A compound decoloring agent for recovering crude styrene from pyrolysis gasoline

Abstract

This invention discloses a compound decolorizing agent for recovering crude styrene from cracked gasoline. The compound decolorizing agent consists of a solvent, a decolorizing agent, a polymer dispersant, and a styrene polymerization inhibitor; wherein the mass ratio of solvent to decolorizing agent is 64%~79%:21%~36%, the amount of polymer dispersant added is 0.1%~0.2% of the total mass of solvent and decolorizing agent, and the amount of styrene polymerization inhibitor added is 0.05%~0.15% of the total mass of solvent and decolorizing agent. The solvent is 1,2-propanediol diacetate or 1,3-propanediol diacetate. This invention, through the compounding of a specific solvent and decolorizing agent, and the synergistic use of a polymer dispersant and a composite polymerization inhibitor, results in a stable compound decolorizing agent capable of efficient decolorization at room temperature, significantly reducing polymerization side reactions, and yielding superior grade styrene with a color ≤10 and a purity ≥99.8%, achieving a styrene recovery rate of over 96.0%, while effectively solving the equipment blockage problem caused by polymer coking.

Description

Technical Field

[0001] This invention relates to the field of petrochemicals, and more particularly to a compound decolorizing agent for recovering crude styrene from cracked gasoline. Background Technology

[0002] Styrene is an important chemical raw material, used as a key monomer in synthetic resins, ion exchange resins, and synthetic rubber, and also in pharmaceuticals, dyes, pesticides, and mineral processing. In recent years, with the development and large-scale expansion of the ethylene industry, the technology of extracting and recovering styrene from pyrolysis gasoline has become a highly sought-after technology for increasing styrene production. Because pyrolysis gasoline has a very complex composition, the crude styrene product obtained by its extraction and distillation is yellow, with the main coloring substances being conjugated dienes with boiling points and polarities similar to styrene. These dienes cannot be completely separated from styrene during ordinary distillation or extractive distillation, requiring chemical decolorization.

[0003] Currently, there are two main industrial processes for styrene decolorization: the first-generation process uses concentrated nitric acid (Nitric Acid Decolorization), and the second-generation process uses organic anhydride (Acid Anhydride Decolorization). The nitric acid method produces styrene with a color intensity (Pt-Co colorimetric value) no greater than 0, requires low decolorizing agent dosage, and has good decolorization effect, but it causes environmental problems related to the discharge of acidic wastewater. For the organic anhydride method, maleic anhydride is currently the preferred anhydride, as it produces no wastewater and is environmentally friendly. However, when using pure maleic anhydride as a decolorizing agent, its freezing point is 52.8℃, requiring heating to melt it into a liquid and mix it with styrene. The heating temperature is around 65℃, but at this temperature, maleic anhydride easily undergoes a polymerization reaction with styrene. The resulting polymer causes the following problems: 1. Blockage of the decolorizing agent injection pipes and injection points, preventing normal injection of the decolorizing agent and affecting product quality. Second, clogging of the styrene refining tower packing: High concentrations of organic acids in the refining tower cause polymers to easily adhere to the packing surface, severely clogging it. Third, clogging of the reboiler heat exchange tubes in the refining tower bottom reduces reboiler heating efficiency, preventing the refining tower bottom from providing timely heat, hindering continuous product output from the top, and limiting production capacity. Fourth, clogging of filters: The inlet and outlet filters of the refining tower bottom pump require frequent cleaning, and the cleaned polymers are large-particle coke residues, mostly formed by the polymerization reaction between the decolorizing agent and styrene. Furthermore, the frequency of bottom filter cleaning is directly related to the concentration of the decolorizing agent; higher concentrations lead to more severe polymerization reactions, requiring more frequent filter cleaning and increasing styrene loss. Fifth, high tar viscosity: Tar mainly consists of a small amount of high-boiling-point substances produced by the decolorization reaction of coloring substances with maleic anhydride, polymers of styrene and maleic anhydride, styrene self-polymers, unreacted maleic anhydride, and polymerization inhibitors. This tar needs to be metered and discharged into the tar tank through the refining tower. Due to the high viscosity of the tar, a certain amount of styrene is required for dilution to ensure its fluidity, resulting in significant styrene product loss. Meanwhile, to prevent tar from condensing in the tank, the storage temperature of the tar tank is generally controlled at 50°C. At this temperature, styrene, acting as a diluent, continues to react with excess decolorizing agent in the tank, producing heavy polymers that further increase the viscosity of the tar, hindering its transport to the coking unit.

[0004] CN101429090B discloses a scheme that uses oxalic acid, maleic anhydride, and acetic anhydride as decolorizing agents, and adds the decolorizing agents to the reflux styrene at the top of the styrene tower to make the color of pure styrene meet the quality requirements. However, this method still uses pure acid anhydride as a decolorizing agent and cannot fundamentally solve the problem of equipment blockage.

[0005] CN101429091B discloses an extractive distillation decolorization method using maleic anhydride and acetic anhydride as decolorizing agents and N-formylmorpholine, N-methylpyrrolidone and sulfolane as solvents. However, the N-methylpyrrolidone and sulfolane solvents used in this method are prone to blackening and deterioration (they turn black in just one day). In actual production, the extractant needs to be regenerated, which makes the process complicated.

[0006] CN101514138B discloses a composite decolorizing agent composed of at least one of maleic anhydride, methylmaleic anhydride, fumaric anhydride and their derivatives, and a monoolefin compound with an adjacent electrophilic group (at least one of vinyl acetate, acrylic acid, or acrylate compounds). This decolorizing agent can react directly with styrene-containing streams in a reactor, and the reaction product can be distilled to obtain a product with the required color. When the decolorizing agent of this invention is used for decolorizing styrene-containing streams, no pretreatment of the raw materials is required, and there are no requirements on the concentration of styrene in the raw materials. However, this invention does not mention whether the polymer generated during the decolorization reaction process causes blockage of the equipment or its solution.

[0007] CN109422615B addresses the problem of reboiler clogging in styrene refining towers during organic acid anhydride decolorization processes. It proposes using dienophilic compounds (maleic anhydride, acrylates, or benzoquinone) as decolorizing agents and employing a falling film evaporator in the refining tower. This allows various polymers to enter the refining tower by gravity and be pumped out. This method effectively removes heavy components and polymers from the reboiler tubes, reducing scaling and extending the stable operating cycle of the crude styrene decolorization system. However, using conventionally packed structured packing in the refining tower results in easy clogging of the lower packing section, leading to a still short operating cycle. The research group disclosed a decolorization process in CN114805003A that uses maleic anhydride or cinnamaldehyde and its derivatives as decolorizing agents and adds styrene polymerization inhibitors (polymerization inhibitors selected from 2-sec-butyl-4,6-dinitrophenol and / or nitroxide radicals). Furthermore, addressing the problem of existing decolorization and refining towers being entirely filled with structured packing and prone to clogging, the group replaced the existing packing section with a few low-pressure-drop plate trays (sieve plates or floating valve plates) in the lower section of the tower. Special designs were also implemented for the tower internals at the most prone to clogging points, significantly enhancing the anti-clogging properties of the trays. This effectively solved the problems of high pressure drop in plate towers and easy clogging in packed towers, and significantly extended the stable operating time of the decolorization unit.

[0008] CN111205158B discloses an improved maleic anhydride decolorization process. This process first removes moisture from crude styrene in a dehydration tower, then uses maleic anhydride as a decolorizing agent in a decolorization reaction tank at 0.3–0.5 MPa and 55–65°C for 8–12 hours. The material then enters a refining tower for distillation separation. This process employs multiple methods to ensure styrene product quality, prevent polymerization blockage, and reduce equipment corrosion. These include adding the polymerization inhibitor 2-sec-butyl-4,6-dinitrophenol to the dehydration tower feed line and the refining tower feed line; adding the polymerization inhibitor p-tert-butylcatechol to the top of the refining tower; adding a decolorizing aid to the refining tower feed line or the inlet of the second reboiler; adding flash evaporation treatment to the reboiler material; and improving the unit's regulation and control methods. However, the process does not specify the composition of the decolorizing aid used.

[0009] CN104276926B discloses a method for decolorizing crude styrene obtained from the extractive distillation of the C8 fraction of cracked gasoline. The crude styrene is fed into a dehydration tower for distillation and dehydration. Water is separated from the top of the tower through azeotropic distillation, and dehydrated styrene is obtained from the bottom. The dehydrated styrene is mixed with a decolorizing agent and placed in a static mixer or stirred mixer, where it is held at 40–90°C for 10–60 minutes for a decolorization reaction. Then, it is fed into a styrene refining tower for distillation, obtaining styrene product at the top and the heavier components discharged from the bottom. The azeotropic agent used is an aromatic or cycloalkanes with a boiling point less than 150°C as the dehydrating agent. The decolorizing agent used is a diephilic compound with an electron-withdrawing group (selected from one or more of maleic anhydride, acrylonitrile, acrylate, acrolein, nitroethylene, benzoquinone, and butynediate). The decolorizing agent is added either by heating and melting it before directly adding it to the dehydrated styrene, or by dissolving the decolorizing agent in a solvent with a boiling point greater than 200°C before adding it to the dehydrated styrene. The solvent with a boiling point greater than 200°C is selected from one or more of C9+ aromatics, triethylene glycol, tetraethylene glycol, sulfolane, N-formylmorpholine, and dioctyl phthalate. This process can reduce the degree of hydrolysis of the decolorizing agent, thereby reducing the amount of acid produced by hydrolysis, preventing equipment corrosion caused by organic acids, and effectively reducing wastewater discharge. However, it does not mention the effectiveness in solving clogging problems or the stability of the solvent.

[0010] Therefore, developing a novel compound decolorizing agent that is stable, has good decolorization effect, can reduce and disperse polymers from the source, thereby completely solving the problem of equipment blockage and improving styrene recovery rate has important industrial application value. Summary of the Invention

[0011] The present invention aims to overcome the shortcomings of the prior art and provide a compound decolorizing agent with stable properties, good decolorization effect, effective prevention of equipment blockage, and improved styrene recovery rate, as well as its preparation method.

[0012] To achieve the above objectives, the present invention adopts the following technical solution: A compound decolorizing agent for recovering crude styrene from cracked gasoline comprises a solvent, a decolorizing agent, a polymer dispersant, and a styrene polymerization inhibitor; the mass ratio of the solvent to the decolorizing agent is 64%~79%:21%~36%; the amount of the polymer dispersant added is 0.1%~0.2% of the total mass of the solvent and the decolorizing agent; the amount of the styrene polymerization inhibitor added is 0.05%~0.15% of the total mass of the solvent and the decolorizing agent; the solvent is selected from 1,2-propanediol diacetate and 1,3-propanediol diacetate.

[0013] The decolorizing agent is selected from maleic anhydride, acrylic acid, and methyl acrylate.

[0014] The polymer dispersant is selected from polyacrylate and polyvinyl acrylate.

[0015] The styrene polymerization inhibitor is a polymerization inhibitor composed of 4-hydroxy-2,2,6,6-tetramethylpiperidine nitroxide radical (OH-TEMPO, trade name Inhibitor 701) and 2-sec-butyl-4,6-dinitrophenol (DNBP), with a mass ratio of 1:1.

[0016] The preparation method of the compound decolorizing agent includes the following steps: weighing each component according to the ratio; mixing and stirring the solvent and decolorizing agent evenly at room temperature to obtain an organic acid anhydride / acid solution; adding a polymer dispersant and a styrene polymerization inhibitor to the organic acid anhydride / acid solution, stirring and dissolving thoroughly to obtain a colorless and transparent liquid compound decolorizing agent, which is then sealed for later use.

[0017] The present invention also provides the application of the compound decolorizing agent in the decolorization of crude styrene recovered from cracked gasoline.

[0018] The compound decolorizing agent of this invention achieves efficient decolorization and thorough anti-clogging through the synergistic effect of its components. Its mechanism is detailed below: First, the decolorizing reactive component of the compound decolorizing agent, the organic acid anhydride series, undergoes a typical cycloaddition reaction, the Diels-Alder (DA) reaction, with the color-developing substances in crude styrene, such as cyclopentadiene. In this reaction, the enoyl group in the organic acid anhydride undergoes an addition reaction with the conjugated double bond of the cyclopentadiene or other conjugated dienes, generating a new cyclic compound. A schematic diagram of the reaction principle is shown below. Figure 1 This new compound has a higher boiling point than styrene, thus allowing it to be separated from styrene using distillation.

[0019] Secondly, in the decolorization process, besides conjugated olefins undergoing a DA reaction with maleic anhydride, styrene readily undergoes a DA reaction with maleic anhydride to form a copolymer (SMA). This polymer is poorly soluble in styrene. In addition, the self-polymers produced by the self-polymerization reaction of styrene will accumulate and clog equipment and pipelines. Therefore, a solvent component is added to the decolorizing agent formulation to dissolve these polymers. According to the principle of like compatibility, the solvent is selected from 1,2-propanediol diacetate compounds. These compounds are structurally similar to the organic acid anhydride and SMA in the decolorizing agent, have high solubility, and have a good dissolving effect.

[0020] In addition, the addition of compound polymerization inhibitors and polymer dispersants to the decolorizing agent formulation serves to inhibit polymerization from the initial contact between maleic anhydride and styrene, minimizing the self-polymerization reaction of styrene and the copolymerization reaction with maleic anhydride, thereby fundamentally reducing polymer formation. Simultaneously, polymer dispersants such as polyacrylates and polyvinyl esters prevent polymer agglomeration into large particles that settle and cause blockages.

[0021] Through the synergistic effect of the above-mentioned decolorization and anti-clogging mechanisms, the compound decolorizing agent of the present invention, while ensuring excellent decolorization effect and product purity, revolutionarily solves the equipment clogging problem that is common in the organic acid anhydride decolorization process, and realizes the stable operation of the device with long cycle, high efficiency and high yield.

[0022] The beneficial effects of this invention are as follows: 1. Extremely stable properties: Using 1,2-propanediol diacetate and other solvents, the resulting compound decolorizing agent does not deteriorate or change color after being stored in a sealed container at room temperature for 300 days, solving the problem of some solvents in the prior art easily turning black and deteriorating.

[0023] 2. Excellent decolorization effect: Styrene products treated with this compound decolorizing agent have a color (Pt-Co) ≤10 and a purity ≥99.8%, meeting the superior grade standard.

[0024] 3. Significantly improved recovery rate: The compounded decolorizing agent can be used at room temperature without heating, greatly reducing the self-polymerization of styrene and its copolymerization reaction with the decolorizing agent. At the same time, the solvent can effectively dissolve the generated polymer, avoiding the loss caused by styrene as a diluent, and keeping the styrene recovery rate stable at over 96.0%, which is significantly improved compared to traditional methods (93%-95%).

[0025] 4. Fundamentally solves the clogging problem: Through the triple synergistic effect of "polymerization inhibitor at the source + dispersant to prevent aggregation + solvent for effective dissolution", this compound decolorizing agent can effectively prevent polymer coking and deposition. Industrial tests show that after three weeks of continuous operation, the pressure of key equipment (such as the distillation column bottom pump) remains normal without clogging, while serious clogging usually occurs within one week when using pure maleic anhydride.

[0026] 5. Simple process, green and energy-saving: The preparation method is simple, operates at room temperature, and requires no complex equipment. The decolorization process is carried out under mild conditions, reducing energy consumption and minimizing material loss and waste emissions caused by polymerization and dilution. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the Diels-Alder reaction principle in the decolorization reaction.

[0028] Figure 2 This is a photograph of the morphology of the residual liquid at the bottom of the bottle after distillation in Example 1.

[0029] Figure 3 This is a photograph of the morphology of the residue at the bottom of the flask after distillation in Comparative Example 1. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] Example 1: Preparation of the compound decolorizing agent: At room temperature, measure 100 ml of 1,2-propanediol diacetate solvent (density approximately 1.05 g / ml) into a beaker. Add 60.00 g of maleic anhydride while stirring until saturated. Filter out 0.94 g of undissolved maleic anhydride to obtain a saturated maleic anhydride solution with a mass percentage of 36%. Then, add 0.2% (by mass) of polyacrylate (0.32 g) and 0.15% (by mass) of the compound polymerization inhibitor (0.25 g, which is a mixture of polymerization inhibitor 701 and DNBP in a 1:1 mass ratio). Stir thoroughly to dissolve, obtaining a colorless and transparent liquid, which is the compound decolorizing agent.

[0032] Decolorization experiment: 200 g of crude styrene (purity 93.5%) with a color of 250 after dehydration was measured and placed in a rotary evaporator. 5.00 g of the above-mentioned compound decolorizing agent (where the mass ratio of maleic anhydride to styrene was 9:1000) was added. The mixture was stirred and reacted at room temperature for 60 minutes. Subsequently, distillation was carried out under reduced pressure at 78℃ and 6-8 kPa. Finally, 180.53 g of styrene product was obtained, with a recovery rate of 96.49%, a color of 5, and a purity of 99.95%. The residual liquid at the bottom of the distillation flask was uniform, and no precipitate formed after cooling (e.g., ...). Figure 2 (As shown).

[0033] Example 2: Other conditions were the same as in Example 1, except that the mass percentage of maleic anhydride was adjusted to 30%. The decolorization experiment yielded 180.40 g of styrene, with a recovery rate of 99.23%, a color of 6, and a purity of 99.90%.

[0034] Example 3: Other conditions were the same as in Example 1, except that the mass percentage of maleic anhydride was adjusted to 21%. The decolorization experiment yielded 180.25 g of styrene, with a recovery rate of 96.37%, a color of 10, and a purity of 99.85%.

[0035] Example 4: Under the same conditions as in Example 1, the polyacrylate was adjusted to polyvinyl acrylate. The decolorization experiment yielded 180.31g of styrene, with a recovery rate of 96.34%, a color of 6, and a purity of 99.91%.

[0036] Example 5: Under the same conditions as in Example 1, a mixture of solvent and 0.05% (0.080 g) of maleic anhydride inhibitor 701 and DNBP was added. The decolorization experiment yielded 180.04 g of styrene, with a recovery rate of 96.18%, a color of 8, and a purity of 99.90%.

[0037] Example 6: Other conditions were the same as in Example 1. 0.10% (0.16 g) of polyacrylate and 0.05% (0.080 g) of polymerization inhibitor 701 mixed with DNBP were added. The decolorization experiment yielded 180.07 g of styrene, with a recovery rate of 96.22%, a color of 7, and a purity of 99.92%.

[0038] Example 7: Other conditions were the same as in Example 2, except that the solvent was changed to 1,3-propanediol diacetate. The decolorization experiment yielded 180.35 g of styrene, with a recovery rate of 96.32%, a color of 9, and a purity of 99.87%.

[0039] Example 8: Preparation of decolorizing agent: At room temperature, measure 100 ml of 1,2-propanediol diacetate solvent into a beaker, add 59.06 g of acrylic acid and stir until homogeneous to obtain a solution with an acrylic acid mass percentage of 36%. Then, add 0.2% of the total solution mass of polyacrylate (0.32 g) and 0.15% of the compounded polymerization inhibitor (0.25 g, composed of polymerization inhibitor 701 and DNBP mixed at a mass ratio of 1:1), and stir thoroughly to dissolve, obtaining a colorless and transparent liquid compounded decolorizing agent.

[0040] Decolorization experiment: 200g of crude styrene (purity 93.5%) with a color of 250 after dehydration was placed in a rotary evaporator, and 5.00g of the above-mentioned compound decolorizing agent was injected. The decolorization reaction was carried out at 40℃ for 12h, and then vacuum distilled at 78℃ (6-8KPa) to obtain 180.29g of styrene, with a recovery rate of 96.30%, a color of 9, and a purity of 99.88%.

[0041] Example 9: Other conditions were the same as in Example 8, except that acrylic acid was replaced with methyl acrylate, and the decolorization reaction was carried out at 60°C for 16 hours to obtain 180.13g of styrene with a recovery rate of 96.16%, a color of 10, and a purity of 99.83%.

[0042] Comparative Example 1 (Decolorization of pure maleic anhydride) Crude styrene from the same source and in the same quantity as in Example 1 was used, but pure maleic anhydride was used as the decolorizing agent. The maleic anhydride was first melted at 65°C, and then added to 200g of crude styrene at the same effective decolorizing agent ratio as in Example 1 (w maleic anhydride:w styrene = 9:1000). The reaction was carried out for 60 minutes under the same stirring and temperature (maintained at 65°C to simulate heating), followed by vacuum distillation. The final styrene recovery rate was 93.9%, and a large amount of hard polymer clumps (e.g., [missing information]) were observed at the bottom of the distillation flask. Figure 3 (As shown). In actual industrial installations, this clumping is a direct cause of blockages in pipes and towers.

[0043] The above embodiments demonstrate that the compound decolorizing agent provided by this invention, through the scientific compounding of specific solvents, decolorizing agents, polymer dispersants, and styrene polymerization inhibitors, can achieve efficient decolorization at room temperature, resulting in styrene products with low color and high purity. More importantly, this formulation system works synergistically, effectively controlling polymer formation and deposition from both source inhibition and process dispersion and dissolution levels, thereby significantly extending the equipment operating cycle and increasing the styrene recovery rate to over 96%. Its overall performance is significantly superior to the traditional pure acid anhydride decolorization method.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A compound decolorizing agent for recovering crude styrene from cracked gasoline, characterized in that, It is composed of a solvent, a decolorizing agent, a polymer dispersant, and a styrene polymerization inhibitor; the mass ratio of the solvent to the decolorizing agent is 64%~79%:21%~36%; the amount of the polymer dispersant added is 0.1%~0.2% of the total mass of the solvent and the decolorizing agent; the amount of the styrene polymerization inhibitor added is 0.05%~0.15% of the total mass of the solvent and the decolorizing agent; the solvent is selected from 1,2-propanediol diacetate and 1,3-propanediol diacetate.

2. The compound decolorizing agent according to claim 1, characterized in that, The decolorizing agent is selected from maleic anhydride, acrylic acid, and methyl acrylate.

3. The compound decolorizing agent according to claim 1, characterized in that, The polymer dispersant is selected from polyacrylate and polyvinyl acrylate.

4. The compound decolorizing agent according to claim 1, characterized in that, The styrene polymerization inhibitor is a polymerization inhibitor composed of 4-hydroxy-2,2,6,6-tetramethylpiperidine nitroxide radical and 2-sec-butyl-4,6-dinitrophenol.

5. The compound decolorizing agent according to claim 4, characterized in that, The mass ratio of the 4-hydroxy-2,2,6,6-tetramethylpiperidine nitroxide radical to the 2-sec-butyl-4,6-dinitrophenol is 1:

1.

6. A method for preparing a compound decolorizing agent as described in any one of claims 1 to 5, characterized in that, The process includes the following steps: weighing each component according to the specified ratio; mixing and stirring the solvent and decolorizing agent at room temperature to obtain an organic acid anhydride / acid solution; adding a polymer dispersant and a styrene polymerization inhibitor to the organic acid anhydride / acid solution, stirring thoroughly to dissolve, and obtaining a colorless and transparent liquid compound decolorizing agent.

7. The application of the compound decolorizing agent according to any one of claims 1 to 5 in the decolorization of crude styrene recovered from cracked gasoline.

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