KR19990014859A - Liquid Cyclization by Titanium Dioxide Catalyst of 6-Aminocapronitrile to Caprolactam - Google Patents

Abstract

Based on the total amount of titanium dioxide, aminocarbonitrile in the liquid phase in the presence of a titanium dioxide based heterogeneous catalyst having a rutile content in the range of 0.1 wt% to 95 wt% and an anateate in the range of 99.9 wt% to 5 wt% A method for producing a cyclic lactam by reacting with water is disclosed.

Description

Liquid phase cyclization by titanium dioxide catalyst of 6-aminocapronitrile to caprolactam.

The present invention relates to a novel process for preparing cyclic lactams by reacting amino carbonitrile with water in the presence of a catalyst.

US-A 4 628 085 discloses a gas phase reaction of 6-aminocapronitrile with water on an acidic silica gel at 300 ° C. This reaction occurs quantitatively with an initial selectivity of 95% for caprolactam, but the productivity and selectivity are drastically reduced. A similar process in which a very dilute gas stream comprising 6-aminocapronitrile, adiponitrile, ammonia, water and carrier gas passes through silica gel and a copper / chromium / barium-titanium oxide catalyst layer is described in US-A No. 4 625 023. Caprolactam is obtained with a selectivity of 91% with a conversion of 85%. It is once again observed that the activity of the catalyst is drastically reduced.

US-A 2 301 964 relates to the noncatalytic conversion of 6-aminocapronitrile to caprolactam in an aqueous solution at 285 ° C. The yield is less than 80%.

FR-A 2 029 540 describes a process for cyclizing 6-aminocapronitrile to caprolactam in yields of up to 83% using homogeneous metal catalysts from the zinc and copper groups in liquid solutions. However, the complete removal of the catalyst from the required product caprolactam is problematic because caprolactam forms complexes with the metal used.

It is an object of the present invention to provide a process for preparing cyclic lactams by reacting amino carbonnitrile with water, which does not involve the above mentioned disadvantages.

The inventors have found that this object is based on the total amount of titanium dioxide, respectively, in the presence of a titanium dioxide based heterogeneous catalyst having a rutile content in the range of 0.1 wt% to 95 wt% and an anate content in the range of 99.9 wt% to 5 wt%. It was finally discovered that this was achieved by carrying out the reaction in the liquid phase.

Preferred embodiments of the method according to the invention are apparent from the dependent claims of the claims.

The starting material used in the process according to the invention is an amino carbonitrile, preferably a compound of formula (I).

Wherein n and m may each have a value of 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9, and the sum of n + m is 3 or more, preferably 4 or more.

R ¹ and R ² may in principle be any type of substituent, provided that it is ensured that the required cyclization reaction is not affected by substituents. R ¹ and R ² are preferably independently of each other a C ₁ -C ₆ -alkyl or C ₅ -C ₇ -cycloalkyl group or C ₆ -C ₁₂ -aryl group.

Particularly preferred starting compounds are amino carbonnitriles of the formula:

H ₂ N- (CH ₂ ) _m -C≡N

Wherein m has a value of 3, 4, 5 or 6, in particular 5. If m = 5, the starting compound is 6-aminocapronitrile.

In the process according to the invention, the amino carbonnitrile described above is reacted with water in the liquid phase using a heterogeneous catalyst to give cyclic lactams. By using amino carbonitriles of formula (I), the corresponding cyclic lactams of formula (II) are produced.

In formula, n, m, R <^1> and R <^2> have the meaning mentioned above. Particularly preferred lactams are compounds wherein n is 0 and m is 4, 5 or 6, in particular 5, in which case caprolactam is produced.

The reaction is generally carried out in the liquid phase at a temperature of 140 ° C. to 320 ° C., preferably 160 ° C. to 280 ° C., and generally in the range of 1 bar to 250 bar, preferably 5 bar to 150 bar, and the reaction mixture is Attention is drawn to the absence of a catalyst which is predominantly liquid, i. The residence time is generally in the range of 1 to 120 minutes, preferably 1 to 90 minutes, in particular 1 to 60 minutes. In some cases, residence times of 1 to 10 minutes have proven very appropriate.

In general, at least 0.01 mol, preferably 0.1 mol to 20 mol, in particular 1 mol to 5 mol, of water is used per mol of amino carbonitrile.

The amino carbonitrile is prepared from 1 wt% to 50 wt%, especially from 5 wt% to 50 wt%, particularly preferably from 5 wt% to 30 wt%, of an aqueous solution (in this case the solvent is also a reactant) or of a water / solvent mixture. It is advantageously used in the form. Examples of the solvent include methanol, ethanol, alkanols such as n- and i-propanol, n-, i- and t-butanol, polyols such as diethylene glycol and tetraethylene glycol, petroleum ether, benzene, toluene and xylene and Hydrocarbons such as, lactams such as pyrrolidone or caprolactam, or alkyl substituted lactams such as N-methylpyrrolidone, N-methylcaprolactam or N-ethylcaprolactam, and capric acid esters, preferably Is a carboxylic acid having 1 to 8 carbon atoms. Ammonia may also be present in the reaction. It is of course also possible to use mixtures of organic solvents. Mixtures of water and alkanols in water / alkanol ratios of 1/75 wt% to 25/99 wt%, preferably 1/50 wt% to 50/99 wt% have been found to be particularly advantageous in some cases.

The process according to the invention generally comprises a rutile content of from 0.1 wt% to 95 wt%, preferably from 1 wt% to 90 wt% and 99.9 wt% to 5 wt%, preferably based on the total amount of titanium dioxide, respectively. Is carried out in the presence of a titanium dioxide catalyst having an anate content of 99 wt% to 10 wt%.

In a preferred embodiment, the reaction is carried out in a fixed bed using a catalyst in the form of tablets or extrudates, preferably 1 mm to 10 mm in diameter.

The extrudate and tablet forms already have the required content of anatees and rutiles, or from mixed forms containing pure anatees or an anate and rutile phase, from mixtures of pure anatees and rutiles Starting and pyrolysis during the appropriate temperature and residence time (both known to the person skilled in the art, for example, described in Catalysis Today 14 (1992) 225-242) for the required ratio of anate to rutile to be reached. It can be produced by a conventional method using a titanium dioxide powder obtained by.

Corresponding powders such as titanium dioxide powder P25 (registered) from Degussa (20 wt% to 30 wt% rutile and 80 wt% to 70 wt% Anatate) and Pinty-Kemira S150® and S140® (100 wt% of anatease each) from Finti-Kemira are commercially available.

Titanium dioxide generally has a large surface area and can be used on its own or as a supported catalyst that can be applied to a mechanical or chemically stable support.

Titanium dioxide can be prepared by precipitation from an aqueous solution, for example, by other methods such as the sulfate process or the exothermic method of commercially available fine titanium dioxide powder.

If necessary, titanium dioxide containing rutile / anatate may be mixed with other oxides such as aluminum oxide, zirconium oxide or cerium oxide. Various methods are available for preparing mixtures of various oxides. Oxides or their precursor compounds which can be converted to oxides by firing can be prepared, for example, by precipitation together from solution. This results in a very good dispersion of the two commonly used oxides. Precipitation of the oxide or precursor mixture may also occur by precipitating one oxide or precursor in the presence of a second oxide or precursor in the form of a suspension of finely dispersed particles. Another method involves mechanically mixing the oxide or precursor powder, in which case the mixture can be used as starting material for producing the extrudate or tablet.

Various methods are available for preparing supported catalysts. Thus, titanium dioxide can be applied to the support in the form of a sol by simple impregnation. Drying and firing generally remove the volatile components of the sol from the catalyst. This type of titanium dioxide sol is commercially available.

Another possibility for applying an active titanium dioxide layer includes hydrolysis or pyrolysis of organic or inorganic compounds. Thus, the ceramic support can be coated with titanium dioxide in a thin layer by hydrolyzing titanium isopropylate or other Ti alkoxides. Another stable compound is TiCl ₄ . Suitable supports are powders, extrudates or tablets of titanium dioxide per se or other stable oxides such as silicon dioxide. The support used can be designed to be macroporous to improve mass transfer. It is important to note that during the pyrolysis of titanium dioxide both rutile and anate phase are in this range.

The process according to the invention produces cyclic lactams, in particular caprolactam, with good selectivity, homeostasis of catalytic activity and high yields.

<Examples 1 to 7>

6-aminocapronitrile (ACN) in water and ethanol, in the weight ratios set forth in the table below, in a 25 mL capacity heated tubular reactor (diameter: 6 mm, length: 800 mm) filled with titanium dioxide in the form of tablets or extrudates. ) Was passed under a pressure of 100 bar. The product stream exiting the reactor was analyzed by gas chromatography. The results are likewise shown in the table.

Example catalyst shape Sulfate Content (%) Rutile (%) Anatate (%) BET (㎡ / g) Y C S One P25 3 mm extrudates 0.01 93 7 15 92 95 97 2 P25 / DT51 ¹ 3 mm extrudates 0.5 18 82 41 90 98 93 3 P25 / S150 ² 3 mm extrudates 0.06 16 84 50 89 97 92 4 P25 1.5 mm extrudates n.d. 20 80 48 91 99 93 Comparative example 5 VKR611 (registered trademark) ³ 1.5 mm extrudates n.d. 100 0 5 5 10 53 6 DT51 3 mm extrudates n.d. 0 100 36 78 90 85 7 S150 3 mm extrudates 0.17 0 100 108 90 99 91 ^A mixture (Rhone-Poulenc) in which 1 P25® powder is 2/3 parts by weight and the remainder is DT51®. ^{2 A} mixture of P25® powder, 2/3 parts by weight, the remainder being S150® (Finti-Kemira). ³ Rutile from Sachtleben heat treated at 875 ° C. for 2 hours. n.d. = Not measurable. Y = yield; S = selectivity; C = conversion rate. BET = BET surface area by the DIN 66 131 method.

Claims (5)

Amino carbonitrile in the liquid phase in the presence of a titanium dioxide based heterogeneous catalyst having a rutile content in the range of 0.1 wt% to 95 wt% and an anatease in the range of 99.9 wt% to 5 wt%, respectively, based on the total amount of titanium dioxide Reacting with water to produce cyclic lactam. The process of claim 1 wherein the reaction is carried out at a temperature in the range from 140 ° C. to 320 ° C. 3. The process according to claim 1 or 2, wherein amino carbonnitrile of the formula is used. H ₂ N- (CH ₂ ) _m -C≡N Wherein m is 3, 4, 5 or 6. 4. The process of claim 3, wherein 6-aminocapronitrile is used as amino carbonitrile. The process according to claim 1, wherein 1 wt% to 50 wt% of an amino carbonitrile solution in water or a water / organic solvent mixture is used.