Abstract
The objective of this thesis was to examine different pretreatment and saccharification processes of the agriculture residue (i.e. wheat straw) for enhanced production of biobutanol. The purpose was to define the best conditions to obtain maximum sugar yield during the saccharification and butanol yield during the simultaneous saccharification and fermentation (SSF). Three different pretreatment methods for the wheat straws were examined in the present work in comparison with no chemical pretreatment as a reference. This included water, acidic, and alkaline pretreatment. For all cases, physical pretreatment represented by 1 mm size reduction of the straws was applied prior to each pretreatment. Results showed that 16.91 g/L glucose concentration and 100% glucose yield were produced from saccarification with just the physical pretreatment (i.e. no chemical pretreatment). This represented ~5-20% lower sugar release in saccarification compared to the other three pretreatment processes. Saccharification with acid pretreatment obtained the highest sugar concentrations, which were 18.77 g/L glucose and 12.19 g/L xylose. Water pretreatment with SSF was compared with SSF alone (i,e. no chemical pretreatment with SSF). Both processes converted more that 10% of wheat straw into butanol product. This was 2% higher that previous studies. The results illustrated that SSF with no chemical pretreatment obtained 2.61 g/L butanol. Kinetic model was developed for both processes to determine concentration profile of butanol. The SSF with no chemical pretreatment obtained 1.21% root mean square error in comparison with the kinetic model. Similarly, SSF with water pretreatment obtained 1.21% root mean square error in comparison with the kinetic model. Similarly, SSF with water pretreatment obtained 0.83% root mean square error.
Highlights
This thesis examines different pretreatment, saccharification, and fermentation processes for producing biobutanol from agriculture residue
All of these saccharification processes were performed after dilute acidic pretreatment. These results demonstrated that highest sugar concentrations were achieved through separate hydrolysis and fermentation (SHF)
This thesis study achieved its objective of producing butanol from biomass in an inexpensive process without generating air pollution or inhibitors at optimum sugar yields
Summary
This thesis examines different pretreatment, saccharification, and fermentation processes for producing biobutanol from agriculture residue. Attaining butanol from biomass in an inexpensive process without generating air pollution or inhibitors is a complex chemical engineering problem because optimizing the yield is difficult. Typical processes for developing butanol from biomass such as acid pretreatment with enzymatic hydrolysis is expensive and generates air pollution. Pretreatment processes develop inhibitors that suppress butanol fermentation with 33% of the total cost for butanol production (Perez et al, 2008). During large scale butanol production, pretreatment catalysts such as sulfuric acid are hazardous and cause air pollution that lead to acid rain (Hill, 2010). Inhibitors such as hydroxymethylfurfural (HMF) and furfural are promoted by sulfuric acid through acid degradation reactions (Kootstra et al, 2009). Agricultural waste is used as a low cost biomass, but it has a limited availability of polysaccharides
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