WO1996022975A1

WO1996022975A1 - Process for producing aziridines

Info

Publication number: WO1996022975A1
Application number: PCT/EP1996/000165
Authority: WO
Inventors: Ulrich Steuerle; Georg Schuh; Jürgen Schweinzer; Uwe Dingerdissen
Original assignee: Basf Aktiengesellschaft
Priority date: 1995-01-25
Filing date: 1996-01-17
Publication date: 1996-08-01
Also published as: DE19502165A1

Abstract

A process for producing aziridines of the formula (I) in which R?1, R2, R3, R4 and R5¿ are mutually independently H, C¿1?-C8 alkyl or aryl and R?5¿ is in addition benzyl, C¿1?-C8 hydroxyalkyl or C1-C8 aminoalkyl, by the intramolecular catalytic dehydration of alkanol amines of the formula (II) in which the constituents R?1, R2, R3, R4 and R5¿ have the meanings given in formula (I), in the gas phase at temperatures of at least 250 °C on solid catalysts in a fluidised bed at a pressure of 1 to 500 mbar, in which, while maintaining the fluidised bed, a part of the solid catalyst is removed from the reactor, regenerated and fed back into the generator and the aziridines are isolated from the reaction mixture.

Description

Process for the preparation of aziridines

description

The invention relates to a process for the preparation of aziridines of the formula

R5

.N

R ⁱ - - R ³

R2 R4 (I)

means where R ^1, R ^2, R ^3, R ⁴ and R ⁵ are independently H, Cι ~ C to _ß-Al yl or aryl, and R ⁵ additionally represents benzyl, Ci to Cβ-hydroxyalkyl or Cι ~ to Cs Aminoalkyl is by intramolecular catalytic dehydration of alkanolamines of the formula

R ^l R ³

HO CICI NH R ⁵ (II),

I I

R ² R ⁴

in which the substituents R ¹ , R ² , R ³ , R ⁴ and R ^{5 have} the meaning given for them in formula I, in the gas phase at temperatures of at least 250 ° C. over solid catalysts in a fluidized bed below reduced pressure and isolating the aziridines from the reaction mixture.

Various catalysts are used to prepare aziridines, in particular ethyleneimine, by dehydrating alkanolamines in the gas phase. For example, SU-A-230 166 discloses ethyleneimine by reacting ethylene oxide and ammonia to form ethanolamine and dehydrating the ethanolamine at temperatures of about 450 ° C. with calcium phosphate impregnated with, for example, copper chloride or cobalt (II) chloride to produce as a catalyst.

JP-B-50/10593 discloses the production of ethyleneimine by dehydrating ethanolamine in the gas phase over tungsten oxide and oxides of catalysts containing Li, Mg, Ni, Mo, Bi, Sn, Si or Al. According to the teaching of WO-A-89/05797 used in the dehydration of ethanolamine in the Gas phase molecular sieves made of aluminum silicates, aluminum phosphates or silicon aluminum phosphates.

US-A-4,289,656, US-A-4,301,036, US-A-4,337,175, US-A-4,358,405, US-A-376,732 and US-A-4,477,591

Describe catalysts based on niobium / tantalum oxide with the addition of alkaline earth metal oxides and / or iron / chromium oxides for the catalytic gas phase dehydration of monoethanolamine to ethyleneimine.

Further catalysts for the intramolecular elimination of water from alkanolamines in the gas phase are oxide materials which contain silicon or phosphorus as essential components. Catalysts of this type are described, for example, in EP-B-0 227 461, EP-B-0 228 898 and EP-B-0 230 776.

If the catalysts described in the abovementioned references are used in the production of aziridines, oligomers and polymers of aziridine are formed to an undesirable extent.

The service lives of the catalysts described above leave something to be desired. Carbonaceous deposits form on the catalysts, which, for example in a fixed bed reactor, lead to a continuous increase in the pressure loss in the reactor and ultimately to occupation of the active centers on the catalyst, so that the alkanolamine conversion drops sharply. In order to achieve the space-time yields required for the industrial production of aziridines, the catalysts have to be regenerated at regular intervals. This is done, for example, by burning off the carbon-containing deposits by passing air over them at temperatures above 400 ° C. The regeneration of the catalyst is usually time-consuming and means that production is interrupted if only one reactor is available. In principle, the dehydration can also be carried out in a multi-reactor system in which, for example, at least 2 reactors are connected in parallel and the catalyst is regenerated in one reactor and the other reactor used for production. However, fluctuations in the product volume flow can occur, which have a negative effect on the continuous processing of the reaction products by distillation.

The present invention is therefore based on the object of providing a process for the preparation of aziridines, it being possible to produce practically continuously without doing so

SPARE BLADE (RULE 26) to have to switch off the reactor for regeneration of the catalyst.

The object is achieved according to the invention with a process for the preparation of aziridines of the formula

in which R ¹ , R ² , R ³ , R ⁴ and R ⁵ independently of one another denote H, Ci to Cβ-alkyl or aryl and R ⁵ additionally for benzyl, C to C _θ -hydroxyalkyl or Cι ~ to Cβ-aminoalkyl stands by intramolecular catalytic dehydration of alkanolamines of the formula

R ^l R ³

I I

HO CC NH R ⁵ (II),

I I

R ² R "

in which the substituents R ¹ , R ² , R ³ , R ⁴ and R ^{5 have} the meaning given for them in formula I, in the gas phase at temperatures of at least 250 ° C. over solid catalysts in a fluidized bed below reduced pressure and isolating the aziridines from the reaction mixture if the dehydration is carried out under a pressure of 1 to 500 mbar and part of the solid catalyst is removed from the reactor while maintaining the fluidized bed, regenerated and then returned to the reactor.

Surprisingly, it was found that when moving from the fixed catalyst bed, in which the aziridines formed are removed relatively quickly from the hot reaction zone owing to the flow conditions prevailing there, to a stationary, fluid-forming catalyst fluidized bed in which a wider residence time distribution similar to a stirred tank prevails, nevertheless comparable or even higher selectivities with regard to the aziridine formation from alkanolamines can be achieved.

Aziridines are high-energy compounds that easily undergo subsequent reactions with ring opening at temperatures above 100 ° C.

SPARE BLADE (RULE 26) If the residence times on catalysts in the dehydration of alkanolamines in the gas phase at high temperatures are too long, the selectivity of the aziridine formation is reduced because of the subsequent reactions of the aziridines. In the process according to the invention, high selectivities with regard to the formation of ethyleneimine from monoethanolamine are achieved. In order to technically implement the synthesis of aziridines from alkanolamines in the gas phase, the selectivity of the reaction is of great importance. Unwanted by-products are at the expense of the economics of the process. It is therefore often more sensible to carry out the reaction with a lower conversion than a maximum but with higher selectivity than with a high conversion and low selectivity. The unreacted alkanol amine can be recovered and fed back into the synthesis process.

A fluidized bed has the advantage over a fixed catalyst bed that the heat transfer coefficient between indirect heat transfer surfaces and the reaction zone is better. In the fluidized bed there is a significantly more uniform temperature distribution than in the fixed bed, ie there are no significant temperature gradients in the reactor cross section and thus practically no local overheating. In contrast to the fixed catalyst bed, coking-related pressure loss increases do not cause any problems when operating a fluidized bed catalyst. Superficial carbon-like deposits on the catalyst particles can be mechanically removed by the friction of the catalyst particles with one another. The fluidized bed can be operated at different gas velocities in the entire range of existence of a fluidized bed between the minimum fluidization speed of the catalyst used and a pneumatic conveying of the fluidized bed. At low gas velocities, the reaction is carried out, for example, in a stationary, bubble-forming fluidized bed. Discharged fine fraction of catalyst particles is retained with the help of filter candles or cyclones. At high gas velocities, the reaction is advantageously carried out in a circulating fluidized bed in a riser. The catalyst-reaction gas mixture is separated with the aid of cycles after passing through the riser and the catalyst is returned to the reaction vessel. The dehydration of alkanolamines is carried out under a pressure of 1 to 500, preferably 10 to 350 mbar. The alkanolamines can be evaporated separately and the steam, which may also be overheated, can be introduced into the fluidized catalyst bed. However, it is also possible to bring the alkanolamines to be dehydrated into contact with the fluidized bed in liquid form. For example wise happen by introducing them with the help of a tube that ends in the middle of the fluidized bed or metering them onto the surface of the fluidized bed.

The alkanolamines used in the process according to the invention can be used, for example, with the aid of the formula

ⁱ R ³

HO— c— C — NH— R ⁵ (II) in which R ² R ⁴

the substituents R ¹ , R ² , R ³ , R ⁴ and R ⁵ independently of one another are H, C - to Cs-alkyl or aryl and

R ⁵ also stands for benzyl, Cι ~ to Cs-aminoalkyl.

If the alkyl groups of the substituents R ¹ to R ^{5 have} at least 5 carbon atoms, they can also represent a cycloalkyl group, for example cyclohexyl. Examples of suitable alkanolamines are monoethanolamine, 1- or 2-methylmonoethanolamine, diethanolamine and N- (2-aminoethyl) monoethanolamine. Monoethanolamine is preferably used. This produces aziridines of the formula by intramolecular catalytic dehydration

in which R ¹ , R ² , R ³ , R ⁴ and R ⁵ independently of one another denote H, Ci- to Cs-alkyl or aryl and R ⁵ additionally for benzyl, Ci- to Cs-hydroxyalkyl or Ci- to Cβ-aminoalkyl stands. Ethyleneimine, 2-methyl aziridine, N- (2-hydroxyethyl) aziridine and N- (2-aminoethyl) aziridine are thus formed from the alkanolamines mentioned by name.

The alkanolamines are dehydrated in the gas phase at temperatures of at least 250 ° C. For example, temperatures up to 500 ° C can be used. The dehydration reaction is usually carried out in the temperature range from 350 to 450.degree. The dehydration takes place in the gas phase on solid Catalysts that have an average particle size of 10 to 1000 μm, preferably 40 to 500 μm. All catalysts which are known, for example, for the production of ethyleneimine can be used as catalysts. For this, reference is made to the literature references mentioned at the beginning. Active catalyst layers can, however, also be deposited on metallic supports such as meshes, fabrics, foils or steel chips. However, the active catalyst layers can also be deposited on other inert materials, such as silicon carbide, or used in the form of powders, for example, as a fluidized bed catalyst. Catalysts suitable for the dehydration of alkanolamines of the formula II are known, for example, from SU-A-230 166, JP-B-50/10593, WO-A-89/05797, EP-B-0 227 461, EP-B-0 228 89 and EP-B-0 230 776. Preference is given to using alkali, alkaline earth and / or lanthanide compounds which are stable under the conditions of aziridine synthesis and in particular are non-volatile and do not form volatile compounds. Examples include phosphates, sulfates, niobates, tungstates, vanadates, manganates, molybdates, rhenates, titanates and salts of heteropoly acids. In addition to the elements of the alkali, alkaline earth and / or lanthanide group of the periodic system, the catalytically active compositions preferably contain phosphorus and / or transition metals. Examples of such catalytically active materials are lithium-doped tungsten oxide, sodium-doped calcium tungstate, cesium or barium-doped iron sulfate or nickel sulfate.

Catalytically active compositions are characterized, for example, in EP-B-0 227 461 using the following formula

Si _a X _x Y _y O _b (III),

in which Si is silicon, X is at least one element from the group of the alkali and alkaline earth metals, Y is an element from the group B, Al, Ti, Zr, Sn, Zn and Ce and 0 is oxygen, and the indices a, x, y and b indicate the respective atomic ratios of the elements Si, X, Y and 0, where a = 1, x = 0.005-1, y = 0-1 and b has a value which is given by a, x and y is determined.

According to EP-B-0 228 898, the catalytically active compositions have the composition

X _a P _b X _c O _d (IV). In formula IV, X denotes at least one element from the group of the alkali and alkaline earth metals, P phosphorus, Y at least one element from the group B, Al, Si, S, Sc, Ti, Cu, Y, Zr, Nb, Mo , Sn, Sb, La, Ce, Ta, W, Ti, Pb, Bi and Th and 0 oxygen. The indices a, b, c and d and the atomic ratios of the elements X, P, Y and 0 have the following meaning: if a is 1, b is 0.01-3 and c = 0-100, d is a value, which is given by a, b and c and the binding state of the individual elements. According to EP-B-0 230 776, catalytically active compositions have the formula

X _a P YcO _d (V),

in which X is at least one element selected from Group IIIA elements, Group IVA elements, Group VA elements, transition metal elements from Groups I to VIII, lanthanide and actinide elements of the periodic table, P = phosphorus, X is at least one element , which is selected from alkali and alkaline earth metals, 0 means oxygen and the indices a, b, c and d indicate the atomic ratios of the elements X, P, Y and 0 and, if a - 1, b = 0.01-6 and c = 0-3 and d is a value determined by a, b and c and the binding state of the respective elements.

Further suitable catalytically active compositions are those from US-A-4,337,175, US-A-4,289,656, US-A-4,310,036, US-A-4,337,175, US-A-4,358,405, US Pat. A-4 376 732 and US-A-4 477 591 known oxides of tantalum or niobium with an alkaline earth metal oxide as a promoter. Also suitable are catalysts of the composition M ₀ Feo, 5-2.9 Cr _0f3 -7, ₇ or M _{0 0} Fe ₀ , ₀ -2, Cr ₀ , 6-1.7 with M - niobium, tantalum.

Instead of alkaline earth metal oxides, alkali metal oxides and or oxides of elements of the lanthamide group of the periodic system can also be used.

In the process according to the invention, part of the catalyst used is removed continuously or in portions from the fluidized bed. The amounts of catalyst discharged from the fluidized bed reactor practically do not adversely affect the dehydration reaction of the alkanolamines, so that the reaction can be continued regardless of the removal of the catalyst. The removal of the catalyst from the fluidized bed can advantageously be coupled with the addition of a fresh or regenerated catalyst to the fluidized bed, the withdrawn and added amounts of catalyst corresponding to one another. The catalyst discharged from the fluidized bed is regenerated in another reactor. This can be done, for example, under reduced pressure or also under normal pressure or even increased pressure. be taken. In order to regenerate the catalyst, it is heated, for example, in a fluidized bed to temperatures in the range from 300 to 800, preferably 400 to 600 ° C. in the presence of oxygen. Oxygen is preferably used in the form of a mixture of nitrogen and air. The reaction space in which the dehydration takes place and the regeneration space in which the finely divided catalysts coming from the reactor are treated with oxygen must be separate from one another. After regeneration has been completed and the remaining oxygen has been removed, the finely divided catalyst is returned to the fluidized bed reactor. The rate at which the amounts of catalyst are circulated is preferably adapted to the deactivation kinetics of the catalyst. If the conversion achievable with the catalyst decreases, the reasons for this lie not only in the formation of coking on the catalyst but also in a loss of active components. If it should be necessary, the catalyst discharged from the fluidized bed reactor can also be impregnated with an active catalyst component after treatment with oxygen and then returned to the fluidized bed reactor, if necessary after heating to temperatures of 400 to 600 ° C become. The amount of the discharged catalyst depends, as already indicated above, on the service life of the catalyst. The amounts of catalyst discharged from the fluidized bed reactor are, for example, 0.1 to 100, preferably 0.5 to 50% of the amount of catalyst per 24 hours.

Aziridines are preferably prepared by dehydrating the alkanolamines of the formula II in a stationary or circulating fluidized bed. Regardless of the fluidized bed used, be it a stationary or a circulating fluidized bed, the resulting aziridines of the formula I are isolated from the reaction mixture. For this purpose, for example, the aziridines can be absorbed with the aid of an aqueous alkaline absorption liquid and the aziridines can be separated off in a subsequent distillation, and the aqueous alkaline absorption liquids can then be used again to absorb aziridines. Suitable liquids of this type are, for example, aqueous NaOH or KOH solutions.

Because of the high reactivity of the aziridines, it is advisable to cool the hot reaction products as quickly as possible. For example, the hot reaction products emerging from the fluidized bed reactor can be separated from the gas phase with condensed reaction products whose temperature is at most 40 ° C. The temperature of the condensed reaction products used for cooling is preferably in the range from -78 ° C. to + 20 ° C. Unreacted alkanolamines are isolated from the reaction mixture and used again for dehydration.

The selectivity given in the examples in percent means moles of ethyleneimine formed per mole of converted monoethanolamine times 100. The conversion in percent is calculated from the converted amount of monoethanolamine in moles per mole of the monoethanolamine used, multiplied by 100. The yield in% becomes ¬ calculated by mole of the ethyleneimine formed per mole of the monoethanolamine used multiplied by 100.

example 1

72 ml of a fluidized bed catalyst with an average particle size of 200 μm were introduced into an electrically heated quartz tube with an inner diameter of 60 mm. The catalyst was a barium-cesium phosphate on silicon dioxide and was produced according to Example 19 in EP-B-0 228 898. The finely divided catalyst was heated to an internal temperature of 410 ° C. under a pressure of 50 mbar. Monoethanolamine was then passed through the catalyst bed at a gas velocity of 20 cm / sec through an inflow floor from below. During the operation, 10 vol.% Of the catalyst were removed from the fluidized bed reactor at intervals of 1 hour via a descending tube and conveyed to a second fluidized bed reactor. The discharged catalyst was then regenerated at temperatures of 550 ° C. while passing air through at normal pressure and then inerted with nitrogen. The inertized pulverulent catalyst was returned to the reactor using a solids feed pump. The reaction mixture coming from the reactor was absorbed by means of aqueous 0.1 N sodium hydroxide solution and analyzed by gas chromatography. The reactor was operated for a total of 120 hours, the reaction mixture obtained being analyzed after every 12 hours and after 120 hours. The selectivity was 88%, the monoethanolamine conversion was 43% and the ethyleneimine yield was 38% with a single ethanolamine throughput.

Example 2

Example 1 was repeated with the exception that the dehydration was carried out at a temperature of 400 ° C. The selectivity of ethyleneimine formation was 93%, the monoethanol conversion was 36% and the ethyleneimine yield with simple ethanolamine throughput was 34%.

Claims

claims

1. Process for the preparation of aziridines of the formula

in which R ¹ , R ² , R ³ , R ⁴ and R ⁵ independently of one another are H, C: ~ bi Cs-alkyl or aryl and R ⁵ additionally for benzy Ci to Cβ-hydroxyalkyl or Cχ ~ to Cβ-aminoalkyl stands by intramolecular catalytic dehydration of alkanolamines of the formula

R ⁱ R ³

HO CC NH R ⁵ (II),

R ² R ⁴

in which the substituents R ¹ , R ² , R ³ , R ⁴ and R ^{5 have} the meaning given for them in formula I, in the gas phase at temperatures of at least 250 ° C. over solid catalysts in a fluidized bed under reduced pressure and isolating the Aziridines from the reaction mixture, characterized in that the dehydration is carried out under a pressure of 1 to 500 mbar and, while maintaining the fluidized bed, a part of the solid catalyst is removed from the reactor, regenerated and then returned to the reactor.

2. The method according to claim 1, characterized in that one continuously carries out the discharge and recycling of the catalyst.

3. The method according to claim 1 or 2, characterized in that one carries out the dehydration under a pressure of 10 to 350 mbar.

4. The method according to any one of claims 1 to 3, characterized gekenn¬ characterized in that the dehydration is carried out in a stationary or a circulating fluidized bed.

5. The method according to any one of claims 1 to 4, characterized gekenn¬ characterized in that the resulting aziridines are absorbed with aqueous alkaline absorption liquids and the aziridines are separated in a downstream distillation and then the aqueous alkaline absorption liquids are used again to absorb aziridines .

6. The method according to any one of claims 1 to 5, characterized gekenn¬ characterized in that the hot reaction products with condensed reaction products, the temperature of which is at most 40 ° C, separated from the gas phase.

7. The method according to any one of claims 1 to 6, characterized gekenn¬ characterized in that the unreacted alkanolamines are isolated from the reaction mixture and used again.