Thermochemistry of alkyl derivatives of urea

Kabo, G. Ya.; Мирошниченко, Е. А.; Frenkel, M. L.; Kozyro, Alexander A.; Simirskii, V. V.; Krasulin, A.P.; Воробьева, В. П.; Lebedev, Yu. A.

doi:10.1007/bf00960321

Cited by 44 publications

(30 citation statements)

References 2 publications

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“…Knowledge of equilibrium dry gas compositions is useful to the experimentalist as they can be directly compared to measurements from on-line and off-line analyses of the process gas products. Sublimation of urea (solid to gas phase change), with a H of 97.6 kJ/mol, is reported to occur at around 354 K [34], but to streamline the calculation of equilibrium condition, the urea feed was input in gaseous phase in the EQUIL code, and the enthalpy change of sublimation was subsequently accounted for in the 'urea H' term of the total enthalpy balance 'H total '. Similarly, the water feed was input in the gaseous phase.…”

Section: Resultsmentioning

confidence: 99%

Thermodynamics of hydrogen production from urea by steam reforming with and without in situ carbon dioxide sorption

Dupont

Twigg²,

Rollinson

et al. 2013

International Journal of Hydrogen Energy

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The thermodynamic effects of molar steam to carbon ratio (S:C), of pressure, and of having CaO present on the H 2 yield and enthalpy balance of urea steam reforming were investigated.At a S:C of 3 the presence of CaO increased the H 2 yield from 2.6 mol H 2 /mol urea feed at 940 K to 2.9 at 890 K, and decreased the enthalpy of bringing the system to equilibrium. A minimum enthalpy of 180.4 kJ was required to produce 1 mole of H 2 at 880 K. This decreased to 94.0 kJ at 660 K with CaO-based CO 2 sorption and, when including a regeneration step of the CaCO 3 at 1170 K, to 173 kJ at 720 K. The presence of CaO allowed widening the range of viable operation at lower temperature and significantly inhibited carbon formation. The feasibility of producing H 2 from renewable urea in a low carbon future is discussed.

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Section: Resultsmentioning

confidence: 99%

Thermodynamics of hydrogen production from urea by steam reforming with and without in situ carbon dioxide sorption

Dupont

Twigg²,

Rollinson

et al. 2013

International Journal of Hydrogen Energy

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“…According to the Brack mechanism, 13 this is mainly due to the reaction urea(l) -HNCO(l) + NH 3 (g). At this temperature, the vapor pressure of isocyanic acid is already more than 26 bar according to eqn (20). Unless HNCO(l) reacts very fast to form biuret or triuret, it would evaporate, leaving no caloric contribution of HNCO(l) in a DSC experiment.…”

Section: Ureamentioning

confidence: 99%

Thermodynamics and reaction mechanism of urea decomposition

Tischer

Börnhorst

Amsler

et al. 2019

Phys. Chem. Chem. Phys.

114

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“…Several studies investigated the enthalpies and entropies of fusion and solid-solid transition of urea, and its derivatives, including NMU where only the enthalpy of fusion of NMU has been reported. [9][10][11] Hence, one can notice that the thermal programs applied in these studies consisted in first cooling down the NMU sample then heating up to melting.…”

Section: Introductionmentioning

confidence: 99%

Trimorphism of N-methylurea: crystal structures, phase transitions and thermodynamic stabilities

et al. 2016

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International audiencea Melt crystallization of N-methylurea (NMU) was investigated by X-ray and differential scanning calorimetry (DSC) techniques. In addition to the known orthorhombic stable Form I, two new polymorphic forms (II and III) crystallizing in the centrosymmetric space group P2 1 /c were obtained at different quenching temperatures. The crystal structures of Forms II and III were determined from X-ray powder diffraction data. The crystallographic results for the monoclinic forms are presented in this study, as well as a detailed comparison of crystal structures of the three polymorphs. The nature of hydrogen bonds in Form II and Form III were found to be similar; hence, a first order mechanism governed by means of shear movements is suggested where a transition via nucleation and growth could occur at low temperatures. The relative ther-modynamic stabilities of the three forms of NMU were investigated by DSC analyses. Form II and Form III exhibited a reversible solid solid phase transition at circa −118 °C. Both forms were found to be mono-tropically related to the stable Form I

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Thermochemistry of alkyl derivatives of urea

Cited by 44 publications

References 2 publications

Thermodynamics of hydrogen production from urea by steam reforming with and without in situ carbon dioxide sorption

Thermodynamics of hydrogen production from urea by steam reforming with and without in situ carbon dioxide sorption

Thermodynamics and reaction mechanism of urea decomposition

Trimorphism of N-methylurea: crystal structures, phase transitions and thermodynamic stabilities

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