RU2139910C1 - Method of isolating aromatic hydrocarbons from deparaffined fraction having 200-320 c - Google Patents

Abstract

FIELD: organic chemistry. SUBSTANCE: described is method of isolating aromatic hydrocarbons from deparaffined fraction by liquid extraction. Extraction agent is methyl cellulose containing 0.3-10.0 wt % of water and second solvent immiscible with extracting agent is n-pentane. EFFECT: higher selectivity, greater degree of isolation and concentration of aromatic hydrocarbons in extract. 3 ex, 2 tbl

Description

The invention relates to the refining industry and can be used for the separation of aromatic hydrocarbons from the dewaxed fraction of 200 - 320 ^o C - denormalization units "Parex". Denormalizes obtained as a result of adsorption of liquid n-paraffins on zeolites are used as a component of diesel fuels. However, the concentration of aromatic hydrocarbons in denormalizates is 25-30 wt.%, And for this indicator they do not meet the environmental requirements for diesel fuels.

 In accordance with TU 38.1011348-90, amendment 1, the content of aromatic hydrocarbons in the environmentally friendly summer diesel fuel DLEC-V is limited to no more than 20 wt.%, In most foreign countries - not more than 10 wt.%, And in Sweden - 5 wt. % With an increase in the content of aromatic hydrocarbons in diesel fuel, the emission of solid particles in exhaust gases and their smokiness rapidly increase, and the cetane number decreases. In accordance with Russian requirements, the cetane number of diesel fuel should be at least 45, and in some European countries - at least 58.3.

 Reducing the content of aromatic hydrocarbons in diesel fuel is possible by hydrogenation methods, however, instead of traditional hydrotreating units operating at a pressure of 3.5-4 MPa, it is necessary to create new units designed for a pressure of 7-10 MPa, while capital investments are doubled and energy costs are increasing 65-77%. A decrease in the content of arenas to 10 wt.% Is possible at a hydrogen pressure of about 30 MPa.

 In order to reduce energy costs and investment, it is proposed to use the extraction method to reduce the content of aromatic hydrocarbons in denormalizes to a level that meets the environmental requirements for diesel fuels.

The extraction of aromatic hydrocarbons from denormalizates is a more difficult task than from straight-run middle distillate fractions or from n-alkanes. Saturated hydrocarbons in denormalizates are represented by cycloalkanes and isostructural alkanes, which are better soluble in polar extractants than n-alkanes. For example, the critical dissolution temperature of methyl cellosolve (2-methoxyethanol) with methyl cyclohexane is 25 ^o C, and with n-heptane 48 ^o C, with isooctane 46 ^o C, and with n-octane 67.5 ^o C. Therefore, the selectivity of the solvents relative to arenes when extracting them from denormalizes, it is lower than when extracting from fractions enriched with n-alkanes.

Patents for extraction methods for the separation of hydrocarbons from the dewaxed fraction 200-320 ^o C (denormalization units "Parex") were not found.

 A known method of dearomatization of heavy gasoline and kerosene using acetone with 1-15 wt.% Water as extractant [Pat. 153738 Poland, 1991]. The disadvantage of this method is the low selectivity of aqueous acetone, and therefore the concentration of arenes in the extract is only 38 - 50 wt.% And as a result, the yield of raffinate decreases.

The closest in technical essence and the achieved effect to the proposed invention is a method of separating arenes from oil fractions 120-380 ^o C by liquid extraction with methyl cellosolve with the addition of up to 30% water per extractant [SU 349674. 09/11/72]. The disadvantage of this method is the inability to obtain highly concentrated extracts with a high degree of extraction of arenes due to insufficient selectivity and dissolving ability of aqueous methylcellosolve.

 In order to increase the selectivity and efficiency of the process of separation of aromatic hydrocarbons from denormalizates, it is proposed to use a heterogeneous mixture of methyl cellosolve-water-pentane solvents as an extractant. In this mixture, aqueous methylcellosolve is selective with respect to arenes and pentane with saturated denormalizate hydrocarbons; as a result, the selectivity of the separation process increases.

As a raw material, a denormalizate fraction of 200 - 320 ^° C with a refractive index of n $\genfrac{}{}{0ex}{}{\text{20}}{\text{D}}$ 1.4656, density ρ $\genfrac{}{}{0ex}{}{\text{20}}{\text{4}}$ 0.839, containing 27.5 wt.% Arenes.

 Due to the fact that the comparison of the effectiveness of different extractants should be carried out using the same raw materials and with the same number of theoretical extraction stages, in table. 1 (at the end of the description) presents the results of a single-stage extraction of arenas from denormalizate with methyl cellosolve with different water contents (in the presence of pentane and without it) and acetone with 11 wt.% Water (such water content in acetone is recommended as preferred in the patent [Pat. 153738 Poland , 1991]). As follows from the results presented in table. 1, methyl cellosolve with an optimum water content of 5 wt.% In all respects exceeds aqueous acetone: the yield of raffinate, the concentration of arenes in the extract and the degree of their extraction. The use of the methylcellosolve-water-pentane extraction system can improve all extraction indicators compared to aqueous methylcellosolve extraction.

To further increase the concentration of arenes in the extract and reduce their content in the raffinate, a five-stage countercurrent extraction with methylcellosolve with 5 wt.% Water was studied at a volume ratio of 5: 1 to denormalizate in the presence of pentane (volume
ratio to denormalizate 1: 1) (Table 2 at the end of the description). For comparison, the results of a five-step extraction with methylcellosolve with 5 wt.% Water are presented with a volume ratio of 5: 1 to denormalizate.

 As follows from the data table. 2, the proposed solvent mixture based on methylcellosolve and pentane is much more effective than aqueous methylcellosolve. The ratio of the concentrations of arenes in the extract and raffinate when using the proposed method is 28, and for aqueous methylcellosolve - 5.7, which indicates a significantly higher selectivity of the proposed extraction method.

 An advantage of the proposed method is also a significantly higher density difference between the extract and raffinate phases and their rapid delamination. The duration of the separation of the equilibrium phases when using aqueous methylcellosolve is about 1 minute, and for the proposed mixture of solvents - 10 seconds, which allows the use of smaller extractors.

The regeneration of methyl cellosolve and pentane can be carried out by distillation, because methylcellosolve (mp. 124.5 ^o C) does not form azeotropic mixtures with denormalizate hydrocarbons and with pentane.

 Example 1

In a sealed container with a magnetic stirrer, 50 cm ^{3 of} denormalizate (41.95 g) and 150 cm ³ (145 g) of a mixture of methyl cellosolve and water (137.75 g of methyl cellosolve and 7.25 g of water) are loaded. The mixture was thermostated for 30 minutes at 40 ^° C. with vigorous stirring. After settling, the raffinate and extract phases are separated, water and methylcellosolve are distilled off on a distillation column with an efficiency of 20 theoretical plates. Obtain 33.06 g of raffinate containing 18.8 wt. % arenas and 8.89 g of extract containing 59.9 wt.% arenas.

 Example 2

In a sealed container with a magnetic stirrer, load 120 cm ³ (100 g) of denormalizate, 360 cm ³ (348.5 g) of a mixture of methyl cellosolve and water, composition 95: 5 wt. %, respectively, and 120 cm ^{3 of} pentane. The mixture was thermostated for 30 minutes at 40 ^° C. with vigorous stirring. After sedimentation, the raffinate and extract phases are separated, pentane, water and methylcellosolve are distilled off on a distillation column. Obtain 84.4 g of raffinate containing 19.0 wt.% Arenes and 15.6 g of extract containing 73.6 wt.% Arenes.

 Example 3

At the temperature of 40 ^° C., denormalizate (flow rate 100 cm ³ / h) and pentane (100 cm ³ / h) are fed to the lower part of the packed extraction column with an efficiency of 5 theoretical stages, and methyl cellosolve with 5 wt.% Water (flow rate 500) cm ³ / h). As a result of countercurrent extraction, after reaching a stable regime, the raffinate and extract phases are simultaneously selected. From the equilibrium phases, pentane, water and methylcellosolve are distilled off on a distillation column with an efficiency of 20 theoretical plates, and the obtained extract and raffinate are analyzed. The arene content in the raffinate is 3.2 wt.%, In the extract - 89.6 wt. % The yield of raffinate and extract 72.3 and 27.7 wt.%, Respectively, to the missed denormalizate.

Claims (1)

A method of separating aromatic hydrocarbons from a dewaxed fraction of 200-320 ^° C. by liquid extraction using an extractant methyl cellosolve, water and a second solvent, characterized in that methyl cellosolve containing 0.3-10.0 wt.% Water is used as an extractant. as a second solvent not miscible with the extractant, n-pentane.

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