Joan G. Lynam

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.

Pretreatment of rice hulls by ionic liquid dissolution

As a highly available waste product, rice hulls could be a starting block in replacing liquid fossil fuels. However, their silica covering can make further use difficult. This preliminary study investigates effects of dissolving rice hulls in the ionic liquids 1-ethyl-3-methylimidazolium acetate (EMIM Ac), 1-hexyl-3-methylimidazolium chloride, (HMIM Cl), and 1-allyl-3-methylimidazolium chloride (AMIM Cl), and what lignocellulosic components can be precipitated from the used ionic liquid with water and ethanol. EMIM Ac dissolution at 110 °C for 8 h was found to completely remove lignin from rice hulls, while ethanol was capable of precipitating lignin out of the used EMIM Ac. With 8h dissolution at 110 °C using HMIM Cl, approximately 20% of the cellulose in the rice hull sample can be precipitated out using water as co-solvent, while more than 60% of the hemicellulose can be precipitated with ethanol.

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.