| One of the challenges in the production of bioethanol from lignocellulosic biomass is disruption of the complex structure of the biomass to obtain monomeric sugars via pretreatment. Chemical pretreatments that utilize homogeneous chemicals such as H2SO4 are attractive due to the higher reaction rates and mass transfer efficiencies. However acid pretreatment requires special downstream processing in the form of neutralization, which involves costly and inefficient separation from homogeneous reaction mixtures, resulting in a sulfate waste. Therefore, "green agents" such as solid acid catalysts can address some of these challenges by facilitating use of mild operating conditions with higher selectivity, thereby and allowing easy separation from products and catalyst reusability. Hence for the present research, it was hypothesized that solid acid catalysts can pretreat and hydrolyze biomasses. Therefore, in this research, supported sulfonic acid catalysts were evaluated as pretreatment and hydrolysis agents for Switchgrass, Gamagrass, Miscanthus x giganteus, and Triticale hay. The objectives were to (1) synthesize, evaluate, and compare sulfonic acid catalysts for pretreatment of switchgrass, (2) evaluate p-toluenesulfonic acid catalyst for direct hydrolysis of switchgrass, and (3) test the efficiency of magnetic p-toluenesulfonic acid catalysts for pretreatment of four types of lignocellulosic biomasses, viz, switchgrass, miscanthus x giganteus, gamagrass, and triticale hay.;For the first objective, three supported sulfonic acid catalysts were synthesized using activated carbon as support and sulfuric acid, p-toluene sulfonic acid, and methane sulfonic acid as precursors to obtain sulfonic acid catalyst (AC-SA), methane sulfonic acid catalyst (AC-MAS) and p-toluene sulfonic acid catalyst (AC-pTSA). The catalysts were evaluated in batch experiments using three temperatures (30, 60 and 90 °C) and two reaction times (90 and 120 minutes) and switchgrass as feedstock (0.25 g/g raw switchgrass). A proc mixed model was employed to analyze the data along with slice effects test. Results suggested that glucose yields produced after enzymatic hydrolysis ranged between 31.5 and 61.5%, with the maximum yield obtained from switchgrass treated with AC-pTSA at 90 °C for 120 min. Further, results from characterization of catalysts via Boehm titration, BET surface area, TGA, and FTIR analyzers indicated that sulfonation improved the total acidity and lowered pore volume. In addition, the catalyst was reused three times with no significant difference in glucose yields (p > 0.05).;For the second objective, AC-pTSA was employed as a catalyst for direct hydrolysis of biomass. For this part of the research, baseline experiments were performed using pure feedstocks including cellulose, starch, and cellobiose. Subsequently switchgrass was used as a feedstock for hydrolysis. In addition, effects of conventional pretreatments such as ultrasonication, NaOH, and H 2SO4 were also employed prior to catalytic hydrolysis of switchgrass. Results indicated that for model biomasses, i.e., starch and cellobiose, catalytic hydrolysis resulted in glucose yields of 190.07 +/- 2.02 mg g-1 and 237.1 +/- 0.86 mg g-1, respectively. However, for cellulose, the catalyst exhibited poor activity perhaps, due to strong hydrogen bonding and higher crystallinity resulting in low solubility in the liquid. For raw switchgrass, a glucose yield of 72.67 +/- 1.03 mg g-1 (conversion of 23.25 +/- 0.33 %) was obtained. In addition, ultrasonication prior to catalytic hydrolysis yielded 16.91 +/- 0.05 % of glucose. Interestingly, chemical pretreatments (NaOH and H2SO4) of switchgrass actually inhibited the subsequent catalytic hydrolysis and the glucose yields were in the range of 0.26 -- 2.48 mg g-1.;Finally, to enhance the separation of the catalyst from biomass (after pretreatment), the catalyst was magnetized via chemical impregnation. The catalyst was tested for pretreatment of four types of biomasses viz., Switchgrass, Gamagrass, Miscanthus x giganteus and Triticale hay at 90 °C for 2 h and followed by enzymatic hydrolysis using Ctec2. Data analysis via Proc Glimmix suggested that the glucose yields of magnetic catalysts were similar to regular catalyst, with a maximum yield of 65.07 +/- 1.63 % (for Switchgrass). In addition, results from reusability studies using magnetic catalysts indicated that there was a slight reduction in catalytic activity during the second run.;Overall, results from this research suggest that sulfonic acid catalysts have high potential to replace conventional acids for pretreatment and with further improvement in catalytic activity, may possibly be used for direct hydrolysis, making the biomass to alcohol processes more efficient and environment friendly. |
