US2355057A

US2355057A - Apparatus for deaerating viscose compositions

Info

Publication number: US2355057A
Application number: US403007A
Authority: US
Inventors: Norman A Copeland
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1941-07-18
Filing date: 1941-07-18
Publication date: 1944-08-08
Anticipated expiration: 1961-08-08
Also published as: FR927413A; GB561050A; GB564153A

Description

I 8- ,1 N. A. CQPELAND 2,355,057

APPARATUS FOR DEAERATING VISCOSE COMPOSITIONS Filed July 18, 1941 i 3 Sheets-Sheet l BY I 4 I ATTORNEY 8, 1944. N. A. COPELAND ,3

I APPARATUS FOR DEAERATING VISCOSE COMPOSITIONS Filed July 18, 1941 3 Sheets-Sheet 2 Norman A. Copeland INVENTOR MM-i ' ATTORNEY Aug. 8, 1944. N. A COPELAND I 2,355,057

APPARATUS FOR DEAERATING VISCOSE COMPOSITIONS Filed July 18, 1941 3 Sheets-Sheet a TTORNEY viscose layer becomes.

. Patented Aug. 8, 1944 AiP-AEATUS Foa DEAERATING vrscosn COMPOSITIONS Norman A. Copeland, Wilmington,

DeL, aasignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware Application July is, 1041, Serial No. 403,007

'1 Claim.

The present invention relates to apparatus for the removal of air, or other gases, contained in liquids. More specifically, it' relates to the removal of air and other gases from viscose in a continuous manner.

While it is apparent that the app a of n?- present invention is suitable for remoyingah from various liquids, for convenience, the invention will be discussed with specific reference to the deaeration of viscose.

In the production of articles such as yarns or pellicular structures" from viscose compositions, it is necessary to remove the air, or other gases, from the compositions before spinning the yarn or casting the film. If this air is not removed,

. th air bubbles pass through the extrusion oriflcescausing broken filaments during the spinning orjin the caseof films, air bubbles, or holes, will be formed in the film.

Air is present in viscose in two forms, that is, as occluded air which appears as bubbles and dissolved air. If a body of viscose is subjected to a vacuum, the bubbles present becomes larger becauseof the decreased pressure and tendto rise more rapidly tothe surface. The dissolved air forms bubbles and gradually comes out of solution at the surface of the viscose. These actions, of course, become faster the thinner the If a film of viscose is passed continuously over a vertical surface, the same actions take place, but at any reasonable filmvelocity, under low vacuum, i. e.', a pressure below atmospheric pressure but above that at which the viscose boils at any given temperature, air bubbles formed at the film are folded back into the viscose and do not escape; If a high vacuum is employed, such that the pressure is below the vapor pressure given temperature, water is boiled from, the viscose and the removal of airjs greatly accelerated ,since water vapor evaporates into the air bubbles causing themto swell and burst. Also, dissolved air is removed by the sweeping efiect of water being boiled from the film. Deaeration of the film will be complete if the film is sufliciently thin and the boiling sufficiently violent that evaporation takes place throughout the full depth of the A number of methods have used to remove the air from viscose compositions. In one of these, the viscose was treated under the action of a vacuum in a kneading machine. In

been proposed and inches of mercury, while holding it in large rest tanks during the ri ng of the viscose. During this period, the viscose may be passed through a series of rest tanks under this high vacuum. It is further'known to cause the viscose to be spread in a thin film in a container and to subject it to a vacuum which preferably does not cause boiling of the viscose.

There have been a number of disadvantages in the above prior art processes. In most cases, the air is not completely removed. While'the occluded air is diflicult to remove completely, it is of the'viscose at any another method, the one which is probably the most commonly used, the solution is subjected to 'a high vacuum, insome cases as high as 28 even more diflicult to remove a substantial part of the dissolved air. In cases where it is desired to spin a high index viscose, the time necessary for removing the air is sometimes so long that the desired index is passed before th air is removed. The known types of apparatus for removing air from viscose will gradually build up skins on the walls of the apparatus as the result of the spattering of the viscose. In some'cases, large particles of gelled viscose from the skin formation fall into the solution causing filtering difilc'ulties. It is also necessary to clean the apparatus often because of the skin formation.

It is, therefore, an object of this invention to provide an improved apparatus for removing occluded and dissolved air, or other gases, from liquids.

Itis a further object of this invention to provide an apparatus for the continuous deaeration of viscose.

It is another object of this invention to proover the. side walls of a chamber, subjecting the ,film to a high vacuum such that the viscose boils,

collecting the deaerated viscose in the bottom of .the tank, and continuously withdrawing the solution from the vacuum chamber. This chamber is preferably so designed that all wetted portions of said chamber are washed by a continuous flow of viscose and that sputtering of the boiling solution on dry portionsof the chamber is substantially eliminated, thereby substantially preventing the vacuum in the chamber,

' with parts shown 19. The bulb transmits ture reading to the temperature gauge 5|. similar temperature bulb 53 Preferably, the temperature differential between the incomingviscose and the boiling point of the viscose is maintained constant byregulatwhereby .the quantity of water eve-ported per unit volume of viscose will remain substantially constant.

The details the invention Will be better unto the following detailed description when taken in connection with the accompanying illustrations, in which:

Figure l is a vertical sectional view of a deaerating apparatus suitable for use in accordance with the present invention.

Figure 2 is a top plan view of the apparatus shown in Figure l.

Figure 3 is an enlarged sectional view showing a detail of the viscose distributing device of the deaeration apparatus.

Figure 4 is an enlarged sectional view. of a modified form of distributor device.

Figure 5 is a diagrammatic elevational: view, in section, of a modified form of deaeration apparatus constructed in accordance with the present invention. 1

Referring to the drawings. reference numeral derstood by reference H designates a deaeration tank having concave top and bottom sections and constructed sumciently heavy to withstand a high vacuum. A conduit 13 is connected to the top of the tank H. The conduit l3 is provided with a pressure gauge I4 and a throttling valve 15 and a vacuum pump l'l whereby to impart a vacuum to the tank. A manifold 19 is positioned about the upper periphery of the tank. 'A header conduit 21 is connected to the manifold at opposite sides of the tank. A viscose composition fed to the header 2| through conduit 23. A plu rality of connecting conduits 25 are connected between the manifold l9 and the tank H. As

shown in Figure l. the connecting conduits 25' pass through the cylindrical wall of the tank ll into the distributor 21 which is described in greater detailbelow. The distributor 21 is. positioned a. sufllcient distance below the top of the tank II to prevent spattered particles of viscose, due to the boiling of thelatter, from contacting the top of the tank. The distributor directs the viscose downwardly into contact with the side wall 33 of the tank. The tank is preferably rovided with an annular ring 35 which will func ion to redistribute the flow of the viscose to avoid the formation of rivulets. The viscose is designated by line 31. maintained substantially level in the tank II This level is preferably constant.

from the tank H through conduit 39 positioned in the bottom of'the tank. The conduit 39 is provided with valve 40 and pump 4|. II is also provided with a glass gauge 45 which will indicate the level of the viscose. If desired, the gauge 45 may be connected to the viscose outlet conduit 38 by'means of by-pass conduit 41. The bypass conduit 41 functions to pass viscosefrom the outlet line back into the tank H to avoid building up 'coagulated viscose in the conduits leading to the gauge 45. A temperaturebulb 49 is positioned in the manifold an accurate temperais positioned against the internalperiphery of the tank at a distance slightly above the level 1 the viscose 31. The

temperature bulb '53 is connected to a temperature gauge 55 whereby to transmit an accurate The deaerated viscose is withdrawn overlapping relationship to. lip 6| so that the vis- 3 since the flow of viscose along greater diameter than the header 2| and from face of the viscose as it flows cose flowing from between the two lips is directed downwardly along the lip 6! into the tank. A flow shield 69 is positioned between the bottom of lip BI and the internal periphery of the tank II. The viscose will follow flow shield 159 and will then flow along the internal periphery of the tank wall.

Referring to Figure 4, numerals II and Ila designate a tank in which the upper section is of lower section. The internal periphery of.the upper section II and the internal periphery of the top of lower section Ha form the two legs of the U-shaped member of the distributing device. ber 1| is bent inwardly at right angles to contact the lower section lla thereby completing the U-shaped member. In this modification the connecting conduits 25 are preferably provided, at the end projecting within the U-shaped member, with an opening 13 on only one side thereof. It will be readily apparent that the series of connecting conduits 25, each provided with openings on only one side of their inwardly projecting ends issuing viscose downwardly along the wall of the tank Ila. It will be noted that in ,this form of device the viscose will flow solely in a vertical film since the internal periphery of the tank is a continuation of the lip 6|. This form of device is preferred over that shown in Figure the internal periphery of the tank wall is found to be more uniform.

The operation of the above-described device is as follows: The viscose from a feed tank (not shown) is passed into conduit 23, then into header 2| through manifold is and connecting conduits 25 into the distributor 21. The vacuum pump [1, in the meantime, has evacuated the tank II to a suflicient amount that the viscose at the temperature at which it passes into the distributor is caused to boil. In other words, the pressure on the surfrom the distributor is slightly less than the vapor pressure of the viscose. The viscose as it issues from between the lips 6i and G1 boils and froths with a considerable amount of spattering and at the same time ilows'downwardly along the lip Si in a continuous film. The film flows down along the flow shield 89, unless the device is constructed as shown in Figure 4, and then downwardly along the internal periphery of the wall of the tank. As a result of the boiling and frothing of the viscose, the contained air is removed together with a. very small amount of water. The evaporation of the water induces a cooling of the vis- The bottom of mem- -reaches the constantly maintained and the boiling point of the viscose.

sure of the surrounding atmosphere the boiling will cease. The vacuum imparted to the tankis preferably such that the boiling point o'fth'e viscose is at a temperature of from 10 to 35 C.

below the temperature of the incoming viscose. The film of viscose flowing along the internal wall of the tank is preferably caused to fiow over an obstruction such as ring 35 whereby the film is re-formed to prevent the formation of rivulets on the wall of the tank. The viscose, before it level 37, is caused to pass a temperature bulb 53 on the internal peripheryof the tank. The vacuum may be manually adjusted by throttling valve l5. The vacuum will be adjusted from the temperature readings of temperature gauges and 55 to maintain constant the temperature diiferential between these two readings. By 'maintaining this temperature differential constant, the amount of water removed from the viscose will remain constant and the viscose composition will be maintained uniform. The viscose is constantly withdrawn through outlet conduit 39 controlled by valve and pump 4|. The level of the viscose in the tank will be maintained substantially constant by observation of the gauge glass and control of the pump 4|. The conduits of the gauge glass may be occasionally.

cleaned by passing viscose from the outlet conduit 39 through by-pass 41. It may also be desirable at intervals to pass a cleaning fluid such as water through the entire length ofthe gauge glass to maintain the viscose therein free from gelation.

The operation of the apparatus provided with the construction of the distributor shown in Figure 4 will be identical to that above described. The film of viscose will be maintained with a more uniform thickness since the flow along the internal periphery of the device will have no change in direction.

1 Referring to Figure 5 of the drawings, the deaerating apparatus is provided with automatic means for maintaining constant the temperature differential between the incoming viscose The conduit l3 through which the tank II is evacuated is connected with a small tube 93 which leads to a pressure gauge 95 by means of which the vacuum in the tank may be visually determined. The conduit i3 is also provided with a butterfly valve 83 by means of which the suction of the vacuum pump may be throttled. The butterfly valve 83 is autmatically operated by motor diaphragm 85. The motor diaphragm is in turn operated by means of the pressure contained in tube 81 leading thereto. The pressure in the 53. Inasmuch as the controller per se is'no part of the present invention, the details thereof are not set forth herein. One example of an instrument suitable for use in this capacity .is the Taylor Fulscope controller adjustable sensitivity type with automatic reset (I22R) differentially connected with the two temperature bulbs as shown and described on page V-6 of the in-' struction booklet published in 1939 by the Taylor Instrument Companies, Rochester, New York. The vacuum conduit I3 is also provided with a. shutoff valve l5 and a three-stage steam jet pump 8|. The apparatus otherwise shown in Figure 5 is substantially identical to that shown in Figure 1 of the drawings above described,

The operation of the device disclosed in Figure 5 is as follows: The tank II is evacuated to the point where the vacuum is sufliciently high to cause a boiling of the viscose composition which is to be deaerated. The viscose is passed into the distributor and into the tank in the same manner as above described with reference to the apparatus of Figure 1. The viscose froths and boils and spatters towards the center of the tank and at; the same time a film of the viscose passes downwardly into the body of the viscose contained in the lower portion of the tank. The temperatures of the viscose in the manifold and in the tank adjacent'the level of the body of the viscose in the lower portion of an expansion or contraction of the hydrocarbon liquid in the

bulbs

49 and 53 respectively. In case of an increase in temperature, the expanded liquid in bulb 49 is forced through capillary conduit 59 into the controller device 9|, and the expanded hydrocarbon liquid in bulb 53 passes through capillary conduit 52 into controller 9|. The controller 9| is provided with air under a constant pressure which pressure is used by the controller mechanism 9| to operate the motor diaphragm 85 through conduit 81 to open or shut the butterfly valve 83 thereby controlling the pres sure in the tank 1 I. Should the viscose flowing into manifold l9 having a gradually rising tem- 85 to slightly close the butterfly valve 83 thereby tube 81 is determined by the temperature differential between

bulbs

49 and 53 positioned respectively in the manifold l9 and on the inter nal periphery of the tank slightly above the level of the viscose. The-temperature'bulb 49 is provided with a capillary tube 50 containing an expansible hydrocarbon liquid and said capillary tube is connected to'a differential temperature controller 9|. The temperature bulb 53 is similarly provided with a capillary tube 52 which is also connected with the controller 9|. The controller 9| may be any device w ch ill function to regulate an air pressure acting 0 motor diaphragm 85 in accordance with the temperature decreasing the evacuation in the tank I to maintain constant the amount of boiling of the viscose flowing. into the tank. The film of viscose having the slightly increased temperature will flow into contact with bulb 53 which will compensate the controller mechanism to again maintain constant the temperature differential between the incoming viscose in the manifold and the boiling point of the viscose on the internal periphery of the tank slightly above the viscose level 31., Should the temperature of the viscose remain the same but the volume of viscose increase, there will be no immediate function of the bulb 49. From the increased flow of the viscose more water vapor will be formed than can escape through the outlet throttled by the butterfly valve, so the pressure will increase and the boiling point of the viscose will increase. The temperature of the viscose at the bulb 53 will rise causing the controller 9| to slightly open the valve 83 thereby reducing the pressure in the tank to again establish the temperature differential selected. The vacuum in the tank can always be checked visually by the pressure gauge connected to the vacuum con- I'he viscose is withdrawn through outlet conduit 39 provided with valve 40 and pump 4| in the same manner as above described with referdiflerential of the two temperature bulbs 49 and the tank ca use "to cause boiling of the viscose,

small bubbles formed present, there will be some ence to the apparatus of Figure 1. The pump ll used to remove the deaerated viscose continuously. from the tank H is preferably a standard constant flow gear pump.

The following specific example. is given to illustrate the process of the present invention, it being understood that the details set forth in this example are not to be considered as lilniting the invention thereto.

, Example I u A 7% cellulose, 6% caustic viscose having a salt index of e and having is pumped into the continuous deaerating tank at a rate of 245 pounds per minute. The viscose is directed downwardly against the side walls of the tank and fiows in a continuous film having a thickness of approximately inch down the side walls of the tank and into the body of viscose in the lower portion" of the tank. The body of visa temperature 'of 21 C. 1

" a; a vacuum cose is maintained at a substantially constant level in the lower portion of the tank. The tank is subjected initially to a vacuum corresponding to 29.2 inches of mercury, and the viscose film boils and froths as the air and a small quantity of water 25 are removed therefrom. The evaporation of the water induces a cooling of the viscose andthe viscose film, as it reaches thebody of 'viscose in the lower portion of the tank, has cooled toa temperature of 18 The deaerated viscose is continuously pumped from the bottom of the tank at the-rate of 244 pounds per minute and sent to a supply tank for a viscose rayon spinning machine. The almost negligible decrease in the amount of viscose withdrawn from the ank per minutefrom the amount introduced per inute is caused by the small amount of water evaporated during deaeration. This very small quantity of watermay be added to the viscose before -deaeration. Temperature readings are frequently taken of the incoming viscose and viscose just before it passes into the body of viscose in theitank. The vacuum in'the tank is regulated to maintain the temperature differential between th two readings at 3 0., whereby the amount of water evaporated per unit volume of viscose is maintained substantially constant. I I

The followlng'prbcedure may be'us'ed to determine whether the dissolved air as well as the,

deaerator device.

0., and has ceased to boil.

vacuum,'but not sufliciently high to cause boiling. If air is present, either cluded, it becomes evident by the formation of small bubbles which rise to the surface and burst. This takes place slowly so that the sample should be left under vacuum for three or four minutes.

The invention is not limited to the use of any. particular evacuating device since any means of obtaining the vacuum may be used, which will produce a vacuum high enough to cause boilin of the viscose. While the three-stage steam jet vacuum pump is preferred, other devices such as a piston vacuum pump, a centrifugal vacuum pump, and other pump or used. It is desirable to use a large cylindrical tank chamber and as a surface over which the viscose film may flow. Preferably, the tank is sufilciently large to prevent the spattering of the viscose onto any surfaces which are not continuously washed with the flowing film of viscose. The top of the tank is preferably at least 18 inches above the distributor device to avoid spattered particles from contacting the top. A suitably sized tank maybe one having a diameter of 6 feet anda. height of 92/ feet. Although cylindrical tanks are preferred other shaped containers may, however, also be used; for example, a tank having on its inner surface large corrugations wherein the line of .corrugation is parallel to the axis of the tank may be used as a means of increasing the surface area over which the viscose flows without increasing the diameter of the tank. It is also possible to use multiple tanks such as one large tank with a smaller tank inside wherein a film of viscose is provided on the inside surface "of the large tank and on the outside surface of the small tank.

The capacity of vacuum, provided said vacuum is sufiicient to .50 occluded air has been removed by the -continuous when using a" bright viscose,

i.e., a viscose which does not contain a pigment or delusterant, a 125 cc. Ehrlenmeyer fiask is filled to a depth of /2 inch. The fiask is then subjected for half a minute to a vacuum sufficiently higli that is, the pres sure on the viscose is lowered to or pressure of I air present, there is very, little foaming and any;

vacuum is released. If there is any dissolved air of small'bubbles will form in the body of the viscose. These bubbles do not disappear when the vacuum is released, but require an appreciable length of time to redissolve'. several minutes to two or three hours depending "upon the amount of air present in the bubbles and upon the condition of the viscose, such as viscosity, temperature and so forth.

Since small bubbles cannot be seen under the surface of dull viscose, a slightly different procedureds used from that similar sample is taken and The thickness of cause boiling of the viscose. The output of the device may be varied depending mainly upon the rate at which the viscose is introduced into the tank provided suitable deaeration is obtained.

this film of viscose flowin! down the sides of the tank will vary with the amount of viscose fed to said tank. The film should not be so thick that only part of the thickness of the film boils during its fiow inside the tank. The entire film should boil to obtain suit- & able results.

I below the vapor} the viscosew If there is no dissolved.

foaming and a number This may vary from w ture of 21 collapse immediately as the In the above specific example, the viscose was brought into the deaeratio'n' tank at a tempera- C. and was removed at a temperature of 18*. C., a temperature differential of 3 C. Since the temperature drop of the viscose as it passes throughthe tank is a measure of the amount of water evaporated therefrom, the temperature drop is regulated and should not be too great. It would be possible to operate this device with a temperature differential as much as 20 C.,

, but it is preferred that the temperature drop not described above. A I

subJectedto-ahigh 76 exceed 7 C. The temperatureefat which thr viscose may be introduced into the tank..may vary from 15 C. to 40 C. or in some cases ever higher. At temperatures lower than'15" C., the viscose become; so viscous that it flows too slowli for pr'actical operation. he effect of tempera ture on ripening of'the viscose should be taker dissolved or 00- jet action devices may 1 from 0.3 to 3 pounds of e into consideration when operating at the higher temperatures. In deaerating liquids other than viscose, temperatures other than those given above may be used depending upon the properties 01 the liquid.

I While the apparatus of the present invention has been described in termsoi' its use in deaerat: ing viscose, it is understood that it is not'limited thereto and that it may be used to treatpther viscous liquids, such as soiutionsof cellulose derivamves, vinyl compounds, including polyvinyl acetate, polyvinyl alcohol, polyvinyl acetal, etc: resins, either synthetic or natural, including rosin, dammar, alkyd, methacrylates, etc.; and synthetic linear polymeric materials including polyamides, polyesters, and the like. I

1 By the use of the process and apparatusoi the present invention, numerous advantages in the deaeration ofviscosmare obtained. The viscose may now be deaerated almost instantaneously although for operating reasons it remains in the tank for about 20 minutes, whereas heretofore it took about 20 to 30 hours in most cases. The flow oi viscose through the system is continuous which is an improvement over the vacuum rest tank process inmost common current use. Much less equipment and space is needed for the pres ent apparatus than heretofore. Improved de aeration is obtained since not only is all of the occluded air removed, but practically all of the dissolved air aswell. c

Viscose tends to form skins and to gel if left I, stagnant. The-present apparatus is so designed that all wetted portions of the' tank wall are washed bya continuous flow oi and spatterlng on dryvportions is eliminated. By this means, stagnant areas in the deaeration system are eliminated thereby permitting the apparatus to operate for long periods or time without stopping for cleaning said apparatus.

It is well-known that viscose ripening is a function of both time and temperature. 'lf'he more accurately the t e element can be controlled, the higher the temperature which can be used. Since viscose undergoes some cooling as it enters the deaerator because of evaporation of water, it is possible to ripen at a considerably higher temperature than at present and control a if desired. By this means, it is possible in the preparation of the viscose to use an excess of carbon disulfide andto subsequently recover this excess from the viscose in the deaerating system.

. the internal periphery of the container In the past, considerable care has been taken not to use, any viscose preparation procedures which would tend to cause air to be occluded in the viscose. Because Of the high efiiciency of the present process and apparatus for removing 'air, many procedures not heretofore practical may be used. For example, centrifuges and disintegrators which tend to beat or throw air into the viscose may behsed provided the viscose is later deaerated according to the present invention.

Since it is obvious that many changes and modifications can be made in the above-described process and apparatus without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to the above-described details except as set forth in the appended claim.

I claim:

A viscose deaerating apparatus compris cylindrical container, a vacuum pump conne ted to said container, a viscose maniiold,a plurality of viscose inlet means connecting said manifold to said container near the top thereof, a U-shaped annular viscose distributing trough positioned on mediately adjacent said inlet means, and a i'rustum-shaped viscose-directing member contacting and extending downwardly from the inner bottom edge of the trough to the side wall of said container whereby to direct the flow of viscoseissuing .trom said trough in the form of afilm downwardly and into contact with the uppermost exposed portion 01' the side wall below said trough.

' NORMAN A. COPELAND.

and im-'