CONSTITUTION OF ASPHALTENES AND RELATED STUDIES

CHEMICAL CHARACTERISTICS OF BITUMEN WAS ATTEMPTED BY EXAMINATION OF THE ASPHALTENE FRACTION. A SERIES OF ASPHALTENES FROM A WIDE RANGE OF STRAIGHT-RUN, PRECIPITATED AND BLOWN BITUMENS WAS PREPARED. ALL THE ASPHALTENES WERE SUBJECTED TO ELEMENTAL ANALYSIS, INFRARED AND NUCLEAR MAGNETIC RESONANT SPECTROSCOPIC EXAMINATION AND MOLECULAR WEIGHT AND COLOR INTENSITY DETERMINATIONS. A ROUGH CORRELATION IS DEMONSTRATED BETWEEN AROMATICITY AND COLOR INTENSITY. CERTAIN STRUCTURAL DIFFERENCES BETWEEN THE VARIOUS ASPHALTENES WERE SHOWN BY THE NMR STUDIES. THE N-PENTANE ASPHALTENES SHOWED MORE HYDROGEN, LOWER AROMATICITIES, COLOR INTENSITIES AND APPARENT MOLECULAR WEIGHTS, MORE AROMATIC SUBSTITUTION, SHORTER ALIPHATIC CHAINS AND FEWER AROMATIC GROUPINGS THAN THE CORRESPONDING N-HEPTANE ASPHALTENES. TESTS SHOW THAT THE N-HEPTANE ASPHALTENES CAN BE RAGARDED AS BEING A GOOD CRITERION OF THE HARD CORE CENTRE OF THE ASPHALTENES MICELLE IN THE BITUMEN COLLOIDAL SYSTEM. THERMAL DEGRADATION STUDIES ON KUWAIT N- HEPTANE ASPHALTENES HAVE SHOWN THAT MOST OF THE ORIGINAL NITROGEN AND SULPHUR OCCURS IN THE MORE STABLE RING SYSTEMS OF THE ASPHALTENE MOLECULES, AND INDICATE THAT THE AROMATIC GROUPINGS CONTAIN AT LEAST 6 FUSED BENZENE NUCLEII. THE EFFECT OF AIR-BLOWING OF BITUMEN AT 450 F. ON THE TOTAL ASPHALTENE IS TO DECREASE THE CARBON, NITROGEN AND SULPHUR CONTENTS, AROMATICITY AND COLOR, BUT TO RAISE THE APPARENT MOLECULAR WEIGHT OF THE MIDDLE EAST ASPHALTENES UP TO THE LEVEL OF THE STRAIGHT-RUN VENEZUELAN ASPHALTENES. SULPHURIZATION AND BLOWING OF KUWAIT PPA RESULT IN THE GENERAL CHANGES REPORTED FOR BLOWING, EXCEPT THAT THE SULPHUR CONTENT AND COLOR INTENSITY OF THE ASPHALTENES INCREASE ON SULPHURIZATION. BITUMEN BLOWING AT 600 F RESULTS IN THE FORMATION OF ASPHALTENES WHICH ARE MORE SIMILAR TO THOSE ALREADY PRESENT IN THE BITUMEN, THAN ARE THOSE PRODUCED AT 450 F. WORK ON THE MECHANISM OF THE BLOWING PROCESS INDICATES THAT AT LEAST THREE TYPES OF REACTION OCCUR: (1) FORMATION OF HIGH MOLECULAR WEIGHT ASPHALTENES BY DEHYDROGENATION, POLYMERIZATION, AND POSSIBLY ESTERIFICATION, OF THE ASPHALTENES ORIGINALLY PRESENT, (2) FORMATION OF LOW MOLECULAR WEIGHT ASPHALTENES (OF HIGHER HYDROGEN CONTENT) FROM THE RESINS PRESENT IN THE BITUMEN, AND SOME POLYMERIZATION OF THESE, AND (3) SPLITTING OF SIDE CHAINS FROM THE ASPHALTENE MOLECULES TO GIVE FREE RADICAL INTERMEDIATES, FOLLOWED BY FURTHER OXIDATION AND/OR RECOMBINATION REACTIONS. THE MECHANISMS INVOLVED ARE CONSIDERED TO VARY WITH TEMPERATURE.