Controle de qualidade de biodieseis de macaúba e algodão e suas misturas com o diesel usando espectrometria no infravermelho médio e cartas de controle multivariadas

Abstract

The Law No. 13.033/2014 establishes the addition of 7 ± 0.5% (v/v) of biodiesel to the diesel used in the road system and prohibits the addition of vegetable oils or any solvents to this mixture. However, there are cases of irregular addition of vegetable and/or waste oils in diesel, mainly due to the low cost of these raw materials when compared to the final or contaminated product during transportation and storage. Thus, analyzes are necessary to provide immediate and efficient responses in order to ensure the quality of the marketed fuels. In this sense, the present study proposed the quality monitoring of biodiesel/diesel blends (7% biodiesel and 93% diesel) through the use of the Medium Infrared Spectrometry associated with Multivariate Control Charts based on the liquid analytical signal (NAS). Biodiesel was produced from macaúba (acrocomia aculeate) and cotton oils using methanol and ethanol. For each model, three charts were developed: the NAS Chart, which corresponds to the analyte of interest (in this case biodiesel); the interfering chart, related to the contributions of other components in the sample (diesel); and the waste chart, corresponding to non-systematic variation in spectra (instrumental noise). A total of 1508 samples were used for the calibration and validation of the six models (ethyl and cotton biodiesel, macaúba almond (acrocomia aculeate) methyl biodiesel, macaúba mesocarp (acrocomia aculeate) methyl and biodiesel, and also commercial B7 biodiesel). At the calibration stage, 103 samples were used within the quality specifications, these samples were used to establish the statistical limits for each chart. The validation step was carried out with samples within and out of the quality specifications (1405 samples). The validation with non-standard quality samples was carried out in two ways: in relation to the biodiesel content in diesel and the presence of adulterants in biodiesel, diesel and blend. The presence of adulterants was due to the partial replacement of biodiesel by soybean, corn and residual oils; the partial replacement of diesel by lubricating oil, kerosene and gasoline; and by direct addition of the adulterants mentioned in the biodiesel/diesel blend (B7) in the range of 3.5 to 43.5% (v/v) corresponding to an adulteration range of 0.2 to 30% (v/v) in the blend. Thus, it was possible to separate the conforming and non-conforming samples, both regarding the biodiesel content in diesel and the presence of adulterants, since the samples within the specifications were within the established limits, and the samples out of the specifications have exceeded the limit in least one of the charts. Thus, the results have showed that the method described in this study is a viable, efficient and fast alternative to the biofuel quality control.