SU399103A1 - METHOD OF ISOLATION OF BENZENE - Google Patents

Description

one

The present invention relates to a method for separating benzene from its mixtures with non-aromatic and carbohydrate compounds.

A known method for isolating benzene from its mixtures of ic with non-aromatic hydrocarbons is that the initial mixture is subjected to extractive legonagon in the presence of N-methylpyrrolidone.

However, in carrying out this process, it is not possible to get benzene with a residual impurity content of less than 0.001 wt. %

In addition, special studies on this issue lead to the following conclusion: in the preparation of high-purity benzene, it was advisable to determine the vaporization ratio and the ratio of solvents instead of flbbmottoy numbers.

Under the vaporization coefficient V, we should understand the amount of heat supplied to the lower part of the coloine of the extractive distillation necessary to peel pure benzene V times.

The ratio of solvent L here should be understood: L-times the amount of solvent by weight attributed to the pure benzene obtained. It was found that in the case of

the production of pure benzene by one increase in the vaporization ratio does not achieve an improvement in the purity of benzene, if the solvent ratio is also not caught at the same time.

Thus, the object of the present invention is to increase the purity of the product obtained, as well as to intensify the whole process of extractive distillation — as a whole. According to the proposed method, this goal is achieved due to the fact that between the coefficient of vaporization V and the ratio of solvent-dependence is maintained by determining the following formula:

, 6L + C,

where C has a value (-0.5) (-j-1.5);

L is 1 to 10;

and in the raffinate phase, the head product of the extractive non-distillation, the benzyl content is kept by 10–30 wt. %

By increasing the concentration of benzene in the overhead product, the content of nonaromatic hydrocarbons in pure benzene can be even more significantly reduced, without changing the solvent circulation, heat consumption, and the number of plates. However, this is only possible up to a content of 30% benzene in the main product. A further increase in the benzene content does not lead to a noticeable decrease in the content of non-aromatic hydrocarbons in pure benzene. For processing the benzene fraction, with a content of from 0.1 to 1 weight. % of non-aromatic hydrocarbons 01B and with a boiling range from 95 to 105 ° C, 0, a sufficient amount of benzene IB in the head product is 10 vol.s. % It was further found that the benzene content in the circulating solvent affects the purity of benzene. If the content of non-aromatic hydrocarbons in pure benzene is 0.1 weight. %, the increase in benzene content in the circulating solvent from 1% to 5% is compensated by increasing the benzene content in the head product of extractive distillation, for example, from 13% to 17%. O; sufficient content from 1 to 5 wt. The% benzene in the solvent after the distillation of pure benzene prevents the thermal decomposition of the solvent, so that in turn allows refusing from distillation under reduced pressure. If you want to get benzene with a content of nonaro, matic hydrocarbons of 0.003 weight. %, the amount of benzene in the circulating solvent should in no case exceed 1%. Further, for a given concentration ratio of non-aromatic hydrocarbons in the benzene fraction as the initial product n in pure benzene as an extract, 10–13 practical plates in the distant column are needed for every tenth degree of the required concentration ratio. Therefore, if the benzene fraction of the starting product contains 10% non-aromatic hydrocarbons and a content of 0.01% by weight is required. % of non-aromatic hydrocarbons in pure benzene, the concentration ratio is 10 and, depending on the design of the plates and the size of the columns, usually 30-39 practical plates are used in the distant column. The number of plates of the reinforcing column, in contrast, does not depend on the operating conditions and requirements for the purity of the product, and is 10-15 practical plates. Finally, the purity of benzene obtained by extractive distillation depends not only on the influencing parameters described so far: solvent circulation, heat supply, benzene content in the upper portion of the extractive distillation column, benzene content in the solvent and the number of plates in the column, but also the boiling level non-aromatic hydrocarbons, which are contained in the original: product for extractive distillation. At: the boiling level of non-aromatic hydrocarbons may be affected by pre-distillation, in which benzene fraction is taken into account. It turned out that the purity of benzene is significantly affected by the content in the applied benzene fraction of the highest boiling non-aromatic compounds, methyl diclohexane and isooctanes. If the required content of non-aromatic hydrocarbons in pure benzene is less than 500 pime, then in most cases only these components will appear as friables. It was found that with average industrial costs for extractive distillation, with regard to capital costs, operating media and loss of benzene, the content of methylcyclohexane and isooctanes can be reduced to 0.1 of their content in the starting product. It is also possible to reduce the content of these compounds to 0.01 of their content in the starting product. But in this case, the required cost reaches the limit of efficiency. It follows that for the manufacture of pure benzene, in which the benzene fraction is obtained for introducing extractive distillation into the column, it is advisable to carry out preliminary distillation so that the content of methyl cyclohexane and isooctane in it is below 1%, and at higher demands on the purity of the product obtained - below 0, G%. The drawing shows as an example the technological scheme of the installation for carrying out the method according to the invention. The benzene fraction is fed through conduit 1 after heat exchange with hot, recovered by preparing the extract in the heat exchanger 2 to the extractive distillation column 3 at medium height. On a few plates under the top of the extractive distillation column, recovered solvent is fed from line 4. The head product of the extractive distillation column is a raffinate consisting mainly of non-aromatic hydrocarbons. It is taken through line 5 and condensed. Part of the condensate is removed from the plant through line 6, the rest is fed back through line 7 as reflux to the top of the column. An extract is taken from the bottom of the extractive distillation column 3 - a mixture of solvent and benzene, and is fed through pipe 8 into the column to distill light fractions 9 into its medium. As the distillation residue, a recovered solvent remains here, which through line 10, heat exchanger 2 and line 4 is returned to the extractive distillation column. Non-solvent benzene vapors are obtained as the head product of the column for distilling off light ends. They condense. One part is discharged through line 11 as the pure benzene obtained, while the other part is returned through line 12 as reflux to the stripping column 10,

Pr-imer 1. Pure benzene is obtained from COKE benzene, from which sulfur is removed as a result of hydrogenation treatment. TaiK as a benzene fraction of coke benzene contains only a small amount of non-aromatic hydrocarbons, a relatively high concentration of benzene in the raffinate can be tolerated, e ter appreciable amounts of benzene.

The solvent ratio is L 2.5 and the coefficient of α-vapor formation is 0, so that the value of 0.5 is obtained for C. From coke benzene, from which sulfur has been removed, hydrogen is cracked by pressure with hydrogen, and the benzene fraction is obtained by distillation. The number and composition of this is as follows:

This fraction is directed through the pipeline 1 to the plant, the IB of the heat exchanger 2 is heated from 25 ° C to 80 ° C and then fed to the extractive column (neretoic 3 on the 20th plate. The column of extract gas 3 has 40 practical plates and works with three normal pressure Through conduit 4, 2500 kg of selective solvent, which consists of 95% K-methyl1py | rrol-idone (hereinafter referred to as NMP) and 5% benzene, is supplied to this coloin of extractive leregonka 3 at the 35th plate at 110 ° C.

190000 kcal of heat are supplied to the secondary steam and pint of extractive distillation 3, 3 pairs are drawn off at the top of the extractive distillation column through a pipeline. 5 and condense. Part of the condensate is as follows, quantity and with the following composition:

ten

15

output through tr}: bw 6 of install. The rest is returned back through the pipeline 7 to the upper part of the head of the extractive distillation.

A mixture of solvent and benzene in the amount of 3500 kg / h is withdrawn from the bottom of the extract-distillation distillation 3 column and sent through line 8 to the distillation column 9 to the 5th plate.

Column 9 has 25 plates and operates at normal pressure. In the evaporation ap1pa; rath columns for the distillation of light fractions 9 serves 210,000 kcal of heat. Resulting in

In the upper part of the light ends distillation column, 9 pairs are withdrawn through the pipeline and are condensed. Part of the condensate in the next quantity and with the following composition:

35

40

45

taken as pure benzo.l. from the installation. The remainder is sent back through duct 12, to the top of the 4M-iuiii f lung stripping column.

The bottom 1 type of column for the distillation of light fractions consists of NMP with 5% benzene.

This benzene content reduces the temperature of the lower part to 165 ° C. The bottom product is withdrawn in an amount of 2500 kg / ch.s, heated in the heat exchanger 2 the initial product to 80 ° C and, if required, is cooled in a refrigerator to 1 W ° C and returned to lipogdoinp-water 4 back to “Olone Extractive Distillation 3.

Example 2. In this example, a fully hydrogenated benzene fraction of pyrolysis gasoline is introduced into the extractive distillation column. Cleanliness requirements correspond to a maximum of 0.01 wt. % Of aromatic hydrocarbons in Pure benzene. As a consequence, the operating conditions for the extractive neron-i IB counterposition to the first embodiment are altered. The ratio of solvent L is 6.0; coefficient of parity, 0; for C Get a value of 0.4.

From the pyrolysis gasoline treated with hydrogen, a benzene fraction is obtained by distillation. The number and composition of this fraction are as follows:

output through line 6 of the installation. The rest of the return through the pipeline 7 in the upper part of the column extractive distillation.

The bottom of the extractive distillation column 3 removes a mixture of solvent and benzene in the amount of 7000 kg / h and passes it through pipe 8 to the column for distilling light fractions 10 to the 8th plate. Column 9 has 25 plates and operates at a pressure of 0.35 atm in the upper part. 23000 kcal of heat is supplied to the stripper of the stripping column. The vapor at the top of the stripping column 9 is taken off through a T-pipe and condensed.

Part of the condensate in the following quantity and with the following composition (vom:

This fraction is fed through a Tpyooinvod 1 to the unit, heated in a tent-exchanger 2 from 25 ° C to 80 ° C, and then fed to an El1Stractive distillation column 3 on a 40th plate. The extra-reflux column 3 has 60 practical plates and operates at normal pressure. Pipeline 4 into this column by distillation of distillate 3 to the 55th plate at a temperature of 110 ° C serves 6000 south of selective solvent, which consists of 99% N-methylpyrrolidone and 1% benzene.

In the head apparatus of the extractive distillation column 3, 38000 kcal of teile is supplied. The resulting 3 pairs of the extractive distillation column of the column are withdrawn through conduit 5 and condensed. Part of the condensate in the following quantities and with the following composition;

taken as pure benzene from the plant. The rest of the pipe is fed back to the upper part of the column to distill off the light fractions 9.

The bottom product of the light ends distillation column consists of ML with 1% benzene. This benzene content and applied vacuum reduce the temperature of the bottom part to 65 ° C. The bottom product is removed in an amount of 6000 kg / h, the initial product is heated in the heat exchanger 2 to 80 ° C and, if required, cooled in the refrigerator to 110 ° C and then returned back to the extractive distillation column 3 via pipe 4, the subject invention 1 Method of separating -benzene -from its mixtures with non-aromatic hydrocarbons by extractive distillation B in the presence of selective solvents, characterized in that, in order to increase the purity of the target product and intensify the process, between the coefficient, vaporization V and weights with the ratio of solvent to benzene isolated, the dependence described by the following formula is maintained:

/ 2 10, 6L + C, where C Has a value of (-0.5) -; - (+: 1.5), L has a value of 1-f-lO and in the raffinate phase — the head product of extractive distillation, the benzene content is maintained 10-30 weight. % 2. The method according to claim 1, characterized in that L-methyLpyrrolidone is used as a selective solvent, and the ratio of solvent L is 2h-6.