Literaturestudieshave demonstrated the effectiveness of supercritical CO2, particularly in conjunction with a co-solvents), to extract a wide variety of compounds from coal for the purpose beneficiation or the production liquified fuels, aromatics, rare earth elements, and other specialty/valuable chemicals. With pressure building to capture and sequester CO2 in response to greenhouse gas emission concerns, the availability of potentially low cost scCO2 is expected to increase dramatically over the coming decade. Further, with the introduction and demonstration of the scCO2 power cycle, engineering/technical know-how is being developed that can be extended/adapted to large-scale industrial scCO2 extractions. Hence, limitations associated with both sCO2 supply and industrial process scaleup are being addressed. However, one of the remaining primary disadvantages of scCO2 extraction which is magnified with co-solvents use) is the high capital and operating costs associated with product recovery and solvent recycle. In general, a phase change is required, so that evaporative heat losses co-solvent) and recompression costs CO2) are excessive, particularly in the context of the high solvent to substrate ratios necessary to achieve adequate extraction rates. Overcoming this economic barrier would open the door to large scale industrial sCO2 extraction of not only coal but also a range of other potential feeds such as waste materials, biomass, etc. To solve the phase change problem,we propose the use of MPT high performance ceramic microporous membranes as a basic unit operation in scCO2 extraction/processing. The product separation is achieved with only a modest pressure loss, for instance up to several bars, relative to the scCO2 operating pressure. Hence, the vast bulk of the sCO2 and co-solvent) is recycled to the extractor at temperature with only a modest pressure boost required. During the Phase I program we will be conducting bench scale testingof MPT membranes in the scCO2+co-solvent at the expected extraction pressure and temperature to validate membrane performance and performance stability. The upgrading performance of the extraction solvent and membrane separator will be assessed with several coal samples.With this data, an extractor and separator process model will be developed and technoeconomic analysis will be conducted/refined. This information will be used to establish the program technical approach in the Phase II pilot scale demonstration. Our proposed process for coal upgrading offers an array of advantages to conventional approaches and represents a way forward for implementation of scCO2 extraction not only in coal upgrading but also in a range of other industrial process where the thermal and recompression cycles dominate the process economics. In coal upgrading, the technology would be suitable for a range of possible commercial applications including for instance i) clean fuel for advanced combustion approaches with the promise of higher efficiency, significantly reduced emissions, and longer equipment life; ii) production of low cost coke/anode coke; iii) preparation of carbon nanomaterials at substantially reduced cost; iv) the recovery of base, strategic, and rare earth elements from the residual coal.
