CN102115432A - Method for preparing and separating p-hydroxybenzaldehyde, vanillin and syringaldehyde from lignin - Google Patents

Abstract

The invention relates to a method for preparing and separating p-hydroxybenzaldehyde, vanillin and syringaldehyde by using lignin, comprising the following process steps: (1) preparing a LaB _1-x Cux _{O 3} perovskite-type composite oxide catalyst; (2) The crude product of aromatic aldehyde is centrifuged, acidified, and vacuum-dried to obtain a mixture of p-hydroxybenzaldehyde, vanillin, and syringaldehyde after being extracted with chloroform; The mixture was dissolved in absolute ethanol, ammonia water was added to form a precipitate, filtered, the ethanol solution obtained by filtration was adjusted to pH with sulfuric acid solution, and the crude product of syringaldehyde was obtained; the liquid obtained by filtration was concentrated under reduced pressure to obtain a solid, which was Carry out rectification under protection, collect fractions at different temperatures respectively, and obtain vanillin and p-hydroxybenzaldehyde. The invention improves the comprehensive utilization rate of wood fiber, reduces the cost of wood fiber fuel ethanol, and has great economic and social significance.

Description

Method for preparing and separating p-hydroxybenzaldehyde, vanillin and syringaldehyde by using lignin

technical field

The invention relates to a method for preparing and separating p-hydroxybenzaldehyde, vanillin and syringaldehyde by utilizing lignin, and belongs to the technical field of biomass chemical industry.

Background technique

In order to alleviate the dual pressure of energy and environment in the future, countries all over the world attach great importance to the development and utilization of renewable resources, especially biomass resources. Biomass resources, as an ideal substitute for fossil resources such as petroleum and coal, have attracted widespread attention around the world. Biomass resources can be used as energy and processed into chemicals. Therefore, how to effectively convert biomass resources into energy and chemicals is one of the current research hotspots. Plant biomass is an important component of biomass resources, and its main components are cellulose, hemicellulose and lignin. Among them, cellulose and hemicellulose are the raw materials for manufacturing fuel alcohol and other fermentation products and papermaking, while lignin, as a non-fibrous compound, is mostly regarded as industrial waste except for a few industrial applications and has not been efficiently utilized. Biomass The transformation of waste lignin into high value-added chemical products is an economical and environmentally friendly way to improve the efficiency of biomass utilization.

Lignin can be degraded into small aromatic or aliphatic organic molecules under appropriate conditions. The chemical methods for degrading lignin mainly include: acid hydrolysis, alcoholysis, hydrogenolysis, pyrolysis, oxidative degradation, enzymatic hydrolysis, etc. The most studied are the pyrolysis, hydrogenolysis and oxidative degradation of lignin. Under alkaline conditions, p-hydroxybenzaldehyde, vanillin, and syringaldehyde can be obtained in relatively high yields through weak oxidation of lignin. Vanillin obtained from coniferous wood lignosulfonate began to be used in industry in 1936, and was later replaced by eugenol oxidation. However, in some countries, especially some European countries, lignin is used as raw material to prepare vanillin. Lansu's craftsmanship is still used. With the emphasis on the utilization of renewable resources, the oxidative degradation of lignin to produce high value-added chemicals still has important industrial application prospects.

The oxidation reaction of lignin under alkaline conditions may also be referred to as wet oxidation reaction (WAO) of lignin. WAO (Wet aerobic oxidation) technology was proposed by FJ Zimmermann, also known as the Zimmermann method. It uses oxygen in the air as the oxidant under the conditions of high temperature (120-320°C) and high pressure (0.5-10MPa). A method of oxidizing organic substances into inorganic substances or small molecular organic substances such as CO ₂ and H ₂ O in the liquid phase. For the wet oxidation of lignin under alkaline conditions, the use of oxidation catalysts can significantly increase the yield of aromatic aldehydes. At present, the catalysts used for the catalytic oxidation of lignin mainly include noble metal catalysts and transition metal-based catalysts. The former is limited in practical application due to its high cost, and the latter mainly includes copper sulfate and some salts of transition metal ions. Among them Copper sulfate has attracted much attention due to its high activity, but it is difficult to recycle and easily produce secondary pollution, so it has not been used in industry so far. Therefore, finding an efficient and recyclable heterogeneous catalyst is of great significance for the development and utilization of lignin-based biomass waste.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing and separating p-hydroxybenzaldehyde, vanillin and syringaldehyde by using lignin, which has low cost and can improve the comprehensive utilization rate of wood fiber.

According to the technical scheme provided by the present invention, the method for utilizing lignin to prepare and separate p-hydroxybenzaldehyde, vanillin, and syringaldehyde is characterized in that it comprises the following processing steps:

(1), preparation of LaB _1-x Cux _{O 3} catalyst, wherein B is Fe, Co or Mn, 0<x<1:

a, by molar ratio lanthanum nitrate: ferric nitrate, cobalt nitrate or manganese nitrate: copper nitrate=1: 1-x: x takes by weighing nitrate, wherein 0＜x＜1;

B, dissolving nitrate in water makes nitrate solution, the mass concentration of nitrate total amount in aqueous solution is 20%～30%;

C, in nitrate solution, add citric acid and make complexing agent solution, the mol ratio of metal ion total amount in citric acid and nitrate solution is 1: 1～2;

d. Add dropwise ammonia water with a concentration of 10-30% in the complexing agent solution to adjust the pH value of the complexing agent solution to 5-6, and stir and heat the complexing agent solution after adding ammonia water to obtain a wet gel; heat The temperature is 80-100°C, the stirring speed is 200-500 rpm, and the stirring time is 8-10 hours;

e. Drying the wet gel in an oven at 100-220°C for 2-4 hours to obtain a dry gel;

f. keeping the xerogel in a high-temperature sintering furnace at 450-800°C for 4-10 hours to obtain a LaB _1-x Cux _{O 3} catalyst;

(2), the preparation of aromatic aldehyde crude product:

a. Add lignin, catalyst and NaOH into the reaction kettle, the NaOH is 0.1-2.0mol/L, the lignin is 10-200g/L, the catalyst is 1-10g/L, and the rest is water;

b. Introduce 0.1-0.2MPa nitrogen into the reactor for protection, heat the reactor to 120-180°C; continue feeding nitrogen to make the total pressure of the reactor 1.5-2.0MPa, then switch nitrogen to oxygen, Adjust the pressure of oxygen to 2.0-4.0 MPa, and start stirring at the same time, the stirring speed is 600-1200 rpm, and after stirring for 10-120 minutes, the salt solution of p-hydroxybenzaldehyde, vanillin and syringaldehyde, that is, aromatic aldehyde crude product;

(3), separation of p-hydroxybenzaldehyde, vanillin and syringaldehyde:

a. Centrifuge the aromatic aldehyde crude product obtained in step (2), the centrifugation speed is 1000-4000 rpm, and the centrifugation time is 1-10min; add a concentration of 20-30% to the liquid A obtained by centrifugation The sulfuric acid solution acidifies the liquid A to a pH value of 2 to 3 to obtain a suspension liquid B; the suspension liquid B is precipitated overnight, and after filtration, a solid C is obtained, and the solid C is a mixture of unreacted lignin and aromatic aldehyde; the obtained Solid C was vacuum-dried at 50-60°C for 12-24 hours to obtain yellow solid D; the yellow solid D was extracted with chloroform for 6-8 times, the extracted extracts were combined, and the extracts were heated at a temperature of 40 Concentrate under reduced pressure at ~50°C and a pressure of 500-1000Pa to obtain solid E, which is a mixture of p-hydroxybenzaldehyde, vanillin, and syringaldehyde;

b, the solid E obtained in the above step a is dissolved in absolute ethanol to form an ethanol solution of solid E, and the mass ratio of solid E to absolute ethanol is 10% to 40%; 30% ammonia forms a light yellow precipitate, and ammonia accounts for 1 to 10% of the volume of absolute ethanol; the ethanol solution of solid E is filtered to obtain solid F and liquid G, and liquid G is a mixed solution of p-hydroxybenzaldehyde and vanillin; The solid F is put into the ethanol solution with a concentration of 30-50%, and the pH value of the alcohol solution of the solid F is adjusted to 3-4 with a sulfuric acid solution with a concentration of 20-30%, so as to obtain the crude product of syringaldehyde; the crude product of syringaldehyde Using ethanol to recrystallize at 60-80°C to obtain syringaldehyde crystals;

c. The liquid G obtained in the above step b is concentrated under reduced pressure at a temperature of 50-60°C and a pressure of 500-1000Pa to obtain solid H, which is refined under the protection of nitrogen at a pressure of 0.01-0.1MPa. Distillation, collect the first fraction at 150-170°C, and collect the second fraction at 180-190°C; recrystallize the first fraction with ethanol at 60-80°C to obtain vanillin crystals; the second fraction at 60 Recrystallized with ethanol at ~80°C to obtain crystals of p-hydroxybenzaldehyde.

The present invention uses lignin as a raw material and adopts a perovskite type composite oxide that has high catalytic activity and can be reused LaB _1-x Cux _{O 3} (B is Fe, Co or Mn, 0<x<1) The synthesis of p-hydroxybenzaldehyde, vanillin, and syringaldehyde as a catalyst and the development of product separation technology have improved the comprehensive utilization rate of lignocellulosic fibers and reduced the cost of lignocellulosic fuel ethanol, which has great economic and social significance.

Detailed ways

The present invention will be further described below in conjunction with specific examples.

The lignin used in the present invention is a variety of industrial lignins, including alkali lignin and sulfonated lignin in the paper industry; and lignocellulose enzymatic residues in the cellulose alcohol industry.

The catalyst used in the present invention is LaB _1-x Cux _{O 3} perovskite composite oxide, wherein B is Fe, Co or Mn, 0<x<1.

Embodiment one: a kind of method utilizing lignin to prepare and separate p-hydroxybenzaldehyde, vanillin, syringaldehyde comprises the following process steps:

(1), preparation of LaFe _0.9 Cu _0.1 O ₃ catalyst:

a, lanthanum nitrate in molar ratio: ferric nitrate: copper nitrate=1: 0.9: 0.1 takes by weighing nitrate;

B, dissolving nitrate in water makes nitrate solution, the mass concentration of nitrate total amount in aqueous solution is 20%;

C, in nitrate solution, add citric acid and make complexing agent solution, the mol ratio of metal ion total amount in citric acid and nitrate solution is 1: 1.5;

d. Add dropwise ammonia water with a concentration of 10% to the complexing agent solution to adjust the pH value of the complexing agent solution to 5, and stir and heat the complexing agent solution after adding ammonia water to obtain a wet gel; the heating temperature is 80°C , the stirring speed is 200 rpm, and the stirring time is 8 hours;

e. Drying the wet gel in an oven at 100°C for 4 hours to obtain a dry gel;

f. Keep the xerogel in a high-temperature sintering furnace at 450°C for 10 hours to obtain a LaFe _0.9 Cu _0.1 O ₃ catalyst;

(2), the preparation of aromatic aldehyde crude product:

a. Add lignin, catalyst and NaOH into the stainless steel reaction kettle, NaOH is 0.1mol/L, lignocellulose enzymolysis residue is 16.67g/L, and the content of Klassen lignin in the lignocellulose enzymolysis residue is 60 %, which is 10g/L, the catalyst is 1g/L, and the rest is water;

b. Introduce 0.1MPa nitrogen into the reactor for protection, heat the reactor to 120°C; continue to feed nitrogen to make the total pressure of the reactor 1.5MPa, switch nitrogen to oxygen, and adjust the pressure of oxygen to 2.0 MPa, start stirring at the same time, the stirring speed is 600 revs/min, after stirring and reacting for 120min, obtain the salt solution of p-hydroxybenzaldehyde, vanillin and syringaldehyde, that is, the crude product of aromatic aldehyde; wherein the productive rate of vanillin is 10.5 %(p-classen lignin), the productive rate of syringaldehyde is 15.2% (p-classen lignin), and p-hydroxybenzaldehyde yield is 5.5% (p-classen lignin);

(3), separation of p-hydroxybenzaldehyde, vanillin and syringaldehyde:

a, the aromatic aldehyde crude product that step (2) is obtained is centrifuged, and the rotating speed of centrifugal separation is 1000 rpm, and centrifugation time is 10min; In the liquid A that centrifugation obtains, add the sulfuric acid solution that concentration is 20% to make liquid A Acidify to pH 2 to obtain suspension liquid B; precipitate suspension liquid B overnight, obtain solid C after filtration, solid C is a mixture of unreacted lignin and aromatic aldehyde; obtain solid C at 50°C Dry in vacuum for 24 hours to obtain a yellow solid D; extract the yellow solid D with chloroform for 6 times, combine the extracted extracts, and concentrate the extracts under reduced pressure at a temperature of 40 °C and a pressure of 500 Pa to obtain a solid E, the mixture of p-hydroxybenzaldehyde, vanillin and syringaldehyde;

b. Dissolving the solid E obtained in the above step a in absolute ethanol to form an ethanol solution of solid E, the mass ratio of solid E to absolute ethanol is 10%; adding a concentration of 10% ammonia to the ethanol solution of solid E Form pale yellow precipitate, ammoniacal liquor accounts for 1% of dehydrated alcohol volume; The ethanol solution of solid E is filtered to obtain solid F and liquid G, and liquid G is the mixed solution of p-hydroxybenzaldehyde and vanillin; Solid F is put into concentration In a 30% ethanol solution, use a sulfuric acid solution with a concentration of 20% to adjust the pH value of the alcohol solution of solid F to 3 to obtain a crude syringaldehyde product; recrystallize the crude syringaldehyde product using ethanol at 60°C to obtain cloves Aldehyde crystals, the content of syringaldehyde is 99%, and the yield is 12.5% (to Klassen lignin);

c. The liquid G obtained in the above step b is concentrated under reduced pressure at a temperature of 50°C and a pressure of 500Pa to obtain solid H, and the solid H is rectified under the protection of nitrogen with a pressure of 0.01MPa. The first fraction was collected at 170°C, and the second fraction was collected at 180-190°C; the first fraction was recrystallized with ethanol at 60°C to obtain vanillin crystals; the second fraction was recrystallized with ethanol at 60°C to obtain the Hydroxybenzaldehyde crystals; the productive rate of vanillin is 7.5% (p-classen lignin), and p-hydroxybenzaldehyde yield is 3.6% (p-classen lignin), and the content of vanillin and p-hydroxybenzaldehyde are both Above 99%.

Embodiment two: a kind of method utilizing lignin to prepare and separate p-hydroxybenzaldehyde, vanillin, and syringaldehyde comprises the following process steps:

(1), preparation of LaCo _0.1 Cu _0.9 O ₃ catalyst:

a, lanthanum nitrate by molar ratio: cobalt nitrate: copper nitrate=1: 0.1: 0.9 takes by weighing nitrate;

B, dissolving nitrate in water makes nitrate solution, the mass concentration of nitrate total amount in aqueous solution is 30%;

C, in nitrate solution, add citric acid and make complexing agent solution, the mol ratio of metal ion total amount in citric acid and nitrate solution is 1: 2;

d. Add dropwise ammonia water with a concentration of 30% in the complexing agent solution to adjust the pH value of the complexing agent solution to 6, and stir and heat the complexing agent solution after adding ammonia water to obtain a wet gel; the heating temperature is 100°C , the stirring speed is 500 rpm, and the stirring time is 10 hours;

e. Drying the wet gel in an oven at 220°C for 2 hours to obtain a dry gel;

f. Keep the xerogel in a high-temperature sintering furnace at 800°C for 4 hours to obtain a LaCo _0.1 Cu _0.9 O ₃ catalyst;

(2), the preparation of aromatic aldehyde crude product:

a. Add lignin, catalyst and NaOH into the stainless steel reaction kettle, NaOH is 2.0mol/L, alkali lignin is 222.22g/L, and the content of Klasen lignin in alkali lignin is 90%, which is 200g/L , the catalyst is 10g/L, and the rest is water;

b. Introduce 0.2MPa nitrogen into the reactor for protection, heat the reactor to 180°C; continue to feed nitrogen to make the total pressure of the reactor 2.0MPa, switch nitrogen to oxygen, and adjust the pressure of oxygen to 4.0 MPa, start stirring at the same time, the stirring speed is 1200 rev/min, after stirring and reacting for 10min, obtain the salt solution of p-hydroxybenzaldehyde, vanillin and syringaldehyde, that is, the crude product of aromatic aldehyde; wherein the productive rate of vanillin is 12.5 %(p-classen lignin), the productive rate of syringaldehyde is 11.2% (p-classen lignin), and p-hydroxybenzaldehyde yield is 7.5% (p-classen lignin);

(3), separation of p-hydroxybenzaldehyde, vanillin and syringaldehyde:

a, the aromatic aldehyde crude product that step (2) is obtained is centrifuged, and the rotating speed of centrifugation is 4000 rpm, and centrifugation time is 1min; In the liquid A that centrifugation obtains, add the sulfuric acid solution that concentration is 30% to make liquid A Acidify to a pH value of 3 to obtain a suspension liquid B; precipitate the suspension liquid B overnight, and obtain a solid C after filtration; vacuum-dry the obtained solid C at 60° C. for 12 hours to obtain a yellow solid D; Methane chloride was extracted 8 times, and the extract obtained by the extraction was combined, and the extract was concentrated under reduced pressure at a temperature of 50 ° C and a pressure of 1000 Pa to obtain solid E, which is the product of p-hydroxybenzaldehyde, vanillin, and syringaldehyde. mixture;

b. Dissolving the solid E obtained in the above step a in absolute ethanol to form an ethanol solution of solid E, the mass ratio of solid D to absolute ethanol is 40%; adding a concentration of 30% ammonia to the ethanol solution of solid E A light yellow precipitate is formed, and ammonia water accounts for 10% of the volume of absolute ethanol; the ethanol solution of solid E is filtered to obtain solid F and liquid G, and solid F is put into a 50% ethanol solution, and the concentration is 30% sulfuric acid The solution adjusts the pH value of the alcohol solution of solid F to 4 to obtain the crude product of syringaldehyde; the crude product of syringaldehyde is recrystallized with ethanol at 80°C to obtain crystals of syringaldehyde, the content of syringaldehyde is 99%, and the yield is 8.5% % (to Klassen lignin);

c. The liquid G obtained in the above step b is concentrated under reduced pressure at a temperature of 60 ° C and a pressure of 1000 Pa to obtain solid H, which is rectified under the protection of nitrogen with a pressure of 0.1 MPa, respectively The first fraction was collected at 170°C, and the second fraction was collected at 180-190°C; the first fraction was recrystallized with ethanol at 80°C to obtain vanillin crystals; the second fraction was recrystallized with ethanol at 80°C to obtain the Hydroxybenzaldehyde crystal;, the productive rate of vanillin is 9.3% (p-Klasen lignin), p-Hydroxybenzaldehyde yield is 5.6% (p-Hydroxybenzaldehyde), the content of vanillin and p-Hydroxybenzaldehyde All above 99%.

Embodiment three: a kind of method utilizing lignin to prepare and separate p-hydroxybenzaldehyde, vanillin, and syringaldehyde comprises the following process steps:

(1), preparation of LaMn _0.5 Cu _0.5 O ₃ catalyst:

a, lanthanum nitrate by molar ratio: ferric nitrate: copper nitrate=1: 0.5: 0.5 takes by weighing nitrate;

B, dissolving nitrate in water makes nitrate solution, the mass concentration of nitrate total amount in aqueous solution is 25%;

C, in nitrate solution, add citric acid and make complexing agent solution, the mol ratio of metal ion total amount in citric acid and nitrate solution is 1: 1.8;

d. Add dropwise ammonia water with a concentration of 20% to the complexing agent solution to adjust the pH value of the complexing agent solution to 5, and stir and heat the complexing agent solution after adding ammonia water to obtain a wet gel; the heating temperature is 90°C , the stirring speed is 300 rpm, and the stirring time is 9 hours;

e. Drying the wet gel in an oven at 150°C for 3 hours to obtain a dry gel;

f. Keep the xerogel in a high-temperature sintering furnace at 600°C for 6 hours to obtain a LaMn _0.5 Cu _0.5 O ₃ catalyst;

(2), the preparation of aromatic aldehyde crude product:

a. Add lignin, catalyst and NaOH to the stainless steel reaction kettle, NaOH is 1mol/L, sulfonated lignin is 108.70g/L, and the content of Klassen lignin in the sulfonated lignin is 92%, which is 100g/L L, the catalyst is 5g/L, and the rest is water;

b. Introduce 0.15MPa nitrogen into the reactor for protection, heat the reactor to 150°C; continue feeding nitrogen to make the total pressure of the reactor 1.8MPa, then switch nitrogen to oxygen, and adjust the pressure of oxygen to 3.0 MPa, start stirring at the same time, the stirring speed is 1000 revs/min, after stirring and reacting for 60min, obtain the salt solution of p-hydroxybenzaldehyde, vanillin and syringaldehyde, that is, the crude product of aromatic aldehyde; wherein the productive rate of vanillin is 4.9 % (p-classen lignin), the yield of syringaldehyde is 30.6% (p-classen lignin), and the yield of p-hydroxybenzaldehyde is 3.2% (p-classen lignin). ;

(3), separation of p-hydroxybenzaldehyde, vanillin and syringaldehyde:

a, the aromatic aldehyde crude product that step (2) is obtained is centrifuged, and the rotating speed of centrifugation is 3000 rpm, and centrifugation time is 5min; In the liquid A that centrifugation obtains, add the sulfuric acid solution that concentration is 25% to make liquid A Acidify to a pH value of 2 to obtain a suspension liquid B; precipitate the suspension liquid B overnight, and obtain a solid C after filtration; vacuum-dry the obtained solid C at 55° C. for 18 hours to obtain a yellow solid D; Methyl chloride was extracted 7 times, and the extracts obtained by the extraction were combined, and the extracts were concentrated under reduced pressure at a temperature of 45 ° C and a pressure of 800 Pa to obtain solid E, which is the product of p-hydroxybenzaldehyde, vanillin, and syringaldehyde. mixture;

b, the solid E obtained in the above step a is dissolved in absolute ethanol to form an ethanol solution of solid E, and the mass ratio of solid E to absolute ethanol is 30%; adding a concentration of 20% ammonia to the ethanol solution of solid E A light yellow precipitate is formed, ammonia water accounts for 5% of the volume of absolute ethanol; the ethanol solution of solid E is filtered to obtain solid F and liquid G, solid F is put into a 40% ethanol solution, and the concentration is 25% sulfuric acid The solution adjusts the pH value of the alcohol solution of solid F to 3 to obtain the crude product of syringaldehyde; the crude product of syringaldehyde is recrystallized with ethanol at 70°C to obtain crystals of syringaldehyde, the content of syringaldehyde is 99%, and the yield is 28.5% % (to Klassen lignin);

c. The liquid G obtained in the above step b is concentrated under reduced pressure at a temperature of 55°C and a pressure of 800Pa to obtain solid H, and the solid H is rectified under the protection of nitrogen with a pressure of 0.06MPa. The first fraction was collected at 170°C, and the second fraction was collected at 180-190°C; the first fraction was recrystallized with ethanol at 70°C to obtain vanillin crystals; the second fraction was recrystallized with ethanol at 70°C to obtain the Hydroxybenzaldehyde crystals; the productive rate of vanillin is 3.3% (p-Claesen lignin), and p-Hydroxybenzaldehyde yield is 1.6% (p-Claesen lignin), and the content of vanillin p-Hydroxybenzaldehyde is all in More than 99%.

Claims (1)

1. one kind is utilized xylogen to prepare the method for separating p-Hydroxybenzaldehyde, vanillin food grade,1000.000000ine mesh, syringic aldehyde, it is characterized in that, comprises following processing step:

(1), preparation LaB _1-xCu _xO ₃Catalyzer, wherein B is Fe, Co or Mn, 0＜x＜1:

A, lanthanum nitrate in molar ratio: iron nitrate, Xiao Suangu or manganous nitrate: cupric nitrate=1: 1-x: x takes by weighing nitrate, wherein 0＜x＜1;

B, nitrate is dissolved in makes nitrate solution in the water, the mass concentration of nitrate total amount in water is 20%～30%;

C, add citric acid make enveloping agent solution in nitrate solution, the mol ratio of metal ion total amount is 1: 1～2 in citric acid and the nitrate solution;

D, to drip concentration in enveloping agent solution be that the pH value that 10～30% ammoniacal liquor is regulated enveloping agent solution is 5～6, drips enveloping agent solution to be carried out stirring heating behind the ammoniacal liquor and obtain wet gel; Heating temperature is 80～100 ℃, and stirring velocity is 200～500 rev/mins, and churning time is 8～10 hours;

E, with wet gel in baking oven in 100～220 ℃ the oven dry 2～4 hours, obtain xerogel;

F, xerogel was kept 4～10 hours at 450～800 ℃ in high temperature sintering furnace, obtain LaB _1-xCu _xO ₃Catalyzer;

(2), the preparation of aromatic aldehyde crude product:

A, xylogen, catalyzer and NaOH are joined in the reactor, NaOH is 0.1～2.0mol/L, and xylogen is 10～200g/L, and catalyzer is 1～10g/L, and all the other are water;

B, the nitrogen that feeds 0.1～0.2MPa in reactor are protected, and reactor is heated to 120～180 ℃; After continuation feeding nitrogen makes the total pressure of reactor be 1.5～2.0MPa, nitrogen is switched to oxygen, the pressure of regulating oxygen is 2.0～4.0MPa, open simultaneously and stir, stirring velocity is 600～1200 rev/mins, behind stirring reaction 10～120min, obtain the salts solution of p-Hydroxybenzaldehyde, vanillin food grade,1000.000000ine mesh and syringic aldehyde, i.e. the aromatic aldehyde crude product;

(3), the separation of p-Hydroxybenzaldehyde, vanillin food grade,1000.000000ine mesh, syringic aldehyde:

A, with the aromatic aldehyde crude product centrifugation that step (2) obtains, the rotating speed of centrifugation is 1000～4000 rev/mins, centrifugation time is 1～10min; Adding concentration and be 20～30% sulphuric acid soln in the liquid A that centrifugation obtains, to make liquid A be acidified to the pH value be 2～3 to obtain suspension liquid B; Suspension liquid B precipitation is spent the night, obtain solid C after the filtration, solid C is the intact xylogen of unreacted and the mixture of aromatic aldehyde; The solid C vacuum-drying under 50～60 ℃ condition that obtains was obtained yellow solid D in 12～24 hours; Yellow solid D is extracted 6～8 times with trichlorine Party A alkane, merge the extraction liquid that extraction obtains, extraction liquid 40～50 ℃ of temperature, is carried out concentrating under reduced pressure under the condition of pressure 500～1000Pa, obtain solid E, i.e. the mixture of p-Hydroxybenzaldehyde, vanillin food grade,1000.000000ine mesh, syringic aldehyde;

B, the solid E that obtains among the above-mentioned steps a is dissolved in the ethanolic soln that dehydrated alcohol forms solid E, the mass ratio of solid E and dehydrated alcohol is 10～40%; Add concentration and be 10～30% ammoniacal liquor in the ethanolic soln of solid E and form faint yellow precipitation, ammoniacal liquor accounts for 1～10% of dehydrated alcohol volume; The ethanolic soln filtration of solid E is obtained solid F and liquid G, and liquid G is the mixing solutions of p-Hydroxybenzaldehyde and vanillin food grade,1000.000000ine mesh; It is 30～50% ethanolic soln that solid F is put into concentration, is that the pH value that 20～30% sulphuric acid soln is regulated the alcoholic solution of solid F is 3～4 with concentration, obtains the syringic aldehyde crude product; Utilize ethanol under 60～80 ℃, to carry out recrystallization the syringic aldehyde crude product, obtain the syringic aldehyde crystal;

C, it is 50～60 ℃ in temperature with the liquid G that obtains among the above-mentioned steps b, pressure is to carry out concentrating under reduced pressure under the condition of 500～1000Pa to obtain solid H, solid H carries out rectifying under the nitrogen protection of 0.01～0.1MPa, collect first cut at 150～170 ℃ respectively, in the time of 180～190 ℃, collect second cut; First cut is carried out recrystallization at 60～80 ℃ with ethanol, obtain the vanillin food grade,1000.000000ine mesh crystal; Second cut is used ethyl alcohol recrystallization at 60～80 ℃, obtains the p-Hydroxybenzaldehyde crystal.