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Solvent extraction and ultrafiltration have been proposed to extract lignocellulosic compounds from the spent liquors of pulping processes (Liu et al., 2011a); however, these process may not be industrially attractive due to a high operational cost and technical issues (e.g. blocking). Alternatively, adsorption can be considered for removing lignocellulosic compounds from spent liquors (Chaichanawong et al., 2010; Radovic et al., 2000). In one study, XAD-4 resin was employed as adsorbent for lignin in hydrolysis liquor produced from hot water extraction of mixed northern hardwood chips (Schwartz and Lawoko, 2010), approximately 90% of acid-soluble lignin and less than 10% of hemicelluloses were removed from the hydrolysis liquor via treating 5 ml of hydrolysis liquor with 4 g of XAD-4 for 5 min at room temperature. Also, the desorption analysis demonstrated an 85% lignin recovery from XAD-4 in 75 vol.% acetone at room temperature (Schwartz and Lawoko, 2010). In another study, 10.4 g furfural was adsorbed on 36.1 g XAD-4 at 30 C (the adsorption of glucose on XAD-4 was not determined) from a synthetic solution containing 0.5 wt.% glucose and 15.3 g furfural, and more than 95% of adsorbed furfural was recovered from XAD-4 in pure ethanol solution at 50 C (Weil et al., 2002). Activated carbon (AC) possesses a high adsorption capacity for various lignocelluloses (Lee et al., 2011; Montane et al., 2006). If desorption of lignocelluloses from the AC is performed,the AC can be readily recycled and reused. Previously, we demonstrated that the AC was an efficient adsorbent of the lignocelluloses of PHL, and its adsorption capacity could be increased via oxidation (Liu et al., 2011b). Cationic polymers, e.g. polydiallyldimethylammonium chloride (PDADMAC), were able to interact with lignocelluloses of PHL via patch flocculation, form complexes and be eventually removed from PHL (Saeed et al., 2011a). In one study, the concentration of PDADMAC (with a molecular weight ranging from 50 to 100 kDa) in a hydrolysis solution (produced from the hot water hydrolysis of mixed northern hardwood) was maintained at 47.3 ppm at room temperature for 120 min, resulting in 36% lignin and 3% hemicellulose removals (Duarte et al., 2010). One objective of the current work was to introduce a detoxification process that could be integrated into the existing configuration of kraft-based dissolving pulp production based on adsorption and flocculation. Another objective was to evaluate the efficiency of the introduced process in removing lignin from PHL at laboratory scale. The experimental analysis of this work was carried out on industrially produced PHL via unmodified AC and oxidized AC/PDADMAC in subsequent adsorption stages in order to maximize removal of lignin from PHL. |
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