Methyl acrylate production wastewater recovery treatment process and treatment equipment

Abstract

The invention relates to the technical field of chemical production, and discloses a methyl acrylate production wastewater recovery treatment process and treatment equipment. The invention relates to a methyl acrylate production wastewater recovery treatment process, which comprises: carrying out a reaction on methyl acrylate production wastewater and an excessive amount of methanol to convert formaldehyde, acetic acid and acrylic acid in the wastewater into corresponding methylal, methyl acetate and methyl acrylate; the methylal, the methyl acetate, the methyl acrylate and the unreacted methanol are separated from the wastewater through rectification and are recycled. A mixture of methylal, methyl acetate, methyl acrylate and methanol is extracted from the tower top of the reactive distillation tower, and corresponding substances can be recovered after separation; after methanol is separated from wastewater extracted from the bottom of the reactive distillation tower, the wastewater has a low COD value and can be sent to a sewage treatment device.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical production, and in particular to a methyl acrylate production wastewater recovery and treatment process and treatment equipment. Background Art

[0002] When methyl acrylate is produced from methyl acetate and formaldehyde, the wastewater produced contains not only esters, alcohols and hydrocarbons, but also a small amount of side reaction products such as acetic acid and acrylic acid, as well as formaldehyde raw materials that did not participate in the reaction.

[0003] The wastewater from methyl acrylate production contains many types of substances and has a complex composition. The existing conventional distillation separation and evaporation concentration cannot effectively treat it. The COD concentration in the treated wastewater is high, which does not meet the concentration requirements for sewage treatment. It cannot be directly sent to the sewage treatment device, and the substances in the wastewater cannot be effectively recovered. Summary of the Invention

[0004] The main purpose of the present invention is to provide a methyl acrylate production wastewater recovery and treatment process and treatment equipment, aiming to solve the problems of high COD concentration in wastewater treated by the prior art and inability to effectively recover substances in the wastewater.

[0005] To achieve the above object, the present invention provides a process for recycling and treating methyl acrylate production wastewater, comprising: reacting the methyl acrylate production wastewater with excess methanol to convert formaldehyde, acetic acid and acrylic acid in the wastewater into corresponding methylal, methyl acetate and methyl acrylate; The methylal, methyl acetate, methyl acrylate and unreacted methanol are separated from the waste water by distillation and recycled.

[0006] Optionally, the methyl acrylate production wastewater recovery and treatment process comprises the following steps: S10, providing methyl acrylate production wastewater and methanol; S20, feeding the methyl acrylate production wastewater and the methanol into a reactive distillation tower, where formaldehyde, acetic acid, and acrylic acid in the wastewater react with methanol respectively under the action of a catalyst, and reaction products include methylal, methyl acetate, and methyl acrylate; a light component mixture comprising methylal, methyl acetate, methyl acrylate, and methanol is extracted from the top of the reactive distillation tower, and wastewater containing methanol and heavy components is extracted from the bottom of the tower; S30, distilling and separating the light component mixture extracted from the top of the reaction distillation tower; and separating methanol from the wastewater extracted from the bottom of the reaction distillation tower.

[0007] Optionally, the separated and recovered methanol is returned to the system as a reaction raw material for the methyl acrylate production wastewater recovery treatment; the separated and recovered methyl acetate is returned to the system as a reaction raw material for the production of methyl acrylate.

[0008] Optionally, in step S20, the methanol concentration in the wastewater containing methanol and heavy components extracted from the bottom of the reactive distillation tower is 10-30 wt%. Within this range, formaldehyde, acetic acid, etc. in the wastewater can fully react. However, excessive methanol concentration will result in a large amount of methanol circulating in the system, affecting production efficiency. Preferably, the methanol concentration at the bottom of the reactive distillation tower is between 12-20 wt%, for example, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%.

[0009] Optionally, in step S20, the reactive distillation tower is operated at normal pressure, the bottom temperature is 100-110°C, and the top temperature is 40-50°C.

[0010] Optionally, in step S20, the reactive distillation tower is a plate tower or a packed tower, the reflux ratio of the reactive distillation tower is 2-5, and the reactive distillation tower is filled with a solid acid catalyst.

[0011] Optionally, in step S30, after methanol is separated from the wastewater extracted from the bottom of the reactive distillation tower, the COD of the wastewater does not exceed 2000 mg / L.

[0012] The present invention also provides a methyl acrylate production wastewater recovery and treatment device, comprising: A reactive distillation tower is used to react formaldehyde, acetic acid, and acrylic acid in methyl acrylate production wastewater with methanol, respectively, and to separate the methylal, methyl acetate, and methyl acrylate generated by the reaction, as well as the unreacted methanol, from the wastewater through distillation; A methanol recovery tower is connected to the bottom of the reaction distillation tower through a pipeline and is used to separate methanol from the wastewater produced at the bottom of the reaction distillation tower; At least one distillation tower, multiple starting feed ports of the distillation towers are connected to the top of the reactive distillation tower through pipelines, and are used to separate the light component mixture extracted from the top of the reactive distillation tower to separate methylal, methyl acetate, methyl acrylate and methanol.

[0013] Furthermore, the methyl acrylate production wastewater recovery and treatment equipment also includes a phase separation tank, and the feed port of the phase separation tank is connected to the bottom of the methanol recovery tower through a pipeline.

[0014] Furthermore, the top of the methanol recovery tower is connected to the feed inlet of the reactive distillation tower through a pipeline.

[0015] The technical solution of the present application adopts the method of reactive distillation, which can make the formaldehyde in the wastewater react with several acidic substances to generate formic acid aldehyde, methyl acetate and methyl acrylate. Compared with formaldehyde and several acidic substances, formic acid aldehyde, methyl acetate and methyl acrylate are easier to separate from the wastewater. A mixture of methylal, methyl acetate, methyl acrylate and methanol is extracted from the top of the reactive distillation tower. After further separation, the corresponding substances can be recovered to achieve the recycling of resources. The wastewater containing methanol extracted from the bottom of the reactive distillation tower is sent to a methanol recovery tower. After distillation separation, a methanol solution is extracted from the top of the methanol recovery tower, and the wastewater extracted from the bottom of the tower is sent to a phase separation tank to separate the oil substance. The COD of the separated wastewater is ≤2000mg / L and can be directly sent to a sewage treatment device. After treatment, it meets the emission standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural schematic diagram of an embodiment of a methyl acrylate production wastewater recovery and treatment equipment provided by the present invention.

[0017] Description of Figure Numbers: 1. Reaction distillation tower; 2. Methanol recovery tower; 3. Phase separation tank; 4. Multiple distillation towers.

[0018] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), such directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0021] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the meaning of "and / or" appearing throughout the text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0022] The wastewater from methyl acrylate production contains many types of substances and has a complex composition. The existing conventional distillation separation and evaporation concentration cannot effectively treat it. The COD concentration in the treated wastewater is high, which does not meet the concentration requirements for sewage treatment. It cannot be directly sent to the sewage treatment device, and the substances in the wastewater cannot be effectively recovered.

[0023] In view of this, the present invention proposes a methyl acrylate production wastewater recovery and treatment process and corresponding treatment equipment to solve the problems in the prior art of high COD concentration in the treated methyl acrylate production wastewater and inability to effectively recover substances in the wastewater.

[0024] See also Figure 1 In the present invention, the methyl acrylate production wastewater recovery and treatment equipment includes a reaction distillation tower 1, a methanol recovery tower 2, and multiple distillation towers 4. The reaction distillation tower 1 is used to allow formaldehyde, acetic acid and acrylic acid in the methyl acrylate production wastewater to react with methanol respectively, and the methylal, methyl acetate and methyl acrylate generated by the reaction, as well as the unreacted methanol mixture, are separated from the wastewater through distillation; the feed port of the methanol recovery tower 2 is connected to the bottom of the reaction distillation tower 1 through a pipeline, and the methanol recovery tower 2 is used to separate methanol from the wastewater produced from the bottom of the reaction distillation tower 1; the starting feed ports of the multiple distillation towers are connected to the top of the reaction distillation tower 1 through pipelines, and are used to separate the light component mixture produced from the top of the reaction distillation tower 1 to separate methylal, methyl acetate, methyl acrylate and methanol.

[0025] In the technical solution of the present invention, wastewater and methanol are fed into a reactive distillation tower 1, which is operated at normal pressure. Under the action of a catalyst, the following reaction occurs: The formaldehyde in the wastewater reacts with methanol to form methylal. 2CH3OH +CH2O→CH3OCH2OCH3+H2O; Acetic acid reacts with methanol to produce methyl acetate. CH3COOH + CH3OH→CH3COOCH3+ H2O; Acrylic acid and methanol react to form methyl acrylate. CH2CHCOOH+ CH3OH→CH2CHCOOCH3+ H2O; In order to ensure complete reaction between formaldehyde and several acidic substances, an excess of methanol enters the reaction distillation tower 1. A mixture of methylal, methyl acetate, methyl acrylate and methanol is produced from the top of the reaction distillation tower 1, and wastewater containing methanol is produced from the bottom of the tower. The concentration of methanol in the wastewater is 10-30wt%.

[0026] This application proposes a new technical solution, namely, using a reactive distillation tower, and under normal pressure, the formaldehyde and organic acid in the wastewater can be completely reacted. Considering that the reaction between methanol and formaldehyde, and methanol and organic acid is an equilibrium reaction, while the reaction is proceeding in the forward direction, the reaction can also be carried out in the reverse direction. Therefore, in order to completely react the formaldehyde and organic acid in the wastewater and promote the forward reaction, this application adopts an excess of methanol. Therefore, this application has achieved the technical effect of being able to completely react the formaldehyde and organic acid in the wastewater and promote the forward reaction.

[0027] The material extracted from the bottom of the reactive distillation tower 1, i.e., the wastewater containing methanol, is sent to the methanol recovery tower 2. After distillation separation, the methanol solution is extracted from the top of the methanol recovery tower 2, and the wastewater extracted from the bottom of the tower is sent to the phase separation tank 3. The upper layer of the phase separation tank 3 is wastewater, and the lower layer is heavy component tar. The COD of the upper layer wastewater is ≤2000 mg / L. The upper layer wastewater can be directly sent to the sewage treatment device. It is understandable that the methyl acrylate production wastewater recycling and treatment equipment also includes a phase separation tank 3, and the feed port of the phase separation tank 3 is connected to the bottom of the methanol recovery tower 2 through a pipeline.

[0028] The material extracted from the top of the reactive distillation tower 1, i.e., a mixture containing methylal, methyl acetate, methyl acrylate, and methanol, is sent to the starting feed ports of multiple distillation towers 4. The mixture is then distilled through the corresponding distillation towers in sequence to separate methylal, methyl acetate, methyl acrylate, and methanol for recycling. It will be understood that methylal, methyl acetate, methyl acrylate, and methanol are distilled and separated through different distillation towers.

[0029] The methanol solution extracted from the top of the methanol recovery tower 2 and the methanol separated from the multiple distillation towers 4 are all sent to the reactive distillation tower 1 as reaction feedstock. It will be understood that a wastewater inlet and a feed port are provided in the middle of the reactive distillation tower 1. The wastewater to be treated enters the reactive distillation tower 1 through the wastewater inlet, and fresh methanol, the methanol solution extracted from the top of the methanol recovery tower 2, and the methanol separated from the multiple distillation towers 4 all enter the reactive distillation tower 1 through the feed port.

[0030] The reaction distillation tower 1 is a plate tower or a packed tower with a reflux ratio of 2 to 5. The middle of the reaction distillation tower 1 is filled with a solid acid catalyst. The reaction distillation tower 1 is operated at normal pressure. The methanol recovery tower 2 is a plate tower or a packed tower with a reflux ratio of 2 to 5.

[0031] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0032] The wastewater used in the examples of this application comes from the production wastewater of an MMA (methyl methacrylate) production enterprise (10,000 tons / year) (hereinafter referred to as "wastewater"), which contains 20wt% formaldehyde, 6.5wt% acetic acid, and 1.25wt% acrylic acid. The COD of the wastewater is 30g / L. Example 1

[0033] A methyl acrylate production wastewater recovery and treatment process comprises the following steps: The wastewater and fresh methanol are fed into the reactive distillation tower 1, which is a packed tower. The middle part of the reactive distillation tower 1 is filled with a solid acid catalyst. The reflux ratio of the reactive distillation tower 1 is 2. The reactive distillation tower 1 is operated at normal pressure, with a bottom temperature of 110°C and a top temperature of 45°C. A mixture of methylal, methyl acetate, methyl acrylate and methanol is produced from the top of the reactive distillation tower 1, and wastewater containing methanol and heavy components is produced from the bottom of the tower.

[0034] The ratio of the total molar amount of methanol feed (including fresh methanol and recovered methanol) in the reactive distillation tower to the sum of the molar amounts of formaldehyde, acetic acid and acrylic acid in the wastewater is 14.4:1. By controlling the addition ratio of methanol to wastewater, the methanol content in the wastewater at the bottom of reactive distillation tower 1 is maintained at 10wt% under stable operation.

[0035] The methylal, methyl acetate, methyl acrylate and methanol mixture taken out from the top of the reactive distillation tower 1 is sequentially separated by passing through multiple distillation towers 4. The recovered methyl acetate is returned to the system as a raw material for methyl acrylate production, the recovered methyl acrylate is used as a methyl acrylate product, and the recovered methanol is returned to the reactive distillation tower 1 as a raw material.

[0036] The wastewater containing methanol and heavy components extracted from the bottom of the reactive distillation tower 1 is sent to the methanol recovery tower 2. The methanol recovery tower 2 is a packed tower. The reflux ratio of the methanol recovery tower 2 is 3. The methanol recovery tower 2 is operated at normal pressure, the tower bottom temperature is 99°C, and the tower top temperature is 65°C. Methanol is extracted from the top of the methanol recovery tower 2 and refluxed to the reactive distillation tower 1 as a raw material. Wastewater is extracted from the bottom of the tower and sent to the phase separation tank 3. The detection results of the separated wastewater components are as follows: Formaldehyde: 0.1wt%; Acetic acid: 0.16wt%; Acrylic acid: 0.11wt%; COD: 1842 mg / L. The separated wastewater does not contain methanol. Example 2

[0037] A methyl acrylate production wastewater recovery and treatment process comprises the following steps: The wastewater and fresh methanol are fed into the reactive distillation tower 1, which is a packed tower. The middle part of the reactive distillation tower 1 is filled with a solid acid catalyst. The reflux ratio of the reactive distillation tower 1 is 2. The reactive distillation tower 1 is operated at normal pressure, with a bottom temperature of 100°C and a top temperature of 40°C. A mixture of methylal, methyl acetate, methyl acrylate and methanol is produced from the top of the reactive distillation tower 1, and wastewater containing methanol and heavy components is produced from the bottom of the tower.

[0038] The ratio of the total molar amount of methanol feed (including fresh methanol and recovered methanol) in the reactive distillation tower to the sum of the molar amounts of formaldehyde, acetic acid and acrylic acid in the wastewater is 23:1. By controlling the addition ratio of methanol to wastewater, the methanol content in the wastewater at the bottom of reactive distillation tower 1 is maintained at 15wt% under stable operation.

[0039] The methylal, methyl acetate, methyl acrylate and methanol mixture taken out from the top of the reactive distillation tower 1 is sequentially separated by passing through multiple distillation towers 4. The recovered methyl acetate is returned to the system as a raw material for methyl acrylate production, the recovered methyl acrylate is used as a methyl acrylate product, and the recovered methanol is returned to the reactive distillation tower 1 as a raw material.

[0040] The wastewater containing methanol and heavy components extracted from the bottom of the reactive distillation tower 1 is sent to the methanol recovery tower 2. The methanol recovery tower 2 is a packed tower. The reflux ratio of the methanol recovery tower 2 is 3. The methanol recovery tower 2 is operated at normal pressure, the tower bottom temperature is 99°C, and the tower top temperature is 65°C. Methanol is extracted from the top of the methanol recovery tower 2 and refluxed to the reactive distillation tower 1 as a raw material. Wastewater is extracted from the bottom of the tower and sent to the phase separation tank 3. The detection results of the separated wastewater components are as follows: Formaldehyde: 0.08wt%; Acetic acid: 0.12wt%; Acrylic acid: 0.1wt%; COD: 1204 mg / L. The separated wastewater does not contain methanol. Example 3

[0041] A methyl acrylate production wastewater recovery and treatment process comprises the following steps: The wastewater and fresh methanol are fed into the reactive distillation tower 1, which is a packed tower. The middle part of the reactive distillation tower 1 is filled with a solid acid catalyst. The reflux ratio of the reactive distillation tower 1 is 2. The reactive distillation tower 1 is operated at normal pressure, with a bottom temperature of 100°C and a top temperature of 40°C. A mixture of methylal, methyl acetate, methyl acrylate and methanol is produced from the top of the reactive distillation tower 1, and wastewater containing methanol and heavy components is produced from the bottom of the tower.

[0042] The ratio of the total molar amount of methanol feed (including fresh methanol and recovered methanol) in the reactive distillation tower to the sum of the molar amounts of formaldehyde, acetic acid and acrylic acid in the wastewater is 55:1. By controlling the addition ratio of methanol to wastewater, the methanol content in the wastewater at the bottom of the reactive distillation tower is maintained at 30wt% under stable operation.

[0043] The methylal, methyl acetate, methyl acrylate and methanol mixture taken out from the top of the reactive distillation tower 1 is sequentially separated by passing through multiple distillation towers 4. The recovered methyl acetate is returned to the system as a raw material for methyl acrylate production, the recovered methyl acrylate is used as a methyl acrylate product, and the recovered methanol is returned to the reactive distillation tower 1 as a raw material.

[0044] The wastewater containing methanol and heavy components extracted from the bottom of the reactive distillation tower 1 is sent to the methanol recovery tower 2. The methanol recovery tower 2 is a packed tower. The reflux ratio of the methanol recovery tower 2 is 3. The methanol recovery tower 2 is operated at normal pressure, the tower bottom temperature is 99°C, and the tower top temperature is 65°C. Methanol is extracted from the top of the methanol recovery tower 2 and refluxed to the reactive distillation tower 1 as a raw material. Wastewater is extracted from the bottom of the tower and sent to the phase separation tank 3. The detection results of the separated wastewater components are as follows: Formaldehyde: 0.06wt%; Acetic acid: 0.11wt%; Acrylic acid: 0.1wt%; COD: 1026 mg / L. The separated wastewater does not contain methanol.

[0045] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A process for recycling wastewater from methyl acrylate production, characterized in that: include: The methyl acrylate production wastewater is reacted with methanol to convert formaldehyde, acetic acid and acrylic acid in the wastewater into corresponding methylal, methyl acetate and methyl acrylate; wherein the ratio of the molar amount of methanol to the sum of the molar amounts of formaldehyde, acetic acid and acrylic acid in the wastewater is (14.4-55.0):1; The methylal, methyl acetate, methyl acrylate and unreacted methanol are separated from the waste water by distillation and recycled.

2. The methyl acrylate production wastewater recovery and treatment process according to claim 1, characterized in that: The following steps are involved: S10, providing methyl acrylate production wastewater and methanol; S20, sending the methyl acrylate production wastewater and the methanol into a reactive distillation tower, under the action of a catalyst, the formaldehyde, acetic acid and acrylic acid in the wastewater react with the methanol respectively, and the reaction products include methylal, methyl acetate and methyl acrylate, and the light component mixture containing methylal, methyl acetate, methyl acrylate and methanol is extracted from the top of the reactive distillation tower, and the wastewater containing methanol and heavy components is extracted from the bottom of the tower; S30, distilling and separating the light component mixture taken out from the top of the reaction distillation tower; and separating methanol from the wastewater taken out from the bottom of the reaction distillation tower.

3. The methyl acrylate production wastewater recovery and treatment process according to claim 1 or 2, characterized in that: The separated and recovered methanol is returned to the system as a reaction raw material for the recovery and treatment of the methyl acrylate production wastewater; the separated and recovered methyl acetate is returned to the system as a reaction raw material for the production of methyl acrylate.

4. The methyl acrylate production wastewater recovery and treatment process according to claim 2, characterized in that: In the step S20, the concentration of methanol in the wastewater containing methanol and heavy components extracted from the bottom of the reactive distillation tower is 10-30wt%.

5. The methyl acrylate production wastewater recovery and treatment process according to claim 2, characterized in that: In step S20, the reaction distillation tower is operated at normal pressure, the bottom temperature is 100-110°C, and the top temperature is 40-50°C.

6. The methyl acrylate production wastewater recovery and treatment process according to claim 2, characterized in that: In the step S20, the reaction distillation tower is a plate tower or a packed tower, the reflux ratio of the reaction distillation tower is 2-5, and the reaction distillation tower is filled with a solid acid catalyst.

7. The methyl acrylate production wastewater recovery and treatment process according to claim 2, characterized in that: In the step S30, after methanol is separated from the wastewater taken out from the bottom of the reactive distillation tower, the COD of the wastewater does not exceed 2000 mg / L.

8. A methyl acrylate production wastewater recovery and treatment equipment, characterized in that: include: A reactive distillation tower, used to react formaldehyde, acetic acid and acrylic acid in methyl acrylate production wastewater with methanol respectively, and to separate methylal, methyl acetate and methyl acrylate generated by the reaction and unreacted methanol mixture from the wastewater by distillation; wherein the ratio of the molar amount of methanol to the sum of the molar amounts of formaldehyde, acetic acid and acrylic acid in the wastewater is (14.4-55.0):1; A methanol recovery tower, connected to the bottom of the reaction distillation tower through a pipeline, and used to separate methanol from the wastewater produced from the bottom of the reaction distillation tower; At least one distillation tower, a plurality of starting feed ports of the distillation towers are connected to the top of the reaction distillation tower through pipelines, and are used to separate the light component mixture extracted from the top of the reaction distillation tower to separate methylal, methyl acetate, methyl acrylate and methanol.

9. The methyl acrylate production wastewater recovery and treatment equipment according to claim 8, characterized in that: The methyl acrylate production wastewater recovery and treatment equipment also includes a phase separation tank, and the feed inlet of the phase separation tank is connected to the bottom of the methanol recovery tower through a pipeline.

10. The methyl acrylate production wastewater recovery and treatment equipment according to claim 8, characterized in that: The top of the methanol recovery tower is connected to the feed inlet of the reactive distillation tower through a pipeline.

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