Jung Myoung Lee

Autohydrolysis pretreatment of Coastal Bermuda grass for increased enzyme hydrolysis

Coastal Bermuda grass (GBG) was pretreated using an autohydrolysis process with different temperatures and times, and the pretreated materials were enzymatically hydrolyzed using a mixture of cellulase, xylanase and beta-glucosidase with different enzyme loadings to evaluate sugar yields. Compared with untreated CBG, autohydrolysis pretreatments at all elevated temperatures and residence times tested enhanced enzymatic digestibility of both cellulose and hemicellulose. Increasing the temperature and residence time also helps to solubilize hemicelluloses, with 83.3% of the hemicelluloses solubilized at 170 degrees C for 60 min treatment. However, higher temperatures and longer times resulted in an overall lower sugar recovery when considering monosaccharides in the prehydrolyzate combined with the enzyme hydrolyzate. Autohydrolysis at 150 degrees C for 60 min provided the highest overall sugar yield for the entire process. A total of 43.3 g of sugars, 70% of the theoretical sugar yield, can be generated from 100g CBG, 15.0 g of monosaccharide in the prehydrolyzate and 28.3 g in the enzyme hydrolyzate. The conversion efficiency could be further improved by optimizing enzyme dosages and xylanases:cellulases ratio and pretreatment conditions to minimize sugar degradation.

A comparison of the autohydrolysis and ammonia fiber explosion (AFEX) pretreatments on the subsequent enzymatic hydrolysis of coastal Bermuda grass.

Two distinct pretreatment technologies, autohydrolysis and AFEX, have been applied to coastal Bermuda grass (CBG) followed by enzymatic hydrolysis in order to compare the effects of pretreatment on the subsequent sugar generation. Furthermore, the influence of structural features from each pretreatment on biomass digestibility was characterized with SEM, ATR-FTIR, and XRD. Enzymatic conversion of pretreated solids from the pretreatments increased with elevated temperature and longer residence times. AFEX pretreatment at 100 degrees C for 30 min produced a sugar yield of 94.8% of theoretical possible with 30 FPU/g enzymatic loading, the maximum achieved with AFEX. It was also shown that with autohydrolysis at 170 degrees C for 60 min that 55.4% sugar yield of the theoretical possible was produced with a 30 FPU/g enzymatic loading, the maximum with autohydrolysis. AFEX pretreatment does not change the chemical composition of CBG but autohydrolysis reduces hemicellulose content in the pretreated solids. Both pretreatments cause re-localization of lignin components. There was no observed correlation between crystallinity and enzyme digestibility of the pretreated solids. AFEX pretreatment developed more enzymatic accessibility to pretreated solids of CBG than did autohydrolysis pretreatment, leading to more sugar generation through the whole process. The total amount of sugars accounted for with autohydrolysis decreases with increasing temperature, consistent with increased byproduct generation via thermal degradation reactions.

Effects of hardwood structural and chemical characteristics on enzymatic hydrolysis for biofuel production

This study investigated the influence of various hardwood characteristics on enzymatic hydrolysis. Important hardwood species, including three Eucalyptus species, were comprehensively characterized using quantitative (13)C NMR, image analysis and fiber quality analysis. Hydrolysis efficiency from all the hardwoods was correlated to the wood chemical composition and lignin characteristics. Among the key wood components that control enzymatic hydrolysis efficiency, lignin content, enzyme adsorption on substrate and, the ratio of syringyl/guaiacyl (S/G) of the pretreated feedstock were identified as the most important. No wood morphological feature was found to have a significant influence on enzymatic conversion of the pretreated samples.

Impact of hardwood species on production cost of second generation ethanol.

The present work targeted the understanding of the influence of nine different hardwood species as feedstock on ethanol production yield and costs. It was found that the minimum ethanol revenue (MER) (

RHEOLOGY OF CARBOXYMETHYL CELLULOSE SOLUTIONS TREATED WITH CELLULASES

per gallon to the producer) to achieve a 12% internal rate of return (IRR) on invested capital was smaller for low lignin content samples and the influence of species characteristics remained restricted to high residual lignin content. We show that if the pretreatment being applied to the feedstock targets or is limited to low lignin removal, one can expect the species to have a significant impact on overall economics, playing important role to project success. This study also showed a variation of up to 40% in relative MER among hardwood species, where maple, globulus and sweet gum varied the least. Sensitivity analysis showed ethanol yield per ton of feedstock had the largest influence in MER, followed by CAPEX.

Dimensional and hygroexpansive behaviors of cellulose microfibrils (MFs) from kraft pulp-based fibers as a function of relative humidity

The effect of cellulase treatments on the rheology of carboxymethyl cellulose (CMC) solutions was studied using a rotational viscometer. The rheological behaviors of CMC solutions of different molecular mass and degrees of substitution where studied as a function of time after various treatments. These solutions were subjected to active and heat-denatured cellulase, a cationic polyelectrolyte (C-PAM), as well as different shear rates. A complex protein-polymer interaction was observed, leading to a potential error source in the measurement of enzymatic activity by changes in the intrinsic viscosity. The interaction was termed a polymeric effect and defined as a reduction in viscosity of the substrate solution without significant formation of reducing sugars from enzymatic hydrolysis. The cause of the reduction in viscosity appears to be related to the interaction between the enzymes as amphipathic particles and the soluble CMC. Thus, the polymeric effect may cause a considerable experimental error in the measurement of enzymatic activity by viscometric methods.

Detoxification of woody hydrolyzates with activated carbon for bioconversion to ethanol by the thermophilic anaerobic bacterium Thermoanaerobacterium saccharolyticum

Abstract Cellulose aggregate fibrils (CAFs) with dimensions of 100,000×3000×300 nm from unbleached kraft pulp (KP), oxygen delignified KP (KPox.del), and fully bleached kraft pulp (BKP) were liberated by a series of high shear and fractionation operations. The CAFs served as microfibril model material to evaluate their dimensional and hygroexpansive behaviors when submitted to variable relative humidities (RHs). The atomic force microscopy images of CAFs from different sources of kraft fibers were obtained during a RH cycle from 50% RH to 78% RH and then to 21% RH while being kept at 23°C. The resulting images were analyzed to determine dimensional changes in length, its concurrent cross-sectional area, width, and height. The mean value of changes in length and width was in the range of 2.3–3.2% and 1.9–3.3%, respectively. The changes in area and height were in the range of 14.5–18.2% and 12.4–17.3%, respectively. The length of CAFs showed a negative correlation with RH, whereas cross-sectional area, width, and height changes correlated positively with RHs. In the out-of-plane direction, such as area and height, the hygroexpansivity was one order of magnitude larger than the in-plane hygroexpansivity, i.e., in terms of length and width.