CA2485261C - Apparatus for processing materials - Google Patents

Abstract

The present invention relates to an apparatus for processing materials, a process for mixing, finishing and de-volatizing polyamide to make 66 nylon and the 66 nylon made by this process. The apparatus comprises an agitator section (12) hav-ing an outlet (14) adjacent the bottom thereof; a transfer screw (20) disposed adjacent the outlet of the agitator section; a spiral ribbon (24) extending upwardly from the transfer screw; a ring (26) dis-posed vertically above the spiral ribbon, at least one baffle (32a, 32b) disposed vertically above the spiral ribbon and connected to the ring and a wall-wiping spur connected to the ring. Preferably, the apparatus has two baffles - an upper one (32a) for pumping the material downwardly and a lower one (32b) for pumping the material up-wardly. The diameter of each baffle is preferably about 80 % of the diameter of the agitator sec-tion.

Description

APPARATUS FOR PROCESSSN(3 MATERIALS
BACRGItt?Lfl1ri bP TSE TNVENTION
1. f'A1d of rhQ raYo-n=3or, :'he F:reeent. __nvention relates to an apparatus for processing at least one material, ar.d is particul arl y sv:ited for mixing, finishing and de-volatizing polytaers.

2. i~,~rrinti on of the Relaced A
The corrmarcXal nxeparatien of moest linear condensation polymers, such as polyamides or polyesters, ty:ai.cally involves heating monomeric starting materials to cause progreasive condensation of the polymers. This px,ocess is ixsua:.ly carried out in several stages, with the in_ezrediate format.i.on of 1ow-moleCular weight, low viscosity polymeric lic-aid by the removal of volatiles.
The low-molecular weight, low-viscosity polymeric liquid then passes through a t inishing zone which Yu controlled at vari.ous vacuum and residence times and temperatures to allow the polymer to reach the desired final molecular weight and viscosity.
Undesirable side reactions, such as thermal.
dearadation and discalo.ration of polymers in ~al erization e i men: car. occur in the p ym ~u p. preparation of polymers. Such side reactions have long been recognized in the field of polymer processing. Finishers auch as those described in U.S. Patent No, 3,361,537 to Ferrante and U.S. Patent No. 4,139,736 to Hammond have produced polymers of uniform viscosity, with less thermal 3C tiaqradat.inn, discoloration and gel build-up than finishers whieh had been previously available.
Separators have also baan uaed in thp art of polymer processing for producing polymers of lower molecular weight than finishers produce. Separators are devicee which operate at one atmosphere, while finishers operate at one atmosphere or lower with vacuum. It is knowr. to operate a-polvmerization device as both a separator and b tinzaher, ae exdmplifed by U.S. Patent No.

3,71.7,330 to Pinney. It is alao known is, the art to provide a separator which comprises a spiral ribbon exr.endina upwardly from a transfer screw and a ring c.isprs8d above t'tte Bps-ral ribbon, as described in U.S.
Fatent No. 3,087,.4?5 to Boucher, with baffles which are connected to a plurality of spokes attached r_o the transfer screw arid disposed below the ring. These battles have a helical shape and have holes formed thereir., and always pump downwardly. The use of a baffle in a reactor, or finisher, is also disclosed in U.S. Patent Nc.

4,460,278 to Mat$ubara et al.,, U.S, Patent No. 4,007,016 to Weber, U.S. Patent 1vTo. 3,822,999 to Pope and U.S.
Pacent Nc. ::,8C4,379 to Wistrich et al.
P._ major design consideration in polymerizing eguipmentt is flow pattern, which influences final pclymer :-5 color and gliality. Areas of stagnation or channe;.xng are ;cnown flow problems ar.d are indicative of non-ideal flow.
ideally, the polymer should flow through a series of several .vell-mixe3 stages throughout its residence time in the ecr,dpme.nt-, while maintaining plug-f}.ow, i.eõ
substantiGzlly unifcrrn '~.igu,id flow velocities of all the polymer in a giver, transverse cross-section of the equipmer.;:. ?'he separaGOrs and finishers described above do ziot; provide uniform mixing and ideal flow conditions.
A_,sc;, thzse finishers and separator$ exhibit significant gel formation above the surface of L.be polymer and thermal degradati.on of the polya:er.
As demand increaaes for polymers of higher molecular weight: and for more flexible polymer producing operations with higher throughputs, ne-ither the separators nor the finishers as described above are able to produce desired polymers. With such desired higher molecular-weight poWyme_s ar.d higher throughputs, gel, color and other polymer qual.ity specifications such as thermal degradation index and oxidative degradation index become an increasing prolilem. To achieve the increased throughput, larger fa.r,Lshers or separators are required.
To achieve higher moleaular weight, higher viacosity polymer must be prvicess+ed. The larger finishers or separatora and the ?iigher-v:.scoaity polymers require increased power, Whicr xesults in increased energy inpu:~.
Thie increased energy requirement is obviously undesirable from an economic standpoint, and haa the additional disadvantagee of reguiring stronger structures for the E, finishers or separat:ors and overheating the polymer in the fi-.Ai.sher, ultimately resulting in a=-hermal].y degraded, inferior product.
SLFMMnRY DF '3TiE _TNVEr7'PT['3N
The raresent invention solves the problems ldi associated with the prior art by providing an apparatus fo: processing at least one ma:.erial which is particularly useful as a mixer for mixing polymer, and/or as a finisher for prer,aring high molecular weigiit, high-vi.acosity pQlyn.er and/ar as a de-volatizer for removing volatiles 15 from the polymer.
The present invention also so2.ves the problems associated with the prior art by providing an apparatus which minimizes the etiargy ;.nput. and ccst rec.[.:ired to operate the apparatus, and which has maximized mechanical 20 strength.
The present invention also solves the problems associated with the prior art by providing an apparatus which reduces gel formation.
The present invention also solves the problems 25 associated with the prier art by providing an apparatus which provides unifr.rm sr.ixing and prevents excessive channeling and stagnation of the material.
In order to achievw the foregoing solutions, in accordance with the present invention, there is provided 30 an apparatus for processing at least one material. The apparatus compriees an agitator section having an outlet adjacent the bottom thereof; a transfer screw disposed adjace.qt the outlet of the agitator section; a spiral ribbon extending upwardly from the transfez screw; a ring 35 disposed vertically above tha spiral ribbon; and at least one: baffle disposed vertically above Lhe spiral ribbon and c,onnected tO the ring. -Further in accordance with the present invention, it ie preferable that the at least or.e baffle comprises a first baffle for pumping the material downwardly, and a second baffle disposed below the first baffle for pumping the material upwardly. It is further preferable that the diameter of the first and second baffles is about 80% the diameter of the agitator section.
RRTRF gESCRIPTI(ZN OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate the presently preferred embodiments of the invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.
Fig. 1 is an elevational view of the apparatus of the present invention.
Fig. 2 is a cut away, elevational view of the apparatus of Fig. 1, showing the'agitator section and the top of the transfer screw.
Fig. 3 is a cross-sectional view, taken across lines 3 - 3 of Fig. 2, of the ring of the apparatus of the present invention.
Fig. 4 is a plan view showing a preferred desicrn of the top baffle of the present invention.
Fig. 5 is a cross-sectional view, taken across lines 5 5 of Fig. 2, showing the diagonal supports of the apparatus having a generally tear-drop shape according to one embodiment of the present invention.
Fig. 6 is a cross-sectional view, taken across lines 6 - 6 of Fig. 2, showing a major spoke of the apparatus having a generally trapezoidal shape according to a further embodiment of the present invention.
DETAILED DESCRIPTION OF THE PRF-FERRED EMF3ODIMF.'NTS
Reference will now be made in detail to the present preferred embodiments of the invention as illustrated in the accompanying drawings:
In accordance with the present invention, there is provided an apparatus for processing at least one material. The apparatus of the present invention is shown generally at 10 in Figs. 1 and 2. ."Processing" may mean mixing, or alternatively, or in addition, finishing, (i.e., producing a reaction and converting a low viscositv material to a high viscosity material), or alternatively, or in addition, de-volatizing (i.e., stripping out gas) in a material. The apparatus of the present invention may process either one material or a mixture of materials, at least one of which is a liquid. In general, the apparatus of the present invention is ideal for handling a foamy material. Materials suitable for mixing and finishing with the apparatus of the present invention include 6 nylon, whereby water and caprolactan are removed, 6,6 nylon, whereby water is removed, polyarylates, whereby acetic acid and phenol is removed and polyesters, where glycols are removed. A material suitable for mixing and de-volatizing with the apparatus of the present invention includes polyethylene, whereby ethylene gas is removed.
The apparatus of the present invention comprises an upright tubular agitator section 12 as shown in Figs. 1 and 2 having an outlet 14 adjacent the conically-shaped bottom of the agitator section. Material enters the apparatus at the top thereof, usually through a central nozzle 16 as shown in Fig. 1, as indicated by the arrow going into the nozzle. Alternately, several entry nozzles may be employed. When the apparatus of the present invention is used as a finisher or a de-volatizer, by-product gas from the nozzle or from the material flows upwardly and out through a vent 18. A transfer screw 20 is disposed adjacent the outlet of the agitator section as shown in Fig. 1. Transfer screw 20 extends through the bottom of the agitator section and terminates in an auger screw element 21 as shown in Fig. 2, which may have one or more turns. The purpose of the transfer screw is to remove the material from the apparatus and transport it to a downstream transfer line 22 as indicated by the arrow in line 22 and then to a gear pump, not shown. Further downstream operations, such as spinning and casting, may then be performed on the material. Agitator section 12 has an agitator 13 as-shown by the dashed lines in Fig. 1 which extends upwardly from the transfer screw and is driven thereby. The agitator section is joined to the transfez screw by a key and screw joint (not shown), allowing ease af disassembly for routine maint.enance. ::t is of course within the scope of the present invention to use,cther attachment mechanisms between the agitator section and the transfer screw.
A spiral ribbon 24 extends upwardly from the Mransfer screw as shown in Fig. 2. Spiral ribbon 24 mixes t1ie material in the lower portion of the agitator section.
It blends out any non-uniformities generated by upstream process upsets, sw that very uniform matexial is fed to downstreac. operationa. The spiral ribbon also wipes the walls of the agitator section, thus preventing ge"s. build-up. F'urtbermore, the geometry of the spiral ribbon within t"tle agitator section encourages downward pumping of the material, further enhancing the gel-inhibiting characteristics of the ribbon and thus the quality of the material. For very large apparatus, for example when the agitator section diameter is greater than 50 in4hes, the horsepower requirement to rotate the ribbon becomes unreasonably high. This excessive horsepower requirement causes the temperature of the material to increase, resulting in thermal degradati.on, Therefore, for large apparatus, it is preferred to limit the spiral ribbon to be disposed below the 50-inch diameter portior. of the agitator section. For small apparatus, where the horsepower requirement is less of a concern, it may be preferred to allow the ribbon to extend through the entire material zone in the agitator section.
A ring 26 is disposed vertically above the spiral 3C ribbon. The ring provides mechanical integrity to the entire agitator section. The preferred cross-section of the ring is wedge-shaped on the top, as can be seen from Fig. 3. The advantage of providing a wedge-shaped cross eectwon is that the material flows over the wedge and does not stagnate there, which would result in gel foxznatior..
A plurality of diagonal supporu$ 30 as shown in Fig. 2 connect the spiral ribbon to the ring. The supports are welded to the ribbon and the ring, although other attachment methods may be chosen.. The diagonal supports may have a generally tear-drop shape, as shown in Fig. 5. A tear-drop shape enables the laminar flow of the material to flow in a stream line with respect to the walls of the agitator section. This eliminates stagnant or void zones, which lead to gel formation.
The diagonal supports are provided for additional mechanical strength to avoid twisting and distortion of the agitator section. For low-viscosity applications, these diagonal supports may be unnecessary. However, when used, the diagonal supports must be located in positions that will not contribute to gel build-up or cause improper flow patterns, such as channeling.
The apparatus of the present invention further comprises at least one baffle disposed vertically above the spiral ribbon and connected to the ring. The apparatus further includes a plurality of baffle support members 38 for connecting the baffle to the ring. Each baffle is bolted a baffle support member. The at least one baffle comprises a first, or upper, baffle 32a for pumping the low-viscosity material downwardly. Upper baffle 32a serves several purposes. Incoming material drops down and encounters baffle 32a and is radially distributed, resulting in an improved flow pattern within the apparatus. Without a baffle, the material would tend to channel down through the material in the agitator section, the outer region would stagnate and severe degradation would result. In addition, gel stalactites often form on the apparatus. As the stalactites become heavier, they.eventually drop off into the material. The upper baffle catches these stalactites and acts as a filter, not allowing them to pass into the downstream processes, which causes severe problems. In polymerizing processes that cause foam formation, such as nylon polymerization, the upper baffle is designed to pump downwardly and thereby serves the purpose of pumping the contents of the apparatus downwardly, and compressing the foam formed during the polymeric reaction.

The at least one baffle may further comprise at least one second, or lower, baffle 32b, as shown in Fig. 2 by dashed lines, for pumping the material upwardly.
Inclusion of lower baffle 32b is preferred, but is not an essential-feature of the invention. In contrast to the upper baffle 32a, the helical geometry of the lower baffle causes lower baffle 32a to pump material upwardly, which enhances flow pattern and residence time distribution. In a preferred embodiment, the lower baffle is located eight to twelve inches below the upper baffle. Although only two baffles are illustrated, additional lower baffles for pumping the material upwardly may be added as the apparatus height is increased. For instance, if more than two baffles are used with the present invention, all the lower baffles pump would upwardly and the middle baffle would be oriented 180 from the top baffle. In this case, the upper baffle, such as baffle 32a, would be bolted to the lower baffle, such as 32b.
The diameter of the first and second baffles is in the range of about 50% to 990 of the diameter of the agitator section, measured at the height of the baffle.
The upper value for the baffle diameter is limited only by the necessary clearance between the baffle and the wall of the agitator section. Preferably, the diameter of the baffle is preferably about 80% of the diameter of the agitator section, measured at the height of the baffle.
The static level of the material is horizontal at zero rotational speed. Upon rotation the surface of the material assumes the shape of a parabola, in that the material at the wall above the agitator section climbs several inches up the wall and the material at the center of the agitator section drops several inches. In a preferred embodiment, the top of the upper baffle is ideally located four to five inches below the static level of the material to prevent the center'of the baffle from becoming dry. If this occurs, then gel will form in the dry area, due to stagnation and degradation.
Each baffle is made of a corrosion-resistant material, such as metal. It has been found that any solid baffle, made of any material, will cause flow stagnation and polymer degradation. Therefore, each baffle has a plurality of holes formed therein in order to reduce the surface area of the baffle which is exposed to the material being processed. As shown in the top baffle of Fig. 4, a plurality of holes 34a are formed therein, it being understood that similar holes, although not shown, are formed in the bottom baffle. The formation of holes in the baffle prevents stagnation, resulting in better quality material (i.e., one with virtually no gel formation) to a much greater degree than what could be achieved by a baffle with no holes formed'therein. The formation of holes in the baffle also creates better flow patterns, i.e., there is very effective pumping of the material across the surface of the baffle, thereby also preventing gel formation. Enough holes may be formed in the baffle so that the material from which the baffle is made may comprise only 5s of its surface area. The holes may be round, or preferably, rectangular as shown in Fig.
4. It has been found that this configuration of rectangular holes as shown in Fig. 4 produces significant lowering of gel deposition on the baffle.
A spur 36 is connected to the ring as shown in Fig.
2. The purpose of spur 36 is to wipe the walls of the agitator section to improve flow patterns by reducing the tendency for the material to create a beach line of gel on the walls above the material surface. Also, by positioning the spur opposite the cut in the baffle as shown in Fig. 2, it provides additional radial mixing and '30 decreases the tendency for stagnation to occur. By canting the spur forward, it can also serve to pump material downwardly. The spur is optional, and may not be required in some polymer applications. However, in the case of the present invention where two or more baffles are used, the spur is necessary to provide radial mixing at the surface of the material, so that the central feed of the material does not channel down through the apparatus. Preferably, the top of the spur is below the surface of the material, preferably about 1/2 inch, to avoid protrus:ion above the level of the material, which wou.d pT'ovlde a dry region on the spur where gel would form. Preferably, the spur :.s trapezoidal in shape. A
trapezoidal shape enables the laminar flow of the material to flow ir- a stream lina with respect to the waY1s of the agztatcr sectior.. This eliminates stagnant or void zones, which leads to gel. Although mor.e than one spur may be provided, a single spur has the advantage of minimal power raquirements, since spur horsepowQr is directly _0 proportional to the number of spurs used. The spur may be unbolted from the ring and interchanged with a spur of a different height, so that its height can be easily changed if a change in the level of the material is required.
Throtighput changes require diff erent hold-up volume.s, i5 which are achieved by changing the level of material in the agitator section. Hold-up volume can be adjuated by changing the height of the spur and the number and position of the baffiea, which can be changed by unbolting them from the baffle supports as noted above.
20 Each baffle is cut along a radial line and extends above and below a horizontal plane at an angle, 0/2, so that it has a helical shape as shown in Fig. 2. Various pitches, either right or left handed, may be chosen for the baffles. As shown in particular in Figs. 2 and 4, the 25 first, o-r top baffle, is cut along a radial line 40a i:itersecting the vertical center :.ine of the spur, The second, or bottom, baffle is cut along a radial line 40b which ir.tersects the top end point of the spiral ribbon.
The helical shape of the baffles promotes proper flow 3C patterns, by avoiding excessive channeling at the center of the baff;.e. 7n addition, the orientation of the helical baffles with respect to each other, when 3nore than one baffle is used, creates compartments of well-mixed flow which move downwardly through the apparatus.
35 As shown in Fig. 2 ir. particular, a plurality of radially spaced major spokes 42 extend between the ring and the=transfer screw. This configuration of the major spokes is optimal for high visoosity materials. The major spokes are positioned very close to the wail of agitator section 12 to provide wall wiping and reduction of gel at the wall and the supports. The clearance between the major spokes and the agitator section wall can be varied, with the ideal clearance being less than one inch for the preferred embodiment. As can be seen in Fig. 6, the wall side' of the major spokes has the same contour as the agitator section wall to avoid gel and reduce inward mechanical pressure which would produce stress on the supports, resulting in failure. It is preferred to use the minimum number of major spokes necessary to achieve the required mechanical stability for a particular application in order to minimize power requirements.
The apparatus of the present invention also includes a plurality of radially spaced minor spokes 44 which extend between the spiral ribbon and the transfer screw. As shown in Fig. 2 in particular, the major and the minor spokes are disposed on the outside of the spiral ribbon. It should be noted that the baffle may alternatively be connected to the spokes below the ring. The major and the minor spokes preferably have a trapezoidal shape, a major spoke being shown in cross-section in Fig. 6. As noted above, a trapezoidal shape enables the laminar flow of the material to flow in a stream line with respect to the walls of the agitator section, thereby eliminating stagnant or void zones, which lead to gel.
For applications using materials not subject to gel formation, alternatively, the major and minor spokes may have a tear-drop shape, similar to the teardrop shape for the diagonal supports as shown in Fig. 4. Since tear-drop shaped spokes cost less to manufacture than trapezoidal spokes, they are preferred for such applications.
The total number of major and minor spokes is strictly a function,of the viscosity of the material being processed. For processing materials with low viscosities, say below 50 poise, the apparatus of the present invention needs only three spokes. As the viscosity of the material and the size of the apparatus increases, more spokes are needed.
Preferably, the total number of major and minor spokes is six when processing materials with relatively high viscosities.

Preferably, the major and the minor spokes are made of a carrosion-res:.stant material, such as 300 or 400 series stainless steel, In eituatZons were lower viscosity materia3.s are proceased, the entire apparatus may be made from 300 or 400 series stainless steel.
However, in situarions whexe higher viscosity materials are processed, the major and minor spokes may be made of 17-4 pH stainlesa steelõ which is an extremely high strength, corrosion resistant material, while the rest of i.0 the apparatus can still be made of 300 or 400 series stainless steel.
The apparatus of the present invention may fur.thex, comprise at least one fillet for filling in an open space in the apparatus with metal, thereby preventing cavitation. A plurality of fillets 46 is shown underneath the api.ral ribbon at the joint of the spokes in Fig. 2, while a pluralit.y of fillets 48 is showm below the ring in Fig. Z. Alternatively, or in addition, a fillet may be provided at each location of where the upoke is welded into the ring.
'n opexation, the material flow through nozzle 16, agitator secta.on 12, ttansfer screw 20 and out line 22.
The apparatus of the present invention produces a sariee of vertically segmented zones in the material as it flow through the apparatus, The upper vertical zones formed by the baffle allow lower viscosity to be maintained in the upper zcnes of the apparatus, and higher viscosities to be maintained in the lower zones, near the spiral ribbon.
This flow distribution has the advantages of better quality product, i,e., one with virtually no gel or discoloration, greater reaction efficiency (when the apparatus is usad as a finisher) and reduced power consumption. Lower power consumption results in lower heat rise in the material and subsequent iower thermal.
degradation. Also, it has been found that the residence time distribution i,r. the apparatus of the present invention is superior to finishers of the prior art, thus reducing channeling, stagation and gel formation.

A preferred use for the apparatus of the present inventi,on is as a mixer, finisher and de-volatizer in a continuous process for the preparation of a synthetic, linear, riber-forming polyamide by the melt polymerization 5=of an aQupous solution of a polyamide-form,ing salt of an aliphatic diamine and a dicarboxylic acid. Thus, in accordance with the present invention, there is provided an ymprovement in a continuous process for preparing a synthetic, linear, fiber-forming pa:.yamide by the melt 1o polymexxzation of an aqueous solution of a polyamide-forming salt of an aliphatic diamine andi a dicarboxylic acid. The imp_ovQmer.t comprises the step of processing the polyamide in an apparatus as described above comprising a transfer screw disposed adjacent an outle4 ef 15 ar agitator section, a spiral ribbon extending upwardly from che transter screw, a ring disposed vertacally above the spiral r:.bbon and at least one baffle dispoeed vert i-r.al_y above the spiral ribbon and connected to the _rinõ to thereby mix, finish and de-volatize the 20 polyamide. The pr.oGeesing step includes the sub-step of vacuiim finishing and separating the polyamide in one stage. Most preferred is the use of the apparatus of the present invention as a mixer, finisher and de-volatizer in a continuous process for the preparation of 25 polyhexarnathylane adipamide (66 nylon) from an aqueous solution of a hexame;.hylenediammonium adipate (66 nylon salt ). Therefore, in the preferred process of the present invention, the synthetic, linear, fiber-forming polyamide a.s poiyhexamethylene adipamide. The result is 30 polyhexamethylene adipamide made by the process of the present invention.
Tlta_t_ Ma_tIJ2ds The following test mathods were used to evaluate the 66 nylon finished by finiehing apparatus of the prior 35 art and the apparatus of the present invention as described i-i the Examples below.
Thermal degradation index ~'1=pI) is a measurement that correlates with a polymer's thermal history. A lower TDI indicates less severe temperature history during manufacture. It is determined by measuring the optical absor:oar.ce cf a 1t (by wexght) sol=.:tion cf the po"iymer ir:
90t foYmic acid at 292 nm,.
Oxidatiti=e degradation iradex (aDI) is a measurement S that eorrelates with a po.lymer's exposure to oxidating condiGiQr:s during its high temperature manufacture. A
lower OL7I indicaces less severe oxidative degradation during manufacture. l.t is determined by measuring the optical aassorba.nce of a:t (by weight) solution of the po1ynzer in 90;r formic acid at 260 nm, Relative visccsity refers to the ratio of solutian and solvent viscosities meusured in a capillary viscometer at 250C. The solvent is formic acid containing 10W by weight water. The solution is 8.4 s by weight polyamide polymer dissaived in the solvenc.
~,~ Procedur~Q
A typical reaction syStgm for the preparation of 66 nylon, euch as those describe& in U.S. Patent No.
3,113,843 to Li and U.S. Patent No. 3,900,450 to Jaswal et al, and used in the Examples as described below, compriees, sequerstially, a reactor atage, a flasher stage, a steam/polymer separator stage and a vacuum fiiiishing stage. The reaction system nay be preceded by an evapcrator to adjust the conGentration of the 66 nylcar.
salt solution prior to the reactor. The apparatus of the present inver.tion as used in Example 3 carried out both the nteam/polymer separation, such as in separator 14 of Li, and the vacuurn finis'r.ing, such as in finisher 16 of Li.
In a typical 66 nylon process, an acqueous solution of hexamethylenediammonium adipate (6,6 nylon salt) varies between 35 and 65t by weight. Strength may be adjusted .i_n the optional evaporator upstream of the rea.ctor stage.
The effluent from the flasher stage (which is also referr.ec3 to as the secondary reactor) comprises polyamide pre-polymer, typically 9-20 RV (relative vz.scocity) . This stream is fed tc a finishing apparatus. Contrc], variables in the Finishing apparatus are temperature, pressure and hold-up volume. These control variables can be varied such t hat a final polymer of the desired Ftv, typically in the range of 30 to 100, is obtained, Temperature in the finishing apparatus is maintained in the range of 270 to 290 C. Pressure is maintained at 250 to 640 millibar.s.
Hold-up vo]uttes are approximately 20 to 40 minutes.
The process and the product of the present :.nvention will be clarified by the following Examples, which are irat:anded to be purely exemplary of the invention.
Ira EacacripJ,.Ks 1- 3 below, three different reaction systerns for the preparation of polyhexamethylene adipadipamide (66 nylon) using finishers are compared.
one continuous process for preparing 66 nylon is disclosed in U. S. Paterar. No. 3,947,424 to Tomek. This procasb was carried out :,n ar apparatus for separating a vapor from a viscous material disclosed in U.S. Patent No. 3,113,843 to Li, as described below in Comparative Example 1. Another continuoua process for preparing 66 nylon was carried out in a continuous polymerization system as disclosed in U.S.
Patent No. 3,900,450 to Jaswal et a1. Comparative Example 2 used the continuous polymerization system, including rectifying zone 10, first reaction zone 12 of Fig. 1 and flasner 53 of Fig. 3 of Jaswal et al. and a combined separator/finishar such as that shown in U.S. Patent No.
3,717,330 to Pinney. Example 3 used the continuous polymerization system, including rectifyirlg aone 10, first reacting zone 12 of Fig. 1 of oaewal Qt al, and a flashing reactor such as reactor 12 of Li inatead of flasher 53 of Fig. 3 of Jaewal et al. and the apparatus of the present invention in place cf firiisYher 64 of Jaswal et a1. The apparatus of the present invention was used to mix, finish and de-volatize.

Qm r i veRxzmple 1 An approximately 50% by weight aqueous solution (as adjueted in ari evaporator) of hexamethylenediammonium adipate (6,6 nylon salt), a polyaaride-forming salt solution, was fed to a coriventiotial continuous polymeiization process similar to the type disclosed in Tomek, e3:cept that r_o aciditxve:s were employed. The equipment configurat.ion of the polymerization system was as described above. Co:nditions were adjusted such that final polymer exhibited a relative viscosity (RV) of approximately 50, Quality parameters are shown below in Table 1.

(Iomi?a ra r 5 va An approximately 54k by weight aqueous solution of hexamethylenediammonium adipate (6,6 nylon salt), a polyamide-foz-ming salt solution was fed to a conventional continuous polymerization process similar to the type disclosed in :omek, except that no additives were added.
The equipment configuration of the polymerization system was as cescribed above, Conditions were adjusted such that final polymer exhibited a relative viscosity (RV) of approximately 50. Quality parameters are showrl below in Table 1.

:Y M
An approximately 63% by weight ac;ueous solution of hexamethylenediammonium ada.pate (6,6 nylori salt) , a polyamide-forming salt solution was fed to a cor.ventional ,.-...
continuous polymerizatiqn process similar to the type disclosed Tomsk, except nc additives were used. The equipment configuration of the poiymerization system was as described above. Conditions were adjusted such that final polymer exhibited a relative viscosity (RV) of approximately 50. Temperature in the apparatus of th*
present invention was malntained at a temperature in the range of 2701 to 290 C. Pressure was maintained at 250 millibars. Residence time in the apparatus was approximately 30 minutes. The improvements in the 66 nylon product made by the process of the present invention are shown below in Table 1.

Tah1 1 Comparative Examp:e 1 51.1 0.33 0.31 Comparative Example 2 51.7 U.37 0.30 Exa-nple 3 50.9 0.32 0.24 As can be seen from Table 1, when the process of t'-xe pxeseat invention was carxied out (i.e., using the apparatus of the p.r.esect invention), the resulting pol}rmpr nhowed decx-eaeea degradation when compared to polymer processed by the finishing apparatus oF the prior art.
Thi= irriurpvement relates both to thermal degradation, which leads to gzi f~rma--ion (cross linking) and to thermally-induced oxidative degradation, which leads to discoloxation.

Additional advantages and modif icatione will x,eadily oecur to those skilled in the art. The ir.vention in its broader aspects is, tnerefore, not limited to the ~Gspecifi~ details, representative apparatus and il:.ustrative Examples shown and described. Accordingly;
deparwures rnay be made from such cietaile without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

What is claimed is:

1. An apparatus for processing a material, wherein gel stalactites are formed in the material, comprising:

(a) an agitator section having a bottom and an outlet adjacent the bottom thereof;
(b) a transfer screw attached to the agitator section;

(c) a spiral ribbon extending upwardly from the transfer screw and attached thereto;
(d) a ring disposed vertically above the spiral ribbon and connected thereto;

(e) a plurality of major spokes extending between the ring and the transfer screw;
(f) a plurality of minor spokes extending between the spiral ribbon and the transfer screw; and (g) means for catching gel stalactites formed in the material baffle disposed vertically above the spiral ribbon and connected to the major and minor spokes below the ring.