Charles J. Coronella

Effect of thermal pretreatment on equilibrium moisture content of lignocellulosic biomass

The equilibrium moisture content (EMC) of raw lignocellulosic biomass, along with four samples subjected to thermal pretreatment, was measured at relative humidities ranging from 11% to 97% at a constant temperature of 30 °C. Three samples were prepared by treatment in hot compressed water by a process known as wet torrefaction, at temperatures of 200, 230, and 260 °C. An additional sample was prepared by dry torrefaction at 300 °C. Pretreated biomass shows EMC below that of raw biomass. This indicates that pretreated biomass, both dry and wet torrefied, is more hydrophobic than raw biomass. The EMC results were correlated with a recent model that takes into account additional non-adsorption interactions of water, such as mixing and swelling. The model offers physical insight into the water activity in lignocellulosic biomass.

Acetic acid and lithium chloride effects on hydrothermal carbonization of lignocellulosic biomass

As a renewable non-food resource, lignocellulosic biomass has great potential as an energy source or feedstock for further conversion. However, challenges exist with supply logistics of this geographically scattered and perishable resource. Hydrothermal carbonization treats any kind of biomass in 200 to 260°C compressed water under an inert atmosphere to produce a hydrophobic solid of reduced mass and increased fuel value. A maximum in higher heating value (HHV) was found when 0.4 g of acetic acid was added per g of biomass. If 1g of LiCl and 0.4 g of acetic acid were added per g of biomass to the initial reaction solution, a 30% increase in HHV was found compared to the pretreatment with no additives, along with greater mass reduction. LiCl addition also reduces reaction pressure. Addition of acetic acid and/or LiCl to hydrothermal carbonization each contribute to increased HHV and reduced mass yield of the solid product.

Reaction kinetics of hydrothermal carbonization of loblolly pine.

Hydrothermal carbonization (HTC) is a pretreatment process to convert diverse feedstocks to homogeneous energy-dense solid fuels. Understanding of reaction kinetics is necessary for reactor design and optimization. In this study, the reaction kinetics and effects of particle size on HTC were investigated. Experiments were conducted in a novel two-chamber reactor maintaining isothermal conditions for 15s to 30 min reaction times. Loblolly pine was treated at 200, 230, and 260°C. During the first few minutes of reaction, the solid-product mass yield decreases rapidly while the calorific value increases rapidly. A simple reaction mechanism is proposed and validated, in which both hemicellulose and cellulose degrade in parallel first-order reactions. Activation energy of hemicellulose and cellulose degradation were determined to be 30 and 73 kJ/mol, respectively. For short HTC times, both reaction and diffusion effects were observed.

Glycerol as an ionic liquid co-solvent for pretreatment of rice hulls to enhance glucose and xylose yield

Rice hulls, a widely-available secondary agricultural residue, can be pretreated with ionic liquids (IL) prior to enzymatic hydrolysis to enhance glucose and xylose yields. The high cost of ILs is a deterrent to commercial deployment at present. ILs 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium formate, 1,3-dimethylimidazolium dimethylphosphate, and 1-ethyl-3-methylimidazolium diethylphosphate were investigated for rice hull pretreatment. Effects of diluting ILs with glycerol were investigated for biomass pretreatment efficacy, and for solvent recovery. When diluted with 50% glycerol, rice hulls treated in 1-ethyl-3-methylimidazolium formate was found to give glucose and xylose yields after enzymatic hydrolysis better than rice hulls treated in pure 1-ethyl-3-methylimidazolium formate. Dilution in glycerol resulted in an increased rate of solvent recovery after pretreatment, as much as six times that when pure 1-ethyl-3-methylimidazolium formate was used. Diluting 1-ethyl-3-methylimidazolium formate with 50% glycerol was found to decrease solvent viscosity at the pretreatment temperature (110 °C) helping explain improved biomass pretreatment.

A novel method for isokinetic measurement of particle flux within the riser of a circulating fluidized bed

Abstract Previous workers have shown that the net particle flux within the riser of a circulating fluidized bed (CFB) may be measured by a simple technique with a suction probe facing upwards and then downwards. However, this technique does not give accurate measurements of the upward and downward particle fluxes independently. A probe similar to that of previous workers is used here to measure the flux of the upflow. However, the flux of the downflow is measured with a probe through which no external air flow is imposed. The method presented here uses an 8-mm tubular probe, penetrating the riser wall and rising at a sharp angle. The probe is constructed of sections of steel tube and 400 mesh screen. Particles fall into the probe and then into a sealed reservoir for subsequent analysis. The gas flow in the riser passes through the screen sections of the tube, so that the gas flow at the tip of the probe is virtually undisturbed by the presence of the probe. The method is verified in a CFB riser of diameter 115 mm, fluidizing sand of average size 209 μm, with a solids circulation rate in the range of 10–30 (m2s) and air velocity in the range of 3.4–5.4 m/s, corresponding to a nominal solids concentration (based on pressure-drop measurements) of 0.5–2.5%. The technique presented here allows for accurate and independent measurements of both the upward flux and the downward flux, and thus represents an improvement on previous methods. Previous workers have specified that a critical surface where the time-averaged net flux is zero demarcates the dilute core from the dense annulus. However, the total particle flux, defined as the sum of the upward and downward fluxes, is proportional to the time-averaged local particle concentration, and so is indicative of physical phenomena in the riser. Trends for the total flux are presented.