Abstract
Effects of a catalyst in the presence of a hydrogen donor solvent on cracking reactions for upgrading Arabian Heavy vacuum residue were studied using a small scale (0.1BPD) pilot plant (Fig. 1).
For the study, three types of cracking were studied:
Case A: no catalyst present
Case B: relatively low activity demetallization catalyst and high LHSV
Case C: relatively high activity demetallization catalyst and low LHSV
The properties and structural changes of the 545°C residues were analyzed.
Based on the comparative studies on the following hydrogen consumption and formation of toluene insolubles (Table 1), general properties (Table 2), elemental analyses of toluene insolubles (Table 3), and compositions of the residues (Fig. 2), it was found that, by increasing the activity of the catalyst, the following observations were made:
(1) Formation of asphaltenes and toluene insolubles can be reduced.
(2) Hydrogenation and desulfurization can be promoted and, as a result, H/C of the cracked residues and that of toluene insolubles are increased.
(3) Chemical hydrogen consumption is increased. To investigate more in detail, the effects of the presence of a catalyst, molecular weight and 1H-NMR measurements of the 545°C residues were carried out.
It was found that:
(1) By adding a catalyst, cleavage of the side chains is milder, but the extent of hydrogenation of the aromatic rings is increased (Table 4, Fig. 3).
(2) However, when relatively low activity catalysts were used as in these runs, differences in the cracking reactions of the three cases mentioned are not so distinct (Table 4, Fig. 3).
(3) In these cases, the main cracking reactions are the cleveage of the side chains and naphthene rings, although some differences can be recognized among the cases (Table 4, Fig. 3).
From observations made, it can be concluded that thermal cracking is predominant in the cracking reactions when a hydrogen donor solvent and a demetallization catalyst are present together, and the catalyst seems to stabilize the free radicals formed. Therefore, the chemical hydrogen consumption remains smaller by virtue of controlling excessive hydrogenation of the aromatic rings compared to catalytic cracking. These results can support the conclusions described in our previous paper (part 1).1)
To make clearer the conclusion described above, decreases in the reaction rate constants for cracking, desulfurization and vanadium removal were checked for Case C (a similar check has already been made for another run in a previous paper).1) The reaction rate constants at base temperatures for desulfurization and vanadium removal gradually decreased with increasing time of run: however, the reaction rate constants of cracking did not decrease except during the period immediately after the start of the run (Fig. 5). These observations support the conclusion that the catalyst does not appreciatively contribute to the cracking reactions.
