EP3523018B1 - Mixing elements with reduced installation depth for static mixer - Google Patents

Description

The invention relates to mixing elements with reduced overall depth for static mixers, static mixers comprising at least two mixing elements with reduced overall depth, and a method for mixing fluids by means of a mixing element with reduced overall depth or a static mixer comprising at least two mixing elements with reduced overall depth.

In the production of polymers, it is often necessary to mix highly viscous fluids, for example polymer melts, with one another. For example, it may be necessary to mix a polymer melt with another polymer melt containing additives. So-called static mixers, among others, have been used for this for a long time. These are then placed, for example, in tubular housings in such a way that the polymer melts to be mixed flow through the static mixers in a main flow direction, which corresponds to the longest axis of such a tube, and are mixed in the process. The viscosities of such highly viscous fluids are usually in the range from 0.1 to 10,000 Pas, measured using commercially available viscometers known to those skilled in the art, such as capillary, plate-cone or plate-plate viscometers. If the viscosity of a fluid is independent of shear, it is called a Newtonian fluid. If the viscosity of a fluid depends on shear, it is called a non-Newtonian fluid. If the viscosity of a fluid decreases with increasing shear, it is said to be a shear-thinning fluid. If the viscosity of a fluid increases with increasing viscosity, it is referred to as a shear-thickening fluid. A brief overview of the rheological properties of polymer melts can be found, for example, in " Kohlgrüber: The co-rotating twin-screw extruder, Hanser-Verlag, 2007", Chapter 3, pages 37 to 57 .

The static mixers are made up of several mixing elements, for example. These mixing elements are usually designed in one piece and can have an outer sleeve into which one or more cross braces are introduced. These transverse struts essentially have the shape of an elongated body, for example an elongated cuboid, cylinder or an elongated body with a triangular, elliptical or other type of base, which is introduced into the outer sleeve with the long side, i.e. the length of the transverse strut, perpendicular to the main flow direction and at in which one of the two shorter sides, i.e. the width of the cross brace, is at right angles to the long side and at right angles to the main direction of flow. The thickness of the cross strut, i.e. the thickness of the cross strut, extends at right angles to the width of the cross strut, but parallel to the main direction of flow. If there is more than one transverse strut, these are arranged parallel to one another in two planes, viewed in the main direction of flow. At least one web extends from these one or more crossbars on each side of the respective crossbar to the inner surface of the outer sleeve and/or to the nearest crossbar, such that the width of the openings through the webs in the free cross-section of the static mixer is equal to the width of the lands. The webs, which run from the same crossbar in different directions, enclose an angle that is less than 180°, the opening angle O.

The webs also essentially have the shape of an elongated body, for example an elongated cuboid, cylinder or an elongated body with a triangular, elliptical or other type of base. The webs go essentially at right angles with their long side, ie the web length, from the cross brace. The extent of the side of the ridges facing the flow of fluid is the ridge width, the extent of the ridges perpendicular to both the ridge length and the ridge width is the ridge thickness.

The outer sleeve serves on the one hand to enable the mixing element to be inserted into a pipe, for example, without tilting, and on the other hand to increase the mechanical strength of the mixing element. However, the sleeve can also be dispensed with if the transverse struts and webs withstand the expected mechanical load and are suitably connected to one another or are placed one on top of the other in such a way that they do not slip. Such conventional mixing elements are known, inter alia, from Lars Frye "Characterization of static mixers for highly viscous single-phase media", diploma thesis, University of Karlsruhe (TH), Institute for Mechanical Process Engineering and Mechanics, Applied Mechanics Department, February 1999; see in particular pp. 6 and 7 and Figs. 2.7 and 2.8 .

It is also known from the prior art that the ridges of a first mixing element of two identical mixing elements arranged one behind the other are aligned one behind the other with the interstices of a second mixing element, one of the two mixing elements being opposite the other mixing element by its axis perpendicular to the main flow direction and parallel to the transverse struts lying axis is rotated by 180 °, but the two identical mixing elements lying one behind the other have no rotation in the plane lying normal to the main flow direction with respect to the other mixing element. A possible third mixing element directly adjoining the second mixing element then generally has the same orientation as the first mixing element and a possible fourth mixing element immediately adjoining the third mixing element then generally has the same orientation as the second mixing element. However, other orientations of the mixing elements in a static mixer are also possible.

The sides of the transverse struts of these mixing elements, which face away from the webs of the respective mixing element, lie directly on top of one another.

Typically, the mixing elements are installed in a 4+4 arrangement, i.e. four mixing elements arranged directly one behind the other are arranged as described above, wherein the second four mixing elements are immediately adjacent to the first four mixing elements, but the second four mixing elements are rotated through 90° with respect to the first four mixing elements in the plane normal to the main flow direction. Of course, 2+2, 2+3, 3+2, 3+3, 3+4, 4+3 or any other arrangement is also possible. Arrangements of at least two mixing elements arranged directly one behind the other are also called static mixers. In the 3+3 arrangement of a static mixer, the number of mixing elements is preferably a multiple of 3. In the 4+4 arrangement, the number of mixing elements is preferably a multiple of 4. In the x+x arrangement, the number of Mixing elements preferred x. In the x+y arrangement, where x is not equal to y, the number of mixing elements is preferably a multiple of x+y, where x and y are identical or different integers greater than or equal to 2 in each case.

According to the state of the art DE2943688A1 a static mixer is known which consists of a tubular housing and contains at least one mixing element arranged therein. The mixing element consists of intersecting bars which are at an angle to the pipe axis. The bars of the mixing elements are arranged in at least two groups. The ridges within each group are essentially parallel. The webs of one group intersect with the webs of the other group.

DE4428813A1 shows a static mixer, which in contrast to DE2943688A1 has intersecting webs that overlap in the area of the crossing points. This local widening of the ridges in the DE4428813A1 are formed as sheet steel rods, serves to reinforce and / or to form a form-fitting connection of adjacent webs. A groove is cut into the extension, which accommodates an adjacent sheet steel bar. EP0856353A1 shows a module that is part of a static mixer that is provided for a residence time-critical, plastically flowable mixture. The device comprises a tubular housing in which webs are arranged. The webs are inclined towards the longitudinal axis of the housing; they essentially intersect on a straight line perpendicular to the longitudinal axis. The module includes a sleeve that can be pushed into the housing. The inner wall of the static mixer, which conducts the material to be mixed, is formed by the inner sides of the sleeve. The webs are dome-shaped, each with an apex pointing against the direction of movement of the material to be mixed and a base fastened to the inside of the sleeve. Each apex forms a space with respect to the inner wall of the device. EP0526393A discloses a mixing element according to the preamble of claim 1.

In the past, attempts have repeatedly been made to use these mixing elements known from the prior art in terms of improving the mixing result and reducing the To improve pressure loss during the mixing process, without a resounding success could be achieved.

A proposal for improving the mixing elements is, for example, in WO2009000642A1 disclosed. The WO2009000642A1 discloses mixing elements in which there are at least partial gaps between adjacent webs. In this way, an improvement in the mixing result is to be achieved while at the same time reducing the pressure loss during the mixing process.

However, it has been found that for many mixing requirements in the production of polymers, a further improvement in the mixing result while at the same time reducing the pressure loss during the mixing process is desirable.

The reduction in pressure loss can advantageously be achieved by reducing the specific effect of the mixing element or static mixer.

The specific effect is a dimensionless index for describing mixing elements and static mixers, in which the pressure loss in the mixing element or static mixer and the residence time of the fluid in the mixing element or static mixer are included in the numerator and the viscosity of the fluid is included in the denominator. Detailed explanations of the specific effect can be found in Dolling, E.: "On the presentation of mixing processes in highly viscous liquids", dissertation RWTH Aachen, 1971.

wobei W die spezifische Wirkung, Δp der Druckverlust, V das Volumen, η die dynamische Viskosität und V̇ der volumetrische Durchsatz bzw. t_v die Verweilzeit.The specific effect is defined as $$W=\frac{\mathit{\Delta p}V}{n\dot{V}}=\frac{\mathit{\Delta p}{t}_v}{n}$$

where W is the specific effect, Δ p the pressure loss, V the volume, η the dynamic viscosity and V̇ the volumetric throughput or t _v the residence time.

Pressure loss and residence time are inversely proportional to each other with Newtonian behavior of the flow, i.e. the product of the two variables is constant for one and the same mixer under otherwise identical conditions. The residence time is the quotient of the free volume of the mixing element or static mixer and the volume flow through the mixer.

Depending on the technical task, different sizes can be important.

For example, there can be a certain available pressure loss for a given mixing task with a given product, which must not be exceeded for technical reasons. Under these conditions, one would like to minimize the volume of the static mixer, thus the size of the apparatus (and thus the costs of the static mixer) and the residence time, which at the high temperatures of polymer processing typically leads to a deterioration in product properties.

A further technical task can be to accomplish a given mixing task with as little pressure loss as possible with the apparatus size and dwell time specified for quality and plant reasons, in order to save energy.

Furthermore, it can be a technical task to lower the temperature in order to increase the quality with the required throughput, mixing quality and permissible pressure loss. As those skilled in the art know, reducing the temperature in polymer melts typically slows down harmful side reactions and thus increases the product quality, but at the same time the viscosity of polymer melts also increases when the temperature is reduced, so that a limitation in the pressure drop can occur.

All of these tasks can be summarized in such a way that a given mixing task should be solved while minimizing the specific effect.

Furthermore, for example, in an industrial production process such as the production of polymers, both the fluid and thus its viscosity and the volume flow, for example due to the size of the plant and production requirements, and thus also in a tube in which the mixing element or the static mixer is located , are fixed, the specific effect can only be reduced by increasing the free volume of the mixer or static mixing element. However, this increased the residence time of the fluid in the mixer, which is undesirable since a longer residence time, for example in the production of polymers, generally leads to a deterioration in the quality of the polymers. In addition, a larger free volume of a mixing element or static mixer can often only be achieved by a larger diameter of the mixing element or static mixer with an otherwise identical geometry. This in turn has the disadvantages that the pipe into which the mixing element or the static mixer is installed has to be designed to be larger and therefore more expensive, and that changing from the production of one polymer to the production of another polymer is made more difficult.

It is therefore the object of the present invention to provide a mixing element which has a lower pressure drop with the same or better mixing result. This lesser Pressure drop should be achieved without increasing the residence time or increasing the diameter or free volume of the mixing element or static mixer.

The mixing result can be evaluated, for example, by measuring a concentration distribution at the outlet from the static mixers. For this purpose, the concentration distribution is often summarized to form an integral mixing quality. gives an overview" Kohlgrüber: The co-rotating twin-screw extruder, Hanser-Verlag, 2007" in Chapter 9 on pages 184 to 188 .

The object is achieved by a mixing element according to claim 1, which has at least one crossbar from which at least three webs extend at right angles to the longest extent of the crossbar, with at least one web of these at least three webs alternating with at least two webs with respect to the longest extent of the crossbar and the webs lying on opposite sides of the transverse strut enclose an angle (aperture angle O) of 60° to 120°, preferably 75° to 105°, particularly preferably 85° to 95°, in particular 90°, characterized in that that the thickness of the cross brace (dQ) at its thickest point corresponds to 0.9 to 1.1 times the thickness of the webs (dS) multiplied by the cosine of half the opening angle O divided by the sine of the full opening angle O, i.e. dQ = dS * cos (0.5 * O) / sin O +/- 0.1 * dS * cos (0.5 * O) / sin O = (1 +/- 0.1) * dS * cos (0.5 * O) / sin O, where the thickness of the crossbar (dQ) extends parallel to the main flow direction.

The thickness of the transverse strut (dQ) at its thickest point is preferably 0.95 to 1.05 times the thickness of the webs (dS) multiplied by the cosine of half the opening angle O divided by the sine of the full opening angle O, i.e. dQ = (1 +/- 0.05) * dS * cos (0.5 * θ)/sin θ, very particularly preferably 0.98 to 1.02 times the thickness of the webs (dS) multiplied by the cosine of half the opening angle θ divided by the sine of the full opening angle O, i.e. dQ = (1 +/- 0.02) * dS * cos (0.5 * O) / sin O, in particular the thickness of the cross brace is dQ = dS * cos (0.5 * O) / sin O

Furthermore, the thickness dQ of the cross strut is preferred over a continuous distance including the middle of the cross strut length of 90%, preferably over 95%, particularly preferably over 98%, very particularly preferably over 99% of the cross strut length with a maximum deviation of 5% a maximum of 2%, particularly preferably a maximum of 1%.

Also preferably, at least the side of a cross strut (cross strut side) that faces away from the webs has the shape of a rectangle, with this rectangle lying at right angles to the main direction of flow of the fluids.

Furthermore, the thickness of the webs (dS) is preferably 0.01 to 0.07, preferably 0.015 to 0.06 and very particularly preferably 0.02 to 0.05 times the diameter of the mixing element at right angles to the main flow direction.

The mixing element according to the invention can have a sleeve. If the mixing element according to the invention has a sleeve, the outer surfaces of the cross braces and the end faces of the sleeve lie in one plane.

Surprisingly, it was found that such a mixing element not only produces a better mixing result than prior art mixing elements, but also that the pressure loss during mixing is lower without increasing the residence time or the diameter or the free volume of the mixing element or static mixer is enlarged. It is therefore possible to work with a reduced inlet pressure in front of the mixing element.

On the one hand, the reduced pressure loss saves energy that has to be used to generate the pressure, and on the other hand, the reduced pressure loss leads to a lower temperature rise during the mixing process. This in turn reduces temperature-related damage to the fluid to be mixed or to the fluids to be mixed with one another. In addition, in the case of a higher pressure loss, greater expenditure on equipment must be made, for example in the form of more powerful pumps and thicker walls.

In addition, it was surprisingly found that the pressure loss through the mixing element according to the invention can be additionally reduced with the same or better mixing result if the width of the opening between two adjacent webs in the main flow direction, which are on the same side of the crossbar from which they depart, is larger is than the width of a ridge. In this case, this web width of these two webs is essentially the same.

The mixing element according to the invention is additionally advantageous in that it has a smaller overall depth than a comparable mixing element from the prior art. Thus, a mixing element according to the invention has an overall depth that is twice the thickness of the transverse strut. With an opening angle θ of 90° and a normal ratio of the diameter of the static mixer to the thickness of the web of 20:1, this can result in a construction depth that is about 20% less. The space saving resulting from this is technically desirable, in particular because, as a rule, not only one mixing element according to the invention, but many mixing elements according to the invention are installed in a pipe through which the fluids to be mixed flow. Analogously to the static mixers from the prior art already described above, these then form a static mixer according to the invention.

This solves the additional problem of making available a mixing element which has a smaller installation depth than comparable mixing elements from the prior art, while the mixing result is the same or better and the pressure loss is reduced at the same time.

The smaller overall depth of the mixing element according to the invention results in a shorter dwell time of the fluid to be mixed or of the fluids to be mixed with one another in the mixing element. This in turn reduces the thermal loads and thus in turn temperature-related damage to the fluid to be mixed or to the fluids to be mixed with one another.

In addition, it was surprisingly found that if at least two of the mixing elements according to the invention are arranged directly adjacent to one another in such a way that their mutually facing transverse strut sides are aligned one behind the other and touch each other over their entire surface, one of the two mixing elements being in relation to the other mixing element by its axis perpendicular to the main flow direction and parallel to the transverse struts lying axis is rotated by 180°, but the two identical mixing elements lying one behind the other are not twisted in relation to the other mixing element in the plane lying normal to the main flow direction, the mechanical strength of the static mixer according to the invention made up of the at least two mixing elements according to the invention is in comparison to a static mixer, which is made up of the same number of conventional mixing elements in the same arrangement as the mixing elements according to the invention, is not reduced in the direction of flow, but even increased, while it remains at least the same in the other directions.

In such an arrangement according to the invention, the cut surfaces of the imaginary extensions of the outer contours of the webs in the area of the cross section of a cross brace form a rhombus, the cut being made at right angles to the length of the cross brace and at right angles to the width of the cross brace, i.e. parallel to the cross brace thickness (dQ). For an opening angle of O = 90°, this rhombus is a square.

This arrangement according to the invention has the effect that there is a uniform flow of forces. In particular, the flow of forces through the webs are transmitted directly from a mixing element according to the invention to the following mixing element according to the invention without deflection, whereby moments at the transition between web and cross brace and the additional shear stresses associated therewith are avoided. As already explained above, this increases the strength. Further advantages of the mixing element according to the invention and the static mixer according to the invention are the saving of material in the manufacture of the mixer and that increased throughput can be tolerated.

When using the mixing elements according to the invention, there is no need to fear that a mixing element according to the invention or a static mixer made up of at least two mixing elements according to the invention will be compressed under the load of the flowing fluid. On the contrary, the mixing element according to the invention is suitable for higher loads than a corresponding mixing element from the prior art and a static mixer constructed from at least two mixing elements according to the invention is suitable for higher loads than a corresponding static mixer from the prior art.

The advantages of the mixing element according to the invention--ie the improved mixing result, the lower pressure loss and the higher mechanical strength--are particularly apparent when at least two of the mixing elements according to the invention are present in a static mixer. In particular, the advantages of the mixing element according to the invention become apparent when the at least two mixing elements according to the invention are directly adjacent and a mixing element according to the invention is rotated by 180° relative to the respective adjacent mixing element about its axis perpendicular to the main flow direction and parallel to the transverse struts, so that the transverse strut sides of the mixing elements , which are turned away from the webs of the respective mixing element, lie directly on top of each other and touch each other over their entire surface. The advantages of the mixing element according to the invention are particularly evident when at least two of the mixing elements according to the invention form a static mixer, ie when the static mixer is made up exclusively of the mixing elements according to the invention.

The subject matter of the present invention is therefore also a static mixer comprising at least two mixing elements according to the invention. In particular, the subject of the present invention is also a static mixer which is constructed exclusively from the mixing elements according to the invention.

One or more or all of the mixing elements according to the invention may or may not have a sleeve. The static mixer according to the invention can also have a sleeve or not.

Such a sleeve can have marking grooves or marking pins on the outside, which make it difficult or prevent incorrect installation or assembly of the mixing element or the static mixer in a pipe through which the fluids to be mixed flow.

Another object of the present invention is also a method for mixing fluids using a mixing element according to the invention. In particular, a further subject matter of the present invention is also a method for mixing using a static mixer according to the invention.

Fluids which can advantageously be mixed using a mixing element according to the invention or a static mixer according to the invention are the polymer melts already mentioned at the outset or other fluids with a viscosity of 0.1 to 10,000 Pas. Thus, a mixing element according to the invention or a static mixer according to the invention can also be used to mix, for example, a polymer melt with another polymer melt to which additives have been added, or to mix a polymer melt with a solvent. This process takes place, for example, in the production of polymers or mixtures of polymers. Thus, the mixing element according to the invention and the static mixer according to the invention also serve to produce polymers and mixtures of polymers and polymer solutions. The components to be mixed can form a homogeneous mixture (no phase boundary between the components can be observed) or a disperse mixture (phase boundary between the components can be observed). If a component is dispersed, this disperse phase can be solid, liquid or gaseous. The components to be mixed can have the same viscosity or different viscosities. Viscosity ratios can be as high as 1 in 10,000. The proportions, in the case of solids and liquids in parts by weight, in the case of gases in parts by volume, are from 0.1 to 99.9% to 50 to 50%, preferably 3 to 97% to 15 to 85% the polymer melts are a melt of a thermoplastic polymer or melts of several thermoplastic polymers. A thermoplastic polymer is also referred to below for short as a thermoplastic.

Particularly preferred with a mixing element according to the invention or with a static mixer according to the invention are thermoplastic polymers from the series comprising polycarbonate, polyamide, polyester, in particular polybutylene terephthalate or polyethylene terephthalate, polyether, thermoplastic polyurethane, polyacetal, fluoropolymer, in particular polyvinylidene fluoride, polyether sulfones, polyolefin, in particular polyethylene or polypropylene , Polyimide, polyacrylate, in particular poly(methyl) methacrylate, polyphenylene oxide, polyphenylene sulfide, polyether ketone, polyaryl ether ketone, styrene polymers, in particular polystyrene, styrene copolymers, in particular styrene acrylonitrile copolymer, acrylonitrile butadiene styrene block copolymers or polyvinyl chloride processed. So-called blends of the listed polymers are also preferably processed with a mixing element according to the invention or with a static mixer according to the invention, by which the person skilled in the art understands a combination of two or more polymers. Particular preference is given to polycarbonate and blends containing polycarbonate, with the polycarbonate being very particularly preferably obtained by the phase interface process or the melt transesterification process.

It is also known that with a mixing element according to the invention or with a static mixer according to the invention, other fluids such as oils, epoxy resins, polyurethanes, foods, lacquers and paints, creams, pastes, metal melts, salt melts or glass melts can be processed.

Examples of polymer solutions which can be processed as products using a mixing element according to the invention or using a static mixer according to the invention are rubbers or thermoplastics with their monomers and/or solvents. With a mixing element according to the invention or with a static mixer according to the invention, solutions of polymers are preferably selected from the series comprising styrene-acrylonitrile copolymer with styrene, acrylonitrile and/or ethylbenzene, acrylonitrile-butadiene-styrene block copolymers with styrene, acrylonitrile, butadiene and/or ethylbenzene, polycarbonate with chlorobenzene and/or methylene chloride, Polyamide processed with caprolactam or water, polyoxymethylene with formaldehyde, poly(methyl) methacrylate with methyl methacrylate and polyethylene with hexane or cyclohexane. A mixing element according to the invention or a static mixer according to the invention is particularly preferably used for processing polymer solutions containing polycarbonate in chlorobenzene and/or methylene chloride.

For the purposes of the present invention, polycarbonates are both homopolycarbonates and copolycarbonates and/or polyester carbonates; the polycarbonates can be linear or branched in a known manner. Mixtures of polycarbonates are also meant according to the invention.

The polycarbonates can be prepared in a known manner from diphenols, carbonic acid derivatives, optionally chain terminators and branching agents. Details of the manufacture of polycarbonates have been well known to those skilled in the art for at least about 40 years. An example is here Schnell, Chemistry and Physics of Polycarbonates, Polymer Reviews, Volume 9, Interscience Publishers, New York, London, Sydney 1964 , on D. Freitag, U. Grigo, PR Müller, H. Nouvertné, BAYER AG, Polycarbonates in Encyclopedia of Polymer Science and Engineering, Volume 11, Second Edition, 1988, pages 648-718 and finally up U. Grigo, K. Kirchner and PR Müller Polycarbonate in Becker/Braun, Kunststoff-Handbuch, Volume 31, Polycarbonate, Polyacetal, Polyester, Celluloseester, Carl Hanser Verlag Munich, Vienna 1992, pages 117-299 referred.

Aromatic polycarbonates are produced, for example, by reacting diphenols with carbonic acid halides, preferably phosgene, and/or with aromatic dicarboxylic acid dihalides, preferably benzenedicarboxylic acid dihalides, by the phase interface process, optionally using chain terminators and optionally using trifunctional or more than trifunctional branching agents.

Production via a melt polymerization process by reacting diphenols with, for example, diphenyl carbonate is also possible. Examples of diphenols suitable for producing the polycarbonates are hydroquinone, resorcinol, dihydroxydiphenyls, bis(hydroxyphenyl)alkanes, bis(hydroxyphenyl)cycloalkanes, bis(hydroxyphenyl) sulfides, bis(hydroxyphenyl) ether, bis( hydroxyphenyl) ketones, bis(hydroxyphenyl) sulfones, bis(hydroxyphenyl) sulfoxides, α,α'-bis(hydroxyphenyl)diisopropylbenzenes, phthalimidines derived from isatin or phenolphthalein derivatives and their nucleus-alkylated, nucleus-arylated and nucleus-halogenated compounds.

Preferred diphenols are 4,4'-dihydroxydiphenyl, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,4-bis(4-hydroxyphenyl)-2-methylbutane, 1,1-bis- (4-hydroxyphenyl)-p-diisopropylbenzene, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, dimethyl bisphenol A, bis(3,5-dimethyl-4-hydroxyphenyl)methane, 2 ,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, bis(3,5-dimethyl-4-hydroxyphenyl)sulfone, 2,4-bis(3,5-dimethyl-4- hydroxyphenyl)-2-methylbutane, 1,1-bis(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropylbenzene and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

Particularly preferred diphenols are 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 1,1-bis(4 -hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and dimethyl bisphenol A.

These and other suitable diphenols are, for example, in US-A 3,028,635 , US-A 2,999,825 , US-A 3,148,172 , US-A 2,991,273 , US-A 3,271,367 , US-A 4,982,014 and US-A 2,999,846 , in DE-A 1 570 703 , DE-A 2063 050 , DE-A 2 036 052 , DE-A 2 211 956 and DE-A 3 832 396 , in FR-A 1 561 518 , in the Monograph H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964 as in JP-A 62039/1986 , JP-A 62040/1986 and JP-A 105550/1986 described.

In the case of homopolycarbonates only one diphenol is used, in the case of copolycarbonates several diphenols are used.

Examples of suitable carbonic acid derivatives are phosgene or diphenyl carbonate.

Suitable chain terminators that can be used in the production of the polycarbonates are monophenols. Examples of suitable monophenols are phenol itself, alkylphenols such as cresols, p-tert-butylphenol, cumylphenol and mixtures thereof.

Preferred chain terminators are the phenols which are mono- or polysubstituted by linear or branched C ₁ - to C ₃₀ -alkyl radicals, preferably unsubstituted, or substituted by tert-butyl. Particularly preferred chain terminators are phenol, cumylphenol and/or p-tert-butylphenol. The amount of chain terminator to be used is preferably 0.1 to 5 mol% based on Moles of diphenols used in each case. The chain terminators can be added before, during or after the reaction with a carbonic acid derivative.

Suitable branching agents are the trifunctional or more than trifunctional compounds known in polycarbonate chemistry, in particular those having three or more than three phenolic OH groups.

Examples of suitable branching agents are 1,3,5-tri-(4-hydroxyphenyl)benzene, 1,1,1-tri-(4-hydroxyphenyl)ethane, tri-(4-hydroxyphenyl)phenylmethane, 2,4- bis-(4-hydroxyphenylisopropyl)-phenol, 2,6-bis-(2-hydroxy-5'-methyl-benzyl)-4-methylphenol, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl) -propane, tetra-(4-hydroxyphenyl)methane, tetra-(4-(4-hydroxyphenylisopropyl)phenoxy)methane and 1,4-bis-((4',4-dihydroxytriphenyl)methyl)benzene and 3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.

The amount of any branching agent to be used is preferably 0.05 mol % to 3 mol %, based on moles of diphenols used in each case. The branching agents can either be initially introduced with the diphenols and the chain terminators in the aqueous-alkaline phase or, dissolved in an organic solvent, can be added before the phosgenation. In the case of the transesterification process, the branching agents are used together with the diphenols.

Particularly preferred polycarbonates are the homopolycarbonate based on bisphenol A, the homopolycarbonate based on 1,3-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and the copolycarbonates based on the two monomers bisphenol A and 1,1 -bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

In addition, based on the weight of the thermoplastic, up to 50.0% by weight, preferably 0.2 to 40% by weight, particularly preferably 0.10 to 30.0% by weight, of other customary additives can optionally be present.

This group includes flame retardants, anti-drip agents, thermal stabilizers, mold release agents, antioxidants, UV absorbers, IR absorbers, antistatic agents, optical brighteners, light scattering agents, colorants such as pigments, including inorganic pigments, carbon black and/or dyes, and inorganic fillers in the customary for polycarbonate Amounts. These additives can be added individually or as a mixture.

Such additives, as are usually added to polycarbonates, are, for example, in EP-A 0 839 623 , WO-A 96/15102 , EP-A 0 500 496 or " Plastics Additives Handbook", Hans Zweifel, 5th Edition 2000, Hanser Verlag, Münch en described.

In the production of a polycarbonate, the mixing elements according to the invention or static mixers according to the invention are preferably used after the last degassing stage of the polycarbonate. This is generally the case after a tubular or strand evaporator in the production of polycarbonate by the phase interface process and after a high-viscosity reactor in the production of polycarbonate by the melt polymerization process. In the direction of flow upstream of a mixing element according to the invention or static mixer according to the invention, a secondary flow of polycarbonate containing no additives is fed to a main flow of unadditized polycarbonate. The mixing ratio here is in a range from 99:1 to 80:20, preferably from 98:2 to 85:15, particularly preferably from 95:5 to 90:10, in each case by weight.

If a mixing element according to the invention or a static mixer according to the invention is used in the production of polycarbonate, this causes less temperature damage to the polycarbonates. This in turn makes available a polycarbonate which has less yellowing and higher transparency than a polycarbonate which was produced under otherwise identical conditions without using a mixing element according to the invention or a static mixer according to the invention.

The subject matter of the present invention is therefore also a method for the production of polycarbonate, in which a mixing element according to the invention is used. The subject matter of the present invention is therefore also a process for the production of polycarbonate, in which a static mixer according to the invention is used.

Fig. 1

zeigt ein Mischelement aus dem Stand der Technik mit Hülse im Querschnitt und in der Draufsicht. Die Bemaßung von Strecken ist in Millimeter, die Bemaßung des Winkels in Grad; es sind:
1.1 Dicke der Hülse
1.2 Durchmesser des Mischelements einschließlich Hülse
1.3 Dicke dQ der Querstrebe
1.4 Breite der Querstrebe
1.5 Dicke dS des Stegs
1.6 Breite des Stegs
1.7 Breite der Öffnung zwischen zwei Stegen
1.8 Öffnungswinkel O
1.9 Querstreben
1.10 Hauptströmungsrichtung

Fig. 2

zeigt einen Querschnitt eines statischen Mischer bestehend aus zwei Mischelementen aus dem Stand der Technik mit eingezeichneten Pfeilen, die die Kraftflüsse durch die Stege und die Querstrebe andeuten, wenn die Kraft senkrecht von oben auf das Mischelement wirkt; es sind:
2.1 Hülse des oberen Mischelements
2.2 Querstreben des oberen Mischelements
2.3 Stege des oberen Mischelements
2.4 Hülse des unteren Mischelements
2.5 Querstreben des unteren Mischelements
2.6 Stege des unteren Mischelements
2.7 Kraftflüsse (durch Pfeile angedeutet)
2.8 Dicke dQ der Querstrebe des oberen Mischelements
2.9 Breite der Querstrebe des oberen Mischelements
2.10 Dicke dQ der Querstrebe des unteren Mischelements
2.11 Breite der Querstrebe des unteren Mischelements
2.12 IIauptströmungsrichtung

Fig. 3

zeigt einen Längsschnitt durch ein Rohr mit einem statischen Mischer gebildet aus einer doppelten 4+4-Anordnung von Mischelementen aus dem Stand der Technik; es sind:
3.1 erstes Mischelement
3.2 zweites Mischelement, gegenüber dem ersten Mischelement um seine zur Hauptströmungsrichtung senkrechte und parallel zu den Querstreben liegende Achse um 180° gedreht
3.3 drittes Mischelement, ausgerichtet wie erstes Mischelement
3.4 viertes Mischelement, ausgerichtet wie zweites Mischelement
3.5 fünftes Mischelement, ausgerichtet wie erstes Mischelement 3.1, aber in Strömungsrichtung betrachtet um 90° in Umfangsrichtung gegen den Uhrzeigersinn gedreht
3.6 sechstes Mischelement, gegenüber dem fünften Mischelement um seine zur Hauptströmungsrichtung senkrechte und parallel zu den Querstreben liegende Achse um 180° gedreht
3.7 siebtes Mischelement, ausgerichtet wie fünftes Mischelement
3.8 achtes Mischelement, ausgerichtet wie sechstes Mischelement
3.9 neuntes Mischelement, ausgerichtet wie erstes Mischelement
3.10 zehntes Mischelement, ausgerichtet wie zweites Mischelement
3.11 elftes Mischelement, ausgerichtet wie erstes Mischelement
3.12 zwölftes Mischelement, ausgerichtet wie zweites Mischelement
3.13 dreizehntes Mischelement, ausgerichtet wie fünftes Mischelement
3.14 vierzehntes Mischelement, ausgerichtet wie sechstes Mischelement
3.15 fünfzehntes Mischelement, ausgerichtet wie siebtes Mischelement
3.16 sechszehntes Mischelement, ausgerichtet wie achtes Mischelement
3.17 Hauptströmungsrichtung
3.18 Rohr, in dem die Mischelemente eingebaut sind

Fig. 4

zeigt einen Querschnitt eines erfindungsgemäßen Mischelements gemäß dem Schnitt A-A aus Fig. 5; es sind:
4.1 Hülse
4.2 Querstreben
4.3 Stege

Fig. 5

zeigt die Draufsicht eines erfindungsgemäßen Mischelements; es sind:
5.1 Hülse
5.2 Querstreben
5.3 Stege

Fig. 6

zeigt einen Querschnitt eines erfindungsgemäßen statischen Mischers bestehend aus zwei erfindungsgemäßen Mischelementen mit eingezeichneten Pfeilen, die die Kraftflüsse durch die Stege und die Querstrebe andeuten, wenn die Kraft senkrecht von oben auf das Mischelement wirkt; es sind:
6.1 Hülse des oberen Mischelements
6.2 Querstreben des oberen Mischelements
6.3 Stege des oberen Mischelements
6.4 Hülse des unteren Mischelements
6.5 Querstreben des unteren Mischelements
6.6 Stege des unteren Mischelements
6.7 Kraftflüsse (durch Pfeile angedeutet)
6.8 Dicke dQ der Querstrebe des oberen Mischelements
6.9 Breite der Querstrebe des oberen Mischelements
6.10 Dicke dQ der Querstrebe des unteren Mischelements
6.11 Breite der Querstrebe des unteren Mischelements
6.12 Hauptströmungsrichtung

Fig. 7

zeigt einen Querschnitt eines statischen Mischer bestehend aus zwei erfindungsgemäßen statischen Mischelementen mit einem Öffnungswinkel O von etwa gleich 90°; es sind:
7.1 Hülse des oberen Mischelements
7.2 Querstreben des oberen Mischelements
7.3 Stege des oberen Mischelements
7.4 Hülse des unteren Mischelements
7.5 Querstreben des unteren Mischelements
7.6 Stege des unteren Mischelements
7.7 Öffnungswinkel O

Fig. 8

zeigt einen Querschnitt eines statischen Mischer bestehend aus zwei erfindungsgemäßen statischen Mischelementen mit einem Öffnungswinkel O größer 90°; es sind:
8.1 Hülse des oberen Mischelements
8.2 Querstreben des oberen Mischelements
8.3 Stege des oberen Mischelements
8.4 Hülse des unteren Mischelements
8.5 Querstreben des unteren Mischelements
8.6 Stege des unteren Mischelements
8.7 Öffnungswinkel O

Fig. 9

zeigt einen Querschnitt eines statischen Mischer bestehend aus zwei erfindungsgemäßen statischen Mischelementen mit einem Öffnungswinkel O kleiner 90°; es sind:
9.1 Hülse des oberen Mischelements
9.2 Querstreben des oberen Mischelements
9.3 Stege des oberen Mischelements
9.4 Hülse des unteren Mischelements
9.5 Querstreben des unteren Mischelements
9.6 Stege des unteren Mischelements
9.7 Öffnungswinkel O

Fig.10

zeigt links einen Längsschnitt durch einen herkömmlichen statischen Mischer und rechts einen Längsschnitt durch einen erfindungsgemäßen statischen Mischer mit verringerter Bauhöhe. Die um etwa 23 % verminderte Bauhöhe des erfindungsgemäßen statischen Mischers gegenüber der Bauhöhe des statischen Mischers aus dem Stand der Technik ist gut zu erkennen. Auch ist gut zu erkennen, dass eines der beiden Mischelemente gegenüber dem anderen Mischelement um seine zur Hauptströmungsrichtung senkrechte und parallel zu den Querstreben liegende Achse um 180° gedreht ist, so dass die Querstrebenseiten dieser Mischelemente, die den Stegen des jeweiligen Mischelements abgewandt sind, unmittelbar aufeinander liegen und sich vollflächig berühren.

Fig. 11

zeigt eine Vollansicht eines erfindungsgemäßen statischen Mischers.

The invention is explained below by means of drawings, without being restricted to the embodiments shown in the drawings.

1

FIG. 12 shows a mixing element from the prior art with a sleeve in cross section and in plan view. Lines are measured in millimeters, angles are measured in degrees; there are:
1.1 Thickness of sleeve
1.2 Diameter of mixing element including sleeve
1.3 Thickness dQ of the crossbar
1.4 Width of the crossbar
1.5 Thickness dS of the web
1.6 Width of the web
1.7 Width of the opening between two webs
1.8 opening angle O
1.9 cross braces
1.10 Main flow direction

2

shows a cross section of a static mixer consisting of two mixing elements from the prior art with arrows drawn in which indicate the flow of forces through the webs and the cross brace when the force acts perpendicularly from above on the mixing element; there are:
2.1 Upper mixing element sleeve
2.2 Cross braces of the upper mixing element
2.3 Bars of the upper mixing element
2.4 Lower mixing element sleeve
2.5 Cross braces of the lower mixing element
2.6 bars of the lower mixing element
2.7 Power flows (indicated by arrows)
2.8 Thickness dQ of the cross brace of the upper mixing element
2.9 Width of crossbar of upper mixing element
2.10 Thickness dQ of the cross brace of the lower mixing element
2.11 Width of crossbar of lower mixing element
2.12 Main flow direction

3

Figure 12 shows a longitudinal section through a tube with a static mixer formed from a prior art double 4+4 arrangement of mixing elements; there are:
3.1 first mixing element
3.2 Second mixing element, rotated by 180° relative to the first mixing element about its axis, which is perpendicular to the main flow direction and parallel to the transverse struts
3.3 third mixing element, aligned like the first mixing element
3.4 fourth mixing element, aligned like the second mixing element
3.5 fifth mixing element, aligned like the first mixing element 3.1, but rotated counterclockwise by 90° in the circumferential direction, viewed in the direction of flow
3.6 sixth mixing element, rotated by 180° relative to the fifth mixing element about its axis, which is perpendicular to the main flow direction and parallel to the transverse struts
3.7 seventh mixing element, aligned like the fifth mixing element
3.8 eighth mixing element, aligned like the sixth mixing element
3.9 ninth mixing element, aligned like the first mixing element
3.10 tenth mixing element, aligned like the second mixing element
3.11 eleventh mixing element, aligned like the first mixing element
3.12 twelfth mixing element, aligned like the second mixing element
3.13 Thirteenth mixing element, aligned like the fifth mixing element
3.14 Fourteenth mixing element, aligned like the sixth mixing element
3.15 Fifteenth mixing element, aligned like seventh mixing element
3.16 Sixteenth mixing element, aligned like eighth mixing element
3.17 Main flow direction
3.18 Pipe in which the mixing elements are installed

4

shows a cross section of a mixing element according to the invention according to section AA figure 5 ; there are:
4.1 sleeve
4.2 Cross braces
4.3 webs

figure 5

shows the plan view of a mixing element according to the invention; there are:
5.1 sleeve
5.2 Cross braces
5.3 webs

6

shows a cross section of a static mixer according to the invention consisting of two mixing elements according to the invention with arrows drawn in which indicate the flow of forces through the webs and the cross brace when the force acts perpendicularly from above on the mixing element; there are:
6.1 Upper mixing element sleeve
6.2 Cross braces of the upper mixing element
6.3 Bars of the upper mixing element
6.4 Lower mixing element sleeve
6.5 Cross braces of the lower mixing element
6.6 Bars of the lower mixing element
6.7 Force flows (indicated by arrows)
6.8 Thickness dQ of the cross brace of the upper mixing element
6.9 Width of crossbar of upper mixing element
6.10 Thickness dQ of the crossbar of the lower mixing element
6.11 Width of crossbar of lower mixing element
6.12 Main flow direction

7

shows a cross section of a static mixer consisting of two static mixing elements according to the invention with an opening angle θ of approximately 90°; there are:
7.1 Upper mixing element sleeve
7.2 Cross braces of the upper mixing element
7.3 Bars of the upper mixing element
7.4 Lower mixing element sleeve
7.5 Cross braces of the lower mixing element
7.6 Bars of the lower mixing element
7.7 Opening angle O

8

shows a cross section of a static mixer consisting of two static mixing elements according to the invention with an opening angle O greater than 90°; there are:
8.1 Upper mixing element sleeve
8.2 Cross braces of the upper mixing element
8.3 Bars of the upper mixing element
8.4 Sleeve of the lower mixing element
8.5 Cross braces of the lower mixing element
8.6 Bars of the lower mixing element
8.7 Opening angle O

9

shows a cross section of a static mixer consisting of two static mixing elements according to the invention with an opening angle O less than 90°; there are:
9.1 Upper mixing element sleeve
9.2 Cross braces of the upper mixing element
9.3 Bars of the upper mixing element
9.4 Lower mixing element sleeve
9.5 Cross braces of the lower mixing element
9.6 Bars of the lower mixing element
9.7 Opening angle O

Fig.10

shows a longitudinal section through a conventional static mixer on the left and a longitudinal section through a static mixer according to the invention with a reduced overall height on the right. The overall height of the static mixer according to the invention, reduced by about 23% compared to the overall height of the static mixer from the prior art, can be clearly seen. It is also easy to see that one of the two mixing elements is rotated by 180° relative to the other mixing element about its axis, which is perpendicular to the main flow direction and parallel to the transverse struts, so that the transverse strut sides of these mixing elements, which face away from the ribs of the respective mixing element, directly lie on top of each other and touch each other over their entire surface.

11

shows a full view of a static mixer according to the invention.

Claims (13)

1. Mixing element which has at least one transverse strut (1.9) from which there originate, at right angles to the longest extent of the transverse strut, at least three webs, at least one web of these at least three webs lying in alternation relative to at least two webs with respect to the longest extent of the transverse strut, and the webs lying on opposite sides of the transverse strut enclosing an opening angle O of 60° to 120°, characterized in that the thickness of the transverse strut (dQ) at its thickest point is not more than 0.9 to 1.1 times the thickness of the webs (dS) multiplied by the cosine of half the opening angle O divided by the sine of the full opening angle O, the thickness of the transverse strut (dQ) extending parallel to the main flow direction.
2. Mixing element according to Claim 1, characterized in that the webs lying on opposite sides of the transverse strut enclose an opening angle O of 75° to 105°, more preferably of 85° to 95°, more particularly of 90°.
3. Mixing element according to Claim 1 or 2, characterized in that the thickness of the transverse strut (dQ) at its thickest point is 0.95 to 1.05 times the thickness of the webs (dS) multiplied by the cosine of half the opening angle O divided by the sine of the full opening angle O, i.e. dQ = (1 +/- 0.05) * dS * cos (0.5 * O) / sin O, very preferably 0.98 to 1.02 the thickness of the webs (dS) multiplied by the cosine of half the opening angle O divided by the sine of the full opening angle O, i.e. dQ = (1 +/- 0.02) * dS * cos (0.5 * O) / sin O, and in particular the thickness of the transverse strut dQ = dS * cos (0.5 * O) / sin O.
4. Mixing element according to any of Claims 1 to 3, characterized in that the width of the opening (1.7) between two adjacent webs which lie on the same side of the transverse strut from which they depart is greater, in the main flow direction, than the width of a web (1.6) .
5. Mixing element according to any of Claims 1 to 4, characterized in that it has a sleeve.
6. Static mixer comprising at least two mixing elements according to any of Claims 1 to 5.
7. Static mixer according to Claim 6, characterized in that the mixing elements according to any of Claims 1 to 5 are directly adjacent.
8. Static mixer according to Claim 6 or 7, characterized in that it is constructed exclusively of mixing elements according to any of Claims 1 to 5.
9. Static mixer according to any of Claims 1 to 8, characterized in that at least one mixing element and preferably all the mixing elements have a sleeve.
10. Method for mixing fluids, characterized in that a mixing element according to any of Claims 1 to 5 is used.
11. Method for mixing fluids, characterized in that a static mixer according to any of Claims 6 to 9 is used.
12. Method for producing polymers or polymer mixtures, characterized in that a mixing element according to any of Claims 1 to 5 is used.
13. Method for producing polymers or polymer mixtures, characterized in that a static mixer according to any of Claims 6 to 9 is used.

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