KR20140012146A - Method for preparing hydroxylamine - Google Patents

Abstract

The present invention includes the production of hydroxylamine by supplying nitrate and phosphate in an acidic aqueous liquid to the reaction zone and reducing the nitrate with hydrogen, wherein the nitrate concentration in the reaction zone is determined in the liquid exiting the reaction zone. When the hydroxylamine is produced in a continuous process when the molar ratio of nitrate to phosphate is 0.5 or less in the reaction zone of 0.5 or less and the molar ratio of ammonia to nitrate is 2.2 to 7; It relates to an oxime production method and a lactam production method including the hydroxyl production method.

Description

Production method of hydroxylamine {METHOD FOR PREPARING HYDROXYLAMINE}

The present invention relates to a process for preparing hydroxylamine, a process for preparing oxime, and a process for preparing lactam in a continuous process.

Hydroxylamine (hereinafter also referred to herein as "HYAM") is a reagent commonly used in myriad organic and inorganic reactions. It is particularly suitable for use in the preparation of oximes, in particular cyclohexanone oximes, which can then be converted to caprolactam via a Beckmann potential. Beckman's potential process for preparing caprolactam is commonly described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, eg, 7th edition (2005), Chapter on Caprolactam DOI: 10.1002 / 14356007.a05.031 (February 2011). 18th Amendment). Other oximes that have been described using hydroxylamines include cyclododecanone oximes (eg EP-A 1,329,448) and butanone oximes.

Processes for preparing hydroxylamine are also commonly known in the art. In addition, various patents have been registered on this subject. For example, GB-A-1,287,303 and US-5,364,609 relate to methods of reducing nitrate in phosphate buffer solutions using molecular hydrogen.

HPM ^® cyclohexanone oxime method of DSM (e.g., HJ Damme, JT van Goolen and AH de Rooij, Cyclohexanone oxime made without by-product (NH ₄₎ ) ₂ SO ₄ , July 10, 1972, Chemical Engineering, pp 54/55; Or Ullmann's encyclopedia of industrial chemistry (2005), Chapter Caprolactam, pp 6/7; DOI: 10.1002 / 14356007.a05.031 (revised February 18, 2011) uses two recycled liquids, inorganic liquids and organic liquids, of which several reactions and operations take place. An inorganic liquid, that is, an aqueous solution of phosphoric acid and an ammonium nitrate-containing solution, is fed to a hydrogenation reactor, where hydroxylamine is produced. Hydroxylamines are produced through the reduction of nitrate ions with hydrogen, which is facilitated by heterogeneous catalysts (palladium-containing catalysts with carbon as carrier).

In a gas-liquid reactor, gaseous hydrogen is contacted with a circulating inorganic liquid containing nitrate ions together with a buffer acid and a catalyst. The hydrogen containing gaseous phase is circulated throughout a bubble column type reactor by a circulation compressor. Fresh hydrogen is supplied to the circulating gas, with a small amount removed from the system to maintain a constant hydrogen pressure. Inert gaseous components and fresh gaseous by-products N ₂ and N ₂ O in fresh hydrogen are removed via gas purge.

By the Mammoth pump principle, the gas-liquid from the gas-fed reactor zone through the gas-liquid separator to the filter candle in the filtration zone, and also through the heat exchanger to remove the heat of reaction, back to the gas-fed reactor zone Circulate the suspension.

The inorganic liquid obtained after filtration is then contacted with an organic liquid which is a mixture of toluene and cyclohexanone in the oxime zone. Here, cyclohexanone is actually converted to cyclohexanone oxime quantitatively. The cyclohexanone oxime-containing organic phase obtained is distilled off to recover toluene.

The inorganic liquid exiting the oxime zone is completely purified to protect the catalyst of the hydroxylamine reactor. This is done by extracting with toluene and then stripping with water vapor. In the stripping column, the co-generated water and cyclohexanone oxime are also removed during the preparation of the hydroxylamine. A small amount of ammonia by-product remains in the solution, but is prevented from accumulating by converting ammonia to nitrogen in an absorber for a gas mixture of NO and NO ₂ (ie, nitrogen oxides and nitrogen dioxide; hereafter also referred to as nitrogen gas).

Finally, the amount of nitrate consumed must be replenished. The nitrogen gas required for this is produced in the ammonia combustion unit.

EP 1947056 A1 describes a process for preparing hydroxylamine by reducing nitrate with hydrogen gas in the presence of a catalyst in an inorganic process solution containing an acidic buffer as part of a combined hydroxylamine and oxime system. This teaches that such a recycling system can reduce the loss rate of hydroxylamine in the inorganic process solution and can reduce organic impurities.

US 2006/0079678 A1 describes a process for producing hydroxylammonium by part of a system for producing cyclohexanone oximes by reducing nitrate or nitric oxide with a catalyst using hydrogen. This teaches improved distillation of the cyclohexanone oxime product stream, including recycling of distilled cyclohexanone to the cyclohexanone oxime synthesis zone.

Although the manufacture of hydroxylamine from nitrates has been known for decades and how many years have been studied to improve the known production process, currently known industrial processes of generally continuous nature have been found in existing plants or There are still disadvantages when trying to increase production capacity in new plants based on known designs.

A method of increasing productivity in a reactor (fixed hydroxylamine concentration) is to reduce the liquid residence time, for example with increased catalyst concentration and / or increased temperature and / or increased hydrogen partial pressure. At some point it is no longer possible to further increase the liquid feed rate without requiring a high investment in other parts of the loop.

A way to further increase productivity is by increasing the hydroxylamine concentration as described, for example, in EP-1,303,480-B1 and US-6,759,556. Increasing the hydroxylamine concentration achieves more efficient hydroxylamine conversion in the reaction with cyclohexanone in subsequent oxime reaction steps. In addition, by increasing the phosphate concentration (phosphate / hydroxylamine ratio> 2 mol / mol), less carbonyl, which acts as a poison to the catalyst, is introduced into the inorganic process loop, which leads to high activity of the hydrogenation catalyst and It is advantageous for selectivity.

However, the inventors have realized that increasing the hydroxylamine concentration is problematic. For example, during a proprietary study in a conventional plant, the inventors found that increasing the feed rate of reagents to increase the hydroxylamine production capacity, particularly caused contamination problems due to crystallization of hydrogen phosphate (mono) ammonium salt (s). It was found that it can cause. Contamination can, for example, block the filter or cooling pipe after the reaction zone. Specifically, the present inventors have found that in the processes described in EP-1,303,480-B1 and US-6,759,556, the crystallization of the process liquid present in the inorganic process loop by maintaining the process conditions at advantageous values while increasing the hydroxylamine product concentration. The temperature was found to be high.

When the temperature of the reaction mixture drops below its crystallization temperature, crystals form. If this occurs at the surface of the reactor where cooling takes place, the crystals insulate the reactants from the cooling and lose process control. This can easily be accelerated to severe contamination and the need to shut down the reactor for cleaning (ie, severe disturbances). In order to avoid contamination and process anomalies, the crystallization temperature of the reaction mixture should ideally be kept higher than the temperature of the cooling water used to remove the heat of the hydrogenation reaction. This limits the maximum hydroxylamine product concentration at which the nitrate hydrogenation reactor can be operated.

It is an object of the present invention to provide a novel process for preparing hydroxylamine in a continuous process that can serve as an alternative to known processes, in particular compared to conventional methods operating in the same production equipment while avoiding crystallization of salts such as ammonium hydrogen phosphate salts. It is to provide a new method that can be operated with increased hydroxylamine production capacity.

Another object of the present invention is to provide a process for the preparation of hydroxylamine which requires less catalyst per tonne of hydroxylamine to be produced.

From the description herein below, one or more other objects that can be addressed by the present invention will become apparent.

Recently, it has been surprisingly found to address one or more of these objectives by carrying out the preparation of hydroxylamine in a range of nitrate concentrations, nitrate to phosphate ratios and ammonia to nitrate ratios in the reaction zone where hydroxylamine is produced. .

Accordingly, the present invention relates to a process for preparing hydroxylamine in a continuous process comprising feeding nitrate and phosphate in an acidic aqueous liquid to the reaction zone and reducing the nitrate to hydrogen to produce hydroxylamine. Wherein the feed of nitrate and phosphate, hydrogen and temperature is less than 1.0 mol / kg when the nitrate concentration in the reaction zone is determined in the liquid exiting the reaction zone and the molar ratio of nitrate to phosphate in the reaction zone is 0.5 And a molar ratio of ammonia to nitrate of 2.2 to 7 or less. Reduction of nitrate is usually a catalysed reaction.

In accordance with the present invention, it has been found that production capacity can be increased by intensifying the manufacturing process of hydroxylamine. It is surprising that improved production capacity is possible at relatively low nitrate concentrations and at relatively low nitrate to phosphate ratios. After all, the nitrate hydrogenation reaction is believed to follow the behavior of the Langmuir-Hinshelwood class of kinetics and the reaction rate is thought to increase with increasing nitrate concentration in the reaction zone. Thus, one would expect that the rate of nitrate reduction, and therefore hydroxylamine production capacity, would be reduced by decreasing the nitrate concentration.

Specific parameters of the nitrate concentration in the reaction zone of less than 1.0 mol / kg, the molar ratio of nitrate to phosphate in the reaction zone of 0.5 or less, and the molar ratio of ammonia to nitrate of 2.2 to 7 when determined in the liquid exiting the reaction zone The variable results in a reaction mixture having a particularly low crystallization temperature but a high conversion to hydroxylamine.

Thus, the present invention surprisingly provides a process for preparing hydroxylamine at an advantageous production capacity in which the risk of contamination due to crystallization of components in the reaction zone is reduced.

Specifically, according to the present invention, hydroxylamine in the reaction liquid (out of the reaction zone) can be obtained at a concentration of at least 1.2 mol / kg, preferably at least 1.3, more preferably at least 1.4, or at least 1.5. It is thought to be. Such high hydroxylamine concentrations are advantageous because the reaction system is thus strengthened and productivity is improved. In a preferred embodiment, the hydroxylamine concentration is at most 2 moles, in particular at most 1.9 moles and more particularly at most 1.8 moles per kg of liquid reaction product. However, it is not obvious to operate at increased hydroxylamine concentrations in nitrate reduction reactors because of the expected risk of crystallization and contamination.

In addition, the process according to the invention is advantageous in that it may require less catalyst (based on the amount of hydroxylamine produced) to achieve a specific production capacity.

Furthermore, it has been found that the process according to the invention is advantageous in that later use of hydroxylamine in the preparation of oximes, such as cyclohexanone oximes. Hydroxylamines typically exit the reaction zone in the product reaction mixture, which is typically an aqueous liquid comprising hydroxylamine, phosphate, any unreacted nitrate and ammonia. Reaction product mixtures from hydroxylamine preparation have been found to be particularly suitable as feeds for the process for preparing oximes, an advantage being oxime extraction from more effective oxime and / or oxime reaction product mixtures.

As used herein, the term "or" means "and / or" unless stated otherwise.

The term "one" means "one or more" unless otherwise specified.

When referring to “noun” (eg, compound, additive, etc.) in the singular, the plural is intended to be included unless otherwise specified.

The preparation of hydroxylamine can suitably be carried out in known continuous reactors for the preparation of hydroxylamine. In one embodiment, the reaction is carried out in a reactor providing a well mixed gas / liquid system. Such systems are well known in the art and include stirred tank reactors, inner loop reactors, outer loop reactors and bubble column reactors. In a preferred embodiment, a bubble column reactor is used. Particularly good results have been achieved using a bubble column reactor with an external gas-lift.

Parameters derived from concentrations or concentrations of components in the reaction zone (eg, ratios of concentrations of components) can be determined by determining the parameters in a sample taken from the process liquid exiting the reaction zone.

As indicated above, according to the invention, the nitrate concentration in the reaction zone is less than 1.0 mol / kg as determined in the liquid exiting the reaction zone. In a preferred embodiment, the nitrate concentration is at most 0.9 mol / kg, in particular at most 0.8 mol / kg. Particularly good results were obtained using nitrate concentrations below about 0.70. Typically, the nitrate concentration is at least 0.3 mol / kg, in particular at least 0.4 mol / kg. Preferably, the nitrate concentration is at least 0.45 mol / kg, more preferably at least 0.50 mol / kg.

The molar ratio of ammonia to nitrate is from 2.2 to 7. A molar ratio of 6 or less, especially 5 or less, is particularly preferred for high productivity. In particular, it is believed that this is advantageous for the high promoting activity of the catalyst with respect to promoting the reduction of the nitrate to produce hydroxylamine. A molar ratio of ammonia to nitrate of at least 2.3, in particular at least 2.4, or at least 2.5 is particularly preferred for low contamination tendencies. In particular, a molar ratio of 2.3 to 6, more preferably 2.4 to 5, or most preferably 2.5 to 5 is advantageous for the high promoting activity of the catalyst with respect to promoting the reduction of the nitrate to produce hydroxylamine. I think.

Phosphates are usually provided as phosphoric acid or hydrogen phosphate salts, which can be formed by adjusting the pH of the phosphoric acid solution with a suitable base such as hydroxide or ammonia. The molar ratio of nitrate to phosphate is usually at least 0.05, preferably at least 0.10. Excellent results are achieved at values of at least 0.15, more particularly at least 0.20. The molar ratio of nitrate to phosphate is preferably at most 0.40, in particular at most 0.35, more particularly at most 0.30.

Hydrogen can be fed to the reaction zone in a manner known per se and also at such concentrations (hydrogen pressure). Preferably, the pressure is at least about 0.5 MPa, more preferably at least about 1.0 MPa. Usually, hydrogen pressure is 10 Mpa or less.

In an advantageous embodiment, the buffer ratio is selected within certain ranges. Here the buffer ratio is defined as:

([H ⁺ ] + [HYAM]) / [phosphate]

Wherein [H ⁺ ] is the molar concentration of H ^{+ in} the aqueous liquid exiting the reaction zone (mol / kg); [HYAM] is the concentration of hydroxylamine in the aqueous liquid exiting the reaction zone (mol / kg); [Phosphate] is the total concentration (in mol / kg) of phosphate (including H ₃ PO ₄ , monohydrogen phosphate and phosphate in dihydrogen phosphate) in an aqueous liquid exiting the reaction zone.

[H ⁺ ], [HYAM] and [Phosphate] concentrations were all titrated at 25 ° C. with subsequent titration of the liquid sample from the reaction zone with 0.25 N aqueous NaOH solution to [H ⁺ ] concentration at the first equilibrium point (pH of about 4.2). Determined by equilibrium titration of one sample by obtaining (“free acid”); A molar excess of acetone is then added to the sample to convert the hydroxylamine to oxime and H ⁺ , and the equilibrium titration is continued to reach three additional equilibrium points, the first equilibrium point being derived from hydroxylamine. Corresponding to the free acid (which thus gives a value of [HYAM] in the sample), the second equilibrium point gives the [phosphate] value and the final equilibrium point gives the value of ammonium. However, the last value is not necessary here.

In order to reduce the risk of crystallization at a relatively high production capacity, the buffer ratio is preferably 0.4 to 0.8, in particular 0.45 to 0.70, more particularly 0.50 to 0.65 mol / mol.

The H ⁺ molar concentration during the reaction is usually 0.4 to 0.8 mol / kg, in particular 0.45 to 0.70 mol / kg, more particularly 0.50 to 0.65 mol / kg.

The preparation of hydroxylamines according to the invention is usually facilitated by metal catalysts. Suitable catalysts are commonly known in the art. Specifically, a catalyst containing palladium can be used. The catalyst may comprise one or more (catalyst) metals, in particular palladium. The catalyst is usually provided on a carrier. In particular, good results have been achieved with a catalyst comprising palladium on carbon. Typically, the catalyst is provided with a catalyst accelerator such as germanium oxide. Accelerators may be added as desired at any time during the process for preparing hydroxylamine.

Other conditions for producing hydroxylamine can be as known in the art per se. The temperature may in particular be 20 to 70 ° C, preferably 30 to 60 ° C, in particular 35 to 55 ° C.

The hydroxylamines prepared according to the invention can be recovered from the reaction product mixture obtained in the reaction zone by conventional techniques, or the reaction product mixture can be fed (optionally) to further processes, such as to prepare oximes. After treatment to remove one or more undesirable components). The invention therefore also relates to the use of the hydroxylamine obtained in the process according to the invention for the preparation of oximes.

Oximes can be prepared from hydroxylamine in a manner known per se. This method typically involves reacting the hydroxylamine obtained in the process according to the invention with an alkanone. Alkanones may be cyclic or non-cyclic. Preferred cycloalkanones are cyclohexanone (to obtain cyclohexanone oxime), and cyclododecanohexanone (to obtain cyclododecanone oxime). Butanone is a preferred non-cyclic alkanone, followed by butanone oxime.

In particular, the present invention relates to a process for the preparation of cyclohexanone oxime, comprising reacting the hydroxylamine obtained in the process according to the invention with cyclohexanone. This method can be carried out in a manner known per se, for example as described in the above identified prior art, which is hereby incorporated by reference with regard to suitable conditions.

The (cyclic) oximes obtained according to the invention can be used in particular for preparing lactams. This can be achieved by Beckman potential in a manner known per se.

Thus, cyclohexanone oximes obtained according to the invention can be used for the preparation of caprolactam. The present invention thus relates to a process for the preparation of caprolactam, comprising producing a caprolactam by carrying out a Beckman potential on the cyclohexanone oxime obtained in the process according to the invention. The preparation of caprolactam can be carried out in a manner known per se, for example as described in the prior art identified above, which is incorporated herein by reference in connection with suitable conditions.

Similarly, laurolactam is obtained in an embodiment of the present invention by a method comprising performing a Beckman potential on the cyclododecanone oxime obtained according to the present invention to produce laurolactam. This manufacturing step can also be carried out in a manner known per se.

Methods of preparing (cyclic) oximes, such as cyclohexanone oximes, and, if necessary, methods of making lactams, such as caprolactam, are typically integrated in a single plant for preparing hydroxylamine, oxime and, if necessary, lactams in a continuous process. .

The method is now illustrated by the following examples.

Example

Example  1 to 5

Part of the liquid circulating as product from the riser zone, the liquid-gas separation zone, the gas recycle zone, the catalyst-containing reactor liquid supplied with gas (the concentrations listed in Table 1 were determined; these correspond to the concentrations in the reaction zone) The nitrate reduction was carried out in an industrial gas lift loop reactor consisting of a filtration zone for separating the. Fresh hydrogen was fed to the reactor and a gas purge was added to maintain a partial pressure of hydrogen of about 1.4 MPa in the upper zone of the reactor. The average reactor temperature was maintained at about 50 ° C. 10 wt% Pd / C was used as catalyst. About 45 g of GeO ₂ per kg of Pd was added as activator. The catalyst (as anhydrous Pd / C) concentration based on the inorganic process liquid present in the reactor was about 1% by weight. The feed rate and feed composition of the inorganic process liquid fed to the reactor varied within a wide range as described in Table 1, resulting in different compositions and different hydroxylamine production rates of the reactor product. Table 1 shows nitrates in the process according to the invention in which the nitrate concentration and the nitrate to phosphate ratio are reduced together with the performance data of the nitrate reduction reactor under reference conditions ('reference plant') and the increased ammonia to nitrate ratio values. Performance data of the reduction reactor ('E1' to 'E5') are described. The activity in Table 1 is based on the amount of catalyst (as anhydrous Pd / C) present in the riser zone fed with the gas of the hydrogenation reactor. The inorganic liquid product composition illustrated in Table 1 from 'E1' to 'E5' was obtained in seven experiments (crystallization temperature was determined by the inventors) given in US-6,759,556 and the composition of the inorganic liquid product described in Table 2 Can be compared.

[Table 1]

Plant experiments at reference conditions and plant experiments at reduced nitrate and nitrate to phosphate ratios

Control Example  1 to 7

[Table 2]

Liquid composition of nitrate reduction reactor for high hydroxylamine concentrations according to US-6,759,556

Control Example  8 to 10

Product mixtures were prepared to simulate the effect of product concentration on the obtained crystallization temperature of the product mixture. The composition of the product mixture was adjusted for key performance figures such as the desired levels of H ⁺ and buffer ratios, and the NO ₃ ⁻ concentration was at the level expected by the practitioner. Table 3 is comparable to the results described in Table 1 in process windows that are conventional in other respects but now have relatively high NO ₃ ⁻ concentrations, relatively high NO ₃ ⁻ to phosphate ratios and relatively low NH ₄ ⁺ to NO ₃ ⁻ ratios. At increasing hydroxylamine product concentration, the crystallization temperature of the product mixture increases. It should be noted that for proper plant operation the crystallization temperature should preferably be controlled below 25 ° C, in particular below 20 ° C. The results listed in Table 3 demonstrate that operation at high hydroxylamine concentrations usually results in increased crystallization risk under conditions at levels where high reaction rates are expected by those skilled in the art.

[Table 3]

Example of the effect of increased hydroxylamine product concentration on the crystallization temperature of the product mixture at a process window of NH ₄ ⁺ / NO ₃ ⁻ <2.2 mol / mol

Claims (15)

A process for preparing hydroxylamine in a continuous process, comprising supplying nitrate and phosphate in an acidic aqueous liquid to the reaction zone and reducing the nitrate with hydrogen to produce hydroxylamine, wherein the reaction zone The nitrate and the nitrate concentration of less than 1.0 mole / kg when determined in the liquid exiting the reaction zone, the molar ratio of nitrate to phosphate in the reaction zone of 0.5 or less and the molar ratio of ammonia to nitrate of 2.2 to 7 A method of controlling the feed of phosphate, hydrogen and temperature. The method of claim 1,
The molar ratio of said ammonia to nitrate is 2.3 to 6, in particular 2.5 to 5. 3. The method according to claim 1 or 2,
The nitrate concentration is between 0.3 and 0.9 mol / kg, in particular between 0.4 and 0.8 mol / kg. 4. The method according to any one of claims 1 to 3,
The molar ratio of said nitrate to phosphate is from 0.1 to 0.4, in particular from 0.10 to 0.30. 5. The method according to any one of claims 1 to 4,
The buffer ratio in said reaction zone is between 0.4 and 0.8, in particular between 0.45 and 0.70, more in particular between 0.50 and 0.65. 6. The method according to any one of claims 1 to 5,
A method of catalyzing the preparation of said hydroxylamine with a palladium-containing catalyst. The method according to claim 6,
Wherein said catalyst is provided on a carbon carrier. The method according to claim 6 or 7,
Wherein said catalyst further comprises platinum. 9. The method according to any one of claims 1 to 8,
Said H ⁺ molar concentration is between 0.4 and 0.8 mol / kg, in particular between 0.45 and 0.70 mol / kg, more particularly between 0.50 and 0.65 mol / kg. 10. The method according to any one of claims 1 to 9,
The temperature in said reaction zone is 20 to 70 ° C, preferably 30 to 60 ° C, in particular 35 to 55 ° C. A process according to any one of the preceding claims, comprising reacting an alkanone, in particular cyclohexanone, cyclododecahexaone, and butanone, with hydroxylamine selected from the group of How to prepare an oxime. The method of claim 11,
And said alkanone is cyclohexanone and said oxime is cyclohexanone oxime. 13. A method according to claim 12, comprising performing a Beckmann rearrangement on cyclohexanone oxime. The method of claim 11,
And said alkanone is cyclododecanhexanone and said oxime is cyclododecanone oxime. A method according to claim 14, followed by performing a Beckman potential for cyclododecanone oxime.