S?ntese do biodiesel: estudo da influ?ncia de sais de metais alcalinos na cin?tica da metan?lise em meio b?sico

• Autor(a) principal: Campos, Daniel Ananias Reis de
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFRRJ
• Texto Completo: https://tede.ufrrj.br/jspui/handle/jspui/4356
• topic: refratometria; transesterifica??o; cat?lise alcalina; biocombust?veis; refractometry; transesterification; alkaline catalysis; biofuels; Qu?mica

To evaluate the influence of sodium and potassium ions on the kinetics of soybean oil methanolysis with CH3ONa, a study was carried out using different salts (CH3COOK, CH3COONa, KI, KBr, KCl and NaCl) in this reaction. The conditions employed were: 40.0, 50.0 and 60.0 ? C temperatures and speed agitation of 400 and 800 rpm. The observed velocity constants (kobs) were determined from the data obtained by the on-line monitoring of the refractive index of the reaction mixture. The kobs were compared and it was concluded that the stirring speed has a greater influence on the kobs than the effects caused by the temperature increase or the additives employed. Both alkaline ions (K+ and Na+) provided an increase in the values of the kobs by the stabilization of the transition state structure. CH3COOK was the most efficient additive because it increases the kobs values at all three temperatures and in both speed agitation. The increase in kobs ranged from 21% (400 rpm and 40.0 ?C) to 90% (800 rpm and 40.0 ?C) and the most substantial increase occurred at 800 rpm. CH3COONa was less effective than CH3COOK so the increase of kobs was from 3.1% (800 rpm and 60.0 ?C) to 60% (800 rpm and 40.0 ?C). The K+ ion gave better results because it forms a less stable ionic pair with the methoxide in relation to Na+, which provides less activation energy for reactions with potassium salts. In general, chlorides (KCl and NaCl) negatively affected methanolysis at 400 rpm, but KCl increased kobs at 400 rpm and 40.0 ?C. The KI brought improvements in kobs values similar to those of the CH3COOK at 400 rpm, but they were indifferent at 800 rpm. The use of KBr provided an increase in the kobs value in 34% at 800 rpm and 40.0 ?C and statistically null effect in the other reactional conditions studied.