RU2430085C1 - Method of producing ethanolamines - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: triethanolamine can be used in production of surfactants, detergents and cosmetic agents. The method involves reaction of ethylene oxide and excess anhydrous ammonia in two serial mixing and displacement apparatus at high temperature and pressure while returning monoethanolamine to the displacement reactor. Reagents are fed in molar ratio of ammonia to ethylene oxide fed into the mixing reactor equal to 6-10:1, while maintaining conversion of ethylene oxide in the mixing reactor at 75-80%. ^ EFFECT: method enables to obtain reaction mixtures with high content of triethanolamine which virtually do not contain high-boiling products of oxyethylation thereof, which enables to avoid decomposition of triethanolamine due to high temperature at the fractionation step and obtain triethanolamine with high content of the base substance and low colour index. ^ 1 tbl, 9 ex

Description

The invention relates to the field of production of amino alcohols, and in particular to methods for producing ethanolamines, in particular triethanolamine (TEA).

TEA is used in the manufacture of polymeric materials, surfactants, detergents, and in the manufacture of cosmetics.

The specifics of the TEA application areas determine the requirements for its quality - a high content of the main substance (≥99.0%) and a low color index (<20 units of the ARNA platinum-cobalt scale).

Obtaining a TEA of this quality is associated with a number of technological problems.

TEA is a high boiling point (boiling point 360 ° C) thermolabile substance with the onset of decomposition of 170 ° C. Under the influence of high temperatures, TEA decomposes to form a volatile crotonic aldehyde, which, when interacting with ethanolamines (EA), gives Schiff bases polymerizing into colored products [GGSmirnova et al., J. Of Applied Chemistry of USSR 61, pp.1508-9 (1988); Chemical & Engineering News 1966, scp 16. h.42, middle column], so TEA after rectification is colored if the reaction mixtures contain TEA oxyethylation products that increase the heating temperature.

The formation of crotonaldehyde can also occur from ethylene oxide (OE) at high synthesis temperatures. In this case, colored reaction mixtures are obtained, the separation of which does not make it possible to obtain a colorless TEA without the use of special processing steps for the reaction mixtures or isolated TEA. Therefore, it is important both at the synthesis stage and at the stages of rectification to use temperature conditions to avoid these processes.

The most common way to obtain TEA is the synthesis of ethylene oxide and aqueous ammonia in a mixture containing simultaneously monoethanolamine (MEA) and diethanolamine (DEA). The hydroxyethylation of ammonia and amines is accompanied by a high thermal effect (~ 26 kcal / mol OE). The processes for the preferred preparation of TEA require a reduction in the NH ₃ / OE ratio, i.e. high concentrations of MA.

To reduce heat generation and increase the thermal stability of the reactor unit, EA synthesis is usually carried out using aqueous ammonia by fractional injection of OE along the length of the reactor at temperatures up to 160 ° C, pressure up to 12 MPa [US 5/545/751, cl. С07С 209/60, publ. 08/13/96] either in two stages, with the first stage being carried out with an increased molar ratio of ammonia (OE: NH ₃ = 1: 10–16) at temperatures up to 130 ° C, and in the second stage at temperatures up to 180 ° C MEA is ethoxylated and DEA [US 1453762, cl. С07С 91/10, publ. 02/15/74].

Under these conditions, by-products of the decomposition of OE and the interaction of OE with water and ethanolamines are formed, which requires the use of special additives and the use of special techniques at the stages of synthesis and rectification to purify by-products and reduce the color index of individual ethanolamines.

The introduction of additives and treatments affects the economy of the process, increases the number of stages, requires studying the effect of additives on the sanitary-hygienic properties of marketable products.

Known low-temperature methods for the synthesis of EA by the special organization of the reactor unit, which allows in the absence of water and heterogeneous catalysts to carry out the synthesis of a mixture of EA at low temperatures in the environment of the reaction products.

The authors of the patent [RU 1681489, cl. С07С 215/08, publ. 10.20.99] offer the process of obtaining EA, aimed at increasing the yield of TEA. The synthesis process is carried out in two sequential apparatuses: first in the mixing apparatus at a temperature of 50-80 ° C until the OE is incompletely converted, and then until the complete conversion in the displacement apparatus, the temperature of which is 70-20 ° C higher than in the first. The ratio of NH ₃ : OE in the first reactor is 2 ÷ 4: 1. The content of TEA in the reaction mixture increases to 45.0%. However, the practical implementation of the method shows that at low ammonia concentrations in the reactor unit (in the first reactor, the molar ratio NH ₃ / OE = 2 ÷ 4: 1, in the second reactor ammonia is distilled off by increasing temperature) OE reacts with ethanolamines, including with tea. As a result, the formation of a high-boiling TEA oxyethylation product occurs, which increases the cube temperature during rectification and the degree of TEA decomposition. In addition, partial decomposition of OE at high temperatures in the second reactor leads to the formation of colored reaction mixtures (60-80 Hazen units), from which it is impossible to isolate colorless TEA.

The authors of the methods [RU 2141475 C1, cl. С07С 213/04, publ. 11/20/99; RU 2268255 C1, C07C 213/04, publ. 01/20/2006] receive mixtures of EA with a predominant content of MEA and / or DEA by the interaction of OE and anhydrous ammonia in a system consisting of two successive mixing and displacement reactors at a temperature of 40-85 ° C, a pressure of 35-46 atm, a molar ratio of OE / NH ₃ = 1/15 ÷ 25, recycle of MEA in an amount of 0.01 ÷ 1.5 mol per 1 mol of OE in the mixing reactor or distributing it between the mixing and displacement reactors, with the conversion of OE in the mixing reactor 50-85%. The methods are implemented on an industrial scale.

The indicated synthesis conditions are aimed at the synthesis of MEA and DEA and make it possible to obtain a mixture of EA containing 60-40% MEA, 30-50% DEA and not more than 20% TEA (mainly 5-15%). The ratio of the formed MEA and DEA can be changed by returning the MEA to synthesis.

The authors of the patent RU 2225388 C1, cl. С07С 213/04, publ. 03/10/04 (prototype), a method for the production of ethanolamines by reacting OE with a stoichiometric excess of ammonia at elevated temperature and pressure in a system of mixing and displacement reactors at a temperature of 70-85 ° C, a pressure of 35-46 atm, a molar ratio of OE: NH ₃ = 1 : 15 ÷ 25 and the conversion of ethylene oxide in the mixing apparatus is not less than 70%. By returning monoethanolamine to the mixing reactor in an amount of 0.1-1.0 mol per mole of supplied OE, the ratio of MEA and DEA can be changed, the amount of obtained TEA does not exceed 20%.

The task of the authors of the proposed method is the synthesis of a mixture of ethanolamines with a predominant content of triethanolamine.

It is known that the ratio of EA obtained is determined by the molar ratio of NH ₃ : OE. A decrease in the molar ratio of NH ₃ : OE leads to an increase in the content of TEA in the reaction mixture. The return of the IEA changes the ratio of IEA and DEA in favor of DEA.

When the molar ratio of NH ₃ : OE is reduced to 2-5, the TEA content can increase to 40-60%, however, at the same time up to 10% of high-boiling TEA oxyethylation products are formed, which makes it difficult to isolate TEA from the reaction mixture as a marketable product by rectification from for the need to increase the heating temperature, initiating decomposition. Therefore, the claimed method proposed a set of parameters to increase the content of TEA and to avoid the formation of high-boiling products of hydroxyethylation.

The molar ratio of NH ₃ : OE = 6 ÷ 10.

The conversion in the mixing apparatus is 75-80%.

IEA recycling (all or part) to the displacement reactor.

In the proposed method, an increase in the yield of TEA is achieved practically without the formation of by-products - ethoxylated triethanolamine - due to the optimal combination of synthesis parameters: molar ratio NH ₃ : OE, degree of OE conversion in the mixing reactor, and MEA recycling method.

The proposed method allows to obtain with a high yield of TEA, which can be isolated in the form of a practically colorless commercial product by conventional vacuum distillation, i.e. synthesis and rectification conditions do not allow decomposition of OE and TEA.

The essence of the invention lies in the fact that a mixture of EA with a predominant content of TEA is obtained by the interaction of OE and anhydrous ammonia in two successive mixing and displacement apparatus at elevated temperature and pressure, a molar excess of ammonia with MEA recycling. In this case, a certain combination of synthesis parameters must be observed: the molar ratio of ammonia to ethylene oxide fed to the 1st reactor is maintained at 6 ÷ 10, the OE conversion in the mixing reactor is 75-80%, all or part of the MEA is recycled to the displacement reactor.

The proposed method differs from the prototype synthesis parameters:

- molar ratio of NH ₃ : OE is 6 ÷ 10;

- OE conversion of 75-80%;

- MEA recycling is carried out in the displacement reactor.

The advantages of the claimed method:

- the organization of synthesis in a specific narrow framework of parameters allows one to obtain reaction mixtures with a high TEA content, practically containing no high boiling TEA oxyethylation products;

- the separation of such mixtures is carried out by conventional vacuum distillation at the boiling point of TEA. The absence of high-boiling impurities avoids elevated heating temperatures and prevents decomposition processes that cause an increase in the color index of a commodity TEA.

The claimed benefits are achieved only when using all three features:

- molar ratio of NH ₃ : OE should not be less than 6: 1, because with smaller excesses of ammonia in the mixing reactor, along with an increase in the TEA content, the amount of high-boiling products of its hydroxyethylation at any degree of OE conversion increases;

- the conversion of MA in a displacement reactor within no more than 80% minimizes the formation of high-boiling compounds. At a molar ratio of NH ₃ : OE = 6 ÷ 10: 1, high-boiling compounds are produced in the mixing reactor if the OE conversion exceeds 80%; when the OE conversion is <75%, it is not possible to ensure the predominant content of TEA in the mixture of ethanolamines;

- it is necessary to recycle the MEA only into the displacement reactor, increasing the concentration of MEA for the reaction with the residual OE and preventing the hydroxyethylation of TEA in the displacement reactor.

Without MEA recycling, the residual OE reacts with TEA in the displacement reactor, because TEA concentration is highest in comparison with other components. The MEA recycling to the mixing reactor, as well as distributed to both reactors, increases the content of TEA oxyethylation products in comparison with the MEA recycling option only to the displacement reactor.

Thus, the optimal combination of the molar excess of ammonia and the degree of OE conversion in the mixing apparatus allows one to obtain reaction mixtures enriched in TEA without the products of its hydroxyethylation, and the return of MEA to the displacement reactor prevents the production of TEA oxyethylation products in the displacement reactor. The mixture of ethanolamines, leaving the reactor block, has a high TEA content and practically does not contain products of its hydroxyethylation.

The process is carried out as follows. OE and ammonia are continuously fed into the mixing reactor. The temperature in the mixing reactor is kept constant within 70-90 ° C, the molar ratio of NH ₃ : OE is 6 ÷ 10: 1. A conversion of 75-80% is supported by the feed rate of the reagents. The pressure corresponds to the pressure of its own vapor. From the mixing reactor, the reaction mixture enters the displacement reactor operating at the same temperature as the first reactor, and the conversion of ethylene oxide is completed. Returnable MEA is fed to the displacement reactor, where it reacts with OE, successfully competing with TEA due to the higher reaction rate of OE with MEA in comparison with the rate of reaction of OE with TEA.

Ammonia is distilled off from the reaction mixture by the method of [RU 2162461, cl. С07С 213/04, publ. January 27, 2001] and individual ethanolamines are isolated by vacuum distillation on a column with a regular packing and a film evaporator. TEA is isolated with a basic substance content of ≥99%. Chroma is measured photometrically on a platinum-cobalt scale in Hazen units.

Examples of specific implementations of the method are given in the table. The above examples illustrate the claimed method, but do not limit it.

No. Molar ratio
NH ₃ : OE Temperature in mixing and displacement reactors, ° С OE conversion in the mixing reactor,% Supply of MEA to the displacement reactor, mol / mol of OE fed to the synthesis The ratio of the resulting products of hydroxyethylation in the reaction. mixtures TEA color index ≥99%, units Hazen (Pt-Co scale) IEA DEA Tea VK. one 5 89-90 76 0.02 9,4 32.1 58.2 0.3 twenty 2 7 88-89 75 0.05 20.3 28.7 50.9 0.1 <10 3 7.5 85 78 0.2 6.4 37.3 56.1 0.2 12 four 8 78-90 80 1,1 - 28.1 71,4 0.5 fifteen 5 10 70-71 80 1,1 1.9 37.8 60.0 0.3 <10 6 four 85-87 70 0.1 28.0 26.0 40.9 5.1 150 7 6 82-85 70 0.08 41.2 26.7 32.1 - <10 8 6 86 85 0,03 9.9 33.1 55.0 2.0 70 9 8 80 80 - 21.9 27.0 48.0 3,1 110

Examples 1-5 show that the reaction mixture with a predominant content of TEA practically does not contain high-boiling products of its hydroxyethylation, if the synthesis parameters are maintained within the stated limits; triethanolamine isolated from such reaction mixtures has a low color index.

Examples 6-9 show that the syntheses carried out under conditions outside the stated limits for any of the declared parameters do not allow to obtain reaction mixtures with a high TEA content without the simultaneous formation of products of its hydroxyethylation.

Claims (1)

The method of producing ethanolamines, in particular triethanolamine, by the interaction of ethylene oxide and anhydrous ammonia, used in excess, at elevated temperature and pressure, in a system of two successive mixing and displacement reactors with the return of the resulting monoethanolamine, characterized in that ammonia and ethylene oxide are fed into the mixing reactor in a molar ratio of 6 ÷ 10: 1, the conversion of ethylene oxide in the mixing apparatus is maintained at the level of 75-80%, the MEA is returned to the displacement reactor.