(430c) Optimal Composition of Biogas for Methanol Production Via Dry Reforming
Biogas already has CO2 within its composition. However, the syngas produced is expected to show a low ratio H2:CO. To tune this ratio we can follow different alternatives. Biogas composition is variable and can be adjusted. Furthermore, traditionally dry reforming of methane has been combined with other reforming modes [4-6].
In this paper, we present a mathematical optimization approach for the optimal dry reforming of biogas for the production of methanol. The raw biogas is cleaned up before reforming. We allow for the use of steam and variable biogas composition to increase the hydrogen content of the syngas. Part of the biogas is used to provide energy for the process. Next, the unreacted hydrocarbons and CO2 are removed. Subsequently, its composition may be adjusted (using either water gas shift reaction or pressure swift adsorption if there is an excess of hydrogen). Finally, methanol is synthesized. The problem is formulated as an NLP with simultaneous heat integration for the optimal biogas composition and methanol production. Two objective functions are considered: a simplified production cost and we proposed an environmental one based on carbon footprint considering the contributions to CO2 emissions due to the water usage as cooling agent, raw material or steam production and CO2 consumption and release across the process.
Biogas is expected to have around 50-52% of CH4 and 45-47% of CO2, depending on the objective. The production cost of methanol is $1.7/gal, for a plant size that uses 10% of the potential biogas to be produced in Madrid (Spain), with an investment of $46 MM. The production cost is becoming competitive with the current price of methanol ($0.9/gal) with the advantage of its sustainability. The results obtained for both optimizations show a negative carbon footprint, creating a net capture of CO2 while producing a valuable intermediate for chemicals or fuels.
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