# Cleaner Processes for Making Laundry Soap from Vegetable Oils and an Essential Oil
## 1 Introduction  
For household laundry, the use of detergents is preferred. Laundry detergents are obtained by mixing several ingredients: surfactants (with synthetic origin), builders (to extend the cleaning performance), and multiple additives (bleaches, bleach activators, softeners, enzymes, scouring agents, fabric brighteners, anticaking agents, thickening agents, pearlescent agents and opacifying agents) [1]. Detergents have a high capacity to remove dirt from laundry but they heavily pollute wastewater, which is why it is necessary to find a solution to eliminate this inconvenience [2, 3]. The components used in the manufacture of detergents affect flora and fauna through both direct and indirect effects on ecosystems. The presence ofphosphate salts (between 35% and 75%) in the composition of some detergents causes a variety of water pollution problems because phosphates tend to inhibit the biodegradation of organic substances or can contribute to water pollution by promoting excessive algae growth, which can lead to oxygen depletion in the water, and, consequently, the survival of marine life becomes impossible [4; 5; 6]. In order to reduce wastewater pollution, since 2004, the European Union countries, with the support of environmentalists, have developed a regulation (Regulation (EC) No. 648/2004 of the European Parliament and of the Council) to limit the phosphate content of a laundry detergent [7]. Another option would be to replace synthetic detergents with natural cleaning products, which are more sustainable and environmentally friendly due to the biodegradable nature of the ingredients in their composition [8; 9; 10]. Therefore, replacing synthetic detergents with natural cleaning products would be beneficial [8; 9]. A natural cleaning product is one made only from natural ingredients, without synthetic or artificial ingredients [11]. Natural soap is made from ingredients originating from fruit/plants in nature, while detergents are manufactured from synthetic sources (petroleum fractions). Generally, a detergent contains a surfactant, chelators, dispersing agent, stabilizers and perfume, which cause the wastewater to be loaded with non-ecological products, some of which are non-biodegradable [12]. The design of a laundry soap formulation recipe should take into account the participation in the saponification process of a small number of non-polluting chemicals, such as vegetable oils or animal fats, and an alkali such as NaOH [13; 14]. It is known that, during saponification, a hydrolysis reaction occurs due to the nucleophilic attack of the hydroxyl ion (from alkalis) on the C=O group in the ester bonds existing in the triglyceride molecule. As a result, these ester bonds break (between glycerol and the three fatty acids linked to it), resulting in fatty acid salts (soaps) and glycerin [15]. A similar hydrolysis reaction occurs if enzymes (such as lipases) are used under certain conditions (lower temperatures and neutral pH); so, enzymatic hydrolysis can be considered an alternative to conventional saponification [16; 17; 18]. To further minimize the environmental impact or improve the efficiency of soap, eco-friendly alternatives can be used that target both the substances used in saponification (sustainable, biodegradable, natural, ethically sourced and plant-based fats/oils and additives) and the processing techniques (more energy-efficient, such as cold processing or in microreactors equipped accordingly to minimize water consumption and waste generation). Non-irritating, non-polluting soaps can be obtained through cleaner saponification processes in which the use of auxiliaries and additives (compounds containing Fe, Cu, Zn, Cr, and Mn ions, borax, ethyl alcohol, stearic acid, pigments, etc.) is avoided [19; 20]. The ions mentioned should be avoided in soap formulation because they can generate insoluble soaps, ineffective for washing [21]. The nature of the metal ion influences the solubility and stability of the soap in solutions.