Enhancement of cold flowability of waxy crude oil using eco-friendly PPDs synthesized from stearic acid and lauric acid – Experimental, modelling, and mechanistic approach

Abstract

Waxy crude oil suffers from several flow assurance issues due to wax deposition, which results in poor cold flowability and complex rheological behavior, particularly at lower temperatures. To address these problems, several costly non-biodegradable chemicals are used, which make the project unprofitable and non-environmentally. There are very few application studies on biodegradable PPDs in field crude oil, particularly in Indian field crude oil. So, present studies focus on the synthesis of novel biodegradable Polyethylene glycol-based fatty esters utilizing stearic acid (PEGS) and lauric acid (PEGL) and used as environmentally friendly pour point depressants (PPDs) to overcome wax deposition issue. Comparative impact and effectiveness of PEGS and PEGL on flow assurance were evaluated using pour point, wax deposition, DSC, and rheological investigations that included viscosity, yield stress, rheomalaxis, and viscoelastic characteristics. Due to differences in the chain lengths of synthesized PPDs, impacts were also dissimilar. The mechanism of interaction between PPDs and wax particles was also explored using XRD and microscopic analysis. At a minimum concentration of 600 ppm, the addition of PEGL and PEGS depress the pour point of waxy crude oil by 12 °C to 15 °C respectively. A substantial decrease in viscosity was observed (54 % to 76 % respectively for PEGL and PEGS addition) and yield stress decreased by more than 70 % at 30 °C. Rheological modeling analysis revealed a transition from Bingham plastic to shear-thinning Casson behavior after dosing with PEGS and PEGL. PEGS outperformed PEGL because of longer carbon chain that is better co-crystallized with wax crystals and prevents the wax crystallization process. Biodegradability and toxicity were tested using BOD (OECD 301) and toxicity test (OECD 203 Standard) and it was confirmed that the synthesized PPDS (PEGS and PEGL) both are biodegradable and nontoxic in nature. So, synthesized PPDs may be used as a cost-effective, environmentally friendly solution for addressing wax deposition problem for enhancing the cold flowability of waxy crude oil with a minimal dosage.