The Inhibition of Calcium Sulfate Dihydrate Crystal Growth By

NACE-85-357

THE INHIBITION OF CALCIUM SULFATE DIHYDRATE CRYSTAL GROWTH BY

POLYACRLATES AND THE INFLUENCE OF MOLECULAR WEIGHT

Zahid Amjad, PhD and William F. Masler III, PhD Noveon, Inc. (formerly BFGoodrich Performance Materials) 9911 Brecksville Road Cleveland, OH 44141

ABSTRACT INTRODUCTION A seeded growth method has been used to study the influence of low molecular The precipitation and dissolution of weight (MW 710-12,800) polyacrylates on the the sparingly soluble alkaline earth metal crystallization of calcium sulfate dihydrate sulfates from aqueous solutions is of from stable supersaturated solution at considerable scientific and technological temperature ranging from 30-50oC. The importance. The precipitation of calcium results indicate that the crystallization in the sulfate hydrates are of particular interest presence of polyacrylates is preceded by an because of their importance in many induction period following which crystal scale/deposit control applications such as . growth of CaSO4 2H2O proceeds with a rate geothermal, industrial water treatment, oil close to that in pure supersaturated solution. production, and desalination. In many cases Temperature changes, polyacrylate the deposition of hard crystalline scale on heat concentration, and polymer molecular weight transfer surfaces results in decreased thermal greatly affect the duration of the induction efficiency of the system. To preclude an period. The optimum effectiveness as excessive rise of operating costs, scale determined by induction period duration deposition has to be prevented. occurs with a polyacrylate having a molecular weight (MW) of 2,100. The observed A number of methods can be utilized induction periods for the growth of to reduce or prevent fouling of heat transfer . CaSO4 2H2O in the presence of polyacrylates surfaces by mineral scales. These common strongly suggest that the polymer is techniques include (a) operating a system incorporated into the crystal lattice as the under conditions where the solubility of scales crystal grows. forming salt is not exceeded, (b) reducing the cation concentrations of the scale

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