Modeling pyrolysis kinetics of plastic mixtures

Modeling pyrolysis behavior of waste plastic mixtures is of importance for design and operation of reactors which convert these waste plastics into valuable chemicals. However, because of limited understanding of their degradation behavior even for single component plastic wastes, modeling degradation kinetics of plastic mixtures is a challenging task.In this work, we report modeling of binary and ternary mixture degradation kinetics of polyethylene terephthalate (PET), low density polyethylene (LDPE) and polypropylene (PP). A simple mixing rule approach was used with one cross-kinetic degradation parameter per each binary. Ternary kinetics were completely predictive and showed good agreement with the experimental data.     

Reexamination of the intimate ion pair mechanism in the gas phase pyrolysis kinetics of ethyl 4-bromobutyrate

The gas phase pyrolysis of ethyl 4-bromobutyrate in the temperature range of 354–375 °C and pressure range of 47–152 Torr obeys a first-order rate law. The rate coefficient for the unimolecular elimination is expressed by the following Arrhenius equation: log k₁(s^–1)=(13.71±±0.60)–(209.9±7.3) kJ mol^–1/2.303 RT. A more complete analysis for the parallel elimination and consecutive reactions of the bromoester confirms the argument of an intimate ion pair type of mechanism for the debromination processes. The carboethoxy substituent through neighbouring group participation exerts a small but significant accelerating effect in some of the parallel eliminations.

---

4- 354–375°C 47–152 . : log k₁(^–1)=(13,71±0,60)–(209,9±7,3) ·^–1/2,303 RT. . - , .

     

Pyrolysis kinetics of ethyl fluoroacetate in the gas phase

The kinetics of the gas phase pyrolysis of ethyl fluoroacetate have been measured over the temperature range of 340–365 °C and pressure range of 66–187 Torr. The reaction, in a static system seasoned with allyl bromide, and in the presence or absence of propene inhibitor, is homogeneous, unimolecular, and obeys a first-order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equation: log k₁ (sec^–1)=(12.57±0.26)–(194.0±3.1 kJ/mol)/2.303 RT. The result of this work confirms that the sequence of the -halo substituent effects follows the order of their electronegativity differences.

---

340–365 °C 66–187 . , , , , . ; log k₁ (cek^–1)=(12,57±0,26) –(194,0±3,1) //2,303RT. - .

     

The maximally catalyzed pyrolysis kinetics of methyl 3-bromopropionate in the gas phase

The kinetics of the gas phase pyrolysis of methyl 3-bromopropionate, under maximum catalysis of HBr, were found to be of order 1.0. The reaction appears to undergo a molecular elimination of HBr, which follows first-order kinetics. The products are methyl acrylate and HBr. The pyrolysis, in s static system and seasoned vessel, was examined over the temperature range of 330.5–378.5°C and pressure range of 64–145 Torr. The rate coefficients, under maximum catalysis, are given by the Arrhenius equation log k₁(s^–1)=(11.19±0.64)–(171.6±7.7) kJ/mol/2.303 RT. The mechanism of the catalyzed pyrolysis of the bromoester appears to proceed through a six-membered cyclic transition state.

---

3- HBr- , 1,0. HBr . HBr. 330,55–378, 5°C 64–145 . : log k₁ (cek^–1)=(11,9±0,64)–(171,6±7,7) //2,303 RT.

     

The pyrolysis kinetics of ethyl esters in the gas phase. The alkyl substituent effect at the acyl carbon

The gas-phase elimination of ethyl 3-methylbutanoate and ethyl 3,3-dimethylbutanoate has been studied, in a static system, over the temperature range of 360–420°C and in the pressure range of 71–286 torr. The reactions are homogeneous, unimolecular, and follow a first-order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for ethyl 3-methylbutanoate, log k₁ (s^?1) = (12.70 ± 0.36) – (202.5 ± 4.4) kJ/mol/2.303RT, and for ethyl 3,3-dimethylbutanoate, log k₁ (s^?1) = (13.04 ± 0.08) – (207.1 ± 1.0) kJ/mol/2.303RT. Alkyl substituents at the acyl carbon of ethyl esters yield very close values in rates. Consequently it is rather difficult to offer some conclusion concerning the effect of these substituents.     

The pyrolysis kinetics of 4-chloro-2-butanone in the gas phase

The rates of pyrolysis of 4-chloro-2-butanone in the gas phase have been determined in a static system seasoned with the products of decomposition of allyl bromide. The reaction is catalyzed by hydrogen chloride. Under maximum catalysis of HCl, the kinetics were found to be of order 1.5 in the substrate suggesting that a complex elimination is involved. The reaction, when maximally inhibited with propene, appears to undergo a unimolecular elimination and follows a first-order law kinetics. The products are methylvinyl ketone and hydrogen chloride. The kinetics have been measured over the temperature range of 402.0–424.4°C.The rate coefficients are given by the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$ \log k_1 (\sec ^{ - 1}) = (13.67 \pm 0.69) - (225.2 \pm 8.6)\,{\rm kj}/{\rm mol}/2.303RT\angle $\end{document}. Thepyrolysis of 4-chloro-2-butanone is 31 times greater in rate than that of ethyl chloride at 440°C. This large difference in rate may be attributed to the -M effect of the acetyl substituent in the pyrolysis of the former halo compound.     

Homogeneous oxidation kinetics of aqueous ferrous iron at circumneutral pH

Oxidation of aqueous Fe(II) was investigated at circumneutral pH and 23°C in the absence of ligands (other than H₂O, OH^–, and Cl^–) and catalysts (e.g., microbes or solids surfaces). Enzymes (superoxide dismutase and catalase) were used as specific catalytic probes to determine whether superoxide and hydrogen peroxide are intermediates in oxygen reduction by Fe(II). The kinetic evidence suggests that Fe(II) and D.O. react in a termolecular transition state complex, the reaction produces hydrogen peroxide (probably without intermediation by superoxide), and Fe(II) and H₂O₂ react in a termolecular reaction or in a two-step sequence of bimolecular reactions. The rate data permit modeling the overall Fe(II) oxidation reaction at pH7.0 with a rate law that has non-integer orders with respect to [Fe(II)] and [OH^–].     

TG-FTIR analysis of switchgrass pyrolysis

Switchgrass is a high yielding perennial grass that has been designated as a potential energy crop. One method of converting switchgrass to energy is by thermochemical conversion to syngas. This requires that the rate of thermal decomposition of switchgrass and the rate of production of components of the syngas be quantified. Ground switchgrass was pyrolyzed at heating rates of 10–40 °C/min in a thermogravimetric analyzer coupled to a Fourier Transform infrared spectrometer. The amount of gases (ppm) that were volatilized during the duration of experiment was quantified. The pyrolysis process was found to compose of four stages: moisture evaporation, hemicellulose decomposition, cellulose decomposition and lignin degradation. The peak temperature for hemicellulose (288–315 °C) and cellulose degradation (340–369 °C) increased with heating rate. FTIR analysis showed that the following gases were given off during the pyrolysis of switchgrass: carbon dioxide, carbon monoxide, acetic acid, ethanol, and methane.     

Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

The thermal decomposition of the atmospheric constituent ethyl formate was studied by coupling flash pyrolysis with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet (VUV) radiation at the Swiss Light Source (SLS). iPEPICO allows photoion mass-selected threshold photoelectron spectra (ms-TPES) to be obtained for pyrolysis products. By threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformer having a cis (eclipsed) configuration of the O = C (H)– O – C (H₂)–CH₃ and trans (staggered) configuration of the O= C (H)– O – C (H₂)– C H₃ dihedral angles. We observed the following ethyl formate pyrolysis products: CH₃CH₂OH, CH₃CHO, C₂H₆, C₂H₄, HC(O)OH, CH₂O, CO₂, and CO, with HC(O)OH and C₂H₄ pyrolyzing further, forming CO + H₂O and C₂H₂ + H₂. The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH₃CH₂O + CHO and CH₃CH₂ + HC(O)O, were studied computationally at the M06-2X-GD3/aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and newly suggest carbon monoxide as a competitive primary fragmentation product at high temperatures.     

Homogeneous high-temperature oxidation of methane

The kinetics of homogeneous deep oxidation of methane in lean mixtures (up to 2 vol % CH₄ in air) in ceramic tubes and fixed beds of ceramic spheres was studied. Experiments with the homogeneous reaction have shown that the methane oxidation occurs via a consecutive scheme through CO formation. The reaction rate of CH₄ oxidation was found to depend upon the equivalent pass diameter with a significant reaction inhibition in packing of small tubes and spheres, reflecting the influence of mass transfer on the radical-chain termination at the ceramic surfaces. It was also found that CO oxidation practically does not depend upon the mass exchange conditions, but it is visibly inhibited by methane. Recommended kinetic equations and their parameters are presented.     

Neighboring group participation in the pyrolysis kinetics of 4-chloro-1-butanol in the gas phase

The pyrolysis of 4-chloro-1-butanol has been studied in a static system, seasoned with allyl bromide, and in the presence of the free radical suppressor toluene. The working temperature and pressure ranges were 400–450°C and 43–164 Torr, respectively. The reaction is homogeneous, unimolecular, and follows a first-order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equation: log k₁(s^?1) = (13.34 ± 0.50) ? (221.1 ± 6.7) kJ mol^?1 (2.303RT)^?1. The products tetrahydrofuran, formaldehyde, and propene, arise by the participation of the neighboring OH group in 4-chloro-1-butanol pyrolysis. The reaction is best explained in terms of an intimate ion pair type of mechanism.     

竹材非等温热解动力学

利用热重分析技术对竹材在高纯N2条件下,从室温至1273K进行了非等温热解分析,研究了升温速率(5、10、20和40K/min)对热解过程的影响,探讨了其热解机理。研究表明,竹材非等温热解过程主要分为失水干燥、快速热解和缓慢分解三个阶段组成,其中第二阶段是整个过程的主要阶段,析出大量挥发分造成明显失重。升温速率对热解过程有显著影响,随着升温速率的增加,最大热解速度增大,对应的峰值温度升高,热滞后现象加重,热解各阶段向高温侧移动。热解机理满足一维扩散Parabolic法则,反应机理函数为g(α)=α2。不同升温速率下活化能为75.32-82.99kJ.mol-1,指前因子为1.17×105-1.12×106min-1。     

Cyanoacetic ester pyrolysis in the gas phase

The gas-phase thermal decomposition of isopropyl cyanoacetate at 292–325°C and 44–178 Torr reveals a homogeneous unimolecular elimination with a first-order rate law. The rate constants are given by the Arrhenius equation: log k(sec^–1)=(13.01±0.54)–(43,100±1400 cal/mol)/2.303 RT. The data are compared with those for the corresponding -haloacetic esters.

---

292–325°C 44–178 . : log k (^–1)=(13,01±0,54)–(43100±1400 /)/2,303 RT. , - .

     

Homogeneous nucleation of particles from the vapor phase in thermal plasma synthesis

Particle nucleation and growth are simulated for iron vapor in a thermal plasma reactor with an assumed one-dimensional flow field and decoupled chemistry and aerosol dynamics. Including both evaporation and coagulation terms in the set of cluster-balance rate equations, a sharply defined homogeneous nucleation event is calculated. Following nucleation the vapor phase is rapidly depleted by condensation, and thereafter particle growth occurs purely by Browntan coagulation. The size and number of nucleated particles are found to be affected strongly by the cooling rate and by the initial monomer concentration. An explanation is presented in terms of the response time of the aerosol to changing thermodynamic conditions.This work appears in abbreviated from in the proceedings of the International Symposium on Combustion and Plasma Synthesis of High Temperature Materials, San Francisco, Oct. 24–26, 1988, to be published asCombustion and Plasma Synthesis of Hig Temperature Materials, Z. A. Munir and J. B. Holt (eds.), VCH, New York (in press).     

Synthesis and kinetics of non-isothermal degradation of acetylene terminated silazane

Novel acetylene terminated silazane compounds,with three types of substituent,were synthesized by the aminolysis of dichlorosilane with 3-aminophenylacetylene(3-APA).Thermal property of the compounds is studied by thermogravimetry analysis (TGA).It shows that the acetylene terminated silazane has high temperature resistance.The char yield at 1000℃is 77.6,81.9 and 68.7 wt%for methyl,vinyl,and phenyl substituted silazane,respectively.The pyrolysis kinetics of the silazane is investigated by non-isothermal thermogravimetric measurement.The pyrolysis undergoes three stages,which is resolved by PEAKFTT.The kinetic parameters are calculated by the Kissinger method.The role of functionalities on the thermal resistance is discussed.The vinyl-silazane exhibits higher thermal stability because of higher cross-linking density.     

Biomass pyrolysis kinetics: A comparative critical review with relevant agricultural residue case studies

Biomass pyrolysis is a fundamental thermochemical conversion process that is of both industrial and ecological importance. From designing and operating industrial biomass conversion systems to modeling the spread of wildfires, an understanding of solid state pyrolysis kinetics is imperative. A critical review of kinetic models and mathematical approximations currently employed in solid state thermal analysis is provided. Isoconversional and model-fitting methods for estimating kinetic parameters are comparatively evaluated. The thermal decomposition of biomass proceeds via a very complex set of competitive and concurrent reactions and thus the exact mechanism for biomass pyrolysis remains a mystery. The pernicious persistence of substantial variations in kinetic rate data for solids irrespective of the kinetic model employed has exposed serious divisions within the thermal analysis community and also caused the broader scientific and industrial community to question the relevancy and applicability of all kinetic data obtained from heterogeneous reactions. Many factors can influence the kinetic parameters, including process conditions, heat and mass transfer limitations, physical and chemical heterogeneity of the sample, and systematic errors. An analysis of thermal decomposition data obtained from two agricultural residues, nutshells and sugarcane bagasse, reveals the inherent difficulty and risks involved in modeling heterogeneous reaction systems.     

Kinetics and mechanism of 2-pyridylacetic acid pyrolysis in the gas phase: A joint experimental and theoretical study

A combination of the experimental and theoretical study was carried out on the reaction mechanism associated with the pyrolysis of 2-pyridylacetic acid in the gas phase. Methylpyridine and carbon dioxide were analyzed as the products, using a static system over the pressure range of 18–55 torr and the temperature of 541.2–583.4 K. The experimental kinetic data show that the pyrolysis process is homogeneous, unimolecular and proceeds through a concerted mechanism. Theoretical studies at the B3LYP level using the 6-31G^* basis set confirmed an asynchronous concerted mechanism for the reaction. Computed kinetic and activation parameters are in good agreement with the experimental one.     

Study on pyrolysis kinetics of walnut shell

Slow pyrolysis of walnut shell which is a cheap and abundantly available solid waste was carried out using thermogravimetric analysis. The effects of raw material heating rate on the pyrolysis properties and kinetic parameters were investigated. A two-step consecutive reaction model were used to simulate the pyrolysis process. The kinetic parameters were established by using the pattern search method. Comparison between experimental data and the model prediction indicated that the two-step consecutive reaction model can better describe the slow pyrolysis of walnut shell as the formation of an intermediate during the pyrolysis process was taken into account.