Study On Coal Extraction With Polar Solvents And Coal Depolymerization Over SO₄^2-/ZrO₂

Water and methanol are polar solvents which can dissolve micromolecular polar compounds in coal at certain temperature and selectively break the covalent bonds of coal structure with the catalysis of certain acid, which is of great importance in both understanding of coal structure and extracting of relatively simply composed chemicals from coal. Taking water and methanol as solvents respectively and employing methods of extraction under normal atmosphere and super solid acidic catalyst depolymerization via analytical means of GC/MS and FTIR, we studied the extraction rate and composition of extracts from four medium and low ranks of coals.Results of extraction under normal atmosphere with water as solvent indicate that the lower the coal rank, the higher the extraction rate as well as the percentage of oxygenated chemicals. The extracts are simple, mainly including four major kinds of compounds, namely, heteroatom and aromatic compounds, long-chain alkane and alkene compounds, among which oxygenated chemicals and long-chain alkane compounds account for the majority. Water can break the hydrogen bond of the network structure inside coal macromolecules and can catalyze to fracture the ether bond to some extent. Interaction between the hydrated polar organic and non-polar organic possibly leads to a certain amount of non-polar compounds in the extracts. Since water has a ralatively low infiltrating rate to coal, it is not easy to enter the millipore and network structure. Thus what water can dissolve is part of micro- molecules at free state.Methanol has higher infiltrating rate to coal than water, so its molecule can readily approach coal surface or macro pore surface of coal structure before entering the millipore and network structure. Extraction under normal atmosphere with methanol as solvent is therefore characterized by the following features: aromatics take up a greater part among the extracts, which is also the case in phenols and olefin compounds while long-chain alkanes account for relatively low proportion. This shows that small-molecular aromatics and olefin compounds of the coal structure in the mobile phase mainly exist in the microporous parts of the coal, while the long-chain alkenes dissociates on the surface of the coal or the macroporous parts but seldom in the millipore.The synthesized super solid acidic catalyst SO₄^2-/ZrO₂(SZ) has a relatively high catalytic activity to the selected coal model preparaed. With catalysis of SZ, the coal was depolymerized to single composed phenolic compounds in high amount, which is a kind of monomer that can be used to synthesize organic polymer. The above method is therefore a good way to get single composed chemicals from coal. The type and quantity of the catalytical depolymerization extracts by solid super acid SZ are related to the type of coal. Higher yields of phenolic compounds can be obtained from low ranked and highly oxygenated coal. Phenols, acid and ester derivatives of larger molecular weight should have been detected in the depolymerized products without the restrictions of GC/MS detection range.Polar solvents can dissolve the polar and non-polar material in mobile phase in the coal structure. That cracking of part of hydrogen bond of the original coal structure owning to strong polar solvents is respossible for the dissolvement of the polar material, while the dissolvement of the non-polar material is a result of interaction between the polar organic and non-polar organic molecules that are dissolved in water. Super solid acid can be used to catalyse coal depolymerization to get single composed and the high amount of phenolic compounds. This implies that coal macromolecules network structure is rich for ether and ester bond and resorting to solid super acid to catalyzed coal depolymerization is an effective approach to obtain phenolic compounds.