Integration of kraft pulping on a forest biorefinery by the addition of a steam explosion pretreatment

Abstract

Steam explosion has been proposed for a wide range of lignocellulosic applications, including fractionation of biomass, pre-treatment of biomass for ethanol production, or as an alternative to conventional mechanical pulping. Nevertheless, a steam explosion process could also be used as pretreatment before chemical pulping, expecting a reduction in cooking time due to the open structure of the exploded chips. Thus, to evaluate the effect of steam explosion as a pretreatment in the kraft pulping of Eucalyptus globulus, steam exploded chips and control chips were subjected to kraft cookings. Steam exploded chips provided pulps with reductions of kappa number by up to 70% with no significant change in viscosity. Therefore, the cooking time could be shortened by 60%, increasing the productivity and obtaining pulps with similar delignification degree to those of the control pulp. Furthermore, not only the production rate could be increased, but also most of the hemicelluloses could be recovered before pulping and converted to a value-added product. Finally, although exploded pulp had inferior mechanical strength, the optical properties, which are more important in eucalyptus pulps, were found to be better.

Steam Explosion as a Pretreatment of Cynara cardunculus Prior to Delignification

“…Again this is not as discussed in the literature, where steam explosion is said to induce modifications on the lignin structure 37 with a decrease of methoxyl groups due to demethoxylation reactions and degradation of syringyl units, 15 leading to a S/G ratio reduction in steam exploded samples. 4 The steam explosion conditions were chosen to prevent a large mass loss, with removal of nonstructural components and less of structural components. The results obtained are consistent with this idea.…”

“…3 Steam explosion promotes the breakdown of the biomass matrix, making the structural polymers more accessible for subsequent treatments such as hydrolysis or fermentation. 1,4 Two types of reactions occur during steam explosion: in the beginning there is a fast depolymerization of lignin and hemicelluloses by acid hydrolysis, but as temperature increases, condensation and repolymerization reactions dominate, promoting an increase of acid insoluble lignin. 5 The hemicelluloses are released from the cell wall matrix, also liberating acetic acid that will enhance hydrolysis and further sugar reactions; for example, xylose is mainly degraded into furfural.…”

“…7 Condensation reactions can also occur, and fragments can be deposited onto the fibers surface. 4,8 The most important variables during steam explosion are time and temperature as well as chip size since in larger chips the heat transfer is less efficient, and they are less degraded in the interior and overcooked in the exterior. 9 Therefore, chip size is usually small e.g.…”

“…5,9 Overall, steam explosion is an attractive biomass pretreatment since (i) it uses only a limited number of chemicals, (ii) it requires relatively low energy, and (iii) depending on the conditions applied, most of the original cellulose and hemicelluloses-derived carbohydrates can be recovered for fermentation. 10,11 The effect of steam explosion has been reported for several lignocellulosic materials such as wheat straw, 10 eucalyptus wood, 4,12 or pine wood. 5 The objective was mainly not only to recover sugars for bioethanol production but also to increase the heating value, bonding properties, and hydrophobicity before pelletization.…”

Eucalyptus Amplifolia and Corymbia Torelliana in the Southeastern USA: Genetic Improvement and Potential Uses

“…Eucalyptus energywood uses have been demonstrated [16]. Eucalyptus has been considered as a feedstock for energy generation at pulp mills in Florida, and it has potential for use in biorefineries associated with pulp mills [17]. Eucalyptus has been proposed as the primary feedstock for stand-alone biomass power plants in Florida [18].…”