A method for catalytically converting lignin to synthesize pyridine bases

Abstract

The present invention discloses a method for catalytically converting lignin into pyridine bases. In the present invention, an aqueous solution of fatty amine is used to pretreat lignocellulosic sources to achieve an excellent lignin removal rate. Subsequently, a lignin-rich washing solution is obtained through a simple water washing step. Finally, the obtained washing solution is directly hydrocracked to obtain a hydrocracking solution containing pyridine bases. The present invention reports for the first time an efficient conversion method from real lignin to pyridine bases. This method has the characteristics of simple steps, no use of organic solvents in the depolymerization process, and high yield of pyridine base monomers.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic conversion of lignin, and particularly relates to a method for catalytically converting lignin to synthesize pyridine bases. Background Art

[0002] Lignin is the most abundant renewable resource with an aromatic ring structure on Earth. Due to the importance of lignin in biorefining, its high-value utilization has attracted extensive attention. All along, the conversion products of lignin have been mostly limited to compounds containing C, H, and O, and there have been few reports on lignin conversion strategies for products of high-value heteroatom-containing compounds. In order to expand the product pool of lignin conversion, endow biorefining with more possibilities, and improve the economic feasibility of future biorefining, the development of nitrogen-involved lignin conversion routes has received extensive attention from scholars in recent years. Nitrogen-containing chemicals have been widely used in fields such as dyes, polymer synthesis, and medicinal chemistry. However, current related research mostly focuses on the synthesis of nitrogen-containing chemicals from simple lignin model compounds (synthetic monomers and dimers) (Nat. Commun. 2022, 13, 3365; Green Chem. 2022, 24, 2919-2926; Angew Chem. Int. Ed. 2021, 60, 20666-20671; Green Chem. 2021, 23, 8441-8447). However, due to the more complex structure and larger molecular weight of real lignin (extracted from lignocellulose), those strategies that perform well in the conversion of model compounds may not be applicable to real lignin. A small amount of research work has begun to attempt the conversion of real lignin. In these literatures, lignin is first extracted from lignocellulose by pretreatment with a low-solid-content acidic organic solvent, and a large amount of water is added to precipitate lignin from the extract. Subsequently, the lignin conversion strategy can be divided into the following two routes: 1. The obtained lignin is catalytically depolymerized at high temperature into low-molecular-weight lignin oil, and then the lignin oil is converted into benzylamine with an amine and Pd / C under an argon atmosphere (Angew Chem. Int. Ed. 2021, 60, 20666-20671). Similarly, Ruijten et al. (ACS Sustainable Chem. Eng. 2023, 11, 4776-4788) used reductive catalytic fractionation (RCF) to replace the traditional pretreatment method to refine lignocellulose to obtain lignin oil, followed by sugar extraction and heptane / ethyl acetate extraction to obtain a monomer-rich fraction, and finally applied a Cu-SiO2-based amination strategy to convert this fraction into tertiary amine monomers. 2. The second scheme is to first obtain nitrogen-modified lignin through three-step reactions (oxidation, oximation, and acetylation), and then photocatalytically depolymerize the nitrogen-modified lignin to synthesize non-phenolic aromatic amine products (ACS Catal. 2019, 9, 8843-8851). It can be found that there are still some disadvantages in the current nitrogen-involved lignin conversion schemes, such as cumbersome steps, the use of organic solvents in the conversion, and low yields of nitrogen-containing monomers (<10 wt%).Therefore, it is of great significance to develop a method for catalytic conversion of real lignin that is green and simple, uses an aqueous solution as the conversion solvent, and has a high yield of nitrogen-containing monomers. Summary of the Invention

[0003] To solve the drawbacks and deficiencies of the prior art, the purpose of the present invention is to provide a method for catalytic conversion of lignin to synthesize pyridine bases.

[0004] The present invention performs heat pretreatment on lignocellulosic sources with an aqueous solution of fatty amine to achieve an excellent lignin removal rate. Subsequently, a lignin-rich washing solution is obtained through a simple water washing step. Finally, copper acetate and palladium on carbon are directly added to the obtained washing solution for hydrogenolysis to obtain a hydrogenolysis solution containing pyridine bases. The present invention reports for the first time a highly efficient conversion method from real lignin to pyridine bases, which has the characteristics of simple steps, no use of organic solvents in the depolymerization process, and high yield of pyridine base monomers.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] A method for catalytic conversion of lignin to synthesize pyridine bases, comprising the following steps:

[0007] (1) After mixing the lignocellulosic source and the aqueous solution of fatty amine, perform heat pretreatment reaction. After the reaction ends, wash the product mixture with water, and after solid-liquid separation, obtain a lignin-rich washing solution;

[0008] (2) Mix the lignin-rich washing solution, copper acetate, and palladium on carbon, and perform hydrogenolysis reaction under a hydrogen atmosphere to obtain a hydrogenolysis solution containing pyridine derivatives.

[0009] Preferably, the lignocellulosic source in step (1) is at least one of corncob, corn straw, pinewood, eucalyptus, poplar, Manchurian ash, seabuckthorn, fir, Chinese fir, birch, wheat straw, bagasse, rice straw, rice husk, edible mushroom substrate, and peanut shell; more preferably at least one of corn straw, poplar, and pinewood.

[0010] Preferably, in the aqueous solution of fatty amine in step (1), the fatty amine is at least one of dimethylamine, diethylamine, ethylamine, methylamine, propylamine, and diisopropylamine; more preferably at least one of dimethylamine and diethylamine.

[0011] Preferably, in the heat pretreatment reaction in step (1), the mass ratio of the lignocellulosic source, fatty amine, and water is 10 - 50:2 - 360:8 - 360; more preferably 30 - 50:28 - 150:42 - 150; most preferably 30:28:42 or 50:100:150 or 50:150:150.

[0012] Preferably, the conditions for the heating pretreatment reaction in step (1) are: reacting at 100-180 °C for 1-8 h under normal pressure; more preferably reacting at 130-180 °C for 1-3 h under normal pressure.

[0013] Preferably, in the water washing of the product mixture in step (1), water is added for water washing according to the mass ratio of lignocellulosic source to water added for water washing of 10-50:100-1500; more preferably 30-50:800-1500; most preferably 30:800 or 50:1300 or 50:1500.

[0014] More preferably, the water washing can be carried out by adding water in 2-5 times. After each addition of water, solid-liquid separation is carried out, and then water is added for washing the solid and the washing liquid is collected.

[0015] Preferably, the solid-liquid separation method in step (1) is at least one of extrusion separation, centrifugal separation and filtration separation.

[0016] Preferably, the mass ratio of the lignin-rich washing liquid, copper acetate and palladium-carbon in step (2) is 400-2000:2-10:1-10; more preferably 400-1500:2-4:1-8; most preferably 400:2:1 or 1000:4:4 or 1500:4:8.

[0017] Preferably, the mass fraction of palladium in the palladium-carbon in step (2) is 5-30%; more preferably 10%.

[0018] Preferably, the conditions for the hydrogenolysis reaction in step (2) are: reacting at 200-300 °C for 2-15 h under 0.5-4 MPa of hydrogen; more preferably reacting at 250-300 °C for 4-6 h under 1-3 MPa of hydrogen.

[0019] Preferably, the rotation speed of the hydrogenolysis reaction in step (2) is 30-600 rpm.

[0020] Preferably, the pyridine derivative is obtained by purifying the hydrogenolysis solution containing the pyridine derivative in step (2); the purification method is: first adjusting the pH of the hydrogenolysis solution containing the pyridine derivative to acidic with an acid solution, then extracting with ethyl acetate, and collecting the aqueous phase after extraction layering and carrying out vacuum distillation to obtain the pyridine derivative.

[0021] More preferably, the acid solution is at least one of hydrochloric acid, sulfuric acid and phosphoric acid, and the mass concentration of the acid solution is 2-8%; the pH of the hydrogenolysis solution containing the pyridine derivative after acidification is 1.5-3.0; the volume of the ethyl acetate is 2-4 times the volume of the hydrogenolysis solution containing the pyridine derivative; the vacuum distillation conditions are: the vacuum degree is 0.08-0.1 MPa, and the temperature is 55-80 °C.

[0022] Preferably, the pyridine derivative in the hydrolysate containing pyridine derivative in step (2) is at least one of 2-methyl-5-ethylpyridine, 3-ethyl-4-methylpyridine, and 3-hydroxypyridine.

[0023] The mechanism of the present invention is as follows: First, the pretreatment based on aqueous fatty amine solution is used to destroy the ultrastructure of the lignocellulose cell wall, promote the fragmentation and repositioning of lignin, and utilize the nucleophilicity of the amine to capture the lignin active intermediate with a nucleophilic site, thereby achieving the efficient removal of lignin from the lignocellulose matrix. At the same time, the high catalytic depolymerization activity of lignin is maintained by inhibiting the recondensation reaction of lignin intermediates. Then, during the hydrocracking reaction, the lignin side chains with aldehyde and ketone groups are broken to generate aliphatic aldehydes and ketones. The formed aldehydes and ketones undergo a condensation reaction with ammonia obtained from the high-temperature decomposition of fatty amine in the washing solution to form imine intermediates. Various imine intermediates further condense to form diaminimine. Diaminimine easily loses ammonia and undergoes a cyclization reaction to form the intermediate tetrahydropyridine. The active hydrogen atoms in tetrahydropyridine then react with the aldehyde imine molecules, undergo rearrangement, and simultaneously lose two ammonia molecules to synthesize 2-methyl-5-ethylpyridine and 3-ethyl-4-methylpyridine; or the imine intermediate further condenses to form triaminimine. Triaminimine loses three ammonia molecules and is synthesized to obtain 3-hydroxypyridine after cyclization reaction.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] (1) In the present invention, using real lignin (lignin extracted from lignocellulose) as the substrate and water as the solvent, pyridine derivatives can be obtained by directly hydrocracking the washing solution after pretreatment. The synthesis method is green and simple.

[0026] (2) The present invention reports for the first time the technical route for catalytic conversion of real lignin to synthesize pyridine derivatives.

[0027] (3) Through the technical route provided by the present invention, the efficient catalytic conversion of lignin can be achieved, and the yield of N-containing monomers is significantly higher than that of the prior art. Description of the Drawings

[0028] Figure 1 It is the reaction mechanism for the hydrocracking of lignin in the washing solution to generate monophenols and pyridine derivatives.

[0029] Figure 2 It is the two-dimensional gas chromatography-mass spectrometry spectrum of the hydrolysate obtained in Example 1. Detailed Embodiments

[0030] The present invention will be further described in detail below in conjunction with examples and drawings, but the embodiments of the present invention are not limited thereto.

[0031] In the embodiments of the present invention, those not specified with specific conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. Raw materials, reagents, etc. that are not specified with the manufacturer can be obtained as conventional products through commercial purchase.

[0032] Example 1

[0033] 1. Preparation of lignin-rich washing liquid:

[0034] Add 42 parts by mass of water to 28 parts by mass of diethylamine. Subsequently, add the aqueous diethylamine solution to 30 parts by mass of corn straw and mix. Carry out heat pretreatment reaction. The reaction conditions are: normal pressure, 130 °C, 1 h. After the reaction, add a total of 800 parts by mass of water and wash three times equally. For the second and third times of adding water, the solid is washed again. After each washing, solid-liquid separation is carried out by extrusion separation. Collect the liquid part obtained by mixing the three times of washing to obtain the lignin-rich washing liquid.

[0035] 2. Preparation and synthesis of pyridine base:

[0036] Add 2 parts by mass of copper acetate and 1 part by mass of palladium carbon (mass fraction of palladium is 10%) to 400 parts by mass of the washing liquid obtained in step 1. Carry out hydrogenolysis reaction under a hydrogen atmosphere. The reaction conditions are: 2 MPa hydrogen, 250 °C, 4 h, stirring speed of 400 rpm. After the reaction, the hydrogenolysis liquid containing pyridine derivatives can be obtained.

[0037] The yield of pyridine derivative monomer obtained by the above method is 21.3 wt%, and the yield of monophenol is 15.6 wt%. Among them, the yield of monophenol is calculated by GC-FID detection, and the yield of pyridine derivative is calculated by two-dimensional gas chromatography-mass spectrometry detection.

[0038] 3. Purify the hydrogenolysis liquid containing pyridine derivatives obtained in step 2: First, adjust the pH of the hydrogenolysis liquid to acidic with an acid solution, then extract with ethyl acetate, and collect the aqueous phase after extraction layering and carry out vacuum distillation to obtain pyridine derivatives; the acid solution is hydrochloric acid with a mass concentration of 5%; the pH of the acidified hydrogenolysis liquid is 2.0; the volume of ethyl acetate added is 3 times that of the hydrogenolysis liquid; the vacuum distillation conditions are: vacuum degree of 0.09 MPa, temperature of 55 °C.

[0039] Example 2

[0040] 1. Preparation of lignin-rich washing liquid:

[0041] Add 150 parts by mass of water to 100 parts by mass of dimethylamine. Subsequently, add the dimethylamine aqueous solution to 50 parts by mass of poplar sawdust and mix. Then, carry out a heat pretreatment reaction. The reaction conditions are: atmospheric pressure, 150 °C, 3 h. After the reaction, add a total of 1300 parts by mass of water and wash three times equally. For the second and third water additions, the solid is washed again. After each water wash, solid-liquid separation is carried out by centrifugation. Collect the liquid parts obtained from the three water washes to obtain a water wash solution rich in lignin.

[0042] 2. Preparation and synthesis of pyridine base:

[0043] Add 4 parts by mass of copper acetate and 4 parts by mass of palladium carbon (10%) to 1000 parts by mass of the water wash solution obtained in Step 1. Carry out a hydrogenolysis reaction under a hydrogen atmosphere. The reaction conditions are: 3 MPa hydrogen, 290 °C, 5 h, stirring speed of 600 rpm. After the reaction, a hydrogenolysis solution containing pyridine derivatives can be obtained.

[0044] The yield of the pyridine derivative monomer obtained by the above method is 24.1 wt%, and the yield of monophenol is 18.1 wt%. Among them, the yield of monophenol is calculated by GC-FID detection, and the yield of pyridine derivatives is calculated by two-dimensional gas chromatography-mass spectrometry detection.

[0045] 3. Purify the hydrogenolysis solution containing pyridine derivatives obtained in Step 2. First, adjust the pH of the hydrogenolysis solution to acidic with an acid solution, then extract with ethyl acetate. Collect the aqueous phase after extraction layering and carry out vacuum distillation to obtain pyridine derivatives; the acid solution is 3% sulfuric acid; the pH of the acidified hydrogenolysis solution is 1.5; the volume of ethyl acetate added is 2 times that of the hydrogenolysis solution; the vacuum distillation conditions are: vacuum degree of 0.1 MPa, temperature of 70 °C.

[0046] Example 3

[0047] 1. Preparation of a water wash solution rich in lignin:

[0048] Add 150 parts by mass of water to 150 parts by mass of diethylamine. Subsequently, add the diethylamine aqueous solution to 50 parts by mass of pine sawdust and mix. Then, carry out a heat pretreatment reaction. The reaction conditions are: atmospheric pressure, 180 °C, 3 h. After the reaction, add a total of 1500 parts by mass of water and wash three times equally. For the second and third water additions, the solid is washed again. After each water wash, collect the water wash solution rich in lignin by centrifugation.

[0049] 2. Preparation and synthesis of pyridine base:

[0050] Take 4 parts by mass of copper acetate and 8 parts by mass of palladium on carbon (10%) and add them to 1500 parts by mass of the washed solution obtained in Step 1. Carry out a hydrogenolysis reaction under a hydrogen atmosphere. The reaction conditions are: 1 MPa of hydrogen, 300 °C, 6 h, and a stirring speed of 300 rpm. After the reaction ends, a hydrogenolysis solution containing a pyridine derivative can be obtained.

[0051] The yield of the pyridine derivative monomer obtained by the above method is 18.5 wt%, and the yield of the monophenol is 14.1 wt%. Among them, the yield of the monophenol is calculated by GC-FID detection, and the yield of the pyridine derivative is calculated by two-dimensional gas chromatography-mass spectrometry detection.

[0052] 3. Purify the hydrogenolysis solution containing the pyridine derivative obtained in Step 2. First, adjust the pH of the hydrogenolysis solution to acidic with an acid solution, then extract it with ethyl acetate, and collect the aqueous phase after extraction layering and perform vacuum distillation to obtain the pyridine derivative; the acid solution is 7% phosphoric acid; the pH of the hydrogenolysis solution after acidification is 2.5; the volume of ethyl acetate added is 4 times that of the hydrogenolysis solution; the vacuum distillation conditions are: a vacuum degree of 0.1 MPa and a temperature of 65 °C.

[0053] Comparative Example 1

[0054] 1. Preparation of the washed solution rich in lignin:

[0055] Take 42 parts by mass of water and add it to 28 parts by mass of diethylamine. Subsequently, add this aqueous diethylamine solution to 30 parts by mass of corn straw and mix. Carry out a heat pretreatment reaction. The reaction conditions are: normal pressure, 130 °C, 1 h. After the reaction ends, add a total of 800 parts by mass of water and divide it into three equal parts for washing. Among them, the second and third times of adding water are used to wash the solid again. After each washing, solid-liquid separation is carried out by extrusion separation, and the liquid part obtained by mixing the three washings is collected to obtain the washed solution rich in lignin.

[0056] 2. Preparation and synthesis of pyridine base:

[0057] Take 1 part by mass of palladium on carbon (the mass fraction of palladium is 10%) and add it to 400 parts by mass of the washed solution obtained in Step 1. Carry out a hydrogenolysis reaction under a hydrogen atmosphere. The reaction conditions are: 2 MPa of hydrogen, 250 °C, 4 h, and a stirring speed of 400 rpm. After the reaction ends, a hydrogenolysis solution containing a pyridine derivative can be obtained.

[0058] The yield of the pyridine derivative monomer obtained by the above method is 12.2 wt%, and the yield of the monophenol is 7.9 wt%. Among them, the yield of the monophenol is calculated by GC-FID detection, and the yield of the pyridine derivative is calculated by two-dimensional gas chromatography-mass spectrometry detection.

[0059] Comparative Example 2

[0060] 1. Preparation of the washed solution rich in lignin:

[0061] Add 295 parts by mass of water to 5 parts by mass of sodium hydroxide. Subsequently, add the aqueous sodium hydroxide solution to 30 parts by mass of corn straw and mix. Conduct a heat pretreatment reaction. The reaction conditions are: atmospheric pressure, 130 °C, 1 h. After the reaction, add a total of 800 parts by mass of water and wash three times equally. For the second and third water additions, wash the solid again. After each water wash, perform solid-liquid separation by extrusion separation. Collect the liquid part obtained by mixing the three water washes to obtain a lignin-rich wash liquor.

[0062] 2. Preparation and synthesis of pyridine bases:

[0063] Add 2 parts by mass of copper acetate and 1 part by mass of palladium-carbon (mass fraction of palladium is 10%) to 400 parts by mass of the wash liquor obtained in step 1. Conduct a hydrogenolysis reaction under a hydrogen atmosphere. The reaction conditions are: 2 MPa hydrogen, 250 °C, 4 h, stirring speed of 400 rpm. After the reaction, a hydrogenolysis liquor containing pyridine derivatives can be obtained.

[0064] The yield of the pyridine derivative monomer obtained by the above method is 0 wt%, and the yield of the monophenol is 6.8 wt%. The monophenol yield is calculated by GC-FID detection, and the pyridine derivative yield is calculated by two-dimensional gas chromatography-mass spectrometry detection.

[0065] Figure 1 This is the reaction mechanism of the hydrogenolysis of lignin in the wash liquor to produce monophenols and pyridine derivatives. Pyridine bases are exemplified by 2-methyl-5-ethylpyridine, 3-ethyl-4-methylpyridine, and 3-hydroxypyridine. Other pyridine derivative monomers are also synthesized through similar pathways.

[0066] Figure 2 This is the two-dimensional gas chromatography-mass spectrometry combined spectrogram of the hydrogenolysis liquor obtained in Example 1. The successful synthesis of pyridine bases was demonstrated by high-resolution two-dimensional gas chromatography-mass spectrometry technology.

[0067] The above embodiments are preferred embodiments of the present invention. However, the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for catalytically converting lignin to synthesize pyridine bases, characterized in that, It includes the following steps: (1) Mix the lignocellulose source and the aqueous fatty amine solution, heat for pretreatment reaction, end the reaction, wash the product mixture with water, and obtain the water-washed solution rich in lignin after solid-liquid separation; (2) Mix the water-washed solution rich in lignin, copper acetate and palladium-carbon, and carry out a hydrogenolysis reaction under a hydrogen atmosphere to obtain a hydrogenolysis solution containing pyridine bases; In the aqueous fatty amine solution described in step (1), the fatty amine is at least one of dimethylamine, diethylamine, ethylamine, methylamine, propylamine and diisopropylamine; The pyridine bases described in step (2) are 2-methyl-5-ethylpyridine, 3-ethyl-4-methylpyridine, 3-hydroxypyridine, 3-methylpyridine, pyridine-2-carboxaldehyde, 2-pyridinecarboxylic acid, 3-ethylpyridine, 2,6-dimethyl-3-ethylpyridine, 3-hydroxy-6-methylpyridine and 2-ethyl-6-isopropylpyridine.

2. The method for catalytically converting lignin to synthesize pyridine bases according to claim 1, wherein The mass ratio of the water-washed solution rich in lignin, copper acetate and palladium-carbon described in step (I) is 400-2000:2-10:1-10; The mass fraction of palladium in the palladium-carbon described in step (2) is 5-30%; 3. The method for catalytically converting lignin to synthesize pyridine bases according to claim 2, wherein The mass ratio of the water-washed solution rich in lignin, copper acetate and palladium-carbon described in step (2) is 400-1500:2-4:1-8; 4. The method for catalytically converting lignin to synthesize pyridine bases according to claim 1, characterized in that, In the heating pretreatment reaction described in step (1), the mass ratio of the lignocellulose source, fatty amine and water is 10-50:2-360:8-360; In the water washing of the product mixture described in step (1), water is added for washing according to the mass ratio of the lignocellulose source to the water added for washing of 10-50:100-1500; 5. The method for catalytically converting lignin to synthesize pyridine bases according to claim 4, wherein, In the heating pretreatment reaction described in step (1), the mass ratio of the lignocellulose source, fatty amine and water is 30-50:28-150:42-150; In the water washing of the product mixture described in step (1), water is added for washing according to the mass ratio of the lignocellulose source to the water added for washing of 30-50:800-1500; 6. The method for catalytically converting lignin to synthesize pyridine bases according to claim 1, wherein The conditions of the heating pretreatment reaction described in step (1) are: reacting at 100-180°C for 1-8 h under normal pressure; the conditions of the hydrogenolysis reaction described in step (2) are: reacting at 200-300°C for 2-15 h under 0.5-4 MPa hydrogen; 7. The method for catalytically converting lignin to synthesize pyridine bases according to claim 6, characterized in that, The conditions of the heating pretreatment reaction described in step (1) are: reacting at 130-180°C for 1-3 h under normal pressure; the conditions of the hydrogenolysis reaction described in step (2) are: reacting at 250-300°C for 4-6 h under 1-3 MPa hydrogen; 8. The method for catalytically converting lignin to synthesize pyridine bases according to claim 1, wherein The lignocellulose source described in step (1) is at least one of corncob, corn straw, pine wood, eucalyptus wood, poplar wood, Manchurian ash, seabuckthorn, cypress, Chinese fir, birch, wheat straw, bagasse, rice straw, rice husk, edible mushroom substrate and peanut shell; 9. The method for catalytically converting lignin to synthesize pyridine bases according to claim 1, characterized in that, The hydrogenolysis solution containing pyridine derivatives described in step (2) is purified to obtain pyridine derivatives; the purification method is: first adjust the pH of the hydrogenolysis solution containing pyridine derivatives to acidic with an acid solution, then extract with ethyl acetate, and collect the aqueous phase after extraction layering and carry out vacuum distillation to obtain pyridine derivatives.

10. The method for catalytically converting lignin to synthesize pyridine bases according to claim 9, wherein The acid solution is at least one of hydrochloric acid, sulfuric acid and phosphoric acid, and the mass concentration of the acid solution is 2-8%; the pH of the hydrogenolysis solution containing pyridine derivatives after acidification is 1.5-3.0; the volume of the ethyl acetate is 2-4 times the volume of the hydrogenolysis solution containing pyridine derivatives.

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