CS202892B1 - Method for the separation of butadiene or isoprene from hydrocarbon mixtures containing diolefines - Google Patents

Description

(54) A method for separating butadiene or isoprene from diolefin-containing hydrocarbon mixtures

The present invention relates to a process for separating butadiene or isoprene from diolefin-containing hydrocarbon mixtures.

Said diene hydrocarbons, butadiene and isoprene, are the main monomers for the preparation of synthetic rubber and various polyether materials. Butadiene and isoprene are used in particular for the preparation of synthetic rubbers which are very similar in nature to natural rubber. In this preparation, the quality of the starting monomer is critical. The high quality requirements of the monomer are associated with additional cleaning costs. Reducing the cost of butadiene and isoprene requires more economical processes for their preparation or separation from available and cheap raw materials.

To the main ceilings from which butadiene can be separated. and isoprene, include hydrocarbon mixtures containing diolefins (C and / or C 1 - fractions), which are obtained, for example, from the pyrolysis and cracking of petroleum fractions or which arise from the dehydrogenation of paraffin or olefinic hydrocarbons. As paraffinic hydrocarbons, butane or isopropanite may be used, and as olefinic hydrocarbons, butenes or isoamylenes may be used.

Diene hydrocarbons can be separated from the fractions containing these hydrocarbons in various ways. One particularly excellent method by which a high concentration pulp hydrocarbon can be prepared is the extraction rectification process.

Extraction rectification to remove pulp hydrocarbons is usually carried out at elevated temperatures. Diene hydrocarbons tend to self-polymerize at these temperatures, forming thermopolymers. However, the formation of this polymer results in the loss of valuable monomer and also in increased consumption of the extractant. In addition, the resulting thermopolymer settles on the surface of the device, deteriorates heat transfer and causes the device to clog, resulting in downtime.

Thermal polymerization inhibitors are used to reduce spontaneous thermal polymerization of the pulp hydrocarbons when separated by extraction rectification.

A method is known for separating diene hydrocarbons, in particular butadiene or isoprene, from diolefin-containing hydrocarbon mixtures, in which, in particular, furfural, aromatic nitro compounds and benzaldehyde are used as inhibitors of the resulting thermopolymers. In the presence of these inhibitors, spontaneous thermal polymerization is substantially reduced.

However, the inhibitors used in this method do not have sufficient efficacy, resulting in the loss of the separated diene and extracting agent.

When furfural and benzaldehyde are used as inhibitors, it becomes resinous. Resin formation causes loss of the extraction agent. In addition, the use of furfural may create an aggressive corrosive environment.

They are used in admixture with a compound such as sodium nitrite to increase the inhibitory effect of said inhibitors. The use of sodium nitrite in admixture with said compounds makes it possible to significantly increase the monomer yields. However, hazardous explosive organic nitro compounds may form when separating diene hydrocarbons in the presence of sodium nitrite. When lower carboxylic acid alkyl amides are used as the extracting agent in the presence of sodium nitrite, a highly toxic product, nitrosodimethylamine, is formed when separating the diolefin.

A method for separating butadiene and isoprene by means of extraction rectification is also known, wherein aromatic mercaptans and thiodipropionitrile are used as thermal polymerization inhibitors. The presence of these compounds also decreases by thermal polymerization of diene hydrocarbons, but these compounds are thermally unstable and difficult to access.

Yet another method for separating isoprene or butadiene from hydrocarbon mixtures containing diolefins is known. The method comprises subjecting diolefin-containing hydrocarbon mixtures to an extraction rectification with lower carboxylic acid alkyl amides as the extracting agent, in the presence of a thermal polymerization inhibitor. The diolefin-containing hydrocarbon mixture is fed to the central part of the extraction rectification column.

An extraction agent, for example dimethylformamide containing 5 wt.%, Is introduced into the top of the extraction rectification column. furfural and 0.1 7 wt. sodium nitrite. The temperature at the top of the column is about 30 to 50 ° C, the temperature at the bottom of the column is 138 to 154 ° C. The pressure in column ae is maintained between 0.1 and 0.6 MPa. A gas phase containing mainly paraffin and olefinic hydrocarbons is removed from the top of the column and condensed. A portion of the condensate is returned to the column as reflux. A liquid consisting of an extraction agent saturated with diene hydrocarbons and containing traces of acetylene hydrocarbons is removed from the bottom of the column. The liquid is subjected to desorption, fed to a desorption column operating at a pressure of 0.1 to 0.3 MPa, at a head temperature of 5 to 50 ° C and at the bottom of the column of about 165 ° C,

Under these conditions, the pulp hydrocarbon with traces of acetylene hydrocarbons is separated from the extracting agent and removed as the gas phase from the head of the desorption column, the concentration of the diene obtained being 98.5 to 99.4% by weight, the total acetylene hydrocarbon content being 0.9% by weight. .

An extraction agent is removed from the bottom of the desorption column and recirculated to the extraction rectification column.

In carrying out this method, as with the other methods mentioned above, diene and extractant losses are observed. In this case, the inhibitory effect is achieved mainly by the use of sodium nitrite. As mentioned above, working conditions worsen with the use of sodium nitrite and lower carboxylic acid alkyl amides as the extracting agent, since organic nitro compounds may be formed, and working hygiene conditions also deteriorate due to the possible formation of nitrosodimethylamine as a highly toxic product.

It is an object of the invention to overcome these disadvantages.

SUMMARY OF THE INVENTION It is an object of the present invention to provide such a process for separating butadiene or isoprene from diolefin-containing hydrocarbon mixtures which allows to reduce diene and extractant losses, improve working conditions and avoid corrosion of the apparatus.

This object is achieved by the proposed process according to the invention, in which butadiene or isoprene is separated from hydrocarbon mixtures containing diolefins by means of extraction rectification using lower carboxylic acid alkylamides as extraction agent, at a temperature of 30 to 150 ° C, at a pressure of 0.1 to 0 6 MPa, in the presence of a thermal polymerization inhibitor, to obtain a gas phase and a liquid phase containing an extraction agent saturated with butadiene or isoprene, said gas phase is condensed and the liquid phase is subjected to desorption by heat treatment at a temperature of 5 to 165 ° C and at a pressure of from 1 to 0.3 MPa to obtain a gas phase containing butadiene or isoprene and a liquid phase consisting of an extraction agent. The invention is based on the use of a mixture consisting of 0.005 to 0.5 wt. % Of sodium formaldehyde sulfoxylate or zinc formaldehyde sulfoxylate, 0.1 to 1.0 wt. From amines, for example diethylamine, triethanolamine, dicyclohexylamine, diethylaminoethanol, 0.005 to 0.5 wt. Of the carbonates or bicarbonates of the corresponding amines, the percentage of the individual components of the mixture being based on the weight of the extractant. Extraction The reagent separated from the liquid phase after heat treatment is brought to the stage of rectification extraction.

The starting materials used are hydrocarbon mixtures containing diolefins, which are obtained, for example, by pyrolysis or cracking of petroleum fractions, and also hydrocarbon mixtures containing diolefins, which are obtained by dehydrogenation of butane or isopentane, butenes or isoamylene. Fractions containing butane, n-butenes, isobutane,

1,3-butadiene, vinylation of ethylene, ethylacetylene and 1,2-butadiene, and C1-fractions, mainly comprising pentanes, n-pentenes, isoamylene, cyclopentene, isoprene, trans- and cis-1,3-pentadiene, cyclopentadiene and higher acetylene hydrocarbons.

Dimethylformamide and dimethylacacetamide, for example, can be used as alkylamides of lower carboxylic acids as extraction agents.

As mentioned above, rectification extraction is carried out at temperatures ranging from 30 to 150 ° C and at a pressure of 1 to 6 bar. These conditions are optimal. When the temperature is lowered below the lower limit, it is necessary to use expensive coolant to condense the gas phase that is discharged from the head of the rectification column. Increasing the temperature above the upper limit causes considerable loss of the pulp, since the extracting agent degrades and the rates of side reactions such as resin formation and polymerization increase. Said amounts of thermal polymerization inhibitors are sufficient to provide their inhibitory effect.

In the butadiene separation, the rectification extraction step is preferably carried out at a pressure of 0.4 to 0.6 MPa, in the isoprene separation at a pressure of 0.1 to 0.3 MPa, the desorption step in the butadiene separation is carried out at a pressure of 0.11 MPa and in the separation of isoprene at 0.15 MPa.

The paraffinic and olefinic hydrocarbons, for example butane, isobutane, n-butenes or pentanes, n-pentenes and isoamylenes, which are part of the diolefin-containing hydrocarbon feedstock, are not extracted when the rectification is extracted and removed as a gaseous stream from the rectification zone to condensation.

Marrow hydrocarbons (butadiene or isoprene) as well as small amounts of acetylene hydrocarbons are extracted from the starting mixture by means of said extracting agents. The obtained liquid phase, containing diene hydrocarbon, traces of acetylene hydrocarbons, thermal polymerization inhibitors, as well as small amounts of resin products and polymers, leads to desorption by heat treatment of said liquid phase at a temperature between 5 ° C and 165 ° C and under pressure Under these conditions, the diene hydrocarbon is separated from the extractant.

More preferably, the extraction of the reagent separated after heat treatment of the liquid phase containing the extraction of the reagent saturated with butadiene or isoprene is introduced into the rectification extraction step.

As inhibitors, thermal polymerization in the hydrocarbon separation by rectification extraction, as mentioned above, is a mixture consisting of sodium or zinc formaldehyde sulfoxylate in an amount of 0.005 to 0.5 Z, based on the weight of the extractant, of amine carbonates or bicarbonates in an amount of 0.005 to 0.5 Z, based on the weight of the extracting agent, and amines in an amount of 0.1 to 1 Z, based on the weight of the extracting agent. Sodium or zinc formaldehyde sulfoxylate are potent inhibitors of the thermal polymerization of butadiene and isoprene. Under the above conditions, degradation of said inhibitors may occur to form aggressive corrosive agents.

Sodium or zinc formaldehyde sulfoxylate in admixture with amines and carbonates and / or hydrogen carbonate amines are used to prevent corrosion and to increase the effect of the inhibitors. In addition, hydrolysis of the lower carboxylic acid alkylamides is observed under the conditions of extraction of rectification and desorption even in the presence of a small amount of water. .

Thus, for example, dimethylformamide is formed by hydrolysis of formic acid and acetic acid by dimethylacetamide. Amines, which are part of a mixture of inhibitors, are also used to neutralize the acids formed. Said amounts of inhibitors are sufficient to achieve a high inhibitory effect. Reducing the amount of substances belonging to the mixture of inhibitors does not provide a high inhibitory effect, increasing the amount of inhibitors does not lead to an increase of the inhibitory effect, but causes uneconomic consumption of the inhibitors.

Suitable amines are, for example, diethylamine, triethanolamine, dicyclohexylamine or diethylaminoethanol.

The amine carbonates and bicarbonates used are those of the abovementioned amines.

The inhibitor mixture used in the process according to the invention, which contains sodium or zinc formaldehyde sulfoxylate, amines and amine carbonates or bicarbonates, has a high inhibitory effect. Therefore, in the process according to the invention, an insignificant amount of thermopolymer is produced, resulting in slight losses of the dienes and the extraction agent. Furthermore, the use of such inhibitors avoids the possibility of the formation of explosive hazardous and toxic products. Substances which are included in the used mixture of inhibitors _/ are available and relatively inexpensive. .

The diene hydrocarbons separated by the process of the invention have a concentration of about 99.5% by weight.

The method of separating butadiene or isoprene is simple due to its technological design and is carried out as follows:

A hydrocarbon mixture containing diolefins is fed to the central part of the continuous rectification extraction rectification column. An extraction agent containing thermal polymerization inhibitors is fed to the top of the column. The individual streams are fed continuously. Under the conditions of the present invention, butadiene or isoprene with a small amount of acetylene hydrocarbons is extracted with an extraction agent. Paraffin and olefinic hydrocarbons such as butane, isobutane, n-butenes, or pentanes, n-pentenes, isoamylenes are removed from the top of the column by extraction rectification and condensed. Extracting agent containing diene hydrocarbons, small amounts of acetylene hydrocarbons, and thermal polymerization inhibitors are removed from the bottom of the column. as well as small amounts of polymer and resin products.

The saturated extractant is introduced into the desorber. Within the temperature and pressure range of the present invention, the pulp hydrocarbon is desorbed from the extractant. The gaseous phase containing mainly pulp hydrocarbon is discharged from the desorber head and the extractant from which the hydrocarbon has been removed and which contains a thermal polymerization inhibitor and traces of polymer and resin products is removed from the bottom of the desorber and re-introduced if necessary into an extraction rectification column.

In order to better elucidate the process according to the invention, specific examples are given below.

Example 1

A diolefin-containing hydrocarbon mixture consisting of 15 wt. n-butane, 55 wt. butenes and 30 wt. The mixture was fed at a rate of 200 ml / h. To the top of the column was added dimethylformamide containing 0.05 Z sodium formaldehyde sulfoxylate based on the extractant weight, 0.005 Z dicyclohexylamine carbonate, based on the extractant weight, and 1.0 Z dicyclohexylamine based on the extractant weight. . The extractant was circulated at 1500 ml / h. The temperature at the top of the column is 35 ° C, the temperature at the bottom of the column is 138 ° C, and the column pressure is 0.42 MPa. A gas phase consisting of 21.5 wt. n-butane, 78 wt. % of butenes and 0.5 wt. butadiene, and subjected to condensation. A portion of the condensate at 250 ml / h is returned to the top of the column as reflux and a portion of the condensate at 120 ml / h is discharged from the system.

A liquid phase consisting of dimethylformamide containing 5.3 wt. butadiene, and fed at 1580 ml / h to the central part of the desorber with continuous operation. Desorber has 48 floors with a diameter of 32 mm. The temperature in the desorber head is 5 ° C, the temperature in the lower part of the desorber is 165 ° C and the pressure in the desorber is 0.11 MPa.

A gaseous phase containing 99.0 wt. butadiene and condensed. The condensate was collected at a rate of 60 ml / h. The liquid phase is removed from the bottom of the desorber

Consisting of dimethylformamide containing traces of thermopolymer, and dimethylformamide passed back to the rectification extraction column. Butadiene losses due to thermal polymerization were 1.6 g / day and dimethylformamide losses 1.7 g / day.

Example 2

The butadiene separation is carried out analogously to Example 1, except that a mixture consisting of zinc formaldehyde sulfoxylate in an amount of 0.005% by weight of the extracting agent, and dicyclohexylamine bicarbonate in an amount of 0.5 Z, calculated as by weight of the extracting agent, and from dicyclohexylamine in an amount of 0.5 Z, based on the weight of the extracting agent. Butadiene losses due to thermal polymerization were 2.0 g / day and dimethylformamide losses 2.5 g / day.

Example

The butadiene separation is carried out analogously to Example 1, except that dimethylacetamide is used as the extracting agent and diethyl amine carbonate carbonate in an amount of 0.5 Z, based on the weight of the extracting agent, of diethylamine carbonate as a thermal polymerization inhibitor. 0.1 Z, based on the weight of the extracting agent, and from diethylamine in an amount of 0.4%, based on the weight of the extracting agent.

Butadiene losses due to thermal polymerization were 2.1 g / day and dimethylacetamide losses 2.6 g / day.

Example á

A continuous hydrocarbon extraction rectification column having 20 trays of 32 mm diameter is fed with a diolefin-containing hydrocarbon mixture consisting of 65 wt. % of isoamylenes and from 35 wt. isoprene. The mixture was fed at a rate of 50 ral / h. To the top of the column was added dimethylformamide containing 0.05 Z sodium formaldehyde sulfoxylate based on the weight of extracting agent, 0.1 Z diethylaminoethanol carbonate based on the weight of the extracting agent, and 0.3 Z diethylaminoethahol calculated on weight extracting agent. The extraction agent was circulated at a rate of 1500 ml / h. The temperature at the top of the column is 30 ° C, the temperature at the bottom of the column, 35 ° C, and the pressure in the column is 0.15 MPa,

The isoamylene fraction containing 1 wt. isoprene and condensed. A portion of the condensate at 200 ml / h is fed back to the top of the column as reflux and a portion of the condensate at 95 ml / h is discharged from the system. A liquid phase consisting of dimethylformamide containing isoprene is removed from the bottom of the column and fed to the central part of the desorber.

The temperature at the desorber head is 40 ° C, the temperature at the bottom of the desorber is 165 ° C and the pressure at the desorber is 0.15 MPa. A gaseous phase containing 95 wt. isoprene and 5 wt. isoamylenes, and condenses. The condensate is collected at a rate of 55 ml / h. Dimethylformamide is removed from the bottom of the desorber and fed back to the top of the rectification column. Isoprene losses due to thermal polymerization are 2.6 g / day and dimethylformamide losses 2.6 g / day.

Example

The isolation of isoprene is carried out analogously to Example 4, except that zinc formaldehyde sulfoxylate in an amount of 0.05 Z based on the weight of the extracting agent, triethanolamine bicarbonate in an amount of 0.01 Z, calculated on the weight of the extracting agent, is used as thermal polymerization inhibitor. , and triethanolamine in an amount of 0.4 Z, based on the weight of the extractant. The losses of propylene due to thermal polymerization are 2.3 g / day and the losses of dimethylformamide 2.5 g / day.

Claims (2)

the subject of the invention A method for separating butadiene or isoprene from diolefin-containing hydrocarbon mixtures by means of extraction rectification using lower carboxylic acid alkylamides as the extracting agent, at a temperature of 30 to 150 ° C and at a pressure of 0.1 to 0.6 MPa, in the presence of a thermal polymerization inhibitor to obtain a gas phase and a liquid phase containing an extraction agent which is saturated with butadiene or isoprene, said gas phase is condensed and the liquid phase is subjected to desorption by heat treatment at a temperature of 5 to 165 ° C and a pressure of 0.1 to 0.3 MPa to obtain a gas phase containing butadiene or isoprene and a liquid phase consisting of an extraction agent, characterized in that a mixture consisting of 0.005 to 0.5 wt. % sodium formaldehyde sulfoxylate or zinc formaldehyde sulfoxylate, 0.1 to 1.0 wt. From amines, for example diethylamine, triethanolamine, dicyclohexylamine, diethylaminoethanol, 0.005 to 0.5 wt. 7. carbonates or bicarbonates of the corresponding amines, wherein the percentage of the individual components of the mixture is based on the weight of the extractant. 2. The method of claim 1 wherein the extracting agent separated from the liquid phase after heat treatment is brought to the extraction rectification step.