The Use of Chemicals in the Treatment of Produced Oily Waters
Authors: González Gaspar , Feder Angelo L. , Teixeira Carmen L. S. , Lucas Elizabete F. 
Published: December 2007

Oil production is normally accompanied by a concomitant production of large amounts of water. The separation of produced water and its purification prior to discarding, represent an important technological challenge for the oil production industry. For instance a well producing, 20,000 m3/day of oil with a BSW (Basal Sediments and Water) of 50% and a TOG (Total Oil and Grease) of 300 mg/L would produce 3 tons of oil and grease per day. In order to minimize environmental impacts, these residues must be reduced to acceptable levels; this being partic ularly important in offshore operations where the most obvious destination of the produced waters are the oceans.

The oil contained in produced oily waters often is in the form of very stable emulsions. For these systems oil/water separation by the usual physical procedures is difficult; in particular in offshore operations, where space, production facilities and residence times are limited. The use of chemicals as flocculants or flotation agents is common practice in these cases. The products generally recommended are cationic polyelectrolytes however; the field use of these polymers is limited due to the formation of solid residues that in the form of oily sludge accumulate in the treatment plant facilities reducing, after some time, the efficiency of the equipments. In this contribution, other polymers like poly(ethylene oxide) (PEO) or poly(vinyl alcohol) (PVA), that present a good performance as flocculating agents1 for other systems and fictionalized PVA containing hydrophobic alkyl chains and/or carbamate groups are assayed for oil-water separation. Furthermore some studies to identify the causes of sludge formation are also presented.

Experimental Part

Materials

The nonionic polymers used in this work were commercial samples kindly supplied by the manufacturers and were used without further purification. PVA1 is a poly(vinyl alcohol) (PVA) presenting a molecular weight of around 72,000, (Vetec, Química Fina Ltd. Rio de Janeiro, Brazil). PVA2 and PVA3 are products manufactured by Air Products and Chemicals. Inc. (Allentown, PA. USA), commercialized as Airvol 165 and 540 respectively. Both polymers present molecular weights between 140,000 and 180,000 but PVA2 is 100% hydrolyzed and PVA3 has a hydrolysis degree between 87 and 89%. Ucarfloc 302, 304 and 309 are water-soluble poly(ethylene oxide), (PEO), polymers, presenting molecular weights of 5, 7 and 8 × 106, respectively, produced by Union Carbide (Union Carbide Corporation, Denbury, CT, USA).

Two PVA samples presenting molecular weights of 72,000 (PVA1) and 140,000 (PVA2) were chemically modified by fuctionalization with carbamate groups and hydrophobic alkyl chains. The incorporation of carbamate groups (urethanes) in the structure of PVA was made by reaction of urea with PVA in the ratio of 1:1, using dimethylformamide as solvent2. The reaction temperature was fixed at 145°C and the time varied from 30 to 180 minutes. The esterification was carried out subsequently, following Schotten-Baumann reaction3 using acyl chlorides with hydrocarbon chain length varying from 12 to 18 carbon atoms. The temperature was fixed at 145°C and the reaction time was 2 hr. The solvent was also dimethylformamide for this reaction. The reaction schemes are presented in Figure 1.

Three samples of crude oil, here called Crude Oil 1, 2 and 3, were used to prepare synthetic emulsions.