Abstract
Wax crystallization and deposition is a major flow assurance problem in production and transportation of waxy crude oil. Conventional flow improvers are mainly high molecular weight synthetic polymers, many of which are eco-toxic. Bio-based flow improvers derived from natural products are promising as inexpensive, eco-friendly alternatives to existing products. In this study, natural cashew nut shell liquid (CNSL) extracted from waste shells of Anacardium occidentale was esterified with polyethylene glycol (PEG). CNSL derivative reduced the pour point of waxy crude oil by 12 °C at 1000 ppm. The effects of CNSL derivatives on wax crystal morphology and micro-structure were studied by cross-polarized microscopy. Micrographs were processed and analyzed with ImageJ software. Addition of CNSL derivatives to oil resulted in changes in wax crystal morphology and micro-structure evidenced by a reduction in average crystal Feret diameter and aspect ratio and increase in boundary fractal dimension, indicative of formation of increasing number of smaller, rounder crystals. Effect of the additives on flow properties of the waxy oil was determined using a co-axial cylinder rotational viscometer. Dynamic viscosity of oil at shear rate of 17 s−1 was reduced by 79.7–90.5%. CNSL-PEG esters show good prospects as low-cost additives for production, storage and pipeline transportation of waxy crude oil.
Highlights
Petroleum accounts for a large proportion of global energy consumption and is a major revenue source for many exporting nations [33]
We report the preparation and application of natural cashew nut shell liquid-polyethylene glycol (PEG) derivatives as pour point depressants and low-temperature flow improvers for waxy crude oil
The sharp band at 1699 cm−1 in the spectrum of natural cashew nut shell liquid (CNSL) is due to the C=O of carboxylic acid, which is confirmed by the C–O stretch vibrations of the acid at 1211.4 cm−1 [6, 13, 19]
Summary
Petroleum accounts for a large proportion of global energy consumption and is a major revenue source for many exporting nations [33]. Paraffinic crude oils are desirable due to ease of refining and high yield of automotive fuel, but their production and transportation are often encumbered by flow. Waxes crystallize from oil when temperature falls below the wax appearance temperature (WAT). Wax crystals grow and agglomerate in oil with decreasing temperature, forming a large three-dimensional network which changes oil flow behavior. Other unfavorable outcomes of wax crystallization which can cause mechanical failure in production and transportation systems include the deposition of wax on internal surface of tubings and pipelines, resulting in flow constriction as well as high risk of oil gelation if flow is temporarily stopped [1, 14]. Pour point depressants (PPDs)/flow improvers are added to waxy crude oils as a mitigative measure to save cost [23, 31]. High cost of pour point depressant formulations, selectivity of pour point depressants to crude oils and negative environmental impact
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