Objective
TO ESTABLISH EMPIRICAL CORRELATIONS ALLOWING PREDICTIONS TO BE MADE ON COKE FORMATION AND ON THE ENSUING CATALYST DEACTIVATION IN HEAVY PETROLEUM FEEDSTOCK HYDROPROCESSING. TO POSSIBLY IDENTIFY PROCESS CONDITIONS - CATALYST FORMULATIONS THAT WILL SUPPRESS OR DELAY SAID HARMFUL EFFECTS.
Catalysts used for the hydrotreating of heavy petroleum fractions suffer very rapid initial coke build up as a result of strong initial adsorption of the polyaromatic fractions including the nitrogen containing aromatic compounds on the surface.
Some sulphur may be located in the coke, but contrary to nitrogen compounds, the sulphur containing molecules are not adsorbed on the surface.
The fact that the product sulphur concentration stays constant through this initial period shows that the hydrodesulphurization (HDS) activity is not affected by initial coking within the first hour of vaccum gas oil (VGO) hydrotreating.
The hydrodenitrification (HDN) activity may appear to decrease, but more likely this is a result of nitrogen removal by initial adsorption of nitrogen species combined with a constant HDN conversion.
On the basis of studies by temperature programmed techniques it can be concluded that the majority of the nitrogen appears to be present as strongly adsorbed organic nitrogen species, which are oxidized at a relatively high temperature. Some coke may cover these species. Evidence of a small amount of adsorbed nitrogen hydrogen species is also found. The majority of these species is to be found in the active phase of the catalyst.
Nuclear microprobe methods have been developed that allow the measurement of the distribution of carbon, hydrogen, nitrogen and heavier elements in coked catalyst pellets.
Applications have included studies of the variability of profiles in batches of used pellets, investigation of interrelationships between coke components and limited kinetic studies. Many of these applications have proven to be successful and nuclear microprobe methods will continue to be used in the study of catalyst coking.
Solid state carbon-13 cross polarization-magic angle spinning nuclear magnetic resonance (CP-MAS NMR) has in priciple been found to be a powerful tool for the characterization of coke samples.
The application has included calculati ons of aromaticity and hydrogen to carbon ratios of the coke deposits. A careful interpretation of the results is very important since this kind of study involves a lot of assumptions. Correlations, however, begin to emerge and a continued research as concerns methods and application will secure a better understanding of the coke formation at the molecular level.
THERE IS A NEED FOR MORE STABLE CATALYSTS FOR THE HYDROPROCESSING OF HEAVY PETROLEUM FRACTIONS. AMONG THE DEACTIVATING PROCESSES, COKE FORMATION HAS AN IMPORTANT ROLE. A MULTIPHASE STUDY IS ENVISAGED TO SHED LIGHT ON THIS PHENOMENON.
A SUITABLE SAMPLING DEVICE WILL FIRST BE DEVELOPED ALLOWING THE MONITORING OF THE COKE ON THE CATALYST AS A FUNCTION OF TIME (2 TO 12 MONTHS) AND OF ITS POSITION IN THE REACTOR UNDER INDUSTRIALLY MEANINGFUL REACTION CONDITIONS (UP TO 15 MPA H2 PRESSURE, 650-730 KELVIN DEGREES FOR RESIDUAL OILS).
CHARACTERIZATION OF COKE STRUCTURES ON THE CATALYST PARTICLES WILL THEN BE PERFORMED BY SUITABLY DEVELOPED EXTRACTION TECHNIQUES, 13C NMR, HNMR, MAS NMR AS WELL AS TEMPERATURE PROGRAMMED REDUCTION (TPR) IN COMBINATION WITH MASS-SPECTROMETRY OF THE REDUCTION PRODUCTS.
PARTICULARLY USEFUL RESULTS ARE EXPECTED FROM THE COMBINED USE OF SOLID-STATE 13C NMR AND TPR. COKE PRECURSORS CHARACTERIZATION WILL ALSO BE ATTEMPTED. THE SLUDGES FORMED BY UNSTABLE FEEDSTOCK WILL FIRST BE LOOKED INTO. THE POSSIBLE ROLE OF HETEROATOMS IN THEIR FORMATION WILL BE CONSIDERED. USEFUL INFORMATION IS EXPECTED TO STEM FROM CATALYST TESTING WITH MODEL COMPOUNDS LIKE BIPHENYL, DIBENZOTHIOPHENE, INDOLE AND VARIOUS PHENOLS AS WELL AS FROM A PROPER USE OF EXTRACTION TECHNIQUES IN SPENT CATALYSTS. COKE PROFILE MEASUREMENTS WILL BE EFFECTED BY SUITABLY DEVELOPED NUCLEAR MICROPROBE ANALYSIS. FROM SIMULTANEOUS CARBON METAL PROFILES, USEFUL CORRELATIONS BETWEEN THE DISTRIBUTIONS OF VARIOUS CONTAMINANTS ARE EXPECTED.
IN THE SECOND PHASE IT IS INTENDED TO IDENTIFY THE CRITICAL VARIABLES, RESPONSIBLE FOR COKE FORMATION, THROUGH A NUMBER OF SPECIALLY DESIGNED HYDROPROCESSING EXPERIMENTS.
BESIDES OBTAINING USEFUL EMPIRICAL CORRELATIONS, EFFORTS WILL BE MADE TO GET A FUNDAMENTAL UNDERSTANDING OF THE OBSERVATIONS MADE.
MODELS WILL BE OBTAINED RELATING COKE GROWTH AND THE CHANGES IN ITS STRUCTURE TO THE EXTENT OF THE OIL CONVERSION AND, AT A LATER STAGE, TO THE NATURE OF THE FEEDSTOCK AND OF THE CATALYST.
FINALLY A MODEL FOR CATALYST DEACTIVATION BY COKE SHOULD BE DEVELOPED,LINKING THE DEACTIVATION RATES TO FEEDSTOCK PROPERTIES, OPERATING CONDITIONS AND CATALYST PROPERTIES. THIS MODEL SHOULD PROBABLY BE INCORPORATED INTO AN EXISTING MODEL FOR METAL DEACTIVATION, THAT HAS BEEN DEVELOPED BY THE INDUSTRIAL PARTNER.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- agricultural sciences agricultural biotechnology
- engineering and technology environmental engineering energy and fuels fossil energy petroleum
- natural sciences chemical sciences catalysis
- natural sciences chemical sciences organic chemistry aromatic compounds
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Coordinator
2800 Lyngby
Denmark
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