Optimization-based identification of CO2 capture and utilization processing paths for life cycle greenhouse gas reduction and economic benefits

This paper introduces a mathematical formulation to identify promising CO₂ capture and utilization (CCU) processing paths and assess their production rates by solving an optimization problem. The problem is cast as a multi-objective one by simultaneously maximizing a net profit and life cycle greenhouse gas (GHG) reduction. Three case studies are illustrated using an exemplary CCU processing network. The results indicate the optimal solution is greatly influenced by the scale of CO₂ emission source, market demand, and hydrogen availability. Moreover, with the current system of measuring the GHG reduction regarding a business-as-usual level, if the aim is to achieve a GHG reduction within a national boundary, the question of whether CCU plants producing a product of same functionality through conventional means, which the CO₂-based product can replace, exists in the country can come into consideration. This systematic identification will assist decision-making regarding future R&D investment and construction of large-scale CCU plants.     

Assessment of Industrial Greenhouse Gas Reduction Strategies Within Consistent System Boundaries

With respect to the climate goals of the greenhouse gas (GHG) neutrality in 2050, different GHG reduction strategies are discussed for industrial processes. For a comparison of the strategies carbon direct avoidance (CDA), carbon capture and storage, and carbon capture and utilization (CCU), the method system expansion is applied. Exemplarily, the CO₂ reduction potential and the energy demand are determined. The Carbon2Chem® project is described as an example of CCU for the steel and chemical production. The direct reduction with H₂ represents the CDA strategy for the steel industry.     

An optimization‐oriented green design for methanol plants

BACKGROUND: A new design for a methanol plant is proposed in which CO₂ addition, as one of the important parameters, is used to optimize the synthesis gas composition. An attempt has been made to assess the environmental features as well as the process operability of the proposed plant, in which the required CO₂ is provided from reformer flue gas. As a starting point, simulation of a conventional reference methanol case (RMC) and also the proposed green integrated methanol case (GIMC) are performed to obtain operational and kinetic parameters. In order to compare properly GIMC and RMC, the objective function is defined so that SynGas production, and thereby methanol production, in the GIMC is equal to that of the RMC. RESULTS: In the optimization the optimum values of decision variables are calculated using a genetic algorithm. In the best case, the eco‐efficiency indicators of GIMC would decrease to 330.3 kg CO₂ tonne^?1 MeOH, which is 15% lower than that of RMC. The environmental damage cost of 2.9 million dollars could also be prevented in GIMC when compared with RMC. CONCLUSION: It was found that the CO₂ needed in GIMC could be provided by an environmentally friendly process and that the GIMC is a cleaner process compared with RMC. Furthermore, the proposed GIMC would be capable of reducing CO₂ emission while its mitigation potential depends significantly on the type of solvent employed in the GIMC. The results obtained show that environmental damage cost would be important and should be considered in the process design. Copyright © 2012 Society of Chemical Industry     

A multi-scale framework for CO2 capture,utilization, and sequestration: CCUS and CCU

We present a multi-scale framework for the optimal design of CO₂ capture, utilization, and sequestration (CCUS) supply chain network to minimize the cost while reducing stationary CO₂ emissions in the United States. We also design a novel CO₂ capture and utilization (CCU) network for economic benefit through utilizing CO₂ for enhanced oil recovery. Both the designs of CCUS and CCU supply chain networks are multi-scale problems which require decision making at material, process and supply chain levels. We present a hierarchical and multi-scale framework to design CCUS and CCU supply chain networks with minimum investment, operating and material costs. While doing so, we take into consideration the selection of source plants, capture processes, capture materials, CO₂ pipelines, locations of utilization and sequestration sites, and amounts of CO₂ storage. Each CO₂ capture process is optimized, and the best materials are screened from large pool of candidate materials. Our optimized CCUS supply chain network can reduce 50% of the total stationary CO₂ emission in the U.S. at a cost of $35.63 per ton of CO₂ captured and managed. The optimum CCU supply chain network can capture and utilize CO₂ to make a total profit of more than 555 million dollars per year ($9.23 per ton). We have also shown that more than 3% of the total stationary CO₂ emissions in the United States can be eliminated through CCU networks at zero net cost. These results highlight both the environmental and economic benefits which can be gained through CCUS and CCU networks. We have designed the CCUS and CCU networks through (i) selecting novel materials and optimized process configurations for CO₂ capture, (ii) simultaneous selection of materials and capture technologies, (iii) CO₂ capture from diverse emission sources, and (iv) CO₂ utilization for enhanced oil recovery. While we demonstrate the CCUS and CCU networks to reduce stationary CO₂ emissions and generate profits in the United States, the proposed framework can be applied to other countries and regions as well.     

Co‐Metal Catalysts on SiO2‐TiO2 for Methanol Production from CO2 – Effect of Preparation Methods

The effect of quantity, composition, and different impregnation sequences on the catalytic properties of Cu‐Zn‐Al/SiO₂‐TiO₂ in the CO₂ hydrogenation for methanol production was investigated. The Cu‐Zn‐Al catalysts supported on SiO₂ and TiO₂ were prepared by incipient wetness impregnation. Then, their performances in CO₂ hydrogenation were tested under defined conditions. The composition variation of Cu and Zn catalysts resulted in a high methanol production for Cu catalysts with a higher content of Cu, which was the active site for CO₂ activation. Regarding the metal quantity of catalysts, a relatively low loading of co‐metal (Cu‐Zn‐Al) led to the maximum methanol yield when compared with higher loadings as a result of the largest surface area.     

Optimal Design Issues of a Methanol Synthesis Reactor from CO2 Hydrogenation

Methanol production through CO₂ hydrogenation was investigated in a series of fixed-bed reactors. Staging of the reactor into several smaller reactors is considered to enhance methanol production, in addition to maximizing a measure of annual profit. The degrees of freedom of the reactor system are the number of stages, the cooling medium temperature, the heat transfer area, and the volume of the stages. Depending on the objective function (OF) criteria, staging of the reactor increases the OF values to various extents. When the objective is to maximize the methanol production, the OF of a three-stage reactor system with an inlet H₂/CO₂ ratio of 2 is 2.61 % higher than in the single-stage configuration. Staging of the reactor also increases the synthesis gas conversion to methanol. However, if maximizing the annual profit is the objective, the profitability of the two-stage configuration is 2.05 % greater than in the case with one reactor, due to the higher methanol production of the staged reaction system.     

Design framework for dimethyl ether (DME) production from coal and biomass-derived syngas via simulation approach

A comprehensive thermodynamic study was conducted to evaluate the comparative efficacy of methanol and dimethyl ether (DME) synthesis using CO₂ rich syngas feed. The first part of our study included assessing the relative performances of the methanol synthesis system, two step DME synthesis system, and one step DME synthesis system in terms of the CO_x conversion and product yield (methanol/DME) based on the Gibbs free energy minimization approach. The wide range of composition of CO₂-enriched syngas feed produced by the coal and biomass gasification was simulated using Aspen Plus and the following evaluation parameters were analyzed for a broad parameter range: reaction temperature (180–280°C), reaction pressure (10–80 bar), stoichiometry number (SN) (0–11), and CO₂/(CO₂ + CO) molar feed ratio (0–1) for isothermal as well as adiabatic conditions. Based on the equilibrium yield, one-step DME synthesis was discovered as the most viable process to utilize the co-gasification derived syngas effectively. In the second part of our study, the overall process efficiency was inspected through the process design of 1 tonnes per day (TPD) DME plant inclusive of heat integration, resulting in significant CO₂ abatement and DME production with high product purity and minimum energy consumption. Consequently, one-step DME production via CO₂-enriched syngas obtained through the coal or biomass gasification process is identified as the leading technology based on energy utilization and CO₂ abatement.     

A methodology for the sustainable design and implementation strategy of CO2 utilization processes

This work presents a systematic methodology that has been developed for the design of sustainable CO₂ utilization processes that can mitigate CO₂ and also guarantee profitability. First, the three-stage methodology, evaluation criteria and applicable tools are described. Especially, the process design and analysis is discussed as only limited amounts of process data is available for determining the optimal processing path and in the third stage the issue of implementation strategy is considered. As examples, two CO₂ utilization methods for methanol production, combined reforming and direct synthesis are considered. Methanol plants employing such methods are developed using synthesis-design and simulation tools and their evaluation indicators are calculated under various implementation strategies. It is demonstrated that integrating or replacing an existing conventional methanol plant by a combined reforming method represents a sustainable solution. Additionally, producing methanol through direct hydrogenation is a promising way to convert CO₂ when cheap H₂ feeds are available.     

Wind und Kohle: Die technische Photosynthese

The increasing energy demand, the associated CO₂ emissions, and the concurrently decreasing reserves of fossil fuels require new concepts for sustainable energy production. The so‐called Adam‐and‐Eve principle for CO₂‐free production of methanol from coal and nuclear energy is revisited and adapted to today's circumstances. Electrolysis of water using renewable electricity is applied for H₂ production. Simultaneously, coal and the oxygen formed during electrolysis are burned in an oxyfuel process, generating electricity and relatively pure CO₂. Hydrogen from electrolysis and CO₂ are converted to methanol, which can then be used as chemical‐ and energy feedstock.     

High Temperature Co-Electrolysis as a Key Technology for CO2 Emission Mitigation – A Model-Based Assessment of CDA and CCU

The mitigation of CO₂ emissions is a major challenge for modern society. While the mitigation of energy-related emissions can be achieved comparatively easy by switching to renewable energy sources, reduction of process-related industrial emissions is considerably more challenging. To reduce industrial CO₂ emissions, two basic routes are available: carbon direct avoidance (CDA) and carbon capture and utilization (CCU). It is shown that in terms of efficiency, CDA is to be favored when applicable. However, for applications where emissions cannot be avoided, CCU can be a viable approach allowing for emission mitigation.     

The difference in the active sites for CO2 and CO hydrogenations on Cu/ZnO-based methanol synthesis catalysts

The effect of Zn in copper catalysts on the activities for both CO₂ and CO hydrogenations has been examined using a physical mixture of Cu/SiO₂+ZnO/SiO₂ and a Zn-containing Cu/SiO₂ catalyst or (Zn)Cu/SiO₂. Reduction of the physical mixture with H₂ at 573–723 K results in an increase in the yield of methanol produced by the CO₂ hydrogenation, while no such a promotion was observed for the CO hydrogenation, indicating that the active site is different for the CO₂ and CO hydrogenations. However, the methanol yield by CO hydrogenation is significantly increased by the oxidation treatment of the (Zn)Cu/SiO₂ catalyst. Thus it is concluded that the Cu–Zn site is active for the CO₂ hydrogenation as previously reported, while the Cu–O–Zn site is active for the CO hydrogenation.     

CO2 capture by methanol,ionic liquid,and their binary mixtures: Experiments,modeling, and process simulation

The CO₂ solubility data in the ionic liquid (IL) 1‐allyl‐3‐methylimidazolium bis(trifluoromethyl sulfonyl)imide, methanol (MeOH), and their mixture with different combinations at temperatures of 313.2, 333.2, and 353.2 K and pressures up to 6.50 MPa were measured experimentally. New group binary interaction parameters of the predictive universal quasichemical functional‐group activity coefficient (UNIFAC)‐Lei model, which has been continually advanced by our group, were introduced by correlating the experimental data of this work and the literature. The consistency between experimental data and predicted results proves the reliability of UNIFAC‐Lei model for CO₂‐IL‐organic solvent systems. The newly obtained parameters were incorporated into the UNIFAC property model of Aspen Plus software to optimize a conceptual process developed for the purification of a CO₂‐containing gas stream. The simulation results indicate that the use of IL either mixed with MeOH or purely considerably lowers the process power consumption and improves the process performance in terms of CO₂ capture rate and solvent loss. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2168–2180, 2018     

Exploring the Effects of the Interaction of Carbon and MoS2 Catalyst on CO2 Hydrogenation to Methanol

Hydrogenation of CO₂ to form methanol utilizing green hydrogen is a promising route to realizing carbon neutrality. However, the development of catalyst with high activity and selectivity to methanol from the CO₂ hydrogenation is still a challenge due to the chemical inertness of CO₂ and its characteristics of multi-path conversion. Herein, a series of highly active carbon-confining molybdenum sulfide (MoS₂@C) catalysts were prepared by the in-situ pyrolysis method. In comparison with the bulk MoS₂ and MoS₂/C, the stronger interaction between MoS₂ and the carbon layer was clearly generated. Under the optimized reaction conditions, MoS₂@C showed better catalytic performance and long-term stability. The MoS₂@C catalyst could sustain around 32.4% conversion of CO₂ with 94.8% selectivity of MeOH for at least 150 h.     

Economic Assessment of the Hydrogenation of CO2 to Liquid Fuels and Petrochemical Feedstock

To remove high concentrations of CO₂ from the off‐gas of coal‐driven power plants, a new process was proposed. The catalytic hydrogenation of the CO₂ leads to the production of C₂ – C₄ (petrochemical feedstock) and liquid C₅₊ hydrocarbons (fuel). Thus, environmentally harmful CO₂ may be converted sustainably to useful products. On the basis of a process flow sheet, the costs for processing the CO₂ are estimated for different plant sizes. The price of hydrogen contributes significantly to the overall production costs. Further price reductions may be achieved by final engineering optimization of the process as a whole and specific unit operations.     

Combined Decarbonization of Electrical Energy Generation and Production of Synthetic Fuels by Renewable Energies and Fossil Fuels

Power generation from renewable energy sources and fossil fuels are integrated into one system. A combination of technologies in the form of a carbon capture utilization (CCU)-combined power station is proposed. The technology is based on energy generation from fossil fuels by a coal power plant with CO₂ recovery from exhaust gases, and pyrolysis of natural gas to hydrogen and carbon, completed by reverse water-gas shift for the conversion of CO₂ to CO, which will react with hydrogen in a Fischer-Tropsch synthesis for synthetic diesel. The carbon from the pyrolysis can replace other fossil carbon or can be sequestered. This technology offers significant CO₂ savings compared to the current state of technology and makes an environmentally friendly use of fossil fuels for electricity and fuel sectors possible.     

Modeling and Simulation for Post-Combustion Carbon Dioxide Capture from Power Plant Flue Gas with Economic Analysis

In this study three configurations, viz. conventional MEA, interstage absorber, and interstage absorber with two stripper configuration have been techno-economically evaluated for the optimized result by carrying out simulations using ASPEN PLUS. An economic model defined for carbon capture using 30 wt% MEA to reduce CO₂ in flue gas to 0.5 mol% of 550 MWe coal fired power plant resulted in increase in COE of power plant by 20.6, 17.4, and 15.6 percents for the three configurations, respectively. The CO₂-avoided cost for the three configurations are 65.94, 64.05, and 63.09 ($ /tonne of CO₂ avoided), respectively.     

CO2 hydrogenation over micro‐ and mesoporous oxides supported Ru catalysts

We prepared relatively uniform supported Ru catalysts by ion‐exchange and CVD methods, using an NaY zeolite and a mesoporous FSM‐16 as substrates, and carried out CO₂ hydrogenation. They showed high activity for CO₂ hydrogenation. A Ru‐ion‐exchanged catalyst showed high activity for methanol production. Co addition promoted methanol formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Techno-economic evaluation of a PVAm CO2-selective membrane in an IGCC power plant with CO2 capture

Published data for an operating power plant, the ELCOGAS 315 MWe Puertollano plant, has been used as a basis for the simulation of an integrated gasification combined cycle process with CO₂ capture. This incorporated a fixed site carrier polyvinylamine membrane to separate the CO₂ from a CO-shifted syngas stream. It appears that the modified process, using a sour shift catalyst prior to sulphur removal, could achieve greater than 85% CO₂ recovery at 95 vol% purity. The efficiency penalty for such a process would be approximately 10% points, including CO₂ compression. A modified plant with CO₂ capture and compression was calculated to cost €2320/kW, producing electricity at a cost of 7.6 € cents/kWh and a CO₂ avoidance cost of about €40/tonne CO₂.     

On the Issue of the Active Site and the Role of ZnO in Cu/ZnO Methanol Synthesis Catalysts

The problem concerning the active site and the role of ZnO in Cu/ZnO-based methanol synthesis catalysts can be consistently explained based on the literature results by distinguishing CO₂ and CO hydrogenations. Although only metallic copper has some activities for methanol synthesis by the hydrogenation of CO₂, Cu-Zn alloying in Cu particles is responsible for the major promotional role of ZnO in industrial Cu/ZnO-based catalysts. The morphology effect reported in the literature will probably appear for the system of highly dispersed Cu particles supported on ZnO. As for the hydrogenation of CO, Cu⁺ species or Cu-O-Zn sites are the active sites for methanol synthesis. The spillover effect of the Cu-ZnO system is not significant compared to the effect of ZnO on the creation of the Cu-O-Zn site.     

CO2 Hydrogenation to Methanol Over Cu/ZnO/Al2O3 Catalysts Prepared by a Novel Gel-Network-Coprecipitation Method

A novel gel-network-coprecipitation process has been developed to prepare ultrafine Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from CO₂ hydrogenation. It is demonstrated that the gel-network-coprecipitation method can allow the preparation of the ultrafine Cu/ZnO/Al₂O₃ catalysts by homogeneous coprecipitation of the metal nitrate salts in the gel network formed by gelatin solution, which makes the metallic copper in the reduced catalyst exist in much smaller crystallite size and exhibit a much higher metallic copper-specific surface area. The effect of the gel concentration of gelatin on the structure, morphology and catalytic properties of the Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from hydrogenation of carbon dioxide was investigated. The Cu/ZnO/Al₂O₃ catalysts prepared by the gel-network-coprecipitation method exhibit a high catalytic activity and selectivity in CO₂ hydrogenation to methanol.