No abstract

The evolution of 4-O-methylglucuronic (GlcA) and hexenuronic (HexA) acids contents during kraft pulping of Eucalyptus globulus was investigated. Different operating conditions were considered in the range of 80-165 °C for temperature, 10-45 g of Na 2 O/100 g of oven-dried wood for effective alkali charge, and 15-75% for sulfidity, with a liquid-to-wood ratio of 8 L/kg. The GlcA content was about 5% in the native wood and decreased continuously throughout the cook. Up to 87% of this component was consumed, being dissolved together with the xylan chain or converted to HexA. The latter were detected for temperatures higher than 110 °C. The highest HexA values (∼40 mmol/kg of oven-dried pulp) were observed for delignification degrees close to those of industrial bleachable pulps, and the subsequent decrease in their content was only noticeable for lower lignin amounts. The temperature and the effective alkali charge were confirmed to have a strong influence on the HexA content profiles and on the degradation/ dissolution of GlcA, but the effect of sulfidity revealed to be negligible on any of them.

The heterogeneous nature of the kraft pulping of wood is experimentally demonstrated in this paper, and a new methodology for kraft pulping investigation is presented. The strategy proposed here enables the measurement of alkali and of lignin concentrations in the pulping liquor, both inside and outside of the wood chips. With this procedure, it is possible to independently determine, in both entrapped and free liquors, the time histories of the concentrations of alkali and lignin as well as total dissolved solids, which are a direct result of the mass transfer and of the chemical reactions that take place during this heterogeneous process. The influence of the chip thickness and of temperature on the relative rates of these two phenomena is also highlighted. This experimental methodology establishes the foundations for the development of a macroscopic heterogeneous kraft pulping model that can be experimentally validated in pulping conditions, even for modified digester processes.

A kinetic model considering simultaneously the removal of methylglucuronic acids (GlcA), the formation of hexenuronic acids (HexA), and their degradation/dissolution is proposed. In the model, the effective alkali concentration in the entrapped liquor was used instead of that in the bulk liquor, accounting for the heterogeneous nature of wood pulping. The results are very satisfactorily explained by assuming that GlcA are composed of two subgroups: the fast GlcA, which disappear early in the cook with a low activation energy (58 kJ/mol), and the slow GlcA, which are degraded/dissolved (E a ) 91 kJ/mol) or produce HexA, not being totally consumed. The degradation/dissolution reactions of both GlcA subgroups are second-order with respect to their content, while HexA formation (E a ) 92 kJ/mol) and degradation (E a ) 110 kJ/mol) are first-order with respect to slow GlcA and HexA contents, respectively. The effective alkali concentration influences the reactions that involve the slow GlcA and HexA, with a greater contribution to HexA degradation. The sulfidity is not relevant on any of these reactions. The model was experimentally validated with varying temperature, alkali, and sulfidity profiles and predicts reasonably well the GlcA and HexA contents during kraft pulping of Eucalyptus globulus.

The cottonseed oil (CSO) extraction and processing areas including biodiesel (CSB) production created the need for density availability over wide ranges of temperature and pressure. In this work, densities of CSO and CSB were measured. The measurement of CSO density under pressure has never been reported in the literature. To address this limitation, this work reports new experimental data of densities of CSO measured at temperatures from 278 to 358 K and pressures from atmospheric up to 30 MPa using a vibrating tube densimeter. The measured densities of CSO were correlated with the Goharshadi−Morsali−Abbaspour equation of state (GMA EoS) with an absolute average relative deviation of 0.02%. The coefficients of GMA EoS for CSO and CSB were used to calculate the thermal expansivity and isothermal compressibility which influence power and fuel injection and they are rarely presented for vegetable oils and biodiesel, especially at high pressures. The group contribution method GCVOL, Halvorsen model, and Zong fragmentbased approach were used to evaluate the predictive abilities of CSO density data. Good predictions of oil densities were achieved with Halvorsen model for which absolute deviations are in the range of uncertainty of the measurements.