CN1241165A - Process for preparing hydroxylammonium salts - Google Patents

Abstract

The present 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 square meter of palladium and/or platinum area.

Description

Process for the preparation of hydroxylammonium salts

The present invention relates to a process for the preparation of hydroxylammonium salts by catalytic reduction of nitrate ions in an acid medium in the presence of supported palladium and/or platinum catalysts.

A method of this type is known from NL-A-7902291. However, this method has the disadvantage that the catalysts used no longer exhibit good selectivity after a prolonged period of time, ie more than a week. This is particularly disadvantageous in the industrial production of hydroxylammonium salts.

An important application of hydroxylammonium salts is the preparation of oximes from ketones or aldehydes, especially cyclohexanone oxime from cyclohexanone. For the preparation of, for example, cyclohexanone oxime, a cyclization process is known. Thereafter, the reaction medium is buffered with an acid, for example with phosphoric and/or sulfuric acid and salts of these acids, such as alkali metal and/or ammonium salts.

In hydroxylammonium synthesis, nitrate ions are converted to hydroxylammonium ions with hydrogen gas; this proceeds according to the following formula:

It is an object of the present invention to provide a process in which a catalyst is used which maintains an enhanced selectivity to hydroxylammonium salts even after prolonged use and exposure to synthesis conditions.

Said object is surprisingly achieved by incorporating at least 0.00025 mmol of halide ions per square meter of palladium and/or platinum surface area of the catalyst used.

The upper limit of the amount of halide ion used is at most 0.004 mmol per square meter of palladium and/or platinum surface area. Preferably the halide ion is present at a level of 0.001 to 0.002 mmol per square meter of palladium and/or platinum surface area.

Any halogen of iodine, bromine, chlorine and fluorine can be used. Preference is given to using iodine and/or bromide ions. The halide ions can be applied to the catalyst, for example, by treatment with a halide compound. Examples of such halogen compounds include alkali (or alkaline earth) metal salts of the elements I ₂ , Br ₂ , Cl ₂ , F ₂ and compounds such as HI, HBr, iodine, bromine, chlorine and/or fluorine as well as iodide, bromide, Chlorinated and/or fluorinated aliphatic, aromatic, branched or linear hydrocarbons having 1 to 12 carbon atoms (eg methyl iodide, ethyl iodide) or mixtures thereof. Preference is given to using iodine- and/or bromine-containing compounds.

Catalyst treatment may be performed before the (halogen-containing) catalyst is introduced into the reactor. Alternatively, this treatment can also be carried out in situ with the catalyst (whether halogen-containing or not) already present in the reactor. The aforementioned halogen compounds can be used in pure form or in diluted form, optionally dissolved in a suitable solvent. Preferably said treatment is carried out before said catalyst is introduced into the reactor.

The amount of palladium and/or platinum in the catalyst is generally 0.5-20% by weight relative to the total weight of the catalyst.

If a catalyst containing both palladium and platinum is used, the weight ratio of palladium to platinum is generally between 6:4 and 9.9:0.1. Preferably said ratio is between 7:3 and 9.5:0.5.

For platinum and/or palladium catalysts, a solid support is generally used. In principle, any stable material, ie a material which does not dissolve, pulverize, become slime, swell, agglomerate or decompose in the reaction medium, can be used as carrier. Examples of suitable supports include activated carbon or graphite.

The palladium and/or platinum are applied to the support in the form of metal particles. The surface area of these metal particles is that of the palladium and/or platinum. This area can be determined by means of CO adsorption. Typically the area of palladium and/or platinum is between 0.5 and 20 square meters per gram of catalyst.

The catalyst is generally known from NL-A-7604669 by introducing at least one of the metal elements Cu, Ag, Au, Cd, Ga, In, Tl, Ge, Sn, Pb, As, Sb and Bi or a mixture thereof. Compounds containing said elements, such as oxides, nitrates, phosphates, sulfates, tartrates, oxalates, formates and acetates, may also be used. It is also possible to use more than one such compound in admixture. The element or compound can then be applied directly onto the catalyst or it can be added to the reaction medium. Very suitable results are obtained if 0.01 to 5 mg of the above-mentioned activating elements are present per gram of palladium and/or platinum.

Activation with one or more of the aforementioned elements can be carried out before or after the treatment with the halogen compound.

The _H2 pressure in carrying out the catalytic reduction of nitrate ions is generally between 0.1 and 5 MPa, preferably between 0.5 and 2.5 MPa. The _H2 used can be pre-purified. Purification can be carried out by means of, for example, activated carbon for removal of organic components, palladium catalysts for oxygen removal and/or zinc oxide for sulfur removal and ruthenium compounds for conversion of any CO and _CO2 present. Different gases such as helium, methane or nitrogen can optionally be mixed with _H2 .

The hydroxylammonium salts are generally prepared at a pH of 1-6, preferably at a pH of 1-4.

The temperature used is generally 20-90°C; preferably a temperature of 30-70°C is used.

The invention will be further illustrated on the basis of the following examples, which, however, are not intended to limit the invention.

Embodiment and comparative experiment

The examples and comparative experiments were carried out in a constant temperature chromium-nickel steel autoclave with an inner diameter of 80mm and a volume of about 300ml. The autoclave was equipped with four 8 mm wide baffles and a 6-blade turbo stirrer with 40 mm diameter and 10 x 10 mm impeller. The autoclave was operated as a three-phase slurry reactor with continuous flow of liquid and gas phases while solid powder catalyst was retained in the autoclave by means of a polytetrafluoroethylene (PTFE) filter membrane at the liquid discharge.

The autoclave is fed with an aqueous feed containing 3.2 mol/l NO ₃ ^- and 3.3 mol/l phosphate buffer plus 0.1 mol/l NaOH by means of a pump. The phosphate buffer was removed before use and before addition to a ^solution containing _NO in the form of nitric acid and/or sodium nitrate by treatment with H in the presence of a hydrogenation catalyst, _palladium on activated carbon and then filtration and purification of impurities adsorbed on the catalyst.

A constant liquid volume of 115 ml was maintained in the autoclave.

The pressure of the autoclave is maintained at a constant level by means of a pressure regulator at the gas outlet; the outlet gas is cooled before the pressure regulator and the total flow of the outlet gas is measured after the pressure regulator.

The pH in the autoclave was kept constant at 1.8. The supply of acid feedstock for this target is adjusted to the amount consumed by the reaction by means of pH measurement in the discharge liquid and regulation of the feed flow. All products in the outlet gas are analyzed online. The concentrations of all gases N ₂ , NO and N ₂ O formed as a result of various side reactions and post-reactions in the outlet gas were determined by means of gas chromatography. The concentrations of hydroxylammonium salts and NH ₄ ⁺ formed in side and post-reactions plus residual H ⁺ were determined by an automatic titrator.

In each experiment, the catalyst was weighed before being introduced into the autoclave. The catalyst concentration was chosen such that the overall reaction rate was virtually the same in all examples and comparative experiments. This can readily be determined by a person skilled in the art by simple experiments. Next, the autoclave was closed and passivated by means of helium.

After passivation of the autoclave, a _H2 pressure of 4 MPa was established and 115 ml of aqueous feed was charged into the autoclave by means of a pump to start the reaction. All experiments were performed at a temperature of 55 °C, a pressure of 4 MPa and a stirring speed of 1300 revolutions per minute (rpm). The experiment was carried out for two weeks with the doses mentioned above.

The catalyst was activated stepwise during the experiment by means of Ge, which could be in the form of a solution of _GeO2 in water, or dissolved in an aqueous feedstock separate from the supply of liquid feedstock. _GeO2 was used at a concentration of 90 or 225mg/l, where 5-10ml was added to the autoclave per activation step. In the first step the dosing rate was 2 ml/min and in the next step it was 1.5-5 ml/min. Upon activation, the supply of liquid feed to the autoclave was stopped. The first dose of about 0.0625Ge ML (monolayer) was added within a few minutes (1-10 minutes) after the start of each experiment, followed by the same amount after 48 hours for a total of 0.125ML; then every 48 hours Add 0.06ML Ge to reach a total of 0.25ML.

The term "monolayer" is defined as follows: the entire Ge monolayer is equal to the number of Pd and/or Pt atoms on the metal surface. This number can be determined by means of CO chemisorption based on the assumption that one CO molecule can be adsorbed per palladium and/or platinum atom on the surface.

Because the optimum degree of activation cannot be known in advance, activation is performed in steps.

According to the activity of the catalyst, the flow rate of the aqueous raw material is 0.9-5 ml/min, and the concentration of hydroxylammonium formed each time is generally 0.9-1.0 mol/l.

The activity A represented by converted NO ₃ ^-mmol /g _met h is calculated according to the sum of the product yields of formula (1):

A＝Y-HYAM+Y-NH ₄ ⁺ +YN ₂ +Y-NO+YN ₂ O (1)

In the formula, HYAM stands for hydroxylammonium, and Yi stands for the amount of NO ₃ ⁻ converted to product i per gram of palladium and/or platinum per hour, where i=hydroxyl ammonium, NH ₄ ⁺ , N ₂ , NO or N ₂ O. The amount of palladium and/or platinum expressed in grams in the catalyst is g _met . The yield of the product in the liquid phase is based on the titration concentration (c) in mol/l, the liquid flow Q _feed in ml/min and the weight of palladium and/or platinum in the catalyst in g (g _met ) , calculated according to formula (2):

Y(x)=c(x)×Q _feed ×60/g _met (2) where Y is the yield, and x can be hydroxylammonium or NH ₄ ⁺ . The Q _feed is calculated from the weight loss of the raw material supply (g) over time and the density (g/ml) of the liquid measured before use.

The yield of the product in the gas phase is determined from the concentration (C) in % (volume) by gas chromatography, the outlet gas flow Q _gas in Nl/h and the amount of palladium and/or platinum (g _met ) Calculate according to formula (3):

Y(y)=a×[c(y)/100]×Q _gas ×1000/(24.04×g _met ) (3) where y represents N ₂ , NO or N ₂ O and where in the case of NO a= 1 a=2 in the case of _N2 and _N2O . The factor 24.04 is the molar gas volume in units of 1 at 0.1 MPa, 20°C.

Q _gas is calculated by the gas flow of the supplied feed gas (measured), plus the gas flow of the gas products formed (calculated), minus the sum of the _H consumption of all products (calculated).

The selectivity S of each catalyst expressed in mol% is calculated according to formula (4) by means of the output Y and activity A of previous measurement:

S(z)=100×Y(z)/A (4) In the formula, z represents one of the products hydroxylammonium, NH ₄ ⁺ , N ₂ , NO or N ₂ O.

The selectivity is therefore based on the amount of _NO3- converted, ^calculated on the basis of the measured products.

Example I

A 15% by weight Pd/activated carbon E1053 R/W supplied by Degussa was previously loaded with 0.0014 mmol of iodine per square meter of palladium area. This can be done by introducing the catalyst into water and adding 0.063 g HI/l of iodine as an aqueous solution dropwise while passing a constant amount of _H2 . The catalyst was then removed by filtration under _H2 and dried. Iodine had been completely absorbed as apparently iodine no longer appeared to be present in the filtrate (<50 ppb). Furthermore, the area of the metal particles proved to have decreased from the original 12.4 to 11 ^m2 /g _catalyst after the addition of iodine, which is consistent with the hypothetical dose aimed at making two Pd atoms no longer available for CO chemisorption per iodine ion absorbed. consistent. The results are listed in Table I.

Comparative experiment A

15% (weight) of Pd loaded on activated carbon of Example 1 was used. No iodine treatment was performed. The results are listed in Table I.

Table I Example/comparative experiment Ge activation [ML] S of p-hydroxyammonium[mol%] I 0.06250.1250.19 878683.5 A 0.06250.1250.19 84.581.679.5

The comparison of Example I and Comparative Experiment A clearly shows that the catalyst of the present invention also significantly improves the selectivity to hydroxylammonium after a longer period of use (here two weeks of operation).

Example II

Example I was repeated using a catalyst EF 1055 R/W supplied by Degussa with 8% by weight Pd and 2% by weight Pt on activated carbon. The metal surface is 7.1 square meters per gram of catalyst. After treatment with iodine, the surface of the metal particles proved to have been reduced to 6 m ² /g catalyst.

Activated with Ge up to 0.31Ge ML. The second activation was performed after 24 hours. Then do it every 48 hours. The results are shown in Table II.

Comparative experiment B

Example II was repeated without iodine treatment. The results are shown in Table II.

Table II Example/comparative experiment Ge activation [ML] S of p-hydroxyammonium[mol%] II 0.06250.1250.190.250.31 838482.58487 A 0.06250.1250.19810.25800.31 7980818083

Comparison of Example II and Comparative Experiment B also shows a significant increase in the selectivity to hydroxylammonium when the catalyst is treated with iodine.

Claims (10)

1. The method for preparing hydroxylammonium salts by catalytic reduction of nitrate ions in an acid medium in the presence of a palladium and/or platinum catalyst loaded on a carrier, characterized in that the catalyst comprises palladium per square meter and/or halide ions at the level of at least 0.00025 mmol of platinum surface area. 2. Process according to claim 1, characterized in that halide ions are present at a level of at most 0.004 mmol per square meter of palladium and/or platinum surface area. 3. Process according to claim 1 or 2, characterized in that 0.001-0.002 mmol of halide ions per square meter of palladium and/or platinum surface area. 4. Process according to any one of claims 1-3, characterized in that the halide ions are introduced into the catalyst before the catalyst is introduced into the reactor. 5. Process according to any one of claims 1-4, characterized in that the halide ions are iodine and/or bromide ions. 6. Process according to any one of claims 1-5, characterized in that the catalyst is supported on a support material of activated carbon or graphite. 7. According to the method for preparing a catalyst for the preparation of hydroxylammonium salts according to any one of claims 1-7, it is characterized in that the catalyst is selected from I ₂ , Br ₂ , Cl ₂ , F ₂ , HI, HBr and alkali (or alkaline earth) metal salts of iodine, bromine, chlorine and/or fluorine and iodized, brominated, chlorinated and/or fluorinated aliphatic, aromatic, branched or Halogen compound treatment of linear hydrocarbons (e.g. methyl iodide, ethyl iodide) or mixtures thereof. 8. Process according to claim 7, characterized in that said halogen compound is an iodine and/or bromine containing compound. 9. According to the method according to any one of claims 1-8, it is characterized in that the catalyst is selected from Cu, Ag, Au, Cd, Ga, In, Tl, Ge, Sn, Pb, As, Activated by the presence of compounds of Sb and Bi elements. 10. The method substantially as described in the introduction and examples.