Column with separative installations for separating a mixture of hydrocarbons and/or hydrocarbon derivatives by means of an extractive distillation using a selective solvent

Abstract

What is proposed is a column (K) comprising separatory internals (E) for separating a mixture of hydrocarbons and/or hydrocarbon derivatives (1) by extractive distillation with a selective solvent (2), with supply of the selective solvent (2) in the upper region of the column and supply of the mixture of hydrocarbons and/or hydrocarbon derivatives to be separated (1) below the supply of the selective solvent (2), the selective solvent (2) becoming laden in the column (K) with the components from the mixture to be separated (1) for which it has greater affinity and being withdrawn from the lower region of the column as laden selective solvent (3),
while, by contrast, the components from the mixture to be separated for which the selective solvent (2) has a lower affinity remain in the vapor phase and are withdrawn as top stream (4),
which is completely or partially condensed to obtain a condensate (5),
some of which is withdrawn as product stream (6), the remainder being reintroduced to the column (K) as reflux (7),
wherein said column comprises in the region of the column above the separatory internals (E) a first, substantially horizontal feed pipe (R1) for supplying the selective solvent, wherein the first, substantially horizontal feed pipe (R1) exhibits a cross-sectional narrowing to a narrowest point (V), said pipe widening again downstream of the cross-sectional narrowing, and wherein said column comprises a second feed pipe (R2) for supplying the reflux (7), said pipe joining the first, substantially horizontal feed pipe (R1) in the region of the narrowest point (V) of the cross-sectional narrowing.

Claims

1. A column (K), comprising separatory internals (E) for separating a mixture of hydrocarbons and/or hydrocarbon derivatives (1) by extractive distillation with a selective solvent (2), with supply of the selective solvent (2) in the upper region of the column and supply of the mixture of hydrocarbons and/or hydrocarbon derivatives to be separated (1) below the supply of the selective solvent (2), the selective solvent (2) becoming laden in the column (K) with the components from the mixture to be separated (1) for which it has greater affinity and being withdrawn from the lower region of the column as laden selective solvent (3), while, by contrast, the components from the mixture to be separated for which the selective solvent (2) has a lower affinity remain in the vapor phase and are withdrawn as top stream (4), which is completely or partially condensed to obtain a condensate (5), some of which is withdrawn as product stream (6), the remainder being reintroduced to the column (K) as reflux (7), wherein said column comprises in the region of the column above the separatory internals (E) a first, substantially horizontal feed pipe (R1) for supplying the selective solvent, wherein the first, substantially horizontal feed pipe (R1) exhibits a cross-sectional narrowing to a narrowest point (V), said pipe widening again downstream of the cross-sectional narrowing, and wherein said column comprises a second feed pipe (R2) for supplying the reflux (7), said pipe joining the first, substantially horizontal feed pipe (R1) in the region of the narrowest point (V) of the cross-sectional narrowing.

2. The column (K) according to claim 1, wherein there is a liquid distributor (F) disposed above the separatory internals (E) in the column (K).

3. The column (K) according to claim 1, wherein said column has a diameter of >0.5 m.

4. The column (K) according to claim 1, wherein the ratio of the cross section of the first, substantially horizontal feed pipe (R1) upstream of the cross-sectional narrowing to the cross section of the first, horizontal feed pipe (R1) at the narrowest point (V) of the cross-sectional narrowing is chosen such that the pressure inside the first, substantially horizontal feed pipe (R1) at the narrowest point (V) of the cross-sectional narrowing is lower than the pressure outside the first, substantially horizontal feed pipe (R1) immediately proximal to the narrowest point (V) of the cross-sectional narrowing.

5. The column (K) according to claim 1, wherein the diameter of the first, substantially horizontal feed pipe (R1) upstream of the cross-sectional narrowing is chosen such that the flow velocity in the first, substantially horizontal feed pipe (R1) upstream of the cross-sectional narrowing is in the range of from 0.1 to 5.0 m/s.

6. The column (K) according to claim 1, wherein the second feed pipe (R2) that joins the first, substantially horizontal feed pipe (R1) in the region of the narrowest point (V) of the cross-sectional narrowing preferably protrudes into said pipe by a protrusion depth of from 0.1 to 0.8 times the diameter of the second feed pipe (R2).

7. The column (K) according to claim 6, wherein the second feed pipe protruding into the first, substantially horizontal pipe terminates slantedly at an angle to the longitudinal axis of said second feed pipe in the range of from 4? to 65?.

8. The column (K) according to claim 1, wherein the first, substantially horizontal feed pipe has disposed in it, downstream of the narrowest point of the cross-sectional narrowing and substantially transversely to the longitudinal axis of said pipe, a static mixing element (M) that partially blocks the cross section of said pipe.

9. The column (K) according to claim 8, wherein the static mixing element (M) is spaced apart from the point of the narrowest cross section (V) in the first, substantially horizontal feed pipe (R1) by at least double the diameter of the first, substantially horizontal feed pipe (R1) at the point of the narrowest cross section (V).

10. The column (K) according to claim 8, wherein the static mixing element (M) is eccentrically disposed in the cross section of the first, substantially horizontal feed pipe (R1) and is in contact with the interior wall of said pipe or is close to the wall thereof but in the upper region of the first, substantially horizontal feed pipe (R1) is spaced apart from the interior wall of said pipe.

11. The column (K) according to claim 10, wherein the static mixing element (M) eccentrically disposed in the first, substantially horizontal feed pipe (R1) is in the shape of an annulus.

12. The column (K) according to claim 11, wherein the static mixing element (M) eccentrically disposed in the first, substantially horizontal feed pipe (R1) is in the shape of an annulus which is open at the top, said annulus preferably being secured to the interior wall by means of supports in the upper region of said interior wall.

13. A process for separating a mixture of hydrocarbons and/or hydrocarbon derivatives (1) by extractive distillation with a selective solvent (2) in a column (K) according to claim 1, with supply of the selective solvent (2) in the upper region of the column and supply of the mixture of hydrocarbons and/or hydrocarbon derivatives to be separated (1) below the supply of the selective solvent (2), the selective solvent (2) becoming laden in the column (K) with the components from the mixture to be separated for which it has greater affinity and being withdrawn from the lower region of the column as laden selective solvent (3), while, by contrast, the components from the mixture of hydrocarbons and/or hydrocarbon derivatives (1) to be separated for which the selective solvent (2) has a lower affinity remain in the vapor phase and are withdrawn as top stream (4), which is completely or partially condensed to obtain a condensate (5), some of which is withdrawn as product stream (6), the remainder being reintroduced to the column as reflux (7), wherein the selective solvent (2) is supplied into the upper region of the column above the separatory internals (E) via a first, substantially horizontal feed pipe (R1), wherein the first, substantially horizontal feed pipe (R1) exhibits a cross-sectional narrowing to a narrowest point (V), said pipe widening again downstream of the cross-sectional narrowing, and wherein the reflux (7) is supplied via a second feed pipe (R2) which joins the first, substantially horizontal feed pipe (R1) at the narrowest point (V) of the cross-sectional narrowing.

14. The process according to claim 13, wherein said process is an extractive distillation of C.sub.4 cuts to obtain butanes and/or butenes and/or 1,3-butadiene with a selective solvent selected from N-methylpyrrolidone or mixtures thereof with water, dimethylformamide and acetonitrile or an extractive distillation of aromatics-containing mixtures to obtain benzene and/or toluene and/or xylene.

Description

(1) The invention is more particularly elucidated hereinbelow with the aid of a drawing and working examples.

(2) In the drawing, in particular,

(3) FIG. 1 shows a schematic diagram of a preferred embodiment of a column according to the invention,

(4) FIG. 2 shows a schematic diagram of a preferred embodiment for a first feed pipe, said pipe being substantially horizontally disposed in the column, in the region of the narrowest point of the cross-sectional narrowing in the first, substantially horizontal feed pipe and with a static mixing element downstream of the narrowest point of the cross-sectional narrowing in the first, substantially horizontal feed pipe and

(5) FIGS. 3A and 3B show examples of preferred embodiments of static mixing elements

(6) FIG. 1 shows a preferred embodiment for an inventive column K for performing an extractive distillation of a mixture of hydrocarbons and/or hydrocarbon derivatives 1 by running said mixture in countercurrent to a selective solvent 2 over separatory internals E, with a liquid distributor F disposed above said internals, the selective solvent 2 becoming laden in the column K with the components from the mixture to be separated 1 for which it has greater affinity and being withdrawn from the lower region of the column as laden selective solvent 3 while, by contrast, the components from the mixture to be separated for which the selective solvent 2 has a lower affinity remain in the vapor phase and are withdrawn as top stream 4 which is condensed to obtain a condensate 5, some of which is withdrawn as product stream 6, the remainder being reintroduced to the column K as reflux 7.

(7) The selective solvent 2 is fed into the column via a substantially horizontal feed pipe R1 above the internals E and the liquid distributor F. The substantially horizontal feed pipe R1 has a geometry that induces a Venturi effect, i.e. the feed pipe R1 has a cross-sectional narrowing to a narrowest point after which said pipe widens again, the reflux 7 being aspirated from a second feed pipe R2 in the region of the narrowest point of the cross-sectional narrowing, without the need for a feed pump or static pressure.

(8) The schematic diagram in FIG. 2 elucidates the invention-essential admixing element for admixing the reflux 7 into the selective solvent 2: the selective solvent 2 is supplied via a first feed pipe R1 which exhibits a cross-sectional narrowing to a narrowest cross section V and subsequently widens again. In the region of the narrowest point V of the cross-sectional narrowing, the second feed pipe R2 is arranged through which the reflux 7 is passed and admixed into the stream 2 of the selective solvent. The preferred embodiment shown achieves an additional improvement in mixing quality when a static mixer M is disposed downstream of the narrowest point V of the cross-sectional narrowing and transversely to the main flow direction through the first feed pipe R1.

(9) Preferred geometric configurations for static mixers M are shown in FIGS. 3A and 3B: in the shape of an annulus which is open at the top and is in contact with the lower interior wall of the pipe R1 in FIG. 3A, and in the shape of an eccentrically disposed annulus likewise in contact with the lower interior wall of the first feed pipe R1 but spaced apart from the upper interior wall of said pipe and secured thereto with supports in FIG. 3B.

WORKING EXAMPLES

(10) Into an extractive distillation column K having an internal diameter of 5.33 m is fed, above the separatory internals E and at a mass flow rate of 417 t/h, a stream of selective solvent 2 comprising an N-methylpyrolidone/water mixture having a density of 1013.7 kg/m.sup.3 and a viscosity of 1.179 mPa.Math.s. The reflux 7 introduced at a mass flow rate of 22 t/h comprises a mixture of butanes and butenes having a density of 572.1 kg/m.sup.3 and a viscosity of 0.14 mPa.Math.s.

Comparative Example

(11) For comparison, the extractive distillation column K has a commercially available perforated plate liquid distributor disposed in it above the separatory internals E. In the plane of the openings for issuance of liquid from the liquid distributor, mixing quality X.sub.max/X.sub.av, as defined hereinbelow, has a value of 6.8.

(12) When reporting mixing quality, X.sub.max presently describes the highest value in the measurement zone for the mass fraction of stream 7.

(13) Correspondingly, X.sub.av describes the average value in the measurement zone for the mass fraction of stream 7, i.e. the value to be found in the entire measurement zone in the case of perfect mixing.

(14) Mixing quality is defined by the ratio X.sub.max/X.sub.av. Accordingly, mixing quality is 1 in the case of ideal mixing.

(15) The ratio X.sub.min/X.sub.av is defined analogously, i.e., as the ratio of the lowest value in the measurement zone to the average value in the measurement zone, in each case for the mass fraction of stream 7.

Inventive Examples

Example 1

(16) Admixing apparatus provided above the separatory internals E is a first, substantially horizontally disposed feed pipe R1 exhibiting a cross-sectional narrowing to a narrowest point V, said pipe widening again afterwards. In the region of the narrowest point V of the cross-sectional narrowing, a second feed pipe R2 joins therewith, partially protrudes into the first, substantially horizontal feed pipe R1 and has a slanted end.

(17) The specific measurements are as follows: diameter of the first, substantially horizontal feed pipe R1=304.8 mm, cross-sectional narrowing of the first, substantially horizontal feed pipe R1 extends over a length of 150 mm in the longitudinal direction of said pipe, region of the narrowest point V of the cross-sectional narrowing: extends over 75 mm in the longitudinal direction of the first, substantially horizontal feed pipe R1, diameter at the narrowest point V of the first, substantially horizontal feed pipe R1=130 mm, an adjacent widening to the original diameter of 304.8 mm extending over a length of 480 mm of the first, substantially horizontal feed pipe R1.

(18) In the region of the narrowest point V of the cross-sectional narrowing, a second feed pipe R2 having an internal diameter of 50.8 mm protrudes into the first, substantially horizontal feed pipe R1 to a protrusion depth of 49.2 mm at the upstream end and to a protrusion depth of 29.2 mm at the downstream end, i.e. the second feed pipe R2 is slanted.

(19) The mixing quality values which follow are determined in a measurement zone defined as a cross section of the first, substantially horizontal feed pipe R1 at a distance of 2 m downstream of the downstream-facing end of the narrowest point V of the cross-sectional narrowing:
X.sub.max/X.sub.av equals 1.09 and
X.sub.min/X.sub.av equals 0.85.

Example 2

(20) The setup in Example 2 is the same as the setup in Example 1 except that, in addition, disposed downstream of the feed pipes R1 and R2, there is a static mixing element M corresponding to the schematic diagram in FIG. 3B, which is in the shape of an eccentrically disposed ring and is made of a steel sheet and is of 4 mm in thickness, 260 mm in external diameter and 200 mm in internal diameter, said ring being in contact with the lower interior wall of the first, substantially horizontal feed pipe R1 and being secured to the upper interior wall of said pipe with two supports.

(21) The mixing quality determined in this case is 1.02 for X.sub.max/X.sub.av and 0.99 for X.sub.min/X.sub.av.

LIST OF REFERENCE NUMERALS

(22) Streams:

(23) 1 mixture of hydrocarbons and/or hydrocarbon derivatives 2 selective solvent 3 laden, selective solvent 4 top stream 5 condensate 6 product stream 7 reflux
Apparatuses and Apparatus Parts: K column E separatory internals F liquid distributor R1 first, substantially horizontal feed pipe R2 second feed pipe V narrowest point of cross-sectional narrowing