Life-changing Research and Development Cellulosic Biomass Chemical Pretreatment Technologies September 6, 2007 Keith Pauley Keith.Pauley@matricresearch.com 800-611-2296 Chemical and Environmental Technologies Health and Life Sciences Advanced Engineering Systems www.matricresearch.com
Industrialization of Cellulosic Ethanol Five factors control the ability for cellulosic ethanol to become economically viable: Process rate slow process step kinetics requires larger capital equipment costs Conversion efficiency poor utilization of feed materials drives higher operating costs Capital equipment costs exotic MOC, high pressure or temperature materials drive adversely impact cost of goods produced Operating costs high temperatures or pressures require significant amounts of energy Product quality/consistency Inconsistency increases the cost of the overall process MATRIC 2
Fermentation Based Cellulosic Ethanol Process Pretreatment phase, to make the lignocellulosic material such as wood or straw amenable to hydrolysis Cellulose hydrolysis (cellulolysis), to break down the molecules into sugars Separation of the sugar solution from the residual materials, notably lignin Microbial fermentation of the sugar solution Distillation to produce 99.5% pure alcohol Chart courtesy of the National Renewable Energy Lab and appears on the Renewable Fuels Association website. MATRIC 3
Key Processing Cost Elements www.everythingbiomass.org MATRIC 4
Pretreatment Technologies Pretreatment technologies are mostly used as precursor to cellulose hydrolysis Acid Hydrolysis Steam Explosion Ammonia Fiber Expansion (AFEX) Alkaline Wet Oxidation Ozone Pretreatment (Ozonolysis) Each method has advantages and disadvantages No one method is best for all types of feedstock Optimum reaction parameters of the various pretreatments, like temperature, pressure, and reaction time, are specific to each feedstock Mosier et al., Bioresour. Technol. 2005 High yield of sugars does not always result in high conversion to ethanol lignocellulosic components or chemicals used in pretreatment may form compounds that inhibit fermentation MATRIC 5
Acid Hydrolysis Concentrated or dilute mineral acids penetrate biomass, breaking down hemicellulose into monomeric sugars, and removing part of the lignin First cellulosic pretreatment technology dating from Germany in 1898 Reaction is carried out at elevated temperatures Sulfuric acid is most often used, because it is available at low cost Low moisture content is preferred, since less energy is needed to heat the biomass http://www1.eere.energy.gov/biomass/images/photo_0 5208_sugar_platform.jpg MATRIC 6
Acid Hydrolysis Advantages good hemicellulose sugar yields high cellulose digestibility removal of hemicellulose and lignin exposes more cellulose for enzymes to attack can solubilize heavy metals that may contaminate the feedstock Disadvantages requires downstream neutralization some degradation of hemicellulose sugars lower yield of sugars may form compounds such as acetic acid and furfural which inhibit bacteria or yeasts during fermentation equipment costs are high reactors must be corrosion resistant, suitable for high temperature and pressures MATRIC 7
Steam Explosion Physico-chemical pretreatment in which biomass is subjected to high-pressure saturated steam, followed by rapid depressurization Expansion of water vapor exerts force, causing mechanical breakdown of biomass degrades hemicellulose and lignin, thus increasing the potential of cellulose hydrolysis acids or bases may be incorporated into the steam to increase hydrolysis www.biogasol.dk/2me2.htm MATRIC 8
Steam Explosion Advantages economical for hardwoods effectively hydrolyzes hemicellulose promotes delignification enlarges pore size in plant cells which is beneficial for subsequent cellulose hydrolysis Disadvantages increases crystallinity of amorphous regions of cellulose, which decreases cellulose digestibility high equipment costs need for high temperature and high pressure reactors MATRIC 9
Ammonia Fiber Expansion (AFEX) Physico-chemical pretreatment in which prewetted lignocellulosic material is treated with liquid anhydrous ammonia at high temperature and pressure, then pressure is rapidly released Created and patented by Michigan State University In contrast to most pretreatments, AFEX does not significantly solubilize hemicellulose Pressures exceeding 12 atm are required for operation at ambient temperature MATRIC 10
Ammonia Fiber Expansion (AFEX) Advantages Much less sugar degradation than acid pretreatment inhibitor formation is very limited Fast reaction time (~5min) Improves hydrolysis rates of hemicellulose and cellulose in herbaceous crops and grasses Ammonia can serve as a nitrogen source for organisms downstream Ammonia is all volatilized and can be recovered as gas neutralization is not necessary Disadvantages High energy utilization to achieve very high pressures Relatively new and undeveloped process Not proven effective on hardwoods or softwoods AFEX effectiveness decreases with increasing lignin content MATRIC 11
Alkaline Wet Oxidation Water, sodium carbonate, and oxygen at elevated temperature and pressure interact with biomass by breaking ester bonds Mechanism believed to be saponification of intermolecular ester bonds that crosslink hemicelluloses with other components Porosity of the material is increased due to the removal of the crosslinks, so enzymes can attack sugars more easily MATRIC 12
Alkaline Wet Oxidation Advantages Readily oxidizes lignin Significant decrease in cellulose crystallinity more accessible to enzymes Low formation of furfural, a microbial inhibitor often produced by other pretreatment methods Disadvantages Degradation of lignin and hemicellulose to produce carboxylic acids hemicellulose sugars largely decompose, thus cannot be converted to ethanol MATRIC 13
Ozone Pretreatment (Ozonolysis) Sugimoto et al., Ozone Pretreatment for Ethanol Production Using Lignocellulose Materials, Forestry and Forest Products Research Institute Ozone acts primarily by degrading lignin, via attack and cleavage of aromatic ring structures In one study using wheat straw, ozone pretreatment removed 60% of lignin, which increased enzymatic hydrolysis rates fivefold MATRIC 14
Ozone Pretreatment (Ozonolysis) Advantages Effective delignification Ozone does not form any toxic compounds that inhibit hydrolysis ozone can be easily decomposed to oxygen using a catalytic bed or high temperatures, thus extensive downstream processing is avoided Can be conducted at ambient temperature and pressure Disadvantages Requires large amounts of ozone, which is expensive Generation of carboxylic acids from extensive lignin degradation MATRIC 15
Summary None of the current pretreatment technologies described in this presentation meet the criteria for economic viability Each of these technologies is currently being demonstrated at scale Further information may change the verdict MATRIC is currently developing a proprietary chemical pretreatment technology that has the potential to satisfy all of the requirements outlined herein MATRIC 16