FR2651776A1 - PROCESS FOR THE SYNTHESIS OF MONOMETHYLHYDRAZINE IN AQUEOUS SOLUTION. - Google Patents

Abstract

The present invention relates to a process for the synthesis of monomethylhydrazine in aqueous solution by reacting, for a period D1, in aqueous medium and under an oxygen-free atmosphere, of monochloramine with a molar excess of monomethylamine in the presence of a strong base. The reaction medium is then heated, under an oxygen-free atmosphere, between 30 and 100 degrees C, for a period of time D2 such that D2 / D1 is greater than 10, while maintaining the pH greater than 13.5, so as in particular to eliminate methyldiazene, a particular explosive and dangerous by-product. The reaction medium is then purified and concentrated, so as to obtain a concentrated aqueous solution of monomethylhydrazine. The elimination of methyldiazene considerably improves the operating conditions and the safety of implementation of the process. Monomethylhydrazine is used in particular as a synthetic intermediate and as an oxidizer for rocket engines.

Description

The present invention relates to the synthesis of monomethylhy-

  drazine (MMH) in aqueous solution by reaction, in an aqueous medium

  sic, monochloramine with an excess of monomethylamine. Its aim is to improve operating conditions and

  the security of implementation of this process.

  MMH is used in particular as a synthesis intermediate in agrochemistry and in pharmacy, as well as as an oxidizer for

rocket engines.

  We know how to prepare MMH industrially in aqueous solution

  according to a technique derived from the RASHIG process relating to hydrazi-

ne and alkylhydrazines.

  We can schematize this process by the two main reactions

  following blades: 1) NH3 + NaOCil NH2Cl + NaOH 2) NH2Cl + CH3NH2 + NaOH CH3 - NH - NH2 + NaCl + H2O These two reactions are generally carried out successively in two different reactors which are connected to each other so

  take into account the limited shelf life of monochloramine.

  After these two reactions, the medium is purified and concentrated

  reaction, generally by stripping then distillation, in order to obtain

  keep a pure aqueous solution in MMH and relatively concentrated,

around 30% for example.

  The industrial implementation of this process poses many

  many problems which have all been widely studied.

  A major problem is that of training, in quantity re-

  later, volatile by-products, some of which are toxic and others which may decompose thermally or in the presence of oxygen, which may cause explosions

  during the MMH concentration and purification step.

  These volatile by-products also limit the return

and the purity of the finished product.

  The toxic or explosive nature of some of these

  products which can accumulate during the implementation of the process

  dice continuously, entails serious risks during operation

  industrial, especially during the purification and

  fMMH centering since it is during the implementation of this-

  te stage that the thermal risks, and of oxidation by inadvertent air intake, are the most important and that the recycling of

  excess light reagents from stripping promotes this accumulation

  tion. US 3,394,184 and US 3,423,464 remedy the risk presented by the presence of azomethane (CH3-N = N-CH3) as a by-product in the

  reaction medium by eliminating it by azeotropic distillation

  before the MMiH concentration and purification step.

  This improvement only partially solves the problem

  insofar as we discovered that it is mainly the present-

  ce of methyldiazene (CH3-N = NH) as a by-product in the medium

  reaction which makes the process potentially dangerous. Indeed-

  the methyldiazene is very unstable; it explodes on contact with

  oxygen and decomposes thermally from 22 C into nitrogen and metha-

  ne, while azomethane is thermally stable up to 200 C,

  that is to say at the operating temperatures of the various states

  pes of the process of synthesis of the MMH, including the stage of purification

  tion and concentration. To the knowledge of the Applicant, the safety problem posed by the presence of methyldiazene as

  by-product during the synthesis of MMH in aqueous solution se-

  the two main reactions mentioned above have never been mentioned,

  and even less, as a result, resolved. A first part of the pre-

  his invention therefore consists in the discovery of this problem.

  A second aspect of the present invention consists in solving

this issue.

  To this end, the Applicant has discovered that, unexpectedly

  stretched, all or part of the volatile by-products is eliminated, in particular

  methyldiazene, realizing, after reaction of the monochlo-

  ramine with monomethylamine and before purification and concentration

  tion of the reaction medium, an additional finishing step consisting of heating the reaction medium, under an oxygen-free atmosphere, under very specific conditions of time, temperature and pH. The yield and the operating safety of the process are thus improved by limiting the amount of volatile toxic or explosive by-products, and in particular methyldiazene, before the purification and concentration step, a step which presents the

  highest explosion risks for the above reasons.

  The present invention therefore relates to a method of synthesizing

  of monomethylhydrazine in aqueous solution by which it is reacted, for a period D1, in an aqueous medium and under an atmosphere

  free of oxygen, monochloramine with a molar excess of mono-

  methylamine in the presence of a strong base, preferably sodium hydroxide,

  to form monomethylhydrazine and volatile by-products

  then in that the reaction medium is purified and concentrated,

  preferably by stripping then distillation, to obtain a so-

  aqueous solution concentrated in monomethylhydrazine.

  According to the invention, this process is characterized in that after

  reaction of monochloramine with monomethylamine and before puri-

  fication and concentration of the reaction medium, a

  additional finishing pe consisting in heating the reaction medium

  under an oxygen-free atmosphere at a temperature

  taken between 30 C and 100 C, preferably between 70 C and C, for a period D2 such that Dz / Di is greater than 10, preferably between 50 and 1000, while maintaining the pH of the reaction medium greater than 13.5, so as to eliminate all or

  part of the aforementioned volatile by-products and in particular methyl-

  diazene which is broken down into nitrogen and methane during this

finishing step.

  In a particularly preferred manner, this process is implemented

  lives continuously, but it can also be implemented

lives discontinuously.

  The reaction time Di of the monochloramine with the monomer-

  thylamine is generally on the order of a few seconds or ten-

  nes of seconds because longer durations cause a decrease in the

  yield and the presence, in larger quantities, of the

toxic or explosive products.

  Generally, chloramine, monomethylamine,

  ne and the strong base in aqueous solutions. We can also use

  these products in their pure state, in particular monomethylamine. These pro-

  pure products or solutions are preferably stored in an atmosphere

  re free of oxygen, under nitrogen for example. In particular-

  Preferably, an overpressure allows the feeding of these solutions.

  tions or pure liquid products to the reactor in which they will react. This reaction and the additional finishing step

  take place in an oxygen-free atmosphere. During an implementation

  vre discontinuously, this is achieved for example by bubbling a gas

  inert, nitrogen or argon, in the reactor.

  During continuous processing, the volatile by-products

  tils formed and excess reagents, allow to establish such a

the atmosphere in the reactor.

  According to the invention, it is necessary to maintain the pH of the mid

  reaction site greater than 13.5 during the additional finishing step. This is achieved for example by adding a strong base to the

  during this stage. However, particularly preferably

  The amount of strong base present during the reaction between monochloramine and monomethylamine is such that it allows the pH of the reaction medium to be kept above 13.5 during

  the additional finishing step, without the need to a-

  add a base during this step. This simplified way of operating

  relies on the implementation of the method according to the invention.

  The pH of the reaction medium can easily be controlled at

  using known pH measurement probes.

  To carry out the final purification step and concentrate

  tion of the reaction medium, it is preferably carried out, in a pre-

  first, a pressure stripping to remove the im-

  light purities, in particular the excess of reagents which may be

  you recycle, and secondly, a distillation of

  the dilute aqueous solution of monomethylhydrazine, approximately 1% in general

  mineral, resulting from stripping, so as to collect at the top of

  distillation column a concentrated azeotropic aqueous solution

  very low, about 30%, of monomethylhydrazine.

  According to a preferred variant of the method according to the invention, the

  monochloramine is obtained in basic aqueous medium having a pH

  taken between 10 and 14, in an oxygen-free atmosphere, by reaction

  tion, at a temperature between -10 C and +10 C, of ammonium

  niac with an alkaline hypochlorite, preferably sodium hypochlorite. Preferably, according to this variant, ammonia and

  alkaline hypochlorite in aqueous solutions.

  In a particularly preferred manner, always according to this va-

  laughing, the basic aqueous medium is an ammonia buffer NH3-NH4Cl

  playing the double role of buffer and source of ammonia. The solutions

  These are preferably stored in an oxygen-free atmosphere.

  ne, under nitrogen for example. Particularly preferably, a

  overpressure allows these solutions to be fed to the reac-

in which they will react.

  According to a particularly preferred embodiment of this-

  variant, monochloramine is obtained in a first reaction

  tor comprising an entry for the introduction of the aqueous medium

  alkaline hypochlorite and ammonia and an outlet by

  which, after formation of the monochloramine, removes the mid-

  reaction site using appropriate known means, channeled

  stainless steel for example, towards the entrance of a second

  reactor which is also supplied with a strong base and with monomethyl

  laminate and in which monomethylhydrazine and volatile by-products are thus formed, this second reactor having an outlet

  whereby, after formation of the monomethylhydrazine and the

  volatile products, the reaction medium is removed using suitable known means, stainless steel pipes by

  example, towards the entrance of a third reactor in which we

  the additional finishing step, this third reactor,

  preferably a piston reactor fitted with a double jacket allows

  both the circulation of a fluid, comprising an outlet through which

  the, at the end of this additional finishing step, we evacuate

  the reaction medium using suitable known means, canali-

  stainless steel stations for example, towards known means for purifying and concentrating this medium, preferably

stripping and then distillation.

  According to a variant, after formation of the monochloramine in the first reactor, the reaction medium is removed using suitable known means, pipes made of stainless steel for example, towards the inlet of a mixer which is also supplied with monomethylamine, the mixture thus obtained being discharged using suitable known means, stainless steel pipeline by

  example, towards the entrance of the second reactor which is also supplied

strong base.

  According to another variant, the preceding variant is replaced

  split the monomethylamine by the strong base and the strong base by the

monomethylamine.

  According to another variant, the molar ratio between the base

  strong and the alkaline hypochlorite is greater than or equal to 2. This ratio

  port can also be less than 2.

  Generally when the process is carried out

  lon the invention continuously, it is preferred, after the additional step

  finishing and before purification and concentration of the medium

  reaction site, regulate the pressure of the reaction medium in such a way

  We want it to be of the order of a few l05 Pa (a few bars).

  The following nonlimiting examples 1 to 8 carried out so

  continue to illustrate the implementation of the invention.

  Example 1 was implemented in the apparatus

shown schematically in Figure 1.

  This apparatus includes: - a first reactor 1, of the SULZER type, with a volume of 1 cm 3,

  - a second reactor 2, of the SULZER type, with a volume of 1 cm 3, if

killed downstream of reactor 1,

  - a third reactor 3, located downstream of reactor 2, constitutes

  with a coil 10 m long and 200 cm3 in volume, the temperature of which is fixed by that of the thermostatically controlled bath 4 in which it is immersed, - continuous supply devices 5, 6, 7 and 8 of aqueous solutions:

  * device 5 allows the supply of an ammonia buffer

  D cal NH3-NH4Cl whose temperature is set at -7 C a-

  of a cryostat, a buffer for which the concentration to-

  tale of NH3 + NH4Cl is 6.2 mol / kg and the NH4Cl / NH3 molar ratio is equal to 0.5 * device 6 allows the supply of an aqueous solution of sodium hypochlorite (bleach), the concentration is 1.65 mol / kg and the temperature is -11 C * the device 7 allows the supply of an aqueous solution of monomethylamine whose concentration is 13.0 mol / kg and the temperature of the order of 20 C * the device 8 allows the supply of an aqueous sodium hydroxide solution whose concentration is 7.7 mol / kg and the temperature is of the order of 20 C * the devices 5 and 6 feed the first reactor 1 and the devices 7 and 8 feed the second reactor 2, the device 7 being located upstream of the device 8

  * dosing pumps not shown in the diagram fig-

  re 1 set the flow rates to the desired values

tees,

  - a mixer 9 with a volume of 1 cm3 located between the feeds

  tions 7 and 8, - a stripper 10 located downstream of the reactor 3, - a distillation apparatus 11 located downstream of the stripper 10, - a device, not shown in the diagram in figure 1, of

  pressurization and inerting of various aqueous feed solutions

lie,

  - a set, not shown in the diagram in Figure 1, of cap-

  temperature, pressure and pH measurement probes, - devices, not shown in the diagram in FIG. 1, for sampling the reaction medium (liquid and / or gas phases)

allowing its analysis.

  - pipes 12, 13 with an internal diameter of about 1 mm, made of stainless steel, allowing the introduction of reagents and the

  circulation of the reaction medium in the direction indicated by the arrows

  ches on the diagram figure 1 - a device 14 making it possible to regulate at approximately 4 105 Pa (4 bar) the pressure of the reaction medium upstream of the third

reactor 3.

  The reactor 1 is firstly supplied with ammonia buffer with a flow rate of 8.2 g / min using the device 5 and secondly with sodium hypochlorite solution with a flow rate of g / min using the device 6, which makes it possible to form, in this

  reactor 1, monochloramine. The temperature of the reaction medium

  nel in this reactor 1 is 0 C. The reaction medium is then evacuated towards the mixer 9 which is also supplied with an aqueous solution of monomethylamine with a flow rate of 13 g / min using the device 7. After mixing , the reaction medium is evacuated towards the

  reactor 2 which is also supplied with an aqueous solution of

  of with a flow rate of 4.7 g / min using the device 8. We form

  thus in this reactor 2, monomethylhydrazine and subpro-

  volatile products. The reaction medium is then evacuated to the reaction

  tor 3 whose temperature is fixed at 40 ° C. The reaction medium is then evacuated towards the stripper 10 o are eliminated in particular, at the top of the column 15, the ammonia and the monomethylamine in excess, then towards the distillation apparatus 11 o is collected at the head

  from column 16 a pure and concentrated aqueous solution (about 30%

  ron) to monoméhtylhydrazine. The stripping and dis-

  tillation are those usually implemented and well con-

naked of the skilled person.

  To implement Example 2, the supplies 7 and 8 were reversed and for Examples 3 to 8, the mixer 9 was

  removed, the reaction medium therefore being evacuated directly from the reaction

  1 to reactor 2 fed simultaneously with monomethylami-

  ne and soda by devices 7 and 8.

  In addition, for examples 3 to 5, the flow rate of the feed is fixed.

  mentation in aqueous sodium hydroxide solution at 3.3 g / min respectively,

  4.3 g / min and 5.3 g / min, instead of 4.7 g / min for the other examples

  ples. As a result, the molar ratio between soda and hypochli-

  te of sodium is for examples 3 to 5 respectively 1.54, 2.0

  and 2.46 instead of 2.2 for the other examples.

  Furthermore, for examples 7 and 8, the temperature of reactor 3 is fixed at 60 ° C. and 76 ° C. respectively, instead of 40 ° C.

for the other examples.

  For all the examples, the relationship between the duration D2 of se-

  day of the reaction medium in reactor 3, that is to say the

  of the additional finishing step, and the duration Di of se-

  day of the reaction medium in reactor 2, that is to say the

  reaction during which the monochloramine formed in reactor 1 is reacted with a molar excess of monomethylamine in the presence

  of a strong base, is close to 250.

  The pH of the reaction medium in reactor 3 during the

  additional finishing pe is 14.3 for examples 3 and 4, 14.4 for example 5, 14.5 for examples 7 and 8 and 14.6 for

examples 1, 2 and 6.

  Various samples of the reaction medium were carried out, to

  analyzes. The MMH content was determined by logging. To me-

  thyldiazene, demonstrated qualitatively in all examples

  ples by coupling gas chromatography / mass spectrometry on samples of the reaction medium carried out between reactors 2 and 3, was not directly assayed. Given that

  that the methyldiazene decomposes in the reactor 3 into nitrogen of

  thane, we measured methane and nitrogen by pha-

  is gaseous in the gas phase of the reaction medium at the outlet of the reactor 3. The amount of methane formed can be compared to the amount of methyldiazene destroyed since, to the knowledge of the

  Applicant methane can only come from this decomposition alone

  On the contrary, nitrogen can also come, for example,

  full of decomposition of other by-products.

  The MMH assay results are expressed on the one hand in concentration (% by weight) in the reaction medium and on the other hand in moles per mole of sodium hypochlorite introduced, this

  the latter value therefore being equal to one hundredth of the yield in MMH.

  The results of the determination of nitrogen and methane are expressed

  moles per mole of sodium hypochlorite introduced.

D

  Table 1 below presents, for each example, the result

status of these dosages.

I I [

  Ex N2 CH4 MMH | MMH N (mol) (mol) (mol) | () | J I iI

I 1 0.23 0.09 0.53 1 1.12

I I II

2 0.24 0.04 0.59 1.27

! I!

I 3 0.47 0.07 0.45 1.01

t l t t J

4 0.20 0.11 0.47 0.97

I i l

I5 I0.20 0.12.471 0.96

JI I 1

I 6 0.15 0.03 0.55 1.12 1

J I I t t J 7 | 0.08 o, OD 0.54 1.11

! I I

I 8 0.03 0.06 0.61 J 1.23

* ItI I I Table 1

  A comparison of Examples 6 to 8 shows that, unexpectedly

  tense, better elimination of the methyldiazene is obtained, therefore better efficiency of the additional finishing step, and

  a better yield in MMH, when, all other things being equal

  their, the temperature of implementation of this step is increased.

  Furthermore, the comparison of Examples 1, 2 and 6 shows that, all

  your things equal, we destroy, unexpectedly, a lot more methyldiazene when we operate according to the modalities

from example 1.

Claims (9)

Claims   1. A process for the synthesis of monomethylhydrazine in aqueous solution by which, for a period D], is reacted, in an aqueous medium and under an oxygen-free atmosphere, monochloramine with an ex-   molar cesium of monomethylamine in the presence of a strong base, of pre-   ference soda, to form monomethylhydrazine and   volatile products, then in that we purify and concentrate the medium   reaction, preferably by stripping and then distillation, to obtain   hold a concentrated aqueous solution of monomethylhydrazine charac-   terized in that after reaction of the monochloramine with the monomer   thylamine and before purification and concentration of the reaction medium-   nel, an additional finishing step is carried out consisting of heating the reaction medium, under an oxygen-free atmosphere,   at a temperature between 30 C and 1000 C, preferably   taken between 70 C and 100 C, for a period D2 such that D2 / Di is greater than 10, preferably between 50 and 1000, while maintaining the pH of the reaction medium greater than 13.5, so as to   eliminate all or part of the aforementioned volatile by-products and no- especially methyldiazene.   2. Process for the synthesis of monomethylhydrazine in aqueous solution according to claim 1, characterized in that this process is carried out implemented continuously.   3. Process for the synthesis of monomethylhydrazine in aqueous solution   according to any one of the preceding claims, characterized   in that monochloramine is obtained in basic aqueous medium   having a pH between 10 and 14, preferably an ammonia buffer   cal NH3-NH4C1, in an oxygen-free atmosphere, by reaction, at a temperature between -10 C and + 100C, ammonia with   an alkaline hypochlorite, preferably sodium hypochlorite.   4. Process for the synthesis of monomethylhydrazine in aqueous solution according to claim 3 characterized in that the monochloramine is obtained in a first reactor comprising an inlet for the introduction of the basic aqueous medium, alkaline hypochlorite and ammonia and a outlet by which, after formation of the monochloramine, the reaction medium is removed using suitable known means towards the inlet of a second reactor which is also supplied with a strong base and with monomethylamine and in which   the monomethylhydrazine and the volatile by-products are thus formed   tils, this second reactor comprising an outlet by which, after formation of the monomethylhydrazine and volatile by-products,   the reaction medium is removed using known means suitable for   requested towards the entrance of a third reactor in which we realize   the additional finishing stage, this third reactor comprises   both an exit by which, at the end of this additional step   re finishing, the reaction medium is removed using means   known suitable to known means of purification and   centering of this medium, preferably stripping and then distilling   lation. 5. Process for the synthesis of monomethylhydrazine in aqueous solution   according to claim 4 characterized in that the third reaction   tor is a piston reactor provided with a double jacket allowing circulation of a fluid.   6. Process for the synthesis of monomethylhydrazine in aqueous solution   according to any one of claims 4 and 5 characterized in that   that, after formation of the monochloramine in the first reactor,   the reaction medium is removed using known means suitable for   required towards the inlet of a mixer which is also supplied with monomethylamine, the mixture thus obtained being discharged using known means suitable towards the inlet of the second reactor which is also supplies a strong base.   7. Process for the synthesis of monomethylhydrazine in aqueous solution   according to any one of the preceding claims, characterized   in that the amount of strong base is such that it makes it possible to maintain the pH of the reaction medium above 13.5 during   the additional finishing step.   8. Process for the synthesis of monomethylhydrazine in aqueous solution   according to any one of claims 2 to 7 characterized in that   only after the additional finishing step and before purification   and concentration of the reaction medium, the pressure of the medium is regulated   reaction place so that it is on the order of a few Pa (a few bars).   9. Process for the synthesis of monomethylhydrazine in aqueous solution   according to any one of claims 3 to 8 characterized in that   that the molar ratio between the strong base and the hypochlorite alka- linen is greater than or equal to 2.