COLUMN FOR THERMAL TREATMENT OF FLUID MIXTURES, ESPECIALLY THOSE COMPRISING (METH)ACRYLIC MONOMERS

Abstract

The present invention relates to a column (1) for thermal treatment of fluid mixtures, having a cylindrical, vertical column body (2) which forms a column cavity (3), a plurality of trays (8) mounted in the column cavity (3) and spaced apart vertically from one another, at least one stub (11) disposed within the column body (2) and extending away from the column body (2), and a closable inspection orifice (9) formed in the stub (11). The characteristic feature of the column of the invention is that a spray device (20) disposed in the column body (2) can spray liquid (22) at least against the surface (15) of the stub (11) directed into the column cavity (3).

Claims

1. A column for thermal treatment of fluid mixtures, the column comprising: a cylindrical, vertical column body which forms a column cavity, a plurality of trays mounted in the column cavity and spaced apart vertically from one another, at least one stub disposed within the column body and extending away from the column body, and a closable inspection orifice formed in the stub, wherein a spray device disposed in the column body can spray liquid at least against the surface of the stub directed into the column cavity.

2. The column according to claim 1, wherein the spray device has a spray nozzle, an inlet a spray liquid feed device, the spray liquid feed device being designed to draw spray liquid from the column cavity, to feed the spray liquid withdrawn through the inlet to the spray nozzle and to spray it by means of the spray nozzle at least against the surface of the stub directed into the column cavity.

3. The column according to claim 1, wherein the spray liquid feed device has an intake orifice disposed immediately above a tray adjacent to the stub.

4. The column according to claim 1, wherein: the column body forms a vertical inner surface:, and in the case of a vertical cross section of the column the line of the lower line of intersection of the stub directed into the column cavity or a tangent to the line of the lower line of intersection of the stub directed into the column cavity at least in sections forms an angle within a range from 210 to 267 with the vertical inner line of the column body.

5. The column according to claim 4, wherein in the case of a vertical cross section of the column at least 50% of the line of the lower line of intersection of the stub directed into the column cavity or the tangent to 50% of the line of the lower line of intersection of the stub directed into the column cavity forms an angle within a range from 225 to 267 with the vertical inner line of the column body.

6. The column according to claim 4, wherein the stub has an upper half and a lower half and in the lower half the surface of the stub directed into the column cavity or the tangent to the surface of the lower half of the stub forms an angle within a range from 210 to 267 with the vertical inner surface of the column body.

7. The column according to claim 4, wherein the stub is rotationally symmetric about a horizontal axis and the surface of the stub directed into the column cavity or the tangent to the surface of the stub forms an angle within a range from 210 to 267 with the vertical inner surface of the column body.

8. The column according to claim 4, wherein the stub is frustoconical and the surface of the stub directed into the column cavity forms an angle within a range from 210 to 267 with the vertical inner surface of the column body.

9. The column according to claim 1, wherein: the inspection orifice is a manhole orifice which is formed in the stub and can be closed with a cover, at least one of the trays is mounted in the region of the manhole orifice; and a plate is disposed in the region of the stub between the one tray and the closed cover.

10. The column according to claim 9, wherein the entire horizontal cross section of the column at the height of the one tray in the region of the manhole orifice is essentially filled by the one tray and the plate.

11. The column according to claim 9, wherein the one tray in the region of the manhole orifice is a mass transfer tray having orifices and the plate is a mass transfer plate having orifices.

12. The column according to claim 9, wherein the one tray in the region of the manhole orifice and the plate are aligned essentially horizontally.

13. A thermal separation process between at least one gas ascending within the column according to claim 1 and at least one liquid descending within the column.

14. The process according to claim 13, wherein the ascending gas, the descending liquid, or both, comprises (meth)acrylic monomers.

Description

[0093] There follows an elucidation of working examples of the inventive column and working examples of the process according to the invention with reference to the drawings.

[0094] FIG. 1 shows a schematic view of a column in a working example of the invention,

[0095] FIG. 2 shows a detail of a vertical cross section of the column shown in FIG. 1 in the region of an inspection orifice,

[0096] FIG. 3 shows a detail of a vertical cross section of a further working example of the column of the invention,

[0097] FIG. 4 shows a detail of a vertical cross section of yet a further working example of the column of the invention and

[0098] FIG. 5 shows a horizontal cross section of the column shown in FIG. 4 in the region of the inspection orifice.

[0099] The working example described hereinafter relates to a separating column 1 as used, for example, in a process for fractional condensation for separation of acrylic acid from a product gas mixture comprising acrylic acid from a heterogeneously catalyzed gas phase partial oxidation of a C.sub.3 precursor compound (especially propene and/or propane) of the acrylic acid with molecular oxygen to give acrylic acid.

[0100] FIG. 1 shows the separating column 1 known per se in schematic form. It comprises a cylindrical column body 2, the axis of which is aligned vertically. The column body 2 is essentially a hollow cylinder. This means that the shell 7 of the column body 2 forms a column cavity 3. The column body 2 is manufactured from stainless steel. On the outside, the separating column 1 is normally thermally insulated in a conventional manner. The height of the separating column 1 is 40 m. The internal diameter of the shell 7 of the column body 2 is 7.4 m throughout.

[0101] In the vertical direction, the separating column 1 is divided into three regions: the upper region A is referred to as the column head. At the column head is provided a feed 4 through which a liquid can be introduced into the column cavity 3. In addition, an offgas line 13 for withdrawal of the gaseous mixture is formed at the top.

[0102] Beneath the column head, a region B is formed. In this region, the fractional condensation is conducted. A withdrawal line 14 is disposed within this region, through which crude acrylic acid is withdrawn.

[0103] Beneath region B, the column bottom is formed in region C. In the column bottom, there is an inlet 5 for introduction of the product gas mixture into the column cavity 3. In addition, there is an outlet 6 for the bottoms liquid in the column bottom.

[0104] In region B, several trays 8 are secured in the column cavity 3. The trays 8 of the column 1 are horizontal and are mounted with vertical spacing in the column cavity 3. This forms horizontal surfaces facing downward in the trays 8. The trays 8 serve as separating internals which improve separation in the separating column 1. The trays 8 are dual-flow trays. It is also possible to use other trays among those mentioned by way of introduction.

[0105] In order to be able to undertake inspection and cleaning operations when the column 1 is not in operation, at least one inspection orifice 9 is formed in the column body 2. For this purpose, the shell 7 or the column body 2 has an orifice. The cross section of the orifice is circular. If required, however, other cross-sectional shapes may also be used. At the edge of this orifice is secured a frustoconical stub 11 in a liquid- and gas-tight manner. The axis of symmetry of the stub 11 is aligned horizontally, such that the stub 11 extends away from the column body 2. The end of the stub 11 pointing away from the column body 2 forms the inspection orifice 9. At this end, a cover 12 is also provided. The cover 12 is secured in the stub 11 so as to be pivotable. In the closed state, the cover 12 closes the inspection orifice 9 in a liquid- and gas-tight manner. In the pivoted-open state of the cover 12, the column cavity 3 is accessible from outside via the inspection orifice 9.

[0106] FIG. 1 shows only one stub 11. Typically, the common body 2 comprises several stubs 11 spaced apart in vertical direction with the corresponding inspection orifices 9.

[0107] The diameter of the inspection orifice 9 is guided by the purpose of the inspection orifice 9. In the working example described here, the inspection orifice 9 takes the form of a manhole orifice. The diameter of this manhole orifice is within a range from 400 mm to 800 mm.

[0108] FIG. 2 shows the configuration of the inspection orifice 9 in detail. The column body 2 has a vertical inner surface 16 aligned into the column cavity 3. In addition, the stub 11 also has a surface 15 directed into the column cavity 3. This is the inner surface of the stub 11.

[0109] Below and above the inspection orifice 9 is disposed a mass transfer tray 8-1 and 8-2. Since the inspection orifice 9 is a manhole orifice, the distance between these two mass transfer trays 8-1 and 8-2 is relatively large, for example 1000 mm. This relatively large distance between the two mass transfer trays 8-1 and 8-2 can lead to unwanted polymer formation. In order to prevent polymerization in the region between the mass transfer trays 8-1 and 8-2, especially in the stub 11, a spray device 20 is disposed in the column body 2. By means of the spray device 20, it is possible to spray a liquid 22 at least against the surface 15 of the stub 11 directed into the column cavity 3. For this purpose, the spray device 20 has a spray nozzle 21 which is fed with liquid via an inlet 23. The inlet 23 passes through the column body 2 through a gas- and liquid-tight leadthrough 24. Outside the column body 2 is disposed a pump 25 connected to the inlet 23. On the other side, the pump 25 is connected to a line 26 which enters the column cavity again through a further gas- and liquid-tight leadthrough 27. The line 26 has an intake orifice 28 is disposed immediately above the mass transfer tray 8-1. In this case, the mass transfer tray 8-1 is adjacent to the inspection orifice 9 and the stub 11.

[0110] In the working example illustrated here, this mass transfer tray 8-1 is immediately below the inspection orifice 9. By means of the spray device 20, liquid which has collected on the mass transfer tray 8-1 is withdrawn and sprayed by the spray nozzle 21 against the surface 15 of the stub 11 and the inner surface of the cover 12. This prevents liquid from collecting and polymerizing in this region.

[0111] In the vertical cross section of the column 1 shown in FIG. 2, the surface 15 of the lower line of intersection of the stub 11, which is shown as a line in FIG. 2 because of the sectional representation, forms the angle a with the vertical inner surface 16 of the column body 2 which extends downward from the stub 11 and which is also shown as a line in FIG. 2 because of the sectional representation. At the vertex of the angle, the vertical inner surface 16 of the column body 2 and the lower line of intersection of the stub 11 are thus connected. Correspondingly, this surface 15 of the stub 11 forms the angle 13 with the horizontal H, the sum of the angles a and 13 being 270.

[0112] In the configuration shown in FIG. 2, the angle 13 is greater than 0, meaning that the surface 15 in the case of the lower line of intersection of the vertical cross section of the column 1 is not aligned horizontally but inclined. The angle of inclination in the present working example is 3, although the drawings are not a true reproduction of the angles for better illustration. The angle a in this case is thus 267.

[0113] It is pointed out that the angle a may also be smaller, resulting in a more significant inclination of the surface 15. The angle a is, for example, within a range from 210 to 267, especially within a range from 225 to 267 and preferably within a range from 255 to 267.

[0114] The inclination of the surface 15 of the lower line of intersection of the stub 11 in the case of a vertical cross section of the column 1 has the effect that liquid on the surface 15 runs off downward and especially does not remain on this surface 15. In this way, it is possible to prevent the polymerization of liquid comprising (meth)acrylic monomers.

[0115] The inclination of at least 3 is advantageous especially in the lower region of the stub 11, in order that liquid can run off. More particularly, the lower half of the stub 11 is at this angle to the inner surface 16 of the column body 2. For manufacturing reasons, however, the stub 11 is preferably rotationally symmetric, such that the angle between the surface of the stub 11 directed into the column cavity 3 and the inner surface 16 of the column body 2 is the same over the entire circumference of the stub 11. In terms of cross section, the inner line which is part of the inner surface 15 of the stub 11 is a straight line. In other working examples, however, this line may also be curved. In this case, for the angle or the angle , the tangent to the surface 15 of the lower line of intersection of the stub 11 with the vertical inner surface 16 of the column body 2 is considered. In the case of a curved line, the alignment of these tangents changes. The above-specified angle in this case is within the angle range specified at least in 50% and preferably over a greater region, for example 70% or 90%. The angle is especially not 270 or greater in any region.

[0116] In the working example of the column 1 of the invention shown in FIG. 3, the angle a is 270, meaning that the surface 15 in this case is aligned horizontally at the lower line of intersection of the vertical cross section of the column 1 and not inclined as in the working example shown in FIG. 2. The stub 11 is cylindrical. However, polymer formation is prevented in this working example as well by the spray device 20.

[0117] With reference to FIGS. 4 and 5, a further working example of the column 1 of the invention is described:

[0118] As in the working example shown in FIGS. 1 to 3, the inspection orifice 9 is a manhole orifice. The distance between the mass transfer trays 8-1 and 8-2 is relatively large in this case, for example 1000 mm. This relatively large distance between the two mass transfer trays 8-1 and 8-2 can lead to unwanted polymer formation. For this reason, in the working example of FIGS. 4 and 5, a mass transfer tray 8-3 is also disposed in the region of the inspection orifice 9. The distance between the two mass transfer trays 8-1 and 8-3 and between the two mass transfer trays 8-3 and 8-2 in that case is 500 mm. The mass transfer tray 8-3 in the working example described is a dual-flow tray having orifices 17, as shown in FIG. 5.

[0119] Additionally disposed in the region of the inspection orifice 9 is a plate 18 which prevents ascending gas in particular, but also descending liquid, from flowing upward or downward past the mass transfer tray 8-3 through the horizontal orifice formed by the stub 11. The plate 18 has orifices 19, such that it acts as a mass transfer plate. The plate 18 is aligned horizontally, flush with the mass transfer tray 8-3. The plate 18 is thus disposed horizontally at the same level as the mass transfer tray 8-3. The shape of the plate 18, as shown in FIG. 3, is matched to the horizontal cross-sectional shape of the stub. Since the stub in the present working example is frustoconical, the plate 18 is trapezoidal. In order to keep the gap or join between the plate 18 and the mass transfer tray 8-3 as narrow as possible, the long edge of the trapezium of the plate 18 could also be matched to the rounding of the mass transfer tray 8-3 in this region or, conversely, the rounding of the mass transfer tray 8-3 in this region could be truncated to match the long edge of the trapezoidal plate 18.

[0120] According to the size of the inspection orifice 9 and the desired distance between the mass transfer trays 8, it is also possible for several plates 8 to be present in the region of the inspection orifice 9. In that case, one plate 18 is assigned to each of these mass transfer trays 8.

[0121] The plate 18 is secured on the pivotable cover 12, such that it is pivoted away with the cover 12 when the inspection orifice 9 is opened. This has the advantage that the plate 18 need not be detached when inspection or cleaning operations have to be conducted in the column 1. Equally, the mass transfer tray 8-3 is also detachable, such that a person can get through the inspection orifice 9 in the form of a manhole into the column cavity 3.

[0122] As shown in FIGS. 4 and 5, the stub 11 is frustoconical as in the previous working examples. Alternatively, however, it could also be cylindrical as shown in FIG. 3.

[0123] The spray device 20-2 of the working examples of FIGS. 4 and 5 differs from the spray unit 20 of the above-described working examples in that the inlet 23 branches into an upper inlet 23-1 and a lower inlet 23-2 which then enter the column cavity 3 through the leadthroughs 24-1 and 24-2. The upper inlet 23-1 is disposed above the tray 8-3, and the lower inlet 23-2 below the tray 8-3. The upper inlet 23-1 opens into a spray nozzle 21-1, by means of which liquid 22 is sprayed against the upper surface 15 of the stub 11 and the inner surface of the cover 12. The lower inlet 23-2 opens into a spray nozzle 21-2, by means of which liquid 22 is sprayed against the lower surface 15 of the stub 11 and the inner surface of the cover 12.

[0124] In this working example too, a pump 25 connected to the inlet 23 is disposed outside the column body 2. On the other side, the pump 25 is connected to the line 26 which enters the column cavity again via a further gas- and liquid-tight leadthrough 27. The intake orifice 28 of the line 26 in this case is disposed directly above the mass transfer tray 8-1. The mass transfer tray 8-1 here is the closest mass transfer tray beneath the stub 11.

[0125] In further working examples, the spray device 20, proceeding from the inlet 23, may also comprise a line system which sprays the inner surfaces of further inspection orifices with liquid. In this case, the composition of the liquid withdrawn via the intake orifice 28, however, is not always essentially the same as the composition of the liquid in the region of the respective inspection orifice 9 in the operation of a separation process where, more particularly, gas ascends and a liquid descends.

[0126] There follows a description of a working example of the process according to the invention which is executed with the above-described separating column 1.

[0127] The process is a thermal separating process between at least one gas ascending in the separating column 1 and at least one liquid descending in the separating column 1. The ascending gas and/or the descending liquid especially comprises (meth)acrylic monomers.

[0128] In the separation process, a fractional condensation for separation of acrylic acid from a product gas mixture comprising acrylic acid from a heterogeneously catalyzed gas phase partial oxidation of a 0.sub.3 precursor compound (especially propene and/or propene) of the acrylic acid with molecular oxygen to give acrylic acid is conducted in a separating column 1 comprising separating internals. The separating column comprises, from the bottom upward, first dual-flow trays and then crossflow capped trays, which are supported from beneath as described above. Otherwise, the process is conducted as described in documents DE 19924532 A1, DE 10243625 A1 and WO 2008/090190 A1.

[0129] The term C.sub.3 precursor of acrylic acid encompasses those chemical compounds which are obtainable in a formal sense by reduction of acrylic acid. Known C.sub.3 precursors of acrylic acid are, for example, propane, propene and acrolein. However, compounds such as glycerol, propionaldehyde, propionic acid or 3-hydroxypropionic acid should also be counted among these C.sub.3 precursors. Proceeding from these, the heterogeneously catalyzed gas phase partial oxidation with molecular oxygen is at least partly an oxidative dehydrogenation. In the relevant heterogeneously catalyzed gas phase partial oxidations, the C.sub.3 precursors of acrylic acid mentioned, generally diluted with inert gases, for example molecular nitrogen, CO, CO.sub.2, inert hydrocarbons and/or water vapor, are passed in a mixture with molecular oxygen at elevated temperatures and optionally elevated pressure over transition metal mixed oxide catalysts, and converted oxidatively to a product gas mixture comprising acrylic acid.

[0130] Typically, the product gas mixture comprising acrylic acid from a heterogeneously catalyzed gas phase partial oxidation of C.sub.3 precursors (e.g. propene) of acrylic acid with molecular oxygen over catalysts in the solid state, based on the total amount of the specified constituents present (therein), has the following contents:

[0131] 1% to 30% by weight of acrylic acid,

[0132] 0.05% to 10% by weight of molecular oxygen,

[0133] 1% to 30% by weight of water,

[0134] 0% to 5% by weight of acetic acid,

[0135] 0% to 3% by weight of propionic acid,

[0136] 0% to 1% by weight of maleic acid and/or maleic anhydride,

[0137] 0% to 2% by weight of acrolein,

[0138] 0% to 1% by weight of formaldehyde,

[0139] 0% to 1% by weight of furfural,

[0140] 0% to 0.5% by weight of benzaldehyde,

[0141] 0% to 1% by weight of propene, and

[0142] as the remainder, inert gases, for example nitrogen, carbon monoxide, carbon dioxide, methane and/or propane.

[0143] The partial gas phase oxidation itself can be performed as described in the prior art. Proceeding from propene, the partial gas phase oxidation can be performed, for example, in two successive oxidation stages, as described, for example, in EP 700 714 A1 and in EP 700 893 A1. It will be appreciated, however, that it is also possible to employ the gas phase partial oxidations cited in DE 19740253 A1 and in DE 19740252 A1.

[0144] In general, the temperature of the product gas mixture leaving the partial gas phase oxidation is 150 to 350 C., frequently 200 to 300 C.

[0145] Direct cooling and/or indirect cooling cools the hot product gas mixture appropriately at first to a temperature of 100 to 180 C., before it is conducted, for the purpose of fractional condensation, into region C (the bottom) of separating column 1. The operating pressure which exists in the separation column 1 is generally 0.5 to 5 bar, frequently 0.5 to 3 bar and in many cases 1 to 2 bar.

LIST OF REFERENCE NUMERALS

[0146] 1 column, separating column

[0147] 2 column body

[0148] 3 column cavity

[0149] 4 feed

[0150] 5 inlet

[0151] 6 outlet

[0152] 7 shell

[0153] 8 trays

[0154] 8-1, 8-2, 8-3 trays

[0155] 9 inspection orifice

[0156] 11 stub

[0157] 12 cover

[0158] 13 draw point

[0159] 14 withdrawal line

[0160] 15 surface

[0161] 16 inner surface

[0162] 17 orifice

[0163] 18 plate

[0164] 19 orifice

[0165] 20 spray device

[0166] 21 spray nozzle

[0167] 22 liquid

[0168] 23 inlet

[0169] 24 leadthrough

[0170] 25 pump

[0171] 26 line

[0172] 27 leadthrough

[0173] 28 withdrawal orifice