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Physical Properties of Agrochemicals
Published in John H. Montgomery, Thomas Roy Crompton, Environmental Chemicals Desk Reference, 2017
John H. Montgomery, Thomas Roy Crompton
Pelizzetti et al. (1990) studied the aqueous photocatalytic degradation of atrazine (ppb level) using simulated sunlight (λ > 340 nm) and titanium dioxide as a photocatalyst. Atrazine rapidly degraded from 2 ppb to <0.1 ppb in a few minutes. The following intermediates were identified via HPLC and/or GC/MS: 2,4-diamino-6-hydroxy-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine, ammeline (2,4-diamino-6-hydroxy-1,3,5-triazine), ammelide (2-diamino-4,6-dihydroxy-1,3,5-triazine), 2,4-diamino-6-chloro-1,3,5-triazine, 2,4-diamino-6-chloro-N-(1-methylethyl)-1,3,5-triazine, 2,4-diamino-6-chloro-N-ethyl-1,3,5-triazine, 2-amino-4-chloro-6-hydroxy-1,3,5-triazine, 2-chloro-4,6-dihydroxy-1,3,5-triazine, cyanuric acid (2,4,6-trihydroxy-1,3,5-triazine), and 2-acetylamino-4-amino-6-chloro-N-(1-methylethyl)-1,3,5-triazine. Complete degradation of atrazine gave cyanuric acid (2,4,6-trihydroxy-1,3,5-triazine), chloride, and nitrate ions. Mineralization of cyanuric acid to carbon dioxide was not observed (Pelizzetti et al., 1990). Nearly identical photodegradation products were reported by Pelizzetti et al. (1992). They studied the photocatalytic degradation of atrazine in water containing a suspension of titanium dioxide (0.5 g/L) as the catalyst. Irradiation was carried out in Pyrex glass cells using a 1500-W xenon lamp (λ cutoff = 340 nm). The major photoprocesses of degradation were alkyl chain oxidation and subsequent oxidation, leading to the formation of hydroxy derivatives. Dehalogenation was also observed but this was considered a minor degradative pathway. Cyanuric acid was the major photoproduct formed. There was only a partial conversion or mineralization to carbon dioxide (Pelizzetti et al., 1992).
Urea and Melamine Aminoresin Adhesives
Published in A. Pizzi, K. L. Mittal, Handbook of Adhesive Technology, 2017
Ammeline and ammelide can be regarded as partial amides of cyanuric acid. They are acidic, and have no use in resin production. They are very undesirable by-products of the manufacture of melamine, because of their catalytic effect in subsequent MF resin production, due to their acidic nature. If present, both must be removed from crude melamine by an alkali wash and/or crystallization of the crude melamine.
Application of a FIGAERO ToF CIMS for on-line characterization of real-world fresh and aged particle emissions from buses
Published in Aerosol Science and Technology, 2019
M. Le Breton, M. Psichoudaki, M. Hallquist, Å. K. Watne, A. Lutz, Å. M. Hallquist
Gas phase measurements of HNCO indicated inefficient hydrolysis of HNCO, enabling HNCO to further react via several pathways, a known major problem of SCR technology (Bernhard et al. 2012; Wentzell et al. 2013). Upon initial analysis of the HNCO byproducts, the RMEHEV fuel appeared to emit more mass than the diesel buses, with biuret and triuret dominating, whereas the diesel emissions were composed mainly of cyanuric acid, HNCO and triuret. HNCO was a significant particle phase mass contributor for all SCR related peaks, which is unexpected due to its partitioning significantly to the gas phase. HNCO began to come off the filter at 84 °C and exhibited two maximum in desorption temperature (Tmax) at 182 °C and 200 °C. The desorption profile did not return to background levels after the final Tmax value and continued reporting a constant amount of counts after a small dip, suggesting a number of sources of HNCO from the filter. HNCO has a boiling point of 23.5 °C, therefore should begin to come off from the filter if present in the particle phase much earlier than observed. Urea has a melting point of 133 °C and vaporization starts around 140 °C. Upon vaporization it can decompose to form HNCO which can either further react with the remaining urea to form biuret or trimerise and form cyanuric acid. HNCO can further react with biuret to form ammelide and ammeline at temperatures up to 190 °C, with further reactions of biuret contributing to their production and cyanuric acid. At temperatures up to 250 °C, melamine can be formed via reaction of ammeline with ammonia. The ramping of temperature in the FIGAERO to 250 °C may add an unsolvable level of complexity due to the formation rates of a number of these compounds. A standard thermogram for these compounds is displayed in the supplementary (SI Figure S5) confirming the detection of these products, although production of HNCO complicates their direct quantification. We conclude that it is not possible to diagnose the exact composition of the emissions via analyzing relative desorption profiles observed by the CIMS. The high concentration of HNCO could simply be via consumption of byproducts to produce HNCO. Nevertheless, the ability for CIMS to identify these compounds enables the technique to positively confirm the production of these byproducts formed from incomplete hydrolysis of HNCO. Their detection by CIMS also confirms the emission of SCR system particle phase products into the urban atmosphere in forms other than urea and HNCO.