Carbonic Acid Retreatment of Biomass Page: 3 of 65
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This project sought to address six objectives, outlined below. The objectives were met
through the completion of ten tasks.
1) Solidify the theoretical understanding of the binary CO2/H20 system at reaction
temperatures and pressures. The thermodynamics of pH prediction have been improved
to include a more rigorous treatment of non-ideal gas phases. However it was found that
experimental attempts to confirm theoretical pH predictions were still off by a factor of
about 1.8 pH units. Arrhenius experiments were carried out and the activation energy for
carbonic acid appears to be substantially similar to sulfuric acid. Titration experiments
have not yet confirmed or quantified the buffering or acid suppression effects of carbonic
acid on biomass.
2) Modify the carbonic acid pretreatment severity function to include the effect of
endogenous acid formation and carbonate buffering, if necessary. It was found that the
existing severity functions serve adequately to account for endogenous acid production
and carbonate effects.
3) Quantify the production of soluble carbohydrates at different reaction conditions and
severity. Results show that carbonic acid has little effect on increasing soluble
carbohydrate concentrations for pretreated aspen wood, compared to pretreatment with
water alone. This appears to be connected to the release of endogenous acids by the
substrate. A less acidic substrate such as corn stover would derive benefit from the use
of carbonic acid.
4) Quantify the production of microbial inhibitors at selected reaction conditions and
severity. It was found that the release of inhibitors was correlated to reaction severity and
that carbonic acid did not appear to increase or decrease inhibition compared to
pretreatment with water alone.
5) Assess the reactivity to enzymatic hydrolysis of material pretreated at selected reaction
conditions and severity. Enzymatic hydrolysis rates increased with severity, but no
advantage was detected for the use of carbonic acid compared to water alone.
6) Determine optimal conditions for carbonic acid pretreatment of aspen wood. Optimal
severities appeared to be in the mid range tested. ASPEN-Plus modeling and economic
analysis of the process indicate that the process could be cost competitive with sulfuric
acid if the concentration of solids in the pretreatment is maintained very high (-50%).
Lower solids concentrations result in larger reactors that become expensive to construct
for high pressure applications.
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university, Baylor. Carbonic Acid Retreatment of Biomass, report, June 1, 2003; Golden, Colorado. (https://digital.library.unt.edu/ark:/67531/metadc785336/m1/3/: accessed May 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.