DISTILLATION DEVICE COMPRISING A COLUMN WHICH HAS THREE OR A PLURALITY OF CELLS IN SERIES THROUGH WHICH FLUID FLOWS AND METHOD FOR DISTILLING OR EXTRACTIVE DISTILLATION BY USE OF THE DISTILLATION DEVICE

Abstract

A distillation device comprising a column for separating a feed stream into a head product stream, a bottom product stream and optionally one or more side extraction streams, having three or more cells in 5 series through which fluid flows, wherein at least the first cell is integrated into the bottom of the column, for multi-stage heating and partial evaporation of the liquid flowing through the cells with the exception of the liquid from the last cell in an evaporation stage.

Claims

1. A distillation apparatus comprising a column for fractionating a feed stream into a tops product stream, a bottoms product stream, and optionally one or more side draw streams, having three or more serially liquid-traversed cells, wherein at least the first cell is integrated into the bottom of the column for multistage heating and part-evaporation of the liquid traversing the cells, with the exception of the liquid from the last cell, in one evaporator stage in each case, wherein liquid from each of the three or more serially liquid-traversed cells with the exception of the last cell, is passed through an evaporator stage and part-evaporated therein to obtain a part-evaporated stream in each case, which is completely or partially supplied to the respective next downstream cell, and wherein a liquid reflux from one or more of the three or more cells, with the exception of the first cell, into a respective immediately preceding cell is provided.

2. The distillation apparatus according to claim I, wherein the heating and part-evaporation is effected by in-process and/or external energy sources.

3. The distillation apparatus according to claim 1, wherein the heating and part-evaporation is effected by mass flows.

4. The distillation apparatus according to claim 3, wherein the mass flows are steam or hot condensate.

5. The distillation apparatus according to claims 1, wherein the heating and part-evaporation of the liquid traversing the first cell is effected using in-process mass flows, and the heating and part-evaporation of the liquid traversing the penultimate cell is effected using external energy sources.

6. The distillation apparatus according to claim 1, wherein all of the three or more serially liquid-traversed cells are integrated into the bottom of the column.

7. The distillation apparatus according to claim 6, wherein three cells are integrated into the bottom of the column.

8. The distillation apparatus according to claims 1, wherein the evaporator stages are heat exchangers.

9. The distillation apparatus according to claim 1, wherein the liquid reflux is designed as a direct liquid overflow over a weir, as an immersed feed or as a siphon.

10. A process for performing a distillation or an extractive distillation using a distillation apparatus according to claims 1, in which a feed stream comprising a plurality of components is fractionated into a tops product stream, a bottoms product stream, and optionally one or more side draw streams.

11. The process according to claim 10 for separating a feed stream into a tops product stream comprising butane(s) and a bottoms product stream comprising butene(s), and optionally butadiene(s) by extractive distillation.

12. The process according to claim 10 for separating a feed stream into a tops product stream comprising butene(s) and optionally butane(s) and a bottoms product stream comprising butadiene(s) by extractive distillation.

13. The process according to claim 11, wherein the process is an extractive distillation for fractionating a reaction mixture from the dehydrogenation of butanes to produce butenes or from an oxydehydrogenation of butanes to produce butadiene.

Description

[0048] In the figures identical reference numerals describe respective identical or corresponding features.

[0049] In particular:

[0050] FIG. 1 shows a schematic representation of a preferred embodiment of a distillation apparatus according to the invention having a bottom divided into three parts, cross-sectional representations for preferred configurations of the dividing walls in the column bottom being shown in FIGS. 1A to 1C;

[0051] FIG. 2 shows a schematic representation of a further preferred embodiment of a distillation apparatus according to the invention having two cells integrated into the column bottom and a third cell III disposed outside the column and configured as a phase separator, further variants for the cell III disposed outside the column K with heat exchanger WT2 (depicted in detail in FIG. 2A) being shown in FIGS. 2B and 2C;

[0052] FIG. 3 shows a schematic representation of a further embodiment for a preferred distillation apparatus having two cells II and III disposed outside the column K;

[0053] FIG. 4 shows a further variant for a preferred distillation apparatus having two cells II and III disposed outside the column K;

[0054] FIG. 5 shows a further variant for a preferred distillation apparatus having two cells II and III disposed outside the column K;

[0055] FIG. 6 shows a schematic representation of a distillation apparatus having column-integrated cells I and III and a cell II disposed outside the column;

[0056] FIG. 7 shows a prior art distillation apparatus with two-stage heating of the liquid from the column bottom in two heat exchangers arranged vertically one on top of the other;

[0057] FIG. 8 shows a schematic representation of a further embodiment of a prior art distillation apparatus with two-stage heating of the liquid from the column bottom in two horizontally serially arranged heat exchangers;

[0058] FIG. 9 shows a schematic representation of a further embodiment of a prior art distillation apparatus having a bottom divided into two parts and

[0059] FIG. 10 shows a schematic representation of a preferred embodiment of a distillation apparatus according to the invention with a bottom divided into three parts.

[0060] FIG. 1 shows a schematic representation of a preferred embodiment of a distillation apparatus according to the invention with a column K for fractionating a feed stream 1 into a tops product stream 2 with a bottoms product stream 3, with three serially liquid-traversed cells I, II and III, wherein all liquid-traversed cells I-III are integrated into the bottom of the column K and are separated from one another by weirs W1, W2. The bottoms stream from the cell I which is first in the direction of flow is withdrawn and supplied to the heat exchanger WT1 in which the stream is heated and partially evaporated to obtain a part-evaporated stream 4 which is supplied to the second cell II. The bottoms stream from the second cell II is likewise withdrawn in liquid form and heated in an external heat exchanger WT2 and partially evaporated and supplied as part-evaporated stream 5 to the third liquid-traversed cell III.

[0061] The cross-sectional representations in the FIGS. 1A-1C each show preferred arrangements for the dividing walls for dividing the column bottom into the three serially arranged liquid-traversed cells I-III: a concentric arrangement of the dividing walls in FIG. 1A, an arrangement in the shape of circle chords in FIG. 1B and an arrangement in the shape of circle radii in FIG. 1C.

[0062] FIG. 2 shows a schematic representation of a further preferred embodiment of a distillation apparatus according to the invention having two cells I and II disposed in the bottom of the column K and a third cell III disposed outside the column K and configured as a separate apparatus, namely as a phase separator. From said cell a vapor stream 6 is once again recycled into the lower region of the column K, above the liquid level therein, and a substream of the liquid is recycled into the cell II integrated into the bottom of the column K.

[0063] FIG. 2A is a detail view of the plant from FIG. 2, namely of the arrangement composed of cell III and the associated heat exchanger WT2.

[0064] This arrangement may be replaced with the alternatives depicted in FIGS. 2B/2C: As an alternative FIG. 2B shows a falling film evaporator having an integrated tube bundle heat exchanger which in this embodiment constitutes the evaporator stage WT1 and a liquid-traversed bottom region which constitutes the liquid-traversed cell III. In this embodiment the liquid flows through the heated tubes of the integrated heat exchanger, partially evaporates, and is divided into a vapor stream 6 and two liquid substreams 7 and 3.

[0065] The embodiment in FIG. 2C shows a kettle evaporator which comprises a tube bundle disposed in a container and corresponds to the evaporator stage WT1. The tubes heated with a secondary heat-transfer medium heat the liquid and partially evaporate said liquid to afford a gaseous stream 6 and two liquid streams 7 and 3 in the region of the kettle evaporator which is separated by a weir from the region in which the tube bundle heat exchanger is disposed.

[0066] FIG. 3 shows a schematic representation of a further preferred embodiment of a distillation apparatus having two cells II and III which are disposed outside the column K and are both phase separators. From the cell II the vapor stream 8 is recycled into the lower region of the column K, above the liquid level therein, and a substream of the liquid, stream 9, is recycled into the column K below the liquid level, into the cell I. From the cell III the vapor stream 6 is likewise recycled into the lower region of the column K, above the liquid level therein, and a substream of the liquid, stream 7, is recycled into the cell II, below the liquid level therein.

[0067] FIG. 4 shows a variant of the embodiment depicted in FIG. 3, wherein the two units which are disposed outside the column K and are each formed from a cell and an evaporator are falling film evaporators. Here the tube bundle heat exchanger of the falling film evaporator in each case forms the evaporator stage (WT1, WT2) and the bottom region of the falling film evaporator forms the liquid-traversed cells II/III. Unlike in the embodiment in FIG. 3, the vapor stream from the cell III is supplied as stream 10 to the cell II above the liquid level therein and not to the column K as in the embodiment in FIG. 3.

[0068] FIG. 5 shows a further preferred embodiment of a distillation apparatus according to the invention having two cells II and III disposed outside the column K and having a common circulation. In this embodiment the complete liquid stream from the cell II is supplied to the second heat exchanger WT2.

[0069] FIGS. 7 and 8 show prior art configurations.

[0070] According to the embodiment depicted in FIG. 7, the column bottom is merely divided into two parts, into two cells I and II, and the bottoms liquid withdrawn from cell I is heated in two stages in two tube bundle heat exchangers arranged one on top of the other. This further increases the in each case considerable height of a corresponding large industrial scale distillation plant to ranges that may become critical for stability reasons.

[0071] The embodiment depicted in FIG. 8 shows a further variant of a prior art distillation apparatus likewise having a column K bottom divided into two parts. The bottoms liquid from the first cell I is supplied in two stages to two serially disposed tube bundle heat exchangers. The biphasic vaporous/liquid mixture needs to be supplied to the second horizontal tube bundle heat exchanger from below and thus enters into the interior of the tube bundle heat transferor via one or more punctiform sites via the cylinder shell. The surface that said mixture flows against expands continuously until it reaches the maximum width corresponding to the diameter of the apparatus, and subsequently contracts again. It is thus not possible to achieve a uniform distribution of the biphasic vapor/liquid mixture for this embodiment.

[0072] The embodiment depicted in FIG. 9 shows a further variant of a prior art distillation apparatus likewise having a column K bottom divided into two parts. The bottoms stream from the cell I which is first in the direction of flow is withdrawn in liquid form. The bottoms stream is applied via a conveying pump to heat exchanger WT1 in which the bottoms stream is heated. The bottoms stream is then decompressed and thus partially evaporated. The thus obtained part-evaporated stream 4 is supplied to the second cell II. The heating medium supplied to heat exchanger WT1 is regenerated extractant 15.

[0073] FIG. 10 shows a schematic representation of a preferred embodiment of a distillation apparatus according to the invention with a column K for fractionating a feed stream 1 into a tops product stream 2 with a bottoms product stream 3, with three serially liquid traversed cells I, II and III, wherein all liquid-traversed cells I-III are integrated into the bottom of the column K and are separated from one another by weirs. The bottoms stream from the cell I which is first in the direction of flow is withdrawn in liquid form. The bottoms stream is applied via a conveying pump to heat exchanger WT1 in which the bottoms stream is heated. The bottoms stream is then decompressed and thus partially evaporated. The thus obtained part-evaporated stream 4 is supplied to the second cell II. The bottoms stream from the second cell II is likewise withdrawn in liquid form. The bottoms stream withdrawn from the second cell II is applied via a conveying pump to heat exchanger WT2 in which the bottoms stream is heated. The bottoms stream is then decompressed and thus partially evaporated. The thus obtained part-evaporated stream 5 is supplied to the third cell III. The heating medium supplied to heat exchanger WT1 is regenerated extractant 15 and the heating medium supplied to heat exchanger WT2 is partially cooled regenerated extractant 16.

Illustrative Embodiments

[0074] The examples which follow relate in each case to an extractive distillation for butanes/butenes separation using an aqueous N-methylpyrrolidone (NMP) solution in a column, as described in WO 2012/117085 A1. Due to a previous absorption step the butanes/butenes are already partially dissolved in an NMP solution and due to a decompression of this solution to a lower pressure the feed (stream 1) into the extractive distillation is biphasic and comprises a gas phase composed predominantly of butanes and butenes and the NMP solution comprising a dissolved butane/butene component.

[0075] It is a requirement of the separation in the extractive distillation column to obtain a tops product stream 2 which comprises 6 mol % of dissolved butenes and butadienes. It is also a requirement that a bottoms product stream be obtained where the fraction of dissolved butenes and butadienes is 82.9 mol % based on the total amount of non-solvent components. This separation is achieved with all variants described hereinbelow.

[0076] The setup was calculated with a simulation program proprietary to BASF (similar to the commercially available simulator ASPEN plus) based on phase equilibrium models. Simulation of the distillation column was performed using the equilibrium step model. The phase equilibria were described using the non-random two-liquid model (Renon H., Prausnitz J. M.: Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures, AlChE J., 14(1), pp. 135-144, 1968).

[0077] The results of the simulation calculation which follow in each case consider a distillation column having 32 theoretical plates (i.e. equilibrium stages). The numbering proceeds from bottom (1) to top (32) and does not include the column bottom. The evaporators are modelled as equilibrium stages. The gas streams from the evaporators, the outlet of which is directly connected to the column, are introduced directly onto plate 1 of the column. The cells are a constituent of gas-liquid separators and are likewise represented as equilibrium stages. Only liquid streams are introduced into these equilbrium stages and gas thus formed is likewise introduced into the column onto plate 1.

COMPARATIVE EXAMPLE 1

[0078] Table 1 gives a summary of the phases, concentrations, temperatures and pressures of the streams corresponding to FIG. 7 according to the prior art (with two serially connected heat exchangers) where the evaporator at the bottom of the column is divided into two evaporators WT1 and WT2 in order to be able to use energy from the regenerated solvent in WT1 before said solvent is cooled further, one part thereof is recycled as solvent for the absorption step and the other part thereof is recycled as stream 13 into the extractive distillation column (see WO 2012/117085 A1).

[0079] At the top of the column (onto the uppermost plate) reflux (stream 14) from the subsequent condensers is fed into the column, said reflux being composed essentially of butane. At a point somewhat lower than this feed point (about 1-3 theoretical plates lower, here: 2) the regenerated aqueous NMP solution is introduced as extractant (stream 13). The liquid fraction of the feed stream (stream 1) is introduced onto plate 18 and the gaseous fraction is introduced onto plate 19.

[0080] The solvent 11 which flows out of the column and is laden with essentially butanes and butenes is mixed with the overflow from cell II and gas thus formed goes onto the lowest plate of the column. The evaporator WT1 is supplied with liquid from cell I. The biphasic (gaseous and liquid) stream 4 needs to be uniformly distributed onto the heat exchanger WT2 to ensure uniform and effective heat transfer. The stream is further heated and partially evaporated in evaporator WT2. The gas phase formed ascends to the first plate of the column and the liquid is passed into cell II. Therein the bottoms product 3 is withdrawn and the excess liquid flows over the weir into cell 1. The liquid circulation rate (mass flow of stream 11) is often of a magnitude such that between 2% and 20% of the stream, in particular 5-15%, is converted into the gas phase in the evaporators.

EXAMPLE 1 (INVENTIVE)

[0081] The streams in the variant according to the invention with partial recycling of the liquid from the cells II and III into the respective preceding cells (I and II) are shown in table 2 which follows and in FIG. 1.

EXAMPLE 2 (INVENTIVE)

[0082] A further inventive variant where only liquid from cell III is partially recycled into cell I is shown in table 3 which follows and in FIG. 6.

[0083] Both variants achieve the same separation as according to the comparative example 1 but do not have the disadvantage that either the biphasic stream needs to be distributed or else the column needs to be made extremely tall due to an arrangement of one evaporator on top of another as vertical evaporators.

[0084] The variants according to the invention have the further advantage that both the inlet temperature and the outlet temperature for the heat exchanger WT1 is lower than in the comparative example 1 although the same amount of heat is transferred. These temperatures are shown in table 4. The variance both at the inlet and at the outlet is more than 10 degrees Kelvin for the variant according to FIG. 1 and about 4 degrees Kelvin for the variant according to FIG. 6. Hence a higher driving temperature gradient is available and transfer of the same amount of heat thus requires a smaller heat-transfer surface area. Alternatively, it would in principle also be possible in these variants either to obtain more heat from the regenerated solvent used for heating, i.e. said solvent could be cooled further or else heat could be recovered from another process stream at a temperature level about 10 degrees lower (for the variant according to FIG. 1).

EXAMPLE 3 (INVENTIVE)

[0085] An extractive distillation process for extracting 1,3-butadiene from a C.sub.4 mixture (butanes, butenes, butadiene, C.sub.4 acetylenes+small amounts of C.sub.3, C.sub.5+ molecules) was simulated for a distillation apparatus according to FIG. 10 with a bottoms product stream (stream 3) of 380 t/h. The temperatures of individual streams are reported below:

[0086] Regenerated extractant 15: 150.4 C.

[0087] Partially cooled regenerated extractant 16: 138.6 C.

[0088] Cooled extractant 17: 90.2 C.

[0089] The bottoms streams were heated from 68 C. to 180 C. in WT1 and from 95 C. to 106 C. in WT2 (the temperatures achieved upon heating relate to the bottoms stream flowing out from the respective heat exchanger prior to the decompression thereof). The temperature of the liquid bottoms product stream 3 was 104 C. On account of the high driving temperature gradients a total area of only 878 m.sup.2 is required for heat transfer.

COMPARATIVE EXAMPLE 2

[0090] Performing the same simulation as for example 3 but with a distillation apparatus according to FIG. 9 showed that under the same criteria (same composition, amount and temperature of the streams flowing in and flowing out) a 13.6% larger area is required for heat transfer.

TABLE-US-00001 TABLE 1 stream 1 1 13 14 11 4 stream type liquid gas liquid liquid liquid liquid from cell I WT1 to column, column, column, column, WT1 WT2 plate 18 plate 19 plate 30 plate 32 temperature C. 55 55 35.308 40.185 82.221 121.002 pressure bar 5.4 5.4 7 5.4 5.41 5.51 flow rate kmol/h 7429 304.4 9452 25.37 22200 21290 mass flow kg/h 524300 16890 681900 1456 1545000 1499000 concentrations unit low boilers mol/mol 0.002171 0.067389 0.000027 0.018012 0.000078 0.000062 C5+ mol/mol 0.000754 0.000196 0.00076 0.00016 0.000824 0.000816 butanes mol/mol 0.052575 0.637443 0 0.91135 0.012787 0.005979 butenes (inc. mol/mol 0.043933 0.284611 0.000042 0.062215 0.061195 0.03518 butadiene) H2O mol/mol 0.300366 0.00992 0.332384 0.008228 0.324499 0.332066 NMP mol/mol 0.600202 0.000441 0.666785 0.000035 0.600616 0.625897 stream 4 8 8 5 3 stream type gas liquid gas gas liquid from WT1 WT2 WT2 column, cell II plate 32 to WT2 cell II column, plate 1 temperature C. 121.002 148.346 148.346 49.375 148.346 pressure bar 5.51 5.41 5.41 5.3 5.41 flow rate kmol/h 911.5 20477 1722 622.4 16590 mass flow kg/h 46700 1467700 77270 35150 1189000 concentrations unit low boilers mol/mol 0.000451 0.000054 0.000369 0.058598 0.000054 C5+ mol/mol 0.001001 0.000769 0.001475 0.000151 0.000769 butanes mol/mol 0.171766 0.00387 0.118826 0.873327 0.00387 butenes (inc. mol/mol 0.668687 0.022766 0.518169 0.060001 0.022766 butadiene) H2O mol/mol 0.147818 0.323807 0.332736 0.007893 0.323807 NMP mol/mol 0.010276 0.648735 0.028424 0.000033 0.648735

TABLE-US-00002 TABLE 2 stream 1 1 13 14 11 4 stream type liquid gas liquid liquid liquid liquid from cell I WT1 WT1 to column, column, column, column, WT1 cell II plate 18 plate 19 plate 30 plate 32 temperature C. 55 55 35.308 40.185 67.023 110.016 pressure bar 5.4 5.4 7 5.4 5.41 5.41 flow rate kmol/h 7429 304.4 9451 25.37 19460 18190 mass flow kg/h 524300 16890 681800 1456 1355000 1287000 concentrations unit low boilers mol/mol 0.002171 0.067389 0.000027 0.018012 0.000091 0.000065 C5+ mol/mol 0.000755 0.000197 0.000761 0.00016 0.000795 0.000794 butanes mol/mol 0.052575 0.637442 0 0.91135 0.021143 0.007906 butenes (inc. mol/mol 0.043933 0.284611 0.000042 0.062213 0.081794 0.040048 butadiene) H2O mol/mol 0.300365 0.00992 0.332384 0.008228 0.309476 0.323995 NMP mol/mol 0.600201 0.000441 0.666784 0.000035 0.5867 0.627191 stream 4 8 8 5 5 3 stream type gas liquid liquid gas gas liquid from cell II WT2 column, cell III plate 32 to column, WT2 column, plate 1 plate 1 temperature C. 110.016 113.016 148.342 148.342 49.375 148.342 pressure bar 5.41 5.41 5.41 5.41 5.3 5.41 flow rate kmol/h 1270 18680 18091 589.8 622.4 16590 mass flow kg/h 67210 1323000 1296600 26470 35150 1189000 concentrations unit low boilers mol/mol 0.000473 0.000064 0.000054 0.000369 0.0513598 0.000054 C5+ mol/mol 0.000813 0.000792 0.00077 0.001477 0.000151 0.00077 butanes mol/mol 0.210724 0.0075 0.00387 0.118832 0.873326 0.00387 butenes (inc. mol/mol 0.679686 0.038412 0.022767 0.518198 0.06 0.022767 butadiene) H2O mol/mol 0.101526 0.324087 0.323806 0.332703 0.007893 0.323806 NMP mol/mol 0.006779 0.629145 0.648733 0.028421 0.000033 0.648733

TABLE-US-00003 TABLE 3 stream 1 1 13 14 11 12 stream type liquid gas liquid liquid liquid liquid from cell I B1, cell II to column, column, column, column, WT1 WT2 plate 18 plate 19 plate 30 plate 32 temperature C. 55 55 35.308 40.185 78.65 117.38 pressure bar 5.4 5.4 7 5.4 5.41 5.51 flow rate kmol/h 7429 304.4 9450 25.37 22110 21140 mass flow kg/h 524300 16890 681800 1456 1550000 1500000 concentrations unit low boilers mol/mol 0.002171 0.067389 0.000027 0.018012 0.00008 0.000063 C5+ mol/mol 0.000755 0.000197 0.000761 0.00016 0.000795 0.00079 butanes mol/mol 0.052575 0.637443 0 0.91135 0.015456 0.00715 butene,s (inc. mol/mol 0.043933 0.284611 0.000042 0.062215 0.06447 0.036904 butadiene) H2O mol/mol 0.300365 0.00992 0.332384 0.008228 0.315461 0.32406 NMP mol/mol 0.600201 0.000441 0.666784 0.000035 0.603737 0.631034 stream 8 5 5 2 3 stream type gas liquid gas gas liquid from B1 WT2 WT2 column, cell III plate 32 to column, cell III column, plate 1 plate 1 temperature C. 117.38 148.342 148.342 49.375 148.342 pressure bar 5.51 5.41 5.41 5,3 5.41 flow rate kmol/h 970.3 20540 603.1 622.4 16590 mass flow kg/h 50430 1472200 27070 35150 1189000 concentrations unit low boilers mol/mol 0.000456 0.000054 0.000369 0.058598 0.000054 C5+ mol/mol 0.000911 0.00077 0.001477 0.000151 0.00077 butanes mol/mol 0.196414 0.003869 0.118833 0.873326 0.003869 butene,s (inc. mol/mol 0.66508 0.022768 0.518202 0.06 0.022768 butadiene) H2O mol/mol 0.128118 0.323806 0.332698 0.007893 0.323806 NMP mol/mol 0.009021 0.648733 0.028421 0.000033 0.648733

TABLE-US-00004 TABLE 4 WT1 WT2 variant Tin/ C. Tout/ C. Tin/ C. Tout/ C. FIG. 7 82.2 121.0 121.0 148.3 FIG. 1 67.0 110.0 110.0 148.3 FIG. 6 78.7 117.4 117.4 148.3

LIST OF REFERENCE NUMERALS

[0091] 1, 13, 14 feed streams

[0092] 2 tops product stream

[0093] 3 bottoms product stream

[0094] 4, 5 part-evaporated streams

[0095] 6, 8, 10 vapor streams

[0096] 7, 9, 11, 12 liquid substreams

[0097] 15, 16, 17 regenerated extractant streams

[0098] K column

[0099] WT1, WT2 heat exchangers

[0100] W1, W2 weirs

[0101] I, II, III liquid-traversed cells