RU2243960C2 - Method of separating c5-hydrocarbon fractions - Google Patents

Abstract

FIELD: petroleum processing and petrochemistry.

SUBSTANCE: C₅-hydrocarbons with different degrees of saturation are separated by extractive rectification in extractive rectification column using dimethylformamide as extractant followed by desorption of pentenes or pentadienes therefrom and passing desorbed extractant to extractive rectification column. Part of hot desorbed extractant is subjected to liquid-phase mixing with starting hydrocarbons at vigorous stirring, after which resulting mixture is introduced into column in liquid form.

EFFECT: reduced power consumption.

2 dwg, 1 tbl, 5 ex

Description

The invention relates to the separation of C ₅ hydrocarbons of varying degrees of saturation, in particular pentanes, pentenes and pentadienes contained in fractions of various origin (dehydrogenation, pyrolysis of hydrocarbons, etc.), in the presence of polar organic extractants and can be widely used in the synthetic rubber industry in the production of the main monomer isoprene.

A known method of separation of C ₅ hydrocarbons obtained by dehydrogenation of hydrocarbon feeds by successive separation from the target hydrocarbon fraction of light (C ₁ -C ₄ ) and heavy (C ₆ and higher) hydrocarbons by distillation, followed by isolation of isoamylenes and (or isoprene) by extractive distillation [1] .

Closest to the invention, the technical essence is a method for separating fractions of C ₅ hydrocarbons, which consists in separating light and heavy hydrocarbons in conventional rectification columns and separating the residue in the presence of a polar organic extractant (dimethylformamide) by two-stage extractive rectification (er) and desorption [ 2]. Thus obtained C ₅ fractions: isopentane - isoamylene after the first stage of dehydrogenation - are sent for separation by extractive distillation.

Isopentane - the isoamylene fraction is separated into isopentane returned to the first stage of dehydrogenation and the isoamylene fraction sent to the second stage of dehydrogenation. The isoamylene - isoprene fraction is divided into return isoamylenes returned to the second stage of dehydrogenation and isoprene sent for purification. The content of isoamylene in the return isopentane is 1.8 wt.%, And the content of isoprene in the return isoamylene is up to two wt.%. The concentration of extractant (DMF) on the plates at both stages of er reaches 60-80 wt.%.

Due to the high concentration of extractant, the temperature in the cubes of the columns reaches 100 or more ° C, which, combined with the use of hydrocarbon recycling, leads to the formation of thermopolymers (the formation of which begins on the surface of the liquid condensation) [3], as well as to the need to use steam with high temperature.

OBJECT OF THE INVENTION IS:

Reducing energy consumption and increasing the efficiency of the separation process by changing the method of heating the initial fractions of hydrocarbons C ₅ .

This goal is achieved by the fact that part of the hot stripped extractant (DMF) with a temperature of at least 124 ° C is mixed with the initial C ₅ fraction in the liquid state in the ratio of 3.0: 1.0 in the first and second stages of er with vigorous stirring of the resulting mixtures under a pressure of 6-6.5 atm before entering the column. Missing to a ratio of 4-8: 1 with raw materials, DMF is fed to the top of the columns.

In the production of separation of C ₅ hydrocarbon fractions, a method of heating and evaporating hydrocarbons in heat exchangers using steam is used, the disadvantage of which is the deposition of polymers on the tubes of the apparatus and the need to remove them while reducing their efficiency.

The method of heating and evaporation of C ₅ hydrocarbons by a hot stripped DMF extractant in heat exchangers already has three drawbacks, since on the walls of the heat exchangers, tar is deposited from the extractant on the one hand and thermopolymers are deposited from the raw materials with an increased heat transfer surface, which complicates the cleaning problem even more heat exchangers (evaporators).

The most effective is the proposed method of heating raw materials, in which the secondary heat of the hot stripped extractant DMF is used to a greater extent, which completely eliminates the use of water vapor for heating and evaporation of raw materials and evaporators. The proposed method is devoid of the disadvantages of the used methods of heating raw materials and is as follows.

For heating (without evaporation before entering the column), the initial fraction of C ₅ hydrocarbons must be fed to direct mixing (liquid – liquid type) with the hot extractant DMF. Raw materials must be fed for mixing through a cone head equipped with a large number of holes with a diameter of up to 4 mm (since the raw materials are always cleaner compared to the DMF extractant). The extractant for heating the initial fraction of C ₅ hydrocarbons must be supplied in such an amount that the temperature of the resulting mixture is within 100 ° C and is equal to the amount of heat introduced into the column by the evaporated feed. In this case, due to intensive mixing of the liquid mixture, the process of liquid extraction under pressure up to 6.5 atm will occur and most of the initial fraction of C ₅ hydrocarbons will be associated with the DMF extractant.

According to the nature of saturation with DIMETHYLFORMAMIDE, pentadienes stand in front of pentenes, and pentenes stand in front of pentanes even when a liquid mixture is introduced into an er column. and a decrease in pressure to 2 atm and lower, those components of C ₅ hydrocarbons that have the highest relative volatility coefficient begin to evaporate first, i.e. it turns out that in the vapor phase on the plate of the mixture in the columns of er the first stage contains a smaller amount of pentenes, and in the columns of er. the second stage in the vapor phase above the input plate contains a smaller amount of pentadiene, which leads to a decrease in their losses [4-6].

In FIG. 1 and 2 show the implementation scheme of the proposed method.

EXAMPLE 1

Determine the required amount of heat for heating 500 grams of hydrocarbons from ₅ to 100 ° C and the required amount of DMF extractant for heating by mixing at a temperature of DMF of at least 124 ° C. According to the heat balance formula, we have:

Q = Gx · Cx (t ₂ -t ₁ ) -Gg · Cg · (T ₁ -T ₂ ), where:

Gx and Gg - the amount of heated (cold) and hot liquid, g;

Cx and Cg — average heat capacity of cold and hot liquid, cal / g ° C;

T ₁ and T ₂ - the initial and final temperature of the heating fluid, ° C;

t ₁ and t ₂ - initial and final temperature of the heated fluid, ° C.

Then: Qi = Gi · Ci (t ₂ -t ₁ ) = 500 · 0.4 · (100-10) = 18000 cal.

G ₂ = Q _i / C2 · (T ₁ -T ₂ ) = 18000 / 0.5 · (124-100) = 1500 g.

EXAMPLE 2

1500 g of DMF is poured into a device with a capacity of 3 l, the stirrer is turned on, and heating to a temperature of at least 124 ° C is performed. The heating is turned off and 500 g of C ₅ hydrocarbons of the first dehydrogenation stage are introduced into the apparatus. The mixture is stirred for three minutes. The device is set to a temperature of 98 ° C and a pressure of 4 ata. When the stirrer is stopped and three minutes of sedimentation, a liquid sample is taken, and the vapor phase is taken until the pressure in the apparatus drops to 2 atm. 39.7 g of C ₅ hydrocarbons are trapped. The compositions of the liquid and vapor phases are analyzed and summarized in table 1.

EXAMPLE 3

1500 g of DMF is poured into a device with a capacity of 3 l, the stirrer is turned on, and heating to a temperature of at least 124 ° C is performed. Heating is turned off and 500 g of C ₅ hydrocarbons of the second dehydrogenation stage are introduced. Mixing is performed (60 rpm) with a stirrer for three minutes. The device is set to a temperature of 100 ° C and a pressure of 3.6 atm. Without stopping the mixer, the liquid and vapor phases are taken. 18 g of product passes into the vapor phase. After the stirrer stops and the pressure drops to 2 ata, a liquid sample is taken. The composition of the samples analyzed and summarized in table 1.

Thus, water heat is saved and the target products are bonded in the liquid phase prior to introduction of er.

EXAMPLE 4

The condensed and separated isopentane - isoamylene fraction is sent for separation according to the scheme shown in figure 1. The hydrocarbons C _{5 of the} first stage of isopentane dehydrogenation are fed through line 1 to heating by direct mixing with hot desorbed extractant (DMF), which is fed through line 9 with a temperature not less than 124 ° C. The resulting liquid mixture in a ratio of 1: 3 with a temperature of 100 ° C after stirring in line 2 is fed into the column 3 in the pocket 18 of the plate. At 48 (56), a plate is fed through line 4 to the rest of the DMF to a ratio of 4-6: 1 and a temperature of 50 ° C.

Column 3 has 150 cap plates and operates with a reflux ratio of 1.2. The temperature of the top of the column is 44 ° C, and in the cube - 136 ° C. Isopentane with an isoamylene content of up to 1 wt.% Is taken from the top of column 3 through line 5. An extractant saturated with pentene-pentadiene is taken from line 3 of the column 3 cube and fed to column 7 for desorption of DMF. The pentene - pentadiene fraction is taken from the top of column 7 along line 8 and sent to the second separation stage. From the cube of column 7, the desorbed DMF extractant is again fed via line 9 to direct mixing with the feed in a ratio of 3: 1, and the rest of DMF via line 4 is fed back to the separation process.

EXAMPLE 5

Condensed and isolated isoamylene - isoprene fraction of the first stage of dehydrogenation and isoamylene - isoprene fraction of the second stage of dehydrogenation are sent in a ratio of 1: 2 or 1: 1 for separation according to the scheme shown in figure 2.

Raw materials (a mixture of poor + rich raw materials in a ratio of 1: 1) is fed through line 1 to heating by direct mixing with a hot desorbed extractant DMF in a ratio of 1: 3 with a temperature of at least 124 ° C, which flows through line 9. The resulting liquid mixture through line 2 with a temperature of 100 ° C is fed into column 3 on 85 (55) pocket plates. When meeting with the upper, liquid stream, the temperature of the mixture decreases from 100 ° C to 72 ° C. On a 120 (105) plate, line 4 is fed with the rest of the DMF extractant to a ratio of 5-8: 1 with the input feed and a temperature of 50 ° C. Column 3 has 150 cap plates and works with a reflux ratio of 1.6.

The top temperature of column 3 is equal to 37 ° C, and in the cube of the column up to 120 ° C (depending on the supply of recycle isoprene). A pentene fraction with an isoprene content of up to 0.5% by weight is taken from the top of column 3 along line 5. The DMF extractant saturated with pentadienes is taken from the cube of column 3 and sent to desorption column 7 through line 6. Raw isoprene is taken from the top of column 7 along line 8, which is then sent for clear distillation. Desorbed DMF is withdrawn from the cube of column 7 through line 9, which is again sent to the process of mixing, heating and binding of the target components of the feedstock, and along line 4 to the top of column 3.

Using the proposed method of heating raw materials allows you to:

1. By changing the method of heating the feedstock, exclude from the scheme the evaporators of the feedstock and the use of water vapor for evaporation of the feedstock. This leads to the saving of thermal energy not only at the stage of evaporation of raw materials, but also at the stage of separation in columns of er.

2. To reduce the loss of isoamylene with pumped isopentane, as well as to reduce the loss of isoprene with pumped isoamylene both at the stage of heating the raw materials and at the stage of separation in er columns

3. Heating of the raw material with a new direct mixing method with the DMF extractant leads to saturation of the extractant with the target components of the raw material and linking them before entering the er column, which allows you to raise the food plate to a higher one in the first stage and lower the food plate in the second stage, and unload columns from an excess of the top product (phlegmy) with less energy, which leads to improved results.

Used sources of information.

1. Ogorodnikov S.K., Idlis G.S. sec; Isoprene Production.sec; L .: Chemistry. 1973, p.129.

2. Copyright certificate SU 803343 A1, 12/20/2000.

3. Copyright certificate No. 642322, 1979.

4. a) Ogorodnikov S.K., Kogan V.V., Nemtsov M.S. sec; The equilibrium between the liquid and vapor of the mixture of dimethylformamide - isoprene - trimethylene .sec; Housing estate 34, No. 11, 2441 (1961).

b) Karev V.G., Baranov A.V. Proceedings of the conference of the Siberian Technological Institute based on the results of 1962. Issue 2, Krasnoyarsk, 49 (1963) sec; Equilibrium between liquid and vapor dimethylformamide-isopentane-trimethylethylenesec .;

5. Pavlov K.F., Romankov P.G., Noskov A.A. sec; Examples and tasks on the course of processes and apparatuses of chemical technologysec ;. L .: Chemistry. 1970, p. 212.

6. Pavlov S.Yu. other. Isoprene recovery from the C ₅ fraction of gasoline pyrolysis. sec; Chemical industry.sec; 1971, No. 4.

TABLE 1
COMPOSITIONS OF SAMPLES FROM EXPERIENCE No. 1 and EXPERIENCE No. 2 weight% No. Product name Sample 1 Sample 2 Sample 3 DMF Sample 4 Sample 5 Sample 6 Cat. 1 tbsp. DMF Trap 1 Desorbed. Cat 2 DMF Trap 2 raw materials saturated raw materials saturated 1. Hydrocarbons C4 0.3 0.02 2.79 0.5 0.09 3.9 2. Isopentane 65.5 14.86 91.4 0.9 0.08 16.3 3. 2 Methyl - 1 Butene 2.7 0.68 0.60 3.9 0.93 5.9 4. nPentane 3,1 0.73 3.02 2,8 0.67 4.6 5. 1 Penten 0.5 0.12 0.25 1.8 0.42 3.9 6. 3 Methyl - 1 Butene 8.8 2.23 0.63 18.9 4.47 33.3 7. 2 Penten 1.9 0.47 0.5 4.8 1.14 7.3 8. 2 Methyl - 2 Butene 14.5 3.69 0.5 35.8 8.83 22.7 9. Isoprene 2 0.51 0.2 27.4 6.9 1,5 10. 1.3 Pentadiene 0.4 0.1 0.1 1.8 0.45 0.1 eleven. Cyclopendadiene 0.2 0.05 0.02 1 0.25 12. Hydrocarbons C ₆ 0.1 0.02 0.4 0.1 thirteen. DMF 76.52 75.67 0.5 Sample size 500,0 1960,3 39.7 1,500.0 500,0 1982,0 18.0

Claims (1)

The method of separation of C ₅ hydrocarbons of varying degrees of saturation by extractive distillation in an extractive distillation column using dimethylformamide as an extractant with further desorption from the last pentenes or pentadienes and feeding the desorbed extractant to the extractive distillation column, characterized in that a portion of the hot desorbed extractant is fed to the column mixing with the original hydrocarbons, mixing is carried out in the liquid phase with vigorous stirring and getting hydrochloric mixture is introduced into the column in liquid form.

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