Kongkiat Suriye

NaOH modified WO3/SiO2 catalysts for propylene production from 2-butene and ethylene metathesis

A WO3/SiO2 catalyst is used in industry to produce propylene from 2-butene and ethylene metathesis. Catalysts with various WO3 loading (4% to 10%) were prepared by impregnation and tested for the metathesis of ethene and trans-2-butene. Ion exchange of NaOH onto the WO3/SiO2 catalyst was used to mitigate the acidity of the catalysts in a controlled way. At low WO3 loading, the treatment with large amounts of NaOH resulted in a significant decrease in metathesis activity concomitant with significant W leaching and marked structural changes (XRD, Raman). At higher WO3 loading (6% to 10%), the treatment with NaOH mainly resulted in a decrease in acidity. FT-IR experiments after adsorption of pyridine showed that the Lewis acidic sites were poisoned by sodium. Nevertheless, the metathesis activity remained constant after the NaOH treatment. This suggested that the remaining acidity on the catalyst was enough to ensure the efficient formation of the carbene active sites. Interestingly, Na poisoning resulted in some modification of the selectivity. The mitigation of acidity was shown to favor propene selectivity over the formation of isomerization products (cis-2-butene, 1-butene, etc.). Moreover, treatment with NaOH led to a shorter induction period and reduced coke formation on the WO3/SiO2 catalyst.

Production of propylene from an unconventional metathesis of ethylene and 2-pentene over Re2O7/SiO2-Al2O3 catalysts

Abstract An unconventional metathesis of ethylene and 2-pentene over Re2O7/SiO2-Al2O3 catalysts has been studied as an alternative route for the production of propylene. Complete conversion of 2-pentene and propylene yield as high as 88 wt% were obtained under mild reaction conditions at 35°C and atmospheric pressure. Unlike the conventional metathesis of ethylene and 2-butenes in which isomerization is a competing side reaction, the isomerization of 1-butene product from the unconventional metathesis of ethylene and 2-pentene to 2-butenes can further react with excess ethylene in the feed, resulting in additional increase in propylene yield. The secondary metathesis reaction was found to be favored under ethylene/2-pentene (E/2P) molar ratio ≥3 and gas hourly space velocity (GHSV) ≤1000 h−1 at the reaction temperature of 35°C. No catalyst deactivation was observed during the 455 min time-on-stream under the selected reaction conditions.

Role of support nature (γ-Al2O3 and SiO2-Al2O3) on the performances of rhenium oxide catalysts in the metathesis of ethylene and 2-pentene

Abstract The metathesis of ethylene and 2-pentene was studied as an alternative route for propylene production over Re 2 O 7 /γ-Al 2 O 3 and Re 2 O 7 /SiO 2 -Al 2 O 3 catalysts. Both NH 3 temperature-programmed desorption (NH 3 -TPD) and H 2 temperature-programmed reduction (H 2 -TPR) results showed that Re 2 O 7 /SiO 2 -Al 2 O 3 exhibited stronger acidity and weaker metal-support interaction than Re 2 O 7 /γ-Al 2 O 3 . At 35–60 °C, isomerization free metathesis was observed only over Re 2 O 7 /γ-Al 2 O 3 , suggesting that the formation of metal-carbene metathesis active sites required only weak acidity. Our results suggest that on the Re 2 O 7 /SiO 2 -Al 2 O 3 , hydrido-rhenium species ([Re]-H) were formed in addition to the metathesis active sites, resulting in the isomerization of the initial 1-butene product into 2-butenes. A subsequent secondary metathesis reaction between these 2-butenes and the excess ethylene could explain the enhanced yields of propylene observed. The results demonstrate the potential for high yield of propylene from alternative feedstocks.

Effect of Nano-sized TiO2 Additional Support in WO3/SiO2 Catalyst Systems on Metathesis of Ethylene and Trans-2-Butene to Propylene

TiO2 was employed as an additional support by physical mixing with the WO3/SiO2 catalysts and used in the metathesis of ethylene and trans-2-butene for propylene production. Having nano-sized TiO2 as the additional support could enhance trans-2-butene conversion and propylene yield. The results suggested that tungsten could migrate from an original support and form more well-dispersed surface tetrahedral tungsten oxide species on the additional support, leading to a better dispersion. It was also shown that TiO2 having nano size could provide better spreading of the tungsten species than the micro size. A smaller crystallite size evidenced from XRD and a higher ratio between surface tetrahedral tungsten oxide species over crystalline WO3 evidenced from FT-Raman spectra of the nano-sized TiO2 systems were, among other things, advantageous to metathesis activity improvement of the catalyst. This study offers a guidance of supplementing the existing catalysts as one simple way of improvement in the catalytic performances which can easily be applied in the real metathesis reaction process.Graphical Abstract

Effect of Dispersion of the Active Phase on the Activity and Coke Formation over WO3/SiO2 Catalysts in the Metathesis of Ethylene and 2-Butene

WO3/SiO2 catalysts with various tungsten loadings were prepared by the incipient wetness impregnation method and studied in the metathesis of ethylene and trans-2-butene as feed to produce propylene. Two different calcination methods were used to modify the dispersion of the tungsten active phase. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, nitrogen physisorption, ion-exchange titration, FT-Raman, ammonia temperature programmed desorption and temperature programmed oxidation. Better dispersion is obtained from low heating rate calcination. The dispersion of tungsten showed a direct effect on coke formation and was the key factor to improve the stability of the catalysts.Graphical Abstract

Catalytic performance improvement of styrene hydrogenation in trickle bed reactor by using periodic operation

We investigated the catalytic performance improvement of styrene hydrogenation in a trickle bed reactor by using periodic operation. The effects of cycle period and split on relative conversion, which is defined as styrene conversion obtained from periodic operation over that from steady state operation, were examined at various operating conditions including gas and average liquid flow rates, pressure and temperature. The experimental results reveal that both cycle period and split have strong influence on the catalytic performance. The fast mode (short cycle period) is a favorable condition. The improvement by the periodic operation becomes less pronounced for operations at high average liquid flow rate, pressure and temperature. From this study, a maximum improvement of styrene conversion of 18% is observed.

In situ-DRIFTS study: influence of surface acidity of rhenium-based catalysts in the metathesis of various olefins for propylene production

Various olefins including 1- and 2-butene, 2-pentene, and ethylene were used as the reactants for producing propylene by self- and cross-metathesis reactions at 60 °C on supported Re-based catalysts (4 wt% Re). A similar surface structure of rhenium oxides in the form of isolated ReO4 species was observed on Al2O3 and SiO2–Al2O3 supported rhenium oxide catalysts. The catalysts, however, differed in terms of the types (Lewis/Bronsted) and strengths of the acidic sites, as revealed by ammonia temperature programmed desorption (NH3-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) of NH3 adsorption and thermodesorption results. Weak Lewis acidity, especially high ratios of Lewis acid bands at 1280 cm−1/1622 cm−1, led to high metathesis activity of the Re-based catalysts. The additional isomerization activity, however, required strong Bronsted acid sites. The product distribution from the various feeds depended largely on the size of the olefins, and not only on the acid properties of the catalysts. Re2O7/SiO2–Al2O3 appeared to be a versatile catalyst for obtaining a high yield of propylene using either a single reactant (1- or 2-butene) or an ethylene mixed feed.

Effect of the calcine condition on surface structure of titania nanocrystal photocatalyst

In this work, effects of atmosphere during calcination process on photoactivities for decomposition of ethylene were investigated. TiO 2 were prepared by sol-gel and then calcined under N 2 plus increasing amounts of O 2 at temperature 723 K. Conversion of ethylene increased with increasing surface defect. Increasing this defect occurred when amount of O 2 during calcination process increased. Surface defect of TiO 2 samples was determined by CO 2 -TPD and ESR, while XRD, SEM, TEM and BET were used to characterize other physical properties of TiO 2 samples.

Ethylene and mixed 2-butene cis/trans isomers metathesis: Influence of lanthanum as a second metal on the WO3/SiO2 catalysts

Lanthanum (0.5, 0.6, 0.75, 0.9 and 1 wt%) was added as a second metal on the 9 wt% WO3/SiO2 catalysts by the incipient wetness impregnation method. The catalysts were tested in the metathesis reaction of ethylene and 2-butene using either pure 2% trans-2-butene and the mixture of 1% cis- and 1% trans-2-butene as the reaction feed and were characterized by X-ray diffraction (XRD), nitrogen physisorption (BET), inductively coupled plasma optical emission spectrometry (ICP-OES), scanning electron microscopy, ion-exchange titration, FT-Raman, ammonia temperature programmed desorption (NH3-TPD) and reactant temperature programmed desorption (reactant-TPD). An optimum lanthanum loading at 0.5 wt% could improve dispersion of tungsten active phase and adsorption properties of the reactants on the catalysts. The adsorption of the mixed cis/trans-2-butene isomer was much improved on the La-WO3/SiO2 catalysts with 0.5 wt% La.

Synthesis and Characteristics of CaO/MgO Mixed Oxides for the Double Bond Isomerization of 1-Butene

The MgO catalysts containing only weak/medium basic sites were doped with a strong basic oxide CaO by co-precipitation method with 0.19-3.64 wt% CaO. While the amount of strong basic sites linearly increased with wt.% CaO, the activity for isomerization of 1-butene to 2-butenes of the CaO-doped MgO catalysts was maximized at 1.77 wt% CaO. Addition of a small amount of CaO-dopant altered the MgO structure (i.e., the formation of step, edge, and corner sites), resulting in different OH- adsorption abilities and enhanced catalytic activities.