2.1.3 Scanning Electron Microscopy (SEM) Analysis of Asphalt

Grind the asphalt particles obtained by reflux extraction into powder and slice them, observe them in SEM, and analyze their structure. The results are shown in Figure 3.

The surface of the asphalt particle aggregates obtained through extraction is relatively smooth, with a small number of small cracks and protrusions, and the overall shape and flatness are relatively concentrated and fixed. The image shows that asphaltene is a solid with a regular morphology, and the structure formed by molecular association and sedimentation is quite dense, which also proves that asphaltene aggregates can hinder the flow of crude oil.

2.2 Development of Efficient Asphalt Dispersant

2.2.1 Optimal selection of single organic solvents

It is necessary to comprehensively consider and screen organic solvents for high asphaltene sediment from multiple factors such as cost, effectiveness in dissolving asphaltene, impact on crude oil, and environmental protection. This experiment selected 12 organic solvents for evaluation through preliminary research. The specific experimental steps refer to 1.3, and the results are shown in Table 3.

The above 12 organic solvents all have a certain solubility for asphaltene deposits, among which the aromatic solvent LY has a dissolution rate of 83%, and the dissolution effect is higher than other organic solvents. This is because the aromatic solvent LY belongs to polar solvents containing aromatic rings, while the molecular structure of asphaltene contains groups such as methylene, methyl, amino, hydroxyl, carboxyl, as well as aromatic rings or heterocycles, with higher polarity;Based on the principle of similar solubility, the aromatic solvent LY helps to weaken the interaction force of π - π bonds between asphaltene molecules, effectively inhibiting the deposition of asphaltene. Subsequent experiments selected aromatic solvent LY as the main agent to investigate the effect of adding different types of surfactants on the performance of dissolving asphaltene deposits.

2.2.2 Selection and dosage optimization of surfactants

(1) Optimal selection of different types of surfactants

The selection of surfactants requires that they can not only dissolve and disperse asphaltene, but also have good miscibility with the main organic solvent without affecting the various properties of the main solvent. At the same time, they should have a certain inhibitory effect on asphaltene deposition and hinder the aggregation of asphaltene molecules.This experiment uses calcium alkyl salicylate, N-N-di (hydroxyethyl) cocoamide, nonylphenol span-80、span-60、op-4、op-10、AEO-9、 Nine types of inhibitory dispersing surfactants, including petroleum sulfonate, were compounded with aromatic solvent LY. At the same time, in order to improve the penetration of surfactants and main agents into asphalt and enhance the dissolution effect of asphalt, alcohol or alcohol ether mutual solvents were selected.Four commonly used mutual solvents were selected, namely 1,6-hexanediol, ethylene glycol butyl ether, n-pentanol, and n-octanol. Add 1.0% surfactant to the selected aromatic solvent LY, and calculate the solubility of asphaltene in organic solvents containing surfactants. The experimental results are shown in Table 4.

When adding the surfactant nonylphenol to the main agent op-4、 When petroleum sulfonate and n-pentanol are used, the solubility of asphalt is significantly increased, indicating that these four surfactants have a good synergistic effect with the main aromatic solvent LY.When nonylphenol op-4、 When the mass fraction of these three surfactants, n-pentanol, is 1.0%, the dissolution rate increases by 2% to 3%. Among them, the main aromatic solvent LY combined with petroleum sulfonate has the best effect on dissolving asphalt, with a dissolution rate of up to 87%.The above four surfactants enhance the effectiveness of the additives by generating a synergistic effect and promoting mutual solubility with the main aromatic solvent LY.

Generally speaking, while ensuring the oil solubility of chemical additives, increasing the polarity and acidity of the functional groups at the head of the additive can enhance the interaction between the additive and asphaltene, thereby further improving its stability.Wiehe et al. compared the effects of dispersants with phenolic, amino, sulfonic acid, and carboxyl groups as the head group based on dodecylbenzene, and the results showed that the dispersant had the best effect when the head group was sulfonic acid.The reason is that sulfonic acid groups are more acidic than amino groups, and more polar than carboxyl and phenolic groups, indicating the importance of polar and acidic head groups in additives.This experiment also confirmed that sulfonic acid groups with strong polarity and acidity can enhance the solubility and dispersion ability of the main aromatic solvent LY on asphaltene molecules.This group not only promotes the formation of hydrogen bonds, but also further stabilizes the interaction between asphaltene molecules and dispersant molecules, thereby forming a certain steric hindrance. This helps to disrupt the interactions between asphaltene molecules in the aggregate and achieve the goal of inhibiting asphaltene deposition.

(2) Optimization of surfactant dosage

Further investigation was conducted on the optimal dosage of surfactants. Add 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% of nonylphenol to the selected main aromatic solvent LY, respectively op-4、 Petroleum sulfonate and n-pentanol, experimental results are shown in Figure 4.

With the increase of the dosage of n-pentanol and nonylphenol additives, the dissolution effect of the main aromatic solvent LY on asphalt deposits is improved, and the dissolution rate increases to 85% when the dosage is 1.0%; But with the increase of op-4 and petroleum sulfonate dosage, the dissolution effect of the main aromatic solvent LY complex system no longer changes significantly, and the optimal dosages are 0.8% and 0.2%, respectively.This is because the surfactant only acts as a dispersant when the dosage exceeds a certain value, and its effect becomes more effective with the increase of dosage. However, when the dosage is below the critical value, the surfactant will co settle with the asphaltene aggregates, acting as a flocculation settling agent.Lima et al. studied the stabilizing effect of polycashew phenols with different relative molecular weights and sulfonated polystyrene with different degrees of polymerization on asphalt, and found that these substances were coagulants at low concentrations and dispersants at high concentrations.

2.2.3 Optimization of Efficient Asphalt Dispersant Formula

According to the experimental results in the previous section, two asphalt dispersant formulations based on aromatic solvent LY were obtained, namely LYH-1 (aromatic solvent LY+1.0% n-pentanol+1.0% nonylphenol+0.2% petroleum sulfonate) and LYH-2 (aromatic solvent LY+1.0% n-pentanol+1.0% nonylphenol+0.8% op-4).The fixed reaction time was 2 hours and the reaction temperature was 30℃. The dissolution rate of asphalt deposits in formulations LYH-1 and LYH-2 was measured as a function of temperature, and the effects of reaction temperature and time on the two formulations were investigated. The results are shown in Figure 5.

In Figure 5 (a), with a fixed reaction time of 2 hours, the dissolution rates of both formulations showed an upward trend with increasing temperature. When the temperature is within the range of 30-50℃, the dissolution rate rapidly increases to over 90%; When the temperature is within the range of 50-90℃, the dissolution rate of the formula does not increase significantly.The fixed reaction temperature was set at 30 ℃. In order to visually observe the changes in the effects of LYH-1 and LYH-2 over time, the changes in the dissolution rate of asphalt sediment after 1-8 hours of reaction were examined, as shown in Figure 5 (b).The dissolution rates of the two formulas showed a trend of first increasing and then tending to flatten with the extension of reaction time. After a reaction time exceeding 4 hours, both formulations achieved a dissolution rate of over 93% for asphaltene deposits, and there was no significant increase in dissolution rate as the reaction time continued to increase, indicating that asphaltene dissolution had reached saturation.

The formula LYH-1 has a significant dissolution effect on asphaltene deposits, with the optimal reaction temperature of 50℃ and the optimal reaction time of 4 hours. Under these conditions, the dissolution rate is 97%. This indicates that LYH-1 has undergone stronger intermolecular interactions with asphaltene molecules, breaking up the aggregates formed by overlapping planes through hydrogen bonding penetration and π - π interactions, making the molecular spacing looser and inhibiting the aggregation of asphaltene deposits.