Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2002-10-17
2004-09-14
Davis, Brian (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S413000, C564S415000, C564S448000, C564S487000, C564S492000, C564S493000, C502S325000
Reexamination Certificate
active
06790996
ABSTRACT:
The invention relates to a process for preparing primary amines by hydrogenating nitrites in the presence of a supported catalyst comprising cobalt and optionally, in addition, nickel. The invention further relates to the use of this catalyst in a process for preparing primary amines by hydrogenating nitrites.
The hydrogenation of nitrites provides, depending on the reaction conditions and the catalyst used, primary, secondary or tertiary amines, although in general, a mixture of all three amine types is obtained. In the past, intensive research was carried out toward controlling selective hydrogenation to give one type of amine. The removal of secondary and tertiary amines from, for example, the desired primary amines requires additional apparatus and additional energy. It was found that improved selectivity to give primary amines may be achieved by adding ammonia to the reaction mixture. The hydrogenation of dinitriles suffers from the problem of condensation reactions which lead to cyclic products or oligomers.
Selectivity of nitrile hydrogenation is also influenced by the nature of the catalyst. The nature of the catalyst also influences the temperature necessary for the hydrogenation of the nitrites. For instance, in particular in the case of nitrites which are unstable under severe conditions such as high temperatures or in the case of hydrogenation of nitrites where, for example, a certain isomeric ratio is desired, hydrogenation at very low temperatures under protective conditions is desirable. According to the prior art, the most suitable catalysts for hydrogenating nitrites at very low temperatures and with high selectivity are Raney nickel and Raney cobalt.
For instance, U.S. Pat. No. 4,721,811 relates to a continuous process for preparing linear polyamines by hydrogenating polynitriles. The catalyst used is granular Raney cobalt which is obtainable by leaching of corresponding nuggets of the alloy.
U.S. Pat. No. 5,869,653 also relates to a process for catalytically hydrogenating nitrites. The catalyst used is a Raney cobalt catalyst and the hydrogenation takes place in the presence of catalytic quantities of lithium hydroxide and water.
However, the use of Raney catalysts and the preparation thereof brings disadvantages. For instance, Raney catalysts are pyrophoric, so they may only be transported, stored and introduced into the reactors under liquid or with the exclusion of air. The preparation of Raney catalysts is also very complicated, since a starting alloy first has to be prepared by melting, which then has to be leached using considerable quantities of concentrated bases. Afterwards, washing with water results in strongly basic waste water which, for ecological reasons, has to be worked up in a complicated manner or disposed of.
Accordingly, there is a great interest in replacing the Raney catalysts by other, less problematically handled catalysts.
A possibility is the use of supported catalysts. However, according to the prior art, these generally have low selectivities. However, supported catalysts are also known for which selectivity improvement by doping or by the use of cocatalysts is suggested.
For instance, EP-A 0 566 197 relates to a process for preparing primary amines by hydrogenating mono- and/or dinitriles using hydrogen in the presence of nickel and/or cobalt catalysts on a support material, preferably in combination with at least one solid cocatalyst which is insoluble in the reacton medium and the catalyst and/or cocatalyst are substantially nonacid. According to the examples, it was found that the addition of alkali metals or of alkaline earth metals results in a selectivity increase at an only slightly reduced activity. However, these reactions take place at 130 or 140° C., i.e. under conditions which are unsuitable for thermally labile nitrites.
The use of a cocatalyst leads to increased complication, in particular when alkali metals or alkaline earth metals are used.
EP-A 0 424 738 relates to a process for preparing linear triamino compounds by reacting 1,3,6-tricyanohexane over a catalyst comprising cobalt oxide and also an oxide of alkali metals, alkaline earth metals, rare earths or scandium or yttrium. The catalyst may be unsupported or supported. The catalyst has insufficient activity which is noticeable by low space-time yields and the severe hydrogenation conditions (in particular, pressure of 300 bar).
DE-A 1 518 118 relates to a process for hydrogenating nitrites which employs cobalt catalysts comprising magnesium oxide. These may be unsupported or supported catalysts. According to Example 1 of DE-A 1 518 118, the active catalysts used are those in which 55% of the cobalt is present as cobalt metal. According to the examples, hydrogenation is carried out at temperatures of from 100 to 140° C. Accordingly, this process is likewise unsuitable for hydrogenating thermally labile nitrites.
WO 97/10052 relates to a process for hydrogenating nitrites which employs hydrogenation catalysts comprising at least one divalent metal in partially reduced form (preferably Ni or Co) and at least one doping metal selected from the group consisting of Cr, Mo, Fe, Mn, Ti, V, Ga, In, Bi and rare earths in oxidic form. WO 97/10052 also relates to the catalysts themselves. The catalysts disclosed by WO 97/10052 are unsupported catalysts which consist predominantly of the active metal and are accordingly very expensive.
It is an object of the present invention to provide a process for preparing primary amines by hydrogenating nitrites which employs catalysts which are easy to handle and provide better value for money than unsupported catalysts, have high activities and selectivities for hydrogenating nitrites and are usable either as a powder in a suspension process or else as a shaped article in a fixed bed process. These catalysts shall also have high activity and selectivity toward primary amines even at low temperatures, so that the process is suitable for hydrogenating thermally labile nitrites.
We have found that this object is achieved by a process for preparing primary amines by hydrogenating nitrites in the presence of a catalyst comprising cobalt and optionally, in addition, nickel and also at least one further doping metal on a particulate support material.
The process according to the invention is characterized by the cobalt and, if present, the nickel having an average particle size of from 3 to 30 nm (nanometers) in the active catalyst.
Preference is given to the average particle size in the active catalyst being from 3 to 20 nm, more preferably from 3 to 15 nm, most preferably from 3 to 10 nm. The average particle size was determined by X-ray diffraction (Siemens D5000 diffractometer, TOPAS evaluation software). This catalyst used according to the invention has high activities owing to its large active surface area and small crystals and is notable for its long lifetime. To achieve the high activities, even small quantities of the catalytically active species are sufficient which allows inexpensive catalysts to be obtained.
The catalysts used according to the invention are prepared by a process comprising the following steps:
a) coprecipitation of cobalt and optionally, in addition, nickel and also at least one further doping metal from a solution comprising the corresponding salts of the metals mentioned onto a particulate support material,
b) subsequent drying and/or calcining,
c) optionally, molding, and
d) reduction.
a) Coprecipitation of Cobalt and, if Present, Nickel and also at Least One Further Doping Metal
The catalysts used according to the invention are prepared by coprecipitation (mixed precipitation, coprecipitation) of their components onto a particulate support material. To this end, an aqueous salt solution comprising the catalyst components is generally admixed with stirring and heating at temperatures of from 20 to 100° C., preferably from 40 to 80° C., with an aqueous mineral base, preferably an alkali metal base, for example, sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide or ammonium carbo
Ansmann Andreas
Benisch Christoph
BASF - Aktiengesellschaft
Davis Brian
Keil & Weinkauf
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