EP2401045A1

EP2401045A1 - Method for the distillative processing of a methanol/water mixture and method for producing alkali methylates

Info

Publication number: EP2401045A1
Application number: EP10703905A
Authority: EP
Inventors: Gerd Kaibel; Tilmann Sirch; Raimund Felder; Josef Guth
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2009-02-26
Filing date: 2010-02-17
Publication date: 2012-01-04
Also published as: AR075612A1; WO2010097318A1; US20110313207A1; CA2751983A1; JP2012518667A; BRPI1007998A2; CN102333575A

Abstract

The invention relates to a method for the distillative processing of a methanol/water mixture, wherein a methanol/water mixture is added to a distillation column (1), a vapor stream substantially comprising methanol is removed at the head of the distillation column (1), and a bottom stream substantially comprising water is withdrawn at the base of the distillation column (1), at least part of the vapor stream substantially comprising methanol is condensed and the condensed vapor stream is added as heating vapor to an evaporator (11), in which at least part of the methanol/water mixture to be separated is vaporized. The invention further relates to a method for producing alkali methylates in a reaction column (31), wherein methanol and alkaline lye are added to the reaction column (31). At the lower end of the reaction column (31), alkali methylate dissolved in methanol is withdrawn, and a methanol/water mixture is withdrawn at the upper end of the reaction column (31) and the methanol/water mixture is processed by way of the method for distillative processing.

Description

Process for the distillative work-up of a methanol / water mixture and process for the preparation of alkali metal methoxide

description

Di e invention relates to a process for the distillative workup of a methanol / water mixture. Furthermore, the invention relates to a process for the preparation of Alkalimethanolaten in a reaction column, wherein the reaction column methanol and lye is added, at the lower end of the reaction column in methanol solubilized alkali is removed and at the upper end of the reaction column, a methanol / water mixture is removed , The methanol / water mixture is worked up by the process for distillative work-up.

A mixture containing methanol and water is obtained, for example, in the preparation of alkali metal methylates from aqueous alkali metal hydroxide, optionally mixed with methanol, and methanol. Such a process for the preparation of alkali metal methoxides is described, for example, in EP-A 1 242 345. In this case, the reaction is carried out in a reaction column, which at the top is fed with an aqueous, optionally methanol-mixed, alkali-leach stream and methanol in the lower region. At the top of the reaction column, a water-containing methanol stream escapes. This is worked up in a rectification column. The methanol and water-containing stream is the distillation column, in which the workup is carried out as a side stream, preferably in the form of vapor. In the distillation column, a separation of the methanol / water mixture into a substantially methanol-containing stream which is withdrawn at the top of the column, and a substantially water-containing stream, which is withdrawn at the bottom of the column. In order to supply the energy necessary for the distillation, at least part of the substantially water-containing stream withdrawn at the bottom of the column is evaporated in an evaporator. The evaporator is usually heated for this purpose with heating steam. However, this has the disadvantage that the process from outside a large amount of energy must be supplied. Thus, in particular when heating with heating steam, first the generation of the heating steam is necessary. The methanol recovered at the top of the distillation column is partly condensed in a condenser and returned to the column, the remainder being fed as feed into the reaction column.

Another process for the preparation of alkali metal methoxide is known from EP-A 1 997 794. In this process as well, the methanol / water mixture obtained in the reaction column is fed to a distillation column in which the mixture is passed into an essentially methanol-containing overhead stream and essentially Water containing bottom stream is separated. The heating also takes place at the bottom of the column via a conventionally heated evaporator.

The object of the present invention is to provide a process for the treatment of a methanol / water mixture, which can be operated with a reduced compared to the known methods need to be supplied to heating steam.

The object is achieved by a process for the distillative workup of a methanol / water mixture, comprising the following steps:

(a) adding the methanol / water mixture to a distillation column,

(b) removing a substantially methanol-containing vapor stream at the top of the distillation column and a substantially water-containing bottom stream at the bottom of the column,

(c) compressing at least a portion of the substantially methanol-containing vapor stream,

(D) adding the compressed vapor stream as heating steam in an evaporator in which at least a portion of the methanol / water mixture to be separated is evaporated.

By compressing at least part of the essentially methanol-containing vapor stream and adding the compressed vapor stream as heating steam into an evaporator in which at least a portion of the methanol / water mixture to be separated is evaporated, the amount required to operate the distillation column greatly reduced in heating steam or possibly even completely saved. It is only necessary to supply energy for the operation of the compressor for compressing the vapor stream. Since at least part of the vapor stream gives off energy for vaporization and not the entire vapor stream is removed from the process, this also simultaneously reduces the amount of energy to be supplied from the outside.

In the context of the present invention, "substantially methanol-containing" means a proportion of methanol of at least 99% by weight, preferably of at least 99.9% by weight and in particular of at least 99.99% by weight.

Substantially containing water means a proportion of water in the stream of at least 95 wt .-%, preferably of at least 99 wt .-% and in particular of at least 99.99 wt .-%. The removal of the vapor stream at the top of the distillation column means in the context of the present invention that the vapor stream is removed as top stream or as a side draw above the internals in the distillation column. The removal of the substantially water-containing bottoms stream at the bottom of the column is usually carried out at the bottom of the column, but the removal can also take place via a side draw in the bottom.

Any distillation column known to those skilled in the art can be used as the distillation column. Usually used distillation columns have internals. Suitable internals are, for example, trays, unstructured packs or structured packings. As trays usually bubble trays, trays, valve trays, tunnel trays or slot floors are used. Unstructured packages are generally packed beds. Suitable packing elements are customarily as Raschig rings, Pall rings, Berl saddles or Intalox ^® saddles used. Structured packings are sold for example under the trade name Mellapack ^® Sulzer. In addition to the above-mentioned internals further suitable internals are known in the art and can also be used.

Preferred internals have a low specific pressure loss per theoretical separation stage. For example, structured packing and packing have a much lower pressure drop per theoretical plate than plates. This has the advantage that the pressure loss in the distillation column remains as low as possible and thus the mechanical performance of the compressor and the temperature of the methanol / water mixture to be vaporized remain low.

If structured packings or unstructured packs are contained in the column, they may be divided or there may be a continuous packing. Usually, however, at least two packs are provided, one pack above the feed point of the methanol / water mixture and one pack below the feed point of the methanol / water mixture. If an unstructured packing is used, for example a packed body, the fillers are usually located on a suitable sieve bottom or grid floor.

In a preferred embodiment, the evaporator, which is heated with the compressed part of the substantially methanol-containing vapor stream, an intermediate evaporator. This means that the evaporator is arranged above the bottom of the distillation column. This has the advantage that the temperature of the methanol / water mixture to be evaporated, which is taken from the distillation column and passed through the evaporator, has a lower evaporation temperature has as the withdrawn at the bottom of the column, substantially water-containing bottom stream. For vaporization of the methanol / water mixture in an intermediate evaporator, the vapor stream must therefore be compressed less strongly, which makes a lower energy supply necessary for compression.

In addition to the heating of an intermediate evaporator with the compressed vapor stream, however, it is also possible to heat an evaporator with which at least a portion of the bottom stream of the distillation column is heated. However, this requires a stronger compression of the vapor stream and thus a larger amount of energy that is required to compress the vapor stream.

Preferably, therefore, the evaporator to which the compressed vapor stream is added as heating steam, an intermediate evaporator.

The evaporator is usually arranged outside the distillation column. About a deduction from the column to be evaporated in the evaporator methanol / water mixture is withdrawn and fed to the evaporator. Via an inlet, the vaporized mixture is optionally returned to the distillation column with a residual liquid. If the evaporator is a Zwischenverdamp- fer, the trigger through which the methanol / water mixture is withdrawn and fed to the evaporator, a side draw and the inlet through which the vaporized methanol / water mixture is fed back to the column, a side feed. When the evaporator heats the bottom of the column, at least part of the bottom withdrawal stream is fed to the evaporator, evaporated in the evaporator and returned to the column in the region of the bottom. Alternatively, however, it is also possible to form, for example, on a suitable base when using an intermediate evaporator or in the bottom of the column tubes, which are flowed through by the compressed vapor stream. In this case, the evaporation takes place on the bottom or in the bottom of the column. However, it is preferred to arrange the evaporator outside the column.

Suitable evaporators which can be heated with the compressed vapor stream are, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, steam boilers, falling film evaporators or thin-film evaporators. As a heat exchanger for the evaporator usually a tube bundle or plate apparatus is used in natural circulation evaporators and forced circulation evaporators. When using a Rohrbündelübertragers the compressed vapor stream can either flow through the tubes and the methanol / water mixture to be evaporated flow around the tubes or flows around the compressed vapor stream flows around the tubes and the methanol / water mixture to be evaporated the pipes. In a falling film evaporator, the methanol / water mixture to be evaporated is usually added as a thin film on the inside of a pipe, and the pipe is heated from the outside. In contrast to a falling-film evaporator, a rotor with wipers is additionally provided in a thin-film evaporator, which distributes the liquid to be evaporated on the inner wall of the tube into a thin film.

In addition to those mentioned, however, it is also possible to use any other type of evaporator known to those skilled in the art, which is suitable for use in a distillation column.

If the evaporator, which is operated with the compressed vapor stream as heating steam, is an intermediate evaporator, it is preferred if the intermediate evaporator is arranged in the stripping section of the distillation column or in the region of the feed point of the methanol / water mixture. Due to the arrangement of the intermediate evaporator in the stripping section of the distillation column or in the region of the feed point of the methanol / water mixture, a predominant part of the heating energy can be introduced through the intermediate evaporator. For example, it is possible to introduce over 80% of the energy via the intermediate evaporator. According to the invention, the intermediate evaporator is preferably arranged and / or designed such that more than 50%, in particular more than 75%, of the total energy required for the distillation is introduced therewith.

When using an intermediate evaporator, it is particularly advantageous if the intermediate evaporator is arranged such that the distillation column below the intermediate evaporator has from 1 to 50 theoretical plates and above the intermediate evaporator from 1 to 200 theoretical plates. In particular, it is preferred if the distillation column below the intermediate evaporator has 2 to 10 theoretical plates and above the intermediate evaporator 20 to 50 theoretical plates.

The side draw stream through which the methanol / water mixture is fed to the intermediate evaporator and the side feed via which the vaporized methanol / water mixture from the evaporator is returned to the distillation column may be positioned between the same trays of the distillation column. However, it is also possible that the side print and the page feed are at different heights.

In a preferred embodiment, when using an intermediate evaporator, the diameter of the distillation column above the intermediate evaporator is greater than the diameter of the distillation column below the intermediate evaporator. This has the advantage that investment costs can be saved.

The compression of the vapor stream in step (c) can be carried out in any manner known to those skilled in the art. For example, the compaction can be carried out in one or more stages. In a multi-stage compression several compressors of the same design or compressors of different types can be used.

The use of single-stage compression or multi-stage compression depends on the pressure at which the vapor stream is to be compressed. When the compressed vapor stream is used for heating an intermediate evaporator, the pressure difference to be overcome with the compressor is smaller than when using the vapor stream for heating a compressor at the bottom of the distillation column. The larger pressure difference to be overcome can be overcome by additional compressor stages or by a more powerful compressor. Usually, however, additional compressor stages are used.

As a compressor for compressing the vapor stream is any, known in the art compressor with which can compress gas streams. Suitable compressors are, for example, single-stage or multi-stage turbines, reciprocating compressors, screw compressors, centrifugal compressors or axial compressors.

In a multi-stage compression suitable compressors are used for each to be overcome pressure levels.

In addition to the evaporator operated with the compressed vapor stream, another conventionally heated vaporiser is preferably used, which is arranged at the bottom of the distillation column. If the evaporator heated with the vapor stream is likewise arranged at the bottom of the column, the conventionally heated evaporator can be used, for example, to additionally supply heat during operation of the distillation column. In general, however, the conventionally heated evaporator is used to start the column. When starting the column is still not sufficient vapor available, with which the evaporator can be heated, so that first must be supplied from outside heat. After starting the distillation column takes the amount of vapor that can be removed at the top of the column, and the operation can be switched to the heated with the compressed vapor stream evaporator. In this case, it is possible, on the one hand, to slowly start up the evaporator, which is heated with the vapor stream, and to heat the conventionally heated evaporator correspondingly less, or it waits until a stationary operating state is reached the distillation column has been set, and then switched from the conventionally heated evaporator to the heated with the compressed vapor stream evaporator.

If an intermediate evaporator is heated with the compressed vapor stream, the additional, conventionally heated evaporator is used to introduce further heat at the bottom of the column in the distillation column. In this case, the conventionally heated evaporator is operated over the entire operating life of the distillation column. Again, to start the column, a larger amount of heat must first be introduced into the distillation column via the conventionally heated evaporator until the intermediate evaporator can be supplied with a sufficiently large vapor stream in order to heat it. Then the amount of heat that is introduced into the distillation column with the conventionally heated evaporator can be reduced. Alternatively, if an intermediate evaporator is used, it is also possible to use two conventionally heated evaporators at the bottom of the column. The additional conventionally heated evaporator is then used to start the column and the other conventionally heated evaporator continues to operate during operation of the column.

The methanol / water mixture to be separated in the distillation column can be fed in liquid or gaseous form. Preferably, however, the methanol / water mixture is supplied in gaseous form. The addition of the methanol / water mixture is preferably carried out via a side feed.

When the methanol / water mixture to be separated in the distillation column originates from the preparation of alkali metal methoxides, the methanol / water mixture is preferably added in gaseous form to the distillation column.

The pressure at which the distillation column is operated is preferably in the range from 0.2 to 10 bar, in particular in the range from 0.5 to 3 bar.

In one embodiment of the invention, a portion of the substantially methanol-containing vapor stream is condensed and returned to the distillation column. The condensed and returned to the distillation column part of the Brü- denströmen can be taken on the one hand the compressed vapor stream, with which the evaporator is heated, or alternatively an additional part, which is not compressed. When a portion of the vapor stream at which the evaporator is operated is condensed and returned to the distillation column, the portion recycled to the distillation column is preferably expanded to the operating pressure of the distillation column prior to addition to the distillation column. By the Returning the condensed vapor stream to the top of the column increases the concentration of methanol and achieves improved separation of methanol and greater purity of the methanol in the vapor stream.

When a portion of the substantially methanol-containing vapor stream is condensed and returned to the distillation column, the reflux ratio is preferably at least 0.4, more preferably 0.8 to 1.4.

In order to prevent inert gases from accumulating, it is advantageous to connect a liquid separator downstream of the vapor compressor. Gases separated off in the liquid separator can then be discharged in partial streams or completely out of the process, whereby inert gases also contained are removed.

When the process for the distillative workup of the methanol / water mixture is used in a process for the preparation of alkali metal methates, the methanol / water mixture is usually taken from a reaction column for the preparation of the alkali metal methylates as overhead stream. The methanol / water mixture taken off as top stream can then be fed directly into the distillation column. Alternatively, however, it is also possible to use a vapor compressor, in which the withdrawn overhead methanol / water mixture is compressed and then fed to the distillation column. By compressing the methanol / water mixture, the energy required for the distillation of the distillation column is further reduced.

In addition to the process for distillative workup of the methanol / water mixture, the invention also relates to a process for the preparation of alkali metal methoxides in a reaction column, wherein the reaction column methanol and alkali metal hydroxide are added. At the lower end of the reaction column dissolved in methanol methanolate is taken. At the upper end of the reaction column, a methanol / water mixture is removed, which is then worked up by distillation according to the method described above for working up a methanol / water mixture.

The methanol used for the preparation of the alkali metal methoxide can in the inventive embodiment of the method also commercially available methanol with a methanol content of more than 99.8% and a proportion of water of up to

0.1%. The methanol can be fed either in the rectifying section of the distillation column or directly at the top. The optimal feed point depends on the

Water content of the methanol used and on the other hand of the desired residual water content in the distillate. The higher the water content in the methanol used and the higher the purity requirement in the distillate, the more favorable is a feed to some theoretical plates below the top of the distillation column. Preference is given to up to 20 theoretical plates below the top of the distillation column and in particular 1 to 5 theoretical plates.

The reaction column in which the alkali metal methoxide is prepared preferably comprises at least 2, in particular 15 to 40 theoretical plates between the feed point of the alkali metal hydroxide solution and the addition point of the methanol.

In general, the reaction column contains internals. Suitable internals are, for example, trays, structured packings or disordered packings. If the reaction column contains trays, bubble trays, valve trays or trays are suitable. If the reaction column contains soils, preference is given to those soils in which a maximum of 5%, preferably less than 1%, of the liquid pass through the respective trays. The constructive measures required to minimize the Durchregnens the liquid are familiar to the expert. For valve floors, for example, particularly tight-fitting valve types are selected. By reducing the number of valves, it is also possible to increase the vapor velocity in the bottom openings up to twice the value that is usually set. When using sieve trays, it is particularly advantageous to reduce the diameter of the bottom openings and to maintain or even increase the number of openings.

When using structured or unstructured packages, structured packages are preferred in view of uniform distribution of the liquid. In this embodiment, moreover, in all parts of the column cross section corresponding to more than 2% of the total column cross-section, the average ratio of liquid to vapor stream with respect to the liquid must not be exceeded by more than 15%, preferably not more than 3%. This low volume of liquid makes it possible for the capillary effect on the wire mesh to be local

Excludes peaks in the liquid sprinkling density.

In the case of columns with unstructured packings, in particular with packings, and in columns with structured packings, the desired characteristic of the liquid distribution can be achieved by the fact that in the edge region of the column cross section adjacent to the column jacket, which corresponds to about 2 to 5% of the total column cross section Fluid Sprinkling over the other cross-sectional areas up to 100%, preferably by 5 to 15%, is reduced. This can be achieved, for example, by the targeted distribution of the drip points of the liquid distributors or their bores with simple means. The preparation of the alkali metal methoxide can be carried out both continuously and discontinuously. Preferably, the preparation is carried out continuously. In continuous processes, the alkali metal hydroxide, usually in aqueous form, optionally mixed with methanol, is fed at the top of the reaction column. The reaction column is operated as a pure stripping column. In the lower part of the column, methanol is fed in vapor form. About the bottom take-off to obtain specification-appropriate alkali metal. The methanol stream still containing water at the top of the column, referred to above as the methanol / water mixture, is worked up by distillation as described above. The methanol obtained in the distillation is then fed back to the reaction column.

The amount of methanol used is chosen so that it also serves as a solvent for the resulting alkali metal. Preferably, the amount of methanol is chosen so that the desired concentration of the alkali metal methoxide solution is present in the bottom of the reaction column.

Usually used alkali lye are caustic soda and potassium hydroxide.

The reaction column is preferably operated without reflux. This means that the entire vapor taken methanol / water mixture is fed to the distillation column. The methanol / water mixture is preferably fed to the distillation column in vapor form.

If a portion of the methanol is added in vapor form at the top or near the top of the reaction column, the dimensions at the bottom of the reaction column can be reduced. If a portion of the methanol at the upper end or in the region of the upper end of the reaction column is added in vapor form, only a partial amount of 10 to 70%, preferably from 30 to 50% at the lower end of the reaction column is fed and the remaining portion in a single stream or distributed in several streams, preferably 1 to 10 theoretical plates, more preferably 1 to 3 theoretical plates below the feed point of the alkali added in vapor form.

By arranging one or more intermediate evaporators in the upper region of the reaction column, the dimensions in the lower region of the reaction column can be reduced. In the embodiment with intermediate evaporators, it is also possible to supply partial streams of the methanol in liquid form in the upper region of the reaction column. The reaction column is preferably operated at a pressure in the range from 0.5 to 40 bar, preferably in the range from 1 to 5 bar, particularly preferably in the range from 1 to 3 bar, since lower heating powers and smaller amounts of methanol can be realized at a higher pressure ,

In the composite of the reaction column and the distillation column in the preparation of alkali metal methates, the distillation column is preferably operated at a pressure chosen to provide the pressure drop between the columns in the case of vapor compression for the methanol / water mixture or, alternatively, that for the reaction column Methanol flow is possible with little effort.

The methanol required for the reaction and the dilution of the alkali metal methoxide solutions is added at temperatures up to the boiling point, preferably at room temperature, at the top of the distillation column. In this case, a separate feed may be provided for the additional methanol or, on the return of a portion of the methanol taken off at the top of the distillation column, after the condensation, be mixed with it and fed together into the column. In this case, it is particularly preferred that the fresh methanol is added to a condensate tank in which the methanol condensed from the vapor stream is collected.

In an advantageous embodiment of the invention, the reaction column and the distillation column for working up the methanol / water mixture are housed in a column jacket, wherein the lower portion of the column is divided by a partition wall. In this case, in a part of the column, the reaction is carried out to Alkimimethylat, wherein the caustic is added approximately at the level of the upper end of the dividing wall and the methanol is added in vapor form at the lower end. The above the addition point of the alkali metal resulting methanol / water mixture is then distributed above the dividing wall over the entire column area, which serves as a reinforcing part of the distillation column. The second, separated by the partition lower part of the column is the stripping section of the distillation column. The energy necessary for the distillation is then fed via an evaporator at the lower end of the second part of the column separated by the dividing wall, wherein this evaporator can be conventionally heated or heated with the compressed vapor stream. If the evaporator is conventionally heated, then an intermediate evaporator is additionally provided, which is heated with the compressed vapor stream.

As a result of the reflux at the upper part of the column above the dividing wall, a part of the methanol / water mixture to be separated also runs into the column which is the reaction column. back part of the dividing wall column. By means of a suitable design of the bottom directly above the part of the dividing wall column which serves as the reaction column, this proportion, which runs back into the reaction column, can however be minimized.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.

Show it:

FIG. 1 shows a process flow diagram of the process according to the invention for the distillative workup of a methanol / water mixture,

FIG. 2 shows a process flow diagram for a process for the preparation of alkali metal methoxide in a first embodiment,

FIG. 3 shows a process flow diagram for a process for the preparation of alkali metal methoxide in a second embodiment,

FIG. 4 shows a process flow diagram for a process for producing an alkali metal in a third embodiment.

FIG. 1 shows a process flow diagram for a process according to the invention for the distillative workup of a methanol / water mixture.

A distillation column 1 is fed via a feed 3, a methanol / water mixture. The distillation column 1 can be equipped with trays, unstructured packings, in particular random packings, or structured packings. If the distillation column contains 1 packs, then it is preferable to provide two packs, one pack above the inlet 3 and one pack below the inlet 3. Also, in each case more than one pack may be provided above the inlet 3 and below the inlet 3.

The feed 3 is preferably a side feed and is preferably arranged so that below the feed 3 1 to 50, in particular 2 to 10 theoretical plates and above 1 to 200, in particular 20 to 50 theoretical plates are.

In the distillation column 1, the methanol / water mixture is separated into a substantially methanol-containing vapor stream and a substantially water-containing bottom stream. The essentially methanol-containing vapor stream is removed via a vapor withdrawal 5 at the top of the column. The vapor withdrawal 5 can be located at the top of the distillation column 1 as in the embodiment shown here, but it is also possible to carry out the vapor withdrawal 5, for example, as a side draw of the distillation column 1. The execution of the vapor draw 5 as a side draw also allows the use of methanol, which has low-boiling shares, such as alkanes such as butanes. The low-boiling fractions can be discharged at a low methanol loss at the top of the distillation column 1 in a vapor draw 5 designed as a side draw. However, it is preferred to position the vapor withdrawal 5 at the top of the distillation column 1. In order to discharge any liquid with the vapor from the distillation column 1, it is preferable to provide below the vapor withdrawal 5, a droplet separator, which is included as an additional installation in the distillation column 1. For example, an additional packing element or any commercially available droplet separator known to the person skilled in the art can be used as the droplet separator.

About a bottom outlet 7 of the substantially water-containing bottom stream is removed. A portion of the substantially water-containing bottom stream is withdrawn via an outlet 9 from the process. Another part of the substantially water-containing bottom stream is at least partially vaporized in an evaporator 11 and fed to the distillation column 1 at the lower end via an inlet 13. The ratio of the recirculated flow and the flow withdrawn via the outlet 9 can be adjusted via a valve 15.

According to the invention, the evaporator 11 is heated with the vapor stream removed via the vapor withdrawal 5 and essentially containing methanol. For this purpose, the essentially methanol-containing vapor stream is compressed in a vapor compressor 17. The pressure to which the substantially methanol-containing vapor stream in the vapor compressor 17 is compressed, is dependent on the temperature required for the evaporation of the substantially water-containing bottom stream 13. The vapor compression can be done in one stage in a vapor compressor 17 or multi-stage by several successive vapor compressor. Also, a multi-stage compression is possible in an apparatus having a plurality of compressor stages. Due to the heat emission for evaporating the substantially water-containing bottom stream in the evaporator 11 at least a portion of the vapor stream is condensed. In a throttle 19, the vapor stream is depressurized to the operating pressure of the distillation column 1 and recycled via an inlet 21 at the top of the distillation column 1 in this. A portion of the essentially methanol-containing vapor stream is removed from the process via a methanol outlet 23. The ratio of the vapor stream containing methanol fed back into the distillation column 1 and the vapor stream containing methanol substantially withdrawn from the process via the methanol outlet 23 is conveyed via a valve 25 set. The ratio of recirculated and withdrawn vapor stream is dependent on the desired purity of the methanol in the vapor stream.

FIG. 2 shows a process flow diagram for a process for the preparation of alkali methylate in a first embodiment.

For the preparation of alkali metal methoxide, a reaction column 31 is fed via an inlet 33 with aqueous alkali metal hydroxide, which is optionally mixed with methanol or a methanol / water mixture. The alkali metal hydroxide solution can also be supplemented with methanol or a methanol / water mixture in a separate feed stream. In the inlet 33, a heat exchanger 35 is received, through which the aqueous alkali metal hydroxide solution is passed before it flows into the reaction column 31. In the heat exchanger 35, the aqueous alkali solution is heated to the temperature of the feed point. Optionally, the aqueous alkali solution is partially evaporated in the heat exchanger 35. The feed 33 for adding the aqueous alkali metal hydroxide, which is optionally admixed with methanol or a methanol / water mixture, is positioned at the upper end of the reaction column 31.

Via a methanol inlet 37, which is positioned at the lower end of the reaction column 31, vaporous methanol is introduced into the reaction column 31. In addition to the feed with the methanol feed 37 at the lower end of the column, further vaporous methanol can be fed at the upper end of the reaction column via one or more further methanol feeds 39. The further methanol feeds 39 are preferably 1 to 10 theoretical plates, in particular 1 to 3 theoretical plates below the feed 33 for the aqueous alkali.

Via a bottom outlet 41, the alkali methylate produced in the reaction column 31 is removed. A portion of the Alkalimethylats is recycled via an evaporator 43 and a return 45 in the reaction column 31, so as to adjust the concentration of the bottoms outflow 41 withdrawn Alkalimethanolatlösung.

At the top of the reaction column 31, a methanol / water mixture is removed in vapor form via a vapor withdrawal 47.

For workup, the methanol / water mixture removed at the top of the reaction column 31 is fed via the feed 3 to the distillation column 1. In the distillation column 1, a separation of the methanol / water mixture into a substantially water-containing bottom stream and a substantially methanol-containing overhead stream. About the bottom outlet 7 of the substantially water-containing bottom stream is removed from the distillation column 1. A portion of the substantially water-containing bottom stream is at least partially evaporated in the evaporator 49 and returned to the distillation column 1 via the inlet 13. The part of the substantially water-containing bottom stream which is not recycled to the distillation column 1 is withdrawn via the outlet 9.

In the embodiment shown here, the evaporator 49, in which the substantially water-containing bottom stream is at least partially evaporated, is a conventionally heated evaporator. The heating of the evaporator 49 is preferably carried out with heating steam. But it is also any other, known in the art way conceivable to heat the evaporator 49.

The essentially methanol-containing vapor stream is taken off via the vapor withdrawal 5 at the top of the distillation column 1. From the vapor withdrawal 5 branches off a line 51, in which the vapor compressor 17 is positioned. In the vapor compressor 17, the substantially methanol-containing vapor stream is compressed to heat the evaporator 11. In the embodiment shown here, the evaporator 11 is an intermediate evaporator, in which part of the methanol / water mixture to be separated in the distillation column 1 is evaporated. For this purpose, for example, a portion of the methanol / water mixture to be separated is removed via a side draw at the distillation column 1, passed through the evaporator and returned to the distillation column. The outlet and the inlet, over which the methanol / water mixture to be evaporated is passed, can be at the level of the same theoretical separation stage or else at different positions on the distillation column 1. If inlet and outlet are at different positions, then it is preferred if the withdrawal, via which the evaporator 1 1 is supplied with the methanol / water mixture, is above the feed into the distillation column 1, through which the evaporated methanol / water mixture is returned to the distillation column 1 ,

The evaporator 1 1, which is used here as an intermediate evaporator, is preferably positioned so that below the evaporator 1 1 2 to 10 theoretical plates and above the evaporator 20 to 50 theoretical plates of the distillation column 1 are.

In the evaporator 1 1, the substantially methanol-containing vapor stream is cooled by the heat transfer to the methanol / water mixture to be evaporated and optionally partially or even completely condensed. The cooled, optionally at least partially condensed methanol stream is then passed over the Run 21 at least partially returned to the distillation column 1. The uncondensed in the evaporator 1 1 part of the substantially methanol-containing vapor stream is returned via a steam line 53 behind the branch of the line 51 back into the vapor withdrawal 5. The vapor vent 5 then opens into a condenser 55. Alternatively, it is also possible that the vapor line 53 opens into the condenser 55 in addition to the vapor vent 5 and separated from it. In the condenser 55, a portion of the substantially methanol-containing vapor stream is condensed and fed back via the inlet 21 into the distillation column 1. In this case, the part of the vapor stream containing essentially methanol condensed in the condenser 55 can first open into the inlet 21 coming from the evaporator 11 and all of the condensed methanol can be recycled together to the distillation column or the inlet 21 coming from the evaporator 11 Irrespective of the originating from the condenser 55 methanol flow into the distillation column 1. The uncondensed in the condenser 55 portion of the substantially methanol-containing vapor stream is recycled via the methanol inlet 37 and optionally the at least one further methanol inlet 39 into the reaction column 31. Methanol consumed in the reaction column 31 is added via a methanol inlet 57 at the top of the distillation column 1. By adding the methanol via the methanol inlet 57 at the top of the distillation column, the purity of the vapor stream substantially withdrawn via the vapor withdrawal 5 and substantially containing methanol can be further increased. In this way, the proportion of water introduced into the reaction column 31 with the methanol is further reduced. In addition to the addition of the methanol via the methanol inlet 57 at the top of the column, it is also possible to arrange the methanol feed 57 up to 10 theoretical stages below the top of the distillation column 1.

From the emerging from the condenser 55 vapors, a part can be discharged. In this way, for example, inert substances that are introduced into the process can be discharged. For example, the inert substances enter the process in the form of gases dissolved in methanol and / or lye. Also, small amounts of sealing gas can enter the process via seals. For discharging the inert branches off in the embodiment shown here after the condenser 55 from a line 63, via which a portion of the uncondensed vapor stream is removed. In a further capacitor 65, the vapor stream is further cooled. As the cooling medium in the condenser 65, for example, water or brine is used. Preferred as a cooling medium is brine. By using brine, a lower temperature can be achieved than with water, so that a larger proportion of the vapor can condense. The portion not condensed in the condenser 65, which contains the gaseous inerts, is removed from the process and can be supplied, for example, to a torch or an exhaust gas scrubber for further treatment. The condensed The resulting fraction is recycled via a reflux 67 in the distillation column. The reflux 67 can, as shown here, open into the feed 21 or be formed as a separate feed into the distillation column 1.

When using the further capacitor 65, the capacitor 55 can be dispensed with in one embodiment. In this case, the return necessary to achieve the desired purity of the methanol is realized via the condenser 65. The capacitor 65 may be either single-stage or multi-stage, preferably three-stage. In this case, it is cooled in one stage with air, in another stage with water and in the third stage with brine.

In one embodiment, not shown here, it is also possible, with the condensed in evaporator 1 1 portion of the substantially methanol-containing vapor stream further withdrawn from the condenser 55 withdrawn vaporous portion of the substantially methanol-containing vapor stream, before this via the methanol feeds 37, 39 is fed into the reaction column 31.

The vapor stream fed into the reaction column 31 via the methanol feed 37 and the further methanol feeds 39 and withdrawn via the vapor draw 5 from the distillation column 1 can be compressed in a vapor compressor 59. However, it is also possible to feed the vaporous methanol into the reaction column 31 without the use of the vapor compressor 59.

FIG. 3 shows a process flow diagram for a process for the preparation of alkali methylate in a second embodiment.

The embodiment illustrated in FIG. 3 differs from the embodiment shown in FIG. 2 in that the vapor compressor 59, with which the fraction of the vaporous methanol withdrawn via the vapor withdrawal 5 from the top of the distillation column 1 and not condensed out in the condenser 55, is not compressed is included.

However, in the embodiment shown in FIG. 3, a further vapor compressor 61 is positioned in the vapor withdrawal 47 from the reaction column 31, which discharges into the distillation column 1 as feed 3. In the vapor compressor 61, the methanol / water mixture removed via the vapor withdrawal 47 from the reaction column 31 is additionally supplied with energy for the distillation. On the one hand, the methanol / water mixture can be compressed to the pressure of the distillation column 1 when the distillation column 1 is operated at a higher pressure than the reaction column 31. Alternatively, it is also possible for the methanol / water mixture to be To compress a higher pressure than the pressure at which the distillation column 1 is operated, so that the methanol / water mixture on entry into the distillation column 1 suddenly relaxes.

FIG. 4 shows a process flow diagram for a process for the preparation of alkali methylate in a third embodiment. In contrast to the embodiment shown in Figure 2, not a separate reaction column 31 and a distillation column 1 are provided, but the columns are housed in a common column jacket in the form of a dividing wall column 71.

In the dividing wall column 71, the lower region is separated by a dividing wall 73 into a first partial region 75 and a second partial region 77. The first portion 75 serves as a reaction column and the second portion 77 as a stripping section of the distillation column.

At the upper end of the first portion 75 is heated via the inlet 33 in the heat exchanger 35 aqueous alkali solution, which is optionally mixed with methanol or a methanol / water mixture supplied. In the lower region of the first portion 75, methanol is fed in vapor form via the methanol inlet 37. In addition, as also shown in FIG. 2, methanol can also be fed in vapor form via further methanol feeds 39.

At the bottom of the first section 75, the product, alkali metal methylate in methanol, is withdrawn via the bottom outlet 41. A portion of the stream removed via the bottom outlet 41 is returned to the first section 75 of the dividing wall column 71 via the evaporator 43 and the return line 45. The reflux 45 preferably opens below the methanol inlet 37 into the first portion 75 of the dividing wall column 71. The methanol / water mixture formed in the reaction flows in vapor form over the upper end of the dividing wall 73 into the upper part 79 of the dividing wall column, which serves as the reinforcing part of Distillation column 1 acts. The second portion 77 of the dividing wall column 71 serves as a stripping section for the distillation of the methanol / water mixture. About the vapor withdrawal 5 at the upper part 79 of the dividing wall column 71 of the methanol containing vapors is removed from the distillation. As shown in Figures 2 and 3, a partial stream of the substantially methanol-containing vapor stream is fed via the line 51 to the vapor compressor 17, in which the vapor stream containing substantially methanol is compressed. The compressed vapor stream then serves as heating steam in the evaporator 1 1. The evaporator 1 1 is also arranged in the embodiment shown here as an intermediate evaporator in the stripping section of serving as a distillation column portion of the dividing wall column 71. By the heat transfer to the destil- lating methanol / water mixture condenses a portion of the substantially methanol-containing vapor stream. The condensed part is recycled via the inlet 21 in the upper part 79, preferably at the top of the dividing wall column 71. Also at the top of the dividing wall column opens the methanol feed 57, with the fresh methanol can be added to replace methanol consumed in the reaction to alkali metal. The uncondensed in the evaporator 11 portion of the substantially methanol-containing vapor stream is fed via the vapor line 53 to the condenser 55. In the condenser 55, the portion of the vapor stream essentially containing methanol and the fraction of the vapor stream essentially comprising methanol are not partially condensed via the vapor line 53 and the vapor fraction which is not passed via the vapor compressor 17. The condensed fraction is also recycled via the top of the dividing wall column 71 into the dividing wall column 71. The uncondensed part is recycled via the vapor compressor 59 and the methanol feeds 37 and 39 in the first portion 75, which serves as a reaction column, in the dividing wall 71 column.

The dividing wall column is preferably operated at a pressure in the range from 0.2 to 10 bar, in particular at a pressure in the range from 0.5 to 3 bar.

At the bottom of the second portion 77 a substantially water-containing bottom stream is removed via the bottom outlet 7. A portion of the substantially water-containing bottom stream is at least partially vaporized in the evaporator 49 and returned to the second portion 77, preferably at the bottom. The second evaporator 49 is conventional, preferably heated with heating steam.

As a vapor compressor in all embodiments, for example, a single or multi-stage turbocompressor or a screw compressor can be used. The technical detail of the vapor compressor 17 is generally based on the manufacturer's instructions and is familiar to the expert. Thus, it is possible, for example, to connect the vapor compressor 17 with a mist eliminator.

If an evaporator 11 serving as an intermediate evaporator is heated with the vapor stream essentially compressed in the vapor compressor 17, the area of the evaporator 11 is preferably dimensioned so that the temperature difference is not more than 50 K, in particular not more than 30 K. By low temperature differences, the required drive power of the vapor compressor 17 can be reduced. The compression of the substantially methanol-containing vapor stream in the vapor compressor 17 preferably takes place by a factor in the range of 1.5 to 19, in particular in the range of 2 to 4. The exact value of Pressure increase in the vapor compressor 17 depends on the dimensioning of the heat transfer surface of the evaporator 11.

However, as shown here, the dividing wall may either divide the column cross-section into two circular segments, but alternatively it is also possible to form the dividing wall coaxially, in which case it is preferable for the stripping section of the distillation to be of the internal region and the reaction in which the annular wall surrounding the partition is performed.

In the embodiment illustrated in FIG. 4, it is also possible, with the condensate fraction of the essentially methanol-containing vapor stream withdrawn from the evaporator 11, to further heat the vapor fraction of the essentially methanol-containing vapor stream removed from the condenser 55 in a suitable heat exchanger.

Inert outs can be carried out in the same way in the embodiments shown in FIGS. 3 and 4 as in the embodiment shown in FIG. Alternatively, it is also possible to position a condenser for discharging the inerts following the vapor compressor 11 in the conduit 53.

LIST OF REFERENCE NUMBERS

1 distillation column

3 inlet

5 vapor withdrawal

7 sump drain

9 process

1 1 evaporator

13 inlet

15 valve

17 vapor compressor

19 throttle

21 inlet

23 methanol exhaust

25 valve

31 reaction column

33 inlet

35 heat exchanger

37 methanol feed

39 additional methanol feed

41 sump drain

43 evaporator

45 return

47 vapor withdrawal

49 evaporator

51 line

53 steam line

55 capacitor

57 methanol feed

59 vapor compressor

61 further vapor compressors

63 line

65 capacitor

67 return

71 dividing wall column

73 Partition wall

75 first subarea

77 second subarea

79 upper part

Claims

claims

1. A process for the distillative workup of a methanol / water mixture, comprising the following steps:

(a) adding the methanol / water mixture to a distillation column (1),

(b) removal of a substantially methanol-containing vapor stream at the top of the distillation column (1) and a substantially water-containing bottom stream at the bottom of the distillation column (1),

(D) adding the compressed vapor stream as heating steam in an evaporator

(1 1), in which at least part of the methanol / water mixture to be separated is evaporated.

2. The method according to claim 1, characterized in that the evaporator (1 1) is an intermediate evaporator.

3. The method according to claim 2, characterized in that the intermediate evaporator (1 1) in the stripping section of the distillation column (1) or in the region of the feed point (3) of the methanol / water mixture is arranged.

4. The method according to claim 2 or 3, characterized in that the intermediate evaporator (1 1) is arranged so that the distillation column (1) below the intermediate evaporator (11) 1 to 50 theoretical plates and above the intermediate evaporator (11) 1 to 200 theoretical plates.

5. The method according to any one of claims 2 to 4, characterized in that the diameter of the distillation column (1) above the intermediate evaporator (1 1) is greater than below the intermediate evaporator (11).

6. The method according to any one of claims 1 to 5, characterized in that at the bottom of the distillation column (1), a further, conventionally heated evaporator (49) is arranged.

7. The method according to any one of claims 1 to 6, characterized in that the methanol / water mixture of the distillation column (1) is supplied in gaseous form.

8. The method according to any one of claims 1 to 7, characterized in that the distillation column (1) is operated at a pressure in the range of 0.2 to 10 bar.

9. The method according to any one of claims 1 to 8, characterized in that a part of the substantially methanol-containing vapor stream is condensed and returned to the distillation column (1).

10. The method according to any one of claims 1 to 9, characterized in that the methanol / water mixture is removed from a reaction column (31) for the preparation of alkali metal methoxides as overhead stream.

1 1. A process for the preparation of alkali metal methoxides in a reaction column (31), wherein the reaction column (31) methanol and alkali metal hydroxide are added, at the lower end of the reaction column (31) in methanol dissolved alkali metal is removed and at the upper end of the reaction column (31) a methanol / water mixture is removed and the methanol / water mixture is worked up by a process according to any one of claims 1 to 10.

12. The method according to claim 1 1, characterized in that the reaction column (31) and the distillation column (1) for working up the methanol / water mixture are accommodated in a column jacket, wherein the lower region of the column (71) is divided by a partition (73).