Rick Hendrickson

Pretreatment of yellow poplar sawdust by pressure cooking in water

The pretreatment of yellow poplar wood sawdust using liquid water at temperatures above 220°C enhances enzyme hydrolysis. This paper reviews our prior research and describes the laboratory reactor system currently in use for cooking wood sawdust at temperatures ranging from 220 to 260°C. The wood sawdust at a 6–6.6% solid/liquid slurry was treated in a 2 L, 304 SS, Parr reactor with three turbine propeller agitators and a proportional integral derivative (PID) controller, which controlled temperature within ±1°C. Heat-up times to the final temperatures of 220, 240, or 260°C were achieved in 60–70 min. Hold time at the final temperature was less than 1 min. A serpentine cooling coil, through which tap water was circulated at the completion of the run, cooled the reactor’s contents within 3 min after the maximum temperature was attained. A bottoms port, as well as ports in the reactor’s head plate, facilitated sampling of the slurry and measuring the pH, which changes from an initial value of 5 before cooking to a value of approx 3 after cooking. Enzyme hydrolysis gave 80–90% conversion of cellulose in the pretreated wood to glucose. Simultaneous saccharification and fermentation of washed, pretreated lignocellulose gave an ethanol yield that was 55% of theoretical. Untreated wood sawdust gave less than 5% hydrolysis under the same conditions.

Pretreatment of corn fiber by pressure cooking in water

The pretreatment of corn fiber using liquid water at temperatures between 220 and 260°C enhances enzymatic hydrolysis. This paper describes the laboratory reactor system currently in use for cooking of corn fiber at temperatures ranging from 200 to 260°C. The corn fiber at approx 4.4% solid/liquid slurry was treated in a 2-L, 304 SS, Parr reactor with three turbine propeller agitators and a Proportional-Integral-Derivative (PID), controller that controlled temperature within ±1°C. Heat-up times to the final temperatures of 220, 240, or 260°C were achieved in 50 to 60 min. Hold time at the final temperature was less than 10 s. A serpentine cooling coil, through which tap water was circulated at the completion of the run, cooled the reactor’s contents to 180°C within 2 min after the maximum temperature was attained. Ports in the reactor’s head plate facilitated sampling of the slurry and monitoring the pH. A continuous pH monitoring system was developed to help observe trends in pH during pretreatment and to assist in the development of a base (2.0M KOH) addition profile to help keep the pH within the range of 5.0 to 7.0. Enzymatic hydrolysis gave 33 to 84% conversion of cellulose in the pretreated fiber to glucose compared to 17% for untreated fiber.

Fractionation of cellulase and fermentation inhibitors from steam pretreated mixed hardwood.

The purpose of liquid hot water and steam pretreatment of wood is to fractionate hemicelluloses, partially solubilize lignin, and enhance enzyme hydrolysis of cellulose. The pretreatment also solubilizes sugar oligomers, lignin-derived phenolic compounds, acetic acid, and furan derivatives that inhibit cellulase enzymes and/or impede fermentation of hydrolysates by yeasts. This work extends knowledge of the relative contribution of identified inhibitors, and the effect of temperature on their release when pretreated materials are washed and filtered with hot water. Dramatic yield improvements occur when polymeric or activated carbon adsorbs and removes inhibitors. By desorbing, recovering, and characterizing adsorbed molecules we found phenolic compounds were strong inhibitors of enzyme hydrolysis and fermentation of concentrated filtrates by Saccharomyces cerevisiae wine yeast NRRL Y-1536 or xylose fermenting yeast 424A (LNH-ST). These data show that separation of inhibitors from pretreatment liquid will be important in achieving maximal enzyme activity and efficient fermentations.

Liquid Hot Water Pretreatment of Cellulosic Biomass

Lignocellulosic biomass is an abundant and renewable resource for fuel ethanol production. However, the lignocellulose is recalcitrant to enzymatic hydrolysis because of its structural complexity. Controlled-pH liquid hot water (LHW) pretreatment of cellulosic feedstock improves its enzymatic digestibility by removing hemicellulose and making the cellulose more accessible to cellulase enzymes. The removed hemicellulose is solubilized in the liquid phase of the pretreated feedstock as oligosaccharides. Formation of monomeric sugars during the LHW pretreatment is minimal. The LHW pretreatment is carried out by cooking the feedstock in process water at temperatures between 160 and 190 degrees C and at a pH of 4-7. No additional chemicals are needed. This chapter presents the detailed procedure of the LHW pretreatment of lignocellulosic biomass.

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.

Effect of compositional variability of distillers' grains on cellulosic ethanol production.

In a dry grind ethanol plant, approximately 0.84kg of dried distillers grains with solubles (DDGS) is produced per liter of ethanol. The distillers grains contain the unhydrolyzed and unprocessed cellulosic fraction of corn kernels, which could be further converted to ethanol or other valuable bioproducts by applying cellulose conversion technology. Its compositional variability is one of the factors that could affect the overall process design and economics. In this study, we present compositional variability of distillers grains collected from four different dry grind ethanol plants and its effect on enzymatic digestibility and fermentability. We then selected two sources of distillers grains based on their distinctive compositional difference. These were pretreated by either controlled pH liquid hot water (LHW) or ammonia fiber expansion (AFEX) and subjected to enzymatic hydrolysis and fermentation. Fermentation of the pretreated distillers grains using either industrial yeast or genetically engineered glucose and xylose co-fermenting yeast, yielded 70-80% of theoretical maximum ethanol concentration, which varied depending on the batch of distillers grains used. Results show that cellulose conversion and ethanol fermentation yields are affected by the compositions of distillers grains. Distillers grains with a high extractives content exhibit a lower enzymatic digestibility but a higher fermentability.

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.