A method for extracting xylose from papermaking waste liquid

Abstract

The invention discloses a method for extracting xylose from papermaking waste liquid, wherein a certain proportion of flocculant is added to the papermaking waste liquid, the filtrate is filtered and collected, and then the filtrate is physically decolorized to obtain a decolorized filtrate, and then the decolorized filtrate is sequentially subjected to ion exchange, nanofiltration, evaporation concentration, cooling crystallization, centrifugation and drying to finally obtain finished xylose. The invention can remove lignin in the papermaking waste liquid, improve the purification degree of the papermaking waste liquid, and simultaneously improve the purity of xylose in the papermaking waste liquid to obtain crystalline xylose, and no other harmful byproducts are produced during the production process.

Description

Technical Field

[0001] The invention relates to the technical field of xylose processing, and in particular to a method for extracting xylose from papermaking waste liquid. Background Art

[0002] Xylose belongs to pentose. Natural D-xylose exists in plants in the form of polysaccharides. The most common is that xylose is hydrogenated and reduced to xylitol under the action of a catalyst. This type of xylose is called raw material grade xylose. This type of xylose is prone to Maillard reaction at higher temperatures, giving food an attractive color and special aroma. Xylose can also be used in food, medicine, pet food and other fields.

[0003] Wood is an important raw material for papermaking. In the process of producing dissolving pulp, most of the hemicellulose enters the pulping waste liquid through prehydrolysis, and the discharge of pulping waste liquid will cause environmental pollution and waste of resources. Xylose is the main component of hemicellulose in wood. Using papermaking wastewater generated in the wood prehydrolysis process to prepare xylose not only reduces the production cost of xylose, but also turns waste into treasure and reduces the pollution of papermaking wastewater. Since the content of xylose in papermaking waste liquid cannot achieve the crystallization effect, it is necessary to further treat the papermaking waste liquid to improve the purity of xylose in the papermaking waste liquid.

[0004] For example, Chinese patent: CN112877273A, a yeast that decomposes miscellaneous sugars such as galactose and mannose, uses yeast to remove miscellaneous sugars in papermaking waste liquid. However, when this method is used to obtain xylose from papermaking waste liquid, fermentation by-products such as organic acids that are harmful to the environment are produced during the fermentation process and cannot be discharged directly.

[0005] Therefore, how to improve the method of extracting xylose from papermaking waste liquid to avoid the production of harmful fermentation by-products such as organic acids is a technical problem that technicians in this field need to solve urgently. Summary of the invention

[0006] The purpose of the present invention is to provide a method for extracting xylose from papermaking waste liquid to remove lignin in the papermaking waste liquid, improve the purification degree of the papermaking waste liquid, and at the same time improve the purity of xylose in the papermaking waste liquid to obtain crystalline xylose, and there are no other harmful by-products in the production process.

[0007] To achieve the above object, the present invention provides a method for extracting xylose from papermaking waste liquid, comprising the following steps:

[0008] Step 1, dilute the papermaking waste liquid with water to a refractive index of 18-20%, adjust the temperature to 45-55°C, and adjust the pH value to 5.5-6.0, and then add 0.5-1% flocculant according to the volume ratio;

[0009] Step 2, filtering the solution prepared in step 1 after standing for 30-60 minutes to collect the filtrate;

[0010] Step 3, the filtrate in step 2 is subjected to physical decolorization treatment to obtain a decolorized filtrate;

[0011] Step 4, filtering the decolorized filtrate in step 3 using a nanofiltration membrane to obtain a nanofiltration permeate;

[0012] Step 5, subjecting the nanofiltration permeate in step 4 to cation exchange and anion exchange to obtain an ion exchange filtrate with a pH value greater than 4.0 and a transmittance greater than 90%;

[0013] Step 6, vacuum evaporating and concentrating the ion exchange filtrate in step 5 to obtain a concentrated solution, wherein the refractive index of the concentrated solution is controlled at 78-82% and the evaporation temperature is controlled at 80-90° C.;

[0014] Step 7, cooling the concentrated solution in step 6 to room temperature at a rate of 0.5-1°C / h to obtain massecuite;

[0015] Step 8, centrifuging the massecuite in step 7 to obtain semi-finished xylose;

[0016] Step 9, drying the semi-finished xylose in step 8 to obtain finished xylose.

[0017] Further, in step 1, sodium carbonate is added to the papermaking waste liquid diluted with water to adjust the pH value.

[0018] Further, in step 2, the step of filtering the feed solution prepared in step 1 after standing for 30-60 minutes comprises:

[0019] The liquid prepared in step 1 is allowed to stand for 30-60 minutes and then filtered at a filtration pressure of 0.2-0.4 MPa.

[0020] Further, in step 2, the slurry prepared in step 1 is allowed to stand for 30-60 minutes and then filtered through a plate and frame filter.

[0021] Further, in step 4, the filtration pressure of the nanofiltration membrane is not greater than 30 Bar.

[0022] Further, in step 8, the step of centrifuging the massecuite in step 8 comprises:

[0023] The massecuite in step eight is centrifuged in a centrifuge at a speed of 1000-1200 r / min.

[0024] Further, in step 3, the filtrate in step 2 is decolorized, comprising:

[0025] Primary decolorization; heating the filtrate in step 2 to 60-70°C, adding 0.5% activated carbon by volume, and then stirring and filtering in sequence to obtain an intermediate filtrate;

[0026] Secondary decolorization: the primary decolorized filtrate is passed through a granular carbon column to obtain a decolorized filtrate with a transmittance of >40%.

[0027] Further, the step of performing cation exchange and anion exchange on the nanofiltration permeate in step 4 comprises:

[0028] The nanofiltration permeate in step 4 is subjected to a primary cation exchange, a primary anion exchange, a secondary cation exchange and a secondary anion exchange in sequence.

[0029] The method for extracting xylose from papermaking waste liquid of the present invention comprises adding a certain proportion of flocculant to the papermaking waste liquid, filtering and collecting the filtrate, and then physically decolorizing the filtrate to obtain a decolorized filtrate, and then sequentially performing ion exchange, nanofiltration, evaporation concentration, cooling crystallization, centrifugation and drying on the decolorized filtrate to finally obtain finished xylose;

[0030] The present invention can remove impurities from papermaking waste liquid to obtain purified papermaking waste liquid, and then obtain crystalline xylose through subsequent processes. The present invention can effectively remove impurities in papermaking waste liquid by adding a high-efficiency decolorizing flocculant to obtain purified papermaking waste liquid, and then improve the purity of xylose in the purified papermaking waste liquid through a nanofiltration membrane filtration process, filter out most of other miscellaneous sugars, reduce the content of other miscellaneous sugars, and facilitate obtaining crystalline xylose; in addition, the flocculated lignin can be sold as a by-product, which reduces pollution to the environment and increases economic benefits. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail in the following embodiments.

[0032] The present invention discloses a method for extracting xylose from papermaking waste liquid, comprising the following steps:

[0033] Step 1, dilution and flocculation; dilute the papermaking waste liquid with water to a refractive index of 18-20%, adjust its temperature to 45-55°C, and adjust the pH value to 5.5-6.0, and then add 0.5-1% of flocculant according to the volume ratio; this step 1 can be carried out in a stirring tank to make the mixing faster by stirring; wherein, heating the temperature to 45-55°C can make the papermaking waste liquid fully stirred; wherein:

[0034] If the refractive index is lower than the range of 18-20%, the amount of flocculant added is large, which increases the cost; if the refractive index is higher than the range of 18-20%, the flocculation effect is poor.

[0035] If the temperature is lower than the range of 45-55℃, the flocculation effect is poor; if the temperature is higher than the range of 45-55℃, the flocculation effect is not obvious.

[0036] If the pH value is lower than the range of 5.5-6.0, the flocculation effect is poor; if the pH value is higher than the range of 5.5-6.0, some xylose will be isomerized, affecting the yield of xylose.

[0037] Furthermore, if the amount of flocculant added is lower than 0.5-1%, the flocculation effect is poor; if it is higher than 0.5-1%, the flocculant effect is not obvious; according to the above-mentioned refractive index, temperature, and pH range, more impurities in the papermaking waste liquid can be flocculated and precipitated, and then filtered.

[0038] Step 2, filtering; the feed solution prepared in step 1 is allowed to stand for 30-60 minutes and then filtered to collect the filtrate;

[0039] Step 3, decolorization: subjecting the filtrate in step 2 to physical decolorization to obtain a decolorized filtrate;

[0040] Step 4, nanofiltration: filtering the decolorized filtrate in step 3 using a nanofiltration membrane to obtain a nanofiltration permeate;

[0041] Step 5, cation and anion exchange; the nanofiltration permeate in step 4 is subjected to cation exchange and anion exchange to obtain an ion exchange filtrate with a pH value of more than 4.0 and a light transmittance of more than 90%; the cation and anion exchange is achieved by passing the nanofiltration permeate through an ion exchange resin. How to use the ion exchange resin is common knowledge in the art and will not be described in detail; setting the ion exchange filtrate with a pH value of more than 4.0 and a light transmittance of more than 90% can improve the purity of the ion exchange liquid and remove the pigment group to ensure that the finished xylose after crystallization meets the taste requirements;

[0042] Step 6, evaporation and concentration; the ion exchange filtrate in step 5 is vacuum evaporated and concentrated to obtain a concentrated solution, wherein the refractive index of the concentrated solution is controlled at 78-82%, which can reach the crystallization concentration of xylose, and the evaporation temperature is controlled at 80-90°C;

[0043] Step 7, cooling and crystallizing; cooling the concentrated solution in step 6 to room temperature at a rate of 0.5-1°C / h to obtain massecuite; cooling within this range allows the crystals to grow fully and ensures the particle size of the crystals;

[0044] Step 8, centrifugation: centrifuging the massecuite in step 7 to obtain semi-finished xylose;

[0045] Step 9, drying: drying the semi-finished xylose in step 8 to obtain finished xylose.

[0046] Embodiment 1:

[0047] Step 1, dilute the papermaking waste liquid with water to a refractive index of 18%, adjust the temperature to 45° C., and adjust the pH value to 5.5, and then add 0.5% flocculant according to the volume ratio;

[0048] Step 2, filtering the solution prepared in step 1 after standing for 30 minutes to collect the filtrate;

[0049] Step 3, the filtrate in step 2 is subjected to physical decolorization treatment to obtain a decolorized filtrate;

[0050] Step 4, filtering the decolorized filtrate in step 3 using a nanofiltration membrane to obtain a nanofiltration permeate;

[0051] Step 5, subjecting the nanofiltration permeate in step 4 to cation exchange and anion exchange to obtain an ion exchange filtrate with a pH value greater than 4.0 and a transmittance greater than 90%;

[0052] Step 6, vacuum evaporating and concentrating the ion exchange filtrate in step 5 to obtain a concentrated solution, wherein the refractive index of the concentrated solution is controlled at 78% and the evaporation temperature is controlled at 80° C.;

[0053] Step 7, cooling the concentrated solution in step 6 to room temperature at a rate of 0.5°C / h to obtain massecuite;

[0054] Step 8, centrifuging the massecuite in step 7 to obtain semi-finished xylose;

[0055] Step 9, drying the semi-finished xylose in step 8 to obtain finished xylose.

[0056] Embodiment 2:

[0057] Step 1, dilute the papermaking waste liquid with water to a refractive index of 19%, adjust the temperature to 50° C., and adjust the pH value to 5.8, and then add 0.8% flocculant according to the volume ratio;

[0058] Step 2, filtering the solution prepared in step 1 after standing for 45 minutes to collect the filtrate;

[0059] Step 3, the filtrate in step 2 is subjected to physical decolorization treatment to obtain a decolorized filtrate;

[0060] Step 4, filtering the decolorized filtrate in step 3 using a nanofiltration membrane to obtain a nanofiltration permeate;

[0061] Step 5, subjecting the nanofiltration permeate in step 4 to cation exchange and anion exchange to obtain an ion exchange filtrate with a pH value greater than 4.0 and a transmittance greater than 90%;

[0062] Step 6, vacuum evaporating and concentrating the ion exchange filtrate in step 5 to obtain a concentrated solution, wherein the refractive index of the concentrated solution is controlled at 80% and the evaporation temperature is controlled at 85° C.;

[0063] Step 7, cooling the concentrated solution in step 6 to room temperature at a rate of 0.8°C / h to obtain massecuite;

[0064] Step 8, centrifuging the massecuite in step 7 to obtain semi-finished xylose;

[0065] Step 9, drying the semi-finished xylose in step 8 to obtain finished xylose.

[0066] Embodiment 3:

[0067] Step 1, dilute the papermaking waste liquid with water to a refractive index of 20%, adjust the temperature to 55° C., and adjust the pH value to 6.0, and then add 1% flocculant according to the volume ratio;

[0068] Step 2, filtering the solution prepared in step 1 after standing for 60 minutes to collect the filtrate;

[0069] Step 3, the filtrate in step 2 is subjected to physical decolorization treatment to obtain a decolorized filtrate;

[0070] Step 4, filtering the decolorized filtrate in step 3 using a nanofiltration membrane to obtain a nanofiltration permeate;

[0071] Step 5, subjecting the nanofiltration permeate in step 4 to cation exchange and anion exchange to obtain an ion exchange filtrate with a pH value greater than 4.0 and a transmittance greater than 90%;

[0072] Step 6, vacuum evaporating and concentrating the ion exchange filtrate in step 5 to obtain a concentrated solution, wherein the refractive index of the concentrated solution is controlled at 82% and the evaporation temperature is controlled at 90° C.;

[0073] Step 7, cooling the concentrated solution in step 6 to room temperature at a rate of 1°C / h to obtain massecuite;

[0074] Step 8, centrifuging the massecuite in step 7 to obtain semi-finished xylose;

[0075] Step 9, drying the semi-finished xylose in step 8 to obtain finished xylose.

[0076] When the method for extracting xylose from papermaking waste liquid provided by the present invention is applied, the papermaking waste liquid is put into a stirring tank, and the papermaking waste liquid is heated to be fully stirred, and then a certain proportion of flocculant is added, and the filtrate is filtered and collected, and then the filtrate is physically decolorized to obtain a decolorized filtrate, and then the decolorized filtrate is sequentially subjected to ion exchange, nanofiltration, evaporation concentration, cooling crystallization, centrifugation and drying to finally obtain a finished xylose product;

[0077] The present invention can remove impurities from papermaking waste liquid to obtain purified papermaking waste liquid, and then obtain crystalline xylose through subsequent processes. The present invention can effectively remove impurities in papermaking waste liquid by adding a high-efficiency decolorizing flocculant to obtain purified papermaking waste liquid, and then improve the purity of xylose in the purified papermaking waste liquid through a nanofiltration membrane filtration process, filter out most of other miscellaneous sugars, reduce the content of other miscellaneous sugars, and facilitate obtaining crystalline xylose; in addition, the flocculated lignin can be sold as a by-product, which reduces pollution to the environment and increases economic benefits.

[0078] On the basis of the above embodiment, in step 1, sodium carbonate is added to the papermaking waste liquid diluted with water to adjust the pH value.

[0079] On the basis of the above embodiment, step 2, wherein the slurry prepared in step 1 is allowed to stand for 30-60 minutes and then filtered, comprises:

[0080] The liquid prepared in step 1 is allowed to stand for 30-60 minutes and then filtered at a filtration pressure of 0.2-0.4 MPa.

[0081] If the filtration pressure is lower than this range, the pre-coat layer will easily fall off, causing filtration penetration; if the filtration pressure is higher than this range, the flow rate will be smaller.

[0082] On the basis of the above embodiment, in step 2, the feed solution prepared in step 1 is allowed to stand for 30-60 minutes and then filtered through a plate and frame filter.

[0083] On the basis of the above embodiment, in step 4, due to the material requirements of the components of the nanofiltration membrane, the filtration pressure of the nanofiltration membrane is not greater than 30 Bar.

[0084] Based on the above embodiment, step 8, centrifuging the massecuite in step 8 comprises:

[0085] The massecuite in step eight is centrifuged in a centrifuge at a speed of 1000-1200 r / min.

[0086] On the basis of the above embodiment, in step 3, the decolorization treatment of the filtrate in step 2 comprises:

[0087] Primary decolorization; heating the filtrate in step 2 to 60-70°C, adding 0.5% activated carbon by volume, and then stirring and filtering in sequence to obtain an intermediate filtrate;

[0088] Secondary decolorization: the primary decolorized filtrate is passed through a granular carbon column to obtain a decolorized filtrate with a transmittance of >40%.

[0089] Based on the above embodiment, the step of performing cation exchange and anion exchange on the nanofiltration permeate in step 4 comprises:

[0090] The nanofiltration permeate in step 4 is subjected to a primary cation exchange, a primary anion exchange, a secondary cation exchange and a secondary anion exchange in sequence.

[0091] In addition, the following comparative tests were conducted in this application:

[0092] Experiment 1: Three experimental groups with different concentrations of papermaking waste liquid were set up, each experimental group was divided into group A and group B, and the papermaking waste liquid in group A and group B only had different pH values, so as to obtain the effect of papermaking waste liquid in different experimental groups passing through a 0.45μm filter membrane after flocculation. In the specific implementation, the volume of each experimental group was 400ml, the temperature was 50℃, and the experimental results were as shown in Table 1:

[0093] Table 1

[0094]

[0095] From the data in Table 1, we can conclude that:

[0096] 1) Under the same pH value, when the concentration is 17-21%, the higher the concentration of papermaking waste liquid, the longer the filtration time of the filtrate after flocculation, and the more impurities on the filter membrane. When the concentration is 17%, the flocculation effect is lower than that of 18%; when the concentration is 21%, the filtration time of the filtrate after flocculation is greatly increased. Therefore, the flocculation effect is better when the concentration is 18-20%;

[0097] 2) At the same concentration, the flocculation effect of pH 3.0 and pH 6.2 is worse than that of pH 5.5, and too high pH will cause xylose isomerization. Therefore, pH 5.5-6.0 is selected as the appropriate pH range for flocculant addition.

[0098] Experiment 2: Comparison of various components in papermaking wastewater before and after nanofiltration with chromatographic separation and fermentation methods. The experimental results are shown in Table 2:

[0099] Table 2

[0100]

[0101] From the data in Table 2, we can conclude that:

[0102] The papermaking waste liquid treated by nanofiltration has a low content of miscellaneous sugars and a high content of xylose, that is, the effect of removing miscellaneous sugars by nanofiltration is better than that by chromatography and fermentation, and there are no fermentation by-products such as organic acids that are harmful to the environment.

[0103] In summary, the process for purifying xylose solution provided by the present invention has the following advantages:

[0104] 1. Through the implementation of the present invention, impurities in papermaking waste liquid can be effectively removed, reducing pollution to the environment;

[0105] 2. The xylose purity of papermaking waste liquid is improved by using the present invention, and xylose can be extracted from the papermaking waste liquid by using subsequent processes;

[0106] 3. The filtered lignin can be sold as a by-product, reducing production costs;

[0107] 4. The concentrated phase of nanofiltration can be sold as caramel color to reduce production costs.

[0108] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0109] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0110] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for extracting xylose from papermaking waste liquid, characterized in that: The following steps are involved: Step 1, dilute the papermaking waste liquid with water to a refractive index of 18-20%, adjust the temperature to 45-55°C, and adjust the pH value to 5.5-6.0, and then add 0.5-1% flocculant according to the volume ratio; Step 2, filtering the solution prepared in step 1 after standing for 30-60 minutes to collect the filtrate; Step 3, the filtrate in step 2 is subjected to physical decolorization treatment to obtain a decolorized filtrate; Step 4, filtering the decolorized filtrate in step 3 using a nanofiltration membrane to obtain a nanofiltration permeate; Step 5, performing cation exchange and anion exchange on the nanofiltration permeate in step 4 to obtain an ion exchange filtrate with a pH value greater than 4.0 and a transmittance greater than 90%; Step 6, vacuum evaporating and concentrating the ion exchange filtrate in step 5 to obtain a concentrated solution, wherein the refractive index of the concentrated solution is controlled at 78-82% and the evaporation temperature is controlled at 80-90° C.; Step 7, cooling the concentrated solution in step 6 to room temperature at a rate of 0.5-1°C / h to obtain massecuite; Step 8, centrifuging the massecuite in step 7 to obtain semi-finished xylose; Step 9, drying the semi-finished xylose in step 8 to obtain finished xylose.

2. The method for extracting xylose from papermaking waste liquid according to claim 1, characterized in that: Step 1, adjusting the pH value by adding sodium carbonate to the papermaking waste liquid diluted with water.

3. The method for extracting xylose from papermaking waste liquid according to claim 1, characterized in that: Step 2, wherein the feed solution prepared in step 1 is allowed to stand for 30-60 minutes and then filtered, comprises: The liquid prepared in step 1 is allowed to stand for 30-60 minutes and then filtered at a filtration pressure of 0.2-0.4 MPa.

4. The method for extracting xylose from papermaking waste liquid according to claim 1 or 3, characterized in that: Step 2: The slurry prepared in step 1 is allowed to stand for 30-60 minutes and then filtered through a plate and frame filter.

5. The method for extracting xylose from papermaking waste liquid according to claim 1, characterized in that: Step 4: The filtration pressure of the nanofiltration membrane is not greater than 30 Bar.

6. The method for extracting xylose from papermaking waste liquid according to claim 1, characterized in that: Step 8, the step of centrifuging the massecuite in step 8 comprises: The massecuite in step eight is centrifuged in a centrifuge at a speed of 1000-1200 r / min.

7. The method for extracting xylose from papermaking waste liquid according to claim 1, characterized in that: Step 3, the filtrate in step 2 is decolorized, comprising: Primary decolorization; heating the filtrate in step 2 to 60-70°C, adding 0.5% activated carbon by volume, and then stirring and filtering in sequence to obtain an intermediate filtrate; Secondary decolorization: the primary decolorized filtrate is passed through a granular carbon column to obtain a decolorized filtrate with a transmittance of >40%.

8. The method for extracting xylose from papermaking waste liquid according to claim 1, characterized in that: The step of performing cation exchange and anion exchange on the nanofiltration permeate in step 4 comprises: The nanofiltration permeate in step 4 is subjected to a primary cation exchange, a primary anion exchange, a secondary cation exchange and a secondary anion exchange in sequence.

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