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- A brief review of the supercritical antisolvent (SAS) technique for the preparation of nanocatalysts to be used in biodiesel productionPublication . Santos, Samuel; Puna, Jaime; Gomes, João F. P.In an era where sustainability is becoming the main driving force for research and development, supercritical fluids-based techniques are presented as a very efficient alternative technology to conventional extraction, purification, and recrystallization processes. Supercritical antisolvent (SAS) precipitation is a novel technique that can replace liquid antisolvent precipitation techniques. Additionally, through the optimization of precipitation operating conditions, morphology, particle size, and particle size distribution of nanoparticles can be controlled. As an antisolvent, supercritical carbon dioxide (scCO2) is far more sustainable than its conventional liquid counterparts; not only does it have a critical point (304 K and 73.8 bar) on its phase diagram that allows for the precipitation processes to be developed so close to room temperature, but also its recovery and, consequently, the precipitated solute purification stage is considerably simpler. This technique can be used efficiently for preparing nanocatalysts to be used in biodiesel production processes.
- New process for simultaneous removal of CO2, SOX and NOXPublication . Santos, Samuel; Duarte, A. P.; Bordado, João; Gomes, JoãoA method for simultaneous removal of CO2, SOX and NOX from industrial flue gases through the injection of ozone diluted in nitrogen, oxygen or nitrogen/oxygen mixtures, as an oxidizing agent and with the addition of specific sequestrants, that induce the precipitation of nitrates and sulphates, is presented. This new process is related with the conventional CO2 removal method using chemical absorption, but presents as main innovation the possibility to remove also simultaneously SOX and NOX.
- A review on bio-based catalysts (immobilized enzymes) used for biodiesel productionPublication . Santos, Samuel; Puna, Jaime; Gomes, JoãoThe continuous increase of the world's population results in an increased demand for energy drastically from the industrial and domestic sectors as well. Moreover, the current public awareness regarding issues such as pollution and overuse of petroleum fuel has resulted in the development of research approaches concerning alternative renewable energy sources. Amongst the various options for renewable energies used in transportation systems, biodiesel is considered the most suitable replacement for fossil-based diesel. In what concerns the industrial application for biodiesel production, homogeneous catalysts such as sodium hydroxide, potassium hydroxide, sulfuric acid, and hydrochloric acid are usually selected, but their removal after reaction could prove to be rather complex and sometimes polluting, resulting in increases on the production costs. Therefore, there is an open field for research on new catalysts regarding biodiesel production, which can comprise heterogeneous catalysts. Apart from that, there are other alternatives to these chemical catalysts. Enzymatic catalysts have also been used in biodiesel production by employing lipases as biocatalysts. For economic reasons, and reusability and recycling, the lipases urged to be immobilized on suitable supports, thus the concept of heterogeneous biocatalysis comes in existence. Just like other heterogeneous catalytic materials, this one also presents similar issues with inefficiency and mass-transfer limitations. A solution to overcome the said limitations can be to consider the use of nanostructures to support enzyme immobilization, thus obtaining new heterogeneous biocatalysts. This review mainly focuses on the application of enzymatic catalysts as well as nano(bio)catalysts in transesterification reaction and their multiple methods of synthesis.