Adsorption/desorption of polymers from Saudi Arabian limestone

Review on Polymer Flooding: Rheology, Adsorption, Stability, and Field Applications of Various Polymer Systems

“…The isoelectric point of kaolinite (sandstone) is 4.7 29 and the isoelectric point of limestone is 8.2. 30 If the pH is greater than 4.7, adsorption of an anionic polymer will be low on sandstone and decreases further with increasing pH. A pH greater than 4.7 will induce negative charges on the mineral surface and adsorption will decrease due to electrostatic repulsion.…”

“…In the presence of salts, negatively charged pyruvate molecules wrap around the main chain to make a rigid rod like structure. 30,170 Resistance of xanthan to shear and mechanical degradation is much better than polyacrylamide due to the rigidity of the chain. 83,[171][172][173] In deionized water, xanthan has a lower viscosity when compared to PAM copolymers at equivalent molecular weight and concentration.…”

“…But the increase of the ionic strength increases the adsorption of AM-AMPS copolymer due to the decrease in electrostatic repulsion between kaolinite and the copolymer caused by charge shielding in the presence of salts. 40 Adsorption of the sulfonated polymer on limestone, (isoelectric point of limestone is 8.2), has been studied by Celik et al 30 at a pH of 8. Below the isoelectric point, the surface charge on limestone is positive while above it the surface charge is negative.…”

“…Salts may increase or decrease the adsorption of xanthan gum, and above the plateau region, adsorption of xanthan gum increases by the addition of salt and vice versa. 30 This is due to the competing effects of salting-out and electrostatic attraction. Increasing the temperature, which causes coiling of xanthan gum, helps in the reduction of xanthan adsorption on limestone due to lesser exposure of negative side chains of coiled xanthan to rock surfaces.…”

“…However, the side chain consists of β-D-manose-1,4-β-D-glucuronic acid-1,2-α-D-manose and the terminal manose is normally a 4,6-linked pyruvic acid ketal. 168,169 Xanthan gum proved to be tolerant to divalent cations and can maintain its viscosity under conditions of high salinity, 30 which is due to the ordering of xanthan molecules at high salinities. In the presence of salts, negatively charged pyruvate molecules wrap around the main chain to make a rigid rod like structure.…”