A process for recovering heavy acrylic components

Abstract

The present application relates to a kind of acrylic acid heavy component recovery method, comprising the following steps: (1) heavy component diluent mixing process;(2) light component de aldehyde process;(3) light component de maleic anhydride process;Optionally, (4) waste gas recycling process.The process solves the problem that the heavy component pyrolysis tar ratio is high in the current acrylic acid industry, and the impurities in the recovered light component are many.At the same time, the waste heat of acrylic acid oxidation section waste gas is recycled.

Description

Technical Field

[0001] This invention relates to a novel method for recovering heavy acrylic acid components, applicable to deep pyrolysis recovery processes of heavy acrylic acid components. Background Technology

[0002] Acrylic acid is an unsaturated fatty acid and an important organic chemical raw material. Acrylic acid and its esters have a wide range of applications, primarily in the textile, coating, adhesive, synthetic fiber, paper, and leather industries. Currently, the most widespread use of acrylic acid is in the production of thickeners, superabsorbent polymers, flocculants, and detergent builders. Industrially, the most significant role of acrylic acid is in the synthesis of acrylates, such as butyl acrylate, methyl acrylate, and ethyl acrylate. Acrylic esters are mainly used in coatings, plastic modifiers, and rubber. In short, acrylic acid and its esters have a wide range of applications and high demand, making them an important component of today's petrochemical industry.

[0003] The amount of tar (heavy components) per ton of product is a key factor determining the propylene consumption per ton of acrylic acid. The acrylic acid industry commonly adds heavy component crackers to recover heavy acrylic acid components, but due to limitations in cracking technology, the tar ratio in the industry is generally around 45 kg / t. The discharged heavy components still contain a large amount of recoverable acrylic acid, resulting in significant raw material waste. There are two key factors restricting the recovery of heavy acrylic acid components: first, further reducing the tar ratio leads to excessively high viscosity of the heavy components, making them unsuitable for transport through low-temperature pipelines; second, as the temperature of the cracker increases, the impurity content in the recovered light components also increases, while the removal capacity of the refining system is limited.

[0004] The light components recovered from the deep pyrolysis of acrylic acid mainly contain aldehyde impurities such as furfural and benzaldehyde, which are difficult to remove in the refining process. Chemical aldehyde removal involves introducing a aldehyde-removing agent or resin to catalytically condense these impurities with furfural and benzaldehyde, followed by purification to obtain a low-aldehyde-content acrylic acid product. This method is simple, requires minimal equipment investment, and has low operating costs.

[0005] In addition, the most abundant impurity in the light components is maleic anhydride, accounting for about 20-30% of the recovered light components. If it is not treated, the maleic anhydride in the recovered light components will enter the refining process and eventually enter the product, affecting the product quality.

[0006] The waste gas generated in the acrylic acid oxidation section releases heat after catalytic combustion, but this hot gas is directly discharged, resulting in significant heat waste. Furthermore, deeper pyrolysis of acrylic acid components requires higher temperature conditions. Therefore, the hot gas generated by the waste combustion system can be used to provide the heat source needed for the pyrolysis of these recombinant components.

[0007] Therefore, there is a need to find a method for recovering heavy acrylic acid components, to solve the technical problems that prevent the heavy acrylic acid components from being further cracked, and to reduce the impurity removal pressure of subsequent refining processes and realize the rational use of heat sources. Summary of the Invention

[0008] The purpose of this invention is to provide a method for recovering heavy acrylic acid components, enabling further pyrolysis and recovery of acrylic acid from these components. This process involves adding a diluent to the deeply pyrolyzed heavy components to reduce their viscosity and meet transportation requirements; removing aldehydes and maleic anhydride impurities from the recovered light components before they enter the refining process, thus reducing the impurity removal pressure in the refining stage. Simultaneously, the waste gas from the oxidation process can be recycled to recover residual heat, further reducing energy consumption for the deep pyrolysis of the heavy components.

[0009] A method for recovering heavy acrylic acid components includes the following steps: (1) a heavy component diluent blending process; (2) a light component formaldehyde removal process; (3) a light component maleic anhydride removal process; and (4) a waste gas recycling process.

[0010] As a preferred embodiment, a method for recovering heavy acrylic acid components includes the following steps: (1) adding methanol diluent to the large circulation pipeline of heavy acrylic acid components to reduce the viscosity of the heavy components, so that the heavy components after deep cracking meet the requirements of pump and pipeline transportation; (2) setting up a formaldehyde removal process using phenylenediamine as a formaldehyde removal agent in the process of recovering light components to remove aldehyde impurities in the recovered light components, and the light components after impurity removal enter the maleic anhydride removal process, and the wastewater enters the wastewater tank; (3) setting up a maleic anhydride removal process after the formaldehyde removal process to remove maleic anhydride impurities, and the light components after impurity removal enter the acrylic acid refining process, and the wastewater enters the wastewater tank; optionally, it also includes step (4) adding an E-O preheater before the heavy component cracker (the heavy component cracker is used to crack the heavy components generated in the refining section into light components again, and return the light components to the refining process to recover and utilize the acrylic acid in the light components.), and introducing the waste gas from the waste combustion system of the acrylic acid oxidation process as the heat source of the heat exchanger to preheat the heavy components. The light components recovered through the above steps enter the refining process. The refining process involves dehydration in a first refining tower, removal of acetic acid in a second refining tower, and removal of other trace impurities in a third refining tower, ultimately yielding the acrylic acid product. (Since the refining process is a routine operation in the acrylic acid process, it will not be elaborated here. Please refer to "Liu Li, Yu Chunmei. Process Improvement of Acrylic Acid Refining Unit [J]. Chemical Engineering Design, 2011, 21(06):47-48".) This process recovers acrylic acid from the heavy components into the acrylic acid product, reducing acrylic acid loss.

[0011] In this invention, in step (1), the diluent mixing ratio is: the flow rate of the recovered light component: the mass flow rate of methanol = 2:1-1:1.

[0012] In this invention, in step (2), the formaldehyde removal operation temperature is 40-50℃ and the residence time is 30-60min.

[0013] In this invention, in step (2), the amount of formaldehyde removal agent added is: 40-60 kg of formaldehyde removal agent is added for every ton of light components recovered.

[0014] In this invention, in step (3), two crystallization tanks and one buffer tank are set at the rear end of the light component dealdehyde removal device; after the liquid level in the crystallization tank reaches 60-80% of the tank level, it is left to stand for 60-120 minutes; water is used as a solvent to dissolve the precipitated maleic anhydride, and the dissolution time is 10-20 minutes. Maleic anhydride is a white crystal at room temperature and can crystallize and precipitate at room temperature. It is also very soluble in water and does not require heating or other conditions. Therefore, the addition of maleic anhydride crystallization tanks does not require complicated operating conditions, and the precipitated maleic anhydride impurities can be recovered by dissolving in water. Attached Figure Description

[0015] Figure 1 This is a process flow diagram of the deep pyrolysis and recovery of light components from the heavy acrylic acid components of the present invention.

[0016] Figure 2 This is a process flow diagram of the waste gas reuse process for deep pyrolysis of acrylic acid heavy components according to the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments and accompanying drawings. The embodiments described herein are merely illustrative and do not limit the scope of the invention.

[0018] One of the objectives of this invention is to solve the problem that the viscosity of heavy components after deep pyrolysis of acrylic acid is too high to be transported, and to provide a new process using methanol as a diluent.

[0019] The second objective of this invention is to solve the problem of high aldehyde impurities in the recovery of light components from the deep pyrolysis of acrylic acid heavy components, and to provide a new process for removing aldehyde impurities using phenylenediamine.

[0020] The third objective of this invention is to solve the problem of excessive maleic anhydride in the recovery of light components from the deep cracking of acrylic acid heavy components, and to provide a new process for removing maleic anhydride by crystallization precipitation and water dissolution.

[0021] The fourth objective of this invention is to solve the problem of excessive heat required for the deep cracking of acrylic acid heavy components and to provide a new process for recovering waste heat from oxidative waste combustion systems.

[0022] To achieve the first aspect of the invention's objective, methanol is introduced as a diluent in the large circulation pipeline downstream of the acrylic acid recombination and decomposition reactor, as shown in the attached process flow diagram. Figure 1 As shown.

[0023] Currently, the residual liquid from the bottom of the R-1 column of the existing acrylic acid recombinant cracker is pumped into the main circulation pipeline for heavy components via pump P-1, and then transferred to storage tank T-1. From there, pump P-2 pumps the liquid into the main circulation pipeline, completing the circulation. The heavy components are cooled to 85-90°C via heat exchanger E-2. After cracking, the heavy components are discharged from tank T-1 and enter the incineration system. Methanol is introduced into the main circulation pipeline (see attached...). Figure 1 (At the middle circle) to reduce the viscosity of the material in the large circulation pipeline and prevent transportation difficulties due to high viscosity after further reducing the tar ratio.

[0024] Currently, the R-1 tower bottom output is 1.2 t / h, with a tar ratio of 30 kg / t. The tar ratio is expected to be reduced to a minimum of 20 kg / t, at which point the tower bottom output will be 0.8 t / h, requiring a methanol supplement of 0.4 t / h to 0.2 t / h. After dilution, the material viscosity can be kept below 60 cp, solving the transportation problem of sufficiently heavy components from deep cracking. Using this process, an additional 0.4 t / h of light acrylic acid components can be recovered, with an estimated annual revenue of 25 million RMB.

[0025] To achieve the second aspect of the aforementioned invention objective, a formaldehyde removal process is added to the light component recovery process to remove aldehyde impurities from the light components using a formaldehyde removal agent. The process flow is shown in the attached figure. Figure 1 As shown.

[0026] Currently, there are many types of formaldehyde removal agents. Hydrazine and amine compounds have strong formaldehyde removal reactivity. Among them, hydrated hydrazine and phenylhydrazine can achieve high formaldehyde removal rates without acid catalysis, while thiols and nitrophenylhydrazine require the addition of strong acids as catalysts to achieve formaldehyde removal. Phenylenediamine has good formaldehyde removal effect, but because this type of formaldehyde removal agent cannot withstand the operating conditions of the recombinant decomposition reactor (above 130℃), the aldehyde impurities formed by decomposition are returned to the purification system, resulting in a deterioration in the formaldehyde removal effect. Therefore, formaldehyde removal agents cannot be directly added to the recombinant decomposition reactor. In this process, a formaldehyde removal agent tank is partially installed after the E-3 heat exchanger for recovering light components. The operating temperature is 40-50℃, the residence time is 30-60 min, and the amount of phenylenediamine added is 2-3 times the content of aldehyde impurities in the light components. The aldehyde removal rate can reach over 96%. The flocculent material formed by the formaldehyde removal agent and aldehyde impurities separates by gravity sedimentation. After settling in the sedimentation zone at the bottom of the tank, it is directly discharged into the T-2 wastewater tank.

[0027] Aldehyde impurities are primarily removed in the third column (purification column) of the acrylic acid refining section, where acrylic acid is directly produced at the top. After the tar ratio from the acrylic acid recombinant cracking process is reduced to below 30 kg / t, the aldehyde impurities in the recycled light components will increase beyond the removal capacity of the purification column. This means the aldehyde impurities will directly enter the top product, affecting product quality. Improving the aldehyde impurity removal rate by changing the column structure or adjusting operating parameters involves significant equipment modifications and can even affect process stability. However, by adding an aldehyde removal tank to the light component recovery process in the acrylic acid recombinant cracking unit, the amount of aldehyde impurities entering the rectification section can be reduced directly at the source. Furthermore, this process is relatively independent and does not affect the stable operation of the rectification section.

[0028] To achieve the third aspect of the aforementioned invention objective, a maleic anhydride removal crystallization process is added to the light component recovery process to remove maleic anhydride impurities. The process flow is shown in the attached figure. Figure 1 As shown.

[0029] The light component flowing out from the formaldehyde removal module contains approximately 20-30% maleic anhydride. Taking advantage of maleic anhydride's easy precipitation and high water solubility, two crystallization tanks are added downstream of the light component, one in operation and one on standby. When the liquid level in crystallization tank 1 reaches 60-80% of its capacity, it is allowed to stand for 60-120 minutes. Simultaneously, crystallization tank 1 is closed, and crystallization tank 2 is opened. After the specified time has elapsed in crystallization tank 1, the liquid is drained into the light component buffer tank, and water is introduced into the crystallization tank at 80% capacity. After dissolving for 10-20 minutes, the maleic anhydride solution is drained into wastewater tank T-2. The operation of crystallization tanks 1 and 2 is repeated. Because this crystallization operation is intermittent, a light component buffer tank is required downstream of the crystallization tank to ensure a consistently high liquid level, guaranteeing continuous light component recovery.

[0030] After recombinant splitting, maleic anhydride accounts for approximately 20-30% of the light component. If this material directly enters the refining and purification tower, it will severely affect the composition of the material within the tower, causing fluctuations in the operating parameters of the distillation tower. Furthermore, this material will circulate internally in the purification tower bottom and the acrylic acid recombinant splitting unit, gradually accumulating and eventually entering the product, affecting product quality. Therefore, utilizing the properties of maleic anhydride, a maleic anhydride removal crystallization process is added to the light component recovery process, which can remove more than 98% of the maleic anhydride from the light component.

[0031] To achieve the fourth aspect of the aforementioned invention objective, the waste heat from the oxidation waste gas is used as a heat source for the recombinant splitter tower, and the process flow is as follows: Figure 2 As shown.

[0032] Currently, the bottom temperature of the R-1 column in the acrylic acid recombining and splitting reactor is 130℃ (tar ratio 30kg / t). When the tar ratio is reduced to 20kg / t, the bottom temperature needs to be 190-220℃. The waste gas from the acrylic acid oxidation section, at a temperature of 550-600℃, is directly discharged into the air. This hot gas can be used to preheat the material in the bottom of the acrylic acid recombining and splitting reactor, recovering heat. In this new process, an E-0 preheater is added to the bottom of the acrylic acid recombining and splitting reactor. The waste heat from the waste gas from the oxidation section is used to preheat the liquid in the bottom of the recombining and splitting reactor to 115℃ before it is heated to 190-220℃ by the E-1 preheater. This reduces the amount of steam required for the E-1 reboiler to heat the liquid in the bottom of the reactor, recovers heat, and reduces energy consumption.

[0033] The composition of the light and heavy components was analyzed by gas chromatography using an Agilent-7890B instrument. A gradient temperature ramp was employed (initial temperature 50℃, gradient one 10℃ / min to 150℃, gradient two 15℃ / min to 245℃, held for 15 min), with an injection volume of 1 μL and a split ratio of 5:1. The viscosity of the heavy components was measured using a viscometer, a DV2FLV instrument, which can be connected to an external circulating oil bath to test the viscosity of the heavy components at different temperatures.

[0034] Example 1

[0035] The feed rate of the acrylic acid recombination and decomposition unit R-1 is 1.2 t / h (from the acrylic acid refining unit of Wanhua Chemical Group Co., Ltd.), and the temperature of the tower bottom is controlled at 195℃. At this time, the recombination fraction flow rate of the tower bottom is 0.8 t / h, and the light fraction flow rate of the tower top is 0.4 t / h.

[0036] The viscosity of the heavy component in the reboiler is 128 cp at 195℃, meeting the transport requirements of pump P-1. After passing through the main circulation pipeline and cooling to 90℃ via heat exchanger E-2, the viscosity of the heavy component rapidly increases to 769 cp, making pump P-2 unable to transport it. Furthermore, severe blockage occurs in the main circulation pipeline, causing pressure buildup. (To be continued...) Figure 1 When 0.4 t / h of methanol is introduced at the indicated location (circled area) for dilution, the viscosity of the heavy components drops to 30 cp at 90℃, which meets the requirements for pump P-2 transportation, and there is no blockage in the large circulation pipeline.

[0037] The light component at the top of the column was cooled to 45°C via heat exchanger E-3. Analysis of the sample revealed approximately 1.2 wt% aldehyde impurities in the light component. The cooled light component then entered the formaldehyde removal tank, into which 14.4 kg / h of phenylenediamine was added. The formaldehyde removal tank operated at 45°C for 35 minutes. The precipitate at the bottom of the tank was discharged to wastewater tank T-2 via pump P-4 at a flow rate of 19.2 kg / h. The light component overflowed from the top of the tank into the crystallization tank. Analysis of this overflow showed that the aldehyde impurities had decreased to 400 ppm.

[0038] A sample of the light component from the top of the formaldehyde removal tank was analyzed, revealing a maleic anhydride content of 23 wt%. The light component was introduced into crystallization tank 1. Once the liquid level reached 80%, the light component was switched to crystallization tank 2. After standing in tank 1 for 60 minutes, the light component was discharged into a buffer tank. Water was then added to crystallization tank 1 until the liquid level reached 80%, and after standing for 10 minutes, it was discharged into wastewater tank T-2. At this point, the light component feed was switched back from crystallization tank 2 to crystallization tank 1, and the above operation was repeated for crystallization tank 2. A sample of the light component from the buffer tank was analyzed, revealing a maleic anhydride content reduced to 90 ppm. The liquid level in the buffer tank was maintained at 40%, and the light component was continuously fed into the acrylic acid refining process at a rate of 308 kg / h.

[0039] The waste gas from the oxidation process at 580°C enters heat exchanger E-0 to preheat the recombinant components entering the acrylic acid recombination and decomposition unit to 115°C.

Claims

1. A method for recovering heavy acrylic acid components, characterized in that, The process includes the following steps: (1) adding a diluent to the large circulation pipeline after the recombinant splitter to reduce the viscosity of the heavy components; (2) using a formaldehyde remover in the recovered light components from the recombinant splitter to remove aldehyde impurities from the recovered light components; (3) the recovered light components after impurity removal enter the maleic anhydride removal process to remove maleic anhydride impurities, and the recovered light components after impurity removal enter the acrylic acid refining process; in step (3), two crystallizers are set up at the back end of the formaldehyde removal device for the recovered light components for switching and one buffer tank is set up; after the liquid level in the crystallizer reaches 60-80% of the tank level, it is left to stand for 60-120 minutes and then enters the buffer tank, where water is used as a solvent to dissolve the maleic anhydride that has been precipitated. The dissolution time is 10-20 minutes, and the amount of water added accounts for 60-80% of the liquid level in the crystallizer; in step (4), a preheater is added before the recombinant splitter, and the waste combustion gas from the acrylic acid oxidation process is introduced as the heat source of the preheater to preheat the heavy components.

2. The recycling method according to claim 1, characterized in that, The diluent in step (1) is methanol.

3. The recycling method according to claim 2, characterized in that, In step (1), the diluent mixing ratio is: the flow rate of the recovered light component: the mass flow rate of methanol = 2:1-1:

1.

4. The recycling method according to claim 1, characterized in that, In step (2), the formaldehyde removal agent is phenylenediamine.

5. The recycling method according to claim 4, characterized in that, In step (2), the formaldehyde removal operation temperature is 40-50℃ and the residence time is 30-60min.

6. The recycling method according to claim 4 or 5, characterized in that, In step (2), the amount of formaldehyde removal agent added is 40-60 kg per ton of light components recovered.

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