Green Production of a High-Value Branched-Chain Diester: Optimization Based on Operating Conditions and Economic and Sustainability Criteria  
[PERSON]. have a biocatalytic alternative [3], which may be also eco-friendlier, as has been pointed out by studies of Life Cycle Assessment [4] or green calculations [5]. In addition, the use of enzymatic biotransformations in the cosmetic sector can contribute to achieving a \"natural\" designation [6], which has proved to be an increasingly effective marketing claim, as consumers often perceive natural cosmetics as safer, healthier, and more respectful with the environment [7]. In this sense, many examples of the lipase-based synthesis of compliant monoesters can be found in the literature [8; 9; 10; 11], and even some processes have successfully been implemented at an industrial scale [12]. In recent years, the interest in BCEs to obtain everyday-use products has increased due to their technical features at low temperatures [13]. In some cases, they contribute to expanding the concept of sustainability to the product itself: some BCEs are studied for obtaining greener alternatives to mineral-based lube bases due to their biodegradability [14; 15]; others can be used as biodiesel additives to improve their pour and cloud point and their low-temperature filterability [16; 17]. In addition, several BCEs have been described as adequate substitutes for cyclomethicones [18], whose use as a cosmetic ingredient has been banned in the European Union at concentrations above 1% from January 2020 [19]. Actually, BCEs such as NPGDL are widely used in the cosmetic industry as embollients, surfactants, and emulsifying or skin-conditioning agents [20]. In light of the above-mentioned, biocatalysis appears to be an interesting eco-friendly alternative for obtaining BCEs. In the case of the synthesis of esters from polyols, lipases from different origins have been tested with different outcomes [21; 22; 23; 24]. For example, [PERSON] et al. [21] studied the production of bioblubricants from neopentyl glycol and soybean biodiesel catalyzed by two lipases from _Rhizomuocor miehei_ (Rml) and _Candida antarctica_ (CalB), obtaining better results with the first one. On the contrary, a conversion of 98% was achieved by [PERSON] et al. [22] using the same CalB preparation in transesterification reactions with neopentyl glycol and trimethylolpropane. In fact, these enzymes have different structural features that may be decisive for their catalytic activity under certain conditions. According to [PERSON] et al. [25], the binding pocket of Rml has the shape of a bowl with a long axis that makes room for long fatty acids. On the other hand, CalB has a funnel-like binding site, which makes it more appropriate for short and medium fatty acids up to C13. Nevertheless, [PERSON] et al. [26] describe those enzymes as completely the opposite: CalB's active site would have a large acyl binding cleft but narrow space for alcohols, while Rml may find restrictions to accommodate the acid part but not the alcohol. As it seems unlikely to establish a priori the best lipase-based catalytic preparation, this work studies the performance of two commercial biocatalysts, Novozym(r) 40086 (Rml) and Novozym(r) 435 (CalB), in the esterification process of neopentyl glycol (NPG) and lauric acid (LA) under solvent-free conditions to produce NPGDL, a BCE used in the cosmetic industry (Figure 1). The main objective of this present study is the proposal of a new way of manufacturing NPGDL for commercial exploitation. Therefore, it is important to include an economic study in order to select the most profitable alternative. The calculation of the process' direct costs should include energy consumption, raw materials, and the biocatalyst. As with any process using immobilized enzymes, the reuse of the enzymes must be possible to be economically attractive.