EP3325121A1 - Column for thermally treating fluid mixtures, particularly those that contain (meth)acrylic monomers - Google Patents

Abstract

The invention relates to a column (1) for thermally treating fluid mixtures, comprising a cylindrical, vertically-aligned column body (2) that forms a column cavity (3) and a vertical inner surface (16), a plurality of trays (8) which are mounted in said column cavity (3) and vertically spaced apart from one another, at least one neck (11) arranged in the column body (2) and extending away from said column body (2), and a closeable inspection opening (9) formed at the neck (11). The claimed column is characterised in that, in a vertical cross-section of the column (1), the surface (15) of the lower intersection line of the neck (11), directed into the column cavity (3), or a tangent to the surface (15) of said lower intersection line of the neck (11), forms, together with the vertical inner surface (16) of the column body (2) which extends downwards from said neck (11), an angle in the range of 210° to 267°, at least in some sections.

Description

 Column for thermal treatment of fluid mixtures, in particular those containing (meth) acrylic monomers The present invention relates to a column for the thermal treatment of fluid mixtures. It has a cylindrical, vertically oriented column body which forms a column cavity and a vertical inner surface. The column further comprises a plurality of column cavities mounted vertically spaced from each other. Furthermore, the column comprises at least one stub which is arranged in the column body and which extends away from the column body, and a closable access opening, which is formed at the stub. The column is in particular a separation column. Furthermore, the invention relates to a thermal separation process between at least one gas rising in a column and at least one liquid descending in the column.

In separation columns, gaseous (ascending) and liquid (descending) streams are often passed in countercurrent, with at least one of the streams containing in particular a (meth) acrylic monomer. As a result of the imbalances between the streams, a heat and mass transfer takes place, which ultimately causes the separation (or separation) desired in the separation column. In this document, such separation processes should be referred to as thermal separation processes. Examples of and thus element of the expression "thermal separation processes" used in this document are the fractionating condensation (cf., for example, DE 19924532 A1, DE 10243625 A1 and WO 2008/090190 A1) and the rectification (in both cases the ascending vapor phase is in countercurrent to descending The separation effect is due to the fact that the vapor composition is different in equilibrium from the liquid composition), the absorption (at least one ascending gas is led to at least one descending liquid in countercurrent, the separation effect is based on the different solubility of the gas components in the Liquid) and desorption (the reverse process for absorption; the liquid dissolved in the liquid phase is separated by partial pressure reduction; the partial pressure reduction of the liquid phase solute is at least partially characterized by passing a carrier gas through the liquid phase et this thermal separation process as stripping; alternatively or additionally (at the same time as a combination), the partial pressure reduction can be effected by lowering the working pressure). For example, the separation of (meth) acrylic acid or (meth) acrolein from the product gas mixture of the catalytic gas phase oxidation can be carried out so that the (meth) acrylic acid or the (meth) acrolein by absorption into a solvent (eg water or an organic solvent ) or by fractionation-forming condensation of the product gas mixture is first separated in bulk and the resulting absorbate or condensate is subsequently further separated to give more or less pure (meth) acrylic acid or (meth) acrolein (cf., for example, DE-10332758 A1, DE No. 10243625 A1, WO 2008/090190 A1, DE 10336386 A1, DE 19924532 A1, DE 19924533 A1, DE 102010001228 A1, WO 2004/035514 A1, EP 1 125912 A2, EP 982289 A2, EP 982287 A1 and DE 10218419 A1).

The notation (meth) acrylic monomers in this document is abbreviated to "acrylic monomers and / or methacrylic monomers". The term acrylic monomers is used in this document to shorten "acrolein, acrylic acid and / or esters of acrylic acid".

The term methacrylic monomers is used in this document to shorten "methacrolein, methacrylic acid and / or esters of methacrylic acid".

In particular, the (meth) acrylic monomers mentioned in this specification are to comprise the following (meth) acrylic esters: hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, glycidyl acrylate, glycidyl methacrylate, methyl acrylate, methyl methacrylate, n-butyl acrylate, isobutyl acrylate, isobutyl Butyl methacrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, N, N-dimethylaminoethyl acrylate and N, N-dimethylaminoethyl methacrylate.

(Meth) acrylic monomers are important starting compounds for the preparation of polymers which are e.g. be used as adhesives or as water super absorbent materials in hygiene articles use.

On an industrial scale, (meth) acrolein and (meth) acrylic acid are predominantly produced by catalytic gas-phase oxidation of suitable C3 / C4 precursor compounds (or precursors thereof). In the case of acrolein and acrylic acid, propene and propane are preferably used as such precursor compounds. In the case of methacrylic acid and methacrolein, iso-butene and iso-butane are the preferred precursor compounds. In addition to propene, propane, isobutene and isobutane, suitable starting materials are, however, other compounds containing 3 or 4 carbon atoms, for example isobutanol, n-propanol or precursor compounds thereof, for example the methyl ether of isobutanol. Acrylic acid can also be produced by gas-phase catalytic oxidation of acrolein. Methacrylic acid can also be produced by gas-phase catalytic oxidation of methacrolein.

In the context of such production processes, product mixtures are normally obtained from which the (meth) acrylic acid or the (meth) acrolein must be separated off.

Esters of (meth) acrylic acid are e.g. by direct reaction of (meth) acrylic acid and / or (meth) acrolein with the corresponding alcohols. However, in this case as well, product mixtures are first of which make up the

(Meth) acrylic acid esters must be separated.

The separation columns in which these separation processes are carried out contain separating internals. These pursue in the thermal separation process the purpose of increasing the surface area for the separation in the separation column causing heat and mass transfer ("the exchange surface").

As such internals come e.g. Packings, packing and / or trays, which are also referred to as mass transfer trays, into consideration. Often, the separation columns used are those which contain at least one sequence of mass transfer trays, at least as part of the separating internals.

Mass transfer trays pursue the purpose of providing areas in the separation column in the form of liquid layers which form on them, with substantially closed liquid phases. The surface of the vapor or gas stream rising in the liquid layer and thereby dispersing in the liquid phase is then the relevant exchange surface.

A succession of mass transfer trays is understood to mean a succession (one after the other) of at least two superimposed in the separation column, generally identically constructed (ie, identical) mass transfer trays. In terms of application technology, the clear distance between two mass transfer trays directly following one another in such a series (series) of mass transfer trays is made uniform (ie, the mass transfer trays are arranged equidistantly one above the other in the separation column). The simplest embodiment of a mass transfer tray is the so-called Regensiebboden. This is a plate or plate segments joined together to form a plate which, for the ascending gas or vapor phase (the terms "gaseous" and "vaporous" are used interchangeably in this document) is distributed over the plate and substantially planar Through openings, for example, round holes and / or slots, has (see eg DE 10230219 A1, EP 1279429 A1, US-A 3988213 and EP 1029573 A1). Exceeding openings (eg at least one downcomer (at least one drain segment)) do not have rain screen bottoms. As a result of this absence of downcomers, both the gas ascending in the separation column (the vapor rising in the separation column) and the liquid descending in the separation column must move oppositely in the temporal change through the (same) passage openings (through the open cross sections of the passage points) , One also speaks of the "dual-flow" of rising gas and descending liquid through the passage openings, which is why in the literature for such mass transfer trays often the term "dual-flow trays" is used.

The cross section of the passages of a dual-flow tray is adapted in a conventional manner its load. If it is too small, the ascending gas flows through the passage openings at such a high speed that the liquid descending in the separation column is entrained substantially without separation effect. If the cross section of the passages is too large, ascending gas and descending liquid move past one another substantially without replacement, and the mass transfer tray runs the risk of running dry.

That is, the separating effective working area of a Regensiebbodens (dual-flow floor) has two limits. A minimum limiting speed of the ascending gas must be present in order to keep a certain liquid layer on the rain sieve bottom, in order to enable a segregation work of the rain sieve bottom. The upper limit of the velocity of the rising gas is determined by the flood point, when the gas velocity leads to congestion of the liquid on the Regensiebboden and their rain is prevented.

The longest extent of the passage openings of a technical dual-flow floor (= longest direct line connecting two on the outline of the cross section of the

Passage point lying points) is typically 10 to 80 mm (see, for example, DE 10156988 A1). Normally, the passages within a rain screen are identical (ie, they all have the same geometric shape and cross section (cross sectional area)). In terms of application, its cross-sectional areas are circles. That is, preferred Passage openings of rain screen floors are circular holes. The relative arrangement of the passage openings of a Regensiebbodens advantageously follows a strict triangular division (see, for example, DE 10230219 A1). Of course, the passages within one and the same Regensiebbodens also different borrowed be designed (vary over the Regensiebboden).

In terms of application technology, a sequence of rain sieve bottoms in a separation column comprises identical (identical) rain sieve trays, which are preferably arranged equidistantly one above the other.

However, according to DE 10156988 A1, it is also possible to use sequences of rain sieve bottoms in separation columns whose cross-section (preferably circular) within a dual-flow tray is uniform but varies within the sequence (for example decreases from bottom to top).

In general, each dual-flow bottom of a corresponding bottom sequence concludes flush with the wall of the separation column. But there are also variants in which there is a gap between column wall and floor, which is only partially interrupted by bridges. In addition to the actual passage openings, a rain sieve bottom usually still has at most openings which serve to fasten the floor to support rings or the like (cf., for example, DE 10159823 A1).

In the normal operating range of a series of rain screen bottoms, the liquid descending in the separation column is raining in drops from dual flow soil to dual flow soil, i.e., the gas phase rising between the dual flow trays is permeated by a divided liquid phase. The falling on the respective bottom Regensiebboden drops are partially sprayed on impact. The gas stream flowing through the passage openings bubbles through the liquid layer formed on the surface of the floor, whereby an intensive mass and heat exchange takes place between the liquid and the gas.

Depending on the liquid and gas load, rain sieve trays with a column diameter of> 2 m tend to cause small uneven distributions of liquids to swell and thus liquid uptake of a soil can fluctuate over a large area or a rotating wave can form, resulting in a negative mechanical stability of the column body on the other hand, the separation effect is reduced, since the liquid distribution under these conditions is then greatly different in time and place. In order to avoid such instar rarities, it has therefore proved to be advantageous to distribute flow breakers in the form of vertically standing sheets on the bottom cross section, which causes the balls to swell Prevent or at least greatly reduce the liquid inside the column body. The height of the sheets should correspond approximately to the height of the forming liquid bubbling layer. This is about 20 cm under normal loads. The cross section of a separation column is usually circular. This applies in a corresponding manner to the associated mass transfer trays.

Dual-flow trays suitable for the purposes of this document are e.g. in Technical Progress Reports, Vol. 61, Fundamentals of the Dimensioning of Column Trays, pages 198 to 21 1, Verlag Theodor Steinkopf, Dresden (1967) and described in DE 10230219 A1.

From the above-described sequence of rain sieve trays, comprising mass transfer trays without forced guidance of the soil-descending liquid on the soil, sequences of mass transfer trays are distinguished with such forced liquid trays.

These mass transfer trays are characterized in that, in addition to the passages already described, they additionally have at least one downcomer. This is at least one drainage opening located in the mass transfer tray, which retains the liquid (eg, a drain weir (this may in the simplest embodiment extend the drain opening with a throat (a chimney, in the case of a circular drain opening of a tube) above)), and which discharges into a passage which runs down to the mass transfer tray below, which as a rule is centrally symmetrical with respect to an axis pointing in the column longitudinal direction. The cross-section of the well may vary along this axis (e.g., taper) or be constant. Through the at least one downcomer of the mass transfer tray, the liquid descending from a higher mass transfer tray can, independently of the gas or vapor rising through the passages of this mass transfer tray as at least one feed of liquid to the next lower mass transfer tray within a sequence of such mass transfer trays descend the sequence.

The essential basis for this separation of the flow paths of descending liquid and rising gas is the hydraulic closure (the liquid closure or shaft closure) of the respective downcomer for the rising gas (a downcomer must not bypass the rising gas Make passageways past; the gas flow (the steam flow) must not rise through a drainage shaft past the passage openings).

Such a hydraulic lock can e.g. can be achieved by pulling the downcomer downwards (so far downwards) that it dives deep enough into the liquid layer located on the next lower mass transfer tray of the sequence (such a closure is also referred to in this document as " static closure "). The liquid level required for this purpose can be determined on the lower mass transfer tray, e.g. be ensured by the height of appropriate weirs.

However, such a design has the disadvantage that the region of the lower mass transfer tray, which is located directly below the outlet cross section of a downcomer of the overlying mass transfer tray (the so-called inflow area), can not have any passage openings for the rising gas and thus not for the Substance and heat exchange between the formed on the lower mass transfer tray liquid layer and the rising gas is available. In an alternative embodiment, the lower outlet end of the downcomer is raised so far that it no longer dips into the liquid layer located on the underlying mass transfer tray. In this case remains between the lower end of the at least one downcomer and the mass transfer tray on which the downcomer tapers, a sufficiently large intermediate space in which form a bubble layer and a mass and heat exchange between a (on the lower mass transfer tray) accruing Liquid layer and a (by this soil) ascending gas can take place. That is, in this case, the "inflow area" of the at least one downcomer on the mass transfer tray below may also have through openings, thus increasing the available exchange area of the mass transfer tray, and thus its separating effect.

A static fluid closure of the downcomer can be effected in this case, for example, by means of a mounted below the outlet end of the downcomer collecting cup. In terms of application technology, in this case, the jacket wall of the collecting cup is pulled up so far that the outlet end of the downcomer dips into the collecting cup (it is also possible to allow the bottom edge of the downcomer to end at the upper edge of the collecting cup). During operation of the column, the liquid flowing down through the downcomer accumulates in the collecting cupboard until it reaches above the upper edge of the shell wall of the collecting tray. se drains off. The lower edge of the downcomer dips into the liquid in the collecting cup and the collecting cup forms a siphon-like liquid cap of the downcomer. Alternatively, a raised drainage shaft can also be closed dynamically. For this purpose, the downcomer can be closed, for example, at its lower end with a bottom, which is provided with outlet openings which are dimensioned such that the liquid accumulates in the downcomer and the penetration of gas is prevented (cf., for example, EP 0882481 A1 and DE 10257915 A1 ). In this case, the shaft closure is produced dynamically by the pressure loss that arises at the outlet openings. That is, in the static seal, the closure of the drainage shaft is characterized in that its outlet end immersed in jammed liquid, and dynamic closure effect constructive features at the outlet end of the downcomer that the exiting (leaking) liquid suffers a pressure loss in the downcomer backlog in selbigem descending liquid causes, which causes the closure. In the simplest case, such a pressure loss can be caused by the fact that one selects the cross section of the outlet opening of the downcomer small compared to the average cross section of the shaft.

For a separation-effective operation of a sequence of such mass transfer trays, the execution of the at least one downcomer is relevant. On the one hand, the cross-section of the at least one downcomer must be sufficiently large (usually the corresponding cross-sectional area is greater than the cross-sectional area of a passage opening), so that the liquid can safely descend through the at least one downcomer even at the maximum load of the separation column does not back up to the overlying ground. On the other hand, it must be ensured that the hydraulic closure of the at least one downcomer still exists even with minimal liquid load.

At low gas load there is also the risk of raining through of the liquid through the openings. In addition, the liquid in a downcomer must be able to accumulate until the weight of the accumulated liquid column is sufficient to carry the liquid into the headspace below the mass transfer tray associated with the downcomer. This backwater height determines the minimum required length of the downcomer and thus determines the ground clearance required in a sequence of corresponding mass transfer trays. The main factor contributing to the above-mentioned backflow height (backflow length) is the pressure drop ΔΡ of a mass transfer tray. This pressure loss is suffered by the ascending gas as it flows through the passages and the hydrostatic pressure. It is responsible for increasing the pressure in the gas phase of a sequence of such mass transfer trays from top to bottom, so that for the "hydrostatic" pressure h _p of the fluid of a mass transfer tray accumulated in the downcomer, at least the condition - its supply h _p> met ΔΡ the mass transfer tray These relationships are the skilled person, for example from EP 1704906 A1 also known as the way to ensure with an inlet weir on the underlying mass transfer tray that under static closure of the downcomer of the upward mass transfer tray in. However, the use of a Zulaufwehrs increases the backwater level, which is required in the downcomer to the jammed in the same liquid on de n push lower mass transfer soil. Overall, the element of the downcomer allows a widening of the separating working area compared to Regensiebboden. A favorable flow rate of the liquid accumulated in the downcomer out of the downcomer in the method according to the invention is, for example, 1.2 m / s.

In addition, it allows positive guidance of the liquid descending onto a mass transfer tray on this floor.

For example, B. only one half of a (preferably circular) mass transfer tray at least one downcomer (ie, all drain holes are located with their full extent within the corresponding circle segment) and are arranged in a sequence of at least two identical such mass transfer trays the mass transfer trays in a separation column one above the other in that two top-to-bottom successive mass transfer trays in the separating column are each rotated by 180 ° about the column longitudinal axis (rotated) so that their downcomers are on opposite sides (in opposite halves) of the separating column the liquid descending from an upper mass transfer tray through its at least one downcomer to the mass transfer tray below it, on said lower mass transfer tray, over the lower mass transfer tray viewed from the at least one en inflow surface of at least one downcomer of the upper (of the above attached) mass transfer tray (from the at least one inlet through the at least one downcomer of the upper mass transfer tray) in a necessary manner (ie forced) to flow to the at least one downcomer of this lower mass transfer tray. That is, the liquid descending from the upper floor to the lower floor is forcibly led across the floor from the at least one inlet to the at least one outlet. Such a liquid guide on a mass transfer tray within a sequence of identical mass transfer trays shall be referred to herein as a cross flow, the sequence of such identical mass transfer trays as a succession of equivalent crossflow mass transfer trays and the single mass transfer tray within the sequence as cross flow mass transfer trays.

In the simplest case, the cross-flow mass transfer tray is a cross-flow sieve tray. Apart from the at least one downcomer, it has passage openings for the gas rising in a separating column, for the design of which basically all the embodiments mentioned in the rain screen floor come into consideration. Preferably, a cross-flow sieve bottom as through-openings also has circular bores which, in terms of application technology, advantageously also have a uniform radius. As already mentioned, the at least one downcomer makes it possible for the liquid descending in a separation column to pass through a succession of crossflow trays independently of the flow path of the successive rising vapor (through the passage openings) from a higher crossflow sieve tray to the next descend lower-lying cross-flow sieve tray can. On the lower floor, the liquid flows in cross-flow from the at least one inlet of the lower floor formed by the at least one outlet of the higher cross-sieve tray to the at least one downcomer (to the at least one drain) of the lower floor, e.g. the height of at least one drain weir, via which the liquid can flow to the at least one downcomer, ensures the desired liquid level on the lower cross-flow sieve bottom. In addition, the

Liquid held by the dynamic pressure of rising in the separation column steam on the cross-flow sieve tray. However, if the vapor load of a cross-flow sieve bottom drops below a minimum value, the liquid may rain through the passage openings, which reduces the separating effect of the cross-flow sieve bottom and / or leads to dry running of the cross-flow sieve bottom.

This risk of dry running can be counteracted by the fact that the outlet opening of the at least one downcomer is drained and the respective passage opening is extended upwards by a neck (a chimney, in the case of a circular passage opening of a tube).

Above the neck are usually Dampfumlenkhauben (bells, inverted cups) attached (these can in the simplest case with the neck (eg front and rear) screwed sit down and are practically put over the neck), which dive into the pent-up liquid on the ground. The one through the respective passage Opening ascending steam initially flows through the neck into the associated hood, in which it is diverted to subsequently, in contrast to the cross-flow sieve bottom, parallel to the bottom surface of the hood in the self-accumulated liquid to flow (such a "parallel outflow" is In the case of processes according to the invention, it is generally advantageous insofar as it can "blow off" polymer particles formed in an undesired manner and thereby cause a self-cleaning effect). The gas streams (vapor streams) emerging from neighboring hoods, which are preferably distributed equidistantly over the trays, swirl the liquid accumulated on the bottom and form a bubbling layer in the same, in which the material and heat exchange takes place. Such cross-flow mass transfer trays are also referred to as cross-flow bubble trays or cross-flow tray trays. Since they also contain liquid accumulated with low rising gas (vapor) and thus run the risk of running dry, they are also referred to as hydraulically sealed cross flow trays. In comparison to cross-flow sieve trays, they usually require higher investment costs and cause higher pressure losses of the gas rising through them. In contrast to the simple sieve passage opening of a sieve tray, the through-opening of these trays, which is designed as described, is also referred to as bell passage opening or hood passage opening.

The most important component of the cross-flow bubble tray is the bell (cf., for example, DE 10243625 A1 and Chemie-Ing.-Techn. 45th Jahrg. 1973 / No. 9 + 10, pages 617 to 620). Depending on the shape and arrangement of the bells (Dampfumlenkhauben, hoods) distinguishes cross flow bell bottoms z. The cross-sections of the passage opening, chimney (neck) and bell (steam deflection hood) are round (eg the cylinder bell bottom or the flat bubble bottom), tunnel cross flow trays (the cross sections of the passage opening, chimney and bell ( Hood) are rectangular, the passage points with their bells are arranged within juxtaposed rows one behind the other, wherein the longer rectangular edge is aligned parallel to the transverse flow direction of the liquid) and cross-flow

Thormann ^® floors (the cross-sections of the passage opening, chimney and bell (hood) are rectangular, the passage points with their bells are arranged within juxtaposed rows one behind the other, with the longer rectangular edge is aligned perpendicular to the cross-flow direction of the liquid). Cross-flow Thormannböden are z. For example, DE 19924532 A1 and DE 10243625 A1 and the prior art appreciated in these two publications.

The bell edge can have very different shapes in the case of crossflow bubble trays (compare DE 10243625 A1 and Chemie-Ing. Techn. 45th Jahrg. 1973 / No. 9 + 10, pages 617 to 620). Figure 3 from Chemie-Ing. Techn. 45 years. 1973 / No. 9 + 10, p. 618 shows some examples of the serrated and slotted edge. The serrations and slots are usually shaped so that the steam entering the mass stored on the mass transfer tray out of the bell dissolves as easily as possible into a large number of bubbles or jets of steam. The aforementioned Figure 3 and various figures of DE 10243625 A1 also show exemplary embodiments of bell edges, which have a sawtooth-like structure whose teeth are additionally equipped with guide vanes (guide surfaces) ("bent-slots"). The guide vanes are to impose a tangential exit direction on the gas stream (vapor stream) emerging from the bent sawtooth-like slots (direct the gas exit into the liquid in an oblique direction), whereby the surrounding liquid receives a directed impulse of movement, which interacts with the arrangement of the bells (steam deflection hoods). can result in a directional liquid flow on the cross-flow bubble tray overlaying the cross-flow established across the mass transfer tray (often such upturned slots are also referred to as drive slots). For example, in a sequence of cross-flow Thormann floors, the liquid does not flow on a lower cross-flow Thormann bottom directly across the ground, but driven in a manner described above, meandering from the at least one inlet to the at least one drain. The space between two in cross-flow direction successively arranged hoods of a cross-flow Thormannbodens each forms a groove in which the liquid flows. The details of a cross-flow Thormannbodens also usually takes place so that the liquid flows in two in the cross-flow direction respectively successive grooves in countercurrent (see, for example, Figure 3 DE 10243625 A1). The resulting meandering of the cross-flow extends the flow path of the liquid from the at least one inlet to the at least one drain, which favors the separation effect of a cross-flow Thormannbodens.

As already stated, in a cross-flow bubble tray, the gas emerging from the bell, in contrast to the cross-flow sieve bottom, is introduced parallel to the bottom surface in the liquid accumulated on the crossflow bubble tray. Frictional and buoyant forces then ensure that with increasing distance of the leaked gas flow from the bell edge more and more partial flows thereof are deflected in a direction perpendicular to the crossflow bell bottom and finally escape from the liquid layer. As the gas loading of a bell increases, the velocity of the gas stream leaving it increases, which increases the distance from the edge of the bell ("the area of action of the bell") up to which deflection has been described above. This dependence of the effective range of a rigid bell on the gas load can be counteracted by configuring (executing) the passage opening of a cross-flow mass transfer tray as a valve (as a valve passage opening). The resulting cross-flow mass transfer trays are referred to as cross-flow valve trays (see, for example, DD 279822 A1, DD 216633 A1 and DE

102010001228 A1).

The term cross-flow valve floors subsumes in this document thus cross-flow mass transfer trays, the passage openings (bottom holes) with stroke-limited plate, ballast or lifting valves (floating flaps) that adjust the size of the steam passage opening of the respective column load.

In a simple embodiment, the passage openings of the floor for the aforementioned purpose are covered with upwardly movable lids or plates (disks). During the passage of the rising gas, the lids (plates, disks) are raised by the gas flow in an additionally via the respective passage opening mounted (which is usually firmly anchored to the ground) corresponding guide frame (guide cage) and finally reach a gas load corresponding lifting height (instead of Guide cage, the disc can also have anchored with the floor upwardly movable valve legs whose upward mobility is limited upwards). The ascending through the passage opening gas flow is deflected at the bottom of the raised lid (plate, disc) in a similar manner as in the bell (at a bell passage opening) and emerges from the under the raised plate (lid, disc) resulting emergence area and as in the Bubble tray parallel to the bottom into the liquid stored on it. The plate stroke thus controls the size of the gas outlet area and adapts itself to the column load until the upper end of the guide cage limits the maximum possible lifting height. The plates may have downwardly directed spacers, so that at low gas load, the valve closes only so far that created by the spacers space still allows intensive mixing of the horizontal gas outflow with the cross-flow liquid. Spacers also counteract adhesion of the valve disc on the ground. By suitable design of the valve elements of a cross-flow valve bottom, the blowing direction of the valve element can be adjusted and thus the forced liquid flow on the cross-flow valve bottom can be additionally influenced (cf., for example, DD 216 633 A1). The principle of cross-flow valve trays and usable for the purposes of the present document valve bottoms is found, for. B. in Technical Progress Reports, Volume 61, Basics of Dimensioning Column Trays, page 96 to 138 executed. In addition to the above-described movable valves, the expert also knows fixed valves. These are usually disc-shaped, or trapezoidal or rectangular units punched out of the bottom plate and connected thereto via upstanding fixed legs. Especially with larger diameters of a separation column is formed on cross-flow mass transfer trays from the at least one inlet starting to reach the drain weir of the at least one course in a natural way to be observed liquid gradient (the gradient of the damming height of the liquid feeds (conditionally) the cross flow). As a result, in regions with a lower liquid level, due to the resulting lower resistances, the rising vapor (the rising gas) can pass through the liquid layer comparatively easily. This can eventually result in an uneven gas load on the crossflow mass transfer tray (the areas with a lower liquid height (a lower flow resistance) are preferably flowed through), which impairs the separating action thereof. By the application of z. B. in their seat height adjustable bells (alternatively, the bell size can be changed) in cross-flow bubble trays or by using z. B. plates (lids) with different weight in cross-flow valve floors can be compensated in this regard, so that the Stoffaus- exchange floor over its cross-section substantially uniform guest (where the liquid level is smaller on the cross-flow mass transfer tray, the seat height of the bell The seat height of the bell can also be lowered, for example, by lowering the length of the corresponding chimney, at the end of which the bell is optionally screwed, in a targeted manner Alternatively or additionally, for example, the serration / slot structure of the bell rim may also be varied to provide the desired flow resistance compensation, ideally, adjustment via the crossflow mass transfer tray is such that, during operation of the separation column, each of the units located on a crossflow bell oden located bell caused the same flow resistance for the rising gas). Incidentally, the passage points (the passage openings) of a cross-flow mass transfer tray are generally designed advantageously uniform. Through a cross-flow mass transfer bottom through openings (from top to bottom), the cross-sectional area is usually more than 200 times smaller than the total cross-sectional area of all other openings of the Querstromstoffaustauschboden (the cross section of the at least one downcomer not included) form no (effective) Passage openings for the gas rising through the crossflow mass transfer tray and are therefore not attributed to the same. For example, such openings may be tiny idle bores through which hydraulically sealed crossflow trays may run empty when a separation column is switched off. Also, such openings can serve Verschraubungs- purposes.

Sequences of at least one downcomer having mass transfer trays in which the at least one inlet and the at least one sequence z. B. in the same half of the (circular) mass transfer tray or in which there is at least one inlet in the middle of the floor and the at least one drain at the edge of the soil, do not form a sequence of cross-flow mass transfer soils in the registration (inventive) sense.

The efficiency of cross-flow mass transfer trays designed as described is usually below that of a theoretical tray (a theoretical separator). As the theoretical soil (or theoretical separation stage) is to be understood in this document quite generally that one unit of space used for a thermal separation process, separating internals containing separation column, which causes a material enrichment in accordance with the thermodynamic equilibrium. In other words, the term "theoretical soil" can be applied both to separating columns with mass transfer trays and to separation columns containing packings and / or random packings.

The prior art recommends the use of sequences of at least two identical (identically designed) cross-flow mass transfer trays u. a. separation columns containing separating internals which are used to carry out thermal separation processes between at least one gas stream rising in the separation column and at least one liquid stream descending in the separation column, and wherein at least one of the streams contains at least one (meth) acrylic monomer. For example, DE 19924532 A1, DE 10243625 A1 and WO 2008/090190 A1 recommend the use of a sequence of structurally identical hydraulically sealed crossflow mass transfer trays in a separation column for carrying out a fractional condensation process of a product gas mixture comprising acrylic acid of a heterogeneously catalyzed gas phase partial oxidation C3 precursors of acrylic acid with molecular oxygen containing from bottom to top first dual-flow trays and then hydraulically sealed cross-flow mass transfer trays.

It is characteristic of the sequences of the cross-flow mass transfer trays recommended in the prior art that the respective lower of two sequential cross-flow mass transfer trays in the direction of the transverse flow of its at least one inlet to its at least one downcomer only in the region between the at least one inlet and the at least one downcomer (the at least one drainage opening) has passage openings (see, eg, Figures 3 and 4 of DE 10243625 A1, Figure 1 of DD 279822 A1, Figure 1 of DD 216633 A1 and Figure 1 from Chemistry-Ing.-Techn.Vintage 45, 1973 / No. 9 + 10, page 617-620).

The invention particularly relates to columns in which the aforementioned trays are used.

A problematic property of (meth) acrylic monomers is their tendency to undesired polymerization, which, especially in the liquid phase, can not be completely suppressed even by the addition of polymerization inhibitors.

A disadvantage of known separation columns is that, when the thermal separation process is carried out continuously over a longer period of operation, the mass transfer trays are comparatively frequently used to form unwanted polymer. This is particularly disadvantageous because the operator of the thermal separation process due to the unwanted Polymerisatbildung must interrupt the thermal separation process again and again to remove the polymer formed. The same can indeed partially or completely close the passages of the mass transfer tray. In addition, radical polymerization of (meth) acrylic monomers is usually highly exothermic, i. H. under strong heat. There is a risk that the polymerization proceeds so vigorously that the separation column containing the polymerization mixture explodes.

In order to make certain revision work in the column or to clean the column cavity, usually inspection openings are provided in the column body. Such an inspection opening is formed for example in a nozzle which is arranged in the column body. The diameter of the inspection opening is adapted to the intended function of the inspection opening. It may be a so-called hand hole, through which a person can insert their hand, for example, together with a cleaning device. Furthermore, the inspection opening can be designed as a manhole, in which the diameter of the opening is so large that in non-operation, a worker can get into the cavity of the columns to perform there inspection and cleaning. By way of example, the polymerizate of the acrylic acid which has been formed in an undesired manner during operation of the column can also be removed via the inspection opening. The floors mounted in the column cavity are usually arranged so that the inspection opening is located between two floors. However, if the inspection opening is designed as a manhole, this has the disadvantage that the distance between the floors is undesirably large. If no separation-effective internals are provided in the area of the inspection opening, unwanted polymer can form in this area.

In order to solve this problem, it has been proposed in WO 2013/139590 A1 to also apply separable internals in the manhole area of a condensation column and in this way to reduce the distance to the transition floor. However, the problem remains that undesired polymer forms in the area of the inspection opening.

It is an object of the present invention to provide a column and a thermal separation process of the type mentioned above in which polymerization of the substance present in the separation column can be prevented or at least reduced.

According to the invention this object is achieved by a column having the features of claim 1 and a thermal separation method having the features of claim 13. Advantageous embodiments and further developments emerge from the dependent claims.

Accordingly, a column for the thermal treatment of fluid mixtures has been found, comprising a cylindrical, vertically oriented column body forming a column cavity and a vertical inner surface, a plurality of column vials mounted vertically spaced from each other, at least one nozzle in the column body is arranged and which extends away from the column body, and has a closable access opening, which is formed at the nozzle, wherein the column is characterized in that in a vertical section of the column directed into the column cavity line of the lower section line Stutzens or a tangent to this line of the lower line of intersection of the neck at least in sections, with the vertical inner line of the column body extending from the neck down, an angle in a range of 210 ° to 267 ° includes. In an advantageous embodiment, this angle is in a range of 225 ° to 267 ° and preferably in a range of 255 ° to 267 °.

The line of the lower cut line of the neck, which is directed into the column cavity in the case of a vertical section of the column, is part of the surface of the neck. Further, the vertical inner line of the column body extending downwardly from the nozzle is a part of the inner surface of the column body.

The spatial terms "top", "bottom", "horizontal" and "vertical", unless explicitly stated otherwise, refer to the orientation of the column during operation.

It has been found that undesired polymer forms in particular in so-called dead zones in the column. In such dead zones, the residence time of the fluid in the column is particularly long. Such a long residence time favors the polymerization. It has been found that dead zones can form in particular in the region of the inspection opening, in particular in the lower part of the nozzle. Usually, the bottom wall of the nozzle extends horizontally away from the column body. On this horizontal surface, however, liquid can accumulate, which lingers longer in the column. If a polymerizable material is treated in the column, there is thus on this horizontal surface of the nozzle of the inspection opening to an unwanted polymerisation. According to the invention, this polymerisation can be prevented by tilting the lower part of the neck so that liquid, which deposits on the surface of the neck pointing into the column cavity, runs back into the column cavity. The angle of inclination should be at least 3 °, in which case the angle of the column cavity line is the bottom line of intersection of the neck with the vertical inside line of the column body extending downwardly from the neck 267 °. The inclination is preferably even greater, too large inclinations lead to larger openings in the column body for the nozzle. The choice of angle thus represents a compromise between a suitable inclination of the lower surface of the nozzle to the horizontal on the one hand and a suitable diameter of the nozzle on the other hand. According to another embodiment of the column according to the invention closes at a vertical cross-section of the column at least 50% of the in the column cavity directed line of the lower cut line of the nozzle or the tangent to at least 50% of this line of the lower cut line of the nozzle with the vertical inner line of the column body extending downwardly from the nozzle, an angle in a range of 210 ° to 267 °, prefers an angle in a range of 225 ° to 267 °, and more preferably an angle in a range of 255 ° to 267 °. In this case, sections, the inclination, ie the angle to the horizontal, the lower surface of the nozzle may also be lower, that is, the above-mentioned angle greater than the specified angle. Before- However, 70%, more preferably 90%, and in particular 100%, of the lower cutting line of the connecting piece fall into the aforementioned angular range.

The neck of the column has an upper half and a lower half. In the column according to the invention, in particular in the lower half, the column cavity surface of the nozzle or the tangent to the surface of the nozzle with the vertical inner surface of the column body extending downwardly from the nozzle forms an angle in a range of 210 ° to 267 °, preferably an angle in a range of 225 ° to 267 °, and more preferably an angle in a range of 255 ° to 267 °. Namely, the undesired polymer is formed especially at the surfaces of this lower half of the nozzle. Said choice of the angle to the vertical inner surface of the column body prevents liquid from remaining on the surfaces of the lower half of the nozzle and forming polymer.

In terms of application technology, however, the connection piece is rotationally symmetrical about a horizontal axis. In this case, the entire surface of the nozzle directed into the column cavity or the tangent on the surface of the nozzle with the vertical inner surface of the column body encloses an angle in the range of 210 ° to 267 °, preferably an angle in the range of 225 ° ° to 267 ° and most preferably an angle in a range of 255 ° to 267 °.

About a horizontal axis rotationally symmetrical nozzles have opposite oblique nozzle, ie for example nozzles with parallel side surfaces which are mounted obliquely in the wall of the column body, the advantage that they are easier to install manufacturing technology. Further, the advantage of having the spout forming a hand hole is that this hand hole makes it easier to reach into the column cavity and see in it. This is not so easily possible, especially with oblique nozzles, if their axis is not aligned horizontally, ie not perpendicular to the column wall. In addition, such nozzles have the advantage that the liquid runs from the inner wall of the column cavity above the nozzle to the inner wall of the nozzle, there continues to run down further to finally run off again from the inner wall of the column cavity below the nozzle. If the nozzle has an inner wall which is inclined upwards in this running direction, this process would be hindered and liquid would accumulate on one edge. There the liquid will drip off partly. However, there is a risk that liquid will accumulate at this edge. This is especially at oblique nozzle with parallel side surfaces of the danger. Namely, they have an inner surface which slopes upwards in the direction of travel. The nozzle may be formed, for example, frustoconical. The surface of the spigot directed into the column cavity then encloses an angle with the vertical inner surface of the column body which lies in the above-mentioned range. With a frusto-conical neck, liquid that deposits on the surface of the neck can drain particularly well back into the column cavity.

The nozzle is arranged in particular in the vertical direction between two trays mounted in the column cavity. These two floors do not necessarily have to be adjacent. There may also be other floors between these two floors in the area of the nozzle.

According to a further embodiment of the column according to the invention, the inspection opening is a manhole opening, which is formed at the nozzle and which can be closed with a lid. If in this case at least one of the floors is mounted in the region of the manhole opening, a plate is advantageously arranged in the region of the connecting piece between the one floor and the closed cover.

By this plate can be advantageously prevented that ascending gas or descending liquid flows past a horizontal opening in the region of the manhole opening at the bottom, which is mounted in the region of the manhole opening.

Preferably, the entire cross-section of the column body in the region of the nozzle is substantially filled by the one bottom in the region of the manhole opening and the plate. Only at the joints may openings remain. If the bottom in the region of the manhole opening is a mass transfer tray with openings, the plate is preferably designed as a mass transfer plate. In particular, this mass transfer plate also has openings through which gas can rise and liquid can descend, whereby a mass transfer is effected.

The one bottom in the region of the manhole opening and the plate are, in particular, aligned substantially horizontally. The lid may be pivotally attached to the neck. Further, the plate may be attached to the lid so that it is removed when the lid is removed from the neck or swung away.

The inspection opening formed in the neck in particular has a circular cross-section. However, other round, oval or, more rarely, even rectangular cross sections are possible. The clear width of the inspection opening is in a range of 100 mm to 800 mm. If the inspection opening is designed as a manhole opening, the clear width is in particular in a range of 400 mm to 800 mm. Only if it is planned to take large tools or other large parts with through the manhole opening, this opening can be made even larger. If the inspection opening is designed as a hand hole opening, the clear width is smaller, in particular in a range of 100 mm to 300 mm.

The soil used in the column according to the invention is in particular a dual-flow tray. For dual-flow trays, the risk of polymerization is when using a fluid mixture which

Contains (meth) acrylic monomers, especially high. By the column according to the invention, the formation of polymer and thus the risk of explosion can be reduced in this case particularly effectively.

However, the trays which are mounted in the column can also be other trays, as described in the introduction. Between the floors further separation-effective internals can be arranged. Due to the separation-effective internals, the separation of substances in a column, which is used as a separation column, improved. These further installations can be provided, for example, in the form of packages, in particular structured or ordered packages, and / or fillings. Among the beds, those with rings, spirals, saddles, Raschig, Intss or Pall rings, Berl or Intalox saddles, Top-Pak etc. are preferred. For example, for the extraction columns to be used according to the invention particularly suitable packages are z. B. packs of Julius Montz GmbH in D-40705 Hilden, such. For example, the pack Montz-Pak B1 -350. Preferably used perforated structured packages of stainless steel sheets. Packing columns with ordered packs are known in the art and z. In Chem.-Ing.Tech. 58 (1986) No. 1, pp. 19-31 as well as in the Technical Review Sulzer 2/1979, p. 49 et seq. Of the Brothers Sulzer Aktienge- Seilschaft in CH-Winterthur.

According to another embodiment of the column according to the invention, no separating internals and no bottom are arranged in the region of the inspection opening. Advantageously, in this case, a spraying device is arranged in the column body, with which liquid can be sprayed at least against the surface of the nozzle, ie the inner surface of the nozzle, directed into the column cavity. By spraying the inner surface of the nozzle prevents liquid from staying longer at the inner surface of the nozzle. However, it is also possible for the spraying device to be arranged in the column body, with which liquid can be sprayed at least against the inner surface of the nozzle, if in the region of the inspection Opening a floor is arranged. In this way, in each case the undesired formation of polymer is prevented.

According to one embodiment, the spraying device has a spray nozzle, a feed line and a spray liquid feed device. The spray liquid

Feeding device is designed to remove spray liquid from the column cavity, to supply the extracted spray liquid via the feed line of the spray nozzle and to spray at least against the inner surface of the nozzle by means of the spray nozzle. In particular, the spray liquid is removed above a base mounted in the column cavity and in particular not in the column sump. The use of the liquid in the column cavity as the spray liquid affords the advantage that the spray liquid has substantially the same composition as the liquid washed away at the inner surface of the nozzle.

In particular, the spray liquid supply device has an inlet opening which is arranged directly above a bottom which is adjacent to the nozzle. Preferably, the inlet opening is arranged directly above the bottom, which is arranged directly below the nozzle. In this case, the spray liquid is taken from the column cavity in an area which is adjacent to the height of the nozzle, in particular directly under the nozzle. This has the advantage that the spray liquid is removed at the same stage of the column, so that the spray liquid and the liquid to be rinsed off at the inner surface of the nozzle have the same composition. This has a positive effect on the separation effect of a process which is carried out with the column according to the invention.

The column according to the invention can be used in particular as a separation column. The separation column has a sequence of soils. The clear distance between two directly successive trays within the column according to the invention is in particular not more than 700 mm, preferably not more than 600 mm or not more than 500 mm. In terms of application, the clear distance within the floor sequence is 300 to 500 mm. As a rule, the ground clearance should not be less than 250 mm.

The height of the column body is, for example, greater than 5 m, in particular greater than 10 m. However, it is also possible that the height of the column body exceeds 30 m or 40 m. The invention further relates to a thermal separation process between at least one gas rising in a column as described above and at least one liquid descending in the column. In particular, the ascending gas and / or the descending liquid contains

(Meth) acrylic monomers.

The thermal separation process according to the invention may e.g. a fractional condensation process for separating acrylic acid from a product gas mixture containing acrylic acid of a heterogeneously catalyzed gas phase partial oxidation of a C3 precursor compound (in particular propene and / or propane) of the acrylic acid with molecular oxygen to acrylic acid.

The separation column (condensation column) can be designed as described in DE 10243625 A1 or WO 2008/090190 A1.

Exemplary embodiments of the column according to the invention and exemplary embodiments of the method according to the invention are explained below with reference to the drawings.

FIG. 1 shows a schematic view of a column according to an embodiment of the invention,

 FIG. 2 shows a detail view of a vertical cross section of the column shown in FIG. 1 in the region of an inspection opening,

 FIG. 3 shows a horizontal cross section of the column shown in FIG

 Area of the inspection opening,

 FIG. 4 shows a detailed view of a vertical cross section of a further embodiment of the column according to the invention and FIG

 FIG. 5 shows a detailed view of a vertical cross section of yet another

 Embodiment of the column according to the invention.

The embodiment described below relates to a separation column 1, as z. B. in a process of fractional condensation for the separation of acrylic acid from an acrylic acid-containing product gas mixture of a heterogeneously catalyzed gas phase partial oxidation of a C3 precursor compound (in particular propene and / or propane) of acrylic acid is used with molecular oxygen to acrylic acid.

In Fig. 1, the known separation column 1 is shown schematically. It comprises a cylindrical column body 2 whose axis is vertically aligned. The column body 2 is essentially a hollow cylinder. This means, the jacket 7 of the column body 2 forms a column cavity 3. The column body 2 is made of stainless steel. Outwardly, the separation column 1 is normally thermally isolated in a conventional manner. The height of the separation column 1 is 40 m. The inner diameter of the jacket 7 of the column body 2 is 7.4 m throughout.

In the vertical direction, the separation column 1 is subdivided into three regions: the upper region A is referred to as the column head. When the column head an inlet 4 is provided, via which a liquid can be introduced into the column cavity 3. Further, an exhaust pipe 13 is formed at the top for removing the gaseous mixture.

Below the column head a region B is formed. In this area, the fractional condensation is carried out. In region B, a removal line 14 is arranged, via which crude acrylic acid is removed.

Below the region B, the bottom of the column is formed in region C. At the bottom of the column there is a feed line 5 for introducing the product gas mixture into the column cavity 3. Furthermore, there is a drain 6 for the bottom liquid in the bottom of the column.

In area B, several trays 8 are fixed in the column cavity 3. The trays 8 of the column 1 are horizontally aligned and mounted vertically spaced from each other in the column cavity 3. In this case, 8 downwardly oriented horizontal surfaces are formed in the soils. The trays 8 serve as separating internals, which improve the material separation in the separation column 1. The floors 8 are dual-flow floors. However, it is also possible to use other of the initially mentioned soils.

In order to be able to carry out inspection and cleaning work in the non-operation of the column 1, at least one inspection opening 9 is formed in the column body 2. For this purpose, the jacket 7 or the column body 2 has an opening. The cross section of the opening is circular. However, other cross-sectional shapes may be used as needed. At the edge of this opening is a liquid-tight and gas-tight a frustoconical nozzle 1 1 attached. The symmetry axis of the nozzle 1 1 is oriented horizontally, so that the nozzle 1 1 extends away from the column body 2. The remote from the column body 2 end of the nozzle 1 1 forms the inspection opening 9. At this end, a lid 12 is provided. The lid 12 is pivotally attached to the nozzle 1 1. When closed, the lid 12 closes the inspection opening 9 liquid and gas tight. In the opened, opened pivoted state of the lid 12, the column cavity 3 via the access opening 9 is accessible from the outside.

In Figure 1, only a nozzle 1 1 is shown. Usually, the column body 2 comprises a plurality of spaced apart in the vertical direction nozzle 1 1 with the associated inspection openings. 9

The diameter of the inspection opening 9 depends on the purpose of the inspection opening 9. In the embodiment described here, the inspection opening 9 is formed as a manhole opening. The diameter of this manhole opening is in a range of 400 mm to 800 mm.

In Figure 2, the configuration of the inspection opening 9 is shown in detail. The column body 2 has a vertical inner surface 16 directed into the column cavity 3. Furthermore, the nozzle 11 also has a surface 15 directed into the column cavity 3. This is the inner surface of the nozzle 1 1. FIG. 2 shows a vertical cross section of the column 1 shown. In this cross-section, the surface 15 of the lower section of the nozzle 1 1, which is shown in Figure 2 because of the sectional view as a line, closes with the vertical inner surface 16 of the column body 2, which extends from the nozzle 1 1 downwards and in FIG 2 is also shown as a line because of the sectional view, the angle α. At the apex of the angle, the vertical inner surface 16 of the column body 2 and the lower cutting line of the nozzle 1 1 are thus connected. Accordingly, this surface 15 of the nozzle 1 1 with the horizontal H encloses the angle ß, the sum of the angles α and ß is 270 °.

According to the invention, the angle ß is greater than 0, d. H. the surface 15 is not horizontally aligned at the lower line of intersection of the vertical cross section of the column 1, but inclined. The angle of inclination is 3 ° in the present exemplary embodiment, with the drawings not rendering the angles true to reality for better illustration. The angle α is thus 267 ° in this case.

It should be noted that the angle α can also be smaller, so that a greater inclination of the surface 15 results. According to the invention, the angle α is in a range of 210 ° to 267 °, in particular in a range of 225 ° to 267 ° and preferably in a range of 255 ° to 267 °.

The inclination of the surface 15 of the lower cutting line of the nozzle 1 1 in a vertical cross section of the column 1 causes liquid on this surface 15 runs down and in particular does not remain on this surface 15. On the- In this way, the polymerization of liquid containing (meth) acrylic monomers can be prevented.

The inclination of at least 3 °, in particular in the lower region of the nozzle 1 1 is required so that liquid can drain. In particular, the lower half of the neck 1 1 has this angle to the inner surface 16 of the column body 2. For manufacturing reasons, however, the nozzle 1 1 is preferably rotationally symmetrical, so that the angle between the directed into the column cavity 3 surface of the nozzle 1 1 with the inner surface 16 of the column body 2 over the entire circumference of the nozzle 1 1 is the same. In cross-section, the inner line, which is part of the inner surface 15 of the nozzle 1 1, a straight line. In other embodiments, however, this line may also be bent. In this case, for the angle α or the angle β, the tangent to the surface 15 of the lower cutting line of the nozzle 11 with the vertical inner surface 16 of the column body 2 is considered. A curved line changes the orientation of this tangent. The above-mentioned angle α is in this case at least 50%, preferably over a larger range, such as. B. 70% or 90% in the specified angular range. The angle α is in particular in no area 270 ° or larger. In the embodiment of the column 1 according to the invention shown in Figures 1 to 3 below and above the access opening 9, a mass transfer tray 8-1 and 8-2 is arranged. Since the inspection opening 9 is a manhole opening, the distance between these 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 an undesirable formation of polymer. For this reason, in the exemplary embodiment of FIGS. 1 to 3, a mass transfer tray 8-3 is also arranged in the area of the inspection opening 9. The distance between the two mass transfer trays 8-1 and 8-3 or between the two mass transfer trays 8-3 and 8-2 is then 500 mm. The mass transfer tray 8-3 in the exemplary embodiment described is a dual-flow tray which has openings 17, as shown in FIG.

Furthermore, a plate 18 is arranged in the region of the inspection opening 9, which prevents gas rising in particular, but also descending liquid, from flowing upward past the mass transfer tray 8-3 through the horizontal opening formed by the nozzle 11 flowing down. The plate 18 has openings 19 so that it acts as a mass transfer plate. The plate 18 is oriented horizontally, being flush with the mass transfer tray 8-3. The plate 18 is thus arranged horizontally at the same height as the mass transfer tray 8-3. The shape of the plate 18 is as shown in Figure 3 to the horizontal cross-sectional shape of Adapted tail. Since the neck in the present embodiment is truncated cone-shaped, the plate 18 is trapezoidal. In order to keep the gap between the plate 18 and the mass transfer tray 8-3 as narrow as possible, the long side of the trapezoid of the plate 18 could also be adapted to the rounding of the mass transfer tray 8-3 in this area or vice versa the rounding the mass transfer tray 8-3 be flattened adapted in this area to the long side of the trapezoidal plate 18.

Depending on the size of the inspection opening 9 and the desired distance between the material exchange floors 8, a plurality of plates 8 may also be located in the region of the inspection opening 9. These mass transfer trays 8 are then each assigned a plate 18.

The plate 18 is fixed to the pivotable cover 12 so that it is pivoted out with the lid 12 when the inspection opening 9 is opened. This has the advantage that the plate 18 does not have to be dismantled when inspection or cleaning work in the column 1 must be performed. Similarly, the mass transfer tray 8-3 is removable, so that a person can pass through the formed as a manhole access opening 9 in the column cavity 3.

With reference to FIG. 4, a further exemplary embodiment of the column 1 according to the invention is described: The exemplary embodiment shown in FIG. 4 differs from the exemplary embodiment shown in FIGS. 1 to 3 in that no mass transfer tray 8-3 is arranged in the region of the inspection opening 9. The inspection opening 9 is also not formed as a manhole, but as a hand hole. The diameter of the inspection opening 9 is thus substantially smaller than in a manhole. It is designed so that the hand or the arm of a person together with z. B. a cleaning device in the column cavity 3 can be introduced. The diameter is z. B. in a range of 100 mm to 300 mm. The geometry of the nozzle 1 1 and in particular the inclination of the directed into the column cavity 3 surface 15 of the nozzle 1 1, in particular the lower section line of the nozzle 1 1 in a vertical cross-section of the column 1, is the same as in the embodiment of Figure 1 to 3.

With reference to FIG. 5, a further embodiment of the column 1 according to the invention is described: As in the exemplary embodiment described with reference to FIG. 4, no mass transfer tray 8-3 is arranged in the region of the inspection opening 9 in this case. However, the inspection opening 9 is also designed as a manhole. In order to prevent polymerization in the region between the mass transfer trays 8-1 and 8-2, in particular in the case of the nozzle 11, a spray device 20 is arranged in the column body 2. By means of the spray device 20 is a liquid 22 at least against the directed into the column cavity 3 surface 15 of the nozzle 1 1 sprayable. For this purpose, the spraying device 20 has a spray nozzle 21, which is supplied via a supply line 23 liquid. The supply line 23 passes through a gas and liquid-tight passage 24 through the column body 2. Outside the column body 2, a pump 25 is arranged, which is connected to the supply line 23. On the other hand, the pump 25 is connected to a line 26 which re-enters the column cavity via another gas and liquid-tight passage 27. The conduit 26 has an inlet opening 28, which is arranged immediately above the mass transfer tray 8-1. The mass transfer tray 8-1 is adjacent to the inspection opening 9 or the nozzle 11.

In the embodiment shown here is this mass transfer tray 8-1 immediately below the access opening 9. By means of the spray 20, liquid which has collected on the mass transfer tray 8-1, removed and from the spray nozzle 21 against the surface 15 of the nozzle 11 and the Inner surface of the lid 12 sprayed. This prevents liquid from accumulating and polymerizing in this area. As shown in Figure 5, the nozzle 1 1 as in the previous embodiments is frustoconical. The spraying device 20 can be used in other embodiments, however, at inspection openings 9 with smaller clear width and / or in columns 2, in which a bottom 8-3 is arranged in the region of the inspection opening 9.

The spraying device 20, starting from the supply line 23, may also comprise a line system which sprays the inner surfaces of further inspection openings with liquid. In this case, however, the composition of the liquid withdrawn via the inlet opening 28 is not always substantially the same as the composition of the liquid in the region of the respective inspection opening 9 during operation of a separation process in which, in particular, gas rises and a liquid descends.

In the following, an embodiment of the method according to the invention will be described, which is carried out with the separation column 1 described above. The process is a thermal separation process between at least one gas rising in the separation column 1 and at least one liquid descending in the separation column 1. In particular, the ascending gas and / or the descending liquid contains (meth) acrylic monomers.

In the separation process, a fractionating condensation is carried out to separate acrylic acid from a product gas mixture containing acrylic acid a heterogeneously catalyzed gas phase partial oxidation of a C3 precursor compound (especially propene and / or propane) of the acrylic acid with molecular oxygen to acrylic acid in a separation column 1 containing separating internals. The separation column contains from bottom to top first dual-flow trays and then cross-flow hood floors, which are supported from below as described above. Otherwise, the method is carried out as described in DE 19924532 A1, DE 10243625 A1 and WO 2008/090190 A1.

The term "C3 precursor" of acrylic acid is taken to mean those chemical compounds which are obtainable formally by reduction of acrylic acid. Known C3 precursors of acrylic acid are e.g. Propane, propene and acrolein. But also compounds such as glycerol, propionaldehyde, propionic acid or 3-

Hydroxypropionic acid belongs to these C3 precursors. From them, the heterogeneously catalyzed gas phase partial oxidation with molecular oxygen is at least partially an oxidative dehydrogenation. In the relevant heterogeneously catalyzed gas phase partial oxidations, said C3 precursors of acrylic acid, typically with inert gases such as e.g. molecular nitrogen, CO, CO 2, inert hydrocarbons and / or steam diluted, passed in admixture with molecular oxygen at elevated temperatures and optionally elevated pressure over transition metal mixed oxide catalysts and oxidatively converted into an acrylic acid-containing product gas mixture.

The acrylic acid-containing product gas mixture typically comprises a heterogeneously catalyzed gas-phase partial oxidation of C3 precursors (eg propene) of acrylic acid with molecular oxygen over catalysts in the solid state, based on the total amount of the constituents (contained in it) Contents on:

From 1 to 30% by weight of acrylic acid,

From 0.05 to 10% by weight of molecular oxygen,

From 1 to 30% by weight of water,

0 to 5% by weight of acetic acid, 0 to 3% by weight of propionic acid,

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

 0 to 2% by weight of acrolein,

 0 to 1% by weight of formaldehyde,

 0 to 1% by weight furfural,

 0 to 0.5% by weight of benzaldehyde,

0 to 1% by weight of propene, and

as residual amount of inert gases, e.g. Nitrogen, carbon monoxide, carbon dioxide, methane and / or propane.

The partial gas phase oxidation itself can be carried out as described in the prior art. On the basis of propene, the partial gas phase oxidation may e.g. in two consecutive oxidation steps, e.g. in EP 700 714 A1 and in EP 700 893 A1. Of course, however, the gas phase partial oxidations cited in DE 19740253 A1 and in DE 19740252 A1 can also be used.

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.

By direct and / or indirect cooling, the hot product gas mixture is expediently first cooled to a temperature of 100 to 180 ° C, before it is conducted for the purpose of fractional condensation in the region C (the bottom) of the separation column 1. The pressure prevailing in the separation column 1 operating pressure is usually 0.5 to 5 bar, often 0.5 to 3 bar and often 1 to 2 bar.

LIST OF REFERENCE NUMBERS

1 column, separation column

 2 column body

 3 column cavity

 4 inlet

 5 supply line

 6 expiration

 7 coat

 8 floors

 8-1, 8-2, 8-3 trays

 9 inspection opening

 1 1 nozzle

 12 lids

 13 deduction

 14 sampling line

 15 surface

 16 inner surface

 17 opening

 18 plate

 19 opening

 20 spraying device

 21 spray nozzle

 22 liquid

 23 supply line

 24 implementation

 25 pump

 26 line

 27 implementation

 28 removal opening

Claims

claims

Column (1) for the thermal treatment of fluid mixtures with

 a cylindrical, vertically oriented column body (2) forming a column cavity (3) and a vertical inner surface (16),

 a plurality of trays (8) mounted in the column cavity (3) and spaced vertically from each other,

 at least one stub (11) disposed in the column body (2) and extending away from the column body (2), and

 a closable access opening (9) which is formed at the neck (1 1),

 characterized in that

 in a vertical cross-section of the column (1) in the column cavity (3) directed line of the lower section line of the nozzle (1 1) or a tangent to the in the column cavity (3) directed line of the lower section line of the nozzle (1 1) the vertical inner line (16) of the column body (2), which extends from the nozzle (1 1) downwards, at least partially encloses an angle in a range of 210 ° to 267 °.

Column (1) according to claim 1, characterized in that

 in a vertical cross-section of the column (1) at least 50% of the line in the column cavity (3) directed line of the lower section of the nozzle (1 1) or the tangent to 50% of the in the column cavity (3) directed line of the lower section line of the nozzle (1 1) with the vertical inner line (16) of the column body (2), which extends from the nozzle (1 1) downwards, encloses an angle in a range of 225 ° to 267 °.

Column (1) according to claim 1 or 2, characterized in that

 the nozzle (1 1) has an upper half and a lower half and that in the lower half of the in the column cavity (3) directed surface (15) of the nozzle (1 1) or the tangent to the surface (15) of the lower half of the nozzle (1 1) with the vertical inner surface (16) of the column body (2), which extends from the nozzle (1 1) downwards, an angle in a range of 210 ° and 267 °.

Column (1) according to one of the preceding claims, characterized in that

the nozzle (1 1) is rotationally symmetrical about a horizontal axis and the in the column cavity (3) directed surface (15) of the nozzle (1 1) or the tangent on the surface (15) of the nozzle (1 1) the vertical inner surface (16) of the column body (2) extending downwardly from the nozzle (1 1) encloses an angle in a range of 210 ° to 267 °.

Column (1) according to one of the preceding claims, characterized in that

 the nozzle (11) is of frusto-conical shape and the surface (15) of the nozzle (11) directed into the column cavity (3) with the vertical inner surface (16) of the column body (2) has an angle in a range of 210 ° to 267 ° ° includes.

Column (1) according to one of the preceding claims, characterized in that

 the inspection opening (9) is a manhole opening which is formed in the neck (1 1) and which is closable with a cover (12),

 at least one of the bottoms (8-3) is mounted in the region of the manhole opening and

 in the region of the nozzle (1 1) between the one bottom (8-3) and the closed lid (12), a plate (18) is arranged.

Column (1) according to claim 6, characterized in that the entire horizontal cross section of the column (1) at the level of the one bottom (8-3) in the manhole opening of the one bottom (8-3) and the plate (18 ) is substantially filled.

Column (1) according to one of claims 6 or 7, characterized in that one bottom (8-3) in the region of the manhole opening is a mass transfer tray with openings (17) and the plate (18) is a mass transfer plate with openings (19) ,

Column (1) according to one of claims 6 to 8, characterized in that the one bottom (8-3) in the region of the manhole opening and the plate (18) are aligned substantially horizontally.

Column (1) according to one of the preceding claims, characterized in that in the column body (2) a spraying device (20) is arranged, with the liquid (22) at least against the in the column cavity (3) directed surface (15) of the nozzle (1 1) is sprayable.

1 1. Column (1) according to Claim 10, characterized in that the spraying device (20) has a spray nozzle (21), a feed line (23) and a spray liquid feed device, wherein the spray liquid feed device is designed to deliver spray liquid to the column cavity (3) remove the extracted spray liquid via the feed line (23) of the spray nozzle (21) and spray by means of the spray nozzle (21) at least against the in the column cavity (3) directed surface (15) of the nozzle (1 1).

12. Column (1) according to claim 11, characterized in that the spray liquid feeding device has an inlet opening (28), which is arranged directly above a bottom (8-1) which is adjacent to the connecting piece (11). is.

13. Thermal separation process between at least one in the column (1) according to one of claims 1 to 12 rising gas and at least one in the column (1) descending liquid.

14. The method according to claim 13, characterized in that the rising gas and / or the descending liquid contains (meth) acrylic monomers.