Ariane Leites Larentis

Modeling and optimization of the combined carbon dioxide reforming and partial oxidation of natural gas

The optimization of the combined carbon dioxide reforming and partial methane oxidation over a 1% Pt/-Al2O3 catalyst was studied in order to produce synthesis gas with hydrogen/carbon monoxide ratio close to 1, for applications in metallurgical and polycarbonates processes and for production of oxygenated compounds and hydrocarbons. The study was performed with the help of experimental design and two mathematical modeling approaches: empirical and phenomenological. Empirical polynomial models were employed to analyze the effects of the process variables on the response factors and the final correlation coefficients obtained were above 95%. The phenomenological model was obtained from individual mass balances and the obtained correlation coefficients were above 95% for CH4 and N2, 90% for CO2 and H2O and near 70% for H2 and CO. The empirical modeling approach was found to be more efficient, simpler and led to better results than those obtained with the phenomenological model approach. Therefore, the empirical modeling was used for optimization of the process operation conditions. At an oxygen/methane ratio of 0.55 gmol/gmol and temperature of 950 ◦ C, optimized process conditions were obtained with complete methane conversion, maximum carbon monoxide selectivity of 43% and minimum hydrogen/carbon monoxide ratio of 1.3, in absence of water.

Evaluation of growth, carbazole biodegradation and anthranilic acid production by Pseudomonas stutzeri

The proportion of nitrogenated compounds such as carbazole in heavy fractions of crude oil is higher in Brazil than in other parts of the world. The degradation of this compound by microorganisms has already been described for bacteria such as Pseudomonas stutzeri ATCC 31258. Assays were undertaken to assess the influence of different carbazole concentrations on cell growth, carbazole degradation and the formation of anthranilic acid (an intermediate in the carbazole degradation pathway). The results indicated that there was an accumulation of anthranilic acid in the medium with the higher concentration of substrate (10 g/L), which could be related to the inhibition of Pseudomonas stutzeri growth in an excess of carbazole. With 1 g/L of carbazole, growth was found to be ten times greater (0.37 g dry cell weight/L) and there was no accumulation of anthranilic acid (formation of around 7 mg/L), with complete carbazole degradation after three days.

Analysis of experimental errors in catalytic tests for production of synthesis gas

The proper determination of experimental errors in catalytic processes may be very important because experimental errors can exert a major impact upon the analysis of experimental results. For this reason, the influence of temperature upon the experimental errors observed during the combined carbon dioxide reforming and partial oxidation of methane over Pt/-Al2O3 is studied here. It is shown that fluctuations of output stream compositions may decrease more than one order of magnitude as reactor temperature increases in the range from 600 to 1100 ◦ C during catalytic tests. Additionally, it is shown that the covariance matrix of composition measurements is not diagonal, as usually assumed, and may change very significantly with the experimental conditions. Therefore, experimental errors should not be regarded as constant and covariance matrices should not be assumed to be diagonal a priori for kinetic model building and parameter estimation. It is also shown that the covariance matrix may contain significant amount of information about the reaction mechanism, which can be used for model building and interpretation of kinetic experiments. Particularly, it is shown that the actual experimental error may be much smaller than usually obtained when covariance terms are neglected and that fluctuation of catalyst activity may concentrate most of the experimental fluctuations observed experimentally.

Expression and homology modeling of 2′-aminobiphenyl-2,3-diol-1,2-dioxygenase from Pseudomonas stutzeri carbazole degradation pathway

The enzyme 2′-aminobiphenyl-2,3-diol-1,2-dioxygenase (CarB), encoded by two genes (carBa and carBb), is an α2β2 heterotetramer that presents meta-cleavage activity toward the hydroxylated aromatic ring in the carbazole degradation pathway from petroleum-degrader bacteria Pseudomonas spp. The 1082-base, pair polymerase chain reaction product corresponding to, carBaBb genes from Pseudomonas stutzeri ATCC 31258 was cloned by site-specific recombination and expressed in high levels in Escherichia coli BL21-SI with a histidine-tag and in native form. The CarB activity toward 2,3-dihydroxybiphenyl was similar for these two constructions. The α2β2 3D model of CarB dioxygenase was proposed by homology modeling using the protocatechuate 4,5-dioxygenase (LigAB) structure as template. Accordingly, His12, His53, and Glu230 coordinate the Fe(II) in the catalytic site at the subunit CarBb. The model also indicates that His182 is the catalytic base responsible for deprotonating one of the hydroxyl group of the substrate by a hydrogen bond. The hydrophobic residues Trp257 and Phe258 in the CarB structure substituted the LigAB amino acid residues Ser269 and Asn270. These data could explain why the CarB was active for 2,3-dihydroxybiphenyl and not for protocatechuate.