JPH0455410B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for separating and purifying olefins, dienes, etc. from naphtha thermal decomposition products containing acetylenic hydrocarbons. Technical background of the invention and its problems Olefins such as ethylene and propylene are
It is a very important compound as a starting material for petrochemistry. Such olefins are mainly produced by thermally decomposing raw material hydrocarbons such as naphtha in a thermal cracking furnace. By the way, when raw material hydrocarbons such as naphtha are thermally decomposed, the resulting thermal decomposition products (hydrocarbons) contain acetylene hydrocarbons, especially those containing 3 carbon atoms.
It contains acetylene hydrocarbons such as methylacetylene, vinylacetylene, and ethylacetylene, which contain ~4 acetylenes, although in small amounts. In order to separate and refine useful olefins or dienes such as ethylene, propylene, and butadiene from hydrocarbons containing such acetylenic hydrocarbons, the hydrocarbons must be separated and purified using a depropanizer, cryogenic equipment, etc. The olefins are supplied to an olefin recovery section consisting of a hydrogen separation device, a demethanizer, a deethanizer, an ethylene separation tower, a propylene separation tower, a debutanizer, etc., and each olefin and diene are separated at high purity in this olefin recovery section. It is being collected. However, when trying to separate and recover olefins and dienes from the above-mentioned hydrocarbons in an olefin recovery section, acetylenic hydrocarbons polymerize significantly more easily than olefins or dienes, so for example, a depropanizer, In the olefin recovery section where hydrocarbons are initially supplied, such as in a deethanizer tower, acetylenic hydrocarbons polymerize and accumulate on trays or downcomers, clogging the flow path within the tower. There was a problem that there was. In order to solve the problems caused by the polymerization of acetylenic hydrocarbons, conventional methods have been to inject chemicals called antifouling agents into hydrocarbons containing olefins and dienes, or to use distillation columns. The system was a two-column type, in which one column, which suffered from severe fouling, was temporarily disconnected to remove the polymer that had accumulated in the column, and the remaining column was operated during that time. However, methods that use anti-fouling agents have the problem that anti-fouling agents pose a risk of having an adverse effect on the human body when handled, and that a large amount of the agent is required, so the cost cannot be ignored. It was hot. On the other hand, in the system where the distillation column is a two-column type, two distillation columns must be prepared.
There were problems in that the equipment cost was high and it took time and effort to remove the polymer deposited in the column. In addition, acetylenic hydrocarbons having 3 to 4 carbon atoms are
In this state, even if it were recovered, it would have no useful use, and moreover, vinyl acetylene is an explosive decomposition compound. Therefore, it is desirable to convert acetylenic hydrocarbons having 3 to 4 carbon atoms into other useful compounds. Purpose of the Invention The present invention aims to solve the problems associated with the prior art as described above, and is aimed at solving the problems associated with the prior art as described above. Even without using chemicals such as anti-fouling agents, the distillation separation column in the olefin recovery section will not be contaminated or clogged due to polymerization of acetylene hydrocarbons, and a backup distillation separation column can be installed. Provides a method for separating and refining olefins, dienes, etc. from hydrocarbons including acetylenic hydrocarbons, which eliminates the need to store and further converts acetylenic hydrocarbons into other useful compounds. It is intended to. Summary of the Invention The method of separating and refining the thermal decomposition products of naphtha containing acetylenic hydrocarbons according to the present invention includes the following steps when separating and refining olefins from the thermal decomposition products of naphtha containing acetylenic hydrocarbons: This thermal decomposition product of naphtha is supplied to a distillation column for separation and purification of olefins, and all of the fraction in the column is extracted as a side stream from an intermediate stage of this distillation column, and the acetylene-based carbonization contained in this side stream is After hydrogen is hydrogenated in the presence of a selective hydrogenation catalyst for acetylenes, this side stream is again returned to the lower stage from the intermediate stage from which the side stream was extracted from the distillation column. The method for separating and purifying olefins from the pyrolysis product of naphtha containing acetylenic hydrocarbons according to the present invention is a method for separating and refining olefins from the pyrolysis product of naphtha containing acetylenic hydrocarbons. The above naphtha thermal decomposition product is supplied to a distillation column for separation and purification of olefins, and the entire fraction in the column is extracted as a side stream from an intermediate stage of this distillation column, and the acetylene carbonization contained in this side stream is After hydrogen is selectively hydrogenated, this side stream is returned to the lower stage from the intermediate stage where the side stream was extracted from the distillation column, so acetylene carbonization can be achieved without using chemicals such as anti-fouling agents. The distillation separation column in the olefin recovery section will not be contaminated or clogged due to hydrogen polymerization, and there is no need to install a spare distillation separation column. It can be converted into a chemical compound. DETAILED DESCRIPTION OF THE INVENTION The method of separating and purifying olefins from the thermal decomposition product of naphtha containing acetylenic hydrocarbons according to the present invention will be described in detail below. olefins such as ethylene, propylene, butene, and butadiene are separated and recovered with high purity from the resulting hydrocarbons containing acetylene hydrocarbons. This will be explained using steam cracking as an example. In steam cracking, raw hydrocarbons such as naphtha, kerosene, and gas oil are pyrolyzed in a pyrolysis furnace, and olefins such as ethylene and propylene are separated and purified from the resulting pyrolysis gas. However, steam cracking itself, which is a method for producing olefins by thermally decomposing hydrocarbons, is conventionally known. A device for this purpose, namely a steam cracker device, will be explained. The steam cracker equipment is capable of converting hydrocarbons such as naphtha, kerosene, and gas oil into ethylene,
Among the well-known devices for producing propylene and butadiene, the present invention uses a steam cracker device of any type, such as the one shown in Revised Manufacturing Process Chart Complete Collection, 1978, published by Kagaku Kogyosha. An example flowchart is shown in FIG. In this steam cracker device 1, raw material hydrocarbons such as naphtha are introduced into a thermal cracking furnace 3 together with steam 2, and about
It is thermally decomposed at a temperature of about 800℃. The hydrocarbons discharged from the thermal cracking furnace 3 are rapidly cooled to prevent polymerization, and then led to a rectification column 4, where tar is separated from the top and bottom, and gas oil is separated from the top and bottom, while gas oil is obtained from the top of the column. The hydrocarbons are sent to a compressor 6 equipped with a drive machine 5 and compressed. The compressed hydrocarbons then pass through a sulfur removal equipment consisting of an alkali washing section 7 and a drying section 8, and are then sent to a hydrogen separation device such as a depropanizer, a deep cooling device, a demethanizer, a deethanizer, and an ethylene separation tower. , a propylene separation tower, a debutanizer, etc. are sent to the olefin recovery section 9, where high purity ethylene of approximately 99.95% is produced.
Olefins such as propylene and butadiene with a high purity of approximately 99.0% are separated and recovered, as well as methane, ethane, propane, hydrogen, etc. By the way, when raw material hydrocarbons such as naphtha are pyrolyzed together with steam 2 in a thermal cracking furnace 3, the resulting pyrolysis gas contains olefins such as ethylene, propylene, butene, and butadiene, as well as ethane, propane, and butane. Contains paraffins such as and acetylene hydrocarbons such as acetylene, methylacetylene, vinylacetylene, and ethylacetylene. Among these, acetylenic hydrocarbons may polymerize in a distillation separation column in an olefin recovery section such as a depropanizer or a deethanizer, thereby contaminating or clogging the inside of the column. Therefore, in the present invention, as shown in Fig. 2, hydrocarbons containing such acetylenic hydrocarbons are supplied to the first distillation separation column in the olefin recovery section, such as a depropanizer or a deethanizer. At this time, all of the fraction in the column is extracted from intermediate stage A of this distillation column 10 as a side stream by a pump 11, and this side stream is introduced into a hydrogenation column 12 where a selective hydrogenation catalyst for acetylenes is present. , where the acetylenic hydrocarbons contained in the side stream are selectively hydrogenated.
In this way, vinyl acetylene and ethyl acetylene, which are acetylenic hydrocarbons, are converted to butadiene and butene-1, respectively,
Also, acetylene is converted to ethylene, and methylacetylene is converted to propylene. After selectively hydrogenating the acetylenic hydrocarbons as described above, the side stream is returned to the distillation column 10 again. At this time, the place where the side stream is returned is the distillation column 10.
This is the lower stage than the intermediate stage A from which the side stream was extracted. Catalysts that selectively hydrogenate acetylene in hydrocarbons include alumina-supported palladium catalyst (trade name T-2423) and Dow-K method catalyst, which are conventionally known as selective hydrogenation catalysts for acetylene. A catalyst can be used. In addition, in the hydrogenation column 12, the pressure is generally 5 to 30
Kg/cm ² G, the temperature is 50 to 150° C., and it is preferable to hydrogenate in the liquid phase, but these conditions do not limit the present invention. The intermediate stage A from which the internal fraction is extracted as a side stream in the distillation column 10 is preferably located at or above a point in the distillation column 10 where contamination due to polymerization of acetylene hydrocarbons begins to be observed. In this way, when the distillation column 10 is drawn out as a side stream and the internal fraction is extracted, and the acetylenic hydrocarbons contained in this side stream are selectively hydrogenated, the acetylenic hydrocarbons in the side stream have a significantly high concentration. Therefore, acetylenic hydrocarbons can be hydrogenated extremely efficiently. In some cases,
The reaction heat from the hydrogenation reaction can also be used as a heat source for the bottom reheater 13 of the distillation column 10, and energy saving can also be achieved. Note that this distillation column 10 generally has a condenser 14 at its upper part. On the other hand, when the pyrolysis products obtained from the pyrolysis furnace are directly hydrogenated in the presence of an acetylenic hydrocarbon catalyst, the concentration of acetylenic hydrocarbons in the pyrolysis products is low, and the temperature is also low. It is too low to carry out the addition reaction, so it is not possible to efficiently hydrogenate acetylenic hydrocarbons. There are several types of arrangement of distillation columns for separation and purification of olefins in the olefin recovery section.
There are some in which the depropanizer is placed first, some in which the deethanizer is placed first, and some in which the demethanizer is placed first. When the depropanizer is placed first, it is preferable that the hydrogenation of acetylenic hydrocarbons as described above is carried out in the depropanizer, and the deethanizer or demethanizer is placed first. In this case, it is preferable that the above-mentioned hydrogenation of acetylenic hydrocarbons be carried out in this deethanizer or depropanizer. In the above explanation, we have explained the case where the hydrocarbons containing acetylenic hydrocarbons are hydrocarbons obtained by thermal decomposition of naphtha. Alternatively, it can be widely applied for the purpose of increasing the production of high value-added fractions by hydrogenating acetylene. Effects of the Invention The method for separating and purifying olefins from the pyrolysis product of naphtha containing acetylenic hydrocarbons according to the present invention supplies the above-mentioned pyrolysis product of naphtha to a distillation column for separating and purifying olefins. Then, all of the fraction in the column is extracted as a side stream from the middle stage of this distillation column, and after selectively hydrogenating the acetylenic hydrocarbons contained in this side stream, this side stream is passed back into the distillation column. Since the side stream is returned to the lower stage from the intermediate stage where it was extracted, there is no need to use chemicals such as anti-fouling agents to prevent acetylene hydrocarbons from polymerizing and contaminating or clogging the distillation separation column in the olefin recovery section. In addition, there is no need to prepare a standby distillation separation column.
Acetylenic hydrocarbons can be converted into other useful compounds. EXAMPLES The present invention will be explained below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Comparative Example 1 A hydrocarbon fraction containing acetylenic hydrocarbons obtained by thermal decomposition of naphtha was supplied from the bottom to the 27th stage of a carbon steel distillation apparatus having 38 stages.
Distilled. Distillation was carried out at a tower top pressure of 11.6 Kg/cm ² G,
The reaction was carried out under reflux conditions with a tower bottom temperature of 91°C and a tower top temperature of -30°C. The mass balance data for this run is shown in Table 1.
After continuing the above operation for 30 days, the distillation column was opened,
The polymeric scale deposited inside the tower was removed. The amount of scale was 88g in weight. The areas where the accumulation occurred were from the bottom of the tower including the reheater to the 20th stage, and were particularly heavy around the reheater and from the bottom of the tower to the 10th stage. Example 1 The 22nd column from the bottom of a carbon steel distillation column with 38 plates.
A side flow nozzle is attached to the stage, and this side flow nozzle and a stainless steel cylindrical hydrogenation reaction tower (Pd
- Alumina catalyst packing) were connected via a line and a reciprocating mini-pump, and the outlet of the reaction column and the 21st stage from the bottom of the distillation column were connected via a line. Using such a distillation column, a hydrocarbon fraction containing acetylenic hydrocarbons obtained by thermal decomposition of naphtha was supplied from the bottom of the distillation column to the 27th stage. Distillation was carried out at a top pressure of 11.6 kg/cm ² G and a bottom temperature of 91
The reaction was carried out under reflux conditions at a tower top temperature of -30°C. The liquid phase hydrocarbon fraction in the 22nd stage of this distillation column (temperature 60
℃) was extracted by a pump, and after hydrogen was introduced from outside the system and combined, the mixture was fed into a hydrogenation reaction tower. The product at the outlet of the reaction column was returned to the 21st stage of the distillation column. The operating conditions around the reaction tower were as follows. LHSV 15 Temperature (inlet/outlet) 60℃/61℃ Pressure 12Kg/cm ² G Hydrogen/Acetylene (mole ratio) 1.8 After setting the conditions, continue operation for 30 days, then open the distillation column and remove the deposits inside the column. I took it out. As a result, the amount of scale was reduced to 38 g compared to the comparative example. In the comparative examples and examples above, the vinyl acetylene concentration and metal acetylene concentration in each tray were investigated, and the concentrations were determined in Figures 3 and 4.
As shown in the figure. The solid line in the figure is a comparative example, and the dotted line is an example. From FIG. 3 and FIG. 4, it can be seen that according to the example, the concentrations of methyl acetylene and vinyl acetylene below the 21st stage are drastically reduced compared to the comparative example. Further, Table 1 shows the composition of the hydrocarbons supplied, the composition of the top product, and the bottom product in Comparative Examples and Examples. Furthermore, in the Examples, the composition of the hydrocarbons fed to the hydrogenation reaction tower and the composition of the hydrocarbons at the outlet of the hydrogenation reaction tower are shown in Table 2.

【table】

【table】

[Table] From Tables 1 and 2, it is clear that, according to the present invention, when all of the fraction in the column is extracted from the middle stage of the distillation column as a side stream and acetylene hydrocarbons are selectively hydrogenated, the acetylene hydrocarbons are It can be seen that hydrocarbons are almost completely removed and are not included in the bottom product.

[Brief explanation of the drawing]

Figure 1 is a schematic explanatory diagram of a steam cracking device used in the present invention, and Figure 2 is a steam cracking device for selectively hydrogenating acetylenic hydrocarbons among hydrocarbons containing acetylenic hydrocarbons. FIG. 3 and FIG. 4 are explanatory diagrams of the distillation column of methyl acetylene and C4 in the distillation column, respectively.
It is a figure showing the concentration of acetylene. 1... Steam cracker device, 2... Steam, 3... Thermal cracking furnace, 4... Rectification column, 6... Compressor, 9... Olefin recovery section, 10... Distillation column in the olefin recovery section , 12...hydrogenation tower.

Claims (1)

[Scope of Claims] 1. When separating and refining olefins from a pyrolysis product of naphtha containing acetylenic hydrocarbons, the pyrolysis product of naphtha is supplied to a distillation column for separating and refining olefins, All of the fraction in the column is extracted as a side stream from the intermediate stage of this distillation column, and after hydrogenating the acetylenic hydrocarbons contained in this side stream in the presence of a selective hydrogenation catalyst for acetylenes, this side stream is A method for separating and purifying olefins from a naphtha thermal decomposition product containing acetylenic hydrocarbons, characterized in that the stream is returned to a lower stage from an intermediate stage from which a side stream of a distillation column is extracted. 2. The method according to claim 1, wherein the distillation column for separating and purifying olefins is a de-ethanizer and/or de-propanizer in a steam cracking device.