No abstract

A review and analysis of opportunities for long-term carbon dioxide removal and storage in biomass-derived products.

Decarbonization of transportation fuels represents one of the most vexing challenges for climate change mitigation. Biofuels derived from corn starch have offered modest life cycle greenhouse gas (GHG) emissions reductions over fossil fuels. Here we show that capture and storage of CO2 emissions from corn ethanol fermentation achieves ∼58% reduction in the GHG intensity (CI) of ethanol at a levelized cost of 52 $/tCO2e abated. The integration of an oxyfuel boiler enables further CO2 capture at modest cost. This system yields a 75% reduction in CI to 15 gCO2e/MJ at a minimum ethanol selling price (MESP) of $2.24/gallon ($0.59/L), a $0.31/gallon ($0.08/L) increase relative to the baseline no intervention case. The levelized cost of carbon abatement is 84 $/tCO2e. Sensitivity analysis reveals that carbon-neutral or even carbon-negative ethanol can be achieved when oxyfuel carbon capture is stacked with low-CI alternatives to grid power and fossil natural gas. Conservatively, fermentation and oxyfuel CCS can reduce the CI of conventional ethanol by a net 44–50 gCO2/MJ. Full implementation of interventions explored in the sensitivity analysis would reduce CI by net 79–85 gCO2/MJ. Integrated oxyfuel and fermentation CCS is shown to be cost-effective under existing U.S. policy, offering near-term abatement opportunities.

Strategies to remove carbon from the atmosphere are needed to meet global climate goals. Promising strategies include the conversion of waste biomass to hydrogen, methane, liquid fuels, or electricity coupled with CO2 capture and storage (CCS). A key challenge for these projects is the need to connect geographically dispersed biomass supplies with geologic storage sites by either transporting biomass or CO2. We assess the cost of transport for biomass conversion projects with CCS using publicly available cost data for trucking, rail, and CO2 pipelines in the United States. We find that for large projects (order of 1 Mt/yr CO2 or greater), CO2 by pipeline is the lowest cost option. However, for projects that send most of the biomass carbon to storage, such as gasification to hydrogen or electricity production, biomass by rail is a competitive option. For smaller projects and lower fractions of carbon sent to storage, such as for pyrolysis to liquid fuels, CO2 by rail is the lowest cost option. Assessing three plausible example projects in the United States, we estimate that total transport costs range from $24/t-CO2 stored for a gasification to hydrogen project traversing 670 km to $36/t for a gasification to renewable natural gas project traversing 530 km. In general, if developers have flexibility in choosing transport mode and project type, biomass sources and storage sites can be connected across hundreds of kilometers for transport costs in the range of $20-40/t-CO2 stored. Truck and rail are often viable modes when pipelines cannot be constructed. Distances of 1,000 km or more can be connected in the same cost range when shared CO2 pipelines are employed.

We have developed a new class of sodium carbonate/silicone composite sorbents that selectively capture carbon dioxide (CO2) and can purify biogas to natural gas pipeline-quality biomethane. These nontoxic composites can be three-dimensionally printed or extruded at low costs, can have high specific CO2 sorption rates (in excess of 5 μmol s–1 g–1 bar–1) and high selectivity due to their chemical mechanism, and can be regenerated with low-energy air stripping. Therefore, these composite sorbents combine the high selectivity of liquid sorbents with the high specific sorption rates and low regeneration energies found in many solid sorbents. We characterized these composite sorbents with X-ray computed tomography, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Furthermore, we measured composite sorption capacities of up to 0.62 mol CO2 kg–1 and recorded breakthrough curves in a flow-through, fixed-bed reactor using both simulated biogas and locally sourced industrial biogas. Additional tests of the composite sorbent were carried out with pure CO2 in a sealed pressure drop apparatus. This experimental data was used to validate a numerical model of the setup and to simulate an industrial-scale biogas upgrading process. Finally, we performed a preliminary technoeconomic analysis for this upgrading process and found that this composite sorbent can upgrade biogas at a lower cost (∼$0.97 per GJ) than other currently implemented techniques.