Mechanism study on effect of sulfur ion on the viscosity of polyacrylamide solution

Key words:  polyacrylamide  sulfur ion  mechanism of viscosity loss  breakage  coil

Abstract:

Sulfur ion in the waste water leads to the viscosity loss of polymer solution significantly, which reduces the oil displacement efficiency. In order to uncover the mechanism of sulfur ion on reducing polymer viscosity and prevent viscosity loss of polymer solution, the effect of different concentrations of sulfur ion on the polymer viscosity and reversibility were investigated. Scanning electron microscopy (SEM) was used to observe the polymer microstructure. GPC-refractive index detector was used to analyze the molecular weight distribution of the polymer, in which the quantum chemistry and molecular dynamics method were applied to study the break and coil of molecular chain of the polymer caused by sulfur ion. The results show that 7 mg/L sulfur ion can cause more than 80％ loss of viscosity of 1.7 g/L polymer solution. Weight average molecular weight and mean square radius of gyration drop down to 1.277×10⁶ g/mol and 91.4 nm from 3.677×10⁶ g/mol and 191.7 nm respectively. The molecular weight distribution is widened and the size of the polymer molecules is decreased. The main reason of polymer viscosity loss is the free radical chain reaction induced by sulfur ion, which causes the breakage of polymer chain. Also, sulfur ion causes coil and shrinkage of polymer molecular chain, which destroys the spatial network structure of macromolecules.