CS230053B1 - Process for producing ethylene - Google Patents

Abstract

It is an object of the invention to utilize excess or waste gaseous alkenes from pyrolyay or catalytic cracking to produce ethylene. According to the invention, the process for producing ethylene from gaseous hydrocarbons is carried out in the presence of water vapor at a temperature of 800 to 900 ° C and a residence time of less than 1 second with addition of hydrogen sulfide or elemental sulfur in an amount of 0.05 to 0.3. % wt. raw material. A mixture of hydrocarbon gas with a boiling point in the range of -50 to 29 ° C, consisting of C3 and C4 alkenes, is used as the feedstock for pyrolysis. or a mixture of alkanes and alkenes C, and C 1-4. Furthermore, gasoline and / or kerosene and / or gaseous oil in an amount of 10 to 50% by weight can be added to the gaseous feed.

Description

According to the invention, the method for producing ethylene from gaseous hydrocarbons is carried out by pyrolysis in the presence of water vapor at a temperature of 800 to 900 °C and a residence time of less than 1 second with the addition of hydrogen sulfide or elemental sulfur in an amount of 0.05 to 0.3 wt. % per raw material. As raw material for pyrolysis, a mixture of gaseous hydrocarbons with a boiling point in the range of -50 to 29 °C, consisting of C3 and C4 alkenes, or a mixture of C4 alkanes and alkenes, is used. Furthermore, it is possible to add naphtha and/or kerosene and/or gas oil to the gaseous feed in an amount of 10 to 50 wt. %.

230,053

230 0S3

The invention relates to a method for producing ethylene from C8 and _C4 alkenes or from a mixture of C8 and _C4 alkenes and olefins by pyrolysis in the presence of steam at a temperature of 800 to 900 C and a residence time of less than 1 second.

In the refining and petrochemical industry, a large amount of saturated and unsaturated hydrocarbons Cg and C ₄ is produced, the combustion of which under current conditions should be limited only to cases of clear production or social necessity. Maximum efforts are focused on the effective chemical utilization of these petroleum fractions, especially for the synthesis of monomers and other basic petrochemical raw materials and intermediates.

From this point of view, it is also important to reassess the sources of raw materials for pyrolysis itself. In addition to the usual raw materials, especially ethane, propane, gasoline and kerosene, saturated Cg and C ₄ hydrocarbons, which are not used for heating purposes, are being used more and more intensively, and the raw material base is expanding to include high-boiling and high-boiling petroleum fractions, such as gas oil, atmospheric and possibly vacuum.

The basic difficulty in conducting the pyrolysis process is the formation of coke, which is formed with varying intensity depending on the thermal stability of the raw materials used and which settles in difficult places of production equipment, especially in the pipes of pyrolysis furnaces.

This reduces the heat transfer in the equipment, increases the hydraulic resistance of the equipment, loses working time due to more frequent cleaning and increases maintenance costs.* The determining process of coke deposit formation is the interaction of unsaturated radicals with the polymer surface of the monolayer of coke-forming deposits, which are formed at various

230 053 places of the device to varying extents can create. The main coke-forming precursors are, for example, vinyl or phenyl radicals, unsaturated compounds - mainly acetylenic and polyolefinic hydrocarbons. These substances undergo rapid condensation and oligomerization reactions, for example, 1,4-addition of the Diels-Alder type, with the growing coke layer and the reaction accelerates with increasing degree of surface coverage. The most effective action of these radicals is that they are formed in the immediate vicinity of the surface of the growing coke layer.

Coke deposits are permanently covered with a continuous layer of polymer material, which gradually converts into coke. The polymer layer significantly limits the increased surface activity and catalytic effect of the reactor wall, or possibly metals, contained in the coke deposits in accelerating coke formation processes. This catalytic effect is applied mainly at the beginning of the process and is effectively suppressed by some components that act as inhibitors.

The need to inhibit coke-forming reactions is all the more important, the more susceptible the starting material for pyrolysis is to coking. Acetylenes and polyolefins must always be removed because their tendency to polymerize and oligomerize and thus to form coke precursors is enormous and practically cannot be inhibited under normal pyrolysis conditions. In the pyrolysis of gaseous alkane hydrocarbons such as ethane and propane, hydrogen sulfide is used in practice as a retardant for gasification with water vapor (gasification) to carbon oxides /British patent 1,077,918; 1967/. Olefinic feeds are usually not pyrolyzed, but are either converted to saturated raw materials by hydrogenation, or the increased risk of their coking is prevented or limited by special measures, as is known, for example, from Czechoslovak Patent Application No. AO No. by mixing the olefinic portion after the convection section or by mixing a limited amount of olefins - e.g. known from Czechoslovak Patent Application No. AO No. Xl^éoX or Bronner C., Derrien M., Lassau C.: Hydrocarbon Processe. 56, No. 1, 131 /1977/ or Duium F.; KTI Newsletter, Spring 1980, p. 17.

230,053

The above-mentioned shortcomings are eliminated according to the invention by a method of producing ethylene from gaseous hydrocarbons by pyrolysis in the presence of water vapor at a temperature of 800 to 900°C and a residence time of less than 1 second with the addition of hydrogen sulfide or elemental sulfur in an amount of 0.005 to 0.3% by weight per raw material. Its essence lies in the fact that a mixture of gaseous hydrocarbons with a boiling point in the range of -50 to 29°C, consisting of C3 and C4 alkenes or a mixture of C3 and C4 alkenes and alkenes, is used as the raw material for pyrolysis. According to another feature of the invention, naphtha and/or kerosene and/or gas oil are added to the gaseous injection in an amount of 10 to 50% by weight.

The basic effect of the method according to the invention is to suppress the side condensation and oligomerization reactions during the pyrolysis of C5 and C4 olefinic hydrocarbons, which ultimately lead to the formation of coke, which settles on the inner surface of the pyrolysis tubes. Another effect is that the addition of sulfur or hydrogen sulfide increases the yield of ethylene during pyrolysis. In contrast to these two effects, according to British patent 1077918, hydrogen sulfide is used to inhibit the formation of carbon oxides during the pyrolysis of ethane and propane (saturated hydrocarbons).

According to Czechoslovak Patent Application No. AO 180 859, hydrogen sulfide and elemental sulfur are used in the pyrolysis of individual hydrocarbons and petroleum fractions with a boiling point of 30 to 400°C that do not contain olefins.

The method according to the invention is described in more detail using several typical examples of pyrolysis of olefinic fractions.

Pyrolysis was carried out on an experimental device consisting of a tank for raw material and water, pumps, preheater, mixer, direct heating of the tubular reactor, cooler and condenser. The device modeled the real pyrolysis process. C4 fractions freed from diolefins and acetylenes, with different contents of unsaturated hydrocarbons, were pyrolyzed. The tendency to coke-forming reactions was effectively suppressed by continuous addition of hydrogen sulfide or sulfur to the reaction mixture.

Example 1

The saturated feedstock was pyrolyzed under the following conditions: Temperature: 835°C

Mass ratio H20/sur.: 0.4

Dwell time: 0.9 s

H ₂ s content _in the raw material /% wt./: 0.1

230,053

The composition of the feedstock and pyrolysis products was as follows:

Composition /% wt./ Input raw material Pyrolysis product methane 30.3 ethane 2>9 ethylene 40.1 propane 7.6 0.8 propylene 11.3 Cg-unsaturated 1.2 isobutane 33.1 0.8 n-butane 59.3 1.8 -unsaturated 0.6 isobutylene + 1-butene 2.3 trans-2-butene 0.2 cis-2-butene 1.1 1,3-butadiene 3.5 C _c + heavier hydrocarbons 0 3.1

Example 2

In the same manner and under the same reaction conditions as in Example 1, a raw material with a total content of unsaturated hydrocarbons up to 25 wt.% was pyrolyzed.

The composition of the feedstock and pyrolysis products was as follows:

Composition /% nom./ Input raw material Pyrolysis product methane 31.4 ethane 3.1 ethylene 34.1 propane 0.3 0.4 propylene 13.6 Cg-unsaturated ο,ι isobutane 28.4 i.5 n-butane 43.1 2.7 C^-unsatd. 0.6 isobutylene + 1-butene 23.7 4.2 trans-2-butene 2.8 0.2

230 053 cis-2-butene 1,3-butadiene Cg + heavier carbon

1.7

1.3

3>4

3.6

Example 3

In the same manner and under the same conditions as in Example 1, a raw material with a total content of unsaturated C ₄ hydrocarbons up to 50 wt.% was pyrolyzed.

The composition of the input raw material and gas products (with a negligible amount of liquid products) was as follows:

Composition /% wt./ Input raw material Pyrolysis product methane 35.5 ethane 3.0 ethylene 33.7 propane 0.3 0.2 propylene 11.1 Cg unknown. 0.7 isobutane 21.0 0.7 n-butane 37.1 1.5 C ₄ ~unsatisfied. 1.7 isobutylene + 1-butene 34.8 4.2 trans-2-butene 4.1 0.2 cis-2-butene 2.3 1.5 1,3-butadiene 3.4 C ₅ + heavier hydrocarbons 2.6

In the same experimental device, a mixture of C ₄ fraction with a higher content of unsaturated hydrocarbons was pyrolyzed together with virgin gasoline. The tendency of unsaturated hydrocarbons to coke was effectively suppressed by adding elemental sulfur to virgin gasoline in an amount of 0.001 to 0.3 wt. %, preferably 0.06 wt. %, /relative to the hydrocarbon feedstock/. The composition of the mixed feedstock was, for example, 25 wt. % gasoline and 75 wt. % fraction with a 25% content of C ₄ alkenes.

I

Example 4

230,053

The equipment for the co-pyrolysis of the fraction and gasoline was, in contrast to the previous cases, equipped with a separate gasoline pump. The pyrolysis temperature was 820°C; other reaction conditions were the same as in examples 1-3. A mixture of 25% wt. gasoline and 75% wt. fraction with a content of approximately 25% wt. olefins was pyrolyzed.

The composition and characterization of the input raw materials and pyrolysis product were as follows:

Raw material Pyrolytic Gasoline C^-fraction product n-alkanes 40.95 methane - 32.7 i-alkanes 37.68 ethane - 3.8 cyclanes 19.44 ethylene - 36.3 flavors 1.49 propane 0.3 0.2 contents S 0.013 propylene - 11.2 density 680 C^nenas. - 1.3 average mol.wt. . 80.4 i-butane 28.4 0.4

precipitation curve:

it started to rain. 43° n-butane 43.1 0.8 10% 53° unhappy - 0.4 30% 60° i-butene - 1-butene 23.7 1/9 50% 73° trans-2 butene 2.8 0.1 70% 87° cis-2 butene 1/7 1/0 90% 106° 1,3-butadiene- 2.95 addition heavier coal - 6.95 element.sulfur 0.006 % wt.

A basic comparison of the raw materials in terms of their tendency to coke and confirmation of the retarding effect of hydrogen sulfide was carried out on the same device, but in which the direct reactor was replaced by a U reactor. The amount of solid pyrolysis deposits during the pyrolysis of pure raw materials (without the presence of water) was measured, both

230 0S3 with and without continuous addition of hydrogen sulfide.

Example 5

Raw material composition /% wt./ propane 0.3 iso-butane 21.0 n-butane 37.1 iso-butylene + 1-butene 34.8 trans-2- -butene 4.1 cis-2-butene 2.3 A

was pyrolyzed both in a pure state and with the continuous addition of 0.1 wt. % H ₂ S, for 15, 30, 60 and 90 minutes under the following conditions: temperature 83O°C, residence time 0.2 s.

The following yields of solid pyrolysis deposits were achieved:

Pyrolysis time Weight of pyrolysis products /g/ pure raw material raw material + 0.1% H ₂ s 15 0.8 0.05 ³⁰ 1.1 0.05 60 1.75 0.05 90 2.1 0.05

P È S I£ Ž T OF THE INVENTION

230 0S3

Claims (2)

Process for producing ethylene from gaseous hydrocarbons by pyrolysis in the presence of water vapor at a temperature of 800 to 900 ° C and a residence time of less than 1 second with the addition of hydrogen sulfide or elemental sulfur in an amount of 0.005 to 0.5% by weight. to a feedstock, characterized in that a mixture of gaseous hydrocarbons boiling in the range of -50 to 29 ° 0, consisting of C? alkenes, is used as pyrolysis feedstock; and O? or from a mixture of alkanes and alkenes of C? and C ₄ . 2. The process for producing ethylene according to claim 1, characterized in that the gasoline feed is added with a quantity of 10 to 50 wt.