FR2625193A1 - PROCESS AND PLANT FOR DEGRADATION OF NITROGLYCERIN IN NITRATION RESIDUAL ACIDS - Google Patents

Abstract

The invention relates to a method and to an installation for degrading nitroglycerin in the residual acids resulting from the nitration of glycerin. The process according to the invention consists in thermally treating these residual acids by microwave and makes it possible to separately recover concentrated acids. The process consists in adding water or sulfuric acid diluted in the residual acids to improve the solubility of the nitroglycerin and in circulating these residual acids in an installation constituted by a circulation circuit comprising successively in the direction of circulation acids, an inlet of said acids after addition of water or dilute sulfuric acid, a microwave heating system for the acids, an outlet of the mixture thus treated, and an outlet of the nitrous vapors.

Description

Process and installation for degrading nitroglycerin in

  residual nitration acids The production of nitroglycerin, carried out by the action of a nitration bath on glycerin, requires large quantities of nitric acid.

  Only a small fraction of this acid is fixed by glycerol

  most of which is eliminated without any form of effluent.

  In addition to nitric acid, these effluents hereinafter called residual acids "also contain other compounds such as acid.

  sulfuric and water as well as a small amount of nitroglyc-

  rine. The presence of too much water and a subs-

  Explosive tance, in proportions generally varying from 2% to 3%, has the effect of making them dangerous and not directly reusable. They must therefore be treated to eliminate this explosive compound and possibly allow separation of sulfuric acid.

  and nitric acid before recycling in the nitra- process

  tion. The subject of the present invention is a process for the degradation of nitroglycerin in waste acids originating from a process

  of nitration, a process which consists in thermally treating these a-

  waste acids by microwave and allowing separate recovery

concentrated acids.

  The degradation of nitroglycerin must be very rapid. The conventional methods for treating residual acids are based

  on rapid heating of the reaction medium by direct injection

  of live steam in the reaction medium.

  French Patent No. 2,265,675 describes a process for removing nitrous oxides from a mixture containing, for example, acid

  nitric. This process involves passing the residual acids

  areas in a denitrator that is to say in a device in the-

  which they are subjected to steam training,

  under vacuum. The major drawback of the use of this denitrator is the dilution of the acids, because during the water vapor entrainment operation, most of the water gets

  condenses in acids. It is therefore necessary to dehydrate them.

  ter in order to bring them to a concentration making them reusable

sands.

  It is therefore known to those skilled in the art to use water vapor

  to remove nitroglycerin from residual nitra-

  tion. More precisely, the treatment is done in several stages.

  pes. The first step is to add water to the mixture,

  at the outlet of the nitration installation in order to improve the

  nitroglycerin solution and thus avoid a phenomenon of

  release. This so-called wbr lage step is very delicate because it

  the must be adapted to many parameters such as the temperature

ture.

  The mixture must then be stored in a buffer tank to

security reasons.

  The residual acids are then treated, for example, against the current, in a distillation column, fed at the bottom with

  steam at a pressure of 5 to 7 bars in order to carry the acids

  waste at 140'-150'C and cause decomposition to-

  nitroglycerin level by reaction with pre-nitric acid

  feels in these waste acids. The general formula, generally accepted, of this decomposition is as follows:

CH2-O-N02

  CH-O-NO2 + 5HN03 _ "6NO2 + 2NO + 5H20 + 2C02 + CO

CH2-O-NO2

  ÂO This very exothermic reaction produces around 1600 Kcal / kg of

  nitroglycerin dissolved in residual acids.

  In addition to a distillation column, the installation is completed by a device for condensing the vaporized nitric acid and by an absorption column for the nitrous vapors (NO and NO2) produced.

  by the decomposition reaction, and not condensed.

  From residual acids having the following average composition

  boasts: - sulfuric acid 71% - nitric acid: 11% - nitroglycerin: 2.5% - water 15% - nitrous vapors 0.5% we obtain: at the bottom of the column a relatively dilute sulfuric acid (60% acid sulfuric), at the outlet of the condenser a nitric acid containing 80-85% of pure acid, at the bottom of the absorption column of nitric acid containing 50-55%

pure acid.

  The conventional process therefore leads to a distillation of the residual acids which causes the separation of the nitric acid and

  sulfuric acid and a destruction of nitroglycerin.

  This process is effective since the nitroglycerin is destroyed,

  but the injection of water into the reaction medium, on the one hand,

  during the burning stage and above all, in the form of water vapor, when passing through the distillation column, causes a dilution of the outgoing sulfuric acid, which is a major drawback for its recycling: in fact to be able to be reused in a

  sulfonitric bath for the nitration of glycerin, sulfuric acid

  risk must be brought from a concentration of 60-70% to a concentration

  greater than or equal to 95%. The recycling stage of the a-

  sulfuric acid therefore consumes a lot of energy and

very costly sequent.

  The subject of the present invention is a method for treating

  residual acids from a nitration bath allowing re-

  to collect concentrated acids which can be reused directly or pres-

than.

  The method according to the invention is defined according to the following steps:

  touted. The first stage consists of a classic dilution (bralage) stage, i.e. the addition of water or sulfuric acid

  diluted in variable proportions according to the operating conditions

  roofs and in particular according to the outside temperature. This step aims to bring all the nitroglycerin in homogeneous phase within the residual acids and thus to avoid the accumulation of

  nitroglycerin in free form, saturated with acids, therefore unstable.

  The second step consists in circulating the residual acids after dilution in an installation constituted by a circuit comprising successively in the direction of circulation of the mixture: - an inlet for the residual acids after dilution, - an external microwave heating system, - an outlet from the mixture thus treated,

- an outlet for nitrous vapors.

  A mode of implementation of the process and the installation of

  gradation of nitroglycerin in the residual acids of ni-

  tration according to the present invention is now described in se

  referring to the functional diagram of figure 1.

  The residual acids, having undergone a dilution step, are

  stored in one or more tanks 1 connected to a heating circuit

  wind to avoid the emission of nitrous vapors near the

personnel and equipment.

  A dosing pump 2 supplies the tactor 3 constituted

  a supply tube 4 and a degasser 5 in pyrexD The flow of a-

  the feed is 8.7 kg / h. When passing through tube 4, the residual acids are subjected to the action of microwaves. In this

  effect a microwave generator 6 with a power of 800 W, mu-

  nor of a waveguide 7 is disposed at this tube. The brass waveguide has a rectangular section of

  43 m X 86 m and is connected by a flange to the output of the general

  microwave and to the reaction medium by a piston

  glable. It is crossed by the supply tube 4. The action of

  microwave to heat the residual acids to a temperature

  rature from 110- to 130C, and preferably close to 120C, at which the reaction

CH2-O-N02

  CH-O-NO2 + 5HN03-> 6N02 + 2NO + 5H20 + 2C02 + CO

CH2-O-N02

  is initiated. This very exothermic reaction raises the temperature

  medium at 140'-160 C, depending on the flow rate of the metering pump 2.

  Degradation of nitroglycerin results in a change

  of color of the reaction medium. Untreated waste acids

  tees are green (temperature below 140 ° C) and yellow after

  treatment (temperature above 150 * C).

  The degasser 5 which receives the residual acids immediately after they have undergone the action of the microwaves is provided with the following equipment: - at the base: an inlet 8 for the residual acids during treatment, - in the middle part: a outlet tube 9 by overflow of treated residual acids connected to a container 10 by a tube,

  - in the upper part: an outlet pipe 11 for the vapors ni-

  treuses produced by boiling of the reaction medium.

  * According to a conventional method, part of the gas mixture from

  The boiling of residual acids is then partial-

  ment condensed by cooling in the form of nitric acid. AT

  this title an exchanger 13, for example with a glass coil

  mented in water, is disposed at the outlet 11 of the degasser. A reci-

  pient 12 collects nitric acid. Uncondensed vapors in exchanger 13, i.e. uncondensed nitrogen oxides (NO, NO2), traces of nitric acid as well as monoxide and

  carbon dioxide, produced by the breakdown of nitrogly-

  cerine, are introduced at the base of an absorption column 14

  and are then brought into contact against the current with water.

  The nitric acid recovered at the bottom of the absorption column is collected in a tank 15 while the vapors not absorbed

are eliminated by the vent.

  According to a preferred characteristic of the invention, the acids

  waste can be preheated to an intermediate temperature

  between the storage temperature and the de-

  gradation of nitroglycerin. For security reasons this

  temperature should not be higher than 110 * C and, preferably-

  less than or equal to 80C. In the mode of implementation

  shown in Figure 1 this intermediate temperature is

  color thanks to a heater 16 mounted between the metering pump 2 and the tube 4 and supplied k co-current or against the current by the tube 9 fixed to the overflow of the reactor and conveying the

2,625,193

  treated and hot residual acids.

  This allows the temperature to pass through heat exchange

  residual acids of 14C & 55-57'C.

Claims (7)

Claims   1. Continuous process of degradation of nitroglycerin in   residual acids from the nitration of glycerin consist-   both add water or dilute sulfuric acid in them-   so-called residual acids to improve the solubility of nitro-   glycerin, and circulating said residual acids in an installation constituted by a circulation circuit comprising successively in the direction of circulation of the acids, an inlet of said acids after addition of water or dilute sulfuric acid,   an external acid heating system, an outlet from the   diaper thus treated and an outlet for nitrous vapors characterized in that said external heating system is a microwave system.   2. Method according to claim 1 characterized in that the pour-   the concentration of nitroglycerin in said waste acids is at more equal to 3% by volume.   3. Method according to claims 1 or 2 characterized in that   said residual acids are brought to a temperature comprised   between 110 * C and 130'C, preferably close to 120C, by ac- tion of microwaves.   4. Method according to claims 1 to 3 characterized in that   said residual acids are preheated to a temperature   taken between 15'C and 80C before undergoing the action of microwaves.   5. Method according to claim 4 characterized in that said residual acids are preheated by heat exchange with the treated residual acids.   6. Installation for continuous degradation of the nitroglycerin in the residual acids resulting from the nitration of the glycerin, constituted by a circulation circuit comprising successively in the direction of circulation of the acids, an inlet for said acids   after addition of water or dilute sulfuric acid, an external system   laughter for heating acids, an outlet for the mixture thus treated and an outlet for nitrous vapors, characterized in that said external heating system is a microwave system. 7. Installation according to claim 6 characterized in that the microwave system comprises a waveguide which is connected to   a microwave generator and which is crossed by a tube of a- conducted residual acids.