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Pretreatment of Guayule Biomass Using Supercritical CO2-based Method for Use as Fermentation Feedstock

Srinivasan, Narayanan
http://rave.ohiolink.edu/etdc/view?acc_num=akron1289782016

Abstract Details

2010, Doctor of Philosophy, University of Akron, Chemical Engineering.
Guayule is a commercial desert shrub grown in the dry regions of Arizona and California. Its resin and latex products are non-allergenic to most people unlike the products made from the rubber from Hevea brasiliensis. Latex and resins, however, make up only about 20% of biomass. Converting the waste bagasse to biorefinery feedstock makes good economic sense. A supercritical CO2-based process had been developed for pre-treating the guayule. Our approach used supercritical CO2 and moisture for mild hydrolysis and subsequent explosion, created by sudden pressure release. The pretreatment involved: adding water to the bagasse, raising system temperature, pressurizing using supercritical CO2, holding the system for a period of time, and exploding the bagasse. The different pretreatments were compared based on the sugar yield from the enzyme hydrolysis and our method was more effective than other techniques such as acid hydrolysis and delignification. No inhibitory/toxic effects were apparent in terms of growth of Trichoderma reesei Rut C-30. A factorial design was performed to find the optimum working conditions for maximum sugar yields from the supercritical CO2 pretreatment of the guayule. The optimum yields of glucose and pentose were 55% and 60% from enzyme hydrolysis at a temperature of 170 °C, 3800 psi, 57% moisture and 32 minutes of holding time. Additional solvents like acetone and ethanol were tried in place of water as solvents. Although acetone and ethanol gave yields 50% and 54% which are comparable with that of water, only in case of acetone the working conditions were milder (60 °C). A study involving the removal of lignin from the biomass was performed using the supercritical CO2 method. A Supercritical carbon dioxide-ethanol- water system was studied to extract the lignin present in the bagasse. The extraction process was not efficient and removed very little lignin (30%). Guayule has a lot of hemicelluloses and so micro-organisms that can metabolize xylose efficiently in addition to glucose were chosen and were tested for their ethanol tolerance and ability to withstand the hydrolyzate toxicity. Three yeast species were found to consume xylose and have high ethanol tolerance. But the highest yield of ethanol was from the simultaneous saccharification fermentation of the pretreated bagasse with the K.marxianus yeast, 0.36 g ethanol/ g of hydrolysable sugars. The process as a whole aims at using a non food crop as a source of fermentation feedstock. There is no competing use as a food crop and hence no increase in food prices. The supercritical pretreatment process preserves all kinds of sugars including the hemicelluloses. The process does not destroy any sugars compared to the widely used dilute acid pretreatment. The fermentation process involves the use of yeasts that can metabolize hemi-cellulosic sugars in addition to the six carbon sugars and produce ethanol. The thermotolerant K.marxianus yeast gave a high ethanol yield compared to the others. Its ability to grow at higher temperatures enabled the use of SSF process at 42 °C where the enzyme activity is high enough for faster sugar release. The yield of the whole process is 8% (0.08 g ethanol/ g bagasse).
Lu-Kwand Ju, Dr. (Advisor)
Richard Elliott, PhD (Committee Member)
Lingyun Liu, PhD (Committee Member)
Teresa Cutright, PhD (Committee Member)
Donald Ott, PhD (Committee Member)
219 p.
Chemical Engineering
bagasse; PRETREATMENT; lignin; GUAYULE; SUPERCRITICAL; hydrolysis; sugar

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Citations

  • Srinivasan, N. (2010). Pretreatment of Guayule Biomass Using Supercritical CO2-based Method for Use as Fermentation Feedstock [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1289782016

    APA Style (7th edition)

  • Srinivasan, Narayanan. Pretreatment of Guayule Biomass Using Supercritical CO2-based Method for Use as Fermentation Feedstock. 2010. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1289782016.

    MLA Style (8th edition)

  • Srinivasan, Narayanan. "Pretreatment of Guayule Biomass Using Supercritical CO2-based Method for Use as Fermentation Feedstock." Doctoral dissertation, University of Akron, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1289782016

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.