Classifications

• • 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
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
  • B01J19/122—Incoherent waves
  • B01J19/126—Microwaves
• • 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
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/08—Preparation of carboxylic acid esters by reacting carboxylic acids or symmetrical anhydrides with the hydroxy or O-metal group of organic compounds
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C69/00—Esters of carboxylic acids; Esters of carbonic or haloformic acids
  • C07C69/76—Esters of carboxylic acids having a carboxyl group bound to a carbon atom of a six-membered aromatic ring
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C69/00—Esters of carboxylic acids; Esters of carbonic or haloformic acids
  • C07C69/76—Esters of carboxylic acids having a carboxyl group bound to a carbon atom of a six-membered aromatic ring
  • C07C69/80—Phthalic acid esters
  • C07C69/82—Terephthalic acid esters
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D213/00—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members
  • C07D213/02—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members
  • C07D213/04—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom
  • C07D213/60—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
  • C07D213/78—Carbon atoms having three bonds to hetero atoms, with at the most one bond to halogen, e.g. ester or nitrile radicals
  • C07D213/79—Acids; Esters
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/64—Heating using microwaves
  • H05B6/70—Feed lines
  • H05B6/701—Feed lines using microwave applicators
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/64—Heating using microwaves
  • H05B6/80—Apparatus for specific applications
  • H05B6/806—Apparatus for specific applications for laboratory use
• • 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
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/12—Processes employing electromagnetic waves
  • B01J2219/1203—Incoherent waves
  • B01J2219/1206—Microwaves
  • B01J2219/1209—Features relating to the reactor or vessel
  • B01J2219/1212—Arrangements of the reactor or the reactors
  • B01J2219/1215—Single reactor
• • 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
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/12—Processes employing electromagnetic waves
  • B01J2219/1203—Incoherent waves
  • B01J2219/1206—Microwaves
  • B01J2219/1209—Features relating to the reactor or vessel
  • B01J2219/1221—Features relating to the reactor or vessel the reactor per se
  • B01J2219/1224—Form of the reactor
  • B01J2219/1227—Reactors comprising tubes with open ends
• • 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
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/12—Processes employing electromagnetic waves
  • B01J2219/1203—Incoherent waves
  • B01J2219/1206—Microwaves
  • B01J2219/1248—Features relating to the microwave cavity
  • B01J2219/1272—Materials of construction
• • 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
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/12—Processes employing electromagnetic waves
  • B01J2219/1203—Incoherent waves
  • B01J2219/1206—Microwaves
  • B01J2219/1275—Controlling the microwave irradiation variables
  • B01J2219/1281—Frequency
• • 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
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/12—Processes employing electromagnetic waves
  • B01J2219/1203—Incoherent waves
  • B01J2219/1206—Microwaves
  • B01J2219/1275—Controlling the microwave irradiation variables
  • B01J2219/1284—Intensity

Definitions

• the present invention relates to a continuous process for the production of esters of aromatic carboxylic acids under microwave irradiation on an industrial scale.
• Esters are an industrially very important group of substances which is widely used and is used, for example, as a plasticizer, lubricant and as a component of cosmetics and pharmaceuticals.
• a proven and widely used method for preparing esters is the condensation of carboxylic acids with alcohols in the presence of catalysts. The reaction mixture is usually heated for several hours and discharged the forming water.
• WO 2007/126166 discloses a conventional thermal esterification of fatty acids with alcohols at temperatures of 200 to 350 0 C and pressures of up to 10 bar. In the reaction of several hours, in the course of which the resulting water of reaction is continuously discharged with excess alcohol, however, only an incomplete reaction to
• Microwave energy are esterified. It is in a special
• Embodiment that is located in a template reaction material continuously pumped and thereby passed through a stirred in a microwave applicator stirred container. Only after repeated passage through the microwave applicator high degrees of esterification are achieved.
• Plasma formation set narrow limits. Furthermore, prepares the leading in multi-mode microwave ovens to local overheating of the reaction material, caused by more or less uncontrolled reflections of the microwaves irradiated in the microwave oven on the walls and the reaction mixture caused inhomogeneity of the microwave field problems in scale-up. In addition, the microwave absorption coefficient of the reaction mixture, which often changes during the reaction, presents difficulties in terms of a safe and reproducible reaction.
• WO 90/03840 discloses a continuous process for carrying out
• Microwave power can cause unwanted plasma discharges or so-called thermal runaway effects. Furthermore, the spatially varying spatial inhomogeneities of the microwave field in the applicator space, referred to as hot spots, make a safe and reproducible
• single-mode or single-mode microwave applicators are known in which a single wave mode is used, which propagates in only one spatial direction and is focused by precisely dimensioned waveguides on the reaction vessel. Although these devices allow higher local
• Reaction tube is not possible due to the geometry of the applicator and due to the low penetration depth of microwaves and not suitable for up-scaling.
• Pipus et al. disclose homogeneously as well as heterogeneously catalyzed esterifications of benzoic acid with ethanol in a continuous, microwave radiation heated tubular reactor. At a pressure of 7 atm and a temperature of 140 0 C, a turnover of 30% is achieved with a residence time in the reactor of 127 seconds.
• Wilson et al. (Org. Process Res. Dev. 2004, 8, 535-538) disclose a continuous microwave reactor in which a mixture of
• Carboxylic acids sought in the aromatic carboxylic acid and alcohol can also be reacted on an industrial scale under microwave irradiation to the ester. It should as high as possible, that is up to quantitative
• the method should continue to allow the most energy-saving production of the esters, that is, the microwave power used should be absorbed as quantitatively as possible from the reaction mixture and the process thus a high energy
• esters should also have the lowest possible metal content and a low intrinsic color.
• the process should ensure a safe and reproducible reaction.
• esters are more aromatic Carboxylic acids by direct reaction of aromatic carboxylic acids with alcohols in a continuous process by only brief heating by irradiation with microwaves in a reaction tube, the longitudinal axis is in the propagation direction of the microwaves of a single-mode microwave applicator can produce in technically relevant quantities.
• the inventive method also has a high security in the implementation and offers a high reproducibility of the set
• esters prepared by the process according to the invention show a comparison with conventional
• the invention relates to a continuous process for the preparation of carboxylic acid esters in which at least one aromatic carboxylic acid of the formula (I)
• R 2 is an optionally substituted hydrocarbon radical having 1 to 100 carbon atoms and
• n 1 to 10
• Microwave irradiation in a reaction tube whose longitudinal axis is in the Propagation direction of the microwaves of a single-mode microwave applicator is converted to the ester.
• Ar is preferably an aryl radical bearing at least one carboxyl group bonded to an aromatic system.
• aromatic systems is meant cyclic (4n + 2) ⁇ electron conjugated systems in which n is a natural integer and preferably 1, 2, 3, 4 or 5.
• aromatic system may be mono- or polycyclic, such as di- or tricyclic.
• the aromatic system has 6 to 25 atoms, more preferably 6 to 18 atoms.
• the aromatic system is preferably made
• Carbon atoms formed contains, in addition to carbon atoms, one or more heteroatoms, such as
• aromatic systems For example, nitrogen, oxygen and / or sulfur.
• aromatic systems are benzene, naphthalene, indole, phenanthrene, pyridine, furan, pyrrole, thiophene and thiazole.
• the aromatic system may carry, in addition to the carboxyl group, one or more, for example, one, two, three or more identical or different further substituents.
• Suitable further substituents are, for example, alkyl, alkenyl and halogenated alkyl radicals, hydroxy, hydroxyalkyl, alkoxy, poly (alkoxy), halogen, carboxyl, amide, cyano, nitrile and / or nitro groups.
• substituents may be attached at any position of the aromatic system.
• the aryl radical carries at most as many substituents as it has valencies.
• the aryl radical Ar of the formula (I) carries further carboxyl groups.
• the process according to the invention is likewise for the reaction of aromatic carboxylic acids with, for example, two or more
• Suitable carboxyl groups can be controlled, for example, via the stoichiometry between acid (I) and alcohol (II) in the reaction mixture.
• the process according to the invention is particularly suitable for the esterification of alkylarylcarboxylic acids, for example alkylphenylcarboxylic acids.
• alkylarylcarboxylic acids for example alkylphenylcarboxylic acids.
• aromatic carboxylic acids in which the carboxyl group bearing aryl radical Ar additionally bears at least one alkyl or alkenyl radical.
• the process is particularly advantageous in the esterification of
• Alkylbenzoic acids which carry at least one alkyl radical having 1 to 50 carbon atoms, preferably having 2 to 20 carbon atoms and in particular 1 to 12 carbon atoms such as 1 to 4 carbon atoms.
• esterification in particular with at least equimolar amounts of alcohol of the formula (II), one finds selectively
• Suitable aromatic carboxylic acids are, for example, benzoic acid,
• R 2 is an aliphatic radical. This has preferably 1 to 24, particularly preferably 2 to 18 and especially 3 to 6 C-atoms.
• the aliphatic radical may be linear, branched or cyclic. It may also be saturated or unsaturated, preferably it is saturated.
• Hydrocarbon radical may carry substituents such as, for example, halogen atoms, halogenated alkyl radicals, hydroxyl, C 1 -C 5 -alkoxyalkyl, cyano, nitrile, nitro and / or C 5 -C 20 -aryl groups, for example phenyl radicals.
• C 5 -C 2 o-aryl radicals may in turn optionally substituted with halogen atoms, halogenated alkyl radicals, hydroxyl, -C 2 o alkyl, C 2 -C 2 o-alkenyl, C- ⁇ -C 5 alkoxy such as methoxy , Ester, amide, cyano, nitrile, and / or nitro groups.
• Particularly preferred aliphatic radicals are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl, n-hexyl, cyclohexyl, n-octyl, n-decyl, n-dodecyl, tridecyl, Isotridecyl, tetradecyl, hexadecyl,
• R 2 is an optionally substituted or an optionally substituted one
• heteroaromatic group with 5 to 12 ring members.
• Preferred heteroatoms are oxygen, nitrogen and sulfur.
• the aryl or heteroaromatic group may thus be mono- or polycyclic.
• suitable substituents are halogen atoms, halogenated alkyl radicals and also alkyl, alkenyl, hydroxy, hydroxyalkyl, alkoxy, ester, amide, nitrile and nitro groups.
• the radical R 2 carries one or more, for example two, three, four, five, six or more further hydroxyl groups, but not more hydroxyl groups than the radical R 2 C-atoms or as the
• Aryl group has valencies.
• the hydroxyl groups may be attached to adjacent C atoms or to further carbon atoms of the
• the inventive method is also suitable for the esterification of polyols such as ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, neopentyl glycol, glycerol, sorbitol, pentaerythritol, fructose and glucose.
• the esterification can be carried out to complete esters or partial esters.
• the degree of esterification can be controlled, for example, via the stoichiometry between carboxylic acid and alcohol in the reaction mixture.
• R 4 is an alkylene group having 2 to 18 C atoms, preferably having 2 to 12 and in particular 2 to 4 C atoms, such as, for example, ethylene,
• R 5 is hydrogen or a hydrocarbon radical having 1 to 24 C atoms or a group of the formula -R 4 -NR 10 R 11 ,
• n is a number between 1 and 500, preferably between 2 and 200 and in particular between 3 and 50 such as between 4 and 20 and
• R 10 , R 11 independently represent an aliphatic radical with 1 to
• Poly (oxyalkylene) group having 1 to 50 poly (oxyalkylene) units, wherein the polyoxyalkylene units of alkylene oxide units with 2 to
• Suitable alcohols are methanol, ethanol, n-propanol,
• fatty alcohol mixtures obtained from natural raw materials such as, for example, coconut fatty alcohol, palm kernel fatty alcohol and tallow fatty alcohol.
• the method is particularly suitable for the production of
• aromatic carboxylic acid (I) and alcohol (II) can be reacted with one another in any ratio.
• the reaction between carboxylic acid and alcohol preferably takes place with molar ratios of from 20: 1 to 1:20, preferably from 10: 1 to 1:10 and especially from 3: 1 to 1: 3, for example from 1.5: 1 to 1: 1, 5, each based on the
• Embodiment carboxylic acid and alcohol are used equimolar. If the aromatic carboxylic acid (I) carries one or more hydroxyl groups takes place the reaction preferably with at least equimolar amounts of alcohol (II), more preferably in the ratio of aromatic carboxylic acid (I) to alcohol (II) of 1: 1, 01 to 1: 50, especially in the ratio 1: 1, 5 to 1: 20 such as 1: 2 to 1:10.
• Carboxyl groups virtually quantitatively converted to the ester. This process is particularly advantageous when the alcohol used is highly volatile. Volatile here means that the alcohol has a boiling point at atmospheric pressure of preferably below 200 0 C and more preferably below 160 0 C such as below 100 0 C and thus can be separated by distillation from the ester.
• esterifications are carried out in the present process in the presence of homogeneous catalysts, heterogeneous catalysts or mixtures thereof. Both acidic and alkaline catalysts are suitable.
• Preferred esterification catalysts according to the invention are acidic inorganic, organometallic or organic catalysts and mixtures of several of these catalysts.
• acidic inorganic catalysts for the purposes of the present invention are sulfuric acid, phosphoric acid, phosphonic acid, hypophosphorous acid, aluminum sulfate hydrate, alum, acidic silica gel and acid
• Aluminum compounds of the general formula AI (OR 15 ) 3 and titanates of the general formula Ti (OR 15 J 4 can be used as acidic inorganic catalysts, where the radicals R 15 can each be identical or different and are selected independently of one another from C 1 -C 10 -alkyl radicals, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1, 2-dimethylpropyl, iso-amyl, n-hexyl, sec-hexyl, n-heptyl, n-octyl, 2-Ethylhexy, n-nonyl or n-decyl, C3-Ci2 cycloalkyl, for example, cyclopropyl, cyclobuty
• Preferred acidic organometallic catalysts are, for example, selected from dialkyltin oxides (R 15 J 2 SnO, where R 15 is defined standing as above.
• dialkyltin oxides R 15 J 2 SnO, where R 15 is defined standing as above.
• a particularly preferred representatives of acidic organometallic catalysts is di-n-butyltin oxide, which as a so-called Oxo-tin or as Fascat ® Brands is commercially available.
• Preferred acidic organic catalysts are acidic organic compounds with, for example, phosphate groups, sulfonic acid groups, sulfate groups or phosphonic acid groups.
• Particularly preferred sulfonic acids contain at least one sulfonic acid group and at least one saturated or unsaturated, linear, branched and / or cyclic hydrocarbon radical having 1 to 40 carbon atoms and preferably having 3 to 24 carbon atoms.
• Particularly preferred aromatic sulfonic acids and especially alkylaromatic monosulfonic acids with one or more C- ⁇ -C 28 alkyl radicals and especially those with C 3 -C 22 -alkyl are.
• Suitable examples are methanesulfonic acid, butanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, xylenesulfonic acid, 2-mesitylenesulfonic acid, 4-ethylbenzenesulfonic acid, isopropylbenzenesulfonic acid, 4-butylbenzenesulfonic acid, 4-octylbenzenesulfonic acid; Dodecylbenzenesulfonic acid, didodecylbenzenesulfonic acid, naphthalenesulfonic acid. Also acid
• Ion exchangers can be used as acidic organic catalysts, for example poly (styrene) resins bearing sulfonic acid groups, which are crosslinked with about 2 mol% of divinylbenzene.
• Boron acid, phosphoric acid, polyphosphoric acid and polystyrenesulfonic acids are particularly preferred for carrying out the process according to the invention.
• the microwave irradiation is carried out in the presence of acidic solid catalysts.
• Heterogeneous catalysts can be suspended in the reaction mixture and pumped together with the reaction mixture through the reaction tube.
• the reaction mixture can be suspended in the reaction mixture and pumped together with the reaction mixture through the reaction tube.
• Reaction tube fixed fixed bed catalyst and thereby exposed to microwave radiation are examples of suitable solid catalysts.
• suitable solid catalysts are zeolites, silica gel, montmorillonite and (partially) crosslinked polystyrenesulphonic acid, which may optionally be impregnated with catalytically active metal salts.
• Solid phase catalysts can be used, for example, from Rohm & Haas under the brand name Amberlyst ® available.
• the inventive production of the esters is carried out by mixing of carboxylic acid, alcohol and catalyst and subsequent irradiation of the
• the irradiation of the reaction mixture with microwaves preferably takes place in a largely microwave-transparent reaction tube, which is located within a waveguide connected to a microwave generator.
• the reaction tube is aligned axially with the central axis of symmetry of the waveguide.
• the acting as a microwave applicator waveguide is preferred as
• Cavity resonator formed. Further preferred are those in the waveguide unabsorbed microwaves reflected at its end. Preferably, the length of the cavity resonator is dimensioned so that it forms a standing wave in it.
• the microwave applicator as a reflection-type resonator, a local increase in the electric field strength is achieved with the same power supplied by the generator and an increased energy utilization.
• the cavity resonator is preferably operated in mode n E i 0, where n is an integer and represents the number of field maxima of the microwave along the central axis of symmetry of the resonator.
• the electric field is in the direction of the central axis of symmetry of the
• Cavity resonator directed. It has a maximum in the area of the central axis of symmetry and decreases to the lateral surface to the value zero.
• Field configuration is rotationally symmetrical about the central axis of symmetry.
• n is an integer
• N is preferably an integer from 1 to 200, particularly preferably from 2 to 100, in particular from 4 to 50, especially from 3 to 20, for example three, four, five, six, seven, eight, nine or ten.
• the E 0 in mode of the cavity resonator is also referred to as TMoin mode in English, see, for example, K. Lange, KH Löcherer,
• the irradiation of the microwave energy into the waveguide acting as a microwave applicator can take place via suitably dimensioned holes or slots.
• the irradiation of the reaction mixture with microwaves takes place in one
• Reaction tube located in a waveguide with coaxial transition of Microwave is located.
• microwave devices are from a cavity resonator, a
• Cavity resonator and constructed with one opening at two opposite end walls for passing the reaction tube through the resonator.
• the coupling of the microwaves in the cavity resonator is preferably carried out via a coupling pin, which projects into the cavity resonator.
• the coupling pin is preferably shaped as a preferably metallic inner conductor tube functioning as a coupling antenna.
• this coupling pin protrudes through one of the frontal openings into the cavity resonator.
• the reaction tube connects to the inner conductor tube of the coaxial transition and in particular it is guided through its cavity into the cavity resonator.
• the reaction tube is aligned axially with a central one
• the cavity resonator preferably each has a central opening on two opposite end walls for passing the reaction tube.
• Coupling antenna acting inner conductor tube can be done for example by means of a coaxial connecting cable.
• the microwave field is supplied to the resonator via a waveguide, wherein the protruding from the cavity resonator end of the coupling pin is guided into an opening which is located in the wall of the waveguide in the waveguide and the waveguide takes microwave energy and in the Resonator couples.
• Reaction tube which is axially symmetric in an eoin circular waveguide with coaxial transition of the microwaves.
• the reaction tube is guided through the cavity of an inner conductor tube acting as a coupling antenna into the cavity resonator.
• Microwave transparent reaction tube which is passed through an eoin cavity resonator with axial feeding of the microwaves, wherein the length of the
• Microwave transparent reaction tube which is passed through an E 0 in cavity resonator with axial feeding of the microwaves, wherein the length of the
• the irradiation of the reaction mixture with microwaves in a microwave-transparent reaction tube which is axially symmetrical in a circular cylindrical eoin cavity resonator with coaxial transition of the microwaves, wherein the length of the
• Microwave generators such as the magnetron, the klystron and the gyrotron are known in the art.
• Reaction tubes are preferably made of largely microwave-transparent, high-melting material. Non-metallic reaction tubes are particularly preferably used. Substantially microwave-transparent materials are understood here which absorb as little microwave energy as possible and convert it into heat. As a measure of the ability of a substance to absorb microwave energy and convert it into heat, the dielectric is often used
• Loss factor tan ⁇ ⁇ ' V ⁇ ' used.
• the dielectric loss factor tan ⁇ is defined as the ratio of dielectric loss ⁇ " and
• Dielectric constant ⁇ ' Dielectric constant ⁇ ' .
• tan ⁇ values of various materials are given, for example, in D. Bogdal, Microwave Assisted Organic Synthesis, Elsevier 2005.
• materials having tan ⁇ values measured at 2.45 GHz and 25 ° C. of less than 0.01, in particular less than 0.005 and especially less than 0.001 are preferred.
• Preferred microwave-transparent and temperature-stable materials are primarily materials based on minerals such as quartz, alumina, sapphire, zirconium oxide, silicon nitride and the like into consideration.
• temperature-stable plastics such as in particular fluoropolymers such as Teflon, and engineering plastics such as polypropylene, or polyaryletherketones such
• PEEK glass fiber reinforced polyetheretherketone
• reaction tubes have an inner diameter of one millimeter to about 50 cm, in particular between 2 mm and 35 cm and especially between 5 mm and 15 cm as
• reaction tubes are understood here to be vessels whose ratio of length to diameter is greater than 5, preferably between 10 and 100,000, particularly preferably between 20 and 10,000, for example between 30 and 1,000.
• the length of the reaction tube is understood here as the distance of the reaction tube on which the microwave irradiation takes place.
• baffles and / or other mixing elements can be installed.
• Eo-i cavity resonators preferably have a diameter which corresponds to at least half the wavelength of the microwave radiation used.
• the diameter of the cavity resonator is the 1, 0- to
• the E 0 i cavity resonator has a round cross-section, which is also referred to as Eoi round waveguide. Particularly preferably it has a cylindrical shape and especially a circular cylindrical shape.
• the reaction tube is usually provided at the inlet with a metering pump and a pressure gauge and at the outlet with a pressure holding device and a heat exchanger. This allows reactions in a very wide range of pressure and temperature.
• Catalyst can be carried out continuously, batchwise or else in semi-batch processes.
• the preparation of the reaction mixture can be carried out in an upstream (semi) -batch process such as
• the educts carboxylic acid and alcohol and the catalyst are mixed shortly before they enter the reaction tube.
• the catalyst can be added as such or as a mixture with one of the reactants to the reaction mixture. So it has proven particularly useful to make the mixture of carboxylic acid, alcohol and catalyst in a mixing section, from which the reaction mixture in the
• Reaction tube is promoted. Further preferred are the starting materials and
• Catalyst supplied to the process according to the invention in liquid form For this purpose, higher-melting and / or higher-viscosity starting materials, for example in the molten state and / or with solvent, for example, can be used as solution, dispersion or emulsion.
• the catalyst is added to one of the educts or else to the educt mixture before it enters the reaction tube. Heterogeneous systems can also be reacted by the process according to the invention, with corresponding technical devices for conveying the reaction mixture being required.
• the reaction mixture may be fed into the reaction tube either at the end guided through the inner conductor tube, as well as at the opposite end.
• the reaction mixture may thus be parallel or antiparallel to Propagation direction of the microwaves are guided by the microwave applicator.
• length of the irradiation zone (this is understood to mean the distance of the reaction tube in which the reaction mixture
• the reaction conditions are preferably adjusted so that the maximum
• Reaction temperature is reached as quickly as possible and the residence time at maximum temperature remains so short that so few side or subsequent reactions occur as possible.
• the reaction mixture can be passed through the reaction tube several times to complete the reaction, optionally after intermediate cooling. At slower reactions, it has often proven that
• Reaction product immediately after leaving the reaction tube z. B. is cooled by jacket cooling or relaxation. It has also been proven to deactivate the catalyst immediately after leaving the reaction tube. This can be achieved, for example, by neutralization or by heterogeneously catalyzed
• the temperature increase caused by the microwave irradiation is, for example, regulated by controlling the microwave intensity
• Flow rate and / or by cooling the reaction tube for example, by a nitrogen stream, limited to a maximum of 500 0 C.
• the microwave irradiation over a Period of less than 30 minutes, preferably between 0.01 seconds and 15 minutes, more preferably between 0.1 seconds and 10 minutes and in particular between one second and 5 minutes, for example between 5 seconds and 2 minutes.
• the intensity (power) of the microwave radiation is adjusted so that the reaction material when leaving the cavity resonator has the desired maximum temperature.
• the reaction product is cooled as soon as possible after completion of the microwave irradiation to temperatures below 120 0 C, preferably below 100 0 C and especially below 60 0 C.
• the reaction is preferably carried out at pressures between 1 bar (atmospheric pressure) and 500 bar, particularly preferably between 1, 5 and 200 bar, in particular between 3 bar and 150 bar and especially between 10 bar and 100 bar, for example between 15 and 50 bar.
• Working has proven particularly useful under elevated pressure, wherein above the boiling point (at normal pressure) the reactants, products, the optionally present solvent and / or the reaction water formed during the reaction is worked.
• the pressure is set so high that the
• Reaction mixture during the microwave irradiation remains in the liquid state and does not boil.
• an inert protective gas such as nitrogen, argon or helium.
• Solvents which are preferred for the process according to the invention have a dielectric loss ⁇ "of less than 10 and preferably less than 1, for example less than 0.5, measured at room temperature and 2450 MHz
• ⁇ dielectric loss
• solvents having ⁇ "values below 10 such as N-methylpyrrolidone, N, N-dimethylformamide or acetone, and in particular solvents having ⁇ " values below 1.
• solvents having ⁇ "values below 1 aromatic and / or aliphatic hydrocarbons such as toluene, xylene, ethylbenzene, tetralin, hexane, cyclohexane, decane, pentadecane, decalin, and commercial hydrocarbon mixtures such as petroleum fractions, kerosene, solvent naphtha, ® Shellsol AB, Solvesso ® 150, Solvesso ® 200, Exxsol ® , Isopar ® and Shellsol ® -. types solvent mixtures, the ⁇ "values preferably below 10 and especially below 1, are of the present invention for carrying out
• the process according to the invention is carried out in solvents having higher ⁇ "values of, for example, 5 and higher, in particular with ⁇ " values of 10 and higher.
• Embodiment has particularly in the implementation of Reaction mixtures proven that even, ie without the presence of solvents and / or diluents show only a very low microwave absorption.
• this embodiment has proved particularly useful in reaction mixtures which have a dielectric loss ⁇ "of less than 10 and preferably less than 1.
• the accelerated heating of the reaction mixture which is often observed as a result of the solvent addition, requires measures to maintain the maximum temperature.
• reaction mixture is preferably between 1 and 95 wt .-%, more preferably between 2 and 90 wt .-%, especially between 5 and 85 wt .-% and
• the reaction is carried out solvent-free.
• the reaction mixture in the insoluble, strongly microwave absorbing substances are added.
• Heat collector is graphite, for example.
• microwaves are electromagnetic radiation having a wavelength between about 1 cm and 1m and frequencies between about 300 MHz and
• microwave radiation with the frequencies released for industrial, scientific, medical, domestic or similar applications is preferably used, for example with frequencies of 915 MHz, 2.45 GHz, 5.8 GHz or 24.12 GHz.
• Cavity resonator to be irradiated microwave power is particularly dependent on the desired reaction temperature, but also of the
• Geometry of the reaction tube and thus the reaction volume and the Flow rate of the reaction mixture through the heating zone It is usually between 200 W and several 100 kW and in particular between 500 W and 100 kW such as between 1 kW and 70 kW. It can be generated by one or more microwave generators.
• reaction is carried out in a pressure-resistant, chemically inert tube, wherein the water of reaction forming and optionally starting materials and, if present, solvent to a
• the excess pressure can be used by relaxation for volatilization and separation of water of reaction, excess starting materials and, if appropriate, solvents and / or for cooling the reaction product.
• the water of reaction formed after cooling and / or venting by conventional methods such as phase separation, distillation, stripping, flashing and / or absorption is separated.
• Reactor design according to the invention, the implementation of reactions even at very high pressures and / or temperatures.
• Microwave method of the prior art provides.
• the inventive method also allows a controlled, safe and reproducible reaction. Since the reaction mixture is moved in the reaction tube parallel to the propagation direction of the microwaves, become known
• reaction water formed in the esterification can be achieved.
• reaction mixtures in a flow tube of the same dimensions under thermal jacket heating to achieve suitable reaction temperatures extremely high wall temperatures which led to the formation of undefined polymers and colored species, but at the same time interval significantly less esterification cause.
• the products produced by the process according to the invention have very low metal contents without the need for further processing of the crude products. So are the metal contents of the after
• products according to the invention based on iron as the main element usually below 25 ppm, preferably below 15 ppm, especially below 10 ppm, such as between 0.01 and 5 ppm iron.
• the inventive method thus allows a very fast,
• cylindrical cavity resonator (60 x 10 cm) was located. On one of the end faces of the cavity resonator, the ceramic tube passed through the cavity of an inner conductor tube acting as a coupling antenna. The microwave field generated by a magnetron with a frequency of 2.45 GHz was coupled by means of the coupling antenna in the cavity resonator
• the microwave power was adjusted over the duration of the experiment in such a way that the desired temperature of the reaction mixture was kept constant at the end of the irradiation zone.
• the in the test descriptions Therefore, the microwave powers mentioned represent the time average of the irradiated microwave power.
• Reaction mixture was directly after leaving the reaction zone (about 15 cm distance in an insulated stainless steel capillary, 0 1 cm) using PtIOO
• Temperature sensor made. Microwave energy not directly absorbed by the reaction mixture was reflected at the end face of the cavity resonator opposite the coupling antenna; the microwave energy not absorbed by the reaction mixture also in the return and mirrored back in the direction of the magnetron was conducted by means of a prism system (circulator) into a vessel containing water. From the difference between
• Reaction material registered microwave energy calculated.
• reaction mixture was placed in the reaction tube under such a working pressure, which was sufficient to all educts and products or
• Carboxylic acid and alcohol prepared reaction mixtures were pumped at a constant flow rate through the reaction tube and set the residence time in the irradiation zone by modifying the flow rate.
• the resulting mixture was pumped continuously at 5 l / h through the reaction tube at a working pressure of 35 bar and subjected to a microwave power of 2.0 kW, of which 96% was absorbed by the reaction mixture.
• the Residence time of the reaction mixture in the irradiation zone was about 34 seconds.
• the reaction mixture had a temperature of 260 ° C.
• the reaction mixture was cooled to room temperature immediately after leaving the reactor with an intensive heat exchanger.
• the mixture thus obtained was continuously pumped through the reaction tube at 3 l / h at a working pressure of 25 bar and subjected to a microwave power of 3.2 kW, of which 92% was absorbed by the reaction mixture.
• the residence time of the reaction mixture in the irradiation zone was
• reaction mixture had a temperature of 272 0 C.
• the reaction mixture was cooled immediately after leaving the reactor with an intensive heat exchanger to room temperature. It was a turnover of 82% d. Th. Reached.
• the reaction product was virtually colorless and contained ⁇ 5 ppm iron.
• the homogeneous solution thus obtained was continuously pumped at a working pressure of 38 bar at 6.2 l / h through the reaction tube and a
• Irradiation zone was about 27 seconds. At the end of the reaction tube, the reaction mixture had a temperature of 267 ° C. The reaction mixture was cooled to room temperature immediately after leaving the reactor with an intensive heat exchanger.
• Methyl p-hydroxybenzoate was obtained in a mixture with ammonium sulfate and unreacted educt. By recrystallization from methanol, the product was isolated with a purity of> 99%.
• the homogeneous solution thus obtained was continuously pumped at a working pressure of 30 bar at 6 l / h through the reaction tube and a
• Irradiation zone was about 28 seconds. At the end of the reaction tube, the reaction mixture had a temperature of 255 ° C. The reaction mixture was cooled to room temperature immediately after leaving the reactor with an intensive heat exchanger. The reaction product was clearly viscous and virtually colorless. It contained ⁇ 5 ppm iron. Before the reaction, an acid number of 471 (mg KOH / g sample) was using
• the resulting mixture was pumped through the reaction tube continuously at 4 l / h at a working pressure of 35 bar and subjected to a microwave power of 2.4 kW, of which 93% was absorbed by the reaction mixture.
• the residence time of the reaction mixture in the irradiation zone was
• reaction mixture had a temperature of 240 ° C.
• the reaction mixture was cooled to room temperature immediately after leaving the reactor with an intensive heat exchanger. It was a turnover of 83% d. Th. Reached.
• the reaction product was virtually colorless and contained ⁇ 5 ppm iron.

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