(36f) Natural Vs Engineering CO2 Capture and Utilization | AIChE

(36f) Natural Vs Engineering CO2 Capture and Utilization


Martin, M., University of Salamanca
Grossmann, I., Carnegie Mellon University
The very large increase in CO2 emissions from industrial development, transport, and other activities, as well as its accumulation in the atmosphere, above 32Gt CO2 annually (EPA, 2022), make it necessary to remove it, either by storing it in geological deposits or by using it as a synthesis reagent to produce chemicals, i.e. methanol (Martin & Grossmann, 2017) or methane (David & Martin, 2014). The production of methane and methanol from renewable CO2 and H2 is potentially attractive because they are valuable products in the market. Methanol constitutes one of the seven fundamental primary chemical products in the chemical industry (IEA, 2022). Methane can also be employed for domestic use in boilers and heating systems. In both cases, CO2 and renewable H2 are required. On the one hand, the CO2 can be captured by employing the technology based on direct air capture (DAC) as the better option to remove it from the atmosphere compared to the use of biomass. On the other hand, H2 is generated by water electrolysis through the use of renewable energy from PV panels or wind turbines (Martin & Grossmann, 2016). Solar and wind can provide the energy required by the water electrolysis and supply some part of the totality of the energy needed for the process, but this is influenced by the location and its climatic conditions.

We address the problem of deciding which chemical to produce, and the location of the power sources and production facilities accounting for the requirements of the market and the availability of energy. To accomplish this goal, a multi-scale optimization model based on the work by Heras & Martín (2021) is developed to assess the feasibility of producing methane and methanol based on the availability of capturing CO2 (using DAC or biomass) and water, solar and wind energy, available surface to establish the production plant and the photovoltaic panels and/or wind turbines, product transport networks, and the necessary investment. At the process scale, a techno-economic analysis is performed to determine the yield, as well as the investment and product cost of DAC, renewable H2, methane, and methanol production. All the processes are modeled in detail following an equation-based approach. The conventional DAC process employs alkaline solutions based on KOH, which is emerging as the most appropriate alternative from the point of view of process operation and economics to the BPMED process based on bipolar membranes. The CO2 is hydrogenized in each of the products. Water electrolysis, powered by renewable energy from PV panels or wind turbines is considered. H2 is purified from traces of O2 and H2O. The O2 stream can provide credit for the entire system. Methanation of CO2 with renewable hydrogen allows producing synthetic natural gas. The process also generates water that can be recycled for the electrolyzer. Alternatively, CO2 can be hydrogenized to methanol. The process is governed by equilibria that require unreacted H2 and CO2 to be recycled. At the macro scale, the KPIs of the different processes are used to formulate a network optimization problem to decide on the installation of the different technologies across the land/country for a given budget. A multi-period, multi-objective problem MINLP is formulated including social issues related to the generation of wealth and jobs in the region where the facilities are installed. A study of the required supply chain is carried out to determine the most appropriate area in which to locate the CO2 capture and methane/methanol synthesis plants, as well as the type of technology necessary for the generation of solar energy and/ or wind and the area or region in which to locate said technology.

As a case study, Spain is considered, except for the autonomous cities of Ceuta and Melilla and other Spanish enclaves in the Mediterranean due to their small area. At the same time, the social and economic aspects of the use of CO2 capture plants, the generation of methane and methanol, and its distribution, and the use of photovoltaic panels and wind turbines are considered to mitigate the impact of climate change on the areas to be treated and developed the local and national economy.

The production of solar energy are located in the central-southern peninsular areas since they present higher rates of solar radiation and the wind turbines in the coastal area of the Strait of Gibraltar, the northern third of the peninsula, which are the areas with higher wind velocities. In the case of methane, the existence of a pre-existing transportation network dedicated to transportation, as well as the existence of regasification plants, allows its adequate distribution at a national and even international level. Several target prices and different budget allocations are analyzed to assess the infrastructure to be installed. The target sales prices of methane and methanol correspond with the market prices, which are 0.48 €/kgMethane (Eurostat, 2022), and 0.4 €/kgMethanol (Methanol Institute, 2022), respectively. As will be shown, these values can be achieved through the supply of state subsidies and grants, as well as indirect aid to facilitate reaching these prices.


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