A molecular distillation separation method of a plant-derived bio-oil

Abstract

The present application relates to the technical field of high-value chemical separation in plant source biological oil, and discloses a molecular distillation separation method of plant source biological oil, wherein pine sawdust of plant source is used as a biomass raw material to prepare biological oil; a component rich in levoglucosan is separated from the biological oil through a molecular distillation method; a functional monomer is pre-assembled with a template molecule levoglucosan through hydrogen bond action, using an alkenyl type multiple hydrogen bond grafting monomer and methyl methacrylate modified on a PVDF microfiltration membrane as a composite functional monomer; under the action of a crosslinking agent and an initiator, the polymerization monomer is polymerized on the PVDF microfiltration membrane to form a polymer; after removing the template molecule, a levoglucosan molecularly imprinted PVDF microfiltration membrane is prepared; the levoglucosan monomer is separated from the component rich in levoglucosan through the levoglucosan molecularly imprinted PVDF microfiltration membrane, and the purity of the obtained levoglucosan monomer is greater than or equal to 99.5%.

Description

Technical Field

[0001] This invention relates to the field of high-value chemicals in plant-derived bio-oils, specifically a molecular distillation separation method for plant-derived bio-oils. Background Technology

[0002] Among numerous plant-based biomass raw materials, pine sawdust, with its natural characteristics of low ash content, low alkali metal content, and high cellulose, perfectly matches the core requirements of rapid pyrolysis technology for raw materials, and can directly produce bio-oil rich in L-glucan.

[0003] L-glucan has a lactone ring molecular structure, which provides a stable, chiral six-membered ring skeleton. It is an ideal precursor for the synthesis of chiral drugs, antibiotics, vitamins and vanillin. Furthermore, the one secondary hydroxyl group and two primary hydroxyl groups retained on the ring have different reactivity, allowing for selective functionalization without the need for protection-deprotection steps, thus simplifying the synthetic route and enabling the derivation of numerous compounds.

[0004] When processing pine sawdust bio-oil using molecular distillation, L-glucan is mainly concentrated in the distillate. Purifying L-glucan from the molecular distillation enrichment distillate to high purity is no longer a simple separation problem, but a high-precision purification problem for high-value-added fine chemicals. It usually requires a combination of multiple purification techniques such as solvent washing, recrystallization, and column chromatography. This will increase the production cost of high-purity L-glucan and limit its large-scale commercial application. Therefore, developing efficient, low-cost, and scalable purification processes has huge market potential. Summary of the Invention

[0005] This invention uses 1,3,5-tris(6-isocyanohexyl)-1,3,5-triazine-2,4,6-trione, a compound containing a 1,3,5-triazine heterocycle, as the molecular backbone. It introduces urea functional groups by sequentially reacting 2-amino-4-hydroxy-6-methylpyrimidine and 3-buten-1-amine, compounds containing pyrimidine heterocycles, with the urea group via isocyanate-amino addition reactions to obtain a heterocyclic compound containing multiple hydrogen bonds. This heterocyclic compound serves as a functional monomer for preparing L-glucan molecularly imprinted membranes.

[0006] Based on this, the present invention provides a molecular distillation separation method for plant-derived bio-oils. The method utilizes molecular distillation technology to separate components rich in L-glucan from plant-derived pine sawdust bio-oils, and uses a self-developed L-glucan molecularly imprinted membrane to specifically identify and extract high-purity L-glucan monomers from the L-glucan-rich components, thereby achieving the technical goal of converting inexpensive biomass raw materials into high-value chemicals.

[0007] A molecular distillation separation method for plant-derived bio-oils includes the following steps:

[0008] Step 1: Using plant-derived pine sawdust as biomass raw material, bio-oil is produced;

[0009] Step 2: Separate the component rich in L-glucan from the bio-oil obtained in Step 1 by molecular distillation.

[0010] Step 3: Using an alkenylated multi-hydrogen-bonded graft monomer and methacrylic acid as composite functional monomers, the functional monomers and the template molecule L-glucan are pre-assembled through hydrogen bonding to form polymeric monomers. Under the action of a crosslinking agent and an initiator, the polymeric monomers undergo a polymerization reaction on the PVDF microfiltration membrane to form a polymer. The template molecule is removed with an eluent to obtain a L-glucan molecularly imprinted PVDF microfiltration membrane.

[0011] Step four: Separate L-glucan monomers from L-glucan-rich components using a L-glucan molecularly imprinted PVDF microfiltration membrane.

[0012] Preferably, the preparation method of the alkenylated multiple hydrogen-bonded graft monomer is as follows:

[0013] Based on the addition reaction mechanism between isocyanate functional groups and amino functional groups, 1 molar equivalent of 1,3,5-tris(6-isocyanoylhexyl)-1,3,5-triazine-2,4,6-trione is first reacted with 0.91-0.95 molar equivalents of 2-amino-4-hydroxy-6-methylpyrimidine, and then reacted with 0.95-0.99 molar equivalents of 3-butene-1-amine to prepare an alkenylated multi-hydrogen-bonded graft monomer.

[0014] Preferably, in step three, the method of chemically grafting the alkenylated multiple hydrogen bond type grafted monomer onto the PVDF microfiltration membrane is as follows: the isocyanate group in the alkenylated multiple hydrogen bond type grafted monomer undergoes an addition reaction with the hydroxyl functional group on the surface of the hydrophilic PVDF microfiltration membrane, thereby completing the modification effect of the alkenylated multiple hydrogen bond type grafted monomer on the surface of the PVDF microfiltration membrane.

[0015] Preferably, the method for preparing the L-glucan molecularly imprinted PVDF microfiltration membrane is as follows:

[0016] A 50mm×50mm hydrophilic PVDF microfiltration membrane was added to anhydrous toluene solvent. Under nitrogen protection, an anhydrous toluene solution containing 3.5 parts by weight of alkenylated multiple hydrogen bond grafted monomers was added. The temperature was raised to 75-85℃ and the reaction was stirred for 10-14 hours. The membrane sample was taken out and washed with anhydrous toluene to obtain an alkenylated multiple hydrogen bond PVDF microfiltration membrane.

[0017] 0.8-2.4 parts by weight of L-glucan, 3.4 parts by weight of methacrylic acid and alkenylated multi-hydrogen bonded PVDF microfiltration membrane were added to a mixed solvent consisting of 1-2 parts by volume of chloroform and 1 part by volume of methanol. The mixture was stirred at room temperature for 1.5-3.5 h and allowed to stand for 20-30 h to obtain a pre-assembled polymer monomer loaded on the PVDF microfiltration membrane.

[0018] Add 25g of crosslinking agent and 1g of initiator to the pre-assembled polymer monomer loaded on the PVDF microfiltration membrane, degas with ultrasound, and stir the reaction at 55-65℃ for 20-25h under nitrogen protection. Take out the membrane sample, rinse it with deionized water, and then perform Soxhlet extraction with eluent until the L-glucan template molecules are completely removed to obtain the L-glucan molecularly imprinted PVDF microfiltration membrane.

[0019] Preferably, the pore size of the hydrophilic PVDF microfiltration membrane is one of 0.22μm, 0.45μm, and 0.65μm.

[0020] Preferably, the specific method for separating the L-glucan monomer is as follows:

[0021] A 50mm×50mm L-glucan molecularly imprinted PVDF microfiltration membrane is fixed in the cavity of an H-type permeation device, which divides the H-type permeation device into a raw material pool and a receiving pool.

[0022] The component rich in L-glucan was dissolved in a mixed solvent consisting of 1-2 parts by volume of chloroform and 1 part by volume of methanol to form a solution of the component rich in L-glucan;

[0023] The component solution rich in L-glucan is added to the raw material tank, and a mixed solvent consisting of 1-2 parts by volume of chloroform and 1 part by volume of methanol is simultaneously added to the receiving tank.

[0024] Under static conditions, a PVDF microfiltration membrane with a molecularly imprinted levoglucan adsorbs levoglucan. The membrane is then removed and desorbed using an eluent to obtain levoglucan monomers.

[0025] Preferably, the crosslinking agent is ethylene glycol dimethacrylate.

[0026] Preferably, the initiator is azobisisobutyronitrile or azobisisoheptanenitrile.

[0027] Preferably, the eluent is a mixed solvent composed of formic acid and methanol;

[0028] Preferably, the volume ratio of formic acid to methanol in the eluent is (1-2):(8-9).

[0029] Beneficial effects:

[0030] This invention applies molecular imprinting technology to the high-precision purification of L-glucan, a high-value-added fine chemical. Specifically, it provides a new purification scheme for the preparation of ultra-high purity L-glucan monomers using molecular imprinting technology, as detailed below:

[0031] Using 1,3,5-tris(6-isocyanohexyl)-1,3,5-triazine-2,4,6-trione, 2-amino-4-hydroxy-6-methylpyrimidine, and 3-buten-1-amine as raw materials, heterocyclic compounds containing multiple hydrogen bonds, namely alkenylated multi-hydrogen bond grafted monomers, were synthesized through isocyanate group-amino addition reaction.

[0032] Using a hydrophilic PVDF microfiltration membrane as the base membrane, an alkenylated multi-hydrogen-bonded graft monomer was modified onto the surface of the PVDF microfiltration membrane based on the isocyanate group-hydroxy addition reaction mechanism to obtain an alkenylated multi-hydrogen-bonded PVDF microfiltration membrane.

[0033] Using levoglucan as a template molecule, an alkenylated multi-hydrogen-bonded graft monomer modified on a PVDF microfiltration membrane, and methacrylic acid as a composite functional monomer, the levoglucan template molecule and the functional monomer are pre-assembled on the surface of the PVDF microfiltration membrane through hydrogen bonding to form a polymer monomer. Then, under the action of ethylene glycol dimethacrylate crosslinking agent and azobisisobutyronitrile initiator, a polymerization reaction occurs. Finally, the template molecule is removed to obtain a levoglucan molecularly imprinted PVDF microfiltration membrane.

[0034] The PVDF microfiltration membrane with L-glucan molecular imprinting was used to separate the L-glucan-rich component from pine sawdust bio-oil by molecular distillation and then purified it to obtain L-glucan monomers with a purity of ≥99.5%. Detailed Implementation

[0035] Example 1:

[0036] Preparation of pine sawdust bio-oil: Pine sawdust with a particle size of 3 mm was used as raw material and fly ash as heat carrier. The bio-oil was rapidly pyrolyzed in a downflow fluidized bed reactor at a pyrolysis temperature of 500℃ and a heating rate of 500℃ / min. The bio-oil was collected after water cooling.

[0037] The chemical composition of pine sawdust bio-oil was analyzed using a Trace DSQ II gas chromatography-mass spectrometry (GC-MS) system. The chromatographic column used was an Agilent DB-WAX polar capillary column (30m×0.25mm×0.25μm). The temperature program was as follows: the column temperature was first held at 40℃ for 1 min, and then heated to 240℃ at a rate of 8℃ / min and held for 10 min. The compositional analysis results of the pine sawdust bio-oil are shown in Table 1.

[0038] Table 1. Component analysis results of pine sawdust bio-oil

[0039] Compound Name Chemical structural formula relative content (%) Acetic acid 3.52 Succinaldehyde 2.87 5-Hydroxymethylfurfural 2.05 Vanillin 2.96 1-Hydroxy-2-acetone 3.43 3-Methylcyclopentane-1,2-dione 2.38 4-Methyl-3-penten-2-one 3.64 4-Hydroxy-4-methyl-2-pentanone 1.85 Isopropyl propionate 1.68 2,5-Dimethoxytetrahydrofuran 2.37 Guaiacol 4.15 phenol 6.82 2-Methylphenol 1.54 4-Methylphenol 2.03 2,3-Dimethylphenol 1.93 1,2-Ceramide 3.24 L-glucan (1,6-dehydro-β-D-glucopyranose) 18.65 D-Allose 3.34 D-mannose 1.28

[0040] Example 2:

[0041] The fraction rich in L-glucan was separated from pine sawdust bio-oil using molecular distillation techniques, including the following processes:

[0042] Process 1: The pine sawdust bio-oil prepared in Example 1 is pretreated by vacuum filtration through a PVDF microfiltration membrane with a pore size of 0.45 μm to remove solid particulate impurities from the bio-oil and prevent clogging of the instrument;

[0043] Process 2: The pretreated pine sawdust bio-oil was separated using a KDL-5 molecular distillation apparatus. First, 100g of the pretreated bio-oil was weighed and added to the feeder at a rate of 2mL / min. After preheating, it was fed to the evaporation device at 50℃. Under centrifugal force, the oil was evenly distributed on the heated evaporation surface, forming a 1mm thin liquid film under the action of a roller scraper. The evaporation temperature was 70℃, the evaporation pressure was 1000Pa, the scraper speed was 150rpm, the first-stage condensation temperature was 10℃, and the second-stage condensation temperature was -25℃. The distilled fraction from the bio-oil was collected by condensation and denoted as Component 1, with a yield of 61.25wt%. The undistilled fraction was collected directly as the residual fraction, denoted as Component 2, with a yield of 38.75wt%.

[0044] The chemical composition of component one and component two was analyzed by a Trace DSQ II gas chromatography-mass spectrometry system under the same detection conditions as in Example 1.

[0045] The test results show:

[0046] Component 1 contains acetic acid, succinaldehyde, 5-hydroxymethylfurfural, vanillin, 1-hydroxy-2-acetone, 3-methylcyclopentane-1,2-dione, 4-methyl-3-penten-2-one, 4-hydroxy-4-methyl-2-pentanone, 2,5-dimethoxytetrahydrofuran, guaiacol, phenol, 2-methylphenol, 4-methylphenol, and 2,3-dimethylphenol.

[0047] Component 2 contains guaiacol, phenol, 2-methylphenol, 4-methylphenol, 2,3-dimethylphenol, isopropyl propionate, L-glucan, D-alokose, and D-mannose components;

[0048] Therefore, component two is rich in L-glucan.

[0049] Molecularly imprinted membranes are a type of specific separation membrane that couples molecular imprinting technology with membrane separation technology. Molecularly imprinted sites are integrated into the membrane surface and the inner wall of the pores. The specific recognition of the sites is used to achieve specific adsorption of target molecules, thereby achieving selective separation of specific target substances in a mixed system. It is a highly efficient, low-cost, and scalable purification process.

[0050] Accordingly, this invention designs and synthesizes an alkenylated multi-hydrogen bond graft monomer capable of forming multiple hydrogen bond interactions with levoglucan molecules. This monomer is used to modify a PVDF-based membrane to obtain an alkenylated multi-hydrogen bond PVDF microfiltration membrane. Levoglucan is selected as a template molecule to prepare a levoglucan molecularly imprinted PVDF microfiltration membrane, which has high selectivity and excellent specific recognition ability. It can be used to extract pine sawdust bio-oil and separate levoglucan compounds from component two, which is rich in levoglucan, using molecular distillation technology.

[0051] Example 3:

[0052] Preparation of alkenylated multi-hydrogen-bonded graft monomers: Using 1,3,5-tris(6-isocyanohexyl)-1,3,5-triazine-2,4,6-trione as the base material, the isocyanate group of 1 molar equivalent of 1,3,5-tris(6-isocyanohexyl)-1,3,5-triazine-2,4,6-trione first undergoes an addition reaction with the amino functional group of 0.94 molar equivalent of 2-amino-4-hydroxy-6-methylpyrimidine, and then undergoes an addition reaction with the amino functional group of 0.97 molar equivalent of 3-buten-1-amine to generate an alkenylated multi-hydrogen-bonded graft monomer with the following chemical structure:

[0053] ;

[0054] The specific experimental steps for preparing the alkenylated multiple hydrogen-bonded graft monomer are as follows: Under nitrogen protection, 5.0 g of 2-amino-4-hydroxy-6-methylpyrimidine, 1.2 g of 2-amino-4-hydroxy-6-methylpyrimidine and 60 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask, stirred and dissolved at room temperature for 30 min, heated to 70 °C and stirred for 6 h, cooled to room temperature, and then 10 mL of anhydrous N,N-dimethylformamide solution containing 0.7 g of 3-buten-1-amine was added to the three-necked flask. The solution was stirred and dissolved at room temperature for 10 min, heated to 70 °C and stirred for 5 h, cooled to room temperature, evaporated under reduced pressure, and dried to obtain the alkenylated multiple hydrogen-bonded graft monomer.

[0055] The 1H NMR characterization of the alkenylated multi-hydrogen-bonded graft monomers is as follows: 1H NMR (DMSO-d6, 400MHz) δ: 1.31-1.53 ​​(m, 16H), 1.62-1.72 (m, 8H), 2.24-2.29 (m, 2H), 2.54 (s, 3H), 2.98-3.10 (m, 8H), 3.75-3.79 (t, 6H), 5.08-5.11 (d, 2H), 5.64-5.74 (m, 1H), 5.88 (s, 1H), 5.96-5.99 (t, 1H), 6.33 (s, 1H), 6.39-6.42 (t, 1H), 7.36-7.39 (t, 1H), 9.96 (s, 1H).

[0056] Example 4:

[0057] The preparation process of the L-glucan molecularly imprinted PVDF microfiltration membrane MIM-Ⅰ is as follows:

[0058] (1) Preparation of alkenylated multi-hydrogen bonded PVDF microfiltration membrane: Using PVDF microfiltration membrane as base membrane, the alkenylated multi-hydrogen bonded grafted monomer is modified on the surface of PVDF microfiltration membrane by the addition reaction between the isocyanate group in the alkenylated multi-hydrogen bonded grafted monomer and the hydroxyl functional group on the surface of the hydrophilic PVDF microfiltration membrane to obtain alkenylated multi-hydrogen bonded PVDF microfiltration membrane;

[0059] The specific experimental steps for preparing the alkenylated multiple hydrogen bond PVDF microfiltration membrane are as follows: A hydrophilic PVDF microfiltration membrane (also known as a polyvinylidene fluoride microfiltration membrane, with a pore size of 0.45 μm, a thickness of 100 μm, a size of 50 mm × 50 mm, and negligible mass) is added to 50 mL of anhydrous toluene. Under nitrogen protection, 20 mL of anhydrous toluene solution containing 3.5 g of alkenylated multiple hydrogen bond grafted monomer is added. The mixture is heated to 80 °C and stirred for 12 h. After cooling to room temperature, the membrane sample is removed, washed with anhydrous toluene, and dried to constant weight to obtain the alkenylated multiple hydrogen bond PVDF microfiltration membrane.

[0060] (2) Preparation of pre-assembled polymer monomer I loaded on PVDF microfiltration membrane: using dextran as template molecule, alkenylated multi-hydrogen bonded graft monomer grafted on PVDF microfiltration membrane and methacrylic acid as composite functional monomer, the dextran template molecule and the functional monomer are pre-assembled on the surface of PVDF membrane through hydrogen bonding to obtain pre-assembled polymer monomer I loaded on PVDF microfiltration membrane;

[0061] The specific experimental steps for preparing pre-assembled polymer monomer I loaded on PVDF microfiltration membrane are as follows: 1.6g of L-glucan, 3.4g of methacrylic acid and the alkenylated multi-hydrogen bonded PVDF microfiltration membrane prepared in process one are added to a mixed solvent consisting of 30mL of chloroform and 20mL of methanol. The mixture is stirred at room temperature for 2h and allowed to stand for 24h to obtain pre-assembled polymer monomer I loaded on PVDF microfiltration membrane.

[0062] (3) Preparation of L-dextran molecularly imprinted PVDF microfiltration membrane MIM-Ⅰ: Ethylene glycol dimethacrylate crosslinking agent and azobisisobutyronitrile initiator were added to the pre-assembled polymer monomer Ⅰ loaded on the PVDF microfiltration membrane to cause the polymer monomer to undergo a polymerization reaction on the surface of the PVDF membrane. Then, the template molecules were removed by using a formic acid-methanol mixed solution as the eluent to obtain L-dextran molecularly imprinted PVDF microfiltration membrane MIM-Ⅰ.

[0063] The specific experimental steps for preparing the L-glucan molecularly imprinted PVDF microfiltration membrane MIM-Ⅰ are as follows: 25g of ethylene glycol dimethacrylate and 1g of azobisisobutyronitrile were added to the pre-assembled polymer monomer Ⅰ prepared in step 2 and loaded on the PVDF microfiltration membrane. The mixture was ultrasonically degassed for 5 min, and then heated to 60℃ and stirred for 24 h under nitrogen protection. The membrane sample was then removed, rinsed with deionized water, and then subjected to Soxhlet extraction for 24 h using a formic acid-methanol mixed solution (the volume ratio of formic acid to methanol was 1:9). The L-glucan compounds in the Soxhlet extract were detected using a Trace DSQ II gas chromatography-mass spectrometry (GC-MS) instrument (the detection conditions were the same as in Example 1) until the L-glucan template molecules were completely removed. After drying, the L-glucan molecularly imprinted PVDF microfiltration membrane MIM-Ⅰ was obtained.

[0064] Example 5:

[0065] The L-glucan molecularly imprinted PVDF microfiltration membrane MIM-II was prepared. The only difference between it and the L-glucan molecularly imprinted PVDF microfiltration membrane MIM-I is that the amount of L-glucan used is 0.8g.

[0066] Example 6:

[0067] The L-glucan molecularly imprinted PVDF microfiltration membrane MIM-Ⅲ was prepared. The only difference between it and the L-glucan molecularly imprinted PVDF microfiltration membrane MIM-Ⅰ is that the amount of L-glucan used is 2.4g.

[0068] Example 7:

[0069] The adsorption capacity of the L-glucan molecularly imprinted PVDF microfiltration membrane was tested using the following method:

[0070] Prepare 100 mL of a 1 mg / mL L-glucan methanol solution, add 1 g of L-glucan molecularly imprinted PVDF microfiltration membrane, stir at room temperature for 12 h, separate the membrane sample, and take the supernatant to determine the final mass concentration of L-glucan in the solution using a Trace DSQ II gas chromatography-mass spectrometry (GC-MS) instrument (the detection conditions are the same as in Example 1). Calculate the adsorption capacity using the following method:

[0071] Adsorption capacity (mg / g) = [(ρ0-ρ e )×V]÷m

[0072] Wherein, ρ0 is the initial mass concentration of L-glucan, and its unit is mg / mL;

[0073] ρ e This represents the final mass concentration of L-glucan, expressed in mg / mL.

[0074] V is the volume of the L-glucan methanol solution, in mL;

[0075] m represents the mass of the L-glucan molecularly imprinted PVDF microfiltration membrane, and its unit is g;

[0076] The performance test results are shown in Table 2.

[0077] Table 2. Adsorption capacity test results of L-glucan molecularly imprinted PVDF microfiltration membrane

[0078] Types of magnetic adsorbents Adsorption capacity (mg / g) L-glucan molecularly imprinted PVDF microfiltration membrane MIM-Ⅰ 41.6 L-glucan molecularly imprinted PVDF microfiltration membrane MIM-II 19.1 L-glucan molecularly imprinted PVDF microfiltration membrane MIM-III 60.5

[0079] Example 8:

[0080] Component II, containing L-glucan, was purified from pine sawdust bio-oil using molecular distillation technology via a L-glucan-molecular-imprinted PVDF microfiltration membrane MIM-I. The specific process was as follows: The L-glucan-molecular-imprinted PVDF microfiltration membrane MIM-I was fixed in the center of an H-type permeation apparatus, dividing the apparatus into two identical pools (a feed pool and a receiving pool). A solution of component II dissolved in a mixed solvent of chloroform and methanol (3:2 volume ratio) was added to the feed pool. The receiving pool was then filled with... A mixed solvent of equal volumes of chloroform and methanol (volume ratio of chloroform to methanol 3:2) was used. After standing at room temperature for 24 hours, the membrane sample was removed to obtain a L-glucan molecularly imprinted PVDF microfiltration membrane MIM-I with adsorbed L-glucan molecules. The membrane was first washed with deionized water, and then Soxhlet extracted for 24 hours with a formic acid-methanol mixed solution (volume ratio of formic acid to methanol 1:9) to obtain an extract of L-glucan molecules. The solvent (formic acid and methanol) was removed by rotary evaporation, and the L-glucan monomer was obtained after drying. Its purity was quantitatively analyzed by Trace DSQ II gas chromatography-mass spectrometry (the detection conditions were the same as in Example 1). The results showed that the purity of L-glucan was 99.8%.

[0081] Example 9:

[0082] Component II containing L-glucan was separated from pine sawdust bio-oil using molecular distillation technology using a L-glucan molecularly imprinted PVDF microfiltration membrane MIM-II. The specific process was the same as that in Example 8, except that L-glucan molecularly imprinted PVDF microfiltration membrane MIM-II was used instead of L-glucan molecularly imprinted PVDF microfiltration membrane MIM-I. The purity was quantitatively analyzed using a Trace DSQ II gas chromatography-mass spectrometry (GC-MS) instrument (the detection conditions were the same as in Example 1). The results showed that the purity of L-glucan was 99.5%.

[0083] Example 10:

[0084] Component II containing L-glucan was purified from pine sawdust bio-oil by molecular distillation using a L-glucan molecularly imprinted PVDF microfiltration membrane MIM-III. The specific process is the same as that in Example 8, except that L-glucan molecularly imprinted PVDF microfiltration membrane MIM-III was used instead of L-glucan molecularly imprinted PVDF microfiltration membrane MIM-I. The purity was quantitatively analyzed using a Trace DSQ II gas chromatography-mass spectrometry (GC-MS) instrument (the detection conditions were the same as in Example 1). The results showed that the purity of L-glucan was 99.7%.

Claims

1. A method for molecular distillation separation of plant-derived bio-oils, characterized in that, Includes the following steps: Step 1: Using plant-derived pine sawdust as biomass raw material, bio-oil is produced; Step 2: Separate the component rich in L-glucan from the bio-oil obtained in Step 1 by molecular distillation. Step 3: Using an alkenylated multi-hydrogen-bonded graft monomer and methacrylic acid as composite functional monomers, the composite functional monomers and the template molecule L-glucan are pre-assembled through hydrogen bonding to form polymeric monomers. Under the action of a crosslinking agent and an initiator, the polymeric monomers undergo a polymerization reaction on the PVDF microfiltration membrane to form a polymer. The template molecule is removed with an eluent to obtain a L-glucan molecularly imprinted PVDF microfiltration membrane. The chemical structural formula of the alkenylated multiple hydrogen-bonded graft monomer is as follows: ； Step four: Separate L-glucan monomers from L-glucan-rich components using a L-glucan molecularly imprinted PVDF microfiltration membrane.

2. The molecular distillation separation method for plant-derived bio-oil according to claim 1, characterized in that, The preparation method of the alkenylated multiple hydrogen-bonded graft monomer is as follows: Based on the addition reaction mechanism between isocyanate functional groups and amino functional groups, 1 molar equivalent of 1,3,5-tris(6-isocyanoylhexyl)-1,3,5-triazine-2,4,6-trione is first reacted with 0.91-0.95 molar equivalents of 2-amino-4-hydroxy-6-methylpyrimidine, and then reacted with 0.95-0.99 molar equivalents of 3-butene-1-amine to prepare an alkenylated multi-hydrogen-bonded graft monomer.

3. The molecular distillation separation method for plant-derived bio-oil according to claim 1, characterized in that, Step three, the method of modifying the PVDF microfiltration membrane with the alkenylated multiple hydrogen bond type grafted monomer by chemical grafting, is as follows: the isocyanate group in the alkenylated multiple hydrogen bond type grafted monomer undergoes an addition reaction with the hydroxyl functional group on the surface of the hydrophilic PVDF microfiltration membrane, so that the alkenylated multiple hydrogen bond type grafted monomer completes the modification effect on the surface of the PVDF microfiltration membrane.

4. The molecular distillation separation method for plant-derived bio-oil according to claim 1, characterized in that, The preparation method of the L-glucan molecularly imprinted PVDF microfiltration membrane is as follows: A 50mm×50mm hydrophilic PVDF microfiltration membrane was added to anhydrous toluene solvent. Under nitrogen protection, an anhydrous toluene solution containing 3.5 parts by weight of alkenylated multiple hydrogen bond grafted monomers was added. The mixture was heated to 75-85℃ and stirred for 10-14 hours. The membrane sample was then removed and washed with anhydrous toluene to obtain an alkenylated multiple hydrogen bond PVDF microfiltration membrane. 0.8-2.4 parts by weight of L-glucan, 3.4 parts by weight of methacrylic acid and alkenylated multi-hydrogen bonded PVDF microfiltration membrane were added to a mixed solvent consisting of 1-2 parts by volume of chloroform and 1 part by volume of methanol. The mixture was stirred at room temperature for 1.5-3.5 h and allowed to stand for 20-30 h to obtain a pre-assembled polymer monomer loaded on the PVDF microfiltration membrane. Add 25g of crosslinking agent and 1g of initiator to the pre-assembled polymer monomer loaded on the PVDF microfiltration membrane, degas with ultrasound, and stir the reaction at 55-65℃ for 20-25h under nitrogen protection. Take out the membrane sample, rinse it with deionized water, and then perform Soxhlet extraction with eluent until the L-glucan template molecules are completely removed to obtain the L-glucan molecularly imprinted PVDF microfiltration membrane.

5. A molecular distillation separation method for plant-derived bio-oil according to claim 3 or 4, characterized in that, The hydrophilic PVDF microfiltration membrane has a pore size of 0.22 μm, 0.45 μm, or 0.65 μm.

6. The molecular distillation separation method for plant-derived bio-oil according to claim 5, characterized in that, The specific method for separating the L-glucan monomer is as follows: A 50mm×50mm L-glucan molecularly imprinted PVDF microfiltration membrane is fixed in the cavity of an H-type permeation device, which divides the H-type permeation device into a raw material pool and a receiving pool. The component rich in L-glucan was dissolved in a mixed solvent consisting of 1-2 parts by volume of chloroform and 1 part by volume of methanol to form a solution of the component rich in L-glucan; The component solution rich in L-glucan is added to the raw material tank, and a mixed solvent consisting of 1-2 parts by volume of chloroform and 1 part by volume of methanol is simultaneously added to the receiving tank. Under static conditions, a PVDF microfiltration membrane with a molecularly imprinted levoglucan adsorbs levoglucan. The membrane is then removed and desorbed using an eluent to obtain levoglucan monomers.

7. The molecular distillation separation method for plant-derived bio-oil according to claim 1, characterized in that, The crosslinking agent is ethylene glycol dimethacrylate.

8. The molecular distillation separation method for plant-derived bio-oil according to claim 1, characterized in that, The initiator is azobisisobutyronitrile or azobisisoheptanenitrile.

9. The molecular distillation separation method for plant-derived bio-oil according to claim 1, characterized in that, The eluent is a mixed solvent composed of formic acid and methanol.

10. The molecular distillation separation method for plant-derived bio-oil according to claim 9, characterized in that, The volume ratio of formic acid to methanol in the eluent is (1-2):(8-9).

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