The method of purification of benzene

 

(57) Abstract:

The invention relates to a method of purification of benzene from coke production and benzene obtained from fractions of pyrolysis oil from impurities saturated and unsaturated hydrocarbons, thiophene and carbon disulfide. Purification of benzene from saturated and unsaturated non-aromatic hydrocarbons, thiophene and carbon disulfide carried out by extractive distillation using as the extractant mixture of dimethylformamide and toluene at a mass ratio of dimethylformamide 90 - 95; toluene 5 - 10. 1 Il., table 4.

The invention relates to the petrochemical industry, for the purification of benzene obtained in the coking of coal, and benzene, obtained from the liquid fraction of the pyrolysis oil.

In several petrochemical industries that use benzene as raw materials for synthesis, purity requirements is very high. For example, in the production of cyclohexane, the source of raw materials for caprolactam, adipic acid and diamine, all admixture of saturated, unsaturated and sulfur-containing compounds are harmful, because they contaminate the resulting cyclohexane.

Used in the hydrogenation of benzene in the W, since their first adsorbed, the second polymerized, closing the active catalytic centers.

Upon receipt of benzosulfimide the sulfonation of benzene in the vapor phase of all sulfur-containing impurities, limit and unsaturated hydrocarbons adversely affect the process, so as to cause the deoxidation of sulfuric acid and resinification of sulfatase.

Similar circumstances in these and other petrochemical synthesis, using benzene, forced to limit the content of saturated and unsaturated hydrocarbons, thiophene and carbon disulfide.

Although benzene coke is a double stage distillation purification from impurities hydrocarbons and carbon disulfide, the obtained product, the benzene brand "for nitrile", contains up to 0.30 wt.%. impurities nah (marginal and non-marginal), thiophene - to 0.04 wt.%. , disulphide - up to 0.005 wt.%. the temperature of crystallization - 5,20oC, the rate of coloration with sulphuric acid, 0.15 (GOST 8448-78), which indicates the presence of unsaturated compounds.

Another source of benzene for petrochemical synthesis - benzene, obtained from the liquid fraction of the pyrolysis oil is impurities, contains not less than 94,0% wt. the main substance of sulfur-containing impurities is just thiophene to 0.01 wt.%, 0,1-0,12% wt. toluene, the rest of non-aromatic impurities limit and unsaturated hydrocarbons.

So from the above raw materials to obtain benzene brand "synthesis", corresponding to GOST 8448-78 and GOST 9572-77 on the benzene coke and petroleum production, additional methods of cleaning, as the fewer impurities in benzene, the more problematic their separation.

The complex composition and the formation of azeotropic mixtures of impurities non-aromatic hydrocarbons with benzene make the extraction of benzene of high purity by using clear and azeotropic distillation is very energy intensive, requiring highly technological equipment.

A known method of purification of benzene, obtained from the pyrolysis condensate fraction, from impurities non-aromatic unsaturated hydrocarbons and thiophene on natural adsorbents at a temperature of 150-250oC, a pressure of 2-2,8 ATA followed by separation of the benzene by distillation [A. D. Berens and other Processing of liquid products of pyrolysis. - M.: Chemistry, 1985, S. 216]. The purified benzene contains 99,90% wt. and above basic substance

Under the unit raw the need for periodic disposal of spent adsorbents in landfills.

The known method of purification of benzene, obtained from crude oil or coking coal containing up to 98% wt. the main substances of natural adsorbents from unsaturated non-aromatic compounds and sulfur compounds in catalysts based on metals of the VI and VIII groups of the Periodic system [U.S. patent N 3642927, C 07 C 7/00, 15/04, Appl. 07.02.68, publ. 15.02.72). The method is not without disadvantages previously described and further includes energy-intensive stage hydrotreatment.

You know the combination of adsorption and catalytic purification of benzene pyrolysis origin, containing up to 0,0072% wt. nah limit and unsaturated hydrocarbons and 0,002% wt. thiophene, one-step process for hydrogenation plants using specially designed catalysts [C. A. Dynin and other Fine purification of benzene fraction of pyrolysis condensate fraction from olefins and thiophene. Refining and petrochemicals. 1988, No. 9, S. 19-21].

The method allows of cleaning products, followed by distillation to isolate benzene, meets the requirements of GOST 9572-77 on the benzene brand "high purity" content osnovnaya of thiophene in the original benzene at a level of 0.002 wt.%, nah is 0.01% wt. and problems associated with the use of adsorbents, additionally, the degree of conversion of unsaturated is 84.3-93,7% wt

Using methods of chemical binding of impurities present in benzene, for example, carbon disulphide, the alkali in methyl alcohol [C. E. Privalov. Coke and chemistry. 1961, No. 3, S. 361], thiophene, unsaturated compounds with sulfuric acid [A. P. Kolesov, B. H. Sokolov. Coke and chemistry. 1962, No. 5, S. 41], thiophene - chlorine, formaldehyde, hypochlorite associated with the use of large quantities of reagents, with the problems of disposal of waste products of condensation of impurities with the reagent, the loss of the target product [L. J. of Colander. The production of pure benzene. - M.: metallurgy, 1966, S. 64-69].

For the separation of benzene from hydrocarbon impurities using liquid extraction, of benzene solvent is removed then the rectification.

As extractants used glycols, dimethyl sulfoxide, sulfolane [A. A. Miroshnichenko and other coke and chemistry. 1974, No. 8, S. 35-37], N-organic mixed with ethylene glycol and water [A. A. Miroshnichenko and other coke and chemistry. 1958, No. 3, S. 61]. Get the benzene content of the basic substance 99,90% wt. and above the crystallization temperature of 5.40o

Method of extractive distillation is used to achieve deep purification of benzene, this method requires prior separation of most of the impurities.

The known method benzene purification from admixtures of non-aromatic hydrocarbons by extractive distillation using a binary solvent mixture of N-methylpyrrolidone and water at a mass ratio of 3 : 1 [C. H. Sokolov, D. kharlampovich. The production and use of aromatic hydrocarbons. - M.: Chemistry, 1980, S. 240 - 241].

The ratio of extractant/raw is 4.5 : 1 (wt.). As raw materials use of benzene fraction of raffinate temperature Hydrotreating containing 0,73% wt. non-aromatic saturated hydrocarbons. After distillation separation of the cubic product emit benzene containing 99.97% of the basic substance.

However, the method is directed only to the purification of saturated hydrocarbons as raw materials pre-pirical benzene using the solvent N-pyrrolidone removed thiophene and carbon disulfide [A. A. Miroshnichenko, etc. Coke and chemistry. 1975, No. 8, S. 21-25. A. A. Miroshnichenko and other coke and chemistry. 1975, No. 10, S. 35-40].

The disulphide of coking benzene brand "for nitrile" is displayed completely due to the formation of the condensation products with amines, formed by partial hydrolysis of N-methylpyrrolidone. The residual content of thiophene, but, significantly, not reaching the level required for benzene brand "synthesis".

The closest to the technical nature of the claimed method is benzene purification by extractive distillation using as a solvent of dimethylformamide [French patent 2224425, class C 07 C 7/02, Appl. 06.04.73,, publ. 31.10.74].

As raw materials use benzene catalytic reforming gasoline fractions containing 70% of the basic substance and the 30% limit nah C6-C8with their boiling temperature 65-102oC. Cleaning is performed in a column 5 cm in diameter with 60 practical plates Oldershaw, the temperature of the top of the column - 80oC Cuba - 160oC. On 25 th bottom plate serves a mixture of raw materials with formamide at 55 plate serves dimethylformamide. The ratio of arriving in a convoy of dimethylformamide (DMF) and raw materials is 4.5 to 5.5 : 1 (mA) output from the column pairs supplied for irrigation.

CBM product containing 78,1% wt. DMF and 21.0% wt. benzene, directed to the selection of purified benzene and regeneration DMF in 2 columns with resin HEH 284 type K.

The purified benzene contains 99.99% of wt. and above basic substance and less than 0.01% wt. non-aromatic saturated hydrocarbons.

The method relates to the purification of benzene from the limit nah. The original benzene, obviously, in the catalytic reforming process has passed the stage of purification (adsorption or catalytic hydrogenation) of thiophene and unsaturated hydrocarbons, otherwise, their presence in the raw materials is inevitable.

Since the selectivity of dimethylformamide with respect to a mixture of thiophene - benzene large enough 1,93-1,50 when the concentration of the solvent 98-80 mol.% [A. C. the USSR 245134, class C 07 D 63/18, publ. 04.06.1969], while the corresponding modes extractive rectification with dimethylformamide can be separated thiophene from benzene, which is confirmed by the practical experience of the authors of this application. However, the residual content of higher than required for benzene brand "synthesis" according to GOST 9572-77 and GOST 8448-78 for benzene oil and coke, respectively. As for the purification of benzene from the non-is ctice reach their full separation from benzene, bringing the head fraction with saturated hydrocarbons. The content of benzene in the head fraction increases. If the branch limit nah when extractive distillation with DMF ratio benzene/saturated hydrocarbons is 0,40-0,45 : 1, in the case of separation of unsaturated hydrocarbons, this ratio increases to 3.5 to 3.8 : 1.

The carbon disulfide in extractive purification of benzene with dimethylformamide as solvent removed easily enough, its residual content does not exceed 0,00005% max., that meets benzene brands "synthesis". The removal of carbon disulphide is due to its chemical interaction with dimethylamine, invariably accompanying DMF as an impurity and additionally produced from DMF due to the moisture present in the DMF and raw materials.

Thus, the disadvantages of the method benzene purification from impurities limit and unsaturated hydrocarbons, thiophene and carbon disulfide by extractive distillation using DMF as solvent is insufficient purification of benzene from thiophene and increased loss of benzene in the head of the faction in the allocation limit and Marsala, loss reduction of benzene when cleaning.

This goal is achieved by the fact that the purification of benzene from non-aromatic impurities limit and unsaturated hydrocarbons, thiophene and carbon disulfide carried out by extractive distillation using as the extractant binary solvent mixture of toluene and dimethylformamide (DMF) at a ratio of components (% wt.):

toluene - 5-10

DMF - 90-95

The ratio (wt.) the extractant/raw is 4.5 to 6 : 1.

As raw materials use benzene coke brand "for nitrile and benzene allocated distillation distillation of the "heavy" and "light" hydrocarbons from a liquid hydrocarbon, C6-C7pyrolysis fractions propylene production corresponding to THE 33.402-62-144-93.

Impurities marginal and non-aromatic unsaturated hydrocarbons when carrying out extractive distillation with dimethylformamide are derived from benzene, the top product in a mixture with benzene. The head fraction is 9,80-10,00% wt. feedstock benzene content in it 51-53% wt. Thiophene is displayed in the VAT product with DMF and toluene. When the continuous process of cleaning CBM product from him periodically clean Argonauts filtering on the line output of the cubic product.

Part of the toluene contained in the initial benzene, also displayed kubovy product, so as it accumulates in DMF in the amount of more than 10% wt. the extractant is subjected to "regeneration" is a distillation distillation of excess toluene.

Refined marginal and non-aromatic unsaturated hydrocarbons, thiophene and benzene carbon disulfide contains 99.99% of wt. the basic substance and in terms corresponds Marche "cleaned" according to GOST 9572-77 "oil Benzene, and the benzene coke marque "synthesis" of the highest grade according to GOST 8448-78.

The method is carried out according to the following scheme (see drawing).

In the extractive distillation column efficiency 140-160 practical plates (valve) 70-th plate (counting from the bottom of the column) are served raw, in the upper part of the column at a temperature of 90oC serves the extractant is a mixture of dimethylformamide (DMF) and toluene, the content of toluene 5-10% wt.

The ratio of extractant/raw materials (wt.) is 4.5 to 6 : 1.

The mode column: reflux number (PL. h) 2, the temperature of the top (totop) 80oC at 1 ATA, the temperature of the cube (tocube) 125-130oC.

40 plates deduce the purified benzene in pansol.

The extractant recycle from the bottom of column 1, or through desorber 2 is directed to the upper part of the extractive distillation column.

Head of the faction of desorber use as a component of a fuel or share it on thiophene and benzene distillation column 3, directing the selected benzene recycle column 1.

When a continuous process of purification of the extractant from the thiophene in the adsorber conduct or continuously, or periodically, with the accumulation of thiophene to 25-30 kg per tonne of extractant (approximately 200 or more revolutions of the extractant).

The accumulation in the extractant toluene (more than 10% wt.) spend the allocation of excess toluene in a distillation column 4.

Below are examples of benzene purification by the present method and with the use of the extractant by a known method.

Example 1 (using well-known extractant).

1000 g of benzene separated from the liquid fraction of the pyrolysis oil corresponding to THE 38.402-62-144-93, two clear rectification to remove basic impurities limit and unsaturated hydrocarbons, are sent to the 70-th plate extractive distillation column 1 (drawing) efficiency 150 brakepedal 2,23% wt., toluene is 0.06 wt.%, thiophene is 0.01% wt. (table 1).

Column mode: PL. h 2, totop80oC at 1 ATA, tocube130oC.

In the upper part of the column 140-th plate serves heated to 90oC dimethylformamide. The mass ratio of the extractant/raw materials is 5 : 1.

The output 40 of the plates cleared benzene has a composition (wt.%):

benzene - 98,630

limit non-aromatic hydrocarbons - 0,006

toluene - 0,046

thiophene - 0,002

The yield of benzene 86,80% wt

The head fraction is 14,10% wt. benzene content in it - 66,18% wt

The compositions of the initial benzene and factions in extractive distillation are shown in table 1.

Example 2.

1000 g of benzene composition of example 1 is fed to the extractive distillation column 1 (drawing), running the example 1.

In the upper part of the column 1 (140-th plate) at the 90oC serves extractant composition (% wt.):

DMF - 95,0

toluene - 5,0

The ratio of extractant/raw is 5.0 : 1 (wt.).

40 plates of the column in the vapor phase output of purified benzene composition (% wt.):

benzene - 99,990

toluene - 0,002

n-heptane - 0,002

meticulate less than 0.05 (GOST 2706-74).

The yield of benzene 90,07% wt

The head fraction is 9,81% wt. feedstock benzene content in it - 51,37% wt

CBM product containing the extractant, 0,002% wt. thiophene, 0,009% wt. benzene, recycling through desorber 2 is sent to the extractive distillation column 1.

Desorber mode: so so 40; FL.h. 1,0; totopan 80.2oC, a pressure of 0.7-1 ATA, the temperature at the 5th plate (bottom) 140oC.

Head of the faction of desorber sent to the distillation column 3, from the top of which is allocated benzene return recycle in column 1 with the flow of raw materials.

The compositions of the initial benzene and factions in extractive distillation are shown in table 2.

Example 3.

1000 g of benzene coke production brand "for nitrile" containing 99,69% wt. the main substance of 0.015 wt.%. thiophene, 0,003% wt. carbon disulphide, the rest is marginal and non-aromatic unsaturated hydrocarbons, sent to the extractive distillation column 1 (drawing) at 70 plate.

The efficiency of the column 140 Ave so, the mode of operation: FL.h. 2,0; totop80oC at 1 ATA, tocube125oC.

In the upper part of the column of naol - 10,0

The ratio of extractant/raw materials (mass) is 6 : 1.

40 plates of the column display in the vapor phase purified benzene composition (% wt.):

benzene - 99,990

toluene - 0.003

n-heptane - 0,002

cyclohexane - 0,062

methylcyclohexane - 0,002

the disulphide - 0,00005

thiophene

0,00018

The crystallization temperature of 5.50oC.

Coloration with sulphuric acid less than 0.1.

The yield of benzene 99,44% wt

The output of the head fraction is 4.21% wt., benzene content in it - 50,95% wt

The compositions of the initial benzene and fractions during the purification are shown in table 3.

CBM product of the column 1 is directed to a regeneration treatment in column 4 for the distillation of excess toluene from which CBM product enters the supply line of the extractant, the content of toluene in the extractant flow into the column 1 is not less than 5.0 wt.%

Example 4.

1000 g of benzene coke production brand "for nitrile" containing efficiency of 99.78% wt. benzene is passed to the 70-th plate extractive distillation column 1 efficiency 160 other so-Column mode example 1.

In the upper part of the column at 150 plate served at the 90ois a 4.5 : 1 (wt.).

40 column plate deduce the purified benzene in the vapor phase composition (% wt.):

benzene - 99,993

toluene - 0,002

n-heptane - 0,002

cyclohexane - 0,002

methylcyclohexene - tracks

the disulphide - 0,00005

thiophene - 0,0001

The crystallization temperature of the 5,52oC.

The yield of benzene 99,54% wt

Head of the faction is to 3.92% wt. benzene content in it - 52,67% wt

The extractant direct recycling in the upper part of the column 1.

The cleaning results are shown in table 4.

The analysis of the results of the purification of benzene using the proposed extractant known and shows the advantage of the first against the best degree of purification from thiophene (residual content in purified benzene 0,00010-0,00018% wt. compared to 0,002% wt. when using the known extractant).

By the present method of purification on to 4.52% wt. (in the calculation of the original benzene) reduced loss of benzene in the head of the faction when sufficiently complete separation of all non-aromatic hydrocarbons. Benzene content in the bottom product is about 4 times smaller than when using the known extractant. The residual content of carbon in the coke Ben is Brazauskas under the action of moisture present in the DMF.

So, THE 6-09-3720-74 in dimethylformamide provides the content of moisture to 0.07 wt.%, dimethylamine - up to 0.02 wt.%

When testing the proposed method cleanup on pilot plant extractant periodically (via 200-250 rpm) undergoes regeneration distillation removal of thiophene and toluene, with corrosive decomposition products DMF it is not found.

The toluene contained in the extractant and raw materials, does not reduce the coefficients of relative volatility systems benzene-n-heptane, benzene-methylcyclohexane, as it happens when using the known extractants, for example N - methylpyrrolidone [L. J. of Colander. New ways of processing of crude benzene. - M.: metallurgy, 1976, S. 104].

When the content of toluene in the solvent in a quantity less than 5.0 wt.%, increased loss of benzene in the head of the faction and VAT product and the content of thiophene in refined benzene. When the content of toluene in the extractant more than 10% wt. quality cleaning from marginal and non-aromatic unsaturated hydrocarbons is deteriorating.

When submitting extractant at mass ratio and raw materials less than 4.5 : 1 is not achieved the required quality cleaning butsa unjustified from the point of view of the achieved improvement of the quality of cleaning, energy.

Modes columns provide the required complete separation of the impurities in the upper stream and minimal loss of benzene as the product and in the head of the faction.

Thus, the advantage of the proposed method of purification of benzene is carried out in the possibility of simultaneous purification from non-aromatic and sulfur-containing impurities with less loss of benzene in the head of the faction and VAT product using technologically simple and less energy-intensive process compared to, for example, with a catalytic hydrotreatment.

Used in examples 1-4 dimethylformamide corresponds to THE 6-09-3720-74, toluene - GOST 14710-78.

The method of purification of benzene from non-aromatic impurities limit and unsaturated hydrocarbons, thiophene and carbon disulfide by extractive distillation using as the solvent of dimethylformamide, characterized in that use solvent, optionally containing toluene, in the following ratio, wt.%:

Dimethylformamide - 90,0 - 95,0

Toluene - 5,0 - 10,0

 

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