acid-hydrolyzed corn mashes can be clarified readily by centrifugation when such mashes are treated with 1 to 2% (by volume) of various halogenated hydrocarbons at pH 6.0 to 7.0 and at any temperature below the steam distillation points of the latter.
A
hand, the clarification of its related products, distillery residues, has received much attention, especially since the repeal of prohibition. Unfortunately, most of the processes suggested are too costly when applied on an industrial scale and consequently find little, if any, application in the modern fermentation plants. Cooley ( 1 ) and Willkie and Prochaska (6) described separation methods in their discussions of modern by-product recovery systems; the usual method of separating suspended solids in distillery residues utilizes screens, presses, centrifuges, 'and filters, with little or no preliminary physical or chemical treatment of suspensions. Fulton (2) points out, however, t h a t in certain cases bentonite treatment provides a simple and efficacious solution of t h e spent-mash clarification problem and, therefore, should not be overlooked. Consequently, the present investigation was concerned chiefly with laboratory filtration and centrifugation of various corn mashes. PREPARATION OF CORN MASHES
The unfermented batch-cooked acid-hydrolyzed n:n>li was prepared from a mixture of 2800 grams of ground corn (approximately SOYo retnined on KO.30 screen) in 7 liters of 0.33 S sulfuric acid solution. This was heated in a Pyrex carboy by direct steam injection t o 307" F., held for 4 minute?, he:itrd t o 324' F., held another 4 minutes, and blown throuph :i copl)er cooling coil into a sterilized glass container. The mash \vas diluted to 15.84 liters (38 gnllons/bushel), which resultcd in a suqar content totaling approximately l l . O ~ o and euqwnded solids totaling 2.0 t o 2 . 5 7 , . The unfermented continuous-cooked mash was prepared on a pilot plant m i l e by the continuous cooking proems described by Unger and Grubb (4). The rates of flow t ~ i 'corn, water, and steam were adjusted t o give a 40 to 44 gnllon per bushel mash : the result was approximately 10.070 sucnr content a n d 2.05; suspended solids. The fermented continuous-cooked mash was prepared from the unfermented continuous-cooked mash described, by fermentation with Aerobacfer aerogenes (Seagram 7 7 6 ) . The resulting beer hnd a butylene glycol content of approximattaly 3.87, i n t i totnl suspendetl solids of approximately 3.0Yc.
T PRESEST one of the principal components in the pro-
duction of synthetic rubber is butadiene. T h e two nisin processes for the manufacture of this gas utilize, as a starting material, ethyl alcohol on the one hand and butane or butylene on t h e other. T h e latter two are petroleum refinery products which have also attained importance as starting materials for high octane gasoline. A third process, in the pilot plant stage, is intended to by-pass the alcohol production step and obtain butadiene b y direct fermentation of grains or other fermentable materials to a butadiene intermediate, 2,3-butanediol. Once this intermediate has been separated from the fermented mash, it can be easily processed to butadiene. A method which has been seriously considered for the separation of 2,3-butanediol from fermented grain mash (called glycol beer) utilizes liquid-liquid extraction with n-butanol as solvent. This process requires a \veil clarified beer before extraction can be effected. Very small amounts of undissolved solids in the beer feed cause excessive foaming in the extraction column and consequent loss of appreciable amounts of both ;]vent and solute. This paper is concerned Jvith the elimination of these troublcsorne srispendcd solids in acid-hydrolyzed corn mashes. Since the cooking and use of acid-hydrolyzed corn mash are still i n the development stage, there is no reference to the clarification of this particular product in the literature. On the other Present address, I;. I . d u P u n t de
SFiniiiirs
APPARATUS AND PROCEDURE
The nppnrntus used in filtration experiments consisted of a &inch Biichner funiwl connected t o a 250-ml. graduated cylinder maintpinrd at 15.0 inches of mercury (vacuum) by means of a n automatic regulator. I n centrifugation experiments the apparatus consisted of a Clay-hdams Senior variable-speed 15.0ml. test t u b e centrifuge (centrifugal force = 820 X gravity a t 2000 revolutions per minute maximum speed) and a De Lava1 high speed centrifuge (centrifugal force = 30,000 X gravity a t 18,000 r.p.m. masimum speed) employing 15.0-ml. conicnl centrifuge tubes graduated t o the nearest 0.002 cc. at their elongated tips, Treatment of mash samples and temperature control were effected in n one-liter three-neck flask equipped with npit:itor, elccti,ic he:iting jacket, thermostat, and reflux condenser. .\I:ish snniples were trcated with concentrated sodium hytlroside or sulfuric acid solution, and p H measuremmrs \ v c w made a t 70 * 2" F. From 300 to 500,ml. of this mridi Lvc'i'e
a n d C o m p a n y , Inc., ivilrning-
t ,n. Del.
721
2%
.
I
- - - --
I
-=
v1
a
FERMENTEDCONTINUOUS-COOKED ACID-HYDROLYZED(GLYCOL) BEER, The changes in composition, etc., of acidhydrolyzed corn mash during fermentation became apparent when an attempt was made to clarify the resulting product. Thus, although a definite optimum point mas again indicated a t p H 4.8 and 210" F., it proved impossible to obtain any but extremely turbid filtrates without resorting to chemical treatment. When bentonite was used, this fermented material became quite easy to clarify. The filtrates thus obtained proved to be crystal-clear and light amber in color. Highest rates of filtration rvere obtained between p H ,1.6 to 3.2 but decreased sharply beyond this
TURBID FILTRATES
CLEAR F I L T R A T E S
0
,o m
293
u3 0
BEER
+
I
1.00% B E N T O N I T E a625
z -
BEER
-
ZlOOF.
W
+
~
!
15c
0
w 0 2
i
\+\
v
V y_
IQC
.
.-------- - +\. - - -.-\
c Q
+\
+ CL
2
LL
.
jQ
+ .
2
2
0
0 -
I ' 1 UhTREATED BEER
, ' -, ---
-&
~
qi----L
70%:
--A-A
-ir----&
______
-@
-A
0 P H O F BEER
Figure 1.
Effect of pH and Temperature on Filtration of Lntreated Bentonite-Treated Pilot Plant Beer
I n explanation of the previous observations it should be pointed out that cereal grains contain considerable amounts of various proteins and, because of their amphoteric nature, exhibit some Unusual electrochemical Phenomena. Thus, in general, proteins are least soluble and most easily precipitable b i heat at or near their isoelectric points. It is conceivable, therefore, that the maximum filtration rates secured near pH values of 5.0 and 6.2 may be due to the precipitation of certain troublesome proteins at their isoelectric points, On this basis it also seems to assume that the added to mash and beer for PH adjustment begin to form certain colored akali-Protein combinations a t these isoelectric points; this would explain the sudden increases in color density at maximum filtration points, This is also borne out by the fact t h a t ammonium sulfate or trichloroacetic acid (precipitants for proteins) will precipitate these dark colored compounds and leave light colored filtrates such aa
poured into the three-neck flask; the required amounts of Or liquid treating powdered (Volclay were added slowly with vigorous agitation. I n the filtration experiments the apparatus was brought to 15.0 inches (Hg) of vacuum. A new disk of dampened filter paper (IVhatman S o . 40, 9.0 cm. in diameter) was inserted in the Buchner funnel. Mash samples were poured over the filter paper, and the amount of filtrate was cpllected in lo-second intervals as noted by stopwatch. I n the centrifugation experiments 10-ml. mash samples w r t ' withdrawn from the three-neck flask and centrifuged a t 2000 r.p.m. for periods of 10 t o 80 seconds with a fresh sample for enrh centrifugation. The superjacent liquid was transferred to ccntrifuge tubes of the high speed machine and rotated a t 18,000 r.p.m. for 2 minutes. Practically all suspended solids remaining from the first centrifugation were thus separatetl and measured. RESULTS O F FILTRATION EXPERIMENTS
UNFERMESTEDBATCH-COOKEDACID-HYDROLYZED CORNh l . 4 ~ ~The . most pronounced efferts noted in filtration studies on acid hydrolyzed corn material were those of temperature and hydrogen ion concentration on filtration rates. Greatest rates of flow were obtained at 210" F. and p H 5.0. Also, the filtrates obtained in the pH range 3.1 to 7.0 were quite clear but attained increasing cloudiness as the p H diverged from these limits. A peculiarity which may relate to the filtration characteristics of this mash was its variation in color with changes in pH. Klett-Summerson colorimeter readings indicated no color change until a pH of 5.0, the optimum filtration point, was reached. Beyond this point the color became progressively darker. UNFERMENTEDCONTINUOUS-COOKED ACIDHYDROLYZED CORNMASH. Mash cooked by the continuous process also exhibited an optimum filtration point at a p H of 5.0. However, in contrast t o that produced batchwise, an even better optimum point was obtained a t pH 6.2. Greatest changes in color density occurred a t pH 6.2 to 6.3. I n a n effort to obtain greater clarity and higher rates of flow, the mashes were subjected to bentonite treatment as outlined in the work of Steiger (3) and Fulton ( 2 ) . Excellent improvement in clarity and rates of flow resulted in the p H range 2.5 to 3.5. Above pH 4.0, however, clarification by this method became rather difficult.
DISCUSSION O F FILTRATION RESULTS
a11d
U N T R E A T E D MASH,pH
5.94,
=
TEMP.
IBOOF.
+TI---
\ WASH pH
/
=
+
2.0% IVOLUKE)
6.70,
TEMP.
-
\ d
'9
=
I TRICCLORETHVLENE,
!
ISO'F.,
! I
i
I
I
1
I
,
ENTONITE #325,PH TEMP.
,
a
= =
1.61 IBOOF.
A
,
.01 T I M E OF. C E N T R I F U G A T I G N (SECONCS)
Figure 2.
Time of Centrifugation vs. Turbidity of Treated and Untreated Pilot Plant >lash
Near optimum oonditions of pH, temperature, and doncuotrution
4
July, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
those usually found in the pH range bthlow
723
4.0
-
D
optimum filtration points. The high rates of filtration obtainable by the use of bentonite in mash or beer a t low p H and the relative inefficiency of the same addition agent a t any p H above 4.0 may well be attributed to the electronegative nature of the colloidally dispersed bentonite particles; thc latter readily ncutralize and agglomcrate the electropositively charged proteins (at low pH) ill the mash. KOeffort was madc to determine the identity of the proteins responsible for these phenomen;r except for an attempt a t correlating the observed optimum filtration points with published d a t a on isoelectric points. Unfortunately, published d a t a on isoelectric points vary widely. Although zein and glutelin are strongly suspetted t o be the responsible proteins, it was impossible to arrive a t any definite conclusions. RESULTS O F CENTRIFUGATION EXPERIMENTS
3
0 2,0 ~
t
z
W
V 4
1.0 a m
g -
0.8 0.6 0.4
2
0 ffl
s
0.2
0
z
W
a.
ffl 1
-
0.1
5 2
.06
u)
.08
W
0
5 .04
*
>.
c e M
1
.02
1
0 P H OF HASH
The use of bentonite as a mash clarification Figure 3. pH C S . Turbidity of Treated and ITntreated Pilot Plant Mash (30 Seronds at 2000 R.P.\l., 820 X (;ravity) agent was further investigated by subjecting the suspensions to centrifugal force. In an effort t o improve existing methods of treatment, various other chemicals (principally nitropropanes, polar ketones, and trichloroethylene are 0.8% by weight and 2.0% by volume, respectively. trichloroethylene, Celite filter aid, and activated charcoal) were FERMENTED COXTIXUOVS-COOKED ACID-HYDROLYZED (GLYalso tried as clarifying agents. Of these, only trichloroethylenc COL) BEER. Similar centrifugation experiments were carried and the related halogenated hydrocarbons were found to increases the rate and degree of clarification obtainable by centrifugation out on fermented beer. Contrary t,o expectations, trichloroof this type of mash. Table I shows that this effcct is especially ethylene and all the other halogenated hydrocarbons which had noticeable with some of the chlorinated and brominatod hydrobeen establishcd as effective clarifying agents for unfermcnted carbons of higher molecular weight. Thus, unfermented mash mash proved to he ineffective in the clarification of fermented material. not treated wit.h any clarifying agent could not be clarified below Bentonite treatment resulted in excellent clarification, optia suspended solids content of 0 . 2 5 , even after 80 seconds ni' centrifugation a t 2000 r.p.m. The use of 2.0% (by volumr) mum condit,ions being pH 2.0 to 3.0, 210" F., and 0.4% (by of hexachIoropropylene, however, causcd the deposition of' :ill w i g h t ) or more of bentonite. but 0.045% solids in onlv 10 seconds - suspended . under the same conditions. I;NFERI\IEP;TED CONTISCOW-COOKEDACIDHYDROLYZED CORNMASH. Figure 2 illustrates 0 -3 4 0 the effect of centrifugation time upon unfer0 2 mented mash treated with bentonite and tric chloroethylene a t optimum pH, temperature, 2.0 0 and concentration. Both of these are effective 4 7 a clarifying agents for unfermented a6d hydroW 4 I .o lyzed corn mash. v) I Figure 3 shows the effect of p H upon the clari- 0.8 0.6 fication of treated uhfermented mash. Bentonite-treated samples are most easily rlarified 0.4 in the pH range 1.5 to 5.0, wheizas trichloroD a W ethylene-treated samples clarify best at or near 3 0.2 their isoelectric point, p H 6.7. a. a The effect of temperature upor) unfermented ffl mash treated with bentonite and trichlorow 0.1 ethylene is indicated in Figure 4. In both SO8 cases higher mash temperatures result in greater .Ob clarity. I n the latter, however, this rffect nudA denly disappears a t 150" F. and above because I .04 * r of the removal of trichloroethylenc by steam a distillation. .02 It is usually desirable to keep t h r amounts of 3 70 90 IIO I30 I50 170 I90 210 IMASH TEMPERATURE ( " 6 ) treating agents a t a minimum; Figure 5. illustrates the effect of their concentrations upon clariFigure 4. Temperature us. Turbidity of Treated Pilot Plant hlash fication. Optimum concentrations of bentonite (30 Seconds at 2000 R.P.R.I., 820 X Gravity)
-
u)
-
z
724
,
INDUSTRIAL AND ENGINEERING CHEMISTRY S (VOLUME) TRICHLORETHYLENE 1;. I .i5 2i0
Vol. 38, No. 7
to the unfermented acid-hydrolyzed mash, centrifugation with halogenated hydrocarbons will simplify subsequent fermentation and glycol separation problems. 0 -I The minimum concentrations of treating agents IL 2.0 found necessary for efficient clarification of these W Y materials in the laboratory might be reduced still 2 further by the use of industrial type equipment. e w 3 1.0 Certain commercial centrifuges are designed to operate In C.8 a t higher-than-atmospheric temperatures and pressures. 0.6 Such equipment would allow best exploitation of bene0 -I ficial temperature effects and would no doubt result in 0 0.4 notable economy of treating agents. 0 The experiments indicate that the effect of halo8 z genated hydrocarbons on centrifugation of unfermented 0.2 acid-hydrolyzed mash is not due to any coagulating 3 action such tm is noted in the use 'of bentonite. It is more likely that their effect is due to the combination of low surface tensions, excellent solvent action, .06 and high specific gravities. Because of the first two dp characteristics these chemicals probably displace the 'I*- .04 water and corn oil on the surface and in the interstices 0 of the solids, By virtue of the third characteristic m a .02 this displacement results in an increase in apparent a I0 0.2 0.4 0.6 0.8 I .o I.2 specific gravity of the mash particles, which allows % (WEIGHT) BENTOYITE #325 extremely rapid settling when the particles are subFigure 5. Effect of Concentration of Bentonite and Trichlorojected to centrifugal action. Also, judging from the ethylene on Clarification of Pilot Plant Rlash varying effectiveness of these chemicals upon fermented N e a r optimum oenditiona of pH and temperature; 30 seconds a t 2000 r.p.m., and unfermented mashes, this wetting and displacing 820 X gravity action is dependent upon certain unknown charncteristics of the suspended particles. It is hoped that DISCUSSION O F CENTRIFUGATION RESULTS similar experiments on more diversified clarification problems will ultimately explain these effects. Probably the most important observation resulting from these
2
0
4.0
0
0,s
liO
2i5
-
v)
v)
v)
3
v)
E
centrifugstion experiments is t h a t concerning the effect of halogenated hydrocarbons on the rate and degree of clarification obtainable on unfermented acid-hydrolyzed corn mash. It is possible t h a t this property will find application in other clarification problems as well. The use of halogenated hydrocarbons instead of the usual clarifying agents such as bentonite, etc., offers some definite advantages. This group of chemicals is immiscible with water and can, therefore, be easily recovered from the clarified products by flashing or steam distillation. Thus, the final products obtained are devoid of contamination and the treating agents can be recycled in the process. Although applicable only
T A B L EI. EFFECTOF HALOGENATED HYDROCARBONS ON SusPENDED SOLIDSREMAINING IN SUPEIUACENT LIQUIDAFTER CENTRIFUGATION AT 2000 R.P.M. A N D 150" F." Chemical Treatinp: Agentab
10 sec.
Suspended Solids Remaining, 20 30 40 50 60 70 sec. sec.. aec. sec. sec. sec.
80 sec,
ACKNOW LEDG.MENT
The authors wish to express their appreciation to Paul Kolachov for his guidance in this project and to Joseph E. Seagram & Sons, Inc., through whose sponsorship this work was made possible. LITERATURE CITED
Cooley, L. C., IND.ENG.CHEX.,30, 615-21 (1938). Fulton, R. R., Chem. & M e t . Eng., 51, 184 (1944). Steiger, W., Brit. Patent 465,693 (May 13, 1937). Cnger, E, D., and Grubb, H. W,, Div. ot Sugar Chem. and Tech., 107th Meeting of A.C.S., Cleveland, 1944. (5) Willkie, H. F., and Prochaska, J . A , , "Fundamentals of Distillery Practice", 1st-ed., Joseph E. Seagram & Sons, Ino.,
(1) (2) (3) (4)
1943.
PREBESTED o n the program of the Division of Agriculture and Food ChemiaCHEMICAL SOCIETY. try of the 1945 Meeting-in-Print, AMERICAN
Pilot Plant PropDgator hlashd, p H 5.76 None Hexachloropropylene Polyohloropropane Tetrachloroethylene Hexachlorobutadiene Trichloroethylene Carbon tetrachloride Chlorobenzene
3 1.5 1.0 0.6 0.6 0.4 0.3 0.2 0.045 0.03 0.02 0.02 0.015 0.015 0.01 0.01 0.1 0.03 0.02 0.018 0.01 0.018 0.01 0.01 0.1 0.04 0.03 0,025 0.018 0.02 0.01 0.015 0.1 0.04 0.02 0.02 0,015 0.02 0.02 0.02 0.2 0.04 0.03 0.025 0.02 0.02 0.02 0.03 0.25 0.07 0.04 0.03 0.02 0.02 0.018 0.015 1 0.9 0.3 0.25 0.3 0.2 0.2 3 Pilot Plant Acid-Hydrolyaed Corn Mash, p H 6.10
None Tribromoethylene a.8-Dibromoethylene
7 2 2
5 4 ... 3 . . . 2.5 0 . 3 0:15 0.00 0.035 0.035 0.02 0.02 0 6 0.4 0 3 0.12 0.08 0.06 0.04
Initial temperature just prior to centrifugation. 2 0% of mash volume. lkzum8 liated are oercentanes bv volume as determined by special De Ea% centrifuge a t f8.000 r,.p.,m. d An acid-hydrolysed mash similar to t h a t described except for It8 reater dilution (90 t o 94 gallons per bushel instead of 40 t o 44 gallons per bus%el). 4
b
e
~
Molecular Weight-Physical Property Correlation for Petroleum FractionsCorrection An error has been called t o our attention in this article which AND ENGINEERappeared in the April, 1946,issue of INDUSTRIAL ING CHEMISTRY.In Table X, page 447, the figure 610 in t h e molecular weight column should read 620.
1. W. MILLS .4.E. HIRSCHLER S. S. KURTZ,JR.
