Packings for Vinegar Generators RUDOLPH J. ALLGEIER, REUBEN T. WISTHOFF,
AND
FRANK M. HILDEBRANDT
U. S. lndusfrial Chemicab Co., Division of Nafional Distillers Producfs Corp., Bulfimore, Md.
M
ODERN vinegar generators of the circulating type gener-
ally employ beechwood shavings as packing. However, the type of packing material used in the generators ha3 varied considerably during the period in which this kind of equipment has been employed. Often the filling that is most readily available or cheapest in the region selected for manufacture has been used, such as coke, pumice, rattan, grape and other twigs, corncobs, etc. (6). Frequently, operators of vinegar plants, particularly those using specially denatured alcohols as feed, would like to change the type of packing for reasons of economy, or because the conventional beechwood shavings are not readily obtainable. While it is known that performance of a generator changes when the packing is changed, the authors are not aware of a study of the reasons for the variations. This paper deals with a series of experiments that were made in small scale generators over a period of several years using different types of packing. Marked differences in performance resulted from the use of the several kinds of packing. More important, it was possible t o obtain efficiencies almost equal to that of beechwood shavings if appropriate measures were used in handling the generators. This eyperimental work may be useful to vinegar manufacturers as a guide to realizing the most efficient operation of generators packed with materials other than conventional shavings. Experimental Generators Are Replicas of Commercial Circulation-Type Units
The apparatus used in these pilot plant studies has been dcscribed (1, 2, 3 ) . The generators are small replicas of cominercial circulation-type tanks and are operated under conditions as nearly comparable to factory conditions as possible. Experience over a number of years of operation has shown that the results ohtained in this pilot plant can be applied t o plant size generators of either the modern continuous or the older single-pass type. The feed for the generators was prepared by diluting S.D. 3 5 h formulated according to U. S. Government specifications. Five volumes of 85 to 88% ethyl acetate (technical) was added to 100 volumes of 190-proof alcohol to make S.D. 35A. This was then diluted with tap water to a concentration of 9.0 to 9.2 grams of alcohol per 100 ml. for use as generator feed. A fermented solution of a malt concentrate (Diamalt, marketed by Standard Brands for use of bakers) was used as a basic nutrient. The concentrate was diluted to 15 grams per 100 ml., fermented by yeapt, and filtered through No. 12 Whatman paper. The filtrate m-as added a t the rate of 25 ml. per 2000 ml. of diluted alcohol charge. This nutrient, referred to as normal malt nutrient, was developed over a period of years in order to attain optimum alcohol conversion in the 7-day cycle. When nutrients were increased the gene.-ators were speeded up and overoxidation occurred. Other nutrients were added, as described. The method of operation has been described (1, 2, 3). The cycle of operation, consisting of introduction of the charge, fermentation, withdrawal of product, and addition of next charge,
October 1954
was 7 days, except when otherwise specified. The i-day cyc’le resulted in the highest efficiencies ( 1). Presentation of Data. This study of packing materials covers a period of several years. The result,s are given graphically rather than in tabular form to show changes in generator behavior and the relation of these to the management of the generator. Tn-o procedures for presentation of data, described in detail in previous papers (1, 2 ) have also been used in this paper. These are th(. expression of the performance of t’heexperimental generators as pt!rcent,ages of a control, and the use of a moving average of four periods in plotting the graphs. The first procedure rules out factors that affect the whole battery of generators arid the seeonti ensures that variations associated with a single c y r l e of operation will not have a disproport,ionate influence on the results. Coke, rattan, and Berl saddles were studied. Beech shavings served as a control. Coke and rattan are of interest tiecause t,hey may be easily obtained in this country and Berl saddles were included in order to investigate the relation between surfnee are:: of packing and convernion capacity. Surface Area and Impurities Are Critical Factors in Use of Coke a5 Packing
The first coke experiment employed a packing of lwge pier.c.5, ll/z to 2 inches in diameter, prepared by washing Rith water for 2
days. After a preliminary inoculation, the regular S.D. 35.4 charge containing malt nutrient was fed to the generator. S o appreciable growth of organisnis or satisfactory yield Tas 01)tained after several months, and the experiment was discontinurti. The next experiment, run 2, employed a packing composed of alternate layers of coke from run 1, reduced to 1/* inch in d i a m eter, and beechwood shavings. There were seven layers, fo;u~ of shavings and three of coke, in 36 inches of packing. Nutric-nt added was the same as in the control generator. After 10 .ivceic+ of operation the mixed packing generator equaled the conti,ol i n efficiency and remained constant thereafter (Figure 1). In thi. light of subsequent experiments, it would appear that the sh:iTings kept the generator “seeded” with an adequate bacterial population for normal performance. Since this good result W A F ohtained, the coke of this generator was placed in a ncr- generator. Run 3 was set up by filling the lower half of a generator ~ i t h uninoculated, 1/2-incli-diameter coke. The coke separated from the chips in run 2 was placed in the upper half. Apparently ail inadequate population of organisms was retained in the coke R S the new generator dropped sharply in efficiency, :is shown in Figure 1 . The experiment was, therefore, discontinued niter :3 running weeks. These experiments demonstrated that the employment of coke presented difficulties, presumably due to the fact that the organisms did not readily establish themselves on the surface of the packing. In subsequent rum, therefore, impurities were removed by acid washing the coke and the surface was increased by using smaller pieces. iiddition of large amounts of nutrient to
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
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C O K E PACKING - R U N S
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WEEKLY CYCLES I I 1 25 30 20
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Performance of Vinegar Generator Packings
promote bacterial multiplication, and a special effort to get the acetic bacteria established by liberally adding warm vinegar (fresh untreated vinegar from an active generator) were also undertaken. Run 4 employed coke, inch in diameter, washed with 10% hydrochloric acid and water (Figure 1). During the first 4 weeks (period A ) , a 50:50 mixture of warm vinegar and regular S.D. 35A was fed. The yield dropped rapidly, and for the next four cycles (period B ) only warm vinegar mas circulated in order to increase the flora in the generator. When alcohol was reintroduced into the fecd and efficiency calculations were made, the starting point was 85%. Even though the malt nutrient was doubled, efficiency dropped t o 15% in about 6 weeks and remained a t that level for the following 5 weeks, as shown in period C. Sutrient additions of steep water a t the rate of 5 grams per feeding were made for 1 week (period D),10 grams were added the next week (period E ) , followed for 3 weeks (period F) by additions of a mixture of 5 grams of steep water and 5 grams of autolyzed yeast (autolyzed yeast extract, Type No. 75, Vico Products Co., Chicago, Ill.). The relative efficiency increased in a striking fashion to 92%. Ten-gram lots of autolyzed yeast were used per charge for four more cycles (period G) to establish an active film of organisms on the coke. Double amounts of malt nutrients were fed for 4 weeks (period H ) . Since the generator was not up to the control, the nutrients were varied further. For three cycles (period I ) a mixture of 0.2 gram of steep water and normal malt nutrients wa9 used, after which addition of 0.5 gram of steep plus normal malt maintained the efficiency between 94 and 99% for the remaining 8 weeks of the test (period J ) . The response of the generator to the nutrients, especially t o the yeast autolyzate-stcep water miuture, was remarkable and showed that the difficulties viith the packing were definitely related to maintenance of a good pupulation of organisms on the surfaces exposed in the generator. Coke Run 5 , started after Run 4 was operating properly, employed small (1/1 inch in diameter) coke as packing. This run was initiated by feeding a mixture of 50% warm vinegar and 50% S.D. 3 5 4 fortified by 5 grams of steep water and the normal addition of malt extract, for three cycles (period A ) . The efficiency rose to 76% very quickly. Double malt extract for 2 weeks (period B ) , followed by 0.2 gram of steep water plus normal malt extract raised the relative efficiency to 98% a t 10 weeks from starting time, as shown in period G. Minor variations in the type of nutrient were then made, but there was no significant change in efficiency. Operating results expressed as percentages of the control, for the 21 weelrr are shown in Figure 1. I n coke Run 6, employing coke obtaincd locally, the packing was sized to approximately 1/4 inch in diameter and washed with water (no hydrochloric acid treatment). No warm vinegar wash was added, but a 50: 50 warm vinegar-alcohol feed was circulated. Feed for the initial 3 weeks was 50% regular S.D. 3 5 8 plus 50% warm vinegar For the next three cycles, 0.5 gram of steep Tyater plus normal malt nutrient was added, as shown in period A . During cycles 3 t o 14
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PILOT PLANTS (period B ) the nutrient was composed of a mixture of 0.5 gram of steep water, 0.1 gram of Cerelose and normal malt nutrient, Work on this generator had to be discontinued a t this time, but, like the others, this experiment showed the beneficial effect of steep water as a nutrient. Specially Prepared Rattan lo Suitable Packing if Proper Nutrients Are Used
Rattan was employed in one generator of the vinegar pilot plant. In order to obtain conditions comparable to those existing in commercial generators, half of the material was tied in small bundles containing 10 to 12 loops about 3 to 4 inches in length. The remainder was cut in small lengths and used to pack interstices between bundles. The generator was seeded by circulating several gallons of warm vinegar over the rattan packing and by feeding regular S.D. 35A with fermented malt extract as a nutrient. After four cycles, the relative efficiency was 83% but the residual alcohol was high. This behavior, shown in Figure 1, was interpreted to mean that the population of organisms was inadequate to convert the charge in 7 days. For the next six cycles the same feed and nutrients were employed but the cycling time was lengthened to about 10 days. This did not improve yield but lowered residual alcohol (period A ) . At cycle 10 autolyzed yeast a t the rate of 0.5 gram per feeding was added to the nutrient. The relative efficiency rose in 4 weeks to over 98% and remained near that level until cycle 29 (period B), a t which time autolyzed yeast addition was discontinued. A gradual decrease in efficiency to 92% was noted in period C as the yeast nutrient leached from the rattan. At cycle 36 autolyzed yeast was again added a t the rate of 0.5 gram per feeding, and in nine cycles the relative efficiency reached 97 to 98% and has since remained a t that level, as shown in period D. Apparently ally inadequacy of surface of the rattan has been nearly compensated for by the increased nutrient. Runs with Berl Saddles Provide Estimation of Effective Surface Area and Conversion Capacity
Berl saddles of the type employed in distillation columns were tried as a packing for a vinegar generator. Twenty-six pounds of unglazed 1/2-inch porcelain saddles were required. These weigh 56 pounds per cubic foot arid have a known surface area of 155 26 square feet per cubic foot. Thus, this generator had X 156,
a
or 72 square feet of surface. The saddles were soaked 72 hours in 5% hydrochloric acid, rinsed five times Kith water by alternately filling and emptying the generator, and finally washed by running mater. They were covered with 100-grain warm vinegar and allowed to soak 48 hours. Operation similar to that employed for rattan packing was tried-Le., feeding with 50% warm vinegar and 50% S.D. 35A diluted to a concentration of 9 to 9.1 grams of aIcohoI per 100 ml. Four weeks of operation on the usual 7-day cycle failed to establish a normal operation. Since residual alcohol was high, a 14day cycle was tried (period A ) . However, this did not improve performance. Bt cycle 5 the addition of 0.5 gram of autolyzed yeast was started with the results shown by period B. The efficiency rose from 62 to 82% in 2 months but leveled off a t that point, High residuals showed that the organisms were unable to utilize all the alcohol in the feed, and the amount of alcohol in the charge was, therefore, decreased a t cycle 18 by adding regular S.D. 35A feed, except that the charge was diluted with an equal volume of warm vinegar from the preceding production of the generator, A 7-day cycle was also adopted and continued for period C. No increase above the 80 to 82% level of efficiency was noted during the ensuing 13 cycles. A mixture of 50% warm vinegar from another active generator and 50% S.D. 35A alcohol (9 grams per 100 ce.) was used throughout period D to help estab-
October 1954
lish an active film of bacteria. The nutrient was then raiped $0 double the quantity of fermented malt extract employed in the control generator. After five cycles (period E ) the efficiency showed signs of falling and 1 gram of autolyzed yeast was added to each charge during period F. After several cycles the efficiency had risen to 98% and remained steady a t that point for the subsequent seven cycles. Apparently, the effectivesurface area in this generator is about half that in the control generator containing beechwood packing. Since the Berl saddle generator packing has a converting area of 72 square feet, it may be assumed that the beechwood shaving generator has a converting area of about 145 square feet, These pilot plant generators contain 0.54 cubic feet of shavings. This corresponds to an effective surface of about 268 square feet per cubic foot of shavings in the beechwood generator, From this it may be calculated that each square foot of bacteria-coated surface converts about 0.2 gram of alcohol per day. These figures, 81though not of any practical use, are of interest as an index of the bacterial activity in the generators. The Berl saddle generator responded well to the autolyzed yeast. Where hard surfaces are involved, as in the case with both coke and Berl saddles, recourse must be had to a high nutrient level in order to maintain t,he film of acetic organisms, Proper Addition of Nutrients Is Key to Efficient Performance of Generator Packing
Discussions of generator packing in the literature are for the most part limited to descriptive statements. I t i s explained that the acetic organisms have to grow on a support with a large surface area, considerable mechanical strength, and sufficient porosity to hold appreciable amounts of the circulating feed in contact with the bacteria. These obvious matters are, however, not of much use to the plant operator who is in difficulty because he has had to change to a type of packing to which he is not accustomed. The essential practical consideration is to provide information relating the type of packing to bacterial growth and behavior in the generator. So far as type of packing is concerned, i t has been noted that wood shavings are employed almost exclusively in the United States. Shavings made from beechwood have advantages that account for their wide use in the industry. The shavings are curled in a way that allows openings for circulation over as much of the surface as possible (6, 6). As demonstrated by the experiments described in this paper, nutrient requirements change with the type of packing, and periods of Circulation with vinegar from an active generator are necessary along with special nutrient additions in order to bring coke or ceramic saddles into satisfactory production. Like other biological relationships, this one is not simple, and the experimental work could be extended to touch on various aspects of the matter. For instance, it would be helpful to know from direct observation how much of a part is played by the abiIity of organisms to adhere to such surfaces as coke, rattan, or ceramics. In the absence of such observation, the nutrient additions which gave beneficial results in this work were tried on the assumption that the bacterial film is more difficult to maintain on hard surface packings than on the surface of shavings. The nutrients were sekcted because they have been shown to favor the growth of many bacteria and molds. Malt extract is an old stand-by for vinegar production. Corn steep mater and autolyzed yeast are known to be excellent ingredients in culture media. The former was made the subject of a patent in which use as a nutrient for acetic organisms is specifically mentioned (4). The use of Rpecial nutrients favoring bacterial multiplication is required by packings that are deficient in extent of surface or bg packings with surfaces that are not readily coated with bacteria. If such nutrients are used, these packings may be brought to a level of performance essentially the same as shown by beechwood shavings. Autolyzed yeast is especially useful and, in every case
INDUSTRIAL AND ENGINEERING CHEMISTRY
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT where it was employed, the generators responded with a rise in efficiency. The general practice of running vinegar generators calls for holding the nutrients a t a level where the organisms are maintained but not st,imulated to form slime. I n applying the results of these experiments, therefore, the amounte of nutrient should be kept a t the minimum required to give good generator activity. I t is believed that stimulat,ion of bacterial multiplication is required by coke and ceramic saddle packings because the film of organisms sluffs off, whereas beechwood shavings not’ only present more surface per unit volume, but present a surface to which the bacteria can readily adhere. Packings ot,her than shavings may be used to obtain performance equal to beech shavings, volume for volume. However, the nutrient level may have to be raised in order to maintain an
adequate alcohol-converting bacterial film in the generator when certain hard surface packing materials are employed. literature Cited (1) Allgeier. R. J., Wisthofi, R. T., and Hlldebrandt, F. >I,, 1311. EN&.CHEM.,44, 669-72 (1952,.
(2) Ihid., 45, 489-94 (1953). (3) Hildebrandt, F. >I., Food Inds., 13, No. 8, 47-8 (1941) (4) Myers, R. P., and Speck, 31. L , C . S.Patent 2,448,690 (Sept. 7,
1918). ( 5 ) Gnderkofler, 1,. A . , and Hickey, R. J.. “Industrial Fermentations,” Vol. 1, pp. 510-11, 516-17, Chemical Publishing Co., Kew York, 1954. (6) Wustenfeld, H., “Lehrbuch der Essigfabrikation,” pp, 100-2, Paul Parey. Berlin, 1930.
RECEIVED for review April 2, 1954
ACCEPTEDJ u n e 4 , 1954.
Manufacture over Platforming Catalyst EFFECT O F SULFUR ON CATALYST LIFE WILLIAM K. MEERBOTT, ALAN H. CHERRY, BENJAMIN CHERNOFF, JAMES CROCOLL, JULIUS D. HELDMAN’, AND CYRIL J. KAEMMERLEN2 Shell Oil Co., Houston Manufacfuring-Research loborofory, Housfon, Jew.
I
KCREBSIXG demand? on the petroleum industry for monocyclic aromatics and for higher octane fuels have hmulated extensive investigations in the field of catalytic reforming. Recently, several new processes have been described ( 1 , 4, 6 , 7 , 3, 14, 16, 17, 80, 21, 25, 25) whereby narrow boiling petroleum fractions or wider boiling range petroleum naphthas may be converted into monocyclic aromatics such as benzene, toluene, or xylenes, or into fuels of improved octane rat’ing. The catalytic reforming processes involve (1) dehydrogenat,ion of naphthenes t,o aromatics, (2) isomerization of naphthenes and paraffins, (3) hydrocracking of paraffine, (4) desulfurization, and ( 5 ) dehydrocyclization of paraffins. The mechanisms of these reactions have been discussed by several authors in recent years (3, 8, 10, 28). Most of the st,udieshave been carried out in ehort processing periods, eit8herx i t h pure hydrocarbons or with synthetic mixtures of these materials. Only limited information has been available on the effect of operating variables on catalyst life in the production of aromatics via catalytic reforming. This paper is concerned particularly Tvith the pilot plant preparation of concentrates of benzene and t’oluene using the Plat’forniing process developed by the Universal Oil Products Co., including pilot plant, produetion of aromatics from a narrow boiling Cg t o C7 (140’ to 228” F.) East-Kest Texas (ETVT) crude oil fraction, and the factors involved in the selection of operating conditions for an optimum aromatic yield-catalyst life relationship.’ laboratory Recycle Hydrogen Platforming Unit Is Used in lnvestigalions
The experimental apparatus, based on a design supplied by the Universal Oil Products Co., consists of an oil feed system, recycle gas compressor and metering facilities, and a dual external 1 2
Present address, Shell Oil Co., New P o r k , K. Y . Present address, Celanesc Corp. of America, Charlotte, N. C.
2026
preheater-react,or system, together with condensing and produrt recovery vessels. A simplified flow diagram of t,he apparatus is shown in Figure 1. The recycle gas stream, consisting principally of hydrogen, is passed over sodium-calcium hydrate for the rcmoval of hydrogen sulfide and gaseous mercaptans prior to re-use in the process. I n order to simulate the pressure drop that occurs in a commercial installation an interstage pressure control is used between tEir, two laboratory reactors to provide a differential of 50 pounds por square inch. Miniature motor valves and pressure controllers, manufactured by the Research Control Instrument Co. of Tulsa,, Okla., are used for pressure control. The reactor temperature control is semiadiabatic. An aluminum block furnace, into Tvhich the reactor is inserted, is maintained a t a constant block temperature by mean3 of a Celectray temperature controller. Homver, because of the endothermic nature of the dehydrogenation reactions and the type of reactor and furnace construction, it is impracticable to control temperntures within the catalyet bed. During a catalyst life study, a temperature profile of the catal>rst bed is recorded once every 24 hours. Temperature3 a t selectrd points are recorded hourly, as are other process measurements. The temperature profile of the catalyst bed gives an excellent indication of the catalyst activity decline. Catalyst. Universal Oil Products Co. Type R-5 spherical Platforming catalyst is used in all experiments. The total cat,alyst charge is divided equally betv-een the two reactors. Analyses. The recycle gas stream is analyzed by mass spectrometer. The unstabilized liquid product is fractionated by low temperature Podhielniak distillation into a ‘(‘2; and lighter” and a “hexanes plus” cut. Mass spectrometer analyses are obtained on both fractions. The hexanes plus material is analyzed for total aromatics by a fluorescent indicator adsorption technique (5). Individual aromatics are calculated from the
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 10
