Effect of mesopore spatial distribution of HZSM-5 catalyst on zinc state and product distribution in 1-hexene aromatization

1-hexene aromatization is a promising technology to convert excess olefin in fluid catalytic cracking(FCC)gasoline to high-value benzene(B),toluene(T),and xylene.Besides,the increasing market demand of xylene has put forward higher requirements for new generation of catalyst.For increasing xylene yield in 1-hexene aromatization,the effect of mesopore structure and spatial distribution on product distribution and Zn loading was studied.Catalysts with different mesopore spatial distribution were prepared by post-treatment of parent HZSM-5 zeolite,including NaOH treatment,tetra-propylammonium hydroxide(TPAOH)treatment,and recrystallization.It was found the evenly distributed mesopore mainly prolongs the catalyst lifetime by enhancing diffusion properties but reduces the aromatics selectivity,as a result of damage of micropores close to the catalyst surface.While the selectivity of high-value xylene can be highly promoted when the mesopore is mainly distributed interior the catalyst.Besides,the state of loaded Zn was also affected by mesopores spatial distribution.On the optimized catalyst,the xylene selectivity was enhanced by 12.4%compared with conventional Zn-loaded parent HZSM-5 catalyst at conversion over 99%.It was attributed to the synergy effect of mesopores spatial distribution and optimized acid properties.This work reveals the role of mesopores in different spatial positions of 1-hexene aromatization catalysts in the reaction process and the influence on metal distribution,as well as their synergistic effect two on the improvement of xylene selectivity,which can improve our understanding of catalyst pore structure and be helpful for the rational design of high-efficient catalyst.

Measurement and Correlation of Liquid-liquid Equilibria for 1-Hexene-n-Hexane-3-Methysulfolane

Utilizing solvent extraction to separate alkanes and olefins from catalytic light gasoline is an effective method for maximizing the utility of gasoline fractions.This study presents the determination of liquid-liquid equilibrium data for the ternary system of 1-hexene-n-hexane-3-methylsulfolane at 30℃,40℃,and 50℃under atmospheric pressure.The obtained data facilitated the construction of a ternary phase diagram for the system.The results showed that the extraction selectivity of 1-hexene/n-hexane exceeded 1.5 when using 3-methylsulfolane as the extraction solvent.Furthermore,the thermodynamic consistency of the experimental data was examined using Hand’s equation and the Othmer-Tobias method.The correlation coefficient,R^(2)≥0.9578,indicated the acceptable reliability of the phase equilibrium data.Subsequently,the NRTL(non-random two liquid)model was used to correlate the liquid-liquid phase equilibrium data and derive the binary interaction parameter.Notably,the results demonstrated that the root mean square deviation of the NRTL model correlation values from the experimental values did not exceed 2.5%.

Effects of the Amount of Tetrapropyl Ammonium Hydroxide in Synthesis on TS-1 Properties and Catalytic Performance in Epoxidation of Propylene

Titanium silicalite-1(TS-1) was synthesized by a hydrothermal synthesis method with different amounts of tetrapropyl ammonium hydroxide(TPAOH) as template.The as-prepared TS-1 was characterized by scanning electron microscopy,X-ray powder diffraction,Fourier-transform infrared resonance spectroscopy,ultravioletvisible diffuse reflectance spectroscopy and nitrogen physical adsorption and desorption,and studied in the propylene epoxidation with hydrogen peroxide in a fixed bed reactor.The results showed that the amount of TPAOH had a strong influence on the grain morphology,the amount of framework Ti,and the average particle sizes of TS-1.With the increase of TPAOH amount in the synthesis(the molar ratio of TPAOH/SiO_2 increasing from 0.25 to 0.45),the morphology changed gradually from ellipsoids to cubes,the particle sizes of TS-1 decreased slightly,the amount of the framework Ti increased appreciably,and the catalytic stability in the propylene epoxidation increased markedly.Moreover,all the catalysts had the same selectivity to propylene epoxide.However,when the molar ratio of TPAOH/SiO_2 was further increased to 0.55,the particles became large hexagons with the size distribution in a wide range,and the catalytic stability decreased sharply although the amount of the framework Ti increased further,which can be attributed to the long diffusion paths of the reactants in the zeolite.

Effect of TS-1 Treatment by Mixed Alkaline on Propylene Epoxidation

Titanium silicate-1(TS-1) was treated with a mixed alkaline of tetrapropyl ammonium hydroxide(TPAOH) and NaOH. It was characterized by XRD, nitrogen physical adsorption, SEM, FT-IR, UV-Vis and ICPOES, and studied in propylene epoxidation. The mixed alkaline treatment with TPAOH/NaOH solution did not destroy the MFI structure of TS-1. With increasing NaOH concentrations, the relative crystallinity and the framework titanium decreased to some extent while the mesopore volume, mesopore diameter, and extra-framework titanium increased appreciably. When NaOH concentration was 0.0333 mol L^(-1), the best catalytic performance was obtained.

自模板法制备大孔-微孔等级孔TS-1分子筛及其1-己烯环氧化性能

针对等级孔钛硅分子筛TS-1合成方法存在步骤复杂及成本高等难题,使用二氧化硅纳米球同时作为硅源和大孔模板,结合蒸汽辅助结晶方法,通过“硅源溶解-分子筛结晶”过程形成大孔结构,得到大孔-微孔TS-1分子筛。通过调控二氧化硅纳米球的尺寸,可以系统调变大孔直径(100~500 nm)。此外,合成的大孔-微孔TS-1分子筛硅/钛摩尔比可调(30、50、100)。HTS-1-200-30分子筛样品在1-己烯催化环氧化反应中,温度343 K、反应时间6 h条件下1-己烯转化率可达41%,高于微孔TS-1分子筛的催化性能。研究所采用的自模板法使用低成本St9ber法制备二氧化硅纳米球,相较于高成本介孔二氧化硅纳米球,降低了等级孔钛硅分子筛的合成成本,适用于工业大规模生产。

Green and efficient epoxidation of methyl oleate over hierarchical TS-1

The epoxidation of methyl oleate(MO)was conducted in the presence of aqueous H2O2 as the oxidant and hierarchical TS-1(HTS-1)as the catalyst;the catalyst was synthesized using polyquaternium-6 as the mesopore template.The effects of various parameters,i.e.,H2O2/C=C molar ratio,oxidant concentration,amount of the catalyst,reaction temperature,and time,were systematically studied.Furthermore,response surface methodology(RSM)was used to optimize the conditions to maximize the yield of epoxy MO and to evaluate the significance and interplay of the factors affecting the epoxy MO production.The H2O2/C=C molar ratio and catalyst amount were the determining factors for MO epoxidation,wherein the maximum yield of epoxy MO reached 94.9%over HTS-1 under the optimal conditions.

Synergetic photo-epoxidation of propylene with molecular oxygen over bimetallic Au–Ag/TS-1 photocatalysts

Au-Ag bimetallic nanoparticle‐supported microporous titanium silicalite‐1catalysts were prepared via a hydrothermal‐immersion method,and their structures were examined.These materials serve as efficient catalysts for the photosynthesis of propylene oxide via the epoxidation of propene.The Au/Ag mass ratio and reaction temperature were demonstrated to have significant effects on the catalytic activity and selectivity of propylene oxide.The optimal formation rate(68.3μmol/g·h)and selectivity(52.3%)toward propylene oxide were achieved with an Au:Ag mass ratio of4:1.Notably,the strong synergistic effect between Au and Ag resulted in superior photocatalysis of the bimetallic systems compared with those of the individual systems.A probable reaction mechanism was proposed based on the theoretical and experimental results.

Engineering three-layer core–shell S-1/TS-1@dendritic-SiO_(2) supported Au catalysts towards improved performance for propene epoxidation with H_(2) and O_(2)

The advocacy of green chemical industry has led to the development of highly efficient catalysts for direct gas-phase propene epoxidation with green,sustainable and simple essence.The S-1/TS-1@dendritic-SiO_(2) material with three-layer core–shell structure was developed and used as the support for Au catalysts,which showed simultaneously fantastic PO formation rate,PO selectivity and stability(over 100 h)for propene epoxidation with H_(2) and O_(2).It is found that silicalite-1(S-1)core and the middle thin layer of TS-1 offer great mass transfer ability,which could be responsible for the excellent stability.The designed dendritic SiO_(2) shell covers part of the acid sites on the external surface of TS-1,inhibiting the side reactions and improving the PO selectivity.Furthermore,three kinds of SiO_(2) shell morphologies(i.e.,dendritic,net,mesoporous shell)were designed,and relationship between shell morphology and catalytic performance was elucidated.The results in this paper harbour tremendous guiding significance for the design of highly efficient epoxidation catalysts.

Post-treatment of TS-1 with Mixtures of TPAOH and Ammonium Salts and the Catalytic Properties in Propylene Epoxidation

TS-1/SiO_2 extrudate was post-treated with mixed solution of tetrapropyl ammonium hydroxide(TPAOH)and various ammonium salts solution(NH_4F,(NH_4)_3PO_4,(NH_4)_2CO_3,(NH_4)_2SO_4,NH_4CH_3CO_2,NH_4NO_3,NH_4Cl and(NH_4)_2TiF_6).The obtained hierarchical TS-1 catalysts were characterized by many techniques and tested for propylene epoxidation using hydrogen peroxide as an oxidant in a fixed-bed reactor.It was shown that the physicochemical and catalytic properties of the treated TS-1/SiO_2 extrudate depended on the types of ammonium salts added.Compared to the treatment with TPAOH alone,the treatment with a mixed solution of TPAOH and some ammonium salts can greatly improve the catalytic properties of the treated TS-1/SiO_2 extrudate.Some of these ammonium salts were favorable for the incorporation of titanium in the framework,and the beneficial effect depended on the types of ammonium salt.TS-1/SiO_2 extrudate treated with a mixed solution of TPAOH and(NH_4)_3PO_4 exhibited the highest catalyst stability in propylene epoxidation.Such catalytic property can be correlated to high crystallinity,more framework titanium,large specific surface area and large external surface area.

Effect of H_2S on the transformation of 1-hexene over NiMoS/γ-Al_2O_3 with hydrogen

The effect of H2S contents on the transformation of 1-hexene with hydrogen over NiMoS/γ-Al2O3 catalyst was investigated.Inhibition of H2S on both hydrogenation and isomerization reactions of olefin has been demonstrated.And the promotion effect of H2S on the formation of C6 thiols and C12 thioethers has also been observed.It was found out that there was only one type of active site on the NiMoS/γ-Al2O3 for reactions which include hydrogenation reaction,isomerization reaction and sulfides formation reaction,and the formation reactions of sulfides were superior to both hydrogenation and isomerization reactions.The reaction network for the conversion of 1-hexene in the presence of H2S was proposed.

STUDY ON 1-HEXENE POLYMERIZATION BASED ON ZIEGLER-NATTA CATALYSTS WITH DOPED SUPPORT

A series of Ti/Mg supported catalysts are prepared by using ball-milled mixtures of MgCl2-ethanol adducts and NaCl as supports, and 1-hexene polymerizations catalyzed by the novel catalysts are studied. It is found that the molecular weight distribution of poly(1-hexene) becomes apparently narrower when catalysts with doped supports are used, indicating that changing the structure of the support is an effective way to regulate the active center distribution of heterogeneous Ziegler-Natta catalyst.

Liquid-Liquid Equilibrium for Extraction of Benzene from 1-Hexene Using Two Different Solvents

Two different solvents had been used to separate benzene from 1-hexene under atmosphere pressure by employing one of the following two solvents, viz.: dimethyl sulfoxide (DMSO) at 298.15 K and 318.15 K, and furfural at 298.15 K. A series of liquid-liquid equilibrium (LLE) data had been obtained and the distribution coefficient together with the separation factor were calculated from them. Both the NRTL and the UNIQUAC models could fit in with the experimental data quite well.

Synthesis of TS-1 Films on Porous Supports for Epoxidation ofAllyl Chloride by Hydrogen Peroxide

Titanium silicalite-1(TS-1)films were synthesized on stainless steel plate,glass slide and monolith supports via an in-situ hydrothermal method.Characterization data showed that the formation of TS-1 films was easier on the porous flat support with rough surface such as monolith than on the smooth non-porous supports like glass slide and stainless steel plate.The film on the monolith had the highest uniformity and smallest size of crystals.The catalytic property of monolithsupported film was tested for epoxidation of allyl chloride(ACH)by H2O2in a fixed bed reactor.Under the condition of a methanol(solvent)/ACH(90% )/H2O2(30% )ratio of 12:1:1,a LHSV of 1.35 h-1and a temperature of 318 K,the conversion of allyl chloride and the selectivity to epichlorohydrin reached 79% and 51% ,respectively.

Highly Effective Propylene Epoxidation over TS-1/SiO_(2) Hydrothermally Treated

The propylene epoxidation over TS-1/SiO2 catalyst hydrothermally treated was investigated. It was found by EPR characterization that two types of Ti (IV)-superoxide radicals, A (gz=2.0271; gy=2.0074; gx=2.0010) and B (gz=2.0247; gy= 2.0074; gx= 2.0010), were observed for TS-1/SiO2. The superoxo species A converted to B after TS-1/SiO2 catalyst was hydrothermally treated. The results show that over TS-1/SiO2 catalyst hydrothermally treated at 170℃, about 95% conversion of H2O2 with above 94% PO selectivity is obtained during continuous running for 300 h under the conditions of reaction temperature 45℃, 0.5 h-1WHSV of propylene.

Thermodynamic Investigation on the Pyrolysis of 1-Hexene

The pyrolysis of 1-hexene can act as a prototype of pyrolytic mechanism in petro- leum processing. Details of C-C bond cleavage in the 1-hexene pyrolysis were investigated at the MP2/6-31 I＋＋G^＊＊ basis set level. The equilibrium geometries and key thermodynamic parameters such as Gibbs free energies and thermal enthalpies were gained. Our theoretical results show that the entropy effect plays a significant role in dissociative processes. The dissociation of 1-hexene-4-yl radical into C4H6 and C2H5 is not an H-transfer and C-C rupture elementary reaction, but a process involving H-transfer and C-C rupture.

Skeletal Isomerization of 1-Hexene over MCM-22 Zeolite Catalyst

The performance of MCM-22 zeolite for catalytic isomerization of 1-hexene has been studied. At a n(H2)/n(1-hexene) ratio of 8, the influence of steam treatment temperature, reaction temperature and reaction pressure on the performance of MCM-22 zeolite for catalytic skeletal isomerization of 1-hexene was examined. The experimental results showed that at a steam treatment temperature of 500℃, a reaction temperature of 270℃, a space velocity of 1.0 h-1 and a reaction pressure of 0.2 MPa, the MCM-22 zeolite exhibited excellent performance for catalytic skeletal isomerization of 1-hexene with the i-hexene yield reaching 66.15%. Compared with other commonly used molecular sieve catalysts, the MCM-22 zeolite catalyst exhibited better catalytic performance for skeletal isomerization of 1-hexene.

STUDY ON THE ADDITION REACTION OF 1-IODO-4-CHLOROPERFLOROBUTANE TO 1-HEXENE UNDER REDUCTIVE CONDITIONS

Promoted by various reductants,the addition of 1-iodo-4-chloro- perfluorobutane to 1-hexene giving 1:1 adduct is reported.Based on these facts,several new redox systems are proposed.

Effects of the Water in Mixed Solvent on the Epoxidation Reaction of Propylene with TS-1 Catalyst

The epoxidation reaction of propylene and hydrogen peroxide with zeolite catalyst containing titaniumsilicalite (TS-1)has been studied, and the reaction in the mixed solvent of water/methanol has been discussed. It is shown that the selective of epoxidation propylene decreases while the selective of propylene glycol increases, when the water content increases in the mixed solvent of methanol/water.

多级孔TS-1分子筛的制备及催化1-辛烯环氧化性能研究

以P123为辅助试剂,制备了一系列分级孔TS-1分子筛.利用红外、紫外、XRD、BET、ICP等对所得样品进行了表征.对样品在过氧化氢环氧化1-辛烯反应中的催化性能进行了评价.结果表明,所得分级孔TS-1沸石均具有典型的MFI结构,其形貌和结构随P123分子量不同有一定的变化.在优化的反应条件下,用P123(MW=5800)合成的样品可以有效地将1-辛烯转化为相应的环氧化物,相应产率可达56.05%,环氧化物选择性可达59.2%.

制备WO_(3)/TS-1分子筛及催化环戊烯环氧化反应研究

利用湿法浸渍制备了一系列WO_(3)/TS-1分子筛.利用SEM、TEM、XRD、IR、UV-Vis、XPS、BET、ICP等多种分析手段对催化剂的结构、形貌和性质等进行了表征.考察了这一系列分子筛对环戊烯环氧化反应的催化性能,其中以W占分子筛质量分数为4%时浸渍制备的分子筛的催化性能最好.催化剂循环4次后,1,2-环氧环戊烷的选择性和产率保持在68.7%和55.5%左右.