CN114907366B - Method for preparing LGO by catalytic pyrolysis - Google Patents

Abstract

The invention belongs to the field of biomass energy utilization, and particularly relates to a method for preparing levoglucosone (LGO, 1, 6-dehydrated-3, 4-dideoxy-beta-D-glucopyranose-2-one) by catalytic pyrolysis. The invention takes phosphorus-containing composite metal oxide as a catalyst, cellulose/biomass as a raw material, adopts mechanical mixing, carries out quick pyrolysis in an inert anaerobic or anoxic environment at 300-500 ℃, and can obtain a liquid product rich in LGO through quick condensation of pyrolysis gas. In addition, the catalyst has stable performance and is easy to regenerate, and can be recycled for multiple times by roasting in air.

Description

A method for preparing LGO through catalytic pyrolysis

Technical field

The invention belongs to the field of utilization of biomass energy, and specifically relates to a method for preparing LGO through catalytic pyrolysis.

Background technique

Levoglucosone (LGO, 1,6-anhydro-3,4-dideoxy-β-D-pyranosen-2-one) is derived from the dehydration reaction of cellulose and part of hemicellulose during the pyrolysis of biomass. An important anhydrous sugar derivative formed. LGO has highly active ketone groups and acetal centers. It is an important raw material in chemical industry, medical and other fields, and has high application and commercial value. Generally, LGO can be produced by depolymerization, dehydration and other reactions during the pyrolysis of cellulose. However, the conventional pyrolysis products of cellulose are very complex, and the LGO yield and selectivity are extremely low, making further extraction and separation very difficult. Therefore, the cellulose/biomass pyrolysis process must be controlled by appropriate means to promote the production of LGO while inhibiting the production of other products, thereby achieving high yield and high selectivity of LGO preparation.

Studies have shown that adding appropriate acid catalysts during the pyrolysis of cellulose or biomass can significantly promote the production of LGO. Chinese patent application 201110134871.9 discloses a method using sulfuric acid as the core to prepare a series of liquid acids or solid acids to catalyze the pyrolysis of cellulose/biomass to prepare LGO. However, considering that the catalyst prepared from sulfuric acid is highly acidic, during the pyrolysis process Due to the presence of water vapor, the loss of acidic sites is easy to occur, and it will also cause secondary reactions of LGO, making it difficult for it to exist stably. In addition, Chinese patent application 201110430778.2 discloses a method for preparing LGO through the pyrolysis of cellulose/biomass catalyzed by magnetic solid phosphoric acid. The solid phosphoric acid catalyst is prepared by using silicon oxide or alumina combined with a magnetic matrix as a carrier and an equal volume impregnation method. It not only solves the problem of strong acid catalysts polluting the environment and causing secondary reactions of LGO, but also relies on external magnetic fields to achieve catalyst recovery. However, the productivity and selectivity of LGO need to be further improved. On this basis, Chinese patent application 201710092409.4 discloses a method for biomass-based phosphoric acid-activated activated carbon to catalyze the pyrolysis of biomass to prepare LGO. Biochar is used as a carrier and impregnated with phosphoric acid to prepare a phosphoric acid-activated activated carbon catalyst. Poplar wood is used as the raw material for thermal In the solution experiment, the yield of LGO was 10.4wt%. However, the use of biochar carrier made the catalyst unable to be recycled and regenerated, and the economic performance was restricted. In addition to traditional catalysts, Chinese Invention Patent 202011332857.9 discloses a method for preparing LGO by catalyzing the pyrolysis of cellulose using waste strongly acidic macroporous resin Amberlyst-15. This method avoids the complex catalyst preparation process and also provides a waste resin. However, considering that the yield and acidity of waste resin are not stable, it cannot meet industrial needs. Therefore, it has become a top priority to provide a green, pollution-free preparation method with strong regeneration ability and high LGO yield.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing LGO by catalytic pyrolysis.

The invention provides a method for preparing LGO by catalytic pyrolysis. First, the phosphorus-containing heteropolyacid or heteropoly acid salt is impregnated into acidic metal oxides using an equal volume impregnation method, and then the phosphorus-containing composite metal oxide is obtained by high-temperature roasting. Catalyst for catalytic pyrolysis of cellulose/biomass to achieve high yield and selective preparation of LGO. In addition, the phosphorus-containing composite metal oxide has stable catalytic performance and a simple regeneration method. After the solid product is separated and recovered, it can be directly roasted in an air atmosphere for regeneration, and it still has catalytic ability after repeated use.

Specifically, the present invention uses phosphorus-containing composite metal oxide as the catalyst and cellulose/biomass as the raw material. The two are mechanically mixed. The mass ratio of the raw material to the catalyst satisfies (5:1) to (1:5). At 300 Rapid pyrolysis is carried out in an inert oxygen-free environment of ~500°C, with a heating rate of not less than 100°C/min and a decomposition reaction time of not more than 60 seconds. The pyrolysis gas is rapidly condensed to obtain a liquid product rich in LGO.

The preparation method of the catalyst of the present invention is as follows: first, take a certain amount of acidic metal oxide as a carrier, and then use an equal volume impregnation method to load phosphorus-containing heteropolyacid or heteropolyacid salt on the acidic oxide, ultrasonic 0.5 h and then let it stand overnight, put it into an oven to dry at 100°C for 10h, and then bake it at a temperature of 400 to 550°C for 5h to obtain a phosphorus-containing composite metal oxide catalyst.

Preferably, the acidic metal oxide is SnO ₂ , ZnO, TiO ₂ , ZrO ₂ or γ-Al ₂ O ₃ .

More preferably, the acidic metal oxide is SnO ₂ .

Preferably, the phosphorus-containing heteropolyacid or heteropolyacid salt is phosphomolybdic acid, phosphotungstic acid, phosphomolybdotungstic acid, ammonium phosphomolybdate or ammonium phosphotungstate.

More preferably, the phosphorus-containing heteropolyacid or heteropolyacid salt is phosphomolybdic acid or phosphotungstic acid.

Preferably, the mass percentage of the phosphorus-containing heteropoly acid or heteropoly acid salt impregnated in the phosphorus-containing composite metal oxide catalyst is 20 to 80%.

More preferably, the mass percentage of the impregnated phosphorus-containing heteropolyacid or heteropolyacid salt is 45 to 55%.

The cellulose includes microcrystalline cellulose or α-cellulose; the biomass includes wood, crop straw or herbaceous biomass. Raw materials should be crushed to a particle size less than 1mm before use.

The inert oxygen-free condition means that the carrier gas in the reaction is nitrogen, argon or helium.

The beneficial effects of the present invention are:

The present invention uses phosphorus-containing composite metal oxide as a catalyst, and can obtain a liquid product rich in LGO by mechanically mixing it with cellulose/biomass and then performing pyrolysis at medium and low temperatures. Studies have shown that acidic catalysts with phosphorus-containing active sites can promote the formation of LGO. The phosphorus-containing acidic group of the catalyst can promote the formation of unsaturated structure and bicyclic structure. The acidity of the acidic oxide itself can promote the depolymerization and dehydration of cellulose. In addition, the Mo ⁶⁺ or W ⁶⁺ species of the catalyst have good deoxygenation and hydrogenation capabilities. The general deoxygenation reaction activity of the oxygen functional group is C-OH>C=O>COC, which reduces the CO bond energy and promotes cellulose depolymerization. It plays a key role in promoting the secondary conversion of levoglucosan, the main pyrolysis product of cellulose, into LGO. The above many advantages jointly achieve high yield and selective preparation of LGO.

The beneficial effect of the present invention is also manifested in avoiding the use of highly acidic catalysts. Strongly acidic catalysts will not only cause environmental pollution and other problems, but more importantly, due to the presence of water vapor during the pyrolysis process, the loss of acidic sites will easily occur, and it will also cause secondary reactions of LGO, making it difficult for it to exist stably. This results in the loss of LGO and also brings great difficulties to the preservation of pyrolysis liquid products. Phosphorus-containing composite metal oxide catalysts mainly rely on the combination of an appropriate amount of phosphoric acid sites (PO ₄ ^3- species and P ⁵⁺ species embedded in the acidic oxide carrier) and various metal oxides inside the catalyst. The synergy between aspects enables the preparation of LGO with high yield and high selectivity.

In addition, the phosphorus-containing composite metal oxide catalyst is easy to regenerate. After the catalytic pyrolysis reaction, it can be regenerated by roasting in an air atmosphere, and the catalytic effect will not be significantly reduced after repeated use. The environmentally friendly, low-cost, and high-efficiency preparation of LGO is achieved.

Detailed ways

The present invention provides a method for preparing LGO by catalytic pyrolysis. The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

The liquid product yield calculation method in the following examples is as follows:

Liquid product yield = (mass of collected liquid product ÷ mass of raw materials) × 100%.

In the following examples, the content of LGO is analyzed by gas chromatography/mass spectrometry and quantified using the external standard method. The calculation method of LGO yield is as follows:

The yield of LGO = (mass of LGO ÷ mass of raw materials) × 100%.

The percentages in the following examples are mass percentages unless otherwise specified.

The experimental methods in the following examples are conventional methods unless otherwise specified.

Example 1

Weigh 50g SnO ₂ and 20g phosphomolybdic acid respectively, then dissolve the phosphomolybdic acid in a certain amount of deionized water to form a solution, use the equal volume impregnation method to load the phosphomolybdic acid on SnO ₂ , ultrasonic for 0.5h and let it stand overnight. , then placed in an oven at 100°C to dry for 10h, taken out and calcined at 550°C for 5h to obtain a phosphorus-molybdenum-tin composite metal oxide.

Take 10g of the phosphorus-molybdenum-tin composite metal oxide prepared above, use commercial microcrystalline cellulose as raw material (average particle size 0.09mm), mechanically mix the two, and control the mass ratio of cellulose to catalyst to be 1:1, and then The mixture was pyrolyzed at 350°C (heating rate not less than 100°C/min) for 30 seconds in a nitrogen atmosphere. The yield of the liquid product obtained was 52.8%. The LGO content was analyzed by gas chromatography mass spectrometry, and the LGO was calculated. The yield was 18.7%.

Example 2

Weigh 50g ZnO and 30g phosphomolybdic acid respectively, then dissolve the phosphomolybdic acid in a certain amount of deionized water to form a solution, use the equal volume impregnation method to load the phosphomolybdic acid on ZnO, ultrasonic for 0.5h and let it stand overnight, then Place it in an oven at 100°C to dry for 10 hours, take it out and bake it at 450°C for 5 hours to obtain a phosphorus-molybdenum-zinc composite metal oxide.

Take 10g of the phosphorus-molybdenum-zinc composite metal oxide prepared above, use α-cellulose as raw material (average particle size 0.25mm), mechanically mix the two, control the mass ratio of cellulose to catalyst to 5:1, and then The mixture was pyrolyzed at 320°C (heating rate not less than 100°C/min) for 30 seconds in an argon atmosphere. The yield of the liquid product was 49.5%. The LGO content was analyzed by gas chromatography mass spectrometry, and the LGO was calculated. The yield was 15.6%.

Example 3

Weigh 50g γ-Al ₂ O ₃ and 25g phosphomolybdic acid respectively, then dissolve the phosphomolybdic acid in a certain amount of deionized water to form a solution, and use the equal volume impregnation method to load the phosphomolybdic acid on γ-Al ₂ O ₃ . After ultrasonic for 0.5h, let it stand overnight, then place it in a 100°C oven to dry for 10h, take it out and bake it at 400°C for 5h to obtain a phosphorus-molybdenum-aluminum composite metal oxide.

Take 10g of the above-prepared phosphorus-molybdenum-aluminum composite metal oxide, use commercial microcrystalline cellulose as raw material (average particle size 0.05mm), mechanically mix the two, and control the mass ratio of cellulose to catalyst to be 1:3. The mixture was then pyrolyzed at 400°C (heating rate not less than 100°C/min) in a nitrogen atmosphere for 40 seconds. The yield of the liquid product obtained was 57.1%. The content of LGO was analyzed by gas chromatography/mass spectrometry and calculated. It was found that the yield of LGO was 17.9%.

Example 4

Weigh 50g SnO ₂ and 25g phosphotungstic acid respectively, then dissolve the phosphotungstic acid in a certain amount of deionized water to form a solution, use the equal volume impregnation method to load the phosphotungstic acid on SnO ₂ , ultrasonic for 0.5h and let it stand overnight. , then placed in an oven at 100°C to dry for 10h, taken out and calcined at 550°C for 5h to obtain a phosphorus-tungsten-tin composite metal oxide.

Take 10g of the phosphorus-tungsten-tin composite metal oxide prepared above, use α-cellulose as the raw material (average particle size 0.25mm), mechanically mix the two, control the mass ratio of cellulose to catalyst to 1:2, and then The mixture was pyrolyzed at 350°C (heating rate not less than 100°C/min) for 60 seconds in a helium atmosphere. The yield of the liquid product obtained was 53.2%. The LGO content was analyzed by gas chromatography mass spectrometry, and the LGO was calculated. The yield is 17.5%.

Example 5

Weigh 50g γ-Al ₂ O ₃ and 20g phosphotungstic acid respectively, then dissolve the phosphomolybdic acid in a certain amount of deionized water to form a solution, and use the equal volume impregnation method to load the phosphomolybdic acid on γ-Al ₂ O ₃ . After ultrasonic for 0.5h, let it stand overnight, then place it in a 100°C oven to dry for 10h, take it out and bake it at 550°C for 5h to obtain the phosphorus tungsten aluminum composite metal oxide.

Take 10g of the phosphorus tungsten aluminum composite metal oxide prepared above, use commercial microcrystalline cellulose as raw material (average particle size 0.05mm), mechanically mix the two, and control the mass ratio of cellulose to catalyst to be 1:1, and then The mixture was pyrolyzed at 500°C (heating rate not less than 100°C/min) in a nitrogen atmosphere for 20 seconds. The yield of the liquid product obtained was 70.3%. The content of LGO was analyzed by gas chromatography/mass spectrometry, and the calculation was It is known that the yield of LGO is 14.1%.

Example 6

Weigh 50g TiO ₂ and 40g ammonium phosphomolybdate respectively, then dissolve the ammonium phosphomolybdate in a certain amount of deionized water to form a solution, use the equal volume impregnation method to load phosphotungstic acid on TiO ₂ , ultrasonic for 0.5h and then let stand Leave it overnight, then dry it in an oven at 100°C for 10h, take it out and bake it at 500°C for 5h to obtain a phosphorus tungsten titanium composite metal oxide.

Take 10g of the phosphorus-molybdenum-titanium composite metal oxide prepared above, use α-cellulose as raw material (average particle size 0.25mm), mechanically mix the two, control the mass ratio of cellulose to catalyst to 1:5, and then The mixture was pyrolyzed at 300°C (heating rate not less than 100°C/min) for 60 seconds in a nitrogen atmosphere. The yield of the liquid product obtained was 47.9%. The LGO content was analyzed by gas chromatography mass spectrometry, and the LGO content was calculated. The yield is 16.8%.

Example 7

Weigh 50g ZrO ₂ and 10g ammonium phosphotungstate respectively, and then dissolve the ammonium phosphotungstic acid in a certain amount of deionized water to form a solution. Use the equal volume impregnation method to load the phosphotungstic acid on ZrO ₂ , ultrasonic for 0.5h and then let stand. Leave it overnight, then dry it in an oven at 100°C for 10h, take it out and bake it at 550°C for 5h to obtain a phosphorus-tungsten-zirconium composite metal oxide.

Take 10g of the above-prepared phosphotungsten-zirconium composite metal oxide, use commercial microcrystalline cellulose as raw material (average particle size 0.05mm), mechanically mix the two, and control the mass ratio of cellulose to catalyst to be 2:1. The mixture was then pyrolyzed at 370°C (heating rate not less than 100°C/min) in a nitrogen atmosphere for 20 seconds. The yield of the liquid product obtained was 52.3%. The content of LGO was analyzed by gas chromatography/mass spectrometry and calculated. It was found that the yield of LGO was 17.3%.

Example 8

Weigh 50g SnO ₂ and 30g phosphomolybdotungstic acid respectively, and then dissolve the phosphomolybdotungstic acid in a certain amount of deionized water to form a solution. Use the equal volume impregnation method to load the phosphomolybdotungstic acid on SnO ₂ and ultrasonic for 0.5h. Let it stand overnight, then place it in an oven at 100°C to dry for 10 hours. After taking it out, it is roasted at a temperature of 550°C for 5 hours to obtain a phosphorus-molybdenum-tungsten-tin composite metal oxide.

Take 10g of the phosphorus-molybdenum-tungsten-tin composite metal oxide prepared above, use commercial microcrystalline cellulose as raw material (average particle size 0.05mm), mechanically mix the two, and control the mass ratio of cellulose to catalyst to be 1:2. The mixture was then pyrolyzed at 350°C (heating rate not less than 100°C/min) for 30 seconds in a nitrogen atmosphere. The yield of the liquid product obtained was 48.2%. The content of LGO was analyzed by gas chromatography/mass spectrometry and calculated. It was found that the yield of LGO was 15.1%.

Example 9

The solid product after pyrolysis in Example 1 was directly calcined at a temperature of 550°C for 1 hour in an air atmosphere to obtain a regenerated phosphorus-molybdenum-tin composite metal oxide catalyst. Use commercial microcrystalline cellulose as raw material (average particle size 0.09mm), mechanically mix the two, control the mass ratio of cellulose to catalyst to be 1:1, and then heat the mixture at 350°C (the heating rate is not less than 100°C /min), pyrolysis under nitrogen atmosphere for 30 seconds, the yield of the liquid product obtained was 50.9%. The content of LGO was analyzed by gas chromatography/mass spectrometry, and the yield of LGO was calculated to be 17.1%.

Example 10

Take 10g of the phosphorus-molybdenum-tin composite metal oxide prepared in Example 1, use poplar wood as raw material (average particle size 0.1mm), mechanically mix the two, and control the mass ratio of poplar wood to catalyst to be 1:5, and then The mixture was pyrolyzed at 320°C (heating rate not less than 100°C/min) under an argon atmosphere for 30 seconds. The yield of the liquid product obtained was 47.6%. The LGO content was analyzed by gas chromatography mass spectrometry and calculated. The yield of LGO was 10.2%.

Example 11

Take 10g of the phosphorus-molybdenum-zinc composite metal oxide prepared in Example 2, use bagasse as raw material (average particle size 0.1mm), mechanically mix the two, control the mass ratio of bagasse to catalyst to 2:1, and then The mixture was pyrolyzed at 300°C (heating rate not less than 100°C/min) for 40 seconds in a nitrogen atmosphere. The yield of the liquid product obtained was 41.5%. The LGO content was analyzed by gas chromatography mass spectrometry, and the LGO was calculated. The yield was 8.9%.

Example 12

Take 10g of the phosphorus-molybdenum-aluminum composite metal oxide prepared in Example 3, use pine wood as raw material (average particle size 0.1mm), mechanically mix the two, control the mass ratio of pine wood to catalyst to be 1:5, and then mix the mixture After pyrolysis at 350°C (heating rate not less than 100°C/min) for 60 seconds in a nitrogen atmosphere, the yield of the liquid product obtained was 52.2%. The LGO content was analyzed by gas chromatography mass spectrometry, and the LGO production was calculated. The rate is 9.5%.

Example 13

Take 10g of the phosphorus tungsten aluminum composite metal oxide prepared in Example 5, use poplar wood as the raw material (average particle size 0.1 mm), mechanically mix the two, and control the mass ratio of poplar wood to catalyst to be 5:1, and then The mixture was pyrolyzed at 320°C (heating rate not less than 100°C/min) for 40 seconds in a nitrogen atmosphere. The yield of the liquid product obtained was 42.3%. The LGO content was analyzed by gas chromatography mass spectrometry, and the LGO was calculated. The yield was 9.6%.

Example 14

Take 10g of the phosphorus-molybdenum-titanium composite metal oxide prepared in Example 6, use wheat straw as the raw material (average particle size 0.1mm), mechanically mix the two, and control the mass ratio of the wheat straw to the catalyst to be 1:4, and then The mixture was pyrolyzed at 350°C (heating rate not less than 100°C/min) for 30 seconds in a nitrogen atmosphere. The yield of the liquid product obtained was 53.8%. The LGO content was analyzed by gas chromatography mass spectrometry, and the LGO was calculated. The yield was 8.6%.

In the above embodiments, the pyrolysis raw materials include cellulose raw materials such as microcrystalline cellulose and α-cellulose and biomass raw materials such as wood, crop straw or herbs. The cellulose content in the biomass raw materials is about 30 to 50%. , therefore compared with the example using cellulose as the raw material, the LGO yield has decreased, but it does not affect the description of the example of the present invention.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. within the spirit and principles of the present invention shall be included in the present invention. within the range.

Claims (4)

1. The method for preparing the LGO by catalytic pyrolysis is characterized in that phosphorus-containing composite metal oxide is used as a catalyst, cellulose/biomass is used as a raw material, and the two are mechanically mixed; the mass ratio of the cellulose/biomass to the catalyst is (5:1) - (1:5); carrying out quick pyrolysis in an inert anaerobic or anoxic environment at 300-500 ℃, wherein the heating rate of the pyrolysis reaction is not lower than 100 ℃ per minute, the pyrolysis reaction time is not more than 60s, and the pyrolysis gas is quickly condensed to obtain a liquid product rich in LGO;

the preparation method of the phosphorus-containing composite metal oxide catalyst comprises the following steps: taking a certain amount of acidic metal oxide as a carrier, loading phosphorus-containing heteropolyacid or heteropolyacid salt on the acidic metal oxide by adopting an isovolumetric impregnation method, carrying out ultrasonic treatment and drying, and then roasting at 400-550 ℃ for 5h to obtain the phosphorus-containing composite metal oxide catalyst;

the heteropolyacid or heteropolyacid salt containing phosphorus is phosphomolybdic acid, phosphotungstic acid, phosphomolybdic acid, ammonium phosphomolybdate or ammonium phosphotungstic acid;

wherein the acidic metal oxide is SnO ₂ 、ZnO、TiO ₂ 、ZrO ₂ Or gamma-Al ₂ O ₃ ；

The mass percentage of the heteropolyacid or heteropolyacid salt impregnated with the phosphorus-containing composite metal oxide catalyst is 20-80%.

2. The method of preparing LGO by catalytic pyrolysis according to claim 1, wherein the cellulose comprises microcrystalline cellulose or α -cellulose.

3. The method of claim 1, wherein the biomass comprises wood, crop straw, or herbaceous biomass.

4. The method of claim 1, wherein the inert oxygen-free or oxygen-deficient environment is nitrogen, argon or helium as carrier gas.