Luca Matteo Martini

Conversion of CH4 /CO2 by a nanosecond repetitively pulsed discharge

A possible way to store both renewable energy and CO2 in chemical energy is to produce value-added chemicals and fuels starting from CO2 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 CO2 and CH4 in a 1:1 mixture at atmospheric pressure, and compared our results with literature data obtained by other discharges. The main products are CO, H2, C2H2, water and solid carbon. We estimate an energy efficiency of 40% for syngas (CO and H2) 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.

Laser induced fluorescence in atmospheric pressure discharges

This paper offers an outline of laser induced fluorescence (LIF) diagnostics and practical recommendations for its use in atmospheric pressure discharges. LIF principles, technical requirements and rationalization of experimental outcomes by modelling are addressed. Important issues that are particularly relevant to small scale, spatially inhomogeneous discharges, like plasma-jets, are emphasized. For the first time, all collision processes and the spatial non-homogeneity of the laser beam are together accounted for in the LIF model. Saturation characteristics are discussed and used for the assessment of model parameters. A calibration procedure is discussed and implemented. Gas temperature measurements by LIF are also addressed. The whole description of the technique is given, without loss of generality, through the example of its application to the OH radical. Notes on other diatomic radicals, CH, NO and CN, are given along the paper. Some results in a RF plasma-jet are presented as an example of application in a discharge system where all the concepts developed in the paper are applied.

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

The 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.

Molecular growth of PAH-like systems induced by oxygen species: experimental and theoretical study of the reaction of naphthalene with HO (2Π3/2), O (3P), and O2 (3Σ−g)

To 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 (2Π3/2) and the diradicals O (3P) and O2 (3Σ−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.