Method for separating and refining fusel oil in Fischer-Tropsch synthesis

Abstract

The invention discloses a method for separating and refining fusel oil in Fischer-Tropsch synthesis, and belongs to the technical field of chemical separation. In order to solve the problems of difficult separation and high energy consumption of fusel oil due to the existence of azeotrope, the invention provides a rectification and membrane separation coupled process. The method comprises the following steps: firstly, pretreating a fusel oil raw material through a two-stage rectifying tower, and sequentially removing water, heavy components and light components; then carrying out neutralization desalination treatment on the obtained mixed alcohol solution, and then feeding the mixed alcohol solution into a steam permeable membrane system for deep dehydration to obtain mixed alcohol steam with low water content; and finally, sequentially feeding the dehydrated alcohol steam into a subsequent rectifying tower, and separating to obtain high-purity ethanol, n-propyl alcohol and n-butyl alcohol products. Through energy integration design, high-temperature material flow is used for preheating raw materials and providing a heat source for the rectifying tower, and energy consumption is remarkably reduced. The method is reasonable in process, effectively breaks through the alcohol-water azeotropic limitation, and realizes efficient and low-cost separation of high-added-value components in fusel oil.

Description

Technical Field

[0001] This invention belongs to the field of chemical separation technology, specifically relating to a method for separating and refining valuable components such as ethanol, n-propanol, and n-butanol from fusel oil, a byproduct of Fischer-Tropsch synthesis, and particularly to a separation and refining process that couples distillation and membrane separation. Background Technology

[0002] Fischer-Tropsch synthesis is an important process route for synthesizing liquid fuels and chemicals using syngas (CO and H2) as raw materials. During Fischer-Tropsch synthesis, in addition to generating the target hydrocarbon products, a large amount of oxygenated compound aqueous solutions, commonly known as fusel oil, is produced as a byproduct. Fusel oil has an extremely complex composition, typically containing water, methanol, ethanol, n-propanol, n-butanol, higher alcohols (C4+ alcohols), and trace amounts of aldehydes, ketones, acids, esters, and other impurities. Among these, ethanol, n-propanol, and n-butanol are important chemical raw materials and solvents with high economic value.

[0003] However, the separation and purification of fusel oils faces significant challenges. First, alcohols readily form various binary or multi-component azeotropes with water and other alcohols (such as ethanol-water azeotropes), making it difficult to obtain high-purity products using traditional distillation methods. To obtain anhydrous ethanol, azeotropic distillation, extractive distillation, or molecular sieve adsorption are typically required. These methods suffer from high energy consumption, long process flows, potential introduction of third components, or large equipment investments. Second, the acidic substances in fusel oils can corrode equipment; improper handling can lead to scale formation due to the salts produced during neutralization.

[0004] In recent years, membrane separation technology, especially steam permeation technology, has shown great potential in the field of alcohol dehydration. This technology utilizes the selective permeation of membranes to achieve separation, and is particularly suitable for azeotropic systems, offering advantages such as low energy consumption and mild operating conditions. However, how to effectively couple membrane separation technology with traditional distillation processes to meet the requirements of full-component separation in complex fusel oil systems, while simultaneously addressing the impact of impurities (such as acids and salts) on membrane performance and optimizing the energy consumption of the entire separation process, remains a pressing technical challenge in this field.

[0005] Therefore, there is an urgent need to develop a new, efficient, energy-saving, and stable method for separating and refining fusel oils from Fischer-Tropsch synthesis, so as to achieve efficient recovery and high-value utilization of various high-value components in fusel oils. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing fusel oil separation technologies, such as high energy consumption, complex processes, and difficult dehydration, and to provide a method for separating and purifying fusel oils in Fischer-Tropsch synthesis. This method optimizes the separation sequence and energy utilization through the organic coupling of distillation and membrane separation technologies, and can efficiently separate high-purity ethanol, n-propanol, and n-butanol products from complex fusel oil systems.

[0007] A method for separating and purifying fusel oils in Fischer-Tropsch synthesis includes the following steps:

[0008] (a) The fusel oil feedstock containing water and various alcohols is fed into the first distillation column for atmospheric distillation. The top distillate rich in methanol, ethanol, propanol and butanol is obtained from the top of the first distillation column, and the bottom liquid mainly composed of water and C4+ higher alcohols is discharged from the bottom of the column.

[0009] (b) The distillate from the top of the column is fed into a second distillation column for vacuum distillation. Light components, mainly methanol, aldehydes, ketones and esters, are collected from the top of the second distillation column, and a mixed alcohol liquid mainly containing ethanol, propanol, butanol and water is obtained from the bottom of the column.

[0010] (c) The mixed alcohol liquid is neutralized by adding alkali, and then the neutralized material is sent to an evaporator for vaporization and desalination. The resulting gaseous material enters a membrane separation system for steam permeation dehydration to obtain dehydrated mixed alcohol vapor with reduced moisture content.

[0011] It also includes the following steps:

[0012] (d) The dehydrated mixed alcohol vapor obtained in step (c) is fed into a third distillation column for vacuum distillation. The ethanol product is collected from the top of the third distillation column, and the bottom liquid is a mixture of propanol and butanol.

[0013] It also includes the following steps:

[0014] (e) The liquid obtained in step (d) is sequentially fed into the fourth and fifth distillation columns for distillation to separate n-propanol and n-butanol products.

[0015] In step (a), the fusel oil feedstock liquid is preheated by heat exchange with the bottom liquid discharged from the bottom of the first distillation column before entering the first distillation column.

[0016] In step (d), the dehydrated mixed alcohol vapor obtained in step (c) is first introduced into the auxiliary reboiler of the third distillation column to provide heat, and then condensed and fed into the third distillation column as feed.

[0017] The alkali neutralization treatment in step (c) is to adjust the pH value of the material to 7.0-8.5.

[0018] The membrane separation system in step (c) uses a hydrophilic zeolite membrane or a polymer membrane, with an operating temperature of 90-120℃, an absolute pressure of 120-200 kPa on the feed side, and an absolute pressure of less than 5 kPa on the permeate side.

[0019] The first distillation column operates under atmospheric pressure of 100-110 kPa; the second distillation column operates under absolute pressure of 60-80 kPa; and the third distillation column operates under absolute pressure of 30-50 kPa.

[0020] The components of the fusel oil feedstock liquid, by weight percentage, include: water: 25-45%; ethanol: 20-35%; methanol: 10-18%; n-propanol: 8-15%; n-butanol: 5-10%; C4+ higher alcohols and other impurities: balance.

[0021] The method further includes using a prediction algorithm model to predict the separation factor of the membrane separation system, wherein the formula of the prediction algorithm model is:

[0022]

[0023] in: This is the total alcohol concentration. It is the total concentration of other organic matter. It is time; , , , These are the parameters to be fitted.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention employs a coupled process combining distillation and membrane separation, effectively solving the problem of azeotropic distillation of alcohol and water. Pre-distillation removes a large amount of impurities and some water, reducing the load on membrane separation; membrane separation provides efficient and deep dehydration, avoiding the high energy consumption and complex operation of traditional azeotropic distillation or pressure swing distillation. Ultimately, ethanol, n-propanol, and n-butanol products with a purity greater than 99.5 wt% can be obtained.

[0026] 2. This invention achieves ingenious energy integration by using the bottom liquid of T101 to preheat the raw materials and innovatively using the high-temperature retained steam after membrane separation as the heat source for the auxiliary reboiler of T103, thus fully recovering the latent heat and significantly reducing the overall process energy consumption.

[0027] 3. Through neutralization treatment and evaporator desalination, the corrosion of equipment by acidic substances and the pollution and scaling of membrane system by salt are effectively prevented, ensuring the long-term stable operation of the unit.

[0028] 4. By quantifying the effects of operating time, alcohol and impurity concentrations on membrane performance, a predictive model for the separation factor was constructed. This model can accurately predict the dynamic decay of the separation factor. It provides scientific guidance for real-time optimization of process parameters and formulation of maintenance strategies, effectively ensuring the long-term stable operation of the separation unit and significantly extending the service life of the membrane. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process flow for the separation and purification of fusel oils in Fischer-Tropsch synthesis according to the present invention.

[0030] Figure 2 This is a comparison chart of the experimental and predicted values ​​of the separation factor prediction model.

[0031] In the diagram: 1-Preheater; T101-First distillation column; T102-Second distillation column; T103-Third distillation column; T104-Fourth distillation column; T105-Fifth distillation column; M1, M2-Membrane modules; CP1, CP2-Permeate condensers; F1-Feed; D1~D5-Top product; W1~W5-Bottom product; P1, P2-Membrane permeate; R2-Membrane retentate vapor. Detailed Implementation

[0032] In a typical implementation, such as Figure 1 As shown, fusel oil (mainly composed of 30.9 wt% water, 30.12 wt% ethanol, 14.09 wt% methanol, 11.52 wt% n-propanol, 7.33 wt% n-butanol, 4.22 wt% C4+ alcohols (referring to n-pentanol, n-hexanol, n-heptanol, etc.) and small amounts of isopropanol, acetates (referring to methyl acetate and ethyl acetate), ketones (referring to acetone, butanone, etc.), aldehydes (referring to acetaldehyde, propionaldehyde, butyraldehyde, etc.) and acids (referring to acetic acid, propionic acid, n-butyric acid, n-valeric acid, etc.) from the Fischer-Tropsch synthesis process is pumped into the preheater. After exchanging heat with the bottom liquid of column T101, it enters column T101 from the column. T101 is an atmospheric pressure column, which removes most of the water, acids, C4+ alcohols and other heavy components. The distillate from the top of the column enters column T102. T102 removes light components (methanol, aldehydes, ketones, esters, etc.) through vacuum distillation. A portion of the condensed vapor from the top of the column is returned to the column as reflux, while the remainder is collected. The bottom liquid is neutralized and temporarily stored in a transfer tank before being pumped into the membrane separation system.

[0033] The neutralized material is temporarily stored in a transfer tank and then pumped into an evaporator with a packed section. After desalination, it enters the membrane separator in gaseous form. The membrane separator consists of multiple membrane modules connected in series. Moisture and a small amount of solvent in the feed permeate from the upstream side of the membrane to the downstream side. The dehydrated intermediate product vapor enters the auxiliary reboiler of T103 after passing through the last membrane module on the upstream side, serving as part of the heat source for T103. The vapor after membrane condensation enters T103. On the downstream side of the membrane, vacuum and condensation are used to create a vapor pressure difference between the upstream and downstream components. On the inner side of the membrane, vacuum and condensation generate driving force, and the permeate vapor enters the permeate condenser under the suction of the vacuum unit. The permeate flows to the permeate tank and is pumped out for treatment.

[0034] T103 removes propanol and butanol through vacuum distillation. After the vapor at the top of the column is condensed, part of it is returned to the column as reflux liquid to improve the ethanol recovery rate, and part of it is used to produce finished ethanol (serial number D3).

[0035] The bottom liquid is pumped into T104. Isopropanol is removed by atmospheric distillation in T104. A portion of the condensed vapor from the top of the column is returned to the column as reflux, while the remainder is collected. The bottom liquid is pumped into T105. n-Propanol and n-Butanol are separated by atmospheric distillation in T105. n-Propanol (D5) is obtained at the top of the column, and n-Butanol (W5) is obtained at the bottom.

[0036] In some specific implementations, the processing steps include:

[0037] (1) The Fischer-Tropsch synthesis fusel oil feedstock liquid (F1) is fed into the first distillation column (T101) for atmospheric distillation to remove most of the water, C4+ higher alcohols and most of the acids and other heavy components; the heavy components are discharged from the bottom of the first distillation column (W1), and the mixture enriched with methanol, ethanol, propanol, butanol and light components is distilled from the top of the first distillation column (D1).

[0038] (2) The distillate (D1) obtained in step (1) is sent to the second distillation column (T102) for vacuum distillation to remove light components such as methanol, aldehydes, ketones, and esters; the light components are collected from the top of the second distillation column (D2), and the bottom liquid of the second distillation column is mainly ethanol, propanol, butanol and the remaining water and trace amounts of acid.

[0039] (3) The bottom liquid of the second distillation column obtained in step (2) is neutralized with alkali to remove the residual acidic substances; the neutralized material enters the evaporator for vaporization and desalination, and the resulting gaseous material (F2) enters the membrane separation system for steam permeate dehydration; the membrane separation system consists of one or more membrane modules (M1, M2); by evacuating the membrane permeate side, water molecules preferentially permeate through the membrane and are condensed on the permeate side to obtain permeate (P1, P2); the material that does not permeate through the membrane is the dehydrated mixed alcohol vapor (R2).

[0040] (4) The dehydrated mixed alcohol vapor (R2) obtained in step (3) is introduced into the auxiliary reboiler of the third distillation column (T103) to provide some heat and then condense (F3), and then sent to the third distillation column for vacuum distillation; high-purity ethanol product (D3) is taken from the top of the third distillation column, and the bottom liquid (W3) is mainly a mixture of propanol and butanol.

[0041] (5) The bottom liquid (W3) of the third distillation column obtained in step (4) is sequentially fed into the fourth distillation column (T104) and the fifth distillation column (T105) for atmospheric distillation; isopropanol and other impurities are removed in T104 (D4); the bottom liquid (W4) of T104 enters T105; n-propanol and n-butanol are separated in T105, n-propanol product (D5) is obtained from the top of T105 column, and n-butanol product (W5) is obtained from the bottom of the column.

[0042] Further, in step (1), the fusel oil feedstock liquid (F1) enters the preheater (1) before entering the first distillation column (T101) to exchange heat with the heavy components (W1) discharged from the bottom of the first distillation column in order to recover heat.

[0043] Furthermore, in step (1), the operating pressure of the first distillation column (T101) is atmospheric pressure (100-110 kPa), the top temperature of the column is controlled at 78-85℃, and the bottom temperature of the column is controlled at 100-110℃.

[0044] Furthermore, in step (2), the operating pressure of the second distillation column (T102) is 60-80 kPa (absolute pressure), and the top temperature is controlled at 40-50℃.

[0045] Further, in step (3), the membrane separation system preferably uses a hydrophilic zeolite membrane (such as a NaA type zeolite membrane) or a polymer membrane; the operating temperature is 90-120℃, the feed side pressure is 120-200 kPa (absolute pressure), and the permeate side vacuum is preferably less than 5 kPa (absolute pressure).

[0046] Furthermore, in step (3), the neutralization by adding sodium hydroxide or potassium hydroxide solution is used to adjust the pH value of the material to 7.0-8.5.

[0047] Furthermore, in step (4), the operating pressure of the third distillation column (T103) is 30-50 kPa (absolute pressure), and the top temperature of the column is controlled at 40-50℃.

[0048] Example 1

[0049] Fusel oil feedstock (F1) from the Fischer-Tropsch synthesis process is pumped into the preheater (1) to exchange heat with the high-temperature material (W1) from the bottom of column T101. After preheating, it enters the first distillation column T101. T101 operates at atmospheric pressure and is used to remove heavy components (water, C4+ alcohols, acids). The distillate (D1) from the top of column T101 enters the second distillation column T102.

[0050] The T102 depressurization operation is used to remove light components (methanol, aldehydes, ketones, esters), which are collected from the top of the column (D2). After the T102 column bottom liquid is discharged, it enters the alkali neutralization system to neutralize the residual acidic substances, and then enters the transfer tank for temporary storage.

[0051] The neutralized material is pumped into the evaporator, where it is heated and vaporized. The vaporized material (F2) then enters the membrane separation system (M1, M2) in gaseous form. The membrane separation system uses steam permeation technology for dehydration. A vacuum system is used to maintain low pressure on the downstream side of the membrane (permeate side). The permeate containing water vapor is condensed by condensers (CP1, CP2) to obtain permeate (P1, P2), which is then discharged.

[0052] After deep dehydration via membrane separation, the retained material (R2) that does not permeate the membrane is a high-temperature mixed alcohol vapor. This high-temperature vapor is introduced into the auxiliary reboiler of the third distillation column T103 as part of the heat source for T103. After releasing latent heat, it is condensed (F3) and then enters T103.

[0053] The T103 reduced pressure operation is used to separate ethanol from propanol and butanol. The top product, high-purity ethanol (D3), is collected.

[0054] The liquid in the bottom of column T103 (W3) is pumped into the fourth distillation column T104. T104 operates at atmospheric pressure and is used to remove impurities such as isopropanol (D4). The liquid in the bottom of column T104 (W4) enters the fifth distillation column T105. T105 operates at atmospheric pressure, and n-propanol is obtained at the top of the column (D5), while n-butanol is obtained at the bottom (W5).

[0055] The feedstock, fusel oil (F1), has a flow rate of 1000 kg / h and the following composition: water: 30.90%; ethanol: 30.12%; methanol: 14.09%; n-propanol: 11.52%; n-butanol: 7.33%; C4+ alcohols: 4.22%; other (acids, aldehydes, ketones, esters total): 1.82%. T101 operates at atmospheric pressure with 40 theoretical plates. The top pressure is 101.3 kPa, the top temperature is 82℃, the bottom temperature is 105℃, and the reflux ratio is 1.5. T102 operates under reduced pressure with 50 theoretical plates. The top pressure is 20 kPa (absolute pressure), the top temperature is 35℃, and the reflux ratio is 2.0. In the neutralization step, 10% NaOH solution is added to adjust the pH to 7.5. The membrane separation process uses a two-stage series operation with hydrophilic NaA zeolite molecular sieve membranes. Feed temperature 105℃, feed pressure 150 kPa (absolute pressure), permeate side absolute pressure 3 kPa; T103 operates under reduced pressure, with 60 theoretical plates. Top pressure 40 kPa (absolute pressure), top temperature 52℃, reflux ratio 2.5; T104 operates at atmospheric pressure, with 40 theoretical plates. Top temperature 95℃, reflux ratio 5.0; T105 operates at atmospheric pressure, with 50 theoretical plates. Top temperature 97.5℃, reboiler temperature 118℃, reflux ratio 2.0.

[0056] The operational data results for key logistics are shown in the table below:

[0057] Logistics label Flow rate (kg / h) water(%) Ethanol (%) Methanol (%) n-Propanol (%) n-Butanol (%) other(%) F1 (Raw Material) 1000.0 30.90 30.12 14.09 11.52 7.33 <![CDATA[6.04 # ]]> W1 (T101 kettle) 349.7 83.90 0.01 0.00 0.01 0.01 <![CDATA[16.08 △ ]]> D1 (T101 top) 650.3 2.30 46.30 21.66 17.71 11.27 0.76 D2 (T102 top) 151.6 0.20 2.65 92.80 0.00 0.00 <![CDATA[4.35 ▽ ]]> F2 (membrane feed) 498.7 3.00 59.60 0.01 23.05 14.33 0.01 P1 + P2 (osmotic fluid) 13.5 95.00 5.00 0.00 0.00 0.00 0.00 F3 (T103 feed) 485.2 0.41 61.25 0.01 23.75 14.57 0.01 D3 (finished ethanol product) 298.0 0.25 99.70 0.01 0.04 0.00 0.00 W3 (T103 kettle) 187.2 0.70 0.10 0.00 61.38 37.80 0.02 D5 (n-Propanol finished product) 114.5 0.10 0.00 0.00 99.50 0.40 0.00 W5 (n-Butanol finished product) 72.0 0.10 0.00 0.00 0.42 99.48 0.00

[0058] # Other components in F1 include C4+ alcohols (4.22%) and other impurities (1.82%). △ The other components in W1 are mainly C4+ alcohols and acids. ▽ The other components in D2 are mainly light components (aldehydes, ketones, esters). The bottom liquid W3 of the T103 tower passes through T104 before entering T105 to remove approximately 0.7 kg / h of material containing impurities such as isopropanol (D4).

[0059] As shown in Example 1, the method of the present invention successfully separated high-purity products from complex fusel oil feedstocks: ethanol purity reached 99.70%, n-propanol purity reached 99.50%, and n-butanol purity reached 99.48%. The total recovery rates of ethanol, n-propanol, and n-butanol reached 98.5%, 99.3%, and 98.2%, respectively. Approximately 95% of the water was pre-removed by the first distillation column T101, and then the water content in the alcohol mixture was efficiently removed from 3.00% to 0.41% using membrane separation technology, breaking the azeotropic limitation.

[0060] Example 2

[0061] This embodiment examines the impact of fluctuations in feed composition (increased water content) on separation efficiency. The feedstock, fusel oil (F1), has a flow rate of 1000 kg / h. The feedstock composition is as follows: water 40.00 wt%, ethanol 25.00 wt%, methanol 12.00 wt%, n-propanol 10.00 wt%, n-butanol 6.00 wt%, C4+ alcohols 4.00 wt%, and others 3.00 wt%. Adaptive adjustments were made to the process operating parameters: T101 operated at atmospheric pressure, and the reflux ratio was increased to 2.0 to ensure effective dehydration; the total membrane area of ​​the membrane separation system was increased by 20% to cope with the increased water load. The operating temperature was 105℃, and the absolute pressure on the permeate side was 3 kPa. Other distillation column operating parameters were fine-tuned according to the material load.

[0062] Execution result:

[0063] Logistics Name Flow rate (kg / h) water(%) Ethanol (%) n-Propanol (%) n-Butanol (%) F1 (Raw Material) 1000.0 40.00 25.00 10.00 6.00 F2 (membrane feed) 410.5 4.50 59.80 24.30 11.40 F3 (T103 feed) 393.8 0.50 62.34 25.34 11.82 D3 (finished ethanol product) 245.8 0.30 99.60 0.10 0.00 D5 (n-Propanol finished product) 99.3 0.10 0.00 99.50 0.40 W5 (n-Butanol finished product) 59.4 0.10 0.00 0.40 99.50

[0064] As shown in Example 2, even when the moisture content of the raw material increases to 40%, the method of the present invention can still maintain a good separation effect and obtain a high-purity target product by adjusting the operating parameters and membrane system configuration, demonstrating that the process of the present invention has strong operational flexibility and adaptability.

[0065] Example 3

[0066] This embodiment, based on Embodiment 1, illustrates the application effect of energy integration technology. The raw material composition and flow rate are the same as in Embodiment 1. During the raw material preheating process, the raw material (F1) is preheated from 25°C to approximately 80°C using the 105°C T101 column bottom liquid (W1) through a preheater (1). Through this measure, the external heat source load required by the T101 reboiler is reduced by approximately 28%. Simultaneously, during the membrane separation process, the dehydrated alcohol mixture vapor (R2) obtained from the retrieval side of the membrane separation system at approximately 105°C and 150 kPa is first introduced into the auxiliary reboiler of T103 to provide heat to T103. After the vapor condenses to a saturation temperature of approximately 85°C, it enters the T103 column for distillation. Through this measure, the total external heat source load required by the T103 reboiler is reduced by approximately 35%. Through the above energy integration measures, the total energy consumption of the overall process is significantly reduced, while the purity and recovery rate of the final product remain consistent with those of Embodiment 1, significantly improving the economic efficiency of the process.

[0067] Example 4

[0068] This embodiment illustrates the construction of a predictive model for the time-varying process of separation factors in the separation of fusel oils using a polymer separation membrane.

[0069] The membrane separation system processes material F2 with extremely high total alcohol concentrations, exceeding 95%. In polymer-based membranes, alcohol vapors swell the membrane matrix, increasing free volume. This plasticization typically leads to a greater increase in membrane permeability to alcohols than to water, thus reducing selectivity. Simultaneously, the upstream alkali neutralization step generates non-volatile salts. Although removed by an evaporator, trace amounts of salt may still be entrained into the membrane module, accumulating over time to form a fouling layer. To describe the separation factor... With alcohol concentration and time The changes in are represented by a multiplicative model structure, assuming that the effects of these two factors can be approximately decoupled:

[0070]

[0071] in, It is the initial benchmark separation factor; It is a concentration-dependent plasticizing effect factor; It is a time-related fouling effect factor.

[0072] The fouling effect is a cumulative effect over time. To describe the performance degradation process over time, a common phenomenological model, the hyperbolic model, is used to describe the trend of membrane performance decline over time, yielding the following result:

[0073]

[0074] in, It is the performance degradation rate constant.

[0075] The plasticization mechanism is described based on the free volume theory. Since the materials to be processed in this patent contain other organic compounds besides alcohols, such as esters and ketones, these compounds can cause adsorption on the membrane surface, competing with alcohols, and also occupy diffusion channels, affecting alcohol permeation. Therefore, the influence of the concentration of other organic compounds on the separation process needs to be considered, and the concentration inside the membrane is calculated using the competitive adsorption theory. According to the solubility-diffusion model, permeability is the product of solubility S and diffusion coefficient D. Plasticization, mainly caused by alcohols, increases the diffusion coefficient of the components by increasing the free volume of the membrane matrix. According to the free volume theory, the components... diffusion coefficient Its concentration inside the membrane It exhibits an exponential relationship:

[0076]

[0077] in, It is the diffusion coefficient without plasticization. This is the plasticizing coefficient. Assuming plasticization is primarily caused by alcohols, therefore... This refers to the concentration of alcohol adsorbed within the membrane. .

[0078] Separation factor It is the ratio of the permeability of water (W) to that of organic matter (Org). Assuming that the solubility S is minimally affected by plasticization, the change in the separation factor is mainly determined by the change in the diffusion coefficient:

[0079]

[0080] Define the benchmark separation factor as Then the plasticizing effect factor for:

[0081]

[0082] Because plasticization increases the diffusivity of organic matter more than that of water, that is... Define the comprehensive plasticizing strength coefficient ,but:

[0083]

[0084] Next, the intramembrane alcohol concentration was further determined. In fusel oil systems, alcohols (Alc) and other organic compounds (Others) compete for the limited adsorption sites within the membrane material. This phenomenon is described using a competitive Langmuir adsorption model.

[0085]

[0086] in, It is the total saturated adsorption capacity of the membrane. It is a component The adsorption affinity constant, This is the feed-side concentration, used to approximate fugacity or activity, applied to alcohols, and assuming that competition between organic compounds is primarily considered while neglecting competition from water for adsorption sites, then we obtain:

[0087]

[0088] Substituting Equation 8 into Equation 6 of the plasticizing mechanism model, we get:

[0089]

[0090] Define a maximum plasticizing potential constant. Then formula (9) can be written as:

[0091]

[0092] Substituting the revised Equation 10 and the fouling effect term Equation 2 into the overall model framework Equation 1, we obtain the final dynamic model considering the competitive adsorption effect:

[0093]

[0094] Furthermore, considering that in the membrane separation unit of this patent, the feed F2 is a highly concentrated organic material, for example, in Example 1, the total concentration of organic matter is 97%, and it is further concentrated to over 99.5% during membrane separation. At such high organic matter concentrations, assuming the adsorption sites of the membrane material are close to saturation, the denominator of the Langmuir adsorption model... In this context, "1" represents the relative proportion of free adsorption sites, while the following terms represent the proportion of occupied sites. If the membrane is close to saturation, then the number of occupied sites far exceeds the number of free sites, and thus...

[0095] Based on the above assumptions, the denominator of the Langmuir model can be simplified to:

[0096]

[0097] Substituting the simplified denominator into the plasticizing effect term In the expression:

[0098]

[0099] Reorganize the parameters of the terms within the exponent and divide both the numerator and denominator by . :

[0100]

[0101] Let's introduce a new parameter—relative affinity ratio ( ):

[0102]

[0103] It is a dimensionless parameter that directly quantifies the competitive adsorption capacity of other organic compounds (aldehydes, ketones, esters, etc.) relative to alcohols.

[0104] Will Substituting into formula (15), we obtain the simplified plasticizing effect term:

[0105]

[0106] By introducing the high concentration saturation assumption and the relative affinity ratio parameter, we successfully transformed the original three parameters ( Reduced to two parameters () ).

[0107] Substituting the simplified plasticizing effect term (Equation 17) into the overall model framework, we obtain the final four-parameter dynamic model:

[0108]

[0109] The simplified model contains four parameters to be fitted, whose physical meanings are: It is the separation factor under ideal conditions that is free from plasticization and fouling; the maximum plasticization potential constant. The inherent resistance to plasticization of the membrane material determines the upper limit of the plasticizing effect. When the feed contains only alcohols, the plasticizing effect factor is... Relative affinity ratio The score in the index term reflects the competitive effect. This can be understood as the fraction of adsorption sites occupied by alcohols under saturated adsorption conditions. This indicates that other organic compounds are more readily adsorbed onto the membrane than alcohols, and they strongly compete for adsorption sites, effectively inhibiting alcohol adsorption; if This indicates that alcohols are more easily adsorbed, and other organic compounds have difficulty competing for them; therefore, the plasticizing effect is mainly determined by the alcohol concentration. The rate at which the separation factor decreases over time due to salt accumulation is limited.

[0110] Based on the process and operating parameters of Example 1, polyvinyl alcohol membrane separation was used, and the effect of run time on the separation factor was tested under different feed composition conditions. The following test data were obtained:

[0111] serial number Runtime (h) Average alcohol concentration Average concentration of other organic matter Measured separation factor T1 100 0.960 0.020 1043.9 T2 300 0.960 0.020 925.3 T3 600 0.960 0.020 820.1 T4 900 0.960 0.020 780.6 T5 50 0.980 0.005 1035.2 T6 50 0.970 0.015 1063.1 T7 50 0.950 0.030 1092.4 T8 50 0.930 0.050 1124.0 T9 50 0.900 0.080 1077.6 T10 200 0.975 0.010 941.8 T11 400 0.940 0.040 951.1 T12 700 0.950 0.030 867.6 T13 800 0.910 0.070 839.5 T14 1000 0.970 0.015 732.6

[0112] The following test results were used for verification:

[0113] serial number Runtime (h) Average alcohol concentration Average concentration of other organic matter Measured separation factor V1 50 0.960 0.020 1065.4 V2 150 0.940 0.040 1014.7 V3 250 0.970 0.015 989.0 V4 500 0.950 0.030 917.1 V5 750 0.920 0.060 852.0 V6 850 0.960 0.020 807.0 V7 950 0.980 0.005 728.3 V8 1000 0.900 0.080 820.0

[0114] Summary of parameter fitting results

[0115] Parameter name Fitted values Standard error (StdErr) 1170.17 52.52 0.1489 0.0445 49.584 73.391 0.000458 0.000035

[0116] Summary of Model Performance Metrics

[0117] index Fit set Validation set R² (coefficient of determination) 0.9674 0.9574 Mean Absolute Percentage Error (MAPE) 2.02% 2.16%

[0118] The model's R² values ​​on both the fitting and validation sets are higher than 0.95, indicating that the model fits the data well and has strong explanatory power. The MAPE values ​​on the fitting and validation sets are 2.02% and 2.16%, respectively, with similar error levels, indicating that the model's generalization ability is relatively stable.

Claims

1. A method for separating and purifying fusel oils in Fischer-Tropsch synthesis, characterized in that, Includes the following steps: (a) The fusel oil feedstock containing water and various alcohols is fed into the first distillation column for atmospheric distillation. The top distillate rich in methanol, ethanol, propanol and butanol is obtained from the top of the first distillation column, and the bottom liquid mainly composed of water and C4+ higher alcohols is discharged from the bottom of the column. (b) The distillate from the top of the column is fed into a second distillation column for vacuum distillation. Light components, mainly methanol, aldehydes, ketones and esters, are collected from the top of the second distillation column, and a mixed alcohol liquid mainly containing ethanol, propanol, butanol and water is obtained from the bottom of the column. (c) The mixed alcohol liquid is neutralized by adding alkali, and then the neutralized material is sent to an evaporator for vaporization and desalination. The resulting gaseous material enters a membrane separation system for steam permeation dehydration to obtain dehydrated mixed alcohol vapor with reduced moisture content.

2. The method according to claim 1, characterized in that, It also includes the following steps: (d) The dehydrated mixed alcohol vapor obtained in step (c) is fed into a third distillation column for vacuum distillation. The ethanol product is collected from the top of the third distillation column, and the bottom liquid is a mixture of propanol and butanol.

3. The method according to claim 2, characterized in that, It also includes the following steps: (e) The liquid obtained in step (d) is sequentially fed into the fourth and fifth distillation columns for distillation to separate n-propanol and n-butanol products.

4. The method according to claim 1, characterized in that, In step (a), the fusel oil feedstock liquid is preheated by heat exchange with the bottom liquid discharged from the bottom of the first distillation column before entering the first distillation column.

5. The method according to claim 2, characterized in that, In step (d), the dehydrated mixed alcohol vapor obtained in step (c) is first introduced into the auxiliary reboiler of the third distillation column to provide heat, and then condensed and fed into the third distillation column as feed.

6. The method according to claim 1, characterized in that, The alkali neutralization treatment in step (c) is to adjust the pH value of the material to 7.0-8.

5.

7. The method according to claim 1, characterized in that, The membrane separation system in step (c) uses a hydrophilic zeolite membrane or a polymer membrane, with an operating temperature of 90-120℃, an absolute pressure of 120-200 kPa on the feed side, and an absolute pressure of less than 5 kPa on the permeate side.

8. The method according to claim 2, characterized in that: The first distillation column operates under atmospheric pressure of 100-110 kPa; the second distillation column operates under absolute pressure of 60-80 kPa; and the third distillation column operates under absolute pressure of 30-50 kPa.

9. The method according to claim 1, characterized in that, The components of the fusel oil feedstock liquid, by weight percentage, include: water: 25-45%; ethanol: 20-35%; methanol: 10-18%; n-propanol: 8-15%; n-butanol: 5-10%; C4+ higher alcohols and other impurities: balance.

10. The method according to claim 1 or 7, characterized in that, The method further includes using a prediction algorithm model to predict the separation factor of the membrane separation system, wherein the formula of the prediction algorithm model is: in: This is the total alcohol concentration. It is the total concentration of other organic matter. It is time; , , , These are the parameters to be fitted; the other organic compounds refer to the total of acids, aldehydes, ketones, and esters.

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