DE1198345B - Process for the removal of small amounts of higher molecular weight acetylenes and allenes from a predominantly 1,3-butadiene or isoprene containing C or C hydrocarbon mixture - Google Patents

Description

Process for removing small amounts of high molecular weight acetylenes and allenes from a predominantly 1,3-butadiene or isoprene containing C4 or C4 C6 hydrocarbon mixture For the production of diolefins, especially of 1,3-Butadiene and isoprene are increasingly used in pyrolysis processes. This gives gas mixtures which, in addition to the desired diolefins, also contain other unsaturated ones Contain compounds including acetylenes and allenes. For the polymerization of the conjugated diolefins with organometallic catalysts become diolefins required that are free of acetylene and allene compounds. With the known separation processes The acetylenes are usually removed first of the gas mixtures so that they do not have any Cause disturbances in the subsequent diolefin isolation and purification.

There are also processes that involve the diolefins and acetylenes initially separated off together and the acetylenes are subsequently removed. These procedures but are relatively expensive. In the known methods in which the Acetylenes are separated from the diolefin insulation, one uses different Procedural principles. The acetylenes have been selectively hydrogenated. Here lets cannot avoid that even a small part of the conjugated diolefin hydrogenates becomes and is therefore lost. Another known method is the acetylenes removed with a selective extractant. The use of ammoniacal copper salt solution. In this process, apart from the acetylenes also some of the diolefins are dissolved and they have to be recovered. Here comes it very easily forms easily decomposable copper-acetylene compounds.

In addition, there are noticeable losses of diolefin.

It has now been found that higher molecular weight acetylenes and allenes from a predominantly 1,3-butadiene or isoprene-containing C4 or C5 hydrocarbon mixture by treatment with a selective extractant in a simple manner very low losses of 1,3-butadiene or isoprene from these hydrocarbon mixtures can be removed if furfural is used as a selective extractant.

The method can be applied, for example, to C4 or C5 fractions apply that by thermal treatment of hydrocarbons and appropriate Fractionation are obtained and which contain primarily 1,3-butadiene or isoprene, but also small amounts, e.g. B. up to a total of 5 O / o, higher molecular weight, d. H. 4 or acetylenes containing more carbon atoms and / or higher molecular weight, d. H. Allenes containing 4 or more carbon atoms. As examples of these acetylenes and allenes are: 1-butyne, 2-butyne, vinylacetylene, 3-methylbutyne, 1,2-butadiene and 3-methyl-1,2-butadiene.

The furfural can be used in pure form or with the addition of water use, with water contained in the mixture to saturation at room temperature can be. The addition of water increases the selectivity.

Although it is known for the separation of hydrocarbons with different degrees of saturation to use furfural as a selective solvent. It is surprising, however, that one can also use hydrocarbons that are equally highly unsaturated are, such as acetylenes and conjugated diolefins or allenes and conjugated diolefins, can separate with furfural.

The process is mainly carried out by absorption and subsequent desorption, z. B. carried out by washing out of the vapor phase. You can do the procedure also perform as a liquid-liquid extraction.

Depending on the desired form of treatment, the process can be at lower temperature, whereby the hydrocarbons are liquid, or higher Temperature, but not above 1500 C.

It can be pressureless or under slightly increased pressure, e.g. B. at 5 at, run.

The advantage of using the furfural is that the losses can be kept extremely low in diolefins. Besides, does not exist the danger that easily decomposable compounds are formed which lead to explosions being able to lead.

The procedure is based on a drawing in an exemplary manner Embodiment explained in more detail.

The diolefin to be freed from the impurities becomes gaseous introduced through line 1 at the lower end into a wash column 2, while at the upper end The selective solvent flows in through line 3 at the end of this wash column. That The diolefin freed from the acetylenes and allenes is at the top of this washing tower withdrawn via line 4 and can be used to remove solvent vapors with water or with liquid diolefin which is fed to washing zone 6 through line 5, washed the scrubbing liquid is then fed to the column 2. That with the allenes and acetylenes loaded solvent leaves the wash column on Bottom of line 7 and is passed to the top of a second separating column 8. The gas mixture obtained at the top of this column 8, which consists of the diolefin and part of the acetylenes and allenes is via line 9 together with the Crude diolefin to be purified again - fed to the scrubbing column 2 at the bottom. the Acetylenes and allenes are fed to column 8 at a suitable height through a side offtake taken from line 10. This gas flow can help avoid solvent losses be passed through a water wash, which is supplied with water through line 12 will. The wash water is fed through line 14 to the bottom of column 8. Appropriately the gas mixture produced at 14 is mixed with worthless, flammable gases and burned. The high content of water vapor prevents polymerization of inconsistent connections, e.g. B. of diacetylene.

At the bottom of the column 8, the solvent is passed through the heater 15 heated and thereby freed from all gaseous compounds, it can after cooling are fed to the separation column 2 via line 3.

The process can be designed in such a way that the separation column 2 and the Separation column8 can be operated under the same pressure. In this case, the two can Columns can be combined into a single column. However, if the column 8 is Lower pressure than the column 2 operated, it is from Head of the column 8 the bottom of the column 2 fed gas mixture by means of a compressor on the The pressure of the column 2 is compressed.

Example Into a separating column 2 of 150 filled with random packing mm clear width and 6 m height is a raw butadiene at the sump, which is obtained from a crack cut has been isolated and about 500 ppm 1,2-butadiene, 250 ppm 1-butyne, 50 ppm 2-butyne as well as 50ppm vinyl acetylene, introduced in an amount of 3 mSh. The inflow of furfural, saturated with water at room temperature, is at the top of the column 2 100 l / h. The temperature of the solvent is + 200 C. The pressure in the columns is 1.05 ata. A butadiene can be drawn off at the top of this wash column, which only contains -45 to 50 ppm 1,2-butadiene, while the other contaminants are no longer detectable by gas chromatography. The loaded selective solvent is fed to a second column 8. It also consists of a packed column 150 mm in diameter and 8 m in length. The acetylenes and allenes are used in this Column withdrawn above its lower fifth and to avoid solvent losses washed with water. This washing water is fed to the bottom of the column 8. The temperature of the bottom of the column 8 is kept at 140 to 145.degree. The butadiene content of the side stream is 300/9 the butadiene loss is thus less than 0.5% des butadiene used.

Claims (1)

Claim: Process for removing small amounts of higher molecular weight Acetylenes and allenes from a predominantly 1,3-butadiene or isoprene containing C4 or C5 hydrocarbon mixture by treatment with a selective extractant, d u r c h e k e n n -z ei ch n e t that one is used as a selective extraction agent Furfural uses. Publications considered: Petroleum Rafiner, 34 (1955), P. 196.