A dispersant for mto wash water and a method of using the same

Abstract

The application discloses a dispersant for MTO washing water and a use method thereof, and the dispersant is composed of 10-25% of sodium cocoyl monoethanolamide ether carboxylate, 2-12% of lauryl amidopropyl hydroxyl sulfobetaine, 2-13% of polyvinyl alcohol and solvent water according to mass percentage, can effectively prevent the catalyst in the washing tower from being scaled with polymethylbenzene substances, eliminate the generated scale layer, prevent the tray from being blocked, thereby prolonging the operation cycle of the washing tower and improving the economic benefit of the device. Meanwhile, the dispersant has good anti-crystallization performance and cannot cause the crystallization to block the pipeline; the dispersing effect does not change with the change of the catalyst of the MTO device.

Description

Technical Field

[0001] This invention relates to a dispersant for MTO washing water and its application method. Background Technology

[0002] In the methanol-to-olefins (MTO) process, the main products are methane, ethylene, propylene, mixed C4 and mixed C5 compounds, etc.; polymethylbenzene is also produced as a byproduct. The generated polymethylbenzene enters the separation system with the reaction gas. Trimethylbenzene, tetramethylbenzene, and pentamethylbenzene in the polymethylbenzene have high viscosity and poor flowability, and are easily mixed with the catalyst carried in the reaction gas in the water washing tower and deposited on the tray.

[0003] The continuous accumulation and retention of polymethylbenzene in the washing water system gradually leads to a decrease in the heat exchange efficiency of the heat exchange equipment and fluctuations in the pressure differential of the washing tower, affecting the stable operation of the unit. While the unit employs three methods—offline high-pressure water cleaning of the heat exchange equipment, online xylene washing, and online high-pressure water cleaning of the tower trays—to some extent effectively ensure long-term, high-load operation, they fail to fundamentally solve the scaling and clogging problems in the washing water system. Furthermore, frequent cleaning of the air cooler and heat exchangers not only consumes significant manpower and resources but also accelerates equipment wear and tear, increases maintenance costs, and reduces the overall efficiency of the unit.

[0004] To improve the clogging of the washing tower trays in a more environmentally friendly and efficient way, a dispersant can be added to the washing tower periodically to disperse the fine catalyst powder deposited on the washing tower trays into the washing water, effectively reducing the pressure difference of the washing tower. Summary of the Invention

[0005] The purpose of this invention is to develop an MTO (methyl methylbenzene) dispersant for washing water and its application method. This washing water dispersant can effectively inhibit and disperse scale, improve the quality of washing water, enhance the solubility of polymethylbenzene compounds in water, improve the scale-carrying capacity of washing water, peel off and disperse existing dirt, and clean the surfaces of heat exchangers and towers.

[0006] Key points of the invention:

[0007] This invention relates to a dispersant for MTO washing water, comprising, by weight, active ingredients A, B, and C, and a solvent. The characteristic feature is that component A is 10-25% sodium cocoyl ether carboxylate, component B is 2-12% lauramide propyl hydroxysulfonate betaine, component C is 2-13% polyvinyl alcohol, and the solvent is water. Preferably, the composition is: component A: 20% sodium cocoyl ether carboxylate, component B: 6% lauramide propyl hydroxysulfonate betaine, component C: 6% polyvinyl alcohol, and the remainder is water.

[0008] The present invention also provides an efficient method for using the dispersant for MTO water washing water, wherein the dispersant of the present invention is injected into the inlet of the water washing water heat exchanger at a mass concentration of 30-140 ppm.

[0009] During the production process, the temperature at the top of the water washing tower is generally below 50℃, and the temperature at the bottom is between 95-118℃. Polymethylbenzene compounds, such as tetramethylbenzene and mesitylene, have melting points of 76-80℃ and are almost insoluble in water, so they are highly likely to solidify at a suitable temperature within the water washing tower. Hexamethylbenzene, with a melting point as high as 165℃, is also insoluble in water. As the reaction continues, it solidifies at the bottom of the water washing tower or in the washing water, adhering to the trays and causing tray blockage, thus increasing the tower pressure differential. To verify this, FT-IR analysis was performed on the waxy substance removed from the water system. Comparison showed that its main characteristic absorption peaks were basically consistent with the characteristic peaks of the standard infrared spectrum of hexamethylbenzene, thus determining that the main component of the waxy substance causing tray blockage was hexamethylbenzene.

[0010] The main component of the dispersant for washing water in this invention, sodium cocoyl monoethanolamide ether carboxylate, is a nonionic surfactant with excellent dispersing properties. Its functional groups in its molecular structure can form special associations, exhibiting chelating properties to peel and disperse existing scale. It is also environmentally friendly, exhibits stable viscosity at high and low temperatures, and has good antifreeze properties. Lauroamide propyl hydroxysulfonate betaine has good compatibility; when combined with other surfactants, it can improve the quality of washing water, increase the solubility of polymethylbenzenes in water, and enhance scale-carrying capacity. Polyvinyl alcohol has good film-forming properties, forming a separating film on metal surfaces, weakening the adhesion of deposited particles to metal surfaces, and providing passivation protection for equipment and pipelines. The synergistic effect among the components is significant, making it a composite special additive specifically developed for scale buildup in water washing towers.

[0011] The innovation of this invention lies in the following: the dispersant product adopts multifunctional functional groups, which improves the scale inhibition and dispersion performance while enhancing the product's temperature resistance. It does not crystallize or solidify in winter, making it convenient to store and use, thus solving the problem of difficult addition of general dispersants in winter and reducing the energy consumption of the equipment. On the other hand, compared with the limitations of traditional dispersants on the solubility of polymethylbenzene, the multifunctional dispersant of this invention enhances the solubility of polymethylbenzene in water, preventing various suspended solids and heavy oil components in the water from agglomerating and depositing to form scale, improving the scale-carrying capacity of the washing water. At the same time, the product requires a small amount, is low in cost, easy to use, safe and environmentally friendly, and ensures the safe, stable, long-term, and full-load operation of the MTO unit. Detailed Implementation

[0012] Examples 1-7: Under continuous stirring, components A, B, and C were added sequentially to the solvent water according to the group distribution ratio in Table 1, in parts by weight, and mixed evenly to obtain the MTO water washing dispersant of the present invention.

[0013] Table 1: Components and proportions of dispersants in Examples 1-7 (all data in the table are parts by mass)

[0014]

[0015] Scale inhibition and dispersion experiments were conducted on the wash water and scale samples from the washing tower of the MTO unit to verify the treatment effect of the dispersant on the materials in the washing tower of the methanol-to-olefins unit.

[0016] Experimental method: Add 500 mL of wash water to a beaker, weigh approximately 5 g of scale sample and add it to the above solution. Add a dispersant of a certain mass concentration, shake well, and place in a 60℃ constant temperature water bath for 20 minutes. After the bath, observe the water condition, take a sample from the upper layer for COD and oil content analysis, and simultaneously observe the dispersion of scale sample at the bottom of the beaker.

[0017] Example 8:

[0018] The dispersant from Example 1 was added to the evaluation raw material at a concentration of 140 ppm (the evaluation raw material was the wash water and tray scale sample from the actual methanol-to-olefins unit in industry). The material was treated at a constant temperature of 60°C for 20 minutes. The COD value was determined to be 30900 mg / L according to GB / T 11914 standard, and the oil content in the water was determined to be 429.52 mg / L according to GB / T 12152 standard. The dispersion rate was 64.9%.

[0019] Example 9:

[0020] The dispersant from Example 2 was added to the evaluation raw material at 110 ppm (the evaluation raw material was the wash water and tray scale sample from the actual methanol-to-olefins unit in industry). The material was treated at a constant temperature of 60°C for 20 minutes. The COD value was determined to be 33850 mg / L according to GB / T 11914 standard, and the oil content in the water was determined to be 447.26 mg / L according to GB / T 12152 standard. The dispersion rate was 66.3%.

[0021] Example 10:

[0022] The dispersant from Example 3 was added to the evaluation raw material at 80 ppm (the evaluation raw material was the wash water and tray scale sample from the water washing tower of an actual methanol-to-olefins unit in industry). The material was treated at a constant temperature of 60°C for 20 minutes. The COD value was determined to be 34407 mg / L according to GB / T 11914 standard, and the oil content in the water was determined to be 458.01 mg / L according to GB / T 12152 standard. The dispersion rate was 67.8%.

[0023] Example 11:

[0024] The dispersant from Example 4 was added at 80 ppm to the evaluation raw material (the evaluation raw material was the wash water and tray scale sample from the actual methanol-to-olefins unit in industry). The mixture was kept at 60°C for 20 minutes. The COD value was determined to be 38942 mg / L according to GB / T 11914 standard, and the oil content in the water was determined to be 493.64 mg / L according to GB / T 12152 standard. The dispersion rate was 70.2%.

[0025] Example 12:

[0026] The dispersant from Example 5 was added at 50 ppm to the evaluation raw material (the evaluation raw material was the wash water and tray scale sample from the water washing tower of an actual methanol-to-olefins unit in industry). The mixture was treated at a constant temperature of 60°C for 20 minutes. The COD value was determined to be 34106 mg / L according to GB / T 11914 standard, and the oil content in the water was determined to be 449.85 mg / L according to GB / T 12152 standard. The dispersion rate was 67.1%.

[0027] Example 13:

[0028] The dispersant from Example 6 was added at 50 ppm to the evaluation raw material (the evaluation raw material was the wash water and tray scale sample from the water washing tower of an actual methanol-to-olefins unit in industry). The mixture was treated at a constant temperature of 60°C for 20 minutes. The COD value was determined to be 35200 mg / L according to GB / T 11914 standard, and the oil content in the water was determined to be 466.20 mg / L according to GB / T 12152 standard. The dispersion rate was 68.4%.

[0029] Example 14:

[0030] The dispersant from Example 7 was added at 30 ppm to the evaluation raw material (the evaluation raw material was the wash water and tray scale sample from the water washing tower of an actual methanol-to-olefins unit in industry). The mixture was kept at a constant temperature of 60°C for 20 minutes. The COD value was determined to be 34070 mg / L according to GB / T 11914 standard, and the oil content in the water was determined to be 448.06 mg / L according to GB / T 12152 standard. The dispersion rate was 66.9%.

[0031] Blank control experiment

[0032] A blank water sample without dispersant was added to the scale for a comparative experiment. The sample was treated at 60℃ for 20 minutes. The COD value was 20750 mg / L according to GB / T 11914 standard, and the oil content in the water was 287.15 mg / L according to GB / T 12152 standard. The dispersion rate was 0.06%.

[0033] The results of the application evaluation experiments and blank control experiments above show that after adding the dispersant of this invention, the scale at the bottom of the test water sample beaker was significantly and uniformly dispersed without any residue adhering to the walls; the COD and oil content of the water quality changed significantly. This indicates that the dispersant of this invention can emulsify oil droplets in the washing water into smaller droplets, increase the water's oil-dissolving capacity, and reduce the possibility of scaling. In addition, the dispersant is easy to produce and use, does not pollute the environment during use, is easily biodegradable, and has good compatibility with system materials.

Claims

1. A dispersant for MTO washing water, comprising component A, component B, component C, and solvent, characterized in that... Component A is 10-25% sodium cocoyl monoethanolamide ether carboxylate, component B is 2-12% lauramide propyl hydroxysulfonate betaine, component C is 2-13% polyvinyl alcohol, and the solvent is water.

2. The MTO water-washing dispersant according to claim 1, characterized in that: Component A is 20% sodium cocoyl monoethanolamide ether carboxylate, component B is 6% lauramide propyl hydroxysulfonate betaine, component C is 6% polyvinyl alcohol, and the remainder is water as a solvent.

3. A method of using an MTO water washing water dispersant, wherein the dispersant of claim 1 or 2 is added to the inlet of the water washing water heat exchanger at a mass concentration of not less than 30 ppm.

4. The method of using the MTO water-washing dispersant according to claim 3, characterized in that: The dispersant is added to the inlet of the water washing heat exchanger at a mass concentration of 30-140 ppm.

5. The method of using an MTO water-washing dispersant according to claim 4, characterized in that: The dispersant is added to the inlet of the water washing heat exchanger at a mass concentration of 50-80 ppm.

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