An integrated modeling approach for product separation membrane reactors based on thermodynamic equilibrium

Abstract

The present invention discloses an integrated modeling method for a product separation membrane reactor based on thermodynamic equilibrium. It includes a reaction condition input process, a component equilibrium separation process and a performance output process, all of which are implemented and integrated through Matlab code. The reaction condition input process determines the operating conditions, reaction components and physical property models, and determines whether there is a product separation membrane. The component equilibrium separation process divides the membrane reactor into several microelements, and based on the thermodynamic equilibrium of the reaction components with the minimum Gibbs free energy, the reaction and separation processes are calculated in sequence until convergence; for a membraneless reactor, the thermodynamic equilibrium of the reaction is directly calculated. The performance output process shows the proportion of reaction components and related performance of the reactor under thermodynamic equilibrium. The present invention can realize the equilibrium simulation of a reactor with a product separation membrane, and the integrated model has the characteristics of high efficiency, rapidity, generality, and easy coupling.

Description

Technical Field

[0001] The present invention relates to the field of product separation membrane reactors, and in particular to an integrated modeling method of product separation membrane reactors based on thermodynamic equilibrium. Background Art

[0002] The reversible reaction system in the traditional reactor cannot achieve complete conversion of the reactants due to the limitation of thermodynamic equilibrium. As a device that can selectively permeate components, separation membranes are widely used in purification, electrode manufacturing, product separation and other fields. By utilizing the product separation characteristics of the membrane, the target product can be continuously separated during the reaction process of the traditional reactor. Based on the LeChatelier principle, the original thermodynamic equilibrium limitation is broken, a higher target product yield and reactant conversion rate are achieved, and the product purification function is also combined.

[0003] For product separation membrane reactors, there are currently experiments and simulations that demonstrate the potential of membrane reactors in promoting chemical reaction conversion. As a preliminary design of industrial production processes, simulations mainly use some commercial software (such as ANSYS, COMSOL, ASPEN Plus) to study the reaction process in membrane reactors and its enhancement methods, but there are shortcomings such as high computational cost and difficulty in coupling external modules. However, in order to achieve reaction process enhancement, it is usually necessary to perform a large amount of calculations or combine optimization algorithms to obtain the optimal reaction conditions for a specific reaction system.

[0004] In addition, due to different material properties, the properties of product separation membranes are also different, such as hydrogen permeable membranes (palladium-silver composite), oxygen permeable membranes (perovskite), carbon dioxide permeable membranes (zeolite molecular sieves), etc. There are few studies comparing the performance potential of different product separation membranes in reaction systems, and there is a lack of product separation membrane property comparison and membrane design guidance methods.

[0005] Therefore, in order to obtain an efficient and fast product separation membrane reactor calculation model that is suitable for a variety of reaction systems and membrane types, it is necessary to propose an integrated modeling method to apply the corresponding model to the reaction system process design, operating conditions optimization and product separation membrane reactor design guidance, and explore the strengthening mechanism of the product separation membrane on the reactor. Summary of the invention

[0006] The purpose of the present invention is to propose an integrated modeling method for a product separation membrane reactor based on thermodynamic equilibrium. The method proposed in the present invention can establish a corresponding product separation membrane reactor model for efficient and rapid design, optimization and guidance, and can explore the strengthening mechanism of the product separation membrane on the reactor.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] An integrated modeling method for a product separation membrane reactor based on thermodynamic equilibrium is proposed. The modeling method is implemented by Matlab code and integrated into a function that can be called by other codes and software. The entire modeling method is divided into the following steps:

[0009] (1) Establish a data preprocessing module at the head of the modeling program, input the reaction components to be considered in the reversible reaction system corresponding to the reactor, and select a physical property model to calculate the physical properties of each reaction component;

[0010] (2) Input reaction operating conditions: reaction temperature 0-1200° C., reaction pressure 1-50 atm, reactant feed component molar ratio 0-100%, reactant feed flow rate 0-10 mol / h;

[0011] (3) Setting the reactor type, with 0 and 1 representing the reactor with and without a product separation membrane. Through the if statement, if it is set to 0, the calculation of the reactor without a product separation membrane in step 4 is performed; if it is set to 1, the calculation of the reactor with a product separation membrane in step 5 is performed;

[0012] (4) For the reactor without a product separation membrane, the overall Gibbs free energy function is calculated in combination with the physical properties of the reaction components in step 1 and the reaction operating conditions in step 2. The molar proportion of each reaction component when thermodynamic equilibrium is achieved is calculated by the Gibbs free energy minimum principle, and the molar proportion of the reaction component at thermodynamic equilibrium of the reactor without a product separation membrane is output, wherein the Gibbs free energy function is expressed by the following expression:

[0013]

[0014] Where G represents the Gibbs free energy function, g i represents the Gibbs free energy of reaction component i, n i represents the number of moles of reaction component i;

[0015] (5) For reactors with product separation membranes, input membrane thickness of 1 to 100 μm and membrane area of ​​1 to 100 cm 2, membrane side osmotic pressure 0-1atm and its osmotic kinetic parameters; then, the reactor with the product separation membrane is divided into 1-∞ reaction micro-element-separation micro-element groups, and in each reaction micro-element-separation micro-element group, the molar proportion of the reaction component in the thermodynamic equilibrium state of the reaction micro-element is calculated by the Gibbs free energy minimum principle; next, the separation micro-element is further differentiated into smaller micro-element in the separation micro-element, and the product permeation amount calculation formula is iteratively calculated until the single product separation amount result of the separation micro-element meets the convergence criterion; finally, each reaction micro-element-separation micro-element group is calculated in turn according to the cyclic algorithm until the total product separation amount result of the reactor with the product separation membrane meets the convergence criterion, and the molar proportion of the reaction component in the thermodynamic equilibrium state of the reactor with the product separation membrane is output;

[0016] (6) Establishing a result processing module at the end of the modeling program, combining the molar proportion of the reaction components of the reactor under thermodynamic equilibrium outputted from step 4 or 5, and converting it into the flow rate of each reaction component through the law of conservation of mass; then, for the reactor without a product separation membrane, calculating and outputting the performance results such as the reactant conversion rate and the product yield ratio; for the reactor with a product separation membrane, calculating and outputting the performance results such as the reactant conversion rate, the product yield ratio, the product separation amount, the product extraction rate, and the membrane utilization rate;

[0017] In step 1, the reaction components that need to be considered in the reversible reaction system are the main reactants and products of the reversible reaction system, such as the reaction components in the methane steam reforming reaction are CH4, H2O, CO, CO2, H2, the reaction components in the water gas shift reaction are CO, CO2, H2O, H2, and the reaction components in the methanol steam reforming reaction are CH3OH, H2O, CO, CO2, H2.

[0018] In step 1, the physical property model can be selected from SRK, NRTL, PR, WILSON, UNIFAC, and NIST.

[0019] In step 5, the reactor with the product separation membrane is divided into a variable number of reaction micro-element-separation micro-element groups, each reaction micro-element-separation micro-element group calculates the reaction micro-element and the separation micro-element in sequence, and the molar proportion of each reaction component is updated and saved after each calculation;

[0020] In step 5, the convergence criterion for the separation element is that the relative effect of continuing to add a separation element on the result is less than 0.001%; ​​the convergence criterion for the reactor with a product separation membrane is that the relative effect of continuing to add a reaction element-separation element group on the result is less than 0.001%.

[0021] In the reaction element of the reaction element-separation element group, the molar proportion of the reaction components under local thermodynamic equilibrium is obtained by thermodynamic equilibrium calculation, and then the molar proportion of the reaction components under local thermodynamic equilibrium is introduced into the separation element as the initial reaction component condition.

[0022] In the reaction microelement in the reaction microelement-separation microelement group, the amount of separated product is calculated by the product permeation amount calculation formula based on the partial pressure difference of the separated product in the reaction component, wherein the product permeation amount calculation formula is expressed as follows:

[0023]

[0024] In the formula, Q pro is the product separation amount, ε is the product separation membrane effectiveness factor, A mem is the product separation membrane area, α is the permeation kinetic pre-exponential factor, E is the separation activation energy, T is the temperature, P is the product partial pressure (rea and pen represent the reaction side and the permeation separation side, respectively), δ mem is the thickness of the product separation membrane.

[0025] In the separation microelement, the separation microelement is differentiated into 1 to ∞ smaller differential separation microelement, and the product separation amount of each differential separation microelement is iteratively calculated and accumulated as a single product separation amount of the separation microelement, wherein the molar proportion of the reaction components is updated and saved in each calculation.

[0026] Compared with the prior art, the method proposed by the present invention has the following beneficial effects:

[0027] (1) Strong versatility. The reaction condition input process 1 allows the user to customize the operating conditions and reaction components, and the component equilibrium separation process 2 allows the user to customize the membrane parameters and microelement parameters. Therefore, it is suitable for the calculation of reaction systems of various reaction systems and the calculation of various product separation membranes.

[0028] (2) Efficient and fast. All processes are implemented by Matlab code, without coupling with other commercial software, and the calculation results are verified by experiments to ensure accuracy. The single calculation speed is fast (0.2 seconds without membrane and 3 seconds with membrane).

[0029] (3) Good coupling. The integrated design allows the product separation membrane reactor model to be used as a 0-dimensional model or function. The characteristics of the code implementation make it easy to be called by algorithms (such as genetic algorithms, support vector machines, neural networks), and coupled into commercial software that allows external codes (such as ANSYS, COMSOL, ASPEN Plus, Abaqus), etc.

[0030] (4) Product separation membrane performance calculation based on thermodynamic equilibrium can be realized. The theoretical improvement level of product separation membrane in the reaction system can be analyzed and studied to guide the design of product separation membrane reactor; the performance influence mechanism of different operating conditions can be analyzed to implement the optimal operating conditions of the reactor; the performance output can be quickly calculated after input, which can be used for the process flow design of reaction system with multiple reactors, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A flow chart of the integrated modeling method proposed by the present invention;

[0032] Figure 2 This is a schematic diagram of a methane wet reforming reactor model with a hydrogen separation membrane according to an embodiment of the present invention;

[0033] Figure 3 A schematic diagram of a reaction microelement-separation microelement according to an embodiment of the present invention;

[0034] Figure 4 The figure is a comparison chart between the model running results of the embodiment of the present invention and the results of Experiment 1.

[0035] Figure 5 The figure is a comparison chart between the model running results of the embodiment of the present invention and the results of Experiment 2.

[0036] Description of the symbols in the accompanying drawings:

[0037] 1- Reaction condition input process, 2- Component equilibrium separation process, 3- Performance output process. DETAILED DESCRIPTION

[0038] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments, which are only one embodiment of the present invention and do not limit the present invention.

[0039] The following is an explanation of the specific example of modeling a methane wet reforming reactor with a hydrogen separation membrane.

[0040] like Figure 1 As shown, the integrated modeling method of the product separation membrane reactor based on thermodynamic equilibrium provided by the present invention includes a reaction condition input process 1, a component equilibrium separation process 2 and a performance output process 3. The component composition and operating conditions are input in the reaction condition input process 1, such as Figure 2 As shown, in this embodiment, the components of the methane wet reforming reaction system are CH4, H2O, H2, CO, and CO2, wherein CH4 and H2O are reactants, and H2, CO, and CO2 are products. The operating conditions are temperature, reaction side pressure, permeate side pressure, reactant feed ratio, and reactant flow rate. The physical properties of each component and mixed component are determined by the SRK physical property model, including specific heat capacity, density, molar mass, molar enthalpy, and molar entropy.

[0041] Next, the input parameters are imported into the component equilibrium separation process 2, such as Figure 1 As shown in the figure, due to the presence of a hydrogen separation membrane, the if statement is judged as 1 to enter the microelement reaction-separation process based on thermodynamic equilibrium, and enter the membrane-related parameters and microelement parameters. Among them, the membrane thickness is 6μm, the membrane tube diameter is 9.5mm, the membrane tube length is 70mm, the hydrogen separation membrane effectiveness factor is 100%, the activation energy is 16700J / mol, and the pre-exponential factor is 3.4954×10 -5 , the convergence criterion of the microelement is 0.001%. The above parameters are substituted into the product permeation calculation formula to calculate the hydrogen permeation, where the product permeation calculation formula is expressed as follows:

[0042]

[0043] In the formula, Q pro is the product separation amount, ε is the product separation membrane effectiveness factor, A mem is the product separation membrane area, α is the permeation kinetic pre-exponential factor, E is the separation activation energy, T is the temperature, P is the product partial pressure (rea and pen represent the reaction side and the permeation separation side, respectively), δ mem is the thickness of the product separation membrane.

[0044] like Figure 2 As shown, the reactor with product separation membrane is divided into multiple reaction micro-element-separation micro-element groups dL. Figure 3 As shown, in a reaction microelement-separation microelement group dL, the reaction microelement first calculates the molar proportion of the reaction components under thermodynamic equilibrium based on the Gibbs free energy minimum principle, and uses its molar proportion result as the input of the separation microelement. The separation microelement dL is further divided into smaller separation microelement ddL, and H2 is separated for each ddL, and the cycle is repeated until the single H2 separation amount meets the convergence tolerance (less than 0.001%). Subsequently, the convergence calculation of the next reaction microelement-separation microelement group dL component i+1 is started by inheriting the previous microelement dL component i, and the calculation is repeated until the total H2 separation amount meets the convergence tolerance (less than 0.001%), completing the calculation of the component equilibrium separation process 2.

[0045] Finally, the performance output process 3 performs post-processing on the results of the component equilibrium separation process 2, and the output includes but is not limited to the molar proportion of the reaction components, the reactant conversion rate, the H2 separation amount, the H2 yield ratio, the H2 extraction rate, and the membrane utilization rate. More output indicators can be designed in combination with the results such as the molar proportion of the reaction components. Some calculation formulas are shown below:

[0046] Methane conversion rate:

[0047] Hydrogen separation capacity:

[0048] Hydrogen yield ratio:

[0049] Hydrogen extraction rate:

[0050] During the actual model operation, it is only necessary to complete the parameter input in the reaction condition input process 1 to automatically perform subsequent calculations and output results. The following verification of the modeling method of the present invention is carried out in combination with the results of two existing methane steam reforming hydrogen permeable membrane experiments. Experiment 1 measured the hydrogen extraction rate of the reactor with a product separation membrane under the reaction operating conditions of a temperature range of 400-600°C, a reaction pressure range of 100-400kPa, and a reactant space velocity range of 400-2400mL / (g·h); Experiment 2 measured the molar ratio of dry-based reaction components in the reactor with a product separation membrane under the reaction operating conditions of a temperature range of 700-950K. The sources of the two experimental references are as follows:

[0051] Experiment 1: Tong J, Matsumura Y, Suda H, Haraya K. Experimental Study of SteamReforming of Methane in a Thin(6μM)Pd-Based Membrane Reactor. Ind Eng Chem Res2005;44:1454–65.

[0052] Experiment 2: Adris AM, Lim CJ, Grace JR. The Fluidized Bed Membrane Reactor System: A Pilot Scale Experimental Study. Chem Eng Sci 1994; 49:5833-5843.

[0053] like Figure 4 As shown, the calculation results of the reactor model with product separation membrane established in the present invention are compared with the results of Experiment 1, indicating that the model calculation results are in good agreement with the experimental results, proving the reliability of the modeling method.

[0054] like Figure 5 As shown, the calculation results of the reactor model with product separation membrane established in the present invention are compared with the results of Experiment 2, indicating that the model calculation results are in good agreement with the experimental results, proving the reliability of the modeling method.

[0055] Through two experimental comparisons and verifications, it is shown that the feasibility and reliability of the integrated modeling method of the product separation membrane reactor based on thermodynamic equilibrium proposed in the present invention in modeling the methane wet reforming reactor with a hydrogen separation membrane are demonstrated. The integrated implementation is efficient and fast. The entire process is implemented by code, which is efficient and fast, highly versatile, easy to maintain and modify, has low computational cost, and is highly callable.

Claims

1. An integrated modeling method for a product separation membrane reactor based on thermodynamic equilibrium, characterized in that: The modeling methods are all implemented through Matlab code and integrated into a function that can be called by other codes and software. The entire modeling method is divided into the following steps: (1) Establish a data preprocessing module at the head of the modeling program, input the reaction components to be considered in the reversible reaction system corresponding to the reactor, and select a physical property model to calculate the physical properties of each reaction component; (2) Input reaction operating conditions: reaction temperature 0-1200° C., reaction pressure 1-50 atm, reactant feed component molar ratio 0-100%, reactant feed flow rate 0-10 mol / h; (3) Setting the reactor type, with 0 and 1 representing the reactor with and without a product separation membrane. Through the if statement, if it is set to 0, the calculation of the reactor without a product separation membrane in step 4 is performed; if it is set to 1, the calculation of the reactor with a product separation membrane in step 5 is performed; (4) For a reactor without a product separation membrane, the overall Gibbs free energy function is calculated in combination with the physical properties of the reaction components in step (1) and the reaction operating conditions in step (2). The molar proportions of the reaction components when thermodynamic equilibrium is achieved are calculated using the Gibbs free energy minimum principle, and the molar proportions of the reaction components at thermodynamic equilibrium of the reactor without a product separation membrane are output, wherein the Gibbs free energy function is expressed by the following expression: Where G represents the Gibbs free energy function, g i represents the Gibbs free energy of reaction component i, n i represents the number of moles of reaction component i; (5) For reactors with product separation membranes, input membrane thickness of 1 to 100 μm and membrane area of ​​1 to 100 cm 2 , membrane side osmotic pressure 0-1atm and its osmotic kinetic parameters; then, the reactor with the product separation membrane is divided into 1-∞ reaction micro-element-separation micro-element groups, and in each reaction micro-element-separation micro-element group, the molar proportion of the reaction component in the thermodynamic equilibrium state of the reaction micro-element is calculated by the Gibbs free energy minimum principle; next, the separation micro-element is further differentiated into smaller micro-element in the separation micro-element, and the product permeation amount calculation formula is iteratively calculated until the single product separation amount result of the separation micro-element meets the convergence criterion; finally, each reaction micro-element-separation micro-element group is calculated in turn according to the cyclic algorithm until the total product separation amount result of the reactor with the product separation membrane meets the convergence criterion, and the molar proportion of the reaction component in the thermodynamic equilibrium state of the reactor with the product separation membrane is output; (6) A result processing module is established at the end of the modeling program, and the molar proportions of the reaction components of the reactor under thermodynamic equilibrium outputted from step (4) or (5) are converted into the flow rates of the reaction components by the law of conservation of mass; then, for the reactor without a product separation membrane, the performance results of the reactant conversion rate and the product yield ratio are calculated and outputted; for the reactor with a product separation membrane, the performance results of the reactant conversion rate, the product yield ratio, the product separation amount, the product extraction rate, and the membrane utilization rate are calculated and outputted.

2. The integrated modeling method of a product separation membrane reactor based on thermodynamic equilibrium according to claim 1, characterized in that: In step 1, the reaction components that need to be considered in the reversible reaction system are the main reactants and products of the reversible reaction system, among which the reaction components in the methane steam reforming reaction are CH4, H2O, CO, CO2, H2, the reaction components in the water gas shift reaction are CO, CO2, H2O, H2, and the reaction components in the methanol steam reforming reaction are CH3OH, H2O, CO, CO2, H2.

3. The integrated modeling method of a product separation membrane reactor based on thermodynamic equilibrium according to claim 1, characterized in that: In step 1, the physical property model can be selected from SRK, NRTL, PR, WILSON, UNIFAC, and NIST.

4. The integrated modeling method of a product separation membrane reactor based on thermodynamic equilibrium according to claim 1, characterized in that: In step 5, the reactor with the product separation membrane is divided into a variable number of reaction micro-element-separation micro-element groups, each reaction micro-element-separation micro-element group calculates the reaction micro-element and the separation micro-element in turn, and the molar proportion of each reaction component is updated and saved after each calculation.

5. The integrated modeling method of a product separation membrane reactor based on thermodynamic equilibrium according to claim 1, characterized in that: In step 5, the convergence criterion for the separation element is that the relative effect of continuing to add a separation element on the result is less than 0.001%; ​​the convergence criterion for the reactor with a product separation membrane is that the relative effect of continuing to add a reaction element-separation element group on the result is less than 0.001%.

6. The integrated modeling method of a product separation membrane reactor based on thermodynamic equilibrium according to claim 4, characterized in that: In the reaction element of the reaction element-separation element group, the molar proportion of the reaction components under local thermodynamic equilibrium is obtained by thermodynamic equilibrium calculation, and then the molar proportion of the reaction components under local thermodynamic equilibrium is introduced into the separation element as the initial reaction component condition.

7. The integrated modeling method of a product separation membrane reactor based on thermodynamic equilibrium according to claim 4, characterized in that: In the reaction microelement in the reaction microelement-separation microelement group, the amount of separated product is calculated by the product permeation amount calculation formula based on the partial pressure difference of the separated product in the reaction component, wherein the product permeation amount calculation formula is expressed as follows: In the formula, Q pro is the product separation amount, ε is the product separation membrane effectiveness factor, A mem is the product separation membrane area, α is the permeation kinetic pre-exponential factor, E is the separation activation energy, T is the temperature, P is the product partial pressure, rea and pen represent the reaction side and the permeation separation side respectively, δ mem is the thickness of the product separation membrane.

8. The integrated modeling method of a product separation membrane reactor based on thermodynamic equilibrium according to claim 7, characterized in that: In the separation microelement, the separation microelement is differentiated into 1 to ∞ smaller differential separation microelement, and the product separation amount of each differential separation microelement is iteratively calculated and accumulated as a single product separation amount of the separation microelement, wherein the molar proportion of the reaction components is updated and saved in each calculation.

Images