A study of the thermal decomposition of urea, of related compounds and thiourea using DSC and TG-EGA

Stradella, L.; Argentero, Massimo

doi:10.1016/0040-6031(93)80508-8

Cited by 136 publications

(66 citation statements)

References 7 publications

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“…The absorption bands at 2204 and 1233 cm −1 correspond to isocyanic acid (HNCO) [35]. The presence of lactam compounds could explain the appearance of the additional band at 1674 cm −1 , and the band at 1084 cm −1 is related to biuret (C 2 H 5 O 2 N 2 ) [36]. CaCO 3 is responsible for the bands at 2873, 2515, 1795, 1429, 873, and 711 cm −1 [31,37].…”

Section: Possible Mechanism Of Synergetic Inhibitionmentioning

confidence: 99%

“…The hydrolysis of HNCO with trace amounts of water could produce NH 3 and CO 2 . The lactam compound might be the ammelide (C 3 H 4 O 2 N 4 ), which could be formed by the reaction between HNCO and biuret [36,38]. The formation of H 2 O and CO 2 could be the reason why addition of urea facilitated the formation of CaCO 3 .…”

Section: Possible Mechanism Of Synergetic Inhibitionmentioning

confidence: 99%

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Synergetic inhibition of PCDD/F formation from pentachlorophenol by mixtures of urea and calcium oxide

et al. 2016

Journal of Hazardous Materials

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h i g h l i g h t s• Mixed CaO/urea have a synergetic inhibition effect for PCDD/Fs formation from PCP.• 5-20% urea reaction systems obtained the better synergetic inhibition effect.• 2,3,7,8-PCDD congeners were the dominant products in eight reaction systems.• Intermediates could promote the acid-base reaction to realize synergetic inhibition. a r t i c l e i n f o b s t r a c tChlorophenols are structurally similar to PCDD/Fs and have been considered as highly potential precursors for PCDD/Fs formation. The suppressing effects of PCDD/F formation from pentachlorophenol (PCP) were investigated on various mass ratios of CaO and urea. The total concentration of 2,3,7,8-PCDD/Fs, mostly dominated by OCDD, was determined to be 48.58-10186 ng/mg in inhibitor-reaction systems, being much lower than that in blank reaction system (75654 ng/mg). Interestingly, compared with pure CaO and urea reaction system, the concentration and TEQ of formed 2,3,7,8-PCDD/Fs in mixed urea/CaO reaction system were lower, especially with 5-20% urea reaction systems being respectively at decrease by 96.5-99.4% and 99.2-99.7%. The suppression efficiency of TEQ in 5-20% urea reaction systems could be always approximately 100% under 250-350• C. These results suggested that mixed inhibitors, especially 5-20% urea inhibitors, have a synergetic inhibition effect for PCDD/Fs formation from PCP. Mixed inhibitor generated several intermediates, involving CO 2 , H 2 O, NH 3 , Ca(OH) 2 , CaCO 3 , HNCO, biuret and ammelide. The complex between PCP and Ca, N-doped species, lower chlorinated phenols and benzenediol, and organic acids were also determined. Synergetic inhibition mechanism may be attributed to accelerated facilitation of acid-base reaction and N doping. The decomposition of PCP itself also contributes to prevent PCDD/Fs formation.

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Section: Possible Mechanism Of Synergetic Inhibitionmentioning

confidence: 99%

Section: Possible Mechanism Of Synergetic Inhibitionmentioning

confidence: 99%

Synergetic inhibition of PCDD/F formation from pentachlorophenol by mixtures of urea and calcium oxide

et al. 2016

Journal of Hazardous Materials

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“…Urea thermolysis begins when the water content evaporates completely. Stradella and Argentero (1993) and Chen et al (1998) found that ammonia and iso-cyanic were produced during the urea thermolysis process. High molecular compounds such as biuret, CYA, ammelide, and ammeline also appeared in their investigation.…”

Section: Introductionmentioning

confidence: 99%

“…Incomplete decomposition of the UWS leads to spray wall interaction and the formation of a wall film. Side reactions may take place in the wall film producing undesired deposit by-products such as biuret, cyanuric acid (CYA), ammelide, ammeline, melamine, and more complex polymerization products (Stradella and Argentero, 1993;Chen and Isa, 1998;Zhong et al, 2013). These undesired by-products are the main components of solid deposits which may block the exhaust pipe and catalyst leading to higher exhaust pressure and lower conversion efficiency of urea decomposition.…”

Section: Introductionmentioning

confidence: 99%

Quasi 1D modeling of two-phase flow and deposit formation for urea-selective catalytic reduction systems

Gan

Yao

et al. 2016

J. Zhejiang Univ. Sci. A

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A quasi 1D model of two-phase flow for a urea-selective catalytic reduction (SCR) system is developed which can calculate not only the generation of reducing agent but also the formation of deposits in the exhaust pipe. The gas phase flow is solved through Euler method, variables are stored on staggered grids, and the semi-implicit method for pressure-linked equation (SIMPLE) algorithm is applied to decouple the pressure and velocity. The liquid phase is treated in a Lagrangian way, which solves the equations of droplet motion, evaporation, thermolysis, and spray wall interaction. A combination of a direct decomposition model and a kinetic model is implemented to describe the different decomposition behaviors of urea in the droplet phase and wall film, respectively. A new 1D wall film model is proposed, and the equations of wall film motion, evaporation, thermolysis, and species transport are solved. The position, weight, and components of deposits can be simulated following implementation of the semi-detailed kinetic model. The simulation results show that a decrease in the exhaust temperature will increase the wall film region and the weight of deposits. Deposit components are highly dependent on temperature. The urea-water-solution (UWS) injection rate can affect the total mass of wall film and expand the film region, but it has little influence on deposit components. An increase in exhaust mass flow can decrease the total weight of deposits on the pipe wall because of the promotion of the mass and heat transfer process both in the droplets and wall film.

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“…There are several possible decomposition routes for thiourea in the aqueous alkaline solution. One that has been used most commonly and is well elucidated is [64] ( 2 ) 2 + − ⇋ − + 2 2 + 2 which generates hydrogen sulfide ions. The cyanamide complex, CN2H2, hydrolyzes further, however, it does not take part in the rest of the chemical film growth of chalcogenides, hence is ignored in further discussion.…”

Section: Sulphidementioning

confidence: 99%

Mid-IR Range Photosensitive Device Based on Chemically Deposited Nanocrystalline Chalcogenide Thin Films with Tunable Opto-electrical properties

Slonopas

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Past several decades have driven modernization of technology and machinery. This modernization has pushed the limits of our technology and increased our dependence on the energy. Additional side-effect of this rapid growth has been an exponential increase in the generated heat of the modern machinery.In most cases this waste heat is simply released into the environment. Numerous research groups have pursued an idea of capturing and converting the waste heat. Thermoelectric, pyroelectrics, organic Rankine cycle (ORC), and several other methods have been proposed to capture and convert the waste heat into electricity. Presently, all methods, however, have low conversion efficiency and are not economically feasible.In this work we focused on a practical approach to convert mid-IR electromagnetic waves to electricity. It is based on inexpensive thin film technology utilizing a junction between a narrow bandgap lead salt and wide bandgap chalcogenide film.Lead sulfide (PbS) was chosen as the narrow band semiconductors for the IR energy conversion.Lead salt photodetectors uniquely demonstrate high room temperature sensitivity to black-body sources in low temperatures and high internal quantum efficiency (QE). Further, the peculiar band structure of the lead salt allows for small Auger recombination and minimized losses.Due to its favorable opto-electrical properties and band compatibility with PbS, cadmium sulfide (CdS) was chosen as the wide bandgap semiconductor for this work.This work has shown that high quality nanocrystalline thin films of lead sulfide (PbS) and cadmium sulfide (CdS) can be grown cost efficiently using chemical bath deposition (CBD) method. Chemical bath seeding procedure was also developed in order to achieve reproducibility in the transport phenomena of the advanced materials. Seeding also allows these films to be deposited on any surface, including smooth flexible materials. Seeded kernels have shown to become the crystallization centers for both nanocrystalline films.Opto-electrical properties of the films were tuned in such a way to make the materials useful in a broad-band of the IR spectrum. We have shown that altering the parameters of the chemical bath deposition alters the grains hence changing the transport characteristics of the materials. We have shown that parameters of the chemical bath deposition can be optimized to produce highly sensitive thin films tuned to a specific range of the electromagnetic spectra.Novel transparent conducting oxide, Iridium (Ir) doped Titanium Oxide (TiO2) was developed in this work for the use in the optoelectronic device. Ir has been shown to be one of the most efficient dopants in thin films. Ir doped TiO2 has shown to have transport characteristics similar ii to those of the commonly used TCOs, with much higher optical transmittance in the infra-red range.Lastly devices were manufactured from the developed materials. TiO2/CdS/PbS/Au heterojunctions were manufactured and showed photoresponsivity. Device efficiencies were shown to depend on the...

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A study of the thermal decomposition of urea, of related compounds and thiourea using DSC and TG-EGA

Cited by 136 publications

References 7 publications

Synergetic inhibition of PCDD/F formation from pentachlorophenol by mixtures of urea and calcium oxide

Synergetic inhibition of PCDD/F formation from pentachlorophenol by mixtures of urea and calcium oxide

Quasi 1D modeling of two-phase flow and deposit formation for urea-selective catalytic reduction systems

Mid-IR Range Photosensitive Device Based on Chemically Deposited Nanocrystalline Chalcogenide Thin Films with Tunable Opto-electrical properties

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