Potentiometric titration as a method of determining the stoichiometric dissociation constants of weak acids from the thermodynamic dissociation constants of aqueous solutions at 298.15 K

The simple single-ion activity coefficient equation originating from the Debye-Hückel theory was used to determine the thermodynamic and stoichiometric dissociation constants of weak acids from data concerning galvanic cells. Electromotive force data from galvanic cells without liquid junctions, which was obtained from literature, was studied in conjuction with the potentiometric titration data relating to aqueous solutions at 298.15 K. The dissociation constants of weak acids could be determined by the presented techniques and almost all the experimental data studied could be interpreted within the range of experimental error. Potentiometric titration has been used here and the calculation methods were developed to obtain the thermodynamic and stoichiometric dissociation constants of some weak acids in aqueous solutions at 298.15 K. The ionic strength of titrated solutions were adjusted using an inert electrolyte, namely, sodium or potassium chloride. Salt content alonedetermines the ionic strength. The ionic strength of the solutions studied varied from 0.059 mol kg-1 to 0.37 mol kg-1, and in some cases up to 1.0 mol kg-1. The following substances were investigated using potentiometric titration: aceticacid, propionic acid, L-aspartic acid, L-glutamic acid and bis(2,2-dimethyl-3-oxopropanol) amine.

Gas-phase photocatalytic oxidation of volatile organic compounds

Substances emitted into the atmosphere by human activities in urban and industrial areas cause environmental problems such as air quality degradation, respiratory diseases, climate change, global warming, and stratospheric ozone depletion. Volatile organic compounds (VOCs) are major air pollutants, emitted largely by industry, transportation and households. Many VOCs are toxic, and some are considered to be carcinogenic, mutagenic, or teratogenic. A wide spectrum of VOCs is readily oxidized photocatalytically. Photocatalytic oxidation (PCO) over titanium dioxide may present a potential alternative to air treatment strategies currently in use, such as adsorption and thermal treatment, due to its advantageous activity under ambient conditions, although higher but still mild temperatures may also be applied. The objective of the present research was to disclose routes of chemical reactions, estimate the kinetics and the sensitivity of gas-phase PCO to reaction conditions in respect of air pollutants containing heteroatoms in their molecules. Deactivation of the photocatalyst and restoration of its activity was also taken under consideration to assess the practical possibility of the application of PCO to the treatment of air polluted with VOCs. UV-irradiated titanium dioxide was selected as a photocatalyst for its chemical inertness, non-toxic character and low cost. In the present work Degussa P25 TiO2 photocatalyst was mostly used. In transient studies platinized TiO2 was also studied. The experimental research into PCO of following VOCs was undertaken: - methyl tert-butyl ether (MTBE) as the basic oxygenated motor fuel additive and, thus, a major non-biodegradable pollutant of groundwater; - tert-butyl alcohol (TBA) as the primary product of MTBE hydrolysis and PCO; - ethyl mercaptan (ethanethiol) as one of the reduced sulphur pungent air pollutants in the pulp-and-paper industry; - methylamine (MA) and dimethylamine (DMA) as the amino compounds often emitted by various industries. The PCO of VOCs was studied using a continuous-flow mode. The PCO of MTBE and TBA was also studied by transient mode, in which carbon dioxide, water, and acetone were identified as the main gas-phase products. The volatile products of thermal catalytic oxidation (TCO) of MTBE included 2-methyl-1-propene (2-MP), carbon monoxide, carbon dioxide and water; TBA decomposed to 2-MP and water. Continuous PCO of 4 TBA proceeded faster in humid air than dry air. MTBE oxidation, however, was less sensitive to humidity. The TiO2 catalyst was stable during continuous PCO of MTBE and TBA above 373 K, but gradually lost activity below 373 K; the catalyst could be regenerated by UV irradiation in the absence of gas-phase VOCs. Sulphur dioxide, carbon monoxide, carbon dioxide and water were identified as ultimate products of PCO of ethanethiol. Acetic acid was identified as a photocatalytic oxidation by-product. The limits of ethanethiol concentration and temperature, at which the reactor performance was stable for indefinite time, were established. The apparent reaction kinetics appeared to be independent of the reaction temperature within the studied limits, 373 to 453 K. The catalyst was completely and irreversibly deactivated with ethanethiol TCO. Volatile PCO products of MA included ammonia, nitrogen dioxide, nitrous oxide, carbon dioxide and water. Formamide was observed among DMA PCO products together with others similar to the ones of MA. TCO for both substances resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide and water. No deactivation of the photocatalyst during the multiple long-run experiments was observed at the concentrations and temperatures used in the study. PCO of MA was also studied in the aqueous phase. Maximum efficiency was achieved in an alkaline media, where MA exhibited high fugitivity. Two mechanisms of aqueous PCO – decomposition to formate and ammonia, and oxidation of organic nitrogen directly to nitrite - lead ultimately to carbon dioxide, water, ammonia and nitrate: formate and nitrite were observed as intermediates. A part of the ammonia formed in the reaction was oxidized to nitrite and nitrate. This finding helped in better understanding of the gasphase PCO pathways. The PCO kinetic data for VOCs fitted well to the monomolecular Langmuir- Hinshelwood (L-H) model, whereas TCO kinetic behaviour matched the first order process for volatile amines and the L-H model for others. It should be noted that both LH and the first order equations were only the data fit, not the real description of the reaction kinetics. The dependence of the kinetic constants on temperature was established in the form of an Arrhenius equation.

Transformation of carbon dioxide to diethyl carbonate over ceria and ceria-supported catalysts

Carbon dioxide is regarded, nowadays, as a primary anthropogenic greenhouse gas leading to global warming. Hence, chemical fixation of CO2 has attracted much attention as a possible way to manufacture useful chemicals. One of the most interesting approaches of CO2 transformations is the synthesis of organic carbonates. Since conventional production technologies of these compounds involve poisonous phosgene and carbon monoxide, there is a need to develop novel synthetic methods that would better match the principles of "Green Chemistry" towards protection of the environment and human health. Over the years, synthesis of dimethyl carbonate was under intensive investigation in the academia and industry. Therefore, this study was entirely directed towards equally important homologue of carbonic esters family namely diethyl carbonate (DEC). Novel synthesis method of DEC starting from ethanol and CO2 over heterogeneous catalysts based on ceria (CeO2) was studied in the batch reactor. However, the plausible drawback of the reaction is thermodynamic limitations. The calculated values revealed that the reaction is exothermic (ΔrHØ298K = ─ 16.6 J/ ) and does not occur spontaneously at rooms temperature (ΔrGØ 298K = 35.85 kJ/mol). Moreover, co-produced water easily shifts the reaction equilibrium towards reactants excluding achievement of high yields of the carbonate. Therefore, in-situ dehydration has been applied using butylene oxide as a chemical water trap. A 9-fold enhancement in the amount of DEC was observed upon introduction of butylene oxide to the reaction media in comparison to the synthetic method without any water removal. This result confirms that reaction equilibrium was shifted in favour of the desired product and thermodynamic boundaries of the reaction were suppressed by using butylene oxide as a water scavenger. In order to obtain insight into the reaction network, the kinetic experiments were performed over commercial cerium oxide. On the basis of the selectivity/conversion profile it could be concluded that the one-pot synthesis of diethyl carbonate from ethanol, CO2 and butylene oxide occurs via a consecutive route involving cyclic carbonate as an intermediate. Since commercial cerium oxide suffers from the deactivation problems already after first reaction cycle, in-house CeO2 was prepared applying room temperature precipitation technique. Variation of the synthesis parameters such as synthesis time, calcination temperature and pH of the reaction solution turned to have considerable influence on the physico-chemical and catalytic properties of CeO2. The increase of the synthesis time resulted in high specific surface area of cerium oxide and catalyst prepared within 50 h exhibited the highest amount of basic sites on its surface. Furthermore, synthesis under pH 11 yielded cerium oxide with the highest specific surface area, 139 m2/g, among all prepared catalysts. Moreover, CeO2─pH11 catalyst demonstrated the best catalytic activity and 2 mmol of DEC was produced at 180 oC and 9 MPa of the final reaction pressure. In addition, ceria-supported onto high specific surface area silicas MCM-41, SBA-15 and silica gel were synthesized and tested for the first time as catalysts in the synthesis of DEC. Deposition of cerium oxide on MCM-41 and SiO2 supports resulted in a substantial increase of the alkalinity of the carrier materials. Hexagonal SBA-15 modified with 20 wt % of ceria exhibited the second highest basicity in the series of supported catalysts. Evaluation of the catalytic activity of ceria-supported catalysts showed that reaction carried out over 20 wt % CeO2-SBA-15 generated the highest amount of DEC.

Modification of commercial poly-lactide for extrusion coated food packaging applications

Poly-L-lactide (PLLA) is a widely used sustainable and biodegradable alternative to replace synthetic non-degradable plastic materials in the packaging industry. Conversely, its processing properties are not always optimal, e.g. insufficient melt strength at higher temperatures (necessary in extrusion coating processes). This thesis reports on research to improve properties of commercial PLLA grade (3051D from NatureWorks), to satisfy and extend end-use applications, such as food packaging by blending with modified PLLA. Adjustment of the processability by chain branching of commercial poly-L-lactide initiated by peroxide was evaluated. Several well-defined branched structures with four arms (sPLLA) were synthesized using pentaerythritol as a tetra-functional initiator. Finally, several block copolymers consisting of polyethylene glycol and PLLA (i.e. PEGLA) were produced to obtain a well extruded material with improved heat sealing properties. Reactive extrusion of poly-L-lactide was carried out in the presence of 0.1, 0.3 and 0.5 wt% of various peroxides [tert-butyl-peroxybenzoate (TBPB), 2,5-dimethyl-2,5-(tert-butylperoxy)-hexane (Lupersol 101; LOL1) and benzoyl peroxide (BPO)] at 190C. The peroxide-treated PLLAs showed increased complex viscosity and storage modulus at lower frequencies, indicating the formation of branched/cross linked architectures. The material property changes were dependent on the peroxide, and the used peroxide concentration. Gel fraction analysis showed that the peroxides, afforded different gel contents, and especially 0.5 wt% peroxide, produced both an extremely high molar mass, and a cross linked structure, not perhaps well suited for e.g. further use in a blending step. The thermal behavior was somewhat unexpected as the materials prepared with 0.5 wt% peroxide showed the highest ability for crystallization and cold crystallization, despite substantial cross linking. The peroxide-modified PLLA, i.e. PLLA melt extruded with 0.3 wt% of TBPB and LOL1 and 0.5 wt% BPO was added to linear PLLA in ratios of 5, 15 and 30 wt%. All blends showed increased zero shear viscosity, elastic nature (storage modulus) and shear sensitivity. All blends remained amorphous, though the ability of annealing was improved slightly. Extrusion coating on paperboard was conducted with PLLA, and peroxide-modified PLLA blends (90:10). All blends were processable, but only PLLA with 0.3 wt% of LOL1 afforded a smooth high quality surface with improved line speed. Adhesion levels between fiber and plastic, as well as heat seal performance were marginally reduced compared with pure 3051D. The water vapor transmission measurements (WVTR) of the blends containing LOL1 showed acceptable levels, only slightly lower than for comparable PLLA 3051D. A series of four-arm star-shaped poly-L-lactide (sPLLA) with different branch length was synthesized by ring opening polymerization (ROP) of L-lactide using pentaerythritol as initiator and stannous octoate as catalyst. The star-shaped polymers were further blended with its linear resin and studied for their melt flow and thermal properties. Blends containing 30 wt% of sPLLA with low molecular weight (30 wt%; Mwtotal: 2500 g mol-1 and 15000 g mol-1) showed lower zero shear viscosity and significantly increased shear thinning, while at the same time slightly increased crystallization of the blend. However, the amount of crystallization increased significantly with the higher molecular weight sPLLA, therefore the star-shaped structure may play a role as nucleating agent. PLLA-polyethylene glycol–PLLA triblock copolymers (PEGLA) with different PLLA block length were synthesized and their applicability as blends with linear PLLA (3051D NatureWorks) was investigated with the intention of improving heat-seal and adhesion properties of extrusion-coated paperboard. PLLA-PEG-PLLA was obtained by ring opening polymerization (ROP) of L-lactide using PEG (molecular weight 6000 g mol-1) as an initiator, and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy (1H-NMR). The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology, and differential scanning calorimeter (DSC). All blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity, higher shear thinning and increased melt elasticity (based on tan delta). Nevertheless, no significant changes in thermal properties were distinguished. High molecular weight PEGLAs were used in extrusion coating line with 3051D without problems.