Device and method for absorbing and recycling devolatilization tail gas

Abstract

The invention relates to the technical field of devolatilization tail gas absorption and cyclic utilization, in particular to a devolatilization tail gas absorption and cyclic utilization device and method. Comprising the steps that tail gas generated by primary devolatilization and tail gas generated by secondary devolatilization are introduced into a primary devolatilization tail gas absorption tower and a secondary devolatilization tail gas absorption tower respectively, absorption liquid is mother liquid separated by a Meso crystallizer, and the absorbed tail gas is discharged to a vacuum system outside a boundary area; the fresh absorption liquid is sprayed to absorb L-lactide in the tail gas, and the absorption liquid absorbing the L-lactide is sequentially subjected to Meso rectification and Meso crystal separation; and finally, L-lactide produced by the Meso rectifying tower is returned to the L-lactide rectifying tower of the previous process, a Meso-lactide product obtained after Meso crystallization and purification is sent out of a boundary area, and mother liquor obtained after Meso crystallization and separation serves as fresh absorption liquid and is returned to the devolatilization tail gas absorption tower, so that efficient cyclic utilization of effective components in the devolatilization tail gas under the low-temperature working condition is achieved, and the purpose of recycling the effective components in the devolatilization tail gas is achieved. And the utilization value of the Meso-lactide crystallization mother liquor is fully exerted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of absorption and recycling of devolatilization tail gas, and particularly relates to a device and method for absorption and recycling of devolatilization tail gas. BACKGROUND

[0002] Polylactic acid (PLA) is a new type of biodegradable material, which is suitable for various processing methods such as extrusion, injection molding, film drawing and spinning, and is convenient to process, and thus can be applied to the fields of food packaging, fast food boxes, non-woven fabrics, industrial and civil fabrics, agricultural fabrics and 3D printing; in the production process of polylactic acid, devolatilization tail gas is generated in the devolatilization process of polylactic acid, and the tail gas mainly consists of gaseous L-lactide monomers that have not participated in the polymerization reaction and most of the non-condensable gases.

[0003] At present, the mainstream method for treating devolatilization tail gas is to directly condense the L-lactide with a relatively high condensation point in the heat exchange pipe of a condenser, and one condenser is used as a backup, when the amount of L-lactide condensate in the used condenser reaches a certain amount, the standby condenser is put into use by switching the valve, and the condenser switched out of the system is quickly heated to melt the L-lactide condensed in the heat exchange pipe for standby, and the operation is cycled in turn.

[0004] However, the current method is complicated to operate, and the vacuum of the system is easily affected by fluctuations, which is not conducive to the stability of production. SUMMARY

[0005] The present application aims to provide a device and method for absorption and recycling of devolatilization tail gas, which aims to solve the technical problem of the current method in the prior art, which is complicated to operate and the vacuum of the system is easily affected by fluctuations, which is not conducive to the stability of production.

[0006] To achieve the above-mentioned purpose, the present application adopts a device for absorption and recycling of devolatilization tail gas, which comprises a first devolatilization tail gas feed pipe, a first devolatilization tail gas outlet pipe, a first devolatilization tail gas absorption tower discharge pipe, a second devolatilization tail gas feed pipe, a second devolatilization tail gas outlet pipe, a second devolatilization tail gas absorption tower discharge pipe, a Meso rectifying column feed pipe, a Meso crystallizer mother liquor discharge pipe, a first devolatilization tail gas absorption tower, a second devolatilization tail gas absorption tower, a Meso rectifying column, a Meso crystallizer, and a supporting heat exchanger for heating or cooling, a machine pump for conveying materials, and a storage tank for storing materials.

[0007] The first-stage devolatilization tail gas feed pipe is connected with the gas inlet of the first-stage devolatilization tail gas absorption tower, the first-stage devolatilization tail gas outlet pipe is connected with the gas phase outlet at the top of the first-stage devolatilization tail gas absorption tower, the first-stage devolatilization tail gas absorption tower discharge pipe is connected with the liquid phase outlet at the bottom of the first-stage devolatilization tail gas absorption tower, the second-stage devolatilization tail gas feed pipe is connected with the gas inlet of the second-stage devolatilization tail gas absorption tower, the second-stage devolatilization tail gas outlet pipe is connected with the gas phase outlet at the top of the second-stage devolatilization tail gas absorption tower, the second-stage devolatilization tail gas absorption tower discharge pipe is connected with the liquid phase outlet at the bottom of the second-stage devolatilization tail gas absorption tower T201, the first-stage devolatilization tail gas absorption tower discharge pipe and the second-stage devolatilization tail gas absorption tower discharge pipe are merged into the Meso rectification tower feed pipe and then enter the feed inlet of the Meso rectification tower, the Meso rectification tower top discharge pipe is connected with the feed inlet of the Meso crystallizer, the L-lactide produced by the Meso rectification tower discharge pipe is discharged to the L-lactide rectification or crystallization unit outside the boundary area, and the Meso crystallizer mother liquor discharge pipe is connected with the first-stage devolatilization tail gas absorption tower and the second-stage devolatilization tail gas absorption tower through a flow divider.

[0008] The flow divider is a first Meso crystallizer mother liquor pipe and a second Meso crystallizer mother liquor pipe, wherein the first Meso crystallizer mother liquor pipe is connected with the absorption liquid pipe inlet of the first-stage devolatilization tail gas absorption tower, and the second Meso crystallizer mother liquor pipe is connected with the absorption liquid pipe inlet of the second-stage devolatilization tail gas absorption tower.

[0009] The application also provides a devolatilization tail gas absorption recycling method applied to the above-mentioned devolatilization tail gas absorption recycling device, which comprises the following steps:

[0010] Step S1: the devolatilization tail gas produced by the first-stage devolatilization and the second-stage devolatilization is respectively introduced into the first-stage devolatilization tail gas absorption tower and the second-stage devolatilization tail gas absorption tower, and the absorption liquid is the mother liquor separated by the Meso crystallizer;

[0011] Step S2: the absorption liquid is sprayed from the upper part of the tower and countercurrently absorbs the L-lactide in the tail gas, the absorbed tail gas is discharged to the vacuum system outside the boundary area, and the absorption liquid after absorbing the L-lactide is sequentially separated by the Meso rectification and the Meso crystallization;

[0012] Step S3: the L-lactide produced by the Meso rectification tower is returned to the L-lactide rectification tower in the previous process;

[0013] Step S4: the mother liquor separated by the Meso crystallizer is returned to the first-stage devolatilization tail gas absorption tower and the second-stage devolatilization tail gas absorption tower as fresh absorption liquid.

[0014] The de-volatilization tail gas is a tail gas rich in L-lactide monomers in a polylactic acid production process, mainly containing L-lactide and nitrogen, and the de-volatilization tail gas contains 2-10 vol% of L-lactide, and the inlet gas pressure is 0.1-1.0 KPaA.

[0015] In step S1, the first de-volatilization absorption tower corresponds to the first de-volatilization, and the circulating absorption liquid temperature is 20-40 DEG C; the second de-volatilization absorption tower corresponds to the second de-volatilization, and the circulating absorption liquid temperature is 20-40 DEG C.

[0016] In step S3, the circulating absorption liquid discharged from the first de-volatilization tail gas absorption tower and the second de-volatilization tail gas absorption tower is combined with the Meso-lactide-rich stream produced by the L-lactide rectification tower in the previous lactide separation and purification process and enters the Meso rectification tower.

[0017] In step S4, the Meso-lactide product purified by crystallization in the Meso crystallizer has a purity of ≥99.0%, the fresh absorption liquid of the first de-volatilization tail gas absorption tower and the second de-volatilization tail gas absorption tower is the Meso crystallization mother liquor, the content of Meso-lactide is ≤70%, and the freezing point is ≤40 DEG C.

[0018] The Meso crystallizer is one or a combination of static crystallizers, falling film crystallizers or suspension crystallizers.

[0019] The device and method for recycling de-volatilization tail gas absorption of the application comprise a first de-volatilization tail gas inlet pipe, a first de-volatilization tail gas outlet pipe, a first de-volatilization tail gas absorption tower outlet pipe, a second de-volatilization tail gas inlet pipe, a second de-volatilization tail gas outlet pipe, a second de-volatilization tail gas absorption tower outlet pipe, a Meso rectification tower inlet pipe, a Meso crystallizer mother liquor outlet pipe, a first de-volatilization tail gas absorption tower, a second de-volatilization tail gas absorption tower, a Meso rectification tower, a Meso crystallizer, and a supporting heat exchanger for heating or cooling, a machine pump for conveying materials, and a storage tank for storing materials. The design solves the problem of frequent switching of heat exchangers in traditional de-volatilization tail gas treatment, and realizes the operation of the tail gas absorption tower at low temperature, thereby reducing the emission amount of lactide in the discharged tail gas, and improving the utilization rate of the Meso crystallization mother liquor generated in the polylactic acid production process. In this way, the technical problems of the current method, such as complicated operation and unstable system vacuum, are effectively solved, and the stability of production is improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0021] Figure 1 Fig. 1 is a schematic diagram of a booster impeller cover.

[0022] Figure 2 Fig. 5 is a flow chart of a method for recycling and absorbing the devolatilization tail gas according to the present application.

[0023] T101-first devolatilization tail gas absorption tower, T201-second devolatilization tail gas absorption tower, T301-Meso rectification tower, C401-Meso crystallizer, 01-first devolatilization tail gas feeding pipe, 02-second devolatilization tail gas feeding pipe, 03-first devolatilization tail gas outlet pipe, 04-second devolatilization tail gas outlet pipe, 06-first devolatilization tail gas absorption tower outlet pipe, 07-second devolatilization tail gas absorption tower outlet pipe, 08-Meso rectification tower feeding pipe, 09-Meso rectification tower outlet pipe, 10-Meso rectification tower top outlet pipe, 11-second Meso crystallizer mother liquor pipe, 12-Meso crystallizer mother liquor outlet pipe, 13-first Meso crystallizer mother liquor pipe. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in detail below, examples of which are shown in the drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0025] Please refer to Figure 1 The present application provides a device for recycling and absorbing devolatilization tail gas, which comprises a first devolatilization tail gas feeding pipe 01, a first devolatilization tail gas outlet pipe 03, a first devolatilization tail gas absorption tower outlet pipe 06, a second devolatilization tail gas feeding pipe 02, a second devolatilization tail gas outlet pipe 04, a second devolatilization tail gas absorption tower outlet pipe 07, a Meso rectification tower feeding pipe 08, a Meso crystallizer mother liquor outlet pipe 12, a first devolatilization tail gas absorption tower T101, a second devolatilization tail gas absorption tower T201, a Meso rectification tower T301, a Meso crystallizer C401, and a supporting heat exchanger for heating or cooling, a machine pump for conveying materials, and a storage tank for storing materials.

[0026] In the present embodiment, the primary devolatilization tail gas absorption tower T101 is used to absorb the tail gas generated by primary devolatilization; the secondary devolatilization tail gas absorption tower T201 is used to absorb the tail gas generated by secondary devolatilization; the Meso rectification tower T301 is used to separate L-lactide in the circulating absorption liquid discharged from the absorption tower; and the Meso crystallizer C401 is used to separate Meso-lactide product and crystallization mother liquor used as fresh absorption liquid.

[0027] Further, the primary devolatilization tail gas feed pipe 01 is connected with the gas inlet of the primary devolatilization tail gas absorption tower T101, the primary devolatilization tail gas outlet pipe 03 is connected with the gas phase outlet at the top of the primary devolatilization tail gas absorption tower T101, the primary devolatilization tail gas absorption tower discharge pipe 06 is connected with the liquid phase outlet at the bottom of the primary devolatilization tail gas absorption tower T101, the secondary devolatilization tail gas feed pipe 02 is connected with the gas inlet of the secondary devolatilization tail gas absorption tower T201, the secondary devolatilization tail gas outlet pipe 04 is connected with the gas phase outlet at the top of the secondary devolatilization tail gas absorption tower T201, the secondary devolatilization tail gas absorption tower discharge pipe 07 is connected with the liquid phase outlet at the bottom of the secondary devolatilization tail gas absorption tower T201, the primary devolatilization tail gas absorption tower discharge pipe 06 and the secondary devolatilization tail gas absorption tower discharge pipe 07 are merged into the Meso rectification tower feed pipe 08 and then enter the feed inlet of the Meso rectification tower T301, the Meso rectification tower overhead discharge pipe 10 is connected with the feed inlet of the Meso crystallizer C401, the L-lactide produced by the Meso rectification tower discharge pipe 09 is discharged to the L-lactide rectification or crystallization unit outside the boundary region, and the Meso crystallizer mother liquor discharge pipe 12 is connected with the primary devolatilization tail gas absorption tower T101 and the secondary devolatilization tail gas absorption tower T201 through a flow divider.

[0028] Further, the flow divider is a first Meso crystallizer mother liquor pipe 13 and a second Meso crystallizer mother liquor pipe 11, wherein the first Meso crystallizer mother liquor pipe 13 is connected with the absorption liquid pipe of the primary devolatilization tail gas absorption tower T101, and the second Meso crystallizer mother liquor pipe 11 is connected with the absorption liquid pipe of the secondary devolatilization tail gas absorption tower T201.

[0029] Please refer to Figure 2 The present application also provides a method for recycling devolatilization tail gas absorption, which is applied to the above-mentioned device for recycling devolatilization tail gas absorption and includes the following steps.

[0030] Step S1: the devolatilization tail gas generated by primary devolatilization and secondary devolatilization is respectively introduced into the primary devolatilization tail gas absorption tower T101 and the secondary devolatilization tail gas absorption tower T201, and the absorption liquid is the mother liquor separated by the Meso crystallizer C401;

[0031] Step S2: The absorption liquid is sprayed from the upper part of the tower to absorb L-lactide in the tail gas countercurrently, and the absorbed tail gas is discharged to the vacuum system outside the boundary area. The absorption liquid after absorbing L-lactide is separated by Meso rectification and Meso crystallization in turn;

[0032] Step S3: The L-lactide produced by the Meso rectification tower T301 is returned to the L-lactide rectification tower in the previous process;

[0033] Step S4: The mother liquor separated by the Meso crystallizer C401 is returned to the first and second devolatilization tail gas absorption towers T101 and T201 as fresh absorption liquid.

[0034] Further, in step S1, the devolatilization tail gas is the tail gas rich in L-lactide monomer in the production process of polylactic acid, mainly containing L-lactide and nitrogen, and the devolatilization tail gas contains 2-10 vol% of L-lactide, and the inlet pressure is 0.1-1.0 KPaA.

[0035] Further, in step S1, the first devolatilization absorption tower corresponds to the first devolatilization, and the circulating absorption liquid temperature is 20-40°C; the second devolatilization absorption tower corresponds to the second devolatilization, and the circulating absorption liquid temperature is 20-40°C.

[0036] Further, in step S3, the circulating absorption liquid discharged from the first and second devolatilization tail gas absorption towers T101 and T201 is combined with the Meso-lactide-rich stream produced by the L-lactide rectification tower in the previous lactide separation and purification process to enter the Meso rectification tower T301.

[0037] Further, in step S4, the Meso-lactide product purified by crystallization in the Meso crystallizer C401 has a purity of ≥99.0%, the fresh absorption liquid of the first and second devolatilization tail gas absorption towers T101 and T201 is Meso crystallization mother liquor, the content of Meso-lactide is ≤70%, and the freezing point is ≤40°C.

[0038] Further, the Meso crystallizer C401 is one or a combination of static crystallizer, falling film crystallizer or suspension crystallizer.

[0039] In the application, the first devolatilization tail gas first enters the gas inlet of the first devolatilization tail gas absorption tower T101 from the first devolatilization tail gas feeding pipe 01, and is countercurrently sprayed and absorbed with the first Meso crystallizer mother liquor as absorption liquid from the top of the tower. At this time, the operating pressure of the first devolatilization tail gas absorption tower T101 is 0.2 KPaA, and the operating temperature is 30°C. The tower bottom is output to the Meso rectification tower T301, and the gas phase at the top is sent to the vacuum pump outside the boundary area.

[0040] In the invention, the secondary devolatilization tail gas from the secondary devolatilization tail gas feed pipe 02 enters the gas inlet of the secondary devolatilization tail gas absorption tower T201, and is sprayed and absorbed countercurrently with the absorption liquid from the second Meso crystallizer mother liquor at the top, at this time, the operating pressure of the secondary devolatilization tail gas absorption tower T201 is 0.2 KPaA, the operating temperature is 30°C, the tower bottom is the absorption liquid after absorbing the L-lactide in the feed stream, and is output to the Meso rectification tower T301; the top is the gas phase after removing the L-lactide in the feed stream, and is sent to the vacuum pump outside the boundary area.

[0041] In the invention, the tower bottom materials from the primary devolatilization tail gas absorption tower T101 and the secondary devolatilization tail gas absorption tower T201 are separated in the Meso rectification tower T301, the operating pressure of the Meso rectification tower T301 is 0.2 KPaA, the top temperature is 80°C, the operating temperature is 131°C, the tower bottom output contains the L-lactide stream from the devolatilization tail gas, which is returned to the L-rectification tower outside the boundary area for further recovery, and the Meso-lactide at the top after removing part of the L-lactide is sent to the Meso crystallizer C401 for treatment.

[0042] In the invention, the Meso-lactide at the top of the Meso rectification tower T301 after removing part of the L-lactide is crystallized, separated and purified in the Meso crystallizer C401, the concentrated Meso-lactide is returned to the primary devolatilization and secondary devolatilization as fresh absorption liquid, and the separated mother liquor is discharged to the L-rectification tower outside the boundary area for further recovery of useful components.

[0043] The above only discloses one preferred embodiment of the present application, and of course cannot limit the scope of the present application, and those skilled in the art can understand that all or part of the above-mentioned embodiments can be implemented, and equivalent changes made according to the claims of the present application still belong to the scope covered by the present application.

Claims

1. A device for recycling devolatilization tail gas absorption, characterized in that it comprises a first devolatilization tail gas feed pipe, a first devolatilization tail gas outlet pipe, a first devolatilization tail gas absorption column discharge pipe, a second devolatilization tail gas feed pipe, a second devolatilization tail gas outlet pipe, a second devolatilization tail gas absorption column discharge pipe, a Meso rectification column feed pipe, a Meso crystallizer mother liquor discharge pipe, a first devolatilization tail gas absorption column, a second devolatilization tail gas absorption column, a Meso rectification column, a Meso crystallizer, and a set of heat exchangers for heating or cooling, pumps for conveying materials, and storage tanks for storing materials.

2. The device for recycling devolatilization tail gas absorption according to claim 1, characterized in that the first devolatilization tail gas feed pipe is connected to the gas inlet of the first devolatilization tail gas absorption column, the first devolatilization tail gas outlet pipe is connected to the gas phase outlet at the top of the first devolatilization tail gas absorption column, the first devolatilization tail gas absorption column discharge pipe is connected to the liquid phase outlet at the bottom of the first devolatilization tail gas absorption column, the second devolatilization tail gas feed pipe is connected to the gas inlet of the second devolatilization tail gas absorption column, the second devolatilization tail gas outlet pipe is connected to the gas phase outlet at the top of the second devolatilization tail gas absorption column, the second devolatilization tail gas absorption column discharge pipe is connected to the liquid phase outlet at the bottom of the second devolatilization tail gas absorption column T201, the first devolatilization tail gas absorption column discharge pipe and the second devolatilization tail gas absorption column discharge pipe are combined into the Meso rectification column feed pipe, which enters the feed inlet of the Meso rectification column, the Meso rectification column top discharge pipe is connected to the feed inlet of the Meso crystallizer, the L-lactide produced by the Meso rectification column discharge pipe is discharged to the L-lactide rectification or crystallization unit outside the boundary area, and the Meso crystallizer mother liquor discharge pipe is connected to the first devolatilization tail gas absorption column and the second devolatilization tail gas absorption column through a flow divider.

3. The device for recycling devolatilization tail gas absorption according to claim 2, characterized in that the flow divider is a first Meso crystallizer mother liquor pipe and a second Meso crystallizer mother liquor pipe, wherein the first Meso crystallizer mother liquor pipe is connected to the absorption liquid pipe inlet of the first devolatilization tail gas absorption column, and the second Meso crystallizer mother liquor pipe is connected to the absorption liquid pipe inlet of the second devolatilization tail gas absorption column. The method comprises the following steps: Step S1: The devolatilization tail gas produced by the first devolatilization and the second devolatilization is respectively introduced into the first devolatilization tail gas absorption column and the second devolatilization tail gas absorption column, and the absorption liquid is the mother liquor separated by the Meso crystallizer; Step S2: The absorption liquid is sprayed from the upper part of the column and countercurrently absorbs L-lactide in the tail gas, the absorbed tail gas is discharged to the vacuum system outside the boundary area, and the absorption liquid after absorbing L-lactide is sequentially separated by Meso rectification and Meso crystallization; 4. The method for recycling the absorption of the devolatilization tail gas, applied to the device for recycling the absorption of the devolatilization tail gas according to claim 3, characterized in that, Step S3: The L-lactide produced by the Meso rectification column is returned to the L-lactide rectification column of the previous process; Step S4: The mother liquor separated by the Meso crystallizer is returned to the first devolatilization tail gas absorption column and the second devolatilization tail gas absorption column as fresh absorption liquid.

5. The method for recycling devolatilization tail gas absorption according to claim 4, characterized in that ​ ​ ​ In step S1, the devolatilization tail gas is a L-lactide monomer-rich tail gas in a polylactic acid production process, mainly containing L-lactide and nitrogen, and the devolatilization tail gas contains 2-10 vol% of L-lactide, and the inlet pressure is 0.1-1.0 KPaA.

6. The method for recycling devolatilization tail gas according to claim 5, wherein, In step S1, the first-stage devolatilization absorption tower corresponds to the first-stage devolatilization, and the circulating absorption liquid has a temperature of 20-40°C; and the second-stage devolatilization absorption tower corresponds to the second-stage devolatilization, and the circulating absorption liquid has a temperature of 20-40°C.

7. The method for recycling devolatilization tail gas according to claim 6, wherein, In step S3, the circulating absorption liquid discharged from the first-stage devolatilization tail gas absorption tower and the second-stage devolatilization tail gas absorption tower is combined with a Meso-lactide-rich stream produced by an L-lactide rectification tower in a previous lactide separation and purification process, and then introduced into a Meso rectification tower.

8. The method for recycling devolatilization tail gas according to claim 7, wherein, In step S4, the Meso-lactide product purified by crystallization in the Meso crystallizer has a purity of ≥99.0%, the fresh absorption liquid of the first-stage devolatilization tail gas absorption tower and the second-stage devolatilization tail gas absorption tower is a Meso crystallization mother liquor, the content of Meso-lactide is ≤70%, and the freezing point is ≤40°C.

9. The method for recycling devolatilization tail gas according to claim 8, wherein, The Meso crystallizer is one or a combination of a static crystallizer, a falling film crystallizer, or a suspension crystallizer.

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