Kinetic characterization for pretreatment of timber varieties and switchgrass using diluted acid hydrolysis

In recent years, growing attention has been devoted to the use of lignocellulosic biomass as a feedstock to produce renewable carbohydrates as a source of energy products, including liquid alternatives to fossil fuels. The benefits of developing woody biomass to ethanol technology are to increase the long-term national energy security, reduce fossil energy consumption, lower greenhouse gas emissions, use renewable rather than depletable resources, and create local jobs. Currently, research is driven by the need to reduce the cost of biomass-ethanol production. One of the preferred methods is to thermochemically pretreat the biomass material and subsequently, enzymatically hydrolyze the pretreated material to fermentable sugars that can then be converted to ethanol using specialized microorganisms. The goals of pretreatment are to remove the hemicellulose fraction from other biomass components, reduce bioconversion time, enhance enzymatic conversion of the cellulose fraction, and, hopefully, obtain a higher ethanol yield. The primary goal of this research is to obtain kinetic detailed data for dilute acid hydrolysis for several timber species from the Upper Peninsula of Michigan and switchgrass. These results will be used to identify optimum reaction conditions to maximize production of fermentable sugars and minimize production of non-fermentable byproducts. The structural carbohydrate analysis of the biomass species used in this project was performed using the procedure proposed by National Renewable Energy Laboratory (NREL). Subsequently, dilute acid-catalyzed hydrolysis of biomass, including aspen, basswood, balsam, red maple, and switchgrass, was studied at various temperatures, acid concentrations, and particle sizes in a 1-L well-mixed batch reactor (Parr Instruments, ii Model 4571). 25 g of biomass and 500 mL of diluted acid solution were added into a 1-L glass liner, and then put into the reactor. During the experiment, 5 mL samples were taken starting at 100°C at 3 min intervals until reaching the targeted temperature (160, 175, or 190°C), followed by 4 samples after achieving the desired temperature. The collected samples were then cooled in an ice bath immediately to stop the reaction. The cooled samples were filtered using 0.2 μm MILLIPORE membrane filter to remove suspended solids. The filtered samples were then analyzed using High Performance Liquid Chromatography (HPLC) with a Bio-Rad Aminex HPX-87P column, and refractive index detection to measure monomeric and polymeric sugars plus degradation byproducts. A first order reaction model was assumed and the kinetic parameters such as activation energy and pre-exponential factor from Arrhenius equation were obtained from a match between the model and experimental data. The reaction temperature increases linearly after 40 minutes during experiments. Xylose and other sugars were formed from hemicellulose hydrolysis over this heat up period until a maximum concentration was reached at the time near when the targeted temperature was reached. However, negligible amount of xylose byproducts and small concentrations of other soluble sugars, such as mannose, arabinose, and galactose were detected during this initial heat up period. Very little cellulose hydrolysis yielding glucose was observed during the initial heat up period. On the other hand, later in the reaction during the constant temperature period xylose was degraded to furfural. Glucose production from cellulose was increased during this constant temperature period at later time points in the reaction. The kinetic coefficient governing the generation of xylose from hemicellulose and the generation of furfural from xylose presented a coherent dependence on both temperature and acid concentration. However, no effect was observed in the particle size. There were three types of biomass used in this project; hardwood (aspen, basswood, and red maple), softwood (balsam), and a herbaceous crop (switchgrass). The activation energies and the pre-exponential factors of the timber species and switchgrass were in a range of 49 - 180 kJ/mol and from 7.5x104 - 2.6x1020 min-1, respectively, for the xylose formation model. In addition, for xylose degradation, the activation energies and the preexponential factors ranged from 130 - 170 kJ/mol and from 6.8x1013 - 3.7x1017 min-1, respectively. The results compare favorably with the literature values given by Ranganathan et al, 1985. Overall, up to 92 % of the xylose was able to generate from the dilute acid hydrolysis in this project.

Federal and state policy influence on woody biomass utilization

A considerable portion of public lands in the United States is at risk of uncharacteristically severe wildfires due to a history of fire suppression. Wildfires already have detrimental impacts on the landscape and on communities in the wildland-urban interface (WUI) due to unnatural and overstocked forests. Strategies to mitigate wildfire risk include mechanical thinning and prescribed burning in areas with high wildfire risk. The material removed is often of little or no economic value. Woody biomass utilization (WBU) could offset the costs of hazardous fuel treatments if removed material could be used for wood products, heat, or electricity production. However, barriers due to transportation costs, removal costs, and physical constraints (such as steep slopes) hinder woody biomass utilization. Various federal and state policies attempt to overcome these barriers. WBU has the potential to aid in wildfire mitigation and meet growing state mandates for renewable energy. This research utilizes interview data from individuals involved with on-the-ground woody biomass removal and utilization to determine how federal and state policies influence woody biomass utilization. Results suggest that there is not one over-arching policy that hinders or promotes woody biomass utilization, but rather woody biomass utilization is hindered by organizational constraints related to time, cost, and quality of land management agencies’ actions. However, the use of stewardship contracting (a hybrid timber sale and service contract) shows promise for increased WBU, especially in states with favorable tax policies and renewable energy mandates. Policy recommendations to promote WBU include renewal of stewardship contracting legislations and a re-evaluation of land cover types suited for WBU. Potential future policies to consider include the indirect role of carbon dioxide emission reduction activities to promote wood energy and future impacts of air quality regulations.

Small-scale timber stand management techniques : a case study of woodlots in Isangati, Tanzania

Small-scale village woodlots of less than 0.5ha are the preferred use of land for local farmers with extra land in the village of Isangati, a small community located in the southern highlands of Tanzania. Farmers view woodlots as lucrative investments that do not involve intensive labor or time. The climate is ideal for the types of trees grown and the risks are minimal with no serious threats from insects, fires, thieves, or grazing livestock. It was hypothesized that small-scale village woodlot owners were not maximizing timber outputs with their current timber stand management and harvesting techniques. Personal interviews were conducted over a five month period and field data was collected at each farmer’s woodlots over a seven month period. Woodlot field data included woodlot size, number of trees, tree species, tree height, dbh, age, and spacing. The results indicated that the lack of proper woodlot management techniques results in failure to fully capitalize on the investment of woodlots. While farmers should continue with their current harvesting rotations, some of the reasons for not maximizing tree growth include close spacing (2m x 2m), no tree thinning, extreme pruning (60% of tree), and little to no weeding. Through education and hands-on woodlot management workshops, the farmers could increase their timber output and value of woodlots.