EP2867339B1 - Method for producing olefins through thermal water splitting - Google Patents

Description

The present invention relates to a process for the conversion of hydrocarbon feedstocks by thermal vapor cracking to at least one olefin-containing product stream which contains at least ethylene and propylene, wherein a hydrocarbon feed is at least partially reacted in at least one cracking furnace.

Thermal steam cracking (also known as steam cracking or steam cracking) is a long-established petrochemical process. The classical target compound in thermal vapor cracking is ethylene (also: ethene), which is an important starting material for a number of chemical syntheses.

As an insert for the thermal vapor cracking both gases such as ethane, propane or butane and corresponding mixtures as well as liquid hydrocarbons, such as naphtha, and hydrocarbon mixtures can be used.

For details of the devices and reaction conditions used in thermal steam cracking and the reactions that occur, as well as details of the refining technology, refer to corresponding articles in reference works such as Zimmermann, H. and Walzl, R .: Ethylene. In: Ullmann's Encyclopedia of Industrial Chemistry. 6th edition Weinheim: Wiley-VCH, 2005 , and Irion, WW and Neuwirth, OS: Oil Refining. In: Ullmann's Encyclopedia of Industrial Chemistry. 6th edition Weinheim: Wiley-VCH 2005 , referenced. Processes for the preparation of olefins are, for example, also in US 3 714 282 A and the US Pat. No. 6,743,961 B1 disclosed.

Furthermore, here is the US 2008/0194900 which discloses a process for steam cracking an aromatics-containing naphtha feed, wherein the aromatics are removed from the pretreated naphtha feed prior to thermal steam cracking in the aromatics extraction of the steam cracker and the raffinate recovered in the aromatics extraction is fed into the kiln with hydrocarbons of six to eight carbons.

For thermal vapor cracking cracking furnaces are used. The cracking furnaces, together with Quechenheit and downstream facilities for the workup of the product mixtures formed, integrated into corresponding larger plants for olefin production, which are referred to in the context of this application as "steam cracker".

An important parameter in thermal steam cracking is the so-called cracking severity (cracking severity), which determines the cracking conditions. The cracking conditions are particularly influenced by the temperature and the residence time and the partial pressures of hydrocarbons and water vapor. The composition of the hydrocarbon mixtures used as a feed and the type of cracking furnaces used also influence the cracking conditions. Due to the mutual influences of these factors, the fission condition is usually determined by the ratio of propylene (also referred to as propene) to ethylene in the fission gas.

In thermal steam cracking, depending on the feed mixture and cracking conditions, in addition to the classical target compound ethylene, considerable amounts of by-products can sometimes be separated off from a corresponding product stream. These are, inter alia, lower alkenes such as:. Propylene and butenes, as well as dienes such as butadienes, and aromatics such as e.g. Benzene, toluene and xylenes. These have a comparatively high economic value, so that their formation as so-called value-added products (English High Value Products) is desired.

From the US 2008/194900 A1 For example, a naphtha vapor cracking process is known in which recirculated propane stream or recycle C5 stream is recleavable from the product preparation of the steam cracking under normal to severe fission conditions.

The US Pat. No. 6,743,961 B2 discloses a process for producing olefins in which crude oil is partially vaporized in a combined evaporation and splitting unit. The formed vapor and the remaining liquid are split at different cleavage conditions.

In the US 2004/209964 A1 a method is proposed in which a Fischer-Tropsch product stream is fractionated. Hydrocarbons of different chain lengths are split at different cracking conditions.

The object of the present invention is to improve the possibilities for obtaining olefin-containing product mixtures from hydrocarbons by thermal steam cracking.

Disclosure of the invention

Against this background, the invention proposes a process for the conversion of hydrocarbon feedstocks by thermal vapor cracking to at least one olefin-containing product stream which comprises at least ethylene and propylene, wherein a hydrocarbon feedstock is at least partially reacted in at least one cracking furnace, having the features of the independent patent claims. Preferred embodiments are the subject of the subclaims and the following description.

Advantages of the invention

According to the invention, a process is proposed in which the hydrocarbon feed in the cracking furnace is reacted under mild cracking conditions, mild cracking conditions meaning that propylene to ethylene is present at the cracking furnace exit in a ratio of 0.85 to 1.6 kg / kg, and the hydrocarbon feed predominantly Hydrocarbons having a maximum carbon number of 5 contains.

For the purposes of this invention, cracking furnace is understood to mean a splitting unit in which the cracking conditions are defined. It is possible that there is a subdivision into two or more cracking furnaces in a total furnace. One then often speaks of furnace cells. Several furnace cells belonging to a total furnace generally have independent radiation zones and a common convection zone as well as a common smoke outlet. In these cases, each furnace cell can be operated with its own gap conditions. Each furnace cell is thus one Column unit and is therefore referred to here as cracking furnace. The total furnace then has a plurality of column units or, in other words, it has a plurality of cracking furnaces. If there is only one furnace cell, this is the splitting unit and thus the cracking furnace. Cracking furnaces can be combined into groups, which are supplied, for example, with the same use. The fission conditions within a furnace group will usually be set the same or similar.

In the thermal cracking of hydrocarbons of conventional composition, such as naphtha, under mild cleavage conditions produces a very large amount of pyrolysis gasoline, which is very difficult to handle due to the large amount. This is a result of the comparatively lower implementation of the use in the cracking furnace under mild cracking conditions. However, mild cleavage conditions are desirable because a cleavage under mild conditions has a larger ratio of propylene to ethylene than cleavage under normal cleavage conditions as commonly used.

With the method according to the invention, it becomes possible to operate a cracking furnace under mild cracking conditions, since the use and the cracking conditions are adapted to one another. Only by adjusting the use and fissure conditions is it possible to circumvent the disadvantages described above. These disadvantages and the solution shown were recognized within the scope of the invention.

The inventive method thus makes it possible to operate a plant for steam cracking in such a way that more propylene is produced in relation to the fresh feed than in a conventional plant in which the process according to the invention is not used.

The higher the ratio of propylene to ethylene for the cracking conditions in the second cracking furnace, the more propylene is produced in relation to the fresh feed. This is within the scope of the invention advantageous. However, a higher ratio of propylene to ethylene is accompanied by a lower conversion of the use, so that for the values upwards technical and economic limits occur. Within the limits specified in the claims, it is ensured that on the one hand adjust the inventive advantages and on the other hand, the steam cracker is technically manageable and economically operable.

For the specified limit values for the cracking conditions in the cracking furnace which converts under mild cracking conditions, it is true that within these crackers a technically and economically advantageous vapor cracking is possible in which ethylene and propylene are produced as primary products of value.

The term "predominate" is used in this application to make it clear that the feed or fraction does not consist exclusively of hydrocarbons of the specified carbon number, but hydrocarbons of the specified carbon number, hydrocarbons with other carbon numbers and other impurities may also be present can. In the separation and work-up of the product stream, an output stream and / or the fractions and / or fresh-use fractionation always remains of the component (s) in the product stream or in the fraction. Other impurities remain, so that a processed product or fraction stream always contains residues. Since the effort for separation and work-up increases extremely sharply with the purity to be achieved, it depends on economic factors, which proportion of residues may be contained in a stream. How high this proportion is, must be weighed from economic point of view. As a rough guideline for the proportion of unwanted hydrocarbons and other impurities, it will generally be the case that they may be present in the product stream and / or in the fraction with a maximum of 40 percent by weight. Usually even a maximum value of 20% by weight or less is achieved. Ideally, a maximum value of 10% by weight is achieved. The just said applies to all process plants, not only in steam crackers but also in oil refineries. Consequently, for the hydrocarbon feed which is conducted into the cracking furnace which converts under mildly cracking conditions, it is at least 60% by weight, preferably at least 80% by weight and more preferably at least 90% by weight and more preferably at least 95% by weight and most preferably at least 98% by weight hydrocarbons Carbon number of at most 6, preferably of at most 5 contains. Also, for the recycled fractions and fractions recovered from the fresh feed fractionation (see below), these are the desired hydrocarbons of at least 60 weight percent, preferably at least 80 weight percent, and more preferably at least 90 weight percent and more preferably at least 95 weight percent, and most preferably at least 98 weight percent.

In a particularly advantageous embodiment of the invention, one or more fractions, which are obtained from the product stream and which predominantly contains hydrocarbons having a maximum carbon number of 5, are fed as a hydrocarbon feed to the cracking furnace which converts under mild cracking conditions. By returning such fractions, the amount of suitable feed to the second cracking furnace increases, or such fraction constitutes a suitable hydrocarbon feed to the cracking furnace which converts under mild cracking conditions. Also, a fraction having hydrocarbons having a carbon number of 4 and a fraction having a carbon number of 5 obtained in the work-up of the product stream in steam crackers, which can be recycled after the separation of the desired products directly or after further treatment steps.

In an advantageous embodiment of the invention, the recycled fractions are largely free of diolefins when they are fed to the cracking furnace which converts under mild cracking conditions as a hydrocarbon feed. Diolefins have an adverse effect in the cracking furnace. For this purpose, the diolefins are predominantly removed from the fractions which are recycled to the second cracking furnace by preceding conversion processes or separation steps. The removal can take place either before or after the separation of the fractions which are recycled.

The procedures that are necessary for separation and workup are known in the art. These are conventional measures in steam crackers for separating and working up product and fraction streams.

With particular advantages, saturated hydrocarbons are used as the hydrocarbon feed to the cracking furnace which converts under mild cracking conditions. Saturated hydrocarbons are particularly suitable for thermal vapor columns.

Advantageously, the hydrocarbon feed in the cracking furnace is reacted under mild cleavage conditions which result in a ratio of propylene to ethylene of up to 1.2 kg / kg at the cracking furnace exit.

In an advantageous embodiment of the invention, a hydrocarbon feed is reacted under normal cracking conditions in a further cracking furnace, wherein normal cracking conditions mean that at the cracking furnace exit propylene to ethylene in a ratio of 0.25 to 0.85 kg / kg, preferably from 0.3 to 0 , 75 kg / kg, more preferably from 0.4 to 0.65 kg / kg, wherein the ratio of propylene to ethylene for the cracking furnace operating under mild cracking conditions always has a value greater than the value for the ratio of propylene to ethylene for the cracking furnace which converts under normal conditions. In particular, the values for the ratio of propylene to ethylene are at least 0.1 kg / kg, preferably at least 0.15 kg / kg, more preferably at least 0.2 kg / kg apart, so that the advantages of the invention in particular Adjust dimensions.

With special advantages, the steam cracker therefore has at least one cracking furnace which converts under normal cracking conditions. These are used as the insert those hydrocarbons out, which are disadvantageous for the cracking furnace which converts under mild cleavage conditions. Owing to the presence of at least one cracking furnace which converts under normal cracking conditions, the operation of the cracking furnace which converts under mild cracking conditions becomes economically advantageous if a mixture of hydrocarbons which does not satisfy the condition stated in claim 1 is present as a fresh feed.

Thus, with particular advantage, a hydrocarbon feedstock is used for the cracking furnace which converts under normal cracking conditions and deviates in its composition from the hydrocarbon feedstock used for the cracking furnace which converts under mild cracking conditions.

Since the cracking furnace, which converts under normal conditions, is very well suited for the conversion of long-chain hydrocarbons, the cracking furnace which converts under normal cracking conditions is at least one fraction separated and recycled from the product stream, which predominantly contains hydrocarbons a carbon number of at least 6 has supplied. Since certain hydrocarbons accumulate in recirculated fractions through the circulation, hydrocarbons having a carbon number of 6 under normal cracking conditions are recommended for recycled fractions. However, it is also possible to recycle these into the cracking furnace which converts under mildly cleavage conditions.

In a particularly advantageous embodiment of the invention, a fresh use is used, which is fractionated into at least a first and a second fresh-use fraction and the first fresh-use fraction at least partially, advantageously completely, in the under normal gap conditions implementing cracking furnace and the second fresh-use fraction at least partially, advantageously completely, is conducted into the cracking furnace which converts under mild cleavage conditions. Fractionation of the fresh feed makes it possible to provide, in particular for the cracking furnace which converts under mild cracking conditions, an insert with which the advantages according to the invention are set in an outstanding manner.

At this point, it should be emphasized once again that the above-mentioned operations recirculated fractions, fresh-use fraction and fresh inserts of hydrocarbons having a carbon number of at most 6, preferably of at most 5, are particularly suitable as an insert for the cracking furnace which converts under mild cleavage conditions. In order to achieve the advantages of the invention, the inserts proposed here can be carried out individually or as a mixture in the cracking furnace which converts under mild cleavage conditions. As hydrocarbon feed, one or more recirculated fractions or a fresh feed fraction or another feed of hydrocarbons having a carbon number of not more than 6, preferably of not more than 5, can thus be used. Also recycle fraction (s) and a fresh feed fraction or recycle fraction (s) and another feed may be hydrocarbons having a maximum carbon number of 6 or a fresh feed fraction and another use of hydrocarbons having a maximum carbon number of 6 or a mixture from all possible uses as a hydrocarbon feed to the cracking furnace operating under mild cracking conditions.

As explained in the beginning, the ratio of propylene to ethylene in thermal vapor cracking results from a number of different influencing factors in which the cracking furnace exit temperature, i. the temperature of a product stream as it leaves the reactor coil (coil output temperature) plays an important role. The cracking furnace exit temperature for the reaction in the cracking furnace operating at mild cracking conditions is advantageously between 680 ° C and 820 ° C, preferably between 700 ° C and 800 ° C and more preferably between 710 ° C and 780 ° C and more preferably between 720 ° C and 760 ° C. The cracking furnace exit temperature for the reaction in the cracking furnace which converts under normal cracking conditions is advantageously between 800 ° C and 1000 ° C, preferably between 820 ° C and 950 ° C and more preferably between 840 ° C and 900 ° C. The cracking furnace exit temperature of the cracking furnace which converts under normal cracking conditions is at least 10 ° C., preferably at least 20 ° C., above that of the cracking furnace which converts under mild cracking conditions.

In the cracking furnace which converts under mild cracking conditions, it is also possible to use a lower vapor dilution than in the cracking furnace which converts under normal cracking conditions. This reduces the amount of dilution steam required and saves energy. However, a lower vapor dilution in the second cracking furnace is not necessary to show the significant advantage of the invention. Advantageously, 0.3 to 1.5 kg of steam per kg of hydrocarbon feed and 0.15 to 0.8 kg of steam per kg of hydrocarbon feed are used in the cracking furnace operating under mild cracking conditions in the cracking furnace which converts under normal cracking conditions.

It is also advantageously possible to convert, in particular saturated hydrocarbons having a carbon number of 2 to 3, present in the product stream, advantageously by means of thermal vapor columns in a cracking furnace for gaseous use. For this purpose, the saturated gaseous hydrocarbons are recovered from the product stream and recycled to the cracking furnace for gaseous use and implemented there.

Advantageously, as a fresh use in the cracking furnace which converts under mild cracking conditions, there are formed outgas condensates or / and one or more partial cuts an oil refinery and / or synthetic and / or biogenic hydrocarbons and / or mixtures derived therefrom.

As fresh use for the cracking furnace which converts under normal cracking conditions and / or as fresh feed for fresh fractionation, both gases or gas fractions such as ethane, propane or butane and corresponding mixtures and condensates as well as liquid hydrocarbons and hydrocarbon mixtures can be used. The gas mixtures and condensates mentioned include in particular so-called natural gas condensates (English: Natural Gas Liquids, NGL). The liquid hydrocarbons and hydrocarbon mixtures can originate, for example, from the so-called gasoline fraction of crude oil. Such crude naphthas (NT) and kerosene are mixtures of preferably saturated compounds with boiling points between 35 and 210 ° C. However, the invention is also advantageous in the use of middle distillates, atmospheric residues and / or mixtures thereof derived from crude oil processing. Middle distillates are so-called light and heavy gas oils, which can be used as starting materials for the production of light heating and diesel oils as well as heavy fuel oil. The compounds contained have boiling points of 180 to 360 ° C. Preferably, these are predominantly saturated compounds which can be reacted during thermal vapor cracking. Furthermore, fractions obtained by known distillative separation processes and corresponding residues, but also the use thereof respectively, for example by hydrogenation (hydrotreating) or hydrocracking, derived fractions can be used. Examples are light, heavy and vacuum gas oil (English: Atmospheric Gas Oil, AGO, or Vacuum Gas Oil, VGO) as well as mixtures and / or residues (hydrotreated vacuum gas oil, HVGO, Hydrocracker Residue, HCR or Unconverted Oil, UCO).
In particular, natural gas condensates and / or crude oil fractions and / or mixtures derived therefrom are used as fresh feed.

Advantageously, the invention thus encompasses the use of hydrocarbon mixtures having a boiling range of up to 600 ° C as a hydrocarbon feed as fresh feed for the hydrocarbon feed to be used under normal cracking conditions. Within this total area can It is also possible to use hydrocarbon mixtures with different boiling ranges, for example with boiling ranges of up to 360 ° C. or up to 240 ° C. The reaction conditions in the cracking furnace are matched to the hydrocarbon mixtures used in each case.

However, the invention can be used to advantage with any other fresh inserts, which have comparable properties, such as biogenic and / or synthetic hydrocarbons.

Short description of the drawing

The inventive method in a particularly advantageous embodiment will be explained in more detail with reference to the process diagrams, which show the essential process steps schematically. For a better understanding, first by means of FIG. 1 set forth the known method.

FIG. 1 shows a schematic representation of a known procedure for olefin production. FIG. 2 shows a schematic representation of the essential steps of the method according to the invention in a particularly advantageous embodiment and FIG. 3, 4 and 5 show, also schematically, the essential steps of a particularly advantageous embodiment of the invention. In the figures, corresponding elements carry identical reference numerals.

The schematic process diagram 100 of FIG. 1 for the known method includes a cracking furnace 1, in which the fresh use A (for example, naphtha) and the recycled fractions S and P are performed as a hydrocarbon feed. In the cracking furnace 1, the hydrocarbon feed is heated and converted into convection and radiation zone. In the cracking furnace water vapor is added, usually 0.5 to 1 kg of process steam per kg of hydrocarbon. From the cracking furnace 1, a product stream C exits, which is also referred to as a fission product stream directly at the outlet from the cracking furnace. When leaving the cracking furnace, this cracking product stream has a temperature which is normally between 840 ° C and 900 ° C. The ratio of propylene to ethylene is usually 0.35 to 0.6 kg / kg. After a first quench (not shown), the product stream is processed in a processing unit 4. From the Working-up unit are obtained as essential product fractions E to N the following fractions: hydrogen E, spent liquor F, methane G, ethylene H, propylene I, gaseous hydrocarbons L having a carbon number of 4, pyrolysis gasoline M and pyrolysis N. The gaseous hydrocarbons L having a hydrocarbon number of 4 are further treated in a C4 workup unit 5, which is used for the processing of hydrocarbons having a carbon number of 4. Such a C4-processing unit 5 further treats the fraction having a carbon number of 4 such that butadiene O can be discharged. The remaining hydrocarbons having a carbon number of 4 represent a fraction P, which is recycled to the cracking furnace 1. The pyrolysis gasoline M, which comprises hydrocarbons having a carbon number of 5 or more, is further processed in a pyrolysis gasoline upgrading unit 6, and aromatics Q and hydrocarbons R having a carbon number of, for example, more than 9 are discharged. The remaining hydrocarbons having a carbon number of 5 or more are recycled as fraction S into the cracking furnace 1. The workup unit 4 and the C4 workup unit 5 and the pyrolysis gasoline workup unit 6 comprise conventional units for further processing of the product stream or product fractions, which serve to carry out various process steps, such as compression, condensation and cooling, drying, distillation and fractionation, extraction and hydrogenation , The process steps are customary in olefin plants and known to the person skilled in the art.

The schematic process diagram 10 of FIG. 2 now shows the inventive method in its essential steps. In the cracking furnace 2, which converts under mild conditions, a fresh feed BL is fed. From the cracking furnace 2 enters the product stream X, which has a temperature which is advantageously between 700 ° C and 800 ° C. The ratio of propylene to ethylene is advantageously between 0.7 to 1.5 kg / kg. The product stream X is further processed in the processing unit 4. The processes for further treatment and work-up in the processing unit 4 are known and have just been described. Thus, the workup unit 4 also leads, as just described, to the product fractions E to N. The product fractions L and M are further treated, as just described, in the special workup units 5 and 6. Unlike the in FIG. 1 described method is now advantageously the fraction P, which contains hydrocarbons having a carbon number of 4, in the Cracking furnace 2 recycled. In the pyrolysis gasoline working-up unit 6, in addition to the above-mentioned fractions Q and R, the fraction T is recovered. The fraction T, which contains hydrocarbons having a carbon number of 5, is advantageously recirculated to the cracking furnace 2, which reacts under mild cracking conditions.

The schematic process diagram 10 of FIG. 3 now shows the inventive method in a particularly advantageous embodiment and its essential process steps. In addition to the cracking furnace 1, which reacts under normal conditions, there is a cracking furnace 2 which converts under mild cracking conditions, and advantageously a fresh fractionation unit 7. Fresh batch B (for example, naphtha) is now fractionated in the fresh-use fractionation unit 7 and the first fresh-use fraction B1 is fed into the cracking furnace 1, while the second fresh-use fraction B2 is fed into the cracking furnace 2. The fresh fraction fractionation processes use the usual methods of separating and treating hydrocarbon streams known from refinery olefin plants. This knows the expert and he knows how to use it. In the cracking furnace 1 in addition a fraction U and in the cracking furnace 2 in addition the fractions T and P are recycled (for more details see below). Furthermore, the slit furnace 2, which converts under mild cracking conditions, is supplied with a further feedstock BL comprising hydrocarbons having a maximum carbon number of 6, preferably a maximum of 5, as fresh feed. From the cracking furnace 1, in turn, the cleavage product stream C exits with the above-mentioned properties. From the cracking furnace 2, the cleavage product stream X exits. The cleavage product stream X has a temperature which is advantageously between 700 ° C and 800 ° C. The ratio of propylene to ethylene is between 0.85-1.6 kg / kg. The product streams C and X are further processed in the workup unit 4 and combined at a suitable point to a common product stream. The processes for further treatment and work-up in the processing unit 4 are known and have just been described. Thus, the workup unit 4 also leads, as just described, to the product fractions E to N. The product fractions L and M are further treated, as just described, in the special workup units 5 and 6. Unlike the in FIG. 1 described method is now advantageously also the fraction P, which contains hydrocarbons having a carbon number of 4, not recycled into the cracking furnace 1 but in the cracking furnace 2. In the pyrolysis gasoline workup unit 6, fractions T and U are recovered in addition to the above-mentioned fractions Q and R. The fraction T, which contains hydrocarbons having a carbon number of 5, is advantageously returned to the cracking furnace 2, while the fraction U, which contains hydrocarbons having a carbon number of 6 and more, in particular between 6 and 9, advantageously recycled to the cracking furnace 1 becomes. In FIG. 3 Various operations are performed for the cracking furnace. These then form the second hydrocarbon feed. It should be noted that the list of different missions is not exhaustive and in particular that the in FIG. 3 shown inserts for the second cracking furnace B2, BL, T and P does not always have to be performed all in the cracking furnace 2, but that it is sufficient in many cases, to lead a portion of the possible uses in the implementing in mild gap conditions cracking furnace 2, for example a recirculated fraction T of hydrocarbons having a carbon number of 5 and a fresh feed BL of hydrocarbons having a carbon number of at most 6, preferably a maximum of 5 or for example recirculated fractions T and P with hydrocarbons having carbon numbers of 5 and 4 and LPG BL. Briefly, the following operations are possible in the second cracking furnace: B2, BL, T, P, B2 + BL, B2 + T, B2 + P, BL + T, BL + P, T + P, B2 + BL + T, B2 + BL + P, B2 + P + T, BL + P + T or B2 + BL + P + T.

Also, a particularly advantageous embodiment of the invention includes Figure 4. Figure 4 has the same schematic process diagram as it does FIG. 3 shows. This is supplemented by a cracking furnace 3 for gaseous use, in which a fraction V is performed as an insert. The fraction V contains saturated gaseous hydrocarbons having a carbon number of 2 or 3, which are also obtained in the workup unit 4.

Also in FIG. 5 an advantageous embodiment of the invention is shown. FIG. 5 includes the same schematic process diagram on how FIG. 3 but here the fresh-use fractionation is missing. Fresh use is here as Frischseinsatz B the first cracking furnace 1 added and the second cracking furnace 2, a fresh use BL of hydrocarbons having a carbon number of at most 6, preferably a maximum of 5 added. The further process steps were already in the description of the figures FIG. 2 and 3 explained.

LIST OF REFERENCE NUMBERS

1

Cracking furnace (normal cracking conditions)

2

Cracking furnace (mild cracking conditions)

3

Cracking furnace for gaseous use

4

reprocessing unit

5

C4 reprocessing unit

6

Pyrolysis gasoline reprocessing unit

7

Fresh Feed-fractionation

10

schematic process diagrams for a known method

100

schematic process diagrams for the inventive method in particularly advantageous embodiments

A, B, BL

fresh Feed

B1, B2

Fresh feed fractions

C, D, X

product streams

E-V

product fractions

Claims (15)

1. Process for converting hydrocarbon inputs by thermal steamcracking to give at least one olefin-containing product stream comprising at least ethylene and propylene, by at least partly converting a hydrocarbon input in at least one cracking furnace (2), characterized in that the hydrocarbon input is converted under mild cracking conditions in the cracking furnace (2), mild cracking conditions meaning that propylene to ethylene are present in a ratio of 0.85 to 1.6 kg/kg at the cracking furnace exit, and the hydrocarbon input comprising predominantly hydrocarbons having a maximum carbon number of 5.
2. Process according to Claim 1, characterized in that the cracking furnace (2) which converts under mild cracking conditions is supplied with one or more recycled fractions (P, T) which are obtained from the product stream and which comprise predominantly hydrocarbons having a maximum carbon number of 5 as the hydrocarbon input.
3. Process according to Claim 1 or 2, characterized in that the recycled fractions (P, T) are substantially free of diolefins when they are supplied to the cracking furnace (2) which converts under mild cracking conditions as the hydrocarbon input.
4. Process according to any of Claims 1 to 3, characterized in that the cracking furnace (2) which converts under mild cracking conditions is supplied with predominantly saturated hydrocarbons as the hydrocarbon input.
5. Process according to any of Claims 1 to 4, characterized in that the hydrocarbon input is converted in the cracking furnace (2) under mild cracking conditions that lead to a ratio of propylene to ethylene of up to 1.2 kg/kg, at the cracking furnace exit.
6. Process according to any of Claims 1 to 5, characterized in that a hydrocarbon input is converted under normal cracking conditions in a further cracking furnace (1), normal cracking conditions meaning that propylene to ethylene are present in a ratio of 0.25 to 0.85 kg/kg, preferably of 0.3 to 0.75 kg/kg and more preferably of 0.4 to 0.65 kg/kg at the cracking furnace exit, the ratio of propylene to ethylene for the cracking furnace (2) which converts under mild cracking conditions always having a greater value than the value for the ratio of propylene to ethylene for the cracking furnace (1) which converts under normal cracking conditions.
7. Process according to Claim 6, in which the values for the ratio of propylene to ethylene differ by at least 0.1 kg/kg, preferably by at least 0.15 kg/kg, more preferably by at least 0.2 kg/kg.
8. Process according to either of Claims 6 and 7, characterized in that the composition of a hydrocarbon input which is used for the cracking furnace (1) which converts under normal cracking conditions differs from that of the hydrocarbon input which is used for the cracking furnace (2) which converts under mild cracking conditions.
9. Process according to any of Claims 6 to 8, characterized in that the cracking furnace (1) which converts under normal cracking conditions is supplied with at least one fraction (U) which has been separated from the product stream and recycled, comprising predominantly hydrocarbons having a carbon number of at least 6.
10. Process according to any of Claims 6 to 9, characterized in that a fresh input is used, which is fractionated into at least one first and one second fresh input fraction (B1, B2), and the first fresh input fraction (B1) is conducted at least partly into the cracking furnace (1) which converts under normal cracking conditions and the second fresh input fraction (B2) at least partly into the cracking furnace (2) which converts under mild cracking conditions.
11. Process according to any of Claims 6 to 10, in which the cracking furnace exit temperature for the conversion in the cracking furnace (2) which converts under mild cracking conditions is between 680°C and 820°C, preferably between 700°C and 800°C and further preferably between 710°C and 780°C and more preferably between 720°C and 760°C, and the cracking furnace exit temperature for the conversion in the cracking furnace (1) which converts under normal cracking conditions is between 800°C and 1000°C, preferably between 820°C and 950°C and more preferably between 840°C and 900°C, the cracking furnace exit temperature of the cracking furnace (1) which converts under normal cracking conditions being at least 10°C above, preferably at least 20°C above, that of the cracking furnace (2) which converts under mild cracking conditions.
12. Process according to any of Claims 6 to 11, in which 0.3 to 1.5 kg of steam per kg of hydrocarbon input is used in the cracking furnace (1) which converts under normal cracking conditions, and 0.15 to 0.8 kg of steam per kg of hydrocarbon input in the cracking furnace (2) which converts under mild cracking conditions.
13. Process according to any of Claims 1 to 12, in which at least one fraction (V) comprising predominantly hydrocarbons having a carbon number of 2 or 3 is obtained from the product stream and at least partly converted in a cracking furnace (3) for gaseous input.
14. Process according to any of Claims 1 to 13, characterized in that the fresh input (BL) conducted into the cracking furnace (2) which converts under mild cracking conditions comprises natural gas condensates or/and one or more cuts from a mineral oil refinery and/or synthetic and/or biogenic hydrocarbons and/or mixtures derived therefrom.
15. Process according to Claim 10, characterized in that the fresh input (B) used for the cracking furnace (1) which converts under normal cracking conditions or/and for the fresh input for the fresh input fractionation comprises natural gas condensates and/or crude oil fractions, especially naphtha, and/or synthetic and/or biogenic hydrocarbons and/or mixtures derived therefrom.

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