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Study On The Crosslinking Mechanism And Dynamics Of Gelation Of Partially Hydrolyzed Polyacrylamide/Cr(Ⅲ) Systems

Posted on:2003-07-11Degree:DoctorType:Dissertation
Country:ChinaCandidate:H D DuanFull Text:PDF
GTID:1101360062475898Subject:Chemical Engineering
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Water based gels, comprising partially hydrolyzed polyacrylamide (HPAIvI) cross-linked with chromium(ffi), are now finding widespread use for near well-bore water and gas shut-off in the oil industty. The studies on the mechanism and kinetics of the cross-linking reaction and structure and properties of crosslinked gel are very important to understand and improve the in-situ application of the gels technology.There are many factors influncing the gelation dynamics of HPAMICr(il1) gelling system, such as concentrations of polymer and crosslinking agents, pH, concentration of NaCI, temperature and shear on the system. We used viscosity measurement~ Uv-visible spectroscopy and rheological methods to investigate the effect of the above factors on the gelation dynamics.The apparent reaction rate equation of HPAM/Cr(I[1) gelation was obtained by viscosity measurement The gelalion time and gelation balance time decreased, nevertheless the steady gelalion rate and balance viscosity increased, with increasing the salinity of the systent The gelation process can be divided into two periods: fast and slow gelatiom The crosslinking ratio between HPAM/Cr(1Jl) was 3:1.Rheological measurements have been performed on a system of HPAM with Cr(lll) as a crosslinking agent For the HPAM solution, the viscous modulus G" is higher than the elastic modulus G' . Both values don't change with time and the solution is a viscous system. For the crosslinking system G' value increased and exceeded the G" value and the gelling solution has more solid or elastic properties. The kinetics of the gelation was detentiined from measured time dependence of 0' . The gelation process consists of three periods, i.e. the first increasing period, slow increasing period and the second increasing period. The relative gelation rates of the HPAM/Cr (Ill) systems can be measured by usingVthe Initial 0' versus time slopes to represent the rates of gelalion. We found the gelationrates increased with the concentrations of 1]PAM and Cr (111), and the 0' - 0" crossing time became shoiter. We observed the first-order reaction for Cr (III) under the conditions that carboxylate groups are superfluous. The elastic effective crosslinking density of thegelling fluid increases with the polymer concentration and with the gelation process. The average molecular weight of the chains adjacent crosslinks decreases slightly with the cosslinker concentration and with the gelation process. The pH of the gelation solution has strong influence on the gelalion rate, which is inversely to the lf' concentration. The gelation rates also increase with the temperature, and the apparent activity energy is 36.9 KJ/mol, indicating that the gelation rate is very fast at ambient temperature. When NaCI concentration is zero or low in the gelling fluid, gel forms quickly and the white floccule appears. At the same time, the gel strongly dehydrates. There is no evident influence on gelation rate when the concentration of NaCI change from 8 gIL to 20 g,'L.The hydrolysis and the chain structure of HPAM are the important factors affecting the gel performance and application. We used '3C NMR method to determine the hydrolysis of three samples of HPAM with ultrahigh molecular weight and to study the sequence distribution. The number sequence length was calculated. The reactive groups of HPAM were determined by FT-LR spectra. The viscosity and the transmittance of the gelling fluids were also measured through crosslinking process. It was found that the chromium ions react mainly with the carboxylic groups of HPAM and the hydrolysis degree (lID) of HPAM samples has a pronounced influence on the reaction rates. Differential scanning calorimetry (DSC) and thermogravimetiy (TO) were used to study the thermal stability of the resulting gels which exhibit much higher thermal stability than HPAM samples.The crosslinking density was an important parameter. The cross]inking density reflects the the number of the crosslinks in microstr...
Keywords/Search Tags:partially hydrolyzed polyacrylamide(HPAM), Cr(Ⅲ), Gel, Kinetics of crosslinking reaction, Mechanism of crosslinking reactionl Rheological measurements, Viscoelasticity, Surfactants
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