Volatile organic compounds thermal oxidation

Holzer, F., Roland, U. and Kopinke, F.-D. (2002) Combination of non-thermal plasma and heterogeneous catalysis for oxidation of volatile organic compounds Part 1. Accessibility of the intra-particle volume, Appl. Cat. B Env. 38, 163-81. 

Incineration systems are based on the principle that all volatile organic compounds are combustible and can, in principle, be eliminated simply by being burned. Combustion can be achieved without catalysts (thermal systems) or with catalysts (catalytic systems). In either case, flue gases are passed into a chamber where they are heated in an excess of air, resulting in the oxidation of VOCs. Thermal systems operate at temperatures of 750°C-1,000°C, while catalytic systems operate at temperatures of about 350°C-500°C. 

The System 64MT low-temperature thermal desorption (LTTD) system is a commercially available ex situ thermal desorption technology. This system uses a countercurrent flow rotary drier to heat soils contaminated with volatile organic compounds (VOCs) to temperatures sufficient to cause contaminants to volatilize and physically separate from the soU. Filter bags remove particulate matter and afterbumers/oxidizers are used to destroy organic constituents that remain in the filtered airstream. 

The HRUBOUT process is a mobile in situ or ex situ thermal desorption process designed to remediate soils contaminated with volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs). For the ex situ process, excavated soil is treated in a soil pile or in a specially designed container. Heated compressed air is injected into the soil, evaporating soil moisture and removing volatile and semivolatUe contaminants. Heavier hydrocarbons are oxidized as the soil temperature is increased to higher levels over an extended period of time. The vapor is collected and transferred to a thermal oxidizer (incinerator) for destruction. 

King, Buck Technologies, Inc. s, MultiMode combustion (MMC) system treats volatile organic compound (VOC) emissions from soil vapor extraction (SVE) operations. The sequential operation of a thermal oxidizer (ThermOx) followed by a catalytic oxidizer (CatOx) is the basic concept of the MMC system. The CatOx technology is discussed in a separate technology summary (T0780). 

The GEiM-lOOO low-temperature thermal desorption unit is an ex situ technology that treats soils contaminated with volatile organic compounds (VOCs). This process involves a countercurrent drum, pulse-jet baghouse, and a catalytic oxidizer mounted on a single portable trailer. As the soil is heated in the GEM-1000 unit, contaminants are vaporized. The contaminants are then directed to the system s catalytic oxidizer, which is designed to convert virtually all of the VOCs to carbon dioxide and water vapor. The oxidizer contains approximately 4.9 ft of noble metal catalyst and can destroy between 95 and 99% of the hydrocarbons when operating between 600 and 1250°F. 

As discussed in other chapters of this book and summarized in Chapter 16, the formation of tropospheric ozone from photochemical reactions of volatile organic compounds (VOC) and oxides of nitrogen (NC/) involves many reactions. Concentrations are therefore quite variable geographically, temporally, and altitudinally. Additional complications come from the fact that there are episodic injections of stratospheric 03 into the troposphere as well as a number of sinks for its removal. Because 03 decomposes thermally, particularly on surfaces, it is not preserved in ice cores. All of these factors make the development of a global climatology for 03 in a manner similar to that for N20 and CH4, for example, much more difficult. In addition, the complexity of the chemistry leading to O, formation from VOC and NOx is such that model-predicted ozone concentrations can vary from model to model (e.g., see Olson et al., 1997). 

Huang, K., Z. Zhao, G. Hoag, A. Dahmani, and B. Block (2005). Degradation of volatile organic compounds with thermally activated persulfate oxidation. Chemosphere 61, 551-560. 

Since natural sunlight can only penetrate a few microns depth, the use of thin films of titania applied to ceramic or metallic supports as maintenance free decontamination catalysts for the photocatalytic oxidation of volatile organic compounds is of interest for the abatement or control of these emissions. The sol-gel technology can be readily incorporated as a washcoating step of the catalyst supports that may be subsequently heat-treated to fix the titania to the support. The surface area, porosity and crystalline phases present in these gels is important in controlling their catalytic activity. Furthermore, the thermal stability and development of porosity with heat-treatment was important if the sol-gel route is to be used as a washcoating step to produce thin films. 

The increasing amounts of chlorinated volatile organic compounds (VOC), such as 1,2-dichloroethane (DCE) and trichloroethylene (TCE), released in the environment, together with their suspected toxicity and carcinogenic properties, have prompted researchers world-wide to find clean effective methods of destruction [1]. The abatement of chlorinated volatile organic compounds by catalytic combustion has been widely utilised in several technical processes. The lower temperatures required for catalytic combustion result in a lower fuel demand and can therefore be more cost effective than a thermal oxidation process [2]. In addition, the catalytic process also exerts more control over the reaction products and is less likely to produce toxic by-products, like dioxins, which may be generated by thermal combustion [3]. 

Catalytic total oxidation of volatile organic compounds (VOC) is widely used to reduce emissions of air pollutants. Besides supported noble metals supported transition metal oxides (V, W, Cr, Mn, Cu, Fe) and oxidic compounds (perovskites) have been reported as suitable catalysts [1,2]. However, chlorinated hydrocarbons (CHC) in industrial exhaust gases lead to poisoning and deactivation of the catalysts [3]. Otherwise, catalysts for the catalytic combustion of VOCs and methane in natural gas burning turbines to avoid NO emissions should be stable at higher reaction temperatures and resists to thermal shocks [3]. Therefore, the development of chemically and thermally stable, low cost materials is of potential interest for the application as total oxidation catalysts. 

Afterburning processes enable the removal of pollutants such as hydrocarbons and volatile organic compounds (VOCs) by treatment under thermal or catalytical conditions. Combinations of both techniques are also known. VOCs are emissions from various sources (e.g. solvents, reaction products etc. from the paint industry, enaml-ing operations, plywood manufacture, printing industry). They are mostly oxidized catalytically in the presence of Pt, Pd, Fe, Mn, Cu or Cr catalysts. The temperatures in catalytic afterburning processes are much lower than for thermal processes, so avoiding higher NOx levels. The catalysts involved are ceramic or metal honeycombs with washcoats based on cordierite, mullite or perovskites such as LaCoOs or Sr-doped LaCoOs. Conventional catalysts contain Ba-stabilized alumina plus Pt or Pd. 

The formation of char during the thermal decomposition of polymers can be a result of crosslinking reactions taking place in the solid phase. One of the beneficial effects of char formation is that polymer carbon is retained in the solid phase and, as a consequence, is not available for the formation of oxides of carbon, volatile organic compounds and of course smoke. Hence, substances which interact with the polymer to increase char formation during burning are in fact smoke suppressants, and only a few elements in the periodic table are known to react in this way. Zinc, molybdenum, iron and possibly tin compounds are known smoke suppressants and have been available commercially for use in PVC formulations. 

---