US2287897A - Manufacture of organic derivatives of cellulose materials - Google Patents

Description

June 30, 1.942. H. E. MARTIN 2,287,897

MANUFACTURE OF ORGANIC DERIVATIVE 0F GELLUxOE MATERIALS y Original Filed May 13, 19.58 2 Sheets-Sheet 1 .r INVENTOR i". y lser-bevil1 EMori'in.

wrm@ ATTORNEYS H. E. MARTIN v 2,287,897

MANUFACTURE OF ORGANIC DERIVATIVE OF CELLULOSE MATERIALS y June 30, 1942.

Original Filed May 13, 1938 2 Sheets-Sheet 2 INVENTOR Her' er. E.Mor+m. 7 ,"/w

TTORNEYS ateniedv june 9,1%42

MNUACTURE OFAORG-ANIC DERIVATIVES A F CELLULOSE MATERIALSl Herbert E. Martin, Cumberland, Md., assignorvto Celanese Corporation of America, a corporation ci Delaware Original application May 13, 1938, Serial No. 207,696. Divided and this application March 30, 1940, Serial No. 326,911

2 Claims.4 (Cl. 259-68) This invention relatessto the production of organic derivatives of cellulose, and more parl ticularly to a device for precipitating organic esters of cellulose from a solution in which they are formed. This invention is a division of the invention described in my application S. No.

207,696 filed May 13, 1&38, which matured into Patent 2,239,753, Apr. 29I 1941.

An object of this invention is to provide an improved apparatus for precipitating organic esters of cellulose in a continuous manner and under conditions which may be so controlled as to produce any desired type of ber.

Another object of the invention is the prevention or" the escape of acid fumes into the work rooms, which acid fumes cause discomfort and inconvenience to employees and great corrosive damage to buildings and machinery.

@ther objects of this invention will appear from the :following detailed description and drawings.

in the drawings, wherein like reference numerals refer to the same or similar elements in l the several views:

Fig. l is a side View of a continuous precipitator constructed in accordance with this invention,

Fig. 2is a sectional view of the precipitator,

Fig. 3 is a diagrammatic view showing the vdriving elements of the precipitator,

Ng. 4 is Aa -sectional view, taken on line li-li of Fig. 2,

Fig. 5 is a sectional view, taken on line 5 5,

tinuous precipitator and that the. physical structure of the precipitate may be controlled.

In accordance with my invention, Iconstruct a device for continuously precipitating derivativesof cellulose in which the derivative of cellulose, continuously fed thereto, `passes through a plurality'of 4zones where a precipitating liquid is added and thoroughly mixed with the derivative of cellulose and solvent. By controlling the type and amount of precipitating liquid and the speed of the material through the various zones, there are produced precipitates having any desired physical form from fine fibers, coarse fibers and crumbs to gelled lumps.

This invention is applicable to the production of organic derivatives of cellulose such as the organic esters of cellulose and the cellulose ethers. Examples of the organic esters of ce1- lulose are cellulose acetate, cellulose formate, cel.

lulose propionate and cellulose butyrate, while examples of the ethers of cellulose are ethyl cellulose, methyl cellulose and benzyl cellulose. Al-- though the invention is applicable to the production of any organic derivative of` cellulose, it will be described with reference to the production of the commercially most important organic derivative of cellulose, namely cellulose acetate.

winne, in accordance with this invention, the

. cellulose acetate or other organic ester of celthe solution in which the derivatives of cellulose `is produced contains a catalyst and side products of the reaction. The esteriiication of cellulose with an organic acid results in a solution of the derivative of cellulose in an acid solvent. These derivatives of cellulose are precipitated by adding water until .the concentration of the acid reaches a point below which the acid will not has been carried out by batch processes in huge bowls equipped with power driven beaters. I have found that the derivative of cellulose may be precipitated on a commercial scale in a.A conlulose may be precipitated from any solution such as, for instance, solutions formed by dissolving the prepared cellulose acetate in suitable solvents. it is particularly important in connection with the precipitation of cellulose acetate orl other organic esters of cellulose from esterifying mixtures, that is to say from solutions formedby the esterication of cellulose by means of formic acid or the anhydride or chloride of acetic acid, propionic acid, butyric acid and the like in the presence of ai catalystsuch as sulphuric acid,

phosphoric acid or other acid catalysts, and also f in the presence of a sufficient amount of solvent such as acetic acid, propionic acid, butyric acid, etc. to cause the resulting cellulose ester to dissolve to form a heavy viscous solution of the consiitency of molasses.

In making cellulose acetate by the so-called solution method, cellulose is acetylated by means of acetic anhydride anda catalyst in the presence of a relatively large amount of acetic acid which dissolves the cellulose acetate that is formed to produce a very heavy viscous solution. This solution, usually after hydrolysis or ripening to develop the desired solubility characteristics, is

then precipitated by the addition of a precipitating liquid, such as water, which dilutes the acetic acid to such an extent that it is no longer capable of holding the cellulose acetate in solution. However, since the solution of cellulose acetate is very viscous the precipitating liquid draws the solvent from the cellulose acetate such that it forms a `gel if no stirring accompanies the addition of the precipitating liquid. If the precipitating liquid is beaten into the batch the precipitating liqud acts on the particles of streams of the cellulose acetate to precipitate the same in shreds with sort of a case hardening eiect with the result that the acid used as catalyst or as reagent becomes thoroughly removed by washing. However, if more vigorous stirring and beating is employed and the precipitant is diluted with solvent for the cellulose acetate, the cellulose acetate is precipitated in the form of ner and softer fibers which may readily be stabilized by washing and quickly redissolved.

By employing the apparatus of this invention cellulose acetate may be precipitated in such a manner as to obtain any desired type of precipitation. For instance, there may be obtained large fibers which are not completely hardened and which may be hardened by passing them A into a more concentrated bath of precipitant such as water employed in washing the fibers.l Aithough this typeV of liber is sometimes desired, it is rather difiicult to dissolve in acetone and similar solvents employed in the production of artificial silk from the cellulose acetate. However, by treating the cellulose acetate in several stages or zones and controlling the time that the cellulose acetate remains in each of the various zones andthe concentration of the precipitating liquid added thereto in each zone fibers vof smaller size may be produced. The fiber produced is not only more uniform than that obtained by the use of the batch process and the fiber produced may be,

as pointed out above, completely hardened when.

discharged from the precipitator of applicants invention. The finer bers formed by the addition of weaker precipitating solutions, especially in' the first three zones, are more easily stabilized cellulose is in solution. The receptacle I is con-- nected through a feed line 2 to a pump 3 which may be of any suitable type, but is preferably of the double worm gear type. A feed line 4 connects the pump 3 to the continuous precipitator generally indicated by reference numeral 5. A

` valve 3 may be interposed in the line 4 for controlling the feed rate of the solution to the precipitator.

The precipitator is formed of a rectangular housing 1 having a roof 8 and is preferably provided with windows 3 therein such that the operations within the precipitator may be watched. The precipitator 5 is divided into a plurality 'of zones II, I2, I3, I4, I5 and I8. Inthe zone II is mounted two troughs I1 and vIII each containing a shaft I8 and 2I. Similarly zone I2 is divided into two troughs 22 Vand 23 each containing a shaft 24 and 25. Zone I3 is also' divided into twov troughs 25 and 21 each containing a shaft 28 and` 29. Similarly zone I is divided into two trapped within the particles and cannotbe aasaaov troughs 3I and 32 each containing two shafts 33 and 34. Zone I5 consists of a single trough 35 containing a shaft 38, while zone I8 consists of a single trough 31 containing a shaft 38. Between the various zones are partitions such as those indicated by the reference numerals 39, 4 I,-

42, 43 and 44.

In operation the solution of cellulose acetate to be precipitated enters the precipitator 5 through feed line Hgo the first trough I1 of the rst zone I I and is carried from there through the various troughs and zones until it is ejected from the precipitator through the opening 45 into a sluiceway 46. The precipitated material along with the diluted acid is discharged from the sluiceway 43 into a settling tank A1 wherein the dilute acid is withdrawn and the precipitated cellulose acetate is deposited through conduits 48 and 49 into stabilizing vats or washers 5I or 52.

The advantage of dividing the precipitator into zones and troughs is that individual stirrers may be provided having individual speeds which may be varied from one section to the other depending upon the time necessary to hold the solution or fibers in each section. Furthermore, one stirrer may be'stopped for cleaning or repairing without stopping the others.

Upon each shaft operating in the, various troughs are mounted stirrers. These stirrers are different in design according to thespecial function in the process. For'instance, the shafts I9 and 2| in the zone II and shafts 24 and 25 in zone I2l have mounted thereon a stirrer 53 as shown more in detail in Fig. 4. This stirrer consists of blades set on the shaft at about 9..'30" angle and staggered around the shaft so as to give a screw effect. The blades 54 are set in a spiral so as to'carry the solution back and forth across the precipitator thus giving more uniform mixing of the solution and the dilute precipitating acid which is added at that zone. 'Ihe stirrers in zones II and I2 turn toward each other so as to pull the viscous solution towards the center of the two stirrers. As the solution of the derivative of cellulose becomes sufficiently worked with the dilute liquid it passes through a narrow slot 50 in the partition 39. After the solution of cellulose acetate has been further diluted or thinned and uniformly mixed with the precipitating liquid in zone I2, it is forced to rise over the partition 4I through an opening 55. in one end thereof.

'I'he solution of the derivative of cellulose is held in zones II and I2 and has added thereto suiiicient precipitating liquid to thin down the solution in which condition it is passed through the cutaway portion 55 into zone I3. In the zone I3 suihcient precipitating liquid is added to commence the precipitation of the derivative of cellulose. In this zone the shaft 28 operating in the first trough 26 is provided with a spiral screwlike stirrer 58. The stirrer 58 may be a strip of stainless steel or other metal twisted into a spiral. Due to the radius of troughs 26 and 21 overlapping one another the precipitated derivative of cellulose is pulled or stretched at the same time that it is being well mixed with the precipitating liquid. The beater-stirrer 51 is formed by threading a plurality of hubs 58 on the shaft, each hub containing an extending' shaft 53 at the end of which is mounted a paddle 5I. These paddles act to grab the precipitated derivative of cellulose from the stirrer 58 and pull it out or stretch it such that the tendency is to form a fibrous precipitate. The material is discharged from zone I3 through an opening 62 in the partition 42 to zone I4 containing an identical set of stirrers and beaters as in zone' I3. In zone I4 additional precipitatingl liquid is added while the Fig. 6 beat the material and tend to harden the f fibers, iinally discharging them into zone I6 where a similar action takes place. The length of time the fibers are held in zones I and I6 will regulate to a substantial extent the hardness of the fibers precipitated from the machine.` For cellulose acetate is precipitated in a fairly coarse fiber. A fine fiber and onewhich is completely .hardened at vdischarge from the precipitator may be obtained by thinning the solution in zones II and I2 with a 10% solution of acetic acid and adding a 10% solution acetic acid to zones I3, I4 and I 5. By this method cellulose,

acetate is precipitated readily upon passing'into zone I3 and it is completely hardened before passing out of the device. Obviously other concentrations of acid or other solvents and prethis reason each of the shafts 36' and 38 in these zones are provided with an individual drive 64 and 65. As shown inKFig. 3 each zone of the other zones is also provided with an individual drive 66, 6l, 68 and 39. However, one or more of these zones may be, geared together and driven from a single source of power in timed relation to each other. It is obvious, however, that a greater latitude of adjustment may be made if each zone in the machine is separately driven.

The precipitating liquid may be introduced into the various zones by means of a feed` line III which has a header I2 running along the side of the machine with branch lines I3, '14, I5 and l5 entering into zones II, I2, I3 and Iii, respectively. It may be desired in certain cases to have each of the feed lines 13, 14, 'I5 and 'i6 connected to a separate source of supply such that the concentration of the precipitating liqu.d may be varied in each compartment. These feed-in lines are controlled by suitable valves.

As an illustration of the operation of the device, cellulose acetate dissolved in substantially glacial acetic acid coming from an acetylizer is pumped into zone II and thinned with a 30% solution of acetic acid in water. The thin solution passes under partition 3S through slot 5@ into zone I2 where it is further thinned with a 20% solution of acetic acid in water.v This solution then passes over the cut-away portion in partition 4I into zone I3 Where it is precipitated by the addition of a 10% solution of acetic acid in water. The precipitated iibervthen passes into zones III,A I5 and I6 where 'it is hardened with the further addition of 10% solution of acetic acid in water and finally discharged from the sluiceway B6' as a fiber suspended in a 40% acetic acid solution. By controlling the amount of cellulose acetate solution pumped to the device and the quantities and concentration of precipitating liquid added a uniform concentra- *tion of acid is obtained from the sluiceway 66 which greatly facilitates the recovery of the acetic acid. This is distinguished from the prior batch processes wherein the first acid was relatively strong while the last of the acid had a concentration of about 10% which had to be lstored 65 and blended in large storage tanks prior to entering the recovery system, whereas in the present invention the acid may be'drawn from the'` precipitated cellulose acetate and vrun directly to the recovery system.

In the above example the fact that 30% the first zone prevents the bringing of the solution of cellulose acetate to the precipitating point in zone I2 so that upon passing into zone I3 the dilute acetic acid was used for thinning the solution in cipitants may be employed. It is preferable, however, to employ water as the precipitant and a similar solvent to that employed in the original solution of the derivative of cellulose as this greatly facilitates recovery of the solvent and makes an economy in the process. For

instance, cellulose acetate may be precipitated from its solution in acetone by adding in the various zones asolution of acetone and water. It isl not necessary that the precipitating liquid be a true solution for mixtures of solvent and precipitant also may be employed. In a similar manner alkali-soluble cellulose ethers may be precipitated from this solution in alkali by thev addition of dilute aqueous alkali solutions in the various zones, which precipitating liquid may be considered a solution of solvent (concentrated alkali) in a precipitating liquid (water).

If desired, sodium carbonate or other such chemical reagent may be introduced into either zone II or I2 to substantially neutralize the inorganic acid catalyst, if any was used, andalso to produce a gas. This latter step tends to make a more voluminous precipitate. It will be seen from the above description that a uniform type of fiber may be obtained and a constant strength of the weak acetic acid maintained. It is possible to keep the' precipitator entirely closed thus eliminating fumes escaping into the plant. To a large degree the size of iiber depends upon the rate of throughput and the concentration or the amount of precipitant added in thinning the solution of the derivative of cellulose before precipitation. The greater the throughput the larger the fiber or if the throughput is too fast a lump is produced. The precipitator being continuous may be hooked directly to a rotary washer as the feeder therefor` thus eliminating the feeder compartment now necessary in rotary Washers. give better stabilizing and Washing during the processing of the cellulose acetate.

It is to be understood that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein without departing from the spirit of my invention. n

Having described my invention, what I desire to secure by Letters Patent is:

l. A machine suitable for precipitating an organic derivative of cellulose from solution, ccmprising a series of contiguous troughs -for the solution, certain adjacent troughs forming zones and certain single troughs forming zones, inlet means at one end of said series of troughs, outlet means at the other end of said series of troughs,

inlet means for the precipitant near the inlet means for the solution, and a series of rotary members, one in each trough, the rotary meml' bers in at least one zone near the inlet comprising a pair of stirrers having plates set in a spiral, said stirrers being adapted to mix material as it passes through said zone to the next zone, the rotary members in at least one further zone com- The uniform type of ber obtainedv prising a helical plate cooperating with a paddle member to draw out material as it passes to the next zone, and the rotary member in at least one zone near the-outlet comprising paddles.

2. A machine suitable for precipitating an organic derivative of cellulose from solution, comprising a series `of contiguous troughs for the solution,'certain adjacent troughs forming zones and certain single troughs forming zones, inlet means at one end of said series of troughs, outlet means at, the other end of said series of troughs, a plurality of inlets for the precipitant,

each inlet communicating with a dilerent zone i and one of .said inlets communicating with the comprising paddles.

HERBERT E. MARTIN.

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