Experimental measurements and theoretical modeling of high-pressure mass densities and interfacial tensions of carbon dioxide + n-heptane + toluene and its carbon dioxide binary systems

Experimental determination and theoretical predictions of the isothermal (344.15 K) mass densities and interfacial tensions for the sys tem carbon dioxide (CO2) with heptol (n - heptane + toluene) mixtures varying liquid volume fraction compositions of toluene (0, 25, 50, 75, 100 % v/v) and over the pressure range 0.1 to 8 MPa are reported. Measurements are carried out on a high - pressure dev ice that includes a vibrating tube densimeter and a pendant drop tensiometer. Theoretical modeling of mass densities phase equilibria and interfacial properties (i.e., interfacial tension and interfacial concentration profiles) are performed by employing t he Square Gradient Theory using an extension of the Statistical Associating Fluid Theory equation of state that accounts for ring fluids. The experimental bulk phase equilibrium densities and interfacial tensions obtained are in very good agreement with th e theoretical predictions. Although there are no previous experimental data of these mixtures at the conditions explored herein, the results follow the same trends observed from experimental data at other conditions. The combination of experimental and mod eling approaches provides a route to simultaneously predict phase equilibrium and interfacial properties within acceptable statistical deviations. For the systems and conditions studied here, we observe that the phase equilibrium of the mixtures display z eotropic vapor - liquid equilibria with positive deviations from ideal behavior. The mass bulk densities behave ordinarily whereas the interfacial tensions decrease as the pressure or liquid mole fraction of CO2 increases and/or the ratio toluene/heptane dec reases. The interfacial concentration along the interfacial region exhibits a remarkable high excess adsorption of CO2, which increases with pressure and it is larger in n - heptane than in toluene. Toluene does not exhibit any special adsorption activity wh ereas n - heptane displays surface activity only at low pressure in a very narrow range for the case of CO2 + (25% n - heptane + 75% toluene) mixture

Natural gas and BECCS: A comparative analysis of alternative configurations for negative emissions power generation

There is a reliance on negative emissions technologies (NETs), primarily in the form of Bioenergy with Carbon Capture and Storage (BECCS) in most Integrated Assessment Model (IAM) scenarios which are capable of limiting the maximum global temperature rise to 1.5–2 °C. Two currently independent features of transition pathways are fuel switching from a coal to gas, and the deployment of BECCS. The former makes natural gas an important transition fuel which at the same time could be combined with biomass to further abate emissions. To date the majority of studies have considered BECCS in the context of a conversion from coal-fired base configuration. There is therefore a pressing need to identify routes for the effective utilization of biomass-derived fuels in the context of gas-fired power generation infrastructure. In this contribution, we study three distinct CCS-based processes which combine natural gas and biomass capable of producing low-, or carbon-negative power. Both fuel supply chains are considered in order to quantify the net overall CO2 emissions. An important insight is the configuration-specific impact of biomass co-combustion on the overall carbon intensity of power generated. We found that an external biomass combustion configuration was the most carbon negative, removing between 0.5–1 ton of CO2 per MWh of power generated. Results revealed a trade-off between carbon negativity and efficiency of the processes. The generation of net carbon negative power is observed to be highly sensitive to the carbon footprint of the biomass supply chain