RU2296736C1 - Propene/propane separation process - Google Patents

Abstract

FIELD: petrochemical processes.

SUBSTANCE: invention relates to separation of saturated and unsaturated hydrogenation-hydrocarbon, in particular propane and propene contained in starting hydrocarbon blend. Process is carried out in vertical countercurrent contact zone, wherein stream with elevated concentration of propene is withdrawn from concentration section and stream with elevated concentration of propane is withdrawn from exhausting section connected to boiler. Separation is effected in presence of hydrocarbon diluent containing mainly one or several saturated C₄-C₁₀-hydrocarbons having boiling point at least by 30°C above that of propane. Preferred content of the diluent in liquid phase ranges from 20 to 90 wt %. Separation is accomplished through rectification and/or selective absorption with partial stripping of stream in boiler, stripped fraction being recycled into rectification or absorption zone. C₂-Hydrocarbon impurities and diluent are separated in additional rectification zones.

EFFECT: reduced operational expenses and improved separation efficiency.

12 cl, 2 dwg, 8 ex

Description

The invention relates to the field of separation of propene and propane contained in a hydrocarbon mixture, possibly also containing partially other hydrocarbons. In particular, the invention relates to the field of separation of concentrated propene from a hydrocarbon mixture comprising at least propane and possibly hydrocarbons with higher boiling points.

Known [I.R. Cherny. "The production of raw materials for petrochemical syntheses", M., Chemistry, 1983, S. 79-81]. The method of separation of propene and propane by conventional distillation in highly effective distillation zones, in which propene having a lower boiling point (its normal boiling point at a pressure of 1 bar, T _kn = 42.1 ° C) is isolated as or in the composition of the distillate, and more high-boiling propane (its T _kn = 44.1 ° C) is isolated as or in the composition of the bottom residue.

A clear separation of propene and propane and obtaining highly concentrated propene requires distillation zones with an extremely large number of plates (200 or more) and very large reflux numbers (18-20). Usually, such a large number of plates cannot be provided in one distillation zone (column) and 2 or 3 columns are used for separation, connected by countercurrent flows of liquid and steam so that they together serve as one very large distillation column. The process requires very high capital and energy costs.

The reason for the difficulty of separation by conventional distillation is deviations from ideality (Raul's law) in the propene-propane system formed by hydrocarbons of varying degrees of unsaturation (with a different number of multiple bonds in the molecules). These deviations, usually expressed by the values of activity coefficients (γ), are comparable with the ratio of the vapor pressure of pure propene (P ° _PE ) and propane (P ° _PA ). This ratio at 40 ° С is 1.20, however, at a high concentration of propene, the value of γ _{PA is} ≈1.13 (in this case, γ _PE ≈ 1). As a result, the value of the relative volatility (α _{PE / PA} ) of propene and propane, defined by the equation:

at a high concentration of propene (which corresponds to the top of the distillation zone) is only 1.06-1.07, i.e. is very low.

Known [S.Yu. Pavlov. "Isolation and purification of monomers for synthetic rubber." L., Chemistry, 1987, p.51-75] a method for the separation of hydrocarbons that differ in the number of multiple bonds in the molecules by extractive distillation in the presence of highly polar solvents (extractants). At the same time, the relative volatility of more saturated hydrocarbons, which are isolated as (or in the composition) of the distillate, increases. In relation to the propene-propane system, the use of polar extractants would mean to select higher boiling hydrocarbon-propane into the distillate, which requires additional costs. The processes of extractive distillation with polar agents are complex, leading to contamination of products with impurities of the extractant and products of its decomposition and / or hydrolysis. Working with polar extractants requires cleaning them from accumulating impurities, which further complicates the process.

The purpose of the invention is to propose a method for the separation of propene and propane, not requiring an excessively large number of plates and high energy consumption during rectification, not associated with the use of expensive polar extractants.

We found that it is possible to significantly increase the relative volatility (α _{PE / PA} ) and reduce separation costs if vapor-liquid separation is carried out in the presence of saturated hydrocarbon (s) with a boiling point of at least 30 ° C higher than that of propane.

We declare: A method for separating a hydrocarbon mixture comprising predominantly propene and propane by distillation with the outlet of a stream having an increased concentration of propene as distillate from the upper part of the distillation zone and with the outlet of a stream with an increased concentration of propane relative to the sum of C ₃ hydrocarbons from the bottom distillation zone, in which the distillation is carried out in the presence of a hydrocarbon diluent containing mainly one or more saturated hydrocarbons with a boiling point at least 30 ° C higher than the boiling point of propane.

As dependent on this method, we also declare methods in which:

- in most of the specified zone (s) of contact (zones) in the liquid phase support from 20 to 90 wt.% the specified diluent;

- as or in the composition of the specified diluent use saturated (e) hydrocarbon (s) with the number of carbon atoms from 4 to 10;

- the mixture to be separated is fed into the section (s) separated by at least 10 theoretical plates from the input of the indicated diluent and at least 8 theoretical plates from the output of the stream with an increased relative concentration of propane;

- in the presence of the specified diluent, the separation of propane and propene is carried out by distillation and / or selective absorption with partial stripping in the boiler of the stream returned to the specified rectification or absorption zone;

- said hydrocarbon diluent is fed to the upper part of said contact zone and / or to the condensation zone of at least a part of the steam stream removed from it and / or to the upper part of the additional absorption zone connected to said contact zone by gas and liquid flows;

- the output stream with a high concentration of propene is subjected to separation from the impurity of the diluent and / or separation from the impurity of C ₂ hydrocarbons in the additional distillation zone (s);

- from the bottom of the exhaustive part of the contact zone, a stream containing the indicated diluent, a large part of the propane and a smaller part of the propene supplied with the mixture to be separated is withdrawn, C ₃ hydrocarbons are distilled from the specified stream in an additional distillation zone, the bottom residue containing mainly the specified diluent, which is preferably recycle to the specified contact zone and / or the condensation zone of the steam stream removed from it and / or absorption connected to the specified contact zone hydrochloric zone;

- from the exhaustive part of the contacting zone, a side stream is withdrawn containing most of the propane coming from the initial hydrocarbon mixture, which is preferably distilled off from the diluent in an additional distillation zone, and a stream containing mainly said diluent, which is preferably recycled to the specified contacting zone, is removed from below and / or a condensation zone of the steam stream removed from it, and / or an absorption zone connected to said contacting zone;

- as a diluent, a mixture of hydrocarbons is used, which differ in boiling points by at least 25 ° C, the diluent, during or after distillation of C ₃ hydrocarbons from it, is divided into low-boiling and high-boiling parts, which are recycled separately, and the higher-boiling part of the diluent is fed to the section less spaced from the outlet of the stream having an increased concentration of propene;

- in the process of rectification of C ₃ hydrocarbons from a diluent, its low-boiling part is withdrawn as side extraction below the power supply, and the high-boiling part of the diluent is withdrawn as bottoms;

- as the product receive propene concentration above 97 wt.%, preferably above 99.9 wt.%.

The term "countercurrent vapor-liquid contacting zone" used in claim 1 of the claims and hereinafter means a zone with a certain technological function (separation of propene and propane), in which the flow of liquid from the top of the zone and the stream of steam from the bottom in the presence of the necessary mass transfer devices are contacted . This does not mean counterflow in each of the mass transfer devices present in the zone, but refers specifically to the counterflow in the zone as a whole. The zone of countercurrent vapor-liquid contacting is not necessarily implemented in a single apparatus (column). It is possible to use two or more columns connected in such a way that the vapor stream from the top of one ("lower") column enters another column from below, and the liquid stream discharged from the bottom of the indicated other ("upper") column enters the top of the specified "lower" columns, etc. Together, such columns function as a single separation zone. These columns are not necessarily located one above the other (for example, they can be on the same level). In this case, the terms “lower” and “upper” are understood precisely in the functional meaning.

Zones in which technological functions are carried out beyond the concentration of diluent and C ₃ hydrocarbons defined by claim 2: the separation of C ₃ hydrocarbons from the diluent, the initial absorption stage, etc., are understood as additional zones not directly related to the specified ( f) zone (s) of separation of propene and propane.

The specified diluent may contain, in addition to saturated hydrocarbons, other substances (unsaturated hydrocarbons, alcohols, etc.) in a limited amount, so that their presence does not reduce α _{PE / PA} below 1.12 (preferably not lower than 1.15).

The essence and application of the invention is illustrated by figures 1-2 and examples 1-8. These figures and examples do not exhaust the possible applications of the invention, subject to the essence of the invention set forth in paragraph 1 of its claims.

According to figure 1, the separation of the original hydrocarbon mixture, comprising mainly propene and propane, is carried out in zone K-1. The initial hydrocarbon mixture is fed through line 1. The hydrocarbon diluent obtained by combining the fresh diluent stream introduced through line 2 and the circulated diluent fed through line 11 is sent along line 3 and then along lines 3a and / or 3b to zone K-1 above the supply of the shared hydrocarbon mixture and / or via line 3c to the vapor condensation zone from the top of the column.

A vapor stream is discharged from the top of the K-1 column through line 4, which, after adding diluent via line 3c, is subjected to at least partial condensation. In case of incomplete condensation, the non-condensed stream is withdrawn through line 5, the condensate, at least partially, is withdrawn through line 6a as a distillate, and its remaining amount is returned to zone K-1 as reflux. It is possible that water is expelled from the condensate in a separator-settler. Possibly, from the exhaustive part of zone K-1, a side stream is withdrawn along line 7, which is fed to the distillation zone K-2.

The bottom residue of zone K-1 is withdrawn along line 8 and then sent along line 8a to the distillation zone K-2 to separate predominantly propane from the diluent and / or (if the propane-containing stream is withdrawn through line 7) along line 8c and further along line 11, recycle to the distillate of the distillation column K-2 (if used), containing the main amount of propane coming from a shared hydrocarbon mixture, withdrawn through line 9a and / or line 9b, and still bottoms containing mainly diluent are withdrawn through line 10 and then along lines 11, 3, 3a or 3b as diluent to the K-1 zone and / or along line 3c to the condensation zone. Part of the bottoms product K-2 can be removed from the system through line 11b to prevent the accumulation of impurities in the circulating diluent.

The distillate of zone K-1, containing the main amount of propene, can be sent via line 6c to an additional distillation zone K-3 to separate from higher boiling components, mainly from a diluent, as a distillate of zone K-3, a stream containing mainly propene, and the bottom residue of zone K-3 (mainly diluent) is withdrawn via line 14 and preferably recycled to zone K-1 and / or the condensation zone (lines 11, 3, 3b).

The hot diluent circulated through line 11 can be fully or partially used to supply heat to zone K-1 through a heat exchanger-boiler (line 11).

According to figure 2, the separated mixture is fed through line 1 to the column K-1. A high boiling part of diluent is fed to the top of the K-1 column through line 3 or into a counter-flow column K-1A connected to it through line 3a, and a low-boiling part of diluent is fed through line 7 below the inlet of stream 3 or through line 7a below the inlet of stream 3a. The loss of diluent is compensated by feeding it through line 2.

On top of K-1 or K-1A, a steam stream 4 or 4A enriched in propene is discharged through the heat exchanger through line (s) 5a and / or 5b as a product. It is possible that part of the condensate is returned to K-1 or K-1A, respectively (in K-1A - along line 6).

Bottom from K-1 output stream 8 (diluent propane and, possibly, partially propene), which is fed into the column K-2.

On top of K-2, a stream containing propane, partially propene, and, possibly, in a limited amount, a low-boiling part of the diluent is withdrawn via line 9. A stream containing a high boiling part of the diluent (in this case, the light part of the diluent is withdrawn as side extraction along line 11) or a mixture of low boiling and high boiling parts of diluent is discharged from K-2 from line K below.

If a mixture of low-boiling and high-boiling parts of a diluent is withdrawn via line 10, then the mixture is fed to a K-3 column. If the high boiling part of the diluent is withdrawn via line 10, then it is recycled along line 10a and then along line 3 to K-1 or K-1A.

If a K-3 column is used, then distillate containing mainly the low-boiling part of the diluent, which is further recycled to K-1 through line 7 or 7a, is discharged on top of it. Bottom K-3 through line 13 remove the high-boiling part of the diluent, which is then recycled through line 3 to K-1 (input above the input of stream 7) or K-1A.

In the following examples, for brevity, use the conventions:

F (stream 1) is the initial (separated mixture), D is the distillate, W is the bottoms stream (residue), R is the reflux ratio (the ratio of the reflux returned to the distillate selection), TT are theoretical plates, the plate counting is carried out when designating the feed. from top to bottom, the efficiency is the efficiency of the plates. Concentrations are indicated everywhere in mass percent (indicated by%).

As the boiling point temperature (T _c ) of the components, their normal (at 1 ata) boiling points (in ° C) are indicated. For columns: P _in - top pressure, T _in - top temperature, T _to - cube temperature.

Example 1

The separation of the propene-propane mixture F (75% propene, ~ 25% propane) is carried out according to figure 1. The K-3 column is not used. Of the dashed lines, 3a, 6b, 8a, 10, 11b are used.

Column K-1 has 55 TT (73 prakt. Plates with efficiency = 75%), column K-2 - 20 TT. The reflux ratio in K-1 is R = 4.5; in K-2 - R = 4.

The diluent (P) is n.pentane, Т _к = 36.1 ° С. It is fed into a section that is 7 TT apart from the top; its concentration in the liquid on most plates is maintained below the feed P - 60-70%. In K-1: P _in = 16.5 ata, T _in = 41 ° C, T _to = 142 ° C; in K-2: P _in = 14.0 ata, T _in = 41 ° C, T _to = 183 ° C.

The distillate D1 is removed via line 6a in an amount of 0.74 kg / h. It contains 99.8% propene and 0.2% propane. Below K-1 (line 8), a stream containing 96.7% of diluent, 3.2% of propane and less than 0.1% of propene, which is fed to K-2, is withdrawn in an amount of 7.8 kg. On top of K-2, a flow of 9a (desorbate) containing 96.5% propane, ~ 3% propene and 0.5% N is withdrawn in an amount of 0.26 kg / h. pentane.

Example 2 (comparative)

The separation of the propene-propane mixture F (75% propene, 25% propane) is carried out by conventional distillation.

The distillation column (serial connection of 3 columns with countercurrent flows of liquid and vapor) has 200 TT. The reflux number is 20. P _in = 17.0 ata, T _in = 42 ° C, T _to = 56 ° C.

The amount of distillate is 0.75 kg / h (99.1% propene, 0.9% propane).

The amount of bottoms - 0.25 kg / h (96% propane, 4% propene).

Example 3 (comparative)

The separation of the propene-propane mixture F (75% propene, 25% propane) is carried out by conventional distillation.

The distillation column has 75 TT, R = 4.5, P _in = 17.0 ATA, T _in = 40 ° C, T _to = 51 ° C.

The amount of distillate is 0.81 kg / h (90.6% propene, 9.4% propane).

The amount of bottoms 0.19 kg / h (89.7% propane, 10.3% propene).

It can be seen from examples 2 and 3 that the known rectification method either requires extremely large columns and reflux numbers for the separation of concentrated propene, i.e. it is expensive (example 2), or with a moderate number of plates in the column and a moderate reflux number, it is unable to provide the necessary clarity of separation (example 3).

Example 4

The separation of the propene-propane mixture (75% propene, 25% propane) is carried out according to figure 1 similarly to that specified in example 1 (the same diluent, the same number of plates, flow rates of reflux streams in K-1 and K-2 and the concentration of diluent on the plates of the column separation of propene from propane).

In contrast to the example, the diluent is fed into the condensation system of the steam stream discharged from above from K-1. For the subsequent separation of the stream, containing mainly propene, from the impurity of the diluent, an additional distillation column K-3 is used. By supplying a diluent in the condensation system in column K-1 minimal support pressure (P _a = 8.1 atm) and, respectively (with the same _T = 41 ° C) significantly lower temperature on the trays K-1 and its cube (T _k = 100 ° C).

1.73 kg / h of a stream containing 30.97% propene, 0.03% propane, 69.0% N are discharged through line 6a (hereinafter 6c). pentane.

At the top of the K-3 column, 0.74 kg / h of distillate containing 99.9% propene and 0.1% propane are discharged. Bottom K-3 output 0.99 kg / h n. pentane (recycle to the condensation system of steam withdrawn from the K-1 column.

As a desorbate, ~ 0.26 kg / h of a stream containing 96.6% propane, ~ 2.9% propene and 0.5% N are removed from K-2. pentane.

Example 5

The separation of the propene-propane fraction containing 74.2% of propene, 24.9% of propane and 0.9% of hydrocarbons C ₂ (mainly ethylene and ethane) is carried out. The separation is carried out under conditions practically similar to those described in example 1.

0.74 kg / h of a stream containing 98.7% propene, ~ 0.1% propane, 1.2% C ₂ hydrocarbons, which are fed to an additional K-3 column through line 6b, is discharged through line 6a.

On top of K-3 (stream 13), 0.09 kg / h of distillate containing 90.5% C ₂ and 9.5% propene are removed. Bottom K-3 output 0.65 kg / h of stream 14 containing 99.9% propene and 0.1% propane.

Example 6

The C ₃ fraction containing 39% propene, 58% propane and 3% C4 hydrocarbons (mainly isobutane) is subjected to separation. The separation is carried out according to figure 1. Dotted lines 3a, 6a, 6b, 8b are used. Thinner - n. butane (T _c = -0.6 ° C). Column K-1 has 70 TT (93 prakt. Plates at an efficiency of ≈75%). On the plates of the column below the supply of diluent (line 3A) in the liquid, the concentration of diluent is maintained at 40-50%. Reflux value 7. Supply of diluent 2.22 kg / h. P _in = 16.5 ata, T _in = 41 ° C, T _to = 100 ° C.

0.40 kg / h, containing 97% propene, 2.9% propane, 0.1% n butane, is removed via line 6a. 2.82 kg / h of a stream containing 20.1% propane, 0.1% propene, 78.7% N butane, 1.1% isobutane are discharged from line 8b below.

Example 7

Separate the C ₃ fraction containing 40% propene and 60% propane. The separation is carried out according to figure 1. Of the dashed lines, 3a, 6b, 7, 8c are used. The diluent - cyclohexane (with an admixture of hexanes) (T _c = 80.6 ° C) is supplied via line 3 in an amount of 3 kg / h

Column K-1 has 70TT (93 prakt. Plates with efficiency = 75%), R = 6.0.

On the plates of the K-1 column (below the diluent supply), a diluent concentration of 50-60% is maintained. P _in = 15 ata, T _in = 37 ° C, T _to = 215 ° C.

On top of K-1, 0.41 kg / h of distillate is removed, containing 97.1% propene and 2.9% propane.

A line-side stream containing 96.0% propane, 0.5% propene and 3.5% cyclohexane is withdrawn via line 7 in an amount of 0.61 kg / h.

Bottom K-1, through line 8, 2.98 kg / h of solvent are withdrawn (mainly cyclohexane), which is then recycled along lines 8b, 11, 11b, 3a to the K-1 column.

Alternatively, stream 7 is subjected to rectification from cyclohexane in a K-2 column (11 TT) and distillate containing 99.5% propane and 0.5% propene is removed via line 9a in an amount of 0.59 kg / h. The bottom residue (0.02 kg / h of cyclohexane) is added to stream 8c.

Example 8

Separate the propene (70%) - propane (30%) mixture. The separation is carried out according to figure 2. Of the dashed lines, lines 3a, 4a, 5a, 7a, 11 are used (Column K-3 is not used). Thinner - a mixture containing 40% pentanes and 60% hexanes and heptanes (in a ratio of ~ 1: 1).

In the K-1 column - 60 TT, in the K-1A column - 7 TT, in the K-2 column - 20 TT. In the column K-1, the concentration of diluent in the liquid on the plates is maintained at 65-70%. In K-1A: Pb = 18 ata, TV (flow 3a) = 45 ° C. In K-1: Tk = 155 ° C.

On top of K-1A, a stream containing 99.9% propene and 0.1% propane is withdrawn in an amount of 0.75 kg / h from line 5a.

Bottom K-1 output in the amount of 8 kg / h stream 8 containing 96.5% of a mixed diluent and 3.5% propane (with impurities of propene). Stream 8 is fed to a distillation column K-2. In K-2: P _in = 15.0 ata, T _in = 44 ° C, T _to = 182 ° C.

Top K-2 output in the amount of 0.25 kg / h of distillate containing 97.5% propane and 2.5% propene.

Bottom K-2 output in the amount of 4.25 kg / h VAT residue, consisting practically of hexanes and heptanes. The specified stream is recycled to the top of the column K-1A.

A side stream 11 containing 88.6% of a mixture of pentanes and 11.4% of a mixture of hexanes and heptanes was discharged to the side of the K-2 column in an amount of 3.5 kg / h. The specified stream is recycled along lines 11 and 7a to the upper part of the column K-1.

Alternatively, the lateral output (line 11) is not used. Stream 10 from K-2 is fed through line 106 to the K-3 column. On top of K-3, 3.2 kg / h of distillate, which contains mainly pentanes, are discharged, from the bottom of K-3, 4.55 kg / h of bottom residue, which contains mainly hexanes and heptanes, is discharged. In this case, in K-2: T _to = 165 ° C. In K-3: P _in = 1.5 ata, T _in = 44 ° C, T _to = 85 ° C.

Claims (12)

1. The method of separation of propane and propene contained in the original shared hydrocarbon mixture in the vertical zone (s) countercurrent vapor-liquid contact with the output from the reinforcing part of the stream having an increased concentration of propene, and the conclusion from the exhaustive part connected to the boiler, the stream having an increased relative concentration of propane in the amount of C ₃ hydrocarbons, in which the separation is carried out in the presence of a hydrocarbon diluent containing predominantly saturated (e) hydrocarbon (s ) with a boiling point of at least 30 ° C higher than the boiling point of propane. 2. The method according to claim 1, in which in most of the specified (s) zone (s) of contact in the liquid phase support from 20 to 90 wt.% The specified diluent. 3. The method according to claim 1, in which as or in the composition of the specified diluent use saturated (e) hydrocarbon (s) with the number of carbon atoms from 4 to 10. 4. The method according to claim 1, wherein the separated mixture is fed into section (s) separated by at least 10 theoretical plates from the input of said diluent and at least 8 theoretical plates from the output of the stream with an increased relative concentration of propane. 5. The method according to claim 1, in which in the presence of the specified diluent, the separation of propane and propene is carried out by distillation and / or selective absorption with partial stripping in the boiler of the stream returned to the specified rectification or absorption zone. 6. The method according to claim 1, wherein said hydrocarbon diluent is fed to the upper part of the specified contact zone, and / or to the condensation zone of at least part of the steam stream removed from it, and / or to the upper part of the additional absorption zone connected to the specified zone contacting gas and liquid streams. 7. The method according to claim 1, in which the output stream with a high concentration of propene is subjected to separation from the impurity of the diluent and / or separation from the impurity of hydrocarbons C ₂ in the additional distillation (s) zone (s). 8. The method according to claim 1, in which a stream containing said diluent, a large part of propane and a smaller part of propene, supplied with the mixture to be separated, is discharged from the exhaustive part of the contacting zone; C ₃ hydrocarbons are distilled from the specified stream in a distillation zone; a residue containing predominantly said diluent, which is preferably recycled to said contact zone and / or a condensation zone of the steam stream removed from it, and / or connected to said zone ontaktirovaniya absorption zone. 9. The method according to claim 1, wherein from the exhaustive part of the contacting zone a side stream is withdrawn containing most of the propane coming from the initial hydrocarbon mixture, which is preferably distilled off from the diluent in an additional distillation zone, and a stream containing mainly said diluent, which preferably recycled to the specified contact zone, and / or the condensation zone of the steam stream removed from it, and / or the absorption zone connected to the specified contact zone . 10. The method according to claim 1, wherein the diluent is a mixture of hydrocarbons differing in boiling points of at least 25 ° C, the diluent, during or after distillation of C ₃ hydrocarbons from it, is divided into low-boiling and high-boiling parts, which are recycled separately moreover, the higher boiling part of the diluent is fed into a section less spaced from the outlet of the stream having an increased concentration of propene. 11. The method according to claim 1, wherein in the process of rectification of C ₃ hydrocarbons from a diluent, its low boiling part is withdrawn as side extraction below the power supply, and the high boiling part of the diluent is withdrawn as bottoms. 12. The method according to claim 1, in which the product is obtained propene concentration above 97 wt.%, Preferably above 99.9 wt.%.

Images