A method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation

Abstract

This invention relates to the fields of biomass oil processing and liquid hydrocarbon refining technology, and discloses a method for refining crude oil from pyrolysis of Ulva prolifera based on multi-stage membrane separation. The method includes: mixing crude oil from pyrolysis of Ulva prolifera with a n-alkane solvent to perform solvation reconstruction; inducing the precipitation of large-molecule polar impurities by utilizing differences in solubility parameters and performing solid-liquid separation; introducing the resulting degummed hydrocarbon oil into a multi-stage membrane separation system; performing component screening using a modified polytetrafluoroethylene membrane; and applying periodic pressure pulses to the permeate side. This invention utilizes the negative pressure difference generated during the pressure drop phase to drive a reverse flushing action, stripping adsorbates from the membrane interface, maintaining the distribution of hydrophobic components at the interface, and in principle avoiding thermally excited free radical polymerization reactions. This effectively solves the technical obstacle of difficult separation of polar components and hydrocarbon molecules, achieving membrane interface maintenance without downtime, and ensuring the thermodynamic stability of the refined hydrocarbon oil product.

Description

Technical Field

[0001] This invention belongs to the field of biomass oil processing and liquid hydrocarbon refining technology, and particularly relates to a method for refining crude oil from the pyrolysis of Ulva prolifera based on multi-stage membrane separation. Background Technology

[0002] Currently, crude oil produced from the pyrolysis of Ulva prolifera is used as a raw material for the preparation of liquid fuels. Conventional thermal processing methods such as distillation or pyrolysis are typically employed to separate hydrocarbons from impurities by utilizing the differences in boiling points between components. Since crude oil from Ulva prolifera pyrolysis is a microemulsion system composed of polar molecules and hydrocarbons, there is a complex network of hydrogen bonds between its molecules. In production practice, in order to remove bound water and organic acids, it is usually necessary to increase the refining temperature to break the interfacial tension balance. However, this heat input will activate the conjugated double bonds in the crude oil, thereby inducing uncontrolled free radical polymerization reactions, resulting in increased oil viscosity and coking on the surface of refining equipment.

[0003] Industry experts have attempted to increase filtration pressure differential or use modified membrane modules, but analysis has revealed that, under the existing thermodynamic equilibrium, effective desorption between polar impurities and hydrocarbon molecules is difficult to achieve. This leads to the rapid formation of a flexible filter cake layer at the membrane interface and may even cause physical collapse of the membrane pores, making it difficult to achieve high-purity refining while ensuring production continuity. For example, Chinese invention patent CN105419841B discloses a method for preparing renewable energy bio-oil from *Ulva prolifera* by pyrolysis with Jerusalem artichoke alcohol. This method introduces Jerusalem artichoke alcohol as a reaction medium and performs programmed temperature pyrolysis in a high-pressure reactor. This scheme does not deviate from the framework of high-temperature pyrolysis technology. Its thermodynamic input induces coking and polymerization of thermosensitive components, making subsequent washing and distillation processes lengthy and difficult to solve the deep coupling between hydrocarbon molecules and polar impurities at the microscopic level. System operation and product quality are often constrained by the reaction environment.

[0004] Therefore, the technical problem to be solved by this invention is how to achieve the directional migration of components by adjusting the thermodynamic state of the system under normal temperature conditions and construct an interface energy state with self-healing properties to solve the problem of deep separation of polar impurities. Summary of the Invention

[0005] This invention provides a method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation, comprising the following steps: Step 101: Mix the crude oil from the pyrolysis of Ulva lactuca with a n-alkane solvent at a volume ratio of 1:1 to 5:1. Utilize the difference in solubility parameters between the n-alkane solvent and the components of the crude oil from the pyrolysis of Ulva lactuca to carry out solubilization reconstruction, inducing the precipitation of gums, asphaltenes, and large molecular polar impurities and forming micro-aggregates. Step 102: Perform solid-liquid separation on the mixed system obtained in step 101, remove the precipitated micro-aggregates, and obtain a degummed hydrocarbon oil mixture with an acid value of less than 10 mg KOH / g. Step 103: The degummed hydrocarbon oil mixture is fed into a multi-stage membrane separation system. A modified polytetrafluoroethylene membrane is used as the separation medium. The components are screened by utilizing the hydrophobic field formed on the surface of the modified polytetrafluoroethylene membrane by the n-alkane solvent and the oleophilic properties of the modified polytetrafluoroethylene membrane. Step 104: Apply periodic pressure pulses to the permeate side of the multi-stage membrane separation system. The frequency of the periodic pressure pulses is 0.1 Hz to 5 Hz, and the pressure amplitude is 0.01 MPa to 0.2 MPa. Utilize the negative pressure difference generated during the pressure drop phase of the periodic pressure pulses to guide the hydrocarbon oil components that have permeated from the permeate side to the retention side of the modified polytetrafluoroethylene membrane for reverse flushing. This removes large polar impurities and water molecules adsorbed at the membrane interface and maintains the hydrophobic component distribution at the retention side interface of the modified polytetrafluoroethylene membrane, thereby obtaining refined hydrocarbon oil.

[0006] Preferably, the n-alkane solvent in step 101 is n-hexane, n-heptane, n-octane, n-decane, or n-dodecane; during the mixing process, the mixing temperature is controlled at 20°C to 50°C, and the mechanical stirring speed is 100 r / min to 500 r / min, inducing the macromolecular polar impurities to complete sedimentation within 30 min to 120 min.

[0007] Preferably, obtaining the degummed hydrocarbon-oil mixture in step 102 includes the following steps: placing the reconstructed mixture in a settling tank and letting it stand for 2 to 6 hours, using the density difference between the micro-aggregates and the liquid phase for gravity stratification; and removing the sedimentation bottom layer components by using a centrifuge with a separation factor of 3000 to 8000 to remove micro-aggregates with a particle size greater than 0.5 μm.

[0008] Preferably, in step 103, long-chain lipophilic functional groups are grafted onto the surface of the modified polytetrafluoroethylene membrane, so that the contact angle of the modified polytetrafluoroethylene membrane with n-alkane solvent is less than 10° and the contact angle with water molecules is greater than 120°.

[0009] Preferably, in step 104, the periodic pressure pulse is generated by a pressure regulating unit on the permeate side pipeline. The pressure regulating unit removes the polar adsorption layer at the membrane interface by controlling the instantaneous flux of the reverse flush to be 1% to 5% of the forward permeate flux.

[0010] Preferably, after obtaining the refined hydrocarbon oil in step 104, the method further includes the following steps: introducing the refined hydrocarbon oil into a flash distillation tower for solvent recovery, controlling the top temperature of the flash distillation tower to be the boiling point temperature of the n-alkane solvent, and returning the recovered n-alkane solvent to step 101 for recycling.

[0011] Preferably, in step 104, the intensity of the periodic pressure pulse is adjusted by monitoring the real-time permeate flux of the multi-stage membrane separation system, and the adjustment follows the formula: K=J real / J set Where K is the pulse adjustment coefficient; J real For the monitored real-time permeation flux; J set J is the preset standard permeation flux. set Crude oil from the pyrolysis of Ulva prolifera was pre-calibrated based on the corresponding components under standard membrane flux testing; when the K value was below 0.85, the pressure amplitude of the periodic pressure pulse was increased.

[0012] Preferably, the multi-stage membrane separation system adopts a two-stage series structure, wherein the first-stage membrane module has a molecular weight cutoff of 500 Da to 1000 Da and is used to remove metal components and bound water from the degummed hydrocarbon oil mixture; the second-stage membrane module has a molecular weight cutoff of 200 Da to 500 Da and is used to intercept organic acid molecules.

[0013] Preferably, in the purification process of the multi-stage membrane separation system, the operating pressure is controlled to be between 0.5 MPa and 2.0 MPa, and the operating temperature is between 25°C and 45°C.

[0014] Preferably, the kinetic energy generated by the periodic pressure pulse in step 104 is used to eliminate the concentration polarization at the interface of the modified polytetrafluoroethylene film, so that the viscosity change rate of the refined hydrocarbon oil after being kept at 180°C for 48 hours is less than 5%, and the water mass fraction is less than 0.05%.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: 1. In the refining process of crude oil from the pyrolysis of Ulva prolifera, alkane solvents are used to solubilize and reconstruct the crude oil system. By utilizing the difference in solubility parameters between alkane molecules and crude oil components, a physical induction effect is generated, causing stable colloidal substances and large polar molecules to precipitate physically and form micro-aggregates. This transforms the traditional high-temperature chemical separation into physical phase regulation at room temperature, avoiding free radical polymerization reactions triggered by heat during crude oil refining, preventing a sudden increase in system viscosity and coking, and thus ensuring the thermodynamic stability of the hydrocarbon oil products.

[0016] 2. By leveraging the hydrophobic field established by the alkane solvent and the intrinsic properties of the modified polytetrafluoroethylene membrane, a synergistic gain is generated. The chemical potential gradient formed on both sides of the membrane is used to drive the preferential permeation of hydrocarbon molecules, while simultaneously enhancing the association tendency between bound water molecules and organic acid molecules. The oleophilic barrier on the membrane surface enables the spontaneous enrichment of polar impurities, achieving deep decoupling of amphiphilic complex systems without the intervention of external heat sources. This solves the technical obstacle of effectively separating polar components and hydrocarbon molecules due to their similar solubility parameters during the refining of biomass oils.

[0017] 3. By utilizing the pressure modulation pulse applied to the permeate side, controlled reverse osmosis is generated. The refined hydrocarbon oil is then used for reverse backflushing to instantaneously dilute the stagnant layer at the membrane interface, destroy the interfacial convolution structure formed by the enrichment of polar components, and rebuild the chemical potential energy gradient from the inside to the outside. This inhibits the physical adsorption of water molecules and organic acids at the membrane interface, eliminates the interfacial thermodynamic collapse caused by concentration polarization, realizes the dynamic self-maintenance of the filtration interface, and inhibits membrane pore blockage. This ensures that the acid value and water content of the refined hydrocarbon oil are maintained at a constant low level throughout the entire operation cycle. Attached Figure Description

[0018] Figure 1 This is a flow chart of the process for the solvation reconstruction and multi-stage membrane separation refining of crude oil from the pyrolysis of Ulva lactuca in this invention; Figure 2 This is a block diagram of the intelligent pulse compensation and data processing logic for real-time flux feedback of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0020] A method for refining crude oil from the pyrolysis of Ulva prolifera based on multi-stage membrane separation is proposed. This method involves solvation reconstruction of the crude oil system, solid-liquid separation to remove micro-aggregates, component screening using a multi-stage membrane separation system, and reverse osmotic pressure pulse flushing. This achieves deep decoupling of the complex microemulsion system containing polar impurities and hydrocarbon molecules at room temperature, ensuring the thermodynamic stability of the refined hydrocarbon oil product. Specifically, a stable microemulsion system is constructed from the polar components and hydrocarbon molecules in the crude oil through a hydrogen-bonded network, exhibiting extremely strong microscopic stability. The system's inherent properties cause conventional gravity settling methods to fail. Furthermore, this complex system is highly susceptible to activating active components and inducing uncontrolled free radical polymerization under high-temperature refining conditions. In this embodiment, crude oil from the pyrolysis of *Ulva prolifera* and a n-alkane solvent are introduced into the reconstruction reaction unit at a volume ratio of 1:1 to 5:1. The n-alkane solvent is selected from one or more of n-hexane, n-heptane, n-octane, n-decane, or n-dodecane. Solvative reconstruction is achieved by utilizing the difference in solubility parameters between the n-alkane solvent and the components of the crude oil from the pyrolysis of *Ulva prolifera*, while maintaining a mixing temperature of 2... Under process conditions of 0℃ to 50℃ and mechanical stirring speed of 100r / min to 500r / min, stable resins, asphaltenes, and large polar impurities undergo physical precipitation through a physical induction effect, and aggregate to form micro-aggregates within an induction period of 30min to 120min, thus constructing a heterogeneous material basis for subsequent physical sieving. The volume ratio of n-alkane solvent to crude oil from Ulva lactuca pyrolysis is set within the range of 1:1 to 5:1. When the volume ratio is lower than 1:1, the difference in solubility parameters of the mixed system cannot be considered. Disruption of the hydrogen bond network in crude oil prevents gums and asphaltenes from forming micro-aggregates with a particle size greater than 0.5 μm, resulting in an acid value of the degummed hydrocarbon oil mixture exceeding 15 mg KOH / g and causing irreversible blockage at the membrane interface. When the volume ratio is higher than 5:1, the dilution effect increases the condensation load of the flash distillation tower and no longer reduces the product acid value. By maintaining the volume ratio within the range, the physical induction effect generated by the solvent causes large molecular polar impurities to complete sedimentation within an induction period of 30 min to 120 min, achieving directional decoupling of the microemulsion system under ambient temperature conditions.

[0021] Because the reconstructed mixture contains microaggregates that can easily cause physical blockage of membrane pores, the system places the mixture in a settling tank and allows it to stand for 2 to 6 hours. Preliminary gravity stratification is achieved using the density difference between the microaggregates and the liquid phase. The bottom layer is then treated with a centrifuge with a separation factor of 3000 to 8000 to remove microaggregates larger than 0.5 μm, resulting in a degummed hydrocarbon oil mixture with an acid value below 10 mg KOH / g. This process effectively removes most of the heat-sensitive precursors from the crude oil, preventing them from being present in the later stages. A flexible filter cake layer is generated at the membrane separation interface. To address the challenge of decoupling polar heteroatoms and hydrocarbon molecules in crude oil from *Ulva prolifera* pyrolysis at room temperature due to their similar solubility parameters, the resulting degummed hydrocarbon oil mixture is fed into a multi-stage membrane separation system. A modified polytetrafluoroethylene (PTFE) membrane with long-chain oleophilic functional groups grafted onto its surface is used as the separation medium. The modified PTFE membrane has a contact angle of less than 10° with n-alkane solvents and a contact angle greater than 120° with water molecules. The system utilizes the hydrophobic field formed by the n-alkane solvent on the membrane surface and the membrane's inherent oleophilic properties to construct a... A chemical potential gradient, at an operating pressure of 0.5 MPa to 2.0 MPa and an operating temperature of 25°C to 45°C, drives hydrocarbon molecules to preferentially permeate through the membrane pores, while the stagnant side spontaneously accumulates polar components such as organic acids and bound water. To address the concentration polarization and interfacial thermodynamic collapse issues caused by the accumulation of polar components at the membrane interface during continuous production, this embodiment applies periodic pressures with a frequency of 0.1 Hz to 5 Hz and a pressure amplitude of 0.01 MPa to 0.2 MPa to the permeate side of the multi-stage membrane separation system. Force pulses, periodic pressure pulses are generated by the pressure regulating unit on the permeate side pipeline. The negative pressure difference generated during the pressure drop phase guides the hydrocarbon oil components that have permeated on the permeate side to the retention side of the modified polytetrafluoroethylene membrane for reverse flushing. By controlling the instantaneous flux of the reverse flushing to 1% to 5% of the forward permeate flux, the large molecular polar impurities and water molecules adsorbed at the membrane interface are instantly diluted and stripped. This ensures that the viscosity change rate of the refined hydrocarbon oil after being kept at 180°C for 48 hours is less than 5% and the water mass fraction is less than 0.05%.

[0022] To achieve dynamic self-maintenance of the membrane interface energy state, the system acquires the real-time permeate flux during each stage of membrane separation via a monitoring device, and adjusts the intensity of periodic pressure pulses based on the following calculation formula: K=J real / J set Where K is the pulse adjustment coefficient, J real To monitor the real-time permeation flux, J setBased on the pre-calibrated standard permeate flux of the corresponding components under standard membrane flux testing, when the K value is below 0.85, the system increases the pressure amplitude of the periodic pressure pulse through a feedback loop until the polar adsorption layer at the membrane interface is effectively removed and the flux recovers to the preset range. This ensures that the hydrophobic component distribution at the filtration interface is maintained without interrupting production. In the overall refining architecture, the multi-stage membrane separation system adopts a two-stage series structure. The first-stage membrane module has a molecular weight cutoff of 500 Da to 1000 Da and is used to remove metal components and bound water from the degummed hydrocarbon oil mixture. The second-stage membrane module has a molecular weight cutoff of 200 Da to 500 Da and is used to intercept organic acid components. After obtaining refined hydrocarbon oil, it is introduced into a flash distillation tower. To balance the heat and product purity during the solvent recovery process in the flash distillation tower, the system controls the liquid residence time at the bottom of the flash distillation tower to be 15 to 30 minutes. This ensures that the mass fraction of residual n-alkane solvent in the refined hydrocarbon oil is less than 0.1% and the acid value is less than 2 mg KOH / g. At the same time, a circulating pump in the bottom of the tower is used to maintain the controlled circulation of the refined hydrocarbon oil. The boiling point of the system is lowered by a reduced pressure environment to maintain the operating temperature below 120°C, preventing secondary self-polymerization of residual polar precursors in the refined hydrocarbon oil caused by local temperature rise. The recovered n-alkane solvent is returned to the reconstitution process for recycling, thus constructing a fully closed-loop hydrocarbon oil purification path.

[0023] Example 1: When processing highly polar Ulva prolifera pyrolysis crude oil with a water content of 8.5% and an acid value of 28.6 mgKOH / g, for the microemulsion system constructed by polar heteroatoms and hydrocarbon molecules through hydrogen bonding networks in this material, n-heptane was used as the n-alkane solvent and mixed at a volume ratio of 2:1 at 45°C. The mechanical stirring speed was set to 400 r / min, and the solubility parameter of the system was changed by the n-heptane solvent, inducing the gum and asphaltenes to aggregate within 90 min to form micro-aggregates with a particle size greater than 0.6 μm. The micro-aggregates were removed by a centrifuge with a separation factor of 6000 to obtain a degummed hydrocarbon oil mixture with an acid value of less than 10 mgKOH / g. The degummed hydrocarbon oil mixture was then pumped into a multi-stage membrane separation system composed of two-stage modified polytetrafluoroethylene membranes.

[0024] At an operating pressure of 1.5 MPa and an operating temperature of 35°C, a periodic pressure pulse with a frequency of 0.8 Hz and a pressure amplitude of 0.12 MPa is applied by the pressure regulating unit on the permeate side. This periodic pressure pulse drives the permeate-side components to perform a 4% reverse flush at the pressure trough, diluting and stripping the polar convolution structure at the membrane interface. The system adjusts the pulse intensity according to the following formula: K = J real / J set Where K is the pulse adjustment coefficient, J real The real-time permeation flux is measured in L / m³. 2 ·h,J setThe pre-calibrated standard permeation flux is expressed in L / m³. 2 After flash evaporation to recover the solvent, the water content of the refined hydrocarbon oil is less than 0.04% and the acid value is less than 2 mg KOH / g. Due to the stripping of the heat-sensitive polar precursor that induces polymerization at room temperature, the viscosity change rate of the refined hydrocarbon oil after being stored at 180°C for 48 hours decreased from 45% before refining to 2.8%. The hydrophobic field provided by solvation reconstruction and the reverse flushing driven by pressure pulse jointly maintain the chemical potential gradient distribution at the membrane interface.

[0025] Example 2: The flux stability and thermodynamic properties of crude oil from the pyrolysis of *Ulva prolifera* with different polarities were verified during the refining process on a membrane separation test platform equipped with pressure adaptive regulation. The experimental data were collected from sensors on the physical test platform, with the flow sensor measuring from 0 to 50 L / m³. 2 •h, with a resolution of 0.01L / m 2 The temperature control unit has an accuracy of ±0.5℃, the pressure transmitter has an accuracy of 0.02MPa, and the sampling period is set to 1s. This is used to balance the capture accuracy of transient flux changes with the data throughput pressure of the monitoring system, and to meet the real-time reconstruction of the response process of periodic pressure pulses with a frequency of 0.1Hz to 5Hz. Gaussian white noise with a signal-to-noise ratio of 20dB is injected into the acquisition loop to simulate electromagnetic and mechanical interference in the industrial environment. In view of the differential effects of acid value and water content in crude oil from the pyrolysis of Ulva lactuca on the degree of polar convolution at the membrane interface, the experiment set up three experimental groups with different intensities and three corresponding control groups. The experimental groups used n-heptane solvation reconstruction combined with periodic pressure pulses. Control group 1 removed the solvation reconstruction step and directly performed membrane separation. Control group 2 removed the periodic pressure pulse mechanism and maintained a constant operating pressure. Control group 3 set the volume ratio of n-heptane to crude oil to 0.5:1. The key performance data of the test oil with an acid value of 28.6mgKOH / g were examined.

[0026] Table 1: Comparison of Technical Effects of Different Refining Methods

[0027] Referring to the data in Table 1, control group 1 lacked the pre-removal of resins and asphaltenes during the solvation reconstruction stage, leading to the accumulation of micro-aggregates at the membrane interface. The permeate flux decreased by more than 60% within 10 hours, indicating that single membrane separation cannot cope with the physical clogging risk of the unreconstructed system. Although control group 2 completed reconstruction, the lack of pressure pulse-driven reverse flushing caused thermodynamic collapse in the polar molecular layer enriched at the interface, resulting in a K value dropping to 0.49 and exceeding the water content limit of the purified product. The experimental group, through the hydrophobic field provided by solvation reconstruction and the pressure pulse-driven 4% flow rate reverse flushing, produced… Synergistic gain was achieved, maintaining a high chemical potential gradient at the membrane interface, and the product indicators were superior to those of the control groups. The experiment investigated the trend of the change in the volume ratio of n-heptane from 1:1 to 6:1, determined the nonlinear effect of solvent ratio on the purification effect and the performance inflection point. When the volume ratio increased from 1:1 to 5:1, the acid value of the degummed hydrocarbon oil mixture decreased linearly from 9.2 mgKOH / g to 5.6 mgKOH / g. However, when the volume ratio increased to 6:1, the rate of decrease in acid value tended to slow down, and the dilution effect led to an increase in membrane separation energy consumption, indicating that the upper limit of the 5:1 ratio is close to the physical saturation region of solvation reconstruction.

[0028] Table 2: Gradient validation data for crude oils with different acid values

[0029] According to the gradient data in Table 2, when the polarity of the material increases regularly, the system adjusts the periodic pressure pulse amplitude to counteract the intensified concentration polarization, so that crude oils with different initial values ​​are maintained at a low acid value level and viscosity change rate range after refining. This proves that the method of the present invention achieves dynamic compensation of the thermodynamic state of the membrane interface through parameterized logic feedback based on the change of polar component loading in the material, and deeply decouples the complex microemulsion system into a highly stable refined hydrocarbon oil. The entire experimental process confirms that at room temperature, the interface self-maintenance mechanism driven by the reconstruction of the system solubility parameters by n-alkane solvent and the permeate side pressure pulse effectively removes the heat-sensitive polar precursors in the crude oil from the pyrolysis of Ulva prolifera.

[0030] Example 3: This example combines Figures 1 to 2 This paper describes a method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation, as follows: Figure 1As shown, step 101 involves mixing the crude oil from the pyrolysis of *Ulva prostrata* with a n-alkane solvent at a volume ratio of 1:1 to 5:1. The difference in solubility parameters between the solvent and the crude oil components is used for solvation reconstruction, inducing the precipitation of gums, asphaltenes, and large-molecule polar impurities, which then form micro-aggregates. Step 102 involves solid-liquid separation of the mixture, removing the precipitated micro-aggregates to obtain a degummed hydrocarbon oil mixture with an acid value below 10 mg KOH / g. Step 103 then sends the degummed hydrocarbon oil mixture into a multi-stage membrane separation system. A modified polytetrafluoroethylene membrane is used as the separation medium, utilizing the hydrophobic field formed by the n-alkane solvent and the oleophilic properties of the membrane for component screening. Finally, step 104 applies periodic pressure pulses of 0.1-5 Hz and 0.01-0.2 MPa to the permeate side, using the negative pressure difference during the fallback phase to drive reverse flushing, stripping away large-molecule polar impurities and water molecules adsorbed at the membrane interface to obtain refined hydrocarbon oil.

[0031] like Figure 2 As shown, the raw flow / pressure analog signals generated by the field sensor cluster are transmitted to the data acquisition and signal filtering module to generate real-time permeation flux data J. set The flux attenuation coefficient is then fed into the intelligent calculation unit, which simultaneously reads the standard flux setting J from the A1 standard flux reference library. set The two are combined and calculated to output the adjustment coefficient status to the pulse compensation strategy generation logic. This logic then issues an amplitude step command to the pressure regulation unit to perform physical cleaning feedback. At the same time, the flux offset record generated by the flux attenuation coefficient intelligent calculation unit is transmitted to the historical trend learning update module. After processing, archived operation data is generated and stored in the A2 operation log database.

[0032] Example 4: In the production scenario of crude oil from the pyrolysis of *Ulva prolifera* whose composition fluctuates due to its growth cycle, the kinematic viscosity of the material changes from 12.5 mm... 2 / s offset to 18.4mm 2 The flux baseline drift generated per second, the system's standard permeation flux J setThe determination procedure includes: selecting a degummed hydrocarbon-oil mixture sample after treatment by the reconstructed reaction unit; recording the stable permeation flux of the modified polytetrafluoroethylene membrane within the initial 15 minutes under operating conditions of 35℃ and constant operating pressure P of 1.2MPa; and determining the standard permeation flux of the current batch according to the following calibration formula: the standard permeation flux equals the structural permeation constant multiplied by the pressure and then divided by the dynamic viscosity, where the standard permeation flux is the system's preset target permeation flux, and its unit is L / m2h; the structural permeation constant is an intrinsic permeation property parameter of the membrane module, and its physical unit is micrometers, representing the effective average path length of the membrane pores. This constant is obtained by converting the flux value measured by running pure heptane at 1.0MPa pressure for 30 minutes and is stored in the controller's register; the pressure is the real-time operating pressure, and the unit is MPa; the dynamic viscosity is in mPa·s; by setting the structural permeation constant as a physical quantity with the dimension of length, the physical dimensions on both sides of the formula are logically consistent. set J set =Φ·(P / η), where J set Standard permeation flux, in L / m 2 •h; Φ is the inherent structural constant of the membrane module, with its physical unit being micrometers; P is the constant operating pressure, with the unit being MPa; η is the dynamic viscosity of the material, with the unit being mPa·s. This procedure establishes a dynamic benchmark for specific material properties, avoiding false alarms caused by single empirical values.

[0033] Before using a multi-stage membrane separation system for purification, PTFE-based membranes were modified using an electron beam irradiation grafting process. The distribution density of long-chain lipophilic functional groups on the surface of the modified PTFE membrane was measured to be 0.15 mol / m³. 2 Up to 0.25 mol / m 2 This microscopic functional group distribution results in a lower arithmetic mean roughness R on the film surface. a The hydrophobic molecular density was increased from 0.12 μm before grafting to 0.45 μm. This was achieved by utilizing the van der Waals attraction of long-chain lipophilic functional groups to n-alkane solvents, constructing a continuous and stable hydrophobic solvent molecular film on the membrane surface. This physically prevents bound water molecules from contacting the membrane substrate. The modified polytetrafluoroethylene (PTFE) membrane was prepared using an electron beam irradiation grafting process. The PTFE membrane was placed in a reaction chamber with a vacuum level below 10 Pa, and a grafting solution containing octadecyl acrylate monomer was introduced. The irradiation dose was controlled at 100 kGy to 150 kGy, allowing the octadecyl functional groups to form covalent bonds on the base membrane surface. After grafting, the membrane module was washed with anhydrous ethanol at 40°C for 24 hours to remove residual monomers. The distribution density of long-chain lipophilic functional groups on the modified membrane surface was measured to be 0.15 mol / m³. 2 Up to 0.25 mol / m 2This maintains the membrane's contact angle with the n-alkane solvent at less than 10°. ∘ When the system detects that the pulse regulation coefficient K drops to 0.82 during continuous operation, the polar component loading at the membrane interface exceeds the carrying capacity of the hydrophobic field on the modified polytetrafluoroethylene membrane surface, causing hydrogen bond network convolution at the membrane pore inlet and resulting in increased permeation resistance. To overcome this physical obstacle, the system initiates an amplitude adaptive regulation program, increasing the pressure amplitude of the periodic pressure pulse in 0.02 MPa increments until the K value recovers to above 0.90. The basis for setting 0.85 as the regulation threshold is that when K is below this value, the bound water molecule clusters at the interface begin to form a continuous polar film. If the reverse scouring intensity is not enhanced in time through pressure amplitude compensation, it will cause a change in the thermodynamic state of the membrane interface.

[0034] Example 5: In the scenario of initial operation of a multi-stage membrane separation and purification system or deployment of a modified polytetrafluoroethylene membrane module, the system executes an offline calibration procedure for the inherent structural constant Φ of the membrane module. This procedure selects n-heptane with a purity of not less than 99.5% as the standard reference fluid. Under an environment where the operating temperature is maintained at 25°C and the operating pressure is constant at 1.0 MPa, the volumetric permeate flux J of the membrane module is recorded within 30 minutes of stable operation. ref , where J ref Volumetric permeability, in L / m³ 2 The measured value of Φ is determined based on the linear relationship between fluid viscosity and pressure, and this value is stored in the controller's memory so that the filter medium corresponds to the intrinsic permeation parameters under a single-component flow field.

[0035] In the scenario of processing crude oil from the pyrolysis of Ulva prolifera with an initial moisture content fluctuation exceeding 2%, the system initiates an online parameter initialization procedure with a startup duration of 15 minutes before refining. The controller instructs the pressure regulating unit to apply a preset median pressure pulse, and the real-time permeation flux J is acquired through a monitoring device. real The pulse regulation coefficient was then corrected using a step-by-step adjustment method, compared with the aforementioned offline calibrated volumetric permeability baseline. K The initial search vector, the permeation resistance of the membrane separation interface and the compensation step of the dynamic pressure pulse are aligned with the corresponding physical parameters under full range coverage.

[0036] Example 6: In a production scenario where the kinematic viscosity of crude oil from the pyrolysis of *Ulva prolifera* fluctuates between different batches during the operation of a multi-stage membrane separation system, the kinematic viscosity of the material is targeted at 10 mmHg. 2 / s to 20mm 2The system initiates a pre-calibration procedure for the periodic pressure pulse frequency f, considering the impact of the offset between / s on filtration kinetics. The real-time dynamic viscosity η of the degummed hydrocarbon-oil mixture is measured using a viscometer. Based on the kinetic equilibrium conditions of non-polar fluid displacement within the membrane pores, the periodic pressure pulse frequency is determined as follows: frequency equals the frequency conversion factor divided by the dynamic viscosity, where the frequency unit is Hz; the dynamic viscosity unit is mPa·s; and the frequency conversion factor unit is mPa. The calibration method for this factor is as follows: during system startup, the controller drives the pressure regulation unit in 0.1Hz increments. The frequency range of 0.1Hz to 5.0Hz was scanned, and the fluctuation amplitude of the membrane permeation flux was monitored simultaneously. The product of the frequency at which the fluctuation amplitude first reached 5% of the stable permeation flux and the real-time dynamic viscosity was selected as the frequency conversion coefficient for this batch of materials. In this embodiment, this coefficient was calibrated to 22.8 mPa. f is defined as: f = σ / η, where f is the frequency of the periodic pressure pulse in Hz; η is the dynamic viscosity of the degummed hydrocarbon-oil mixture in mPa·s; and σ is the frequency coupling constant in mPa. The kinematic viscosity was determined to be 15.2 mm at 35℃. 2 The frequency setting for the mixed liquid is 1.5Hz, which physically matches the period of the periodic pressure pulse with the peeling time of the interfacial polar adsorption layer.

[0037] When the system detects a drift in the pulse regulation coefficient K due to trace accumulation of fouling on the surface of the modified polytetrafluoroethylene membrane module during the continuous refining of refined hydrocarbon oil, the controller instructs an online maintenance scheme based on the rate of change of the K value. The real-time permeation flux is obtained through the flux monitoring device, and the average descent slope of the K value within a continuous 1-hour sampling window is calculated. When the average descent slope exceeds 0.05 / h, the system automatically increases the pressure amplitude of the periodic pressure pulse, increasing the pressure amplitude from 0.12MPa to 0.18MPa in 0.01MPa increments to enhance the interfacial shear force generated by reverse scouring, until the real-time permeation flux at the membrane interface recovers to 95% of the standard permeation flux, and the water content of the refined hydrocarbon oil stabilizes at around 0.038%. The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation, characterized in that, Includes the following steps: Step 101: Mix the crude oil from the pyrolysis of Ulva lactuca with a n-alkane solvent at a volume ratio of 1:1 to 5:

1. Utilize the difference in solubility parameters between the n-alkane solvent and the components of the crude oil from the pyrolysis of Ulva lactuca to carry out solubilization reconstruction, inducing the precipitation of gums, asphaltenes, and large molecular polar impurities and forming micro-aggregates. Step 102: Perform solid-liquid separation on the mixed system obtained in step 101, remove the precipitated micro-aggregates, and obtain a degummed hydrocarbon oil mixture with an acid value of less than 10 mg KOH / g. Step 103: The degummed hydrocarbon oil mixture is fed into a multi-stage membrane separation system. A modified polytetrafluoroethylene membrane is used as the separation medium. The components are screened by utilizing the hydrophobic field formed on the surface of the modified polytetrafluoroethylene membrane by the n-alkane solvent and the oleophilic properties of the modified polytetrafluoroethylene membrane. Step 104: Apply periodic pressure pulses to the permeate side of the multi-stage membrane separation system. The frequency of the periodic pressure pulses is 0.1 Hz to 5 Hz, and the pressure amplitude is 0.01 MPa to 0.2 MPa. Utilize the negative pressure difference generated during the pressure drop phase of the periodic pressure pulses to guide the hydrocarbon oil components that have permeated from the permeate side to the retention side of the modified polytetrafluoroethylene membrane for reverse flushing. This removes large polar impurities and water molecules adsorbed at the membrane interface and maintains the hydrophobic component distribution at the retention side interface of the modified polytetrafluoroethylene membrane, thereby obtaining refined hydrocarbon oil.

2. The method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation according to claim 1, characterized in that, In step 101, the n-alkane solvent is n-hexane, n-heptane, n-octane, n-decane, or n-dodecane; during the mixing process, the mixing temperature is controlled at 20°C to 50°C, and the mechanical stirring speed is 100 r / min to 500 r / min, inducing the macromolecular polar impurities to complete the sedimentation within 30 min to 120 min.

3. The method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation according to claim 1, characterized in that, Step 102 involves obtaining the degummed hydrocarbon-oil mixture by the following steps: placing the reconstructed mixture in a settling tank and allowing it to stand for 2 to 6 hours, using the density difference between the micro-aggregates and the liquid phase for gravity stratification; and removing the sedimentation bottom layer components by using a centrifuge with a separation factor of 3000 to 8000 to remove micro-aggregates with a particle size greater than 0.5 μm.

4. The method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation according to claim 1, characterized in that, In step 103, long-chain lipophilic functional groups are grafted onto the surface of the modified polytetrafluoroethylene membrane, making the contact angle of the modified polytetrafluoroethylene membrane with n-alkane solvent less than 10° and the contact angle with water molecules greater than 120°.

5. The method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation according to claim 1, characterized in that, In step 104, the periodic pressure pulses are generated by the pressure regulating unit on the permeate side pipeline. The pressure regulating unit removes the polar adsorption layer at the membrane interface by controlling the instantaneous flux of the reverse flush to be 1% to 5% of the forward permeate flux.

6. The method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation according to claim 1, characterized in that, After obtaining the refined hydrocarbon oil in step 104, the following steps are also included: introducing the refined hydrocarbon oil into a flash distillation tower for solvent recovery, controlling the top temperature of the flash distillation tower to be the boiling point temperature of the n-alkane solvent, and returning the recovered n-alkane solvent to step 101 for recycling.

7. The method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation according to claim 1, characterized in that, In step 104, the intensity of the periodic pressure pulses is adjusted by monitoring the real-time permeate flux of the multi-stage membrane separation system, following the formula: K=J real / J set Where K is the pulse adjustment coefficient; J real For the monitored real-time permeation flux; J set J is the preset standard permeation flux. set Crude oil from the pyrolysis of Ulva prolifera was pre-calibrated based on the corresponding components under standard membrane flux testing; when the K value was below 0.85, the pressure amplitude of the periodic pressure pulse was increased.

8. The method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation according to claim 1, characterized in that, The multi-stage membrane separation system adopts a two-stage series structure. The first-stage membrane module has a molecular weight cutoff of 500 Da to 1000 Da and is used to remove metal components and bound water from the degummed hydrocarbon oil mixture. The second-stage membrane module has a molecular weight cutoff of 200 Da to 500 Da and is used to intercept organic acid molecules.

9. The method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation according to claim 1, characterized in that, In the purification process of the multi-stage membrane separation system, the operating pressure is controlled to be between 0.5 MPa and 2.0 MPa, and the operating temperature is controlled to be between 25°C and 45°C.

10. The method for refining crude oil from *Ulva prostrata* pyrolysis based on multi-stage membrane separation according to claim 1, characterized in that, The kinetic energy generated by the periodic pressure pulse in step 104 is used to eliminate the concentration polarization at the interface of the modified polytetrafluoroethylene film, so that the viscosity change rate of the refined hydrocarbon oil after being kept at 180°C for 48 hours is less than 5%, and the water mass fraction is less than 0.05%.

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