Automated and Manual Methods for the Determination of Polyacrylamide and Other Polyacrylamide and Other Anionic Polymers
Summary.
The concentration of polyacrylamides is determined by precipitation with Hyamine 1622 Reagent I and by measurement of the amount precipitation with Hyamine 1622 Reagent I and by measurement of the amount of light scattered by the resulting turbidity. The analysis can be automated as well as adapted for field trials. The effects of anionic surfactants, changes in polyacrylamide molecular weight, and salinity are discussed.
Introduction
In this age of EOR, the use of polyacrylamides in the oil field is increasing steadily. Polyacrylamides are used in the viscosification of drilling muds, polymer-augmented mobility control, and the crosslinking of polymers for profile modification. Implementation of these techniques profile modification. Implementation of these techniques requires fast and accurate determination of polyacrylamides in a wide range of aqueous solutions. The method presented meets these criteria by being simple, accurate, and free presented meets these criteria by being simple, accurate, and free from most interferences. The analysis of polyacrylamide in water has historically been based on one of three principles: hydrolysis, with detection of the resulting ammonia; the starch iodide method (redox titration); and turbidimetry. Of these, the first two suffer interferences from background nitrogen compounds and redox processes, respectively. We have applied Crummett and Hummel, S turbidimetric method to the analysis of polyacrylamides in oilfield brine and production core tests. Hyamine 1622 (diisobutylphenoxyethoxyethyldimethylbenzylammonium chloride, Fig. 1) precipitates anionic polyacrylamides very effectively, providing detection limits of 0.5 to 1.0 ppm polyacrylamide. The reaction is shown in Fig. 2. Sodium polyacrylamide. The reaction is shown in Fig. 2. Sodium citrate is used to buffer the pH at 8.2. The sodium citrate also acts as a masking agent to prevent the precipitation of anionic surfactants (a potential interference) so that they can be tolerated up to the 200-ppm level. Changes in salinity and the presence of biocides (formaldehyde and/or glutaraldehyde) have no effect on the analysis. The presence of iron does interfere with the method. presence of iron does interfere with the method.
Manual Method
The manual method is straightforward and simple. The procedure for analysis follows. procedure for analysis follows.Pipette the appropriate aliquot of sample to a 50-mL mixing cylinder.Dilute to 30 mL with deionized water.Add 10 mL of 5% sodium citrate and mix.Add 10 mL of 0.4% Hyamine 1622 reagent and mix.Wait for 30 minutes for turbidity to develop.Measure turbidity in a 5-cm [1.97-in.] cell at 500 nm [5,000 A] with any standard colorimeter.
The concentration of polyacrylamide in the sample is determined by extrapolation from the turbidity on a previously constructed calibration curve, such as that shown previously constructed calibration curve, such as that shown in Fig. 3. Observe in Fig. 3 that the method is linear to 20 ppm polyacrylamide. For higher levels of polyacrylamide, it may be necessary to dilute the sample further. polyacrylamide, it may be necessary to dilute the sample further. Because of the ease of manipulation, this method has been adapted to a field test, The turbidity development over 1 hour is shown in Fig. 4. Evidently, the reaction does not occur instantaneously and 40 minutes is required to achieve maximum turbidity. There is an acceptable error of 0. 1 ppm/min when the absorbance is measured at 30 minutes. Because the concentrations measured could be time-related, it is advantageous to automate the procedures; this adaptation is described in the following section.
Adaptation to AutoAnalyzer
The use of an AutoAnalyzer-type instrument ensures that the measurement is recorded at consistent reaction times because the same pump speed is used for both standards and samples. This gives identical times for mixing the reagent with the standard or sample, allowing the reaction to occur in the delay coil and the material to be introduced to the detector cell. The AutoAnalyzer manifold was set up as shown in Fig. 5. The standards and samples, in 2-mL cups, were loaded into the sampler tray with the samples placed immediately after the standards. With the system at reagent equilibrium (adjusted to steady baseline), the samples were aspirated and mixed with citrate and air. Reagent was then added and the mixing continued through a single mixing coil, where the turbidity complex forms.
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