## 1 Introduction  
The industrial growth and modernization of the world have progressively caused the depletion of fossil resources and serious environmental problems, which has led to a global interest in the search for alternative fuels that can be used in diesel engines. These new fuels must be characterized by coming from renewable resources, minimizing environmental impact, and being economically viable [1,2]. Biodiesel appears to be a promising solution, as it allows the continued use of existing technology of internal combustion engines, either purely or combined with diesel [3]. Other advantages of using biodiesel are its lower sulfur and aromatic content, and higher flash point compared to diesel. These characteristics make biodiesel safer to handle, and biodegradable [4]. In addition, its chemical composition contributes to a reduction in carbon monoxide, carbon dioxide, hydrocarbons, and soot emissions [5]. Among the different products for the production of biodiesel, palm oil stands out due to its properties similar to diesel from regular petroleum [6; 7]. These characteristics have caused the biodiesel derived from palm oil to be been widely investigated. However, the use of edible vegetable oils is related to environmental problems, such as deforestation, soil destruction, and consumption of much of the arable land [8]. In addition, biofuels are criticized for the use of feedstocks that could also be used as food resources. Therefore, not all of them are economically profitable, as they can be considered to be food crops [9]. Because of this, the selection of edible vegetable oils as a potential biodiesel feedstock cannot be considered a long-term option. A researched alternative is the production of biodiesel through the use of residual palm oil, which can eliminate the problems associated with the use of edible oils and reduce pollution from this type of waste [10]. In particular, the palm oil industry produces a large amount of waste in the liquid or solid form [11]. It is reported that only 10% of the biomass produced in palm oil farms is converted for edible use; the remaining 90% is polluting waste material [12; 13]. Among the by-products of palm, oil residues are residual palm oil, fatty acid residues, residual oil from the empty futon cluster, residual oil from the palm decenter cake, and industrial liquid waste [14]. The use of palm oil residues, in addition to positively impacting the environment, have certain economic advantages. Studies show that the cost of production of palm oil residues is 20% to 30% lower when compared to refined vegetable oil [15], the raw material is abundant and at a reduced price [16]. Additionally, a large amount of waste from used cooking oil (UCO) is progressively generated by homes, restaurants, and food processing industries. This type of waste has been investigated for the production of biodiesel [17; 18; 19]. However, the higher content of fatty acids, the percentage of water, and the lower calorific value compared to standard diesel have caused a reduction in the viability of using UCO as a raw material for the production of biodiesel [14]. Due to the above, alternative forms are required for the use of UCO as a raw material in the generation of biodiesel, which would contribute to the reduction of pollution problems associated with the UCO. Among the different types of residual cooking oils, sunflower oil has a relatively high energy density, which makes it a promising material for biofuel production [20; 21]. [PERSON] and [PERSON] [22] concluded that the properties of biodiesel produced from sunflower oil are within the ASTM (American Society for Testing and Materials) international standards. However, high viscosity remains a problem for its massive implementation. The production of biodiesel from blends of different types of raw material is one of the methods investigated to produce biodiesel with properties closer to conventional diesel. [PERSON] et al. [23] investigated several blends of biodiesel produced from sunflower oil and soybean oil.