Absorption of NOx

Dutch State Mines (Stamicarbon). Vapor-phase, catalytic hydrogenation of phenol to cyclohexanone over palladium on alumina, licensed by Stamicarbon, the engineering subsidiary of DSM, gives a 95% yield at high conversion plus an additional 3% by dehydrogenation of coproduct cydohexanol over a copper catalyst. Cyclohexane oxidation, an alternative route to cyclohexanone, is used in the United States and in Asia by DSM. A cyclohexane vapor-cloud explosion occurred in 1975 at a co-owned DSM plant in Flixborough, UK (12) the plant was rebuilt but later closed. In addition to the conventional Raschig process for hydroxylamine, DSM has developed a hydroxylamine phosphate—oxime (HPO) process for cyclohexanone oxime no by-product ammonium sulfate is produced. Catalytic ammonia oxidation is followed by absorption of NOx in a buffered aqueous phosphoric acid... 

Kafarov W, Shestopalov EA, Novikov EA, Belkov VP. Mathematical model of absorption of NOx in production of weak nitric acid. Soviet Chem Ind 1975 7 1224-1226. 

In this section, four examples illustrating the application of the rate-based modeling approach discussed above are presented. First three reactive absorption processes -namely absorption of NOx, coke gas purification and CO2 absorption by aqueous... 

Bart H, Morr R, Burtscher K (1991) Absorption of NOx and SO2 without waste products Abstract 35-13, 4th World Congress in Chem Eng, Karlsruhe... 

Hodjati, S., Petit, C., Pitchon, V. et al. (2000) Absorption/Desorption of NOx Process on Perovskites Nature and Stability of the Species formed on BaSn03, Appl. Catal. B Environ., 27, 117. 

C-doped Ti02 was employed for the photocatalytic removal of NOx. The presence of carbon, in the form of coke-like species, was responsible for visible light absorption and thus for the good activity of the photocatalyst under green light irradiation [133]. 

Apart from the economic significance of such loss there are potentially adverse effects on the environment arising from acidification of rain and soil. Ammonia may react with hydroxyl radicals in the atmosphere to produce NOx contributing to the acidification of rain (4). Wet and dry deposition of NH3/NH4+ inevitably contributes to soil acidification through their subsequent nitrification. This effect can be accentuated in woodland by absorption of aerosols containing NH4+ within the canopy followed by transport to the soil in stem flow (5). In more extreme cases, NH3 emission from feedlots, pig and poultry... 

Hodjati, S Petit, C Pitehon, V Kieimemaim, A. Absorption/desorption of NOx process on perovskites impaet of SO2 on the storage capacity of BaSnOs and strategy to develop thioresistanee. Appl. Catal, B Environmental, 2001, Volmne 30, Issues 3-4, 247-257. 

Nitrosylsulfuric acid also is made from absorption of nitrogen oxides (NOx) in oleum (fuming sulfuric acid) ... 

Infrared absorption bands attributable to methyl thioformate have been observed in the oxidation of DMS by OH in the absence of NOx but not when NOx was present (Barnes et al., 1996 Patroescu et al., 1999). Reaction (51) appears to be quite slow (k < 1 X 10 15 cm2 molecule-1 s-1), so that the dominant fate of CH3SCH20 is decomposition to HCHO + CH3S Turnipseed et al. (1996) measured the production of CH3S in the reaction of OH with DMS and also suggest, based on its relatively high yield, that the thermal decomposition (50) predominates over reaction (51) with 02 to form methyl thioformate. The methyl thioformate observed in laboratory systems in the absence of NO is thus likely due to cross reactions of CH3SCH200 with itself or other R02 (Barnes et al., 1994a), and the abstraction channel in the OH + DMS... 

Absorption of the nitrogen oxide components (NOx) of the process gas stream is conducted in a sieve tray-type absorption column. This tower contains 59 sieve trays, of which the top 45 trays contain herringbone cooling coils to remove heat of reaction/dilution and maintain low absorption temperatures. 

NONE No Flow 1. Pump failure. High emission of NOx in tail gas. a) Install LOW LEVEL ALARM on LIC at the base of the absorption column. 

Suchak NJ, Jethani KR, Joshi JB. Modeling and simulation of NOx absorption in pilot-scale packed columns. AIChE J 1991 37 323-339. 

The primary pollution problem in nitric acid plants is the abatement of NOx in tail gases. Three options exist to reduce these emissions to acceptable levels 1) Capture the NOx and convert it to additional nitric acid, 2) Capture the NOx and convert it to nitrate-nitrite sales, or 3) Render the NOx harmless by converting it to non-polluting compounds. The processes that have been developed to reduce emissions at existing and new plants can be classified into four general categories Absorption, Adsorption, Selective Catalytic Reduction (SCR) and Non-Selective Catalytic Reduction91. 

Reproduced by permission of Monsanto Enviro-Chem Systems, Inc.) a DCN Destmction by Catalysis of NOx HEA High Efficiency Absorption... 

Monsanto Enviro-Chem offers NOx abatement technology that is licensed from Rhodia of France. It includes a high efficiency absorption (HEA) section for extended absorption and a catalytic reduction section (SCR) for catalytic destruction of NOx (i.e., the DCN technology).99 Additional process details are given in Reference 99. The operating conditions for the steps in the Monsanto technology are compared in Table 22.19. 

DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Moderately toxic by ingestion, skin contact, intravenous, and subcutaneous routes. Mildly toxic by inhalation. A skin and severe eye irritant. Excessive absorption can cause urticaria, vomiting, diarrhea, blurred vision, and weakness. Combustible when exposed to heat or flame can react vigorously with oxidizing materials. Explodes on contact with dicyanofurazan. To fight fire, use alcohol foam, mist, dr) chemical, water spray. When heated to decomposition it emits highly toxic fumes of NOx. 

Removal of NOx from tail gases is often more difficult than improving the absorption technology... 

Among the manifold reactions in snow the photolysis of nitrate (NO3 ) is now the best characterized reaction due to a range of laboratory experiments. These studies have been used to extract information about the absorption coefficients and quantum yields of NO3 in ice as a function of wavelength, the formation of products like the hydroxyl radical (OH) and nitrite (N02), and the release of NOx to the gas phase. Limited information regarding the absorption coefficients and the formation of OH radicals can also be found for the photolysis of H202. " Investigations regarding the photolytic decomposition of further compounds with a potential relevance for photochemical processes in surface snow are limited to studies, in which reactions of HCHO and NO2 have been examined. 

At variance, Wl-650 pellet was immediately oxidized by NO2 (see Fig. 5a), with decrease of the electron population of the Vo a broad, weak and negative absorption was already evident after a contact time of 2 sec, at the same time weak vibrational peaks related to the formation of a variety of NOx surface species appeared. At higher contact times the electronic... 

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