共查询到19条相似文献,搜索用时 187 毫秒
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Olah等曾以氯化铝等作催化剂研究了邻氯甲苯的均相异构化.近年又有专利报道用氢型丝光沸石和HZSM-5沸石为催化剂使邻氯甲苯在≥20kg/cm2压力下异构化.为了有效地利用"杀草丹"生产过程中量大价廉的副产物邻氯甲苯,本文以P-HZSM-5沸石作催化剂,在常压流动微反-色谱装置上研究了邻氯甲苯的气-固相异构化反应. 相似文献
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化学液相沉积法调变沸石孔径及异构体择形分离 总被引:4,自引:0,他引:4
本文用化学液相沉积方法精细调变NaY沸石孔径, 在适当的溶剂中硅酯与沸石吸附水或表面羟基作用而沉积于沸石外表面, 沸石孔口有效地被缩小。制备了一系列氧化硅沉积量不同的SiNaY沸石, 红外光谱、比表面和孔体积测量结果表明随着沉积量增加沸石孔径逐渐缩小, 但沸石骨架结构、孔容和内表面性质基本不变。测定了SiNaY样品对于对二甲苯/1, 3, 5-三甲苯, β-甲基萘/α-甲基萘, 1, 2, 4-三甲苯/1, 3, 5-三甲苯, 对二甲苯/间二甲苯和对甲酚/间甲酚五类分子尺寸不同的液体混合体系的择形吸附行为, 发现SiNaY沸石对分子尺寸与沸石孔径相近的混合体系具有良好的择形选择吸附分离性能。 相似文献
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表面强酸分布——影响HZSM-5沸石对位选择性的主要因素 总被引:2,自引:0,他引:2
考察了交换剂和改性处理对HZSM-5沸石在甲苯乙基化反应中对位选择性的影响,检测了反应初级产物的组成,用原位TPD法研究了沸石表面酸中心的催化性质。结果表明,孔径和酸性分布都是影响沸石对位选择性的重要因素,但是表面酸性的调变对提高HZSM-5沸石的对位选择性更为重要。对-甲乙苯是甲苯乙基化反应的初级产物,在表面异构化反应后生成间-甲乙苯。烷基化和异构化两种反应活性中心在酸强度上的差异很小,仅仅是所处位置不同。由于改性处理同时抑制了这两类活性中心,使HZSM-5沸石在甲苯乙基化反应中的对位选择性上升而活性下降,表现出反向变化关系。 相似文献
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为了考察多级孔丝光沸石中介孔的存在对丝光沸石吸附平衡和动力学的影响,选择甲苯分子作为探针分子,对其在具有不同介孔孔隙度的多级孔丝光沸石上的吸附等温线和吸附动力学曲线进行了测试。结果表明,甲苯在多级孔丝光沸石上的吸附等温线可以很好地用双位Toth吸附模型进行描述,由拟合参数以及亨利常数(KH)和初始吸附热(Qst)的计算得知,相对于微孔丝光沸石,介孔的引入增大了甲苯在丝光沸石内的吸附量,但减弱了甲苯与沸石表面的相互作用力;另外,甲苯在多级孔沸石表现出高的吸附速率,并随介孔孔隙度的增加而增大,反映了沸石内介孔的存在可有效促进沸石的传质能力。 相似文献
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A series of nickel-exchanged catalysts based on ZSM-5, USY, and Mordenite zeolites has been prepared by the ionic exchange method. The NiZeol catalysts have been characterized by XRD and BET. The exchange levels and nickel contents of the catalysts have been determined by chemical analysis. The acidity of the zeolite supports has been investigated using NH3 adsorption microcalorimetry. The number of acidic sites was found to decrease according to the following sequence: HUSY > HZSM-5 > HMOR. The temperature programmed reduction studies showed that the most reducible catalyst is NiZSM-5. The Ni-exchanged zeolites presented good catalytic performance in the methane reforming by CO2. At a temperature of 650°C, CH4 conversions of 71 and 54% were achieved on NiUSY and NiZSM-5 respectively. At 400°C, CO2 FTIR adsorption has shown that CO2 decomposes into CO and oxygen on NiZSM-5 which explains its reactivity at such a low temperature, while no decomposition of this probe molecule was observed on the NiUSY catalyst. The catalytic performance was found to vary in the following sequence at 650°C: NiUSY > NiZSM-5 > NiMOR. Moreover, the catalytic performances were found to depend strongly on the CO2/CH4 ratio in the feed and were markedly improved for CO2/CH4 greater than 1. 相似文献
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以TPD和质谱检测的TPSR、IR及微型反应器等手段探讨了X型沸石的表面酸、碱性质对甲醇、甲苯侧链烷基化反应的作用及可能的反应历程。 相似文献
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测定了Na-β氧化铝管在NaOH、NaOH-KOH、NaOH-(CH_3)_4NOH以及NaOH-NaCl四种溶液的浓差电池体系中的电动势, 求得Na-β氧化铝与NaOH水溶液之间的界面电势Δφ。结果表明: 在NaOH、NaOH-NaCl水溶液中, Δφ与loga_2(Na~+)/a_1(Na~+)之间的关系服从Nernst公式; K~+离子的存在影响Δφ值, 而OH~-、(CH_3)_4N~+贴无影响。探讨了用β氧化铝在高浓碱性Na~+水溶液中做Na~+离子选择性电极的可能性。 相似文献
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TianboZhao HuiyingZhang FengyanLi ChaoYang BaoningZong 《天然气化学杂志》2005,14(2):95-100
ZSM-5/β co-crystalline zeolites with different content of ZSM-5 have been synthesized by adding different amount of ZSM-5 to the synthetic system of β zeolite with NaAlO2, silica sol as the source of aluminum and silica, respectively, and TEA as the template under controlled condition of the synthesis. The ZSM-5/β co-crystalline zeolite was studied by XRD, SEM, BET and NH3-TPD. The reaction activity of toluene alkylation was investigated with a mixture of toluene-methanol as the feedstock in a pulse micro-reactor over the ZSM-5/β co-crystalline zeolite. It is found that ZSM-5/β co-crystalline zeolite has two kinds of zeolite structure including ZSM-5 and β zeolite, not in the form of a physical mixture. The pore structure of ZSM-5/β co-crystalline zeolites is different from that for β zeolite, ZSM-5 and their physical mixture. In addition, the peaks of both high and low temperature desorption of ammonia over the ZSM-5/β co-crystalline zeolite shift 23 ℃ to lower temperatures and the acid amount of its strong acid is 3% more than the physical mixture. So the ZSM-5/β co-crystalline zeolite produces the highest content of xylene, which is 10.4% higher than the physical mixture. And the ZSM-5/β co-crystalline zeolite has better selectivity for toluene alkylation and weaker de-methylation than β zeolite, ZSM-5 and their physical mixture. 相似文献
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Ionophores selectively sensitive to primary amines have been synthesized which display low potentiometric selectivity coefficients for K~+, Na~+ and NH_4~+ ions, secondary and tertiary amines as well as quaternary ammonium ions. These ionophores include macrocyclic polyethers with dinaphthyl subunits and azocrown ether with nitrogen donor atoms. The feasibility of these ionophores for preparing primary amine drug selective electrodes was investigated in detail. Practically usable PVC membrane electrodes sensitive to primary amine drugs, such as mexiletine, dopamine, metaraminol and tryptamine, and aliphatic primary amines have been prepared with these ionophores as neutral carriers. Direct potentiometric methods for assaying these drugs have been proposed by using the prepared electrodes. The proposed primary amine drug selective electrodes are remarkably superior to those based on ion-associates. Compared with the electrodes based on common ethers, the interference by K~+, Na~+ and NH_4~+ ions is subst 相似文献
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Pillai RS Peter SA Jasra RV 《Langmuir : the ACS journal of surfaces and colloids》2007,23(17):8899-8908
The adsorption isotherms for nitrogen, oxygen, and argon in various NaCaA zeolite samples were calculated theoretically using the grand canonical Monte Carlo simulation method. The adsorption capacity, selectivity, and heat of adsorption of nitrogen increase with an increasing number of calcium cations in zeolite A. The heat of adsorption of nitrogen showed a sudden increase when the calcium ion exchange to zeolite A was around 60%. Adsorption isotherms, determined experimentally by the volumetric adsorption method, support theoretically predicted isotherms. These observations have been explained in terms of the interaction of the nitrogen molecule with Ca2+ ions and their locations in zeolite A. 相似文献
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碱性X分子筛催化甲苯与甲醇侧链烷基化自由基机理研究 总被引:3,自引:0,他引:3
苯乙烯是重要的工业原料,年消耗量约3000万吨。传统工艺中,苯乙烯由乙苯催化脱氢得到。由于传统工艺高能耗,高污染,甲苯与甲醇侧链烷基化合成苯乙烯引起了人们广泛关注,但是目前该路线进入工业化还有很多问题需要解决,甚至催化机理仍不明确。本文对甲苯侧链烷基化机理及提高反应选择性等方面进行了研究。采用离子交换法制备CsX分子筛,在固定床反应器上进行甲苯与氘代甲醇的同位素示踪实验和硝基甲苯的侧链烷基化实验,结合量子计算明确反应机理。采用IGA-002系统测定甲醇在CsX, KX和NaX上的等温吸附线,考察甲醇在分子筛不同笼结构中的吸附情况。将氘代甲苯与甲苯在CsX, KX和活性炭催化下进行氢氘交换实验,检验自由基在不同催化剂上的稳定性。以CO2为载气进行甲苯与甲醇侧链烷基化实验,考察CO2对反应的影响。甲苯与氘代甲醇进行侧链烷基化反应时,大多数氘出现在甲苯上,仅少数氘存在于苯乙烯及乙苯上,表明甲苯氢与甲醇的甲基氘进行了氢氘交换。量子化学计算表明,甲苯与甲醇的氢氘交换沿自由基路径的能垒远小于沿离子路径的。氘代实验和量子计算结果表明,甲苯侧链烷基化过程中存在自由基,但并不能证明侧链烷基化是自由基反应。为了验证甲苯侧链烷基化反应是否为自由基机理,以4-硝基甲苯(NO2-Ph-CH3)代替甲苯与甲醇进行侧链烷基化反应。硝基是强吸电子基团,能稳定苄基负离子,如果甲苯侧链烷基化是离子反应,硝基甲苯侧链烷基化产物收率会升高。另外,硝基又能与活泼自由基生成稳定自由基,若反应为自由基机理,则硝基甲苯不发生侧链烷基化反应。分析结果表明,反应液中不存在侧链烷基化产物,确定了甲苯侧链烷基化反应为自由基机理,而不是离子机理。热力学上甲醇更容易进行生成CO和H2等的副反应,从而减少CH3?与H?碰撞甲醇的几率。甲醇等温吸附线显示甲醇在NaX和KX上的吸附容量相近且远大于CsX上的,表明Cs+阻碍了甲醇进入X分子筛的β-笼。由于甲苯不能进入β-笼, NaX和KX的β-笼内甲醇与甲基自由基接触发生副反应。 CsX催化时Cs+阻碍甲醇进入β-笼而抑制了副反应的发生,提高了甲醇利用率。甲苯与氘代甲苯在CsX, KX和活性炭上进行氢氘交换,反应物用GC-MS分析。结果表明,在CsX上氢氘交换进行得更彻底,在活性炭上几乎没有氢氘交换。 X分子筛活化甲苯为自由基的效果优于活性炭,这可能是推拉效应造成的。当甲苯进入分子筛后, Lewis酸性阳离子与苯环络合并吸引电子,催化剂阴离子骨架与甲苯的甲基作用并供给电子,推电子与吸电子共同作用使甲苯更容易生成苄基自由基,并使其更稳定。 CsX对甲苯的活化作用强于KX,表明CsX的酸碱搭配更有助于甲苯生成自由基。这也是CsX催化甲苯与甲醇侧链烷基化效果优于KX的原因。以CO2替代N2作为载气能显著提高苯乙烯的选择性,这是由于CO2的存在降低了H?和CH3?的浓度,提高了?CH2OH的浓度。?CH2OH与甲苯生成苯乙烯, H?的减少降低了苯乙烯加氢生成乙苯。 相似文献
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银离子交换沸石Y修饰电极(Ag+-沸石Y)的循环伏安(CV)行为, 不同于溶液中的银离子在固体银电极表面上的CV行为. Ag+-沸石电极中银离子还原电位明显受沸石体内银簇影响. 依据Ag+-沸石修饰电极在含有能够与银离子形成难溶盐的电解质中的CV行为, 本文发现了沸石对溶液中阴离子具有尺寸选择效应, 并解释了银离子交换沸石修饰电极的循环伏安反应特性. 相似文献