**Pretreatment and Enzymatic Hydrolysis Project**

**Feedstock Qualification**

Stage Gate Review

Advanced Materials

6/1/05

**Abstract**

To achieve a goal of displacing 30% of current petroleum use by 2030
will require a consistent, robust, annual supply of feedstocks to
biorefineries for the production of biofuels and other biomass products.
Pretreatment is the initial operation necessary to convert feedstocks to
fuels and products. Pretreatment must provide an economical means to
open and expose the biomass surface structure to enzymatic hydrolysis to
yield fermentable sugars for biofuel production. Pretreatment and
enzymatic hydrolysis are two of the most capital-intensive processes in
the production of bioethanol, with pretreatment effectiveness also
strongly influencing enzymatic hydrolysis effectiveness. The current
research strategy is to reduce the cost for both processes, thereby
enabling biorefinery deployment.

Advancing this strategy requires an understanding of pretreatment and
feedstock chemistry, as diverse feedstocks' compositions may require
different pretreatment approaches. The goal for the Feedstock
Qualification Project is to select specific feedstocks representative of
feedstocks present in potentially sufficient quantities to meet a major
portion of the petroleum displacement goal, and to determine their
pretreatment reactivity across a broad range of pH, time, and
temperature. Towards that end we have selected wheat-straw residue and
energy-crop switchgrass. We will also likely select a third feedstock
representing a forest resources derived from harvesting residues or fuel
treatments. We intend to complete preliminary assessments of the
performance of various pretreatment conditions on these feedstocks by
the end of FY 2005 and final assessment by the end of FY 2006.

**Introduction**

In 2002, the Biomass Research and Development Technology Advisory
Committee published two reports, "Vision for Bioenergy and Biobased
Products in the United States" and "Final Road Map for Biomass
Technologies in the United States" (1, 2). These reports outlined the
strategy, goals, and technology to displace 30% of the current petroleum
consumption in the United States by 2030 using biomass to supply fuels,
chemicals, and power. The report estimated that more than one billion
tons of biomass would be needed annually to achieve this goal. In 2004,
the U.S. Department of Energy and the United States Department of
Agriculture released a draft report of "Biomass as Feedstock for a
Bioenergy and Bioproducts Industry: The Technical Feasibility of a
Billion-Ton Annual Supply" (billion-ton study) (3). The report surveyed
the forest and agricultural resources in the United States to determine
whether the resource base was available for a sustainable
billion-ton-per-year bioindustry. The positive finding estimated that
1.3 billion tons of sustainable biomass are available from a wide range
of feedstocks, crop residues, and processed waste. Of the 1.3 billion
tons of biomass needed, more than 380 million tons would come from
forestlands and more than 930 million tons from agricultural lands.
Combined processing of the projected feedstocks represents a six-fold
increase in current biomass production and consumption.

One of the major objectives listed in the 2002 Biomass Vision was:

*"Develop economically and environmentally sound bioconversion
processes/*

*technologies for commercial application of a range of biobased fuels
and products*"

Examples of research needs were improved methods for physical and
chemical pretreatment of biomass feedstocks prior to fermentation.
Pretreatment is a key first step, opening the biomass structure,
exposing it to enzymatic hydrolysis. While many unknowns and barriers
exist for biomass pretreatment, effective biochemical conversion of
these feedstocks is a key to achieving cost-effective yields. The
Feedstock Qualification Survey (FQS) will:

-   Identify feedstocks with the greatest potential to meet the
    billion-ton vision

-   Screen representative feedstocks for their pretreatment and
    saccharification response across time, temperature, and pH range

-   Continue to develop pretreatment knowledge using improvements in
    enzyme economics.

While several different pretreatment approaches are already in various
stages of process development on a few feedstocks, a broader assessment
of pretreatment chemistries across feedstock categories is still needed.
Different pretreatment and enzymatic hydrolysis approaches may be well
suited to certain feedstock types but not as applicable to other
feedstock types. Work under the Consortium for Applied Fundamentals and
Innovation has demonstrated how alternative pretreatments affect
pretreatment chemistries. In pretreating herbaceous biomass, for
example, ammonia fiber explosion depolymerizes by cleaving
lignin-carbohydrate bonds, leading to significant delignification (4,5).
Dilute acid hydrolysis, on the other hand, removes most of the
hemicellulose fraction along with a modest amount of lignin.
Additionally, evaluating selected feedstocks at acidic, neutral, and
alkaline pH regimes may identify different pretreatment chemistries
impacting enzymatic saccharification.

**Biomass Availability**

######## 

######## Forest Feedstocks

According to the billion-ton study, more than 193 million tons of
biomass are currently used for fuels, products, and power. Of this, 142
million tons come from forestlands with the balance coming from
biofuels, bioproducts, and biomass from crop residues. Of the 142
million tons of forest-derived biomass used yearly, 31% comes from wood
residues, 37% is from forest products, and 25% is from fuelwood. The
analyses and assumptions listed in the billion-ton biomass survey
project an increase of 2.5 times the current biomass extracted from
forestlands and forest products, to more than 380 million tons of
sustainable, annual biomass. As Figure 1, taken from the billion-ton
study, shows, the increase in biomass comes from using uncollected
forest residues produced during harvesting, from forest thinnings for
fire hazard suppression, and from urban wood wastes. These unexploited
materials have the potential to contribute to healthier forests and
reduced forest fire hazard. Unfortunately, forest feedstocks from
thinnings, harvesting residues, and urban wood wastes are likely to be
diverse in species, proportion of bark and ash in the overall feedstock,
and other ways. This makes selection of a single representative
feedstock from this feedstock category, as necessary for conducting the
FQS experimental screening, difficult. For the experimental screening
study, it would be necessary to define a representative feedstock type.

The tonnage of sustainable harvest extracted from forest thinnings for
fire hazard suppression and logging residues accounts for a 49% (Figure
3) increase from unexploited resources, and 26% of the total forest
biomass resource. Other biomass sources in forestlands have existing use
such as fuelwood, pulping liquors, and wood residues. Level growth in
these areas is expected, fully exploiting any added resources.

![](media/image1.wmf)

Figure 1. Projected biomass from the forest resource based on existing
use and inventory of unexploited residues, harvesting fuel treatments
and forest products. *(3) A Billion-Ton Feedstock Supply for a Bioenergy
and Bioproducts Industry*

######## Agricultural Feedstocks 

About 10% of the current total of 193 million tons per year of U.S.
agricultural crops is now used for biobased products and biofuels.
Starch-based ethanol from corn and other grains and biodiesel from
soybeans are the largest current bioenergy uses. Growing perennial
energy crops and harvesting crop residues make the agricultural sector
the largest potential contributor of biomass feedstocks, according to
the billion-ton study. With certain changes in land use practices,
technology, and crop management, the United States could produce more
than 960 million tons of agricultural derived biomass per year. These
changes would include:

-   Achieving a 50% increase in crop yields

-   Introducing perennial crops such as switchgrass, willows, and poplar

-   Obtaining harvesting and collection efficiency of 75% for crop
    residues

-   Implementing no-till practices for all croplands

-   Increasing soybean residues/seed ratio.

Incorporation of these assumptions increases the potential agricultural
feedstocks to 960 million tons of annual sustainable production (2), a
four-fold increase over the current total biomass production of 193
million tons. Figure 2 shows the potential contribution of primary
agricultural resources, by sector, from incorporating changes in land
practices and crop managements.

The largest increase in available biomass comes from planting and
harvesting perennial crops (29%), followed by harvesting corn stover
(16%) and harvesting small grain residues (12%). Corn stover, is the
largest potential crop residue feedstock, but is not selected for direct
inclusion in the FQS experimental study because of continuing
programmatic efforts involving this feedstock. We expect that with a few
appropriate control experiments, the data from programmatic research on
corn stover would serve as a basis for comparison to the FQS
pretreatment and enzymatic hydrolysis data.

Wheat straw combined with other crop residues adds up to 150 million
tons of potential biomass, approaching the feedstock volume potential of
corn stover. Therefore, as a representative small grains crop residue
feedstock, wheat straw was chosen for the FQS experimental study.

According to the draft billion-ton study, perennial crops have the
potential to become the largest source of available biomass, with well
over 350 million tons/year potentially available. Switchgrass was
selected as a representative perennial crop feedstock for the FQS
experimental study because of its potential for multiple yearly
harvests, low harvesting cost, and potential for widespread distribution
(6). However, it is unclear how much of the perennial crop feedstock
category would consist of switchgrass and other grasses and how much
would consist of woody perennial energy crops, such as poplar or willow.
In addition, a perennial woody energy crop would provide a woody
feedstock for the FQS experimental study with less varied compositional
characteristics than forest residues. Further guidance on expected
policy and other drivers is needed to decide if a woody perennial crop
(i.e. poplar) or a representative forest residue feedstock is the best
choice for a woody feedstock for inclusion in the FQS experimental
study.

![](media/image2.wmf)

**Figure 2. Projected biomass from the agricultural resource based on
increased yields, higher residue collection, and introduction of
perennial crops. (3)**

**Feedstock Composition**

Feedstock composition directly affects the efficacy of biomass
pretreatment and saccharification. Pretreatment chemistry and the ease
of saccharification of biomass reflect lignocellulosic structure and
composition. While many crop and forest residues make excellent
feedstocks for power and products from thermochemical conversion, the
scope of this survey is limited to biochemical conversion.
Cost-effective biochemical conversion of potential feedstocks to fuels
and products needs appropriate levels of cellulose, hemicellulose,
accessory sugars, and lignin. Extractives, high ratios of lignin to
carbohydrates, or high ash content will negatively impact the process
economics. Understanding the effect of feedstock composition on
pretreatment chemistry and ultimately feedstock reactivity, is one key
to achieving the robust conversion processes able to handle the variety
of feedstocks and biomass compositions a biorefinery could receive at
the plant gate.

The variability in chemical composition across individual varieties and
environmental growth conditions is another characteristic to consider in
selecting feedstocks for suitable conversion processes. Figure 3 shows
the average agricultural feedstock composition from 53 varieties taken
from the EERE Biomass Feedstock Composition and Property Database (7).
Comparing the average composition of sample feedstocks (wheat straw,
corn stover, and switchgrass), the percentage mass for glucan, xylan,
and lignin fractions are all within sample variability. Wheat straw,
however, has higher ash content than the other two, as do other straw
feedstocks, such as rice straw. The ash content reflects silica and
potassium content, which has a history of boiler fouling, abrading
mechanical and processing equipment, and neutralizing acidic catalysts
(8). The Market Target Corn Stover composition used in Aspen Plus^®^
models for material and energy balances serves as a benchmark feedstock
composition. These models analyze process scenarios for ethanol
production. Variation in the major lignocellulosic polymers from the
Target Case can serve as a first screening to select a thermochemical or
biochemical conversion path for future feedstocks. We selected wheat
straw as a representative small grain residue for this early survey in
part because of the impact of its higher ash content, not present in
forest residues, switch grass, or corn stover.

![](media/image3.wmf)

**Figure 3. Feedstock Composition of Varieties of Corn Stover, Bagasse,
Switchgrass and Wheat Straw Taken from the EERE Database**

In contrast to agricultural resources, forest residues and
thinnings---typically pine or other softwoods---can vary greatly in
feedstock composition. As shown in Figure 4, ponderosa pine composition
varies considerably with the part of the tree/means of collection. Such
variation in composition presents challenges in selecting a
representative "feedstock type" of forestland biomass. Hybrid poplar, on
the other hand, is more uniform and also shares some composition
attributes of agricultural resources, with respect to xylan and
extractives content. Using hardwoods, such as hybrid poplar, to
represent a "woody" resource would avoid some of the feedstock issues
from the diverse composition of forest residues and thinnings. However,
additional policy and program guidance is needed regarding selecting
forest residues for the FQS. Future considerations may include selection
of feedstocks spanning a range of compositional and structural features,
producing differing responses to pretreatment chemistries and resulting
enzymatic hydrolysis needs.

![](media/image4.wmf)

**Figure 4. Composition of Ponderosa Pine Thinnings Components and Whole
Hybrid**

**Poplar (9)**

**Existing Pretreatment and Saccharification Data**

The goal of the feedstock qualification survey is to evaluate biomass
feedstocks with potential to achieve the stated goal for petroleum
displacement. The data from these feedstocks, once selected and
evaluated, will populate a feedstock survey database describing a
particular feedstock performance across experimental boundaries. Other
studies that have systematically examined feedstocks in this manner
would be included in that database as well. For example, for the past
six years NREL has evaluated corn stover and corn stover varieties for
their composition, pretreatment performance, and saccharification using
dilute acid pretreatment. Also, for the past three years, the Consortium
for Applied Fundamentals and Innovation (CAFI) has worked to understand
pretreatment chemistry effects on corn stover, as embodied in the
specific CAFI pretreatment processes, spanning the acidic, neutral, and
alkaline regions. We expect that data from these efforts will complement
the FQS experimental data. Thus, while corn stover was not included in
this first feedstock selection, the data from past and continuing
research efforts on corn stover feedstocks will be incorporated.

**Path Forward**

Switchgrass and wheat straw were selected as the first feedstocks for
evaluation of their respective pretreatment chemistries. The major
criterion for the selection was the potential amount of biomass that
could be produced to meet the goal for petroleum displacement. A third
feedstock, representing the forestry resources, was identified but not
selected yet due to additional program and policy guidance needed to
reach consensus. These three feedstocks (if forest residues are selected
as the woody feedstock) could contribute more than 60% of biomass needed
to meet the programmatic petroleum displacement goal. Adding the
contribution of collected corn stover residue could potentially bring
the total biomass collection to about 80% of the billion ton
requirement.

The work plan for the FQS experimental study is to generate a broad data
set to determine the effect of different pretreatment chemistries,
ranging from acidic to alkaline, on the selected feedstocks. These
pretreatment conditions are robust enough to provide process-relevant
information regarding the time, temperature, and pH for the pretreatment
conditions for each feedstock. Results from these experiments will
include component mass balances (solubilization of components and
recovery of solubilized liquid products) and the response of pretreated
process streams (washed pretreated solids and any oligomer-containing
liquid fractions) to enzymatic hydrolysis using a baseline enzyme
preparation. We will also conduct studies to determine what types of
enzyme activities are better suited to various pretreated samples. The
sugar yield from pretreatment and the total sugar yield from the
combined pretreatment and saccharification assay, along with the amount
of monomeric and oligomeric composition of the released sugars, will
provide the baseline for pretreatment chemistry for the specific
feedstocks. This data on yields from various process conditions for the
selected feedstocks would provide feedstock reactivity across the
selected pretreatment conditions and relative differences between
feedstocks. This can guide stakeholders and technology developers in
formulating pretreatment-saccharification strategies for specific
feedstocks.

**Milestones**

*FY05*

Selection of three candidate feedstock opportunities across captive,
residue, and energy crop feedstock categories **-** 3/31/05 (Completed)

Interim report of pretreatment and enzymatic saccharification
results---initial feedstocks and/or pretreatment chemistries-9/31/05

*FY06*

Completion of laboratory pretreatment chemistry screening on a set of
biomass feedstocks and reporting of pretreatment and enzymatic
saccharification performance -7/29/06

**Out-year efforts**

Evaluation of additional feedstocks and feedstock varieties are planned
for the FY06 and into FY07. Feedstocks with promising pretreatment
chemistries will be moved to larger scale bench pretreatment and
saccharification studies.

For FY07 and beyond, the focus will be to construct a reactor with
multiple-pretreatment-chemistry capability to conduct alternative
pretreatments across a broad range of pH, time, and temperature.

**References**

> 1\. Biomass Research and Development Technology Advisory Committee.
> *Vision for Bioenergy & Biobased Products in the United States*. Oct.
> 2002.
> <http://www.bioproducts-bioenergy.gov/pdfs/FinalBiomassRoadmap.pdf>

2.  Biomass Research and Development Technology Advisory Committee.
    *Final Roadmap for Biotechnologies in the United States*. Dec. 2002.
    <http://www.bioproducts-bioenergy.gov/pdfs/FinalBiomassRoadmap.pdf>

3.  *A Billion-Ton Feedstock Supply for a Bioenergy and Bioproducts
    Industry: Technical Feasibility of Annually Supplying 1 Billion Dry
    Tons of Biomass*.

<http://www.eere.energy.gov/biomass/pdfs/final_billionton_vision_report2.pdf>

4.  Mosier, N., Wyman, C., Dale, B., Elander, R., Lee, Y.Y., Holtzapple,
    M., Ladisch, M., 2004. "Features of promising technologies for
    pretreatment of lignocellulosic biomass." *Bioresource Technology*
    96 (2005) 673--686.

> 5\. Wyman, C., Dale, B., Elander, R., Holtzapple, M., Ladisch, M.,
> Lee, Y.Y., 2005. "Coordinated development of leading biomass
> pretreatment technologies"
>
> *Bioresource Technology*. In press.
>
> 6\. Personal communication with Robert Perlack, Oak Ridge National
> Laboratory, Oak Ridge, TN, Environmental Sciences Division, Bioenergy
> Systems Group 3/3/05.

7.  EERE Biomass Feedstock Composition and Property Database.

> <http://www.eere.energy.gov/biomass/feedstock_databases.html>

8.  Vlasenko, E., Ding, H., Labavitch, J., Shoemaker, S. "Enzymatic
    hydrolysis of pretreated rice straw." *Bioresource Technology*
    59 (1997) 109-119

9.  Personal Communication with Bonnie Hames, National Renewable Energy
    Laboratory. Wet Chemicals Analysis of Softwood and Hardwood
    Thinnings. 4/5/05.