Aeration in the Production of Compressed Yeast

It is also believed that aeration takes away fermentation products from the surface of the cells and sub- stitutes fresh nutrients for them. Staub (31...
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The photograph shows an aerating system of the perforated tube type for a huge propagating tub, where compressed yeast is produced by aeration in a European factory.

SHENLEY RESEARCH INSTITUTE, LAWRENCEBURG, IND.

propagation of the yeast, and that the yeast call utilize only the oxygen dissolved in the liquid. The solubility of oxygen is low-O.O009Q/, a t 20” C. Aeration is necessary to replace used, dissolved oxygen. I t is also believed that aeration takes away fermentation products from the surface of the cells and substitutes fresh nutrients for them. Staub (SI) believes that the yield of yeast is in direct proportion to the cube root of the aerating intensity. This and similar conclusions may be true only to a limited extent. On the other hand, there are facts which may at least modify the oxygen supply theory, Yeast may also multiply in the absence of air. In several experiments made on a pilot-plant scale in 1930-33, one of the authors obtained considerable yield$ of compressed yeast in mashes in which carbon dioxide or nitrogen was passed through instead of air. These yields were three to four times larger than those obtained in identical mashes in which no gas was distributed. Weleminsky and Butschowita (56) obtained the same yield in aerated wort as in unaerated but rapidly circulated wort I n the first case there was no alcohol, in the second case, normal alcohol yield in addition to yeast. Meyer (18) describes propagation of yeast without aeration. I n closed tubs the wort is well agitated under vacuum to eliminate alcohol and carbon dioxide; in addition to alcohol, the same amount of yeast was obtained as in aerated wort. Jansen ( 2 1 ) recommends intensive circulation of the beer in a closed fermenter. All the beer is passed through a pump every 10 minutes. Besides excellent alcohol yield, a good yield of yeast is claimed. Willkie and Prochaska (68) concluded: “In the absence of oxygen, growth is slow and fermentation is the predominant reaction. Whereas agitation with inert gases increases both growth and fermentation rate through better contact of yeast with mash ingredients, dispersion of air throughout the medium induces yeast growbh specifically a t the expense of fermentation. Pure oxygen is not as good a growth stimulant as air.”

OMPRESSED yeast, originally a by-product of alcohol and beer, has gained in importance during the past thirty years. Yeast is being consumed wet or dry, natural or irradiated, alone or mixed with other food substances and flavoring materials. I n wartime yeast has become a partial substitute for meat. With the advent of the aeration of the wort in the early part of this century, the production of compressed yeast became independent from alcohol or beer manufacture. Aeration of the nutrient liquids in which the yeast propagates enabled manufacturers not only to multiply former yields four or five times, but also to control the quality of the product. Since the time of the old-fashioned foam yeast process early in this century, hundreds of new methods of producing compressed yeast have been developed; all have one principal step in common, aeration of the wort. Air was generally believed to be a raw material which could be obtained free of cost. The cost of energy necessary to compress air, however, proved that a considerable amount (10-2001,) of the total producticn expenses is due to aeration. Manufacturers, eager to reduce costs, began to study the attainment of optimum yield with a reduced amount of air. Especially between 1925 and 1940 dozens of patents were applied for, chiefly in Europe. Research was concentrated on proper technology rather than on the biological effect of aeration. The primary purpose of this paper is to provide a basis for further research by discussing the facts connected with aeration in the production of compressed yeast, by enumerating some of the aerating systems used or recommended, and by tracing the course of their development. I n recent years the interest of fermentologists has turned toward microbiological processes other than compressed yeast production, where aeration of the wort is essential. For those processes also, useful directions can be obtained from the methods used in aerating the yeast wort. Tittle is known about the biochemical mechanism of aeration. The general belief is that oxygen is important chiefly for the

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INDUSTRIAL AND ENGINEERING CHEMISTRY

October, 1944

YIELD

The yield of compressed yeast is generally expressed as weight per cent of the carbohydrate-containing raw material, occasionally as weight per cent of the actual sugar used. The weight of yeast is normally given a t 30% solids content. The carbohydrate-containing raw material is most often molasses and seldom grain; it is more frequently beet molasses than cane molasses. In the true yield statement, the fermentable sugar content of the molasses is also given. In continental Europe, if not otherwise specified, the yield is given as kilograms of yeast with 30% solids content obtained from 100 kg. of molasses containing 50 weight % fermentable sugar (expressed as sucrose). The yield based on this specificat impoitant, because the yield on seed yeast as well as the air requirement for its production is usuallp much lower than t h x t 011 the final product. QUALITYOF AIR. The quality of the air is more important, t,o the yield than the quantity. It is even more difficult to define quality of air exactly than to define quantity. An attempt will lie made to interpret the term by discussing its most important components. The conditions under which air is introduced, distributed, and kept in the wort determine quality. I t is essential that t,he air (A) should pass through the entire height of the liquid, (R) should be distributed equally through the entire cross section of the tub, (C) should contact the wort at the largest, possible surface, and (D) should be in contact with the wort for the longest possible time. A. The air is generally introduced into the liquid a t the deepc~st,point,, close to the bottom of the tub. By this means both tub and air capacity are best utilized. 13. A well-balanced network of aerating tubes covering t'he entire tub bottom, the proper position of the aerating candles or hodies, or the agitation of the mash are the means employed t o maint,ain homogeneous dist'rihution of air. If the air passes

tion periods, the amount of air supplied to the tub is usually constant, regardless of the changes in volume of wort or in yeast concent,ration during the main propagation period (10-12 hours). Under the influence of a number of variants, only one particular phase can be characterized by this third typc of report. The production man likes to report and compare the air requirement in cubic feet per weight unit, of raw material used or per weight unit of new yeast (methods IV and V). At first glance method V in particular seems a good way to compare production results. S o proper . comparison, however, based on this type of specifica.tion,can be obtained hecause of two major variants-height of liquid and yield. It has already been mentioned that, the utilizat'ion of air Table 111. Air Requirements of Yeast Production in Various Systems depends considerably on the size and shape of the Air Requirement, Cu. Ft. fermenter. Each method of propagation, in combination wit,h a special method of aeration, may reach the. optimum yield in a manner charact)eristic of the met,hod. There are methods in which a 6 5 7 0 % yield can be increased only slightly even if the quantity of air is doubled. There are other methods in which a 65-70% yield can easily. be increased to S5-90% simply by increasing the quantity 530 12 6.0 13,000 1. a l'erfomted tuhes 0.20 375 72 74 280 24 12.5 20,000 9. Perforated tubes 0.3 210 of air by 50%. These figures demonstrate that yield 78 400 20 10.5 20,000 3. Perforated tubes 0.21 315 and liquid level cannot be eliminated from the defi85 .. .... 5,100 275 4. ( 6 8 ) Perforated tubes 0.20 235 , . .. .... .. .. .. 5. ( 6 ) Perforated tubes 0.06 260 nition of air requirement. 333 .. .... 10,000 6. ( 5 ) Perforated tuhes 0.11 ... 7. ( 2 6 ) Perforated tubes In spite of the fact, then, that it is commoii 67 (assumed) 0.14 290 360 ,. .... 7,000 practice, the quantity of air cannot be satisfdctorily R, Xechaniral air dia91 zoo i 3.0 550 tributor 0.40 180 relat,ed to a single characteristic of a method. For 0. (30) N o . 60 carbon ~. . .. ,. . . .. 0.13 sparger 0.40 .,. correct evaluation, quantity of air must be reported .. ,. . . .. 0.13 10. (50) B,erkefeld candle he liquid a t any , ,

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October, 1944

through only one section of the tub, that part will be overaerated while the other part will be underaerated. I n the over-aerated mash the utilization of air is poor, and in the under-aerated mash the propagation is slow.

Figure

1.

E a r l y Forms of P e r f o r a t e d T u b e Systems A . Inverted T B . Perforated ring C. Spiral marger

(:. I n aeration t,Iie inost important fac.t,or in t,o establish the largest possible contact,ing surfaw between air and liquid per unit of air. The largest possible surface of a given amount of a,ir is offered by bubbles of the smallest size. The surface area of 1 cubic foot in a single bubble will be 697 square inches. If t,his is divided into bubbles 1 inch in diameter, its total surface mea will be 10,368 square inches. Going farther, the total contacting ,siirf:tce of 1 cubic foot of air divided into bubbles with a diameter of 0.1 inch will be 103,680 square inches; with a diameter of 0.01 iiich, it will be 1,036,800 square inches, etc. The total surface area of a definite amount of air will increase in inverse proportion to the diamet,er of the individual bubbles. I n t,he practical aeration of yeast mashes, the diameter of the ziir bubbles is est,imated t,o be from 0.0001 to 1 inch. By the old xerating systems, practically every size between these limits was represented. The greater part passed in the form of large bubbler, and only a small fraction of air formed the smallest hubblrs. The total contacting surface per unit of air was relatively small. Those methods which produce only the small hubhle. are called “fine aerating systems”, and they result in yields identical with or larger than the old systems, while using only 10-50% of their air requirement. Naturally, the yield does not increase in direct proportion to the contacting surface. Several of the aerating systems disperse the liquid in the air in the form of a fine spray. The contacting surface increases with the decreased size of the liquid drops. I>. The next important, factor in aeration is the cont,acting time, the time the bubbles spend in the wort. Fine aeration cnreates not only a large contacting surface, but also a longer cvntaoting time. The floating time is much longer for a small bubble than for a larger one because of its lower elevating power. .I small bubble may spend minutes in the liquid before leaving i t ; a. large one may pass through within a few seconds. In order to lengthen the floating time, several systems keep the liquid in a slow rotat>ingmovement, the bubbles thus reaching the surface of the liquid through a long spiral cour8e instead of by a straight vertical line. The floating time is also influenced by the height of the liquid. That is the explanation of the lower air requirement in cubic feet per gallon of wort in a tall vat. The floating time is not in direct proportion to the height of the liquid, because the rising speed is constantly accelerated by the elevating power of the bubbles. Even the elevating power increases with the course of elevation, because the size of the bubbles will inhease as the liquid pressnre decreases in the upper liquid 1ayer.s.

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ENERGY REQUIREMENT

The investigator in the laboratory ax well as the indudtrial operator will profit by an analysis of the air requirements. The production man will look only for the energy requirement of the aeration. He will report it in horsepower or kilowatts per 100 pounds of yeast produced. The energy requirement is dependent upon the quantity and the pressure of air used, and the energy requirement of the agitators, mechanical distributors, or circulating pumps. The quantity of air per unit of product depends mainly upon the height of the liquid level and the contacting surfaces of the air. For the higher liquid level, the producer pays with the higher pressure; for the smaller bubbles he pays with additional air pressure when porous air-distributing bodies are used, anti with additional energy when mechanical air clistributors are ut,ilizetl. When energy requirements ai’e held t o the minimum, local conditions must be carefully considered. Generally t,he actual energy consumption due to unbalanced local conditions is higher than the theoretical cwnsumpt,ion calculated from minimum air requirement. On the other hand, local conditions may reduce the cost of the energy requirement below the theoret,ical. When, as is customary, steam-driven air (’o~npressorsare used, utilization of exhaust steam for sterilization, distillation, etc., will considerably reduce the costs of air compression. Next t,o the energy requirement,, the production man is interested in the necessary maximum air pressure, because the price of the air compressor, air cooler, filter, conducting pipe lines, et(’., is higher for high-pressure than for low-pressure operation. CLASSIFICATION OF METHODS

Methods developed by processing engineers have geiierally aimed at high yields and low air requirements. Methods developed by machine factories have generally produced simple, dependable devices designed for large consumption without requiring many changes in other equipment. Many of the recommended methods are simple reproductions of previous one&,with only slight improvements. Most patents seek to secure advantages over existing patents or to protect promising ideai.

, Figure

I.

N e t w o r k of PerForated T u b e s

Groupings of the systems recommended or used may be approached from different angles-for instance: Grouping 1: (a) syst.ems where air is distribut,ed in the liquid; (b) systems where liquid is dishibuted in the air; ( c ) systems where air and liquid are placed in cont,act on bodies wit,h large surfaces. Grouping 2: (a) systems where the liquid is aerated in t,he tub; ( b ) systems where part of the liquid is withdrawn from the tub and, after being subjected t,o intensive aeration, is returned. Grouping 3: (a)air distributors with moving parts; ( b ) air distribut,ors without moving parts. Grouping 4: (a) rough

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Figure

3. Position of Holes in Tubes

aeration; ( b ) fine aeration. Such and similar groupings may be set up to classify the various aerating systems according to one or another basic point. Disregarding systematic classification, the folloffing grouping will deal with the various systems in seven major groups, according to the simifarity of the devices used to distribute air. KOsharp line can be drawn even between these groups. I. Compressed air enters the liquid through perforated metallic plates, tubes, or tube systems fixed on the bottom of the tub. XI. Air enters the liquid through hollow bodies, plates, tubes, candles, or false bottoms, made of porous material such as ceramic substances, porous carbon, porous copper, hard rubber, soft rubber, fibrous substances, etc. 111. Air enters the liquid through hollow bodies, plates, or tubes made of metal and provided with openings other than bored holes. IV. Mechanical air distributors. V. Liquid spray aerators. VI. Packed columns. VII. hliscellaneous. I. FIXED M E T A L L I C DISTRIBUTORS W I T H BORED H O L E S

deveral attempts were made to aerate the wort through the holes of a perforated false bottom or through the holes of perforated plates of hollow bodies; however, they were impractical because liquid sank through the holes into the bodies below or between the double bottoms, caused irregularity in the aeration, and became a source of infection. The perforated tube system has been most frequently used by manufacturers. Kumerous attempts have been made to break away from this classical aerating system, but its simplicity, dependability, and relatively low cost have assured preference over other methods. The present form of perforated tube system is the result of a long series of improvements. In the beginning air was introduced into the liquid through the two open ends of an inverted-T pipe line (Figure I A ) . This vias soon replaced by perforated rings and spiral spargers. The next arrangement was a network of perforated tubes covering the bottom of the tub; individual parallel tubes branched out on both sides of a horiaontal main line, into which the air passed through one or more vertical lines inside the tub (Figure 2). The iron pipes originally used were replaced by tin-coated copper, occasionally by brass, and recently by stainless steel tubes. The tubes, few in number at first, increased rapidly until the bottom surface was nearly covered by them. Union connections, later well-grooved surface connections, were applied. The diameter of the tubes varied, according to the size of the tubs, from 1/4 to 2 inches. The holes were moved from the top to the bottom of the

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tubes in order to prevent the flow of liquid into them. Later the holes were placed on two sides or a t the lower part of the tubes 90" apart. Recently very small holes occupy the upper surface of the tubes (Figure 3). The size of the holes as a rule was '/25-'/25 inch. The number of holes was increased and their diameter reduced. Shortly before World War 11, tubes were produced with holes less than 0.1 inch in diameter. Through these holes, fine aeration was closely approached. Because the perforated tube system has been in use since aeration became common practice, only a few patents or trademarked models have been claimed. I n one trade-marked model of hlaschinenbau A,-G. Golzern-Grimma (15), the individual perforated tubes are connected to the main air line in such a way that they are easily turned in an upright position without the use of union connections (Figure 4). According to two other trade marks (16) air channels located a t the bottom of the tub are closed by metal plates perforated by very small holes. In another model (17) tubes are applied with a finely perforated, horizontal top plate (Figure 3E). A patent (@) of Strauch & Schmidt specifies an aerating system in which the individual Derforated tubes branch out from submain lines which, in turn, stem from the main air line. By this arrangement the individual tubes are parallel to the main air line. I n another patented system (46) the aerating tubes are provided with water and steam connections for cleansing and sterilizing. A4eratingsystems are built, by Strauch & Schmidt for vats up to 200,000-gallon capacity. They claim 3 0 4 0 % less air requirement for their latest models and still less for double-tube aerating systems (Figure 5). Aerating MYStems built by Golzern-Crimma are also generally used in European yeast factories. II. FINE A E R A T I O N T H R O U G H P O R O U S SUBSTANCES

By devices classified in this group, air enters the liquid IKI the form of fine bubbles through the tiny openings of porous substances. The air may be compressed into hollow botiieh. into tubes placed on the bottom of the propagating tub, or between double bottoms, the upper of which is built of the poroup substance. Practically all mateiials used in bacteriological and aerological filtration have been tested for fine aeration. The earlier reoonlmendation of Peter ($3) that, porous subFicrure 4. Placement stance be used did not receive much attention. Stich is credited with calling the attention of yeast manufacturers to the importance of fine aeration and with presenting practical ways of attaining it. His baric. patent (36) recommends the introduction of air into the wort through diaphragm bodies with orifices 0.16 to 0 . 6 ~ in size, and the lengthening of the floating time by slow rotation of the liquid. This was a revolutionary recommendation a t that time, when the diameter of the holes of the perforated tubes varied from 1000 to 2000,~. I Stich's basic patent was followed by many others. F ~ example, pore sizes in the diaphragm plates are increased to I-25p in order to reduce the pressure requirement of the air ($2). The diaphragm plates or bodies are built with two layers (38). The thick inside layer with large holeP amures mrrhanicai

October, 1944

INDUSTRIAL A N D ENGINEERING CHEMISTRY

strength; the thin outside layer with small pores assures the fine distribution of air. This change was necessary to reduce the resistance of the ceramic plates and candles. At the beginning of propagation, the wort is converted into a foam by fine aeration (41). During the course of propagation, enough finely distributed air is supplied to the wort to maintain its foamy consistency; development and maintenance of foam are aided by special ingredients added to the liquid. In order to increase the mechanical strength inside the ceramic candles, perforated metal tubes are applied (39). A number of candles made of porous ceramic material are screwed to the air lines in the bottom of the tub (43). They are placed at various angles and can be of different sizes. Certain parts of the tub bottom may hold more candles than others, in order to maint,ain natural circulation in the liquid. The diaphragm-like aerating bodies are made of hard rubber, soft rubber, glass powder, metal, or fibrous material (40). The individual elements of the fine-aerating system are provided with separate air control and liquid-releasing devices (86); if liquid gets into the candles or other aerating bodies, it is returned to the tub. A fine perforated rubber tube covers the perforated metal pipes of any conventional aerating system (3.9). The holes of the rubber tube are tight and open only under an excess of air pressure. The porous, ceramic, aerating candles are mounted a t the outside surface of the perforated metallic pipes (34). The pipes are covered by elastic rubber rings or perforated rubber t,ubes which allow air from the metal pipe to go through the cwdles, but they close when inside pressure decreases. Almost every yeast factory in Europe in 1930 and the following years attempted to apply Stich’s method or to avoid his patents. A number of laboratory and semipilot-plant tests were made, but only a few factories made actual use of the process. They placed hundreds of ceramic candles upright in the bottoms of the tall yeast tubs and used screw connections to the copper :4,ir-linesystems. Several disadvantages of the met,hod handicapped its broader une. If the ceramic candles were strong enough, excess air pressure (8-14 or more pounds per square inch) was required; v,ith t,he resistance of the liquid, this amounted to 14-20 pounds 01’ more. Thus, despite the greatly reduced amount of air, the energy requirement was just below that of other methods developed at the same time. The air compressors of the older plants were designed for a maximum pressure of about 6-8 pounds per square inch. When a plant was converted to the Stich method, the compressors had to be replaced. The maintenance expense of the easily broken candles, the danger of spoiling a mash if any of the candles broke during aeration, cleaning and sterilization difficulties, and the frequent changing of t,he candles because of clogging kept, manufacturers from using them generally. Numerous methods embody the elements of the Stich method or improvements upon it; several will be mentioned as examples. Rraasch and Braasch (4) improved the fine-aerating process by adding small amounts of organic acid (acetic or lactic) to the wort. The addition of 0.01% or more lactic acid changes the surface tension of the mash so that the dimensions of the air bubbles will decrease to a fraction of their original size. By this method ceramic candles can be used with much larger pores, and less excess air pressure is required. Gosda (10) provided the candles with safet,y valves, introduced the air a t both ends of the crtndles, and improved the screw connections between candles and metallic air lines. Bermann (5) recommended glass filter plates with pores of 40 to 70p for fine aeration. Schattaneck (16) recommended porous plates made of copper. In the United States a number of devices made of ceramic substances or porous carbon available for filtration purposes are twily adapted to fine aeration. They are used for filtering twverages, serological, bacteriological, and other preparations,

Figure 5.

889

Double-Tube Aerating System of Strauch &

Schmidt

and air. Recently some of them were specially designed and used for distributing gas in liquids. Carbon dioxide is dispersed through such porous substances in carbonated beverage production. Porous substances are marketed in the form of plates, candles, or tubes. Plates are used as false bottoms. Tubes are connected on one or both ends to the air line for aeration. Tubes in horizontal position are also prepared with porous flat upper plates for fine aeration, when the semicylindrical part of the tube facing the side and bottom of the tub is impermeable. The characteristics of most of these devices are described in the commercial bulletins of the producers (19, 28). Carbon tubes are made up to 36 inches in length and 6/8-33/4 inches in inside diameter, with porosity from 5 to 19Op. Air permeability of the various porosities per square foot per minute at various pressures is presented in charts. I n recent yeLrs American scientists have reported the use of porous substances to distribute air in yeast worts on a laboratory and pilot-plant scale. Pavcek, Peterson, and Elvehjem ($1) used a silicon carbide tube as air distributor in a fermenter which dispersed 100 liters of air per minute. They obtained ten and a half to thirteen times as great a yield in aerated as in uuaerated wort. Stark, Kolachov, and Willkie (30)used aloxite stones, No. 30 and No. 60 carbon spargers, Berkefeld candles, and open glass tubes as air distributors in 500-ml. fermenters. Many of their data connected with air distribution prove the great importance of fine aeration. Their results also confirm that data on air requirement reJated to a single factor such as cubic feet per minute per gallon have limited value. The extremely low air consumption when Berkefeld filters are used correlated with facts previously stated. The orifices of a Berkefeld filter are very small and result in very fine air distribution a t the cost of high air pressure. Stark, Scalf, and Kolachov (57) report the effect of aeration OIL the growth of distiller’s yeast. I n selected experiments (which included their earlier work, 30) they used aloxite stone, Berkefeld candles, glass tube, and No. 30 and No. 60 carbon spargers as air distributors to provide the wort with 3, 0.8, 0.4, and 0.07 cubic foot of air per gallon per minute. They report optimum results when 0.4 cubic foot of air per minute per gallon of wort is distributed through 17 square inches of effective area of No. 60 carbon sparger. The National Carbon Company (19) discloses that No. 60 carbon tubes contain pores of 33p diameter and require 34 pounds of air pressure per square inch for every 5 cubic feet per minute per square foot. Table 11 indicates the relation between pressure and power consumption.

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l-riger, Stai,k, S i d f , and Kolachov (.$i)rpport that in a 300gallon pilot-plant wort, hFst aeration \vas ohtained when 3 ,-;quare inches of sparger area of ;"io. BO teartlropshaped carbon rpargei' were used per gallon. Air consumption ~ v a i 0.25 cubic foot of a i l . per gallon; 80 ~ 4 l o t i of mash cvntaine.tl 1 bushel of grain. 'Chey proposed for inciiistrial plants 0.25 cubic foot of air per minute per gallon of wort, 10 cwhic, feet of air piJi* niiiiutc, per square f0I)t (If hpargei' sui f:ic,t:, :iniI Figure 6. Fast-Rotating M e c h a n i c a l A i r Distributor of V o s e l b u s c h ( 5 4 )

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pouirtii pei a q i i L i i e l'e:i\t c*oiicen-

inch.

in number of cells per milliliter. The experiments of the four reports (81,SO, 4 7 , 5 7 ) \vert, made on a laboratory or pilot-plant scale. In one ( X J ) gro\vtli , factors and vitamin €3, content of yeast were studied: in tiic ot)her three, the production of distiller's yeast (.~imultaneously with alcohol). The same critical attention cannot be paid to the oconorny of aeration in propagating yeast for snch puip(~se8as i n cmnpressed yeast production. %or instance, the power requirement where high air pressure \vas used is extremely high. Thew reports are still of great importance because fine aeration through porous substances \vas nsetl arid close sperifications of conditions werc reported. 111.

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IY. M E C H A N I C A L AIR DISTRIBUTOXS

I kvices in this group use mechanical Force to produce air t)uhbles of the smallest possible size in the wort. The air entering the liquid through relatively large openings forms tiny bubbles iibe of thc differenw in speed between liquid and air which ih ted by rotating bodies. Llechanical air distrihutorh ran he divided into the i'ollo\ving types: The liquid is niovetl with cwnsiderable speed above the fixed openings of the air supply; the openings of t,he air supply are moved with considerable speed i n the liquid; t,he air bubbles are iirtrotluccd into the liquid in ilie form of large bubbles aiitl are t1ihintegr:Lte'd tlirre by fastriioving agitators. Iilipfel ( I S ) describes equipment t o atrriit e liquids Cor hreiveries or cornpressed yeast production. It consists of a hollow vertiimal shaft connected with perforated tuhes in horizontal position rlose to the bottom of the propagating tub. The air passina through the rotating shaft and the hoi~ixoritaltubes is dispersed thi~oughout~ tlic (:ross sertion of the liqiiitl. This tfevire has the elements of a modern mechanical ail, distributor. Peter (22) i,ecwmmentls a slow-movins agii atoi' which force;. fine air bubhlrs inti.oduceci at the bottom of the tub in a slon. rotating movement instead of a rapid upright p m d i . He improved this method (63) by in:rotlucing air het \ v w n the tiorihle bottoms of the tub, the upper bottom of which is porous. 'This patent (6J)contains the eiements of both Group? JI and IV. The correct technical application of both groups, himever, \vas made &out ten years later hy Stich ttnd f(rI1niver~ :urd hy T'ogelbusch miti followers.

FIXED DISTRIBUTORS W I T H VARIOUS O P E N I N G S

The large reduction in the air 1,equiremerit achieved by i3t icli'h r!>rthod left no doubt about the economical possibilities of fine aeration. To overcome the disadvantages of a nonmetallic rubhtance, a number of devices were constructed in which the ail, \vas forced into the liquid as fine bubbles, through the small y~ac*c! between well-fitting metallic surfaces. Vogelbusch (52) recommends winding the large openings ot nlet,allic tubes or other bodies with wire or fibrous substances. 'fhe air compressed into the tubes or other hollow bodies will enter the liquid between the narrow space of the joining wires 01' fibers. He also compresses the perforated surface of a metallic, tube (60) so that the round holes will be deformed into narron. openings. A number of rings cut from sheet metal (.CtJ) are cwmpressed next to one another to form a t,ube-like body. Dra~viiig the compressed air into the hollow space causes it to escape into the liquid between the rings, in the form of fine bubbles. According to Lockey ( l h ) , the air is forced into the liquid through the lengthy cuts of two metallic tubes. The snialler tube fits into the larger, and one of them is rotated. Rank and Hahn (24) describe aerating bodies made of pa~allel ivire of square cross section. Using lorn excess pressure, 0.5 pound per square inch, the air enters the liquid between the \vires i n the form of fine bubbles. The fineness of bubbles ii increased by the sharpness of the edge of the wires. They claim that 18.7 horsepower are sufficient to supply 450 cubic feet of air per minute in mash 1 1 . 5 feet high, in the form of fine bubbles. They also state that 29 horaepo\Ver are required n ' h r i i diaphragm bodies are used undei, iclentical conditions.

U I

Figure

7. Simple

F i n e - A e r a t i n g D e v i c e of d e B e c z e

(1)

\.70gelbuscli (64) describes equipnieiit in which air passes into the liquid through the holes of a fast-rotating, hollow metal device. Air i8 drawn into this rontainer through a hollow vertical shaft, which a l ~ oprovides the revolving motion. Baffle plntes prevent t,he rotation of the liquid (Figure 6). Voge!Ijusch ronstructed several (ievices; the final form is a hollow !)impeller of perforated metal rotated at high speed (800-2000 : ~ . ~ i . m , )The . speed of rotation permits the air passing through i he relatively large holes (0.5 to I mni.) to enter the liquid in the f o m of very fine bubbles, which are further divided by the fastmoving propeller into microscopic particles. The fineness of the air bubbles increases with the difference in speed between liquid a n d propeller.

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after eiiiulsifying it with air by passage through centrifuge-like equipment similar to yeast separators. No air compressors are required because the centrifuge sucks the necessary air. All the wort passes through the aerator every 25 minutes. Jonas claims that oniy 20 horsepower are needed to provide enough air for 13,200 gallnns of wort. ACKNOWLEDGMENT

huLhors wish to express their appreciation t o Isidoro Caldav, h., for the drawings. BIBLIOGRAPHY

Becae, 6 .de, Hungarian Patent 110,202 (1934). Becae. G. de, U. S.Patent 2,199,722 (1940). Bermann, Viktor (to Verband der Csl. Presshefefabriken), Czechosiovak, Patent 51,832 (1935). Braasch, H., and Braasch, A., German Patent 605,912 (1934). Bratton, G. S.(to Anheuser-Busch, Inc.), U. S. Patent 1,732,921 (1929).

Foth, Georg, Handbuch der Spiritusfabrikation, Berlin. Paul Parey, 1929. Giesecke, E., Austrian Patent 65,676 (1915). Ibid., 65,677 (1915). Ibid., 65,678 (1915).

Gosda, Julius, Brit. Patent 412,842 (1934). Jansen, S., Ibid.,366,753 (1932). Jonas, V., Austrian Patent Application 479/34 (1934), Klipfel, C., Swiss Patent 21,295 (1901). Lockey, J. (to Distillers Co., Ltd.), Brit. Patent 387,486 (1933). Maschinenbau A.-G. Golaern-Grimma, German Patent 246,708 ( 19 14).

Maschinenbau A.-G. Golzern-Grimma, German Trade Marks 1,238,254 (1932) and 1,301,483 (1934). Zbid., 1,253,788 (1933).

Meyer, A,, Dutch Patent 8368 (1921). Natl. Carbon Co., “Porous Carbon and Graphite”, Catalog Section M8900 (1943). N.-V. Internationale Suiker en Alcohol Cis-ipagnie, Hungarian Patent Application 516,617 (1937). Pavcek, P. L., Peterson, W. H., ani‘ slvehjem, C. A.. IKD. ENG.CHEM.,29, 536 (1937). Peter, Ludwig, German Patent 336,246 (1922). Ibid., 338,886 (1921).

Rank, W., and Hahn, W., German Patent Application N31.839 (1931).

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Reader’s Digest, “Something’s Brewing”, Bet., 1943 (condensed from Time, Aug. 9, 1943). Schattaneck, E., Austrian Pat>eniApplication 1631/34 ( I 934). Schula, M., German Patent 91,50i (1898). Selas, Co., Bull. 706-12 (1943) and 912 (1943). Sigmond, A. V., German Patent (ii,328 (1893). Stark, W. ELt Kolachov, P. J., and Wiilkie, 1-1. F., Am. Soc. Brevi. ing Chem., Proc. 4th Ann. Meeting 1941, 49-56. Staub, E., Chem-Ztg., 52, 189 (1928). Stich, E. G., Brennerei-Ztg., No. 1761 (1927) Stich. E. G.. German Patent 507.284 I19XI). Ihid., 543,776 and 545,345 (1932) Ibid., 567,518 (1933). Stich, E, G. (to Norddeutsche Hefeindustri A.-G.). Ibid.. 553.231 (1932): German Patent 526.951 (1931): (to Wire schaftliche Vereinigung der deut. Hefeinduatriej, Ibid., 561,978 (1932). Stich, E. G. (to Norddeutsche Hefeinduatri A.-G.), Ibid., 590,560 (1934). Ibid., 594,192 (1934). Ibid., 594,193 (1934). Ibid., 594,195 (1934). Ibid., 594,361 (1934). [bid., 594,671 (1934). Stich, E. G. (to Wirtschaftiiche Vereinigung der deut. Hefeindustrie), Ibid., 622,962-3 (1935). Stich, E. G., Wochschr. Brauerei, 48 (1926). Strauch & Schmidt, German Patent 552,241 (1932). [bid., 597,953 (1934). Unger, E. D., Stark, TV. €Scalf, I.,B, E., and Kolachov, P. J , , IND.ENG.CHEM..34. 1402 (1942). Vogelbusch, W., Austrian Patent 122,951 (1934;. Ibid., 123,393 (1934). Thid., 126,573 (1933). Ibid., 127,365 (1934). [bid.. 128.825 (1935). [bid.; 136,’969 (1934). Ibid., 142,217 (1935). 1

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Walter, F. G., “Manufacture of Compressed Yeast”, London. Chapman and Hall, 1940. Weleminsky, F., and Butschowitz, E., Zentr. Baht. Parasitenk., I I , 78, 178-91 (1929). Willkie, H. F., and Kolachov, P. J., “Food for Thought”, Indianapolis, Ind. Farm Bur. (1942). R7illkie, H. F., and Prochaska, J. A,, “Fundamentals of Distillery Practice”, Louisville, 30s. E. Seagram & Sons, 1943. Zscheile, A., “Mitteilungen iihpr Presshefefabrikation”, 1935.

ASE OX1

ON OF

J

ROBERT W. LEWIS’ AND OLIVER W. BROWN

T

HE purpose of this investigation was to study the vaporphase oxldation of the picolines over vanadate catalysts in a n effort t o determine the most favorable conditions for obtaining the pyridine carboxylic acids. The production of these acids by vapor-phase catalytic methods has not been reported previously. p-Picoline has received most attention in this study since its partial oxidation product, nicotinic arid, is of considerable importance. The vanadates have been useful as catalysts in the oxidation of various organic compounds. I n 1928 Maxted and Dunsby (3) oxidized several nitro and halogen derivatives of toluene t o the corresponding benzoic acids over tin vanadate. Later Maxted (2) oxidized benzaldehyde, benzyl alcohol, and a number of 1 Present

address, Shell Oil Company, Inc., Wood River, Ill.

Indiana University, Bloomington, In& aromatic hydrocarbons over bismuth and tin vanadates. Bismuth vanadate was also used as a catalyst in the oxidation of furfural to maleic anhydride by Milas and Walsh (6). Kiprianov and Shostak (1) used bismuth, tin, and silver vanadates in the oxidation of benzene to maleic anhydride. Sulfur dioxide was also oxidized to sulfur trioxide over several vanadate catalysts by Neumann (6) and Maxted (4). I n this study the vanadates of five representative metals from different families of the periodic table were used as catalysts. From the results obtained a comparison of the catalytic activities of these various vanadates can be madc. Figure 1 is a diagram of the reaction chamber. Air was the oxidizing agent in all cmes and was taken from a compressed air line. The rate of flow of air was measured by a differential level