The method of purification of benzene from unsaturated hydrocarbons

 

(57) Abstract:

The invention relates to the petrochemical industry, for the purification of benzene, obtained from a liquid hydrocarbon, C6-C7- fractions of pyrolysis oil from impurities unsaturated hydrocarbons. Describes a new method of purification of benzene from unsaturated hydrocarbons, which consists in that the unsaturated hydrocarbons are separated from the upper benzene product when extractive distillation with dimethylformamide, then they are subjected to oligomerization at 150 - 170oC in the presence of 0.0001 is 0.001 wt.% benzosulfimide based on benzene with subsequent unification fight off the oligomers of benzene with benzene, extracted from the bottom product of the extractive distillation column and purified from thiophene known methods. The technical result is to simplify the process and its effectiveness to obtain the desired product of high purity with a basic substance content of not less than 99,90 wt. %. 1 Il., 3 table.

The invention relates to the field of chemistry, in particular to methods for removal of benzene from impurities unsaturated hydrocarbons.

The industry of organic synthesis imposes high requirements to the RCTs "cleared", produced in accordance with GOST 9572-77, coloration with sulphuric acid should not exceed 0.1 in non-model scale, and the content of thiophene and 0.0001% wt

A known method of purification of benzene obtained by distillation of the benzene-toluene fraction of the pyrolysis condensate fraction ethylene-propylene production from unsaturated, including conjugated dienes, non-aromatic hydrocarbons by treating them with a cleansing system based on aluminum and carbon tetrachloride (ed. mon. USSR N 615053, C 07 C 7/148, 1978). The method allows you to clean from unsaturated compounds to their residual content of 0.05% wt. when the source of 1.5 - 2.0% wt.

Modification cleansing complex due to its application to the activated surface of the aluminum oxide can improve the quality of cleaning at higher impurity content of unsaturated hydrocarbons in the raw material - up to 5.0% wt. (ed. mon. USSR N 1825355, class C 07 C 7/148, 15/04, Appl. 01.04.91, publ. 30.06.93).

Disadvantages ways adsorption purification is large specific consumption of adsorbent per unit of product, recurring problem of disposal of spent adsorbent, the duration of the cleaning process. If the content of thiophene in benzene period sluzbacelna compounds on natural adsorbents, for example, active clays, with subsequent isolation of the desired product by distillation [A. D. Berens and other Processing of liquid products of pyrolysis. M, Chemistry, 1985, S. 216; ed. mon. The USSR 1065392, class C 07 C 15/04, 7/148, 1984].

In the industrial production of benzene, the most effective method of purification of benzene from unsaturated compounds is a catalytic Hydrotreating, including processing of raw materials with hydrogen (hydrogen-containing gas in the presence of catalysts, oxides of metals of the VIII, VI groups of the Periodic system at a temperature of 140-180oC, a pressure of 3-5 ATA on stage I treatment, at a temperature of 350-480oC and a pressure of 3-5 ATA II on stage with subsequent purification from impurities unsaturated compounds on the active clay and allocation of saturated aromatic hydrocarbons, in which the number of the Hydrotreating increases, azeotropic or extractive distillation [Composition and processing of liquid pyrolysis products in the domestic installations. Thematic review. M, Tsniiteneftehim, 1977, S. 76-77]. The method ensures the production of high-purity benzene content of the basic substance 99,90% wt. and above) with high yield.

However, a significant disadvantage of not allowing you to use it on Malaconda the volumes, associated with the provision of hydrogen, very energy intensive process - the factors that make the process of obtaining high-purity benzene unprofitable.

Method of catalytic Hydrotreating in the period of its development, is provided instead of the first stage of targetirovanija for treatment of unsaturated compounds, thermal polymerization used, for example, at facilities of the company Solivan-Chemie, Lurgi [L. J. of Colander. Obtaining pure benzene for synthesis. M, metallurgy, 1966, S. 120-122].

The polymerization of unsaturated compounds in the crude benzene coke production (later - benzene-toluene-xylene fraction) was carried out at 200oC, pressure up to 60 ATA in the presence of coke gas with subsequent distillation of the benzene from the polymer, which was only a waste when cleaning.

However, the method of thermal polymerization were not successful, despite the hard mode of polymerization, did not provide a fairly complete selection of unsaturated compounds, which resulted in a coating apparatus in the next stage Hydrotreating resinous deposits, impeding the operation of the installations. Therefore, thermal polymerization was widely replaced rode the high-purity benzene, including liquid pyrolysis products, after Hydrotreating, along with the clearing of marginal nah required fine purification of unsaturated compounds and thiophene known methods - adsorption, crystallization, catalytic purification with the use of special catalysts, khimochistka [C. A. Dynin and other Fine purification of benzene fraction of pyrolysis condensate fraction from olefins and thiophene. Refining and petrochemicals, N 9, 1988, S. 19-21].

Thus, all known methods of purification from unsaturated non-aromatic hydrocarbons are based on adsorption processes, hydrogenation or chemical interaction with a cleaning agent, which bears also the adsorption nature (ed. mon. 615053, ed. mon. 1825355, class C 07 C 15/04, 7/148).

Information about different treatment methods from unsaturated hydrocarbons, not based on the above processes, in the technical and patent literature is not found.

Proposed method of purification of benzene from unsaturated non-aromatic hydrocarbons by extractive distillation using dimethylformamide as solvent, the output produced by this top product of unsaturated hydrocarbons podyma distillation of the benzene from oligomerizate. The ratio (mass) of dimethylformamide (DMF) to raw materials is 4.5 to 6 : 1.

VAT product of the extractive distillation column that does not contain impurities of unsaturated hydrocarbons, after the separation of dimethylformamide are sent to homochitto from thiophene, purified from thiophene benzene connect with benzene, selected after cleaning the head fraction from unsaturated hydrocarbons.

Get a benzene of high purity with a basic substance content of not less than 99,90% wt

As a source of raw materials use benzene, a dedicated two-stage rectification of liquid C6-C7pyrolysis fractions of ethylene-propylene production (EPP) and past the purification of marginal and unsaturated non-aromatic hydrocarbons by azeotropic distillation with methanol.

As major impurities benzene contains thiophene is 0.01% wt. and cyclodiene aromatic hydrocarbons (2-2,6% wt.), don't separate when cleaning azeotropic distillation with the use of known solvents (methanol, acetone).

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

Benzene is sent to the middle part of the extractive distillation column 1. Efficiency is>) - 80oC, a pressure of 0.8-1 ATA temperature of the cube (tcubeo) - 160oC.

In the upper part of the column served at a temperature of 90oC dimethylformamide (DMF) at a mass ratio to raw 4.5 to 6:1.

The top product of the column containing 75-80% wt. benzene, which is a 9.6 - 12% wt. from the source directed to polymerization 2, in which at a temperature of 150-170oC and in the presence of 0.001 and 0.0001% wt. sulfonic acids are oligomerization of unsaturated hydrocarbons.

This unsaturated compound form, mainly dimers, sodemare, trimers, the boiling point of the cubic product - 210-240oC. Oligomerized sent to the distillation column 3 for isolation of purified benzene, which is combined with benzene selected from the cubic product.

VAT product of the extractive distillation column 1 is directed in desorber 4, from which the dimethylformamide direct recycle to the column 1, and the head of the faction in the purification unit from thiophene.

The removal of thiophene spend formaldehyde way [L. J. of Colander. Obtaining pure benzene for synthesis. M, metallurgy, 1966, S. 66-67].

Purified from thiophene benzene is combined with the upper benzene product is less than 99,90% wt., with a crystallization temperature of not less than the 5.45oC, density 0,8778 g/cm3at 20oC, figure painting sulfuric acid is less than 0.1 (GOST 2706.3-74).

Benzene corresponds Marche "cleaned" according to GOST 9572-77 "Benzene oil".

The yield of benzene 95-95,6% wt. in the calculation of the original product or 97,5 of 97.8% wt. in the calculation contained in the benzene. The main loss of benzene occurs at the stage of chemical treatment of the cubic product from thiophene (more than 2.0% wt.).

The following are examples of practical implementation benzene purification by the present method.

Example 1.

10000 g of benzene containing 2,09% wt. non-aromatic unsaturated hydrocarbons, 97,84% wt. the main substance is directed in the middle part of the extractive distillation column 1 (Fig. 1), in the upper part of the column serves dimethylformamide, heated to 90oC. the Efficiency of the column 140 practical plates (so so ), reflux number (PL. h)-2, the temperature of the top of the column (ttopo)-80oC, the temperature of the cube (tcubeo)-160oC. the Mass ratio of dimethylformamide/benzene is 4.5 : 1. The top product of the column constituting 9,62% wt. from the source directed to polymerization 2. Sod and 0,00096 g (0,0001% wt.) sulfonic acids, pre-mixed with 300 g of benzene, purified from impurities unsaturated hydrocarbons (for an equal distribution of sulfonic acids in the charge of polymerizatio).

Unsaturated non-aromatic hydrocarbons contained in the top product of the column 1, while quantitatively form compounds, which are mainly dimers, sodemare and trimers of diene hydrocarbons with a small amount (about 1.0 to 1.5%) more than high molecular entities.

Time oligomerization - 30 minutes at a mixing intensity of 900 rpm

Oligomerized sent to the distillation column 3 for distillation of benzene, which is combined with the benzene separated from the cubic product of the column 1. From the cubic product of columns 1 benzene first, select the top product of desorber 4, then it is sent to the purification unit from thiophene 5.

Selected kubovy product of desorber dimethylformamide recycling guide in column 1.

The mode of operation of desorber: 40 Ave so, FL.h. - 1,0, ttopo-80,2oC, a pressure of 0.8-1 ATA, the temperature at the 5th plate (bottom of column) - 150oC.

The cleaning head of the faction of desorber from thiophene spend formaldehyde way in when the C of the stirring speed 900 rpm for 40 minutes, followed by settling prior to discharge of the reagent for 45 minutes.

The purified benzene, not containing thiophene, combined with purified oligomerization benzene the top product of the column extractive distillation 1.

The content of the basic substance in purified product 99,94% wt., saturated hydrocarbons and 0.06 wt.%, unsaturated nonaromatic hydrocarbons, including cyclodiene, no. Crystallization temperature of - 5,46oC, density 0,8787 g/cm3at 20oC, coloration with sulphuric acid in the rooms exemplary scale of less than 0.05 (GOST 2706.3-74).

The yield of benzene - 95,51% wt. in terms of the original product or 97,58% wt. in the calculation contained in the benzene.

The content of components in the original benzene and at all stages of purification are shown in table 1.

The purified benzene indicators corresponds Marche "cleaned" according to GOST 9572-77.

Example 2.

10000 g of benzene containing 2,69% wt. non-aromatic unsaturated hydrocarbons, 97,21% wt. the main substance is sent to the extractive distillation column 1 (Fig. 1) operating in the mode of example 1.

In the upper part of the column serves n is the shining 12,11% wt. from the supplied cleaning, send to polymerizaton 2.

The content of benzene in the top product - 77,37% wt

The oligomerization is carried out at 170oC in the presence of a 0.012 g (0,001% wt.) benzosulfimide, pre-mixed with 300 g of purified benzene. Time oligomerization 30 minutes, stirring speed 900 rpm Oligomerized served in the distillation column 3, the top product which is distilled pure benzene, then combine with purified benzene cubic product of the column 1.

From the cubic product of columns 1 benzene produce the top product of desorber 4, running the example 1.

The top product of desorber sent to a purification unit of thiophene in the conditions of example 1 in the presence of 165 g of 28% formalin and 95,7 g 94% sulfuric acid. The purified benzene containing 0,0001% wt. thiophene, combined with benzene, purified oligomerization from unsaturated hydrocarbons.

Get a benzene containing 99,90% wt. the basic substance not containing unsaturated non-aromatic hydrocarbon having a temperature of crystallization of 5.45oC, density 0,8787 g/cm3at 20oC, color sulfuric acid below 0.10.

The yield of benzene 95,27% wt. in races which m corresponds to the brand "cleaned" according to GOST 9572-77.

The content of components in the original benzene and at all stages of purification are shown in table 2.

Example 3.

10000 g of benzene composition in example 1 was subjected to purification in the extractive distillation column 1 (Fig. 1) operating in the mode of example 1. The ratio of dimethylformamide/purified benzene 5.5 : 1,0. The top product of the column 1, comprising 9,98% wt. from the source directed to polymerization 2. The content of benzene in the top product - 78,46% wt. The oligomerization is carried out at 160oC in the presence 0,006 grams (0,0006% wt.) sulfonic acids under the conditions of example 1.

Oligomerized sent to the distillation column 3 for isolation of purified benzene, which combined with the benzene separated from the cubic product of the column 1.

CBM product of the column 1 is directed in desorber, which in the conditions of example 1 emit benzene, which is then channelled to the removal of thiophene.

The removal of thiophene is carried out in the conditions of example 1 in the presence of 163 g of 28% aqueous formalin and 96 g of 94% sulfuric acid. The purified benzene, not containing thiophene, together with a purified benzene the top product of the column 1. Get a benzene containing 99,94% wt. the basic substance not containing unsaturated hydrocarbons and the second acid is below 0.10.

The yield of benzene 99,57% wt. from the original product or 97,70% wt. on the contained benzene.

The content of components in the original benzene and at all stages of purification are shown in table 3.

Thus, the inventive cleaning method provides deep cleaning of benzene, obtained from the pyrolysis liquid fractions Epps, from unsaturated impurities, including cyclodienes hydrocarbons. The yield of benzene is 97,6 - 97,9% wt. in the calculation contained in the feedstock benzene.

Known methods of cleaning these hydrocarbons are separated methods, including adsorption processes or catalytic hydrotreatment. These methods are uneconomical in the case of benzene producing the highest-grade cleaning for light-duty, semi-industrial plants, especially if they do not have available sources of hydrogen in the case of Hydrotreating.

The inventive method allows for simpler and lower-cost technology, which requires a much smaller capital investment and energy than catalytic Hydrotreating, and more effective intensity of the cleaning process and less waste-free technology than adsorption, which is important in objevent.

The separation of the purified benzene in the extractive distillation column into two streams allows for a deep cleaning from thiophene known methods with relatively small losses of benzene, as there are no capable to resin formation or polymerization of unsaturated compounds.

Since the selectivity of dimethylformamide with respect to the mixture cyclodiene hydrocarbons - benzene, low, then bring them from benzene head fraction ratio benzene/cyclodiene hydrocarbons increases to 3.5-3,75:1 compared with its value 0,40-0,50:1 in the allocation of saturated hydrocarbons. That is why there is the problem of extracting benzene from a mixture with cyclodiene hydrocarbons and return it to its target product. Conducting the oligomerization cyclodienes hydrocarbons with subsequent distillation of the benzene from oligomers to return in the final product 7,6 -9,6% wt. benzene in the calculation of the benzene contained in the original product, that is to significantly reduce the loss of benzene in the process of purification by extractive rectification.

The reaction of oligomerization of olefin and diene non-aromatic hydrocarbon selected from benzene, under the action of the sulfonic acids of Priya with a significant prevalence of the mechanism of cationic polymerization. The resulting oligomeric structures include cyclodiene and olefinic hydrocarbons. Relatively low boiling point of the resulting mixture of oligomers (210 - 240oC) confirms the practical absence of more high-molecular formations than dimers, trimers.

Olefinic unsaturated hydrocarbons also come in the oligomerization reaction with diene hydrocarbons, so they can not be removed from the purified benzene before feeding it to purification by extractive rectification.

However, they are removed enough from benzene when cleaning from the limit of non-aromatic hydrocarbons by extractive distillation with methanol or acetone. It should be noted that the oligomerization in the present conditions proceeds in the absence of olefinic hydrocarbons with greater speed, which is important for continuous cleaning process.

When the temperature of the oligomerization below 150oC the rate of polymerization slows down, the time is significantly increased.

When the temperature of the oligomerization above 170oC formed by partially crosslinked oligomeric structure, the boiling point of the mixture of oligomers increases to 310-320oC, CC Otsa, especially at low temperatures.

With the introduction of sulfonic acids in the quantity < 0,0001% wt. for benzene, the output of the head fraction of the column 1, the proportion of unsaturated hydrocarbons do not react oligomerization, warded off from oligomers benzene contains 15,0-20,0% wt. them from the original number. A slight excess amount of sulfonic acids in excess of 0.001% wt. impractical because it does not affect the speed and completeness of polymerization of unsaturated hydrocarbons, with considerable increase in the number of sulphonic acids, the rate of polymerization increases, along with the linear form cross-linked structure comprising diene, olefin hydrocarbons and benzene, that is part of the benzene is lost with the oligomers.

Used in the examples of practical implementation 1-3 dimethylformamide corresponds to THE 6-09-3720-74, sulfuric acid, technical - GOST 2184-77, formaldehyde - GOST 1625-89.2

The method of purification of benzene from unsaturated hydrocarbons, characterized in that the unsaturated hydrocarbons are separated from the upper benzene product when extractive distillation with dimethylformamide, then they are subjected to oligomerization at 150 - 170oC in the presence of 0.0001 is 0.001 wt.% benzols elenim from the bottom product of the extractive distillation column and purified from thiophene known methods.

 

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