Citation: R˘ aducanu, C.E.; Dobre, T.; Mih˘ aiescu, D.E.; Moro¸ san, A.; Jidveian, R.; Cioroiu Tîrpan, D.R.; Vasiliu, A.D.; Gogoa¸ s˘ a, C.I.; Pârvulescu, O.C.; Tric˘ a, B. Synthesis of Guanidine and Its Deposition on Bacterial Cellulose as Green Heterogeneous Catalyst for Transesterification to Methyl Esters. Energies 2024, 17, 1344. https:// doi.org/10.3390/en17061344 Academic Editor: Eugenio Meloni Received: 24 January 2024 Revised: 25 February 2024 Accepted: 1 March 2024 Published: 11 March 2024 Copyright: © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Synthesis of Guanidine and Its Deposition on Bacterial Cellulose as Green Heterogeneous Catalyst for Transesterification to Methyl Esters Cristian Eugen Răducanu 1 ,Tănase Dobre 1,2, *, Dan Eduard Mihăiescu 3 , Alina Moro¸ san 3 , Roxana Jidveian 1 , Doinit , a Roxana Cioroiu Tîrpan 4 , Alexandru Dan Vasiliu 1 , Cristina Ionela Gogoa¸ să 1 , Oana Cristina Pârvulescu 1 and Bogdan Trică 5 1 Department of Chemical and Biochemical Engineering, National University of Science and Technology Politehnica Bucharest, 1-7 Gheorghe Polizu St., 011061 Bucharest, Romania; cristianrdcn1@yahoo.com (C.E.R.); rjidveian@gmail.com (R.J.); vasiliudanalexandru1994@yahoo.com (A.D.V.); cristina_ionela_92@yahoo.com (C.I.G.); oana.parvulescu@yahoo.com (O.C.P.) 2 Technical Sciences Academy of Romania, 26 Dacia Blvd., 030167 Bucharest, Romania 3 Department of Organic Chemistry, National University of Science and Technology Politehnica Bucharest, 1-7 Gheorghe Polizu St., 011061 Bucharest, Romania; dan.mihaiescu@upb.ro (D.E.M.); alina.morosan@upb.ro (A.M.) 4 Department of Chemistry and Chemical Engineering, Ovidius University of Constan¸ ta, 124 Mamaia Blvd., 900527 Constan¸ ta, Romania; tirpanroxana@gmail.com 5 National Institute for Research Development for Chemistry and Petrochemistry-ICECHIM, 202 Spl. Independentei, S6, 060021 Bucharest, Romania; bogdan.trica@icechim.ro * Correspondence: tghdobre@gmail.com Abstract: Green catalysts used in the transesterification reaction of biodiesel must have biodegrad- ability and non-toxicity as their main characteristics, being thus friendly to the environment, since they perform in processes in which the content of CO 2 , which is increasing from year to year, should be reduced. As a consequence, their manufacture can be extremely rigorous. This work presents the two-step construction, synthesis, and deposition of such a green heterogeneous catalyst and its testing in the catalysis of the transesterification of triglycerides with methanol, resulting in methyl esters. A CSTR-type reactor was used to perform transesterification, and the biodiesel yields obtained had values in the range of 91.7–95.7%, using 2, 3, and 4 g/g catalyst to oil, under conditions like those for obtaining commercial biodiesel in homogeneous catalysis, i.e., a 65 ◦ C process temperature and a 4:1, 5:1 or 6:1 methanol-to-oil molar ratio. Keywords: bacterial cellulose; superbase synthesis; synthesis of guanidine; green heterogeneous catalyst; transesterification; methyl esters 1. Introduction Typical diesel fuel is obtained from oil, which is responsible for a major part of the greenhouse effect and is non-renewable, so in 50–100 years it could become unexploitable [1–3]. Currently the profitable exploitation of oil is characterized by the following: (i) non- uniform availability; (ii) best availability mostly in areas of permanent conflict; (iii) financial instability in specific markets; (iv) quasi-dependence on politics; (v) huge extractive or refining facilities, whose costs (execution or maintenance and especially security today) become real barriers for some and allow only certain actors to play in this field. Biofuels, on the other hand, do not produce a greenhouse effect through use, so they are of particular interest. Biodiesel, the second most produced biofuel, has properties similar to classic diesel and features that can recommend it as an alternative: (i) it can be obtained in any quantity, so it does not necessarily require huge facilities, although production capacity is currently only governed by demand or certain environmental regulations imposed; (ii) it can be obtained Energies 2024, 17, 1344. https://doi.org/10.3390/en17061344 https://www.mdpi.com/journal/energies