Effects of temperature on methanol adsorption on functionalized graphite: saturation of functional groups

Grand Canonical Monte Carlo simulation of methanol adsorption on a graphite model with two hydroxyl groups grafted on the surface has been carried out to investigate the effects of temperature in the range of 278–360 K. The spacing between the OH groups was chosen so that two hydrogen bonds could be formed with the first methanol molecule. In the Henry law region, the isosteric heat at zero loading is greater than the condensation heat. When the loading is increased, the isosteric heat at low temperatures decreases slightly and exhibits a shoulder, which is associated with the formation of a cluster of methanol molecules around one OH group. On further increase in loading, the adsorbate–adsorbate interactions decrease because methanol begins to adsorb on the other OH group, resulting in a sharp decrease in the isosteric heat to a minimum, at which point both OH groups are covered with methanol molecules. At higher temperatures the isosteric heat at zero loading decreases but remains higher than the condensation heat. The shoulder heat is progressively diminished with temperature because methanol molecules are distributed over the two OH groups, due to the entropic effects. Interestingly, the minimum heat still occurs when the functional groups are covered and is even more pronounced at high temperatures

Adsorption of carbon dioxide on hydrotalcite-like compounds of different compositions

The adsorption of carbon dioxide on hydrotalcite-like compounds was investigated. Two different powdered hydrotalcites were used containing the cations nickel and iron. The powdered materials were screened for carbon dioxide adsorption using a thermogravimetric method and it was found that NiMgAl (Sample 1) hydrotalcite has the largest capacity for CO2, adsorbing 1.58 mmol g−1 at 20 °C, and highest rate of adsorption of up to 0.17 mmol g−1 min−1. This represented an increase of 53% in adsorption capacity, compared with NiMgAlFe (Sample 2). In order to improve the rheological behaviour of hydrotalcite paste for extrusion, hydrotalcite powders were combined with boehmite alumina (70:30 and 50:50 ratios of hydrotalcite:boehmite) before extrusion into pellets suitable for use in a fixed bed adsorber. These pellets were then re-crushed and further tested by thermogravimetric methods. The effects of temperature, composition and pre-treatment of the hydrotalcites on the adsorption of carbon dioxide and nitrogen are reported. At 20 °C, the amount of carbon dioxide adsorbed was between 2.0 and 2.5 mmol g−1 for all the hydrotalcite/alumina samples in this study, although this decayed rapidly with increasing temperature. The results are compared with silica gel as a common sorbent reference, and with literature values. Hydrotalcite/alumina samples have thermal stability and a high adsorption capacity for carbon dioxide over a wide range of temperatures. The composition of the hydrotalcite/alumina pellets investigated in this study has less effect upon the adsorption behaviour compared with the non-calcined hydrotalcite powder, thus allowing a wide choice of pellet compositions to be used

Coupling Reactions of Carbon Dioxide with Epoxides Catalyzed by Vanadium Aminophenolate Complexes

A series of vanadium compounds supported by tetradentate amino-bis(phenolate) ligands were screened for catalytic reactivity in the reaction of propylene oxide (PO) with carbon dioxide, [VO(OMe)(O2NOBuMeMeth)] (1), [VO(OMe)(ON2OBuMe)] (2), [VO(OMe)(O2NNBuBuPy)] (3), and [VO(OMe)(O2NOBuBuFurf)] (4) (where (O2NOBuMeMeth) = MeOCH2CH2N(CH2ArO-)2, Ar = 3,5-C6H2-Me, tBu]; (ON2OBuMe) = -OArCH2NMeCH2 CH2NMeCH2ArO-, Ar = 3,5-C6H2-Me, tBu; (O2NNBuBuPy) = C5H4NCH2N(CH2ArO-)2, Ar = 3,5-C6H2-tBu2; (O2NOBuBuFurf) = C4H3OCH2N(CH2ArO-)2, Ar = 3,5-C6H2-tBu2). They showed similar reactivities but reaction rates were greater for 2, which was studied in more detail. TOF for conversion of PO over 500 h-1 were observed. Activation energies were determined experimentally via in situ IR spectroscopy for propylene carbonate (48.2 kJ mol-1), styrene carbonate (45.6 kJ mol-1) and cyclohexene carbonate (54.7 kJ mol-1) formation

The capture and activation of CO2 for the production of sustainable chemical feedstocks

With the considerable increase in both the consumption and demand of fossil fuels, carbon dioxide emissions in the atmosphere will increase correspondingly, causing global warming. However, carbon dioxide (C02) as a chemical has many advantages chemically; it is non-toxic, non-combustible, and can also be the starting material for the synthesis of fine chemicals. Among the possible processes which utilise carbon dioxide as a reagent, the synthesis of five-membered cyclic carbonates is very appealing, due to their vast potential for use as polar solvent, chemical intermediates and monomers in polymerisation. Therefore, this research aims to capture and activate carbon dioxide to produce cyclic carbonates. Carbon dioxide absorption III several imidazolium-based IOnIC liquids, pyridinium-based ionic liquids, and a tetramethylammonium-based ionic liquid, poly[ (p-vinylbenzyl)trimethylammonium hexafluorophosphate] (P[[VBTMA] [PF 6]]) and its monomer was studied in comparison with glycerol trioctanoate and powdered materials (such as hydrota1cites, mixed oxides and boehmite). The thermal stability, long-term stability, decomposition kinetics and the evaporation of ionic liquids were also investigated. The influence of many parameters on sorption capacity such as sorption isotherm, stability on cycle operation, gas selectivity and sorption kinetics of samples were considered in this research. Bench-scale CO2 capture was also carried out to determine the thermodynamic properties and energy required for CO2 absorption and desorption. The results show that the highest thermal stability was exhibited by the imidazolium cation and bis(trifluoromethylsulfonyl)imide anion, compared with the other ionic liquids studied. All the ionic liquids studied can have a detectable vapour pressure in the temperature range 80-120 °C as determined by thennogravimetric analysis. The functional groups of the ionic liquids had strong effects on CO2 sorption capacity and selectivity. The largest effect on CO2 solubility was associated with the ionic liquid anion. The activation energy values of CO2 sorption mainly arise from the different viscosities in all the ionic liquids, whereas those of the poly(ionic liquid) and ionic liquid monomer mainly depend on the morphological structure. The lowest energy required for CO2 recovery was in the poly(ionic liquid) when compared to all the ionic liquids and the MEA solution process. The different energy required for all the ionic liquids and the MEA solution process could be reduced by increasing the amount of ionic liquids. A novel non-symmetrical aluminium(III) chloride salen complex [AICI( salenac )OH] was synthesised and investigated in the catalytic cyc1oaddition of CO2 into styrene oxide. The influence of temperature on reactivity and the reaction kinetics using this catalyst was compared with a binary catalyst system. The AICI(salenac)OH showed the better catalytic activity in the synthesis of styrene carbonate at atmospheric CO2 pressure, when compared to a symmetrical aluminium salen complex reported in literature. The cycloaddition reaction was favoured at high temperature, although tetrabutylammonium bromide (Bu4NBr) was used to enhance the catalytic reaction with the AICI(salenac)OH. The styrene carbonate synthesis by a binary catalyst system required a lower activation energy, when compared to the AICI(salenac)OH alone. iiEThOS - Electronic Theses Online ServiceGBUnited Kingdo