Nickel/alumina catalyst, its preparation and use

Abstract: The invention provides a nickel/alumina catalyst, with an atomic ratio of nickel/aluminum between 10 and 2, an active nickel surface area between 70 and 150 m²/g nickel and an average pore size, depending on the above atomic ratio, between 4 and 20 nanometers. Preferably the nickel/alumi­ nium atomic ratio is between 10 and 4, Preferably the catalyst has a specific porous structure. The invention also provides a method for preparing the catalyst by a two step process involving precipitating nickel ions and adding during a second, so-called ageing step a soluble aluminium compound. The catalyst is useful for hydrogenating unsaturated organic compounds in particular oils.

Description: The application relates to a hydrogenation catalyst containing nickel and alumina, as well as to the preparation and use thereof. Catalysts containing nickel/alumina are known and are mainly applied for the preparation of methane-containing gas. It is usual to prepare such catalysts by co-precipitating nickel- and alumium ions from a solution with an alkaline reagent like, e.g., ammonium carbonate is as disclosed in US-A-3 320 182 (Esso Research). According to this co-precipitation method, catalysts are obtained which have reasonably good properties, but the filterability of the catalyst precursor (green cake) and catalytic properties, particularly in the hydrogenation of unsaturated triglyceride oils, are inadequate. The BET total surface area of these catalysts is typically below 200 m 2 /g of catalyst and the average pore size is in the order of a few nanometers. Furthermore Applied Catalysis, 7 (1983), p. 85-90, (Doesburg, Hakvoort, Schaper and Professor van Reyen) discloses a nickel/alumina catalyst confining 0.3 g Al 2 O 3 per gram of catalyst which indicates that 0.7 g of nickel and nickel oxide were present, so that. In view of the fact that reduced catalysts are never completely reduced, the amount of free nickel in the catalyst must have been below 70%. It is also stated that these catalysts have an open porous structure and have an active nickel surface area of 25 m 2 /gram catalyst, and that the size of the nickel crystallites was 15 nanometers on the average (bottom of page 89) and 20 nanometers assuming spherical particles (middle of page 89). These catalysts were prepared by co-precipitating nickel ions and aluminium ions. The present invention provides a novel nickel/alumina catalyst satisfying the following combination of features 1) a nickel/aluminium atomic ratio between 4 and 10; 2) an average pore size between 4 and 20 nanometers; 3) an active nickel surface between 90 and 150 m 2 /g nickel; 4) nickel crystallites with an average diameter between 1 and 5 nanometers characterized as set a in claim 1. The atomic ratio of nickel to aluminium of these catalysts is between 10 and 4 because this results in a higher hydrogenation selectivity of the catalyst i.e. less formation of completely saturated triglycerides which is probably due to a higher average mesopore size. Further these catalysts preferably have an open, porous structure with macropores of 100-500 nanometers and mesopores having an average size between 8 and 20 nanometers. As is apparent from electronmicroscopy the macropores are formed by interconnected catalyst platelets. The BET total surface area is usually between 90 and 450 m 2 /g of catalyst. The above-mentioned improved catalysts can be prepared by a process in which an insoluble nickel compound is precipitated from an aqueous solution of a nickel salt with an excess alkaline precipitating agent, which precipitate is subsequently allowed to mature in suspended form and is then collected, spray dried and reduced, wherein, after the nickel ions have been precipitated, a soluble aluminium compound is added. The soluble aluminium compound can be added as a solution but also as undissolved crystals. The soluble aluminium compound being added after the nickel ions have been substantially precipitated is e.g. aluminium nitrate, sodium aluminate or alumina which dissolves at least partly in the excess alkali. After precipitation and maturing according to the invention, the precipitate is separated from the liquid, usually washed, spray dried and activated with hydrogen at an elevated temperature, this by usual procedures. Nickel compounds which can be used as starting material for the catalysts according to this invention are water-soluble nickel compounds such as nitrate, sulphate, acetate, chloride and formate. The solutions which are charged to the precipitation reactor preferably contain between 10 and 80 g nickel per litre; especially preferred are solutions which contain between 25 and 60 g nickel per litre. Alkaline precipitation agents which can be used as starting material for the catalysts according to the present invention are alkali metal hydroxides, alkali metal carbonate, alkali metal bicarbonate, the corresponding ammonium compounds and mixtures of the above-mentioned compounds. The concentration of the alkaline solution which is fed into the precipitation reactor is preferably between 20 and 300 g alkaline material (calculated as anhydrous material) per litre (in as far as the solubility allows this), more particularly between 50 and 250 g per litre. It is convenient to use both solutions (of metal salt and alkaline compound) in almost the same concentrations (expressed in equivalents), so that approximately the same volumes can be reacted. The metal-containing solution and the alkaline solution are added in such amounts per unit of time that a small excess of alkaline compound is present during the precipitation step, so that the normality of the liquid is between 0.05 and 0.5, preferably between 0.1 and 0.3 (this normality is determined by titrating a solution of hydrochloric acid, with methyl-orange as indicator). Sometimes it is necessary to add some more alkaline solution during the maturing step, in order to keep the normality within the range indicated above. The precipitation reactor has such dimensions with respect to the amounts of liquid pumped in, that short average residence times can be obtained. As a rule, average residence times of between 0.1 sec. and 10 minutes, preferably between 0.2 sec. and 4.5 minutes are used in the precipitation reactor. In a preferred embodiment, in which the precipitation step (step 1) is carried out continuously, the amounts of solutions fed into the precipitation reactor are controlled by measuring, optionally continuously, the normality or pH of the reactor effluent. The temperature at which the precipitation takes place can be controlled by adjusting the temperatures of the liquids fed in. The required vigorous agitation of the liquid in the precipitation reactor preferably takes place with a mechanical energy input of between 5 and 2000 watts per Kg of solution. More preferably the agitation takes place with a mechanical energy input of 100 to 2000 watts per kg of solution. The reaction mixture obtained from the precipitation reactor preferably goes within 15 minutes to a stirred post-reactor of a significantly higher capacity in which the suspension is agitated and matured. At this stage soluble aluminium, compounds and possible other compounds are added, and optionally carrier material and promoters if any. The amount of aluminium compound added is 0.1 to 0.25 mol aluminium ions per gram atom of nickel in the suspension. Preferably, a soluble compound such as aluminium nitrate or sodium aluminate is added. Preferably the liquid in the ageing reactor, thus during the maturing step, is kept at a temperature between 40 and 100°C, preferably between 60 and 98°C. The precipitation step and also the maturing step can be carried out batchwise (=discontinuously), continuously and semi-continuously (e.g. according to the Cascade method). Preferably the precipitation is carried out continuously by dosing an aqueous metal salt solution and an alkaline precipitating agent solution together in a small, vigorously agitated mixing device and thereafter pumping the suspension into one or more post-reactors. Usually the normality of the liquid in the maturing reactor during the ageing step (step 2) is kept in the same range as during the precipitation step (step 1); if necessary by adding some more alkali. The maturing step can be carried out in one or more reactors, the (total) average residence time being maintained between 20 and 180 minutes, preferably between 30 and 150 minutes. If two or more reactors are used, it is preferred to have the temperature in the second or further reactor 5 to 15 centigrades lower than in the preceding maturing reactor. After the ageing step has been completed, the solid material is separated from the mother liquor, usually washed, spray dried, optionally ground and calcined and thereafter activated with hydrogen at a temperature, between 250 and 600, preferably between 350 and 500°C. This activation can take place at atmospheric pressure or at increased pressure. The present process involving separate precipitation and ageing steps results in a catalyst precursor/green cakes which has a considerably improved filterability than a co-precipitated precursor at least a four fold improvement. Preferably before spray drying, or during a step preceding that, promoters can be added. Suitable amounts of promoters are from 0.5 to 10%, calculated on the weight of nickel, of elements such as molybdenum, cobalt, copper, iron, lanthanum, magnesium, or other elements and combinations thereof. The solid material is preferably washed with water; sometimes some alkaline material or a surface active material is added to the washing water. Also an organic solvents e.g. acetone can be advantageously used during washing. Drying preferably takes place with hot air. The catalyst thus obtained is especially suitable for the hydrogenation of unsaturated organic compounds particularly oils, fats, fatty acids and fatty acid derivatives like nitriles. This hydrogenation is carried out with hydrogen at an increased temperature (80-250°C) and optionally an increased pressure (0.1-5.0 10 6 Pa). The hydrogenated products thus obtained, e.g. hydrogenated oils, show favourable properties such as low tri-saturated content, sometimes combined with a steep dilatation curve. The invention is illustrated by the following examples: Example 1 Solutions of Ni(NO 3 ) 2 (35 g Ni per litre) and Na 2 CO 3 anh. (100 g/l) were continuously pumped at equal flow rates into a vigorously stirred precipitation reactor, where nickel hydroxide/carbonate was precipitated at a temperature of 20°C. The pH of the suspension in this reactor was 9.4. In this precipitation reactor (volume 25 ml), the suspension had an average residence time of 0.5 min. The suspension was then transferred continuously to a second, ageing reactor (volume 1500 ml), in which the average residence time was 30 min. and the temperature was 97°C. Simultaneously, an amount of aluminium ions was continuously dosed into this reactor, as an aqueous solution of aluminium nitrate, at a rate of 0.13 g aluminium per min. The average Al/Ni atomic ratio was 0.3 (comparative). The pH of the suspension in the second reactor was 9.0. The volume of the liquid in the second reactor was kept constant. In Table I this is tabulated. The maturing step was terminated after 90 min. (3× the average residence time), and the suspension in the reactor filtered. The green filter cake thus obtained was washed with distilled water. The washed cake was: A) dried at 120°C in a drying oven; B) spray dried; C) washed with acetone and dried at room temperature. Thereafter the catalyst was activated for 30 minutes with hydrogen at a temperature of 400°C. From the determination of a nickel surface area by hydrogen chemiabsorption an average nickel crystallite size of 2.0 nanometers was calculated. The filterability of the green cake was determined as follows: 1 litre of a green cake aqueous suspension with 4% (w.w.) solids from the maturing reactor was filtered over a Büchner funnel with a Schleicher and Schüil (trade name) black band filter with a diameter of 125 mm. The vacuum applied was 3-4,000 Pa, and obtained with an aspirator. The time of filtration in minutes necessary for filtering 4 litres of distilled water over the bed of green cake obtained was taken as a yardstick of the filterability of the green cake. This time of filtration is dicated i.a. in Table I. The activity of the catalyst in the hydrogenation of fish oil (iodine value 165) was determined as follows: 150 g fish oil was hydrogenated at 180°C and a hydrogen pressure of 1.10 5 Pa with 0.07% (w.w.) of catalyst. The decrease in the refractive index of the fish oil was compared with the decrease obtained in a similar hydrogenation with a known standard catalyst and the activity was expressed as a percentage of the activity of the standard catalyst. As to the selectivity of the catalyst: 250 g fish oil (iodine value 165) were hydrogenated to an iodine value of 85 with 0.1% (w.w.) catalyst and 60 litres H 2 /hour at a pressure of 1.10 5 Pa at 180°C. The melting point of the hydrogenated oil was determined and the time required to reach an iodine value of 85. Together they are a yardstick for the selectivity. The oil filtration of the catalyst was determined as follows: After the hydrogenation the suspension, i.e. the hydrogenated oil containing the catalyst, was cooled to 90°C and pumped to a closed, double-walled filtration vessel which was connected to a thermostat at 90°C. The bottom of this vessel contained a cotton filter cloth of 30 cm diameter. After pumping the oil and the catalyst into the filtration vessel an overpressure of 3.10 5 Pa. was applied. During the filtration this pressure was maintained with a Kendall (tradename) pressure regulator. After increasing the pressure to 3.10 5 Pa (t=o) the time of filtration time was measured. The weight of the filtered oil was determined as a function of time. Subsequently, the weight of the filtered oil (x-axis) was plotted graphically against the filtration time divided by the relevant weight of the oil (y-axis). The slope of the line obtained was taken as a yardstick for the filter reistance of the cake. These values are indicated in Table II for 150 g oil in min./g. Example 2 and Comparative Example 3 In accordance with the procedure described in Example 1, more catalysts according to the invention were prepared, variations being made, however, in the amounts of starting materials and conditions, as indicated in Table I below. The properties of these catalysts are summarized in Table II. It is noteworthy that on an average, short hydrogenation times could be used and the catalyst retained its activity for a prolonged period when compared with a co-precipitated catalyst. An excellent selectivity was also observed, i.e. there was less tri-saturated triglyceride formed especially in the hydrogenation of soya bean oil. Further, the melting point of the hydrogenated oils appeared to be practically independent of the atomic ratio of Al to Ni and of the conditions of washing and drying. Finally, also the filtration properties of green cake and catalyst after hydrogenation were particularly favourable. Examples 4, 5 and 6 The procedure followed was identical to that of Example 1. In this case solutions of NiSO 4 (35 g/l Ni) and Na 2 CO 3 anh.(100 g/l) were brought together at equal flow rates (32 ml/min. -1 ) at 20°C. The pH of the suspension in the precipitation reactor was 9.4. This suspension was subsequently transferred continuously to a second, maturing reactor (volume 1920 ml). Simultaneously, an amount of aluminium ions was dosed continuously into this second reactor. In the case of Example 4 an aqueous sodium aluminate was dosed (0.068 g Al/min.) whereas in the case of Examples 5 and 6 a solution of aluminium oxide in 4 N aqueous sodium hydroxide was dosed (0.13 g Al/min). Figure 1 which is an electron micrograph of the catalyst of Example 6 at a magnification of 10 4 shows the open spongy structure with the interconnected catalyst platelets forming the macropores. The catalyst preparation is summarized in Table III and the properties in Table IV. Comparative Experiments 1-2 The preparation was carried out according to Example 1. In this case a solution of aluminium nitrate in water was dosed into the precipitation reactor. The results are tabulated in Tables V and VI. Example 7 Herein the hydrogenation of C18-nitrile to amine is described. The catalyst was prepared according to Example 2. The reaction was carried out in an autoclave of 200 ml, charged with 70 ml nitrile (acid value 0.2) and amount of catalyst corresponding with 0.12% Ni at a hydrogen pressure of 2.5 10 6 Pa. The temperature was 110°C at the start of the reaction and increased to 120°C due to the heat of reaction and maintained for 2.5 hours. The ratio H 2 :NH 3 was 1:1. The conversion of the nitrite was 92%. The yield of primary amine was 91% and the selectivity for primary amine 99%. The selectivity and rate of filtration of the spent catalyst were higher than those which were obtained after hydrogenation with the catalyst according to Comparative Experiment 2. Example 8 The catalyst prepared according to Example 6 was tested in the hydrogenation of soybean oil. In a so-called loop jet reactor soybean oil (IV 132) was hydrogenated using 0.02% (w.w.) of Ni, at a hydrogen pressure of 6.10 5 Pa and a temperature of 110°C. The reaction rates of the hydrogenation obtained with various amounts of said catalyst showed this catalyst to be more active than a commercially available nickel-on-guhr catalyst at equal nickel levels. Moreover, the selectivity of the reaction using said catalyst (i.e. low saturated C 18 content (C 18:0 ) and low solid fat contents at 30°C at an IV of 90 (N 30 )) was excellent compared to values obtained with known Ni-on-guhr catalysts as is shown in Table VII. Example 9 The same catalyst as used in Example 8 was tested in the hydrogenation of rapeseed oil (IV 117.5). In a so-called BUSS (trade name) reactor rapeseed oil was hydrogenated using 0.05% (w.w.) Ni at a hydrogen pressure of 4.10 5 Pa and a temperature of 175°C. A high selectivity with respect to C 18:0 content and N 30 values was obtained with said catalyst compared with the two Ni-on-guhr catalysts. (N 30 values: 1.5% and 3.3% respectively and C 18:0 :10.0% and 11.5% respectively). Example 1 2 3 Ni/Al atomic ratio 3.33 10.0 2.0 Molarity of the soda solution 1.0 1.0 1.0 Molarity of the nickel solution 0.6 0.6 0.8 Precipitation temperature (°C) 20 20 20 Average precipitation time (min.) 0.5 0.5 0.5 pH value 9.4 9.4 9.4 Maturing temperature (°C) 97 97 97 Average maturing time (min.) 30 30 30 pH value 9.0 9.0 9.0 Filterability of green cake (min.) 3 1 4 Properties of the catalyst A B A B A B Active Ni surface area (m 2 /g Nil 115 139 95 100 95 120 Ni crystallite size (nm) 1.7 2.3 4.0 1.5 4.0 2.8 Average pore size (nm) 6 16 5.5 BET-total surface area (m 2 /g catalyst) 320 180 320 Example 1 2 3 Fish oil activity after washing with water (%) 98 90 45 Fish oil activity after spray-drying (%) 150 128 120 Fish oil activity after washing with acetone (%) 154 133 132 Selectivity: Hydrogenation time (min.) Water drying, 198 220 330 Spray-drying 100 120 130 Acetone drying 84 84 84 Melting point (°C) Water drying 32.0 32.5 32.0 Spray-drying 32.0 33.0 33.0 Acetone drying 31.5 32.0 32.0 Oil filtration after hydrogensting 150 g oil (min.g -1 ) Water drying 0.1 0.1 0.1 Spray-drying 0.2 0.2 0.2 Acetone drying 0.25 0.25 0.2 Example 4 5 6 Ni/Al atomic ratio 10 6 5 Molarity of the soda solution 1.0 1.0 1.0 Molarity of the nickel solution 0.6 0.6 0.6 Precipitation temperature (°C) 20 20 20 Average precipitation time (min.) 0.5 0.5 0.5 pH value 9.4 9.4 9.4 Maturing temperature (°C) 98 98 98 Average maturing time (min.) 30 30 30 pH value 9.7 9.3 9.4 Filterability of green cake (min.) 2.5 2 2 Properties of the catalyst A B A B A B Active Ni surface area (m 2 /g NI) 80 100 110 140 110 140 NI crystalline size (nm) 4.0 1.5 2.3 2.0 2.3 2.0 Average pore size (nm) 16 11 11 BET-total surface (m 2 /g catalyst) 180 250 250 Example 4 5 6 Fish oil activity after washing with water (%) 100 100 110 Fish oil activity after spray-drying (%) 125 140 150 Selectivity: Hydrogenation time (min.) Water drying 200 150 120 Spray-drying 130 97 80 Melting point (°C) Spray-drying 32.0 33.0 33.0 Oil filtration after hydrogenating 150 g oil (min.g -1 ), Water drying 0.12 Spray-drying 0.18 Comparative experiment 1 2 Ni/Al atomic ratio 5 5 Molarity of the soda solution 1.0 1.0 Molarity of the nickel solution 0.6 0.6 Precipitation temperature (°C) 20 20 Average precipitation time (min.) 0.5 0.5 pH value 9.4 9.4 Ageing temperature (°C) 97 97 Average maturing time (min.) 30 30 pH value 11.0 9.4 Filterability of green cake (min.) 32 32 Properties of the catalyst A B A B Active Ni surface area (m 2 /g Ni -1 ) 70 125 70 135 Ni crystallite size (nm) 3.0 1.6 3.6 1.6 Average pore size (nm) 5 5 BET-total surface area (m 2 /g catalyst) 380 380 Comparative experiment 1 2 Melting point (°C) 31.0 32.0 Hydrogenation time (min.) Spray-drying 150 120 Oil filtration after hydrogenating 150 g oil (min. g -1 ) Spray-drying 0.17 0.17 Fish oil activity Spray-drying (%) 110 110 Catalyst Hydrogenation rate (IV decrease/min.) C 18:0 (%) N 30 (%) Example 6 2.2 8.2 0.7 Ni-on-guhr-1 1.8 10.5 4.3 Ni-on-guhr-2 1.7 9.5 3.2

Claims: A nickel/alumina catalyst satisfying the following combination of features 1) a nickel/aluminium atomic ratio between 4 and 10; 2) an average pore size between 4 and 20 nanometers; 3) an active nickel surface is between 90 and 150 m 2 /g nickel; 4) nickel crystallites with an average diameter between 1 and 5 nanometers; characterized in that the catalyst is obtainable by a process for the preparation of a nickel/alumina catalyst, in which process an insoluble nickel compound is precipitated from an aqueous solution of a nickel salt with an excess alkaline precipitating agent, which precipitate is subsequently allowed to mature in suspended form and is then collected, spray-dried and reduced, and where after the nickel ions have been precipitated, a soluble aluminium compound is added to the suspended nickel precipitate as a solution or undissolved crystals. A catalyst according to claim 1, characterized in that the BET total surface area is between 90 and 450 m 2 /g. A catalyst according to claim 1 or 2, characterized in that the catalyst has an open, porous structure with macropores of 100-500 nanometers and a mesopore structure having an average pore size between 8 and 20 nanometers. A catalyst according to claim 3, characterized in that the macropores are formed by interconnected catalyst platelets. A process for the preparation of a nickel/alumina catalyst satisfying the following combination of features 1) a nickel/aluminium atomic ratio between 4 and 10; 2) an average pore size between 4 and 20 nanometers; 3) an active nickel surface is between 90 and 150 m 2 /g nickel; 4) nickel crystallites with an average diameter between 1 and 5 nanometers. in which process an insoluble nickel compound is precipitated from an aqueous solution of a nickel salt with an excess alkaline precipitating agent, which precipitate is subsequently allowed to mature in suspended form and is then collected, spray-dried and reduced, wherein after the nickel ions have been precipitated, a soluble aluminium compound is added to the suspended nickel precipitate as a solution or undissolved crystals. A process according to claim 5, characterized in that the soluble aluminium compound is added to the suspension within 15 minutes after precipitation of the nickel ions. A process according to any of claims 5 or 6, characterized in that the soluble aluminium compound is added in an amount of 0.1 to 0.25 mol aluminium ions per gram atom of nickel in the suspension. A process according to any of claims 5-7, characterized in that the maturing is carried out during a period of 20 to 180 minutes. A process according to any of claims 5-8, characterized in that the maturing is carried out at a temperature between 40 and 100°C. A process according to any of claims 5-9, characterized in that the precipitation is carried out continuously by dosing an aqueous nickel salt solution and an alkaline precipitating agent solution together in a small, vigorously agitated mixing device and thereafter pumping the suspension into one or more post-reactors. A process according to claim 10, characterized in that two or more post-reactors are used, the temperature in the second and possibly following post-reactor being 5-15°C lower than that in the preceding post-reactor. A process for the hydrogenation of unsaturated organic compounds, characterized in that a catalyst is used according to any of claims 1-4.

Inventors: GANGULI KESHAB LAL, LOK CORNELIS MARTINUS, NOOTENBOOM PETER, GANGULI, KESHAB LAL, LOK, CORNELIS MARTINUS, NOOTENBOOM, PETER
Applicants: UNICHEMA CHEMIE BV, UNICHEMA CHEMIE B.V.
Application year: 1985
Main classification: B01J23
IPC codes: C07C209, C07C67, B01J21, C11C3, C07B61, B01J35, C07B31, B01J23, C07B35, C07C211