Green C2-C4 hydrocarbon production through direct CO2 hydrogenation with renewable hydrogen: Process development and techno-economic analysis
Graphical abstract
Introduction
C2-C4 hydrocarbons, such as light olefins, are important chemical building blocks for a variety of useful derivatives in the petrochemical industries [1], [2]. In particular, ethylene and propylene production in the petrochemical industries has shown significant growth in the global market during the past decades [3]. The global market demand for ethylene and propylene is predicted to reach 184 and 127 MMton, respectively, by 2022, corresponding to a 20% and 25% increase over 2017 [3], [4]. Conventionally, C2-C4 hydrocarbons have primarily been produced using oil fractions from petroleum refineries and natural gas processing plants [3], [5], [6], [7]. With the rapid depletion of petroleum sources [8], many alternative feedstock (e.g. biomass-based [9]) and technological pathways (e.g. methanol-to-olefin [10] or coal-to-olefin routes [11], [12]) have been investigated to satisfy the demand growth of C2-C4 hydrocarbons.
A concern about climate change and global warming is increasing as CO2 emission has been predicted to continually and rapidly increased [13]. Since a recent report of the Intergovernmental Panel on Climate Change (IPCC) [14] suggested on the limiting global warming less than 1.5 °C by reducing global CO2 emissions, more attempts have been made to mitigate climate change [15]. In this context, the environmental friendliness is one of the prioritized criteria in the light hydrocarbons production such as developing clean technologies, using renewable energy sources, or proactively utilizing CO2 as a source for high-value chemicals [16]. Especially, the direct utilization of CO2 has been considered as one of the most effective initiatives to mitigate climate change. A number of studies in the literature have examined new processes which utilizes CO2 as a source (e.g., the direct CO2 hydrogenation) as a promising route to value-added chemicals from a captured CO2, especially coupled with renewable H2 [17]. Do et al. developed the eco-friendly process for methanol production through the direct hydrogenation of CO2 with a renewable H2 [18]. Similarly, the techno-economic analysis of the power-to-dimethyl ether conversion using the CO2 hydrogenation was examined by Michailos et al. [19]. Meiri and the colleagues studied the catalyst performance of the direct CO2 hydrogenation for the hydrocarbon production and developed simulation models for techno-economic analysis [20], [21]. Najari et al. proposed and analyzed an advanced membrane reactor for the CO2 hydrogenation to the hydrocarbon production [22]. While various studies on the CO2 direct hydrogenation for producing value-added hydrocarbons are found in the literature, most studies focused on the long-chains hydrocarbon, or liquid fuels production [23]. Particularly, Smejkal et al. [24] performed a techno-economic evaluation of direct CO2 hydrogenation technology to produce petrochemical and liquid fuel hydrocarbons. Zhang et al. [25] analyzed the technological and economic performance of a process for co-production of synthetic natural gas and liquid fuel hydrocarbons via direct CO2 hydrogenation. Recently, a few studies have focused on light C2-C4 hydrocarbons via direct CO2 hydrogenation. For instance, Najari et al. [26] estimated the kinetic parameters for the modeling and optimization of the hydrogenation reaction of CO2 to C1-C4 hydrocarbons over a K-promoted Fe catalyst using an algorithm-based method. To the best of our knowledge, there is little study in the open literature to propose a complete process producing light C2-C4 hydrocarbons via direct CO2 hydrogenation, and to analyze the technical, economic and environmental capability. Thus, it is necessary to develop rigorous models and examine the techno-economic and environmental performance of the light C2-C4 hydrocarbons via direct CO2 hydrogenation to obtain further perspectives for industrial applications.
This work aims to develop and evaluate a complete process for the C2-C4 hydrocarbons production via direct CO2 hydrogenation. One of the distinct features of the proposed process is a green route to C2-C4 hydrocarbons, which is obtained from the synergy of using a captured CO2 and renewable H2. In this work, the catalyst of Fe-K/γ-Al2O3 was introduced in the catalytic conversion unit to produce light hydrocarbons [26]. The diverse mixture of products with different physicochemical characteristics (e.g., a wide distribution of hydrocarbons, undesired by-products such as CO, and unreacted CO2 and H2) results in a complex separation scheme which is also another critical featured of the study. To achieve the goal, a conceptual but rigorous process model for the C2-C4 hydrocarbon production, including the reaction and separation sections, has been developed using the software Aspen Plus V10.0 [27]. Then, a techno-economic analysis study was performed to evaluate the technical and economic feasibility of the proposed process using different criteria: technical performance (carbon element efficiency and energy efficiency), environmental performance (emission CO2-eq), and economic performance (unit production cost). In addition, major cost parameters, in particular the price of renewable H2 as the most critical factor, were evaluated in a sensitive analysis study that identifies the key strategies to make the proposed process more economically.
Section snippets
Process overview
The conceptual design for the process of producing light hydrocarbons via direct CO2 hydrogenation is introduced in this section. Fig. 1 shows a simplified block diagram of the proposed process for light hydrocarbon production using captured CO2 and renewable H2 as the raw materials. The feedstock materials are as follows:
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CO2: is captured from flue gas (21 mol% CO2, 3 mol% O2, 66 mol% N2, and 11 mol% H2O) from a coal-fired power plant [28].
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Renewable H2: is produced via water electrolysis using
Process modeling
In this study, the direct hydrogenation of CO2 to light hydrocarbon production process was modeled and simulated using Aspen Plus V10 [27]. The parameters and assumptions for the modeling and simulation are presented in Table 1, including the catalytic conversion unit for direct hydrogenation, the multiple separation technologies integrated for C2-C4 hydrocarbon purification, and the recycling of CO2, CO, and H2. In the CO2 hydrogenation stage, the kinetic of the series of reactions to produce
Carbon and energy efficiency
Fig. 3 presents the carbon and energy efficiencies of the proposed process. The carbon flow of the process is broken down into the major components, CO2, CO, CH4, C5+ and C2-C4 hydrocarbons, as shown in Fig. 3(a). As discussed before, a high recycling stream volume (66,644 kmol/h) was required to improve the carbon efficiency () due to the low conversion of the CO2 hydrogenation reaction. Within 11,050 kmol/h CO2 feed stream, 8771 kmol/h of carbon element are presented in form of the C2-C4
Conclusion
This study aimed to propose a new green process for the production of C2-C4 hydrocarbons from captured CO2 and renewable H2. To achieve this goal, direct CO2 hydrogenation was used as the main reaction to produce C2-C4 hydrocarbons, and a complex separation scheme including membrane, absorption, PSA, and distillation technologies and an onsite combined heat and power plant were integrated to achieve highly energy-efficient, economical, and low-CO2-emission C2-C4 hydrocarbon production. In
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This research was supported by “Next Generation Carbon Upcycling Project” (Project No. 2017M1A2A2043137) through the National Research Foundation (NRF) funded by the Ministry of Science and ICT, Republic of Korea.
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