Preparation of lignin-based intumescent nanogel and its mechanism of inhibiting coal spontaneous combustion

An environment-friendly intumescent nanogel was developed to prevent spontaneous combustion in coal mines. Acrylamide (AM) was introduced into the lamellae of organic nano-montmorillonite (OMMT) with layered structure, and sodium lignosulfonate was introduced as a carbon source. Ammonium polyphosphate (APP), which integrates acid source and gas source, was added into gel carrier to form an intumescent nanogel (CFR). The effects of gel components on gel properties were optimized by orthogonal experiment using gelation time, yield and permeability as evaluation indexes. Scanning electron microscope (SEM) was used to observe the micro-morphology of the coal samples after calcination. Fourier transform infrared spectroscopy (FTIR) was employed to analyze the evolution of active radical groups. Characteristic temperature points of coal samples were analyzed by thermogravimetric experiments (TGA). The results showed that the calcined coal treated with CFR was covered with a uniform and dense intumescent char layer, and the carbon residue rate was more than 2.9 times that of the raw coal. The content of active carbonyl (CO), hydroxyl (-OH) and alkyl (-CH3, –CH2) in coal samples was effectively reduced by the intumescent nanogel (CFR), and the content of ether bond (C–O–C) was increased. The characteristic temperature points of the coal samples were all increased to different degrees. Therefore, the intumescent nanogel (CFR) can effectively prevent the coal spontaneous combustion.