JPS62246991A - Thermal cracking treatment for cracked heavy fraction - Google Patents

Abstract

PURPOSE:To continuously obtain cracked gas oil at a high thermal cracking reaction efficiency and high yield, by thermally cracking heavy fraction of cracked oil, obtained from thermal cracking of petroleum heavy oil, in the presence of a specific aromatic solvent while inhibiting occurrence of coking. CONSTITUTION:Petroleum heavy feed stock oil is introduced into a cracking furnace 1 from a line 7, where it is thermally cracked, and further cracked in the first tank reactor 2. Gaseous matter containing cracked oil is transmitted into a fractional distillation column 4, while liquid pitch is mixed with a thermal cracking product of the cracked heavy fraction from a line 14 to be introduced into the second tank reactor 3 and the mixture is thermally cracked under the same conditions as those of the previous step. A gaseous matter containing the cracked oil is transmitted into the column 4 and a liquid pitch is discharged. Subsequently the gaseous matter containing the cracked oil is put under fractional distillation in the column 4, and the cracked gas and cracked gas oil are discharged from lines 20 and 19, respectively. After passing through a line 18, the cracked heavy fraction is mixed with an aromatic solvent from a line 21 containing a component not containing toluene-isoluble ingredient, the solvent parameter of which is 8.0-10.0 and presents a liquid phase in the reaction. The mixture is thermally cracked in the second cracker 5, and further cracked in the third tank reactor 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for continuously pyrolyzing a heavy fraction of cracked oil obtained by pyrolysis of petroleum heavy oil.

[Prior art]

When pyrolyzing heavy petroleum oil to obtain cracked oil and pitch,
It is known that the heavy fraction of cracked oil (cracked heavy oil) is further pyrolyzed to obtain more light fractions, for example,
According to JP-A No. 59-157180, in order to obtain a light fraction, the cracked heavy fraction is passed through a reaction system different from the cracking reaction system of raw material heavy oil, that is, a cracking heating furnace and a soaker. A method of thermal decomposition treatment using a reaction system consisting of a combination of the following has been proposed.

In this case, the cracked heavy fraction is thermally cracked under conditions that are more severe than the thermal cracking conditions of the feedstock heavy oil, that is, at a higher temperature.

By the way, when trying to increase the thermal decomposition reaction rate in order to increase the yield of light fractions in the thermal decomposition treatment of such decomposed heavy fractions, the polycondensation reaction proceeds rapidly at the same time as the thermal decomposition reaction. As a result, polycondensation compounds typified by n-hebutane-insoluble matter are produced. Since this polycondensation compound has poor compatibility with aliphatic cracked oil, it causes phase separation and adheres to the tube of the cracking heating furnace, causing coking trouble. In addition, in thermal decomposition treatment in a soaker, as the reaction progresses, the amount of n-hebutane insoluble components increases, and toluene insoluble components that have undergone further polycondensation are also produced, causing changes in the temperature of the decomposition reaction system and hydrocarbons. Depending on the partial pressure, if the pyrolysis reaction rate exceeds a certain limit, coking in the soaker becomes significant. Therefore, in the conventional method, it is necessary to suppress the thermal decomposition reaction rate below a certain limit value, which is still unsatisfactory in terms of equipment design and economic efficiency.

〔the purpose〕

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for thermally decomposing a cracked heavy fraction, which overcomes the above-mentioned drawbacks found in the prior art.

〔composition〕

According to the present invention, the heavy fraction of cracked oil obtained by pyrolysis of petroleum-based heavy oil is treated with a solubility parameter of 8.0 to 10.
0, is substantially free of toluene-insoluble components, and contains components that exhibit a liquid phase in the reaction system. A method for thermally decomposing a cracked heavy fraction is provided, the method comprising thermally decomposing a heavy fraction using a combination of the following methods.

The cracked heavy fraction used in the present invention refers to the heavy fraction of cracked oil obtained by thermally cracking petroleum heavy oil, and usually has a boiling point in the range of 370 to 550°C. In this case, petroleum-based heavy oils include, in addition to residual oils from normal pressure or vacuum distillation of crude oil, various fractional residue oils, solvent deasphalted asphalt, natural asphalt, oil refinery residues obtained from tar sands, and the like.

In the present invention, when the 1-cracking heavy fraction is thermally decomposed using a decomposition heating furnace or a decomposition heating furnace and a seed reactor,
Thermal treatment of the cracked heavy fraction.

The reaction is carried out in the presence of an aromatic solvent having a solubility parameter of 8.0 to 10.0, substantially free of toluene-insoluble components, and containing components exhibiting a liquid phase in the reaction system. According to the research of the present inventors, in the thermal decomposition treatment of such cracked heavy fractions, coking troubles in the single cracking heating furnace can be effectively prevented, and the problem of coking in the cracking heating furnace and the barrel reactor can be effectively prevented. It has been found that coking troubles in the barrel reactor can also be effectively prevented when the combination is used.

The aromatic solvent used in the present invention has a solubility parameter in the range of 8.0 to 10.0. If the solubility parameter is less than 8.0, the effect of effectively preventing coking troubles in the decomposition heating furnace will be weakened, making it necessary to use a large amount of solvent, which is economically undesirable.

The solubility parameters shown herein are defined by the following formula. Although the solubility parameter expressed by this formula is somewhat different from the solubility parameter in the strict sense that includes temperature factors, it is sufficiently effective as an approximate formula for determining the solubility parameter of hydrocarbon compounds ( Literature: D,M.

Riggs, R.J., Diefendorf: ”
14th Biennial, Conf, onCar
bon”, Extended Abstract
, USA, p. 407.1979).

δ=-11,8(1/(1+C/1())+M,8
(I) δ: Solubility parameter C/H: Atomic ratio of carbon and hydrogen of hydrocarbon Next, the solubility parameters of petroleum hydrocarbons represented by the above formula are shown in the table below.

Table 1 In addition, the solvent used in the present invention is one that does not substantially contain toluene-insoluble components, and when it contains toluene-insoluble components,
The toluene-insoluble components are heated in a decomposition heating furnace and become higher molecular components, which themselves become the cause of coking. Furthermore, the aromatic solvent used in the present invention needs to contain a component that exhibits a liquid phase under one reaction condition.

Even if the solubility parameter is 8.0 or higher, those that become a gas phase under the reaction conditions do not exhibit a solvent effect.
It cannot be used effectively. The amount of solvent used in the present invention is:
Usually, the ratio is such that the component exhibiting a liquid phase in the reaction system is 1 to 50% by weight, preferably 5 to 20% by weight, based on the cracked heavy fraction. The specific type of solvent and its addition ratio are as follows: When the mixed oil obtained by adding the solvent to the cracked heavy fraction is maintained under the reaction conditions of a pyrolysis furnace, the boiling point (T( The solubility parameter of the fraction above 760)) should be selected to be 7.7 or higher. In this case, the normal pressure equivalent boiling point (T(760)) This indicates the flash conditions for the product, and is determined by the temperature and hydrocarbon partial pressure, and is expressed by the following linear equation.

T (760): Boiling point converted to normal pressure (°F) TP: Operating temperature (°) P = Hydrocarbon partial pressure (a7,) C1 = 8.4682 C2 = -6625,2 C:l = 0.21528X10 ' Specific examples of the solvent used in the present invention include, for example.

Fluid catalytic cracking residual oil (solubility parameter 28.8-9.6
), ethylene bottom (solubility parameter: 9.0-9.9
), liquefaction solvents recycled in the coal liquefaction process (solubility parameter 2: 8.0 to 9.1), and the like. Fluid catalytic cracking residue oil is distilled to obtain a fraction with a boiling point of 420 to 538°C (solubility parameter: 8.5 to 9
．． 1) is a particularly preferred solvent that can be used in the present invention.

In the present invention, first, the mixture of the solvent and the decomposed heavy fraction is thermally decomposed in a decomposition heating furnace. In the case of the present invention, the thermal decomposition reaction rate of the 1-cracking heavy fraction can be set higher than that in a conventional cracking heating furnace, and the thermal decomposition reaction rate of the 1-cracking heavy fraction can be set higher than the thermal decomposition reaction rate of the 1-cracking heavy fraction. It is carried out at a pyrolysis reaction rate. This limit thermal decomposition reaction rate means the maximum thermal decomposition reaction rate that does not cause coking when the cracked heavy fraction is heat-treated in a decomposition heating furnace without adding a solvent.
It is defined as the maximum thermal decomposition reaction rate without the by-product of sludge (solid phase polycondensation compound) in the thermal decomposition product obtained from the decomposition heating furnace. Generally speaking, when a cracked heavy fraction is pyrolyzed without adding a solvent, if the pyrolysis reaction rate is increased above a certain limit value, the polycondensation reaction will continue to occur in the pyrolysis product. Sexual sludge will now be generated. It is known that coking troubles occur when such reaction conditions are adopted. Therefore, the limit thermal decomposition reaction rate corresponds to the upper limit thermal decomposition reaction rate without producing this sludge as a by-product. This critical thermal decomposition reaction rate is related to the properties of the decomposed heavy fraction; those with high aliphaticity tend to cause coking, so the value is small, while those with high aromaticity tend to cause coking. Its value becomes larger.

The reaction conditions in the decomposition heating furnace are generally a temperature of 450 to 520°C, preferably 480 to 520°C.

Pressure crab 0.3-100kg/cnTG, reaction time:
Conditions of 0.5 to 10 minutes are adopted. 1 in this decomposition heating furnace.

As described above, the thermal decomposition treatment is carried out at a temperature above the critical thermal decomposition reaction rate, and this thermal decomposition reaction rate can be adjusted by adjusting the reaction temperature, reaction pressure, and residence time.

In the present invention, if necessary, the product from the decomposition heating furnace can be further thermally decomposed using a seed reactor after the decomposition heating furnace.

In this case, the reaction conditions in the seed reactor are a temperature of 380
~450℃, hydrocarbon partial pressure 20.5~5 atm (absolute pressure)
, reaction time: 5 to 360 minutes, preferably 30 to 180 minutes. The thermal decomposition reaction rate in this seed type reactor can be controlled by the reaction temperature, hydrocarbon partial pressure, and reaction time, and when the reaction temperature and reaction pressure are held constant, it can be controlled by the reaction time. In this type of reactor, liquid pitch and gaseous products containing cracked light oil are produced.

As the decomposition heating furnace, one equipped with an external heating large tube type reactor is used, and the barrel type reactor is a single reaction type, and the reactor structure is not particularly limited, and continuous type, semi-batch type, etc. Either of the complete mixing type and the extrusion flow type may be used.

Preferably, it is of the seed type with an internal stirring device.

This seed type reactor may be of a type using a wet wall system or a scraper, etc., in order to keep the reactor wall clean, if necessary. One barrel reactor may be used, or two or more barrel reactors may be used in combination. If one seed reactor is used, it is advantageous to use a thoroughly mixed type. In the present invention, when performing thermal decomposition treatment using a decomposition heating furnace and one seed reactor, the conditions for the seed reactor are: reaction temperature: 400 to 450°C, hydrocarbon partial pressure 1 to 5 atm. , a reaction time of 30 to 180 minutes is preferably employed.

Next, the present invention will be explained in more detail with reference to the drawings. 1st
In the figure, ■ is the first decomposition heating furnace, 2 is the first barrel reactor, 3 is the second tank reactor, 4 is the fractionating column, 5 is the second decomposition heating furnace, and 6 is the third tank reactor. Each vessel is shown.

The raw material oil is introduced into the decomposition heating furnace 1 through line 7, where it is subjected to thermal decomposition treatment, and then through line 8, where it is subjected to thermal decomposition treatment in the first barrel reactor 2. This first tank reactor 2
The gaseous material containing cracked oil generated in the line 12
through line 11 to fractionation column 4, while liquid pitch is withdrawn through line 11, mixed with the pyrolysis products of the cracked heavy fraction from line 14, and passed through line 13 to a second Introduced into a tank reactor. The gaseous material containing cracked oil produced in this second tank reactor 3 is extracted through line 16 and sent to the fractionating column 4 through line 17, and the liquid pitch is passed through line 15 to produce products. It is extracted as a pitch.

The gaseous material containing cracked oil sent to the fractionating column 4 is fractionated here, and the cracked gas is extracted from the top of the column through line 20, and the cracked light fraction is extracted through line 19. served,
A cracked heavy fraction is withdrawn through line 18. The cracked heavy fraction extracted through this line 18 is
After being mixed with the aromatic solvent from the line 21, it is introduced into the second decomposition heating furnace 5, where it is subjected to a thermal decomposition treatment.
It is introduced into the third tank reactor 6 through line 22, where it is further subjected to thermal decomposition treatment. The gaseous material containing the cracked light oil produced in this third tank reactor 6 is transferred to the line 23.
and is sent to the fractionating column 4 through line 17, while the thermal decomposition products of the generated cracked heavy fraction are introduced into the second tank reactor 3 through line 14.

In the present invention, the aromatic solvent mixed into the cracked heavy fraction through the line 21 has a solubility parameter of 8.0 to 1000, preferably 8.5 to 10.0, and substantially Use one that does not contain toluene-insoluble components.

In the present invention, when the mixture of the aromatic solvent and the decomposed heavy fraction is thermally decomposed in the decomposition heating furnace 5, the thermal decomposition reaction rate of the decomposed heavy fraction is as follows.

The pyrolysis reaction rate can be higher than that in a conventional decomposition heating furnace, and the pyrolysis reaction rate is usually higher than the limit pyrolysis reaction rate for one cracked heavy fraction.

Note that the thermal decomposition reaction rate referred to here in relation to the critical decomposition reaction rate is expressed by the following formula.

HaR: Boiling point 370°C or higher component-based thermal decomposition reaction rate (%) A:
Weight B of components with a boiling point of 370° C. or higher in the feedstock oil: Weight cracking of components with a boiling point of 370° C. or higher in the pyrolysis treatment product When the heavy fraction alone is pyrolyzed in a decomposition heating furnace,
When the thermal decomposition reaction rate becomes 30 to 35%, a large amount of n-heptane insoluble components are produced, and coking becomes significant. The solubility parameter of the liquid phase product at this time is the normal pressure equivalent boiling point (T
(760))), but 1 usually 7.4 ~
It is 8.0. On the other hand, the solubility parameter of the n-hebutane insoluble component is 8.9 to 9.5, which is higher than that of the liquid phase product, so the n-hebutane insoluble component is not dissolved in the liquid phase product as a matrix. It is thought that this causes the solid phase to separate as a solid phase, and as a result, coking occurs. In contrast, according to the present invention, the solubility parameter 8.
In the case of thermal decomposition treatment with the aromatic solvent of 0 to 1010, even if the thermal decomposition reaction rate is as high as 40 to 45%,
Caulking does not occur. In this case, the amount of n-hebutane insoluble components was about 0.6 to 6.0%, and although it does not mean that the n-hebutane insoluble components were significantly suppressed by the addition of the aromatic solvent, The solubility parameter of the liquid phase product increases. Therefore, this is the reason why caulking does not occur in the case of the present invention.

It is thought that this is because separation of the n-hebutane-insoluble component from the liquid phase is prevented as a result of the improvement in the dissolving power of the liquid-phase component for the rho-hebutane-insoluble component due to the increase in the solubility parameter of the liquid-phase component.

Further, the aromatic solvent used in the present invention also undergoes a thermal decomposition reaction under the above thermal decomposition treatment conditions, and its solubility parameter becomes even higher, thereby preventing coking trouble in the subsequent third tank reactor 6. It acts effectively. In the second decomposition heating furnace 5, the n-hebutane insoluble component in the thermal decomposition product is generally 10% by weight or less, preferably 3.0 to 6% by weight.
．． It is preferable to carry out thermal decomposition treatment so that the content is in the range of 0% by weight.

In the third tank reactor 6, the thermal decomposition product obtained in the 1-decomposition heating furnace 5 is further subjected to thermal decomposition treatment. In this type reactor 6, the toluene insoluble component in the liquid decomposition product is 3.5
The thermal decomposition treatment is preferably carried out so that the amount is less than 2.5% by weight, preferably less than 2.5% by weight.

If the amount of toluene-insoluble components exceeds this range, it will be difficult to prevent coking troubles in the seed reactor 6.

In this third barrel-shaped reactor 6, the 1-decomposition heavy fraction is further thermally decomposed, but at the same time, the polycondensation reaction proceeds, and the amount of n-hebutane insoluble components further increases, and toluene insoluble components are also produced. Begin to. In the case of a conventional seed reactor, the reaction pressure is generally low, so that the aliphatic light cracked oil is flushed out of the reaction system, and the solubility parameter of the liquid phase product increases. However, under such low pressure conditions, it is difficult to proceed with the thermal decomposition reaction of the 1-cracking heavy fraction. Generally speaking, in order to effectively thermally decompose a cracked heavy fraction to make it lighter, it depends on the reaction temperature, but
The hydrocarbon partial pressure of the reaction system is 1 atm or more, preferably 1.5
It is necessary to adopt conditions such that the pressure is higher than atmospheric pressure; if the hydrocarbon partial pressure is too low, the hydrocarbon components to be decomposed will not remain in the reaction system and will be stripped. However, under the conditions of high hydrocarbon partial pressure as described above, although the thermal decomposition reaction proceeds, more toluene-insoluble components are produced, and coking occurs in the liquid phase of the reactor. However, in the present invention, as mentioned above, since a specific aromatic solvent is present in the reaction system, in the seed reactor,
Even if the hydrocarbon partial pressure is increased to further advance the thermal decomposition reaction, coking can be prevented from occurring. That is, 1
In the case of the present invention, an aromatic solvent having a high dissolving power for polycondensation compounds such as toluene-insoluble components is present in the reaction system, and this aromatic solvent is itself thermally decomposed in the decomposition heating furnace in the previous stage. As a result of the reaction, its solubility parameter increases and its ability to dissolve toluene-insoluble components further improves, so that coking can be effectively suppressed even under hydrocarbon partial pressure conditions of 1.5 atmospheres or higher.

The liquid decomposition product obtained in the third tank reactor 6 is introduced into the second tank reactor 3. Note that depending on the properties of the liquid decomposition product, it may be introduced into the first barrel reactor 2.

Next, regarding the thermal decomposition treatment conditions employed in the thermal decomposition treatment of feedstock oil, the reaction conditions in the decomposition heating furnace I are generally temperature = 450 to 52 (Ic, preferably 485 to 520°C, The conditions of pressure crab normal pressure ~ 20 kg/cjG and reaction time = 0.5 ~ 5 minutes are adopted.In this decomposition heating furnace, the thermal decomposition reaction rate based on the raw material oil is 10
~50%, preferably 20-40%.

The thermal decomposition reaction rate based on the raw material oil is expressed by the following formula.

R': Thermal decomposition reaction rate based on the component with a boiling point of 538°C or higher A' Weight of the component with a boiling point of 538°C or higher in the two feedstock oils B' : Weight of the component with a boiling point of 538°C or higher in the thermal decomposition product First tank The reaction conditions in the type reactor 2 and the second tank type reactor 3 are: reaction temperature = 380-450°C, reaction pressure = 100°C.
m+++I1g~5kg/a#G, reaction time: 5~1
20 minutes, preferably 30 to 60 minutes. These seed reactors can be supplied with reduced pressure or steam to reduce the hydrocarbon partial pressure l.
It is operated under conditions of oo to SOOmmHg. The total thermal decomposition reaction rate of the first tank reactor 2 and the second tank reactor 3 is 20 to 55% based on the raw material oil.

As the decomposition heating furnaces 1 and 5, those equipped with externally heated large tube type reactors are used, and the seed type reactors 2゜3 and 6 are
The reaction type and reactor structure are not particularly limited, and may be either a continuous type or a semi-batch type, a complete mixing type, or an extrusion flow type. This type of reactor is preferably equipped with an internal stirring device, and if necessary, it can be of a type using a wet wall system, a scraper, etc. in order to keep one reactor wall clean.

Various modifications are possible when carrying out the invention; for example, in the pyrolysis treatment of cracked heavy fractions.

The third tank type reactor 6 can be omitted and the decomposition treatment can be performed using only the decomposition heating furnace 5, and when the raw oil is thermally decomposed, one One or more seed reactors may be used; in addition, aromatic solvents may be added to the cracked heavy fraction in line 18;
At the same time, it can also be added to the feedstock oil in line 7. Furthermore, the aromatic solvent can be added only to the feedstock in line 7 instead of being added to the cracked heavy fraction in line 18. In this case, the aromatic solvent is used in the first decomposition heating furnace 1. It passes through the first and second tank reactors 2 and 3, passes through the inlet 17 and enters the fractionating column 4, and the line 18
It is extracted in the form of a mixture with the cracked heavy fraction and introduced into the cracking heating furnace 5. When an aromatic solvent is added to the feedstock oil as described above, the aromatic solvent is added to the first and second decomposition heating furnaces 1 and 5, and the first . 2nd and 3rd
Since it is introduced into each of the barrel reactors 2 and 3.6, it is possible to effectively suppress the occurrence of coking troubles in the entire apparatus.

In addition, when an aromatic solvent is added to feedstock oil, the thermal decomposition treatment in the 1-cracking heating furnace 1 is performed at a rate higher than the critical cracking reaction rate of 1M feedstock, as in the case of addition to the cracked heavy fraction. It is preferable to do so. Also.

As the fractionating column 4, one consisting of a plurality of fractionating columns can also be used.

〔effect〕

As described above, the present invention thermally decomposes the cracked heavy fraction in the presence of a specific aromatic solvent, thereby achieving a high thermal decomposition reaction rate and preventing the occurrence of coking. As a result, the yield of lightened cracked oil can be significantly improved.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example I Middle East vacuum residual oil was thermally decomposed using a combination of a decomposition heating furnace and a seed reactor, and the resulting cracked oil was subjected to fractional distillation. A cracked heavy fraction with the properties shown was obtained.

Table 2 (Properties of cracked heavy fraction) Next, 30 parts by weight of the aromatic solvent (fluid catalytic cracking residual oil) shown in Table 3 below was mixed with 70 parts by weight of the cracked heavy fraction. This mixed oil (dissolution parameter: 8.1) was supplied to a decomposition heating furnace at a flow rate of 500 g/hour, and thermally decomposed at a temperature of 500°C, a pressure of 10 kg/aJG, and a reaction time of 2 minutes. completely mixed reactor (inner volume 1.2
g) at a reaction temperature of 425°C and a reaction pressure of 1.03k.
Further thermal decomposition treatment was carried out under the conditions of g/cjG and average residence time of 130 minutes.

Table 3 (Properties of solvent) When the reaction was carried out continuously for 12 hours as described above, no increase in the supply pressure of the cracked heavy fraction to the cracking heating furnace was observed, and the operation was terminated. Afterwards, the inside of the reaction tube of the decomposition heating furnace was inspected, but almost no coking was observed.

Next, the thermal decomposition products obtained by the above thermal decomposition treatment were analyzed, and the thermal decomposition reaction rate based on the decomposed heavy fraction was determined to be 42.4%, and the residual oil produced was 42.4%. The toluene-insoluble component in the solution was 14.6%. In addition, during the pyrolysis reaction, a part of the product from the decomposition heating furnace was sampled and analyzed, and the pyrolysis reaction rate based on the decomposed heavy fraction was determined to be 32.9%. The amount of toluene-insoluble components in the produced oil was 0%.

In addition, in the said thermal decomposition process, as a raw material oil.

Continuous operation was performed for 6 hours in the same manner except that only the aromatic solvent was used. The thermal decomposition reaction rate in the decomposition heating furnace at this time was 5.2%, and the overall thermal decomposition reaction rate including the seed reactor was 7.4%.

Comparative Example 1 Only the cracked heavy fraction shown in Example 1 was used as the raw material oil, and was supplied to a cracking heating furnace at a flow rate of 500 g/hour, and the temperature was 500 g/hour.
When thermal decomposition treatment was carried out under the conditions of ℃, pressure 10 kg/cJG, and reaction time 2 minutes, a rapid decrease in the amount of generated gas was observed, indicating that rapid coking was progressing in the decomposition heating furnace. When the product was analyzed 8 hours after the start of operation, the thermal decomposition reaction rate had reached only 15%.

Comparative Example 2 The thermal decomposition treatment was carried out in the same manner as in Example 1 except that no aromatic solvent was added. A temperature difference between the outer wall temperature of the seed reactor and the liquid temperature occurred 4 hours after the start of operation, and this temperature difference gradually increased, so 8 hours after the start of operation, the operation of the seed reactor was stopped and decomposition heating was started. Only the furnace was operated for 12 hours. Further, when the product after 12 hours was analyzed, the thermal decomposition reaction rate in the decomposition heating furnace was 17%, and the toluene-insoluble component in the product was 0%.

After the operation was stopped, we inspected the inside of the seed reactor and found that
Severe coking was observed on the inner wall of the reactor and stirring blades.

Example 2 In order to further clarify the effect of adding an aromatic solvent to the cracked heavy fraction according to the present invention, the cracked heavy fraction 70 weight shown in Table 2 above and the weight of the cracked heavy fraction shown in Table 3 above were added. A mixed oil with 30 parts by weight of an aromatic solvent was heated in a decomposition heating furnace at a temperature of 525°C, a pressure of 25.8 kg/cofG, and a flow rate of 0.
Thermal decomposition treatment was carried out under conditions of 5 m/sec and 30% decomposition reaction rate.

For comparison, only the decomposed heavy fraction was thermally decomposed in the same manner except that no aromatic solvent was added.

In the above thermal decomposition treatment, the amount of coke adhering to the reaction tube was investigated, and this is shown in FIG. 2 in relation to the reaction time. In FIG. 2, curve-1 shows the results of the present invention;
2 shows the results of a comparative example.

As is clear from the results shown in Figure 2, it can be seen that the present invention effectively prevents the occurrence of coking when an aromatic solvent is added to the decomposed heavy fraction for thermal decomposition treatment. .

[Brief explanation of drawings]

FIG. 1 shows an example of an apparatus system diagram for implementing the present invention. FIG. 2 is a graph showing the experimental results shown in Example 2. 1.5... Decomposition heating furnace, 2, 3, 6... Seed reactor, 4... Fractionation column.

Claims (1)

[Claims] (1) A heavy fraction of cracked oil obtained by thermal decomposition of petroleum heavy oil has a solubility parameter of 8.0 to 10.0,
In the presence of an aromatic solvent that does not substantially contain toluene-insoluble components and contains components that exhibit a liquid phase in the reaction system,
1. A method for thermally decomposing a cracked heavy fraction, the method comprising thermally decomposing a cracked heavy fraction using a cracking heating furnace or a combination of a cracking heating furnace and a tank reactor.