CN114496106A - Construction method of diesel oil steam cracking reaction network - Google Patents

Abstract

The invention discloses a method for constructing a diesel steam cracking reaction network. The compound molecule is used as the heteroatom composition of diesel; the reaction network generation tool Reaction Mechanism Generator is used to automatically generate a single-molecule reaction network for each molecule in the hydrocarbon composition and heteroatom composition; all the generated hydrocarbon composition molecules and heteroatoms are generated. The reaction networks of atoms that make up the molecules are merged to construct the overall reaction network of diesel steam cracking. The invention can obtain the reaction network at the level of the diesel steam cracking radical mechanism at low cost and in a short time, and the required time is only the running time of the RMG program, and no additional manual carding work is required.

Description

A kind of construction method of diesel steam cracking reaction network

technical field

The invention relates to the petrochemical field, in particular to a low-cost and rapid construction method of a diesel steam cracking reaction network.

Background technique

In recent years, the overcapacity of diesel has become obvious, and many refineries have used diesel as one of the important raw materials for steam cracking units to produce high value-added low-carbon olefins. The patent specifications with publication numbers of CN101139529A and CN105622310A respectively carry out steam cracking reaction of coking diesel oil and Fischer-Tropsch synthetic diesel oil to expand the source of steam cracking to produce olefin raw materials.

It is well known that the thermal cracking of hydrocarbons follows a free radical mechanism, and the reaction process is highly random and complex. Diesel is a complex hydrocarbon mixture, and the cracking reaction path is extremely complex. For the kinetic modeling of complex reaction processes, the traditional reaction kinetic model building method generally aggregates multiple components, and manually organizes the reaction paths and estimates the kinetics according to the known reaction rules or templates of each family composition. parameter. The patent specification with publication number CN108108572A adopts six lumped kinetic models for the hydrocracking process of wax oil to reduce the complexity of the reaction network. The patent specification with publication number CN109698014A establishes a plurality of reaction rules for catalytic reforming raw materials, and the reaction paths between the raw materials and products are determined according to the established reaction rules. For the steam cracking process of complex mixtures such as diesel, the traditional reaction kinetic model construction method is time-consuming and labor-intensive, and the cost is extremely high, and the lumped kinetic model or the kinetic model of the molecular reaction level is difficult to accurately describe the interaction at the free radical level. effects, especially the regulation mechanism of heteroatom components on olefin products.

With the rapid development of computer technology, the automatic generation tool of reaction network emerges as the times require. With the help of the automatic reaction network generator, detailed reaction networks at the free radical level can be obtained in a short time and with the least consumption of human and material resources. In the existing literature reports, the automatic reaction network generation technology is mostly used for the reaction network generation of pure substances, and the composition of relatively pure naphtha fractions.

Compared with the traditional naphtha cracking feedstock, diesel fuel has a more complex composition, higher content of heavy components, and contains a certain proportion of heteroatom compounds represented by sulfur-containing compounds and nitrogen-containing compounds. The number of carbon atoms in the diesel fraction can reach 22, and the isomers increase exponentially with the increase of carbon number, which makes the scale of the steam cracking reaction network extremely large. In addition, the thermal cracking of sulfur-containing compounds and nitrogen-containing compounds is more complex and changeable than that of hydrocarbons, and the intermediate products also have a modulating effect on the coking process of steam cracking to olefins.

Therefore, the use of automatic reaction network generation technology can not only quickly build a diesel steam cracking reaction network at low cost, but also interpret the interaction of hydrocarbons in diesel with sulfur-containing compounds and nitrogen-containing compounds from the radical level, and predict diesel steam cracking. product distribution.

SUMMARY OF THE INVENTION

The invention provides a method for constructing a diesel steam cracking reaction network, which has low construction cost and high speed. The constructed overall reaction network of diesel steam cracking includes heteroatoms represented by sulfur-containing compound molecules and nitrogen-containing compound molecules. The reaction network couples the reaction network of hydrocarbon molecules with the reaction network of sulfur-containing compounds and nitrogen-containing compounds.

A method for constructing a diesel steam cracking reaction network, comprising the steps of:

(1) Carry out component analysis on diesel oil, and screen representative hydrocarbon molecules as the hydrocarbon composition of diesel fuel, and representative sulfur-containing compound molecules and nitrogen-containing compound molecules as the heteroatom composition of diesel fuel;

(2) Using the reaction network generation tool Reaction Mechanism Generator (RMG) to automatically generate a single-molecule reaction network for each molecule in the hydrocarbon composition and heteroatom composition;

(3) The reaction networks of all the generated hydrocarbon constituent molecules and heteroatom constituent molecules are combined to construct the overall reaction network of diesel steam cracking.

In step (1), a chromatographic technique can be used to analyze the components of the diesel oil.

In step (1), the hydrocarbon molecules include straight-chain alkanes, iso-alkanes, alkenes, cycloalkanes and aromatic hydrocarbons. Although straight-chain alkanes and iso-alkanes belong to the same alkanes, their cracking paths and cracking product distributions are quite different, so the present invention divides them into two subclasses for molecular statistics. Alkynes are negligible due to their extremely low content in diesel fuel.

The lower the mass fraction threshold is set, the more representative components of diesel are screened out, and the more realistic the diesel composition can be described, but the more the number of single-molecule reaction networks that need to be constructed, the longer the overall calculation time is. Moreover, molecules with too low content have little effect on the diesel steam cracking reaction process. Therefore, in order to be able to describe the diesel composition almost realistically, taking into account the efficiency, in step (1):

The representative hydrocarbon molecules are hydrocarbon molecules whose mass ratio in diesel oil is not less than 0.3% (preferably not less than 0.5%);

The representative sulfur-containing compound molecules and nitrogen-containing compound molecules are sulfur-containing compound molecules and nitrogen-containing compound molecules whose mass ratio in diesel fuel is not less than 0.05% (preferably not less than 0.1%).

In step (2), the automatic generation process of the single-molecule reaction network is to specify the temperature, pressure, species and proportion of reactant molecules, termination conditions and user-defined tolerance factors of the corresponding single-molecule reaction system, and start the reaction network generation tool Reaction Mechanism. Generator performs automatic reactive network generation for this reactive system.

During the automatic generation of the reaction network of the single molecule, the temperature of the reaction system can be set to 780-900°C, which belongs to the normal operating range of the steam cracking furnace. For automatic reaction network generation, high-temperature reaction systems can be compatible with low-temperature reaction systems. The higher the temperature setting, the more detailed the reaction network is, but the calculation time of a single reaction network is also longer. Based on this, the temperature of the reaction system is preferably set to 800 to 850°C, more preferably 820 to 850°C.

During the automatic generation of the single-molecule reaction network, the pressure of the reaction system can be set to 0.1-0.3 MPa, which belongs to the conventional steam cracking furnace pressure operating range.

In the process of automatic generation of a single-molecule reaction network, the feed composition is preferably the corresponding hydrocarbon constituent molecules or heteroatom constituent molecules and water molecules, wherein the water molecules only serve as the feed constituent molecules and have no reactivity. The mass ratio of the corresponding hydrocarbon constituent molecules or heteroatom constituent molecules and water molecules can be 1-2:1, and this dilution ratio range belongs to the conventional steam cracking furnace dilution ratio operation range.

The higher the molar conversion of the termination conditions, the more detailed the reaction network, but the longer the calculation time. In the process of automatically generating the reaction network of the single molecule, the termination condition is preferably that the molar conversion rate of the corresponding hydrocarbon constituent molecule or heteroatom constituent molecule is greater than 85%, and more preferably the molar conversion ratio of the corresponding hydrocarbon constituent molecule or heteroatom constituent molecule is. 90% to 95%.

The user-defined tolerance factor is a criterion for distinguishing the core reactions included in the reaction network from the marginal reactions that are excluded. This value has a great influence on the scale of the reaction network and the calculation time. The smaller the tolerance factor, the more detailed the reaction network, but the longer the computation time of a single reaction network. In the process of automatic generation of single molecule reaction network, the user-defined tolerance factor is preferably set to 0.5～0.01. It is more preferable to set it as 0.1-0.01, and it is still more preferable to set it as 0.05-0.03.

Considering that the first merged network has priority in the merging process, that is, the same reaction path will be subject to the first merged network, in step (3), the merging rule of the total reaction network is the sulfur-containing compound reaction network and the nitrogen-containing compound reaction network. The reaction network is first merged into network 1, the purpose is to keep the reaction network of sulfur-containing compounds and nitrogen-containing compounds intact, and the aromatic hydrocarbon reaction network is merged on the basis of network 1 to obtain network 2, the purpose is to keep the aromatic hydrocarbon reaction network as much as possible, in network 2. On the basis of combining the naphthenic reaction network to obtain the network 3, the purpose is to keep the naphthenic reaction network as much as possible. On the basis of the network 3, the straight-chain alkane reaction network is combined to obtain the network 4. The reaction path is placed in network 3 and then merged. On the basis of network 4, the isoparaffin reaction network is combined to obtain network 5. The isoparaffin reaction network will contain a part of the reaction paths of aromatic hydrocarbons, naphthenes and linear alkanes, so it is placed in the network 4. Network 4 is then merged, and finally the olefin reaction network is combined on the basis of network 5 to obtain the overall reaction network of diesel steam cracking. The reaction network of paraffins already contains some important olefin cracking paths, so the olefin reaction network is placed in the last merge, so that the olefin cracking paths of other types of hydrocarbon molecules remain intact.

Compared with the prior art, the main advantages of the present invention include:

(1) The reaction network and the corresponding kinetic parameters of the diesel steam cracking radical mechanism level can be obtained at low cost and in a short time, and the time required is only the running time of the RMG program, and no additional manual carding work is required;

(2) The chromatographic analysis results are used as the basis for selecting representative molecules of diesel oil, and the minimum mass content thresholds are respectively set for hydrocarbon composition and heteroatom composition as the standard for selecting molecules, and the composition of diesel oil participating in the steam cracking reaction is almost truly described;

(3) Taking the reaction network of heteroatom compound molecules as the first step of RMG network merging, it avoids that the elementary reactions related to sulfur-containing compounds and nitrogen-containing compounds are covered during the network merging process.

Description of drawings

Fig. 1 is a flow chart of constructing a diesel steam cracking reaction network proposed by the present invention.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. The operation method without specifying the specific conditions in the following examples is usually in accordance with the conventional conditions, or in accordance with the conditions suggested by the manufacturer.

As shown in Figure 1, the diesel sample is sent to a chromatographic analyzer for component analysis. According to the chromatographic results, representative hydrocarbon molecules are screened as the hydrocarbon composition of diesel, as well as representative sulfur-containing compound molecules and nitrogen-containing compounds. Molecules are used as the heteroatom composition of diesel; the reaction network generation tool RMG is used to automatically generate a single molecule reaction network for the hydrocarbon composition and heteroatom composition of each diesel; all diesel hydrocarbons are composed of molecules according to specific merging rules. Combined with the reaction network of heteroatom constituent molecules to obtain the overall reaction network of diesel steam cracking. The hydrocarbon constituent molecules include linear paraffins, isoparaffins, olefins, naphthenes and aromatics. The merging rule is that the reaction network of sulfur-containing compounds and the reaction network of nitrogen-containing compounds are first merged into network 1, the aromatic hydrocarbon reaction network is merged on the basis of network 1 to obtain network 2, the cycloalkane reaction network is merged on the basis of network 2 to obtain network 3, and the network 3 On the basis of merging the linear alkane reaction network to obtain network 4, merging the isoparaffin reaction network on the basis of network 4 to obtain network 5, and finally merging the olefin reaction network on the basis of network 5 to obtain the total reaction network of diesel steam cracking.

Example 1

The diesel sample is sent to a chromatographic analyzer for component analysis. The chromatographic analyzer has the functions of analyzing hydrocarbon molecules, sulfur-containing compound molecules and nitrogen compound molecules. According to the obtained chromatographic analysis results, the mass fractions of all detected diesel components are normalized, and the hydrocarbon molecules with a mass fraction of not less than 0.3% are taken as the hydrocarbon composition of diesel oil, and the mass fraction of not less than 0.05% The sulfur-containing compound molecules and nitrogen-containing compound molecules are composed of heteroatoms of diesel fuel, and together they are used as representative molecules to describe the composition of diesel fuel. A total of 121 kinds of hydrocarbon molecules were screened, with the number of carbon atoms ranging from 10 to 22; 9 kinds of sulfur-containing compound molecules, namely mercaptans, sulfides, thiophenes, benzothiophenes, etc.; 4 kinds of nitrogen-containing compounds Compound molecules are pyridines, pyrroles, tetrahydropyrroles, etc.

The reaction network generation tool Reaction Mechanism Generator was used to automatically generate single-molecule reaction networks for the above 134 representative molecules of diesel. The temperature of all single-molecule reaction systems is uniformly set to 900°C, the pressure is set to 0.2MPa, the feed composition is the corresponding diesel hydrocarbon molecules or heteroatom molecules and water molecules, and the mass ratio of the two is set to 1:1. The custom tolerance factor was set to 0.01, and the termination condition was set to achieve 99% molar conversion of the corresponding diesel hydrocarbon constituent molecules or heteroatom constituent molecules. Start the reaction network generation tool Reaction MechanismGenerator to perform automatic reaction network generation for each single-molecule reaction system. The average time taken to generate the 134 single-molecule reaction networks was 12.1 hours, and the average size of the reaction networks was 316 species with 6894 reactions.

The 134 single-molecule reaction networks obtained above were merged according to the following merging rules: the reaction networks of 9 kinds of sulfur-containing compound molecules and 4 kinds of nitrogen-containing compound molecules were first merged into network 1, and the scale of network 1 was 3898. Species, 60,156 reactions; 8 kinds of aromatic hydrocarbon molecules in hydrocarbon molecules were merged on the basis of network 1. Reaction network was obtained to obtain network 2, and the scale of network 2 was 6011 species, 98,995 reactions; on the basis of network 2, carbon The reaction network of 14 kinds of cycloalkane molecules in hydrogen compound molecules is obtained, and network 3 is obtained. The scale of network 3 is 10,231 species and 113,754 reactions; on the basis of network 3, the reaction network of 13 kinds of linear alkane molecules in hydrocarbon molecules is merged , obtain network 4, the scale of network 4 is 13131 species, 147565 reactions; on the basis of network 4, the reaction network of 79 isoalkane molecules in hydrocarbon molecules is merged, and network 4 is obtained, and the scale of network 4 is 16523 species , 171322 reactions; on the basis of network 5, 7 kinds of olefin molecular reaction networks in hydrocarbon molecules were merged and finally the total reaction network of diesel steam cracking was obtained. The total reaction network scale was 17344 species and 174325 reactions.

The overall reaction network of diesel steam cracking obtained above uses a lower mass fraction threshold to screen representative molecules, and at the same time adopts a higher reaction temperature, a lower user-defined tolerance factor, and a higher target conversion rate, so The scale of the reaction network is huge, the number of species in the reaction network reaches about 17,000, and the number of reactions is as high as about 170,000, which can describe the diesel steam cracking radical reaction process in great detail.

Example 2

The same diesel sample as in Example 1 was used to send the chromatographic analyzer to analyze the content of hydrocarbon molecules, sulfur-containing compound molecules and nitrogen compound molecules. According to the obtained chromatographic analysis results, the mass fractions of all detected diesel components are normalized, and the hydrocarbon molecules with a mass fraction of not less than 0.5% are taken as the hydrocarbon composition of diesel oil, and the mass fraction of not less than 0.1% The sulfur-containing compound molecules and nitrogen-containing compound molecules are composed of heteroatoms of diesel fuel, and together they are used as representative molecules to describe the composition of diesel fuel. A total of 92 kinds of hydrocarbon molecules, the number of carbon atoms ranges from 10 to 22; 5 kinds of sulfur-containing compound molecules, namely mercaptans, sulfides, thiophenes, benzothiophenes, etc.; 2 kinds of nitrogen-containing compound molecules , respectively, pyridines, pyrroles, etc.

The reaction network generation tool Reaction Mechanism Generator was used to automatically generate single-molecule reaction networks for the above 99 representative molecules of diesel. The temperature of all single-molecule reaction systems is uniformly set to 850°C, the pressure is set to 0.2MPa, the feed composition is the corresponding diesel hydrocarbon molecules or heteroatom molecules and water molecules, and the mass ratio of the two is set to 1:1. The custom tolerance factor was set to 0.01, and the termination condition was set to achieve 99% molar conversion of the corresponding diesel hydrocarbon constituent molecules or heteroatom constituent molecules. Start the reaction network generation tool Reaction MechanismGenerator to perform automatic reaction network generation for each single-molecule reaction system. The average time taken to generate the 99 single-molecule reaction networks was 11.9 hours, and the average size of the reaction networks was 325 species and 6822 reactions.

The 99 single-molecule reaction networks obtained above were merged according to the following merging rules: the reaction networks of 5 kinds of sulfur-containing compound molecules and 2 kinds of nitrogen-containing compound molecules were first merged into network 1, and the scale of network 1 was 2101. Species, 32,076 reactions; 5 kinds of aromatic hydrocarbon molecules in hydrocarbon molecules were merged on the basis of network 1. Reaction network was obtained, and network 2 was obtained. The scale of network 2 was 3,799 species and 60,655 reactions; on the basis of network 2, carbon The reaction network of 10 kinds of cycloalkane molecules in hydrogen compound molecules was obtained, and the scale of network 3 was 6569 species and 99231 reactions; on the basis of network 3, the reaction network of 13 kinds of linear alkane molecules in hydrocarbon molecules was merged , obtain network 4, the scale of network 4 is 9469 species, 133042 reactions; on the basis of network 4, the reaction network of 64 isoalkane molecules in hydrocarbon molecules is merged to obtain network 4, the scale of network 4 is 12754 species , 149952 reactions; on the basis of network 5, 7 kinds of olefin molecular reaction networks in hydrocarbon molecules were merged and finally the total reaction network of diesel steam cracking was obtained. The total reaction network scale was 13365 species and 152134 reactions.

Compared with Example 1, the overall reaction network of diesel steam cracking obtained in this example adopts a relatively high mass fraction threshold to screen representative molecules, so that the number of representative molecules is reduced from 134 to 99, and the final overall reaction network The number of medium species was reduced to about 13,000, and the number of reactions was reduced to about 150,000, which was consistent with the experimental results. The network can also describe the diesel steam cracking radical reaction process in detail.

Example 3

The same diesel sample and the same mass fraction threshold as in Example 2 are used to screen representative molecules, that is, hydrocarbon molecules with a mass fraction of not less than 0.5% are taken as the hydrocarbon composition of diesel oil, and the mass fraction of not less than 0.1% of the hydrocarbon molecules Sulfur compound molecules and nitrogen-containing compound molecules are composed as heteroatoms of diesel fuel. A total of 92 kinds of hydrocarbon molecules, the number of carbon atoms ranges from 10 to 22; 5 kinds of sulfur-containing compound molecules, namely mercaptans, sulfides, thiophenes, benzothiophenes, etc.; 2 kinds of nitrogen-containing compound molecules , respectively, pyridines, pyrroles, etc.

The reaction network generation tool Reaction Mechanism Generator was used to automatically generate single-molecule reaction networks for the above 99 representative molecules of diesel. The temperature of all single-molecule reaction systems is uniformly set to 850°C, the pressure is set to 0.2MPa, the feed composition is the corresponding diesel hydrocarbon molecules or heteroatom molecules and water molecules, and the mass ratio of the two is set to 1:1. The custom tolerance factor was set to 0.05, and the termination condition was set to achieve 90% molar conversion of the corresponding diesel hydrocarbon constituent molecules or heteroatom constituent molecules. Start the reaction network generation tool Reaction MechanismGenerator to perform automatic reaction network generation for each single-molecule reaction system. The average time taken to generate the 99 single-molecule reaction networks was 9.3 hours, and the average size of the reaction networks was 239 species and 4821 reactions.

The 99 single-molecule reaction networks obtained above were merged according to the following merging rules: the reaction networks of 5 kinds of sulfur-containing compound molecules and 2 kinds of nitrogen-containing compound molecules were first merged into network 1, and the scale of network 1 was 1203. Species, 22345 reactions; merging 5 kinds of aromatic hydrocarbon molecular reaction networks in hydrocarbon molecules on the basis of network 1, obtaining network 2, the scale of network 2 is 2210 species, 41523 reactions; on the basis of network 2, merging carbon The 10 kinds of cycloalkane molecules in the hydrogen compound molecules reacted to the network, and the network 3 was obtained, and the scale of the network 3 was 4021 species and 69,231 reactions; on the basis of the network 3, the 13 kinds of linear alkane molecules in the hydrocarbon molecules were merged. The reaction network , obtain network 4, the scale of network 4 is 6112 species, 93326 reactions; on the basis of network 4, the reaction network of 64 isoalkane molecules in hydrocarbon molecules is merged, and network 4 is obtained, and the scale of network 4 is 8044 species , 104252 reactions; on the basis of network 5, 7 kinds of olefin molecular reaction networks in hydrocarbon molecules were merged, and finally the total reaction network of diesel steam cracking was obtained, and the total reaction network scale was 8116 species and 105713 reactions.

Compared with Example 2, the overall reaction network of diesel steam cracking obtained in this example adopts a moderate reaction temperature, a moderate user-defined tolerance factor, and a low target conversion rate, and the number of representative molecules remains unchanged. On the basis of , the number of species in the final total reaction network was further reduced to about 8,000, and the number of reactions was further reduced to about 100,000, which was consistent with the experimental results. The network is still able to describe the diesel steam cracking radical reaction process in detail.

In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims (10)

1. a construction method of diesel steam cracking reaction network, is characterized in that, comprises the steps: (1) Carry out component analysis on diesel oil, and screen representative hydrocarbon molecules as the hydrocarbon composition of diesel fuel, and representative sulfur-containing compound molecules and nitrogen-containing compound molecules as the heteroatom composition of diesel fuel; (2) Using the reaction network generation tool Reaction Mechanism Generator to automatically generate a single-molecule reaction network for each molecule in the hydrocarbon composition and heteroatom composition; (3) The reaction networks of all the generated hydrocarbon constituent molecules and heteroatom constituent molecules are combined to construct the overall reaction network of diesel steam cracking. 2. construction method according to claim 1, is characterized in that, in step (1), described hydrocarbon molecule comprises straight chain alkane, isoalkane, alkene, cycloalkane and aromatic hydrocarbon. 3. construction method according to claim 1, is characterized in that, in step (1): The representative hydrocarbon molecules are hydrocarbon molecules whose mass ratio in diesel is not less than 0.3%; The representative sulfur-containing compound molecules and nitrogen-containing compound molecules are sulfur-containing compound molecules and nitrogen-containing compound molecules whose mass ratio in diesel fuel is not less than 0.05%. 4. construction method according to claim 1 is characterized in that, in step (2), the reaction network automatic generation process of monomolecular is to specify temperature, pressure, reactant molecular species and ratio, termination of corresponding monomolecular reaction system Conditions and user-defined tolerance factors, start the reaction network generation tool Reaction Mechanism Generator to perform automatic reaction network generation for the reaction system. 5 . The construction method according to claim 4 , wherein, during the automatic generation of the reaction network of the single molecule, the temperature of the reaction system is set to 780-900° C. 6 . 6 . The construction method according to claim 4 , wherein, during the automatic generation of the reaction network of the single molecule, the pressure of the reaction system is set to 0.1-0.3 MPa. 7 . 7. construction method according to claim 4 is characterized in that, in the automatic generation process of the reaction network of monomolecular, feed is composed of corresponding hydrocarbon composition molecule or heteroatom composition molecule and water molecule, and the mass ratio of the two is 1 to 2:1. 8 . The construction method according to claim 4 , wherein, in the process of automatically generating the reaction network of the single molecule, the termination condition is that the molar conversion rate of the corresponding hydrocarbon constituent molecule or heteroatom constituent molecule is greater than 85%. 9 . 9 . The construction method according to claim 4 , wherein, in the process of automatically generating the reaction network of the single molecule, a user-defined tolerance factor is set to 0.5-0.01. 10 . 10. construction method according to claim 2 is characterized in that, in step (3), the merging rule of total reaction network is that sulfur-containing compound reaction network and nitrogen-containing compound reaction network merge into network 1 first, in network 1 basis. On the basis of network 2, combining the cycloalkane reaction network to obtain network 3, combining the linear alkane reaction network on the basis of network 3 to obtain network 4, and combining the isoparaffin reaction network on the basis of network 4 to obtain network 2 Network 5. Finally, the olefin reaction network is combined on the basis of network 5 to obtain the overall reaction network of diesel steam cracking.

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