Abstract
In the BCL process, the CLB, non-distillable fractions of the primary hydrogenation products is treated in the solvent de-ashing section to remove ash and parts of preasphaltenes.
Then the recovered de-ashed oil (DAO) is mixed together with the solvent fraction, followed by hydrotreatment of the mixture at a fixed bed reactor in the secondary hydrogenation section. The secondary hydrogenation reactivity is affected by the primary hydrogenation conditions producing the CLB. In this paper, effects of the chemical structure of DAO on the secondary hydrogenation were inestigated by using a fixed bed reactor with DAO produced under the different primary hydrogenation conditions in the 50t/d pilot plant.
Several experiments were carried out to investigate the effect of catalyst bed length and liquid velocity on the rate of secondary hydrogenation of DAO. The rate of secondary hydrogenation reaction can be expressed by a liquid hold-up model in trickle bed reactors proposed by Henry and Gilbert. DA0 conversion decreased with fa and N/C atomic ratio in DAO, and increased with the amount of HI-BS and 0/C atomic ratio in DAO, while the selectivity of the reaction products and the aparent activation energy were almost constant.
The calculated values from the regression analysis for DAO conversion were agreement with experimental values. The characteristic structual parameters showed that the aromaticity of DAO increased with reaction temperature in the primary hydrogenation section, whereas the average molecular weight of DAO measured by VPO and the amount of preasphaltenes decreased. From results of structural analysis, the average molecular structure of DAO may be considered to consist of roughly 2 unit structure of clusters including 3 to 4 aromatic rings. These results indicated that the rate of DAO coversion to 420°C fractions decreased with the increase of aromaticity, such as the number of aromatic ring in the unit structure of DAO, affected by the reaction temperature in the primary hydrogenation section producing the CLB.
