The Impact of Xylanase and Hot Acid Pretreatment on HexAs in Eucalyptus Kraft Pulp Bleaching

Abstract

The influence of the presence of hexenuronic acid (HexA) in eucalyptus kraft pulp on the efficiency of D 0 EpD 1 was investigated by separately using both commercial cellulase-free xylanase and hot acid pretreatments. In comparison to the xylanase pretreatment, the hot acid pretreatment was more than four-fold effective in removing the HexAs (61%) and concomitantly reduced the kappa number, but resulted in lower viscosity. After subsequent D 0 EpD 1 bleaching, the final brightness and its stability were improved remarkably, especially under xylanase pretreatment. At the same brightness of 85% ISO, the xylanase pretreatment reduced the consumption of active chlorine (35.6%) more than the acid pretreatment did (27.5%). The total relative active chlorine savings for the xylanase pretreatment over the acid pretreatment was therefore nearly 23%. The HexA component can be removed considerably in both D 0 and D 1 stages during the D 0 EpD 1 bleaching sequence, while only slightly in the Ep stage. The use of xylanase and acid pretreatment both resulted in insignificant physical strength losses for the bleached pulps.

Toward Valorization of the Effluent from Xylanase Prebleaching of Eucalypt Kraft Pulp Using a Nanofiltration Purification Step

“…Since one of xylanase bleach-boosting mechanisms consists of the release of LCCs (lignin-carbohydrate complexes) from pulp, − it is expected that some lignin fragments, which act as the main chromophores in pulp, are leached out of the fibers together with the xylan fragments they are linked to. Indeed, the liberation of chromophores from pulp due to xylanase action has been reported. − This was also confirmed in this work through absorbance profile analysis of the diluted filtrates from the various treatments (Figure ). Lignin maximal absorption occurs commonly at 237, 254, and 280 nm, related to the absorption maxima of this aromatic biopolymer, due to the known n-π* and π–π* electronic transitions .…”

“…It is noteworthy that in addition to residual lignin, residues of hexenuronic acid (HexA), derived from MeGlcA under kraft pulping conditions, can also contribute to the absorptivity of the effluents. The partial release of HexA structures in the xylanase-assisted biobleaching of hardwood kraft pulps is well-documented elsewhere. ,− …”

Enhancing Enzyme-Mediated Cellulose Hydrolysis by Incorporating Acid Groups Onto the Lignin During Biomass Pretreatment

“…The pretreated Aspen was subsequently subject to mechanical pulping/refining using a twin-gear juicer (super angel juicer model 8500) in a total volume of 10 L of water. The acid wash of the pretreated Aspen mechanical pulp (MP) was conducted according to Meng et al (2015). The cellulose-rich delignified Kraft pulp was donated by Fortress Ltd.…”

“…The pretreated Aspen slurry was subsequently pulped using a twin-gear juicer to simulate mechanical pulping. As initial conductometric titration had indicated that the pretreated mechanical pulp (MP) still contained some weak acids, the pulp was subsequently acid washed to remove any residual uronic acid groups that were potentially located on the residual hemicellulose (Meng et al, 2015). After this series of treatments, the pulps contained less than 10% hemicellulose and any associated acid groups were below detectable levels ( Table 1).…”

Perfil transcricional da xilogênese em <i>Eucalyptus grandis</i>

“…Como já mencionado os pontos críticos envolvidos no processo de polpação são a deslignificação e o branqueamento, sendo ambos problemáticos devido aos resíduos de lignina. Meng et al (2015) ressalvam que os processos mais modernos de branqueamento demandam uma alta alvura e estabilidade nas polpas produzidas, com a preservação das propriedades de resistência física intrínsecas da mesma. Ao mesmo tempo em que se busca minimizar os compostos químicos, a energia e o consumo de água dispendidos na produção da celulose.…”