E ). (12) United States Patent Fleury et a]. US 8,222,355 B2. Jul. 17, (10) Patent N0.: (45) Date of Patent:

Transcription

1 US B2 (12) United States Patent Feury et a]. (10) Patent N0.: () Date of Patent: Ju. 17, 12 (54) PROCESS AND APPARATUS FOR TREATNG VSCOUS PRODUCTS (75) nventors: Pierre-Aain Feury, Raminsburg (CH); Pierre Lichti, MuttenZ (CH) (73) Assignee: List Hoding AG, Arisdorf (CH) Notice: (21) App. No.: 12/295,094 Subject to any discaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 437 days. (22) PCT Fied: Mar. 28, 07 (86) PCT No.: PCT/EP07/ (87) 371 (0X1) (2), (4) Date: Oct., 08 PCT Pub. No.: WO07/ PCT Pub. Date: Oct. 11, 07 (65) Prior Pubication Data US 10/ A1 Jun. 17,10 () Foreign Appication Priority Data Mar. 31, 06 (DE) (51) nt. C. C08F 2/00 (52) (58) (06.01) B01J19/18 (06.01) B01J19/00 (06.01) US. C /88; 422/135; 422/224; 422/2 Fied of Cassi?cation Search /71, 526/88; 422/135, 224, 2 See appication?e for compete search history. (56) References Cited U.S. PATENT DOCUMENTS 3,880,7 A 4/1975 List 3,927,983 A * 12/1975 Gordon et a /110 4,141,934 A * 2/1979 Winger et a /53 5,372,418 A 12/1994 Biesenberger et a. 6,039,469 A 3/00 Pamer 6,710,141 B1 3/04 Heide et a. FOREGN PATENT DOCUMENTS DE A 5/01 EP /1992 EP /01 GB /1978 WO /06 OTHER PUBLCATONS Wang, Ning He. Poymer Extrusion DevoatiiZation. Chem. Eng. Techno. vo. 24. ssue p. 957.* Wang, Chem. Eng. Technoogy, Poymer Extrusion DevoatiiZation, vo. 24, ssue 9, 01, p. 957.* nternationa Preiminary Report on Patentabiity for PCT/EP07/ , issued Sep., 08. * cited by examiner Primary Examiner * David W Wu Assistant Examiner * Eizabeth Eng (74) Attorney, Agent, or Firm * Bachman & LaPointe, PC. (57) ABSTRACT n a process for treating viscous products, especiay for per forming poymerization processes, especiay for homo- or copoymerizing thermopastics and eastomers, Wherein monomer(s) and/or cataysts and/or initiators are added to a backmixed mixing kneader, especiay With a ength/diameter ratio of , heat is suppied to the product Which is backmixed With aready reacted product and the reacted prod uct is removed from the mixing kneader, the product in the mixing kneader sha be heated up to its boiing temperature, portions of the product sha be evaporated and exothermicity of the product sha be absorbed by evaporative cooing. 12 Caims, 1 Drawing Sheet E ). L 18

2 Ju. 17, 12 US. Patent 1 i _.._.WMW...E ' N. i E z E t 1

3 1 PROCESS AND APPARATUS FOR TREATNG VSCOUS PRODUCTS BACKGROUND OF THE NVENTON This invention reates to a process for treatment of viscous products, in particuar for performance of poymerization processes, in particuar for homo- or copoymerization of thermopastics and eastomers, Wherein monomer(s) and/or cataysts and/or initiators are added to a backmixed mixing kneader, in particuar having a ength/diameter ratio of , heat is suppied to the product, and backmixed With aready reacted product, and the reacted product is WithdraWn from the mixing kneader, and to apparatus therefor. A considerabe proportion of poymerization reactions, in particuar for production of homo- and copoymeric thermo pastics and eastomers, are commerciay performed as a surry or soution process in one or more series-connected, continuous-?ow, backmixed, vertica stirred tank reactors known as CSTRs. These stirred tank reactors have the task of ensuring that the monomers, the cataysts and initiators be distributed in a sovent/diuent under precisey de?ned processing condi tions, such as temperature and pressure, as homogeneousy as possibe in order that the reaction may proceed in a poiced manner, that a uniform product quaity having the desired moar mass may be formed and that, in addition, the heat of reaction may be controed. The probem With these stirred tank reactors, then, is that ony products having a ow apparent viscosity can be pro cessed. As the concentration of the poymer in the sovent/ diuent increases, the apparent viscosity of the reaction mass increases to such an extent that the stirrer utimatey cannot generate su?icient convective?ow. The consequence thereof is an inhomogeneous distribution on the part of the mono mers. This eads to cumping, poor moar mass distribution, caking, oca overheating up to and incuding a runaway reaction for the entire reactor contents. A further probem With stirred tank reactors is that some products give rise to foaming, Which can ead to bockages in the vapor outet ports. The abovementioned processing risks expain Why stirred tank reactors can ony be operated With a arge excess of sovent/diuent of up to about 90% of the reaction mass, or ony conversions of ess than % are achievabe in the case of buk poymerizations. As a consequence thereof, addi tiona operations become necessary for mechanica/therma remova of the diuent/sovent/monomer or for postreaction. This is generay accompished in dewatering screws, evapo ration and drying systems, and aso ripening tanks. They require high capita, energy and operating costs. Moreover, there are new poymers Which are not processabe using a Water stripping process. Buk poymerizations are aso performed continuousy in singe- or muti-shaft extruders (for exampe from Werner P?eiderer, Buss-Kneter, Weding Engineers, etc.). These apparatuses are designed for poymerizations in the viscous phase up to high conversions. They are constructed as con tinuous pug-?ow reactors and accordingy have a arge L/D ratio of from >5 to about. Here the foowing probems arise: a) n the case of sow poymer reactions With reaction times >5 minutes during Which the reaction mass remains in the iquid state for a ong period, pug?ow cannot be maintained. The very different rheoogica properties between the monomers and poymers prevent uniform product transportation, and this eads to undesirabe?uctuations in quaity. b) The substantia exothermicity of many poymerization processes and aso the dissipated kneading energy fre quenty make it necessary to remove these energies via evaporative cooing. n evaporative cooing, some of the monomer or of an admixed sovent/ diuent is evapo rated, condensed in an externa condenser and returned as condensate into the reactor. OWing to the arge L/D ratio and the arge screw cross-section necessitated by the design, ony very imited free cross-sectiona areas are avaiabe for the Withdrawa of vapors. This eads to the undesirabe entrainment of poymers into the vapor ines and into the re?ux condenser and, as a consequence thereof, to bockages. c) An additiona compicating factor With the production of (co)poymers from two or more different monomers is that it is mainy the monomer Which has the owest evaporating point that evaporates for the evaporative cooing, so that there is a shift in the monomer concen trations in the reactor, in particuar in the region of the entry ori?ce for the condensate re?ux. This is generay undesirabe. d) t is aso disadvantageous that the free product voume of screws is imited to about 1.5 m3 for mechanica engi neering reasons, so that ony ow throughputs can be achieved in the case of reactions having residence times >5 minutes, Which requires the instaation of a puraity of parae ines at correspondingy high capita and operating costs. A further Way of performing buk poymerizations up to high conversions is described in US. Pat. No. 5,372,418. Here, co- or contrarotating muti-screw extruders having non meshing screws, or pairs of screws, Which convey in opposite directions are described for the poymerization of monomers by backmixing With the poymer in the viscous phase. These apparatuses are in principe capabe of performing poymer ization processes up to high conversions and at the same time of avoiding the above-described disadvantages a) (coapse of pug?ow) and c) (recipe shift through re?ux) of the pug-?ow extruder. HoWever, the above-described probems b) (re duced free cross-section) and d) (capacity) sti remain unsoved. The abovementioned processes are aso carried out in so caed mixing kneaders in Which appropriate kneading and transporting eements transport the product from an inet to an outet and at the same time ensure that the product comes into intensive contact With the heat-exchanging surfaces. Such mixing kneaders are described for exampe in DE patent ,EP A1 and DE A1. SUMMARY OF THE NVENTON n accordance With the present invention, We have found that the object is achieved When the product in the mixing kneader is heated to its boiing temperature, portions of the product are vaporized and an exotherm of the product is absorbed by evaporative cooing. This means that the heating of the product to its boiing temperature is utiized not ony for vaporizing corresponding sovents, cataysts and/or initiators or the ike, but aso to condense, i.e., coo, some or a of the vaporized products and return them as condensate into the mixing kneader. Since product in the mixing kneader has a arge surface area, the condensate can form a?m over the entire area of the product and thus ead to e?icient cooing. Preferaby, the condensate

4 3 is returned at the ocation of the vaporization itsef. When, for exampe, the mixing kneader is subdivided into a puraity of chambers or open ces, it Wi ikey be advisabe aso to provide a corresponding number of vapor domes through Which the condensing fractions of product are WithdraWn. The condensate is then aso fed back into the mixing kneader at this ocation of the vapor domes. The optima boiing temperature is adjusted according to the product, by varying the pres sure. t is known, for exampe, that PMMA (poymethy methacryate) has an optima boi ing temperature of 10 C. at 3.5 bar. BeoW this temperature, the viscosity increases, Which has a deeterious effect on the torque to be accommodated; above the temperature, there is a risk of depoymerization. A preferred buid-up of a vacuum for WithdraWing vapors in the mixing kneader has the advantage that air and inert gas, for exampe nitrogen, is Withdrawn, but voatiizing monomer condenses in the condenser and can be fed back into the mixing kneader for cooing. n a further iustrative embodiment of the process, for Which independent protection is sought but Which is particu ary effective to carry out in connection With the process thus described, the product is to be backmixed unti it has reached a predetermined viscosity and this viscosity is maintained by continuous addition of further monomer and/ or cataysts and/ or initiators. A ow viscosity is an indication to the operator of a corre sponding mixing kneader that there is ony or essentiay monomer in the mixing kneader that is iquid. As the poy merization progresses, the more the viscosity increases. Once the product has reached a predetermined viscosity, this is a signa for the fact that a certain percentage of the product has become transformed into poymer. This is a signa to operate the mixing kneader in a continuous process, such that the viscosity and hence the conversion/degree of poymerization remains the same. Essentiay, this is determined by reference to the torque. n the case of PMMA, Which is processed under 3.5 bar at 1 C. reaction temperature and revoutions of the shaft per minute, a viscosity pateau at Which changeover to continuous operation is effected is attained at a torque of 100 Nm. The process of the invention is additionay improved by a further step When the product is vaporized, by energy input consisting of mechanica kneading energy and heat transfer via contact With kneader heat-exchange surfaces, up to just above the point of coapse of the vaporization rate, and the thus pre-evaporated viscous bed of product is continuousy admixed With new ow-viscous product soution such that the vaporization rate remains above the point of coapse. f the product is initiay sti very iquid on account of the high sovent content, the vaporizing essentiay takes pace via the contact heat Which comes from a heated housing she, a heated shaft and/or heated kneading counter-eements. The greater the viscosity of the product due to evaporation, the more the contact heat transfer decreases and the more the shearing heat increases, the sum tota of the two passing through a maximum. HoWever, once the percentage of iquid constituents has been diminished by a certain extent, the vaporization rate decreases very appreciaby, since it is no onger possibe for su?icient sovent to come up in the interior of the product to the surface. According to the invention, therefore, the proportion of, for exampe, sovents sha be maintained in a processing range Which is cose to the maxi mum but absoutey sti above this point of coapse of the vaporization rate. This process of the invention provides the advantage that, at the enhanced mechanica intensity, any foaming due to the ?ash addition of the product into the mixing kneader is dis rupted, Which further improves the heat energy input. The vaporization energy needed for evaporation is accordingy maximized by the combination of contact heat and shearing heat. The possibiity of keeping the product temperature con stant via the vaporization of sovent aows a high degree of freedom in reation to the reguation of the shearing heat via the rotary speed (shear gradient) and the?age of the mixing kneader. When, in a preferred iustrative embodiment, a second mixing kneader, extruder or the ike foows, devoatiization takes pace in it additionay. For exampe, in such an extruder, the product can be subjected to pug?ow via an appropriate geometry on the part of the kneading eements. Mass-transfer-imited evaporation takes pace in this extruder, Which therefore preferaby takes the form of two shaft mixing kneaders Which are described in the prior art. n this mixing kneader With pug How, it is essentia that the surface of the product be renewed as quicky as possibe, since the iquid evaporates off this surface. Since the evapo ration sites retreat more and more into the product interior, the product surface has to be permanenty renewed by more intensive kneading. Another requirement is good product temperature poicing. The need for a arger product surface area can aso be met in particuar by the product being comminuted, for exampe via an appropriate perforated pate as comminuting device, before entry into the extruder. When the product after dis charge from the mixing kneader is forced, for exampe by a gear pump, through the perforated pate, it Wi pass into the extruder in spaghetti-ike form, Which resuts in the formation of a very arge surface area. HoWever, the concept of the invention sha comprehend other comminuting devices as We. Heat absorption is sef-evidenty aso improved by the arger surface area. A throtte vave up stream of the gear pump cooperates With a? eve indicator for the mixing kneader and thereby ensures that the product contents are kept approximatey con stant in the mixing kneader itsef. At the same time, the gear pump and the throtte vave serve to bock any transfer from the mixing kneader into the extruder and vice versa. n this Way, for exampe, the mixing kneader can be operated under reduced pressure and the extruder under superatmospheric pressure, or vice versa. BREF DESCRPTON OF THE DRAWNGS Further advantages, features and detais of this invention Wi be apparent from the foowing description of a preferred iustrative embodiment and aso from reference to the draw ing; it shows in its singe FGURE a schematic depiction of a pant for treating viscous products, in particuar for perform ing poymerization processes, Which is in accordance With the present invention. DETALED DESCRPTON Monomer(s), cataysts, initiators and possiby sma amounts of sovents are continuousy metered into a singe shaft mixing kneader 1 equipped With backmixing stirrer shaft geometry, surrounded by a heating jacket 6 and party?ed With reacted product, via appropriate metering devices 2 and backmixed in the processing space. This is indicated by the broken-ine arrow 10. The mixing kneader 1 is subdivided into four chambers Which are formed by cooperating knead ing counter-eements 11 and, mounted on a shaft 12, kneading eements 13. Here the term chamber sha be understood as

5 5 meaning not cosed chambers but open ces between Which the product can be backmixed. The reaction product is WithdraWn by means of an attached discharging device 3. ts motor M is connected to a measuring device 8 for the?age of the mixing kneader 1. The With drawing is preferaby effected such that the?age in the mixing kneader 1 remains constant. The viscosity of the reaction mass in the mixing kneader 1 is adjusted through the choice of the reaction parameters, throughput, temperature, pressure and so on, such that the product is directy devoatiized in a subsequent LST residua devoatiizer or extruder 4, or the unreacted monomer can be reacted to competion in a downstream apparatus, for exampe a ripening tank. Reaction temperature and reaction pres sure are preferaby chosen such that the monomer excess or the sovent content is in the boiing range. The appropriate temperature range depends on the product itsef. For exampe, the boiing temperature of a certain monomer can be optima at 1 C. and a pressure of 3.5 bar, i.e., the monomer sti has a reativey ow viscosity, so that the shaft 12 has to accommodate reativey itte torque. n this case, the optima reaction temperature is at this temperature and this pressure. f this product Were to be treated under a pressure of 2 bar ony, for exampe, the boiing temperature Wi be 10 C., for exampe, Which eads to a higher product viscosity, so that a higher torque Woud have to be accommodated for the shaft 12, and this is atogether Worse for the process. f, however, the pressure Were to be increased to 4 bar, for exampe, the boiing temperature Woud be 180 C., and at this temperature an undesirabe depoymerization occurs. This process just described makes it possibe to remove the heat of reaction and the dissipated kneading energy through the vaporization of the sovent/monomer. This vapor is con densed in a re?ux condenser 5 donned on the kneader 1, and returned into the reaction mass. t is aso possibe for a pu raity of re?ux condensers to be distributed aong the ength of the mixing kneader 1. t is conceivabe, in particuar, that each chamber is assigned a re?ux condenser. The condensation can incidentay aso be reaized exter nay, and the condensate is metered With various nozzes back into the monomer/poymer mass in a homogeneous manner. The sma L/D (ength/diameter) ratio of preferaby 0.5 to 3.5 of the mixing kneader 1 causes the back?owing condensate to be mixed optimay uniformy back in the reac tor, and this is an immense probem With previousy used backmixing extruders having a arge L/D ratio. The backmixed mixing kneader 1 can operate under reduced pressure, under atmospheric pressure or under super atmospheric pressure. n the case of poymerization systems Which are operated under reduced pressure, a vave 23 is opened and the ine 24 is attached to a vacuum pump. n this Way, air and nitrogen as inert gas is WithdraWn, but the mono mer condenses in the condenser 5 and can pass back into the mixing kneader 1. For poymerization systems Which are operated under atmospheric pressure, the vave 23 is opened and the ine is eft under these atmospheric conditions. For poymerization systems Which are operated at pres sures higher than ambient pressure, preference is given to controing the system pressure to a particuar vaue With an inert gas (nitrogen for exampe), and this is done by means of a vave 14. The vave 23 is cosed in this case. A discharge of the discharging device 3 is foowed by a throtte vave 16 Which in turn is foowed by a gear pump 17. Throtte vave contro is ikewise effected in agreement With the? eve of the mixing kneader 1, as determined via the 6 measuring device 8. The gear pump 17 is foowed by a perforated pate 18, through Which product can be introduced from the discharging device 3 into the extruder 4 in spaghetti ike form. An arrow ahead of the throtte vave 16 indicates that, in this region, it is aso possibe for a stripping agent to be introduced into the discharging device 3. The devoatiizer 4 is assigned a motor M via Which one or more stirrer shaft(s) 21 With stirring/kneading eements 22 are driven in the devoatiizer 4. The stirrer shaft geometry is engineered so as to bring about pug?ow. n addition, the devoatiizer 4 is donned With one or more vapor domes 19 via Which evaporating products can be WithdraWn. The devoatiizer 4 is foowed by a further discharging screw Which in turn is driven by a motor M. The invention caimed is: 1. A poymerization process, comprising: (a) providing a mixing kneader having a backmixing stirrer shaft, Wherein the mixing kneader has a ength/diameter ratio of between ; (b) continuousy feeding to the mixing kneader monomers, cataysts and initiators to form a mixed product; and (c) heating the mixed product in the mixing kneader to its boiing temperature, Wherein portions of the product are vaporized and an exotherm of the product is absorbed by evaporative cooing, incuding vaporizing the product by providing energy input consisting of mechanica kneading energy and heat transfer via contact With kneader heat-exchange surfaces, up to just above the point of coapse of the vaporization rate, and the thus pre-evaporated viscous bed of product is continuousy admixed With new ow-viscous product soution such that the vaporization rate remains above the point of coapse. 2. A process according to caim 1 Wherein the vaporized portions of the product are at east party condensed and returned as condensate back into the mixing kneader to coo the remaining product. 3. A process according to caim 2 Wherein the condensate is returned to the mixing kneader at a ocation Where product is evaporated. 4. A process according to caim 2 Wherein the boiing temperature in the mixing kneader is adjusted by changing the pressure in the mixing kneader. 5. A process according to caim 1 incuding buiding up a vacuum in the mixing kneader so as to WithdraW vapors. 6.A process according to caim 1 incuding backmixing the mixed product to attain a predetermined viscosity for the product and maintaining the viscosity by the continuous addi tion of further monomers, cataysts and initiators. 7. A process according to caim 1 incuding in?uencing the kneading energy by varying the rotary speed of the stirrer shaft of the mixing kneader. 8. A process according to caim 1 incuding continuousy backmixing the product in the mixing kneader. 9. A process according to caim 1 incuding continuousy discharging the product from the mixing kneader and intro ducing the discharge product into a second mixing kneader or extruder. 10. A process according to caim 9 incuding heating the discharged product from the mixing kneader prior to intro duction into the second mixing kneader or extruder. 11. A process according to caim 10 Wherein the discharged product from the mixing kneader is fed to an extruder and subjecting the extruder to pug?ow. 12. A process according to caim 11, incuding subjecting the product in the extruder to surface renewa. * * * * *