首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
碱金属盐对ZSM-5分子筛晶化的影响   总被引:7,自引:0,他引:7       下载免费PDF全文
Effect of different alkali metal salts on the crystal size and the crystallization rate of ZSM-5 zeolite was de-tailedly investigated in this paper. The samples prepared by adding the different alkali metal salts were character-ized by using XRD, TEM, TG-DSC, BET and IR techniques. The XRD results showed that, for the nanosized ZSM-5 zeolite, the characteristic peaks broadened on the XRD patterns in comparison with the microsized ZSM-5 zeolite. The SEM results verified that the crystal size of zeolites prepared by adding different alkali metal salts had different results, and adding NaCl, NaC2H3O2 and KCl showed the better effect of reducing crystal size, which are about of 40~60nm size. The crystallization curve of adding the different alkali metal salts suggested that the crystallization rate was significantly affected by the anions in the alkali metal salt besides the cations. Moreover, the crystal size likewise depended on the anion in the alkali metal salt. In addition, the BET results suggested that the nanosized ZSM-5 zeolite possessed a larger outer surface area in comparison with the microsized ZSM-5 zeolite. The thermostability of the samples was determined by TG-DSC technique, indicating that the nanosized ZSM-5 zeolite had a poor thermostability as compared with the microsized ZSM-5 zeolite. The possible difference of the samples with different crystal sizes on IR spectra was also given.  相似文献   

2.
The carbon nanotubes-coated cordierite (CNTs-cordierite) was fabricated by pyrolysis of ethine on cordierite with iron catalyst, which was penetrated into the cordierite substrate by vacuum impregnation. The cordierite substrate, carbon naontubes, and CNTs-cordierite were characterized by SEM. TEM/HREM. BET, and TGA. The results show that the carbon nanotubes were distributed uniformly on the surface of cordierite. A significant increase in BET surface area and pore volume was observed, and a suitable pore-size distribution was obtained. On the CNTs-cordierite, carbon nanotubes penetrated into the cordierite substrate, which led to a remarkable stability of the CNTs against ultrasound maltreatment. Growth time is an important factor for thermostability and texture of the sample. The mass increased but the purity decreased with the growth time, which caused the exothermic peak shift to low temperature, and the corresponding full width half maximum (FWHM) of the peak in DTG increased.  相似文献   

3.
微波场中A型分子筛及分子筛膜合成的研究   总被引:8,自引:0,他引:8  
Effects of aging time and alkalinity as well as cation concentration(Na+) on the synthesis of A type zeolite and zeolite membrane were investigated in this paper. The results showed that aging time for synthesis of A type zeolite and zeolite membrane had remarkable influence and alkalinity could accelerate the formation of zeolite but was disadvantage to zeolite membrane synthesis. Cation concentration(Na+) also couldn′t accelerate the synthesis of zeolite and zeolite membrane but it was probable an important factor to accelerate crystal growth .Moreover, more compact zeolite membranes could be synthesized by this method while the thickness of membrane was thinner than that of convention. Zeolites and zeolite membranes were characterized by XRD, TEM as well as IR characterization techniques.  相似文献   

4.
Carbon deposition during methanol to hydrocarbons leads to the quick deactivation of ZSM-5 catalyst and it is one of the major problems for this technology. Decreasing the crystal size or introducing mesopores into ZSM-5 zeolites can improve its diffusion property and decrease the coke formation. In this paper, nano-sized ZSM-5 zeolite with intercrystalline mesopores combining the mesoporous and nanosized structure was fabricated. For comparison, the mesoporous ZSM-5 and nano-sized ZSM-5 were also prepared. These catalyst samples were characterized by XRD, BET, NH3-TPD, TEM, Py-IR and TG techniques and used on the conversion of methanol to gasoline in a fixed-bed reactor at T = 405 °C, WHSV = 4.74 h-1and P = 1.0 MPa. It was found that the external surface area of the nano-sized ZSM-5 zeolite with intercrystalline mesopores reached 104 m2/g, larger than that of mesoporous ZSM-5(66 m2/g) and nanosized ZSM-5(76 m2/g). Catalytic lifetime of the nano-sized ZSM-5 zeolite with intercrystalline mesopores was 93 h, which was only longer than that of mesoporous ZSM-5(86 h), but shorter than that of nanosized ZSM-5(104 h). Strong acidity promoted the coke formation and thus decreased the catalytic lifetime of the nano-sized ZSM-5 zeolite with intercrystalline mesopores though it presented large external surface that could improve the diffusion property. The special zeolite catalyst was further dealuminated to decrease the strong acidity. After this, its coke formation rate was slowed and catalytic lifetime was prolonged to 106 h because of the large external surface area and decreased weak acidity. This special structural zeolite is a potential catalyst for methanol to gasoline reaction.  相似文献   

5.
A novel EVA/unmodified nano-magnesium hydroxide(NMH)/silicone rubber ternary nanocomposite was prepared by using a special compound flame retardant of NMH and silicone rubber(CFR).The flammability of the ternary composite was studied by cone calorimeter test(CCT).Synergistic effect on flame retardancy was found between silicone rubber and NMH.EVA/CFR ternary nanocomposite showed the lowest peak heat release rate(PHRR)and mass loss rate (MLR)among the samples of virgin EVA,EVA composites.The synergistic flame retardancy of silicone rubber and NMH in EVA system is attributed to the enhanced char layers in the condensed phase that prevents the heat and mass transfer in the fire.  相似文献   

6.
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   

7.
吕春祥 《高分子科学》2010,28(3):367-376
<正>Thermal properties of acrylonitrile(AN)-acrylamide(AM) copolymers for carbon fibers were studied by DSC and in situ FTIR techniques in nitrogen(N_2) and air flows.The cyclization mechanism and stabilization behavior of polyacrylonitrile(PAN) were discussed.In N_2 flow,it was found that AM had the ability to initiate and accelerate cyclization process,which was confirmed by the fact that the initiation of nitriles shifted to a lower temperature.Compared to AN homopolymer,the initiation temperature of cyclization was ahead 32 K by introducing 3.59 mol%AM into the copolymer.The exothermic reaction was relaxed due to the presence of two separated exothermic peaks.Accompanied by DSC,in situ FTIR and calculation of activation energy,the two peaks were proved to be caused by ionic cyclization and free radical cyclization,respectively,and the corresponding cyclization mechanism was proposed.With increasing in AM content,the ionic cyclization tends to be dominant and the total heat liberated first increases and then decreases.For AN homopolymer,the activation energy of cyclization is 179 kJ/mol.For AN-AM copolymer(containing 3.59 mol%AM),the activation energy of ionic cyclization is 96 kJ/mol and that of free radical cyclization is 338 kJ/mol.In air flow,similar cyclization routes occur and the difference is the contribution of oxidation.The oxygen in environment has no remarkable effect on cyclization of AN homopolymer but retards the cyclization of AN-AM copolymers.For AN-AM copolymer with 3.59 mol%AM,the cyclization temperature is postponed 10℃in air.  相似文献   

8.
A series of 3. OMo/(Hβ γ-Al2O3) samples with γ-Al2O3 contents in the range of 0-100% (mass fraction) was studied by means of XRD, NH3-TPD, TPR and BET determinations for characterizing their structures. The Hβ zeolite structure in the 3.0Mo/Hβ sample can be effectively stabilized by adding some γ-Al2O3 to Hβ zeolite. γ-Al2O3 mainly favors the formation of polymolybdate or multilayered Mo oxide, while Hβ mainly forms the Al2(MoO4)3 species, as evaluated by the TPR technique. When used as the catalyst for the metathesis of butylene-2 and ethylene to propylene, there exists a close correlation between the specific surface area and stability of the catalyst. The specific surface area of the catalyst shows the maximum when (Hβ γ-Al2O3) contains 30%γ-Al2O3, which is in agreement with that of the time needed for the reaction stablization. In the case of maximum surface area, the rate of coke deposition is the minimum.  相似文献   

9.
The thermal decomposition behavior and nonisothermal reaction kinetics of the double-base gun propellants containing the mixed ester of triethyleneglycol dinitrate(TEGDN) and nitroglycerin(NG) were investigated by thermogravimetry(TG) and differential thermogravimetry(DTG), and differential scanning calorimetry(DSC) under the high-pressure dynamic ambience. The results show that the thermal decomposition processes of the mixed nitric ester gun propellants have two mass-loss stages. Nitric ester evaporates and decomposes in the first stage, and nitrocellulose and centralite II(C2) decompose in the second stage. The mass loss, the DTG peak points, and the terminated temperatures of the two stages are changeable with the difference of the mass ratio of TEGDN to NG. There is only one obvious exothermic peak in the DSC curves under the different pressures. With the increase in the furnace pressure, the peak temperature decreases, and the decomposition heat increases. With the increase in the content of TEGDN, the decomposition heat decreases at 0.1 MPa and rises at high pressure. The variety of mass ratio of TEGDN to NG makes few effect on the exothermic peak temperatures in the DSC curves at different pressures. The kinetic equation of the main exothermal decomposition reaction of the gun propellant TG0601 was determined as: dα/dt=1021.59(1-α)3e-2.60×104/T. The reaction mechanism of the process can be classified as chemical reaction. The critical temperatures of the thermal explosion(Tbe and Tbp) obtained from the onset temperature(Te) and the peak temperature(Tp) are 456.46 and 473.40 K, respectively. ΔS≠, ΔH≠, and ΔG≠ of the decomposition reaction are 163.57 J·mol^-1·K^-1, 209.54 kJ·mol^-1, and 133.55 kJ·mol^-1, respectively.  相似文献   

10.
The composite ZSM—5 zeolite/vermiculite catalyst,in which tiny ZSM—5 zeolite parti-cles embedded in the vermiculite substrate,has been synthesized by hydrothermal method with vermiculite assilicon source.The catalytic behavior of resulting catalyst for xylene isomerization,propylene aromatizationand toluene disproportionation is better than that of HZSM—5 zeolite.  相似文献   

11.
高硅无铝Mo-Beta沸石的合成与结构表征   总被引:2,自引:0,他引:2  
用水热晶化法合成了无铝Mo-Beta沸石,讨论了合成条件对无铝Mo-Beta沸石晶化的影响,通过化学分析、XRD、IR、DTA/TGA、TEM、NMR、ICP和UV-Vis紫外漫反射光谱测定了样品的n(SiO2)/n(MoO3)比,并对其结构进行了表征,结果表明,所合成的Mo-Beta沸石晶粒均匀,Mo存在于沸石骨架中,由于Mo的掺入,引起Beta沸石红外光谱、差热分析曲线及晶胞参数, 29SiMASNMR谱等发生变化。  相似文献   

12.
ERB-1分子筛的合成与表征   总被引:2,自引:0,他引:2  
 分别以白炭黑、硼酸和氢氧化钠为硅源、硼源和碱源,以六亚甲基亚胺为模板剂,系统地研究了硅硼比、碱量、模板剂用量和水量对合成ERB-1分子筛的影响,并采用N2物理吸附、吸附NH3的程序升温脱附、热重和差热分析、 X射线衍射和傅里叶变换红外光谱等手段对样品的表面性质、酸性和热稳定性进行了表征. 结果表明,合成ERB-1分子筛较好的原料组成为 n(SiO2)/n(B2O3)=0.6~2, n(H2O)/n(SiO2)=40, n(NaOH)/n(SiO2)=0.1~0.2和n(HMI)/n(SiO2)=0.8~1; ERB-1分子筛上的酸中心以弱酸为主,且酸强度较低; ERB-1的结构在800 ℃以下保持稳定.  相似文献   

13.
一种新型共生沸石(T-L)的合成与表征   总被引:2,自引:0,他引:2  
在Na2O-K2O-Al2O3-SiO2-H2O体系中水热合成了一种新型的共生沸石, 它由L型沸石生长在T型沸石的一端而形成, 称之为T-L型沸石. 通过XRD, SEM, TEM, EDX, IR等手段对其进行了初步的表征. SEM相片表明这种沸石具有特殊的铆钉状外形; 在TEM相片上可以清楚地看到L型沸石的大孔道, 此孔道与L型沸石的表面垂直. 通过EDX的数据计算发现共生沸石的两相有不同的骨架硅铝比: T型沸石部分Si/Al=3.71, L型沸石部分Si/Al=3.41. 在该样品中B酸大于L酸.  相似文献   

14.
徐孝文汪靖  龙英才 《中国化学》2006,24(12):1725-1730
Tin dioxide (SnO2) nano-particles were prepared on high silica TON, MFI and FAU type zeolites by impregnation of SnC12 solution and subsequent calcination at 873 K. XRD and SAED were used to characterize the crystalline phase, and TEM was used to characterize the morphology, the particle size and the agglomerative state of the formed nano-materials. The nano-particles, which possess 8 nm, 10-80 nm and 6 nm in size, were found to form on the outer surface of TON, MFI and FAU zeolites, respectively. SnO2 microcapsules and SnOz netlike nanostructure were obtained by decomposition of SnO2-TON and SnO2-MFI in 40% hydrofluoric acid at room temperature. Compared with the nano-particles formed on NaY zeolite, the special morphology and the agglomerative state of SnO2 nanostructures on TON and MFI type zeolites with one and two dimension channel system indicate that the heterogeneous framework, surface structure and property perform important function for forming and growing SnO2 nanostructure on the outer surface of the zeolites.  相似文献   

15.
16.
用(NH_4)_3AlF_6溶液对Y型沸石进行铝化,得到了不同硅铝比的铝化Y型沸石。XRD实验表明Al原子进入Y型沸石骨架,晶胞常数α_0增大,而且晶胞常数α_0的增大与铝化程度有一定的关系。铝化Y型沸石的吸附量略有降低。IR研究表明,骨架振动,表面羟基谱峰变化不明显。在铝化Y型沸石上存在B酸和L酸,其主要是B酸中心。  相似文献   

17.
乙苯工艺技术开发及工业应用进展   总被引:1,自引:0,他引:1  
乙苯是重要的基本有机化工原料,主要用于生产苯乙烯,进而作为合成橡胶和塑料等高分子材料的单体.乙苯的生产主要采用苯和乙烯的烷基化工艺.传统的AlCl3法由于存在设备腐蚀和环境污染等问题己逐步被环境友好的分子筛烷基化法取代.分子筛烷基化法分为气相法和液相法.气相烷基化催化剂为ZSM-5分子筛,例如Mobil-Badger气相烷基化工艺;液相烷基化催化剂有Y,Beta和MCM-22分子筛,例如Lummus/UOP的EBOne工艺和Mobil-Raythen的EBMax工艺.近年来,随着经济的发展,全球范围内乙苯需求量逐年增加,产能也逐渐扩大.尤其在中国大陆,目前乙苯产能居世界首位,其乙苯工艺技术的开发也最为活跃.经过20多年的发展,苯烷基化制乙苯工艺取得了长足发展.中国科学院大连化学物理研究所在成功合成ZSM-5/ZSM-11分子筛的基础上,与中国石化、中国石油联合开发了苯与干气气相烷基化制乙苯工艺;中国石化上海石油化工研究院则以ZSM-5分子筛为基础,开发了适应原料多样性的苯气相烷基化制乙苯催化剂和工艺技术,可以采用石油苯、焦化苯、纯乙烯、乙醇和稀乙烯为原料;石油化工科学研究院则开发了基于Beta分子筛的苯与乙烯液相烷基化催化剂及液相循环烷基化工艺.以上催化剂及工艺技术均己工业化应用.此外,实现催化烷基化与分离同时进行的催化蒸馏工艺以及乙烷脱氢再与苯烷基化的两段法制乙苯工艺的研究也取得了一定进展.在苯烷基化制乙苯工艺中,气相法操作温度高,苯与乙烯进料摩尔比高,因而能耗高,同时二甲苯含量高,产品纯度低.液相烷基化工艺则具有温度低和苯/烯比低的特点,其能耗控制及产品质量均优于气相法工艺.但是,液相反应中的扩散阻力大,孔道为10元环的ZSM-5分子筛失活迅速,因而选用了具有12元环孔道的Y,Beta和具有表面12元环碗状半超笼的MCM-22分子筛为催化剂.然而,液相法工艺的苯与乙烯进料摩尔比仍然远高于理论化学计量比,其产品中含有一定比例的多乙基苯(主要是二乙苯),需采用烷基转移过程将多乙基苯与苯反应生成乙苯.进一步降低苯/烯比、提高单乙苯选择性是未来乙苯工艺开发的努力方向.研究表明,介孔分子筛及纳米片状分子筛在苯烷基化反应中具有优于常规分子筛的催化表现,即更高的乙烯转化率和乙苯选择性.其原因在于,扩散是影响苯烷基化反应性能的关键因素,扩散性能的改善使得产物从活性位解吸后更容易扩散出去,进而空出活性位并进一步催化新的底物.同时,单烷基化产物与新的烷基化试剂进一步发生烷基化的几率降低,提高了单烷基化产物的选择性.因而,采用扩散性能更好的催化剂催化苯烷基化反应前景看好,关键问题在于如何简单并廉价地获取该类材料.另外,虽然分子筛催化苯烷基化是一个环境友好的工艺过程,但是在分子筛催化剂制备过程中会产生环境污染.同时,失活催化剂的处理也是需要考虑的问题.开发分子筛的绿色合成技术,减轻甚至消除环境污染是一个值得努力的方向;开发失活催化剂的综合利用技术,如采用失活催化剂为原料用于分子筛的合成,可以作为环境保护的有效手段.  相似文献   

18.
通过优化水热陈化条件制备纳米L沸石,再采用水热合成结合原位二次晶化法,合成具有微-介复合孔结构的高效ZSM-5-L二元复合分子筛.考察了体系pH、二次晶化温度等因素对ZSM-5-L复合分子筛合成的影响,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和傅里叶变换红外光谱(FTIR)等技术对复合分子筛进行表征,确定了最佳复合条件:pH=10.5~11.5,晶化温度170℃,晶化时间24 h.ZSM-5-L复合分子筛具有不同于ZSM-5沸石、L沸石及两者机械混合物的物性特征,且具有微-介复合孔结构.以正戊烷催化转化为探针反应,评价了ZSM-5-L复合分子筛轻烃芳构化反应性能.在相同反应条件下,ZSM-5-L复合分子筛具有优于2种单分子筛及二者机械混合物的正戊烷芳构化催化性能.  相似文献   

19.
程志林  万惠霖刘赞 《中国化学》2004,22(12):1454-1455
Zeolite A rods by self-assembly of zeolite A microcrystal were successfully synthesized by microwave-assisted hydrotherrnal synthesis. The average size of zeolite crystals consisting of self-assembling materials was about 300 nm and the length of zeolite rods was in the range of 15--30μm.  相似文献   

20.
Two mixed-matrix NiMo/Al2O3 catalysts containing nano-and micro-sized zeolite Y have been prepared to explore the size effect of zeolite Y particle on the hydrodesulfurization(HDS)and hydrodenitrogenation(HDN)activities of fluid catalytic cracking(FCC)diesel.They were characterized by SEM,BET,XRD,H2-TPR,NH3-TPD and HRTEM.The results show that the catalyst containing nano-sized zeolite Y possesses larger average pore diameter,higher pore volume,weaker and lesser acid sites,more easily reducible metal phases,shorter MoS2 slabs and more slab layers than the catalyst containing micro-sized zeolite Y.The catalysts were also evaluated with a high-pressure fixed-bed reactor using real FCC diesel as feed.The results display that the catalyst containing nano-sized zeolite Y bears higher HDS and HDN activities and exhibits higher relative rate constant for the removal of total sulfur or nitrogen than the one containing micro-sized zeolite.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号