TWI532681B - A method for recovering ethylene glycol and acetaldehyde from polyester wastewater - Google Patents

Description

Method for recovering ethylene glycol and acetaldehyde in polyester wastewater

The invention relates to a method for recovering and reusing organic matter in polyester wastewater in a chemical process, in particular to a method for recovering ethylene glycol and acetaldehyde in polyester wastewater.

At the same time as the rapid development of the polyester industry, a large amount of industrial wastewater is also produced, especially in the process of important esterification, a large amount of esterification wastewater is produced, and since these esterification wastewaters contain acetaldehyde and ethylene glycol, Organic substances such as 2-methyl-1,3-dioxocyclopentane (where the volatile component acetaldehyde accounts for about 50% of the total organic pollutants), and the COD (chemical oxygen demand) concentration of the wastewater is as high as 20000-30000 mg/ L, this not only increases the downstream treatment cost of wastewater, but also exacerbates the conflict between the resources, environment and benefits faced in the development of the polyester industry.

At present, the treatment of esterification wastewater at home and abroad is mainly carried out in the following ways.

The wastewater is treated by an anaerobic-aerobic process. However, due to the very high toxicity of aldehydes, it is not conducive to bacterial growth, resulting in low biochemical treatment efficiency. For such high COD wastewater, biological treatment alone is not only expensive but also expensive to process. .

The wastewater is treated by steaming and then incinerating. After stripping, the COD value drops below 5000mg/L, and then the top material is introduced into the hot coal furnace for incineration, and the heat energy is comprehensively utilized, but the carbon dioxide generated by incineration causes a greenhouse effect, and incomplete combustion will also cause secondary pollution. And the incineration requires a high safety factor or it is prone to explosion and burns as a whole. These valuable organics are not the most economical way.

John. Brown German Engineering Co., Ltd. uses continuous vacuum distillation, such as the Chinese patent number (CN16854A), to obtain high purity ethylene glycol, which is costly and consumes a lot of energy.

Reverse osmosis membrane method, such as Chinese patent number (CN1301238C) recycling esterification waste Ethylene glycol in water, the method obtains high purity of ethylene glycol but can not separate acetaldehyde, especially the reverse osmosis membrane is imported from abroad, with high technical dependence and high cost. Moreover, the above method does not take into account the recovery of acetaldehyde, especially the influence of the relatively large amount of by-product 2-methyl-1,3-dioxolane on water pollution or COD value.

Recently, as reported in the Chinese Patent No. (CN1974508A), the 2-methyl-1,3-dioxolane by-product was intermittently treated by catalytic ion exchange after stripping, and then the recovery of acetaldehyde and ethylene glycol was separately processed. A method of esterifying ethylene glycol and acetaldehyde in wastewater. The method can obtain ethylene glycol with high purity, but uses water to directly absorb acetaldehyde vapor, which causes industrial water to increase and the concentration of the obtained acetaldehyde solution is too low, which requires subsequent treatment, which increases the processing cost, and the method is The batch process, especially the introduction of the 2-methyl-1,3-dioxolane by-product of the intermittent acid catalysis, is highly demanding for industrial equipment due to the corrosive nature of the acid, and due to the 2-methyl-1 The formation of acetaldehyde and ethylene glycol by 3-dioxolane is a reversible reaction. After the batch treatment, it is difficult to ensure that acetaldehyde and ethylene glycol will not form 2-methyl-1,3-di in the next step. Oxolane.

Based on the solution to the above-mentioned shortcomings of the prior art, the present invention is a method for recovering ethylene glycol and acetaldehyde in polyester wastewater, the main purpose of which is to recover and reuse organic matter in polyester wastewater in a chemical process, in particular A method for recovering ethylene glycol and acetaldehyde in a polyester wastewater.

The invention also receives good economic benefits and the purpose of energy saving and consumption reduction:

(1) The present invention is capable of obtaining an ethylene glycol solution having a purity of more than 95% and an acetaldehyde product of more than 98%.

(2) The COD value of the treated esterification wastewater is greatly reduced, and the COD value is reduced from not less than 20,000 mg/L to less than 3000 mg/L, and the discharge is achieved.

(3) Simplified the technical process of acetaldehyde and ethylene glycol recovery, making full use of the original unit facilities for ethylene glycol recovery, eliminating the input and consumption and control system of the new device, and directly recovering the recovered ethylene glycol into the ester. The reaction kettle continues the esterification reaction, eliminating the steps of collecting, purifying, and then converting the ethylene glycol into a reaction, thereby realizing the continuous loop operation of the esterification reaction and the wastewater treatment and recycling, realizing energy saving and consumption reduction. .

In summary, the present invention not only can obtain high-purity ethylene glycol and acetaldehyde products, but also reduces subsequent processing techniques, and has good economic and environmental benefits. At the same time, the improvement of technical process has also set an example for the recovery of acetaldehyde and ethylene glycol in the industry in terms of energy saving.

1‧‧‧Flat Tower

101‧‧‧Steam

2‧‧‧acetaldehyde distillation tower

201‧‧‧Steam

202‧‧‧Waste collection device

203‧‧‧Steam recovery unit

3‧‧‧ glycol distillation tower

301‧‧‧Glycol heating device

302‧‧‧Steam recovery unit

1 is a flow chart of an improved pre-processing technique; and FIG. 2 is a flow chart of an improved processing technique.

The detailed structure of the present invention and its connection relationship will be described in conjunction with the following drawings to facilitate an understanding of the audit committee.

In order to achieve high purity acetaldehyde and ethylene glycol recovery, and further reduce the energy consumption of the device operation, the present invention further simplifies the technical process by further making bold improvements on the basis of the prior application, such as the Chinese patent application number (201010602167.7). The purpose of energy saving and consumption reduction.

The invention provides a method for recovering ethylene glycol and acetaldehyde in a polyester wastewater, wherein the recovery of ethylene glycol is recovered according to the decomposition principle of 2-methyl-1,3-dioxolane. During the treatment of wastewater, high concentrations of acetaldehyde and ethylene glycol are continuously recovered and recovered, so that the hydrolysis of 2-methyl-1,3-dioxolane under high temperature conditions proceeds to the positive reaction direction, and the final hydrolysis is complete. The decomposition principle is as follows:

The present invention is achieved by the following technical solution: a method for recovering ethylene glycol and acetaldehyde in polyester wastewater, which is a continuous collection process, which is achieved by the following steps: (1) Ethylene glycol from esterification unit The esterification wastewater and steam from the separation tower are processed into the stripping tower, and the organic gas and water vapor collected at the top of the tower enter the acetaldehyde rectification tower; (2) after being treated by the acetaldehyde rectification tower, collected at the top of the tower. High-purity acetaldehyde, the bottom wastewater is directly passed through the reflux or separate traces to the glycol separation column of the esterification unit. Separation of ethylene glycol and water and other organic substances in the separation column, the recovered ethylene glycol directly enters the esterification reactor to continue the esterification reaction; (3) the organic ester-derived ester from the top of the esterification separation column The wastewater or steam is recycled to the stripping tower for treatment.

The stripping tower in the step (1) needs to add heat mass transfer, preferably the heat source is water vapor, the pressure is 0.1-1.0 MPa, the top pressure is 0.1-1.0 MPa, the top temperature is 60-140 ° C; The temperature is 80-160 °C.

The esterification wastewater in the step (1) comprises mixed water of the original esterified water and the newly added organic component, and the COD thereof is not less than 20,000 mg/L; the stripping wastewater collected at the bottom of the tower is COD. Waste water with a value of less than 3000 mg/L. After the wastewater treated by the stripping tower, the COD value is less than 3000 mg/L, and the sewage treatment can be directly performed.

The organic gas collected at the top of the column described in the step (1) is condensed and pumped into the acetaldehyde rectification column in a liquid manner or directly into the acetaldehyde rectification column without condensation.

The acetaldehyde rectification column described in the step (2) needs to be added with mass transfer, preferably the heat source is water vapor, the pressure is 0.1-1.0 MPa, the top pressure is 0.1-1.0 MPa, and the temperature at the top of the column is 20-80 ° C, the tower The bottom temperature is 80-160 ° C, the reflux ratio is 0.1-50, and the operating pressure is 0-1.0 MPa.

The acetaldehyde rectification column described in the step (2) has a purity of acetaldehyde collected at the top of the column of more than 98%.

The bottom wastewater of the acetaldehyde rectification column described in the step (2) is returned to the ethylene glycol separation tower through the reflux of the ethylene glycol separation column or additionally through the pipeline, and no new ethylene glycol recovery device is required. The bottom of the acetaldehyde rectification column bottom water is passed between the columns 1 to 12, preferably between the 4th to 8th trays.

Preferably, in order to ensure the quality of the recovered ethylene glycol, the ratio of the amount of waste water in the bottom of the acetaldehyde distillation column to the original reflux flow rate of the separation column does not exceed one.

The purity of the ethylene glycol collected in the bottom of the ethylene glycol separation column of the original esterification unit in the step (2) is greater than 95%.

The bottom wastewater of the acetaldehyde rectification column in the step (2) contains a small amount of undecomposed 2-methyl-1,3-dioxolane and acetaldehyde vapor and re-enters the esterification unit ethylene glycol separation column. The stripper and the acetaldehyde rectification column are subjected to loop decomposition and further processing.

The esterification wastewater or steam from the ethylene glycol separation column in the step (3) is again introduced into the stripping column to form a loop circuit.

The recovery of ethylene glycol is based on the principle of reversible reaction of 2-methyl-1,3-dioxolane to acetaldehyde and ethylene glycol under heating conditions, and the esterification wastewater is passed through a stripping column at the temperature. During the acetaldehyde rectification column and the ethylene glycol separation column, 2-methyl-1,3-dioxolane is continuously hydrolyzed, and acetaldehyde vapor is continuously collected in the acetaldehyde rectification column and the ethylene glycol separation column, respectively. The ethylene glycol solution continuously causes the hydrolysis reaction to proceed to the positive reaction direction.

Example 1

(1) The esterification wastewater (COD value: 20000 mg/L) from the esterification unit ethylene glycol separation tower and steam are treated in the stripping tower. The heat transfer mass of the stripping tower is water vapor, and the pressure is 0.1 MPa. The top pressure is 0.1 MPa, the temperature at the top of the column is 60 ° C; the temperature at the bottom of the column is 80 ° C. The organic matter gas and water vapor collected at the top of the column enter the acetaldehyde rectification column, and the COD value of the wastewater collected at the bottom of the stripping tower is 2655mg/L; (2) The heat source of the acetaldehyde rectification column is water vapor, the pressure is 0.1 MPa, the pressure at the top of the column is 0.1 MPa, the temperature at the top of the column is 20 ° C, the temperature at the bottom of the column is 80 ° C, the reflux ratio is 0.1, and the operating pressure is 0.1 MPa. . After being treated by the acetaldehyde rectification column, high-purity acetaldehyde is collected at the top of the column, and the bottom wastewater is directly passed through the ethylene glycol separation tower which is refluxed into the esterification unit, and the amount of waste water in the bottom of the acetaldehyde distillation column and the original column of the separation tower The ratio of the flow rate is 1; the separation of ethylene glycol and water and other organic substances is completed in the separation tower, and the recovered ethylene glycol directly enters the esterification reaction kettle to continue the esterification reaction; (3) The esterified wastewater or steam from which the organic matter is collected from the top of the esterification separation column, and again enters the stripping column for treatment.

The product components and their contents were obtained by the technical flow device provided by the present invention, as shown in Table 1.

Example 2

(1) The esterification wastewater (COD is 30,000 mg/L) from the esterification unit ethylene glycol separation tower and steam are treated in the stripping tower. The heat transfer mass of the stripping tower is water vapor, the pressure is 1 MPa, and the pressure at the top of the tower is It is 1 MPa, the temperature at the top of the tower is 140 ° C; the temperature at the bottom of the column is 160 ° C. The organic matter gas and water vapor collected at the top of the tower enter the acetaldehyde rectification tower, and the COD value of the wastewater collected at the bottom of the stripping tower is 2875 mg/L. ; (2) The heat source of the acetaldehyde rectification column is water vapor, the pressure is 1 MPa, the pressure at the top of the column is 1 MPa, the temperature at the top of the column is 80 ° C, the temperature at the bottom of the column is 160 ° C, the reflux ratio is 50, and the operating pressure is 1 MPa. After being treated by the acetaldehyde rectification column, high-purity acetaldehyde is collected at the top of the column, and the bottom wastewater is directly passed through another separate line to enter the ethylene glycol separation tower of the esterification unit, and the line enters the separation tower body at a position The first tray; the ratio of the amount of wastewater at the bottom of the acetaldehyde distillation column to the original reflux of the separation column is 0.5; the separation of ethylene glycol and water and other organic substances is completed in the separation column, and the recovered ethylene glycol directly enters the esterification. The reaction kettle continues the esterification reaction; (3) The esterified wastewater or steam from which the organic matter is collected from the top of the esterification separation column, and again enters the stripping column for treatment.

The product components and their contents were obtained by the technical flow device provided by the present invention, as shown in Table 2.

Example 3

(1) The esterification wastewater (COD is 25000 mg/L) from the esterification unit ethylene glycol separation tower and steam are treated in the stripping tower, and the heat transfer mass of the stripping tower is water vapor. The pressure is 0.6MPa, the top pressure is 0.5MPa, the temperature at the top of the tower is 100°C, the temperature at the bottom of the column is 120°C, and the organic gas and water vapor collected at the top of the tower enter the acetaldehyde rectification tower at the bottom of the stripping tower. The collected wastewater has a COD value of 2595 mg/L; (2) The heat source of the acetaldehyde rectification column is water vapor, the pressure is 0.6 MPa, the pressure at the top of the column is 0.6 MPa, the temperature at the top of the column is 100 ° C, the temperature at the bottom of the column is 120 ° C, the reflux ratio is 4, and the operating pressure is 0.5 MPa. . After being treated by the acetaldehyde rectification column, high-purity acetaldehyde is collected at the top of the column, and the bottom wastewater is directly passed through another separate line to enter the ethylene glycol separation tower of the esterification unit, and the line enters the separation tower body at a position The 12th tray; the ratio of the amount of waste water in the bottom of the acetaldehyde rectification tower to the original reflux flow rate of the separation tower is 0.6; the separation of ethylene glycol and water and other organic substances is completed in the separation tower, and the recovered ethylene glycol directly enters the esterification. The reaction kettle continues the esterification reaction; (3) The esterified wastewater or steam from which the organic matter is collected from the top of the esterification separation column, and again enters the stripping column for treatment.

The product components and their contents were obtained by the technical flow device provided by the present invention, as shown in Table 3.

Example 4

(1) The esterification wastewater (COD is 28000 mg/L) from the esterification unit ethylene glycol separation tower and steam are sent to the stripping tower for treatment. The heat transfer mass of the stripping tower is water vapor, and the pressure is 0.6 MPa. The pressure is 0.5MPa, the temperature at the top of the tower is 100°C, the temperature at the bottom of the column is 120°C, the organic gas and water vapor collected at the top of the tower enter the acetaldehyde rectification tower, and the COD value of the wastewater collected at the bottom of the stripping tower is 2455mg. /L; (2) The heat source of the acetaldehyde rectification column is water vapor, the pressure is 0.6 MPa, the top pressure is 0.6 MPa, the top temperature is 100 ° C, the bottom temperature is 120 ° C, the reflux ratio is 6, and the operating pressure is 0.5 MPa. . After being treated by the acetaldehyde rectification column, high-purity acetaldehyde is collected at the top of the column, and the bottom wastewater is directly passed through another separate line to enter the ethylene glycol separation tower of the esterification unit, and the line enters the separation tower body at a position The sixth tray; the ratio of the amount of waste water in the bottom of the acetaldehyde distillation tower to the original reflux flow of the separation tower is 0.6; the separation of ethylene glycol and water and other organic substances is completed in the separation tower, and the recovered ethylene glycol directly enters the esterification. The reaction kettle continues the esterification reaction; (3) The esterified wastewater or steam from which the organic matter is collected from the top of the esterification separation column, and again enters the stripping column for treatment.

The product components and their contents were obtained by the technical flow device provided by the present invention, as shown in Table 4.

Example 5

The effect of the implementation of the processing technology flow before the improvement.

The technology and equipment before the improvement (using the process of Figure 1) have been put into practical use in well-known enterprises in the polyester industry. Taking the esterification wastewater produced by an annual output of 150,000 tons of polyester as an example, the specific technical results before the improvement are as shown in Table 5: Table 5 Esterification wastewater and the content of each component of the product

Example 6

The present invention (improved) processes the technical process implementation effects.

The technology and device of the present invention (using the flow of FIG. 2) have been put into practical use in well-known enterprises in the polyester industry, and the operating conditions are as described in Embodiment 4. Taking the esterification wastewater produced by an annual output of 150,000 tons of polyester as an example, the specific technical results after improvement are as follows: According to the actual production conditions, the obtained esterified wastewater was treated by the technical flow device provided by the present invention to obtain the product components and their contents, as shown in Table 6.

It can be seen from the processed results that after treatment with the wastewater treatment system of the technical process, regardless of the output of acetaldehyde and ethylene glycol or the discharge wastewater index, the products have no influence on the various indexes, and the recovery is obtained. The purity of the ethylene glycol is rather higher, which fully demonstrates that the improved inventive process is successful and feasible.

Table 7 Comparison of steam consumption before and after improvement (converted to steam consumption)

Table 7 lists the steam consumption before and after the improvement. It is easy to see through two comparisons. After the improvement, the steam consumption is significantly reduced by 26%, achieving the goal of energy saving. Therefore, the technical process and device of the present invention can make the promotion of the technology to a new stage, thereby creating greater benefits for enterprises and society.

The above description is to be construed as illustrative and not restrictive Other embodiments of the invention will be apparent to those skilled in the art from this disclosure. It should be noted that the present specification and examples are to be considered as illustrative only, and the actual scope of the invention is determined by the scope of the claims.

1‧‧‧Flat Tower

101‧‧‧Steam

2‧‧‧acetaldehyde distillation tower

201‧‧‧Steam

202‧‧‧Waste collection device

203‧‧‧Steam recovery unit

Claims (10)

A method for recovering ethylene glycol and acetaldehyde in polyester wastewater is a continuous collection process, which is characterized by the following steps: (1) the esterification wastewater is treated in a stripping tower, and stripping is obtained at the bottom of the column. The wastewater is treated by sewage, and the organic gas collected at the top of the tower enters the acetaldehyde rectification column; (2) after being treated by the acetaldehyde rectification column, high-purity acetaldehyde is collected at the top of the tower, and the wastewater collected at the bottom of the tower enters the original a glycol separation column having an esterification unit, which separates ethylene glycol from water and other organic substances in the separation column, and the recovered ethylene glycol directly enters the esterification reactor to continue the esterification reaction; and (3) The esterification wastewater or steam collected from the ethylene glycol separation tower of the esterification unit is collected and returned to the stripping column for treatment. The method for recovering ethylene glycol and acetaldehyde in the polyester wastewater according to claim 1, wherein the esterification wastewater described in the step (1) comprises the original esterification wastewater and is obtained in the step (3). The wastewater or steam has a COD value of not less than 20,000 mg/L. The method for recovering ethylene glycol and acetaldehyde in the polyester wastewater according to claim 1, wherein the heat source of the stripping tower described in the step (1) is water vapor, and the pressure is 0.1-1.0 MPa. The top pressure is 0.1-1.0 MPa, the top temperature is 60-140 ° C, and the bottom temperature is 80-160 ° C. The method for recovering ethylene glycol and acetaldehyde in the polyester wastewater according to claim 1, wherein the organic gas collected at the top of the step described in the step (1) is condensed and pumped in a liquid manner. Into the acetaldehyde rectification column, or directly into the acetaldehyde rectification column without condensation. The method for recovering ethylene glycol and acetaldehyde in the polyester wastewater according to claim 1, wherein the waste water collected by the stripping tower at the bottom of the tower has a COD of less than 3000 mg/L. The method for recovering ethylene glycol and acetaldehyde in the polyester wastewater according to claim 1, wherein the heat source of the acetaldehyde rectification column described in the step (2) is water vapor, and the pressure is 0.1-1.0 MPa. The pressure at the top of the column is 0.1-1.0 MPa, the temperature at the top of the column is 20-80 ° C, the temperature at the bottom of the column is 80-160 ° C, the reflux ratio is 0.1-50, and the operating pressure is 0.1-1.0 MPa. The method for recovering ethylene glycol and acetaldehyde in the polyester wastewater according to claim 1, wherein the acetaldehyde distillation tower bottom wastewater is refluxed by the ethylene glycol separation column or In addition, it enters the glycol separation column through a pipe. The method for recovering ethylene glycol and acetaldehyde in the polyester wastewater according to claim 7, wherein the ratio of the bottom amount of the acetaldehyde distillation column to the original reflux flow rate of the ethylene glycol separation column is not more than 1. The method for recovering ethylene glycol and acetaldehyde in the polyester wastewater according to claim 7 of the patent application, wherein the bottom of the acetaldehyde distillation tower bottom water is additionally connected to the ethylene glycol separation tower by a pipeline. Between 12 trays. A method for recovering ethylene glycol and acetaldehyde in a polyester wastewater according to any one of claims 1 to 9, characterized in that the acetaldehyde distillation column bottom wastewater described in the step (2) contains A small amount of undecomposed 2-methyl-1,3-dioxolane and acetaldehyde vapors are re-entered into the esterification unit ethylene glycol separation column, stripping column, and acetaldehyde rectification column for loop decomposition and further processing.