Fossil fuel resources are not limitless so alternative renewable recourses are needed to fill the void that inevitably will be created once the supplies of this resource start do dwindle. Biomass has the potential to fill this void. Today only a small part of the world annual production of biomass is utilized by humankind, while the rest is allowed to decay naturally. To utilize this renewable resource in the production of fuel and chemicals, the so called bio-refineries specialized in fractionation and making use of all component of the biomass are needed. Ionic liquids could aid in this task. Ionic liquids (ILs) have shown great potential in the field of biomass processing in general and in the pretreatment of (ligno)-cellulose in particular. However, a few things need to be addressed before any large-scale processing can be considered: Finding new routes for IL synthesis that make "on-site" production possible; Investigation into the challenges facing IL pretreatment of (ligno)-cellulose such as possible depolymerization of cellulosic material during the pretreatment and investigating what influence different ILs have on the pretreatment of cellulosic material by methods like enzymatic hydrolysis. This work aims to address these issues and will present a route for IL synthesis making use of alcohols and carboxylic acids both commonly found in a biorefinery. Some of these ILs have also been tested for their ability of dissolve cellulose. Furthermore, this work will address the possibilities but also challenges upon IL-mediated (ligno)-cellulose processing. This includes investigating several ILs and their efficiency as a pretreatment solvent for enzymatic hydrolysis; these studies involve a large variety of different cellulosic materials. This work demonstrated that depolymerization during the IL pretreatment is a possibility and that this can complicate the recovery processes. Furthermore, this work gives guidance into what type of ILs might be suited as pretreatment solvents for different cellulosic materials, including amorphous and crystalline cellulose, processed and native lignocellulose, different types of wood samples and hemicellulose.

No description available.

No description available.

The effect of ionic strength (I), pCO2, and temperature on the reaction kinetics of calcite was investigated in magnesium-free, phosphate-free, low calcium (mCa^2 ≈ 0.01 – 0.02 molal) simple KCl and NaCl solutions from both undersaturated and oversaturated conditions. First order kinetics were found sufficient to describe the dissolution rate data. Dissolution rates decreased with increasing I and were faster in KCl than NaCl solutions at the same I indicating that Na^ interacts more strongly with the calcite surface than K^ or that water is less available in NaCl solutions. Rates increased with increasing pCO2 and temperature, and their influence diminished at high I. Arrhenius plots yielded a relatively high activation energy (Ea ≈ 20 ± 2 kJ mol-1) which indicated that dissolution was dominated by surface controlled processes. These results are consistent with the hypothesis that the mole fraction of "free" solvent plays a significant role in the dissolution kinetics of calcite with a minimum value of ~45-50 percent required for dissolution to proceed in undersaturated solutions at 25-55 degrees C and pCO2 = 0.1 – 1 atm. Precipitation rates were modeled using the general and Davies and Jones rate equations yielding similar results. Reaction orders were found to typically range between 0.8 and 2.5 for both rate equations regardless of electrolyte. For both solutions, rate constants were found to range between 100.8 and 101.7 mmole m-2 hr-1 (general rate equation) and 101.5 and 102.2 mmole m-2 hr-1 (Davies and Jones rate equation). Under the experimental conditions employed and the resultant precision (~20-25 percent), I and pCO2 do not have a significant influence on the precipitation rate of calcite. Precipitation rates increased with temperature although Arrhenius plots yield a broad range of activation energies (Ea ≈ 15 – 28 kJ mol-1, R2 = 0.72). The relatively low calculated activation energies coupled with the precision of the results suggest the possibility of surface nucleation in the present results. Overall, these findings may be useful in understanding and predicting the interaction and reactivity of the host carbonate minerals in subsurface reservoirs to the injection of CO2 although much work needs to be completed at elevated temperatures and pressures.

ABSTRACT Hydrophobic organic pollutants (HOPs) are in general characterized by high toxicity, long environmental half-life and high bio-accumulation factors. Due to their hydrophobicity, HOPs tend to sorb onto particulates in natural aquatic environment and their degradation pathways and rates are altered with the change of the reaction media and the settlement of these particles. The influence of the dissolved organic matters (DOMs), termed as the third phase, on the sorption partition coefficient is observed because of their interactions with HOPs. This binding (between DOM and HOP) increases apparent solubility and mobility of the HOP and the sorption coefficient of HOP in aquatic system is reduced. On the purpose of obtaining data closer to the real world, many aquatic factors, such as the concentration and types of DOM, pH value and ionic strength, are studied intensively recently. Nevertheless, it is difficult to clarify the influence of ionic strength because the relationship between binding constant of DOM-HOP and ionic strength is ambiguous in the literature. As such, by applying fluorescence quenching method, we investigate the influence of ionic strength on the partition coefficient (Kdom) of PAHs (phenanthrene¡Bpyrene)-humic acid (HA) system. Results show that the interaction of HA and cations is the primary factor in the variations of the partition coefficient. It is believed that, as cations reacting with specific binding sites on HA, the molecules' configuration of HA is changed and the binding mechanism of PAHs and HA is altered. A "four-stage variation model" is then proposed to explain the relationship between the ionic strength and partition coefficient. Therefore, a non-constant trend of ionic strength effect is resulted and is used to explain the controversial findings in the literature. Furthermore, Mg++ is found to cause stronger effect than K+ owing to higher charge density. The introduction of Br- would complicate the fluorescence quenching mechanism of phenanthrene-HA system because it's a fluorescence quencher. However, effects of anions on the variation of Kdom are not as significant as cations in our system. The effects of ionic strength on the variation of Kdom for four humic acids are LHA¡ÖPHA¡]Peat humic acid¡^¡ÖSHHA¡]Summit Hill humic acid¡^¡ÖSRHA. Results from different humic acids indicate that the Suwannee River humic acid (SRHA) is not as sensitive as Leonardite humic acid (LHA) on the ionic strength effect because of lower hydrophobicity. The influence of ionic strength on the variation of Kdom for pyrene-HA system is also amplified because of pyrene's higher hydrophobicity compared with phenanthrene.

Thesis--M. Phil., University of Hong Kong, 1982.

Thesis (M. Phil.)--University of Hong Kong, 1978. / Typescript.

The release of ionic solute from melting seasonal snow produces an influx of ion laden water into hydrologic systems at the start of spring snowmelt. The spatial and temporal variability of meltwater and solute release from melting snow was investigated at different spatial scales to assess the magnitude and variability of this process. Four laboratory experiments were performed where an 0.4 m³ volume of snow was placed in a plexiglass box and melted from above. NaCl and dye tracer experiments revealed contemporaneous areas of concentrated dye and dilute meltwater in flow fingers, indicating that meltwater in preferential flow paths is diluted by low concentration water from the top of the snowpack. Meltwater discharge and meltwater electrical conductivity were measured in snow lysimeters, and snow accumulation and electrical conductivity of samples from snowpits were measured over four snowmelt seasons at an alpine field site. Peak snow-water equivalent ranged from 0.57 to 2.92 m, and lysimeter discharges ranged from 20 to 205% of the mean flow; however mean lysimeter flow was representative of snow ablation observed in snow pits. The electrical conductivity in snowpit samples and lysimeter meltwater averaged 2-3 μS cm⁻¹. Peak meltwater electrical conductivity ranged from 6 to 14 times that of the bulk premelt snowpack. The highest conductivities were observed during the first few days following the onset of flow, and the lysimeters that began flowing earliest tended to have the highest conductivities at the onset of flow. A mathematical model for solute transport in snow was developed that includes the effects of mass transfer between mobile and immobile liquid phases, advection, hydrodynamic dispersion, and melt—freeze episodes. The ability of the model to accurately simulate solute movement and release depends on the validity of the assumption of one—dimensional flow and on the accuracy of modeling the snowpack energy balance. This model is preferable to the empirical models of solute elution currently in use for investigations of watershed hydrogeochemical response because it has the ability to respond directly to changes in snow accumulation or meteorlogical conditions.

published_or_final_version / Biochemistry / Master / Master of Philosophy

No description available.