Atlantic Biomass Conversions
Sequential Enzymatic Pretreatment and Sacacharification System
Produces Highly Efficient Conversion of Sugar Beet Pulp to Biofuel Sugars
January 2010
Abstract
The fundamental barriers to overcoming the biomass recalcitrance that causes low
efficiencies in simple sugar production from complex carbohydrates include: 1) limited
enzyme access to biomass components within the cell wall matrix, and 2) inhibition of
the conversion processes by conversion products.
In our work with sugar beet pulp we have developed a proprietary enzyme process that
overcomes these barriers. We call this the Sequential Enzymatic Pretreatment and
Sacacharification System. With this system we are able to convert very high
percentages of sugar beet pulp, and in the future other low-cost field crops and
agricultural residues into C-5 and C-6 sugars suitable for biofuel production using
fermentation or other biochemical conversion technologies.
Sugar Beet Pulp
Beet pulp from sugar beets (Beta vulgaris), which is a residue of commercial sucrose
(table sugar) production has the potential to be a valuable biofuel crop. In addition to the
commercially produced sucrose contained in the plant’s root, which is approximately
17% of total dry weight, the remaining beet pulp is rich in other carbohydrate
components that could be used for biofuels (Table 1).
Table 1: Post Process Beet Pulp Composition & Annual Yield
(Average values obtained from Crystal Sugar, composition may vary with strain or
growing conditions)
Biomass Component
Pectin
Arabinose
Xylose
Cellulose
Sucrose
Proteins
Minerals
Non-Characterized
Total Available for
Biofuels
Potential Biofuels
(gallons) @65%
Conversion Efficiency
% Composition
24.0%
16.0%
16.0%
20.0%
4.0%
11.0%
4.0%
5.0%
76.0%
US Production
(Dry Tons)
600,000
400,000
400,000
500,000
100,000
Europe & Asia
(Dry Tons)
960,000
640,000
640,000
800,000
160,000
2,000,000
3,200,000
371,000,000
594,000,000
In both the US and the EU current sugar beet harvests are limited by government
regulations to maintain sugar prices. Therefore, current harvest totals are considerably
below totals of the mid-20th century. Higher yields would therefore be possible in
response to market demands, policy changes, and through the use of new “energy”
sugar beet varieties.
In commercial beet sugar processing, sucrose is
released from the biomass matrix by soaking
chopped up sugar beets in 600-650C (140-1500F)
water for approximately two hours in counter-flow
diffusers systems. Beet pulp remains.
An enzymatic system that produces biofuel
precursors from the remaining pulp biomass within
the two hour operating time would produce a lowcapital system that: 1) would utilize the relatively
high temperature to speed up reactions, and 2)
would not require large storage tanks for the pulp
awaiting conversion.
Sugar beet pulp is also ideally suited for biofuel
production because of the following production
characteristics.
Beet Pulp from the Diffuser
•
Beet pulp is a low-value ($.03-.05/lbs) agricultural residue of sucrose production.
•
Beet pulp production is concentrated at a small number of large capacity plants.
•
Therefore, biomass transportation and storage costs have already been
optimized.
•
Sugar beet plants have extensive process control, steam production, and water
quality systems already in place. This lowers the infrastructure costs of
expanding the facilities into biofuel production.
•
The residual beet pulp left over from sugar hydrolysis is high in protein content
and may be used as a high-value animal feed.
Raw (Unprocessed) Beet Pulp
2.0
Post-Processed Beet Pulp
Sequential Enzymatic Pretreatment and Sacacharification System
In order to overcome biomass recalcitrance, which will greatly decrease the amount of
time needed for plant cell wall hydrolysis leading to reduced biofuel production costs, a
specific order of enzyme treatment is required. We have developed a proprietary
enzymatic system based on the research that led to this discover.
Enzyme treated beet pulp
Untreated beet pulp
This system is able to quickly convert a very high percentage of sugar beet pulp into C5 and C-6 sugars suitable for biofuel production using fermentation or other biochemical
conversion technologies. A summary of current results, produced with enzymes still
being optimized, is presented in Table 2 below.
Table 2: Calculated Conversion Ratios
Composite Results With 1st Generation Enzymes
1. Initial Cellulose Concentration
Cellobiose Produced
Glucose Produced
Estimated Conversion Rate
20 gm/l
2.92 gm/l
16.03gm/l
94.8%
2. Initial Hemicellulose Concentration
Arabinose Produced
Estimated Conversion Rate
16 gm/l
11.6 gm/l
72.5%
3. Initial Pectin Concentration
Galactose Produced
Gal-Acid Produced
Total Converted
Estimated Conversion Rate
3.0
24 gm/l
2.77 gm/l
17.40 gm/l
20.17gm/l
84.0%
Sequential Enzyme System: Safety/Environmental/Operational Advantages
Because our Sequential Enzymatic Pretreatment and Sacacharification System can
be retrofitted to existing beet sugar plants and uses enzymes that will be produced in
closed bioreactors at facilities certified for safety, instead of genetically modified
organisms (GMO), it will have the following safety, environmental, and operational
advantages.
•
No organisms will be used at beet processing plants. Therefore, no GMO
(genetically modified organisms) issues are involved. This means no extra
environmental impact statements (EIS), USDA, or state and local permitting
required.
•
With no organisms being used, individual species tolerances to production
conditions, temperature, pH, etc. are not operational concerns.
•
By adding our system to existing production facilities, rather than building new
stand-alone plants, permitting costs are significantly reduced.
4.0
To The Future
Atlantic Biomass is working to expand the use of the Sequential Enzymatic
Pretreatment and Sacacharification System to other biomass feedstocks. Our first
targets are sorghum, both sweet and “energy” varieties, and perennial field grasses
such as switchgrass and salt resistant spartina spieces.
The production goals for these new enzyme systems are those of the Atlantic Biomass
portable “Follow-the-Crop” biofuel precursor system. The combination of these two
systems will greatly increase the availability of biofuel feedstocks. Together, they will
efficiently converting widely dispersed small stands of grasses and other field crops
grown on marginal lands into a liquid biofuel feedstock that can transported by truck or
rail hundreds of miles to large, efficient biofuel producers.