Diane Thomas

The absorption-oxidation of NOx with hydrogen peroxide for the treatment of tail gases

Abstract Absorption of NOx up to partial pressures of 500 Pa was experimented at 20°C and atmospheric pressure with aqueous and nitric acid solutions containing hydrogen peroxide. Various NOx oxidation ratios in the gas phase, and different concentrations of nitric acid and hydrogen peroxide in the scrubbing liquid were investigated. It was shown that the absorption rate was enhanced by H 2 O 2 but remains constant if increasing excess quantities of H 2 O 2 are used. Absorption of NOx into H 2 O 2 is considerably catalyzed by nitric acid. A mathematical model was developed in which all these experimental observations were included, and overall kinetic parameters for different NOx species were determined. Favorable agreement was shown between the model predictions and the experimental results obtained both in a laboratory-scale and a pilot-scale absorption column.

Nitrogen Oxides Scrubbing with Alkaline Solutions

The absorption of NOx into sodium hydroxide solutions was studied in a small packed column. A simple mathematical model developed for this absorption was used for the determination of rate parameters relative to NOx species in such solutions. While hydrolysis is the main controlling step for NO2, N2O4 and N2O3 species, nitrous acid HNO2 plays an essential role for the NOx absorption in NaOH solutions. Our mechanistic and kinetic findings were validated as the model has worked with fair success in predicting both NOx removal efficiencies and liquid phase compositions.

Removal of tetravalent NOx from flue gases using solutions containing hydrogen peroxide

The absorption of NO x (IV) into nitric acid solutions containing a low concentration of hydrogen peroxide was studied in a small packed column. A simple mathematical model developed for this absorption was used for the determination of kinetic parameters relative to NO 2 and N 2 O 4 in such solutions. Results obtained at 10, 20, 30°C lead to the same interpretation: hydrolysis is the main controlling step for tetravalent nitrogen oxides absorption and there is no sensible effect of the acidity on the absorption efficicency. Hydrogen peroxide, however, plays an essential role in solution by preventing the HNO 2 decomposition. The mechanistic and kinetic findings were validated as the model has worked with fair success in predicting NO x removal efficiencies in a pilot-scale packed column.

Highly efficient, long life, reusable and robust photosynthetic hybrid core-shell beads for the sustainable production of high value compounds.

An efficient one-step process to synthesize highly porous (Ca-alginate-SiO2-polycation) shell: (Na-alginate-SiO2) core hybrid beads for cell encapsulation, yielding a reusable long-life photosynthetically active material for a sustainable manufacture of high-value metabolites is presented. Bead formation is based on crosslinking of an alginate biopolymer and mineralisation of silicic acid in combination with a coacervation process between a polycation and the silica sol, forming a semi-permeable external membrane. The excellent mechanical strength and durability of the monodispersed beads and the control of their porosity and textural properties is achieved by tailoring the silica and alginate loading, polycation concentration and incubation time during coacervation. This process has led to the formation of a remarkably robust hybrid material that confers exceptional protection to live cells against sheer stresses and contamination in a diverse range of applications. Dunaliella tertiolecta encapsulated within this hybrid core-shell system display high photosynthetic activity over a long duration (>1 year). This sustainable biotechnology could find use in high value chemical harvests and biofuel cells to photosynthetic solar cells (energy transformation, electricity production, water splitting technologies). Furthermore the material can be engineered into various forms from spheres to variable thickness films, broadening its potential applications.

Green and sustainable production of high value compounds via a microalgae encapsulation technology that relies on CO2 as a principle reactant

A very promising and facile one-pot synthesis pathway is presented for the microencapsulation of live cells in a very porous core–shell system based upon a robust matrix. (Alginate–SiO2–polycation) shell@(alginate–SiO2) core hybrid beads, on the millimeter scale, containing live cells are obtained through cross-linking chemistry and the polycondensation of silicic acid in conjunction with the use of a polycation to negate the surface charge on silica. Very interestingly it is revealed that the polycation used (PDADMAC) plays a very important role in the formation of highly robust core–shell beads. PDADMAC acts as a catalyst in the polycondensation of silicic acid, leading to the formation of a resistant double layer shell comprising of an interior layer of alginate–SiO2 with a very homogeneous distribution of porous SiO2 and an external layer of porous PDADMAC that confines SiO2 within the bead. The photosynthetic chlorophyta Dunaliella tertiolecta, which produces high value metabolites (such as anti-oxidants, pharmacologically active compounds, neutraceuticals etc.) via photosynthesis, has been encapsulated within this core–shell system. Oximetry and fluorescence measurements highlight how this algal culture can remain photosynthetically active over an extraordinarily long period of 13 months for high value compound production, whilst entrapped within a highly porous, mechanically and chemically stable, optically transparent matrix, with no observable leaching of the cells from the core of the beads. HPLC has been employed to highlight the presence of excreted metabolites, based on neutral sugar building blocks such as arabinose, galactose and xylose, in the surrounding media. These results reveal how this kind of high performance, low-cost, and easily scaleable core–shell living material could be employed in large scale photobioreactors (PBRs), to potentially facilitate metabolite harvesting whilst protecting the culture from external contamination and for green energy production and environmental (CO2) remediation.

Influence of Shaping on Pd and Pt/TiO2 Catalysts in Total Oxidation of VOCs

The catalytic performance of a commercial TiO2 was investigated towards the total oxidation of toluene. A variety of two titania supports was used in this work, shaped (pellets) and non-shaped (powder) materials. 0.5wt% Pd or Pt were impregnated onto both types of titania supports using the wet impregnation method. A decrease in the surface area of the obtained catalysts was noticed after the catalytic test, although it was still much higher than that of classical titania supports. The catalysts were tested in the total oxidation of toluene, and a major decrease in activity was noticed for Pt impregnated “shaped” supports.