Improved Demulsifier Chemistry: A Novel Approach in the Dehydration of Crude Oil

Abstract

Summary With the ever-growing demand for more efficient dehydration and desalting of crude oil, classic demulsifiers no longer perform satisfactorily in most cases, and new chemical systems are required. This paper describes new emulsionbreakers, generally polyester amines, and paper describes new emulsionbreakers, generally polyester amines, and gives detailed laboratory studies of their advantages, over classic demulsifiers: more complete migration to theinterface, improved emulsion breaking and coalescence, improved effluent waterquality, and partial corrosion inhibition. These new demulsifiers combined withclassic emulsion breakers have been successfully tested. Introduction Almost 60 million B/D of crude oil is produced worldwide. At least 60million B/D of water is coproduced from the oil-bearing reservoirs. Modem oil production requires efficient dehydration and desalting of crudeoil, as well as treatment of effluent water to an environmentally acceptablelevel. To ensure smooth oil productio operations, demulsifiers must be used, but only at low dosage levels. Chemical demulsifiers are specially tailored toact where they are needed-at the oil/water interface. Their high efficiencymakes their use a very attractive, economic way to separate oil and water. Over the years, better products and processes have resulted in a greatreduction in the demulsifier concentration required. This trend is stillcontinuing. Improvements in demulsification technology are concentrated in thefollowing areas: synthesis of new demulsifiers; development of laboratory andfield techniques for testing demulsifier combinations; and better design of surface treating facilities--i.e., more favorable conditions for chemical emulsiondestabilization, forced coalescence in pipelines and treating units, settling, and cleaner phase separation. Demulsifier Chemistry Table 1 is a brief listing of the chemicals used to demulsify crude oilemulsions since the beginning of the century. The industrial availability of ethylene oxide (EO) in the 1940's allowed the production of fatty acid, fattyalcohol, and alkylphenol ethoxylates. production of fatty acid, fatty alcohol, and alkylphenol ethoxylates. This was the first time that nonionics were usedfor this purpose. With the creation of ethylene oxide/propylene oxide (EO/PO) blockcopolymers, the first "genuine" demulsifiers were available. Addition of EO and/or PO to linear or cyclic (acid or base catalyzed) p-alkylphenolformaldehyde resins and to diamines or higher functional amines yields classes of modified polymers that perform quite well at relatively low concentrations. Furthermore, these demulsifier bases were converted to high-molecular-weightproducts by reaction of one or more with difunctional compounds such productsby reaction of one or more with difunctional compounds such as diacids, diepoxides, di-isocyanates, and aldehydes, delivering a host of potentialemulsion breakers. However, a need still exists for new, more efficient demulsifiers andfinishing agents. We synthesized such a system from commercially availableproducts. Fig. 1 shows the basic chemistry of these compounds. The newdemulsifiers are best described as "poly-esteramines"; they areobtained by polycondensation of an EO/PO poly-esteramines"; they areobtained by polycondensation of an EO/PO block copolymer, an oxalkylated fattyamine, and a dicarboxylic acid. A linear terpolymer with this idealizedstructure results. The nitrogen atoms are accessible to cationization. Polyesteramines are converted by alkylation to quaternized polyesteramine withno problems. problems. This three-component system obviously offers a broadrange of variations. By altering the molar ratios and interchanging one or more of the three agents, we can quite easily control the molecular weight, theshape of the polymer, and the hydrophile/lipophile balance value. For example, it is possible to create a highly branched polyesteramine by incorporation of apolyfunctional EO/PO polyesteramine by incorporation of a polyfunctional EO/POpolymer. The hydro- and oleophobic properties are determined by the polymer. The hydro- and oleophobic properties are determined by the EO/PO ratios, thelength of the alkyl chain in the fatty amine, and the type of carboxylicacid. Fig. 2 illustrates the approximate molecular-weight distribution of singlecomponents, EO/PO blocks, and polyesteramines. It reinforces the idea thatthese effective demulsifiers are not clearly defined molecules, but polymerswith a broad molecular-weight distribution. The degree of quaternization andcharge density also can be influenced. With this chemical "box ofblocks," it is possible to construct or to tailor demulsifiers for nearlyall problems possible to construct or to tailor demulsifiers for nearly allproblems in crude oil dehydration and desalting. The development of multiform structures from single blocks in Fig. 1 appearsrather complex. The chosen structure of these high-performance polyesteraminedemulsifiers becomes clearer once the properties and functions of the singleprecursors involved are properties and functions of the single precursorsinvolved are examined individually. It has been known for a long time that EO/PO-block copolymers and all theirvariants are exceptionally active interfacially. Therefore, they are the activecomponents in the demulsification process; they effect the migration to andspreading at the interface of process; they effect the migration to andspreading at the interface of oil-in-water emulsions. The dominant property of fatty amines and their quaternary cationicderivatives is their substantiveness. They adhere to all types of surfaces, acharacteristic behavior used in demulsification. At interfaces of crude oil emulsions, organic matter (asphaltenes, oilresins, naphthenic acids, paraffins, and waxes) and inorganic material (clay, carbonates, silica, and metallic salts) accumulate. Fatty amines andquaternaries adsorb preferentially at these surfaces. The dicarbonic acid ismainly a chemical link that helps combine the above-mentioned compounds andthus their properties. The mechanism of demulsification by polyesteramines maybe deduced from these properties. After migration to the oil/water interface, the oligomeric or poly-mericdemulsifier molecule is fixed by the amine quaternary component poly-mericdemulsifier molecule is fixed by the amine quaternary component by adsorption. The EO/PO-block copolymer is not freely mobile because it is attached to theamine by the dicarbonic acid. Consequently, it is held at the interface, wherethe emulsion destabilization occurs. Thus, the interfacial activity isincreased. This concept provides a plausible explanation for the good performance ofthese polyesteramines at low concentrations. The fast, performance of thesepolyesteramines at low concentrations. The fast, complete, and lastingadsorption of the polyesteramine at the metal surface is caused by its highdegree of substantiveness. The amines and moieties also contribute to a sharp interface and to asmaller oil-in-water turbidity. They may be viewed as partial structures of aclassic invert emulsion breaker attached to a classic demulsifier. The resultsof our laboratory work and field testing support this statement. Laboratory Testing Improved evaluation methods play an important role in the development of newdemulsifiers. Demulsification tests must be carefully designed to simulateexisting oilfield dehydration and desalting conditions as closely aspossible. SPEPE P. 334