| 1. |
- Häggström, Caroline, et al.
(författare)
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Catalytic methanol synthesis via black liquor gasification
- 2012
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Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 94:1
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Tidskriftsartikel (refereegranskat)abstract
- Biofuel production from gasified black liquor is an interesting route to decrease green house gas emissions. The only pressurised black liquor gasifier currently in pilot operation is located in Sweden. In this work, synthesis gas was taken online directly from this gasifier, purified from hydrocarbons and sulphur compounds and for the first time catalytically converted to methanol in a bench scale equipment. Methanol was successfully synthesised during 45 h in total and the space time yield of methanol produced at 25 bar pressure was 0.16-0.19 g methanol/(g catalyst h). The spent catalyst exposed to gas from the gasifier was slightly enriched in calcium and sodium at the inlet of the reactor and in boron and nickel at the outlet of the reactor. Calcium, sodium and boron likely stem from black liquor whereas nickel probably originates from the stainless steel in the equipment. A slight deactivation, reduced surface area and mesoporosity of the catalyst exposed to gas from the gasifier were observed but it was not possible to reveal the origin of the deactivation. In addition to water, the produced methanol contained traces of hydrocarbons up to C 4, ethanol and dimethyl ether. © 2011 Elsevier B.V. All rights reserved.
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| 2. |
- Rownaghi, Ali A., et al.
(författare)
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Selective dehydration of methanol to dimethyl ether on ZSM-5 nanocrystals
- 2012
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 119-120:7, s. 56-61
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Tidskriftsartikel (refereegranskat)abstract
- The effects of crystal size and mesoporosity on the performance of various synthesized ZSM-5 zeolites in catalytic dehydration of methanol to dimethyl ether (DME) reaction have been investigated. The reactions were carried out in a continuous flow fixed-bed reactor at temperatures between 180 to 320 °C and 1.1 bar. It was found that methanol conversion enhances by decreasing crystal size and increasing the reaction temperature. Uniform nanocrystal catalysts showed highest activity and stability for methanol dehydration to dimethyl ether in the temperature range studied. On the other hand, both the activity and selectivity of large crystals were low. The high activity and DME yield for the nanocrystals is due to smaller mass transport resistance for the Nano-ZSM-5 sample, due to the small crystal size. Furthermore, it was found that the selective dehydration of methanol to dimethyl ether on ZSM-5 catalyst is based on the product selectivity inside the pore channels; in other words, the selectivity to dimethyl ether should be 100% if there is no acid site on the external surface. From this evidence, it is concluded that in methanol dehydration to DME, the reaction activity is related to the crystal size, whereas the DME selectivity is determined by the uniformity of Al distribution, which determines acidity of external surface and low mass transport resistance of small crystal size. Therefore, a decrease in the number of acid sites on the external surface and reduction in crystal size are key ways to enhance catalytic selectivity and activity, respectively.
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| 3. |
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| 5. |
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| 6. |
- Rownaghi, Ali, et al.
(författare)
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Innovative process for the synthesis of vanadyl pyrophosphate as a highly selective catalyst for n-butane oxidation
- 2010
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 165:1, s. 328-335
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Tidskriftsartikel (refereegranskat)abstract
- Vanadyl pyrophosphate (VPO) catalysts are used for the selective oxidation of light alkanes, which are based on vanadyl hydrogen phosphate hemihydrate (VOHPO40.5H2O) as the precursor. Catalyst precursor with well-defined crystal size has been successfully synthesized for the first time, using a simple one-step high-pressure autoclave that was surfactant-free and water-free method with significantly lower temperature and shorter reaction time. VOHPO40.5H2O was prepared from V2O5 using an isobutanol, 1-pentanol, 1-heptanol and 1-dectanol as both solvent and reducing agent at elevated temperatures (100, 120, and 150°C). This new method significantly reduced the preparation time and lowered production temperature (50%) of catalyst precursor (VOHPO40.5H2O) when compared to conventional hydrothermal synthesis methods. VOHPO40.5H2O can be obtained at temperature far below 150°C. It was found that the presence of 1-heptanol and 1-decanol in the reaction mixtures is crucial for obtaining a well-defined crystal size of precursor phase and solely generated impurity, [VO(H2PO4)2]. Our findings show that both the phase composition and morphology of vanadium phosphate can be influenced by the use of different reducing agent and temperature during the preparation process. This new methodology produces catalysts with a much higher surface area (ca. 23m2g-1) compared with those materials prepared by slow hydrothermal synthesis (ca. 9.5m2g-1). Finally, the yield of maleic anhydride was significantly increased from 21.3% for conventional catalyst to 37.9% for the new solvothermal catalyst.
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| 7. |
- Rownaghi, Ali, et al.
(författare)
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Methanol to gasoline-range hydrocarbons : influence of nanocrystal size and mesoporosity on catalytic performance and product distribution of ZSM-5
- 2011
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 50:21, s. 11872-11878
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Tidskriftsartikel (refereegranskat)abstract
- Improvement of synthesis methods for ZSM-5 zeolite, as a heteregeneous catalyst, is essential for a wide variety of different reactions in the chemical industry. Decreasing zeolite crystal size and introducing mesoporosity into the zeolite structure can improve its performance in catalytic reaction through decreasing the micropore diffusion path length and increasing the external surface area. In this study, three different ZSM-5 zeolites (Nano-ZSM-5, Meso-ZSM-5, and Con-ZSM-5) were prepared by a single-templating procedure, and the reaction of methanol to gasoline-range hydrocarbons was evaluated over synthesized ZSM-5 crystals in a fixed bed continuous flow reactor. Good correlation was observed between catalytic performance, product distribution, mesoporosity, and crystal size of ZSM-5 zeolites. Both nanocrystal and mesoporous ZSM-5 zeolites showed long-term catalytic stability compared with the conventional one. In contrast to conventional ZSM-5 catalyst, the nanocrystal and mesoporous ZSM-5 catalysts showed high selectivities for light olefins and alkyl aromatics, respectively, in the conversion of methanol to gasoline. These results dearly indicate that both crystal size and mesoporosity significantly influence the ZSM-5 lifetime and product distribution
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| 8. |
- Rownaghi, Ali, et al.
(författare)
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Novel synthesis techniques for preparation of ultrahigh-crystalline vanadyl pyrophosphate as a highly selective catalyst for n-butane oxidation
- 2010
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 49:5, s. 2135-2143
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Tidskriftsartikel (refereegranskat)abstract
- The vanadyl hydrogen phosphate hemihydrate (VOHPO40.5H2O), with well-defined crystal size, has been successfully synthesized for the first time, using a simple one-step solvothermal process that was free of surfactants and water and had a short reaction time and low temperature. The synthesis was performed via the reaction of V2O5 and H3PO4 with an aliphatic alcohol (1-propanol or 1-butanol) at high temperatures (373, 393, and 423 K) in a high-pressure autoclave. The mixture of reactions directly gave the VOHPO40.5H2O, which is a valuable commercial catalyst precursor for the selective oxidation of n-butane to maleic anhydride. The catalyst precursors were dried by microwave irradiation. The reaction conditions (by varying the reducing agent and reaction temperature) were used further for optimization of the crystallite size, surface area, morphology, and activity of the nanostructure of vanadium phosphate oxide [(VO)2P2O7] catalyst. This new method significantly reduced the preparation time and lowered the production temperature (50%) of catalyst precursor (VOHPO40.5H2O), when compared to conventional hydrothermal synthesis methods. The as-prepared (VO)2P2O7 catalyst under various conditions exhibited remarkably different physical and chemical properties, indicating the potential of the suggested method in tuning the crystalline structure and surface area of (VO)2P2O7 to improve its catalytic performance. It was found that the length of the carbon chain in an alcohol and reaction temperature in the solvothermal condition had a great impact on the chemical and physical properties of resulting catalysts. Interestingly, there was no trace of VO(H2PO4)2, which is an impurity noted to be readily formed under solvothermal preparation conditions. The precursors and catalysts were characterized using a combination of powder X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area measurement, scanning electron microscopy (SEM), and temperature-programmed reduction in hydrogen (H2-TPR). A correlation between the surface area of the catalyst and the activity was observed. Finally, the yield of maleic anhydride was significantly increased from 21% for conventional catalyst to 38% for the new solvothermal catalyst.
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| 9. |
- Rownaghi, Ali, et al.
(författare)
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Selective formation of light olefin by n-hexane cracking over HZSM-5 : influence of crystal size and acid sites of nano- and micrometer-sized crystals
- 2012
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 191, s. 528-533
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Tidskriftsartikel (refereegranskat)abstract
- A series of HZSM-5 catalysts with different characteristics (size, texture, surface acid site density) was prepared by hydrothermal method and their performances were investigated in catalytic cracking of n-hexane (as a model compound of light naphtha) at 370 and 470 ˚C. Uniform nano-sized HZSM-5 (ca.∼ 0.1 μm) was found to be a very attractive catalyst, showing a selective formation of propylene and light olefin (about 83% at WHSV = 3 h−1) and a high resistance to the deactivation. Under similar conditions micro-size HZSM-5 (ca.∼ 2.0 μm) produced higher amount of other hydrocarbons i.e., C5+) and coke. This is because nano-size crystals have a larger external surface area, which offers a higher number of pore entrances and enhances the reaction occurring inside the pore channels compared with large miro-size crystals. In addition, it is found that the selectivity to light olefin increases by decreasing the number of acid sites on the external surface. This leads to the conclusion that in n-hexane cracking to light olefin, the activity and selectivity are related to the crystal size and the ratio of surface acid sites to total acid sites. As shown, reducing crystal size and decreasing acid sites on the external surface are remarkable ways to enhance catalytic activity and selectivity, respectively.
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| 10. |
- Rownaghi, Ali, et al.
(författare)
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Solvothermal synthesis of vanadium phosphate catalysts for n-butane oxidation
- 2009
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 155:1-2, s. 514-522
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we have developed a simple, low-cost, template-free and surfactant-free solvothermal process for synthesis of vanadyl hydrogen phosphate hemihydrate (VOHPO4·0.5H2O) with well defined crystal size. The synthesis was performed by reaction of VPO4·2H2O with an aliphatic alcohol (isobutyl alcohol, 1-pentanol, 1-hexanol, 1-heptanol or 1-decanol). This afforded well crystallized VOHPO4·0.5H2O by solvothermal methods at 120°C temperature. This new method significantly reduced the preparation time and lowered production temperature (50%) of catalyst precursor (VOHPO4·0.5H2O) when compared to conventional hydrothermal synthesis methods. By varying the reducing agent, the solvothermal evolution process from layered tetragonal phase VOPO4·2H2O to orthorhombic phase VOHPO4·0.5H2O was observed. It was found that the length of carbon chain in an alcohol in the solvothermal condition had a great impact on chemical and physical properties of resulting catalysts. Interestingly, there was no trace of VO(H2PO4)2an impurity noted to be readily formed under solvothermal preparation condition. Therefore, this study introduces a more facile synthetic pathway to V(III) compounds. In addition, the microwave-synthesized catalysts exhibited some properties superior to those of conventionally synthesized catalyst such as better stability, crystallinity, and catalytic activity in the production of maleic anhydride. The characterization of both precursors and calcined catalysts was carried out using X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometer (ICP-AES), N2physisorption, temperature programmed reduction (H2-TPR) and scanning electron microscopy (SEM). The XRD pattern of the active catalyst prepared by this solvothermal method confirmed the presence of smaller crystal size (between 6 and 13nm along 020 planes) of vanadium phosphate catalyst with higher specific surface area. Finally, the yield of maleic anhydride was significantly increased from 29% for conventional catalyst to 44% for the new solvothermal catalyst.
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