WO2005110572A1

WO2005110572A1 - Divided edc column

Info

Publication number: WO2005110572A1
Application number: PCT/EP2005/005000
Authority: WO
Inventors: Peter Kammerhofer
Original assignee: Vinnolit Gmbh & Co. Kg
Priority date: 2004-05-07
Filing date: 2005-05-09
Publication date: 2005-11-24
Also published as: DE102004022735A1

Abstract

The invention relates to a distillation column, in particular, one that can be used for separated out high-boiling fractions, for example, for purifying 1,2-dichloroethane (EDC). As a result, impurities and/or byproducts whose boiling point differs only slightly from that of the product are separated out in a nearly quantitative manner in one part of the column. To this end, a vertical baffle plate is inserted into the column in order to achieve a sales EDC quality.

Description

Split EDC column

description

Distillation column, use thereof and process for distillation, in particular of 1,2-dichloroethane (EDC)

The invention relates to a distillation column, in particular for separating high-boiling fractions from product mixtures, which column can be used, for example, to purify 1,2-dichloroethane (EDC). This means that impurities and / or by-products can be separated almost quantitatively, even if their boiling point differs only slightly from that of the product.

1, 2-dichloroethane (ethylene dichloride, EDC) is produced on a large scale as a preliminary product for the production of vinyl chloride (VC) by two different processes. One method is the so-called direct chlorination (DC), in which ethylene and chlorine in the liquid phase using a homogeneous

Catalyst system to be implemented EDC. Another process is the so-called oxychlorination (OC), in which ethylene, hydrogen chloride and oxygen in the gas phase are converted to EDC using a heterogeneous catalyst system. The raw EDC (DC-EDC or OC-EDC) produced by both processes must be subjected to purification by distillation before it is processed into VC by thermal cleavage (EDC cleavage, pyrolysis). In EDC cleavage, usually 40-50% of the total EDC used is not converted, which can be recovered as a so-called "re-EDC", but can be contaminated by various by-products. That too Re-EDC must be purified by distillation before it can be returned to the manufacturing process.

The cleaning of raw EDC (DC or OC EDC) and back EDC is done in the prior art with the help of at least three

Distillation columns carried out, as described for example in the patent DE 199 53 762 C2 and shown in Figure 1. OC-EDC 1 is pre-cleaned by separating so-called low boilers and water 5 in a combined low boiler and dewatering column 4. Here and also in the present invention, the term “low boilers” denotes all components with a boiling point below that of EDC, ie all components with a boiling point which is lower than 8 ^a C; the term “high boilers” accordingly designates all components with a boiling point above that of EDC, ie all components with a boiling point which is higher than 84 ² C.

In a central high boiler column 6, the EDC feed streams of OC-EDC, DC-EDC (2) and re-EDC (3) are distilled in a continuous process in order to separate the high boilers. The bottom stream of the high boiler column is concentrated in an additional vacuum distillation column 7 for the recovery of EDC. The main disadvantage of this process is that it does not succeed in by-products and impurities whose boiling point is similar to that of the EDC, such as benzene and 1,1-dichloroethane from the back EDC, and / or low-boiling impurities from the DC-EDC (such as ethylene and hydrogen chloride), so completely separated that the EDC obtained meets the internationally customary specifications of an EDC (sales EDC) intended for sale in terms of high boiler and low boiler content. The Specifications for sales EDC are an EDC purity of approximately 99.9% with a high boiler content of <500 ppm (w / w) and a low boiler content of <350 ppm. Table 1 shows a typical EDC quality that was achieved with a system according to the described prior art.

Table 1: Composition of EDC after high boiler removal in columns 6 and 7 according to the prior art; all figures are in ppm by weight.

In order to achieve the required sales EDC quality, the reprocessing of re-EDC and raw EDC is carried out in two different columns according to the prior art

High boiler separation carried out to remove the by-products and impurities mentioned above. In particular, benzene and 1, 1-dichloroethane are not permitted in the amount incurred in the sales EDC. Due to the separate distillation in two columns, an EDC quality is produced in one column, which is used again as "feed EDC" in the cleavage, and in the other column the EDC is purified from DC and OC in such a way that pure or sales - EDC can be won.

The disadvantage of this is that two distillation columns with circulation evaporators result in high investment costs and increased operating costs and additionally cause a higher cleaning effort and associated higher costs. Furthermore, the maintenance and cleaning of the second column of the continuous process are interrupted, which leads to additional downtimes of the system.

An object of the invention is to provide a device in which a separation of high-boiling and other contaminants, for example boiling at or near the boiling point of the product, can be carried out economically. In addition, it is an object of the invention to disclose the use of such a column and to provide a process for the separation of high-boiling and other impurities from product mixtures which boil approximately at or near the boiling point of the product.

This object is achieved by the subject matter of the independent and dependent claims and the description in connection with the figures.

The invention thus relates to a vertical distillation column with a plurality of trays (separation stages), at least two column feed lines, at least one, preferably two, three or even more product discharge lines, a buoyancy or intensifying column, a stripping column and a bottom section at the lower end of the column, the Column has at least one vertical partition, which divides the entire buoyancy or intensifying column and at least part of the stripping column, but not the bottom part of the column, into at least two areas (distillation chambers), each area having at least one column feed line and the areas over the Stand sump part in fluid communication with each other. The invention also relates to the use of the column for the distillation (purification) of EDC. The invention further relates to a method for distillation (Purification) of two, three or more different product mixtures, the two, three or more different product mixtures being passed into or through the column feed lines of a column according to the invention and one, two, three or more distillates being separated off. Finally, the invention relates to a process for the distillation (purification) of EDC, the EDC being subjected to a fractional distillation in a vertical distillation column with several trays, at least two EDC feed streams and at least one column discharge line.

Surprisingly, it was found that the device according to the invention enables separate, improved separation of different product streams, a product stream containing by-products which are difficult to remove by distillation.

It was also found that a column according to the invention, in particular for continuous fractional distillation, shows a higher separation efficiency than a column which has no vertical dividing wall, despite the number of separation stages remaining the same.

Surprisingly, it was found in particular that EDC with a quality suitable for sale can be produced using only one distillation column if at least one vertical partition is provided in the column which separates the upper part of the column into at least two areas.

The product mixtures to be separated each comprise a halogenated hydrocarbon, preferably a polychlorinated hydrocarbon, in particular EDC. According to an advantageous embodiment, the raw EDC and the back EDC are distilled separately in the regions (distillation chambers) separated by the at least one vertically retracted partition. For this purpose, the raw EDC and the back EDC are each fed into different areas, preferably continuously, formed by the at least one vertical partition. In principle, the feed can take place at any point in the column, but back-EDC and raw EDC are advantageously fed in in the middle part of the column, ie between the top and bottom parts, preferably about halfway up the column.

Particularly preferably, the EDC from the oxychlorination is first separated from low boilers and water in a column, before it is combined with the EDC from the direct chlorination or fed separately into a region of the column according to the invention.

In particular, according to the invention it is possible, depending on the amount and composition of the column feeds to be purified, to the distillation chambers to obtain different distillate purities in one column. This is made possible in particular by condensation of the vapors from different parts and / or areas of the column. It is also possible to set a desired distillate quality by mixing the two distillate streams.

The distillation column according to the invention and the at least one dividing wall are arranged vertically, arrangements also being included by the invention which are not completely aligned vertically; so are z. B. Arrangements of Co lons that deviate from the vertical by 5, 10 or 20 degrees are possible, but not preferred.

According to one embodiment of the column, at least one product discharge is on the side, ie. H. arranged between the top and bottom of the column. Particularly pure product can be obtained if not only high-boiling but also low-boiling contaminants are removed. According to the invention, one, two or more vertical partition walls are provided, which can have the same or different lengths, a partition wall being preferred. The invention is therefore explained below using an example of a partition.

According to one embodiment of the column, the lower part of the vertical dividing wall can be shortened or lengthened so that it extends over more or less horizontally arranged dividing plates and the volume of the separate distillation chambers can be adjusted as required.

According to a further embodiment, the vertical dividing wall preferably extends from the lowest column plate or from another column plate in the stripping column to the top part of the column, the two separate vertical distillation chambers having a common bottom part.

According to a further embodiment, the purity of the distillate or the distillates is regulated in particular by the amount and / or composition (s) of the EDC feed streams also on the individual distillation chambers.

According to one embodiment of the invention, a column according to the invention has at the lower end of at least one vertical partition at least one horizontal slide to change the amount of steam flowing into at least one area of the column. The column particularly preferably has a slide at the lower end of each region. Each slide can preferably be controlled individually, so that the amount of steam flowing into the respective area of the column can be controlled individually.

According to a further embodiment, the bottom of the column is used for all areas of the column for energy input (for example by means of a circulation evaporator) and for high boiler removal. This results in an economically particularly interesting synergy effect.

The material for the vertical partition can be chosen arbitrarily, for example it can be made of unalloyed or alloy steel. The material is chosen according to the requirement.

According to the invention, the column feed lines can be arranged such that one feed line with one area and two further feed lines are in fluid communication with another area of the column. For example, return EDC can be introduced into one area via one inlet line and OC-EDC and DC-EDC into the other area via the two further inlet lines. Alternatively, OC-EDC and DC-EDC can also be initiated in different areas, which are different from the area for reverse EDC.

A product discharge line for high boilers is preferably arranged in the bottom; additionally or alternatively, at least one product derivation is preferably arranged in at least one area of the column in the top part. The Product from the bottom section can be further separated or purified via a further distillation column. According to a preferred embodiment, product discharge lines are arranged in at least two areas of the column, via which at least a part of the feed EDC and ultrapure EDC are particularly preferably derived. High-purity EDC is preferably derived from the part of the column into which OC-EDC and possibly also DC-EDC are introduced, while feed EDC is derived from the area of the column into which the return EDC is introduced.

As an alternative or in addition, ultrapure EDC can also be derived from the area into which OC-EDC and possibly also DC-EDC are introduced via a product derivation at the level of the buoyancy or booster column.

The invention is explained in more detail below with the aid of two flow diagrams which show the structure of two embodiments of an EDC cleaning system. In addition, the results and analysis values which are obtained by the cleaning method according to the invention are shown in comparison with the values which are obtained by the conventional cleaning method for EDC, which is known in particular from DE 199 53 762.

As shown in the two Figures 2 and 3, the cleaning of EDC according to these embodiments of the invention is carried out in a column which is divided into two parts by a vertical separating plate. The EDC feed stream of unreacted EDC from the pyrolysis (back-EDC) is fed on one side of the column and the EDC feed stream from oxychlorination (OC) and direct chlorination (DC) (together the raw EDC) on the other side of the column , The swamp the column is used jointly for energy input (circulation evaporator) and for high boiler discharge to the downstream vacuum distillation column.

The flow diagrams in FIG. 2 / FIG. 3 show the following:

In three vertical columns 1, 2 and 3, distillation is carried out in a continuous process. EDC produced by oxychlorination is fed into column 1 via line 11. At the top of this column, the

Low boilers and water separated via line la. From the bottom section 1b, the pre-cleaned OC-EDC is fed via line 1b into the left half of column 2 (the so-called sales EDC side) for laterally separating high boilers, preferably approximately halfway up the column. Also laterally, preferably at about half the height of the column, the DC-EDC obtained from the direct chlorination is fed into this half of column 2 via line 12. This left half of column 2 is referred to in the present case as the distillation chamber of the sales EDC, in

Contrary to the right half, the distillation chamber of the Feed EDC is called. In the present flow diagrams, there are two halves, with a different division at any time, on the one hand in more than two distillation chambers and on the other hand in differently sized distillation chambers, in the sense of the invention. The return EDC, which has been recovered from the conversion of EDC to vinyl chloride, is likewise fed laterally, preferably also approximately halfway up the column, via line 13 into the distillation chamber of the Feed EDC of column 2.

The product of the right or feed EDC side of column 2 is separated from head section 2a via line 15 and used again as feed EDC for the production of vinyl chloride.

The Feed-EDC can be used without prior removal of hydrogen chloride and other low boilers such as Ethylene can be used directly for the splitting of EDC to VC.

The high boiler fraction, which may also contain feed EDC, is separated off from the bottom section 2b of column 2 and fed into the vacuum column 3 for further high boiler removal.

The high boiler fraction is separated off from the bottom section 3b of the vacuum column 3 via the line 16, while feed EDC from the top section 3a is brought together in line 15 with the feed EDC from the top section 2a of the column 2.

Only Figure 2: From the sales EDC side of column 2 above the feeds of raw EDC from OC and DC, preferably in the upper third of the column amplifier section, that

Sales EDC with a 99.99% purity separated via line 14. A part of the preferably completely condensed product from the top part 2a of the column 2 on the left or sales EDC side is discontinuously discharged to prevent accumulation of low boilers and water, the remaining part is returned to the left side of the column.

Furthermore, part of the stream taken from the top part la of the column 1 is returned to the column 1. Part of the stream taken from the top part 2a of the right or feed side of the column 2 is also returned to the column 2.

Only FIG. 3: In order to further increase the purity of the product from the top part 2a of the column 2 on the left or sales EDC side, this product is fed via line 2a into a further cleaning column, a so-called EDC stripper column 5 , fed. Sales EDC with an increased purity is then obtained from the bottom part of column 5. Low boilers can be returned to the column 3, preferably in the upper region, from the top of the column 5.

In a vinyl chloride plant according to the flow diagram in FIG. 2, comprising direct chlorination, oxychlorination, EDC distillation, EDC pyrolysis (splitting) and VC distillation, the following quantities are produced in the sub-plants:

Direct chlorination: 56000 kg / h EDC oxychlorination: 29500 kg / h EDC vinyl chloride: 37500 kg / h sales (export) EDC: 25000 kg / h

Table 2: The composition of the sales EDC (product of column side draw via line 14) is as follows: All figures are in ppm by weight

The composition of the top product 15 on the feed product side of column 2 is shown in Table 3.

Table 3: The purity of the feed product (line 15) is as follows: All data are in ppm by weight

In a vinyl chloride system according to the flow diagram in FIG. 3, comprising direct chlorination, oxychlorination, EDC distillation, EDC pyrolysis (splitting) and VC distillation, the following quantities are produced in the subsystems: direct chlorination: 45300 kg / h EDC oxychlorination: 21600 kg / h EDC vinyl chloride: 27500 kg / h sales EDC: 22500 kg / h

The top product 2a of the sales EDC side according to FIG. 3 of column 2 is listed in table 4.

Table 4 (All figures are in ppm by weight)

The composition of the top product 2a of the feed EDC side of column 2 is listed in Table 5.

Table 5: The purity of the Feed EDC (line 15) is as follows:

All figures are in ppm by weight

The top product of stripping column 5 is recycled as feed EDC via line 15 to the vinyl chloride process for the recovery of valuable materials.

The purity of the sales EDC (line 14) after the low boiler stripping in column 5 is listed in Table 6:

Table 6: The purity of the sales EDC at the bottom of the EDC stripping column (line 14) is as follows: All data are in ppm by weight

Table: Evaluation of the sales EDC qualities of the different processes

Definitions: EDC = 1, 2-dichloroethane VC = vinyl chloride high boilers = by-products with a boiling point of> 84 ° C at atmospheric pressure low boilers = by-products with a boiling point of <84 ° C at atmospheric pressure buoyancy column or booster column of a column = the column section that is above the Column inlet tray is the stripping column of a column = the part of the column which lies below the column inlet tray.

The present invention overcomes the disadvantages of the prior art, in particular that the internationally required product quality for sales EDC is achieved with a column connection which is no more complex than that described in DE 199 53 762. In particular, the investment costs are reduced by reducing the number of devices. Furthermore, the downtimes are reduced by reducing the cleaning effort due to the reduced number of devices and, furthermore, the energy consumption is significantly reduced.

Claims

claims

1. Vertical distillation column with a plurality of trays and column feed lines, at least one product discharge line, a lifting or intensifying column, a stripping column and a bottom part at the lower end of the column, the column having at least one vertical dividing wall which comprises the entire lifting or intensifying column and at least one Part of the stripping column, however, does not divide the bottom part of the column into at least two areas, each area having at least one column feed line and the areas being in fluid communication with one another via the bottom part.

2. Column according to claim 1, wherein the vertical

Partition extends from the bottom bottom of the stripping column over the entire lifting or intensifying column or from another bottom of the stripping column over the entire lifting or intensifying column of the column.

3. Column according to one of the preceding claims, wherein the column has a plurality of vertical partitions either of the same or different lengths.

4. Column according to one of the preceding claims, wherein the material for the vertical dividing walls comprises or consists of metal.

5. Column according to one of the preceding claims, wherein the column feed lines are arranged so that a

Inlet line with one area and two inlet lines with another area of the column are in fluid communication.

6. Column according to claim 5, wherein the one feed line for reverse EDC and the two feed lines for OC-EDC and DC-EDC are provided.

7. Column according to one of the preceding claims, wherein at least one product derivative is arranged in the bottom part.

8. Column according to one of the preceding claims, wherein at least one product derivative is arranged in at least one area of the column in the top part.

9. Column according to claim 8, wherein a product derivative is arranged in each area of the column in the top part.

10. Column according to one of the preceding claims, wherein at least one product derivative is arranged in a region of the column at the level of the buoyancy or booster column.

11. Column according to one of the preceding claims, wherein a product derivation for feed EDC and / or high boilers in

Bottom part of the column is arranged.

12. Column according to one of the preceding claims, wherein a product derivation for feed EDC are arranged in a region of the column in the top part.

13. Column according to claim 12, wherein a product department for ultrapure EDC is arranged in another area of the column in the top part or at the level of the buoyancy or booster column.

14. Column according to one of the preceding claims, wherein at the lower end of at least one vertical partition at least one horizontal slide is provided for changing the amount of steam flowing into at least one area of the column.

15. A method for the distillation of at least two different product mixtures, the at least two different product mixtures being passed into the column feed lines of a column and distilled according to one of the preceding claims and at least one product being separated off.

16. The method according to claim 15, wherein at least two or three products are separated.

17. The method according to any one of claims 15 or 16, wherein the product mixtures each contain a halogenated hydrocarbon.

18. The method according to any one of claims 15-17, wherein the product mixtures each have a multi-chlorinated

Contain hydrocarbon.

19. The method according to any one of claims 15-18, wherein the product mixtures each contain EDC.

20. The method according to any one of claims 15-19, wherein the distillation is a fractional distillation.

21. The method according to any one of claims 15-20, wherein the

Purity of the distillate is regulated by the location of the supply of the EDC feed streams in the column.

22. The method according to any one of claims 15-21, wherein crude EDC, which comprises OC-EDC and / or DC-EDC, and re-EDC, which comprises EDC from a pyrolysis of EDC to vinyl chloride, distilled separately in the regions become.

23. The method according to any one of claims 15-22, wherein the bottom of the column is used for all areas together for energy input and high boiler separation and the at least one vertical partition extends down to the bottom.

24. The method according to any one of claims 15-23, wherein the amount of steam can be changed at least in a column area by at least one slide installed horizontally with respect to the flow direction of the steam, preferably at the lower end of at least one vertical partition, and thus independently of the EDC feed amount and purity, the required distillate quality can be set in at least one column area.

25. Use of a column according to one of claims 1 to 14 for the purification of EDC.