MXPA99003980A - Process for preparing hydroxylammonium salts - Google Patents

Abstract

The invention relates to a process for preparing a hydroxylammonium salt through catalytic reduction of nitrate ions in an acid medium in the presence of a palladium and/or platinum catalyst on a carrier in which at least 0.00025 mmol halogen ions are present per m2 of palladium and/or platinum area.

Description

PROCEDURE FOR PREPARING HYDROXYLAMONIUM SALTS The invention relates to a process for preparing a hydroxylammonium salt by means of the catalytic reduction of nitrate ions, with hydrogen, in an acid medium, in the presence of a palladium or platinum catalyst on a carrier. This type of procedure is already known from NL-A-7902291. However, a disadvantage of this method is that, after being carried out for a relatively long time, that is, longer than one week, the catalysts used do not show good selectivity. This is particularly disadvantageous in the commercial production of hydroxylammonium salts. An important application of the hydroxylammonium salts is in the preparation of oximes from ketones or aldehydes, in particular the preparation of cyclohexanone oxime from cyclohexanone. A cyclic process is known for the preparation, for example, of cyclohexanone oxime. Subsequently, the reaction medium is regulated with acid, for example, with phosphoric acid and / or sulfuric acid regulators, and the salts derived from these acids, for example, the alkali and / or ammonium salts.

In the synthesis of hydroxylammonium, the nitrate ions are converted, with hydrogen, to hydroxylammonium ions; this proceeds according to the following equation: 2 H + + N03"+ H2 -> NH3OH + + 2 H20 The purpose of the invention is now to provide a process in which use is made of catalysts that retain an increased selectivity towards the hydroxylammonium salt, even after prolonged use and exposure to the synthesis conditions. Surprisingly, the purpose is achieved by the incorporation of at least 0.00025 mmol of halogen ions per square meter of palladium surface area and / or platinum in the catalyst used. The upper limit for the amount of halogen ions is at most 0.005 mmol per m2 of palladium surface area and / or platinum. Preferably the halogen ions are present at a level between 0.001 and 0.002 mmoles of halogen ions per square meter of the surface area of the palladium and / or platinum. Any of the halogens can be used: iodine, bromine, chlorine and fluorine. Preferably, iodine and / or bromine ions are used. Halogen ions can be applied to the catalyst, for example, by treatment with a halogen compound. Examples of said halogen compounds include elemental I2, Br2, Cl2, F2, and compounds such as H1, HBr, alkali (alkaline-earth) salts of iodine, bromine, chlorine and / or fluorine; aliphatic, aromatic, linear or branched, iodinated, brominated, chlorinated and / or fluorinated hydrocarbons having from 1 to 12 carbon atoms (for example, methyl iodide, ethyl iodide) or mixtures thereof. Preferably, compounds containing iodine and / or containing bromine are used. The catalyst treatment can be carried out before introducing the catalyst (containing halogen) into the reactor. Alternatively, this treatment can also be carried out in situ, with the catalyst (containing or not containing halogen) already present in the reactor. The aforementioned halogen compound (s) can be used either in pure form or in diluted form; optionally dissolving in a suitable solvent. Preferably the treatment takes place before introducing the catalyst into the reactor. The amount of palladium and / or platinum in the catalyst is usually 0.5-20% by weight, based on the total weight of the catalyst.

If a catalyst containing both platinum and palladium is used, the weight ratio of palladium to platinum will generally be between 6: 4 and 9.9: 0.1. Preferably the ratio will be between 7: 3 and 9.5: 0.5. Generally, a solid carrier is used for the platinum and / or palladium catalyst. In principle you can use as carrier any material that is stable, that is, that does not dissolve, pulverize, become lime, swell, coagulate or disintegrate in the reaction medium. Examples of suitable carriers include activated carbon or graphite. Palladium and / or platinum is applied to the carrier in the form of metal particles. The surface area of these metal particles is the area of palladium and / or platinum. This area can be determined with the help of CO adsorption. Usually the area of palladium and / or platinum will be between 0.5 and 20 m2 per gram of catalyst. Usually the catalyst is activated, as is already known from NL-A-7604669, by introducing the presence of at least one of the metal elements of the group consisting of Cu, Ag, Au, Cd, Ga, In, TI, Ge, Sn, Pb, As, Sb and Bi, including mixtures of them. It is also possible to make use of compounds containing the aforementioned elements, for example, the oxides, nitrates, phosphates, sulfates, tartrates, oxalates, formates and acetates thereof. More than one such compound can be used in a mixture. The elements or compounds can be applied directly to the catalyst or, alternatively, they can be added to the reaction medium. A very suitable result can be obtained if 0.01-5 mg of the element or the activating elements, of the previous group, per gram of palladium and / or platinum is present. The activation with one or more of the elements mentioned above can be carried out before and after the treatment with the halogen compound (s). The hydrogen pressure at which the catalytic reduction of the nitrate ions takes place will generally be between 0.1 and 5 MPa, preferably between 0.5 and 2.5 MPa. The hydrogen that is going to be used can be previously purified. Purification can be carried out with the aid, for example, of activated carbon for the purpose of removing the organic components, with a palladium catalyst, for the purpose of removing oxygen, and / or with zinc oxide to remove the sulfur and with a ruthenium compound for the purpose of converting any CO and C02 present. Optionally a different gas can be mixed with the hydrogen, for example, helium, methane or nitrogen.

Usually the hydroxylammonium salt will be prepared at a pH of between 1 to 6, preferably between 1 and 4. Usually the temperature will be between 20 and 90 ° C, preferably a temperature between 30 and 70 ° C is used. The invention will be further clarified with reference to the following examples; however, it is not limited to them.

EXAMPLES AND COMPARATIVE EXPERIMENTS The examples and comparative experiments were carried out in a chromium-nickel steel autoclave, with a thermostat, with an internal diameter of 80 mm and an approximate volume of 300 ml. This autoclave was equipped with four deflectors 8 mm wide and a turbine agitator, six blades, with a diameter of 40 mm and blades of 10 x 10 mm. The autoclave was operated as a three-phase suspension reactor, with a continuous flow of the liquid and gaseous phases, while the solid catalyst powder was retained in the autoclave with the aid of a membrane filter of polytetrafluoroethylene in the liquid drain.

The autoclave was fed with the aid of a pump, with an aqueous feed containing 3.2 mol / liter of N03 ~ and 3.3 mol / liter of phosphoric acid regulator plus 0.1 mol / liter of NaOH. This phosphoric acid buffer was purified before use and before adding a solution containing 03 ~ in the form of nitric acid and / or sodium nitrate, treating it with hydrogen in the presence of a palladium on activated carbon hydrogenation catalyst, and then it was filtered to remove the catalyst and the impurities adsorbed on the catalyst. A constant liquid volume of 115 ml was maintained in the autoclave. The autoclave pressure was maintained at a constant level, with the help of a pressure regulator at the gas outlet; the outlet gas was cooled before the pressure regulator, while the total flow rate of the exit gas was measured behind the pressure regulator. The pH of the autoclave was kept constantly at 1.8. For this purpose, the supply of the acid feed was adjusted to the amount consumed in the reaction, with the help of a pH meter in the liquid drain and the adjustment of the flow rate of the feed. All products in the gas outlet were analyzed online. The concentrations of the gases N2, NO and N20, formed as a result of all kinds of lateral and posterior reactions in the exhaust gas, were measured with the help of a gas chromatograph. The concentrations of the hydroxylammonium salt and the NH ~ formed in the lateral and posterior reactions, plus the residual H +, were determined by an automatic titrator. In each experiment, the catalyst was weighed before introducing it into the autoclave. The catalyst concentration was selected so that the total reaction rate was virtually the same in all the examples and comparative experiments. This can easily be determined by a person skilled in the art, in a simple experiment. Then the autoclave was closed and made inert with the help of helium. After the autoclave was made inert, a hydrogen pressure of 4 MPa was established and the autoclave was filled with 115 ml of aqueous feed with the aid of a pump, which leads to the start of the reaction. All the experiments were carried out at a temperature of 55 ° C, a pressure of 4 MPa and an agitation speed of 1300 rotations per minute (r.p.m.). The experiments were continued for two weeks, with the dosage described above.

The catalyst was activated with the aid of Ge, which was dosed as a Ge02 solution in water, or dissolved in the aqueous feed separately from the liquid feed, in steps, in the course of the experiments. Ge02 was used at concentrations of 90 or 225 mg / 1, of which 5 to 10 ml were added to the autoclave at each activation step. The dosage regimen was 2 ml / minute in the first step, 1.5-5 ml / minute in the following steps. During the activation the supply of the liquid feed to the autoclave was stopped. The first dose of approximately 0.0625 Ge ML (monolayer) was added in a few minutes (between 1 and 10 minutes) after the start of each experiment, followed by a similar amount after 48 hours, to a total of 0.125 ML; then 0.06 Ge ML every 48 hours up to a total of 0.25 ML. The term ML ("monolayer") is defined as follows: a total monolayer of Ge is equal to the number of Pd and / or Pt atoms on the metal surface. This number can be determined with the help of CO chemisorption with the assumption that each palladium and / or platinum atom on the surface can adsorb a molecule of CO.

Activation was carried out in steps because the optimal degree of activation was not known in advance. Depending on the activity of the catalyst, the flow rate of the aqueous feed was between 0.9 and 5 ml / minute, with the concentration of the hydroxylammonium formed each time being typically 0.9-1.0 mol / liter. Activity A, expressed in mmoles of N03"converted / gmet.hour, is calculated as the sum of the product yields, according to equation (1): A = Y-HYAM + Y-NH4 + + Y-N2 + Y-NO + Y-N20 (1) Where "HYAM" represents hydroxylammonium; "Y-i" the amount of NO2- converted to product i per hour, per gram of palladium and / or platinum; where i = hyam, NH +, N2, NO or N20. The amount of palladium and / or platinum in the catalyst, in grams, is gmet. The yield of the products in the liquid phase was calculated on the basis of the concentrations (c) titrated in mol / liter, the liquid flow rate Qfeed in ml / minute and the amount of palladium and / or heavy platinum with the catalyst, expressed in g (gmet) / according to equation (2): Y (X) = C (X) * Qfeed * 60 / graet (2) where Y is the yield and x can be hydroxylammonium or NH4 +. Qfeed is calculated from the heavy decrease in the feed supply (in g) with the time and density of the liquid (g / ml) measured before use. The yields of the products in the gas phase are calculated from the concentrations (c) in% by volume, determined by gas chromatography; the output gas flow Qgas in Nl / h and the amount of palladium and / or platinum (gmet) according to equation (3): Y (y) = a * [c (y) / 100] * Qgas * 1000 / (24.04 * gmet) (3) where y represents N2, NO or N20, and where: a = 1 in the case of NO, a = 2 with N2 and N20. The factor 24.04 is the molar volume of gas in liters to 0.1 MPa, 20 ° C. Qgas is calculated by summing the gas flow rates of the supplied (measured) gasses and the gaseous products formed (calculated) minus the summed (calculated) hydrogen consumptions for all the products.

The selectivity S, expressed in molar% of each catalyst, was calculated with the help of the previously determined Y yield and activity A, according to equation (4): S (z) = 100 * Y (z) / A (4) where z represents one of the hydroxylammonium products, NH4 +, N2, NO or N20. Therefore, the selectivities are based on the amount of N03 ~ converted, when calculated on the basis of the measured products.

EXAMPLE I A Pd at 15% by weight on activated carbon, supplied by Degussa, E1053 R / W, was loaded in advance with 0.0014 mmol of iodine per square meter of palladium area. This was done by introducing the catalyst into water and adding the iodine dropwise, in the form of an aqueous solution of 0.063 g of Hl / liter, while constantly passing hydrogen through it. Then the catalyst was removed by filtration, under hydrogen, and dried. Iodine had been completely adsorbed, as is evident from the fact that iodine was no longer demonstrable in the filtrate (less than 50 parts per billion). The area of the metal particles also showed that it had decreased after the addition of the iodine from 12.4 originally, to 11 m2 / g of catalyst, which is in accordance with the dose sought, on the assumption that, by adsorbed iodide ion, two Pd atoms are no longer available for CO chemisorption. The results are shown in table I.

COMPARATIVE EXPERIMENT A The 15% by weight Pd was used on activated carbon of Example I. No treatment was carried out with iodine. The results are shown in table I.

TABLE I -10 The comparison of Example I and Comparative Experiment A clearly shows that the selectivity to hydroxylammonium has increased significantly, also to a -45 longer term, in this case, the operation for two weeks.

EXAMPLE II -20 Example I was repeated with a catalyst supplied by Degussa, EF 1055 R / W, which has 8% by weight of palladium and 2% by weight of platinum, on activated carbon. The metal area was 7.1 square meters per gram of catalyst. After treatment with iodine, it was demonstrated that the area of the metal particles had decreased to 6 m2 / g of catalyst. Activation with Ge continued to 0.31 Ge ML. The second activation was made almost after 24 hours. Then every 48 hours. The results are shown in table II.

COMPARATIVE EXPERIMENT B Example II was repeated, but without the iodine treatment. The results are shown in table II.

TABLE II H) ?5 The comparison of Example II and Comparative Experiment B also shows a significant increase in hydroxylammonium selectivity when the COQ catalyst was treated.

Claims (8)

NOVELTY OF THE INVENTION CLAIMS

1. - Process for preparing a hydroxylammonium salt by means of catalytic reduction of nitrate ions with hydrogen in an acid medium, in the presence of palladium and / or platinum catalyst on a carrier, characterized in that the catalyst includes halogen ions at a level of when minus 0.00025 and at most 0.004 mmol of halogen ions per square meter of surface area of the palladium and / or platinum.

2. Method according to claim 1, further characterized in that the halogen ions are present at a level between 0.001 and 0.002 mmol of halogen ions per square meter of surface area of the palladium and / or platinum.

3. Method according to any of claims 1 and 2, further characterized in that the halogen ions are introduced into the catalyst before the introduction of the catalyst into the reactor.

4. Method according to any of claims 1-3, further characterized in that the halogen ions are iodine and / or bromine ions.

5. - Method according to any of claims 1 to 4, further characterized in that the catalyst is on a carrier material of activated carbon or graphite.

6. Method according to any of claims 1 to 5, further characterized in that the catalyst is treated with a halogen compound, selected from the group consisting of I2, Br2, Cl2, F2, Hl, HBr, alkali salts (alkaline) -carriers) of iodine, bromine, chlorine and / or fluorine; aliphatic, aromatic, branched or linear, iodinated, brominated, chlorinated and / or fluorinated hydrocarbons having 1 to 12 carbon atoms, or mixtures thereof.

7. Process according to claim 6, further characterized in that the halogen compound is a compound containing iodine and / or bromine.

8. Method according to any of claims 1 to 7, further characterized in that the catalyst is activated by the presence of one or more compounds of the elements of the group consisting of Cu, Ag, Au, Cd, Ga, In, TI, Ge, Sn, Pb, As, Sb and Bi.