Process and apparatus for the preparation of hydroxylamine

Abstract

This document relates to a process and a device for the preparation of hydroxylamine. The invention relates to a continuous process for the preparation of hydroxylamine in a phosphoric acid buffered aqueous solution by hydrogenation of a nitrate salt with hydrogen in the presence of suspended palladium-containing hydrogenation catalyst particles at a pressure above atmospheric pressure in a looped Venturi reaction device comprising a hydrogenation reactor and an external circulation loop, wherein the hydrogenation reactor comprises a downward gas-suspended sparger in an upper region of the hydrogenation reactor. The invention also relates to a looped Venturi reaction device for the continuous preparation of hydroxylamine in a phosphoric acid buffered aqueous solution by hydrogenation of a nitrate salt with hydrogen in the presence of suspended palladium-containing hydrogenation catalyst particles at a pressure above atmospheric pressure. The invention also relates to the use of the looped Venturi reaction device of the invention as a stand-alone unit for the production of hydroxylamine or as part of a chemical plant for the production of oxime compounds.

Description

Technical Field

[0001] This invention relates to a process for the continuous industrial-scale production of hydroxylamine in a phosphoric acid-containing buffered aqueous solution by hydrogenation of nitrate with hydrogen in the presence of palladium-containing hydrogenation catalyst particles in a circulating Venturi reactor. Furthermore, this invention relates to a circulating Venturi reactor for the production of hydroxylamine, and the use of the circulating Venturi reactor as a stand-alone unit for the production of hydroxylamine or as part of a chemical plant for the production of oximes. Background Technology

[0002] Hydroxylamine (CAS No. 7803-49-8) is a commonly used reagent in numerous organic and inorganic reactions. It is particularly well-suited for the preparation of oximes, especially cyclohexanone oximes, which can subsequently be converted to caprolactam via the Beckmann rearrangement. The Beckmann rearrangement process used to prepare caprolactam is well-known in the art, such as in the "Caprolactam" section of Ullmann's Encyclopedia of Industrial Chemistry (May 25, 2018, Wiley-VCH VerlagGmbH & Co. KGaA, Weinheim, Germany), available electronically at https: / / doi.org / 10.1002 / 14356007.a05_031.pub3. Other oximes prepared using hydroxylamine have been described, including cyclododecanone oximes (e.g., EP-A 1329448) and butanone oximes.

[0003] Methods for preparing hydroxylamine are also well known in the art. For example, GB1287303A, US5364609A and US4328198A relate to methods for reducing nitrate / salt or nitric oxide in phosphate buffer solution using molecular hydrogen.

[0004] HPO licensed by Fibrant ® and HPO ®plus Oxime production techniques (see, for example, HJ Damme, JT van Goolen and AH de Rooij, Cyclohexanone oxime made without byproduct (NH4)2SO4, July 10, 1972, Chemical Engineering, pp. 54 / 55, or JT Tinge, MHLGroothaert, Y.-HE Sheu (2023), The Fibrant Hydranone) ®and HPO plus Technologies for Cyclohexanone and -Caprolactam Production (Case Study). An Overview of the Technology and Outlook; pp. 971-1006; Ch. 33 in: Industrial Arene Chemistry: Markets, Technologies, Sustainable Processes and Cases. Studies of Aromatic Commodities (Ed. J. Mortier; available at https: / / doi.org / 10.1002 / 9783527827992.ch33) utilizes two recycled liquids (inorganic and organic liquids) in which multiple reactions and operations are carried out. The inorganic liquid is an aqueous solution containing phosphate and ammonium ions, which is fed into a hydrogenation reactor to produce hydroxylamine. Hydroxylamine is formed by reducing nitrate ions or nitric oxide with hydrogen, a process catalyzed by a heterogeneous hydrogenation catalyst (a palladium and / or platinum-containing catalyst supported on a solid (usually carbon) substrate). Promoters are typically added for heterogeneous hydrogenation catalysts to improve catalyst performance. The organic liquid is a solution containing alkane ketones, which is fed into an oximation reactor for the production of alkane ketone oximes.

[0005] When hydroxylamine is formed using a solution of phosphoric acid and nitrate as starting materials, the following chemical reaction occurs: The reaction for preparing hydroxylamine in the hydroxylamine-forming region is as follows: In acidic aqueous solutions, hydroxylamine exists mainly as hydroxyammonium cations, with only a very small amount of hydroxylamine remaining unprotonated.

[0006] Despite HPO ® and HPO ®plus The process is known for its high selectivity for the desired product hydroxylamine, but it still generates small amounts of byproducts (i.e., ammonium, N2O and N2).

[0007] The byproduct can be generated according to the following reaction: The hydroxylamine formation reaction is carried out using platinum (Pt), palladium (Pd), or a mixture thereof supported on a solid support as a heterogeneous catalyst in the presence of an activator. Typically, the catalyst exists as a finely dispersed solid phase in the liquid reaction mixture. The mixture obtained from the first reaction is an acidic aqueous solution containing phosphate, which includes a suspension of solid catalyst particles in a hydroxylamine solution.

[0008] At Fibrant's HPO ® and HPO ®plus In the cyclohexanone oxime process, the generated hydroxylamine solution, after catalyst removal, is contacted with an organic liquid containing cyclohexanone and solvent in the oximation section. At this point, cyclohexanone reacts with hydroxylamine to form cyclohexanone oxime. Subsequently, the cyclohexanone oxime is separated from the phosphoric acid solution and, after purification, converted to ε-caprolactam.

[0009] The acidic aqueous solution containing phosphate exiting the oxime stage must be thoroughly purified to protect the catalyst in the hydroxylamine reactor. A small amount of ammonia, a byproduct, will remain in the solution, but its accumulation is prevented by converting it to nitrogen in a nitrite (NO2 and NO mixture) absorber.

[0010] Water generated in the hydrogenation process is removed by evaporation, as well as water introduced into the process by fresh nitric acid or a mixture of nitrogen oxides.

[0011] When nitrates are hydrogenated in the hydroxylamine generation zone, the phosphoric acid solution separated from cyclohexanone oxime is added with fresh nitric acid or nitrogen oxides before being recycled back to the hydroxylamine generation zone. The nitrogen oxides required in the process are generated in the ammonia combustion unit. Optionally, the nitric acid required in the process is produced in a nitric acid unit.

[0012] Replenish HNO3 to compensate for the depletion of nitrate ions: Currently serving as an HPO ® and HPO ®plus In the nitrate reduction process, a portion of the cyclohexanone oxime process, gaseous hydrogen is contacted in a three-phase (i.e., gas-liquid-solid) bubble column reactor with a circulating inorganic liquid containing nitrate ions, as well as a buffer acid and catalyst. Nitrate hydrogenation is carried out under high pressure. The hydrogen-containing gaseous phase is circulated within the bubble column reactor via a circulating compressor. Fresh hydrogen is fed into the circulating gas while a small amount of gas is vented from the system to maintain a constant hydrogen partial pressure. Inert gas components in the fresh hydrogen, as well as the generated gaseous byproducts nitrogen (N2) and nitrous oxide (N2O), are removed by gas purging. Using a Mammoth pump, the gas-liquid suspension is circulated from the aerated reactor section through a gas-liquid separator to the filter candles in the filtration section. After the heat of reaction is removed by a heat exchanger, it is returned to the aerated reactor section.

[0013] The method of preparing hydroxylamine from nitrate ions has been known for decades, and for many years people have been dedicated to further researching ways to improve the known preparation methods.

[0014] WO98 / 18717A1 describes a process for producing hydroxylamine via nitrate ion catalytic reduction and mentions the subsequent production of cyclohexanone oxime via reaction with cyclohexanone. The document notes that the selectivity of palladium or platinum reduction catalysts can be improved by incorporating small amounts of halogen.

[0015] EP0773189A1 also describes a process for producing hydroxylamine and subsequently cyclohexanone oxime. Furthermore, it mentions the cyclohexanone rearrangement to ε-caprolactam. This document teaches that nitrate reduction catalysts with essentially the same platinum and palladium concentrations lead to improved selectivity.

[0016] EP1275616A1 also describes a process for producing hydroxylamine via catalytic reduction of nitrate ions. The efficiency of the system is improved by extracting the gas mixture from the reaction, removing non-hydrogen compounds from the feed stream, and recycling the hydrogen-rich phase back to the reaction. US 5,155,081A describes a graphite-supported platinum catalyst and its use in a process for producing hydroxylamine by reducing nitrogen oxide gases (rather than from a nitrate solution). This document notes that the selectivity of the catalyst deteriorates over time, as indicated by the increasing nitrous oxide (N₂O) content in the tail gas.

[0017] However, the known industrial processes for producing hydroxylamine (usually continuous processes) still have some shortcomings. In particular, there is a trend in the ε-caprolactam production industry to increase single-line capacity to 300,000 tons or more of ε-caprolactam per year.

[0018] Increasing the size of the three-phase bubbling tower reactor, the heat exchanger for removing reaction heat, and the capacity of the gas recirculation compressor lead to a variety of technical problems and increased investment costs. Constructing multiple parallel-operating three-phase bubbling tower reactors and auxiliary equipment is also undesirable, as this increases investment and maintenance costs, including the additional operational attention and costs required during hydrogenation stage operation.

[0019] Therefore, there is a need to utilize a simple device design to increase the production capacity of hydroxylamine, a design that can be scaled up on a single production line without parallelization or increasing the number of lines, to achieve a production capacity of at least 90,000 tons of hydroxylamine, which is sufficient for the annual production of 300,000 tons of ε-caprolactam.

[0020] In addition, it is necessary to further improve the selectivity of converting nitrate to hydroxylamine and reduce the selectivity of converting to byproducts ammonium, N2O and N2, as this will further reduce the variable cost of the entire ε-caprolactam production process and reduce the loss of valuable starting materials that are not converted to hydroxylamine, both of which will help improve the carbon footprint of the entire ε-caprolactam process. Summary of the Invention

[0021] One object of the present invention is to satisfy one or more of the above-mentioned needs and to overcome or mitigate the disadvantages associated with existing technology processes.

[0022] In particular, an object of the present invention is to provide an improved hydroxylamine production process that increases production capacity (i.e., increases space-time yield) while satisfying one or more of the aforementioned requirements (i.e., increasing selectivity for hydroxylamine and reducing selectivity for conversion to byproducts), and overcoming or mitigating the disadvantages associated with prior art processes. As used herein, space-time yield is defined as the total mass of hydroxylamine produced per hour per reactor working volume.

[0023] Furthermore, another object of the present invention is to provide an improved hydroxylamine production apparatus that allows for a simple apparatus design and process scale-up on a single production line, while overcoming or mitigating one or more disadvantages associated with prior art apparatuses.

[0024] One or more other purposes can be found in the rest of the instruction manual.

[0025] The aforementioned objective is achieved through the process described in claim 1 and the apparatus described in claim 9.

[0026] A continuous process for preparing hydroxylamine in a phosphate-buffered aqueous solution by hydrogenating nitrate with hydrogen in the presence of suspended palladium-containing hydrogenation catalyst particles at pressures above atmospheric pressure in a loop venturi reactor, the loop venturi reactor comprising a hydrogenation reactor and an external circulation loop, wherein the hydrogenation reactor includes a downward gas suspension injector in its upper region, the injector comprising a reaction mixture inlet, a motive fluid nozzle, a suction chamber, a throat, a divergent outlet diffuser, and optionally a converging inlet nozzle, the process comprising the following steps: a) Charge the hydrogenation reactor and / or external circulation loop with a fresh nitrate-containing phosphate buffer solution; b) Fresh hydrogen-containing gas is introduced into the circulating Venturi reactor, preferably into the hydrogenation reactor; c) Under the action of palladium-containing hydrogenation catalyst particles, the nitrate introduced in step b) is hydrogenated using the hydrogen introduced in step a), wherein the hydrogenation is carried out at a temperature in the range of 20 to 65°C, preferably in the range of 25 to 55°C, and most preferably in the range of 30 to 45°C, to provide a reaction mixture comprising a hydroxylamine-containing phosphoric acid buffer aqueous solution, hydrogenation catalyst particles, and hydrogen-containing gas. d) Circulate the reaction mixture through the circulating Venturi reactor; e) Cooling the reaction mixture, wherein cooling is performed by water in an indirect heat exchanger located in the external circulation loop; f) Discharge the hydroxylamine-containing phosphoric acid buffered aqueous solution from the circulating Venturi reaction apparatus, wherein the reaction mixture is filtered in a filter device inserted into the external circulation loop or through a pipeline branching off from the external circulation loop and connecting the external circulation loop to the filter device before a portion of the hydroxylamine-containing phosphoric acid buffered aqueous solution is separated from the reaction mixture. g) Exhaust N2O-containing gas from the circulating Venturi reactor; in: The gas holdup of the reaction mixture flowing through the external circulation loop is at least 5% by volume, preferably at least 8% by volume, more preferably at least 12% by volume, and most preferably at least 15% by volume. In step f), the phosphate concentration measured in the phosphate-buffered aqueous solution containing hydroxylamine discharged from the circulating Venturi reactor is 2 to 4 mol / kg, preferably 2.8 to 3.8 mol / kg. In step f), the acid concentration measured in the hydroxylamine-containing phosphoric acid buffer solution discharged from the circulating Venturi reactor is 0.3 to 0.7 mol / kg, preferably 0.4 to 0.6 mol / kg.

[0027] Surprisingly, it has been found that a continuous process for preparing hydroxylamine in a phosphate-buffered aqueous solution by hydrogenating nitrates with hydrogen in a circulating venturi reactor at pressures above atmospheric pressure in the presence of suspended palladium-containing hydrogenation catalyst particles, using the specific process steps and conditions mentioned above, can produce hydroxylamine in a direct and cost-effective manner, with selectivity superior to that of existing processes. Simultaneously, the selectivity for byproducts is reduced, thereby decreasing the costs associated with removing these byproducts. The process of the present invention enables the industrial-scale production of hydroxylamine with a capacity superior to that of existing processes, and can produce hydroxylamine efficiently, thus reducing the environmental burden of the product. In particular, the process of the present invention can produce hydroxylamine that can be used to produce polyamide 6 intermediates, with a carbon footprint superior to that of existing processes. Therefore, by applying the process of the present invention, not only is the carbon footprint of hydroxylamine reduced, but the carbon footprint of all compounds derived from it (such as cyclohexanone oxime, ε-caprolactam, polyamide 6, and products containing polyamide 6, such as stockings, carpets, and sportswear) is also reduced.

[0028] The present invention also provides a circulating Venturi reactor for the continuous preparation of hydroxylamine in a phosphate-buffered aqueous solution by hydrogenation of nitrates with hydrogen in the presence of suspended palladium-containing hydrogenation catalyst particles at a pressure higher than atmospheric pressure. The circulating Venturi reactor comprises: (a) A hydrogenation reactor, preferably with an aspect ratio of at least 2, more preferably at least 4, the hydrogenation reactor comprising: For use as an inlet for fresh hydrogen; The outlet of N2O-containing gas in the upper region of the hydrogenation reactor; The reaction mixture outlet is located in the lower region of the hydrogenation reactor; A downward gas suspension injector in the upper region of a hydrogenation reactor, wherein the downward gas suspension injector includes a reaction mixture inlet, a motive fluid nozzle, a suction chamber, a throat, a divergent outlet diffuser, and optionally includes a convergent inlet nozzle. Optionally, a splitter is arranged below the injector in the lower region of the hydrogenation reactor; Optionally, a circulation pipe is arranged below the ejector in the lower region of the reactor; Optionally, an inlet containing a nitrate-containing phosphate-buffered aqueous solution; (b) An external loop, comprising: Water-cooled indirect heat exchanger; Circulating pump; A filtration device comprising an outlet for a phosphate-buffered aqueous solution containing hydroxylamine inserted into an external circulation loop, or a pipeline connecting the external circulation loop to the outlet of the phosphate-buffered aqueous solution containing hydroxylamine, branching off from the external circulation loop; and Optionally, the inlet is a nitrate-containing phosphate-buffered aqueous solution, and The external circulation loop connects the reaction mixture outlet of the hydrogenation reactor to the reaction mixture inlet of the gas suspension injector.

[0029] Surprisingly, the circulating venturi reactor of this invention can replace the three-phase bubble column reactor in a continuous, industrial-scale production process, allowing for a simpler plant design and process scale-up on a single production line. This eliminates the need for parallelization or increased scale-up to achieve a yield of at least 90,000 tons of hydroxylamine, resulting in improved selectivity for hydroxylamine (i.e., fewer byproducts). This is particularly surprising because circulating venturi reactors are typically well-suited for rapid reactions involving pure, expensive gaseous reactants, requiring relatively high reaction pressures and heat dissipation. Their most common application is in end-user systems using expensive, pure gases. In contrast, the process of this invention is a continuous process capable of handling hydrogen-containing gas mixtures with hydrogen content as low as 25% by volume. Furthermore, the high cost of circulating venturi reactors limits their application to multi-purpose, campaign-based manufacturing of high-value chemicals. However, hydroxylamine produced by the process of this invention is merely an inexpensive intermediate for the bulk chemical ε-caprolactam (a monomer of polyamide 6, also known as nylon 6). However, due to the improved selectivity for hydroxylamine and the ability to scale up the process on a single production line, it remains profitable to replace the three-phase bubble column reactor in existing production facilities, resulting in overall economic benefits.

[0030] Advantageous embodiments of the invention are embodied in the dependent claims and will be explained in more detail below. Detailed Implementation

[0031] This invention provides a continuous process for preparing hydroxylamine in a phosphate-buffered aqueous solution by hydrogenating nitrate with hydrogen in the presence of suspended palladium-containing hydrogenation catalyst particles in a circulating venturi reactor at a pressure higher than atmospheric pressure.

[0032] The process of this invention is a continuous process. As used herein, the term "continuous process" refers to a process in which the feed stream (i.e., a hydrogen-containing gas stream from outside the circulating Venturi reactor and a nitrate-containing phosphate-buffered aqueous solution from outside the circulating Venturi reactor) is continuously fed into the circulating Venturi reactor, and the product stream (i.e., a hydroxylamine-containing phosphate-buffered aqueous solution to outside the circulating Venturi reactor) is continuously discharged to outside the circulating Venturi reactor. Therefore, "continuous mode" can be understood as the opposite of "batch mode". The hydroxylamine-containing phosphate-buffered aqueous solution described herein is an aqueous solution mainly containing hydroxylamine, nitrate ions, and a phosphate-buffered aqueous solution in the form of hydroxylamine cations. When used herein, the phosphate-buffered aqueous solution is a solution containing an aqueous solution of hydrogen phosphate and ammonium ions.

[0033] The process of this invention is carried out in a circulating Venturi reactor. The circulating Venturi reactor comprises a circulating reaction mixture, to which a phosphate-buffered aqueous solution containing nitrate and a hydrogen gas stream are introduced, and from which a phosphate-buffered aqueous solution containing hydroxylamine is extracted as a product stream and a gas stream containing the byproduct N₂O is extracted. The apparatus typically includes a gas suspension injector to generate a three-phase system comprising a phosphate-buffered aqueous solution, a hydrogen gas phase, and solid palladium-containing hydrogenation catalyst particles. The circulating Venturi reactor used in the continuous nitrate hydrogenation process according to the invention comprises a hydrogenation reactor, an external circulation loop, an indirect heat exchanger, and a filter, wherein the filter is inserted into the external circulation loop or passes through a line branching from the external circulation loop and connecting the external circulation loop to the filter, and the hydrogenation reactor includes a downward gas suspension injector in its upper region, the injector comprising a reaction mixture inlet, a motive fluid nozzle, a suction chamber, a throat, a divergent outlet diffuser, and optionally a converging inlet nozzle. The circulating Venturi reactor may also include other components common in the art and well known to those skilled in the art. Preferably, the circulating Venturi reactor is the circulating Venturi reactor described in this invention, which will be further described below. It should be understood that all features described below in the context of the circulating Venturi reactor of this invention also apply to the Venturi reactor used in the process of this invention.

[0034] In step a) of the process of the present invention, a fresh nitrate-containing phosphate buffer aqueous solution is introduced into the hydrogenation reactor and / or external circulation loop of the circulating Venturi reactor.

[0035] In step b) of the process of the present invention, fresh hydrogen-containing gas is introduced into the circulating Venturi reactor, preferably into the hydrogenation reactor. The fresh hydrogen-containing gas can be introduced into the circulating Venturi reactor in a manner and concentration (hydrogen partial pressure) known per se.

[0036] Generally, the hydrogen-containing gas introduced into a circulating Venturi reactor is not completely pure and may contain one or more inert substances, such as nitrogen, water, helium, argon, carbon dioxide, methane, ethane, and propane. The type and concentration of these inert substances depend largely on the technology used to prepare and purify the hydrogen-containing gas. For economic reasons, partially pure hydrogen is preferred. Generally, the hydrogen concentration in the hydrogen-containing gas can be greater than 50% by volume, preferably greater than 85% by volume, more preferably greater than 95% by volume, and most preferably greater than 99% by volume. A high hydrogen partial pressure in the circulating Venturi reactor is preferred because it can have a positive impact on both the activity and selectivity of the palladium-containing hydrogenation catalyst particles.

[0037] In the preparation of hydroxylamine, the partial pressure of hydrogen in the hydrogenation reactor can be adjusted by regulating the inflow of fresh hydrogen-containing gas in step b) and the outflow of N2O-containing gas in step g). Due to hydrogen consumption and byproduct formation, the partial pressure of hydrogen in the outflow of N2O-containing gas is lower than that of the inflow of fresh hydrogen-containing gas. Increasing the inflow of fresh hydrogen-containing gas in step b) and the outflow of N2O-containing gas in step g) will increase the partial pressure of hydrogen in the hydrogenation reactor. Conversely, decreasing the inflow of fresh hydrogen-containing gas in step b) and the outflow of N2O-containing gas in step g) will decrease the partial pressure of hydrogen in the hydrogenation reactor.

[0038] The total gas pressure within the hydrogenation reactor can vary over a wide range. A higher total gas pressure is advantageous because it limits the flow of N₂O-containing gas exiting the circulating Venturi reactor, thereby improving hydrogen utilization, i.e., less hydrogen is lost from the purge stream leaving the circulating Venturi reactor. On the other hand, excessively high pressure within the hydrogenation reactor is undesirable due to the higher equipment cost. A lower total gas pressure within the hydrogenation reactor is advantageous in terms of equipment cost, but on the other hand, it requires the exit of a large flow of N₂O-containing gas from the circulating Venturi reactor, thus reducing hydrogen utilization, i.e., more hydrogen is lost from the N₂O-containing gas exiting the circulating Venturi reactor. According to a preferred embodiment of the invention, the total gas pressure within the hydrogenation reactor during the reaction ranges from 1 to 200 bar, preferably 2 to 100 bar, more preferably 3 to 75 bar, and most preferably 10 to 50 bar.

[0039] By maintaining the hydrogen partial pressure in the hydrogenation reactor within the range of 1 bar to 40 bar during hydroxylamine preparation, particularly within the range of 5 bar to 25 bar, and most notably within the range of 10 bar to 20 bar, very good results were obtained in terms of selectivity for hydroxylamine and catalyst productivity.

[0040] The partial pressure of the inert gas within the hydrogenation reactor can vary over a wide range. A higher partial pressure is advantageous because it limits the flow of N₂O-containing gas exiting the circulating Venturi reactor, thereby improving hydrogen utilization, i.e., less hydrogen is lost in the purge stream leaving the circulating Venturi reactor. On the other hand, excessively high partial pressures of the inert gas within the hydrogenation reactor are undesirable due to the high equipment cost. A lower partial pressure of the inert gas within the hydrogenation reactor is advantageous due to equipment cost. On the other hand, this requires the discharge of a large flow of N₂O-containing gas from the circulating Venturi reactor, thereby reducing hydrogen utilization, i.e., more hydrogen is lost in the N₂O-containing gas leaving the circulating Venturi reactor. Particularly good results were obtained by maintaining the partial pressure of the inert gas in the hydrogenation reactor during the reaction in the range of 0.5 to 50 bar, preferably in the range of 2 to 40 bar, and most preferably in the range of 5 to 30 bar.

[0041] In step c) of the process of the present invention, the nitrate introduced in step a) is hydrogenated using hydrogen introduced in step b) under the action of palladium-containing hydrogenation catalyst particles. The hydrogenation is carried out at a temperature in the range of 20 to 65°C, preferably in the range of 25 to 55°C, and most preferably in the range of 30 to 45°C, to provide a reaction mixture comprising a hydroxylamine-containing phosphoric acid buffer aqueous solution, hydrogenation catalyst particles, and hydrogen-containing gas. The hydrogenation reaction results in the generation of heat of reaction, which is at least partially stored in the phosphate-containing buffer aqueous solution (i.e., the solution temperature rises). In addition to hydroxylamine, nitrous oxide (N₂O) is also generated during the reaction.

[0042] The palladium-containing hydrogenation catalyst particles used in the preparation of hydroxylamine according to the process of the present invention are primarily composed of palladium as the active component, supported on a support material (such as carbon). The catalyst can be activated in the presence of one or more catalyst activators. The catalyst activator can be an element from the group consisting of Cu, Ag, Cd, Hg, Ga, In, Ti, Ge, Sn, Pb, As, Sb, and Bi. Most preferably, the catalyst activator is Ge. Compounds containing the aforementioned elements can also be used as catalyst activators, such as oxides, nitrates, phosphates, sulfates, halides, and acetates. These elements or compounds thereof can be part of the palladium-containing hydrogenation catalyst particles as described in U.S. Patent 3,767,758 A, or they can be added to the reaction medium. Preferably, the palladium-containing hydrogenation catalyst comprises palladium supported on a support or a combination of palladium and platinum. The palladium:platinum weight ratio can vary, but pure palladium is generally preferred. Pure palladium may contain some platinum impurities. Preferably, the palladium-containing hydrogenation catalyst particles contain less than 25 wt% platinum, more preferably less than 5 wt% platinum, and even more preferably less than 2 wt% platinum. Preferably, the support comprises carbon (e.g., graphite, carbon black, or activated carbon) or an alumina support, more preferably graphite or activated carbon. Relative to the total weight of the support and catalyst particles, the palladium-containing hydrogenation catalyst particles preferably contain 1 to 25 wt% palladium or palladium with platinum, more preferably 5 to 15 wt% palladium or palladium with platinum. Generally, the amount of palladium-containing hydrogenation catalyst present in the reaction mixture can be 0.05 to 25 wt%, preferably 0.2 to 15 wt%, more preferably 0.5 to 5 wt%, relative to the entire reaction mixture. Preferably, the average particle size of the palladium-containing hydrogenation catalyst particles, as determined by laser diffraction, is typically 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. The term "average particle size" refers to 50% by volume of particles larger than a specified diameter.

[0043] Preferably, the amount of catalyst activator is 0.01 to 100 mg per gram of palladium hydrogenation catalyst particles, more preferably 0.05 to 50 mg per gram of palladium hydrogenation catalyst particles, more preferably 0.1 to 10 mg per gram of palladium hydrogenation catalyst particles, and most preferably 1 to 7 mg per gram of palladium hydrogenation catalyst particles.

[0044] According to the invention, the promoter or palladium-containing hydrogenation catalyst particles can be added continuously or intermittently to the circulating Venturi reactor. Preferably, the promoter and palladium-containing hydrogenation catalyst particles are added intermittently. Adding a promoter is particularly advantageous for increasing the hydroxylamine production rate per kilogram of catalyst in the circulating Venturi reactor, as it enhances the activity of the catalyst already present in the reactor. Adding palladium-containing hydrogenation catalyst particles is particularly advantageous for increasing hydroxylamine production without impairing selectivity. If desired, the promoter and palladium-containing hydrogenation catalyst particles can be added simultaneously. Preferably, the palladium-containing hydrogenation catalyst particles are added together with the promoter, but the promoter can also be advantageously added without the palladium-containing hydrogenation catalyst particles. The addition point of the palladium-containing hydrogenation catalyst particles and / or the promoter can be located anywhere within the circulating Venturi reactor. Those skilled in the art can select the optimal addition point of the palladium-containing hydrogenation catalyst particles and / or the promoter in the circulating Venturi reactor. Preferably, palladium-containing hydrogenation catalyst particles and / or promoters are introduced (i.e. metered in) into the hydrogenation reactor. As an equally preferred alternative, palladium-containing hydrogenation catalyst particles and / or promoters may be introduced (i.e. metered in) into an external circulation loop.

[0045] The addition of palladium-containing hydrogenation catalyst particles and / or promoters can be carried out in continuous or batch mode. The activity and selectivity of the catalyst-promoter system remain at a high level for a long period of time, meaning that no additional amount of palladium-containing hydrogenation catalyst particles and / or promoters is required, or only a very limited amount needs to be added. According to a preferred embodiment of the invention, the palladium-containing hydrogenation catalyst particles are added to the hydrogenation reactor [A] and / or external circulation loop in batch mode.

[0046] In step d) of the process of the present invention, the reaction mixture is circulated through the circulating Venturi reactor. The reaction mixture is circulated through the loop by a circulation pump. Preferably, the circulation rate of the reaction mixture is 10 to 500 times per hour, more preferably 15 to 300 times per hour. This circulation rate has proven particularly advantageous for hydrogen-liquid mass transfer because it allows for vigorous mixing of the gas and liquid phases. The reaction mixture circulated through the external circulation loop of the circulating Venturi reactor is a liquid-gas-solid three-phase system, comprising a hydroxylamine-containing phosphoric acid buffered aqueous solution, a hydrogen-containing gas phase, and solid palladium-containing hydrogenation catalyst particles. For the reaction mixture containing a minimal amount of gas phase, very good results have been achieved in improving or at least maintaining the catalyst performance in terms of activity and selectivity over a longer period of time. Furthermore, the circulation of the three-phase system avoids or reduces the need to separate gas bubbles from the suspension of hydrogenation catalyst solid particles and the phosphate buffered aqueous solution before entering the external circulation loop. Therefore, according to the present invention, the gas retention rate of the reaction mixture flowing through the external circulation loop is at least 5% by volume, preferably at least 8% by volume, more preferably at least 12% by volume, and most preferably at least 15% by volume.

[0047] In step e) of the process of the present invention, the reaction mixture is cooled, wherein the cooling is achieved using water in an indirect heat exchanger located in the external circulation loop. The cooling process removes the heat of reaction stored in the phosphate-containing buffer solution. Generally, the heat transfer effect in the indirect heat exchanger is improved by increasing the flow rate of the reaction mixture. Preferably, the flow rate of the reaction mixture inside the tubes of the shell-and-tube indirect heat exchanger is at least 1 m / s.

[0048] According to step f) of the process of the present invention, an aqueous solution containing hydroxylamine and a phosphoric acid buffer is discharged from the circulating Venturi reactor, wherein the reaction mixture is filtered in a filter device inserted into an external circulation loop before a portion of the aqueous solution containing hydroxylamine and a phosphoric acid buffer is separated from the reaction mixture, or the reaction mixture passes through a pipeline branching off from the external circulation loop and the filter device. According to the present invention, the concentration of hydroxylamine measured in the aqueous solution containing hydroxylamine and a phosphoric acid buffer discharged from the circulating Venturi reactor in step f) can be selected within a wide range. For example, the concentration of hydroxylamine in the aqueous solution containing hydroxylamine and a phosphoric acid buffer discharged from the circulating Venturi reactor in step f) can vary in the range of 0.1 to 2.5 mol / kg. Excellent results are obtained at values ​​in the range of 0.50 to 2 mol / kg, particularly at a concentration of about 1 mol / kg of the aqueous solution containing hydroxylamine and a phosphoric acid buffer.

[0049] According to step g) of the process of the present invention, N2O-containing gas is discharged from the circulating Venturi reactor. Continuous discharge of N2O-containing gas from the circulating Venturi reactor is advantageous because it prevents the continuous accumulation of gaseous non-hydrogen compounds within the reactor, thereby reducing the hydrogen partial pressure when the reactor operates at a constant total pressure. The accumulation of gaseous non-hydrogen compounds is caused by two processes. First, hydrogen is consumed during nitrate hydrogenation, while inert substances present in the feed are not consumed. Therefore, the ratio of hydrogen to non-hydrogen compounds decreases over time. Second, inert substances such as nitrogen and nitrous oxide (N2O) are generated as byproducts during nitrate hydrogenation. Again, the ratio of hydrogen to non-hydrogen compounds decreases over time. It is well known that hydrogen and N2O can form explosive mixtures. Therefore, the nitrate hydrogenation process is always carried out well below the lower explosive limit (LEL) of the gas mixture. This is another reason why the circulating Venturi reactor is equipped with an outlet for discharging gaseous non-hydrogen compounds, including N2O. In a preferred embodiment of the process of the present invention, the concentration of nitrous oxide in the N2O-containing gas discharged in step g) ranges from 0 to 2 vol%, particularly from 0.01 to 1 vol%, more particularly from 0.05 to 0.5 vol%, and most particularly from 0.08 to 0.3 vol%. By recovering hydrogen from the N2O-containing gas discharged in step g) and at least partially reusing the recovered hydrogen (preferably, at least partially reusing the recovered hydrogen for the preparation of hydroxylamine in the process according to the present invention), the economy and sustainability of the process can be improved. It is desirable to remove at least a portion of the N2O from the N2O-containing gas discharged in step g) before reusing it for the preparation of hydroxylamine in the process according to the present invention. According to a preferred embodiment of the present invention, the N2O-containing gas discharged in step g) is purified, and at least a portion of the discharged N2O-containing gas is reused for hydrogenation reaction. The purification is preferably carried out by adsorption or membrane separation, thereby removing at least a portion of the N2O from the N2O-containing gas.

[0050] The hydrogenation reaction in the process according to the invention is carried out in a phosphate-buffered aqueous solution. This solution provides phosphate in the form of phosphoric acid or hydrogen phosphate, which can be formed by adjusting the pH of the phosphate-buffered solution with a suitable base (e.g., hydroxide or ammonia). According to the invention, the phosphate concentration measured in the hydroxylamine-containing phosphate-buffered aqueous solution discharged from the circulating Venturi reactor in step f) is in the range of 2 to 4 mol / kg, preferably 2.8 to 3.8 mol / kg. This has proven particularly advantageous because a phosphate concentration below 2 mol / kg results in a more dilute hydroxylamine content, while a phosphate concentration above 4 mol / kg causes the crystallization temperature to rise to an undesirable level.

[0051] According to the invention, the acid concentration (sometimes referred to as free acid concentration) measured in the hydroxylamine-containing phosphate buffer aqueous solution discharged from the circulating Venturi reactor in step f) ranges from 0.3 to 0.7 mol / kg, more specifically from 0.4 to 0.6 mol / kg.

[0052] Acid concentration refers to the concentration of H+ in the liquid leaving the circulating Venturi reactor. + Molar concentration, expressed in moles per kilogram, refers to the total concentration of phosphates (including H3PO4, monohydrogen phosphate, and dihydrogen phosphate) in the liquid leaving the circulating Venturi reactor, expressed in moles per kilogram.

[0053] The concentrations of acid, hydroxylamine, and phosphate can all be determined by equilibrium titration of the same sample. Specifically, the sample containing a phosphate buffer solution is titrated with a 0.25N sodium hydroxide aqueous solution at 25°C to obtain the acid content at the first equilibrium point (pH approximately 4.2). Then, excess acetone is added to the sample to convert hydroxylamine to oxime and H+. + Then, the equilibrium titration continues to reach three more equivalence points, where the first equivalence point corresponds to the free acid from hydroxylamine (thus obtaining the value of hydroxylamine in the sample); the second equivalence point yields the value of phosphate concentration; and the last equivalence point yields the value of ammonium content, although the value of ammonium is not needed here.

[0054] According to the present invention, the nitrate concentration measured in the hydroxylamine-containing phosphate buffer aqueous solution discharged from the circulating Venturi reactor in step f) can vary over a wide range.

[0055] Typically, the nitrate concentration measured in the phosphate-buffered aqueous solution containing hydroxylamine discharged from the circulating Venturi reactor in step f) is 2 mol / kg or less, particularly 1.0 mol / kg or less. In a preferred embodiment, the nitrate concentration measured in the phosphate-buffered aqueous solution containing hydroxylamine discharged from the circulating Venturi reactor in step f) is 0.9 mol / kg or less, particularly 0.8 mol / kg or less. Particularly good results are achieved when the nitrate concentration measured in the phosphate-buffered aqueous solution containing hydroxylamine discharged from the circulating Venturi reactor in step f) is approximately 0.70 mol / kg or less. Typically, the nitrate concentration measured in the phosphate-buffered aqueous solution containing hydroxylamine discharged from the circulating Venturi reactor in step f) is at least 0.3 mol / kg, particularly at least 0.4 mol / kg. Preferably, the nitrate concentration measured in the hydroxylamine-containing phosphate buffer aqueous solution discharged from the circulating Venturi reactor in step f) is at least 0.45 mol / kg, more preferably at least 0.50 mol / kg.

[0056] According to the invention, the molar ratio of nitrate to phosphate in the phosphate-buffered aqueous solution containing hydroxylamine discharged from the circulating Venturi reactor in step f) is typically at least 0.05 mol / kg, preferably at least 0.10 mol / kg. Excellent results are obtained when this value is at least 0.15 mol / kg, more particularly at least 0.20 mol / kg. The molar ratio of nitrate to phosphate is preferably 0.40 mol / kg or lower, particularly 0.35 mol / kg or lower, and even more particularly 0.30 mol / kg or lower.

[0057] According to the present invention, the ratio of nitrate concentration in the hydroxylamine-containing phosphate buffer solution discharged from the circulating Venturi reactor in step f) to the nitrate concentration in the fresh nitrate-containing phosphate buffer solution introduced into the circulating Venturi reactor in step a) can be selected within a wide range. Experiments show that the depletion of nitrate in the reaction mixture has a negative impact on the catalyst productivity. Experiments show that if the ratio of nitrate concentration (in moles / kg solution) in the hydroxylamine-containing phosphate buffer solution discharged from the circulating Venturi reactor in step f) to the nitrate concentration (in moles / kg solution) in the nitrate-containing phosphate buffer solution introduced into the circulating Venturi reactor in step a) is in the range of 1:2 to 1:6, more preferably in the range of 1:2.5 to 1:5, very good results can be obtained.

[0058] Another object of the present invention is to provide a circulating Venturi reactor for the continuous preparation of hydroxylamine in a phosphate-buffered aqueous solution by hydrogenation of nitrates with hydrogen in the presence of suspended palladium-containing hydrogenation catalyst particles at pressures above atmospheric pressure. All apparatus features described below in conjunction with this apparatus also correspond to specific embodiments of the process of the present invention, and vice versa. Therefore, this apparatus is preferably suitable for carrying out the process of the present invention, and it should be understood that the descriptions related to the process of the present invention also apply to embodiments of this apparatus.

[0059] The circulating Venturi reactor of the present invention includes a hydrogenation reactor, preferably with an aspect ratio of at least 2, more preferably at least 4, comprising an inlet for fresh hydrogen, an outlet for N2O-containing gas in the upper region of the hydrogenation reactor, a reaction mixture outlet in the lower region of the hydrogenation reactor, and a downward gas suspension injector in the upper region of the hydrogenation reactor, wherein the downward gas suspension injector comprises a reaction mixture inlet, a motive fluid nozzle, an intake chamber, a throat, a divergent outlet diffuser, and optionally a converging inlet nozzle, optionally a diverter arranged below the injector in the lower region of the hydrogenation reactor, and optionally a circulation pipe arranged below the injector in the lower region of the reactor, and optionally an inlet for a nitrate-containing phosphate buffered aqueous solution.

[0060] The hydrogenation reactor, as part of a circulating venturi reactor, comprises a reaction vessel and a downward gas suspension injector located in the upper region of the hydrogenation reactor. The reaction vessel can be any type suitable for containing a suspension of phosphate-buffered aqueous solution and palladium-containing hydrogenation catalyst particles, as well as hydrogen gas. Preferably, the reaction vessel is a vertically upright column with a length greater than its diameter; more preferably, the column has an aspect ratio of at least 2; and most preferably, the aspect ratio is at least 4. This is advantageous because the hydrogenation reactor needs to operate under pressurized conditions (i.e., pressures above atmospheric pressure). The terms "length" and "diameter" as used herein refer to the internal length and internal diameter of the column, respectively. Preferably, the reaction vessel does not contain any built-in devices such as baffles, circulation pipes, distributors, coils, or heat exchanger coils, thereby minimizing the required volume of the reaction vessel to operate at pressures above atmospheric pressure. It should be understood that the dimensions of the reaction vessel correspond to the dimensions of the hydrogenation reactor, and therefore the terms "reaction vessel" and "hydrogenation reactor" are used interchangeably herein.

[0061] During operation of a hydrogenation reactor, the lower part of the reaction vessel typically contains a three-phase system as the reaction mixture: a suspension consisting of a hydroxylamine-containing phosphoric acid buffer solution and palladium-containing hydrogenation catalyst particles as the continuous phase, along with hydrogen-containing bubbles; while the upper part of the reaction vessel primarily contains hydrogen-containing gas. The upper part of the reaction mixture may be foamy, thus exhibiting a very high gas volume fraction.

[0062] The hydrogenation reactor includes a downward gas suspension injector in its upper region, which comprises a reaction mixture inlet, a motive fluid nozzle, a suction chamber, a throat, a divergent outlet diffuser, and optionally a converging inlet nozzle. The primary purpose of the gas suspension injector is to form a dispersion of hydrogen-containing gas in a suspension containing a phosphate buffer solution and palladium-containing hydrogenation catalyst particles. The gas suspension injector offers the advantage of rapid gas-liquid mass transfer. High energy dissipation rates can be easily achieved by employing a jet stream. These characteristics enable higher productivity using the circulating Venturi reactor of the present invention under similar conditions (e.g., catalyst loading, hydrogen partial pressure, and temperature) compared to prior art devices such as stirred tanks and bubble columns. Alternatively, in the circulating Venturi reactor of the present invention, higher productivity can be achieved in exchange for lower catalyst loading while maintaining productivity. Finally, compared to prior art devices such as stirred tanks and bubble columns, the circulating Venturi reactor of the present invention achieves higher selectivity for hydroxylamine in nitrate hydrogenation.

[0063] Unwilling to be bound by theory, the inventors believe that the improved heat transfer effect is due to the heat exchanger inserted in the external circulation loop of the circulating Venturi reactor of the present invention, compared to heat transfer in prior art devices such as stirred tank reactors and bubble column reactors. This improved heat transfer effect allows nitrate hydrogenation to proceed at a lower reaction temperature with a fixed cooling water flow rate, thereby increasing the selectivity for hydroxylamine. The gas-liquid mass transfer of hydrogen in the circulating Venturi reactor of the present invention is improved compared to the gas-liquid mass transfer in prior art devices such as stirred tank reactors and bubble column reactors. This ensures a higher hydrogen concentration in the reaction mixture under similar conditions (e.g., catalyst loading, hydrogen partial pressure, and temperature), thereby improving the selectivity for hydroxylamine.

[0064] Preferably, the gas suspension ejector is a self-priming gas suspension ejector. This gas suspension ejector includes a reaction mixture inlet, a motive fluid nozzle (also called a liquid nozzle), an intake chamber, an optional converging inlet nozzle, a throat, and a diverging outlet diffuser. This type of gas suspension ejector is often referred to as a Venturi ejector. A circulation pump inserted into an external circulation loop supplies fluid through the motive fluid nozzle, thereby obtaining a high-speed jet. This creates a negative pressure, so hydrogen-containing gas is drawn into the intake chamber and carried by the jet into the converging inlet nozzle and throat, where the phases mix violently. The three-phase reaction mixture containing extremely fine bubbles then flows through the diverging outlet diffuser and into the main body of the hydrogenation reactor. Preferably, the hydrogen-containing gas drawn into the intake chamber is a mixture of fresh hydrogen-containing gas from outside the circulating Venturi reactor and hydrogen-containing gas extracted from the top of the hydrogenation reactor. It has been shown that the outflow rate of the three-phase flow, comprising a hydroxylamine-containing phosphoric acid buffer solution, a hydrogen-containing gas phase, and solid particles of the hydrogenation catalyst leaving the liquid nozzle, determines the gas intake rate in the intake chamber. Studies have shown that when the outlet flow rate from the liquid nozzle is below 10 m / s, insufficient intake in the suction chamber results in a very limited observed nitrate hydrogenation rate and excessively low selectivity for the desired hydroxylamine compound, leading to a large amount of byproducts. When the outlet flow rate from the liquid nozzle is above 10 m / s, a positive correlation is observed between the outlet flow rate and the observed nitrate hydrogenation rate, and the selectivity for hydroxylamine formation reaches the desired level. When the outlet flow rate from the liquid nozzle is above 500 m / s, no improvement is observed in either the nitrate hydrogenation rate or the selectivity for hydroxylamine. In a preferred embodiment of the invention, the outlet flow rate of the reaction mixture from the liquid nozzle is at least 10 m / s, preferably above 20 m / s, and hydrogen-containing gas is drawn in from the suction chamber.

[0065] Preferably, a gas suspension injector with a downward-facing nozzle is arranged in the upper part of the hydrogenation reactor, through which a suspension containing a phosphate buffer solution and palladium hydrogenation catalyst particles, as well as hydrogen gas, are fed into the hydrogenation reactor. The outlet of the diffuser can be located above or below the surface of the three-phase system (i.e., the suspension containing the phosphate buffer solution and hydrogenation catalyst particles, and hydrogen gas bubbles) within the main body of the hydrogenation reactor.

[0066] The design of the gas suspension jet is crucial for achieving initial dispersion at the nozzle, while the kinetic energy of the liquid jet is essential for entraining gas and subsequent dispersion. Those skilled in the art can select or design the optimal type of gas suspension jet.

[0067] Optionally, the hydrogenation reactor is equipped with more than one gas suspension injector. Preferably, these gas suspension injectors can operate in parallel. Alternatively, instead of using a gas suspension injector comprising a single channel (with a nozzle and a diffuser), a multi-channel injector with multiple independent channels within a single universal injector body can be used. The advantage of multiple gas suspension injectors or channels is increased throughput and reduced size, i.e., shorter length.

[0068] Optionally, a flow divider (also known as a counterflow device or flow deflector) is positioned below the injectors in the lower region of the reactor to divert the reaction mixture within the reaction vessel, thereby improving the mixing efficiency of the reaction mixture within the reaction vessel. The liquid circulation pattern and highly turbulent flow within the reaction vessel provide favorable conditions for catalyst suspension, thus preventing catalyst particle settling. Another advantage of the flow divider is that it reduces the gas hold-up in the reaction mixture entering the external circulation loop from the reaction vessel.

[0069] Optionally, in addition to the distributor, a circulation pipe is provided below the injector in the lower region of the reactor to distribute the reaction mixture within the reaction vessel, thereby further improving the mixing efficiency of the reaction mixture within the reaction vessel.

[0070] The circulating venturi reactor of the present invention includes an external circulation loop comprising a water-cooled indirect heat exchanger, a circulation pump, a filter (the filter comprising an outlet of a hydroxylamine-containing phosphate-buffered aqueous solution inserted into the external circulation loop, or a pipeline branching off from the external circulation loop and connecting the external circulation loop to the filter containing the hydroxylamine-containing phosphate-buffered aqueous solution outlet), and optionally an inlet of a nitrate-containing phosphate-buffered aqueous solution. The external circulation loop connects the reaction mixture outlet of the hydrogenation reactor to the reaction mixture inlet of the gas suspension injector.

[0071] As used herein, the term "heat exchanger" refers to a device for transferring heat from one fluid stream to another. Heat exchangers can be direct (where fluid streams are mixed) or indirect (where fluid streams are kept separate by a partition wall). All heat exchangers mentioned herein are indirect heat exchangers. An indirect heat exchanger comprises at least two chambers with partition walls. Its simplest form comprises two chambers, with heat transferred from the fluid in the first chamber through the partition wall to the fluid in the second chamber. Each chamber may independently have a longer path and a larger surface area to volume ratio to facilitate heat transfer. Indirect heat exchangers are well known to those skilled in the art. The function of the heat exchanger is to transfer the sensible heat of a hydroxylamine-containing phosphate buffer solution to a cooling fluid, thereby lowering the temperature of the hydroxylamine-containing phosphate buffer solution. This can be achieved by one or more heat exchangers operating in series and / or parallel. In a preferred embodiment of the circulating Venturi reactor according to the invention, the water-cooled indirect heat exchanger is selected from shell-and-tube heat exchangers or plate heat exchangers, preferably shell-and-tube heat exchangers. Plate indirect heat exchangers are preferred because they can handle large flow rates and result in a small logarithmic mean temperature difference (LMTD) between the liquids transferring heat. Shell-and-tube indirect heat exchangers are particularly preferred because their shape makes them robust and durable. Even more preferred are multi-tube shell-and-tube indirect heat exchangers, in which the tubes of the heat exchanger are arranged in a tube bundle.

[0072] According to the present invention, particularly good results can be achieved when the heat exchanger is inserted into an external circulation loop. The advantages of this are that the heat exchanger can be built large enough as needed, without being limited by the reactor's working volume. Furthermore, due to the higher flow rate, the heat transfer efficiency on the process side of the heat exchanger inserted into the external circulation loop is much higher than that of a heat exchanger inserted into the reactor, meaning a smaller heat transfer surface area is required, and therefore the heat exchanger can be made smaller. Moreover, the heat exchanger inserted into the external circulation loop is easier to maintain and repair. And, regardless of the reactor's working volume, the entire surface area of ​​the heat exchanger on the process side is always available for heat transfer. Finally, the cost of a heat exchanger inserted into the external circulation loop can be lower than that of a heat exchanger built into the reactor.

[0073] In principle, any type of coolant can be used to remove heat from the indirect heat exchanger of a circulating Venturi reactor. However, for cost reasons, cooling water is used as the coolant in the indirect heat exchanger of the circulating Venturi reactor of this invention. Single-pass cooling is the simplest and earliest form of water cooling. In this case, water is drawn from rivers, lakes, groundwater, or seawater, then pumped to the heat exchanger, and the heated water is returned to its source. Alternatively, a cooling loop can be provided to circulate the cooling water. Generally, the cooling water is not ordinary water and usually contains a regulator.

[0074] The primary purpose of the circulating pump (also called the circulator pump) in the external circulation loop of the circulating venturi reactor of the present invention is to generate a large reaction mixture velocity throughout the entire external circulation loop, as it provides the power input to the ejector. The circulating fluid is forced through the ejector nozzle, where it is accelerated to form a jet, which, by its momentum, entrains the reactant gas into the mixing tube. Furthermore, the large reaction mixture velocity through the external circulation loop and through the heat exchanger improves the heat transfer effect (on the process side) in the indirect heat exchanger. Moreover, at a larger reaction mixture velocity, the settling of palladium-containing hydrogenation catalyst particles in the external circulation loop is reduced due to the high degree of turbulence, meaning that fouling is also reduced. Finally, by increasing the flow rate, the operation of the cross-flow filtration unit (which is preferably a filtration device inserted into the external circulation loop) is improved, as this reduces any filter cake buildup on the filter surface (filter cake buildup would hinder the filtrate from passing through the filter media).

[0075] The circulating pump in the external circulation loop can be any type of pump suitable for pumping a reaction mixture containing a hydroxylamine-containing phosphate buffer solution, palladium-containing hydrogenation catalyst particles, and hydrogen-containing gas. Preferably, the hydrogen-containing gas is present in the form of bubbles. Preferably, the circulating pump is specifically designed to provide high flow rates and low head. Those skilled in the art can select the optimal type of circulating pump, as pump selection is a routine task. Unique impellers and special hydrodynamic pump casing shapes enable the pumping of liquids with high solids content and high carrier gas volumes without the need for an inducer, thus avoiding wear problems when using heterogeneous catalysts. Preferably, a centrifugal pump without an inducer is selected to avoid wear problems when using heterogeneous catalysts.

[0076] The circulating Venturi reactor of the present invention includes a filtration device comprising an outlet for a hydroxylamine-containing phosphoric acid buffered aqueous solution inserted into an external circulation loop, or a pipeline connecting the external circulation loop to the filtration device containing the hydroxylamine-containing phosphoric acid buffered aqueous solution and branching off from the external circulation loop. This filtration device is used to remove palladium-containing hydrogenation catalyst particles from the solution before it comes into contact with the organic liquid and solvent containing cyclohexanone in the oxime stage. This is advantageous because the recovered palladium-containing hydrogenation catalyst particles can be reused during hydrogenation and downstream blockage and other types of process interference can be prevented. The filtration device can be a cross-flow filtration device or a dead-end filtration device.

[0077] In dead-end filtration systems, the feed passes through a membrane or filter bed, palladium-containing hydride particles deposit on the filter media, and the filtrate exits from the other end. Generally, these filtration systems require the formation of a filter cake to function effectively. Typically, the effective pore size of the filter cake is smaller than the pore size of the individual filters, which helps improve particle-fluid separation and cake buildup. However, the filter cake cannot become too thick, otherwise the filtrate throughput will be excessively restricted, and hydroxylamine may decompose within the cake due to the absence of hydrogen. Therefore, the filter cake must be removed periodically. Removing the filter cake, for example, through backwashing, is a laborious task and can disrupt continuously operating processes. In practice, to avoid this problem, dead-end filters are often designed in multiple parallel configurations for continuous processing. During backwashing, the pressure on both sides of the filter is periodically reversed, causing the permeate to flow back to the feed side, stripping the particle layer from the filter surface.

[0078] Cross-flow filtration (also known as tangential flow filtration) is a technique in which the solution to be purified flows parallel to the filter medium. As the filtrate passes through the filter medium, little or no filter cake forms because solid particles are washed away by the flow of the solution. Because no or almost no filter cake forms, the operating time of the filtration unit can be increased. Cross-flow filtration can be a continuous or batch process, unlike intermittent dead-end filtration. Optionally, catalyst particles accumulated on the cross-flow filter can be removed by backwashing.

[0079] Optionally, one or more protective filters may be installed downstream of the hydrogenation catalyst particulate filtration section. Generally, protective filters are dead-end filtration based filters with smaller pore sizes. Their primary purpose is to capture particles that leak from the main filter during normal operation, or to capture particles in the event of damage or leakage to the main filter.

[0080] In a preferred embodiment of the circulating venturi reaction apparatus of the present invention, a filter is inserted into the external circulation loop and is a cross-flow filter unit.

[0081] The circulating venturi reactor may include additional modules before, between, or after the modules listed above. For example, the reactor may also include measuring instruments for measuring pressure, temperature, flow rate, and concentration. Preferably, online measuring devices are installed.

[0082] Preferably, the circulating Venturi reactor includes means for adding a catalyst and / or activator to the phosphate-buffered aqueous solution. Preferably, the circulating Venturi reactor includes means for adding a catalyst and / or activator to the phosphate-buffered aqueous solution, operated in a batch manner. Preferably, the means includes a vessel and a stirrer, which are inertized or maintained in a hydrogen atmosphere during operation. In a preferred embodiment of the process of the present invention, the circulating Venturi reactor further includes means for adding a catalyst and / or activator to the phosphate-buffered aqueous solution, operated in a batch manner.

[0083] The circulating Venturi reactor of the present invention can be constructed using steel because steel has high tensile strength. A problem with using a reaction solution containing nitric acid is that it tends to corrode the steel in the circulating Venturi reactor using that solution. Most steels contain a certain amount of molybdenum. It is well known that molybdenum is detrimental to the selectivity of the hydroxylamine reaction; for example, the presence of 1 ppm of molybdenum in the reaction medium can lead to a reduction in hydroxylamine selectivity of more than 2%.

[0084] When used in this document, "hydroxylamine selectivity" (selectivity for hydroxylamine production) is defined as follows: the amount of hydroxylamine produced in a circulating Venturi reactor divided by the amount of hydrogen ions (H+) consumed in the circulating Venturi reactor. + The molar ratio is half of the total amount. Low selectivity means that more byproducts will be generated, which is an undesirable situation.

[0085] In this paper, the activity of a catalyst is defined as the number of grams of hydroxylamine produced per gram of catalyst per hour. In other words, the activity is related to the production rate of hydroxylamine.

[0086] A range of steels are well-known for manufacturing containers, pipes, and reactors used in the production of hydroxylamine. These include steels known as 304, 316, 304L, or 316L. Different grades of steel contain varying amounts of molybdenum and other metals. Furthermore, the levels of carbon and other elements also affect their corrosion resistance.

[0087] The maximum carbon content for 304 and 316 grade steel is 0.08 wt%, while the maximum carbon content for 304L and 316L grade steel is 0.030 wt%. The content ranges for all other elements are substantially the same (e.g., the nickel content ranges from 8.00 to 10.50 wt% for 304 steel and from 8.00 to 12.00 wt% for 304L steel).

[0088] Low-carbon "variants" (316L) emerged as alternatives to the "standard" (316) carbon content range, aiming to overcome the risk of intergranular corrosion (weld corrosion), a problem identified in the early applications of these steels. This corrosion can occur if the steel is kept at temperatures between 450 and 850°C for several minutes (the exact duration depends on the temperature) and then exposed to a highly corrosive environment. The corrosion occurs near the grain boundaries.

[0089] Preferably, the carbon content of the steel is 0 to 0.03 wt% C. If the carbon content is below 0.030 wt%, then this intergranular corrosion will not occur after exposure to these temperatures, especially for the duration typically experienced by the heat-affected zone of a "thick" section of the steel. Low-carbon steels may also be easier to weld than steels with standard carbon content.

[0090] Steel can also undergo annealing. Annealing is a heat treatment process that alters the material, causing changes in its strength, hardness, and other properties. It involves creating specific conditions by heating the material above its recrystallization temperature, holding it at a suitable temperature, and then cooling it. For steel, this process typically involves heating the material thoroughly (usually to a red-hot state) for a period of time, followed by cooling. Annealing does not reduce the carbon content, but it makes the elemental distribution more uniform, thereby improving corrosion resistance.

[0091] More preferably, austenitic steel is used. Austenite, also known as γ-phase iron, is a metallic, non-magnetic allotrope of iron, or a solid solution of iron with an alloying element. In ordinary carbon steel, austenite exists above its eutectoid critical temperature of approximately 1000 K; other alloy steels have different eutectoid temperatures.

[0092] According to a preferred embodiment of the invention, the walls of the circulating Venturi reactor comprise steel containing 0 to 0.08 wt% carbon and 0 to 0.03 wt% molybdenum. According to a particularly preferred embodiment, the walls of the circulating Venturi reactor comprise steel, and the steel is selected from the group consisting of: Quenched and annealed steel A contains 0 to 0.08 wt% carbon, 0 to 2.0 wt% manganese, 0 to 2.0 wt% silicon, 0 to 0.045 wt% phosphorus, 0 to 0.03 wt% sulfur, 17 to 21 wt% chromium, 0 to 0.03 wt% molybdenum, 8.0 to 13 wt% nickel, with the remainder being iron and unavoidable impurities; Low-carbon steel B contains 0-0.03 wt% carbon, 0 to 2.0 wt% manganese, 0 to 1.0 wt% silicon, 0 to 0.045 wt% phosphorus, 0 to 0.03 wt% sulfur, 17 to 21 wt% chromium, 0 to 0.03 wt% molybdenum, 8.0 to 13.0 wt% nickel, with the remainder being iron and unavoidable impurities; Stabilized steel C contains 0 to 0.08 wt% carbon, 0 to 2.0 wt% manganese, 0 to 2.0 wt% silicon, 0 to 0.045 wt% phosphorus, 0 to 0.04 wt% sulfur, 17 to 21 wt% chromium, 0 to 0.03 wt% molybdenum, 9.0 to 13.0 wt% nickel, and contains titanium (minimum: 5 times the carbon (C) content to maximum: 0.8 wt%) or niobium + tantalum (minimum: 8 times the carbon (C) content to maximum: 1.1 wt%), with the remainder being iron and unavoidable impurities.

[0093] Using this steel with a limited molybdenum content further improves the selectivity of the hydrogenation reaction for hydroxylamine.

[0094] The circulating venturi apparatus of the present invention is configured to implement an industrial-scale process and is an industrial-scale apparatus. "Industrial-scale" refers to production capacity, or a apparatus capable of producing at least 100 tons of hydroxylamine annually if continuously operating. In a preferred embodiment, the apparatus according to the present invention has an annual hydroxylamine production capacity of at least 1,000 tons, preferably at least 25,000 tons, more preferably at least 50,000 tons, even more preferably at least 75,000 tons, and most preferably at least 100,000 tons.

[0095] Finally, another object of the present invention is the use of the circulating Venturi reactor of the present invention as a stand-alone unit for the production of hydroxylamine, or as part of a chemical plant for the production of oxime compounds, preferably as part of a chemical plant for the production of oxime compounds, more preferably as part of a chemical plant for the production of butanone oxime, cyclopentanone oxime, cyclohexanone oxime and / or cyclododecanone oxime, and most preferably as part of a chemical plant for the production of cyclohexanone oxime.

[0096] The advantage of using it as a standalone unit is that the hydroxylamine in the phosphate-buffered aqueous solution containing hydroxylamine can be directly used in various chemical reactions without the need for complex and expensive separation and purification steps. The advantage of using it as part of a chemical plant producing oxime compounds is that the phosphate-buffered aqueous solution formed after the hydroxylamine reaction in the phosphate-buffered aqueous solution containing hydroxylamine can be reused, preferably after purification according to the process of the present invention and the addition of nitrates. This is beneficial because the valuable compounds (especially nitrates and phosphates) contained in the hydroxylamine in the phosphate-buffered aqueous solution containing hydroxylamine are not lost. Attached Figure Description

[0097] The following will refer to Figure 1-5 The present invention and the prior art are described below.

[0098] Figure 1 : Applicable to the production of oxime compounds using HPO® and HPO® plus A schematic diagram of a device for the technical production of oximes.

[0099] Figure 2 HPO® and HPO® for the production of oxime compounds according to existing technology plus The technology, as part of an apparatus suitable for the production of oximes, is illustrated in the diagram of an apparatus suitable for the production of hydroxylamine.

[0100] Figure 3 : A schematic diagram of the structure of an example of the gas suspension injector of the present invention.

[0101] Figure 4 HPO® and HPO® are suitable for the production of oxime compounds. plus A schematic diagram of a circulating Venturi reaction apparatus suitable for producing oximes according to the present invention, as part of a technical production apparatus for oximes.

[0102] Figure 5 HPO® and HPO® are suitable for the production of oxime compounds. plus A schematic diagram of a cyclic Venturi reaction apparatus for the technical production of oximes, applicable to the production of hydroxylamine according to the present invention.

[0103] However, the invention is defined by the claims and as generally described herein. It should not be limited to the following. Figures 3 to 5 The implementation methods shown are for illustrative purposes.

[0104] Figure 1 This indicates that HPO® and HPO® are suitable for use in the production of oxime compounds. plusA schematic diagram of the apparatus for the technical production of oximes. Hydrogen-containing gas is delivered to the hydroxylamine generation zone [1] via pipeline

[11] . A phosphate-buffered aqueous solution containing nitrates is supplied via pipeline

[25] . A gas mixture containing hydrogen and non-hydrogen compounds (such as N2O) is discharged via pipeline

[26] . A phosphate-buffered aqueous solution containing hydroxylamine is delivered to the hydroxylamine removal zone [2] (also known as the oxime section) via pipeline

[12] . Ketones are supplied via pipeline

[13] . After reaction in the oxime section, the generated oximes are removed in the organic phase via pipeline

[14] . A phosphate-buffered aqueous solution is delivered to the separation unit [3] via pipeline

[15] . A portion of the phosphate-buffered aqueous solution is periodically delivered to the neutralization section [4] via pipeline

[16] . Ammonia supplied via pipeline

[17] is used for neutralization. The resulting neutralized solution is discharged via pipeline

[18] . The remaining phosphate-containing buffer solution is transported via pipeline

[19] to the dehydration zone [6], where the solution is concentrated by dehydration. The removed water is discharged via pipeline

[20] . The resulting concentrated phosphate-containing buffer solution is transported via pipeline

[21] to the ammonia conversion zone [6], where nitrous gas supplied via pipeline

[22] is used to convert ammonia. The resulting phosphate-containing buffer solution with reduced ammonia content is transported via pipeline

[23] to the addition unit [7], where nitrous gas and / or nitric acid are added via pipeline

[24] and dissolved in the solution. The resulting nitrate-containing phosphate-containing buffer solution is transported via pipeline

[25] to the hydroxylamine generation zone [1], and then the process is repeated.

[0105] Figure 2 HPO® and HPO® are used to produce oxime compounds according to existing technology. plusThe technology, as part of an apparatus for the production of oxime, is a schematic diagram of an apparatus for the production of hydroxylamine. It includes a high-pressure autoclave three-phase bubbling tower reactor [a], a cooling element [b], a first gas distributor [c], a second gas distributor [d], a gas suspension separator [e], a gas recirculation compressor [f], and a catalyst filtration unit [g]. The high-pressure autoclave three-phase bubbling tower reactor [a] is placed vertically and equipped with a water-cooled shell-and-tube heat exchanger [b] to remove heat from the hydrogenation reaction. Cooling water enters the heat exchanger [b] through pipeline

[201] , absorbs heat, and is discharged through pipeline

[202] . The high-pressure autoclave three-phase bubbling tower reactor [a] is also equipped with a first gas distributor [c] for generating hydrogen-rich bubbles below the heat exchanger [b], and a second gas distributor [d] for generating hydrogen-rich bubbles in the lower part of the main body of the bubbling tower reactor [a]. Fresh hydrogen-containing gas is supplied to the hydrogenation unit through pipeline

[203] . A portion of fresh hydrogen-containing gas is introduced into the reactor via a first gas distributor [c], and the remainder is introduced via a second gas distributor [d]. A gas mixture containing hydrogen and non-hydrogen compounds (such as N₂O) is discharged from the top of the bubble column reactor [a] via line

[204] . This gas mixture is combined with a gas mixture discharged from one of the gas suspension separators [e] (only one is shown in the figure) via one of the lines

[205] (only one is shown in the figure). A portion of the combined gas mixture is discharged from the device via line

[206] . The remaining gas mixture is introduced into the gas recirculation compressor [f] via line

[207] . The gas mixture discharged from the gas recirculation compressor [f] is combined with a portion of fresh hydrogen-containing gas introduced via line

[203] and introduced into the reactor via line

[208] . The gas mixture is dispersed in a phosphate-buffered aqueous solution reaction mixture via the second gas distributor [d]. A phosphate-buffered aqueous solution containing nitrates is supplied via line

[209] . The nitrate-containing phosphoric acid buffer solution is obtained by adding fresh nitric acid or nitrogen oxides to the phosphoric acid buffer solution (not shown in the figure). A multiphase mixture containing the hydroxylamine-containing phosphoric acid buffer solution, hydrogenation catalyst particles, and hydrogen gas flows into the gas suspension separator [e] through one of the lines

[210] (only one shown in the figure). In the gas suspension separator [e], the gas phase is separated from the multiphase mixture and discharged through one of the lines

[205] (only one shown in the figure). The remainder of the multiphase mixture is discharged from the bottom of the gas suspension separator [e] through one of the lines

[211] (only one shown in the figure) and then fed into one of the catalyst filtration units [g] (only one shown in the figure). In the catalyst filtration unit [g], the hydroxylamine-containing phosphoric acid buffer solution, which contains almost no catalyst particles, is separated and conveyed to the oxime section (not shown in the figure) through one of the lines

[212] (only one shown in the figure).A mixture containing a hydroxylamine-containing phosphate buffer solution and catalyst particles is discharged from the catalyst filtration unit [g] through a line

[213] (only one is shown in the figure) and then fed into the bottom of the bubble column reactor [a].

[0106] Figure 3 This is a schematic diagram of an example of the gas suspension injector [F] of the present invention. The gas suspension injector [F] includes a suspension inlet [G], a fluid nozzle [H], an intake chamber [I], a converging inlet nozzle [J], a throat [K], and a diverging outlet diffuser [L]. A suspension [α] containing hydroxylamine, a phosphate buffered aqueous solution, and catalyst particles enters the gas suspension injector [F] through the suspension inlet [G]. Preferably, the stream [α] entering the gas suspension injector [F] also contains bubbles. The suspension (preferably with bubbles) then enters the intake chamber [I] through the fluid nozzle [H]. In the intake chamber [I], fresh hydrogen-containing gas [β] is introduced through the inlet [M]. Here, fresh hydrogen-containing gas refers to hydrogen-containing gas originating from outside the circulating Venturi reactor [X]. Fresh hydrogen-containing gas can originate from various sources and be produced through different processes, such as steam methane reforming, water electrolysis, methanol dehydrogenation, (lignite) gasification, biomass gasification, methane pyrolysis, hydrocarbon feedstock cracking, and underground hydrogen extraction. Alternatively, fresh hydrogen-containing gas can be produced by removing non-hydrogen compounds from hydrogen-containing and N₂O-containing gases discharged from the circulating venturi reactor [X]. In addition to fresh hydrogen-containing gas, hydrogen-containing gas accumulating at the top of the reaction vessel [Z] can also be fed into the intake chamber [I] (not shown in the figure). The suspension stream drags the gas from the intake chamber [I] to the converging inlet nozzle [J], then through the throat [K] to the diverging outlet diffuser [L], thereby forming an extremely fine hydrogen-containing bubble dispersion in a suspension of hydroxylamine-containing phosphoric acid buffer solution and catalyst particles. The resulting dispersion [γ] is discharged from the gas suspension injector [F] and charged into the reaction vessel [Z] (not shown in the figure).

[0107] Figure 4This is a schematic diagram of a circulating Venturi reactor [X] suitable for the production of hydroxylamine according to the present invention. The circulating Venturi reactor [X] comprises a vertically placed hydrogenation reactor [A] with an aspect ratio of at least 2, an external circulation loop [B], a water-cooled indirect heat exchanger [C], a circulation pump [D], a catalyst filter [E], a downward gas suspension injector [F], a suspension inlet [G], a fresh hydrogen-containing gas inlet [M], a gas discharge line [N], a suspension outlet [O], a distributor [P], a circulation pipe [Q], an outlet of a phosphate-buffered aqueous solution containing hydroxylamine [R], equipment connection segments [S], an inlet of a phosphate-buffered aqueous solution containing nitrate [T], a gas circulation line [U], a cooling water inlet [V], a cooling water outlet [W], and a reaction vessel [Z]. The autoclave hydrogenation reactor [A] is placed vertically and is equipped with a downward gas suspension injector [F] on top of the reaction vessel [Z]. The gas intake chamber of the gas suspension injector [F] is located outside the reaction vessel [Z]. This allows for easy connection and disconnection of the pipeline supplying fresh hydrogen to the gas inlet [M]. A gas recirculation line [U] connects the upper part of the reaction vessel [Z] to the gas intake chamber of the gas suspension injector [F]. Hydrogen-containing gas flows into the gas intake chamber of the gas suspension injector [F] through the gas recirculation line [U]. A suspension of hydroxylamine-containing phosphoric acid buffer solution and palladium hydrogenation catalyst particles enters the downward gas suspension injector [F] through the suspension inlet [G]. The reaction mixture is injected into the upper region of the reaction vessel [Z] and then flows into the recirculation pipe [Q] inserted centrally along the longitudinal direction of the reactor. Optionally, the reactor [A] may not be equipped with the recirculation pipe [Q] (not shown in the figure). A splitter [P] is located in the lower region of the reaction vessel [Z], below the injector. Both the recirculation pipe [Q] and the splitter [P] improve the mixing of the reaction mixture within the reaction vessel [Z]. Optionally, reactor [A] may not be equipped with a splitter [P] (not shown in the figure). The outlet of the gas suspension injector [F] that injects the reaction mixture into the upper region of the reaction vessel [Z] may be located above or below the surface of the reaction mixture (i.e., a suspension of hydroxylamine-containing phosphoric acid buffered aqueous solution and palladium hydrogenation catalyst particles, as well as hydrogen-containing bubbles) within the reaction vessel [Z]. Optionally, the reaction vessel [Z] may be equipped with more than one downward gas suspension injector [F] (not shown in the figure). This has the advantage of allowing for a shorter nozzle length compared to a single nozzle. A gas mixture containing hydrogen and inert substances (such as N₂O) is discharged from reactor [A] through a gas exhaust line [N]. Optionally, the gas mixture discharged through the gas exhaust line [N] may be purified to remove at least some of the inert substances, and then at least part of the discharged hydrogen-containing gas may be recharged into reactor [A], optionally through a fresh hydrogen-containing gas inlet [M] (not shown in the figure).A phosphate-buffered aqueous solution containing hydroxylamine, hydrogenation catalyst particles, and a suspension that typically also contains hydrogen bubbles are discharged from reactor [A] through suspension outlet [O] and enter external circulation loop [B]. This outlet can be located at any desired location in reactor [A], but is preferably located at the bottom of reactor [A]. External circulation loop [B] connects the suspension outlet [O] of reactor [A] to the suspension inlet [G] of gas suspension injector [F]. A circulation pump [D], a catalyst filter [E], and a water-cooled indirect heat exchanger [C] are sequentially inserted into external circulation loop [B]. The devices are connected via equipment connection segments [S]. The order of the circulation pump [D], catalyst filter [E], and water-cooled indirect heat exchanger [C] in external circulation loop [B] may vary. Figure 3 The sequence may differ. For example, the sequence might begin with a circulation pump [D], followed by a water-cooled indirect heat exchanger [C], and finally a catalyst filter [E]. The circulation pump [D] circulates the hydroxylamine-containing phosphoric acid buffer solution within the circulating Venturi reactor [X]. The circulation rate of the hydroxylamine-containing phosphoric acid buffer solution within the circulating Venturi reactor [X] can vary over a wide range. Generally, the circulation rate of the hydroxylamine-containing phosphoric acid buffer solution varies between 10 and 500 times per hour, preferably between 15 and 300 times per hour, and most preferably between 20 and 250 times per hour. The circulation rate (expressed in cycles per hour) here is defined as the flow rate (in cubic meters per hour) of the hydroxylamine-containing phosphoric acid buffer solution through the external circulation loop divided by the total volume (in cubic meters) of the hydroxylamine-containing phosphoric acid buffer solution in the circulating Venturi reactor [X]. In a preferred embodiment of the process of the present invention, the circulation rate of the phosphate buffer aqueous solution ranges from 10 to 500 times per hour, preferably from 15 to 300 times per hour.

[0108] In the catalyst filtration unit [E], a hydroxylamine-containing phosphoric acid buffer solution [R] containing almost no catalyst particles is separated. The catalyst filtration unit [E] can be of any type. Preferably, the catalyst filtration unit employs cross-flow filtration or dead-end filtration technology, with cross-flow filtration technology being the most preferred. Optionally, the stream [R] is further filtered in a second filtration unit (not shown) located downstream to remove remaining catalyst particles. The circulating Venturi reactor [X] is equipped with a water-cooled shell-and-tube heat exchanger [C] to remove the heat generated by the hydrogenation reaction. Cooling water enters the heat exchanger [C] through a line [V], absorbs heat, and is discharged through a line [W]. A nitrate-containing phosphoric acid buffer solution is supplied through a line [T] to an external circulation loop [B] downstream of the catalyst filtration unit [E]. Alternatively, the nitrate-containing phosphoric acid buffer solution is supplied through a line [T] to other locations in the circulating Venturi reactor [X], such as to the reaction vessel [Z]. A phosphate buffer solution containing nitrates is obtained by adding fresh nitric acid or nitrogen oxides to a phosphate buffer solution (not shown in the figure).

[0109] Figure 5 This is a schematic diagram of another circulating Venturi reactor [X] suitable for the production of hydroxylamine according to the present invention. A vertically placed hydrogenation reactor [A] with an aspect ratio of at least 2 and an external circulation loop [B] are shown. Figure 4 The vertically placed hydrogenation reactor [A] with an aspect ratio of at least 2 and the external circulation loop [B] shown are substantially similar, except that the catalyst filter [E] is not inserted into the external circulation loop [B], but rather into a branch line [Y] from the external circulation loop [B]. In the catalyst filter [E], a hydroxylamine-containing phosphate buffer aqueous solution [R] containing almost no palladium hydrogenation catalyst particles is separated. The catalyst filter [E] can be any type of catalyst filter. Preferably, the catalyst filter employs cross-flow filtration or dead-end filtration, with dead-end filtration being the most preferred. Optionally, the stream [R] is further filtered in a second downstream filtration unit (not shown) to remove any remaining catalyst particles. Optionally, the stream containing palladium hydrogenation catalyst particles or a stream containing a suspension of palladium hydrogenation catalyst particles in an aqueous solution (e.g., a phosphate buffer aqueous solution) is discharged from the catalyst filter [E] and introduced into any desired location in the circulating venturi reactor [X].

[0110] While the invention has been described through several preferred embodiments, those skilled in the art will recognize that modifications, equivalent substitutions, and improvements can be made without departing from the scope and spirit of the invention. The invention can be operated on an industrial scale. Apparatus suitable for the production of hydroxylamine can be operated in continuous mode. Therefore, no limitation is intended for the invention except as defined in the appended claims.

[0111] The invention will be described in further detail in the following embodiments, which are not intended to limit the scope of the invention as defined by the appended claims.

[0112] Example Comparative Example 1 This comparative example was conducted in a commercial nitrate hydrogenation unit, specifically an HPO® plant used to produce cyclohexanone oxime (which is subsequently converted to ε-caprolactam). plus Part of the factory. HPO® plus Factory and Figure 1 The basic correspondence shown is that the nitrate hydrogenation unit and Figure 2 The basic correspondence is shown. Extensive data on this nitrate hydrogenation unit has been collected over the years. During this period, the actual hydroxylamine production rate of the nitrate hydrogenation unit was not constant and varied primarily due to market conditions. Converted to annual production, the hydroxylamine production rate varied between approximately 25,000 tonnes to approximately 50,000 tonnes per year. The catalyst used for the selective reduction of nitrate is activated carbon containing 10% palladium (10% Pd / C). The nitrate concentration in the phosphate buffered aqueous solution containing nitrate fed to the nitrate hydrogenation unit varied between 2 and 3 mol / kg of phosphate buffered aqueous solution. The nitrate concentration in the phosphate buffered aqueous solution containing hydroxylamine discharged from the nitrate hydrogenation unit varied between 0.5 and 1.0 mol / kg of phosphate buffered aqueous solution. The acid concentration in the phosphate buffered aqueous solution containing hydroxylamine discharged from the nitrate hydrogenation unit varied between 0.4 and 0.6 mol / kg of phosphate buffered aqueous solution. The phosphate concentration in the hydroxylamine-containing phosphate buffer solution discharged from the nitrate hydrogenation unit varied between 2.8 and 3.8 mol / kg of the phosphate buffer solution. The hydroxylamine concentration in the hydroxylamine-containing phosphate buffer solution discharged from the nitrate hydrogenation unit remained consistently at approximately 1 mol / kg of the phosphate buffer solution.

[0113] During this period, the hydrogen partial pressure of the feed stream entering the three-phase bubble column through the gas distributor above the heat exchanger varied between 10 and 20 bar, while the partial pressure of fresh hydrogen remained at approximately 25 bar. The coolant used in the heat exchanger below the main body of the bubble column was cooling water drawn from a cooling water network. During this period, the average temperature of the phosphate buffer solution within the three-phase bubble column fluctuated between 42 and 50°C. Furthermore, the selectivity for hydroxylamine varied between 82% and 89% during this time.

[0114] Comparative Example 2 The operation of the aforementioned system was transformed into a numerical model developed using GNU Octave version 7.1.0. This model describes the system by combining hydrogen-liquid mass transfer, hydrogen-liquid-solid mass transfer, reaction kinetics, material balance, and heat balance. The simulation results obtained using this program include numerical values ​​for the productivity and selectivity of the target product hydroxylamine and undesired byproducts. The model predicts the effects of numerous variables, including temperature, hydrogen partial pressure, nitrate content, gas retention rate, apparent gas velocity, liquid residence time, catalyst retention rate, and catalyst particle size. The description of the reaction kinetics was obtained through laboratory-scale experiments under representative conditions, using an extended version of the equations given by A. Schumpe et al. in Chem.-Ing.-Tech. (Vol. 59, No. 1, 1987, pp. 72-73 and Vol. 60, No. 4, 1988, pp. 302-304). The description of the nitrate hydrogenation unit is based on production data from the commercially operating hydrogenation unit described in Example 1, calibrated. The model was adapted to simulate the performance of nitrate hydrogenation in a circulating Venturi reactor. The performance of these alternative units was characterized by numerical values ​​of the productivity and selectivity of the target product hydroxylamine and undesired byproducts. These simulation results were compared with the performance of the commercial nitrate hydrogenation unit described in Comparative Example 1.

[0115] Example 1 The effect of enhanced heat transfer This embodiment is based on... Figure 3 It was carried out in a device that is basically similar to the one shown.

[0116] The simulation model described in Comparative Example 2, developed to describe the process shown in Comparative Example 1, is for... Figure 3The equipment configuration shown has been modified. Almost all parameters are identical to those of the prior art unit described in Comparative Example 1, including the total liquid retention rate, hydrogen partial pressure, hydrogen-liquid mass transfer, hydrogen-liquid-solid mass transfer, catalyst concentration, average liquid residence time, nitrate concentration in the nitrate-containing phosphate buffer aqueous feed to the nitrate hydrogenation unit, and the size of the heat exchanger. When comparing the two units, the type of coolant (cooling water drawn from the cooling water network), the temperature of the coolant, and the coolant feed rate into the heat exchanger are all constant. The main difference between the two simulated units lies in the liquid flow rate on the process side of the heat exchanger. For the circulating venturi reactor unit with a heat exchanger in the external circulation loop, a much higher liquid flow rate can be achieved (on the process side) compared to the conventional unit with a heat exchanger located below the main body of the bubbling tower.

[0117] Simulation results show that, under a range of process conditions, the average temperature of the hydroxylamine-containing phosphate buffer solution in the circulating venturi apparatus can be easily reduced by several degrees Celsius compared to conventional apparatus. The main consequence of this temperature reduction is an approximately 2% increase in selectivity for the target product hydroxylamine, while the selectivity for undesirable byproducts decreases by the same percentage.

[0118] Example 2 Effects on improving gas-liquid mass transfer This embodiment is based on... Figure 3 It was carried out in a device that is basically similar to the one shown.

[0119] The simulation model described in Comparative Example 2 and developed for Comparative Example 1 is aimed at Figure 3 The equipment configuration shown has been adjusted. Almost all parameters are valued in the same way as those in the prior art device described in Comparative Example 1, including the total liquid retention rate in the device, the hydrogen partial pressure in the device, the hydrogen-liquid-solid mass transfer, the catalyst concentration, the nitrate concentration in the nitrate-containing phosphate buffer aqueous solution feed of the nitrate hydrogenation device, and the heat transfer rate of the heat exchanger.

[0120] The main difference between the two simulations lies in the different hydrogen-liquid mass transfer rates resulting from the use of different types of equipment. In the case of the circulating Venturi reactor, a Venturi jet gas distributor is used, which produces smaller hydrogen-containing bubbles compared to conventional devices using bubbling gas distributors.

[0121] Simulation results show that, under a wide range of process conditions, the hydrogen-liquid mass transfer rate in the circulating venturi unit is improved compared to that of conventional units. The most important result of this enhanced gas-liquid mass transfer is an approximately 2% increase in selectivity for the target product hydroxylamine, a similarly reduced selectivity for undesirable byproducts, and an approximately 30% increase in hydroxylamine productivity.

[0122] Example 1 shows that in the circulating venturi reactor device according to the present invention, the average temperature of the reaction liquid can be reduced, and therefore, the selectivity of nitrate hydrogenation to hydroxylamine can be significantly improved compared with the prior art process.

[0123] Example 2 shows that in the circulating venturi reactor device according to the present invention, enhanced hydrogen-liquid mass transfer can be achieved. Therefore, compared with the prior art process, the selectivity of nitrate hydrogenation to hydroxylamine and the productivity of hydroxylamine can be significantly improved.

[0124] These examples demonstrate that overall selectivity for hydroxylamine can be improved by enhancing heat transfer and / or hydrogen-liquid mass transfer during nitrate hydrogenation in a phosphate-buffered aqueous solution. This reduces the consumption of nitrate and hydrogen feedstocks during hydroxylamine production, decreases the variable costs of hydroxylamine production, and improves the carbon footprint of hydroxylamine production. Furthermore, the reduced amount of byproducts generated also lowers the costs associated with removing these byproducts.

[0125] Furthermore, improving hydrogen-liquid mass transfer during nitrate hydrogenation in a phosphate-buffered aqueous solution has been shown to increase hydroxylamine production. This allows the entire nitrate hydrogenation process to produce more hydroxylamine, thereby reducing the fixed costs of hydroxylamine production—that is, the cost is spread across a larger hydroxylamine yield.

[0126] Therefore, Examples 1 and 2 demonstrate significant improvements over existing technology processes.

Claims

1. A continuous process for preparing hydroxylamine in a phosphate-buffered aqueous solution by hydrogenating nitrate with hydrogen in a circulating Venturi reactor ([X]) at a pressure above atmospheric pressure in the presence of suspended palladium-containing hydrogenation catalyst particles, the circulating Venturi reactor ([X]) comprising a hydrogenation reactor ([A]) and an external circulation loop ([B]), wherein the hydrogenation reactor ([A]) includes a downward gas suspension injector ([F]) in the upper region of the hydrogenation reactor ([A]), the injector ([F]) comprising a reaction mixture inlet ([G]), a kinetic fluid nozzle ([H]), an intake chamber ([I]), a throat ([K]), a divergent outlet diffuser ([L]), and optionally a converging inlet nozzle ([J]), wherein the process comprises the following steps: a) A fresh nitrate-containing phosphate buffer solution is introduced into the hydrogenation reactor ([A]) and / or the external circulation loop ([B]); b) Fresh hydrogen-containing gas is introduced into the circulating Venturi reactor ([X]), preferably into the hydrogenation reactor ([A]); c) Under the action of palladium-containing hydrogenation catalyst particles, the nitrate introduced in step a) is hydrogenated using the hydrogen introduced in step b), wherein the hydrogenation is carried out at a temperature in the range of 20 to 65°C, preferably in the range of 25 to 55°C, and most preferably in the range of 30 to 45°C, to provide a reaction mixture comprising a hydroxylamine-containing phosphoric acid buffer aqueous solution, hydrogenation catalyst particles, and hydrogen-containing gas. d) Circulate the reaction mixture through the circulating Venturi reactor ([X]); e) Cooling the reaction mixture, wherein the cooling is performed by water in an indirect heat exchanger ([C]) located in the external circulation loop ([B]); f) Discharge of a hydroxylamine-containing phosphoric acid buffered aqueous solution from the circulating Venturi reactor ([X]), wherein the reaction mixture is filtered in a filter device ([E]) inserted into the external circulation loop ([B]) or through a line ([Y]) branching off from the external circulation loop ([B]) and connecting the external circulation loop ([B]) to the filter device ([E]); g) Discharge of N2O-containing gas from the circulating Venturi reactor ([X]); in: The gas retention rate of the reaction mixture flowing through the external circulation loop ([B]) is at least 5% by volume, preferably at least 8% by volume, more preferably at least 12% by volume, and most preferably at least 15% by volume. In step f), the phosphate concentration measured in the phosphate-buffered aqueous solution containing hydroxylamine discharged from the circulating Venturi reactor is 2 to 4 mol / kg, preferably 2.8 to 3.8 mol / kg. The acid concentration in the phosphate-containing buffer solution is 0.3 to 0.7 mol / kg, preferably 0.4 to 0.6 mol / kg.

2. The process of claim 1, wherein the circulation rate of the reaction mixture is 10 to 500 times per hour, preferably 15 to 300 times per hour.

3. The process according to claim 1 or 2, wherein the partial pressure of the inert gas in the hydrogenation reactor ([A]) is in the range of 0.5 to 50 bar, preferably in the range of 2 to 40 bar, and most preferably in the range of 5 to 30 bar.

4. The process according to any one of the preceding claims, wherein the nitrate concentration in the hydroxylamine-containing phosphate buffer aqueous solution discharged from the circulating Venturi reactor ([X]) in step f) is expressed in moles per kilogram of solution, and the nitrate concentration in the nitrate-containing phosphate buffer aqueous solution charged into the circulating Venturi reactor [X] in step a) is expressed in moles per kilogram of solution, in the range of 1:2 to 1:6, more preferably in the range of 1:2.5 to 1:

5.

5. The process as described in any of the preceding claims, wherein palladium-containing hydrogenation catalyst particles are fed into the hydrogenation reactor ([A]) and / or the external circulation loop ([B]) in an intermittent mode.

6. The process as described in any of the preceding claims, wherein the N2O concentration in the N2O-containing gas discharged in step g) is in the range of 0 to 2 vol%, particularly in the range of 0.01 to 1 vol%, more particularly in the range of 0.05 to 0.5 vol%, and most particularly in the range of 0.08 to 0.3 vol%.

7. The process as described in any of the preceding claims, wherein the concentration of hydroxylamine in the phosphate-buffered aqueous solution containing hydroxylamine discharged from the circulating Venturi reactor ([X]) in step f) ranges from 0.50 to 2 mol per kilogram of the phosphate-buffered aqueous solution, more preferably about 1 mol per kilogram of the phosphate-buffered aqueous solution.

8. The process according to any one of the preceding claims, wherein the N2O-containing gas discharged in step g) is purified, and at least a portion of the discharged N2O-containing gas is reused in the hydrogenation reaction, preferably, the purification is carried out by adsorption or membrane separation, thereby removing at least a portion of the N2O from the N2O-containing gas.

9. A circulating Venturi reactor ([X]) for the continuous preparation of hydroxylamine in a phosphate-buffered aqueous solution by hydrogenation of nitrates with hydrogen in the presence of suspended palladium-containing hydrogenation catalyst particles at a pressure above atmospheric pressure, wherein the circulating Venturi reactor ([X]) comprises: (a) A hydrogenation reactor ([A]), preferably having an aspect ratio of at least 2, more preferably at least 4, said hydrogenation reactor ([A]) comprising: Inlet for fresh hydrogen ([M]); The outlet ([N]) containing N2O gas in the upper region of the hydrogenation reactor ([A]); The reaction mixture outlet ([O]) is located in the lower region of the hydrogenation reactor ([A]); The downward gas suspension injector (F) in the upper region of the hydrogenation reactor ([A]) includes a reaction mixture inlet ([G]), a kinetic fluid nozzle ([H]), an intake chamber ([I]), a throat ([K]), a divergent outlet diffuser ([L]), and optionally includes a convergent inlet nozzle ([J]). Optionally, a splitter ([P]) is arranged below the ejector in the lower region of the hydrogenation reactor ([A]); Optionally, a circulation pipe ([Q]) is arranged below the ejector in the lower region of the reactor ([A]); Optionally, the inlet is a phosphate-buffered aqueous solution containing nitrates ([T]). (b) The outer loop ([B]), which includes: Water-cooled indirect heat exchanger ([C]); Circulating pump ([D]); A filtration device ([E]) comprising an outlet ([R]) of a hydroxylamine-containing phosphate-buffered aqueous solution inserted into the external circulation loop ([B]), or a line ([Y]) branching from the external circulation loop ([B]) and connecting the external circulation loop ([B]) to the outlet ([R]) of the filtration device ([E]) containing the hydroxylamine-containing phosphate-buffered aqueous solution; and Optionally, the inlet ([T]) is a nitrate-containing phosphate buffer solution, and The external circulation loop ([B]) connects the reaction mixture outlet ([O]) of the hydrogenation reactor ([A]) to the reaction mixture inlet ([G]) of the gas suspension injector ([F]).

10. The circulating Venturi reactor ([X]) as claimed in claim 9, wherein the outlet flow rate of the reaction mixture exiting the liquid nozzle ([H]) is at least 10 m / s, preferably greater than 20 m / s, and wherein hydrogen-containing gas is drawn in from the intake chamber ([I]).

11. The circulating venturi reaction apparatus ([X]) as described in any of the preceding claims, wherein the filtering device ([E]) is inserted into the external circulation loop ([B]) and is a cross-flow filtering unit.

12. The circulating Venturi reactor ([X]) as described in any of the preceding claims, wherein the water-cooled indirect heat exchanger ([C]) is selected from a shell-and-tube heat exchanger or a plate heat exchanger, preferably a shell-and-tube heat exchanger.

13. The circulating Venturi reactor ([X]) as described in any of the preceding claims, wherein the walls of the circulating Venturi reactor ([X]) comprise steel, and the steel is selected from the group consisting of: Quenched and annealed steel A contains 0 to 0.08 wt% carbon, 0 to 2.0 wt% manganese, 0 to 2.0 wt% silicon, 0 to 0.045 wt% phosphorus, 0 to 0.03 wt% sulfur, 17 to 21 wt% chromium, 0 to 0.03 wt% molybdenum, 8.0 to 13 wt% nickel, with the remainder being iron and unavoidable impurities; Low-carbon steel B contains 0-0.03 wt% carbon, 0 to 2.0 wt% manganese, 0 to 1.0 wt% silicon, 0 to 0.045 wt% phosphorus, 0 to 0.03 wt% sulfur, 17 to 21 wt% chromium, 0 to 0.03 wt% molybdenum, 8.0 to 13.0 wt% nickel, with the remainder being iron and unavoidable impurities; Stabilized steel C contains 0 to 0.08 wt% carbon, 0 to 2.0 wt% manganese, 0 to 2.0 wt% silicon, 0 to 0.045 wt% phosphorus, 0 to 0.04 wt% sulfur, 17 to 21 wt% chromium, 0 to 0.03 wt% molybdenum, 9.0 to 13.0 wt% nickel, and contains titanium (minimum: 5 times wt% of carbon (C) to maximum: 0.8 wt%) or niobium + tantalum (minimum: 8 times wt% of carbon (C) to maximum: 1.1 wt%), with the remainder being iron and unavoidable impurities.

14. The circulating Venturi reactor ([X]) as described in any of the preceding claims, wherein the hydroxylamine production capacity is at least 100 tons per year, preferably at least 25,000 tons per year, more preferably at least 50,000 tons per year, even more preferably at least 75,000 tons per year, and most preferably at least 100,000 tons per year.

15. The circulating venturi reactor ([X]) as described in any one of claims 9 to 14 is used as a separate unit for the production of hydroxylamine or as part of a chemical plant for the production of oxime compounds, preferably as part of a chemical plant for the production of oxime compounds, more preferably as part of a chemical plant for the production of butanone oxime, cyclopentanone oxime, cyclohexanone oxime and / or cyclododecanone oxime, and most preferably as part of a chemical plant for the production of cyclohexanone oxime.

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