Biotransformation technology
The biotransformation of coal belongs to the category of biological processing, which refers to the depolymerization of macromolecules in coal with the participation of microorganisms, which is called biodegradation or dissolution. The transformation of microorganisms such as fungi, bacteria and actinomycetes is mainly used to realize the dissolution, liquefaction and gasification of coal, so that it can be transformed into water-soluble substances or hydrocarbon gases, from which chemicals with special value can be extracted to prepare clean fuels, industrial additives and agricultural plant growth promoters, and finally the dissolution, liquefaction and gasification of coal can be realized. For example, dissolved coal products are converted into single low molecular weight aromatic hydrocarbons with high added value and methane, methanol and ethanol which can replace petroleum as clean fuels. The gas methanation technology of converting cellulose into alcohol and cellulose into biogas, hydrogen and carbon monoxide by microorganisms is basically mature and can be carried out at normal temperature and pressure. The research on microbial degradation of petroleum and lignin has made rapid progress. Coal is homologous to petroleum and lignin, especially young low-rank coal contains a lot of lignin, which has been proved to be biodegradable by microorganisms.
Microbes that degrade and transform coal
The source of microorganisms that can degrade and transform coal is based on their metabolites, such as secreted enzymes and chelating agents, which can attack some components and structures in coal or organic compounds similar to coal and can be screened from various existing microorganisms. For example, the structure of lignin is similar to that of low-rank coal, so microorganisms that can degrade lignin, such as Phanerochaete chrysosporium, can be selected to study microbial coal dissolution, and some achievements have been made. Another example is that there is aromatic ring structure in coal, so bacteria that can degrade aromatic rings, such as Pseudomonas, can be selected to study coal dissolution. In addition, strains can be isolated from microorganisms that grow on natural coal. There is a certain matching relationship between different microorganisms and different coal samples, so it is very important to screen out microorganisms that can dissolve and degrade coal from different coal species. There are many kinds of coal in China, and the reserves of low-rank coal are very large, so it is of great practical significance to screen the matching of bacteria and coal.
Biodegradation and transformation types of coal
Weathered lignite, lignite and even young bituminous coal have been tested. The degree of coal dissolution seems to be more related to the type of coal, followed by the type of microorganism, while most untreated lignite and young bituminous coal cannot be degraded by the tested fungi. Generally speaking, the order of coal dissolution degree from large to small is: weathered coal, coal exposed to air, and newly mined coal not exposed to air.
Experiments show that low-priced coal is more easily degraded and transformed by bacteria after pretreatment. Therefore, people have tried various oxidation pretreatment methods, such as nitric acid soaking oxidation treatment, microwave radiation treatment, high temperature air oxidation of coal (150℃), hydrogen peroxide and ozone (or combination) oxidation pretreatment, etc., and the biological solubility of lignite has been greatly enhanced.
Han Wei and Yang Haibo of Dalian University of Technology in China oxidized Pingzhuang and Zhalainuoer lignite with nitric acid and used Coriolus versicolor for biological action. The weight loss of coal and the analysis of collected products show that the dissolution reaches 30%-60%. The late Professor Wang of Anhui University of Science and Technology used white rot fungi to degrade and transform nitric acid to treat Yima lignite and Huainan sub-bituminous coal. The experimental results also show that acid treatment is helpful to the biodegradation and transformation of coal.