The Use of Chemicals in the Treatment of Produced Oily Waters

Abstract

Introduction 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 particularly 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, Qu mica 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. 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, Qu mica 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.

Correlation between Methods to Determine Total Oil and Grease in Synthetic Oily Water Using Heavy Oil: Gravimetry vs Fluorimetry

“…It is important that all the oil added is mixed with the brine, so that we can trust in the amount of oil in the water. Usually, the mixture of oil and brine is done using a mechanical stirrer. , However, the heavy oil adheres on the rod and removing it is not easy, mainly when using n -hexane as the extraction solvent. Therefore, our procedure used manual shaking and preparation of the oily water directly in the separation funnel used for the extraction by an organic solvent.…”

“…Such water must contain an oil concentration as low as possible for either being discarded or reinjected . Many countries establish rules for disposing of water produced by the oil industry, which can be treated by different processes. − ,− In this context, TOG must be accurately determined by specific methods. For example, Brazilian regulations require the use of gravimetric methods to determine TOG, while other methodologies may be accepted when providing their correlation with the gravimetric one .…”