Biomass gasification presents highly interesting possibilities for expanding the utilization of biomass as power generation using internal combustion engines or turbines. However, the need to reduce the tar in the producer gas is very important. The successful application of producer gas depends not only on the quantity of tar, but also on its properties and compositions, which is associated with the dew-point of tar components. Class 5, 4, and 2 tar become a major cause of condensation which can foul the engines and turbines. Hence, the selectivity of tar treatment method to remove or convert class 5, 4, and 2 tar is a challenge in producer gas utilization. This review was conducted to present the recent studies in tar treatment from biomass gasification. The new technologies with their strengths and the weaknesses in term of tar reduction are discussed.

Tar reduction in biomass producer gas via mechanical, catalytic and thermal methods: A review

Non-thermal plasmas for non-catalytic and catalytic VOC abatement.

Manganese dioxide (MnO2 ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO2 single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO2 -based composites via the construction of homojunctions and MnO2 /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO2 -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO2 -based materials for comprehensive environmental applications is provided.

MnO2 -Based Materials for Environmental Applications.

A multidisciplinary approach to understand the interactions of nonthermal plasma and catalyst: A review

Packed-bed plasma reactors, constructed by packing noncatalytic dielectric pellets inside nonthermal plasma reactors, have been demonstrated to effectively alleviate the major bottleneck encountered by nonthermal plasma, i.e., the energy efficiency needs to be further improved. As far as the environmental issues are concerned, packed-bed plasma reactors are mainly applied to ozone generation and gaseous pollutant removal. According to the available experimental data, for a given specific energy density, the energy efficiency for ozone generation and gaseous pollutant abatement obtained with packed-bed reactors, if compared to that of nonpacked reactors, could be 1.1−4.3 and 1.1−12 times higher, depending on the type of pollutant, the reactor geometry, and the packing pellets used. Nevertheless, it is worth noticing that the packing pellets suitable for ozone generation and pollutant removal are quite different. The influences of material, dielectric constant, size, and shape of the packing pellets on the ...

Review of Packed-Bed Plasma Reactor for Ozone Generation and Air Pollution Control

The removal of two volatile organic compounds (propane and isopropyl alcohol) by a nanosecond pulsed corona discharge serially combined with Al2O3–MnO2 catalytic post-treatment has been investigated in air at atmospheric pressure and room temperature. The degradation mechanism of VOCs in the non-thermal plasma is a serious problem: several hazardous organic compounds (acetone and formaldehyde) are produced, and the formation yield of CO is higher than CO2. The high concentration of ozone (up to 800 ppm) produced in the corona discharge can be used to further oxidize the VOCs on the catalyst. The efficient decomposition of O3 on MnO2 at ambient temperature leads to the formation of reactive oxygen species susceptible to react with residual pollutants in the effluent. This results in a significant increase of VOCs destruction and removal efficiency. Moreover, the catalytic post-treatment greatly enhances the conversion of propane into CO2. The study of ozone-promoted decomposition mechanism of C3H8 on the catalyst has shown that organic by-products are adsorbed and gradually oxidized on the surface. However, concerning isopropyl alcohol, the oxidation remains incomplete: the formation yield of acetone increases after catalytic post-treatment, and the concentration of carbon oxides remains very low. The treatment of immobilized C3H7OH by ozone could be an alternative technique. Finally, the influence of the gas composition on the decomposition rate of ozone was also investigated.

Plasma-enhanced catalysis of propane and isopropyl alcohol at ambient temperature on a MnO2-based catalyst

Increasing concerns over atmospheric pollution has motivated research into technologies able to remove volatile organic compounds (VOC’s) from gas streams. The aim of this paper is to understand the chemical and physical mechanisms implied in the decomposition of VOC’s in a filamentary nonthermal plasma discharge. Experiments have been carried out on three pollutants (propane, propene, and isopropyl alcohol) in dry air at atmospheric pressure using a wire to cylinder corona discharge generated by a homemade nanosecond rise time high voltage pulse generator. The resulting plasma efficiently destructs propane, propene, or isopropyl alcohol at a concentration of 500ppm with low specific input energies (less than 500J∕L), but the poor oxidation rate leads to the formation of numerous by-products (acetone, formaldehyde, formic acid, and methyl nitrate) whose concentration can reach some hundreds of ppm. We also investigated the effect of pulse parameters on VOC removal efficiency. Neither pulse peak value nor rise time (in the range of 4–12ns) appears to have a significant influence on the VOC decomposition rates. Therefore, we believe that the way the energy is deposited in the plasma does not modify the density of active species (radicals, ions) in the streamers. The production of energetic electrons is not enhanced by the external applied field, and the only effective parameter may be the local field in the streamer head, which is almost the same (around 500Td) whatever the voltage (above the inception value).

Decomposition of three volatile organic compounds by nanosecond pulsed corona discharge: Study of by-product formation and influence of high voltage pulse parameters

The effectiveness of applying a pulsed corona discharge to the destruction of olfactory pollution in air was investigated. This paper presents a comparative study of the decomposition of three representative sulfide compounds in diluted concentrations: hydrogen sulfide (H2S), dimethyl sulfide (DMS), and ethanethiol (C2H5SH), which could be completely removed when a sufficient but reasonable energy density was deposited in the gas. DMS showed the lowest energy cost (around 30 eV/molecules); C2H5SH and H2S had an EC of respectively 45 eV and 115 eV. The efficiency of the non-thermal plasma process increased with decreasing the initial concentration of sulfide compounds, while the energy yield remained almost unchanged. SO2 was the only identified byproduct of H2S decomposition, but the sulfur balance suggests the formation of undetected SO3. The byproducts analyzed during the degradation of DMS and C2H5SH enabled to propose a reaction mechanism, starting with radical attack and breaking of C–S bonds.

Julien Jarrige

Papers

Plasma-enhanced catalysis of propane and isopropyl alcohol at ambient temperature on a MnO2-based catalyst

Decomposition of three volatile organic compounds by nanosecond pulsed corona discharge: Study of by-product formation and influence of high voltage pulse parameters

Decomposition of Gaseous Sulfide Compounds in Air by Pulsed Corona Discharge