A separation and recovery process for by-product mixed alcohols in polyester units

Abstract

The present invention provides a separation and recovery process for by-product mixed alcohols of a polyester device, comprising: (1) the mixed alcohols from the polyester device as by-products enter a light-removal tower, a first light component is extracted from the tower top, and a first heavy component is extracted from the tower bottom and enters an evaporation tower; (2) a second heavy component is extracted from the tower bottom of the evaporation tower, and the second light component is extracted from the tower top and enters an ethylene glycol refining tower; (3) an ethylene glycol product is extracted from the side line of the ethylene glycol refining tower, a third light component is extracted from the tower top, and the third heavy component from the tower bottom enters a diethylene glycol refining tower; (4) a diethylene glycol product is extracted from the side line of the diethylene glycol refining tower, a fourth light component is extracted from the tower top, and a fourth heavy component is extracted from the tower bottom; the separation and recovery process optimizes the existing separation process according to the characteristics of the by-product mixed alcohol mixture of the polyester device, and the improved separation and recovery process has the advantages of being able to flexibly cope with changes in feed composition, while being able to improve product quality and recovery rate, and has good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical engineering, and in particular relates to a separation and recovery process of by-product mixed alcohol from a polyester device. Background Art

[0002] Conventional polyester usually refers to polyethylene terephthalate (PET), which is obtained by esterification and polycondensation of terephthalic acid (PTA) and ethylene glycol (EG). In recent years, with the continuous expansion of polyester production capacity, market products have become seriously homogeneous, and the pursuit of differentiated product competition has become an important direction for the development of the industry. Differentiated polyesters usually introduce a third monomer or a fourth monomer on the basis of conventional polyester for modification to synthesize different functional polyesters. In order to prepare high molecular weight polyesters, high vacuum is usually used to remove small molecular monomers in the polycondensation and final polymerization stages. In this process, excess unreacted monomers will be pumped into a steam jet pump and reused after condensation. If the third monomer introduced is a diol (such as diethylene glycol), the unreacted mixed alcohol must be refined and separated before it can be recycled.

[0003] Ethylene glycol and diethylene glycol (also known as diethylene glycol) in mixed alcohols are usually separated by distillation equipment. In the polyester polymerization process, the polycondensation and final polymerization stages use a high vacuum process. The unreacted mixed alcohol extracted contains moisture, light components, oligomers and other substances. When the proportion of ethylene glycol in the material is relatively high, the oligomers dissolved in ethylene glycol will not affect the distillation process. Ethylene glycol is a heat-sensitive substance that is prone to condensation and coking at high temperatures, affecting the stable operation of the device and the quality of the product. Therefore, vacuum operation is often used for the distillation separation of ethylene glycol to reduce the operating temperature of the tower bottom. Due to the low operating temperature of the distillation tower, as ethylene glycol is continuously extracted, the oligomers dissolved in ethylene glycol will precipitate and block the filler or tower plate, affecting the distillation separation effect. There are many by-products in the polymerization reaction, and the change of the mixed alcohol feed composition has a great influence on the distillation separation effect. For example, there are intermediate components with boiling points between water and ethylene glycol, and intermediate components with boiling points between ethylene glycol and diethylene glycol. The conventional method of separating ethylene glycol and diethylene glycol in order of boiling points requires a large number of towers, a complex process, and high operation difficulty. If the separation towers are set in order according to the boiling points of water, ethylene glycol, diethylene glycol, and oligomers, it is difficult to ensure that the product purity reaches more than 99%.

[0004] CN109179542A provides a distillation system and process for ethylene glycol and diethylene glycol in polyol waste liquid. The polyol waste liquid is collected and then treated uniformly, and has a stable composition. The melting point of oligomers in the polyol device is lower than that of the oligomers in the polyester device, and it is not easy to clog fillers or tower plates. Therefore, its treatment process is not suitable for the separation of mixed alcohols in the polyester device.

[0005] CN105085165A provides a method for separating ethylene glycol and diethylene glycol, wherein the feed composition is a crude ethylene glycol flow in a process of producing ethylene glycol from coal-based synthesis gas, and by-products such as methanol, ethanol, water, 1,2-propylene glycol, and 1,2-butylene glycol have been removed before entering an ethylene glycol and diethylene glycol separation system. The feed composition is stable and does not contain oligomers. The content of diethylene glycol produced in the process of producing ethylene glycol from coal-based synthesis gas is much lower than the content of diethylene glycol in by-product alcohol of a polyester device. It is difficult to obtain stable product quality by using this method to process mixed alcohols of a polyester device.

[0006] In summary, how to learn from the existing polyol separation and recovery process to achieve efficient separation of mixed alcohols as by-products of polyester plants has become a technical problem that needs to be solved urgently. Summary of the invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a separation and recovery process for mixed alcohol by-products of polyester devices. The separation and recovery process optimizes the existing separation process according to the characteristics of the mixed alcohol by-products of polyester devices. The improved separation and recovery process has the advantage of being able to flexibly respond to changes in feed composition, while improving product quality and recovery rate, and has good application prospects.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a separation and recovery process for a by-product mixed alcohol of a polyester device, the separation and recovery process comprising the following steps:

[0010] (1) The mixed alcohol by-product from the polyester unit enters the light component removal tower, the first light component is extracted from the top of the tower, and the first heavy component in the bottom of the tower enters the evaporation tower;

[0011] (2) The second heavy component is taken out from the bottom of the evaporation tower, and the second light component is taken out from the top of the tower and enters the ethylene glycol refining tower;

[0012] (3) According to the composition of the second light component in step (2), the ethylene glycol product is produced from the side line of the ethylene glycol refining tower, the third light component is produced from the top of the tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower;

[0013] Or the ethylene glycol product is taken out from the top of the ethylene glycol refining tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower;

[0014] (4) The diethylene glycol product is taken out from the side line of the diethylene glycol refining tower, the fourth light component is taken out from the top of the tower, and the fourth heaviest component is taken out from the bottom of the tower.

[0015] The following are preferred technical solutions of the present invention, but are not intended to be limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0016] As a preferred technical solution of the present invention, the mixed alcohol in step (1) includes water, ethylene glycol, diethylene glycol and oligomers.

[0017] Preferably, the mixed alcohol in step (1) comprises, by mass percentage, 1-10 wt% of water, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%; 70-95 wt% of ethylene glycol, for example, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt% or 95 wt%; 5-20 wt% of diethylene glycol, for example, 5 wt%, 10 wt%, 15 wt% or 20 wt%; and 0.01-10 wt% of oligomer, for example, 0.01 wt%, 0.05 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%; the selection of the above numerical values ​​is not limited to the listed numerical values, and other numerical values ​​not listed within the respective numerical ranges are equally applicable.

[0018] As a preferred technical solution of the present invention, the mixed alcohol in step (1) also includes at least one of a first intermediate component, a second intermediate component or a third intermediate component, for example, a first intermediate component and a second intermediate component, a first intermediate component, a second intermediate component and a third intermediate component, a first intermediate component and a third intermediate component, etc.

[0019] Preferably, the first intermediate component includes a component having a boiling point lower than that of water, and a component having a boiling point between water and 110°C.

[0020] Preferably, the second intermediate component comprises a component having a boiling point between 110°C and ethylene glycol.

[0021] Preferably, the third intermediate component comprises a component having a boiling point between ethylene glycol and diethylene glycol.

[0022] Preferably, the fourth intermediate component comprises a component having a boiling point between diethylene glycol and oligomers.

[0023] Preferably, in the mixed alcohol of step (1), the content of the first intermediate component is 0-5wt%, for example, 0wt%, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%; the content of the second intermediate component is 0-5wt%, for example, 0wt%, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%; the content of the third intermediate component is 0-5wt%, for example, 0wt%, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%; the content of the fourth intermediate component is 0-5wt%, for example, 0wt%, 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, etc. The selection of the above numerical values ​​is not limited to the listed numerical values, and other unlisted numerical values ​​within their respective numerical ranges are equally applicable.

[0024] As a preferred technical solution of the present invention, the theoretical plate number of the lightness removal tower in step (1) is 5 to 25, for example, 5, 10, 15, 20 or 25, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the top operating pressure of the lightness removal tower in step (1) is -0.01 MPaG to -0.09 MPaG, for example, -0.01 MPaG, -0.02 MPaG, -0.03 MPaG, -0.04 MPaG, -0.05 MPaG, -0.06 MPaG, -0.07 MPaG, -0.08 MPaG or -0.09 MPaG, but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0026] Preferably, the operating temperature of the bottom of the lightness removal tower in step (1) is 110-180°C, for example, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C or 180°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the reflux ratio of the lightness removal tower in step (1) is 0.1 to 10, for example 0.1, 1, 2, 4, 6, 8 or 10, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, in step (1), the first light component includes water and / or a first intermediate component.

[0029] As a preferred technical solution of the present invention, the top operating pressure of the evaporation tower in step (2) is -0.04 MPaG to -0.099 MPaG, for example, -0.04 MPaG, -0.05 MPaG, -0.06 MPaG, -0.07 MPaG, -0.08 MPaG or -0.099 MPaG, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the operating temperature of the bottom of the evaporation tower in step (2) is 110-200°C, for example, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, in step (2), the second component comprises oligomers and / or a fourth intermediate component.

[0032] As a preferred technical solution of the present invention, the theoretical plate number of the ethylene glycol refining tower in step (3) is 10 to 40, for example, 10, 15, 20, 25, 30, 35 or 40, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] Preferably, the top operating pressure of the ethylene glycol refining tower in step (3) is -0.04 MPaG to -0.099 MPaG, for example, -0.04 MPaG, -0.05 MPaG, -0.06 MPaG, -0.07 MPaG, -0.08 MPaG or -0.099 MPaG, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the operating temperature of the bottom of the ethylene glycol refining tower in step (3) is 110-200°C, for example, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the reflux ratio of the ethylene glycol refining tower in step (3) is 0.1 to 10, such as 0.1, 1, 2, 4, 6, 8 or 10, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] As a preferred technical solution of the present invention, when the second light component in step (3) does not contain the second intermediate component, one of the following extraction schemes is selected, namely, the ethylene glycol product is extracted from the side line of the ethylene glycol refining tower, the third light component is extracted from the top of the tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower; or the ethylene glycol product is extracted from the top of the ethylene glycol refining tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower.

[0037] Preferably, when the second light component in step (3) contains the second intermediate component, the ethylene glycol product is extracted from the side line of the ethylene glycol refining tower, the third light component is extracted from the top of the tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower.

[0038] Preferably, the ethylene glycol product in step (3) is extracted at the side line position of the 2nd to 10th theoretical plates from top to bottom, such as the 2nd theoretical plate, the 3rd theoretical plate, the 4th theoretical plate, the 5th theoretical plate, the 6th theoretical plate, the 7th theoretical plate, the 8th theoretical plate, the 9th theoretical plate or the 10th theoretical plate, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the third light component in step (3) includes the second intermediate component.

[0040] As a preferred technical solution of the present invention, the theoretical plate number of the diethylene glycol refining tower in step (4) is 5 to 30, for example, 5, 10, 15, 20, 25 or 30, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the top operating pressure of the diethylene glycol refining tower in step (4) is -0.04 MPaG to -0.099 MPaG, for example, -0.04 MPaG, -0.05 MPaG, -0.06 MPaG, -0.07 MPaG, -0.08 MPaG or -0.099 MPaG, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the operating temperature of the bottom of the diethylene glycol refining tower in step (4) is 110-200°C, for example, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the reflux ratio of the diethylene glycol refining tower in step (4) is 0.1 to 10, such as 0.1, 1, 2, 4, 6, 8 or 10, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the diethylene glycol product in step (4) is extracted at the side line position of the 3rd to 10th theoretical plates from top to bottom, such as the 3rd theoretical plate, the 4th theoretical plate, the 5th theoretical plate, the 6th theoretical plate, the 7th theoretical plate, the 8th theoretical plate, the 9th theoretical plate or the 10th theoretical plate, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] Preferably, the fourth light component in step (4) comprises ethylene glycol and diethylene glycol.

[0046] In step (4) of the present invention, the components extracted from the top of the diethylene glycol refining tower are a mixture of part of ethylene glycol and diethylene glycol (i.e., the fourth light component). The top extraction amount is adjusted according to the composition change of the feed mixed alcohol in step (1) to ensure the purity of the diethylene glycol product.

[0047] As a preferred technical solution of the present invention, the evaporation tower in step (2) includes any one of an evaporation tower with a wire mesh without reflux, an evaporation tower with a section of filler without reflux, an evaporation tower with a section of filler with reflux, or an evaporation tower with a tower plate with reflux.

[0048] Preferably, in the evaporation tower without reflux and the evaporation tower with reflux, the height of the filler is independently 1 to 3 m, for example, 1 m, 1.5 m, 2 m, 2.5 m or 3 m, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] Preferably, the number of theoretical plates of the evaporation tower with reflux plates is 2 to 10, such as 2, 4, 6, 8 or 10, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] As a preferred technical solution of the present invention, the separation and recovery process of the by-product mixed alcohol produced by the polyester device is a continuous process.

[0051] In the present invention, the lightness removal tower, the ethylene glycol refining tower and the diethylene glycol refining tower all independently include a reboiler.

[0052] Preferably, the reboiler comprises any one of a forced circulation reboiler and a falling film reboiler, or a combination of the two.

[0053] As a preferred technical solution of the present invention, the fourth monomer introduced into the polyester device is a diol with a boiling point between ethylene glycol and diethylene glycol, which can be extracted from the top of the diethylene glycol refining tower described in step (4) and introduced into a new separation tower for separation, which belongs to the extended technology of the present invention.

[0054] As a preferred technical solution of the present invention, the fourth monomer introduced into the polyester device is a diol with a boiling point higher than that of diethylene glycol, which can be extracted from the bottom of the diethylene glycol refining tower described in step (4) and introduced into a new separation tower for separation, which also belongs to the extended technology of the present invention.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) The separation and recovery process of the present invention removes oligomers before separating alcohol substances, thereby avoiding blockage of the tower plates or fillers in the later stage, prolonging the life of the device and saving costs;

[0057] (2) The separation and recovery process of the present invention is aimed at the characteristics that there are many by-products in the polymerization reaction and the change of the mixed alcohol feed composition has a great influence on the distillation separation effect. The extraction positions of various components, including components with a boiling point lower than water, intermediate components with a boiling point between 110°C and ethylene glycol, and intermediate components with a boiling point between ethylene glycol and diethylene glycol, are reasonably set. Without changing the tower, the extraction amount at each location can be adjusted to meet the purity and yield of ethylene glycol and diethylene glycol, so that the purity of ethylene glycol reaches more than 99.2wt% and the yield reaches more than 95.8%, and the purity of diethylene glycol reaches more than 99.2wt% and the yield reaches more than 86.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 The present invention provides a flowchart of a process for separating and recovering by-product mixed alcohols from a polyester device in accordance with a specific embodiment of the present invention.

[0059] Among them, C-101 is a lightness removal tower, C-102 is an evaporation tower, C-103 is an ethylene glycol refining tower, C-104 is a diethylene glycol refining tower, E-101 is a lightness removal tower condenser, E-102 is a lightness removal tower reboiler, E-103 is an evaporation tower condenser, E-104 is an evaporation tower reboiler, E-105 is an ethylene glycol refining tower condenser, E-106 is an ethylene glycol refining tower reboiler, and E-107 is a diethylene glycol refining tower condenser. E-108 is the reboiler of diethylene glycol refining tower, P-101 is the reflux pump of lightness removal tower, P-102 is the bottom liquid pump of lightness removal tower, P-103 is the bottom liquid pump of evaporation tower, P-104 is the reflux pump of ethylene glycol refining tower, P-105 is the ethylene glycol product extraction pump, P-106 is the bottom liquid pump of ethylene glycol refining tower, P-107 is the reflux pump of diethylene glycol refining tower, P-108 is the diethylene glycol product extraction pump, and P-109 is the bottom liquid pump of diethylene glycol refining tower. DETAILED DESCRIPTION

[0060] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0061] In a specific embodiment, the present invention provides a separation and recovery device for by-product mixed alcohol of a polyester device, the separation and recovery device comprising a lightness removal tower C-101, an evaporation tower C-102, an ethylene glycol refining tower C-103 and a diethylene glycol refining tower C-104 connected in sequence;

[0062] The lightness removal tower C-101 includes a lightness removal tower condenser E-101, a lightness removal tower reflux pump P-101, a lightness removal tower reboiler E-102 and a lightness removal tower kettle liquid pump P-102;

[0063] The evaporation tower C-102 includes an evaporation tower condenser E-103, an evaporation tower reboiler E-104 and an evaporation tower kettle liquid pump P-103;

[0064] The evaporation tower C-102 includes any one of an evaporation tower without reflux and a wire mesh, an evaporation tower without reflux and a section of filler, an evaporation tower with a reflux and a section of filler, or an evaporation tower with a reflux and a tray;

[0065] Furthermore, in the evaporation tower without reflux and with a section of filler and the evaporation tower with reflux and with a section of filler, the height of the filler is independently 1 to 3 m;

[0066] Furthermore, the number of theoretical plates of the evaporation tower with reflux plates is 2 to 10;

[0067] The ethylene glycol refining tower C-103 includes an ethylene glycol refining tower condenser E-105, an ethylene glycol refining tower reflux pump P-104, an ethylene glycol refining tower reboiler E-106, an ethylene glycol product extraction pump P-105 and an ethylene glycol refining tower bottom liquid pump P-106;

[0068] The diethylene glycol refining tower C-104 includes a diethylene glycol refining tower condenser E-107, a diethylene glycol refining tower reflux pump P-107, a diethylene glycol refining tower reboiler E-108, a diethylene glycol product extraction pump P-108 and a diethylene glycol refining tower bottom liquid pump P-109.

[0069] The present invention also provides a separation and recovery process for a by-product mixed alcohol of a polyester device, which is based on the separation and recovery device in the above specific embodiment. The separation and recovery process is as follows: Figure 1 As shown, the following steps are included:

[0070] (1) The mixed alcohol by-product from the polyester unit enters the light component removal tower C-101, the first light component is extracted from the top of the tower, and the first heavy component in the bottom of the tower enters the evaporation tower C-102;

[0071] The mixed alcohol comprises, by mass percentage, 1-10 wt% of water, 70-95 wt% of ethylene glycol, 5-20 wt% of diethylene glycol, and 0.01-10 wt% of oligomers; and further comprises 0-5 wt% of a first intermediate component, 0-5 wt% of a second intermediate component, 0-5 wt% of a third intermediate component, and 0-5 wt% of a fourth intermediate component;

[0072] Further, the first intermediate component includes components with a boiling point lower than water, and components with a boiling point between water and 110°C; the second intermediate component includes components with a boiling point between 110°C and ethylene glycol; the third intermediate component includes components with a boiling point between ethylene glycol and diethylene glycol; the fourth intermediate component includes components with a boiling point between diethylene glycol and oligomers;

[0073] Furthermore, the number of theoretical plates of the lightness removal tower C-101 is 5 to 25, the operating pressure of the tower top is -0.01 MPaG to -0.09 MPaG, the operating temperature of the tower bottom is 110 to 180° C., and the reflux ratio is 0.1 to 10;

[0074] Further, the first light component includes water and / or a first intermediate component;

[0075] (2) The second heavy component (including oligomers and / or the fourth intermediate component) is taken out from the bottom of the evaporation tower C-102, and the second light component is taken out from the top of the tower and enters the ethylene glycol refining tower C-103;

[0076] The top operating pressure of the evaporation tower C-102 is -0.04 MPaG to -0.099 MPaG, and the bottom operating temperature is 110 to 200°C.

[0077] (3) When the second light component in step (2) contains the second intermediate component, the ethylene glycol product is produced from the side line (the position of the 2nd to 10th theoretical plates from top to bottom) of the ethylene glycol refining tower C-103, the third light component (including the second intermediate component) is produced from the top of the tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower C-104;

[0078] When the second light component in step (2) does not contain the second intermediate component, the ethylene glycol product is extracted from the side line (the position of the 2nd to 10th theoretical plates from top to bottom) of the ethylene glycol refining tower C-103, the third light component is extracted from the top of the tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower C-104; or the ethylene glycol product is extracted from the top of the ethylene glycol refining tower C-103, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower C-104;

[0079] The number of theoretical plates of the ethylene glycol refining tower C-103 is 10 to 40, the operating pressure of the tower top is -0.04 MPaG to -0.099 MPaG, the operating temperature of the tower bottom is 110 to 200°C, and the reflux ratio is 0.1 to 10;

[0080] (4) The diethylene glycol product is produced from the side line (the position of the 3rd to 10th theoretical plates from top to bottom) of the diethylene glycol refining tower C-104, the fourth light component (including ethylene glycol and diethylene glycol) is produced from the top of the tower, and the fourth heavy component is produced from the bottom of the tower;

[0081] The number of theoretical plates of the diethylene glycol refining tower C-104 is 5 to 30, the operating pressure of the tower top is -0.04 MPaG to -0.099 MPaG, the operating temperature of the tower bottom is 110 to 200° C., and the reflux ratio is 0.1 to 10.

[0082] In addition, the boiling points of the various materials in the mixed alcohol involved in the following examples and comparative examples are shown in Table 1.

[0083] Table 1

[0084] Acetaldehyde water Dioxane Ethylene glycol monoethyl ether Ethylene glycol Diethylene glycol Triethylene glycol Oligomer Boiling point / ℃ 20.1 100 101 135 197.3 245 289.4 ＞300

[0085] The following are typical but non-limiting embodiments of the present invention:

[0086] Examples 1 to 6 respectively provide a separation and recovery process for a by-product mixed alcohol of a polyester device. The separation and recovery process is based on the separation and recovery process in a specific implementation manner. The raw material composition of the specific mixed alcohol and the parameter conditions in the separation process are shown in Tables 2 and 3, respectively.

[0087] Table 2

[0088]

[0089] Table 3

[0090]

[0091]

[0092] Comparative Example 1

[0093] This comparative example provides a separation and recovery process for mixed alcohol by-products of a polyester device. The separation and recovery process refers to the separation and recovery process in Example 1, except that: no evaporation tower C-102 is provided, that is, the operation of evaporation tower C-102 in step (2) is not performed, and the first heavy component in the bottom of light removal tower C-101 in step (1) is directly introduced into ethylene glycol refining tower C-103.

[0094] The separation and recovery process in the above comparative example is used for separation, which is easy to clog the packing, and increases the operating temperature of the tower bottom, the required heat medium temperature is increased, and the tower bottom reboiler is easy to coke and affect the product quality; if the purity of ethylene glycol is to reach 99.2wt%, the yield will be less than 80%, and if the purity of diethylene glycol is to reach 99.2wt%, the yield will be less than 70%.

[0095] It can be seen from the above embodiments and comparative examples that the separation and recovery process of the present invention removes the oligomers before the alcohol substances are separated, thereby avoiding the blockage of the later tower plates or fillers, improving the life of the device and saving costs; the separation and recovery process is aimed at the characteristics that there are many by-products in the polymerization reaction and the change of the mixed alcohol feed composition has a great influence on the distillation separation effect. The extraction positions of various components, including components with a boiling point lower than water, intermediate components with a boiling point between 110°C and ethylene glycol, and intermediate components with a boiling point between ethylene glycol and diethylene glycol are reasonably set. Under the condition of not changing the tower, the extraction amount at each location can be adjusted to meet the purity and yield of ethylene glycol and diethylene glycol, so that the purity of ethylene glycol reaches more than 99.2wt%, the yield reaches more than 95.8%, and the purity of diethylene glycol reaches more than 99.2wt%, and the yield reaches more than 86.8%.

[0096] The present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the operation of the present invention, addition of auxiliary operations, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A separation and recovery process for mixed alcohol by-products of a polyester device, characterized in that: The separation and recovery process comprises the following steps: (1) The mixed alcohol by-product from the polyester unit enters the light component removal tower, the first light component is extracted from the top of the tower, and the first heavy component in the bottom of the tower enters the evaporation tower; The mixed alcohol includes water, ethylene glycol, diethylene glycol and oligomers; The mixed alcohol further comprises at least one of a first intermediate component, a second intermediate component, a third intermediate component, or a fourth intermediate component; The first intermediate component is a component having a boiling point lower than water, and a component having a boiling point between water and 110°C; The second intermediate component is a component with a boiling point between 110°C and ethylene glycol; The third intermediate component is a component with a boiling point between ethylene glycol and diethylene glycol; The fourth intermediate component is a component having a boiling point between diethylene glycol and oligomers; (2) The second heavy component is taken out from the bottom of the evaporation tower, and the second light component is taken out from the top of the tower and enters the ethylene glycol refining tower; (3) According to the composition of the second light component in step (2), the ethylene glycol product is produced from the side line of the ethylene glycol refining tower, the third light component is produced from the top of the tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower; Or the ethylene glycol product is extracted from the top of the ethylene glycol refining tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower; The number of theoretical plates of the ethylene glycol refining tower is 10 to 40; the ethylene glycol product is extracted at the side line position of the 2nd to 10th theoretical plates from top to bottom; (4) The diethylene glycol refining tower produces a diethylene glycol product from the side line, produces a fourth light component from the top of the tower, and produces a fourth heavy component from the bottom of the tower; The number of theoretical plates of the diethylene glycol refining tower is 5 to 30; the diethylene glycol product is extracted at the side line position of the 3rd to 10th theoretical plates from top to bottom.

2. The separation and recovery process according to claim 1, characterized in that: The mixed alcohol in step (1) comprises, by mass percentage, 1 to 10 wt % of water, 70 to 95 wt % of ethylene glycol, 5 to 20 wt % of diethylene glycol, and 0.01 to 10 wt % of oligomers.

3. The separation and recovery process according to claim 2, characterized in that: In the mixed alcohol of step (1), the content of the first intermediate component is 0-5wt%, the content of the second intermediate component is 0-5wt%, the content of the third intermediate component is 0-5wt%, and the content of the fourth intermediate component is 0-5wt%.

4. The separation and recovery process according to claim 3, characterized in that: The number of theoretical plates of the lightness removal tower in step (1) is 5 to 25; The top operating pressure of the lightness removal tower in step (1) is -0.01 MPaG to -0.09 MPaG; The operating temperature of the bottom of the lightness removal tower in step (1) is 110-180° C. The reflux ratio of the light component removal tower in step (1) is 0.1 to 10; the first light component in step (1) includes water and / or a first intermediate component.

5. The separation and recovery process according to claim 3 or 4, characterized in that: The top operating pressure of the evaporation tower in step (2) is -0.04 MPaG to -0.099 MPaG; The operating temperature of the bottom of the evaporation tower in step (2) is 110-200° C.; the second heavy component in step (2) includes oligomers and / or a fourth intermediate component.

6. The separation and recovery process according to claim 3, characterized in that: The top operating pressure of the ethylene glycol refining tower in step (3) is -0.04 MPaG to -0.099 MPaG; The operating temperature of the bottom of the ethylene glycol refining tower in step (3) is 110-200° C. The reflux ratio of the ethylene glycol refining tower in step (3) is 0.1 to 10.

7. The separation and recovery process according to claim 3, characterized in that: In step (3), when the second light component does not contain the second intermediate component, the ethylene glycol product is extracted from the side line of the ethylene glycol refining tower, the third light component is extracted from the top of the tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower; or the ethylene glycol product is extracted from the top of the ethylene glycol refining tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower; In step (3), when the second light component contains the second intermediate component, the ethylene glycol product is extracted from the side line of the ethylene glycol refining tower, the third light component is extracted from the top of the tower, and the third heavy component in the bottom of the tower enters the diethylene glycol refining tower; The third light component in step (3) includes the second intermediate component.

8. The separation and recovery process according to claim 1, characterized in that: The top operating pressure of the diethylene glycol refining tower in step (4) is -0.04 MPaG to -0.099 MPaG; The operating temperature of the bottom of the diethylene glycol refining tower in step (4) is 110-200° C. The reflux ratio of the diethylene glycol refining tower in step (4) is 0.1 to 10; the fourth light component in step (4) includes ethylene glycol and diethylene glycol.

9. The separation and recovery process according to claim 1, characterized in that: The evaporation tower in step (2) includes any one of an evaporation tower without reflux and a wire mesh, an evaporation tower without reflux and a section of filler, an evaporation tower with a reflux and a section of filler, or an evaporation tower with a reflux and a tray; In the evaporation tower without reflux and with a section of filler and the evaporation tower with reflux and with a section of filler, the height of the filler is independently 1 to 3 m; The number of theoretical plates of the evaporation tower with reflux plates is 2 to 10.

10. The separation and recovery process according to claim 1, characterized in that: The separation and recovery process of the by-product mixed alcohol of the polyester device is a continuous process.

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