| Description |
The reactions for conversion of methane to benzene suffer from low yield and are equilibrium-limited by excess hydrogen, which can be resolved by using a hydrogen-selective membrane. Data from lab-scale experiments were used to obtain reaction rate constants used in a rigorous thermodynamic reactor model written in MATLAB and integrated into an Aspen Plus process model with thermal pinch analysis for an efficient heat exchanger design. Aspen Process Economics Analyzer was used to assess sensitivity to economic conditions and determine economic viability. The results indicate that the venture is profitable (profitability index of 1.17, internal rate of return of 35.5%, net rate of return of 18.2%). The capital cost was found to be $35,500 per daily standard barrel of benzene. Additionally, the process remains economically attractive, as long as either the price of benzene remains above $470/mt, or the price of hydrogen remains above $0.8/kg. A custom system was built for pyrolysis of Green River shale cores to evaluate the effect of heating rate and pressure on oil yield and quality. In tandem with this, a phase equilibrium model was written in MATLAB to explore the effect of these operational parameters on a global reaction system. Condensable oil was collected in five temperature intervals and an Excel macro was written to track over 140 identified and classified species concentrations using GC-MS and GC chromatograms. The oil condensed between 300 °C and 340 °C from the 0.008 °C/min experiment contained a lower paraffin concentration (31 mol% vs 63 mol%) and higher aromatic concentration than the 0.03 °C/min experiment iv (43 mol% vs. 22 mol%). Additionally, the alkene concentration was higher in the 0.008 °C/min experiment compared to the 0.03 °C/min experiment for oil from all temperature intervals. Weight-loss data from the load cell was used to estimate rate parameters and the possibility of exploring phenomena not evident from thermogravimetric analysis of powders was highlighted. The model predicts that when low quantities of evolved vapor exist the system, the maximum oil yield is attained when pyrolyzing under high pressure and high heating rate rather than low pressure and low heating rate for systems where most vapor is allowed to exit. |
