ABSTRACT

This study is focused on the evaluation of polyepoxysuccinic acid (PESA), 2-phosphonobutane 1,2,4-tricarboxyMic acid (PBTC), and PESA/PBTC blends for calcium sulfate dihydrate (gypsum) and calcium carbonate scale inhibition for aqueous systems. For comparison, synthetic, bio-, and hybrid polymers were also tested for their efficacy as scale inhibitors. It has been observed that performance of inhibitors depends on inhibitor dosage and functional groups. Results also reveal that PBTC exhibits synergistic effect on the performance of polymers containing carboxyl group. Scanning electron microscopic studies of the gypsum crystals grown in the presence of anionic inhibitors show that structures of these crystals are highly modified. XRD data collected for calcium carbonate in the presence and absence of inhibitors confirm the presence of calcite as the major phase.

INTRODUCTION

Many industrial water systems struggle with accumulation of unwanted deposits on equipment surfaces. Commonly encountered deposits include: (a) mineral scales (i.e., carbonates, sulfates, phosphates, fluorides salts of alkaline earth metals) (b) corrosion products (i.e., oxides/hydroxides of iron, aluminum, zinc, copper), (c) suspended matter (i.e., precipitated salts, clay, sit), (d) microbiological mass, and (e) process contaminants i.e., oil, grease, cationic flocculant-anionic polymer salt, etc.1

The problem of scale formation is intensified at higher temperatures because of the peculiar inverse-temperature-solubility profiles of these minerals in water. The deposits that form can markedly reduce heat transfer causing energy losses or material damage, especially when coupled with corrosion. Various factors such as bubble formation, suspended matter, and water chemistry have been shown to play a role on the crystallization and deposition of scales on the metal surfaces. In desalination of brackish/sea water by reverse osmosis (RO) membrane-based process, the formation of scale on RO membrane surface often leads to poor quality produced water, increased energy costs, increased operating pressure, and premature membrane replacement. In oil-producing wells, unwanted scale deposits decrease flow through the tubes, thereby affecting oil production. In geothermal applications, factors such as variable fluid compositions, different plant operating conditions, and the complex nature of scale deposits make deposit control a challenging problem.

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