Preparation and optimization of thermosensitive hydrogels for inhibiting coal oxidation

Currently, the prevention and control of coal spontaneous combustion (CSC) mainly depend on liquid or inert gas injection. In this study, the mixed sol solution was prepared with methylcellulose (MC), polyethylene glycol (PEG), and surfactant sodium dodecyl sulfate (SDS). It has the advantages of in-situ, nontoxicity, easy biodegradation, etc., and can retain a large amount of water by sol-gel transition. The effect of each component on the gel properties was analyzed by using central composite design (CCD) of response surface methodology (RSM). The optimal values of independent variables were 1.99 wt% MC, 6 wt% PEG, and 8 mM/L SDS, under which the response values were obtained as gelation temperature 70°C, gelation time 75 seconds, gel strength 20.32 kPa, and seepage rate 28.51%. The obtained thermosensitive hydrogel (TSH) was characterized by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The results showed that the hydrogel was formed by physical cross-linking of MC-PEG-SDS ternary system. The gelation temperature of MC increased in the coexistence of SDS and PEG. The temperature-programmed experiment of coal samples treated with inhibitors showed that the CO inhibition rate of 8 wt% MC-PEG-SDS was higher than that of 20 wt% MgCl2 at 90-120°C. Besides, TSH and l-ascorbic acid (VC) were mixed to form a composite inhibitor (8 wt% MC-PEG-SDS/4 wt% VC) based on physical cooling and chemical inhibition. The experiment results showed that the composite inhibitor had a significant inhibitory effect on coal oxidation, and the corresponding CO inhibition rate (RTi) values fluctuated in the range of 47.68% to 83.57%. Therefore, TSH can act as a carrier of antioxidants and their combination can be used to prevent CSC.