CN113861437A - A method for fractionating lignin from straw pulping black liquor - Google Patents
A method for fractionating lignin from straw pulping black liquor Download PDFInfo
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- 229920005610 lignin Polymers 0.000 title claims abstract description 123
- 239000010902 straw Substances 0.000 title claims abstract description 31
- 238000004537 pulping Methods 0.000 title claims abstract description 29
- 238000000034 method Methods 0.000 title claims abstract description 27
- 238000003756 stirring Methods 0.000 claims abstract description 127
- 239000007788 liquid Substances 0.000 claims abstract description 39
- 238000009826 distribution Methods 0.000 claims abstract description 9
- 239000007787 solid Substances 0.000 claims abstract description 9
- 238000005119 centrifugation Methods 0.000 claims abstract description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 51
- 238000000926 separation method Methods 0.000 claims description 26
- 229920002472 Starch Polymers 0.000 claims description 25
- 235000019698 starch Nutrition 0.000 claims description 25
- 239000008107 starch Substances 0.000 claims description 25
- 238000005303 weighing Methods 0.000 claims description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 13
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 12
- 238000006467 substitution reaction Methods 0.000 claims description 11
- 125000002091 cationic group Chemical group 0.000 claims description 9
- CSPHGSFZFWKVDL-UHFFFAOYSA-M (3-chloro-2-hydroxypropyl)-trimethylazanium;chloride Chemical compound [Cl-].C[N+](C)(C)CC(O)CCl CSPHGSFZFWKVDL-UHFFFAOYSA-M 0.000 claims description 6
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 6
- 238000005227 gel permeation chromatography Methods 0.000 claims description 5
- 230000003113 alkalizing effect Effects 0.000 claims description 3
- 238000001914 filtration Methods 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- 239000000843 powder Substances 0.000 claims description 3
- 230000001376 precipitating effect Effects 0.000 claims description 3
- 238000002360 preparation method Methods 0.000 claims description 3
- 238000010008 shearing Methods 0.000 claims description 3
- 238000002791 soaking Methods 0.000 claims description 3
- 238000001291 vacuum drying Methods 0.000 claims description 3
- 238000005406 washing Methods 0.000 claims description 3
- 238000005189 flocculation Methods 0.000 abstract description 20
- 230000016615 flocculation Effects 0.000 abstract description 20
- 230000000694 effects Effects 0.000 abstract description 4
- 239000012528 membrane Substances 0.000 description 20
- 239000006228 supernatant Substances 0.000 description 13
- 239000002253 acid Substances 0.000 description 7
- 239000002904 solvent Substances 0.000 description 5
- 238000001556 precipitation Methods 0.000 description 4
- 238000000638 solvent extraction Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 239000002028 Biomass Substances 0.000 description 2
- 238000003916 acid precipitation Methods 0.000 description 2
- 239000003513 alkali Substances 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 238000005194 fractionation Methods 0.000 description 2
- 238000009776 industrial production Methods 0.000 description 2
- 230000007935 neutral effect Effects 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 238000000108 ultra-filtration Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 125000003118 aryl group Chemical group 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 230000005591 charge neutralization Effects 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000008394 flocculating agent Substances 0.000 description 1
- 231100001261 hazardous Toxicity 0.000 description 1
- 231100000086 high toxicity Toxicity 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 230000020477 pH reduction Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
- C08H6/00—Macromolecular compounds derived from lignin, e.g. tannins, humic acids
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Biochemistry (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
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Abstract
本申请公开一种从秸秆制浆黑液中分级分离木质素的方法，选用秸秆造纸制浆黑液，调节pH=8~10，称取后黑液倒入烧杯；配制10‑20g/L的St‑CTA溶液；移液枪移取St‑CTA溶液加入烧杯中；搅拌后静置；然后离心分离，获得木质素组分L1，收集离心后的液体；pH调至6~8后，加入絮凝剂搅拌后静置；然后以离心分离，获得木质素组分L2，收集离心后的液体；pH调至4~6后，加入絮凝剂搅拌后静置；然后离心分离，获得木质素组分L3；将获得的木质素组分L1、L2和L3，冷冻干燥，得到不同分子量分布的木质素固体；本发明分级目标明确，处理效果显著，操作工艺简单，所需设备及投资较小，综合生成成本低。
The application discloses a method for classifying and separating lignin from straw pulping black liquor. The straw pulping black liquor is selected, pH is adjusted to 8-10, and the black liquor is weighed and poured into a beaker; St-CTA solution; pipette the St-CTA solution into the beaker; stir and let stand; then centrifuge to obtain lignin fraction L1, collect the centrifuged liquid; after pH is adjusted to 6~8, add flocculation Then, centrifuge to obtain lignin component L2, and collect the liquid after centrifugation; after pH is adjusted to 4~6, add flocculant and stir and let stand; then centrifuge to obtain lignin component L3 The obtained lignin components L1, L2 and L3 are freeze-dried to obtain lignin solids with different molecular weight distributions; the present invention has clear grading objectives, remarkable treatment effect, simple operation process, small required equipment and investment, and comprehensively generates low cost.
Description
Technical Field
The application relates to the technical field of biomass resource recycling, in particular to a method for separating lignin from straw pulping black liquor in a grading manner.
Background
The biomass resource has the characteristics of low pollution, regeneration and wide distribution range, and is a potential substance capable of replacing fossil resources. As a big agricultural country in China, more than 7 hundred million tons of straws can be generated every year, and the characteristics of 20-25 percent of lignin in the straws, high carbon content of the lignin, low cost and aromatic characteristic enable the lignin to have great potential advantages in the aspects of preparing fireproof materials, synthesizing flocculating agents, water reducing agents and the like. However, lignin has the disadvantages of complex structure, difficult separation and extraction, high extraction cost and the like, so that mass production on a large scale is difficult, and the efficient utilization efficiency of lignin is remarkably reduced.
Fractionation of lignin has been an important means to obtain lignin fractions with narrow molecular weight distribution, well defined chemical composition and function. The main lignin fractionation methods at present are the following four: (1) acid addition selective precipitation; (2) membrane-assisted ultrafiltration; (3) and (4) solvent extraction.
The acid precipitation is to add strong acid to gradually acidify the alkaline black liquid to precipitate the lignin, but the acid precipitation condition is not easy to control, a large amount of acid needs to be added, the equipment requirement is high, the treated alkali liquor is easy to cause secondary pollution, and the recovered lignin has high viscosity and is not easy to separate. The membrane-assisted ultrafiltration uses differential pressure as a driving force to fractionate the black liquor through membranes with different membrane molecular weight cut-offs, but the equipment requirement is high, the energy demand is large, the cost is high, and the membrane pores are easy to block to cause membrane pollution. The solvent extraction is to extract lignin by using different organic solvents, but most of the solvents are based on dangerous solvents, and have the disadvantages of complex solvents, high toxicity, high grading cost and high risk, so the solvent extraction is not suitable for industrial production.
Content of application
The technical problem to be solved is as follows:
the technical problems to be solved by the application are that in the prior art, the acidification condition is not easy to control, a large amount of acid needs to be added, the equipment requirement is high, the alkali liquor after treatment easily causes secondary pollution, the recovered lignin has high viscosity and is not easy to separate, the equipment requirement is high, the energy requirement is high, the cost is high, membrane pores are easy to block to cause membrane pollution, the method is based on a hazardous solvent, the solvent is complex, the toxicity is high, the grading cost is high, the risk is large, and the method is not suitable for industrial production and the like.
The technical scheme is as follows:
a method for separating lignin from straw pulping black liquor in a grading way comprises the following steps:
the first step is as follows: selecting straw papermaking pulping black liquor, measuring the pH value of untreated black liquor, adding concentrated hydrochloric acid to adjust the pH value to be = 8-10, weighing 100mL of black liquor by using a measuring cylinder, and pouring the black liquor into a beaker;
the second step is that: weighing St-CTA starch-based flocculant with a cationic substitution degree of 70-95%, dissolving the St-CTA starch-based flocculant in 100mL of pure water, and preparing a St-CTA solution with the concentration of 10-20 g/L;
the third step: 3-14mL of St-CTA solution is transferred by a liquid transfer gun and added into the beaker in the first step while stirring;
the fourth step: firstly, stirring at a stirring speed of 200-250r/min for 3-10min, then stirring at a stirring speed of 40-60r/min for 10-20min, and finally standing for 2-10 h; then centrifuging at the rotating speed of 7000-;
the fifth step: continuously adding a hydrochloric acid solution into the centrifuged liquid collected in the fourth step, adjusting the pH of the solution to 6-8, adding a 2-8mLSt-CTA solution, stirring at a stirring speed of 200-250r/min for 3-10min, stirring at a stirring speed of 40-60r/min for 10-20min, and standing for 2-10 h; then centrifuging at the rotating speed of 7000-;
and a sixth step: continuously adding a hydrochloric acid solution into the centrifuged liquid collected in the fifth step, adjusting the pH of the solution to 4-6, adding a 2-8mLSt-CTA solution, stirring at a stirring speed of 200-250r/min for 3-10min, stirring at a stirring speed of 40-60r/min for 10-20min, and standing for 2-10 h; then centrifuging at the rotating speed of 7000-;
the seventh step: the obtained lignin components L1, L2 and L3 were freeze-dried to obtain lignin solids with different molecular weight distributions.
As a preferred technical scheme of the application: the molecular weight distribution ranges of the different molecular weight lignin components L1, L2 and L3 obtained in the seventh step are respectively greater than 5000Da, 1000 to 5000Da and less than 1000Da as evidenced by GPC gel permeation chromatography.
As a preferred technical scheme of the application: and in the second step, the preparation method of the St-CTA starch-based flocculant comprises the steps of dissolving 0.25g of KOH in 15mL of pure water to prepare a KOH solution, weighing 1.62g of starch to dissolve in the KOH solution, alkalizing for half an hour at 50-100 ℃ in a four-necked flask, adding 0.4-0.41g of (3-chloro-2-hydroxypropyl) trimethyl ammonium Chloride (CTA) powder into 5mL of the alkalized starch solution for half an hour, continuously reacting for 2 hours at 50-100 ℃, adding 0.5mL of concentrated HCl to adjust the pH, continuously stirring for 5 minutes, precipitating and washing in acetone, pouring into an ethanol solution, shearing, stirring and soaking in ethanol for 1 hour, filtering, and vacuum drying at 60 ℃ overnight to obtain the product.
As a preferred technical scheme of the application: in the second step, the concentration of St-CTA was 20g/L, the degree of substitution 90%.
As a preferred technical scheme of the application: in the first step, the pH =9, and in the third step, the amount of St-CTA added is 3 mL; in the fourth step, the mixture is quickly stirred for 5min at the stirring speed of 250 r/min; stirring at a low speed of 50r/min for 20 min; standing for 8 h; the centrifugation speed is 8000rpm, and the time is 8 min.
As a preferred technical scheme of the application: in the fifth step, pH =7, St-CTA was dosed in 4 mL.
As a preferred technical scheme of the application: in the sixth step, pH =5, St-CTA was dosed in 4 mL.
As a preferred technical scheme of the application: the pH of the untreated black liquor in the first step, pH = 13.
Has the advantages that:
compared with the prior art, the method for separating lignin from straw pulping black liquor by stages has the following technical effects:
1. the starch-based flocculant has the advantages of wide availability, low cost, environmental friendliness, biodegradability and the like;
2. can be carried out under neutral condition without adding a large amount of acid or acid-resistant equipment;
3. the structure of lignin is not damaged, and the pollution is small;
4. the invention has the advantages of clear grading target, obvious treatment effect, simple operation process, less required equipment and investment and low comprehensive generation cost.
5. The flocculation-precipitation method is to separate lignin by adding flocculant for precipitation, and has the advantages of capability of separation under neutral condition, reduced acid consumption, no need of acid-proof equipment, low cost, less pollution, and easy acquisition of lignin with concentrated molecular weight distribution. Starch-3-chloro-2-hydroxypropyl triethyl ammonium chloride (St-CTA) is a cationic starch-based flocculant, and St-CTA has strong charge neutralization and bonding bridging effects and can effectively polymerize and precipitate substances in water.
Drawings
FIG. 1 is a gel permeation chromatogram of black liquor lignin;
FIG. 2 is a gel permeation chromatogram of lignin component L1;
FIG. 3 is a gel permeation chromatogram of lignin component L2;
FIG. 4 is a gel permeation chromatogram of lignin component L3;
FIG. 5 shows the lignin content of different molecular weights in the components L1, L2 and L3 of example 1;
FIG. 6 is the content of lignin of different molecular weights in the components L1, L2, L3 of example 2;
FIG. 7 is the content of lignin of different molecular weights in the components L1, L2, L3 of example 3;
FIG. 8 is the content of lignin of different molecular weights in the components L1, L2, L3 of example 4;
FIG. 9 shows the content of lignin of different molecular weights in the components L1, L2 and L3 of example 5;
FIG. 10 is the content of lignin of different molecular weights in the components L1, L2, L3 of example 6;
FIG. 11 is a graph of turbidity removal results of supernatants after each flocculation of examples 1-6.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention, but it should not be understood that the scope of the present invention is limited to the following examples. Various substitutions and alterations can be made by those skilled in the art and by conventional means without departing from the spirit of the method of the invention described above.
Example 1:
a method for separating lignin from straw pulping black liquor in a grading way comprises the following steps:
the first step is as follows: selecting straw papermaking pulping black liquor, measuring the pH =13 of the untreated black liquor, adding concentrated hydrochloric acid to adjust the pH =10, weighing 100mL of lignin solution to be treated by a measuring cylinder, and pouring the lignin solution into a beaker;
the second step is that: weighing 2g of St-CTA starch-based flocculant with a cationic substitution degree of 70 percent, dissolving in 100mL of pure water, and preparing 20g/L of St-CTA solution;
the third step: 3mL of St-CTA solution is transferred by a liquid transfer gun and added into the black liquor in the first step while stirring;
the fourth step: firstly, quickly stirring for 5min at the stirring speed of 250 r/min; then slowly stirring for 15min at the stirring speed of 50 r/min; and finally standing for 6 hours. Then carrying out centrifugal separation at the rotation speed of 8000rpm for 8min to obtain a lignin component L1, and collecting centrifuged liquid;
the fifth step: hydrochloric acid solution was further added to the centrifuged liquid collected in the fourth step, and after the pH of the solution was slowly adjusted to 8, 4mL of St-CTA solution was added with stirring. Firstly, quickly stirring for 5min at the stirring speed of 250 r/min; then slowly stirring for 15min at the stirring speed of 50 r/min; and finally standing for 6 hours. Then carrying out centrifugal separation at the rotation speed of 8000rpm for 8min to obtain a lignin component L2, and collecting centrifuged liquid;
and a sixth step: and (3) continuously adding a hydrochloric acid solution into the centrifuged liquid collected in the fifth step, slowly adjusting the pH of the solution to 6, and adding a 3mLSt-CTA solution while stirring. Firstly, quickly stirring for 5min at the stirring speed of 250 r/min; then slowly stirring for 15min at the stirring speed of 50 r/min; and finally standing for 6 hours. Then centrifugally separating at 8000rpm for 8min to obtain lignin component L3;
the seventh step: the obtained lignin components L1, L2 and L3 were freeze-dried to obtain a lignin solid. Passing the supernatant through 5000Da and 1000Da membranes before and after each flocculation, and testing TOC before and after the membranes, wherein FIG. 5 shows the content of lignin with different molecular weights in components L1, L2 and L3; and turbidity before and after flocculation was measured, and fig. 11 is a graph showing the turbidity removal rate of the supernatant after each flocculation.
The preparation method of the St-CTA starch-based flocculant comprises the steps of dissolving 0.25g of KOH in 15mL of pure water to prepare a KOH solution, weighing 1.62g of starch to dissolve in the KOH solution, alkalizing for half an hour at 50-100 ℃ in a four-necked flask, adding 0.4-0.41g of (3-chloro-2-hydroxypropyl) trimethylammonium Chloride (CTA) powder into 5mL of the alkalized starch solution for half an hour, continuously reacting for 2 hours at 50-100 ℃, adding 0.5mL of concentrated HCl to adjust the pH, continuously stirring for 5 minutes, precipitating and washing in acetone, pouring into an ethanol solution, shearing, stirring and soaking in ethanol for 1 hour, filtering, and vacuum-drying at 60 ℃ overnight to obtain a product.
Example 2
A method for separating lignin from straw pulping black liquor in a grading way comprises the following steps:
the first step is as follows: selecting straw papermaking pulping black liquor, measuring the pH =13 of the untreated black liquor, adding concentrated hydrochloric acid to adjust the pH =9, weighing 100mL of lignin solution to be treated by a measuring cylinder, and pouring the lignin solution into a beaker;
the second step is that: weighing 2g of St-CTA starch-based flocculant with a cationic substitution degree of 95 percent, dissolving the St-CTA starch-based flocculant in 100mL of pure water, and preparing 20g/L of St-CTA solution;
the third step: 5mL of St-CTA solution is transferred by a liquid transfer gun and added into the beaker in the first step while stirring;
the fourth step: firstly, quickly stirring for 5min at the stirring speed of 240 r/min; then slowly stirring for 15min at the stirring speed of 50 r/min; and finally standing for 2 hours. Then carrying out centrifugal separation at the rotating speed of 7500rpm for 8min to obtain a lignin component L1, and collecting centrifuged liquid;
the fifth step: continuously adding hydrochloric acid solution into the centrifuged liquid collected in the fourth step, slowly adjusting the pH of the solution to 7, adding 4mLSt-CTA solution while stirring, and quickly stirring for 5min at a stirring speed of 240 r/min; then slowly stirring for 15min at the stirring speed of 50 r/min; and finally standing for 2 hours. Then carrying out centrifugal separation at the rotating speed of 7500rpm for 8min to obtain a lignin component L2, and collecting centrifuged liquid;
and a sixth step: continuously adding a hydrochloric acid solution into the centrifuged liquid collected in the fifth step, slowly adjusting the pH of the solution to 5, adding 4mL of St-CTA solution while stirring, and quickly stirring for 5min at a stirring speed of 240 r/min; then slowly stirring for 15min at the stirring speed of 50 r/min; and finally standing for 2 hours. Then carrying out centrifugal separation at the rotating speed of 7500rpm for 8min to obtain a lignin component L3;
the seventh step: the obtained lignin components L1, L2 and L3 were freeze-dried to obtain a lignin solid. Passing the supernatant through 5000Da and 1000Da membranes before and after each flocculation, and testing TOC before and after the membranes, wherein FIG. 6 shows the content of lignin with different molecular weights in components L1, L2 and L3; and turbidity before and after flocculation was measured, and fig. 11 is a graph showing the turbidity removal rate of the supernatant after each flocculation.
Example 3
A method for separating lignin from straw pulping black liquor in a grading way comprises the following steps:
the first step is as follows: selecting straw papermaking pulping black liquor, measuring the pH =13 of the untreated black liquor, adding concentrated hydrochloric acid to adjust the pH =9, weighing 100mL of lignin solution to be treated by a measuring cylinder, and pouring the lignin solution into a beaker;
the second step is that: weighing 2g of St-CTA starch-based flocculant with 90% cationic substitution degree, dissolving the St-CTA starch-based flocculant in 100mL of pure water, and preparing 20g/L of St-CTA solution;
the third step: transferring 7mL of St-CTA solution by a liquid transfer gun, and adding the St-CTA solution into the beaker in the first step while stirring;
the fourth step: firstly, quickly stirring for 5min at the stirring speed of 250 r/min; then slowly stirring for 10min at the stirring speed of 50 r/min; and finally standing for 8 hours. Then carrying out centrifugal separation at the rotating speed of 8500rpm for 10min to obtain a lignin component L1, and collecting centrifuged liquid;
the fifth step: continuously adding hydrochloric acid solution into the centrifuged liquid collected in the fourth step, slowly adjusting the pH of the solution to 7, adding 5mLSt-CTA solution while stirring, and quickly stirring for 5min at a stirring speed of 250 r/min; then slowly stirring for 10min at the stirring speed of 50 r/min; and finally standing for 8 hours. Then carrying out centrifugal separation at the rotating speed of 8500rpm for 10min to obtain a lignin component L2, and collecting centrifuged liquid;
and a sixth step: continuously adding hydrochloric acid solution into the centrifuged liquid collected in the fifth step, slowly adjusting the pH of the solution to 5, adding 2mLSt-CTA solution while stirring, and quickly stirring for 5min at a stirring speed of 250 r/min; then slowly stirring for 10min at the stirring speed of 50 r/min; and finally standing for 8 hours. Then carrying out centrifugal separation at the rotating speed of 8500rpm for 10min to obtain a lignin component L3;
the seventh step: the obtained lignin components L1, L2 and L3 were freeze-dried to obtain a lignin solid. Passing the supernatant through 5000Da and 1000Da membranes before and after each flocculation, and testing TOC before and after the membranes, wherein FIG. 7 shows the content of lignin with different molecular weights in components L1, L2 and L3; and turbidity before and after flocculation was measured, and fig. 11 is a graph showing the turbidity removal rate of the supernatant after each flocculation.
Example 4
A method for separating lignin from straw pulping black liquor in a grading way comprises the following steps:
the first step is as follows: selecting straw papermaking pulping black liquor, measuring the pH =13 of the untreated black liquor, adding concentrated hydrochloric acid to adjust the pH =8, weighing 100mL of lignin solution to be treated by a measuring cylinder, and pouring the lignin solution into a beaker;
the second step is that: weighing 2g of St-CTA starch-based flocculant with 80% cationic substitution degree, dissolving in 100mL of pure water, and preparing 20g/L of St-CTA solution;
the third step: transferring 3mL of St-CTA solution by a liquid transfer gun, and adding the St-CTA solution into the beaker in the first step while stirring;
the fourth step: firstly, quickly stirring for 10min at the stirring speed of 200 r/min; then slowly stirring for 20min at the stirring speed of 50 r/min; and finally standing for 8 hours. Then carrying out centrifugal separation at the rotation speed of 8000rpm for 10min to obtain a lignin component L1, and collecting centrifuged liquid;
the fifth step: continuously adding hydrochloric acid solution into the centrifuged liquid collected in the fourth step, slowly adjusting the pH of the solution to 6, adding 2mLSt-CTA solution while stirring, and quickly stirring for 10min at the stirring speed of 200 r/min; then slowly stirring for 20min at the stirring speed of 50 r/min; and finally standing for 8 hours. Then carrying out centrifugal separation at the rotation speed of 8000rpm for 10min to obtain a lignin component L2, and collecting centrifuged liquid;
and a sixth step: continuously adding hydrochloric acid solution into the centrifuged liquid collected in the fifth step, slowly adjusting the pH of the solution to 4, adding 2mLSt-CTA solution while stirring, and quickly stirring for 10min at the stirring speed of 200 r/min; then slowly stirring for 20min at the stirring speed of 50 r/min; and finally standing for 8 hours. Then carrying out centrifugal separation at the rotating speed of 8000rpm for 10min to obtain a lignin component L3;
the seventh step: the obtained lignin components L1, L2 and L3 were freeze-dried to obtain a lignin solid. Passing the supernatant through 5000Da and 1000Da membranes before and after each flocculation, and testing TOC before and after the membranes, wherein FIG. 8 shows the content of lignin with different molecular weights in components L1, L2 and L3; and turbidity before and after flocculation was measured, and fig. 11 is a graph showing the turbidity removal rate of the supernatant after each flocculation.
Example 5
A method for separating lignin from straw pulping black liquor in a grading way comprises the following steps:
the first step is as follows: selecting straw papermaking pulping black liquor, measuring the pH =13 of the untreated black liquor, adding concentrated hydrochloric acid to adjust the pH =8, weighing 100mL of lignin solution to be treated by a measuring cylinder, and pouring the lignin solution into a beaker;
the second step is that: weighing 2g of St-CTA starch-based flocculant with 90% cationic substitution degree, dissolving the St-CTA starch-based flocculant in 100mL of pure water, and preparing 20g/L of St-CTA solution;
the third step: a liquid transfer gun transfers 4mL of St-CTA solution and adds the St-CTA solution into the beaker in the first step while stirring;
the fourth step: firstly, quickly stirring for 3min at the stirring speed of 230 r/min; then slowly stirring for 20min at the stirring speed of 60 r/min; and finally standing for 10 hours. Then carrying out centrifugal separation at the rotation speed of 8000rpm for 9min to obtain a lignin component L1, and collecting centrifuged liquid;
the fifth step: continuously adding hydrochloric acid solution into the centrifuged liquid collected in the fourth step, slowly adjusting the pH of the solution to 6, adding 3mLSt-CTA solution while stirring, and quickly stirring for 3min at a stirring speed of 230 r/min; then slowly stirring for 20min at the stirring speed of 60 r/min; and finally standing for 10 hours. Then carrying out centrifugal separation at the rotation speed of 8000rpm for 9min to obtain a lignin component L2, and collecting centrifuged liquid;
and a sixth step: continuously adding hydrochloric acid solution into the centrifuged liquid collected in the fifth step, slowly adjusting the pH of the solution to 4, adding 4mLSt-CTA solution, and rapidly stirring for 3min at a stirring speed of 230 r/min; then slowly stirring for 20min at the stirring speed of 60 r/min; and finally standing for 10 hours. Then carrying out centrifugal separation at the rotating speed of 8000rpm for 9min to obtain a lignin component L3;
the seventh step: the obtained lignin components L1, L2 and L3 were freeze-dried to obtain a lignin solid. Passing the supernatant through 5000Da and 1000Da membranes before and after each flocculation, and testing TOC before and after the membranes, wherein FIG. 9 shows the content of lignin with different molecular weights in components L1, L2 and L3; and turbidity before and after flocculation was measured, and fig. 11 is a graph showing the turbidity removal rate of the supernatant after each flocculation.
Example 6
A method for separating lignin from straw pulping black liquor in a grading way comprises the following steps:
the first step is as follows: selecting straw papermaking pulping black liquor, measuring the pH =13 of the untreated black liquor, adding concentrated hydrochloric acid to adjust the pH =9, weighing 100mL of lignin solution to be treated by a measuring cylinder, and pouring the lignin solution into a beaker;
the second step is that: weighing 2g of St-CTA starch-based flocculant with a cationic substitution degree of 95 percent, dissolving the St-CTA starch-based flocculant in 100mL of pure water, and preparing 20g/L of St-CTA solution;
the third step: transferring 3mL of St-CTA solution by a liquid transfer gun, and adding the St-CTA solution into the beaker in the first step while stirring;
the fourth step: firstly, quickly stirring for 5min at the stirring speed of 250 r/min; then slowly stirring for 15min at the stirring speed of 50 r/min; and finally standing for 8 hours. Then carrying out centrifugal separation at the rotating speed of 8500rpm for 8min to obtain a lignin component L1, and collecting centrifuged liquid;
the fifth step: continuously adding hydrochloric acid solution into the centrifuged liquid collected in the fourth step, slowly adjusting the pH of the solution to 7, adding 4mLSt-CTA solution while stirring, and quickly stirring for 5min at a stirring speed of 250 r/min; then slowly stirring for 15min at the stirring speed of 50 r/min; and finally standing for 8 hours. Then carrying out centrifugal separation at the rotating speed of 8500rpm for 8min to obtain a lignin component L2, and collecting centrifuged liquid;
and a sixth step: continuously adding hydrochloric acid solution into the centrifuged liquid collected in the fifth step, slowly adjusting the pH of the solution to 5, adding 3mLSt-CTA solution while stirring, and quickly stirring for 5min at a stirring speed of 250 r/min; then slowly stirring for 15min at the stirring speed of 50 r/min; and finally standing for 8 hours. Then carrying out centrifugal separation at the rotating speed of 8500rpm for 8min to obtain a lignin component L3;
the seventh step: the obtained lignin components L1, L2 and L3 were freeze-dried to obtain a lignin solid. The supernatant before and after each flocculation was subjected to 5000Da and 1000Da membranes, and the TOC before and after the membranes were tested, and FIG. 10 shows the contents of lignin with different molecular weights in the components L1, L2 and L3; and turbidity before and after flocculation was measured, and fig. 11 is a graph showing the turbidity removal rate of the supernatant after each flocculation.
From the turbidity removal results of examples 1-6, it can be seen in FIGS. 11 and 5-10 that the >5000Da (L1 fraction) lignin content in example 1 was 9.87g/L, with a removal rate of 49%; the lignin content of 1000-5000 Da (L2 component) is 2.34g/L, and the removal rate is 63%; the lignin content of <1000Da (L3 fraction) was 4.9g/L with a total removal of 75% (see FIG. 5). The lignin content of >5000Da (L1 fraction) in example 2 was 9.32g/L, the removal rate was 45%; the lignin content of 1000-5000 Da (L2 component) is 2.44g/L, and the removal rate is 61%; the lignin content of <1000Da (L3 fraction) was 3.2g/L with a total removal of 75% (see FIG. 6). The lignin content of >5000Da (L1 fraction) in example 3 was 14.4g/L, with a removal of 57%; the lignin content of 1000-5000 Da (L2 component) is 3.98g/L, and the removal rate is 73%; the lignin content of <1000Da (L3 fraction) was 4.9g/L with a total removal of 95% (see FIG. 7). The lignin content of >5000Da (L1 fraction) in example 4 was 12.74g/L, with a removal rate of 55%; the lignin content of 1000-5000 Da (L2 component) is 3.69g/L, and the removal rate is 70%; the lignin content of <1000Da (L3 fraction) was 4.04g/L, with a removal rate of 88% in total (see FIG. 8). The lignin content of >5000Da (L1 fraction) in example 5 was 13.67g/L, with a removal of 56%; the lignin content of 1000-5000 Da (L2 component) is 3.99g/L, and the removal rate is 72%; the lignin content of <1000Da (L3 fraction) was 5.01g/L, with a total removal of 92% (see FIG. 9). The lignin content of >5000Da (L1 fraction) in example 6 was 13.03g/L, with a removal of 56%; the lignin content of 1000-5000 Da (L2 component) is 4.1g/L, and the removal rate is 72.5%; the lignin content of <1000Da (L3 fraction) was 4.9g/L with a total removal of 90% (see FIG. 10). The gel permeation chromatography in the graph 1-4 can also be used for obtaining that the flocculation-precipitation can realize the classification of different molecular weights of lignin in the black liquor, and the molecular weight distribution is mainly more than 5000Da, 1000-5000 Da and less than 1000 Da.
Claims (8)
1. A method for separating lignin from straw pulping black liquor in a grading way is characterized by comprising the following steps:
the first step is as follows: selecting straw papermaking pulping black liquor, measuring the pH value of untreated black liquor, adding concentrated hydrochloric acid to adjust the pH value to be = 8-10, weighing 100mL of black liquor by using a measuring cylinder, and pouring the black liquor into a beaker;
the second step is that: weighing St-CTA starch-based flocculant with a cationic substitution degree of 70-95%, dissolving the St-CTA starch-based flocculant in 100mL of pure water, and preparing a St-CTA solution with the concentration of 10-20 g/L;
the third step: 3-14mL of St-CTA solution is transferred by a liquid transfer gun and added into the beaker in the first step while stirring;
the fourth step: firstly, stirring at a stirring speed of 200-250r/min for 3-10min, then stirring at a stirring speed of 40-60r/min for 10-20min, and finally standing for 2-10 h; then centrifuging at the rotating speed of 7000-;
the fifth step: continuously adding a hydrochloric acid solution into the centrifuged liquid collected in the fourth step, adjusting the pH of the solution to 6-8, adding a 2-8mLSt-CTA solution, stirring at a stirring speed of 200-250r/min for 3-10min, stirring at a stirring speed of 40-60r/min for 10-20min, and standing for 2-10 h; then centrifuging at the rotating speed of 7000-;
and a sixth step: continuously adding a hydrochloric acid solution into the centrifuged liquid collected in the fifth step, adjusting the pH of the solution to 4-6, adding a 2-8mLSt-CTA solution, stirring at a stirring speed of 200-250r/min for 3-10min, stirring at a stirring speed of 40-60r/min for 10-20min, and standing for 2-10 h; then centrifuging at the rotating speed of 7000-;
the seventh step: the obtained lignin components L1, L2 and L3 were freeze-dried to obtain lignin solids with different molecular weight distributions.
2. The method for the fractional separation of lignin from straw pulping black liquor according to claim 1, characterized in that: the molecular weight distribution ranges of the different molecular weight lignin components L1, L2 and L3 obtained in the seventh step are respectively greater than 5000Da, 1000 to 5000Da and less than 1000Da as evidenced by GPC gel permeation chromatography.
3. The method for the fractional separation of lignin from straw pulping black liquor according to claim 1, characterized in that: and in the second step, the preparation method of the St-CTA starch-based flocculant comprises the steps of dissolving 0.25g of KOH in 15mL of pure water to prepare a KOH solution, weighing 1.62g of starch to dissolve in the KOH solution, alkalizing for half an hour at 50-100 ℃ in a four-necked flask, adding 0.4-0.41g of (3-chloro-2-hydroxypropyl) trimethyl ammonium Chloride (CTA) powder into 5mL of the alkalized starch solution for half an hour, continuously reacting for 2 hours at 50-100 ℃, adding 0.5mL of concentrated HCl to adjust the pH, continuously stirring for 5 minutes, precipitating and washing in acetone, pouring into an ethanol solution, shearing, stirring and soaking in ethanol for 1 hour, filtering, and vacuum drying at 60 ℃ overnight to obtain the product.
4. The method for the fractional separation of lignin from straw pulping black liquor according to claim 1, characterized in that: in the second step, the concentration of St-CTA was 20g/L, the degree of substitution 90%.
5. The method for the fractional separation of lignin from straw pulping black liquor according to claim 1, characterized in that: in the first step, the pH =9, and in the third step, the amount of St-CTA added is 3 mL; in the fourth step, the mixture is quickly stirred for 5min at the stirring speed of 250 r/min; stirring at a low speed of 50r/min for 20 min; standing for 8 h; the centrifugation speed is 8000rpm, and the time is 8 min.
6. The method for the fractional separation of lignin from straw pulping black liquor according to claim 1, characterized in that: in the fifth step, pH =7, St-CTA was dosed in 4 mL.
7. The method for the fractional separation of lignin from straw pulping black liquor according to claim 1, characterized in that: in the sixth step, pH =5, St-CTA was dosed in 4 mL.
8. The method for the fractional separation of lignin from straw pulping black liquor according to claim 1, characterized in that: the pH of the untreated black liquor in the first step, pH = 13.
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| CN1920170A (en) * | 2006-09-18 | 2007-02-28 | 同济大学 | Method for lignin extraction by papermaking black liquor acidification and flocculation precipitation |
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Application publication date: 20211231 |