CO2 utilization for methanol production; Part I: Process design and life cycle GHG assessment of different pathways

Selective scission of glucose molecule by a Pd-modulated Co-based catalyst for efficient CO2 reduction under mild conditions

Combining terrestrial biomass as the reductant with submarine-type hydrothermal environments for CO2 reduction represents a possible approach for novel energy production systems that sustainably circulate carbon. However, increasing the reductive power of biomass is the main limitation of this potential method. Herein, we demonstrate that Co-doped with small amounts of Pd enhances the reduction of CO2 by selectively producing an active intermediate from carbohydrates. This catalytic reaction utilized glucose as a reductant to achieve high formate production efficiency (458.6 g kg-1) with nearly 100% selectivity with 7.5 wt% Pd1Co20/γ-Al2O3 at a moderate temperature of 225 °C. The regulation of the electronic structure of the catalytic Co surface by the dopant Pd plays a key role in promoting the C-C bond cleavage of glucose and hydrogen transfer for CO2 reduction. The findings presented here indicate that biomass can serve as the hydrogen source for CO2 reduction and provide insight into the potential utilization of CO2 in sustainable industrial applications.

Recent advances in CO2 reduction with renewable reductants under hydrothermal conditions: towards efficient and net carbon benefit CO2 conversion

The ever-growing atmospheric CO2 concentration threatening the environmental sustainability of humankind makes the reduction of CO2 to chemicals or fuels an ideal solution. Two priorities are anticipated for the conversion technology, high efficiency and net carbon benefit, to ensure the mitigation of the CO2 problem both promptly and sustainably. Until now, catalytic hydrogenation or solar/electro-chemical CO2 conversion have achieved CO2 reduction promisingly while, to some extent, compromising to fulfill the two rules, and thus alternative approaches for CO2 reduction are necessary. Natural geochemical processes as abiotic CO2 reductions give hints for efficient CO2 reduction by building hydrothermal reaction systems, and this type of reaction atmosphere provides room for introducing renewable substances as reductants, which offers the possibility to achieve CO2 reduction with net carbon benefit. While the progress in CO2 reduction has been abundantly summarized, reviews on hydrothermal CO2 reduction are relatively scarce and, more importantly, few have focused on CO2 reduction with renewable reductants with the consideration of both scale of efficiency and sustainability. This review provides a fundamental and critical review of metal, biomass and polymer waste as reducing agents for hydrothermal CO2 reduction. Various products including formic acid, methanol, methane and multi-carbon chemicals can be formed, and effects of operational parameters such as temperature, batch holding time, pH value and water filing as well as detailed reaction mechanisms are illustrated. Particularly, the critical roles of high temperature and pressure water as reaction promotor and catalyst in hydrothermal CO2 conversion are discussed at the mechanistic level. More importantly, this review compares hydrothermal CO2 reduction with other methods such as catalytic hydrogenation and photo/electrocatalysis, evaluating their efficiency and potential for net carbon benefit. The aim of this review is to promote the understanding of CO2 activation under a hydrothermal environment and provide insights into the efficient and sustainable strategy of hydrothermal CO2 conversion for future fundamental research and industrial applications.

Simultaneous Optimization and Integration of Multiple Process Heat Cascade and Site Utility Selection for the Design of a New Generation of Sugarcane Biorefinery

Biorefinery plays a crucial role in the decarbonization of the current economic model, but its high investments and costs make its products less competitive. Identifying the best technological route to maximize operational synergies is crucial for its viability. This study presents a new superstructure model based on mixed integer linear programming to identify an ideal biorefinery configuration. The proposed formulation considers the selection and process scale adjustment, utility selection, and heat integration by heat cascade integration from different processes. The formulation is tested by a study where the impact of new technologies on energy efficiency and the total annualized cost of a sugarcane biorefinery is evaluated. As a result, the energy efficiency of biorefinery increased from 50.25% to 74.5% with methanol production through bagasse gasification, mainly due to its high heat availability that can be transferred to the distillery, which made it possible to shift the bagasse flow from the cogeneration to gasification process. Additionally, the production of DME yields outcomes comparable to methanol production. However, CO2 hydrogenation negatively impacts profitability and energy efficiency due to the significant consumption and electricity cost. Nonetheless, it is advantageous for surface power density as it increases biofuel production without expanding the biomass area.

Life cycle assessment of biostimulant production from algal biomass grown on piggery wastewater

Piggery wastewater has become a large source of pollution with high concentrations of nutrients, that must be managed and properly treated to increase its environmental viability. Currently, the use of microalgae for treating this type of wastewater has emerged as a sustainable process with several benefits, including nutrient recovery to produce valuable products such as biostimulants, and CO2 capture from flue gases. However, the biostimulant production from biomass grown on piggery wastewater also has environmental impacts that need to be studied to identify possible hotspots. This work presents the life cycle assessment by IMPACT 2002+ method of the production of microalgae-based biostimulants, comparing two different harvesting technologies (membrane in scenario 1 and centrifuge in scenario 2) and two different technologies for on-site CO2 capture from flue gases (chemical absorption and membrane separation). The use of membranes for harvesting (scenario 1) reduced the environmental impact in all categories (human health, ecosystem quality, climate change, and resources) by 30 % on average, compared to centrifuge (scenario 2). Also, membranes for CO2 capture allowed to decrease environmental impacts by 16 %, with the largest reduction in the resource category (∼33 %). Thus, the process with the best environmental viability was achieved in scenario 1 using membranes for CO2 capture, with a value of 217 kg CO2 eq/FU. In scenario 2 with centrifugation, the high contribution of the cultivation sub-unit in all impacts was highlighted (>75 %), while in scenario 1 the production sub-unit also had moderate contribution in the human health (∼35 %) and climate change (∼30 %) categories due to the lower concentration and high flow rates. These results were obtained under a worst-case situation with pilot scale optimized parameters, with limited data which would have to be further optimized at industrial-scale implementation. The sensitivity analysis showed a little influence of the parameters that contribute the most to the impacts, except for the transportation of the piggery wastewater to the processing plant in scenario 2. Because of the relevant impact of biostimulant transportation in scenario 1, centrifugation becomes more favourable when transportation distance is longer than 321 km.

Climate and biodiversity impacts of low-density polyethylene production from CO2 and electricity in comparison to bio-based polyethylene

Plastics are essential materials for modern societies, but their production contributes to significant environmental issues. Power-to-X processes could produce plastics from captured CO₂ and hydrogen with renewable electricity, but these technologies may also face challenges from environmental perspective. This paper focuses on environmental sustainability assessment of CO₂-based low-density polyethylene (LDPE) compared to bio-based LDPE. Life cycle assessment has been applied to study climate impacts and land use related biodiversity impacts of different plastic production scenarios. According to the climate impact results, the carbon footprint of the produced plastic can be negative if the energy used is from wind, solar, or bioenergy and the carbon captured within the plastic is considered. In terms of biodiversity, land-use related biodiversity impacts seem to be lower from CO₂-based polyethylene compared to sugarcane-based polyethylene. Forest biomass use for heat production in CO₂-based polyethylene poses a risk to significantly increase biodiversity impacts. Taken together, these results suggest that CO₂-based LDPE produced with renewable electricity could reduce biodiversity impacts over 96 % while carbon footprint seems to be 6.5 % higher when compared to sugarcane-based polyethylene.

Net-zero transition of the global chemical industry with CO2-feedstock by 2050: feasible yet challenging

Carbon capture, utilization and storage (CCUS) have been projected by the power and industrial sectors to play a vital role towards net-zero greenhouse gas emissions. In this study, we aim to explore the feasibility of a global chemical industry that fully relies on CO₂ as its carbon source in 2050. We project the global annual CO₂ demand as chemical feedstock to be 2.2-3.1 gigatonnes (Gt), well within the possible range of supply (5.2-13.9 Gt) from the power, cement, steel, and kraft pulp sectors. Hence, feedstock availability is not a constraint factor for the transition towards a fully CO₂-based chemical industry on the global basis, with the exception of few regions that could face local supply shortages, such as the Middle East. We further conduct life cycle assessment to examine the environmental benefits on climate change and the trade-offs of particulate matter-related health impacts induced by carbon capture. We conclude that CO₂ captured from solid biomass-fired power plants and kraft pulp mills in Europe would have the least environmental and health impacts, and that India and China should prioritize low-impact regional electricity supply before a large-scale deployment of CCUS. Finally, two bottom-up case studies of China and the Middle East illustrate how the total regional environmental and health impacts from carbon capture can be minimized by optimizing its supply sources and transport, requiring cross-sectoral cooperation and early planning of infrastructure. Overall, capture and utilization of unabatable industrial waste CO₂ as chemical feedstock can be a feasible way for the net-zero transition of the industry, while concerted efforts are yet needed to build up the carbon-capture-and-utilization value chain around the world.

Hybrid Renewable Hydrogen Energy Solution for Remote Cold-Climate Open-Pit Mines

Contemporary off-grid mining operations rely on diesel fuel for the provision of their total energy including electricity, heat, and haulage. Given the high cost of diesel and its imposed greenhouse gas emissions, mining companies are looking for more affordable and cleaner sources of energy for their operations. Although renewable energy systems, such as solar photovoltaic and wind provide efficient solutions to address this challenge, full decarbonization has shown to be very challenging, mainly due to the high cost of battery storage along with the inability to meet total site energy demand. Integrating hydrogen and thermal storage with battery banks can facilitate a full transitioning off diesel. In this sense, the present study intends to offer an innovative decarbonized solution by integrating wind turbines with a multi-storage system (battery, hydrogen, and thermal storage) to supply the total energy (electricity, heat, and haulage) for remote open-pit mines. Among the different proposed fully decarbonized configurations in this study, it is shown that a renewable system with a hydrogen-powered fleet and hybridized battery/hydrogen storage configuration can present the most economically viable case for open-pit mines with a considerably less life-of-mine cost.

Environmental and energetic analysis of coupling a biogas combined cycle power plant with carbon capture, organic Rankine cycles and CO2 utilization processes

Greenhouse gas emissions from power plants that use fossil fuels cause a serious impact to the environment, for this reason the use of renewable energy technologies is an important alternative as a way of combatting climate change. The production of power via biomass is considered as a carbon neutral energy resource, but it is well known that the non-fossil CO₂ emitted from this type of processes can also be captured. In order to do so, in this work it is proposed a match between a Biogas combined cycle power plant and postcombustion carbon capture process, to capture the CO₂ produced by the biogas combustion, and also it considered a match with an organic Rankine cycle that uses the wasted energy of the combustion gases. Additionally, it is considered that the captured carbon is used to produce some value-added chemicals and fuels. Environmental and energetic evaluations were carried out for the coupling of those technologies. The implementation of the carbon capture plant, results on a diminution of the 87% of the emission of the combined cycle power plant. The life cycle analysis results show that the study case of Syngas production via dry reforming of methane, presents the lower global warming potential (0.088 CO₂-eq kg/kg) and it was also found that the global warming potential has a reduction with the help of the mass integration between the different alternatives of CO₂ utilization. Finally, it was found an annual reduction of 0.055 CO₂-eq t for the system with mass integration compared with the cases without mass integration.