Liquid fuel production using solar-thermal energy: Process development and technoeconomic evaluation

Jiyong Kim, Terry A. Johnson, James E. Miller, Ellen B. Stechel, Christos Maravelias

Research output: Chapter in Book/Report/Conference proceedingConference contribution


We have previously described a novel solar-based concept for the production of methanol from carbon dioxide and water. This system applies concentrated solar energy to thermochemically reenergize CO 2 into CO, and then water-gas shift (WGS) to produce syngas (a mixture of CO and H 2) that is fed to a methanol synthesis reactor. Aside from the thermochemical reactor, which is currently under development at Sandia National Laboratories, the approach is based on well-established industrial processes and component designs. Our previous work included an assessment of energy efficiency and economic feasibility of this baseline configuration for an industrial-scale methanol plant. We determined that an overall process energy efficiency (solar-to-fuel) of 7.1% could be achieved and a break-even price of the methanol produced using this approach would be 1.22 USD/kg. Our current work focuses on improvements to the baseline system. We propose several avenues for improvement: 1) alternative pathways to syngas including water splitting and combined CO 2 and H 2O splitting, 2) improved separations, and 3) alternative hydrocarbon products. For alternative pathways and products, we studied three systems in addition to the baseline system previously reported: (i) H 2O water splitting, followed by reverse water-gas shift (RWG) reaction, followed by methanol synthesis (MS) (ii) Simultaneous CO 2 and H 2O splitting (mixed pathway) followed by MS (iii) Simultaneous CO 2 and H 2O splitting (mixed pathway) followed by Fischer-Tropsch (FT) synthesis In all designs, we employed amine-based separation systems to remove CO 2 from CO/CO 2 or H 2/CO/CO 2 mixtures. However, we also studied the effect of replacing the CO 2 separations system with an analogous CO separations system. We found that CO separations could provide a significant improvement in energy efficiency and utility costs for the CO 2 splitting and mixed pathways. To compare the improved systems to our baseline, we performed rigorous process simulations to determine equipment sizing and costing, as well as operational expenses (e.g., raw material and utility costs). We then performed detailed profitability calculations. We determined that the mixed pathway (i.e., simultaneous splitting of CO 2 and H 2O) has a number of advantages over the CO 2-splitting or H 2O-splitting pathways. Also, the production of methanol is slightly more attractive than the production of FT diesel. Using the mixed pathway with MS as our new baseline, we then carried out sensitivity analysis studies to identify the main cost drivers. We found that the primary economic drivers are the high capital investment associated with the solar concentrator/reactor sub-system which accounts for more than 90% of the capital expenditure, and the high utility consumption for CO/CO 2 separation. Economic parameters such as tax rate and interest rate are also important. Rather than use a cost of CO 2 as had been done previously, we expanded the boundaries of our system to include CO 2 capture at a power plant. We determined that the effect of CO 2 capture leads to small increases in the minimum selling price (i.e., break-even price) of methanol. We also studied how the minimum selling price (MSP) of methanol increases as a function of the distance between the power plant and the solar facility and the transportation technology. The energy efficiencies of the different systems were also analyzed. Along with lower cost, the mixed pathway with MS demonstrated the highest efficiency. The primary energy efficiency (= chemical energy out (HHV) over total primary energy in) was calculated as 12.7% if process heat and electricity are provided from fossil fuels and 10.7% if solar power is the sole primary energy source. This 10.7% system efficiency is significantly higher than what can currently be achieved with photosynthesis-based processes, and illustrates the potential for solar thermochemical based strategies to overcome the resource limitations that arise for low-efficiency approaches. Finally, the analysis indicates that a solar-thermochemical pathway to fuels has significant potential, and points towards future research opportunities to increase efficiency and reduce cost. Particularly, it is evident that there is much room for improvement in the development of a less expensive and more efficient solar concentrator/reactor sub-system, an opportunity that will benefit from the increasing deployment of concentrated solar power. In addition, significant advances are achievable through improved separations, different end products, and different degrees of process integration and distribution. Our investigation establishes a methodology for comparison and assessment of impact on both the economics and the efficiency for advanced system designs.

Original languageEnglish (US)
Title of host publication11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings
StatePublished - 2011
Externally publishedYes
Event2011 AIChE Annual Meeting, 11AIChE - Minneapolis, MN, United States
Duration: Oct 16 2011Oct 21 2011

Publication series

Name11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings


Other2011 AIChE Annual Meeting, 11AIChE
Country/TerritoryUnited States
CityMinneapolis, MN

All Science Journal Classification (ASJC) codes

  • Chemical Engineering(all)


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