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As intelligent mining operations evolve, stringent standards for gas management and extraction are imperative. To mitigate the risks associated with coal and gas outburst and to prevent gas concentration from exceeding safe limits, a comprehensive three-dimensional gas extraction system is introduced. This method, exemplified by the 1075 intelligent working face at the Yangliu coal mine, integrates temporal and spatial considerations for comprehensive extraction. Utilizing COMSOL and UDEC simulations, the extraction parameters for both pre-extraction and mid-mining extraction have been meticulously optimized. The optimal strategy involves boreholes with a diameter of 113 mm, spaced 3 m apart, and an initial negative pressure of 31 kPa, which is subsequently reduced to 13 kPa as gas levels decrease. The positioning of directional high-level boreholes is determined by the fracture zone distribution in the goaf's overlying strata, placed 19–25 m above the roof and 0–65 m from the return airway. Directional interception boreholes are optimally located 54–73 m above the roof. Surface wells are strategically positioned 15 m above the roof, with a horizontal distance of 30–65 m from the return airway. After extraction of the system, the maximum gas concentrations recorded in the return airway and the upper corner are 0.26% and 0.27%, respectively. The average daily production reached 5258 t, nearly doubling the overall efficiency. This gas extraction technique not only enhances the efficiency of intelligent mining operations but also serves as a valuable reference for future research in the field. [ABSTRACT FROM AUTHOR]

Polyurethane is a group of block copolymer which is composed of diisocyanate, chain extender, and polyol, including polyurethane foam, polyurethane elastomer, waterborne polyurethane, etc. This research focused on thermoplastic polyurethane elastomer (TPU) which is formed with 4,4’-diphenylmethane diisocyanate (MDI), poly(1,4-butanediol-hexanedioic acid) diolpolyester(PBA) and extended with 1,4-butanediol(BDO).The degradation of TPU was carried out with the help of methanol as the supercritical solvent. The SEM of the reaction residues revealed the process of the depolymerisation. The products were measured by GC-MS and found out to be PBA, BDO and 4,4’-methylene diphenyl carbamate(MDC) which is themethylate of MDI.GC-FID, HPLC-UV and GPC were used to further analysis. The experimental results showed that supercritical methanol performed outstandingly in TPU recycling, it needed lower temperature and shorter time than regular methods. At 230°C/70min, over 90% raw materials of TPU could be recovered.