It is well known that crude oil is one of the most important energy sources. The oil-in-water emulsion is often produced during oil exploitation due to waterflooding and groundwater. This emulsion causes damage to the transmission pipeline and environment. Therefore, the separation of oil and water is an essential step in the petroleum industry. Chemical demulsification is currently the most widely employed due to its convenient operation and quick response. However, the extensive use of chemical emulsifiers has brought potential harm to the environment, so it is necessary to explore novel environmentally friendly demulsifiers. Recently, nanoparticle (NP) demulsifiers have been widely concerned in the application of demulsification for crude oil emulsion. NP demulsifiers usually refer to chemically synthesized nanoparticles or modified natural nanoparticle minerals. While graphene oxide and reduced graphene oxide are reported to exhibit an excellent demulsification performance of more than 99.9%, the high cost of raw materials limits their widespread use. As a result, economical mineral materials such as attapulgite, kaolinite, and nano-silica are employed to develop NP demulsifiers.

Ordinary mineral nanomaterials typically consist of a single hydrophilic part (e.g., quartz, silicate, etc.). Therefore, they require complex surface modifications to adjust their hydrophilicity and hydrophobicity, enabling them to be excellent demulsifiers. Recently, researchers found a novel mineral material called Micro-nano silicon-carbon ore (Si–C). The Si–C particles consist primarily of hydrophilic quartz and hydrophobic carbon, so it is expected that they can be used to prepare a novel NP demulsifier.

The Nano silicon-carbon ore utilized was sourced from a mining site named Shilukeng in Fengcheng City, Jiangxi Province, China. Initially, bulk samples of Si–C were ground, and the resulting mineral particles were subsequently screened to obtain samples less than about 1 um. The demulsifiers (OSi–C) were prepared through a simple oxidation treatment.

The major elemental composition of the Si–C includes O (40.35%), Si (35.33%), C (9.15%), Al (2.18%), Fe (1.3%), K (0.33%), and the loss on ignition is 9.57%. The average particle size of Si–C was 343.4 nm. The Zeta potential of OSi–C was considerably lower than that of the Si–C for all pH conditions. This is due to the introduction of oxygen-containing functional groups on the OSi–C surface after oxidation treatment. The content of C–OH, C–O–C, and O=C–O increased compared to that of the Si–C, suggesting that the OSi–C was successfully oxidized, resulting in increasing oxygen-containing functional groups. After oxidation, the obtained OSi–C nanoparticles showed good amphiphilicity, interfacial activity, and low interfacial tension (IFT) properties, which enable the particles easily to arrive at the oil–water interface. And it was believed that the self-assembly behavior of OSi–C at the oil-water interface is due to its good interfacial activity and the ability to reduce the oil-water IFT. At a demulsifier dosage of 1000 mg/L, OSi–C exhibited a demulsification efficiency exceeding 98.94% at pH 6, with the oil concentration in the separated water less than 97.33 mg/L.

An OSi–C nanoparticle demulsifier was prepared by a simple oxidation treatment of natural Si–C nanoparticles to achieve highly efficient demulsification for the crude oil-in-water emulsion at room temperature (25 ℃). The OSi–C nanoparticles exhibit superior demulsification performance than the original Si–C at the optimal conditions, and have a demulsification efficiency of 98.94% at pH 6. The mechanism behind emulsion breaking was revealed through analyses of Zeta potential, interfacial activity, surface wettability, dynamic IFT, self-assembling at the oil–water interface, and microscopic observation of the demulsification process. On the one hand, the OSi–C nanoparticles have good amphiphilicity, interfacial activity and the ability to self-assembly at the oil–water interface, which makes it easy to arrive at the oil–water interface. On the other hand, the OSi–C material has abundant Oxygen-containing functional groups and aromatic ring structures, which can promote the binding of nanoparticles with emulsified molecules of asphaltenes and resins at the oil–water interface through hydrogen bonding and π–π interactions. Furthermore, with the help of external forces such as stirring and oscillation, the protective film at the oil-water interface ruptures, thereby achieving oil–water separation. Therefore, the OSi–C nanoparticles can rapidly break the emulsion with high efficiency at room temperature. Due to the natural composition advantage and nontoxicity of the raw Si–C, this work provides a new approach for synthesizing environmentally friendly natural mineral NP demulsifiers.