ABSTRACT This work aims to develop and validate a model based on chemical equilibrium to predict the composition of syngas produced by gasification of woody biomass (sawdust). The model uses Gibbs Energy minimization to evaluate the composition of the system in chemical equilibrium. The results are validated by comparison between experimental data from a gasification experiment and those of other similar models in the literature. The study shows good agreement among experimental results and elucidates the role of solid unburned carbon in such systems, which is present in considerable amount. It can be concluded that equilibrium models can be used to predict carbon conversion in gasification systems.

ABSTRACT: Essential oils are complex mixtures of volatile compounds found at low levels in aromatic plant specific parts. Soluble in organic solvents, these oils are characterized by their fragrance and antimicrobial activity, being widely used in industries. The mathematical modeling of essential oil extraction is a relevant step in the project of industrial plants because it is about achieving optimized operational conditions. A model is available in the literature describing the extraction process of basil essential oil, based on diffusion within the leaf. Parametric equations were tested for the variable diffusion coefficient with the concentration, resulting in a significant improvement in the description process, when compared to papers presented in the literature.

Óleos essenciais são compostos químicos voláteis, característicos por sua fragrância e frequentes atividades antimicrobianas e antioxidantes. São extraídos dos tricomas de plantas aromáticas a partir de diversos métodos diferentes de extração. As indústrias dão preferência à extração por arraste a vapor (destilação a vapor), por ser um processo tradicional, de simples operação e baixo custo. A modelagem matemática deste processo é um passo inevitável para projetar plantas industriais de extração de óleo essencial visando a boas condições operacionais. O modelo empregado neste trabalho é baseado na difusão do óleo no interior da folha. Apresentam-se o procedimento de discretização deste modelo por método de diferenças finitas e a validação deste por comparação com a solução analítica. Dados da literatura de perfis de rendimento por tempo de extração foram empregados para a estimação do coeficiente de difusão. Propôs-se a melhoria do modelo por meio da estimação de parâmetros de equações empíricas para a descrição do coeficiente de difusão como função da concentração de óleo. A partir desta modificação, o modelo não possui mais solução analítica, o que justifica o procedimento numérico adotado. O modelo foi validado através de um conjunto de dados disponíveis na literatura.

Essential oils are volatile chemical compounds, characteristic for its fragrance and frequent antimicrobial and antioxidant activities. Essential oils are extracted from the glandular trichomes of herbs from various extraction methods. Industries give preference to extraction by steam distillation, for its traditional method, simple operation and low cost. The mathematical modeling of this process is an inevitable step for designing industrial plants of essential oil extraction with good operating condition. The model used in this article is based on the diffusion of the oil within the leaf. The discretization procedure of this model is presented through finite differences and its validation by comparing with the analytical solution. Data of profiles yield by extraction time were used to estimate the diffusion coefficient. In order to improve the model empirical equations were applied to describe de diffusion coefficient as a function of the oil concentration and the parameters of these equations were estimated. Using this modification, the model has no longer analytical solution, which justifies the adopted numerical procedure. The model was validated using data from literature.