Effect of water and organic pollutant in CO2/CH4 separation using hydrophilic and hydrophobic composite membranes

Membrane technology is a simple and energy-conservative separation option that is considered to be a green alternative for CO2 capture processes. However, commercially available membranes still face challenges regarding water and chemical resistance. In this study, the effect of water and organic contaminants in the feed stream on the CO2/CH4 separation performance is evaluated as a function of the hydrophilic and permselective features of the top layer of the membrane. The membranes were a commercial hydrophobic membrane with a polydimethylsiloxane (PDMS) top layer (Sulzer Chemtech) and a hydrophilic flat composite membrane with a hydrophilic [emim][ac] ionic liquid–chitosan (IL–CS) thin layer on a commercial polyethersulfone (PES) support developed in our laboratory. Both membranes were immersed in NaOH 1M solutions and washed thoroughly before characterization. The CO2 permeance was similar for both NaOH-treated membranes in the whole range of feed concentration (up to 250 GPU). The presence of water vapor and organic impurities of the feed gas largely affects the gas permeance through the hydrophobic PDMS membrane, while the behavior of the hydrophilic IL–CS/PES membranes is scarcely affected. The effects of the interaction of the contaminants in the membrane selective layer are being further evaluated.This research was funded by the Spanish Ministry of Science and Innovation; project CTQ2016-76231-C2-(AEI/FEDER, UE) and project PID2019-108136RB-C31)

Absorption of coal combustion flue gases in ionic liquids using different membrane contactors

Carbon dioxide (CO2) and sulfur dioxide (SO2) are typical gases produced during coal combustion and their emissions have to be controlled and minimized in order to reduce environmental risks. Organic solvents are commonly used as absorption liquids for the chemical absorption of CO2 and SO2, and their use in combination with a membrane device is being studied recently. The volatile character of common solvents produces solvent losses due to their evaporation into the gas stream. Thus, the use of solvents with lower vapor pressure such as ionic liquids as absorption liquids may contribute to the performance of a zero solvent emission process. In the present study, mass transfer of CO2 is studied in a polypropylene hollow fiber membrane contactor when the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate is used as the absorption liquid. Mass transfer coefficients are compared with those obtained with a ceramic hollow fiber contactor for SO2 absorption. The overall mass transfer coefficient takes a value of K overall = (3.69 ±0.18) ×10-7 m s-1 and K overall = (3.38 ±0.09) ×10-6 m s- 1 in CO2 and SO2 systems, respectively. Main resistance to mass transfer has been found to be the membrane itself. In CO2 absorption a theoretical effective diffusivity was estimated as D eff = 4.94 ×10-7 m2 s-1 which differs from diffusivity obtained from experimental results (D eff = (1.717 ±0.18) ×10-11 m2 s-1).This research has been funded by the Spanish Ministry of Science and Technology (Project CTM2006-00317 and Project EUI2008-03857)

Life cycle assessment of bottom ash management from a municipal solid waste incinerator (MSWI)

Thermal treatment of Municipal Solid Waste (MSW) results in various types of solid wastes, distinguishing mainly bottom, boiler and fly ashes and slag. To minimise waste generation it necessary to carry out primary measures for controlling residue outputs that involve optimising control of the combustion process. Obviously, after primary measures a secondary treatment is required. The conventional bottom ash management is to carry out a solidification process. This solidification or stabilization process produces a material with physical and mechanical properties that promote a reduction in contaminant release from the residue matrix. Solidification methods commonly make use of inorganic binder reagents such as cement, lime and other pozzolanic materials. Once waste is stabilized, it is usually sent to the landfill. However, despite the heavy metal content, it is getting more and more common the use of this waste as a natural aggregate. In particular, it could be used as a raw material for clinker production, cement mortar or frit production. Other possible management options included its utilization as a drainage layer on a landfill and as a sub-base material in a road construction. In this work it was assessed different bottom ash management options. In this work the Life Cycle Assessment (LCA) methodology was applied to assess the environmental impact of different bottom ash management options. Specifically, the conventional ash solidification was compared with the ash recycling in Portland cement production

Continuous electroreduction of CO2 towards formate in gas-phase operation at high current densities with an anion exchange membrane

The carbon dioxide (CO2) electroreduction to formate is nowadays considered as a promising approach to convert CO2 into a value-added product and simultaneously, in the context of strategies for mitigating climate change. However, there is a scarce number of studies published in the literature operating with a current density higher than 200 mA cm- 2 , and there is the need of operating at higher current densities, with acceptable performance and low penalty in terms of energy consumption, for future implementation at industrial scale. Thus, in this work, a novel configuration is studied using a filter press reactor in a continuous mode, with a single pass of the reactants through the cell, employing a Sustainion anion exchange membrane and working with a current density up to 600 mA cm-2 . Using the same electrocatalysts, the configuration shows a similar performance to the GDE configuration with liquid electrolyte, but with the advantage of operating only with a vapour input to the cathode and avoiding the need for a liquid catholyte. Although at the expense of obtaining a more diluted product, excellent combinations of Faradaic Efficiency for formate (73.7 %), energy consumptions (342 kWh-kmol-1), and product rates (22.9 mmol m- 2 -s -1) can be achieved at high current densities. Therefore, the configuration with Sustainion membranes reported in this manuscript can be particularly interesting for future applications that do not involve a very concentrated formate product.Authors fully acknowledge the financial support received from the Spanish State Research Agency (AEI) through the projects PID2019-108136RB-C31 (AEI/10.13039/501100011033) and PID2020-112845RB-I00 (AEI/10.13039/501100011033). We are also grateful for the nanoparticles prepared and provided by the group of Prof. V. Montiel and Dr. José Solla-Gullón from the Institute of Electrochemistry of the University of Alicante. The authors also thank BioRender.com online software as this science illustration tool has allowed to create some of the figures of this manuscript

Toward the decarbonization of hard-to-abate sectors: a case study of the soda ash production

Decarbonizing the so-called "hard-to-abate" sectors is considered more technically challenging than others such as energy or transportation because they entail emissions not only from heat and power generation but also from manufacturing and process industries. The opportunities for them are less obvious and the challenges are greater, so their shift or transition to zero emissions is still relatively unexplored. In this case study, we aim to analyze the environmental impact and the technoeconomic viability of the integration of a carbon capture and utilization (CCU) plant that produces CO2-based methanol (CO2-MeOH) by means of electrochemical reduction (ER) in the hard-to-abate sector of synthetic soda ash. With a rigorous emphasis on the goal of net zero CO2 emissions, life cycle assessment (LCA) and technoeconomic assessment (TEA) were used as tools in order to guide further research and development toward its potential final commercialization. LCA and TEA results have demonstrated that it is possible to reduce the carbon footprint (CF) of the synthetic soda ash production at a reasonable cost within proper medium/long-term developments. Several scenarios have been assessed considering the future innovation of the CCU-ER technology and the future evolution of the electricity and CO2 market prices because of the application of instruments such as Power Purchase Agreements (PPAs) and the European Union Emissions Trading System. The scenarios analyzed suggest that the complete electrification of the integrated plants of soda ash through electric heat (EH) is positive from the environmental perspective. This EH represents the direct conversion of renewable electricity to industrial heat. The results displayed a reduction in the CF of soda ash up to 74% as long as the entire integrated plant was run on renewable electricity and considering the commercialization of the ER side products such as H2 and O2. Not considering the selling of these two products leads to more modest reduction around 41%. However, this complete electrification has major implications on the economic profile under the current combination of electricity and CO2 market prices. Low-cost electricity, for example, using surpluses of renewable electricity and/or PPAs, and a higher CO2 price, which can be expected in the short/mid-term, are required to ensure economic feasibility. A 50% reduction of the current average wholesale electricity price that was used as a reference in the present study (43 €·MW h-1) will ensure economic feasibility under the proper ER technology development. The insights gained in this study may be of assistance in the sustainable implementation of CCU in energy-intensive manufacturing processes.Authors thank to Spanish Ministry of Economy and Competitiveness (MINECO) for the financial support through the project CTQ2016-76231-C2-1-R. We would like also to thank MINECO for providing Marta Rumayor with a Juan de la Cierva postdoctoral contract (IJCI-2017-32621)

Innovative alternatives to methanol manufacture: carbon footprint assessment

Finding and implementing more sustainable alternatives to the fossil-dependence routes for methanol (MeOH) manufacturing is undoubtedly one of the challenges of our model of society. Some approaches can be used to convert CO2 into MeOH as direct hydrogenation or electrochemical reduction (ER). These alternatives lead to lower natural resources consumption respect the conventional routes, but they are still found at different technological readiness levels (TRLs). Therefore some remaining challenges need to be overtaken to achieve a carbon neutral cycle respect the conventional route, especially in the case of ER, which is currently found at its infancy. This would indicate their final industrial competitiveness in a sustainable mode. This study uses Life Cycle Assessment as the main tool in order to compare these two CO2-based manufacture alternatives (found at different TRLs) with the fossil-route. The results allow for evaluating the potential challenges inherited to the alternative based on ER. Utilization of renewable energy is one of the most important key issues to achieve a carbon neutral product using these options. However, its benefit could be neglected due to the high requirement of steam in the purification step, particularly in ER. It was demonstrated that a future scenario using ER leads to a lower natural resources consumption (mainly natural gas) compared to the conventional fabrication, which represents an important step towards more green and efficient MeOH synthesis.Authors thank to Spanish Ministry of Economy and Competitiveness (MINECO) for the financial support through the project CTQ2013-48280-C3-1-R. We would like also to thank MINECO for providing Marta Rumayor with a Juan de la Cierva postdoctoral contract (FJCI-2015-23658)

A case study for environmental impact assessment in the process industry: municipal solid waste incineration (MSWI)

Life Cycle Assessment (LCA) has been introduced in the evaluation of chemical processes and or products in order to take into account the Supply Chain and its environmental constraints and burdens. Regarding to the environmental assessment of chemical processes and/or products two main variables need to be taken into account: Natural Resources Sustainability (NRS) and Environmental Burdens Sustainability (EBS). NRS includes the use of energy, water and materials whereas EBS is given by the environmental sustainability metrics developed by the Institution of Chemical Engineers (IChemE). The main components of EBS have been classified in 5 environmental impacts to the atmosphere (acidification, global warming, human health effects, stratospheric ozone depletion and photochemical ozone formation), 5 aquatic media impacts (aquatic acidification, aquatic oxygen demand, ecotoxicity (metals), ecotoxicity (others) and eutrophication) and 2 land impacts (hazardous and non-hazardous waste disposal). To reduce the number of variables and thus, the complexity, the development of a normalisation and weighting procedure is required. This work proposes the normalization of EB based on the threshold values of the European Pollutant Release and Transfer Register (E-PRTR) and a similar procedure based on the values given by the BREF document on waste incineration for the NRS normalisation. This procedure will help in the decision making process in the waste management field and in the particular, in Municipal Solid Waste Incineration (MSWI)

Tailoring gas-phase CO2 electroreduction selectivity to hydrocarbons at Cu nanoparticles

Copper-based surfaces appear as the most active catalysts for CO2 electroreduction to hydrocarbons, even though formation rates and efficiencies still need to be improved. The aim of the present work is to evaluate the continuous gas-phase CO2 electroreduction to hydrocarbons (i.e. ethylene and methane) at copper nanoparticulated-based surfaces, paying attention to particle size influence (ranging from 25–80 nm) on reaction productivity, selectivity, and Faraday efficiency (FE) for CO2conversion. The effect of the current density and the presence of a microporous layer within the working electrode are then evaluated. Copper-based gas diffusion electrodes are prepared by airbrushing the catalytic ink onto carbon supports, which are then coupled to a cation exchange membrane (Nafion) in a membrane electrode assembly. The results show that the use of smaller copper nanoparticles (25 nm) leads to a higher ethylene production (1148 μmol m−2 s−1) with a remarkable high FE (92.8%), at the same time, diminishing the competitive hydrogen evolution reaction in terms of FE. This work demonstrates the importance of nanoparticle size on reaction selectivity, which may be of help to design enhanced electrocatalytic materials for CO2 valorization to hydrocarbons.The authors gratefully acknowledge the financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through the projects CTQ2013-48280-C3-1-R and CTQ2016-76231-C2-1-R. Ivan Merino-Garcia and Jonathan Albo would also like to thank the MINECO for the Early Stage Researcher Contract (BES-2014-070081) and Ramón y Cajal programme (RYC-2015-17080), respectively

From linear to circular integrated waste management systems: A review of methodological approaches

The continuous depletion of natural resources related to our lifestyle cannot be sustained indefinitely. Two major lines of action can be taken to overcome this challenge: the application of waste prevention policies and the shift from the classical linear Integrated Waste Management Systems (IWMSs) that focus solely on the treatment of Municipal Solid Waste (MSW) to circular IWMSs (CIWMSs) that combine waste and materials management, incentivizing the circularity of resources. The system analysis tools applied to design and assess the performance of linear IWMSs were reviewed in order to identify the weak spots of these methodologies, the difficulties of applying them to CIWMSs, and the topics that could benefit from further research and standardization. The findings of the literature review provided the basis to develop a methodological framework for the analysis of CIWMSs that relies on the expansion of the typical IWMS boundaries to include the upstream subsystems that reflect the transformation of resources and its interconnections with the waste management subsystems