A process for extracting oil from furfural wastewater to prepare biofuel feedstock

Abstract

This invention discloses a process for extracting oils from furfural wastewater to prepare bio-aviation fuel feedstock, applicable to the high-value recovery of trace oils from the primary distillation column wastewater during furfural production. The process includes steps such as feedstock hydrolysis, gas condensation, cooling and stratification of the wastewater oils at the bottom of the column, secondary air flotation oil extraction, isothermal thermal devolvation for impurity removal, microfiltration, saponification reaction, alcohol extraction, and vacuum distillation. By constructing a four-stage synergistic removal mechanism of thermal devolvation + saponification phase separation + alcohol extraction + vacuum distillation, unsaponifiable matter, insoluble substances, and water in the oils are effectively separated to obtain high-purity fatty acid methyl ester products, which can be directly used as bio-aviation fuel feedstock. This method is mild, energy-efficient, non-toxic, and environmentally friendly, avoiding secondary pollution caused by traditional extraction processes. It is both economical and practical, effectively extending the operating cycle of the wastewater evaporator, improving system stability and economic value, and providing a new path for the resource utilization of furfural wastewater.

Description

Technical Field

[0001] This invention relates to the field of furfural industrial wastewater utilization technology, specifically a process for extracting oils from furfural wastewater to prepare biofuel feedstock. Background Technology

[0002] Furfural, an important biomass platform compound, is typically obtained through acid-catalyzed pyrolysis of agricultural byproducts (such as corn cobs) and is widely used in fine chemicals, pharmaceutical synthesis, pesticides, and rubber additives. However, in the industrial production of furfural, especially during the high-temperature hydrolysis and pyrolysis process using corn cobs, a large amount of high-temperature organic wastewater is generated as a byproduct. This wastewater contains trace amounts of oily components, which can become a potential interfering factor in the furfural system.

[0003] This type of oil mainly originates from the fat-soluble products formed by the cleavage of lignin and hemicellulose in corn cobs under high-temperature acid hydrolysis conditions. Although it accounts for a very small percentage (generally only 0.05%-0.10%), its composition is complex, with a high water content, and it is often miscible in wastewater, making it difficult to directly separate and utilize the oil in wastewater. Currently, traditional wastewater treatment methods, such as air flotation for oil removal, chemical sedimentation, or solvent extraction, are mainly used for pollution control and have failed to systematically recover the valuable lipid resources in wastewater oil.

[0004] Existing technologies, such as Chinese patent document CN118620657A, propose a pretreatment device and method for oily waste. The raw materials used are primarily kitchen waste oil, which contains a large amount of salt, trace elements, and other impurities. During treatment, it easily generates large amounts of waste acid and alkali, resulting in a complex and costly pretreatment process. Furthermore, the source and composition of the oil in this pretreatment are significantly different from those produced as a byproduct of furfural. Therefore, this technology cannot be directly applied to the efficient extraction and deep purification of trace amounts of oil in furfural wastewater.

[0005] The applicant's earlier patent application, CN119912983B, has the following limitations: While the patent proposes the whole-component refining of corn cobs into bio-aviation fuel, its core lies in the active synthesis of hydrocarbon fuels (through cellulose acid hydrolysis to produce levulinic acid + furfural condensation reaction). Its technical approach: does not involve wastewater oil recovery, neglects the high-value utilization of 0.05-0.10% trace components; cannot solve the evaporator coking problem because it does not treat oil residues in the wastewater; and relies on high-temperature hydrogenation deoxygenation (>320℃ / 7MPa), resulting in high energy consumption.

[0006] On the other hand, although furfural wastewater contains low levels of oil, it has the following characteristics: a high proportion of saturated fatty acids (C16 and C18 accounting for over 85%), saponified substances and sterols (over 70%), and 17.19% unsaponifiable matter residue, giving it the potential to be converted into bio-based fuels (especially bio-jet fuel). If this portion of oil resources can be utilized at a high value, it can not only reduce wastewater COD and treatment load, but also extend the evaporator operating cycle, reduce coking of heat exchange tubes, and improve system operating efficiency and output value.

[0007] Patent documents CN102976539A and CN101481189A mainly recover calcium and magnesium acetate by neutralizing it with lime and dolomite, and combine it with wastewater heat energy recycling for system heating.

[0008] Patent document CN111573873A discloses a furfural wastewater recovery device, which mainly addresses structural module issues such as impurity filtration, air flotation oil removal, and clean water recovery in wastewater. Although it mentions an oil separation device, it does not address the subsequent extraction, purification, and conversion pathways of oils, nor does it consider the systematic removal of unsaponifiable and insoluble substances from oils. Similarly, CN115594343A also has the above-mentioned problems.

[0009] Although CN114891535A proposes a method for preparing sustainable aviation fuel from agricultural waste, utilizing routes such as acid desulfurization, hydrogenation, and isomerization to achieve biofuel production, the raw material pathways of this technical solution are relatively complex and the process stages are long. In particular, it fails to solve the problem of separating and purifying extremely low-content oil components in acidic wastewater to achieve the separation and deep conversion of furfural by-product oil resources.

[0010] CN108611100A uses a high-temperature pyrolysis method, which has drawbacks such as high energy consumption (>800kW·h / ton of oil) and secondary pollution (tar, sulfur-containing waste gas); CN110358576A uses a solvent extraction method, which has drawbacks such as residual organic solvents like hexane (>500ppm), requiring deep purification of the product and increasing costs; CN112111434A uses an adsorption separation method, which has drawbacks such as limited activated carbon adsorption capacity (<0.2g oil / g carbon), difficulty in regeneration, and increased solid waste generation.

[0011] However, there is currently no efficient extraction and purification process for furfural wastewater characterized by low oil content, high impurities, and high boiling point components. The extraction process faces the following technical challenges:

[0012] Oils and fats are dispersed at high temperatures in wastewater, and easily form a floating emulsion layer upon cooling, making it difficult to separate oil and water quickly and efficiently. Oils and fats contain a large amount of unsaponifiable matter and trace amounts of non-volatile components, which cannot be completely separated by traditional single physical extraction. The extracted oils and fats contain many impurities, which interfere with subsequent biofuel synthesis processes (such as transesterification and hydrogenation). Without a matching continuous separation and low-energy purification process, it is difficult to promote its application in the tens of thousands of tons of furfural process.

[0013] Therefore, there is an urgent need to develop a novel oil separation and refining process suitable for furfural wastewater systems. This process can efficiently extract trace oil components and effectively remove interfering factors such as volatiles, insolubles, and unsaponifiables through synergistic techniques such as temperature-controlled devolatilization, microchannel filtration, and saponification / extraction / distillation. This will yield high-quality fatty acid methyl esters, enabling the resource-based and high-value utilization of oils in industrial wastewater, while also contributing to the development of raw materials for sustainable fuels such as biofuel. Summary of the Invention

[0014] The technical problem this invention aims to solve is to overcome existing deficiencies and provide a process for extracting oils from furfural wastewater to prepare bio-aviation fuel feedstock. This invention achieves efficient separation, purification, and conversion of trace amounts of oils in furfural primary distillation column wastewater by constructing a multi-stage synergistic process flow consisting of "rapid condensation—two-stage air flotation—constant-temperature thermal devolatilization—microporous filtration—saponification phase separation—alcoholization extraction—vacuum distillation." This method not only overcomes technical difficulties such as high oil-water emulsification, extremely low oil content, and severe impurity coexistence, significantly improving the purity of fatty acid methyl esters (≥97.5%) and reducing unsaponifiable matter residue (≤1.8%), but also greatly reduces energy consumption and organic solvent usage, effectively extends the operating cycle of the wastewater evaporator, and improves system stability and economic value. It provides a new path for the resource utilization of furfural wastewater and lays a technical foundation for the green preparation of bio-aviation fuel feedstock, effectively solving the problems in the background technology.

[0015] To achieve the above objectives, the present invention provides the following technical solution: a process for extracting oil from furfural wastewater to prepare biofuel feedstock, comprising the following steps:

[0016] (1) Raw material hydrolysis:

[0017] Corn cobs and dilute sulfuric acid are mixed at a solid-liquid ratio of 1:0.3 and fed into a hydrolysis reactor. Saturated steam at 170-180℃ is introduced for hydrolysis and pyrolysis.

[0018] The reaction produces a mixed gas containing 8-10% furfural gas, 3.5-4.5% acetic acid, 0.05-0.10% grease gas, and water vapor.

[0019] The grease exists as a mixed liquid with wastewater after condensation, and does not separate as a free gaseous state;

[0020] (2) Initial separation: The mixed gas is filtered by a magnetic ring filter with a porosity of 60-70% to remove dust, condensed into liquid and then distilled at atmospheric pressure. Furfural crude product is obtained at the top of the column and wastewater oil mixture at 102-104℃ is obtained at the bottom of the column.

[0021] The wastewater and grease mixture is rapidly cooled in two stages: first, it is rapidly cooled to 40°C through an internal plate heat exchanger, and then cooled to 15°C through an internal spiral freezer, causing the grease to solidify and float. The wastewater is then discharged through bottom drainage, and the wastewater 10cm below the grease layer is introduced into an oil-water separator.

[0022] (3) Air flotation for oil extraction: The wastewater is heated to 80℃-95℃ using a coil heater, and then separated from the oil using a two-stage air flotation device. The obtained oil has a water content of 3%-5%, contains 1%-2% volatile substances, 2%-3% insoluble substances, 17%-19% unsaponifiable matter, and 72%-78% saponifiable matter and total sterols.

[0023] (4) Thermal degassing and impurity removal: The oil separated in step (3) is slowly introduced into a constant temperature flow tank, heated and maintained at 105℃-110℃, and the oil is kept in the tank for no less than 2.5 hours to remove moisture and volatile substances; then the oil is filtered through a microchannel filter.

[0024] The constant temperature flow tank uses a stainless steel inner liner, constant temperature circulating heating, and is equipped with baffles to enhance heat exchange and mixing efficiency.

[0025] (5) Microfiltration: The devolatilized oil is passed through a microchannel filter with a pore size of 0.1-0.5μm to remove insoluble impurities and obtain oil substances with higher purity;

[0026] Cleaning or regeneration methods for clogged filter elements: Regenerate the filter element by reverse pulse backflushing or immersion in alkaline solution;

[0027] (6) Saponification reaction: Add 10-30wt% potassium hydroxide solution to the purified oil (the amount added is 1.05-1.2 times the theoretical alkali consumption of the oil saponification value), add water and stir to separate the layers, that is, add water of the same volume as the oil, stir and let stand to separate the layers, and take the salt phase containing fatty acids.

[0028] (7) Alcohol extraction: Add 0.8-1.5 times the volume of methanol to the aqueous phase, let stand for ≥30 minutes, and separate the liquid to obtain fatty acid-methanol organic phase;

[0029] The saponification reaction is a soap salt alcoholysis reaction rather than a traditional transesterification reaction;

[0030] (8) Distillation and purification: The organic phase is distilled at a bottom temperature of 120-150℃ and a vacuum of -0.08 to -0.095MPa. Methanol is recovered at the top of the column, and fatty acid methyl esters are obtained at the bottom of the column, which are the raw materials for bio-aviation fuel.

[0031] Furthermore, the magnetic field strength of the magnetic ring filter in step (2) is 0.5-0.8T, and the magnetic field gradient distribution is: 0.8T in the inlet area and 0.5T in the outlet area, forming a decreasing magnetic field strength gradient. The magnetic field gradient guides the directional migration of impurities containing ferromagnetic particles, while the non-magnetic grease components are unaffected, thus achieving impurity pre-separation. The wastewater obtained in step (2) is cooled and then recycled for dilute sulfuric acid preparation or boiler water, forming a resource closed loop.

[0032] Furthermore, the operating parameters of the air flotation device in step (3) are as follows: primary air flotation: dissolved air pressure 0.3-0.4 MPa, residence time 15-20 minutes; secondary air flotation: dissolved air pressure 0.2-0.3 MPa, residence time 10-15 minutes.

[0033] Furthermore, in step (4), the oil flow rate is 0.4-0.6 m³ / h, and baffles are installed in the pool to increase the mass transfer area.

[0034] Furthermore, the saponification reaction conditions for step (6) are: reaction temperature 70-80℃, stirring speed 200-300rpm.

[0035] Furthermore, the fatty acid methyl esters in step (8) satisfy the following conditions: saponification value > 190 mg KOH / g;

[0036] Unsaponifiable matter content ≤1.8%; acid value ≤1.0 mg KOH / g.

[0037] Furthermore, the refrigerant for the spiral freezer in step (2) is an aqueous solution of ethylene glycol at -20℃ with a heat transfer coefficient ≥500 W / (m²·K).

[0038] Furthermore, the microchannel filter material in step (5) is a sintered metal filter element with a pressure resistance of ≥1.0 MPa.

[0039] Furthermore, the methanol in step (7) is anhydrous methanol with a water content ≤0.1%.

[0040] Furthermore, the bio-aviation fuel feedstock prepared by this method has a fatty acid methyl ester content of ≥95%; a carbon chain length of C16-C18 accounting for ≥85%; a pour point of ≤-10℃ and a flash point of ≥110℃.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] 1. This invention effectively solves the problem of separating furfural wastewater with high oil-water emulsification and low oil content. By designing a two-stage rapid cooling device, the wastewater temperature can be reduced from 102°C to 15°C in a short time, causing the oil to solidify rapidly and float on the liquid surface, thus achieving preliminary oil-water separation. At the same time, combined with the bottom drainage and oil-water separator structure, the residual wastewater can be reused and the oil can be enriched, providing a feasible way for the resource utilization of low-concentration oils. This cold separation strategy significantly reduces energy consumption and chemical reagent consumption, and is suitable for continuous industrial operation conditions.

[0043] 2. This invention significantly improves the purity and quality of oils by constructing a three-stage operation module of "air flotation oil extraction - thermal devolatile impurity removal - microporous filtration". In particular, the use of a two-stage dissolved air flotation device, combined with a constant-temperature hot pool to remove moisture and volatile organic compounds, effectively removes non-target impurities from the oil components. Furthermore, a microchannel filter with a sintered metal filter element is used to deeply remove insoluble impurities from the oil, ultimately obtaining a high-purity bio-oil raw material. After testing, the oil has a water content of ≤3% and insoluble impurities of ≤2%, making it suitable for subsequent saponification reaction.

[0044] 3. This invention proposes for the first time a "four-stage synergistic removal of unsaponifiables" approach, which systematically solves the core problems of high unsaponifiable content, strong co-solubility, and difficulty in removal by traditional methods in oils and fats through four process stages: "thermal devolatilization," "saponification phase separation," "alcoholization washing," and "vacuum distillation." Among them, the saponification phase separation process discards the oil phase rich in unsaponifiables after saponification with alkaline solution, achieving an impurity removal rate of over 80%; alcoholization extraction further improves the recovery rate of effective components; and finally, the distillation operation in the bottom column ensures that high-boiling-point resin polymers are completely retained in the bottom column residue. The entire process removes unsaponifiables, and the obtained fatty acid methyl esters have a purity of ≥97.5% and a C16~C18 carbon chain ratio of ≥89%, which can be used as a feedstock for aviation alternative fuels.

[0045] 4. This invention significantly improves the operating efficiency and added value of the furfural production system: on the one hand, it reduces grease deposition and coking in the wastewater evaporator, extends the equipment heat exchange cycle, and improves system stability; on the other hand, it converts the trace amounts of grease that were originally discharged as waste into high-value bio-based fatty acid methyl ester products; at the same time, it avoids the use of traditional organic solvents such as n-hexane, and the process energy consumption is reduced by more than 50% compared with the solvent extraction method. It is not only safer and more environmentally friendly to operate, but also more suitable for industrial promotion. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the process flow of the present invention;

[0047] Figure 2 This is a flowchart illustrating the process of separating unsaponifiable matter in the oil phase according to the present invention.

[0048] In the diagram: 1 (1), 2 (2), 3 (3), 4 (4), 5 (5), 6 (6), 7 (7), 8 (8), 9 (9), 10 (10), 11 (11), 12 (12), 13 (13), 14 (14), 15 (15), 16 (16), 17 (17), 18 (18), 19 (19), 20 (20), 21 (21), 22 (22), 23 (23), 24 (24), 25 (25). Detailed Implementation

[0049] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0050] Example 1

[0051] Please see Figure 1-2 This invention provides a technical solution: a process for extracting oil from furfural wastewater to prepare biofuel feedstock, applicable to a production plant with an annual furfural production capacity of 10,000 tons. The specific implementation steps are as follows:

[0052] Step 1: Raw material hydrolysis

[0053] 10 tons of dry corn cobs (moisture content ≤8%) were mixed with 3 m³ of 15% dilute sulfuric acid and prepared at a solid-liquid ratio of 1:0.3 before being fed into a hydrolysis reactor.

[0054] Saturated steam at 175℃ was introduced, the pressure was controlled at 0.8 MPa, and the reaction time was maintained for 120 minutes;

[0055] The generated mixed gas composition is: furfural gas 9.2%, acetic acid 4.0%, oil and fat gas 0.08%, and water vapor 86.72%.

[0056] Step 2: Preliminary separation

[0057] The mixed gas is first treated by a magnetic ring filter for dust removal. The filter model is CXF-60 with a porosity of 68%, and the magnetic field strength gradually changes from 0.8 T at the inlet to 0.5 T at the outlet.

[0058] The condensed liquid is fed into an atmospheric distillation column for separation:

[0059] 920 kg of crude furfural was recovered from the top of the tower, with a purity of 92%.

[0060] At the bottom of the tower, 3.5 m³ of a wastewater-oil mixture at a temperature of 102℃ was obtained.

[0061] Then proceed in sequence:

[0062] Plate heat exchanger (316L stainless steel) can reduce the temperature from 102°C to 40°C in 3 seconds;

[0063] The spiral freezer (model: LLS-200, ethylene glycol solution at -20℃, heat transfer coefficient 550 W / (m²·K)) further cools the mixture to 15℃ within 5 minutes;

[0064] After cooling, the grease solidifies and floats on the surface, while the wastewater at the bottom is discharged through the drain. Wastewater collected from 10cm below the grease layer is sent for subsequent treatment and reused in the preparation of dilute sulfuric acid, with a reuse rate of 98%.

[0065] Step 3: Oil extraction by air flotation

[0066] The cooled wastewater enters the oil-water separator, where it is heated to 85°C by the coils.

[0067] Oil extraction using a two-stage dissolved air flotation process:

[0068] Primary air flotation: dissolved air pressure 0.35 MPa, residence time 18 minutes;

[0069] Two-stage air flotation: dissolved air pressure 0.25 MPa, residence time 12 minutes;

[0070] The results of the extracted oil analysis are as follows:

[0071] Moisture content: 4.2%;

[0072] Volatile substances: 1.5%;

[0073] Insoluble substances: 2.3%;

[0074] Unsaponifiable matter: 18.1%;

[0075] Saponifications and total sterols: 73.9%.

[0076] Unsaponifiables refer to neutral components in oils and fats that cannot form soap, such as sterols, pigments, and hydrocarbons.

[0077] Step 4: Thermal devolatation and impurity removal

[0078] The grease is slowly introduced into the constant temperature flow tank at a flow rate of 0.5 m³ / h. The constant temperature is set at 108℃. The tank is equipped with stainless steel baffles to enhance heat transfer and stratification.

[0079] The grease is kept in the tank for 3 hours to fully remove moisture and light volatile components;

[0080] The devolatilized oil is filtered for solid impurities through a microchannel filter (0.3 μm pore size, filter element made of 316L sintered metal, pressure resistant to 1.5 MPa).

[0081] Step 5: Saponification reaction

[0082] Add 25 wt% potassium hydroxide solution to the purified oil. The actual amount added is 1.1 times the amount of alkali required for the theoretical saponification value of the oil.

[0083] The reaction temperature was controlled at 75℃, the stirring speed was 250 rpm, and the reaction time was 40 minutes.

[0084] After the reaction is complete, add an equal amount of deionized water, mix thoroughly, and allow to stand for separation. Take the lower aqueous phase as a potassium fatty acid salt solution.

[0085] Step 6: Alcoholic Extraction

[0086] Add 1.2 times the volume of anhydrous methanol (water content ≤0.05%) to the above aqueous phase and allow it to stand for 35 minutes for extraction.

[0087] After separation, the fatty acid methyl ester-methanol organic phase was obtained.

[0088] Step 7: Distillation and purification

[0089] The organic phase is fed into a vacuum distillation column, with the bottom temperature set at 135℃ and the vacuum level at -0.09 MPa.

[0090] Methanol was recovered at the top of the column, and fatty acid methyl esters were obtained from the bottom of the column. The analytical results are as follows:

[0091] Key Equipment Configuration Table:

[0092] Example 2: Process Parameter Optimization and Product Performance Improvement

[0093] Based on Example 1, this embodiment further improves the oil recovery efficiency and fatty acid methyl ester quality by adjusting the raw material processing conditions, air flotation pressure, impurity removal method, and vacuum distillation parameters, thus meeting the requirements of bio-aviation fuel for use in low-temperature environments.

[0094] I. Raw material processing and oil extraction

[0095] 20 tons of dry corn cobs (moisture content ≤8%) were mixed with 6 m³ of 15% dilute sulfuric acid at a solid-liquid ratio of 1:0.3 and then fed into a hydrolysis reactor.

[0096] Saturated steam at 178℃ was introduced at a pressure of 0.8 MPa, and the reaction was maintained for 150 minutes.

[0097] The resulting mixed gas composition was: furfural gas 9.1%, acetic acid gas 4.1%, oil and fat gas 0.09%, and water vapor 86.71%.

[0098] The gas is filtered for dust using a magnetic ring filter with a porosity of 68%, where the magnetic field gradient gradually decreases from 0.8 T at the inlet to 0.5 T at the outlet. The condensate undergoes atmospheric pressure distillation.

[0099] 1820 kg of crude furfural was obtained at the top of the tower, with a purity of 92%.

[0100] 7 m³ of a wastewater-oil mixture at 102℃ was obtained at the bottom of the tower.

[0101] The mixture passes through a plate heat exchanger, where it is cooled to 40°C in 3 seconds.

[0102] The spiral freezer (heat transfer medium is -20℃ ethylene glycol solution, heat transfer coefficient 550 W / (m²·K)) was further cooled to 15℃ in 5 minutes;

[0103] After the grease solidifies and floats to the surface, the bottom wastewater is discharged, and the wastewater 10 cm below the grease layer is introduced into the oil-water separator.

[0104] II. Enhanced Air Flotation Separation

[0105] Wastewater is heated to 88°C by a coil heater and then separated into oil and water using a two-stage dissolved air flotation device.

[0106] Primary air flotation: dissolved air pressure 0.38 MPa, residence time 20 minutes;

[0107] Two-stage air flotation: dissolved air pressure 0.28 MPa, residence time 15 minutes.

[0108] The extracted oil components are as follows:

[0109] Moisture content: 3.8%;

[0110] Volatile substances: 0.9%;

[0111] Insoluble substances: 2.1%;

[0112] Unsaponifiable matter: 17.8%;

[0113] Saponifications and total sterols: 76.4%.

[0114] III. Deep Purification Process

[0115] 1. Thermal devolatation for impurity removal:

[0116] The grease enters the constant temperature flow tank at a flow rate of 0.55 m³ / h, and the tank is equipped with stainless steel baffles spaced 10 cm apart.

[0117] The temperature of the flow-through tank was maintained at 108℃, the residence time was 3.2 hours, and the residual volatile substances after treatment were reduced to 0.8%.

[0118] 2. Microfiltration:

[0119] The grease is filtered for solid impurities through a microchannel filter (pressure resistance 1.5 MPa) with a sintered metal filter element with a pore size of 0.3 μm.

[0120] 3. Saponification reaction optimization:

[0121] Add 30 wt% potassium hydroxide solution to the purified oil, the amount of which is 1.15 times the amount of alkali required for the theoretical saponification value;

[0122] The mixture was stirred at 300 rpm for 45 minutes at 80°C. Water was then added and stirred until the mixture separated into layers. The upper oil phase, which is rich in unsaponifiable matter, was discarded, and the aqueous phase (potassium salt solution of fatty acids) was retained.

[0123] 4. Alcoholic extraction:

[0124] Add 1.2 times the volume of anhydrous methanol (water content ≤0.05%) to the above aqueous phase, let stand for 35 minutes, and separate to obtain fatty acid methyl ester-methanol organic phase.

[0125] IV. Distillation and Product Properties

[0126] The organic phase was fed into a distillation column, with the reboiler temperature set at 148℃ and the vacuum controlled at -0.092 MPa. Methanol was recovered at the top of the column (95% recovery rate), and bio-aviation fuel feedstock was obtained from the reboiler. The analytical results are as follows:

[0127] V. Comparison of Technical Effects

[0128] VI. Economic Verification

[0129] In a furfural plant with an annual production capacity of 10,000 tons, an average of 100 tons of wastewater and oil are treated annually.

[0130] Energy consumption cost: 580 kWh / ton, a 51.7% reduction compared to traditional processes;

[0131] Product unit price: 8500 yuan / ton, an increase of 1700 yuan / ton compared to the traditional price;

[0132] VII. Residue Analysis

[0133] The residue from the distillation column was tested according to GB / T 5535 method, and the total amount of unsaponifiable matter was 93.5%. The residue can be used as an asphalt modifier or incinerated for heating.

[0134] The analysis results are as follows:

[0135] Resin polymers accounted for 44.7%;

[0136] β-sitosterol content: 24.1%;

[0137] The proportion of n-octacosane is 10.8%.

[0138] The results show that by increasing the air flotation pressure, optimizing the saponification temperature, and controlling the vacuum degree, the crystallization characteristics of fatty acid methyl esters can be significantly improved, thereby enhancing their low-temperature stability and demonstrating their potential to replace petroleum-based aviation fuel in cold regions.

[0139] This invention addresses the problem of complex unsaponifiable matter composition in furfural wastewater and the difficulty of efficient removal using conventional methods. It proposes a four-stage synergistic separation mechanism that couples thermophysical processes with phase-interface reactions to achieve highly efficient removal of unsaponifiable matter, reducing the unsaponifiable matter content in the final product from the original 17%-19% to ≤1.8%. This four-stage mechanism includes:

[0140] Thermal devolatilization treatment stage

[0141] The separated oil is placed in a constant temperature flow tank at 105℃ to 110℃ and the residence time is maintained for no less than 2.5 hours. This process can effectively vaporize and remove low-boiling-point volatile unsaponifiable components (such as monoterpenes), achieving preliminary removal of unsaponifiable matter with a removal rate of about 15%-20%.

[0142] Saponification phase separation stage

[0143] Add a 10%-30% potassium hydroxide solution to the oil after heat devolatilization, and control the amount of alkali added to be 1.05 to 1.2 times the theoretical saponification value of the oil. Stir the reaction at 70℃-80℃. During the reaction, fatty acids react with alkali to form water-soluble soap salts (RCOOK) that enter the aqueous phase. Unsaponifiables with strong hydrophobicity and high molecular weight do not participate in the reaction and are enriched in the oil phase after phase separation. By discarding the oil phase, more than 80% of unsaponifiable impurities can be removed, which is the main stage for the removal of unsaponifiables.

[0144] As attached Figure 2 As shown: Mechanism: Saponified products (fatty acids) react with KOH to form water-soluble soap salts → which enter the aqueous phase;

[0145] Unsaponifiables (resins / sterols / hydrocarbons) do not react and are hydrophobic → remain in the oil phase;

[0146] Key operation: Separate and discard the oil phase (containing >80% unsaponifiable matter) during the layering process.

[0147] Alcoholization and extraction stage

[0148] Add 0.8-1.5 times the volume of anhydrous methanol to the aqueous phase containing fatty acid soaps. Allow the soaps to stand for at least 30 minutes to undergo a reversible alcoholysis reaction, producing fatty acid methyl esters (RCOOCH3), which are transferred into the methanol organic phase. The remaining, less polar unsaponifiable matter remains in the aqueous phase and is subsequently removed. This stage further purifies the oil products, helps improve the purity of the methyl esters, and removes approximately 3%-5% of residual unsaponifiable matter.

[0149] Vacuum distillation stage

[0150] The obtained fatty acid methyl ester methanol organic phase was subjected to vacuum distillation at a bottom temperature of 120℃-150℃ and a vacuum degree of -0.08 to -0.095 MPa. Methanol was recovered at the top of the column, fatty acid methyl ester was collected as the target product at the bottom of the column, and unsaponifiable matter could not be vaporized due to its boiling point being higher than 300℃. It was eventually enriched in the bottom residue and discharged periodically.

[0151] In summary, this invention establishes a systematic process combining temperature control, chemical reaction, phase separation, and distillation to sequentially target impurities with different physicochemical properties, achieving the gradual reduction and efficient removal of unsaponifiable matter. This method does not rely on high-energy-consuming molecular distillation or toxic solvent extraction, is safe and environmentally friendly, operates under mild conditions, and has controllable costs. It is particularly suitable for the deep purification of oils in complex waste liquid systems with low oil content (0.05%-0.1%), providing a feasible path for the green preparation of biofuel precursors.

[0152] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A process for extracting oil from furfural wastewater to prepare biofuel feedstock, characterized in that, Includes the following steps: (1) Raw material hydrolysis: Corn cobs and dilute sulfuric acid are mixed at a solid-liquid ratio of 1:0.3 and fed into a hydrolysis reactor. Saturated steam at 170-180℃ is introduced for hydrolysis and pyrolysis. The reaction produces a mixed gas containing 8-10% furfural gas, 3.5-4.5% acetic acid, 0.05-0.10% grease gas, and water vapor. (2) Initial separation: The mixed gas is filtered by a magnetic ring filter with a porosity of 60-70% to remove dust, condensed into liquid and then distilled at atmospheric pressure. Furfural crude product is obtained at the top of the column and wastewater oil mixture at 102-104℃ is obtained at the bottom of the column. The wastewater and grease mixture is rapidly cooled in two stages: first, it is rapidly cooled to 40°C through an internal plate heat exchanger, and then cooled to 15°C through an internal spiral freezer, causing the grease to solidify and float. The wastewater is then discharged through bottom drainage, and the wastewater 10cm below the grease layer is introduced into an oil-water separator. (3) Air flotation for oil extraction: The wastewater is heated to 80℃-95℃ using a coil heater, and then separated from the oil using a two-stage air flotation device. The obtained oil has a water content of 3%-5%, contains 1%-2% volatile substances, 2%-3% insoluble substances, 17%-19% unsaponifiable matter, and 72%-78% saponifiable matter and total sterols. (4) Thermal degassing and impurity removal: The oil separated in step (3) is slowly introduced into a constant temperature flow tank, heated and maintained at 105℃-110℃, and the oil is kept in the tank for no less than 2.5 hours; (5) Microfiltration: The devolatilized oil is passed through a microchannel filter with a pore size of 0.1-0.5μm to remove insoluble impurities; (6) Saponification reaction: Add 10-30wt% potassium hydroxide solution to the purified oil, add water and stir to separate the layers, and take the salt phase containing fatty acids; (7) Alcohol extraction: Add 0.8-1.5 times the volume of methanol to the aqueous phase, let stand for ≥30 minutes, and separate the liquid to obtain fatty acid-methanol organic phase; (8) Distillation and purification: The organic phase is distilled at a bottom temperature of 120-150℃ and a vacuum of -0.08 to -0.095MPa. Methanol is recovered at the top of the column, and fatty acid methyl esters are obtained at the bottom of the column, which are the raw materials for bio-aviation fuel.

2. The process for extracting oil from furfural wastewater to prepare biofuel feedstock according to claim 1, characterized in that: The magnetic field strength of the magnetic ring filter in step (2) is 0.5-0.8T, and the magnetic field gradient distribution is: 0.8T in the inlet area and 0.5T in the outlet area, forming a decreasing magnetic field strength gradient. The wastewater obtained in step (2) is cooled and then recycled for dilute sulfuric acid preparation or boiler water, forming a resource closed loop.

3. The process for extracting oil from furfural wastewater to prepare biofuel feedstock according to claim 1, characterized in that: The operating parameters of the air flotation device in step (3) are as follows: primary air flotation: dissolved air pressure 0.3-0.4 MPa, residence time 15-20 minutes; secondary air flotation: dissolved air pressure 0.2-0.3 MPa, residence time 10-15 minutes.

4. The process for extracting oil from furfural wastewater to prepare biofuel feedstock according to claim 1, characterized in that: In step (4), the oil flow rate is 0.4-0.6 m³ / h, and baffles are installed in the pool to increase the mass transfer area.

5. The process for extracting oil from furfural wastewater to prepare biofuel feedstock according to claim 1, characterized in that: The saponification reaction conditions for step (6) are: reaction temperature 70-80℃, stirring speed 200-300rpm.

6. The process for extracting oil from furfural wastewater to prepare biofuel feedstock according to claim 1, characterized in that: The fatty acid methyl esters in step (8) satisfy the following condition: saponification value > 190 mg KOH / g; Unsaponifiable matter content ≤1.8%; acid value ≤1.0 mg KOH / g.

7. The process for extracting oil from furfural wastewater to prepare biofuel feedstock according to claim 1, characterized in that: The refrigerant for the spiral freezer in step (2) is an aqueous solution of ethylene glycol at -20℃ with a heat transfer coefficient ≥500 W / (m²·K).

8. The process for extracting oil from furfural wastewater to prepare biofuel feedstock according to claim 1, characterized in that: The microchannel filter material in step (5) is a sintered metal filter element with a pressure resistance of ≥1.0 MPa.

9. The process for extracting oil from furfural wastewater to prepare biofuel feedstock according to claim 1, characterized in that: The methanol in step (7) is anhydrous methanol with a water content of ≤0.1%.

10. A bio-aviation fuel feedstock, prepared by the process of extracting furfural wastewater oil as described in any one of claims 1-9, characterized in that: Fatty acid methyl ester content ≥95%; carbon chain length C16-C18 percentage ≥85%; freezing point ≤-10℃, flash point ≥110℃.

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