Crude oil dehydration method based on molecular dynamics simulation

Abstract

The invention discloses a crude oil dehydration method based on molecular dynamics simulation, and relates to the technical field of petroleum processing, and the method comprises the following steps: constructing an atom and molecule model, and carrying out initial structure configuration; establishing a nano-droplet model, and placing the nano-droplet model in a set rectangular box for relaxation so as to minimize energy; setting a time step length and a force field parameter of the liquid drop, and carrying out molecular dynamics simulation by selecting a veociity-verlet integral algorithm; applying an electric field in the x-axis direction, and setting periodic boundary conditions; and each physical quantity of the water drops is obtained through cyclic calculation until the set time step length is reached. Therefore, by the adoption of the crude oil dehydration method based on molecular dynamics simulation, water drops are modeled on the atomic level, the micro mechanism of different variables on dehydration efficiency and accurate representation of liquid drop coalescence and separation is effectively revealed by accurately controlling the size of the water drops, electric field parameters and the like, and reference is provided for efficient dehydration in the petroleum industry.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum processing, in particular to a crude oil dehydration method based on molecular dynamics simulation. Background Art

[0002] Crude oil often contains a certain amount of water, which is usually dispersed in the crude oil in the form of small droplets to form an oil-in-water emulsion. The presence of water not only affects the quality of crude oil and reduces the heating value of crude oil, but also causes corrosion of equipment and increases transportation and processing costs. Therefore, effective dehydration of crude oil is one of the important links in oil processing.

[0003] Traditional methods for crude oil dehydration mainly include sedimentation, heating, chemical separation and centrifugal separation, etc. However, these methods have certain limitations in terms of energy consumption, chemical pollution and efficiency, especially for tiny water droplets, which are difficult to achieve efficient separation by traditional physical methods.

[0004] At present, electrostatic coalescence is an emerging dehydration method. It charges water droplets under the action of an electric field and causes them to collide and coalesce to form larger water droplets, which is easy to separate. Electrostatic coalescence has the advantages of high efficiency, environmental protection and strong adaptability, and has been widely used in the field of oil-water separation. However, the existing electrostatic coalescence technology still faces some challenges. For example, the influence mechanism of parameters such as electric field intensity, water droplet concentration and water droplet size on the coalescence effect is not fully understood, which limits its application range and separation efficiency.

[0005] Therefore, studying the coalescence behavior of water droplets under the action of electric field is of great significance to improve the dehydration efficiency. In order to more systematically study the influence of these factors on the dehydration process, it is necessary to provide a simulation model based on molecular dynamics to study the movement and coalescence behavior of water droplets under the action of electric field, reveal the key factors affecting the coalescence efficiency from a microscopic perspective, optimize the electric field parameters, overcome the limitations of traditional methods, and solve the limitations of traditional methods in terms of efficiency and stability. Summary of the invention

[0006] The purpose of the present invention is to provide a crude oil dehydration method based on molecular dynamics simulation, which can accurately control the water droplet size, electric field parameters, etc. through a simulation model based on molecular dynamics, effectively reveal the influence of different variables on the dehydration efficiency, and realize efficient dehydration in the petroleum industry.

[0007] To achieve the above object, the present invention provides a crude oil dehydration method based on molecular dynamics simulation, comprising the following steps:

[0008] S1. Build atomic and molecular models and perform initial structural configuration;

[0009] S2. Build a model of the nanodroplet and place it in a set rectangular box for relaxation to minimize the energy;

[0010] S3, set the time step and force field parameters of the droplet, and use the velocity-verlet integration algorithm for molecular dynamics simulation;

[0011] S4, applying an electric field in the x-axis direction and setting periodic boundary conditions;

[0012] S5. Obtain various physical quantities of the water droplet through cyclic calculation until the set time step is reached.

[0013] Preferably, in step S2, establishing the model of the nanodroplets includes establishing a rectangular box, in which three spherical nanodroplets are evenly placed, and the three droplets are in a straight line.

[0014] Preferably, in step S2, the energy minimization adopts the NVT ensemble, where N, V, and T represent the number of atoms, volume, and temperature in the simulation system, respectively, and the initial values ​​of the three parameters are set and kept unchanged in the simulation.

[0015] Preferably, in step S3, the velocity-verlet integration algorithm uses Taylor to perform expansion calculation as follows:

[0016]

[0017] Then we get:

[0018]

[0019] In the formula, are the displacement, velocity, and acceleration of the atom at time t, respectively. Δt is the time step. O(Δt 2 ) is the remainder of Taylor’s formula.

[0020] Preferably, in step S3, the force field of the droplet adopts the Lennard-Jones 12 / 6 potential function, as follows:

[0021]

[0022] In the formula, q i ,q j are the charges of atoms i and j respectively; r ij represents the distance between atoms i and j, i.e. the bond length; ε ij is the energy parameter, σ ij is the distance parameter.

[0023] Therefore, the present invention adopts the above-mentioned crude oil dehydration method based on molecular dynamics simulation, which has the following technical effects:

[0024] (1) The established theoretical model can quickly and accurately calculate physical quantities such as the particle distribution and droplet motion state of nanodroplets in oil-in-water, greatly improving efficiency. It provides a new method for exploring the microscopic behavior of droplets in nanoemulsions and provides basic data support for designing more efficient dehydration equipment. It has significant industrial application prospects and reduces the high cost and difficulty of experiments.

[0025] (2) During the simulation process, the NVT ensemble is selected, that is, a constant number of atoms, volume, and temperature, which can ensure the stability of the system. By selecting a reasonable time step and using the velocity-verlet integration algorithm, the dynamic behavior of nanoscale water droplets under the action of an electric field can be simulated, ensuring computational stability and efficiency.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of molecular dynamics simulation in an embodiment of a crude oil dehydration method based on molecular dynamics simulation;

[0028] Figure 2 is a schematic diagram of an initial model after relaxation is completed in an embodiment of a crude oil dehydration method based on molecular dynamics simulation;

[0029] Figure 3 It is a schematic diagram of the state of droplet coalescence at 106ps in an embodiment of a crude oil dehydration method based on molecular dynamics simulation;

[0030] Figure 4 The microscopic schematic diagram of a nano droplet at 250ps in an embodiment of a crude oil dehydration method based on molecular dynamics simulation;

[0031] Figure 5 The microscopic schematic diagram of a nano droplet at 500ps in an embodiment of a crude oil dehydration method based on molecular dynamics simulation;

[0032] Figure 6 It is a schematic diagram of the relationship between the number of Na ions and Cl particles at various positions of a droplet at the atomic level at 106ps in an embodiment of a crude oil dehydration method based on molecular dynamics simulation;

[0033] Figure 7 It is a mean square displacement of the whole process in an embodiment of a crude oil dehydration method based on molecular dynamics simulation. DETAILED DESCRIPTION

[0034] The present invention can be explained in more detail by the following examples. The purpose of disclosing the present invention is to protect all changes and improvements within the scope of the present invention. The present invention is not limited to the following examples.

[0035] like Figure 1 As shown, the present invention provides a crude oil dehydration method based on molecular dynamics simulation, comprising the following steps:

[0036] S1. First, use Materials Studio for molecular modeling, then use Packmol to build a system model, and then use Lammps for simulation. It can achieve large-scale parallel computing, which is suitable for nanoscale simulation and effectively improves simulation efficiency.

[0037] S2. According to the size requirements in the project, a nanodroplet model is established, and the NVT ensemble is used for energy minimization (the maximum iteration number is 500 and the maximum energy estimation value of 1000 kcal / mol, and the total relaxation time is 600 ps). Among them, N, V, and T represent the number of atoms, volume, and temperature in the simulation system, respectively, and the initial values ​​of the three parameters are set and kept unchanged in the simulation to ensure the stability of the system. Among them, the relaxation completion results are shown in Figure 2 The droplet diameter has no substantial effect on the actual simulation results. Therefore, in order to save computing power, the radius of the droplets is 3nm, the center distance between the droplets is 10nm, and a box with a length, width and height of 120nm*24nm*24nm is built on the periphery.

[0038] S3. First, set the droplet potential function. Here, the Lennard-Jones 12 / 6 potential function (LJ 12-6) is selected as follows:

[0039]

[0040] In the formula, q i ,q j are the charges of atoms i and j respectively; r ij represents the distance between atoms i and j, i.e. the bond length; ε ij is the energy parameter, σ ij is the distance parameter.

[0041] Secondly, the time step of the calculation is set. The whole simulation process is 500ps, the integration step is 1fs, and the molecular position information and thermodynamic information of the system are output every 1000fs for analysis.

[0042] Then, based on the velocity-verlet integration algorithm and using Taylor expansion, the model is iteratively calculated to simulate the dynamic behavior of nanoscale water droplets under the action of electric field. The expansion formula is as follows:

[0043]

[0044] In the formula, are the displacement, velocity, and acceleration of the atom at time t, respectively. Δt is the time step. O(Δt 2 ) is the remainder of Taylor’s formula.

[0045] Using the above two formulas, we get:

[0046]

[0047] Before iterative calculation, it is necessary to set the coordinates and their initial velocities, and obtain the coordinate data of the atoms in the system after calculation through a cyclic calculation of the time step t+Δt.

[0048] S4, apply an electric field E in the x-axis direction. In this example, the droplet concentration is set to 1.197M / L and the electric field strength is set to 0.48V / nm. It should be noted that in actual production, the electric field strength used for dehydration is on the order of 10 5 V / m, but in order to save computing power and make it react faster, the electric field strength is increased by an order of magnitude, but this does not affect the rigor of the simulation. Afterwards, periodic boundary conditions are set for the simulation system so that it will not fly out of the set range during the calculation process, thereby calculating the x, y, z coordinates of each atom in the system, the speed and acceleration in the x, y, z directions, and other physical quantities; and the output physical quantities are averaged to obtain the result data at different times.

[0049] Although the electric field strength selected in this embodiment is 0.48 V / nm, the critical electric field strength for droplet aggregation is subsequently obtained to be 0.50 V / nm by changing the single factor of the electric field strength. In actual production, the electric field strength is controlled within a certain range as much as possible.

[0050] like Figure 3 As shown in Figure 1, at 106ps, the coalescence behavior between water droplets can be clearly observed, that is, the contact moment when the droplets first coalesce; Figure 4 As shown in Figure 2, after 250 ps, ​​the droplets aggregate for the second time. Figure 5 As shown, after 500ps, the droplet reaches a balanced convergent state.

[0051] At 106ps, the relationship between the number of Na ions and Cl particles in the droplet at the atomic level x coordinate is as follows: Figure 6 In the whole process, the mean square displacement of each atom is shown as Figure 7 As shown, ① to ④ is the process of the first coalescence of droplets, and ⑤ to ⑧ is the process of the second coalescence of droplets, which is manifested by the increase in the slope of the curve.

[0052] S5, when the set time step t is reached max , stop calculating and outputting the final data; otherwise, repeat steps S3-S4.

[0053] Therefore, the present invention adopts the above-mentioned crude oil dehydration method based on molecular dynamics simulation, and by optimizing the electric field strength and simulation parameters, the water droplet coalescence efficiency can be improved, providing a reference for reducing the dehydration time and reducing energy consumption in the actual process.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for dehydrating crude oil based on molecular dynamics simulation, characterized in that: The following steps are involved: S1. Build atomic and molecular models and perform initial structural configuration; S2. Build a model of the nanodroplet and place it in a set rectangular box for relaxation to minimize the energy; S3, set the time step and force field parameters of the droplet, and use the velocity-verlet integration algorithm for molecular dynamics simulation; S4, applying an electric field in the x-axis direction and setting periodic boundary conditions; S5. Obtain various physical quantities of the water droplet through cyclic calculation until the set time step is reached.

2. The method for dehydrating crude oil based on molecular dynamics simulation according to claim 1, characterized in that: In step S2, establishing a model of nanodroplets includes establishing a rectangular box, in which three spherical nanodroplets are evenly placed, and the three droplets are in a straight line.

3. The method for dehydrating crude oil based on molecular dynamics simulation according to claim 1, characterized in that: In step S2, the NVT ensemble is used for energy minimization, where N, V, and T represent the number of atoms, volume, and temperature in the simulation system, respectively. The initial values ​​of the three parameters are set and kept unchanged during the simulation.

4. The method for dehydrating crude oil based on molecular dynamics simulation according to claim 1, characterized in that: In step S3, the velocity-verlet integration algorithm uses Taylor to perform expansion calculation as follows: Then we get: In the formula, are the displacement, velocity, and acceleration of the atom at time t, respectively. Δt is the time step. O(Δt 2 ) is the remainder of Taylor’s formula.

5. The method for dehydrating crude oil based on molecular dynamics simulation according to claim 1, characterized in that: In step S3, the force field of the droplet adopts the Lennard-Jones 12 / 6 potential function, as follows: In the formula, q i ,q j are the charges of atoms i and j respectively; r ij represents the distance between atoms i and j, i.e. the bond length; ε ij is the energy parameter, σ ij is the distance parameter.

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