EP1285903B1 - Process for the preparation of paraffines from educts containing cyclic hydrocarbons - Google Patents

Abstract

Production of paraffins comprises reaction of feed containing cyclic hydrocarbons on a zeolite catalyst under isothermal conditions in a cooled reactor.

Description

The invention relates to a process for the preparation of paraffins from cyclic hydrocarbon-containing feedstocks such as mineral oil fractions and / or fractions from thermal or catalytic conversion systems containing alkanes, alkenes, cyclic alkanes and / or aromatics by reacting with a zeolite catalyst.

For environmental reasons, a reduction of the aromatic content in fuels is sought. Therefore, aromatics-rich fractions previously added to octane-numbering fuels will have to be reused in future. This also applies to the aromatics-rich pyrolysis heavy gasoline obtained in the production of ethylene and propylene in olefin plants. In DE 199 49 211 A1, it is proposed for this purpose to react such fractions by means of a zeolite catalyst to form n-alkanes, in particular ethane, propane and n-butane. Finally, these substances can be mixed back into the use of the olefin plant. WO 93/08145 discloses a continuous isomerization / ring opening process.

The present invention has for its object to provide a method of the type mentioned in such a way that high yields can be achieved in an economical manner.

This object is achieved in that the reaction is carried out under isothermal conditions in a cooled reactor.

By observing isothermal conditions, account is taken of the fact that the temperature difference between a minimum temperature required for sufficient catalytic activity (eg 340 ° C) and a maximum temperature (410 ° C) permissible for economic selectivity is related to an adiabatic Temperature increase of z. B. 325 ° C is very low. Under isothermal conditions is to be understood in the context of the present invention that the temperature increase in the closed catalytic zone is limited to values that are significantly below the corresponding adiabatic temperature increase and significantly within said operating window, ie, for example, be controlled at 40 ° C.

In isothermal catalytic conversion, i. In reactions such as ring opening and cracking, accumulating heat is dissipated at a high temperature level and can be fed to a meaningful use. In contrast, in an adiabatic reaction and cooling by liquid injection of the reaction products no meaningful waste heat utilization would be possible. In addition, the isothermal procedure offers control engineering and economic advantages. Subsequent separation of the reaction products is greatly facilitated. The temperature control according to the invention makes it possible to optimize the selectivity.

Conveniently, the reaction of the starting materials is carried out in externally cooled tubes of the reactor. For this purpose, the starting materials are passed through the pipes, while the pipe jacket is cooled by means of a heat carrier. As a heat carrier in particular melts and heat transfer oils are.

According to a particularly preferred embodiment of the invention, the reaction of the starting materials is carried out in a reactor with wound tubes. Such a reactor is described for example in DE 34 12 482 A1.

Advantageously, the feedstocks containing cyclic hydrocarbons are hydrogenated in a pretreatment step to a feed stream containing predominantly naphthenes and up to 40 vol.% Aromatics. For hydrogenation, a nickel catalyst is suitably used. For procedural reasons, it may be advantageous to reduce the proportion of aromatics in the feed stream to less than 5% by volume, preferably at most 2% by volume.

According to a further development of the invention, an adiabatic catalyst bed with a hydrogenation catalyst is connected directly upstream of the cooled reactor, reaction heat being obtained by hydrogenation of hydrocarbons being used for further preheating of the starting materials for the subsequent isothermal reaction. In this way, the use of external energy for Heating of the starting materials are minimized to the reaction temperature necessary for the isothermal reaction, and it can be dispensed with a furnace.

In the following, the invention will be explained in more detail with reference to an exemplary embodiment shown schematically in the figures:

Figur 1

ein Fließschema der Vorbehandlungsstufe

Figur 2

ein Fließschema der isothermen katalytischen Umsetzung

Figur 3

ein Fließschema der Nachbearbeitungsstufe.

Figur 4

eine Auflistung der Produktbestandteile

Show it

FIG. 1

a flow chart of the pretreatment step

FIG. 2

a flow chart of the isothermal catalytic reaction

FIG. 3

a flowchart of the postprocessing stage.

FIG. 4

a list of product components

The pretreatment stage shown in FIG. 1 serves for the hydrogenation of the starting materials containing the cyclic hydrocarbons. A stream of C5 + hydrocarbons from an olefin plant is fed to selective hydrogenation and desulfurization as well as fractionation 1. The resulting pyrolysis heavy gasoline with predominantly C7 + hydrocarbons has an aromatic content of typically 60 to 90 vol.%, In the present example, 87 vol.% To. By means of a pump 2, the pyrolysis heavy gasoline is compressed to a pressure of about 30 bar and divided into two partial streams 3 and 4. The partial stream 4 is heated via a heat exchanger 5 and fed at a temperature of 80 to 120 ° C a hydrogenation stage 6 with three catalyst beds containing a nickel catalyst. The other partial stream 3 is distributed to the hydrogenation stage 6. In the hydrogenation stage 6, the aromatics are hydrogenated to napthenes. The product obtained, which may contain up to 40 vol.% Aromatics, but in the present example less than 0.5 vol.% Aromatics, is withdrawn at a temperature of 120 to 160 ° C by means of line 7, in the heat exchangers 5 and 8 cooled, wherein the heat exchanger 8 is operated with cooling water, and finally fed to a gas liquid separation 9. Liquid product is partly recycled via line 10 and serves to dilute the starting material for the hydrogenation stage 6. Hydrogen gas is produced in a pressure swing adsorption plant (PSA). 11 produced hydrogen mixed. The naphthene-containing product stream in line 12 is fed to the isothermal reaction stage shown in FIG.

As shown in FIG. 2, the product stream containing the naphthenes is compressed by means of a pump 13 to approximately 25 to 70 bar, preferably 50 to 60 bar, in the present example to approximately 60 bar, preheated by means of heat exchangers 14 and 15 and a heating stage 16 fed. The heated to about 380 ° C feedstocks are introduced into the isothermal reactor 17. In the present embodiment, the isothermal reactor 17 is designed as a straight tube reactor. The tubes arranged in the reactor 17 are cooled with a heat transfer oil from the outside, which circulates in the conduit 18. The heat of reaction in the reactor 17 is removed by means of the heat carrier oil to an external steam generator 19. The isothermal reactor 17 contains a zeolite catalyst. In the reactor, the naphthenes are converted to paraffins under isothermal conditions at a consistently high conversion rate. The reaction products are removed via line 20 and cooled by means of the heat exchangers 15 and 14. At a temperature above the dew point of 144 ° C, the reaction products are transferred to the post-processing stage shown in Figure 3.

In the post-processing stage shown in FIG. 3, the reaction products are fractionated. For this purpose, the reaction products are fed via line 21 to a scrubber 22. The gaseous product is removed from the head of the scrubber 22 by means of line 23, cooled in a heat exchanger 24 against cooling water and fed to a gas-liquid separation 25. The gaseous product obtained is fed via line 26 to a further gas-liquid separation stage 27. The resulting in this separation stage gaseous product is passed at a temperature of about 15 ° C via a dryer 28 to a plate heat exchanger 29. In a further gas-liquid separation stage 30 gaseous hydrogen is separated and fed by means of line 31 into the process. The resulting in the separation stage 30 liquid product is finally removed via line 32 from the post-treatment stage and is available as a feedstock with a very high paraffin content for the steam cracker of the olefin plant available. The condensate accumulating in the scrubber 22 contains partially propane, and is fed via line 33 to a propane stripping in a stripping column 34. This accumulating aromatics are finally by means of a return line 35 returned to the pretreatment stage shown in Figure 1.

FIG. 4 shows the product composition of the product stream leaving the plant, which is used as an insert for the steam cracker of the olefin plant (SC feedstock).

Claims (6)

1. Process for preparing paraffins from feedstocks comprising cyclic hydrocarbons, e.g. mineral oil fractions and/or fractions from thermal or catalytic conversion plants comprising alkanes, alkenes, cyclic alkanes and/or aromatics, by reaction over a zeolite catalyst, characterized in that the reaction is carried out under isothermal conditions, i.e. the temperature increase in the closed catalytic zone is limited to values which are below the corresponding adiabatic temperature increase and within the operating window, in a cool reactor.
2. Process according to Claim 1, characterized in that the reaction is carried out in externally cooled tubes of the reactor.
3. Process according to Claim 1, characterized in that the reaction is carried out in a reactor having coiled tubes.
4. Process according to any of Claims 1 to 3, characterized in that the feedstocks comprising cyclic hydrocarbons are hydrogenated in a pretreatment stage to give a feed stream which comprises predominantly naphthenes and up to 40% by volume of aromatics.
5. Process according to Claim 4, characterized in that the feed stream contains less than 5% of aromatics.
6. Process according to any of Claims 1 to 5, characterized in that an adiabatic catalyst bed comprising a hydrocarbon catalyst is installed directly upstream of the cooled reactor, with heat of reaction evolved in the hydrogenation of hydrocarbons being used for preheating the feedstocks for the subsequent isothermal reaction.

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