| 1. |
- Haglund, R., et al.
(author)
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Upgrading of hydropyrolysis coal tar by hydroprocessing
- 1991
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In: Erdöl Erdgas Kohle. - 0179-3187. ; 107:5, s. 232-235
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Journal article (peer-reviewed)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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| 2. |
- Otterstedt, J-E, et al.
(author)
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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
-
In: Applied Catalysis. - 0166-9834 .- 1873-3867. ; 70:1, s. 43-52
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Journal article (peer-reviewed)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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| 3. |
- Persson, A-E, et al.
(author)
-
The synthesis of discrete colloidal particles of TPA-silicalite-1
- 1994
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In: Zeolites. - : Elsevier BV. - 0144-2449. ; 14:7, s. 557-567
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Journal article (peer-reviewed)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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| 4. |
- Schoeman, B.J., et al.
(author)
-
Analysis of the crystal growth mechanism of TPA-silicalite-1
- 1994
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In: Zeolites. - : Elsevier BV. - 0144-2449. ; 14:7, s. 568-575
-
Journal article (peer-reviewed)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.
(author)
-
Colloidal zeolite suspensions
- 1994
-
In: Zeolites. - : Elsevier BV. - 0144-2449. ; 14:2, s. 110-116
-
Journal article (peer-reviewed)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, B.J., et al.
(author)
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Synthesis and size tailoring of colloidal zeolite particles
- 1993
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In: Journal of the Chemical Society. Chemical communications. - 0022-4936. ; :12, s. 994-995
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Journal article (peer-reviewed)abstract
- A novel method is presented whereby it is possible to synthesize colloidal zeolite particles of a pre-determined size
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| 7. |
- Schoeman, B.J., et al.
(author)
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The synthesis of colloidal zeolite hydroxysodalite sols by homogeneous nucleation
- 1994
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In: Zeolites. - : Elsevier BV. - 0144-2449. ; 14:3, s. 208-216
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Journal article (peer-reviewed)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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| 8. |
- Sterte, Johan
(author)
-
Preparation and properties of large-pore La-Al-pillared montmorillonite
- 1991
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In: Clays and clay minerals. - 0009-8604 .- 1552-8367. ; 39:2, s. 167-1737
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Journal article (peer-reviewed)abstract
- Large-pore La-Al-pillared montmorillonite was prepared by reacting montmorillonite with hydrothermally treated mixtures of aluminum chlorohydrate and lanthanum chloride. The large-pore La-Al-pillared montmorillonite is characterized by basal spacings of about 26 Å, surface areas of 300-500 m2/g, and pore volumes in the range 0.2-0.3 cm3/g. The most favorable pillaring solution had an OH/Al ratio of 2.5, a La:Al ratio of 1:5, and was 2.5 M with respect to Al.
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| 9. |
- Sterte, Johan
(author)
-
Preparation and properties of pillared interstratified illite/smectite
- 1990
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In: Clays and clay minerals. - 0009-8604 .- 1552-8367. ; 38:6, s. 609-616
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Journal article (peer-reviewed)abstract
- Pillared, regularly and randomly interstratified illite/smectite (I/S) was prepared by interacting aluminum chlorohydrate with I/S in aqueous dispersion. I/S samples from Kinnekulle, Sweden, ranging in composition from 30-60% smectite layers, were used as starting clays. The pillaring resulted in a separation of the smectite layers in the I/S of about 9 Å, as estimated by X-ray powder diffraction and by nitrogen adsorption studies. Only the smectite layers of the clay were modified by the pillaring procedure. The pillared products had surface areas of 200-260 m2/g and pore volumes of about 0.18 cm3/g. The uptake of Al by the clay and the micropore surface area of the pillared products were proportional to the fraction of smectite layers in the I/S. The thermal and hydrothermal stability of the pillared I/S was similar to that of pillared montmorillonite prepared using the same procedure.
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