共查询到19条相似文献,搜索用时 47 毫秒
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采用小型固定流化床装置(ACE Model C),研究了在反应温度460-540℃下,模型化合物十氢萘在Y分子筛催化剂上的裂化反应路径及生焦机理。结果表明,十氢萘裂化的初始阶段,H+进攻十氢萘上与叔碳原子相连的C-H键和C-C键形成非经典五配位叔正碳离子是其最主要的引发反应;十氢萘裂化产物主要是丙烯、丙烷、异丁烷、异戊烷、甲基环戊烷、甲苯、二甲基苯等;产物的收率在催化剂上由大到小为,非芳烃、单环芳烃、双环芳烃;十氢萘催化生焦的机理是碳正离子机理,随反应温度和分子筛酸量的升高,双分子氢转移以及脱氢缩合能力增强,焦炭产率和转化率也随之升高。 相似文献
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平朔煤热解过程中PAHs的释放特性 总被引:1,自引:0,他引:1
平朔煤热解过程中PAHs的释放特性 《燃料化学学报》2013,41(11):1281-1286
利用热解-气质联用仪(PY-GC-MS)研究了平朔煤在不同热解温度下多环芳烃(PHAs)的释放规律,并探讨了该过程中PAHs的生成机理。研究结果表明,16种PAHs的生成总量随着热解温度的升高先增大后减少,在800℃达到最大值。且PAHs环数分布规律对热解温度具有显著的依赖性,不同环数的PAHs,其最大生成量时所对应的热解温度亦不同。随着热解温度的升高,煤结构中的桥键、芳香环上的脂肪侧链以及较难断裂的甲基、酚羟基等依次断裂,使得PAHs的生成量不断增加,当温度升高至1 000、1 200℃时,伴随着缩合反应加剧,大环PAHs的生成量继续增加。由总体趋势看出,平朔煤大分子网络结构的热裂解主要发生在600~800℃,热解缩合反应主要发生在高温下。平朔煤热解过程中的PAHs除小部分来自煤中可萃取的芳烃结构挥发外,主要来自煤中大分子芳香结构裂解以及热解生成自由基碎片的高温聚合。 相似文献
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应用密度泛函理论研究了Mo/MCM-22分子筛上碳化钼活性中心的几何结构和电子结构,以及甲烷在该活性中心上的活化机理. 设计了两种结构的活性中心模型: Mo(CH2)2(模型A)和Mo(CH)CH2(模型B); 它们都嫁接在MCM-22分子筛超笼边缘的T4位的Brnsted-酸性位上,用3T簇模型代替分子筛的骨架,对所设计的模型进行了几何结构优化和电子结构分析. 结构优化结果显示, Mo与CH2端基以双键结合,键长为0.18~0.19 nm, 而Mo与CH端基以叁键结合,键长为0.17 nm. 通过自然键轨道分析,证明中心钼原子以配位键与骨架氧原子结合. 根据前线分子轨道的分析,预测了甲烷活化反应将发生在甲烷分子的HOMO和钼活性中心的LUMO之间,即 C-H 键的电子流向 Mo-C 键的π*轨道. 甲烷 C-H 键发生异裂, H+和H3C-基团分别与 Mo-C 键上的Mo和C成键. 在模型A上,甲烷活化反应的活化能为119.97 kJ/mol; 在模型B上,甲烷的H原子可以分别结合到CH2端基和CH端基上,对应的活化能分别为91.37和79.07 kJ/mol. 相似文献
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吸热型碳氢燃料正癸烷热裂解机理、热沉及产物分布的理论研究 总被引:1,自引:0,他引:1
采用密度泛函理论(DFT)的B3LYP方法在6-311G(d,p)基组水平上对正癸烷裂解过程中涉及的反应物、产物及过渡态进行了几何构型优化和振动频率计算,运用B3LYP/aug-cc-pVTZ方法计算单点能并构建势能剖面图。利用TheRate程序包及Eckart校正模型计算了各反应速率常数k。采用统计热力学原理求得不同温度下的热容Cp,mθ及熵S298 Kθ,并通过设计等键反应获得了各物种的标准生成焓△fH298 Kθ。用Chemkin II程序模拟预测了产物分布,理论计算了热沉值,并讨论了温度、压力对产物分布和热沉的影响。结果表明,C-C键断裂过程是反应的初始步骤,且抽氢反应较β键断裂反应更易进行。裂解起始温度为500 ℃,反应主要发生在600~700 ℃,其主要产物为氢气、甲烷、乙烯、乙烷、丙烯和1,3-丁二烯,且产物分布随温度不同而变化。模拟计算获得正癸烷在温度600 ℃、压力2.5 MPa条件下的总热沉值为2.334 MJ/kg,对应的热裂解转化率为25.9%,该热沉值可以满足速率为5~6马赫数的飞行器的冷却要求。 相似文献
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甲苯热解机理的AM1研究(Ⅰ)热力学分析 总被引:2,自引:0,他引:2
在实验的基础上,本文用Gaussian98程序包中AM1法UHF计算,对碳材料用碳前驱体甲苯的热裂解反应机理进行了研究。在对反应物,产物自由基的结构进行能量梯度法全优化的同时,计算了不同温度下的标准热力学参数(298-1073K)。热力学计算结果表明:(1)当甲苯的热裂解温度相对较低时(773K左右),热力学计算结果首先支持苯环上甲基C-H键的断裂生成苯基自由基并继而生成联二甲苯的反应;随着温度的提高(达1073K时),生成苯自由基和甲基自由基的反应比例将大生成苄基自由基的比例;该反应机理与实验结果基本一致。(2)采用Gaussian98程序包中AM1法中的UHF计算,较适合低级芳香烃热裂解反应机理的理论研究。 相似文献
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反应温度对聚二甲基硅烷高压合成聚碳硅烷性能的影响 总被引:4,自引:0,他引:4
以聚二甲基硅烷(PDMS)为原料,在高压釜内高温高压合成了聚碳硅烷(PCS)先驱体.研究了反应温度对合成的PCS的Si—H键含量、支化度、Si—Si键含量、分子量及其分布、软化点及产率的影响.研究表明,随着反应温度的提高,分子量及软化点均明显增加,分子量分布变宽,支化度升高,Si—Si键含量明显降低.当反应温度低于460℃时,Si—H键含量及产率随反应温度的升高逐渐升高,当反应温度高于460℃时,由于分子间的缩合及热交联二者逐渐降低.在反应过程中PDMS首先转化为小分子量的PCS,然后是小分子PCS分子间发生脱氢及少量脱甲烷缩合使分子量长大.当反应温度高于450℃时,PCS分子量分布出现中分子量峰,Si—Si键含量较低,在室温空气中比较稳定. 相似文献
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现行高中化学课本(必修)第二册(人教社版),关于石油裂化的实验是一个很难做的实验,耗时太多,现象也不明显,我们认为该实验并不难做,主要是在运用反应原理上略有欠缺,只要稍加改进就是一个很好的实验。石油热裂化是在高温下石油(实际是石油产品)中的大分子链烃被断裂为小分子烃。裂化的关键条件是温度,只有达到一定温度时才能发生裂化。石蜡的裂化温度是500℃左右,石蜡的沸点是360℃以 相似文献
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采用水热法制备FeCrAl丝网负载FAU沸石膜,考察了合成液老化、载体预涂晶种以及晶种液中添加聚乙烯醇(PVA)等因素的影响,评价了FeCrAl丝网负载FAU沸石膜对模型吸热燃料正辛烷裂解的催化活性。结果表明,载体表面预涂Y分子筛晶种后有助于增加载体表面分子筛负载量,采用老化后的合成液,效果更显著,并且更易在金属丝上生长出一层连续致密的FAU沸石膜。在相同水热合成条件下,载体表面用含PVA的晶种液预涂晶种后,可增加分子筛负载量。正辛烷在FeCrAl丝网负载FAU沸石膜上的初始裂解转化率(7.2%~13.2%,500 ℃)高于其在空白载体上的裂解转化率(4.4%),FAU沸石膜的初始催化活性不仅与载体表面分子筛负载量有关,也与分子筛膜的形貌有关。 相似文献
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十氢萘在分子筛催化剂上的开环反应研究 《燃料化学学报》2012,40(12):1422-1428
在小型固定流化床(FFB)装置中研究了Y分子筛与ZSM-5分子筛催化剂上的十氢萘裂化开环反应性能,考察了温度和剂油比对Y分子筛开环反应催化性能的影响。结果表明,十氢萘在分子筛催化剂上通过环烷环开环反应生成丙烷、丙烯、丁烷、丁烯、甲基戊烷和环戊烷、环己烷等非芳烃以及苯、C1~4烷基取代苯等单环芳烃,并通过脱氢缩合反应生成四氢萘、萘、甲基萘和菲、芘等多环芳烃甚至焦炭等。由于扩散和吸附性能的影响,ZSM-5分子筛催化剂的裂化开环反应选择性比Y分子筛催化剂的高,因此,十氢萘环烷环开环与脱氢缩合反应的相对比例(NRO/DHC)在ZSM-5分子筛催化剂上较高。在Y分子筛催化剂上,温度为450~550 ℃、剂油比为3~9,反应温度升高或者剂油比增加,双分子氢转移以及脱氢缩合反应增强,从而导致环烷环开环产物选择性降低。 相似文献
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Konstantin Khivantsev Nicholas R. Jaegers Libor Kovarik Miroslaw A. Derewinski Ja-Hun Kwak Janos Szanyi 《Molecules (Basel, Switzerland)》2022,27(7)
Steamed zeolites exhibit improved catalytic properties for hydrocarbon activation (alkane cracking and dehydrogenation). The nature of this practically important phenomenon has remained a mystery for the last six decades and was suggested to be related to the increased strength of zeolitic Bronsted acid sites after dealumination. We now utilize state-of-the-art infrared spectroscopy measurements and prove that during steaming, aluminum oxide clusters evolve (due to hydrolysis of Al out of framework positions with the following clustering) in the zeolitic micropores with properties very similar to (nano) facets of hydroxylated transition alumina surfaces. The Bronsted acidity of the zeolite does not increase and the total number of Bronsted acid sites decreases during steaming. O5Al(VI)-OH surface sites of alumina clusters dehydroxylate at elevated temperatures to form penta-coordinate Al1O5 sites that are capable of initiating alkane cracking by breaking the first C-H bond very effectively with much lower barriers (at lower temperatures) than for protolytic C-H bond activation, with the following reaction steps catalyzed by nearby zeolitic Bronsted acid sites. This explains the underlying mechanism behind the improved alkane cracking and alkane dehydrogenation activity of steamed zeolites: heterolytic C-H bond breaking occurs on Al-O sites of aluminum oxide clusters confined in zeolitic pores. Our findings explain the origin of enhanced activity of steamed zeolites at the molecular level and provide the missing understanding of the nature of extra-framework Al species formed in steamed/dealuminated zeolites. 相似文献
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Reactivity of isobutane on zeolites: a first principles study 总被引:1,自引:0,他引:1
In this work, ab initio and density functional theory methods are used to study isobutane protolytic cracking, primary hydrogen exchange, tertiary hydrogen exchange, and dehydrogenation reactions catalyzed by zeolites. The reactants, products, and transition-state structures are optimized at the B3LYP/6-31G* level, and the final energies are calculated using the CBS-QB3 composite energy method. The computed activation barriers are 52.3 kcal/mol for cracking, 29.4 kcal/mol for primary hydrogen exchange, 29.9 kcal/mol for tertiary hydrogen exchange, and 59.4 kcal/mol for dehydrogenation. The zeolite acidity effects on the reaction barriers are also investigated by changing the cluster terminal Si-H bond lengths. The analytical expressions between activation barriers and zeolite deprotonation energies for each reaction are proposed so that accurate activation barriers can be obtained when using different zeolites as catalysts. 相似文献
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Ni-Mg复合催化剂催化裂解CH制氢动力学研究 《燃料化学学报》2017,45(2):249-256
基于定温热重实验,建立了甲烷催化裂解反应动力学模型和催化剂表面积炭失活动力学模型。其中,甲烷催化裂解动力学模型将初始产氢速率视为催化剂未积炭条件下的动力学基础数据;催化剂表面积炭失活动力学则基于甲烷催化裂解速率的降低。实验使用Ni-Mg复合催化剂,分别在535、585、635℃,甲烷分压10~4、2×10~4、3×10~4Pa条件下展开甲烷催化裂解动力学特性研究。结果表明,甲烷催化裂解的反应级数为0.5,活化能为82 k J/mol;Ni-Mg复合催化剂反应失活级数为0.5,催化剂失活活化能为118 k J/mol。实验条件下均制得了多壁碳纳米管。 相似文献
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lntroductionThesmallolefinslikeethylene,propeneandbutenearethec0mmerciallydesirablepetrochemicalfeedstocksandarefoundincreasingusageinchemicalindustry.Theyareusuallyobtainedfromthepyrolysis0fpetroleumhydrocarb0nswithsteaInatveryhightemPeratUreandarealsoavailablefromFCCprocess.TheimProvedFCCcatalystforeIhancingtheolefinproducthasbeenreportedll].However,FCCisalrnostimPossiblefortheshortchainalkanefeedstockscutfrompetroleum0robtuinedfromrefinerygasornatUralgassincecrackingofhydrocarbonsbeco… 相似文献
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Effects of Calcination Temperature on the Acidity and Catalytic Performances of HZSM-5 Zeolite Catalysts for the Catalytic Cracking of n-Butane 下载免费PDF全文
The acidic modulations of a series of HZSM-5 catalysts were successfully made by calcination at different treatment temperatures, i.e. 500, 600, 650, 700 and 800 ℃, respectively. The results indicated that the total acid amounts, their density and the amount of B-type acid of HZSM-5 catalysts rapidly decreased, while the amounts of L-type acid had almost no change and thus the ratio of L/B was obviously enhanced with the increase of calcination temperature (excluding 800 ℃). The catalytic performances of modified HZSM-5 catalysts for the cracking of n-butane were also investigated. The main properties of these catalysts were characterized by means of XRD, N2 adsorption at low temperature, NH3-TPD, FTIR of pyridine adsorption and BET surface area measurements. The results showed that HZSM-5 zeolite pretreated at 800 ℃ had very low catalytic activity for n-butane cracking. In the calcination temperature range of 500-700 ℃, the total selectivity to olefins, propylene and butene were increased with the increase of calcination temperature, while, the selectivity for arene decreased with the calcination temperature.The HZSM-5 zeolite calcined at 700 ℃ produced light olefins with high yield, at the reaction temperature of 650 ℃ the yields of total olefins and ethylene were 52.8% and 29.4%, respectively. Besides, the more important role is that high calcination temperature treatment improved the duration stability of HZSM-5zeolites. The effect of calcination temperature on the physico-chemical properties and catalytic performance of HZSM-5 for cracking of n-butane was explored. It was found that the calcination temperature had large effects on the surface area, crystallinity and acid properties of HZSM-5 catalyst, which further affected the catalytic performance for n-butane cracking. 相似文献