| 1. |
- Persson, A.E., et al.
(författare)
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Synthesis of stable suspensions of discrete colloidal zeolite (Na, TPA)ZSM-5 crystals
- 1995
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Ingår i: Zeolites. - 0144-2449. ; 15:7, s. 611-619
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of zeolite ZSM-5 in the form of stable suspensions of colloidal crystals from clear homogeneous solutions has been achieved from synthesis mixtures with low sodium and high TPAOH concentrations. The ultimate size of the discrete crystals is in the range 130-230 nm with a narrow particle size distribution. The crystal growth was monitored by the direct method of dynamic light scattering. An increasing alumina concentration was found to decrease the crystal growth rate, the number of crystals produced, and the ZSM-5 yield. The final crystal size was found to increase with increasing alumina concentration in the synthesis solution. The number of crystals produced decreased with an increased alkalinity in contradiction to what has been found for colloidal TPA-silicalite-1. This together with the presence of the two competing processes, crystal growth and crystal dissolution, which are both catalyzed by hydroxide ions, suggests the presence of an optimum alkalinity (depending on the alumina concentration).
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| 2. |
- Persson, A-E, et al.
(författare)
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The synthesis of discrete colloidal particles of TPA-silicalite-1
- 1994
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Ingår i: Zeolites. - : Elsevier BV. - 0144-2449. ; 14:7, s. 557-567
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Tidskriftsartikel (refereegranskat)abstract
- Discrete colloidal particles of TPA-silicalite-1 with an average particle size of less than 100 nm and with a narrow particle-size distribution have been synthesized in clear homogeneous solutions. The factors influencing particle size have been investigated. High silica contents in conjunction with high alkalinities favor the synthesis of colloidal silicalite suspensions. Polymeric silica sources result in larger particles compared to those synthesized with tetraethoxy silane-presumably due to the different nucleation kinetics. It was found that the base concentration influences nucleation behavior in that high alkalinities result in the nucleation of a relatively large number of particles. The growth rates are constant for a given silica content irrespective of the alkalinity, at least within the alkalinity range studied. This result is ascribed to a rate-limiting surface reaction step that is a consequence of the synthesis mixture composition. The linear growth rates recorded are lower than those typically reported in the literature.
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| 3. |
- Elvin, F.J., et al.
(författare)
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Processes for demetalization of fluid cracking catalysts
- 1988
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Ingår i: Fluid catalytic cracking. - Washington, DC : American Chemical Society (ACS). - 0841215340 ; , s. 229-236
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Konferensbidrag (refereegranskat)abstract
- Three processes, Demet III, Demet X and New Demet, for demetallization of metal poisoned octacat fluid cracking catalysts were investigated. These processes removed a significant part of the V (30-40%) from the catalyst. The New Demet and Demet III were very effective in removing Ni (88% and 80%, respectively) while practically no Ni could be removed by Demet X. The Demet procedures also proved effective in removing other contaminants like Fe and Cu. All Demet methods resulted in increased cracking activities as determined by the micro-activity test. The conversions increased from 65% for the untreated catalyst to 76-78% for samples treated according to the different Demet procedures. The increase in activity was accompanied by a corresponding increase in gasoline yield of 5.0-6.5%.
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| 4. |
- Schoeman, B.J., et al.
(författare)
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Analysis of the crystal growth mechanism of TPA-silicalite-1
- 1994
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Ingår i: Zeolites. - : Elsevier BV. - 0144-2449. ; 14:7, s. 568-575
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Tidskriftsartikel (refereegranskat)abstract
- The method of chronomal analyses (dimensionless time analyses) according to Nielsen has been applied to the growth of discrete colloidal particles (particle sizes of less than 100 nm) of TPA-silicalite-1 to gain information on the crystal growth mechanism. The increase in particle size in the range 30-95 nm was monitored by dynamic light scattering and yielded the result that the increase in crystal size is a linear function of synthesis time. The linear growth rate of the almost spherical particles at 100°C is 3.79 nm/h - a low value that is ascribed to the synthesis conditions employed. Furthermore, the particle number concentration was shown to be constant, indicating that no secondary nucleation event occurs during the growth process. The crystallization kinetics recorded in the temperature interval 80-100°C correlate with a first-order surface reaction controlled growth mechanism in which the corresponding apparent energy of activation is 42 kJ/mol. A diffusional mechanism as well as a compound growth mechanism in which both surface reaction and diffusion compete for rate control can be ruled out as being operative.
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| 5. |
- Schoeman, B.J., et al.
(författare)
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Colloidal zeolite suspensions
- 1994
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Ingår i: Zeolites. - : Elsevier BV. - 0144-2449. ; 14:2, s. 110-116
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented whereby it is possible to synthesize colloidal zeolite sols containing discrete zeolite particles with an average particle size of less than 150 nm and with a narrow particle-size distribution. The zeolite sols exhibit typical colloidal characteristics such as Tyndall light scattering and a low rate of sedimentation and coagulation due to electrolyte concentrations in excess of the critical coagulation concentration. The effect of sodium on the crystallization kinetics, product distribution, and particle size has been investigated. Relatively high Na2O AL2O3 ratios favor the formation of large crystals of zeolite A. Low Na2O AI2O3 ratios result in colloidal crystals of zeolite Y, whereas intermediate ratios yield zeolite Y and/or zeolite A with particle sizes of ca. 100 nm. Midsynthesis addition of sodium allows for a fivefold increase in zeolite yield.
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| 6. |
- Schoeman, Brian J., et al.
(författare)
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Dynamic light scattering applied to the synthesis of colloidal zeolite
- 1995
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Ingår i: Journal of porous materials. - 1380-2224 .- 1573-4854. ; 1:2, s. 185-198
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Tidskriftsartikel (refereegranskat)abstract
- The use of dynamic light scattering as an analysis method within the field of zeolite synthesis has proved to be a powerful and robust tool with which the particle size and the corresponding particle size distribution can be determined. The method has been employed in the evaluation of the crystallization of several types of colloidal zeolite from 'clear homogeneous' solutions. Examples of such zeolites are zeolite N-Y, hydroxysodalite, and TPA-silicalite-1. The fact that the particle size can be determined in as-synthesized zeolite sols as a function of synthesis time enables one to follow, for example, the crystallization process in terms of particle size increase, the process of particle size tailoring as well as to obtain information on the growth mechanism in zeolite synthesis. The colloidal nature of sols following redispersion of zeolite powders and colloidal zeolite organosols has been assessed using dynamic light scattering. The advantages as well as problems associated with the use of dynamic light scattering for characterization of colloidal zeolites are discussed. © 1995 Kluwer Academic Publishers.
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| 7. |
- Schoeman, B.J., et al.
(författare)
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Synthesis and size tailoring of colloidal zeolite particles
- 1993
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Ingår i: Journal of the Chemical Society. Chemical communications. - 0022-4936. ; :12, s. 994-995
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Tidskriftsartikel (refereegranskat)abstract
- A novel method is presented whereby it is possible to synthesize colloidal zeolite particles of a pre-determined size
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| 8. |
- Schoeman, B.J., et al.
(författare)
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The synthesis of colloidal zeolite hydroxysodalite sols by homogeneous nucleation
- 1994
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Ingår i: Zeolites. - : Elsevier BV. - 0144-2449. ; 14:3, s. 208-216
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal suspensions of discrete particles of microcrystalline hydroxysodalite have been synthesized from clear homogeneous solutions wherein the average particle size determined by dynamic light scattering is 37 nm with a narrow particle-size distribution. Particle-size analysis performed with various methods yield results that are in agreement. The growth-limiting nutrient has been identified as alumina. As a result, the midsynthesis addition of alumina results in further particle growth to 48 nm with the corresponding increase in zeolite yield. Hence, the fine control of particle size and thereby zeolite yield without the formation of a secondary particle population is shown to be possible. Direct measurements of zeolite yield and particle size allow for a detailed evaluation of the events that occur during crystallization.
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| 9. |
- Sterte, Johan, et al.
(författare)
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Characterization of alumina-montmorillonite complexes
- 1988
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Ingår i: Applied Catalysis. - 0166-9834 .- 1873-3867. ; 38:1, s. 119-129
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Tidskriftsartikel (refereegranskat)abstract
- Changes in pore structure on thermal and hydrothermal treatment of three different alumina-montmorillonite complexes were investigated using nitrogen adsorption-desorption measurements, thermogravimetric analysis, adsorption of condensed aromatic molecules and acidity measurements by pyridine adsorption. The surface area retention of the alumina-montmorillonites after thermal and hydrothermal treatment increased with increasing temperature of hydrothermal treatment of the aluminum chlorohydrate solution used in the preparation of the materials. Hydrothermal treatment of the alumina-montmorillonites at 750°C for 18 h resulted in increased average layer distances in the materials primarily due to a collapse of micropores. The acidity retentions of the alumina-montmorillonites, measured by pyridine adsorption, were approximately proportional to the corresponding surface area retentions.
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| 10. |
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| 11. |
- Haglund, R., et al.
(författare)
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Upgrading of hydropyrolysis coal tar by hydroprocessing
- 1991
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Ingår i: Erdöl Erdgas Kohle. - 0179-3187. ; 107:5, s. 232-235
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Tidskriftsartikel (refereegranskat)abstract
- Upgrading of a hydropyrolysis coal tar by hydroprocessing was investigated using different process conditions. The response of the hydropyrolysis tar to hydroprocessing was compared to those of a conventional coal tar and two heavy oil fractions. At comparable conditions, the removal of heteroatoms from the hydropyrolysis tar was more effective than from the conventional tar and, in particular, than from the oil fractions. Using conditions typical for hydroprocessing of heavy oil fractions, the contents of N, O as well as S in the hydropyrolysis tar were reduced by more than 90%. Hydroprocessing also resulted in a considerable increase in the gasoline fraction of the tar.
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| 12. |
- Otterstedt, J-E, et al.
(författare)
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Catalytic cracking of heavy oil over catalysts containing different types of zeolite Y in active and inactive matrices
- 1988
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Ingår i: Applied Catalysis. - 0166-9834 .- 1873-3867. ; 38:1, s. 143-155
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Tidskriftsartikel (refereegranskat)abstract
- The effects of addition of alumina to the matrices of cracking catalysts containing different types of zeolite Y, on their cracking performance, were investigated using a micro activity test and two different feed oils. For the heavier feed oil, the alumina addition resulted in a higher conversion at the same catalyst to oil ratio independent of the type of zeolite. This higher conversion was accompanied by a greater selectivity for coke and a lower selectivity for gasoline. For the lighter feed oil the effect of alumina addition on the total conversion was much less pronounced while the effects on the selectivity were similar to those observed using the heavier feed. The performance of the catalysts in a commercial fluid catalytic cracking unit is discussed in view of their coke forming tendencies and the heat balance of the cracker.
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| 13. |
- Otterstedt, J-E, et al.
(författare)
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Catalytic cracking of heavy oils
- 1988
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Ingår i: Fluid catalytic cracking. - Washington, DC : American Chemical Society (ACS). - 0841215340 ; , s. 266-278
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Konferensbidrag (refereegranskat)abstract
- The effects of composition of heavy oils derived from petroleum and biomass, on their response to cracking over catalysts of various composition were investigated. The contribution to the conversion from different types of cracking was estimated and the effect of temperature on the product distribution was studied. Heavy fractions of Wilmington crude contained more aromatics and polars compared with a conventional HVGO. The conversion of the Wilmington fractions increased with boiling point range. The zeolitic contribution to the conversion decreased while the matrix contribution remained constant and the contribution from thermal cracking increased. The low H/C-ratio of FCC feed derived from liquefied biomass led to low conversion and poor gasoline selectivity. Addition of alumina to the matrix resulted in a catalyst more active for heavy oil cracking but with a poor selectivity. Alumina-montmorillonite catalysts showed activities for heavy oil cracking comparable to that of a conventional, zeolite based, cracking catalyst. Effects of matrix composition and zeolite type on the heavy oil cracking performance are discussed.
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| 14. |
- Otterstedt, J-E, et al.
(författare)
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Colloidal components in solutions of alkali silicates
- 1987
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 115:1, s. 95-103
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Tidskriftsartikel (refereegranskat)abstract
- The particle size of colloidal silica in 1 to 5 M SiO2 solutions of lithium, sodium, potassium, and cesium silicates in the ratio range 1.5-20 moles of SiO2 per mole of M2O was determined by reaction with molybdic acid and by Sears titration. The particle size increased from 1.0 to 4.5 nm with increasing ratio but did not depend on the type of alkali-metal cation. The amount of monomeric silicate ions decreased sharply with increasing ratio from 35% for ratio 2 to 2% for ratio 15 in 5 M SiO2 solutions. The polymeric particles were extracted into tetrahydrofuran or tertiary butylalcohol at pH 2, without changing the particle size, in yields which increased to more than 95% for the highest ratios. Previous dilution caused the particle size to grow in high-ratio solutions but to decrease in low-ratio solutions.
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| 15. |
- Otterstedt, J-E, et al.
(författare)
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Effects of matrix alumina-silica ratio on the performance of heavy oil cracking catalysts containing zeolite Y in matrices of amorphous silica-alumina
- 1991
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Ingår i: Applied Catalysis. - 0166-9834 .- 1873-3867. ; 70:1, s. 43-52
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Tidskriftsartikel (refereegranskat)abstract
- The effects, on the activity and selectivity for cracking heavy oils, of varying the alumina-silica ratio in amorphous aluminosilicate matrices for CREY, REUSY, USY, and LZ zeolites were studied using a microactivity test and two different feedstocks. With a heavy aromatic feedstock gasoline yields and octane numbers showed a pronounced maximum for matrix alumina-silica weight ratios in the range 90:10-70:30 and with CREY zeolite as the main active component. With a lighter aliphatic feedstock the gasoline yields and octane numbers were much less dependent on the alumina-silica weight ratio. The effects on pore structure and selectivity of hydrothermal treatment of conventional amorphous aluminosilicate catalysts and zeolite catalysts with amorphous silica-alumina matrices having alumina-silica weight ratios in the range 90:10-70:30 are discussed.
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| 16. |
- Sterte, Johan, et al.
(författare)
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A study on the preparation and properties of fibrillar boehmite
- 1986
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Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 21:10, s. 1159-1166
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Tidskriftsartikel (refereegranskat)abstract
- Effects of temperature, time and Al2O3 Cl molar ratio on the structure and porous nature of synthetic fibrillar boehmite prepared by hydrothermal treatment of aluminum chlorohydrate solutions were investigated. Fibrillar boehmite crystallized at temperatures above 120°C in a solution with an Al2O3 Cl ratio of 0.93 employing a reaction time of 24 h. The ultimate particles in a sample prepared at 160°C had a length of approximately 1000 Å and a diameter of about 50 Å. Increasing crystallinity with increasing temperature up to 220°C and with increasing reaction time up to 24 h was observed while differences in Al2O3 Cl ratio resulted in minor effects. The deionized and freeze dried or directly freeze dried products possessed surface areas in the range 50-250 m2/g and pore volumes in the range 0.1-1.0 cm3/g. Pore volume distributions were calculated for some samples. Effects of deionization are discussed.
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| 17. |
- Sterte, Johan, et al.
(författare)
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Catalytic cracking of heavy oil : use of alumina-montmorillonites both as catalysts and as matrices for rare earth exchanged zeolite Y molecular sieve
- 1988
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Ingår i: Applied Catalysis. - 0166-9834 .- 1873-3867. ; 38:1, s. 131-142
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Tidskriftsartikel (refereegranskat)abstract
- Three types of alumina-montmorillonite complexes were evaluated as cracking catalysts, alone and in admixture with rare earth exchanged zeolite Y (REY), using the micro activity test and three different feed oils. Prior to the test, all catalysts were steam treated at 750°C for 18 h. For cracking of heavy oils, the alumina-montmorillonites showed conversions similar to that of a reference catalyst containing 20% REY in a kaolin-binder matrix. The alumina-montmorillonites showed higher coke and lower gas yield when compared with the reference catalyst while the gasoline yields were essentially the same over the two types of catalysts. The selectivity for light cycle oil was considerably greater for the alumina-montmorillonites. When used as matrices for REY, the alumina-montmorillonites resulted in considerably more active catalysts at the same zeolite content compared with a catalyst having a kaolin-binder matrix, while the selectivity properties differed very little between the two types of catalysts.
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| 18. |
- Törncrona, A., et al.
(författare)
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Preparation of a novel fibrous catalyst support
- 1995
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 5:1, s. 121-126
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Tidskriftsartikel (refereegranskat)abstract
- A method for preparing wash-coated silica fibres is described. Colloidal silica particles (22 nm) were deposited onto the surface of 2 μm amorphous silica fibres, surface-modified by deposition of a thin film of amorphous silica with a high density of silanol groups and with the charge reversed by adsorption of a water-soluble cationic polymer. This deposition resulted in an increase in specific surface area from 0.9 m2 g-1 for the fibre to 40 m2 g-1 for the fibre with deposited silica particles. Hydrothermal treatment at 750°C in 100% steam for 24 h fixed the silica particles onto the fibre surface and made them coalesce into a strong porous structure. During this process, the specific surface area decreased from 40 to 30 m2 g-1. Particles of fibrillar boehmite were deposited onto the surface of silica fibres. The boehmite particles were fixed by thermal treatment at 550°C, during which the boehmite was transformed into γ-Al2O3. The specific surface area of the alumina wash-coated silica fibres was 28 m2 g-1. Wash-coated fibres were characterized by nitrogen adsorption-desorption analysis, scanning and transmission electron microscopy (SEM and TEM).
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