CN109160660B - Method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater - Google Patents

Abstract

The invention relates to the field of sodium carboxymethylcellulose wastewater treatment, in particular to a method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater, which comprises the following steps: 1) adding a flocculating agent into the wastewater, and performing flocculation separation to obtain a mother solution; 2) adding macroporous adsorption resin into the mother liquor, oscillating for 2-5h at 20-40 ℃, and filtering to obtain an effluent liquid; 3) carrying out reduced pressure distillation on the effluent to remove precipitated salt substances to obtain a concentrated solution; 4) adding methanol and exchange resin into the concentrated solution for esterification, rectifying, and collecting distillate at 90-120 deg.C to obtain esterified product; 5) heating and hydrolyzing the esterified substance for 3-5h, and distilling under reduced pressure to remove alcohol substances and water to obtain glycolic acid. The invention has the following priority: can effectively recover the glycolic acid in the CMC production wastewater, and is economical and environment-friendly.

Description

Method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater

Technical Field

The invention relates to the field of sodium carboxymethylcellulose wastewater treatment, in particular to a method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater.

Background

The only pollutant produced in the sodium carboxymethylcellulose (CMC) industry is wastewater, and is characterized by high salt content and high COD (20000-40000 mg/L). About 2.5-3 tons of waste liquid is generated every 1 ton of CMC is produced, the treatment of CMC production waste water is an important subject in the world, and developed countries pay particular attention to the treatment. For example, a hydrogen peroxide treatment process is adopted in Japan, and a resin exchange method is adopted in Germany, but the respective defects still exist, and zero emission of surface water cannot be realized. China has no mature technical patent in this aspect, and has a gap which is enlarged compared with developed countries. The problem is very important to solve at present when energy conservation, emission reduction and environmental protection, particularly the water protection system is raised to become national strategy in China.

China is in a rapid economic growth period, and the CMC products are developing at a higher annual growth rate at present. The demand of China is expected to increase to 80-100 million tons in the last 5 years, and the market growth is good, so that the urgency and the necessity of implementation are highlighted by recycling of emissions of the CMC industry.

The patent with application number CN201610346447.3 describes a method for treating CMC waste water, firstly filtering a large amount of salt in an evaporation mode to remove, and then reducing COD by a biochemical method, thereby meeting the discharge requirement, but the COD content in the CMC waste water is very high, and part of substances have poor biodegradability, meanwhile, chloroacetic acid is used for replacing hydroxyl in the production process of CMC, excessive chloroacetic acid is needed, under the alkaline condition, the excessive chloroacetic acid forms sodium glycolate, and the glycolic acid and the esterified substance thereof are important fine chemical intermediates, and are widely applied to the industries of adhesives, dyeing, spinning and daily chemicals. Therefore, the separation or conversion of the glycolic acid contained in the wastewater has great significance for the treatment of the CMC wastewater, not only can greatly reduce the COD in the solid waste and be beneficial to environmental protection, but also can change waste into valuables. Glycolic acid is generally obtained by esterifying glycolic acid in wastewater and then hydrolyzing the glycolic acid, and there are two main methods for synthesizing glycolic acid esters: one is that glycolic acid and alcohol generate ester under the catalysis of acid; the other is ester which is produced by reacting glycolic acid with halogenated hydrocarbon under alkaline condition to form ester, and separating and purifying by rectification. The first method has the disadvantages of low conversion rate, resulting in low utilization rate of raw materials; the second method has the disadvantages that the used halogenated hydrocarbon is generally higher in price than the corresponding alcohol, at least an equivalent amount of alkali is consumed to promote the reaction, new solid waste is generated, and industrial production is not economical.

Disclosure of Invention

Aiming at the problems, the invention provides a method for recovering glycolic acid in sodium carboxymethylcellulose (CMC) production wastewater, which can effectively remove most organic matters and salts in the sodium carboxymethylcellulose wastewater, recover glycolic acid, realize environment-friendly discharge and effectively recycle wastes.

To achieve the above object, the present invention is achieved by: a method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater comprises the following steps:

(1) adding a flocculating agent into the wastewater, and performing flocculation separation to obtain a mother solution;

(2) adding macroporous adsorption resin into the mother liquor, oscillating for 2-5h at 20-40 ℃, and filtering to obtain an effluent liquid;

(3) carrying out reduced pressure distillation on the effluent to remove precipitated salt substances to obtain a concentrated solution;

(4) adding methanol and exchange resin into the concentrated solution for esterification, rectifying, and collecting distillate at 90-120 deg.C to obtain esterified product;

(5) heating and hydrolyzing the esterified substance for 3-5h, and distilling under reduced pressure to remove alcohol substances and water to obtain glycolic acid.

The main components of the sodium carboxymethylcellulose wastewater are high in salinity and COD, the method is characterized by firstly carrying out flocculation treatment on the wastewater, mainly removing residual sodium carboxymethylcellulose and suspended matters, then effectively removing more than 90% of organic matters in the wastewater by using macroporous adsorption resin, reducing the COD value, effectively removing the salinity in the wastewater by secondary distillation, adding alcohol for esterification, obtaining an esterified substance with higher purity by rectification, and finally obtaining the glycolic acid by hydrolysis.

Preferably, the flocculant is a fenton reagent, the flocculation separation is implemented by centrifuging in a centrifuge for 5-10min, sodium carboxymethylcellulose can be remained in sodium carboxymethylcellulose wastewater, the sodium carboxymethylcellulose can be mixed in the wastewater and discharged, which is one of main reasons causing water pollution and COD standard exceeding, the fenton reagent can be used for effectively degrading the sodium carboxymethylcellulose on one hand, and in addition, suspended impurities in water can be removed by flocculation operation, so that the pretreatment is carried out on subsequent resin, and the service life of the resin is prolonged.

Preferably, the rotating speed of the centrifuge is 4500-.

Preferably, the average particle size of the macroporous adsorption resin is 0.32-0.76mm, the average pore diameter is 10-20nm, and the macroporous adsorption resin with the parameters can effectively remove organic matters in sodium carboxymethylcellulose and reduce COD.

Preferably, the reduced pressure distillation in the step (3) is carried out twice, the first reduced pressure distillation is carried out at the pressure of-0.08 to-0.085 MPa and the temperature of 50 to 80 ℃, the distillate is subjected to the second reduced pressure distillation at the pressure of-0.085 to-0.095 MPa and the temperature of 50 to 80 ℃ to obtain a concentrated solution, and sodium chloride can be removed in large quantity and the desalination rate can be improved by carrying out reduced pressure distillation twice and controlling parameters.

Preferably, the exchange resin is strong acid ion exchange resin, and the strong acid ion exchange resin is used for replacing acid to be used as a catalyst for esterification reaction, so that a series of side reactions caused by acid addition and subsequent processes such as acid removal are avoided, and the yield and the purity of a final product are improved.

Preferably, the strong acid ion exchange resin can be reused after being activated by strong acid, the strong acid ion exchange resin is used as a catalyst of reaction and does not participate in the reaction, and the resin can be reused after being physically cleaned and reduced by strong acid, so that the cost is saved.

Preferably, the esterification in the step (4) has the exchange resin content of 100-200 g/L.

Preferably, the rectification in the step (4) has the space velocity of 0.01-0.015/min, the temperature interval for collecting the distillate is 80-95 ℃, and the esterification reaction also occurs in the rectification process, wherein under the parameters provided by the invention, the esterification rate of the hydroxyacetic acid can reach 96%.

Preferably, the hydrolysis temperature in the step (5) is controlled to be 70-90 ℃, the temperature is lower than 70 ℃, and the slow hydrolysis reaction has low yield; the temperature is higher than 90 ℃, and the hydrolysate is easy to re-esterify.

The invention has the following priority:

(1) the waste water is pretreated by adopting a fenton reagent, residual sodium carboxymethylcellulose and partial organic matters are removed, and the residual organic matters are removed by using macroporous adsorption resin, so that the COD can be efficiently reduced.

(2) According to the invention, glycolic acid is obtained by esterifying and hydrolyzing glycolic acid in wastewater, because impurities in sodium carboxymethylcellulose wastewater are more, the glycolic acid is difficult to purify directly, and the purity of the obtained product is lower, the yield and the purity of the glycolic acid can be greatly improved by using a method of catalyzing esterification by ion exchange resin, rectifying, collecting and esterifying.

(3) The wastewater treated by the method can obtain glycolic acid, effectively reduce the COD and salt content of the wastewater, reach the discharge standard and have practical economic benefits.

Detailed Description

The present embodiments are to be considered in all respects as illustrative and not restrictive. Any changes that may be made by one of ordinary skill in the art after reading the specification herein are, within the purview of the appended claims, to fall within the scope of the patent laws.

The production wastewater is obtained by using excessive chloroacetic acid to replace hydroxyl to produce sodium carboxymethyl cellulose, and the excessive chloroacetic acid can form ammonium glycolate to be dissolved in the wastewater and is accompanied with impurities such as sodium carboxymethyl cellulose, lignin and the like.

Example 1:

a method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater comprises the following steps:

(1) h is added into the waste water₂O₂And FeSO₄Composed fenton reagent, wherein H₂O₂And FeSO₄In a molar ratio of 30: 1, stirring and mixing uniformly, centrifuging for 10min in a centrifuge at the rotating speed of 5000r/min, and separating to obtain mother liquor;

(2) adding macroporous adsorbent resin into the mother liquor, with average particle diameter of 0.32-0.56mm and average pore diameter of 10-15nm, oscillating at 30 deg.C for 2 hr, and filtering to obtain effluent liquid, wherein at this time, a large amount of organic matter has been removed, and COD in the wastewater is reduced remarkably;

(3) carrying out reduced pressure distillation on the distillate, wherein the first reduced pressure is-0.08 MPa, the temperature is 80 ℃, carrying out second reduced pressure distillation on the distillate, the pressure is-0.095 MPa, the temperature is 80 ℃, obtaining a concentrated solution, and removing a large amount of sodium chloride;

(4) adding methanol into the concentrated solution at a ratio of 5kg/L, adding strong acid ion exchange resin at a ratio of 200g/L for esterification, rectifying after 24h, controlling the space velocity of the rectifying tower at 0.01/min, and collecting distillate at 90-120 deg.C to obtain esterified product;

(5) heating and hydrolyzing the esterified product at 70 deg.C for 3h, and distilling under reduced pressure to remove alcohol and water to obtain glycolic acid.

Example 2:

a method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater comprises the following steps:

(1) h is added into the waste water₂O₂And FeSO₄Composed fenton reagent, wherein H₂O₂And FeSO₄In a molar ratio of 40: 1, stirring and mixing uniformly, centrifuging for 10min in a centrifuge at the rotating speed of 4500r/min, and separating to obtain mother liquor;

(2) adding macroporous adsorbent resin into the mother liquor, with average particle diameter of 0.52-0.76mm and average pore diameter of 15-20nm, oscillating at 20 deg.C for 5 hr, and filtering to obtain effluent liquid, wherein at this time, a large amount of organic matter has been removed, and COD in the wastewater is reduced remarkably;

(3) carrying out reduced pressure distillation on the distillate, wherein the first reduced pressure is-0.08 MPa, the temperature is 80 ℃, carrying out second reduced pressure distillation on the distillate, the pressure is-0.095 MPa, the temperature is 80 ℃, obtaining a concentrated solution, and removing a large amount of sodium chloride;

(4) adding 3kg/L methanol into the concentrated solution, adding 100g/L strong acid ion exchange resin for esterification, rectifying after 24h reaction, controlling the space velocity of the rectifying tower at 0.012/min, and collecting distillate at 90-120 deg.C to obtain esterified product;

(5) heating and hydrolyzing the esterified product at 90 deg.C for 5h, and distilling under reduced pressure to remove alcohol and water to obtain glycolic acid.

Example 3:

a method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater comprises the following steps:

(1) h is added into the waste water₂O₂And FeSO₄Composed fenton reagent, wherein H₂O₂And FeSO₄In a molar ratio of 25: 1, stirring and mixingHomogenizing, centrifuging for 5min in a centrifuge at a rotation speed of 5000r/min, and separating to obtain mother liquor;

(2) adding macroporous adsorbent resin into the mother liquor, with average particle diameter of 0.32-0.56mm and average pore diameter of 10-20nm, oscillating at 40 deg.C for 3 hr, and filtering to obtain effluent liquid, wherein at this time, a large amount of organic matter has been removed, and COD in the wastewater is reduced remarkably;

(3) carrying out reduced pressure distillation on the distillate, wherein the first reduced pressure is-0.085 MPa, the temperature is 50 ℃, carrying out second reduced pressure distillation on the distillate, the pressure is-0.095 MPa, the temperature is 50 ℃, obtaining a concentrated solution, and removing a large amount of sodium chloride;

(4) adding methanol into the concentrated solution at a ratio of 5kg/L, adding strong acid ion exchange resin at a ratio of 200g/L for esterification, rectifying after 24h, controlling the space velocity of the rectifying tower at 0.015/min, and collecting distillate at 90-120 deg.C to obtain esterified product;

(5) heating and hydrolyzing the esterified product at 80 deg.C for 4h, and distilling under reduced pressure to remove alcohol and water to obtain glycolic acid.

The glycolic acid obtained from the three examples was analyzed and examined to obtain the data shown in the following table, wherein the recovery rate was the content of glycolic acid product in 1 ton of wastewater.

The purity of the glycolic acid obtained by the invention is about 75 percent, and the recovery rate is about 10-15kg glycolic acid per 1 ton waste water. The process of the invention can effectively reduce COD and salt in the wastewater and is beneficial to scientific discharge of the wastewater.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (9)

1. A method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater is characterized by comprising the following steps: the method comprises the following steps:

(1) adding a flocculating agent into the wastewater, and performing flocculation separation to obtain a mother solution;

(2) adding macroporous adsorption resin into the mother liquor, oscillating for 2-5h at 20-40 ℃, and filtering to obtain an effluent liquid;

(3) carrying out reduced pressure distillation on the effluent to remove precipitated salt substances to obtain a concentrated solution;

(4) adding methanol and exchange resin into the concentrated solution for esterification, rectifying, and collecting distillate at 90-120 deg.C to obtain esterified product; the exchange resin is strong acid ion exchange resin;

(5) heating and hydrolyzing the esterified substance for 3-5h, and distilling under reduced pressure to remove alcohol substances and water to obtain glycolic acid.

2. The method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater according to claim 1, characterized in that: the flocculant is a fenton reagent, and the flocculation separation is centrifugation for 5-10min in a centrifuge.

3. The method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater according to claim 2, characterized in that: the rotating speed of the centrifuge is 4500-.

4. The method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater according to claim 1, characterized in that: the average grain diameter of the macroporous absorption resin is 0.32-0.76mm, and the average pore diameter is 10-20 nm.

5. The method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater according to claim 1, characterized in that: and (3) carrying out reduced pressure distillation twice, wherein the first pressure is-0.08 to-0.085 MPa, the temperature is 50 to 80 ℃, and the distillate is subjected to reduced pressure distillation for the second time, the pressure is-0.085 to-0.095 MPa, and the temperature is 50 to 80 ℃ to obtain a concentrated solution.

6. The method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater according to claim 1, characterized in that: the strong acid ion exchange resin can be repeatedly used after being activated by strong acid.

7. The method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater according to claim 1, characterized in that: the content of the exchange resin in the esterification in the step (4) is 100-200 g/L.

8. The method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater according to claim 1, characterized in that: and (4) rectifying in the step (4), wherein the space velocity is 0.01-0.015/min, and the temperature interval for collecting the distillate is 80-95 ℃.

9. The method for recovering glycolic acid from sodium carboxymethylcellulose production wastewater according to claim 1, characterized in that: the temperature of the hydrolysis in the step (5) is controlled to be 70-90 ℃.