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Previous issue date: 2014-09-24 === Um dos principais problemas relacionados ? utiliza??o do ?leo diesel como
combust?vel ? a presen?a de enxofre (S) que provoca polui??o no meio ambiente e
corros?o nos motores. Com o intuito de minimizar as consequ?ncias decorrentes da
libera??o deste poluente, a legisla??o brasileira estabeleceu limites m?ximos de teor de
enxofre que os combust?veis podem apresentar. Para atender ?s exig?ncias, o ?leo
diesel com concentra??o m?xima de enxofre igual a 10 mg/kg (S10) vem sendo
amplamente comercializado no pa?s. Entretanto, a redu??o no teor de enxofre pode
acarretar mudan?as nas propriedades f?sico-qu?micas do combust?vel, as quais s?o
essenciais para o desempenho dos ve?culos. Este trabalho tem como objetivo a
identifica??o das principais mudan?as nas propriedades f?sico-qu?micas do ?leo diesel
e como elas est?o relacionadas ? redu??o do teor de enxofre. Foram testadas amostras
de ?leo diesel dos tipos S10, S500 e S1800 de acordo com as metodologias da
American Society for Testing and Materials (ASTM). As propriedades f?sico-qu?micas
de massa espec?fica, ponto de fulgor, viscosidade cinem?tica e propriedades a baixa
temperatura foram determinadas. Os ?leos tamb?m foram caracterizados por
termogravimetria (TG) e submetidos ? destila??o f?sica (ASTM D86) e destila??o
simulada por cromatografia gasosa (ASTM D2887). Os resultados da caracteriza??o
f?sico-qu?mica mostraram que a redu??o do enxofre tornou os combust?veis mais leves
e fluidos, permitindo uma maior aplicabilidade a ambientes com baixas temperaturas e
uma maior seguran?a para o transporte e armazenamento. Atrav?s dos dados de
destila??o simulada foi observado que a diminui??o do teor de enxofre provocou
aumento das temperaturas de ebuli??o das fra??es iniciais e a redu??o das
temperaturas de ebuli??o das fra??es m?dias e pesadas. A TG revelou um evento de
perda de massa, atribu?do ? volatiliza??o ou destila??o de hidrocarbonetos leves e
m?dios. A partir destes dados, o comportamento cin?tico das amostras foi estudada e
verificou-se que as energias de ativa??o (Ea) pouco variaram ao longo da convers?o.
v
Considerando a m?dia dessas energias, o S1800 apresentou a Ea mais elevada no
decorrer da convers?o e o S10 os menores valores === One of the main problems related to the use of diesel as fuel is the presence of sulfur
(S) which causes environmental pollution and corrosion of engines. In order to
minimize the consequences of the release of this pollutant, Brazilian law established
maximum sulfur content that diesel fuel may have. To meet these requirements, diesel
with a maximum sulfur concentration equal to 10 mg/kg (S10) has been widely
marketed in the country. However, the reduction of sulfur can lead to changes in the
physicochemical properties of the fuel, which are essential for the performance of road
vehicles. This work aims to identify the main changes in the physicochemical
properties of diesel fuel and how they are related to reduction of sulfur content.
Samples of diesel types S10, S500 and S1800 were tested according with the methods
of the American Society for Testing and Materials (ASTM). The fuels were also
characterized by thermogravimetric analysis (TG) and subjected to physical distillation
(ASTM D86) and simulated distillation gas chromatography (ASTM D2887). The
results showed that the reduction of sulfur turned the fuel lighter and fluid, allowing a
greater applicability to low temperature environments and safer for transportation and
storage. Through the simulated distillation data was observed that decreasing sulfur
content resulted in higher initial boiling point temperatures and the decreasing of the
boiling temperature of the medium and heavy fractions. Thermogravimetric analysis
showed a loss event mass attributed to volatilization or distillation of light and medium
hydrocarbons. Based on these data, the kinetic behavior of the samples was
investigated and it was observed that the activation energies (Ea) did not show
significant changes throughout conversion. Considering the average of these energies,
the S1800 had the highest Ea during the conversion and the S10 the lowest values
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