Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
  • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D9/00—Crystallisation
  • B01D9/0004—Crystallisation cooling by heat exchange
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D9/00—Crystallisation
  • B01D9/0018—Evaporation of components of the mixture to be separated
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D9/00—Crystallisation
  • B01D9/0018—Evaporation of components of the mixture to be separated
  • B01D9/0022—Evaporation of components of the mixture to be separated by reducing pressure
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
  • B01F27/80—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis
  • B01F27/808—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis with stirrers driven from the bottom of the receptacle
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
  • B01F27/80—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis
  • B01F27/86—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis co-operating with deflectors or baffles fixed to the receptacle
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
  • B01F27/80—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis
  • B01F27/86—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis co-operating with deflectors or baffles fixed to the receptacle
  • B01F27/861—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis co-operating with deflectors or baffles fixed to the receptacle the baffles being of cylindrical shape, e.g. a mixing chamber surrounding the stirrer, the baffle being displaced axially to form an interior mixing chamber
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
  • B01F27/80—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis
  • B01F27/91—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis with propellers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/71—Feed mechanisms
  • B01F35/712—Feed mechanisms for feeding fluids
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/0053—Details of the reactor
  • B01J19/006—Baffles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/0053—Details of the reactor
  • B01J19/0066—Stirrers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/18—Stationary reactors having moving elements inside
  • B01J19/1868—Stationary reactors having moving elements inside resulting in a loop-type movement
  • B01J19/1875—Stationary reactors having moving elements inside resulting in a loop-type movement internally, i.e. the mixture circulating inside the vessel such that the upwards stream is separated physically from the downwards stream(s)
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F2215/00—Auxiliary or complementary information in relation with mixing
  • B01F2215/04—Technical information in relation with mixing
  • B01F2215/0413—Numerical information
  • B01F2215/0418—Geometrical information
  • B01F2215/0422—Numerical values of angles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F2215/00—Auxiliary or complementary information in relation with mixing
  • B01F2215/04—Technical information in relation with mixing
  • B01F2215/0413—Numerical information
  • B01F2215/0418—Geometrical information
  • B01F2215/0431—Numerical size values, e.g. diameter of a hole or conduit, area, volume, length, width, or ratios thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/00049—Controlling or regulating processes
  • B01J2219/00182—Controlling or regulating processes controlling the level of reactants in the reactor vessel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/00049—Controlling or regulating processes
  • B01J2219/00189—Controlling or regulating processes controlling the stirring velocity
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/00049—Controlling or regulating processes
  • B01J2219/00243—Mathematical modelling

Definitions

• the invention relates to processes for the preparation of free-flowing dicarboxylic acid crystallizates from an aqueous solution or suspension of the dicarboxylic acid in a crystallizer.
• Dicarboxylic acids and especially adipic acid are important monomers for the preparation of polymers, in particular of polyamides.
• Dicarboxylic acids can be z. Example by oxidation of cyclic alcohols, cyclic ketones or mixtures of these alcohols and ketones with oxidizing agents such as concentrated nitric acid or air.
• the quantitatively most important dicarboxylic acid is adipic acid, which is obtained industrially in two reaction steps from cyclohexane. In the first step, cyclohexane is oxidized with air to a cyclohexanol / cyclohexanone mixture (anolone mixture). After removal of unreacted cyclohexane, the anolone mixture is oxidized with concentrated nitric acid.
• the industrial-scale oxidation of the cyclohexanol / cyclohexanone mixtures is carried out with excess 40-70% by weight, in particular concentrated (60% strength by weight) nitric acid at from 40 to 90 ° C. and atmospheric pressure.
• the catalysts used are copper and vanadium salts.
• the reaction product contains adipic acid (93-96 mol%) as by-products, succinic acid and glutaric acid (4-5 mol%) and small amounts of monocarboxylic acids, such as, for example, As acetic acid.
• the reaction effluent is passed into an outflow column, into which air is blown from below.
• the exhaust gas withdrawn at the top of the column is worked up to nitric acid.
• the bottom product is then dehydrated in a second column to the extent that the nitric acid content increases to 56 wt .-%. About 90% by weight thereof is recycled to the oxidation reactor, about 10% by weight purified by crystallization from water, see DE-A-1 238 000.
• adipic acid is accessible from glucaric acid.
• Dicarboxylic acids having preferably two to twelve carbon atoms, such as.
• oxalic, malonic, succinic, maleic, glutaric, adipic, pimelic, suberic, sebacic, decanedicarboxylic and dodecanedicarboxylic are crystalline compounds with melting points between 98 ° C and 185 ° C. When heated, they can decay, such.
• B. adipic acid form a cyclic ketone (cyclopentanone).
• the dicarboxylic acids are usually crystallized into crystal powders (crystallizates).
• crystals should not have too low an average crystal size distribution in order to reduce or avoid, for example, dust formation during handling.
• Adipic acid usually crystallizes from pure solutions in the form of thin sheets, which have a large contact area and thus allow good adhesion between adjacent crystals due to attractive interactions between the individual contact surfaces. Adipic acid crystals are described, for example, in RJ Davey et al, J. Chem. Soc. Faraday Trans. 88 (23), 3461-3466 (1992).
• the surface of pure adipic acid crystals is essentially determined by the ⁇ 100 ⁇ -oriented crystallographic surfaces, the physical properties of which result from the hydrophilic carboxyl groups lying there.
• ⁇ 100 ⁇ faces When two such ⁇ 100 ⁇ faces are brought into contact with each other, they can immediately adhere weakly to each other through the formation of hydrogen bonds.
• Such facets are generally saturated with a "monofilm" of water, and the contacting of two such surfaces saturated with water substantially enhances their cohesiveness.
• US Pat. No. 5,296,639 describes a process for the purification of adipic acid during crystallization, in which the crystal morphology is modified in such a way that the uptake of impurities during crystallization is reduced.
• caproic acid or selected surfactants such as sodium dodecyl sulfate, sodium dodecylsulfonate or sodium dodecylbenzenesulfonate are added for this purpose.
• a disadvantage of this method is that the additives typically have to be added in concentrations of more than 100 ppm up to 3% in order to achieve the desired effect. As a result, the product is usually inadmissibly contaminated.
• the use of surfactants still has the disadvantage that in the case of an accumulation by internal recycling of the solvent (usually water) in systems for foaming, so that an application in concrete technical processes in the rule is difficult or even über- home is not possible.
• additives are considered to be fundamentally disadvantageous. They only act if they adsorb on the interface and so inevitably appear in the dicarboxylic acid crystals as impurities.
• the object of the present invention is to provide a process for the preparation of free-flowing dicarboxylic acid crystallizates from an aqueous suspension of the dicarboxylic acid in a crystallizer, wherein the co-use of additives can be dispensed with and Nevertheless, good storage and free-flowing crystals are obtained, which are not prone to caking.
• the crystals should preferably not only be larger than the known crystals. Moreover, they should not be in the form of thin crystallographic surfaces oriented in the ⁇ 100 ⁇ direction, but in a more favorable, compact crystal form.
• the crystals should have a good trickling and not lose their flowability during prolonged storage. In addition, they should have no tendency to form fines and high purity.
• the object is achieved by a process for the preparation of free-flowing Dicarbonklarekristallisaten from an aqueous solution or suspension of dicarboxylic acid in a crystallizer, characterized in that a stirred container is used as a crystallizer, a vertical, cylindrical tank with side walls and a bottom , Means for supplying and discharging the solution or suspension, a coaxially arranged in the cylindrical tank guide tube and a coaxial arranged on the tank bottom blade stirrer with rotating coaxial shaft and Rrindermeasuren which promotes the solution or suspension in the radial direction, so that a Adjusting the flow of the solution or suspension in the manner of a loop reactor, wherein the peripheral speed of Blattrrockers 0.5 to 6 m / s and the power input into the solution or suspension through the blade stirrer is 0.01 to 5 kW / m 3 .
• solution or suspension includes solutions, suspensions, and mixed solutions / suspensions.
• solution and suspension preferably include these three meanings, and “suspension” thus also means solutions.
• free-flowing denotes dicarboxylic acid crystallizates which do not have the form of thin leaves described at the outset, but represent three-dimensional crystal agglomerates which are characterized by an irregular surface structure and therefore do not tend to cake, and which are free-flowing even after prolonged storage.
• aqueous solution or suspension denotes a solution or suspension in which the majority of the solvent or suspension medium consists of water, preferably the suspension medium contains at least 60% by weight of water, more preferably at least 80% by weight of water. in particular at least 95% by weight of water. Particular preference is given to using only water as the solvent or suspension medium.
• flow of the suspension in the manner of a loop reactor means that the suspension flows within the guide tube in the axial direction, between the guide tube and side walls of the cylindrical tank also flows in the axial direction with opposite orientation and at the bottom of the cylindrical tank and above the As a result, based on a cross-sectional view of the cylindrical tank in the form of a vertical section a loop-shaped flow of the suspension, which thus flows in the manner of a loop reactor.
• flow of the suspension in the manner of a loop reactor thus refers to an annular flow of the suspension in a loop, is introduced into the suspension and discharged from the suspension.
• the loop is between cylindrical tank and With respect to the vertical direction of the cylindrical tank, there is an axial flow direction through the vertical cylindrical tank except at the top and bottom reversal points is limited in the direction of the tank bottom so that substantially or exclusively results in a radial conveying direction on the tank bottom.
• the distance between the stirrer bottom edge and the bottom of the tank is chosen as small as possible.
• the parameters according to the invention ensure a sufficiently large flow rate and a sufficiently low shear introduction into the suspension.
• Any suitable dicarboxylic acids which form a suspension in water can be used in the process according to the invention.
• the dicarboxylic acid is selected from C2-i2 dicarboxylic acids, preferably C4-8 dicarboxylic acids.
• the dicarboxylic acid is preferably aliphatic, linear and terminal or aromatic.
• dicarboxylic acids examples include terephthalic acid or isophthalic acid and oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, decanedicarboxylic acid and dodecanedicarboxylic acid.
• the dicarboxylic acids may be saturated, unsaturated or branched.
• the dicarboxylic acids further functional groups such.
• terephthalic acid adipic acid or succinic acid.
• adipic acid in particular was prepared by oxidation of cyclohexanol, cyclohexanone or mixtures thereof with nitric acid. After removal of excess nitric acid, nitrogen oxides and water, it is preferably subjected to at least one crude crystallization, preferably two crude crystallizations.
• the adipic acid content of this prepurified adipic acid is preferably 95-99% by weight, preferably 97-98% by weight (based on dry substance).
• the cyclohexanol or cyclohexanone used for the oxidation with nitric acid can be prepared by oxidation of cyclohexane with air or oxygen, by hydrogenation of phenol or by hydration of cyclohexene.
• adipic acid which was prepared by single-stage oxidation of cyclohexane with air or by saponification of adipic diesters.
• adipic acid can also be used, starting from renewable raw materials, eg. B. from muconic acid or glucaric acid, is accessible.
• the dicarboxylic acid suspensions used in the process are preferably obtained according to the following steps: a) oxidation of cyclic alcohols, ketones or mixtures thereof with nitric acid, oxygen or air to give corresponding dicarboxylic acids, b) working up the oxidation effluent, using water and unused oxidizing agent separated from the dicarboxylic acids formed completely or partially, c) at least one coarse crystallization of the dicarboxylic acids from water as the solvent.
• Crude adipic acid, prepared on the said routes, is preferably also subjected to at least one crude crystallization from water before the pure crystallization.
• Crystallization generally takes place when a supersaturated solution of the dicarboxylic acid is present in a solvent.
• a supersaturated solution of a dicarboxylic acid can be produced in various ways: Once it is possible to bring about the supersaturation of the solution by evaporation of solvent, at atmospheric pressure or in vacuo.
• the pure crystallization of the dicarboxylic acids preferably takes place from water as solvent. It can be carried out batchwise, preferably continuously.
• the dicarboxylic acids used for the pure crystallization preferably have a dicarboxylic acid content of 90-99 wt .-% after at least one crude crystallization.
• the crystallization is preferably carried out at temperatures of 30 to 90 ° C, preferably 40 to 80 ° C, particularly preferably 50 to 70 ° C.
• the concentration of the aqueous dicarboxylic acid solution which is fed to the crystallizer preferably 20 to 70 wt .-%, preferably 30 to 60 wt .-%.
• the residence time of the dicarboxylic acid suspension in the crystallizer is preferably 0.25 to 8 hours, preferably 0.5 to 4 hours, more preferably 1 to 3 hours.
• adipic acid solution containing undissolved adipic acid suspended as seed crystals.
• the temperature in the crystallizer is z. B. maintained at 50 to 70 ° C.
• crystal-free adipic acid solution is supplied.
• Adipic acid suspension is withdrawn continuously via a product take-off, so that the level of the crystallizer remains constant.
• crystallizers used according to the invention are known in a general form from the prior art. For this purpose, reference may be made, for example, to WO 2004/058377.
• WO 2004/058377 A1 (DuPont, Priority Dec. 16, 2002) describes an apparatus which is suitable for the production of particles by precipitation or crystallization (FIG. 1 in FIG.
• This apparatus can be designed to crystallize biological products such as proteins and enzymes, small organic molecules such as pharmaceuticals, fine chemicals and inorganic materials such as mineral salts (page 1, lines 8 to 15).
• the apparatus shown in Figure 1 consists of a crystallisation apparatus comprising: a) a container,
• a radial stirrer optionally containing a top and a bottom plate
• the apparatus can produce crystals of different sizes ranging from about 0.5 to about 3000 microns (page 6, lines 24 to 30).
• WO 2004/058377 enables the production of larger crystals with a narrower size distribution or finer crystals with narrower size distribution. Increasing the RPM value often results in finer particles, adjusting the addition rate of the feed to change the particle size (page 21, lines 22-25).
• the size of the crystals can be varied by changing the chemical composition of the liquid streams, the stirrer speed (RPM) and the ratio of the different liquid flows to each other.
• WO 2004/058377 A1 gives no indication as to how to proceed in the crystallization of dicarboxylic acids and in particular of adipic acid in order to achieve the object of the invention.
• FIG. 2 shows the schematic structure of a crystallizer used according to the invention in a cross-sectional view.
• the parameters listed below are given in FIG. FIG. 2 relates to a crystallizer used according to the invention with a radial stirrer arranged near the bottom.
• the numbers 1 to 7 given on the right in FIG. 2 have the following meanings:
• FIG. 3 shows a schematic representation of a horizontal cross-sectional view of the crystallizer according to FIG. 2.
• the reference numbers 2 to 7, which are recorded on the right-hand edge of FIG. 3, have the meanings given above.
• FIGS. 4 and 5 A possible embodiment of an inclined blade stirrer can be taken from FIGS. 4 and 5.
• FIG. 4 shows a crystallizer not used according to the invention, in which a inclined blade stirrer (axial stirrer) is not arranged close to the ground, but in the guide tube with a significant ground clearance.
• FIG. 4 shows a schematic cross-sectional view of the crystallizer
• FIG. 5 shows a horizontal cross section through the crystallizer at the level of the
• FIG. 5 shows the arrangement of the oblique blade stirrer in the crystallizer.
• the inclined blade stirrer per se can also be used in the process according to the invention.
• the reference numerals 1 to 7 used in Figures 4 and 5 at the right edge have the following meaning:
• FIG. 1 also shows photographic images of adipic acid crystals obtained by the process according to the invention (FIG. 1, top) or customary adipic acid crystals obtained by a process not according to the invention (FIG. 1, bottom).
• a cylindrical basic shape is selected according to the invention, which is closed with a bottom and preferably with a lid.
• bottom and lid forms are preferably dished bottoms, semi-elliptical soils and basket bottom floors use. But it can also be flat and conical bottoms for the lower end.
• the molds for floor and lid can also be manufactured according to the ASME standard (American Society of Mechanical Engineering).
• H / D of the container is given by the ratio between the total container height H (including the bottom and the lid) and the container diameter D. Values for H / D between 1 and 6 are preferably suitable for the stirred tank or container, preferably from 2 to 4.
• the degree of filling of the container is defined, which is defined dimensionless by the reference of the liquid level Hf to the total container height H.
• a common range for Hf / H is preferably between 0.5 and 0.9, preferably from 0.6 to 0.8.
• a plug-in tube also called guide tube
• guide tube is arranged concentrically or coaxially, which serves for the defined alignment of the circulation flow generated by the stirrer.
• An important design criterion with which the process parameters can be favorably influenced is the ratio di_ / D between the guide tube diameter di_ and the container diameter D. Smaller diameter ratios promote a dispersing function, larger diameter ratios are more likely to counteract a gentle treatment of the material to be stirred. Diameter ratios di_ / D are preferably between 0.2 and 0.8, preferably from 0.3 to 0.7.
• the distance between the lowest point of the container bottom and the lower edge of the Einsteckrohres Ahi_, i is chosen to be large enough to operate the arranged in this space stirrer with a safe distance to the ground or to the plug-in tube. At the same time, this influences the deflection of the fluid flow between the plug-in tube and the annular space and thus the pressure loss in the loop.
• the ratio between the ground clearance and the container diameter Ahi_, i / D is preferably
• the overlap of the upper edge of the Einsteckrohres with liquid Ahi_, 2 is advantageous to achieve a favorable flow deflection and to keep the resulting pressure loss low.
• a well-designed covering can also favor the intake of floating solids or foams.
• the covering Ahi_, 2 / D based on the container diameter is preferably selected between 0.05 and 0.5, preferably between 0.1 and 0.3. According to the design of the container height H, the level Hf, the Leitrohrêtabstandes Ahi_, i and the Leitrohr- coverage Ahi_, 2 results in the length of the Einsteckrohres li_.
• baffles in the draft tube and / or between the draft tube and side walls of the cylindrical tank.
• the baffles are important to break the tangential twist of the fluid flow caused by the impeller rotation and redirect it in an axial flow direction.
• the arrangement of the baffles on the pressure side of the stirrer should be carried out, which, similar to pumps, is the side to which the stirrer conveys the fluid.
• the pressure side of the guide tube interior is above the propeller stirrer. If an axial stirrer conveys the fluid down the guide tube, the pressure side is the area between the bottom of the stirrer and the bottom of the container.
• the reinforcement can then be arranged both in the diameter range of the guide tube and / or in the region of the annular space.
• the suction side is the region of the Leitrohrinnenraumes above the stirrer, as well as for the concentric arranged in the guide tube axial stirrer, which promotes downward in the guide tube. If the flow direction of an axial stirrer in the guide tube is directed upwards, the suction side is the area below the stirrer.
• the number of baffles per pressure and suction side is preferably from 3 to 12, preferably from 4 to 8.
• the width of the baffles bs / i_ in the guide tube is dimensionless relative to the guide tube diameter di_.
• bs / i_ / di_ between 0.05 and 0.5, preferably from 0.1 to 0.35.
• the length of the baffles in the guide tube IS, L can be max. correspond to the length of the plug-in tube IL and should preferably be at least half the diameter of the guide tube dL to ensure a sufficient reinforcement effect.
• the ground clearance of the Leitrohrstrombrecher AhS, L is, in particular for the execution with the ground-level blade stirrer, preferably minimally the distance of Leitrohrunterkante to the container bottom AhL, 1 and max. AhL, 1 + half the stirrer outer diameter dR / 2.
• the width of the baffles in the annulus bS, R can be max. the annulus width (D-dL) / 2 amount, which results from the clear distance between the guide tube and container wall.
• the distance of the annular space baffle to the inner wall of the container AS, R1 is 0.02 x D by default, but may also have values from 0 x D to 0.1 x D.
• the distance of the annular space-stream breaker to Leitrohrinnenwand AS, R2 be dimensioned by default with 0.02 x D, depending on the version but also from 0 x D to 0.1 x D.
• the length of the Ringraumstrombrecher IS, R is based on achieving a sufficient reinforcement effect and should be similar to the Leitrohrstrombrecher minimal half container diameter D.
• the maximum length results from the conclusion of the annular space with the Leitrohroberkante AhL, 3.
• the distance between the annular space flow breaker and the container bottom AhS, R can preferably be designed with dimensions between 0 ⁇ D and 1 ⁇ D, preferably from 0.02 ⁇ D to 0.5 ⁇ D. According to the invention, it has been found that the size and above all form (morphology) of the dicarboxylic acid crystals can be drastically improved by the speed or peripheral speed of the stirrer (RPM) and the power input, preferably also by the type of stirrer used.
• RPM peripheral speed of the stirrer
• the crystallizer content should be stirred intensively.
• the blade stirrer used in the crystallizer used according to the present invention has a rotating shaft and stirrer blades attached thereto, which may have any desired angle of attack with respect to the agitator shaft.
• Corresponding stirrer geometries are known per se and are explained in more detail, for example, in the publications listed below. Each stirrer becomes a radial stirrer when placed according to the invention near the ground.
• EP-A-1 208 905 describes a stirred vessel for producing a suspension of solids in a liquid having a uniform concentration, the agitator having turbine blades on a rotating shaft.
• Textbooks and publications on stirrer design are z. B. K. Kipke, "Power consumption and flow optimized in Leitrohrpropellern", Maschinenre, Würzburg 88 (1982) 52, Ekato Handbook of Stirring Technology "(1990); F. Liepe et al., "Rhaktechnike”, 1st edition 1998, self-published University of Applied Sciences Kothen
• the stirrer in Figure 1 of WO 2004/058377 may have any shape, provided that this allows the necessary circulation of liquid ..
• Suitable are "radial flow impeller", at the head and / or at the bottom of the guide tube have an axial “flow propeller” or a “marine propeller”, a “double propeller” or a “multi propeller”.
• the stirrer is preferably a "radial flow agitator”, preferably a “radial flow impeller” with at least one blade, a bottom plate and optionally a cover plate (page 10, line 27 to page 11, line 11).
• the number of stirrer blades, the size of the vanes, the vane angle of attack and the number of stirrer revolutions per minute (RPM) can be varied by means of these parameters of the mixture (page 1 1, lines 17 to 25).
• the "impeller” comprises the configurations shown in Figures 2, 3, 4 and 5.
• WO 2004/058377 can, for. B. have any shape, as long as the content of the crystallization apparatus is pumped through the apparatus at the necessary speeds.
• the height of the stirrer blades is about one-sixth of the agitator diameter.
• the width of the at least one wing varies with the wing angle (page 12, lines 7 to 17).
• the stirrer blades can have any angle that will cause the necessary circulation in the apparatus.
• the wing angle in WO 2004/058377 A1 is typically about 45 to 65 degrees, preferably about 55 degrees (page 12, lines 7 to 17).
• the linear velocity of the slurry is about 0.1 to about 1.8 meters per second, preferably about 0.9 meters per second (page 19, lines 12 to 14).
• each stirrer type used becomes a radial stirrer, since the suspension flow can only be conducted to the outside, since an axial direction of flow through the tank bottom is hindered.
• the terms according to the invention are to be understood “close to the ground” and “on the tank bottom”.
• any suitable blade stirrers with rotating coaxial shaft and stirrer blades can be used.
• the blade stirrer can be selected from radial stirrers, inclined blade stirrers, turbine stirrers, propeller stirrers, anchor stirrers, spiral stirrers and helical stirrers.
• the design and arrangement of the agitator is important in terms of achieving optimal crystal morphology.
• a radial stirrer which is placed on the tank bottom / container bottom or between the container bottom and lower edge of the insert tube and thus below the guide tube.
• a single-stage stirrer design is selected, however, the subdivision of the stirrer into several individual stages is also possible.
• Radial stirrers are characterized in that the stirrer blades are arranged perpendicular to the horizontal plane at an angle ⁇ of 90 °. Typical representatives are disc or blade stirrers.
• the number of stirrer blades nRb may preferably be from 2 to 16, preferably from 4 to 8.
• the stirrer height hR depends on the ground clearance of the lower Einsteckrohrunterkante AhL, 1 taking into account a sufficient ground clearance of the stirrer lower edge AhR, 1 itself and a sufficient distance between R industrialeroberkante and guide tube AhR, 2.
• the stirrer may preferably be designed with a height hR between 0.1 x D and 0.58 x D, preferably from 0.25 x D to 0.5 x D.
• the values for AhR, 1 and AhR, 2 may preferably be between 0.01 x D and 0.3 x D, preferably from 0.03 x D to 0.2 x D.
• the distances AhR, 1 and AhR, 2 can differ from each other. If necessary, the shape of the stirrer blades can be adapted to the bottom shape to achieve a uniform distance AhR, 1.
• the diameter of the radial agitator dR is largely determined by the diameter of the guide tube dL, but may also be designed smaller or larger than this.
• Interpretations for dR are usually 0.1 x D to 0.98 x D, preferably from 0.15 x D to 0.9 x D possible, preferably from 0.3 x D to 0.7 x D.
• a certain volume-specific power input is to be applied by the agitator, which ensures complete suspension of the solid particles and a stable circulation flow between the guide tube and annulus.
• the volume-specific power input is to be understood below as the ratio P / V between the stirrer power P and the filling volume V of the container.
• Power inputs are from 0.01 W / l to 5 W / l, preferably from 0.05 W / l to 2 W / l, in particular from 0.1 to 0.5 W / l or kW / m 3 .
• the circumferential speed with respect to the outside diameter of the stirrer results.
• the stirring speed necessary for the formation of the compact agglomerates according to the invention is 0.5 to 6 meters per second, preferably 1 to 5 meters per second, more preferably 1.2 to 4 meters per second, particularly preferably 1.5 to 3 , 5 meters per second.
• the inventive method has the advantage that it solves the task in a conventional apparatus solely by using an unconventional stirrer assembly and coordinated peripheral speed and tuned power input, but without the aid of additives.
• the compact crystals formed according to the invention remain free-flowing because they do not cake because of their shape as the normally resulting thin dicarboxylic acid leaflets to larger units.
• an inclined blade stirrer mounted centrally in the guide tube and having an angle of attack of more than 20 degrees with the same energy input as in the case of the blade stirrer, substantially smaller dicarboxylic acid crystals are formed in the form of thin platelets. These platelets caked within weeks to non-free-flowing lumps.
• dicarboxylic acid suspension Small amounts of dicarboxylic acid suspension are withdrawn continuously via a draw-off tube, so that the level of the crystallizer remains constant.
• the dicarboxylic acid crystals are z. B. separated on a centrifuge and optionally dried.
• the variant of the suspension withdrawal is preferably selected on the container bottom, other deduction variants such as in Leitrohrinnern or in the region of the annulus are in principle also possible.
• a radial or axial stirrer arrangement is selected between the tank bottom and the bottom edge of the plug-in pipe, or an axial stirrer conveying downwards in the draft pipe at the bottom of the tank.
• the metered dicarboxylic acid solution is preferably metered into the annulus to avoid short circuit currents between Zudosierstelle and drain. Due to the upward flow in the annular space and the subsequent downward flow in the guide tube, the metered volume elements are forced to pass through the circulation area of the container at least once before they can leave the crystallizer.
• the number of mixing points in the annulus can be from 1 to 100, preferably it corresponds to the number of baffles in the annulus.
• the Zudosierstellen can be distributed both in the vertical direction over the annulus height and distributed in the horizontal direction over the circumference of the annulus.
• the position of the Zudosierstellen should preferably be positioned in a horizontal plane in the direction of rotation of the stirrer in front of the baffles in an angle ß between 1 and 45 °, preferably from 5 to 20 °.
• the invention is further illustrated by the following examples. Examples
• a cylindrical glass laboratory crystallizer (DN300) with an internal height of about 350 mm and an internal diameter of 300 mm with a diameter of 206 mm (DN200) can be equipped with different stirrers.
• the crystallizer is charged with a 35% suspension of adipic acid in water and heated to 60.degree. Partial dissolution of the crystals results in a solids content of about 23%. These initially present crystals of 100-200 ⁇ medium size serve as seed crystals.
• a 35% strength, crystal-free solution of adipic acid at 82 ° C. is conveyed into this crystallizer from a temperature-controlled storage container.
• the crystallizer In order to keep the temperature in the crystallizer at a constant 60 ° C at the delivery rate of 1 1, 7 kg / h, it is cooled over its walls. By periodically subtracting small amounts of suspension via a bottom outlet valve, the level in the crystallizer is kept constant. After 10 hours of operation of the experiment, the originally contained suspension has been replaced to less than 1% of the starting amount; in terms of particle size and shape, a new steady state equilibrium has been established. The suspended crystals are separated by centrifuging for three minutes on a Siebbecherzentrifuge at 600g, freed by rapid spreading on an absorbent filter paper from adhering mother liquor and finally dried overnight at 60 ° C in a vacuum oven.
• FIG. 1 Figure 2 and Figure 3 show the crystallizer used in the process schematically.
• the crystals obtained in the crystallizer shown in FIGS. 2 and 3 by the process according to the invention have a mean size of 1 .100 ⁇ m determined by laser diffraction and show the shape of compact agglomerates. When stored in a closed screw-cap glass (height 0.2 m), the crystals remain free-flowing for weeks. They are shown in Figure 1 above. Comparative Example 1
• a five-blade inclined blade turbine (angle of attack 38 °) of 185 mm diameter is used at a height of about 80 mm above the tank bottom and inside the guide tube.
• a speed of 12RPM as in Example 1 crystallization can not be performed because the pump power of the stirrer and the power input are insufficient to produce a stable flow and to suspend the seed crystals.
• a speed of 300RPM is set, corresponding to a peripheral speed of about 2.9 meters per second.
• Figure 4 and Figure 5 show a schematic representation of the crystallizer used in Comparative Example 1 and Schrägblattrlochers. The crystals obtained in the experiment were again measured and examined.
• the crystals have a mean size of 450 ⁇ and have the shape of thin platelets.
• the bed is clearly cohesive and moderately baked after only 24 hours, strongly caked after a few weeks in the form of large, hard lumps. They are shown in Figure 1 below.
• the crystallizer described in Example 1 of the continuous crystallization of adipic acid and depicted in FIGS. 2 and 3 is now filled with 9.6 kg of succinic acid and 20.4 kg of water. Its 32% solution has a saturation temperature of 68.5 ° C. After dissolution of all crystals at 75 ° C, the crystallizer is cooled to 68.3 ° C and seeded at this temperature with 96g succinic acid crystals, cooled another 0.5K and stirred at this temperature for half an hour.
• the still thin suspension is then cooled in the course of 3.5 h from 68 ° C to 30 ° C, the cooling initially begins slowly with 2K / h, then slowly increased and finally reaches the final temperature with a maximum cooling rate of 16K / h ,
• the separation and work-up of the suspension is identical to the previously described procedure for adipic acid.
• a five-blade inclined blade turbine (angle of attack 38 °) of 185 mm diameter is used at a height of about 80 mm above the tank bottom and inside the guide tube, as shown in FIGS. 4 and 5. Again, it is not possible at all to achieve stable flow and suspension of all crystals at the low RPM of 90 RPM.
• a speed of 245RPM is set. At the end of the experiment, the crystals have a laser diffraction average size of 700 ⁇ and are in the shape of highly rounded platelets. Under the same storage conditions, the bed appears clearly cohesive after only 24 hours, moderately baked after a few weeks in the form of large lumps.

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• 2014
  • 2014-03-14 EP EP14710549.8A patent/EP2970082A1/de not_active Withdrawn
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