Tobacco stem raw material treatment method

Abstract

The invention discloses a treatment method of a tobacco stem raw material. The treatment method comprises the following steps: (1) preparing a eutectic solvent; (2) uniformly mixing the eutectic solvent and the tobacco stem powder according to a certain proportion, and heating for reaction; (3) cooling to room temperature, and carrying out solid-liquid separation to obtain solid residues; and (4) carrying out enzyme hydrolysis on the obtained solid residues. The method is low in cost, high in treatment efficiency and environmentally friendly.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of comprehensive utilization of biomass, and particularly relates to a processing method of tobacco stem raw material. BACKGROUND

[0002] With the continuous depletion of fossil resources and the increasing pressure of environmental pollution, developing new renewable green energy has become a major issue of global strategic significance. Tobacco stem is a byproduct of tobacco production and processing, and its yield is huge. It is usually discarded directly and not fully utilized. Therefore, the development and utilization of such byproducts as tobacco stem can improve economic and social benefits. Wood fiber biomass such as tobacco stem is mainly composed of cellulose, hemicellulose and lignin. In the process of biomass conversion, cellulose and hemicellulose can be converted into monosaccharides such as glucose and xylose through enzymatic hydrolysis. However, due to the complex structure of lignocellulose, there are a large number of hydrogen bonds and covalent bonds between cellulose and lignin and hemicellulose molecules, forming a dense structure that is difficult to decompose and utilize, which is the main reason for limiting the utilization of lignocellulosic biomass. The main raw materials for the utilization of lignocellulosic biomass on the current market are agricultural products and some woody plants, and the utilization scheme for tobacco stem material is extremely limited.

[0003] Effective separation of lignin components in tobacco stem cell wall is beneficial to the application of tobacco stem raw material in the production of reconstituted tobacco, and has extremely high utilization value. There are various pretreatment methods for lignocellulosic biomass. The lignin and hemicellulose wrapped in cellulose are removed, the dense three-dimensional structure is destroyed, and the cellulose is fully exposed, so as to further increase the binding site and accessibility of cellulase to improve the hydrolysis efficiency of enzyme. Traditional methods include acid treatment, alkali treatment, steam explosion, physical and chemical treatment methods, but all have many shortcomings such as high cost, environmental pollution, and large equipment pressure.

[0004] Deep Eutectic Solvents (DES) is also known as deep eutectic solvent, as a new type of ionic liquid composed of hydrogen bond acceptor and hydrogen bond donor in recent years has attracted attention; its advantage lies in its large amount, simple preparation, cheap. Because a large number of hydrogen bond donors and hydrogen bond acceptors can be selected, and at the same time has great adjustability; so choose deep eutectic solvent as a pretreatment reagent, it is a very valuable pretreatment system, such as Industrial Crops & Products, 206(2023)117691 and Carbohydrate Polymers 208(2022)119105. The literature "Research on the pretreatment of sugarcane bagasse based on deep eutectic solvent system" (Luo Liang, Jinan University master thesis, 2019) uses deep eutectic solvent of choline chloride and oxalic acid to pretreat sugarcane bagasse to explore the influence of different molar ratio of deep eutectic solvent on enzymolysis, wherein the lignin removal rate is 53.15%, and the enzyme hydrolysis efficiency is 79.51%. But the deep eutectic solvent needs to combine with glycerol, ethylene glycol, or polyethylene glycol (PEG 400); the lignin removal rate and enzyme hydrolysis efficiency need to be improved.

[0005] In order to find a simple, green and environmentally friendly way to process tobacco stem raw materials, the present application is proposed. SUMMARY

[0006] The present application discloses a processing method of tobacco stem raw materials. The present application uses microwave-assisted deep eutectic solvent to pretreat tobacco stem, which has the characteristics of simple operation, low cost and high efficiency and green; and the removal rate of lignin and hemicellulose in the pretreated tobacco stem is significantly improved, and the enzyme hydrolysis efficiency is significantly improved.

[0007] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0008] A processing method of tobacco stem raw materials, comprising the following steps:

[0009] (1) preparing a deep eutectic solvent;

[0010] (2) mixing the deep eutectic solvent and tobacco stem powder uniformly according to a certain proportion, heating and reacting;

[0011] (3) cooling to room temperature, and solid-liquid separation to obtain solid residues;

[0012] (4) enzyme hydrolysis of the obtained solid residues.

[0013] Preferably, the preparation method of the deep eutectic solvent is: mixing the hydrogen bond donor and the hydrogen bond acceptor uniformly according to a certain molar ratio at a certain temperature to obtain a uniform transparent solution; that is, the deep eutectic solvent.

[0014] Preferably, the hydrogen bond donor is oxalic acid dihydrate, and the hydrogen bond acceptor is choline chloride; the molar ratio of the two is 1: (1-3); preferably 1:2; and no other chemical reagent is added for auxiliary treatment.

[0015] Preferably, the mixing temperature of the hydrogen bond donor and the hydrogen bond acceptor is 70-100℃.

[0016] Preferably, the solid-liquid mass ratio of the tobacco stem powder and the deep eutectic solvent in step (2) is 1: (10-30); the microwave heating reaction temperature is 80-120℃, and the time is 5-10 min.

[0017] Preferably, the tobacco stem powder is a powder after steam explosion and drying of the tobacco stem, the particle size is 20-80 mesh, and the water content is ≤5wt%.

[0018] Preferably, the steam explosion conditions are as follows: flow rate is 1400kg / h, steam pressure is 1.3-1.5bar; water content of the discharged material is 32-36wt%, and the discharged material temperature is 63-73℃.

[0019] Preferably, step (3) uses a vacuum filtration method for solid-liquid separation; and the solid residue is washed to neutral with deionized water and then dried.

[0020] Preferably, the enzyme in step (4) is cellulase; the hydrolysis time is not less than 4h, and the temperature is 40-60℃.

[0021] The beneficial effects of the present application are as follows:

[0022] 1. The treatment method of the present application uses a deep eutectic solvent for tobacco stem raw material, which does not need to combine with glycerol, ethylene glycol, or polyethylene glycol (PEG 400) compared with the prior art; and compared with the traditional ionic liquid method, the deep eutectic solvent is simple to prepare, low in cost, high in processing efficiency, and green and environmentally friendly.

[0023] 2. The treatment method of the present application for tobacco stem raw material realizes good separation of lignin and hemicellulose, and can completely protect the original structure of cellulose, thereby ensuring excellent hydrolysis and conversion effect. The glucose yield after enzyme hydrolysis can reach more than 80%. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The content of cellulose, hemicellulose and lignin in the tobacco stem after treatment at different temperatures in the examples.

[0025] Figure 2 The glucose yield after 72h cellulase hydrolysis of the tobacco stem after treatment at different temperatures in the examples.

[0026] Figure 3are scanning electron microscope images of TS-0, TS-80, TS-100, TS-120 under different processing conditions of the examples. DETAILED DESCRIPTION

[0027] The application will be further described in detail through specific embodiments, but this should not be understood as limiting the scope of the application to the following examples. Various replacements and changes made according to ordinary technical knowledge and conventional means in the art without departing from the above-mentioned method idea of the application should be included in the scope of the application.

[0028] A processing method of tobacco stem raw material according to the application comprises the following steps:

[0029] S1: synthesis of eutectic solvent:

[0030] The hydrogen bond donor oxalic acid dihydrate and the hydrogen bond acceptor choline chloride are placed in a conical flask in a molar ratio of 1:2, heated and stirred at 500 rpm under a water bath at 80℃, and the mixture is melted into a uniform transparent solution, which is the prepared eutectic solvent. ；

[0031] S2: microwave-assisted eutectic solvent treatment of tobacco stem: tobacco stem powder with water content ≤5wt% and particle size of 20-80 mesh is mixed with eutectic solvent in a mass ratio of 1:20, then placed in a microwave reaction kettle and mixed uniformly before reaction; the microwave heating temperature is 80-120℃, the power is 600W, and the treatment time is 5min;

[0032] S3: after the reaction is completed, the microwave reaction kettle is taken out and cooled to room temperature, the treated material of S2 is filtered under vacuum using a vacuum filtration device, and solid residues are obtained, then washed with distilled water until neutral, and dried;

[0033] S4: the obtained solid residues are subjected to enzymatic hydrolysis; the enzyme reagent is cellulase, the hydrolysis time is 72h, the temperature is 50℃, and the rotation speed is 150rpm; the glucose yield of enzyme hydrolysis is determined.

[0034] The contents of cellulose, hemicellulose and lignin in the tobacco stem components are determined, and the cellulose recovery rate and the lignin and hemicellulose removal rate are calculated.

[0035] The component determination of the tobacco stem used the standard analysis procedure of the U.S. National Renewable Energy Laboratory; the steps were: 0.3 g of tobacco stem was mixed with 72% sulfuric acid solution, and after being kept in a 30°C water bath for 1 h, 84 mL of distilled water was added, and it was put into a 121°C high-pressure steam sterilization pot for 45 min, and finally the vacuum filtration device combined with a G3 sand core crucible funnel was used to separate the solid-liquid after the reaction; the solid component was washed to neutral with distilled water and then dried, and was put into a muffle furnace, ashed at 600°C, and the lignin content was calculated, and the liquid part was analyzed for glucose (cellulose) and xylose (hemicellulose) content by high performance liquid chromatography.

[0036] The calculation formula is as follows:

[0037] Solid recovery rate: ;

[0038] Cellulose recovery rate: ;

[0039] Hemicellulose removal rate: ;

[0040] Lignin removal rate: ;

[0041] Enzymatic hydrolysis glucose yield: ;

[0042] Wherein, glucose yield: g / L; system volume: L; sample mass: g; 0.9-coefficient.

[0043] The tobacco stem powder is the powder after drying the steam exploded tobacco stem. The steam explosion conditions of the tobacco stem are shown in the following table:

[0044]

[0045] Example 1:

[0046] 5 g of steam exploded tobacco stem powder with a particle size of 60 mesh and water content of 3 wt% (named TS-0) was added to a reaction kettle, mixed with 50 g of eutectic solvent, mixed uniformly to ensure that the eutectic solvent and the powder were fully contacted; the reaction kettle was put into a microwave reactor, the working frequency was set to 600 W, the reaction time was 5 min, and the reaction temperature was 80°C; the mixture after reaction was vacuum filtered to obtain solid residue, which was washed with distilled water to neutral, dried, and then TS-80 was obtained;

[0047] The lignin, cellulose, and hemicellulose contents of the tobacco stems treated in this example were 37.78%, 63.15%, and 0%, respectively. The solid recovery rate, lignin removal rate, hemicellulose removal rate, and cellulose recovery rate were 24.7%, 51.8%, 100%, and 100%, respectively. The glucose yield after 72 h enzymatic hydrolysis was 51.85%.

[0048] Example 2

[0049] 5 g of steam-exploded tobacco stem powder (TS-0) was added to a reaction kettle and mixed with 50 g of deep eutectic solvent. The mixture was mixed evenly to ensure that the deep eutectic solvent and the powder were in full contact. The reaction kettle was placed in a microwave reactor, and the working frequency was set to 600 W. The reaction time was 5 min, and the reaction temperature was 100°C. After the reaction, the mixture was vacuum filtered to obtain a solid residue, which was then washed with distilled water until it was neutral. The residue was dried to obtain TS-100.

[0050] The lignin, cellulose, and hemicellulose contents of the tobacco stems treated in this example were 19.86%, 62.76%, and 0%, respectively. The solid recovery rate, lignin removal rate, hemicellulose removal rate, and cellulose recovery rate were 29.95%, 69.28%, 100%, and 100%, respectively. The glucose yield after 72 h enzymatic hydrolysis was 83.37%.

[0051] Example 3

[0052] 5 g of steam-exploded tobacco stem powder (TS-0) was added to a reaction kettle and mixed with 50 g of deep eutectic solvent. The mixture was mixed evenly to ensure that the deep eutectic solvent and the powder were in full contact. The reaction kettle was placed in a microwave reactor, and the working frequency was set to 600 W. The reaction time was 5 min, and the reaction temperature was 120°C. After the reaction, the mixture was vacuum filtered to obtain a solid residue, which was then washed with distilled water until it was neutral. The residue was dried to obtain TS-120.

[0053] The lignin, cellulose, and hemicellulose contents of the tobacco stems treated in this example were 36.41%, 55.73%, and 0%, respectively. The solid recovery rate, lignin removal rate, hemicellulose removal rate, and cellulose recovery rate were 21.55%, 59.47%, 100%, and 82%, respectively. The glucose yield after 72 h enzymatic hydrolysis was 65.6%.

[0054] Figure 1 The lignin, cellulose, and hemicellulose contents of the tobacco stems treated in this example were 37.78%, 63.15%, and 0%, respectively. The solid recovery rate, lignin removal rate, hemicellulose removal rate, and cellulose recovery rate were 24.7%, 51.8%, 100%, and 100%, respectively. The glucose yield after 72 h enzymatic hydrolysis was 51.85%. Figure 2 The lignin, cellulose, and hemicellulose contents of the tobacco stems treated in this example were 19.86%, 62.76%, and 0%, respectively. The solid recovery rate, lignin removal rate, hemicellulose removal rate, and cellulose recovery rate were 29.95%, 69.28%, 100%, and 100%, respectively. The glucose yield after 72 h enzymatic hydrolysis was 83.37%. Figure 3are TS-0, TS-80, TS-100, TS-120 scanning electron micrographs under different processing conditions of examples.

[0055] By Figure 1 and Figure 2 It can be seen that the treated samples maintain a high cellulose recovery rate and its original structure, and the cellulase hydrolysis efficiency is also maintained at a high level, reaching more than 80%. The steam exploded tobacco stem powder raw material has a loose structure itself, so the enzyme hydrolysis efficiency is also good (>60%). By Figure 3 It can be seen that the aqueous and oxalic acid-based deep eutectic solvent has a significant component separation and structure disintegration effect on the tobacco stem sample, and the phenomenon is more obvious at a higher treatment temperature. The sample treated at 120℃ has the most serious structure disintegration, which is beneficial to the removal of lignin and hemicellulose and cellulase hydrolysis; however, the cellulose recovery rate and glucose yield after cellulase hydrolysis are reduced. Therefore, the temperature of the aqueous and oxalic acid-based deep eutectic solvent is not the higher the better for the steam exploded tobacco stem sample. The exploded tobacco stem is beneficial to the treatment of the aqueous and oxalic acid-based deep eutectic solvent at a low temperature.

[0056] The above description is only used to specifically introduce the embodiments of the present application, but the technical solutions proposed by the present application are not limited to the above methods. Equivalent modifications and changes made by those skilled in the art to the technical solutions proposed by the present application should be covered in the scope of the claims of the present application without departing from the basic principles of the present technology.

Claims

1. A method for processing tobacco stem raw materials, characterized in that, Includes the following steps: (1) Preparation of eutectic solvent; (2) Mix the eutectic solvent and tobacco stem powder in a certain proportion and heat to carry out the reaction; (3) Cool to room temperature and separate the solid and liquid to obtain a solid residue; (4) The obtained solid residue is subjected to enzymatic hydrolysis.

2. The processing method according to claim 1, characterized in that, The method for preparing the eutectic solvent is as follows: hydrogen bond donors and hydrogen bond acceptors are mixed uniformly at a certain temperature according to a certain molar ratio to obtain a homogeneous and transparent solution; this is the eutectic solvent.

3. The processing method according to claim 2, characterized in that, The hydrogen bond donor is oxalic acid dihydrate, and the hydrogen bond acceptor is choline chloride; the molar ratio of the two is 1:(1-3).

4. The processing method according to claim 2, characterized in that, The mixing temperature of hydrogen bond donors and hydrogen bond acceptors is 70-100℃.

5. The processing method according to claim 1, characterized in that, Step (2) The solid-liquid mass ratio of tobacco stem powder and eutectic solvent is 1:(10-30); the microwave heating reaction temperature is 80-120℃ and the time is 5-10min.

6. The processing method according to any one of claims 1 or 5, characterized in that, The tobacco stem powder is the powder obtained after drying tobacco stems by steam explosion, with a particle size of 20-80 mesh and a water content of ≤5wt%.

7. The processing method according to claim 5, characterized in that, The conditions for steam explosion are as follows: flow rate: 1400 kg / h, steam pressure: 1.3-1.5 bar; discharge water content: 32-36 wt%, discharge temperature: 63-73℃.

8. The processing method according to claim 1, characterized in that, Step (3) Solid-liquid separation is performed by vacuum filtration; the solid residue is washed with deionized water until neutral and then dried.

9. A method for pretreating tobacco stems according to claim 1, characterized in that, The enzyme used in step (4) is cellulase; the hydrolysis time is no less than 4 hours and the temperature is 40-60℃.

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