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DEVELOPMENT OF A PROCESS FOR CONVERTING HEAVY CRUDE OILS AND PETROLEUM REFINING RESIDUES.

Ziel

TO DEVELOP A PROCESS FOR OBTAINING HIGH YIELDS OF VALUABLE LOWBOILING FRACTIONS FROM HEAVY REFINERY AND COAL-TAR RESIDUES AS WELL AS FROM PROBLEMATICAL HEAVY CRUDES, BY EXTRACTION WITH GASES UNDER HYPERCRITICAL CONDITIONS;
Research was carried out to develop a process which with the aid of supercritical gas extraction allowed high amounts of low boiling and thus high value fractions to be recovered from difficult to process crude oils, residues from primary petroleum processing and residues from coal based chemical processes. Extraction using supercritical water was seen as a promising approach.

Results showed that when using supercritical water as extraction agent it was not possible to achieve a higher extract yield than that obtained when using the straight hydrocarbon mixture of n-butane and isobutane. The quality of the extract in terms of ash and heavy metal content deteriorated.

Preliminary tests using pure asphaltenes showed that even without the addition of hydrogenating gases and/or catalysts, supercritical water was capable of converting high molecular weight, n-heptane insoluble compounds into oil like, n-heptane soluble products under temperature and pressure conditions such as were applied in the extraction tests. That there was still no increase in the extract yield is explained by the fact that superimposed on the first effect is a thermally induced conversion of n-heptane soluble compounds into n-heptane insoluble products (formation of 'secondary asphaltenes'). In the processing of vacuum residues, for example, the n-heptane soluble constituents would have to be separated prior to extraction with supercritical water. Preliminary extraction using supercritical butane is well suited to this purpose.

Based on the results obtained a profitability study was carried out. From this the following can be stated:
2 stage extraction of the vacuum residue using butane and subsequently using supercritical water is advantageous in comparison with single stage extraction using supercritical butane only given high prices for both the feed and the extract recovered;
in the case of both process variants a profit can only be attained if the extracts recovered are at least DM 100/t extract more expensive than the vacuum residue charged;
the conversion of heavy oil residues by extraction using supercritical water (viewed in isolation) is uneconomical as processing costs over DM 700/t extract would be incurred. Combination with extraction using butane yields only slight advantages if any.
OWING TO THE HIGH CONTENT OF ASPHALTENES,SULPHUR AND HEAVY METALS PRESENT IN REFINERY RESIDUES, THE REFINING OF HEAVY CRUDES POSES PROBLEMS. THE MOST PROMISING WAY OF INCREASING THE LIGHT-FRACTION YIELD SEEMS TO BE STEAM EXTRACTION UNDER HYPERCRITICAL CONDITIONS. SUCH AN OPERATION INVOLVES CHEMICAL TRANSFORMATIONS TOO, SINCE WATER REACTS, GIVING RISE TO HYDROLYSIS AND HYDROGENATION OF CRACKED SPECIES. IN THE FIRST SUBPROGRAMME, AN ATMOSPHERIC RESIDUE, A VACUUM RESIDUE AND A HEAVY CRUDE WILL FIRST BE SUBJECTED TO EXTRACTION WITH HYPERCRITICAL PROPANE AND PETROLEUM EITHER IN ORDER TO PROVIDE A BASIS FOR COMPARISON.
EXTRACTIONS WITH HYPERCRITICAL STEAM WILL THEN BE CARRIED OUT AT DIFFERENT PARAMETER VALUES. THE STEAM-DISSOLVED PHASE WILL THEN BE BROUGHT IN CONTACT WITH HYDROGEN IN A CATALYST BED, NAMELY (NI, MO) S ON GAMMA-ALUMINA. TEMPERATURES FROM 390 TO 450 CELSIUS DEGREES, PRESSURES FROM 260 TO 320 BAR AND CONTACT TIME FROM 10 TO 30 MIN. WILL BE USED. IN THE SECOND SUBPROGRAMME, SIMILAR STUDY WILL MAKE USE OF HOMOGENEOUS CATALYSIS BY THE SAME METAL IONS. THE VALUE OF CONVERSION RESIDUES AS FEEDSTOCKS FOR COKE OR GAS PRODUCTION WILL BE ASSESSED. FINALLY, COAL AND PETROLEUM PITCHES WILL BE EXTRACTED WITH HYPERCRITICAL STEAM + PROPOANE, WITH THE AIM OF RENDERING THEM SUITABLE FOR FURTHER PROCESSING (E.G. TO CARBON FIBERS) THROUGH REMOVAL OF ASH AND QUINOLEINE-INSOLUBLE RESIDUES. FRACTIONAL CONDENSATION OF THE EXTRACT LEADS TO INTERESTING FRACTIONS OF GOOD PURITY. THE PROBLEM OF WASTEWATER DISPOSAL AFTER RECOVERY OF DISSOLVED VALUABLE MATERIALS OR OXIDATION WILL BE CONSIDERED. DATA FOR THE DESIGN OF A PILOT PLANT WILL BE MADE AVAILABLE.

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