Transformation of ethanol into hydrocarbons on ZSM-5 zeolites modified with iron in different ways

ZSM-5 zeolites modified by iron incorporation through post-synthesis ion exchange and those synthesized with iron addition to the synthesis medium were compared in the reaction of liquid hydrocarbons production from ethanol. AA, TPR, FTIR, XRD, SEM, nitrogen adsorption and photoacoustic spectroscopy were used for the samples characterization. Acid leaching and ammonium exchange were tested for obtaining the acid form of the zeolite, with similar results, the major difference being a faster deactivation in the latter case. The best yield of liquid hydrocarbons was obtained with the samples with low iron content. The product distribution in both gaseous and liquid phases was independent of the way the zeolite was obtained or the iron was introduced, with major variations only with time (due to deactivation).     

Effect of crystal size and surface modification of ZSM-5 zeolites on conversion of ethanol to propylene

The conversion of ethanol to propylene was carried out over ZSM-5 zeolites (Si/Al ratio ≈ 20) with a small crystal size of ca. 30 nm. Catalyst deactivation was significantly suppressed over the nanometer-sized ZSM-5 zeolite, indicating that the small crystal was more tolerant to coking. On the other hand, the selectivity of this zeolite to propylene was lower than that of conventional ZSM-5 zeolites (ca. 2 μm). It was suggested that the large external surface area of the nanometer-sized ZSM-5 zeolite catalyzed undesired reactions. To elucidate the reason for the decreased selectivity, the external surfaces of the nanometer-sized crystals were covered with a very thin pure-silica ZSM-5 layer by a hydrothermal synthesis. The obtained crystal maintained the same crystal size and had a silica-rich surface (Si/Al ratio ≈ 50). After the surface modification, the selectivity to propylene was improved without any decrease in the catalyst life.     

A LUMPED KINETIC MODEL FOR DEHYDRATION OF ETHANOL TO HYDROCARBONS OVER HZSM-5

A kinetic model for the conversion of ethanol to hydrocarbons over HZSM-5 catalyst has been developed. The model is based on data from ethanol dehydration experiments conducted in a fixed-bed integral reactor at atmospheric pressure and temperatures of 150°C to 360°C, and is the first which integrates the major reaction pathways of both dehydration and higher hydrocarbon formation over ZSM-5 zeolite. In the model C₃-C₆ olefins, C₃-C₅ paraffins, and C₆⁺ hydrocarbons are treated as lumped species, while ethanol, diethyl ether, ethylene, and ethane are treated individually. Nonlinear parameter estimation using quasilinearization and least squares as the objective function has been implemented to estimate rate constants, adsorption equilibrium constants, and activation energies. The Langmuir-Hinshelwood rate expressions successfully correlated the experimental data.     

甲醇制烃催化剂及其反应机理研究进展

综述了改性和非改性ZSM-5、β和SAPO-34等多种催化剂在甲醇制烃类物质中的应用。ZSM-5主要用于甲醇制汽油过程以及甲醇芳构化反应,甲醇在β沸石上主要转化成乙烯、丙烯、丙烷、异丁烷、六甲基苯和少量五甲基苯,而SAPO-34对乙烯和丙烯等低碳烯烃具有较高的选择性（90%）。总结了甲醇制烃机理的研究进展,主要包括初始C—C的形成以及烃池物种的研究,讨论了甲醇制烃催化剂及其研究方向。     

Nitrous oxide as an oxidant for ethane oxydehydrogenation

Waste nitrous oxide was used as an oxidant for ethane oxydehydrogenation performed at the range of temperature from 350 to 450 °C over iron modified zeolite catalysts. Different zeolite matrices (zeolite ZSM-5 of different Si/Al ratio, H-Y, mordenite) modified with iron cations introduced into zeolite by means of ionic exchange were applied as catalysts for the reaction under study. Additionally, amorphous silica and alumina silica as well as silicalite of MFI structure were also used as a matrix for iron ions accommodation and they were tested for oxydehydrogenation reaction. It was found that only iron modified zeolites showed activity for reaction under study. Amorphous oxide supports and crystalline neutral silicalite modified with iron cations by means of impregnation were completely inactive for oxydehydrogenation reaction. The best catalytic performance was found on iron modified zeolites of MFI structure. The Si/Al ratio of the ZSM-5 matrix influenced the activity for ethane oxydehydrogenation reaction insignificantly. N₂O oxidant was partly utilized for ethane oxidation (towards ethene or carbon oxides), while some part of the oxidant was decomposed to nitrogen and oxygen. Performing the reaction at 450 °C resulted in a high ethene yield and complete N₂O removal.     

轻烃低温芳构化制取高辛烷值汽油

考察了反应温度、空速和高径比条件对轻烃在分子筛催化剂上低温芳构化制取高辛烷值汽油性能的影响。结果表明,反应温度和空速对催化剂的催化性能有明显影响,提高反应温度有利于提高芳烃收率,增加进料空速,催化剂芳构化性能下降,芳烃二次反应也减少。在450 ℃、1.0 h^-1和高径比为6.0的条件下,此轻烃在ZSM-5催化剂作用下,可得到高辛烷值汽油,其初馏点为49 ℃,干点为203 ℃,烯烃质量分数为13.42%,芳烃质量分数为84.24%,辛烷值为101,可作汽油调和组分,也可直接作汽油使用。     

Production of Propylene from Ethanol Over ZSM-5 Zeolites

In this work, we studied the conversion of ethanol to propylene over ZSM-5 zeolites. The catalytic performance of H-ZSM-5 (Si/Al₂ = 30, 80, and 280) and ZSM-5 (Si/Al₂ = 80) modified with various metals was investigated. H-ZSM-5(Si/Al₂ = 80) afforded high propylene yield, which indicates that a moderate surface acidity favored propylene production. Zr-modified ZSM-5(80) gave the highest yield (32%) of propylene at 773 K. Furthermore, the catalytic stability of the zeolite was improved by the modification of zirconium. The surface acidity and the presence of metal ions played important roles on the production of propylene.     

ZSM-5/MCM-41复合分子筛的制备及对乙醇脱水的催化活性

以微孔ZSM-5分子筛为母体,采用NaOH溶液对其进行预处理,再在水热条件下以十六烷基三甲基溴化铵（CTMAB）为模板剂制备了ZSM-5/MCM-41介微孔复合分子筛,考察了预处理温度、晶化温度等因素对复合分子筛结构和形貌的影响。进一步考察了该复合分子筛催化剂在乙醇脱水反应中的催化活性。结果表明,ZSM-5分子筛在2.0 mol/L NaOH溶液中于110℃预处理20 h,再于110℃水热晶化20 h制备的分子筛具有良好的介微孔复合结构;该复合分子筛经NH4NO3溶液离子交换制备的氢型催化剂在乙醇脱水催化反应中表现出良好的性能。当乙醇WHSV=0.5 h-1时,最佳反应温度为240～255℃,乙醇转化率〉99%,乙烯选择性〉96%。     

以TPABr为模板剂的ZSM-5分子筛膜的合成与表征

以四丙基溴化铵(TPABr)为模板剂,直接在多孔的α-A1_2O_3陶瓷管外表面,经过重复合成制得了渗透通量较大的ZSM-5沸石分子筛膜。以合成ZSM-5沸石的DTA/TGA分析结果为依据,确定了去除ZSM-5沸石膜中模板剂的热处理制度。用X R D和S E M对Z S M-5沸石分子筛膜进行了表征,膜的分离因子用单一的氢气和氮气的渗透通量的比值表示。X RD分析表明陶瓷基质表面的膜层是ZSM-5沸石晶相,S E M结果显示合成的沸石膜层晶体相互交连,形成一种连续的多晶层,厚度约10μm。H_2、N_2对分子筛膜的气体渗透表明,合成的ZSM-5沸石膜的H_2/N_2理想分离因子为2.87。     

Production of high-octane gasoline from straight-run gasoline on ZSM-5 modified zeolites

The acid and catalytic properties of ZSM-5 zeolites modified with tungsten heteropolycompounds were studied in the process of production of high-octane gasoline from straight-run gasoline. It was shown that introducing cobalt tungsten-bismuthate, cobalt tungsten-phosphate, and iron tungsten-phosphate heteropolycompounds in zeolite in amount of 1–3 wt % makes it possible to increase the yield of high-octane gasoline by 5–10% and that of alkyl aromatic hydrocarbons by 5–7% from straight-run gasoline compared to initial H-ZKE-G zeolite. The interrelation between acid and catalytic properties of zeolite catalysts modified with cobalt tungsten-bismuthate, cobalt tungsten-phosphate, and iron tungsten-phosphate heteropolycompounds was established for the process of producing high-octane gasoline from straight-run gasoline.     

Mn and Zn doped ZSM-5 zeolite catalysts

Manganese was incorporated into a ZSM-5 zeolite by a special impregnation method which practically prevented the deposition of the metal ions on the internal surface of the zeolite pores. As a result, the production of light olefins increased sharply while that of aromatics did not significantly change. The double incorporation of Zn (by ion-exchange) and of Mn (by this impregnation technique) led to catalysts which could produce more aromatics and more light olefins (mainly ethylene and propylene) than the parent ZSM-5 zeolite.     

Direct Hydrothermal Conversion of High-Silica Faujausite and Zeolite β to ZSM-5 and Its Catalytic Performance

In the absence of a structure-directing organic molecule, aluminosilicate ZSM-5 is produced directly from high-silica zeolite Y or zeolite by a simple hydrothermal treatment of the alkali metal hydroxide-treated starting zeolite material. NMR and FTIR results clearly suggest that the majority of the Al(III) species is present in the framework yielding Brønsted acid sites. Addition of an appropriate organic molecule such as tetrapropylammonium bromide or tetrabutylammonium bromide facilitates the formation of ZSM-5 and ZSM-11, respectively. The protonated form of all the ZSM-5 catalysts shows very good catalytic activity for the conversion of methanol to hydrocarbon.     

Fischer–Tropsch Synthesis Using Zeolite-supported Iron Catalysts for the Production of Light Hydrocarbons

Fischer–Tropsch synthesis (FTS) for the production of olefins from syngas was investigated on FeCuK impregnated on zeolite catalysts such as ZSM-5, Mordenite and Beta-zeolite. ZSM-5 supported catalyst showed the best activity among the three catalysts due to the high reducibility of iron oxides. It also exhibited high olefin selectivity compared to a catalyst prepared by physical mixing of the two components, due to the presence of moderate number of acid sites.     

磷改性ZSM-5分子筛物化性质和裂解制乙烯性能的研究

The physicochemical features of phosphorus-modified ZSM-5 zeolites (SiO2/Al2O3 molar ratio is 25) were characterized by XRD(X-ray diffraction), BET(Brunauer, Emmett and Teller spcific surface area measurement), NH3-TPD(ammonia temperature-programmed desorption) and MASNMR(magic angle spinning nuclear magnetic resonance), and the performance on catalytic pyrolysis to produce ethylene was investigated with a light hydrocarbon fixed bed micro-reactor with n-octane as feed. The results show that the acid site density, acid intensity and hydrothermal stability of ZSM-5 zeolite were improved by phosphorus modification. When P205 content in ZSM-5 zeolite is higher than 2.5%, phosphorus modification can prevent ZSM-5 zeolite crystal structure transformation from orthorhombic to monoclinic. In addition, the dealumination of ZSM-5 zeolite framework was moderated by phosphorus modification under high temperature hydrothermal treatment. The results of n-octane pyrolysis on phosphorus-modified ZSM-5 zeolites show that ethylene yields of zeolites with different phosphorus content are almost the same under the same n-octane conversion. However, the modified zeolites with higher pyrolysis activity give lower yield of propene, butene and total olefin than lower pyrolysis activity under the same n-octane conversion.     

Storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere by the sealing of the micropore outlet

The storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere was examined by hydrogen filling into the micropore and the following sealing of the micropore outlet to prevent the release of hydrogen to the outside. The surface grafting of 1,4-bis(hydroxydimethylsilyl)benzene onto ZSM-5 zeolite was applied to the sealing of the micropore outlet. Pressurized hydrogen (10 MPa) was filled into the micropore of ZSM-5 at liquid nitrogen temperature (−196 °C), and then the sample was heated at 150 °C for forming strong binding between the zeolite surface and the disilane compound under the hydrogen pressure. The hydrogen sorption isotherm at −196 °C showed that the adsorption of hydrogen onto the disilane-grafted ZSM-5 thus obtained was reduced to less than 20% from the original ZSM-5. The remarkable hysteresis between the adsorption and desorption branches of the isotherm indicated that the kinetic trap of hydrogen occurred by the narrowed outlets of the micropores of ZSM-5 with the disilane compound. Even after exposing the disilane-grafted ZSM-5 to the atmosphere over a few months, hydrogen could be discharged by heating over 150 °C. This result demonstrated that molecular hydrogen was successfully stored into ZSM-5 zeolite in the ambient atmosphere for a long time.     

Control of acid-site location of ZSM-5 zeolite membrane and its application to the MTO reaction

ZSM-5 zeolite membrane, which shows high selectivity toward olefins in the methanol conversion, was developed by controlling the location of the acid sites. First, the ZSM-5 zeolite catalyst membrane without pinholes was successfully prepared by synthesizing a ZSM-5 zeolite layer on an outer surface of a cylindrical alumina ceramic filter. The membrane was used as the catalytic membrane reactor to recover olefins from methanol. Though the olefins were successfully produced from methanol with high selectivity (ca. 80%), production of paraffin and aromatics was observed at the feed side of the zeolite membrane. To prevent the such production, the location of the acid site of the ZSM-5 zeolite membrane was controlled by a new method called the catalytic cracking of silane (CCS) method. Selective deactivation of acid sites at the outer surface of the zeolite membrane (feed side of reactant) by the CCS method allowed us to increase the selectivity of the olefins by 10% as compared to the untreated membrane.     

Visible light photoreduction of Cr(VI) in aqueous solution using iron-containing zeolite tubes

In this study, a novel visible light photocatalyst consisting of iron-loaded zeolite tubes was designed to reduce Cr(VI) to Cr(III) in aqueous solution. Iron was incorporated into hollow, porous ZSM-5 tubes using two different methods. In the first method, the iron-encapsulated ZSM-5 tubes were prepared by introducing iron into the mesoporous silica template prior to the formation of the hollow ZSM-5 tubes resulting in an encapsulated iron species. In the second method, iron was ion-exchanged into the ZSM-5 shell during a post-synthesis treatment. The iron-loaded ZSM-5 structures were extensively characterized by powder X-ray diffraction (XRD), elemental analysis, solid-state ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR), electron paramagnetic resonance (EPR), electron microscopy with energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy (XPS). The iron in the iron-exchanged ZSM-5 tubes tended to aggregate compared to the iron in the iron-encapsulated ZSM-5 tubes. Both the iron encapsulated and iron-exchanged ZSM-5 hollow tubes were active for the visible light photoreduction of Cr(VI) to Cr(III) in aqueous solution. The iron-exchanged ZSM-5 tubes were very active initially but suffered from substantial iron leaching after the first use in aqueous Cr(VI) photoreduction relative to the iron-encapsulated ZSM-5 tubes which showed very little leaching of the iron.     

SELECTIVE FORMATION OF ALKYLAROMATICS OVER ZEOLITE CATALYSTS: ALKYLATION OF TOLUENE WITH ETHANOL

Selective formation of para-ethyltoluene by alkylation of toluene with ethanol was studied using as catalysts ZSM-8 Type zeolite which is another member of ZSM-5 family. Disproportionalion of toluene to produce xylenes increased with increasing reaction temperature, A temperature programmed desorption study snowed very strong acid sites were absent on Mg or Ba modified HZSM-8. Increased para-ethylloluene selectivity over modified ZSM-8 catalysts is interpreted in terms of a reduction in the strong acid sites and increased diffusional resistance.     

Estimation of crystalline phase in ZSM-5 zeolites by infrared spectroscopy

A fast and accurate method for identification and determination of purity of Zeolite Socony Mobil 5 (ZSM-5) zeolite was developed using the IR optical density ratio of the bands at 550 and 450 cm^?1 in the mid-IR region of the structure spectra. The optical density values obtained from the proposed method, for ZSM-5 zeolite synthesized, are compared with those of the Bayer ZSM-5 zeolite used as reference material. For well-crystallized calcined ZSM-5 zeolite, this ratio is circa 0.8. This ratio is found to be less, if amorphous silicate is present in zeolite. The presence of a band at 550 cmSUP>?1 in addition to the one at 450 cm^?1 shows that ZSM-5 zeolite has been formed even if the material is X-ray amorphous. The absence of the structure-sensitive band at 550 cm^?1 unambiguously indicates that such a zeolite has not been formed.     

Yield of gasoline-range hydrocarbons as a function of uniform ZSM-5 crystal size

Uniform ZSM-5 nanocrystals were synthesized by a single-templating procedure. The samples were then characterized by a variety of physical techniques such as XRD, SEM, BET, ICP and TPD. The dehydration of methanol over synthesized ZSM-5 zeolite was studied in a fixed-bed continuous flow reactor at 370 °C and WHSV of 2.6 gg⁻¹ h under ambient pressure. The effect of crystal size of zeolite catalysts on product distribution in methanol dehydration reaction was investigated. Good correlation was observed between catalytic performance, product distribution and size of ZSM-5 crystals. It was found that the decrease in crystal size significantly influences light olefins (ethylene and propylene) and paraffins (C₁–C₄) selectivity in methanol dehydration reaction. Furthermore, nanocrystal ZSM-5 showed long-term catalytic stability compared with conventional ZSM-5 provided that the reaction activity is strongly dependent on the crystal size in methanol dehydration process. The results indicated that crystal size significantly affects the catalyst lifetime and hydrocarbon distributions in product stream. Based on the obtained results, it is concluded that the use of uniform ZSM-5 nanocrystals improves the yield of propylene and alkyl aromatics in methanol conversion reaction at mild conditions.