DE102016200561A1 - Process for recovering ethylene from methane - Google Patents

Abstract

A process (100) for recovering ethylene from methane is provided by providing, using a process for the oxidative coupling of methane (1), a product mixture comprising at least ethylene, ethane and methane and lower than methane and higher than ethane Contains compounds. It is envisaged that from the product mixture first by means of an adsorptive process (4) 60 to 90 mole percent of the methane and at least a portion of the lower than methane boiling components are removed and the product mixture is then subjected to one or more further treatment steps and then to give a The separation process comprises a demethanization (9), which is subjected to at least a portion of the product mixture as a separation insert, and in the first part of the methane and the major part of the ethane and of ethylene and higher than Ethane boiling compounds are washed out by means of an absorption liquid from the separation insert.

Description

The invention relates to a process for the production of ethylene from methane according to the preamble of patent claim 1.

State of the art

The oxidative coupling of methane is described in the literature, for example in JD Idol et al., "Natural Gas", in: JA Kent (ed.), "Handbook of Industrial Chemistry and Biotechnology", Volume 2, 12th Edition, Springer, New York 2012 ,

According to the current state of knowledge, the oxidative coupling of methane comprises a catalyzed gas phase reaction of methane with oxygen, in which one hydrogen atom is split off from each of two methane molecules. The resulting methyl radicals initially react to form an ethane molecule. In the reaction, a water molecule is further formed. With suitable ratios of methane to oxygen, suitable reaction temperatures and the choice of suitable catalytic conditions, then an oxydehydrogenation of the ethane to ethylene, a target compound in the oxidative coupling of methane. In this case, another water molecule is formed.

The reaction conditions in the oxidative coupling of methane classically include a temperature of 500 to 900 ° C and a pressure of 1 to 10 bar and high space velocities. More recent developments are also moving towards the use of lower temperatures. The reaction can be carried out homogeneously and heterogeneously in a fixed bed or in the fluidized bed. In the oxidative coupling of methane, higher hydrocarbons having up to six or eight carbon atoms can also be formed; However, the focus is on ethane or ethylene and optionally propane or propylene.

In particular, due to the high binding energy between carbon and hydrogen in the methane molecule, the yields in the oxidative coupling of methane are comparatively low. In addition, the relatively harsh reaction conditions and temperatures required to cleave these bonds also favor the further oxidation of the methyl radicals and other intermediates to carbon monoxide and carbon dioxide.

Although the low yields and the formation of carbon monoxide and carbon dioxide can be counteracted in part by the choice of optimized catalysts and reaction conditions, a gas mixture formed in the oxidative coupling of methane in addition to the target compounds such as ethylene and possibly propylene contains considerable amounts of unreacted methane and water , Carbon monoxide and carbon dioxide. Such a gas mixture is hereinafter also referred to as "product mixture" of the oxidative coupling of methane, although it contains not only the desired products, but also unreacted starting materials and by-products.

In the oxidative coupling of methane reactors can be used, in which a catalytic zone is followed by a non-catalytic zone. The product mixture formed in the catalytic zone is transferred to the non-catalytic zone, where it is initially still at the comparatively high temperatures used in the catalytic zone. In particular, by the presence of the water formed in the oxidative coupling of methane, the reaction conditions here resemble those of conventional steam cracking processes. Therefore, ethane and higher paraffins can be converted to olefins. In the non-catalytic zone and other paraffins can be fed so that the residual heat of the oxidative coupling of methane can be exploited in a particularly advantageous manner. Such vapor cracking in a catalytic zone downstream non-catalytic zone is also referred to as "post bed cracking". Subsequently, the term "post-catalytic vapor cracking" is used for this purpose.

With regard to the reaction conditions prevailing in the steam cracking, it is also to be found in specialist literature such as Article "Ethylene" in Ullmann's Encyclopedia of Industrial Chemistry, Online Edition, 15 April 2007, DOI 10.1002 / 14356007.a10_045.pub2 , referenced. For example, steam cracking is used to obtain short chain olefins such as ethylene and propylene, diolefins such as butadiene or aromatics, but is not limited thereto.

Is below a "reactor, which is adapted for the oxidative coupling of methane," the speech, this is to be understood as a reactor having at least in a reactor zone a catalyst (for example in the form of a fixed bed or fluidized bed catalyst), which is suitable for oxidative coupling of methane is suitable. At least in this reactor zone, temperature and pressure conditions can be created by suitable means, for example by burners and upstream compressors, which lead to an oxidative coupling of methane under the influence of the catalyst, as explained above. A corresponding reactor may, in addition to the illustrated reactor zone further reactor zones, for example, a non-catalytic zone, which is used for the above-mentioned post-catalytic steam cracking ("Post Bed Cracking").

Correspondingly, when it is mentioned below that a product mixture is formed "using a process for the oxidative coupling of methane", it should be understood that a process is involved which comprises the reactions explained above, in particular the formation of methyl radicals, their coupling to ethane and the subsequent oxydehydrogenation. In addition, however, other methods or method steps may be included, in particular the post-catalytic cracking ("post-bed cracking") discussed above. To this or these further methods or method steps, further inserts can be supplied, which are at least partially converted into products which are found in the product mixture. In other words, the formation of the product mixture which is done "using" the process for the oxidative coupling of methane does not necessarily involve only the oxidative coupling of methane.

Product mixtures formed using a process for the oxidative coupling of methane contain, for the reasons explained above, in particular large amounts of methane, which should advantageously be separated and recycled to the oxidative coupling. Due to the high methane content of the comparatively low content of target products, the separation-technical processing of a corresponding product mixture turns out to be extremely complicated.

The present invention therefore seeks to provide a process in which, in particular, the processing of a corresponding product mixture is improved over the prior art.

Disclosure of the invention

Against this background, the present invention proposes a process for the production of ethylene from methane with the features of claim 1. Embodiments are each the subject of the dependent claims and the following description.

Before explaining the features and advantages of the present invention, some basics and the terms used will be explained.

Common processes for the separation of product streams from processes for producing hydrocarbons, such as the oxidative coupling of methane, involve the formation of a series of fractions based on the different boiling points of the components contained. In the art, abbreviations are used which indicate the carbon number of the predominantly or exclusively contained hydrocarbons. Thus, a "C1 fraction" is a fraction which contains predominantly or exclusively methane (and conventionally also lower than methane-boiling compounds, then also called "C1minus fraction"). By contrast, a "C2 fraction" contains predominantly or exclusively ethane, ethylene and / or acetylene. A "C3 fraction" contains predominantly or exclusively propane, propylene, methyl acetylene and / or propadiene. A "C4 fraction" contains predominantly or exclusively butane, butene, butadiene and / or butyne, it being possible for the respective isomers to be present in different proportions, depending on the source of the C4 fraction. The same applies to a "C5 fraction" and the higher fractions. Several fractions can be summarized. For example, a "C2plus fraction" contains predominantly or exclusively hydrocarbons with two and more and a "C2minus fraction" predominantly or exclusively hydrocarbons having two carbon atoms and methane and optionally lower than methane boiling compounds.

When referring to "higher-boiling" or "lower-boiling" or "lower-boiling" compounds in comparison with a compound, these are compounds which have a higher or lower boiling point than the compound with which these compounds are compared. For example, carbon monoxide, hydrogen, nitrogen and argon are compounds that boil lower than methane. On the other hand, acetylene and hydrocarbons having three or more carbon atoms are compounds boiling higher than ethane.

Corresponding fractions can also be used as refrigerants, such as the C2 or C3 fractions or components thereof. The temperature levels provided by respective C2 or C3 refrigerants are commonly referred to as "C2 cold" or "C3 cold". These refrigerants are fed into refrigeration circuits, where they are first compressed to a specific final pressure level and, on the basis of this pressure, subsequently decompressed to different pressure levels for refrigeration at corresponding temperature levels. By means of a C3 refrigerant (in particular propane and propylene) can be generated in this way, for example, refrigerant flows at about -40 ° C and +10 ° C.

Liquid and gaseous mixtures, as used herein, may be rich or poor in one or more components, with "rich" for a content of at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99, 9% or 99.99% and "poor" for a content of not more than 50%, 25%, 10%, 5%, 1%, 0.1% or 0.01% of molar, Weight or volume can stand. The term "predominantly" can correspond to the definition of "rich". Liquid and gaseous mixtures may also be enriched or depleted in one or more components as used herein, which terms refer to a corresponding content in a starting mixture from which the liquid or gaseous stream was obtained. The liquid or gaseous mixture is "enriched" if it is at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times, 100 times or 1000 times, "depleted" when it contains not more than 0,9 times, 0,5 times, 0,1 times, 0,01 times or 0,001 times the content of a corresponding component, relative to the starting mixture. In the present case, for example, the term "methane" or "hydrogen" or an "ethylene product" is meant, including a mixture which is rich in the corresponding component. However, it can also be the respective clean gas.

A liquid or gaseous mixture is "derived" from, or formed from, this mixture or using this mixture of any other liquid or gaseous mixture (also referred to as the starting mixture) if it contains at least some components contained in or from the starting mixture. A mixture formed in this sense may be formed from the starting mixture by separating or branching off a partial stream or one or more components, enriching or depleting one or more components, chemically or physically reacting one or more components, heating, cooling, pressurizing and the like. However, "forming", for example, a feed mixture for a subsequent separation process, may also simply represent passing a corresponding mixture in a suitable conduit and feeding it to the separation process.

The present application uses the terms "pressure level" and "temperature level" to characterize pressures and temperatures, thereby indicating that corresponding pressures and temperatures in a given plant need not be used in the form of exact pressure or temperature values to realize the innovative concept. However, such pressures and temperatures typically range in certain ranges that are, for example, ± 1%, 5%, 10%, 20% or even 50% about an average. Corresponding pressure levels and temperature levels can be in disjoint areas or in areas that overlap one another. In particular, for example, pressure levels include unavoidable or expected pressure drops, for example, due to cooling effects. The same applies to temperature levels. The pressure levels indicated here in bar are absolute pressures.

For the design and specific design of distillation columns and absorption columns, as they can also be used in the context of the present application, reference is made to relevant textbooks (see, for example K. Sattler, "Thermal Separation Methods: Fundamentals, Design, Apparatus", 3rd edition, Wiley-VCH, Weinheim 2001 ).

A "distillation column" in the language used here is a separation unit which is set up at least partially for a gaseous or liquid or in the form of a two-phase mixture with liquid and gaseous fractions, possibly also in the supercritical state To separate, ie from the mixture each pure substances or mixtures to produce, which are enriched relative to the mixture with respect to at least one component or depleted in the above-mentioned sense. Distillation columns are well known in the field of separation technology. Typically, distillation columns are formed as cylindrical metal containers equipped with internals, such as sieve trays or ordered or disordered packages. A distillation column is characterized, inter alia, by the fact that a liquid fraction is deposited in its lower region, also referred to as a sump. This liquid fraction, also referred to as bottom product, is heated in a distillation column by means of a bottom evaporator, so that continuously evaporates a portion of the bottom product and rises in gaseous form in the distillation column. A distillation column is also typically provided with a so-called top condenser into which at least part of a gas mixture enriched in an upper region of the distillation column or a corresponding clean gas, also referred to as top product, is fed in, liquefied therein and fed as liquid reflux at the top of the distillation column ,

In contrast to a distillation column, an "absorption column" does not have a bottom evaporator. Absorption columns are also generally known in the field of separation technology. Absorption columns are used for absorption in the phase countercurrent and therefore also referred to as countercurrent columns. In countercurrent absorption, the donating gaseous phase flows upwardly through an absorption column. The receiving solution phase flows, abandoned from the top and withdrawn below, the gas phase. In a corresponding absorption column internals are also typically provided, which are suitable for a gradual (soils, spray zones, rotating plates, etc.) or continuous (random packing of packing, packing, etc.) provide phase contact.

In an absorption in countercurrent, as it takes place in an absorption column, a gaseous stream is sent to a particular finely divided liquid stream. The liquid stream absorbs components from the gaseous stream, which are washed out of the gaseous stream in this way. The leaching may be partial or complete.

Advantages of the invention

The present invention is based on the recognition that it is particularly advantageous to process a product mixture produced in a process for the oxidative coupling of methane or a separation insert formed therefrom, which has already been prepared using suitable treatment steps, by means of absorptive demethanization, i. the compounds contained boiling higher than methane, in particular ethane and ethylene, but also hydrocarbons having three and possibly more carbon atoms, at least predominantly wash out of this separation using an absorption liquid. This leaves a gas mixture containing predominantly methane and lower than methane-boiling compounds, if they were included in the product mixture or separation insert. However, this gas mixture may also contain leached compounds and, if appropriate, parts of the absorption liquid which have passed into the gas phase.

Conventional methods for demethanization, which are not absorptive but predominantly or exclusively work by distillation, have in common that here temperatures of -100 ° C and less for the separation of methane and possibly lower than methane boiling compounds must be used, which is the use of ethylene as a refrigerant ("C2 cold") required. Optionally, the use of turboexpanders to achieve temperatures of -130 ° C and less is required, especially when a corresponding gas mixture contains a higher proportion of lighter compounds, as is conventional when using predominantly or exclusively gaseous or ethane-rich inserts in steam cracking the case is. This proves to be complicated and extremely costly due to the materials and equipment required here. In particular, when using turbo expanders, a corresponding method also proves to be extremely maintenance-prone.

In order to avoid correspondingly low temperatures, corresponding absorptive processes have previously been proposed in other processes.

For example, in the EP 0 675 094 A2 proposed to first feed a gas mixture from a steam cracking process into an absorber (absorption column) and to wash out the hydrocarbons having two carbon atoms by means of an absorption liquid leaving a gas mixture containing predominantly or exclusively methane and hydrogen. In addition to the hydrocarbons having two carbon atoms, fractions of the methane and of the hydrogen from the starting mixture also pass into the absorption liquid. Methane and hydrogen are therefore first expelled from the loaded absorption liquid before it is recovered from the hydrocarbons having two carbon atoms. Other partially absorptive methods in a different embodiment, for example, from the US Pat. No. 2,815,650 A , of the US 5 710 357 A , of the WO 2014/064172 A2 and the US 2,933,901 A1 known.

Above all, absorptive demethanization has the advantage that significantly higher temperatures can be used for separating off methane and possibly hydrogen than are possible in predominantly or exclusively distillative processes. As mentioned above with regard to distillation columns, there must be condensed a gaseous top product, in the demethanization of a methane-rich gas mixture, at a correspondingly low temperature so that it can serve as reflux to the distillation column. In an absorptive demethanization, however, a condensing to a much higher temperature absorption liquid is used, by means of which the compounds which are heavier than methane, are washed out. Methane does not need to be condensed here. In the absorptive demethanization can therefore be dispensed with C2 refrigerant and it can be used, for example, C3 refrigeration.

However, the use of absorptive demethanization initially appears problematic due to the high methane content of the product mixture from the process for the oxidative coupling of methane. According to the invention, however, it could be recognized that with a suitable choice of the treatment steps used, including a suitable depletion of the product mixture of methane by means of an adsorptive process, the absorptive demethanization can be used with particular advantage.

Overall, the present invention provides a process for recovering ethylene from methane in which a product mixture is provided using a method for the oxidative coupling of methane. As discussed above, providing "using" the process for the oxidative coupling of methane may also include other processes or process steps, including a treatment of a corresponding gas mixture. The product mixture contains at least ethylene, ethane and methane and lower than methane and higher than ethane boiling compounds. As mentioned above, product mixtures usually obtained in processes for the oxidative coupling of methane typically also contain water, carbon dioxide and carbon monoxide. Further, hydrogen and, for example, inert gases unreacted in the process of oxidative coupling of methane may be contained.

According to the invention, 60 to 90 mole percent, in particular 70 to 85 mole percent, of the methane and at least some of the components boiling lower than methane are first removed from the product mixture by means of an adsorptive process, in particular by means of pressure swing adsorption and / or by means of thermal swing adsorption. This is a "fuzzy", separation technology and energy but particularly inexpensive, removal of methane, in which the product mixture is advantageously depleted to a methane content of only 45 to 60 mol percent. The methane contained is therefore not completely removed from the product mixture. Subsequent to the pressure swing adsorption, the product mixture is subjected to one or more further treatment steps and then subjected to separation technology to obtain a product rich in ethylene. The ethylene-rich product can be made from the process. As mentioned, the separation processing is made much easier by the partial removal of methane.

The separation technology processing of the product mixture according to the invention comprises a demethanization, which is subjected to at least a portion of the product mixture as a separation insert, and in the first part of the methane and the majority of the ethane and ethylene and the higher than ethane boiling compounds by means of an absorption liquid from the Separation insert to be washed out. The leaching of the part of the methane and the major part of ethane and ethylene and the higher than ethane boiling compounds by means of the absorption liquid from the product mixture is hereinafter also referred to as "absorptive demethanization".

The absorption liquid used contains hydrocarbons having at least three or four carbon atoms, for example hydrocarbons having three and / or hydrocarbons having four and / or hydrocarbons having five and / or hydrocarbons having six carbon atoms. In particular, it may be butane. Methods for absorptive demethanization, which can also be used in the context of the present invention, are known in principle, for example from the EP 0 675 094 A2 , However, their use in the processing of product mixtures from the oxidative coupling of methane for the reasons mentioned above has not hitherto been considered.

Particularly in combination with the depletion of methane by the adsorptive process according to the invention, the use of an absorptive process of demethanization offers advantages. Absorptive demethanization would require more than ten times more wash liquid, such as butane, to process the product mixture to be demethanized without depletion of methane. Therefore, if a product mixture obtained by means of oxidative coupling of methane were treated directly with an absorptive demethanizer, then very large amounts of washing liquid would be required. By depletion by means of the adsorptive process in the context of the present invention, this amount can be significantly reduced, for example, three to four times the demethanizing product mixture.

Advantageously, in the demethanization in the context of the process according to the invention, a first fraction and a second fraction are formed, wherein the first fraction contains at least the majority of the methane and lower than methane boiling compounds from the demethanization subject separation and the second fraction at least the predominant Part of the ethane and ethylene and the higher than ethane boiling compounds from the demethanization subject separation insert. The composition of the fractions formed in this demethanization (the first and the second fraction) results from the fact that the separation insert contains the higher than ethane-boiling compounds. In other words, in the context of the present invention, it is a "demethanizer first" method. Although in a "deethanizer first" process the second fraction might contain most of the ethane and ethylene, but not the majority of the higher than ethane boiling compounds of the separation insert. These would have been previously separated.

In the context of the process according to the invention, an adapted absorptive demethanization is advantageously used, as also with reference to the attached 2 explained is. Here, by washing out by means of the absorption liquid, a liquid fraction is formed, which is the partially washed out methane, the predominantly washed out ethane, the predominantly washed out ethylene, the predominantly washed out, higher than ethane boiling compounds and at least the majority of the hydrocarbons with at least three or four Containing carbon atoms from the absorption liquid. The first fraction remains gaseous and can then be further processed.

The next step is now to recover the hydrocarbons having at least three or four carbon atoms of the absorption liquid, so that the absorption liquid can be regenerated in this way. Therefore, the hydrocarbons having at least three or four carbon atoms of the absorption liquid are first separated from the liquid fraction. The remainder of the remainder, which essentially still contains the above-mentioned washed-out compounds, is then advantageously in the context of the present invention in the second fraction (see above) and another fraction, the washed methane and another, lower part of the ethane and ethylene from the separation insert contains, separated. This separation is "out of focus" (one part of ethane and ethylene does not go exclusively to the second, but also to the other). However, this makes it possible to dispense with C2 refrigerant. However, the second fraction, that is, those containing at least the majority of ethane and ethylene, as well as higher than ethane boiling compounds from the separation feed, is free or nearly free of lower boiling compounds such as methane and hydrogen. It can therefore be transferred to a downstream separation step. The further fraction which contains the washed out methane and a further part of the ethane and the ethylene from the separation insert, however, can be recycled and added to the separation insert. It is again subjected to the absorption with the absorption liquid. In this way, heavier compounds contained here are not lost in the process.

Advantageously, the separation processing comprises a (combined) deethanization and ethane / ethylene separation which is subjected to at least part of the second fraction (see above) and in which the ethylene-rich product of the process as a whole, one rich in ethane and one to the higher than ethane boiling compounds rich fraction can be formed. The combined deethanization and ethane / ethylene separation may be advantageously carried out in a single separation apparatus as described with reference to U.S. Pat 2 shown, in particular a dividing wall column. This is possible because in a product mixture of a process for the oxidative coupling of methane comparatively small amounts of higher than ethane boiling compounds are included. The ethane-rich fraction obtained in the combined deethanization and ethane / ethylene separation can in particular be attributed to the process for the oxidative coupling of methane.

In the present invention, in particular, the absorptive demethanization may cause the first fraction in addition to the (not washed out) methane and lower than methane boiling compounds still a small portion of the higher than ethane boiling compounds from the separation and gas-phase transition compounds contains from the absorption liquid used. In this case, the separation processing advantageously comprises a further pressure swing adsorption, which is subjected to at least a portion of the first fraction, and in which the higher than ethane boiling compounds (from the separation insert and the absorption liquid) are at least predominantly separated. Here recovered compounds can each be fed to the process again at a suitable point.

Advantageously, it is provided that the gas mixture before performing the adsorptive method for partially removing methane of a first compression from a first to a second pressure level and after performing the adsorptive method for partially removing methane of a second compression of a third to a fourth Pressure level is subjected. The second compression is advantageously carried out before the further processing steps and in particular before the separation processing. By compressing from the first to the second pressure level, the pressure swing adsorption can be performed more effectively, or is required for the same degree of depletion of methane, a smaller-sized pressure swing adsorption.

The present invention solves the problem by the proposed measures, which results from the fact that in the oxidative coupling of methane remain relatively large amounts of methane in a corresponding product mixture, which can not be readily supplied to a separation part of a conventional plant conventionally. Due to the large quantities of methane, the dimensions of the compressors, columns and the like used for direct processing of a corresponding product mixture would have to be significantly expanded compared to known processes.

In the pressure swing adsorption, as mentioned, 60 to 90 mole percent, in particular 70 to 85 mole percent of the methane, but also at least a portion of the lower than methane boiling components are removed. These lower than methane boiling components include in particular carbon monoxide and hydrogen. This gas mixture can therefore be advantageously fed to a methanation in which carbon monoxide can be reacted with hydrogen to form methane. This additionally formed methane can be recycled with the separated methane to the process for the oxidative coupling of methane. In this way, the overall efficiency of the process can be improved. If the content of hydrogen over carbon monoxide is more than stoichiometric, the methanation can also carbon dioxide, which is separated in the further treatment steps from the product mixture, are supplied. The first compression is particularly advantageous in connection with such a methanation, because through them the mentioned, lower than methane boiling components directly, ie without further compression, can be supplied to the second pressure level of methanation.

In the context of the present invention, advantageously, the first pressure level is 4 to 10 bar, in particular 6 to 8 bar, and / or the second pressure level is 13 to 19 bar, in particular 15 to 17 bar, and / or the third pressure level is 1 up to 3 bar, in particular at 1.2 to 2 bar and / or the fourth pressure level at 20 to 40 bar, in particular at 25 to 35 bar. In the case of pressure swing adsorption, it is known to introduce a gas mixture at a defined pressure level, in this case the second pressure level, into one or more vessels which have a suitable adsorption material. In the context of the present invention, where the depletion of methane is the main purpose, molecular sieve is advantageously used as the adsorption material. At this predominantly heavier than methane boiling compounds adsorb. By contrast, the remaining compounds pass through the container or containers during the adsorption phase at the second pressure level. For desorption of the adsorbed components, a pressure reduction takes place in a pressure swing adsorption, here to the third pressure level.

In the process according to the invention, the product mixture may in particular contain carbon dioxide. The or the further treatment steps therefore include, in particular, an acid gas removal. Advantageously, the gas mixture is subjected in the course of the second compression of the sour gas removal. Sauergasentfernungsschritte, which serve in particular for the separation of carbon dioxide and optionally other compounds such as hydrogen sulfide, are known for example from the field of steam cracking process. An acid gas removal can therefore be carried out "in the course" of the second compression, because typically a corresponding gas mixture fed to a compressor, taken on an intermediate stage, then introduced into a gas scrubbing process and finally the compression on the intermediate stage is fed again. Within the scope of the present invention, sour gas removal therefore takes place within the scope of the present invention advantageously at an intermediate pressure level between the third and the fourth pressure level.

An acid gas removal, as can also be used in the context of the present invention, may in particular comprise an amine wash and a caustic wash. In such an amine scrubbing, a corresponding gas mixture is brought into contact with an amine-containing scrubbing solution (wash liquor), by means of which, in particular, carbon dioxide and other acid gases are scrubbed out of the gas mixture. An acid gas removal downstream of the second compression and thus also downstream of the pressure swing adsorption is particularly advantageous because in the context of depletion of methane, the volume of the gas mixture has been considerably reduced and therefore the required devices can be made smaller. As mentioned above, carbon dioxide separated off during acid gas removal can be used partially or completely in the case of methanation.

In the process according to the invention, as mentioned, the product mixture may in particular contain water. In this case, the or the further treatment steps include in particular a drying of the product mixture. Advantageously, in the context of the present invention, the product mixture after the second compression and in particular after the removal of acid gas is subjected to such drying.

In the process according to the invention, the compounds which boil higher than ethane in the product mixture may comprise acetylenes and / or diolefins. Therefore, it is of particular advantage if the or the further treatment steps include hydrogenation of the acetylenes and / or the diolefins to the corresponding (mono) olefins. Such hydrogenation is of particular advantage because corresponding compounds in downstream steps such as the described demethanization can no longer have any negative effects. For example, the diolefin butadiene tends to polymerize and contribute to the separation conditions used in downstream separation processing, particularly distillation columns operated at higher temperatures to so-called fouling. This is prevented by the hydrogenation.

The method according to the invention advantageously provides for water washing upstream of the pressure swing adsorption and upstream of the above-mentioned first compression. The provision of the product mixture therefore advantageously comprises such a water wash. Such water washing is used in particular for the removal of heavy hydrocarbons or oil-like components, as they can be formed as by-products of the oxidative coupling of methane. Corresponding water-washing processes are known in the field of steam-cracking processes. A water wash is also known in English as "scrubbing". A water wash upstream of the first compression and the pressure swing adsorption is particularly advantageous, because in this way corresponding components in the pressure swing adsorption can not interfere.

The present invention also relates to a plant adapted to carry out a process as previously explained. Such a plant has all the means to enable it to carry out such a process. The corresponding explanations and advantages are therefore expressly referred to.

The invention will be explained in more detail in preferred embodiments with reference to the accompanying drawings.

Short description of the drawing

1 illustrates a process according to an embodiment of the invention in the form of a schematic flowchart.

2 Figure 4 illustrates a demethanization according to an embodiment of the invention in the form of a schematic flow chart.

Detailed description of the drawing

In 1 a process according to a particularly preferred embodiment of the invention is illustrated in the form of a schematic flow chart and in total with 100 designated.

The process 100 includes a process for the oxidative coupling of methane, which is here in total with 1 is designated. As mentioned, a corresponding method can be carried out in a suitable reactor, which in particular can also be set up in addition to post-catalytic steam splitting ("post-bed cracking"). For details refer to relevant literature.

The process for the oxidative coupling of methane 1 an oxygen-rich stream a and a methane-rich stream b are supplied. The methane-rich stream b may be formed using an externally supplied methane stream c and one or more recirculated methane streams d. The externally provided methane stream c may in particular also contain certain amounts of other components besides methane, which are customary in natural gas or purified natural gas fractions, for example. The recirculation of a methane stream is explained below. For example, a recycle, high-ethane stream f may be fed into a post-catalytic steam cracking step.

Using the process for the oxidative coupling of methane 1 a gas mixture ("product mixture") is formed, which contains at least methane, ethane and ethylene, lower than methane and higher than ethane boiling compounds, especially water and carbon dioxide. This product mixture can be used as stream g of a water wash 2 be supplied. In the water wash 2 can wash out using the use of wash water heavy components from the product mixture of the current g and withdrawn in the form of a stream h. A water flow which also accumulates here is denoted by i.

The product mixture correspondingly freed of heavy components can be in the form of a stream k of a first compression 3 where it is compressed in the context of an embodiment of the present invention from a first pressure level to a second pressure level. The compressed product mixture, as illustrated here in the form of a stream 1, can subsequently undergo pressure swing adsorption 4 be supplied. In pressure swing adsorption 4 For example, the product mixture of stream I can be depleted in methane and in compounds which boil lower than methane. A gas mixture obtained in this case, which may contain, for example, carbon monoxide, hydrogen and inert gases, may be in the form of a stream y of a preparation of suitable type, in the example shown a methanation 13 to be subjected. If necessary, a corresponding gas mixture can be suitably conditioned, for example by removal or addition of components, so that it can be used for the return to the process for the oxidative coupling of methane 1 and / or methanation 13 suitable. In the example shown, the current y is combined with a current w explained below. The stream y and the stream w can be separated or treated together. Even only one of the streams y and w can undergo methanation 13 be supplied. In the methanation 13 or another and / or further treatment step, the mentioned methane-rich stream d can be obtained, which can be used in the process can be attributed to the oxidative coupling of methane.

In the methanation 13 Carbon monoxide can be converted in the streams y and w with hydrogen also contained to methane. This additionally formed methane can be supplied to the method for the oxidative coupling of methane in the form of the current d again with the originally separated by means of pressure swing adsorption methane. In this way, the overall efficiency of the process can be improved. If the content of hydrogen over carbon monoxide in the streams y and / or w is more than stoichiometric and therefore in the methanation 13 not completely consumed, can methanation 13 Also, carbon dioxide, which is separated from the product mixture in further treatment steps supplied (see below to stream x). The first compression 3 is associated with such methanation 13 particularly advantageous, because through them, the above, lower than methane boiling components directly, ie without further compression of the separated gas mixture of the stream y, the methanation 13 can be supplied. In this way, you save yourself an additional compression step or compressor.

A product mixture depleted of methane in this way can take the form of a stream m of a second compression 5 be subjected. In the course or after this second compression can be an acid gas removal 6 take place by adding a corresponding product mixture at an intermediate stage of compaction 5 withdrawn, a washing step in the sour gas removal 6 subjected, and then the second compression 5 is fed again on the intermediate stage. As mentioned, gas scrubbing processes known for acid gas removal, in particular amine scrubbing and alkaline scrubbing, can be used. Carbon dioxide formed in the sour gas removal can be withdrawn in the form of a stream n and, for example, in the form of the above-mentioned stream x, partly for methanation 13 be added, as explained above.

The compressed product mixture, which has been freed of acid gases, can be in the form of a stream of drying and precooling 7 be subjected to, in the water, for example adsorptive, can be separated from the product mixture of the current o. In this way, the product mixture can then be supplied in the form of a stream p in a substantially anhydrous state of a cold separation part, without that water can freeze.

A hydrogenation step 8th can be provided, in which in the product mixture of the stream p acetylenes and / or diolefins can be hydrogenated to the corresponding olefins. Downstream of the hydrogenation, the product mixture can be in the form of a stream q of a demethanization 9 are fed, in which a first (light) fraction and a second (heavy) fraction are formed. Demethanization 9 is carried out in an embodiment of the invention absorptive, ie hydrocarbons boiling higher than methane, are washed out using an absorption liquid, which is provided here in the form of a stream r, predominantly from the product mixture of the stream q. A portion of the methane contained in the product mixture of the stream q and possibly other, lower than methane boiling compounds are also partially washed out of the product mixture. The gaseous first (light) fraction remaining on washing therefore contains methane and lower than methane-boiling compounds, but also a residue of higher-boiling compounds (inter alia hydrocarbons having at least three carbon atoms). It is subtracted in the example shown in the form of a current e and treated as explained below.

Leaching in absorptive demethanization 9 is discussed in detail with reference to 2 explained. As shown there, the second (heavy) fraction contains absorptive demethanization 9 the hydrocarbons that boil higher than methane. Because a hydrogenation 8th These are paraffins and monoolefins, including ethane, ethylene and hydrocarbons having at least three carbon atoms. This second (heavy) fraction is in the form of the stream s of a combined deethanization and ethane / ethylene separation 10 fed, which also in 2 is illustrated in detail.

In the combined deethanization and ethane / ethylene separation 10 a fraction is formed which is rich in hydrocarbons with three and possibly more carbon atoms. This is carried out in the form of a stream t. Their treatment is not illustrated in detail and takes place in a known manner. In the combined deethanization and ethane / ethylene separation 10 Furthermore, an ethane fraction, which is attributed to the mentioned stream f for the oxidative coupling of methane, and an ethylene-rich product in the form of the current u formed.

The first (light) fraction from the (absorptive) demethanization 9 is in the form of the current e in the illustrated example of another pressure swing adsorption 11 fed. In the further pressure swing adsorption 11 in particular in the first (light) fraction still contained, higher methane boiling compounds are separated. These can be recycled in the form of the stream v in the process, for example, upstream of the second compression 5 , In the further Pressure Swing Adsorption 11 Unadsorbed compounds (methane and lower boiling compounds) can be combined in the form of stream w with stream y and treated as already explained above for stream y.

Due to the use of absorptive demethanization 9 is to cover the refrigeration needs of in 1 shown method 100 or a corresponding system only a C3 refrigerant circuit required. Such a C3 refrigerant circuit is greatly simplified as a block 12 shown.

In 2 is a demethanization 9 and a combined deethanation and ethane / ethylene separation 10 according to an embodiment of the invention in the form of a simplified process flow diagram illustrated. This can, for example, in 1 shown process 100 be used. To clarify the involvement in such a process 100 be on the synonymous in 1 shown currents e, f and q to w referenced. In contrast to conventional demethanization processes, according to the in 2 illustrated embodiment by using an absorption liquid in the form of a current G, as explained, a waiver of very low temperatures, as they can be provided only by means of C2 refrigerants possible. In 2 is also the further pressure swing adsorption 11 shown also in 1 is shown.

In the in 2 demethanization shown 9 is the gas mixture of the stream q, in particular by the second compression 5 , is present at a pressure level of, for example, about 25 to 30 bar, in a heat exchanger 101 cooled and then in the lower part of an absorption column 102 transferred. The heat exchanger 101 For example, it can be operated with a refrigerant at approx. -38 ° C, cooling the flow q down to approx. -35 ° C. In the lower part of the absorption column 102 Furthermore, a stream A is fed, the provision and composition of which is explained below.

At the top of the upper part of the two-part absorption column 102 the absorption liquid is given up in the form of a stream G via a valve which is not separately marked. Hydrocarbons, which boil higher than methane, are predominantly washed out by this absorption liquid. However, there remains a non-washed out remainder. Further, a portion of the methane and lower than methane boiling compounds from the injected fluid of the streams q and A is washed out. On a shelf 103 the absorption column 102 Therefore falls to a liquid fraction, in addition to the hydrocarbons of the absorption liquid of the current G and the majority of higher than methane boiling hydrocarbons from the streams q and A, but also a portion of the washed methane and lower than methane boiling compounds from the streams q and A can contain.

Due to the heat of solution in the absorption of the leached compounds, the liquid fraction described is at a significantly higher temperature than the currents fed into the absorption column, for example at about -10 to -5 ° C. Therefore, it is advantageous to cool the liquid fraction to minimize the circulating amount of the absorbing liquid. For this purpose, the liquid fraction can be withdrawn in the form of a stream B and in a heat exchanger 104 be cooled, for example by means of low-pressure C3 refrigerant. Subsequently, the stream B is in the lower part of the absorption column 102 fed.

At the top of the upper part of the absorption column 102 For example, a "first" fraction containing predominantly methane and lower than methane-boiling compounds can be taken off in the form of the stream e, which is already present in 1 is shown. This can in the further pressure swing adsorption 11 be edited as previously explained.

From the lower part of the absorption column 102 For example, a liquid fraction can be withdrawn in the form of a stream E which, in addition to the hydrocarbons of the absorption liquid of stream G, also contains the hydrocarbons heavier than methane from streams q and A and the methane leached from streams q and A. The current E is in a pump 107 pressure increased, through a heat exchanger 108 passed, and an unspecified valve in a distillation column 109 fed. In the distillation column 109 For example, the hydrocarbons of stream G, ie the absorption liquid, which are for example hydrocarbons with four carbon atoms (butane), can be recovered here.

The distillation column 109 has for this purpose a bottom evaporator, which can be operated with medium pressure steam. From the top of the distillation column 109 withdrawn gas can in a heat exchanger 111 be cooled with low pressure C3 refrigerant. In a condensate container 112 separated liquid can by means of a pump 113 via a not separately marked valve on the distillation column 109 be transported back. By contrast, a portion which remains in gaseous form can flow in the form of a stream F via a valve, not separately identified, into a further distillation column 116 be guided. The stream F contains essentially the hydrocarbons, which are heavier than methane, from the streams q and A and the washed methane from the streams q and A, as already contained in the stream E.

In the stream F, however, little or no hydrocarbons of the absorption liquid of the stream G are more contained. The latter hydrocarbons are withdrawn from the bottom of the distillation column and then in a water cooler 114 and the heat exchanger 108 cooled. After combining with fresh absorption liquid from the stream r and further cooling in another, cooled with medium-pressure C3 refrigerant heat exchanger 115 is the absorption liquid in regenerated form again to the task on the absorption column 102 to disposal.

In the further distillation column 116 For example, the fluid of stream F may be "out of focus", but at the pressure level of the absorption column 102 and only using C3 refrigeration, into a gaseous overhead fraction and a liquid bottoms fraction. The separation here is fuzzy because essentially all of the methane and the compounds boiling lower than methane, but also part of the hydrocarbons having two carbon atoms of the stream F are converted into the top fraction. The top fraction is returned to the absorption column in the form of the stream A mentioned 102 fed. The hydrocarbons with two carbon atoms are therefore not lost here.

The bottom fraction of the further distillation column 116 subtracted in the form of a stream s (see also 1 ), however, contains predominantly or exclusively ethane and ethylene and the still contained hydrocarbons having three carbon atoms. The current s will, as already in 1 shown in the deethanization 10 with integrated ethane / ethylene separation, here using a dividing wall column 119 is carried out. The further distillation column 116 is heated in the example shown with high-pressure C3 refrigerant in the sump. For this purpose, a heat exchanger 117 provided. At the top is the further distillation column 116 cooled with low-pressure C3 refrigerant. The stream s can by means of a heat exchanger 115 be warmed up, before he enters the dividing wall column 119 is fed.

The dividing wall column 119 has in the part shown on the left a first bottom evaporator 120 on, which is operated with process water. In the part shown here on the right is a sump evaporator 121 which can be operated with high-pressure C3 refrigerant. A heat exchanger 122 at the top can be operated with low pressure C3 refrigerant. In an upper part is the dividing wall column 119 formed in one piece; Here, a liquid fraction separates on an intermediate bottom, which can be returned to the lower part or its halves via valves which are not separately marked.

At the top of the upper part of the dividing wall column 119 For example, a fraction containing predominantly or exclusively ethylene may be withdrawn. This can in the mentioned heat exchanger 122 be totally condensed, leaving in a return tank 123 a liquid, ethylene-rich fraction separates. This can be done via a pump 124 via a not separately marked valve partly on the upper part of the dividing wall column 119 attributed and partly as the already mentioned current u (see 2 ) as an ethylene-rich product. From the bottoms of the two parts of the dividing wall column, the stream t of hydrocarbons having three carbon atoms and the stream rich of ethane f can be withdrawn. The currents f and u can be in the already mentioned heat exchanger 115 be cooled.

The pressure in the absorption column 102 is for example about 25 to 30 bar and the pressure in the distillation column 109 for example, about 28 to 30 bar, the pressure in the further distillation column 116 is at or slightly above the pressure in the absorption column 102 , Therefore, for the transfer of the stream A from the further distillation column 116 in the absorption column 102 no pressure increase necessary.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0675094 A2 [0028, 0034]
• US 2815650 A [0028]
• US Pat. No. 5,710,357 A [0028]
• WO 2014/064172 A2 [0028]
• US 2933901 A1 [0028]

Cited non-patent literature

• JD Idol et al., "Natural Gas", in: JA Kent (ed.), "Handbook of Industrial Chemistry and Biotechnology," Volume 2, 12th Edition, Springer, New York 2012 [0002]
• Article "Ethylene" in Ullmann's Encyclopedia of Industrial Chemistry, Online Edition, April 15, 2007, DOI 10.1002 / 14356007.a10_045.pub2 [0008]
• K. Sattler, "Thermal Separation Methods: Fundamentals, Design, Apparatus" 3rd Edition, Wiley-VCH, Weinheim 2001 [0021]

Claims (14)

Process ( 100 for the recovery of ethylene from methane using a process for the oxidative coupling of methane ( 1 ) a product mixture is provided which comprises at least ethylene, ethane and methane and lower than methane and higher than ethane boiling compounds, characterized in that from the product mixture first by means of an adsorptive process ( 4 ) 60 to 90 mole percent of the methane and at least a portion of the lower than methane boiling components are removed and the product mixture is then subjected to one or more further treatment steps and then subjected to separation to obtain an ethylene-rich product, wherein the separation processing is a demethanization ( 9 ), which is subjected to at least a portion of the product mixture as a separation insert, and in the first part of the methane and the majority of ethane and ethylene and the higher ethane boiling compounds are washed out by means of an absorption liquid from the separation insert. Process ( 100 ) according to claim 1, wherein the absorption liquid contains hydrocarbons having at least three or four carbon atoms. Process ( 100 ) according to claim 1 or 2, wherein the adsorptive process ( 4 ) comprises a pressure and / or a temperature swing adsorption. Process ( 100 ) according to any one of the preceding claims, wherein in demethanization ( 9 a first fraction and a second fraction are formed, wherein the first fraction at least the majority of the methane and lower than methane boiling compounds and the second fraction at least the majority of the ethane and ethylene and the higher than ethane boiling compounds from the Separation insert contains. Process ( 100 ), according to claim 4, wherein the leaching by means of the absorption liquid, the first fraction remains gaseous and a liquid fraction is obtained, the washed out methane, the washed out ethane, the washed out ethylene, the leached, higher than ethane boiling compounds and at least the predominant Part of hydrocarbons containing at least three or four carbon atoms from the absorption liquid. Process ( 100 ) according to claim 5, wherein first of all the hydrocarbons having at least three or four carbon atoms of the absorption liquid are separated from the liquid fraction and the remainder is subsequently separated into the second fraction and another fraction comprising the leached methane and a further part of the ethane and the Separated ethylene is added, wherein the further fraction is added to the separation insert and again subjected to absorption. Process ( 100 ) one of claims 4 to 6, wherein the separation processing a deethanization and ethane / ethylene separation ( 10 ), which is subjected to at least a portion of the second fraction, and in which the ethylene-rich product, a rich in ethane and a higher than ethane boiling compounds fraction are formed. Process ( 100 ) according to one of claims 4 to 7, wherein the first fraction contains a portion of the higher than ethane boiling compounds from the separation insert, wherein the separation processing a further pressure swing adsorption ( 11 ), which is subjected to at least a portion of the first fraction, and in which the higher than ethane boiling compounds are separated. Process ( 100 ) according to one of the preceding claims, wherein 70 to 85 mole percent of the methane are removed by means of the adsorptive process, whereby the product mixture is depleted in particular to a methane content of 45 to 60 mole percent. Process ( 100 ) according to any one of the preceding claims, wherein the product mixture before the adsorptive process ( 4 ) of a first compression ( 3 ) from a first to a second and after the adsorptive process ( 4 ) and before or after the further processing steps of a second compression ( 5 ) is subjected from a third to a fourth pressure level. Process ( 100 ) according to claim 10, wherein the first pressure level at 4 to 10 bar, the second pressure level at 13 to 19 bar, the third pressure level at 1 to 2 bar and / or the fourth pressure level at 20 to 40 bar. Process ( 100 ) according to one of the preceding claims, in which the product mixture contains carbon dioxide, the further preparation step or steps comprising an acid gas removal ( 6 ). Process ( 100 ) according to any one of the preceding claims, in which the product mixture contains water, wherein the or the further treatment steps a drying ( 7 ) of the product mixture. Process ( 100 ) according to any one of the preceding claims, wherein the higher than ethane boiling compounds acetylenes and / or diolefins in which the further treatment step (s) comprises hydrogenation ( 8th ) of the acetylenes and / or the diolefins to the corresponding olefins.

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