US2420356A - Degasification - Google Patents

Description

Patented May 13, 1947 UNITIEZD: STATES- PATENT; OEFzl CE;

DE GASIFICATI ON Russell Edwardv'Compa, Bogota; N. J.,- assignortorn Colgate-Palmolive-Peet flornpany, J ersey- City, N. J., a corporation of Delaware Application August 29, 1942; 'sei'ial Nt'ii-456319 3 Claimsr (Cl. 183 -2.5)Y

The present invention relates to. a process for degasifying'liquid compositions'and', more particularly, to-a process for deaeratingwiscousicom positions, especiallyqdental creams: and pastes;-

and to an apparatustherefor;

Heretofore, great a difficulty has been. eXperi= enced withmany heavy; viscous:compositions;v

especially pastes Land. creams, in that, during;

mixing operations in their manufacture andzespe cially where dried ingredients are addedpa con? siderable volumerof airisbeaten into these com;

positions andremains thereinin the form of .bub

bles in the 'final product: .Bubbles: are 'aISOZ fI'G- quently incorporated a in: these compositions by the liberation-of variousgasesvby chemical: re-

action in l the manufacturing i-floperationr. The presence of bubbles in atcomposition requires that r.

the processor furnish a, .-;larger container: fOl'J a given weight 7 oi? material and, is moreover, :ithe;

product is undesirableziromza merchandising 2 g] weeksfi manufacture. Other proposals and sugagestions :have-rbeenmade for solvingpthis problem;; but none 10f these suggestions :and proposals, so. far: asis -known; has: been zentirelyrisatisfactoryri r when :employed-= in industrial-5; operationlruponza commercialzscale.

It is an object Of'thB'JIJIGSBHtElIIVGIItlOII to"pro-:-- vide a-novel method .for:degasifyingviscoustcome't positions, which method-is:rapid;andieffi'cientiinwoperation:

It isranotherlrobject:ofrzthe inventionitolprovide a new methodiiforvremovin'gabubbles from'tfiui'd' compositions andsr'plasti'c materials;.especiallyz-a' those having =ra low but ivisually perceptible-irate l of efiow at moderate temperatures; wwithoutssubs stantial "change; inv their1:composition. 1.

Itiis also an .iobject'. of zthe: invention to provide :1 an. improved: method for deaeratingsscreams: and: p especially dental creams andipastes; witnv out appreciably-lowering: their: moisture or l sol vent content;

aspect; .Thus; upon standing for a :considerableiir periodof time upon-the shelvesof..dea1ersi1ori-" upon thepremises of 'the consumer; :there' is a a tendenc for theselgas bubbles slowly to collect f in larger bubbles. For this reason, even. though the proper weight of materiallis in the container,

the appearance of the :material whe'niput :intouse is unsatisfactory... Even: inthose cases where thematerial is usedwpromptly;:so "that the bub-'- only partially coalesce; their presence bles throughout the compositionugivesiitl'a, 'coarse and unsatisfactory appearance: .Where: gas bub'-' bles occur in the product as; a' result of chemical reaction, there is also the disadvantage that the presence of said gases ma) modify the properties-'- of the compositiom- The .prior art hasattempted to: rid such com positions of': the bubbles: contained" 1 therein by various means, For-example, the' compo'sitionis permitted" to stand in. bulkifor a few days and is then stirred on the theory that the small bubbles collect into bubbles ofv somewhat large-r size' and that theyucan then be released by the'stirring operation; In the case of lightercompositions;- heat is sometimesfiapplied in conjunction with the standingyandstirring; After stirringr' the material is permitted-to stand for a few days" longer andisthen stirred again; With heavier compositions; such' as pastes and creams; this op eration is repeated three or four times within a period of a couplevofxweeks. Itwillbeapparentthat such a process has -considerable-disadvantages: from a practical: standpoint in: 1arge'-sca1e operation; as-storage; faci1ities-;;musttbe-provided in .theufactory;for: the product s'of a "couple 0f The :invention further: provides: i'aniimprov'ed apparatusaior. degasifying; viscous compositionsa Other objects :and advantagesofithe invention-- will be apparent'ito those'iskille'd in the art: fromthe following descriptionp-takentim conjunction withzthe.accompanyingidrawing, wherein:

Fig-cl is a vertical:ise'ctional view pf an embodiment of a device accordingzto the presentirr ,vention be subjected to therloweripressure for a sufiicient time to permit expansion::of the-gas-bubbles: which breakathroughf and leave the material;

Thedegasifiedrmaterialsis quickly collected in areceiveni thei promptcfcollection giving volati1' liquid; constituents ttherein insufiicient time i -to" volatilize:

The orificesimay be-disposedin I any suitable 1 foraminous body for 'holding-the-viscous material?- Thus, a perforated plate or a perforated'pipe :sealed at oneend thereof 'may be" used," one, fine" sieve or screen may be employed. If desired, a series of perforated plates and/or screen may be provided, and a vacuum may be applied either below the bottommost member of such series or between other members as well. In using a perforated pipe, the pressure differential may be obtained by applying a high pressure upon the material within the pipe, or, preferably, the pipe may be enclosed in an evacuated vessel.

Although the mechanism of operation of this process is not to be limited to the following theory,

it is believed that, where the material to bedegasified is passed through a perforated plate into a low pressure zone, the material is divided into a multiplicity of filaments, thus providing a large surface area for exposure to the expansive effect of the low pressure, and the gas bubbles in the extruded filaments expand and break through the material. A fine screen has a similar effect, as the material is supported by the screen and, upon applying a vacuum therebeneath, the gas bubbles are released from the material at the screen surface and pass through the screen, while the viscous composition comes through at an appreciably slower rate, thus furnishing a series of large areas of material at the screen surface for exposure to the lower pressure. vides a shearing efiect upon the composition similar to that of passage through the orifices of a perforated plate, although, when employing a screen, the material cannot be retained in separate streams for any appreciable time after passage therethrough. It will be understood that the theory of operation set forth in the present paragraph isnot necessary to an understanding of the invention disclosed herein and that the same is advanced merely as an aid to the further development of the art.

When using a screen or sieve, selection of one of sufficient fineness to support the composition for an appreciable time should be made, having due regard to operating conditions, including viscosity and apparent density characteristics of the material to be degasified as well as the pressure differential employed. Screens of about 80 mesh or having larger openings to about 200 mesh or having smaller openings may be used, especially with heavy solutions containing substantially no solid matter. Indeed, the use of screens generally in this connection is more applicable to the degasification of such viscous so' lutions than to the treatment of plastic materials of the type of dental creams and pastes.

The use of screens may be advantageously combined with perforated plates, and a suitable apparatus for degasifying viscous compositions, especially heavy solutions, may comprise a degasifying vessel having a pair of close-fitting, horizontal, perforated plates therein with one or more close-fitting, horizontal screens of fine mesh disposed therebetween, means for providing a low pressure zone in the lower portion of the degasifying vessel below the lower plate, and a receiving vessel below the degasifying vessel for collecting the degasified material.

The degasification of viscous compositions, particularly pastes and creams, is preferably carried out in an apparatus comprising a tank having a constricted lower portion and a. close-fitting,

perforated plate horizontally disposed therein above said constricted portion, means for providing a low pressure zone in the constricted portion below the plate, and a receiver disposed below the tank and communicating therewith. The

Passage through a screen also prov tank may be closed at the top for feeding material to be degasified to the upper surface of the plate under pressure, but it is preferred to have the tank open to the atmosphere where practicable and, where it is desired to equalize the pressure on the material during the operation, to employ mechanical means for effecting such equalization. The operation is preferably carried out at room temperature, although slight- 1y higher temperatures may be desirable in some instances; in such case, a jacket, steam coil or other means for controlling the temperature of the material in the tank can be used, or preheating of the material can be employed. It may also be desired in the case of certain compositions, especially those which, upon drying, are apt to form films upon their upper surfaces, to furnish a scraper means for clearing the orifices in the plate from time to time.

The orifices should be fine and are preferably, but not necessarily, smaller in diameter than the gas bubbles to be removed. They may vary from about inch in diameter or smaller to about inch in diameter and may be any suitable distance, say, from about 10 diameters to about 40 diameters or farther, apart. larly satisfactory results have been obtained with orifices of about a e inch in diameter, spaced about inch apart.

The thickness of the plate and the length of drop of the material extruded therethrough are also factors in the operation. The rate at which a particular material is extruded for a given pressure differential is dependent, at least in part, upon the thickness of the plate, and this rate is partly determinative of the length of time during which the gas bubbles in the material are subjected to the expansive effect of the lower pressure zone. The length of drop of the extruded material also influences this effect, and the longer the drop provided, the thinner may be the plate, all other conditions being equal. The plate may vary considerably in thickness, a preferred range being from about se inch to about inch, and-the distance through which the material must fall after extrusion through the plate and before collection may vary from a few inches to a, few feet or more, depending upon various other factors and conditions, as aforesaid and as will appear hereinafter.

The receiver is preferably a long cylinder, which it is preferred to keep about three-quarters full, more or less, in order to maintain a sufflcient head to insure flow of the material to a pump which removes the degasified material from the receiver. It is preferred to provide means, such as a valve between the constricted portion of the tank and the receiver, for allowing the receiver to be evacuated at the start of the operation without subjecting the underside of the perforated plate to this gradual evacuation. After the receiving tank is evacuated, the valve is preferably opened as quickly as possible, so that the material extruded at the beginning of the operation is immediately subjected to almost the minimum pressure, employed. The provision of means, such as a :by-pass valve, for partially equalizing the pressure and allowing the large valve to be opened more easily may also be desirable.

In degasifying a given composition, the physical condition of the material isalso to be considered. Thus, in the case of creams and pastes and other relatively viscous materials, the age of the material plays an important part in the rate of de- Particu- 5: gasification. Ageing of, someof these compositions: for even two or three days sets up a stiffer consistency which-can be :made to pass through the fine orificesof the plate only at a considerably slower rate than when the compositions aretfresh. On the other hand, when such compositions are freshly prepared, the bubbles therein are very finely dispersed and are more difiicult to remove. For thisreason, it may be necessaryin'thecase of very fresh compositions to block'off part of the orifices iii-the plate. and thereby to slow down ,the rate. A'preferred meth d of operation isto permit the composition to age'for a-few hours, say, about four to about eight'hours, before-degasifying. During this short ageingperiod, the finelydispersed gas bubbles appear to coalesce into somewhat larger, visible bubbles, which makes thecomposition more easily degasified. Such, compositions are frequently thixotropic, and the degree of stirring to which they are subjectedbefore being degasified may also influence the rateof degasification.

The .processof the invention will now be describedin connection with an apparatus for carryme the same into practice. Referring to Fig. 1, reference character I indicates a tank having a perforated plate 2 horizontally disposed therein atitscentral portionand adapted for containing abovesaid plate aquantity of a material to be degasified. The .plate Zis about inch in thicknessand isperforatedwith orifices of about inch in diameter. The plate contains about four orifices per square inch and is supported upon an annular bracket .3 which is affixed to the inside of the ,tank. (See also Fig. 2.)

The lower section of the tank, below the centrally disposed perforated plate 2, is constricted andhas an outlet 4 which communicates through a gate valve with a cylindrical receiver 6. A nozzle ,pipe 1 which connects the gate valve 5 with the receiver extends down into the receiver forsome distance. At the side of the receiver, above the lower endcfthe nozzle pipe 7, a connection ,8 to a vacuum apparatus is provided. This connection is equipped with a vacuum breaker 9, .a trap III for the purpose of detecting any of the composition which is carried through the connection by entrainment in the gas stream, and a vacuum gauge l I. The vacuum apparatus may be of the jet type or may comprise a vacuum pump, in which latter case. a dehumidifier for removing any slight amount of water vapor volatilized from the composition may advantageously be employed.

The receiveris ,also constricted at the bottom thereof, and the outlet i2 of the receiver communicates through a small .gate valve 3 with the chamber of a pump M. The pump is driven by a motorJS. Atthe lower portion of the receiver, there is a connection 16 with a liquid level indicator and control l'l whichis in turn connected witha motor control! 8 through a hand and automatic station ,l 9. The. motor control is connected with the motor I5 and isadapted to operate the motor'so as to providev suflicient material in the receiver to maintain agoodhead.

It will be observed that the operation of this device-is extremely simple. The composition to be degasified is run into the top of the tank I and upon the upper surface of the perforated plate 2. The material may be delivered to. the tank continuously, intermittently or in batches. After the tank has beenfilled to a desired level, the-receiver 6 ,is evacuated, both valves 5 and. l3fbei-ng closed. A vacuum of about 28'to about 2.9 inches ofmercury is applied, and,- after. this:

vacuum has been attained, valve -5* is opened. The material to be degasified isiforced by; thepressure -difi'erential through the orifices of the plate. 7 and falls in long filaments to. the bottom of the tank I. During-its fall, the material is subjected to the low pressure and the gas bubbles expand and :breakthrough the surface of the material.

The gas is withdrawn through the connection .8-

directly into the pump chamber-and is delivered. by the pump-tothe storage tanks. It is preferred to provide a rise in the-pump discharge line in order that an-external fluid seal may :be obtained. A conventional automatic control,diagrammatically indicated in the drawing, can be provided, and this is so set that the .pump canbe shut off when the. level of material in-the receiver fallsbelovv a certain point, or the speedof the pumpsfcan be. increased to remove more material from the receiver when the level of material therein is higher than apredetermined point,

Thoseskilled. in the art will recognize that the novel device described-canbe made in any re-. quired size and that the thickness of the perforated plate, the number of orifices-therein, thespacing of these orifices, the distance through:

which the. extruded material is required to fall,

and .various other factors will be varied, depending upon the material to be degasified and upon .the size of the unit. For example, using a unit comprising. a-tank of 28 inches diameter andz33 inches in height on the straight side witha 45 degree conical .bottom and ,a cylindrical receiver of about 18 inches in diameter and-about 12-feet in height, designedfor a capacity of about .750 pounds of dental creamat aspecific gravityof about 1.45 when approximately three-quarters full, it has beenfound that the provision of a inch plate having fourorifices, each of about inch diameter, per square inch, a drop-formaterial extruded averaging about 1 foot and the applicationoi a vacuum of about 28. inchesat room temperature give satisfactory results in del aerating. pastes and creams of about the consistency of dental cream and furnish-about 3,000 pounds per hour of deaerated material.

A feature of the process is that viscous materials can be degasifiedwithout appreciable change in their composition. In operating with adental cream containing a large proportion of air bubthe upper portion of a receiver 6 are shown. As- Y in the apparatus depicted at Fig. 1, there is a tight-fitting, perforated plate 2 horizontally mounted upon an annular bracket -3 within the tank, and an outlet 4 at the bottom of the tank communicates with the receiver through a, valve 5. In this modification, a vertical lifting rod 20 having its lower end rotatably journaled in a bearingat the center of the plateZ is provided,

and a nut 2|. engages the end of-the' rod just.

below the plate. A hub 22 is fixedly mounted upon the rod just above the plate, and a horizontal scraper arm 23 shorter than the radius of the plate but longer than the radius of its perforated area is attached to one side of said hub. The scraper arm is adapted to make scraping contact with the upper surface of the plate 2 upon rotation of the lifting rod 20. Although the rod 20 may normally be manually rotated, means for rotating the same may be provided, if desired. Means for raising and lowering the lifting rod may also be furnished.

A removable floating plate 24 (shown in operative position) is also provided. This floating plate is of slightly smaller diameter than the tank I and has an upward-extending annular flange 25 at it perimeter. There is an aperture at the center of the floating plate surrounded by a collar 26, through which the rod 20 is adapted to pass as a guide therefor.

The use of the modification depicted at Fig. 2 is preferred where very viscous compositions of the type of dental creams and pastes or heavier are to be degasified. Such compositions frequently form films upon exposed surfaces, and such films, forming upon the top surface of material in the tank, cause clogging of the orifices. After the last of the material has passed through the orifices, the lifting rod 20 is rotated, and the scraper arm 23, attached to the rod by means of the hub 22, rotates therewith and makes scraping contact with the entire perforated area of the plate 2. In this manner, the skin formed can be removed before addition of new material. The floating plate 24 may be laid upon the upper surface of the material to be degasified after the last of the batch has been fed into the tank, and the weight of the floating plate provides a relatively constant pressure upon the material, whereby the composition is fed substantially uniformly to the orifices in the plate.

Referring to Fig. 3, wherein another modification of the degasifying tank is shown, there are a pair of perforated plates, 2A and 2B, horizontally disposed within the tank I, and two screens, 21A and 21B, placed in horizontal position between said plates. Both plates are about 1 inch in thickness, the upper plate 2A having orifices of about inch diameter and the orifices in the lower plate 2B being about 1% inch in diameter. The upper screen 27A is approximately 150 mesh and the lower screen 273 is approximately 100 mesh. A vacuum of about 28 inches to about 29 inches of mercury is applied below the system through the connection 8 at the top of the receiver 6.

The -material is be degasified is run into the tank at the top and collects upon the upper surface of the upper plate 2A. The vacuum is applied, and at the start of the operation substantially the full pressure differential of the entire system (viz., about 28 to about 29 inches of mercury) is effective to force the material through this upper plate. The partially degasified material through plate 2A collects upon the upper screeen 21A, and, when this screen is covered, the pressure difference through plate 2A is reduced by substantially the pressure difierence through screen 21a. Similarly, a further reduction in pressure through each plate or screen in the series occurs as the material collects on each successively lower plate or screen. When the system reaches equilibrium, the material, as it passes through each member of the series of plates and screens, is partially degasified, and

the gas released passes through the next lower member in bubbles of larger size. Upon passing through the lower plate 23, the material is substantially completely degasified, and the gas is evacuated.

The system is of particular value in the degasification of viscous solutions wherein the viscosity is appreciably higher because of the presence of gas bubbles. Thus, a concentrated aqueous solution of coconut oil monoglyceride monosulphate sodium salt and sodium sulphate containing minute bubbles of air and having an apparent specific gravity of 0.98 is heated to about 65 C. and run through the modification of the apparatus illustrated at Fig. 3, employing a vacuum of about 25 inches of mercury. A degasified product having a specific gravity of about 1.28 at about 40 C. is obtained.

Fig. 4 shows a modification of the apparatus designed for removing gas from the system as soon as released from the composition being degasified. This has the advantage of not remixing the gas with the composition during the operation. According to this modification, a screen 27 is placed in the tank I in horizontal position between a pair of perforated plates, 2A and 2B, substantially parallel thereto. The upper plate 2A is separated from the screen 21 by a conical collector 28 having a central outlet 29, and the screen is separated from the lower plate 23 by a similar collector 30 having a central outlet 3!. The tank is provided at the side thereof with two connections, 8A and SE, to vacuum apparatus. The upper connection 8A is located below the collector 28 but at a point above the outlet 29, and the lower connection 8B is similarly located with respect to the collector 30 and its outlet. A third connection SC to a vacuum apparatus is provided in the receiver 6 below the degasifying tank. as has been described supra. By this means, a suitable pressure can be applied in any zone in the system. Thus, with atmospheric pressure above the plate 8A, a vacuum of about 12 inches of mercury is applied between this plate and the screen. About 21 inches of mercury vacuum is applied between the screen and the lower plate, and the receiver is under a vacuum of about 29 inches.

The material is partially degasified after passage through the plate 2A, and the gas removed therefrom is withdrawn from the tank through connection 8A. Further degasification takes place on passing through the screen, the removed gas being withdrawn through connection 83. Upon passing through the plate 23, substantially all of the remaining gas bubbles are removed, the degasified material being collected in the receiver, as described supra, and the gas leaving the system through connection 80.

The present invention has been described with reference to particular embodiments, but it will be understood that other variations and modifications can be made and that various equivalents can be substituted therefor without departing from the principles of the present invention. Such variations and modifications are believed to be within the scope of the present specification and within the purview of the appended claims.

I claim:

1. A process for deaerating dental creams which comprises ageing a freshly made dental cream containing air bubbles and moisture for about 4 to about 8 hours, extruding said aged dental cream through a multiplicity of fine orifices into a reduced pressure zone, said orifices being sufliciently far apart to permit the cream to fall freely in a multiplicity of fine streams, subjecting said fine streams to the pressure of the reduced pressure zone for a time interval suflicient to deaerate the dental cream, and promptly collecting the deaerated cream whereby insuflicient time is provided for vaporization of any substantial amount of moisture contained therein.

2. A device for deaerating dental creams which comprises a degasifying vessel, a plurality of substantially horizontally disposed foraminous members closely fitting Within said vessel and separating the Vessel into a plurality of superposed zones, said members having foramina of increasing size from the uppermost member to the lowermost member and each of said members being adapted to hold a quantity of a dental cream containing air bubbles upon its upper surface during operation, and means for establishing during operation successively lower pressures in said zones from the uppermost to the lowermost thereof.

3. A process for deaerating" dental creams which comprises passing dental cream containing air bubbles and moisture into a series of superposed zones through a multiplicity of orifices between succeeding zones, said zones being of REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,146,532 Crane et al Feb. 7, 1939 199,785 Burgin Jan, 29, 1878 2,080,151 Powell et a1 May 11, 1937 2,306,265 Heald Dec. 22, 1942 2,020,250 Stephens et a1. Nov. 5, 1935 1,667,139 Borden Apr. 24, 1928 1,418,002 Kothny May 30, 1922 2,257,943 Fraser Oct. 7, 1941

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