Background
Lignin is one of three major components in plant cell walls and is widely found in vascular bundles of plants. The lignin has the advantages of being natural, renewable, biodegradable, non-toxic and the like, and is regarded as an important substitute raw material of petrochemical resources. In China, with the rapid development of paper making industry and renewable energy industries such as fuel ethanol and the like, lignin is often discharged or combusted for energy supply as pulping and paper making waste liquid and byproducts which are difficult to utilize in biorefinery, so that the environment is seriously polluted, and the lignin is a great waste of resources.
The method realizes effective separation of lignin by biomass refining, and is an effective way for high-value utilization of lignin at present. Pulping-oriented lignin separation methods include a caustic soda method, a sulfate method, a formic acid method and the like, which are generally carried out under severe reaction conditions, and the content of lignin beta-O-4 is generally low, and the reaction activity is weak; emerging sugar-oriented lignin separation methods such as weak acid, weak base, organic solvent treatment and the like have low lignin removal rate due to mild conditions, and can limit high-value conversion. Therefore, the development of a simple, green and efficient lignin separation method becomes a current research hotspot.
At present, the prior art generally adopts a cooking method to separate lignin. For example, CN108086028A discloses a method for producing solvent lignin, which comprises the following specific steps: pretreating the plant fiber raw material by adopting organic acid or an organic acid aqueous solution; taking an organic acid aqueous solution as a cooking solvent, adding a catalyst, and cooking the pretreated plant fiber raw material; after the cooking is finished, carrying out solid-liquid separation to obtain cooking liquor and plant fibers; the cooking liquor is pumped into an evaporation concentration device for negative pressure evaporation concentration, and the value of the pressure P satisfies 0.7 multiplied by 10 5 Pa≤P≤1×10 5 Pa, the concentration temperature is 65-200 ℃, the concentration degree is stopped when the concentrated solution is concentrated until the total mass of the concentrated solution is 5-300% of the weight of the absolute dry raw materials, and the recovered organic acid solution and the concentrated solution are collected; adding distilled water into the concentrated solution, stirring, standing, and filtering to obtain solid precipitate as solvent lignin.
CN105274894A discloses a method for separating lignocellulose components by metal catalysis of organic acid, wherein a lignocellulose raw material is put into a cooking system consisting of organic acid and a metal catalyst for cooking; after cooking, recovering the metal catalyst, carrying out solid-liquid separation, and washing the solid with an organic acid solution and water respectively to obtain paper pulp; mixing the cooking waste liquid and the pickling waste liquid, evaporating and concentrating, condensing steam, distilling again, and recovering organic acid and furfural; adding water washing waste liquid into the evaporation concentrated solution for precipitation, carrying out solid-liquid separation, washing and drying the solid to obtain lignin, evaporating, concentrating and drying the liquid to obtain oligosaccharide and monosaccharide, and being more suitable for component separation of wood and non-wood fiber raw materials.
However, the prior art adopts a cooking method to separate lignin, which not only has the disadvantages of high energy consumption, complex operation and the like, but also wastes a large amount of organic reagents, increases the cost of raw materials, and is not suitable for large-scale popularization and use. Therefore, in order to solve the problems of low lignin separation yield, high chemical reagent recovery cost and the like, a method for separating lignin by recycling solid organic acid is urgently needed to be developed at present, a high-value lignin product can be separated, the lignin separation yield is more than or equal to 90%, the DLS size is 225-230nm, the zeta potential is stabilized at-38 to-44 mV, the organic reagent can be recycled, the recovery cost is low, the environmental pollution is small, the separation cost is greatly reduced, and the method is convenient for large-scale popularization and use.
Disclosure of Invention
In view of the problems in the prior art, the invention provides a method for separating lignin by recycling solid organic acid, which can separate a high-value lignin product, so that the lignin separation yield is more than or equal to 90%, the DLS size is 226-231nm, the Zeta potential is stabilized at-38 to-44 mV, an organic reagent can be recycled, the recovery cost is low, the environmental pollution is small, the separation cost is greatly reduced, the large-scale popularization and use are facilitated, and the proper recycling times of the solid organic acid are further researched by the inventor.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention aims to provide a method for separating lignin by recycling solid organic acid, which comprises the following steps:
(1) Mixing a wood fiber raw material with a solid organic acid aqueous solution for heating reaction, and performing first solid-liquid separation to obtain a first filtrate and a solid;
(2) Carrying out anti-solvent dilution on the first filtrate obtained in the step (1), and carrying out secondary solid-liquid separation to obtain a separation mother liquor and lignin;
(3) And (3) cooling and recrystallizing the separation mother liquor obtained in the step (2), carrying out solid-liquid separation for the third time to obtain the recovery type solid organic acid, and using the recovery type solid organic acid to prepare the solid organic acid aqueous solution obtained in the step (1) for recycling.
The method for separating lignin by recycling the solid organic acid can separate a high-value lignin product, so that the lignin separation yield is more than or equal to 90 percent, the DLS size is 226-231nm, the Zeta potential is stabilized at-38 mV to-44 mV, an organic reagent can be recycled, the recovery cost is low, the environmental pollution is small, the separation cost is greatly reduced, the method is convenient for large-scale popularization and use, and the inventor further researches the recycling times suitable for the solid organic acid.
As a preferred technical scheme of the invention, the wood fiber raw material in the step (1) comprises any one or a combination of at least two of wood, straw or bamboo, and typical but non-limiting examples of the combination are as follows: combinations of wood and straw, straw and bamboo, or wood and bamboo, and the like.
As a preferred technical solution of the present invention, the solid organic acid in the aqueous solid organic acid solution in step (1) comprises any one or a combination of at least two of maleic acid, crotonic acid, benzenesulfonic acid or o-aminobenzenesulfonic acid, and typical but non-limiting examples of the combination are: combinations of maleic acid and crotonic acid, crotonic acid and benzenesulfonic acid, benzenesulfonic acid and orthanilic acid, or maleic acid and orthanilic acid, and the like.
In a preferred embodiment of the present invention, the mass concentration of the aqueous solid organic acid solution in step (1) is 30 to 95wt.%, for example, 30wt.%, 35wt.%, 45wt.%, 50wt.%, 60wt.%, 70wt.%, 75wt.%, 85wt.% or 95wt.%, but is not limited to the recited values, and other values not recited in the above-mentioned numerical ranges are also applicable.
In a preferred embodiment of the present invention, the mass ratio of the lignocellulosic raw material to the solid aqueous organic acid solution in step (1) is 1 (5 to 40), for example, 1.
As a preferred embodiment of the present invention, the temperature of the heating reaction in the step (1) is 60 to 120 ℃, for example, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃ or 120 ℃, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the heating reaction time in step (1) is 10 to 120min, such as 10min, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min or 120min, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the first solid-liquid separation in the step (1) is suction filtration.
As a preferred technical scheme of the invention, the anti-solvent in the anti-solvent dilution in the step (2) comprises water.
It is worth noting that the anti-solvent dilution according to the present invention refers to the process of adding anti-solvent to the first filtrate.
Preferably, the mass ratio of the antisolvent in the antisolvent dilution in the step (2) to the first filtrate is 1 (1 to 4), such as 1.
Preferably, the temperature of the anti-solvent in the anti-solvent dilution described in step (2) is in the range of 20 to 30 ℃, such as 20 ℃,21 ℃, 22 ℃, 23 ℃, 25 ℃, 26 ℃, 27 ℃, 28 ℃ or 30 ℃ and the like, but is not limited to the recited values and other non-recited values within this range are equally applicable.
It is worth to say that, the first filtrate in the step (1) does not need to be subjected to cooling treatment, and the anti-solvent with the temperature of 20-30 ℃ can be directly added into the first filtrate, and then the anti-solvent is diluted at room temperature, so that the aim of basically precipitating lignin can be completely fulfilled.
Preferably, the second solid-liquid separation of step (2) comprises centrifugal separation.
It is worth to explain that the solid volume in the first solid-liquid separation is larger, and the separation purpose can be achieved by adopting simple suction filtration; DLS size of solid (lignin) in the second solid-liquid separation is in nanometer level, and centrifugal separation effect is best; the solid (solid organic acid) in the third solid-liquid separation has larger particle size, and the separation effect can be achieved by adopting suction filtration.
As a preferred embodiment of the present invention, the initial temperature of the cooling recrystallization in the step (3) is 20 to 30 ℃,21 ℃, 22 ℃, 23 ℃, 25 ℃, 26 ℃, 27 ℃, 28 ℃ or 30 ℃, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the temperature at the end of the cooling recrystallization in step (3) is 0 to 10 ℃, for example 0 ℃, 1 ℃,2 ℃, 4 ℃, 5 ℃, 6 ℃, 7 ℃, 9 ℃ or 10 ℃, but not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the incubation time for the cooling recrystallization in the step (3) is 20 to 24 hours, such as 20 hours, 20.5 hours, 21 hours, 21.5 hours, 22 hours, 22.5 hours, 23 hours, 23.5 hours or 24 hours, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.
It should be noted that the holding time for the cooling recrystallization in the step (3) of the present invention is a holding time after the end temperature of the cooling recrystallization is reached.
In a preferred embodiment of the present invention, the number of recycling in step (3) is 1 to 10, for example, 1, 3, 5, 7, 9 or 10, but the number is not limited to the recited values, and other values not recited in the above range are also applicable, preferably 1 to 5.
It should be noted that, through many experimental studies, the inventors found that, although the physicochemical properties and yield of the lignin product are not affected by preparing the solid organic acid aqueous solution required for the next round by using the recovered solid organic acid, the recovered solid organic acid is inevitably doped with impurities generated by further degradation such as glucose, xylose, furfural, formic acid, acetic acid, and the like, so as to reduce the recovery rate of the recovered solid organic acid, and the inventors prefer that the recycling is performed for 1 to 5 times, taking the recovery cost and energy consumption into comprehensive consideration.
As a preferred technical scheme of the invention, the method comprises the following steps:
(1) Mixing a wood fiber raw material with a solid organic acid aqueous solution with the mass concentration of 30-95 wt.% according to the mass ratio of 1 (5-40), carrying out heating reaction at 60-120 ℃ for 10-120 min, and carrying out suction filtration to obtain a first filtrate and a solid matter; wherein the wood fiber raw material comprises any one or combination of at least two of wood, straw or bamboo; the solid organic acid in the solid organic acid aqueous solution comprises any one or the combination of at least two of maleic acid, crotonic acid, benzenesulfonic acid or o-aminobenzenesulfonic acid;
(2) Adding water with the temperature of 20-30 ℃ into the first filtrate obtained in the step (1) for anti-solvent dilution, wherein the mass ratio of the water to the first filtrate is 1 (1-4), and obtaining separation mother liquor and lignin through centrifugal separation;
(3) And (3) cooling and recrystallizing the separated mother liquor obtained in the step (2), wherein the initial temperature of the cooling and recrystallization is 20-30 ℃, the final temperature of the cooling and recrystallization is 0-10 ℃, the heat preservation time is 20-24 hours, and the recovered solid organic acid is obtained through third solid-liquid separation and is used for preparing the solid organic acid aqueous solution obtained in the step (1) for 1-10 times of recycling.
Compared with the prior art, the invention at least has the following beneficial effects:
the method for separating lignin by recycling the solid organic acid can separate a high-value lignin product, so that the lignin separation yield is more than or equal to 90 percent, the DLS size is 226-231nm, the Zeta potential is stabilized at-38 mV to-44 mV, an organic reagent can be recycled, the recovery cost is low, the environmental pollution is small, the separation cost is greatly reduced, the method is convenient for large-scale popularization and use, and the inventor further researches the recycling times suitable for the solid organic acid.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
To better illustrate the invention and to facilitate the understanding of the technical solutions thereof, typical but non-limiting examples of the invention are as follows:
example 1
The embodiment provides a method for separating lignin by recycling solid organic acid, which comprises the following steps:
(1) Mixing 1g of wood fiber raw material with 10g of benzenesulfonic acid aqueous solution with the mass concentration of 80wt.% according to the mass ratio of 1; wherein the wood fiber raw material is ground wood powder;
(2) Adding water with the temperature of 25 ℃ into the first filtrate obtained in the step (1) for anti-solvent dilution, wherein the mass ratio of the water to the first filtrate is 1;
(3) And (3) cooling and recrystallizing the separation mother liquor obtained in the step (2), wherein the initial temperature of the cooling and recrystallization is 25 ℃, the final temperature of the cooling and recrystallization is 5 ℃, the heat preservation time is 24 hours, the recovered benzenesulfonic acid is obtained through third solid-liquid separation, the recovered benzenesulfonic acid is dried and weighed, the recovery rate is calculated, and then the recovered benzenesulfonic acid is prepared together with fresh benzenesulfonic acid to prepare the benzenesulfonic acid aqueous solution obtained in the step (1) for recycling, and the benzenesulfonic acid aqueous solution is recycled for 10 times according to the steps.
Example 2
The embodiment provides a method for separating lignin by recycling solid organic acid, which comprises the following steps:
(1) Mixing 1g of wood fiber raw material and 40g of maleic acid aqueous solution with the mass concentration of 50wt.% according to a mass ratio of 1; wherein the wood fiber raw material is ground wood powder;
(2) Adding water with the temperature of 20 ℃ into the first filtrate obtained in the step (1) for anti-solvent dilution, wherein the mass ratio of the water to the first filtrate is 1;
(3) And (3) cooling and recrystallizing the separated mother liquor obtained in the step (2), wherein the initial temperature of the cooling and recrystallization is 20 ℃, the final temperature of the cooling and recrystallization is 0 ℃, the heat preservation time is 24 hours, the recovered maleic acid is obtained through third solid-liquid separation, the recovered maleic acid is dried and weighed, the recovery rate is calculated, and then the recovered maleic acid and fresh maleic acid are used together to prepare the maleic acid aqueous solution obtained in the step (1) for recycling, and the maleic acid aqueous solution is recycled for 10 times according to the steps.
Example 3
The embodiment provides a method for separating lignin by recycling solid organic acid, which comprises the following steps:
(1) Mixing 1g of wood fiber raw material with 25g of an o-aminobenzenesulfonic acid aqueous solution with the mass concentration of 30wt.% according to the mass ratio of 1; wherein the wood fiber raw material is ground bamboo powder;
(2) Adding water with the temperature of 30 ℃ into the first filtrate obtained in the step (1) for anti-solvent dilution, wherein the mass ratio of the water to the first filtrate is 1;
(3) And (3) cooling and recrystallizing the separation mother liquor obtained in the step (2), wherein the initial temperature of the cooling and recrystallization is 30 ℃, the final temperature of the cooling and recrystallization is 10 ℃, the heat preservation time is 24 hours, the recovered o-aminobenzenesulfonic acid is obtained through third solid-liquid separation, the recovered o-aminobenzenesulfonic acid is dried and weighed, the recovery rate is calculated, and then the o-aminobenzenesulfonic acid is prepared together with fresh o-aminobenzenesulfonic acid to be recycled in the step (1), and the o-aminobenzenesulfonic acid aqueous solution is recycled for 10 times according to the steps.
The solid organic acid recovery rates calculated under different recycling times in the methods described in the above examples 1 to 3 are shown in table 1; it is worth to be noted that the recovery rate of the solid organic acid in each cycle is calculated according to the following formula: solid organic acid recovery = dry mass of the recovery type solid organic acid/mass of the solid organic acid in the aqueous solution of the solid organic acid × 100%.
TABLE 1
Number of times of cyclic utilization
|
1 time of
|
2 times (one time)
|
3 times of
|
4 times (twice)
|
5 times (twice)
|
6 times of
|
7 times (twice)
|
8 times (by volume)
|
9 times of
|
10 times of
|
Example 1 (benzenesulfonic acid)
|
97%
|
92%
|
88%
|
81%
|
75%
|
71%
|
67%
|
62%
|
58%
|
52%
|
Example 2 (maleic acid)
|
98%
|
96%
|
95%
|
93%
|
88%
|
86%
|
83%
|
80%
|
76%
|
70%
|
Example 3 (Orthoaminobenzenesulfonic acid)
|
96%
|
94%
|
90%
|
86%
|
85%
|
83%
|
80%
|
74%
|
72%
|
67% |
As can be seen from table 1, the recovery rate of maleic acid corresponding to example 2 was higher at the same number of recycling times; when the maleic acid is recycled for 10 times, the recovery rate of the maleic acid corresponding to the embodiment 2 is 70%, while the recovery rates of the solid organic acid containing the sulfonic acid group, namely the o-aminobenzenesulfonic acid and the benzenesulfonic acid, are relatively low, and after the maleic acid is recycled for 10 times, the recovery rates are respectively reduced to 67% and 52%; when the solid organic acid is recycled for 5 times, the recovery rates of the solid organic acid corresponding to the embodiments 1 to 3 are all over 75%, but the recovery rates of the solid organic acid are all reduced with the increase of the number of the recycling times, and the number of the recycling times is preferably 1 to 5 times in consideration of the recycling cost and the energy consumption.
The lignin obtained in the method of example 1 with different recycling times was characterized as follows, and the lignin separation yield, DLS size, zeta potential and molecular weight, and the specific characterization results are shown in table 2.
TABLE 2
As can be seen from Table 2, in the process of recycling 10 times of the benzenesulfonic acid adopted in example 1, the lignin separation yield is above 90%, the Dynamic Light Scattering (DLS) size and Zeta potential of the lignin obtained by separation are respectively maintained at 226-231 nm and-38 to-44 mV, and the weight average molecular weight and the number average molecular weight are respectively maintained at about 3000 and 1500, which indicates that the recycling of the benzenesulfonic acid does not affect the quality of the lignin obtained by separation, including the size, the surface property, the molecular weight and the like. In addition, fig. 1 shows the morphology of lignin obtained by reaction and separation of benzenesulfonic acid with a wood fiber raw material for 1 time of recycling, fig. 2 shows the morphology of lignin obtained by reaction and separation of benzenesulfonic acid with a wood fiber raw material for 10 times of recycling, and comparing fig. 1 with fig. 2, it can be seen that the two are basically the same in morphology and equivalent in size, which indicates that the morphology of lignin obtained by separation is not affected by recycling of benzenesulfonic acid.
Comparative example 1
This comparative example provides a method for separating lignin under exactly the same conditions as in example 2, except that the end temperature of the cooling recrystallization described in step (3) of example 2 was changed from 0 ℃ to 15 ℃. The calculated primary recovery rate is only 57%, and is not recycled.
Comparative example 2
This comparative example provides a process for isolating lignin under exactly the same conditions as in example 2, except that the end temperature of the cooling recrystallization in step (3) of example 2 was changed from 0 ℃ to-5 ℃. The visually-measured recovered maleic acid is yellow, which indicates that more impurities are doped, and the purity of the recovered maleic acid does not reach the standard and is not recycled.
Comparative example 3
This comparative example provides a method for isolating lignin under exactly the same conditions as in example 2, except that the incubation time was changed from 24 hours to 12 hours in step (3) of example 2. The first recovery rate calculated was only 62% and was not recycled.
In conclusion, the method for separating lignin by recycling solid organic acid can separate high-value lignin products, so that the lignin separation yield is more than or equal to 90%, the DLS size is 226-231nm, the zeta potential is stabilized at minus 38-minus 44mV, organic reagents can be recycled, the recovery cost is low, the environmental pollution is small, the separation cost is greatly reduced, the method is convenient for large-scale popularization and use, and the inventor further researches the suitable recycling times of the solid organic acid.
The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are all within the protection scope of the present invention.
It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.