SK154897A3 - Method for the preparation of cyclic lactams - Google Patents

Abstract

Production of cyclic lactams by the reaction of amino carboxylic acid nitriles with water, performed in the liquid phase in the presence of heterogeneous catalysts based on titanium dioxide with a rutile content in the range from 0.1 to 95 wt.% and an anatase content in the range from 99.9 to 5 wt.% in relation to the total titanium dioxide content.

Description

Process for the preparation of cyclic lactams

Technical field

The invention relates to a process for preparing cyclic lactams by reacting aminocarboxylic acid nitriles with water in the presence of a catalyst.

BACKGROUND OF THE INVENTION

US-A-4,628,085 discloses the reaction of 6-aminocapronitrile with water in the gaseous state on acidic silica gel at 300 DEG C. 95% of the caprolactam is obtained with an initial selectivity, but it is noted rapid decline in productivity and selectivity. A similar process is described in U.S. Pat. No. 4,625,023, which discloses a strongly diluted flow of gases consisting of 6-aminocapronitrile, adipic acid dinitrile, ammonia and water vapor and a carrier gas through the catalyst beds, which consists of silica gel and a copper (chromium) barium-titanium dioxide system. Caprolactam with a selectivity of 91% is obtained in 85% yield. Also in this case, rapid deactivation of the catalyst is observed.

The object of the invention according to U.S. Pat. No. 2,301,964 is the non-catalysed reaction of 6-aminocapronitrile in aqueous solution to caprolactam at 285 ° C. yields are below 80%.

FR-A 2 029 540 discloses a process for cyclizing 6-aminocapronitrile to caprolactam using homogeneous metal catalysts consisting of a group of zinc and copper in an aqueous solution, whereby the caprolactam is obtained in a yield of up to 83%. However, the complete separation of the catalysts from the valuable caprolactam product presents difficulties because caprolactam forms complexes with the metals used.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a process for the production of cyclic lactams by reacting aminocarboxylic acid nitriles with water, which does not have the above drawbacks.

SUMMARY OF THE INVENTION

The process for preparing cyclic lactams by reacting aminocarboxylic acid nitriles with water, in the presence of a catalyst, according to the invention comprises carrying out the reaction in the liquid phase in the presence of heterogeneous titanium dioxide catalysts having a rutile content of 0.1 to 95% by weight. and having an anatase content of 99.9 to 5% by weight, based on the total titanium dioxide content.

Preferably, the reaction is carried out at a temperature of 140 to 320 ° C using aminocarboxylic acid nitriles of the general formula

H ₂ N - (CH ₂ ) _m - C = N wherein the m index is 3, 4, 5 or 6, especially 6-aminocarponic acid nitrile. Preferably, 1 to 50 wt. of a solution of the aminocarboxylic acid in water or in a mixture of water and an organic solvent.

Aminocarboxylic acid nitriles, preferably of the general formula I, are used as starting materials in the process according to the invention.

<-1 P $ - 1_ c <2 R ² ch ₂

(I) wherein n and m are in each case 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 and the sum of n + m is at least 3, preferably at least 4.

The symbols R ¹ and R ² substituents can be of any kind, while ensuring that the desired reaction is the cyclic substituents affected. Preferably, R ^{@ 1} and R @ ² independently of one another are alkyl of 1 to 6 carbon atoms, cycloalkyl of 5 to 7 carbon atoms, or aryl of 6 to 12 carbon atoms.

Particularly preferred starting compounds are aminocarboxylic acid nitriles of the general formula

H ₂ N - (CH ₂ ) _m - C n where m has a value of 3, 4, 5 or 6, in particular 5. For m = 5, the starting compound is 6-aminocaproic acid nitrile.

The process according to the invention reacts the above-described aminocarboxylic acid nitriles with water in the liquid phase, using heterogeneous catalysts to obtain cyclic lactams. The use of aminocarboxylic acid nitriles of the formula I gives the corresponding cyclic lactams of the formula II

H wherein n, m, R ¹ and R ² are as defined above. Particularly preferred are the lactams of formula II, wherein n is zero and m is 4, 5 or 6, especially 5 (in the latter case caprolactam is obtained).

The reaction is carried out in the liquid phase at temperatures generally 140 to 320 ° C, preferably 160 to 280 ° C; the pressure is generally 0.1 to 25 MPa, preferably 0.5 to 15 MPa, while keeping the reaction mixture liquid under the conditions used, i.e. without the solid-phase catalyst. The residence times are generally 1 to 120, preferably 1 to 90, and most preferably 1 to 60 minutes. In some cases, a residence time of 1 to 10 minutes has been found to be quite sufficient.

In general, at least 0.01 mol, preferably 0.1 to 20 mol and in particular 1 to 5 mol of water are used per mole of aminocarboxylic acid nitrile.

Preferably, aminocarboxylic acid nitrile is used in the form of 1 to 50 wt%, preferably 5 to 50 wt%. % and most preferably 5 to 30 wt. aqueous solution (where water is also the reaction partner) or in water / solvent solution mixtures. Solvents include, for example, alkanols such as methanol, ethanol, n-propanol and isopropanol, n-butanol, isobutanol, tert-butanol and polyols such as diethylene glycol and tetraethylene glycol, hydrocarbons such as petroleum ether, benzene, toluene, xylene, lactams such as pyrrolidone or caprolactam or alkyl-substituted lactams such as N-methylpyrrolidone, N-methylcaprolactam or N-ethylcaprolactam as well as esters of a carboxylic acid, preferably a C 1 -C 8 carboxylic acid. Ammonia may also be present in the reaction mixture. Of course, mixtures of organic solvents may also be used. Mixtures of water and alkanols in a water / alkanol ratio of 1 to 75, 25 to 99, preferably 1 to 50 to 50 to 99, have proven to be particularly advantageous in individual cases.

The process according to the invention is carried out in the presence of titanium dioxide catalysts having a rutile content of 0.1 to 95% by weight, preferably 1 to 90% by weight. and with an anatase content of 99.9 to 5% by weight, preferably 99 to 10% by weight, in each case based on the total titanium dioxide content.

According to a preferred embodiment, the reaction is carried out in a fixed bed, wherein the catalysts are in the form of rods or tablets, preferably the tablets and rods have a diameter of 1 to 10 mm.

For the preparation of bars and tablets which can be produced by conventional methods, titanium dioxide powder which already has the desired content of anatase and rutile is used, or is prepared by pyrolysis based on a pure modification of anatase or a mixture containing anatase and rutile phase or a mixture of pure anatase and rutile phases, or a mixture of anatase and rutile modifications, by pyrolyzing at a corresponding temperature and residence time (as known to those skilled in the art, for example, from Catalysis Today 14: 225-242, 1992) until the desired ratio of anatase to rutile is achieved.

Corresponding powders are commercially available, for example titanium dioxide powder P25 ^R (20 to 30% by weight rutile and 80 to 70% by weight anatase) from Degusa or S150 ^R and S140 ^R (each containing 100% anatase) from Finti- Kemira.

Titanium dioxide can be used as such or as a supported catalyst, and can be applied to a mechanically and chemically stable support, usually with a large surface area.

The titanium dioxide can be produced by precipitation from an aqueous solution, for example after a sulphation process or other process such as pyrogenic production of fine titanium dioxide powders, which are commercially available.

Alternatively, titanium dioxide containing anatase and rutile may be mixed with other oxides such as alumina, zirconia and cerium oxide. Various methods can be used to produce the compositions. The oxides or precursors thereof that are convertible into oxides by calcination can be prepared, for example, by co-precipitation from solutions. In general, a very good distribution of the two oxides used is achieved. The oxides or precursors thereof may be precipitated by precipitation of one oxide or precursor in the presence of a suspension of finely divided particles of the other oxide or precursor. Another method consists in mechanically mixing the oxide powder or the precursor product, which mixture can be used as a starting material for the manufacture of bars or tablets.

The supported catalysts can be produced in various ways. For example, titanium dioxide can be applied in the form of a sol by simply impregnating it onto a carrier. Drying and calcining remove the volatile components of the sol in the usual manner. Such soles are commercially available for titanium dioxide.

Another possibility of deposition of active titanium dioxide layers is the hydrolysis or pyrolysis of organic or inorganic compounds. Titanium dioxide can be coated in a thin layer, for example, with a ceramic carrier by hydrolysis of titanium isopropyl or other titanium alkoxides. Another preferred compound is titanium tetrachloride. Suitable carriers are powders, sticks or tablets of titanium dioxide alone or other stable oxides such as silica. The carriers used may be macroporous to facilitate transport. It is important that the pyrolysis of titanium dioxide ensures that both the rutile and anatase phases are formed in the proportions indicated.

The process according to the invention yields cyclic lactams, in particular caprolactam in high yield, with good selectivity and good stability of the catalytic action.

The following examples illustrate the invention without limiting it in any way. Percentages are by weight unless otherwise indicated.

DETAILED DESCRIPTION OF THE INVENTION

Examples 1 to 7

To a heated 25 ml tube reactor (6 mm diameter, 800 mm length) filled with titanium dioxide in the form of tablets or rods, a solution of 6-aminocapronitrile (ACN) in water and ethanol in the weight ratios indicated above is introduced at 10 MPa. in the table. The product stream leaving the reactor is analyzed by gas chromatography. The results are shown in the table.

table

At- EXAMPLE Kata- Shape and catalysts Content> sulphate [%] Rútil Anatas BET [n ² / g] A U WITH [%] [%] 1 P25 3 mm chopsticks 0.01 93 7 15 92 95 97 2 P25 / DT51 ¹ 3 mm rods 0.5 18 82 41 90 98 93 3 P25 / S150 ² 3 mm sticks 0.06 16 84 50 89 97 92 4 P25 1.5 mm N.B. 20 80 48. 91 99 93

chopsticks

For comparison

5 VKR611 ^R3 1.5 mm sticks N.B. 100 0 5 5 10 53 6 DT51 3 mm sticks N.B. 0 100 36 78 90 85 7 S150 3 mm sticks 1.17 0 100 108 90 99 91

¹ 2/3 parts by weight of P25 ^R powder, remainder DR51 ^R (Rhône-Poulenc) ² 2/3 parts by weight of P25 ^R powder, remainder S150 ^R (Finti-Kemira) o

Rushed from the firm. Sachtleben processed 2 h at 97 ° C

N.B. = not determined

A = Yield; S = selectivity; U = decomposition

BET = BET surface according to DIN 66 131

Industrial usability

Preparation of cyclic lactams, especially caprolactam with high yields with good selectivity and good catalyst stability.

Claims (5)

PATENT CLAIMS Process for preparing cyclic lactams by reacting aminocarboxylic acid nitriles with water in the presence of a catalyst, characterized in that the reaction is carried out in the liquid phase in the presence of heterogeneous titanium dioxide catalysts having a rutile content of 0.1 to 95% by weight. and having an anatase content of 99.9 to 5% by weight, based on the total titanium dioxide content. Process according to claim 1, characterized in that the reaction is carried out at a temperature of 140 to 320 ° C. Process according to claims 1 and 2, characterized in that aminocarboxylic acid nitriles of the general formula (I) are used. H ₂ N - (CH ₂ ) _m - C = N where m is 3, 4, 5 or 6. Process according to Claim 3, characterized in that the aminocarboxylic acid nitrile used is 6-aminocapronitrile. Process according to claims 1 to 4, characterized in that 1 to 50 wt. solution of aminocarboxylic acid nitrile in water or in a mixture of water and an organic solvent.