Synthesis and demulsification performance of a novel low-temperature demulsifier based on trimethyl citrate

With the advancement of oil displacement technology, oil recovery has improved significantly [1], [2], [3]. However, as oil reserves are depleted and enhanced oil recovery (EOR) technologies become more popular, there is increasing production of high water content crude oil emulsions [4], [5]. These undesirable emulsions have various harmful effects such as: E.g. increased transportation costs, increased viscosity, pipeline corrosion and corrosion of associated equipment [6], [7], [8]. Stabilized by the interaction of natural surface-active substances, these emulsions can persist for long periods of time without oil-water separation [9], [10], [11]. To address these challenges, demulsification and dehydration of the emulsions is required before further processing.

The existing demulsification processes mainly consist of physical demulsification and chemical demulsification [12], [13]. However, traditional physical methods such as heating and demulsification by electric fields require a lot of energy and time, resulting in increased costs, waste of resources and high equipment load [14], [15]. In chemical demulsification, demulsifiers are added directly to the emulsions, which means efficient demulsification can be achieved in a shorter time. Due to its straightforward operation and high demulsification efficiency (DE), chemical demulsification is widely used as a viable solution in the oilfield industry [16], [17], [18]. In recent years, researchers have been actively working on the development of various chemical demulsifiers to effectively address the growing challenges in demulsification of crude oil emulsions. However, many of these demulsifiers are not suitable for practical applications due to complex local conditions. In addition, existing demulsification processes still face some critical problems such as: B. high emulsion viscosity, poor solubility of the demulsifier, low demulsification performance, high demulsification temperature and extended demulsification times [19], [20]. Therefore, further efforts are still required to synthesize novel and efficient demulsifiers to improve their practical application in demulsification of oilfield emulsions.

Chemical demulsifiers are typically designed as amphiphilic compounds with interfacial activity. Common examples include ionic liquids, block copolymers and nanoparticles [9], [21], [22]. Husain et al. synthesized three types of ionic liquid demulsifiers named 1-butyl-4-methylpyridinium tetrafluoroborate (BMPT), 1-butyl-4-methylpyridinium hexafluorophosphate (BMPH), and 1-butyl-4-methylpyridinium iodide (BMPI) and used them for W/O emulsions Demulsification. Among them, BMPH achieved a DE of 99% at 75 °C and a concentration of 1000 mg/L [23]. An et al. developed a polyether demulsifier with anthocyanin as raw material and achieved a DE of 94.4% at 70 °C [24]. Agah et al. prepared four cellulose demulsifiers for demulsification at 80 °C and achieved an optimal DE of 99.5% after 12 hours at a concentration of 3000 mg/L [25]. These demulsifiers all demonstrated an exceptional DE of over 95%. However, they often require a longer demulsification time and a high demulsification temperature, which limits their widespread application. Therefore, it is crucial to develop and synthesize demulsifiers with high DE at low demulsification temperature conditions [26], [27]. In addition, the selection of raw materials and synthesis processes should also be based on the requirements for cost-effectiveness and environmental friendliness.

Based on previous literature results [28], [29], [30], [31]Demulsifiers with hydrophilic center and hydrophobic areas show excellent demulsification performance. Currently, some commercial demulsifiers such as SP169 use ethylene oxide (EO) as the hydrophilic center and propylene oxide (PO) as the hydrophobic part. SP169 contains both a hydrophilic center and a hydrophobic branched chain, leading to its excellent DE in W/O emulsions. However, the manufacturing process of EO-PO polymers is dangerous and complex. Demulsification typically requires temperatures above 60 °C, resulting in significant energy consumption. On the one hand, trimethyl citrate, derived from citric acid, offers the advantages of cost effectiveness and wide availability. On the other hand, the currently synthesized demulsifier has excellent amphiphilicity and a simple and safe manufacturing process. Therefore, in this study, a novel demulsifier (TCED) with trimethyl citrate as the hydrophilic center was synthesized by a simple two-step method. The demulsification experiments revealed that TCED exhibited remarkable DE at a low temperature of 40 °C, indicating its broad potential for various applications in oil–water separation processes.