description

Process and plant for the production of ethylene

The present invention relates to a method for producing ethylene and a corresponding plant according to the preambles of the independent claims.

State of the art

Olefins such as ethylene or propylene, but also diolefins such as butadiene and aromatics can be produced from paraffins by steam cracking. Corresponding processes have been known for a long time. For details, refer to specialist literature such as the article "Ethylene" in Ullmann's Encyclopedia of Industrial Chemistry,

Online edition, April 15, 2007, DOI 10.1002 / 14356007. a10_045.pub2, referenced.

During steam cracking, what is known as cracked gas is obtained which, in addition to the target products, contains unconverted hydrocarbons and undesired by-products. In known processes, this cracked gas is first subjected to treatment before it is fractionated or separated

Obtaining different hydrocarbons or fractions is fed. Details are described in the cited article, in particular in Section 5.3.2.1, "Front-End Section" and 5.3.2.2., "Hydrocarbon Fractionation Section".

Corresponding processing includes, in particular, what is known as

Sour gas removal, in which components such as carbon dioxide, hydrogen sulfide and mercaptans are separated from the cracked gas. The cracked gas is typically compressed before and after an appropriate treatment. For example, the cracked gas can be taken from a so-called crude gas compressor at an intermediate pressure level, subjected to the acid gas removal, and then in the

Raw gas compressor can be further compressed.

It is sometimes desirable to convert ethane-rich feedstocks into ethylene by means of steam cracking, with the formation of the smallest possible amounts of by-products. In this context, in addition to unconverted ethane, hydrocarbons with three and four carbon atoms formed during steam cracking are typically returned to the reactor or reactors used. In order to avoid a single hydrogenation of these recycled fractions, the entire cracked gas can be hydrogenated in the course of processing (so-called crude gas hydrogenation).

Since the recycled hydrocarbons with three and four carbon atoms typically make up a small proportion of the total input to be converted, these hydrocarbons are typically split together with the freshly supplied or recycled ethane. In other words, there is no need to provide separate units for steam splitting.

In FIG. 1, a corresponding method is shown in the form of a schematic flow chart and is explained in detail below with reference to FIG. As indicated there, however, a separation is carried out in this process which is more complex than would be necessary for the purposes explained.

Against this background, the present invention sets itself the task of improving a corresponding method and making it simpler in terms of separation technology and thereby reducing the investment and / or operating costs.

Disclosure of the invention

Against this background, the present invention proposes a method for the production of ethylene and a corresponding plant according to the preambles of the respective independent claims. Preferred configurations are in each case

Subject of the dependent claims and the following description.

Before explaining the advantages of the present invention, some terms used in the description of the invention are defined in more detail below.

As used herein, component mixtures can be rich or poor in one or more components, the term “rich” for a content of at least 75%, 80%, 90%, 95% or 99% and the term “poor” for a content of at most 25%, 20%, 10%, 5% or 1% by molar, weight or

Volume base can stand. In the language used here, component mixtures can also be enriched or depleted in one or more

Be components, these terms referring to a corresponding content in another component mixture using which the component mixture under consideration was formed. That looked at

Component mixture is "enriched" if it is at least 1, 5 times, 2 times, 5 times, 10 times, 100 times or 1,000 times the content of the specified

Component (s) has, and "depleted" if it is at most 0.75 times, 0.5 times, 0.1 times, 0.01 times or 0.001 times the content of the designated

Having component (s). A component mixture "predominantly" containing one or more components is particularly rich in this or these components in the sense just explained.

If it is said here that a component mixture is "formed" using another component mixture, this is to be understood as meaning that the component mixture under consideration is at least some of that in the other

Has components mixture contained or these formed components. Forming one component mixture from another can, for example, divert part of the component mixture, feed in one or more further components or component mixtures, a chemical or

physical conversion of at least some components, as well as heating, cooling, evaporation, condensation, etc. include. A "making" one

However, the component mixture from another component mixture can also merely comprise the provision of the other component mixture in a suitable form, for example in a container or a line.

The present application used to characterize pressures and

Temperatures the terms "pressure level" and "temperature level", which is intended to express that corresponding pressures and temperatures in a corresponding system do not have to be used in the form of exact pressure or temperature values. However, such pressures and temperatures typically move in certain ranges, for example ± 1%, 5%, 10%, 20% or 25% around a mean value. Corresponding pressure levels and temperature levels can lie in disjoint areas or in areas that overlap one another. The same pressure level can still exist, for example, if there are unavoidable pressure losses. The same applies to temperature levels. The pressure levels specified here in bar are absolute pressures.

Advantages of the invention

Overall, the present invention proposes a process for the production of ethylene in which a first feed gas (fresh feed) and a second feed gas

(recycled feed gas) fed to a reactor and processed in this by steam cracking while obtaining a product mixture (cracked gas). The first feed gas can in particular consist of so-called crude ethane with conventional

Specifications exist and, in particular, are supplied from the system boundary. The first feed gas has more than 90 percent by weight, in particular more than 95 percent by weight, of saturated hydrocarbons and more than 80 percent by weight, in particular more than 85, 90 or 95 percent by weight, of ethane. A propane content in the first feed gas is in particular up to 15 percent by weight, for example up to 10 or up to 5 percent by weight.

The first feed gas is in particular low in or (essentially) free of heavier hydrocarbons, the content of which in particular is a maximum of 5

Weight percent or 1 percent by weight may be. Under "heavier

Hydrocarbons "are understood here to mean, in particular, hydrocarbons with four or more carbon atoms.

The first feed gas can contain methane in a content of up to 5 percent by weight. In particular, it is free from or at least low in carbon dioxide and other trace components. All explanations relating to a “feed gas” relate to the fresh feed directly at the reactor, ie a corresponding feed gas can, if necessary, have already been pretreated, for example depleted in CO 2.

The steam cracking in the context of the present invention is used in particular to avoid the excessive formation of by-products with a medium or low ethane conversion of, for example, 65% or less, 60% or less, 55% or less, 50% or less or 45% or less and 10 % or more,

20% or more or 30% or more carried out. Therefore, a comparatively large amount of ethane remains in the product mixture. The specialist can make further parameter settings for steam splitting as required. In particular, appropriate settings such as steam dilution and reactor pressure are selected such that

a comparatively large amount of ethylene is produced from the converted ethane and comparatively few hydrocarbons with three or more carbon atoms are produced.

If "one" reactor is used here, it goes without saying that, instead of just one reactor, several reactors can also be used in series or parallel operation, to which one or more corresponding feed gases can then be fed. Several of these reactors ("cracking furnaces") can be operated identically or differently.

In the context of the present invention, the product mixture which is withdrawn from the reactor, or a part thereof, is obtained with a subsequent mixture which

Contains hydrogen, methane, ethane, ethylene and hydrocarbons with three, four and at least five carbon atoms and in particular (essentially) consists of these components, subjected to a treatment. The processing can in principle take place in a known manner (see above). In particular, such a work-up can also be a hydrogenation of acetylene and a partial hydrogenation

Hydrogenation of especially monounsaturated and polyunsaturated

Include hydrocarbons with three carbon atoms to avoid corresponding hydrogenation in the recycle of components. A correspondingly formed subsequent mixture or a part thereof is then subjected to separation in the context of the present invention.

The present invention is characterized in that the separation comprises an ethylene separation step, the at least the ethane, the ethylene and the

Hydrocarbons with three carbon atoms from the subsequent mixture or a part thereof are fed in unseparated from one another in a common separating insert. In contrast to known ethylene separation steps, which in the prior art typically consist essentially of separating ethane and ethylene from one another (in a so-called C2 splitter), in the context of the present invention, ethylene is separated from a remaining fraction in a corresponding separation step which, however, contains not only ethane, but also substantial parts of the heavier hydrocarbons from the product mixture. Since in the context of the present invention, due to the composition of the first feed gas, overall comparatively small amounts of

Hydrocarbons with three carbon atoms are formed and thus im

Product mixture are present, the remaining fraction comprises in particular more than 50 percent by weight, in particular more than 60 percent by weight, more than 70 percent by weight, more than 80 percent by weight or more than 85 percent by weight, and in particular up to 95 percent by weight or up to 90 percent by weight ethane and otherwise heavier Hydrocarbons, at least those with three

Carbon atoms. The heavier hydrocarbons are upstream of the

However, ethylene separation step is not separated as in conventional processes. This applies at least to the hydrocarbons with three carbon atoms, as in

Indicated below.

Depending on the configuration of the method according to the invention, the

Ethylene separation step also with hydrocarbons with four and possibly five

Carbon atoms are fed, as explained in detail below. The ethylene separated off here or a light fraction from the ethylene separation step can be carried out as an ethylene product from the process. An essential aspect of the present invention consists in the unseparated feeding of the components mentioned into the ethylene separation step. This makes it easier

upstream separation and contributes to a reduction in the separation effort.

Does this mean that at least the ethane, the ethylene and the

Hydrocarbons with three carbon atoms from the subsequent mixture or a part of it are fed "unseparated" to the ethylene separation step, this is understood to mean that these components are at least partly in a continuous stream (of which, however, a part or certain components, including partly the hydrocarbons with three carbon atoms, can be separated) from the reactor to the ethylene separation step. The separation insert for the ethylene separation step can, depending on the specific design of the process, in particular also hydrocarbons with four carbon atoms or

Include hydrocarbons with four and at least five carbon atoms, which are thus also fed to the ethylene separation step without being separated.

In the ethylene separation step, the mentioned light fraction, which contains more than 95 mol percent, in particular more than 99 mol percent, of ethylene and can in particular (essentially) consist of ethylene, and a heavy fraction, which contains at least part of the ethane from the separation insert (p , V, X) and at least 15 percent by weight of the hydrocarbons with three and four carbon atoms (possibly also heavier hydrocarbons). The heavy fraction can

in particular more than 20 percent by weight, more than 30 percent by weight, more than 40 percent by weight, more than 50 percent by weight, more than 60 percent by weight, more than 70 percent by weight, more than 80 percent by weight or more than 90

Have percent by weight of the hydrocarbons with three and four carbon atoms (possibly also heavier hydrocarbons), the last-mentioned information also being able to indicate upper limits of corresponding value ranges. The values ​​result from the comparatively strong dilution of these components with ethane. The heavy fraction can be (essentially) free of ethylene. The heavy fraction from the ethylene separation step or a part thereof is used (directly or with separation of any heavier components contained) to form the second feed gas.

To reduce the separation effort, in the context of the present invention, in particular, a "soft" or "fuzzy" deethanization can take place in which, as is known from the prior art, a fraction is not formed which contains ethane and ethylene, but (in Essentially) free of other, especially heavier, components. This is combined with demethanization. However, only demethanization can take place.

Thus, within the scope of the present invention, the separating insert that the

Ethylene separation step is fed, are formed using a first pre-separation step and a second pre-separation step, the secondary mixture or its part being separated is fed to the first pre-separation step in unchanged composition, a light fraction and a heavy fraction being formed in the first pre-separation step, wherein the light fraction from the first pre-separation step or a part thereof is fed to the second pre-separation step, wherein a light fraction and a heavy fraction are formed in the second pre-separation step, and the heavy fraction from the second

Pre-separation step or part thereof as the separation insert or part of the

Separation insert is used, which is fed to the ethylene separation step. The first pre-separation step corresponds to the already mentioned fuzzy one

Deethanization, the second pre-separation step (as far as the usual

corresponding) demethanization.

The separation limits in the fuzzy deethanization used according to the invention can be set differently. In a first alternative, the light fraction from the first pre-separation step can contain a total of less than 1 mol percent of hydrocarbons with four and at least five carbon atoms and the remainder methane, ethane, ethylene and hydrocarbons with three carbon atoms. The heavy fraction from the first pre-separation step can in this case contain a total of less than 1 mol percent hydrogen, methane and ethylene and the remainder ethane, hydrocarbons with three, four and at least five carbon atoms. The task of this separation step in the first alternative is in particular the separation of ethylene and hydrocarbons with four and at least five carbon atoms, whereas the hydrocarbons with three carbon atoms are contained in both fractions. In this first alternative, the light fraction from the second pre-separation step, i.e. from the demethanization, contains a total of more than 99 mol percent methane and hydrogen, and the heavy fraction from the second pre-separation step contains less than 1 mol percent methane and hydrogen and the remainder ethane, Ethylene and hydrocarbons with three carbon atoms.

In a second alternative, the separation limit in the fuzzy deethanization can be set in such a way that the light fraction from the first pre-separation step has less than 1 mol percent of hydrocarbons with at least five carbon atoms and the remainder is methane, ethane, ethylene and hydrocarbons with three and four carbon atoms, and the heavy fraction from the first

Pre-separation step contains a total of less than 1 mol percent of hydrogen, methane and ethylene and the remainder ethane and hydrocarbons with three, four and at least five carbon atoms. The task of this separation step in the second alternative is in particular the separation of ethylene and hydrocarbons with at least five carbon atoms. In this second alternative, the light fraction from the second pre-separation step, i.e. the demethanization, basically contains a total of more than 99 mol percent methane and hydrogen, as above. The heavy fraction from the second pre-separation step also contains a total of less than 1 mol percent methane and hydrogen, but the remainder is ethane, ethylene and hydrocarbons with three and four carbon atoms.

In both of the alternatives explained above, the heavy fraction from the first pre-separation step or a part thereof can each be subjected to a further separation step in which a light fraction and a heavy fraction are again formed. The light fraction here either contains less than 1 mol percent of hydrocarbons with at least six carbon atoms and the remainder

Hydrocarbons with three, four and five carbon atoms or less than 1 mole percent of hydrocarbons with at least five carbon atoms and the remainder hydrocarbons with three and four carbon atoms. In this case, the heavy fraction can either be predominantly or exclusively, in accordance with the first alternative just given for the composition of the light fraction

Hydrocarbons with at least six carbon atoms or, according to the second alternative just given for the composition of the light fraction, predominantly or exclusively hydrocarbons with at least five

Contain carbon atoms.

The task of the separation step explained last is to generate a suitable recycling. At least hydrocarbons with six carbon atoms should be removed, if necessary also hydrocarbons with five carbon atoms. This further separation step is therefore a typical one in the latter case

Debutanization step, as it is basically known from the prior art.

According to a third alternative, however, the separation insert which is fed to the ethylene separation step can also be formed using only a single pre-separation step to which the subsequent mixture of unchanged composition is fed. This is also a demethanization. In this single pre-separation step, a light fraction that contains more than 99 mol percent methane and hydrogen is formed. Due to the additionally supplied

Hydrocarbons contain a heavy fraction, which is formed in the single pre-separation step, but a total of less than 1 mol percent methane and hydrogen and the remainder ethane, ethylene and hydrocarbons with three, four and at least five carbon atoms. This heavy fraction from the single pre-separation step or part thereof is used as the separation insert or as part of the separation insert which is fed to the ethylene separation step.

If, instead of a first and second pre-separation step, as in the third alternative just explained, a single pre-separation step is used, at least part of the heavy fraction that remains after the ethylene separation step is advantageously fed to a further separation step in which a light fraction and a heavy fraction are formed. The light fraction here either contains less than 1 mole percent of hydrocarbons with at least six

Carbon atoms and the remainder hydrocarbons with three, four and five

Carbon atoms or less than 1 mole percent of hydrocarbons with at least five carbon atoms and the remainder hydrocarbons with three and four carbon atoms. The heavy fraction can in this case either, according to the first alternative just given for the composition of the light fraction, predominantly or exclusively hydrocarbons with at least six carbon atoms or, according to the second alternative just given for the composition of the light fraction, predominantly or exclusively

Contain hydrocarbons with at least five carbon atoms.

Here, too, the task of the separation step explained last is to generate a suitable recycle, in which at least hydrocarbons with six

Carbon atoms, possibly also hydrocarbons with five carbon atoms, are removed. In the latter case, this further separation step is again a typical debutanization step, as is basically known from the prior art.

It goes without saying that in each of the cases in which, as explained above and below, hydrocarbons with at least six carbon atoms are converted into a fraction, these hydrocarbons are contained in the product mixture.

In all cases in which a separation step previously referred to as a "further separation step" is used, its light fraction or a part thereof is used to form the second feed gas, since it is poor in or free of

Hydrocarbons with six and possibly more carbon atoms and possibly also with five carbon atoms and contains hydrocarbons that are suitable for recirculation in the steam cracking. This is particularly the case when the processing of the cracked gas, which has been explained several times, includes a hydrogenation. The light fraction from the further separation step can be combined in the first and second alternative with the heavy fraction from the ethylene separation step.

The heavy fraction from the further separation step, on the other hand, is typically discharged from the process together with a fraction from the processing which contains hydrocarbons with at least five or at least six carbon atoms. This is what is known as pyrolysis gasoline, which after

Processing in a manner known per se, for example as fuel or for

Extraction of aromatics can be used.

The three alternatives of the present invention explained above (with the first and second pre-separation step with different separation limits in the first pre-separation step and the alternative without the first pre-separation step) each have different advantages in terms of production and operating costs, which are summarized below. The person skilled in the art therefore selects the alternatives explained above depending on the requirements.

Under the first alternative, a reduction in the required

Shaft power by 3.6 MW, in the second alternative by 6.3 MW and in the third alternative by 6.9 MW (here and below the "reduction" refers to a method not according to the invention, as illustrated in FIG. This can be traced back to the less precise or no separation in the deethanizer. There is also a reduction in the amount of low-pressure steam required (expressed in the amount of energy required to provide it) by 10.8 MW (first alternative), 13 MW (second

Alternative) or 16 MW (third alternative 3). This is due to the reduced resp.

no heating output in the deethanization.

In the second alternative, the deethanization can take place at a significantly lower pressure than in the first alternative and in the embodiment not according to the invention, which in addition to the lower compressor output also in particular

Results in material savings. The same applies to the number of trays in the deethanization, which can also be reduced in the second alternative. In the third alternative, it may be advantageous to equip the debutanization with an additional low-pressure absorber.

In the third alternative, a reduction in the rib plate heat exchanger surface by approx. 600 kW / K is possible, in particular because deethanization is no longer necessary. A reduction in the block-in-shell heat exchanger surface is approx. 750 kW / K in the first alternative, approx. 1,450 kW / K in the second alternative and approx. 1,800 kW / K in the third alternative. The tube bundle heat exchanger surface can be reduced by approx. 2,600 kW / K in the first alternative, by approx. 4,300 kW / K in the second alternative and by approx. 5,700 kW / K in the third alternative.

The present invention also extends to a plant for the production of ethylene, with respect to which reference is made to the corresponding independent patent claim. Regarding the features and advantages of such a system, which can be designed in particular to carry out a method, as described above in

different configurations has been explained in detail, reference is made to the explanations above.

The invention is explained in more detail below with reference to the accompanying drawings, which illustrate embodiments of the present invention in comparison with an embodiment not according to the invention.

Brief description of the drawings

Figure 1 illustrates a method according to one not according to the invention

Embodiment.

Figure 2 illustrates a method according to an embodiment of the invention.

FIG. 3 illustrates a method according to an embodiment of the invention.

FIG. 4 illustrates a method according to an embodiment of the invention.

Detailed description of the drawings

In the following figures, structurally or functionally corresponding elements are indicated with identical reference symbols. The same applies to the material flows marked with capital letters. It goes without saying that corresponding components experience different structural designs or

corresponding material flows can sometimes be composed differently without being designated differently in each case.

Methods according to embodiments not according to the invention and embodiments according to the invention are described below in each case. However, the corresponding explanations relate to devices for carrying out corresponding methods in the same way. If, therefore, reference is made below to method steps, the corresponding explanations apply in the same way to system components that are provided for implementing corresponding method steps.

In Figure 1, a process for the recovery of ethylene according to one is not

embodiment of the invention in the form of a schematic

Process diagram illustrated and designated as a whole by 400.

In method 400, a feed gas A is fed to a reactor 1 from the system boundary (as illustrated by an arrow symbol). This feed gas A was previously and is hereinafter referred to as the “first” feed gas. For example, it is essentially pure ethylene. To possible

The ethylene content of a corresponding first feed gas is based on the above

Explanations referenced. Furthermore, a further feed gas, previously and hereinafter referred to as "second" feed gas, is fed to the reactor. This second feed gas is one that is fed back from the method 400

Gas mixture, which in particular contains ethane and hydrocarbons with three and four carbon atoms. For the formation of the second feed gas, reference is made to the following explanations.

The first feed gas A and the second feed gas B are fed to the reactor 1 and processed there with steam (not illustrated) by steam cracks. In this way, a product mixture C is obtained, which is also known in the art as cracked gas. In addition to products and by-products of the steam cracking, the product mixture C also contains, in particular, unreacted starting materials, in the present case in particular ethane, and also water from the added steam. The product mixture C is used to remove corresponding undesired components

therefore a processing with the process steps 2 to 4 and a total of 10 combined separation.

The treatment initially includes a water quench for cooling and process steam condensation as well as compression in a typically multi-stage compressor in a process step 2. In this case, hydrocarbons with five or more carbon atoms can be deposited from the product mixture C, i.e. components of the so-called pyrolysis gasoline. Corresponding components can be withdrawn from process step 2 in the form of a stream D. Sour gas can also be removed. A compressed and correspondingly of at least a part of the hydrocarbons with five

Gas mixture freed from carbon atoms, which is now designated by E, can now be fed to a pre-cooling and drying 3. In the course of this pre-cooling and drying, a hydrogenation 4, the so-called crude gas hydrogenation, can be carried out, in which acetylene in particular is converted to ethylene and monounsaturated and polyunsaturated hydrocarbons with three or more carbon atoms and heavier components are partially converted to less unsaturated components. A hydrogenation can also take place in the separation 10 described below, but this would have the disadvantage that in most configurations

Acetylene and to be returned to the reactor, initially still unsaturated

Hydrocarbons with three and four carbon atoms have to be hydrogenated separately (not further described). A gas mixture F processed in method steps 2 to 4, previously and hereinafter referred to as “secondary mixture”, is fed to separation 10.

In the example shown, the separation 10 initially comprises one

Dethanization step 5 ', previously and hereinafter also referred to as "first pre-separation step", in which a light fraction H, which essentially contains ethane, ethylene and lower-boiling compounds, and a heavy fraction G, which is contained in

Substantially hydrocarbons with three or more carbon atoms are formed. The former is fed to a demethanization 6, previously and hereinafter also referred to as a “second pre-separation step”, the latter to a debutanization 8, previously and hereinafter also referred to as a “further separation step”.

In the second pre-separation step 6, the light fraction H becomes from the first

Pre-separation step 5 ', which, as mentioned, essentially ethane, ethylene and

Contains lower boiling compounds, freed from the lower boiling compounds. In this way, a light fraction I is formed which essentially contains methane and hydrogen and which can be withdrawn from the process 100 and / or used, for example, to fire the reactor 1. It is also possible to recover hydrogen from a corresponding gas mixture. It should be pointed out here that the sequence of pre-separation step 5 '(or pre-separation step 5 and 5 "in the subsequent examples according to the invention) and pre-separation step 6 can be interchanged in their order. A heavy fraction K from the second pre-separation step 6, one of methane and Hydrogen-freed gas mixture which still essentially contains ethane and ethylene in process 400, is then fed to an ethylene separation step 7 ', which here corresponds to a classic C2 separation, where a light fraction L essentially comprising ethylene and a heavy fraction M essentially comprising ethane are formed. The former can be delivered in the form of a material flow L to the system boundary illustrated by the arrow symbol; the latter is used in the form of a material flow M to form the second feed gas B.

In the further separation step 8, the heavy fraction G from the first pre-separation step becomes a light fraction N, which essentially contains hydrocarbons with three and four (and possibly five, see explanations above) carbon atoms, and a heavy fraction O, which essentially contains Contains hydrocarbons with five and possibly more carbon atoms. The former is combined with the heavy fraction M from the ethylene separation step and thus to form the second

Feed gas B used. The heavy fraction O from the further separation step 8 is combined with the stream D and carried out in the form of a pyrolysis gasoline stream P.

As already mentioned above, in the process 400 illustrated in FIG. 1, a complete separation of hydrocarbons having three and four carbon atoms from ethane, which is in itself superfluous, is carried out. In particular, an unnecessary separation effort is carried out in the deethanization 5. The present

The invention therefore proposes a method in different configurations in which a corresponding separation effort is reduced.

In FIG. 2, a method according to an embodiment of the present invention is illustrated and designated as a whole by 100. This embodiment corresponds to the "first alternative" mentioned several times above.

The method 100 according to FIG. 2 differs from that in FIG. 1

illustrated method 400 not according to the invention with regard to FIG

Process steps 1 to 4 not necessarily. With regard to these process steps, reference is therefore made to the explanations above. In the method 100 according to FIG. 2, however, a method that deviates from the method 400 according to FIG. 1 is used

Dethanization carried out as the first separation step, which is therefore denoted here by 5 differently. In contrast to a gas mixture containing essentially ethane, ethylene and lighter components (cf. light fraction H according to FIG. 1) on the one hand and an essentially hydrocarbons with three or more

Gas mixture containing carbon atoms on the other hand (cf. light fraction G according to FIG. 1) is here a light fraction Q, which in addition to ethane, ethylene and lighter components also contains some of the hydrocarbons with three

Contains carbon atoms from the secondary mixture F supplied to the first pre-separation step 5, and a heavy fraction R, which contains only some of the hydrocarbons with three carbon atoms and otherwise the heavier hydrocarbons from the secondary mixture F and possibly ethane, is formed. The light fraction Q is in particular essentially free of hydrocarbons with four or more carbon atoms. Conversely, the heavy fraction R withdrawn fraction is poor in or free of ethylene and lower-boiling components.

Here too, the light fraction Q is fed to the second pre-separation step 6, in which a light fraction H containing essentially methane and hydrogen is formed. A remaining heavy fraction S, however, in contrast to the heavy fraction K from the second pre-separation step 6 of the process 400 according to FIG. 1, contains not only ethane and ethylene but also hydrocarbons with three carbon atoms. It is fed to an ethylene separation step 7. In contrast to that

Ethylene separation step 7 ″ of process 400 according to FIG

Hydrocarbons with three carbon atoms. This can occur in particular in the bottom of a rectification column used in the ethylene separation step 7. The heavy fraction T from the ethylene separation step 7 is used in the formation of the second feed gas B in the manner illustrated.

The further separation step 8 according to the method 100 essentially corresponds to the separation step 8 according to the method 400 according to FIG and from the first pre-separation step 5 and the heavy fraction S from the second

Pre-separation step 6 has passed into the heavy fraction T from the ethylene separation step 7.

In FIG. 3, a method according to a further embodiment of the present invention is illustrated and designated as a whole by 200. The method 200 corresponds to the “second alternative” mentioned several times above. It differs from the method 100 according to FIG. 2 essentially in the different execution of the first pre-separation step 5. The first pre-separation step 5 is therefore denoted by 5 ″ in the method 200 according to FIG.

In contrast to the first pre-separation step 5 according to the method 100, in the first pre-separation step 5 ″ according to the method 200, a light fraction U is formed which, in addition to ethane, ethylene and the lower-boiling components, not only contains some of the hydrocarbons with three carbon atoms, but also contains some of the hydrocarbons with four carbon atoms from the subsequent mixture F. This is fed to the second pre-separation step 6. While a light fraction H formed in the second pre-separation step 6 is predominantly or

contains only methane and hydrogen, the remaining heavy fraction V contains ethane, ethylene and hydrocarbons with three and four

Carbon atoms. In the ethylene separation step, which is designated here as above with 7, a light fraction K containing essentially ethylene and a heavy fraction W containing essentially ethane, hydrocarbons with three and hydrocarbons with four carbon atoms are formed.

A heavy fraction R formed in the first pre-separation step 5 ″ does not contain the hydrocarbons with three and four carbon atoms which are transferred via the fractions U and V into the fraction W, so that they also do not transfer to the light fraction N of the further separation step 8.

FIG. 4 illustrates another embodiment of the present invention, indicated generally at 300. The method 300 corresponds to the “second alternative” mentioned several times above. As with the method 300 in FIG. 4

illustrated, a first pre-separation step 5 ', 5 or 5 "(see previous FIGS. 1 to 3) can also be completely dispensed with in an embodiment according to the invention A heavy fraction X obtained here thus contains not only ethane and ethylene but also hydrocarbons with three, four and at least five carbon atoms

Fraction X is fed to the ethylene separation step 7, in which the

Light fraction K containing predominantly or exclusively ethylene can be formed and withdrawn. A remaining heavy fraction Y can be fed to a further separation step, which can be designed in a manner comparable to the separation step 8 according to the present figures and is therefore denoted by 8 '. The light fraction formed in this separation step 8 'contains ethane and hydrocarbons with three and four (and possibly five) carbon atoms. It is therefore used directly as the second feed gas B. The composition of the heavy fraction O

does not differ from that according to the previously explained embodiments of the invention.

Claims

1. Method (100, 200, 300) for the production of ethylene, in which a first

Feed gas (A) and a second feed gas (B) fed to a reactor (1) and processed in this to obtain a product mixture (C) by steam cracks, the first feed gas (A) more than 90 percent by weight of saturated hydrocarbons and more than 80 percent by weight Has ethane, and where the product mixture (C) or a part thereof is processed (2, 3, 4 ) and the secondary mixture (F) or a part thereof is subjected to a separation (10), characterized in that the separation (10) comprises an ethylene separation step (7) to which at least the ethane,the ethylene and the hydrocarbons with three carbon atoms from the secondary mixture (F) or a part of it in each case in a common separation insert (S, V, X) are fed in unseparated from one another, with a light fraction (K) in the ethylene separation step (7) containing more than 95 mole percent ethylene, and a heavy fraction (T, W, Y) containing at least some of the ethane from the separation insert (S, V, X) and at least 15 percent by weight of the hydrocarbons with three and fourX) and at least 15 percent by weight of the hydrocarbons with three and fourX) and at least 15 percent by weight of the hydrocarbons with three and four

Carbon atoms from the separation feed (S, V, X), and wherein the heavy separation product (T, W, Y) from the ethylene separation step (7) or a part thereof is used as part of or to form the second feed gas (B) .

2. The method (100, 200) according to claim 1, wherein the separation insert (S, V), which is fed to the ethylene separation step (7), using a first one

Pre-separation step (5, 5 ") and a second pre-separation step (6) is formed, wherein the first pre-separation step (5, 5") the subsequent mixture (F) or its

Separation (10) subject part is fed in unchanged composition, wherein in the first pre-separation step (5, 5 ") a light fraction (Q, U) and a heavy fraction (R) are formed, the light fraction (Q, U) from the first pre-separation step (5, 5 ") or a part of it from the second

Pre-separation step (6) is fed, wherein in the second pre-separation step (6) a light fraction (H) and a heavy fraction (S, V) are formed, and the heavy fraction (S, V) from the second pre-separation step (6) or part

thereof as the separation insert (S, V) or as part of the separation insert (S, V) which is fed to the ethylene separation step (7).

3. The method (100) according to claim 2, wherein the light fraction (Q) from the first pre-separation step (5) a total of less than 1 mol percent of hydrocarbons with four and at least five carbon atoms and the remainder methane, ethane,

Contains ethylene and hydrocarbons with three carbon atoms, and in which the heavy fraction (R) from the first pre-separation step (5) in total less than 1 mol percent hydrogen, methane and ethylene and the remainder ethane,

Contains hydrocarbons with three, four and at least five carbon atoms.

4. The method (100) according to claim 3, wherein the light fraction (H) from the

second pre-separation step (6) a total of more than 99 mol percent methane and hydrogen and the heavy fraction from the second pre-separation step (6) contains less than 1 mol percent methane and hydrogen and the remainder ethane, ethylene and hydrocarbons with three carbon atoms.

5. The method (200) according to claim 2, wherein the light fraction (U) from the first pre-separation step (5 ") a total of less than 1 mol percent of hydrocarbons with at least five carbon atoms and the remainder methane, ethane, ethylene and hydrocarbons with three and contains four carbon atoms and in which the heavy fraction (R) from the first pre-separation step (5) has a total of less than 1 mol percent of hydrogen, methane and ethylene and the remainder ethane and

Contains hydrocarbons with three, four and at least five carbon atoms.

6. The method (100) according to claim 5, wherein the light fraction (H) from the

second pre-separation step (6) a total of more than 99 mol percent methane and hydrogen and the heavy fraction from the second pre-separation step (6) contains less than 1 mol percent methane and hydrogen and the remainder ethane, ethylene and hydrocarbons with three and four carbon atoms.

7. The method (100, 200) according to any one of the preceding claims 3 to 6, in which the heavy fraction (S, V) from the first pre-separation step (5, 5 ") or a part thereof is subjected to a further separation step (8), in which a light fraction (N) and a heavy fraction (O) are formed, the light fraction either having less than 1 mol percent of hydrocarbons with at least six carbon atoms and the remainder hydrocarbons with three, four and five carbon atoms or less than 1 mol percent

Hydrocarbons with at least five carbon atoms and the rest

Contains hydrocarbons with three and four carbon atoms.

8. The method (300) according to claim 1, wherein the separation insert (X), the

Ethylene separation step (7) is fed, is formed using a single pre-separation step (6) to which the secondary mixture (F) is fed in unchanged composition, and in which a light fraction (H), which contains a total of more than 99 mol percent methane and hydrogen , and a heavy fraction (X) which in total contains less than 1 mol percent methane and hydrogen and the remainder ethane, ethylene and hydrocarbons having three, four and at least five carbon atoms, are formed, the heavy fraction (X) from the single pre-separation step (6) or a part thereof is used as the separation insert (X) or as a part of the separation insert (X) which is fed to the ethylene separation step (7).

9. The method (300) of claim 8, wherein at least a portion of the heavy

Fraction (X) from the only pre-separation step (6), which occurs after the

Ethylene separation step (7) remains, is fed to a further separation step (8 '), in which a light fraction (B) and a heavy fraction (O) are formed, the light fraction either being less than 1 mol percent

Contains hydrocarbons with at least six carbon atoms and the remainder hydrocarbons with three, four and five carbon atoms or less than 1 mole percent of hydrocarbons with at least five carbon atoms and the remainder hydrocarbons with three and four carbon atoms.

10. The method (100, 200, 300) according to any one of the preceding claims 7 or 9, in which the light fraction (N, B) from the further separation step (8) or a part thereof is used to form the second feed gas (B) .

1 1. The method according to any one of the preceding claims 7, 9 or 10, wherein the heavy fraction (O) from the further separation step (8, 8 ') together with a fraction (D) from the preparation (2), the hydrocarbons with contains at least five or at least six carbon atoms, from which method (100, 200, 300) is carried out.

12. Plant for the production of ethylene, which is set up to feed a first feed gas and a second feed gas (B) to a reactor (1) and to process them in this by means of steam cracks while obtaining a product mixture (C), the plant also being set up for this purpose is to provide the first feed gas (A) in such a way that it has more than 90 percent by weight of saturated hydrocarbons and more than 80 percent by weight of ethane, and the product mixture (C) or a part thereof to obtain a secondary mixture (F), the hydrogen, methane, Ethane, ethylene and hydrocarbons with three, four and at least five

Contains carbon atoms, a preparation (2, 3, 4) and the subsequent mixture (F) or a part thereof to be subjected to a separation (10), thereby

characterized in that the separation (10) comprises an ethylene separation step (7) that means are provided which are adapted to the

Ethylene separation step (7) at least the ethane, the ethylene and the

To supply hydrocarbons with three carbon atoms from the secondary mixture (F) or a part thereof in a common separating insert (S, V, X) unseparated from one another, that means are provided which are set up for a light fraction (K ), which contains more than 95 mole percent ethylene, and a heavy fraction (T, W, Y), which consists of at least some of the ethane from the separation insert (S, V, X) and at least 15 percent by weight of the hydrocarbons with three and four carbon atoms the separation insert (S, V, X), and that means are provided which are adapted to form the heavy separation product (T, W, Y) from the ethylene separation step (7) or a part thereof as part or for the formation of the second feed gas (B) to be used.

13. Plant according to claim 12, which is set up to carry out a method according to one of the preceding claims 1 to 11.