Nicoletta Panariti

Petroleum residue upgrading with dispersed catalysts: Part 1. Catalysts activity and selectivity

The results of a study aimed at the identification of the relevant chemical aspects involved in the process of upgrading heavy feedstocks in the presence of dispersed catalysts are discussed. The catalytic activity of different compounds was compared in terms of products yields and quality. Moreover, a detailed and systematic characterization of the catalysts recovered at the end of the reactions was achieved. The experimental work provided quite a large set of data, allowing to investigate the factors that may affect catalyst activity (precursor solubility, rate of activation, degree of dispersion, presence of promoters etc.). The results of this study demonstrate that the best performances are obtained by the microcrystalline molybdenite generated in situ by oil-soluble precursors. The nature of the organic ligand does not play a very relevant role in influencing the hydrogenation activity. The presence of phosphorus, however, significantly enhances hydrodemetallation, at least in terms of vanadium removal. Bimetallic precursors show a slight synergistic effect towards the hydrodesulfurization reaction. Microsized powdered catalyst precursors have a much lower catalytic activity compared to the oil-soluble ones.

Thermal cracking of petroleum residues: 1. Kinetic analysis of the reaction

Abstract In order to define a kinetic scheme and to calculate the kinetic parameters of the thermal cracking of petroleum residues, a vacuum residue of Belaym crude was thermally cracked at 410, 430, 450 and 470 °C for reaction times up to 120 min. The concentration of three pseudo-components, namely vacuum residue, distillate and coke, was detected during conversion and the data from these experiments were used for the definition of the kinetic model. Distillate production can be described as a simple first-order reaction while coke formation seems to be the consequence of consecutive reactions, in particular involving asphaltenes. A study of the structural changes of asphaltenes as a function of severity was also performed and the variations of the average molecular parameters with conversion were correlated. The results of this work have been used as reference data for a subsequent study of residue conversion in the presence of hydrogen-donor solvents.

Petroleum residue upgrading with dispersed catalysts: Part 2. Effect of operating conditions

The hydrotreatment of a petroleum residue in the presence of dispersed molybdenite was carried out within a wide range of operating conditions and catalyst loading. The effect of reaction severity as well as of molybdenum concentration on product distribution and quality was studied. Based on the experimental results, a simplified reaction scheme was proposed. The hydroprocessing of the residue was described in terms of the competition between two reactions: the direct conversion of the feedstock to distillate and coke, and the catalytic hydrogenation. Compared to thermal conditions, the presence of dispersed molybdenite controls very well coke formation; however, a trend of increasing formation of solids was observed at high catalyst concentrations. The overall upgrading of the feedstock requires significant amounts of molybdenum as well as relatively high hydrogen pressure.

THERMOCATALYTIC HYDROCONVERSION OF HEAVY PETROLEUM CUTS WITH DISPERSED CATALYST

Abstract This report concerns the use of unsupported dispersed catalysts in upgrading heavy feeds. The conversion of heavy crudes and resids into valuable products requires an efficient hydrogen activation. A method recently investigated deals with the use of metallic or organometallic (water- or oil-soluble) compounds, which under a thermal treatment decompose and give rise to a slurry of fine solid particles. This active form of catalyst promotes locally the spill-over of the hydrogen and therefore enhances the conversion of resids to distillate, reducing the coke formation. The primary objective of this report is to assess the current state of knowledge on this field, in order to identify new directions and strategies for Research.

The role of MoS2 nano-slabs in the protection of solid cracking catalysts for the total conversion of heavy oils to good quality distillates

The total conversion of the oil barrel to good quality fuels and distillates has been an overriding goal in the oil refinery industry. Today, it is even more important to improve the effective use of the energy fossil reserves. The actual technologies still produce variable amounts of low quality fractions (e.g. fuel oil, bunker oil) or by-products (e.g. coke). The evolution of the slurry hydrocracking technology can open the way to achieve the objective. This technology was originally developed in Germany in the first half of the last century and reconsidered by several research groups in the past decades. The catalyst used in the slurry process is still constituted by the same materials developed by German scientists in the last century, i.e. bulk, crystalline, nano-sized iron, molybdenum or tungsten sulfide. We have demonstrated now that it is possible to improve the catalytic performances by combining the excellent hydrogenation, hydrodesulfurization and hydrodemetallation properties of dispersed MoS2 catalyst with those of a conventional cracking catalyst. This dual catalyst system demonstrates for the first time the ability of dispersed MoS2 particles to protect the cracking catalyst against rapid decay due to coke accumulation and metal poisoning.

Thermal cracking of petroleum residues: 2. Hydrogen-donor solvent addition

Abstract The thermal cracking of a petroleum vacuum residue mixed with 20 wt% of a hydrogen-donor solvent (dihydrophenanthrene, DHP) was studied within the temperature range 390–450 °C and reaction times up to 4 h. The concentration of three pseudo-components, i.e. vacuum residue, distillate and coke, was observed during conversion and a simple kinetic model of the reaction was proposed. The comparison of these results with corresponding data previously recorded for simple thermal cracking shows that the presence of the donor solvent : 1. (1) decreases the rate of vacuum residue conversion with a particular effect on coke deposition reactions that are strongly inhibited; 2. (2) enhances the maximum distillate production by about 10–15 wt%; 3. (3) allows operation at higher severities while maintaining the visocity of the residual oil (tar) at low values.