Ethylene pyrolysis and oxidation: A kinetic modeling study

Ethylene oxidation and pyrolysis was modeled using a comprehensive kinetic reaction mechanism. This mechanism is an updated version of one developed earlier. It includes the most recent findings concerning the kinetics of the reactions involved in the oxidation of ethylene. The proposed mechanism was tested against ethylene oxidation experimental data (molecular species concentration profiles) obtained in jet stirred reactors (1–10 atm, 880–1253 K), ignition delay times measured in shock tubes (0.2–12 atm, 1058–2200 K) and ethylene pyrolysis data in shock tube (2–6 atm, 1700–2200 K). The general prediction of concentration profiles of minor species formed during ethylene oxidation is improved in the present model by using more accurate kinetic data for several reactions (principally: HO₂ + HO₂ → H₂O₂ + O₂, C₂H₄ + OH → C₂H₃ + H₂O, C₂H₂ + OH → Products, C₂H₃ → C₂H₂ + H).     

Detailed experimental and kinetic modeling study of 3-carene pyrolysis

3-Carene is an important potential biofuel with properties similar to the jet-propellant JP-10. Its thermal decomposition and combustion behavior is to date unknown, which is essential to assess its quality as a fuel. A combined experimental and kinetic modeling study has been conducted to understand the initial decomposition of 3-carene. The pyrolysis of 3-carene was investigated in a jet-stirred quartz reactor at atmospheric pressure, at temperatures varying from 650 to 1050 K, covering the complete conversion range. The decomposition of 3-carene was observed to start around 800 K, and it is almost complete at 970 K. Online gas chromatography shows that primarily aromatics are generated which suggests that 3-carene is not a good fuel candidate. The potential energy surface for the initial decomposition pathways determined by KinBot shows that a hydrogen elimination reaction dominates, giving primarily cara-2,4-diene. Next to this molecular pathway, radical pathways lead to aromatics via ring opening. The kinetic model was automatically generated with Genesys and consists of 2565 species and 9331 reactions. New quantum chemical calculations at the CBS-QB3 level of theory were needed to calculate rate coefficients and thermodynamic properties relevant for the primary decomposition of 3-carene. Both the conversion of 3-carene and the yields of the primary products (ie, benzene and hydrogen gas) are well predicted with this kinetic model. Rate of production analyses shows that the dominant pathways to convert 3-carene are hydrogen elimination reaction and radical chemistry.     

Thermal and kinetic study of tyre waste pyrolysis via TG-FTIR-MS analysis

The world production of tyre waste amounts to 5·10⁶ ton year^–1, 2·10⁶ tons of which are produced in Europe, but the final destination of nearly 65–70% of them is the landfill, despite the high added value materials lost and the consequent environmental impact. Treatments alternative to landfilling take into account reconstruction and reuse of the tyres or the matter and/or energy recovery by means of thermal treatment processes (incineration, gasification and pyrolysis). Among these, pyrolysis seems to be a promising and realistic alternative to attain the conversion of tyre waste into valuable and reusable products. Present work relates to experimental tests and results obtained for the study of tyre waste pyrolysis, conducted by means of thermo-gravimetric analysis (TG) of the material and the simultaneous determination, through Fourier transform infrared (FTIR) and mass spectrometry (MS), of the decomposition products. The analysis of the volatile fraction allows to isolate, within the thermograms, the evolution of products referable to specific tyre components and therefore it suggests the application of a multi-component decomposition model. The kinetic model consequently developed agrees fairly well with the experimental data.     

碳源甲基苯热裂解机理的密度泛函动力学研究

在热力学研究的基础上,用UB3LYP/3-21G^*方法对甲苯热裂解机理进行了动力学研究。计算得到了甲苯的5种热裂解路径的活化能。用过渡状态理论,计算得到了这些路径在298～1223K温度范围内的速率常数。动力学计算结果表明：甲苯在热解温度低于963K时的主反应路径为甲苯热裂解生成苄基自由基的反应,其速控步的活化能△E~0^θ^≠=402.27kJ/mol;当温度高于963K达1223K左右时,主反应路径转为苯环上脱甲基生成苯基和甲基自由基的路径,该路径的活化能△E~0^θ^≠=456.91kJ/mol。以上研究结果与实验结果相一致。     

Thermal characterization and isothermal kinetic analysis of commercial Creosote decomposition process

Isothermal decomposition process of commercial Creosote was analyzed by thermogravimetric technique in a nitrogen atmosphere, at four different operating temperatures (T = 230, 250, 270, and 290 °C). It was found that the two-parameter autocatalytic ?esták–Berggren kinetic model best describes the investigated process. It was established that the applied logistic function can successfully perform a given kinetic predictions of investigated process, at all operating temperatures. The experimental density distribution function of the apparent activation energy values was evaluated. Based of the characteristic shape of distribution curve, it was concluded that the isothermal pyrolysis of commercial Creosote represent a complex process, which probably includes primary and secondary (autocatalytic) pyrolysis reactions, together with various decomposition reactions and radicals recombination pathways.     

Thermodynamic and thermokinetic study on pyrolysis process of heavy oils

Enthalpy of pyrolysis and its variation in the pyrolysis process of four heavy oils: Daqing vacuum residue (DQVR), Karamay vacuum residue (KRVR), Liaohe vacuum residue (LHVR), and Venezuela vacuum residue (VNVR), have been quantitatively studied by differential scanning calorimetry associated with thermogravimetry. The results indicate that overall enthalpies at different heating rates show a linear trend with respect to the final coke yields in the thermal analysis. Classical kinetic method (Friedman method) is used to further analyze pyrolysis enthalpy variation in the pyrolysis process and determine the thermokinetic parameters. The main stage of thermal reaction (conversion ranges from 0.1 to 0.9) could be described by 1.5 order reaction model for four heavy oils. The mean activation energies determined by Friedman method are 216.3, 194.9, 173.9, and 168.7 kJ mol^?1 for DQVR, KRVR, LHVR, and VNVR, respectively. It means that endothermic enthalpy of pyrolysis in the thermal process of VNVR is easier to change compared with other oil sample cases. For the sake of simplification of kinetic treatment, Sharp method is tentatively used to perform kinetic analysis. The comparison between results from two methods indicates that activation energies from Sharp method are valid to a certain degree under the condition that the mechanism of thermal process is properly chosen although isoconversional method (Friedman method) is recommended and thought to be the better way.     

A kinetic model for pyrolysis of CF2HCl

Thermal decomposition of CF₂HCl has been modeled using 2,269 thermally activated reactions and 63 chemically activated processes. Thermochemical properties for the species involved are calculated using statistical mechanics and group contribution theory, and reaction rate constants are determined using transition state theory. The theoretical predictions, obtained without fitting any parameter values, afree closely with available experimental data. Also, the reactions that control the distribution of reaction products are identified, and this, in turn, permits simplification of the reaction set. Sensitivity studies show that uncertainties in the calculations do not alter the predicted trends in behavior or the main reaction pathways. © 1995 John Wiley & Sons, Inc.     

Shock tube pyrolysis of pyrrole and kinetic modeling

The kinetics of pyrolysis of pyrrole dilute in argon have been studied in a single pulse shock tube, using capillary column GC, together with GC/MS and FTIR for product identification, over the temperature range 1200–1700 K, total pressures of 7.5–13.5 atm and nominal mixture compositions of pyrrole of 5000 and 700 ppm (nominal concentrations of 5 × 10^?7 and 7 × 10^?8 mol cm^?3). Time-resolved measurements of the rate of disappearance of pyrrole behind reflected shock waves have been made by absorption spectroscopy at 230 nm, corresponding to the lowest ¹π* ← ¹π transition of pyrrole at pressures of 20 atm and mixture compositions between 1000–2000 ppm pyrrole (1.7–3.0 × 10^?7 mol cm^?3) over the temperature range of 1300 to 1700 K. At the lower end of the studied temperature range, the isomers of pyrrole, allyl cyanide and cis- and trans-crotononitrile, were the principal products, together with hydrogen cyanide and propyne/allene. At elevated temperatures, acetylene, acetonitrile, cyanoacetylene, and hydrogen became important products. The rate of overall disappearance of pyrrole, as measured by absorption spectrometry, was found to be first order in pyrrole concentration, with a rate constant k_dis(pyrrole) = 10^14.1±0.7 exp(?74.1 ± 3.0 kcal mol^?1/RT) s^?1 between 1350–1600 K and at a pressure of 20 atm. First order dependence of pyrrole decomposition and major product formation was also observed in the single pulse experiments over the range of mixture compositions studied. A 75-step reaction model is presented and shown to substantially fit the observed temperature profiles of the major product species and the reactant profile. In the model the initiation reaction is postulated to be the reversible formation of pyrrolenine, (2H-pyrrole). Pyrrolenine can undergo ring scission at the C2? N bond forming a biradical which can rearrange to form allyl cyanide and crotononitrile or undergo decomposition to form HCN and C₃H₄ or acetylene and a precursor of acetonitrile. The model predicts an overall rate of disappearance of pyrrole in agreement with the experimental measurements.     

钾对松木热解特性影响实验研究

采用管式炉热解实验装置对浸渍K2CO3松木进行直接热解,并将松木热解气通过含钾石英砂层、含钾焦层以模拟钾对热解气体反应的影响。结果表明,松木中浸渍K后会促进热解固体焦生成,提高H2/CO比,低温下K会降低液相产率、提高气相产率,而热解温度较高时则使气体产率下降、液体产率提高。松木热解气经过含K石英砂后发生催化裂解,液体产率降低,CO、CO2和H2产量上升。松木焦也可以催化裂解焦油,使气体产物增加,H2和CO2产量提高,CO、CH4和C2产量降低。K与松木焦共同作用,不仅使焦油发生裂解而且促进更多焦参与气固反应。钾对松木热解作用是通过对松木的直接热解、对气体中间产物再反应的均相催化及对固体焦气化的非均相催化等复杂过程实现的。     

Kinetics of pyrolysis and combustion of pine needles and cones

A wide kinetic study has been carried out under different conditions in TG and TG–MS for each material, at different operating conditions. Runs were carried out at three different atmospheres: N₂, N₂:O₂ 4:1 and N₂:O₂ 9:1. In addition to the dynamic runs carried out at constant heating rate, other runs were performed in an isothermal regime (constant heating rate until the set temperature is reached and then the set temperature is maintained constant).In addition, a study of the thermal decomposition for both materials was also carried out in a dynamic run using TG–MS in order to observe the evolution of the major compounds and to discuss the information that could be obtained.From the overall analysis of the data, schemes of reactions and kinetic values were calculated by integration of the differential equations and minimizing the squared differences between the experimental and calculated values. It is important to emphasise that the same set of parameters is proposed for the runs for each material, and depends on neither the heating rate in dynamic runs nor whether the run is carried out in a dynamic or isothermal mode.     

Investigation of the bioenergy potential of microalgae Scenedesmus acuminatus by physicochemical characterization and kinetic analysis of pyrolysis

In this work, the bioenergy potential of green microalgae Scenedesmus acuminatus was evaluated through the psychochemical characteristics and kinetic study of pyrolysis, where the results indicate a good candidate for application in the thermochemical process due to its low moisture and ash content and high calorific value. Its thermal behavior under a heating rate of 10 °C min^?1 and inert atmosphere shows that decomposition occurs in two stages. Stage I (125–309 °C) involves the pyrolysis of carbohydrates and protein and stage II (309–501 °C) the pyrolysis of lipids. The Starink isoconversional method showed a better application for simulation curves, compared with methods of FWO and KAS. The average values of activated energy were 107.1 and 132.6 kJ mol^?1 for stages I and II, respectively, which indicates that pyrolysis occurs more easily in stage I than in stage II. The conversion rate curves show that the calculated kinetic parameters are satisfactory for the evaluation of the thermochemical systems.

     

Detailed chemical kinetic modeling of butylbenzene pyrolysis

A chemical kinetic model was constructed for the pyrolysis of butylbenzene. The mechanism was based on free radical reactions. All relevant reactions were considered, and a final selection of 60 reactions involving 29 molecules and free radicals was made. The rate constants and thermodynamic parameters were taken from the literature or estimated using accepted literature methods such as group additivity. The results from the model were compared to experimental rates and product selectivity for butylbenzene pyrolysis over a temperature range of 778 K to 868 K and to an experimental rate at 923 K. The rates agreed within a factor of two and were usually much closer. The experimental and theoretical yields of the major products, styrene, ethane, toluene, and propylene, agreed within two percentage points. The agreement for seven minor products was not quite as good, with the worst case being an overprediction of the yield of allylbenzene by a factor of 2.6.     

磷酸和水蒸气联合改性的HZSM-5的物化表征及催化研究

研究了磷和水蒸气联合改性HZSM-5样品的物化和催化性能。XRD和IR研究表明，没有新的晶相出现。NH3-TPD研究样品的酸性表明，经过磷改性后的样品的酸量明显下降。经过水热处理的样品的BET比表面明显降低，这可能归因于磷物种和铝物种对孔道的堵塞。氮吸附－脱附等温线研究表明，等温线为I型和IV型的复合型，滞后环为H4型。联合改性样品的正庚烷裂化转化率高于仅仅由水蒸气改性样品的正庚烷裂化转化率，从而显示出磷物种对沸石分子筛高温水蒸气脱铝的抑制作用。     

Physicochemical characterization and compatibility study of roflumilast with various pharmaceutical excipients

Journal of Thermal Analysis and Calorimetry - To rich flavor additive species of pyrazines, two new compounds of 3,6-dimethyl-2,5-pyrazinedicarboxylic acid 1-octen-3-yl ester (DMPOE) and...     

棉秆催化热解特性及动力学建模研究

通过不同添加剂处理棉秆的热重实验,分析NaOH、Na₂CO₃、Na₂SiO₃、NaCl、TiO₂、HZSM-5六种添加剂催化棉秆热解动力学特性,结合原料的组分分析,建立三组分独立平行一级反应热解动力学模型对试样热失重行为进行模拟,采用非线性最小平方算法求解热解动力学参数。研究发现,添加剂的加入改变了三组分动力学参数,在碱性添加剂作用下,纤维素和半纤维素热解活化能都有较大程度降低,且碱性越强,纤维素热解活化能越低,而半纤维素热解活化能越高;中性添加剂NaCl对纤维素和半纤维素热解活化能的影响不大;酸性添加剂使纤维素和半纤维素的热解活化能有所增大,但所有添加剂对木质素热解活化能的影响不明显。     

Physicochemical characterization of interfaces

Reversed-flow inverse gas chromatography (RF-IGC) was used to measure, directly from experimental data, adsorption energies, local adsorption isotherms, the probability density function for the adsorption energies, and lateral interaction parameters, as distributed over experimental time. Local isotherms and the distribution energy function were correlated with adsorption energy. The results obtained are comparable to those calculated on the basis of the well-known integral equation. The RF-IGC method was used with the two most common hydrocarbons, acetylene and 1-butene, as probe gases, in the presence and absence of ozone, and with magnesium oxide and silicon oxide as solid adsorbents.