Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/10—Preparation of derivatives of isocyanic acid by reaction of amines with carbonyl halides, e.g. with phosgene
• • 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
  • B01J19/24—Stationary reactors without moving elements inside
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C265/00—Derivatives of isocyanic acid
  • C07C265/14—Derivatives of isocyanic acid containing at least two isocyanate groups bound to the same carbon skeleton

Definitions

• the invention relates to a process for the preparation of isocyanates by reacting the corresponding amines with phosgene in the gas phase, wherein in the conversion of the amine into the gas phase, a diluent containing between 90.0000 mass% and 99.9999 mass% in the phosgenation process inert substances and between 0.0001 mass% and 10.0000 mass%) oxygen (O 2 ), is present and the molar ratio of amine to oxygen (0 2 )> 1000: 1.
• Isocyanates and especially diisocyanates are produced in large quantities and serve mainly as starting materials for the production of polyurethanes. They are usually prepared by reacting the corresponding amines with phosgene. The reaction of the amines with the phosgene can be carried out in the liquid phase or by phosgenation in the gas phase.
• the present invention relates exclusively to the phosgenation in the gas phase.
• reaction conditions are selected so that at least the reaction components amine, isocyanate and phosgene, but preferably all starting materials, products and reaction intermediates, are gaseous at the selected reaction conditions.
• Advantages of the gas phase phosgenation include a reduced phosgene hold-up, the avoidance of difficult phosgenable intermediates and increased reaction yields.
• EP 0 289 840 B1 discloses for the first time a process for the preparation of aliphatic diisocyanates by phosgenation of the corresponding diamines in the gas phase, in which the vaporous diamines, optionally diluted with an inert gas or with the vapors of an inert solvent, and phosgene separated from each other to temperatures of 200 ° C heated to 600 ° C and continuously reacted in a heated to 200 ° C to 600 ° C reaction space with each other.
• Preferred inert gas is nitrogen.
• Suitable inert solvents whose vapors may also be used to dilute the diamine include monochlorobenzene, ortho-dichlorobenzene, xylene, chloronaphthalene, decahydronaphthalene or mixtures thereof.
• the amount of inert gas optionally used as a diluent or solvent vapor is not critical. If a dilution of the diamine takes place, this can be done, for example, while maintaining a volume ratio of Diamine vapor to inert gas or solvent vapor of 1: 0, 5 to 1: 2 take place. Beyond the requirement that the diluent should be inert, no further details are given on its purity.
• EP 0 593 334 B1 describes for the first time a process for the preparation of aromatic diisocyanates in the gas phase.
• the reactants contacted in the reaction i. H. at least one diamine and phosgene are used alone or in the presence of a diluting gas stream.
• a diluting gas stream (“gas dilution vector”) is meant any gas which is diluent and inert to the reactants and reaction products
• the inert gases such as nitrogen
• the vapor of a solvent especially benzene, xylene, monochlorobenzene or
• no further details are given about its purity.
• diluents inert gases or the vapors of inert solvents
• the dilution of the amine is common practice.
• suitable inert substances often nitrogen, act as an entraining agent and facilitate vaporization of the amine, thereby reducing decomposition reactions (for example, with ammonia cleavage).
• TDA toluenediamine
• the addition of 4% by mass of nitrogen results in a reduction in the evaporation temperature of the TDA of about 8 K.
• a diluent are sufficient to lower the evaporation temperature.
• the substance added to reduce the boiling point should be inert to the amine and the later reaction products and / or intermediates because reaction of the amine and / or the reaction products and / or the reaction intermediates with the adjuvant would reduce the yield on the one hand and on the other hand lead to the formation of deposits and / or make the distillative purification of the isocyanate more difficult.
• oxidizing substances can change the properties of an isocyanate such that discoloration occurs in the isocyanate itself or in the resulting polyurethane foam (see, for example, WO 2005/010066, page 1, lines 24 to 26).
• nitrogen is one of the preferred diluents for lowering the temperature required for the evaporation of the amine.
• Technical nitrogen is available in different purities and accessible through different manufacturing processes.
• air is used as the feedstock.
• Common methods of air separation are deep-freeze distillation, membrane processes and pressure swing adsorption. Deep-freeze distillation is the most effective technology for producing large quantities of nitrogen.
• Pressure swing adsorption and membrane processes are considered the more economical processes for the production of less pure nitrogen (up to 99.8% purity with a minimum of 0.2% remaining oxygen content) at medium flow rates (25-500 Nm 3 / h).
• the amount of nitrogen required, and in particular the nitrogen purity required has a significant impact on the selection of the nitrogen production process (see above, Figure 1) and thus on the costs to be taken into account for nitrogen supply,
• nitrogen is to be used as a diluent in a gas phase isocyanate production process
• purities of less than 99.9% by volume are acceptable, and there are several nitrogen production options available, even less than 93 vol% allowed, so there is the advantage that a Tiefklaltedestillation in one
• a single-column apparatus can be used which produces nitrogen with an oxygen content of 7% by volume (Linde AG: Cryogenic air separation, development and technical development).
• noble gases in particular argon is to call, which is the cheapest noble gas.
• Argon like nitrogen, is recovered by air separation, in particular by deep-freeze distillation. Since argon boils only 3 K lower than oxygen, the production of oxygen-poor argon succeeds again only by the application of downstream steps for oxygen removal, such as selective adsorption, reaction with hot metal or by catalyzed reaction with hydrogen to water and subsequent drying. Although these steps can raise the purity of argon from 98% after deep-freeze distillation to as much as 99.999%, it requires high costs for the additional equipment and its operation and maintenance (Kirk-Othmer Encyclopedia of Chemical Technology, 2001 by John Wiley & Co.).
• Organic solvents also contain certain amounts of dissolved oxygen in standard commercial purity levels, and without special measures, oxygen is also present in the vapors of organic solvents which can be used as diluents facilitating the evaporation of the amine in the prior art.
• EP 0 954 549 B1 in section [0002] describes that compounds containing amino groups in general tend to discolor on contact with oxygen.
• ortho-toluenediamine such as 2,3-diaminotoluene or 3,4-diaminotoluene, indicated that this already darkened immediately after the action of air, while other amines, eg. As aniline, although more stable, but also become dark over time.
• Aliphatic compounds with amino groups also discolor over time at room temperature; in general, however, according to EP 0 954 549 B1, they discolor at a much lower rate than compounds containing aromatic amino groups.
• the object of the present invention was therefore to provide a process for the preparation of isocyanates by reacting the corresponding amines with phosgene in the gas phase, in which an inert material in the phosgenation process can be used to facilitate the conversion of the amine into the gas phase without the purity requirements for the substance which is inert in the phosgenation process adversely affect the economic efficiency of the process.
• the object can be achieved by a process for the preparation of isocyanates by reacting the corresponding amines with phosgene in the gas phase, in which (i) the amine in an evaporation space in the presence of> 0.10% by mass to 25% by mass), preferably from> 0.10% by mass> to 10% by mass, more preferably from
• step (ii) the gaseous stream containing from (i), amine and diluent is reacted with a gaseous phosgene stream in a reaction space to the corresponding isocyanate; wherein the diluent used in step (i) is between 90.0000 mass% and 99.9999 mass%, preferably between 99.0000 mass% and 99.9950 mass%, particularly preferred between 99.5000 mass% and 99.9900% by mass of substances which are inert in the phosgenation process and between 0.0001% by mass and 10.0000% by mass, preferably between 0.0050% by mass and 1.0000% by mass, particularly preferably between 0.0100% by mass and 0.5000 mass% of oxygen, in each case based on the mass of the diluent, and the molar ratio of amine to oxygen (O 2 ) in step (i) in the evaporation space
• reaction in the gas phase is meant that the amines react in the gaseous state to the isocyanates and in the course of the reaction, all components present (starting materials, products, intermediates, by-products, if necessary inert substances) during the passage through the reaction space at least 95.0% by mass, preferably at least 98.0% by mass, more preferably at least 99.0% by mass and most preferably at least 99.9% by mass, in each case based on Total mass of all existing components, remain in the gas phase.
• Vaporization space is understood to mean the space in which the primary amine is transferred to the gas phase.
• the evaporation space is located in a technical device for transferring liquids to the gas phase, the evaporator.in the simplest case, the evaporation space is identical to the internal volume of the evaporator.
• inert substance a substance which is inert in the phosgenation process
• inert substance a substance which is gaseous in the reaction space at the reaction temperature and as such (ie in the case of which it is not attainable in practice) % purity) preferably not at all or only insignificantly (ie without measurable impairment of the process) with the compounds occurring in the course of the reaction (amine, phosgene, intermediates, by-products, products).
• the inert substance together with impurities contained in it forms the diluent. It is also possible to use mixtures of several substances which are inert in the phosgenation process.
• reaction space is meant the space in which the gas phase reaction of primary amine (or intermediates) with phosgene to the desired isocyanate takes place, starting where the starting materials are first mixed and ending where the conditions for a gas phase reaction of primary amine (or intermediates) with phosgene to the desired isocyanate are no longer given (for example, by stopping the reaction due to temperature reduction or “quenching” (see below), etc.).
• the achievement of the object according to the invention is particularly surprising since it is known that oxygen reacts with amines and thus in no way represents an inert compound or does not behave in an inert manner.
• the state of the art of gas phase phosgenation can be improved, since as a diluent in the conversion of the amine into the gas phase, a substance less than heretofore conventional purity (i.e., with higher oxygen contents) can be used, thereby improving the economics of the process.
• the solution according to the invention is surprising because it is known that oxygen also reacts with the reaction product isocyanate and thus does not behave inertly with respect to the reaction product.
• the diluent according to the invention is thus a mixture of the actual inert substance and oxygen in small amounts.
• the reaction of the oxygen with the amine will result in the formation of monomeric and binary oxidation products whose boiling points are not are substantially higher (ie only by a few K, generally not more than 20 K, preferably not more than 10 K, more preferably not more than 5 K) than that of the original amine.
• the monomeric and binary oxidation products remain in the gas phase and enter the reaction space for gas phase phosgenation together with the amine stream.
• the reaction of the oxygen with the amine in addition to the monomeric and binary oxidation products, also leads to high-boiling oligomeric oxidation products .
• the proportion of oligomeric oxidation products to tarry products increases as the oxygen content in the gaseous amine increases.
• the oligomeric oxidation products have a boiling point that is well above the boiling point of the original diamine. Thus, condensation and clogging of the lines containing gaseous amines may occur.
• Blockages or pressure loss-causing cross-sectional constrictions have massive effects on the service life of the gas phase reactor and on the availability of the process for the preparation of isocyanates in the gas phase and are highly critical.
• water can also be formed as a product of the oxidation.
• the presence of water is likewise undesirable in the phosgenation reaction, since this leads to the decomposition of the phosgene under evolution of hydrogen chloride, and thus the stoichiometry desired within the reaction space is negatively influenced.
• phosgene losses are the result.
• water is undesirable in phosgenation reactions, as this results in the risk of corrosion, unless very high quality (and therefore very expensive) materials are used.
• the amine is converted into the gas phase in at least one evaporation space in the presence of a diluent containing an inert substance and to temperatures of 200 ° C to 600 ° C, preferably 200 ° C to 500 ° C, more preferably 250 ° C heated to 450 ° C and fed to the reaction space.
• a diluent is used which contains between 90.0000% by mass and 99.9999% by mass, preferably between 99.0000% by mass and 99.9950% by mass, more preferably between 99.5000% by mass.
• the diluent is used in amounts of from 0.10% by mass to 25% by mass, preferably from 0.10% by mass to 10% by mass, more preferably from 0.20% by mass to 5.0 % By weight, based on the total mass of amine and diluent, with a molar ratio of amine to oxygen (O 2 ) of> 1000: 1, preferably in the range between 1000: 1 and 1,000,000: 1, particularly preferred between 10,000: 1 and 50,000: 1, is complied with.
• suitable inert substances are, for example, those substances which are already gaseous at room temperature, for example nitrogen, noble gases such as helium or argon, other gases such as carbon dioxide.
• suitable inert substances are those which are gaseous only at temperatures above room temperature, for example aromatics such as chlorobenzene, chlorotoluene (0-, m-, p-isomers), dichlorobenzene (0-, m -, p-isomers), toluene, xylene (0-, m-, p-isomers), chloronaphthalene (all isomers) or decahydronaphthalene.
• nitrogen is particularly preferred because it satisfies the criteria with regard to chemical inertness extremely well and is substantially less expensive than noble gases.
• a diluent comprising an inert material which is already gaseous at room temperature, preferably N 2 , He, Ar, particularly preferably N 2, is used.
• the diluent contains, in addition to the inert substance, at least oxygen, in concentrations between 0.0001 mass% and ⁇ 10.0000 mass%, preferably between 0.0050 mass% and 1.0000 mass%, more preferably between 0.0100% by mass) and 0.5000% by mass, based on the mass of the diluent.
• diluents of lower purity often also contain other substances that do not necessarily interfere with amine evaporation. So z. B. nitrogen of lower purity nor argon, helium and water.
• the oxygen content of the diluent to be used is preferably determined before it is introduced into the evaporation space. This includes the taking note of certificates of analysis of the respective suppliers of diluents, if they are purchased from the isocyanate manufacturer without their own analysis. If oxygen-containing gases such as nitrogen or argon, preferably nitrogen, are used as the diluent, the oxygen content of the diluent is preferably determined by a gas chromatographic online analysis familiar to the person skilled in the art.
• the maintenance of the molar ratio of amine to oxygen (0 2 ) in step (i) (conversion of the amine into the gas phase) in the Verdamphengsraum of> 1000: 1, preferably in the range between 1000: 1 and 1,000,000: 1, more preferably between 10,000: 1 and 50,000: 1, achieved by reducing the absolute flow rate of the evaporation space supplied diluent (see also Example 3) ,
• the diluent used in step (i) is a mixture of different lots of diluent having different oxygen contents.
• the purer charge of the diluent may be obtained, for example, by recovering and recycling the diluent which has already passed the reaction space and its contained oxygen by reaction with amine or other substances present in the reaction mixture.
• any suitable evaporator can be used as the evaporator for the amine evaporation.
• Preference is given to tube-bundle heat exchangers, plate heat exchangers or falling-film evaporators, optionally with pumped circulation. It is also possible to use micro-heat exchangers or micro-evaporators as described in WO 2005/016512 A or in DE 10 2005 036870 A1.
• evaporation systems are used, in which a small work content with a high circulation rate is passed through a falling film evaporator.
• the conversion of amines into the gas phase according to the invention is primarily important for the gas phase phosgenation of the amines to the corresponding isocyanates. In principle, however, the considerations of the purity of the diluent can also be transferred to other applications of amine evaporation.
• other applications include amine evaporation e.g. Example, the evaporation for the purpose of distillation, such as the separation of ortho- and meta-TDA isomers, or the distillative removal of TDA residue.
• Other applications of TDA evaporation may include applications include, in which TDA is only partially evaporated, z. As in the expulsion of dissolved gases, such as ammonia, with an inert gas. Partial evaporation is also present during storage and transport of TDA in a molten state, where inert gases can be used for over-veiling.
• both the evaporation of the amine and an optionally required overheating can be carried out in one stage; but they can also be done in multiple stages.
• the vaporous amine stream can be passed through a mist eliminator.
• the average residence time from leaving the evaporation space until it enters the reaction space is more than 0.01 second, preferably more than 0.1 second, and especially preferably more than 0.5 second.
• the residence time is preferably not more than 60 seconds until it enters the reaction space. This residence time is sufficiently long at the temperatures given in the evaporation to ensure that the oxygen present in the inert diluent supplied for evaporation reacts completely with the amine.
• the evaporator and / or superheater and the pipes for generating the vaporous Diaminstroms to the gas phase reactor can be made of any metallic material, for. As steel, stainless steel, titanium, Hastelloy, Inconel or other metallic alloys.
• the reaction of the primary amine with phosgene takes place in at least one reaction space arranged in a reactor.
• the reaction space is understood as meaning the space in which the gas phase reaction of primary amine (or intermediates) with phosgene takes place to give the desired isocyanate.
• the term "reactor" is understood to mean the technical apparatus which contains the reaction space.
• a reactor can also contain several reaction spaces. It is also possible to connect a plurality of reactors with one or more reaction spaces in succession or in parallel.
• the inventive method is in principle applicable to any reaction space and reactor geometry.
• the reactor has, subsequent to the reaction space in which, after the mixture of the starting materials, a conversion of the amine groups to the isocyanate groups of 80.0%, preferably 90.0%, particularly preferably 99.0%, very particularly preferably 99.5% is achieved, a further, rotationally symmetrical reaction space with a constant and / or extended flowed through cross-sectional area.
• the method according to the invention is applicable in principle to any procedure of gas phase phosgenation. Preference is given to the adiabatic procedure described in EP 1 935 876 A1. However, the method described is also applicable in an isothermal mode.
• the selected residence time for the reaction of the amine groups with the phosgene to the isocyanate is preferably between 0.050 seconds and 15 seconds, depending on the type of amine used, the starting temperature, optionally the adiabatic temperature increase in the reaction chamber, the molar ratio of amine used and Phosgene, type and amount of at least one inert substance and the selected reaction pressure.
• phosgene in excess with respect to the amine groups to be reacted.
• a molar ratio of phosgene to amine groups of 1.1: 1 to 20: 1, more preferably from 1.2: 1 to 5: 1, before.
• the phosgene is heated to temperatures of 200 ° C to 600 ° C and optionally diluted with an inert gas such as N 2 , He, Ar or with the vapors of an inert solvent, for.
• an inert gas such as N 2 , He, Ar or with the vapors of an inert solvent, for.
• aromatic hydrocarbons with or without halogen substitution such as.
• chlorobenzene or dichlorobenzene fed to the reaction space.
• the phosgene is also treated with a diluent, its oxygen content must be kept as low as possible (usually lower than the oxygen content of the diluent of the amine), because oxygen in the phosgene can lead to the formation of residues in the reaction chamber or even to the formation of explosive mixtures according to the so-called quenching (see below). Preference is therefore given to using recycled and thus oxygen-free inert material for the dilution of the phosgene.
• the gaseous reaction mixture which preferably comprises at least one isocyanate, phosgene, an inert substance and hydrogen chloride, is preferably freed from the isocyanate formed. This can be done, for example, by subjecting the reaction mixture continuously leaving the reaction mixture, a condensation in an inert solvent, as has already been recommended for other gas phase phosgenations (EP 0 749 958 AI).
• the condensation preferably takes place in that the reaction space used in the process according to the invention has at least one zone into which the reaction is stopped one or more suitable liquid streams ("quench liquids") are sprayed in.
• quench liquids suitable liquid streams
• the at least one zone is in a quenching stage, as z.
• a quenching stage as z.
• the at least two cooling zones are used. Integration and operation of these at least two cooling zones are preferably carried out with a quenching stage. This is disclosed in structure and operation in EP 1 935 875 A1.
• condensation or quenching step leaving solutions or mixtures are then preferably worked up by distillation and thus recovered the isocyanate in the required purity.
• the gas mixture leaving the condensation or quenching stage is preferably freed from residual isocyanate in a downstream gas scrubber with a suitable scrubbing liquid, preferably subsequently freed of excess phosgene in a manner known per se.
• a suitable scrubbing liquid preferably subsequently freed of excess phosgene in a manner known per se.
• This can be done by means of a cold trap, absorption in an inert solvent (eg chlorobenzene or dichlorobenzene) or by adsorption and hydrolysis on activated charcoal.
• the hydrogen chloride gas passing through the phosgene recovery stage can be recycled in a manner known per se for the recovery of the chlorine required for the phosgene synthesis.
• the washing liquid obtained after its use for gas scrubbing can then be used, preferably at least partially, as quench liquid for cooling the gas mixture into the corresponding zone of the reaction space.
• the inert gas passes through the condensation or quenching stages and optionally downstream gas scrubbing and phosgene recovery in gaseous form together with the gaseous hydrogen chloride.
• the gaseous hydrogen chloride can, for. B. by absorption separated in water, and thus recovering the inert gas used in the evaporation.
• this stream of inert gas optionally after drying and optionally after destruction of remaining traces of phosgene, can be recycled to the evaporation space to facilitate the transfer of the amine into the gas phase.
• This stream of inert gas is free of oxygen, since originally existing oxygen has already reacted with the amine before the reactor for gas phase phosgenation. Any losses of inert gas may be supplemented with fresh diluent, which preferably contains the same inert gas, and the supplemental fresh diluent may have a high oxygen content of up to 10% by mass, as this gas stream dilutes with the oxygen-free recycled gas becomes.
• the content of oxygen in the inert gas used as diluent must be such that the molar ratio of amine to oxygen according to the invention of> 1,000: 1, preferably in the range between 1,000: 1 and 1,000,000: 1, particularly preferred between 10,000: 1 and 50,000: 1, is complied with.
• the diluent used in step (i) conversion of the amine into the gas phase
• Examples of preferred aliphatic or cycloaliphatic amines are 1,4-diaminobutane, 1,6-diaminohexane (HDA), 1,11-diaminoundecane, 1-amino-3,5,5-trimethyl-3-aminomethylcyclohexane (IPDA). , 4,4'-diaminodicyclohexylmethane or 4,4'-diaminodicyclohexylpropane-2,2.
• HDA 1,6-diaminohexane
• IPDA 1-amino-3,5,5-trimethyl-3-aminomethylcyclohexane
• diamines of the abovementioned type with exclusively aliphatically or cycloaliphatically bonded amino groups such as isophoronediamine (IPDA), hexamethylenediamine (HDA) or bis (p-aminocyclohexyl) methane (PACM 20) are particularly preferred.
• IPDA isophoronediamine
• HDA hexamethylenediamine
• PAM 20 bis (p-aminocyclohexyl) methane
• TDA toluenediamine
• 2,4-TDA and 2,6-TDA diaminobenzene
• NDA naphthylenediamine
• 2,2'-, 2,4 "- or 4,4 Particularly preferred is toluenediamine (TDA), in particular 2,4-TDA and 2,6-TDA, and mixtures thereof are very particularly preferred 2,4- / 2,6-TDA isomer mixtures of Isomer ratios 80/20 and 65/35.
• Example 1 > 99.999% purity ( ⁇ 0.0001 mass% 0 2 )
• Example 2 99.32% purity (0.68 mass% O 2 )
• Example 5 92, 12% purity (7.88 mass% O 2 )
• Example 6 dried air (78% by mass o N 2 , 22% by mass o 0 2 )
• an m-toluenediamine isomer mixture containing 80.3% 2,4-TDA and 19.7% 2,6-TDA is evaporated.
• approx. 100 g of the TDA isomer mixture are weighed exactly into a 250 mL round-bottomed flask which is connected to a distillation apparatus which can be operated under reduced pressure and consists of a Reitmeyer batch, a bridge and a cooled distillation template.
• a distillation apparatus which can be operated under reduced pressure and consists of a Reitmeyer batch, a bridge and a cooled distillation template.
• the round bottom flask protrudes a boiling capillary, which ends immediately above the liquid level of the filled TDA isomer mixture.
• the diluent is introduced into the round bottom flask at 4 or 10 L / h (at 1013 hPa and 20 ° C) while heating it with a hot air blower.
• the TDA vapor which forms is fed together with the diluent at an absolute pressure of 100 mbar through Reitmeyer attachment and bridge into the distillation receiver where it is condensed and collected.
• the distillation is continued until the submitted TDA has completely evaporated. This is the case at the set absolute pressure of 100 mbar after a time of 16 to 17 minutes and also recognizable by the fact that the internal temperature in the round bottom flask exceeds 180 ° C. Due to the absence of the distillation and the known volume flow of the diluent, the molar amount of oxygen with which the TDA vapor came into contact can be calculated.
• TDA vapor and oxygen oxidation products Formed by contact with TDA vapor and oxygen oxidation products whose boiling point is much higher than that of m-TDA, they remain in the round bottom flask or in the Reitmeyer attachment and can be reweighed there.
• Example 1 Comparative Example: Oxygen Content of Diluent ⁇ 0.0001% by Weight; Amine Amine Ratio: Oxygen> 1000: 1)
• the amount of residue in the round bottom flask was 1300 mg, the amount of residue in the distillation receiver 70 mg.
• Example 2 (according to the invention: oxygen content of the diluent> 0.0001 mass%, molar ratio amine: oxygen> 1000: 1)
• Example 3 (according to the invention: oxygen content of the diluent> 0.0001 mass%, molar ratio amine: oxygen> 1000: 1 - reduction of the absolute amount of diluent)
• Example 2 The procedure is the same as in Example 1. During the 16.25 minute distillation of 106.2 g of m-TDA (0.87 mol) only 4 L / h of nitrogen with 1.91 mass% of oxygen were used. Due to the smaller amount of diluent, the molar ratio of amine to oxygen is still greater than 1000, namely calculated 1010: 1. The amounts of residue in the round bottom flask was 1296 mg, the amount of residue in the distillation receiver 72 mg. Both residue values are as low as when using the pure oxygen in Example 1.
• Example 4 Comparative example: oxygen content of the diluent> 0.0001% by mass, molar ratio amine: oxygen ⁇ 1000: 1)
• Example 3 The procedure is the same as in Example 3. During the 17-minute distillation of 105.6 g of m-TDA (0.86 mol), 10 L / h of nitrogen with 1.91 mass% of oxygen were used. The molar ratio of amine to oxygen is now mathematically 384: 1. The amounts of residue in the round bottom flask was 1408 mg, the amount of residue in the distillation receiver 81 mg. Both residue values are significantly increased compared to Examples 1 to 3, which would be noticeable as a loss of yield in the industrial scale implementation. The example shows that changing the molar ratio of m-TDA to oxygen to a value of less than 1000 has a negative effect on the yield.
• Example 5 comparative example: oxygen content of the diluent> 0.0001% by mass, molar ratio amine: oxygen ⁇ 1000: 1)
• Example 2 The procedure is the same as in Example 1. During the 17-minute distillation of 106.0 g of m-TDA (0.87 mol), 10 L / h of nitrogen with 7.88 mass% of oxygen were used. The molar ratio of amine to oxygen is calculated 93: 1. The amounts of residue in the round bottom flask was 1393 mg, the amount of residue in the distillation template 91 mg. Both residue values are significantly increased compared to Example 1 to 3, which would be noticeable in the industrial scale implementation as yield loss.
• Example 1 Compared with Example 1, the residue in the distillation template (content of oxidation products whose boiling point is not is much higher than that of m-TDA) increased by 30%, which in the large-scale implementation of this method in addition to yield losses can lead to accelerated clogging of the TDA steam leading lines.
• Example 6 comparative example: oxygen content of the diluent 22% by mass; molar ratio amine: oxygen ⁇ 1000: 1)
• the volume of residue in the round bottomed flask was 1477 mg, the amount of residue in the distillation receiver was 113 mg. This represents an increase of 13% in the round bottom flask (oxidation products with a much higher boiling point than m-TDA) and of 61% in the distillation receiver (oxidation products whose boiling point is not significantly higher than that of m-TDA) compared to Example 1.
• the significant increase in oxidation products, the boiling point of which is not significantly higher than that of m-TDA, would result in the large-scale implementation of this method in addition to yield losses to accelerated clogging of the TDA-steam lines leading.
• Table 1 summarizes for examples 1 to 6 how the formation of oxidation products with a similar or substantially higher boiling point than m-TDA depends on the ratio of m-TDA to oxygen during the distillation. Table 1 :

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