Abstract

Water-in-oil (w/o) emulsions are widely used in the food and pharmaceutical industries, among others. Moreover, the most common type of emulsion produced and handled in the oil industry processes is the w/o emulsion. This study investigates the features of a water-in-mineral oil macro-emulsion formulated with mineral oil as the continuous phase and Span 83 as the nonionic surfactant. Emulsions are prepared at room temperature according to the hydrophilic–lipophilic difference (HLD) theory and were tested for the mean droplet size and droplet size distribution, viscosity, and kinetic stability. An empirical correlation was introduced that estimates the viscosity of the water-in-mineral oil macro-emulsions and captures the non-Newtonian behavior at larger water fractions. The effect of electrolyte and internal phase concentration was specifically assessed on the emulsion flocculation and the stability of the system. Stability tests show a threshold electrolyte concentration exists after which droplets coalesce upon collision and flocculation. Salting out is most likely the responsible mechanism of phase separation in the emulsions with higher electrolyte concentrations. The results imply that sedimentation is accountable for the formation of different layers in emulsion with time. The sedimentation rate was intensified for emulsion with smaller water content (64% variation in 3 days between 10% emulsion and 40% emulsion) and concentrated emulsions were found to be more stable. Also, the size of the droplets was influenced by the NaCl concentration, surfactant concentration, and phase ratio.

摘要

油包水 (w/o) 乳液广泛用于食品和制药行业等。此外，在石油工业过程中生产和处理的最常见类型的乳液是 w/o 乳液。本研究研究了以矿物油为连续相、Span 83 为非离子表面活性剂配制的矿物油包水大乳液的特性。根据亲水-亲油差异 (HLD) 理论在室温下制备乳液，并测试平均液滴尺寸和液滴尺寸分布、粘度和动力学稳定性。引入了一种经验相关性，用于估计矿物油中水的宏观乳液的粘度并捕捉较大水份的非牛顿行为。具体评估了电解质和内相浓度对乳液絮凝和体系稳定性的影响。稳定性测试显示存在阈值电解质浓度，之后液滴在碰撞和絮凝时聚结。盐析很可能是电解质浓度较高的乳液中相分离的主要机制。结果表明，随着时间的推移，乳液中不同层的形成是沉降的原因。对于含水量较小的乳液（10% 乳液和 40% 乳液之间 3 天的 64% 变化），沉降速率加快，浓缩乳液被发现更稳定。此外，液滴的大小受 NaCl 浓度、表面活性剂浓度和相比的影响。