聚甲基丙烯酸甲酯等温燃烧反应的动力学研究

使用锥形量热仪研究了 3mm厚、10 0× 10 0mm2 的透明聚甲基丙烯酸甲酯 (PMMA)板在不同温度下的燃烧反应 ,采用化学动力学法拟合了PMMA燃烧过程中质量损失率a与时间t的单方程速率模型 .结果显示 ,在PMMA燃烧过程中 ,质量损失速率受产物的解吸附和扩散过程控制 .PMMA在 5 84～ 80 0℃燃烧时 ,合适的反应动力学方程为 [-ln(1-a) ]1/4=Ae-E/RTt ,其中指前因子A约等于 0 .12 39s-1,平均表观活化能E约为2 2 .81kJ/mol,并与温度的变化基本无关 ,计算结果与实验数据吻合较好     

生物油及其重质组分的热解动力学研究

采用热重分析法对生物油及其三种重质组分模型化合物的热解特性进行了对比研究,并对动力学参数进行了求解.结果表明:生物油的热解包括挥发组分的蒸发及重质组分的裂解两个阶段,反应级数都是4级,活化能分别为29～36kJ/mol及13～19 kJ/mol;三种重质组分模型化合物中左旋葡聚糖也存在两个失重区间,反应级数分别为1和2,且表观活化能最高;3,4二甲氧基苯甲醛和丁香酚则只有一个失重区间,且相应的反应级数分别为0.8和0.5,表观活化能也依次降低.     

溴酸钾氧化甲基红褪色分光光度法的动力学

依据褪色分光光度法对BrO3--甲基红-NaCl体系进行了研究,实验表明,在518nm为最大吸收波长下,测定了该反应的动力学参数,确定了反应速率方程式,得知该反应的总反应级数为2.5级,表观活化能为55.82k J/mol,活化能为66.87kJ/mol,实验还测定了其他离子对该反应的催化作用,达到了预期的结果.     

食用菌生产废弃物热反应机理与活化能

利用TG-FTIR联用分析仪对食用菌生产废弃物的热解特性进行了研究;并采用分布式活化能模型求解了主要热懈段的活化能,探讨了活化能随转化率的变化关系;利用FTIR结果分析了食用菌生产废弃物的热反应机理.研究结果表明;食用菌生产废弃物主要分三段热解;第一段热解在23~100℃;失重率在12.33%~14.36%左右;主要为C=O键的断裂和CO_2的形成,伴随着少量的苯环从长链分子中断裂.第二失重段约在220~390℃,失重率约为45.09%~47.29%;主要为C=O键的断裂和CO_2的形成、大量苯环从分子成分的长链脱离,同时伴有O-H键断裂、烷烃类的C-H键和取代苯的C-H键的断裂.第三失重段约在380~800℃之间,这阶段失重率为15.01%~15.34%,主要为C=O键断裂,且强度比第二段有所增加.主要热解段第二段的热解活化能在105~165 kJ变化,呈先递增后减小的变化规律,在转化率0.7处达到最大值.     

水合乙酸锌脱水反应的动力学

用等温热重法和非等温热重法研究了Zn(CH3COO) 2·2H2 O的脱水反应 .在 61.1、62 .8、66.2、69.9℃下的等温热重数据 ,由等转化率下的lnt=E/RT +ln[g(α) /A]进行拟合 ,确定了活化能的大小 ;升温速率为 10℃ /min的非等温热重曲线显示 ,Zn(CH3COO) 2·2H2 O的脱水反应发生在 71～ 10 2℃间 ,其数据通过Doyle Zsako法进行拟合 ,以线性相关系数为判据 ,并结合等温热分析拟合结果 ,得到该脱水反应的积分动力学模式函数g(α) =[-ln( 1-α) ]2 / 3、活化能E =10 0 .8kJ/mol、指前因子ln(A/s-1) =3 6.0 9、动力学补偿效应方程为lnA =0 .3 3 3 9E + 2 .0 10 .     

抗癌药β-榄香烯分子内部运动的13C核自旋弛豫研究

首次应用变温实验方法和¹³C核自旋弛豫方法研究了抗癌药β-榄香烯小分子的内部运动状况。结果表明β-榄香烯分子的六元环在所研究的温度范围(298~318K)内几乎是刚性的。该分子的整体滚动自扩散活化能为14kJ/mol.其六元环外侧链基团CH₂=CCH₃-和CH₂=CH-的整体内旋转扩散活化能均为19kJ/mol.而与该六元环直接相连的甲基的内旋转扩散活化能为18kJ/mol.这个数值大大高于连在六元环上不同位置的两个侧链基团CH₂=CCH₃一中甲基的内旋转扩散活化能(其数值分别为了7kJ/mol和2.8KJ/mol).3个不同位置的甲基的内旋转扩散活化能有很大差别可能是由它们所处的分子空间环境不同而引起的。     

地开石热分解过程及非等温动力学研究

用傅利叶变换红外光谱仪研究了湖南晨溪地开石热分解前后的红外光谱,加热反应后原矿粉红外光谱在3620.73、3695.34cm-1处的地开石羟基伸缩振动吸收峰和在916.06、1009.33cm-1处的羟基弯曲振动吸收峰都消失,表明其质量失重为羟基脱水.在298～1123K,用TG DTA综合分析仪研究了地开石在程序升温下的热分解行为.结果表明,在600～1000K,其质量损失为13.7%,与理论计算的脱水量相近.根据TG DTG曲线上的基础数据,联合运用积分法(Coats Redfern方程、HM方程、MKN方程)和微分法(Achar方程)对地开石脱水反应过程进行了非等温动力学研究,结果显示,地开石热分解反应的机理函数为F2,求得反应的动力学参数:反应级数为2.1,表观活化能为131.62kJ/mol,指前因子为108.3s-1.作为一种验证方法,使用Ozawa方程对不同升温速率TG曲线上相同分解率处的绝对温度进行线性回归分析,求出的表观活化能值为133.07kJ/mol,此值不仅与上述各种方法的表观活化能值相近,也与确定机理函数时的表观活化能值相近.说明实验求得的动力学参数在很大程度上是可靠的.     

TX-100和CTAB交换动力学的核磁共振研究

运用核磁共振(NMR)方法分别测定了表面活性剂辛基苯聚氧乙烯醚(TX-100)和十六烷基三甲溴化铵(CTAB)在不同温度下的临界胶束浓度.阐述了应用1D NMR线型分析方法对表面活性剂快交换体系平均停留时间的定量测量.实验测量了TX-100和CTAB胶束溶液中表面活性剂分子在不同温度下的平均停留时间.结果显示,平均停留时间随温度的增加逐渐减小,说明TX-100和CTAB分子进出胶束的速率随温度的增加逐渐加快.利用阿伦尼乌斯公式拟合,获得了TX-100和CTAB的表观交换活化能,TX-100的表观交换活化能为17.6 k J/mol,CTAB的表观交换活化能为75.3 k J/mol.对TX-100和CTAB平均停留时间和表观交换活化能进行分析,得出平均停留时间和表观交换活化能与分子结构的关系:表观交换活化能反映的是疏水相互作用和静电斥力的大小;而平均停留时间不仅受活化能的影响,还与分子结构有关.     

Hydrolysis of New Transplatin Analogue Containing One Aliphatic and One Planar Heterocyclic Amine Ligand: A Density Functional Theory Study

用密度泛函理论对一种新式反铂抗癌药物trans-[PtCl2(3-pico)(isopropylamine)]的水解机理进行了研究．研究中选用两个模型,即模型一为反应物和产物均为孤立状态,模型二为反应物和产物处于络合状态．运用B3LYP/6-31G**泛函方法对反应物、产物和过渡态的几何结构进行了全面优化．发现水解过程中过渡态结构与文献中报道的三角双锥结构吻合．反应络合物与产物络合物中所包含的进入基团(水分子)和离去基团(氯离子)对反应的热力学和动力学都产生了很大影响：模型二的两步反应活化能垒分别比模型一提高了约26.3和23.8 kJ/mol,吸热量比模型一分别降低了约420.5和771.2 kJ/mol．采用IEF-PCM模型进行水溶液计算,模型一两步反应的活化能垒比气相值分别提高约27.6和6.7 kJ/mol,模型二则分别降低约7.9和29.3 kJ/mol．经过熵修正后整个体系第一步水解的反应活化能全部上升了而第二步则恰好相反,第二步水解的活化能垒始终高于第一步．     

纳米金属粉对高氯酸铵热分解动力学的影响

用TG和DSC研究了普通级和纳米级的铝、镍金属粉对普通高氯酸铵热分解特性的影响 .结果表明 ,普通级和纳米级铝粉对普通高氯酸铵热分解几乎没有影响 ,纳米镍粉对普通高氯酸铵的热分解 ,特别是高温阶段的促进作用最明显 .这种促进作用随着纳米镍粉含量的减少而逐渐减弱 .利用Coats Redfern积分法计算了超细高氯酸铵热分解的动力学参数 ,结果显示纳米镍粉使超细高氯酸铵热分解的表观活化能从 15 7.9kJ/mol下降为134.9kJ/mol,而其热分解的机理函数都同属于“成核和核成长”的Avrami Erofeev方程系列的函数 ,同时还探讨了纳米镍粉对高氯酸铵热分解促进作用的机理 .     

A novel single particle study of steam gasification kinetics of a coal-derived char at high temperatures and pressures

A novel single particle experiment was developed to allow for detailed char gasification measurements in pure steam at temperatures from 1000 °C to 1400  °C and pressures from 1  bar to 15  bar. A coal-derived activated carbon was thoroughly characterized with respect to its composition, physical structure, and reactivity revealing properties consistent with chars reported in the literature. The single particle approach allowed for the boundary and initial conditions to be well known and for the mass of the particle to be accurately measured before and after testing to provide high-quality conversion data. The resulting conversion data were analyzed using the random pore model and the shrinking core model, of which the random pore model provided the best fit. Apparent activation energies were calculated using the random pore model which provided values ranging from 57.1 kJ/mol to 129 kJ/mol which are nominally half of the magnitude of the values reported in the literature under kinetically controlled conditions, thus demonstrating that regime II conditions were present. Additionally, the activation energies decreased with increasing temperature further demonstrating the presence of regime II conditions. The calculated reaction order ranged from 0 to 0.5 and decreased with increasing pressure agreeing well with literature values and trends.     

Thermal Degradation Kinetics of Plasticized Poly (Vinyl Chloride) with Six Different Plasticizers

Plasticized PVC formulated with different kinds of normally used plasticizers, including bis(2-ethylhexyl) phthalate (DOP), dioctyl terephthalate (DOTP), acetyl tri-n-butyl citrate (ATBC), acetyl trioctyl citrate (ATOC), trioctyl trimellitate (TOTM), and a new vegetable devived plasticizer, isosorbide ester (ID-37), were prepared by a melt blending method. The effect of plasticizer on the thermal degradation behavior of plasticized PVC was investigated by thermal gravimetric analysis (TGA). The activation energies were calculated by three well known methods, developed by Flynn-Wall-Ozawa (FWO), Friedman and Kissinger, respectively. The TGA conducted in N₂ atmosphere showed that the type of plasticizer had an obvious influence on the thermal stability of plasticized PVC. It was found that the peak temperatures (T_P) of the thermal degradation processes shifted to higher temperature with the increase of the heating rate, with two processes being shown. The activation energy of the first thermal decomposition process (E₁), calculated by the Kissinger method, was between 118 and 130 kJ/mol, while the activation energy of the second thermal decomposition process (E₂) was between 261 and 305 kJ/mol, except 499 kJ/mol for the PVC/TOTM formulation. The corresponding values of E₁ and E₂ obtained by the Flynn-Wall-Ozawa method were similar to the above data. E of the sample with TOTM also showed a higher value than the others; the results demonstrated that the PVC plasticized with TOTM was more thermally stable than with the others. The activation energies for certain conversion degrees were calculated by the Friedman method and the FWO method. The value of activation energy for 20%, 50%, and 80% conversion calculated by the Friedman method, exhibited an apparent difference from that calculated by the Flynn-Wall-Ozawa method; the results showed that the value of E obtained by the Friedman method was much more reasonable than that obtained by the Flynn-Wall-Ozawa method.     

Non-isothermal kinetics of styrene-butadiene-styrene asphalt combustion

The combustion characteristics of styrene-butadiene-styrene （SBS） asphalt are studied by thermogravimetric analysis （TG/DTG） at four different heating rates. According to the saturates/aromatics/resins/asphaltenes （SARA） fractionation method, the combustion process of SBS asphalt can be divided by Gaussian peak fitting into three main stages： oil content release, resin pyrolysis, and asphaltene and char combustion. When the heating rate increases, the mass losses of the oil content and resin pyrolysis increase, and less asphaltenes are formed at a higher temperature. The activation energy values are calculated by the Coats-Redfern method to be in the range 61.6 kJ/mol-142.9 kJ/mol. The Popescu method is used for the kinetic analysis, and the result shows that the three stages of asphalt combustion can be explained by the sphere phase boundary reaction model, the second order chemical reaction model, nucleation, and its subsequent growth model, respectively.     

Effect of operational parameters on degradation of Malachite Green by ultrasonic irradiation

The aim of the present study was to apply ultrasonic technique to remove Malachite Oxalate Green (MG) from aqueous solution. An ultrasonic bath with frequency of 35 kHz was used to investigate the effect of different operational parameters such as MG concentration, power density, temperature, mechanical agitation and addition of EtOH, 2-PrOH and iso-BuOH. Decolorization of MG follows a first order kinetics and hydroxyl radicals have an important role in degradation of MG. The apparent reaction rate constant (k(ap)) was influenced by variation of operational parameters. The activation energy was 30.95 kJ/mol in temperature range of 21-34 degrees C, suggesting a diffusion-controlled reaction. Alcohols act as hydroxyl radicals scavengers having undesirable contribution. UV-vis spectral change of MG showed hypsochromic shift occurred with increasing sonication time, proposing N-demethylation process of MG.     

Correlation between burning surface temperature and regression rate for polymethylmethacrylate

Prediction of the regression rate of polymeric fuels is important, especially for the optimal design of solid fuel ramjets or hybrid rocket motors. The burning surface temperature and the surface activation energy in the Arrhenius pyrolysis equation are required for prediction of the regression rate. As a typical polymeric fuel, polymethylmethacrylate (PMMA) was chosen for the present study. The burning surface temperature of PMMA was measured for both end-burning and sandwich-burning experimental devices. In the end-burning experiment, the oxygen flow impinged on the top of the specimen to burn the PMMA. In the sandwich-burning experiment, PMMA sheets were sandwiched between AP pellets. Temperature profiles near the burning surface were measured with a thermocouple embedded in the specimen. Simultaneously, the emergence of the thermocouple from the burning surface was determined with a video camera. The burning surface temperature obtained in the present study was found to be almost independent of the regression rate. The surface activation energy of PMMA was more than 1000 kJ/mol. Our measured surface temperature or the activation energy differs from the values measured with a thermocouple in previous studies. This difference probably is a result of mistaken identification of the burning surface temperature in the previous studies, because it was found that the sudden change or tiny plateau of the slope, in the temperature profile of PMMA, did not signal the burning surface.     

Thermal Stability and Degradation Kinetics of Poly(Methyl Methacrylate)/Sepiolite Nanocomposites by Direct Melt Compounding

Poly(methyl methacrylate) (PMMA) nanocomposites based on sepiolite modified with trimethyl hydrogenated tallow amine by an adsorption process were prepared by melt compounding using a corotating twin screw extruder. The morphology and dispersion of sepiolite in the PMMA were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermal stability and the activation energies were investigated by thermogravimetric analysis/differential thermogravimetric (TGA/DTG). The XRD and TEM results show that the sepiolite was dispersed homogeneously in the PMMA matrix at a nanometer scale. The TGA analysis revealed that the addition of sepiolite improved the thermal stability of PMMA. The apparent activation energies were calculated by the method of Flynn–Wall–Ozawa in nitrogen at four different heating rates, showing that sepiolite increased the apparent activation energies by about 20 kJ/mol within the degree of conversion (α) of 0.35–0.9, as compared with the reference PMMA sample.     

Diffusion and thermite reaction process of film-honeycomb Al/NiO nanothermite:Molecular dynamics simulations using ReaxFF reactive force field

The diffusion and thermite reaction process of Al/NiO nanothermite composed of Al nanofilm and NiO nano honeycomb are investigated by molecular dynamics simulations in combination with the Reax FF. The diffusion and thermite reaction are characterized by measuring energy release, adiabatic reaction temperature, and activation energy. Based on time evolution of atomic configuration and mean square displacement, the initialization of the thermite reaction process of Al/NiO nanothermite results from the diffusion of Al atoms. Under the microcanonical ensemble, it is found that the adiabatic reaction temperature of the thermite reaction process of Al/NiO nanothermite reaches over 5500 K, and activation energy is 8.43 k J/mol. The release energy of the thermite reaction process of Al/NiO nanothermite is 2.2 k J/g, which is in accordance with the available experimental value. With the same initial temperature, the adiabatic reaction temperature of the thermite reaction process of Al/NiO nanothermite has a tendency to decrease dramatically as the equivalence ratio increases. On the basis of chemical bond analysis, the initial temperature and equivalence ratio have great effects on the thermite reaction process, but do not significantly affect the average length of Al–Ni nor Al–O bond. Overall, the thermite reaction of film-honeycomb Al/NiO nanothermite is a complicated process instead of a theoretical equation.