MXPA99011846A - React distillation - Google Patents

Abstract

The reactive distillation is carried out in a column (1) with a filler (2) which is designed at least partially as a catalyst carrier (23). The fluids (3, 4), which form phases of different densities, flow through the filling. A flow (300) of internal volume is established for the densest fluid (3), the value of which is in a range (I) around a differentiated value (a), where this value is associated with a distribution ( 32) of drying time of the densest fluid. For the differentiated value, the variance (s) of the drying time distribution -as a function of the internal volume flow- requires a minimum, and the limits of the mentioned internal volume flow interval do not differ from the differential value in more of 30%, preferably more than 1

Description

REACTIVE DISTILLATION DESCRIPTION OF THE INVENTION The invention relates to a reactive distillation, according to the preamble of claim 1, with uses of the reactive distillation and with a filler column to carry out the reactive distillation. By reactive distillation is meant a process in which catalytic reactions are carried out in a column in the presence of simultaneous distillation. In this process, the column can be operated as a fill column. The filling of the column typically comprises a large number of partial spaces containing solids and cavities between the partial spaces, with the cavities and the partial spaces extending mainly along a column axis or at angles to the latter and the spaces In each case, partials are formed by a packed bed which contains catalytically active substances. A denser fluid flows in the partial spaces of packed bed with a volume flow which is designed as an internal volume flow. A less dense fluid flows countercurrent through the cavities. The partial spaces of the packed bed are joined by walls which are permeable for fluids. On the one hand, catalytic reactions take place in the packed bed, and on the other hand, an exchange of material takes place between the two fluids. The undesirable byproducts that arise in reactive distillation, the concentration of which depend on the operating parameters. As a rule, product treatment is required, which is more complicated and costly as more byproducts arise. The operating parameters are therefore advantageously chosen so that the production of by-products that are generated is as low as possible. However, the objective of a production speed as large as possible of the reactive distillation carried out, per unit volume of the filling, is also sought. In order to obtain this, it must be provided to the entire filling surface, which is potentially available, covered (wetted) by a denser fluid. Reactive distillation is known from US-A 5 120 403 in which the filling is "flooded" with a liquid phase and a gaseous phase which forms a foam with the liquid phase which is transported through the filling. The object of the invention is to provide an additional method to carry out a reactive distillation for which the production of by-products is a minimum or at least is in the vicinity of a possible minimum and for which the production speed of the products that are made is as big as you can. This objective is satisfied by the reactive distillation which is defined in claim 1. Reactive distillation is carried out in a column with a filler which is formed at least partially as a catalyst carrier. The fluids which form the two phases of different densities, flow through the filling.

An internal volume flow is established for the densest fluid, the value of which is in an approximate range of a differentiated value, where this value is associated with a more dense fluid drying time distribution: for the differentiated value , the variance of the distribution of the drying time - as a function of the internal volume flow - requires a minimum; and the limits of the aforementioned range, the internal volume flow differs from the differentiated value by no more than 30%, preferably not more than 10%. The dependent claims relate to advantageous embodiments of the invention. The objective of claim 8 is the use of the method according to the invention. Claim 9 is directed to a corresponding filler column. In the following, the invention will be described with reference to the drawings. In which they are shown: figure 1, the lower part of a column by means of which reactive distillation can be carried out, figure 2, partially a package for carrying out the reactive distillation, figure 3, a diagram for the explanation of a time distribution of drying, figure 4, an experimentally determined curve which illustrates the dependence of the variance of the distribution of drying time on the internal volume flow, figure 5, wall sections for a mattress-like filling part, the Figure 6, a carrier structure with a cylindrical filling part, and Figure 7, partially a filling with two kinds of filling structures.

Column 1 of figure 1 contains a filler 2 such as is known from patent specification EP 0 640 385 (= P.6592). The filling 2 comprises filling elements 2 'which are placed in a similar manner to stacking and which is constituted by layers 2"which are directed along the main flow direction 10, with the layers 2" formed of substantially cylindrical filler portions 23. Between the filling parts 23 there are flow conduits which pass through each other and which are open with respect to each other. The filler portions 23 are placed on a grid-like carrier structure, which is not illustrated in Figure 1. The adjacent filler elements 2"in each case are mutually offset by an angle of 90 °. Collars 12 form obstacles of deviation for the fluids 3 and 4 which participate in the reactive distillation (see figure 2) Now the aspects of the reactive distillation which are required for the explanation of the invention will be explained with reference to figures 2 and 3. The fluids 3 and 4, which form two phases of different densities, flow through the backfill 2 backflow in the direction of the z axis, which is parallel to a column axis The filling 2 comprises cavities 24 and partial spaces 23 which extend mainly along the axis of the column or which can also be oriented at angles with respect to the axis of the column.The partial spaces 23 in each case form a bed 20 Packed, in particular a body poured from a granulate which is a carrier of the catalytically active substances. The partial spaces 23 are joined by walls 22 which are permeable for the fluids 3, 4. These walls 22 can be made, for example, of wire gratings (in the form of trusses, meshes or nets). The fluid 3 flows with a flow 300 of internal volume through the packed bed 22. The arrows 30 indicate the trajectories on which the molecules of the substances which are contained in the fluid 3 move. Through the reactions at the points 21 (inside the packed bed 20), the initial substances are converted into desired products or in undesirable by-products (arrow 30 X.) An exchange of material (arrows 40, 41) takes place between the fluids 3 and 4 on the surfaces of the packed bed 20 which are formed by the walls 22. A distillation by means of this exchange of material The molecules which are contained in the fluid 3 have different drying times in the packed bed 20. A molecule which is carried to the bed 20 packed at the point z = 0 and in time t = 0 - see the diagram in figure 3 - it is located in the vicinity of a point with z = z: at a subsequent time point t = tj The two dashed lines 301 and 302 indicate the scattering region from the trajectories on which the molecules move through the packed bed 20. A frequency distribution of the z positions of the molecules at a time point t = t is provided by a bell-shaped curve 31, which is qualitatively illustrated as a function curve c = c (z; t = tj If one registers at the lower end of the packed bed 20 - specifically at z 0 z2 - the emergence of labeled molecules which are introduced simultaneously at the time point t = 0 or at the packed bed 20, one obtains a curve 32 at Bell shape: c '= c' (t; z = z) For this curve 32, a variance s can be determined This variance s depends on the internal volume flow 300. The labeled molecules can be, for example, ions, whose Concentration can be determined at the end of the packed bed z = z2 as a result of measurements of electrical conductivity Measurements of the variance s are in dependence on the internal volume flow 300 which generates a curve 33 which has a minimum : see fig ura 4. A differentiated value a of the internal volume flow in which the quantity produced of the by-products in the same way is a minimum, corresponds with the minimum of s. At an internal volume flow much smaller than that of a, a stagnation of the fluid 3 arises in the packed bed 20 and therefore partially higher drying times are generated, which results in an expansion of the curve 32 and by therefore an increase in the variance s. In an internal volume flow much larger than that of a, a liquid derivation arises on the surface of the packed bed 20 which is formed by the walls 22. This liquid flows past the packed bed catalytically active and is placed in a very small contact with it. The fluid 3 has partially higher drying times, which likewise lead to an extension of the curve 32 and an increase of the variance s. In order for a predetermined production rate of the reactive distillation to be carried out, an ideal process is obtained when the column is dimensioned such that the internal volume flow is taken with a differentiated value a. Deviations from this value a, which are in a restricted range I around the value of a performance, do not substantially worsen the method: within the limits of this interval I, the internal volume flow may differ from the value 5 differentiated by up to about 30%. Of course, it is preferable that the amount constitute 10% or less. An additional suitable packing for carrying out the reactive distillation is known from the patent specification EP 0 631 813 (= P.6579). The filling portions 23 Those which form parallel layers are formed in the form of mattresses comprising two fluid-permeable walls 22 'and 22": see Figure 5. The interior space of the filling portion 23 contains a granulate 200 with catalytically active substances. parallel on the walls 22 'and 22", which are shaped like reliefs, form the interior space. These conduits 25 pass through each other and are open relative to each other. At the edge of the filling part 23, they close. As a result of profiling the walls 22 'and 22", similar cavities are also produced ducts in the same way, in each case between adjacent layers which pass through each other and are open one with respect to the other. Figure 6 shows a suitable additional packaging, which is known from the document mentioned above, EP 0 640 385. A static mixing structure 5 of surfaces 51 and 52, which are bent in a zigzag manner, is used as a carrier structure for the filling portions 23. In the whole or in addition only in the individual conduits which are formed by the zigzag bending can, in each case, contain a filling part 23. As a rule, a film of the denser fluid is also formed on the carrier structure. Through this, the surface which is available for distillation is increased. In order to generate an even larger surface available for distillation, the filler 2 can be designed as follows: see Figure 7. In the column, zones 6 and 7 of a first and second class are placed in a sequence alternating in the direction of the axis of the column. In the zones 6 of the first class, filling structures 5 are contained (see Figure 6) in which only an exchange of material between the two fluids takes place. In the zones 7 of the second class are contained 5 'filling structures, 23 in which the reactive distillation takes place. The lengths of zones 6 and 7 may vary in order to render surfaces of different sizes available. A production quantity is predetermined for the reactive distillation, for the packed column. The filling capacity of the column, according to the invention, should be designed in such a way that the internal volume flow which is provided for the operation of the column corresponds, on the one hand, mainly with the predetermined production quantity and , on the other hand, so that it is in the mentioned interval I around the value differentiated. The reactive distillation according to the invention can be used, for example, for the production or for the decomposition of esters, ethers and alcohols. Other uses may be the selective hydration of olefins or aromatics; in addition, the realization of isomerizations. An example for the explanation of the reactive distillation according to the invention: the synthesis of methyl-tert-butyl ether (MTBE) can be carried out in a reactive distillation with catalytically active fillers (see EP-A 0 396 650) . In this, isobutene is converted to MTBE from a flow of C4 with methanol. The acid ion exchange resin can be used in this as a catalyst. In addition to the main reaction, three side reactions can mainly occur. On the one hand, the flow of C4 may contain traces of water, whereby isobutene reacts to form terbutanol. On the other hand, isobutene can react with itself to form diisobutene; in addition, condensation of methanol to dimethyl ether can take place. The last two side reactions mentioned arise in the case of a large excess of a reaction partner or in the absence of another reaction partner.

In a reactive distillation which is operated with catalytically active fillers, with a small internal volume flow there is a stagnation of the liquid phase and therefore partially higher drying times in the reaction zone of the column at different positions. In these zones of stagnation, the mentioned side reactions occur to a greater degree in the case of an excess of a reaction partner or in the absence of another reaction partner which is caused by the reaction. In the case of an internal volume flow which exceeds the upper limit of the interval I, the zones of stagnation in the same way admitted are avoided, but the reaction exchanges decrease considerably, however. In the reactive distillation, according to the invention, the internal volume flow of the column adjusts such that the catalytically active solid flows through and uniformly through the fluid phase part and the stagnation zones in the fluid phase are avoided. catalytically active solid bed. In this way, the catalyst is completely wetted and the mentioned side reactions are partially suppressed.

Claims (10)

1. A reactive distillation in a column comprising a filler, which is designed at least partially as a catalyst carrier, with fluids which form two phases of different densities flowing through the filler, characterized in that the internal volume flow is it adjusts for the densest fluid, the value of which is in a range approximately at a differentiated value which is associated with the distribution of drying time of the densest fluid; and where, for this differentiated value, the variance of the distribution of the drying time, as a function of the internal volume flow, requires a minimum; and wherein within the limits of the aforementioned range, the internal volume flow does not differ from the differentiated value by more than 30%, preferably 10%.

2. Reactive distillation, as described in claim 1, characterized in that the column contains a filler which comprises a large number of partial spaces containing solid substances and cavities between the mentioned partial spaces, wherein the cavities extend mainly along of a column axis or at angles to the latter, where the partial spaces mentioned in each case are formed by a packed bed which contains catalytically active substances and with these partial spaces of packed bed joined by walls which are permeable to the fluids.

3. Reactive distillation, as described in claim 2, characterized in that the zones of a first and second classes are placed in the column in an alternating sequence in the direction of the axis of the column, with filling structures in which only place an exchange of material between the two fluids that are contained in the zones of the first class, while the packed packing structures in which the reactive distillation is carried out are contained in the zones of the second class.

4. The reactive distillation, as described in claim 2 or claim 3, characterized in that the filling of the filling structures which are provided to carry out the reactive distillation, are constituted of layers which are oriented in the direction of the axis from the column; and wherein the adjacent layers in each case form cavities similar to ducts which cross each other and are open with respect to each other.

5. The reactive distillation, as described in claim 4, characterized in that the layers, in each case, are formed by a plurality of filler portions containing catalytically active substances which are placed inside a carrier structure; and wherein the filler portions are substantially cylindrical.

6. The reactive distillation, as described in claim 4, characterized in that the layers, in each case, are formed by mattress-like filling portions which comprise two fluid-permeable walls; and wherein the interior spaces of the filling parts are formed by parallel conduits containing catalytically active substances which are present in the form of a profile similar to relief of the walls with these conduits passing through each other, and which are open one with respect to to another and that are closed at the edge of the filling part.

7. The use of the reactive distillation, according to one of claims 1 to 6, for the preparation or for the decomposition of esters, ethers or alcohols.

8. The use of the reactive distillation, according to one of claims 1 to 10, for the selective hydration of olefins or aromatic compounds.

9. The use of the reactive distillation, according to one of claims 1 to 10, to carry out isomerizations.

10. A filling column for carrying out a reactive distillation according to one of claims 1 to 3, characterized in that the production quantity is predetermined for the reactive distillation; and where the capacity of the filler column is designed in such a way that the internal volume flow which is predetermined for the operation of the column, corresponds, on the one hand, mainly with the predetermined production amount and is based, by another part, in the mentioned interval around the differentiated value.