TY JOUR TI Extraction of coal and sludge from the Pechora coal basin in an autoclave at elevated temperature and pressure in an organic solvent environment KW hard coal KW coal sludge hypercoal KW extraction with N-methylpyrrolidone KW thermogravimetry KW elemental composition JO Vestnik of geosciences AU Kuzmin, D.V. AU Burdelnaya, N.S. AU Burtsev, I.N. AU Beliy, V.A. PY 2025 IS 0 PB FSBI FIC "Komi Scientific Center of the Ural Branch of the Russian Academy of Sciences"