A method for predicting the conversion rate of hydrogen sulfide pyrolysis to produce hydrogen

Abstract

A method for predicting the conversion rate of a hydrogen sulfide pyrolysis hydrogen production reaction relates to the technical field of hydrogen production and gas purification, and mainly comprises the following steps: step S1: establishing a hydrogen sulfide pyrolysis hydrogen production reaction equilibrium constant prediction model from the molecular structure level, and step S2: calculating the conversion rate of the hydrogen sulfide pyrolysis hydrogen production reaction through the hydrogen sulfide pyrolysis hydrogen production reaction equilibrium constant prediction model; compared with the prior art, the method for predicting the conversion rate of a hydrogen sulfide pyrolysis hydrogen production reaction in the present invention can construct a hydrogen sulfide pyrolysis reaction equilibrium constant model from the molecular structure level, and the calculated equilibrium constant value is in good agreement with actual data and is better than the calculated value of the existing model. In addition, the model overcomes the defect that the traditional model cannot predict the influence of pressure on the equilibrium conversion rate, and provides a new technical solution for accurately calculating the conversion rate of the hydrogen sulfide pyrolysis hydrogen production reaction; the method of the present invention is suitable for hydrogen production by hydrogen sulfide pyrolysis and recovery of elemental sulfur in the energy industry.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogen production and gas purification, and in particular to a method for predicting the conversion rate of hydrogen production reaction by pyrolysis of hydrogen sulfide. Background Art

[0002] Hydrogen production by pyrolysis of hydrogen sulfide (chemical reaction equation: ) is an effective method for producing hydrogen and removing the environmental pollutant hydrogen sulfide. It can effectively remove the heavy pollutant hydrogen sulfide that is widely present in the energy industry and manufacturing industry, and meets the current needs for environmental protection and green development. The hydrogen sulfide pyrolysis reaction is a reversible endothermic reaction. From the perspective of reaction kinetics, increasing the temperature is conducive to accelerating the reaction rate and the conversion rate of hydrogen sulfide, but high temperature conditions will undoubtedly increase energy consumption and equipment tolerance, and increase economic costs. Therefore, the research and prediction of the conversion rate of hydrogen sulfide pyrolysis reaction is one of the foundations for the industrialization and large-scale application of hydrogen sulfide pyrolysis reaction.

[0003] Generally speaking, the study of conversion rate often involves chemical equilibrium, which plays an important role in the design and optimization of chemical reaction processes. As an important parameter of chemical equilibrium, the equilibrium constant is of great significance for understanding and controlling the equilibrium state of chemical reactions and predicting the direction and rate of reactions. Therefore, establishing the relationship between the reaction equilibrium constant and temperature and pressure is crucial for dynamically mastering the conversion rate in the hydrogen sulfide pyrolysis process and further guiding the practical application of hydrogen sulfide pyrolysis to produce hydrogen.

[0004] However, existing methods for determining the equilibrium constant of hydrogen sulfide pyrolysis reaction, such as empirical expressions, require fitting a large amount of experimental data to obtain, and have shown some problems in practical applications. For example, at certain temperatures, the deviation between the equilibrium constant value calculated using these empirical expressions and the experimental data exceeds the error range required by the project. At the same time, various empirical formulas established over the past 100 years only use temperature as a variable but not pressure as a variable, and cannot be used to calculate the conversion rate of hydrogen sulfide pyrolysis under different pressures. In addition, there are inconsistencies in the values ​​of the equilibrium constant of hydrogen sulfide pyrolysis reaction calculated by different empirical formulas at different temperatures, which in turn affects the accuracy of the prediction of the conversion rate of hydrogen sulfide pyrolysis reaction based on this basis. In practical applications, it is difficult to decide which empirical formula is the best. Summary of the invention

[0005] In view of this, in order to improve the accuracy of the prediction of the conversion rate of hydrogen sulfide pyrolysis reaction to produce hydrogen, the present invention proposes a method for predicting the conversion rate of hydrogen sulfide pyrolysis reaction to produce hydrogen, which obtains the equilibrium constant of hydrogen sulfide pyrolysis reaction to produce hydrogen from the perspective of molecular dynamics, and further ensures the accuracy of the conversion rate of hydrogen sulfide pyrolysis reaction predicted based on the equilibrium constant.

[0006] In order to solve at least one of the above technical problems, the technical solution provided by the present invention is:

[0007] The technical solution adopted by the present invention to solve the above-mentioned problem is a method for predicting the conversion rate of hydrogen production by pyrolysis of hydrogen sulfide, comprising the following steps:

[0008] Step S1: establishing a prediction model for the equilibrium constant of hydrogen sulfide pyrolysis reaction;

[0009] Step S2: calculating the conversion rate of hydrogen sulfide pyrolysis reaction to produce hydrogen by using a hydrogen sulfide pyrolysis reaction equilibrium constant prediction model;

[0010] The equilibrium constant prediction model for hydrogen sulfide pyrolysis reaction is shown in formula (1):

[0011]

[0012] In formula (1), K is the equilibrium constant of hydrogen sulfide pyrolysis reaction; e is the natural constant; R is the universal gas constant, which is 8.3143 J·K -1 mol -1 ; T is Kelvin temperature, unit K; is the total molar Gibbs free energy of H2 produced in the hydrogen sulfide pyrolysis reaction, in J / mol; is the total molar Gibbs free energy of the product S2 in the hydrogen production reaction by pyrolysis of hydrogen sulfide, in J / mol; It is the total molar Gibbs free energy of H2S produced by the pyrolysis of hydrogen sulfide, in J / mol.

[0013] The technical effects of the present invention are:

[0014] Compared with the prior art, the method for calculating the equilibrium constant of the hydrogen sulfide pyrolysis reaction provided by the present invention can obtain an effective analytical expression of the Gibbs free energy of reactants and products from the molecular structure level, and construct a hydrogen sulfide pyrolysis reaction equilibrium constant model. It only needs to input several basic molecular constants of the products and reactants to directly perform algebraic operations to obtain accurate results, which reduces the dependence on a large amount of experimental data of related reactions. The calculated equilibrium constant value is in good agreement with the actual data and is better than the calculated value of the existing model, thereby providing a new way to accurately calculate the conversion rate of the hydrogen sulfide pyrolysis hydrogen production reaction, improving the accuracy of predicting the conversion rate of the hydrogen sulfide pyrolysis hydrogen production reaction, and is conducive to guiding the application of the hydrogen sulfide pyrolysis hydrogen production reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 The calculation results of the thermal cracking conversion rate of hydrogen sulfide under different conditions in the embodiments of the present invention;

[0017] Figure 2 is the relative deviation of the embodiment of the present invention when comparing different equilibrium constant prediction models with experimental data in the range of 1023K to 1405K;

[0018] Figure 3 It is the relative deviation when comparing the embodiment of the present invention with different equilibrium constant prediction models and experimental data in the range of 1362K to 1667K. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below in conjunction with the embodiments and drawings.

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention.

[0021] Example:

[0022] A method for predicting the conversion rate of hydrogen sulfide pyrolysis to produce hydrogen, comprising the following steps:

[0023] Step S1: establishing a prediction model for the equilibrium constant of hydrogen sulfide pyrolysis reaction;

[0024] The method for establishing the equilibrium constant prediction model for the hydrogen production reaction by pyrolysis of hydrogen sulfide is mainly aimed at the three substances (H2, S2, and H2S) in the hydrogen sulfide pyrolysis reaction. Starting from the molecular structure, appropriate oscillator models are used to describe the internal vibrations of the molecules of the three substances. By solving the Schrödinger equation, the vibration energy level expression is obtained, and then the corresponding partition function is obtained. Then, combined with the basic thermodynamic formulas, the analytical expressions of the Gibbs free energy of the three substances are obtained respectively. According to the relationship between the equilibrium constant and the reaction Gibbs free energy, a new analytical prediction model for the equilibrium constant of the hydrogen sulfide pyrolysis reaction is constructed.

[0025] (1) Establishment of the analytical expression of Gibbs free energy of S2

[0026] Starting from the molecular structure of S2, the Fu-Wang-Jia potential energy model is used to characterize the intramolecular vibration, and the analytical expression of the molar Gibbs free energy of S2 is established, as shown in formula (21). The variables in formula (21) satisfy the relationship between formulas (22) to (29), and then:

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036] Among them, for equations (21) to (29), is the molar Gibbs free energy of S2, in J / mol; is the dissociation energy of S2, in J; is the coupling constant of S2, in m -1 ; is the equilibrium bond length of S2, in m; is the equilibrium vibration frequency of S2, in m -1 ; is the reduced mass of S2, in kg; is the mass of S2, in kg; c is the speed of light, which is 2.99793×108 m / s; h is Planck's constant, which is 6.6260755×10 -34 J·s; k is the Boltzmann constant, which is 1.380658×10 -23 J / K; R is the universal gas constant, which is 8.3143 J·K -1 mol -1 ; T is Kelvin temperature, unit K; p is gas pressure, unit Pa.

[0037] At the same time, based on the prior art in this field, the experimental values ​​of the three basic molecular constants of the molar Gibbs free energy of S2 can be respectively

[0038] (2) Establishment of the analytical expression of Gibbs free energy of H2

[0039] Starting from the molecular structure of H2, the analytical expression of the molar Gibbs free energy of the H2 molecule is constructed, as shown in formula (31). The variables in formula (31) satisfy the relationship of formulas (32) to (39). At this time, we have:

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049] Among them, for equations (31) to (39), is the molar Gibbs free energy of H2, in J / mol; is the dissociation energy of H2, in J; It is a dimensionless parameter and is taken as 1.0; is the equilibrium bond length of H2, in m; is the equilibrium vibration frequency of H2, in m -1 ; is the reduced mass of H2, in kg; is the mass of H2, in kg; c is the speed of light, which is 2.99793×10 8 m / s; h is Planck's constant, which is 6.6260755×10 -34 J·s; k is the Boltzmann constant, which is 1.380658×10 -23 J / K; R is the universal gas constant, which is 8.3143 J·K -1 mol -1 ; T is Kelvin temperature, unit K; p is gas pressure, unit Pa.

[0050] At the same time, based on the prior art in this field, the experimental values ​​of the three basic molecular constants of the molar Gibbs free energy of H2 can be respectively

[0051] (3) Establishment of the analytical expression of Gibbs free energy of H2S

[0052] Starting from the molecular structure of H2S, the modified Tietz oscillator model is used to describe the symmetric stretching vibration within the H2S molecule, while the conventional asymmetric stretching vibration and bending vibration are described by the harmonic oscillator model. The energy level of the symmetric stretching vibration within the H2S molecule is obtained, and then the partition function of the symmetric stretching vibration within the H2S molecule is obtained. Then, combined with the translational coordination function and rotational partition function of the H2S molecule, the analytical expression of the molar Gibbs free energy of H2S can be established, as shown in formula (41). The variables in formula (41) satisfy the relationship between formulas (42) to (48). At this time,

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061] In formulas (41) to (48), is the molar Gibbs free energy of H2S, in J / mol; is the dissociation energy of SH bond, unit is J; is a dimensionless parameter, taking -0.80; r eSH is the equilibrium bond length of the SH bond, in m; ω es is the symmetric stretching vibration frequency of H2S, in m -1 ;ω ea is the antisymmetric stretching vibration frequency of H2S, unit: m -1 ;ω eb is the bending vibration frequency of H2S, in m -1 ;μ SH is the reduced mass of hydrogen atoms and sulfur atoms, in kg; is the mass of H2S, in kg; c is the speed of light, which is 2.99793×10 8 m / s; h is Planck's constant, which is 6.6260755×10 -34 J·s; k is the Boltzmann constant, which is 1.380658×10 -23 J / K; R is the universal gas constant, which is 8.3143 J·K -1 mol -1 ; T is Kelvin temperature, unit K; p is gas pressure, unit Pa, I a , I b , I c They are the moments of inertia of H2S molecules around the three principal axes, in kg·m 2

[0062] At the same time, based on the prior art in this field, the experimental values ​​of the five basic molecular constants of the molar Gibbs free energy of H2S can be respectively r eSH =1.3356×10 -10 m,ω es =2.165×10 5 m -1 ,ω ea =2.626×10 5 m -1 ,ω eb =1.183×10 5 m -1 , I a =2.70767×10 -47 kg·m 2 , I b =3.09691×10 -47 kg·m 2 , I c =5.80459×10 -47 kg·m 2 .

[0063] The reaction Gibbs free energy is used to represent the equilibrium constant of the hydrogen sulfide pyrolysis reaction to produce hydrogen. That is, the equilibrium constant prediction model of the hydrogen sulfide pyrolysis reaction to produce hydrogen is shown in formula (1):

[0064]

[0065] In formula (1), K is the equilibrium constant of hydrogen sulfide pyrolysis reaction; e is the natural constant; R is the universal gas constant, which is 8.3143 J·K -1 mol -1 ; T is Kelvin temperature, unit K; is the total molar Gibbs free energy of H2 produced in the hydrogen sulfide pyrolysis reaction, in J / mol; is the total molar Gibbs free energy of the product S2 in the hydrogen production reaction by pyrolysis of hydrogen sulfide, in J / mol; It is the total molar Gibbs free energy of H2S produced by the pyrolysis of hydrogen sulfide, in J / mol.

[0066] The total molar Gibbs free energy of S2 in the equilibrium constant prediction model for hydrogen production from hydrogen sulfide pyrolysis The calculation formula is shown in formula (2):

[0067]

[0068] In formula (2), is the standard formation enthalpy of S2, in J / mol; is the molar enthalpy of S2 at 298.15K, in J / mol; is the molar Gibbs free energy of S2, in J / mol.

[0069] Standard enthalpy of formation of S2 Take 128600 J·mol -1 , is the molar enthalpy of S2 at 298.15 K, which is 13441.301 J·mol -1 .

[0070] The total molar Gibbs free energy of H2 in the equilibrium constant prediction model of hydrogen sulfide pyrolysis reaction The calculation formula is shown in formula (3):

[0071]

[0072] In formula (3), is the standard formation enthalpy of H2, in J / mol; is the molar enthalpy of H2 at 298.15K, in J / mol; is the molar Gibbs free energy of H2, in J / mol.

[0073] Standard enthalpy of formation of H2 Take the molar enthalpy at 0 J / mol and temperature 298.15 K Take 34996.098 J / mol.

[0074] The total molar Gibbs free energy of H2S in the equilibrium constant prediction model for hydrogen production from hydrogen sulfide pyrolysis The calculation formula is shown in formula (4):

[0075]

[0076] In formula (4), is the standard formation enthalpy of H2S, in J / mol; is the molar enthalpy of H2S at 298.15K, in J / mol; is the molar Gibbs free energy of H2S, in J / mol.

[0077] Standard enthalpy of formation of H2S Take -20502 J·mol -1 , is the molar enthalpy of H2S at 298.15K, which is 49499.134 J·mol -1 .

[0078] Step S2: calculating the conversion rate of hydrogen sulfide pyrolysis reaction to produce hydrogen by using a hydrogen sulfide pyrolysis reaction equilibrium constant prediction model;

[0079] The method for calculating the conversion rate of hydrogen sulfide pyrolysis to produce hydrogen in this embodiment is: the hydrogen sulfide pyrolysis to produce hydrogen equilibrium constant K calculated by the hydrogen sulfide pyrolysis to produce hydrogen equilibrium constant prediction model under the corresponding temperature and pressure conditions is used to calculate the hydrogen sulfide pyrolysis to produce hydrogen equilibrium constant K p , substitute into the equilibrium equation of H2S thermal cracking reaction to calculate the degree of reaction, that is, the conversion rate of hydrogen sulfide thermal decomposition to hydrogen.

[0080] Based on the equilibrium composition of the H2S thermal cracking reaction, the equilibrium equation of the H2S thermal cracking reaction is shown in formula (5):

[0081]

[0082] In formula (5), n is the initial molar number of H2S, in mol; α is the degree of reaction, ranging from 0 to 1, 0 means no reaction, 1 means complete reaction; P tot is the total reaction pressure during the H2S pyrolysis reaction, in Pa

[0083] Assuming that the initial molar number of hydrogen sulfide is 1, the percentage progress of the reaction (α%) corresponds to the conversion rate of hydrogen sulfide. According to the above equation, the pyrolysis conversion rate of hydrogen sulfide under specific conditions can be quickly calculated by substituting the reaction equilibrium constant obtained under the conditions.

[0084] The present invention predicts and calculates the conversion rate of hydrogen sulfide pyrolysis at different temperatures and pressures. The experimental conditions and prediction results are shown in Table 1:

[0085] Table 1 Effect of pressure on H2S conversion rate from hydrogen sulfide pyrolysis

[0086]

[0087]

[0088] From Table 1, it can be observed that the conversion rate of H2S decreases gradually with the increase of pressure. If the results are expressed in the form of a curve, it can be more clearly seen that the conversion rate of H2S increases with the increase of temperature and the decrease of pressure. Figure 1 shown.

[0089] Evaluation of the Equilibrium Constant Prediction Model for Hydrogen Production from Hydrogen Sulfide Pyrolysis

[0090] According to the equilibrium constant prediction model for hydrogen sulfide pyrolysis reaction to produce hydrogen established in the embodiment, the predicted values ​​of the equilibrium constant model at different temperatures, the calculated values ​​of the existing empirical expressions and the experimental data published in the prior art in the field are compared and analyzed, and the specific results are shown in Table 2 and Table 3, respectively, wherein the experimental data are the data after the original experimental data given by Preuner and Schupp and Randall and Bichowsky are inversely processed. Figure 2 , Figure 3 is the relative deviation between the predicted values ​​of the equilibrium constant prediction model established in the present invention in different temperature ranges and the calculated values ​​of the four empirical expressions in the prior art and the experimental data (K 实验 -K 计算 / K 实验 ).

[0091] Table 2 Comparison of equilibrium constants of hydrogen sulfide pyrolysis reaction in the temperature range of 1023K to 1405K

[0092]

[0093] Table 3 Comparison of equilibrium constants of hydrogen sulfide pyrolysis reaction in the temperature range of 1362K to 1667K

[0094]

[0095]

[0096] Combining Table 2, Table 3 and Figure 2 , Figure 3 It can be seen from the results that the prediction results of the hydrogen sulfide pyrolysis reaction equilibrium constant prediction model established by the present invention are in good agreement with the experimental data, and the average relative deviations are better than the empirical expressions in the prior art. This model has significant advantages over the same type of empirical expressions in the prior art: 1) Only the experimental values ​​of several basic molecular constants of reactants and products need to be input to directly perform algebraic operations, overcoming the dependence on a large amount of experimental data for related reactions; 2) Starting from the molecular structure, the accuracy of the calculation is improved; 3) Temperature and pressure are used as variables to enhance applicability. This technology of constructing a formulaic representation of the equilibrium constant also provides a new way to calculate the equilibrium constant in other chemical reaction processes. At the same time, the conversion rate of the hydrogen sulfide pyrolysis reaction to produce hydrogen obtained by using the equilibrium constant prediction on this basis is correspondingly more accurate, and can more accurately reflect the real results and the overall reaction process, which is conducive to guiding the practical application of the hydrogen sulfide pyrolysis reaction to produce hydrogen.

[0097] In the description of the present invention, it should be pointed out that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside" and "outside" etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and should not be understood as a limitation on the present invention.

[0098] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for predicting the conversion rate of hydrogen production by pyrolysis of hydrogen sulfide, characterized in that: The following steps are involved: Step S1: establishing a prediction model for the equilibrium constant of hydrogen sulfide pyrolysis reaction; Step S2: calculating the conversion rate of hydrogen sulfide pyrolysis reaction to produce hydrogen by using a hydrogen sulfide pyrolysis reaction equilibrium constant prediction model; The equilibrium constant prediction model of hydrogen sulfide pyrolysis reaction is shown in formula (1): In formula (1), K is the equilibrium constant of hydrogen sulfide pyrolysis reaction; e is the natural constant; R is the universal gas constant, which is 8.3143 J·K -1 mol -1 ; T is Kelvin temperature, unit K; is the total molar Gibbs free energy of H2 produced in the hydrogen sulfide pyrolysis reaction, in J / mol; is the total molar Gibbs free energy of the product S2 in the hydrogen sulfide pyrolysis reaction, unit J / mol; is the total molar Gibbs free energy of H2S produced in the hydrogen sulfide pyrolysis reaction, in J / mol; The total molar Gibbs free energy of S2 in the hydrogen sulfide pyrolysis hydrogen production equilibrium constant prediction model The calculation formula is shown in formula (2): In formula (2), is the standard formation enthalpy of S2, in J / mol; is the molar enthalpy of S2 at 298.15K, in J / mol; is the molar Gibbs free energy of S2, in J / mol; The total molar Gibbs free energy of H2 in the equilibrium constant prediction model of the hydrogen sulfide pyrolysis hydrogen production reaction The calculation formula is shown in formula (3): In formula (3), is the standard formation enthalpy of H2, in J / mol; is the molar enthalpy of H2 at 298.15K, in J / mol; is the molar Gibbs free energy of H2, in J / mol; The total molar Gibbs free energy of H2S in the hydrogen sulfide pyrolysis hydrogen production equilibrium constant prediction model The calculation formula is shown in formula (4): In formula (4), is the standard formation enthalpy of H2S, in J / mol; is the molar enthalpy of H2S at 298.15K, in J / mol; is the molar Gibbs free energy of H2S, in J / mol; The method for calculating the conversion rate of hydrogen sulfide pyrolysis reaction is as follows: the equilibrium constant K of hydrogen sulfide pyrolysis reaction calculated by the equilibrium constant prediction model of hydrogen sulfide pyrolysis reaction under the corresponding temperature and pressure conditions is converted into p , the equilibrium equation of the H2S thermal cracking reaction is brought into play to calculate the degree of reaction, that is, the conversion rate of hydrogen sulfide thermal decomposition to hydrogen, wherein the equilibrium equation of the H2S thermal cracking reaction is shown in equation (5): In formula (5), n is the initial molar number of H2S, in mol; α is the degree of reaction, ranging from 0 to 1, 0 means no reaction, 1 means complete reaction; P tot It is the total reaction pressure during the H2S pyrolysis reaction, in Pa.

Images