A comparative study of polystyrene decomposition in supercritical water and air environments using diamond anvil cell

Abstract

Polystyrene (PS) decomposition in supercritical water (SCW) and in air was studied with the diamond anvil cell (DAC) technique coupled with microscopy and FTIR. Apparent concentrations were calculated by using digital imaging analysis. When PS ϩ water systems (11.8 -22.6 wt % PS) were rapidly heated at a rate of 2.3°C/s, the PS particle melted at 279.8 -320.2°C. After formation of a globule at 409.3-452.5°C, the globule started to dissolve in color to yellow at 496.1°C. At 570.3°C and 742.5 MPa, solubility reached the maximum of 91.5 wt % (11.8 wt % PS). The soluble material was a styrenelike liquid, which was identified by IR after cooling. In isothermal runs at 400 and 450°C, two heterogeneous liquid phases consisting of water and decomposed PS were found. Styrenelike liquid products were identified after the reactions. PS decomposition stages in air consisted of melting, gas generation, liquid ring configuration, and finally yellow volatile products formation at 583.2°C. The results show conclusively that PS can be dissolved in SCW above 496.1°C and homogenous reaction is likely to occur above 570.3°C. Reactions in SCW at 400 and 450°C take place in heterogeneous liquid phases, while in the PS ϩ air system, a formed liquid ring undergoes depolymerization.

Production of Chemicals in Supercritical Water

“…Siskin also showed some polymer-related reactions in superheated water, but mainly under subcritical condition [2]. Fang treated polystyrene in SCW, and found that it is dissolved above 769.3 K, and then homogeneous reaction takes place above 843.5 K to produce styrenelike product [53]. Kronholm also treated polystyrene, and obtained styrene recovery of 57 wt% with NaOH addition in 20 min at 673 K [54].…”

Continuous distribution kinetics for degradation of polystyrene in sub- and supercritical toluene

“…In the reaction system, the radicals, produced from the random scission of polystyrene, produce volatile products (also named as styrenelike products [19]) undergoing chain-end scission including depolymerization, intramolecular transfer and followed b-scission. Among the styrenelike products, styrene is the main component [18].…”

Degradation of poly(butylene terephthalate) in different supercritical alcohol solvents

“…The exploration of supercritical fluids as solvents and as reaction media for polymer degradation has attracted particular interest over the past decade 2–4. Because of their unique physical and chemical properties, they have many advantages when they are used in polymer degradation, such as reaction in the homogeneous phase and high decomposition rates 5, 6.…”