Title

A Study of Concentrated Acid Hydrolysis Conversion of Lignocellulosic Materials to Sugars Using a Co-Rotating Twin-Screw Reactor Extruder and Plug Flow Reactor

Date of Award

2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Roger Hester

Advisor Department

Polymers and High Performance Materials

Abstract

Concerns about the ability of petroleum to continue supplying ever increasing global energy demands, at a price capable of generating continued economic growth, have spurred innovative research in the field of alternative energy. One alternative energy option that has the ability to provide long-term sustainable energy supplies for the global energy market is the conversion of lignocellulosic materials, via acid hydrolysis, to fermentable sugars for the production of fuel grade ethanol. This research demonstrates the ability of a co-rotating twin-screw reactor extruder and plug flow reactor to continuously convert lignocellulosic materials to fermentable sugars using high temperature concentrated acid hydrolysis. In addition to demonstrating continuous operation of the two-stage concentrated acid hydrolysis system, a number of design of experiments were conducted to model the twin-screw performance and maximize its ability to effectively solubilize lignocellulosic feedstocks in the high shear, elevated temperature, concentrated acid environment. These studies produced a base case twin-screw operating condition used to generate a standard extrudate composition for an extensive high temperature acid hydrolysis batch reactor kinetic modeling study. In this study a number of nonlinear and linear regression analyses were undertaken so that the concentration of less resistant cellulose, or the amount of solublilized extrudate cellulose, resistant cellulose, or non-solubilized extrudate cellulose, glucose, and decomposition products could be obtained as a function of time, temperature, and acid concentration. This study demonstrated that the theoretical cellulose conversion of 51% was limited by the amount of solubilized polysaccharides that could be produced in the twin-screw pretreatment. Further experimentation, showing twin-screw pretreatment lignocellulosic versatility, produced nearly identical results as the southern yellow pine sawdust experiments that were conducted in the previous studies. From this experimentation it is believed that the current conversion yields achievable are limited by the twin-screw geometry used. Future screw designs that incorporate a tapered screw intermeshing depth will compensate for solids to liquids conversions as the extrudate travels the length of the screw. This will ensure that the extrudate receives the necessary shear forces to produce higher lignocellulosic solubilization.