Abatement of VOCs with alternate adsorption and plasma-assisted regeneration : a review

Energy consumption is an important concern for the removal of volatile organic compounds (VOCs) from waste air with non-thermal plasma (NTP). Although the combination of NTP with heterogeneous catalysis has shown to reduce the formation of unwanted by-products and improve the energy efficiency of the process, further optimization of these hybrid systems is still necessary to evolve to a competitive air purification technology. A newly developed innovative technique, i.e., the cyclic operation of VOC adsorption and NTP-assisted regeneration has attracted growing interest of researchers due to the optimized energy consumption and cost-effectiveness. This paper reviews this new technique for the abatement of VOCs as well as for regeneration of adsorbents. In the first part, a comparison of the energy consumption between sequential and continuous treatment is given. Next, studies dealing with adsorption followed by NTP oxidation are reviewed. Particular attention is paid to the adsorption mechanisms and the regeneration of catalysts with in-plasma and post-plasma processes. Finally, the influence of critical process parameters on the adsorption and regeneration steps is summarized

Recent advances in the abatement of volatile organic compounds (VOCs) and chlorinated-VOCs by non-thermal plasma technology: A review

Most of the volatile organic compounds (VOCs) and especially the chlorinated volatile organic compounds (Cl–VOCs), are regarded as major pollutants due to their properties of volatility, diffusivity and toxicity which pose a significant threat to human health and the eco-environment. Catalytic degradation of VOCs and Cl–VOCs to harmless products is a promising approach to mitigate the issues caused by VOCs and Cl–VOCs. Non-thermal plasma (NTP) assisted catalysis is a promising technology for the efficient degradation of VOCs and Cl–VOCs with higher selectivity under relatively mild conditions compared with conventional thermal catalysis. This review summarises state-of-the-art research of the in plasma catalysis (IPC) of VOCs degradation from three major aspects including: (i) the design of catalysts, (ii) the strategies of deep catalytic degradation and by-products inhibition, and (iii) the fundamental research into mechanisms of NTP activated catalytic VOCs degradation. Particular attention is also given to Cl–VOCs due to their characteristic properties of higher stability and toxicity. The catalysts used for the degradation Cl–VOCs, chlorinated by-products formation and the degradation mechanism of Cl–VOCs are systematically reviewed in each chapter. Finally, a perspective on future challenges and opportunities in the development of NTP assisted VOCs catalytic degradation were discussed

Ontwikkeling van heterogene plasmakatalyse voor de verwijdering van gezondheidsbelastende organische micropolluenten in binnenlucht

Onvoldoende ventilatie en een stijgend aantal emissiebronnen binnenshuis resulteren in een algemeen slechte binnenluchtkwaliteit. Aangezien mensen ongeveer 85% van hun tijd binnenskamers doorbrengen, heeft dit een ernstige impact op de gezondheid. Doordat conventionele technieken niet in staat blijken binnenlucht op een efficiënte manier te zuiveren, groeit de laatste jaren de interesse in geavanceerde oxidatie processen. Deze technologie is in staat een groot gamma vluchtige organische stoffen (VOS) af te breken onder atmosferische omstandigheden. In dit werk werd het potentieel van niet-thermische plasma onderzocht als innovatieve technologie voor de verwijdering van VOS in binnenlucht. Onderzoek inzake binnenlucht is enkel mogelijk door middel van innovatieve, opconcentrerende bemonsteringsmethodes. In dit werk werd een innovatieve versnelde Solid-Phase Dynamic Extraction (ASPDE) procedure ontwikkeld, ASPDE blijkt een factor 6 efficiënter te zijn dan Solid-phase microextraction (SPME) monstername. Tijdens dit doctoraatsonderzoek werd een DC positieve streamer ontlading gegenereerd door middel van een 4-pins-rooster plasma reactor. Deze plasmareactor werd ontwikkeld, geoptimaliseerd en gevaloriseerd aan de hand van tolueenoxidatie. De meest optimale resultaten werden bekomen in lucht met een relatieve vochtigheid van 26%. Tijdens tolueenoxidatie werden reactieproducten geïdentificeerd zoals azijnzuur, benzaldehyde, benzylalcohol, nitrofenolen,... Op basis van deze informatie, is voor de eerste keer het reactiemechanisme voorgesteld waarop tolueen door een niet-thermisch plasma afgebroken wordt. OH-radicalen blijken hierbij een belangrijke rol te spelen via H-abstractie en OH-additie. In dit werk werd aangetoond dat een meer efficiënte exploratie van plasmatechnologie mogelijk is door combinatie met heterogene katalyse. Zowel in-plasma (IPC) als post-plasma (PPC) katalyse werd onderzocht om twee redenen: het reduceren van bijproducten (bv. ozon, stikstofoxides, VOS oxidatieproducten) en een verbetering van de VOS afbraak-efficiëntie. Er is aangetoond dat het toevoegen van CuOMnO2/TiO2 in post-plasma positie (PPC), de ozonconcentratie sterk doet dalen. De tolueenverwijderingsefficientie van de PPC configuratie blijkt tevens tot 40 keer hoger te zijn dan met plasma alleen. In vochtige gasstromen, daalt de PPC tolueenverwijdering echter door competitieve adsorptie. In dit werk is ook beschreven dat deactivatie van katalysatoren mogelijk kan veroorzaakt worden door de vorming van HNO3 in de plasma-ontlading. Om de impact van luchtvochtigheid op een meer systematische manier te bestuderen werden tijdens dit doctoraat een zestal katalysatoren getest stroomafwaarts van de DC corona ontlading (PPC). Terwijl het effect van vocht niet altijd belangrijk blijkt voor ozondegradatie, wordt een vochtafhankelijk effect waargenomen op PPC tolueenverwijdering. De mate van vochtafhankelijkheid door water blijkt sterk gecorreleerd aan de invloed op Van der Waals interacties. Sorptiemetingen gebaseerd op de Equilibrium Partitioning in Closed Systems (EPICS) methodologie, toonden aan dat evenwichts-constanten en overeenkomstige verwijderings-efficiënties voor tolueen logaritmisch gecorreleerd zijn (R²= 0.966 ± 0.012 (n=4))

Recent advances in the catalytic oxidation of volatile organic compounds: a review based on pollutant sorts and sources

It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field

Plasma Processes for Renewable Energy Technologies

The use of renewable energy is an effective solution for the prevention of global warming. On the other hand, environmental plasmas are one of powerful means to solve global environmental problems on nitrogen oxides, (NOx), sulfur oxides (SOx), particulate matter (PM), volatile organic compounds (VOC), and carbon dioxides (CO2) in the atmosphere. By combining both technologies, we can develop an extremely effective environmental improvement technology. Based on this background, a Special Issue of the journal Energies on plasma processes for renewable energy technologies is planned. On the issue, we focus on environment plasma technologies that can effectively utilize renewable electric energy sources, such as photovoltaic power generation, biofuel power generation, wind turbine power generation, etc. However, any latest research results on plasma environmental improvement processes are welcome for submission. We are looking, among others, for papers on the following technical subjects in which either plasma can use renewable energy sources or can be used for renewable energy technologies: Plasma decomposition technology of harmful gases, such as the plasma denitrification method; Plasma removal technology of harmful particles, such as electrostatic precipitation; Plasma decomposition technology of harmful substances in liquid, such as gas–liquid interfacial plasma; Plasma-enhanced flow induction and heat transfer enhancement technologies, such as ionic wind device and plasma actuator; Plasma-enhanced combustion and fuel reforming; Other environment plasma technologies

Roles of Non-thermal Plasma in Gas-phase Glycerol Dehydration Catalyzed by Supported Silicotungstic Acid

Acrolein is an indispensable chemical intermediate with a rising demand in recent years. The concern of the increase of propylene prices due to the shrinking supply of nonrenewable crude oil makes the acid-catalyzed gas-phase glycerol dehydration to acrolein a prime candidate for research. Our analysis showed that the sustainable acrolein production from glycerol was both technically and economically viable. Alumina2700® (Al) and Silica1252® (Si) loaded with silicotungstic acid (HSiW) possessed distinct features while provided equally good acrolein yield (73.86mol% and 74.05mol%, respectively) optimally. Due to the unique non-equilibrium characteristics, non-thermal plasma (NTP) could promote a variety of chemical reactions; however, its application in a dehydration process remained blank. This study used the reaction of glycerol dehydration to acrolein to probe whether NTP could 1) improve acrolein yield during dehydration, 2) suppress the coke formation and regenerate the catalyst, and 3) modify the properties of the catalyst. The dielectric barrier discharge configuration was used to generate NTP; various NTP field strengths and also their interaction with temperature and the catalyst were investigated. The results showed that NTP improved the glycerol conversion and that NTP with a proper field strength increased acrolein selectivity. The optimal acrolein yields of 83.6 mol% and 83.1 mol% were achieved with 3.78 kV/cm NTP and 4.58 kV/cm NTP at 275°C for HSiW-Al and HSiW-Si, respectively. The application of NTP-O2 (5% oxygen in argon, 4.58 kV/cm) during glycerol dehydration significantly suppressed coke formation on HSiW-Si. NTP-O2 could regenerate the deactivated HSiW-Si at low temperatures by removing both soft and hard coke at various rates. NTP-O2 with higher field strength, at medium operation temperature (150ºC) and in argon atmosphere was more effective for coke removal/catalyst regeneration. Applying NTP to the catalyst fabrication showed some capabilities in modifying catalyst properties, including enlarging surface area, preserving mesopores, increasing acid strength and Brønsted acidity. NTP with argon as the discharge gas performed better in these modifications than NTP with air as the discharge gas