CS233235B1 - The method of evaporating acetic acid with a vinyl acetate concentration of 0.1 to 5% by weight - Google Patents

Abstract

The invention solves the evaporation of acetic acid with a low concentration of vinyl acetate, and is particularly suitable for the process of synthesizing vinyl acetate by adding acetic acid to acetylene or by splitting ethylidene diacetate. To prevent deterioration of heat transfer or clogging of parts of the technological equipment, at least one antioxidant and/or inhibitor of free-radical reactions is added to the acetic acid containing vinyl acetate in an amount of 1.10-^ to 1.10"' % by mass and the vapors are removed at a linear speed of 8 to 16 m.s"1. Certain oxidation residues, intermediate products, e.g. from the production of phenol, are listed as particularly suitable antioxidants.

Description

233235 2

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the evaporation of acetic acid with a low concentration of vinyl acetate at defined rates of liquid and vapor phase.

The industrial scale evaporation of acetic acid is generally not associated, with severe corrosion effects, with no technological difficulties. However, it has been shown that the evaporation of acetic acid in the production of vinyl acetate does not occur in accordance with the foreseen course of the process, since the transfer processes of heat transfer to the connecting pipes and in many cases the technological efficiency of the preheating is impaired. These negative effects can cause an accidental situation with Sasu.

Evaporation of acetic acid in the production of vinyl acetate by the addition of acetic acid to ethylene, optionally by thermal and catalytic decomposition of ethylidene diacetate, takes place in the regeneration of acetic acid as well as in the evaporation of acetic acid by a mixture where both recovered acetic acid and fresh acid acetic acid are used.

In both of these operations, in addition to any other possible admixtures, mainly the monomeric vinyl acetate is present in the acetic acid, but in low concentration and, in addition, without any apparent contaminants which could cause its polymerization. However, it has been shown that in the operation it is partially polymerized as well as the formation of other hardly definable liquids, whereby deterioration of the equipment does not usually remove the technical measures, such as continuous or long-term liquid phase draining, thus preventing the increased concentration of these undesirable products. in a digester.

According to the invention, the method of evaporating acetic acid with a concentration of vinyl acetate is 0.1 to 5% by weight. in the process for the production of vinyl acetate by the addition of acetic acid to the ethylene and / or by the ethylene diacetate digestion, its stabilization in the liquid phase or in the vapor phase, by stabilizing the acetic acid solution with at least one antioxidant and / or at least one inhibitor in the TND in an amount of 1.10%. % to 1.10% by weight, calculated on the total amount of the mixture, and part of the liquid phase, the evaporator, preferably discontinuously, with the resulting vapors being removed outside the evaporator body at a linear velocity of 8 to 16 ms -1.

The main advantage of the method according to the invention is to ensure a long-term uniform and efficient operation of the acetic acid evaporator with a positive impact on the whole technological part before the reactor with minimal material costs, as well as removal of the work with cleaning of the respective parts of the technological equipment. The implementation of the process of the invention also provides considerable energy savings in the evaporation of acetic acid and higher working time.

The addition of a stabilizing agent, which is at least one antioxidant or aToradical Reaction Inhibitor, has a complex effect in the process, on the one hand it binds the dissolved oxygen, not only prevents the formation of hydroperoxides and polymers, but also suppresses the formation of dwarf compounds and their negative effects. In order to stabilize the present invention, both antioxidants such as 2,6-di-tert-butyl-p-cresol, N-phenyl-N'-isopropyl-p-phenylenediamine, diphenylamine, cumylphenol and the like can be used both commercially and commercially. OTHER PRODUCTS OF ANTI-OXIDATE PRODUCTS, THE MOST DESTILLATION RESIDUES FROM THE PRODUCTION OF N-PHENYL-N'-ISopropyl-P-PHENYLENEDIAMINE, 2,6-DI-Tert-butyl-P-Cresol, Phenol Distillation Residues, Phenolic Pits, Intermediates production of antioxidants, from the production of alkylphenols and the like. Inhibitors of the tadadical reactions of this invention include, but are not limited to, typical polymerization reaction inhibitors such as divalent phenols, especially hydroquinone, alkoxy-phenols, aromatic and aliphatic nitro compounds and dinitro compounds, 3-hydroxylamine, and derivatives thereof, phenothiazine, sulfur and its compounds. 3 233235

The use of all of these substances, in addition to the technical benefits, is also advantageous from the economic point of view.

Ensuring the desired linear vapor velocity does not represent an increase in investment requirements and is easy to use using conventional chemical calculations between the vaporized acetic acid and the conduit brightness.

Some application possibilities of the invention show the examples below. R e r * L a d 1

A 0.5 L three-necked glass beaker was charged continuously with 30 g / g of acetic acid and 30 g / h of regenerated acetic acid from the production of vinyl acetate containing 0.24% w / w. % of vinyl acetate as well as 1.2.10 wt. pyrocatechin after its addition as an inhibitor in the noradical reactions. After 120 hours of continuous evaporation at a constant level in the evaporation flask, the residue in the flask was increased to 47.2% by weight. In the comparative experiment without the addition of an inhibitor, the residue was increased by 132.7% by weight over the same period at the same acetic acid flow rates. EXAMPLE 2 30 g / h of dry acetic acid and 30 g / h of regenerated acetic acid containing 0.57% by weight were continuously injected in the same apparatus as in Example 1. % vinyl acetate and 1.1.10-2 wt. p-methoxyphenol as an inhibitor in the heteradical reactions. After 120 hours of continuous evaporation, the residue in the contents of the flask was increased by 37.2% by weight. In the comparative procedure under the same conditions, but without the inhibitor, the residue is increased by 154.7% by weight. EXAMPLE 3 Residues from the manufacture of an N-phenyl-N'-isopropyl-p-phenylenediamine (antioxidant CD) containing 4 wt. p-aminodiphenylamine, 8 mg / kg palladium, at a concentration of 8.10% by weight. After 120 hours of continuous evaporation, the evaporation was increased to 30.6% by weight. The comparative experiment as in Example 2 has an increase in the evaporator of 154.7% by weight. Example 4

The procedure is similar to that of Example 3 but except 5.10% by weight. 5.10% w / w of N-phenyl-N'-isopropyl-p-phenylenediamine (CD) antioxidant was added. phenol sm61 from the distillation of phenol produced by the so-called cumene process. Phenolic salts have the following composition (% by weight): alpha-methylstyrene = 0.2; acetophenone = 21.6; phenol = 4.6; cumylphenol = 22.8; dimethylphenylcarbinol = 11.5, the remainder up to 100% being predominantly dimers of alpha-methylstyrene and phenyl-trimethylindene.

After 120 hours of continuous evaporation, the 21.2% residue was increased, while the comparative experiment as in Example 2 had an evaporator increase of 154.7%.

Claims (3)

OBJECT OF THE INVENTION 1.10 to 1.10 ~ ³ ~ 96 ¹ wt., Calculated on the total amount of the mixture of, and often the liquid phase is remitted, preferably discontinuous, wherein the generated steam is discharged outside the body of the evaporator at a linear velocity m s 8 and 16 '. Process for evaporating acetic acid with a vinyl acetate concentration of 0.1-596% by weight. in the process of producing vinyl acetate by catalyzing the addition of acetic acid to acetylan and / or by cleaving ethylidene diacetate, stabilizing it in the liquid phase or even in the vapor phase, characterized in that said acetic acid solution is stabilized by at least one antioxidant and / or at least one inhibitor in a radical reaction quantity 2. The method of claim 1, wherein 2,6-di-tert-butyl-p-cresol, 2,4-di-tert-butylphenol, cumylphenol, diphenylamine, N-phenyl-N 'are used as antioxidants. -isopropyl-p-phenylenediamine, preferably distillation residues from the production of antloxidants and / or intermediates from the production of N-phenyl-N '-isopropyl-p-phenylenediamine, and the distillation residues from the production of phenol. 3. A method according to claim 1 or 2, wherein alkoxyphenols having a carbon number of 1 to 4 and an alkoxy group, divalent phenols, nitrosoamines, hydroxylamines and derivatives thereof, sulfur and compounds thereof are used as inhibitors of the radical reactions.