(287d) Biomaterials of Tomorrow: The Rheology of Liquefied Feedstocks and the Impact of Feedstock Variability

PhD dissertation: “High Solids Loading Aqueous Slurry Formation of Corn Stover Before Pretreatment in a Fed-Batch Bioreactor”, advised by Michael Ladisch, Agricultural and Biological Engineering, Purdue University

With an increase in population, the world will depend on renewable sources to meet the increasingly energy needs. The use of lignocellulosic biomass as a renewable source has been proven efficient for conversion to cellulosic ethanol and capable of contributing to achieve the threshold on energy demand while reducing greenhouse gases in 90% compared to fossil fuels. However, biomass processing encounters limitations in feeding and flow within biorefineries due to system plugging by compaction and slurry high yield stress, preventing transport of biomass materials and in some cases unexpected plant shutdowns that result in high operational costs.

Different solutions for biomass handling and slurry formation have been studied from densified materials such as pellets. Cellulosic biomass residues are typically processed in pretreatment reactors to which acid or base is added. Other pretreatments, such as liquid hot water (LHW) and steam explosion that act without the addition of chemicals, use pressures above the saturation vapor of water, to disrupt biomass structure. Although these methods are widely known, the use of pretreatments like acid digestion and LHW presents challenges like waste disposal and could be energy inefficient. Alternatively, other approaches such as enzyme liquefaction have been applied for the transformation of biomass into slurries with promising results without the use of pretreatments.

However, the implementation of enzyme liquefaction faces difficulties due to the recalcitrant properties of biomass, its variability, and the release of enzyme inhibitors. Although it has been proven that the properties of the chemical composition in biomass have effects on enzyme inhibition, hindering the efficiency of liquefaction, not much research has been conducted in understanding physical properties such as particle size, porosity, water adsorption retention and their effect on the ability to form a slurry at high solids concentration.

To improve the handling of lignocellulosic biomass and the formation of biomass slurries, the primary focus of this research is to identify the key indicators and most important physical characteristics of corn stover that determine its ability to form a slurry at high solids concentrations up to 300 mg/ml. This is achieved by understanding the formation of slurry from densified materials such as pellets that hold different physical and chemical properties and how these properties change and interact during the liquefaction process (Figure 1). Pellets and slurries characteristics

Furthermore, this research explores the hypothesis that the initial and final slurry rheology depends on the initial physical characteristics of the corn stover biomass such as the shape, size and free water of the particles, and the final rheology also is a function of its history during processing. Additionally, enzymatic assisted slurry formation improves enzyme hydrolysis of untreated and pretreated slurries; for what this work conducted experimental investigation of physical changes and chemical reactions that occur during and after enzyme-assisted slurry formation, which in turn could enhance enzyme accessibility to cellulose. Enzyme-assisted liquefaction for solid loadings of up to 300g/L was conducted on a fed-batch process using commercial enzymes Celluclast 1.5L or Ctec-2 at 1FPU/g or 3 FPU/g of dry solids in a 10 mM sodium citrate buffer solution (pH 4.8). Samples were characterized with respect to their composition, rheology, and water absorption. Slurries achieved yield stresses of 178±7 Pa (3 FPU, Celluclast 1.5L) and 79±6 Pa (3 FPU, Ctec-2) for corn stover at 24 hours, compared to 6,000 Pa for samples without enzyme. Yield stress was 155± 29 Pa (3FPU, Ctec-2) and 257 ± 72 Pa (1 FPU, Celluclast 1.5L) for corn cobs at 24 hours. Particle size reduction for deaggregated pellets and final slurries was measured. Particle size and water absorption are analyzed as a predictor factor for liquefaction in combination with lignin content, and impact of an integrated process on biorefinery operations is discussed.

Acknowledgments: DOE Cooperative Agreement 8652 and 8910

Research Interests:

My career has been focused on the research of renewable energy and renewable resources engineering. I have been part of several research projects that had contributed to the field, from working with small farmers in Colombia during my first job as a research engineer, to helping small farmers in Indiana and Africa to manage their specialty crops to currently working with the United States Department of Energy to study the use of corn stover as biomass to produce bioethanol. In each of this project’s major advances were made in terms of research, for the small farmers in Colombia different technologies where designed and transferred and a logistics characterization was published to help understand the challenges in the region. For the small farmers in Indiana and Africa a patent of a solar dryer was generated and tested to understand the impact on the dehydration of products with three different publications as result of this works. Recently two publications for the work on biofuels have been published in terms of new strategies to treat biomass and enhance its liquefaction to improve the production of bioethanol in the US. From these projects I have learned that I would like to peruse a research career related to biological products and my goal as a faculty would be to pursue projects related with sustainability and removable resources from agricultural waste. From the different research experiences, I have identified four main research areas I would like to work on:

1. Biological materials physical and chemical characterization
2. Biomass transformation
3. Fermentation
4. Rheology of biological materials