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Filtration of Hydrocarbons containing asphaltenes and resins - Bea

Published 12 February 2018 | By Bea Technologies SpA

The high-boiling constituents of petroleum are influencing the physical properties of crude oil , especially in case of filtration.

In particular Asphaltenes and resins are characterized , as high molecular weight materials, with the tendency to form aggregates in the crude-oil.

The aggregates are produced by the presence of intermolucar hydrogen bonding between the asphaltenes and the resins. It appears that when resins and asphaltenes are present together , hydrogen bonding are one of the mechanism by which resin-asphaltenes are achieved and resin-asphaltene interactions are preferred over asphaltene-asphaltene interactions. As a result asphaltenes and resins are forming a complex mixture of constituents of higher molecular weight.

The interactions between polar aromatics ( resins ) and non-polar are leading to the formation of MICELLES. The micelles center is formed from polar molecules of asphaltene ( with pronounced aromatic nature ) which are progressively surrounded by other more soluble molecules ( of less aromatic mature ) places between the center and the periphery.

It has been observed that the resins play an important function in stabilizing the asphaltenes in the crude oil. Since the asphaltenes are incompatible with the oil fractions, asphaltenes dispersion is attributable mainly to the resins. Under unfavourable conditions the asphaltenes species might aggregate into clusters that are unstable and can precipitate or may easily stuck to any surface during filtration or any separation process.

The model require that the asphaltene micelles are composed of an insoluble molecular core that associates with the resins, thereby providing steric stabilization against flocculation and precipitation. The elementary micelles units can further cluster into larger particles similar to flocs.

Asphaltene molecules ---- micelle ----micelle clusters ----- flocs

An important corollary of petroleum composition is that the mole fraction of the resins is always larger than that of the asphaltenes and hence the micelles are expected to be richer in resins.

The addition to crude.oil of non-polar solvents can procure the reduction of solubility parameters or polarity of hydrocarbon medium. The solubilization of the resins is leading to dissociation of the resin-asphaltene complexes, resulting in destabilization of the asphaltenes and relative precipitation/phase separation.

The size of the asphaltene agglomerate varies as a function of the temperature, the asphaltene concentration, and the presence of the resins. This establishes that the self-association of the asphaltenes is reversible and that the molecular size in the solution state result from a thermodynamic equilibrium between primary particles and reversible aggregates.

Filtration

It has been recorded that in presence of both asphaltenes and resins, the formation of micelles and aggregates is highly probable. The amount and size of the aggregates are influenced by the temperature. For temperature over 150°C the aggregates are reduced and generally dissolved.

For temperature below 80 - 125°C the formation of aggregates might be consistent procuring a fast clogging of the filter media.
The temperature and process conditions are even influencing the average size of the aggregates. Generally was seen that a filtration rating of 75 micron is less sensible to the clogging by retention of ashaltene /resin conglomerates due to the fact that as pressure drop through the media is increasing then the aggregates are partially disrupted and the asphaltenes should be able to be extruded on the other side of the filter media while this fact it is not possible for really solid particles and contaminants.

The situation to be avoided is the formation of a compact layer of asphaltenes /resin aggregates on the surface of filter media which can lead to a fast clogging of the filter surface with rapid increase of the pressure drop and sudden decrease of the flow.
In this case the backwashing cannot wash out the compact layer , manual cleaning is necessary or soaking in a low molecular weight solvent /gasoil to soften the compact layer.

BEA Technologies S.p.A - TECHNICAL ASSISTANCE