High-quality oil and gas from pyrolysis of Powder River Basin coal catalyzed by an environmentally-friendly, inexpensive composite iron-sodium catalysts

The objective of this research is to develop a cost-effective catalytic pyrolysis process for producing high-quality oil and gas from coal with low CO2 emission. Catalytic pyrolysis of the Powder River Basin coal using composite Na2CO3-FeCO3 catalysts has been investigated in a fixed bed reactor between 500 and 800 °C under atmospheric pressure to evaluate effects of catalyst on quantity and quality of the resulting oils and gases. The results indicate that high-quality oil and gas can be obtained with use of 4% Na2CO3 and 3% Na2CO3–1% FeCO3 catalyst. Use of 3% Na2CO3–1% FeCO3 catalyst can improve coal conversion by ~ 4.5% and 5% for Na2CO3 catalyst. The H/C ratio of the oil products obtained with catalysts are higher, while their O and S concentrations are reduced by as much as 36.1% and 50.6% for 4% Na2CO3 and 23.27% and 50.6% for 3% Na2CO3–1% FeCO3 catalyst, respectively. The respective heating values of oil obtained with the 4% Na2CO3 and 3% Na2CO3–1% FeCO3 catalysts increase by 833.3 kJ/kg and 541.7 kJ/kg. Moreover, these catalysts can reduce CH4 and increase H2 and CO concentrations of the produced gases at 700 °C, while 3% Na2CO3–1% FeCO3 obtain better quality syngas (H2/CO) at higher temperature. At 700 °C,4% Na2CO3 can reduce CH4 concentration in the gas by 23.11% and increase H2 and CO by 70.22% and 6.54%, respectively, 3% Na2CO3–1% FeCO3 can reduce CH4 concentration by 20.80% and increase H2 and CO by 58.90% and 2.18%. All these results demonstrate that 4% Na2CO3 and 3% Na2CO3–1% FeCO3 are both promising coal pyrolysis catalysts. The composite catalyst can not only synergize the advantages, but also overcome the challenges of pure iron or pure sodium based catalytic coal pyrolysis processes. In addition, GCMS test results show that Na2CO3 can change the reaction pathway way of pyrolysis, resulting in a decrease in the generation of furan and esters and increases in the productions of phenols, ketones, straight-chain olefins, and alicyclic hydrocarbons. The associated catalytic mechanism with addition of Na2CO3 is proposed.