Preparation of a low-temperature poly (amino acids) demulsifier and its demulsification mechanism

To improve the universality and efficiency of polymer demulsifiers at low temperatures, a unique type of biodegradable poly (ε-carbobenzyloxy-L-lysine) -block-poly (L-phenylalanine) (PZLL-b-PPA) demulsifier with stronger polarity and higher aromaticity was developed. The molecular structure and weight of PZLL-b-PPA were determined using Fourier transform infrared (FT-IR) spectroscopy, 1H nuclear magnetic resonance hydrogen spectra (NMR) and gel permeation chromatography (GPC). A bottle test was used to evaluate the demulsification performance of PZLL-b-PPA with different block ratios, structure and interfacial activity. Numerous critical variables, such as demulsifier structure and dosage, pH levels, emulsion salinity, oil content and oil type, were carefully examined. The demulsification results showed that PZLL5-b-PPA25 has excellent low-temperature demulsification capability and can effectively separate oil from water emulsions with different pH values (4.0 ∼ 11.0) and oil contents ranging from 1.0 ∼ 20.0 wt% within 2 min at room temperature. The best demulsification efficiency reached 99.98 %, with only 6.0 mg/L of residual oil in the separated water. The analysis of interfacial self-assembly behavior revealed that PZLL-b-PPA has a strong affinity for aromatic molecules and exhibits high interfacial activity. The quantum chemical calculation indicated that the main chain polyamide skeleton of PZLL-b-PPA has a stronger interaction for asphaltene, resin and naphthenic acid molecules than conventional oxygen-containing skeleton polymers. Furthermore, the microscopy analysis indicated that PZLL-b-PPA has excellent capacity for flocculation and coalescence of oil droplets in an O/W emulsion. As a result, when PZLL-b-PPA is added to the emulsion, it can quickly migrate to the oil-water interface and interact with and displace the emulsion's stabilizers (asphaltenes and resins), promoting oil droplet coalescence and separation from water at low temperature.