Efficient Way of Carbon Dioxide Utilization in a Gas-to-Methanol Process: From Fundamental Research to Industrial Demonstration

Efficient utilization of CO₂ to produce clean liquid fuels and various petrochemicals has attracted significant attention during the past decades. This review mainly focuses on our efforts and main achievements during the development of a CO₂-utilizing Gas-to-Methanol (CGTM) process, which is composed of CO₂/steam-mixed reforming and methanol synthesis via CO₂ and CO hydrogenation. Experimental apparatus at different scales, ranging from lab to demonstration, have been established to pursue an efficient CGTM process with enhanced energy efficiency and reduced CO₂ emissions. The proposed CGTM process employs a proprietary coke-resistant Ni-based catalyst in the reforming section, which is very stable under a 1000-h accelerated stability test. Based on the results of the process simulation and optimization obtained by using Aspen Plus, a CGTM demonstration plant with a methanol-production capacity of 10 t/day is designed and constructed, which comprises a reforming section (co-feeding CO₂ into the reformer), a methanol synthesis section, and a recycling section. During the continuous operation for 1000 h, the CGTM demonstration plant exhibited a satisfactory performance, which is in good agreement with the design values. The overall thermal efficiency is shown to be superior to that of the conventional Gas-to-Methanol (GTM) processes, and the CGTM process is economically feasible given that the NG price, methanol price, and the plant scale are located in the following range of 1–5 $/MMBTU, 350–500 $/Mt, and 2500–5000 TPD, respectively. Furthermore, the proposed CGTM process would be even more competitive in the case of a higher carbon tax.     

The process design and simulation for the methanol production on the FPSO (floating production,storage and off-loading) system

A process for methanol production from 100 MM scfd of stranded gas and CO₂ is proposed and simulated using a commercial process simulator, PRO/II v.9.1, for a FPSO (floating production, storage, off-loading) system. The process consists of Steam-CO₂ Reforming (SCR), methanol synthesis, a Reverse Water-Gas Shift (RWGS) reaction and ancillaries with recycle streams to SCR and RWGS. All reactors were simulated using the Gibbs reactor model. Also, the Plug Flow Reactor (PFR) model with reaction rate equations was used for the methanol reactor and the result was compared to the Gibbs reactor model. To maximize the use of the carbon source in stranded gas and CO₂ while avoiding an undesirable increase in process size, the optimum recycle ratios were calculated with a satisfying constraint, a steam-to-carbon ratio ≥ 1 in the SCR. In the proposed Methanol-FPSO process the RWGS reactor can maximize CO₂ utilization and case studies were performed to analyze the influence of RWGS.     

Environmental and economic analysis of methanol production process via biomass gasification

We have researched and simulated the BTL (biomass to liquid process) in which woody biomass is converted to transportation liquid fuels. In the present study, methanol (MeOH) was considered as a liquid fuel. The BTL-MeOH was designed and the environmental and economic analysis of the process was performed from the viewpoint of CO₂ emission and capital and operating costs. A case study focusing on heat and power resources was conducted. The result revealed that the process required an independent case of heat and power for CO₂ reduction; however, the cost of this was high due to the cogeneration with a steam turbine. Therefore, the introduction of a low-cost cogeneration, e.g., with a gas turbine, was required for commercialization.     

CO2 utilization for methanol production; Optimal pathways with minimum GHG reduction cost

Mitigating CO₂ emissions from industries and other sectors of our economy is a critical component of building a sustainable economy. This paper investigates two different methanol synthesis routes based on CO₂ utilization (CO₂ capture and utilization [CCU], and tri-reforming of methane [TRM]), and compares the results with the conventional methanol production using natural gas as the feedstock (NG-MeOH). A comprehensive techno-economic analysis (TEA) model that includes the findings of the life cycle assessment (LCA) models of methanol production using various CO₂ utilization pathways is conducted. Economic analysis is conducted by developing a cost model that is connected to the simulation models for each production route. Compared to the conventional process (with a GHG emission of 0.6 kg CO₂/kg MeOH), the lifecycle GHG reduction of 1.75 and 0.41 kg CO₂/kg MeOH are achievable in the CCU and TRM pathways, respectively. Furthermore, the results indicate that, under current market conditions and hydrogen production costs, methanol production via CO₂ hydrogenation will result in a cost approximately three times higher than that of the conventional process. The integrated TEA–LCA model shows that this increased cost of production equates to a required life cycle GHG reduction credit of $279 to $422 per tonne of CO₂ utilized, depending on construction material and selected pathway. Additionally, when compared to the CO₂ hydrogenation route, the tri-reforming process (TRM-MeOH) can result in a 42% cost savings. Furthermore, a minimum financial support of $56 per tonne utilized CO₂ will be required to make the TRM-MeOH process economically viable.     

Analysis of carbon dioxide-to-methanol direct electrochemical conversion mediated by an ionic liquid

An intensified process for carbon dioxide capture and conversion is proposed and analyzed, considering an electrochemical parallel plate reactor which processes a CO₂-charged stream from an absorption unit at 40 °C and atmospheric pressure and where the target product of the conversion is methanol.The task-specific ionic liquid 1-(3-aminopropyl)-3-methylimidazolium bromide was selected, synthesized and characterized. This ionic liquid has shown a good absorption capacity, high ionic conductivity, high chemical–electrochemical stability and acts as a charged intermediate (CO₂^*−) stabilizer, enabling the electrochemical reduction of absorbed CO₂.The electrical energy in the electrochemical reactor was estimated to be 8.683 kWh kg (CO₂)⁻¹ or 115.16 g (CO₂) kWh⁻¹, too high to ensure the environmental sustainability of the process. A low concentration of carbon dioxide in the liquid phase, at ambient conditions, implies the need for a high electrode area for the process and is a major hindrance to improving the economy of the process.     

Exclusion of CO and CO2 from ammonia synthesis gas by an electrocatalytic process

A new exclusion process for CO and CO₂ from ammonia synthesis gas has been proposed: this takes place at room temperature and atmospheric pressure. The process is based on the electrochemical reduction of CO and CO₂ to methanol proceeding at a mediated electrode via homogeneous catalysis. The maximum percentages of CO and CO₂ excluded from the initial gas were about 1.5 and 4.1%, respectively, with a mediated electrode of 82.8 cm² area in a reaction time of 5 h. The amount of excluded CO and CO₂ was equivalent to the sum of moles of methanol formed and gases dissolved into the solution alone. The electroreduction of CO and CO₂ was more efficient at three-phase (electrode/solution/gas) and at two-phase (electrode/solution) interfaces, respectively.     

Syngas Stoichiometric Adjustment for Methanol Production and Co-Capture of Carbon Dioxide by Pressure Swing Adsorption

Methanol is an important raw material in industry and is commonly produced from syngas. The stoichiometric ratio (H₂–CO₂)/(CO + CO₂) of the methanol synthesis reactor feed stream must be adjusted to approximately 2.1. In this study, the replacement of the solvent unit within a coal to methanol process by a pressure swing adsorption (PSA) unit is proposed. The PSA produces a hydrogen enriched stream, to adjust the stoichiometric ratio of the methanol feed stream, and simultaneously captures the carbon dioxide for future sequestration. The feed flow rate is sub divided into eight 4-bed PSA units, operated with a defined phase lag between them in order to flatten the products (composition and flow rate) oscillations. The results show that the stoichiometric adjustment is possible and that oscillations on the products flow rate and composition are reduced to less than 3%. A carbon dioxide stream of 95.15% is obtained with a recovery of 94.2% and a productivity of 82.7 mol CO₂/kg/day. The power consumption of the global process is 119.7 MW, which includes the requirements for the rinse stream (64.4 MW) and the compression of the CO₂ product to 110 bar for sequestration (55.3 MW).     

Methane Pyrolysis for CO2-Free H2 Production: A Green Process to Overcome Renewable Energies Unsteadiness

The Carbon2Chem® project aims to convert exhaust gases from the steel industry into chemicals such as methanol to reduce CO₂ emissions. Here, H₂ is required for the conversion of CO₂ into methanol. Although much effort is put to produce H₂ from renewables, the use of fossil fuels, especially natural gas, seems to be fundamental in the short term. For this reason, the development of clean technologies for the processing of natural gas with a low environmental impact has become a topic of utmost importance. In this context, methane pyrolysis has received special attention to produce CO₂-free H₂.     

Transient Optimization of Coproduction Systems for Steel and Value-Added Chemicals

A mixed-integer linear programming model for methanol production from steelmaking byproduct gases is presented, considering dynamic constraints of process units. Renewable energy is used to produce hydrogen for the process via electrolysis. A case study incorporates dynamic market prices and the CO₂ footprint of the electric power consumption, revealing a CO₂ saving potential of 18.5 % for the scenarios and configurations studied. The results indicate that upgrading the model to a design optimization in the future will increase savings.     

Effects of zirconia promotion on the activity of Cu/SiO2 for methanol synthesis from CO/H2 and CO2/H2

The effect of zirconia promotion on Cu/SiO₂ for the hydrogenation of CO and CO₂ at 0.65 MPa has been investigated at temperatures between 473 and 573 K. With increasing zirconia loading, the rate of methanol synthesis is greatly enhanced for both CO and CO₂ hydrogenation, but more significantly for CO hydrogenation. For example, at 533 K the methanol synthesis activity of 30.5 wt% zirconia-promoted Cu/SiO₂ is 84 and 25 times that of unpromoted Cu/SiO₂ for CO and CO₂ hydrogenation, respectively. For all catalysts, the rate of methanol synthesis from CO₂/H₂ is higher than that from CO/H₂. The apparent activation energy for methanol synthesis from CO decreases from 22.5 to 17.5 kcal/mol with zirconia addition, suggesting that zirconia alters the reaction pathway. For CO₂ hydrogenation, the apparent activation energies (~12 kcal/mol) for methanol synthesis and the reverse water-gas shift (RWGS) reaction are not significantly affected by zirconia addition. While zirconia addition greatly increases the methanol synthesis rate for CO₂ hydrogenation, the effect on the RWGS reaction activity is comparatively small. The observed effects of zirconia are interpreted in terms of a mechanism which zirconia serves to adsorb either CO or CO₂, whereas Cu serves to adsorb H₂. It is proposed that methanol is formed by the hydrogenation of the species adsorbed on zirconia.     

Multi-objective optimization design of hydrogen infrastructures simultaneously considering economic cost,safety and CO2 emission

Recently increasing attention has been given to a hydrogen infrastructure (HI) including producing, transporting, and delivering H₂, the next generation alternative renewable energy source to users. This paper is concerned with designing the HI considering multiple perspectives of economic cost efficiency, safety and low CO₂ emission simultaneously. An optimization modeling approach is thus proposed to address such multiple objectives of cost efficiency of H₂ supply, safety guarantee and cost efficiency of CO₂ mitigation in the HI design. The proposed model employs fuzzy multiple objective programming to compute a compromising solution among multiple objectives. A case study of the future HI in Korea is presented to demonstrate the applicability of the proposed model with some comments. The proposed modeling work can be further utilized for developing systematic decision-making tools for policy makers to determine investment strategies for developing HIs.     

Recent advances on the membrane processes for CO2 separation

Membrane separation technology has popularized rapidly and attracts much interest in gas industry as a promising sort of newly chemical separation unit operation. In this paper, recent advances on membrane processes for CO₂ separation are reviewed. The researches indicate that the optimization of operating process designs could improve the separation performance, reduce the energy consumption and decrease the cost of membrane separation systems. With the improvement of membrane materials recently, membrane processes are beginning to be competitive enough for CO₂ separation, especially for post-combustion CO₂ capture, biogas upgrading and natural gas carbon dioxide removal, compared with the traditional separation methods. We summarize the needs and most promising research directions for membrane processes for CO₂ separation in current and future membrane applications. As the time goes by, novel membrane materials developed according to the requirement proposed by process optimization with increased selectivity and/or permeance will accelerate the industrialization of membrane process in the near future. Based on the data collected in a pilot scale test, more effort could be made on the optimization of membrane separation processes. This work would open up a new horizon for CO₂ separation/Capture on Carbon Capture Utilization and Storage (CCUS).     

Methanol Synthesis from CO2, CO,and H2over Cu(100) and Ni/Cu(100)

The catalytic activity of Cu(100) and Ni/Cu(100) with respect to the methanol synthesis from various mixtures containing CO₂, CO, and H₂have been studied in a combined UHV/high pressure cell apparatus at reaction conditions,P_tot=1.5 bar andT=543 K. For the clean Cu(100) surface it is found that admission of CO to a reaction mixture containing CO₂and H₂does not lead to an increase in the rate of methanol formation, which indirectly suggests that the role of CO in the industrial methanol process relates to the change in reduction potential of the synthesis gas. For the Ni/Cu(100) surface it is found that Ni does not promote the rate of methanol formation from mixtures containing CO₂and H₂. In opposition, admission of CO to the reaction mixture leads to a significant increase in the rate of methanol formation with a turnover frequency/Ni site∼60×the turnover frequency/Cu site at Ni coverages below 0.1 ML making it a rather substantial promoting effect. It is found that the admission of CO to the synthesis gas creates segregation of Ni to the surface, whereas this is not the case for a reaction involving CO₂and H₂. It is suggested that CO acts strictly as a promotor in the system and we ascribe the increase in activity to a promotion through gas phase induced surface segregation of Ni.     

Electrochemical synthesis of dimethyl carbonate from methanol,CO2 and propylene oxide in an ionic liquid

BACKGROUND: Dimethyl carbonate (DMC) can be used effectively as an environmentally benign substitute for highly toxic phosgene and dimethyl sulfate in carbonylation and methylation, as well as a promising octane booster owing to its high oxygen content. Two‐step transesterification from epoxide, methanol, and CO₂ is widely used in the bulk production of DMC. However, major disadvantages of this process are high energy consumption, and high investment and production costs. A one pot synthesis of DMC from carbon dioxide, methanol, and epoxide was, therefore, developed. But the yields of DMC are below 70% due to the thermodynamic limitation. RESULTS: Electrochemical synthesis of DMC was conducted with platinum electrodes from methanol, CO₂ and propylene oxide in an ionic liquid was conducted. The bmimBr (1‐butyl‐3‐methylimidazolium bromide)‐methanol‐propylene oxide system with CO₂ bubbling allows DMC to be effectively synthesized and a high yield (75.5%) was achieved. CONCLUSION: In this electrolysis, redox reactions of substrates, CO₂, methanol, and propylene oxide, on Pt electrodes were carried out, producing the activated particles, CH₃O^?, CH₃OH⁺, CO₂^? and PO^?, resulting in the effective synthesis of DMC with a 75.5% yield in an ionic liquid (bmimBr). Finally, a mechanism for this synthesis reaction was proposed, which is very different from those reported in the literature. Copyright © 2011 Society of Chemical Industry     

Sorption-enhanced dimethyl ether synthesis—Multiscale reactor modeling

As an opportunity for the attenuation of atmospheric CO₂ emissions, conversion of carbon dioxide into valuable oxygenates as fuel additives or fuel surrogates was explored conceptually in terms of a potentially feasible dimethyl ether (DME) conversion process. Incentives for application of conventional CO₂–DME conversion process are insufficient due to low CO₂ conversion, and DME yield and selectivity. In-situ H₂O removal by adsorption (sorption-enhanced reaction process) can lead to the displacement of the water gas shift equilibrium and therefore, the enhancement of CO₂ conversion into methanol and the improvement of DME productivity. A two-scale, isothermal, unsteady-state model has been developed to evaluate the performance of a sorption-enhanced DME synthesis reactor. Modeling results show that under H₂O removal conditions, methanol and DME yields and DME selectivity are favoured and the methanol selectivity decreases. The increase of methanol and DME yields and DME selectivity becomes more important at higher CO₂ feed concentration because a relatively large amount of water is produced followed by a large quantity of water removed from the system. Also, the drop in the fraction of unconverted methanol becomes more important when CO₂ feed concentration is higher and the dehydration reaction is favoured. Therefore, application of the sorption-enhanced reaction concept allows the use of CO₂ as a constituent of the synthesis gas as the in-situ H₂O removal accelerates the reverse water gas shift reaction.     

Impact of liquid absorption process development on the costs of post-combustion capture in Australian coal-fired power stations

Australian power generators produce approximately 170 TWh per annum of electricity using black and brown coals that accounts for 170 Mtonne of CO₂ emissions per annum or over 40% of anthropogenic CO₂ emissions in Australia. This paper describes the results of a techno-economic evaluation of liquid absorption based post-combustion capture (PCC) processes for both existing and new pulverised coal-fired power stations in Australia. The overall process designs incorporate both the case with continuous capture and the case with the flexibility to switch a CO₂ capture plant on or off depending upon the demand and market price for electricity, and addresses the impact of the presently limited emission controls on the process cost. The techno-economic evaluation includes both air and water cooled power and CO₂ capture plants, resulting in cost of power generation for the situations without and with PCC. Whilst existing power plants in Australia are all water cooled sub-critical designs, the new power plants are deemed to range from supercritical single reheat to ultra-supercritical double reheat designs, with a preference for air-cooling. The process evaluation also includes a detailed sensitivity analysis of the thermodynamic properties of liquid absorbent for CO₂ on the overall costs. The results show that for a meaningful decrease in the efficiency and cost penalties associated with the post combustion CO₂ capture, a novel liquid sorbent will need to have heat of absorption/desorption, sensible heat and heat of vaporisation around 50% less in comparison with 30% (w/w) aqueous MEA solvent. It also shows that the impact of the capital costs of PCC processes is quite large on the added cost of generation. The results can be used to prioritise PCC research in an Australian context.     

Economical assessment of competitive enhanced limestones for CO2 capture cycles in power plants

CO₂ capture systems based on the carbonation/calcination loop have gained rapid interest due to promising carbonator CO₂ capture efficiency, low sorbent cost and no flue gases treatment is required before entering the system. These features together result in a competitively low cost CO₂ capture system. Among the key variables that influence the performance of these systems and their integration with power plants, the carbonation conversion of the sorbent and the heat requirement at calciner are the most relevant. Both variables are mainly influenced by CaO/CO₂ ratio and make-up flow of solids. New sorbents are under development to reduce the decay of their carbonation conversion with cycles. The aim of this study is to assess the competitiveness of new limestones with enhanced sorption behaviour applied to carbonation/calcination cycle integrated with a power plant, compared to raw limestone. The existence of an upper limit for the maximum average capture capacity of CaO has been considered. Above this limit, improving sorbent capture capacity does not lead to the corresponding increase in capture efficiency and, thus, reduction of CO₂ avoided cost is not observed. Simulations calculate the maximum price for enhanced sorbents to achieve a reduction in CO₂ removal cost under different process conditions (solid circulation and make-up flow). The present study may be used as an assessment tool of new sorbents to understand what prices would be competitive compare with raw limestone in the CO₂ looping capture systems.     

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.     

A comparative study of carbon dioxide capture capabilities between methanol solvent and aqueous monoethanol amine solution

Simulations have been performed to compare the performance of CO₂ capture power between 98.5 wt% methanol solvent and 30 wt% MEA aqueous solution. A general purpose chemical process simulator, PRO/II with PROVISION release 8.3 was used for the modeling of CO₂ capture process. For the simulation of CO₂ capture process using methanol as a solvent, NRTL liquid activity coefficient model was used for the estimation of the liquid phase non-idealities, Peng-Robinson equation of state model was selected for the prediction of vapor phase non-idealities, and Henry’s law option was chosen for the prediction of the solubilities of light gases in methanol and water solvents. Amine special thermodynamic package built-in PRO/II with PROVISION release 8.3 was used for the modeling of CO₂ capture process using MEA aqueous solution. We could conclude that the 30 wt% of MEA aqueous solution showed better performance than the 98.5 wt% methanol solvent in CO₂ capture capability. Through this study, we tried to compare the differences between the two processes from the aspects of capital and operating costs using a commercial process simulator. This will guide the optimal process design in the carbon dioxide capture process.