RECOVERY of 2,3=BUTYLENE GLYCOL from FERMENTATIQN LIQUORS R. H.B L O M , D. L. REED', AARON EFRON, AND G. C. MUSTAKAS NORTHERN REOIONAL RESEARCH LAIORATORY.
U.'S. DEPARTMENT OF AGRICULTURE, PEORIA. ILL.
A
possible industrial source of butadiene is 2,3-butylene glycol, produced by t h e fermentation of cereal grains. The recovery of butylene glycol from a fermentation liquor Is difficult because of its comparatively hlgh boillng point and t h e presence in t h e liquor of 2 parts of nonvolatile solids t o 1 part of glycol. A recovery process is described i n which a concentrated liquor is steam-sttrfpped in a paoked column a t a n elevated pressure. Experimental work underlying this step of t h e process i s described.
ACCHARIFIED wheat or corn maslies have been fermented with a strain of Aerobacter aerogenes to produce a beer containing 3.5 to 4.0% meso-dextro-2,3-butyleneglycol (6) boiling a t 183' C., 0.1 to 0.2% acetylmethylcarbinol boiling a t 143' C., 0.3 to 0.5% ethanol boiling a t 78.32' C., and 6 to 8% nonvolatile solids. Acetylmethylcarbinol and water form an azeotrope (8) which boils a t 99.5' C., and the alcohol-water szeotrope boils a t 78.15' C. The principal problem of recovery, therefore, is the separation of the highest-boiling volatile compound, glycol, from the nonvolatile solids, present in the a p proximate ratio of 2 parts of solids to 1 part of glycol. Several methods for accomplishing this step have been studied by various investigators, but few of their results have been published. These methods include solvent extraction, spray drying, kerosene distillation, alcohol precipitation, and drum drying. I n the recovary process developed a t this laboratory the beer is concentrated and the glycol is removed from the concentrate or sirup by Bountercurrent steam stripping. Preliminary consideration of the stripping process led to the conclusion that the operation should be conducted under pressure for purposes of steam economy and greater equipment capacity. Liquid-vapor equilibrium data for the butylene glycol-water system show that the glycol content of vapor from a given liquid increases a t a rapid rate as the pressure on the system is increaaed (1). For example, a water solution containing 10% butylene glycol by weight is in equilibrium with vapor containing 0.33% glycol by weight when the solution is boiled udder an absolute pressure of 2.45 pounds per square inch. When the pressure is atmospheric, the vapor contains 1.0% butylene glycol ; and at 55 pounds per square inch gage it contains 2.5%. Theoretically 30, 10, and 4 pounds of stearn, respectively, would be required to remove the glycol from 1 pound of such a solution by counterourrent stripping. The advantage of stripping a t elevated pressures is obvious.
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tinuous center opening which was plugged with a piece of capped O.Mnch pipe. Figure 1 is a diagram of the column and auxiliary equipment. Sirup was prepared in an evaporator by concentrating the beer, made by the fermentation of malted corn mash. The concentrate contained 13.8% glycol and approximately 30% solids. It was pumped a t a constant rate through a preheater and into the top of the stripping column. Steam was introduced at the base of the column and vapor issued from the top through a flowcontrol valve. The pressure in the column was 110 pounds per square inch gage. The vapor was condensed and the condensate weighed. Stripped sirup was discharged from the base of the column through a throttled valve. For purposes of calculation, the effective steam rate, P, to the base of the column was assumed equal to the rate at which con-
Pressure Gouge
Vapor Temp.
PRELIMINARY -PER1 MENTS
A stripping column 13 feet high was constructed of &inch jacketed pipe and packed with 2.6-inch ceramic spheres to a height of l1.5 feet. The arrangement of packing created a con1 Rwent
WWh.
add-,
Puget Sound Pdp and Timber Company, Bellinfihsm.
1
Stripped
Figure 1.
Sirup
Butylene Glycol Strlpping Column
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densate was formed. This is true only if the column is operated adiabatically and if there is no difference in the latent heats of vaporization of glycol and water. Since the glycol content of the condensate was small, the effect of the difference in latent heats was insignificant. However, because of heat losses there was some condensation of. vapor within the column. I n order to obtain applicable values of the steam rate, the assumption was thus made without serious error. The column was operated until the butylene glycol content of the condensed vapors, as measured by refractive index, became constant. When a steady rate was attained, a sample of the condensate was taken for chemical analysis. Data in Table I show that 95% of the glycol in the sirup was vaporized by the use of 6.08parts of stripping steam to 1 part of sirup.
the experimental curve from the ideal line. Actually, a recovery of 95.8% required a P / F ratio of 6.08. SLUDGE FORMATION. The fermented beer contains both dissolved and suspended solids, and after evaporation 55 to 60% of the total solids in the resulting sirup are insoluble. Approximately 25% of the total solids is ash, composed principally of calcium sulfate and carbonate. Several runs were made to determine whether the insoluble solids of the feed sirup were flowing through the packing, since their accumulation would eventually plug the column. The stripping column was operated until steady-state conditions were established, and the stripped sirup was then collected for a 30-minute period. The following results show that a large part of the solids in the sirup was being deposited in the column: Run No.
TABLE I. VAPORIZATION OF BUTYLENEI GLYCOL BY COUNTERCURRENT STEAM STRIPPING OF GLYCOL EVAPORATOR SIRUPAT 110 POUNDS PER SQUARE INCH GAQBPRESSURE^ Run No.
1 2 3 4 5 0
7 8 9 10 11
F Sirup beed Rate Lb./dr. 25.8 24.0 21.3 23.3 25.6 23.4 23.3 27.0 27.6 27.0 27.4
Glycol idSirup,
%
13.8 13.8 13.8 13.8 12.25 12.25 la.25 12.25 12.25 12.25 12.26
Condensate Rate P Lb./Hr: 5.5 6.2 17.0 29.4 50.0 62.4 80.0 94.6 115.7 138.8 106.7
Y p , Glycol
in Condensate, 3 '6 4.18 4.44 4.62 4.41 2.83 2.32 2.39 2.33 2.44 2.09 1.93
ProductR Glycol Feed Slripped Ratio P / F , from Lb./Lb. Sirup, % 6.5 0.21 8.1 0.25 24.8 0.76 40.2 1.20 45.1 1.95 50.0 2.67 07.4 3.40 65.2 3.43 83.4 4.19 87.8 5.14 05.8 0.08
Figure 2 shows the relation between glycol recovery and the amount of stripping steam used per unit quantity of sirup. The percentage recovery of glycol from the sirup is given by the equation:
vThere P
-
product rate (assumed equal to rate a t which s t r i p ping steam is supplied), lb./hr. F = sirup feed rate, lb./b. Y = butylene glycol content of product, lb./lb. $ = butylene glycol content of feed sirup, lb./lb.
For a given sirup, Xj is constant, and a t any fixed pressure Yp also becomes constant if equilibrium is attained between the liquid and the vapor in the column. Therefore, under conditions of equilibrium, if R is plotted against 100 the ratio P / F a 90 straight line results 80 with a slope equal to 100(Yp/X/).The 70 b r o k e n l i n e of 60 Figure 2 illustrates 50 these ideal operata 40 ing conditions exd 30 trapolated to 100% r e c o v e r y and a 20 corresponding P / F ratio of 3.1. That - o I the column was 0 1 2 3 4 5 6 7 PRODUCT-FEED RATIO, w, L ~ B . grossly ine%hnt-Le., contained aninFigure 2. Change i n Glycol Res a c i e n t number covery i n Vapors from 13-Foot oftheoretical plates Stripping Column with Change in Steam-Sirup Ratio a t a Pressure of isindicatedbYthe 110 Pounds per Square lnoh Gage rapid deviation of
$
g
Vol. 37, No. 9
12 13 14 15
-Soli&, In feed 7.34 0.81 6.91 2.85
Lb./Hr.In atripped sirup 4.58 4.97 3.93 1.66
Solids Acoounted for, % 62.2 73.1 50.9 54.3
Since the column was flushed with water between experiments and the runs did not last long, the amount of solids deposited in the column was not enough to cause noticeable flooding. However, when the column was opened after the experiments were completed, the spaces between the pieces of packing were found to be almost completely filled with sludge. This substance was insoluble in water, but its appearance was entirely different from the insoluble solids of the sirup. A chemical analysis of the sludge gave inconclusive results concerning its composition. It is believed that the deposit is a decomposition product of both soluble and insoluble constituents of the sirup, and that its formation is a function of the temperature of stripping. It was recognized that removal of the insoluble solids by filtration of the beer before concentration to sirup would probably lessen the amount of sludge formed during stripping. However, the various methods of filtering and clarifying were found to be impractical because of low operating rates and the high retention of glycol in the separated solids. PILOT PLANT EXPERIMENTS
The results of the preliminary experiments showed that it was possible to obtain good recoveries of glycol from sirup by the steam stripping process. However, if the process is t o be practicable, a method of operation is required which will provide for the removal of the deposited sludge. The column used in the preliminary experiments was lengthened to 27.5 feet to increase the number of theoretical plates. Experiments were conducted to determine a satisfactory type of packing and the maximum operating pressure which could be used without excessive formation of sludge. The amount of sludge deposited was indirectly estimated by the pressure drop across the column. Although sludge was formed at a pressure of 55 pounds per square inch gage, it had a soft texture and couid be flwhed or washed off the packing by the action of water and steam. The sludges formed at higher operating pressures were harder and more resistant to removal by washing. It was determined that the packing must be large and open in type to minimize the tendency of the sludge to bridge the voids and thus plug the column. For example, iron Raschig rings, 1.9 X 1.9 inches, were found to be a more satisfactory packing than large unglazed ceramic spheres. However, they also plugged or fouled rapidly when packed in a random manner, and were difficult to clean by the countercurrent washing procedure which will be described. An extended experiment proved that by arranging the iwn rings in an orderly manner and incorporating a water washing cycle in the operation of the stripping column, prolonged operation was possible. The column was packed with Raacbig rings made by cutting 1.9-inch pieces from standard 1.5-inoh pipe, These rings were stacked vertically in circlee around a capped 1.5-inch pipe which
September, 1945
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stripping, IIBCBIIS~ pravioua wmlts Iiad indicated that the siudge from im wlkalinc airup waa softer rind more itmenshle to removal
by water w;id,ing than that from an mid sirup. Samples of feed sirup i d sl."pped sirup were t a k n regularly during the run. .411 of the condensate was eolicctcd, mixed, and sampled at the end oi the experiment. During preliminary runs the ~iiiountof condensation within
the colunin was memured. When this wlu added to the oondonsilta oi 210 pounds per hour which wlu oolleeted 88 product, the tot,nl steam used undor the operating conditions was equivsIcnl 1.0 II superficial vapor velocity of approximately 2 feet pet second. Throughout most of the run the sirup feed rate wss 42 poonds per hoar; hence, the ratio of Steam to sirup, P / F , was 5. Those rates were maintined except for the first 24 houm of the mperiment, when 8 slightly lower sirup feed rate WBB used. Tho experiment W&F oonducted for 7 days without in'terrupting I he flow of ~ r o through m the column. During the first 24 houm I hn differential pressure cross the column increased from 0 to 1.5 inches n i mercury. The sirup feed was stopped, and the column wis allon,rd to drain for 15 minuteu. The p m u r e drop, sttribI u l , d to retention of thickened sirup or sludge, WBS then 0.9 inch ai mweory. Water, preheated to ~.pproximately240' F., WBB
Figure 3.
View of Pilot Plant Shewing Triple-Effect Evaporatop and Stripping Column
plugged tha ccntrsl opening. Each layex of rings wa- ru1uli:d ane-half ring in reiwence to lhe adjacent layws. Tlir total height of packing was 23 feet. h circular disk, 4 inclics in diurneter, on which the enlering airup fell, was fixcd in t l w column at approximately 18 inches above the top of the pmkiep. A duplex proportioning pomp was used to iced sirup st a p proximately 80' F. into the top of tho t ~ > w cat r a cwistant rate fmm a sirup storsge tank whioh was set on scales to allow froqueni. rlicoking of t.he feed rat
