Inhibition Of Calcium Sulfate Dihydrate Crystal Growth By Phosphonic Acids - Influence Of Inhibitor Structure And Solution Ph

1979 ◽  
Author(s):  
David W. Griffiths ◽  
Stephen D. Roberts ◽  
Sung-Tsuen Liu
Keyword(s):  
Crystal Growth ◽  
Calcium Sulfate ◽  
Solution Ph ◽  
Phosphonic Acids ◽  
Calcium Sulfate Dihydrate

Kinetics of crystal growth of calcium sulfate dihydrate. The influence of polymer composition, molecular weight, and solution pH

1988 ◽  
Vol 66 (6) ◽  
pp. 1529-1536 ◽  
Author(s):  
Zahid Amjad
Keyword(s):  
Molecular Weight ◽  
Crystal Growth ◽  
Induction Period ◽  
Functional Groups ◽  
Polyacrylic Acid ◽  
Calcium Sulfate ◽  
Polymer Composition ◽  
Supersaturated Solution ◽  
Solution Ph ◽  
Calcium Sulfate Dihydrate

A seeded crystal growth technique has been used to study the influence of solution pH and temperature ranging from 25 to 50 °C on the performance of polymers of varying functional groups as calcium sulfate dihydrate (CaSO4•2H2O, gypsum) crystal growth inhibitors. Results indicate that at constant temperature and at a constant solution pH, crystallization in the presence of polyacrylic acids is preceded by an initial slow growth reaction, hereafter called induction period, following which crystal growth of gypsum proceeds with a rate close to that in pure supersaturated solution. Results suggest that at a constant pH, polyacrylic acid concentration, molecular weight, and temperature greatly affect the duration of induction period. Kinetic data collected as a function of solution pH in the range 2.5 to 9.0 suggest that solution pH has a marked effect on the induction period. The observed dependence of induction period on solution pH may be explained in terms of the degree of ionization of polyacrylic acid. Among the polymers of varying functional groups studied, i.e. carboxyl, sulfonate, acrylamide, dimethyldiallylammonium, etc., only those polymers having carboxyl group showed marked inhibitory activity for the growth of gypsum crystals.

Research on Crystallization Kinetics of Calcium Sulfate Dihydrate Prepared by Bittern under 20°C and 120r/min Condition

2014 ◽  
Vol 926-930 ◽  
pp. 210-213
Author(s):  
Bi Jun Luo ◽  
Hai Hong Wu ◽  
Yu Qi Wang ◽  
Qi Zhang
Keyword(s):  
Experimental Data ◽  
Crystal Growth ◽  
Crystallization Kinetics ◽  
Residence Time ◽  
Calcium Sulfate ◽  
Nucleation Density ◽  
Growth Line ◽  
Calcium Sulfate Dihydrate ◽  
Kinetics Of

Crystallization kinetics experiment of calcium sulfate dehydrates, which is prepared by bittern under 20°C and 120r/min conditions, is carried out. According to the results of the experimental data, nucleation densityn0of gypsum crystals is proportional to the residence time, and the rate of crystal growth lineGis inversely proportional to the residence time. Meanwhile, the crystallization kinetics formula is derived to be:B0= 5.78×102G0.87.

Calcium Sulfate Scale Formation: A Kinetic Approach

1978 ◽  
Vol 18 (02) ◽  
pp. 133-138 ◽  
Author(s):  
George H. Nancollas ◽  
Atal E. Eralp ◽  
Jasbir S. Gill
Keyword(s):  
Crystal Growth ◽  
Ionic Strength ◽  
Specific Surface ◽  
Calcium Sulfate ◽  
Scale Formation ◽  
Phase Changes ◽  
Field Conditions ◽  
Stable Phase ◽  
Calcium Sulfate Dihydrate ◽  
Solid Phases

Abstract The growth and phase transformation of calcium sulfate dihydrate and hemihydrate crystals were studied at temperatures from 70 to 130 deg. C. At 70 deg. C the second-order rate constant for dihydrate crystal growth did not change by more than 20 percent over a pH range of 3.2 to 9.2. It was also independent of ionic strength up to 2.0M. Growth in stable supersaturated calcium sulfate solution was completely inhibited by 7 x 10-7 M phytic acid for about 24 hours at 70 deg. C. The seeded crystallization of calcium sulfate hemihydrate at temperatures from 90 to 140 deg. C and The phase changes from a- to beta-hemihydrate were investigated by X-ray diffraction, specific surface area analysis, and scanning electron microscopy. Organic phosphonates were found to be effective inhibitors of crystal growth of all the phases at high temperatures. Introduction The phases that form during the crystallization of many sparingly soluble salts evidently are determined much more by kinetic factors than by thermodynamic considerations. Thus, in the case of calcium phosphate crystal growth, an amorphous precursor is formed rapidly at the beginning of the precursor is formed rapidly at the beginning of the reaction and undergoes slow transformation to the thermodynamically stable phase, hydroxyapatite. Significant changes with time are observed in such factors as chemical composition, crystallinity, and specific surface areas of the solid phases. The simple equilibrium studies do not reveal the factors that may be important in determining whether these phases will precipitate in the field. phases will precipitate in the field. The case of calcium sulfate, which is important in desalination, geochemistry, and petroleum engineering, is complicated further by the fact that it can crystalize from aqueous solutions in three forms- dehydrate (CaSO4 - 2H2O), hemihydrate (a-CaSO4 1/2 H2O or beta-CaSO4 - 1/2 H2O), and anhy-drite (CaSO4). These phases may be stable or unstable depending on temperature or ionic strength, and they have decreasing solubilities with increasing temperatures above about 40 deg. C. To understand the formation of these scale minerals, high-temperature laboratory methods must be used for the kinetic studies, allowing both solutions and solid phases to be sampled without spurious temperature effects. The kinetics of transformation of one hydrate to another is particularly important in determining the nature of the scale formed under field conditions as a function of both temperature and background electrolyte concentration. This investigation studied the formation and dissolution of calcium sulfate phases under some typical field conditions. Kinetic investigations were emphasized since these frequently can be used to predict the nature of the phases formed under specific conditions of concentration or temperature. Moreover, unlike the results of spontaneous precipitation experiments, such studies are highly reproducible. The effects of factors such as ionic strength, temperature, supersaturation, and effectiveness of scale inhibitors may be studied quantitatively. In addition, the influence of the nature of the seed crystal phase and morphology on the subsequent growth process can be investigated. The morphology of the crystals comprising scale deposits may be particularly important in determining whether they pack together as hard, destructive scale or remain as a sludge to be swept away by the liquid phase. Seeded-crystal growth processes are better models than are spontaneous processes are better models than are spontaneous precipitation studies for the scale formation reactions precipitation studies for the scale formation reactions in which the solid phase is formed heterogeneously either on a foreign substrate or on crystals of scale already present. The growth rate of calcium sulfate dihydrate seed crystals is independent of the fluid dynamics in the system, suggesting that the rate is not diffusion-controlled but depends on a surface reaction rate. This has particular significance for the formation of scale in the oil well because the scaling rate is expected to be independent of the dynamics of fluid flow at the metal surface. SPEJ P. 133

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