Sequential extrusion-ozone pretreatment of switchgrass and big bluestem.

Pretreatment is one of the biggest challenges in utilizing lignocellulosic feedstocks to meet the mandatory requirements for biofuels around the world. Earlier researchers evaluated extrusion and ozone pretreatment separately and found that sugar recovery can be improved significantly from 15-20 to 40-75 % for different feedstocks. To further improve sugar recoveries, extrusion-ozone sequential pretreatment was explored. Accordingly, optimal extruded switchgrass (176 °C, 155 rpm, 20 % moisture, and 8 mm) and big bluestem (180 °C, 155 rpm, 20 % moisture, and 8 mm) at 25-75 % moisture content were exposed to an ozone flow rate of 37-365 mg/h for 2.5 to 10 min. Pretreated samples were then subjected to enzymatic hydrolysis to determine sugar recovery. Statistical analyses confirmed significant effects of the independent variables and their interactions on sugar recoveries for both feedstocks. Maximum glucose, xylose, and total sugar recovery of 66.4, 82.3, and 70.4 %, respectively, were obtained when a low-moisture (25 %) extruded switchgrass was ozonated for 2.5 min at a flow rate of 37 mg/h. Respectively, this represents increases of 3.42, 5.01, and 3.42 times that of the control. When big bluestem at 25 % moisture was extruded and then ozonated for 2.5 min at a flow rate of 365 mg/h, resulting glucose, xylose, and total sugar recoveries of 90.8, 92.2, and 87.5 %, respectively, were obtained. These represent increases of 4.5, 2.7, and 3.9 times than that of the control. It is also noteworthy that furfural and hydroxymethyl furfural were not detected in any of the pretreatments, and only low levels (0.14-0.18 g/l) of acetic acid were measured. The results show that sequential pretreatment using extrusion and ozone is an efficient way to improve sugar recovery from herbaceous biomass feedstocks.

Sequential extrusion-microwave pretreatment of switchgrass and big bluestem.

Developing an effective and economical biomass pretreatment method is a significant roadblock to meeting the ever growing demand for transportation fuels. Earlier studies with different feedstocks revealed that in the absence of chemicals, neither extrusion nor microwave could be standalone pretreatments. However, there is potential that the advantages of these individual methods can be harnessed in a sequential pretreatment process. Accordingly, switchgrass and big bluestem were extruded and then subject to microwave pretreatment, under optimal conditions that had been separately determined in prior studies. Pretreated biomass was then subject to enzymatic hydrolysis to understand the effectiveness of the sequential pretreatment on sugar recovery and generation of fermentation inhibitors. Statistical analysis confirmed that moisture content, microwave power level, and exposure time (and their interactions) had significant influence on sugar recovery. Sequential pretreatment of switchgrass (25% moisture, 450W and 2.5min) resulted in a maximum glucose, xylose, and total sugar recovery of 52.6%, 75.5%, and 59.2%, respectively. This was higher by 1.27 and 2.71, 1.21 and 4.60, and 1.25 and 2.87 times compared to extrusion alone and the unpretreated control, respectively. The same sequential pretreatment conditions achieved maximum glucose, xylose, and total sugar recovery of 83.2%, 92.1%, and 68.1%, respectively, for big bluestem. This was 1.14 and 4.1, 1.18 and 2.7, and 1.20 and 3.0 times higher than extrusion alone and the unpretreated control, respectively. This sequential pretreatment process did not aggravate acetic acid formation over levels observed with the individual pretreatments. Furthermore, furfural, HMF, and formic acid were not detected in any of the treatments. Although the sequential pretreatment process enhanced sugar recovery without increasing the levels of potential fermentation inhibitors, the increased energy input for the microwave treatment may not be economical.

Physiochemical characterization of briquettes made from different feedstocks.

Densification of biomass can address handling, transportation, and storage problems and also lend itself to an automated loading and unloading of transport vehicles and storage systems. The purpose of this study is to compare the physicochemical properties of briquettes made from different feedstocks. Feedstocks such as corn stover, switchgrass, prairie cord grass, sawdust, pigeon pea grass, and cotton stalk were densified using a briquetting system. Physical characterization includes particle size distribution, geometrical mean diameter (GMD), densities (bulk and true), porosity, and glass transition temperature. The compositional analysis of control and briquettes was also performed. Statistical analyses confirmed the existence of significant differences in these physical properties and chemical composition of control and briquettes. Correlation analysis confirms the contribution of lignin to bulk density and durability. Among the feedstocks tested, cotton stalk had the highest bulk density of 964 kg/m(3) which is an elevenfold increase compared to control cotton stalk. Corn stover and pigeon pea grass had the highest (96.6%) and lowest (61%) durability.

Extrusion pretreatment of pine wood chips.

Pretreatment is the first step to open up lignocellulose structure in the conversion of biomass to biofuels. Extrusion can be a viable pretreatment method due to its ability to simultaneously expose biomass to a range of disruptive conditions in a continuous flow process. Extruder screw speed, barrel temperature, and feedstock moisture content are important factors that can influence sugar recovery from biomass. Hence, the current study was undertaken to investigate the effects of these parameters on extrusion pretreatment of pine wood chips. Pine wood chip at 25, 35, and 45 % wb moisture content were pretreated at various barrel temperatures (100, 140, and 180 °C) and screw speeds (100, 150, and 200 rpm) using a screw with compression ratios of 3:1. The pretreated pine wood chips were subjected to standard enzymatic hydrolysis followed by sugar and byproducts quantification. Statistical analyses revealed the existence of significant differences in sugar recovery due to independent variables based on comparing the mean of main effects and interaction effects. Pine wood chips pretreated at a screw speed of 150 rpm and a barrel temperature of 180 °C with a moisture content of 25 % resulted in a maximum cellulose, hemicellulose, and total sugar recoveries of 65.8, 65.6, and 66.1 %, respectively, which was about 6.7, 7.9, and 6.8 fold higher than the control (unpretreated pine chips). Furthermore, potential fermentation inhibitors such as furfural, hydroxyl methyl furfural, and acetic acid were not found in any of the treatment combinations.