1. Konstantin Popov

2. Pyrolysis: thermal decomposition in the absence of oxygenCombustion of solids is gas phase process supplied by gaseous fuel produced during pyrolysis of the solid 3. ~40% of all plastic production 4. why needed? 28.8 mln tons of plastic landfilled yearly (USA) Only 4.77 mln tons recycled and combusted (USA)6.4 mln tons of plastic circles the globe in oceansrecycling 5. why needed? Majority of fire victims are killed by hazardous products of combustionfire safety 6. why needed? Polyethylene and other longchain alkanes: a solid fuel for hybrid rocketssolid rocket fuel 7. initial stages of pyrolysis of polyethylene Reactive Molecular Dynamics studyexperimental study using GC and NMRkinetic modeling 8. initial stages of pyrolysis of polyethylene Reactive Molecular Dynamics studyexperimental study using GC and NMRkinetic modeling 9. 00.511.52 10. 1100ENERGY / KJ MOL-1900 700500 300 100 -100 0123DISTANCE BETWEEN C ATOMS / A45 11. 5ENERGY / KJ MOL-14 3 2 1 0 -10246 DISTANCE / A810 12. temperature range: 2300 3100K density range: 0 0.75 g cm-3 length of polymer chain: 500 monomer units (1000 C atoms) periodic boundary conditions: 13. Millions3100K, normal density350 300Keff / s-1250 200 15050-100 simulations per point100 50 0 0.30.40.50.6 RC0.70.80.9 14. Two-step mechanism: k1(1) R-R [RR] k-1kD(2) [RR] R + R 15. 30kD/keff*10-325 20153100K, normal density10 5 0 0123kD*10-1245 16. 30 short separationskD/keff*10-325 20153100K, normal density10 long 5 separations 0 0123kD*10-1245 17. The effect of density: 9.5vacuum reduced density normal densityLog(k1 / s-1)9 8.58 7.5 76.5 6 0.30.350.4 1000 K/ T0.45 18. The effect of polymer chain length: 8.51log(k1 / s )8.0fixed p fixed d7.57.06.5 2450200number of C atoms in a single molecule1000 19. Although effects of condensed phase were observed, their magnitude is not dramaticGas phase C-C scission rate constant can be used in modeling condensed phase processes This result of the RMD part will be used in kinetic modeling of experimental observations 20. initial stages of pyrolysis of polyethylene Reactive Molecular Dynamics studyexperimental study using GC and NMRkinetic modeling 21. experimental apparatus 22. experimental apparatusthermostat 23. experimental apparatusstirrer 24. experimental apparatusthermocouple 25. experimental apparatusreactor 26. reactorpolyethylene sample 27. temperature range: 400 440oC time: 0 20 mininitial stages: abundances of vinyl groups kept below 1% 28. Gas Chromatography C5H12C2H41-C6H122-C4H8 C2H61-C7H14C3H8 C6H14CH4C7H161-C4H8 C3H6C4H10 C8H18 29. 1HNMR R-CH=CH-RRR1C=CH2-CH2-R-CH=CH2-CH3 30. 13CNMR-CH2--CH3-CH3 CHYCHY 31. examples of gaseous products: 3.00E-05440 CMolar fraction2.50E-05 2.00E-05 1.50E-05methane propane hexane1.00E-05ethylene5.00E-06 0.00E+00 051015Time / min2025 32. condensed phase products: 0.0035440 C0.003Molar fraction0.0025R-CH=CH20.002 vinyl0.0015vinylene vinylidene0.001RRC=CH20.00050 -50-0.0005R-CH=CH-R510Time / min152025 33. initial stages of pyrolysis of polyethylene Reactive Molecular Dynamics studyexperimental study using GC and NMRkinetic modeling 34. initiation of the process:R-R 2RP k1 35. propagation reactions: kPRP C2H4 + RP kHTRP + -CH2- -CH3 + RSkSRS Q + RP long-chain olefins containing vinyl group 36. radical addition to double bonds (propagation reactions): kAPTR P + Q RS kAPNR P + Q RP * kASTRS + Q RS* kASNRS + Q RP** 37. termination reactions: kRPPRP + RP R-RkRPSRP + RS CHYkRSSRS + RS CHH 38. reduced mechanism: initiationk1R-R 2RP kPRP C2H4 + RP kHTpropagationRP + -CH2- -CH3 + RS kSRS Q + R P kASTRS + Q RS* (+CHY) terminationkRSSRS + RS CHH 39. assumptions used:(i) gas phase k1 (supported by RMD) (ii) gas phase kP, kS (iii) steady-state approximation for [RP] and [RS]: 40. kinetic equation for [C2H4]: 440oC 1.8E-05 1.6E-05 C2H4 molar fraction1.4E-05 1.2E-05 1.0E-05 8.0E-06steady-state [RP] determined6.0E-06 4.0E-06 2.0E-060.0E+00 051015Time / min2025 41. kinetic equation for [-CH3]: 440oC 2.0E-02 1.8E-02-CH3 molar fraction1.6E-02 1.4E-02 1.2E-02 1.0E-02 8.0E-03kHT and steadystate [RS] determined6.0E-03 4.0E-03 2.0E-030.0E+00 -5 0510 Time / min152025 42. kinetic equation for [RS]:kinetic equation for [RP]:solution:kRSS determined 43. kinetics of [Q]:solution: 44. kinetics of [Q]:0.0020440oCmolar fraction0.0015kAST determined0.00100.00050200400600time / sec80010001200 45. possible pathway to produce vinylene groups: (i) radical addition to vinyl group(ii) -scission 46. possible pathway to produce vinylidene groups: (i) H abstraction from a tertiary C atom(ii) -scission 47. Rate constant of hydrogen abstraction: 1.341.361.381.4-14.1 -14.3Tsang, 1986Log(kHT)-14.5 -14.7 -14.9 -15.1 -15.3 -15.51000 K / T1.421.44 48. Rate constant of radical recombination: 1.34 -10.5Log(kHT)-111.361.381.4Tsang, 1986-11.5 -12 -12.5 -131000 K / T1.421.44 49. Rate constant of radical addition to double bonds: 1.34 -14.71.361.381.4-14.8 Tsang, 1991 Log(kHT)-14.9 -15 -15.1 -15.2 -15.31000 K / T1.421.44 50. Reactive Molecular Dynamics: Kinetics of C-C bond scission was studied under the conditions of liquid phase Two-step kinetic mechanism enabled decoupling the influence of the cage effect from the kinetics of C-C scission in the liquid phase The influence of the polymer chain length on the kinetics of C-C scission was evaluated for fixed density and fixed pressure Important conclusion: usage of gas phase value of k1 is justified for modeling liquid phase processes 51. experimental study and kinetic modeling: The kinetics of both liquid phase and gas phase products of initial stages of HDPE pyrolysis were studied The kinetics of major products was successfully described using proposed kinetic mechanism The values of rate constants of critical reactions (kHT, kAST, kRSS) were estimated under the conditions of the liquid phasePossible pathways for creation of vinylene (R-CH=CH-R) and vinylidene (RR1C=CH2) were suggested