Development of sustainable coal to liquid processes: Minimising process CO 2 emissions

摘要

Traditional coal-to-liquid ( CTL ) plants are synonymous with the production of carbon dioxide. Coal may be gasified in the presence of steam and oxygen to produce gas comprising carbon dioxide ( CO 2 ), carbon monoxide ( CO ), methane ( CH 4 ), hydrogen ( H 2 ) and steam ( H 2 O ). The gases can be reacted to a myriad of chemicals and fuels via the Fischer-Tropsch ( FT ) reaction. However, excess carbon dioxide is generated via the Water-Gas-Shift reaction during preparation of CO:H 2 ratios for FT . Here, a process development is represented on a CHO phase diagram, where unique regions are identified for autothermal operations for coal conversion. Considerations are given to develop idealised processes for the production of liquid chemicals from coal which emit minimal process CO 2 , require minimal energy input and do not require steam. This is achieved by co-feeding coal with methane and identifying endothermic-exothermic process pairs for methane-coal dry reforming. Furthermore, it is shown that a preferred method to produce liquid fuels from coal is by first creating dimethyl ether ( DME ) as an intermediate, followed by the dehydration of DME to liquid fuels (gasoline range). For this route, via DME , the CO 2 emission was found to be four times less than idealised CTL processes. Graphical abstract Display Omitted Highlights ? CHO diagram is defined for autothermal regions for dry reforming of coal-methane systems. ? Idealised coal to liquids methods are defined. ? Gasoline range FT liquid is obtained via initial production of dimethyl ether. ? Process minimises CO 2 released to the atmosphere and does not require steam.