RU2268254C1 - Method for preparing dimethylethanolamine - Google Patents

Abstract

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a method for preparing dimethylethanolamine. Method involves interaction of anhydrous dimethylamine and ethylene oxide in two successive mixing reactors and displacing under enhanced temperature and pressure. Interaction is carried out under equilibrium pressure 6-13 atm in both reactors connected by gaseous phase. Dimethylamine and ethylene oxide are fed into reactor in the mole ratio = (3-6):1, and interaction is carried out up to achievement the concentration of ethylene oxide 1.4-5% at the mixing reactor outlet, and then the reaction mixture is fed into the displacing reactor. Method allows enhancing safety of the process, to provide high selectivity and increasing the output of the process in combination with simplicity of technological equipment.

EFFECT: improved preparing method.

1 tbl, 1 dwg, 4 ex

Description

The invention relates to organic chemistry, to the field of obtaining compounds containing amino groups and hydroxyl groups associated with acyclic carbon atoms of a saturated carbon skeleton, and in particular to methods for producing dimethylethanolamine (DMEA).

Dimethylethanolamine is used as a starting material in organic synthesis: in the production of flocculants, pharmaceuticals and cosmetics, as polymerization catalysts, absorbents for the purification of natural and industrial gases.

Widely known methods for producing dialkylethanolamine [Chemical encyclopedia; Kirk-Othmer, Encyclopedia of Chem. Techn., 3-ed., V.1, p. 944]. These methods consist in carrying out the interaction of ethylene oxide (hereinafter - OE) and an excess of the corresponding dialkylamine at elevated temperature and pressure. To carry out the interaction, the presence of a certain amount of catalyst is necessary - water or interaction products.

A specific feature of the hydroxyethylation reactions of lower amines is the autocatalytic nature of their progress and high thermal effect (up to 28 kcal / mol). Therefore, there is the problem of organizing effective heat removal from the reaction zone to prevent “auto-acceleration” of the reaction initiating explosive decomposition of ethylene oxide.

To organize effective heat removal of the reaction and ensure the temperature stability of the process in industry, the following methods are used:

- dilution with solvents - water, lower alcohols, excess dimethylamine;

- the use of special apparatus for carrying out the process, for example, a sectional reactor of the displacing type (“pipe in pipe”), with a high ratio of pipe length to its diameter, with the organization of heat removal from each section;

- fractional or batch feed of ethylene oxide into the reactor.

A known method of obtaining [patent GDR 203534, class. C 07 C 91/06, op. 10.26.83] dimethylethanolamine by the interaction of ethylene oxide (OE) and dimethylamine (DMA) with a ratio of OE: DMA of 1: 1.1-3.5. The process is carried out in a batch reactor with a stirrer, in the presence of catalytic amounts of water (0.1-2%), at a temperature of 60-80 ° C and pressure up to 15 atm. The temperature in the reaction zone is maintained by supplying ethylene oxide in certain portions, as well as providing heat removal from the interaction zone.

A known method of obtaining [US patent 5663444, class. C 07 C 209/02, op. 09/02/1997] dialkylethanolamines, which is carried out by the interaction of OE and an excess of dialkylamine from 1 to 50 moles, preferably from 1 to 10, at a temperature of 90-160 ° C and a pressure of 5-70 atm. The process is carried out in the presence of catalytic amounts of water - from 2.5 to 50%, after the reaction, the reaction products are sent for separation, excess dialkylamines are returned to the synthesis stage. The interaction is carried out in a batch tank with a stirrer, with a batch input OE.

The disadvantage of these processes is the use of water, the presence of which causes the formation of by-products - glycols, the isolation of which presents certain difficulties. In addition, DMEA forms a difficult to separate azeotrope with water, which complicates the production of commercial DMEA of the required purity.

Therefore, it seems more optimal to obtain DMEA in anhydrous conditions.

The main problem that has to be solved in the anhydrous synthesis of tertiary amino alcohols, in addition to providing effective heat removal, is selectivity, because a side reaction of the tertiary amine hydroxyethylation to the chain proceeds at a significant rate

This is especially true for the synthesis of DMEA, where the rate of side reactions of hydroxyethylation of the target product into the chain is an order of magnitude higher than in the synthesis of tertiary amino alcohols such as methyldiethanolamine (MDEA) and triethanolamine (TEA).

Known methods for producing tertiary amino alcohols: TEA [RF Patent 1681489, cl. C 07 C 215/08, op. 10.20.1999] and MDEA [RF Patent 1783771, cl. C 07 C 215/12, op. 17.009.1990] are not suitable for the synthesis of DMEA, since the presence of recyclable intermediate products (in the synthesis of MDEA is MEMA, in the synthesis of TEA is MEA, DEA) reduces the formation of by-products of high boiling hydroxyethylation products. There are no intermediates in the synthesis of DMEA.

Known autocatalytic method [patent of Germany 2357076, class. C 07 C 91/06, op. 05.28.75] obtaining alkyl ethanolamines, including dimethylethanolamine - prototype.

According to this method, the interaction of OE and anhydrous dimethylamine is carried out in a pipe-to-pipe displacement reactor. OE and dimethylamine (DMA) are fed to the reactor in a ratio of 1: 2. To provide catalysis with reaction products, a starting mixing reactor with a short residence time is established at the inlet of the tubular reactor, which ensures the conversion of OE of 1-30% or 0.05-0.2 times the reaction mixture is recycled to the inlet from the outlet of the reactor. The synthesis is carried out at a temperature of 100 ± 8 ° C and a pressure of 30 atm.

The disadvantages of this process:

- a high concentration of OE (22-32%) in the displacement reactor causes thermal instability of the process: small temperature fluctuations in the reactor can cause an uncontrolled increase in temperature, since the heat of reaction is more dynamic than heat removal. The same consequences occur in an emergency shutdown of production (shutdown of water, electricity);

- the complexity of the organization of an industrial reactor: the need to provide highly efficient heat removal causes performance limitations when using a displacement reactor, the ratio of the length of the reactor to its diameter in the prototype is 3600: 1;

- the need to maintain pressure in the reactor unit, significantly higher than equilibrium, to prevent the formation of a gas phase in the pipes;

- the high temperature of synthesis, necessary to increase productivity, negatively affects the quality of the product - color.

The objective of the invention is to increase the safety of the synthesis process, as well as providing high selectivity and increasing the productivity of the process in combination with the simplicity of technological design.

The essence of the invention lies in the fact that the method of producing dimethylethanolamine is carried out by the interaction of anhydrous dimethylamine and ethylene oxide in two successive mixing and displacement reactors at elevated temperature and pressure, characterized in that the interaction is carried out at an equilibrium pressure of 6-13 atm in both reactors connected by gas phase, moreover, dimethylamine and ethylene oxide are fed into the mixing reactor in a molar ratio of 3-6: 1, the reaction is carried out until a concentration of 1.4-5% oxy si ethylene at the outlet of the mixing reactor, then the reaction mixture enters the displacement reactor.

A diagram of the reactor unit is shown in the drawing.

The method is as follows. Raw materials - ethylene oxide (1 mol) from the tank pos. 1, anhydrous fresh DMA (1 mol) from the tank pos. 2 and return DMA (2-5 mol) from the tank pos. 3 - is supplied in a molar ratio of 3- 6 moles of DMA and per 1 mole of OE to the mixing reactor, item 4, where mainly (75-95%) the conversion of OE is carried out and the concentration of OE in the mixing reactor is 1.4-5%, which ensures the safety of the process. The low current concentration of MA is provided by the synthesis parameters: temperature, residence time of the reaction mixture in the reactor (ratio of reactor volume to space velocity of the supplied components). A high concentration ratio of DMA and DMEA suppresses the adverse reaction, as MA predominantly reacts with DMA, rather than with DMEA. Then the reaction mixture along the line pos.6 enters the displacement reactor, where the remaining ethylene oxide reacts.

The temperature in the reactors is maintained within the range of 70-90 ° C, it can be the same in the mixing and displacement reactors or different, but the temperature in the displacement reactor must be no lower than the temperature of the mixing reactor. Both reactors freely communicate pos. 7 in the gas phase and operate under equilibrium pressure of the reaction mixture within 6–13 atm created by the reaction mixture at a given temperature. From the reactor, the reaction mixture arrives at the separation stage of pos.8, from where the excess DMA is returned via line pos.9 to the tank pos.3.

Distinctive features of the proposed method are:

- the implementation of the main part of the conversion of MA in the mixing reactor, its current concentration in the mixing reactor is 1.4-5% (in the prototype 22-32%);

- carrying out the synthesis at the same equilibrium pressure of the reaction mixture in both reactors (6-13 atm);

- molar ratio of reagents at the inlet to the reactor DMA: OE = 3-6: 1.

Advantages of the proposed solution:

- a high level of process safety: the conversion of ethylene oxide is carried out mainly in the mixing reactor, the concentration of OE in it is 1.4-5%. This ensures thermal stability of the reactor during operation and safety during emergency shutdowns. An additional guarantee of safety is the process at equilibrium pressure, because the possibility of heat removal by evaporation of part of the DMA prevents the possibility of heating when the process is stopped;

- a simple constructive solution of reactors (capacitive devices) does not limit the performance of the installation;

- low, in comparison with the prototype, the synthesis temperature favorably affects the color of commercial DMEA;

- low pressure in the synthesis and a simple constructive solution provide a reduction in investment during construction and ongoing costs during production operation.

Case Studies

The process in accordance with the scheme shown in the drawing was carried out as follows.

Ethylene oxide and anhydrous amine are fed continuously at a predetermined speed, in a molar ratio of 1: 3-6, to a 1-liter capacitive mixing reactor pos. 4, operating at a temperature of 70-90 ° С. From the mixing reactor, the reaction mixture flows by gravity into the displacement reactor pos. 5 with a volume of 0.5 l, operating at a temperature of 70-90 ° C. Both reactors communicate in the gas phase with each other by the line pos. 7, on which there is a reflux condenser.

The supply of raw components is carried out at such a rate that the OE has time to react at a given temperature by 75-95%, while the concentration of OE in the mixing reactor is 1.4-5.0%. The concentration of ethylene oxide in the mixing reactor is controlled by gas chromatographic analysis of samples taken periodically from the mixing reactor.

The conditions and results of the experiments are shown in the table.

Examples of the method according to the invention Experience No. MA supply, kg / h DMA feed, kg / h DMA / OE molar Synthesis Conditions Mixing reactor Displacement reactor T ° C R atm The composition of the reaction mixture,% weight. MA Conversion OE DMA DMEA Impurities Mixing reactor Displacement reactor MA concentration DMA DMEA Impurities one 0.3 1,2 four 70-73 74 8 5,0 67.7 20.3 7.0 75 0.1 62.5 30.1 7.2 2 0.3 1.8 6 89-90 90 13 1.4 74.0 21,4 3.2 90 - 72.5 24.3 3.2 3 0.3 1.35 4,5 78-82 85 eleven 3,1 68.9 22.9 5.1 83 - 65.8 29.1 5.1 four 0.3 0.9 3 80-81 82 10 2,5 56 33.3 8.2 90 - 53.7 37.5 8.8

Claims (1)

A method of producing dimethylethanolamine by the interaction of anhydrous dimethylamine and ethylene oxide in two successive mixing and displacement reactors at elevated temperature and pressure, characterized in that the reaction is carried out at an equilibrium pressure of 6-13 atm in both reactors connected in the gas phase, and dimethylamine being fed into the mixing reactor and ethylene oxide in a molar ratio of 3-6: 1, the interaction is carried out to achieve a concentration of 1.4-5% ethylene oxide at the outlet of the mixing reactor, then the reaction mixture em into the displacement reactor.