JPS62218487A - Method of thermal cracking for production of petrochemicals from hydrocarbon - Google Patents

Abstract

PURPOSE:To decrease the yield of methane and, at the same time, to improve the yields of ethylene and propylene, by producing petrochemicals through thermal cracking of hydrocarbon in the presence of a high-temp. methane-contg. gas heated at a predetermined temp. or above. CONSTITUTION:A starting hydrocarbon 1 is fed into a thermal cracking reactor 2. At the same time, a methane-contg. gas 4 is heated in a heating section 5 at 850 deg.C or above and fed into the cracking reactor 2, where it is mixed with the starting hydrocarbon 1. After the completion of the thermal cracking reaction, a reaction fluid 6 is fed into a quenching device 7 to quench it. The cooled reaction fluid 8 is fed into a separation-purification system 9, where it is separated into a cracked oil 10, an org. hydrocarbon 12, an olefin product 13, a fuel gas 14, a methane contg. gas 15, etc. A part of the methane-contg. gas 15 is circulated into the reactor 2. This brings about an increase in the methyl radical concn. in the reaction system, and the coupling effect thereof contributes to an improvement in the yield of ethylene.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pyrolysis method for producing petrochemical products such as olefins and aromatic hydrocarbons by pyrolyzing hydrocarbons.

[Conventional technology]

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

[Problem that the invention seeks to solve]

In this method, once the raw material is selected, essentially specific cracking conditions and specific equipment are required depending on the requirements of the raw material and product. For this reason, there is a drawback that the selectivity of raw materials and products is poor and flexibility is lacking.

For example, in the current typical naphtha tube cracking furnace, the main focus is on ethylene production, so other basic chemicals such as co-produced propylene, C4 olefin fraction, and BTX are also produced to balance supply and demand. It is difficult to arbitrarily vary the product yield accordingly (product selectivity). That is, if an attempt is made to increase the propylene yield, the ethylene yield, etc. will decrease, and the overall gasification rate will decrease, the amount of low-value liquid components will increase, and the economic efficiency of the plant will deteriorate.

In particular, in recent years, significant progress has been made in energy conservation in plants, and the energy consumption rate for ethylene production has been significantly improved.As a result, fuels such as methane and cracked oil are in surplus. Effective utilization is required.

[Means for solving problems]

The present inventors focused on the problems of the conventional method of tube cracking, and developed a hydrocarbon thermal cracking method that can selectively obtain desired olefins and BTX with a higher yield than the conventional method. As a result of extensive research, we have found that when hydrocarbons are thermally decomposed, methane-containing gas is heated to 850% by external heating.
By supplying this high-temperature methane-containing gas to a reactor to thermally decompose raw material hydrocarbons, the production of fuel components such as methane is suppressed, and olefins and BT are produced.
It was discovered that the product selectivity was significantly improved as the yield of X increased, and the present invention was developed based on this finding.

That is, the present invention provides a method for producing petrochemical products by thermally decomposing hydrocarbons, in which a methane-containing gas is brought to a high temperature of at least 850°C by external heating, and then supplied to a decomposition reactor. The present invention relates to a pyrolysis method for producing petrochemical products from hydrocarbons, characterized by pyrolyzing the hydrocarbons in the presence of hydrocarbons and rapidly cooling the reaction products.

First, the present invention is characterized in that the methane-containing gas is brought to a high temperature of at least 850° C. by external heating and then supplied to the decomposition reactor. In other words, methane converts into active methyl radicals at high temperatures, but this concentration is lower than 850°C.
In the above cases, the amount of methane increases significantly, producing the revolutionary effects of methane as described below, and also plays a role in supplying the 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 increased (in internal heating, combustion gas is used as the heating medium). (The methane-containing gas is diluted because it is mixed with methane, which is the fluid to be heated.) As a result, methane can be highly activated even if the preheating temperature of the methane-containing gas is relatively low.Secondly, methyl radical This effect can be obtained at relatively low temperatures (that is, if the methane concentration is high, the methyl radical effect can be obtained at low temperatures because it is highly activated even at low temperatures), and the yield of propylene and C4 olefin fractions increases. There are advantages such as

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

Firstly, if the temperature of the reactant fluid at the point where the high-temperature methane-containing gas is supplied is low, the methyl radicals generated at the above-mentioned high temperature will be quenched and lose their effectiveness, and secondly, the feedstock hydrocarbons will be decomposed to some extent. By supplying a high-temperature methane-containing gas to a state where lower olefins are produced, active methyl radicals react with these olefins to achieve the improvement in yield and product selectivity as intended by the present invention. This is because it is possible.

Further, although there is no particular restriction on the amount of methane to be supplied, the higher the temperature of the methane-containing gas to be supplied, the higher the concentration of activated methyl radicals, so the same effect can be achieved with a smaller amount of methane.

On the other hand, there is no particular restriction on the methane concentration in the methane-containing gas to be supplied, but the higher the methane concentration, the higher the concentration of methyl radicals, so it is preferable to supply the gas in a state of as high a concentration as possible. However, when attempting to heat highly concentrated methane to a high temperature of 91,000°C or higher by external heating,
At the same time, coking of methane occurs partially, so it is effective to coexist a small amount of hydrogen. The hydrogen supplied in this way contributes not only to suppressing coking but also to activating methane.

Further, the higher the methane concentration in the methane-containing gas to be supplied, the better, and it is preferable that the methane concentration is at least 20 Oat%.

In addition, the pyrolysis reactor used in the present invention may be an externally heated reactor such as a normal tube cracking furnace that is heated from the outside of the reaction tube, but it is also possible to use an externally heated reactor that heats from the outside of the reaction tube. A thermal reactor may also be used. In particular, when the present invention is applied to an externally heated reactor, rapid heating can be achieved using high-temperature methane-containing gas, increasing the decomposition temperature and shortening the decomposition time. As a result, the production of methane and mold-forming compounds due to side reactions is suppressed, and the yield of useful products increases.

As a heat source for generating high-temperature methane-containing gas in the present invention, for example, a heat source for heating a reactor can be used. In other words, in an internally heated reactor, the desired high temperature can be easily achieved by installing a methane-containing gas supply pipe inside the combustion chamber, and in an externally heated reactor, a methane-containing gas supply pipe is installed inside the combustion chamber. It is possible that

As described above, the purpose of the present invention is to convert methane-containing gas into a high-temperature gas of 850°C or higher by external heating, supply this gas to a decomposition reactor to thermally decompose raw material hydrocarbons, and to use the action of this high-temperature methane to thermally decompose raw material hydrocarbons. The aim is to achieve higher olefin yield and product selectivity than before. That is, by decomposing raw material hydrocarbons 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 (CH311) in the reaction system increases significantly, which, together with the effect of increasing the methane partial pressure,
The decomposition reaction of C4 olefin fractions such as propylene and butene into methane is significantly suppressed. As a result, the yield of methane decreases and the yield of propylene, butene, etc. increases.

■ CH111 + ClH4: C5Ha + H・■ For example, with propylene, normally ethylene and methane are produced by the reaction (■), and as a result, propylene decreases and methane increases, but according to the present invention, the reaction (■) Dipropylene is produced by the reaction, and the yield of propylene increases.

Second, the coupling of the methyl radical increases the yield of C components such as ethane and ethylene (reaction (2)).

■ - Horse C horse・+CHs・→C soot 1 → 2 mountains In normal pyrolysis, the increase in ethylene is achieved by the decrease in propylene and increase in methane due to the reaction (■), but according to the present invention , Reaction (2) can be achieved without reducing the amount of propylene, and product selectivity is greatly improved. In particular, in the present invention, by externally heating the methane-containing gas, the methane concentration can be increased compared to internal heating (internal heating). Radical concentration increases. As a result, the yield of propylene and C4 olefin fractions increases greatly, especially due to the effect of reaction (1).

As mentioned above, Wc3 suppresses the production of methane, resulting in an increase in the hydrogen concentration in the reaction system.

Therefore, along with the presence of methane, the radical concentration in the reaction system increases, which promotes the decomposition of feedstock hydrocarbons and suppresses coking in the cracking furnace due to the hydrogenation effect, increasing the gasification rate. has.

Fourthly, due to the above-mentioned coking suppressing effect, it is possible to increase the partial pressure of the raw material hydrocarbon and operate with a reduced amount of diluent gas, thereby reducing the energy consumption rate.

The methane (methyl radical) effect in the present invention is not due to an increase in olefins due to the decomposition of methane supplied from outside the system, but because the methyl radical functions as a catalyst for intermediate products resulting from decomposition of raw materials. This is due to a number of reasons.

This is clear from the fact that, for example, when methane heated to 850-1000°C is supplied, the raw material is interrupted, and the decomposition products are measured by gas chromatography, no methane decomposition products are detected. It is.

As explained above, the present invention is characterized by focusing on the characteristics of methane at high temperatures and actively utilizing these characteristics to thermally decompose hydrocarbons.

As a result, in the present invention, it is possible to achieve a significantly higher yield of polyethylene than in the past, and also to achieve significantly higher propylene and C4 olefin fractions, thereby improving the yield of valuable components and increasing the selectivity for one product.

Next, the method of the present invention will be explained in detail using an example embodiment.

FIG. 1 is an illustrative diagram of an embodiment in which the method of the present invention is applied industrially. This is merely illustrative and does not limit the invention in any way.

In FIG. 1, feedstock hydrocarbon 1 is replaced by 3 as needed.
After preheating 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 heating reactor in which high-temperature combustion gas and raw materials are directly mixed and heated.

Steam 3 may also be supplied to the decomposition reactor 2 as a diluent gas. Furthermore, to the decomposition reactor 2, there is a line 4)
Methane-containing gas is supplied from This methane-containing gas 4 is heated in a heating section 5 installed in the decomposition reactor 2 8.
After being heated to 50° C. or higher, it is mixed with the raw material hydrocarbon 1 in the decomposition reactor 2. The methane-containing gas 4 is preferably supplied to a reaction fluid temperature range of at least 500°C. The decomposed reaction fluid 6 mixed with the hot methane-containing gas stream 4 leaves the decomposition reactor 2 and enters the quenching device 7 where it is quenched 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 a tube. The reaction fluid 8 that has exited the quenching device 7 enters the separation and purification system 9, where it passes through cracked oil 10, wastewater 11, BTX 12.
It is separated into products, tL/fin 13, fuel gas 14, methane-containing gas 15, etc.

Among these, a part of the methane-containing gas 15 is recycled through line 4 to the decomposition system. Note that the separation and purification system 9 actually consists of several steps including various distillation devices (not shown).

〔Example〕

A reaction tube with an inner diameter of 6IIIφ and a length of 4 m was used, and while the reaction tube was heated from the outside, naphtha (boiling point 40 to 140° C., specific gravity = α675) was supplied as a raw material hydrocarbon for thermal decomposition. Naphtha is steamed (25
wt%) and was preheated to 200 to 300°C and supplied to the reactor, and the front part of the reaction tube was used as a preheating part. Methane is supplied to the middle of the decomposition reaction tube by installing a tube with an inner diameter of 61 wφ on the high temperature region side in the same combustion chamber as the reaction tube,
The temperatures of naphtha and methane were measured before and after mixing. The heating is
This was done by burning kerosene.

The produced gas from the reactor outlet was used to indirectly cool the reaction tube from the outside, and after stopping the reaction, the product was analyzed and quantified by gas chromatography. Further, the residence time was calculated from the volume of the reactor and the reaction conditions.

Figure 2 shows the reactor outlet pressure 2. Oata, reactor outlet @ [850°C, residence time approximately 113 seconds, and the decomposition rate was adjusted to be basically constant, and methane was supplied to the reactor at a ratio of 125 (weight ratio) to the raw material. This figure shows the relationship between the preheating temperature of the methane-containing gas and the product yield. The temperature of the naphtha and steam in the reactor during the feeding of methane to the reactor was 650-750°C. As shown in FIG. 2, it can be seen that when the preheating temperature of the methane-containing gas becomes 850° C. or higher, the yields of olefins and hydrogen increase, and the yield of methane decreases.

Also, the temperature of naphtha before mixing with methane-containing gas was
When the temperature was lowered to below 00°C, the increase in yield decreased considerably,
It was necessary to relatively increase the preheating temperature of the methane-containing gas. On the other hand, by increasing the preheating temperature of the methane-containing gas, the amount of methane supplied could be reduced.

〔Effect of the invention〕

As described in detail above, the present invention has the following features that surpass the prior art. That is, by heating the methane-containing gas to a high temperature by external heating and supplying this high-temperature methane-containing gas to a reactor to thermally decompose hydrocarbons,
You can obtain the following effects.

(1) The concentration of methyl radicals in the reaction system increases, and due to the coupling effect, the yield of ethylene ethane, propylene, and C4 olefin fraction can be increased without decreasing the yield of the fraction.

(2) Due to the effect of methane, the decomposition of propylene and C4 olefin fractions is suppressed, the methane yield decreases, and the yield of propylene and C4 olefin fractions increases.

(3) Due to the above effects, the ethylene yield can be increased compared to the conventional method, and the yield of propylene and C4 olefin fractions also increases, resulting in a marked increase in product selectivity.

(4) Methane yield decreases, resulting in increased hydrogen yield. 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, improving energy consumption.

(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, especially the improvement in the yield of propylene and C4 olefin, can be expected.

(6) It is possible to rapidly raise the temperature of the raw material hydrocarbon, and as a result, the decomposition time is shortened, and the decomposition and reduction of C4 olefins such as propylene and butene due to side reactions can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention, and FIG. 2 is a chart showing the effect of preheating temperature of methane-containing gas as an example of the present invention. Sub-agents 1) Meifuku agent Ryo Hagiwara − Sub-agent Atsushi Anzai Plan 2

Claims (1)

[Claims] A method for producing petrochemical products by thermally decomposing hydrocarbons, in which a methane-containing gas is heated to at least 850% by external heating.
℃, the raw material hydrocarbon is supplied to a pyrolysis reactor, the raw material hydrocarbon is thermally decomposed in the presence of the high-temperature methane, and the reaction product is rapidly cooled. Pyrolysis method.