Lignin Basis Research Articles

Design and Testing of a Pilot-Scale Aqueous Ammonia Soaking Biomass Pretreatment System

Scale‐up of the aqueous ammonia soaking (AAS) biomass pretreatment method to 75‐L soaking vessel size was accomplished in this work. A novel, pilot‐scale AAS system capable of pretreating 4 kg of switchgrass per cycle was designed, fabricated, and tested. The pretreatment process involved soaking biomass in 29.5% aqueous ammonium hydroxide at a liquid: solid ratio of 5 L/kg. Major vessel design criteria included (1) allowing thorough washing of the soaked biomass in the pretreatment reactor; (2) simple, low‐cost fabrication; and (3) limiting safety hazards by minimizing ammonia fumes from the system. Based on these constraints, commercially available 75‐L HDPE tanks were selected as the primary vessels for pretreatment. The pretreatments were conducted outside, without agitation during the summer months in Iowa, with ambient temperatures ranging from 15 C to 33 C. During the first experimental cycle, clogging of the outlet resulted in leakage from the vessel during rinsing, and led to redesign of the washout prevention system. The redesigned system used a “teabag” approach in which dry biomass was preloaded into a cylindrical mesh bag, and the filled bag was placed into the soaking vessel. This modification eliminated outlet clogging, simplified biomass loading and unloading, but slightly reduced washing efficiency. Through five soaking cycles, an average of 22% to 25% delignification was achieved (Klason lignin basis) compared to the 35% removal seen at the bench‐scale as reported by our group. Approximately 50% to 60% of the pretreated switchgrass was recovered, dry basis, compared to 75% previously achieved at the bench‐scale. Overall, the system successfully generated moderate quantities (10 kg/wk) of pretreated biomass for pilot‐scale fermentation experiments while illustrating some of the materials handling challenges that must be addressed as pretreatment methods are scaled‐up.

Aqueous Ammonia Soaking of Switchgrass Followed by Simultaneous Saccharification and Fermentation

Simultaneous saccharification and fermentation (SSF) of switchgrass was performed following aqueous ammonia pretreatment. Switchgrass was soaked in aqueous ammonium hydroxide (30%) with different liquid-solid ratios (5 and 10 ml/g) for either 5 or 10 days. The pretreatment was carried out at atmospheric conditions without agitation. A 40-50% delignification (Klason lignin basis) was achieved, whereas cellulose content remained unchanged and hemicellulose content decreased by approximately 50%. The Sacccharomyces cerevisiae (D5A)-mediated SSF of ammonia-treated switchgrass was investigated at two glucan loadings (3 and 6%) and three enzyme loadings (26, 38.5, and 77 FPU/g cellulose), using Spezyme CP. The percentage of maximum theoretical ethanol yield achieved was 72. Liquid-solid ratio and steeping time affected lignin removal slightly, but did not cause a significant change in overall ethanol conversion yields at sufficiently high enzyme loadings. These results suggest that ammonia steeping may be an effective method of pretreatment for lignocellulosic feedstocks.

Transformation of lignin-related compounds with laccase in organic solvents

The extracellular laccase (benzenediol: oxygen oxidoreductase, EC 1.10.3.2) of Trametes versicolor was isolated from culture medium and immobilized by entrapment of the enzyme in a solvent-resistant hydrophilic matrix like Sepharose-CL-6B. The gel-enzyme association has been shown to be stable in water containing organic solvents. The efficiency of the immobilized laccase in different organic solvents was comparable with the activity shown in a buffered aqueous system. The immobilized laccase in organic solvents showed a good stability and a high tolerance to elevated temperatures. Water-insoluble organosolv lignin (OL), dissolved in dioxane/water, was readily converted by immobilized laccase from Trametes versicolor. The transformed lignin showed an increase in phenolic groups, changes in the quantity of conjugated elements, and a significant modification of both the aliphatic and aromatic carbon moieties of the lignin molecule. The changes in the lignin molecule were analyzed by UV-, IR-spectroscopy, and 13C-NMR solid-state spectroscopy. High-performance size exclusion chromatography (HPSEC) of the lignin transformed with the laccase—Sepharose complex revealed a pronounced increase in weight-average molecular weight. Polymerization of the lignin in the organic solvent proved to be 4 times more effective than polymerization of the same compound in an aqueous system. Water-insoluble organosolv lignin as well as a variety of lignin-related aromatics, solubilized in dioxane-H 2O (7 : 3), was readily converted by laccase preparation either in batch or in continuous flow column. Reaction of laccase with the solubilized lignin generates in the reaction media reduced oxygen species able to reduce the cytochrome c. For the first time it is now possible to perform enzymatically catalyzed reactions with lignin in an organic solvent. This is a first step towards an enzymatically derivatization of lignin, the formation of polymer blends on the basis of lignin by an enzymatically catalyzed reaction.

Multiphase materials with lignin. VIII. Interpenetrating polymer networks from polyurethanes and polymethyl methacrylate

AbstractSeveral types of interpenetrating polymer networks (IPNs) from polyurethane/polymethyl methacrylate (LPU/PMMA) on the basis of lignin were prepared. All composites were judged to possess two phase morphology. The composition and the presence of crosslinking were found to influence the thermal and mechanical properties of the solvent‐cast films. The mechanical properties were assessed by dynamic mechanical analysis and by tensile testing, and they were found to vary consistently with composition and the presence of crosslinks. The modulus behavior of the different IPNs could be explained by models which accounted for either dual phase continuity or phase inversion.