Evaluating the Potential of Biodegradable Carbohydrates and the Aqueous Extract of Potato Pulp to Inhibit Calcium Carbonate Scale in Petroleum Production
Authors: Ortiz Ronald W. P. , Oliveira Jessica , Vaz Guilherme V. , Passos Nayanna Souza , Bispo Felipe J. S. , Gonçalves Vinicius Ottonio O. , Cajaiba Joao , Ortiz-Bravo Carlos A. , Kartnaller Vinicius 
Published: November 2023

Summary
Scale is a significant operational concern in petroleum production that is commonly addressed by using chemical inhibitors. However, commercial inhibitors can potentially be pollutants depending on their composition and method of disposal. Consequently, evaluating the potential of biodegradable molecules to inhibit scale has gained attention. This study evaluates the effect of a series of carbohydrates (i.e., glucose, fructose, sucrose, maltose, maltodextrin, and soluble starch) and the aqueous extract of potato pulp on calcium carbonate precipitation and scale formation. Precipitation tests were conducted by combining aqueous solutions of sodium bicarbonate (3000 mg L−1) and calcium chloride (4000 mg L−1) in the presence of each carbohydrate, the aqueous extract of potato pulp, or a commercial inhibitor (1000 mg L−1). The precipitation was monitored through RGB (red, green, and blue) image analysis and pH measurements. The induction time in the presence of glucose, fructose, maltose, and sucrose is two to three times longer than in the blank test (in the absence of an inhibitor). This effect is slightly more pronounced in the presence of maltodextrin and soluble starch (approximately four times longer). However, the drop in pH and the mass of solids recovered is similar for all the carbohydrates tested (~0.5 mg and 120 mg, respectively), suggesting that carbohydrates slightly influence the precipitation kinetics but do not affect the precipitation equilibrium. Scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analysis reveals that calcium carbonate precipitates as calcite and vaterite in the blank test. In the presence of glucose, fructose, maltose, and maltodextrin, calcium carbonate exclusively precipitates as calcite. However, in the presence of sucrose and soluble starch, calcium carbonate precipitates as both calcite and vaterite. Interestingly, a more prominent amount of vaterite was observed in the presence of soluble starch. All carbohydrates decrease the crystallite size of calcite, while sucrose and soluble starch increase the crystallite size of vaterite. The crystalline phases were also identified by Raman spectroscopy, ruling out the presence of any amorphous calcium carbonate phase. The inhibitory effect of soluble starch and the aqueous extract of potato pulp on calcium carbonate scale formation was evaluated in a dynamic scale loop (DSL) system. Soluble starch slightly delays scale formation even at high concentrations (1000 mg L−1). Conversely, the aqueous extract of potato pulp demonstrates enhanced performance by delaying scale formation by approximately 20 minutes for a 1-psi increase in the pressure of the tube and by more than 40 minutes for a 4-psi increase. As a result, it exhibited an impact on the kinetics of solid deposition. This agrees with the precipitation test in the presence of the potato extract (PE), which increases the induction time (from 2 minutes to 32 minutes), decreases the mass of solids (from 116 mg to 35 mg), and forms more distorted and smaller particles of calcite. These findings suggest a promising approach for the development of green scale inhibitors utilizing aqueous extracts of starchy foods or even starchy foods waste water.