Urea and by-product decomposition

ureaby-productsdeposits
Based on experimental measurements by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) and mass spectroscopy (MS) the mechanism of urea decomposition and by-product formation was extended by a mechanism handling the high-temperature by-product decomposition. Samples substances were urea, ammelide, ammeline, cyanamide, dicyandiamide, melamine, melem, melam and graphitic carbon nitride. The temperature range from room temperature to 750°C is covered.
Reaction type
multi-phase
Reactants
urea
Version
2.0 (Nov 2020)
Reference

C. Kuntz, C. Kuhn, H. Weickenmeier, S. Tischer, M. Börnhorst, O. Deutschmann: Kinetic modeling and simulation of high-temperature by-product formation from urea decomposition; Chemical Engineering Science, doi.org/10.1016/j.ces.2021.116876, 2021

DOI:10.1016/j.ces.2021.116876

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<SPECIES>
    <GASPHASE>
        H2O NH3 CO2 HNCO urea(g) cya(g) HCN(g) N2 mela(g) O2 NO C2N2
    </GASPHASE>
    <PHASE liquid>
        DCSLMAX=25
        urea(l)  1320
        HNCO(l)  1140
        NH3(l)    700
        biu(l)   1470
        triu(l)  1547
        H2NCN(l) 1069
        Dcd(l)   1049
    </PHASE>
    <PHASE aq>
        H2O(l)    998
        urea(aq) 1100
        NH3(aq)   700
        HNCO(aq) 1140
    </PHASE>
    <PHASE solid>
        ammd(s)  1573
        g-C3N4 1900
        ammn(s) 2220
        melam(s) 1900
        mela(s) 1260
        melem(s) 1717
        melon(s) 1900
    </PHASE>
    <PHASE H2NCN_s>
        H2NCN(s) 1282
    </PHASE>
    <PHASE Dcd_s>
        Dcd(s) 1404
    </PHASE>
    <PHASE urea_s>
        urea(s)  1320
    </PHASE>
    <PHASE biu_s>
        biu(s)   1470
    </PHASE>
    <PHASE triu_s>
        triu(s)  1547
    </PHASE>
    <PHASE cya_s>
        cya(s)   2500
    </PHASE>
</SPECIES>

<MECHANISM>
<LIQUID>
    <GLOBAL>
        ammd(s) > 2 HNCO + H2NCN(s)
        <ARRHENIUS>
            A/cm_units = 1.5e11
            Ea/kJ_mol  = 175.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        3 ammd(s) > 2 ammn(s) + H2NCN(s) + 2 CO2
        <ARRHENIUS>
            ammd(s)  1
            A/cm_units = 8.5e10
            Ea/kJ_mol  = 185.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        3 ammd(s) > melem(s) + H2NCN(s) + 3 CO2
        <ARRHENIUS>
            A/cm_units = 9.0e14
            Ea/kJ_mol  = 185.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        ammn(s) > HNCO + 2 H2NCN(s)
        <ARRHENIUS>
            A/cm_units = 3.0e10
            Ea/kJ_mol  = 187.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        3 ammn(s) > melem(s) + 3 HNCO + 3 NH3
        <ARRHENIUS>
            A/cm_units = 8.0e14
            Ea/kJ_mol  = 200.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        2 H2NCN(l) > Dcd(s)
        <ARRHENIUS>
            A/cm_units = 9.0e12
            Ea/kJ_mol  = 115.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        3 Dcd(l) > 2 mela(s)
        <ARRHENIUS>
            Dcd(s) 1
            A/cm_units = 6.0e15
            Ea/kJ_mol  = 165.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        2 mela(s) > melam(s) + NH3
        <ARRHENIUS>
			A/cm_units = 5.0e9
			Ea/kJ_mol  = 140.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        3 Dcd(l) > 6 HCN(g) + 2 NH3 + 2 N2
        <ARRHENIUS>
            Dcd(s) 1
            A/cm_units = 1.7e14
            Ea/kJ_mol  = 165.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        melam(s) > melem(s) + NH3
        <ARRHENIUS>
            A/cm_units = 3.0e14
            Ea/kJ_mol  = 215.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        melam(s) > NH3 + 6 HCN(g) + 2 N2
        <ARRHENIUS>
            A/cm_units = 0.6e14 #1.2
            Ea/kJ_mol  = 215.67
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        melem(s) > 2 g-C3N4 + 2 NH3
        <ARRHENIUS>
            A/cm_units = 1.2e5
            Ea/kJ_mol  = 130.71
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        melem(s) > melon(s) + NH3
        <ARRHENIUS>
            A/cm_units = 2.5e5
            Ea/kJ_mol  = 130.71
        </ARRHENIUS>
    </GLOBAL>

#Homogeneous Reactions proposed by Tischer et al., doi:10.1039/c9cp01529a.
    <REACTION>
        urea(l) + HNCO(l) = biu(s)
        A/SIunits = 1e-4
        Ea/kJ_mol = 0
    </REACTION>

    <REACTION>
        urea(l) + HNCO(l) = biu(l)
        A/SIunits = 1e-4
        Ea/kJ_mol = 0
    </REACTION>

    <REACTION>
         biu(l) + HNCO(l) = triu(s)
         A/SIunits = 1e-4
         Ea/kJ_mol = 0
    </REACTION>

    <REACTION>
        triu(s) > cya(s) + NH3
        A/SIunits  = 1.2e2
        Ea/kJ_mol  = 42
    </REACTION>

    <REACTION>
        triu(s) > ammd(s) + H2O
        A/SIunits  = 0.3e2
        Ea/kJ_mol  = 42
    </REACTION>

</LIQUID>

<INTERPHASE>

    <REACTION>
        mela(s) > mela(g)
        A/SIunits =  9e5
        Ea/kJ_mol  = 141.30
    </REACTION

    <GLOBAL>
        2 g-C3N4 > 3 C2N2 + N2
        <ARRHENIUS>
            g-C3N4  1
            A/SIunits = 2.8E1
            beta = 0
            Ea/kJ_mol = 149.72
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        5 melon(s) > 9 C2N2 + 12 HCN(g) + NH3 + 7 N2
        <ARRHENIUS>
            melon(s)  1
            A/SIunits = 3.0E1
            beta = 0
            Ea/kJ_mol = 149.72
        </ARRHENIUS>
    </GLOBAL>

    <GLOBAL>
        melon(s) > 2 g-C3N4 + NH3
        <ARRHENIUS>
            melon(s)  1
            A/SIunits = 0.75E1
            beta = 0
            Ea/kJ_mol = 149.72
        </ARRHENIUS>
    </GLOBAL>
  
    <REACTION>
        H2NCN(s) = H2NCN(l)
        A/SIunits = 0.088
    </REACTION>

    <REACTION>
        Dcd(s) = Dcd(l)
        A/SIunits = 0.088
    </REACTION>

#Interphase Reactions proposed by Tischer et al., doi:10.1039/c9cp01529a.
    <REACTION> #Reaktion 1 in Brack, geändert
        cya(s) > cya(g)
        A/SIunits =  3e4
        Ea/kJ_mol  = 141.30
    </REACTION>

    <REACTION>
        urea(l) + urea(l) > biu(l) + NH3
        A/SIunits =  3.5e0
        Ea/kJ_mol  = 99
    </REACTION>

    <REACTION>
        biu(l) + urea(l) > triu(s) + NH3
        A/SIunits =  2e2       
        Ea/kJ_mol  = 116.50
    </REACTION>

    <REACTION>
        H2O = H2O(l)
        A/SIunits = 0.086
        beta=0.5
    </REACTION>

    <REACTION>
        urea(g) = urea(l)
        A/SIunits = 0.086
        beta=0.5
    </REACTION>

    <REACTION>
        NH3 = NH3(l)
        A/SIunits = 0.088
        beta=0.5
    </REACTION>

    <REACTION>
        NH3 = NH3(aq)
        A/SIunits = 0.088
        beta=0.5
    </REACTION>

    <REACTION>
        NH3(aq) = NH3(l)
        A/SIunits = 0.088
        beta=0.5
    </REACTION>

    <REACTION>
        urea(aq) = urea(s)
        A/SIunits = 0.047
        beta=0.5
    </REACTION>

    <REACTION>
        urea(aq) = urea(l)
        A/SIunits = 0.047
        beta=0.5
    </REACTION>

    <REACTION>
        HNCO = HNCO(l)
        A/SIunits = 0.055
        beta=0.5
    </REACTION>

    <REACTION>
        HNCO = HNCO(aq)
        A/SIunits = 0.055
        beta=0.5
    </REACTION>

    <REACTION>
        HNCO(aq) = HNCO(l)
        A/SIunits = 0.055
        beta=0.5
    </REACTION>

    <REACTION>
        urea(l) = urea(s)
        A/SIunits = 1e-6
    </REACTION>

    <REACTION>
        biu(l) = biu(s)
        A/SIunits = 1e-6
    </REACTION>
</INTERPHASE>
</MECHANISM>
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