The determinations of cellulose and lignin are important in wood analysis from both perspectives: chemistry composition, commercial and industrial application of woods. In this context, Raman image spectroscopy was applied in the determination of cellulose and lignin distribution in wood surfaces of Swietenia macrophylla King (Mahogany) and Eucalyptus hybrid (E. urophylla × E. camaldulensis). The relative concentration maps were obtained by applying a multivariate curve resolution procedure. The estimated Raman spectra for cellulose and lignin agrees with the ones available in the literature. The cellulose concentration maps showed similar variations for both studied species with an average value of nearly 85% as obtained by the reference method. The lignin concentration maps were somewhat different. The Eucalyptus hybrid presents a broader distribution (20 to 45%) while for Mahogany it is nearly constant, around 25%, with localized regions presenting contents of 45 to 65% of lignin. The reference method showed that the mean lignin content of both species is 27%. The cellulose and lignin concentration maps agree with the biological functions of the anatomic structures observed in the images.
Magnetic mixed iron/cadmium (ICdO) and iron/tin (ISnO) oxide nanoparticles were used as catalysts in relevant reactions for biodiesel production technologies. These compounds were active for hydrolysis and transesterification of soybean oil as well as esterification of soybean oil fatty acids. In the esterification assisted by ISnO high yields, ca. 84%, were achieved, after 1 h reaction at 200 ºC. The oxide was magnetically recovered and reused four times without loss in its activity, while a loss of activity was observed for ICdO catalyst. ISnO also demonstrated catalytic activity for macauba oil, a highly acidic substrate.
Nanopartículas magnéticas compostas por óxidos mistos de ferro/cádmio (ICdO) e ferro/ estanho (ISnO) foram usadas como catalisadores em reações relevantes para diferentes tecnologias de produção de biodiesel. Estes compostos foram ativos para hidrólise e transesterificação de óleo de soja, bem como para a esterificação de ácidos graxos obtidos a partir do óleo de soja. Na esterificação mediada por ISnO foram alcançados altos rendimentos, ca. 84%, após 1 h de reação a 200 ºC. O óxido foi recuperado magneticamente e reutilizado quatro vezes sem perda da sua atividade catalítica, enquanto que uma perda significativa foi observada quando ICdO foi usado. ISnO demonstrou também atividade para a produção de biodiesel a partir de óleo de macaúba, um substrato altamente ácido.
Nb2O5/HX (X = HSO4-, H2PO4-, NO3-) compounds were obtained from the treatment of niobium acid (Nb2O5·xH2O) with sulfuric, phosphoric, and nitric acids as well as Nb2O5 and Nb2O5·xH2O have been investigated as catalysts for the transesterification, esterification and pyrolysis of vegetable oils. The compounds were characterized by thermal analysis (DTA-TGA), spectroscopy (DRX, FT-IR and FT-Raman), surface area (BET) and the acidity (Ho) determined by n-butylamine titration using the Hammet´s indicator method. It was observed that after the acid treatment both the surface area and the acidity decreased as compared to the starting Nb2O5·xH2O. The only exception was a higher acidity verified when nitric acid was used. Among the catalyst investigated, the Nb2O5/H3PO4 presented the highest activity in the alcoholysis of soybean oil with different mono-alcohols (methanol, ethanol, 2-propanol, n-butanol). All tested solids seemed to stabilize the carboxylic acids formed during the pyrolysis, yielding higher acid numbers for the obtained products. Finally, the use of Nb2O5/H3PO4 and Nb2O5/H2SO4 as catalysts for the esterification showed better activity than Nb2O5·xH2O and Nb2O5.
Nb2O5/HX (X = HSO4-, H2PO4-, NO3-) foram obtidos após o tratamento do Nb2O5·xH2O com ácido sulfúrico, fosfórico, nítrico, sendo investigados juntamente com Nb2O5 e Nb2O5·xH2O como catalisadores na reação de transesterificação, esterificação e pirólise de óleos vegetais. Os catalisadores foram caracterizados por análise térmica (DTA-TGA), espectroscopia (DRX, FT-IV e FT-Raman), área superficial (BET), e determinada acidez (Ho) pela titulação com n-butilamina utilizando o método Hammet. Após o tratamento ácido, todas as áreas superficiais e a acidez decresceram comparadas com o Nb2O5·xH2O utilizado inicialmente no tratamento. A única exceção foi a alta acidez verificada quando o ácido nítrico foi utilizado. Entre os catalisadores testados, o Nb2O5/H3PO4 apresentou boa atividade na reação de alcoólise do óleo de soja com diferentes alcoóis (metanol, etanol, 2-propanol, n-butanol). Todos os sólidos testados demonstraram estabilizar ácidos carboxílicos durante a pirólise. Finalmente, o uso de Nb2O5/H3PO4 e Nb2O5/H2SO4 como catalisador na reação de esterificação demonstrou melhor atividade que o Nb2O5 e Nb2O5·xH2O.
The preparation of new materials obtained from the co-precipitation of aluminum, tin and zinc oxides and their use as catalytic system activities for vegetable oils alcoholysis are reported herein. It was observed that these metal-oxides of the type (Al2O3)X(SnO)Y(ZnO) Z are active for soybean oil alcoholysis, uzing several alcohols, including branched ones. Best result was achieved using methanol, with conversion yields up to 80% in 4 h. It was also possible to recycle the catalysts without apparent loss of activity.
Neste trabalho são apresentados a preparação de novos materiais obtidos da co-precipitação de alumina e óxidos de estanho e zinco e seu uso como sistemas catalíticos ativos para alcoólise de óleos vegetais. Foi observado que estes óxidos metálicos do tipo (Al2O3)X(SnO)Y(ZnO) Z são ativos para a alcoólise do óleo de soja usando diversos álcoois, incluindo ramificados. Os melhores resultados foram observados utilizando metanol, sendo atingidas conversões acima de 80% em 4 horas. Foi também possível reciclar estes materiais sem perda aparente de sua atividade catalítica.
In this work, a simple and fast capillary electrophoresis method for the simultaneous analysis of 4-carboxybenzaldehyde (4-CBA), p-toluic acid (pTOL) and benzoic acid (BZ) in industrial batches of crude (CTA) and highly-purified (PTA) terephthalic acid was developed. The electrophoretic conditions comprise: 20 mmol L-1 tetraborate buffer at pH 9, hydrodynamic injection (5 s/17 kPa), applied voltage of +30 kV and direct UV detection at 200 nm. The concentrations of 4-CBA and pTOL in five batches of CTA and four batches of PTA as determined by the proposed CE methodology were in agreement with the results from gas chromatography and polarography methods in current use in Tereftalatos Mexicanos S.A. (TEMEX). Levels of BZ were determined only by the CE methodology and ranged from 60 - 300 ppm in CTA and 5 - 7 ppm in PTA. Several impurities deriving from the incomplete oxidation of p-xylene were investigated. So far the positive identification of 4-hydroxymethylbenzoic acid was accomplished by comparison with pure standards.
Neste trabalho, foi desenvolvido um método simples e rápido, utilizando eletroforese capilar (CE), para a análise simultânea de 4-carboxibenzaldeído (4-CBA), ácido p-toluóico (pTOL) e ácido benzóico (BZ), em lotes industriais de ácido tereftálico cru (CTA) e purificado (PTA). As condições eletroforéticas de análise foram: tampão tetraborato a 20 mmol L-1 (pH 9), injeção hidrodinâmica (5 s, 17 kPa), tensão aplicada de +30 kV e detecção direta em 200 nm. Foram analisados cinco lotes de CTA e quatro lotes de PTA nos teores de 4-CBA e pTOL pela metodologia proposta e as metodologias utilizadas na empresa Tereftalatos Mexicanos S.A. (TEMEX), que são cromatografia gasosa para pTOL e polarografia para 4-CBA, mostrando concordância entre os valores encontrados. Os níveis de BZ foram determinados apenas pela metodologia CE, apresentando no CTA, valores compreendidos entre 60 e 300 ppm, enquanto que no PTA, 5 a 7 ppm. Várias impurezas derivadas da oxidação incompleta do p-xileno foram investigadas, constatando-se a presença do ácido 4-hidroximetilbenzóico por comparação com padrões.
A method is presented for the choice of spectral regions when absorption measurements are coupled to chemometric tools to perform quantitative analyses. The method is based on the spectral distribution of the relative standard deviation of concentration (s c/c). It has been applied to the development of PLS-FTNIR calibration models for the determination of density and MON of gasoline, and ethanol content and density of ethanol fuel. The new method was also compared with the correlation (R²) method and has proved to generate PLS calibration models that present better accuracy and precision than those based on R².
Raman spectroscopy has been used to get some insight into the chemical composition and structure of magnetic fluids based on ferrites. The inner as well as the surface structure of Fe-maghemite and Zn-maghemite have characterized by Raman spectroscopy. It has been shown that different chemical species are present on the maghemite surface by changing the laser excitation energy. Maghemites modified by the adsorption of aspartic and glutamic acids as well as those modified by the adsorption of methylene blue(MB) have also been investigated by Raman spectroscopy. It has been shown that while FTIR (Fourier transform infrared) spectroscopy gives almost no information regarding to the surface species, Raman spectroscopy in and off resonance gives suitable information regarding to the adsorbate structure and bonding. The Raman spectroscopy study of the modified maghemites have shown that the organic acids adsorb on the maghemite surfarce as glutamate and aspartate chemically bounded to Fe(III) ions on the maghemite surface, and that MB, a cation, adsorbs on the maghemite surface as a monomer by ion pair formation with coadsorbed nitrate.
A capillary electrophoresis system using laser induced fluorescence detection is described. A Raman system equipped with a microscope has been used to focus the laser beam on the capillary giving a lateral resolution of 1.5 mm. The fluorescence signal of the analyte (ZnPcTS - tetrasulfonated zinc-phthalocyanine) was collected by the microscope objectives and analysed by a monochromator with confocal characteristics equipped with a CCD detector. Electropherograms obtained with this system were compared to those obtained on a commercial instrument, showing that the described system presents a lower detection limit and better resolution.