RU2568114C2 - Method of separating benzene from mixtures with non-aromatic hydrocarbons - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of separating benzene from mixtures with non-aromatic hydrocarbons to simultaneously obtain a distillate by extractive rectification. The method is characterised by that the selective solvent used is mixtures containing 30-50 wt % mixed solvent of sulfolane and 3-methylsulfolane of the composition 89/11 wt % and 50-70 wt % N-methylpyrrolidone.

EFFECT: use of the present method enables to obtain benzene with a higher degree of extraction and a distillate which can be used as a component of motor petrol or as raw material for the pyrolysis process.

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Description

The invention relates to the refining and petrochemical industries and can be used to isolate benzene and toluene from the benzene fraction of the reformate with the simultaneous production of a gasoline component.

For large oil refineries with reformate resources of more than 1.5 million tons / year, the most economical way to reduce the benzene content in motor gasolines, which should not exceed 1% (vol.) According to Euro-4 standards, is to fractionate the reformate of the gasoline fraction with the subsequent separation of benzene from benzene fraction by extractive distillation [1]. N-methylpyrrolidone [2], N-formylmorpholine [3], and mixed solvent “Tektiv-100” [4, 5] are used as selective solvents for the extractive distillation process in industry.

The process of extractive distillation, developed by the American company Glitch Technology Corporation (GTC) using "Tektiva-100", has been used in a number of foreign plants and since 2011 at KINEF LLC. GTC patented a method for the isolation of benzene and its homologs by extractive distillation with a mixture of sulfolane and 3-methylsulfolane [6]. Sulfolan exhibits high selectivity with respect to arenas and is the most effective extractant used in industry [7]. However, in the process of extractive distillation, the selective solvent should not only be highly selective with respect to the released components, but also, in contrast to extraction, have a high dissolving ability to hydrocarbons: it is undesirable to exfoliate the liquid on the plates of the extractive distillation column, which leads to a decrease in the efficiency of the separation process. 3-Methylsulfolane is significantly less selective than sulfolane with respect to benzene and its homologues, but its addition increases the solubility of sulfolane, and at a sufficiently high content in the mixture promotes homogenization of the system with shared hydrocarbons.

The closest in technical essence and the achieved effect to the proposed invention is a method of separating arenes from hydrocarbon fractions using a mixture of sulfolane with 3-methylsulfolane [7]. The disadvantages of this solvent, adopted as a prototype, are as follows:

- the use of high-boiling selective solvents (table. 1) leads to a high temperature in the extractive distillation column and in the boiler and to a decrease in the selectivity of the separation process;

- the high viscosity of the components of the mixed solvent (table. 1) reduces the efficiency of the plates and the number of theoretical plates of the extractive distillation column;

- difficulties in the regeneration of solvents: the need to use a high pressure and vacuum steam generator in the stripping column;

- the need to use a vacuum-generating system and a vacuum column with a larger diameter compared to an atmospheric stripping column leads to increased capital costs.

As the operating experience of the extractive distillation unit at KINEF LLC showed, the main disadvantage of the mixed solvent used, due to the non-optimal ratio of its components, is the insufficiently high dissolving ability with respect to hydrocarbons. As a result, it is necessary to increase the ratio of solvent to raw material and feed it to the extractive distillation column in an overheated state, which leads to an increase in energy consumption, a decrease in the stability of π-complexes with benzene, and solvent selectivity.

The purpose of this invention is the elimination of these disadvantages. This goal is achieved by adding to the mixture of sulfolane-3-methylsulfolane a relatively low boiling and low viscosity solvent with increased dissolving ability with respect to hydrocarbons - N-methylpyrrolidone (Table 1).

The liquid-vapor balance of binary systems of a non-aromatic hydrocarbon (hexane, 1-hexene, cyclohexane, heptane) (1) - benzene (2) containing 30 wt% was studied. benzene, in the presence of a mixed solvent sulfolane - 3-methylsulfolane 89/11% wt. (solvent I) and mixtures thereof with N-methylpyrrolidone. In all experiments conducted at atmospheric pressure, the mass ratio of selective solvents to hydrocarbon mixtures was 2: 1. Based on the compositions of the equilibrium phases (Table 2), the coefficients of relative volatility and selectivity of mixed solvents with respect to the separated hydrocarbons were calculated (Table 3).

) гексана и бензола), образованием одной жидкой фазы с разделяемыми углеводородами.As follows from the above data, mixed solvent I forms heterogeneous systems with all the separated hydrocarbon mixtures at the boiling point, which leads to low relative volatility coefficients (α _p ) of hydrocarbons. N-methylpyrrolidone is more effective, despite the lower selectivity compared to sulfolane and 3-methylsulfolane with infinite dilution of hydrocarbons with solvents (Table 1). The increased effectiveness of N-methylpyrrolidone is due to its high solvent capacity for hydrocarbons (as evidenced by the relatively low limiting activity factors ( $${\gamma }_i^{\circ }$$

) hexane and benzene), the formation of a single liquid phase with shared hydrocarbons.

In mixtures of solvent I with N-methylpyrrolidone, a synergistic effect is ensured: the relative volatility coefficients of all non-aromatic hydrocarbons with respect to benzene are higher than in solvent I and individual solvents. The maximum values of α _p correspond to the content of N-methylpyrrolidone in mixed solvents, in which there is a transition from a heterogeneous to a homogeneous system with shared hydrocarbons. For example, a more effective mixture of solvent I with N-methylpyrrolidone composition of about 30/70% wt. Only when the 1-hexene-benzene system is separated, does the maximum value of α _p correspond to the composition of the solvent I – N-methylpyrrolidone mixture of about 50/50 wt%. Such a shift in the maximum can be explained by the increased solubility of 1-hexene in polar solvents in comparison with other non-aromatic hydrocarbons used in the work. Therefore, the transition from a heterogeneous to a homogeneous system in this case occurs already when N-methylpyrrolidone is added to the solvent I in a mass ratio of 1: 1.

Non-aromatic hydrocarbons can be arranged in the following ease of removal from a mixture with benzene (by α _p values): 1-hexene>hexane>cyclohexane> heptane.

This series corresponds to the saturated vapor pressure of hydrocarbons; the highest boiling hydrocarbon, heptane, is the most difficult to distill from benzene during extractive distillation.

A comparison of the effectiveness of solvent I and its mixtures with the optimal composition of N-methylpyrrolidone was also carried out in experiments on the isolation of benzene from the benzene fraction of the reformate by extractive distillation. The experimental conditions are given in table. four.

1.4105; плотность при 20°C 0.7220 г/см³; стандартная разгонка, °C: н.к. - 54,10% - 67,50% - 72,90% - 79, к.к. - 87. Индивидуальный углеводородный состав сырья исследовали методом капиллярной газожидкостной хроматографии (табл. 5).The raw material used was the benzene fraction of the reformate processed at the extractive distillation unit of PO Kirishinefteorgsintez LLC according to the process of GTC. This fraction is isolated on the installation of total xylene separation by rectification of the reforming catalysts of gasoline fractions [9]. Characteristics of the reformate benzene fraction: refractive index $$n_D^{\mathrm{twenty}}$$

1.4105; density at 20 ° C 0.7220 g / cm ³ ; standard run, ° C: n.k. - 54.10% - 67.50% - 72.90% - 79, c.k. - 87. The individual hydrocarbon composition of the feed was studied by capillary gas-liquid chromatography (Table 5).

In the same table. Figure 5 shows the composition of the distillates obtained by extractive distillation on a laboratory column with an efficiency of 15 theoretical plates. In all experiments, toluene, which is present in a small amount in the feed, is absent in the distillate, which indicates its almost complete recovery. Part of the benzene is lost with the distillate, especially with its last fractions, in which the higher boiling non-aromatic hydrocarbons - heptane, cycloalkanes and unsaturated C ₇ hydrocarbons are concentrated. Nevertheless, both the degree of benzene extraction and the arene content in the aromatic concentrate isolated from the bottom residue by steam distillation in experiments using a mixture of solvent I with N-methylpyrrolidone are significantly higher than in experiment 1 with solvent I, even with lower ratio of mixed solvent to raw materials.

The results of extractive distillation using mixtures of solvent I with N-methylpyrrolidone can be improved by increasing the number of theoretical plates of the extractive distillation column from 15 to 36, corresponding to the efficiency of an industrial column using GTC technology.

Example 1

1.4772, что свидетельствует о преобладании в ней бензола. Масса объединенных фракций дистиллята 28.8 г, что составляет 79.8% мас. от расхода сырья.In a cube of an extractive distillation column with an efficiency of 15 theoretical plates, 50 ml (36.1 g) of the benzene fraction of 55-85 ° C reformate containing 28.96% wt. benzene, 0.58% wt. toluene and 70.46% wt. non-aromatic hydrocarbons. The contents of the cube are heated to boiling and a mixture of solvent I (sulfolane - 3-methylsulfolane 89/11% wt.) With N-methylpyrrolidone composition 30/70% wt. Is fed to the top of the column. at a temperature of 75-80 ° C and a volumetric ratio to the distillate of about 1.3: 1. The main distillate fraction (35 ml) and three more fractions (2 ml each) were taken. The refractive index of the last fraction of the distillate $$n_D^{\mathrm{twenty}}$$

1.4772, which indicates the predominance of benzene in it. The mass of the combined fractions of the distillate is 28.8 g, which is 79.8% wt. from the consumption of raw materials.

Aromatic hydrocarbons are distilled off from the bottoms with sharp steam to obtain 50.5 g of regenerated mixed selective solvent (mass ratio of solvent to feed 1.4: 1) and 7.9 g of aromatic concentrate. The composition of the distillate and the bottom residue is analyzed by capillary gas-liquid chromatography. The material balance of the experience of extractive distillation is compiled and the degree of extraction of benzene and toluene is calculated (Table 6, experiment No. 3).

Example 2

50 ml (36.1 g) of the benzene fraction of the reformate of the same composition are loaded into a cube of the same extractive rectification column. Extractive distillation is carried out by feeding to the top of the column a mixture of solvent I with N-methylpyrrolidone composition 50/50% wt. (table. 4, experiment No. 3). Selected 27.7 g of distillate, which is 76.7% wt. from the consumption of raw materials. An aromatic concentrate (8.4 g) was distilled off with still water from the bottom residue to obtain 65.0 g of a regenerated mixed selective solvent. The content of benzene and toluene in the distillate and aromatic concentrate is analyzed by gas-liquid chromatography (table. 6, experiment No. 4).

Information sources

1. Mirimanyan A.A., Vikhman A.G., Maryshev I.B. et al. Analysis of options for reducing the share of benzene in reformates // World of Petroleum Products. 2006. No5. S. 26-27.

2. Gaile A.A., Zalishchevsky G.D. N-methylpyrrolidone. Preparation, properties and use as a selective solvent. - St. Petersburg: Khimizdat, 2005.704 s.

3. Gaile A.A., Somov V.E., Zalishchevsky G.D. Morpholine and its derivatives. Obtaining, properties and use as selective solvents. - SPb .: Khimizdat, 2007 .-- 336 p.

4. Gentry J.K., Kumar K.S., Lee H.M., Lee Y.H. Production of aromatic hydrocarbons using GT-BTX ^sm technology // Chemistry and technology of fuels and oils. - 2003. N 1-2. S. 12-17.

5. Gaile A.A. Processes for the separation of petroleum products and mixtures of organic substances using selective solvents. - SPb .: SPbGTI (TU), 2010 .-- 176 p.

6. GTC Technology Inc, Lee F. - M. Aromatic purification from petroleum streams: Pat. 6781026 USA, IPC ⁷ C07C 7/00. Claim 10.21.02. Publ. 08/24/04. RZhKhim., 2006, 15N97P.

7. Gaile A.A., Somov V.E., Warsaw O.M., Semenov L.V. Sulfolan: properties and use as a selective solvent. - SPb .: Khimizdat, 1998 .-- 144 p.

8. Gaile A.A., Somov V.E. The processes of separation and purification of oil and gas products: Textbook. allowance. - SPb .: Khimizdat, 2012 .-- 376 p.

9. Varshavsky O.M., Sulyagin N.V., Zheludev S.G. et al. // 8th St. Petersburg International Forum of Fuel and Energy Complex, St. Petersburg, April 8-10, 2008 - Sat. materials. - SPb., 2008 .-- S. 180-185.

Claims (1)

A method of isolating benzene from mixtures with non-aromatic hydrocarbons while simultaneously producing the distillate by extractive distillation, characterized in that mixtures containing 30-50% by weight are used as a selective solvent. mixed solvent sulfolane - 3-methylsulfolane composition 89/11% wt. and 50-70% wt. N-methylpyrrolidone.