CS250012B1 - A method for obtaining crystalline hexamethylenetetramine - Google Patents

Abstract

The purpose of the invention is to reduce the material complexity of the production process of crystalline hexamethylenetetramine, improve its theological properties and reduce the production of waste water from the process. The stated purpose is achieved by using as a washing medium and/or as its component in the process of separating solid hexamethylenetetramine, preferably by centrifugation, at a temperature of 20 to 70°C under atmospheric pressure, juice condensates from the evaporation process of aqueous solutions of hexamethylenetetramine, in the amount of 0.01 to 1 kg per 1 kg of crystalline hexamethylenetetramine with the following composition: more than 90% by weight water, 0.001 to 1% himot. ammonia, 0 to 4 wt.% methanol and 0.005 to 7 wt.% hexamethylenetetramine.

Description

The invention relates to a process for obtaining crystalline hexamethyltetamine from its aqueous mother liquors.

The production of crystalline hexamethylenetetramine is known and used industrially. Hexamethylenetetramine is mainly used in the manufacture of plastics, explosives, pharmaceutical products and the like.

The basic raw materials are ammonia and formaldehyde, whose mutual condensation reaction can be carried out in the gas or liquid phase, depending on the nature of the raw materials used. Most commonly, however, the so-called. a combined method, i. j. reacting ammonia gas with aqueous formaldehyde solutions or formaldehyde containing gases with aqueous ammonia solutions. The choice of the nature of production depends, in particular, on the process of obtaining the basic raw materials.

The resulting hexamethylenetetramine formation reaction can be expressed as follows:

CH2O + 4 NH3 -> C6H12N4 + 6 H2O - H = - 400 kmolar ¹

The condensation reaction of ammonia with formaldehyde is an exothermic colored process, which is used in every technology because it positively affects the energy intensity of the process.

To obtain a suspension of crystalline hexamethylenetetramine in the mother liquors, crystallization evaporation is used at temperatures of 50-65 ° C and reduced pressure to minimize the heat excretion excrements of hexamethylenetetramine. The aqueous environment is most commonly used, but the use of other solvents is known worldwide, in particular for the purpose of azeotropically draining water from hexamethylenetetramine solutions (U.S. Pat. No. 3,061,608, French Patent No. 1,167,436). A disadvantage of these processes is the necessity of solvent recovery and wastewater contamination with other organic compounds.

In the evaporation process, succulent condensates containing free ammonia and hexamethylenetetramine are also formed, which are entrained in the form of overspray from the vaporized apparatus. These condensates, together with other waste water, are liquidated by passing through a waste water treatment plant, which is one of the disadvantages of the process for the production of hexamethylenetetramine thus conducted.

• Podta jap. pat. no. 7 703 394, after concentrating the reaction mixture in an evaporator to a solution concentration of 43% by weight. recycle the evaporated ammonia solution to the reaction portion. The process requires a solution of the increased energy intensity resulting from the low concentration of ammonia in the recycled solution.

To obtain a solid phase from the suspension, i. j. crystalline hexamethylenetetramine, most commonly centrifugation is used, and after drying the crystalline hexamethylenetetramine, the product is finalized.

As a washing medium in the process of centrifuging the suspension of hexamethylenetetramine, an aqueous solution of hexamethylenetetramine and conc. 25 to 40 wt.

This method has proven to be disadvantageous, in particular in terms of the qualitative parameters of the resulting product, in view of it, since unwanted impurities are introduced into the crystalline phase by the solution during the washing. The product thus prepared could not be used for special explosive applications.

The crystalline product of improved quality parameters can be prepared by a process in which steam condensate is used as the washing medium of the centrifuged solid phase, which means, however, increasing the economic complexity of the process.

Most of these disadvantages can be overcome by the process of the present invention.

The present invention provides a process for separating the solid phase from aqueous mother liquors in a process for producing crystalline hexamethylenetetramine, preferably by centrifugation, wherein the solid phase is washed. The centrifugation process is carried out at 20 to 70 degrees C at atmospheric pressure, and as a separate solid phase wash medium, suction condensates are formed which are formed by the condensation of vapors from the evaporation process of aqueous hexamethylenetetramine solutions at 50 to 65 ° C under reduced pressure.

An essential component of the suction condensates is water, more than 90% by weight, but also contain 0.001 to 1% by weight. % ammonia, 0 to 4 wt. % methanol and 0.005 to 7 wt. hexamethylenetetramine.

Depending on the desired quality parameters of the crystalline hexamethylenetetramine produced, 0.01 to 1 kg of suction condensates are consumed in the solid phase separation process to produce 1 kg of hexamethylenetetramine.

The process according to the invention has a number of technical-economic advantages over the hitherto used.

The most important are: reducing the cost of disposing of suction condensates at a wastewater treatment plant, as they are recycled back into the process; loss of hexamethylenetetramine, since the steam condensate has been replaced by waste suction condensate, which in addition to free ammonia also contains hexamethylenetetramine, which also enters the wastewater from the evaporation process and the free ammonia present reduces the solubility of crystalline hexamethylenetetramine as well as improving theological properties of the product.

The most important advantages are illustrated by the following examples:

Example 1 (comparative)

In the process of producing crystalline hexamethylenetetramine, 4 750 kg of 37% formalin and 637 kg of 100% ammonia are introduced into the condensation reaction. The reaction yielded 5 387 kg of an aqueous solution having a concentration of 25% by weight. of hexamethylenetetramine, which is led to crystallization densification to obtain a 75% suspension of hexamethylenetetramine in the mother liquor, with 2 125 kg of sucrose condensates containing 1.3 kg of ammonia / m ³ , 5.5 kg of hexamethylenetetramine / m ³ and chemical With oxygen consumption of 21 kg Ch / m ^{3 of the} solution, it leaves the evaporation process into the waste water and then passes through a waste water treatment plant where it is cleaned at a cost of 1.4 Kg / kg of chemically bound oxygen. After centrifugation of the suspension, 1,275 kilograms of wet hexamethylenetetramine is obtained, with consumption of 200 kg of steam condensate for washing and drying, 1,250 kilograms of crystalline hexamethylenetetramine are prepared.

Example 2

Under analogous conditions to Example 1, a suspension of hexamethylenetetramine is prepared for centrifugation, where 200 kg of suction condensates are characterized as quantitatively and qualitatively in Example 1, with the residual amount being sent to a sewage treatment plant or treated. otherwise. After centrifuging the suspension, 1277 kg of wet hexamethylenetetramine are obtained, which, after drying, is 1,252 kg of product.

Following the procedure of Example 2, the losses of ammonia and hexamethylenetetramine in the suction condensates are reduced, thereby reducing the specific consumption of raw materials and reducing the wastewater treatment costs of the hexamethylenetetramine production.

Claims (2)

SUBJECT 1. A method of obtaining a crystalline? Ličík hexametyléintetramínu from the aqueous mother liquor, preferably by centrifugation at a temperature of 20 to 70 ^Q C, at atmospheric pressure, characterized in that the separated solid phase is washed of the crystalline hexamethylenetetramine condensate vapors from the process odparovarna aqueous solution of hexamethylenetetramine which it contains 0.001 to 1% of ammo. 0 to 4 wt. % methanol, 0.005 to 7 wt. % hexamethylenetetramine and the remainder to 100 wt. water. 2. A method according to claim 1, characterized in that 0.01 to 1 kg of steam condensate from the evaporation process of aqueous hexamethylenetetramine solutions is consumed to wash 1 kg of the separated light phase of hexamethylenetetramine.