ZSM-35分子筛催化剂用于正丁烯骨架异构的反应性能及失活再生研究

采用高硅铝比ZSM-35分子筛催化剂,在固定床连续反应器中进行了正丁烯骨架异构化稳定性试验,并采用氧气烧炭再生,利用TPO、BET、NH3-TPD、Py-IR等技术,对新鲜催化剂、不同反应时间后及再生的催化剂进行表征,研究了积炭对催化剂活性的影响。结果表明：正丁烯转化率为45%时,异丁烯选择性为95%,经过390 h的运行,异丁烯的收率仍能达到32%,该催化剂具有良好的稳定性及选择性,且再生性能良好。催化剂上积炭主要在反应初期形成,沉积在微孔内,且优先发生在强酸中心上,主要为难以烧除的类石墨炭。     

ZSM-35分子筛催化正丁烯骨架异构的反应性能及失活再生

采用高硅铝比ZSM-35分子筛催化剂,在固定床连续反应器中进行了正丁烯骨架异构化稳定性实验,并采用氧气烧炭再生,利用TPO、BET、NH3-TPD、Py-IR对新鲜催化剂、不同反应时间后及再生的催化剂进行表征,研究了积炭对催化剂活性的影响。结果表明,正丁烯转化率为45%时,异丁烯选择性为95%,经过390 h的运行,异丁烯的收率仍能达到32%,该催化剂具有良好的稳定性及选择性,且再生性能良好。催化剂上积炭主要在反应初期形成,沉积在微孔内,且优先发生在强酸中心上,主要为难以烧除的类石墨炭。     

正丁烯骨架异构镁碱沸石分子筛催化剂的研制与应用

采用水热合成法合成长条状大晶粒镁碱沸石分子筛,采用XRD、SEM及NH_3-TPD程序升温脱附进行表征,结果表明,实验室小试合成、中试放大及工业生产得到的3种分子筛物化指标基本一致,该分子筛催化剂在正丁烯骨架异构反应中均表现出高活性、高选择性和再生性能好等优点。工业应用结果表明,SC518催化剂在重时空速6 h~(-1)和异丁烯收率不低于30%条件下,工业装置运行中单程运行周期不小于43天,副产物收率小于1%。     

正丁烯骨架异构催化剂再生性能

采用小型固定床装置评价自制ZSM-35分子筛催化剂正丁烯骨架异构性能,在反应温度380℃、反应压力0.1 MPa和空速6.0 h-1条件下反应350 h,正丁烯转化率和异丁烯收率均大于35%,异丁烯选择性大于95%,副产物收率在反应进行至120 h时接近0,催化剂正丁烯骨架异构性能稳定。通过程序升温氧化表征研究催化剂积炭过程,采用程序升温氧化烧碳法对催化剂进行再生,采用XRD、NH3-TPD和BET等表征新鲜催化剂和三次再生催化剂的物化性能,结果表明,再生催化剂的物化性质几乎无变化,三次再生催化剂异构性能接近新鲜催化剂,催化剂再生性能良好。     

正丁烯在FER沸石上异构化催化制异丁烯的研究进展

本文综述了镁碱沸石的合成及其在正丁烯骨架异构催化制异丁烯中的研究进展,同时对反应机理作了简要讨论。重点评述了Mobil公司和Shell公司丁烯异构催化过程的专利文献。指出镁碱沸石是一种高效的直链烯烃骨架异构催化剂。     

ZSM-35分子筛催化剂催化正丁烯骨架异构工艺条件研究

采用水热法合成了ZSM-35分子筛,并成型制备成品催化剂。在小型固定床反应器上考察了反应温度、重时空速和原料中正丁烯浓度等对该催化剂的正丁烯骨架异构催化性能的影响,确定最佳工艺条件为:温度380℃,压力0.1 MPa,重时空速6 h-1,原料中正丁烯浓度50%~70%。在最佳工艺条件下,正丁烯骨架异构反应运行600 h后,异丁烯收率仍保持在25%以上,异丁烯选择性反应在25 h后即保持在90%以上,丙烯和重组分收率在反应120 h后接近0,催化剂异构性能良好。     

ZSM－35分子筛催化剂催化正丁烯骨架异构工艺条件研究

采用水热法合成了ZSM－35分子筛,并成型制备成品催化剂。在小型固定床反应器上考察了反应温度、重时空速和原料中正丁烯浓度等对该催化剂的正丁烯骨架异构催化性能的影响,确定最佳工艺条件为：温度380℃,压力0．1 MPa,重时空速6 h^－1,原料中正丁烯浓度50％～70％。在最佳工艺条件下,正丁烯骨架异构反应运行600 h后,异丁烯收率仍保持在25％以上,异丁烯选择性反应在25 h后即保持在90％以上,丙烯和重组分收率在反应120 h后接近0,催化剂异构性能良好。     

正丁烯骨架异构催化剂积碳失活研究

采用实验室自制ZSM-35分子筛催化剂,在小型固定床装置上进行正丁烯骨架异构反应评价,采用NH3-TPD、BET和TG等表征手段分析不同反应时间段催化剂的积碳类型和积碳量,结合表征结果探索催化剂的积碳过程。实验结果表明:催化剂上的大部分积碳在反应初期形成,尤其是高温积碳,导致酸量尤其强酸中心量迅速下降,且比表面积和比孔容不断减小,分子筛微孔堵塞严重,8元环孔道几乎完全被堵塞。     

多级孔ZSM-35分子筛催化正丁烯骨架异构的研究

采用二氧化硅调和方法对ZSM-35分子筛进行改性,对试样进行XRD、BET表征,利用固定床反应器评价考察了多级孔ZSM-35分子筛在正丁烯异构反应中的催化性能。试验结果表明:获得兼具微孔和介孔优势的多级孔分子筛可显著延长催化剂的使用寿命,并在异丁烯收率方面略有提高。     

混合分子筛催化正丁烯骨架异构制异丁烯反应性能

通过对比十元环分子筛SAPO-11和FER催化正丁烯骨架异构反应性能和不同装填方式对反应的影响。探讨了十元环分子筛孔道结构对生成异丁烯的影响。结果表明,具有一维的孔道结构SAPO-11分子筛的异丁烯选择性最好,具有二维孔道结构的FER分子筛更有利于异丁烯的自由扩散,产率高。     

The role of shape selectivity and intrinsic selectivity of acidic sites of the catalysts in the skeletal isomerization of n-butenes

The effect upon kinetic behaviour (activity and selectivity) of the physical properties (pore volume distribution) and acidic characteristics (nature of acidic sites and acidic strength distribution) of acidic catalysts in the skeletal isomerization of n-butenes has been studied. The catalysts studied are the following: γ-alumina, alumina modified by introduction of F, Cl and Br, silica–alumina, HZSM-5 zeolite-based catalyst and SAPO-34-based catalyst. It has been proven that the selectivity of acidic catalysts towards the skeletal isomerization of n-butenes is the result of a compromise between pore shape selectivity and intrinsic selectivity of the acidic sites of different strength, this latter property being more significant. Strong acidic sites are needed for the skeletal isomerization, but sites which are too strong produce important amounts of byproducts. A chlorinated alumina is a highly active and selective catalyst for skeletal isomerization. © 1998 SCI.     

Comparative study of the catalytic properties of ferrierite zeolite exchanged with alkaline earth metals in the skeletal isomerization of n-butene

Ferrierite zeolites ion exchanged with alkaline earth cations (Mg²⁺, Sr²⁺, Ba²⁺) were prepared and examined as catalysts for the skeletal isomerization of 1-butene. The samples were characterized by XRD, atomic absorption spectroscopy, ammonia TPD, FT-IR, BET/pore size distribution and pyridine chemisorption. The acidity studies indicated that acid strength increases in the order H⁺>Mg²⁺>Sr²⁺>Ba²⁺, therefore, the number of weak acid sites follows the opposite trend. At the same time, Brønsted acid sites associated with protons disappear and the number of Lewis acid sites increases with metal content. The presence of bulky cations like Mg²⁺, Sr²⁺, Ba²⁺ leads to a slight reduction of surface area and pore size. Ferrierites containing magnesium exhibit the highest isobutene yield. Lewis acid sites are responsible for improvement in catalyst stability as well as suppression of coke formation.     

Isobutene production from skeletal isomerization of 1-butene on WOx/ferrierite

Both potassium and ammonium ferrierite (FK and FA, respectively) were impregnated with tungsten species using either tungstic acid or ammonium metatungstate as precursors. The skeletal isomerization of 1-butene at 200–400°C, atmospheric pressure and 0.15 atm 1-butene partial pressure, was studied on samples with and without tungsten. Tungsten species on FK promote the isobutene formation while those species on FA generate a synergetic effect over the isobutene production. The presence of tungsten species improves the material stability and mainly, the isobutene yield. Starting the 1-butene feed over the catalytic bed at 200°C and then increasing the reaction temperature to 400°C, makes it possible to avoid the low isobutene selectivity at short times-on-stream. This revised version was published online in August 2006 with corrections to the Cover Date.     

Deactivation of ferrierite during the skeletal isomerization of linear butenes

Deactivation of ferrierite during the skeletal isomerization of 1-butene at atmospheric pressure and 0.15 atm 1-butene partial pressure was studied. At 300°C, the carbon content shows a sharp increase during the first 30 min-on-stream, with a slower growth thereafter. Temperature-programmed oxidation profiles corresponding to different times-on-stream are similar, showing two well-defined combustion peaks centered at about 325 and 640°C, respectively. When starting the 1-butene feed with the catalytic bed at 100 or 200°C and then increasing the temperature up to 300°C, no significant difference is observed, neither in carbon content nor in oxidation profiles. Important differences in the profiles are observed by comparing at the same time at each temperature. The lower the temperature, the higher the reactivity toward oxidation at low temperature. The carbonaceous deposit formed at 100°C shows the main combustion peak at the lowest temperature (135°C) and a more olefinic character; it could be related to a strong adsorption of reactant molecules. At 200°C, the proportion of saturated species associated to oligomers increases; while at 300°C, coke shows both aromatic and olefinic species.     

Monte Carlo simulation of xylene isomerization over zeolite catalysts

The isomerization reaction of xylene was simulated by means of the Monte Carlo method based on the experimentally observed parameters, including the diffusivity, equilibrium adsorption constant and intrinsic rate constant. The dependence of the product selectivity upon the Thiele modulus was examined and the results were satisfactorily consistent with those of the continuous model as well as the experiments. This suggests that the Monte Carlo method is helpful for investigating the nature of shape selectivity in zeolite-catalyzed reactions.     

Skeletal isomerization of octadecane on bifunctional ZSM-23 zeolite catalyst

Octadecane was isomerized over three different Pt/H-ZSM-23 samples. The distributions of methylheptadecane and dimethylheptadecane skeletal isomers obtained on the Pt/ZSM-23 samples were very similar. Positional isomer distributions are fingerprints of the zeolite framework structure. The independence of skeletal isomer distributions from Al-gradients and particle size constitutes a strong argument in favor of pore-mouth catalysis.     

Monte Carlo simulation of complex isomerization. I. Effect of diffusivity on product selectivity

A Monte Carlo method by which actual situations can be approached was developed. The complex isomerization A=B=C in a regular network was simulated, and the effects of intracrystalline diffusivities of molecules on the product selectivity were also investigated.     

Skeletal isomerization of 1-butene into isobutene over Mg-ZSM-22 modified by the deposition of silicon alkoxide

Mg-ZSM-22, modified by the deposition of silicon ethoxide, was prepared and investigated as a catalyst for the skeletal isomerization of 1-butene to isobutene in a fixed-bed flow reactor. The prepared catalysts were characterized by XRD, TPD, SEM-EDX, ICP and FT-IR. The deposition of silicon alkoxide on Mg-ZSM-22 led to a decrease in the amount of strong acid sites, confirmed by TPD experiments with ammonia and γ-collidine. The treatment also affected the size of pore opening, as evidenced by constraint index measurement and chemisorption experiment using -hexane. As the deposition time increased, the conversion of 1-butene decreased as the result of reduced acidity, while selectivity to isobutene increased. The deposition of silicon alkoxide resulted in the suppression of side reactions and coke deposition, thus enhancing the skeletal isomerization. The modification of Mg-ZSM-22 by deposition of silicon alkoxide was very effective in terms of catalytic stability and coke removal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Active copper species in 1-butene skeletal isomerization: comparison between copper-modified MCM-41 and beta catalysts

The role of copper was studied in the skeletal isomerization of 1-butene over copper-modified mesoporous MCM-41 molecular sieve and Beta zeolite. The Cu–H-MCM-41 and Cu–H-Beta catalysts were synthesized in our laboratory and characterized by XRD, nitrogen adsorption, X-ray fluorescence, FTIR of adsorbed pyridine and direct current plasma atomic emission spectrometry. The oxidation state of copper after oxidation and reduction in Cu–H-MCM-41 was evaluated by FTIR with probe molecules. Copper ion-exchanged and the proton forms of MCM-41 and Beta catalysts were tested towards 1-butene skeletal isomerization by varying the weight hourly space velocity and temperature. Quantum chemical calculations at the B3LYP/6-31 + G^** level were performed in order to understand the role of copper at the molecular level.

Copper in Cu–H-MCM-41 pretreated in synthetic air was mostly in the form of Cu²⁺ but reduced during the catalytic experiment to the metallic form Cu⁰ via Cu⁺. Even if the copper exchange decreased the amount of Brønsted acid sites, Cu–H-MCM-41 pretreated in synthetic air was more active than H-MCM-41 towards 1-butene skeletal isomerization. The enhanced catalytic activity is due to copper Cu⁺, which was formed during the reaction. Introduction of copper into H-Beta, however, did not have any effect at all on the performance of the catalyst. The probable reason for this is the high initial activity of copper-modified H-Beta causing a very fast reduction of copper to the inactive metallic form Cu⁰.