Effect of the Chemical Structure of Alkyl Acrylates on Their Defoaming Activity in Crude Oil: Experimental and Theoretical Studies

The study and development of non-silicon-based defoamers for crude oils have been slightly investigated worldwide, despite urgent requirements of the petroleum industry. The suppression of crude oils has usually been resolved using commercial silicone defoamers (polysiloxanes), but these compounds cause serious problems such as catalyst poisoning in petroleum refining processes. In this study, an acrylic homopolymer series with different molecular structures was synthesized by emulsion polymerization, to determine the influence of the chemical repetitive unit on the defoaming capability. The following acrylic homopolymers were considered: poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA), poly(hexyl acrylate) (PHA), poly(2-ethylhexyl acrylate) (PEHA), and poly(dodecyl acrylate) (PDA). These polyacrylates were evaluated as foam suppressors in heavy crude oil, by means of a static method based on the sudden pressure drop of the system, which has the advantage of mimicking the gas/crude oil conditions in a biphasic separation tank. PHA, PEHA, and PDA showed greater antifoaming activity than that of silicones to suppress crude oil foam but only at an appropriate weight-average molecular weight ((M) over bar (w)). The strong influence of the length of pendant groups in the repetitive unit, which constitutes polyacrylates, could be evidenced by this way. The defoaming activity of the series of acrylic homopolymers was correlated with two series of physicochemical parameters obtained by theoretical calculations using HyperChem software and by molecular dynamics simulations. A "pitching off" mechanism of bubble collapse could be clearly established by this last simulation method. These novel antifoaming agents, based on a variety of polyacrylates, are innocuous during crude oil refining, and their fabrication cost is economically competitive, so they can be applied in industrial separation tanks to eliminate petroleum foams.