CN117126632A

CN117126632A - Method for efficiently preparing adhesive by using papermaking black liquor

Info

Publication number: CN117126632A
Application number: CN202311239745.9A
Authority: CN
Inventors: 甘林火; 湛云
Original assignee: Huaqiao University
Current assignee: Huaqiao University
Priority date: 2023-09-25
Filing date: 2023-09-25
Publication date: 2023-11-28

Abstract

The invention relates to a method for efficiently preparing an adhesive by using papermaking black liquor, which comprises the following steps: s1, dropwise adding dilute acid into papermaking black liquor, and separating out lignin fraction A and filtrate B when the pH value reaches 9.5-10.5; s2, continuously dropwise adding dilute acid into the filtrate B, and separating out lignin fraction C when the pH value reaches 5.0-5.5; s3, mixing the lignin fraction A and the lignin fraction C obtained in the steps S1 and S2 according to a certain proportion, adding the mixture into a reaction container together with phenol and sodium hydroxide, heating and preserving heat, adding a first batch of formaldehyde aqueous solution, heating for reaction, adding a second batch of formaldehyde aqueous solution and urea, continuing to react, cooling after the reaction is finished, and discharging. The invention has simple process, low cost and strong feasibility, and the obtained wood adhesive has high bonding strength and good industrial application prospect.

Description

Method for efficiently preparing adhesive by using papermaking black liquor

Technical Field

The invention relates to the technical field of adhesive preparation, in particular to a method for efficiently preparing an adhesive by using papermaking black liquor.

Background

Along with exhaustion of fossil resources and exacerbation of environmental pollution problems, development of bio-based adhesive products is an important way for promoting green sustainable development of adhesives. The preparation of wood adhesives by using lignin, which is a renewable biomass resource with the most abundant aromatic ring-containing structure in nature, to replace petroleum-based phenolic compounds has become a research hotspot.

Meanwhile, the industrial pulping and papermaking process in China mainly comprises alkaline pulping, a large amount of lignin is dissolved in black liquor generated in the alkaline pulping process, and the industrial lignin can be effectively and resource utilized, so that the problem of environmental pollution caused by the black liquor in papermaking can be solved, good economic benefits can be generated, and the method has double important significance on resources and environment.

Papermaking black liquor is typically acid-separated lignin insoluble in water by one-time acid separation (pH < 3.0). Because the residual alkali amount of the black liquor is large, a large amount of acid is required to be consumed, and the filtered black liquor also needs to consume a large amount of alkali to adjust the pH value to be neutral or slightly alkaline again so as to adapt to the environmental requirement of the later biochemical treatment of the black liquor, the method has high running cost. Moreover, the industrial lignin obtained by the traditional one-time acid precipitation has the disadvantages of high molecular dispersity, lack of surface hydrophilic functional groups and reactive sites or uneven distribution and the like, so that the industrial application field is greatly limited.

Currently, in order to develop the industrial application of acid lignin in papermaking black liquor in adhesive production, scientific researchers have carried out a great deal of work on the modification and activation of industrial lignin by adopting a chemical method, and the main methods comprise demethylation, oxidation, methylolation, phenolization and the like. However, due to the harsh chemical modification conditions, the process is complex and tedious and is not environment-friendly, so that the pretreatment cost of the industrial lignin is high, and the industrial lignin is difficult to popularize and apply in the production of adhesives on a large scale.

For example, in patent application CN 103113840A, a wood adhesive is prepared by first performing a methylolation modification reaction on a papermaking black liquor with a solids content of 40% -60% after concentration and a first formaldehyde under stirring at 90±2 ℃, then adding phenol, mixing, and then performing polycondensation reaction with formaldehyde and melamine twice. The technology has high energy consumption of concentrating papermaking black liquor in the early stage, and chemical modification technology steps are added in the later stage, the bonding strength is between 0.75 and 1.15MPa, and the adhesive performance is general. The patent application CN 114686121A regulates the pH value of a system to 3-4 at the temperature of 50-60 ℃ when the papermaking black liquor with the solid content of 15-20%, and dries the disposable acid-separated lignin after washing; acid-separated lignin, an amination agent, an oxidant and N, N-dimethylformamide are subjected to oxidative ammonolysis reaction to obtain a mixed material A; reacting the mixed material A, starch, an initiator and a dispersing agent in an N, N-dimethylformamide aqueous solution, then mixing the mixture with polyvinyl alcohol, and aging to obtain a mixed material B; and (3) carrying out a first reaction on the mixed material B, phenol, formaldehyde and an alkaline compound under the catalysis of metal oxide, and then carrying out a second reaction on the mixed material B, the phenol, the formaldehyde and the alkaline compound with a coupling agent and an amide compound to obtain the wood adhesive. The process steps are complicated, the cost is high, and the bonding strength of the obtained adhesive is only 1.33-1.78MPa.

In summary, in order to promote the recycling application of papermaking black liquor in the adhesive production, the environmental pollution and the dependence on fossil resources are further reduced, and the technical difficulty is how to improve the adhesive performance of the lignin-based adhesive product and simultaneously remarkably reduce the pretreatment process cost of lignin in the papermaking black liquor.

Disclosure of Invention

The invention aims to solve the problems of high cost and low bonding strength of the existing process for preparing an adhesive by using papermaking black liquor, and provides a method for efficiently preparing the adhesive by using the papermaking black liquor. The invention provides a method for efficiently preparing an adhesive by using papermaking black liquor, which has the advantages of simple and convenient process and low cost.

In the invention, the papermaking black liquor does not need to be heated and concentrated, so that the energy consumption can be obviously reduced; compared with the acid amount required by the traditional one-step acid precipitation process (the pH value of the black liquor is adjusted to be 1.0-3.0), the sectional acid precipitation process adopted in the invention can obviously reduce the acid amount. In a specific embodiment, the first stage acid leaching process in S1 is to adjust the pH of the black liquor to 9.5-10.5, and the second stage acid leaching process in S2 is to adjust the pH of the black liquor to 5.0-5.5. In addition, the lignin filter cake after centrifugal filtration does not need to be washed, and can be directly placed in an oven for drying, so that a large amount of washing wastewater is not generated; the black filtrate after centrifugal filtration is close to neutral, basically meets the environmental requirement of later biochemical treatment of black liquor, and does not need to consume a large amount of alkali to adjust the pH value of the system to be neutral or slightly alkaline.

In the invention, lignin fraction A separated out in the first stage (under alkaline condition) has the structural characteristics of larger molecular weight, and lower surface functional group (charge) and reactive site content; the lignin C fraction separated out in the second stage (under the acid condition) has different structural characteristics of smaller molecular weight and higher surface functional group (charge) and reactive site content. By adjusting the ratio of the two components, in the polycondensation reaction with formaldehyde, lignin fraction C and part of lignin fraction A provide phenolic hydroxyl ortho-position and react with formaldehyde to generate phenolic resin, and a small amount of lignin fraction A is permeated and filled into the pores of the plate in the hot pressing process of the adhesive, so that the bonding strength of the adhesive can be obviously enhanced, and the similar additive effects such as nano cellulose and starch are exerted. In a specific embodiment, the lignin fraction a and lignin fraction C in S3 are added in a ratio of 0-2:2, more preferably the lignin fraction a and lignin fraction C are added in a ratio of 1:2.

The specific scheme is as follows:

a method for efficiently preparing an adhesive by using papermaking black liquor comprises the following steps:

s1, adding an acid solution into papermaking black liquor to enable the pH value of a reaction system to reach 9.5-10.5, filtering after reaction to obtain solid and filtrate B, and drying the solid to obtain lignin fraction A;

s2, adding an acidic solution into the filtrate B to enable the pH value of a reaction system to reach 5.0-5.5, filtering after the reaction, and drying the obtained solid to obtain lignin fraction C;

s3, adding the lignin fraction C obtained by the lignin fraction A, S2 obtained by the S1, phenol and sodium hydroxide into a reaction container, heating and reacting for a period of time, adding formaldehyde aqueous solution, increasing the reaction temperature and continuing to react for a period of time, adding formaldehyde aqueous solution and urea, and cooling after heat preservation and reaction to obtain the adhesive, wherein the mass ratio of the lignin fraction A to the lignin fraction C is 0-2:2, and the mass ratio of the lignin fraction C to the mass ratio of the phenol is=0.2-1.5:1.

Further, the solid content of the papermaking black liquor in the S1 is 18-20wt% and the lignin content is 6-8wt%.

Further, the acidic solution in S1 and/or S2 is an aqueous solution of 4-8mol/L hydrochloric acid or sulfuric acid, preferably an aqueous solution of 6mol/L sulfuric acid.

Further, the filtration in S1 and/or S2 is a centrifugal filtration, preferably at a rotational speed of 5000-15000rpm/min for 8-10min.

Further, the drying temperature in S1 and/or S2 is 60-100deg.C, preferably 60-80deg.C.

Further, the mass ratio of the lignin fraction A to the lignin fraction C in S3 is 0.5-2:2, preferably 1:2;

preferably, the mass of lignin fraction C in S3: the mass of phenol=0.2-0.5:1.

Further, the total mass of the lignin fraction A and the lignin fraction C in S3 accounts for 10-60% of the total mass of the lignin fraction A, the lignin fraction C and phenol, i.e., the degree of substitution of phenol is 10-60%, preferably, when the amount of the lignin fraction A is not 0, the degree of substitution of phenol is 20-40%; or when the lignin fraction C is used alone to replace phenol, the degree of substitution of phenol is 40-60%.

Further, mixing the lignin fraction C obtained by the lignin fraction A, S2 obtained by the step S1 in the step S3, adding the mixture into a reaction vessel together with phenol and sodium hydroxide aqueous solution, heating to 70-85 ℃ for reaction for 1-3 hours, adding formaldehyde aqueous solution, and heating to 86-95 ℃ for reaction for 10-100 minutes; then adding formaldehyde aqueous solution and urea, reacting for 10-100min under the heat preservation, and cooling after the reaction is finished to obtain the adhesive.

Further, the concentration of the formaldehyde aqueous solution in the S3 is 30-37wt%, the dosage of the formaldehyde aqueous solution accounts for 90-100% of the total mass of lignin and phenol, the formaldehyde aqueous solution is added for 2 times, and the first adding amount accounts for 30% of the total amount of the formaldehyde aqueous solution; the amount of urea is 5% of the total mass of lignin and phenol.

The invention also protects an adhesive, which is prepared by adopting the method for efficiently preparing the adhesive by using papermaking black liquor, wherein the bonding strength of the adhesive is 2.5-4.0MPa.

The beneficial effects are that:

according to the invention, the papermaking black liquor is directly subjected to the sectional acid precipitation in a specific pH range at room temperature, so that the energy consumption is obviously reduced, the acid consumption is reduced, the pretreatment process of industrial lignin in the papermaking black liquor is greatly simplified, and the unexpected technical effect is obtained, namely, the synergistic mechanism of macromolecular lignin penetration filling is cooperated when lignin active sites react with formaldehyde to generate phenolic resin by optimizing the addition proportion of the two-stage acid precipitation lignin fraction, so that the bonding strength of the prepared adhesive is obviously improved. Under the condition that the substitution degree of phenol reaches 30%, the bonding strength of the obtained adhesive is higher than that of an adhesive prepared by 100% phenol, and the adhesive has obvious technical progress effect.

In a word, the method for efficiently preparing the adhesive by using the papermaking black liquor has the advantages of simple and convenient process, low cost and environmental friendliness, and the prepared adhesive has high bonding strength and strong practicability, is favorable for large-scale popularization and has good industrial application prospect.

Detailed Description

Preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention are described below, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. The specific techniques or conditions are not identified in the examples and are performed according to techniques or conditions described in the literature in this field or according to the product specifications. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention. In the following examples, "%" refers to weight percent and parts refer to parts by weight unless explicitly stated otherwise.

The test methods used below included:

glue strength: in the invention, firstly, the adhesive is made into the plywood, and then the bonding strength is measured, and the specific method comprises the following steps: taking out poplar board with length of 100mm, width of 25mm and thickness of 2mm, uniformly applying glue on the poplar board with glue application amount of 150g/m ² . The plywood was hot pressed at 1.2MPa and 160 ℃. After the hot pressing is finished, the plywood is firstly put at room temperaturePlacing for 24h, soaking in hot water at 63 ℃ for 3h, and cooling at room temperature for 10min. And then testing the bonding strength of the plywood as the bonding strength index of the adhesive.

The main reagents used below include:

bamboo pulp black liquor is derived from New energy Co., atlanto-Bao industry Co., ltd, contains a large amount of alkali, 18-20wt% of solid content and 6-8wt% of lignin.

Example 1

A method for efficiently preparing an adhesive by using papermaking black liquor comprises the following specific steps:

1) Adding 6mol/L sulfuric acid water solution into bamboo pulp black liquor while stirring at room temperature, separating out part of lignin when the pH value of the black liquor reaches 9.7, standing, centrifuging in a centrifuge at 10000rpm/min for 10min, drying the precipitate in an oven at 80 ℃ to obtain lignin fraction A, and collecting filtrate B;

2) Continuously dripping 6mol/L sulfuric acid water solution into the filtrate B obtained after centrifugal filtration while stirring at room temperature, precipitating a large amount of residual lignin when the pH value of the black liquor reaches 5.4, standing, centrifuging in a centrifuge at 10000rpm/min for 10min, and drying the precipitate in an oven at 80 ℃ to obtain lignin fraction C;

3) 2.4g of lignin fraction A, 5.6g of phenol and 2.8mL of 40% sodium hydroxide solution were added to the reaction vessel and stirred at 80℃for 2h. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is 1.75MPa.

Example 2

1) Adding 6mol/L sulfuric acid water solution into 250mL bamboo pulp black liquor while stirring at room temperature, separating out part of lignin when the pH value of the black liquor reaches 9.7, standing, centrifuging in a centrifuge at 10000rpm/min for 10min, drying the precipitate in an oven at 80 ℃ to obtain lignin fraction A, and collecting filtrate B;

3) 2.4g lignin fraction C, 5.6g phenol and 2.8mL, 40% sodium hydroxide solution were added to the reaction vessel and stirred at 80℃for 2h. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is 1.78MPa.

Example 3

1) Adding 6mol/L sulfuric acid water solution into 500mL bamboo pulp black liquor while stirring at room temperature, when the pH value of the black liquor reaches 10.0, separating out part of lignin, standing, centrifuging in a centrifuge at 10000rpm/min for 10min, drying the precipitate in an oven at 80 ℃ to obtain lignin fraction A, and collecting filtrate B;

2) Continuously dripping 6mol/L sulfuric acid water solution into the filtrate B obtained after centrifugal filtration while stirring at room temperature, precipitating a large amount of residual lignin when the pH value of the black liquor reaches 5.2, standing, centrifuging in a centrifuge at 10000rpm/min for 10min, and drying the precipitate in an oven at 80 ℃ to obtain lignin fraction C;

3) 0.8g lignin fraction A, 1.6g lignin fraction C, 5.6g phenol and 2.8mL, 40% sodium hydroxide solution were added to the reaction vessel and stirred at 80℃for 2h. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is up to 3.95MPa.

Example 4

3) 1.2g lignin fraction A, 1.2g lignin fraction C, 5.6g phenol and 2.8mL, 40% sodium hydroxide solution were added to the reaction vessel and stirred at 80℃for 2h. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is 2.85MPa.

Example 5

3) 3.6g lignin fraction A, 4.4g phenol and 2.8mL 40% sodium hydroxide solution were added to the reaction vessel and stirred at 80℃for 2h. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is 1.78MPa.

Example 6

3) 1.6g lignin fraction A, 3.2g lignin fraction C, 3.2g phenol and 2.8mL, 40% sodium hydroxide solution were added to the reaction vessel and stirred at 80℃for 2h. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is up to 2.91MPa.

Example 7

3) 4.8g lignin fraction A, 3.2g phenol and 2.8mL 40% sodium hydroxide solution were added to the reaction vessel and stirred at 80℃for 2h. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is 1.74MPa.

Example 8

3) 3.6g lignin fraction C, 4.4g phenol and 2.8mL, 40% sodium hydroxide solution were added to the reaction vessel and stirred at 80℃for 2h. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is up to 2.72MPa.

Example 9

3) 4.8g of lignin C, 3.2g of phenol and 2.8mL of 40% sodium hydroxide solution were added to the reaction vessel and stirred at 80℃for 2h. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is up to 2.77MPa.

In contrast, the degree of substitution of phenol by lignin fraction C in example 2 was 30%, whereas the degree of substitution of phenol by fraction C alone in examples 8 and 9 was 45% and 60%, respectively, and the test results showed that a high degree of substitution of phenol by C was advantageous for improving the bonding strength.

Comparative example 1

Referring to example 1, except that acid lignin was not introduced, 8.0g of phenol and 2.8mL of 40% sodium hydroxide solution were added to the reaction vessel, and stirred at 80℃for 2 hours. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is only 1.30MPa.

Comparative example 2

With reference to examples 5 and 8, the difference is that the acid-extracted lignin is obtained by a one-time acid-extraction method, and the specific method is as follows:

1) Adding 6mol/L sulfuric acid water solution into bamboo pulp black liquor while stirring at room temperature, precipitating lignin in large quantity when the pH value of the black liquor reaches 5.0-5.5, standing, centrifuging in a centrifuge at 10000rpm/min for 10min, and drying the precipitate in an oven at 80 ℃ to obtain acid-precipitated lignin;

2) 3.6g of acid-separated lignin, 4.4g of phenol and 2.8mL of 40% sodium hydroxide solution were added to the reaction vessel, and stirred at 80℃for 2 hours. Then, 7.168mL of an aqueous formaldehyde solution (37% by mass formaldehyde) was added thereto, and the reaction was stirred at 90℃for 50 minutes. Finally, 0.4g of urea and 3.072mL of formaldehyde aqueous solution (formaldehyde mass concentration: 37%) were added, and the reaction was continued under stirring at 90℃for 40min. After the reaction is finished, the reaction system is rapidly cooled to 70 ℃, then slowly cooled to room temperature and then discharged, the adhesive is obtained, and after the adhesive is pressed, the bonding strength of the plywood is 0.79MPa.

Through observing all examples and comparative example 1, the black liquor lignin is fractionated into two lignin fractions by using a two-step acid precipitation method, and optionally, the bonding strength of an adhesive prepared by one lignin fraction or the two lignin fractions according to a certain addition proportion is higher than that of an adhesive prepared without adding lignin, and the maximum amplification is as high as 204%, so that the two-step fractionation of the industrial lignin in the papermaking black liquor or the reasonable proportioning of the two lignin fractions is favorable for improving the bonding strength of the adhesive, and is far higher than the national corresponding standard (> 0.7 MPa).

Meanwhile, comparative observations of example 5, example 8 and comparative example 2 also found that the two-step acid-leaching process was used to fractionate black liquor lignin into two lignin fractions, optionally one of which produced adhesives (1.78 MPa and 2.72 MPa) had a higher bond strength than adhesives produced from lignin obtained by one-time acid-leaching (0.79 MPa), the latter only reaching the national corresponding standard (> 0.7 MPa).

The invention adopts a simple two-stage acid precipitation process to carry out fractionation pretreatment on the industrial lignin in the papermaking black liquor, and then the bonding strength of the adhesive prepared by reasonably proportioning the two lignin fractions is obviously increased, which is far superior to the corresponding national standard, and has good application value and industrial popularization prospect.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the scope of the technical concept of the present invention, and all the simple modifications belong to the protection scope of the present invention.

In addition, the specific features described in the above embodiments may be combined in any suitable manner without contradiction. The various possible combinations of the invention are not described in detail in order to avoid unnecessary repetition.

Moreover, any combination of the various embodiments of the invention can be made without departing from the spirit of the invention, which should also be considered as disclosed herein.

Claims

1. A method for efficiently preparing an adhesive by using papermaking black liquor is characterized by comprising the following steps: the method comprises the following steps:

s3, adding the lignin fraction C obtained by the lignin fraction A, S obtained by the S1, phenol and sodium hydroxide into a reaction container, heating and reacting for a period of time, adding formaldehyde aqueous solution, increasing the reaction temperature and continuously reacting for a period of time, adding formaldehyde aqueous solution and urea, preserving heat and cooling after reaction to obtain an adhesive, wherein the mass ratio of the lignin fraction A to the lignin fraction C is 0-2:2, and the mass of lignin fraction C: mass of phenol = 0.2-1.5:1.

2. the method for efficiently preparing the adhesive by using the papermaking black liquor according to claim 1, wherein the method comprises the following steps: the solid content of the papermaking black liquor in the S1 is 18-20wt% and the lignin content is 6-8wt%.

3. The method for efficiently preparing the adhesive by using the papermaking black liquor according to claim 2, wherein the method comprises the following steps: the acidic solution in S1 and/or S2 is 4-8mol/L hydrochloric acid aqueous solution or sulfuric acid aqueous solution, preferably 6mol/L sulfuric acid aqueous solution.

4. The method for efficiently preparing the adhesive by using the papermaking black liquor according to claim 1, wherein the method comprises the following steps: the filtration in S1 and/or S2 is carried out by centrifugation, preferably at 5000-15000rpm/min for 8-10min.

5. The method for efficiently preparing the adhesive by using the papermaking black liquor according to claim 1, wherein the method comprises the following steps: the drying temperature in S1 and/or S2 is 60-100deg.C, preferably 60-80deg.C.

6. The method for efficiently preparing the adhesive by using the papermaking black liquor according to claim 1, wherein the method comprises the following steps: the mass ratio of the lignin fraction A to the lignin fraction C in the S3 is 0.5-2:2, preferably 1:2;

preferably, the mass of lignin fraction C in S3: the mass of phenol=0.2-0.5:1.

7. The method for efficiently preparing the adhesive by using the papermaking black liquor according to claim 1, wherein the method comprises the following steps: the total mass of the lignin fraction A and the lignin fraction C in the S3 accounts for 10-60% of the total mass of the lignin fraction A, the lignin fraction C and phenol, namely the substitution degree of phenol is 10-60%, and preferably, when the dosage of the lignin fraction A is not 0, the substitution degree of phenol is 20-40%; or when the lignin fraction C is used alone to replace phenol, the degree of substitution of phenol is 40-60%.

8. The method for efficiently preparing the adhesive by using the papermaking black liquor according to claim 6 or 7, wherein the method comprises the following steps: s3, mixing the lignin fraction C obtained by the lignin fraction A, S2 obtained by the S1, adding the mixture into a reaction vessel together with phenol and sodium hydroxide aqueous solution, heating to 70-85 ℃ for reaction for 1-3 hours, adding formaldehyde aqueous solution, and heating to 86-95 ℃ for reaction for 10-100 minutes; then adding formaldehyde aqueous solution and urea, reacting for 10-100min under the heat preservation, and cooling after the reaction is finished to obtain the adhesive.

9. The method for efficiently preparing the adhesive by using the papermaking black liquor according to claim 8, wherein the method comprises the following steps: the concentration of the formaldehyde aqueous solution in the S3 is 30-37wt%, the dosage of the formaldehyde aqueous solution accounts for 90-100% of the total mass of lignin and phenol, the formaldehyde aqueous solution is added for 2 times, and the dosage of the first addition accounts for 30% of the total mass of the formaldehyde aqueous solution; the amount of urea is 5% of the total mass of lignin and phenol.

10. An adhesive prepared by the method for efficiently preparing the adhesive by using papermaking black liquor according to any one of claims 1-9, which is characterized in that: the bonding strength of the adhesive is 2.5-4.0MPa.