TO IMPROVE KNOWLEDGE OF THE REACTIONS THAT TAKE PLACE DURING THERMAL TREATMENT OF HEAVY PETROLEUM CUTS WITH A VIEW TO ENHANCING THE STABILITY OF PRODUCTS.
In a visbreaking pilot plant residues (both atmospheric and vacuum) obtained from an URAL crude oil were processed by means of a true boiling distillation. Trials were performed at fixed temperature varying the apparent residence time and at different operating temperatures for each residence time value. To underline the influence of the residence time on the kinetics of the reactions, an operating temperature of 460 C was chosen as a reference value for trials performed at 6 various flow rates. 3 trials were performed at 470 C and at 480 C. 1 trial was done at 450 C and 465 C.
The effects of the kinetic parameters (residence time and temperature) on density and viscosity showed a clear proportional dependence on the residence time with temperature greatly increasing such dependence, both for atmospheric and vacuum residues. Sulphur and vanadium content showed no significant variation. Investigation into the relative variation of asphaltene content against flow rate showed the asphaltenes had the same reactivity after treatment at 370 C and 570 C. Variation in the atmospheric residue was greater than that for vacuum residue.
In addition atmospheric residue showed an unusual decrease of relative variation of asphaltene content which was probably due to the influence of the vaporized phase in the reactor. Therefore, a shorter real residence time was obtained and compared with the kinetic equivalent. Contrary to the expected result, in the vacuum residue in which the vaporization effect was negligible, the relative variation of asphaltenes increased from 30 % at 450 C, to near 120% at 480 C.
Finally, the kinetic aspect of the process was investigated, data obtained at different residence time and fixed temperature allowed evaluation of the first order reaction constant; employing data at varying temperatures and a fixed residence time determined the activation energy E and frequency factor A.
Employing the CORBET method, 5 different classes of compounds wer e identified: paraffin, aromatics, light resins, heavy resins and polar resins. The most relevant aspects were the rapid disappearance of heavy polar resins with increasing residence time and an increase in light resins with residence time.
It is thought that heavy and polar resins react mainly to transform themselves into asphaltenes, by means of dealkylation and condensation reactions, and partially into light resins, by means of splitting reactions. Light resins, however, can originate from the vacuum gas oil (VGO) where paraffin and aromatics undergo condensation reactions.
TRADITIONAL TREATMENTS OF HEAVY RESIDUES, SUCH AS COKING, THERMAL CRACKING AND VISBREAKING, RESULT IN GAS OILS AND VACUUM DISTILLATES OF MARKED INSTABILITY, AS IS SHOWN, FOR EXAMPLE, BY THE FORMATION OF INSOLUBLE IN THE FORMER AND BY VISCOSITY CHANGE AND PRECIPITATION OF ASPHALTENES IN THE LATTER. IN COMMERCIAL PLANTS, REDUCING THE SEVERITY AND USING SUITABLE SOLVENTS ARE THE COMMONEST WAYS OF MINIMIZING THESE PHENOMENA. IT IS INTENTED TO GAIN A BETTER INSIGHT INTO THE UNDERLYING REACTIONS AND DEVICE NEW MEANS OF MANAGING THEM THROUGH A COLLABORATIVE RESEARCH PROGRAMME INVOLVING SEPARATE CONTRACTS WITH AGIP PETROLI, SELM AND ERG SPA (SEE EN3C004100-I (A) AND EN3C004600-I (A)). ERG'S CONTRIBUTION WILL CONCERN THE FOLLOWING SUBPROGRAMMES:
- DEVELOPMENT OF ANALYSIS METHODS TO COMPLEMENT TO THOSE DEVELOPED BY THE OTHER COLLABORATING CONTRACTORS, E.G. TBP TECHNIQUES. MUCH EFFORT WILL ALSO BE DEVOTED TO ACQUIRING OPTIMUM ANALYTICAL INFORMATION BY COMBINING HPLC, COUPLED WITH THE CORBET METHOD, WITH CONVENTIONAL SOLID-LIQUID CHROMATOGRAPHY TECHNIQUES.
- DESIGN, CONSTRUCTION AND OPERATION OF A MICRO-REACTOR. THE DESIGN CRITERIA WILL AIM, INTER ALIA, AT TEMPERATURE PROFILES, RESIDENCE TIME, MASS FLOWS (HIGHER THAN 600 LB./SEC.SA.FT.) AND SOAKING FACTORS (NEAR 2 CU. FT. DAY/BARREL) CLOSE TO THOSE APPLIED IN THE DESIGN OF COMMERCIAL REACTORS. FULLY AUTOMATED CONTINUOUS OPERATION, THANKS TO A CENTRAL COMPUTER UNIT WHICH ALSO PERFORMS DATA LOGGING, WILL ENSURE EXELLENT PARAMETER CONTROL AND REPRODUCIBILITY. THUS EACH EFFLUENT COMPOSITION WILL BE RELIABLY CORRELATED WITH VARIATIONS IN PARAMETER VALUES. FEED COMPOSITIONS WILL BE AS SIMPLE AS POSSIBLE SO AS TO MAKE FOR EASIER INTERPRETATION OF THE RESULTS OF THE RUNS AND ENABLE RELIABLE FORECASTS TO BE MADE CONCERNING THE BEHAVIOUR OF MORE COMPLEX FEEDS.
- AN ATTEMPT TO DEVELOP AN ALGORITHM FOR GENERAL USE WHICH WILL ENABLE YIELDS TO BE FORECASTED AND OPTIMIZED ON THE BASIS OF THE TBP COMPOSITION OF FEEDS. FOR THIS PURPOSE, THE RESULTS OBTAINED BY THE OTHER COLLABORATING CONTRACTORS ON TARS AND CRUDES WILL BE TAKEN INTO ACCOUNT.