Optimization of biofuel production from switchgrass with hydrogen peroxide – acetic acid pretreatment method

The aim of this master's thesis is to develop integrated thermochemical and fermentation processes for the production of maximum quantities of two biofuels, ethanol, and methane, with minimum process cost from the energy crop switchgrass. In this master's thesis, firstly, the energy crop switchgrass characterization was carried out and to reach to C5 and C6 sugars in the lignocellulosic structure hydrogen peroxide (H2O2) and acetic acid (CH3COOH - HAc)(HP&HAc) pretreatment was applied. To increase the ethanol and methane production efficiency HP&HAc pretreatment process was optimized for maximum biofuel production. Response surface method (RSM), Central composite design (CCD) were used in HP&HAc pretreatment process optimization. Experimental design of HP&HAc pre-treatment process was done with Design Expert 7.1.5 software. Experiments were conducted according to the pretreatment conditions proposed by the software using parameters of H2O2 amount, HAc amount, reaction time and reaction temperature in the HP&HAc pretreatment process, and the analysis results of the determined response variables were transferred to Design Expert software. In the CCD experiment design, ANOVA test was applied to model the response variable and to test the conformity of the proposed model. The HP&HAc pretreatment process was optimized for maximum ethanol and methane production and maximum ethanol and methane production at minimum process cost, and optimum process conditions were detected. Using HP&HAc pretreated samples, the ethanol production process was optimized with simultaneous saccharification and fermentation process (SSF) and ethanol was produced. After ethanol production, with minimum waste strategy using all wastes including ethanol fermentation medium, the second biofuel, methane production, was carried out by using methane fermentation. Finally, after HP&HAc pretreatment experiments Scanning Electron Microscope (SEM) was used to investigate the changes in surface properties and Fourier Transform Infrared Spectroscopy (FTIR) was used to examine the change in bond characterization of switchgrass. As a result of the characterization analysis, carbon (C) content of the switchgrass was determined as 40.13%. The amount of cellulose and hemicellulose were 33.13% and 34.76%, respectively. High carbon content, cellulose, and hemicellulose content (67.89%) and structural carbohydrate content (2.17 mg / mL) suggest that switchgrass can be used in energy production. At the conclusion of the simultaneous saccharification and fermentation process, maximum ethanol was produced in the HP&HAc pretreatment condition of 100 °C reaction temperature, 24 h reaction time, 0% HAc and 2% H2O2 concentrations in which the maximum sugar concentration was also obtained. 81.65 mgEtOH/gTS ethanol was produced from switchgrass samples treated in this HP&HAc condition. From raw switchgrass samples, 32.62 mgEtOH/gTS ethanol was produced. The amount of ethanol produced by the HP&HAc pretreatment application was 150.36% greater than the amount of ethanol produced from the raw switchgrass sample and reached 49.55% of the theoretical ethanol yield. Ethanol was evaporated via distillation, fermentation medium and liquid phase from pretreatment were combined and biochemical methane potential test (BMP) was performed to produce methane from all wastes. The maximum methane production was obtained as 363.82 mLCH4/gVS from the switchgrass samples pretreated at 100 °C reaction temperature, 6 hours reaction time, 2% HAc and 0% H2O2 concentrations. Average BMP value of the switchgrass variety of Shawneé samples was measured as 195.50 mLCH4/gVS. Methane produced from the samples treated with HP&HAc pretreatment increased by 86.09% compared to methane produced from raw samples of switchgrass. Independent variable values are processed and modeled in Design Expert® 7 software. The R2 values of the models established for ethanol and BMP were calculated as 0.8650 and 0.8508, respectively. In the first approach; optimum HP&HAc pretreatment conditions for maximum ethanol and methane production were found as 100 °C reaction temperature, 22.9 hours reaction time, 2% HAc and 2% H2O2 concentrations. In the second approach; optimum HP&HAc pretreatment conditions for maximum ethanol and methane production at minimum process cost were suggested as 50 °C reaction temperature, 6 hours reaction time, 1.87% HAc and 0% H2O2 concentrations. Validation tests were conducted to test the reliability of the models under optimum HP&HAc pretreatment conditions recommended by the software. The low error between the values estimated by the model and the results obtained from the validation experiments shows that the obtained models can be used safely. In this study, from 1 tonne of switchgrass variety of Shawneé energy crop grown in Turkey and dried on the field; 36.32 L ethanol, 161.15 L CH4 produced from raw samples, 95.6 L ethanol ve 292.89 L CH4 produced from samples pretreated at optimum HP&HAc pretreatment conditions for maximum ethanol and methane production and 38.77 L ethanol, 282.43 L CH4 produced from samples pretreated at optimum HP&HAc pretreatment conditions for maximum ethanol and methane production at minimum process cost. According to this, 163.21% ethanol, 81.75% methane increase in optimum HP&HAc pretreatment conditions for maximum ethanol and methane production, 6.76% ethanol, 75.25% methane increase in optimum HP&HAc pre-treatment conditions for maximum ethanol and methane production at minimum process cost were obtained, compared to ethanol and methane produced from raw switchgrass. Since there are no studies in the literature evaluating the ethanol and methane production processes combined with HP&HAc pretreatment process, determining optimum process conditions for ethanol and methane production and producing two biofuels without waste production using the energy crop switchgrass, the results obtainedfrom studies conducted within the scope of this master's thesis are the values that can be used as reference points in subsequent studies.