High Selectivity To Light Olefins Research Articles

Synthesis of sub-micrometric SAPO-34 by a morpholine assisted two-step hydrothermal route and its excellent MTO catalytic performance.

SAPO-34 with a sub-micrometer crystal size was synthesized by a double hydrothermal treatment employing cost-effective morpholine as a structure directing agent, which presented an enhanced catalytic lifetime (nearly 3 times the conventional one) in the reaction of methanol to olefins with a higher light olefin selectivity (total selectivity of 97.1%). Detailed studies of the sample after different time intervals in the second crystallization with and without additional morpholine were carried out, which offered insight into crystal degradation and re-crystallization phenomena. The samples with different morpholine concentrations during the second hydrothermal treatment were also prepared, in which the sample with 80% MOR aqueous solution exhibited the smallest crystal size and the longest MTO lifetime. Furthermore, the investigation on the additional amount of mother liquor (from the first crystallization) required for the second crystallization showed that the presence of half the amount of the mother liquor (nutrients) could give us the required results effectively.

Modified iron catalyst for direct synthesis of light olefin from syngas

The modified iron catalysts for direct synthesis of light olefins from syngas were investigated. A series of catalysts were prepared by co-precipitation method and characterized by SEM, BET and X-ray diffraction methods. Catalytic performance of the catalysts was tested in a fixed-bed reactor. The experimental results showed that Zn-modified iron catalyst displayed a high selectivity for light olefins and one through CO conversion. Alkali metal modified catalytic performances as electronic promoter that promoted the formation of light olefins. Meanwhile, the combination of Na + and Zn is a key factor to optimize the light olefins selectivity of catalyst in syngas to light olefins. The modified iron catalyst (Fe/Zn molar ratio = 1, prepared by co-precipitation using Na2CO3 as precipitant) displayed a CO conversion of 95.09%, a light olefins selectivity of 53.32%, and an olefin/paraffin ratio up to 6.91. That catalyst has high stability and activity in the performance test time on stream of 100 h.

Nano confinement and catalytic conversion of energy molecules

Catalysis, as a key and enabling technology, plays an increasingly important role in fields ranging from energy, environment and agriculture to health care. Rational design and synthesis of highly efficient catalysts has become the ultimate goal of catalysis research. Thanks to the rapid development of nanoscience and nanotechnology, and in particular a theoretical understanding of the tuning of electronic structure in nanoscale systems, this element of design is becoming possible via precise control of nanoparticles’ composition, morphology, structure and electronic states. In the present paper, we will illustrate the results on the structural and electronic properties of catalytically active centers in the nano-confined systems, as well as their catalytic activities. Based upon the concept of “Nano-Confined Catalysis”, novel catalyst has been designed by embedding low-valent iron atoms within the lattice of silicon dioxide. The active single iron site could catalyze the direct and selective conversion of methane exclusively to ethylene and aromatics. The reaction is initiated by catalytic generation of methyl radicals, followed by a series of gas-phase reactions. The absence of adjacent iron sites prevents catalytic C−C coupling, further oligomerization and hence coke deposition. At 1090 °C, methane conversion reaches a maximum at 48.1% and ethylene selectivity 48.4%, while the total hydrocarbon selectivity exceeded 99%, representing an atom-economical transformation process of methane. The surface-confined iron sites delivered stable performance, with no deactivation observed during a 60-h test. This technology would allow the removal of the energy-intensive process of syngas production from the conventional natural gas utilization technologies. In addition, we recently established the concept of nano-composite catalysts comprising of metal oxides and zeolites, which effectively separates the active sites for CO and H2 activation from those for C−C coupling. CO and H2 are activated over the partially reduced metal oxides forming intermediates, which are subsequently converted to products within the confined pores of zeolites. As such, surface polymerization, a long-standing problem in the conventional Fischer-Tropsch synthesis invented more than 90 years ago, could be circumvented. This novel process for syngas conversion could achieve a high selectivity of light olefins (80%), surpassing the limit of 58% for C2−C4 light hydrocarbons by the ASF distribution. Furthermore such a bifunctional composite catalyst delivers stable performance and no obvious deactivation was observed within a over 3000 h stability test. These achievements open up new avenues for the developments of clean technologies for the efficient utilization of carbon resources, such as natural gas, coal and biomass, and are recognized as the “milestone in the direct synthesis of light olefins”. Now, his team is collaborating with companies to explore industrial applications, starting from a pilot-scale study.

Selectively forming light olefins via macroporous iron-based Fischer–Tropsch catalysts

A highly dispersed macroporous iron-based catalyst (Fe/S80-E) was developed by the modification of a macroporous silica (80 nm) surface with ethylene glycol before the impregnation of iron precursors. Due to higher diffusion efficiency and highly dispersed iron particles, this kind of catalyst presents superb catalytic performance in Fischer–Tropsch synthesis with high selectivity of light olefins (46.2 c-mol%) as well as high activity (CO conv. 63.4 %) without any promoters. The obtained catalysts were characterized by N2 physisorption, mercury intrusion porosimetry, XRD, TEM, XPS, TPR and in situ DRIFT.

Incorporation of mixed metals into SAPO-34 frameworks by the dry-gel conversion method using mixed templates: investigating catalysts characterisation and performance

ABSTRACTThe crystallisation of the MeAPSO-34 material was studied under dry-gel conversion conditions and using two and three templates. This study has been focused on the effect of the incorporation of a mixture of Ni and Mn into the SAPO-34 framework. The MeSAPO-34 samples were characterised by X-ray diffraction, energy-dispersive X-ray spectrometer, scanning electron microscope, temperature-programmed desorption and Brunner–Emmett–Teller. The influence of metal incorporation into the framework of SAPO-34 (MeAPSO-34) on methanol conversion was investigated in this study. The performances on methanol conversion for these catalysts were different according to the properties of metals incorporated into the SAPO-34 structure. The catalytic performance demonstrated high activity and light olefins selectivity for the prepared catalysts. Among the light olefin products, Mn and Ni incorporation is helpful for propylene generation, but samples with a mixture of Ni and Mn favour the ethylene production.

Methanol conversion to light olefins over surfactant-modified nanosized SAPO-34

Ultrasonic and microwave-assisted aging processes were employed in the static hydrothermal synthesis of nanosized SAPO-34 molecular sieve. A series of nanosized hierarchical SAPO-34 samples with different degrees of mesoporosity were utilized to investigate the impacts of mesoporosity on the catalytic performance of the methanol to olefins (MTO) reaction. The so-called series were synthesized in the presence of various mesogenous templates, such as TPOAC, CTAB, and their combinations. These SAPO-34 samples were characterized by XRD, FE-SEM, BET, FT-IR and NH3-TPD techniques. The catalytic activities were studied in a fixed-bed reactor under atmospheric pressure, 450 °C and WHSV of 4 h−1. Comprehending the results, it can be said that in comparison with the typical catalysts, reliable MTO catalytic lifetime (420 min) as well as sufficiently high light olefins selectivity (90 %) was obtained through the nanosized hierarchical porous SAPO-34 templated with a mixture of 50 % CTAB and 50 % TPOAC. This achievement is associated to its effective combination of acidity and porosity.

Hydrothermally stable MOFs for CO2 hydrogenation over iron-based catalyst to light olefins

Two types of hydrothermally stable MOFs, ZIF-8 and MIL-53(Al) with different size and morphology, were prepared and used as supports for catalysts for synthesis of hydrocarbons from CO2 hydrogenation. XRD patterns proves that all these two types of MOFs materials could be stable under the reaction conditions (P=3MPa; T=573K) with water as byproduct. MOFs as a novel porous materials show excellent properties on catalysis compared with traditional supports γ-Al2O3 and the type of MOF supports has a significant impact on the activity and selectivity of Fe catalysts for CO2 hydrogenation. Due to the acidity of supports, ZIF-8 supports show different levels of considerable light olefins selectivity, while all MIL-53 supports nearly could not obtain light olefins. The light olefins selectivity of ZIF-8 is also affected by the secondary reaction of hydrogenation during the internal diffusion process. In this article, catalyst with high active and high light olefins selectivity was obtained just by modulating the MOFs supports.

The effects of SiO2/Al2O3 and H2O/Al2O3 molar ratios on SAPO-34 catalysts in methanol to olefins (MTO) process using experimental design

To investigate the effects of silicon and water content on SAPO-34 catalyst, a number of experiments by using response surface methodology of molar ratios of SiO2/Al2O3=0.1–0.6 and H2O/Al2O3=50–120 were performed. The catalytic performances of prepared SAPO-34 samples at 410°C and 30wt.% methanol in water for MTO process were investigated. Due to relatively high crystallinity and small crystal size (1.3μm); SiO2/Al2O3=0.17 and H2O/Al2O3=109.75 catalyst showed high total light olefins selectivity (71.45%). ANOVA results indicated that the light olefins selectivity was influenced more by changing of SiO2/Al2O3 molar ratio rather of H2O/Al2O3 molar ratio.

Effects of pretreatment on iron-based catalysts for forming light olefins via Fischer–Tropsch synthesis

The effects of ethylene glycol modified co-precipitation were applied to develop a catalyst with higher activity and selectivity of light olefins in the Fischer–Tropsch synthesis. The catalysts prepared by an ethylene glycol (EG) modified co-precipitation realized smaller and homogeneously distributed catalyst particles as 15–25 nm, which was two times smaller than that of the catalyst prepared from conventional co-precipitation. The Fe/Mn-EG catalyst has higher activity and enhanced selectivity to light olefins, as well as the doubled olefin to paraffin ratio (C2=–C4=/C20–C40), comparing to un-pretreated catalyst. Furthermore, the addition of magnesium promoter to the Fe/Mn-EG catalyst inhibits the chain growth ability, and enhances the formation of light olefins (C2=–C4=), realizing the high selectivity of light olefins as 50.1 %. The properties of catalyst structure, active phase, reduction and carburization of obtained catalysts were characterized by N2 physisorption, XRD, SEM, XPS, TPR and DRIFTS measurements.

Nanowire accumulated Fe2O3/SiO2 spherical catalyst for Fischer-Tropsch synthesis

A catalyst consisting of SiO2 nanowires and highly dispersed Fe2O3 (denoted NW-FS) was synthesized in situ by iron-assisted amine-vapor-transport treatment. NW-FS was prepared by the direct transformation of an industrial spherical Fe2O3/SiO2 catalyst (denoted indus-FS). NW-FS was characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, N2-sorption measurements, X-ray photoelectron spectroscopy, and temperature-programmed reduction. NW-FS exhibited a high selectivity for light olefins, especially for ethene in the Fischer-Tropsch synthesis. This was because of the highly dispersed Fe2O3 and low diffusion resistance of its open structure. The C2–C4 olefin/paraffin ratio was 3.3, which was higher than that of indus-FS at 1.9.

Neat dimethyl ether conversion to olefins (DTO) over HZSM-5: Effect of SiO2/Al2O3 on porosity, surface chemistry, and reactivity

This study investigates the unique effect of the SiO2/Al2O3 ratio (30, 80, and 280) on the physicochemical and reactivity properties of the HZSM-5. This catalyst can be used for light olefin production using neat dimethyl ether (DTO). Crystallinity and porosity of the HZSM-5 samples as measured by XRD and N2 isotherms, show minimal effect of the SiO2/Al2O3 ratio. Acidity measurements by NH3-TPD, on the other hand, exhibit weak and strong acid sites, with both their ratio and total acidity being reduced with increasing SiO2/Al2O3. Experiments in the Berty reactor allow analyzing the changes of dimethyl ether (DME) conversion, light olefin selectivity and catalyst stability with SiO2/Al2O3 ratio. Moreover, these studies show that from the three HZSM-5 catalysts considered, the one with the SiO2/Al2O3=280 gives the highest light olefin selectivity. A maximum performance of 59% DME conversion at 1.16% coke load, and 50% light olefins selectivity (5% ethylene, 21% propylene, 24% butane) are observed at 450°C. In addition, this thermal level leads not only to find a promising catalyst performance for the SiO2/Al2O3=280 ZSM5 catalyst but to establish also its unchanged activity with time-on-stream. On the basis of the experimental data obtained it is postulated that an “in series” reaction network is adequate to describe the chemical changes with formed olefins undergoing eventually further transformation to paraffins and heavier aromatic hydrocarbons.

Optimization of catalytic glycerol steam reforming to light olefins using Cu/ZSM-5 catalyst

Response surface methodology (RSM) and multi-objective genetic algorithm was employed to optimize the process parameters for catalytic conversion of glycerol, a byproduct from biodiesel production, to light olefins using Cu/ZSM-5 catalyst. The effects of operating temperature, weight hourly space velocity (WHSV) and glycerol concentration on light olefins selectivity and yield were observed. Experimental results revealed the data adequately fitted into a second-order polynomial model. The linear temperature and quadratic WHSV terms gave significant effect on both responses. Optimization of both the responses indicated that temperature favouring high light olefin formation lied beyond the experimental design range. The trend in the temperature profile concurred commensurately with the thermodynamic analysis. Multi-objective genetic algorithm was performed to attain a single set of processing parameters that could produce both the highest light olefin selectivity and yield. The turn-over-frequency (TOF) of the optimized responses demonstrated a slightly higher value than the one which was not optimized. Combination of RSM, multi-objective response and thermodynamic is useful to determine the process optimal operating conditions for industrial applications.

Hierarchical ZSM-11 with intergrowth structures: Synthesis, characterization and catalytic properties

Hierarchical ZSM-11 microspheres with intercrystalline mesoporous properties and rod-like crystals intergrowth morphology have been synthesized using a spot of tetrabutylammonium as a single template. XRD, FTIR, SEM, TEM and N2 adsorption analysis revealed that each individual particle was composed of nanosized rod crystals inserting each other and the intercrystalline voids existing among rods gave a significant mesopore size distribution. Steam treatment result demonstrated the excellent hydrothermal stability of samples. Various crystallization modes including constant temperature crystallization (one-stage crystallization) and two-stage temperature-varying crystallization with different 1st stage durations were investigated. The results suggested that the crystallization modes were mainly responsible for the adjustable particle size and textural properties of samples while the small amount of tetrabutylammonium bromide was mainly used to direct the formation of both ZSM-11 framework and its intergrowth morphology. Furthermore, the performance of optimal ZSM-11 as an active component for the catalytic pyrolysis of heavy oil was also investigated. Compared with the commercial pyrolysis catalyst, the hierarchical ZSM-11 catalyst exhibited a high selectivity to desired products (LPG + gasoline + diesel), as well as a much lower dry gas and coke yield, plus a high selectivity and yield of light olefins ( C3=-C4=) and very poor selectivity to benzene. Therefore, fully open micropore-mesopore connectivity would make such hierarchically porous ZSM-11 zeolites very attractive for applications in clean petrochemical catalysis field.

Reaction Characteristic of MeAPSO-34 (Me=Mn, Co) Catalysts for Olefins Production from Dimethyl Ether

In DME to olefins (DTO) reaction, SAPO-34 catalyst with CHA structure is well known to be one of the catalysts with good performance. However, the SAPO-34 catalyst is easily deactivated due to coke deposition during DTO reaction. In this study, MeAPSO-34 catalysts (Me=Mn, Co) were prepared for the increase of the catalyst lifetime and their properties have been characterized by XRD and SEM. The DTO reaction was carried out over the MeAPSO-34 catalysts, and the results were compared with the SAPO-34 catalyst. The lifetime of MeAPSO-34 catalysts with high DME conversion and selectivity of light olefins was prolonged than that of the SAPO-34 catalyst. It may be concluded that the decrease of strong acid sites, which were responsible for the formation of coke, affect on the lifetime of the MeAPSO-34 catalysts. In addition, the CoAPSO-34 catalyst with a Co additive showed the best performance in terms of the catalytic lifetime and the selectivity to light olefins.

Control of Product Distribution of Fischer–Tropsch Synthesis with a Novel Rotating Packed-Bed Reactor: From Diesel to Light Olefin

A rotating packed-bed (RPB) reactor has been first applied to the Fischer–Tropsch synthesis (FTS) reaction. The main products of the FTS can be selectively formed by choosing the optimum high gravity level of the RPB reactor, which has opened a door to tailor the product distribution of FTS. The high selectivity of light olefins in RPB reactor provides a novel pathway to directly and effectively form light olefins from syngas, syngas to olefin (STO), which would avoid low-efficiency methanol synthesis and methanol-to-olefin (MTO) process.

Cracking Performance and Feed Characterization Study of Catalytic Pyrolysis for Light Olefin Production

The catalytic pyrolysis of heavy oils, gas oils, cracked diesel and gasoline fractions was investigated in a confined fluidized-bed reactor. The feed with a high H/C atomic ratio and low aromaticity showed good cracking performance, high feed conversion, and high yield and selectivity of total light olefins (i.e., ethene, propene, and butene). The cracked diesel and gasoline fractions with a low H/C atomic ratio and high aromaticity showed poor secondary cracking performance. A characterization parameter (KCP) was proposed to characterize the cracking performance of various feedstocks. The yield of total light olefins increased with an increase in KCP, despite the catalytic or thermal pyrolysis. KCP could be used as a criterion to evaluate the cracking performance of a feed for the production of light olefins. The cracking performance of a feed was considered desirable for KCP above 3.6 and undesirable for KCP below 2.8. Besides KCP, the United States Bureau of Mineral Correlation Index (BMCI) was also su...

High Propylene Selectivity in Methanol-to-olefin Reaction over H-ZSM-5 Catalyst Treated with Phosphoric Acid

H-ZSM-5 zeolite was treated with phosphorus acid by impregnating H-ZSM-5 with aqueous solutions of phosphoric acid at various concentrations. H-ZSM-5 (P-HZSM-5) modified with phosphoric acid was used as a catalyst for the methanol-to-olefin reaction. The molar ratios of P/Si and Si/Al in H-ZSM-5 and P-HZSM-5 were measured by EDX analysis. The Si/Al molar ratios of P-HZSM-5 increased with higher concentration of H3PO4 in the solution, which might be caused by partial dealumination of H-ZSM-5 by the H3PO4 treatment. The P/Si molar ratio of P-HZSM-5 after washing was proportional to the H3PO4 concentrations in the aqueous solutions. The remaining phosphorus species after the washing must be strongly adsorbed by interaction with the pore surface of H-ZSM-5 zeolite. The P-HZSM-5 catalyst showed very high propylene selectivity up to 57% with methanol conversion of 100%. Furthermore, catalyst stability was significantly improved for the P-HZSM-5 catalysts. Ammonia TPD spectra showed that the strong acid sites of H-ZSM-5 disappeared after the phosphoric acid treatment. Consequently, the formation of aromatics and coke was inhibited, resulting in higher light olefin selectivity and catalyst stability.

Light olefin synthesis from carbon dioxide by hydrogenation over Fe3(CO)12 supported on ZSM-5 zeolite catalyst

An Fe3(CO)12 catalyst supported on zeolite ZSM-5, prepared by a ‘multiple-reflux-impregnation’ method, exhibits high catalytic activity for hydrogenation of carbon dioxide and gives a high selectivity for light olefins, with a selectivity for ethene of >90 mol%.

Characterization of K-Fe/silicalite catalyst prepared via SMAI

Highly dispersed supported metal catalyst K-Fe/silicalite are prepared via SMAI method, and characterized by TEM, XRD, XPS and magnetic measurements techniques. Its catalytic properties in the CO hydrogenation making olefin reaction are also studied. The results show that the iron on the surface of the catalyst which has superparamagnetism, almost existed as the Fe0 before reacting. The catalyst exhibited high activity and selectivity for light olefins in CO+H2.

Effects of sodium, aluminium and manganese on the fischer-tropsch synthesis over alumina-supported iron catalysts

Addition of sodium, aluminium or manganese to alumina-supported iron catalysts can influence hydrocarbon distributions produced by hydrogenation of carbon monoxide. Combinations of sodium (Na/Fe = 0.1) with either aluminium (Al/Fe = 0.9) or manganese (Mn/Fe = 0.4) produce stable catalysts with high selectivity for light olefins and concurrent supression of methane selectivity. These effects are probably due to influences on both the dispersion of iron the support, and electronic promotion. Ratios of olefin/paraffin = 10 were observed in the range C3–C5, with methane selectivity reduced to less than 10%.