DD282858A5 - REACTOR FOR THE THERMAL CONVERSION OF HYDROCARBONS - Google Patents

Abstract

The invention relates to a reactor for thermal conversion of hydrocarbons, which is used in the chemical industry for thermal processes in the temperature range of 450 to 1 100C and consists of a pipe system, on the surface of a 0.1 to 50 mm thick silicon-containing layer is disposed, which is first treated with air and then with oxygen-free and / or oxygen-poor nitrogen-containing gases. {Reactor; thermal process; Pipe system; Surface; silicon-containing layer; Air, oxygen-free, nitrogen-containing; Gas}

Description

Field of application of the invention

The invention relates to a reactor for the thermal conversion of hydrocarbons, which is used in the chemical industry for thermal processes in the temperature range of 450 to 1100 ° C.

Characteristic of the known state of the art

For reactors for the thermal conversion of hydrocarbons to olefins and aromatics, high-alloyed steels, which are required to withstand high high temperatures, must be used which, owing to certain alloying constituents, eg. As nickel, the coke formation, which is an undesirable side reaction, favor.

Coke deposits in the reactor lead to drastic deterioration of the heat transfer, to increase the Differenzdruckfcs in the system and ultimately to the deterioration of the economics of the system. Therefore, these deposits must be removed at certain intervals by burning with air and / or water vapor. The service life of the tubes is greatly reduced by the frequent changes of oxidizing and reducing atmosphere in the production cycle, which has a negative effect on the availability of the plant.

According to DE-OS 3206601 a reactor tube for the thermal cracking or reforming of hydrocarbons is used, which is equipped with a nickel-free inner tube. However, this technology is very complicated and industrially difficult to realize for tube reactor systems, which consist of several tubes. In DE-OS 3046412 a process for the high-temperature treatment of hydrocarbonaceous materials is described, in which with Flammsprüh-, Plasmc's'rahl- or baking method SiOrbeschichtete reactors are geset t.

In GB 1483144 a seduction is described in which the pipe surface of the reactor is first oxidized at about 800 ° C with air or water vapor. This is followed at 200 to 1 200 ° C, preferably at 600 to 900 ⁰ C occupancy of the surface with alkoxysilanes.

However, the reactors coated in both said processes inhibit coke formation only over a short period of time. In this case, a rapid activation of the passivated reactor surface takes place and a coke layer with a high coke formation occurs.

Furthermore, methods are known in engineering is Oberflächenvergü.ung that schin share wear-resistant coatings and HartstoffschLhten on highly stressed Mi. such. B. on cutting tools produce.

For the production of hard coatings on machine parts made of unalloyed and low-alloy steels, according to DD 200573, the metal surface is first coated with an oxide and / or i> ydroxidischen primary layer, the elements such. B. Al, Si, Cr, Ti, Mo, W, V, Nb, provided and then subjected to a thermo-chemis.chen treatment in aufstickender and / or carburizing atmosphere.

The primary layer is from the aqueous phase subjected to (usually aqueous electrolyte) was applied to the parts and flowing these are then in the furnace in the presence of NHY, CH _4, CO, CO ₂ of a thermal treatment. As a result, hard nitride and / or carbide-containing layers are obtained on the machine components or tools, so that these no longer have to be made from ho jhlegierten steels' the improvement of their Gebrauchswertigenschafton (increase in strength, increased wear and Korrosionswidersiand).

Object of the invention

The aim of the invention is a reactor for the thermal conversion of hydrocarbons at 450 to 1100 ⁰ C desse surface prevents the formation of coke deposits over a long period of time, thus ensuring high availability of the reactor.

Explanation of the essence of the invention

The object of the invention is to develop a reactor for the thermal conversion of hydrocarbons in which the formation of coke deposits in pyrolysis processes is suppressed by a surface coating.

This object is achieved by a reactor for the thermal conversion of hydrocarbons at 450 to 1100 ° C according to the invention in that the reactor consists of a pipe system, on its surface coming into contact with hydrocarbons, a 0.1 to 50Mm thick silicon-containing layer is arranged at surface temperatures of 600 to 1100 ⁰ C first 1 to 60 hours with flowing air and then 1 to 50 hours with ΰ to 80m / s flowing acid-free and / or oxygen-poor nitrogen-containing gases at 500 to 1100 ⁰ C thermo-treated.

The reactors used for pyrolysis reactions usually order from pipe systems that are constructed as tube bundles and / or branching pipes. On the surface of the tubes, which is contacted by the hydrocarbon, a silicon-containing layer according to the invention with a thickness of 0.1 to 50μπι, preferably 0.1 to 20μηι arranged. This layer is produced by applying one or a mixture of silicon-containing compounds on the pipe surface according to known technologies, for. B. by introducing the silicon-containing compound by means of steam as a diluent.

After applying the silicon-containing compounds, the treatment of the reactor at surface temperatures of 600 to 1100 ⁰ C, preferably at 700 to 900 ⁰ C, 1 to 60 hours with air flowing through and then 1 to 50 hours with oxygen-free and / or oxygen-poor gases in the temperature range 500 to 1100 ⁰ C, preferably from 700 ⁰ C to 900 ⁰ C, at Strörr jngsgeschwindigkeiten of 5 to 80m / s. As ^st: ckstoffhaltige gases are particularly ammonia and nitrogen. The reactor exhibits constant operating conditions over a long period of time with only insignificant coking when the silicon-containing layer disposed on the surface contains from 20 to 60 mass% silicon and from 3 to 20 mass% nitrogen. The reactor is particularly suitable for the pyrolysis of liquid hydrocarbons in the temperature range from 450 to 1100 ^° C. With the use of the reactor according to the invention, an up to 90% reduction of the coke-like deposits on the reactor surface and thus a noticeable extension of the duration of the A '. ilage until a necessary decoking reaches.

This extension of reactor life reduces the number of decoking operations required to operate, thereby reducing the material damage associated with each decoking and significantly extending the life of the reactor, ultimately having a positive effect on the overall economy of the plant. The invention will be explained in more detail with reference to the following 3 examples.

Ausführungsbeispiole

example 1

In a laboratory reactor made of stainless steel (XSCrNiTi 18.10) with the dimensions 200mm x 15mm χ 15mm, a straight-mn gasoline was pyrolyzed at a reactor temperature of 75O ⁰ C, a residence time of 0.25s and a water vapor / hydrocarbon ratio of 0.6. Steam and straight-run gasoline were metered and vaporized separately, combined at the reactor inlet and squeezed in the electrically heated reactor. At the reactor outlet, the reaction product was quenched by indirect cooling, the liquid product condensed and the gas product collected in a storage vessel. The liquid and gaseous reaction products were analyzed by gas chromatography.

To determine the amount of coke formed in the reactor, the tube was burned out for 1 hour with air at 800 ⁰ C. The carbon oxides formed were introduced after conversion of CO to CO ₂ over copper oxide at 700 ^° C. in sodium hydroxide solution and the amount of carbon was determined by back-titration of the unused sodium hydroxide solution with hydrochloric acid. The results are included in Table 1. The amount of coke is given in% by weight, based on the starting material. From Table 1 it can be seen that in a untreated reactor there is a high coking tendency.

Example 2

The laboratory tube reactor according to Example 1 was wetted with silicone oil at room temperature. The liquid film remaining on the tube inner surface was then burned in the air stream for 1 hour at 1000 ° C. with a ring burner.

This was followed by a 5-hour post-treatment with gaseous ammonia at the same temperature and at a flow rate of 20 l / h. This treatment method achieves a long-term stable and effective passivation of the laboratory tube reactor.

The pyrolysis decoking cycles performed with such a reactor resulted in extremely low coking tendencies, as shown in Table 1.

Example 3

The laboratory tube reactor according to Example 1 was coated with hexamethyldisiloxane in the CVD method at 75O ⁰ C and then treated at 1000 ⁰ C for 1 hour in an air stream and then subjected to a continuous aftertreatment with gaseous ammonia at the same temperature and at a flow rate of 20l / h.

With a reactor treated in this way, 50 pyrolysis experiments were carried out with straight-run gasoline under the conditions given in Example 1, followed by decoking in each case. As shown in Table 1, the amount of coke formed is extremely low, and even after 50 cycles of pyrolysis decoking, no increase in coke formation was observed.

Table 1

Coke formation tendency in the pyrolysis of straight-run gasoline in differently treated reactors

number of trials

pyrolysis

Decoking cycle

Untreated reactor

Treated reactor

10 15 20 25 30 35 40 45 50

example 1

Amount of coke (mass fractions

0.61 0.57 0.78

Example 2

coke

(Mass fractions

in%)

0.08

0.08

0.07

0.06

0.05

0.03

0.04

0.05

0.04

0.07

0.06

0.07

0.06

0.05

Example 3

Amount of coke (mass fractions

0.04 0.04 0.05 0.05 0.04 0.06 0.08 0.06 0.05 0.06 0.08 0.10 0.07 0.06

Claims (2)

1. Reactor for the thermal conversion of hydrocarbons at 450 to 1100 ° C, which is arranged from a pipe system, on whose surface coming into contact with hydrocarbons, a silicon-containing layer, characterized in that the silicon-containing layer has a thickness of 0.1 to 50μιη and at surface temperatures of 600 to 1100 ⁰ C first 1 to 60 hours with flowing air and then 1 to 50 hours with 5 to 80 m / s flowing oxygen-free and / or oxygen-poor nitrogen-containing gases at 500 to 1100 ⁰ C is thermo-treated. 2. Reactor according to claim 1, characterized in that arranged on the reactor surface necessary for the hydrocarbon conversion surface layer 20 to 60 parts by mass in% silicon and 3 to 20 parts by mass in% nitrogen.