New approach to the determination of free glycerol in biodiesel based on oxidation with periodate

Autor: Santos, Luana de Oliveira
Přispěvatelé: Rocha Junior, Jose Geraldo, Barra, Cristina Maria, Teixeira, Viviane Gomes, Cordeiro, Fl?vio Couto
Jazyk: portugalština
Rok vydání: 2019
Předmět:
Zdroj: Biblioteca Digital de Teses e Dissertações da UFRRJ
Universidade Federal Rural do Rio de Janeiro (UFRRJ)
instacron:UFRRJ
Popis: Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2022-01-18T03:20:50Z No. of bitstreams: 1 2019 - Luana de Oliveira Santos.pdf: 2002415 bytes, checksum: b8c0a85709898741cd1f79f84fa96f9c (MD5) Made available in DSpace on 2022-01-18T03:20:50Z (GMT). No. of bitstreams: 1 2019 - Luana de Oliveira Santos.pdf: 2002415 bytes, checksum: b8c0a85709898741cd1f79f84fa96f9c (MD5) Previous issue date: 2019-10-29 CAPES - Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior CNPq - Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico The quality standards for biodiesel commercialized in Brazil are set by the National Agency of Petroleum, Natural Gas and Biofuel (ANP), through Brazilian Resolution No. 45 of 2014 (RANP 45/2014). RANP 45/2014 sets the maximum free glycerol content in biodiesel added to diesel oil at 0.02% w/w. The higher free glycerol content could to lead troubles in fuel storage tanks, formation of deposits and clogging in the engine injection system and emission of toxic aldehydes. In this work, a new approach to determine free glycerol in biodiesel from soybean, palmist, macauba (pulp) and used frying oils was developed employing the glycerol oxidation by the periodate and, after, masking of the excess periodate by the molybdate. This provided a decrease in the oxidation time probably due to excess periodate employed. The iodate formed in oxidation of glycerol was quantified by the addition of iodide, forming the tri-iodide anion. The iodometric determination was performed in three days with spectrophotometric and titrimetric techniques. In the spectrophotometric method, the glycerol was extracted by partition in ethanol-water/n-heptane and the tri-iodide was determined in the presence of starch (? = 582 nm). Two analytical curves were constructed after analysis of glycerol standards in a dual and single beam spectrophotometer. The latter had lower precision in the measurements, and its analytical curve presented low limits of detection (1.9 mg L-1) and quantification (5.7 mg L-1), and good coefficient of determination (R2 = 0.9972). The repeatability of spectrophotometric method was satisfactory (CV < 12%), however the intermediate precision was unfavorable (CV < 39%), according to ANOVA free glycerol contents obtained between the days. The analysis of glycerol standards in water by titrimetric method was done by the titration of tri-iodide with Na2S2O3 standard solution, in the presence of starch, and presented excellent accuracy, with relative errors below 3.0%. Detection and quantification limits were 1.2 mg L-1 and 3.5 mg L-1, respectively. Biodiesels were analyzed by titrimetric method after glycerol extraction by partition in water/n-heptane. The precision of this method was good in repeatability (CV < 14%) and intermediate precision (CV < 8%), evaluated by ANOVA. The accuracy of the titrimetric method was evaluated by recovery tests at three fortification levels: 250, 500 and 1000 mg L-1, reaching 91% to 105% of recovery. The average global levels of free glycerol levels in the biodiesels obtained by both methods did not differ significantly at the 95% confidence level, according to the Student's t-test. However, the titrimetric method presented smaller variations between days, lower cost and greater simplicity compared to the spectrophotometric method. In addition, the analyses were quick (10 min) when compared to the other techniques described in the literature and lower detection limit compared to other titrimetric methods. Os padr?es de qualidade para o biodiesel comercializado no Brasil s?o estabelecidos pela Ag?ncia Nacional de Petr?leo, G?s Natural e Biocombust?veis (ANP), por meio da Resolu??o Brasileira n? 45 de 2014 (RANP 45/2014). A RANP 45/2014 estipula o teor m?ximo de 0,02% m/m de glicerol livre no biodiesel adicionado ao diesel. Maiores concentra??es de glicerol podem levar a problemas nos tanques de armazenamento do combust?vel, forma??o de dep?sitos e entupimento no sistema de inje??o do motor, al?m de emiss?o de alde?dos t?xicos. Neste trabalho, uma nova abordagem para a determina??o de glicerol livre em biodieseis provenientes de ?leos de soja, palmiste, maca?ba (polpa) e fritura foi desenvolvida empregando a oxida??o do glicerol com periodato e mascaramento do periodato excedente com molibdato. Isto diminuiu o tempo requerido para a oxida??o, pelo excesso de periodato empregado. O iodato formado na oxida??o do glicerol foi quantificado a partir do ?nion tri-iodeto produzido ap?s adi??o de iodeto. A determina??o iodom?trica foi realizada empregando as t?cnicas espectrofotom?trica e titrim?trica, em tr?s dias de an?lise. O m?todo espectrofotom?trico foi baseado na extra??o do glicerol por parti??o em etanol-?gua/n-heptano, e determina??o do tri-iodeto na presen?a de amido, em ? = 582 nm. Duas curvas anal?ticas foram constru?das a partir da leitura de padr?es de glicerol em espectrofot?metro de feixe duplo e ?nico. Este ?ltimo gerou medidas de maior precis?o e curva anal?tica com baixos limites de detec??o (1,9 mg L-1) e quantifica??o (5,7 mg L-1), e coeficiente de determina??o (R2) de 0,9972. Na an?lise dos biodieseis, a repetibilidade do m?todo foi satisfat?ria (CV < 12%), ao contr?rio da precis?o intermedi?ria (CV < 39%), segundo a ANOVA dos teores de glicerol livre obtidos entre os dias. O m?todo titrim?trico foi aplicado na an?lise de padr?es aquosos de glicerol, a partir da titula??o do tri-iodeto com solu??o padr?o de Na2S2O3, na presen?a de amido, e apresentou excelente exatid?o, com erros relativos inferiores a ? 3,0%. Limites de detec??o e quantifica??o de 1,2 mg L-1 e 3,5 mg L-1, respectivamente, foram encontrados a partir de uma curva de resposta. Para a an?lise titrim?trica dos biodieseis, foi realizada anteriormente, a extra??o do glicerol livre por parti??o em ?gua/n-heptano. A precis?o deste m?todo foi boa em n?vel de repetibilidade (CV < 14%) e em termos de precis?o intermedi?ria (CV < 8%), avaliada pela ANOVA. A exatid?o do m?todo titrim?trico foi avaliada frente a testes de recupera??o em 3 n?veis de fortifica??o: 250, 500 e 1000 mg L-1 e alcan?ou entre 91% e 105% de recupera??o. Os teores m?dios globais de glicerol livre nos biodieseis obtidos pelos dois m?todos n?o diferiram significativamente ao n?vel de confian?a de 95%, segundo teste t de Student. No entanto, o m?todo titrim?trico apresentou menores varia??es entre os dias, menor custo e maior simplicidade em compara??o ao m?todo espectrofotom?trico. Al?m disso, permite quantificar o glicerol no biodiesel em um curto tempo (cerca de 10 minutos), quando comparado ?s demais t?cnicas de an?lise descritas na literatura, e apresenta um menor limite de detec??o, em compara??o a outros m?todos titrim?tricos.
Databáze: OpenAIRE
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