O conteúdo dos artigos e seus dados em sua forma, correção e confiabilidade são de responsabilidade exclusiva dos autores. 2018 Permitido o download da obra e o compartilhamento desde que sejam atribuídos créditos aos autores, mas sem a possibilidade de alterá-la de nenhuma forma ou utilizá-la para fins comerciais.

Current specifications for gasoline impose strong restrictions on the content of aromatic compounds. Isomerization of normal paraffins to isoparaffins is considered an important petroleum reaction for the production of clean gasoline to improve its Research Octane Number (RON) and Motor Octane Number (MON). The isoparaffins are considered as an alternative to the use of oxygenated and aromatic compounds, whose maximum contents are subjected to strict regulations in order to protect the environment. In this work, catalysts supported on mordenite were obtained by competitive ion exchange using aqueous solutions of platinum complexes. Different concentrations of platinum were tested for the isomerization of n-hexane. All the catalysts obtained were shown to be selective to the formation of isomers with high-octane number, which are the products of greatest interest in the oil refining industry. The highest conversion and the best selectivity for 2,3-dmC 4 di-branched component, the isomer with the highest octane number, were found with the 1.10 wt% Pt/HMOR.

Increasing rates of non-carious cervical lesions due to dental erosion, exposure of dentinal tubules, and hypersensitivity to environmental stimuli have led to the development of new prevention strategies. This study evaluated the effects of a low-intensity diode laser (λ = 808 nm) on the dentinal chemical composition and prevention of demineralization. In addition, the study monitored temperature changes during the course of irradiation. Forty dentin specimens were randomly allocated into four groups (n = 10): G1 - No treatment (control), G2 - irradiated with 15 J/cm(2), G3 - irradiated with 30 J/cm(2), and G4 - irradiated with 60 J/cm(2). Each specimen was partially covered with nail varnish, treated according to the group irradiation levels, and exposed to an erosive challenge (1.0 M hydrochloric acid) for 5 min. Afterwards, dentin loss was profilometrically analyzed and examined by scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX). Intrapulpal temperatures were measured during the dentin irradiation. One-way ANOVA and Tukey tests (p < 0.05) were performed to assess differences. For all irradiated groups, intrapulpal temperature changes were less than 3°C. The G2 group showed statistically significant differences when compared to the other groups, representing the lowest temperature increase. A quantitative element analysis via EDX did not significantly differ (p < 0.05) for Ca, P, F, O, or C between the four groups when measured after irradiation/erosion. The mean wear rates (± SD, μm) were 35.66 ± 7.28; 40.70 ± 5.03; 38.17 ± 10.81 and 25.25 ± 6.87 for G1-G4, respectively. The G4 group statistically differed from all other groups representing the lowest wear rate. These results suggest that dentin irradiation, using a diode laser with levels set at 60 J/cm(2), may induce inhibitory effects on root dentin demineralization without causing any harmful thermal effects. However, the exact mechanism of the action of the laser remains unclear.

No abstract

No abstract