Kinetics of Organosolv Delignification in Batch- and Flow-Through Reactors

Abstract

The kinetics of Organosolv delignification of black cottonwood in aqueous methanol was studied in the temperature ränge 130-210°C using 0.00 to 0.05 M sulfuric acid äs catalyst. The bulk delignification phase followed pseudo-first order kinetics with an activation energy of 19.2 kcal/mol (80.3 kJ/mol) suggesting the cleavage of benzyl ether linkages to be the rate determining reaction. At low catalyst concentrations (< 0.02 M sulfuric acid), the bulk rate constant of deashed cottonwood is nearly proportional to the catalyst concentration. When the delignification was carried out in a flow-through reactor, the rate constant was increased by a factor of 1.8 probably äs a consequence of the solubility properties of Organosolv lignins. At any level of delignification, the flow-through reactor produces holocellulose fibers with higher DP values than the batch reactor. The molecular weights of isolated flow-through reactor lignins are substantially higher than those found for the batch reactor lignins, e.g. M w = ~ 50000 versus -9500.

Kinetics of polysaccharide hydrolysis in the acid-catalysed delignification of eucalyptus globulus wood by acetic acid

“…In the hydrolysis of Quercus falcata wood by dilute sulphuric acid, however, the rate constant is only proportional to acid concentration if inorganic components of wood are removed with dilute HC1 prior to hydrolysis; otherwise, these components neutralize part of the HzSO 4 (Harris et al 1984). The fact that in our experiments the rate constants for neither the fast polysaccharide hydrolysis process nor the hydrolysis of lignin (V~zquez et al 1995) showed non-linear [HC1 ]-dependence indicative of partial neutralization may probably be attributed to the presence of acetic acid, which has been proposed as an alternative to HC1 for removal of the undesirable inorganic substances (Tirtowidjojo et al 1988). Fitting Arrhenius' equation to the values of kfc calculated by fitting Eq.…”

The effect of direct and counter‐current flow‐through delignification on enzymatic hydrolysis of wheat straw, and flow limits due to compressibility

“…Flow-through processes have been shown to improve the efficiency of different alkaline and organosolv delignification methods (Kadam et al, 2009;Park and Kim, 2012;Tae and Lee, 2005;Tirtowidjojo et al, 1988). Flow-through treatment is typically performed by percolation through material packed in a column.…”

“…Flow-through treatment is typically performed by percolation through material packed in a column. Compared to batch reactions, higher rate constants for lignin dissolution have been shown for percolation, leading to increased lignin dissolution and a lower degree of cellulose degradation (Tirtowidjojo et al, 1988). In hydrothermal pretreatments, flowthrough processes have also been shown to increase the dissolution of both hemicellulose (Liu and Wyman, 2005;Petersen et al, 2009) and lignin (Liu and Wyman, 2003).…”

“…The liquid flow removes the dissolved lignin, replaces it with fresh reagent and facilitates efficient displacement wash of the solids (Tervola and R€ as€ anen, 2005). Accordingly, the efficiency improvement by flow-through operation has been attributed to the prevention of recondensation of the dissolved lignin and reducing further degradation of the dissolved lignin (Tirtowidjojo et al, 1988).…”

“…It is also considered the optimal reactor configuration for dilute acid saccharification of lignocellulose, and has been suggested as the preferred process for flow-through delignification (Lee et al, 1999;Tirtowidjojo et al, 1988). Countercurrent flow could therefore be envisioned to further reduce the amount of adverse lignin reactions and improve further contact of the residual NaOH with the material compared to regular percolation.…”