(433f) Modification of Biomass Rheology: The Influence of Physical Chemistry

Chemicals derived from lignocellulosic biomass, including liquid fuels, are a sustainable alternative to petroleum derivatives. Many different processes have been proposed to convert lignocellulosic materials to liquid fuels but a common operation required in all of them is heating to high temperatures (110-230 ^oC). Reducing the concentration of water during this step decreases utility costs and decreases overall capital costs by reducing equipment size. Increasing the solids concentration however, results in rheological changes like a rapidly increasing yield stress. Mixing, pumping and pouring biomass slurries becomes difficult, if not impossible, above 20-30 wt% solids.

We have shown previously that the rheology of biomass can be controlled with the use of certain water soluble polymers (WSPs). AFM experiments have revealed that WSPs alter stresses in cellulose fiber suspensions by lubricating the surface of individual fibers. Using these additives, we have been able to mix and convey untreated biomass at solids concentrations up to 50 wt%. However, the efficacy of WSPs is reduced after certain treatments such as acid hydrolysis. How changes in the physical chemistry of biomass during treatment affect rheology modification with WSPs is unknown.

In this presentation our focus will be on the influence of the physical chemistry of both biomass and WSPs on rheological modifications. The physical chemistry of the biomass is altered by the treatment type, e.g. acid hydrolysis, and the treatment severity. Specific changes to the physical chemistry of the biomass are probed with fiber suspensions containing known chemistries, e.g. cellulose fibers vs. hemicellulose-rich fibers. The physical chemistry of the WSPs are altered by varying the type of polymer, the molecular weight, the degree of substitution, and by the addition of chemical additives. We will show how these variables influence not only the instantaneous rheological modification but also its behavior over time.