Paul J. Westgate

Cellulose pretreatments of lignocellulosic substrates.

Cellulose in inedible plant materials, forestry residues, and municipal wastes must be pretreated to disrupt its physical structure, thereby making its hydrolysis to glucose practical. Developments since 1991 are summarized.

Modeling of Equilibrium Sorption of Water Vapor on Starch Materials

The equilibrium behavior of corn grits and corn starch at temperatures above 70° C, a region for which limited data and theory are available, are compared and found to be similar. Sircar’s model and potential theory accurately represent isotherm data for both adsorption systems as well as data for desorption from corn. Values of the model parameters indicate that physical properties of these starch-based sorption materials exhibit a temperature dependence that is likely related to the breaking of hydrogen bonds as water interacts with the sorbent. Modification of the two models with an exponential temperature relation is proposed to account for the experimentally measured temperature dependence of model parameters. The resulting modified Sircar’s model and potential theory equations are shown to fit the data for both starch and corn grits in the high temperature range.

Enzyme conversion of lignocellulosic plant materials for resource recovery in a Controlled Ecological Life Support System.

A large amount of inedible plant material composed primarily of the carbohydrate materials cellulose, hemicellulose, and lignin is generated as a result of plant growth in a Controlled Ecological Life-Support System (CELSS). Cellulose is a linear homopolymer of glucose, which when properly processed will yield glucose, a valuable sugar because it can be added directly to human diets. Hemicellulose is a heteropolymer of hexoses and pentoses that can be treated to give a sugar mixture that is potentially a valuable fermentable carbon source. Such fermentations yield desirable supplements to the edible products from hydroponically-grown plants such as rapeseed, soybean, cowpea, or rice. Lignin is a three-dimensionally branched aromatic polymer, composed of phenyl propane units, which is susceptible to bioconversion through the growth of the white rot fungus, Pluerotus ostreatus. Processing conditions, that include both a hot water pretreatment and fungal growth and that lead to the facile conversion of plant polysaccharides to glucose, are presented.

Sorptive recovery of dilute ethanol from distillation column bottoms stream

Modern ethanol distillation processes are designed to ensure removal of all ethanol from the column bottoms, i.e., to levels <100ppm ethanol, and utilize substantial str ipping steam to achieve this result. An alternate approach using sorption was attempted as a means to reduce energy requirements in the stripping section, and thereby reduce cost. Adsorbents tested for use in such an application showed that carbonaceous supports, in particular Ambersorb XEN 572, gave alcohol-free water as effluent when a 1% (w/w) starting ethanol concentration was passed downflow at 1 bed vol/h over a fixed-bed adsorber at 70°C. Regeneration was readily achieved at 70-90°C using hot air, vacuum, superheated steam, or hot water to strip the ethanol from the column, and yielded ethanol streams containing a maximum of 5.9% alcohol, with average concentrations of 2.5-3.5% depending on the regeneration method used. These experimentally determined operating conditions combined with distillation energy calculations have enabled development of a process concept for sorptive concentration of dilute ethanol which is more energy efficient than distillation alone. The combination of existing distillation and corn grit drying technologies, with sorptive recovery of dilute ethanol (from the column bottoms) shows promise of recovering a fuel grade, 99.4% ethanol product from a 4.5% ethanol broth with an energy requirement of 23,100 BTU/gal. The potential energy saving of 3600 BTU/gal over distillation alone corresponds to 1.8¢ /gal, and provides motivation for further examination of this approach in reducing costs of ethanol production from biomass.

Bioprocessing in space

Two approaches for biomass processing in Controlled Ecological Life Support Systems are compared in a literature survey. The approaches are based on (1) total oxidation of plant matter and (2) the potential of bioregenerative recovery.

Growth of Cephalotaxus harringtonia plant-cell cultures

SummaryCell cultures of Cephalotaxus harringtonia were examined to characterize growth kinetics. The requirement for an undefined medium supplement (coconut water) was eliminated by maintaining high cell concentrations in semicontinuous and batch growth. Sucrose fed to batch-cultured cells was completely hydrolyzed and a diauxic growth pattern was observed corresponding to first glucose and then fructose uptake. Examination of increases in cell concentrations on the basis of fresh and dry weight showed that a substantial lag period existed between the initiation of substrate uptake and increases in cell volume. Specific growth rates were highest during periods of glucose uptake, but cell yields were comparable for the two sugars. In contrast, studies with glucose or fructose as the sole carbon source indicated that cell yields were significantly lower with fructose but specific growth rates were comparable for the two sugars.

Analysis of plant harvest indices for bioregenerative life support systems

Harvest indices, which are measures of the ratio of edible to total plant weight, are redefined to include edible sugars derived from enzymatic hydrolysis of the cellulose content of inedible plant components. Compositional analysis and carbohydrate contents of rapeseed, rice, soybeans, cowpea, wheat, sweet potato, white potato, and lettuce were analyzed to develop such generalized harvest indices. Cellulose conversion is shown to extend considerably the food available from plants otherwise grown for their oil and protein content in a bioregenerative life support system.