SU431150A1 - METHOD OF CLEANING SOLVENTS - Google Patents

Description

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This invention relates to methods for purifying solvents used in hydrocarbon recovery processes.

A known method of purification of solvents used to isolate acetylene from polymer impurities is by distillation in the presence of an additive of an oil fraction with a boiling point 125 ° C above the boiling point of the solvent with a selection of the purified solvent in the form of distillate. Such a method is ineffective in purification of solvents used for the isolation of aromatic or diolefinic hydrocarbons, since in this case the solvent is contaminated with poorly soluble polymeric and other heavy impurities.

In order to eliminate this drawback, it is proposed to use as an additive a hydrocarbon mixture containing aromatic hydrocarbons with a boiling point of 30-80 ° C above the boiling point of the solvent isolated from the high boiling pyrolysis fraction of gasoline.

The solvent is expediently either purified from water and other compounds boiling at a temperature below the boiling point of the solvent, or subjected to repeated distillation after purification.

The hydrocarbon mixture is preferably added in an amount of 0.5-5% by volume of the solvent. The proposed method is particularly suitable.

for the purification of furfural, ethylene glycol and 1,1 dioxytetrahydrothiophene, as well as N-alkyl amides of acids, for example M, N-dimethylformamide, M, N-dimethylacetamide and N-methylpyrrolidone.

The hydrocarbon mixture added according to the invention to the solvent to be purified is 5 to 10 times better dissolving polymers and other non-volatile compounds contained in the solvent than the solvent to be purified. This means that very small amounts of the hydrocarbon mixture should be added to the solvent to be purified, therefore the amount of concentrate withdrawn from the bottom is very small. The advantage of the proposed method is also that the solvent is trapped with almost no loss. Furthermore, the method is economical, since the hydrocarbon mixture added to the solvent is obtained from the by-product of the pyrolysis of gasoline in the production of ethylene. Example 1. From the condensate formed during the pyrolysis of gasoline in the process of producing ethylene, components with a boiling point below 230 ° C were isolated by distillation. 0.15 l

The resulting hydrocarbon mixture, boiled at a temperature above 230 ° C, is collected in a circulation apparatus, on which a column is mounted (height 400 mm, diameter 40 mm), filled with wire spirals (diameter 2 mm). Then, 7.9 l of M, N-dimethylacetamide with a polymer and other non-volatile compounds content of 0.6 weight is introduced into the evaporator at a rate of 0.6 l / h. % purified from water and low-boiling point compounds and used as a solvent in a pilot plant for the production of isoprene by extraction distillation. The mixture is rectified in a column at a pressure of 190 mm RT. Art. and reflux ratio 2: 1. The temperature at the bottom of the column is 74 ° C, at the top 110 ° C.

In flowing concentrate, taken from the evaporator in a hot state, contains 24.6 wt. % of polymers and other volatile components, as well as 2.4 wt. % M, N-dimethylacetamide (0.06 wt.% Of the initial amount of solvent). The solvent obtained at the top of the column is characterized by a high degree of purity (the content of polymers in it is 0.02 wt. 1%).

The initial hydrocarbon mixture is added in an amount of 1.9% by volume of the solvent to be purified.

Example 2. 0.15 l of the hydrocarbon mixture obtained in Example 1 (H. K - 220 ° C) is fed to the circulating evaporator with an impaled column described in Example 1. Then, 28.0 l of M, S-dimethylformamide, which was used as a solvent in a pilot plant for the production of butadiene by extraction distillation and containing (in wt.%): 0.23 polymers, was introduced into it at a rate of 0.6 l / h. and other low volatile compounds, 2.5 water, 0.04 formic acid and 0.06 butadiene oligomers. The mixture is rectified in a column at a pressure of 210 mm Hg. Art. and reflux ratio 3: 1. The temperature at the bottom of the column is 120 ° C, at the top 102 ° C.

The oily concentrate taken from the rotating evaporator in a hot state contains (in wt.%): 29.7 polymers, 2.8 N, N-dimethylformamide (0.03 wt.% Of the initial amount of solvent), 1.22 water and 1, 71 formic acid.

To remove the still-distilled compounds with a boiling point below the boiling point of the solvent, water and possibly azeotropes formed, distillate is fed to the middle of the second column (length 600 mm, diameter 25 mm) under a pressure of 193 mm Hg. also filled with wire spirals (diameter 2 mm). The reflux number of this column is 8: 1, the temperature at the bottom is 107 ° C, the top is 62 ° C. The purified solvent is distilled in a gaseous state by a stream from the middle part of the column, below the point of entry of the distillate, which also contains (in wt.%): 0.02 polymers, 0.04 water, 0.002 formic acid, and 0.008 butadiene oligomers. The lower phase of the second column is continuously recycled to the circulation evaporator of the first column, while the head product consisting of low-boiling compounds, water and possibly azeotropes formed is discarded.

The initial hydrocarbon mixture is added in an amount of 0.93% by volume of the solvent to be purified.

And measure 3. To continuously carry out the method of example 2, the resulting concentrate is collected, enriched with polymers in a circulating evaporator, and 0.6 l of purified N, Ndimethylformamide is added to it every hour, to which 1 vol. % hydrocarbon mixture. The temperature at the bottom of the column support equal to 126 ° C. The solvent with all the low-boiling components is distilled off through the column, and the injected

per unit of time in a circulating evaporator, the amount of hydrocarbon mixture is continuously distilled from it in the form of an oily solution enriched with polymers containing (in wt.%): 16.7 polymers, 3.4

M, N-dimethylformamide (0.03 wt.% Initial amount of solvent), 1.28 water and 1.67 formic acid.

The water leaving the top of the column as a distillate solvent, containing low-boiling components, possibly azeotropes, is further processed in the second column as in Example 2. The purified solvent withdrawn from this column (as

weight. %): only 02 polymers, 0.035 water, 0.016 formic acid, and 0.008 butadiene oligomers. Therefore, it has the same degree of purity as the periodically cleaned solvent in example 2.

The lower phase of the second column is continuously returned, as in Example 2, to the circulation evaporator of the first column, while the head product consisting of low-boiling compounds, water and possibly

the azeotropes formed are discarded.

Example 4. Analogously to example 2, N-methylpyrrolidone, which was used as a solvent in a pilot plant for the production of butadiene by extraction distillation and containing (in wt.%): 0.40 polymers and other volatile ingredients, was purified, 0.8, and 0, 08 oligomers of butadiene.

0.15 L of the hydrocarbon mixture used in Example 1 (N.K. 230 ° C) is fed to a circulation evaporator, to which 16.7 liters of contaminated solvent are then added under the conditions of Example 2 and distilled. The concentrate taken from the evaporator

contains (in wt. |%): 30.8 polymers and other volatile ingredients, as well as 3,4 N-dimethylpyrrolidone (0.02 wt.% of the initial amount of solvent). The solvent obtained as a distillate is introduced to remove low-boiling compounds, water and possibly formed azeotropes in the second column, which is under a pressure of 40 mm Hg. Art. The reflux number of this column is 8: 1, the temperature at the bottom is 93 ° C, the top is 37 ° C. Purified N-methylpyrrolidone, discharged from the column as a side stream, contains (in wt.%): Only 0.015 other polymers and other non-volatile substances, 0.09 water and 0.007 butadiene oligomers.

The lower phase of the second column is continuously recycled to the circulation evaporator of the first column, while the head product consisting of low-boiling compounds, water and possibly azeotropes formed is discarded.

The amount of the original hydrocarbon mixture in terms of the solvent to be purified is 0.5 vol. %

Example 5. Analogously to example 3, purify 1,1-dioxytetrahydrothiophene, used in a pilot plant for the production of aromatic hydrocarbons by solvent extraction and containing (in wt.%): 0.7 polymers and other volatile ingredients, as well as 3.4 water. In a circulating evaporator, 0.15 l of the hydrocarbon mixture prepared according to example 1 (N.K. 315 ° C) is added to it, and 5.0 l of 1,1-dioxytetrahydrothiophene at a rate of 0 is used to absorb polymers and other volatile ingredients. , 6 l / h and then distilled at a pressure of 32 mm Hg. Art. The evaporated solvent is rectified in a column (length 650 mm and diameter 40 mm) filled with wire spirals (diameter 2 mm). Reflux the number of columns 3: 1, the temperature at the bottom 181 ° C, 162 ° C at the top.

For the purpose of isolating low-boiling components contained in the distillate, water and possibly azeotropes formed, the distillate is fed to the middle of the second column (length 600 m, diameter 25 mm), also filled with wire spirals. Below the point of entry of the distillate, a pure solvent gas is withdrawn as a side stream. The lower phase is returned to the Circulating evaporator of the first column, while the head product containing water is discarded. The pressure in the column 26 mm Hg. -st., reflux number 8: 1, temperature below 170 ° C, top 30 ° C.

In order to carry out the process continuously, a concentrate obtained in a circulating evaporator, enriched with polymers and other non-volatile compounds, is fed to the column, and 0.6 l of dioxetrahydrothiophene to be purified is added to it every hour.

5 about. % of the above hydrocarbon mixture.

The amount of hydrocarbon mixture introduced per unit of time into the circulation evaporator is collected in the form of an oily solution enriched with polymers containing (in wt.%): 12.3 polymers and other non-volatile substances, as well as 1,2,1-dioxytetrahydrothiophene (0 , 06 wt.% Of the initial amount of solvent). Purified 1,1-dioxytetrahydrothiophene still contains only 0.018 polymers and 0.008 water.

Subject invention

Claims (3)

1. The method of purification of solvents used in the processes of separation of hydrocarbons, from impurities of polymers and non-volatile compounds by distillation in the presence of an additive boiling at a higher temperature than the solvent of the hydrocarbon mixture, , with the selection of a purified solvent in the form of a distillate, characterized in that, with a view to improving the efficiency of the process during the purification of the solvents used to extract diolefin or aromatic hydrocarbons, a hydrocarbon mixture with a boiling point of 30-80 ° C above the boiling point of the solvent, separated from the high boiling pyrolysis fraction of gasoline, is used as an additive. 2. A method according to claim 1, characterized in that the solvent is advantageously either preliminarily purified from water and other compounds boiling at a temperature below the boiling point of the solvent, or subjected to repeated distillation after the purification step. 3. The method according to claim 1, wherein the hydrocarbon mixture is added in an amount of 0.5-5% by volume of the solvent.