A system and method for recovering waste alkali liquor in the production process of regenerated cellulose fiber

Abstract

The present invention belongs to the field of resource recovery, and specifically relates to a system and method for recovering waste alkali liquor in the process of regenerated cellulose fiber production. The recovery method comprises the following steps: (1) mixing the waste alkali liquor and the catalyst uniformly, and obtaining a first supernatant and a first concentrated slurry after stratification; (2) the first concentrated slurry is further subjected to sedimentation separation, and a second supernatant and a second concentrated slurry are obtained after stratification again; (3) the first supernatant and the second supernatant are combined and distilled to obtain a recovered alkali liquor, and the second concentrated slurry is evaporated and dried to obtain catalyst vapor and hemicellulose solid; (4) the recovered alkali liquor obtained in step (3) is returned to the production process for recycling, and the catalyst vapor is recycled and further recycled. Compared with alcohol precipitants such as methanol and ethanol, the amount of catalyst used can be reduced by 30 to 50%, and the energy consumption used for recycling can be correspondingly saved. The present invention can recover the residual catalyst in the hemicellulose while drying it, thereby reducing the loss of the catalyst and improving the purity of the hemicellulose.

Description

Technical Field

[0001] The invention belongs to the field of resource recovery, and in particular relates to a system and method for recovering waste alkali liquor in a regenerated cellulose fiber production process. Background Art

[0002] Regenerated cellulose fiber is one of the main chemical fiber varieties, and its output accounts for about one-third of the world's total chemical fiber output. It is estimated that my country's regenerated cellulose fiber production capacity is about 4 million tons, and the annual output of viscose fiber accounts for about 60% of the world's total output. With the development of the global economy and the growth of population, the use of regenerated cellulose fiber will continue to grow. The production process of regenerated cellulose fiber includes four stages: viscose preparation, spinning, post-treatment and post-processing. In the process of viscose preparation, a large amount of caustic soda is consumed and a large amount of waste lye is produced. Its main components are water, NaOH and hemicellulose, of which the content of NaOH is as high as 17-25%. In the production process of regenerated cellulose fiber, lye is recycled, but when the concentration of hemicellulose in the lye increases to a certain level, it can no longer be used in production, otherwise it will affect the preparation process of viscose, as well as the properties of viscose, forming conditions and the quality of the final product. In order to control the content of hemicellulose in the lye, the original method is to adjust the content of hemicellulose in the lye by partially discharging the waste lye, which requires a large amount of acid to be consumed for neutralization, which not only increases the operating cost of the sewage treatment plant, but also causes a great waste of resources. Some companies also sell waste alkali liquid to small paper mills at a low price, which is restricted by the production conditions of the paper mills. When the paper mills are shut down or abolished, the disposal of waste alkali liquid is restricted. Therefore, in order to reduce environmental pressure and reduce production costs, the purification and recycling of waste alkali liquid is an issue that must be solved for the sustainable development of regenerated cellulose fiber production companies.

[0003] Since hemicellulose is a complex polysaccharide composed of different monosaccharides, it has a small molecular weight and a complex structure. At the same time, the NaOH content in the waste alkali solution is high, so it is difficult to recycle it using conventional processes. At present, my country mainly uses dialysis and membrane separation processes to purify and recycle waste alkali solution. However, the dialysis process has low efficiency in recovering alkali solution, large water consumption, and large land occupation, and has been gradually eliminated. Relatively speaking, the membrane separation method has low cost and good effect, and is being promoted and applied. However, the membrane separation method is actually a concentration process of hemicellulose in an alkaline aqueous solution. It cannot completely and thoroughly recover and recycle the waste alkali solution. At least 30-50% of the waste alkali solution still needs to be treated by traditional methods. Summary of the invention

[0004] In view of the problems and shortcomings in the prior art, the object of the present invention is to provide a system and method for recovering waste alkali liquor in the production process of regenerated cellulose fiber.

[0005] To achieve the purpose of the invention, the technical solution adopted by the present invention is as follows:

[0006] A first aspect of the present invention provides a waste alkali liquor recovery system, the system comprising a first thickener, the waste alkali liquor and the catalyst enter the first thickener for mixing and then undergoing sedimentation separation, the first supernatant enters a distillation separation device, the first concentrated slurry enters a second thickener for further sedimentation separation, the second supernatant enters a distillation separation device, the second concentrated slurry enters a steam dryer for evaporation and drying to obtain catalyst vapor and hemicellulose solids; the catalyst vapor enters the distillation separation device and is recovered from the top to the catalyst storage tank for recycling, and the recovered alkali liquor flowing out from the bottom of the distillation separation device is returned to the production process for recycling.

[0007] According to the waste alkali liquid recovery system, preferably, the first supernatant liquid is mixed with the second supernatant liquid and then enters the distillation separation device.

[0008] The second aspect of the present invention provides a method for recovering waste alkali liquor in the process of producing regenerated cellulose fibers by the system of the first aspect, comprising the following steps:

[0009] (1) mixing the waste alkali solution in the regenerated cellulose fiber production process with the catalyst uniformly, and obtaining a first supernatant and a first concentrated slurry after layering;

[0010] (2) the first concentrated slurry is further separated by sedimentation, and after further stratification, a second supernatant and a second concentrated slurry are obtained;

[0011] (3) combining the first supernatant and the second supernatant and performing distillation to obtain a recovered alkali solution, and evaporating and drying the second concentrated slurry to obtain catalyst vapor and hemicellulose solids;

[0012] (4) The recovered alkali solution obtained in step (3) is returned to the production process for recycling, and the catalyst vapor is recovered and further recycled;

[0013] The catalyst is a mixed solution of tetrabutylammonium hydroxide, sodium phthalocyanine cobalt sulfonate and ethylenediaminetetraacetic acid.

[0014] According to the recovery method, preferably, the mass ratio of tetrabutylammonium hydroxide, sodium cobalt phthalocyanine sulfonate and ethylenediaminetetraacetic acid is (5-10):(0.1-0.8):(0.01-0.1).

[0015] According to the recovery method, preferably, in step (1), the volume ratio of the waste alkali solution to the catalyst solution is 1:1.3-2.2.

[0016] According to the recovery method, preferably, in step (1), the content of hemicellulose in the waste alkali solution is 12 to 35 g / L.

[0017] According to the recovery method, preferably, the catalyst vapor is recovered by fractional distillation.

[0018] According to the recovery method, preferably, the content of the catalyst in the recovered alkali solution after distillation is less than 0.05 wt %.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention uses tetrabutylammonium hydroxide, sodium phthalocyanine cobalt sulfonate and ethylenediaminetetraacetic acid to form a catalyst. Under the action of the catalyst, hemicellulose and related lipid substances in the alkali solution are gradually precipitated, and the hemicellulose substances are precipitated in the form of solid particles. Compared with alcohol precipitants such as methanol and ethanol, the amount of catalyst used can be reduced by 30-50%, and the energy consumption used for recovery can be correspondingly saved. The present invention can also recover the residual catalyst in the hemicellulose while drying it, reduce the loss of the catalyst, and improve the purity of the hemicellulose. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The invention discloses a waste alkali solution recovery system, wherein 1 is a catalyst storage tank, 2 is a first thickener, 3 is a second thickener, 4 is an evaporator, and 5 is a distillation separation device. DETAILED DESCRIPTION

[0022] The following examples are only for further explanation of the present invention. It should be noted that all technical and scientific terms used in the present invention have the same meanings as in the technical field to which the present invention belongs unless otherwise specified. The experimental methods in the following examples without specifying specific conditions are all based on conventional techniques in the technical field, or according to the conditions recommended by the manufacturer; the reagents or instruments used without specifying the manufacturer are all conventional products that can be purchased commercially.

[0023] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0024] Example 1

[0025] A system for recovering waste alkali liquor in the production process of regenerated cellulose fiber, such as Figure 1As shown, the system includes a first thickener 2, the waste alkali liquor and the catalyst enter the first thickener 2 and mix and then undergo sedimentation separation, the first supernatant enters the rectification separation device 5, the first concentrated slurry enters the second thickener 3 for further sedimentation separation, the second supernatant enters the rectification separation device 5, the second concentrated slurry enters the evaporation dryer 4 and undergoes evaporation and drying to obtain catalyst vapor and hemicellulose solids; the catalyst vapor enters the rectification separation device 5 and is recycled from the top to the catalyst storage tank 1 for recycling, and the recycled alkali liquor flowing out of the bottom of the rectification separation device 5 is returned to the production process for recycling. The first supernatant and the second supernatant are mixed and then enter the rectification separation device 5.

[0026] This embodiment also provides a method for recovering waste alkali liquor in the production process of regenerated cellulose fiber using the above system, which specifically comprises the following steps:

[0027] (1) Add viscose fiber waste alkali liquor containing 13.4 g / L hemicellulose and 155 g / L sodium hydroxide to the first thickener 2, and then add a catalyst composed of tetrabutylammonium hydroxide, sodium cobalt phthalocyanine sulfonate and ethylenediaminetetraacetic acid and mix them evenly, wherein the mass ratio of tetrabutylammonium hydroxide, sodium cobalt phthalocyanine sulfonate and ethylenediaminetetraacetic acid is 6:0.1:0.015, and the volume ratio of waste alkali liquor to catalyst is 1:2.1. After standing for a period of time and separating the solutions, a first supernatant (alkali liquor containing a small amount of hemicellulose) and a first concentrated slurry (containing hemicellulose and catalyst) are obtained, and the first supernatant is passed into the rectification separation device 5.

[0028] (2) The first concentrated slurry is passed into the second thickener 3 for further sedimentation separation, and after stratification, a second supernatant and a second concentrated slurry are obtained. The second supernatant is mixed with the first supernatant and then passed into the distillation separation device 5. The second concentrated slurry is passed into the evaporator 4.

[0029] (3) Through spray drying, the catalyst in the second concentrated slurry enters the distillation separation device 5 in the form of steam, and at the same time, hemicellulose solids with a moisture content of 6.35% are obtained. The catalyst steam is discharged from the top of the tower and enters the catalyst storage tank 1 for recycling, and the alkali liquid flowing out from the bottom of the tower is returned to the alkali liquid storage tank for recycling.

[0030] The catalyst content in the alkali liquid flowing out from the bottom of the distillation separation device of this embodiment is 0.0043%, and the hemicellulose content is 1.67 g / L.

[0031] Example 2

[0032] A method for recovering waste alkali liquor in a regenerated cellulose fiber production process comprises the following steps:

[0033] (1) Add viscose fiber waste alkali liquor containing 24.5 g / L hemicellulose and 244 g / L sodium hydroxide to the first thickener 2, and then add a catalyst composed of tetrabutylammonium hydroxide, sodium cobalt phthalocyanine sulfonate and ethylenediaminetetraacetic acid and mix them evenly, wherein the mass ratio of tetrabutylammonium hydroxide, sodium cobalt phthalocyanine sulfonate and ethylenediaminetetraacetic acid is 7.5:0.38:0.049, and the volume ratio of waste alkali liquor to catalyst is 1:1.9. Mix them evenly, let them stand for a period of time, and after the solution is separated into layers, a first supernatant (alkali liquor containing a small amount of hemicellulose) and a first concentrated slurry (containing hemicellulose and catalyst) are obtained, and the first supernatant is passed into the distillation separation device 5.

[0034] (2) The first concentrated slurry is passed into the second thickener 3 for further sedimentation separation, and after stratification, a second supernatant and a second concentrated slurry are obtained. The second supernatant is passed into the rectification separation device 5, and the second concentrated slurry is passed into the evaporator 4.

[0035] (3) Through spray drying, the catalyst in the second concentrated slurry enters the distillation separation device 5 in the form of steam, and at the same time, hemicellulose solids with a moisture content of 6.35% are obtained. The catalyst steam is discharged from the top of the tower and enters the catalyst storage tank 1 for recycling, and the alkali liquid flowing out from the bottom of the tower is returned to the alkali liquid storage tank for recycling.

[0036] The catalyst content in the alkali liquid flowing out from the bottom of the distillation separation device of this embodiment is 0.0235%, and the hemicellulose content is 3.96 g / L.

[0037] Example 3

[0038] A method for recovering waste alkali liquor in a regenerated cellulose fiber production process comprises the following steps:

[0039] (1) Add viscose fiber waste alkali liquor containing 33.68 g / L hemicellulose and 216 g / L sodium hydroxide to the first thickener 2, and then add a catalyst composed of tetrabutylammonium hydroxide, sodium cobalt phthalocyanine sulfonate and ethylenediaminetetraacetic acid and mix them evenly, wherein the mass ratio of tetrabutylammonium hydroxide, sodium cobalt phthalocyanine sulfonate and ethylenediaminetetraacetic acid is 8.8:0.67:0.076, and the volume ratio of waste alkali liquor to catalyst is 1:1.8. After standing for a period of time and separating the solutions, a first supernatant (alkali liquor containing a small amount of hemicellulose) and a first concentrated slurry (containing hemicellulose and catalyst) are obtained, and the first supernatant is passed into the rectification separation device 5.

[0040] (2) The first concentrated slurry is passed into the second thickener 3 for further sedimentation separation, and after stratification, a second supernatant and a second concentrated slurry are obtained. The second supernatant is passed into the rectification separation device 5, and the second concentrated slurry is passed into the evaporator 4.

[0041] (3) Through spray drying, the catalyst in the second concentrated slurry enters the distillation separation device 5 in the form of steam, and at the same time, hemicellulose solids with a moisture content of 6.35% are obtained. The catalyst steam is discharged from the top of the tower and enters the catalyst storage tank 1 for recycling, and the alkali liquid flowing out from the bottom of the tower is returned to the alkali liquid storage tank for recycling.

[0042] The catalyst content in the alkali liquid flowing out from the bottom of the distillation separation device of this embodiment is 0.0397%, and the hemicellulose content is 5.79 g / L.

[0043] Embodiments 4 to 9

[0044] The present invention also conducted experiments of Examples 4 to 9, which are basically the same as Example 1, except that the amount of catalyst used is different, as shown in Table 1. The contents of hemicellulose and catalyst in the alkali solution recovered in Examples 4 to 9 after two sedimentation separations are also shown in Table 1.

[0045] Table 1 Experimental data related to waste alkali solution recovery

[0046]

[0047] As can be seen from Table 1, there is a certain relationship between the hemicellulose extraction rate and the amount of catalyst used. When the ratio of waste alkali liquid to catalyst is between 1:1.7 and 2.2, the hemicellulose extraction rate is optimal.

[0048] The above embodiments are specific implementation methods of the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any other combination, change, modification, substitution and simplification that does not exceed the design concept of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for recovering waste alkali liquor in a regenerated cellulose fiber production process, characterized in that: The following steps are involved: (1) mixing the waste alkali solution in the regenerated cellulose fiber production process with the catalyst uniformly, and obtaining a first supernatant and a first concentrated slurry after layering; (2) the first concentrated slurry is further subjected to sedimentation separation to obtain a second supernatant and a second concentrated slurry; (3) combining the first supernatant and the second supernatant and performing distillation to obtain a recovered alkali solution, and evaporating and drying the second concentrated slurry to obtain catalyst vapor and hemicellulose solids; (4) The recovered alkali solution obtained in step (3) is returned to the production process for recycling, and the catalyst vapor is recovered and further recycled; The catalyst is a mixed solution of tetrabutylammonium hydroxide, sodium phthalocyanine cobalt sulfonate and ethylenediaminetetraacetic acid.

2. The method according to claim 1, characterized in that: The mass ratio of tetrabutylammonium hydroxide, sodium cobalt phthalocyanine sulfonate and ethylenediaminetetraacetic acid is (5-10):(0.1-0.8):(0.01-0.1).

3. The method according to claim 2, characterized in that: In step (1), the volume ratio of the waste alkali solution to the catalyst solution is 1:(1.3-2.2).

4. The method according to claim 3, characterized in that: In step (1), the content of hemicellulose in the waste alkali solution is 12 to 35 g / L.

5. The method according to claim 4, characterized in that: The catalyst vapor is recovered by fractional distillation.

6. The method according to claim 5, characterized in that: The content of the catalyst in the recovered alkali solution after distillation is less than 0.05wt%.

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