Film-Forming Compounds from Crude Oils, Interfacial Films and Paraffin Deposition

Abstract

ABSTRACT A method was developed to collect interface-active film material from theoil/water interface. The film-forming material was subjected to infrared andmass spectrometric analysis. The combined analysis data indicate that the polarorganic material consists to a large extent of aliphatic esters of aromaticacids. The existence of smaller amounts of ketones, aldehydes, naphthalene andanthrazene derivatives, carboxylic acids and organic nitro compounds was alsoindicated. Long chain aliphatic material was found incorporated within themultilayered film structures. The molecular weight range of the inter faciallyadsorbed organic molecules lies between 200 and 420, with the accent on thehigher mass values. The surface exposed groups of the multilayer films arethought to consist of a closely packed array of CH, groups. A hypothesisconcerning an interrelationship between the formation of interfacial films andparaffin deposition is given. INTRODUCTION THE EXISTENCE OF FILMFORMING COMPOUNDS in crude oils and the possibleimplication to some problems of concern to the petroleum industry has beenrecognized for a number of years. It has been found that the surface exposedgroups of polar-non-polar molecules, adsorbed on a solid or a liquid surface, will completely determine the subsequent wettability characteristics of thelatter (1). The relevancy of this fact to problems such as relativepermeability measurements, secondary recovery methods and paraffin depositionhas been mentioned by several researchers (2, 3, 4). Attempts have been made inthe past to isolate film forming compounds from crude oils and to define theirchemical nature. Metalporphyrins complexes (5, 6), free naphthenic acids, acidanions and their salts (7), and highly oxygenated low molecular weightfractions of the resin and asphalt fractions of crude oils (2) have been listedas interface-active compounds. A severe crystal growth modification in waxslovent mixtures, induced by asphaltic material, has been reported by Birdwell(8), Chichakli (9) and others (10). Patton (11) found, during paraffindeposition studies, that the presence of a high boiling point crude oilfraction, both in the wax solvent system and as a pre-adsorbed film, inhibitedthe formation of paraffin deposits. A film balance study of the physicalcharacteristics of films formed by benzene solutions of crude oils, includingtheir distillation and chromatographic fractions at the oil/water interface, was described earlier (12, 13). The indication was that the 700°F+ distillationresidual and, in turn, their asphaltic sub fractions are the major contributorsof interface-active material to the films formed by the original crude oils.Hence, without trying to adopt any specific model for the structure of acolloidal " asphaltene particle," it seemed that either the asphaltic fractionscontained free polar molecules a priori or the benzene as a solvent played arole in " activating" polar molecules through destruction of a number ofasphaltene particles.