Preparation and use method of defoaming agent for aromatic hydrocarbon extraction unit

Abstract

The invention relates to a preparation method and a use method of a defoaming agent for an aromatic hydrocarbon extraction unit. The defoaming agent has good defoaming and foam inhibition performance, the lauramide derivative and the fatty amine component contained in the defoaming agent can destroy a liquid film structure and shorten the service life of bubbles, the foam breaking speed is high, the foam inhibition capacity is high, the foaming phenomenon in a stripping tower of an aromatic hydrocarbon extraction device can be effectively inhibited, the extraction device can operate stably, and the product quality and yield are guaranteed. Meanwhile, the defoaming agent has high dispersity, stability and alkali resistance, raw materials are easy to obtain, the production cost is low, crystals cannot be separated out to block a pump body and a pipeline in the use process, storage and use are safe and environmentally friendly, and adverse effects on the environment are avoided.

Description

Technical Field

[0001] The present invention relates to the preparation and use method of an antifoaming agent for an aromatic extraction unit. Background Art

[0002] The extraction unit is one of the important links in aromatic production. Its process uses sulfolane as the extraction solvent and consists of a raw material fractionation, extraction, rectification, and solvent oil separation unit. The device raw materials come from the hydrogenated gasoline of the pyrolysis gasoline hydrogenation unit in the olefin plant or the de-pentane oil of the catalytic reforming unit. After removing the C ≥8 components in the fractionation tower, the C 6 and C 7 aromatic and non-aromatic components are contacted and mixed with the solvent in the extraction tower. The aromatic hydrocarbons gradually dissolve, and the non-aromatic hydrocarbons are drawn from the top of the tower. The mixed aromatic hydrocarbons at the bottom of the tower are stripped in the stripping tower to remove the light non-aromatic hydrocarbons and a small amount of benzene, and the latter enters the extraction tower as reflux aromatic hydrocarbons in the reflux tank for replacing and purifying the aromatic hydrocarbons. In the recovery tower, the solvent containing the mixed aromatic hydrocarbons is separated by vacuum steam rectification. The solvent is recycled, and the mixed aromatic hydrocarbons enter the rectification system to sequentially separate benzene, toluene, and xylene products.

[0003] For an aromatic extraction device, affected by factors such as the characteristics of the raw material composition, the processing load of the device, the interface of the extraction tower, and the feed temperature of the stripping tower, the stripping tower is extremely prone to foaming. When the feed rate of the device increases, the load of the stripping tower also increases, and the operating flexibility of the tower decreases, making it easy to generate foaming or flooding phenomena. On the other hand, if the interface at the bottom of the extraction tower is too low, it may also cause a large amount of non-aromatic hydrocarbons to enter the stripping tower and cause foaming. In addition, the feed temperature of the stripping tower is affected by factors such as the solvent circulation rate and the bottom temperature of the benzene recovery tower. When the feed temperature of the stripping tower is high, the flash evaporation amount of the material after entering the tower increases, and the possibility of generating foaming is greater. High olefin content in the backwash liquid, unstable operation of the control valve, and inaccurate indication of the automatic control instrument will also cause frequent foaming phenomena in the stripping tower.

[0004] In the initial stage of foaming, the flow rate of the rich solvent from the bottom of the extraction tower to the solvent recovery tower decreases, the liquid level of the solvent recovery tower drops significantly, and the top pressure and bottom temperature of the extraction tower will continue to rise. If not handled in time, it will cause the solvent to rush to the top of the tower and even enter the reflux tank, resulting in solvent loss, reducing the processing capacity of the stripping tower and causing production fluctuations. Usually, solvent foaming is accompanied by an increase in the content of light non-aromatics in the feed components, and the gas load at the top of the tower suddenly increases. In severe cases, it will cause the safety valve at the top of the tower to trip, affecting the normal production of the device. On the other hand, due to excessive vaporization at the top of the tower, the bottom liquid level will continue to drop, ultimately leading to the stripping tower being unable to maintain the liquid level and shutting down. Therefore, the operation of the stripping tower has become a difficult point for the stable operation of the aromatic extraction device.

[0005] To inhibit the foaming phenomenon in the stripping column and ensure the stable operation of the aromatics extraction unit, relevant anti-foaming measures are proposed in aspects such as controlling the feed composition of the device, improving the operation method, process parameters, enhancing the solvent quality, and process transformation. However, from the current application situation, most of the above countermeasures have problems such as long adjustment cycles and slow effects. Some are only temporary, and the methods that can effectively improve the solvent quality and optimize the internal transformation of the stripping column are costly and have a large solvent processing loss. Therefore, to quickly resume production, an anti-foaming agent is selected to solve the foaming problem. There are various types of anti-foaming agents on the market currently. For example, silicone anti-foaming agents can effectively inhibit the foaming trend of the solvent in the column, but long-term use will cause the precipitation of silicone, which not only leads to the blockage of the tube bundle but also enters the final aromatic products, affecting the production efficiency and quality of the products; polyether anti-foaming agents are safe, non-toxic, and easy to use, but the foam-breaking rate is relatively low, and the already generated foam layer cannot be quickly eliminated. When the foam layer in the stripping column slowly accumulates and rises, the phenomenon of tower flooding may still occur. Summary of the Invention

[0006] The object of the present invention is to provide a preparation method and a use method of an anti-foaming agent for an aromatics extraction unit. This agent is a new generation of multi-functional anti-foaming agent developed to solve the foaming problem in the stripping column of the aromatics extraction device. It is more adaptable to the anti-foaming environment in the sulfolane extraction system, has more comprehensive functions, and can quickly achieve the purposes of foam-breaking and foam inhibition, eliminate the adverse effects brought by solvent foaming, improve the operating state of the stripping column, and ensure the stable operation of the extraction unit of the device.

[0007] Key points of the invention: The anti-foaming agent for the aromatics extraction unit of the present invention is composed of an active ingredient A component, a B component, and an aromatic hydrocarbon solvent. Its characteristics are that by mass percentage, the A component is 15 - 35%, and the B component is 10 - 20%. Among them, the A component is a lauramide derivative, which can be selected from one of N, N-dimethyl lauramide and N, N-bis(hydroxyethyl) lauramide; the B component can be selected from one of tetraethylenepentamine and dimethylaminopropylamine; the solvent is an aromatic hydrocarbon solvent (mainly composed of a mixture of benzene, toluene, and xylene), and its dosage makes up the balance of the composition to 100%. Its characteristics are that it is better if the viscosity of the auxiliary agent remains at 2.2 - 2.5 Pa·s at 25°C.

[0008] When the aromatics extraction device processes raw materials, the stripping column is prone to foaming. This is because in the gas-liquid two-phase flow, there is a continuous force that creates cavities on the liquid surface, and bubbles will be generated. And factors such as the thickness of the foam film, the viscosity of the liquid, and the surface tension will affect the durability and stability of the bubbles. If the mass transfer between the bubbles and the liquid phase increases the surface tension of the liquid phase, the bubbles will become stronger. The stripping column is due to the relatively high surface tension of the mass transfer in the system, which stabilizes the formed foam.

[0009] The surface tension of the defoamer for the aromatics extraction unit of the present invention is lower than that of the foam liquid film. After the defoamer is added to the foam system, it will quickly disperse into fine droplets and form a thin film layer when contacting the foam liquid film. Due to the extremely low surface tension of the defoamer, it will push the liquid with a higher surface tension to flow to the area with a lower surface tension to maintain the surface tension balance of the whole system. Affected by this, the film wall will become thinner and thinner. Eventually, due to the traction of other high-surface-tension film layers and the imbalance of internal forces, the bubble liquid film will rupture. In addition, the introduction of alkyl long chains in the main component increases the hydrophobic group, reduces water solubility, improves surface performance and dispersing ability, promotes the rupture of the foam liquid film, makes the foam tend to be unstable, and is beneficial to the final defoaming effect. On the other hand, the functional molecular structure of polyamine is beneficial to slowing down the diffusion rate of gas in the liquid phase, hindering the dissolution and diffusion of bubbles, so as to achieve the purpose of preventing and inhibiting the generation and stability of bubbles. The former of the two components acts quickly and can rupture bubbles in a short time; the latter acts persistently and has a long effective time, and can slow down the generation of foaming phenomena from the root cause. The coordinated action of the two is significant and the synergistic effect is obvious. It is a multifunctional silicon-free defoamer specially developed for the foaming problem of the stripping tower in the aromatics extraction system.

[0010] The present invention also provides a method for using the defoamer for the aromatics extraction unit. The multi-point injection method is adopted, and the defoamer is continuously injected into the feed line and the top reflux line of the stripping tower in the form of the original solution through a dosing pump. Adding the defoamer here can timely, comprehensively and effectively inhibit the generation of bubbles and solve the foaming problem of the stripping tower. The addition amount of the defoamer is based on the feed amount of the stripping tower, and the recommended injection amount is 8 - 50 ppm.

[0011] The product of the present invention is a highly efficient compound defoamer. Compared with a single agent, the defoamer of the present invention has the dual functions of foam breaking and foam inhibition. The functions of each component cooperate tacitly, and can quickly and effectively eliminate foam. Its performance is superior to that of the same type of defoamer; and it is safe and convenient to use, has good thermal stability and chemical stability, has stronger adaptability to acid-base environments, and has a higher foam breaking rate. This defoaming technology has good effects and low costs, not only maintains the stable operation of the device, but also does not enter the subsequent system to contaminate the product, ensuring the quality and yield of the product. Specific embodiments

[0012] Examples 1 - 8: By mass percentage, add the aromatic solvents in the proportions shown in Table 1 to a reaction kettle equipped with a stirrer. Start the stirrer, and sequentially add Component A and Component B in proportion under continuous stirring. Stir at room temperature until the materials are evenly mixed. Open the discharge valve at the bottom of the kettle to obtain the defoamer for the aromatics extraction unit of the present invention.

[0013] Table 1: Components and ratios of the defoamer in Examples 1 - 8 (the data in the table are all by mass percentage).

[0014]

[0015] The sulfolane solvent for the foaming liquid is prepared, containing 26% of pyrolysis gasoline (taken from the stripping tower material of the aromatics extraction unit of Ningxia Coal Industry Co., Ltd.). The defoaming and foam suppression performance of the defoamer is tested to verify the treatment effect of the defoamer on the stripping tower material of the aromatics extraction unit.

[0016] Defoaming experiment: Add 120 mL of the foaming liquid into a 250 mL ground glass graduated cylinder, tightly press the ground glass stopper and shake it vigorously back and forth 30 times. Immediately record the foam height (h 0 ), then add a certain amount of defoamer. After an interval of 20 seconds, record the foam height (h). Calculate the defoaming rate according to the following formula and compare it with the blank test (without adding defoamer). Defoaming rate = (h 0 -h) ÷ h 0 × 100%.

[0017] Foam suppression experiment: Add a small volume of the foaming liquid into a 250 mL graduated cylinder, continuously bubble with nitrogen, keep the nitrogen flow rate at 1 L / min, record the height of the foam rising to the highest point, and use this as the time reference. Add a certain amount of defoamer and record the change of the foam height with time under the condition of continuous bubbling, and compare it with the blank test. Keep the water bath temperature constant during the experiment.

[0018] Example 9: Add the defoamer of Example 1 into the evaluation material at 50 ppm. Under the condition of a temperature of 55 °C, conduct defoaming and foam suppression experiments, record the height and time of foam generation, measure the defoaming rate to be 74.7%, and the foam volume in the foam suppression experiment is 72 mL.

[0019] Example 10: Add the defoamer of Example 2 into the evaluation material at 30 ppm. Under the condition of a temperature of 55 °C, conduct defoaming and foam suppression experiments, record the height and time of foam generation, measure the defoaming rate to be 77.0%, and the foam volume in the foam suppression experiment is 66 mL.

[0020] Example 11: Add the defoamer of Example 3 into the evaluation material at 20 ppm. Under the condition of a temperature of 55 °C, conduct defoaming and foam suppression experiments, record the height and time of foam generation, measure the defoaming rate to be 82.3%, and the foam volume in the foam suppression experiment is 60 mL.

[0021] Example 12: Add the defoamer of Example 4 into the evaluation material at 20 ppm. Under the condition of a temperature of 55 °C, conduct defoaming and foam suppression experiments, record the height and time of foam generation, measure the defoaming rate to be 88.5%, and the foam volume in the foam suppression experiment is 48 mL.

[0022] Example 13: Add the defoamer in Example 5 at 10 ppm to the evaluation material. Conduct defoaming and foam suppression experiments at a temperature of 55°C. Record the height and time of foam generation, and measure the defoaming rate to be 94.6%. The foam volume in the foam suppression experiment is 22 mL.

[0023] Example 14: Add the defoamer in Example 6 at 10 ppm to the evaluation material. Conduct defoaming and foam suppression experiments at a temperature of 55°C. Record the height and time of foam generation, and measure the defoaming rate to be 92.1%. The foam volume in the foam suppression experiment is 36 mL.

[0024] Example 15: Add the defoamer in Example 7 at 10 ppm to the evaluation material. Conduct defoaming and foam suppression experiments at a temperature of 55°C. Record the height and time of foam generation, and measure the defoaming rate to be 92.8%. The foam volume in the foam suppression experiment is 30 mL.

[0025] Example 16: Add the defoamer in Example 8 at 8 ppm to the evaluation material. Conduct defoaming and foam suppression experiments at a temperature of 55°C. Record the height and time of foam generation, and measure the defoaming rate to be 96.4%. The foam volume in the foam suppression experiment is 18 mL.

[0026] Blank control experiment: Do not add any defoamer to the evaluation material. Conduct defoaming and foam suppression experiments at a temperature of 55°C. Record the height and time of the generated foam, and measure the defoaming rate to be 17.6%. The foam volume in the foam suppression experiment is 170 mL.

[0027] From the results of the above application evaluation and blank control experiment, it can be seen that after adding the defoamer of the present invention, the foam descends rapidly and breaks quickly, while in the blank test, the foam volume descends very slowly and cannot disappear. Therefore, a composite defoamer of the present invention has an obvious effect on suppressing foaming in the stripping column, and is non-toxic, pollution-free, and does not generate any three wastes during the whole process.

Claims

1. A defoamer for an aromatic extraction unit, comprising component A, component B and an aromatic solvent, wherein: Component A is a lauramide derivative, which can be selected from one of N, N-dimethyl lauramide and N, N-di(hydroxyethyl) lauramide; component B is selected from one of tetraethylenepentamine and dimethylaminopropylamine; and the organic solvent is an aromatic hydrocarbon solvent (the main component is a mixture of benzene, toluene and xylene).

2. A defoamer for aromatic extraction unit according to claim 1, characterized in that In terms of mass percentage, component A accounts for 15-35%, component B accounts for 10-20%, and the amount of solvent is sufficient to make up the balance of the composition to 100%.

3. The method for preparing a defoamer for an aromatics extraction unit according to claim 2, characterized in that The dosage of each component is preferably such that the viscosity of the defoamer is maintained at 2.2-2.5 Pa•s at 25°C.

4. A method for using a defoamer for an aromatics extraction unit, wherein the defoamer is continuously added to a stripping tower feed line and a tower top reflux line at a mass concentration of 8-50 ppm.

5. The method for using a defoamer for an aromatics extraction unit according to claim 4, characterized in that: The defoamer is continuously added into the stripping tower feed line and the tower top reflux line at a mass concentration of 8-20 ppm.

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