The effect of Lewis number variation on combustion waves in a model with chain-branching reaction

In this paper we investigate the linear stability and properties of the travelling premixed combustion waves in a model with two-step chain-branching reaction mechanism in the adiabatic limit in one spatial dimension. It is shown that the Lewis number for fuel has a significant effect on the properties and stability of premixed flames, whereas the Lewis number for the radicals has only quantitative (but not qualitative) effect on the combustion waves. We demonstrate that when the Lewis number for fuel is less than unity the flame speed is unique and is a monotonically decreasing function of the dimensionless activation energy. The combustion wave is stable and exhibits extinction for finite values of activation energy as the flame speed decreases to zero. For fuel Lewis number greater than unity the flame speed is a double-valued function. The slow solution branch is shown to be unstable whereas the fast solution branch is either stable or exhibits the onset of pulsating instabilities via the Hopf bifurcation. The evolution of these instabilities leads to flame extinction.     

A novel TMSI-mediated synthesis of Hantzsch 1,4-dihydropyridines at ambient temperature

The synthesis of various substituted Hantzsch 1,4-dihydropyridines has been achieved using the classical Hantzsch procedure and modified Hantzsch conditions for the first time at room temperature in the presence of iodotrimethylsilane (TMSI) generated in situ in CH₃CN, in excellent yields.     

Atom transfer radical copolymerization of acrylonitrile and ethyl methacrylate at ambient temperature

Copolymerization of acrylonitrile (AN) and ethyl methacrylate (EMA) using copper‐based atom transfer radical polymerization (ATRP) at ambient temperature (30 °C) using various initiators has been investigated with the aim of achieving control over molecular weight distribution. The effect of variation of concentration of the initiator, ligand, catalyst, and temperature on the molecular weight distribution and kinetics were investigated. No polymerization at ambient temperature was observed with N,N,N′,N′,N″‐pentamethyldiethylenetriamine (PMDETA) ligand. The rate of polymerization exhibited 0.86 order dependence with respect to 2‐bromopropionitrile (BPN) initiator. The first‐order kinetics was observed using BPN as initiator, while curvature in first‐order kinetic plot was obtained for ethyl 2‐bromoisobutyrate (EBiB) and methyl 2‐bromopropionate (MBP), indicating that termination was taking place. Successful polymerization was also achieved with catalyst concentrations of 25 and 10% relative to initiator without loss of control over polymerization. The optimum [bpy]₀/[CuBr]₀ molar ratio for the copolymerization of AN and EMA through ATRP was found to be 3/1. For three different in‐feed ratios, the variation of copolymer composition (F_AN) with conversion indicated toward the synthesis of copolymers having slight changes in composition with conversion. The high chain‐end functionality of the synthesized AN‐EMA copolymers was verified by further chain extension with methyl acrylate and styrene. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1975–1984, 2006     

Architectural control of polystyrene physical properties using branched anionic polymerization initiated at ambient temperature

Ambient temperature-initiated anionic polymerization has generated branched polystyrenes of varying molecular weights and architectures by inclusion of a distyryl branching comonomer into a conventional sec-Butylithium-initiated polymerization of styrene. Primary chain length control within the branched polymers, and restriction of the branching points to varying segments of the primary chains, led to variations of glass transition temperature with no direct correlation to the branched polymer molecular weight but a strong relationship to the length of individual chains comprising the branched macromolecules.     

The effect of limestone on the combustion of fuel blends

Combustion profiles of coal-limestone-paper blends were studied using thermogravimetric/ Fourier transform infrared spectroscopy (TG/FTIR). The role of limestone in promoting the initial combustion of coal-paper blends and its ability to absorb sulphur oxides were examined.     

Very rapid copper‐mediated atom transfer radical polymerization of benzyl methacrylate at ambient temperature

The ability to do very rapid bulk atom transfer radical polymerization (ATRP) of benzyl methacrylate using a CuX/PMDETA complex at room temperature was demonstrated in this study. The experimental conditions required to synthesize low‐ and high‐molecular‐weight poly(benzyl methacrylate) with low polydispersity are reported here. The controlled/living nature of the polymerization was demonstrated through kinetic studies, and chain‐extension studies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1053–1057, 2004     

The effect of a radical scavenger on the propagation of flames in an exothermic-endothermic system

The propagation of a premixed laminar flame supported by an exothermic chemical reaction under adiabatic conditions but subject to inhibition through parallel endothermic chemical processes is considered. These consist of the endothermic decomposition of an inhibitor W leading to the formation of a ‘radical scavenger’ S, which acts as a catalyst for the removal of active radicals X through an additional termination step. The heat loss through the endothermic reaction and the action of the radical scavenger, represented by the parameters α and ρ, both have a strong quenching effect on wave propagation. The dependence of the flame velocity c on α and ρ is determined by numerical integration of the flame equations for a range of values of the other parameters. The (ρ ,c) curve can have at least one turning point, the (α,c) curve can be monotone or it can have one or three turning points, depending on the values of the parameters β, representing the rate at which inhibitor is consumed, μ, the ratio of the activation energies of the reactants and the Lewis numbers. The additional feature caused by the scavenger is that the (α, c) curve has a turning point for any (μ, β) parameter pair if ρ is sufficiently large. A new feature of the model is that, for non-zero values of ρ, there can be four solutions below critical values of α. This behaviour is confirmed by a high activation energy analysis, which also reveals some additional features of the flame structure resulting from the presence of the radical scavenger.AMS subject classification: 80A25, 35K57, 35B32     

Al2O3负载Pt催化剂的合成及其甲醇低温催化燃烧性能研究

采用一步合成法制备了Al₂O₃负载Pt催化剂Pt/Al₂O₃,以甲醇催化燃烧作为目标反应研究了其催化性能,考察了还原剂浓度、表面活性剂用量、表面活性剂浓度和煅烧温度对Pt/Al₂O₃甲醇低温催化燃烧性能的影响。结果表明,当还原剂浓度为0.1 mol/L、表面活性剂(CTAB)用量为8.53 g/g_cat.、表面活性剂浓度为0.1 mol/L、煅烧温度为600℃时,所得催化剂的活性最高,25℃下甲醇催化燃烧的转化率达到52%。而改进一步合成法制备的负载型催化剂Pt/Al₂O₃具有更高的甲醇催化燃烧活性,25℃下甲醇催化燃烧的转化率为84%。     

外来水分对煤自燃过程影响及作用机制研究

通过浸泡方法制备一系列不同外来水分含量的煤体,利用程序升温氧化实验模拟煤自燃过程,研究外来水分对煤自燃特性的影响;结合热分析和孔结构表征实验,探讨外来水分对煤自燃过程影响作用机制。外来水分对煤自燃过程的作用机制随着煤自燃状态发展而发生变化,主要表现出四个阶段。在缓慢氧化阶段,外来水分主要隔离煤与氧气的接触反应,对煤自燃起到物理抑制作用;在加速氧化阶段,水分可直接参与煤氧反应,起到化学促进作用;经过缓慢氧化阶段和加速氧化阶段,大量外来水分的蒸发导致煤颗粒表面裂隙增大,水分越大的煤生成的活性点位会更多,当煤自燃进入快速氧化阶段,外来水分对煤氧化反应的影响表现出延迟促进效应;当煤体温度达到180℃后,随着煤体温度进一步升高,不同初始外来水分含量的煤体自燃特征逐渐趋于一致。     

超声提取-高温燃烧吸收-离子色谱法测定纺织品中可吸附有机卤化物北大核心CSCD

建立了一种对纺织品中可吸附有机卤化物(AOX)的超声提取-高温燃烧吸收-离子色谱定量检测分析新方法。该方法采用超声方式提取纺织品中的AOX,提取液加入活性炭进行振荡吸附,并用酸性硝酸钠溶液对无机卤化物进行去除。采用程序升温的氧化燃烧方式对吸附AOX的活性炭进行裂解、燃烧及气化,其产生的卤化氢等气体随载气进入吸收液并完全转化为无机卤素阴离子,采用离子色谱分离测定,外标法定量。实验优化了超声提取时间、活性炭用量、燃烧气及其流量、燃烧升温程序、吸收液和吸收方式等前处理条件,并对离子色谱的仪器分析条件如色谱柱、柱温及淋洗液流速等进行优化。结果表明,氟、氯、溴、碘4种卤素离子的标准溶液在0.02~10 mg/L范围内呈线性关系,线性相关系数(R^(2))均在0.999以上;AOX测定的方法定量限为0.10~0.50 mg/kg。以棉、毛和涤纶3种不同种类的阴性纺织样品作为样品基质,选取典型的有机卤化物进行加标,在低、中、高3个加标水平下测得AOX的平均回收率为82.3%~98.7%,相对标准偏差(RSD,n=7)为2.0%~5.7%,表明方法具有良好的回收率和精密度。将该方法应用于实际纺织样品的测定,检出了不同含量的AOX,且重复性好。研究建立的方法通过采用活性炭的振荡吸附、程序升温的高温氧化燃烧方式和多孔吸收瓶的二级吸收方法,提高了AOX转化为无机卤素的回收率;同时利用离子色谱仪器选择性好、灵敏度高的特点成功地一次性分离检测4种AOX,且无杂质离子的干扰。该方法简单、准确、可靠,满足国内外法规和标准对纺织品中AOX的限量要求,适用于纺织品中AOX的分析测定。     

Controlled polymerizations of 2‐(dialkylamino)ethyl methacrylates and their block copolymers in protic solvents at ambient temperature via ATRP

Very well‐controlled polymerizations of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) and 2‐(diethylamino)ethyl methacrylate (DEAEMA) in aqueous and methanolic solutions via atom transfer radical polymerization (ATRP) at ambient temperature were demonstrated. Poly(DMAEMA) and poly(DEAEMA) of low polydispersity index (PDI) of ～1.07 were obtained using the p‐toluenesulfonyl chloride/CuCl/1,1,4,7,10,10‐hexamethyl‐triethylenetetramine (p‐TsCl/CuCl/HMTETA) system. Excellent control of polymerization was achieved even in pure methanol. This is in contrast with the very poor control of DMAEMA ATRP in methanol reported previously using a different intiator/catalyst/ligand system. The initiator p‐TsCl underwent hydrolysis reaction in aqueous methanolic solutions with a second‐order rate constant of 6.1 × 10^?4 dm³ mol^?1 s^?1 at 25 °C. Both poly(DMAEMA) and poly(DEAEMA) retained almost full chlorine‐functionization at the chain ends. Well‐defined block copolymers of DEAEMA and DMAEMA were successfully obtained by starting with either macroinitiators of DEAEMA or DMAEMA. Other well‐defined diblock copolymers could be prepared using these macroinitiators. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5161–5169, 2004     

热重法研究K2CO3与Fe2O3对煤粉燃烧反应性的影响

利用综合热重分析仪分别研究了K₂CO₃、Fe₂O₃对褐煤、烟煤、无烟煤、石墨等不同燃料的催化燃烧反应性的影响。结果表明,催化剂种类、添加量、粒径和燃料的变质程度对催化燃烧具有一定的影响;向无烟煤中加入K₂CO₃、Fe₂O₃两种催化剂,无烟煤的燃点由458℃分别降为319℃、405℃,燃烧速率由11.94%/min分别提高到26.40%/min、17.66%/min。K₂CO₃、Fe₂O₃对褐煤和烟煤的燃点没有明显的降低作用,但是对无烟煤和石墨燃点有明显的降低作用,且随着煤变质程度的增加,燃点降低幅度增大。由于引起燃点和燃速变化的原因不同,所以加入催化剂后造成燃点和燃速的变化也不同。     

4氯化铜对聚氯乙烯燃烧产物的催化作用

用现代色谱分析技术确定了在不同炉温条件下,掺杂有CuCl~2的聚氯乙烯燃烧过程中二噁英和多环芳烃的生成量,研究了氯化铜用量对其生成量的影响。结果表? 鞯ゴ康木勐纫蚁┤忌詹罅康亩嗷贩继蜕倭康亩f英,氯化铜的加入可大大增加二噁英的生成量,并能抑制多环芳烃的产生。金属氯化物可能是促使聚氯乙? ┤忌詹f英的主要因素之一。     

Grafting of methacrylates and styrene on to polystyrene backbone via a “grafting from” ATRP process at ambient temperature

Well defined graft copolymers are prepared by “grafting from” atom transfer radical polymerization (ATRP) at room temperature (30 °C). The experiments were aimed at grafting methacrylates and styrene at latent initiating sites of polystyrene. For this purpose, the benzylic hydrogen in polystyrene was subjected to allylic bromination with N‐bromosuccinimide and azobisisobutrylnitirle to generate tertiary bromide ATRP initiating sites (Br? C? PS). The use of Br? C? PS with lesser mol % of bromide initiating groups results in better control and successful graft copolymerization. This was used to synthesize a series of new graft copolymers such as PS‐g‐PBnMA, PS‐g‐PBMA, PS‐g‐GMA, and PS‐g‐(PMMA‐b‐PtBA) catalyzed by CuBr/PMDETA system, in bulk, at room temperature. The polymers are characterized by GPC, NMR, FTIR, TEM, and TGA. Graft copolymerization followed by block polymerization enabled the synthesis of highly branched polymer brush, in which the grafting density can be adjusted by appropriate choice of bromide concentration in the polystyrene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3818–3832, 2007     

氧体积分数对炭黑燃烧特性影响的热天平研究

利用热天平对天然气扩散火焰中生成的炭黑在不同氧体积分数下（21%、15%、10%和5%）的燃烧特性进行了研究，选用蜡烛炭黑、4种工业炭黑以及无烟煤焦炭作为对比。基于试验结果确定了燃烧特性参数，并分析了燃烧特性。天然气扩散火焰中生成的炭黑明显早于其他试样着火燃烧，着火温度在所有试样中最低，氧体积分数为21%下为483.0℃，比焦炭约低114℃，比蜡烛炭黑低近127.8℃。自制天然气炭黑可燃指数比焦炭低，着火后前期燃烧反应能力较弱。随着氧体积分数的降低，各试样着火温度在50℃内变化。比较各试样的燃尽特性可知自制天然气炭黑在不同燃尽率下的相对燃尽时间最长，氧体积分数为21%下完全燃尽为6.03min，比焦炭长21.3%。蜡烛炭黑相对燃尽时间也较长。随着氧体积分数降低，各试样燃尽时间都延长，尤其是自制天然气炭黑，氧体积分数从21%降到5%，相对燃尽时间延长2.97倍，氧体积分数降低明显延长其燃尽过程。     

环境气氛作用下煤灰在刚玉质耐火板上的表面结渣行为

采用了扫描电镜、能谱分析仪、X射线衍射等方法对不同环境气氛下熔融煤灰在刚玉耐火板上煅烧渣样进行了测试,并就渣样的形貌、成分分布及与刚玉质耐火板之间的高温烧结特性进行了分析研究。研究结果表明,氧化性气氛下,碱性氧化物促进了煤灰在刚玉耐火板上的黏结作用,特别是Al含量较高的耐火板更有利于促进其发生共晶反应。还原性条件下,煤灰中生成的FeO具有很强的助熔效果,促使矿物之间产生低熔点的共熔物,同时Fe、Cr、Ti的扩散偏析减弱,加强了熔融煤灰对耐火板的黏结作用。     

添加剂对燃煤电石渣固硫的促进作用

在煤的燃烧过程中采用钙基固硫技术脱除SO2等气体污染物,是实现煤高效清洁燃烧的有效措施之一。传统钙基固硫剂价格低廉,但普遍存在固硫剂利用率低,固硫反应速率与硫析出速率不一致,以及高温下形成的固硫产物易于分解等缺点。研究表明,在钙基固硫剂中掺入微量添加剂可以有效提高钙基固硫剂的固硫率。添加剂主要起两大作用,一是对煤的燃烧过程有助燃和促进作用,提高钙基利用率;二是在燃烧过程中形成耐热稳定的物相或熔融物相包裹固硫物相,从而抑制固硫物相的分解,阻止SO2的排放。     

The phenomenon of negative temperature coefficient in palladium-initiated combustion of hydrogen–propane–air mixtures

1. Download : Download high-res image (257KB)
2. Download : Download full-size image

     

高温环境下灰中矿物质对长广煤燃烧固硫行为的影响

针对煤粉炉及层燃炉中煤灰固硫特性,以高温固硫物相硫铝酸钙为固硫产物,对掺混不同比例煤灰的三种煤和添加设定比例CaO和Al2O3后煤的高温固硫特性进行了分析。结合XRD晶相分析和SEM表面形态分析发现,相对低比例煤灰而言,高比例煤灰更能提高煤的固硫率,渣样中硫铝酸钙含量明显增多。煤中添加CaO和Al2O3添加剂后,1300℃下的固硫率为24%,此时产物中有固硫物相硫铝酸钙生成。