RU2420509C1 - Method of extracting diethylene glycol and triethylene glycol - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention relates to an improved method of extracting diethylene glycol and triethylene glycol which are widely used in processes of producing polyurethanes and resins, for cleaning natural gas, as plasticisers and antifreeze components, through vacuum rectification from a mixture of ethylene glycols treated with an alkaline alcoholate of polyalkylene glycol or polyether based on alkylene oxide. Usually, the method employs an alkaline alcoholate of polether based on ethylene oxide or propylene oxide, and content of the alkaline alcoholate of polyalkylene glycol or polyether based on alkylene oxide in the mixture of ethylene glycols is equal to 0.00005-0.05 mol/l. ^ EFFECT: method enables to lower content of impurities in extracted di- and triethylene glycols. ^ 3 cl, 13 ex, 2 tbl, 1 dwg

Description

The invention relates to an improved method for the isolation of di- and triethylene glycols, which are widely used in the processes of producing polyurethanes and resins, for drying natural gas, as plasticizers and components of antifreeze agents.

The main industrial method for producing di- and triethylene glycols is to extract them by vacuum distillation from the bottom residue of the process of separating monoethylene glycol obtained by hydration of ethylene oxide (Dyment ON, Kazansky KS, Miroshnikov AM Glycols and other derivatives of ethylene and propylene oxides. M. : Chemistry, - 1976). Considering that the target product of this technology is monoethylene glycol, preferably monoethylene glycol of fiber purity, the described methods for the separation of ethylene glycols are aimed at improving the quality of monoethylene glycol. In particular, in order to improve light transmission in the UV region in the range 220-350 nm and reduce the aldehyde content to the stage of monoethylene glycol extraction, optically active impurities are distilled off with light aldehydes (RF Application No. 97110324/24, IPC ⁶ C07C 31/20, publ. 05/10/1999). It is known to reduce the formation of these impurities by the process of hydration of ethylene oxide using recycled water containing 0.00005-0.001% wt. acetaldehyde at a temperature of 150-190 ° C (RF Patent No. 2186053, IPC ⁷ C07C 31/20, 29/10, publ. 07.27.2002). However, these methods do not ensure the removal of impurities of high boiling aldehydes and acids formed during the hydration of ethylene oxide and during the rectification of monoethylene glycol at high temperatures. These high-boiling impurities during vacuum distillation are distilled off with di- and triethylene glycols, polluting these commercial products. In particular, the content of aldehydes increases. During storage, impurities contribute to the flow of the autocatalytic oxidation process with a decrease in the pH of di- and triethylene glycols.

Known methods for removing acidic impurities by treatment with an alkaline reagent of the reaction mass of hydration of ethylene oxide or an evaporated solution containing monoethylene glycol to a pH of 7.5-12, followed by isolation of monoethylene glycol, di- and triethylene glycols by vacuum rectification (RF Patent No. 2152922, IPC ⁷ C07C 31/20 , 29/10, published on July 20, 2000; RF Patent No. 2145591, IPC ⁷ C07C 31/20, 29/10, published ^on 02.20.2000). The disadvantage of these methods for the isolation of di- and triethylene glycols is the occurrence of condensation of light aldehydes in the early stages of rectification with the formation of heavy products and thermal decomposition of glycols in the presence of free alkali with the formation of carboxyl derivatives. The resulting heavy impurities with boiling points close to the boiling points of di- and triethylene glycols are released during vacuum distillation with a marketable product.

The objective of the invention is to improve the quality of di- and triethylene glycols released by vacuum distillation from a mixture of ethylene glycols.

The problem is solved by the method of separation of diethylene glycol and triethylene glycol from a mixture of ethylene glycols by vacuum distillation, including processing the mixture of ethylene glycols with an alkaline alcoholate of polyalkylene glycol or a polyether based on alkylene oxide.

It is possible to use an alkaline alcoholate of a polyether based on ethylene oxide or propylene oxide.

The alkaline alcoholate content of a polyalkylene glycol or an alkylene oxide based polyether in a mixture of ethylene glycols may be 0.00005-0.05 mol / L.

As the alkaline alcoholate of polyalkylene glycol, an alkali metal alcoholate based on polyethylene glycol is used.

As polyethylene glycol, diethylene glycol or triethylene glycol or mixtures thereof are used. As a mixture of diethylene glycol and triethylene glycol, it is possible to use the bottom residue of the process for extracting monoethylene glycol from a by-product of the production of ethylene oxide of the following composition:

Mass fraction of diethylene glycol 70.0-95.0%, Mass fraction of triethylene glycol 1.0-30.0% Alkaline alcoholate content diethylene glycol and triethylene glycol 0.025-0.75 mol / L.

As the alkylene oxide polyester alkaline alkoxide, an alkali metal alcoholate based on ethylene oxide or propylene oxide with a molecular weight of from 200 to 1000, obtained by anionic polymerization of ethylene oxide or propylene oxide, is used.

As a polyester based on propylene oxide with a molecular weight ranging from 200 to 1000, you can use polyethers of the following grades: Laprol 373 (TU 2226-017-10488057-94), Laprol 502M (TU 2226-012-05766801-93).

As a polyether based on ethylene oxide with a molecular weight ranging from 200 to 1000, for example, PEG 400 polyester (TU 2226-061-05766801) can be used.

Alkylene oxide-based polyethers with molecular weights ranging from 200 to 1000 are prepared by anionic polymerization of ethylene oxide or propylene oxide by the following procedure.

440 g of starting material, monoethylene glycol, 80 g of an alkaline catalyst, sodium hydroxide, are loaded into the reactor. The reactor is purged with nitrogen and, with stirring, is gradually heated to 90-100 ° C over 30 minutes. In this case, the alkali dissolves in the starting substance. Then, alkylene oxide, for example ethylene oxide, begins to be fed into the reactor from a measuring vessel. The process of anionic polymerization of alkylene oxide in the presence of a starting substance and an alkaline catalyst is carried out at a temperature of the reaction mass of 80-110 ° C and a pressure of 3.0-4.0 kgf / cm ² . After feeding 4.38 kg of alkylene oxide, the reaction mixture was kept for 1.0 h at a temperature of 115-125 ° C until a residual content of alkylene oxide in the reaction mass of not more than 0.01 wt.% Was achieved. The resulting reaction mass contains 0.41 mol / l of sodium alcoholate of a polyether based on ethylene oxide (polyethylene glycol) with a molecular weight of 538 (calculated based on the hydroxyl number of the obtained polyethylene glycol - 208 mgKOH / g). Table 1 shows the physicochemical properties of alkaline alkylene oxide polyesters obtained in a similar manner using methanol and ethanol as a starting material, sodium hydroxide and potassium hydroxide as an alkaline catalyst, ethylene oxide and propylene oxide as alkylene oxide .

Evaluation of the effectiveness of the proposed method for the isolation of diethylene glycol and triethylene glycol by vacuum distillation from a mixture of ethylene glycols was carried out on a continuous installation, presented below. This installation includes a distillation column pos. 1 with an efficiency of 20 theoretical plates for distillation of residual monoethylene glycol, a distillation column pos. 2 with an efficiency of 20 theoretical plates for isolating diethylene glycol, a distillation column pos. 3 with an efficiency of 20 theoretical plates for isolating triethylene glycol. Removing the residual monoethylene glycol coming with a mixture of ethylene glycols in a distillation column pos. 1 is carried out in the following modes: column cube temperature 157-160 ° C, column top temperature 100-102 ° C, reflux ratio 1.5, residual pressure at the top of the column 35 -40 mmHg When the column is in this mode, the residual monoethylene glycol content in the bottoms product is in the range of 0.01-0.05% wt. Isolation of diethylene glycol in a distillation column pos. 2 is carried out in the following modes: column cube temperature 165-170 ° C, column top temperature 130-135 ° C, reflux ratio 1.5, residual pressure at the top of the column 15-17 mm Hg Isolation of triethylene glycol in a distillation column pos. 3 is carried out in the following modes: column cube temperature 180-185 ° C, column top temperature 150-155 ° C, reflux ratio 2.5, residual pressure at the top of the column 10-12 mm Hg In addition to these columns, this unit has a capacity of pos. 4 for receiving and supplying bottoms of the monoethylene glycol extraction process; capacity pos. 5 for receiving and supplying an alkaline alcoholate of a polyalkylene glycol or a polyether based on alkylene oxide; reflux containers pos.6, pos.9, pos.12; capacity pos. 7 for collecting distilled off residual monoethylene glycol; containers pos.10 and pos.13 for collecting diethylene glycol and triethylene glycol; containers pos. 8, pos. 11, pos. 14 for collecting bottoms product of columns pos. 1, pos. 2, pos. 3; pumps pos.15, pos.16, pos.17, pos.18; refrigerators pos.19, pos.20, pos.21.

For testing at the indicated installation, a mixture of ethylene glycols was used as a feedstock, which is a cubic product of a monoethylene glycol recovery column obtained by hydration of ethylene oxide at a temperature of 155-160 ° C, followed by evaporation of the reaction mass and isolation of commodity monoethylene glycol. This mixture of ethylene glycols has the following composition: the residual content of monoethylene glycol is 8-12% wt., The content of diethylene glycol, triethylene glycol and tetraethylene glycol, respectively 65-70% wt., 12-20% wt., 2-5% wt. This mixture has a pH in the range of 6.5-7.5 and a mass fraction of aldehydes in terms of acetaldehyde of 0.008-0.012%.

Test conditions are described in the examples. The composition of the streams was determined chromatographically at a column temperature of 150 ° С, an evaporator of 250 ° С with registration by a flame-ionization detector. For chromatography, a metal column 2 m long filled with a sorbent — 5% wt. polyethylene glycol PEG-20,000 on a chromaton of a fraction of 0.16-0.25 mm.

The invention is illustrated by the following examples.

Example 1. During the test, a diethylene glycol alcoholate is obtained preliminarily in a 50 liter stainless steel reactor equipped with a stirrer and a thermo shirt. For this, 35 kg of diethylene glycol and 2540 g of potassium alkali are charged into the reactor. The alkali is dissolved with stirring and heating to 40 ° C. The resulting reaction mass is dried at a temperature of 120 ° C and a residual pressure of 200-250 mm Hg. 36.7 kg of the resulting solution containing 1.45 mol / L of potassium alcohol diethylene glycol is loaded into the container pos.5. Physico-chemical properties of the obtained diethylene glycol alcoholate are presented in table 1.

In the container pos.4 take 3000 kg of the initial mixture of ethylene glycols containing 11.0% wt. monoethylene glycol, 68.3% wt. diethylene glycol, 15.1% wt. triethylene glycol and 5.6% wt. tetraethylene glycol. Raw materials from the tank pos.4 and diethylene glycol alcoholate from the tank pos.5 pump pump pos.15 serves to feed the columns pos.1.

In the vacuum distillation column pos. 1, residual monoethylene glycol is extracted at a column cube temperature of 157-160 ° C, the top of the column 100-102 ° C, a reflux ratio of 1.5, and a residual pressure at the top of the column of 35-40 mm Hg. The column distillate after cooling in the heat exchanger pos.19 is sent to the collection tank pos.6, from where part is returned as reflux, and the rest is taken out to the tank pos.7. Under these conditions, a mixture of ethylene glycols containing 80-85% wt. Is distilled off from the top of the column. monoethylene glycol, 10-15% wt. diethylene glycol (analysis of the distillate from the tank pos.6). VAT liquid columns 1, containing 0.01-0.05% wt. monoethylene glycol, withdrawn to the collection tank pos. 8, from where with the pump pos. 16 they are fed to the column pos. 2.

In a vacuum distillation column pos. 2, diethylene glycol is isolated at a column temperature of 165-170 ° C, a column top of 135-137 ° C, a reflux ratio of 1.5, and a residual pressure in the top of the column of 15-17 mm Hg. The column distillate after cooling in the heat exchanger pos. 20 is sent to the collection tank pos. 9, from where part is returned as reflux, and the rest is taken out to the container pos. 10. Under these conditions, diethylene glycol is distilled off from the top of the column with a basic substance content of 99.9% wt., Aldehydes 0.0002% wt. in terms of acetaldehyde (analysis of the distillate from the tank pos.9) and pH 7.0. VAT liquid columns 2, containing 0.08-0.10% wt. diethylene glycol is withdrawn to the collection tank pos.11, from where the pump pos.17 serves to supply the column pos.3.

In a vacuum distillation column pos. 3, triethylene glycol is isolated at a column temperature of 180-185 ° C, a column top of 150-155 ° C, a reflux ratio of 2.5, and a residual pressure in the top of the column of 10-12 mm Hg. The column distillate after cooling in the heat exchanger pos. 21 is sent to the collection tank pos. 12, from where a part is returned as reflux, and the rest is taken out to the container pos. 13. Under these conditions, triethylene glycol is distilled off from the top of the column with a basic substance content of 99.9% wt., Aldehydes 0.0002% wt. in terms of acetaldehyde, pH 7.3 (analysis of the distillate from the tank pos.12). VAT liquid column 3, containing 14.0-15.0% wt. triethylene glycol, withdrawn to the collection tank pos.14. The test in this mode is carried out for 48 hours.

Example 2. The test is carried out analogously to example 1, and the mixture of ethylene glycols is treated with potassium alcoholate of PEG 400 polyester (No. 8, table 1) by feeding the column pos. 1 from the tank pos. 5 to the pump pos. 15. From the top of the column of pos. 2, diethylene glycol is distilled off with a basic substance content of 99.8% wt., Aldehydes 0.0015% wt. in terms of acetaldehyde (analysis of the distillate from the tank pos.9) and a pH of 7.3. Triethylene glycol with a basic substance content of 99.9% wt., Aldehydes 0.0002% wt. in terms of acetaldehyde, pH 7.4 (analysis of the distillate from the tank pos.12).

Example 3. The test is carried out analogously to example 1, the consumption of raw materials from the tank pos.4 and diethylene glycol alcoholate from the tank pos.5 is 20 kg / h and 0.7 kg / h. At these costs, a dosage of diethylene glycol alcoholate in a mixture of ethylene glycols in an amount of 0.05 mol / L is provided.

Examples 4-13. The test is carried out analogously to example 3. The physicochemical properties of alkaline alcoholates of polyalkylene glycols and polyethers based on alkylene oxide are presented in table 1. The results of the analysis of the isolated di- and triethylene glycols are presented in table 2.

According to the test results, from a mixture of ethylene glycols treated with an alkaline alcoholate of polyalkylene glycol or polyether based on alkylene oxide with a dosage of 0.00005-0.05 mol / L, diethylene glycol and triethylene glycol with aldehyde content of less than 0.0050% wt were isolated by vacuum distillation. and a pH of 7.0-7.4.

Thus, the proposed method for the separation of diethylene glycol and triethylene glycol by vacuum distillation from a mixture of ethylene glycols provides a reduction in the content of impurities and thereby improving the quality of diethylene glycol and triethylene glycol.

Claims (3)

1. A method of separating diethylene glycol and triethylene glycol from a mixture of ethylene glycols by vacuum distillation, comprising treating the mixture of ethylene glycols with an alkaline alcoholate of a polyalkylene glycol or an alkylene oxide polyester. 2. The method according to claim 1, in which an alkaline alcoholate of a polyether based on ethylene oxide or propylene oxide is used. 3. The method according to claim 1, in which the alkaline alcoholate content of a polyalkylene glycol or a polyether based on alkylene oxide in a mixture of ethylene glycols is 0.00005-0.05 mol / L.

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