阅读说明：本技术 聚酯转制可塑剂副产乙二醇的纯化方法 (Purification method of byproduct ethylene glycol of polyester conversion plasticizer ) 是由 廖德超 庄荣仁 陈仲裕 赖秋南 于 2020-02-17 设计创作，主要内容包括：本发明公开一种聚酯转制可塑剂副产乙二醇的纯化方法,其包括：将包含乙二醇及2-乙基己醇的反应废水流通入乙二醇脱水塔；将热水流通入乙二醇脱水塔,以与反应废水流混合、且用以去除反应废水流中的2-乙基己醇,从而将乙二醇与2-乙基己醇予以分离；以乙二醇脱水塔对乙二醇进行脱水作业,以于乙二醇脱水塔的塔底收集到包含乙二醇的粗乙二醇流、且于乙二醇脱水塔的塔顶收集到包含2-乙基己醇的有机物废水流；以及将粗乙二醇流通入乙二醇蒸馏塔,以于乙二醇蒸馏塔的塔顶收集到高纯度的乙二醇溶液。借以让回收的乙二醇溶液具有高的纯度、从而具有高的被利用价值。(The invention discloses a purification method of a byproduct ethylene glycol of a polyester conversion plasticizer, which comprises the following steps: passing a reaction waste water stream comprising ethylene glycol and 2-ethylhexanol to an ethylene glycol dehydration column; passing the hot water stream to an ethylene glycol dehydration tower to be mixed with the reaction wastewater stream and to remove 2-ethylhexanol from the reaction wastewater stream, thereby separating ethylene glycol from 2-ethylhexanol; dehydrating the ethylene glycol by using an ethylene glycol dehydrating tower, so as to collect a crude ethylene glycol flow containing the ethylene glycol at the bottom of the ethylene glycol dehydrating tower and collect an organic matter wastewater flow containing 2-ethylhexanol at the top of the ethylene glycol dehydrating tower; and passing the crude ethylene glycol stream to an ethylene glycol distillation column to collect a high purity ethylene glycol solution at the top of the ethylene glycol distillation column. Thereby the recovered glycol solution has high purity and high value of utilization.)

1. A purification method of by-product glycol of polyester conversion plasticizer is a continuous collection method, and is characterized in that the purification method of by-product glycol of polyester conversion plasticizer comprises the following steps:

(1) passing a reaction wastewater stream to a glycol dehydration column; wherein the reaction wastewater stream comprises: ethylene glycol and 2-ethylhexanol;

(2) passing a hot water stream to said ethylene glycol dehydration column to mix with said reaction wastewater stream and to remove said 2-ethylhexanol from said reaction wastewater stream, thereby separating said ethylene glycol from said 2-ethylhexanol; wherein the hot water stream is heated water and the hot water temperature of the hot water stream is between 40 ℃ and 95 ℃;

(3) dehydrating the ethylene glycol by using the ethylene glycol dehydrating tower, so as to collect a crude ethylene glycol flow at the bottom of the ethylene glycol dehydrating tower and collect an organic wastewater flow at the top of the ethylene glycol dehydrating tower; wherein the crude ethylene glycol stream comprises the dehydrated ethylene glycol and the organic wastewater stream comprises the 2-ethylhexanol; and

(4) feeding the crude ethylene glycol stream to an ethylene glycol distillation column to collect an ethylene glycol solution at the top of the ethylene glycol distillation column.

2. The method of claim 1, wherein in step (2), the temperature of the hot water in the hot water stream is between 50 ℃ and 80 ℃.

3. The method for purifying ethylene glycol as a byproduct in polyester conversion plasticizer according to claim 1, wherein in the step (2), the hot water flow is introduced into the lower half of the ethylene glycol dehydration tower.

4. The method according to claim 1, wherein the organic waste water stream collected from the top of the glycol dehydrating tower in the step (3) has a COD value of not more than 1,200 mg/L.

5. The method according to claim 1, wherein in the step (4), the ethylene glycol solution is collected from the top of the ethylene glycol distillation column and has an ethylene glycol purity of not less than 90%.

6. The method for purifying ethylene glycol as a byproduct in polyester conversion plasticizer according to claim 1, wherein the step (4) further comprises: a high boiling mixture is collected at the bottom of the ethylene glycol distillation column.

7. The method as claimed in claim 6, wherein the high boiling mixture collected from the bottom of the ethylene glycol distillation tower in the step (4) has a recoverable thermal value of incineration, and the recoverable thermal value of incineration is not less than 1,500 kcal/kg.

8. The method as claimed in claim 1, wherein the bottom of the ethylene glycol dehydration tower is heated by a reboiler to provide heat for distillation, and the reboiler is heated by high pressure steam.

9. The method of claim 1 to 8, wherein the pressure at the top of the ethylene glycol dehydration column is not more than 1bar, the reflux ratio of the ethylene glycol dehydration column is between 0.01 and 3, the temperature at the top of the ethylene glycol dehydration column is between 50 ℃ and 100 ℃, and the temperature at the bottom of the ethylene glycol dehydration column is between 80 ℃ and 160 ℃.

10. The method for purifying ethylene glycol as a byproduct in polyester conversion plasticizer according to any of claims 1 to 8, wherein the pressure at the top of the ethylene glycol distillation column is not more than 1bar, the reflux ratio of the ethylene glycol distillation column is between 0.01 and 10, the temperature at the top of the ethylene glycol distillation column is between 120 ℃ and 150 ℃, and the temperature at the bottom of the ethylene glycol distillation column is between 130 ℃ and 170 ℃.

11. The method of claim 1, wherein the reaction waste water stream has a flow rate of 300kg/h to 1,200kg/h when passing into the glycol dehydrating tower, and the hot water stream has a flow rate of 30kg/h to 600kg/h when passing into the glycol dehydrating tower.

12. The method for purifying by-product ethylene glycol from polyester conversion plasticizer according to claim 11, wherein the mass flow ratio of said reaction wastewater stream to said hot water stream S2 is between 1: 0.1 to 1: between 0.5.

Technical Field

The invention relates to a method for purifying ethylene glycol, in particular to a method for purifying a byproduct ethylene glycol of a polyester conversion plasticizer.

Background

In the prior art, polyester waste (such as polyethylene terephthalate (PET)) and raw material 2-ethylhexanol (2-Ethyl-1-hexanol, 2-EH) can be used for preparing plasticizer (such as dioctyl terephthalate (DOTP)) by alcoholysis and ester exchange one-step method under the action of catalyst. The chemical reaction of the process produces Ethylene Glycol (EG) as a byproduct. However, since the by-product ethylene glycol and the raw material 2-ethylhexanol are azeotropic and difficult to separate from each other, the process can distill off the ethylene glycol in the 2-ethylhexanol by water extraction reaction during the synthesis to generate the above-mentioned reaction waste water stream containing the by-product ethylene glycol and a trace amount of the raw material 2-ethylhexanol.

However, in the past, much of the research on the process has focused on the selection of the catalyst or the removal of ethylene glycol, but few have focused on the recovery and purification of the ethylene glycol as a byproduct.

Although ethylene glycol can be recovered, the existing recovery method mainly adopts an evaporation mode to remove moisture in the reaction wastewater stream so as to recover ethylene glycol. However, since ethylene glycol and 2-ethylhexanol azeotroped and were difficult to separate from each other, the ethylene glycol recovered by the conventional method had a low purity, and it was difficult to further use it as a raw material for producing other products (e.g., a raw material for synthesizing polyesters).

Chinese patent publication No. 105936620, proposes a purification device capable of purifying ethylene glycol in the preparation of a plasticizer DOTP. The device utilizes the waste heat of the ethylene glycol and the 2-ethylhexanol generated by the reaction to heat and distill the separated ethylene glycol solution so as to save energy, but the problem of low purity of the ethylene glycol cannot be solved.

The present inventors have considered that the above-mentioned drawbacks can be improved, and have made intensive studies and use of scientific principles, and finally have proposed the present invention which is designed reasonably and effectively to improve the above-mentioned drawbacks.

Disclosure of Invention

In the prior art, polyester waste (such as polyethylene terephthalate (PET)) and raw material 2-ethylhexanol (2-Ethyl-1-hexanol, 2-EH) can be used for preparing plasticizer (such as dioctyl terephthalate (DOTP)) by alcoholysis and ester exchange one-step method under the action of catalyst. The chemical reaction of the process produces Ethylene Glycol (EG) as a byproduct. However, since the by-product ethylene glycol and the raw material 2-ethylhexanol are azeotropic and difficult to separate from each other, the process can distill off the ethylene glycol in the 2-ethylhexanol by water extraction reaction during the synthesis to generate the above-mentioned reaction waste water stream containing the by-product ethylene glycol and a trace amount of the raw material 2-ethylhexanol.

However, in the past, much of the research on the process has focused on the selection of the catalyst or the removal of ethylene glycol, but few have focused on the recovery and purification of the ethylene glycol as a byproduct.

Although ethylene glycol can be recovered, the existing recovery method mainly adopts an evaporation mode to remove moisture in the reaction wastewater stream so as to recover ethylene glycol. However, since ethylene glycol and 2-ethylhexanol azeotroped and were difficult to separate from each other, the ethylene glycol recovered by the conventional method had a low purity, and it was difficult to further use it as a raw material for producing other products (e.g., a raw material for synthesizing polyesters).

Chinese patent publication No. 105936620, proposes a purification device capable of purifying ethylene glycol in the preparation of a plasticizer DOTP. The device utilizes the waste heat of the ethylene glycol and the 2-ethylhexanol generated by the reaction to heat and distill the separated ethylene glycol solution so as to save energy, but the problem of low purity of the ethylene glycol cannot be solved.

The present inventors have considered that the above-mentioned drawbacks can be improved, and have made intensive studies and use of scientific principles, and finally have proposed the present invention which is designed reasonably and effectively to improve the above-mentioned drawbacks.

Drawings

FIG. 1 is a flow diagram of a process for purifying ethylene glycol in accordance with an embodiment of the present invention.

Fig. 2 is a schematic diagram of an ethylene glycol purification process according to an embodiment of the present invention.

Detailed Description

The embodiments of the present invention disclosed herein are described below with reference to specific embodiments, and those skilled in the art will understand the advantages and effects of the present invention from the disclosure of the present specification. The invention is capable of other and different embodiments and its several details are capable of modification and various other changes, which can be made in various details within the specification and without departing from the spirit and scope of the invention. The drawings of the present invention are for illustrative purposes only and are not intended to be drawn to scale. The following embodiments will further explain the related art of the present invention in detail, but the disclosure is not intended to limit the scope of the present invention.

Referring to fig. 1 and 2, an embodiment of the invention provides a method for purifying ethylene glycol as a byproduct in converting polyester into a plasticizer, which is a continuous collection method and includes step S110, step S120, step S130, and step S140. It should be noted that the order of the steps and the actual operation manner carried out in the embodiment can be adjusted according to the requirement, and are not limited to the embodiment.

The step S110 includes: a reaction waste water stream S1 is passed to a glycol dehydration column 100. Wherein the reaction wastewater stream S1 contains Ethylene Glycol (EG) and 2-ethylhexanol (2-Ethyl-1-hexanol, 2-EH).

It should be noted that the wastewater stream S1 refers to a wastewater stream generated in a process for converting a plasticizer (e.g., dioctyl terephthalate, DOTP) into a polyester (e.g., polyethylene terephthalate, PET). In more detail, the process adopts polyester waste and 2-ethylhexanol as a raw material to prepare the plasticizer through a one-step method of alcoholysis and ester exchange under the action of a catalyst. The chemical reaction of the process produces ethylene glycol as a byproduct. However, since the by-product ethylene glycol and the raw material 2-ethylhexanol are azeotropic and difficult to separate from each other, the process can distill off the ethylene glycol in the 2-ethylhexanol by water extraction reaction during the synthesis to generate the above-mentioned reaction waste water stream S1 containing the by-product ethylene glycol and a trace amount of the raw material 2-ethylhexanol.

Since the reaction wastewater stream S1 contains ethylene glycol at a relatively high concentration, the reaction wastewater stream S1 has a relatively high COD value (or Chemical Oxygen Demand), which causes difficulty in wastewater treatment of the reaction wastewater stream S1.

In the conventional glycol recovery method, water is removed from the reaction wastewater stream S1 by evaporation to recover glycol. However, since ethylene glycol and 2-ethylhexanol azeotroped and were difficult to separate from each other, the ethylene glycol recovered by the conventional method had a low purity, and it was difficult to further use it as a raw material for producing other products (e.g., a raw material for synthesizing polyesters). In order to solve the above technical problem, an embodiment of the present invention aims to improve the purity of the recovered ethylene glycol through the following steps S120 to S140, so as to improve the value of the recovered ethylene glycol.

Further, the ethylene glycol dehydration tower 100 is configured to perform dehydration work on ethylene glycol in the reaction wastewater stream S1. The ethylene glycol dehydrating tower 100 has a tower top 101, a tower bottom 102, and a tower body 103 between the tower top 101 and the tower bottom 102. The tower body 103 defines an upper half 1031 connected to the tower top 101 and a lower half 1032 connected to the tower bottom 102, and the upper half 1031 is connected to the lower half 1032. Furthermore, the bottom 102 of the glycol dehydration column 100 is heated by a reboiler (not shown) to provide heat for distillation, and the reboiler uses a high pressure steam as its heat source.

In terms of the operational parameters of the dehydration column, the pressure of the top 101 of the glycol dehydration column 100 is preferably not more than 1bar, the reflux ratio of the glycol dehydration column 100 is preferably between 0.01 and 3, the temperature of the top 101 of the glycol dehydration column 100 is preferably between 50 ℃ and 100 ℃, and the temperature of the bottom 102 of the glycol dehydration column 100 is preferably between 80 ℃ and 160 ℃, but the present invention is not limited thereto.

The step S120 includes: a hot water stream S2 is passed to the above-mentioned ethylene glycol dehydration column 100 to be mixed with the reaction wastewater stream S1 and to remove 2-ethylhexanol in the reaction wastewater stream S1.

Wherein the hot water stream S2 is heated water, and preferably heated pure water. The hot water temperature of the hot water stream S2 is preferably between 40 ℃ and 95 ℃, and particularly preferably between 50 ℃ and 80 ℃. Further, the hot water stream S2 is preferably passed into the lower half 1032 of the ethylene glycol dehydration column 100, but the present invention is not limited thereto.

More specifically, since ethylene glycol is miscible with water and 2-ethylhexanol is not miscible with water, according to this characteristic, the method of this embodiment introduces the hot water stream S2 in the above temperature range into the ethylene glycol dehydration tower 100 to utilize the mixing of the hot water stream S2 with the reaction wastewater stream S1 and the miscibility with ethylene glycol, and the hot water stream S2 can be used to enhance the removal (or elimination) of 2-ethylhexanol (because 2-ethylhexanol is poorly soluble in water) in the reaction wastewater stream S1, thereby effectively separating the ethylene glycol from 2-ethylhexanol.

According to the above configuration, ethylene glycol and 2-ethylhexanol can be separated from each other more efficiently, and thus the problem of azeotropy of ethylene glycol and 2-ethylhexanol can be effectively solved, so that the ethylene glycol solution S5 obtained in the subsequent step can have higher ethylene glycol purity, and the organic matter waste water stream S3 obtained in the subsequent step can have a lower COD value (due to the reduced concentration of ethylene glycol, or even no ethylene glycol), and thus can be directly subjected to waste water treatment.

In an embodiment of the present invention, in order to improve the separation efficiency of ethylene glycol and 2-ethylhexanol, the waste reaction water stream S1 and the hot water stream S2 have a preferred flow rate range when they are introduced into the ethylene glycol dehydration column 100, respectively. Specifically, the reaction wastewater stream S1 has a flow rate of 300kg/h to 1,200kg/h, and preferably 500kg/h to 900kg/h when it is passed into the ethylene glycol dehydration column 100. The hot water stream S2 has a flow rate of between 30kg/h and 600kg/h, and preferably between 60kg/h and 420kg/h, when passed to the ethylene glycol dehydration column 100. From another perspective, the mass flow ratio of the wastewater reaction stream S1 to the hot water stream S2 is between 1: 0.1 to 1: 0.5, and preferably between 1: 0.2 to 1: between 0.35.

The step S130 includes: the ethylene glycol dehydration tower 100 is used to dehydrate ethylene glycol, so that a crude ethylene glycol stream S4 is collected at the bottom 102 of the ethylene glycol dehydration tower 100, and an organic wastewater stream S3 is collected at the top 101 of the ethylene glycol dehydration tower 100. Wherein the crude ethylene glycol stream S4 contains the dehydrated ethylene glycol and the organic wastewater stream S3 contains the 2-ethylhexanol.

More specifically, since the ethylene glycol and 2-ethylhexanol have been more effectively separated from each other through the above-mentioned step S120, the problem of azeotropy between the ethylene glycol and 2-ethylhexanol has been effectively improved. Further, since the boiling point of ethylene glycol (about 197 ℃ C.) is higher than that of 2-ethylhexanol (about 184 ℃ C.) and is also higher than that of water (about 100 ℃ C.). The 2-ethylhexanol and water form an azeotropic mixture at a given ratio (e.g., about 100 ℃ C. for water at about 20% azeotropic mixture). Accordingly, the ethylene glycol dehydration column 100 can separate the mixture into a gas phase and a liquid phase by controlling the temperature according to the difference of the boiling points of the components of the mixture, and at this time, the low boiling point material is vaporized and flows out toward the top 101, and the high boiling point material flows out at the bottom 102 in a liquid state, thereby achieving the effect of separating the components of the mixture from each other.

In this embodiment, the ethylene glycol dehydration tower 100 is capable of dehydrating the ethylene glycol in the reaction wastewater stream S1 to collect the crude ethylene glycol stream S4 at the bottom 102 of the ethylene glycol dehydration tower 100, and the crude ethylene glycol stream S4 contains ethylene glycol and preferably does not contain 2-ethylhexanol (or contains only a very low concentration of 2-ethylhexanol). In other words, the ethylene glycol flows out in the bottom 102 of the column in a liquid state because of its high boiling point.

Furthermore, the glycol dehydration tower 100 azeotropes 2-ethylhexanol with water and then condenses it through a condenser to collect the organic waste water stream S3 at the top 101 of the glycol dehydration tower 100, and the organic waste water stream S3 contains water and 2-ethylhexanol, and preferably contains no glycol (or only a very low concentration of glycol).

Thereby, the crude ethylene glycol stream S4 can be provided to the ethylene glycol distillation column 200 in the subsequent step S140 to continue the purification operation, and the organic wastewater stream S3 can be subjected to the subsequent wastewater treatment. It is worth mentioning that, since the organic wastewater stream S3 contains no glycol or only a very low concentration of glycol, the COD value of the organic wastewater stream S3 can be effectively reduced, thereby facilitating the subsequent wastewater treatment. In an embodiment of the present invention, the organic wastewater stream S3 collected at the top 101 of the glycol dehydrating tower 100 preferably has a COD value of not more than 1,200mg/L, and particularly preferably not more than 1,000mg/L, but the present invention is not limited thereto.

The step S140 includes: the crude ethylene glycol stream S4 is passed to an ethylene glycol distillation column 200 to collect a solution of ethylene glycol S5 at the top 201 of the ethylene glycol distillation column 200 and a high boiling mixture S6 at the bottom 202 of the ethylene glycol distillation column 200.

Wherein the ethylene glycol distillation column 200 has a top 201 and a bottom 202, and the ethylene glycol distillation column 200 is capable of purifying a crude ethylene glycol stream S4.

More specifically, the crude ethylene glycol stream S4 contains a high boiling point mixture S6 (e.g., propylene glycol, butylene glycol …, and other higher boiling fusel alcohols) having a boiling point higher than that of ethylene glycol in addition to ethylene glycol. Therefore, the ethylene glycol distillation column 200 can separate the ethylene glycol from the high boiling point mixture S6 by the principle that the boiling points of the components of the mixture are different.

Further, since the ethylene glycol has a low boiling point, the ethylene glycol can be vaporized in the ethylene glycol distillation column 200 and flows out in the direction of the top 201, and then is condensed by a condenser, so that the ethylene glycol solution S5 with high purity can be collected at the top 201 of the ethylene glycol distillation column 200.

In one embodiment of the present invention, the ethylene glycol solution S5 preferably has an ethylene glycol purity of not less than 90%, and particularly preferably has an ethylene glycol purity of not less than 95%. It is worth mentioning that the recovered glycol has a relatively high purity, so that it can be further used as a raw material for producing other products (e.g., a raw material for synthesizing polyester), thereby enhancing the utility value of the recovered glycol.

Since the boiling point of the high boiling point mixture S6 is high, the high boiling point mixture S6 is in a liquid state and flows out from the bottom 202 of the column. It is worth mentioning that the high boiling mixture S6 has an incineratable recoverable heat value, and the incineratable recoverable heat value is preferably not less than 1,500 kcal/kg. That is, the high boiling mixture S6 can be incinerated directly.

In terms of the operational parameters of the distillation column, the pressure of the top 201 of the ethylene glycol distillation column 200 is preferably not more than 1bar, the reflux ratio of the ethylene glycol distillation column 200 is preferably between 0.01 and 10, the temperature of the top 201 of the ethylene glycol distillation column 200 is preferably between 120 ℃ and 150 ℃, and the temperature of the bottom 202 of the ethylene glycol distillation column 200 is preferably between 130 ℃ and 170 ℃, but the present invention is not limited thereto.

In summary, the ethylene glycol solution S5 collected by the method of this embodiment has high ethylene glycol purity, and thus has high utility value. The organic waste water stream S3 collected in the method of this example has a low COD value, so it can be directly treated with waste water. Furthermore, the high boiling mixture S6 collected in the method of this example has incineratable recoverable calorific value, so it can be incinerated directly. That is, the ethylene glycol purification method provided in this embodiment not only enables the recovered ethylene glycol solution S5 to have high purity and thus high value, but also enables the waste generated in the method to be directly disposed of without causing serious environmental pollution.

[ advantageous effects of the embodiments ]

One of the advantages of the present invention is that the method for purifying ethylene glycol as a byproduct in polyester conversion plasticizer provided by the present invention can separate ethylene glycol from 2-ethylhexanol by "passing a hot water stream into the ethylene glycol dehydration tower to mix with the reaction wastewater stream and to remove the 2-ethylhexanol from the reaction wastewater stream; wherein the hot water flow is heated water, and the hot water temperature of the hot water flow is between 40 ℃ and 95 ℃, the glycol is dehydrated by the glycol dehydration tower, so that a crude glycol flow is collected at the bottom of the glycol dehydration tower, and an organic wastewater flow is collected at the top of the glycol dehydration tower; wherein the crude glycol stream contains the dehydrated glycol and the organic wastewater stream contains the 2-ethylhexanol, and "the crude glycol stream is fed into a glycol distillation column to collect a glycol solution at the top of the glycol distillation column" to make the recovered glycol solution have high purity and thus high utility value, and the waste (such as organic wastewater stream or high boiling mixture) generated in the method can be directly disposed of (such as wastewater treatment or incineration treatment) without causing serious pollution to the environment.

The disclosure is only a preferred embodiment of the invention and should not be taken as limiting the scope of the invention, so that the invention is not limited by the disclosure of the specification and drawings.