Method for preparing aromatic aldehyde chemicals by catalyzing high-selectivity oxidative depolymerization of lignin through continuous high-pressure reaction system

Abstract

The invention discloses a method for preparing an aromatic aldehyde compound mainly containing vanillin by catalyzing high-selectivity oxidative depolymerization of lignin through a continuous high-pressure reaction system, which comprises the following steps: adopting a screw-type continuous reactor and one catalyst of copper chloride, ferric chloride, nickel chloride, manganese chloride and cobalt chloride, and controlling proper material retention time; the aldehyde product selectivity is excellent and is far superior to the aldehyde selectivity level of the traditional batch reaction, and the problems of uncontrollable product distribution and low target product proportion in the traditional technology are effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-value utilization of biomass resources, and particularly relates to a method for preparing aromatic aldehyde chemicals by high-selectivity oxidative depolymerization of lignin in a continuous high-pressure reaction system. BACKGROUND

[0002] Lignin, as the most abundant aromatic renewable resource in nature, its efficient conversion into high-value-added aromatic monomers is one of the core directions of biomass refining. Lignin is mainly composed of phenylpropane basic units connected by C-C and C-O bonds, and the connection mode (β-O-4, β-5, α-O-4, β-β, 5-5, etc.) is complex. Efficient catalytic cleavage of C-C / C-O bonds is the key to depolymerizing lignin. The catalytic oxidation method can selectively cleave C-C bonds, fully utilize the original oxygen-containing groups and aromatic structure of lignin, and obtain aromatic compounds containing oxygen-containing functional groups. In the prior art, batch reaction mode is often used for lignin oxidative depolymerization, which has two key problems: first, the reaction process is difficult to accurately control, which includes the cleavage of different linkages of lignin, the over-oxidation of target monomer products, and the condensation side reaction of active intermediates, resulting in low selectivity of aromatic monomers and unstable product distribution, making it difficult to direct preparation of target products; second, batch reaction includes non-reaction links such as heating, cooling, feeding and unloading, and the effective treatment capacity per unit time is limited, and the production efficiency is low. SUMMARY

[0003] The purpose of the present application is to provide a method for preparing aromatic aldehyde chemicals by high-selectivity oxidative depolymerization of lignin in a continuous high-pressure reaction system, which realizes efficient and directional conversion of lignin resources and solves the problems of low selectivity of aromatic aldehydes and low production efficiency in the prior art.

[0004] The present application is realized by the following technical solutions:

[0005] A method for preparing aromatic aldehyde chemicals by high-selectivity oxidative depolymerization of lignin in a continuous high-pressure reaction system, which is carried out in a high-temperature and high-pressure continuous cracking reaction device based on screw propulsion (patent publication number CN117339476A). The lignin raw material and the alkali solution are introduced into the mixing area respectively, and the mixed reaction is transmitted into the reaction area by the screw rod, and the continuous depolymerization reaction is carried out in the high-pressure oxygen-containing reaction gas atmosphere of 0.1-5 MPa. By fine control of the metal chloride catalyst and the reaction residence time, lignin is prepared into aromatic aldehyde chemicals mainly containing vanillin by high-selectivity oxidative depolymerization. The metal chloride catalyst is selected from one of copper chloride, ferrous chloride, nickel chloride, manganese chloride and cobalt chloride.

[0006] Specifically includes the following steps:

[0007] (1) Raw material preparation and material premixing: the lignin raw material is crushed and sieved and added to a high-pressure feed tank; the catalyst is premixed with the lye to configure a reaction solution; the raw material is added to the mixing area by regulating the speed of the vertical feeding screw, the reaction solution is quantitatively input by a plunger pump, and the system pressure is maintained by connecting an oxygen-containing reaction gas cylinder;

[0008] (2) Material conveying: the material is pushed by the rotation of the screw to move forward along the axial direction of the reactor in the screw-propelled high-temperature and high-pressure continuous cracking reaction device reaction cavity, and the baffles on the screw strengthen the mass transfer and mixing effect of the material;

[0009] (3) Oxidative depolymerization: the reaction area is heated to a preset temperature of 190℃ by the heating module, so that the lignin in the reaction raw material is broken under alkaline oxidation conditions to prepare aromatic aldehyde compounds mainly in the form of vanillin; the residence time of the material in the reaction area is controlled by adjusting the material conveying rate and the screw speed, and the residence time is 2-16 min, preferably 2-12 min;

[0010] (4) Product collection: the reaction products are collected in a product storage tank equipped with a back pressure valve, and after cooling by a cooling coil, the products are discharged by a ball valve, and the liquid phase of the aromatic aldehyde compounds mainly in the form of vanillin is obtained by solid-liquid separation.

[0011] Preferably, in step (1), the lye is a sodium hydroxide or potassium hydroxide aqueous solution with a concentration of 1-4 M, and the catalyst is added in an amount of 0.5%-10% of the mass of the raw material.

[0012] The oxygen-containing reaction gas is selected from oxygen, compressed air, and oxygen-nitrogen mixed gas, and the reaction gas pressure is 0.1-5 MPa.

[0013] Preferably, the lignin raw material is selected from pine, bamboo chips, and lignin sulfonate.

[0014] To ensure stable conveying and uniform reaction of the raw material in the continuous flow reaction system, the raw material is crushed and sieved to a particle powder of not less than 40 mesh to ensure stable conveying and uniform mixing of the raw material and the lye in the screw reactor.

[0015] In the present application, the screw speed of the screw-propelled high-temperature and high-pressure continuous cracking reaction device can be 5-200 rpm.

[0016] The beneficial effects of the present application are as follows:

[0017] 1) The present application adopts a screw propulsion type high temperature and high pressure continuous cracking reaction device and one of copper chloride, iron chloride, nickel chloride, manganese chloride and cobalt chloride as a catalyst, and controls the appropriate material residence time, so that the selectivity of aldehyde products is excellent, which is much better than the selectivity level of traditional batch reaction aldehydes, effectively solving the problems of uncontrollable product distribution and low target product proportion in traditional technology.

[0018] 2) The present application adopts a screw propulsion type high temperature and high pressure continuous cracking reaction device, which has simple structure and good mass transfer mixing effect; the raw material treatment and reaction parameters are easy to standardize control, without special equipment or expensive reagents, and the operation is convenient and stable, and has good feasibility from small test to pilot test to industrialization amplification, and the continuous reaction mode saves the heating, cooling, feeding and discharging and other non-reaction links of batch reaction, so that the effective treatment amount per unit time is greatly improved. Compared with the traditional batch reaction, the monomer production efficiency of the present application is obviously improved, the production cycle is effectively shortened, the energy consumption and time cost per unit product are reduced, and technical support is provided for large-scale production.

[0019] 3) The products of the present application include p-hydroxybenzoic acid, vanillic acid, syringic acid, vanillin and syringaldehyde, etc. a variety of high value-added aromatic monomers, mainly aromatic aldehydes, which can be widely used in medicine, spice, fine chemical industry and other fields, realizing the high value utilization of low value biomass resources, and meeting the green and low carbon development concept. DETAILED DESCRIPTION

[0020] The following is a further description of the present application, but not a limitation of the present application.

[0021] The following is an example of the liquid phase product obtained under different reaction conditions, and the reaction product is quantitatively analyzed by liquid chromatography, and the calculated product yield and selectivity data, wherein the acid selectivity = (vanillic acid + syringic acid + p-hydroxybenzoic acid) / (total amount of five target monomers) x 100%, the aldehyde selectivity = (vanillin + syringaldehyde) / (total amount of five target monomers) x 100%, and the default missing item is 0; the vanillin production efficiency is measured by the mass of vanillin generated per unit volume of lignin raw material reaction liquid per unit time (the batch reaction includes the heating time).

[0022] Example 1:

[0023] (1) Raw material preparation and material premixing: pine wood is crushed and sieved and added to a high-pressure feed tank; 5mM CuCl2 reaction solution is prepared by using 2M NaOH solution as mother liquor, the vertical feeding screw speed is controlled at 30g / min, the raw material is added to the mixing area, the reaction solution is pumped at a speed of 500ml / min through a plunger pump, and the system pressure is maintained at 2MPa through an external oxygen cylinder;

[0024] (2) Material conveying: The material is pushed forward in the reactor cavity of the screw propelling high-temperature and high-pressure continuous cracking reaction device along the axial direction of the reactor by the rotation of the screw, and the baffles on the screw strengthen the mass transfer and mixing effect of the material;

[0025] (3) Oxidative depolymerization: The reaction region is heated to a preset temperature of 190°C by the heating module, so that the lignin in the reaction raw material is broken under alkaline oxidation conditions to prepare aromatic aldehyde compounds mainly composed of vanillin; The residence time of the material in the reaction region is controlled by adjusting the material conveying rate and the screw rotation speed, and the residence time is 2 min;

[0026] (4) Product collection: The reaction products are collected in a product storage tank equipped with a back pressure valve, and after cooling by a cooling coil, they are discharged through a ball valve, and the liquid phase of the aromatic aldehyde compounds mainly composed of vanillin is obtained by solid-liquid separation. The results are shown in Table 1.

[0027] Example 2:

[0028] The reaction conditions are the same as in Example 1, except that the residence time is adjusted to 6 min, and the results are shown in Table 1.

[0029] Example 3:

[0030] The reaction conditions are the same as in Example 1, except that the residence time is adjusted to 12 min, and the results are shown in Table 1.

[0031] Example 4:

[0032] The reaction conditions are the same as in Example 1, except that the residence time is adjusted to 16 min, and the results are shown in Table 1.

[0033] Example 5:

[0034] The reaction conditions are the same as in Example 1, except that the catalyst is FeCl2, and the results are shown in Table 2.

[0035] Example 6:

[0036] The reaction conditions are the same as in Example 5, except that the residence time is adjusted to 6 min, and the results are shown in Table 2.

[0037] Example 7:

[0038] The reaction conditions are the same as in Example 5, except that the residence time is adjusted to 12 min, and the results are shown in Table 2.

[0039] Example 8:

[0040] The reaction conditions are the same as in Example 5, except that the residence time is adjusted to 16 min, and the results are shown in Table 2.

[0041] Example 9:

[0042] The reaction conditions were the same as in Example 1, except that the catalyst was CoCl2, and the results are shown in Table 3.

[0043] Example 10:

[0044] The reaction conditions were the same as in Example 9, except that the residence time was adjusted to 6 min, and the results are shown in Table 3.

[0045] Example 11:

[0046] The reaction conditions were the same as in Example 9, except that the residence time was adjusted to 12 min, and the results are shown in Table 3.

[0047] Example 12:

[0048] The reaction conditions were the same as in Example 9, except that the residence time was adjusted to 16 min, and the results are shown in Table 3.

[0049] Example 13:

[0050] The reaction conditions were the same as in Example 1, except that the raw material was adjusted to poplar, and the results are shown in Table 4.

[0051] Example 14:

[0052] The reaction conditions were the same as in Example 2, except that the raw material was adjusted to poplar, and the results are shown in Table 4.

[0053] Example 15:

[0054] The reaction conditions were the same as in Example 3, except that the raw material was adjusted to poplar, and the results are shown in Table 4.

[0055] Example 16:

[0056] The reaction conditions were the same as in Example 1, except that the raw material was adjusted to bagasse, and the results are shown in Table 4.

[0057] Example 17:

[0058] The reaction conditions were the same as in Example 2, except that the raw material was adjusted to bagasse, and the results are shown in Table 4.

[0059] Example 18:

[0060] The reaction conditions were the same as in Example 3, except that the raw material was adjusted to bagasse, and the results are shown in Table 4.

[0061] Example 19:

[0062] The reaction conditions were the same as in Example 1, except that the raw material was adjusted to bamboo chips, and the results are shown in Table 4.

[0063] Example 20:

[0064] The reaction conditions were the same as in Example 2, except that the raw material was adjusted to be bamboo chips, and the results are shown in Table 4.

[0065] Example 21:

[0066] The reaction conditions were the same as in Example 3, except that the raw material was adjusted to be bamboo chips, and the results are shown in Table 4.

[0067] Example 22:

[0068] The reaction conditions were the same as in Example 1, except that the raw material was adjusted to be sodium lignosulfonate, and the results are shown in Table 4.

[0069] Example 23:

[0070] The reaction conditions were the same as in Example 2, except that the raw material was adjusted to be sodium lignosulfonate, and the results are shown in Table 4.

[0071] Example 24:

[0072] The reaction conditions were the same as in Example 3, except that the raw material was adjusted to be sodium lignosulfonate, and the results are shown in Table 4.

[0073] Comparative Example 1:

[0074] Reference Example 1, except that the reaction was carried out using a stainless steel autoclave with an alkali-resistant liner, and the sample was taken after 2 minutes of heat preservation reaction. The results are shown in Table 5.

[0075] Comparative Example 2:

[0076] Reference Comparative Example 1, except that the sample was taken after 6 minutes of heat preservation reaction. The results are shown in Table 5.

[0077] Comparative Example 3:

[0078] Reference Comparative Example 1, except that the sample was taken after 12 minutes of heat preservation reaction. The results are shown in Table 5.

[0079] Comparative Example 4:

[0080] Reference Comparative Example 1, except that the sample was taken after 16 minutes of heat preservation reaction. The results are shown in Table 5.

[0081] Table 1 Monomer yield of pine in continuous high-pressure screw reactor by CuCl2 alkaline oxidation

[0082] Table 2 Monomer yield of pine in continuous high-pressure screw reactor by FeCl2 alkaline oxidation

[0083] Table 3 CoCl2 basic oxidation monomer yield of pine in continuous high-pressure screw reactor

[0084] Table 4 Monomer yield of different substrates in continuous high-pressure screw reactor

[0085] Table 5 Basic oxidation product yield and selectivity in batch reactor under different conditions

[0086] Examples 1-12 show that in the continuous high-pressure screw reaction system, the catalyst component of metal chloride (CuCl2 / FeCl2 / CoCl2) and the residence time jointly determine the generation and selectivity of aromatic monomers. The general rule is that a shorter residence time is more conducive to the enrichment of aromatic aldehydes and higher aldehyde selectivity. When the residence time is prolonged, aldehydes are more easily further oxidized to acids, resulting in a decrease in aldehyde selectivity and an increase in acid selectivity, indicating that the degradation of target aldehyde products can be inhibited and the selectivity can be regulated by "metal chloride + residence time".

[0087] Examples 13-24 show that the method has good universality: the substrate is expanded from pine to poplar, sugarcane residue, bamboo chips, and sodium lignosulfonate, etc., which can all be used to prepare aromatic monomers in a continuous system and maintain high aldehyde selectivity. The monomer yield of different substrates is different, but overall, aromatic aldehydes represented by vanillin and eugenol can be obtained, indicating that the continuous oxidative depolymerization process is suitable for various biomass and lignin-derived substrates. When the lignin raw material is selected from pine, bamboo chips and lignosulfonate, the aldehyde product selectivity performs well.

[0088] Comparative Examples 1-4 were carried out in a batch high-pressure kettle. The production efficiency of vanillin per unit time (3.56-4.67 g / L / h, see Table 5) and the production efficiency of vanillin in the continuous reaction system of Examples 1-4 (5.57-48.12 g / L / h, see Table 1) were compared at the same reaction time scale. It can be found that the preparation efficiency of aromatic monomers in the continuous conversion process is 13.5, 9.0 and 3.4 times that of the preparation efficiency in the batch process at the corresponding time, which fully embodies the advantages of the method described in the present application.

Claims

1. A method for preparing aromatic aldehydes by highly selective oxidative depolymerization of lignin using a continuous high-pressure reaction system, characterized in that, The reaction is carried out in a high-temperature and high-pressure continuous pyrolysis reactor based on a screw propulsion system, as disclosed in CN117339476A. Lignin raw material and alkaline solution are introduced into a mixing zone, and the mixed reactants are conveyed into the reaction zone via a screw. A continuous depolymerization reaction is carried out in a high-pressure oxygen-containing reaction gas atmosphere of 0.1–5 MPa. Highly selective oxidative depolymerization of lignin is achieved through precise control of the metal chloride catalyst and the reaction residence time to prepare aromatic aldehyde chemicals, primarily vanillin. The metal chloride catalyst is selected from one of copper chloride, ferrous chloride, nickel chloride, manganese chloride, and cobalt chloride.

2. The method according to claim 1, characterized in that, Specifically, the following steps are included: (1) Raw material preparation and material premixing: The lignin raw material is crushed and sieved and added to the high-pressure feed tank; the catalyst and alkali solution are premixed to prepare the reaction solution; the speed of the vertical feed screw is adjusted to add the raw material to the mixing area, and the reaction solution is quantitatively input through the plunger pump. At the same time, the system pressure is maintained by the external oxygen-containing reaction gas cylinder. (2) Material conveying: The material is pushed forward along the reactor axis in the reaction chamber of the screw-driven high temperature and high pressure continuous pyrolysis reactor by the rotation of the screw. The baffle on the screw enhances the mass transfer and mixing effect of the material. (3) Oxidative depolymerization: The reaction zone is heated to a preset temperature of 190°C by the heating module, so that the lignin in the reaction raw material can be efficiently debonded under alkaline oxidation conditions to prepare aromatic aldehyde compounds with vanillin as the main component; the residence time of the material in the reaction zone is controlled by adjusting the material conveying rate and the screw speed, and the residence time is 2-16 min. (4) Product collection: The reaction products are collected into a product storage tank equipped with a back pressure valve, and after being cooled by a cooling coil, they are discharged through a ball valve. Aromatic aldehyde compounds, mainly vanillin, are obtained in the liquid phase through solid-liquid separation.

3. The method according to claim 1 or 2, characterized in that, The alkaline solution is an aqueous solution of sodium hydroxide or potassium hydroxide with a concentration of 1-4 M, and the amount of catalyst added is 0.5%-10% of the raw material mass.

4. The method according to claim 1 or 2, characterized in that, The oxygen-containing reaction gas is selected from oxygen, compressed air, or an oxygen-nitrogen mixture, and the reaction gas pressure is 0.1–5 MPa.

5. The method according to claim 1 or 2, characterized in that, The lignin raw materials are selected from pine wood, bamboo shavings, and lignin sulfonates.

6. The method according to claim 1 or 2, characterized in that, The raw materials are crushed and sieved to a particle size of not less than 40 mesh.

7. The method according to claim 1 or 2, characterized in that, The screw speed of the screw-driven high-temperature and high-pressure continuous pyrolysis reactor is 5 to 200 rpm.

8. The method according to claim 3, characterized in that, Step (3) requires a stay time of 2-12 minutes.

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