Uso do rejeito de vermiculita ativado como adsorvente na purificação de biodiesel de soja catalisado por CaO de cascas de ovos de galinha

Abstract

The growing increase in global warming and environmental pollution resulting from the use of fossil resources available in nature and the scientific-technological advances of society has motivated the study of new renewable sources of energy to meet human needs and at the same time reduce environmental problems. As alternatives to replace petroleum and its derivatives, biofuels appear, especially biodiesel, for being biodegradable, non-toxic and for reducing the emissions of polluting gases. This biofuel is commonly obtained by the transesterification route, where triacylglycerol molecules react with alcohol to form biodiesel and glycerol as a co-product. Usually, this reaction is catalyzed by a strong homogeneous base and its final washing process to remove impurities is done with water. However, heterogeneous catalysis and the adsorbent purification process have been studied because they have, respectively, the advantage of reusing the catalyst and eliminating washing steps. In this sense, the present study aimed to obtain CaO from the calcination of chicken eggshells at different temperatures (650, 700, 800 and 900 °C) for a period of 2 hours, in order to evaluate the potential as a catalyst in the transesterification reactions from soybean oil into biodiesel, in addition to using a new method of purification of this biofuel using vermiculite waste (RVA adsorbent) as an alternative to traditional wet washing. Characterizations by XRD, FTIR, BET, Experimental Density, Zeta potential, Particle size distribution, EDX and TGA/DrTGA were carried out for the residues and the catalysts. The catalytic tests were divided into four (4) steps to evaluate the conversion into esters and the final yield of biodiesel (mass of oil/mass of biodiesel). In the first step, all catalysts achieved high conversion to esters of 98.27, 98.60, 98.58 and 96.96% for OC65, OC7, OC8 and OC9, respectively. However, the final yield results between the mass of soybean oil and the mass of biodiesel obtained from the reaction (m/m) after wet washing were relatively low, with the highest value of 34.30% for biodiesel catalyzed by OC7. Thus, in the consecutive steps, the OC7 catalyst was adopted, however, applying the dry washing process, using vermiculite tailings, to re-evaluate the two aforementioned parameters. In the second stage, the conversion to esters was 98.46% and the final yield increased considerably by 2.8 times when compared to the first stage, obtaining 97.45%. In order to further evaluate the feasibility of the dry cleaning process, in a third and fourth step, modifications were made to the parameters reaction temperature and oil:alcohol molar ratio. The results obtained for both stages were, respectively, 94.40% and 96.94% of conversion into esters, and 95.10% and 84.30% of the final biodiesel yield after dry cleaning, confirming its efficiency. Also, when physical-chemical analyzes of acidity, iodine and density were carried out, these results were identified as required in relation to the limits for commercialization established by regulatory bodies such as the ANP. Therefore, from the results obtained, the OC7 sample, produced with the differential of reducing the energy costs involved with the calcination process, is validated as a potential heterogeneous and environmentally beneficial catalyst for the production of biodiesel in a more sustainable way. In addition to the use of RVA tailings as an adsorbent in dry cleaning, presenting the advantages of increasing the final yield of biodiesel and drastically reducing the generation of aqueous effluents, making the process ecologically correct and reducing costs.