RU2246475C2 - Method for separating c5-hydrocarbon fractions with different degree of saturation - Google Patents

Abstract

FIELD: petroleum chemistry, chemical technology.

SUBSTANCE: fractionation is carried out in two columns. The parent raw is fed on the second column top, in line of its phlegm and isoprene fraction is removed from the second column top and fed its to the first column. Piperylene fraction is removed from the second column vat and isoprene is removed from the first column top, and isoprene-amylene faction is removed from this column vat that is fed for extractive fractionation. Invention provides reducing energy consumptions, enhancing quality of separation products and reducing their losses.

EFFECT: improved separating method.

2 dwg, 6 tbl

Description

The invention relates to the separation of C ₅ hydrocarbons of varying degrees of saturation, in particular pentenes and pentadienes contained in fractions of various origin (dehydrogenation, pyrolysis of hydrocarbons, etc.), and can find wide application in the synthetic rubber industry in the production of the main monomer isoprene.

A known method for the separation of C ₅ hydrocarbons obtained by dehydrogenation of hydrocarbon feeds by sequential 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 isoprene by extractive distillation and further concentration of isoprene by distillation from cyclopentadiene and piperylene and heavy.

Closest to the invention in technical essence is a method for the separation of C ₅ hydrocarbons of varying degrees of distillation saturation, which is carried out first in two distillation columns, then in an e.p. and desorption column. Light and heavy hydrocarbons are separated in distillation columns. The final separation is carried out in the column er and in the desorption column. Distillation and desorption columns have 60 plates each, an er column - 150. The mode of the first distillation column is as follows: the temperature of the cube is 80 ° C, the reflux ratio is 1, the top pressure is 1.5 kg / cm, the second is 90 ° C, 1 and 2, respectively, 1.1 (SU 804620 A, 02/18/1981 ) The raw material obtained after the extractive distillation process (stream I in an amount of 100%) enters column 1 on 16 to 20 plates. The column has 150 plates. The recycle fraction from the top of column 2 (stream II) is fed to the same 16–20 plates in an amount of 50% of the main stream I. From the top of column 1, up to 47% weight is taken. isoprene - rectified (stream III), and up to 53% of the weight is removed from the cube of column 1. from all raw materials and fed into the column 2 to 36 - 38 plates for further separation.

From the top of column 2, an isoprene fraction is taken into column 1 in an amount of 62.5% by weight. from introduced into the column 2 raw materials. Column 2 has 150 cap plates. From the 75th plate from the so-called lateral selection isoprene - amylene - piperylene fraction (stream VI) is removed for extractive distillation in an amount of 25% by weight. From the cube of column 2, the piperylene fraction is removed in an amount of 12.5% by weight. (stream V).

DISADVANTAGES OF THE EXISTING METHOD

1. The withdrawal of a large amount of piperylene (up to 25% by weight) for extractive distillation from the so-called lateral extraction (75 K-2 plate) and again its return to the rectification columns with flow I, which interferes with the normal process of extractive distillation and rectification itself.

2. The high content of piperylene in the raw material, which requires additional energy consumption.

3. Significant losses of isoprene (5% by weight) and amylene (16% by weight) with piperylene fraction removed from the bottom of the column 2.

The proposed method of rectification is as follows. Initially, the feed stream I (in an amount of 100% by weight) is not supplied to K-1, but to the top of K-2 in the reflux line to the 150th plate. This allows you to free the raw materials before the main distillation in K-1 from C ₆ and heavy, piperylene and partially from cyclopentadiene, which immediately remain in K-2. From the top K-2 in an amount of 10 - 12% weight. less from stream I, stream II is discharged into K-1 for 40 to 48 plates, as the feed contains less impurities and more isoprene.

As a result, instead of two streams of raw materials, one remains 40% less, but with the same amount of isoprene, the content of which is 8 - 10% higher in stream II compared to stream I.

From the top of K-1, stream III is discharged with a concentration of isoprene of 99.0% by weight, in an amount of 77.77% by weight, which contains less cyclopentadiene and amylene. Stream IV is removed from K-1 cubes, but it is not supplied to K-2 for 36-38 plates, but for extractive rectification instead of stream VI from K-2 side selection. At the same time, more amylene (up to 46% weight. Instead of 17 - 35% weight.) Is removed for extractive rectification. See tables 3-6 of figure 1 and figure 2.

From the cube K-2, flow V is removed, which already contains isoprene up to 1% weight. instead of 5% weight. and amylene up to 4% weight. instead of 16% weight. At the same time, the consumption of energy resources (electricity) is reduced due to the elimination of the side extraction unit and when replacing a pump with more power with less power when pumping the IV stream.

OBJECT OF THE INVENTION

Reducing energy consumption, increasing the efficiency of the separation process and reducing the number of flows due to changes in the supply of raw material flows to columns 1 and 2.

This goal is achieved by the fact that rectification is carried out both by changing the feed flow of raw materials, and by the height of the columns, which allows to reduce the amount of raw material supplied to K-1 by 40% with the same amount of the main isoprene product. This is due to the fact that stream I is not supplied to column 1, but to the top of K-2 in the reflux line, and the raw material for column 1 is stream II, that is, from two streams I and II (raw material + recycle fraction), one stream II, which is supplied to column 1 for 40 to 48 plates, since the amount of isoprene increased in it and the amount of ballast (piperylene and heavy C ₆ ) decreased. Heavy, niperylene and partially cyclopentadiene immediately remain in K-2 and do not interfere with the rectification process in K-1. Isoprene is an amylene fraction remaining in cube 1 (stream IV) and up to 20% by weight. from raw materials, it is removed immediately to extractive distillation, which contains up to 46% weight. amylene, and which are immediately removed for extractive rectification instead of stream VI, which eliminates lateral selection from the 75 K-2 plate, which contains up to 25% weight. piperylene, which interferes with both the rectification process and the process of extractive distillation (like ballast).

Changing the feed flow to K-1 and K-2 along the way and in the height of the food plates significantly (both in quantity and quality) changes the composition of the feed flows, which allows to improve the quality of all rectification products, starting from flows II, III, IV and ending with stream VI while reducing energy consumption. Moreover, stream II contains 40% less ballast than flows I and II according to the existing method.

Example 1. Calculate a food plate on K-2.

The task. Calculate the rectification process of a mixture of isoprene-amylene (piperylene + cpd + C ₆ ) to simplify the calculation. Food contains 53% of isoprene, 19% of amylene and 28% of piperylene. The residue contains 0.3% isoprene, 0.9% amylene. The reflux number is 10. The calculation is carried out per 100 kmol of food. The material balance for isoprene will have the following form: 53.29 = D * x ¹ +0.003 R = (100-R) x ¹ +0.003 R = 100x ¹ + (0.003-x ¹ ) R.

Taking into account that x ¹ = 0.73897, we get 53.29 = 73.897-0.73897R. Where from

R = (73.897-53.29): 0.73897 = 27.886, whence D = 100-27.886 = 72.114, where

R is the number of moles of bottoms; D is the number of moles of distillate; x ¹ is the molar fraction of isoprene in the distillate. According to these data, you can create a table of material balance.

TABLE 1 Components Raw materials distillate balance kg kmol % mol kmol % mol kmol % mol 1. Isoprene 8480 124.71 53.29 53,206 73,780 0,084 03 2. Amilen 3040 43,43 18.56 18,309 25,389 0.251 0.9 3. Piperylene 4480 65.88 28.15 0.599 0.831 27,881 98.8 TOTAL: 16000 234.02 100.00 72,114 100,000 27,886 100.0

The amount of flowing reflux at V = 10 is 10 * 72.114 = 721.14 = f.

The amount of steam rising in the column: 721.14 + 72.114 = 793.254 = G.

Для изопрена уравнение будет иметь видConsider the movement of mixture components in a depletion column. The equation of the working line of the column of depletion is

For isoprene, the equation will be

Using this equation, we begin the calculation of the cubic part of the rectification column. Using Raoul’s law, we find the composition of the vapor rising from the cube. To do this, let us set the boiling point in a cube of 75 ° C.

Since the content of the components in the liquid phase of the fifteenth plate is approximately the same as in the nutrient liquid, we accept the supply of power to the fifteenth plate. Having found the number of the food plate, we proceed to the enrichment column. For this part of the column, the relation

where f is the amount of phlegm flowing in the column; G is the number of rising vapors in the column, kmol.

You can also write: 1: (V + 1) = D / G, where D is the amount of distillate, taken per unit, in kmol. Equation (II) can be written as follows: y ¹ = f: Gx ¹ + D: Gx $\genfrac{}{}{0ex}{}{\text{one}}{\text{D}}$ .

Where do we have for isoprene

.Where

.

где

.For amylene

Where

.

где

.For piperylene

Where

.

So, we got that the total number of plates (theoretical) in the column is eighteen.

Therefore, the number of plates in the enrichment column will be 18-15 = 3 pieces. And practically the column has 150 plates, and the food plate should be 150: 18 = 8.33333. 15 * 8.33333 = 125 pieces, that is, 125 plates, but not 36-38 plates. P.S. The theoretical calculation shows the validity of the transfer of the power plate from 36 to 125, and the practical analysis data have excellently confirmed this even when applying power to 113 plates (see table 2).

TABLE 2 ANALYSIS OF PUMPING FROM THE KUBA K-2 - 2500 kg / h Name of components
raw materials. Bic₅N₁₀
(isoamylene) iC₅H₈
(isoprene) nC ₅ H ₈ (piperylene) C ₆ + heavy tars Date and time of sampling
K-450 ₂ % Weight, kg % Weight, kg % Weight, kg % Weight, kg 10/29/83
6 hours sampling submission - 113 plate

10/30/83
6 hours sampling submission - 113 plate

10/30/83
18 hours sampling feed - 113 plate

11/18/83
18 hours - sampling feed - 36 plate

11/19/83
6 hours - sampling feed - 36 plate

11/20/83
18 hours - sampling feed - 36 plate

12/31/83
6 hours - sampling feed - 113 plate

01/02/84
6 hours - sampling feed - 113 plate

01/30/84
6 hours - sampling feed - 113 plate

01/31/84
6 hours - sampling feed - 113 plate

02/10/84
6 hours - sampling feed - 113 plate

02.20.84 g.
6 hours - sampling feed - 113 plate

02/29/84
6 hours - sampling feed - 113 plate

03/10/84
6 hours - sampling feed - 113 plate

03/19/84
6 hours - sampling feed - 113 plate

03/31/84
6 hours - sampling feed - 113 plate

And so on until now unchanged, the supply of raw materials to 113 plates.

EXAMPLE 2. Raw materials in an amount of 100% by weight obtained after extractive distillation (stream I) are fed to a K-1 column for 16-20 plates. The recycle stream II, which accounts for 50% of the main stream I, which is discharged from the top of K-2, is fed to these plates. From the top of K-1, flow III is discharged with a concentration of isoprene of 98.4% by weight. From the K-1 cube, stream IV is removed, which enters the 36th plate in K-2. Isoprene - amylene - piperylene fraction (stream VI) is removed from lateral selection (75 plate) of K-2. From the cube K-2 is derived (stream V), sent to the warehouse and then for burning.

DISADVANTAGES OF THE EXISTING METHOD

The feedstock (stream I) contains a lot of amylene and piperylene, which are displayed on er from lateral selection (75 plate) K-2. Column 1 spins a lot of ballast (amylene, piperylene, C ₆ , heavy), which can be reduced if the side sampling unit is completely removed, and the amylenes are removed from the K-1 cube. Large losses of isoprene (5% wt.) And amylene (16% wt.).

EXAMPLE 3. Raw materials in an amount of 100% by weight obtained after extractive rectification (stream I) are fed to the reflux line for 150 plates in K-2. From the top K-2 in the amount of 90% weight. the isoprene fraction (stream II) is removed in K-1 on 40-48 plates. Isoprene is removed from the top of K-1 - rectified in the amount of 77.77% by weight. (99.0% wt.) - stream III. From cubes K-1 isoprene - amylene - piperylene fraction is removed in an amount of 22.23% by weight. extractive rectification (stream IV). From the K-2 cube, the piperylene fraction (stream V) is removed in an amount of 10% by weight. The compositions of the streams I, II, III, IV, V, VI are shown in tables 1-4.

ADVANTAGES OF THE SUGGESTED RECTIFICATION METHOD

1. The number of feed streams is reduced (instead of 6-5) and the quality of the streams in composition is improved.

2. Reduced electricity consumption by 15%.

3. The quality of isoprene - rectified is increased by reducing the content of cyclapentadiene and amylene in it.

4. The lateral selection unit is excluded from the scheme, which allows to exclude the accumulation of amylene and piperylene in rectification columns and on er blocks.

5. Reduced isoprene loss with 5% weight. up to 1% weight. and amylene with 16% weight. up to 4% weight. with piperylene fraction pumped from the K-2 cube, which leads to the saving of isoprene and amylene.

All this happens due to a change in the supply of raw materials from the underlying plates to higher ones. For example, in the proposed method in K-1, the raw materials must be served on 40-48 plates instead of 16-20 plates according to the existing method, because the raw material in its composition contains more isoprene than vapors rising from the cubes of columns. And in K-2, raw materials are fed immediately to 150 plates instead of 36-38 plates according to the existing method. At the same time, the raw material itself serves as additional reflux, which increases the clarity of separation. Figure 1 and 2 presents a diagram of the existing and proposed methods of rectification.

Using the proposed method allows, by changing the flow of raw materials both in place and in the height of the columns, to reduce the number of flows by eliminating the flow of lateral selection; and there will also be a combination of flows I and II, which leads to the separation of heavy, piperylene and, partially, cyclopentadiene from stream I.

At the same time, the side extraction unit is removed from the circuit, due to which piperylene is accumulated in the systems of rectification and extraction. There is a decrease in energy consumption, the quality of isoprene - rectified is increased due to a decrease in the content of amylene and cyclopentadiene in it, as well as losses of isoprene and amylene with the piperylene fraction pumped from the K-2 cube, which leads to savings in isoprene and amylene and a reduction in heat consumption.

SOURCES OF INFORMATION

1. Copyright certificate SU 804620 A, dated February 18, 1981.

2. V.N.Stabnikov. “Distillation apparatus”. Engineering. M., 1965 365 p.

3.K.F. Pavlov, P.P. Romankov, A.L. Noskov. “Examples and tasks on processes and devices.” Chemistry. L., 1970 624 p.

4. Kasatkin A.G. “The main processes and apparatuses of the chemical industry." M., Chemistry, 1971, 783 p.

FLOW COMPOSITIONS.% WEIGHT. FIGURE 1

Table 3 Name of components The composition of the flows according to K-1 I II III IV % weight kg % weight kg % weight kg % weight kg 1. Isoprene 78.0 15600 83.0 8300 98.4 13776 63,275 10124.0 2. Amilen 10.0 2000 10.0 1000 1,56 218.4 17,385 2781.6 3. JRC 1,0 200 1,0 100 0.04 5,6 1,840 294.4 4. Piperylene 10.0 2000 6.0 600 - - 16.250 2600.0 5. Heavy C ₆ 1,0 200 - - - - 1,250 200,0 TOTAL: 100.0 20000 100.0 10,000 100.00 14000 100.00 16000

Table 4 Name of components Compositions of flows according to K-2 IV II VI V % weight kg % weight kg % weight kg % weight kg 1. Isoprene 63,275 10124 83.0 8300 43.35 1734.0 4,5 90 2. Amilen 17,385 2781.6 10.0 1000 36.29 1451.6 16.5 330 3. JRC 1,840 294.4 1,0 100 3.11 124,4 3,5 70 4. Piperylene 16,250 2600 6.0 600 18.75 690.0 65.5 1310 5. Heavy C ₆ 1,250 200,0 - - - - 10.0 200 TOTAL: 100.0 16000 100.0 10000,0 100.0 4000,0 100.0 2000

STRUCTURES OF STREAMS,% WEIGHT, BY FIGURE 2

Table 5 Name of components Compositions of flows according to K-2 I II V % weight kg % weight kg % weight kg 1. Isoprene 78.0 15600 86.64 15595 0.25 5,0 2. Amilen 10.0 2000 11.06 1990 0.50 10 3. JRC 0.9 180 0.66 120 3.00 60 4. Piperylene 10.1 2020 1,64 295 86.25 1725 5. Heavy C ₆ 1,0 200 - - 10.00 200 TOTAL: 100.0 20000 100.0 18000 100.00 2000

Table 6 Name of components The composition of the flows according to K-1 II III IV % weight kg % weight kg % weight kg 1. Isoprene 86.64 15595 99.5 13930 41,625 1665 2. Amilen 11.06 1990 0.49 68.6 48,035 1921.4 3. JRC 0.67 120 0.01 1.4 2,965 118.6 4. Piperylene 1,64 295 - - 7,375 295.0 5. Heavy C ₆ - - - - - - TOTAL: 100.0 18000 100.0 14000 100.0 4000

Claims (1)

The method of separation of C ₅ hydrocarbon fractions of varying degrees of saturation by distillation in two columns, characterized in that the feed is fed to the top of the second column to its reflux line, the isoprene fraction is taken from the top of the second column and sent to the first column, piperylene fraction is taken from the cube of the second column , isoprene is withdrawn from the top of the first column, isoprenamylene fraction is withdrawn from the cube of this column, directed to extractive rectification.

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