## 1 Introduction  
The growing interest in processes that can combine economical savings and environmental preservation has driven not only research groups but also industry to find alternative technologies and methods that conform to Green Chemistry principles [1]. It was not a tough challenge to combine the interests of society, industry, and scientific groups when it has become clear that applying these principles is economically profitable [2]. The first concepts regarding Green Chemistry arose in 1990 and, since its creation, it has been based on improving design to reduce consumption of raw materials rather than treating waste [2, 3]. Anastas and Warner introduced, in 1998, the guidelines necessary to redesign processes and products systematically, more known as The Twelve Principles of Green Chemistry [3]. Even before the introduction of the concepts of Green Chemistry, stimulated by the international petroleum crisis from the 1970s, the search for renewable energy sources led to the discovery of biofuel as the most promising alternative to the use of fossil fuels, since it is appropriate for the transportation sector, responsible for 57% of the global oil demand and for 24% of direct CO\({}_{2}\) emissions [4, 5, 6]. Considering the significant share of the transportation sector on the Greenhouse Gases emissions and on the air quality of cities, replacing fossil fuel with biofuel arises as a promising alternative to diminish emissions, specially where the renewable alternative does not seem to be extensively applied, for instance, in jet and maritime fuel. Biodiesel manufacture is a well-established process with billions of gallons being produced yearly; however, it still has room for improvements to maximize the economic value and minimize the environmental impact, especially in what concerns diminishing waste production [7, 8]. Avoiding the generation of waste is so relevant that it has been highlighted as one of the main issues since the first discussions about environmental preservation. In 1980, Roger Sheldon proposed a metric to measure the production efficiency taking into account the amount of waste generated, the E-factor [9]. The first principle of Green Chemistry, indeed, is waste preservation [3]. The main production process of biodiesel is the catalyzed transesterification of triglycerides with an alcohol (mainly methanol and ethanol), generating an ester (biodiesel) and glycerol (by-product) (Figure 1) [10]. The main environmental disadvantage of the biodiesel industry is the massive amount of glycerol generated as by-product, at a rate of 10-12% and a purity of about 50-55% [11]. Since 68% of the glycerol supply comes from the biodiesel industry, the expected growth in the supply of this commodity follows the tendency of the biofuel industry, with a growth rate of 5.2% until 2027 [12, 13]. In fact, the side production of glycerol, viewed as a problem in the past, helped to alleviate the economic pressure over biodiesel plants as a consequence of the demand reduction by the COVID-19 pandemic, because as less biodiesel was produced, the market felt glycerol supply pressure, and its prices rose to levels not seen in years. However, it is relevant to note that this effect was not due to a lack of glycerol on the market, but due to logistics problems caused by the mobility restrictions. Glycerol is viewed as a safe chemical in terms of supply [12, 14]. Despite that temporary shortcut, glycerol supply continues to expand at a much faster pace than the new applications to absorb it. Many alternatives have been studied to avoid treating this chemical as waste [15]. The alternatives are particularly interesting if the use of crude glycerol is enabled, without the need of purifying it [16]. Refined glycerol has found numerous applications in cosmetics, pharmaceuticals, and food industries for a long time and, by 2019, this segment accounted for 65.1% of the glycerol market [17, 18].