A method for constructing a reaction network and predicting products of heptane steam cracking with hydrocarbons of the same carbon number and application

Abstract

This invention belongs to the field of petrochemical technology, and specifically relates to a method and application for constructing reaction networks and predicting products from the steam cracking of heptane with the same number of carbon atoms. The method for constructing reaction networks and predicting products from the steam cracking of heptane with the same number of carbon atoms includes the following steps: selecting different hydrocarbons with the same number of carbon atoms as representatives of heptane; setting simulation conditions, and using the Reaction Mechanism Generator tool to automatically generate single-molecule reaction networks for each representative, obtaining a steam cracking reaction mechanism file, and completing the construction of the reaction network; importing the steam cracking reaction mechanism file into a reaction kinetics calculation program to establish a plug flow reactor model, simulating the steam cracking reaction process, and obtaining the product distribution. This invention improves the efficiency of reaction mechanism construction, provides high accuracy in prediction results, and requires no additional reagents, resulting in low operating costs.

Description

Technical Field

[0001] This invention belongs to the field of petrochemical technology, and specifically relates to a method and application for constructing a reaction network and predicting products from the steam cracking of heptane and other hydrocarbons with the same number of carbon atoms. Background Technology

[0002] Steam cracking is an important process for producing ethylene, propylene, butene, and aromatics, and is widely used in the petrochemical industry. The feedstock for steam cracking mainly consists of a mixture of hydrocarbons such as naphtha, hydrocracking tail oil, and diesel. Among these, naphtha is used extensively due to its wide availability and low cost. Naphtha has a complex composition, containing a large number of hydrocarbon molecules with different carbon numbers and isomers, primarily composed of alkanes (including n-alkanes, isoalkanes, and cycloalkanes), aromatics, and trace amounts of alkenes. Alkanes are ideal feedstocks for steam cracking. Heptane is an important component of naphtha fractions. Constructing a steam cracking reaction network for heptane-like hydrocarbons and a product prediction method can help us gain a deeper understanding of the relevant chemical reactions in naphtha steam cracking and guide the selection of cracking feedstocks in industrial applications.

[0003] Alkane vapor cracking follows a free radical mechanism, involving numerous simultaneous reactions and mutual initiation, making real-time monitoring difficult. Artificially constructing reaction mechanisms is cumbersome, prone to overlooking important steps, and struggles to handle the complex reaction networks of alkane cracking. While experimental setups are currently a common method for predicting heptane cracking products, these setups require significant investment and maintenance, and consume large quantities of expensive reagents. Therefore, experimental setup-based cracking product prediction is a considerably costly approach.

[0004] In recent years, with the development of computer technology and reaction kinetics, automated reaction network generation technology has been gradually applied to the mechanistic study of complex reaction systems. Automated reaction network generators can generate the required detailed cracking reaction networks in a short time, saving resource costs. Some studies have constructed a diesel vapor cracking reaction network using automated reaction network generators, while others have constructed a liquefied petroleum gas (LPG) cracking reaction network. Based on existing literature, no methods for constructing vapor cracking reaction networks and predicting products for heptane and other hydrocarbons with the same number of carbon atoms have been found.

[0005] Therefore, there is an urgent need to provide a method for constructing reaction networks and predicting products for hydrocarbons with the same number of carbon atoms as heptane, so as to provide a new technical approach for optimizing cracking feedstocks and studying reaction mechanisms. Summary of the Invention

[0006] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial solution. Specifically, the present invention provides a method for constructing reaction networks and predicting products from the vapor cracking of heptane and other hydrocarbons with the same number of carbon atoms. This method improves the efficiency of reaction mechanism construction, provides high accuracy in prediction results, and requires no additional reagents, resulting in low operating costs.

[0007] The inventive concept of this invention: The method for constructing a reaction network and predicting products of steam cracking of heptane with the same number of carbons in this invention includes the following steps: (1) Selecting different hydrocarbons with the same number of carbons as representatives of heptane; (2) Setting simulation conditions and using the reaction network generation tool Reaction Mechanism Generator to automatically generate a single-molecule reaction network for each representative, obtaining a steam cracking reaction mechanism file, and completing the construction of the reaction network; (3) Importing the steam cracking reaction mechanism file into a reaction kinetics calculation program to establish a plug flow reactor model, simulating the steam cracking reaction process, and obtaining the product distribution.

[0008] This invention employs an automated reaction network to generate mechanism files, avoiding the problem of relying on manual experience to add reaction paths one by one in the traditional reaction mechanism construction process, thus improving the efficiency of reaction mechanism construction. The software used in this invention is all open-source and can run on ordinary servers, resulting in low software and hardware investment costs. The predicted pyrolysis product yield of this method has an error of less than 0.3% compared with the experimental setup evaluation results, and requires no additional reagents, posing no safety or environmental issues. It boasts the advantages of high prediction accuracy and low operating costs.

[0009] Therefore, the first aspect of the present invention provides a method for constructing a reaction network and predicting products from the steam cracking of heptane and other hydrocarbons with the same number of carbon atoms.

[0010] Specifically, the method for constructing the reaction network and predicting products of heptane-like hydrocarbon steam cracking includes the following steps: (1) Select different hydrocarbons with the same number of carbon atoms as heptane as representative compounds; (2) Set simulation conditions and use the reaction network generation tool Reaction Mechanism Generator to automatically generate single-molecule reaction networks for each representative substance to obtain the steam cracking reaction mechanism file and complete the construction of the reaction network; (3) Import the steam cracking reaction mechanism file into the reaction kinetics calculation program, establish a plug flow reactor model, simulate the steam cracking reaction process, and obtain the product distribution.

[0011] Preferably, in step (1), the different hydrocarbons with the same number of carbon atoms as heptane include at least one of 3-ethylpentane, 2,2-dimethylpentane, 2,3-dimethylpentane, 3,3-dimethylpentane, cycloheptane, isoheptane, n-heptane, and 2,2,3-trimethylbutane. That is, "hydrocarbons with the same number of carbon atoms as heptane" refers to different hydrocarbons with the same number of carbon atoms as heptane.

[0012] Preferably, in step (2), the simulation conditions include reaction feed, reaction temperature, reaction pressure, termination conditions, and tolerance factor.

[0013] Preferably, the reaction feed comprises different hydrocarbons with the same number of carbon atoms as heptane and water molecules.

[0014] Preferably, the mass ratio of different hydrocarbons with the same number of carbons and water molecules in the heptane is 1:(0.5-0.8); for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, etc.

[0015] Specifically, the mass ratio of each hydrocarbon with the same number of carbon atoms to water molecules is 1:(0.5-0.8).

[0016] Specifically, during the automatic reaction network generation process, the feed species are selected to include corresponding reactant molecules and water molecules. Water molecules are designated as an inert component, acting as a diluent and not participating in the reaction. The water-to-hydrocarbon mass ratio is a commonly used dilution ratio in industrial steam cracking furnaces.

[0017] Preferably, the reaction temperature is 779-848℃; more preferably, the reaction temperature is 818-848℃.

[0018] Specifically, in industrial steam cracking units, the temperature for heptane cracking is in the range of 800-850℃, within which hydrocarbon molecules can undergo effective free radical chain reactions. Therefore, this invention further sets the temperature range to 818-848℃, which ensures that hydrocarbon molecules are fully cracked to form a complete reaction network, avoiding excessive cracking and side reactions caused by excessively high temperatures.

[0019] Preferably, the reaction pressure is 0.18-0.23 MPa.

[0020] Specifically, industrial steam cracking units typically operate under near-atmospheric or slightly positive pressure conditions to ensure rapid cracking of hydrocarbon molecules and reduce the occurrence of side reactions. Therefore, this invention sets the reaction pressure to 0.18-0.23 MPa. Within this pressure range, sufficient cracking of hydrocarbon molecules can be ensured while effectively suppressing free radical recombination reactions and coke formation, thereby facilitating the acquisition of a stable cracking reaction network and improving the accuracy of target product prediction.

[0021] Preferably, the termination condition is that the molar conversion rate of different hydrocarbons with the same number of carbons in heptane is ≥90% or the residence time is 0.5-0.8s.

[0022] Specifically, in the automatic reaction network generation process, the termination conditions determine the reaction network and computational scale. Termination conditions include the reaction termination time or a threshold for the molar conversion rate of reactants. A higher molar conversion rate results in a more detailed reaction network, but also requires a longer computation time. Similarly, a longer reaction time (residence time) results in a larger reaction network. Therefore, the preferred termination conditions of this invention are a molar conversion rate of 90-95% for different hydrocarbons with the same number of carbons in heptane, and a residence time of 0.5 s.

[0023] Preferably, the tolerance factor is 0.008-0.012.

[0024] Specifically, the tolerance factor is used to characterize the ratio of species generation rate to the maximum generation rate of the system. A generation rate threshold is set to filter automatically generated reactions. A smaller tolerance factor results in a more detailed reaction network, but also requires longer computation time and consumes more resources; conversely, an excessively large tolerance factor may miss some important reactions. Therefore, it is necessary to set an appropriate tolerance threshold to construct a complete fragmentation mechanism.

[0025] Preferably, in step (3), the reaction kinetics calculation program includes the Cantera program.

[0026] Preferably, the plug flow reactor model assumes that the reactants flow unidirectionally along the axis of the plug flow reactor model and there is no axial backmixing. The simulation calculation process is set with conditions including reaction temperature, pressure, feed composition, feed rate, and residence time.

[0027] Specifically, a plug flow reactor model was established using a reaction kinetics calculation program to simulate the steam cracking reaction process. The plug flow reactor assumes that the reactants flow unidirectionally along the reactor axis, with thorough radial mixing and no axial backmixing, and that the feed composition, temperature, and pressure gradually change along the length of the reactor.

[0028] Specifically, the obtained reaction mechanism file is imported into the reaction kinetics calculation program Cantera, and operating conditions such as reaction temperature, pressure, feed composition, and residence time are set. By spatially discretizing the reactor, it is divided into multiple micro-reaction units, and the species conservation equation and reaction kinetic equation are solved in each unit to obtain the variation of species concentration along the reactor length or residence time. Based on the obtained species concentration distribution data, the molar yield and selectivity of major cracking products such as ethylene, propylene, methane, and 1,3-butadiene can be further calculated, enabling the prediction of the steam cracking product distribution of different hydrocarbons with the same number of carbons in heptane.

[0029] Preferably, the reaction temperature of the plug flow reactor model includes eight stages of gradient heating: the first stage temperature is 180-220℃, the second stage temperature is 300-320℃, the third stage temperature is 450-470℃, the fourth stage temperature is 590-600℃, the fifth stage temperature is 760-780℃, the sixth stage temperature is 820-830℃, the seventh stage temperature is 830-835℃, and the eighth stage temperature is 835-838℃.

[0030] Preferably, the inlet pressure of the plug flow reactor model is 0.21-0.23 MPa and the outlet pressure is 0.16-0.18 MPa.

[0031] Preferably, the feed composition includes different hydrocarbons with the same number of carbon atoms as heptane and water.

[0032] Preferably, in the feed composition, the mass ratio of different hydrocarbons with the same number of carbon atoms in the heptane to water is 1:(0.5-0.8); for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, etc.

[0033] Specifically, the mass ratio of each hydrocarbon with the same number of carbon atoms to water is 1:(0.5-0.8).

[0034] Preferably, the feeding rate is 2.5-4 kg / h; Preferably, the dwell time is 0.5-0.63s.

[0035] A second aspect of the present invention provides an application of the reaction network construction and product prediction method described in the first aspect of the present invention in the petrochemical field.

[0036] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: (1) The present invention constructs steam cracking reaction networks of different hydrocarbons through an automatic reaction mechanism generation method. It can generate a relatively complete reaction network and corresponding kinetic parameters in a low-cost manner and in a short time, avoiding the problem of relying on manual experience to add reaction paths one by one in the traditional reaction mechanism construction process, and improving the efficiency of reaction mechanism construction.

[0037] (2) By establishing a plug flow reactor model, this invention simulates the reaction process of different hydrocarbons with the same number of carbons in heptane, and can obtain the variation law of reactants and products along the residence time of the reactor, thereby realizing the prediction of the generation trend of target products such as ethylene and propylene.

[0038] (3) The software used in the reaction network construction and product prediction method of this invention is all open source software and can be run on ordinary servers, with low software and hardware investment costs. The error between the predicted pyrolysis product yield and the experimental device evaluation results is less than 0.3%, and no additional reagents are required. There are no safety or environmental issues, and it has the advantages of high prediction accuracy and low operating cost. Attached Figure Description

[0039] Figure 1 This is a flowchart of the method for constructing a steam cracking reaction network and predicting products of hydrocarbons with the same number of carbon atoms as heptane in Example 1 of the present invention. Detailed Implementation

[0040] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0041] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0042] Example 1 This embodiment provides a method for constructing a reaction network and predicting products from the vapor cracking of heptane and other hydrocarbons with the same number of carbon atoms. The specific steps are as follows: (1) n-Heptane, isoheptane, 3-ethylpentane, 2,2-dimethylpentane, 2,3-dimethylpentane, 3,3-dimethylpentane, cycloheptane and 2,2,3-trimethylbutane were selected as research objects; (2) Edit the operating conditions at 848℃ and 0.185MPa respectively, and set the termination time to 0.5s and the molar conversion rate of hydrocarbons to 0.9, and the tolerance factor to 0.01; the feed composition is hydrocarbons and water, with a mass ratio of 1:0.5; start the Reactor Mechanism Generator automatic reaction network generation tool to construct the reaction network for each of the above single molecules, run it simultaneously on a 96-core server, and finally the average time for generating the reaction network of 8 single molecules is 9 days and 8 hours, the average scale of the reaction network is 1086 species and 49968 reactions, obtain the steam cracking reaction mechanism file, and complete the construction of the reaction network; (3) Import the steam cracking reaction mechanism file into the reaction kinetics calculation program to establish a plug flow reactor model, simulate the steam cracking reaction process, and obtain the product distribution. The parameters of the plug flow reactor model are set to a length of 17.868 meters, which is divided into eight sections. The first four sections are preheating sections, and the last four sections are heating sections. The temperature of the first section is 201℃, the temperature of the second section is 319℃, the temperature of the third section is 460℃, the temperature of the fourth section is 590℃, the temperature of the fifth section is 780℃, the temperature of the sixth section is 828℃, the temperature of the seventh section is 832℃, and the temperature of the eighth section is 838℃. The inlet pressure is controlled at 0.23MPa, and the outlet pressure is controlled at 0.18MPa. The feed at the inlet is a single hydrocarbon and water molecules, and the mass ratio of the two is 2:1. The feed rate is 3.36kg / h, and the residence time is 0.57s.

[0043] The mass conversion rates of different hydrocarbons were obtained by calculating the changes in reactant mass, and the mass yields of major cracking products such as ethylene, propylene, methane, 1,3-butadiene, and hydrogen were further calculated. By comparing the differences in product distribution among different hydrocarbons under the same reaction conditions, the influence of molecular structure on the cracking reaction pathway and product formation patterns can be analyzed.

[0044] The formulas for calculating the mass conversion rate and product yield of different hydrocarbons are as follows: ; .

[0045] X W : Mass conversion rate of hydrocarbons, m in The inlet mass of hydrocarbons, m out Y represents the export quality of hydrocarbons. w,i mi represents the product yield. ,out This indicates the quality of exported products.

[0046] The experiment was conducted on a steam cracking ethylene production evaluation device (any conventional device in the field can be used). The feedstock was pumped into eight mutually insulated and independent heating furnace tubes. The heating temperature was the same as the simulated temperature mentioned above. The steam ratio was also set to 1:0.5. The inner diameter of the furnace tube was 6 mm. The feed rate was 3.36 kg / h. The inlet and outlet pressures were controlled at 0.23 MPa and 0.18 MPa, respectively. The product was taken out from the gas phase sampling port. The yield was calculated using the following formula.

[0047]

[0048]

[0049]

[0050]

[0051]

[0052] 100%.

[0053] in, Mass fraction of a certain product The relative molecular mass of a product. The volume of a certain product. Molecular mass of all gaseous products : Average molecular weight of pyrolysis gas Specific gravity of pyrolysis gas Volume of pyrolysis gas after reaction Wet gas gauge pressure, Volume of pyrolysis gas before reaction : Wet gas gauge temperature : Weight of pyrolysis gas Yield of a certain product : Inlet hydrocarbon quality.

[0054] n-Heptane mass conversion rate = (inlet n-heptane mass - outlet n-heptane mass) / inlet n-heptane mass × 100%.

[0055] The accuracy of the simulation was demonstrated by comparing the product yield and mass conversion rate of n-heptane with those obtained from the experimental section. Furthermore, by comparing the experimental values, the pre-exponential factor parameters affecting the main product reaction (the pre-exponential factor parameters are part of the reaction mechanism file; fine-tuning some values ​​can achieve the required accuracy) were manually adjusted to achieve a good fit.

[0056] The flowchart of the method for constructing the steam cracking reaction network and predicting products of heptane with the same number of carbon atoms in Example 1 of this invention is as follows: Figure 1 As shown.

[0057] The product distribution of the simulation and experimental parts in Example 1 is shown in Table 1.

[0058] Table 1: Product Distribution Results of Simulation and Experiment in Example 1

[0059] As shown in Table 1, the simulation has high accuracy, and straight-chain alkanes are more conducive to the formation of ethylene. The higher the degree of branching, the lower the ethylene content and the higher the propylene content. Moderate branching is conducive to the formation of butene, but excessive branching reduces it. Branching and ring structure affect the degree of deep cracking and thus affect the formation of methane. Hydrogen is not significantly affected by branching.

[0060] Example 2 Example 2 uses the single-molecule reaction network generated in Example 1, i.e., the steam cracking reaction mechanism. The steam cracking reaction mechanism file is imported into the reaction kinetics calculation program to establish a plug flow reactor model, and the steam cracking reaction process is simulated. The plug flow reactor model parameters are set as follows: length 17.868 meters, divided into eight sections. The first four sections are preheating sections, and the last four sections are heating sections. The temperature of the first section is 201℃, the second section is 320℃, the third section is 460℃, the fourth section is 590℃, the fifth section is 790℃, the sixth section is 838℃, the seventh section is 843℃, and the eighth section is 848℃. The inlet pressure is controlled at 0.23MPa, and the outlet pressure is controlled at 0.18MPa. The feed at the inlet consists of single hydrocarbons and water molecules in a mass ratio of 2:1, with a feed rate of 3.36kg / h and a residence time of 0.57s.

[0061] Following the same calculation method as in Example 1, the change in the mass of reactants was calculated to obtain the mass conversion rate of hydrocarbons, and the mass yields of major cracking products such as ethylene, propylene, methane, 1,3-butadiene, and hydrogen were further calculated.

[0062] Compared to Example 1, the highest temperature of the plug flow reactor model in Example 2 increased to 848°C, which allows for the analysis of the product distribution differences of hydrocarbon steam cracking reactions under different reaction temperature conditions, thereby verifying the applicability of the method of the present invention for predicting cracking products under different reaction conditions.

[0063] Using the same experimental procedures and calculation methods as in Example 1, the product yield and mass conversion rate of the n-heptane experimental portion were obtained and compared with the simulation results.

[0064] The product distribution of the simulation and experimental parts in Example 2 is shown in Table 2.

[0065] Table 2: Product Distribution Results of Simulation and Experiment in Example 2

[0066] As shown in Table 2, with the increase of cracking temperature, the conversion rate and ethylene yield increased, while the yields of propylene and butene decreased, and the yields of methane and hydrogen also increased.

[0067] It is understood that the method for constructing the reaction network and predicting the products of heptane-like hydrocarbon steam cracking in this invention can realize the automatic construction of the reaction mechanism and the prediction of the distribution of cracking products, and has the advantages of high automation, wide applicability and high computational efficiency.

[0068] In summary, this invention constructs a steam cracking reaction network for heptane hydrocarbons with the same carbon number through an automated reaction mechanism generation method. This method generates a relatively complete reaction network and corresponding kinetic parameters in a low-cost and short-term manner, avoiding the problem of manually adding reaction paths one by one based on experience in traditional reaction mechanism construction, thus improving the efficiency of reaction mechanism construction. By establishing a plug flow reactor model to perform kinetic simulation of the reaction process of the heptane hydrocarbons with the same carbon number, the variation law of reactants and products along the residence time of the reactor can be obtained, thereby enabling the prediction of the formation trend of target products such as ethylene and propylene.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for constructing a reaction network and predicting products from the steam cracking of heptane and other hydrocarbons with the same number of carbon atoms, characterized in that, Includes the following steps: (1) Select different hydrocarbons with the same number of carbon atoms as heptane as representative compounds; (2) Set simulation conditions and use the reaction network generation tool Reaction Mechanism Generator to automatically generate single-molecule reaction networks for each representative substance to obtain the steam cracking reaction mechanism file and complete the construction of the reaction network; (3) Import the steam cracking reaction mechanism file into the reaction kinetics calculation program to establish a plug flow reactor model, simulate the steam cracking reaction process, and obtain the product distribution.

2. The method for constructing reaction networks and predicting products according to claim 1, characterized in that, In step (1), the different hydrocarbons with the same number of carbons as heptane include at least one of 3-ethylpentane, 2,2-dimethylpentane, 2,3-dimethylpentane, 3,3-dimethylpentane, cycloheptane, isoheptane, n-heptane and 2,2,3-trimethylbutane.

3. The method for constructing reaction networks and predicting products according to claim 1, characterized in that, In step (2), the simulation conditions include reaction feed, reaction temperature, reaction pressure, termination conditions, and tolerance factor.

4. The method for constructing reaction networks and predicting products according to claim 3, characterized in that, The reaction feed consists of different hydrocarbons with the same number of carbon atoms as heptane and water molecules.

5. The method for constructing reaction networks and predicting products according to claim 4, characterized in that, The mass ratio of different hydrocarbons with the same number of carbons and water molecules in the heptane is 1:(0.5-0.8).

6. The method for constructing reaction networks and predicting products according to claim 3, characterized in that, The reaction temperature is 779-848℃; and / or the reaction pressure is 0.18-0.23MPa.

7. The method for constructing reaction networks and predicting products according to claim 3, characterized in that, The termination condition is that the molar conversion rate of different hydrocarbons with the same number of carbons in heptane is ≥90% or the residence time is 0.5-0.8 s; and / or, the tolerance factor is 0.008-0.

012.

8. The method for constructing reaction networks and predicting products according to claim 1, characterized in that, In step (3), the reaction kinetics calculation program includes the Cantera program; And / or, the plug flow reactor model assumes that the reactants flow unidirectionally along the reactor axis and there is no axial backmixing, and the simulation calculation process is set with conditions including reaction temperature, pressure, feed composition, feed rate, and residence time.

9. The method for constructing reaction networks and predicting products according to claim 8, characterized in that, The reaction temperature of the plug flow reactor model includes eight stages of gradient heating: the first stage is 180-220℃, the second stage is 300-320℃, the third stage is 450-470℃, the fourth stage is 590-600℃, the fifth stage is 760-790℃, the sixth stage is 820-838℃, the seventh stage is 830-843℃, and the eighth stage is 835-848℃. And / or, the inlet pressure of the plug flow reactor model is 0.21-0.23 MPa, and the outlet pressure is 0.16-0.18 MPa; And / or, the feed composition includes different hydrocarbons with the same number of carbons as heptane and water; And / or, the feed rate is 2.5-4 kg / h; And / or, the dwell time is 0.5-0.63s.

10. The application of the reaction network construction and product prediction method according to any one of claims 1-9 in the petrochemical field.

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