Process of preparation of aliphatic amines

Details Process of preparation of aliphatic amines Process of preparation of aliphatic amines

2003-03-04

2004-10-26

Davis, Brian (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

Reexamination Certificate

active

06809222

ABSTRACT:

TECHNICAL FIELD
Present invention is concerned with a process of preparation of aliphatic amines by ammonia addition to alkenes.
BACKGROUND ART
Most of aliphatic amines are produced by amination of alcohols or possibly by amination of carbonyl compounds. Only currently the addition of ammonia to alkenes starts to be applied according to the scheme
The reaction is exothermic, while the equilibrium constant decreases with increasing temperature. Therefore, active catalysts are sought which would provide for sufficient reaction rate also at a temperature of 200 to 250° C. at which the equilibrium conversion of an alkene to an amine is more favourable.
Of course, increasing pressure improves the equilibrium conversion of an alkene to an amine, and most of the current publications and patents give a pressure higher than 2 MPa, and in several cases even 70 MPa.
The reaction rate depends on the catalyst activity, but also on the alkene reactivity. Isobutene is highly reactive, propene reacts more slowly, and ethylene has the smallest activity. While isobutylene reacts with ammonia on a zeolite catalyst quickly enough already at a temperature of 250° C., ethylene requires a temperature of about 350° C.
Many substances have been tried as homogeneous and heterogeneous catalysts for the ammonia addition to alkenes. The greatest attention has been paid to zeolite type catalysts. From U.S. Pat. Nos. 4,307,250 and 4,375,002 Y- and X-type zeolites, including various modifications, are known as catalysts which work at the following conditions:
pressure
2.06 to 41.3 MPa
temperature
200 to 450° C.
molar ratio NH
3
/alkene
0.2 to 20.
With H-mordenite as a catalyst at a temperature of 300 to 320° C., a pressure of 5 MPa and a molar ratio NH
3
/isobutene of 3.95 isobutylene conversion of 15 to 26% was reached in single experiments, but the conversion selectivity to tert-butylamine was relatively low, reaching 24 to 72%. In the above mentioned patent documents the side products have not been described, and they are probably oligomers of isobutylene. In EP 0305 564 A1 there is described a partially dealuminized zeolite catalyst which has a higher activity and selectivity, leading to a conversion of 3.8 to 13.6% at a temperature of 220 to 260° C., a pressure of 5 MPa and at a molar ratio NH
3
/isobutylene=4.
In DE 33 26 579 A1 there is described a method of amine preparation by alkene amination in the presence of a pentasil-type catalyst. An advantage of this catalyst in comparison with the Y-type is higher selectivity and lower formation of carbonaceous deposits, namely at a relatively small excess of ammonia. The pressure of 30 MPa is considered to be optimal, and the highest isobutylene conversion of 12% has been reached at a temperature of 330° C., a pressure of 59 MPa and at a molar ratio NH
3
/isobutylene=1.5. When aminating isobutylene by the method according to DE 33 27 000 A1 on a boralite-based catalyst at a molar ratio NH
3
/isobutylene=1.5, a temperature of 300° C. and a pressure of 30 MPa an isobutylene conversion of 17.3% has been achieved.
The use of alkali metals and of their hydrides as catalysts for ammonia addition to alkenes is described in U.S. Pat. No. 2,501,556, where pressures of at least 50 MPa and a temperature of 100 to 250° C. are recommended. The use of rare metals of the group VIII, especially of palladium on a carrier, as catalysts of alkene amination is known from U.S. Pat. No. 3,412,158. The use of homogeneous catalysts, based on the solutions of ruthenium and iron complexes, in preparation of aliphatic and aromatic amines by ammonia addition to olefines at a temperature of 100 to 250° C. and a pressure of 0.1 to 83 MPa is described in EP 0039 061 B1, but the results of experiments have been evaluated only quantitatively. The use of ammonium halides as catalysts for the above mentioned reaction is known from EP 0200 923 A2, and that of organic cation exchangers from U.S. Pat. No. 4,536,602. Nevertheless, only thermostable types based on fluorine compounds are suitable. It seams that other types of catalysts of ammonia addition to olefins cannot compete with zeolites. Zeolites have excellent thermal stability and they are easily regenerated with air at a temperature of 400 to 500° C. Some of the homogeneous catalysts show corrosive action, whereas zeolites are practically inert.
Most of the patent literature which concerns the amine preparation by zeolite catalyzed addition of ammonia to olefins recommends to perform the above mentioned reaction at a relatively high pressure. For example, in DE 33 26 579 A1 and DE 33 27 000 A1 a pressure in the range of 4 to 70 MPa is considered, but a pressure of 20 to 30 MPa is recommended. Using a lower pressure, for example 5 MPa (U.S. Pat. Nos. 4,307,250, 4,375,002, EP 0305 564 A1), the alkene conversion to amine of about 10% is achieved only with a high excess of ammonia. The reaction mixture is liquefied by cooling, and the unreacted starting substances are separated by rectification. If a higher ammonia excess is used, even more than 10 kg of ammonia, which has high heat of vaporization, per 1 kg of the prepared amine must be evaporated. At a pressure of 30 MPa a similar isobutylene conversion can be achieved also at a molar ratio NH
3
/isobutylene of 1.5. However, a high-pressure apparatus is very expensive, and injecting the liquids into a high pressure requires much energy for driving the injection pumps.
DISCLOSURE OF INVENTION
At present it has been found that it is possible to produce aliphatic amines by the ammonia addition to alkenes using a method according to the present invention which eliminates the high heat consumption of the known procedures. The nature of the method of preparation of aliphatic amines from ammonia and alkenes in the gas phase using homogeneous or heterogeneous catalysts consists in that the reaction system consists of two sections which are mutually interconnected and conditioned and of one cooling zone which work at a practically equal pressure of 2 to 8 MPa, while the starting ammonia and alkene enter the first section, where they are mixed with the unreacted ammonia and alkene at the pressure of the synthesis, and the gaseous mixture enters the second section, where a partial chemical transformation of reactants to amine takes place, and the reaction mixture leaving the second section passes the cooling zone and returns to the first section, where the separation of the gaseous mixture of unreacted ammonia and alkenes from the liquid crude amine takes place, which crude amine is further purified.
Synthesis of amines from alkenes and ammonia in the system of two mutually conditioned sections working at a practically equal pressure according to the present invention allows that it can be only performed in a relatively narrow range of pressures of 2 to 8 MPa. The term “practically equal pressure” means that the pressure differences in the sections are caused only by the pressure loss in the apparatus and pipes. The upper bound for the working pressure is given by the closeness of the critical pressure of ammonia or of its mixture with an alkene. The function of the first section is namely conditioned by simultaneous existence of the gaseous and liquid phase in it. The critical pressure for ammonia is 11.2 MPa, the critical pressure, for example, for isobutylene is 4.0 MPa.
Only a small part of amines can be separated by a simple partial condensation in the first section at the system pressure. The amine content in the mixture which leaves the second (catalytic) section is namely limited by equilibrium, and it represents only 1 to 3 molar % of the amine. Conversion of alkenes to amine under the conditions according to the invention is 3 to 10%, and the amine content is further decreased by the excess of ammonia. Therefore, according to the present invention the efficiency of the amine separation from the gaseous mixture is preferably increased by a built-in packing which increases the surface of the interfacial contact of the gas and liquid, while the gas and liquid counterfl

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