CS214923B1 - Method of shifting the reactor by pyrolisis - Google Patents

Description

The present invention relates to a process for the passivation of an olefin pyrolysis reactor.

To date, ethylene pyrolysis is one of the basic processes in petrochemistry. In the thermal decomposition of individual hydrocarbons and petroleum fractions to the desired olefins, not only the primary reactions to produce hydrogen, methane, light alkanes and alkenes take place, but also secondary reactions leading to fission, dehydrogenation, hydrogenation and condensation products. For extracts of gaseous, liquid and solid pyrolysis products ie. In addition to the reaction conditions, the type of reactor used also influences the coke. The properties of the construction material, the internal surface to volume ratio and the chemical activation or passivation of the internal surface of the reactor by different chemicals are manifested in the process kinetics and in the composition of the pyrolysis products. For this purpose, pyrolysis of individual hydrocarbons and petroleum fractions was studied in reactors of non-metals (glass, quartz, porcelain), metals (iron, nickel, gold, silver, cobalt, titanium), alloys (monel, ascoloy, incoloy 800) and stainless steel. different composition. The wall effect applies especially where the surface to volume ratio of the reactor is increased. In an iron reactor, the rate of conversion is greater than in a quartz or gold reactor. Iron, cobalt and nickel promote coking, unlike quartz, porcelain, silver or gold.

The formation of pyramid, which in the form of coke deposits on the inner surface of the furnace tubes, leads to a deterioration of heat transfer, a decrease in the yield of the final products, a decrease in the performance of the pyrolysis furnace and a reduced service life of the furnace tubes. From this, it is obvious that a reduction in coking in pyrolysis would result in a significant improvement in economic indicators. Much effort has been devoted to the search for ingredients having an inhibitory effect on coke formation. Several types of chemical compounds have been tested as inhibitors, and their wider application under operating conditions is most often limited by efficiency, availability or cost. Air, steam or a mixture thereof is commonly used to decoke the pyrolysis reactor. These oxidizing agents react with the carbon monoxide to form carbon oxides and hydrogen, while also oxidizing the inner surface to the metal oxides. The oxidized surface in this way increases the course of the secondary reactions mainly to the formation of the carbonate. This is particularly evident when pyrolysis of the hydrocarbon feedstock is started. The oxidatively activated surface causes increased coking, especially at exposed locations such as surface irregularities, bends, tapered cross-sections, heat-stressed parts. The formation of coke can be so intense that the reactor becomes clogged at the points mentioned.

The above drawbacks are overcome by the method of reactor passivation in the pyrolysis of individual hydrocarbons and petroleum fractions boiling at 30 to 400 ° C in the presence of water vapor, characterized in that the internal coating of the pyrolysis reactor is passaged by sulfur or thermally decomposable sulfur compounds prior to pyrolysis. a temperature range of 600 to 900 ° C for a duration of 10 to 180 minutes at a space velocity of from 2 kg / m ³ · h to 3000 kg / m ³ · h based on the sulfur present in the compound used.

Advantages of the method of the reactor passivation according to the invention are that by passivation of the inner surface of the pyrolysis reactor with sulfur compounds prior to pyrolysis of the hydrocarbon feedstock, the conversion of hydrocarbons to the carbon monoxide is effectively prevented from depositing in the form of coke on the inner surface of the reactor. This makes it possible to extend the pyrolysis plant time, thereby improving the performance of the furnace.

The experiments were carried out in a flow-through stainless steel tubular reactor at a temperature range of 600 to 900 ° C. The pressure ranged from 0.05 to 0.5 MPa, preferably from 0.1 to 0.2 MPa, and the residence time was less than 1 s. Hydrocarbons and petroleum fractions having a boiling point of from 30 to 400 ° C, mainly gasolines, kerosene and gas oils, were individually pyrolyzed.

In order to treat the pyrolysis reactor, a greater number of organic and inorganic sulfur compounds was tested. Of the inorganic substances, elemental sulfur, hydrogen sulfide, carbon disulfide, sulfur dioxide, sulfides, sulfates, metal thiosulfates of the first and second groups of the periodic table, or ammonium compounds were added. Among the organic sulfur compounds, these were compounds of the mercaptan, sulfide, sulfoxide, disulfide, xanthate, thiophene type and their aromatic and aliphatic derivatives, the derivatives having 1 to 32 carbon atoms. Furthermore, they were phosphorus and sulfur compounds of the alkenylthiophosphonic acid type or of the 0'-dialkyl-dithiophosphoric acid or their inorganic and organic salts or esters, in particular metal salts of the first and second groups of the periodic table or ammonium salts, the alkyls containing 1 to 16 carbon atoms. .

Method of dosing into the pyrolysis system? it was given to the nature and properties of sulfur compounds. For example, hydrogen sulfide was metered directly into the reactor. Water-soluble compounds (e.g. sulfides, sulfates) were dosed as aqueous solutions. Sulfur substances which are soluble in hydrocarbons were added in the form of hydrocarbon solutions.

The effect of hydrogen sulphide and elemental sulfur on the passivation of the internal surface of the reactor was monitored by pyrolysis of heptane and gasoline under catalytic reforming after aromatic extraction (gasoline raffinate). The petrol raffinate had a boiling point of 37 ° C to 156 ° C, a density of 691 kg / m ³ . The pyrolysis and passivation temperatures of the reactor were 820 ° C. The preheat temperature was 400 ° C in all experiments.

The results of the experiments are shown in Tables 1, 2, 3 and 4.>

T a b u 1 k a 1 Pyrolysis without passivation:

Raw material. · · · petrol raffinate heptane Temperature (° C) 820 820 Retention time (S) 0.25 0.25 Injection (g / h) 30.5 31.02 Experiment Time (min) 60 60 Coke weight (g) 0.9 1.0 Coke increment (% w / w) 2.9 3.2

Reactivation of the reactor was done with pure hydrogen sulfide gas and a solution of elemental sulfur in heptane (0.2 wt%) and gasoline raffinate (0.1 wt%).

Table 2 Hydrogen sulphide passivation:

H ₂ S flow rate (ml / min) * 50 50 Passivation time (min) 10 30 Reactor weight gain after passivation (g) 0.25 0.42

* Flow rate H ₂ S in kg / m ³ . h = 652.3

J a b u I k a 3

Elemental sulfur passivation:

passivator petrol raffinate + 0.1% wt. Elementary. S n-heptane %, 2% wt. Elementary. sulfur Flow rate (g / h) 30.9 31,1- ^{| J} Retention time (s) 0.25 0.24 Passivation time (min) 30 30 Reactor mass gain after passivation (g) 0.5 0.7

4- The spatial velocity of the passivator relative to the amount of sulfur present:

and 4.28 kg / m ³ . h

(b) 8,57 kg / m ³ . h

Table 4

Pyrolysis after reactor passivation:

Passivation with hydrogen sulphide by elemental sulfur in

petrol raffinate heptane spraying (etched petrol raffinate heptane Flow rate (g / h) 31.4 30.6 30.2 30.1 30.6 30.6 Experiment time (min 60 60 30 60 30 60 Retention time (s) 0.25 0.25 0.25 0.25 0.25 0.25 Coke weight (g) 0 10 0.16 0 0.05 0

Comparison of the pyrolysis results before passivation (Example 1) and after passivation (Example 4) of a stainless steel metal reactor shows the decisive influence of sulfur compounds on coke formation in the initial phase after pyrolysis start-up.

Claims (1)

Reactivation of reactor by pyrolysis of individual hydrocarbons and petroleum fractions! with a boiling point of 30 to 400 ° C in the presence of water vapor to olefins, characterized in that the inner surface of the pyrolysis reactor is passivated with sulfur or thermally decomposable sulfur compounds in a temperature range of 600 to 900 ° C for 10 to 180 minutes at room speed before pyrolysis from 2 kg / m ³ . h up to 3000 kg / m ³ . h based on the sulfur present in the compound used.