Wang Xiangsheng

Synthesis of titanium silicalites in different template systems and their catalytic performance

Abstract Titanium silicalites have been synthesized in the TPABr+ammonia, TPABr+hexanediamine, TPABr+ethylenediamine, TPABr+diethylamine, TPABr+TEAOH, TPABr+n-butylamine, TPABr+TBAOH and TBAOH+n-butylamine systems. As-synthesized titanium silicalites were characterized by XRD, IR and 13 C CP MAS NMR. Catalytic performance in epoxidation of propylene and template effect was investigated. It has been shown that both TPABr and TBAOH serve as templating agent in TPABr+TBAOH system. But in other systems, when there is enough TPABr, organic amines or ammoniums only act as the bases. TEAOH or n-butylamine can take the role of template when less TPABr is added. It indicates that the ability of organic amines or ammoniums to direct the Pentasil structure decreases as follows: TPA+>TBA+>TEA+>n-butylamine. Catalysts exhibiting good performance in epoxidation of propylene can be attained using TPABr as the template and ammonia, n-butylamine, diethylamine, hexanediamine or TBAOH as bases.

Characterization of Modified Nanoscale ZSM-5 Zeolite and Its Application in the Olefins Reduction in FCC Gasoline

Nanoscale HZSM-5 zeolite was hydrothermally treated with steam containing 0.8 wt% NH3 at 773 K and then loaded with La2O3 and NiO. Both the parent nanoscale HZSM-5 and the modified nanoscale HZSM-5 zeolites catalysts were characterized by TEM, XRD, IR, NH3-TPD and XRF, and then the performance of olefins reduction in fluidized catalytic cracking (FCC) gasoline over the modified nanoscale HZSM-5 zeolite catalyst was investigated. The IR and NH3-TPD results showed that the amount of acids of the parent nanoscale HZSM-5 zeolite decreased after the combined modification, so did the strong acid sites deactivating catalysts. The stability of the catalyst was still satisfactory, though the initial activity decreased a little after the combined modification. The modification reduced the ability of aromatization of nanoscale HZSM-5 zeolite catalyst and increased its isomerization ability. After 300 h onstream, the average olefins content in the gasoline was reduced from 56.3 vol% to about 20 vol%, the aromatics (C7–C9 aromatics mainly) and paraffins contents in the product were increased from 11.6 vol% and 32.1 vol% to about 20 vol% and 60 vol% respectively. The ratio of i-paraffins/n-paraffins also increased from 3.2 to 6.6. The yield of gasoline was obtained at 97 wt%, while the Research Octane Number (RON) remained about 90.

Epoxidation of Propylene with Dilute H2O2 over Titanium Silicalite Containing Trace Aluminum

Titanium silicalite (TS-1) was successfully synthesized by using TPABr as the template and silica sol as silicon source in a 100 l stainless steel autoclave. IR, XRD, UV--vis, elemental analysis, and 27Al and 31P MAS NMR were used to characterize the synthesized products. The results show that the synthesized material has an MFI structure with high crystallinity and large crystal size and two kinds of titanium species. Trace aluminum in silica sol is also incorporated into the zeolite framework. The synthesized TS-1 exhibits high activity in the epoxidation of propylene with dilute H2O2 with high selectivity to methyl mono-ethers and low selectivity to propylene oxide (PO). The low selectivity toward PO is due to the residual acidity onto TS-1. The selectivity of PO can reach up to 90% through adjusting the pH of the reaction mixture. Extra amounts of base decrease the H2O2 utilization and the H2O2 conversion. However, in over acid-treated TS-1 in which part removal of extra-framework titanium takes place, the utilization of H2O2 is quite different: for the low Si/Ti ratio of TS-1, the H2O2 utilization increases. But the utilization of H2O2 does not change for the high Si/Ti ratio TS-1. Thermal analysis shows that the as-synthesized TS-1 exhibits high activity and thermal stability in the calcined range 540-900 °C.

Side-chain alkylation of toluene with methanol on KX/KZSM-5 binary zeolite catalysts

The side-chain alkylation of toluene with methanol catalyzed by the modified binary zeolite catalysts of KX and Al 2 O 3 , KX, KY, KM, or KZSM-5 has been studied. It was found that the selectives of styrene increased with the partial charge on the (A10 4 ) − tetrahedra in the second zeolite component. The KX/KZSM-5 binary zeolite catalysts had much higher activities than did the separate zeolite catalysts, and the catalytic properties were greatly improved after H 3 BO 3 and KOH modifications. Comparing the alkylation data with the t.p.d. measurements of NH 3 and CO 2 , Sandersons electronegativity, and the partial charge on the (A10 4 ) − tetrahedra, it is concluded that the side-chain alkylation of toluene with methanol on the binary zeolite catalysts is an acid-base cooperative, selective reaction.

Ethylation of ethylbenzene to produce para-diethylbenzene

Abstract HZSM-5 Catalyst was steamed and modified by the impregnation of mixed rare-earth nitrate solution and tetraethyl orthosilicate in cyclohexane solution. The modified catalysts were then applied to the alkylation of ethylbenzene with ethylene, ethanol and crude material containing 65% ethylene to produce diethylbenzene (DEB). Alkylation over the RE-Si-ZSM-5 catalysts yielded 95–98% P-DEB. The high para-selectivity is due to the reduction in acid strength within the pores and the reduction in acid sites on the crystals external surface. These catalysts have good performance in the industrial application.

Epoxidation of Propylene over Small-Crystal TS-1 Extrudate in a Fixed-Bed Reactor

A small-crystal titanium silicalite-1 (TS-1) with a size of 600 nm × 400 nm × 250 nm was synthesized using a nano-sized TS-1 mother liquor as the seed in a tetrapropyl ammonium bromide (TPABr)-ethylamine hydrothermal system,and was extruded with silica sol.The obtained TS-1 extrudate was characterized by X-ray powder diffraction (XRD),Fourier-transform infrared (FTIR) spectroscopy,ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy,and nitrogen physisorption.The reaction conditions,including temperature,pressure,molar ratio of propylene/H2O2 (n(C3H6)/n(H2O2)),the weight hourly space velocities (WHSVs) of propylene,methanol and H2O2,and the concentration of NH3·H2O,were systematically studied to identify ideal conditions for propylene epoxidation over small-crystal TS-1 extrudate.The reaction temperature had little effect on the propylene oxide (PO) yield under the conditions examined.The highest PO yield was obtained when the pressure was 2.0 MPa and the n(C3H6)/n(H2O2) was 4.The PO content in the product was maximized when the WHSVs of propylene,methanol and H2O2 were 0.93,2.5,and 0.25 h-1,respectively.A low concentration of NH3 · H2O was beneficial for a high PO yield.Under the optimized condition,we compared catalytic performances of TS-1 with different crystal sizes and performed a long-term test over the small-crystal TS-1.The tests indicated that H2O2 conversion and PO selectivity could both reach 95%,even after 1000 h on stream.

Scale-Up Synthesis of Hydrogen Peroxide from H2/O2 with Multiple Parallel DBD Tubes

The scale-up synthesis of H2O2 from H2/O2 via a dielectric barrier discharge (DBD) under ambient conditions was studied. A plasma reactor consisting of multiple parallel DBD tubes was designed to scale up the H2O2 synthesis. The number of tubes had no significant effect on the discharge mode, and no decay occurred in H2O2 selectivity during the scale-up process. These advantages made this technology more stable and efficient. The reactors energy efficiency increased with the number of tubes and reached 136 g H2O2/kWh in the four-tube reaction. The total energy efficiency was limited by the extremely low energy transfer efficiency of power supply, and might be enhanced by optimizing the impedance matching between the power supply and the reactor load. As a result, an assembly of multiple DBD tubes may provide a viable route for the scale-up synthesis of H2O2 by a non-equilibrium plasma.

Preparation of titanium-containing large pore molecular sieve from H-Al-Beta zeolite

Abstract Ti-Al-Beta zeolite has been synthesized by gas-solid isomorphous substitution with H-Al-Beta zeolite as precursor. X-ray diffraction pattern showed that its structure was similar to that of zeolite H-Al-Beta. The only difference between their IR spectra was an extra adsorption band appearing at 960cm−1. The study of IR and UV-Vis spectra showed that Ti was incorporated into the framework of Beta zeolite and Ti was tetrahedrally coordinated as part of the framework. After the precursor was treated with acid, the incorporation of titanium became easy. With increasing acid concentration, the content of Ti into the framework increased. In addition, increasing substitution time, the content of Ti into the framework also increased.