Inhibition and dissolution of wax deposition for phet crude in a semi-pilot scale using poly(ethylene-co-vinyl acetate)

Abstract

The most common problem found in petroleum fields is wax depostition, which occurs with all waxy crudes, including Phet crude (PTT Exploration and Production Public Company Limited, Thailand). When wax deposition occurs in the transporting tanks, so-called remaining-on-board or ROB, the volume of crude oil transported is reduced the wax precipitating in the storage tanks. In this work, poly (ethylene-co-vinyl acetate) or EVA analytical grade and EVA commercial grade (EVAFLEX) as a wax inhibitor were investigated in semi-pilot scale. Pour point temperature reduction and ROB were measured, and an economic assessment of the EVA wax inhibitor was also performed. EVA analytical grade with 40% vinyl acetate content at high concentration (1000 ppm) and 25% vinyl acetate content at low concentration (200 ppm) showed good effect on pour point reduction (from 31 to 17C and 31 to 21C) with 90 and 93% ROB reduction, respectively. In comparison, EVAFLEX with 33% vinyl acetate content reduced pour point temperature to 18C at 1000 ppm with 96% ROB reduction, and EVAFLEX with 28% vinly acetate content at low concentration (400 ppm) decreased the pour point temperature to 20C with 91% ROB reduction. In addition, the thermograms from DSC showed that the crystallization temperature of n-paraffins decreased as the concentration increased. Moreover, the amount of inhibitor distribution in oil was more than ROB fraction. Regarding the economic assessment, the addition of an EVAFLEX (28% VA) in a heavy aromatic solution with a concentration of 200 ppm showed a gain of net profit from selling ROB as crude when the initial of amount of working sludge wax solid was at least 2500 tons per year.