Heterogeneous Kinetic Model for the Methylglucuronic and Hexenuronic Acids Reactions during Kraft Pulping of Eucalyptus globulus

Abstract

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.

Catalytic efficiency and stability of tertiary amines in oxidation of methyl 4-deoxy-β-L-threo-hex-4-enopyranosiduronic acid by hypochlorous acid

“…Deposition of models of oxidized carbohydrates or their dehydration products, such as 5-hydroxymethyl-2-furaldehyde (HMF) and 2-furaldehyde (furfural), over different cellulosic substrates have shown the enhancement of chromophore formation upon ageing (Pedroso and Carvalho 2003;Simeonova et al 2007;Brogdon 2009;Rosenau et al 2011). Additionally, the effect of transition metals in ageing reactions has been also confirmed (Granstrom et al 2001;Simão et al 2005;Beyer et al 2006;Lachenal et al 2009).…”

Kinetic Study of Hexenuronic and Methylglucuronic Acid Reactions in Pulp and in Dissolved Xylan during Kraft Pulping of Hardwood

“…7 Their approach was somewhat different, and no analyses were made of the dissolved xylan. As well, they divided the methylglucuronic acid content into different portions in terms of their reactivity.…”

“…The energies of activation shown in Table 3 are all considerably higher than was recently reported by Simao et al for Eucalyptus globulus. 7 Their approach was somewhat different, and no analyses were made of the dissolved xylan. As well, they divided the methylglucuronic acid content into different portions in terms of their reactivity.…”

“…The recipe for minimizing the HexA content of pulp often involves high temperatures and high alkali levels. 7,8 Such cooking conditions, however, also minimize the xylan content of the produced pulp. For a pulp producer, high xylan content is essential, not only due to its contribution to pulp yield 9,10 but also to its ability to improve pulp strength.…”

Heterogeneous studies in pulping of wood: Modelling mass transfer of alkali

“…This paper proposes a model for the mass transfer of alkali from the bulk liquor to the inside of the wood chips that is based on data on the composition of both free and entrapped liquors. The pulping experiments followed the methodology proposed by Egas et al [10] and the relevance of the information gathered on the entrapped liquor has been confirmed by Simão et al [14,15]. This mass transfer model relies on a lumped parameter approximation, in which the concentration profile of alkali inside the chip is represented by its spatial average concentration.…”