Conversion of CH\u3csub\u3e4\u3c/sub\u3e/CO\u3csub\u3e2\u3c/sub\u3e by a nanosecond repetitively pulsed discharge

\u3cp\u3eA possible way to store both renewable energy and CO\u3csub\u3e2\u3c/sub\u3e in chemical energy is to produce value-added chemicals and fuels starting from CO\u3csub\u3e2\u3c/sub\u3e and green electricity. This can be done by exploiting the non-equilibrium properties of gaseous electrical discharges. Discharges, in addition, can be switched on and off quickly, thus being suitable to be coupled with an intermittent energy source. In this study, we have used a nanosecond pulsed discharge to dissociate CO\u3csub\u3e2\u3c/sub\u3e and CH\u3csub\u3e4\u3c/sub\u3e in a 1:1 mixture at atmospheric pressure, and compared our results with literature data obtained by other discharges. The main products are CO, H\u3csub\u3e2\u3c/sub\u3e, C\u3csub\u3e2\u3c/sub\u3eH\u3csub\u3e2\u3c/sub\u3e, water and solid carbon. We estimate an energy efficiency of 40% for syngas (CO and H\u3csub\u3e2\u3c/sub\u3e) production, higher if other products are also considered. Such values are among the highest compared to other discharges, and, although not very high on an absolute scale, are likely improvable via possible routes discussed in the paper and by coupling to the discharge a heterogeneous catalysis stage.\u3c/p\u3

Molecular growth of PAH-like systems induced by oxygen species:experimental and theoretical study of the reaction of naphthalene with HO (\u3csup\u3e2\u3c/sup\u3eΠ\u3csub\u3e3/2\u3c/sub\u3e), O (\u3csup\u3e3\u3c/sup\u3eP), and O\u3csub\u3e2\u3c/sub\u3e (\u3csup\u3e3\u3c/sup\u3eΣ - G)

\u3cp\u3eTo assess if reactions with oxygen species can induce a mass increase of polycyclic aromatic hydrocarbons, we exposed naphthalene molecules to an oxidative gas flow containing the radicals H and HO (\u3csup\u3e2\u3c/sup\u3eΠ\u3csub\u3e3/2\u3c/sub\u3e) and the diradicals O (\u3csup\u3e3\u3c/sup\u3eP) and O\u3csub\u3e2\u3c/sub\u3e (\u3csup\u3e3\u3c/sup\u3eΣ-g). We observed the formation of 1- and 2-naphtol, 1,4-naphthoquinone, naphthalene-derived cyclic ethers, an ester from ring opening, and ether adducts containing two naphthalene units. We investigated the possible reaction pathways as a function of temperature by density functional calculations. We found that the reactivity is characterized by HO, O and H addition to naphthalene, or by H abstraction from it, with roles depending on temperature. In conclusion, oxygen species can promote, under the experimental conditions, mainly naphthalene oxidation and, to a lesser extent, substantial molecular growth, with an efficiency that the calculations indicate to depend on the system temperature. Future experiments should try to quantify key species to allow defining the relative importance of the various reaction mechanisms uncovered by ab initio calculations.\u3c/p\u3

Characterisation of volatile organic compounds (VOCs) released by the composting of different waste matrices

\u3cp\u3eThe complaints arising from the problem of odorants released by composting plants may impede the construction of new composting facilities, preclude the proper activity of existing facilities or even lead to their closure, with negative implications for waste management and local economy. Improving the knowledge on VOC emissions from composting processes is of particular importance since different VOCs imply different odour impacts. To this purpose, three different organic matrices were studied in this work: dewatered sewage sludge (M1), digested organic fraction of municipal solid waste (M2) and untreated food waste (M3). The three matrices were aerobically biodegraded in a bench-scale bioreactor simulating composting conditions. A homemade device sampled the process air from each treatment at defined time intervals. The samples were analysed for VOC detection. The information on the concentrations of the detected VOCs was combined with the VOC-specific odour thresholds to estimate the relative weight of each biodegraded matrix in terms of odour impact. When the odour formation was at its maximum, the waste gas from the composting of M3 showed a total odour concentration about 60 and 15,000 times higher than those resulting from the composting of M1 and M2, respectively. Ethyl isovalerate showed the highest contribution to the total odour concentration (>99%). Terpenes (α-pinene, β-pinene, p-cymene and limonene) were abundantly present in M2 and M3, while sulphides (dimethyl sulphide and dimethyl disulphide) were the dominant components of M1.\u3c/p\u3

Laser induced fluorescence diagnostics of simple radicals in atmospheric pressure plasma jets

\u3cp\u3eIn this paper we give a general description of the LIF technique by way of OH absolute measurements in two atmospheric pressure plasma jet systems, namely a plasma gun and a RF plasma jet. We address in detail: the modelling of the LIF measurement, taking into account collisional processes and the spatial non-uniformity of the laser beam; absolute calibration; rotational temperature measurements.\u3c/p\u3

Reactivity of fatty acid methyl esters under atmospheric pressure plasma jet exposure:an experimental and theoretical study

\u3cp\u3eWe have investigated the treatment of a mixture of fatty acid methyl esters by an RF-plasma jet with He-H\u3csub\u3e2\u3c/sub\u3eO and He-O\u3csub\u3e2\u3c/sub\u3e gas feed. We have measured the concentration of the hydroxyl radical in the jet by laser induced fluorescence, looking for correlation with the lipid reactivity. We have detected four product families, whose yields increase with the OH exposure: volatile products, polymerization products, reduced chains, and oxidized chains. Theoretical calculations give insights on the radical attack to the lipid chain and show that none of the products can be attributed exclusively to reactions with OH. Therefore, the observed reactant conversion as function of the OH exposure must be interpreted as a qualitative relationship with the total amount of radical species present in the plasma jet. PACS: 52.80.Tn, 82.33.Xj, 31.15.E-.\u3c/p\u3