FR3050650A1 - NEW DEVICE FOR DISPENSING GAS AND LIQUID IN CATALYTIC DISTILLATION COLUMNS WITH LIQUID DESCRIPTIVE FLOW - Google Patents

Abstract

The present invention describes a device for feeding the catalytic zone of a reactive distillation column using a liquid flow as a reaction flow, the flow of the liquid in the reactive zone being of descending type, and the gas not meeting the liquid. in the reactive zone.

Description

BACKGROUND OF THE INVENTION The object of this invention is the improvement of the internals used in reactive distillation columns. By internal is meant any element useful for the distribution of gas and liquid fluids within the catalytic zone. We speak of plateau of the catalytic zone to designate all the internals and support elements of the catalytic bed.

Reactive distillation, also called catalytic distillation, consists in carrying out a separation by distillation and then a chemical reaction in the same equipment called reactive distillation column. This operation is particularly indicated for the balanced reactions (for example A + B C + D), thus incomplete. Thus, if one of the constituents is removed during the reaction, the equilibrium will move in the direction of the formation of the latter, thereby improving the reaction conversion.

In the rest of the text, the terms reactive column or catalytic column will be used indifferently.

One embodiment of a reactive distillation column is a succession of catalytic zones and distillation zones (cf. FIG. 1 for the general configuration of a reactive column). A catalytic zone is framed by two distillation zones, a so-called "superior" and a so-called "lower". All 3 zones form a doublet.

In the context of the present invention, the gas and the liquid are only encountered in the distillation zones, and the catalytic zone only relates to the liquid.

The gas must therefore bypass the catalytic zone without any contact with the liquid.

The term "bypass" in the text of the catalytic zone will sometimes be referred to by the gas according to a terminology well known to those skilled in the art.

The new internal scheme described in the present invention differs from that of the prior art due to the change of flow direction of the liquid in the catalytic zone which becomes downward while it is ascending in the prior art. Downflow has certain advantages, including the possibility of higher liquid surface speeds. Typically, according to the prior art. the liquid surface velocity should be less than the superficial fluidization rate of the bed, whereas according to the invention it can exceed it. The fluidization rate of a bed of particles depends essentially on the density, the average diameter of said particles, and the viscosity of the liquid. The person skilled in the art knows in particular the reference: "Perry's Chemical Engineers Handbook, 7th Edition, Mc Graw-Hill" which makes it possible to evaluate the minimum speed of fluidization of given particles.

Brief description of the figures

FIG. 1 is a schematic representation of a catalytic column which makes it possible to visualize the alternation of the distillation zones and the reactive zones. A column can comprise several reactive zones and several alternating distillation zones.

FIG. 2 represents a schematic view of a reactive column plate according to the invention. FIG. 2 shows a liquid supply zone from the upstream distillation zone consisting simply of an upper liquid layer surmounting the catalytic zone (8).

The liquid passes through the catalytic zone (8) in downward flow and is then discharged from said zone by overflow from an annular peripheral zone (5) surrounding said catalytic zone (8). This peripheral annular zone (5) has a vertical wall (12) which acts as a weir.

The liquid joins the downstream distillation zone via a second peripheral zone adjacent to the wall of the dedicated column (6).

The gas circulates in a dedicated peripheral zone adjoining the wall of the column (7) which is entirely separated from the peripheral zone of the liquid (6) by sealed vertical walls as can be seen in FIG. the catalytic column made at the level of the catalytic zone and which makes it possible to visualize the peripheral zone portion dedicated to the liquid (6), and the peripheral zone portion dedicated to the gas (7).

FIG. 2a is a view from above which makes it possible to better visualize the peripheral zones (6) and (7).

FIG. 3 represents a variant of the invention in which the gas no longer flows through the dedicated peripheral zone (7), but through a network of chimneys (9) which passes through the catalytic zone (8). The circulation of the gas is ascending through the chimneys (9).

FIG. 3a is a view from above which makes it possible to visualize the peripheral zone (6).

FIG. 4 represents another variant of the present invention in which the liquid is no longer removed from the catalytic zone by the dedicated peripheral zone (6), but by a network of chimneys (10) passing through the catalytic zone (8), and disposed coaxially with respect to the chimney array (9).

FIG. 4a is a view from above which makes it possible to visualize the gas chimneys (9) and the liquid chimneys (10).

FIG. 5 represents a variant of the diagram according to FIG. 4 in which the liquid evacuation chimneys (10), still substantially coaxial with the "bypass" chimneys (9), are compartmentalised so as to define two zones: - an area (11) which recovers the liquid at the bottom of the catalytic zone (8) and returns it to the compartment (11); - an area (13) which allows the liquid to come down to leave the chimney (10); ) at the lower part of the catalytic zone (8).

Figure 5a shows the gas chimneys (9) and liquid chimneys (10).

Examination of the Prior Art The prior art in the field of reactive columns is essentially represented by the document FR 2737132. This text describes the general scheme of a reactive column and more particularly describes the path followed by the liquid at the level of the reactor. catalytic zone. It does not mention any device to cope with significant variations in the liquid flow and / or gas. The internal described in the patent FR2737132 can be summarized as follows:

A catalytic zone (C) is framed by two distillation zones (B), the vapor of the distillation flowing from bottom to top so as to be practically not in contact with the catalyst, and the liquid circulating from the zone of distillation. higher distillation towards a substantially central zone located at the bottom of the catalytic zone, this by means of a central collector having a conical then cylindrical shape which brings the liquid below the catalytic zone.

The liquid then circulates radially below said catalytic zone by a radial-type means, so as to be introduced into a liquid distribution zone. From this distribution zone, the liquid flows through the catalyst in the catalytic zone in an upward direction, called "upflow", then the liquid is recovered by at least one liquid discharge means in the lower distillation zone.

The catalytic zone is surmounted by a certain layer of liquid which makes it possible to ensure the supply of the discharge means. The liquid supply of the upflow catalytic zone results in reduced flexibility, since the fluidization velocity within the catalytic bed can not be exceeded.

This constraint generally leads to an enlargement of the column diameter in upward flow. By passing to a downward flow according to the invention, therefore without risk of fluidization, this constraint disappears and one can practice lower column diameters.

There can also be a gain in height by disappearance of the collector.

Brief description of the invention

The present invention can be defined as a reactive distillation column constituted by the alternation of catalytic zones (8) and distillation zones (B) in which, at each of the catalytic zones (8), the liquid coming from the downstream distillation zone feeds the upper liquid layer (3) overcoming the catalytic bed (8) and then passes through the catalytic zone (8) in downward flow and is discharged from said catalytic zone by an annular zone (5) terminating in a weir (12) which allows it to join the peripheral zone (6) adjoining the wall of the column, or by a system of chimneys (10) passing through the catalytic zone, the gas passing through the catalytic zone (C) through a zone dedicated device (7), or by a network of vertical chimneys (9) which open above the upper level of the liquid weirs (12), the inner wall of the annular zone (5) exceeding the level of the liquid layer superior (3) to respond to a situation of "overfull".

According to a first variant of the present invention, the liquid is removed from the catalytic zone (8) by a network of chimneys (10), coaxial and surrounding the "bypass" chimneys of the gas (9), these chimneys (10). being compartmentalized in a first annular zone (11) in which the liquid rises and a second annular zone (13) inside which the liquid drops down at the base of the catalytic bed (8).

According to another particular variant of the present invention, the compartmentation of the chimneys (10) has a first half (11) allowing the liquid to rise, and a second half (13) allowing the liquid to go down to the level of the base of the catalytic bed (8).

In the configuration where the gas bypasses the catalytic zone by the network of chimneys (9), the number of stacks (9) per unit section of the catalytic zone is preferably between 1 and 20 stacks / m ^ when the gas stacks do not are not associated with the liquid chimneys (10), that is to say when the evacuation of the liquid is through the peripheral zone (6).

In the configuration where the gas bypasses the catalytic zone (8) by the network of chimneys (9), the number of chimneys (9) per unit section of the catalytic zone is between 20 and 200 stacks / m ^, and preferred way between 100 and 150 chimneys / m ^ when the gas chimneys (9) are surrounded by liquid chimneys (10).

Detailed description of the invention

The present invention can be defined as a reactive distillation column constituted by the alternation of catalytic zones (8) and distillation zones (B). Each catalytic zone is thus framed by an upstream distillation zone and a downstream distillation zone. The general arrangement of the distillation zones and the catalytic zones is not different from that of the prior art according to FIG.

In the context of the present invention, each catalytic zone is the seat of a reaction with the liquid phase only, and the flow of said liquid phase through the catalytic bed is downward.

The following description is made by following Figure 2 according to the invention.

The liquid from the upstream distillation zone directly feeds an upper liquid layer (3) which overcomes the catalytic zone (8).

The catalytic bed is supported by a lower grid (15) delimiting the lower level of the catalytic bed (8).

In the same way, the upper level of the catalytic bed is delimited by an upper grid (16).

The liquid passes through the catalytic zone (8) in downward flow and is discharged from said catalytic zone by overflow over the side wall (12) which defines the upper liquid layer (3).

The liquid rises from the bottom of the catalytic zone (8) by the annular zone (5) whose outer wall ends with the weir (12).

The inner wall of the annular zone (5) exceeds the level of the upper liquid layer (3) so as to respond to a situation of "too full" that can occur in case of too much liquid traffic or delta P too high .

The transfer of the liquid to the downstream distillation zone can be done either by a dedicated peripheral zone (6) adjoining the wall of the column, or by a system of chimneys (10) passing through the catalytic zone.

The gas from the downstream distillation zone bypasses the catalytic zone (8) either by a dedicated peripheral zone (7) or by a network of vertical chimneys (9) which open above the upper level of the liquid spillway (12). ).

According to a first variant of the present invention represented by FIG. (3), the gas bypasses the catalytic zone not by means of the dedicated peripheral zone (7), but by means of a system of chimneys (9) passing through the zone catalytic and emerging at a level above the level of the weir (12). The pitch between chimneys (9) for the crossing of the gas is preferably either square or triangular.

The number of stacks (9) per unit section of the catalytic zone is preferably between 1 and 20 stacks / m ^ when the gas stacks are not associated with the liquid stacks, and preferably between 20 and 200 stacks / m ^, and preferably between 100 and 150 stacks / m 2 when the gas and liquid stacks are associated coaxially.

According to another variant of the distillation column of the invention (not shown), the liquid after passing through the catalytic zone (8) is returned to the downstream distillation zone via a dedicated peripheral zone (6) separated by sealed walls of the peripheral zone (7) dedicated to gas.

According to another variant of the present invention represented by FIG. 4, the liquid is discharged from the catalytic zone (8) by a network of chimneys (10) surrounding the gas bypass chimneys (9).

In this case, the circulation of the liquid inside the chimneys (10) comprises a first ascending portion followed by a second descending portion, the chimneys (10) being divided by means of a vertical wall making it possible to define the upward zone. (11) and the descending zone (13) for the liquid.

This variant with a network of chimneys (9) for the bypass of the gas, and network of coaxial chimneys (10) for the evacuation of the liquid is represented by FIG. 4.

The liquid evacuation chimneys (10) are preferably coaxial with the bypass chimneys (9).

These chimneys (10) have an interior partitioning which makes it possible to define two zones inside the chimneys (10): - - an upward zone (11), - a downward zone (13) which brings back the liquid to the lower level of the catalytic bed (8) from which it flows to the downstream distillation zone. The flow of the liquid in the chimneys (10) is therefore first ascending in the part (11) and then down in the part (13).

The network of chimneys (10) for the evacuation of the liquid therefore has the same pitch characteristics as the network of chimneys (9) of "bypass" of the gas.

In some cases, the chimney array (10) does not exactly cover the chimney array (9), in the sense that some chimneys (9) are not surrounded by the coaxial chimney (10).

In a variant of the present invention shown in FIG. (5), the compartmentalisation of the liquid evacuation stacks (10) is different and defines a first half (11) of the chimney for the upward flow of the liquid, and a second half (13) for the downward flow of the liquid.

Whatever the variant of the present invention, there is an overflow device at the upper part of the wall (12) separating the catalytic bed (8) from the upflow zone of the liquid (5). or (11), according to the variant of the invention. This avoids clogging of the column in case of too high liquid flow, or partial blockage of the bottom of the catalyst bed. In this case, the excess liquid from the upstream distillation zone goes directly into the annular zone (5) or (11) according to the variant chosen.

It remains within the scope of the present invention by combining the different variants, that is to say: - With an evacuation of the liquid by the dedicated peripheral zone (6) and a "bypass" of the catalytic zone by the gas by means of the network of chimneys (9) according to FIG. 3. - With evacuation of the liquid by the network of chimneys (10) and a bypass of the catalytic zone by the gas by means of the dedicated peripheral zone (7). ). - With an evacuation of the liquid by the network of chimneys (10) and a "bypass" of the catalytic zone by the gas by means of the network of chimneys (9) according to Figure 4.

Comparative example

In the example which follows, a column dimensioning according to the prior art (liquid flow in the upflow reaction zone) is compared with a design according to the invention (liquid flow in the reaction zone in "down flow" ).

The reactive column is used in a C4 cut etherification process containing mainly olefins (butene-1, butene-2-cis, butene-2-trans, iso-butene), paraffins (n butane, isobutane).

The examples are established by means of a numerical simulation previously calibrated on a similar industrial case. The Proll simulation software is used. The kinetics of reaction for etherification is based on the study published in "Kinetics and Mechanism of Ethyl Tertiary Butyl Ether Liquide Phase Phase, Françoisse, O. Chemical Engineering and Processing: Process Intensification Volume: 30 Issue 3 (1991) ISSN : 0255-2701 Online ISSN: 1873-3204 ".

In the present example, only the operation of the reactive column is of interest. This reactive column has 5 reactive doublets.

A doublet is constituted by a catalytic zone, the receiving plate of the liquid coming from the catalytic zone, and the distillation plate situated downstream of the catalytic zone in question. More simply, we can consider that a doublet is the set of a catalytic zone and the distillation plate downstream to said catalytic zone.

The column comprises 33 theoretical plates including the reboiler (conventionally noted plateau 33), and the condenser (conventionally noted plateau 1).

The load is introduced tray 24, the doublets are located between the theoretical trays 5et6,7et8,9et10, 11 and 12 and 13 and 14.

The pressure at the top of the column is maintained at 800 kPa, the temperature is 64.9 * 0 at the head and 147 ° C. at the reboiler.

The charge of the reactive distillation column has the following composition as the average composition in Table 1 below:

Table 1 - composition of the charge of the catalytic column

The charge rate is set at 25650 kg / h. In order to obtain high conversions, the column is operated with a high reflux of 38500 kg / h. On the catalytic column, an overall conversion of 63% of the isobutene present in the feed is thus carried out.

At the level of the upper doublet, the liquid flow rate is 92.2 m3 / h at operating conditions, the density of the liquid is 536 kg / m3.

The gas flow rate is 64.5 t / h with a density at 16.1 kg / m3. The molar mass of the gas is 59 g / mol.

The sizing of a doublet according to the prior art is based mainly on 3 criteria: a) The fluidization speed of the catalyst, in this case an Amberlyst A 15 resin. In order to maintain a fixed catalyst bed, it is generally limited to at 1/3 of this fluidization speed. In the present case, with the operating conditions of the upper doublet fixed, there is a fluidization rate of 0.8 cm / s. An upward velocity of the liquid in the catalytic bed is therefore required of 0.25 cm / s maximum. (b) The permissible gas velocity in the gas passage. The usual criterion is 2.5m / s to avoid having a loss of pressure (pressure drop) of the gas by excessive friction. c) The central manifold has a diameter set at 80 cm to have a minimum residence time on the liquid allowing the steam to be released.

The diameter of the upper liquid-side doublet to meet the fluidization velocity criterion (a) is 1.8 m. In order to comply with the criterion of speed on the gas (b), a diameter of the upper doublet on the gas side of 1.88 m is obtained.

The sizing of the trays is carried out according to the usual criteria of those skilled in the art and gives a diameter of 1.8 m. In this case, it is the doublet that sets the diameter of the column.

The distillation column housing this type of system must have an internal diameter of 1.88m to be compatible with the design of the doublet.

According to the "downflow" technology described in the present invention, it becomes possible to limit the diameter of the catalytic bed (hence of the catalytic zone) to a lower value. It is indeed possible to increase the liquid velocity, without worrying about fluidization or excessive pressure loss, up to 1 times the fluidization velocity. The diameter of the catalytic zone thus goes to 1.1 m, instead of 1.8 according to the sizing of the prior art.

Comparative Table 2 below summarizes the differences in sizing between a column according to the prior art and a column according to the invention.

Table 2: Principal dimensions of the column according to the prior art and according to the invention

Claims (5)

1. Reactive distillation column consisting of the alternation of catalytic zones (8) and distillation zones (B) in which, at each of the catalytic zones (8), the liquid from the downstream distillation zone feeds the upper liquid layer (3) surmounting the catalytic bed (8) and then passing through the catalytic zone (8) in downward flow and is discharged from said catalytic zone by an annular zone (5) terminating in a weir (12) which makes it possible to join the peripheral zone (6) adjoining the wall of the column, or by a system of chimneys (10) passing through the catalytic zone, the gas passing through the catalytic zone (C) by a dedicated peripheral zone (7), or by a network of vertical chimneys (9) which open above the upper level of the liquid weirs (12), the inner wall of the annular zone (5) exceeding the level of the upper liquid layer (3) so as to meet to one situation of "overfull". 2. reactive distillation column according to claim 1, wherein the liquid is removed from the catalytic zone by a network of chimneys (10), coaxial and surrounding gas bypass chimneys (9), these chimneys (10) being partitioned into a first annular zone (11) in which the liquid rises and a second annular zone (13) inside which the liquid drops down at the base of the catalytic bed (8). 3. reactive distillation column according to claim 1, wherein the compartmentalization chimneys (10) has a first half (11) allowing the liquid to rise and a second half (13) allowing the liquid to go down to the base of the catalytic bed (8). 4. Reactive distillation column according to claim 1, wherein the number of stacks (9) per unit section of the catalytic zone is preferably between 1 and 20 stacks / m ^ when the gas stacks are not associated with the liquid stacks. (10), that is to say when the evacuation of the liquid is through the peripheral zone (6). 5. reactive distillation column according to claim 1, wherein the number of stacks (9) per unit section of the catalytic zone is between 20 and 200 stacks / m ^, and preferably between 100 and 150 stacks / m when the gas chimneys (9) are surrounded by liquid chimneys (10).