JPH0649867B2 - Pyrolysis method for producing petrochemicals from hydrocarbons - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pyrolysis method for pyrolyzing a hydrocarbon to produce petrochemicals such as olefin and aromatic hydrocarbon.

[Conventional technology]

Conventionally, a tubular pyrolysis method called steam cracking is used as a method for converting light gaseous hydrocarbons such as ethane and propane and liquid hydrocarbons such as naphtha and kerosene into olefins. As is well known.

[Problems to be solved by the invention]

In this method, once a raw material is selected, a specific decomposition condition and a specific device are basically required depending on the requirements of the raw material and the product. For this reason, there is a problem in that the raw materials and products have poor selectivity and lack flexibility.

For example, in the current typical naphtha tube cracking furnace, since ethylene production is the main focus, other basic chemicals such as co-produced propylene, C ₄ olefin fraction and BTX are used as a balance between supply and demand. It is difficult to arbitrarily change the product yield according to the product yield (product selectivity). That is, if an attempt is made to increase the propylene yield, the yield of ethylene and the like will be lowered, and the gasification rate will be lowered overall, the liquid components of low value will be increased, and the economical efficiency of the plant will be deteriorated.

In particular, in recent years, the energy saving of the plant has been greatly advanced, and the energy intensity for producing ethyle has been greatly improved. As a result, the fuels such as methane and cracked oil have a surplus. Effective utilization is required.

[Means for solving problems]

The present inventors have paid attention to such problems of tubular cracking in the conventional method, and have proposed a thermal cracking method for hydrocarbons in which the desired olefin and BTX can be selectively obtained in a higher yield than ever before. As a result of intensive research to develop, methane containing gas was decomposed into iron by 850 by external heating.
As a high-temperature gas of ℃ or higher, and by supplying this high-temperature methane-containing gas to the reactor to pyrolyze the raw hydrocarbons, the production of fuel components such as methane is suppressed, and olefin and BT
It was found that the yield of X is increased and the product selectivity is significantly improved, and the present invention has been completed based on this finding.

That is, the present invention relates to a method for producing a petrochemical product by thermally decomposing hydrocarbons, in which a methane-containing gas is heated to at least 850 ° C. by external heating and then fed to a pyrolysis reactor to detect the presence of the high-temperature methane. The raw hydrocarbons are pyrolyzed under
It relates to a pyrolysis process for producing petrochemicals from hydrocarbons, characterized by quenching the reaction products.

First, the present invention is characterized in that the methane-containing gas is heated to a high temperature of at least 850 ° C. by external heating and then supplied to the decomposition reactor. That is, methane is converted to active methyl radicals at high temperatures, but this concentration is 850 ° C.
By the above, it greatly increases and brings about the epoch-making effect of methane as described later and plays a role of supplying heat necessary for decomposition.

In particular, in the present invention, by heating the methane-containing gas externally, firstly, the methane concentration in the methane-containing gas can be made high (in the internal heating, the combustion gas as a heating medium is , The methane-containing gas is diluted because it is mixed with methane that is a fluid to be heated), and as a result, high activation of methane can be performed even when the preheating temperature of the methane-containing gas is relatively low. Can be obtained at a relatively low temperature side (that is, if the methane concentration is high, it is highly activated even at a low temperature, so that a methyl radical effect can be obtained at a low temperature), and the yield of propylene and C ₄ olefin residue is increased. There are advantages such as

Furthermore, the present invention is characterized in that the methane-containing gas heated to a high temperature is supplied to a thermal decomposition reactor to thermally decompose hydrocarbons. The supply position of the high-temperature methane-containing gas to the decomposition reactor is preferably such that the reaction fluid temperature is at least 500 ° C or higher.

This is because firstly, when the temperature of the reaction fluid at the supply position of the high-temperature methane-containing gas is low, the methyl radicals generated at the high temperature are quenched and lose the effect. Secondly, the raw material hydrocarbon is decomposed to some extent. By supplying a high-temperature methane-containing gas to a state where lower olefins are being produced, active methyl radicals react with these olefins to achieve the intended yield and product selectivity improvement of the present invention. Because you can.

The amount of methane supplied is not particularly limited, but the higher the temperature of the methane-containing gas supplied, the higher the concentration of activated methyl radicals, and the same effect can be achieved with a small amount of methane. On the other hand, the methane concentration in the supplied methane-containing gas is not particularly limited, but the higher the methane concentration, the higher the concentration of methyl radicals, so it is preferable to supply the methane-containing gas in the highest possible concentration. But,
When high-concentration methane is heated to 1000 ° C. or higher by external heating, coking of methane partially occurs at the same time, and it is effective to make a small amount of hydrogen coexist. The hydrogen thus supplied contributes not only to the inhibition of coking but also to the activation of methane. Further, the higher the methane concentration in the supplied methane-containing gas is, the better, and it is preferable that at least 20 vol% is present.

Further, as the thermal decomposition reactor used in the present invention, an external heat type reactor such as an ordinary tube type decomposition furnace which is heated from the outside of the reaction tube is used to decompose the high temperature combustion gas by directly mixing it with the raw material hydrocarbons. It may be a thermal reactor. In particular, when the present invention is applied to an external heat type reactor, a high temperature methane-containing gas enables rapid heating, so that the decomposition temperature can be increased and the decomposition time can be shortened. As a result, the production of methane and the production of liquid polymer due to side reactions are suppressed, and the yield of useful products is increased.

As the heat source for generating the high-temperature methane-containing gas in the present invention, for example, a heat source for heating the reactor can be used. That is, in the internal heat type reactor, the target high temperature can be easily achieved by installing the methane-containing gas supply pipe in the combustion chamber, and in the external heat reactor, the methane-containing gas supply pipe is installed in the combustion chamber. It is possible.

As described above, the object of the present invention is to externally heat a methane-containing gas into a high-temperature gas of 850 ° C. or higher, supply the gas to a cracking reactor to thermally decompose the raw material hydrocarbons, , To achieve higher olefin yield and product selectivity than ever before. That is, by decomposing the raw material hydrocarbon in the presence of methane heated to a high temperature of 850 ° C. or higher, the following effects can be obtained.

First, the concentration of methyl radicals (CH ₃ ·) in the reaction system markedly increased, and in combination with the effect of increasing the partial pressure of methane, the decomposition reaction of C ₄ olefin residues such as propylene and butene into methane was significantly suppressed. It As a result, the yield of methane decreases and the yield of propylene, butene, etc. increases.

For example, in the case of propylene, ethylene and methane are produced by a normal reaction, and as a result, propylene is reduced and methane is increased, whereas according to the present invention, propylene is produced by the reaction of and the yield of propylene is Is increasing.

Secondly, due to the coupling of the methyl radical, the yield of the C component such as ethane and ethylene is increased (reaction).

In normal pyrolysis, the increase of ethylene can be achieved by the decrease of propylene by the reaction and the increase of methane, whereas according to the present invention, the effect of the reaction can be achieved without the decrease of propylene. The selectivity is greatly improved. Particularly, in the present invention, by externally heating the methane-containing gas, the methane concentration can be increased as compared with the internal heating (internal heating type heating), and as a result, methyl at a relatively low temperature side of 850 ° C. or higher can be obtained. Radical concentration increases. As a result, the increase in the yields of propylene and C ₄ olefin residue is increased due to the effect of the reaction.

Thirdly, as described above, as a result of suppressing the production of methane, the hydrogen concentration in the reaction system increases. Therefore, with the presence of the above-mentioned methane, the radical concentration in the reaction system increases, promoting the decomposition of the raw material hydrocarbons and suppressing the coking in the cracking furnace by the hydrogenation effect to increase the gasification rate. Have.

Fourthly, due to the above-mentioned coking suppression effect, the partial pressure of the raw material hydrocarbon can be increased to enable the operation in which the amount of the diluent gas is reduced, and the energy consumption rate can be reduced.

Note that the methane (methyl radical) effect in the present invention does not mean that olefins are increased due to the decomposition of methane supplied from outside the system, and that the methyl radical functions catalytically to the intermediate product due to the decomposition of the raw material. It is by doing.

This is clear from the fact that, when methane superheated at 850 to 1000 ° C. is supplied, the decomposition products are measured by gas chromatography analysis while the raw materials are interrupted, the decomposition products of methane are not detected at all. Is.

As described above, the present invention is characterized by paying attention to the characteristics of methane at high temperature and positively utilizing this to thermally decompose hydrocarbons. As a result, in the present invention, a significantly higher ethylene yield than in the past can be achieved, and the propylene and C ₄ olefin residues can also be made extremely high, the yield of valuable components can be improved, and the product selectivity can be increased.

Next, the method of the present invention will be described in detail with reference to one embodiment.

FIG. 1 is an illustration of an embodiment in which the method of the present invention is applied industrially. This is for illustration only and in no way limits the invention.

In FIG. 1, the raw material hydrocarbon 1 is 3
After preheating up to around 00 to 500 ° C., it enters the decomposition reactor 2.
The decomposition reactor 2 may be an ordinary tube-type decomposition furnace or an internal heat type reactor for directly mixing and heating high temperature combustion gas and raw materials. Steam 3 may be further supplied to the split reactor 2 as a diluent gas. Furthermore, in the decomposition reactor 2,
A methane-containing gas is supplied from line 4. The methane-containing gas 4 is heated by a heating unit 5 provided in the cracking reactor 2 to be heated to 850 ° C. or higher, and then mixed with the raw material hydrocarbon 1 in the cracking reactor 2. The supply position of the methane-containing gas 4 is preferably supplied to the reaction fluid temperature range of at least 500 ° C. The reaction fluid 6 mixed with the high temperature methane-containing gas stream 4 and decomposed exits the decomposition reactor 2 and enters a quenching device 7 where it is rapidly cooled and heat is recovered. Examples of the quenching device 7 include an indirect quenching heat exchanger that exchanges heat between two fluids inside and outside the pipe. Reaction fluid 8 exiting quenching device 7
Enters the separation and purification system 9 and decomposed oil 10, wastewater 11, BT
X12, product olefin 13, fuel gas 14, methane-containing gas 15 and the like are separated. Among them, a part of the methane-containing gas 15 is recycled to the decomposition system through the line 4.
The separation / purification system 9 actually includes several steps including various distillation devices (not shown).

〔Example〕

Using a reaction tube having an inner diameter of 6 mmφ and a length of 4 m, naphtha (boiling point 40 to 140 ° C., specific gravity = 0.675) was fed as a raw material hydrocarbon while heating the reaction tube from the outside to thermally decompose it. Naphtha is steam (25 wt% relative to naphtha)
Together with preheating to 200-300 ° C. and supplying to the reactor,
The front part of the reaction tube was used as a preheating part. For methane, a tube having an inner diameter of 6 mm was also installed on the high temperature region side in the same combustion chamber as the reaction tube, and was supplied in the middle of the decomposition reaction tube, and the temperatures of naphtha and methane before and after mixing were measured. The heating was performed by burning kerosene. With respect to the product gas from the reactor outlet, the reaction tube was indirectly cooled from the outside to stop the reaction, and then the product was analyzed and quantified by gas chromatography. The residence time was calculated from the reactor volume and reaction conditions.

Figure 2 shows the reactor outlet pressure of 2.0ata, the reactor outlet temperature of 830 ° C, the residence time of about 0.3 seconds, and the decomposition rate was adjusted to be basically constant. On the other hand, the relationship between the methane-containing gas preheating temperature and the product yield when supplied at 0.25 (weight ratio) is shown. The temperature of the naphtha and steam of the reactor at the time of supplying methane to the reactor was 650 to 750 ° C. From FIG. 2, it is understood that when the preheating temperature of the methane-containing gas becomes 850 ° C. or higher, the yields of olefin and hydrogen increase and the methane yield decreases.

In addition, the temperature of the naphtha before mixing with the gas containing methane is 5
When the temperature was set to 00 ° C or lower, the increase in yield was considerably reduced,
It was necessary to increase the preheating temperature of the methane-containing gas relatively. On the other hand, when the preheating temperature of the methane-containing gas was increased, the amount of methane supplied could be reduced.

〔The invention's effect〕

As described in detail above, the present invention has the following features over the prior art. That is, the methane-containing gas is heated to a high temperature by external heating, and the high-temperature methane-containing gas is supplied to the reactor to thermally decompose the hydrocarbon,
The following effects can be obtained.

(1) The concentration of methyl radicals in the reaction system is increased, and the coupling effect can increase the yield of ethyleneethane without depending on the decrease in the yields of propylene and C ₄ olefin residues.

(2) Due to the effect of methane, the decomposition of propylene and C ₄ olefin residue is suppressed, the methane yield is reduced, and the yield of propylene and C ₄ olefin residue is increased.

(3) Due to the above effects, the ethylene yield can be increased as compared with the conventional method, and the yields of propylene and C ₄ olefin fractions are also increased, resulting in a marked increase in product selectivity.

(4) The methane yield is reduced, and as a result, the hydrogen yield is increased. Coking is suppressed by the effect of methane and the hydrogenation effect of increasing hydrogen. As a result, it can be operated at a low dilution ratio and the energy consumption rate can be improved.

(5) By externally heating the methane-containing gas, a high concentration of methyl radicals is generated at a relatively low temperature, and the above-mentioned effects of methane, particularly the propylene and C ₄ olefin s yield can be improved.

(6) The temperature of the raw material hydrocarbon can be rapidly raised, and as a result, the decomposition time can be shortened and the decomposition and reduction of C ₄ olefin such as propylene and butene due to a side reaction can be suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention, and FIG. 2 is a table showing an effect of a preheating temperature of a methane-containing gas as an example of the present invention.

Claims (1)

[Claims] 1. A method for producing a petrochemical product by pyrolyzing a hydrocarbon, wherein a methane-containing gas is heated to at least 850 ° C. by external heating and then fed to a pyrolysis reactor in the presence of the high-temperature methane. Pyrolysis method for producing petrochemicals from hydrocarbons, characterized in that raw hydrocarbons are pyrolyzed in the above step and reaction products are rapidly cooled.