HYDROGENATION CATALYST

Abstract: The invention provides a metal (Z = 27-29)/alumina catalyst with an atomic ratio of active metal to aluminium between l2 and l.5, having an active metal content of at least 75% in the activated catalyst, an active metal surface area between 60 and l50 m²/g of metal, characterized in that the soyabean selectivity is below 2%, preferably below l% The invention also provides a process for the preparation of these catalysts and a method for the hydrogeneration of saturated organic compounds using the catalyst.

Description: The invention relates to a metal/alumina catalyst in which the active metal has an atomic number (Z) between 27 and 29, to a process for the preparation of the catalyst and to a process for the hydrogenation of unsaturated compounds, in particular fatty compounds using such a catalyst. Such metal/alumina catalysts are known in the art and they can be prepared by various processes. Two main processes involve: l) Impregnation with a metal salt solution of existing (sometimes pre-shaped) alumina material, followed by drying, calcination and reduction. One example of such a process is EP-A- 92 878 (Unilever). 2) Precipitation from a solution of metal hydroxy carbonate and alumina hydrate or metal aluminium hydroxy carbonate using an alkaline precipitating agent. Often co-precipitation of the active metal and aluminium is effected, as described in US-A- 4 307 248 (Barnett), and sometimes sequential precipitation is disclosed as e.g. EP-A- l68 09l (Unilever). Subsequently the precipitate is filtered, washed, dried, optionally calcined and activated (reduced). The physical properties and catalytic characteristics of the catalyst are dependent on the preparative route and on drying, calcining and activation. There are, of course, certain relations between physical constants like porosity, BET surface area, degree of reduction to active metal, degree of metal dispersion, etc. and catalytic performance like selectivity, activity, lifetime of the catalyst, etc. For catalysts used for the hydrogenation of organic material, in particular of fatty compounds such as unsaturated triglycerides, the selectivity is very important, as the formation of fully saturated triglycerides has been recognized as undesirable because this may cause crystal formation ("sandiness") in products like edible emulsions, e.g. margarine and and low-fat spreads. The selectivity of the catalyst is here expressed as the percentage of solid fat at 30°C in a soyabean oil hydrogenated to an iodine value (I.V.) of 90, which is more fully described below. The present invention provides a selective metal (Z= 27-29)/alumina catalyst with an atomic ratio of active metal to aluminium between l2 and l.5, preferably between l0 and 3, an active metal surface area between 60 and l50 m²/g of nickel and between l and 20 m²/g for copper and/or cobalt, which catalyst has a selectivity below 2% (percentage of solid phase at 30°C obtained after hydrogenating a standard soyabean oil with an I.V. of l30 to an I.V. of 90 under conditions described below). In a preferred embodiment, the selectivity of the catalyst is even below l%. Also the catalysts according to the present invention usually have a BET total surface area between 90 and 450 m²/g and an average pore radius between 2 and 20, preferably between 4 and l5 nanometers. The present invention further provides a convenient method for the preparation of a hydrogenation catalyst which comprises alumina and an active metal (M) having an atomic number (Z) from 27 to 29, characterized in that an ammoniacal metal ion solution is combined with an aqueous solution of an aluminium compound, that ammonia is removed by keeping it at, or near, the boiling point for 20 to l80 minutes, thereby precipitating inter alia M₆Al₂(OH)₁₆CO₃.4H2O. The precipitate is collected, dried and reduced with hydrogen. Suitable aluminium compounds are alkali aluminate and other aluminium salts. Suitable metal (M) compounds for preparing the ammoniacal metal solution are e.g. carbonates etc. Although the invention provides hydrogenation catalysts and a method for the preparation thereof, in which the active metal is cobalt (Z = 27), nickel (Z = 28) or copper (Z = 29), it is preferred to have cobalt and/or nickel as the active metal, and nickel is more preferred. When preparing the catalyst, it is preferred to combine the ammoniacal metal ion solution and the aluminium salt solution at temperatures between l0 and 85°C in order to avoid premature precipitation of aluminium ions. For optimum results it is recommended that an aluminium salt solution is added to an ammoniacal metal ion solution, the solutions being at a temperature between l5 and 50°C. This usually results in a combined solution of the two ingredients from which ammonia is removed by boiling and a precipitate predominantly containing M₆Al₂(OH)₁₆CO₃.4H₂O (depending on the M/Al atomic ratio) is formed. Also metal (M) hydroxy carbonate can be precipitated, especially at high M/Al atomic ratios. The precipitation can be effected under various conditions. Thus, the precipitation temperature of the suspension is generally between 60° and l00°C, preferably between 75° and l00°C. During the precipitation the suspension generally has a pH value between ll.5 and 9.5. The pH value drops during the heating because the ammonium complex slowly decomposes and ammonia is removed. This precipitation by heating usually takes from l5 minutes to 24 hours, preferably l to 8 hours. Further, the precipitation often takes place in concentrations such that the final precipitate contains the active metal (M) in weight percentages between 30 and 60, preferably between 35 and 50. In order to increase resistance of the catalyst to poisoning, (particularly with sulphur and/or carbon), it is often advantageous to incorporate in the catalyst a small amount of another metal (compound) as promotor which often also facilitates activation (lower activation temperature). Suitable promotors contain particularly the elements molybdenum, lanthanum, barium, calcium, copper, (for nickel), potassium and their compounds. The promotor can be incorporated in the starting solution from which it is precipitated but the promotor can also be incorporated in the catalyst by spraying or impregnation. Generally the promotor is present in an amount ranging from between 0.2 and l4% (based on the total catalyst). After the precipitation of the catalyst precursor, the precipitate is generally separated by filtration, and, at choice, the cake is subsequently washed and dried. The catalyst precursor is usually washed with water, but sometimes it is advantageous to use organic solvents or surfactant solutions. Drying can be effected by oven-drying or spray-drying. It was noted that most of the catalysts were not substantially affected as to activity and selectivity by the drying conditions. Sometimes impregnation with an aqueous solution of a promotor compound is carried out subsequently. Optionally, drying and grinding to a powder of the proper particle size is carried out, followed, again optionally, by calcining at a temperature of 250-500°C. Thereafter, the catalyst precursor is activated (= reduced) with hydrogen at a temperature between 250 and 600°C, preferably between 350 and 500°C, and this activation is carried out at (super)atmospheric pressure. The catalysts according to the present invention contain the active metal, which is distributed over the internal and external surface of the alumina support which is formed during calcination and activation of the catalyst precursor. In another embodiment, the present invention provides a method for the hydrogenation, particularly of unsaturated fatty materials, such as fatty acids, their esters, in particular glycerides and fatty nitriles, at temperatures of l00-230°C and pressures of 0.l-0.6 Mpa, for fatty nitriles up to 5 MPa. The nickel-containing catalyst is especially useful in the hydrogenation of polyunsaturated triglycerides such as fish oil, soyabean oil, sunflower oil and the like, and leads to the formation of only minor quantities of fully saturated triglycerides. Such hydrogenated oils with an iodine value of e.g. 88-92 combined with a low solid fat content at 30°C (below l.0%) are novel, valuable ingredients for the manufacture of oleaginous foodstuffs because they do not cause sandiness (small crystals of solid fats). The cobalt (Z = 27) catalyst according to the present invention is especially useful in the hydrogenation of fatty nitrile to fatty amine, wherein high yields of primary amine are obtainable. The copper (Z = 29) catalyst according to the present invention is a selective hydrogenation catalyst. The invention is illustrated by the following examples: Examples l-2 To l litre ammoniacal nickel solution (Ni:NH₃ = l:9 molar ratio) containing 2.2% of nickel, a 500 ml sodium aluminate solution was added dropwise at 25°C in a period of 50 minutes. The aluminium concentration in the sodium aluminate solution was varied in the examples l-2 so as to give an Ni/Al atomic ratio of 5.3 and 3.2, respectively, in the reaction mixture and in the final precipitate. After complete addition of the sodium aluminate solution, the mixture of the two solutions was heated to the boil (l00°C) in a period of 40 minutes while stirring. At this temperature the ammoniacal nickel complex decomposed, ammonia removed and nickel precipitated. The precipitation of nickel was completed in 80 minutes, after which the reaction vessel was closed and the mixture was kept at the boil for 60 minutes at pH = l0.0. Then the precipitate was filtered off using a Büchner funnel. One part of the precipitate was dried in a spray drier at 220-l40°C, while another part was dried in an oven at l20°C. The dried precipitates were activated by reduction in a 0.l MPa hydrogen atmosphere at 450°C. The performance of the resulting catalysts was determined using various methods: l) The activity was determined in the hydrogenation of fish oil at l80°C and 0.l MPa H₂ pressure. The activity was expressed relative to the activity of a standard catalyst (A f = l00%). This method is disclosed in detail in EP-A- 0 l68 09l (Unilever), page 8, lines l5-24. 2) The selectivity was determined in the hydrogenation of a standard soyabean oil (I.V. = l30) at l00°C, 0.l MPa H₂ pressure and 0.l% Ni. The hydrogenation was continued until the resulting oil had an iodine value of 90. The percentage of solid fats present in the hydrogenated oil at 30°C (N₃₀) is taken as a yardstick for the selectivity of the catalyst. Consequently a low percentage of solid fat at 30°C is indicative for highly selective catalyst. The time required to hydrogenate the soyabean oil to an I.V. of 90 was also taken as a measure for the activity. 3) The oil filtration properties of the catalyst were determined after a hydrogenation of fish oil. The time required to filter l50 grams of oil from the catalyst-oil suspension expressed as minutes per grams of oil was taken as a yardstick for the oil filtration properties This method is disclosed in detail in EP-A- 0 l68 09l(Unilever), page 8, line 34, page 9, line l9. The results are given in Table l. Examples 3-5 A l-litre ammoniacal nickel solution (Ni:NH₃ = l:9 molar ratio) containing 2.2.% of nickel was heated to the boil in 40 minutes. At the boiling temperature, the ammoniacal nickel complex decomposed, ammonia removed and nickel compound precipitated. The precipitation was completed in 60 minutes. During this period 500 ml of a sodium aluminate solution were added to the boiling reaction mixture. The aluminium concentration in the sodium aluminate solution was varied in the Examples 3-­ 5, so as to give an Ni/Al atomic ratio of l0, 5.6 and 3.7, respectively, in the reaction mixture and in the final precipitate. After the nickel precipitation and the addition of the sodium aluminate solution were completed, the reaction vessel was closed and the mixture was kept at the boil for 60 minutes at pH = l0.0. Then the precipitate was filtered off on a Büchner funnel. One part of the precipitate was dried in a spray drier at 220-l40°C while another part was dried in an oven at l20°C. The dried green cakes were activated by reduction in a 0.l MPa hydrogen atmosphere at 450°C. The performance of the resulting catalysts was determined by methods as given above (Examples l-2). The results are given in Table 2.

Claims: 1. A metal (Z = 27-29)/alumina catalyst with an atomic ratio of active metal (M) to aluminium between l2 and l.5, an active metal surface area between 60 and l50 m²/g of active nickel and between l and 20 m²/g for copper and/or cobalt, characterized in that the selectivity as defined above is below 2%. 2. A catalyst according to claim l, characterized in that the BET-total surface area is between 90 and 450 m²/g of catalyst and that the average pore radius is between 2 and 20. 3. Process for the preparation of a hydrogenation catalyst which comprises alumina and an active metal (M) having an atomic number (Z) from 27 to 29, characterized in that an ammoniacal metal ion solution is combined with an aqueous solution of an aluminium compound, that ammonia is removed by keeping at or near the boiling point for 20 to l80 minutes, thereby precipitating i.a. M₆Al₂(OH)₁₆CO₃.4H₂O, which precipitate is collected, dried and reduced with hydrogen. 4. Process according to claim 2, characterized in that the average pore radius is between 4 and l5 nanometers. 5. process according to claim l or 2, characterized in that the active metal (M) has an atomic number of 28 (nickel). 6. Process according to any of the claims 3-5, characterized in that the ammoniacal solution and the aluminium salt solution are combined at temperatures between l0 and 85°C. 7. Process according to claim 6, characterized in that to an ammoniacal metal ion solution an aluminium salt solution is added, the solutions being at a temperature between l5 and 50°C. 8. Process for the catalytic hydrogenation of unsaturated fatty compounds, characterized in that a catalyst according to claim l or 2 is used. 9. Process according to claim 8, characterized in that polyunsaturated triglyceride oils are hydrogenated. l0. A hydrogenated oil having an iodine value between 88 and 92 and a solid fat content at 30°C below l.5%,. preferably below l.0%.

Inventors: OUDEJANS, JOHANNES CORNELIS, VERZIJL, DIRK
Applicants: UNILEVER N.V., UNILEVER PLC
Application year: 1987
Main classification: B01J23
IPC codes: C07B35, B01J37, C07C67, B01J23, C07B31, C11C3, B01J35