(554e) Evaluation of Membrane Separations Opportunities within Lignocellulosic Biorefining Processes: Tailoring Membrane Properties

Evaluation of Membrane Separations Opportunities
within Lignocellulosic Biorefining
Processes: Tailoring Membrane Properties

Jennifer Leberknight, Amitkumar Gautam, and Todd J. Menkhaus

South Dakota School of Mines and Technology

Department of Chemical and Biological Engineering

Rapid City, SD
57701

Tel: (605)-394-2422

Email: Todd.Menkhaus@sdsmt.edu

Membrane
separations can be integrated into a biorefinery at many locations and offer
tremendous potential to reduce water usage and energy consumption, decrease
production costs, simplify purification operations, and offer opportunities for
recovery of valuable co-products.  Here we
explore five locations for integration of membrane technology into the basic biochemical
production process for fuels and/or chemicals. 
The biomass is initially pretreated and enzymatically hydrolyzed to
convert the cellulose and hemicellulose into fermentable sugars, after which a
solid-liquid clarification operation to remove solids (primarily lignin) may be
employed (Membrane Separation 1).  The
liquid stream can then be further separated to recycle the hydrolysis enzymes (Membrane
Separation 2) and/or to concentrate the sugars by reverse osmosis (Membrane Separation
3).  Increased fermentation efficiency could
be achieved by integrating a membrane step after fermentation to separate and
recycle the fermentation organism (Membrane Separation 4), while membrane
extraction or pervaporation can be used for in-situ
product recovery (Membrane Separation 5). 
Within the various membrane processes, fouling is a major challenge to
overcome.  We have correlated membrane
fouling tendencies within the different membrane separation locations to
measureable properties of the membrane and foulants such as ionic charge,
hydrophilicity, size, and surface roughness to determine why membranes
foul.   Through a combination of analytical and
modeling approaches we postulate fouling mechanisms and identify methods to
mitigate fouling.  Finally, simple empirical
models using variable concentrations of fouling components and quantitative
membrane properties have been developed to help establish predictive performance
abilities.  As detailed examples, both
microfiltration (Separations 1 and 4) along with pervaporation of ethanol from
a fermentation broth (Separation 5), were evaluated. Both selectivity and flux
must be considered in new fouling-resistant membrane designs.  The unique soluble compounds (phenolics,
furans, and organic acids) in the lignocellulosic derived feeds greatly complicate
the fouling and separation, as will be discussed.