RU2155177C1 - Method of purifying benzene from thiophene - Google Patents

Abstract

FIELD: preparation of highly pure benzene, more particularly cleaning of benzene from thiophene. SUBSTANCE: content of thiophene in benzene used in synthesis on metal- containing catalysts is not more than 0.00005 wt %. Benzene is purified from thiophene with urotropin in amount of 1.5-3.0 moles per 1 mole of benzene in the presence of catalytic amounts of sulfuric acid. EFFECT: lower benzene losses when benzene is purified from thiophene and reduced amount of agent per unit of product. 4 ex

Description

 The invention relates to the petrochemical industry, to the production of high-purity benzene used in petrochemical synthesis.

 Thiophene is an impurity harmful in most processing processes, primarily as a catalytic poison.

 The most sensitive to the thiophene content in the feed is the process of catalytic hydrogenation of benzene. When the thiophene content in benzene is 0.0002%, its hydrogenation rate on nickel-chromium catalysts is halved. Platinum hydrogenation catalysts are no less sensitive to thiophene.

 The thiophene content in benzene going to hydrogenation should not exceed 0.00001 and 0.00005% wt. (GOST 9572-77 and GOST 8448-78).

 During the nitration of benzene, thiophene also forms nitro derivatives, which reduce the quality of the products of the reduction of nitrobenzene and reduce the stability during their storage.

 Thiophene impurities are harmful in the direct catalytic reduction of nitrobenzene to aniline on copper catalysts, in the chlorination of benzene in the presence of iron chloride, in the alkylation of benzene on a number of catalysts, etc.

 Thus, the task of cleaning benzene from thiophene is very relevant for petrochemical plants using benzene.

 Widely used in industry methods of purification of products from impurities — by clear distillation using highly efficient columns, azeotropic distillation using various solvents, and extractive distillation — do not allow to achieve a deep degree of purification of benzene from thiophene.

The most effective is the catalytic hydrotreating under pressure at a temperature of 380 - 500 ^o C, the method provides a deep purification of benzene from thiophene (up to 0.00005% wt.) [Composition and processing of liquid pyrolysis products in domestic plants. Thematic review., M., Central Research Institute of Chemical Technology, 1977, p. 76 - 77].

 However, this cleaning process is very energy-intensive, it justifies itself only in large industrial production of benzene, semi-industrial, small-tonnage plants do not use it for economic reasons.

 Thiophene from benzene cannot be isolated either by ordinary or fractional crystallization, since it forms mixed crystals with benzene [V.M. Kravchenko. ZhPKh, 1950, v. 23, No. 3, p. 288 - 298].

 The proximity of the adsorption properties of thiophene and benzene do not allow them to be divided into ordinary absorbents [S.Yu. Elovich, O.G. Larionov. ZhPKh, 1961, v. 34, No. 9, p. 2067 - 2073].

Complete removal of thiophene can be achieved on active clays at a process temperature of 150 - 250 ^o C, a pressure of 2.0 - 2.08 ata [A.D. Berenz et al. Processing of liquid pyrolysis products. M., Chemistry, 1985, p. 216]. However, the method is limited to the upper thiophene content in the raw material 3 Mill. ^1, a high flow rate per unit adsorbent materials and the necessity to disposal of spent adsorbent.

A known method of purification of benzene from thiophene and indefinite compounds, combining adsorption and catalytic purification in one process [V.A. Dvinin et al. Fine purification of the benzene fraction of pyrocondensate from olefins and thiophene. Oil refining and petrochemistry, 1988, N 9, c. 19-21]. The method allows purification of the products containing thiophene 5,5-22 million. ^-1 subsequent rectification allocate benzene, meets the requirements of GOST 9572-77 on benzene mark "highest purification" (content of thiophene 0.00005 wt.%) When the content of the basic substance is not less than 99.90% wt.

 The disadvantage of this method is the loss of benzene due to its partial alkylation, rather high cost of the cleaning process itself.

 For the deep purification of benzene from thiophene, especially with its small content in the purified benzene, the methods of chemical bonding of thiophene with separation of the resulting reaction products from benzene are widely used. The use of acidic reagents (aluminum chloride, ferric chloride, hydrogen fluoride, boron trifluoride, etc.) for these purposes does not provide the necessary cleaning depth [G.V. Kozhlevich et al. Coke and Chemistry, 1933, N 7, p. 55; B.A. Volkov. Coke and Chemistry, 1957, N 1, p. 53]. In addition, these processes are lengthy, multi-stage, require high reagent consumption, and thorough dehydration of the raw materials.

 The most widespread industry has found a way to clean benzene from thiophene with sulfuric acid [Yu.A. Pustovit, Coke and Chemistry, 1960, N 10, p. 44]. The removal of thiophene in this case is based on the difference in the rates of sulfonation of benzene and thiophene.

 However, practically sulfuric acid purification is always accompanied by partial sulfonation of benzene, the higher the degree of purification, the greater the loss of benzene [L.Ya. Kolyandr. Obtaining pure benzene for synthesis, M., Metallurgy, 1966, p. 111].

 The disadvantage of the process is the need to use highly concentrated sulfuric acid (94 - 100%), the content of organic impurities in the spent sulfuric acid, lack of selectivity.

 The efficiency and selectivity of the process of purification of benzene from thiophene with sulfuric acid increases in the presence of unsaturated compounds or industrial additives - waste products containing them [L.M. Cherkasova, L.K. Gorin. Coke and Chemistry, 1963, N 1, p. 44 to 46; A.P. Kolesov et al. Coke and Chemistry, 1965, N 11, p. 34 - 37]. The reaction products of thiophene with terminal compounds are separated by distillation. The residual thiophene content in benzene is 0.00005% wt. However, there are still problems with the consumption of sulfuric acid, although at a lower concentration (93 - 94%), the need for preliminary drying of the raw materials, regeneration of the spent acid, waste disposal, separation of unsaturated compounds from purified benzene.

 Closest to the claimed method according to the technical essence is a method for purifying benzene from thiophene using formaldehyde in the presence of sulfuric acid [L.M. Cherkasova, L.K. Gorin. Coke and Chemistry, 1963, N 1, p. 44].

The amount of formaldehyde 0.52% wt. to purified benzene 92.5 mol per 1 mol of thiophene), the amount of sulfuric acid with a concentration of 94% wt. - 10.9% wt. to benzene. The source benzene contains 0.056% wt. thiophene. The purification temperature is 80.0 ^° C. 20% of formaldehyde is fed before the sulfuric acid is fed, stirred for 10 minutes, the rest of it is added after the acid is fed, followed by stirring for 40 minutes.

 The resulting mixture of benzene, reagent and powdered condensation products of thiophene with formaldehyde is settled for 45 minutes. The reagent with settled condensation products is lowered. Refined benzene does not contain thiophene. The yield of purified benzene is about 96% wt. from the source.

 The disadvantages of the process are the high consumption of reagent - 114.5 kg per 1 ton of benzene, large losses of benzene during purification, the need to implement a reagent that cannot be regenerated.

 The aim of the invention is to reduce losses of benzene during its purification, reducing the consumption of reagent.

This goal is achieved by the fact that the purification of benzene from thiophene is carried out with urotropine (hexamethylene tetraamine) in the presence of a catalytic amount of sulfuric acid. The amount of urotropin is 1.5 to 3.0 mol per 1 mol of thiophene in the purified benzene. The amount of sulfuric acid (in terms of 100%) - 0.1 - 1.0% wt. in terms of benzene. Cleaning is carried out at a temperature of 20.0 - 80.0 ^o C with vigorous stirring (stirring speed 800 - 1200 rpm.) For 30 to 60 minutes.

 From the condensation products of thiophene with urotropine (gel-like formations of light yellow color) benzene is separated by distillation distillation. The purified benzene does not contain thiophene or the thiophene content does not exceed 0.00005% wt. (depending on the contact time of the purified benzene with the reagent). Refined benzene meets the thiophene content requirements of GOST 9572-77 for "high purity" oil grade benzene and GOST 8448-78 for coal and shale benzene of the highest purification category.

The process is carried out in an intensive mixing apparatus, since the concentrations of thiophene and reagent in benzene are very low. Benzene is distilled off in a distillation column with an efficiency of 30 practical plates (etc.), with a reflux ratio (fl.h.) - 1.0, a column top temperature of 80.0 ^o C, a cube - 84.5 ^o C.

 The yield of benzene 99.50 - 99.60% wt.

 The bottoms product of the distillation column — the formulated product with thiophene and ammonium sulfate, is periodically removed for incineration.

 The following are examples of the practical implementation of the purification of benzene according to the claimed method.

 Example 1

 Into an intensive mixing apparatus, 1000 kg of petroleum grade “for synthesis” benzene of the first grade, containing the main substance 99.50%, thiophene - 0.00035% wt. 8.85 g of urotropine (0.063 mol) and 6100 g of 98% sulfuric acid (0.6% by weight with respect to benzene) are introduced. The molar ratio of urotropine: thiophene is 1.5: 1.

At a temperature of 80 ^o C the contents of the apparatus are stirred at a speed of revolution of the mixer 1000 rpm./min for 30 minutes Then the reaction mixture from the stirring apparatus is fed into a distillation column with an efficiency of 30 pr.t., fl.h. - 1.0, t _top ⁰ - 80.0 ^o C, t _cube ⁰ - 84.5 ^o C.

 Refined benzene does not contain thiophene. The yield of benzene 99.55% wt. based on the source.

 VAT product as it accumulates output periodically for burning.

 Example 2

 Intensive mixing apparatus is charged with 1000 kg of benzene of the coke chemical grade “for synthesis” of the first grade, containing the main substance 99.0% by weight, thiophene - 0.0004% by weight. 20 g of urotropine and 1020 g of 98% sulfuric acid are introduced (0.1% wt. Calculated on benzene).

 The ratio (molar) of urotropin: thiophene is 3: 1.

Stirring is carried out at a temperature of 20 ^o C in the conditions of example 1.

 After 30 minutes of stirring, the thiophene content in benzene is 0.00005% wt. , after 60 minutes of stirring, the purified benzene does not contain thiophene.

 The separation of benzene from the condensation products of thiophene with urotropine is carried out under the conditions of example 1.

 The yield of benzene 99.60% wt. to the source.

 Example 3

 In the apparatus of example 1 load 1000 kg of benzene by-product coke production brand "for synthesis" of the highest grade, containing 0,0002% wt. thiophene, the main substance — 99.70% wt., 8.0 g of urotropine and 10200 g of 98% sulfuric acid are introduced (1.0% wt. based on benzene).

 The ratio of urotropine: thiophene is 2.4: 1 (molar).

The temperature with stirring is 50 ^o C.

 After 25 minutes of stirring, benzene contains 0.00005% wt. thiophene, after 60 minutes of mixing thiophene in benzene is absent.

 The separation of benzene from the condensation products of thiophene with urotropine is carried out under the conditions of example 1. The yield of benzene is 99.50% wt.

 Example 4 (prototype).

 1000 g of benzene in Example 1 is loaded into an autoclave with a stirrer, 3.56 g of formalin of 28% concentration is introduced, stirred for 10 minutes, 109 g of 94% sulfuric acid and 15.0 g of 28% formalin are introduced.

 The stirring speed is 900 rpm.

The mixture in the autoclave is stirred for 40 minutes at a temperature of 80.0 ^o C. After stopping the stirring, the reaction mixture is settled for 45 minutes. The lower layer of the reagent with the condensation products of thiophene with formaldehyde is drained. The benzene content in it is 3.67%, the condensation product of formaldehyde with benzene is 0.43% wt.

 The top product - purified benzene - does not contain thiophene.

 Thus, the inventive purification method allows to achieve complete removal of thiophene from benzene, as well as the known method using formaldehyde.

 However, the loss of benzene in the present method is at the level of 0.50% wt. in terms of the starting benzene (about 4.0% wt. in the known method).

 The consumption of urotropine is at the level of formaldehyde consumption per 1 mol of thiophene, and the consumption of sulfuric acid is reduced by an order of magnitude or more (1.0 - 10.0 kg versus 102 kg in terms of 100% acid per 1.0 ton of benzene). Neither benzene sulfonation products nor reaction products of sulfuric acid with thiophene were found in the reaction mixture. Obviously, the role of sulfuric acid in the claimed process is the implementation of interphase transfer in benzene-thiophene, urotropin-thiophene systems.

 When using urotropin in an amount less than 1.5 mol per 1 mol of thiophene, its complete removal from benzene is not achieved; its greater than 3 mol per 1 mol of thiophene is not practical to use, since this does not lead to an improvement in the quality of purification, and free urotropin is present in the reaction mixture.

 When the amount of sulfuric acid is less than 1.0 kg per 1.0 t of benzene (in terms of 100% acid), the process proceeds sluggishly, the contact time of the reagent with the purified benzene until it reaches the required depth of purification from thiophene is doubled or more.

 An amount of sulfuric acid of more than 10.0 kg per 1.0 ton of benzene does not accelerate the purification process or improve the quality of purification and creates unnecessary ballast in the system.

 The temperature regime of cleaning does not affect its quality, increasing its intensity somewhat with increasing temperature, but not very significantly.

 The urotropine used complies with GOST 1381-73. Sulfuric acid technical - GOST 2184-77.

Claims (1)

 The method of purification of benzene from thiophene by treatment with a chemical reagent in the presence of sulfuric acid followed by isolation of the purified product, characterized in that urotropin is used as a reagent in an amount of 1.5-3.0 mol per 1 mol of thiophene, and sulfuric acid in a catalytic amount.