TWI813796B - An improved process for the production of oximes - Google Patents

Abstract

The present invention provides an improved process for the continuous production of an essentially pure oxime, wherein the oxime is formed by reacting hydroxylamine with an aldehyde or a ketone, wherein the hydroxylamine is formed in an aqueous phosphate-containing acidic solution by hydrogenation of nitrate ions or nitrogen oxides in the presence of titanium ions at a concentration of 0.05 to 25 mg/kg of said aqueous phosphate-containing acidic solution, and in the presence of a hydrogenation catalyst; an essentially pure cyclohexanone oxime obtainable therefrom; and a chemical plant for the continuous production of an essentially pure oxime.

Description

Improved method for producing oxime

Field of invention The present invention relates to an improved process for the production of oximes, in particular to one in which the desired oxime is produced by reducing nitrate ions or nitric oxide with hydrogen in the presence of a catalyst in an acidic medium and in the presence of a controlled amount of titanium ions. Hydroxylamine method.

Background of the invention Oximes are usually produced by the reaction of hydroxylamine with aldehydes or ketones. Examples of oximes are butanone oxime, cyclohexanone oxime and cyclododecanone oxime, which are prepared by the condensation of hydroxylamine with butanone, cyclohexanone and cyclododecanone respectively.

Methyl ketoxime (also known as methyl ethyl ketoxime) is particularly used in the paint industry to inhibit the formation of skin on paint prior to application.

Cyclododecanone oxime is mainly consumed as the precursor of dodecanolide, which is the precursor of polyamide-12 (also known as nylon-12).

Compared to other compounds, cyclohexanone oxime is particularly an intermediate in the production of caprolactam. This monomer is commonly used in the production of polyamide-6 (also known as nylon-6).

Methods for producing hydroxylamine are generally known in the art (see, e.g., J. Ritz, H. Fuchs and H. Perryman; "Ullmann's Encyclopedia of Industrial Chemistry Hydroxylamine" on " Online publication of the article "Hydroxylamine"; Wiley‐VCH Verlag GmbH & Co. KGaA; first published on June 15, 2000; https://doi.org/10.1002/14356007.a13_527; June 14, 2018 day search).

One method for the production of oximes is based on the reaction of a hydroxylammonium phosphate buffer solution with an aldehyde or ketone in the presence of a solvent. Hydroxylammonium phosphate solutions are obtained by selective hydrogenation of nitrate ions or nitrogen oxides in phosphate-containing acidic aqueous solutions, which are also known as inorganic process liquids. This method for producing oximes is generally known as the HPO® method and is licensed by Fibrant®. The HPO ^® method is mainly used in the production of cyclohexanone oxime.

The ^HPO® cyclohexanone oxime process utilizes two recycled liquids - an inorganic process liquid and an organic process liquid, in which several reactions and operations occur (see e.g. HJ Damme, JT van Goolen and AH de Rooij, "No by-products (NH ₄ )" Cyclohexanone oxime made without by-product (NH ₄ ) ₂ SO ₄ ), July 10 _, 1972 _, "Chemical Engineering"; page 54/55 or "Ullmann's Encyclopedia of Industrial Chemistry", online publication of the article on "Caprolactam", pages 8-10, online record version: May 25, 2018, DOI: 10.1002/ 14356007.a05_031, Copyright © 2018 Wiley‐VCH Verlag GmbH & Co. KGaA (Retrieved 4 June 2018). Inorganic process liquids are acidic aqueous solutions containing phosphate and also contain ammonium, nitrate and/or nitric oxide, It is fed to a hydroxylamine formation zone where hydroxylamine is produced. Hydroxylamine is formed by reduction of nitrate with hydrogen over a heterogeneous hydrogenation catalyst, such as a palladium-containing catalyst supported on carbon. The hydrogenation catalyst may be formed by one or more hydrogenation Activated by the presence of a catalyst activator.

In the case where hydroxylamine formation starts from a solution of phosphoric acid and nitrate, the chemical reaction that occurs is represented as follows: Reaction 1) Hydroxylamine is formed in the hydroxylamine formation zone: 2 H ₃ PO ₄ + NO ₃ ^- + 3 H ₂ → NH ₃ OH ⁺ + 2 H ₂ PO ₄ ^- + 2 H ₂ O The resulting mixture of the first reaction is an acidic aqueous phosphate solution containing a suspension of solid hydrogenation catalyst particles in a hydroxylamine solution.

In Fibrant ^{'s HPO} cyclohexanone oxime process, the resulting hydroxylamine solution, after removal of the catalyst, is contacted with an organic process liquid containing cyclohexanone and solvent. Thus, cyclohexanone and hydroxylamine react through the following reaction to form cyclohexanone oxime: Reaction 2) Cyclohexanone oxime is formed in the cyclohexanone oxime formation zone:

Next, the organic process liquid containing the formed cyclohexanone oxime and the inorganic process liquid containing phosphoric acid are separated. Volatile organic compounds and water are removed from inorganic process liquids containing phosphoric acid by steam stripping. Water entering the process, such as water formed from the chemical formation of hydroxylamine, water produced by the formation of cyclohexanone oxime and water from the _HNO3 supply, needs to be removed to avoid accumulation of water in the process. Subsequently, freshly produced nitrate or nitrogen oxide is added to the inorganic process liquid containing phosphoric acid before it is recycled to the hydroxylamine formation zone. Reaction 3) Supply HNO ₃ to compensate for the depletion of the nitrate ion source: H ₃ PO ₄ +H ₂ PO ₄ ^- +HNO ₃ +3H ₂ O → 2H ₃ PO ₄ +NO ₃ ^- +3 H ₂ O New added Nitrate production may be introduced into the process by absorbing _NOx gas, thereby forming nitrate in situ in the inorganic process liquid containing phosphoric acid and/or by adding aqueous nitric acid to the inorganic process liquid containing phosphoric acid.

Although the formation of cyclohexanone oxime by the ^HPO® cyclohexanone oxime process has been known since the 1960s and several improvements have been studied, the industrial-scale continuous version of the process still has some disadvantages.

In particular, selectivity with respect to the conversion to by-products ammonium, N ₂ O and N ₂ is an issue in known continuous processes. Selectivity against these by-products increases over time. By-products can be formed according to the following equation: NO ₃ ^- + 2 H ⁺ + 4 H ₂ → NH ₄ ⁺ + 3 H ₂ O 2 NO ₃ ^- + 2 H ⁺ + 4 H ₂ → N ₂ O + 5 H ₂ O 2 NO ₃ ^- + 2 H ⁺ + 5 H ₂ → N ₂ + 6 H ₂ O In the ^HPO® cyclohexanone oxime method, the inorganic process liquid containing phosphoric acid is a closed loop system with no liquid discharge.

A problem with the above process is that the inorganic process liquid containing phosphoric acid does not have an outlet to remove unstripped undesired components from the process. As mentioned previously, water and volatile organic compounds are removed from the inorganic process liquid containing phosphoric acid by steam stripping, ie by removal through the gas phase. And therefore, components not removed by stripping accumulate in the inorganic process liquid.

The inventors have found that the presence of titanium ions in the inorganic process liquid containing phosphoric acid and nitrate ions or nitrogen oxides and fed to the cyclohexanone oxime formation zone has a negative impact on the selectivity towards hydroxylamine. In fact, more by-products are formed, such as ammonia, N ₂ O and N ₂ .

Reduced selectivity towards hydroxylamine is undesirable because it increases the carbon footprint of the oxime production process due to increased consumption of energy, hydrogen and nitrate or nitrogen oxides required to form hydroxylamine.

Reduced selectivity towards hydroxylamine is further undesirable as it makes the oxime production process less environmentally friendly than without this reduction in selectivity towards hydroxylamine. This is especially the case where it increases the energy and feedstock costs of oxime production due to the increased consumption of energy, hydrogen and nitrate or nitrogen oxides required to form hydroxylamine.

Increased selectivity towards by-products, especially ammonia and _N2O , is also undesirable due to the increased costs associated with the decomposition of these components.

Reducing the selectivity for hydroxylamine over time is undesirable because it simultaneously reduces the product yield of the oxime formation process. Solutions to the problem of reduced product yields of oxime formation processes can be extremely expensive, e.g. in larger scale plants for the production of oximes, compared to the investment required to maintain a constant high level of selectivity towards hydroxylamine. Higher investment.

As is evident from the above reaction equation, the inorganic process liquid may contain neutral and/or protonated species, such as hydroxylamine and/or hydroxylammonium or ammonia and/or ammonium respectively. This means that according to the invention, both hydroxylamine and hydroxylammonium can be read as hydroxylamine and/or hydroxylammonium, and both ammonia and ammonium can be read as ammonia and/or ammonium.

US 3 767 758 discloses a process in which a hydroxylamine salt is prepared by reducing nitric acid with hydrogen in an acidic medium in the presence of a catalyst containing a metal from the platinum group metals and an activator. The reaction catalyst exhibits high selectivity and conversion. With regard to increasing the activity of the catalyst, several elements are mentioned, including titanium (Ti).

This prior art document is therefore defective because it encourages the use of elemental titanium in processes in which hydroxylamine salts are prepared by reducing nitric acid with hydrogen in an acidic medium in the presence of a catalyst containing a metal from the platinum group metals. Therefore, US 3 767 758, remote from the present invention, teaches that the presence of titanium ions in the inorganic process liquid containing phosphoric acid and nitrate ions or nitrogen oxides fed to the cyclohexanone oxime formation zone has a negative impact on the selectivity of the catalyst towards hydroxylamine.

US 4 340 575 discloses hydroxylammonium salts produced by a process comprising the catalytic reduction of nitrogen oxides with hydrogen in a dilute aqueous mineral acid at high temperatures in the presence of a suspended platinum catalyst, wherein the reaction is carried out in a vessel, said vessel The walls are composed of conventional copper-free molybdenum-containing austenitic chromium-nickel steel containing 16 to 28 weight percent (wt%) chromium, 20 to 50 wt% nickel, 1 to 4 wt% molybdenum and up to 0.1 wt% carbon and It additionally contains titanium metal in an amount of at least 5 times but not more than 1.0% by weight of carbon, or niobium or tantalum in an amount of at least 8 times but not more than 1.5% by weight of carbon.

This prior art document encourages the use of austenitic chromium-nickel steel containing a certain amount of titanium metal to construct vessels in which hydroxylammonium salts are produced. It does not mention or indicate the deleterious effect that titanium ions released from the walls of these vessels into the reaction mixture due to, for example, corrosion will have on the selectivity towards hydroxylamine formation.

Summary of the invention It is therefore an object of the present invention to provide an improved process for continuous oxime production, in which the above-mentioned disadvantages, in particular with regard to reduced selectivity towards hydroxylamine, are prevented.

This object is achieved by a process for the continuous production of substantially pure oximes, wherein the oximes are formed in an oxime-forming zone by reacting hydroxylamine with an aldehyde or ketone at a concentration of In the presence of 0.05 to 25 mg of titanium ions in an acidic aqueous solution of radicals, and in the presence of a hydrogenation catalyst, hydrogenation of nitrate ions or nitrogen oxides is formed in the hydroxylamine formation zone in the phosphate-containing acidic aqueous solution, and wherein The acidic aqueous solution containing phosphate is circulated between the hydroxylamine formation zone and the oxime formation zone.

Detailed description of preferred embodiments As used herein, a "continuous process" is a process that operates 24 hours a day, seven days a week except for infrequent interruptions due to, for example, process disturbances, maintenance activities, or for economic reasons. In other words, a continuous process for the production of oximes as used herein is a process in which the aldehyde or ketone is fed without interrupting the process and in which the oxime is removed without interrupting the process. Continuous processes for the production of oximes can be performed at a constant rate or the rate can fluctuate over time.

As used herein, a "substantially pure" compound means a compound that has a purity of at least 92% by weight; preferably at least 97% by weight; more preferably, it is at least 99% by weight; still more preferably at least 99.5% by weight ; Even better at least 99.8% by weight; and most preferably at least 99.9% by weight.

The reaction of hydroxylamine with an aldehyde or ketone means that the aldehyde or ketone is partially or completely converted to form an oxime as the product. Preferably, at least 50 mol%, more preferably at least 80 mol%, still more preferably at least 96 mol% and even better at least 99 mol% of the aldehyde or ketone is converted to the oxime.

As used herein, the terms "phosphate-containing acidic aqueous solution" and "inorganic process fluid" are the same. The inorganic process liquid is a phosphate-containing aqueous solution with varying concentrations of hydroxylammonium salts and ammonium salts.

"Hydrogenation of nitrate ions or nitrogen oxides" means partial or complete conversion of nitrate ions or nitrogen oxides and hydrogen to form a hydrogenation product or a mixture of hydrogenation products of nitrate ions or nitrogen oxides. Preferably, at least 50 mole percent of the converted nitrate ions or nitrogen oxides are converted to hydroxylamine. More preferably, at least 70 mol%; even more preferably, at least 80 mol%; at least 85 mol%; especially at least 90 mol% of the converted nitrate ions or nitrogen oxides are converted to hydroxylamine. Other hydrogenation products that may be formed include the by-products ammonia, N ₂ O and N ₂ .

One source of titanium ions is chemical plant equipment. Chemical plant equipment commonly used to prepare oximes and hydroxylamines is constructed of materials containing titanium metal. Equipment corrosion and circulation of acidic aqueous solutions containing phosphate can lead to titanium ion contamination. The selectivity of nitrate ion or nitric oxide reduction has been found to be reduced in the presence of titanium ion contamination. Other possible sources of titanium ions are impurities contained in raw materials added to the process, such as nitric acid and phosphoric acid.

Selectivity for hydroxylamine is defined as the molar ratio of hydroxylamine production to proton (H ⁺ ) consumption, where one hydroxylamine requires two protons (H ⁺ ). To obtain 100% conversion, "hydroxylamine selectivity" (selectivity with respect to hydroxylamine yield) as used herein is defined as: twice the amount of hydroxylamine produced in the reaction zone divided by the amount of H ⁺ consumed in the reaction zone Morby. Low selectivity means more by-products are produced, which is undesirable.

In principle, the removal of titanium ions from aqueous solutions can be achieved by many techniques, such as cathodic precipitation using mercury surfaces as cathodes; deposition or adsorption on noble metal surfaces; adsorption on adsorbents such as resin, graphite, activated carbon, or silica gel. However, all these technologies suffer from several disadvantages, such as that they are not suitable on an industrial scale, are expensive, have low removal rates or affect the quality of the produced oximes.

The present inventors have discovered an alternative method for removing titanium ions from phosphate-containing acidic aqueous solutions that does not suffer from the above-mentioned disadvantages. In the present invention, titanium ions are removed from the phosphate-containing acidic aqueous solution by introducing ammonia water into the phosphate-containing acidic aqueous solution to form a coprecipitate of titanium ions and iron-ammonium phosphate complex. By forming a coprecipitate of titanium ions with the iron-ammonium phosphate complex, the titanium ions can be removed from the phosphate-containing acidic aqueous solution, which can then be used more efficiently to produce hydroxylamine with higher selectivity.

An additional advantage of the present invention is that the process for the continuous production of oxime can be carried out without disturbing or interrupting already existing continuous oxime production processes.

Generally, in the method of the present invention for the continuous production of oxime, the concentration of titanium ions is maintained at within the stated concentration range.

As used herein, the term "precipitate" refers to an insoluble compound or solid formed in a solution by a chemical reaction.

According to the method of the present invention, the co-precipitation of titanium ions and complex iron-ammonium phosphate can be carried out in a continuous mode or a batch mode.

The ratios between the components in the complex iron-ammonium phosphate precipitate can vary to some extent. Complex iron-ammonium phosphate precipitates typically contain from about 0.8 to about 1.2 moles of iron, from about 0.4 to about 0.7 moles of ammonium, and about 1 mole of water of hydration per mole of phosphate. The complex iron-ammonium phosphate precipitate can be prepared as follows: NH ₄ H(Fe ₂ (OH) ₂ (PO ₄ ) ₂ ]·2 H ₂ O

The presence of titanium ions at any concentration is detrimental to the performance of the hydrogenation catalyst. However, for titanium ion concentrations of less than 0.05 mg/kg phosphate-containing acidic aqueous solutions, the reduction in hydroxylamine selectivity of the hydrogenation catalyst is less than about 0.1%. On the one hand, the cost of removing titanium ions to a concentration of less than 0.05 mg/kg of phosphate-containing aqueous solution outweighs the benefits arising from the associated increase in hydroxylamine selectivity of the hydrogenation catalyst. Therefore, such reduction of low titanium ion concentration is not required as it is uneconomical. On the other hand, for acidic aqueous phosphate solutions with titanium ion concentrations greater than 25 mg/kg, the hydroxylamine selectivity of the hydrogenation catalyst decreases by more than about 20%, which in this case makes the process of producing oximes unattractive from an economic point of view force because it increases the energy and raw material costs of oxime production, for example due to the increased consumption of energy, hydrogen and nitrate or nitrogen oxides required to form hydroxylamine.

In order to achieve an appropriate balance between titanium ion removal and the hydroxylamine selectivity of the catalyst in the presence of titanium ions, preferably the titanium ion concentration is greater than 0.05 mg/kg of the phosphate-containing acidic aqueous solution, and more preferably greater than 0.1 mg/kg of the phosphate-containing acidic aqueous solution. The acidic aqueous solution of phosphate is even preferably greater than 0.15 mg/kg of the acidic aqueous solution containing phosphate.

If preferably, the titanium ion concentration is less than 25 mg/kg phosphate-containing acidic aqueous solution, more preferably less than 10 mg/kg phosphate-containing acidic aqueous solution, even more preferably less than 7 mg/kg phosphate-containing acidic aqueous solution , then an appropriate balance between titanium ion removal and the catalyst's hydroxylamine selectivity in the presence of titanium ions can also be achieved.

When the titanium ion concentration is 0.05 to 25 mg/kg of the phosphate-containing acidic aqueous solution, it is more preferably 0.1 to 10 mg/kg of the phosphate-containing acidic aqueous solution, even more preferably 0.15 to 7 mg/kg. When the amount of phosphate-containing acidic aqueous solution is increased, the optimal balance between titanium ion removal and the hydroxylamine selectivity of the catalyst in the presence of titanium ions can be further achieved.

Co-precipitation of titanium ions with complex iron-ammonium phosphate can be carried out at any temperature between the freezing point and boiling point of the acidic aqueous solution containing phosphate. Good results were obtained for temperatures ranging from 25 to 75°C.

As used herein, the term "precipitation" refers to a process in which an insoluble compound or solid is formed in a solution by a chemical reaction.

Co-precipitation of titanium ions with complex iron-ammonium phosphate can be carried out at any pH value of the phosphate-containing acidic aqueous solution in the range of 3 to 10. Preferably, the co-precipitation of titanium ions with complex iron-ammonium phosphate is at a pH value in the range of 4 to 6.5, more preferably at a pH value in the range of 4 to 5, even more preferably in the range of 4.0 to 5.0 at a pH value within, optimally at a pH value of about 4.2.

The pH value of the phosphate-containing acidic aqueous solution can be adjusted by adding alkali or acid. Preferably, by adding NH ₃ , more preferably by adding NH ₃ aqueous solution, even more preferably by adding less than 25 wt % NH ₃ aqueous solution, optimally by adding less than 10 wt % NH ₃ aqueous solution. The pH value of an acidic aqueous solution containing phosphate. Preferably, the pH value of the phosphate-containing acidic aqueous solution is reduced by adding a phosphate-containing acid or a phosphate-containing acidic salt, more preferably by adding an H ₃ PO ₄ aqueous solution.

Typically, in the method of the present invention, the coprecipitate of titanium ions and complex iron-ammonium phosphate is formed by feeding ammonia into a phosphate-containing acidic aqueous solution containing titanium ions.

Co-precipitation of titanium ions with complex iron-ammonium phosphate can be performed in the presence of hydroxylamine and at any hydroxylamine concentration. However, titanium ion co-precipitation is more efficient at lower hydroxylamine concentrations. Preferably, the co-precipitation of titanium ions and complex iron-ammonium phosphate is less than 1 mole of hydroxylamine per kg of phosphate-containing acidic aqueous solution, more preferably less than 0.1 mole of hydroxylamine per kg of phosphate-containing acidic aqueous solution, even better It is carried out in the presence of less than 0.05 mole of hydroxylamine per kg of acidic aqueous solution containing phosphate.

The desired low concentration of hydroxylamine in the phosphate-containing acidic aqueous solution can be obtained in different ways, for example by thermally treating the phosphate-containing acidic aqueous solution. Preferably, a titanium ion-containing phosphate-containing acidic aqueous solution that already has a low hydroxylamine concentration is used for co-precipitation of titanium ions and complex iron-ammonium phosphate. In the ^HPO® process, preferably, the phosphate-containing acidic aqueous solution downstream of the stripper that removes volatile organic compounds and water from the phosphate-containing acidic aqueous solution containing phosphoric acid, and the phosphate-containing acidic aqueous solution upstream of the hydrogenation reactor is used for titanium Co-precipitation of ions with complex iron-ammonium phosphate.

Typically, in the method of the present invention, before titanium ions are removed, the concentration of hydroxylamine in the titanium ion-containing phosphate-containing acidic aqueous solution is less than 0.1 mole of hydroxylamine per kg of the titanium ion-containing phosphate-containing acidic aqueous solution.

It is not necessary to feed the entire phosphate-containing acidic aqueous solution to the unit in which a co-precipitate of titanium ions and complex iron-ammonium phosphate is formed. Preferably, a portion of the phosphate-containing acidic aqueous solution is fed to the unit in which a co-precipitate of titanium ions and complex iron-ammonium phosphate is formed. Preferably, this fraction is in the range of 0.1 to 50% of the total flow rate of the phosphate-containing acidic aqueous solution, more preferably in the range of 0.2 to 10%, and most preferably in the range of 0.5 to 5%.

Co-precipitation of titanium ions with complex iron-ammonium phosphate can be performed in the presence of phosphate and at any phosphate concentration. However, titanium ion co-precipitation is more efficient at a phosphate concentration of about 2 moles per kg of phosphate-containing acidic aqueous solution. Preferably, the co-precipitation of titanium ions and complex iron-ammonium phosphate is in the range of 0.5 to 4 moles of phosphate per kg of acidic aqueous solution containing phosphates, more preferably in the range of 0.7 to 3 moles of phosphates per kg of acidic aqueous solution containing phosphates. phosphate in the range, even more preferably in the presence of phosphate in the range of 1.0 to 2.4 moles of phosphate per kg of phosphate-containing acidic aqueous solution.

In cases where the phosphate concentration is higher than the preferred phosphate concentration range, water may be added to the phosphate-containing acidic aqueous solution.

Co-precipitation of titanium ions with complex iron-ammonium phosphate can be performed in the presence of iron ions and at any iron ion concentration. However, titanium ion co-precipitation is more efficient at an iron ion concentration of at least about 50 mg per kg of phosphate-containing acidic aqueous solution. Preferably, the co-precipitation of titanium ions and complex iron-ammonium phosphate is in the range of 50 to 4000 mg per kg of phosphate-containing acidic aqueous solution, and more preferably in the range of 100 to 2500 mg per kg of phosphate-containing acidic aqueous solution. Even better it is carried out in the presence of iron ions in the range of 200 to 1000 mg per kg of phosphate-containing acidic aqueous solution.

In the absence of a sufficient concentration of iron ions for co-precipitation of titanium ions with complex iron-ammonium phosphate, the iron compound can be fed into the phosphate-containing acidic aqueous solution. Preferably, iron compounds containing no foreign components are added. Suitable iron compounds are, for example, nitrates, phosphates, hydroxides and oxides of trivalent and ferrous iron. Preferably, these compounds are dissolved in water, such as an aqueous Fe(III) phosphate solution, or a 30 to 36% by weight Fe(III) nitrate aqueous solution.

Generally, in the method of the present invention, the concentration of iron ions in the acidic aqueous phosphate-containing solution containing titanium ions is increased by feeding an iron compound into the acidic aqueous phosphate-containing solution containing titanium ions before removing the titanium ions. concentration.

The co-precipitation of titanium ions and complex iron-ammonium phosphate preferably includes the following steps: - Mix ammonia and an acidic aqueous solution containing phosphate to form a co-precipitate of titanium ions and complex iron-ammonium phosphate; and - Remove co-precipitates of titanium ions and complex iron-ammonium phosphate.

According to one embodiment of the chemical plant of the invention, the separation of said complex from said phosphate-containing acidic aqueous solution is achieved by filtration.

Co-precipitation of titanium ions with complex iron-ammonium phosphate is more efficient when the mixture of ammonia water and phosphate-containing acidic aqueous solution is introduced into a retention vessel after being discharged from the in-line mixing device, where ammonia water and phosphate-containing acidic aqueous solution are The average residence time of the mixture of aqueous solutions in the retention vessel is in the range of 1 to 1000 minutes, preferably in the range of 2 to 250 minutes, more preferably in the range of 3 to 150 minutes, and optimally in the range of 3 to 90 minutes within the range.

The hydrogenation catalyst employed in the preparation of hydroxylamine (reaction 1) in the hydroxylamine formation zone preferably comprises a supported noble metal, preferably supported platinum (Pt), palladium (Pd) or a combination of palladium and platinum.

The Pd:Pt weight ratio can vary, although pure Pd is generally preferred. Pure Pd can contain some Pt impurities. Preferably, Pd contains less than 25% by weight Pt, better still less than 10% by weight, even better still less than 5% by weight and especially less than 1% by weight Pt.

According to an embodiment of the method of the present invention, the hydrogenation catalyst is a Pd-containing hydrogenation catalyst.

Preferably, the support comprises carbon (eg graphite, carbon black or activated carbon) or alumina, more preferably graphite or activated carbon. The hydrogenation catalyst employed in the hydroxylamine formation zone preferably contains 1 to 25 wt%, more preferably 3 to 20 wt%, even more preferably 5 to 15 wt% of the precious metal relative to the total weight of the hydrogenation catalyst.

Preferably, the hydrogenation catalyst used in the hydroxylamine formation zone contains activated carbon as a support and contains 1 to 25 wt% Pd relative to the total weight of the hydrogenation catalyst, more preferably 3 to 20 wt% Pd, and even more preferably 5 to 15% by weight Pd.

"Total weight of hydrogenation catalyst" means the sum of the weight of the support and the weight of the precious metal on the support.

Generally, in the method of the present invention, the hydrogenation catalyst may include activated carbon as a carrier and contain 3 to 20% by weight of Pd relative to the total weight of the hydrogenation catalyst.

Generally speaking, the hydrogenation catalyst may be present in an amount of 0.05 to 25% by weight, preferably in an amount of 0.2 to 15% by weight, more preferably in an amount of 0.5 to 5%, relative to the total weight of the phosphate-containing acidic aqueous solution in the hydroxylamine formation zone. An amount of % by weight is present in the hydroxylamine forming zone.

The average size of the hydrogenation catalyst particles may be between 1 and 150 μm, more preferably between 5 and 100 μm, even more preferably between 5 and 60 μm and most preferably between 5 and 40 μm. "Average particle size" means that 50% by volume of the particles are larger than the specified diameter. The particle size of the hydrogenation catalyst particles can be determined with a Malvern Panalytical particle size analyzer according to ISO 13320 (2009).

The hydrogenation catalyst can be activated by the presence of one or more hydrogenation catalyst activators. The hydrogenation catalyst activator may contain a metal selected from the group including germanium, cadmium, indium and bismuth. Most preferably, the hydrogenation catalyst activator is germanium. Compounds containing the elements in question can also be used as catalyst activators, such as oxides, nitrates, phosphates, sulfates, halides and acetates. The element or its compound can be applied directly to the hydrogenation catalyst or it can be added to the reaction medium.

Preferably, the hydrogenation catalyst activator is 0.01 to 100 mg per g hydrogenation catalyst, more preferably 0.05 to 50 mg per g hydrogenation catalyst, further preferably 0.1 to 10 mg per g hydrogenation catalyst, most preferably per g hydrogenation catalyst Present in amounts from 1 to 7 mg.

Preferably, the hydrogenation catalyst is activated by a hydrogenation catalyst activator containing elemental germanium. The amount of elemental germanium is 0.01 to 100 mg per g of hydrogenation catalyst, more preferably 0.05 to 50 mg per g of hydrogenation catalyst, and further preferably per g. 0.1 to 10 mg of hydrogenation catalyst, optimally 1 to 7 mg per g of hydrogenation catalyst.

Typically, in the method of the present invention, the hydrogenation catalyst is activated by a hydrogenation catalyst activator containing elemental germanium in an amount of 1 to 7 mg per g of hydrogenation catalyst.

According to a preferred embodiment of the method of the present invention, the hydrogenation catalyst includes activated carbon as a carrier and contains 3 to 20% by weight of Pd relative to the total weight of the hydrogenation catalyst, and the hydrogenation catalyst is activated by a hydrogenation catalyst activator containing the element germanium. The amount of germanium is 1 to 7 mg per g of hydrogenation catalyst.

The method of the present invention is suitable for the production of any oxime that can be produced by the reaction of hydroxylamine with an aldehyde or ketone. Preferably, as the oxime, butanone oxime, cyclohexanone oxime or cyclododecanone oxime are respectively formed by the reaction of hydroxylamine and ketobutanone, cyclohexanone or cyclododecanone. More preferably, as the oxime, cyclohexanone oxime is formed by the reaction of hydroxylamine with the ketone cyclohexanone.

According to one embodiment of the method of the invention, the substantially pure oxime is cyclohexanone oxime and the ketone is cyclohexanone.

Preferably, the purity of the substantially pure cyclohexanone oxime obtained is at least 92% by weight; more preferably at least 97% by weight; still more preferably at least 99% by weight; even more preferably at least 99.5% by weight; even more preferably at least 99.5% by weight; More preferably at least 99.8% by weight; and most preferably at least 99.9% by weight. Cyclohexanone, cyclohexanol, toluene and water can be present as impurities.

Typically, in the process of the present invention, the purity of substantially pure cyclohexanone oxime is at least 99.8% by weight.

The method of producing substantially pure oximes is much more environmentally friendly than methods known in the art. Therefore, the products of such methods are also much more environmentally friendly than those produced via other methods. The special characteristics of such products, which are much more environmentally friendly, can be guaranteed by, for example, certification.

The invention further provides substantially pure cyclohexanone oxime obtainable by the process according to the invention.

Typically, the substantially pure cyclohexanone oxime obtainable by the process according to the invention has a purity of at least 99.8% by weight.

The present invention also provides a chemical plant for the continuous production of substantially pure oximes, comprising: a. The oxime formation zone, wherein the oxime is formed by reacting hydroxylamine with an aldehyde or ketone; b. Hydroxylamine formation zone, wherein hydroxylamine is formed by hydrogenation of nitrate ions or nitrogen oxides in the presence of titanium ions and a hydrogenation catalyst at a concentration ranging from 0.05 to 25 mg per kg of phosphate-containing acidic aqueous solution. in the acidic aqueous solution containing phosphate; and c. a titanium ion removal zone, wherein the concentration of titanium ions in the phosphate-containing acidic aqueous solution is maintained within the range by removing titanium ions from the phosphate-containing acidic aqueous solution, and wherein the titanium ions are removed from the phosphate-containing acidic aqueous solution. The removal of titanium ions from the phosphate-containing acidic aqueous solution is achieved by coprecipitating with the complex iron-ammonium phosphate and separating the complex from the phosphate-containing acidic aqueous solution.

What is stated above with respect to the features of the method according to the invention also applies to the features of the chemical plant according to the invention.

The titanium ion removal zone may contain any unit for removing coprecipitates from the aqueous phase. Preferably, the titanium ion removal zone includes a settling device, a hydrocyclone and/or a (membrane) filtration unit. In a preferred embodiment of the chemical plant of the invention, the titanium ion removal zone comprises a filter in which the co-precipitate of titanium ions and complex iron-ammonium phosphate is separated. In a further preferred embodiment of the chemical plant of the invention, the titanium ion removal zone comprises a plate filter in which the coprecipitate of titanium ions and complex iron-ammonium phosphate is separated. According to a preferred embodiment, the titanium ion removal zone of the chemical plant of the present invention further includes: - an in-line mixing device in which ammonia and a phosphate-containing acidic aqueous solution containing titanium ions are mixed to form a co-precipitate of titanium ions and complex iron-ammonium phosphate, and - Retention vessels, in which the retention time is from 3 to 150 minutes.

Preferably, the in-line mixing device is a static mixer. Even better, the in-line mixing device consists of several mixer elements contained in a pipe. According to a particularly preferred embodiment of the chemical plant of the invention, the in-line mixing device is an in-line static mixer consisting of three elements of a spiral static mixer in a pipe.

Generally, the titanium ion removal zone of the chemical plant of the present invention may also include one or more of the following - Dosing unit for metered addition of water to the stripped phosphate-containing acidic aqueous solution, - A quantitative dosing unit for quantitatively adding iron(III) nitrate aqueous solution to the stripped acidic aqueous solution containing phosphate, - Pumps for feeding acidic aqueous solutions containing phosphate into in-line mixers, - Pump for feeding ammonia solution into an in-line mixer, - a pH measuring device located downstream of the in-line mixer, which measures the pH value of the mixture obtained after in-line mixing, and/or - A controller that maintains the pH value of the mixture obtained after in-line mixing at a set value by adjusting the amount of ammonia solution fed to the in-line mixer.

As used herein, a "chemical plant" is any facility that manufactures or otherwise processes required chemical substances. This includes units for one or more chemical or physical operations such as heating, cooling, mixing, distillation, extraction and reaction. It includes all ancillary equipment such as return units, coolant supplies, pumps, heat exchangers and piping systems. The exact apparatus depends inter alia on the type and purity of the starting materials and the desired end product, but also on the scale and type of the process.

The chemical plant is preferably of industrial scale. Industrial scale means an oxime production rate of at least 1,000 kg oxime per hour, more preferably at least 2,000 kg oxime per hour, even better at least 4,000 kg oxime per hour, and most preferably at least 6,000 kg oxime per hour.

The invention is illustrated by, but not intended to be limited to, the following examples. Example 1

An industrial-scale chemical plant operating according to Fibrant ^HPO® technology for the production of substantially pure cyclohexanone oxime operates in a continuous manner over a period of several years. The average output of this plant is greater than 15 tons of cyclohexanone oxime per hour. In this plant, greater than 99% of the feed cyclohexanone reacts with hydroxylamine to form cyclohexanone oxime. Substantially pure cyclohexanone oxime is produced with a purity of at least 99.9% by weight.

In an ammonia combustion plant, a gaseous mixture of NO, _NO2 and water is prepared. As a result, this mixture absorbs into the phosphate-containing acidic aqueous solution containing phosphoric acid, thereby forming nitrate. The resulting phosphate-containing acidic aqueous solution is fed to a nitrate hydrogenation reactor.

Hydroxylamine is prepared by catalytically reducing nitrate ions with hydrogen in a nitrate hydrogenation reactor. The average particle size of the hydrogenation catalyst particles (10 wt% palladium/activated carbon) was approximately 15 μm. Germanium (in the range of 2 to 6 mg/g hydrogenation catalyst) is used as a hydrogenation catalyst activator.

The hydroxylamine concentration in the phosphate-containing acidic aqueous solution containing phosphoric acid discharged from the nitrate hydrogenation reactor is maintained at higher than 1.2 mol per kg of phosphate-containing acidic aqueous solution. The phosphate concentration in the phosphate-containing acidic aqueous solution discharged from the nitrate hydrogenation reactor is maintained at higher than 3 mol per kg of phosphate-containing acidic aqueous solution. Samples of the phosphate-containing acidic aqueous solution fed to the nitrate hydrogenation reactor were taken periodically. A portion of these samples were used in a pilot plant for nitrate hydrogenation operated according to a standard experimental protocol to determine the activity and selectivity of the standard hydrogenation catalyst. And another part of this sample is used to determine the titanium ion concentration.

The pilot plant for nitrate hydrogenation consists of a well-stirred hydrogenation reactor with a continuous feed of hydrogen and a feed of nitrate-containing phosphate-containing acidic aqueous solution. The acidic aqueous product stream containing phosphate and the gaseous exhaust stream are continuously discharged from the nitrate hydrogenation pilot plant. The hydroxylamine concentration in the phosphate-containing acidic aqueous product stream discharged from a nitrate hydrogenation pilot plant is maintained at a fixed value.

The pilot plant for nitrate hydrogenation operates in continuous mode. The main aspects of the standard experimental protocol are: Reaction temperature: 50℃ Hydrogen pressure: 1100 kPa Hydrogenation catalyst: 10 wt% Pd/activated carbon Hydrogenation catalyst concentration: 1.0 wt% Germanium concentration: 3 mg per g of hydrogenation catalyst Hydroxylamine concentration in the outlet: 1.2 mol per kg of acidic aqueous solution containing phosphate Stirring speed: 2250 rpm

The results of various pilot experiments are summarized in Table 1. Table 1: experiment Ti ion concentration Hydroxylamine selectivity A 0.5 ppm 84.9% B 0.6 ppm 84.7% C 2.2 ppm 83.5% D 4.7ppm 81.9% E 6.6ppm 79.7% For experiments A to E, no effect on catalyst activity was observed.

Measurement of titanium ion concentration in a phosphate-containing acidic aqueous solution sample fed to a nitrate hydrogenation reactor was performed using a spectroscopic method using a Thermo Scientific iCAP6500 (ICP-AES) spectrometer.

The term "ppm" of a compound is defined as follows: mg of compound per kg of phosphate-containing acidic aqueous solution.

"Hydroxylamine selectivity" is defined as the molar ratio of twice the amount of hydroxylamine produced in the reactor divided by the amount of H ⁺ consumed in the reactor.

H ⁺ , hydroxylamine and phosphate concentrations were all determined by equilibrium titration of a sample by subsequent titration of a sample of phosphate-containing acidic aqueous solution from the reaction zone with 0.25 N aqueous NaOH at 25°C to obtain the first equilibrium point ( H ⁺ concentration ("free acid") at a pH of approximately 4.2); a molar excess of acetone is then added to the sample to convert the hydroxylamine to the oxime and H ⁺ , and the equilibrium titration is continued to subsequently reach an additional three equivalence points , the first of which corresponds to the free acid from hydroxylamine (and therefore provides a value for the hydroxylamine concentration in the sample); the second of which provides a value for the phosphate concentration, and the last of which provides a value for ammonium. However, the latter value is not required here. Samples were titrated on a Metrohm Dynamic Titrator.

"Activity" refers to the number of moles of nitrate converted per kilogram of catalyst per hour.

"Phosphate concentration" refers to the total concentration of phosphate (including phosphate in H ₃ PO ₄ , monohydrogen phosphate and dihydrogen phosphate) measured in moles per kg of acidic aqueous solution containing phosphate.

Example 1 shows that the hydroxylamine selectivity decreases by increasing the titanium ion concentration while the catalyst activity remains unchanged. The reduction in hydroxylamine selectivity is approximately 0.8% per ppm of titanium ions in aqueous solutions containing phosphoric acid. Example 2

Additional hydrogenation experiments were conducted in the pilot plant for nitrate hydrogenation described in Example 1. Again the standard experimental protocol was used.

For these experiments, several synthetic feeds were prepared by using analytical grade chemicals. The composition of all these aqueous samples is almost similar in terms of phosphate, nitrate, ammonia and H ⁺ concentrations, however, the titanium ion concentration varies from 0 to 90 ppm. Chemicals applied: chemicals structure supplier Purity % Ammonium nitrate NH ₄ NO ₃ VWR Chemicals 99.99 Phosphoric acid 80 wt% H ₃ PO ₄ ICL 99.99 Ammonia solution 25 wt% NH ₄ OH Emsure, Merck 99.99

Titanium(IV) phosphate is prepared in-house by using _TiCl as a source of titanium ions and 80 wt% phosphoric acid (ICL, ultrapure grade).

For dilution purposes, ultrapure water (MilliQ water) should be used.

The results of various pilot experiments are summarized in Table 2. Table 2 experiment Ti ion concentration Hydroxylamine selectivity F 0ppm 88.5% G 4 ppm 85.7% H 10ppm 80.4% I 90 ppm 56.1%

The results of Example 2 show that the hydroxylamine selectivity decreases by increasing the titanium ion concentration, while the amount of ammonium and gaseous products (the sum of _N2O and _N2 ) increases by increasing the titanium ion concentration. A decrease in hydroxylamine selectivity of approximately 0.8% per ppm titanium ion was observed for titanium concentrations in the range of 0 to 10 ppm. A decrease in hydroxylamine selectivity to approximately 56% was observed for a titanium ion concentration of 90 ppm.

No effect of titanium ion concentration on catalyst activity was observed.

Comparison of Example 1 and Example 2 shows that in both cases the hydroxylamine selectivity decreases by increasing the titanium ion concentration, while the catalyst activity remains unchanged. A decrease in hydroxylamine selectivity of approximately 0.8% per ppm titanium ion was observed for titanium concentrations ranging from 0 to about 10 ppm. The observed effects were only caused by the presence of various amounts of titanium ions, since additional analytical grade chemicals were used in Example 2. Example 3

Example 3 was conducted in the same industrial scale chemical plant as Example 1 for the production of cyclohexanone oxime. However, the plant is now expanded by a unit for coprecipitation of titanium ions with complex iron-ammonium phosphate and a filtration unit for removal of the coprecipitate from the resulting phosphate-containing acidic aqueous solution. The main components of the unit for co-precipitation of titanium ions with complex iron-ammonium phosphate, operated in continuous mode, are - a dosing unit for the dosing of water to the stripped phosphate-containing acidic aqueous solution, - a dosing unit for the dosing of A dosing unit for dosing the iron (III) nitrate aqueous solution into the stripped phosphate-containing acidic aqueous solution, - a pump for feeding the phosphate-containing acidic aqueous solution into the in-line mixer, - the in-line mixer, which An in-line static mixer consisting of three elements of a spiral static mixer in a pipe fed with stripped phosphate-containing water and optionally aqueous iron (III) nitrate solution an acidic aqueous solution, and an ammonia aqueous solution, - a pump for feeding the ammonia aqueous solution to the in-line mixer, - a pH measuring device located downstream of the in-line mixer which measures the pH value of the mixture obtained after in-line mixing, - a controller that maintains the pH value of the mixture obtained after in-line mixing at a set value by regulating the amount of ammonia solution fed to the in-line mixer, and - a residence time vessel. Previously (as in Example 1), the phosphate-containing acidic aqueous solution resulting from the formation of cyclohexanone oxime was extracted with toluene and subsequently stripped to remove volatile organic compounds and water, and fed after absorbing _NOx gas (Recirculation) to the nitrate hydrogenation reactor.

A portion of the stripped phosphate-containing acidic aqueous solution is fed to a unit for co-precipitation of titanium ions with complex iron-ammonium phosphate. After removing the co-precipitate of titanium ions and complex iron-ammonium phosphate in the filtration unit, the resulting phosphate-containing acidic aqueous solution is combined with the remainder of the stripped phosphate-containing acidic aqueous solution that is not fed to Unit for co-precipitation of titanium ions with complex iron-ammonium phosphate. The combined resulting phosphate-containing acidic aqueous solution is fed to a nitrate hydrogenation reactor after absorbing _NOx gas.

The feed rate of the stripped phosphate-containing acidic aqueous solution fed to the unit for coprecipitation was approximately 1 ton/hour. The stripped phosphate-containing acidic aqueous solution is diluted with approximately 1.5 tons of water per hour. Optionally, an aqueous iron (III) nitrate solution is added to the stripped phosphate-containing acidic aqueous solution to maintain an iron concentration of at least 200 ppm. The control was set at a pH of 4.2. The concentration of ammonia in the ammonia solution fed to the in-line mixer was 25% by weight. The retention time in the retention container is approximately 30 minutes. An aqueous slurry of coprecipitates of titanium ions and complex iron-ammonium phosphate is fed to a plate filter unit, from which the aqueous phase is discharged as filtrate. The plate filter unit operates in continuous mode. However, when loading the plate filter, the operation of the plate filter was interrupted due to the removal of the fed coprecipitate in batch mode.

The titanium ion removal efficiency of the unit for coprecipitation of titanium ions and complex iron-ammonium phosphate and the filtration unit for removing the coprecipitate from the resulting phosphate-containing acidic aqueous solution was about 65%. This means that the effluent from the filtration unit contains an amount of approximately 35% of the titanium ions present in the stripped phosphate-containing acidic aqueous solution that is fed to the unit for co-precipitation.

Before starting the unit for co-precipitation of titanium ions with complex iron-ammonium phosphate, the concentration of titanium ions in the nitrate hydrogenation reactor was 7 mg per kg of phosphate-containing acidic aqueous solution.

After starting the unit for co-precipitation of titanium ions with complex iron-ammonium phosphate and the filtration unit for removing the co-precipitate, a gradual decrease in the titanium ion concentration in the nitrate hydrogenation reactor was observed. Finally, the titanium ion concentration in the nitrate hydrogenation reactor is maintained in the range of 0.1 to 1 mg per kg of phosphate-containing acidic aqueous solution discharged from the hydrogenation reactor. Additionally, increased hydroxylamine selectivity values and reduced by-product (ammonia, _N2O and _N2 ) formation rates were observed compared to before starting the unit for co-precipitation of titanium ions with complex iron-ammonium phosphate. The purity of the substantially pure cyclohexanone oxime produced is maintained at at least 99.9% by weight and the cost of producing the substantially pure cyclohexanone oxime is reduced.

(without)

Claims (9)

A method for the continuous production of a substantially pure oxime having a purity of at least 92% by weight, wherein the oxime is formed in an oxime-forming zone by reacting hydroxylamine with an aldehyde or ketone, characterized in that the hydroxylamine is formed by Formed in the hydroxylamine formation zone by hydrogenation of nitrate ions or nitrogen oxides in the presence of titanium ions at a concentration of 0.05 to 25 mg per kg of phosphate-containing acidic aqueous solution and in the presence of a hydrogenation catalyst. In an acidic aqueous solution, wherein the phosphate-containing acidic aqueous solution circulates between the hydroxylamine formation zone and the oxime formation zone, and wherein the titanium ion concentration is determined by forming a co-precipitation of titanium ions and complex iron-ammonium phosphate and removing the coprecipitate of titanium ions and the complex iron-ammonium phosphate to maintain within the concentration range. The method of claim 1, wherein the coprecipitate of titanium ions and the complex iron-ammonium phosphate is formed by feeding ammonia into a phosphate-containing acidic aqueous solution containing titanium ions. The method according to any one of claims 1 to 2, wherein before removing the titanium ions, the concentration of hydroxylamine in the phosphate-containing acidic aqueous solution containing titanium ions is The acidic aqueous solution of phosphate is less than 0.1 mole of hydroxylamine. The method according to any one of claims 1 to 2, wherein the concentration of iron ions in the phosphate-containing acidic aqueous solution containing titanium ions is determined by feeding an iron compound into the titanium ion-containing acidic aqueous solution before removing the titanium ions. It is increased by the acidic aqueous solution containing phosphate containing titanium ions. The method according to any one of claims 1 to 2, wherein the hydrogenation catalyst is a Pd-containing hydrogenation catalyst. The method according to any one of claims 1 to 2, wherein the hydrogenation catalyst includes activated carbon as a carrier and contains 3 to 20 wt% Pd relative to the total weight of the hydrogenation catalyst, and wherein the hydrogenation catalyst The catalyst is activated by a hydrogenation catalyst activator containing elemental germanium in an amount of 1 to 7 mg per g of the hydrogenation catalyst. The method of any one of claims 1 to 2, wherein the substantially pure oxime is cyclohexanone oxime and the ketone is cyclohexanone. A chemical plant for the continuous production of substantially pure oximes with a purity of at least 92% by weight as claimed in claim 1, comprising: a. an oxime formation zone, wherein the oxime is formed by reacting hydroxylamine with an aldehyde or ketone; b. .Hydroxylamine formation zone, wherein hydroxylamine is formed in the acidic aqueous solution containing phosphate by hydrogenation of nitrate ions or nitrogen oxides in the presence of titanium ions and a hydrogenation catalyst at a concentration ranging from 0.05 to 25 mg per kg of phosphate-containing acidic aqueous solution. in an acidic aqueous solution of phosphate; and c. a titanium ion removal zone, wherein the concentration of titanium ions in the acidic aqueous solution containing phosphate is maintained in the range by removing titanium ions from the acidic aqueous solution containing phosphate. within, and wherein the removal of titanium ions from the phosphate-containing acidic aqueous solution is achieved by co-precipitating with complex iron-ammonium phosphate and separating the complex from the phosphate-containing acidic aqueous solution, wherein the The titanium ion removal zone further includes: an in-line mixing device, in which ammonia water and a phosphate-containing acidic aqueous solution containing titanium ions are mixed, thereby forming the titanium ions and composite iron-ammonium phosphate Co-precipitate, wherein the in-line mixing device is an in-line static mixer composed of three elements of a spiral static mixer in a pipeline, and a retention vessel, wherein the retention time is 3 to 150 minutes. The chemical plant of claim 8, wherein the titanium ion removal zone includes a plate filter, wherein the coprecipitate of titanium ions and complex iron-ammonium phosphate is separated in the plate filter.