Efficiency of Emission Reduction Technologies for Residential Biomass Combustion Appliances: Electrostatic Precipitator and Catalyst

Residential biomass combustion has been pointed out as one of the largest sources of atmospheric pollutants. Rising awareness of the environmental effects of residential biomass combustion emissions boosted the development of different emission reduction devices that are currently available on the market for small-scale appliances. However, detailed studies on the efficiency of these devices in different combustion systems available in Southern European countries are lacking. In this study, two pollution control devices (catalytic converter and electrostatic precipitator) were tested in two different combustion systems (batch mode operated woodstove and automatically fed pellet stove) in order to assess the emission reduction potential of the devices. Pine firewood was used to fuel the woodstove. One commercial brand of pellets and an agricultural fuel (olive pit) were taken for the experiments in the pellet stove. While the efficiency of the electrostatic precipitator in reducing PM10 was only recorded for woodstove emissions (29%), the effect of the catalyst in decreasing gaseous emissions was only visible when applied to the pellet stove flue gas. For wood pellet combustion, reductions of CO and TOC emissions were in the range of 60–62% and 74–77%, respectively. For olive pit combustion, a lower decrease of 59–60% and 64% in CO and TOC emissions, respectively, was recorded.

A Review of Recovery of Palladium from the Spent Automobile Catalysts

The spent automobile catalysts (SAC) is the major secondary source of palladium and the production of SAC is increasing rapidly over years. The price of palladium keeps rising over the years, which demonstrates its preciousness and urgent industrial demand. Recovering palladium from the spent automobile catalysts benefits a lot from economic and environmental protection aspects. This review aims to provide some new considerations of recovering palladium from the spent automotive catalysts by summarizing and discussing both hydrometallurgical and pyrometallurgical methods. The processes of pretreatment, leaching/extraction, and separation/recovery of palladium from the spent catalysts are introduced, and related reaction mechanisms and process flows are given, especially detailed for hydrometallurgical methods. Hydrometallurgical methods such as chloride leaching with oxidants possess a high selectivity of palladium and low consumption of energy, and are cost-effective and flexible for different volume feeds compared with pyrometallurgical methods. The recovery ratios of palladium and other platinum-group metals should be the focus of competition since their prices have been rapidly increased over the years, and hence more efficient extractants with high selectivity of palladium even in the complexed leachate should be proposed in the future.

Transportation and Air Quality Perspectives and Projections in a Mediterranean Country, the Case of Greece

This study provides a thorough review and analysis of the evolution of the Greek vehicle fleet over the last ~30 years, which is next used for the generation of high granularity fleet projections, the assessment of associated air pollution and the estimation of relevant environmental benefits by 2030. The integrated methodology developed takes also into account vehicle clustering and the Brown’s Double Simple Exponential Smoothing technique that, together with the adoption of COPERT-based emission factors, allow for the estimation of the anticipated emissions in 2030. Expected 2030 emissions levels suggest a reduction across all pollutants compared to 2018, ranging from 3.7% for PM10 to 54.5% for NMVOC (and 46% for CO, 14% for SO2, 28% for NOX and 21% for CO2). We find that Greece is on track with national goals concerning the reduction of air pollution from the transportation sector, which designates the positive contribution anticipated by EVs and new, “greener” vehicles, and sets new challenges for the further improvement of the sector beyond the 2030 outlook.

VOCs Photothermo-Catalytic Removal on MnOx-ZrO2 Catalysts

Solar photothermo-catalysis is a fascinating multi-catalytic approach for volatile organic compounds (VOCs) removal. In this work, we have explored the performance and the chemico-physical features of non-critical, noble, metal-free MnOx-ZrO2 mixed oxides. The structural, morphological, and optical characterizations of these materials pointed to as a low amount of ZrO2 favoured a good interaction and the ionic exchange between the Mn and the Zr ions. This favoured the redox properties of MnOx increasing the mobility of its oxygens that can participate in the VOCs oxidation through a Mars-van Krevelen mechanism. The further application of solar irradiation sped up the oxidation reactions promoting the VOCs total oxidation to CO2. The MnOx-5 wt.%ZrO2 sample showed, in the photothermo-catalytic tests, a toluene T90 (temperature of 90% of conversion) of 180 °C and an ethanol T90 conversion to CO2 of 156 °C, 36 °C, and 205 °C lower compared to the thermocatalytic tests, respectively. Finally, the same sample exhibited 84% toluene conversion and the best selectivity to CO2 in the ethanol removal after 5 h of solar irradiation at room temperature, a photoactivity similar to the most employed TiO2-based materials. The as-synthetized mixed oxide is promising for an improved sustainability in both catalyst design and environmental applications.

Kinetic Analysis for the Catalytic Pyrolysis of Polypropylene over Low Cost Mineral Catalysts

A kinetic analysis of non-catalytic pyrolysis (NCP) and catalytic pyrolysis (CP) of polypropylene (PP) with different catalysts was performed using thermogravimetric analysis (TGA) and kinetic models. Three kinds of low-cost natural catalysts were used to maximize the cost-effectiveness of the process: natural zeolite (NZ), bentonite, olivine, and a mesoporous catalyst, Al-MCM-41. The decomposition temperature of PP and apparent activation energy (Ea) were obtained from the TGA results at multiple heating rates, and a model-free kinetic analysis was performed using the Flynn–Wall–Ozawa model. TGA indicated that the maximum decomposition temperature (Tmax) of the PP was shifted from 464 °C to 347 °C with Al-MCM-41 and 348 °C with bentonite, largely due to their strong acidity and large pore size. Although olivine had a large pore size, the Tmax of PP was only shifted to 456 °C, because of its low acidity. The differential TG (DTG) curve of PP over NZ revealed a two-step mechanism. The Tmax of the first peak on the DTG curve of PP with NZ was 376 °C due to the high acidity of NZ. On the other hand, that of the second peak was higher (474 °C) than the non-catalytic reaction. The Ea values at each conversion were also decreased when using the catalysts, except olivine. At <0.5 conversion, the Ea obtained from the CP of PP with NZ was lower than that with the other catalysts: Al-MCM-41, bentonite, and olivine, in that order. The Ea for the CP of PP with NZ increased more rapidly, to 193 kJ/mol at 0.9 conversion, than the other catalysts.