Method for recovering PVA in waste water of island fiber opening

Abstract

This invention discloses a method for recovering PVA from wastewater in the opening and treatment of island fiber manufacturing, belonging to the field of wastewater treatment. The method involves sequentially adding sodium sulfate, sodium polyphosphate, and boric acid to PVA wastewater to obtain a white PVA product. The PVA recovery rate is as high as 79%, and the recovered PVA exhibits good film-forming properties, transparency, and mechanical properties, as well as a certain degree of flame retardancy, thus realizing the recovery and reuse of PVA from the opening and treatment wastewater.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of wastewater treatment, and particularly relates to a method for recycling PVA in sea-island fiber opening wastewater. BACKGROUND

[0002] Sea-island fiber is a kind of high-value-added and high-performance composite fiber, which has wide application in artificial suede, peach skin, synthetic leather and filter material. The benzene reduction and alkali reduction process used for sea-island fiber opening has problems such as high energy consumption, environmental pollution and resource waste, which does not meet the concept of ecological environmental protection. Therefore, researchers begin to study green and non-toxic water-soluble polyvinyl alcohol (PVA) as a sea component to realize the composite melt spinning of sea-island fiber, and then water-soluble opening is carried out. However, 3% to 5% of PVA is still contained in the opening wastewater. If the wastewater is directly discharged, it will cause environmental pollution. Membrane separation method is one of the commonly used methods for treating PVA wastewater at present, but the filter membrane has short service life, high price and high production cost. Patent CN202210684221.X discloses a recovery process for purifying PVA in waste liquid, but it needs multi-stage preheating negative pressure distillation and multiple evaporation, and has high requirements for equipment, complex process and high energy consumption. Patent CN202111678664.X discloses a method for extracting PVA from slurry by supercritical carbon dioxide, which comprises the steps of waste water filtration, PVA filter cake drying, grinding, supercritical CO2 extraction, CO2 and extract separation, PVA evaporation crystallization, etc. The process is complex and the flow is long, and it is difficult to realize industrialized production at present. The chemical coagulation method is simple, but the PVA recovered by the traditional chemical coagulation method has high water content and low solid content, which needs further treatment. SUMMARY

[0003] [TECHNICAL PROBLEM]

[0004] Direct discharge of PVA wastewater can easily cause environmental pollution and resource waste, and the traditional PVA wastewater treatment technology has problems such as complex process, long flow, high energy consumption or low PVA recovery rate.

[0005] [TECHNICAL SCHEME]

[0006] In order to solve the above technical problems, the application provides a method for recycling PVA in opening wastewater, which is simple and efficient, can significantly reduce the water content of the recovered PVA, improve the PVA recovery rate, and realize the recycling of PVA in wastewater.

[0007] The first object of the application is to provide a method for recycling PVA in opening wastewater, which comprises the following steps:

[0008] A method for recycling PVA in opening wastewater, characterized in that it comprises the following steps:

[0009] (1) heating sodium sulfate to dissolve in deionized water, adding to PVA wastewater, mixing, obtaining mixed solution 1; the mass fraction of PVA in the PVA wastewater is 3%-5%;

[0010] (2) then dissolving sodium polyphosphate in deionized water, adding to the mixed solution 1 of step (1), mixing, reacting at 40-60℃ for 5-20min, obtaining mixed solution 2;

[0011] (3) heating boric acid to dissolve in deionized water, adding to the mixed solution 2 of step (2), stirring and reacting, obtaining white solid, separating and collecting the solid, washing, drying.

[0012] Further, in step (1), the adding amount of sodium sulfate relative to PVA wastewater is (0.2-0.6) g / 30mL. Specifically, 0.5g / 30mL can be selected.

[0013] Further, in step (1), the concentration of sodium sulfate heated and dissolved in deionized water is (0.08-0.24) g / mL. Specifically, 0.2g / mL can be selected.

[0014] Further, in step (2), the adding amount of sodium polyphosphate relative to PVA wastewater is (0.2-0.6) g / 30mL. Specifically, 0.5g / 30mL can be selected.

[0015] Further, in step (2), the concentration of sodium polyphosphate dissolved in deionized water is (0.1-0.3) g / mL. Specifically, 0.25g / mL can be selected.

[0016] Further, the mass ratio of sodium polyphosphate to sodium sulfate is 1:1.

[0017] Further, in step (3), the adding amount of boric acid relative to PVA wastewater is (0.15-0.55) g / 30mL. Specifically, 0.5g / 30mL can be selected.

[0018] Further, in step (3), the concentration of boric acid heated and dissolved in deionized water is (0.03-0.11) g / mL. Specifically, 0.1g / mL can be selected.

[0019] Further, the mass ratio of sodium polyphosphate to boric acid is 1:1.

[0020] Further, the recovery method specifically comprises:

[0021] (1) PVA wastewater: the mass fraction of PVA is 3.33%, the pH value is 9, and 30ml of PVA wastewater is processed in a single test;

[0022] (2) Weigh a certain amount of sodium sulfate, heat and dissolve in 2.5 mL of deionized water at 50°C, add to the above wastewater and stir for 1.0 min to obtain mixed solution 1;

[0023] (3) Weigh a certain amount of sodium polyphosphate, dissolve in 2 mL of deionized water, and then add to mixed solution 1 of step (2) and stir;

[0024] (4) React the wastewater of step (3) in a constant temperature water bath at 50°C for 10 min to obtain mixed solution 2;

[0025] (5) Weigh a certain amount of boric acid, heat and dissolve in 5 mL of deionized water at 50°C, then add to mixed solution 2 of step (4) (ensure that the solution is prepared and used immediately), and stir and continue to react for 5 min to obtain a white product;

[0026] (6) Wash the product with cold deionized water for 3 times, then place it in a vacuum oven, dry and weigh its mass to calculate the PVA recovery rate.

[0027] Further, the addition amount of sodium sulfate in step (2) is 0.2-0.6 g.

[0028] Further, the addition amount of sodium polyphosphate in step (3) is 0.2-0.6 g.

[0029] Further, the addition amount of boric acid in step (5) is 0.15-0.55 g.

[0030] Further, the drying temperature in step (6) is 60°C.

[0031] Further, the PVA wastewater is sea-island fiber opening wastewater, and the mass fraction of PVA is 3%-5%.

[0032] The second object of the present application is to provide a preparation method of recycled PVA film, which comprises:

[0033] S1, recycling PVA according to the above method;

[0034] S2, heating and dissolving the recycled PVA in deionized water, defoaming, and standing to form a film.

[0035] Further, the standing to form a film is placed in a constant temperature and humidity box at 25°C and a relative humidity of 60% for drying for 24 h.

[0036] Further, the defoaming is vacuum defoaming.

[0037] [Beneficial effects]

[0038] The application is directed to a suitable treatment method for sea-island fiber opening wastewater with PVA mass fraction of 3% or more, which improves the PVA recovery rate, and the recovered PVA has good film forming property, transparency and mechanical property and certain flame retardancy, realizing the recycling and reuse of PVA in the wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The cross-linking reaction of sodium polyphosphate and PVA.

[0040] Figure 2 The recovery effect of the anhydrous sodium sulfate / sodium polyphosphate / boric acid system on PVA. DETAILED DESCRIPTION

[0041] The preferred embodiments of the application are described below, and it should be understood that the embodiments are for better explaining the application and are not used to limit the application.

[0042] Test method:

[0043] PVA recovery rate test: the ratio of the mass of the recovered PVA obtained after drying the PVA in the wastewater to the mass of PVA in the wastewater, i.e. PVA recovery rate = mass of recovered PVA / mass of PVA in the wastewater.

[0044] Initial thermal decomposition temperature test: determined by a thermogravimetric analyzer (TG).

[0045] Melting point test: determined by a differential scanning calorimeter (DSC).

[0046] Mechanical property test: determined by a microcomputer-controlled electronic universal testing machine according to the national standard GB / T 1040-92 "Plastics - Determination of tensile properties".

[0047] Micro-combustion calorimetry test: the combustion performance of the sample is tested by a micro-combustion calorimeter. The temperature rising rate is 1℃ / s, and the temperature range is 100-700℃.

[0048] Limiting oxygen index test: the limiting oxygen index (LOI value) of the sample is tested by an oxygen index tester according to GB / T 2406.2-2009 "Plastics - Determination of the burning behavior in an oxygen index apparatus".

[0049] Example 1

[0050] A PVA recovery method in wastewater, comprising the following steps:

[0051] (1) PVA wastewater: PVA mass fraction is 3.33%, the pH value is 9, and 30 mL of PVA wastewater is treated in a single test;

[0052] (2) Weigh 0.5 g of sodium sulfate, dissolve in 2.5 mL of deionized water at 50°C, add to the above wastewater and stir for 1.0 min to obtain mixed solution 1;

[0053] (3) Weigh 0.5 g of sodium polyphosphate and dissolve in 2 mL of deionized water, then add to mixed solution 1 of step (2) and stir;

[0054] (4) React the wastewater of step (3) at 50°C in a constant temperature water bath for 10 min to obtain mixed solution 2;

[0055] (5) Weigh 0.5 g of boric acid, dissolve in 5 mL of deionized water at 50°C, then add to mixed solution 2 of step (4) (ensure that the solution is prepared immediately before use), stir and continue to react for 5 min to obtain a white product;

[0056] (6) Wash the product with cold deionized water 3 times, then place it in a vacuum oven, dry and weigh its mass to calculate the PVA recovery rate, which is 77.82%.

[0057] Comparative Example 1

[0058] Omit sodium sulfate in Example 1, and the rest is the same as Example 1. No PVA is precipitated in the wastewater.

[0059] Comparative Example 2

[0060] Omit sodium polyphosphate in Example 1, and the rest is the same as Example 1. Only a small amount of PVA is precipitated in the wastewater.

[0061] Comparative Example 3

[0062] Omit boric acid in Example 1, and the rest is the same as Example 1. No PVA is precipitated in the wastewater.

[0063] From Example 1 and Comparative Examples 1-3, it can be seen that the absence of any one of sodium sulfate, sodium polyphosphate and boric acid is not conducive to the recovery of PVA in the wastewater, and the combined action of the three helps to precipitate PVA in the wastewater, thereby improving the PVA recovery rate.

[0064] Example 2

[0065] In this example, the optimal recovery method of PVA in wastewater is obtained by further optimizing the experiment, taking sodium sulfate (A), sodium polyphosphate (B) and boric acid (C) as independent variable factors and the PVA recovery rate as response value for response surface experiment. The specific steps are as follows:

[0066] (1) PVA wastewater: PVA mass fraction is 3.33%, and its pH value is 9. Single test PVA wastewater 30 ml;

[0067] (2) Weigh a certain amount of sodium sulfate, heat to dissolve in 2.5 mL of deionized water at 50°C, add to the wastewater above and stir for 1.0 min;

[0068] (3) Weigh a certain amount of sodium polyphosphate, dissolve in 2 mL of deionized water, and then add to the wastewater of step (2) and stir;

[0069] (4) React the wastewater of step (3) in a constant temperature water bath at 50°C for 10 min;

[0070] (5) Weigh a certain amount of boric acid, heat to dissolve in 5 mL of deionized water at 50°C, then add to the wastewater of step (4) (ensure that the solution is prepared and used immediately), and stir, continue to react for 5 min to obtain a white product;

[0071] (6) Wash the product with cold deionized water 3 times, then place it in a vacuum oven, dry, and then weigh its mass to calculate the PVA recovery rate.

[0072] The experimental results are shown in Table 1.

[0073] Table 1 Optimization Experimental Results

[0074] Experimental group (A) Sodium sulfate / g (B) Sodium polyphosphate / g (C) Boric acid / g PVA recovery rate / % 1 0.4 0.5 0.25 61.68 2 0.3 0.3 0.35 60.44 3 0.4 0.4 0.35 76.04 4 0.3 0.4 0.25 56.05 5 0.4 0.4 0.35 75.32 6 0.4 0.3 0.25 58.14 7 0.4 0.4 0.35 76.22 8 0.5 0.4 0.45 78.15 9 0.5 0.3 0.35 72.22 10 0.5 0.4 0.25 62.55 11 0.3 0.4 0.45 64.77 12 0.3 0.5 0.35 63.2 13 0.4 0.4 0.35 76.12 14 0.4 0.3 0.45 70.1 15 0.4 0.5 0.45 72.56 16 0.5 0.5 0.35 73.51 17 0.4 0.4 0.35 75.37

[0075] The response surface experiment results obtained with sodium sulfate (A), sodium polyphosphate (B), and boric acid (C) as the independent variable factors and the PVA recovery rate as the response value are shown in Table 1. It can be seen that with the change of the independent variables, the response value (PVA recovery rate) changes from 56.05% to 78.15%, indicating that sodium sulfate, sodium polyphosphate, and boric acid are key factors affecting the PVA recovery rate. According to the results of the response surface experiment, the response surface function equation model related to the three factors of PVA recovery rate is established as follows:

[0076] PVA recovery rate (%) = 75.81 + 5.25*A + 1.26*B + 5.90*C - 0.3675*AB + 1.72*AC - 0.27*BC - 4.36*A 2 -4.12*B 2 -6.08*C 2 .

[0077] According to the model, the optimal process for PVA recovery is: sodium sulfate 0.471 g, sodium polyphosphate 0.414 g, and boric acid 0.435 g.

[0078] Example 3

[0079] This example uses the optimal recovery process obtained from the response surface experiment of Example 2 to test, and the PVA recovery rate is 79.26%.

[0080] Example 4

[0081] A preparation method of recycled PVA film, comprising the following steps:

[0082] The recycled PVA obtained in Example 3 was heated and dissolved in deionized water, and then poured into a polytetrafluoroethylene plate after vacuum degassing, and then placed in a constant temperature and humidity box with a relative humidity of 60% at 25°C for drying for 24h to form a film.

[0083] The obtained recycled PVA film was tested for performance, and the thickness, transparency, tensile strength and elongation at break thereof were 113μm, 84.2%, 17.9MPa and 61.8%, respectively; the heat release rate peak temperature was increased to 434.5°C, and the LOI value was increased from 19.5% to 25.1%, thereby improving the flame retardant performance and safety of the PVA-based plastic film and realizing the recycling of PVA in the waste water of the water-soluble sea-island fiber.

[0084] Comparative Example 4

[0085] With reference to Example 1, the equivalent amount of sodium polyphosphate in step (3) was replaced by the relevant composition reported in the literature (as shown in Table 2):

[0086] (1) PVA waste water: the mass fraction of PVA was 3.33%, and the pH value thereof was 9; 30ml of PVA waste water was treated in a single test;

[0087] (2) 0.5g of sodium sulfate was weighed and dissolved in 2.5mL of deionized water at 50°C, added to the above waste water and stirred for 1.0min;

[0088] (3) 0.5g of composition (B) was dissolved in 2mL of deionized water, and then added to the waste water of step (2) and stirred;

[0089] (4) The waste water of step (3) was reacted in a constant temperature water bath at 50°C for 10min;

[0090] (5) 0.5g of boric acid was weighed and dissolved in 5mL of deionized water at 50°C, and then added to the waste water of step (4) (to ensure that the solution is prepared and used immediately), and stirred, and the reaction was continued for 5min to obtain a white product;

[0091] (6) The product was washed with cold deionized water for 3 times, and then placed in a vacuum oven for drying, and then weighed to calculate the PVA recovery rate, and the PVA recovery rate was obtained as shown in Table 2.

[0092] Table 2

[0093] Composition (B) PVA recovery rate Sodium polyphosphate (Example 1) 77.82％ Ammonium carbonate 27.43％ Sodium bicarbonate 30.21％ Ammonium carbonate + sodium bicarbonate (mass ratio 1 : 1.5) 30.58％

[0094] The method of using sodium carbonate + sodium bicarbonate as a coagulant, although to some extent helps PVA in wastewater to precipitate, but the precipitated PVA is difficult to form large flocs, and a considerable part is in the form of small colloidal particles suspended in water, which is difficult to collect, and the PVA coagulation and dehydration treatment has a low solid content, and the actual recovered PVA content is not high, so a new coagulant system needs to be developed to improve the PVA recovery rate. The present application is used in combination with sodium polyphosphate, which can esterify and crosslink with the hydroxyl groups in PVA, so that PVA is precipitated and separated out quickly, and the reaction mechanism is as shown in Figure 1 .

[0095] Moreover, it is found in the experiment that only by adding sodium sulfate and boric acid, PVA is difficult to form large flocs, and after continuing to add sodium polyphosphate, PVA in the fiber opening wastewater is quickly precipitated, and it is found that the fiber opening wastewater becomes clear, because the PVA fiber opening wastewater contains a small amount of other additives in addition to PVA, and sodium polyphosphate has strong Ca 2+ complexing ability and ion exchange performance, which can make the suspension into a solution, and the effect is as shown in Figure 2 .

[0096] Comparative Example 5

[0097] Referring to Example 1, the order of steps (3) and (5) is adjusted:

[0098] (1) PVA wastewater: PVA mass fraction is 3.33%, and its pH value is 9, and 30ml of PVA wastewater is treated in a single test;

[0099] (2) 0.5g of sodium sulfate is weighed and dissolved in 2.5ml of deionized water at 50°C, added to the above wastewater and stirred for 1.0min;

[0100] (3) 0.5g of boric acid is weighed and dissolved in 5ml of deionized water at 50°C (to ensure that the solution is prepared and used immediately), and then added to the wastewater of step (2) and stirred;

[0101] (4) The wastewater of step (3) is reacted for 10min under the condition of constant temperature water bath at 50°C;

[0102] (5) 0.5g of sodium polyphosphate is weighed and dissolved in 2ml of deionized water, and then added to the wastewater of step (4) (to ensure that the solution is prepared and used immediately), and stirred and reacted for 5min, to obtain a white product;

[0103] (6) The product is washed with cold deionized water for 3 times, and then placed in a vacuum oven for drying, and then weighed to calculate the PVA recovery rate of 38.62%.

[0104] The above examples are not intended to limit the scope of the present application, nor are the described steps intended to limit the order in which they are performed. Modifications apparent to one skilled in the art in light of the above teachings are intended to fall within the scope of the claims.

Claims

1. A method for recovering PVA in a fiber-opening wastewater, characterized by, The method comprises the following steps: (1) heating and dissolving sodium sulfate in deionized water, adding to PVA wastewater, mixing, obtaining mixed solution 1; the mass fraction of PVA in the PVA wastewater is 3%-5%; (2) then dissolving sodium polyphosphate in deionized water, adding to the mixed solution 1 of step (1), mixing, reacting at 40-60℃ for 5-20 min, obtaining mixed solution 2; (3) heating and dissolving boric acid in deionized water, adding to the mixed solution 2 of step (2), stirring and reacting, obtaining white solid, separating and collecting the solid, washing, drying; The addition amount of sodium sulfate relative to the PVA wastewater is (0.2~0.6) g / 30 mL; the addition amount of sodium polyphosphate relative to the PVA wastewater is (0.2~0.6) g / 30 mL; the addition amount of boric acid relative to the PVA wastewater is (0.15~0.55) g / 30 mL.

2. The method of claim 1, wherein, In step (1), the concentration of sodium sulfate heated and dissolved in deionized water is (0.08~0.24) g / mL.

3. The method of claim 1, wherein, In step (2), the concentration of sodium polyphosphate dissolved in deionized water is (0.1~0.3) g / mL.

4. The method of claim 1, wherein, The mass ratio of sodium polyphosphate to sodium sulfate is 1:

1.

5. The method of claim 1, wherein, In step (3), the concentration of boric acid heated and dissolved in deionized water is (0.03~0.11) g / mL.

6. The method according to any one of claims 1 to 5, characterized in that, The mass ratio of sodium polyphosphate to boric acid is 1:

1.

7. A method for preparing a recycled PVA film, characterized by, The method comprises: S1, recovering PVA according to the method in any one of claims 1-6; S2, heating and dissolving the recovered PVA in deionized water, defoaming, standing and forming a film.

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